Manufacturing and physical properties of all-polyamide composites

Based on the difference in melting points between polyamide 66 (PA66) fiber and polyamide 6 (PA6) matrix, all-polyamide composites were fabricated under various processing conditions. In these all-polyamide composites, the reinforcement and matrix share the same molecular structure unit (–CONH–(CH₂)₅–). Because of the chemical similarity of the two components, good bonding at the fiber/matrix interface could be expected. Effects of processing temperature and cooling rate on the structure and physical properties of composites were investigated by SEM, DMA, DSC analyses, and static tensile test. Fiber/matrix interface strength benefited from elevated processing temperature. The static tensile results showed that the maximum of tensile strength was observed in the processing temperature range of 225–245 °C. At different cooling rates, crystallization temperature of PA6 in the composites was increased compared to the pure PA6 because of the nucleation effect of PA66 fiber surface to the PA6 matrix. A study of the matrix microstructure in a single fiber-polymer composite gave proof of the transcrystalline growth at the fiber–matrix interface, the reason behind which was the similar chemical compositions and lattice structures between PA6 and PA66.