Morphologies of blends of isotactic polypropylene and ethylene copolymer by rapid expansion of supercritical solution and isobaric crystallization from supercritical solution

Isotactic polypropylene (iPP) and ethylene-butene (EB) copolymers were diss olved in supercritical propane and precipitated by rapid expansion of super critical solution (RESS) and isobaric crystallization from SS (ICSS). The c loud-point pressures of the ternary solutions were found to increase as the immiscibility of PP and EB copolymer increased (i.e., as the number of eth yl branches in the EB copolymers decreased). The RESS process resulted in m icrofibers and a trace of microparticles, and the EB copolymer domains in t he blends decreased in size as the ethyl branch content in the EB copolymer s increased. The thermal stability of the copolymer domains was improved by synthesizing thermoplastic vulcanizate (TPV) from PP and ethylene-propylen e-diene terpolymer in a supercritical propane solution followed by RESS. Th e ICSS process produced microcellular polymeric foamlike materials, but the two polymers were precipitated independently by thermally induced phase se paration. (C) 2000 John Wiley & Sons, Inc.