Louis C. Weiss

Density of Modified Cottons Determined with a Gradient Column

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.

Abrasion and Tensile Properties of Cross-Linked Cotton Fabrics

Fiber toughness, fabric construction, and pretreatment were found to affect abrasive wear in permanent-press trouser cuffs. Samples of Pima S-2, Hopi Acala, and Delta pine 15 cottons were processed into twelve constructions of print-cloth weight fabrics. Cross-linking with the dimethylol dihydroxyethyleneurea-type resin was applied as a continuous process to fabrics after scouring and after slack mercerizing. Nitrogen con tents of treated fabrics show that type of cotton, fabric construction, and pretreatment affected the amounts of resin reacted with the fabric. Pima cotton had the lowest and Deltapine the highest level of nitrogen in almost every fabric construction. Pima cotton fabrics showed less wear during conventional abrasion test and laundering and greater crease-recovery angles than did the other cottons. Cuffs of basket-weave fabrics with 0.87% nitrogen showed less crease wear during laundering than did plain weave at 0.64% nitrogen. At comparable nitrogen content, slack-mercerized fabrics were more durable at a higher crease-recovery angle than were cuffs made from scoured fabrics.

Degradation of Cotton Fibers and Yarns by Heat and Moisture

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.

Moduli of Cotton Fibers and Yarns in Relation to X-Ray Angles

Cotton samples with a wide range in fiber properties were chosen. An X-ray measure of the degree of crystallite orientation and/or the secant modulus of fifteen cottons are traced through levels from sub-fibers to single fibers to bundles to yarns. The differences due to sample characteristics gradually become less as the cottons progress through these levels. When the secant modulus of the yarns spun at the appropriate twist for maximum strength is referred to the X-ray measurement, no additional masking, but resolution occurs. The resolution seems to be more pronounced with American upland than with barbadense cottons. Tenacity, secant modulus, and bundle linear density primarily explain the rankings.

Strain-Recovery Properties of of Wash-Wear— Treated Cotton Fabrics:

Scoured and slack-mercerized fabrics were treated with dimethylol ethylene urea, methylated methylol melamine, and formaldehyde. Fabries with differences in resin add-on and differences in stretch during the cure were examined. Changes in tensile modulus caused by addition of resin were smaller than those caused by stretching during treatment. The elongation at break was greater for the slack-mercerized than for the scoured fabries. Also, the recovery from strain during the testing was greater for the slack- mercerized than the scoured fabric. Recovery increased with add-on for both the basket and the plain-weave fabrics. Stretch during treatment had-only minor effects on strain recovery during the testing. The correlation coefficients of fiber strain recovery to fabric strain recovery are lower than those of fabric strain recovery to wrinkle recovery. The correlation coefficient of the latter is increased if recovery is a function of both strain and stress rather than of either used separately.

Physical Properties of Fibers and Yarns of Partially Acety lated Cottons

Samples of cotton of Deltapine, Rowden, and Stoneville varieties were partially acetylated as bulk cotton and as untreated 14/3 yarns to acetyl contents ranging from 9 to 26%. Breaking loads and elongations at break of single fibers, fiber bundles, and yarns were decreased by the partial acetylation up to about 17%, but showed a tendency to increase above 20% acetyl content. Moisture conditions have less effect on tenacity of yarns of 25% than on those with lower acetyl content. Tenacities of the acetylated yarns when wet were slightly lower, and when desiccator-dried were higher than those of the untreated controls. Below 15%, the relation of density to acetyl content was consistent with calculations based on the preferential reaction of amorphous cellulose in the initial stages of the reaction. Resistançe to heat degradation increased with acetyl content up to 25% acetyl. The pH of the water used to rinse the reacted yarns was an important factor influencing heat degradation. Maximum retention of strength occurred when the wash water was in the pH range of 10-11. A slight but consistent difference in heat resistance of the partially acetylated cottons was associated with differ ent varieties.

