A.K. Sengupta

Anisotropy in Some Mechanical Properties of Woven Fabrics

A woven fabric is considered as an anisotropic lamina and initial modulus and crease recovery of cotton woven fabrics have been studied. It is observed that Pattersons relation of anisotropy in initial modulus for nonwoven fahrics is, also, generally valid for woven fabrics. Crease recovery in a bias direction is higher than those in the warp and weft directions. A marked difference exists in crease recovery values with twill woven fabrics for positive and negative direction of bending.

Role of Water in Air-Jet Texturing Part I: Polyester Filament Feeder Yarns with Different Frictional Characteristics

Polyester multifilament yams with different frictional characteristics have been air textured under both dry and wet texturing conditions. Wet textured yams are more stable and have higher bulk, and the surface structure of these yarns shows higher loop frequency, lower loop height, and a higher percentage of protrudes and closed and crossed loops for feeder yams with similar frictional characteristics. For comparable values of dry and wet friction, yams textured after prewetting are far superior in properties than yams textured in the dry state. The study clearly demonstrates that the effect of prewetting is not confined only to the lubricating action of water.

Influence of Interfilament Friction on Structure and Properties of Air Textured Yarns

The structure and properties of air textured yarns are influenced by the dynamic friction of the parent filament yam. We have demonstrated this by texturing under various conditions two similar multifilament yarns with different spin finishes. We have analyzed the effects of water and mechanical stretch on the structure and properties of the air textured yams. We present here a new classification of surface loops of air textured yarns and analyze the effect of interfilament friction and water on different types of loops.

An Analysis of the Air-jet Yarn-texturing Process

The air-jet texturing process for synthetic continuous multifilament yarns is more versatile than any other texturing process and provides the most effective simulation of natural staple spun yarns. The process itself is inadequately understood, and the ultimate goal of the work is to achieve a better understanding of the mechanism of the texturing process and to make suggestions for more efficient nozzle designs in order to increase productivity and thereby reduce production costs. Reviews of historical development of the texturing nozzles and of the previous investigations are reported. Various designs of texturing nozzles are available but, in general, they possess similar flow characteristics i.e., a supersonic, turbulent, asymmetric, and non-uniform flow. Therefore this research was confined mainly to one type of nozzle investigated on a purpose-designed single-head texturing machine. A mathematical flow model of the nozzle was developed to compare with the results of the experimental work; this model was also used as a basis for the design of new texturing nozzles. Experiments were conducted using scaled-up models of the texturing nozzle in order to determine the flow characteristics. Flow visualisation, high-speed cine and still photograhy were among the techniques used in the investigations. The work was extended to include tension and drag force measurements, filament speed measurements and yarn tests. The effects of filament crosssections on the texturing were theoretically studied. The effects of wetting the filaments on the air flow were analysed theoretically whereas their effect on the friction were investigated experimentally. In the light of these experiments and the associated theoretical analyses, a loop formation mechanism has been suggested in order to provide an improved understanding of the process. Effects of process parameters on the yarn properties have also been examined and the results observed to be an good agreement with those predictable by the mechanism postulated, Finally new texturing nozzles were designed, manufactured , and tested, and these proved to be more economic as regards air consumption. Suggestions for future work and further improved nozzle designs have been made,

Effect of Mercerization on the Tensile Properties of Rotor Spun Yarn

Rotor spun 14s cotton yarns were twisted over a range of twist multipliers from 4.25 to 5.5. The yarns were mercerized with sodium hydroxide and stretched to their original length. Tenacity of mercerized yarns was significantly greater than the grey yarns at all twist levels. A substantial improvement of 52.8% in tenacity was observed at the lowest twist. Even slack mercerization improved yarn tenacity at lower twist levels (up to 4.7) close to that for tension mercerized yam. Maximum increase in yarn tenacity by slack mercerization was 46% at the lowest twist. Tension mercerization increases yarn tenacity primarily by improvement of fiber packing at lower twist levels, but at higher twist levels fiber orientation, fiber packing, and improvement in fiber tenacity all affect yarn tenacity.

Effect of Process Variables in Air-Jet Texturing on the Properties of Spun Yarns with Different Structures

We have analyzed the effects of process variables (texturing overfeed, air pressure) and feed material variable (yarn twist) on the important properties of air-jet textured spun yarns of different structural configurations. For this, we adopted a factorial design approach where factors are varied simultaneously in order to find the individual as well as interactive effects. Using this experimental design, we computed general re lationships relating the properties with variables as well as the significant terms in these relationships, and we plotted the response surface graphically.

Studies on Acrylonitrile-Hydrozyalkyl-Methacrylate Copolymer Fibers

The effect cf wet spinning conditions on the properties of acrylonitrile-2-hydroxyethyl methacrylate (AN-HEMA) and acrylonitrile-2-hydroxypropyl methacrylate (AN-HPMA) copolymer fibers were studied. Copolymers containing 1 to 4.8 mole% hydroxyalkylmethacrylate comonomer were synthesized by slurry polymerization using redox initiator. The spinning dope used was a 15% solution of polymer in dimethylformamide. The spinning conditions studied were: extrusion pressure, coagulating bath temperature, take-up velocity, and draw ratio. Low coagulating bath temperature and high draw ratio gave fiber with better strength properties. Sonic modulus and x-ray diffraction were used for study ing the molecular orientation and crystalline organization. The influence of hydrophilic comonomers in polyacrylonitrile on moisture sorption, dyeability, and tensile properties was considered.

Effect of Repeated Laundering on the Properties of Air-Jet Textured Cotton/Filament Composite Fabrics

We describe laundering and wrinkling trials on woven grey and dyed fabrics made from air-jet textured cotton/filament composite yams as weft. The tensile and bursting strength properties of the fabrics are not affected much by the laundering treatments. The textured yarn grey fabrics in general show higher relaxation with laundering, resulting in increased thickness, thermal insulation, and abrasion resistance, and re duced air permeability and tear strength. The greater strain relief due to laundering of the bulkier textured yam structure also helps to improve the crease recovery and wrinkling properties of these fabrics. Fabrics made with textured yams show higher wrinkle recovery than the parent yarn fabrics at various strain levels. The extent of whiteness gain in grey fabrics and color loss in dyed fabrics is almost the same in both the parent and textured yarn fabrics as a consequence of laundering treatments. The textured yarn fabrics, however, show higher color value than those from the parent yarn.

False Twist Texturization of Polypropylene Multifilament Yarns Part IV: Structural Influences on Dye Uptake

Polypropylene fiber and fibers spun from blends of polypropylene and small amounts of polyester and polystyrene incorporated through melt blending prior to spinning were investigated for dyeing performance in both untextured and textured forms. The dyeing performance improved with the addition of these polymers. While the reduction of crystallinity resulted in improved dyeing performance, the nature of the polymeric additive and other structural characteristics of the fibers also played an important role. A negative correlation exists between the number of crystals per unit volume and dye uptake.

Change in Configuration of Fibers During Transfer from Cylinder to Doffer in a Card

An improved technique for the study of change in fiber configuration during transfer from cylinder to doffer in a card is reported. It is observed that the majority of fibers change their configuration during transfer. Hooks are formed and previously formed hooks are removed. Transfer of fibers takes place both with and without reversal of ends. Those fibers that transfer without reversal change their configura tions more. A mechanism for the formation of leading hooks through buckling of front ends is suggested.