Direct injection molding of polypropylene composites reinforced with recycled carbon fibers

The adoption of recycled carbon fiber (RCF) as a reinforcing component in composite materials is driven by several factors, including cost-effectiveness, environmental sustainability, and the growing disparity between supply and demand. This paper studies the tensile and physical properties of composites made from RCF, virgin carbon fiber (VCF), and virgin glass fiber (VGF) using direct injection molding, with fiber content ranging from 0 to 20 wt%. At the 20% fiber loading level, the tensile modulus increased 321%, 314%, and 148% for the RCF, VCF, and VGF composites, respectively, compared with pure polypropylene (PP). The tensile properties were evaluated at different crosshead speeds, and the tensile strength increased when the crosshead speed increased from 5.08 to 50.8 mm/min. Fractured specimen analysis indicates that the primary failure modes were fiber pullout and PP matrix fracture. Furthermore, incorporating 20 wt% RCF enhanced the flame-retarding properties by decreasing the burn rate of PP by 60%. This study shows that using RCF can improve mechanical and physical properties at a lower cost compared to VCF and VGF. Additionally, utilizing RCF helps reduce carbon fiber landfill waste and lessens environmental impact, thereby promoting a circular economy.