Thermal behavior of UV-cured acrylated waste cooking oil coatings: comparative effects of curing time and photoinitiator systems

This study investigates the thermal behavior of UV-LED-cured acrylated waste cooking oil (AWCO) coatings, analyzing the effects of curing time (5, 10, 15, and 20 minutes) on crosslinking and stability. Coatings were polymerized under a 365-nm UV-LED using free radical and cationic photoinitiators. Thermogravimetric analysis (TGA) revealed distinct degradation profiles: the free radical system achieved peak initial decomposition at 362.2 °C (10 min), while ash content peaked at 6.0% (15 min), indicating optimal crosslinking at intermediate times. In contrast, the cationic system exhibited superior thermal stability (initial decomposition: 386.3 °C at 5 min) and progressive ash content increase (5.8% at 20 min), attributed to its oxygen-insensitive living polymerization. Differential scanning calorimetry (DSC) confirmed complete curing within 5 minutes for cationic systems, evidenced by the disappearance of exothermic monomer peaks. These results demonstrate that 10-minute UV-LED curing optimizes free radical coatings, whereas 5 minutes suffice for cationic systems, balancing efficiency and thermal performance. The study highlights the critical role of photoinitiator chemistry and curing duration in upcycling waste oils into robust coatings.