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This ensures accurate measurements are taken, cutting down waste when creating custom-made liners for ponds, coal ash basin projects, etc. ​ Click here for PDF ​ Begin by drawing the perimeter of the pond to the best of your ability. Select a straight line down the bottom, through the center of the length of the pond. Calculate your measurement from the liner termination point at the top of the slope down through the pond to the liner termination point on the opposite side.   Measure dimensions along this centerline on 25' centers (or closer to be more accurate) or where the pond perimeter makes significant changes in shape (ie: Dimensions w, x, y, & z.). Place a stake or flag at these points. Measure down through the pond from the liner termination point perpendicular to the centerline (ie: Dimensions A1 & A2, B1 & B2, etc). Record dimension from liner termination point at top of the slope to the centerline. Record all dimensions on the drawing. These dimensions will allow EPI to provide accurate shop drawings of panels (A, B, C, D) to fit the pond creating as little waste as possible. If you have any questions, please call EPI's team at 1-800- 655-4637 Custom Fabrication Coal Ash Basin Closure

A Discussion of Minimum Geomembrane Thickness 30 mil smooth polyvinyl chloride geomembrane is functionally equivalent to 60 mil textured high-density polyethylene.  by Fred. P. Rohe “Minimum thickness” seems to imply that thicker is better. But in reality thickness is only one of many material properties affecting the ultimate performance and durability of any geomembrane. The discussion of minimum thickness focuses on one parameter and ignores all others, many of them equally as important factors. Here are some facts for you to consider. Let’s explore the following items as they relate to the statement that “30 mil PVC is functionally equivalent to 60 mil HDPE” when it comes to geomembrane containment applications: Material type Slope Stability Manufacturing Tensile Strength Elongation at failure Failure at Yield Multi-axial Stress – Stress Cracking Oxidation Welding Flexibility Chemical Compatibility                       Regulations   1. Material: Polyethylene is a crystalline plastic. PVC is an amorphous plastic. Amorphous means nebulous, fluid, unstructured…that is, it does NOT have a crystalline molecular structure like polyethylene.  This simple difference in the makeup of these two plastics creates significant differences in how they respond to many outside forces and situations in real-world geosynthetic applications.  2. Slope Stability: It has become the industry standard that on slopes steeper than about 6H/1V it is necessary to use textured HDPE for slope stability because smooth HDPE is unacceptable.  This is in comparison to standard, smooth surface PVC geomembrane which is routinely installed on 3H/1V slopes every day.  Textured polyethylene liners were originally developed in order to compete with the slope stability characteristics of smooth PVC, much the same as Low Density Polyethylene (LDPE) liners were developed to compete with the flexibility characteristics of PVC.   Smooth PVC geomembranes are inherently able to provide much higher residual friction angles and to provide stability with soils and other geosynthetics on much steeper slopes than smooth HDPE, and in many cases, textured HDPE.  Research and individual project testing continues to show that smooth 30 mil PVC geomembrane has an equal or higher residual friction angle than textured 60 mil polyethylene. Since the industry standard is to use textured HDPE on all slopes, it is only common sense to compare materials that would be used on a 3H/1V slope… which is 60 mil textured HDPE and 30 mil smooth PVC geomembranes. 3. Manufacturing Thickness Tolerance: A mil, as used to describe a geomembrane, is defined as 1/1000th of an inch (0.001 inch).  The methods of measurement of the thickness of smooth PVC and textured HDPE differ significantly.  In order to fully understand this difference, read ASTM D-5199 for smooth geomembranes and ASTM D-5994 for textured geomembranes. All PVC geomembrane material is manufactured to a thickness tolerance of +/- 5%.  This means the minimum thickness of 30 mil PVC anywhere on the sheet cannot be less than 28.5 mils (specification thickness of 0.030 inches, minus 5% - 0.0015 inches = 0.0285 inches).  So the thickness of PVC geomembrane can only vary below the minimum thickness a maximum of 1.5 mils measured anywhere on the membrane.  For comparison, the clear PVC wrapper on the dry cleaning you picked up recently is about 1 mil thick. HDPE on the other hand is manufactured to a thickness tolerance of +/- 10% which is measured using minimum average roll value (MARV) methods.  This means the minimum thickness of 60 mil textured HDPE should not be less than 54 mils (specification thickness of 0.060 inches, minus 10% -0.006 inches = 0.054 inches) in 8 out of 10 measurements across the roll width.  It should be noted that since minimum average roll value is used in calculating the thickness of the HDPE material, it is considered adequate for thickness measurement of 51 mils (-15%) to be accepted for one or two of the measurements, as long as the minimum average of the measurements is above 0.054 inches. A typical footnote for HDPE:  “The combination of stress concentrations due to coextrusion texture geometry and the small specimen size results in large variation of test results.  Therefore these tensile properties are minimum average values.”  PVC uses minimum values rather than “minimum average” values. While the minimum thickness of 30 mil PVC is minus 5% (-1.5 mils )(0.0015”) the minimum thickness for 60 mil textured HDPE is minus 15% (-9 mils) (0.0090”).  PVC maintains much closer control of the thickness of the material in the manufacturing process. 4. Tensile Strength: Tensile strength at break for 30 mil smooth PVC is 73 lbs/in (2400 psi).  PVC is tested at a speed of 20 inches per minute. Tensile strength at break for 60 mil textured HDPE is 90 lbs/in (1500 psi).  HDPE is tested at a speed of 2 inches per minute. While the thickness of 30 mil PVC is 50% less, the tensile strength at break is only 18% less than the 60 mil textured HDPE.  Doubling the thickness from 30 mil to 60 mil for HDPE provides only slightly higher tensile strength than 30 mil PVC.  5. Elongation at Break: The minimum elongation at break for 30 mil smooth PVC geomembrane is 380%. The minimum elongation at break for 60 mil textured HDPE geomembrane is only 100%. While the thickness of the HDPE is double that of the PVC, the elongation at break of the 60 mil textured HDPE is 60% lower than the 30 mil PVC. Polyethylene proponents may quickly point out that SMOOTH HDPE has a minimum elongation at break of 700%... but remember, smooth HDPE is NEVER used on a slope, so the value is not relevant in the comparison of geomembranes in actual use. 6. Failure at Yield Elongation: Minimum elongation at break for 30 mil PVC is 380%.  PVC does not have a yield point when elongated. The minimum yield elongation for 60 mil textured HDPE is 12% (GRI GM-13).  This is the point at which the HDPE fails. Since PVC is an amorphous material, it does not have a yield failure point like crystalline materials.  PVC is an elastic material.  It remains elastic throughout its elongation all the way up to the breakpoint.  Therefore, the failure elongation for PVC is the breakpoint, which is 380% for 30 mil PVC. HDPE is also elastic, but only through elongation up to it’s yield point, at about 12%.  Then the material becomes plastic.  When the yield point is exceeded, HDPE is no longer the same material.  It is no longer elastic and changes to a plastic state.  Once the HDPE material has elongated beyond the 12% yield point, it can no longer function as a geomembrane. Engineers can safely design using strain limits two or three times higher by using PVC geomembrane. 7. Stress Cracking: Since PVC geomembrane is an amorphous material, it is not subject to environmental stress cracking.  Nor does PVC geomembrane stress crack when exposed to multi-axial stresses. Polyethylene geomembranes are crystalline plastic and ARE subject to environmental stress cracking.  The higher the density of the resin, the more likely the sheet is to stress crack. Stress cracking of HDPE can be compared to the cracking of an automobile windshield.  A windshield is installed with a neoprene or rubber gasket around the perimeter to isolate it from the vehicles metal frame, and cushion it from being twisted or subjected to unequal stresses.  A minuscule stone chip or tiny scratch is all it takes to initiate a crack in a windshield when a small amount of stress is applied (a bump at the car wash, a sudden change in temperature…).  Crystalline plastics like HDPE behave in much the same way. HDPE geomembrane must not be subjected to unequal stresses in order to minimize stress cracking.  An example is that HDPE geomembranes require a neoprene gasket when attaching it to a solid structure such as a concrete wall or steel support.  This will hopefully delay cracking of the HDPE material beyond the service life of the installation.  PVC on the other hand, is not crystalline, is not subject to stress cracking, so therefore does not require the use of neoprene, rubber, or any other cushioning gasket when attaching PVC to concrete or steel structures. Polyethylene manufacturers test their material for environmental stress cracking.  However, it is interesting to read the footnotes.  For instance, one typical note:  “NCTL for HD Textured is conducted on representative smooth membrane samples”.   So this means stress crack testing is never actually performed on textured 60 mil HDPE. 8. Oxidation: 30 mil PVC geomembrane materials do not oxidize on the surface.  When repairs are required or when patches are necessitated by removal of destructive samples, welding can be accomplished by simply cleaning the surface of the PVC of any dirt or moisture.  Mechanical or chemical preparation is not required.  Joining can be done by thermal, chemical, or adhesive seaming.  Abrading the surface of PVC geomembrane is not required. In order to thermally join textured 60 mil HDPE panels for repairs it is necessary to remove the surface oxidation from each of the polyethylene sheets before extrusion welding.  This process is done using handheld electric grinders using heavy grit sanding disks.  Welding specifications limit the amount of surface grinding to a maximum of 10% of the sheet thickness (6 mils in the case of 60 mil textured HDPE).  (For comparison, 5 mils is the thickness of a sheet of stationery paper).  This means a technician with a hand grinder operating at 1200 rpm using 80 or 100 grit sanding disks is limited to a tolerance of 0.006 inches when grinding the surface of a 51 mil thick textured HDPE liner. (51 mils is the minimum thickness to still be called 60 mil textured HDPE).  Considering he never exceeds (?) the 0.006” limit, at the point of each repair weld on a 60 mil textured HDPE liner, the material can be 45 mils thick and still qualify as 60 mil. This is a reduction in thickness of 15 mils, a full 25% of the original thickness.   This is compared with the 30 mil PVC with a 5% tolerance of only 1.5 mils. We believe the EPA was very aware of the welding repair issues when making recommendations concerning the 30 mil minimum for an FML, but increasing the thickness to 60 mil when using polyethylene.  Some European countries require a minimum of 100 mil thickness for HDPE with zero strain allowed. 9. Welding: 30 mil PVC is now routinely welded using dual-track hot air equipment, allowing for air channel testing of all field welds.  This process is virtually identical to the process of welding 60 mil textured HDPE.  The exception is that 30 mil PVC can also be tested for peel strength along the full length of any field seam using simple, proven air channel methods . 