THERMOANALYTICAL STUDIES ON NEW POLYMORPHIC FORMS OF PROPYL, OCTYL AND DODECYL GALLATES

Abstract

• propyl , octyl and dodecyl gallates were submitted to thermal analysis • thermal analysis revealed melting followed by degradation in high temperatures • when cooled just after melting new polymorphic forms crystalized • X-ray diffraction and hot stage microscopy confirmed these polymorphic forms • a complete thermal behavior mechanism was proposed for these antioxidants The thermal behavior of propyl (PG), octyl (OG) and dodecyl (DG) gallates, three antioxidants widely used in fuel and food industries, was evaluated by thermoanalytical techniques (TG, DTA, DSC and hot stage microscopy), and complementary techniques, such as FTIR-ATR and XRD. All of them presented melting in characteristic temperatures during heating. The resulting liquid phases crystallized in different solid forms when cooled just after melting. However, when the samples were heated beyond melting temperature, they decomposed. Although thermal studies were conducted at higher temperature than those in which they are regularly used, this work provided relevant information regarding their thermal behavior at higher temperatures. Data from XRD, FTIR-ATR and hot stage microscopy were used to confirm the presence of new polymorphs. Finally, based on these results mechanisms describing the thermal behavior of PG, OG and DG were proposed.