INVESTIGATION OF MECHANICAL PROPERTIES AND INSTABILITY OF AIR-JET TEXTURED PBT YARNS

Abstract

Air-jet texturing mechanically alters the parallel arrangement of the synthetic filaments within the yarn, transforming them into a bulky, spun yarn like structure. In this technique, with the help of the applied overfeed and supersonic airflow, all kinds of filaments can be textured. In air-jet texturing, the textured yarn is subjected to a slight stretch between two feed-roll units after the exit of the jet. The purpose of this stretch is to stabilize the mechanical properties of the textured yarn by anchoring the loops in the core. Some of the loops in the structure of the air-jet textured yarns can be destroyed by the effect of the applied forces. The amount of the loops remaining on the thread is related to the "stability" of these loops. Polyester fibres are synthetic materials that contain ester bonds in their main chains. These fibres are especially preferred in conventional and industrial applications due to their favourable properties. Among all the polyester fibres, polyethylene terephthalate (PBT) is generally used where elastic behaviour is essential. In this study, mechanical properties and instability of the air-jet textured PBT yarns were investigated. The preliminary studies showed that mechanical stabilization over a 6% stretch ratio deformed the yarn structure. For this reason, PBT yarns were textured with 4 different mechanical stretch (0-2-4-6%) and 3 different overfeed ratios (20-40-60%). Yarn counts, mechanical properties and instability of the yarns were investigated. The results were discussed concerning the optical microscope images. It was concluded that increasing the overfeed, increased the looped structure. This leaded an increase in the yarn count and breaking elongation, while a decrease in the elastic recovery. Filaments in the samples with the least looped structure (yarns textured with 20% overfeed) maintained their parallel arrangement regarding the yarn axis. Therefore for these samples, the properties of their molecular structure came into prominence and the best elastic recovery behaviour was observed in this group of samples.