Rheology of Native Cellulose in Ionic Liquids

Open Access
- Author:
- Jain, Preet K
- Area of Honors:
- Chemical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Ralph H Colby, Thesis Supervisor
Andrew Zydney, Thesis Honors Advisor - Keywords:
- Rheology
Cellulose
Shear-thinning
Ionic Liquids
Polymer Solutions
Green solvents
Solvent quality
Associating polymers
Chain dynamics
Glass-transition temperatures
Time-temperature Superposition - Abstract:
- Cellulose, one of the most abundant polymers on Earth, has many interesting characteristics which can be exploited due to its strong intermolecular and intramolecular hydrogen bonding along with its eco-friendly nature. Dissolving cellulose without derivatizing it has been a quest for many years, and this has led to the discovery of many ionic liquids (ILs) that are able to fully dissolve it. Ionic liquids have a high thermal and chemical stability along with being environmentally friendly for chemical modification and processing of cellulose. Native cellulose fibers spun from ionic liquid solutions have depicted characteristics of having twice the modulus of derivatized cellulose and this was the gateway into gaining a better understanding of cellulose/IL solutions through the characterization of cellulose of different molecular weights (272, 520 and 625 kg/mol) and of different concentrations (0.01-8.00 wt%) in 1-ethyl-3-methyl imidazolium phosphonate (EMImMPO3H). The scaling of specific viscosity and terminal relaxation time depict that EMImMPO3H is a good solvent and this was confirmed by the molecular weight dependence of the overlap and entanglement concentration. The terminal relaxation time data varied to a certain degree from literature and the conjecture is that this deviation is due to associations between polymer chains in the ionic liquid. This dependence of terminal relaxation time on concentration was further investigated by comparing it with the theoretical predictions made by Semenov et al for associating polymers and some correlation was observed. The rheology measurements for understanding the chain dynamics also depict the presence of associations via the Cox-Merz empirical rule failure. Moreover, a non-monotonic trend in glass transition temperature was seen with increasing concentration of cellulose and this was associated with the effect of ionic liquid structures at low concentrations of cellulose and the effect of cellulose at high concentrations. The application that drives this research is to have an environmentally friendly fiber spinning process and therefore, this thesis tries to understand the polymer solution’s viscoelastic behavior through rheology.