Fractional Isolation and Chemical Structure of Hemicellulosic Polymers Obtained from Bambusa rigida Species

Abstract

Water and aqueous alkali sequential treatments of delignified bamboo particles were performed to extract hemicelluloses with a high yield and weight-average molecular mass (Mw). The sequential treatment 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 water-extractable ones (20100-28100 g mol(-1)). Structural determination based on FT-IR and (1)H, (13)C, and 2D-HSQC NMR analyses showed that both the water- and alkali-extractable hemicelluloses shared the 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. A small amount of other minor hemicelluloses (β-glucans) including xylans in the water-extractable hemicelluloses could be identified by NMR and other approaches.