Incorporating Lignin into Polyethylene Glycol Enhanced Its Performance for Promoting Enzymatic Hydrolysis of Hardwood

Polyethylene glycol (PEG) has been widely applied to improve enzymatic hydrolysis of lignocellulose by reducing enzyme nonproductive binding on lignins. To improve the performance of PEG in enzymatic hydrolysis, lignin-based surfactants were synthesized through lignin graft modification with poly(ethylene glycol) diglycidyl ether in this study. More importantly, effects of incorporating lignin into PEG on its behavior in enzymatic hydrolysis were investigated. Enzymatic hydrolysis of poplar results indicated that lignin-based surfactants exhibited better performance compared to PEG for promoting enzymatic hydrolysis. Moreover, a lower lignin-based surfactant loading was needed to achieve equal enzymatic hydrolysis. To explore the potential mechanism, changes of enzyme distribution and residual enzyme activities in supernatant after adding surfactants were determined. Quartz crystal microbalance with dissipation analysis was used to monitor the interaction between surfactants/enzyme and lignin in real-time. It revealed that the binding rates of lignin-based surfactants on lignin surfaces (1.06-1.32 min(-1)) were higher than those of PEG (0.43 min(-1)). Additionally, lignin-based surfactants respectively reduced the enzyme binding rates and maximum enzyme binding capacity on lignin by 36.7-40.9% and 43.3-64.9%, which was more significant than the reduction in enzyme binding rates and maximum enzyme binding capacity with PEG. A better understanding of this beneficial mechanism is a benefit for the design and utilization of surfactant in the lignocellulosic biorefinery process.