Grinding of CF-Reinforced Thermoplastic and Thermoset Composites: Is There Contamination in the Process?

Abstract

The growing demand for carbon fiber-reinforced thermoplastic and thermoset (CFRT) composites, mainly in the aerospace, automotive, and energy industries, is due to obtaining lighter components. However, the amount of waste generated during the CFRT production process and at the end of its useful life has been increasing sharply, urgently requiring viable solutions that create less environmental impact in its final disposal. The mechanical recycling process has been presented as an economically and environmentally viable alternative to minimize the environmental impacts generated by the accumulation of this waste in the environment. Therefore, in this study, possible contaminations arising from the grinding process of waste composites reinforced with carbon fiber (CF) based on thermoplastics, polyamide 6 (CF/PA6), low melting poly (aryl ether ketone) (CF/PAEK), poly (phenylene sulfide) (CF/PPS), and fast-curing epoxy thermoset, are investigated. The composites are ground in a knife mill, resulting in materials measuring (2.6 ± 1) mm. Through differential scanning calorimetry (DSC) analysis, it is observed that the thermal profile of the ground composites is not changed; only the CF/PA6 composite shows an increase of 10% in the value of the degree of crystallinity. X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrometer show no metallic contamination from the grinding process. Only low levels of aluminum contamination are observed (below 2.7 wt%), attributed to the comminution step of the waste using an angle grinder adapted to cutting discs with abrasive aluminum oxide grains before the grounding process in the knife mill.