High strength hydrogel using phenolated lignin

In this experiment, lignin was modified through phenolation and then used to synthesize hydrogels with polyvinyl alcohol (PVA). The highest yield in phenolation was achieved at 120 °C with a Lignin/Phenol ratio of 1/4 and 10% sulfuric acid charge, resulting in a yield of 123%. Successful phenolation of lignin was indicated by the increasing yield and the intensity of the bending vibration of the phenolic hydroxyl group (O–H) at 1356 cm − 1 in the FTIR spectra. A remarkable difference was observed between hydrogels containing phenolated lignin (PhL) and non-phenolated lignin (L). PhL had a yield of 98%, while L yielded 88% at a 1:1 Lignin/PVA ratio. When the PVA/L ratio was changed to 1:2, L was unable to form a stable hydrogel. Instead, it formed a soft, jelly-like liquid after 24 h. On the other hand, PhL was able to form a stable hydrogel up to a 1:5 PVA/PhL ratio with 78% yield. Additionally, the phenolated hydrogel showed higher mechanical stability than the L hydrogel. However, the L-PVA hydrogel had a higher swelling ratio than the PhL-PVA hydrogel.