Wool shrink resistance

In the stepwise synthesis of the unsymmetrical complex dye 13 [ 70236-60-1] [10], the azo dye made from diazotized l-amino-2-hydroxy-5-nitrobenzene and 1-phenyl-3-methyl-5-pyrazolone and the 1 1 chromium complex obtained from 6-nitro-l-diazo-2-hydroxynaphthalene-4-sulfonic acid and 2-naphthol are heated together at 80 °C for 5 h. The adduct is salted out with NaCl. A black powder is obtained that dyes wool and leather in dark brown shades. The resulting colors are fast, particularly on shrink-resistant wool. 

Guise B and Jones F W, Shrink-resisting wool with silicones . Textile Chemist Colorist, 1977, 9(3), 65-69. 

Textile Finishing. Polyethyleneimine-A/-methylolurea derivatives improve the crease and wear resistance of cotton (429,430). The adhesion between individual wool fibers is improved by pretreatment with amines, which leads to improved shrink resistance (431). An antimicrobial finish can be appHed to cotton by using a combination of PEI and ureas to bind zinc pyrithione to the fabric (432). After wool has been provided with a flameproof finish using fluorozirconate or fluorotitanate, the wool can be neutralized with PEI (433). Conventional neutralizing agents caimot be used for this purpose since they impair the flameproof characteristics of the impregnated fabric. 

Some combing plants also produce shrink-resistant treated wool-top. The current process incorporates chlorination, and the appHcation of a shrinkproofing polymer. Chlorination is likely to be replaced soon by mote environmentally friendly treatments. 

The principal oxidi2ing agent used in degradative shrink-resist treatments is chlorine. Free chlorine reacts very rapidly with wool hence it is difficult... 

Fig. 8. Electron micrograph of Merino wool fibers in a fabric that have been treated with a typical shrink-resistance polymer, showing fiber—fiber bond...

To produce easy care wool—polyester blend garments, heat setting of the polyester component will impart set stability to repeated machine washing. A minimum of 20—30% polyester is needed for adequate stability. A fabric shrink-resist treatment such with Synthappret BAP may be necessary to give the required shrink-resistance for easy cate performance. If the polyester content is increased, particularly above 50%, and a suitable fabric constmction is used, heat setting alone will give easy care performance. 

It is more difficult to produce pure wool easy care garments. The problem is to obtain adequate durability of the setting rather than obtaining shrink-resistance, because some wool setting processes are not stable to machine washing. As of ca 1997, the best approach is to combine the Synthappret BAP fabric shrink-resist process with Siroset garment setting. 

Shrink-resistance processes compatible with Zirpro-treated wool have also been developed (166). 

Enzymes can be used to modify the surface of wool fibres in order to improve lustre, softness, smoothness or warmth of the fabric. Since such processes involve attack on the cuticular scales of the fibre, there is clearly a resemblance to shrink-resist treatments and similar methods are used [116] ... 

Enzymes have been proposed as a means of subtractive shrink-resist treatment. Their use has been discussed already in section 10.4-2. There are difficulties, however, in the commercially successful application of enzymes to wool at present. 

High substantivity for wool. This is clearly linked with the foregoing requirement. These two factors are particularly important when application takes place after an AOX-free oxidative stage, since such treatments generally impart lower initial shrink resistance than chlorine-based subtractive treatments. Indeed, these two requirements may need to be fulfilled so effectively that the oxidative stage before polymer treatment can be omitted. 

No shrink-resist polymer developed so far meets all the above requirements [301]. There is clearly some similarity with easy-care finishing of cotton. Although effective crosslinking agents are readily available for application to cotton, the morphological complexity of the wool fibre is such that an equally effective polymer has yet to be identified for wool treatment [304]. 

Polysiloxanes as shrink-resist finishes have been developed from their traditional uses as softeners and water repellents as such their chemistry is discussed in section 10.10.3. This was a natural trend as many shrink-resist finishes tend to impart a harsh handle to wool. 

Table 10.33 Comparison of typical shrink-resist polymers of the non-AOX types for application to wool [301]...

Polyquaternary compound Shrink-resist effect after pre-oxidation Exceptional improvement in fastness All processing stages suitable Improves shrink-resist effect of polyether and polysiloxane types No improvement in handle Shrink-resist effect weaker than with other types Odour possible on chlorinated wool... 

Mention has already been made of the effectiveness of corona or plasma treatment in increasing the influence of subsequent or concurrent polymer treatment. As examples of polymers used in this way, mention can be made of reactive cationic polysiloxane [294] and polymerisation on the fibre of tetrafluoroethylene or hexafluoropropylene [299]. Water repellency was also improved by the fluorinated polymers. Tetrafluoroethylene gave superior shrink resistance this polymer covered the scale edges of the wool, whereas this did not occur with poly(hexafluoropropylene). 

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