The Nature and Function of the Resin in the Chlorine /Resin Shrinkproofing Treatment of Wool Tops

Abstract

The only resin which has been found fully satisfactory for shrinkproofing wool tops by the chlorine/resin process on the industrial scale is a polyamide-epichlorohydrin polymer. A study has been made of the nature and function of this resin, on the wool and in isolation from it, to determine why it is peculiarly suitable. It is accepted as a premise for which there is considerable evidence that most of the shrinkproofing effect is produced by the prechlorination treatment, which softens the scales on the wool fibers, and that chlorination usually leaves some fibers undertreated, with scales hard enough to cause fiber migration and felting. It is shown that the role of the resin is to form a complete sheath over each fiber, burying or "masking" these undertreated scales. This requires an effective mean thickness which depends on the level of chlorination, but is usually greater than 0.5 μm, corresponding to about 10% of resin on the weight of wool. So high an uptake would, however, give too harsh a handle in the dry state. The peculiar advantage of the resin which has been used appears to be its capacity to swell considerably in water, to nearly 5 times its air-dry volume, while remaining solid and adhering to the wool. A 2% uptake of resin solids, measured in the air-dry state, is therefore equivalent approxi mately to the required 10% of resin gel in water. It has sometimes been found that the effectiveness of this treatment is reduced if processing oils are present. It is shown that such "oils," which contain considerable quantities of surfactants, dehydrate both the resin and the chlori nated cuticle cells. This hardens the scales and sharpens their contour while simultaneously thinning the masking films of resin and reducing their mutual adhesiveness; all these changes promote felting. Some suggestions are made as to the nature of the forces which hold the resin on the wool fibers.