Modified chitosan as a multi-functional material in eco-friendly formulation for anti-counterfeit applications

Renewable resources and waste materials can be used as viable raw materials to prepare security formulations devoid of volatile organic compounds and would essentially offer environmental protection. Therefore, chitosan (deacetylated chitin), which is a marine waste material is modified through simultaneous N-conjugation with pyrene-1-carboxaldehyde (PCA) as an aggregation caused quenching fluorophore and fluorene-2-carboxaldehyde (FCA) to obtain a smart fluorescent chitosan-based Schiff base (FCSSB). The covalent attachment could immobilize pyrene onto the chitosan, and the subsequent diluting effect of the biopolymer framework could hinder the aggregation of pyrene and, thereby, the self-quenching of fluorescence. The modified FCSSB could serve as a multi-functional material; both as a binder and a fluorophore in an eco-friendly formulation using aqueous acetic acid as the mild solvent and glycerol as the viscosity regulator. The formulation is used as a security ink to obtain single/multilayer coating/s and further prints using flexography technique. The prints that appeared invisible in daylight exhibited a blue fluorescence under 370 nm UV illumination. Moreover, the ink film presented good rub resistance and colour stability after different cycles of UV exposure. Therefore, FCSSB formulation can be readily utilized as a security ink for information decryption and could also be processed into products of diverse forms, including ink pads, coatings, printed patterns, and films. This simple, but effective approach provides additional impetus to real-life applications of biopolymers from natural/waste materials in anti-counterfeiting.