Preparation and characterization of carbon fiber/polypropylene composites via a tri‐screw in‐line compounding and injection molding

Abstract In this study, a novel process called tri‐screw in‐line compounding and injection molding (TSICM) and corresponding apparatus had been developed for carbon fiber (CF) reinforced polypropylene (PP) composites. The structure and working principle were introduced in detail. Effects of carbon fiber loadings and screw rotation rates on mechanical, thermal, and morphological properties of CF/PP composites were experimentally investigated. Fiber length distributions of the composites were determined by using a vision measuring machine. It was found that the maximum number of fibers observed was in the range of 0–50 μm and the maximum length of the fiber in the composites is about 1 mm. Differential scanning calorimetry results showed that the melting enthalpy crystallinity of the composites decreased slightly with the increase in CF loading. Thermogravimetric analysis results showed that the thermal stability of the composites improved with increasing CF loading. Mechanical test results showed that the tensile, flexural strength, modulus, and impact strength increased with increasing CF loadings. The strain at break decreased with the increase in CF content. The increasing screw rotation rate decreased not only the tensile strength and modulus but also the flexural strength and modulus. However, it increased the strain at break values of composites.