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Geofoam Features | Canadian Environmental Protection by Fred P. Rohe The city of Detroit is in the process of reclaiming its river front. Over the years the area has been dominated by business and industry but the area has become an embarrassment. The Detroit Riverfront Conservancy was created with the mission of revitalizing the waterfront area. The first phase of this undertaking was the Louis Arena to the Douglas MacArthur bridge to Belle Isle. People are to run, walk, bike and roller-blade on the new RiverWalk, which will also include places for people to sit and take in the scenery. A portion of the RiverWalk passes directly between the General Motors (GM) Renaissance Center buildings and the Detroit River. GM retained Albert Kahn Associates to design a suitable plaza and promenade to blend as part of the RiverWalk project. The plaza includes a granite world map showing the GM facility locations world wide. John Carlo, Inc. was selected as the prime contractor to build the plaza as a showpiece for the GM Center.   Planter boxes were lined to create a tree-lined tiered walkway.     Material The area selected for the plaza has seen many varied uses over the past century. There are many unknowns regarding the soils and other materials deposited there. It was known that the area had experienced some subsidence and the fill in the area was over soft soils. The area is bounded on one side by a service areaway and on the other by a concrete sea wall at the river’s edge. The site’s close proximity to the Windsor Tunnel under the Detroit River to Canada was another important consideration.The plaza area needed to be raised approximately four meters above the existing parking lot area it is replacing. The designers selected expanded polystyrene Geofoam for use as fill material. The 1.5 pounds/square foot density Geofoam would save weight, reduce lateral pressures on the adjacent structures, and speed construction at the congested work site.Hydrocarbons have a devastating effect on contact with expanded polystyrene foam. In order to protect the Geofoam from damage by an accidental spill of fuel or other hydrocarbon materials, the designers utilized a geomembrane.8130 XR-5 was selected to cover the top of all areas where Geofoam was installed. XR-5 is a PVC coated fabric formulated using Elvaloy, a chemical resistant polymer which imparts flexibility to the geomembrane.     Protective sand layer was broadcast-spread over geomembrane liner.   Discussion The GM Renaissance Center Plaza and Promenade is a public area in downtown Detroit. GM will be displaying vehicles at the plaza as well as hosting many outdoor events in the area. The plaza will also be heavily landscaped to provide an enhanced look to the park like setting. The plaza is also directly adjacent to a busy city street with all types of vehicles all types of vehicles traveling in the congested area. There is legitimate concern for a possibility of an accidental fuel spill. Therefore it was necessary to take precautions to protect the Geofoam from any adverse exposure to chemicals that would dissolve the foam.Environmental Protection, Inc. (EPI) was selected to provide over 4,700 square meters of XR-5 geomembrane liner for this project. Over one acre of XR-5 was prefabricated to fit the varying shapes of the plaza and the many planter boxes and planting areas that were incorporated into the design. Each area of the plaza where Geofoam was installed had to be covered with geomembrane. The XR-5 material was installed directly over the foam, or over a sand cushion that was installed on top of the foam in some areas.The liner extended up vertically 30 to 50 centimeters on the perimeter concrete walls. The geomembrane was secured to the concrete using an aluminum batten bar 0.3175 centimeters by five centimeters. The batten was anchored to the concrete wall using Ramset three centimeter long powder-actuated fasteners located approximately 15 centimeters centre to centre.Since the geomembrane now acts to collect any fluid, including rainwater, a drain age system had to be implemented above the liner and drain piping to direct the water away from the plaza. The liner was sealed to these drain pipes using prefabricated EPI Tapered Pipe Boots. Boots were custom fabricated of XR-5 for each pipe diameter used on the project. EPI also prefabricated inside and outside corners to simplify the installation of the XR-5 around the many column foundations and intricate corners in the planter areas. Installation of the XR-5 had to be coordinated with the many other subcontractors working on the site. The area was so congested that the installation had to be done in phases in order to allow enough area for everyone to operate efficiently. Summary The XR-5 geomembrane provided an excellent solution for protection of the EPS Geofoam on this project. The material was easily fabricated to fit the unusual shapes and dimensions of the plaza and its many planters. Installation was rapid, with very little field welding required.While unlikely, it is possible that an accidental spill could cause serious damage to the Geofoam underlying the GM Renaissance Center Plaza and Promenade. The foresight to provide protection for the EPS foam will ensure that this area will be use-able and useful to the visitors to the Detroit river front for many years to come. References Curtis, R., Page, D., Peaslee, G. “EPS Geofoam Technology Project”, The Bridge, April/June 2004, Michigan Technological University, Houghton, MI 49931. “Reclaiming The Riverfront.” “GM Riverfront Plaza & Promenade”, The Liner Letter, Vol. 4 – Issue 5, July 7, 2004. Wehrmeyer, S., “Geofoam: Providing new solutions to old challenges”, Geotechnical Fabrics Report, June/July 2001. Nystrom, J., “Applications: Geofoam takes a new track”, Geotechnical Fabrics Report, September 1999. Reuter, G., Rutz, J., “Applications: A lightweight solution for landslide stabilization”, Geotechnical Fabrics Report, September 2000. For more information call   800-OK-LINER  today!

by Richard W. Thomas and Timothy D. Stark  One of the current research topics being pursued by the PVC Geomembrane Institute (PGI) is the thermal welding and subsequent air channel testing of PVC geomembrane seams, which is the focus of this column. Other active research projects include the long-term performance of PVC geomembranes using field case histories, shear behavior of PVC geomembrane interfaces, and the chemical resistance of PVC geomembranes. These projects will be discussed in future columns.  This article focuses on the use of a new seam burst test to evaluate field PVC geomembrane seams. This topic is part of a larger study on the thermal welding of PVC geomembranes and some results from this study are also presented herein. The seam burst test is an excellent indicator of seam quality and has been directly related to seam peel strength ( ASTM D 6392 ). These results allow the burst test to be used in the field to test the entire length of a PVC seam for the specified peel strength instead of using destructive peel tests over a limited portion of the seam. It is anticipated that the use of the burst test will lead to a reduction in the destructive testing required during field installations.  Thermal welding has proven to be an efficient and cost-effective method of field seaming PVC geomembrane liners since 1991 and has been used for factory fabrication since 1982. PVC geomembranes possess excellent thermal welding characteristics such as a wide thermal seaming range, lack of residual stress or stress cracking, and no required surface preparation, such as grinding. Fully automated welding systems can thermally weld PVC geomembranes as thin as 0.5 mm (20 mil). These welding systems allow the operator to adjust welding speed, nip-roller pressure, and welding temperature to create the best quality seam.  In addition, thermal welding can be used to create an air-channel using a dual track wedge and thus conduct air-channel testing of the seam. An important a difference between air-channel testing of PVC geomembranes seams versus high-density polyethylene (HDPE) geomembranes is the flexible nature of a PVC geomembrane, which allows the field technician to see the air channel inflate as the air pressure migrates down the seam. The inflated air channel somewhat resembles an inflated inner tube and this distinctive behavior has been referred to as “inner tubing” of PVC seams. If a weak spot is encountered and leaks, the air pressure may not be fully inflated at this weak spot. It can be seen that the air channel is inflated (inner tubing), readily visible, and maintaining the air pressure. The thermally welded seams used in this study were created in a single day in Austin, Texas at TRI/Environmental on an asphalt subgrade. Two installation crews from two different companies (Colorado Lining International and Environmental Protection, Inc.), one using a hot air welder and the other using a hot wedge welder, created the seventy-two (72) 9.2 m (30 foot) long thermal seams used in this study.  The hot air machine is a Leister Twinnie Model CH6056. The hot wedge machine is a Mini-Wedge made by Plastic Welding Technologies (formerly Columbine, Inc.).  The 0.75 to 1.00 mm (30 and 40 mil) PVC geomembrane used in the thermal seam testing was provided by Canadian General-Tower, Ltd. of Cambridge, Ontario, Canada. The seams were evaluated by the standard peel test at 20 in/min at 73ºF ( ASTM D 6392 , 1999) and by the seam burst test developed during this project. The burst test was performed by sealing off one end of a seam length and pressurizing the other end with compressed air. The seam length tested in the burst test was 2 m (6 feet). The basic test procedure involved selecting a starting air pressure, holding that air pressure constant for 30 seconds, then increasing the air pressure 5 psi at a time, and holding the new air pressure another 30 seconds. This was repeated for each 34.4 kPa (5 psi) air pressure increment. The 34.4 kPa (5 psi) air pressure increment was achieved in a 5 second time period. This procedure of increasing the air channel pressure, holding the air pressure, and then increasing the air pressure by 34.4 kPa (5 psi) continued until the seam “burst”.  Most of the burst failures involved the peel mode, which occurred during the 30 second holding period. However, some seams burst during the 34.4 kPa (5 psi) air pressure increase step.  The seam peel strength is compared to the burst pressure because pressurizing the air channel results in the seam being challenged more in a peel mode than a shear mode. Therefore the seam peel strength, and not the shear strength, was used for comparative purposes. It is important to note that the burst test fails the seam from the inside towards the outside of the seam whereas the peel test fails the seam from the outside towards the inside of the seam. The impact of this difference, if any, is a subject of the ongoing research but it does not impact the results herein because PVC seam requirements are specified in terms of peel strength and the burst pressure is simply being correlated to this specified parameter. The specified value for the peel strength of both 0.75 and 1.00 mm (30 and 40 mil) thick PVC seams according to the PGI material specification (PGI 1997) is 2.6 N/mm (15 ppi).  The main contribution of the air-channel testing research is the development of a relationship between peel strength at room temperature (22.8ºC; 73ºF) and the burst pressure at sheet temperatures ranging from 22.8 to 46.7ºC (73 to 116ºF) as shown in Figure 2. This relationship was developed from the test results obtained during the research program and from Arrehnius modeling that allows the data to be extended to sheet temperatures below 22.8ºC and above 46.7ºC. This relationship allows field personnel to perform seam QA/QC operations without conducting destructive tests because the seam peel strength can be measured indirectly by applying air pressure to the air channel in a dual track weld. This field air channel test can be used instead of destructive seam testing, which has the advantages of NOT cutting holes in the geomembrane, geomembrane surface preparation such as grinding, and patching the resulting geomembrane. The main advantage of the peel strength/burst pressure relationship in Figure 2 is the ability to test the entire seam length instead of a 1 m coupon. This procedure coupled with the flexibility of PVC geomembranes which allows the air channel to expand (inner tube) so field personnel can visually inspect the seam as the air pressure migrates along the channel and the fact that the presence of any defect may not allow the air channel to fully expand or inflate in the vicinity of the defect, results in a excellent means for ensuring the integrity of field thermal seams in PVC geomembranes.  Some of the results from the larger study on the thermal welding of PVC geomembranes include understanding the effects of welding temperature, welding speed, and sheet temperature on seam performance. These variables were evaluated for two geomembrane thicknesses and two types of welder, i.e., hot air and wedge welders, using the results of seam peel tests (ASTM D 6392) and the new burst test. The seam test results show that welding speed has a greater impact on the measured peel strength than welding temperature. Therefore, welding personnel can increase the seam peel strength for a given sheet temperature and welding temperature simply by reducing the speed of the welder. A welding speed in the range of 0.9 to 2.1 m/min provides the best seams under the widest range of sheet temperature, geomembrane thickness, and welding temperature. Welding speeds as high as 3.1 m/min can produce good seams especially if the sheet temperature is high via sunshine and/or the welding temperature is high. The seam test results also show that a welding temperature of 315.6ºC (600ºF) is too low and a welding temperature of 482.2ºC (900ºF) is too high for this 0.75 mm (30 mil) thick PVC geomembrane. Therefore, an optimal welding temperature to initiate welding is 398.9ºC (750ºF) for this 0.75 mm (30 mil) PVC geomembrane. The test results also suggest that an optimal welding temperature might range from 454.4 to 468.3ºC (850 to 875ºF) for a welding speed of 3.1 m/min for 1.00 mm (40 mil) seams.    REFERENCES ASTM D 6392, 1999, “Standard Test Method for Determining the Geomembrane Seams Produced using Thermo-Fusion Methods”, American Society for Testing and Materials, Vol. 04.09, West Conshohocken, Pennsylvania, USA, pp. 1311-1315.  PVC Geomembrane Institute (PGI), 1997, “PVC Geomembrane Material Specification 1197”, University of Illinois, Urbana, IL, www.pvcgeomembrane.com , January 1, 1997. As of 2009, the PVC Geomembrane Institute no longer exists. The Specifications related to PVC fabricated geomembranes are now under the guidance of ASTM International . All relevant information for PVC Fabricated Geomembrane Material, Seams and Field Seam Testing has been covered by specifications developed by the D-35 Geosynthetics Committee of ASTM International. For more information call   800-OK-LINER   today!

LOW TEMPERATURE AIR CHANNEL TESTING OF THERMALLY BONDED PVC GEOMEMBRANE SEAMS Timothy D. Stark 1 Hangseok Choi 2 and Richard W. Thomas 3 A technical paper submitted for review and possible publication in the Geosynthetics International Journal November 29, 2003 1 Professor of Civil and Environmental Engrg., University of Illinois, Newmark Civil Engrg. Laboratory, 205 N. Mathews Ave., Urbana, IL, 61801-2352, (217) 333-7394; E-mail: tstark@uiuc.edu 2 Post-doctoral Research Associate of Civil and Environmental Engrg., University of Illinois, (217) 333-1773; E-mail: hchoi2@uiuc.edu 3 Technical Director, TRI/Environmental, Inc., 9063 Bee Caves Road, Austin, TX 78733-6201, USA, Telephone: 512-263-2101, Telefax: 512-263-2558; E-mail: Rthomas@tri-env.com . ABSTRACT The objective of this paper is development of a procedure for air channel testing of dual track thermal seams at low sheet temperatures and recommendations for reducing destructive testing of field PVC geomembrane seams. This objective is accomplished by developing relationships between seam peel strength and seam burst pressure for sheet temperatures ranging from 0.6 °C to 25.6 °C during field air channel testing. This paper refines the original correlation presented by Thomas et al. (2003) using data for low sheet temperatures and develops a polynomial equation that can be used to convert the sheet temperature during field air channel testing to the air channel pressure required to satisfy the specified seam peel strength instead of graphically finding the air channel pressure from an Arrhenius analysis. Thus, the proposed relationship and equation allow the seam peel strength to be determined from the field air channel testing without conducting destructive tests. KEYWORDS PVC Geomembrane, Air Channel Testing, Seams, Quality Assurance, Quality Control, Thermal Welding, Peel Strength, Burst Pressure, Low Temperature AUTHORS T. D. Stark, Professor of Civil and Environmental Engineering, 2217 Newmark Civil Engineering Laboratory, University of Illinois, 205 N. Mathews Ave., Urbana, IL 61801, USA, Telephone: 1/217-333-7394, Telefax: 1/217-333-9464; E-mail: tstark@uiuc.edu . H. Choi, Post-doctoral Research Associate of Civil and Environmental Engineering, B156 Newmark Civil Engineering Laboratory, University of Illinois, 205 N. Mathews Ave., Urbana, IL 61801, USA, Telephone: 1/217-333-1773, E-mail: hchoi2@uiuc.edu . R. W. Thomas, Technical Director, TRI/Environmental, Inc., 9063 Bee Caves Road, Austin, TX 78733-6201, USA, Telephone: 512-263-2101, Telefax: 512-263-2558, E-mail: Rthomas@tri-env.com . PUBLICATION Geosynthetics International is published by the Industrial Fabrics Association International, 1801 County Road B West, Roseville, Minnesota 55113-4061, USA, Telephone: 1/612-222-2508, Telefax: 1/612-631-9334. Geosynthetics International is registered under ISSN 1072-6349. DATES: Original manuscript received November 29, 2003 REFERENCE Stark, T. D., Choi, H., and Thomas, R. W., 2003, “Low Temperature Air Channel Testing of Thermally Bonded PVC Geomembrane Seams”, Geosynthetics International   INTRODUCTION Thermal welding has proven to be a cost-effective method of field seaming PVC geomembrane liners because PVC possesses excellent thermal welding characteristics such as a wide thermal seaming range and surface preparation/grinding is not required. The thermal welding technique allows PVC geomembranes to be constructed in cold weather when chemical seams are not applicable and utilizes prevalent QA/QC techniques. Thomas et al. (2003) show that fully automated thermal welding systems can weld PVC geomembranes as thin as 0.5 mm at temperatures as low as –8 °C. These systems allow the operator to adjust welder speed, nip-roller pressure, and welding temperature to create the best quality seam. During installation, welder speed is set according to geomembrane thickness. The welder should also be adjusted to account for large variations in ambient temperature. Depending upon the manufacturer of the welder, PVC welding temperatures vary from 315 to 480 °C. The use of thermal welding also allows common QA/QC techniques to be used for PVC geomembranes, such as air channel testing. It is important to emphasize that the amount of field seaming with PVC geomembranes is much less, as much as 80% less, than HDPE geomembranes because most of the required geomembrane seaming is performed in the factory and large panels are shipped to the site. Thomas et al. (2003) present relationships between seam peel strength and seam burst pressure at three different sheet temperatures (i.e., 22.8, 35.0, and 46.7 °C) during field air channel testing. These relationships are used to construct a correlation between the field air channel pressure required to satisfy the specified seam peel strength of 2.6 N/mm and a range of sheet temperatures during air channel testing. The correlation is extended using an Arrhenius analysis of the test results. This correlation can be used to convert the sheet temperature during field air channel testing into the air channel pressure required to satisfy the specified seam peel strength. More importantly, the flexible nature of PVC allows the inflated air channel to be visible and thus the integrity of the seam can be investigated along the entire seam length. In addition, the air channel test is challenging the peel strength along the entire length of the seam instead of a limited seam length that is used in conventional destructive tests. In this study, thirty-seven (37) sets of seam peel strength and seam burst pressure data are used in addition to the data presented by Thomas et al. (2003). The new data corresponds to low sheet temperatures, 0.6 °C to 25.6 °C, during field air channel testing. The data presented by Thomas et al. (2003) corresponds to sheet temperatures ranging from 22.8 °C to 46.7 °C. The main objective of this paper is development of a relationship between seam peel strength and burst pressure at low sheet temperatures. This data is also used to refine the correlation developed by Thomas et al. (2003), which relates the field air channel pressure required to satisfy the specified seam peel strength of 2.6 N/mm to sheet temperatures ranging from 0 °C to 60 °C.  