J.L. Ren

Fractional isolation and structural characterisation of hemicellulosic polymers from delignified and ultrasonic irradiated sugarcane bagasse

Abstract Hemicellulose-type polysaccharides were isolated from the delignified and ultrasonic irradiated sugarcane bagasse by a sequential two-step alkaline extraction. It was found that the successive extractions with 15% and 18% KOH for 2 h, 15% and 18% NaOH for 2 h, 8% and 10% KOH for 15 h, and with 8% and 10% NaOH for 15 h resulted in a total dissolution of 89.6%, 92.8%, 94.9%, and 97.3% of the original hemicelluloses, respectively. Sugar analysis revealed that xylose was the predominant sugar composition of all the hemicelluloses, comprising 57.4- 68.6% of the total sugars. Arabinose (12.3-18.4%) and glucose (10.8- 14.6%) appeared as the second and third major sugar constituents. Galactose (3.9-8.7%), uronic acids, mainly 4-O-methyl-glucuronic acid (2.7-5.8%), rhamnose (1.2-2.6%), and mannose (0.2-1.3%) were observed as minor constituents. The structural studies by 13C-NMR spectroscopy showed that L-arabino (4-O-methyl-D-glucurono) xylans were the major constituents of the hemicellulosic polymers. Furthermore, the current results also showed that the four alkali-soluble hemicellulosic fractions, isolated during the first step treatment with relatively lower concentrations of alkalis, were more branched and acidic, and had larger molecular weights (Mw, 23100-34500), but lower thermal stability than the other four alkali-soluble hemicellulosic preparations (Mw, 21700-28700), extracted during the second stage treatment with relatively higher concentrations of alkalis.

Fractional Separation and Structural Characterization of Chlorophyll and Lignin from Perennial Ryegrass (L. perenne) and Cocksfoot Grass (D. glomerata)

Abstract One chlorophyll rich fraction and two lignin preparations were separated from perennial grass and cocksfoot grass by sequential three‐stage treatments with 80% ethanol containing 0.2% NaOH, 2.5% H2O2−0.2% EDTA containing 1.5% NaOH, and 2.5% H2O2−0.2% TAED containing 1.0% NaOH at 75°C for 3 h, respectively, which released 4.6 and 3.6% chlorophyll rich fraction, 2.3 and 5.8%, and 0.9 and 1.0% lignin preparations, except for releasing 8.0 and 10.4%, 79.1 and 77.0%, and 12.9 and 12.5% of the original hemicelluloses, respectively. The lignin fractions obtained from the two different grasses had very similar molecular weights and structural composition. The NMR spectra of the lignin preparations revealed the presence of p‐hydroxyphenyl, guaiacyl, and syringyl structures, and the lignin in chlorophyll rich fraction contained more guaiacyl and syringyl units than p‐hydroxyphenyl unit, whereas the reverse trend was found in the two lignin preparations. The lignin preparations are distinguished with straw and wood lignins by relatively higher contents of p‐hydroxyphenyl unit and lower amounts of condensed units (β‐5 and 5‐5′) and resinol units (β‐β). This difference in distribution of structural units indicated some structural heterogeneity between grass and straw/or wood lignin.