Selective delignification of low-energy Asplund fibers using peracetic acid: Effects on cellulose supramolecular structure and hemicellulose integrity.

Hybrid pulping strategies combining mechanical and chemical treatments are gaining attention as energy-efficient approaches for lignocellulosic biomass fractionation. In this study, a hybrid pulping concept combining low-energy Asplund pretreatment with peracetic acid (PAA) delignification was investigated at varying chemical charges. Process performance was evaluated based on pulp yield, chemical composition, FTIR analysis, fiber morphology, structural characteristics (WAXS/SAXS), and water retention value. The results demonstrate that mechanical pretreatment improves chemical accessibility, enabling effective delignification under mild conditions. An apparent optimum at intermediate PAA charge was identified, where substantial lignin removal and efficient fiber individualization were achieved while maintaining substantial hemicellulose retention with only limited carbohydrate loss, fiber shortening, and yield reduction. Higher chemical charges resulted in continued delignification but only limited additional benefits relative to the increase in treatment severity, while indications of oxidative modification became more pronounced. Increased swelling together with changes in supramolecular structure indicate enhanced accessibility in the wet state and a more compact fiber structure upon drying. Overall, the hybrid approach enhances the efficiency of PAA delignification and enables effective fiber separation under comparatively mild conditions, offering a promising route for producing high-quality lignocellulosic fibers for bio-based applications.