THERMAL SEAM EVALUATION To make field thermal seams, it is necessary to melt the polymer at the sheet surface using a heat source. The heat can be transferred to the sheets to be welded from hot air or a hot wedge. A hot air welder uses an air blower that blows heated air from an electrical element between the two sheets to be bonded by melting an interface strip. A hot wedge welder generates the heat energy necessary to melt the sheets at the interface by electrical elements placed directly between two sheets. Rollers are used to drive the heating machine and to apply pressure on the heated strip of the sheets. At present, two types of PVC thermal seams are used in practice: dual track and single track seams. Both types of seams can be created with a hot air or a hot wedge and allow destructive and nondestructive testing to be carried out as soon as the seam has cooled. This rapid assessment of quality allows immediate changes to be made in the seaming process to ensure optimal productivity. This paper focuses on non-destructive air channel testing of dual track seams. The seams used in this study were created at two different locations and using two different welders. This first location is TRI/Environmental in Austin, Texas on an asphalt subgrade. The other location is Environmental Protection, Inc. (EPI) in Mancelona, Michigan. The two welders are hot air and hot wedge. The hot air machine is a Leister Twinnie Model CH6056. The hot wedge machine is a Mini-Wedge made by Plastic Welding Technologies (formerly Columbine, Inc.). The sheet temperatures range from 10 to 38 °C during thermal welding. The 0.75 and 1.00 mm thick PVC geomembranes used in the thermal seam testing were provided by Canadian General-Tower, Ltd. of Cambridge, Ontario, Canada. Both welders have a typical, pre-set nip pressure and this was maintained throughout the seaming operation. Table 1 shows the different welding conditions used. After eliminating test results corresponding to a film tearing bond (FTB) failure mode, twenty-five (25) data sets were selected from 9.2 m long thermal seams using a hot air welder and a hot wedge welding machine, which were created at TRI/Environmental. The exclusion of the FTB failure mode is recommended by Thomas et al. (2003) so the peel strength and burst pressure of the seams correspond to a similar failure mode and thus are comparable. Twelve (12) data sets from the nine thermal seams constructed by EPI at low temperature conditions are also used. A hot air welder was used to thermally weld the 0.75 mm thick PVC geomembranes. The sheet temperatures range from –3.9 °C to 2.8 °C during thermal welding. A total of 37 sets of peel strength and burst pressure data, 25 sets from the TRI/Environmental seams and 12 sets from the EPI seams, are used to develop the correlation between sheet temperature, burst pressure, and peel strength. The 37 data sets are divided into four sub-groups according to the sheet temperature at the time of the air channel test as shown in Table 1. The 37 data sets are summarized in descending order of sheet temperature during field air channel testing. Seven data sets are included in Group 1, which has sheet temperatures ranging from 24.4 °C to 25.6 °C with an average value of 25.1 °C. Seven data sets are included in Group 2, which has sheet temperatures ranging from 12.8 °C to 18.3 °C with an average value of 14.8 °C. Eleven data sets are included in Group 3, which has sheet temperatures ranging from 7.8 °C to 11.7 °C with an average value of 9.7 °C. Finally, twelve data sets are included in Group 4, which has sheet temperatures ranging from 0.6 °C to 7.2 °C with an average value of 5.3 °C. The seams were evaluated by the standard peel test at 50 mm/min at 22.8°C (ASTM D 6392, 1999) and by an air channel test developed during this project. The air channel test is performed by sealing off one end of a seam length and pressurizing the other end with compressed air. The full procedure of the air channel test is described in Thomas et al. (2003). Thomas et al. (2003) show that the air channel test fails the seam from the inside towards the outside of the seam whereas the peel test fails the seam from the outside towards the inside of the seam. This difference is not deemed significant because PVC seam requirements are specified in terms of peel strength and the burst pressure during air channel testing is simply being correlated to this specified parameter. The specified value for the peel strength of both 0.75 and 1.00 mm thick PVC seams according to the material specification available through the PVC Geomembrane Institute (2003) is 2.6 N/mm.  RELATIONSHIP BETWEEN SEAM PEEL STRENGTH AND BURST PRESSURE 3.1 Verification of previous relationships Thomas et al. (2003) present relationships between seam peel strength and seem burst pressure during air channel testing for three sheet temperatures. These relationships use the hypothesis that a correlation exists between peel strength and burst pressure because both tests involve peeling apart the seam, albeit in different directions. Figure 1 shows the Thomas et al. (2003) relationships between peel strength and burst pressure for the 72 seams welded at TRI/Environmental, which exhibit a peel failure mode (i.e., non-FTB failure mode), at three sheet temperatures (i.e., 22.8, 35.0, and 46.7°C). To be useful, this relationship should be linear and should include seams that fail in identical ways, i.e., peel versus FTB. Therefore, the non-linear data points, i.e., FTB failure mode, were omitted to develop a relationship between peel strength and burst pressure (Thomas et al. 2003). The relationship between peel strength and burst pressure can be expressed in terms of a ratio of peel strength (N/mm) to burst pressure (kPa), and the ratio is obtained from the slope of each trend line in Figure 1, using a linear regression analysis. Figure 1 shows that with an increase in sheet temperature, the ratio of peel strength to burst pressure, or slope of the trend line, increases. In other words, for a given peel strength, a lower burst pressure is expected as the sheet temperature increases. To confirm the accuracy of the relationship presented by Thomas et al. (2003) between peel strength and burst pressure at a sheet temperature of 22.8 °C (see Figure 1(a)), this ratio between peel strength and burst pressure of 0.0108 is plotted along with the Group 1 data sets in Figure 2. Group 1 data sets have sheet temperatures ranging from 24.4 °C to 25.6 °C with an average value of 25.1 °C whereas the data from Figure 1(a) corresponds to a sheet temperature of 22.8 °C. In general, the relationship between peel strength and burst pressure at a sheet temperature of 22.8 °C (i.e., the ratio of peel strength to burst pressure of 0.0108) is in agreement with the trend of the Group 1 data. The trend line with a slope of 0.0108 lies slightly below most data sets which have sheet temperature greater than 22.8 °C. One data point does not satisfy this trend, which is at 25 °C which plots below the line. The data shows that with a sheet temperature greater than 22.8 °C, the ratio of peel strength to burst pressure must be greater than 0.0108. This trend of higher sheet temperature resulting in a greater the ratio of peel strength to burst pressure is also observed in the relationships presented by Thomas et al. (2003) between the ratio of peel strength to burst pressure and the sheet temperature as shown in Figure 1. Thus, the accuracy of the relationship presented by Thomas et al. (2003) is reinforced.  3.2 Development of new relationships for low temperature In this paper, new relationships between peel strength and burst pressure for air channel testing at temperature ranging from 0.6 °C to 18.3 °C are developed to complement the prior relationships for sheet temperatures of 22.8 °C, 35.0 °C, and 46.7 °C presented by Thomas et al. (2003). Thirty (30) data sets, which are designated Groups 2, 3, and 4 in Table 1, are used to develop the relationships for low sheet temperatures. Average sheet temperatures for Group 2, 3, and 4 data sets are 14.8 °C, 9.7 °C, and 5.3 °C, respectively, as shown in Table 1. As recommended by Thomas et al. (2003), only the peel failure mode is considered in this analysis. The results of linear regression analyses for each data set are plotted in Figure 3. The solid line in Figure 3 represents the relationship between peel strength and burst pressure from the low temperature data and can be expressed in terms of a ratio of peel strength (N/mm) to burst pressure (kPa). The ratio is obtained from the slope of each trend line in Figures 3. The slopes are calculated as 0.0091, 0.0072, and 0.0063 for average sheet temperatures of 14.8 °C, 9.7 °C, and 5.3 °C, respectively. The trend lines show that a ratio of peel strength to burst pressure decreases with a decrease in sheet temperature during air channel testing. In other words, for a given peel strength, a greater burst pressure is expected as the sheet temperature decreases and the PVC geomembrane becomes stiffer. The ratios of peel strength to burst pressure from Figure 3 are summarized in Table 2 together with the ratios for sheet temperatures of 22.8 °C, 35.0 °C, and 46.7 °C presented by Thomas et al. (2003). The dashed line in Figure 3 represents the expected relationship between peel strength and burst pressure from the Arrhenius analysis performed by Thomas et al. (2003). The expected slopes are 0.0083, 0.0070, and 0.0060 for sheet temperatures of 14.8 °C, 9.7 °C, and 5.3 °C, respectively. Comparing the measured and estimated slopes at each sheet temperature, the expected slope from the Arrhenius analysis underestimates the slope obtained by a linear regression analysis. The degree of difference between the two slopes is expressed as follows: (1) Using Equation (1), the degree of difference is calculated to be 8.8%, 2.8%, and 4.8% for sheet temperatures of 14.8 °C, 9.7 °C, and 5.3 °C, respectively. Thus, the results of the Arrhenius analysis performed by Thomas et al. (2003) do not correctly represent the measured relationship between sheet temperature, burst pressure, and peel strength and thus a new relationship is presented herein.  RELATIONSHIP BETWEEN SHEET TEMPERATURE AND REQUIRED AIR CHANNEL PRESSURE It is proposed that the air channel test can be used as a field quality assurance/quality control test instead of destructive testing of PVC geomembrane seams. Therefore, it is necessary to develop a relationship between sheet temperature, burst pressure, and peel strength. This relationship allows field personnel to determine the air channel pressure that is required for a particular sheet temperature to ensure that the specified seam peel strength, e.g., 2.6 N/mm, is satisfied. Table 2 shows that the ratio of peel strength to burst pressure is a function of a sheet temperature during air channel testing. Thomas et al. (2003) use the three ratios for the three sheet temperatures (i.e., 22.8 °C, 35.0 °C, and 46.7 °C) and the specified peel strength of 2.6 N/mm to calculate the minimum air channel pressure required to achieve the specified peel strength at sheet temperatures ranging from 22.8 °C to 46.7 °C. Three data points (solid circles) in Figure 4 denoted as a measured value were obtained by dividing the specified peel strength of 2.6 N/mm by the ratios at the three sheet temperatures (i.e., 22.8 °C, 35.0 °C, and 46.7 °C). These three data points are from Thomas et al. (2003). Thomas et al. (2003) utilize Arrhenius modeling (Koerner et al. 1992, Shelton and Bright 1993) to augment these three data points and extend the applicable temperature range beyond the range of 22.8 °C to 46.7 °C used in the testing. Because it is assumed that most temperature dependent properties vary exponentially, the Arrhenius model was used to extend the measured relationship between peel strength and burst pressure to other sheet temperatures. Arrhenius modeling is typically used to determine the temperature dependence of chemical reactions, including deleterious reactions such as hydrolysis or oxidation and has been frequently used to estimate the service lifetime of geosynthetic products (Koerner et al. 1992, Shelton and Bright 1993, Risseeuw and Schmidt 1990, Salman and DiMillio 1998, Thomas 2002). The results of the Arrhenius analysis performed by Thomas et al. (2003) were used to extend the relationship between sheet temperature, burst pressure, and peel strength to sheet temperatures ranging from 0 to 22.8 °C and from 46.7 to 60.0 °C. Considering the three measured ratios for low sheet temperatures in Table 2, three data points (open circles) are added to Figure 4, which represent the air channel pressure required to satisfy the specified peel strength of 2.6 N/mm for sheet temperatures of 14.8 °C, 9.7 °C, and 5.3 °C. Instead of performing an Arrhenius analysis, all of the six slopes in Table 2 for sheet temperatures of 5.3, 9.7, 14.8, 22.8, 35.0, and 46.7 °C are used to construct the new relationship in Figure 4 between the air channel pressure required to satisfy the specified seam peel strength of 2.6 N/mm and the sheet temperature during air channel testing. The six data points correspond to the following polynomial equation: (2) It is useful to express Figure 4 and Equation (2) in English units because there is still a tendency to use English units in field welding operation. Figure 5 shows the air channel pressures (lb/in 2 ) required to satisfy the specified peel strength of 15.0 lb/in, corresponding to 2.6 N/mm in SI units, for sheet temperatures of 41.5, 49.5, 58.6, 73.0, 95.0, and 116.1 °F. The six data points correspond to the following polynomial equation in English units: (3) These equations can be used to convert a sheet temperature to the air channel pressure required to satisfy the specified seam peel strength instead of graphically estimating the required air channel pressure or performing an Arrhenius analysis. Welding personnel can simply measure a sheet temperature during air channel testing, apply the required air channel pressure calculated from Equation (2) or (3) to the air channel for 30 seconds, and if the air channel maintains this pressure without peeling, it can be assumed that the seam peel strength is greater than or equal to the specified value of 2.6 N/mm (15.0 lb/in). It is proposed that this procedure can be used instead of destructive seam testing, which has the disadvantages of cutting holes in the geomembrane, patching the resulting geomembrane, and not testing 100% of the seam. The technique proposed herein evaluates 100% of the seam length and the flexible nature of a PVC geomembrane allows the inflated seam to be visually inspected over the entire length for defects. In addition, the proposed air channel test can be performed onsite regardless of the sheet temperature.  5 EVALUATION OF RECOMMENDED RELATIONSHIP FOR AIR CHANNEL TEST This section evaluates the accuracy of the proposed relationship in Figure 4 between required air channel pressure to satisfy the specified seam peel strength (i.e., 2.6 N/mm) and sheet temperature during air channel testing. Thomas et al. (2003) performed the verification by predicting the burst pressure for the 72 seams created and tested at the three sheet temperatures during air channel testing (i.e., 22.8 °C, 35.0 °C, and 46.7 °C) and comparing the predicted values to the measured values. This verification utilized a pass/fail criterion to simulate typical QA/QC procedures. In this paper, the same verification procedure is adopted for the additional three average sheet temperatures (i.e., 14.8 °C, 9.7 °C, and 5.3 °C). Table 3 summarizes the verification procedure and the number of seams that would have failed the requirement of peel strength (i.e., 2.6 N/mm) and air channel pressure. The air channel pressure required for a peel strength of 2.6 N/mm is calculated from Figure 4 and Equation (2) at each sheet temperature. For example, two welded seams out of eleven in Group 3 with an average sheet temperature of 9.7 °C fail to satisfy the requirement of peel strength of 2.6 N/mm in standard seam testing. Requirement of air channel pressure corresponding to the specified peel strength is calculated from Equation (2) to be 361.1 kPa for a sheet temperature of 9.7 °C. This required air channel pressure is compared to the actually measured burst pressures in Group 3. Four welded seams out of eleven in Group 3 fail the air channel pressure requirement (see Table 3). Thus, more seams fail the air channel pressure requirement for each of the low sheet temperatures (i.e., 14.8 °C, 9.7 °C, and 5.3 °C) than a destructive seam peel test. Therefore, the result of the air channel test is conservative because it will classify more seams as failed than the conventional peel test. It is anticipated that the extra failures were identified because the burst test challenges the entire seam and not only a limited portion of the seam.  6 CONCLUSIONS The purpose of this study is to develop three relationships between seam peel strength and burst pressure for sheet temperatures of 14.8 °C, 9.7 °C and 5.3 °C during field air channel testing. With these relationships, the relationship presented by Thomas et al. (2003) between the required air channel pressure to satisfy the specified peel strength (i.e., 2.6 N/mm) and the sheet temperature during air channel testing is refined and extended to a sheet temperature of 5.3 °C. The following conclusions are based on the data and interpretation presented in this paper. The ratios of peel strength to burst pressure are measured to be 0.0091, 0.0072, and 0.0063 for average sheet temperatures of 14.8 °C, 9.7 °C, and 5.3 °C, respectively. The expected ratios of peel strength to burst pressure from the Arrhenius analysis presented by Thomas et al. (2003) are 0.0083, 0.0070, and 0.0060 for these sheet temperatures. Comparing these ratios at each sheet temperature indicates that the Arrhenius analysis does not predict the measured relationship between peel strength, burst pressure, and sheet temperature at the low sheet temperatures, 5.3 °C to 14.8 °C. The Arrhenius analysis presented by Thomas et al. (2003) slightly overestimates the air channel pressure required to satisfy the specified seam peel strength of 2.6 N/mm at low sheet temperatures. The error is measured to be 8.8%, 2.8%, and 4.8% for sheet temperatures of 14.8 °C, 9.7 °C, and 5.3 °C, respectively. The data presented herein is used to develop a polynomial equation to refine the relationship presented by Thomas et al. (2003) for a range of sheet temperature of 5.3 °C to 46.7 °C. The equation can be used to convert a sheet temperature during field air channel testing to the air channel pressure required to satisfy the specified seam peel strength of 2.6 N/mm instead of graphically finding the required air channel pressure or performing an Arrhenius analysis. Verification of the proposed equation was performed by comparing the predicted value to the measured value along with a pass/fail criterion to simulate typical QA/QC procedures. Equal or more seams fail the requirement of air channel pressure compared to the requirement of peel strength. Therefore, the air channel test is conservative, and it will classify more seams as failed than the conventional peel test. The proposed relationship in this paper will allow field personnel to perform seam QA/QC operations without conducting destructive tests. This relationship, see Figure 4 and/or Equation (2) (and Figure 5 and/or Equation (3) in English units), allows the seam peel strength to be measured indirectly by applying air pressure to the air channel in a dual track weld, which reduces if not eliminates the need for destructive testing. This coupled with the visibility of an inflated air channel provides assurance of the integrity of the seam.  