In Situ Reduction of Graphene Oxide Nanosheets in Poly(vinyl alcohol) Hydrogel by γ-Ray Irradiation and Its Influence on Mechanical and Tribological Properties

Graphene-oxide-containing poly(vinyl alcohol) (PVA/GO) composites prepared by the freeze-thaw method were irradiated by gamma-rays at doses of 50, 100, 150, and 200 kGy to improve their strength and wear resistance. The effects of irradiation dose on the mechanical, thermal, and tribological properties were evaluated. The microstructure and composition of the PVA/GO hydrogels before and after irradiation were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results reveal that the irradiation can reduce the GO sheets dispersed in the PVA matrix in situ and that the reduced graphene oxide acts as the cross-linking point of the dangling bonds between molecular chains and forms covalent bonds after gamma-ray irradiation, which endows the composites with high strength and improved thermal stability. Compared to the nonirradiated PVA/GO hydrogels, a 270% enhancement in compressive strength was obtained when the applied irradiation dose was 150 kGy. The friction coefficient of the PVA/GO hydrogels increased with increasing irradiation dose because of the loss of hydrophilicity. However, the wear resistance significantly improved upon irradiation treatment.