Presentation on theme: "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."— Presentation transcript:
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.
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
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.
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 Polymer Chains
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.
Classification Of Polymers Inorganic –Siloxanes –Silicones –Sulfur Chains Organic –Natural Polymers Polysaccharides Insulin DNA –Semisynthetic Polymers Rayon Cellulose Acetate –Synthetic Polymers
Synthetic Polymers Synthetic polymers are subdivided into principal categories: –Thermoset Polymers –Thermoplastic Polymers
Thermoset Resins Are polymers, that once are fully cured, cannot be resoftened with heat and reprocessed. Examples –Epoxies –Phenolics –Rubbers –Elastomers
Thermoplastic Resins Are polymers that can be resoftened repeatedly with heat and reprocessed. Examples –Polyolefins –Vinyl polymers –Polyesters –Engineering polymers –Fluorocarbons
Examples Of Polyolefins Polyethylene Polypropylene Polybutylene
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
Grades Of Polypropylene Homopolymer Impact Copolymer (with > 7% PE in PP) Random Copolymer (with < 7% PE in PP)
Chemical Configurations Polyethylene H H | | -- -- C - C -- -- | | H H Polypropylene H H | | -- --- C -- C --- -- | | H CH 3
PE & PP Polymerization Addition Polymerization A Random Process Broad Molecular Weight Distribution
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
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
Controlling Oxidation Antioxidant: inhibitor of oxidation process Polymer and product configuration dictates: –Antioxidant package Chemical composition Mechanism of prevention –Concentration / loading
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)
Consequences Of Hydrolysis Product deterioration –Physical properties Density, appearance, integrity –Mechanical properties Tensile strength and creep resistance Polymer degradation –Molecular breakdown –Reduces molecular weight (MW n ) –Increases carboxyl end groups (CEG)
Controlling Hydrolysis Selection of molecular weight (MW n ) –Coated geogrids & high strength geotextiles : MW n > 25,000 –Non Woven Geotextiles: MW n < 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
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.
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