Study on the Valorization of Oak Bark Biomass - Part II: Organosolv Pulping of Bark Residue after Tannin Extraction

Bark, a significant byproduct of the wood industry accounting for 10-20% of log weight, is typically utilized for low-value applications because of its high ash and lignin contents.Nevertheless, it remains a rich source of cellulose and hemicellulose, offering potential as a high-value bioproduct feedstock through appropriate pretreatment and pulping.In this study, tannin-extracted oak bark residues were subjected to organosolv pulping using either acidic (H 2 SO 4 ) or alkaline (NaOH) catalysts.The pulp yields were 39.4% and 45.6% under Acid 60 (120C, 60 min) and Alkali 90 (120C, 90 min) conditions, respectively.Acidic pulping induced partial hydrolysis of polysaccharides, whereas alkaline treatment facilitated lignin-hemicellulose cleavage and improved carbohydrate preservation.Lignin recovered from black liquor under Acid 60 conditions exhibited the highest purity (82.8%) and recovery yield (37.3%).The resulting pulps were directly micronized by homogenization to produce well-dispersed microfibers without additional pretreatment.Overall, these findings demonstrate that tannin-extracted bark residues are promising precursors for microfibers suitable as bio-based fillers and compatibilizers, contributing to the sustainable valorization of underutilized forest biomass.