Mechanical Recycling Process: An Alternative for CF/PA6 Composite Waste from the Automotive Industry

Abstract

The amount of waste generated by the automotive industry from carbon-fiber-reinforced thermoplastic (CFRTP) has been increasing every year due to the rising demand for these materials, as they lead to weight reduction and improved vehicle performance. Carbon-fiber-reinforced polyamide 6 (CF/PA6) is a thermoplastic matrix composite utilized in this sector, typically fabricated through lamination followed by part cutting. This manufacturing process generates waste with high mechanical properties and comes at a high cost. In this work, we suggest a simple and efficient method to recycle this waste. The waste from CF/PA6 composites was cut into small squares of various sizes and dried in an oven. Laminates measuring 300 × 300 mm were then prepared by randomly arranging the waste in an aluminum mold and subjected to hot compression. Laminates with varying proportions of neat PA6 were also prepared. Standardized specimens were cut using a CNC router cutting machine following processing and subsequently inspected via ultrasound. The recycled laminates were characterized by various mechanical properties, including Charpy impact strength, three-point flexural strength, interlaminar shear strength (ILSS), and Shore D hardness. Thermal properties were evaluated through differential scanning calorimetry, thermogravimetric analysis, Vicat softening temperature (VST), and heat deflection temperature (HDT). Morphological characteristics were analyzed via fractography of specimens post-impact test using scanning electron microscopy. Visual inspection and ultrasound analysis confirmed the quality of the processed laminates. The recycled composites exhibited promising mechanical properties, with average Charpy impact values of 878 J/m, a Shore D hardness of 81, flexural strength of 310 MPa, ILSS of 33 MPa, and HDT and VST exceeding 200 °C. Fractographic analysis indicated excellent fiber–matrix interface bonding. Consequently, the feasibility of mechanical recycling of CF/PA6 composite waste, with 40 wt % neat PA6, was demonstrated as a viable solution for manufacturing new laminates suitable for secondary applications.