Purpose This paper aims to study the colour stability of chlorophyll and the effect of copper (II) nitrate – Cu(NO3)2 – as an additive in natural dye coating films after being exposed to ultraviolet-A (UV-A). Design/methodology/approach The natural dye was extracted from the leaves of Cassia alata L. using absolute ethanol as the solvent. The extract was divided into two parts and, one of it was added with 3 wt.% Cu(NO3)2 as an additive. The polymer blend of poly(methyl methacrylate) (PMMA) and acrylic polyol was used as the coating binder. Both parts of the dye with and without additive were mixed with the blended polymer in a specific ratio. The resulted mixtures were applied as coating films on glass substrates. The colour stability of the coating films on exposure to UV-A with the time of exposure was observed with Commission internationale de l’éclairage (CIE) L*a*b* colour coordinates. The hidden power by the means of reflectivity and glossiness of the coatings was also studied. Statistical standard deviation (STD) was used to analyse the data. Findings The test showed that the coating films containing Cu(NO3)2 had smaller colour differences, (ΔE*) indicating higher colour stability. The analysis on hidden power also showed that the coating film with Cu(NO3)2 was 1.6 times more stable than the film without additive. All the measurements in this study were observed within 35 days of duration. Research limitations/implications This paper implies the potential of using natural dye extracted from Cassia alata L. leaves as a stable dye colourant for coating applications. Practical implications The coating film developed in this study is suitable for glass substrate applications. Originality/value A new method of preparing solvent-based coating film from PMMA–acrylic polyol with chlorophyll colourant is introduced in this study.

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Purpose-The purpose of this paper is to observe the colour and thermal stability of natural red dye consisting of anthocyanin with addition of different aqueous acids and applied as coating films. Design/methodology/approach-The natural red dye was extracted from Hibiscus sabdariffa L. (roselle) flowers and mixed with 1 per cent hydrochloric acid, 5 per cent acetic acid, 5 per cent citric acid and 5 per cent oxalic acid. All the dye samples were exposed to heat and UV-B to observe the colour stability by calculating the half-life and rate of reaction. In coating film application, each of the dye samples was mixed with 25 wt% of poly(vinyl alcohol) (PVA) and applied on to a glass substrate. The coating samples' colour stability was observed by using CIE L ‫ء‬ a ‫ء‬ b ‫ء‬ colour space coordinates. The coating films' weight loss stability against temperature was observed by using thermogravimetric analysis. Findings-Addition of hydrochloric acid enhances the thermal and UV stability of the anthocyanin natural dye. This can be observed from the calculation of the half-life of the dye. The half-life values for the thermal and UV stability studies were 1,155 hours and 210 hours, respectively. In coating films, the sample with addition of acetic acid showed the highest colour stability with colour difference (⌬E ‫ء‬) value 8.95. Research limitations/implications-The coating films developed in this work are not suitable to be applied on metal substrates due to the presence of water, which can contribute to the corrosion formation. Practical implications-The coating films developed in this work are suitable for washable coating application. In other words, they are non-permanent coatings applied on a glass substrate. Originality/value-Development of water-based coatings from PVA binder with anthocyanin colourant is introduced in this study.

Purpose The purpose of this paper is to study the colour stability and water content resistivity of the green colour coating paint film (consisting of chlorophyll) during exposure to ultraviolet A (UV-A). Design/methodology/approach The natural green dye was prepared by immersing Cassia alata L. leaves in absolute ethanol. The extract was prepared in two batches of dye samples where one of it was a pure dye and the other was added with 3 Wt. % Cu(NO3)2 as an additive. Polymer blend as a binder was prepared by mixing poly(methyl methacrylate) (PMMA) and commercial acrylic polyol. The blended polymer was mixed with the natural dye in a specific ratio and applied as coating paint film on glass panel surfaces. The visible spectrum stability (colour stability) and water content resistivity of the coating paint films during exposure to UV-A were monitored. Findings Addition of Cu(NO3)2 had improved the colour stability of the coating paint film. Fourier transform infrared spectroscopy analysis showed that both coating paint films do not absorb water and are resistive to water content. Research limitations/implications The ability of Cu(NO3)2 as an colour stability additive to the natural green dye applied in the coating paint film. Practical implications The coating paint film developed in this work is suitable to be applied on glass substrates. Originality/value The colour stability of the coating paint film was analysed by using the reflectance spectrum.

Purpose-The purpose of this paper is to observe the thermal and colour stabilities of coating films consisting of natural dye anthocyanin colourant with acid and nitrate salt as additives. Design/methodology/approach-The natural dye was extracted from Hibiscus sabdariffa L. (Roselle) by using distilled water as solvent. The extracted dye was mixed with 1 weight per cent hydrochloric acid and 5 weight per cent calcium nitrate to conduct the comparison study. The dye samples were than mixed with poly (vinyl alcohol) (PVA). The mixtures were applied on glass panels to form coating films. The coating films were left to dry for 24 hours. The thermal stability of coating films was investigated by using thermogravimetric analysis (TGA). The amorphousness coating films molecular structures were observed by using x-ray diffraction (XRD). CIE L ‫ء‬ a ‫ء‬ b ‫ء‬ colour coordinate space technique was used to investigate the coating films colour stability against ultraviolet (UV). Findings-The results show that addition of hydrochloric acid (HCl acid) enhanced thermal stability of PVA-anthocyanin coating and shifted the degradation temperature to higher temperature at 300°C. HCl acid also improved UV stability of the coating system significantly with the reduced ⌬E from 26.67 to 16.89. Addition of calcium nitrate (Ca(NO 3) 2) salt promotes good interaction with PVA-anthocyanin system that caused structural changes, improved thermal stability and increased T g from 61.5 to 83.1°C. Research limitations/implications-The potential of using natural dye extracted from plant as renewable material. Practical implications-The coating films developed in this works are suitable for glass substrate application. Originality/value-Development of water-based coating from PVA binder with anthocyanin colourant is introduced in this study.