A method has been found to prepare bulk samples of wool fibers in such a way that reproducible compression tests may be performed upon them. An evaluation of the bulk compression characteristics of 29 widely different wool samples shows that compressive load, rather than resilience, serves to bring out differences among them. This finding suggests that quality differences among wools, as determined by handling, are related to differences in the wools' resistance to compression rather than to differences in compressional resilience. For these 29 wool samples there is an inverse relationship between compressive load and mean fiber diameter. Although this finding is in agreement with similar results re ported for cotton fibers, it conflicts with the predictions from a theoretical model that has been proposed to explain the compressional behavior of wool. The theoretical model, which was based on a consideration of bending forces only during compression, has been claimed to fit results found for 310 samples of Merino wool. There is, therefore, an implication either that there is a different dependency of resistance to compression on fiber diameter within a wool breed as compared to that among different breeds or that the proposed theory is inadequate. When the compressing piston size is varied at a constant sample size for a Targhee 60's wool card sliver, it is found that the effective volume of fibers being compressed is greater than the volume of fibers beneath the piston, probably because of fiber-to-fiber entanglements. The experimental results indicate that a constant area should be added to the compressing piston areas in order to achieve a constant compressive stress. This area increment is independent of sample diameter, providing the sample diameter is suf ficiently greater than that of the compressing piston, and this area increment decreases with increasing degree of compression.
TEXTILE RESEARCH JOt'RNAI. I)~ar .S'ir:.-Some new results have been obtained on the thermal behavior of protein fibers hy means of dif-. ferentia) thermal analysis ( DTA ) . I)T.A involves the measurement of the thermally cletectable transitions or reactions that occur as a substance is heated at a constant rate through the temperature range of interest and the general technique has been wel) described in the literature r 5. 71. The apllication of this technique to textile fibers was the subject of a recent communication to this jourrTal ( fi ~ .Fiber samples of about 150 mg. were heated at a rate of 10° C./min. from room temperature to 550° C. Calcined ahiniintini oxide was employed as the thermally stable referepce material. The apparatus and specific techniques used are fully discussed in a paper to be submitted for puhlication 4n this journal. The properties of the keratin fibers examined are described Nt detail elsewhere ( 2 J . In Figure 1 the I)TA curvts obtained under a nitrogen atmosphere are shown for a series of protein fihers. The major reactions are indicated to be endothermic for all the fibers and, of course, nonoxidativc in nature. The keratin fibers as a group yield similar curves and are distinguished from the curve for silk in the temperature range in which the second major reaction appears to occur (326° C. for silk ) > and in the shape and depth of the peaks. It is suggested that this difference may be due to the melting or disordering of a-and ,a-keratin. Silk is krtowrn to consist of poiypeptide chains in a pre-dominantly extended configuration with intermolecular hydrogen bonding and having a general resernblance to (3-keratin. Keratin fillers in their natural state consist essentially of a-keratin. although some work ( 1, 3j has indicated that small amounts of ~keratin may he present. All the curves show an initial reaction whirh is endothermic and show peak temperatures ranging from 108° C. for silk to 116°C. for human hair. In each case, this reaction represents the loss of sorbed water. As the curves return to the base line, a small shoulder appears alx>ut 1 fi0° C. which is evidence for a second endothermic reaction of a minor nature. W'att et al.181 J have recently shown that a small amount of ahsorbed water in wool fiber is strongly held at hydrophillic sites in the filer and is removed only at relatively high temperatures (up to 150' C. in T'Ufil0l. Thus this second and smaller endothermic reaction may represent the removal of this tightly held water. &dquo; ' In the keratin fibers, the next major reaction is also endothermic and begins around 210° C. A single peak at 251 C. is observed for human hair, whereas in the case of IWS Wool C (an Australian Merino wool) and kid mohair the shape of the endotherms suggests that at least two sequential reactions have occurred. No major reaction appears to occur in the temperature range of 210&dquo;-275° C. in silk. Silk shows an important endothermic reaction starting gradually around 275° C. and accelerating rapidly at 285° C. to reach ...
The acid-catalyzed reaction of formaldehyde with cellulose has been studied under conditions comparable to those of formaldehyde treatments carried out in textile finishing plants. Cotton, Fortisan, and viscose rayon fabrics were treated at different padbath pH values (2.0, 2.2, and 2.4) and formaldehyde concentrations, at different temperatures (110°, 120°, and 130° C.), and for different periods of time.At the higher pH values of 2.2 and 2.4, the cross-linking reaction seems to take place primarily in the amorphous regions of the fibers; at the lowest pH, a very rapid reaction occurs in the amorphous regions, accompanied and followed by diffusion of formaldehyde into the crystalline regions which controls the observed reaction rate. Both the rate and extent of reaction appear to depend on the state of internal order of the cellulosic material, being least for cotton, the material of highest crystallinity. Fortisan and viscose rayon have about the same degree of crystallinity, but the reaction with Fortisan is more rapid which causes the extent of reaction at later times to be greater than that observed for viscose rayon. Two possible explanations are either that the higher orientation of Fortisan facilitates the cross-linking process or that recrystallization occurs during acid hydrolysis, and viscose rayon has a relatively higher rate of recrystallization. The results of X-ray diffraction studies carried out on the variously treated cellulosic fibers are consistent with the proposed reaction mechanisms.
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