K. R. Krishna Iyer

Influence of delignification and alkali treatment on the fine structure of coir fibres (Cocos Nucifera)

The present communication reports the effect of a softening treatment carried out with 18% NaOH on the fine structure and structure-property relations in coir fibres. The effect of successive removal of lignin and hemicelluloses on the fine structure has also been studied. Unlike other cellulosic fibres, alkali treatment failed to produce any increase in fibre elongation in coir. However, the spiral structure was found to be considerably modified by swelling. X-ray and infrared spectral measurements revealed that a part of the noncellulosic components does occupy the intracellular space and plays a significant role on fine structural changes produced during the alkali treatment.

Prediction of Bundle Strength From Single-Fiber Test Data

A theory is developed for predicting the strength of a bundle of sufficiently large number of elements, if the average breaking load and the breaking-elongation distribution of these elements are known. The usefulness of the theory is illustrated with data on cotton fibers.

Inverse Relaxation/Stress Recovery in Cotton Fibers and Yarn

The literature on mechanical properties of textile fibers is replete with data on viscoelastic characteristics like stress relaxation, creep, creep recovery, etc. A closely associated property, &dquo;stress recovery&dquo; or &dquo;inverse relaxation,&dquo; on the other hand, does not seem to have been investigated. If an extended specimen is allowed to recover a part of the deformation and constrained to remain at a length higher than what it is likely to assume if allowed to retract fully, the stress in the specimen tends to increase. This inverse relaxation or stress recovery, which is a function of time, is initially fast but slows down later on. The stress thus rises exponentially with respect to time. Neither a discussion of the significance of stress recovery nor experimental data on this property can be found in literature, though Peters and Woods have mentioned tension build-up [ 1 ]. We record here the stress recovery data on a cotton fiber sample and a cotton yarn sample tested using the Instron Tensile Tester.

Yarn Tension as a Function of Extension: A New Approach

Formulas have been derived for the extension and initial specific modulus of two- filament twisted yarn in terms of the properties of the component filaments. Experi mental data on a few yarn assemblies agree better with these formulas compared to earlier ones reported in the literature.

Sonic Modulus of Cotton Yarn and Its Relationship with Recovery Parameters

Effects of chemical modifications such as mercerization (with and without stretch) and crosslinking (with HCHO and DMDHEU of various concentrations) on me chanical properties such as dynamic (sonic) modulus, immediate elastic recovery (IER), work recovery (WR), and crease recovery angle (CRA) of yam samples were studied. While slack mercerization reduced the dynamic modulus and the recovery parameters, stretch during mercerization brought about a profound increase in their values. The dynamic modulus and recovery parameters also increased progressively with the severity of crosslinking in HCHO and DMDHEU. A high degree of linear correlation existed between the dynamic modulus and IER, WR, and CRA for samples treated with a given reagent; however these relationships were specific to the reagent.

Influence of Mercerization and Crosslinking on the Dynamic and Static Moduli of Cotton Yarns

’ Physical properties of textile materials under the influence of cyclic tensile forces are known as &dquo;dynamic mechanical properties.&dquo; Dynamic modulus is the foremost among the dynamic mechanical properties usually studied. Various techniques for determining the dynamic modulus have been summarized by Woo et al. [ 14], Chaikin and Chamberlain [ 11, and Tipton [ 11 ]. From published literature, very little information is available on the dynamic mechanical properties of cotton fibers and yarns. Hamburger [2], Lyons [4], Typton [ 11 ], and Woo et al. [ 14] employed sonic velocity methods to determine the dynamic modulus of raw cotton fibers. It is well known that chemical modifications such as mercerization and crosslinking treatment affect several physical properties of cotton fibers. In viscoelastic materials, where time effects such as stress relaxation and creep are significant, the ratio of dynamic to static modulus will be high compared to that in perfectly elastic materials where the ratio is unity. The more plastic a material is, the greater will be the ratio of dynamic to static modulus [4]. Our paper discusses the effect of chemical modifications such as mercerization and crosslinking on the dynamic and static moduli of cotton yarn, as well as on the ratio of these two moduli. Leas of cotton Digvijay spun to 30s count with a twist multiplier of 4.0 were dewaxed and kier boiled. These leas formed the control sample (first control) for studying the effect of mercerization. The treatment was carried out in slack as well as stretched conditions. The sample designations are MS-mercerized slack, M 8%-stretched to 8% below the original length, M 0%-stretched to original length, M + 2%-stretched to 2% over original length, and M + 4%-stretched to 4% over original length. The slack mercerized yarn constituted the control sample (second control) for crosslinking with HCHO and DMDHEU. In order to forestall the likely effects of yarn geometry on modulus measurements [7, 15], the yarn was wound on a special metallic frame and maintained at constant length with no twist loss during treatments. Form W process [9] was used for HCHO treatment at three alternative concentrations: 8% (XH 8%), 16% (XH 16%), and 22% (XH 22%). Bound HCHO in the treated sample was estimated chemically. The conventional pad-dry-cure method [ 12] was employed for DMDHEU treatments. Four different concentrations, 5% (XD 5%), 10% (XD 10%), 15% (XD 15%), and 20% (XD 20%), were studied. Nitrogen content (N%) was estimated by infrared method based on the carbonyl absorption [3]. All yarn samples were conditioned at 65% RH before modulus determination.

Reversals in Cotton: A Study with Scanning Electron Microscopy

The fibrillar morphology of the reversal zones in cotton fibers swollen in aqueous zinc chloride (ZnCl 2) is examined using scanning electron microscopy. There are dis tinct differences in the size of fibrillar aggregates on the two sides of structural reversals in some of the ZnCl2 treated fibers in all four varieties of cotton studied. These dif ferences seems to suggest that fibrils flanking a structural reversal could differ in their fineness levels.

X-Ray Orientation of Equatorial Planes in Swollen and Stretched Cellulosic Fibers

X-ray orientation profiles were recorded that pertained to the three equatorial planes from cotton fibers containing both cellulose I and II lattices and from viscose fibers. The changes in orientation brought about by swelling and stretching treatments could be accurately followed by studying the distribution of any one of the diffraction arcs.

Birefringence of Stretched Cellulose Films

Birefringence in three orthogonal directions was determined at normal incidence by the compensator method on thin sections of cellophane sheets, before and after subjecting them to swelling and stretching treatments. Considerable increase in crys tallinity and longitudinal orientation of molecular chain axes was achieved by stretch ing. From the course of variation in the three birefringence values with increasing stretch up to 42.5% imparted during treatment, it was possible to ascertain the biaxial orientation of the molecular chains in the crystalline and amorphous celluloses. If the crystallites are oriented with the (101) plane parallel to the film surface, the glucose rings in the amorphous regions align themselves parallel to the film surface. The stacking tendency of crystallites leading to the planar orientation of the (101) planes parallel to the film surface is also evident from crystallite dimension data.

Changes in Cross-Sectional Dimensions of Cotton Fibers on Crosslinking and on Subsequent Wetting

Changes in cross-sectional dimensions of cotton fibers resulting from crosslinking treatments were studied. One variety of cotton, Sujata, was subjected to crosslinking in dimethyloldihydroxyethyleneurea and in formaldehyde to different add-on levels. The changes in cross-sectional area and perimeter due to crosslinking, as well as the changes in these dimensions resulting from subsequent wetting, were measured. The results were discussed in the light of available information on fiber morphology and the nature of crosslinking reactions.