Improving Mechanical Properties of Nylon and Polyester Yarns by Horizontal Isothermal Bath Metho

Several techniques and treatments have been used for the production of high tenacity polyamide and polyester yarns. The inherent problems of low productivity, high production cost, and high energy consumption, complexity of chemical reaction, mass transfer and waste recovery systems make most of them inappropriate for industrial application. Horizontal isothermal bath (HIB) is an alternative eco-friendly simple treatment that can be utilized during melt spinning process for production of high performance fibers. The method contributes to high tensile properties through developing unique fiber morphology, transformable into highly oriented, order crystalline structures under mild drawing and heating. The drawing can be performed on HIB yarn during (i.e. continuous system) or after (i.e. batch system) the spinning process.;The purpose of this work is to study the effect of HIB method and drawing in improving the mechanical properties of nylon and polyester yarns. To achieve that, several HIB parameters including liquid depth, temperature, viscosity, and type as well as take-up speed, draw ratio and temperature were examined and optimized for the desirable tensile performance. In the first study, such parameters were investigated for a low Mw multi-filament nylon-6 yarn in the batch HIB system. The results showed that such treatment can increase the molecular orientation of the amorphous and crystalline functions up to 0.54 and 0.983 respectively, and raised both the amorphous isotropy and fiber birefringence by 67 and 45%, respectively. Also, hot drawing of the HIB yarn at a very low draw ratio of 1.38, increased the tenacity and modulus up to 10 g/d and 43.9 g/d respectively, and decreased the elongation to 27%.;In the second study, the effect of HIB and post-drawing on the tensile properties of poly trimethylene terephthalate (PTT) yarns was examined. PTT is an interesting polyester for textile products, as it has combined physical properties of nylons (PA-6 and PA-66) and other aromatic polyesters (PET and PBT). PTT filament is the most promising candidate for replacement of PET fiber, due to the properties such as lower melting point, easier processing and dyeing, and higher flexibility. The results showed that the bath treatment increased considerably the fiber orientation and crystallinity up to 0.066 by 66% and 47.94% by 100%, respectively. Drawing the HIB fibers with a low draw ratio of 1.11 increased the tensile strength up to 4.76 g/d and reduced the tensile strain down to 51.76%. Such the strength is greater than the maximum value (3.3 g/d) reported before. The obtained results can widen application of PTT fibers in technical woven/nonwoven products.;The third study is related to the integration of the drawing and the HIB into one-step continuous process for production of high tenacity PET yarn. So far, the drawing and the HIB treatment have been used in two separate steps (i.e. batch system), which is not appropriate for industrial scale due to the low drawing speed (50 mm/min). This problem can be solved in the continuous system, as the drawing could be done on the HIB yarn during melt spinning. The results showed that continuous HIB process increased the tenacity and modulus up to 7.9 and 116.5 g/d, respectively and reduced the strain down to 9%. Such tensile properties obtained simply through entering the filaments into the bath (depth of 24 cm, temperature of 110°C) for some millisecond and applying a very low DR of 1.3 to the yarn at a high drawing temperature of 200°C, which otherwise requires a much higher DR of 5.2 in conventional spin-draw process. The combined effects of high crystallinity, high molecular orientation and compact fibrillar morphology contributed to such high tensile properties.