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No. 1 of 19 Polymers for Geosynthetics by Dr. Don Bright The Tensar Corporation

No. 1 of 19 Polymers for Geosynthetics by Dr. Don Bright The Tensar Corporation The information presented in this document has been reviewed by the Education Committee of the International Geosynthetics Society and is believed to fairly represent the current state of practice.

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No. 1 of 19 Polymers for Geosynthetics by Dr. Don Bright The Tensar Corporation

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  1. No. 1 of 19 Polymers for Geosynthetics by Dr. Don Bright The Tensar Corporation The information presented in this document has been reviewed by the Education Committee of the International Geosynthetics Society and is believed to fairly represent the current state of practice. However, the International Geosynthetics Society does not accept any liability arising in any way from use of the information presented.

  2. Presentation • Polymers • Principal polymers in Geosynthetics • Principal polymer chemical configurations • Polymerization • Molecular weight & its importance • Elements of deterioration and degradation • Controlling impact of deteriorative elements

  3. Polymers: By Definition • Polymers are macromolecular structures formed by the chemical union (polymerization) of many (poly) repeat mono units (mers) of a specific chemical configuration. • The polymerization process results in a long molecular structure of the monomer unit.

  4. Polymer Chains H H H H H H H H H H H H H H H H H H | | polymerization | | | | | | | | | | | | | | | | C = C = - C - C - C - C - C - C - C - C - C - C - C - C - C - C - C - C - | | | | | | | | | | | | | | | | | | H H H H H H H H H H H H H H H H H H MonomerPolymer

  5. Polymers By Classification • Polymers are either inorganic or organic with the latter being the more predominant. • Inorganic polymers comprise only a few compounds. • Organic polymers are principally derivatives of petroleum. • Organic polymers are classified as natural, semisynthetic, or synthetic.

  6. Inorganic Siloxanes Silicones Sulfur Chains Organic Natural Polymers Polysaccharides Insulin DNA Semisynthetic Polymers Rayon Cellulose Acetate Synthetic Polymers Classification Of Polymers

  7. Synthetic Polymers • Synthetic polymers are subdivided into principal categories: • Thermoset Polymers • Thermoplastic Polymers

  8. Thermoset Resins • Are polymers, that once are fully cured, cannot be resoftened with heat and reprocessed. • Examples • Epoxies • Phenolics • Rubbers • Elastomers

  9. Thermoplastic Resins • Are polymers that can be resoftened repeatedly with heat and reprocessed. • Examples • Polyolefins • Vinyl polymers • Polyesters • Engineering polymers • Fluorocarbons

  10. Examples Of Polyolefins • Polyethylene • Polypropylene • Polybutylene

  11. Examples Of Vinyl Resins • Poly(vinyl chloride) • Rigid Grade: Pipe • Plasticized Grade: Geomembrane • Plastisol Grade: Coating • Poly(vinyl dichloride) [clear food wrap] • Poly(vinyl butyral) [Windshield Laminate]

  12. Examples Of Polyesters • Poly(ethylene terephthalate) (PET) • Geotextiles • Geogrids • Tire Cord Tread Belting

  13. Examples Of Engineering Resins • Polyamide [NylonTM] • Polycarbonate [LexanTM] • Poly(methy methacrylate) [PlexiglassTM]

  14. Examples Of Fluorocarbons • Polytetrafluroethylene [PTFE Plumbers Tape] • Polychlorotrifluoroethylene [wire coating]

  15. Grades Of Polyethylene(ASTM D 1248) • Low Density Polyethylene (LDPE) 0.910 < Density < 0.925 • Medium Density Polyethylene (MDPE) 0.926 < Density < 0.940 • High Density Polyethylene (HDPE) 0.941 < Density < 0.965

  16. Grades Of Polypropylene • Homopolymer • Impact Copolymer (with > 7% PE in PP) • Random Copolymer (with < 7% PE in PP)