30 mil PVC field welding quality control is actually now superior to that of textured 60 mil HDPE.  Coupled with an electronic leak location survey, it is now possible to test the strength and integrity of the entire length of all PVC field welds, and the integrity of the entire surface of a 30 mil PVC liner installation. 10. Flexibility: PVC is very flexible due to the addition of plasticizers that make the material ideal for geomembrane applications.  Flexibility = Durability.  Forensic analysis of PVC in application after application shows that PVC will effectively do the job year after year in buried geosynthetic liquid containment applications. PVC material has been exhumed by many different researchers, including: The Bureau of Reclamation  (main index) Environmental Protection, Inc. 25-Year-Old PVC Geomembrane 30-Year-Old PVC Geomembrane Long Term Aging Effects PVC Geomembrane Institute 30-Year-Old PVC Geomembrane In addition, continuous research is being done to ensure plasticizer retention (PDF available at bottom of blog) in PVC geomembranes for many future generations. Research continues by The Bureau of Reclamation, EPI ( Long Term Aging Effects ), and the PGI (PVC longevity). Flexibility also impacts how a geomembrane can be affected by folds, wrinkles, or waves in the material.  Textured 60 mil HDPE requires the management of waves and wrinkles during installation to prevent any folds in the material. Folds and wrinkles are not allowed ever in textured 60 mil HDPE.  Folds in textured HDPE will cause stress cracking in the material.  Forensic analysis has also shown that buried waves in HDPE are likely to remain in place throughout the life of the installation and can serve as conduits for liquid flow above or below an HDPE geomembrane. 30 mil PVC on the other hand is extremely flexible due to its amorphous makeup.  Also, PVC has a 60% lower coefficient of thermal expansion (70 x 10-6 cm/cm/ºC) than textured HDPE.  PVC geomembrane is NOT subject to the formation of waves by changes in ambient temperature during the day as is HDPE. In addition, there has been testing on the effects of folds and wrinkles by the Bureau of Reclamation and forensic analysis of actual exhumed PVC geomembrane material to show conclusively that folds and wrinkles have no adverse effect on the long term durability of 30 mil PVC geomembrane. 11. Chemical Compatibility: 30 mil PVC geomembrane has been successfully used for many years for waste containment applications, including municipal landfills, wastewater treatment, and animal waste containment.  EPA 9090 testing has been performed countless times on PVC geomembrane. PVC has been proven to perform effectively in applications requiring resistance to a wide range of chemicals, including municipal solid waste landfills, anaerobic waste treatment ponds, and oxidation ponds. 12. Regulations: Subtitle D regulations determine the thickness of geomembrane used in waste containment applications in the United States of America. Many people involved in the business of waste containment believe that US Government regulations require a minimum of 60 mil thick HDPE for a liner in a municipal waste containment application.  This is just NOT accurate!  The fact is that US Government Subtitle D regulations and all state regulations which use Subtitle D as their guide require a minimum 30 mil thick flexible membrane liner.  This 30 mil liner is used in conjunction with a compacted clay base or some other form of composite liner system.  The 30 mil liner can be PVC, CPE, or CSPE.  What is true though, is that Subtitle D and all of those individual State Regulations require that if the bottom liner used is polyethylene, then (specifically because it is polyethylene) the HDPE can NOT be 30 mil, but is REQUIRED by REGULATION a to be MINIMUM of 60 mils thick. The bottom line is that 30 mil PVC has already been approved by Subtitle D regulations.  Choosing to use polyethylene requires the use of a minimum of 60 mil thick HDPE. This is an excerpt from the regulation: 40 CFR Ch. I (7–§ 258.29 1–02 Edition) Subpart D—Design Criteria § 258.40 Design criteria. (b) For purposes of this section, composite liner means a system consisting of two components; the upper component must consist of a minimum 30-mil flexible membrane liner (FML), and the lower component must consist of at least a two-foot layer of compacted soil with a hydraulic conductivity of no more than 1x10-7 cm/sec. FML components consisting of high-density polyethylene (HDPE) shall be at least 60- mil thick. Click here for individual State regulations Conclusion: 30 mil smooth polyvinyl chloride geomembrane is functionally equivalent to 60 mil textured high-density polyethylene. The combination of physical properties possessed by 30 mil PVC geomembrane gives it the performance characteristics that make it functionally equivalent to polyethylene geomembranes that are twice as thick.  PVC has proven itself to be an ideal solution for long-term containment applications.

Geogrid vs. Geotextile: The Differences in Geosynthetic Materials Geosynthetic materials play a crucial role in enhancing the performance and longevity of infrastructure projects. Two commonly used geosynthetic materials are geogrids and geotextiles. While they may appear similar at first glance, there are fundamental differences in their composition, functions, and applications. Understanding Geogrids Geogrids are geosynthetic materials composed of high-strength polymers, typically in the form of grids or mesh structures. These grids can be made from various materials such as polyester, polyethylene, or polypropylene. The primary purpose of geogrids is to provide tensile reinforcement and improve the stability of soils or aggregates in civil engineering projects. Key Characteristics of Geogrids: Tensile Strength: Geogrids are designed to exhibit high tensile strength in both longitudinal and transverse directions. This characteristic allows them to distribute loads efficiently and restrain lateral movement of soil particles, preventing deformation or failure. Aperture Size and Shape: Geogrids have uniform apertures, often in the form of rectangular or diamond-shaped openings. This structural design enables efficient interlocking with surrounding soil or aggregate particles, creating an enhanced load transfer mechanism. Rigidity and Stiffness: Geogrids possess a rigid structure due to their manufacturing process, providing them with excellent resistance to deformation and elongation. Soil Interaction: Geogrids rely on interlocking mechanisms with soil particles, engaging them to create a composite material that withstands external forces and improves load distribution. Applications of Geogrids Geogrids find applications in various civil engineering projects, including: Reinforcing retaining walls and slopes Stabilizing roadways and railway embankments Enhancing the load-bearing capacity of foundations Preventing soil erosion and facilitating vegetative growth on steep slopes Understanding Geotextiles Geotextiles are geosynthetic fabrics made from synthetic fibers, such as polyester or polypropylene. These fabrics possess unique properties that make them suitable for diverse applications in civil engineering, environmental projects, and geotechnical applications. Key Characteristics of Geotextiles: Filtration and Drainage: Geotextiles act as filters, allowing water to pass through while preventing the movement of soil particles. They facilitate effective drainage, preventing the buildup of excess pore water pressure. Separation and Reinforcement: Geotextiles are used to separate dissimilar materials, such as soil and aggregate, preventing their intermixing. They also provide moderate reinforcement to the soil by distributing loads and reducing differential settlement. Permeability: Geotextiles have controlled permeability, allowing water and gases to flow through while restraining the migration of fine particles. This characteristic prevents the clogging of drainage systems and maintains the stability of the soil. Erosion Control: Geotextiles are employed to mitigate erosion by stabilizing soil surfaces and protecting them from the erosive forces of wind and water. Applications of Geotextiles Geotextiles have a wide range of applications, including: Soil stabilization and erosion control in landscaping and slope protection Separation and reinforcement of soils in road and railway construction Filtration and drainage systems in landfills and retaining structures Protection of geomembranes in environmental containment projects Geogrids and geotextiles, though both geosynthetic materials, have distinct characteristics and serve different purposes in civil engineering and construction projects. By understanding the unique properties of geogrids and geotextiles, engineers can make informed decisions when selecting the appropriate material for their specific project requirements, ensuring optimal performance and long-lasting infrastructure. Ready to speak with an expert about which geosynthetic material is right for you? Contact the experts at EPI today.

Geomembranes have played a vital role in infrastructure development for decades. As technology continues to advance, new materials and innovative applications are shaping the future of geomembranes. There are emerging trends and industry statistics to take note of that highlight the exciting prospects and advancements in the field of geomembranes. Increased Demand for Sustainable Materials One of the prominent trends in the geomembrane industry is the growing demand for sustainable materials. With a heightened focus on environmental protection, there is a shift towards using geomembranes made from recycled or biodegradable materials. These sustainable alternatives provide effective containment solutions while reducing the ecological footprint of projects. Advancements in Geomembrane Manufacturing The manufacturing processes of geomembranes are continually evolving, leading to improved product quality, performance, and durability. Advanced techniques such as extrusion coating, calendaring, and fusion welding are being refined, resulting in geomembranes with enhanced tensile strength, tear resistance, and dimensional stability. These advancements allow for a wider range of applications and longer service life. Integration of Smart Technologies The integration of smart technologies into geomembranes is an emerging trend with immense potential. Sensor-based monitoring systems and geosynthetic embedded sensors are being developed to provide real-time data on factors such as temperature, strain, and leakage. These technologies enable proactive maintenance, early detection of issues, and improved overall performance of containment systems. Growing Applications in Water Management Water scarcity and the need for efficient water management are driving the increased use of geomembranes in applications such as reservoirs, irrigation ponds, and wastewater treatment facilities. Geomembranes provide impermeable barriers that prevent seepage and contamination, preserving water resources and protecting the environment. Expansion of Geomembrane Use in Mining The mining industry is witnessing a surge in the use of geomembranes for tailings management and heap leach pads. Geomembranes play a crucial role in preventing the migration of potentially harmful chemicals and contaminants into surrounding ecosystems. As regulations become stricter, the demand for geomembranes in mining applications is expected to grow significantly. The future of geomembranes is promising, with emerging trends and advancements shaping the industry. Sustainable materials, manufacturing innovations, smart technologies, and expanding applications in water management and mining are driving the growth of the geomembrane sector. As infrastructure demands and environmental concerns continue to grow, geomembranes will play an increasingly crucial role in providing effective containment solutions and safeguarding our ecosystems for years to come.

