Zirconia/graphene nanocomposites effect on the enhancement of thermo-mechanical stability of polymer hydrogels

Abstract

In this study, the synergy effect of zirconia and graphene oxide (GO) as fillers and their contribution in the thermo-mechanical stability of the polyacrylamide (PAM) hydrogels were investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) (i.e., thermal stability), and dynamic mechanical analysis (DMA) (i.e., rheological properties). The degradation temperature was lowered by 2.2% (shift from 182 °C to 178 °C) upon the addition of zirconia-graphene nanocomposites (ZrGx). The amount of bound water of the PAM-ZrG5 hydrogel, on the other hand, increased as a result of more hydrophilic groups attaching to water molecules, lowering the direct covalent bond between the filler and PAM. This led to decrease in degradation enthalpy of the PAM-ZrG5 hydrogel, further reflecting on the rheological properties of the ZrG5, i.e. storage modulus (G’) reduced from 1890 Pa to 1050 Pa compared to neat-PAM. This could be attributed to slippage of polymer chains across the nanocomposites due to van der Waals associations. However, the effect of ZrG5 was evident in a saline environment whereby the gel strength (ratio of storage modulus to loss modulus) G’/G” of the neat-PAM improved by 160% in the presence of divalent salt (MgCl2) and by 51% when using Arabian seawater. This was achieved at only 0.2 wt% of the ZrG5 in the gelant.