Molded parts peroxide cure

Diallyl Phthalate Resin Thermoset supplied as diallyl phthalate prepolymer or monomer. Has high chemical, heat and water resistance, dimensional stability, and strength. Shrinks during peroxide curing. Processed by injection, compression, and transfer-molding. Used in glass-reinforced tubing, auto parts, and electrical components. Also called DAP. 

When peroxide compounds are cured in contact with air, a tacky surface results because oxygen causes chain scission of the polymer free radical. This can create problems in deflashing molded parts, and prevent the use of peroxide ernes in some extmded or autoclave processes. Peroxide formulations that resist air inhibition of the cure are under development. 

Hand layup. The oldest method is a purely manual operation. (1) The open female mold is first treated with mold release. (2) Optionally, a pigmented gel coat is applied 15 to 20 mils thick and partly cnred. (3) Glass fiber mat, or woven or knitted cloth, is hand-laid into the mold or onto the gel coat. (4) Thixotropic polyester/styrene liquid, containing MEK peroxide and activator, is impregnated into the cloth. (5) The assembly stands and cures at room temperature. This gives a product with one good surface and somewhat irregular thickness. 

Polyurethane in the rubber industry can be used in (1) the thermoplastic elastomer form (TPE), discussed earlier, (2) a two-part liquid system in reaction injection molding (RIM), (3) the cast molding of rubber parts, or (4) as a millable gum that can be processed on a two-roll mill and cured with agents such as peroxides or sulfur, just as with conventional rubber. Although different versions of polyurethane elastomers must be tailor-made for each of these four common applications, the basic chemistry used is very similar in all. 

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