Abstract:

Objective The ideal yarn sensor is both conductive and elastic. The bonding between the conductive layer and the elastic polymer fiber is usually weak, and after repeated stretching, the reduced bonding between the conductive material and the polymer matrix and the detachment of the conductive layer will seriously affect its sensing performance. Therefore, how to improve the bonding fastness of the conductive layer and the yarn is one of the challenges in ensuring the sensing stability.

Method Cotton fibers with good hydrophilicity and spandex with elasticity were blended to prepare core yarns with different levels of twists, then the cotton/spandex core yarns were modified with 3-(aminopropyl) triethoxysilane, and MXene-coated conductive cotton/spandex yarns were prepared by coating MXene using the dip-rolling method. The morphology and structure of the conductive core yarns were characterized, and their mechanical properties, electrical conductivity and tension sensing properties were investigated.

Results Cotton fiber was used as the sheath and spandex as the core to prepare the cotton/spandex core yarns with different twist levels. The characterizations by Fourier transform infrared spectrometer, Raman spectroscopy and water washing resistance showed that 3-(aminopropyl)triethoxysilane successfully modified cotton fibers by amination, and MXene was mainly grafted onto the surface of cotton fibers by chemical bonding. SEM images showed that the diameter of the core yarn was 0.7-0.8 mm, which also proved that MXene coated the cotton fibers to form a dense conductive layer. The chemical bonding between MXene and the cotton fibers resulted in a certain enhancement of the yarn breaking strength, and the strength of the MXene-coated cotton/spandex core yarns gradually increased as the yarn twist icreased. In addition, the MXene coating of the yarns also endowed good conductive properties to the yarns. As the twist of the core yarns was increased, the electrical resistance demonstrated a gradual decrease, with a minimum resistance of 54 kΩ. The strain-relative resistance change curve of MXene-coated cotton/spandex core yarns with a twist of 133 twists/(10 cm) showed linear sensing with a linearity of 0.996, a sensitivity of 28.1, and the sensing stability is good. The obtained sensing yarns were attached to the joints of fingers, elbows and knees for motion monitoring, and the R/R₀ values fluctuated stably between 0.1 and 1.7, indicating that they can be used for monitoring the trajectory and amplitude of limb movements.

Conclusion Hydrophilic cotton fibers with good hydrophilicity and spandex with elasticity were adopted to prepare core yarns, and MXene was encapsulated within cotton/spandex core yarns by dip-rolling with yarn modification technology to obtain MXene-coated cotton/spandex core yarns. MXene and modified cotton fibers produced stable chemical bonding. When the yarn twist is 133 twists/(10 cm), the mechanical properties and electrical conductivity of the MXene-coated cotton/spandex core yarn are better. The above core yarn shows good sensing properties and can be used for monitoring movements such as fingers, elbows and knees. The study of MXene-coated cotton/spandex core yarn provides a new idea for the study of sensing yarn and sensing fabric based on natural fibers.

Key words: cotton/spandex core yarn, modified cotton fiber, sensing yarn, MXene, strain sensing