Characteristics of degraded cellulose obtained from steam-exploded wheat straw

The isolation of cellulose from wheat straw was studied using a two-stage process based on steam explosion pre-treatment followed by alkaline peroxide post-treatment. Straw was steamed at 200degreesC, 15bar for 10 and 33 min, and 220degreesC, 22 bar for 3, 5 and 8 min with a solid to liquid ratio of 2:1 (w/w) and 220degreesC, 22 bar for 5 min with a solid to liquid ratio of 10:1, respectively. The steamed straw was washed with hot water to yield a solution rich in hemicelluloses-derived mono- and oligosaccharides and gave 61.3 %, 60.2 %, 66.2 %, 63.1 %, 60.3 % and 61.3 % of the straw residue, respectively. The washed fibre was delignified and bleached by 2 % H2O2, at 50degreesC for 5 h under pH 11.5, which yielded 34.9 %, 32.6 %, 40.0 %, 36.9 %, 30.9 % and 36.1% (% dry wheat straw) of the cellulose preparation, respectively. The optimum cellulose yield (40.0 %) was obtained when the steam explosion pre-treatment was performed at 220degreesC, 22 bar for 3 min with a solid to liquid ratio of 2:1, in which the cellulose fraction obtained had a viscosity average degree of polymerisation of 587 and contained 14.6 % hemicelluloses and 1.2 % klason lignin. The steam explosion pre-treatment led to a sianificant loss in hemicelluloses and alkaline peroxide post-treatment resulted in substantial dissolution of lignin and an increase in cellulose crystallinity. The six isolated cellulose samples were further characterised by FT-IR and C-13-CP/MAS NMR spectroscopy and thermal analysis. (C) 2004 Elsevier Ltd. All rights reserved.