MICROSTRUCTURAL CHANGES IN HOMOPOLYMERS AND POLYMER BLENDS INDUCED BYELASTIC STRAIN PULVERIZATION

A novel polymer processing technique known as elastic strain pulveriza tion (ESP) involves the simultaneous effects of high pressure and shea r deformation to pulverize polymers. Homopolymers and blends of commer cially important postconsumer plastics, including high-density and low -density polyethylene (HDPE, LDPE), polypropylene (PP), and polystyren e (PS) are studied by several characterization techniques to determine the effects of ESP on the microstructure. Electron spin resonance spe ctroscopy confirms that free radicals are generated by the mechanical rupture of main chain carbon bonds during pulverization by ESP. The po ssibility of these free radicals terminating by heterogeneous combinat ion to form compatibilizing block or graft copolymers in coprocessed p olymer blends establishes the potential of ESP in commingled plastics recycling. Differential scanning calorimetry (DSC) and polarized light microscopy of homopolymers and blends indicate that crystalline struc ture is drastically altered by ESP processing. Spherulite size reducti on is also observed in both crystalline/crystalline and crystalline/am orphous blends after ESP. These results are consistent with homogeniza tion that may be due to the formation of compatibilizing copolymers by heterogeneous macroradical combination. (C) 1995 John Wiley & Sons, I nc.