Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/27890
Title: ULTRASOUND MODIFICATION OF CELLULOSE AND CURDLAN
Authors: WONG SHEN SIUNG
Keywords: ultrasound modification, cellulose, curdlan, polysaccharides modifications, depolymerisation, sulfation
Issue Date: 12-Jan-2011
Source: WONG SHEN SIUNG (2011-01-12). ULTRASOUND MODIFICATION OF CELLULOSE AND CURDLAN. ScholarBank@NUS Repository.
Abstract: Current study aims to elucidate the effectiveness of ultrasound in the modification of polysaccharides, namely cellulose and curdlan. It is anticipated that better understanding will be gained on the effect of ultrasound beyond the conventional concept of polymeric chain fragmentation. The first part of the thesis outlined the physicochemical characterisation of the crystalline cellulose produced via ultrasonication of native bacterial cellulose (BC) and plant cellulose (PC) in a cuprammonium hydroxide solution (CUAM). Ultrasound induced depolymerisation, causing a reduction in molecular weight (MW) as shown by size exclusion chromatography study, yet the molecular structure of sonicated BC and PC were unaltered; they remained as (1&#8594;4)-ß-D-glucan. It was interesting to found that ultrasonication promotes the increment of the crystallinity index (CrI) of sonicated BC in a relatively short period of 30 minutes. Highly crystalline cellulose is desired since there is always a demand for precision engineered cellulosic materials to incorporate in bio-nanocomposites. The subsequent chapter described the same ultrasonication process of BC and PC with prolonged ultrasonication time (up to 90 minutes), with particular focus on elucidating the MW and CrI change of the products. Limiting molecular weight (Mlim) of BC and PC was achieved after 60 minutes of ultrasonication. Ultrasonication significantly (p < 0.05) increased the CrI of both BC and PC. The increment stops at samples (BC and PC) sonicated for 60 minutes. This corresponds with the Mlim values of both samples, confirming the correlation of CrI to the MW of these materials. The final chapter of the thesis describes an alternative, non-conventional method to prepare curdlan sulfate assisted by ultrasonication, based on green chemistry considerations. Curdlan was suspended in 50% (v/v) sulfuric acid at 40 °C with or without sonication. Ultrasonication has significantly (p < 0.05) increased the degree of sulfation (DS) value of sonicated samples by almost fourfold; at the same time, it achieved MW reduction by one order of magnitude. This is due to the combined effect of ultrasonication and sulfuric acid treatment, which successfully produced curdlan sulfate with low MW (~49 kDa) that is of application interest. As final concluding remarks, the current study has demonstrated the ability of ultrasound in modification of cellulose and curdlan. In addition, present projects have also confirmed the ability of utilising ultrasound beyond conventional depolymerisation experiments. It is believed that these results will provide a new insight into polysaccharides modifications and eventually expand the methodologies of polysaccharides modifications.
URI: http://scholarbank.nus.edu.sg/handle/10635/27890
Appears in Collections:Ph.D Theses (Open)

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