Design of mediator-based deep eutectic solvent for targeted modulation of lignin structure for the lignin-enhanced multifunctional gels and fermentable sugar

Abstract

In order to achieve efficient fractionation and valorization of sugarcane bagasse, a p-TsOH-mediated DES was developed by incorporating a small amount of p-toluenesulfonic acid (p-TsOH) into a mixture of choline chloride (ChCl) and lactic acid (LA). This novel DES system can effectively separate and modulate the structure of lignin, and achieve efficient enzymatic hydrolysis of the residual substrate. Under the optimal conditions (100 °C, 2 h, ChCl: LA: p-TsOH = 1:1:0.1), high removal efficiencies of lignin (85.80%) and xylan (91.69%) were achieved. The glucose yield of the residue reached 97.28% after 72 h of enzymatic hydrolysis, representing a 348% increase compared with the sample without p-TsOH addition. In addition, regenerated lignin with distinct structures was obtained precisely by adjusting the pretreatment temperature from 60°C to 120°C. The β-O-4 linkages decreased from 29.81/100Ar to zero, while H-type units increased to 33.67/100Ar. Meanwhile, massive G-type units were converted to catechol structures via demethylation. These lignin samples were incorporated into polyvinyl alcohol (PVA) gels via self-assembly, and the resulting lignin-PVA gels exhibited excellent mechanical strength (10.67–14.86 MPa), Young's modulus (10.48–17.00 MPa), toughness (30.37–89.91 MJ/m3)，representing a significant improvement over the original PVA gel (0.58 MPa, 0.16 MPa, 1.29 MJ/m³). In addition, favorable photothermal conversion performance was also observed. Overall, this work provides a novel strategy for biorefinery, which can be applied for the comprehensive upgradation of lignocellulosic components.