Chain dynamics and glass transition of dry native cellulose solutions in ionic liquids.
basic_science · Level V
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- Record sourced from PubMed, PMID 31774426.
- Also identified by DOI 10.1039/c9sm01587f.
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Abstract
Dry native cellulose solutions in 1-butyl-3-methylimidazolium methylphosphonate (EMImMPO<sub>3</sub>H), 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 (T<sub>g</sub>) 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<sup>-1</sup>. Cellulose/IL solutions showed a minimum in T<sub>g</sub> 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 T<sub>g</sub> were used to construct time-temperature-superposition master curves. The angular frequency shift factor a<sub>T</sub> as a function of temperature indicates Arrhenius behavior within a 9 K range near T<sub>g</sub>, 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 T<sub>g</sub> due to disrupted ionic regularity of ILs, but does not seem to change their fragility.