Thermal hazard assessment of polyimide synthesis at different viscosities using calorimetry.

The thermal hazard assessment of polyimide (PI) synthesis, including polyamide acid (PAA) and PAA imidization, was investigated owing to its uncontrolled viscosity and heat release. The thermal behavior of PAA with different viscosities investigated using a laboratory-scale setup and auto-reaction calorimetry (SIMULAR). The reaction enthalpy of PAA ranged from − 154.54 to − 156.82 kJ mol⁻¹ as the viscosity increased from 7000 to 104,200 Pa s, indicating that heat release and viscosity increment were two opposite processes during PAA synthesis. The thermal behavior of PAA imidization was investigated using differential scanning calorimeter (DSC). The imidization of PAA was found to be an endothermic reaction with a heat absorption of 105.77 J g⁻¹. Hence, the two-step PI synthesis is an exothermic reaction that concentrates on the synthesis of PAA. Second, the decomposition characteristics of PI in the isothermal mode were analyzed using DSC. The decomposition of PI occurred in the temperature range of 842.89–981.28 K, with a heat release of − 380.07 J g⁻¹. The apparent activation energy of PI, calculated using the Ozawa model, ranged from 179.74 to 308.26 kJ mol⁻¹. Finally, the thermal hazard level of PI was found to be Level 1 based on the Stoessel criticality diagram. This suggests that controlling the dosage can avoid implosion during PI synthesis because an increase in viscosity leads to a higher hazard. [ABSTRACT FROM AUTHOR]