Thermal behavior and polymorphism of the antioxidants: BHA, BHT and TBHQ

Thermal behavior of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and tert-butylhydroquinone (TBHQ), widely used as antioxidants in industry and as food additives, was studied using TG/DTG/DTA and DSC, hot stage microscopy and DRX techniques, looking for a meticulous thermal characterization of these substances. The results revealed that the compounds underwent melting followed by evaporation, without decomposition under the conditions of analysis. BHA presented a solid-solid transition before melting. BHT revealed crystallization in different phases from the melting, on cooling or reheating, depending on using or not isothermal treatment after melting. TBHQ showed two events that suggested a cold crystallization, but only one solid phase could be identified by XRD analysis. Polymorphic transformations could be found on heating/cooling processes.