A ternary composite based on polystyrene sulphonic acid, organic dye and hygroscopic inorganic salt for cobalt-free humidity indicating agent

Abstract The composites of polystyrene sulphonic acid (PSS) with various organic dyes were coated on a polyethylene terephthalate (PET) film. The coated film exhibited colour change depending on humidity. The composite of PSS with Neutral Red showed colour change from blue (low humidity) to pink (high humidity) in a similar way to that of conventional cobalt-based humidity indicator. The change of colour was evaluated using L*a*b* coordinates and the results revealed that the composite of PSS with brilliant blue FCF gave the most distinct colour change. Further, addition of hygroscopic inorganic salt such as magnesium chloride was found to be effective in tuning humidity range.

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