A mild process for producing high-performance dissolving pulp toward highly-substituted cellulose acetate: integrated production of lignin nanoparticles and closed-loop solvent recycling

Abstract

High-purity dissolving pulp is essential for synthesizing advanced cellulose derivatives such as cellulose acetate (CA). However, conventional pulping and bleaching methods often involve energy-intensive, high-temperature, and lengthy processes that hinder sustainable production. This study explored four green pulping systems—choline chloride/lactic acid, benzyltriethylammonium chloride/formic acid (BTEAC/FA), p-toluenesulfonic acid, and γ-valerolactone—to sustainably produce high-quality bamboo dissolving pulp, enhancing lignin valorization and solvent recovery. Among these, the BTEAC/FA system (130 °C, 2 h) yielded crude pulp that, after simple two-step bleaching, produced high-grade dissolving pulp with 0.14% hemicellulose, 97.36% cellulose, and 90.20% Fock reactivity. The resulting CA exhibited a high degree of substitution (2.92) and excellent spinning dope transparency (hazen value of 21.5), outperforming bleached kraft-based and commercial CA. Simultaneously, the by-product lignin, with high purity (90.76%) and abundant phenolic hydroxyl groups (3.28 mmol g⁻¹), was readily self-assembled into uniformly dispersed spherical lignin nanoparticles (∼34.89 nm) that effectively stabilized Pickering emulsions. After four cycles, the bleached BTEAC/FA-prepared pulp retained 85.11% α-cellulose. Meanwhile, nanoparticles derived from recycled lignin formed highly durable Pickering emulsions, maintaining droplet sizes of 10.93 μm after 105 days. Additionally, the fourth-recycled DES was valorized into a high-strength wood adhesive, enabling a closed-loop and green processing. Overall, the integrated process provides a mild, low-emission route to produce acetification-grade dissolving pulp while simultaneously offering the strategic employment of the by-product lignin and DES waste liquids, which promote the development of sustainable biorefinery.