Seven cotton and one rayon samples were tested at various gage lengths, using the Stelometer. A method of estimating the slip length of fibers in a flat-bundle test is de rived and applied to these data in order to obtain a "corrected" gage length for use in calculating strain at break. Also, a method similar to that proposed by Platt et al for calculating the maximum possible bundle tenacity from breaking load and elongation at break of single cotton fibers is applied to previous single-fiber tensile data. The resulting derived values of bundle tenacity and per cent elongation are compared with measurements made on fiber bundles at equivalent gage lengths. The flat-bundle values of tenacity and elongation, measured with the Stelometer, show a good correlation with the values measured on single fibers.

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...

A rapid method which compares favorably in accuracy with that of slower methods for measuring the density of cellulosic materials with a gradient column is described. Densities of several cottons before and after chemical modification by partial acetylation, carboxymethylation, aminization, and mercerization are given. Per cent acetyl can be expressed as a function of density in a linear empirical equation over a range of 13 to 42% acetyl with a precision of ± 2%. Density measurements of decrystallized, ball-mill ground, and acid hydrolyzed cottons were in agreement with the generally accepted con cept of the crystalline-amorphous cellulose phase composition in these materials. Cotton from which water was removed by solvent exchange was found to have a high density before, and a low density after, air drying.

Strength and elongation measurements were made on single cotton fibers and on yarns which had been subjected to various temperatures from 110° to 162°C and various moisture conditions from 3% R.H. up to saturation for periods of heating from 2 to 128 hrs. Moisture contents and degrees of polymerization were also determined, the latter being used to calculate cellulose chain rupture. The simultaneous reduction in strength and elongation at break indicates that heat degradation weakens fibers by creating or intensifying weak points along the fiber. An equation similar to that derived by Sippel, relating fiber strength loss to time of heating and percentage of cellulose links broken, is discussed. Yarn strength, although not as readily affected by heat degradation as fiber strength, follows a similar pattern.