AVRAMI-EQUATION AND NONISOTHERMAL CRYSTALLIZATION OF POLYETHYLENE INVESTIGATED BY DSC

The kinetics of the nonisothermal crystallization of polyethylene (alone and crosslinked with a peroxide or filled with silica) has been analyzed assuming a composed crystallization process (primary and secondary) and Avrami coefficients have been determined for each component of the process. It has been shown that the Avrami coefficient n of the secondary process increases from 1.8 to 3 with an increasing degree of polymer cross-linking, which indicates a continuous change in the mechanism of crystallization. Filler (silica) affects this parameter, especially at a content up to l0 wt%, whereas at higher amounts (up to 35 wt%) the crystallization has apparently the same mechanism as in the pure polymer; in the former case the overall rate of the process, however, is lower.