Utomo NW, Saifuddin I, Nazari B, Jain P, Colby RH. Chain dynamics and glass transition of dry native cellulose solutions in ionic liquids.
SOFT MATTER 2020;
16:200-207. [PMID:
31774426 DOI:
10.1039/c9sm01587f]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Dry native cellulose solutions in 1-butyl-3-methylimidazolium methylphosphonate (EMImMPO3H), 1-butyl-3-methylimidazolium acetate (EMImAc), and 1-butyl-3-methylimidazolium chloride (BMImCl) ionic liquids (IL) were investigated using subambient linear viscoelastic oscillatory shear. Glass transition temperatures (Tg) of solutions with various cellulose concentrations up to 8.0 wt% were observed as the peaks of loss tangent tan(δ) and loss modulus G'' in descending temperature sweeps at 1 rad s-1. Cellulose/IL solutions showed a minimum in Tg at ∼2.0 wt% cellulose content before increasing with cellulose concentration, suggesting a perturbation of the strongly structured IL solvents by the cellulose chains. Isothermal frequency sweeps in the vicinity of Tg were used to construct time-temperature-superposition master curves. The angular frequency shift factor aT as a function of temperature indicates Arrhenius behavior within a 9 K range near Tg, allowing calculation of fragility, which was found to be constant up to 8.0 wt% cellulose concentration. This result implied that increasing cellulose concentration initially decreases Tg due to disrupted ionic regularity of ILs, but does not seem to change their fragility.
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