Application of ultrasonic waves in activation of microcrystalline cellulose

Abstract

In this work, microcrystalline cellulose (MCC) was activated with ultrasonic waves. The influences of ultrasonic treatment on the changes of supramolecular structures and morphology structure were studied by WAXS and SEM. The accessibility of the MCC was characterized by water retention value (WRV) and specific surficial area. The influence of ultrasonic treatment on the reactivity of MCC was investigated through the reaction of MCC being oxidized into 2,3-diadehyde cellulose (DAC) by periodate sodium. The mechanism of the reactivity change of ultrasonically treated MCC was examined. The results showed that the degree of crystallinity of MCC decreased and the degree of polymerization showed little change after treatment with ultrasonic waves. The morphologial variation of the treated MCC was significant when compared with the untreated MCC, which contribute to the improvement of accessibility. The aldehyde content of DAC prepared from ultrasonically treated MCC was improved from 64.19 to 85.00%, indicating that the regioselective oxidation reactivity of MCC was significantly improved. The aldehyde content was found to first increase with time of ultrasonic treatment to a point, and then decrease as time progressed. In addition, the aldehyde content was found to increase with an increase in ultrasonic power.

Ultrasound irradiation in the production of ethanol from biomass

“…In a study conducted by Wang et al [43], the degree of crystallinity of MCC after ultrasonic treatment negligibly decreased from 62% to 61%, when the ultrasonic power increased from 0 W to 200 W. However, with increasing ultrasonic power from 200 W to 700 W, a significant decrease in the degree of crystallinity of MCC was observed. It should be noted that although the degree of crystallinity decreased to 54.6% at 700 W for 15 min, the crystal size showed little change under this condition [43]. In another study it was found that both the degree and size of crystalline cellulose did not change so much after ultrasound treatment under 400 W for 12 min [37].…”

“…It seems that the treatment time of cellulosic materials using low-power ultrasound irradiation does not significantly affect the crystallinity of cellulose [43]. Generally, there is no linear relation between crystallinity and treatment time in the different powers of ultrasound waves [37,43,44].…”

“…It seems that the positive effect of ultrasound intensity on accessibility is due to the increase of smaller particles and deeper damage of surface structure [43]. It was reported that the accessibility of cellulose increases from 73% to 119% of WRV, with increasing ultrasound (400 W, 23-25 kHz) treatment time in levels of 0 s, 90 s, 180 s, 360 s and 720 s [37].…”

“…They reported that after treatment with the ultrasound waves, specific surface area and WRV increase which implied the increase of accessibility. Wang et al [43] also found that the specific surface areas of microcrystalline cellulose (MCC) increased dramatically after 5-20 min ultrasonic treatment with a power of 500 W and a frequency of 20 kHz.…”

“…8) [42]. Wang et al [43] believe that when the treating time continually increases, the "hot-spot" effects generated from the collapse of ultrasonic cavitation bubbles can cause the collision and aggregation between particles, resulting in a steady decline of specific surface area.…”