Rheology of Natural Polysaccharides in Ionic Liquids
Open Access
- Author:
- Wattana, Ravisara
- Area of Honors:
- Materials Science and Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Ralph H Colby, Thesis Supervisor
Dr. Robert Allen Kimel, Thesis Honors Advisor - Keywords:
- Rheology
Natural Polysaccharides
Cellulose
Chitosan
Xanthan
Ionic liquids
Urea Effect - Abstract:
- Natural Polysaccharides are produced billions of tons globally from renewable resources that are available up to 85%. With its enormous availability, they are attractive to substitute the use of petroleum-based plastics. Cellulose and chitosan are the most and second most plentiful obtained from the plant cell wall and crustacean shells, respectively. Xanthan is another abundant polysaccharide taken from a bacterium that is water-soluble. These three polysaccharides represent the three systems: cellulose as a neutral polysaccharide, chitosan as a cationic polysaccharide, xanthan as an anionic polysaccharide. The conventional dissolutions of the two former polysaccharides have been long discussed that lead to environmental concerns because they are toxic and expensive. Certain ionic liquids (ILs) are recognized as green, non-derivatizing solvents for cellulose and many natural polysaccharides. They are also nonvolatile due to the negligible vapor pressure allowing them to be recyclable under the processing condition. Thus, this work aims to gain a better understanding of these abundant polysaccharides through their rheological behavior. The three polysaccharides were dissolved in 1-ethyl-3-methylimidazolium acetate (EMImAc), 1-butyl-3-methylimidazolium chloride (BMImCl), and 1-ethyl-3-methylimidazolium methyl-phosphonate (EMImMPO3H) to investigate their rheological responses in ionic liquid solutions. Cellulose dispersed well in all three ILs resulting in a viscoelastic fluid, but chitosan only swells in EMImAc and EMImMPO3H exhibiting a gel-like material. Xanthan formed weak gels when dissolved in BMImCl and EMImMPO3H, but seemed to fully dissolve in EMImAc. The temperature effect strongly influences the xanthan conformation, but EMImAc was found to have the least change in rheology. Due to the high cost of ionic liquids, the addition of urea can potentially help in the processing cost of the natural polysaccharides in ionic liquids. Since urea is very good at competing for hydrogen bonds, it was found to lower the viscosity of the three polysaccharide solutions, and it completely transformed gels to liquids. The interfacial rheology using the Double Wall Ring (DWR) was found to be barely affected by the urea addition, while the intrinsic viscosity decreased as more urea was added. Ultimately, the purposes of these results are to improve the processability of the natural polysaccharides as well as to promote sustainability by reducing our dependence on non-renewable resources.