Self-assembled poly(lactic acid) films with high heat resistance and multi-stage thermochromic properties prepared by blown film-annealing

Abstract

Developing reversible thermochromic films that can achieve thermochromism from low to high temperatures by simple processes is a goal which carries a great deal of potential. They have potential applications in temperature monitoring, information encryption and anti-counterfeiting. For this work, decanedioic acid, 1,10-bis(2-benzoylhydrazide) (TMC-300) was used as a self-assembled organic nucleating agent and was combined with an annealing process to heat-resistant modify the blown polylactic acid films. The thermochromic films would have a higher upper limit to its detection range. Through this method, we obtained thermochromic films with a dense morphological structure. Additionally, the effects of TMC-300 and annealing on various properties of films were studied in detail. Unexpectedly, we found a hindering effect between thermochromic microcapsule (TCM) and TMC-300 at TMC-300 mass fractions below 0.3 wt%. Subsequently, TCM with different color changes in different temperature ranges was added. Films with thermochromic color change in the range of 25–70 °C were successfully prepared by this method. The color of the films also demonstrated a multi-stage thermochromic transition through brown, orange, and red before eventually becoming colorless. The results showed the crystallinity of the films rose to 45.65 %, while the heat resistance temperature and elongation at break increased by 60 % and 170 %, respectively. The prepared thermochromic films had enough transparency and even after 60 heating–cooling cycles, they exhibited outstanding thermochromic properties. Moreover, we have explored the application of films in fields of information encryption and temperature monitoring by utilising their multi-stage thermochromic properties.