Chemo-rheological studies and monitoring of high-Tg reactive polyphtalamides towards a fast innovative RTM processing of fiber-reinforced thermoplastic composites

Abstract In this work, a High Temperature hybrid process coupling “reactive Extrusion” and “Resin Transfer Molding” (HT-ERTM) was designed for the manufacturing of continuous Glass Fiber-Reinforced Thermoplastic Composites (GFRTC) with an elevated glass transition temperature. Hereto, a high-performance polyphtalamide (PPA) obtained from the chain extension reaction of its prepolymer was studied with the optimal stoichiometry ratio and at several temperatures. Due to the extremely fast reaction, the present work highlights that both the reaction kinetics and the increase in viscosity are not easily monitored at short times and at high temperatures by usual techniques such as DSC and titration methods. The chemo-rheological evolutions were first studied ex-situ by coupling rheology with fast scan FTIR. In a second step, the HT-ERTM process was equipped with specific dielectric sensors in order to in-situ track the reaction evolution and the flow properties up to injection inside the cavity. Meanwhile, the viscosity increase was then determined depending on time, temperature and molar mass growth. Specifically, it was possible to model its evolution at less than one minute whereas the reaction conversion reaches 85% on two minutes of processing window. Interestingly, it was found that the in-situ results corroborated their ex-situ counterparts mentioned above. Finally, GFRTC parts with fiber contents up to 60 wt. % were obtained with a better control of both mechanical and thermo mechanical properties intended especially for high service temperature applications such as in the automotive or aerospace industries.