Isolation and characterisation of cellulose obtained by a two-stage treatment with organosolv and cyanamide activated hydrogen peroxide from wheat straw

Seven wheat straw cellulose preparations were isolated by a two-stage acidic organosolv treatment followed by cyanamide activated hydrogen peroxide bleaching. The effects of concentration of acetic and formic acids on the yield of cellulose and degradation of lignin and non-cellulose polysaccharides were investigated. Organic acids were more effective than alcohols on the degradation of lignin and hemicelluloses. Formic acid/acetic acid/water (30/60/10, v/v/v) system was found to be the most effective in delignification and removal of non-cellulose polysaccharides from the straw and did not have any undesirable effects on cellulose properties such as its intrinsic viscosity. In this case, the treatment removed 94.1% of the original lignin and 76.5% of the original hemicelluloses using 0.1% HCl as a catalyst at 85 °C for 4 h. Cyanamide activated hydrogen peroxide bleaching degraded substantial amounts of residual hemicelluloses and lignin, produced the cellulose samples having a relatively high purity. Under a best condition, a cellulose relatively free of lignin (0.7%) and with intrinsic viscosity of 393 ml g−1 and favourable molar mass (213,940 g mol−1) was obtained. Both unbleached and bleached cellulose preparations were further characterised by FT-IR and CP/MAS 13C NMR spectroscopy, and thermal stability.