Green production of dissolving pulp from sugarcane bagasse via carbonate-based oxygen-alkali pulping and enzymatic totally chlorine-free bleaching

Abstract

The increasing demand for dissolving pulp in high-value applications imposes resource constraints on traditional feedstocks and thus necessitates the exploration of eco-friendly non-wood alternatives. However, conventional processes are inappropriate for non-wood biomass, causing cellulose degradation and environmental concerns. Therefore, developing green and efficient pulping techniques for non-wood feedstock is of great significance. This study employed sugarcane bagasse as a raw material and innovatively developed a carbonate-based oxygen-alkali pulping (COAP) process combined with an enzymatic totally chlorine-free (TCF) bleaching sequence, which was successfully integrated to achieve the green and efficient production of dissolving pulp. The mechanism by which sodium carbonate regulates active oxygen species (AOs) to selectively deconstruct lignin during the COAP process was systematically elucidated, and a multivariate quadratic polynomial regression model for the COAP process was established. In addition, the synergistic mechanism of enzymatic treatment and H₂O₂ in the targeted chromophore destruction was analyzed, and a new strategy for selective lignin removal was proposed. The results showed that the prehydrolysis stage achieved selective removal of 83.7% hemicellulose while retaining 89.7% cellulose at 170 °C. During the COAP stage, the partial replacement of NaOH with Na₂CO₃ delayed the superoxide anion radicals (O₂^−·) protonation to regulate AOs. This not only achieved selective oxidative degradation of lignin and maximized cellulose preservation, but also significantly reduced the bleaching demand in the subsequent stage. Moreover, response surface methodology optimization identified the optimal pulping conditions as a sodium carbonate substitution ratio of 50%, a temperature of 105.8 °C, and a reaction time of 3 h, producing pulp with the International Organization for Standardization (ISO) brightness of 47.6%, an 𝛼-cellulose content of 89.1%, and a yield of 36.5%. During the enzymatic bleaching stage, a cascade pretreatment with xylanase and laccase (20 U/g) selectively degraded residual lignin-carbohydrate complexes and lignin chromophoric groups, significantly reducing the subsequent H₂O₂ (3%) bleaching load. Finally, high-quality dissolving pulp with a brightness of 81.2% ISO, high 𝛼-cellulose content (91.02%), high viscosity (248 mL/g), and overall yield (30.8%) was obtained. This study demonstrates a promising green biorefinery route for the valorization of agricultural residues.

Keywords

Sugarcane bagasse / Dissolving pulp / Carbonate-based oxygen-alkali pulping / Enzymatic bleaching / Mechanism

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