Facile Syntheses of Physically Crosslinked Carboxymethyl Cellulose Hydrogels and Nanocomposite Hydrogels for Enhancing Water Absorbency and Adsorption of Sappan Wood Dye

This study was focused on a facile synthesis and comprehensive characterization of carboxymethyl cellulose (CMC)-based hydrogel and their potential absorption. CMC reacted with Al^III as an ionic crosslinker to produce physical hydrogels with better gel strength but gave a low water absorption (WAC). To elucidate this question, we fabricated both the CMC hydrogel and its nanocomposite hydrogel incorporating nano-size calcium carbonate (NCC) particles using a two-step process. The Al^III- crosslinked CMC hydrogel was subsequently filled with NCC particles to give CMC/NCC nanocomposite hydrogels. The CMC/NCC1 hydrogel with NCC 1 %wv⁻¹ gave a three-fold higher equilibrium WAC. To achieve an insight structure-property-function relation, CMC hydrogels were characterized for physically crosslinking interaction. FT-IR confirmed that Al^III ion reacts with the negative charges of carboxylate groups on the CMC chains to form the network structure via bidentate coordination. XPS data of the CMC hydrogels agreed well with the spectroscopic data. The resonance peaks of the C−O of substituent groups−CH₂COO⁻ were shifted upward to 177.9 ppm due to the incorporation of NCC. The higher chain flexibility (low tanδ) in CMC/NCC hydrogel with NCC 1 %wv⁻¹ produced the higher WAC than did the composite hydrogel with NCC 5 %wv⁻¹ adding. The CMC hydrogels were explored whether they are promisingly sustainable adsorbent for dye adsorption from Sappan wood extract while its CMC/NCC hydrogel rendered for better water absorption. Morphological studies revealed that NCC particles distributed mostly on the CMC surfaces to produce nanostructured composites with some particles penetrating through hydrogel pores. The specific surface areas of the CMC hydrogel increased with NCC amounts with lower WACs due to gel stiffness. The CMC hydrogels were confirmed as a promisingly sustainable adsorbent for dye adsorption from Sappan wood extract while its CMC/NCC hydrogel rendered for better water absorption which should be applicable for the dye concentration before CMC hydrogel dye adsorption.