Morphology of cellulose objects regenerated from cellulose-N-methylmorpholine N-oxide-water solutions

International audienceThe precipitation in aqueous media of cellulose from solutions in N-methylmorpholine N-oxide (NMMO) hydrates is an important stage in the process of manufacturing of fibres, films and other cellulose objects. It is responsible for the formation of the structure of the regenerated object and their morphological characteristics significantly influence the properties of the final products. Regeneration of rather large cellulose objects was observed in situ by optical microscopy. It was found that all regenerated objects present an asymmetric structure composed of a dense skin surrounding a sub-layer characterised by the presence of finger-like voids. The porous texture of the cellulose parts between these voids is typical of the one obtained by spinodal decomposition. The morphologies of regenerated cellulose samples are described as a function of various parameters, initial cellulose solutions and composition and temperature of the aqueous regeneration bath. A mechanism of the structure formation during regeneration is proposed

Dissolution, crystallisation and regeneration of cellulose in Nmethylmorpholine N-oxyde

International audienceMixtures of N-methylmorpholine N-oxyde (NMMO) and water are direct solvents for cellulose, used for processing fibres (Lyocell process). The objective of this work is to study three aspects of the preparation of cellulose objects from NMMO-water solutions, the NMMO-water phase diagram in order to follow the dissolution-swelling path, the crystallisation of the cellulose solution that may occur under cooling and the regeneration of the cellulose from a solution

Cellulose swelling and dissolution as a tool to study the fiber structure

International audienceThe swelling and dissolution mechanisms of cotton or wood fibers cellulose fibers in aqueous (as N - methylmorpholine N-oxide and water mixtures, or soda solutions) or in ionic liquids are studied. Some cellulose samples treated by enzyme mixtures are investigated too. Six dissolution modes are found and detailed. The swelling (homogeneous or by ballooning) is the precursor of the dissolution step, which occurs by bursting of balloons or by unwinding of cellulose structure. These phenomena are due to morphological structure of the native cellulose fibres. The balloons formation reveals the elasticity and semi - permeability of primary and S1 layers, which play the role of a membrane. The intern stresses frozen during biosynthesis are revealed by unwinding. The study allows the influence of the solvent quality on the dissolution mechanism

A Flow-induced phase inversion in immiscible polymer blends containing a liquid-crystalline polymer studied by in situ optical microscopy

International audienceThe phase inversion from a morphology of hydroxypropylcellulose in water (HPC50%) droplets in polydimethylsiloxane (PDMS) matrix to a morphology of PDMS droplets in HPC50% matrix can be induced by a change of shear rate, due to a viscosity ratio inversion. Such a process passing through four different transient morphological stages was studied by optical microscopy in a transparent shear device. In a certain concentration region, at a fixed shear rate, after sheets of PDMS were formed, the transition "hesitates" between phase inversion and refined starting morphology. The influence of PDMS concentration, shear rate, elasticity, and phase dimension on the final morphology was investigated and compared with different models given in the literature. The influence of concentration and shear rate on the duration of the transient flow was also studied. We propose a simplified model of breakage of filaments to explain a part of our result

Physics of cellulose xanthate dissolution in sodium hydroxide-water mixtures: a rheo-optical study

Article disponible sur le site de l'éditeur : http://www.cellulosechemtechnol.ro/pdf/CCT44,7-8(2010)/217-221.pdfInternational audienceThe way cellulose xanthate (viscose) fibres dissolve in sodium hydroxide water mixtures is studied in situ, under flow, using a counter rotating optical rheometer. When a bunch of viscose fibres is placed in a solvent, a visco-elastic shell is formed, slowing down the diffusion of the solvent to non-dissolved fibres. It forms a highly concentrated, visco-elastic phase that disperses slowly through a pulling mechanism sucking this visco-elastic solution into the solvent. Due to this mechanism, dispersion and distribution of cellulose xanthate into the solvent is very slow

