Improving interfacial adhesion and mechanical properties of carbon fiber reinforced polyamide 6 composites with environment-friendly water-based sizing agent

In this study, a water-based aminoethylpiperazine-polyamide (AEPPA) is synthesized and its water-based sizing agent is prepared to improve the interfacial properties of carbon fiber reinforced polyamide 6 (CF/PA6) composites. The results show that the AEPPA sizing layer enhances the wettability of CF surface, thereby promoting the sufficient impregnation of PA6 resin on the fiber surface. Meanwhile, a strong interface is formed due to the interdiffusion and hydrogen bond formation between AEPPA and PA6 molecular chains. Accordingly, the interfacial shear strength increases by 29.3% and 20.2% from 41.9 MPa for as-received and 45.1 MPa for desized CF/PA6 composites to 54.2 MPa for 4 wt% AEPPA sizing agent treated CF/PA6 composites. In addition, to clarify the applicability of the resultant sizing agent, unidirectional CF/PA6 prepregs are prepared, and the mechanical properties of CF/PA6 composites are evaluated in detail. The average interlaminar shear strength, tensile strength and flexural strength increase by 14.2%, 10.5% and 20.0% from 73.8, 2198.1 and 1393.6 MPa for desized CF/PA6 composites to 84.3, 2638.7 and 1539.9 MPa for those treated with AEPPA sizing agent due to the effective stress transfer across the interface, respectively. Moreover, the cross-section morphologies and fracture behavior are analyzed to verify the improvement of mechanical properties. Furthermore, the strengthening mechanism of interfacial properties is intensively discussed.