Cross-linked plastics

Abstract

A number of useful cross-linkable or thermosetting plastics are available. When cross-linked, these materials tend to be stiff, but with poor impact strength and low elongation. Normally reinforcing fillers have to be incorporated into the polymers to produce strong, useful materials, known as composites. Selected fillers can be also used to enhance electrical properties, such as volume resistivity, or to reduce the cost of the compounded polymers. Cross-linked polymers used in large volumes include:

• (i) Phenol formaldehydes(PF), including the novolak moulding powders and resol liquid impregnation resins

• (ii) Amino formaldehydes, including urea-formaldehydes (UF) and melamine formaldehydes (MF),(also known asamino-plasts)

• (iii) Unsaturated polyesters,glass-fibre impregnation resins, dough-moulding and sheet-moulding compounds (DMC and SMC respectively), and moulding powders

• (iv) Epoxide resins,normally available as liquid impregnation resins.