05 Chemical and Physical
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Transcript of 05 Chemical and Physical
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Chemical and Physical Properties
MFG 355
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Ultraviolet (UV) Light Degradation
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Oxidation
• Plastic paint
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Chemical resistivity and solubility
None Swelling/softening Dissolving Reacting
PE and H2O Nylon and H2OPVC and ketone
PVOH and water Cellulosics and acids
Increasing Chemical Reactivity to Plastic
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Chemical Resistivity and Solubility
• PS exposed to gasoline
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Chemical Nature and Solvent-solute Interactions
• Polar effects– Like with like
• Steric effects– Crystallinity
• Physical property effects on solvent-solute interactions– Solvent size– Swelling
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Like to like – polar polymer
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Thermodynamics of Solvent Interactions
• EquationΔG = ΔH – TΔS
• Negative ΔG is favorable• Negative ΔH means bonds are forming• Positive ΔS is standard (increasing)
– When does each term dominate to give a negative ΔG?
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Plasticizers
• Increase swelling– Randomness
• Plasticizers can migrate out
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Solvent Welding
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Water Repellent
• Surface tension must be LOW– Silicones = 24 dyne/cm– PTFE = 19 dyne/cm– PVC = 37 dyne/cm
• Water wicking
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Corrosion-Resistant
• Availability of electrons • Polymers are better than metals• Fluoropolymers—tightly attached
– Electron shielded• Chlorine attachment (blocks electron
availability)
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Coatings
• Decorative and protective– Adhesion– Weatherability– Water solubility
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Environmental Resistance and Weathering
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Environmental Stress Cracking
• Hawaii Story– Crosslinked, LLDPE
• Banana Plantation– Drawdown
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Crazing
• Cracks at stress areas
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Permeability
• Diffusion Coefficient D = Doe-A/RT
• Fick’s Laws of diffusion J = -D dc/dx
• Barrier Properties dc/dt = D d2c/dx2
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Gas (vapor) Permeation
• Polar groups (solubility) to solvent or gas• Intermolecular size (distance)• Crosslinking and crystallinity
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Electrical Properties
• Resistivity (1018 – 10-6)• Dielectric Strength• Arc Resistance• Dielectric Constant• Dissipation Factor (heat up)
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Conductive PolymersH
H
H
H
C nC C C( )
H
H
H
H
C nC C C( )
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Conductive PolymersMaterial
Conductivity (Ohm-cm)-1
Silver 6.25 x 105
Copper 5.85 x 105
Gold 4.44 x 105
Polyacetylene (doped) .6.0 x 104 - 1.5 x 105
Steel .6.0 x 104
Silicon 1.56 x 10-3
Carbon, graphite .1.0 x 10-3
Polyacetylene (unmodified) .1.0 x 10-11 to .1.0 x 10-15
Carbon, diamond .1.0 x 10-14
Alumina ceramic .1.0 x 10-15
Epoxy .1.0 x 10-15
Polyethylene, medium density .1.0 x 10-16
Teflon .1.0 x 10-18
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Optical Properties
• Light Transmission– Clear– Translucent– Opaque
• Colorants– Dyes– Pigments
• Surface Reflectance
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Transparency
• Non-crystalline• Index of refraction – low• Total luminous transmittance – high
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Plastic Identification• Spectroscopy
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Flammability• Self-extinguishing
– Halogen effects (oxygen)– Fillers (Al2O3·3H2O) (heat)– Aromatics (fuel)– Silicones (fuel)
Fuel Oxygen
Heat
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Flammability Tests• Vertical
and horizontal burn tests
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Limiting Oxygen Index
Chamber
Sample
Sample holder
Gas manifold
N2O2
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Flammability Tests
• Radiant panel• Cone calorimeter
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Flexibility
• CH2, O are flexible– PE, Polyisoprene, PEO, Siloxanes
• Polybutylene terephthalate is more flexible than PET
• Pendant groups• Crystallinity – reduces flexibility• Copolymers• Plasticizers (soluble)
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Heat Resistance
• Stiffening groups along the chain– Phenyl groups– Tg goes up since it takes more heat to move
molecules• Strong intermolecular H-Bonding• Crystallinity increases heat resistance
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Insulating Polymers
• Non-polar is better• Foams
– Air is an insulator
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Toughness
• Backbone Structure• Pendant Groups
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Thank You
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Flammability Tests
• Limiting oxygen index (LOI)
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Adhesives• Bonding (chemical) between surfaces is best• Crosslinking agents (ie siloxanes)• Solvent based• Latex adhesives – good flow into crevices for
mechanical attachment• Pressure-sensitive – polymer flow (mechanical)• Hot melt – polymer flow• Reactive – low molecular weight to get stronger• End Groups