Rheology of Native Cellulose in Ionic Liquids
Open Access
- Author:
- Utomo, Nyalaliska
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 08, 2019
- Committee Members:
- Ralph H Colby, Thesis Advisor/Co-Advisor
Robert John Hickey, III, Committee Member
Enrique Daniel Gomez, Committee Member - Keywords:
- Cellulose
Ionic Liquids
Native Cellulose
Rheology
Polymer Solutions
Green Solvents
Biopolymers
Molecular Weight Determination
Solvent Quality
Interfacial Rheology
Associating Polymers
Polymer Chain Dynamics - Abstract:
- Cellulose is the most abundant renewable biopolymer on Earth produced in hundreds of billion tons annually. Ionic liquids have been identified as novel solvents that are capable to fully dissolve cellulose without derivatizing it. Ionic liquids (ILs) have low vapor pressure and can be reused for many process cycles, making them strong candidates in replacing traditional solvents for cellulose. Furthermore, native cellulose fibers spun from IL solutions have twice the modulus of derivatized cellulose, since all the native hydrogen bonding groups that make wood strong are still present. The objective of this thesis is therefore to gain a better understanding of cellulose/IL solutions through characterization of cellulose dissolved in 1-ethyl-3-methylimidazolium acetate (EMImAc), 1-butyl-3-methylimidazoilium chloride (BMImCl), and 1-ethyl-3-methylimidazolium methyl-phosphonate (EMImMPO3H). The molecular weights of native cellulose samples were determined through intrinsic viscosity in Cupriethylenediamine hydroxide (Cuen) and EMImAc, as well as through size exclusion chromatography (SEC) of derivatized cellulose tricarbanilates (CTCs) in THF. The use of universal Mark-Houwink exponent of 𝑎 = 1.0 was found to fit well into the determined intrinsic viscosity and molecular weight data. From the scaling of specific viscosity and relaxation time, it was concluded that EMImAc is a θ solvent and BMImCl a good solvent for native cellulose. The determined relaxation times seemed to be affected by the polydispersity of cellulose samples and the predicted cellulose-cellulose associations might have interfered with solvent classifications. The rheology measurements of cellulose/ILs were found to be influenced by both interfacial effects and associations between cellulose chains. The interfacial effect is seen as exaggeration in viscosity value in rotational rheometer geometries that expose samples to an air surface. The associations in cellulose/ILs were observed in an unusual Cox-Merz failure and can be disrupted by the addition of urea into the system. The degree of associations was dictated by IL’s anion size and was quantified by the width of rubbery plateau from time-temperature superposition (tTs) master curves. An unusual, non-monotonic trend in glass transition temperature was also observed in solutions due to cellulose breaking ILs’ ionic structure. Despite the broken ionic structure, solutions’ fragility indices do not vary significantly with increasing cellulose concentration. Overall, this thesis dives into the behavior of cellulose in ionic liquid solutions to gain a comprehensive and thorough knowledge to motivate the large-scale production of cellulose fibers using ILs as solvents. It was done through assessing multiple aspects of the solutions such as molecular weight determination of cellulose, solvent quality of EMImAc and BMImCl, interfacial and associations effects of cellulose/IL solutions, and cellulose chain dynamics in ILs.