Physical Properties of Cotton Treated by Pad-Dry-Cure, Mild-Cure, Poly-Set, and Wet-Fix Processes

This study was directed primarily at the physical property changes in fibers, yarns and fabrics as smooth drying proper ties are developed in cotton by pad-dry-cure, mild-cure, poly-set and wet-fix processes. Bound nitrogen differed appre ciably in the final products, the maximum nitrogen being required in the wet-fix and the minimum in the poly-set cottons. Compared to pad-dry-cure cottons, tensile properties change more rapidly with bound nitrogen during the initial reaction periods for poly-set and wet-fix cottons and in the final reaction period for mild-cure cottons. Tenacity of single fibers had larger differences at the maximum levels of reaction than did those of the yarns or fabrics. In dual step processes, poly-set and wet-fix, strength decreased with each step. Recovery from tensile strain in single fibers was inversely related to retained strength, the wet-fix cottons had the smallest strength loss and the smallest increase in recovery. Incon sistencies between crease recovery for fabrics and strain recovery for fibers indicate that fiber properties other than strain recovery are affecting crease recovery and smooth-drying of fabrics.

Cotton as an Electret

Research to enhance the storage of electrical charge in lint cotton led to imparting electret-like properties to cotton fibers. An electrostatic field introduced stored, oriented charges within a bundle of cotton fibers. The threshold values of temperature, time, and electric field for production of cotton electrets are defined, and specifications for measuring charge-density distribution are presented. The electret nature of the phenomenon is substantiated by findings that cotton fibers exposed to electric fields at elevated temperatures show long-term, charge-retention properties that are enhanced by short-circuiting. These fibers also display a tendency to a charge-polarity reversal after being removed from the electric field. Furthermore, the waxes native to the single fiber seem to be the basis of this new cotton property. These waxes are related to one of the best known electret materials—carnauba wax. A similar effect with analogous characteristics has also been produced in polyester fibers. With both fibers the effect is less than that possessed by ideal electrets.

Influences of Fiber Properties on Yarn Twists

The variation in the twist multiplier for maximum yarn strength in terms of the fiber properties of length. weight fineness, and uniformity of tenacity along bundle length is inferred from data based upon 15 1, 30, 1, and 40/1 yarns of a series of cottons having widely different fiber properties. The optimum twist multipliers that were calculated (1) from the above three fiber parameters (i.e., the tenacity-length uniformity hypothe sis); (ii) from the length and fineness, and (III) from the fiber length alone are com pared to the optimum twist multipliers detemined from the yarn tenacity vs twist curves. The tenacity-length uniformity hypothesis and the Sullivan theory are com pared by utilizing single cotton fiber properties. Considering all comparisons, the cor relation coefficients for theoretical to nommal values of optimum twist range from 0.64 to 0.96. Utilization in yarn twist of the ratio denoting uniformity of tenacity along bundle length in the tenacity-length uniformity hypothesis and of the ratio of single-fiber tenacity transfer in the Sullivan theory is illustrated.

Effects of Tension During Cross-Linking Treatments of Cotton Fabrics

The effects of tension during cross-linking treatments on the physical properties of fabrics were investigated on 80 X 80 print cloth and 48 X 48 sheeting with scour and slack mercerization pretreatments. The treatments were with methylated methylol meka mine and tris(1-aziridinyl)phosphine oxide applied as pad-dry-and-cure resins, and with formaldehyde applied to the cotton in swollen and semi-swollen condition. The effects of tension during treatment with formaldehyde in swollen or semi-swollen condition were achieved only by wet stretching and drying the fabric under tension prior to the treatment. Changes in fabric properties as a result of tension were similar to, but smaller than. changes previously observed in fiber and yarn properties. Large changes in moduli were achieved by tension, especially on slack mercerized fabric. Tension increased strip breaking strength over the untensioned but lowered elongation and toughness index. Tension increased tear strength and had no appreciable effect on wrinkle recovery.