Tartrazine-Intercalated Zn–Al Layered Double Hydroxide as a Pigment for Gel Nail Polish: Synthesis and Characterisation

In the modern world, nail polish, gel polish, in particular, is one of the most commonly used cosmetics. The pigment is a component of gel polish, which determines the toxicity and color of the composition. Zn-Al layered double hydroxides intercalated with food dyes are promising pigments to be used for gel nail polish. Characteristics of Trartazine- intercalated Zn–Al (Zn:Al=4:1 and Zn:Al=4:1) hydroxide prepared at рН=8 and рН=11 have been studied. The crystal structure of the prepared samples has been studied by means of X-ray diffraction analysis and thermogravimetry, pigment properties – by measuring and calculating the color characteristics in CIELab and XYZ. The color characteristics of gel nail polish samples prepared with the synthesized pigments have been studied in the same way. The results of XRD analysis and thermogravimetry revealed that Zn-Al-Tartrazine hydroxide synthesized at Zn:Al=4:1 is a layered double hydroxide with the α-Zn(OH) 2 structure. At рН=8, LDH with low crystallinity is formed, and at рН=11 crystallinity increases. It was discovered that Zn-Al LDH breaks down to ZnO during synthesis at рН=11. As a result, Zn–Al– Tartrazine hydroxide (Zn:Al=4:1), synthesized at pH=11, contains both LDH and ZnO. For Zn–Al–Tartrazine hydroxide (Zn:Al=2:1), synthesized at pH=11, an almost complete breakdown of LDH was observed. It was found that the most promising for the preparation of gel nail polish are Zn-Al-Tartrazine hydroxide synthesized at рН=8. These pigments have an orange color (color tone 596–601 nm) with high monochromaticity (pigment color purity 60–65 %, color purity of gel nail polish 70–75 %). It is proposed that the breakdown of Zn-Al LDH to ZnO, discovered at higher pН can be exploited to prepare pigments with improved grindability