Wool, additives Wetting

In addition to the restrictions on their mobiHty caused by steric and polar interactions between chemical groups, the protein molecules in wool fibers are covalentiy cross-linked by disulfide bonds. Permanent setting only occurs if these disulfide bonds are also rearranged to be in equiHbrium with the new shape of the fiber. Disulfide bond rearrangement occurs only at high temperature (>70° C) in wet wool and at even higher temperatures (above 100°C) in... 

In addition to the natural protein fibres wool and silk, fibres have been produced commercially from other proteins. These materials were introduced as wool substitutes but today have little or no significance. Mention may, however, be made of ArdiP products from the groundnut protein and marketed for some years after World War II by ICI. Compared with wool it had inferior wet and dry strength and abrasion resistance. The inclusion of up to 20% ArdiP into wool, however, yielded a product with negligible loss in wearing properties. 

An additional major transition which is observed in DSC scans of stratum comeum is a doublet endotherm which peaks at 194 °C and 210°C in dry samples and at 120°-130°C in wet samples (Figure 14). These transitions are also characteristic of the more extensively investigated keratin-containing wool (49, 65). Polyamides such as the various nylons also show melting endotherms above 200 °C (63). 

As indicated earlier, wet friction for human hair is higher than dry friction (see Table 8-18). In addition, both static and kinetic friction and the differential friction effect increase with increasing relative humidity. These same phenomena have been observed for wool fiber [126,127]. 

Just as with natural wool, casein wool is sensitive to acids, alkalis, and heat, but possesses less wet strength. In addition, and unlike natural wool, casein wool deforms plastically. 

Another common cause of a metal surface remaining wet is contact with absorbent materials, particularly insulants such as rock-wool, and this again can cause serious attack when seawater or chloride-contaminated water becomes entrained. In addition, the absorbent material itself can be (or may become) corrosive, as in the case of wood. Examples of trouble that can occur from this cause are wooden decks or fenders laid over steel, certain aluminium alloy frames in contact with wooden hulls, and zinc or cadmium-coated fasteners in wooden hulls. The whole subject of the corrosion of metals by wood receives detailed treatment in Section 18.10. 

The farm animals that are most likely to suffer from cold stress are newborn lambs, calves and pigs. They are small and tend to have poor insulation because of low levels of subcutaneous fat or a thin coat of hair or wool. In addition, they are wet when born. If the newborn animal also fails to obtain sufficient milk from its mother, then its heat increment of feeding may be low. Newborn animals have a special type... 

Polyacrylonitrile (PAN) is produced by the additional polymerization of acrylonitrile always, the second and the third monomers are used for the modihcation of dyeability and spinnability. They can then be spun into fibers by dry or wet spinning methods, such as how Orion with a distinctive dumbbell cross section is spun by dry process produced by DuPont, and Acrilan had circular cross section and is spun by the wet extrusion technique produced by Monsanto. PAN fiber can also get the crimp structure like wool by using the bicomponent spinning process in fiber preparation. Properties of PAN fibers are listed in Table 2.27. 

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