The world production of thermoplastic resins averaged 8.6 million metric tons in 1963,35.3 million metric tons in 1975, and is projected to he 136 million metric tons by 1990 ( 1 ) . In 1975,86% of the world production was made up of four polymers; namely, polyethylene (40% polyvinyl chloride (23%), polystyrene (12%), and polypropylene (11%); also, it is estimated that less than 2% of the thousands of new polymers synthesized every year in laboratories all over the world are ever introduced.This trend is expected to continue into the foreseeable future for several reasons among which are economic stresses, technological constraints, government regulatory edicts, and the necessity to conserve the world's dwindling resources. Because of this, there is a resurgence of interest in developing new polymeric materials via the combination of existing commercially proven polymers and the addition of multipurpose additives, pigments, particulate fillers, reinforcing fibers, and coupling agents. This paper concerns itself with polymeric mixtures; mixtures of structurally different homopolymers, copolymers, terpolymers, etc., andlor mixtures thereof. The copolymers, terpolymers, etc., could be random, alternating, graft, block, star-like, or comb-like, so long as the constituent materials exist at the polymeric level. In Table 1, the uolvmer mixtures are classified in terms of their method of pieparation. A mechanical polymer hlend is made by melt blending the polymers either on an open roll or in an extruder or any &hersuitable intensive mix&. The processing temperature must be well above the glass transition temperatures (T,) of each of the constituent polymers for mixtures of amorphous polymers andlor the melting temperature (T,) for mixtures containine semi-crvstalline nolvmers. whichever is higher. commercial6 avai~adle polymer blends'are almost exclusively mechanical blends. Depending on the state of thermal stability of the polymers being mixed, the high shear involved durine nrocessine could initiate uolvmer deeradation reactions resuGibg in the generation of free iadicalsr~he free radicals could react with the other structurally different polymers present resulting in true chemical graft or block copolymers and such mixture is referred to as a mechanochemical hlend. A chemical polymer blend is made by in situ polymerization and cross-linking of the constituent polymers and the result is an interpenetrating cross-linked polymer network of structurally different polymers. The three main categwies are interpenetrating networks (IPNs), simultaneous interprnetrating polymer networks (SINS), and inter~~rnrtratinc elastometric networks (IENsi 12). In eeneral.the I'ENS are made by mixing and coagulating two dyfferent kinds of oolvmer latexes. and crosslinkine the coaeulum to . .
--form a three-dimensional mosaic structure. If the latex coaeulum is not cross-linked. the resultine uroduct is called latex polymer hlend. Solution cast uolvmer blends are ureoared bv dissolving the constituent p~l$m& in a c~m m o~s o i v e n t s...
