Interphase strengthening of carbon fiber/polyamide 6 composites through mixture of sizing agent and reduced graphene oxide coating

In this study, the interfacial bonding of carbon fiber (CF)/polyamide 6 (PA 6) composites is enhanced through the application of a mixture composed of a PA sizing agent and a reduced graphene oxide (RGO) coating onto a CF surface. RGO is introduced from shellac as a biodegradable polymer through an annealing process that is simple, eco-friendly, and inexpensive, resulting in shellac-derived RGO (SRGO) on the CF surface with strong bonding. Furthermore, it can be concluded that the reinforced interphase between the fiber and matrix by subsequent sizing treatment leads to complex physical and chemical bonding mechanisms. The chemical relationship between the sizing agent and SRGO was investigated using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis, differential scanning calorimetry, and thermogravimetric analysis. By modifying the sizing agent and mixture coating, the interlaminar shear strength increased by up to 70.7% for the CF/PA6 composites compared to those obtained without modification. Furthermore, the flexural strength and modulus of the mixture of the modified composites increased by 73% and 84%, respectively. Finally, the storage modulus and absorbed impact energy increased by 200% and 73.3%, respectively. These results suggest an improvement in the interfacial bonding of the composites upon the application of a mixture of PA sizing agent and SRGO coating.