Pleats in a worsted fabric which were fast to relaxation in hot water were readily destroyed by light hand washing. This has been shown to be due to small movements of the fibers, of the order of 0.5-1.0 mm. These movements are the initial stage of felting. They destroy the pleats by blurring the position of the region of maximum set and by imposing temporary opposing sets on the fibers. The shape of the fibers has been studied, and their radius of curvature and two other parameters have been meas ured. Fibers from unpleated regions of the fabric undergo similar movements and deforma tions on washing, but their overall shape is unchanged, since it is determined by the geometry of the fabric.
Examination by transmission electron microscopy of fibers drawn from two card slivers commercially treated by the chlorine-Hercosett® process showed the Hercosett film to be continuous over each fiber. One sliver had passed the Superwash test; almost all of the cuticular scales were flattened or sloping. Most of the fibers retained no steep scales, and none retained more than 20%. Previous work indicates that the modified scales would be much softer in water than unmodified scales. The Hercosett film on these fibers was at least 0.1 μm thick everywhere. The other sliver had failed the Superwash test, half the fibers resembled those in the first sliver, but among the other half a high proportion of the scales (from 30- 70% on different fibers) remained steep (and, correspondingly, relatively hard). On half of these the film thickness was 0. 1 μm or greater; on the other half it was less than 0.05 μm either all over or on the remaining steep scale faces. The character of these differences is such as to explain the failure of the process in the case of the second sliver. The difference in the scale shape indicates that the failure resulted from non-uniformity of chlorination. The resin considerably pene trated the cuticle.
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.
Two types of fabric, a tightly constructed worsted and a woolen of more open con struction, have been milled in laboratory stocks. Curves of (i) shrinkage in both warp and weft directions, as a function of time, and (ii) the mean displacement d of those fiber portions which have moved, also as a function of time, have been determined for each fabric. In the case of the worsted, the latter curve is linear for the first 5 hr of milling, although the former shows acceleration of the rate of shrinkage at about 2 1/2 hr. This indicates that fiber displacement is the primary result of milling and that shrinkage is a secondary result. From these curves the curve of linear shrinkage against d has been determined for each fabric. For the worsted this curve, after d has been corrected for shrinkage, consists of two linear regions. Their intersection marks a change in the mechanism of felting, which is also revealed by the appearance of straightened lengths of fibers and subsequently by the acceleration in the shrinkage-time curve. The configuration of the fibers as milling proceeds has been studied, and in the case of the worsted fabric additional curves have been determined, relating the fraction of the total fiber length which is straightened to the duration of milling, to d, and to the linear shrinkage. The induction period, an interval at the beginning of milling during which no shrinkage occurs, is also discussed.
Following on the observation that the KMnO4/salt shrinkproofing process attacks the scales on the intrados of the crimp of wool fibers preferentially, the “static” friction of wool fibers over polished horn in aqueous media has been measured by the standard capstan method under conditions chosen to ensure that some contact is made with the intrados of the crimp. It has been found that the treatment causes a large increase in the with-scale friction and in some circumstances a decrease in the frictional difference. When the proportion of contact with the intrados of the crimp is reduced, these effects become much smaller. Both types of frictional change are the result of degradation of the material inside the scale-cells, which makes the scales, when wet, softer and less elastic than the scales of untreated fibers. Experimental conditions determine whether this softening is expressed as an increase in with-scale friction or as a decrease in the frictional difference.
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