Cross cotton

From the information on the right side of the C3v eharaeter table, translations of all four atoms in the z, x and y direetions transform as Ai(z) and E(x,y), respeetively, whereas rotations about the z(Rz), x(Rx), and y(Ry) axes transform as A2 and E. Henee, of the twelve motions, three translations have A and E symmetry and three rotations have A2 and E symmetry. This leaves six vibrations, of whieh two have A symmetry, none have A2 symmetry, and two (pairs) have E symmetry. We eould obtain symmetry-adapted vibrational and rotational bases by allowing symmetry projeetion operators of the irredueible representation symmetries to operate on various elementary eartesian (x,y,z) atomie displaeement veetors. Both Cotton and Wilson, Deeius and Cross show in detail how this is aeeomplished. 

Cross-linking cotton Cross-linking systems Cross ozomdes Cross-section shapes Crotarbital [1952-67-6]... 

Polyester blends Polyester carbonates Polyester containers Polyester-cotton blends Polyester, cross-linked Polyester diols... 

Tire Ya.rns, A method to iacrease the strength of viscose yam from the 0.2 N /tex (2.2 gf/den) standard to levels needed ia tires was first patented by Courtaulds ia 1935 (18). By raising the ziac concentration ia the spia bath to 4% the thread could be stretched more by immersing it ia a hot dilute acid bath duting extension. Filament strengths iacreased to about 0.3 N/tex (3.3 gf/den), and the cross section became rounder, with a thicker skin than regular viscose. Pairs of these yams were capable of beiag twisted iato tire cords which outperformed traditional cotton cords. 

Miscellaneous. Flame-resistant cross-linked polyethylene can be made with a number of fluoroborates and antimony oxide. This self-extinguishing material may contain the fluoroborates of NH, Na", K", Ca ", Mg ", Sr ", or Ba " in amounts of 4—20% (76). Magnesium fluoroborate cataly2es the epoxy treatment of cotton fabrics for permanent-press finishes (77) (see Textiles). 

The multiplicity of nylon blends, processing systems, and uses requires a large variety of staple types. Tex per filament may be 0.1—2 (1—20 den), the cross section may be round or modified, the luster may be bright or dull, crimp may be present or absent, and the fiber may be heat-set or not, depending on its use. The staple length is about 4 cm for cotton system processing, 5—7 cm for the woolen system, 8—10 cm for the worsted system, and about 18—20 cm for carpet staple. 

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 wrinkle recovery angle provides a measure of the degree of chemical modification. This is calculated by blending a small sample and measuring the recovery to the flat configuration (180°). Whereas the untreated cotton recovers approximately 90°, the cross-linked cotton sample recovers 120—140°. If this is measured on dry fabric, it is termed conditional wrinkle recovery angle if on wet fabric, it is termed wet wrinkle recovery. At one point, wet wrinkle recovery was important, particularly in Europe. In the United States, the widespread use of clothes dryers has made conditional wrinkle recovery important. 

There is no question that the bane of textile chemists in the area of cross-linking for smooth-dry performance is the loss of abrasion resistance. This has been a continuing problem when durable press is pushed to high levels of performance. Numerous approaches to this problem have been explored (32). However, the simplest solution has been to blend cotton with synthetic fibers. A 50—50 cotton—polyester fabric can have exceUent smooth-dry performance and yet be able to endure numerous launderings. 

The ease of hydrolysis of a DMEU-treated fabric has been used to produce bicolored cotton fabrics. This was accompHshed by applying a thickened DMEU solution in a print configuration to the pile of fabric, curing the resin, and dyeing the fabric. The DMEU-treated areas resisted dyeing because of the cross-links. Subsequendy, the DMEU-crosslinks were removed via an acid hydrolysis and the entire fabric was overdyed to achieve the desired bicolored effect (69). 

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