Search

A technique to measure the dynamic mechanical properties of human skin in vivo is described. The technique measures the propagation and attenuation of shear waves in skin tissue over a range of frequencies (8–1016 Hz). Results show that both the propagation velocity and attenuation of shear waves in skin are highly dependent upon the water content of the stratum corneum. The technique was used to measure the dynamic mechanical properties of the skin on the back of the left hand for a group of 16 men ranging in age from 24–63 years. The results suggest that aged skin has a lower water content than the skin of younger men.

The propagation and attenuation of shear waves in human skin is investigated over a frequency range of near zero to 1000 Hz. The results show that at frequencies below a few hundred Hz, shear waves propagate along the skin surface and thus provide information on the dynamic mechanical properties of the stratum corneum. The surface waves, however, are rapidly attenuated with increasing frequency so that at frequencies above about 500 Hz the energy is propagated only as bulk shear waves. Thus, at high frequencies the properties measured are those of the dermis.

A number of experimental yarns were spun from partially acetylatecl (PA) cotton stock to determine some of the factors that improve its mechanical processing and yarn properties. These studies indicated that blending PA cotton stock with raw cotton was a better method of preparation for mechanical processing than the use of an antistatic treatment on the PA stock. Blending resulted in better mechanical processing and im proved yarn properties at a lower cost. Blending high acetyl PA cotton with 40% raw cotton was considered to be the best method of preparation. PA stock prepared from a rain-grown cotton exhibited better mechanical processing characteristics than stock pre pared from a longer-staple irrigated cotton. However, yarns spun from the latter type of PA cotton had better properties of strength, elongation, and flex abrasion resistance. The use of a higher twist multiplier in spinning and plying resulted in PA cotton yarns having improved properties of elongation and flex abrasion resistance.

High and uniform absorbency of cotton fabrics is a desirable quality in nearly every wet- finishing operation and in many finished fabrics; yet absorbency-measuring tests which have been employed up to the present time are largely inadequate and arbitrary. A test method is described here which is more suitable in that it meets the requirements of wetting the fabric quickly from one side while it is under pressure and allowing the comparison of different fabrics in a readily understandable manner. Using a glass filtering funnel to provide a wet porous plate and a flowmeter for measuring rates, the apparatus is easily assembled and calibrated. The test is simple and rapid and per mits numerical evaluation of both rate of absorption and total or ultimate absorption, largely independently of apparatus characteristics. The separate evaluation of these absorbency factors and the elimination of timing procedures set this test apart from those previously published. The method is readily adaptable to the investigation of many liquid-absorbent relationships. Application of the test to the evaluation of absorbency of purified cotton fabrics has led to a plausible explanation of their absorption behavior as being due largely to spaces within the fabric rather than to absorption characteristics of the fiber itself.

A study was made of means for rapidly preparing specimens from wool tops and grease wool cores for fineness measurement by an electronic particle size analyzer (Coulter Counter). 3 Factors such as types of blades, geometrical relationships of blade, fiber bundle, and anvil, and means of holding the specimen during cutting were varied. A preferred combination of cutting parameters was selected using particle length uni formity as the principal criterion for selection. The new method has the potential of enabling the preparation of specimens for Coulter Counter fineness analysis from wool tops or grease wool cores in about 20 minutes, while introducing less than a 2% increase in the coefficient of variation of fiber diameter.

Fully acetylated cotton (FA cotton), a chemically modified cellulosic fiber made from cotton and retaining its fibrous form, is described. A small-scale method of preparing a completely or nearly completely substituted product from cotton raw stock, yarn, or fabric by the application of acetic anhydride and perchloric acid catalyst in a diluent which minimizes the tendency of the product to dissolve, is reported. Its general prop erties and behavior in laboratory tests show it to have many superior properties to previ ously known cellulosic fibers, including partial acetates and triacetates. FA cotton has good tenacity, both wet and dry, and flex-abrasion endurance; it has some thermo plasticity, yet shows no sticking at ironing temperatures below 250° C.; it has low moisture regain and is dyeable with ordinary acetate colors. Work in progress m- dicates that treatment of yarn and fabric may be carried out satisfactorily in commercial- type stainless steel equipment.

The resistance for months to deterioration by microorganisms (in soil burial) of suitably acetylated fibrous cottons, some with only one-third of the hydroxyl groups substituted, depends upon the distribution of the acetyl groups as well as upon the total number of such groups present.Under usual conditions of acetylation, according to the literature, reaction takes place first in the amorphous cellulose, starting at the most accessible places. According to the present ex perimental acetylations and special dyeing tests, the reaction, which is probably confined at first to the amorphous cellulose, takes place along fibers in various segments and throughout cross sections rather than as a layer increasing in thickness from the surface inward. At one-third substitution the amorphous cellulose is converted to triacetate; the cotton fiber still contains about two-thirds of the original cellulose, which is present as crystalline material surrounded by acetylated cellulose. The swelling capacity of the cotton in water is greatly reduced.While the mode of attack by microorganisms is not completely understood, they apparently begin at the most readily accessible amorphous cellulose. From the literature and from the present experiments, protection by partial acetylation is believed to be due to the blocking of hydroxyl groups, the filling of spaces between chains in the amorphous cellulose, and the sup pression of swelling. It represents a general method of rendering cellulose unsuitable, or at least inaccessible, as a food for microorganisms.A relatively low degree of partial saponification may detract greatly from the rot-resistance of a well-protected acetylated cotton owing to the restoration of amorphous cellulose, with loss of blocking groups and a restoration of swelling capacity.Partial methylenation by treatment with formaldehyde may impart a moderate degree of rot-resistance, which seems best explained as being due to the suppression of swelling by cross linking. Formaldehyde-containing resins which impart rot-resistance apparently act similarly.The evidence obtained indicates that the amorphous cellulose is the part which is normally attacked, and that its ability to swell in water may be a more important factor in microbiological attack than is commonly recognized.The use of dyeing has been exemplified for qualitative tests to supplement other evidence regarding substitution and the composition and properties of substituted cottons.