Polynosic rayon

Standard viscose and polynosic rayons are blended with cotton for improved physico-chemical properties of the blended fabric. The increase in tensile strength brought about by blending wool with viscose is well-known. Fabrics containing around 65% triacetate with viscose may be given durable pleats. Bulked or textured nylon is sometimes used with viscose rayon for fabrics. Table 4.17 shows... 

Interest in the manufacture of different forms of rayon has resulted in the production of regular rayon, hollow viscose, spun-dyed filaments and staple rayon, crimped rayon and surface modified fibers, high tenacity rayon and high wet modulus (polynosic) rayon fibers. In chemical composition, viscose rayon and cotton are alike they are both cellulose. 

An example of the first type is the use of low-acid, low-salt, and low-temperature spin-baths, which slow down the cellulose regeneration sufficiently to yield HWM polynosic rayon [190]. Another example is the Lilienfeld process for which the viscose, made from unaged alkali cellulose with excess carbon disulfide and only a short ripening, is spun into a cold spin-bath containing 50-85% of sulfuric acid. This is a case of stabilizing the xanthic acid. Rayon produced in this way has tenacities greater than 5 g/den. 

The polynosic rayons enjoyed a revival of fortimes in the 1990s when the new lyocell fiber produced by Courtaulds (Tencel )—a solvent spim fiber with polynosic properties— became popular in ladies apparel and denim. By 2001 however the Toyobo Tufcel plant in Japan had been closed and at the time of writing, it is likely to be transferred to China where lower labor costs would allow it to compete more effectively with lyocell (see below). 

Property Cuprammonium rayon rayon Modal Polynosic rayon rayon ... 

High-wet-modulus rayons (polynosic rayons) have been developed in recent years. These fibers are produced from high-grade cellulose starting materials, and the formation and decomposition of cellulose xanthate is carried out under the mildest of conditions to prevent degradation of the cellulose chains. 

Property Cuprammo-niu m Regular rayon Improved rayon Modal Polynosic Y-Shaped a rayon Solvent-spun b rayon... 

FIGURE 10.86 Rayon fibers showing fibrillation on treatment with nitric acid (a) high wet-modulus (b) crimped HWM and (c) polynosic. 

The fibers that were produced were given wide recognition, especially in France where the name polynosics originated. They had a unique fibrillar structure, high strength wet and dry, low elongation (8 11%), relatively low water retention, and very high wet-modulus of 1 g/den (0.9 cN/dtex). Their resistance to caustic soda was exceptional for rayon in fabrics, they had the firm, crisp hand of cotton. 

Polynosic fiber n. A high-wet-modulus rayon staple having a microfibular structure of fibers. The molecular chain length of the cellulose forming the fiber is about twice as long as in conventional rayon. 

Figure 7.28 Melting DSC curve.s for water trapped in various kinds of cellulose [291. Water content (grams of water/gram of sample) = 1.0 g g 1, Kapok 2, linen 3, wood cellulose 4, jute 5, rayon 6, polynosic 7, cotton...

Regenerated fiber viscose, polynosic, cuprammonuium, acetate rayon, Tencel... 

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