Preparation of High-Brightness Wood Pulp Fibers via Synergistic Cooking with Lignin-like Small Molecules and Formic Acid

Efficient separation of the three main components of lignocellulosic biomass is crucial for the preparation of high-quality pulp. However, the intermolecular condensation reactions of lignin during conventional acid cooking increase the difficulty of lignin removal and reduce the efficiency of component separation. In this study, spruce, a softwood species, was used as raw material, and lignin-like small molecules (guaiacol or syringol) were introduced to suppress lignin condensation and improve pulp quality. Experimental results showed that compared with the pure formic acid system, this strategy promoted the separation of lignin and hemicellulose components from cellulose pulp. The cellulose content in pulp was increased to more than 82%, while the lignin content was reduced to less than 2%. The brightness was increased from 40.5% ISO to 56.2% ISO and 55.76% ISO, respectively, and the surface lignin coverage was significantly decreased. Meanwhile, the tensile strength of the prepared pulp was nearly doubled, the total phenolic hydroxyl content of lignin was more than doubled, and the β‑O‑4 linkages were effectively preserved, resulting in highly reactive lignin with significantly enhanced potential for high-value utilization. This work provides a new approach for the efficient separation of lignocellulosic biomass components and the preparation of high-brightness, high-quality pulp materials.