Healing of carbon fibre-epoxy composites using thermoplastic additives

The healing efficiency and healing mechanisms of selected insoluble thermoplastics blended into an epoxy resin and its respective carbon fibre–epoxy matrix composite is investigated. The capacity of two reactive thermoplastic additives (polyethylene-co-methacrylic acid (EMAA) and polyethylene-co-glycidyl methacrylate (PEGMA)) and two non-reactive thermoplastics (ethylene vinyl acetate (EVA) and acrylonitrile butadiene styrene (ABS)) to heal cracks in the epoxy resin network and heal delaminations in carbon–epoxy composite is determined. The thermoplastics were able to partially repair the fractured epoxy, although different healing mechanisms were operative. The thermoplastics (except ABS) were partially or completely effective in restoring the mode I interlaminar fracture toughness and fatigue resistance of delaminated composites. The healing efficiency of the thermoplastics, defined by the percentage recovery to the interlaminar fracture toughness of the composites, increased in the order: ABS (lowest), PEGMA, EVA and EMAA (highest). Healing by the reactive EMAA and PEGMA thermoplastics involves a unique pressure delivery mechanism whereas healing by the non-reactive EVA thermoplastic is controlled by its viscosity and adhesion to the fracture surfaces. ABS was ineffective as a healing agent in the composite due to its high viscosity which impeded flow into the delamination crack.