Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Thermochromic film for cold chain monitoring.

ABSTRACT
This study reports the fabrication of thermochromic polylactic acid (PLA) composites incorporating black thermochromic pigments (TCB) and polyethylene glycol (PEG) plasticizers of different molecular weights (1400, 2250, and 6000) through melt blending. The composites were evaluated for their colorimetric response within the temperature range of −10°C to 50°C, reproducibility across heating/cooling cycles, and stability under thermal aging. Their mechanical and thermal properties were characterized using tensile testing, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results showed that PEG molecular weight influenced both thermochromic behavior and material performance. PLA/PEG6000/TCB exhibited a clear and uniform color change, reaching a ΔE of 32.1 at 50°C. The thermochromic response was rapid upon heating, reversible across cycles, and only slightly affected by thermal aging. Mechanical testing indicated an increase in ductility, with elongation at break rising by up to 242% as PEG molecular weight increased, while tensile strength and modulus decreased. PEG1400 and PEG2250 promoted crystallinity, whereas PEG6000 produced amorphous blends. Thermal stability declined with increasing PEG molecular weight, attributed to phase separation. These findings demonstrate that adjusting PEG molecular weight is a practical approach to designing biodegradable, reusable thermochromic sensors for smart packaging and cold-chain monitoring.