  17. Polyethylene H H | | -- -- C - C -- -- | | H H Polypropylene H H | | -- --- C -- C --- -- | | H CH3 Chemical Configurations

  18. PE & PP Polymerization • Addition Polymerization • A Random Process • Broad Molecular Weight Distribution

  19. Broad Molecular Weight Distribution |_____________________| |__ short__| chain length |_______________________long chain length___________________| |___intermediate chain length__| |____________| |__________________________| |___________________________________| |_________________| |________________________________________|

  20. Chemical Configuration Poly(ethylene terephthalate) (PET) H H | | - C - C - O - C - - C - O - | | || || H H O O

  21. PET Polymerization • Condensation Polymerization • Generation of water molecules • Narrow Molecular Weight Distribution

  22. Narrow Molecular Weight Distribution |____________________Longest Chain Length @ 2X _________________| |_Shortest Chain Length @ 1X _| Molecular Weight Distribution Ratio 2:1

  23. Environmental ExposureNeed To Consider • Weathering • Chemical degradation • Oxidation • Hydrolysis • Biological degradation

  24. Weathering • Exposure to: • Ultraviolet light • Temperature • Oxygen • Humidity • Airborne Agents • Chemical • Biological

  25. Consequences Of Weathering • Product Deterioration • Physical Properties • Density, Appearance, Integrity • Mechanical Properties • Tensile Strength and Creep Resistance • Polymer Degradation • Molecular Breakdown • Lower Molecular Weight • Free Radical Group Formation

  26. Protection From Weathering • Polyolefins • Addition of Carbon Black and/or • UV Stabilizer Package • Polyester • UV Stabilizer Package or • Protective Coating with UV Stabilizer Package

  27. Oxidative Degradation • Degradation of a polymer through its reaction with oxygen • Dependent upon: • Product exposed surface area • Product manufacturing process • In-use environment oxygen concentration • Susceptible geosynthetic polymers • Polyolefins: PE and PP

  28. Consequences Of Oxidation • Product deterioration • Physical properties • Density, appearance, integrity • Mechanical properties • Tensile strength and creep resistance • Polymer degradation • Molecular breakdown • Lower molecular weight • Free radical group formation

  29. Controlling Oxidation • Antioxidant: inhibitor of oxidation process • Polymer and product configuration dictates: • Antioxidant package • Chemical composition • Mechanism of prevention • Concentration / loading

  30. Hydrolytic Degradation • Molecular breakdown due to reaction of a specific monomeric chemical structure with water or water vapor • Susceptibility is dependent upon • Molecular Weight, MW • Carboxyl End Groups, CEG • Susceptible Geosynthetic Polymers • Polyesters (PET)

  31. Consequences Of Hydrolysis • Product deterioration • Physical properties • Density, appearance, integrity • Mechanical properties • Tensile strength and creep resistance • Polymer degradation • Molecular breakdown • Reduces molecular weight (MWn) • Increases carboxyl end groups (CEG)

  32. Controlling Hydrolysis • Selection of molecular weight (MWn) • Coated geogrids & high strength geotextiles : MWn > 25,000 • Non Woven Geotextiles: MWn < 20,000 • Selection of carboxyl end groups (CEG) • Coated geogrids & high strength geotextiles : CEG < 30 • Non Woven Geotextiles: 40 < CEG < 50 • In-use environment 3 < ph < 9

  33. Biodegradation • Micro-organisms • Bacteria, fungi, algae • Physical degradation • Molecular deterioration • Macro-organisms • Rodents, insects • Physical degradation

  34. Controlling Biodegradation • Not a concern for the molecular weight grades of PE, PP, PET, and PVC used in geosynthetics. • Microorganisms are known to attack and digest additives used to plasticize some base polymers.

  35. Summary • Polymers • Principal polymers in Geosynthetics • Principal polymer chemical configurations • Polymerization • Molecular weight & its importance • Elements of deterioration and degradation • Controlling impact of deteriorative elements

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