Partly Sulfonated Polystyrenes Effectively Enhance the Enzymatic Saccharification of Poplar Wood under Green Liquor Pretreatment

Lignosulfonate, as a water-soluble lignin, is famous for weakening the nonproductive adsorption between cellulase and substrate lignin. This study investigated the role of hydrophobic and hydrophilic components of partly sulfonated polystyrene (SPS) as lignosulfonate mimics in enhancing the enzymatic hydrolysis of lignocellulose by minimizing nonproductive cellulase–lignin interactions. SPS samples with varying molecular weights and sulfonation degrees were synthesized, the performance in enzymatic hydrolysis was evaluated, and their interactions with cellulase and lignin were analyzed. The results indicated that reducing the SPS molecular weight and degree of sulfonation significantly improved substrate enzymatic digestibility at 72 h (SED@72 h), with the optimal SPS-MW2700-61.5% enhancing SED@72 h by 20.7% and decreasing the cellulase–lignin adsorption by 81%. SPS with low sulfonation degrees spontaneously adsorbed on cellulase, driven by electrostatic interaction forces. In contrast, SPS with high sulfonation degrees adsorbed on cellulase, driven by van der Waals forces and hydrogen bonding forces. SPS formed a 1:1 complex with cellulase, preserving the enzyme activity. This research provides insights into the development of additives to minimize nonproductive adsorption during lignocellulosic enzymatic hydrolysis.