7 - Additives, fillers and reinforcements

Abstract

Additives are substances added to other substances. In the plastics industry, the term is most often employed for materials added in relatively small amounts to basic resins or compounds to alter their properties. This chapter focuses on antistats, blowing agents, catalysts, fire retardants, mold-release agents, nucleating agents, reinforcements, stabilizers, and surfactants. It also discusses the additives used in plastic foams that serve dual functions. Antistats are chemicals which impart a slight to moderate degree of electrical conductivity to normally insulative plastics compounds thereby, preventing the build-up of electrostatic charges on finished items. Antistats may be incorporated in the materials before molding. These materials function either by being inherently conductive or by absorbing moisture from the atmosphere. Blowing agents are the particular agents that cause plastics to foam. Catalysts are substances that cause or accelerate a chemical reaction when added to the reactants in minor amounts, without being permanently affected by the reaction. A negative catalyst (inhibitor, retarder) decreases the rate of reaction. Fire retardants or flame retardants are materials that reduce the tendency of plastics to burn. They are usually incorporated as additives during compounding but are sometimes applied to surfaces of finished articles.