ACKNOWLEDGMENTS Colorado Lining of Denver, Colorado and Environmental Protection, Inc. of Mancelona, Michigan fabricated the thermal seams used in this study. The support of these organizations and the PVC Geomembrane Institute is gratefully acknowledged.  REFERENCES ASTM D 6392, 1999, “ Standard Test Method for Determining the Geomembrane Seams Produced using Thermo-Fusion Methods ”, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA. Geosynthetic Research Institute (GRI), 1994, “Standard Test Method GM-6: Testing of Geomembrane Materials”, Drexel University, Philadelphia, PA, July. Koerner, R.M., Lord, A., and Hsuan, Y.H., 1992, “Arrhenius Modeling to Predict Geosynthetic Degradation”, Geotextiles and Geomembranes, No. 11, pp. 151-183. Koerner, R.M., 1998. Designing with Geosynthetics , 4th Edition, Prentice Hall, Upper Saddle River, New Jersey, 761 p. PVC Geomembrane Institute (PGI), 2003, “PVC Geomembrane Material Specification 1103”, University of Illinois, Urbana, IL. Risseeuw, P. and Schmidt, H.M., 1990, “Hydrolysis of HT Polyester Yarn in Water at Moderate Temperatures”, Proceedings of the 4 th International Conference on Geotextiles, Geomembranes, and Related Products, The Hague, Netherlands, pp. 691-696. Rollin, A.L., and Fayoux, D., 1991, “Geomembrane Seaming Technique”, Geomembranes: Identification and Performing Testing, Rollin, A.L. and Rigo, J-M, eds., RILEM Report 4, pp. 59-79. Salman, A., Elias, V. and DiMillio, A., 1998, “The Effect of Oxygen Pressure, Temperature and Manufacturing Processes on Laboratory Degradation of Polypropylene Geosynthetics”, Proceedings of the Sixth International Conference on Geosynthetics, Atlanta, pp. 683-690. Shelton, W.S. and Bright, D.G., 1993, “Using the Arrhenius Equation and Rate Expressions to Predict the Long-Term Behavior of Geosynthetic Polymers”, Proceedings of the Geosynthetics ’93 Conference, Vancouver, pp. 789-802. Thomas, R.W., 2002, “Thermal Oxidation of a Polypropylene Geotextile used in a Geosynthetic Clay Liner”, Proceedings of the International Symposium IS Nuremberg 2002, Nuremberg, Germany, pp. 87-96. Thomas, R.W. and Stark, T.D., 2003, “Reduction of Destructive Tests for PVC Seams”, Geotechnical Fabric Report, IFAI, March, pp. 26-29. Thomas, R.W., Stark, T.D., and Choi, H., 2003, “Air Channel Testing of Thermally Bonded PVC Geomembrane Seams”, Geosynthetics International, Vol. 10, No. 2, pp. (in press).  LOW TEMPERATURE AIR CHANNEL TESTING OF THERMALLY BONDED PVC GEOMEMBRANE SEAMS Timothy D. Stark, Hangseok Choi, and Richard W. Thomas Table 1. PVC Seam Testing Data Summary. Group Test ID Burst temp. (°C) Average burst temp. (°C) Burst pressure (kPa) Peel strength (N/mm) PVC thick-ness (mm) Welding details Data source Welder type Welder temp. (°C) Welder speed (m/min) Sheet temp. (°C) 1 1 25.6 25.1 482.3 5.60 1.00 H/A 390 1.9 1.7 EPI 2 25.6 172.3 3.00 1.00 H/A 390 2.8 1.7 EPI 3 25.0 482.3 5.95 1.00 H/A 320 1.1 -3.9 EPI 4 25.0 137.8 1.23 1.00 H/A 320 1.9 -2.2 EPI 5 25.0 34.5 0.70 1.00 H/A 320 2.8 -1.1 EPI 6 25.0 537.4 5.95 1.00 H/A 482 2.8 2.8 EPI 7 24.4 551.2 7.35 1.00 H/A 482 1.9 2.8 EPI 2 8 18.3 14.8 861.3 8.05 1.00 H/W 399 0.9 15.6 TRI/Envir. 9 15.6 82.7 0.88 1.00 H/A 320 1.9 -2.2 EPI 10 15.6 20.7 0.35 1.00 H/A 320 2.8 -1.1 EPI 11 14.4 585.7 4.20 0.75 H/W 371 3.0 32.2 TRI/Envir. 12 13.9 592.5 5.78 1.00 H/A 390 1.9 1.7 EPI 13 13.3 689.0 6.48 1.00 H/A 482 2.8 2.8 EPI 14 12.8 757.9 7.18 1.00 H/A 482 1.9 2.8 TRI/Envir. 3 15 11.7 9.7 275.6 2.63 0.75 H/A 360 3.0 26.7 TRI/Envir. 16 11.1 516.8 4.73 0.75 H/A 390 2.1 10.0 TRI/Envir. 17 11.1 172.3 1.58 0.75 H/A 320 3.0 26.7 TRI/Envir. 18 10.0 413.4 5.08 0.75 H/A 320 2.1 26.7 TRI/Envir. 19 10.0 482.3 3.15 0.75 H/A 360 2.1 26.7 TRI/Envir. 20 9.4 275.6 2.28 1.00 H/A 390 2.8 1.7 EPI 21 9.4 530.5 3.33 1.00 H/A 360 2.1 32.2 TRI/Envir. 22 8.9 702.8 4.38 0.75 H/W 427 5.8 32.2 TRI/Envir. 23 8.9 268.7 3.50 1.00 H/W 399 3.0 37.8 TRI/Envir. 24 7.8 475.4 2.98 0.75 H/W 427 5.8 10.0 TRI/Envir. 25 7.8 757.9 4.20 0.75 H/W 427 3.0 32.2 TRI/Envir. 4 26 7.2 5.3 413.4 2.98 0.75 H/A 390 3.0 10.0 TRI/Envir. 27 6.7 723.5 3.85 0.75 H/W 482 3.0 32.2 TRI/Envir. 28 6.1 254.9 2.80 0.75 H/A 390 3.0 26.7 TRI/Envir. 29 6.1 620.1 5.08 1.00 H/A 390 2.1 15.6 TRI/Envir. 30 6.1 213.6 1.75 1.00 H/A 360 3.0 32.2 TRI/Envir. 31 6.1 551.2 3.33 1.00 H/A 440 3.0 32.2 TRI/Envir. 32 5.6 254.9 2.28 0.75 H/A 360 3.0 10.0 TRI/Envir. 33 5.0 261.8 3.15 1.00 H/A 390 3.0 15.6 TRI/Envir. 34 5.0 475.4 2.45 1.00 H/W 482 3.0 15.6 TRI/Envir. 35 4.4 551.2 2.63 1.00 H/A 390 3.0 32.2 TRI/Envir. 36 4.4 620.1 2.80 1.00 H/W 441 3.0 37.8 TRI/Envir. 37 0.6 551.2 3.68 0.75 H/W 371 5.8 32.2 TRI/Envir. Note: Welder type H/A = Hot air welder and H/W = Hot wedge welder Table 2. Relationship between peel strength and burst pressure. Sheet temperature during burst test ( o C)   Measured value by regression Expected value by Arrhenius analysis (Thomas et al. 2003) 5.3 0.0063 0.0060 9.7 0.0072 0.0070 14.8 0.0091 0.0083 22.8 0.0108* - 35.0 0.0163* - 46.7 0.0215* - *: Data from Thomas et al. (2003) Table 3. Number of failures predicted using the specified seam peel strength of 2.6 N/mm. Sheet temperature during air channel test ( o C) Data set ID (Number of data sets) Peel strength Air channel pressure Requirement (N/mm) Failure number Failure rate (%) Requirement (kPa) Failure number Failure rate (%) 14.8 Group 2 (7) 2.6 2 28.6 285.7 2 28.6 9.7 Group 3 (11) 2.6 2 18.2 361.1 4 36.4 5.3 Group 4 (12) 2.6 3 25.0 412.7 4 33.3 For more information call   800-OK-LINER   today!

THERMALLY BONDED PVC SEAMS Phase II - The Effects of Welding Speed, Welding Temperature, and Sheet Temperature on the Peel Strength and Burst Strength of 30 mil and 40 mil PVC Double-Track Fusion Seams Author:  Richard W. Thomas, TRI/Environmental, Inc. SUMMARY Test welds were made with two types of welding machines, at two different sheet temperatures, on two thicknesses of sheet, at three set point temperatures and at three speeds.  The 72 seams were evaluated by the peel test at room temperature and by burst tests performed at three different temperatures. The results showed the importance of welder set point and speed.  The results also showed that there is a strong relationship between peel and burst and that a non-destructive burst test, performed in the field, could be used to ensure the strength of installed seams.   INTRODUCTION The objective of Phase II was to learn more about the thermal welding process of PVC geomembranes and to develop a window of appropriate conditions for welding.  More specifically, a wider range of welder temperatures and speeds were to be evaluated along with the effects of sheet temperature.  There was also interest to further explore the relationship between bursting the seams from the air channel out and peeling the seams from the outside in.  If this relationship is known, one can eliminate the practice of cutting holes in seams to determine seam strength.   SEAM PREPARATION The 72 prepared seams were made in a single day in Austin, Texas on an asphalt subgrade.  There were two crews, one using a hot air welder and the other a hot wedge welding machine.  The hot air machine was the same one used in Phase I, namely a Leister Twinnie Model CH6056.  The hot wedge machine was a “Mini-Wedge” made by Plastic Welding Technologies (formerly Columbine). The crews each used three welder set points and three welder speeds based on their “normal” conditions, and their experience.  Each crew made a set of 30 mil and 40 mil seams in the shade in the morning. Then, they each made an identical set of seams in the sun in the afternoon.  The sheet temperatures range from 50 to 100°F.  The temperature was monitored by a thermocouple attached to the sheet.  The effect of nip roller pressure on seaming was not examined during this study.  Both welders had a typical pressure pre-set and this was maintained throughout the seaming operation.  The following table shows the different conditions used.     THERMALLY BONDED PVC SEAMS Phase II - The Effects of Welding Speed, Welding Temperature, and Sheet Temperature on the Peel Strength and Burst Strength of 30 mil and 40 mil PVC Double-Track Fusion Seams Author:  Richard W. Thomas, TRI/Environmental, Inc. SUMMARY: Test welds were made with two types of welding machines, at two different sheet temperatures, on two thicknesses of sheet, at three set point temperatures and at three speeds.  The 72 seams were evaluated by the peel test at room temperature and by burst tests performed at three different temperatures. The results showed the importance of welder set point and speed.  The results also showed that there is a strong relationship between peel and burst and that a non-destructive burst test, performed in the field, could be used to ensure the strength of installed seams.   INTRODUCTION The objective of Phase II was to learn more about the thermal welding process of PVC geomembranes and to develop a window of appropriate conditions for welding.  More specifically, a wider range of welder temperatures and speeds were to be evaluated along with the effects of sheet temperature.  There was also interest to further explore the relationship between bursting the seams from the air channel out and peeling the seams from the outside in.  If this relationship is known, one can eliminate the practice of cutting holes in seams to determine seam strength.   SEAM PREPARATION The 72 prepared seams were made in a single day in Austin, Texas on an asphalt subgrade.  There were two crews, one using a hot air welder and the other a hot wedge welding machine.  The hot air machine was the same one used in Phase I, namely a Leister Twinnie Model CH6056.  The hot wedge machine was a “Mini-Wedge” made by Plastic Welding Technologies (formerly Columbine). The crews each used three welder set points and three welder speeds based on their “normal” conditions, and their experience.  Each crew made a set of 30 mil and 40 mil seams in the shade in the morning. Then, they each made an identical set of seams in the sun in the afternoon.  The sheet temperatures range from 50 to 100°F.  The temperature was monitored by a thermocouple attached to the sheet.  The effect of nip roller pressure on seaming was not examined during this study.  Both welders had a typical pressure pre-set and this was maintained throughout the seaming operation.  The following table shows the different conditions used.                                                     Table 1 - Seaming Parameters Used     Welder Type              Sheet      Thickness (mil)               Sheet     Temperature (°F)             Welder       Speed (ft/min)              Welder     Temperature (°F)          Hot Air                 30                 40                50,80               60, 90             4, 7, 10             4, 7, 10         608, 680, 734         680, 734, 824      Hot Wedge                 30                 40               50, 90              60, 100            3, 10, 19            3, 10, 19         700, 800, 900         750, 825, 900   SEAM EVALUATION The seams were evaluated by the standard peel test at 20 in/min at 73°F and by a burst test developed for this project.  The burst test was performed by sealing off one end of a seam length and pressurizing the other end with compressed air.  The basic procedure was to select a starting pressure, hold there for 30 seconds, then ramp 5 psi at a time, holding for 30 seconds for each 5 psi step.  The 5 psi was applied in a 5 second time period.  This went on until failure occurred.  Most of the failures were peels that occurred during the 30 second soak.  However, there were some seams that burst during a 5 psi step. The burst test done at room temperature was done on a 6 feet length of seam.  More seam length was useful to determine the relationship between peel and burst.  The burst test was also performed at two higher temperatures.  These tests were performed in a constant temperature room set for 100°F and 120 °F.  The actual sheet temperatures were 95°F and 116°F.  These elevated temperature tests were performed on 4 feet lengths of seam. The seam was clamped in the center, then both 2 feet halves tested to produce duplicate results.  None of the individual test strips that were pressurized were also peel tested. All tests were performed on as-made strips from the original 30 ft length.   RESULTS The results from testing all of the 72 seams for peel strength and for burst strength at three temperatures are given in Tables 2-9.  The two values listed for peel strength are the two weld tracks. The burst values at room temperature were done once while the higher temperature bursts were done in duplicate. The values presented are the averages of the two burst tests.  Typically, the two results were within 5 psi of one another.  Also, in the hot air seams (“A” series) the numbering is not consistent from 1 to 36, as it is in the hot wedge seams (“W” series). There were two instances where a particular seam burst at a very low value due to specific weak spot in the seam.  They occurred at the temperatures of 800° F and 900° F, and looked like “burn through”.  This is the type of thing that will occur in the field since 100% of the seams will be tested.  In the field, these weak spots would be locations for a patch. Otherwise, the burst behavior was as one might predict.  As more heat got into the seam, the peel  and burst values increased.  Of course, more heat gets into a seam from higher set point temperatures, slower speeds, or an increased sheet temperature.  Experienced welders will often adjust their welding speed to the ambient conditions.  For example, they might increase their speed during the day as the temperature gets warmer.  Or, if clouds suddenly appear, they may slow down because the sheet is cooler in the shade. The strongest seams exceeded the pressure gauge used.  It had a scale up to 120 psi, so above this pressure, the operator made an estimate of the pressure.  The pointer still went higher, but there was no scale to read above 120 psi. Effects of Welder Speed, Welder Temperature, and Sheet Temperature on Peel Strength Since there are so many sets of results, a series of bar graphs was prepared to examine trends in the results.  Figure 1 shows the peel strength results for all the seams made by the Hot Air Welder.  The temperature in the header was the sheet temperature when the seams were made. There are a number of observations one can see in these plots: The effect of speed seems to be greater than the effect of temperature.  This suggests that one should be able to increase the strength under a given set of conditions by slowing down the welder. A speed of 10 ft/min produced seams significantly weaker than those made at 7 ft/min under the same conditions, within the temperature range studied.  In fact, of the 4 seams that did not meet 15 ppi in strength, all were made at a speed of 10 ft/min.  Two other seams made at this speed had peel strengths of exactly 15 ppi. The effect of sheet temperature was greatest at the lowest welder temperature for 30 mil sheet.  This suggests that a temperature of 608 °F is too low for good welds. All these seams made at 734 °F have similar strengths as a function of speed and welder temperature.  This suggests that a temperature near this one (like 750 °F) would be a good starting point for setting up a welding operation. The upper temperature of 824° F produced excellent seams at 4 and 7 ft/min and good seams at 10 ft/min.  This suggests that the temperature can be raised further to provide more heat for a better seam at 10 ft/min.  It is likely that a welder temperature of 850 or 875 °F would produce higher strengths at 10 ft/min.  Of course, burn through and acidic corrosion increase at high temperatures also. Seams that do not peel are obtained at peel strengths around 40 ppi.   The observations one can make about these results include: The 30 mil seams had a maximum peel strength around 25 ppi. Also, the difference in strength with different conditions was small.  This seems to suggest that there is a ceiling on peel strength in this case.  The results for seams welded at 80°F show a difference of only 6 ppi between the highest and lowest strength.  This is odd, in light of the burst test results, which will be discussed in the next section. As before, the effect of speed is greater than the effect of temperature.  A speed of 19 ft/min is obviously too fast for 40 mil but made reasonable 30 mil seams. The effect of ambient temperature was largest in the 40 mil seams, except for the slowest speed.  The temperature difference was also the greatest (40°F).  These results also suggest that good seams can be made at a set point temperature as high as 900° F, but again, the increased possibility of “burn-through” and corrosion increase as the temperature is increased. The only acceptable 40 mil seams made in cooler temperatures were at the slowest speed of 3 ft/min.  This might involve the sheet’s contact with the wedge surface.  A cooler and stiffer sheet may not contact as well under the roller pressure used.   Effects of Welder Speed, Welder Temperature, and Sheet Temperature on Burst Strength The burst test is essentially a peel test from the air channel out.  It should be sensitive to the same conditions as the peel test but may be more indicative of seam quality since it will find the weakest area of the seam.  These results are similar to the peel strength results. Speed has a more dramatic affect than welder temperature, and there is just a small increase in strength when the sheet temperature is changed from 50° F to 80°F. Also, the burst strength of the 40 mil seams is significantly higher than the burst for 30 mil seams.  These results show some significant differences in burst strength for 30 mil seams that did not appear in the peel test results.  Otherwise, the same trends were seen. Speed has the greatest effect and weaker seams are made at cooler temperatures at speeds of 10 ft/min or more. One of the most interesting findings from the last two sections involve the sets of 30 mil seams. Notice that the seams made by the wedge had maximum peel strengths around 25 ppi while the hot air seams had maximum peel strengths of 45 ppi.  