Development of Reusable Halochromic Textile with a Multi-pH Transition Range

Halochromic textiles are one form of halochromic materials that can be applied as a pH indicator to indicate the change in pH by changing colors. In this research project, halochromic textile was developed by surface functionalization of cotton fibers with a mixture of phenolphthalein (PP) and p-nitrophenol (p-NP) in order to provide a muti-pH transition range. The PP and p-NP molecules were covalently immobilized on cotton fabrics via a phenol-formaldehyde-based reaction. The successful dye immobilization was confirmed by ATR-FTIR spectroscopy. By varying several reaction parameters, an optimum reaction condition that provided the clear color change of the halochromic cotton fabrics was determined. At this reaction condition, the halochromic cotton fabrics exhibited off-white color at pH lower than 6, slightly yellow at pH 6-7, yellow at pH 8, orangish pink at pH 9, and pink at pH 10-12. In addition, the color reversibility of the halochromic cotton fabrics and the dye leaching were also investigated. The halochromic cotton fabrics after pH response test exhibited the color reversibility when they were washed by DI water. The halochromic dyes did not leach from the halochromic cotton fabrics when immersed in buffer solutions with pH 8, 10 and 12 for 15 days, suggesting that the developed halochromic cotton fabrics are reusable.