When embarking on a construction project, selecting the right geomembrane is crucial for ensuring longevity, environmental safety, and cost-effectiveness. Geomembranes are widely used for various applications including waste containment, water management, and infrastructure protection. Here’s a comprehensive guide to help you choose the right geomembrane for your construction project.   Understanding Geomembranes Geomembranes are impermeable membranes used as liners and barriers in construction projects to prevent fluid migration. They are made from synthetic materials such as polyethylene (PE), polyvinyl chloride (PVC), and ethylene propylene diene monomer (EPDM).   Factors to Consider When Choosing a Geomembrane Project Requirements : The specific needs of your project, such as the type of containment, environmental conditions, and regulatory requirements, will dictate the choice of geomembrane. Material Selection : High-Density Polyethylene (HDPE) : Known for its chemical resistance and durability, HDPE is ideal for landfill liners and mining operations. Linear Low-Density Polyethylene (LLDPE) : Offers more flexibility compared to HDPE and is suitable for applications requiring a better fit to complex shapes. PVC : Flexible and easy to install, PVC is commonly used in water containment and agriculture applications. EPDM : Highly flexible and resistant to UV exposure, making it perfect for exposed applications like ponds and canals. Thickness and Durability : Thicker geomembranes offer better puncture resistance and longevity, essential for heavy-duty applications. The durability required depends on the exposure conditions and expected lifespan of the project. Installation Considerations : The ease of installation can impact the overall cost and timeline of the project. Materials like PVC and LLDPE are easier to handle and install compared to stiffer options like HDPE. Environmental Impact : Consider the environmental regulations and the potential impact of the geomembrane on the local ecosystem. Opt for materials that are environmentally friendly and comply with industry standards.   Application-Specific Geomembrane Choices Waste Containment : For landfill liners and hazardous waste containment, HDPE is preferred due to its high chemical resistance and durability. Water Management : LLDPE and PVC are commonly used for lining reservoirs, ponds, and irrigation canals because of their flexibility and ease of installation. Mining and Industrial Applications : HDPE is suitable for leachate containment in mining operations, offering excellent resistance to chemicals and harsh conditions.   Selecting the right geomembrane for your construction project involves careful consideration of the material properties, project requirements, and environmental factors. By understanding the different types of geomembranes and their applications, you can make an informed decision that ensures the success and sustainability of your project. For more information on geomembrane products and solutions, visit our Products Page.

EPI - The Liner Company, a pioneer in the geomembrane industry since 1980, stands at the forefront of environmental protection. Specializing in high-quality geotextile and geomembrane products, EPI has been instrumental in advancing landfill and environmental remediation technologies. Geotextiles in Landfill Liners and Caps In the realm of modern landfill design, where precision and durability are paramount, EPI's geotextiles play a critical role. These advanced materials form part of the composite systems that line and cap landfill cells, effectively preventing contamination of surface and groundwater. Their products demonstrate outstanding performance in filtration, separation, and protection of geomembranes, ensuring the long-term integrity of landfill structures. Groundwater Protection and Leachate Control A key concern in landfill operations is the protection of groundwater and efficient control of leachate. EPI's geotextiles are engineered to excel in these aspects. They offer unmatched durability, chemical resistance, and puncture resistance, vital for withstanding the challenges posed by hazardous leachate collection. These properties ensure that EPI's geotextiles are not just effective but also provide a sustainable solution for environmental management. Applications in Environmental Remediation Projects EPI's geotextiles find extensive application in various environmental remediation projects. Their adaptability and superior performance make them ideal for applications ranging from leachate collection to erosion control and slope stabilization. The use of EPI's geotextiles in these projects underscores their contribution to environmental sustainability and protection. EPI - The Liner Company's geotextiles are more than just products; they are integral components in the fight for a cleaner, safer environment. By offering solutions that blend innovation with reliability, EPI continues to set the standard in the geomembrane industry, ensuring that our planet's future remains secure.

Using Geotextiles for Drainage Systems Increased Permeability: When strategically placed within the soil profile in drainage systems, geotextiles significantly enhance soil permeability. This improvement allows water to flow more freely, reducing the risk of waterlogging in agricultural fields, civil engineering projects, and various landscaping applications. Geotextiles contribute to enhanced plant root health, reduced surface runoff, and the prevention of soil erosion in areas prone to water saturation by facilitating efficient water movement. Erosion Control: Geotextiles play a pivotal role in erosion control within drainage systems, providing a protective layer that stabilizes soil and prevents its displacement. This erosion prevention is crucial for maintaining the structural integrity of embankments, retaining walls, and other drainage infrastructure. Beyond erosion control, geotextiles also aid in sediment retention, reducing the transport of soil particles and contaminants in stormwater runoff. This assists in preserving the ecological balance of downstream environments. Reinforcement of Soil Structure: In road construction and embankment projects, geotextiles act as a reinforcing agent for the soil structure. By distributing loads more evenly and reducing settlement, these fabrics enhance the stability of the drainage system and contribute to the longevity of the constructed infrastructure. Additionally, geotextiles minimize the potential for differential settlement, a common issue in road construction, ensuring a smoother and safer surface for vehicular traffic. Filtration Applications of Geotextiles Particle Retention: Geotextiles serve as highly efficient filters, selectively allowing water to pass through while preventing the migration of fine soil particles. This particle retention function is crucial for applications such as subsurface drainage, where maintaining soil structure and preventing clogging are paramount. By providing an effective barrier against soil movement, geotextiles contribute to the overall stability of embankments, ensuring that the drainage system remains free from the detrimental effects of soil intrusion. Sediment Control: Geotextiles excel in sediment control applications by capturing and containing suspended particles, preventing their discharge into water bodies. This sediment control is essential in construction sites where soil erosion and sediment runoff can have adverse environmental impacts. Additionally, geotextiles offer a sustainable solution for mitigating sedimentation in water bodies, promoting responsible land management practices and supporting compliance with environmental regulations. Protection of Drainage Pipes: Geotextiles act as a protective layer around drainage pipes, safeguarding them against the intrusion of fine soil particles. This protective function ensures the optimal functioning and prolonged lifespan of drainage systems, reducing maintenance requirements. By mitigating the risk of pipe clogging, geotextiles contribute to the efficiency of subsurface drainage systems, preventing water stagnation and maintaining the integrity of the overall infrastructure. Benefits of Geotextiles in Preventing Soil Clogging Prolonged Lifespan of Infrastructure: Geotextiles play a pivotal role in preventing soil clogging, thereby significantly extending the lifespan of drainage infrastructure. This longevity is especially crucial in subsurface drainage applications, where clogging can impede water flow and compromise the overall effectiveness of the system. The incorporation of geotextiles in drainage projects ensures sustained functionality, reducing the need for frequent maintenance interventions and minimizing the associated costs for property owners and municipalities. Improved Water Quality: Beyond infrastructure longevity, geotextiles contribute to improved water quality within drainage systems by preventing soil clogging. By minimizing the transport of sediments and contaminants, geotextiles help ensure that the discharged water meets stringent environmental standards. This focus on water quality underscores the importance of geotextiles in sustainable land management practices, promoting environmentally responsible solutions for managing stormwater runoff and preserving the health of aquatic ecosystems. Sustainable Land Management: Geotextiles play a vital role in promoting sustainable land management practices by preventing soil clogging and reducing the need for frequent maintenance. This sustainable approach not only saves costs but also minimizes the environmental impact associated with recurring interventions in drainage infrastructure. Through their role in maintaining optimal water flow and preventing soil erosion, geotextiles contribute to a holistic and environmentally conscious strategy for managing water resources, supporting ecosystems, and ensuring the longevity of infrastructure investments.

Understanding Geonets Geonets are three-dimensional, synthetic drainage materials used to address a variety of environmental and geotechnical challenges. Made from high-density polyethylene (HDPE) or polypropylene, these durable and versatile nets are designed to provide cost-effective and efficient drainage solutions in various industries, including waste management, mining, and construction.   Applications of Geonets Geonets are highly adaptable and can be used in a range of applications: Erosion control : Geonets serve as soil stabilizers, preventing erosion and ensuring the safety of slopes and embankments. Landfill leachate management: As a critical component in landfill liner systems, geonets help collect and remove leachate, thus preventing groundwater contamination. Gas venting: Geonets installed in landfill cover systems allow for safe and effective gas venting, mitigating the risk of explosions and reducing greenhouse gas emissions. Mining: Geonets are employed for heap leaching processes in the mining industry, aiding in the collection and management of leachate and maintaining the integrity of the heap. Road construction: Geonets improve the strength and stability of subgrade soils, extending the lifespan of roads and reducing maintenance costs.   The Benefits of Geonets Geonets offer several advantages over traditional drainage solutions: High flow capacity: Geonets have a high flow capacity, allowing for efficient and rapid drainage even in low permeability soils. Durability: The materials used in geonets are resistant to chemicals and ultraviolet (UV) radiation, ensuring a long service life. Cost-effectiveness: Geonets are lightweight and easy to install, reducing labor and transportation costs. Environmental sustainability: Geonets help prevent soil erosion, groundwater contamination, and greenhouse gas emissions, contributing to environmental protection and sustainable practices.   EPI and Geonets At EPI, we are committed to providing innovative and sustainable solutions for environmental and geotechnical challenges. With years of experience in the industry, we offer high-quality geonets, tailored to the specific needs of our clients. Our team of experts will guide you through the process, ensuring the correct geonet selection, design, and installation for your project. With our dedication to customer satisfaction and environmental stewardship, you can trust EPI to deliver reliable and cost-effective geonet solutions for your needs.   Embrace the Future of Environmental Protection with Geonets Geonets are revolutionizing the way we manage environmental challenges, offering efficient and sustainable solutions across various industries. Choose EPI - Environmental Protection, Inc. for your geonet needs and join us in building a greener, safer, and more sustainable future.

5 Key Factors to Consider When Selecting a Geomembrane Geomembranes play a vital role in environmental protection by acting as barriers for containment and controlling the migration of various substances. EPI is a leading provider of high-quality geomembrane solutions tailored to your project's unique requirements. When choosing a geomembrane, it's essential to consider the following five factors to ensure the right fit and optimal performance. 1. Material Type Different geomembrane materials offer varying levels of durability, flexibility, and chemical resistance. Common materials include high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polyvinyl chloride (PVC), and more. Consider the properties of each material and choose one that best suits your application, taking into account the substances it will be in contact with and the environmental conditions.   2. Thickness Geomembrane thickness is crucial for its overall performance, including puncture resistance and durability. Thicker geomembranes generally offer better protection and longevity, but they may also be less flexible and more challenging to install. Choose a thickness that balances the need for strength and durability with ease of installation and project requirements.   3. Site Conditions Evaluate the site conditions where the geomembrane will be installed. Consider factors such as soil type, groundwater levels, temperature fluctuations, and potential exposure to chemicals or UV radiation. Understanding the site conditions will help you select a geomembrane with the appropriate properties and ensure its long-term performance.   4. Installation Method The method of installation can significantly impact the effectiveness and longevity of a geomembrane. Common installation methods include welding, adhesive bonding, and mechanical fastening. Collaborate with experienced professionals like EPI - Environmental Protection, Inc. to determine the most appropriate installation method for your project and ensure proper installation procedures are followed.   5. Manufacturer and Supplier Reputation Choosing a reliable and reputable geomembrane manufacturer and supplier, such as EPI, is critical. Ensure the manufacturer has a proven track record of providing high-quality products that meet industry standards and certifications. Additionally, consider their customer service, technical support, and warranty offerings to ensure a smooth and successful project.   Selecting the right geomembrane for your project is essential for optimal performance and long-lasting environmental protection. Consider factors such as material type, thickness, site conditions, installation method, and manufacturer reputation when making your decision. EPI is here to assist you in making the best choice for your project and providing unparalleled geomembrane solutions. Contact us today to discuss your needs and let our experts guide you through the process.