Conversely, the hot air seams showed burst strengths less than 80 psi while the wedge seams had maximum burst strengths over 100 psi. This seems to indicate that bursting from the inside out is not the same as peeling from the outside in. If there is a difference, it must be in the initiation of peeling. It looks like the inside of the wedge seams is stronger than the outside. And, the opposite seems true for the hot air seams. Their outsides seem stronger than the insides. More information should be obtained by exploring the relationship between the peel strength and the burst strength.   The Relationship Between Peel Strength and Burst Strength It seems reasonable that there would be a strong relationship between these two properties because they both involve peeling the seam apart, assuming the seam peels.  This section will look at this relationship for all of the seams prepared.  The relationship between peel strength and burst strength for 30 mil seams made with hot air is seen in Figure 5.  This plot uses the lowest peel value of the two tracks and the average burst value.   The value of the slope noted on the graph is the slope after the four points furthest from the original line were removed. The purpose of removing these points is to get a better value for the slope of the line.  Notice that there was very good linear correlation as displayed by the r2 value.  A correlation of 1.0 would indicate a perfect fit.   This time, three points were omitted to better define the line. The selection of these point is largely arbitrary. However, this part of the analysis will give an estimate of the Burst Strength vs. Peel Strength relationship. It will still need to be proven that the relationship is correct. The relationship for the hot wedge welder are somewhat different then the ones just seen.   This plot clearly shows that these seams reach a maximum peel strength even though the burst strength indicates stronger seams. Therefore, only five points were used to define the relationship for this set of seams. Similar behavior is seen in Figure 8, which shows the plot for the 40 mil, hot wedge seams.    Once again, it is observed that a maximum peel strength has been reached. Both of the plots for the wedge welder indicate that the seams are stronger from the air-channel out than from the outside towards the air channel. It is not known at this time if this is specific to the particular welder used or if its a general phenomenon with wedge welders. It is possible that the wedge itself might have a slightly different profile at the air channel than at the outside edges.   If one takes an average of the four slopes, the overall slope is 0.448 ppi/psi.  Alternatively, one can combine all the data for a general line.  Figure 9 shows the combined results before and after the “outliers” are removed.   Relationship Between Burst Strength and Sheet Temperature It is well known that plastics soften with increasing temperature. Not only is the tensile strength lowered, but increased temperature also results in lower peel strengths and lower burst strengths. Since the burst test might be used as a field test one day, it is necessary to know the relationship between burst strength and temperature. Ultimately, one would have to know what burst strength is required at any given temperature to ensure a particular peel strength. This is why a good relationship between peel and burst must be developed. The same exercise that generated the plots in Figure 9 was done for the seams burst at 95°F and those burst at 116°F. The results are shown in Figures 10 and 11. This provides a good estimate for the relationship between room temperature peel strength and the burst strength at different temperatures.   Before and After Removal of “Outliers” Since the room temperature peel strength is common in Figures 9-11, a single plot can be prepared showing the relationships between burst strength and peel strength at all three temperatures. This is seen in Figure 12.   The slopes of the lines are rates of change which makes it appropriate to use the Arrhenius model to determine the temperature dependence of this process.  The first step in this process is to prepare a plot of ln Rate vs. 1/T, where T is the absolute temperature.  This is shown in Figure 13.   This line can now be used to prepare a plot of the required burst strength to equal a given peel strength at any temperature. For example, Figure 14 shows the minimum burst strength required to ensure a 15 ppi peel strength.   So, if this model is correct, one could simply apply the required burst pressure and if the seam holds, then the peel strength was over 15 ppi. This could be done in place of destructive seam testing.  It has the advantages of no cut holes, no patches, and 100% testing.  It also can be done onsite, regardless of the temperature.  Similar curves can easily be prepared for other peel strength values.  COMMENT:   EPI is continuing research on burst strength at lower sheet temperatures. As more points of data are developed, the relationship between burst strength and sheet temperature will likely be a straight line graph.   Evaluation of the Model Now that the model has been developed, it can be checked by seeing if all the 72 seams burst at three temperatures fit the model.  Using the pass/fail criteria defined by the model, all the seams will be evaluated for pass/fail.  The results are shown in tabular form in Tables 10 - 13. Table 10 - Pass/Fail Results for 30 mil Hot Air Seams Seam Number     Actual Peel P/F 15 ppi        Burst Requirement at 73°F = 31 psi    Burst Req. At    95°F = 23 psi    Burst Req. At   116°F = 17 psi A1 P P P P A2 P P P P A3 F (12 ppi) F (20 psi) F (15 psi) F (10 psi) A4 P P P P A5 P P P P A6 F (13 ppi) F (30 psi) F (15 psi) F (15 psi) A7 P P P P A8 P P P P A9 P (17 ppi) P (33 PSI) F (20 psi) P (19.5) A10 P P P P A11 P P P P A12 F (9 ppi) F (20 psi) F (15 psi) F (10 psi) A13 P P P P A14 P P P P A15 P P P P A16 P P P P A17 P P P P A18 P (16 ppi) F (30 psi) P P Failures 3 4 4 3 Each of the three seams less than 15 ppi peel also failed to meet the appropriate burst requirement. Two seams (A9 and A18) had peel strengths greater than 15 ppi but failed the burst requirement at one temperature. Notice that both of these seams were near the 15 ppi requirement. Seams that fail to meet the burst requirement but meet the peel requirement are considered false negatives.   Table 11 - Pass/Fail Results for 40 mil Hot Air Seams        Seam Number      Actual Peel P/F 15 ppi       Burst Requirement      at 73°F = 31 psi    Burst Req. At    95°F = 23 psi    Burst Req. At   116°F = 17 psi A28 P P P P A29 P P P P A30 F (10 PPI) F (25 PSI) P (25 PSI) F (15 PSI) A31 P P P P A32 P P P P A33 P P P P A34 P P P P A35 P P P P A36 P P P P A37 P P P P A38 P P P P A39 P (15 PPI) P (35 PSI) F (19 PSI) F (14.5 PSI) A40 P P P P A41 P P P P A42 P P P P A43 P P P P A44 P P P P A45 P P P P Failures 1 1 1 2 his time, the one seam that was less than 15 ppi in peel (A30) passed one of the three burst requirements.  This would be considered a false positive.  There was  also one false negative (A39) which failed the burst requirement at 116°F.  So, for this set, one seam had a false positive and 1 seam had two false negative values. Table 12 - Pass/Fail Results for 30 mil Hot Wedge Seams        Seam Number       Actual Peel P/F 15 ppi       Burst Requirement      at 73°F = 31 psi    Burst Req. At    95°F = 23 psi    Burst Req. At   116°F = 17 psi W1 P P P P W2 P (18 PPI) F (25 PSI) P (31 PSI) P (22.5 PSI) W3 F (11 PPI) F (25 PSI)   F (15 PSI) F (10 PSI) W4 P P P P W5 P P P P W6 P P P P W7 P P P P W8 P P P P W9 P P P P W10 P P P P W11 P P P P W12 P P P P W13 P P P P W14 P P P P W15 P P P P W16 P P P P W17 P P P P W18 P P P P Failures 1 2 1 1 This set showed one false negative (W2).  Notice that the burst value at 73°F (25 psi) was actually lower than the peel value at 95°F (31 psi).  This indicates that the portion of the seam tested at 73°F had a weak spot that was captured by the burst test.  Interestingly, this was the set that had the fewest results used to construct the model. Table 13 - Pass/Fail Results for 40 mil Hot Wedge Seams        Seam Number       Actual Peel P/F 15 ppi     Burst Requirement      at 73°F = 31 psi    Burst Req. At    95°F = 23 psi    Burst Req. At   116°F = 17 psi W19 P P P P W20 F (6 PPI) F (10 PSI) F (12.5 PSI) F (8 PSI) W21 No Bond No Bond No Bond No Bond W22 P P P P W23 F (6 PPI) F (10 PSI) F (7.5 PSI) F (5 PSI) W24 No Bond No Bond No Bond No Bond W25 P P P P W26 F (14 PPI) F (15 PSI) F (15 PSI) F (10 PSI) W27 No Bond No Bond No Bond No Bond W28 P P P P W29 P (20 PPI) P (35 PSI) F (22.5 PSI) F (12.5 PSI) W30 F (5 PPI) F (7 PSI) F (3.5 PSI) F (5 PSI) W31 P P P P W32 P P P P W33 F (6 PPI) F (15 PSI) F (9 PSI) F (5 PSI) W34 P P P P W35 P P P P W36 F (10 PPI) F (23 PSI) F (15 PSI) F (10 PSI) Failures 6 6 7 7 One seam showed two false negative values (W29).  There is little to be said about W29.  It easily passed the peel test, barely passed the burst test at 73° and failed the burst test at 95°F and 116°F. Table 14 shows a summary of all the false positives and false negatives. Table 14 - Summary of Inconsistent Results           Seam Number                  Actual Peel P/F 15 ppi      Burst Requirement     at 73°F = 31 psi   Burst Req. At   95°F = 23 psi     Burst Req. At    116°F = 17 psi A9 P (17 ppi) P (33 psi) F (20 psi) P (19.5 psi) A18 P (16 ppi) F (30 psi) P (27.5 psi) P (20 psi) A30 F (10 ppi) F (25 psi) P (25 psi) F (15 psi) A39 P (15 ppi) P (35 psi) F (18 psi) F (14 psi) W2 P (18 ppi)) F (25 psi) P (31 psi) P (22.5 psi) W29 P (20 ppi) P (35 psi) F (22.5 psi) F (12.5 psi) False Positives 1 0 1 0 False Negatives 7 in 5 seams 2 3 2 This summary shows that 5 seams had false negatives while one had a false positive.  One can also consider how many total seams would have failed for each of the different pass/fail criteria.  Table 15 shows this information.   Table 15 - Numbers of Failures for Each Different Requirement Requirement    Number of Failures    False Positives       False Negatives Peel Strength of 15 ppi Burst Str. at 73°Fof 31 psi Burst Str. at 95°F of 23 psi Burst Str. at 116°F of 17 psi 11 13 13 13 1 Seam Total 0 1 0 7 Total in 5 seams 2 3 2 This table shows that all the burst tests would have given two additional seams that did not meet a requirement. That suggests that the burst test is conservative; it will error on the side of more failures. One thing worth mentioning is that 3 of the five seams with false negatives had peel values of 15 or 16 ppi. That means that sometimes the seams were very close to the pass/fail boundary. One should expect differences whenever the values are close to a boundary. CONCLUSIONS This two part study contributed to the further knowledge about heat seaming PVC in a variety of ways. First, the effects of set-point temperature, welder speed and sheet temperature were evaluated for two thickness of sheet made by both hot air and hot wedge welders. The results showed that speed was a greater factor than the other variables and temperatures around 600°F are too cool and a temperature of 900°F is likely too high, due to sheet decomposition, burn-through and corrosion. That puts 750°F right in the center, which appears to be a good starting set-point for welding.  As far as welding speeds, the results suggested that a range of 3 to 7 ft/min gives the best seams under the widest variation of conditions. Speeds of 10 ft/min and maybe a little higher can make good seams, especially if there is significant heat in the sheet through sunshine and/or welder set-point. The different sheet temperatures studied showed some differences but the range of temperatures studied was relatively small.  The original research plan called for an additional higher sheet temperature, but this was not possible on the February day chosen to make all the seams. It is clear, however, that as the sheet heats up, the speed may be increased or the set-point lowered without changing the quality of the resulting seams. The largest contribution of this research was the development of the relationship between peel strength at room temperature (standard laboratory environment) and the burst strength at any temperature from 40°F to 140°F. This has resulted in a brand new way to perform construction quality control and quality assurance. It is now possible to measure the peel strength of PVC seams indirectly and non-destructively by applying air pressure to the air channel in a double track seam. This means it is no longer necessary to cut holes in seams to measure their strength.  Additionally, 100% seam testing can be done, which is something no other geomembrane can do. Certainly, it is more valuable to know that 500 ft of seams meet the strength requirement rather than a 1 yard coupon removed from the same 500 ft Some further work to validate this relationship would be valuable. Results so far show the model is good, but some independently made seams tested at a variety of sheet temperatures would strengthen the model.  Seams burst at lower temperatures (50°F) and higher temperatures (135°F) would be particularly valuable to make sure that the model holds at temperatures away from those used to design the model.   For more information call   800-OK-LINER  today!

ASTM D7177 - Air Channel Testing PVC Geomembrane Thermal Welds Years of R&D by EPI have resulted in a NEW Testing Method for PVC geomembranes. In June 2005 a new Air Channel Testing Specification was adopted by ASTM. ASTM D 7177-05 Standard Specification for Air Channel Evaluation of Polyvinyl Chloride (PVC) Dual Track Seamed Geomembranes.  EPI first began hot wedge welding PVC in 1990 and Dual Track Thermal Welding of PVC field seams in 1992.  After years of experimenting, field trials, equipment modifications & improvements, and numerous consultations with equipment manufacturers, EPI made a wholesale change to hot air welders for welding PVC. We received considerable help from Bruno Zurmuhle of Leister and J.B. Budny from Heely-Brown Company .  Developing the procedures for using hot air welders on thinner, more flexible PVC materials was a challenging task. But the problems were conquered and technicians began to develop the skills to professionally weld PVC geomembrane in any thickness in almost any weather condition. What evolved from these problem solving sessions and the reams of test data developed, was the absolute belief that the air channel test could be used to verify the physical strength of a PVC weld. In 2001, TRI Environmental agreed to do some testing and research on PVC thermally welded seams. Rick Thomas also became intrigued that PVC seams could be tested for peel strength using an air channel test. In 2002 burst testing research was initiated at TRI on hot air and hot wedge welded PVC seams in 30 and 40 mil PVC. The result of this testing and other research was a graph of pressure vs. sheet temperature for air channel testing PVC geomembranes that verifies a minimum of 15 lb/in peel strength for the full length of the test section. This temperature and pressure correlation is necessary to correct the test to the same conditions required in the laboratory when peel testing flexible PVC seams (72 degrees Fahrenheit). In 2002 Mark Wolschon, Quality Control Manager of EPI, introduced to ASTM the idea of a standard air channel test for PVC. ASTM Committee D35 established an ASTM Task Group to develop a new standard.  After over two years of extensive discussions, ASTM D7177 Standard Specification for Air Channel Evaluation of Polyvinyl Chloride (PVC) Dual Track Seamed Geomembranes was adopted by ASTM in 2005.  ASTM D7177   is now the recognized standard for air channel testing of PVC field seams. This test method does not apply for HDPE welds due to the rigid nature of that material.   Simply stated, poorly made thermal welds peel open when subjected to air channel testing according to ASTM D7177 . This test stresses the entire length of the seam, so any weak areas, no matter how small, will be immediately located. Any failing seam should be replaced. EPI has also experienced welds with passing destructive samples removed, failing an air channel test in another area of the same seam. Any seam that fails must be rewelded to insure the customer receives the best possible product. Sheet Temperature ºC Air Pressure KPa Sheet Temperature ºF Air Pressure PSI Hold Time 4.5 345 40 50 30 Seconds 7 324 45 47 30 Seconds 10 310 50 45 30 Seconds 13 290 55 42 30 Seconds 15.5 276 60 40 30 Seconds 18 262 65 38 30 Seconds 21 241 70 35 30 Seconds 24 228 75 33 30 Seconds 26.5 214 80 31 30 Seconds 29.5 193 85 28 30 Seconds 32 179 90 26 30 Seconds 35 165 95 24 30 Seconds 37.5 152 100 22 30 Seconds 40.5 138 105 20 30 Seconds 43.5 131 110 19 30 Seconds 46 117 115 17 30 Seconds 48.5 103 120 15 30 Seconds 51.5 90 125 13 30 Seconds 54.5 83 >130 12 30 Seconds The chart above lists the air pressure required to verify 15 lb/in Seam Peel Strength for PVC dual track welds at various sheet temperatures, per ASTM D7177 .   Using a hot air welder with a dual track nozzle, EPI's installation crew can weld seams leaving an air channel  between the welds. EPI has the expertise to complete air channel testing of dual track thermal welded PVC field seams. Testing is accomplished by sealing both ends of the seam and introducing air pressure into the channel between the two parallel welds. The seam is pressurized to the minimum required pressure to verify the minimum of 15 lb/in peel strength, based on the ambient sheet temperature of the PVC geomembrane material.  The pressure is monitored to insure weld integrity throughout the seam.  As a matter of practice, a passing seam will hold pressure immediately, whereas a poor seam will continue to loose pressure as the weld gradually peels open. The minimum pressure is determined according to the graph and chart shown below. Air channel testing a dual track weld is an improved non-destructive testing method for field seams. Air channel testing will find flaws and weak areas that would otherwise be missed by an air lance.  Air lance testing of single welds, whether made by heat or chemical, does not insure the quality of the weld. Pressure used in each test varies with the temperature of the PVC geomembrane. Air channel testing is performed according to EPI QC Standards based ASTM D7177 .  "T" Seams: ALL field seams must be tested and T-seams can be difficult to air channel test if not welded properly.  T-seams are defined as a point in the seam where three layers of material overlap each other.  This occurs at the point that a dual track field weld crosses a factory seam, usually at a 90 degree angle.  (sometimes referred to as butt seams or end seams)   We have had hundreds of questions from engineers and customers regarding the air channel testing of "T" seams, the seam created along the end of a PVC geomembrane panel.  EPI air channel tests ALL field seams, including the seams along the ends of factory panels.                                Specimen of EPI "T" Seam in 30 mil PVC There is a potential at each "T" to have a very tiny hole at the junction of the three layers of material. This is another key reason why air channel testing of every seam is critical to the integrity of the liner system, finding and eliminating these holes. Special care is taken by the welding technicians when setting up the welder to make sure this type of overlap is completely sealed, so the air channel test can be used to verify strength and continuity of these seams also. EPI factory seams have no loose edge, so the process for welding T-seams is relatively easy. Slowing the welding machine's rate of travel will allow the melted PVC material to flow together at the junction of the three layers of material, providing the necessary seal and weld strength.  For fabricators who leave a loose edge on the factory seams, then each loose edge will need to be trimmed, similar to the process used on field welds which intersect other seams.   For more information call  800-OK-LINER  today!

