Influence of ultrasonic wave treatment on structure and accessibility of cellulose fibers

As cellulose reactions take place mostly under heterogeneous conditions that pre-activating treatment is need to improve their accessibility and reactivity. In this paper an attempt was made to treat cellulose fibers from bleached eucalyptus Kraft pulp by ultrasonic wave. The structure changes on morphology, supermolecular were characterized by means of polarized light microscopy, scanning electron microscopy (SEM) and X-ray diffraction. The property changes as accessibility of cellulose characterized as water retention value (WRV) and surface area determined by dye adsorption were also investigated. The results showed that the morphology and fine structure of cellulose fibers had changed during the ultrasonic wave treatment. Removal of S-1 layer, dislocations in the S-2 layer, swelling of the fiber, and then fibrillation in the S-2, layer had been observed on ultrasonic treated cellulose fibers. X-ray diffraction investigation showed that after the ultrasonic treatment: the crystallinity (Xc) of cellulose was increased at some extent which was found to be related to treatment time and ultrasonic power. The maximum Xc of 84 % was obtained when cellulose was treated for 720s with an ultrasonic wave of frequency of 23-25kHz, power of 200W. It was also found that after ultrasonic treatment, the accessibilities were remarkably increased and a large number of pores accessible to water were opened up. These results suggested that along with other classical or non-classical activation methods developed in accordance with "Green Chemistry" requirements, ultrasonic wave treatment might be promising, methods of activation cellulose in cellulose functionatization.