The weaving of cotton fabrics with potential elasticity, obtained by introducing cotton yarn with the addition of PBT (polybutylene terephthalate) filament, differ from cotton fabrics including elastane, e.g. Lycra, both in the production process as well as in its useful properties. The excellent elasticity of PBT filaments is achieved by shrinkage in a hot water treatment, which can be carried out after weaving. The degree of elasticity of the threated fabric depends on the PBT share in its construction, as well as the structural properties of the fabric. The objective of this diploma was to observe the physical mechanical properties of six samples of cotton fabrics, with core spun cotton yarn with PBT filament as core in the weft direction. In order to compare the effect of the PBT component, we simultaneously studied fabrics with identical structure and without a PBT component. Half of the length of the samples was threated in boiling distilled water for 30 minutes before being dried for 24 hours in a relaxed state, in which the PBT develops its elastic properties. The following physical and mechanical properties were measured on all fabric samples, either treated or untreated: shrinkage of yarn and fabric after treatment, breaking strength and elongation of the yarn and fabrics, fabric thickness, yarn density, mass per surface area, air permeability and abrasion resistance. The obtained results showed that all samples containing PBT filaments in the weft had significantly shrunk during treatment. The largest degree of shrinkage was observed in the six-end weft faced twill in accordance with a smaller number of interlaceing points and floating threads. The frequency of interlacement determines the integration of the yarn into the weave thus influencing the friction surfaces between yarns which dictates the degree of shrinkage.
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