Influence of crystallization on microcellular foaming behavior of polyamide 6 in a supercritical CO2-assisted route

摘要

Supercritical CO(2)as a blowing agent has attracted increasing interest in the preparation of microcellular polyamide 6 (PA6) foams. In this work, we developed the supercritical CO2-assisted method to prepare a series of different microcellular PA6 foams by controlling its crystallization properties in two steps and carefully investigated the corresponding crystallization properties of modified PA6 and foams using various techniques. Initially, a multifunctional epoxy-based chain extender (CE) was used to produce high-melt strength-modified PA6 with improved foaming ability; then, the resulting PA6 was foamed to prepare the microcellular foams of PA6 using supercritical CO(2)as a blowing agent in a batch foaming route. The CE effectively enhanced the melt strength of PA6, and CE usage was optimized to obtain a threshold of high branching without crosslinking. The number of crystals was also adjusted by the saturation temperature. Furthermore, these crystals that formed during the saturation process served as high-efficiency bubble nucleating agents and then limited the growth of bubbles at the same time. The microcellular foams of PA6 were successfully obtained with a cell size of 10.0 mu m, and cell density of 2.0 x 10(9)cells/cm(3)at the saturation temperature of 225 degrees C.