Results are reported on tests of breaking load and elongation of single fibers at constant specimen length from the length groups of 6 cotton samples. A description is given of the instrument used in these tests. Average weight fineness of the center section of fibers from each length group was determined, and the tenacity and "stiffness" of the fibers were calculated.A method is described of calculating a single-fiber tenacity "index" for a cotton sample from the tenacity values of 3 modal-length groups. A high correlation is demonstrated between this index and the weighted mean single-fiber tenacity for the whole sample. IN A PREVIOUS PUBLICATION [3J datawere presented on the strength of single cotton fibers from 4 varieties of American Upland cotton. It was demonstrated that fiber breaking load and tenacity (specific strength) increase with increase in length of the individual fibers, and that an inverse relationship exists between fiber tenacity and the length of the section tested. These data were used to interpret some of the variations in flat-bundle test results. While many data have been published on the physical properties of single fibers [2, 4, 6-10~, little information is available on the variation of these properties with fiber length within a single sample for American Upland cottons. In most strength tests made on cotton, whether of the bundle or of the individual-fiber type, the preparation of the sample alters the length distribution, so that the sample broken is not necessarily representative of the actual length distribution of the cotton.The results would therefore not be expected to be truly representative of the strength of the cotton. While this is true of either type of test, results obtained using the bundle-type test are more liable to error than are those from the single-fiber type in the comparison, for example, of chemically modified and raw samples, since the results of the bundle test are dependent to some extent upon the surface characteristics of the sample.In the present paper the results of a more extended investigation on the relation of tenacity of single fibers to fiber length are reported, and the instrument used in making the tests is described. The tenacity of samples from several varieties was determined by first measuring the breaking load and weight fineness of the center section of fibers from each length group. These strengths were weighted in accordance with the length distribution of the cotton, and an &dquo;average tenacity&dquo; was calculated. If a more rapid method is desired for this determination, a characteristic index, bearing a fixed relation to this average tenacity, can be determined by testing only a few length groups. A method of calculating such an index is discussed, and its relation to the average tenacity is demonstrated.The elongation at break of each fiber was recorded, and an average value was determined for every length group. These values were studied in relation to fiber length and strength.The whole-fiber weight fineness and the coefficients...
Four cottons in commercial production, covering a range of such physical properties as strength, length, and fineness, were studied in a comparison of two methods of determining fiber strength—the individual fiber test and the Pressley flat-bundle test. Because of the combing action in bundle preparation, cotton fibers broken in the flat-bundle test represent the longer fibers found in a sample of cotton. These remaining fibers are not representative of the length of the original sample; and since fiber specific strength increases with fiber length, neither are they representative of the strength of the original sample. This increase in specific strength with increase in length is evident whether fibers are broken indi vidually or in aggregates. The relationship between the logarithm of individual fiber tensile strength and the logarithm of the specimen length used is inversely linear. The flat-bundle test represents the strength of fibers whose specimen lengths were deduced to be between 1/16 and 3/32 inch.
Fibers from ginned cotton and from 16/2s yarn of seven cottons of different physical properties were tested as a bundle and as individual fibers in order to determine what changes in properties, if any, could be attributed to the mechanical processing. Determinations of tenac ity, length array distribution, and crystal alignment revealed no consistent differences between the cottons before and after processing. The maturity of carded cottons was slightly lower. The weight fineness and breaking load of individual fibers were unchanged with processing, but elongation at break was decreased. A higher modulus in tension was obtained from load- elongation curves of processed fibers, with the greatest difference found for loads below 2 g.
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