Abstract:

Objective Auxetic components can be used to create functional auxetic composite materials. The helical auxetic yarn (HAY) belongs to the group of auxetic reinforcement materials. Traditional auxetic yarns, made from filaments with a helical structure, often face issues like component slippage that can reduce yarn stability. They also lack the natural crimp and soft texture of staple fibers, which restricts their surface properties and applications. To address these challenges, this paper presents an innovative production method for helical auxetic yarns that incorporates staple fibers into the spiral wrapping structure. The aim is to enhance the yarn's auxetic performance and expand its range of applications.

Method Composite yarn was spun on a modified ring spinning machine to create a helical auxetic yarn based on the wrapping structure, with cotton and polyester filaments wrapped around a spandex filament. Besides, the double-filament helical auxetic yarn without cotton was also produced. The auxetic performance characteristics of these two types of yarns were analyzed and compared. Based on the spinning parameters, the effect of the yarn construction parameters on the negative Poisson's ratio was further investigated.

Results In this study, the negative Poisson's ratio of the new developed three-component and conventional two-component helical auxetic yarns was compared and analyzed. The maximum negative Poisson's ratios of the two yarns were similar, both less than -2, and the negative Poisson's ratio of two-component yarn was slightly better. In addition, the three-component helical auxetic yarn achieved a maximum negative Poisson's ratio at less strain compared with two-component yarn. Furthermore, after achieving the best negative Poisson's ratio, the Poisson's ratio of the three-component helical auxetic yarn was maintained below -0.5 with a tensile strain of 5% to 15%. However, after the two-component yarn reached the maximum negative Poisson's ratio, the negative Poisson's ratio effect of the yarn showed the weaking tread, flattening and approaching zero after 13% tensile strain. The influence of structural parameters of the helical auxetic yarn on the negative Poisson's ratio effect was discussed based on the spinning process parameters. Firstly, at a twist factor of 325, i.e., a helix angle of 27.4°, the negative Poisson's ratio effect was most obvious and its peak is at a 3% tensile strain. As the yarn twist factor increased, the negative Poisson's ratio effect diminished and larger tensile strain was required for reaching the maximum negative Poisson's ratio. Secondly, when the draft ratio of the wrapping filament was higher, the maximum negative Poisson's ratio of the helical auxetic yarn was initially increased and then decreased. When the draft ratio of the wrapped filament was 1.03, the negative Poisson's ratio was -3.24 which was the highest value among all the types of yarns. Thirdly, the draft ratio of the elastic core filament has negative effect on the maximum negative Poisson's ratio of the yarn. When the draft ratio of elastic core filament was 1.01 and 1.02, the negative Poisson's ratio of helical auxetic yarn was the best and similar, both less than -3.

Conclusion The enhancement of ring spinning machinery has facilitated the fabrication of a three-component auxetic yarn incorporating cotton fibers, thereby introducing an innovative approach to the design of auxetic yarns. The spinning process parameters, encompassing the twist factor as well as the drafting ratios of the core filament and the wrapping filament, exert a pronounced influence on the auxetic performance of the yarn. A comparative analysis of the auxetic properties of yarns manufactured under varying process parameters has yielded critical insights for optimizing the production process. This has led to the development of yarns that exhibit superior and consistent auxetic characteristics, thereby expanding the horizons and potential applications of auxetic materials within the textile industry.

Key words: auxetic yarn, helical wrapping structure, complex yarn, yarn structure, process parameter