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In this work, the application of a composite film of polydiacetylenes (PDAs) with poly(vinyl alcohol) (PVA) is reported as an irreversible low-temperature indicator for frozen food and pharmaceutical items. The thermochromic dyes, i.e., functionalized diacetylenes (DAs), were synthesized using the Steglich esterification of 10,12-pentacosadiynoic acid with different aliphatic alcohols (linear and branched chains). The synthesized PDAs show irreversible thermochromic behavior at low temperatures (above 7 °C) because of the lack of intermolecular interactions on the side head groups. Furthermore, composite films are fabricated by incorporating functionalized monomers into the polymer matrix. Monomeric DAs undergo polymerization under UV exposure, forming PDAs within composite films. Different analytical techniques have been used to confirm the formation of the functionalized DA ester moieties. During thermochromic studies, low-temperature color transition (above 7 °C) is achieved by functionalization of head groups with different aliphatic alcohols (linear chain), while in the case of branched-chain head group-functionalized polymers, the thermochromic transition is observed (beyond 25 °C). Additionally, it has been revealed that these PDA-based irreversible low-temperature thermochromic composite films can be used as a warning indicator for packaged food/drug items kept in a frozen environment.
Goyal et al. (Fri,) studied this question.
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