Effects of Nucleophilic Polymer Assistance in Acidic Pretreatment on the Enzyme Digestibility and Fermentability of Pretreated Lignocelluloses

This study presents a novel, cost-effective strategy employing nucleophilic polymers as direct additives during dilute acid (DA) pretreatment (2% H₂SO₄, 170–180 °C) to enhance the bioconversion efficiency of various lignocellulosic biomasses, including poplar (PP), mulberry branches (MB), and corn stover (CS). Screening among nine nucleophilic polymers identified carboxymethyl chitosan (CMS) and gelatin (GE) as exceptional dual-function enhancers to improve both prehydrolysate fermentability and enzymatic hydrolysis yield of pretreated substrates. The addition of CMS in pretreatment significantly detoxified prehydrolysates by reacting with key carbonyl inhibitors (reducing furfural by 19.8–38.6%, 5-hydroxymethylfurfural (HMF) by 3.8–59.1%, vanillin by 16.1–34.2%, syringaldehyde by 15.8–48.2% vs DA prehydrolysate controls). The addition of CMS dramatically boosted the fermentability of prehydrolysates with Saccharomyces cerevisiae, elevating ethanol yields to 7.33 (MB), 6.86 (CS), and 8.36 g/L (PP) from 6.28, 1.66, and 6.95 g/L in DA controls, respectively. Simultaneously, GE addition profoundly improved the enzyme digestibility of pretreated materials, increasing the 72-h enzymatic hydrolysis yields by 64.82 to 49.94%, 38.71 to 97.83%, and 44.26 to 55.15% for MB, CS, and PP, respectively. The findings from XPS and chemical compositional analyses indicated that the better enzyme digestibility might be related to in situ lignin modification with GE assistance. Crucially, both polymers demonstrated consistent efficacy across diverse feedstocks, with CMS also mildly aiding digestibility and GE contributing to the detoxification of pretreated biomasses. This direct addition approach with nucleophilic polymers enhanced enzyme digestibility and fermentation of pretreated materials concurrently without costly post-pretreatment steps, offering a significant advancement for efficient biofuel production.