Fiber mercerization

Use In the manufacture of paper, vulcanized fiber, mercerized cotton, viscose rayon. 

II allomorph is known by the term regenerated cellulose. Regeneration involves either preparing a solution of cellulose in an appropriate solvent or of an intermediate derivative followed by coagulation and recrystallization. This process is used to produce rayon fibers. Mercerization involves intracrystalline swelling of cellulose in concentrated aqueous sodium hydroxide (NaOH), followed by washing and recrystallization. This process is used to improve the properties of natural yams and fabrics. The transition from cellulose I to cellulose II is not reversible, and fliis implies that cellulose II is a stable form as compared with the metastable cellulose I. 

Mercerization is the common method to produce high-quality fibers. Mercerization leads to fibrillation, which causes the breaking down of the composite fiber bundle into smaller fibers and... 

Celluloses can be converted to other useful products by reorientation of their fiber structure. Paper, parchment paper, vulcan fiber, mercerized cotton, and hydrocelluloses belong in this class. 

Chedin J. and Marsaudon A. 1954. Progress in the understanding of liquid reaction mediums, and interpretation of their reactions with cellulosic fibers mercerization-nitration. Chim Ind (Paris) 71 55 8. 

Scheme 15.1 shows the mercerization of C. indica fibers. Mercerization and other surface treatments have also been carried out to alter the properties of different fibers [20]. Scheme 15.2 shows the schematic representation of different surface treatments... 

Mercerization is the most common method to produce high-quality fibers (Ray et al. 2001). Scheme 1 shows the probable mechanism of mercerization of cellulose fibers. Mercerization leads to fibrillation, which causes breaking down of the composite fiber bundle into smaller fibers. Mercerization reduces fiber diameter, which leads to the development of a rough surface topography, resulting in better fiber-matrix interface adhesion and improved mechanical properties (Joseph et al. 2000). Moreover, mereerization increases the number of possible reactive sites and allows better fiber wetting. 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

The largest use of zinc chloride in the United States is in wood preservation, fluxes, and batteries (see Batteries). Zinc chloride solution dissolves vegetable fiber and is widely used in mercerizing cotton (qv), swelling fibers, as a mordant in dyeing, parchmentizing paper, etc (see Fibers, vegetable ... 

Mercerized cellulose fibers have improved luster and do not shrink further. One of the main reasons for mercerizing textiles is to improve their receptivity to dyes. This improvement may result more from the dismption of the crystalline regions rather than the partial conversion to a new crystal stmcture. A good example of the fundamental importance of the particular crystal form is the difference in rate of digestion by bacteria. Bacteria from cattle mmen rapidly digest Cellulose I but degrade Cellulose II very slowly (69). Thus aHomorphic form can be an important factor in biochemical reactions of cellulose as well as in some conventional chemical reactions. 

An older method of cellulose fiber modification is mercerization [22,33-36], which has been widely used on cotton textiles. Mercerization is an alkali treatment of cellulose fibers. It depends on the type and concentration of the alkalic solution, its temperature, time of treatment, tension of the material, and the additives used [33,36]. At present there is a tendency to use mercerization for natural fibers as well. Optimal conditions of mercerization ensure the improvement of the tensile properties [33-35,37] and absorption characteristics [33-35], which are important in the composing process. 

Analog-to-glass fibers silanes are used as coupling agents for natural fiber polymer composites. For example, the treatment of wood fibers with product A-175 improves wood dimensional stability [53]. In contrast, a decrease of mechanical properties was observed for coir-UP composites after a fiber modification with di-chloromethylvinyl silane [54]. The treatment of mercer-... 

Those containing less than 7.5% N show a fiber character and give no X-ray diffraction indicating nitration, but only the pattern of mercerized cellulose... 

Viscose Also known as the Cross-Bevan-Beadle process. A process for making regenerated cellulose fibers. The product has been known by the generic name rayon since 1924. Cellulose, from cotton or wood, is first reacted with sodium hydroxide ( mercerization), yielding alkali cellulose. This is dissolved in carbon disulfide, yielding cellulose xanthate, which is dissolved in sodium hydroxide solution. Injection of this solution (known as viscose... 

Sisson has traced the evolution of current concepts of the crystalline part of cellulose structures. The fiber diagram obtained by X-ray diffraction is now known to be produced by a series of elementary crystals, called crystallites, which have a definite arrangement with respect to the fiber axis. It is also known that the crystallites in regenerated cellulose may be oriented to varying degrees with respect to the fiber axis and that the crystallites in regenerated cellulose and mercerized cotton differ from those in native fibers. These hydrate type crystallites appear to be more reactive chemically than the native type. 

Acetylation rates have also been studied by Centola37 who treated natural and mercerized ramie fibers for varying times with acetic anhydride and sodium acetate and examined the reaction products chemically and by X-ray diffraction. The reagent was considered to penetrate into the interior of fibers. A heterogeneous micellar reaction was believed to occur that converted a semi-permeable elastic membrane around the micelles into the triacetate. The rate of acetylation of mercerized ramie was observed to be faster than that of unmercerized fiber. Centola concluded that about 40 % of the cellulose in native ramie is amorphous and acetylates rapidly. 

Mercerization apparently causes an appreciable increase in the amount of accessible cellulose in cotton while unsubstituted rayons appear to contain a greater proportion of intercrystalline cellulose than either type of cotton. The dye affinities and moisture-regain capacities of these fibers generally seem to be in the order of increasing accessibilities. 

Purification of the reboiled caustic soda is important to remove sizes (raw-mercerization), dyes (mercerization of dyed materials), fibers, and impurities released from the fibers. Important techniques are filtration, centrifugation, flotation processes, and oxidative processes [29-31]. The application of membrane processes for reconcentration is limited to low concentrations of NaOH because of the insufficient chemical stability of the membranes. 

The swelling of native, and mercerized, cellulose fibers in ethyl-enediamine (EDA), with subsequent washing in methanol, changes the cellulose I and II lattices to cellulose II] and III, respectively. The presence of EDA, in excess of that which is necessary for the cellulose-EDA complex to form, is essential for the conversion to occur. Treatment with boiling water or hydrochloric acid converts the III lattices into the respective, parent types. Washing in alkali converts both forms into cellulose II. 

Strong caustic solutions penetrate the crystal lattice of alpha cellulose and produce an alkoxide called alkali, or soda, cellulose. Mercerized cotton is produced by aqueous extraction of the sodium hydroxide from alkali cellulose fibers. Cellulose ethers and cellulose xanthate are produced by reactions of alkyl halides or carbon disulfide, respectively, with the alkali cellulose. 

Cotton treated in this way is almost pure cellulose, and su Is in greal demand by those industries using cellulose. The pure cellulose of the fiber may be dissolved and then precipitated in sheets, giving the familiar thin transparent cellophane. Or the dissolved cellulose may be pressed through fine holes and solidified, giving rayon. If treated wilh concentrated causlic soda, cotton fibers lake on a high degree of luslcr. The product of this process is called mercerized collon, after John Mercer, its discoverer. 

Hot dilute or cold concentrated acids disintegrate the fiber, similar u> cotton. Strong alkaline solutions cause swelling and reduce strength. Can be mercerized. 

As far as we know, apart from a preliminary report about mercerization of cotton fibers (3) and a recent paper about chemically etched PETP filaments (4), high modulus aramide fibers and carbon fibers are practically the only systems with detailed (recently) published work on electron diffraction and dark field of ultrathin sections of textile or paratextile fibers (5, 6,... 

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