Dissolution mechanisms of wood cellulose fibres in NaOH-water

The authors are grateful to the publisher, Springer, for letting the manuscript being archived in this Open Access repository. The final publication is available at http://www.springerlink.comInternational audienceFour wood pulps and a microcrystalline cellulose were dissolved in a NaOH 8%-water solution. Insoluble fractions and clear solution fractions were isolated by centrifugation and were observed by optical microscopy and transmission electron microscopy. Molecular weight distribution, carbohydrate composition and cellulose II content were measured. The dissolution of wood cellulose fibres in NaOH 8%-water solutions occurs by successive dismantlement and fragmentation steps governed by the swelling and the shearing of the original structure. The cellulose from insoluble and clear solution fractions is in both case converted in cellulose II and the insoluble fractions contain embedded mannans. Besides, the molecular weight distributions of cellulose from insoluble and clear solution fractions reveal the existence of heterogeneities in dissolution capacity of the cellulose chains, independent to the degree of polymerization, which are related to the chemical environment of the chains in the fibre structure

Influence of ZnO on the properties of dilute and semi-dilute cellulose-NaOH-water solutions

International audienceThe influence of ZnO as cellulose-8%NaOH-water solution stabilizer against gelation is studied. Cellulose intrinsic viscosity in 8%NaOH-water as a function of solution temperature is investigated in the presence and absence of ZnO. The addition of ZnO did not bring any improvement in terms of solvent thermodynamic quality. Non-dissolved ZnO particles were observed above 0.8-0.9% ZnO in 8%NaOH-water. Gelation of cellulose-8%NaOH solutions with and without ZnO are studied for various cellulose and ZnO concentrations (4-6% and 0-1.5%, respectively) in a wide range of temperatures (-5 °C to 50 °C). Gelation times were exponentially increasing with increasing ZnO concentration and with decreasing cellulose concentration and solution temperature. Gelation times of cellulose-NaOH-water-ZnO systems were found to follow a semi-empirical model correlating these three parameters. We suggest that ZnO is acting as water molecular "binder" stabilizing cellulose-NaOH-water solutions

In situ characterisation of dispersion processes of silica in an elastomer matrix under shear, impact of a filler treatment

International audienceThe dispersion of a filler immersed in a polymer flow submitted to shear is the result of the counterbalance between hydrodynamic forces acting on the agglomerate and its cohesive forces. The nature of the filler, its surface treatment or its degree of infiltration by the polymer should impact its cohesivity. To better understand the influence of these parameters on dispersion, direct observations of dispersion mechanisms under shear were carried out on raw silica, silica treated with a covering agent and fully infiltrated silica agglomerates. Dispersion mechanisms and critical stresses for dispersion were determined and found to be different in those three cases

Structural changes and alkaline solubility of wood cellulose fibers after enzymatic peeling treatment

The authors are grateful to the publisher, Elsevier, for letting the manuscript being archived in this Open Access repository. The final publication is available at http://www.sciencedirect.com/International audienceTwo dissolving sulphite wood pulps were treated by an enzymatic peeling protocol and the changes in terms of structure and alkaline solubility were analyzed. The enzymatic treatment leads to a fast and large decrease of degree of polymerization and of crystallinity, showing that the enzymes do not simply act on the fiber surface. The swelling and dissolution behaviour of the treated samples showed that the enzyme mixture used has two effects at short peeling times (i) a digestion of the primary wall which is seen by the near absence of ballooning and (ii) a destructive action on the inside of the fiber which is seen by the large decrease in the degree of polymerization. At long peeling times, the external walls are totally digested and the fiber structure is totally destroyed, as seen by the absence of birefringence. The alkaline solubility of the different treated samples was investigated in a NaOH 8%-water solution. As expected from thermodynamic considerations, there is a direct correlation between the solubility and the degree of polymerization. However, aside thermodynamics, the removal of the external walls and the macrostructural destructuration of the fibers are key factors in the improvement of the dissolution of wood cellulose fibers. At constant intrinsic viscosities of the cellulose materials, the alkaline solubility is almost two times higher when the external walls are removed. The macrostructural destructuration of fibers by enzymes allows a high degree of polymerization to be preserved while keeping a good alkaline solubility