High-Resolution Thermogravimetric Analysis Is Required for Evaluating the Thermal Stability of Deep Eutectic Solvents

Deep eutectic solvents (DESs) might be used at an elevated temperature; thus, their thermal stability is essential for the high-temperature applications. Thermogravimetric analysis (TGA) is the most widely used technique to characterize thermal stability of DESs. The temperature rise rate could be used to regulate the quality of TGA. DESs might undergo several steps of decomposition and/or evaporation with these processes and usually overlap with time and temperature increase; therefore, it is hard to get subtle information on the decomposition at a rapid heating rate. However, a slow heating rate might cause significant alternation of the composition of DESs because DESs are mixtures of a hydrogen bond donor and hydrogen bond acceptor with different decomposition and/or evaporation rates. High-resolution TGA (HR-TGA) is required for evaluating the thermal stability of DESs. It could provide a better resolution than both the slow heating rate and fast heating rate. In this paper, we used the HR-TGA method to analyze the processes of DES decomposition. By optimizing the resolution of the stability analysis and its influence on the kinetic parameters, the performance of HR-TGA is visibly better than that of the traditional TGA. Moreover, HR-TGA-MS experiments were performed for obtaining decomposition mechanism information. This work provides new information on the thermal decomposition of DES, which is helpful for gaining insights on DES and application of DES in industry. In conclusion, HR-TGA is absolutely necessary to replace the conventional TGA for evaluating the thermal stability of DESs.