Polystyrene reinforced by self-welded glass fibers: Kinetics of polyamide 6 preferential segregation

The encapsulation kinetics of short glass fibers (GFs) by polyamide 6 (PA6) during their melt compounding with polystyrene (PS) was studied. The encapsulation correlates to the mechanical strength of the ternary PS/PA6/GF (50/21/29) composites at temperatures higher than the Tg of the PS matrix. It was observed that many fibers are “welded” together by the minor PA6 phase, and a continuous GF-PA6 network is formed throughout the PS matrix. As a result, the elastic modulus is enhanced remarkably over a wide temperature region from the Tg of PS to the Tm of PA6, and the heat distortion temperature of the composites increases significantly up to 201 °C. We verified that the bulk strength of the GF-PA6 network depends on the encapsulation ratio, NPA6, a parameter denoting the percentage of the PA6 phase encapsulating the fibers. As mixing time increases, NPA6 increases gradually and then remains constant. The PA6 with a lower viscosity shows a rapid increase in NPA6, but a larger difference in viscosity between PA6 and PS results in a higher saturating value. A remarkable increase in NPA6 was observed for samples after isothermal post-treatments. It was concluded that the encapsulation of the GF by polymers and the strength of the GF-PA6 networks are kinetically determined by the migration of the dispersed PA6 domains to the GF surface and the preferential segregation of these PA6 domains to the junction point of fibers under the driving force of capillarity.