Influence of injection molding process conditions on the mechanical properties of CF-PPS/PTFE composites

Carbon Fiber-reinforced Polyphenylene Sulfide (CF-PPS) exhibits mechanical properties similar to aluminum with significantly lower density, making it an interesting alternative in automotive and aerospace applications. However, achieving these mechanical properties is not straightforward in many cases as they depend highly on material processing conditions. Numerous previous studies emphasize the high dependency on the mechanical properties of carbon fiber-reinforced PPS yet only partially analyze the influence of some processing parameters on these mechanical properties. Consequently, some studies present contradictory results regarding the optimal processing conditions. In contrast to previous works, this study simultaneously and interdependently analyzes the influence of the main processing factors, such as injection temperature, injection speed, holding pressure, mold temperature, and annealing treatment. The composite material, containing 30%wt carbon fiber and 15%wt polytetrafluoroethylene (PTFE), was prepared using a controlled injection molding process with pre-drying at 100 degrees C for 4 hours. Post-injection annealing at 180 degrees C for 1 hour with a controlled cooling rate of 25 degrees C per hour significantly improved mechanical properties. This study demonstrates that if the processing conditions correspond to the least favorable parameters within the experimental design, tensile strength, impact strength, and Young's modulus can decrease significantly. Compared to these suboptimal conditions, tensile strength can be up to 78.1% lower, impact strength 109.5% lower, and Young's modulus 72.9% lower, thus severely compromising the structural integrity of the manufactured components. The results of this study determine the processing conditions of carbon fiber-reinforced PPS that optimize each of its main mechanical properties. For fracture strength, it is found that a low injection speed, annealing treatment, low injection temperature, low holding pressure, and high mold temperature are recommended to maximize the strength of Carbon Fiber Reinforced Polyphenylene Sulfide/Polytetrafluoroethylene (CFPPS/PTFE) composites. Regarding Young's modulus, a high mold temperature, elevated injection temperature, and increased holding pressure exhibit significant positive effects. Moreover, impact strength peaks with low injection speed, high holding pressure, and high mold temperature. Regarding hardness, annealing after the injection process, high injection temperature, high injection speed, and high holding pressure are identified as critical factors for maximizing hardness.