Environmental Protection Agency: 600 S2-87/015 Apr. 1987 Evaluation of Flexible Membrane Liner Seams after Chemical Exposure and Simulated Weathering by William R. Morrison and Linda D. Parkhill Strength and durability were tested in presently available seaming systems a for flexible membrane liners (FML). The seams were exposed to selected, simulated environmental conditions over short periods of up to 52 weeks. A total of 37 combinations of supported and unsupported polymeric sheet materials joined by various seaming methods was subjected to 6 chemical solutions. brine and water immersion, freeze/ thaw cycling, wet/dry cycling, heat aging, and accelerated outdoor aging. Effects of these environmental conditions were evaluated using shear and peel strength tests before and after exposure. The tests were performed under dynamic load at room temperature and under static dead load at 50'C. In addition six NDT (nondestructive test) methods were evaluated. This Project Summary was developed by EPA's Hazardous Waste Engineering Research Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction A considerable number of laboratory tests and pilot-scale studies have been conducted by various Government and private-sector groups to assess the effects of chemical waste products on the integrity of FML’s in hazardous waste containment facilities. However, little has been done to assess the performance of the various types of seams used in joining the manufactured roll goods in the factory and the panels seamed in the field. To learn more about the strength and durability of seams mad: by presently available seaming systems, the U.S. Environmental Protection Agency (USEPA) has funded research with the U . S. Bureau of Reclamation (USSR) to evaluate FML seams exposed to selected, simulated environmental conditions over short periods of up to 52 weeks. The seams listed in Tables 1 and 2 were subjected to six chemical solutions, brine and water immersion, freeze/thaw cycling, wet/dry cycling, heat aging, and accelerated outdoor aging. Effects of the environmental conditions in this study were evaluated using shear and peel strength tests before and after exposure. The tests were performed under dynamic load at room temperature, and under static dead load at 50'C (i 22'F). In addition to seam testing. six nondestructive test (NDT) methods were evaluated in this study. The six NDT methods were: Acoustic method - ultrasonic pulse echo (5 to 1 5 MHz) Acoustic method - continuous wave resonant frequency (167 kMz) Air lance - 345 kPa (50 lb/in2) Vacuum chamber Double seam pressurization Mechanical point stress Table 1. Types of Factory Seams Evaluated             Lining Material Scrim Reinforcement Seaming Method Seam Width(in) 36-mil CPE 6 x 6 leno polyester Thermal-hot air 2.25 36-mil CPE 70 x 70 polyester Thermal-hot air 1 30-mil CSPE 8 x 8 polyester Thermal-hot air 2.5 36-mil CSPE 6 x 6 polyester Thermal-hot air 3 36-mil CSPE 10 x 70 polyester Thermal-hot air 2 36-mil CSPE 6 x 6 leno polyester Thermal-hot air 2.25 36-mil CSPE 10 x 10 polyester Bodied Solvent adhesive 3 36-mil CSPE 10 x 10 polyester Thermal-dielectric 1.25 38-mil EIA polyester Thermal-hot air 2 40-mil EPDM 10 x 70 nylon) Vulcanized.34 in. capstrip 1.5 30-mil CPE - Solvent adhesive 1 30-mil CPE - Thermal-dielectric 0.75 30-mil LLDPE - Thermal-hot wedge 0.62 30-mil PVC - Solvent adhesive 1 30-mil PVC - Thermal-dielectric 0.75 30-mil PVC - Thermal-dielectric 0.75 Table 2. Types of Field Seams Evaluated             Lining Material Scrim Reinforcement Seaming Method Seam Width (in) 36-mil CPE 6 x 6 leno polyester Bodied solvent adhesive 3 36-mil CPE 10 x 10 polyester Solvent adhesive 3 30-mil CSPE 8 x 8 polyester Bodied solvent adhesive 4.5 36-mil CSPE 6 x 6 polyester Bodied solvent adhesive 4.5 36-mil CSPE 10 x 10 polyester Adhesive 3 36-mil CSPE 6 x 6 leno polyester Bodied solvent adhesive 3 35-mil CSPE 70 x 10 polyester Solvent adhesive 3 36-mil CSPE 70 x 10 polyester Solvent adhesive 3 36-mil CSPE 70 x 70 polyester Solvent adhesive 3 38-mil EIA polyester Thermal-hot air 2 40-mil EPDM 10 x 10 nylon Gum tape cement 6.5 30-mil CPE - Solvent adhesive 3 30-mil CPE - Solvent adhesive 3.5 30-mil HDPE - Extrusion Fillet weld N/A 80-mil HDPE - Extrusion fillet weld N/A 80-mil HDPE - Extrusion lap weld 1.75 80-mil HDPE - Thermal-hot dual wedge 1 30-mil LLDPE - Thermal-hot wedge 0.63 30-mil PVC - Solvent adhesive 2 30-mil PVC - Solvent adhesive 3.5 30-mil PVC - Solvent adhesive 3 Exposure Methods For chemical immersion, solutions were chosen to represent a wide range of chemical groups. These solutions were: 10 percent phenol (organic acid) 10 percent hydrochloric acid (inorganic acid) 10 percent sodium hydroxide (inorganic base) 10 percent methyl ethyl ketone (ketone)  5 percent furfural (aldehyde)100 percent methylene chloride (halogenated hydrocarbon) Methylene chloride is not soluble in water; therefore, pure solvent was used to avoid the problem of phase separation. Pure chemicals or aqueous chemical solutions were selected for testing rather than simulated or actual wastes from waste sites to simplify verification of testing Procedures. The use of representative groups of chemicals also allows for reasonable interpretation of the data. Chemical, brine, and water immersion of seam samples was accomplished in covered 170-liter (45 gal) capacity polypropylene and polyethylene tanks. These tanks were filled separately with each of the liquids and the seam samples were then suspended in the liquids. Three tanks of room-temperature tap water and six tanks of saturated sodium chloride brine solution (three tanks at room temperature and three at 50° C (122 F) were also set up for immersing samples at the USBR Laboratory. The samples, except for the room temperature brine, were removed and tested after 3, 6 and 12 months of immersion. Due to an error in scheduling. the room temperature brine samples were only tested after 3 and 12 months of immersion. The remaining samples were either placed in running tapwater for 6-month saturation before beginning freeze/thaw or wet dry cycling tests or set aside for heat aging tests. For heat aging, seam samples were subjected for periods of 4, 8, and 13 weeks to oven-aging at 70° C (158° F) in an effort to provide an accelerated test of long-term heat effects on the seam systems. Double-sided exposure of all samples was used to accommodate the large number of samples in minimum space. An advantage of double-sided exposure over single sided exposure was the reduced time needed to see the effects e)f the liquids on the samples. In parallel with the tank immersions, smaller coupons of the parent materials were immersed in small, clear glass jars for periodic weight and thickness measurements. The smaller coupons allowed for easier inspection of the polymeric sheet materials for obvious excessive degradation, swelling, or change in color or surface texture. if any accelerated response was observed in the coupons, the seam samples were removed from the larger tanks before they were destroyed completely. The ratio of the volume of liquid to the surface area for each coupon was 6.2 mL/cm 2 (40 mL/in 2 ). Thirty-two representative seam samples received accelerated outdoor sunlight exposure testing on accelerated weathering test machines located at the Desert Sunshine Exposure Test (DSET) Laboratories in Phoenix, Arizona. The machines are capable of tracking the sun and focusing the sun's rays on the 5-inch-wide seam specimens for optimum UV (ultraviolet) exposure. The accelerated rate of degradation of the sun exposure is approximately eight times that of conventional outdoor exposure. The samples were visually inspected and photographed after 6 months of exposure. After 1 year of exposure, the samples were again inspected and photographed, and then returned to the USBR where they were tested for peel strength retention and observed for any obvious deterioration. Test Methods Coupon samples of some parent materials were measured for weight and thickness before immersion. The 21 coupon samples, each with dimensions. 50 millimeters by 125 millimeters 12 in by 5 in), were measured after 1. 2, 3, 4, 8, 12, 36. and 52 weeks of immersion. Initial physical properties were tested on the unexposed seam samples for all lining materials. The data collected represent the virgin materials and seams in an unexposed state as received from the factory or the field fabrication. After completion of the liquid immersions and the required environmental conditioning intervals, dynamic shear and peel testing and static dead load peel testing were performed to determine changes in physical properties. The dynamic shear and peel tests were conducted in accordance with the test procedures described in ASTM D 454586, "Standard Practice for Determining the Integrity of Factory Seams Used in Joining Manufactured Flexible Sheet Geomembranes. "Test results of exposed seam samples were compared to the test results of original unexposed seam samples for all tests. The mode of failure was evaluated as well as the numerical results of shear, peel, and dead load in lbf/in of seam width. Several methods are available for Qualitatively testing seams without testing samples from a completed lining system. These nondestructive test methods can be used to measure the continuity of a seam but cannot be used to quantitatively measure the relative strength of the joint or the projected future performance. These methods should be used in conjunction with destructive methods in a quality assurance program. Table 3 summarizes the available NDT methods evaluated in this study. Results Results of the study indicate that no direct correlation exists between the seam shear and seam peel strengths. For example, high shear strength does not guarantee high peel strength. The shear test appears to be more indicative of the strengths and weaknesses of the parent material, whereas the peel test is more a measure of the strengths and weaknesses of the seam bond.Dead load peel testing indicates that for the most part, no direct correlation exists between the results of this testing and the dynamic peel testing.For supported FMLs, the seam strength properties within the same generic group [CPE (chlorinated Polyethylene) or CSPE (chlorosulfonated polyethylene) for example] varied depending on the Particular FML chemical formulation and the type of scrim (reinforcing fabric).Chemical immersion tests indicate that changes in weight and thickness of the materials affected occur quite rapidly. In chemical immersion testing the performance of the FML seams was that essentially expected, based on the recommendations of the FML manufacturer and review of the available chemical compatibility data. Results of the accelerated outdoor sunlight exposure testing indicate that the one-year exposure may be too long, resulting in accelerated weathering conditions too severe for some materials. Of the three thermal methods used to field seam HOPE liners. evaluated in this study, the extrusion lap weld produced the highest shear and peel strengths. The extrusion fillet weld produced a slightly higher shear strength than the hot dual wedge, but the peel strengths of these two seams were nearly identical. In the peel tests, however, the hot dual wedge seam exhibited a failure within the seam area, and the other two field seams failed at the seam edge.Of the two factory seaming methods used for the unsupported PVC (polyvinyl chloride) and CPE liners, the seams made with the solvent adhesive exhibited higher shear strengths, whereas those made dielectrically produced higher peel strength values. The higher shear strength was primarily due to the wider factory seam for the solvent adhesive seam. In the shear tests. failure occurred in the parent material. The same was also true for the peel tests, except for the PVC solvent adhesive seam, where the failure occurred within the seam itself. No appreciable difference was noted in the performance of the two seaming methods. Studies on the NDT methods indicate that each method has particular strengths and limitations as a check for seam bonding. However, -none of the methods determine seam strengths. The performance of the individual seams are summarized in tables for sure conditions. Conclusions Peel strength of a seam is an important property that should be tested along with the shear strength to evaluate the quality of a seaming method of Operation. The dead load peel test, as conducted in this study, was not a valid procedure for evaluating the quality of a seaming method or operation. Generic-type material specifications are not sufficient to ensure satisfactory performance of FML seams when used for hazardous waste containment applications. Short-term chemical immersion tests of up to 6 months may not be of enough duration to determine the chemical compatibility of some FML seams. Existing publishing data and manufacturers’ recommendations on chemical compatibility of FML materials give a reasonable basis to make an initial judgment on the expected performance of seams in a given chemical environment. The 1-year accelerated outdoor sun light exposure may be too severe for some FML materials. The two factory seaming methods evaluated in this study for PVC and CPE produced satisfactory seams. As part of this study, the factory seam requirements listed in NSF Standard No. 54 were reviewed for the materials evaluated. Based on the results of this study, and other USBR studies, the shear requirements (breaking factor) are satisfactory, but the peel requirements (peel adhesion) for the unsupported materials such as CPE and PVC appear to be low. The air lance. vacuum chamber, and mechanical Point stressing work well on most seam types with some specific limitations. Recommendations The dead load peel test should be conducted utilizing a certain percentage of the ultimate peel strength. This will require additional testing to establish realistic dead load test values for the various FML seams. The specifications for hazardous waste containment should incorporate special provisions to ensure a specific FML formulation for chemical compatibility with the materials to be contained. The 120-day immersion period specified in EPA Test Method 9090, "Compatibility Test for Waste and Membrane Liner," should be reviewed to ensure that it is of long enough duration to determine chemical compatibility. Additional studies are recommended to determine if the accelerated weather test is truly representative of long-term weathering of FML’s formulated for outdoor exposure. Additional studies are recommended to develop a method for testing HDPE seams for environmental stress cracking.Studies should be conducted on evaluating the thermal-hot air method for factory seaming PVC and CPE materials. This would provide an opportunity to document the results for future specification consideration. The NSF Joint Committee on FML’s should give consideration to increasing the peel adhesion values for CPE and PVC and for supported CPE and CSPE materials.   Table 3: Recommended NDT Methods Based on this Research           Ultrasonic Continuous     Double Mechanical   Thickness pulse echo wave resonant Vacuum seam point FML (mils) (5-15 MHz) frequency (167 kHz) Air lance chamber pressurization Stress Supported 30   * * *   * CSPE 36   * * *   * and 45   * * *   * CPE 60   *   *   *                 Unsupported 20 * * *       CPE 30 * * * *   *                 Unsupported 20 * * *   *   PVC 30 * * * * * *   40 * * * * * *                 Unsupported 20 * *   * *   HDPE 30 * *   * * * HDPE-A 40 * *   * * * LLDPE 60 * *   * * *   80 * *   * * *   100 * *     * *                 Supported 30     * *   * EPDM 45     * *   * and BUTYL 60       *   *                 Supported 38       *   * EIA               1 mil = 0.0254 mm.               EPI can now Air Channel test PVC geomembrane field seams         For more information call   800-OK-LINER  today!

UTILIZING PVC GEOMEMBRANES FOR LANDFILL AND POND LINERS by Fred P. Rohe Environmental Protection Inc. Abstract Flexible PVC liners have been successfully used for containment applications since the 1960’s. This paper will cover the fabrication and installation of a typical PVC geomembrane for containment applications. The multimedia presentation will consist of a PowerPoint presentation using video and photographs. The benefits of using PVC versus some of the alternative geomembranes will be discussed.  Introduction The large scale development of PVC geomembranes began in the 1960’s with the use of PVC film to prevent seepage of water from canals and reservoirs used for irrigation in the western United States. The US Department of Interior, Bureau of Reclamation [1] first began experimenting with PVC geomembranes in 1957. In the Bureau of Reclamation’s 35+ years of geomembrane experience, PVC geomembranes have proven especially effective where limited access, short downtime, long haul distances, and potential for freezing and thawing are factors. The primary use of PVC geomembrane by the Bureau of Reclamation has been for lining irrigation canals in the southwestern United States. Hundreds of miles of canals are in use today lined with 10 mil and 20 mil PVC. These canals are unique structures because: They are long and narrow They have limited access for work They have steep side slopes  Historically, PVC has been the most widely used geomembrane for canal applications for the following reasons: Availability in large sheets - PVC can be factory fabricated into panels up to 30 M wide and 100 M long. Panels can be accordion folded in both directions to facilitate shipping and handling in narrow confines associated with canal construction. These large panels minimize field seaming. PVC is highly flexible and retains this property over a wide range of temperatures, which permits it to conform to the subgrade better than other geomembrane materials, which were available at the time of selection, such as HDPE and EPDM. PVC is easily field-spliced and repaired with a solvent-type cement. PVC also has good puncture, abrasive, and tear-resistant properties, which are important to minimize damage during installation. PVC geomembrane installation does not require sophisticated equipment or skilled labor. These same material properties are advantageous to many other applications requiring containment liners. PVC geomembrane is used in all types of water and waste containment applications, including landfills, wastewater treatment lagoons, oil exploration, aquaculture, and irrigation ponds.  Theory PVC geomembrane film can be factory pre-fabricated into large panels prior to shipment to the project site. Panels as large as 2,000 M 2 (20,000 Ft 2 ) are common. This reduces the amount of field welding required by up to 80% in many installations. Factory fabrication is not affected by the adverse weather conditions often encountered in the field therefore, quality of welding can be controlled and assured. In many situations, a one piece liner can be installed without any requirements for field welding.  Factory Fabrication Calendered PVC film is manufactured in thickness’ of .25 mm (10 mil) up to 1.5 mm (60 mil) and widths from 1.75 to 2.5 M (5 Ft. to 8 Ft.). The most common thickness’ used in containment applications are .5 mm and .75 mm (20 and 30 mil) . Manufacturers are required to provide certifications that the PVC film meets or exceeds all raw material testing requirements of the PVC Geomembrane Institute’s PGI-1197 specification for PVC geomembrane liners. Fabricators are also required to provide certifications that all factory welds meet or exceed material testing requirements. The PVC film is converted into panels by PVC geomembrane fabricators using chemical fusion welding, dielectric welding, hot air or hot wedge welding. The process used depends on the particular fabrication firm, but all materials and welding are required to meet or exceed the PVC Geomembrane Institute PGI-1197 specification for material properties and seam weld strength. Panels of PVC geomembrane are fabricated to fit the particular project dimensions. Panels can be built to fit irregular curves, accommodate unusual geometric shapes, or made into very large panels to minimize welding in the field. Factory weld testing [7] includes destructive testing of samples taken from a minimum of every 1,000 M (3,000 Ft.) of factory seam, or once per panel. Samples are tested for bonded seam strength and seam peel adhesion according to PGI-1197. The PGI Specification 1197 [6] replaces NSF-54, which is no longer supported by the National Sanitation Foundation.  Factory Welding Minimum Peel Strength: 20 mil - 12.5 LB/in 30 mil - 15 40 mil - 15 50 mil - 15 60 mil - 15 Factory Welding Minimum Shear Strength: 20 mil - 38.4 LB/i 30 mil - 58.4 40 mil - 77.6 50 mil - 96 60 mil - 116   Nondestructive testing is also performed over the full length of every weld. Records from each liner panel can be traced from the serial number of each panel back to the original PVC batch produced and to the resin used to produce the material. After completion of the welding, the PVC panel is accordion folded in both directions and placed on a sturdy wooden pallet for transport to the project site. The panel is packaged to protect the material from weather and damage during transportation and storage. Each panel is labeled with a serial number and panel designation corresponding to the panel location drawing for its particular project.  Field Installation PVC panels arrive at the site and are deployed according to a panel layout diagram for that project. The deployment simply involves unfolding the panel in reverse of the fabrication process. The panel is unfolded off the pallet along its length, and then using manpower, it is unfolded across its width, much like placing the tarp on a baseball diamond during a rain delay. This unfolding is quick, simple and allows large areas of liner to be placed each day. Panels are overlapped approximately .3M (12 In.) for field welding. The perimeter of the panel is usually placed in an anchor trench which is backfilled with soil to hold the panel in place during welding and placing of the cover soil on top of the geomembrane. There are three primary methods of field seaming PVC geomembrane panels; Adhesive seaming Chemical fusion seaming Thermal fusion welding  Adhesive seaming of PVC is the oldest and simplest method of sealing geomembrane panels. The process involves coating each surface of the panels to be joined with a bodied solvent adhesive. The coated pieces are then placed together and pressure is applied by a roller or other device to mate the pieces together and create a bond. Chemical fusion welding utilizes a chemical fusion agent (solvent) to dissolve the surfaces of the pieces of material to be joined. The chemical fusion agent is introduced between the two sheets of PVC to be welded, and while the surface of the material is molten, pressure is applied to mate the two surfaces together. This provides a homogeneous bond between the two sheets after the fusion agent evaporates. This method is used extensively in the fabrication and installation of PVC geomembranes. Thermal fusion welding of PVC has been used in Europe for many years. Its use for the field welding of PVC geomembranes in the United States began around 1990. Thermal fusion welders consist of a hot wedge or hot air device that heats the surface of the material to a molten state, while traveling along the length of the seam. Pressure rollers follow the heating device to press the two pieces of PVC geomembrane together while the surfaces of each sheet are melted. This provides a homogenous bond between the two pieces.  There are several advantages to the thermal welding method over the adhesive or chemical methods: Significantly higher peel strength can be achieved. Weld strength is more uniform Two parallel welds can be made allowing for air pressure testing between the welds . After welding is completed, samples are taken from the field seams at a rate of one per 150 M (500 Ft.) for destructive testing of peel and shear strength.  Field Welding Minimum Peel Strength:  All gauges - 10 LB/in   Field Welding Minimum Shear Strength:  All gauges - 80% of specified tensile strength   Each field seam is also non-destructively tested over its entire length to insure continuity and identify any voids in the seam. Non-destructive testing of adhesive and chemical seams is performed using an air lance. This apparatus directs a high pressure stream of air at the edge of the seam in order to detect any voids in the weld. This test requires a minimum of 50 psi air pressure through a 3/16" diameter nozzle. Non-destructive testing of dual track thermal welds [8] is performed by sealing one end of the channel formed between the two parallel welds, and introducing air pressure from the opposite end of the weld. The air pressure varies depending on the thickness of the material. Minimum pressure is 15 psi and maximum is 30 psi. Any drop in pressure is recorded over the two minute duration of the test. A maximum amount of pressure drop is specified for each thickness of PVC geomembrane. Any void in the seam, even as small as a pin hole, will not allow the air pressure to be maintained. After the non-destructive testing has been performed, any defective areas are repaired and then re-tested to insure there are no voids in the field seam. When liner testing has been completed and accepted the geomembrane is then covered with .3 M (12 in.) of clean soil to protect the geomembrane from damage. The soil cover can be sand or clay that is free of stones, roots, rubbish or any other item that may penetrate the liner. Placement of the cover material can be accomplished using rubber tired or tracked machines as long as a minimum layer of cover soil is maintained between the equipment and the liner.  Performance The US Bureau of Reclamation has been the best source of information on the long term durability of PVC geomembranes. Testing conducted by the Bureau [2] on samples of 10 mil PVC in service in irrigation canals for over 29 years indicate the buried material has retained its physical properties and is still performing satisfactorily. Environmental Protection, Inc. and Occidental Chemical Corporation [10] also performed testing 25 year old 10 mil PVC geomembrane used in a golf course irrigation pond in northern Michigan. After 25 years or service the testing confirmed that the material still exceeded today’s specifications for minimum material properties and seam peel and shear strength. The PVC Geomembrane Institute and its member companies along with the Minnesota Department of Natural Resources are conducting a 30 year assessment of the long term durability of PVC geomembrane. This long term test program, begun in 1995, will provide valuable information on the continuing performance of PVC in containment applications.  Conclusions Today’s PVC geomembranes provide an economical solution to today’s rigorous environmental containment needs. Thicknesses of 30 and 40 mils provide more durability than the thinner materials used thirty years ago. PVC is easily fabricated, installed and tested to assure clients receive the highest quality and most secure liner installation available today.  Acknowledgements PVC Geomembrane Institute  References [1] REC-ERC-95-01, USE OF GEOMEMBRANES IN BUREAU OF RECLAMATION CANALS, RESERVOIRS, AND DAM REHABILITATION, US Department of Interior, Bureau of Reclamation, Denver, CO. [2] REC-ERC-84-1, PERFORMANCE OF PLASTIC CANAL LININGS, US Department of Interior, Bureau of Reclamation, Denver, CO. [3] Successful History of PVC Geomembranes Bureau of Reclamation: 1968 - 1995 - March 1996, PVC Geomembrane Institute Technical Bulletin [4] CONSTRUCTION QUALITY CONTROL DOCUMENT, PVC Geomembrane Institute, - Dated April 1995 [5] Technical Guidance Document, "Inspection Techniques for the Fabrication of Geomembrane Field Seams", EPA/530/SW-91/051, U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, Washington, D.C., May 1991. [6] New Standards for PVC Geomembranes Introduced - August 1997, PVC Geomembrane Institute Technical Bulletin   For more information call   800-OK-LINER   today!

