Lubricants and Mold-Release Agents

Abstract

Lubricants are added to most polymers at low levels to increase the overall rate of processing or to improve surface properties [1–4]. They have been used in the past to facilitate extrusion, injection, compression, etc., of many polymers, mainly PVC, acrylonitrile-butadiene-styrene terpolymer (ABS), PS, PMMA, cellulose acetate (CA), polytetrafluoroethylene (PTFE), and so on. Figure 2.1 shows the relative importance of these polymers as far as the use of lubricants is concerned [5]. The most used lubricants and their relative importance in the United States in 1978 were [6]: Ca and Zn stearates, 45% by weight Waxes, 23.5% by weight Fatty acid amides, 19% by weight Fatty acid esters, 12% by weight When used with a good knowledge of the problem to be solved, lubricants often improve the properties of products (brightness, heat stability in the course of a processing operation, light stability, resistance to degradation by corrosive agents and to water absorption, better dispersion of additives, improved electrical, optical, and mechanical properties, etc. [7]). Some examples of lubricants are stearic acid and its Ca, Li, Ba, Al, Pb, etc., salts, natural waxes, microcrystalline paraffins with a high melting point (to avoid a cloudy appearance and greasy touch of finished products), mineral and vegetable oils, and whale fat (used to transform Teflon powder into some products).