Thermochromic Biopolymer Based on Natural Anthocyanidin Dyes

Abstract

Recently a novel thermochromic poly(lactic acid) (PLA)-composite material was presented. Depending on temperature the incorporated anthocyanidin dye was found to be present either in its neutral or anionic anhydrobase form. A reversible formation of PLA-dye complexes triggered by conformational changes of the polymer backbone was proposed to explain this thermochromic effect. In order to study the influence of the dye structure on the PLA-dye complex formation and on the thermochromic properties of the PLA-composite material a variation of the anthocyanidin dye structure was investigated. The results indicate that a hydroxyl group in 3'-position of the anthocyanidin dye resulting in the presence of adjacent hydroxyl groups is mandatory for the PLA-anthocyanidin dye complex formation and thus for the occurrence of thermochromism.

Thermochromic Polymers—Function by Design

“…Scheme of the thermochromic effect and the proposed mechanism. Reproduced from ref . Copyright 2013 Scientific Research Publishing Inc.…”

“…In a further study variations of the anthocyanidin dye structure were carried out by Lötzsch et al Cyanidin chloride was substituted by either pelargonidin chloride or delphinidin chloride to provide a homologous series with one to three hydroxyl groups on the B-ring of the anthocyanidin dyes (Figure ).…”

Green Thermochromic Materials: A Brief Review

“…Anthocyanidins have been studied as thermochromic natural dyes with the potential to replace commonly used leuco dyes in applications such as textiles, inks, or paints. [46,47,59,79,81] Lötzsch et al investigated how the conformational changes in the polylactic acid (PLA) backbone that informed its interactions of cyinidin chloride such that a reversible, nontoxic thermochromic complex could be formed. [79] The most practical application for thermochromic natural dyes is in irreversible temperature indicators for the development of smart food packaging.…”

Functional Polymers and Polymer–Dye Composites for Food Sensing

“…In the past decades, the use of polymer‐dye composites as a design platform of food sensors has attracted great interest, since this methodology is relatively easy to implement and scale‐up. [ 42,45–54 ] In general, this type of sensor could be fabricated through immobilization of dyes into a polymer matrix through either physical blending or covalent chemical bonding. Compared to covalent bonding, the physical blending often encounters the problem of dye leaching from the polymer matrix, which may lead to decreased sensing sensitivity and potential food contamination.…”