Some New Observations on the Effects of Mild Shrinkproofing Treatments on Wool Fibers

Abstract

When wool fibers which have been shrinkproofed by either the KMnO 4 /salt process or a dry chlorination process are examined with the optical microscope, normally, very little effect of the treatment can be seen. However, if they are straightened for the examination, a number of differences between treated and control fibers can easily be seen, especially if water is present. The principal effects are that the scales on the treated fibers, but not on the untreated, become less prominent as the fibers are straightened and that this change is much greater on the side which was the intrados of the crimp curve than on the extrados. Microscopic observation of fibers sliding on each other or over a diffraction grating also reveals effects of the treatment: the deformation of the scales of treated fibers is more plastic and less elastic than that of untreated and the sliding of the treated fibers is more heavily damped. From these and other observations, the conclusion has been drawn that these treatments degrade the protein inside the scales so that it becomes more viscous and less elastic, particularly when it is swollen by or dissolved in water. The epicuticle appears to be unbroken and still elastic.These results throw some light on the well-known disagreement between different workers about the changes produced in the coefficients of friction of wool fibers by the KMnO 4 /salt treatment.

Lipid Role in Wool Dyeing

“…This investigation provided the first unequivocal evidence that dye does, in fact, enter the wool fiber between cuticle cells, and also showed that dye diffuses along the nonkeratinous endocuticle and CMC early in the dyeing cycle. The above finding supports the view that the cuticle (Makinson, 1968), probably the highly crosslinked A-layer of the exocuticle (Hampton & Rattee, 1979;Baumann & Setiawan, 1985), is a barrier to dye penetration, in that dyes are directed to the gaps between the scales in order to reach the cortex. It appears, however, that lipids present at the intercellular junctions are also a barrier to the diffusion of dyes into the nonkeratinous regions of the CMC (Leeder et al, 1985a).…”

Transmission Electron Microscopy Studies of the Permanganate/Salt Shrinkproofing Treatment of Wool

“…After exhaustion of the KMnO,,, the manganese dioxide deposited on the wool was removed with sodium bisulphite. When applied to fabric, this procedure has been shown [7] to give a low level of resistance to felting, with a shrinkage-reduction factor of about 3.4.…”

The Role of Chlorine in Oxidative Antifelting Treatments of Wool

“…The epicuticle is not normall disrupted [8,10,13). If the increase in softening is only slight, its principal effect is to increase the friction of the fibers, reducing their mobility and so reducing their feltability to a limited extent.…”

“…If the increase in softening is considerable, it has the additional effect of reducing the difference between against-scale and with-scale friction; this reduces the tendency of the fibers to migrate continuously in one direction during washing, and it can confer a considerably higher degree of resistance to felting. The lower level of softening can be achieved simply by oxidation [10); the relation between the chemical and physical changes appears to be that scission of disulphide bonds makes the molecular chains more mobile, and increased absorption of water by the newly introduced charged groups plasticizes the protein. The higher level of softening can be achieved if the oxidizing agent is chlorine [11 J; the relation between the chemical and physical changes appears to be that the molecular fragments produced by chlorine, although of a fairly high molecular weight, are soluble in water because of their high content of sulphonic and sulphinic groups, but are mostly too large, after mild chlorination, to diffuse out through the epicuticle [8, 1 i~.…”