Direct impregnation of thermoplastic melt into flax textile reinforcement for semi-structural composite parts

We performed an experimental study to manufacture flax fiber textile reinforced thermoplastic composites by direct impregnation method in a closed mold. To reduce the process time, we adopted compression resin transfer molding resin because of its short flow path during the highly viscous resin impregnation process. Fiber preheating process was introduced before the impregnation process in order to avoid the resin cooling down when contacting the flax fibers. Optimal process temperature conditions such as mold temperature, resin temperature and fiber temperature were experimentally determined while minimizing the effect of thermal degradation of flax fiber and obtaining good impregnation quality. In particular, a sequential pressure cycle was proposed to improve the impregnation quality and to obtain the uniform fiber volume fraction in the final part. The impregnation quality was assessed by the density measurement and by the micrographic image analysis. The mechanical properties of the final parts were comparable with the literature values obtained by the compression molding of matrix-fiber premixed materials such as commingle yarns or film stacking, whereas the process cycle time of was much shorter than the other conventional methods in the literature.