Molecular weight and crystallinity alteration of cellulose via prolonged ultrasound fragmentation

Present investigation aims to study the effect of prolonged ultrasonication (more then 30 min) on the molecular weight (M¯w) and crystallinity index (CrI) of bacterial cellulose (BC) and plant cellulose (PC), and to compare the trend of M¯w reduction and CrI increment. In addition, the kinetics of degradation will be computed based on first order reaction kinetics. BC and PC were dissolved in cuprammonium hydroxide (CUAM) solution prior to ultrasonication at 0, 5, 10, 15, 30, 60 and 90 min. Samples were recovered from solution and lyophilised before subjected to size exclusion chromatography (SEC) measurement and x-ray powder diffraction (XRPD) studies. Ultrasonication significantly (p   < 0.05) reduce the M¯w of both BC and PC, with limiting molecular weight (Mlim) of ∼47 and ∼46 kDa, respectively, after 60 min of ultrasonication. This suggests that CUAM is a more appropriate solvent in ultrasound depolymerisation of cellulose. Kinetics study reveals that degradation of BC is slightly faster than that of PC. A continuous increment of CrI as a function of ultrasonication time was observed for both BC and PC. This increment stops at samples sonicated beyond 60 min, confirming the correlation of CrI to the M¯w of these materials.

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