Kinetic of Thermal Decomposition of Bixin Derived Seeds of Urucum (Bixa orellana L.) using Dynamic Thermogravimetry

摘要

The tropical shrub Urucum internationally known as Annatto (Bixa orellana L.) is a smallrntree with predominant occurence in the regions of South America particularly in Brazil. Bixin isrnthe major component of the coloring matter present in the external surface of its seeds (more thanrn80%) along with Norbixin. These diapocarotenoid pigments are largely used in the food industryrn(mainly in the butter, cheese and margarine branches), condiments, cosmetics, pharmaceutical,rntextile and inks. The increasing on the use of naturally occurring colorants is a consequence ofrnconcerns on the toxicity of synthetic colorants. A sample of the pure diapocarotenoid isolated byrnsolvent extration from the seeds of Annatto was used in the present work. The study reports thernkinetic of the thermal decomposition of Bixin using Dynamic Thermogravimetry. The dynamicrnthermogravimetric curves were obtained in Shimadzu Thermobalance, TGA-50 model, underrnnitrogen atmosphere with flow of 50 mL min~(-1), heating rate of 5, 10 and 15 ℃min~(-1) and range ofrntemperature 25-900 ℃. The DSC curve was obtained in Shimadzu Calorimeter, DSC-50 model,rnunder nitrogen atmosphere with flow of 50 mL min~(-1), heating rate of 10 ℃ min-1 and range ofrntemperature 25-500 ℃. The dynamic termogravimetric curves (TG) presented four steps ofrnthermal decomposition. The DSC curve indicated melting and decomposition of Bixin. Byrnoverview the curves of the TG/DSC reveal that reactions occurred in the liquid phase. Thernkinetic study was performed using dynamic method. For better adjustment of the experimentalrndata the kinetic model F3 was choosed. The kinetic parameters were obtained using integral andrnapproximate methods: Coats-Redfern (CR), Madhusudanan (MD), Horowitz-Metzger (HM) andrnVan Krevelen (VK), whose results had been coherent.