Twist-controlled conductive bicomponent yarns: internal structure and properties analyzed by X-ray computed tomography

Conductive bicomponent yarns suitable for apparel manufacturing were fabricated under various twisting conditions, and the correlation between their internal structures and electrical properties was systematically investigated. Three types of conductive bicomponent yarns with identical linear densities were prepared by varying the combinations of first- and second-twist levels using PET yarn and Ag-coated polyamide filaments. Their mechanical, morphological, and electrical properties were evaluated, and non-destructive X-ray computed tomography (X-ray CT) was used to analyze the three-dimensional internal fiber assemblies. X-ray CT analysis revealed pronounced differences in packing density, helical structure, and turn length depending on the twist combination and sequence. Bicomponent yarns with higher internal packing density and shorter turn length exhibited increased inter-filament contact, resulting in a significant reduction in linear resistance. In particular, the PET-AP70/PET-AP70 structure exhibited the densest internal configuration and the lowest electrical resistance with minimal variation. This paper for the first time, quantitatively establishes a structure–property relationship between twist-induced internal architecture and electrical performance in conductive bicomponent yarns using X-ray CT. The findings provide design guidelines for durable and reliable smart textile applications.