Flow behavior and linear viscoelasticity of cellulose 1-allyl-3-methylimidazolium formate solutions

Engineering chitosan into fully bio-sourced, water-soluble and enhanced antibacterial poly(aprotic/protic ionic liquid)s packaging membrane

The design and facile preparation of water-soluble and eco-friendly polymer packaging membrane materials is a fascinating research topic, particularly in terms of the increasing concerns on potential microplastics pollution in ecosystem. In this study, taking advantages of the structural features of chitosan (CS) and betaine hydrochloride (BHC), fully bio-sourced and water-soluble poly(aprotic/protic ionic liquid)s (PAPILs) were successfully designed and prepared through the reaction of the amino groups in CS and carboxyl groups in BHC. The structure and thermo-properties of the PAPILs were elucidated by a series of characteristic methods. The rheological properties of the PAPILs aqueous solutions were also investigated. Moreover, water-soluble PAPILs membrane with a smooth surface morphology and a tensile strength of 62.9 MPa was successfully prepared. The PAPILs membrane also exhibited satisfactory biocompatibility, excellent antibacterial activities and high oxygen barrier property. Together with these outstanding material performance and functionality, as a "proof of concept", the potential use of the PAPILs membrane as water-soluble packaging material for laundry detergent capsule and pesticide was preliminarily demonstrated. These findings provide significant insights for the design of sustainable and functional packaging materials by using natural resources.

Chain dynamics and glass transition of dry native cellulose solutions in ionic liquids

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 (T_g) 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 T_g 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_g were used to construct time-temperature-superposition master curves. The angular frequency shift factor a_T as a function of temperature indicates Arrhenius behavior within a 9 K range near T_g, 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_g due to disrupted ionic regularity of ILs, but does not seem to change their fragility.

Unique gelation and rheological properties of the cellulose/CO2-based reversible ionic liquid/DMSO solutions

Gelation and rheological behaviors of cellulose/CO₂-based reversible ionic liquid (RIL)/DMSO solutions were investigated. The exponents of specific viscosity η_sp versus concentration c were determined for wood pulp (WP) and microcrystalline cellulose (MCC) solutions. The complex viscosity acquired using oscillatory shear closely follows the steady shear viscosity, thus revealing the applicability of Cox-Merz rule. The influence of RIL content in the solvent on apparent viscosities, activation energy, intrinsic viscosities, specific viscosity-c[η] master curve, and relaxation time were also investigated. Gelation occurred in this cellulose solution system due to thermal-induced CO₂ release from the decomposition of the CO₂-based reversible ionic liquid. The formed gel was stable in air, but re-dissolved when exposed to CO₂, indicating the switch-on and switch-off effects of CO₂ in cellulose dissolution and gelation.

Dissolution and transesterification of cellulose in γ-valerolactone promoted by ionic liquids

Ionic liquids act as promoters for the dissolution of cellulose in GVL and also as catalysts for cellulose derivatization in GVL, providing a green and effective solvent system for cellulose processing and derivatization.

Rheology and microstructure of concentrated microcrystalline cellulose (MCC)/1-allyl-3-methylimidazolium chloride (AmimCl)/water mixtures

Water added to a solution of microcrystalline cellulose (MCC) in 1-allyl-3-methylimidazolium chloride (AmimCl) reduces the solvent quality and causes significant changes in the flow properties and microstructure due to restructuring and aggregation of cellulose molecules. We report an experimental investigation by means of polarization optical microscopy (POM) and rheology of the distinct phases formed in 5-20 wt% MCC/AmimCl solutions due to the addition of water. With increase in the cellulose concentration, the MCC/AmimCl/water mixtures showed different morphologies such as the non-aligned cholesteric liquid crystalline (LC) domain, the coexistence of spherulite-like structures within the LC domain and a space-spanning network of spherulite-like structures at high concentrations of water. In situ microscopy during shear and POM observations pre and post shear revealed a significant increase in the size of the birefringent domains as the shear rate is increased, which continued to exist even after the cessation of shear. With an increase in the concentration of water, the zero shear viscosity of the MCC/AmimCl/water mixtures was found to go through a minimum, beyond which the aggregation of cellulose commenced. The corresponding oscillatory shear response showed a sol-gel transition with an increase in water concentration. Moreover, at high cellulose concentrations (12-20 wt%), the MCC/AmimCl/water gels exhibited self-similarity and followed the Chambon-Winter (CW) criterion. The similar phase behavior and rheological response observed for MCC dissolved in 1-butyl-3 methylimidazolium chloride (BmimCl) indicated the generality of the presented results.

Two-Dimensional FTIR as a Tool to Study the Chemical Interactions within Cellulose-Ionic Liquid Solutions

In this study two-dimensional FTIR analysis was applied to understand the temperature effects on processing cellulose solutions in imidazolium-based ionic liquids. Analysis of the imidazolium ionνC2–H peak revealed hydrogen bonding within cellulose solutions to be dynamic on heating and cooling. The extent of hydrogen bonding was stronger on heating, consistent with greater ion mobility at higher temperature when the ionic liquid network structure is broken. At ambient temperatures a blue shiftedνC2–H peak was indicative of greater cation-anion interactions, consistent with the ionic liquid network structure. Both cellulose and water further impact the extent of hydrogen bonding in these solutions. The FTIR spectral changes appeared gradual with temperature and contrast shear induced rheology changes which were observed on heating above 70°C and cooling below 40°C. The influence of cellulose on solution viscosity was not distinguished on initial heating as the ionic liquid network structure dominates rheology behaviour. On cooling, the quantity of cellulose has a greater influence on solution rheology. Outcomes suggest processing cellulose in ionic liquids above 40°C and to reduce the impacts of cation-anion effects and enhance solubilisation, processing should be done at 70°C.