Optimized mechanical properties of carbon fiber reinforced thermoplastics by tuning polymer chain length based on quad-screw extrusion

There is a need for cost-effective manufacturing methods to optimize the impregnation and mechanical properties of carbon fiber reinforced thermoplastics (CFRTPs) by overcoming the low flowability of thermoplastics due to their high melt viscosity. In this study, to improve the impregnation of the CFRTP by inducing low melt viscosity, a strategy to control the molecular weight (MW) of thermoplastic polymer was developed. Through the quad-screw extrusion (QSE) process, as the rotational speed of the QSE increased, the MW of the polypropylene (PP) matrix decreased, resulting in improved flowability and impregnation characteristics of the matrix, as well as enhanced mechanical strength of the CFRTP. The tensile and flexural strengths of the CFRTP were optimized at 1500 rpm, resulting in 77% and 23% improvements, respectively, compared to the CFRTP with raw PP. Therefore, the applied QSE process effectively controlled the MW, melt viscosity, and flowability of the PP matrix and produced CFRTP with improved mechanical strength. Highlights: Mechanical degradation using QSE was applied to improve flowability of matrix. As polymer chain length decreased, impregnation between CF and matrix was improved. The improved impregnation characteristics resulted in the improved mechanical strengths. There is an optimal matrix MW to optimize the mechanical strengths of CFRTP.