Abstract
In this work, the effect of using zirconium(IV) hydroxide (Zr(OH)4) nanoparticles in the enhancement of the thermal stability and viscoelastic properties of organically cross-linked polyacrylamide (PAM) hydrogels using hydroquinone (HQ) and hexamethylenetetramine (HMT) was studied. The thermal stability and viscoelastic properties of the PAM gels were studied by DSC and DMA, respectively. From the DSC analysis, the bound and free water contents were analyzed along with the degradation enthalpy to give a preliminary clue about the direct vs indirect interactions taking place in the gel. With the addition of 0.2–0.8 wt % Zr(OH)4, the thermal stability of the PAM hydrogel improved by 3–5 °C (reaching 187 °C) compared to PAM alone. Moreover, the elasticity of the PAM hydrogel increased with the addition of Zr(OH)4 which was also supported by the strong interaction bond formed as demonstrated from the higher degradation enthalpy and free water recorded. These interactions were further explained using FTIR and optical microscope images. The TGA results also revealed the functionalization of PAM gel and showed that the gel was thermally stable even at 400 °C. In addition, the effects of calcination, organic cross-linker, salinity, and pH on the gel properties were investigated. From DSC and DMA analysis, it was found that the optimal conditions for the polymer gel were as follows: PAM at 4 wt %, Zr(OH)4 at 0.2–0.8 wt %, organic cross-linkers (OrgCL) at 0.3 wt %, and KCl or MgCl2 at 2 wt %.