Fifth International Conference on Geotextiles, Geomembranes and Related Products Singapore, 5-9 September 1994 Assessment of a PVC Geomembrane Used in a Landfill Cover System K. Badu-Tweneboah & N. D. Williams GeoSyntec Consultants, Boca Raton, FL, USA D. W. Haubeil Mead Paper, Chillicothe, OH, USA   ABSTRACT: A polyvinyl chloride (PVC) geomembrane was used in combination with a geosynthetic clay liner (GCL) as a composite barrier in the cover system for the final closure of a paper mill sludge landfill. The landfill contained very compressible and low shear strength wastewater treatment sludge materials. During placement of a vegetative cover soil layer over an installed cover system panel, localized bearing capacity failure of the underlying sludge material occurred. As a result, the geosynthetics settled up to 2.4 m in a certain area. Geomembrane samples with and without seam were taken from the affected area for laboratory tests. The test results indicated that the mechanical properties of the geomembrane and seam exceeded the minimum requirements of the project specifications and were within the range of conformance test results. These results confirmed that PVC geomembranes are suitable for landfil1 cover system applications where settlement of the underlying waste may result in large stresses and strains in the geomembrane cover system.  INTRODUCTION The purpose of this paper is to present the performance of a PVC geomembrane during construction of a final cover system for a highly compressible sludge landfill. The PVC geomembrane was selected on the basis of its mechanical properties, in particular its ability to tolerate large settlements. During construction of the final cover system, construction equipment caused large settlements of a portion of the installed cover system including the geomembrane. There was therefore concern over the integrity of the geomembrane. The results of the laboratory tests performed on the affected geomembrane and seam are presented and compared with the project specifications and results of conformance tests performed as part of construction quality assurance monitoring.  HISTORY OF THE LANDFILL The landfill was constructed in 1974 for the disposal of wastewater treatment plant primary and secondary sludges, coal ash, and lime mud, which were waste byproducts of the pulp and paper manufacturing process. These waste byproducts, when combined, were typically fully saturated, with water contents in excess of 200 percent and shear strengths that ranged from 1 to 10 kPa. The sludges were very compressible and generated considerable leachate through consolidation under self-weight. Results of laboratory consolidation tests indicated that the modified compression index, Cc , for the sludge was in excess of 0.30. The sludge had a very low bearing capacity because of its low shear strength. This had a direct impact on disposal operations and construction of the cover system for final closure of the facility. The landfill covered approximately 10 hectares and had been developed by constructing a l5-m high embankment at the mouth of a small ravine to create the space for sludge disposal. The maximum depth of sludge in the landfill occurred at the lowest elevation of the ravine and was approximately 15 m; the average depth of sludge was about 9 m. In 1990, an innovative cover system that incorporated eight layers of geosynthetics was designed for final closure of the landfill facility. Construction of the final cover system began in June 1992 and was completed in January 1993 (Badu-Tweneboah et al., 1994).  FINAL COVER SYSTEM COMPONENTS Fig. 1 illustrates the profile of the final cover system, which was designed and constructed for closure of the landfill. The purpose of the 0.75-m thick vegetative cover was to support vegetation as well as protect the underlying layers from root penetration and frost damage. The geocomposite drainage layer immediately below the vegetative cover layer served as an infiltration collection and removal system (ICRS) for the control of precipitation that infiltrated through the vegetative cover layer. The composite barrier consisted of a O.5-mm thick PVC geomembrane placed on top of a GCL. The purpose of the composite barrier was to: (i) minimize leakage of precipitation into the landfill, thereby minimizing the rate and quantity of leachate generation; (ii) minimize upward migration of leachate out of the Iandfill; and (iii) reduce the volume and rate of gas discharged to the atmosphere through the final cover system. Below the composite barrier was a geocomposite layer that served as an underdrain layer for the collection and removal of leachate expelled from the sludge due to consolidation caused by placement of the final cover system and by self-weight. This underdrain layer also served as a gas collection layer for the control of gas migration from the landfill. Each of the two geocomposite drainage layers consisted of a layer of geonet placed between two needle punched nonwoven geotextile layers. The geotextiles functioned as filters and/or separators. The geosynthetics were used as the major components of the cover system in lieu of conventional earthen construction materials in order to reduce the vertical stress applied to the sludge, thereby decreasing the total settlement and the volume of leachate generated due to consolidation of the waste. To facilitate placement of the vegetative cover soil and to support the weight of construction equipment, a 3-m to 6-m thick layer of stabilized sludge was placed above the in-place sludge. The stabilized sludge consisted of sludge mixed with hark and fly ash to provide a minimum undrained shear strength of 24 kPa (Badu-Tweneboah et al., 1994). Construction specifications required the use of low ground pressure dozers with a maximum ground pressure of 34 kPa for placement of the 0.75 m vegetative cover soil layer. Fig. 1 Final cover system profile. PVC GEOMEMBRANE INSTALLATION The PVC geomembrane rolls were factory-fabricated into 40 panels with a width of 21 m. The total area of the PVC geomembrane installed over the landfill was measured to be 102,680 m2. A total of l4 samples were retrieved from the 40 fabricated panels for laboratory conformance testing. The results of the conformance tests were compared with the project specifications to ensure conformance with the material property requirements. Adjacent PVC geomembrane panels were bonded in the field using a solvent-adhesive welding technique. The completed PVC geomembrane seams were visually examined for workmanship and continuity. Nondestructive and destructive tests were performed to evaluate the integrity of the field seams. The air lance testing method was used to nondestructively test the field seams in order to evaluate their continuity. Laboratory destructive testing was performed to evaluate the strength of the field seams. Testing was performed to determine the bonded seam strength and peel adhesion using the test methods provided in ASTM test standards (ASTM, 1991). The overlying layers were immediately installed after acceptable results had been obtained for the field seams.  PLACEMENT OF COVER SOIL Low ground pressure dozers were used to place the O.75-m thick layer of vegetative cover soil over installed panels. The cover soil materials were hauled from the landfill perimeter and spread over the installed geosynthetics using the low ground pressure dozers. It was necessary to use closed portions of the landfill as haul roads to facilitate placement of cover soil in other areas. As a result, closed portions were Subjected to repeated loading from the combined weight of construction equipment and cover soil materials which subsequently led to pumping of the subgrade. Pumping of the very low shear strength, fully saturated sludge into the stabilized sludge layer progressively reduced the shear strength of the stabilized sludge layer. This led to the development of localized bulges, and at times placement of excessive thickness of soil (Badu-Tweneboah et al., 1994). Placement of excessive thickness of soil caused immediate settlement, which was difficult to observe because the depressed (i.e. settled) area was filled immediately with soil as the dozer trafficked the area with cover soil. As a result of placement of excessive thickness of soil, localized bearing capacity failure of the underlying subgrade material occurred in a 60-m long by 18-m wide area of an installed panel; this area is hereafter referred to as the affected area.  FAILURE INVESTIGATIONS AND CORRECTIVE ACTIONS Test holes were excavated to determine the thickness of cover soil placed over the geosynthetics in the affected area. Up to 3.7 m of soil was placed in one area. The 3.7 m of cover soil corresponded to an applied stress of about 70 kPa, which greatly exceeded the design strength of the stabilized sludge subgrade. The settlement of the geosynthetics in the affected area was determined to range from 0.10 to 2.4 m. It was observed that the cohesive nature of the cover soils caused them to stick to the top geotextile component of the ICRS geocomposite drainage layer. These geosynthetic layers were therefore damaged during the cover soil removal process. The geomembrane showed signs of tension in the form of Iateral wrinkling but had no tears, scratches, or separated seams, except for few locations which were torn by the backhoe. However, the underlying geosynthetics, particularly, the GCL were observed to have had seam separation. The affected area was subsequently repaired by: (i) removing all cover soil and geosynthetics; (ii) restabilizing the sludge with bark and regrading the surface; and (iii) reinstalling the cover system using new geosynthetic materials. Placement of the cover soil over this area was performed using low ground pressure dozers much smaller than those used in the initial stages of construction. Additional grade control measures were instituted to ensure that not more than the required 0.75 m of cover soil was placed over the installed geosynthetics.  INTEGRITY OF PVC GEOMEMBRANE In the area where localized bearing capacity failure occurred, a sample from the PVC geomembrane parent material and a sample from the adjacent field seam were taken for laboratory conformance testing to evaluate the integrity of the geomembrane material and field seam. Testing was performed in accordance with ASTM test standards (ASTM, 1991). The results of the laboratory testing are summarized in Tables 1 and 2. Table 1 presents a summary of the results of tests on the physical and mechanical properties of the PVC geomembrane field sample compared with the project specifications and conformance test results. These results indicate that the mechanical properties of the PVC geomembrane which was subjected to the loading from the 3.7 m of cover soil still exceeded the minimum requirements of the specifications and were within the range of conformance test results obtained from the geomembrane panels. Even though visual observations indicated signs of tension in the geomembrane, its mechanical properties were still within the range of conformance test results. Table 2 presents a similar comparison of the PVC geomembrane field seam sample with the project specifications. Again, the mechanical property values of the field seam sample exceeded the specifications. Based upon the results of the laboratory testing and comparison with the specifications, it was concluded that the integrity of the PVC geomembrane had not been affected by the stresses imposed by the loading from the 3.7 m of cover soil. These results confirmed that PVC geomembranes are suitable for landfill cover system applications where settlement of the underlying waste may result in large stresses and strains in the geomembrane cover system.   CONCLUSIONS AND RECOMMENDATIONS The performance of a PVC geomembrane subjected to excess loading during construction of a final cover system over a very compressible, low shear strength waste material has been presented in this paper. Results of laboratory tests and comparison with the specifications and conformance test results showed that the PVC geomembrane and field seam were not impacted enough by the large stresses and strains imposed by the excess loading caused during construction to affect the integrity of the geomembrane. Therefore, PVC geomembranes are acceptable for construction over very compressible, low shear strength waste materials. To facilitate construction, however, stabilization of the upper few meters of the waste material may be required. Also, proper placement of cover soil may be necessary in order to minimize the development of bulges and localized bearing capacity failure. This can be accomplished by using lightweight equipment.  REFERENCES ASTM (1991) Annual Book of ASTM Standards, Philadelphia, Vol. 08.01, 556 p. Badu-Tweneboah, K., Williams, N.D., and Haubeil, D.W. (1994) Closure of a paper mill sludge 1andfill, Proceedings of 1994 International Environmental Conference, TAPPI, Portland, OR, USA, 1: 117-130.      For more information call   800-OK-LINER   today!

PVC's mechanical properties are quite different to those of HDPE:   The uniaxial stress-strain curve does not display a yield point (a point of instability). It is a "predictable" curve of decreasing slope with no discontinuities up to a break of over 300%.The multiaxial stress-strain curve displays a lower break stress than HDPE but a much higher break strain. Much of PVC's deformation (up to the break strain) is recoverable. In HDPE strain in excess of about 12% (the yield point) is not recoverable. PVC will conform to geometrical profiles much more readily than HDPE. HDPE has a higher puncture stress but a lower puncture strain than PVC. Being different, each will perform better in different environments. Neither is the best under all circumstances. Useful strain in HDPE is 10%. Useful strain in PVC is 300%. HDPE yield point is a point of instability.  Figure 4.) Multiaxial Stress vs. Strain For Five Geomembrane Materials PVC has excellent ductility - ability to conform to subgrade.   PUNCTURE TESTING   HDPE has high resistance to puncturing but with little deformation. PVC will deform significantly before puncturing. HYDROSTATIC TESTING: PRESSURE TO FAILURE              PVC conforms to subgrade better than HDPE. HDPE has higher apparent strength but PVC conforms better and maintains an impermeable barrier.   For more information call   800-OK-LINER  today!

