Durable and washable sheath/core-type polyamide 6-RhYK/PP colorimetric bicomponent fiber as reversible hydrogen chloride (HCl) gas sensor

Fiber-based colorimetric sensors for hydrogen chloride (HCl) gas detection are advantageous due to their convenience, distinct visual warning, low cost, and electric power-free operation. Application of these sensors to textiles, such as clothes or gloves, requires consideration of sensing performance and durability, including long-term reusability, washing, and weather resistance. In this study, a colorimetric sheath/core (S/C)-type polyamide 6 (PA6)-RhYK/polypropylene (PP) bicomponent fiber is fabricated for HCl gas detection using a melt-spinning process without any dyeing or printing. The gas sensing performance of the produced fibers with various colorant concentrations and fiber drawing ratios is investigated by exposure to HCl gas (1–100 ppm). The durability of the knitted fabric containing the fiber is demonstrated through washing, cycling, and weather resistance tests. Additionally, an RGB sensor-type portable smart device is constructed using our fiber sensor as the target material. This sensor continuously detects changes in fiber color due to exposure to HCl gas and sounds an alarm when a specific value range is reached, thereby improving risk awareness in dark environments. These results confirm the applicability of the colorimetric fiber-based sensor to clothing and prove that this is a useful method for detecting harmful gases in industrial sites and daily life.