Screen-printed stretchable knitted textile electrodes based on Bio-PTT/PET bicomponent yarns for E-textile applications

Knitted fabrics composed of bio-poly(trimethylene terephthalate)/polyethylene terephthalate (bio-PTT/PET) bicomponent yarns are introduced as sustainable substrates for screen-printed stretchable electrodes. These yarns exhibit inherent stretchability owing to their latent crimps, which provide a structural deformation mechanism distinct from the elastomeric behavior of conventional polyurethane (PU)-based substrates. A systematic investigation of the number of printing passes revealed that three passes yielded optimal performance, enabling the formation of a continuous conductive layer, maintaining electrical stability under repeated strains, and minimizing mechanical degradation. Exceeding this threshold resulted in excessive ink accumulation, as indicated by a 62.4% increase in ink thickness at the fourth pass, which corresponded to significant reductions in tensile strength and flexural rigidity. The optimized electrodes demonstrated superior durability compared with the PU-based counterparts, maintaining a surface resistance of 11.5 Ω/m² after five washing cycles, whereas that of PU electrodes increased to 20.7 Ω/m². Electrical conductivity was preserved under repeated stretching and laundering, enabling reliable surface electromyography (sEMG) monitoring. Clear muscle-activity signals and stable resting baselines were obtained, with root mean square (RMS) values comparable to those of Ag/AgCl gel electrodes and a signal-to-noise ratio of 22.1 dB, confirming sufficient signal quality for practical biosignal interpretation. These findings reveal the potential of bio-PTT/PET bicomponent yarns as robust and sustainable substrates for knitted stretchable electrodes, supporting reliable applications in biosignal monitoring, wearable electronics, and adaptive smart textiles. Moreover, this study provides a foundation for extending this approach to other latent-crimp fiber substrates, broadening the range of viable materials for sustainable and durable smart textiles.