Chemical and Physical Properties
MFG 355
Ultraviolet (UV) Light Degradation
Oxidation
• Plastic paint
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
Chemical Resistivity and Solubility
• PS exposed to gasoline
Chemical Nature and Solvent-solute Interactions
• Polar effects– Like with like
• Steric effects– Crystallinity
• Physical property effects on solvent-solute interactions– Solvent size– Swelling
Like to like – polar polymer
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?
Plasticizers
• Increase swelling– Randomness
• Plasticizers can migrate out
Solvent Welding
Water Repellent
• Surface tension must be LOW– Silicones = 24 dyne/cm– PTFE = 19 dyne/cm– PVC = 37 dyne/cm
• Water wicking
Corrosion-Resistant
• Availability of electrons • Polymers are better than metals• Fluoropolymers—tightly attached
– Electron shielded• Chlorine attachment (blocks electron
availability)
Coatings
• Decorative and protective– Adhesion– Weatherability– Water solubility
Environmental Resistance and Weathering
Environmental Stress Cracking
• Hawaii Story– Crosslinked, LLDPE
• Banana Plantation– Drawdown
Crazing
• Cracks at stress areas
Permeability
• Diffusion Coefficient D = Doe-A/RT
• Fick’s Laws of diffusion J = -D dc/dx
• Barrier Properties dc/dt = D d2c/dx2
Gas (vapor) Permeation
• Polar groups (solubility) to solvent or gas• Intermolecular size (distance)• Crosslinking and crystallinity
Electrical Properties
• Resistivity (1018 – 10-6)• Dielectric Strength• Arc Resistance• Dielectric Constant• Dissipation Factor (heat up)
Conductive PolymersH
H
H
H
C nC C C( )
H
H
H
H
C nC C C( )
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
Optical Properties
• Light Transmission– Clear– Translucent– Opaque
• Colorants– Dyes– Pigments
• Surface Reflectance
Transparency
• Non-crystalline• Index of refraction – low• Total luminous transmittance – high
Plastic Identification• Spectroscopy
Flammability• Self-extinguishing
– Halogen effects (oxygen)– Fillers (Al2O3·3H2O) (heat)– Aromatics (fuel)– Silicones (fuel)
Fuel Oxygen
Heat
Flammability Tests• Vertical
and horizontal burn tests
Limiting Oxygen Index
Chamber
Sample
Sample holder
Gas manifold
N2O2
Flammability Tests
• Radiant panel• Cone calorimeter
Flexibility
• CH2, O are flexible– PE, Polyisoprene, PEO, Siloxanes
• Polybutylene terephthalate is more flexible than PET
• Pendant groups• Crystallinity – reduces flexibility• Copolymers• Plasticizers (soluble)
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
Insulating Polymers
• Non-polar is better• Foams
– Air is an insulator
Toughness
• Backbone Structure• Pendant Groups
Thank You
Flammability Tests
• Limiting oxygen index (LOI)
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