Crystalline properties of melt-processed polyamide 6 matrix multiscale hybrid composites

We investigated the crystalline properties of injection-molded polyamide 6 matrix composites containing carbon nanotubes and microfibers (basalt and carbon). We showed with differential scanning calorimetry tests that microfibers affect crystalline properties differently. Basalt fibers do not have a nucleating effect, while carbon fibers do, to a small extent. Carbon nanotubes acted as nucleating agents themselves, but in composites reinforced with microfibers they increased the crystallinity even more. Due to the nucleating effect of the nanotubes, crystallization started at a higher temperature in each composite. We observed synergistic effects concerning nucleation in hybrid composites. We decomposed the crystalline melting curves to determine the characteristics of the crystallite types and proved that the presence of nanotubes facilitated the formation of α-type crystallites. We showed that nanotubes have a double effect: They have a nucleating effect regarding crystallinity, and they inhibit the movement of polyamide molecules relative to each other, which decreases the tendency to crystallize. Therefore, nanotube content has an optimum concerning crystallization. This is in accordance with tensile mechanic properties.