High wet modulus

Modified Viscose Processes. The need for ever stronger yams resulted in the first important theme of modified rayon development and culminated, technically if not commercially, ia the 0.88 N/tex (10 gf/den) high wet modulus iadustrial yam process. 

Control of the regeneration conditions, together with a wide variety of modification, allows the production of a wide variety of products including high-wet modulus fibers, hollow fibers, crimped fibers, and flame-resistant fibers. While almost all rayon is produced using the... 

The viscose process has some variants depending on the quality of the cellulose and the composition of the regenerating bath, special high added value products can be obtained so-called modal-polynosic fibres, or modal-high wet modulus fibres, for instance. 

Fig. 12.8. Cross-sectional morphologies of some of the rayon fibers, (a) High wet modulus (b) regular rayon (c) crimped HWM (d) hollow (e) cuprammonium (f) trilobal. (Sources All except trilobah Turbak, A., "Rayon" in Encyclopedia of Polymer Science and Engineering, 2nd ed., Vol. 14, p. 55, copyright John Wiley Sons, Inc., New York, 1985 and used with permission of the copyright owner trilobal photo Gupta, B. S. and Hong, C.T., INJ, 7(1), 38 (1995).)...

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. 

FIGURE 10.85 Stained rayon cross section showing skin and core (a) high wet-modulus (b) regular (c) tire cord and (d) crimped. 

Property Regular Intermediate wet-modulus High wet-modulus Polynosic Moflal... 

Two fibers with exceptionally high wet-modulus were developed years ago, but the importance of this property to dimensional stability in fabrics was not recognized at the time. Surprisingly, one of the stronger rayon fibers with conditioned tenacity of 6-7 g/den (5.4-... 

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. 

Fin. 12 (coniinued). (d,e) Theoretical stress-strain plots for composite forms based on plots for crystalline C and disordered D material in (d) wet and (e) dry state, (f) Comparison of theoretical plots with experimental curves for standard rayon S and high-wet-modulus rayon H, dry D and wet W. 

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. 

In processes making regular staple fiber, reactions 5 and 6 occur practically simultaneously, but in high wet modulus processes, reaction 5 predominates in the spin bath, with reaction 6 occurring while stretching the filament in a hot water or steam bath. The carbon disulfide liberated in spinning and stretching can be recovered from the extracted air and from the spin-bath liquor. 

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