Polyvinyl alcohol/methyl orange flexible film as reusable pH indicator

Abstract

Methyl orange (MO) is a synthetic organic semiconductor, which is frequently used as pH indicator in food & beverages, pharmaceuticals, wastewater treatment, laboratory experimentation, agriculture and healthcare etc . It is a toxic and mutagenic substance. This azo dye is very difficult to decompose by common treatment methods and thereby causing environment pollution and health problems. To overcome this problem, a reusable pH indicator flexible film is prepared by the blending of polyvinyl alcohol (PVA) with MO using water as solvent at 100 °C. PVA is a synthetic non-toxic biodegradable polymer with good solution processability in water and it contains hydroxy functional groups. The intermolecular hydrogen bonding exists between PVA and MO will prevent the macro-phase separation of this new polymeric material. All polymeric materials showed good absorbance in the UV–Vis region of the electromagnetic spectrum and intensity of absorption increases with increase in the amount of MO in the polymer matrix. The pH indicating property of polymer film is studied by dipping the film in different acids and bases. It showed red colour in acid solution and orange-yellow in base solution. The absorption spectrum of PVA/MO film in 0.1 N HCl solution showed bathochromic shift of ∼ 42 nm than that measured in water solution due to the existence of MO in two different forms namely benzenoid and quinonoid form. The flexibility and reusability of this novel material will make it excellent pH indicator in many industrial and laboratory applications.