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