Breaking hydrophobic recalcitrance by penetrant and its coupling with external periodic forces in high solids enzymatic hydrolysis of lignocellulose

Experiment and model unveil penetrant mechanism against hydrophobic recalcitrance • A multi-scale model couples surface chemistry, seepage, mass transfer and reaction. • Reveal the synergistic effect between penetrant and external periodic forces High solids enzymatic hydrolysis (≥ 20% w /w) is the precondition for economic cellulosic biorefining, delivering high product concentration with minimal wastewater. At high solids, however, water transport becomes rate-limiting: flow switches from bulk diffusion to unsaturated gas-liquid two-phase flow inside the cell-cavity pore network, sharply impeding cellulase mass transfer. Existing approaches address this bottleneck almost entirely through reactor engineering, leaving substrate surface properties unexamined. Taking this substrate-surface route, we examined the specificity of Tween 20 enhancement on steam-exploded corn stover at high solids, and found that it acts principally as a penetrant governing unsaturated water transport, not merely through its low-solids enzyme-side roles of reducing non-productive adsorption and protecting the enzyme. The conversion gain amplifies sharply with solids loading, from 4.5% at 5% solids to 44.3% at 20%, while the capillary imbibition rate rises 117%, identifying imbibition as the controlling factor. Component-selective amphiphilic adsorption on hydrophobic lignin raises polar surface energy 121%, lowers the lignin contact angle from 68.8° to 50.9°, and doubles the capillary driving force. A four-layer multi-scale model coupling surface chemistry, seepage, mass transfer and hydrolysis reveals a positive feedback loop underlying the enhancement. Recasting this surfactant as a penetrant further exposes its coupling with external periodic force: the capillary pressure adds linearly to the applied compression and offsets a few percent of the mechanical drive. This work reframes penetrant action at high solids as the modulation of unsaturated water transport, opening a new direction for enzymatic-hydrolysis additive design. Download: Download high-res image (222KB) Download: Download full-size image