Showing papers on "N-Methylmorpholine N-oxide published in 2011"

Swelling and dissolution mechanisms of regenerated Lyocell cellulose fibers

Abstract: The swelling and dissolution mechanisms of dry, never-dried and re-wetted Lyocell fibers were investigated using mixtures of N-methylmorpholine N-oxide and water with various contents of water (from monohydrate to 24% w/w). A radial dissolution starting from the outer layers was observed. Dissolution kinetics was dependent on the water content, the drying state and the spinning conditions. A buckling of the core of dry fibers was observed during swelling. This phenomenon was attributed to the deformation of the unswollen core to accommodate the contraction of the swollen parts of the fiber. In purely swelling conditions with no dissolution, a huge swelling of a very thin skin layer was observed in the first stage, followed then by a progressive swelling of the inside of the fiber. We postulate that this mechanism arose from the fact that this skin is much less crystalline than the core.

How does the never-dried state influence the swelling and dissolution of cellulose fibres in aqueous solvent?

Abstract: The swelling and dissolution capacity of dried and never-dried hardwood and softwood pulps and cotton linters was compared in two aqueous solvents, N-methylmorpholine-N-oxide (NMMO)-water at 90 °C with water contents ranging from 16 to 22% and NaOH—water at −6 °C with NaOH contents ranging from 5 to 8%. Swelling and dissolution mechanisms were observed by optical microscopy and dissolution efficiency was evaluated by recovering insoluble fractions. The results show a contrasted picture towards the effect of the never-dried state on the swelling and the dissolution capacity depending on the origin of the fibres and the type of aqueous solvent. In the case of NMMO—water, the presence of water within and around the fibre does not seem to favour dissolution initiation but after 2 h of mixing the dissolution yield appears to be similar for either dried or never-dried state. The limiting factor for dissolution in NMMO—water is not the penetration of the solvent inside the cellulose fibres, but only the local concentration of NMMO molecules around the fibre. For NaOH—water, both optical microscopy observations on individual fibres and dissolution yield measurements show that the never-dried state is more reactive for softwood pulps and cotton linters and has no significant effect on hardwood pulps. In this case, the local decrease of solvent strength is counteracted by the opening of the structure in the never-dried state which should enable the Na+ hydrated ions to penetrate easier.

Morphology of polysaccharide blend fibers shaped from NaOH, N -methylmorpholine- N -oxide and 1-ethyl-3-methylimidazolium acetate

Abstract: The aim of this study was to find newly structured biopolymer blends bearing those adjustable features able to produce innovative materials. Apart from cellulose derivatives (cellulose carbamate and carboxymethyl cellulose), mannans (guar gum, locust bean gum, and tragacanth gum), xylan, starch (cationized), ι-carrageenan, and xanthan were chosen as blend polysaccharides for cellulose as matrix. In order to study their integration into the cellulose skeleton, fibers were shaped from three different solvents: NaOH by a special wet-spinning process, as well as N-methylmorpholine-N-oxide (NMMO) and 1-ethyl-3-methylimidazolium acetate (EMIMac) via Lyocell technology. The structure and morphologies of the fibers were analyzed by X-ray wide-angle scattering and atomic force microscopy. Hydrophilic/hydrophobic properties were determined by means of a contact angle, as well as moisture content and water retention values, while the surface properties throughout zeta-potential measurements. Being very different processes, the wet spinning in NaOH solution and the dry–wet spinning are deeply impacted by the types of solvent and polysaccharide. The X-ray results for NMMO fibers revealed the highest orientation compared with EMIMac having the lowest orientation of NaOH fibrous types. AFM images also show the lowest surface roughnesses for NMMO and EMIMac fibers. The moisture content and water retention values support these trends, while the water contact angle results show insignificant differences between the samples from EMIMac and NaOH, even though the values calculated for NMMO fibers were the lowest.

Dry jet-wet spinning of bagasse/N-methylmorpholine-N-oxide hydrate solution and physical properties of lyocell fibres

Abstract: Sugarcane bagasse, a cheap cellulosic waste material, was investigated as a raw material for producing lyocell fibers at a reduced cost. In this study, bagasse was dissolved in N-methylmorpholine-N-oxide (NMMO) 0.9 hydrate, and fibers were prepared by the dry jet-wet spinning method with coagulation in an aqueous NMMO solution. The effects of NMMO in 0 to 50% concentrations on the physical properties of fibers were investigated. The coagulating bath contained water/NMMO (10%) solution produced fiber with the highest drawability and highest physical properties. The cross-section morphology of these fibers reveals fibrillation due to the high degree of crystallinity and high molecular orientation. In the higher NMMO concentrated baths (30 to 50%), the prepared fibers were hollow inside, which could be useful to make highly absorbent materials. The lyocell fibers prepared from bagasse have a tensile strength of 510 MPa, initial modulus of 30 GPa, and dynamic modulus of approximately 41 GPa. These properties are very comparable with those of commercial lyocell fibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011