Electrospinning of continuous nanofiber hollow yarns for thermal storage and insulation by a multi-step twisting method

In this study, phase change nanofiber hollow yarns were designed. The hollow yarn structure is proposed due to its ability to provide insulation for fabrics, while the phase change material is added due to its capacity to store thermal energy. These yarns are developed by utilizing the classical covering–dissolving strategy, which uses a modified multi-step twisting method. The effects of twisting and winding speed on the yarn morphology, structure, mechanical and heat storage properties are discussed. It is observed that the ultrafine fibers for yarn fabrication are about 100–400 nm in diameter. Their yarn products then undergo obvious shape deformation in the process of hollowing, resulting in a nanofiber hollow yarn with yarn diameter of around 250 µm. To obtain target yarns with desirable structure and strength, the recommended twisting and winding speed should be within 200–260 rpm and 1.2–1.6 rpm, respectively. Their tensile strength and elongation at break under these conditions are tested to be about 30–40 MPa and 20%, respectively, which is acceptable for further weaving. As for the heat storage capacity, it is somewhat weakened but still considerable (20–30 kJ·kg–1) within the temperature range of 30–40℃. By coupling air and phase change materials together, the resultant nanofiber hollow yarns and their fabric products proved to have better heat storage and insulation performance, and may have broad prospects for thermal regulation.

Preparation and fuzzy evaluation of wool hollow yarn

Wool hollow yarn not only has the characteristics of being skin-friendly and warm, it also has good air and moisture permeability; thus, it has great development potential. Here, we first show that the water-soluble (polyvinyl alcohol (PVA)) fiber ratio in core-spun yarn should not exceed 30%; to ensure smooth spinning, a core yarn linear density of 3.4–5.6 tex was selected by theoretical analysis. Second, using rabbit hair fiber with tencel fiber, which has high tenacity, as an environmentally friendly blended outsourcing fiber, and water-soluble (PVA) fiber for the core yarn, we prepared five types of core-spun yarns. Water-soluble (PVA) fiber was removed in 20 min to prepare wool hollow yarn using room temperature water. Finally, properties of the wool hollow yarn produced, such as breaking strength, breaking elongation, evenness of CV (coefficient of variation) value, >3 mm hairiness index, and deviation from linear density after removing PVA, were tested and analyzed, and evaluated comprehensively by means of fuzzy mathematics. The results showed that the hairiness of wool hollow yarn was improved, the mechanical properties and evenness of sliver and hairiness were decreased, and the overall properties of hollow yarns with a core yarn content of 25% were the best.