3-isocyanatopropyltriethoxysilane block-graft engineering tailoring carbon fiber surface to manipulate interface properties of carbon fiber/polyamide 6 composites

Introducing the isocyanate group on carbon fiber (CF) to improve its surface activity is an effective method for CF surface modification. However, its application in industry is limited by the fact that the modification process is harmful to the environment and the isocyanate is prone to fail. In this paper, caprolactam (CPL) was used to block the isocyanate bond of 3-isocyanopropyltriethoxysilane (IPTS). By adjusting the hydrolysis conditions and concentration of the modified coupling agent solution, the CPL-blocked IPTS was grafted onto the surface-oxidized CF, and the CF-reinforced polyamide 6 (PA6) composites were prepared. The results showed that the interlaminar shear strength (ILSS) of the composites reached 52.53 MPa after treating CF with 1.0 wt% of coupling agent solution, which was 23.83% higher than that of the desized CF/PA6 composites. During the composite molding process, the high temperature unblocked the IPTS, and the released isocyanate reacted with the terminal amino group of PA6 by covalent grafting to establish a high-strength composite interface, which was the main reason for the improvement of ILSS. This study shows that this method is simple and environmentally friendly, and can effectively improve the interface properties of CF/PA6 composites.