PVC AND HDPE GEOMEMBRANES IN MUNICIPAL WASTE LANDFILL LINERS AND COVERS: THE FACTS Presented to MICHIGAN DEPARTMENT OF NATURAL RESOURCES  By Dr. I.D. PeggsI-CORP INTERNATIONAL Ocean Ridge, FL THE PVC GEOMEMBRANE INSTITUTE INTRODUCTION The selection and design of the geomembrane components of landfill lining and cover systems are not simple matters if optimum durability is required. A designer cannot blindly take any material of a predetermined regulated (implying satisfactory) minimum thickness "off the shelf" and apply it for all systems, on all slopes, on all subgrades, with all leachates, in all environments, and for all landfill operating procedures. If this practice is followed, and often it is, the liner is not "designed" and will probably fail before its intended service life. And there have been a significant number of geomembrane failures in all types of landfills and liquid impoundments.There is not one universally acceptable geomembrane material because all materials have their Achilles Heel - it is simply a matter of recognizing the negative feature of each material and designing around it, to take advantage of the positive aspects of each material. This is why geomembrane lining systems need to be competently designed in the first place, and then be approved by informed regulatory design engineers. Geomembrane thickness is an integral parameter in the design process and should not be arbitrarily legislated at one value to cover all potential materials. The flexibility to properly design a given system is essential, if optimum performance is to be achieved, and if advances in materials are to be taken advantage of. It is not my intention in this document, and in the associated meeting, to show that PVC is a better geomembrane than HDPE, and that all lining and cover systems can be built with PVC. However, it is my objective to show that PVC, in its variant forms, has a large number of very desirable properties and, therefore, is an excellent candidate material for consideration in all lining systems. HDPE cannot arbitrarily be used in all lining systems. I am in the midst of a failure analysis of an HDPE lining system that failed after 18 months use despite there being a written guarantee from the manufacturer that the material was chemically compatible with the impoundment contents. I have a second failure that occurred after 5 years in a plant that produced the HDPE resin from which the geomembrane was manufactured to line its own waste facilities. In this latter case the resin manufacturers were not aware that their resin was inadequate for geomembrane applications. There is a general feeling at the grass roots level of the regulatory and designing arenas that HDPE is the geomembrane of choice and will meet most waste containment performance requirements. It will not do that, and those who have had failures certainly would not agree with that feeling. I believe that the extreme confidence that the geomembrane users place in HDPE is as unjustified as the lack of confidence they place in other materials such as PVC. And this is somewhat strange since PVC has been so successfully used for waste containment for over 36 years. I would like to dispel the myths of PVC and HDPE so that they will both come out of the starting gate being considered by competent designers on their technical merits (and demerits) only - not with preconceived emotional feelings. The regulatory agencies must play a large part in this procedure by positively requiring comprehensive design processes, and not by imposing restrictions that unintentionally discourage necessary design efforts. Certainly it may be necessary to define the "entry level", or to make the "initial cut", but this must not be done in such a way that the intended minimum criteria be perceived as the only criteria that need to be met. And the minimum criteria should not be written in such a way that, unintentionally, adequate candidate materials, both old and new, are eliminated. In the first draft of Act 641 a single minimum thickness (60 mil) for any geomembrane used in lining and cover systems was proposed. Such a requirement effectively defined that only HDPE could be used as a geomembrane. The Department of Natural Resources is to be commended for recognizing the inadequacies of this draft and for making appropriate, professional allowance for the use of three specific materials and for leaving the door open for new geomembranes as they become available. Such a regulatory approach is like a breath of fresh air for designers and offers the potential for competent, durable lining system designs. There are two groups of people and institutions that always have, and always will lose their battles: those who stick with the old, ignoring new developments, and those who blindly jump to the new, not fully recognizing the problems of the new. Those who remain flexible and take advantage of both will be the winners. The PVC geomembrane manufacturers are recovering from the former. Those who have had HDPE failures are suffering from the latter.As you consider PVC and HDPE geomembranes remember that there are many types and grades of each of them. Saying "HDPE" and "PVC" is like saying "steel": there are many different types of steels (ferritic, austenitic, martensitic, and others) formulated to meet different service conditions. There are many different PVCs formulated with different additives to meet different environmental conditions. HDPEs also are different but they are different not so much by design but by default, due to the different resin types. The factors responsible for the vastly variable fundamental stress cracking resistance (mechanical durability) of HDPE are not yet fully understood, and, therefore, cannot be intentionally engineered. Just because a failure has occurred in a PVC or HDPE geomembrane does not automatically mean that all other PVC and HDPE products will fail under the same circumstances. Except for a relatively small number of failures that have occurred due to the selection of inappropriate materials the majority of geomembrane failures have occurred due to inadequate design, poor installation workmanship, or inattentive CQA. There is no question that, to prevent failures, the emphasis must be placed on proper design and CQA. And this, most certainly, includes proper design after the correct material has been selected. Michigan's Act 641 will certainly help achieve this goal in its second draft form.  PVC PERFORMANCE I will attempt to dismiss some of the myths of PVC and put the performance of HDPE into perspective. The following concerns are usually expressed about PVC : It contains pinholes and therefore a lining cannot be made leak-free. It does not have adequate chemical resistance. It does not have adequate weathering resistance to UV and thermal radiation. It becomes brittle at low temperatures. Plasticizers leach out, or volatilize, causing unacceptable material degradation. The CQA associated with PVC is inadequate. In assessing these features one should keep in mind that the major factor is whether the material concerned continues to function as intended. The fact that some changes occur is irrelevant unless they affect the functional performance of the geomembrane. In other words, different materials may change at different rates as they age, but both could still provide in excess of the required performance. The fact that one changes more than another is irrelevant.   Pinholes Since a geomembrane is intended to be an impermeable barrier, pinholes are not desirable features. However, no geomembrane is absolutely impermeable, and it is doubtful that any sizeable geomembrane will be installed without some construction induced damage and a few sections of inadequate seaming that might leak. After all, the premise of the double lining system is that a single liner cannot be made leak-free. This is, however, no reason to tolerate the existence of pinholes in any geomembrane, but it may put the existence of the one or two pinholes that may exist into practical perspective. In all CQA Plans, project specifications, and regulatory aspects, it is necessary to remember that ideals are unachievable and that the real world (practical) situations require some compromise. PVC sheeting has been made in thin gages (as low as 4 mil) for vapor barriers, swimming pool liners, and other critical medical applications for many years without pinholes. With continuous in-plant backlighting and QC techniques, geomembranes with pinholes should not appear on site. There are ASTM standards (e.g. D4451) and Federal Specifications (e.g. L-P-375C) that demand that PVC membranes in thickness greater than 10 mil contain absolutely no pinholes. Alberta Environment has used many millions of square feet of 20 mil PVC geomembrane irrigation canals and, several years ago, had a specification of 1 pinhole (maximum) per 100 ft2 of geomembrane. After thorough examination of a large amount of geomembrane they concluded that pinholes were statistically non-existent. Improved methods of calendering have effectively eliminated pinholes in PVC sheet and geomembranes. Three or four separate rolling actions ensure there are no holes. Alberta Environment did find a minor problem with gel defects (cold roll) under startup conditions, but discussions with the manufacturers prevented such material being delivered to the site. Similar (gel) problems can occur in HDPE when agglomerates of decomposed HDPE find their way through the extruder into the geomembrane. They can sometimes be identified as bumps, or solid blisters on the surface of the geomembrane. They may also be confused with carbon black agglomerates when making carbon dispersion measurements, if the carbon black is not properly dispersed. Agglomerates of carbon black have been seen to initiate stress cracking. The US Bureau of Reclamation has had similar experience with (the lack of) pinholes in PVC geomembrane. Many years ago (1960's) they experienced a few pinholes in 10 mil material, but after moving to 20 mil geomembrane, found it was unnecessary to have a pinhole specification. They have done a large amount of laboratory testing with 20 mil PVC, such as hydrostatic burst and puncture testing, and have never had a premature test failure due to pinholes. They have also used 20 mil PVC, in 5 x 10 ft panels, to provide critical water proofing in other laboratory tests, without premature failures. It would, however, be foolish to state that PVC geomembrane contains absolutely no pinholes since one cannot be absolute. But the numbers that may escape manufacturing and fabrication QC procedures are very small, and are effectively zero when compared to other construction damage that can produce leakage. It would be even more foolish to state that PVC contains pinholes and HDPE does not. In my last visit to an HDPE geomembrane manufacturing plant I saw holes in geomembrane from a few millimeters diameter to holes one could put one's fist through. In a recent CQA project I.CORP found a 60 ft length of 60 mil HDPE geomembrane that contained about 10 holes up to 80 mils in diameter. Both HDPE and PVC geomembranes can, therefore, appear in the field with holes. However, with appropriate specifications, and good in-plant QC and field CQA, holes in both PVC and HDPE can be effectively eliminated, or be caught and repaired. Chemical Resistance For landfill applications the chemical resistance of the proposed geomembrane to the leachate is assessed by EPA Method 9090 "Compatibility Test for Waste and Membrane Liners". In this test the geomembrane is exposed to leachate at 23 and 50°C for 120 days. Changes in properties are measured every 30 days. If there is no continuing degradation trend, or if changes that reach an equilibrium condition within certain limits occur, the geomembrane is considered to be compatible with the leachate. For practical purposes it is immaterial whether one of two types of the same material, or one of two different materials, degrades more than the other if both still, and will continue to, adequately meet the project specifications. There is no question that for any given chemical containment requirement there is more chance that HDPE (but not all HDPE's), rather than PVC, will provide the better chemical resistance. However, for most municipal waste leachate applications it is probable that, although HDPE may be technically more resistant, PVC may provide more than adequate resistance for the required service. The historical performance of PVC geomembrane in Michigan and elsewhere has proven this. It could be an unreasonable trade off to use the fundamentally more chemically resistant material if it is more expensive, and with poor design, poor installation practice, and poor CQA could lead to other durability problems. Most installers surveyed (Appendix A) for this project feel that PVC is much easier to install correctly than HDPE. A European contact stated, appropriately and realistically: "PVC is not suitable for ALL chemical contacts, but PVC is one of the best materials for the ratio price/properties, mechanical properties, weldability, and permanent elongation." Three laboratories that perform EPA Method 9090 testing were surveyed for this project: GeoSyntec Consultants, Precision Laboratories, and Texas Research Institute. All have