Kushal Sen

Effect of reaction medium on Radical copolymerization of acrylonitrile with vinyl acids

Radical polymerization of acrylonitrile (AN) with methacrylic acid (MAA) and itaconic acid (IA) was carried out in a mixture of dimethylformamide (DMF) and water at 70°C using α, α′-azobisisobutyronitrile (AIBN) as an initiator. Monomer feed in the polymerization vessel was 98:2 (AN:MAA/IA) in the molar ratio, and the DMF:H2O ratio was varied between 20:80 and 80:20 (w/w). Copolymers were characterized by FTIR, carbon, hydrogen, nitrogen elemental CHN analysis, 1H- and 13C-NMR, and viscometry. The rate of polymerization (Rp) was found to decrease with an increase in DMF concentration in the reaction medium, that is, in 20% DMF for AN–MAA system, the Rp is 1.23% min−1 in 1 h of polymerization, while in 80% DMF, Rp is reduced to 0.37% min−1. The nature of the vinyl acid also affects the Rp. It has been shown that the rate of polymerization is higher for an AN–MAA system as compared to an AN–IA system (Rp = 1.0% min−1) and the methacrylic or itaconic acid content in the copolymer increases with an increase in the DMF concentration. The MAA content in the poly(AN–MAA) polymer produced in 20% DMF is 3.2 mol %, which increases to 6.1 mol % (calculated through FTIR spectra) when DMF is increased to 80% in the reaction medium. The intrinsic viscosity [η] of the poly(AN–IA) and poly(AN–MAA) copolymers in DMF was found to be in the range of 0.67–2.90 dLg−1 depending on the reaction medium. In determining the intrinsic viscosity, a definite deviation from rectilinearity of the concentration dependence in the high-dilution region is observed, thereby demonstrating the polyelectrolyte behavior of these polymers. Through FTIR and NMR spectral studies, PAN homopolymer and other copolymers have shown the formation of a small quantity of acrylamide units. In addition copolymer P10, which contains 10.1 mol % IA, has shown anhydride formation.

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.

Studies on electro-conductive fabrics prepared by in situ chemical polymerization of mixtures of pyrrole and thiophene onto polyester

This article reports on development, characterization, and performance of electro-conductive textiles prepared by in-situ chemical polymerization of mixtures of pyrrole and thiophene onto a polyester fabric. It was observed that a mixture of pyrrole and thiophene at 4:1 molar ratio resulted in the lowest surface resistivity among all the mixtures and the individual monomers studied. This electro-conductive fabric exhibited exponential voltage-current relationship. Further, it showed substantial fall in surface resistivity under the exposure of ultra-violet radiation. Under the application of DC voltage across it, an exponential rise in surface temperature was observed and the coefficient of rise in temperature was found to be directly related to the duration of voltage applied. Further, when subjected to mechanical straining, it displayed a decrease in resistivity followed by an increase of resistivity.

Texturing of Polyester-Viscose Blended Yarn by Batch and Continuous Processes:

Union-setting (combined heat-setting and resin-curing) of polyester-viscose blended yarns of varying blend ratios (20/80, 50/50, 65/35, and 80/20) was studied for producing textured yarn by batch (twist-set-detwist) and continuous (false-twist) methods. Basic aluminum chloride and magnesium dihydrogen phosphate were used as catalysts for the setting of the viscose component by dimethylol dihydroxyethylene urea. In the batch process an increase in the curing time from 2.5 to 30 seconds marginally increases the extent of resin fixation with no concommitant increase in the crimp rigidity. The crimp rigidity, however, increases with increase in the polyester component in the blend. The ratios of wet/dry retractability and wet/dry tenacity are maximum in 65/35 polyester-viscose blended yarn. Continuous false-twist texturization of blended yarn with simultaneous setting of both the components was possible even with a residence time of 1 second in the heater.

