N. B. Patil

Quantitative Analysis of Crystalline Phases in Chemically Treated Cotton Fibers

This paper deals with the evaluation of crystal lattice transformations and decrys tallization brought about in cotton fibers by chemical treatments, using x-ray diffiaction techniques. Suitable indices have been evolved to quantify cellulose II and total crys tallinity values, and cotton fibers subjected to widely different chemical treatments have been evaluated. The accuracy of the new indices and their usefulness in routine analysis are enumerated.

Crystallization of Amorphous Cellulose

Recrystallization behavior of the hydrolysates of native and thrice mercerized cotton, ball-milled to yield samples of different amorphity, was studied using x-ray diffraction. For crystallization of amorphous cellulose into cellulose I lattice, the presence of cellulose I nuclei seems to be a prerequisite. In a partially ball-milled cellulose I . sample, crystallization into cellulose II does not start until the amorphous content is as high as 75% or more. Results are discussed on the basis of the current ideas of the fine structure of fibers.

Studies on some Physical Parameters of Cotton Fibers and Their Influence on Breaking Strength

Data on linear density, wall thickness, and breaking strength—all measured for individual fibers from five selected cottons—have been examined in detail. It was observed that (i) the variability in single-fiber tenacity, calculated from the above data, is less than that obtained on the basis of average tex, and (ii) breaking load increases with in creasing linear density, up to the average value of linear density for each cotton, and levels off thereafter. The latter result seems to be due to lack of mutual alignment of lamellae in the wall when the fiber is subjected to loading.

Quantitative X-Ray Phase Analysis in Cottons Through Simple Indices

It is well known that crystal-lattice changes and decrystallization can be brought about in cotton cellulose .by using appropriate chemical reagents. 1-ravdiffraction (XRD) methods have been employed by manv workers to monitor such changes, and different procedures have been followed to evaluate parameters like crystallinity, crystal-lattice composition, etc. In the case of the familiar mercerization treatment, easily-measurable indices such as the lattice-conversion ratio (LCR) E4] and the ratio of the heights of the (101 ) and (002) XRD peaks El] have been used to study the fine structure of the samples. In the case of such treatments with reagents like ethylenediamine (EDA) or zinc chloride, which only increase the disorder in cotton and do .not produce new crystal lattices, the changes have been evaluated by indices like the crystallinity index (CI) [3~. Apart from such indices, more &dquo;absolute&dquo; methods E2] have also been developed. However, they are generally a little more dif~cult to use in routine studies. The purpose of th note is 1) to evaluate the utility of LCR in estimating the cellulose II and amorphous contents in samples consisting of these phases of cellulose as’well as the native cellulose I lattice, and 2) to similarly evaluate the utility of CI in estimating the amorphous contents in samples containing only cellulose I and amorphous phases. For the present study, mercerized and EDA-decrystallized samples were prepared as described by Patil el al. [2]. The XRD diagrams were obtained using Ni-filtered Cu K. radiation from a Philips stabilized x-ray generator PW 1130 with diffractometer and recording accessories, and operating in the reflection

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.

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.

Recrystallization of Cellulose

Hydrolysates of fibers swollen in various intracrystalline swelling agents were ball- milled for separate periods. These samples containing different proportions of cellulose I (C I) Cellulose II (C II) and amorphous (Am) phases were subjected to a mild hy drolysis, and their recrystallization behavior was studied by x-ray diffraction methods. Recrystallization into C I occurs only by nucleation, whereas recrystallization into C II is also caused by accretion of the long disordered molecular segments severed from crystallites.

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.

Structure-Property Relations in Chemically Treated Cotton Fibers

A study has been made of the influence of fine structural parameters on the tensile properties of cottons swollen in slack condition in aqueous solutions of sodium hy droxide and ethylenediamine. The results confirm that lattice type and crystallinity are important in deciding the tensile properties of the treated cottons.