Wet modulus

The wet modulus of fibers at various temperatures influences the creasing and mussiness caused by laundering. Figure 6 shows the change with temperature of the wet modulus of acetate and triacetate, and compares them with a number of other fibers (2). Acetate, triacetate, and rayon behave quite similarly, with a lower sensitivity than acryUc. 

Fig. 6. The effect of water temperature on the wet modulus of fibers. To convert N /tex to gf/den, multiply by 11.33.

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. 

The hydrophilic properties of cellulose confer moisture absorption capacity to fabrics made from blends of rayon and synthetics. This property of moisture absorption is one of the reasons why rayon is used extensively in nonwoven, disposable applications, as the cross-sectional swelling of regular rayon is about three times that for cotton. The main disadvantage of regular rayon in textiles is its low wet-modulus in the wet state, fabrics made from rayon will be weak and easy to stretch and deform. 

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. 

Several proposals have been made, all specifying a minimum wet-modulus around 0.5 g/den (0.45 cN/dtex) for 1.5-denier fiber. Human-made cellulosic fibers that meet this criterion could then legally be called Modal. 

One way to improve the hot wet modulus of acrylics is to introduce cross-links between the chains. Cross-linking is known to limit the decrease in modulus that occurs when a polymer is heated above Tg [360]. The success of attempts to do this will be covered in Section 12.6.4. 

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