Structural and tensile characteristics of reduced graphene oxide/poly (vinyl alcohol) composite films: Influence of ultraviolet irradiation

The influence of ultraviolet (UV) radiation on the structural and uniaxial tensile characteristics of reduced graphene oxide (rGO)/poly(vinyl alcohol) (PVA) composite films produced by using various contents (0-10 wt%) of rGO obtained by a microwave-assisted reduction process was investigated. With increasing rGO content, significant reinforcing effects of the rGO sheets were seen on the tensile characteristics of the unirradiated rGO/PVA composite films, that is, increases in the stiffness and rigidity and decreases in the strain at break values. After UV exposure times from minutes up to 1 hour, for all the rGO contents, the rGO/PVA composite films had improved tensile strength and modulus values as well as considerable improvement in the stress-strain behavior in spite of great decreases in the strain at break values. The structural changes responsible for the improvement in the tensile strength and Young's modulus of the rGO/PVA composite films were associated with the development of strong intermolecular interactions between the rGO sheets and the PVA polymer chains through the formation of hydrogen bonds. Deterioration of the mechanical characteristics, especially strain at break values, was mainly due to the photodegradation of the structural units induced by UV radiation leading to the formation of some free radicals caused by the chemical bond breakages in the polymer chains as well as the weakening of intermolecular interactions such as hydrogen bonds. Correlation between the changes in the tensile properties and the structure of the rGO/PVA composite films were sought by analyzing tensile testing, fourier transform infrared/attenuated total reflectance (FTIR/ATR), and UV-visible spectral results