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Influence of Twist on Selected Properties of Multifilament Yarn

Mertová I., Moučková E., Neckář B., Vyšanská M.

Autex Research Journal

2018

Vol. 18, no. 2

110--120

Owing to twisting of filament fiber bundle, the structure and consequently various parameters and properties of a fiber bundle are changed. The aim of the work is to verify the effect of multifilament yarn twist (or twist coefficient) on selected mechanical properties such as multifilament tenacity, breaking elongation, and coefficient of fiber stress utilization in the yarn. Furthermore, the influence of twist on structural parameters such as the angle of peripheral fibers, the packing density, and the substance cross-sectional area of fiber bundle is observed. Two multifilament yarns with different filament cross-section shape and material were used for the experiment. Experimentally obtained data was compared with the known model dependencies derived decades ago based on the helical model. It can be stated that multifilament yarn retraction can be predicted based on the angle of peripheral fibers using the Braschler’s model. The coefficient of fiber stress utilization in the multifilament yarn determined experimentally corresponds with a theoretical curve, constructed according to Gégauff and Neckář, in the area of Koechlin’s twist coefficient α > 54 ktex1/2 m−1. Results as well as possible causes of deviations of experimental data from the theoretical one are discussed in this work.

The influence of acid dyes upon some structural and physico-mechanical indices of polyamide fibres

Nedkova M., Pavlov P., Pishev D.

Autex Research Journal

2005

Vol. 5, no. 3

162--175

The influence of three acid dyes upon some physico-mechanical indices of polyamide multifilament yarn has been studied as a consequence of the structure modifications which occur during the dyeing process. It has been established that, irrespective of the differences in the chemical composition of the dyes, the modifications in the properties of the samples used are quite similar. Some structural characteristics, tenacity and elongation at break, crease resistance and the critical time of dissolution, have been determined. The dependencies of the indices listed on the dye concentration are of a complex character, which reflects the gradual penetration of the dye molecules into the inter-fibrillar and intra-fibrillar amorphous areas of the structure which are different in solidity. The fluctuations in the course of the dependencies in the area of the lowest concentrations are the result of the combined influence of the processes of improvement of the crystal phase and the relaxation phenomena, occurring in the most accessible amorphous areas of the fibrous structure. With the increase in the dye concentration, the so-called 'cross-linking effect' starts to appear, as a result of the formation of inter-molecular links of the polymer-dye-polymer type, which influence the properties under investigation in a characteristic way. The increase in the dye presence in the substrate provokes the repeated alternation of the above-mentioned phenomena in the thicker amorphous areas of the samples, with a pronounced influence of the 'cross-linking effect' in the highest concentrations.