Crystallization of polyamide confined in sub-micrometer droplets dispersed in a molten polyethylene matrix

The crystallization of submicrometer PA6 droplets dispersed in an ethylene-1-octene copolymer matrix, using PE-g-MA as a compatibilizer agent, is investigated. This system shows a nonconventional mechanical behavior at high temperatures. Up to similar to 100 degrees C above the final melting temperature of the ethylene-1-octene copolymer matrix, the system shows good thermal and mechanical properties including dimensional stability. Because of the dispersed phase morphology of the system, so-called fractionated/homogeneous crystallization takes place leading to an extra supercooling of PA6: similar to 50 degrees C compared to the bulk PA6 crystallization temperature. Thus-though this is most probably just of interest for small-scale research-the system can be processed at lowered temperatures while still providing exceptional high-temperature properties. While the matrix is in the melt state when crystallization of the dispersed PA6 phase occurs, the possibility of matrix induced crystallization is absent, contrary to almost all of the 'dispersed droplets in a matrix' systems reported so far. The kinetics of this phenomenon is investigated in detail by DSC: the existence of fractionated/homogeneous crystallization is shown to be related to the lack of active nuclei in the dispersed droplets by means of self-seeding experiments. The occurrence of extensive cold crystallization of PA6 in the confined environment is studied as is the crystallization kinetics, including the characterization of its time dependences showing its sporadic nature. (c) 2006 Wiley Periodicals, Inc.