Study of a reactive epoxy–amine resin enabling in situ dissolution of thermoplastic films during resin transfer moulding for toughening composites

A reactive solvent composed of an epoxy resin and a liquid amine hardener was used to dissolve thermoplastic films in situ and produce composites modified by thermoplastics via resin transfer moulding (RTM). In order to overcome the high viscosity of the thermoplastic/resin solution, the thermoplastic, in the form of films, was placed between layers of fiber glass in the mould. It was intended that a thermoplastic/thermoset blend be generated in the interply regions after the following events had taken place: impregnation, dissolution of the films and a reaction induced phase separation of the thermoplastic (namely, polyether imide, PEI). Several diamine hardeners (cycloaliphatic and aromatic) were evaluated with regards to their reactivity and solubility. None of the cycloaliphatic amines tested were suitable. Only a liquid aromatic amine (diethyl toluene diamine) was found to satisfy both viscosity, miscibility and reactivity requirements for a RTM process. Finally, a first investigation into the blend morphology was carried out, this reveals dispersed PEI nodules between the fiber glass layers. This morphology may be compared to that observed in other thermoplastic/thermoset blends, i.e. “conventional” blends formed either from epoxy–amine/thermoplastic films (without glass fibers) or epoxy–amine/thermoplastic solutions at fixed concentration.