Reusable flexible halochromic cellulose-based composite tape for visual alkaline leaking point detection: Preparation and property testing

In this study, we focused on developing flexible halochromic cellulose-based composite tape that is reusable and environmentally friendly for alkaline leaking point detection. Phenolphthalein derivative containing hydroxymethyl groups (PP-OH) was synthesized from phenolphthalein (PP), paraformaldehyde (PFA), and ethanolamine (ETA) via Mannich reaction, and then used as a halochromic dye. The chemical structure of PP-OH was confirmed by ¹H-NMR spectroscopy. In the flexible halochromic composite tape fabrication, PP-OH, poly(vinyl alcohol) (PVA), and glutaraldehyde (GA) as a crosslinker were mixed and coated on Whatman qualitative filter paper grade 42 via solution casting at 90 °C for 4 h. The reaction variables including the amount of PP-OH (0.1, 0.5, and 1 wt.% of PVA) and the molar ratio of PP-OH:GA (1:10, 1:20, and 1:30) were studied in order to find an optimum reaction condition that achieves the desired appearance and properties of the developed flexible halochromic composite tape. The properties of the flexible halochromic composite tape such as pH transition range, mechanical properties, color reversibility, and halochromic dye leaching were investigated. In addition, the flexible halochromic composite tape was subjected to test under the simulated conditions by applying it to detect the leaking point of alkaline substances in the form of aqueous solution and vapor. The results of the halochromic dye leaching and color reversibility of the flexible halochromic tape could reflect its reusability property. Therefore, the developed flexible halochromic composite tape has a potential for detecting the leaking points on pipelines in industrial plants and is also reusable.