Comparative study of alkali- and acidic organic solvent-soluble hemicellulosic polysaccharides from sugarcane bagasse

Two-stage treatments of sugarcane bagasse with mild alkali and acidic 1,4-dioxane were performed. Pretreatment with 1 M NaOH aqueous solution at 20, 25, 30, 35, and 40 °C for 18 h released 55.5%, 57.3%, 59.1%, 60.9%, and 62.1% of the original hemicelluloses, respectively. Post-treatment of the corresponding alkali-treated residue with 1,4-dioxane–2 M HCl (9:1, v/v) at 87 °C for 2 h, respectively, degraded 11.6%, 11.9%, 11.4%, 10.9%, and 10.6% of hemicelluloses (% dry starting material). It was found that the five alkali-soluble hemicellulosic preparations contained a much higher amounts of xylose (78.0–82.2%) and slightly higher uronic acids (4.8–5.8%), mainly 4-O-methyl-α-d-glucopyranosyluronic acid, but were lower in arabinose (9.3–11.7%) and glucose (2.2–4.1%) than those of the corresponding five acidic dioxane-degraded hemicellulosic fractions in which xylose (44.9–46.8%), arabinose (35.9–38.1%), and glucose (13.0–13.7%) were the major sugar constituents. The studies revealed that the five alkali-soluble hemicellulosic preparations were more linear and acidic, and had a large molecular weight (35,200–37,430 g mol−1) than those of the hemicellulosic fractions (12,080–13,320 g mol−1) degraded during the acidic dioxane post-treatment. This demonstrated that the post-treatment with acidic dioxane under the condition used resulted in substantial degradation of the hemicellulosic polymers. The 10 hemicellulosic samples were further characterized by FT-IR and 1H and 13C NMR spectroscopy, GPC and thermal analysis, and the results are reported.

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