Enhancing the mechanical performance of PA6 based composites by altering their crystallization and rheological behavior via in-situ generated PPS nanofibrils

Polyamide 6 (PA6) is a popular engineering thermoplastic due to its impressive mechanical and wear resistance properties. However, its poor notched impact performance at room temperature limits its application. Although melt blending with elastomeric materials can improve PA6's toughness, this comes at the expense of its tensile strength and stiffness. In this work, a unique in-situ fibrillation technique was demonstrated to improve the impact performance of PA6 without sacrificing its stiffness. PA6-based in-situ nanofibrillar composites, containing polyphenylene sulfide (PPS) nanofibrillar domains with an average diameter around 60 nm, were produced combining melt compounding and hot stretching. Then, the effect of this fibrillar network on the mechanical properties of PA6 composites was investigated under uniaxial tensile deformation and notched impact. Results indicated no decrease in the tensile modulus in the presence of PPS nanofibrils; however, the nanofibrillar network did induce a significant difference in the stress-strain curves with the evolution of multiple necking and strain hardening. This behavior was explained by the formation of transcrystalline structures and a small crystal size in the presence of the fibril network. The evolution of multiple necking and strain hardening was correlated with the improved elasticity of the nanofibrillar composite through rheological analysis as well. Notched Izod impact tests on the composites demonstrated that 3 wt% PPS nanofibrils improved the impact strength by ~85% compared to neat PA6. Overall, this study gives insight into the design of PA6 composites with tuned impact strength and stiffness through a simple and scalable production method.