Harris M. Burte

A New Theory of Non-Linear Viscous Elasticity

The stress-strain curve of a material is calculated on the hypothesis that when flow occurs a section of the molecular chain constituting the material changes from a configuration A to a con figuration B and thereby becomes unable to elongate again. Except for a small elastic deformation of both structures, the elongation is proportional to the fraction of the material in the B configura tion. The two components are assumed to be in solution with one another, and the rates of trans formation are then proportional to the relative abundance of the transformed species. These rates are written in the manner of the Eyring theory of reaction rates. Systems of more than two com ponents are discussed and several examples are calculated. The calculated curves show good qualitative agreement with stress-strain curves of the nylon-wool-rubber type.

A Non‐Destructive Mechanical Test for Animal Fibers

The slope of the force‐extension curve in the Hookes law region can be measured non‐destructively, for animal fibers, at three to fifteen minute intervals. The change of this Hookean slope with time is used to follow the course of the heterogeneous reaction between wool and a reagent.Data are presented on the interaction between concentrated neutral salt solutions and wool fibers. These results indicate that wo processes occur: (a) Relatively rapid hydration or dehydration of the fiber until equilibrium with the activity of water in the salt solution is attained; (b) Relatively slow absorption of salt ions by the fiber. Very concentrated salt solutions dehydrate the fiber so completely that absorption of salt ions is not possible. Swelling experiments and experiments involving other mechanical properties confirm these hypotheses. The interaction between wool fibers and aqueous solutions of large organic molecules follows a similar pattern.

Properties of Apparel Wools III. The Mechanical Behavior of Top and Roving Made on the French Worsted System

A description is given of the measurement of the tensile force-extension curves of fiber as semblies with no net twist—i.e., top and roving produced on the French worsted system. Typical force-extension curves are presented, and the effects of testing conditions on various parameters of these curves have been determined. These force-extension curves are a measure of the forces required to cause the fibers to slip over one another; they depend on such factors as fiber length, fiber diameter, fiber modulus of elasticity, interfiber coefficient of friction, and fiber crimp, and on density of fiber packing in the assembly, fiber parallelism, and weight per unit length of the assembly. The relationships between the above factors and parameters of the force-extension curve are discussed in the light of the use of these measurements to investigate processes which affect any of these factors or to characterize different fiber types. The variability of parameters of the force-extension curve is discussed. Part of the variability may be ascribed to slight differences in the performance of the machine units producing the assemblies.

The Detection of Modification in Animal Fibers II. Tensile Recovery at 65 % R. H

Methods are described for measuring parameters of the tensile recovery of animal fibers. The effects of fiber crimp on these measurements, and the interpretation of the data obtained with crimpy fibers, are discussed. Data are presented on the fiber-to-fiber variation in tensile recovery and on the effects of various chemical treatments. For wool fibers from a common source there is very little fiber-to-fiber variation in tensile recovery.

Properties of Apparel Wools: VII. The Mechanical Behavior of Roving

1. Anderson, S. L., Cox, D. R., and Hardy, L. D., J. Textile Inst. 43, T362-79 (1952). 2. Barritt, J., J. Textile Inst. 29, P47-59 (1938). 3. Burte, H. M., TEXTILE RESEARCH JOURNAL 23, 469-80 (1953). 4. Evans, T. F., TEXTILE RESEARCH JOURNAL 24, 637-43 (1954). 5. Speakman, J. B., and Greenwood, J. R., J. Textile Inst. 26, P271-88 (1935). 6. Speakman, J. B., and Murthy, C. N. K., J. Soc. Dyers Colourists 56, 252-8 (1940). 7. von Bergen, W., and Wakelin, J. H., TEXTILE RE-

Discussion of Published Papers Remarks on the "Secondary Yield Point" in Wet Wool Fibers

† Fellow of the Textile Research Institute. IN A RECENT ARTICLE,* the secondary yield point (see Figure 1), a feature of the stress-strain diagrams for several of the wool fibers tested, was described. Although the data did not then indicate the following, it now appears that the explanation of this phenomenon is not the molecular one given, but depends upon the macroscopic dimensions of the fiber. The secondary yield point is due to variations of

Properties of Apparel Wools: VI. Aging of Top and Roving Produced on the French Worsted System

The aging of top and roving produced on the French worsted system has been investigated by measuring the dimensional changes and the mechanical properties of these fiber assemblies. The experimental results indicate that one consequence of aging is a relaxation of stresses in the fibers caused by deformation of the fiber crimp during previous processing. A brief high- temperature, high-humidity treatment of the top balls or roving bobbins has many of the same effects on the properties of the top and roving as a long aging period at 65% R.H. and 70° F.

The Detection of Modification in Animal Fibers I. Use of the Ratio (Hookean Slope in H2O/ Hookean Slope in Conditioned Air)

The ratio (Hookean slope in H2O/ Hookean slope at 65% R.H.), where both measurements of the Hookean slope are on the same fiber, is shown to be independent of fiber cross-sectional area, and, for a given fiber type and previous history, the fiber-to-fiber variation of the ratio is small. Since chemical treatments markedly affect this ratio, its use to detect chemical process modification of animal fibers presents attractive possibilities.

The Effect of Dilute Salt Solutions on the Mechanical Properties of Animal Fibers

In a recent paper in this JOURNAL, &dquo;The Relaxation of Stress in Wool Fibers&dquo; [3], Katz and Tobolsky showed that when a water-relaxed fiber was treated with a sodium chloride solution (O.1N to 1.01~’) a slow but relatively large further relaxation of tension took place. However, Sookne and Harris [4] had previously found that the energy required to extend a wool fiber 30% when it is immersed in a O.1N sodium chloride solution was the same as the energy required to extend the fiber when immersed in water. Similarly, in connection with some other work [2], I have found that over the time interval of the Katz and Tobolsky experiment immersion of

The Detection of Modification in Animal Fibers III. Tensile Recovery in Water

The tensile recovery of animal fibers in water has been measured in a manner similar to that previously described [1] for animal fibers at 65% R.H. The tensile recovery measured in water was much less sensitive for detecting chemical modification than the tensile recovery at 65% R.H. Even after very severe chemical modification, water-soaked animal fibers showed almost perfect tensile recovery.