Durable press, cellulose

The most important cotton etherification treatments are those that produce wrinkle resistance in fabrics [331,333,334]. The aldehydes, formaldehydes, and glyoxals, react with the OH groups of two cellulose chains as well as those of one chain. Reaction in which a bond is established between the two cellulose molecules is called cross-linking and is the basis for profound changes in the cotton fiber. Cross-linking produces resiliency in the fiber to give the needed dimensional stabilization, wrinkle resistance, and crease retention for modern durable-press cellulosic fabrics. Cross-links based on etherification reactions traditionally have been used because of their durability to repeated laundering and wear. 

Two different chemical approaches have been used commercially to produce non-swelfing or durable press cellulose fabrics. The original approach is the incorporation of a polymerised finish in the pores of the fibres, so that water molecules cannot easily penetrate the fibre. The newer approach is the reaction of multifunctional crosslinking agents with the hydroxyl groups of adjacent cellulose molecules that hinder the swelfing of the cellulose fibre. 

Figure 1 shows the repeating glucose units of cellulose with the carbons labeled, including those with the reactive 2, 3, and 6 hydroxyls. Ihe most important reactions of cotton cellulose commercially are esterification and etherification, with the products of etherification ranking first. It is generally agreed today among textile scientists that durable press cellulosic textiles ow their smooth-drying and resilient properties to the reactivity of formaldehyde and its amide derivatives with cellulose to produce crosslinks between adjacent cellulose chains (Figure 2). Hovever, the theory that crosslinking was responsible for increased resiliency developed only after the treatmaits were in wide use.

Essentially nonionic soil-release agents comprise polyesters, polyamides, polyurethanes, polyepoxides and polyacetals. These have been used mainly on polyester and polyester/ cellulosic fabrics, either crosslinked to effect insolubilisation (if necessary) or by surface adsorption at relatively low temperature. Polyester soil-release finishes have been most important, particularly for polyester fibres and their blends with cellulosic fibres. These finishes, however, have much lower relative molecular mass (1000 to 100 000) than polyester fibres and hence contain a greater proportion of hydrophilic hydroxy groups. They have been particularly useful for application in laundering processes. These essentially nonionic polymers may be given anionic character by copolymerising with, for example, the carboxylated polymers mentioned earlier these hybrid types are generally applied with durable press finishes. 

Substituted triazinyl derivatives of DAS are usually chosen for pad-dry-bake application to cotton in conjunction with an easy-care or durable-press finish. In these mildly acidic conditions (pH about 4) the FBA must show appreciable resistance towards the catalyst (usually magnesium chloride) necessary to cure the resin. The less substantive products in the upper half of Table 11.1 are important in this respect, as are compounds of type 11.9 where R = OCH3 or CH3NCH2CH2OH. It is likely that the hydroxyethylamino groups present in many of these compounds participate in condensation reactions with N-methylol groups in the cellulose-reactant resin. The performance of an FBA applied in conjunction with a resin finish can be modified and improved by careful formulation of the pad liquor but this lies beyond the scope of the present chapter. Alternatively, FBA and resin can be applied in two separate steps most DAST-type brighteners would be suitable if applied in this way. 

Two factors emeiged to turn the focus of durable press the discovery that incorporation of a level of nylon or polyester in the fabric can substantially increase the garments abrasion resistance, and the realization that the marketplace preferred cotton—polyester blends in delayed cure operations, even though 85% cotton—15% nylon fabric yields a suitable product. The 50% cotton—50% polyester fabric seemed particulady appropriate because it contained sufficient cellulosic to benefit from a chemical finish and sufficient synthetic to provide strength and abrasion resistance. 

In addition to fiber and fabric influences on abrasion resistance, chemical finishes must also be considered. Many thermosetting resins used to impart durable press characteristics to cellulosic fabrics reduce their resistance to abrasion as a result of fiber embrittlement. 

The high-temperature cross-linking of cotton cellulose by polycarboxylic acids, having three to four carboxyls per molecule, has been extensively investigated as a method of formaldehyde-free durable-press finishing. In 1963, Gagliardi and Shippee [383] showed... 

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). 

Easy-care and durable press finishes of cellulosics... 

Easy-care and durable press finishes of cellulosics 59 Table 5.4 Effects of the ether modification of DMDHEU °... 

Other chemical crosslinking agents that have been nsed to provide durable press properties to cellulose include dimethylol ethylene or propylene urea, diglyoxal urea, triazons, urons, carbamates, diepoxides and diisocyanates. However, owing to either high cost or limited technical advantages, very few are actually used commercially, sometimes as minor components of mixtures for special effects. 

In commercial use, easy-care and durable press finishes are frequently combined with other finishes to provide additional properties such as water and oil repellency, flame retardancy, soil release and the like. Often the combination of another finish with the cellulose crosslinking finish will result in a more durable effect from the first finish. Combination with pigment printing is very common because of similar chemistry to cellulose crosslinking agents and binders and the similar application conditions. 

Usable for anti-pilling Hand building finishes, for cellulosics easy-care Durable press finishes Cellulase finishes... 

Elastomeric finishes are often combined with easy-care and durable press finishes. The silicones reduce abrasion, increase tearing strength (Ehnendorf testing apparatus - ASTM D1424), and crease recovery. For equal crease resistance and durable press performance the amount of cellulose crosslinking agents can be markedly reduced in these combinations. ... 

When used on polyester/cellulosic fabrics in conjunction with durable press resins, the silicone emulsion polymer system ... 

---