Isolation and characterization of cellulose obtained from ultrasonic irradiated sugarcane bagasse.

Cell walls of sugarcane bagasse were first delignified with chlorite followed by ultrasonic irradiation and then by two-step sequential extractions at 23 degrees C with 15 and 18% KOH for 2 h, 15 and 18% NaOH for 2 h, 8 and 10% KOH for 12 h, and 8 and 10% NaOH for 12 h and by a single one-stage isolation with 10% KOH for 16 h and with 10% NaOH for 16 h, which released 79.4, 81.8, 83.6, 85.7, 61.5, and 65.6% of the original hemicelluloses, and subsequently yielded 50.7, 49.5, 48.6, 47.8, 57.2, and 55.4% of the cellulose, respectively. The six cellulosic preparations were free of bound lignin and had a purity of 77.1-90.1% with the intrinsic viscosity (eta), viscosity average degree of polymerization, and molecular weight (M(w)) ranging from 534.1 to 631.6 mL g(-1), from 1858.1 to 2238.2 mL g(-1), and from 301000 to 362600 g mol(-1), respectively. The structural features of the isolated six cellulosic samples were comparatively examined by Fourier transform infrared and cross-polarization/magic angle spinning (13)C NMR spectroscopy and X-ray diffraction, and their thermal stability was investigated by using thermogravimetric analysis. It was found that all of the cellulosic preparations have the typical cellulose I structure but the crystallinity of the SCB cellulose was lower than that of flax, cotton, and kenaf.