| Abstract Scope |
Covalent adaptable networks (CANs) or vitrimers represent an emerging self-healing technology ideally suited for high-performance carbon fibre composites. The application of thermal energy to the polymer network activates dynamic covalent bonds which undergo exchange reactions which can either repair damage or entirely reprocess a polymer, much like a thermoplastic. This process is controlled by the vitrimization temperature, Tv, that acts effectively as a control switch. It is critical however, that Tv is above the glass transition temperature, Tg, of the network, to ensure no significant impact upon the static performance of the composite. The challenge, therefore, is to take advantage of this mechanism and design high performance polymer networks, that are both durable, re-processable and repairable.
In this study, the effects of subtle changes in chemical structure of epoxy imine vitrimers were investigated in relation to the cure, final properties, repair and re-processability. Aromatic imine-containing epoxides, varying only by their substitution patterns, were synthesized from vanillin and either para- or meta- aminophenol. They were then cured with the aromatic amine hardener, diethyltoluenediamine (DETDA) and characterised. Both highly aromatic vitrimers displayed dynamic behaviour in terms of thermoreformability and adhesion of cured resins. However, the rigidity inherent in the meta-substituted network was more challenging to repair and re-process, highlighting the competing influences that determine static and dynamic behaviour, arising simply from different substitution patterns. Finally, the practical translation of their dynamic behaviour to carbon fibre composites will be emphasised, illustrating the enormous potential of vitrimers to both multi-functional and sustainable composites. |