Rayon fabrics Finishing

The solution (pad bath) contains one or more of the amino resias described above, a catalyst, and other additives such as a softener, a stiffening agent, or a water repeUant. The catalyst may be an ammonium or metal salt, eg, magnesium chloride or ziac nitrate. Synthetic fabrics, such as nylon or polyester, are treated with amino resias to obtaia a stiff finish. Cotton (qv) or rayon fabrics or blends with synthetic fibers are treated with amino resias to obtain shrinkage control and a durable-press finish. 

A defect of regular rayon fabric in the absence of a cross-linking finish is its solubility in alkali with consequent loss of strength and dimensional stability. These defects have been largely overcome in the high performance rayons. Mitchell and Daul (43) reported that regular textile grade rayon staple fiber accounts for 70-80% of the output of the rayon industry. 

Another category of durable hand builders are formaldehyde-containing thermosetting polymers. These products are usually supplied as dispersions or aqueous solutions of precondensates of urea or melamine with formaldehyde, for example di-methylol urea or di- to hexa-methylol melamine and their methyl ethers. The thermosetting polymers are comparatively inexpensive and provide fabrics with stiffness and resilience. However, they have a tendency to reduce abrasion resistance, yellow after exposure to heat, and release formaldehyde. Melamine-based hand builders are more highly crosslinked than urea-based products and are accordingly more durable. Butylated urea condensates are especially useful for rayon fabrics (see also Chapter 5 Easy-care and durable press finishes of cellulosics). 

Urea-formaldehyde (U/F) products are readily synthesised from water solutions of urea and formaldehyde at pH 7.5-9. The resulting iV,iV-dimethylol urea (DMU) is often modified by further reaction at pH 8-9 with methanol to the more stable and liquid dimethylether of DMU (dimethoxymethyl urea) as shown in Fig. 5.1. These reactions are equilibrium reactions with significant concentrations of the starting compounds. These equilibria are the reasons for the high content of free and easily released formaldehyde found with U/F products. Because of their high reactivity, unmodified U/F finish baths must be used within a few hours. The high stiffness and firmness of the U/F finish can be important for rayon fabrics which often are considered too limp when compared with cotton. The U/F finish gives the best elastic resilience. ... 

KAURIT KFN is recommended for the anticrease and antishrink finishing of rayon, cotton and linen fabrics and blends of these fibres with one another or with wool or synthetics. It also produces good results in the embossed, chintz, Schreiner and plisse finishing of cotton and spun rayon fabrics and in the fixation of filling agents. 

The various TEX-WETS are colloidal aqueous silica dispersions widely used in textile finishing to control yarn slippage, modify hand, and control luster. However applied, these products can be used to stabilize weave and to impart special finish effects to fabrics made of cotton, wool, synthetic fibers and filaments, and to mixtures. Treatment gives outstanding finishes on nylon and Dacron marquisettes, rayon fabrics and viscose rayon suitings. Application requires no special equipment nor curing. The dispersions are not cationic and, therefore, cannot be applied by exhaustion onto the fabric. 

McFarlane, R.A., Processing and Finishing of Rayon Fabrics, London, Courtaulds, 1948. 

The HWM staple fibers have essentially all of the best attributes of regular rayon except for a few important differences. They swell less in water, are somewhat stiffer due to higher cellulose DP (IV) and orientation, and are almost twice as strong and resist dimensional change. Fabrics made from HWM fibers can be dyed and later finished (cross-linked) by much the same techniques as those used for cotton fabrics. In 50-50 blends of polyester and HWM rayon, fabrics can be made that are virtually indistinguishable from some cotton counterparts [282]. 

One of the major advances in textile technology in recent years has been the introduction of resin finishes that impart the wrinkle- and crease-resistant properties associated with wash and wear fabrics. Ordinarily used with cotton and viscose rayon, resin finishes are currently applied to the majority of shirts, blouses, etc. The resin finishes consist of aqueous solutions of urea formaldehyde or melamine formaldehyde precondensates or of cyclic ureas such as dimethylol ethylene urea. It is thought that wrinkle resistance is imparted through the cross-linking of adjacent cellulose chains in the fiber, rather than from resin formation in or between fibers. 

Flame-Retardant Finishes on Cellulosic Substrates. The flame retarding of cotton and viscose-rayon fabrics has been the object of a large worldwide effort on phosphorus-containing finishes (217-219). The commercial cotton finishes are based on tetrakis(hydroxymethyl)phosphonium salts, usually the chloride or sulfate (220). These salts are prepared by reaction of formaldehyde with phosphine in the presence of an acid. 

The abrasion resistance of rayon is fair, and abrasion of rayon fabrics becomes noticeable after repeated usage and launderings. The rayons are resistant to pill formation. Rayon fabrics wrinkle easily and without chemical treatment show poor crease recovery and crease retention. Durable press and wash-and-wear finishes tend to cause less degradation of rayon than found with cotton. Rayon possesses excellent moisture absorbency characteristics, but the weaker rayons swell and deform somewhat in the presence of moisture. 

Considerable effort is being made (ca 1993) to develop satisfactory flame retardants for blended fabrics. It has been feasible for a number of years to produce flame-resistant blended fabrics provided that they contain about 65% or more ceUulosic fibers. It appears probable that blends of even greater synthetic fiber content can be effectively made flame resistant. An alternative approach may be to first produce flame-resistant thermoplastic fibers by altering the chemical stmcture of the polymers. These flame-resistant fibers could then be blended with cotton or rayon and the blend treated with an appropriate flame retardant for the ceUulose, thereby producing a flame-resistant fabric. Several noteworthy finishes have been reported since the early 1970s. 

KAURIT W is recommended for the anticrease and antishrink finishing of spun rayons and cotton cloth, and for the fixation of filling and stiffening agents on wool and other fibrous materials. The product imparts a woolly, full and resilient handle to spun rayons. On polyamide fabrics it produces a good stiff handle, such as is required for polyamide-rayon lace and polyamide tulle. 

KAURIT M90 is used for the antishrink and easy-care finishing of cotton fabrics and spun rayons, for permanent fixation of calender effects, for the fixation of reactive filling and stiff finishes and for the stiff finishing of synthetic textiles, e.g., collar interlinings, petticoat fabrics, and lace. The product is often used in combination with other KAURIT or PIXAPRET types. 

TEXAPRET AM is particularly economical on spun rayons, but it is also used as filling finish for cotton, wool and blended fabrics. 

ARIDRY FC Extra is a new aqueous fluorochemical finish designed to impart lasting high oil and water repellence together with dry soil resistance to all fibers including cotton, rayon, wool, nylon, acrylics, polyester and is especially recommended for upholstery fabrics, drapery, slipcovers and other woven materials where dry-soil resistance is of importance. 

CNC Finish 81 is a synthetic hand builder and weighter used to produce unique finishes on cotton, rayon and polyester blends. In addition to giving weight to the finished fabrics, CNC Finish 81 imparts a full smooth hand with little tendency to mark-off. 

CNC RIBBON FINISH CN may be applied at low temperature minimizing color changes. CNC RIBBON FINISH CN produces a continuous, transparent, non-dusting film. It will not oxidize or decompose on a fabric. CNC RIBBON FINISH CN will not dull the luster of ribbon, acetate or rayon. 

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