Metal triflates as catalytic curing agents in self-healing fibre reinforced polymer composite materials

Abstract

High performance, damage tolerant fibre reinforced polymer (FRP) composite materials are currently required to demonstrate no propagation of any sub-surface structural micro-cracking when under service load, thereby encouraging overdesign and limiting the inherent lightweight nature of such a material. By incorporating selfhealing functionalities, in-situ autonomous repair can be initiated in the event of damage to maintain structural integrity while ultimately realising lighter and more sustainable structures. We have demonstrated metal triflate initiated ring opening polymerisation (ROP) of epoxide resin [1] in FRPs to restore >99% of the host matrix fracture toughness after damage under Mode I tests. Optimising the polymer composition via differential scanning calorimetry (DSC) identified the key parameters to achieve autonomous curing under ambient conditions. Initial and self-healed performance was evaluated using FRP E-glass double cantilever beam (DCB) coupon mechanical test specimens with embedded microvascular channels for self-healing agent delivery. Full recovery of fracture toughness (>99%) was demonstrated while achieving the following requirements: low cost, low toxicity, autonomous curing, autonomous delivery, usability, manufacturing processability and applicability to existing aerospace and automotive maintenance programs. Brittle and ductile cohesive failure mechanisms resulted from inclusion of a solvent (ethyl phenylacetate) within the healing agent under low (10 wt%) and medium (25 wt%) concentrations. Therefore, the failure mechanism can be adapted as the solvent acts as a plasticiser in the self-healing agent. This was further confirmed by imaging fracture plane surfaces via scanning electron microscopy (SEM). The adhesive repair was typically ~100 ?m in thickness, comparable to damage voids present in impact damaged FRP composite materials.