CHEMISTRY OF LONG WEAR

POLYMER DEGRADATION•Oxidation(thermal and light-catalyzed)

•Hydrolysis(ester backbone polymers)

•Loss of polymer components (e.g. plasticizer)

Stable (incl. outdoor)Poly(methyl methacrylate)Bisphenol polycarbonatePoly (vinyl fluoride)

Scratch-resistant coating

Sensitive to UVAromatic polyurethanes(aliphatic more stable)

Sensitive to OxidationPolyolefins

Stabilizers

OXIDATION OF HYDROCARBONSGeneral Mechanism of Oxidation Chain Reaction

Backbiting in Polymers

ANTIOXIDANTSGeneral mode of action – formation of weak radicals

Examples1. Aromatic amines(most active)

R – aliphatic/aromatic

Electron delocalization stabilizes radicals

Disadvantages: staining antioxidants

ANTIOXIDANTS2. Hindered phenols

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Disadvantages: good for gasoline, too volatile for use in plastics

ANTIOXIDANTSHigher molecular weight hindered phenols

Nitrogen-containing phenols (more effective)

Dinitriles

PEROXIDE DECOMPOSERS-Contain S(II), S(IV), P(III)- Act differently than antioxidants- Synergetic with antioxidants, used together

METAL DEACTIVATORS

Propylenediamine

- Work by metal sequestration

Salpn

EDTA Citric Acid

PREVENTION OF PHOTODEGRADATION

-Encapsulation of electroluminescent polymers on resins-Addition of carbon black as a pigment-UV screening agents

NATURAL ANTIOXIDANTS

•Natural phenols from plants (rosemary, black papper, buckweat,

peanut halls)

•Vitamin E

•Plant flavanoids (epigallocatechin gallate)

LUBRICANTSWhat are lubricants?What is their function?

When lubricants are not needed:-Bearings suspended by pressurized gas-Nylon and polytetrafluoroethylene (PTFE, Teflon ©) polymers

Substances used as lubricants or lubricant alternatives-Carbon-graphite-Polymer cross-linking improves abrasion resistance-Silicon oil-Zirconium particles-MbS2

-WS2

HOW WEAR CAN BE REDUCED

-Coatings of polyurethane rubber, ultralight polyethylene (metal surfaces)

-Making surface harder (cross-linked coatings)

- Layer of silica or titania

-High energy ion irradiation of polyethylene, nylon, polystyrene, etc

-Diamond coating (vapor deposition)