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 MgCl 2 at 2 wt %.

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Blends of polylactic acid (PLA) and nanohydroxyapatite (NHA) were prepared through melt‐mixing by varying the composition of NHA from 1 to 5 wt%. The tensile properties of the PLA‐1 wt% NHA nanocomposite exhibited higher values than neat PLA. Beyond 1 wt% NHA, a drop in tensile properties of the PLA–NHA nanocomposites was observed due to agglomeration and poor interfacial adhesion between NHA and PLA. Therefore, NHA was surface modified (mNHA) using three different surface modifiers namely, 3‐aminopropyl triethoxysilane (APTES), sodium n‐dodecyl sulfate (SDS) and polyethylenimine (PEI). The surface treatment of NHA was studied through Fourier transform infrared spectroscopy (FTIR) and energy dispersive X‐ray (EDX). Results revealed that the tensile properties increased in order of PLA‐5 wt% mNHA (APTES) followed by PLA‐5 wt% mNHA (SDS), whereas PEI modified NHA resulted in lower tensile properties. Further, increasing mNHA loading to 30 wt%, decreased the tensile strength due to agglomeration of mNHA. POLYM. COMPOS., 39:2880–2888, 2018. © 2016 Society of Plastics Engineers

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