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

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 degrees 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.