Effect of gamma-irradiation on the mechanical properties of polyacrylonitrile-based carbon fiber

The influence of gamma-irradiation on the structure and mechanical properties of polyacrylonitrile-based carbon fibers was studied. It was observed that the Young’s modulus of the fibers irradiated increased with irradiation dose, increasing to 267 GPa at 300 kGy, a 16.1% improvement compared to that of as-received carbon fiber. However, the tensile strength increased to 5.4 GPa at 30 kGy, i.e., a 17.4% increase, and then dropped to 4.65 GPa at 300 kGy, which is almost the same as for the untreated fiber. Uniform stress model analysis and Raman spectroscopy show that the degree of covalent cross-linking between the graphene planes increased to a maximum at 30 kGy and then remained almost constant with further irradiation. The SEM images show that the degree of surface roughness increased with the increasing irradiation dose. It is believed that when the dose is less than 30 kGy, the increased cross-linking is the dominant effect, and thus improves the tensile strength. On the other hand, further irradiation generates surface flaws, which neutralizes the increase and results in a decrease of tensile strength.