Fiber-Reinforced Thermoplastic Prepregs Using Ionic Liquids: Fabrication and Evaluation of Mechanical Properties

Abstract

Generally, the viscosity of thermoplastic resin is considerably higher than that of thermosetting resin, even if it melts at a high temperature. Furthermore, because the thermoplastic resin is difficult to dissolve in a solvent, it is difficult to prepare a prepreg by the solvent methods used for preparing a thermosetting resin. Therefore, when molding fiber-reinforced thermoplastic (FRTP), impregnation of the thermoplastic resin into the reinforcing fibers has become a serious problem. In this study, we propose a novel method for manufacturing the FRTP prepreg, in that the thermoplastic resin is dissolved with an ionic liquid and impregnated with a reinforcing fiber. Unlike organic solvents, ionic liquids have a low environmental burden and can sufficiently dissolve thermoplastic resins; thus, ionic liquids are suitable for manufacturing FRTP prepregs. In this study, a prepreg was prepared by dissolving polyamide and polyethersulfone resins in an ionic liquid and impregnating it with a glass fiber, and the FRTP was molded using this prepreg. The optimum conditions for polymer dissolution in ionic liquids were found by prototyping and evaluating the prepreg under various polymer-dissolution conditions. It was confirmed that the FRTP using the prepreg showed a good resin impregnation state and mechanical properties superior to those of FRTP produced by the conventional film-stacking method.