The comparison of cellulose regeneration behavior in different solvents after sulfuric acid treatment

Abstract

Background The efficient utilization of cellulose requires certain treatments. Regeneration of cellulose after dissolving it using chemical reagents is one of the commonly used methods. In this study, a high solid/liquid ratio beyond the region normally explored in the conventional processes was applied in the sulfuric acid treatment of cellulose, and different solvents were employed in the cellulose regeneration process. Results Sulfuric acid in the swelling state was effective in disrupting the cellulose structure and breaking its internal hydrogen bonds. The crystal type of the cellulose samples regenerated in water was cellulose II, while samples generated in methanol and ethanol showed amorphous structures. Meanwhile, the degree of polymerization (DP), average particle size (D₅₀), and crystallinity (CrI) values of the samples were ranked as water > methanol > ethanol in terms of the regeneration solvents. This order was correlated with the polarity and molecular size of the solvents. The stronger the polarity, the more the liquid could form hydrogen bonds with the sulfuric acid during the regeneration process, which resulted in a higher degree of cellulose agglomeration. When cellulose was regenerated in ethanol after acid treatment, its DP decreased from 210 to 17 and its CrI decreased from 78.90 to 15.39 which will facilitate the subsequent enzymatic hydrolysis. The results of the enzymatic hydrolysis experiments showed that the glucose productivity of the sample from ethanol was the highest among the three regeneration solvents. Conclusion The regeneration solvents have significant impact on the crystal types and physio-chemical property of regenerated cellulose after acid treatment. Solvents with more polarity have a greater ability to form hydrogen bonds with sulfuric acid, resulting in a higher degree of cellulose re-polymerization, while solvents with smaller molecular size give the cellulose less spatial hindrance in forming hydrogen bonds for re-polymerization. Ethanol is considered to be a better solvent for cellulose regeneration after acid treatment among water, ethanol, and methanol.