Nonisothermal crystallization behaviors of a polyolefin terpolymer and its foam

The nonisothermal crystallization kinetics of a polyolefin terpolymer (poly(propylene-co-ethylene-co-1-butene) and its expanded foam was investigated by differential scanning calorimetry. A kinetic equation for nonisothermal crystallization was employed to analyze the crystallization characteristics of the terpolymer and its foam. The Avrami exponent, n, can be reasonably well determined from the nonisothermal crystallization exotherm. The polarized optical microscopy showed that pristine terpolymer had a well-developed spherulite morphology whereas the foamed terpolymer consisted of elongated entities that subsequently developed as more bundle-like entities. The latter morphology is typical one of the γ phase. The difference in crystallization behavior observed for the pristine and foamed terpolymer samples is attributed to the formation of different morphologies during the foam expansion process.