Design and development of electrically conducting textile sensors for smart textiles and apparel

The thesis presents a systematic study of sensing behaviour of the polypyrrole (PPy)-coated textile materials for large strain sensing purposes. This research is aimed at creating a conducting textile with superior sensing performance including low electrical resistance, high strain sensitivity and good environmental stability. It is also aimed to provide better understanding of the strain sensing mechanism and interaction between the PPy coating and textile substrate. The study covers five related aspects, namely (1) fabrication techniques of the PPy-coated fabrics, (2) sensing performance of the PPy-coated fabrics with various stabilisation treatments, (3) characterisation of the PPy-coated fabrics fabricated under extremely low polymerisation temperature, (4) sensing mechanism of the PPy-coated fabrics and (5) product development using the newly developed flexible fabric strain sensors.; Fabrication techniques including (1) screen printing followed by chemical vapour deposition and (2) padding followed by chemical vapour deposition have been further developed in this project. The chemical vapour deposition method can produce thinner, denser and uniformly distributed PPy coating layer on the textile substrate thereby enhancing the sensing performance.; The study of the PPy-coated fabrics and pure PPy powders with different stabilisation treatments reveals that all the treatment methods can improve thermal stability, PPy chain ordering, surface smoothness and fabric hydrophobicity, resulting in enhancing the environmental stability as well as strain sensitivity. The most promising fabrication process with stabilisation treatments has been identified for producing high sensing capacity.; Electrically conductive fabrics prepared by the chemical vapour deposition process under extremely low polymerisation temperature (<-20°C) exhibit excellent strain sensitivity factor of over 400 at a strain of 50%. It is found that low temperature polymerisation produces smaller particle size of PPy with thinner, denser and smoother PPy coating on textile substrate which is beneficial to the sensing performance.; The present research discovers that the excellent strain sensing behaviour of the PPy-coated Tactel/Lycra knitted fabrics are mainly attributed to the high performance of the PPy-coated PU yarn as well as the excellent property of the knitted fabric structure. In-situ scanning electron microscopy observation demonstrates the crackopening and crack-closing mechanism on the fibre surface.