Innovative method of pure cotton core–shell yarn achieving both softness and high strength

Low-twist cotton yarn is considered a highly promising and environmentally friendly, close-fitting textile, attributed to its softness and skin compatibility. However, relatively low strength has significantly hindered the broader application of low-twist cotton yarn. To achieve low-twist yarn with high enough strength, this paper presents the design of a novel type of core–shell yarn: skeleton yarn. The core structure of the 64.7 tex skeleton yarn consists of a 19.4 tex ring-spun pure cotton single yarn, while the shell comprises a double cotton roving layer. This study investigates the effect of the twist factor ( {α}_t ) of the core yarn on the structure and properties of the skeleton yarn. The mechanism underlying the influence of twist distribution between the core and shell layers on the movement trajectory of the core yarn is elucidated. The variation in diameter, shape, softness, and tensile properties of the skeleton yarn is studied across different twist factors of the core yarn (350–600). The corresponding prediction functions are established, and a comprehensive performance evaluation is carried out. The results reveal that when the twist factor of core–shell yarn is 400/450, the shell layer twist is only 298 T/10 cm, bending rigidity is 0.4 × 10 ⁻⁶ cN·cm ² /cm, breaking strength is as high as 17.37 cN/tex, and the elongation is up to 8.8%. These findings demonstrate that the skeleton yarn structure can effectively balance the need for softness and strength, ensuring improved skin affinity for subsequent textile applications.