Improved interfacial shear strength in carbon fiber enhanced semi-aromatic polyamide 6T composite via in-situ polymerization on fiber surface

The interfacial property of carbon fiber (CF) reinforced semi-aromatic poly (hexamethylene terephthalamide) (PA6T) thermoplastic composite has been improved by in-situ polymerization on fiber surface. On that basis, PA6T oligomer was coated upon fiber to form a reactive polymeric layer and modified fiber surface structure. SEM, FTIR and XPS analysis were conducted to investigate its surface status, finding that CF was perfectly wetted and formed a much rougher surface on which large quantity of polar -CO-NH-groups attached. After poly-merization under 320 oC for 10 min, this layer could bond tightly around fiber. And TGA results demonstrated that polymerized layer had excellent heat-resistance and possessed an initial decomposition temperature over 400 C. A microbond test was implemented to accurately evaluated the interfacial shear strength (IFSS), meanwhile, a facile approach of "spraying " was applied to form microdroplets in quantity onto single carbon fiber within a few minutes. It was found that the fiber and the matrix was efficiently bonded and the interaction was efficaciously enhanced by the polymeric layer, thus 20.9% of IFSS and 20.9% of bulk composites' tensile strength improvement were achieved compared to those without modification. Notably, the in-situ polymeri-zation formed a gradient transition of interfacial modulus and raised the interphase thickness to 800 nm, thus a "buffer " in interphase region was established. Our work provided a facile method to manufacture high-performance thermoplastic composite with outstanding interfacial property and broaden its application in advanced materials field.