V. B. Gupta

Dyeability Characteristics of Textured Polyethylene Terephthalate Yarn

The dyeability characteristics of polyethylene terephthalate (PET) yarn, textured at different temperatures and different contact times, are reported. The dye uptake data is explained in terms of the structural changes taking place on texturing. The results indicate that the degree of crystallinity and the size of the crystallites are the predominant factors controlling dye uptake. The temperature of texturing plays an important role because it determines the crystal linity and the distribution of crystal size in the textured sample.

Changes in the Structure of Polyethylene Terephthalate Yarn on Texturing

The changes in the structure of commercial polyethylene terephthalate yam, when it is textured on a spindle false- twist machine, have been studied over a range of heater temperatures and heater contact times. Compared to the un textured yarn, crystalline content increases on texturing, but crystallite orientation, birefringence, and amorphous orien tation decrease. The changes in these structural parameters with temperature and time of texturing are discussed.

A Nonlinear Viscoelastic Model for Textile Fibers

The viscoclastic characteristics of a three element model, which has two Hookean Springs and a dashpot containing a non Newtonian power-law liquid, are considered, and the equations for creep recovery, stress relaxation and stress strain behavior are developed. These equations, along with the creep equation derived earlier for such a model, can be useful in the characterization of nonlinear viscoelastic behavior shown by textile fibers.

A Model for Nonlinear Creep of Textile Fibers

A model is presented to represent the nonlinear visco-elastic behavior, particularly the creep behavior, of polymeric solids like textile fibers. The equations obtained are shown to predict approximately the creep and creep-rate curves for a nylon 6 filament.

The Nature of Coupling between the Crystalline and Amorphous Phases and its Effect on the Properties of Heat-set Poly(ethylene terephthalate) Fibres

Poly(ethylenc terephthalate) (PET) fibres having a wide range of structures and morphologies were prepared by heat-setting commercial PET yarn at fixed temperatures between 100 and 255°C under two conditions, i.e. while the yarn was free to relax and when it was held taut at constant length. The structural and morphological characteristics of the crystalline and amorphous phases of the fibre were obtained by using standard methods. The sonic modulus, boiling-water shrinkage, recovery during an axial load–elongation test, and uptake of disperse dye by the fibre were determined experimentally. The dependence of these physical properties on structure is critically examined in this paper. It is shown that, in addition to the well-known structural characteristics such as the content and orientation of the amorphous phase, size and size distribution of crystallites, birefringence, etc., the nature of coupling between the crystalline and amorphous phases in the fibre, which differs significantly in the two sets ...

The Effect of Tension and Twist on the Structure and Dyeability of Textured Polyethylene Terephthalate Yarn

The changes in structure and dyeability characteristics of: a) polyethylene terephthalate (PET) yarn, textured at different tensions and various twist levels; and b) the textured samples after being relaxed in water at 80°C for 2 hours, are reported. The crystallinity of all textured samples was found to be higher than that of the untextured yarn, but in general, crystallite orientation, birefringence, and amorphous orientation decreased on texturing. The effect of tension and twist on these structural parameters is discussed in this paper. The textured samples, after being relaxed, show decrease in crystallinity, crystallite orientation, birefringence, and amorphous orientation. The dye uptake of the textured samples is considerably affected by tension in the crimping zone, and water treatment increases the dye uptake of the textured yarn. The structural dependence of dye-uptake data is analyzed.

Dependence of Stiffness and Strength of Cotton Fibers on Crystallite Orientation

Twenty-four varieties each of Gossypium hirsutum and Gossypium arboreum species from the Indian Agricultural Research Institutes farms at New Delhi and its substation at Sirsa, respectively, were studied for their bundle strength on a Pressley strength tester using zero gauge length and for crystallite orientation using X-ray diffraction. The crystallite orientation was expressed in terms of 40% and 50% angles and the Hermans orientation factor; from the latter an average orientation angle α m was computed. Correlations between bundle strength and these orientation parameters were calculated.

Latent Crimp in False-Twist-Textured Polyethylene Terephthalate Yarn

The effect of tension in the winding zone of the false-twist-texturing process on the crimp properties of textured polyethylene terephthalate yarn has been investigated. It was found that, all other conditions remaining unchanged, high wind-up tension results in low crimp retraction. Post-texturing treatments enhance the crimp retraction of these yarns and demonstrate the role of wind-up tension in rendering the crimp latent.

The Dependence of Stiffness and Strength of Gossypium hirsutum Cotton on Crystallite Orientation

The crystallite orientation angle obtained from x-ray diffraction patterns can be used for varietal characterization of cotton at the molecular level. The 40 and 50% x-ray angles are usually taken as representative parameters to correlate with the strength of the fiber. Although the 50% x-ray angle has some theoretical justification, like the use of the half-width of spectral lines, the choice of the 40% x-ray angle is arbitrary. From the study of 24 Gossypium hirsulum cotton varieties reported in this paper, it is observed that the average angle of orientation αm evaluated from the Hermans orientation factor fc gives better correlations with mechanical properties than the 40 and 50% x-ray angles con ventionally used.

Determination of Crystallite Orientation in Polyethylene Terephthalate Fibers

The orientation distribution of crystallites in polyethylene terephthalate (PET) fibers is generally determined using approximate methods. In this paper an exact equation, based on the generalized treatment of Wilchinsky, is developed which makes use of the intensity-distribution curves of three equatorial planes to determine Hermans orientation factor. The orientation factors obtained for a few PET samples using this approach are compared with those obtained by using two approximate methods. It is concluded that for fibers having relatively high orientation. the various approaches give reasonably close values for Hermans orientation factor.