EXAMINATION OF PVC IN A 'TOP CAP' APPLICATION Samuel B. Levin and Mark D. Hammond   REFERENCE: Levin, S. B. and Hammond, M. D., "Examination of PVC in a 'Top Cap' Application," Geosynthetic Testing for Waste Containment Applications, ASTM STP 1081, Robert M. Koerner, Ed., American Society for Testing and Materials, Philadelphia, 1990. ABSTRACT: The PVC liner installed over Phase I of the Dyer Boulevard Landfill provides us with an opportunity to examine the material after 5+ years of exposure to landfill gas and other environmental stresses in a top cap application. Test results for samples extracted from the cap are compared to test results obtained at the time of installation, to material properties included within the original material specification, and to material properties from a 'control' sample of excess PVC material from this closure project kept in a warehouse since 1983/84. INTRODUCTION Thee Dyer Boulevard Landfill services all of Palm Beach County, Florida. It is located over the Turnpike Aquifer, an important local source of drinking water. When initially opened in 1968, it was one of several unlined landfills operated within the County. With time, it became a major disposal area for both municipal solid waste and sewage sludge. In late 1970's, evidence of contamination of the shallow aquifer surrounding this high rise landfill was observed within the site's monitoring network. Under the terms of a consent agreement between Palm Beach County and the Florida Department of Environmental Regulation, executed in 1982, it was agreed that: The Phase I (unlined) landfill was to be closed in an environmentally sound manner. A new lined landfill was to be developed to provide for future solid waste disposal capacity. An alternative means of wastewater treatment plant sludge and septic tank pumpings disposal was to be utilized. Post, Buckley, Schuh & Jernigan, Inc. (PBS&J) was selected by Palm Beach County, and subsequently by the Solid Waste Authority of Palm Beach County (SWA) when it assumed responsibility for the landfill in 1983, to develop the closure design for the existing 190 acres ± of landfill cells in Phase I. The closure design developed for the site included a low permeability 'top cap', well vegetated side slopes, and an integrated drainage system to capture and remove surface runoff, reducing percolation and subsequent leachate generation. The top cap was designed for installation over slopes of less than 10 percent, based on water balance calculations which indicated that only minimal percolation was anticipated through well vegetated landfill side slopes. The selection of a liner material for use in the top cap at the Dyer Boulevard Landfill proved to be an arduous task, with properties of various materials reported in differing units, or obtained using differing test methods. Suppliers assisted in the selection process by noting the superior properties of some liner materials relative to competing materials. Plasticizer loss, ultraviolet degradation, questionable chemical resistance with respect to landfill gas exposure, and more limited elongation properties were cited as reasons to consider materials other than PVC. Environmental stress cracking, seaming difficulties, and poor strength characteristics upon exposure to bidirectional forces were cited as reasons to consider materials other than High Density Polyethylene (HDPE).  PURPOSE AND SCOPE During the past several years, geosynthetics testing has matured to the point at which properties of virgin materials ' are widely available and in many cases readily comparable. Data concerning the properties of liner materials which have been in service remain scarce, although there is a growing body of information concerning exposure in the laboratory to simulated in-service environments [1], [2]. The top cap material in-service at Dyer Boulevard provides an opportunity to examine the properties of material which has been in service for over five years. Properties of this material will be compared to the properties determined by quality assurance testing during its manufacture and installation, in an attempt to assess the change in properties resulting from material exposure. Excess material stored in a warehouse since its purchase in 1983/84 will serve as a control.  DESIGN AND SPECIFICATIONS The site closure design included the placement of PVC sheet, soil bedding and cover material, a passive landfill gas venting system, drainage improvements, and seeding, mulching and sodding of the completed landfill. A typical cross section through the final cover is provided in Figure 1. Physical properties specified for the 20 mil PVC liner are presented in Table 1. Tensile strength at the seam was required to be at least 80 percent of that of the parent material, or 1760 psi. Also required in the specification was the sampling and testing of the production run for tensile strength and elongation at break. General Contractor Crabtree Construction Company, Inc., purchased 3.32 million square feet of PVC material, Product Number 1951, manufactured by Dynamit Nobel of America, Inc. and fabricated by the Watersaver Company, Inc. The surface of the subgrade prepared as liner bedding was treated with Hyvar X-L Herbicide prior to placement and seaming of the liner panels. The coarse grained sand used for liner bedding and backfill was obtained by dredge from a near site borrow area. One hundred and sixty-six panels of PVC, most of which measured 400 feet by 70 feet, were installed by Wright/Kohli Construction Company, a specialty liner subcontractor. Watersaver WS-70 splicing solvent was used for seaming the panels together.   TABLE 1 -- Specified Physical Properties for 20 Mil PVC Physical Property Value ASTM Test       Thickness +/- 10% D 1593 Specific Gravity 1.24 - 1.30 D 792 Tensile Strength 2200 psi D 882 or D 412 Elongation 300% D 882 or D 412 100% Modulus 1000 psi D 882 Graves Tear 270 lbs/in D 1004 Water Extraction 0.35% (max) D 1239 Volatility 0.70% (max) D 1203 Impact Cold Crack -20ºF D 1790 Dimensional Stability 5% max @ 212ºF D 1204-54         PVC SHEET (LINER) TESTING Testing of the properties of the PVC sheet installed over the Dyer Boulevard landfill included: Quality control (QC) testing of the parent material at the time of manufacture by Dynamit Nobel of America, Inc. Non destructive (air lance) testing of all field seams during the time of installation. Destructive testing of the parent material, factory and field seam samples obtained throughout the ten month installation period. Table 2 provides a summary of the manufacturer's QC data. Please note that the data presented is the average for a number of rolls tested. One sample was obtained for testing purposes for each 86,000 square feet of manufactured product.   TABLE 2 -- Manufacturer's QC Data            ASTM Manufacturer's Test Result Test Result Test Result Test Result Properties Test Method Specification (Ave.11 Rolls) (Ave.6 Rolls) (Ave.13 Rollsb) (Ave.7 Rolls) Thickness (mils) D-1593 20 +/- 5% 19.9 19.5 19.8 19.9 Specific Gravity (min.) D-792 1.23 1.25 1.25 1.2 1.25 Tensile Strength D-882 2400 MD 2999 MD 2836 MD 2487 MD 2977 (psi)     TD 2768 TD 2692 TD 2464 TD 2781 Modulus @ 100% D-882 1000 MD 1446 MD 1270 MD 1384 MD 1291 Elong. (psi min.)     TD 1333 TD 1202 TD 1332 TD 1203 Elongation, % min. D-882 300 MD 414 MD 423 MD 336 MD 453       TD 426 TD 435 TD 354 TD 449 Tear Strength (lbs.) D-1004 5.5 MD 7.46 Not 8.51 Not       TD 7.92 Reported 9.18 Reported Low Temperature D-1790 -20 Pass Pass Pass Pass Impact °F             Volatile Loss max. D-1203 1 0.79 0.70% 0.87% 1.13% (@70°C for 24 hrs.)             Water extraction D-1239 0.3 0.08 0.18 0.15 0.3 % Loss max             (1040F, for 24 hrs.)             Dimensional Stability D-1204 ±5.0 MD -1.8 MD -1.8 MD -1.8 MD -1.27 % change, max.     TD 0.6 TD 1.7 TD 0.86 TD 0.51 212?F for 15 min.             a Provided by the Watersaver Company, Inc.     MD - Machine Dire   b Number of rolls tested estimated based upon reported material weight.   TD - Transverse D   Destructive testing of field samples taken throughout the liner installation process was performed by QC Metallurgical Inc., Hollywood, Florida. A total of 236 tensile strength tests were performed on field samples. These test results are summarized in Table 3. All tensile tests were performed in shear.  TABLE 3 -- Summary of Tensile Test Data for Field Samples of PVC when Installed         Specified Values Range of Results Average Value Sample Sample Type Sample Quantity (psi) (psi) (psi) Standard Deviation Field Seam in Shear 195 1760 1490 - 2550 1937 165             Factory Seam in Shear 30 1760 1825 - 2568 2132 186             Parent Material 11 2200 2040 - 4750 2857 712 LINER RESAMPLING/TESTING PROGRAM In December, 1989, the soil overburden was carefully removed from the top cap in several locations of the Phase I area to expose the liner material. According to the Solid Waste Authority's manager of landfills, the exposed material appeared to exhibit few signs of degradation upon visual inspection. The surface of the material exhibited minor undulations, a few millimeters in size, where the material apparently elongated to conform to the surfaces of soil particles. The samples were highly pliable, exhibiting no apparent brittleness. Eight coupons of the parent material and one field seam coupon were sliced from the cap by the Solid Waste Authority's manager of landfills. Added to the package of nine samples was a coupon sliced from a factory panel of PVC stored by the Solid Waste Authority as surplus in a warehouse since its purchase in 1983/84 for capping the Phase I Dyer Boulevard site. The ten samples were transmitted to Geosyntec, Inc., Boynton Beach, Florida for laboratory testing. A summary of test results for these samples is provided in Table 4. The tests were selected to correspond with tests performed by the manufacturer in 1984. Low temperature impact testing was not performed due to its limited applicability to the sub-tropical West Palm Beach environment. Dimensional stability was not determined due to an insufficient quantity of sample material.   TABLE 4 -- Liner Resampling/Testing Program           Specific Tensile Modulus @ 100% Elongation Tear Volatile Loss Water Extraction   Gravity Strength Elongation (%) Strength (%) (%)     (psi) (psi)   (lbs.)     ASTM               Test Method 0-792 0-882 D-882 0-682 D-1004 D-1203 D-1239 Field Seam N/A 2204 shear N/A 407 N/A N/A N/A     1140 peel           Field Panel 1 1.265 MD TD MD TD MD TD MD TD         2744 2642 1865 1721 341 381 10.1 9.3 1.33 2.81 Field Panel 2 1.282 MD TD MD TD MD TD MD TD         3072 2642 1865 1721 341 381 10.1 9.3 0.4 1.08 Field Panel 3 1.267 MD TD MD TD MD TD MD TD         2740 2544 1968 1828 341 334 9.9 9.6 1.41 2.06 Field Panel 4 1.264 MD TD MD TD MD TD MD TD         2614 2633 2043 1904 340 324 9.5 9.8 2.02 1.85 Field Panel 5 1.267 MD TD MD TD MD TD MD TD         2634 2327 1884 1879 311 309 9.5 8.6 3.26 1.99 Field Panel 6 1.252 MD TD MD TD MD TD MD TD         2496 2360 1667 1794 356 270 8.8 8.9 4.23 2.63 Field Panel 7 1.27 MD TD MD TD MD TD MD TD         2446 2149 1746 1672 309 331 9.2 8.5 0.85 1.69 Field Panel 8 1.278 MD TD MD TD MD TD MD TD         2627 2628 1763 1781 362 345 8.9 8.6 0.96 2.58 Warehouse 1.279 MD TD MD TD MD TD MD TD     Panel   2662 2439 1557 1476 429.4 417.4 8.3 7.8 0.78 1.29             MD - Machine Direction             TD - Transverse Direction   COMPARISON/EVALUATION OF TEST RESULTS An insufficient number of field seam samples (one) and warehouse parent material samples (one) were retested to provide for a reliable comparison of test results. Data from the testing of these samples is provided for information only. Emphasis will be placed on comparing the data from the factory QC parent material test results with testing of the eight parent material samples obtained in December, 1989. This data is presented for comparison in Table 5.   TABLE 5 -- Summary of Test Results             Parent Material (Manufacturer's) Parent Material Parent Material(field samples     QC Data (from Warehouse) December 1989) Specific Gravity Range 1.26 - 1.25   1.25 - 1.28     Ave. 1.25 1.28 1.27   Tensile Strength MD Range 2487 -2999 2662 2498 - 3072   (psi) Ave. 2789   2672     TD Range 2464 - 2781 2439 2149 - 2725,     Ave. 2651   2502   Break Elongation MD Range 336 - 453 429 309 - 362   (%) Ave. 395   335     TD Range 354 - 449 417 270 - 381     Ave. 407   327   Tear Resistance MD Range 7.5 - 8.5 8.3 8.9 -10.1 (lbs.) Ave. 8     9.5   TD Range 7.9 - 9.2 7.8 8.5 -9.8   Ave. 8.6     9.1 Secant Modulus MD Range 1270 - 1446 1557 1667 - 2243   (psi) Ave. 1366   1897     TD Range 1202 - 1333 1476 1672 - 2027     Ave. 1287   1826   Volatile Loss (%) Range 0.70 - 1.13 0.78 0.4 - 4.23     Ave. 0.87   1.81   Water Extraction (%) Range 0.08 - 0.30 1.29 1.69 - 2.81     Ave. 0.16   2.09               a Average values presented here are average of the average QC data reported by the manufacturer, weighed by the number of rolls tested.                     The specific gravity of the 'aged' PVC appears to be somewhat greater than that at the time of manufacture. This increase is consistent with a loss of plasticizer in the aged samples, since the specific gravity of the PVC resin (approximately 1.4) exceeds that of the plasticizer (approximately 0.98). Based on the apparent increase in specific gravity, the aged samples have lost approximately 13 percent of their initial (factory) plasticizer content. Plasticizer loss would expectedly be evidenced by an increase in tensile strength. The aged samples did not reflect this, with a loss in the average tensile strength of about 4 and 6 percent, machine direction and transverse direction respectively. Conversely, break elongation results followed a highly predictable path. The average aged sample elongation was 15 percent (machine direction) and 20 percent (transverse direction) less than that reported on the factory QC sheets. The tear resistance test, as its name implies, is a measure of the force necessary to initiate a tear in the plastic sheet. The averaged test sample tear resistance values for the aged samples exceeded the average values observed at the time of manufacture by 6 and 19 percent. Secant modulus at 100% strain provides a measure of the stiffness of the sheet, and should increase as plasticizer is lost from the material. The modulus at 100% strain of the aged samples averaged 42 and 39 percent above the average modulus data reported at the time of manufacture. The volatile loss test is subject to some variability, depending on the type of plasticizer used [4],[5]. The large difference between the average volatile loss tested at the time of manufacture and that of the aged samples likely exceeds variations inherent in the test. The average volatile loss of the aged samples exceeded the average loss reported by DNA by over 100 percent. An even larger increase was observed between average values for the water extraction test. The average loss values for the aged samples exceeded those reported at the time of manufacture by over 1000 percent.  DISCUSSION The above described apparent changes in properties of the PVC sheet, with the possible exception of tensile strength, are consistent with changes associated with plasticizer loss. Since designers, owners, and operators of solid waste landfills are most concerned with the long term effectiveness of the top cap, what we really wish to know is of what point will placticizer loss be sufficient to result in cap failure, and how long will it take for this failure to occur? It would appear from both visual observation and laboratory testing that for a South Florida landfill, this period exceeds five years. With few exceptions, the properties which relate to the ability of the PVC to continue to function as a low permeability moisture barrier, (tensile strength, elongation, tear resistance, secant modulus) exceeded the originally specified values in each of the eight aged samples. How long beyond this five year period will the PVC sheet continue to provide its intended top cap function? Extrapolation of the data obtained by testing the eight aged samples is tenuous, at best. Some insight may be provided through review of the comprehensive study performed by Morrison and Starbuck [5]. Testing was performed on 10 mil PVC linings within eight canals which had been in service for periods ranging from 0.6 to 19 years. The changes in properties observed by Morrison and Starbuck were mostly consistent with those observed in the eight landfill top cap samples, and were attributed to plasticizer loss. The landfill top cap environment does not appear to have been more hostile to PVC than the canal lining environment, although the difference in thickness (10 mil for canal linings, 20 mil for the top cap) may have impacted the relative magnitude of the observed/reported changes in properties. The Morrison and Starbuck study provides data for 10 mil canal lining samples after as many as 18 and 19 years in service. Loss in elongation for the 19 year old sample is as high as 63.3%, with a corresponding loss of plasticizer of 45.7%. These property changes were not sufficient to cause failure of the canal lining. An additional potential difference between the landfill top cap environment and the canal lining environment is temperature. The top cap may be exposed to elevated landfill gas temperatures resulting from waste decomposition. Elevated temperatures are a driving force for plasticizer loss. In-situ temperatures were not noted in the canal lining study, making comparisons with the top cap environment more difficult. How long a service life is required for a landfill top cap? In Florida, the post closure period for a solid waste landfill extends a minimum of 20 years [6]. The latest proposed federal rules [7] require a post closure period which extends for a minimum of 30 years. The stresses imposed on a top cap in a solid waste landfill subsequent to its installation, are in our opinion primarily a result of differential waste settlement. Sufficient elongation to accommodate this settlement is of paramount importance. The rate and uniformity at which landfills settle is highly variable depending to a large extent on the type of waste accepted, compaction procedures, moisture content, and overall landfill height. Landfill settlement tends to be most pronounced in the initial several years after closure. It is during this period that the PVC exhibits its greatest elongation properties.  SUMMARY AND CONCLUSIONS The PVC top cap at the Dyer Boulevard Landfill appears to have maintained its integrity after its initial 5+ years in service. Test values from sample coupons extracted from the top cap differ from test values for sample coupons taken from the parent material at the time of manufacture. These apparent property changes are consistent with those attributed to plasticizer loss, published for PVC which has been in service as canal lining, although the canal lining and top cap environments may differ. The aging of PVC in both the top cap and canal environments appears to be consistent with changes in properties associated with plasticizer loss although other factors in the landfill environment or canal environment may be responsible for these observed changes. In the canal environment, the PVC exhibited significant loss of plasticizer over 18 and 19 years of exposure. Corresponding elongation properties were reduced by as much as 63%. The material was still serving its intended function despite these changes in properties. Additional long term data (preferably from landfill top cap environments) will assist in projecting the anticipated service life of PVC for landfill closures.  ACKNOWLEDGMENTS We wish to express our sincere appreciation to the Solid Waste Authority of Palm Beach County for funding the liner testing program. Additional thanks are due to Art Arena, Technical Director, Huls America, Inc., and Richard Dickenson, a technical consultant to Huls America, Inc.  REFERENCES W.R. Morrison and L.D. Parkhill, Evaluation of Flexible Membrane Liner Seams after Chemical Exposure and Simulated Weathering , U.S. Bureau of Reclamation, Engineering and Research Center, Denver, Colorado, Feburary 1987. Haxo, H.E., et.al ., Liner Materials Exposed to Municipal Solid Waste Leachate, third Interim Report , EPA-600/2-79-038, July 1979.Post , Buckley, Schuh & Jernigan, Inc. , Contract Specifications for Dyer Boulevard Landfill Closure for Palm Beach County, Florida , June 1983. ASTM, 1989 Annual Book of ASTM Standards , Section 8, Volume 08.01.W.R. Morrison and J.G. Starbuck, Performance of Plastic Canal Linings , U.S. Bureau of Reclamation, Engineering and Research Center, Denver, Colorado, January 1984. Florida Administration Code, Chapter 17-701.07. [7] Federal Register, Volume 53, No. 168, Tuesday, August 30, 1988/Proposed Rules, Page 33408.   Mr. Levin is Assistant Manager of the Solid Waste/Resource Recovery Division of Post, Buckley, Schuh & Jernigan, Inc., 800 North Magnolia Avenue, Suite 600, Orlando, Florida 32803. Mr. Hammond is Director of Operations, Solid Waste Authority of Palm Beach County, 5114 Okeechobee Boulevard, Suite 2-C, West Palm Beach, Florida 33417.   For more information call   800-OK-LINER  today!

