Transcript POLYMERS IN GEOSYNTHETICS

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
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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.
Polymer Chains
H H
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C=C
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H H
Monomer
polymerization
=
H H H H H H H H H H H H H H H H
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-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C| | |
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H H H H H H H H H H H H H H H H
Polymer
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
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]
Examples Of Polyesters
• Poly(ethylene terephthalate) (PET)
– Geotextiles
– Geogrids
– Tire Cord Tread Belting
Examples Of Engineering
Resins
• Polyamide [NylonTM]
• Polycarbonate [LexanTM]
• Poly(methy methacrylate) [PlexiglassTM]
Examples Of Fluorocarbons
• Polytetrafluroethylene [PTFE Plumbers
Tape]
• Polychlorotrifluoroethylene [wire coating]
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
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-- -- C - C -- -|
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H H
Polypropylene
H H
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-- --- C -- C --- -|
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H
CH3
PE & PP Polymerization
• Addition Polymerization
• A Random Process
• Broad Molecular Weight Distribution
Broad Molecular Weight
Distribution
|_____________________|
|__ short__|
chain length
|_______________________long chain length___________________|
|___intermediate chain length__|
|____________|
|__________________________|
|___________________________________|
|_________________|
|________________________________________|
Chemical Configuration
Poly(ethylene terephthalate) (PET)
H
H
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-C
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H
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- C -O - C |
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H
O
-C-O||
O
PET Polymerization
• Condensation Polymerization
• Generation of water molecules
• Narrow Molecular Weight
Distribution
Narrow Molecular Weight
Distribution
|____________________Longest Chain Length @ 2X
_________________|
|_Shortest Chain Length @ 1X _|
Molecular Weight Distribution Ratio 2:1
Environmental Exposure
Need To Consider
• Weathering
• Chemical degradation
– Oxidation
– Hydrolysis
• Biological degradation
Weathering
• Exposure to:
– Ultraviolet light
– Temperature
– Oxygen
– Humidity
– Airborne Agents
• Chemical
• Biological
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
Protection From Weathering
• Polyolefins
– Addition of Carbon Black
and/or
– UV Stabilizer Package
• Polyester
– UV Stabilizer Package
or
– Protective Coating with UV Stabilizer Package
Effect of Carbon Black on Resistance to UV Light
for Polyethylene and Polypropylene
100
Percent of Protection (%)
75
Polyethylene
Polypropylene
50
25
0
0
1
2
3
Carbon Black Content (Wt % )
4
5
6
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 (MWn)
– Increases carboxyl end groups (CEG)
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
Biodegradation
• Micro-organisms
– Bacteria, fungi, algae
• Physical degradation
• Molecular deterioration
• Macro-organisms
– Rodents, insects
• Physical degradation
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
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Polymers
Principal polymers in Geosynthetics
Principal polymer chemical configurations
Polymerization
Molecular weight & its importance
Elements of deterioration and degradation
Controlling impact of deteriorative elements