A self-healing and recyclable polyurethane composite film for durable pH responsive coating

Abstract

Wearable pH sensors can offer a visual warning signal of pH changes, making them particularly attractive in health monitoring and environmental detection. However, the fabrication of durable wearable pH sensors remains challenging due to the inevitable damage that sensors suffer in practical applications. Here, a durable pH responsive coating fabric with outstanding self-healing and recyclable capabilities is prepared with a composite film composed of a dynamic boroxine-polyurethane (BPU) and a pH responsive Congo red-based polymeric dye (CRPD). The BPU/CRPD composite film exhibits a high tensile strength of 17.46 MPa, breaking elongation of 407 %, toughness of 31.61 MJ/m3, Young’s modulus of 11.78 MPa, and outstanding elastic restorability. The high reversibility of boroxines and hydrogen bonds enable the composite film with healing efficiency of 87 % at 70 °C for 2 h and recycling efficiency of 97 % under 3 MPa at 80 °C for 5 min. In addition, the BPU/CRPD coated fabric presents outstanding pH responsive property and color fastness. Importantly, the scratched coating fabric can be easily healed at 70 °C, 5 MPa for 5 min or using an electric iron. Furthermore, the BPU/CRPD coatings on the discarded fabric can be recycled and reused many times with similar pH responsive behavior. The outstanding fastness, self-healing and recycling properties promote the durability of the pH responsive coating. This work provides a meaningful strategy for developing durable pH responsive coating fabrics with self-healing and recycling capabilities that will be promising for wearable pH sensors.