Influence of the Relative Humidity on the Physico-Mechanical Properties of Poly(vinyl alcohol)—Graphene Oxide Composite Films

Composite films containing poly(vinyl alcohol) filled with different amounts of graphene oxide (2 and 4 wt %) were prepared by the solution casting technique. Three series of pure poly(vinyl alcohol) and graphene oxide-loaded films with fixed amounts of water were used: films annealed at 70°C for 2 h (2 wt % of water), films equilibrated at 33% relative humidity (5.5% of water) and 65% relative humidity (8% of water), and their physico-mechanical properties were studied. For annealed composite films and films equilibrated at 33% relative humidity the significant increase of the Young’s modulus, yield stress and strength was found with an increase of the filler content. Simultaneously, a sharp decrease of the elongation at break from 50–100% for pure PVA to about 5% for the composite with 2 and 4 wt % of GO was observed, and the film’s brittleness dramatically increased. At the same time PVA composite with 2 and 4 wt % GO equilibrated at 65% relative humidity deformed plastically and were characterized by high values of strain at break (100–190 %) and tensile energy at break. The obtained results have been analyzed taking into account the data on the effect of sorbed water on the T_g of poly(vinyl alcohol).