Thermoplastic self-healing polymer blends for structural composites: Development of polyamide 6 and cyclic olefinic copolymer blends

One of the main limitations of high-performance composite materials is failure due to fatigue crack propagation during service. Traditional repair methods can be expensive and time-consuming. For this reason, the research in the field of self-healing composites has considerably increased in the past decade. At this aim, this work is focused on the production of a polyamide 6 (PA6) matrix with self-healing properties. Cyclic olefinic copolymer (COC) was selected as a healing agent and it was melt compounded with PA6. From scanning electron microscope micrographs, it was possible to highlight the immiscibility and the lack of interfacial adhesion between the constituents. The healing efficiency of the system was evaluated by comparing the blends' fracture toughness (K-IC), both in quasi-static and impact mode, before and after the healing process performed at 140 degrees C by applying a pressure of 0.5 MPa. Through the addition of 30 wt% of COC, the fracture toughness of the virgin samples slightly decreased, passing from 2.3 MPa center dot m(1/2) of neat PA6 to 2.1 MPa center dot m(1/2). However, the presence of the 30 wt% of COC homogeneously distributed within the PA6 matrix led to a healing efficiency of 11% in quasi static mode and 35% in impact mode.