False Twist Texturization of Polypropylene Multifilament Yarns Part III: Reducing Feeder Yarn Crystallinity Through Melt Blending with Small Amounts of Polyester and Polystyrene

Incorporating small amounts of polyester and polystyrene into polypropylene by melt blending prior to spinning reduces crystallinity considerably. An amount as low as 5% polystyrene reduces crystallinity from 70% for the parent fiber to 34% for the blend. A reduction in feeder yam crystallinity results in a greatly improved performance in texturizability of the fiber.

Influence of yarn structures; part A: on carpet compressional performance under static and dynamic conditions

Three different Indian wools viz. Malpura, Magra and Chokla, significantly different in terms of fibre diameter, proportion of medullated fibres and extent of medullation are selected for this study. Two different mixing approaches i.e. homogeneous and strategic mixing of fibres of different characteristics were used. Three-layered yarn structures were developed to exploit the advantages of the strategic mixing, where wool fibres of different characteristics are positioned in different layers of the yarn as proposed by one of the author of this paper. The compressional performances of handloom carpets made from structurally different yarns were studied using newly developed carpet compression tester measured under static and dynamic conditions.

False Twist Texturization of Polypropylene Multifilament Yarns Part II: Reducing Feeder Yarn Crystallinity Through Tension Annealing

Annealing followed by rapid quenching is used to reduce the ctystallinity of poly propylene filaments. The effect of reduced feeder yarn crystallinity on the texturizability of the fibers is studied. The tension-annealed samples show a considerable increase in crimp rigidity values compared to the parent, unannealed samples, particularly when the contact time in the heater during texturing is low.

Flexible non-metallic electro-conductive textiles

ABSTRACT This issue of Textile Progress reviews research carried out on electrically conducting polymers, fibres and fabrics prepared by in situ chemical, electrochemical and vapour-phase polymerisation. It provides information about various inherently conducting polymers prepared from aniline, pyrrole, thiophene and their derivatives that are often used to prepare flexible non-metallic electro-conductive textiles. Several methods for the characterisation of electro-conductive fabrics are included, namely scanning electron microscopy, X-ray diffraction, elemental disruptive X-ray analysis and Fourier transmission infrared spectroscopy. The role of the polymerisation process in determining the electrical properties of electro-conductive textiles is examined. The review highlights applications of flexible non-metallic conductive textiles in electro-magnetic shielding materials, heating pads, sensors and actuators.

False Twist Texturization of Polypropylene Multifilament Yams: Part I: Time-Temperature Effects

The effects of heater temperature and contact time on the properties of textured polypropylene yarn are reported. Increases in both contact time and heater temperature increase crimp rigidity. Enhancing the rate of cooling increases crimp rigidity consid erably, particularly when low contact times are used. Texturization reduces crystallinity of the yarn. The crystallinity is progressively reduced with the increase in contact time. The use of a coolant to rapidly quench the yarn as it emerges from the heater reduces crystallinity even further. The level of crystallinity of the textured yarn is not related to the crimp rigidity value.

Simultaneous Dyeing and Texturing of Polyester/Viscose Blended Yarn

A unique system for simultaneously dyeing and texturing polyester/viscose blended yarn is reported. Dyeing and texturing were accomplished by pad-thermosol and alkali shock treatment. A single bath was used, containing a mixture of disperse and reactive dye, along with dimethyloldihydroxyethyleneurea and an acid catalyst. Dye fixation and texturing were achieved by baking the treated yarn on a Scragg Mini bulk machine using a heater temperature of 210°C for 2.5-5 seconds; however, higher color yields and wash fastness were obtained by post-alkali shock treatment. The results of continuous dyeing and texturing also show a very uniform coloring and high color yield as compared to that obtained by the cross-dyeing involving high temperature dyeing followed by pad-alkali shock treatment of textured yarns. The crimp rigidity and the tensile properties of simultaneously dyed and textured yarns were also not affected in any way, because the dyeing step was incorporated with texturing.