Cellulose fibres, dissolution

Desizing by chemical decomposition is applicable to starch-based sizes. Since starch and its hydrophilic derivatives are soluble in water, it might be assumed that a simple alkaline rinse with surfactant would be sufficient to effect removal from the fibre. As is also the case with some other size polymers, however, once the starch solution has dried to a film on the fibre surface it is much more difficult to effect rehydration and dissolution. Thus controlled chemical degradation is required to disintegrate and solubilise the size film without damaging the cellulosic fibre. Enzymatic, oxidative and hydrolytic degradation methods can be used. 

Cellulose or wool residues in blends with polyester fibres Dissolution of the polyester fibre is carried out in a 50% solution of trichloroacetic acid in chloroform at room temperature for 15 min (liquor ratio 1 50). The sample is then rinsed twice with about 100 ml of a 15% solution of trichloroacetic acid in chloroform. The sample is subsequently rinsed with cold chloroform until, in the case of dyed samples, the solvent is no longer dyed. As a rule about 200 ml of chloroform are required. A final rinse is made with hot water. 

SOY 09] Soykeabkaew N., Nishino T., Peijs T., All-cellulose composites of regenerated cellulose fibres by surface selective dissolution . Composites A, vol. 40, pp. 321-328, 2009. 

In the amorphous cellulose sample the chemical shift of the C4 carbon is as low as 81-6 ppm and very close to the corresponding value of the low molecular weight cellulose in DMSO solution (see Table 4). This sample was prepared by dissolution of Whatman cellulose powder CF-1 in DMSO-paraformaldehyde followed by precipitation in ethanol. Therefore, the molecular chains of this sample must be fully disordered in comparison with those of the regenerated cellulose fibres and native cellulose. The more detailed structure of the noncrystalline components of different cellulose samples will be discussed elsewhere. ... 

Swatloski et al. showed previously that [C4mim]Cl is an excellent solvent in which to solubilise cellulose [47], and recently, it has been demonstrated that ionic liquids based on ethanoate and formate anions are also efficient solvents for this purpose [48, 49]. In particular, [C2mim][02CCH3] has been shown to be a potential solvent for a new commercial process for the preparation of cellulose fibres. Neutron diffraction and complementary MD simulations have been performed on both the [Cimim]Cl and [C2mim][02CCH3]/glucose system in order to increase our understanding of ionic liquid properties relevant to the biomass dissolution... 

It is the direct dissolution of the cellulose in an organic solvent without the formation of an intermediate compound that genetically differentiates lyocell from other cellulosic fibres such as viscose. 

More recently, cellulose fibres have been investigated as potential precursors for self-reinforced polymer composites, as well summarised in a review by Eichhom et al. [191]. Numerous authors have reported the use of cellulose fibres from various sources, including wood pulp fibres [192, 193], filter and Kraft paper [194-197], microcrystalline cellulose fibres [198-202], sisal fibres [203, 204], ramie fibres [205], cotton fibres [206], regenerated cellulose (Lyocell) and cellulose fibres spun from an anisotropic phosphoric acid solution (Bocell) [207], and fibres from bacterial cellulose [208]. Two main technologies have been presented to produce these so-called self-reinforced cellulose or all-cellulose composites, and these are, first, the conventional impregnation of cellulose matrix into cellulose fibres and, second, a novel selective dissolution method in which the cellulose fibre surfaces are partially dissolved to form a matrix phase that bonds fibres together. 

Unlike the thermal processing methods for the consolidation of polymers such as PP, which may use selective fibre surface melting, selective dissolution of cellulose fibres partially dissolves the surface layer of cellulose fibres to form a matrix phase of the all-cellulose composites. Analogous to thermal processing methods described earlier, only the surface of the fibre is intended to be affected by the solvent processing and the core of the fibres maintain their structure in order to provide mechanical reinforcement for the final composite. If performed in a controlled manner, this selective surface dissolution concept can result in a continuous... 

Dissolution of the cellulose in cuprammonium solution followed by acid coagulation of extruded fibre ( cuprammonium rayon —no longer of commercial importance). In this case the acid converts the cuprammonium complex back into cellulose. 

TXRF has also been used for the characterisation of single, colourless textile fibres (polyesters, modified cellulose and wool), yielding a fingerprint trace-element pattern, suitable for forensic purposes [276,277], Sample preparation involved dissolution/predigestion in HN03 and matrix removal (O2 cold plasma). 

These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

It is worth noting that the mercerisation process, bom in the 19th century, produces a cellulose II structure too, but without dissolution of the fibres and therefore with no reshaping. Cotton fibres are soaked in a concentrated (19%) NaOH solution then washed. Mercerised cotton shows a softer touch and more brilliance than natural cotton. 

Cellulose acetates are by far the most important organic esters. The diacetate has DS = 2.4 and is fabricated either in filament form for fibres or in powder form to melt. Diacetate filaments are obtained by dissolution in acetone, extrusion through a spin and then evaporation of the solvent. The obtained fibres are used in textiles (called simply acetate ) and in cigarette filters (tow). The triacetate (DS = 2.9) finds application in brilliant textiles easy to dye. 

The presence of the complex carbohydrates provides the environment with a viscous hydrogel structure water removal gradually yields a mass of bacteria bound by undigested carbohydrates (celluloses) to form the stool. The presence of a hydrogel softens the mass and also provides water for dissolution. Carbon dioxide release is also a fermentation product, and if the redox potential is sufficiently low, bacteria can produce methane and hydrogen that can be detected in the breath particularly after the ingestion of pulses. In the upright position, the gas will rise to the transverse colon It is estimated that an adult produces approximately 2-3 L per day on 20 g fermentable fibre (most of which is eliminated in the breath). ... 

RAD Radugin, M.V., Prasov, A.N., Lebedeva, T.N., and Zakharov, A.G., Heat of dissolution of cellulose in water and water-dimethyl sulfoxide mixtures. Fibre Chem., 40, 533, 2008. 

Cellulose secondary acetate fibres are manufactured from cotton linters by steeping in glacial acetic acid and sulphuric acid-catalysed reaction with acetic anhydride. The reaction is exothermic and the final product in a maximum of 20 hours is cellulose triacetate, which is converted to secondary acetate by adding sufficient water. The hydrolysis is stopped when 1/6 of the acetate groups have been randomly changed to hydroxyl groups. The precipitated polymer flakes are dissoluted in acetone containing small amounts of water or alcohol. The chemical formula of cellulose triacetate and the diacetate fibre production chart are shown in Fig. 4.5. 

Cellulose can be regenerated into textile fibres (Cellulose II) through the dissolution and then precipitation into filaments. The viscose and the Lyocell process are the two main... 

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