Preparation of novel authentication film by screen-printing of anthocyanin biomolecular extract: Thermochromism and vapochromism.

Novel thermochromic and vapochromic paper substrates were prepared via screen-printing with anthocyanin extract in the presence of ferrous sulphate mordant, resulting in multi-stimuli responsive colorimetric paper sheets. Environmentally-friendly anthocyanin extract was obtained from red-cabbage (Brassica oleracea var. capitata L.) to function as spectroscopic probe in coordination with ferrous sulphate mordant. Pink anthocyanin/resin nanocomposite films immobilized onto paper surface were developed by well-dispersion of anthocyanin extract as a colorimetric probe in a binding agent without agglomeration. As demonstrated by CIE colorimetric studies, the pink (λ max = 418 nm) film deposited onto paper surface turns greenish-yellow (λ max = 552 nm) upon heating from 25 °C to 75 °C, demonstrating new thermochromic film for anticounterfeiting applications. The thermochromic effects were investigated at different concentrations of the anthocyanin extract. Upon exposure to NH 3(g) , the color of the anthocyanin-printed sheets changes rapidly from pink to greenish-yellow, and then immediately returns to pink after taking the gaseous ammonia stimulus away, demonstrating vapochromic effect. The current sensor strip showed a detection limit for NH 3(aq) in the range of 50-300 ppm. Both thermochromism and vapochromism showed high reversibility without fatigue. In addition to studying the rheological properties of the prepared composites, the morphological and mechanical properties of the printed cellulose substrates were also studied.