High strength hydrogel using phenolated lignin

Abstract In this investigation, lignin was phenolated and lignin based PVA hydrogels was synthesized. The highest yield in phenolation was found to be 123% at 10% sulfuric acid charge and L/P ratio of 1/4 at 120°C. FTIR spectra showing the increasing intensity of the bending vibration of phenolic hydroxyl group (O–H) at 1356 cm− 1 indicated the successful phenolation of lignin. A remarkable difference was observed in hydrogel preparation between phenolated (PhL) and nonphenolated lignin (L). Phenolated lignin had 98% yield while nonphenolated lignin yielded 88% at 1:1 L/PVA ratio. At L/PVA ratio of 2:1, nonphenolated lignin did not form stable hydrogel and remained very soft galley like liquid after 24 h of reaction. However, phenolated lignin formed stable hydrogel up to 5:1 L/PVA ratio with 78% yield. L/PVA hydrogel had higher swelling ratio in comparison with PhL/PVA hydrogel. At the lignin to PVA ratio of 1:2, the swelling ratio was 3101% and 4417% for phenolated and nonphenolated lignin hydrogels.