The rigid amorphous fraction of cold-crystallized polyamide 6

The rigid amorphous fraction (RAF) of polyamide 6 ordered/crystallized on heating initially fully amorphous glassy samples has been analyzed. Variation of the maximum annealing temperature allowed generation of partially ordered samples with different amount, perfection and morphology of mesophase or crystals. In samples with low fraction of mesophase between 0 and 20 %, the RAF increases with increasing mesophase fraction to reach a maximum value of 50 %. Further increase of the fraction and perfection of the ordered phase achieved by annealing at high temperature leads to a decrease of the RAF. The ratio between mobile and rigid amorphous fractions increases with increasing crystallinity, suggesting increasing decoupling of crystals and amorphous phase in samples of high crystallinity, and confirming results obtained earlier on poly(ethylene terephthalate) and isotactic polypropylene. The study contains a comparison of the RAF estimated from calorimetric analysis of the heat-capacity increment and dynamic-mechanical analysis of the area of the loss-factor peak on devitrification the mobile amorphous fraction, and a discussion of the effect of the phase composition of cold-ordered/crystallized PA 6 on the stiffness.