INTEREST OF A RHEOKINETIC STUDY FOR THE DEVELOPMENT OF THERMOPLASTIC COMPOSITES BY THERMOPLASTIC - RESIN TRANSFER MOLDING

Since thirty years, composite materials began to replace metal in a number of applications, and their introduction into the technical parts is growing steadily. Until today, thermosetting polymer based composites were predominant, but are faced with environmental rules more stringent (COV, recyclability...). They offer good mechanical and chemical performances, recyclability, feasibility... Many development paths are being explored with the aim to get a couple material / robust process to produce at a reasonable cost, structural or semi-structural parts. Indeed, thermoplastic composites have an increased need due to their improved properties compared to thermosets. However, relatively high viscosity of thermoplastic systems poses manufacturing challenges that has traditionally as thermoforming, fiber/tape placement. Another process route offered is the injection of monomers with a low viscosity (around 10mPa.s): Thermoplastic-Resin Transfer Molding (T-RTM). Due to the dramatically increasing viscosity during the injection caused by the polymerization, the reaction time has to be chosen long enough to ensure a complete injection and impregnation in the presence of fibers, but not too long to limit the cycle time. Currently, reactive thermoplastics are not technically matured for industrial applications. Their chemistry and rheology especially in the presence of fibers are not well studied and understood. The reaction time is the most crucial parameter for a well-controlled injection. So, the viscosity should stay low as long that full impregnation is achieved. The other point is the reaction kinetics. The faster the reaction, the more reaction heat is released in less time which results in overheating in the center of very thick parts. In a first approach the pure polymer is investigated. To better understand the reaction time during an injection process, rheological measurements were achieved at different shear rates and temperatures. In parallel, the reaction kinetics through the exothermic reaction during polymerization are modelled and experimentally verified.