Cellulose is the most abundant polymer natural resource on Earth. Mankind has chemically modified cellulose for centuries to make it solution processable. Recently, native cellulose has been shown to fully dissolve in certain ionic liquids and the fibers spun from those solutions have twice the modulus of chemically modified cellulose, since all of the hydrogen bonds that make wood strong are still present. In this work, we show that while the cellulose / ionic liquid solutions are in some ways similar to ordinary polymer solutions, there are both intermolecular association effects in the bulk solution and cellulose adsorbs strongly to the air/solution interface, complicating rheology and processing. 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 oC 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.

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

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.