Kaifang Xie

With the advancement of flexible electronic textiles, electronic braided cords have garnered significant attention in smart wearable fields by integrating electronic functionalities while preserving textile characteristics such as softness, breathability, and comfort. However, their electrical conductivity suffers varying degrees of degradation under mechanical conditions including friction, stretching, and flexure. This study employed polyester braided cord as a substrate and optimized the preparation of polypyrrole (PPy)-modified braided cord through in situ polymerization combined with orthogonal experimental design. The degradation mechanisms of conductivity under different mechanical conditions were systematically investigated. Experimental results demonstrate that the optimal conductivity (63 S·m ⁻¹ ) was achieved when the pyrrole monomer concentration, FeCl₃·6H₂O concentration, pre-immersion time, and polymerization time were set to 0.2, 0.2 mol·L ⁻¹ , 4 h, and 9 h, respectively. Although external forces can damage PPy conductive pathways on the cord surface, leading to conductivity loss, the modified cord exhibits excellent friction resistance, stretch tolerance, flexural durability, and stable conductivity under low-load conditions. This research provides critical scientific insights for prolonging the service life of electronic braided cords and their integrated smart textiles.

Smart textiles have a wide range of applications in all walks of life. Wearable sensors have become the main research hotspot due to their excellent performance in both perception and response. In this paper, polyvinylidene fluoride (PVDF) was used as the raw material to fabricate continuous fiber via melt spinning method, and β-phase crystal PVDF fiber was obtained at a melting temperature of 230°C and draft ratio of 5. The plain weave fabric of PVDF fiber was dipped into hot dimethyl silicone oil for thermal polarization treatment. When the plate was at a distance of 4 mm, the polarization temperature was 90°C and the polarization voltage was 9 kV, the PVDF had the best polarization property. After polarization, the PVDF fabric showed a good piezoelectric response and a PVDF flexible sensor could be applied to chemical fiber and natural fibers fabrics, in human health monitoring equipment in contact with close-fitting clothing or in home textile products for intelligent alarm systems.

In this article, water-based polyurethane (PU) with different concentrations and partial alcoholysis polyvinyl alcohol (PVA) were used to coat polyester (PET) harness cord in turn. The surface and mechanical properties of harness cord before and after coating were evaluated by performing the tests of dynamic contact angle, morphology observation, bending properties, tensile properties, and wearability. It was found that the surface properties of 1.5% PU-coated harness cord tended to be stable, and the mechanical properties of PU(1.5%)/PVA-coated harness cord were optimal. Compared with PVA-coated harness cord, the wearability of PU(1.5%)/PVA-coated harness cord showed a great increment up to 135.7%. This was because the PU coating effectively improved the interfacial properties between the PVA coating and the hydrophobic PET fibers and enhanced the adhesion of the PVA coating to the PET fibers.

Kapok fiber is a natural hollow fiber that has superior biocompatibility and biodegradability and is naturally antibacterial. Because of its unique properties, it has great potential in the application of postoperative repair dressings. The wettability and micro-equilibrium of kapok fibers play a critical role in dressing applications. In this study, the critical adhesion volume and adhesion energy of essence liquid to alkali-treated kapok fiber (AKF) were quantitatively calculated to explore the wettability and micro-equilibrium through the equilibrium wetting theory. Meanwhile, the three-phase contact line (TCL) structure was described. The results showed that the critical adhesion volumes of the three types of essence liquid for AKF were 3.45, 3.81, and 4.12 μL, respectively. Moreover, the critical volumes and low error rates derived from the equilibrium wetting theory were 3.41 μL and 1.16%, 3.99 μL and 4.51%, and 4.60 μL and 10.43%, respectively. Therefore, the critical volume of adhesion could be well calculated by the theoretical model. The average adhesive energies of essence liquid to the AKF were 0.38, 0.45, and 0.56 J, respectively, caused by the difference in liquids properties. The TCL showed a mechanical lock and bonding points at both ends because of the curvature difference and higher surface energy. These results are proposed to inspire the design of a liquid carrier of kapok fibers based on the fiber network structure.

The heat transmission through a fabric during the measurement of thermal resistance was simulated by a novel heterogeneous model that was constructed according to the structure of ThermolabII Tester KES-F7. In this model, the heat transmissions along the longitudinal and transverse directions of yarn were treated independently. The material constants of fabrics, such as mass density, specific heat, thermal conductivity and thickness, were used as parameters for simulation in this fabric model. The validity of this model was then confirmed by the high consistency between the heat flux obtained from experiment and simulation, with the average difference ratio lower than 5%. The simulation results suggested that the guard area could effectively reduce the horizontal heat leakage from the test plate when the experimental fabric was thin. Only less than 8% of heat leaked in the one-layer case, while the leakage was significantly aggravated when more layers of fabric were stacked, resulting in the considerably lower thermal insulation achieved in both experiment and simulation compared with that in real fabrics. The temperature distribution in the model also implied that the longitudinal and transverse thermal conductivity of yarn exerted great effect on the heat leakage during the measurement. Moreover, for multilayers consisting of different fabrics, the laying sequence could obviously influence the heat leakage and, consequently, change the obtained thermal resistance.

In this article, the harness cords were manufactured by braiding, coating and heat setting at the temperatures of 130 and 195℃, respectively. The film formers used in coating process were poly(butyl acrylate), copolymer size and partial alcoholysis polyvinyl alcohol. The pure film formers' spectra were obtained using in-situ infrared test method on a spectrometer. The scanning electron microscope, bending tester and wearing test device were used to measure the morphology, bending rigidity and wearability of harness cords, respectively. The results showed that the temperature of heat setting changed the molecular structure of coatings, and different influences of temperature on the bending rigidity and wearability of coated harness cords were observed. When the heat setting temperature rose from 130 to 195℃, the bending rigidity of poly(butyl acrylate)-coated harness cord almost kept constant. However, the bending rigidity of copolymer size and polyvinyl alcohol-coated harness cords increased by 33.1% and decreased by 47.4%, respectively. The poly(butyl acrylate) coating presented the best adhesivity to hydrophobic polyester harness cord, and the coated harness cord showed the best uniformity and flexibility as well as higher wearability. After heat setting at 195℃, the wearability of harness cords coated with poly(butyl acrylate), copolymer size and polyvinyl alcohol was increased by 380, 120 and 585%, respectively, when compared with the uncoated one.

The wearability of braided harness cord was studied by measuring the tensile properties of worn ones with a universal electronic strength tester and wearing test device developed in our laboratory. The abrasion mechanism of harness cord was investigated, and the fractured schematic diagram was proposed according to the morphology observed by a hand USB microscope and scanning electron microscope. The results indicated the abrasive action could significantly reduce the tensile properties of harness cord, and a negative linear correlation between the tensile properties and the abrasive times was observed. The morphology suggested the fractured process of harness cord could be divided into five stages: surface abrasion of sheath fibers, partial breakage of sheath fibers, structure failure, full breakage of sheath fibers, and breakage of core fibers. In addition, the fibers in harness cord presented different fracture types due to the combined effect of external friction, bending, stretching, and fatigue during the wearability test.