Development of Polyamide 6 (PA6)/Polycaprolactone (PCL) Thermoplastic Self-Healing Polymer Blends for Multifunctional Structural Composites

High-performance composites suffer from fatigue crack propagation during service. Traditional repair methods can be expensive and time-consuming. Therefore, research on composites with self-healing capabilities has considerably increased in the past decade. The aim of this work is to develop a polyamide 6 (PA6) matrix with self-healing properties. Polycaprolactone (PCL) was used as healing agent and melt compounded with PA6. PCL caused a decrease of the mechanical properties of PA6, due to its immiscibility and low mechanical properties. Nevertheless, acceptable fracture toughness values in quasi-static mode were obtained. Samples were thermally mended at 80 and 100 °C, and the healing efficiency was assessed by comparing the fracture toughness of virgin and repaired samples both in quasi-static and in impact mode. The blend with a PCL content of 30 wt% showed limited healing efficiency values (up to 6%) in quasi-static mode, while an interesting repair capability (53%) was detected under impact conditions. This discrepancy was explained through microstructural analysis and correlated to a different fracture morphology. In fact, under quasi-static mode, the PA6 matrix was severely plasticized, while under impact a brittle fracture surface was obtained. This morphology favored the flow of PCL during the thermal healing process.