Direct electrophoretic deposition of waterborne polyurethane and poly(urea-urethane) on epoxy-sized carbon fibers for improved thermoplastic composites

• Main Author: Tan, Nathanael Chih Eng
• Other Authors: Lu Xuehong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Sizing agent; Composite; Carbon fiber
• Online Access: https://hdl.handle.net/10356/174711
• Institution: Nanyang Technological University

Carbon fiber-reinforced polymer composites (CFRPCs) are an industry standard for aerospace/ automobile applications due to their excellent strength-to-weight ratio. However, the overwhelming use of non-recyclable thermoset CFRPCs over thermoplastic CFRPCs has led to mainly thermoset compatible epoxy-sized carbon fiber (CF) being produced, which has poor interfacial interaction with thermoplastic matrices. In order to increase the recyclability of CFRPCs through the use of thermoplastics instead while maintaining mechanical strength, there is a need to treat the CF to make it thermoplastic compatible. Here, we evaluated the potential of two sizing agents, waterborne polyurethane (WPU) and poly(urea-urethane) (WPUU), within a thermoplastic Polyamide 6 (PA6) matrix. In contrast to previous studies, the WPU/WPUU agents were sized directly onto the commercial epoxy-sized CFs for improved efficiency, without a desizing step to remove the epoxy sizing. Our results confirm the long-term stability of WPU/WPUU aqueous emulsions via measurements of zeta potential, as well as the successful direct electrodeposition of the WPU/WPUU from scanning electron microscopy images. Single fiber pull-out test results reveal that both WPU- and WPUU-sized CFs exhibit a 25.4% and 36.8% improvement in interfacial shear strength respectively, compared to commercial epoxy-sized CFs. However, the short beam strength of the WPU/WPUU-sized bulk composite shows no significant improvement over the epoxy-sized bulk composite, likely due to the poor thermal stability of the sizing agents coupled with extended exposures to high temperatures during the hot press process. These results suggest that further measures to improve the thermal stability of WPU and WPUU, or improvement of process parameters, will be required for effective application.