performed, or are presently performing, tests on PVC in hazardous and municipal leachates. None of the PVC geomembranes has failed the test. One of the tests in hazardous leachate has been performed at 85°C and, even though there has been some loss of plasticizer, the PVC geomembrane successfully passed the test. This confirms that it is extremely important to recognize that, even though some changes in properties occur the material may still provide adequate service. Two of the laboratories commented that if owners and regulatory agencies were concerned about the chemical resistance of PVC, a move to Oil Resistant grades of PVC should more than put those concerns to rest. Out of a total of approximately 55 EPA Method 9090 tests recently performed by all three laboratories on PVC, only two displayed problems; with solvent seams. However, not all solvent seams were problematic in EPA Method 9090 testing. None of the dielectric seams tested gave problems. It Is clear, that to obtain the optimum combination of material and performance, it is essential to experimentally assess the leachate resistance of each material and its seams. Semi-crystalline materials, such as HDPE, should, in addition, be tested under stress in the leachate to assess their stress cracking resistances. Chemical resistance work presently underway in France, in which PVC, HDPE, and other geomembranes have been exposed to an MSW leachate for 1 year, has shown that both HDPE and PVC have suffered loss of additives from only a 100 m m surface layer. (Artieres, Sardinia 91 Landfill Conference). The second draft of Act 641 specifies that resistance to leachate shall be assessed by performing the EPA Method 9090 test. On this basis, of the 55 tests performed by the three laboratories surveyed, PVC geomembranes were appropriate for containing 53 of the leachates. PVC is unquestionably a stable material for containing landfill leachates, as has been proven in Michigan. I have investigated three HDPE liner failures in which the standard chemical resistance tables indicate that the HDPE is compatible with the contents of the ponds (nitric acid and black liquor). In one case the liner manufacturer had provided a written guarantee that the HDPE would be resistant to the black liquor for 10 years. The black liquor pond failed after 12 to 18 months by environmental stress cracking. The nitric acid pond failed after 9 months, also by environmental stress cracking. In the latter case there was even sufficient residual stress in the extruded fillet seam bead to initiate stress cracking in the bead, independently of the service stress on the geomembrane. Two of the laboratories commented that municipal waste leachates are getting weaker, as the wastes placed in landfills become more controlled. The third agreed in principal, but identified two municipal leachates they have tested as containing "bad actors". In the recently promulgated Part 258 of 40 CFR "Criteria for Classification of Solid Waste Disposal Facilities and Practice" (colloquially known as Subtitle D), there are indications (pp 24 and 25) that there is little difference in the toxic constituents of leachates generated in true municipal waste landfills (built since 1980) and those operated prior to 1980 that contained industrial wastes in addition to municipal wastes. It is, therefore, possible that in Michigan the municipal landfills that accept industrial wastes may not have significantly more obnoxious leachates than those that accept municipal waste only. Such co-disposal of municipal and industrial wastes can be used to advantage since there is evidence that it can be done in such a way as to promote the degradation of the municipal waste (Sardinia '91 Landfill Conference). There is a large amount of evidence, not only from EPA Method 9090 testing, but also from field experience, that PVC is satisfactorily containing municipal waste leachates. There are more than approximately 30 PVC lined landfills in Michigan that are performing satisfactorily. The few problems that have occurred are, as in most HDPE failures, related to inadequate design, poor installation, and/or poor CQA. Samples of PVC geomembrane removed from the sump of Lycoming County, PA, landfill after exposure to leachate for 11 years are still very flexible and show no visible signs of degradation. In summary, there is no justification for taking the following two approaches to geomembrane chemical resistance; to dismiss PVC out of hand saying it does not have adequate leachate resistance, and; to assume that HDPE will perform adequately without appropriately testing it, even though the manufacturer may provide a written guarantee.  Weathering and Thermal Resistance This is the most confusing area of concern with PVC, and may relate to our need to understand that there are different grades or PVC, since we, in North America, are adamant that PVC should not be left exposed to the elements. Yet, in Europe, PVC is quite regularly left exposed on critical installations, such as the upstream faces of hydroelectric dams. In one installation PVC has provided excellent service for more than 12 years at an elevation of over 6000 ft. In Sicily an exposed PVC roofing membrane has provided a watertight seal at a chemical plant for over 18 years. The US Bureau of Reclamation has investigated 10 mil thick PVC geomembrane that has been installed on irrigation canal side slopes for up to 27 years, and while it has lost some plasticizer, there is still sufficient plasticizer remaining for the geomembrane to have adequate ductility and flexibility for continued service. Once again, the important factor is that material still performs its intended function despite the fact that it has aged. Plasticizers are added in sufficient quantities for the intended service, recognizing that some might be lost in service. Similarly, antioxidant packages are added to HDPE to prevent damaging thermal oxidation during extrusion, seaming, repairing, and service. Just as PVC can lose its plasticizer during aging, HDPE can degrade by consumption of antioxidant as it experiences temperatures as high as 80 o C or more in summer sunshine. In other words it is expected that these additives will be lost during different phases of service, but that fact alone is immaterial provided sufficient additive remains. It has been reported that 40 mil PVC has successfully survived one year EMMAQUA (standard sunlight exposure) testing and that 60 mil HDPE has failed this test. On the other hand it is probable that there will be HDPEs that would survive this test and PVCs that would not. In fact, it has been stated by the US Bureau of Reclamation that a one year EMMAQUA test "may be too long, resulting in accelerated weathering conditions too severe for some materials". All PVCs and all HDPEs are not created equal. Therefore, it is not a matter of simply stating that PVC is better than HDPE (or vice versa) for a specific use; one should also consider that one grade of HDPE may be better than another, or one type of PVC may be better than another. PVC geomembranes are now being successfully heat seamed in the US. They have been successfully heat seamed for many years in Europe. If the geomembrane can tolerate seaming temperatures without degrading in service at the seams, it can tolerate exposure to sunlight for extended service periods, as proven on dams, roots, and canal banks. For landfill uses most weathering/thermal problems are eliminated by the regulatory requirement for covering the liner with various types of soil and other geosynthetic layers. Such layers protect the geomembrane from ultraviolet and severe thermal effects. Act 641 requires that geomembranes be covered by soil within 30 days. Concern has been expressed about the potential problems of a landfill PVC cover material being exposed to weathering when overlying soils are eroded. This should be considered to be a problem with the design of the cover system rather than a potential problem with the geomembrane. It is, surely, unacceptable for any soil cover, on any landfill cover system, to erode to expose the geomembrane, whatever the geomembrane material. Proper separation, filtration, and drainage layers (probably geosynthetics) as required in EPA recommended designs will prevent soil erosion. Act 641 requires that erosion of soil in the cover system shall be prevented.  Low Temperature Brittleness PVC canal liners with an Alberta Environment brittleness temperature specification of -20°C (ASTM D1790) have been successfully installed in Canadian winters. When deployed, a covering layer of stones is dumped onto the geomembrane from a conveyor belt. This is a severe cold impact test. National Sanitation Foundation International Standard 54 "Flexible Membrane Liners" specifies a maximum brittleness temperature of -29°C for the geomembrane. This is even more stringent than the Canadian specifications which have proven satisfactory in harsh service environments. Since most landfill CQA Plans require that geomembrane shall not be seamed (thereby meaning "installed") below 5°C, PVC should be able to withstand most installation environments. Once installed, the soil cover will protect the geomembrane from extremely low temperatures. Even if the temperature does reach the -20°C range under the soil, a PVC geomembrane would continue to provide adequate protection. If the geomembrane is only subject to static loading it will be protective to much lower temperatures than -30 o C, since the brittleness temperature is determined by an impact procedure (ASTM D1790). The measured brittleness temperature of HDPE appears to be considerably lower than that for PVC, but once again, is this really of practical significance? It will depend on the particular installation. (It should also be noted that PVC is tested by impacting a bent strip, while HDPE is tested by striking a single thickness cantilevered specimen. The PVC test is far more severe and will, therefore, show a higher brittleness temperature.) If PVC has other favorable properties, but for some project specific reason must be installed when it is cold, it is only necessary to take a little extra care during its installation. This is no different to the extra care that is required when installing HDPE to minimize its potential for stress cracking in service. A majority of designers and installers surveyed (Appendix A) for this project agree that PVC has better mechanical property characteristics and is easier to install than HDPE. HDPE is a problem because of the yield point in its stress/strain curve that occurs at approximately 12% strain. This point of instability is of major concern to the designer. When allowing for biaxial stress conditions, as occur in geomembranes in the field, and low temperatures, it is necessary to design for maximum strains in the order of 2 or 3%. Since PVC does not have a yield point the designer can make use of strains to the breaking point - in excess of 300% at room temperature under uniaxial conditions. The level of comfort gained by the designer when using a material that has a steadily changing stress/strain curve is significant; the designer is able to give a facility owner a much safer installation, or one with a lower factor of safety and, therefore, a wider range of safe operating conditions. However, once again, mechanical properties are not the only factors that should be considered in liner/cover design. If the subgrade is not subject to settlement, tensile properties may be of little significance. If slopes are steep, and friction angles are high on one side of the geomembrane and low on the other, mechanical properties could be extremely important. Plasticizer Leaching and Volatilization This has been dealt with partially in Section 2.2. Plasticizer loss does occur, but in most cases has been shown to be of no practical consequence. Similarly the consumption of antioxidants in HDPE occurs and has been shown to be of little practical consequence. When the fundamental chemical resistance of the geomembrane to the leachate is correctly assessed, or materials with the correct additive packages are exposed to UV/thermal radiation, both PVC and HDPE will provide adequate durability in landfill liner/cover applications.The Bureau of Reclamation has shown that 30% of the plasticizer in a 10 mil PVC geomembrane may be lost within 4 years, but that after 19 years the geomembrane still contains over 50% of its plasticizer. Such material is still very flexible. As with most processes, the rate of loss of plasticizer decreases with time. A number of studies have shown that even if 75% of the plasticizer is removed from PVC causing the geomembrane strength, and puncture and tear resistances, to increase and the ductility to decrease, the elongation at break may still exceed 100%. This value is still more than 10 times greater than the useful strain allowable in HDPE. In HDPE, once the yield strain has been exceeded the material will continue to elongate at a stress lower than the yield stress. For design purposes HDPE has failed at the yield point. Plasticizer has been claimed as being a desirable food to rodents, which there by chew holes in PVC liners. Where rodents have consumed PVC in the field they have only done it to gain access to the warmth behind the liner, not because they