Process Intensification in Soybean Hull Fractionation: Linking Delignification, Structural Opening, and Fibrillation

Abstract

Efficient fractionation of lignocellulosic biomass remains a major challenge due to the complex and recalcitrant architecture of plant cell walls, requiring process intensification strategies capable of selectively promoting delignification while preserving the cellulosic fraction. This study investigated the combined influence of chemical (NaOH concentration), thermochemical (temperature), mechanical (high-intensity ultrasound), electrical (pulsed electric field, PEF), and physical (particle size) process intensification strategies on soybean hull fractionation using a Plackett–Burman screening design. Cellulose yield, water retention value (WRV), and fibrillation yield were adopted as complementary indicators of delignification efficiency, fiber accessibility, and structural disintegration. Temperature emerged as the dominant factor governing cellulose recovery and fibrillation, whereas particle size and NaOH concentration primarily influenced fiber swelling and structural accessibility, as reflected by WRV. In contrast, PEF showed no measurable contribution to cellulose recovery, WRV, or fibrillation yield within the investigated experimental domain, demonstrating that its influence was negligible compared to the thermochemical variables. The integration of statistical screening with scanning electron microscopy, Fourier transform infrared spectroscopy, and sustainability assessment enabled the organization of representative processing conditions into four empirical structural transformation regimes, describing the progressive evolution of the lignocellulosic matrix from mild delignification to extensive fibrillation. Rather than representing mechanistic transitions, these regimes constitute an empirical process-structure–property framework linking processing conditions, structural responses, and fractionation performance. The findings demonstrate that thermochemical variables should be prioritized for soybean hull fractionation while establishing the operational domain in which PEF is unlikely to provide meaningful gains. This integrated framework contributes to the rational design of intensified lignocellulosic fractionation processes and supports more efficient and sustainable biomass valorization strategies.