Viscoelastic properties and physical gelation of poly (butylene adipate-co-terephthalate)/graphene nanoplatelet nanocomposites at elevated temperatures

A series of biodegradable nanocomposites were prepared by dispersing graphene nanoplatelets (GNPs) in poly (butylene adipate-co-terephthalate) (PBAT). Variations of dynamic and steady shear rheology of the nanocomposites with GNP loading and temperature were investigated via oscillatory measurements. Viscoelastic properties of the matrix exhibited significant enhancement with GNP addition. Solid-like flow behaviour was observed for highly filled samples while pure PBAT and nanocomposites with low GNP loadings showed liquid-like behaviour. Interestingly, the liquid-solid transition was found to occur at lower GNP concentrations with increasing temperature; dropping from 11.5 wt% at 160 °C to 7 wt% at 220 °C. Furthermore, in contrast to ideal melts, viscoelastic properties of some of the nanocomposites increased with increasing temperature. These observations suggest that the percolation did not originate only from network formation between the platelets but may be related to a combined GNP-PBAT gelling network, which enhanced with increasing temperature, leading to a more solid-like response at elevated temperatures. Variation of shear viscosity of nanocomposites with temperature also showed that increasing GNP loading reduces the temperature sensitivity of viscosity, leading to an increase in relative viscosity of nanocomposites with increasing temperature.