find it good to eat. A survey of users identified only one positive case where this has occurred. On the other hand, HDPE is claimed to be inedible by rodents. However, at the Somerset Generating Station of New York State Electric and Gas there is ample evidence, in the form of 1-in. diameter holes, that vole-type rodents find HDPE extremely edible. Both these cases may be the exceptions that prove the rule, but they also identify the danger of generic statements and the resultant possibility of avoiding perfectly adequate materials based on misstatements. Quality Control and Construction Quality Assurance. There is a feeling that the qualities of HDPE geomembranes and geomembrane seams are higher than those of PVC since the HDPE industry has more visible QC documentation, and CQA documentation is more extensive. Comprehensive CQA is absolutely essential for HDPE, particularly in locations such as Michigan, where it can be very cold, since its service performance is critically dependent upon proper installation - it is not as forgiving a material as PVC. HDPE's window of seaming parameters is narrow, allowance for expansion/contraction and wrinkling must be provided, and the conditions that produce stress cracking must be avoided. It is not surprising that more CQA attention is paid to HDPE. Many owners of facilities have demanded detailed CQA Plans for HDPE, but only recently have requested that similar CQA Plans be prepared for PVC installations. The manufacturers and installers of PVC geomembrane, at their own discretion, have also recently generated comprehensive QC documents and CQC Plans. The past absence of CQA Plans for PVC has unquestionably been a function of most designers' experiences with PVC, and the fact that PVC has generally performed satisfactorily without major installation controls. The survey (Appendix A) of nationally recognized designers and geomembrane installers (those who regularly install PVC and HDPE) in the USA and Canada elicited the fact that most felt most comfortable working with PVC, then VLDPE, and finally HDPE.  A number of significant comments returned with the survey were as follows: "Some HDPE resins are a (expletive) to weld and some are easier, the whole gamut of seamability". "PVC is hard to generalize, there are so many types available". "Although the mechanical and temperature characteristics of HDPE are less than ideal, its chemical inertness and weldability make it the material of choice". "PVC has the best overall mechanical properties". "I feel most comfortable with all the types of geomembranes and all design aspects, except repairability". "PVC is low tech seaming high performance product. HDPE is high tech seaming". "Eliminate chemical resistance and long term stability and HDPE doesn't have much going for it".   It is clear that neither PVC nor HDPE is the better geomembrane in all applications. It is also clear that a selection must be made on a project specific basis, with due allowance being made for the less desirable features of each material. Experienced designers will take each material on its own merits and not pre-select it based on generalities. With the promulgation of Subtitle D, and the development of Michigan's Act 641, all geomembrane installations will require comprehensive CQA programs, thereby putting HDPE, PVC, and other materials on an equal footing. However, it will still be necessary to ensure that the correct information is requested in the CQA Plan, and that each Plan is customized to account for the potentially problematic parameters for each material, whether that material is PVC or HDPE.  Seams All geomembranes require some field seaming. It is universally recognized that field prepared seams are potentially the most problematic feature of lining systems. The width of HDPE geomembrane rolls is steadily increasing in order to minimize the number of field seams required. PVC, on the other hand, is seamed under controlled conditions in the fabrication plant to produce larger panels, thereby reducing the number of field seams required. In a given liner area the length of field seam required in PVC may be 20% of that required in HDPE. It is, therefore, a matter of rationalizing whether, for any specific project, it is better to have fewer field seams with the potential problems that PVC might have, or more seams with the problems that HDPE might have. This is a decision only the designer can make. Such a point was concluded by the Bureau of Reclamation in their study on the chemical exposure and weathering of FML field seams, (EPA/600/S2-87/015): "Generic-type material specifications are not sufficient to ensure satisfactory performance of FML seams when used for hazardous waste containment applications".  Thickness For many years EPA has recognized, as now has Michigan DNR, that a single minimum thickness is not an adequate criterion for geomembranes used in landfill liner and cover applications. All materials are not equal, and cannot so simply be reduced to a single common denominator. Due to its semicrystalline nature HDPE is a different breed of geomembrane, and within its ranks are many sub-species. Even if a single thickness requirement is based on HDPE there are many types of HDPE geomembrane that would not perform satisfactorily even at twice a minimum thickness of 60 mil. At this moment I am examining a stress cracking failure that occurred, after five years service, in an HDPE liner 100 mil thick that was not exposed to low temperatures. In such instances thickness has absolutely no influence on the durability of the geomembrane - other parameters must be considered. Other parameters must be considered for every type of traditional and novel geomembrane. A single thickness value, such as 60 mil, is selected based on HDPE, but where realistic technical considerations have been given to other materials, such as PVC and Hypalon, thicknesses in the range of 30 mil are considered adequate. In Subtitle D (p32) a composite bottom liner is required to have a primary geomembrane with a minimum thickness of 30 mil. If the geomembrane is HDPE it must be at least 60 mil thick. A higher thickness for HDPE is required to make allowance for its problematic features; it is extremely difficult to seam at thicknesses less than 40 mil, and the grinding required on preparation for fillet extrusion seaming produces reduced thickness in the notch sensitive area at the edge of the seam. In fact, with a tolerance of +10% (NSF 54) on HDPE geomembrane thickness and the supposed maximum grinding depth (EPA/530/SW-91/051) of 10% of thickness, 60 mil HDPE geomembrane could be almost 40 mil thick adjacent to extruded seams, patches, and penetrations. EPA has stated (EPA/530/SW-91/054): "the design engineer should recognize that some geomembrane materials may require greater thicknesses to prevent failure or to accommodate unique seaming requirements." The norm is the 30 mil figure. HDPE is the exception that requires additional thickness. PVC and the other geomembranes should not be penalized because of HDPE's perceived deficiencies. One disadvantage, therefore, of specifying a minimum thickness is that it may eliminate excellent candidate geomembranes. Even the best available geomembrane, that would perform adequately at lower thicknesses, may be eliminated on the basis of cost at higher thicknesses. The intent of regulations is to provide safer waste containment, not simply more expensive waste containment. And, as we have seen, a minimum thickness may not be functional, even if that thickness is tailored for the specific material selected. The second disadvantage of specifying a minimum thickness, whether or not there are one or two values to suit different materials, is the danger that some "designers" will read it as a specification, i.e. a geomembrane of the minimum thickness will perform the job, and no other factors need be considered. The same sentiment was expressed by Bob Landreth, chief of EPA's Landfill Technology Section in a letter dated 29 September 1989 to the Corps of Engineers in which he stated:  "Thickness of materials should be a function of design which implies site specific information and considerations. Although other thicknesses, 30 and 60 mils, are allowed (page v), this approach, we believe, ties the hands of the designer and will force the use of generic designs and could lead to increases in overall project costs. We also strongly believe and as part of our recommendations to consultants that a minimum thickness of material type should be specified then let the consultants "design" the system. Our recommendations based on seamability, punctureabilty and installability is as follows:  Type          Min Thickness (mil) PVC20-30 (30 is very tough) CPE                     30 CSPE-R 36 Polyethylene*       60 *Polyethylene is set as a 60 mil minimum primarily from a seamability standpoint. It has not been clearly demonstrated to us that PE products less than 60 mil can be constantly seamed in the field. There is also concern that this is at the lower limit for creating conditions that encourages stress cracking. While stress cracking is still under review we are starting to see improvements in seaming techniques. It is interesting to note that the West Germans are now requiring PE thickness greater than 100 mil.   On the other hand, a minimum thickness is a preliminary regulatory means of eliminating totally inadequate designs. However, it should be made perfectly clear that this is only a guide, and that engineering calculations should be made to confirm the thickness required for any liner or cover application.In addition to allowing for different minimum thicknesses of geomembranes Michigan Act 641 requires that a "geomembrane shall be of sufficient tensile strength to withstand anticipated stressed without failure". This provides an opportunity for the regulator to confirm that a proper design has been done and that the related geomembrane thickness is based on design calculations and not the regulations themselves.  CLOSURE A number of geomembranes, including PVC geomembranes, have been used successfully, for many years, to contain municipal and hazardous wastes in Michigan and elsewhere. PVC does not suddenly become inappropriate because HDPE geomembranes have become available. HDPE has many positive attributes, but it also has a number of negative attributes that are not yet fully understood. New materials (e.g. polypropylene/EPDM alloys) that offer specific advantages and, hopefully, fewer disadvantages are appearing and will continue to appear. It is desirable to design geomembrane lining systems using the least expensive material that will best achieve the performance specifications. Regulations should be written, as in the second draft of Act 641, to accommodate all candidate materials that will adequately perform the required function, and the performance of that function should be decided by proper engineering design, not by a regulatory recipe. In no way can a regulation provide a satisfactory design. In the September/October 1990 issue of Geotechnical Fabrics Report Bob Landreth of EPA's Risk Reduction Engineering Laboratory stated:  "The modifications (to chemical analysis techniques and control of wastes) should increase the number of geomembrane compositions available for use. The increased number of geomembrane compositions should now allow the designer to develop innovative designs. We (EPA) believe innovative designs will be more economical, technically viable, and be more reliable."  As designers and Michigan DNR recognize, optimum design cannot be achieved by regulating a single minimum thickness. At least two minimum thicknesses are required to accommodate two fundamental types of materials; amorphous thermoplastics (such as PVC) and semi-crystalline thermoplastics (such as HDPE). The minimum thicknesses, (30 mil and 60 mil respectively), specified in Subtitle D are acceptable to producers of both these classes of materials.  Fortunately, a minimum thickness of 30 mil is also acceptable to those producing elastomeric geomembranes and fully-crosslinked elastomeric alloys, two other classes of materials. There is little doubt that HDPE has become the landfill liner geomembrane of choice, but it has achieved this position with a significant dose of effective marketing and regulatory support. At the same time that the emotive pendulum has swung in favor of HDPE it has unjustifiably swung away from PVC. At present the potential problems of HDPE are overlooked, as are the many advantages of PVC. Michigan's Act 641 has now been written to include three values, rather than one value, of minimum thickness, and to stress the importance of thorough geomembrane design in order that the people of Michigan get optimum cost effective landfill waste containment from the complete range of geomembranes available. This is a responsible approach. A fair technical hearing, should now be given to PVC as well as HDPE. PVC has performed well in the past in Michigan and, as it continues to be improved, it will perform well in municipal solid waste landfills in the future. Designers and regulators can achieve more, and widen the window of environmental protection, by taking advantage of the many unique properties of PVC.   For more information call   800-OK-LINER   today!

