Effect of Ultrafine Grinding Pretreatment on the Cellulose Fibers and Nanocrystals from Wheat Straw

To investigate the effect of ultrafine grinding pretreatment on the isolation of wheat straw cellulose fibers and nanocrystals, wheat straw at cellular scale (50-30 mu m) were produced with different ultrafine grinding time prior to extract cellulose fibers and nanocrystals. Cellulose fibers were obtained by 4% sodium hydroxide and alkaline hydrogen peroxide treatment from ultrafine ground wheat straw. Morphological changes were observed using scanning electron microscopy (SEM). Fourier transform infrared (FTIR) spectroscopy showed the removal of non-cellulosic components and the rearrangement of hydrogen bonds in cellulose. X-ray diffraction (XRD) analysis revealed the decrease of crystalline index with grinding time prolonged and the formation of cellulose II in alkali treated 8.0 h ultrafine ground wheat straw. Cellulose nanocrystals were produced from these cellulose fibers using 64% sulfuric acid hydrolysis treatment. Morphological examination through atomic force microscope (AFM) showed that the length of rod-like CNCs decreased with prolonged ultrafine grinding time in 2.0 h and then increased due to the formation of cellulose II.