Evaluation of Bending Properties and Fiber Matrix Interfacial Properties of Recycled Plain Weave Carbon Fiber Reinforced Polyamide 6

Abstract

Carbon Fiber Reinforced Plastics (CFRP) with thermosetting resin matrix are widely used in sports and aerospace industry. From the perspective of carbon neutrality, the development of carbon fiber recycling technology is essential. The hot air circulation recycling method has been reported to deliver recycled carbon fibers (rCF) from CFRP with an epoxy resin matrix in the state of continuous fibers, which have comparable properties to virgin carbon fibers and are bound together with decomposition products derived from the epoxy resin. We have previously reported that the removal of sizing agents from carbon fiber surfaces or oxidation treatment improve the interfacial shear strength (IFSS) between carbon fibers and polyamide resin. Since rCF is obtained by heat-treatment of CFRP under an oxygen environment, it is expected to have superior interfacial bonding properties to thermoplastic resins, which is similar to heat-treated or oxidized carbon fibers. In this study, single-fiber pull-out tests were conducted using carbon fibers and recycled carbon fibers with Polyamide 6 (PA6) to clarify the effect of heat treatment on IFSS. Additionally, three-point bending tests were performed on CF/PA6 laminates reinforced with these fibers to reveal the relationship between mechanical properties of CF/PA6 laminates and IFSS. For rCF, longer heat treatment results in higher IFSS. For three-point bending tests, however, excessively higher IFSS resulted in lower bending strength, suggesting an optimal IFSS value to achieve maximum bending strength. The recycled carbon fibers used in this study showed equivalent flexural strength to laminates reinforced with unsized carbon fibers, indicating that they are suitable for a reinforcing material for thermoplastics composites, including PA6.