Study on auxetic and mechanical properties of complex yarn with spandex core and nylon wrap based on braiding technology

Abstract

Auxetic textiles have gained prominence for their unique negative Poisson’s ratio (NPR) behavior, emerging as advanced materials for protective and sports textile. This work develops and characterizes auxetic yarns (AYs) made from 1680 D spandex core yarn and 150 D/3 and 210 D/3 nylon-wrapped yarns. A high-speed braiding machine was employed to fabricate AYs with 1–8 core configurations with single nylon wrap yarn at spindle speeds of 20, 30, and 40 rpm. The NPR and deformation behavior were analyzed using real-time imaging and tensile testing. The results show that spindle speed exerts a very strong influence on auxetic performance; the higher this speed (40 rpm), the smaller the NPR owing to tighter helical winding angles. Multicore designs from 7–8 cores exhibited improved structural stability, displaying auxeticity at a strain of 30%. The 150 D/3 wrapped in nylon was more satisfactory than 210 D/3 in NPR magnitude value (–3.64 and –2.99 at 20 rpm, respectively), because it was more flexible and possessed lower linear density. Mechanical testing revealed that multicore configurations increased breaking load (up to 48.33 N for 8-core AYs) while maintaining consistent stress–strain behavior. Nylon’s inherent properties, high tensile strength, abrasion resistance, and fatigue durability were critical in mitigating yarn slippage, a common limitation in auxetic structures. This work establishes a framework for optimizing AY design through material selection (spandex–nylon synergy) and process parameters (spindle speed, core number). The discoveries improve durable auxetic fabrics for athletics and medical braces that require dynamic mechanical responsiveness.