Effect of CNF Added Location on the Interlaminar Fracture Toughness of CFRTP

The objective of this study is to clarify the effect of cellulose nanofiber (CNF) added location on the interlaminar fracture toughness of carbon fiber reinforced thermoplastic composites (CFRTP). In this study, two types of CFRTP specimens were fabricated using the sheet lamination method: CFRTP with CNF added to the resin and CFRTP with CNF added to the carbon fiber. The interlaminar fracture toughness of these specimens was evaluated through End Notched Flexure (ENF) and Edge Crack Torsion (ECT) tests to compare the influence of CNF added location. The test results revealed that CFRTP with CNF added to the resin exhibited higher interlaminar fracture toughness than CFRTP with CNF added to the carbon fiber. When CNF was added to the carbon fiber, even a small amount of CNF led to an increased probability of cohesive failure due to CNF aggregation, resulting in decreased interfacial adhesion. In contrast, adding CNF to the resin improved the shear strength at the fiber/resin interface, thereby enhancing interlaminar fracture toughness. In conclusion, these findings indicate that adding CNF to the resin rather than to the carbon fiber is an effective approach to improve the interlaminar fracture toughness of CFRTP.