Crystallization of glass-fiber-reinforced polyamide 66 composites: Influence of glass-fiber content and cooling rate

This paper reports the effect of glass fibers (GF) and carbon black powder (CB) on the crystallization behavior of polyamide66 (PA66). Particular attention was paid to erasing the thermo-mechanical history related to processing conditions of the composites in order to probe the intrinsic effect of the fillers. The statistical analysis of the experimental data delivers an analytical relationship for the crystallinity ratio as a function of both GF content and cooling rate. Glass fibers are shown to promote a nucleating effect that significantly increases the crystallization kinetics and crystallinity ratio of the PA66 matrix in the composites up to a GF weight fraction of about 30% before to depress both properties above this threshold value. In parallel, CB particles generate a synergistic nucleation effect that increases crystallinity. However, this effect does not compensate the detrimental effect on crystallinity of GF at high content. A discussion is made on the physical origins of the drop of the crystallinity ratio that occurs above the GF threshold content.