Postdoctoral Associate , Massachusetts Institute of Technology
Trying to find green ways to process green materials (i.e. minimizing environmental impacts)
Cellulose and chitosan (the deacetylated form of chitin) are the most abundant renewable polymeric natural resources on our planet. Despite our long history with cellulose and chitin (both discovered over 170 years ago), while the underground carbon source keeps shrinking and concerns toward their environmental impact continue to grow, we now live in a cellulose-chitin renaissance, reconsidering new applications and processes for these two green polymeric materials. This puts an emphasize on the importance of research on finding new solvents for these materials since both polymers only get processed via wet-spinning and not in molten form. Native cellulose and chitosan can dissolve in certain ionic liquids. Having nearly zero vapour pressure and being almost completely recyclable make these liquids strong alternatives for the traditional solvents with quite large environmental impacts and derivative effects on the polymers. It is crucial to gain better understanding of the physical state of cellulose and chitosan in ionic liquids. We report solution rheology of six native cellulose samples of different molecular weight in two different ionic liquids. Based on the concentration dependences of viscosity and longest relaxation time, 1-ethyl-3-methylimidazolium acetate (EMImAc) and 1-butyl-3-methyl imidazolium chloride (BMImCl]) are θ-solvents for cellulose. The strange failure of the Cox-Merz rule (η>η* in the shear-thinning region) for cellulose solutions in ionic liquids suggests that cellulose is not a simple flexible polymer in solution. This was hypothesized to be related to intra-chain hydrogen bonding at shear rates adequate for polymer conformational ordering. Trace amounts of water compete for hydrogen bonds and can impart a yield stress to the solution rheology, which grows in magnitude as more water is incorporated. However, simply heating the solution to 80°C drives off the water and reverts the solutions to viscoselastic liquids with no yield stress. Rheology of five different chitosan samples (with deacetylation ratio ~75% and of different molecular weight) was also studied in EMImAc. Unlike those of dry cellulose, chitosan solutions in the IL contained non-crystalline aggregates, identified using linear viscoelastic tests. This was related to the chemical crosslinks present in the samples due to reaction between amine and hydroxyethyl groups on the chitosan backbone while being manufactured at elevated temperatures.
Abstract: A method is proposed for processing of experimental data which would allow adequately describing the rheological behavior of systems whose disperse phase contains swelling particles of anisometric shape. Polysaccharide films with a high degree of swelling were obtained from dispersions of powdered cellulose in chitosan solutions. The high sorption capacity of the films, good adhesion to skin, lack of toxicity, and possibility of immobilizing drugs in them allow considering these films as promising materials for healing wounds and burns.
Pub.: 01 Nov '00, Pinned: 19 Aug '17
Abstract: Solubility of cellulose, chitin, and chitosan in seven ionic liquids of varied structure was studied. It was found that pressure, temperature, and amount of an aprotic diluent (dimethyl sulfoxide) affect the dissolution of cellulose and chitin in an ionic liquid. The variation of the degree of polymerization of cellulose and chitin in ionic liquid solutions was studied. IR Fourier spectroscopy and X-ray diffraction analysis were used to examine the structural organization of hydrated cellulose and chitin films obtained.
Pub.: 16 Dec '12, Pinned: 19 Aug '17
Abstract: In order to obtain a safe and biodegradable material with antimicrobial properties from cellulose for food packaging, we presented a facile way to graft chitosan onto the oxidized cellulose films. The obtained films had a high transparent property of above 80% transmittance, excellent barrier properties against oxygen and antimicrobial properties against Escherichia coli and Staphylococcus aureus. The antimicrobial properties, mechanical properties, and water vapor permeability of composites are essential characteristics in determining their applicability as food-packaging materials. Moreover, using a sausage model, it was shown that the composites exhibited better performance than traditional polyethylene packaging material and demonstrated good potential as food packaging materials. The results presented a new insight into the development of green materials for food packaging.
Pub.: 01 Dec '15, Pinned: 19 Aug '17
Abstract: Ionic liquid solutions of cellulose or dopes can be spun into Lyocell-type textile fibers by dry-jet wet spinning. An extruded dope is drawn over an air gap into water, where the water hydrates the ionic liquid and cellulose is regenerated. Spinnability studies have concentrated on the deformation and failure modes in the air gap and thus the rheology of the unhydrated spinning dope. Herein, a breach in the bath, another failure mode, is discussed. Dopes are prepared from the good spinning solvents NMMO·H2O and [DBNH]OAc and the poor spinning solvents [emim]OAc and [TMGH]OAc. The diffusion constants for water diffusing inwards and for ionic liquid diffusing outwards the emerging filament are measured offline. The resiliences and strengths of cellulose-ionic liquid solutions with different hydration stoichiometries are measured by means of rheometry. By calculating the diffusion dynamics, the resilience distribution of the forming filament is simulated. Gel strength distribution accounts for the tendency of [emim]OAc dopes to undergo a telescope-type breach, whereas the gelatinous solution state of [TMGH]OAc dopes accounts for their poor spinnability.
Pub.: 15 Dec '15, Pinned: 19 Aug '17
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