1. Polymers for Geosynthetics 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.
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 Monomer Polymer

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. Classification Of Polymers
Inorganic
Siloxanes
Silicones
Sulfur Chains
Organic
Natural Polymers
Polysaccharides
Insulin
DNA
Semisynthetic Polymers
Rayon
Cellulose Acetate
Synthetic 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)
< 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. Chemical Configurations
Polyethylene
H H
| |
-- -- C - C -- --
Polypropylene
H H
| |
C -- C
H CH3

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 2X _________________|
|_Shortest Chain Length @ 1X _|
Molecular Weight Distribution Ratio 2:1

23. Environmental Exposure Need 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 or
Protective Coating with UV Stabilizer Package

28. 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

29. 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

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

31. 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)

32. 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)

33. 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

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

35. 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.

36. 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