Paper Number
SM8 

Session
Polymers Solutions, Melts and Blends

Title
Solution rheology of dry native cellulose in ionic liquids: Weakly associating polymers?

Presentation Date and Time
October 21, 2019 (Monday) 2:20

Track / Room
Track 3 / Room 201

Authors (Click on name to view author profile)

1. Utomo, Nyalaliska (Penn State University, Materials Science and Engineering)
2. Nazari, Behzad (Penn State University, Materials Science and Engineering)
3. Colby, Ralph (Pennsylvania State University, Materials Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Nyalaliska Utomo, Behzad Nazari, and Ralph Colby
Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802

Speaker / Presenter 
Colby, Ralph

Text of Abstract
We report solution rheology of six dry native cellulose samples of different molecular weight in three different ionic liquids; 1-ethyl-3-methylimidazolium acetate [EMIm]Ac, 1-butyl-3-methyl imidazolium chloride [BMIm]Cl and 1-ethyl-3-methylimidazolium methylphosphonate [EMIm][P(OCH3)(H)O2]. These solutions do not crystallize, making it possible to measure the glass transition using oscillatory shear rheology. Trace amounts of water impart a yield stress to these solutions so they experience 20 min at 80 C in the rheometer after loading to remove water. Concentration dependences of specific viscosity and relaxation time make each solution appear to be a ‘normal’ polymer solution, with dilute, semidilute unentangled and entangled regimes of concentration. However, the same cellulose sample in different solvents at the same concentration has a different width of the rubbery plateau and there is a strange failure of the Cox-Merz rule (shear viscosity larger than linear complex viscosity in the shear-thinning region) for cellulose solutions in ionic liquids. Both of those observations suggest that native cellulose is not a simple flexible polymer in solution and that it instead has some inter-chain hydrogen bonds between cellulose chains. Urea is known to compete for hydrogen bonds and adding urea to these solutions lowers the viscosity, most dramatically for the solutions with the widest rubbery plateau. An additional complication with these solutions is that cellulose seems to adsorb to the air interface to create a viscoelastic film and the consequences of that adsorption on literature for the temperature dependence of intrinsic viscosity of cellulose in [EMIm]Ac will be discussed.