POLYMERIC PLASTICIZERS FOR HIGHER PERFORMANCE FLEXIBLE PVC Applications  RONALD D. SVOBODA The C.P. Hall Company Chicago. Illinois 60638   Flexible PVC applications can be categorized as requiring either general or higher performance characteristics. In many application areas. specification requirements are becoming increasingly more severe requiring the use of Polymeric polyester plasticizers in compounding. Polymeric plasticizers provide excellent migration. volatility. fluid chemical extraction. and/or weathering resistance in higher performance applications compared with that obtained from monomeric plasticizers alone. INTRODUCTION End uses for flexible PVC compounds are quite diverse, but they can be loosely categorized as being either general performance or higher performance applications. Each of these performance categories requires a different set of considerations in terms of compounding with plasticizers. For general performance applications, compounders require moderate performance in several areas without particular emphasis on any one. In these applications, good plasticizing efficiency is often desired and this is manifested in processing ease. good compound softening. and modulus and tensile reduction. For economic reasons, compound softening and modulus reduction are ideally obtained using the lowest plasticizer loadings possible. Performance properties are of secondary consideration and general performance applications may or may not require moderate volatility resistance. fluid chemical extraction resistance. and low-temperature properties. Some general performance plasticizers used in the market place today include DIDA. DINP. DIDP. DOP. DBP, and other phthalates made from straight-chain alcohols of seven to eleven carbons-in length. The consumer demand for more durable goods and specifications for higher performance products require many of the same considerations needed in general performance compounding. however. particular emphasis is placed on superior plasticizer permanence in one or more specific areas. Discussed in this paper are how polymeric polyester plasticizers may be used in higher performance applications where superior plasticizer migration. volatility. fluid chemical extraction. and/or weathering resistance are critical.  DISCUSSION Polymeric Plasticizers Polymeric plasticizers are Produced by reacting a dibasic carboxylic acid with a glycol or a mixture of different dibasic carboxylic acids with one or more glycols. When these molecules are reacted. the chain propagation or building may be terminated by the use of monofunctional carboxylic acids or alcohols. Some polymeric plasticizers are also produced using no terminator. Following is a representation of the production of an acid terminated polymeric polyester which assumes that stoichiometrically correct quantities of dibasic carboxylic acid, glycol, and monofunctional carboxylic acid have been reacted together to yield a polymeric plasticizer of a viscosity (or molecular weight) within a given range.  General Synthesis of an Acid Terminated Polyester Dicarboxylic          Acid Glycol             Fatty Acid         O O                                                O      O nHO-C-R-C-OH + (n + I)HO-R'-OH + 2R"C-OH-R"-C- -O-R’-O-C-R-C- -O-R’-OCR"+ By Product (2n + 2)H2O For the purposes of this paper, the polymeric plasticizers discussed are identified by dicarboxylic acid type and typical apparent viscosity In centapoises taken at 25° C. Dicarboxylic acids commonly used to manufacture polymeric plasticizers include the following:  Common Dicarboxylic Acids Used to Manufacture Polymeric Plasticizer. Phthalate Glutarate - 5 Carbons Adipate - 6 Carbons Azelate - 9 Carbons Sebacate - 1 0 Carbons   Mixtures Polymeric plasticizers are manufactured in a wide range of viscosities and provide varied balances of permanence along with handling and processing ease. Generally, as viscosity is increased, processing and handling become more difficult. The polymeric plasticizers we produce range in viscosity from about 900 cps up to 160,000 cps. The polymerics discussed in this paper are identified by the first letter of the acid type used. In other words. A-indicates an adipate, G - a glutarate, and so on. Azelates would be identified with a prefix of Z, but are not discussed in this paper. Acid mixtures are identified by the letter MA. Following the letter identifying acid type is the typical apparent viscosity for the plasticizer. Therefore, an adipate polymeric with a viscosity of 5,600 is identified as A-5,600. Polymeric Plasticizer Identification                 Acid Type                                         Viscosity, cps                 Adipate                                                  5600                                                 A-5600                                                 G-12,000                 Glutarate                                             12,000   Factors Influencing Plasticizer Permanence The permanence of a polymeric plasticizer in a flexible PVC compound depends upon three major factors which include structure, molecular weight/ viscosity, and polarity. Polymerics composed of branched structures are more permanent than those based upon linear structures. Branching tends to hinder movement or entangle the plasticizer within the polymer matrix making it more difficult to migrate or be removed by volatilization or extraction. Although linear structures provide less permanence, they do yield better low temperature properties. The greater the viscosity/molecular weight of a plasticizer, the greater will be its permanence. Simply stated, the longer and bulkier the molecule is, the more difficult for it to be removed. Polarity can be roughly viewed as the ratio of oxygen to carbon atoms in a plasticizer. The greater the ratio of oxygen to carbon atoms, the greater the polarity. It is vital that the polarity of the plasticizer be properly matched to that of the polymer, in this case PVC. If the polarity of the plasticizer is not sufficiently similar to that of PVC, varying degrees of plasticizer incompatibility may result. Plasticizers which are somewhat incompatible are more prone to migration, volatilization, and extraction.  Migration Resistance Migration is the movement of a plasticizer within and from a PVC compound into or onto a substrate to which it is held in intimate contact. Plasticizers which are migratory can have negative effects upon substrates including marring, crazing, discoloring, weakening, and dissolving. Several application areas come to mind where little or no plasticizer migration can be tolerated and where polymeric plasticizers are currently used. Plasticizer used in PVC refrigerator door gaskets cannot mar or discolor the ABS and polystyrene inner cabinets they are held in contact with when the door is closed. Plasticizer used in PVC to construct automotive instrument panels, head rests, and arm rests cannot migrate to the polyurethane backing used in these constructions. If migration occurs, the PVC covering could become brittle and crack or adhesion could be lost at the PVC covering, polyurethane interface. For vinyl electrical tapes, plasticizer cannot migrate through the tape and dissolve the adhesive backing. Furthermore, significant work has been done examining the use of polymeric plasticizers in vinyl medical tubing. In this application area, it has been shown that non-migrating plasticizers can be used so that polycarbonate couplings, unto which the tubings are connected, do not stress crack (1). Using our own laboratory test procedure, we have tested several polymeric plasticizers and a general performance monomeric (DOP) for migration to ABS, polystyrene, and nitrocellulose substrates (2). In Table 1. DOP, and polymerics A-3,300, G-3,700, and G-12,000 are compared for migration resistance to the three aforementioned substrates. Like most all other general purpose monomerics, DOP migrates readily to all three substrates. Polymeric plasticizer A-3,300 provides a respectable balance of migration resistance properties, while G-3,700 and G-12,000 provide excellent resistance to migration. Glutarate polymerics are especially known for their non-migration characteristics (3).  Table 1. Migration Resistance of Selected Plasticizers in PVC.             DOP A-3,300 G-3,700 G-12,000 ABS P G G E Polystyrene P G E E Nitrocellulose P G G G E = Excellent, G = Good, P = Poor   Recipe: PVC-100, BaCd-1, Plasticizer-67.   Volatility Resistance Excellent volatility resistance is particularly important in PVC wire and cable jacketing where specifications (i.e. UL 62 105° C Class 12 Thermoplastic Insulation and Jacket) require minimal losses of elongation and tensile after air aging (4). Newer specifications for interior automotive trim, particularly instrument panels, also require stringent requirements for minimal losses of elongation. Ideally, most compounders for applications requiring low volatility will be in search of the lowest losses of elongation and weight and the least increases in modulus, tensile, and compound hardness. Compared in Table 2. are DOP, and polymerics MA-5,500 and A-6,800 in unfilled PVC compounds which have been air aged for three days at 136° C. As can be seen, much of the DOP has been volatilized from its compound under these test conditions and as a result elongation and tensile changes are excessive. Both polymerics enjoy lower volatility weight losses and, as a result, changes in stress-strain properties are of lesser magnitude (5). Often times a higher performance application may require superior permanence with regards to two or more performance parameters. In Table 3. PVC compounds have been air-aged for up to 500 h at 120° C while in contact with polyurethane (PU) foam. For this type of aging, we will have the combined effects of volatilization and migration. Compared are a compound plasticized entirely with a linear phthalate and another with a blend of polymeric A-1,200 and the same phthalate in a 3:1 ratio. Blending plasticizers such as this is a popular way of getting the best of both worlds for cost and performance. Using the polymeric plasticizer, we have greatly reduced 50% modulus and elongation loss and slightly reduced tensile increase values.  Table 2. Air Oven Volatility Resistance of Select Plasticizers in PVC. Air Oven Aging, 3 days at 136ºC       DOP MA-S,500 A-6,800 Percent-       Weight change -28 -4.3 -1.6 Elongation change >100 -14 -9 Tensile change >100 2 -2 Recipe: PVC-100, BaCd-1, Plasticizer-67.     Table 3. Long Term Air Oven Volatility of Plasticized PVC in Contact With PU Foam.     A-1,200   Linear (75)/Linear   Phthalate Phthalate (25) After 250 h     50% modulus change. % 69 50 Tensile change. % -18 -5 Elongation change. % -36 -17 After 500 h     50% modulus change, % 258 189 Tensile change. % 28 24 Elongation change. % -67 -28   Fluid Chemical Extraction Resistance When studying plasticizers for fluid chemical extraction resistance, we would obviously look for the least PVC compound weight loss. Low plasticizer extraction usually results in the preservation of a PVC part's dimensional stability and surface appearance. Failures due to plasticizer extraction can be as severe as part ripping, disintegration, or cracking. Applications requiring excellent extraction resistance include: hoses and tubing: printing rollers: belting, sheeting and film: and upholstery. Polymeric plasticizers have been successfully used in these applications and blending with monomerics is common to optimize properties. In Table 4 is a comparison of the extraction resistance properties for DOP and polymerics A-1,200, A-20,000, and S-160,000 in unfilled PVC compounds. It can be seen that as viscosity increases, so does resistance to extraction with S- 160,000 having superior permanence in all three test fluids. We consider hexane and cotton seed oil to be relatively low in polarity, while 1% soapy water solution is relatively high. Lower polarity fluids generally have a greater ability to extract lower polarity plasticizers and vice versa. For example, since polymeric plasticizer A-20,000 is higher in polarity compared with A-1,200 and S-160,000, it was found to be more readily extracted in the 1% soapy water solution.  Weathering Resistance Weathering resistance is another application area which requires superior permanence with respect to several performance parameters. Flexible PVC products which are weathered are exposed to a combination of: elevated ambient and surface temperatures: wet-dryout cycles due to rain and dew. humidity exposure: UV exposure: contact with dirt and pollutants: and fungal attack. In weathering applications, we look for several performance properties. Probably the primarv property would be resistance to surface degradation. This could mean least color change if the flexible PVC was pigmented or little yellowing if the compound was clear. Other ideal properties would include little or no microbial attack, surface tack development, and surface dirt pick-up. Compounds which are made containing higher performance polymerics in order to weather well, will generally provide better tensile, modulus, elongation, and hardness retention. Specific application areas, where these properties would be of concern include PVC decals, film and sheeting, and a variety of interior automotive trim applications.  Table 4. Fluid Chemical Extraction Resistance of Select Plasticizers in PVC.   DOP A-1,200 A-20,000 S-160,000 Percent Weight Loss       n-Hexane, 24 h -31 -1.9 -0.65 -0.39   @ 23ºC       Cottonseed oil, 24 h -16 -2.9 -1.6 -0.08   @ 60ºC       1% soapy water, 7 d -19 -5.2 -11 -5.3   @ 90ºC       Recipe: PVC-100, BaCd-1, Plasticizer-67.     To examine the weatherability of polymeric plasticizers we prepared unfilled PVC compounds containing several polymeric plasticizers and two monomeric diesters, DOP and DIDG (Diisodecyl Glutarate). The compounds prepared were based upon 100 pphr PVC resin. 1 pphr Barium/Cadmium stabilizer, 0.5 pphr of a UV stabilizer, 3 pphr of ESO, and 67 pphr of the plasticizer variable. Both "direct" and "underglass" agings were performed. For direct agings, specimens are affixed to a wooden panel held at a 45° angle facing south in Miami, Florida. For this type of weathering, specimens are in direct contact with the elements. For underglass agings, specimens are exposed in a similar manner, however, the samples are encased in a glass box, thereby being protected from rain, dew, etc. Underglass weathering is performed mainly for interior automotive trim applications. As would be expected, samples aged under glass experience significantly greater surface temperatures than do those which are direct aged. As mentioned earlier,color retention of pigmented or yellowing resistance of clear PVC films can be vital. Table 5 compares general performance monomerics DIDG and DOP to polymerics G-4,000 and G-12,000 for yellowness index change after two, four, and six months of direct aging. Both monomerics show relatively high initial and longer term tendencies to yellow. G-4,000 and G-12,000 provide excellent short term and longer term resistance to discoloration by yellowing. Glutarate polymerics in general have a proven history of providing good resistance to weathering for PVC compounds.  Table 5. Direct Weathering of Select Plasticizers in PVC   (450 South, with backing, South Miami).       DIDG DOP G-4,000 G-12,000 Yellow Index Change         2 months 8.25 4.93 0.17 0.5 4 months 9.25 8.93 3.17 1.5 6 months 14.9 9.85 4.55 5.35 Recipe: PVC-100, BaCd-1, UV Stabilizer-0.5, Plasticizer-67, ESO-3.   Table 6. Underglass Weathering of Select Plasticizers in PVC (450 South, with backing, South Miami).     DOP DIDG A-20,000 G-12,000 Yellow Index Change       2 months 2.36 -1.9 -1.08 -2.83 4 months 6.05 2.94 0.57 -0.28 6 months 8.38 6.05 2.72 1.34 Recipe: PVC-100, BaCd-1, UV Stabilizer-0.5, Plasticizer-67, ESO-3. Table 6 provides a similar comparison, however, for underglass weathering. Compared are net changes from initial yellowness values for monomerics DOP and DIDG, and polymerics A-20,000 and G-12,000. The magnitude of short term and longer term yellowness index change values is less overall for the underglass weathered compounds compared with those which were direct aged. Polymeric polyesters A-20,000 and G-12,000 provide about a threefold reduction in yellowness index change compared with the general performance monomerics.   SUMMARY AND CONCLUSIONS In this paper, higher performance parameters for flexible PVC applications including plasticizer performance with respect to migration, volatility, fluid chemical extraction, and weather resistance have been discussed. Ideal compound physical property retentions, application areas, and PVC compound data have been given for each of the four higher performance areas. We have seen that higher performance polymeric polyester plasticizers provide superior permanence properties compared with general performance monomerics in all four of these demanding areas. General purpose monomerics provide greater processing and handling ease, greater compound softening efficiency, and are lower in cost than polymeric plasticizers. Optimization of permanence properties, processing, efficiency, and cost can be obtained by judicious blending of higher performance polymerics with monomeric plasticizers.   ACKNOWLEDGEMENT The author would like to express gratitude to his colleagues in the Technical Service Laboratory for generating much data and information contained in this paper. Thanks also goes to W. H. Whittington for his guidance and useful suggestions.   REFERENCES 1. S.E. O'Rourke, J. Vinyl Tech. , 9, 147 (1987). 2. "Surface Mar-CPH Method 01-80B" (1989). The C.P. Hall Co., 5851 West 73rd St., Chicago, IL 60638. 3. J.L. O'Brien, W.H. Whittington, and G. Chalfant, Plast. Compounding, May/June 1981. 4. Standard for flexible Cord and Fixture Wire, UL-62. 12th ed., pp. 53-56, Underwriters Laboratories, lnc., Northbrook, IN., September 1981. 5. Polymeric Plasticizers for Flexible PVC (brochure), The C.P. Hall Co., 5851 West 73rd St., Chicago, IL 60638.   For more information call   800-OK-LINER  today!

Extract from: "THE TECHNOLOGY OF PLASTICIZERS" BY J. KERN SEARS AND JOSEPH R. DARBY CHAPTER ON "PERMANENCE OF PLASTICIZED PVC"   …from the plasticizers occupying more of the surface area at higher concentrations. The surprisingly low volatility of DBP at 25 to 43% concentration probably results from the case hardening of the sample commonly observed with volatile plasticizers. The high and rapidly increasing volatility of the chlorinated paraffin hydrocarbon plasticizer is what would be expected of a highly inefficient plasticizer (a secondary plasticizer used as a primary plasticizer) whose volatile loss is in large measure controlled by difficulty of migration to the surface. 3. Life Expectancy Reed and Connor (62) went beyond Equation 6.2 with data averaged for several typical monomeric plasticizers to obtain Equation 6.3 which permits estimation of weight loss at one condition from known weight loss at some other condition.     t2d1   W2 = W1 t1d2 K(CT2-T1) where W 2 , t 2 , d 2 , and T 2 are respectively the weight loss, exposure time, sheet thickness, and temperature (° C) under the desired conditions; W 1 , t 1 , d 1 , and T 1 , represent the same under known conditions, and K = e b which is approximately 1.10 or 10 0.042 , according to the average of their data in which e is the base of natural logarithms, and b is a constant, 0.096, the average slope of W versus T From this it also appears that for constant time and thickness, a 7.2° C rise in temperature doubles the volatile loss. Similarly, a reduction of 7.2° C in temperature doubles the time required for a given weight loss. Thus they estimate 29 years for a 4-mil (0.1 -mm) film plasticized with DOP to lose a fourth of its plasticizer content at room temperature. Quackenbos (59) used a different approach for prediction and estimation of service life of plasticized PVC-one based on plasticizer vapor pressure. After assuming arbitrarily that a film may be failed when it has lost 10% of its mass (about 25 to 30% of the plasticizer content), he constructed the log-log plot of vapor pressure versus time for 1O% loss (Fig. 6.12). Figure 6.12) Vapor pressure of plasticizers at 98° C versus time for 10% loss from a 4-mil (0.1-mm) PVC Film at 98° C. The 10% loss is based on total composition and represents about a fourth to a third of the plasticizer lost . Quackenbos (59).   Although the data were all obtained at 98° C the graph applies to any temperature as long as the PVC is flexible. Table 6.2 shows predicted service life at 98° C from measured vapor pressure and at 25° C from vapor pressure extrapolated to room temperature. The simple technique of estimating vapor pressure of plasticizer blends from weighted averages of their individual pressures is usually quite satisfactory at these temperatures. Thinius, Schroeder, and Keatner (76) have shown that at temperatures above 200° C, vapor pressures of blends may begin to depart seriously from values predicted in this way. Predictions seem to be too long for the real world at the time of this writing-hundreds of hours at 98° C and 1000 years at room temperature. Yet Graham (30), using the same method, calculated service lives for PVC plasticized with DOP ranging from 4.2 years to 40° C to 1150 years at 0° C. If DBP were used in place of DOP the service lives were only 0.058 years (21 days) at 40° C to 11 years at 0° C. Service life of a low volatile/high volatile blend is usually longer than predicted on vapor pressure. Autooxidation, photooxidation. and hydrolysis can destroy plasticizers and the PVC itself long before their predicted life-span based on volatility has elapsed. Extraction and migration may supersede volatility and shorten service fife. Yet predictions for some uses can be simple and very helpful. The preceding figures permit rapid graphical estimates of service life. As an example, a specific request was received for estimated service life on the Arabian desert for 125-mil (3-mm) thick objects of PVC plasticized with BBP when volatility was the expected limiting factor. Figure 6.5 (or tables in the Appendix) shows the volatile loss from 40-mil PVC/BBP (100/67) to be about 3% of the total mass in one day at 87° C. Percent loss is essentially independent of plasticizer content. If we should plot this one point on Figure 6.10 and draw a line through it essentially parallel to those shown, we can adjust for temperature. With the average annual maximum temperature for Kuwait City 85° F (29.4° C) and the average maximum for August 104° F (40° C) as guides (17), we should find losses of about 0.005 and 0.02% per day for 40-mil film which would be 1.8 and 7.3% per vear for the 29.4 and 40° C average temperatures. These two points are transferred to our enlargement of Reed and Connor's graph--the lower part of Figure 6.9. Straight dashed lines drawn through them to the lower right comer permit us to read the estimated loss for 3-mm thick material as 0.5 and 2.3% loss per year for these two temperatures. If we then use Quackenbos' criterion that 10% loss is failure, these values suggest a life as long as 20 years at 85° F (29.4° C) or as short as 4.5 years at 10.4° F (40° C). These ballpark estimates are designed to be conservative by the choice of maximum temperatures. The fact that 20-mil black pigmented sheets plasticized with 50 phr of BBP are somewhat stiff but tough after nine years continuous exposure, not only to heat but to sun and rain, in southern Florida tend to confirm the reasonableness of the predictions. The annual average maximum temperature at the Florida test site is 83° F (24.4° C) and the average maximum August temperature is 91° F (33° C). In Figure 6.12 only one data point is seriously out of line; that is the one for polyethylene glycol di(2-ethylhexoate). The polyether structure of this plasticizer makes it very easily oxidized, and in Quackenbos’ volatility tests at 98° C it probably suffered oxidative fragmentation (see later). What he measured, therefore, was pseudovolatility for this one plasticizer. With a proper antioxidant present we would predict its data point would shift to the right until it reached the line at a service life of about 200 hr. Even this may be fictitiously short if his vapor pressure data was influenced by either current or previous oxidation. Decomposition of some plasticizers such as phenol alkylsulfates during vapor pressure measurements has proved to be a problem (76).  C. MIGRATION TO OTHER MATERIALS The mobility of a plasticizer which enables it to soften, flexibilize, and toughen PVC also permits it to leave the PVC and go into other solid materials which are in contact with it, if they have the ability to absorb the plasticizer. In most cases the migration process is complex and difficult to describe precisely. Several controlling factors are at play.  1. Controlling Factors As with volatility, the rate of migration may be controlled by the ease of loss from the PVC surface (surface control) or it may be controlled by the rate of diffusion of plasticizer from the interior of the PVC mass to the surface (diffusion control). Therefore the molecular size and shape of the plasticizer are highly important; small molecules migrate faster than large ones. linear molecules migrate faster than bulky, branched ones, and highly solvating ones that produce an open gel structure migrate faster than those that are "frozen in" to isolated pockets. Since, after the first few moments of contact, plasticizer cannot be lost from the surface faster than it can migrate to the surface, its rate of diffusion establishes the ultimate limit on speed of migration; it may migrate slower but it cannot migrate faster. When a material in contact with the PVC surface is efficient enough as an absorbent to remove plasticizer as rapidly as it reaches the surface, the rate of diffusion will control plasticizer loss. In such cases, loss will theoretically equal the loss by evaporation into a vacuum at that temperature. With diffusion in control, the rate of loss will gradually decrease as the concentration of plasticizer inside the PVC "reservoir" decreases and as plasticizer concentration builds up in the receiving material, since the rate varies with the concentration gradient. Curve A of Figure 6.13 shows the effect. When this type loss is plotted against the square root of time the curve is linear, in keeping with Fick's law and as seen in Equation 6.1. Curve A represents the loss to certain grades of silica gel, such as Linde silica, which not only are highly absorbent but which provide good wicking action to lead the plasticizer from the surface. Few materials have this ability. When a material in contact with plasticized PVC can absorb plasticizer at a rate slightly slower than the rate at which plasticizer can migrate to the surface, migration is at first linear with time as shown in Curve B, Figure 6.13. As time goes on and the concentration of plasticizer in the PVC "reservoir" decreases, the diffusion rate decreases until the receiving material can accept plasticizer as fast…   For more information call 800-OK-LINER today!