Abstract:
Hydrogels are hydrophilic, cross-linked three-dimensional networks of insoluble polymer chains that can retain huge amounts of water and many other organic solvents. Various researchers and scientific communities are trying to explore such types of hydrogel which are ecofriendly and mechanically strong. That is why they have incorporated biopolymer such as cellulose and its derivatives into synthetic polymer to introduce hydrogels. However, most of this work using the cellulose was focused on the functionalization only at the C-6 position of the glucose moiety and they cannot be achieved desired goals. In this research, hydrogels are synthesized with improved mechanical properties using nanocrystalline cellulose functionalized at C-2 and C-3 positions of glucose moiety grafted at poly(acrylic acid) network. Here, microcrystalline cellulose was converted to 2, 3-dicarboxylated nano cellulose via nanocrystalline celluloses and 2, 3-dialdehyde nano cellulose. Finally, this dicarboxylated nanocrystalline cellulose incorporated into acrylic acid to prepare hydrogel. The hydrogel was characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Universal Testing Machine (UTM) and different chemical analysis. Surface morphology and particle size were investigated through FESEM. The analysis showed that all the cellulosic materials are in the form of nano fiber and the average fiber diameter was less than 20 nm with a length of 100 nm to few micrometers. FTIR spectra and hydrazine test confirmed the conversion of nanocrystalline cellulose (NCC) to different functional groups and grafting polymerization of modified nanocellulose onto acrylic acid. Chemical structure and crystallinity of carboxylated nanocrystalline cellulose and synthesized hydrogel were investigated by XRD analysis. The swelling capacity of hydrogel was observed by teabag method which showed prominent result with swelling ratio about 600 g/g. It was shown that water swelling can be tuned by the pH of the reaction media. Finally, mechanical properties of hydrogels including young’s modulus, ultimate strength, toughness, ductility were analyzed by UTM machine. The test of mechanical properties suggested that functionalized nanocrystalline cellulose-poly(acrylic acid) based hydrogel showed higher mechanical properties in terms of Young’s modulus (210.5 kPa), toughness (251.34 kJ/m3) and tensile strength (160.0 kPa) than that compared with poly acrylic acid based hydrogel with Young’s modulus (92.2 kPa), toughness (97.4 kJ/m3), and tensile strength (53.0 kPa). The improved compressive strength of the cellulose grafted hydrogel was also observed.
