Improving the Interfacial Adhesion of Long Carbon Fiber-Reinforced Polyamide 6 Composites by Electrochemical Oxidation and Polyethylenimine-Carboxymethyl Cellulose Grafting

Carbon fiber (CF)-reinforced thermoplastic composites have notable ascents in various sectors and applications. For high-performance composites, strong interfacial adhesion between the polymer matrix and the CF is crucial. This is achieved by introducing functional groups on the CF surface. In this paper, a water-based surface treatment was applied to long carbon fibers to enhance the interfacial bonding with the polyamide 6 (PA6) matrix. For that, PEI and CMC were grafted onto the surface of carbon fibers after electrochemical oxidation. The PEI-CMC sizing reduced the carbon fiber/water contact angle to 26.42° from 111.69°. The clear improvement in wettability resulted in a 164.8% increase in the interfacial strength of 26.7 MPa after the application of PEI-CMC sizing on carbon fibers (CFs). The resultant tensile and flexural strength increased by 19.3 and 11.7% from 2009.6 and 378.3 MPa for desized CF/PA6 composites to 250.3 and 422.7 MPa for PEI-CMC-sized CF/PA6 composites, respectively. Moreover, the fractured surface morphologies were also investigated to confirm the enhancement of mechanical properties. The proposed one-step electrochemical oxidation and water-based sizing procedure is found to be promising for the production of high-performance long-fiber-reinforced thermoplastic composites.