Canadian General Tower CRITICAL PROPERTIES OF RAW MATERIALS   INTRODUCTION AS CAN BE READILY APPRECIATED, THIS TOPIC IS FAR RANGING AND VERY COMPLICATED, A FULL DAY SEMINAR COULD BE SPENT ON EACH MATERIAL CATEGORY, WHAT WE WILL ATTEMPT, AT THIS TIME, IS A PRESENTATION OF A VERY GENERAL NATURE CONCERNING THE CHARACTERISTICS DEEMED IMPORTANT IN THE VARIOUS RAW MATERIAL TYPES AS THEY PERTAIN TO P.V.C. MANUFACTURE AT CGT. WHAT WE WILL BE EXAMINING IS NOT THE PROPERTY RESULTING FROM A MATERIAL BEING USED BUT THE PROPERTIES INHERENT IN THE MATERIAL AS IT IS PURCHASED. WITH GENERALIZATION A MEASURE OF SIMPLIFICATION OCCURS. WITH SIMPLIFICATION THE POSSIBILITY OF OMISSIONS AND SOME DISTORTION CAN ALSO OCCUR. WHERE THIS MIGHT HAPPEN, DURING Carl, FOLLOWING REMARKS, YOUR UNDERSTANDING IS ASKED FOR.  DISCUSSION THE RAW MATERIAL CATEGORIES USED AT CGT CAN BE LISTED AS FOLLOWS: PVC RESINS PLASTICIZERS FILLERS LUBRICANTS PROCESSING AIDS STABILIZERS - HEAT & LIGHT FIRE RETARDANT SANTIMICROBIAL AGENTS SOLVENTS COLORANTS BLOWING AGENTS  NOW EACH OF THESE MATERIAL GROUPINGS HAS A DISTINCTIVE FUNCTION IN THE MANUFACTURE OF A P.V.C. PRODUCT. ONE GROUP MAY AFFECT PRIMARILY END USE PROPERTIES. ANOTHER GROUP MAY AFFECT PRIMARILY PROCESSING PROPERTIES, SOME MAY AFFECT BOTH END USE AND PROCESSING PARAMETERS. THE INCLUSION IN A RECIPE 05 A MATERIAL FROM ANY ONE GROUPING IS DONE WITH A DEFINITE PURPOSE TOWARDS A DEFINABLE RESULT, IT IS NOT THE PURPOSE HERE TO ELABORATE ON THE FUNCTION OF EACH OF THESE MATERIAL CATEGORIES - SUFFICE IT TO SAY THAT TEXTS HAVE BEEN WRITTEN ON SUB GROUPS WITHIN A CATEGORY. AND SO, TO THE CRITICAL PROPERTIES OF THESE RAW MATERIALS, THE MAJOR FACTOR, THE OVERRIDING CONCERN WHICH AFFECTS ALL OF THE RAW MATERIAL GROUPINGS IS THAT OF MATERIAL UNIFORMITY, MATERIAL CONSISTENCY, VARIATION OR VARIABILITY OF RAW MATERIAL REFLECTS DIRECTLY ON PROCESSING AND END USE PROPERTIES.  ALL OF THE RAW MATERIALS CAN BE DESCRIBED IN TWO WAYS: CHEMICAL PHYSICAL  EACH OF THE TWO DESCRIPTIONS IMPACTS MIGHTILY ON MANUFACTURE OF P.V.C. PRODUCTS.  1. THE CHEMICAL FACTOR DESCRIBES: COMPOSITION PURITY  2. THE PHYSICAL FACTOR DESCRIBES: STATE, LIQUID, SOLID, GASVISCOSITY PARTICLE SIZE - DISTRIBUTION, POROSITY, BULK DENSITY COLOR CONTAMINATION  THESE TWO FACTORS DETERMINE: WHAT THE PRODUCT WILL DO HOW WELL THE PRODUCT DOES IT THE INTERDEPENDENCY OF EACH MATERIAL GROUPING WITHIN A RECIPE MUST BE STRESSED, THE PROPERTIES BOTH PHYSICAL AND CHEMICAL OF AN INGREDIENT CAN AND DOES AFFECT THE BEHAVIOR OF SOME OR ALL OF THE OTHER INGREDIENTS IN THAT RECIPE. ANYONE WITH THE SLIGHTEST ACQUAINTANCE WITH PLATEOUT OR BLOOM CAN APPRECIATE THE VALIDITY OF THIS STATEMENT. SO, LET US EXAMINE SOME OF THE RAW MATERIAL CATEGORIES IN A LITTLE MORE DETAIL.  1. P.V.C. RESINS:   MAJOR PROPERTIES EFFECTS EFFECTS   PROCESS END USE MOLECULAR WT.   (SPECIFICVISCOSITY) (R VALUE) x x       PARTICLE SIZE & DISTRIBUTION x - HEAT STABILITY x - FISH EYES, GELS - x CONTAMINATION x x HEAT LOSS x x BRABENDER (DRY TIME) (FUSION TORQUE) x - MOLECULAR WEIGHT IS THE MOST IMPORTANT PROPERTY OF A P.V.C. RESIN AS IT DIRECTLY AFFECTS PROCESSING AND END USE PROPERTIES. PARTICLE SIZE, DISTRIBUTION, POROSITY AFFECT MELT VISCOSITY, DRY BLENDING, FLUXING, DUSTING, DRY FLOW. HEAT STABILITY CONCERNS PROCESSING. FISH EYES AND CONTAMINATION STRONGLY REFLECT ON END USE APPLICATIONS AND DEPENDING ON SEVERITY, PROCESSING.  2. PLASTICIZERS   MAJOR PROPERTIES EFFECTS EFFECTS   PROCESS END USE COMPOSITION - x COLOR - x VISCOSITY x - COMPATIBILITY x x VOLATILITY - x GIVEN THAT THE PLASTICIZER HAS BEEN CHOSEN CORRECTLY, THE CHEMICAL COMPOSITION IS DIRECTLY RELATED TO END USE AND EFFICIENCY, COLOR IMPACTS ON THE USEFULNESS OF THE END PRODUCT. VISCOSITY IS IMPORTANT FOR TRANSPORT DURING COMPOUNDING AND FOR EASE OF DRY BLENDING. COMPATIBILITY RELATES TO END USE (EXUDATION) AND VOLATILITY TO PERMANENCE.  3. STABILIZERS   MAJOR PROPERTIES EFFECTS EFFECTS   PROCESS END USE COMPOSITION x x PHYSICAL STATES x - SOLID, LIQUID, GRANULE   COMPATIBILITY x x THE CHEMICAL COMPOSITION IMPACTS DIRECTLY ON THE PROCESS AND END USE. ALTHOUGH MANY OTHER INGREDIENTS INFLUENCE PRODUCT STABILITY, THE STABILIZERS ARE THE FIRST LINE OF DEFENSE AGAINST DEGRADATION DUE TO HEAT AND LIGHT. VARIATIONS IN CHEMICAL COMPOSITION OR INTRODUCTION OF DILUENTS AND/OR IMPURITIES ARE READILY DISCERNIBLE. THE PHYSICAL STATE - LIQUID, GRANULE, POWDER IS RELATED TO EASE OF DISPERSION THROUGHOUT THE BLEND AND HENCE EFFECTIVENESS. COMPATIBILITY IS ESSENTIAL FOR PERMANENCE (PLATEOUT DURING PROCESSING, BLOOM IN FINISHED PRODUCT).  4. FILLERS, FIRE RETARDANTS   MAJOR PROPERTIES EFFECTS EFFECTS   PROCESS END USE PARTICLE SIZE & DISTRIBUTION x x COLOR - x COMPOSITION x x OIL ABSORPTION x -   PARTICLE SIZE IMPACTS ON DISPERSION AND OPACITY AS WELL AS SUCH END USE PROPERTIES AS COLD CRACK AND HARDNESS. OPACITY AND COLOR OF THESE ADDITIVES ARE VERY CRITICAL IN PIGMENTATION OF THE P.V.C, PRODUCTS. IMPURITIES INTRODUCED BY THIS CLASS OF RAW MATERIAL CAN BE PARTICULARLY DETRIMENTAL TO HEAT STABILITY.   5. LUBRICANTS MAJOR PROPERTIES EFFECTS EFFECTS   PROCESS END USE COMPOSITION x - PHYSICAL STATE x - LIQUID, GRANULE,, POWDER   COMPATIBILITY x x   LUBRICANTS ARE CLOSELY RELATED TO STABILIZERS THEIR FUNCTION AND EFFECT, COMPOSITION AND COMPATIBILITY DETERMINE FUNCTIONALITY AND PERMANENCE (ANTI-PLATEOUT, ANTI-BLOOM). PHYSICAL STATE DETERMINES THE EASE OF DISPERSION.  CONCLUSION CRITICAL PROPERTIES THEN, ARE GENERALLY DEFINED BY PURITY OF CHEMICAL COMPOSITION AND PHYSICAL FORM, SPECIFICATIONS ARE DESIGNED AROUND THESE PARAMETERS. UNIFORMITY, CONSISTENCY OF RAW MATERIAL ARE PARAMOUNT FOR OPTIMUM PROCESSING AND SUITABILITY OF END PRODUCT APPLICATION.   PAUL LUSSIER Canadian General-Tower, Ltd.   COMPARISON OF METHODS OF PVC SHEET AND FILM MANUFACTURE                         Extruder Blown Flex Lip Plastisol     Calendar Calendar Film Extruder Cast Melt Roll Lines installed, USA 155 2 90 40 60 5 Relative Resin Cost Lowest Low Higher Higher Highest Low Machine Cost, $ Million 1-3 1-2.5 0.3-0.6 0.3-0.6 0.3-0.7 0.3-1.3 Rate & range, lb/hr 800-8000 500-1500 600 750 750 100-1000         (4½ in.) (4½ in.) with fluxer Product gauge range, in. .002/.050 .002/.050 .001/.003 .005/.125 .001/.012 .0015/.020 Sheet accuracy, % 3(1-5) 3(1-5) 10 10 7 5(2-10) Time to heat, hr 6 5 3 3 ½ 3 Time for “on stream” 2-5 min 10 min 2 hr 5 hr 10 min 2-5 min Gauge adjust time Sec Sec 5-30 min 5-30 min Sec 1 min Auto gauging capability Yes Yes No No No No Color or product change time 5-30 min 10-40 min 30-60 min 30-60 min 15 min 30-60 min Wind-up speed ypm,             average(max) 80(150) 60(80) 15(20) 15(30) 20(40) 20(30) Limitations High capital Lower rate Poor accuracy, long Fumes, Reduced rate   cost, heat time versatility on stream time, low inefficiency, and range,soft,     problem rate, degradation,   high energy materials only,       reduced versatility cost, resin slow manual           cost, release gauge change           paper cost   Applications & Versatility Accuracy Low investment   Grain reten- Good on wall Advantages high rate gauge adjust multi-plant capability tion(pattern covering, thin   accuracy reduced cost utilization, thin gauge cast in), material, coated   ease & adjust   (.003in. and under) soft hand fabric, accuracy   ease at   and heavy gauge   and drape reduced   re-process   (.050-.125in.)     investment   For more information call   800-OK-LINER  today!

