Abstract:

Objective Polyamide 66 (PA66) filaments are commonly used in workwear and mountaineering clothing due to their high strength, cold resistance, and aging resistance. However, PA66 filaments have poor hygroscopicity, leading to easy generation of static electricity during weaving. Meanwhile fabrics accumulate sweat and breed bacteria, endangering human health during wear. Hydrogel materials exhibit excellent water absorption and retention properties. Composite hydrogel yarns combine these hydrogel properties with the unique adjustability and wearability of traditional yarns. Currently, the primary methods for preparing composite hydrogel yarns are impregnation and coating, which are simple but lack effective control over hydrogel thickness on the yarn surface.

Method Using PA66 filaments as the core yarn and a polyvinyl alcohol and sodium alginate (PVA/SA) as nanofiber shell, with mass fractions of 12% and 3% respectively and a volume ratio of 9∶1, PVA/SA/PA66 nano core-spun yarns with varying shell layers (4, 8, 12, 16) were prepared via nano core-spun yarn technology. These nanofiber core-spun yarns were subjected to chemical crosslinking in a 4% calcium chloride saturated boric acid solution to obtain PVA/SA/PA66 composite hydrogel core-spun yarns. The yarn structure was characterized. Additionally, the droplet penetration rate, core absorption height, and saturated moisture content were tested.

Results The cross-linking of PVA and SA with boric acid and calcium chloride were syudied. The characteristic peaks at 3 306 and 1 336 cm^-1 correspond to the stretching and bending vibrations of —OH in PVA and SA. The characteristic peaks of SA appear at 1 720 and 1 097 cm^-1, correspongding to the antisymmetric stretching vibration of —COOH and the stretching vibration of —C—O—C, respectively. After crosslinking, the four peaks show a significant reduction in strength, and the position of —C—O—C displays an obvious shift(from 1 097 to 1 105 cm^-1), indicating that PVA and SA were crosslinked with boric acid and calcium chloride, respectively. The polarization microscope images reveal the "skin-core" structure of PVA/SA/PA66 composite hydrogel core-spun yarns, with light, transparent skin nanofibers and hydrogels, and dark PA66 filaments as the core. Layer thickness increases with the number of layers, but cross-linked yarns have thinner layers than uncross-linked ones. The scanning electron microscopy images of PVA/SA/PA66 core-spun yarns with different number of layers display that before crosslinking, nanofibers accumulate and interweave with decreasing pores as layers increase. After crosslinking, the "skin-core" structure and nanofiber morphology are maintained, and with the increase of the number of layers, the adhesion and entanglement of nanofibers are more obvious, but they are gel-like, and the nanofibers at the cross section are becoming smoother. Droplet penetration rate and core absorption velocity and height decrease with the number of layers after crosslinking, with 4 > 8 > 12 > 16 layers> PA66 filaments, and this is because as the number of layers increases, the internal structure of the yarns gradually tightens. The saturated moisture content results at 25 ℃ and 90% relative humidity indicate that when the number of layers increases, the gel content of the cortex increases, the hygroscopic capacity of the core-spun yarn increases, and the equilibrium hygroscopic capacity increases. However, after reaching a certain critical value, if the number of layers continues to increase, the exposed hydrophilic groups decrease and the contact probability with water molecules decreases. Thus, the equilibrium moisture absorption decreases. Specifically, the saturated moisture content of PA66 filaments is 0.07 g/g, 4, 8 and 16 layers is 0.23, 0.26 and 0.17 g/g, respectively, while the 12 layers yarn has a saturated moisture content of 0.29 g/g, which can reach 4 times that of the original filaments.

Conclusion The yarns produced by nano core-spun yarn technology exhibit a distinct "skin-core" structure, with effectively regulated and directly proportional thickness of cortical nanofibers and hydrogels. As the layer number increases, the electrostatic spinning nanofibers of PVA/SA/PA66 core-spun yarns accumulate and interweave, reducing pores between nanofibers. After cross-linking, the nanofibers adhered and entangled, binding more tightly and reducing the thickness of the cortex. PVA/SA/PA66 composite hydrogel core-spun yarns with varying layer numbers show differences in morphology, structure, droplet penetration rate, core absorption velocity-height, and saturated moisture content at 25 ℃ and 90% relative humidity. Specifically, droplet penetration rate and core absorption velocity-height decrease with increasing layers, while saturated moisture content peaks at 4 to 16 layers, all higher than that of PA66 filaments. Considering preparation cycle and performance, the 8 layers yarn is optimal. In summary, PVA/SA/PA66 composite hydrogel core-spun yarns exhibit superior hydrophilic hygroscopic properties compared to PA66 filaments, expanding their application range to air-water collection, dehumidification, evaporation, and refrigeration.

Key words: polyamide 66, polyvinyl alcohol, sodium alginate, hydrogel, electrospinning, core-spun yarn, hygroscopic property