Comparative study of hemicelluloses released during two-stage treatments with acidic organosolv and alkaline peroxide from Caligonum monogoliacum and Tamarix spp

Two-stage treatments of Caligonum monogoliacum and Tamarix spp. with acidic organosolv and alkaline peroxide were performed. Pre-treatment with ethanol-H2O (60/40, v/v) under acid catalyst (0.2 N HCl) at 70 degreesC for 4 h released 18.7 and 17.8% hemicelluloses from dewaxed C. monogoliacum and Tamarix spp., respectively, Sequential treatment with 2% H2O2 at pH 11.5 for 16 h at 45 degreesC solubilized 26.2 and 26.5% hemicelluloses from pre-treated C. monogoliacum and Tamarix spp., respectively. Cellulose predominated in the insoluble residues, accounting for 36.7-37.8% of dry materials. It was found that the two alkaline peroxide soluble hemicellulosic preparations contained a much higher amount of xylose (74.1-77.3%) but lower in glucose (7.4-18.6%), galactose (3.0-8.3%), rhamnose (2.3-2.9%), mannose (0.8-2.7%), and arabinose (1.3-1.4%) than those of the two acidic organosolv soluble hemicellulosic fractions in which xylose (31.8-50.8%), glucose (21.4-30.3%), galactose (7.6-24.1%), and rhamnose (5.7-10.1%) were the major sugar components. The content of uronic acids was slightly higher in the two alkaline peroxide soluble hemicellulosic preparations (7.5-8.3%) than the two acidic organosolv soluble hemicellulosic fractions (5.0-6.5%). Furthermore, the studies showed that the two alkaline peroxide soluble hemicellulosic preparations were more linear and acidic, and had a large molecular mass (M-w, 27,220-31,410 g mol(-1)) than the two acidic organosolv soluble hemicellulosic fractions ((M) over bar (w), 13,820-18,380 g mol(-1)). Lignin content and its composition associated in the four isolated hemicelluloses were determined by alkaline nitrobenzene oxidation and monitored with HPLC. No significant differences in lignin content (5.94-9.82%) and its composition were found. Further comparative study of the four hemicellulosic preparations and two cellulosic fractions was carried by both degraded methods such as acid hydrolysis and thermal analysis and non-degradation techniques such as FT-IR and C-13-NMR spectroscopy. (C) 2003 Elsevier Science Ltd. All rights reserved.