GENERAL PVC is the common abbreviation for polyvinylchloride, one member of a large class of polymers, called vinyl. Most versatile of the thermoplastics, vinyl polymers are also among the oldest. They - when suitably compounded - range in form from soft and flexible to hard and rigid, either of which may be solid or cellular. CHEMISTRY Polyvinyl chloride polymer is, of course, produced from vinyl chloride monomer. The classical method of VCl manufacture is from the reaction of H Cl and acetylene:   H Cl + C 2 H 2               CH 2 CHCl Acetylene                  vinyl chloride monomer   This is a somewhat inefficient and expensive process. The method presently used involves the oxychlorination of ethylene to make ethylene dechloride which is subsequently cracked to vinyl chloride.   2 H Cl + ½ O 2 + Cl 2 + 2 C 2 H 4                   2 C 2 H 4 Cl 2 + H 2 O (ethylene)                                                 (ethylene dichloride)                                C 2 H 4 Cl 2                         CH 2 CHCl + HCl                                                                    (vinyl chloride)   The derivations and reactions involved are shown schematically below:     Vinyl chloride monomer, then, is the basic repeating unit of a polyvinyl chloride chain. This monomer is an easily liquefiable gas with a pleasant odor (B.P. - 20° C). The polymerization of this material is then carried out to produce high molecular weight polymer. Polymerization processes available are as follows: Suspension: Monomer is dispersed in water to form a suspension where the reaction occurs. Particle shape is like popcorn and particle size of the order of 50 micrometers. Emulsion: Monomer is emulsified in water. Particle sizes are usually less than 1 micrometer. Chain lengths and hence molecular weight can be controlled by polymerization temperatures. RESIN TYPES AND CHARACTERISTICS PVC resins can be classified as either general purpose or dispersion. General purpose resins are usually produced by suspension polymerization and the calendering resins used at C.G.T. fall into this category. Dispersion resins which are used in plastisols and organosols are produced primarily by emulsion polymerization where the fine particles are obtained. (A)Characteristics of general-purpose suspension PVC: The most important is molecular weight due to its great effect on processing and end product properties. Further, processing may also be affected by molecular weight distribution and by the degree of branching. Particle size and particle-size-distribution will affect compounding, processing and bulk handling. Large, fairly uniform particles are easier to handle and process. Fine particles will absorb plasticizer less evenly during dry blending. For most commercial suspension resins particles range from 50 - 150 micrometers. Gels are large resin particles that failed to fuse completely during processing and appear as small spots or lumps on finished film. There are inherent variations in heat stability amongst vinyl resins. These are attributed to differences in initiators, residual catalysts and impurities. (B) Characteristics of Emulsion Resins or Dispersion Resins: These resins fuse most rapidly because of their fine particle structure. Particle sizes range from 0.5 to 2.0 micrometers. Particle size and particle-size distribution affect the viscosity and stability of plastisols. Complete fusion of dispersion resins is generally considered to indicate complete solvation which is the solution formation of a resin by a solvent or plasticizer.  COMPOUNDING It should be noted that PVC resins, of themselves, are of no practical use. When fused they are hard, brittle compounds. Their inherent limited heat stability make any type of processing difficult if not impossible. Therefore, in order to produce a useful product other ingredients are added to the PVC resin for the purpose of: increasing flexibility providing adequate heat stability improving processability imparting aesthetic appeal Let's consider these ingredients in some detail: 1. PLASTICIZERS: Plasticizers are low boiling liquids or low molecular weight solids that are added to resins to alter processing and physical properties. They increase resin flexibility, softness and elongation. They increase low temperature flexibility but decrease hardness. They also reduce processing, temperatures and melt viscosity in the case of calendering. Plasticizers fall into two categories based on their solvating power and compatibility with resins: A. Primary Plasticizers: are able to solvate resins and retain compatibility on aging. Samples of these would be: DOP -- Dioctyl phthalate S-711 -- Di (n-hexyl; n-octyl; n-decyl) phthalate (linear) DIDP -- Di-iso decyl phthate B. Secondary Plasticizers : are so defined because of their limited solubility and compatibility and are, therefore, used only in conjunction with primary plasticizers. The ratio of primary to secondary depends on the type and quantity of the particular plasticizers. Secondary plasticizers are used to impart special properties such as:  Low temperature flexibility:             - DMODA (di-normal octyl decyl adipate) - DOZ (di-octyl azelate) - DOA (di-octyl adipate) Flame retardance: Reofas 65 (tri-iso propyl phenyl phosphate) Electrical properties: tri-mellitates -Cost reduction: Cereclor, chlorinated paraffins  In a separate category are the polymeric plasticizers. These are long chain molecules and are made from adipic, azelaic, sebacic acids and propylene and butylene glycols. The efficiency of polymerics is poor but volatility and migration are superior. An example of a polymeric plasticizer is Paraplex G-54. The characteristics sought in plasticizers can be summarized as follows: Efficiency - This is the level or concentration needed to give a stated hardness, flexibility or modulus. The effect on low temperature flexibility. Solvating power: This influences the fluxing rate of the compound at a given temperature or at a minimum fluxing temperature. The fluxing rate relates directly to processing time. Permanence: This relates to volatility, extraction resistance, compatibility.  2. HEAT STABILIZERS : The chief purpose of a heat stabilizer is to prevent discoloration during processing of the resin compound. Degradation begins with the evolution of Hydrogen Chloride, at about 200° F Increasing sharply with time and temperature. Color changes parallel the amount of degradation running from white to yellow to brown to black. Therefore, the need for heat stabilizers. The most effective stabilizers have been found to be: Metal soaps: Barium -cadmium solids and liquids : Mark 725, Mark 311 Organo tin compounds: octyl tin mercaptide: Mark OTME Poxies: epoxidized soya oil (G-62)The above are most likely most effective only when used in combination (synergism). What are some of the criteria in choosing a stabilizer system? The ability to prevent discoloration. The amount of lubrication involved. In calandering this can be of critical importance. Mark 725 has low lubricating effect while Mark 311 contributes high lubrication effect. Plate-Out - a potential side-affect of processing and has been linked to certain barium-cadium stabilizers. Compatibility with the resin systems - for obvious reasons. Resistance to sulpher staining: atmospheric discoloration. 3. FILLERS: Essentially fillers are added to formulations to reduce costs, although they may offer other advantages - such as opacity, resistance to blocking, reduced plate-out, improved dry blending. On the other side, fillers can reduce tensile and tear strength, reduce elongation, cause stress whitening, reduce low temperature performance. The most common fillers used with PVC are calcined clays, and water-ground and precipitated calcium carbonates of particle size around 3 micrometers. Other fillers are silicas and talcs.  Examples of fillers used at C.G.T. are: - water ground calcium carbonate : Microwhite 25   Duramite - silica: Cab-O-Sil - Talc: Hi-Fine # 80 4. LUBRICANTS: These materials are of prime importance in PVC processing. They: Improve the internal flow characteristics of the compound. Reduce the tendency for the compound to stick to the process machinery. Improve the surface smoothness of the finished product. Improve heat stability by lowering internal and/or external friction. Examples of lubricants, with which you may be familiar, are stearic acid, calcium stearate, Wax E, polyethylene AC 617 5. PROCESSING AIDS: These may be regarded as low-melt viscosity, compatable solid plasticizers. They are added to lower processing temperature, improve roll release on calendars, reduce plate-out, promote fusion. They are usually added at concentrations of 5.0%. The most widely used processing aids are acrylic resins of which acryloid K 120N is an example.  7. OTHER ADDITIVES There are several other additives which we will list and comment on briefly: Impact Modifiers: These are used in rigid vinyls to improve impact resistance. These are usually acrylic or ABS polymers used at 10 - 15 phr levels. Examples are: Kureha BTA 111, Blendex 301. Light Stabilizers: for resistance to ultraviolet radiation. They are used in low concentrations 0.5 - 1.5 phr. An example is Tinuvin P which is produced by Ciba-Geigy. Flame Retardants: PVC is inherently self-extinguishing. However, the plasticizers and additives are not. Therefore, flame retardants are added. The most widely known one is antimony tri-oxide. Anti-Static AgentsFungicides: Vinyzene BP-5 Foaming Agents : Chemicals that decompose at predetermined temperatures to produce a certain volume of gas within the molten vinyl and thereby create a foam. Colorants: Both pigments and dyes can be used. However, dyes, which are soluble organic substances, are used sparingly due to their tendency toward migration and extract ability. Heat resistance of colorants must be carefully evaluate.  In summary, we have seen that a vinyl compound consists of the following components:- PVC resin - plasticizer - heat stabilizer - lubricant - special additive - colorants.  P. Lussier    For more information call   800-OK-LINER  today!