Viscose rayon final processing

It is produced from a liquid solution in a process similar to that by which viscose rayon is made. The final product consists of long fibers with the lowest density of all commonly used reinforcements. Aramid s rigidity and strength are intermediate between those of glass and carhon. 

The viscosity of the viscose, an important processing parameter, and the final rayon properties are dependent on the average chain length or DP of the cellulose. Control of this variable is achieved by aging the alkali cellulose crumb under conditions yielding the appropriate extent of depolymerization for the type of rayon produced. 

Figure 14.37, shows a block scheme of the viscose/rayon process from the spinning stage to production of the final viscose/rayon material. In this process, two types of surfactant process additives are introduced, i.e. spin bath additives and lubricant finishing additives. 

Fibers are the basic element of nonwovens world consumption of fibers in nonwoven production is 63% polypropylene, 23% polyester, 8% viscose rayon, 2% acrylic, 1.5% polyamide and 3% other high performance fibers [8]. The data in Fig. 10.4 shows the market share of important polymers and fibers in the nonwovens market. Manufacturers of nonwoven products can make use of almost any kind of fibers. These include traditional textile fibers, as well as recently developed hi-tech fibers. Future advancements will be in bicomponent fibers, micro-fibers (split bicomponent fibers or meltblown nonwovens), nano-fibers, biodegradable fibers, super-absorbent fibers and high performance fibers. The selection of raw fibers, to a considerable degree, determines the properties of the final nonwoven products. The selection of fibers also depends on customer requirement, cost, processability, changes of properties because of web formation and consolidation. The fibers can be in the form of filament, staple fiber or even yam. 

In this chapter we will elaborate on recent advances in dissolution and derivatization of cellulose and follow up with a description of new processes that lead to regenerated cellulose fibers. Finally, we will describe viscose processes and rayon fiber properties. 

One common feature of the viscose, euprammonium, and carbamate processes is the chemically modified cellulose is regenerated into cellulose after the extrusion. Fibers made from these processes often are called rayon fibers. However, useful fibers can be produced by derivative methods without the regeneration of cellulose. Two important examples are cellulose acetate and cellulose triacetate fibers. Cellulose acetate can be obtained by aeetylation of cellulose with acetic acid and acetic anhydride with sulfuric acid as a catalyst. Cellulose triacetate, which is partly saponified to get the desired degree of substitution, is produced by a similar process. Both cellulose acetate and cellulose triacetate keep their derivative structure in final fibers. The major difference between these two fibers is that in cellulose acetate fibers, less than 92% but at least 74% of the -OH groups are acetylated, but in triacetate fibers, at least 92% of the hydroxyl groups are acetylated. 

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