b Salehnia - Polymer Engineering Department, Amirkabir University of Technology, Tehran, Iran
f Sharif

Effect of addition of graphene oxide (GO) nanosheets on die swell behavior of homogeneous poly vinyl-alcohol aqueous solutions, with different GO loading (0.25, 0.5 and 0.75 wt%) in PVA solution (15.5 wt%) , have been studied. The solutions, were prepared through vigorous mixing and moderate sonication, at room temperature. Die swell of the flow emerging from capillary dies was studied, with different diameters (0.8, 1.5 mm) and length/diameter ratio (15, 30, 40). The fluid emerged into a buoyancy bath to reduce the influence of the interfacial and gravitational forces. By increasing the shear rates from 0.1 to 1500 , shear-thinning behavior was observed. Addition of GO decreased the power law index (n), but increased the zero shear viscosity at high GO loading. Die swelling increased at higher shear rate and die diameter, and decreased by GO loading. Similar observation was reported recently [Dixit et al.,ICANN.2009]; at low shear rates, for aqueous solutions with GO showing higher die swell in comparison to unfilled solution, whereas at high shear rates, the same composition showed lower die swell compared to the unfilled solution. Surprisingly, die with the lowest length/diameter ratio (15), showed higher sensitivity to the addition of GO. Study of the linear viscoelastic responses of the samples at the room temperature, reveals an increase in the storage modulus and a low frequency plateau at high GO loading that indicates a solid like behavior. Results also show, adding GO nanosheets increases Hydrogen bond concentration which affects rheological properties and die swell behavior of PVA aqueous solution

die swell, PVA solutions, graphene oxide nanosheets, rheology