Physicochemical Properties and Structural Characterization of Water- and Alkali-Extractable Hemicelluloses from Delignified Bambusa rigida species: A Comparative Study

摘要

The most critical procedure to exploit hemicelluloses-based materials is the efficient separation of biomass. Then the isolated hemicelluloses were chemically modified for preparing bio-based materials. The main advantages of the water and alkali extractions are the fact that they are simple to perform and cost-effective. If sequential extractions were performed, the residual biomasses are mainly cellulose with a high purity. Therefore, the delignified biomass could be used for preparative of hemicelluloses and cellulose with high purity. In this case, the sequential extraction method was considered as a feasible procedure to obtain hemicelluloses and cellulose in a large scale. In this study, water and aqueous alkali sequential treatments of delignified bamboo particles were performed to extract hemicelluloses with a high yield and weight averaged molecular mass (Mw). The successively extractions together dissolved 42% of hemicelluloses based on dry holocellulose. GPC results showed that the alkali-extractable hemicelluloses have higher Mw (35000 and 44450 g mol-1) than that of water-extractable ones (20100-28100 g mol-1). Structural determination based on FT-IR, 1H, 13C and 2D-HSQC NMR analysis showed that both the water and alkali-extractable hemicelluloses consist mainly of arabinoglucuronoxylans, and probably had a structure composed of the (1→4)-linked β-D-xylopyranosyl backbone with 4-O-methyl-α-D-glucuronic acid attached to O-2 of the xylose residues and L-arabinose attached to O-3 of the xylose residues. Moreover, it revealed that the water-extractable hemicelluloses retained original structure without cleaving chemical linkages. Furthermore, it was also found that the hemicelluloses with the highest yield and Mw were obtained by the aqueous alkali treatment from the delignified bamboo. Small amount of other minor hemicelluloses (β-glucans) including xylans in the water-extractable hemicelluloses could be identified by NMR and other approaches.