Evaluation of healable epoxy matrices as covalent adaptive networks in uniaxial compression  

Vitrimers provide dynamic bonding that can allow a degree of self-healing capability in cross-linked resins. A commercial amine-cured epoxy resin, Prime 27 was observed to show a compressive yield stress, measured in compression, of 88  2 MPa and a compression modulus of 3.41  0.03 GPa. This base resin was modified by incorporating various proportions of two commercial vitrimers, either Thioplast EPS35 (an aliphatic epoxy-terminated polysulfide) or Vitrimax T130 (an imine-cured DGEBA epoxy resin). The addition of increasing amounts of Thioplast EPS35 into the resin led to a rapid drop in the glass transition temperature of the matrices and also a reduction in compressive performance. After an initial test in quasi-static, uniaxial compression, samples containing vitrimers were heated for 1h at 100°C and then subjected to a second compression test; all of the matrices loaded with Thioplast EPS35 were able to recover their full initial compression performance. Addition of increasing amounts of Vitrimax T130 to the same commercial epoxy resin did not cause any change in its glass transition temperature. However, after initial compression testing, followed by heating (1h at 100°C), only the formulation containing 40 wt% Vitrimax T130-loaded matrix regained its full initial compressive performance. Optimal results in terms of healing capability, measured as the recovery of the initial compression performance during a second identical test, following a heating step, were achieved by incorporating 10 wt% of EPS35 or 40 wt% Vitrimax T130, with little to no drop in glass transition temperature. For these selected formulations, the incorporation of 10% Thioplast EPS35 in Prime 27 gave a yield stress of 83  2 MPa and a compression modulus of 3.13  0.02 GPa, while the addition of 40% Vitrimax T130 gave a yield stress of 79  2 MPa and a compression modulus of 3.30  0.02 GPa.