Thermal behavior and decomposition kinetics of rifampicin polymorphs under isothermal and non-isothermal conditions

Abstract

The thermal behavior of two polymorphic forms of rifampicin was studied by DSC and TG/DTG. The thermoanalytical results clearly showed the differences between the two crystalline forms. Polymorph I was the most thermally stable form, the DSC curve showed no fusion for this species and the thermal decomposition process occurred around 245 °C. The DSC curve of polymorph II showed two consecutive events, an endothermic event (T peak = 193.9 °C) and one exothermic event (T peak = 209.4 °C), due to a melting process followed by recrystallization, which was attributed to the conversion of form II to form I. Isothermal and non-isothermal thermogravimetric methods were used to determine the kinetic parameters of the thermal decomposition process. For non-isothermal experiments, the activation energy (E a ) was derived from the plot of Log β vs 1/T, yielding values for polymorph form I and II of 154 and 123 kJ mol -1 , respectively. In the isothermal experiments, the E a was obtained from the plot of lnt vs 1/T at a constant conversion level. The mean values found for form I and form II were 137 and 144 kJ mol -1 , respectively. Uniterms: Rifampicin. Tuberculosis. Thermal analysis. Thermal decomposition. Kinetic analysis.O comportamento térmico de duas formas polimórficas da rifampicina foi estudado por DSC e TG/DTG. Os resultados termoanalíticos mostraram claramente as diferenças entre as duas formas cristalinas. O polimorfo I é a forma mais estável termicamente, a curva DSC não mostrou a fusão dessa espécie e o processo de decomposição térmica ocorreu próximo a 245 o C. A curva DSC do Polimorfo II apresentou dois eventos consecutivos, um endotérmico (T pico = 193,9 o C) e outro exotérmico (T pico = 209,4 o C), devido à fusão seguida de recristalização, a qual foi atribuída à conversão da forma II à forma I. Métodos termogravimétricos isotérmicos e não-isotérmicos foram empregados para determinar os parâmetros cinéticos do processo de decomposição térmica. Para experimentos não-isotérmicos, a energia de ativação (E a ) foi obtida a partir do gráfico de Log β vs 1/T, e os valores 154 e 123 kJ mol -1 foram encontrados, respectivamente, para os polimorfos I e II. Para os experimentos isotérmicos, a E a foi obtida a partir do gráfico de lnt vs. 1/T a um nível de conversão constante. O valor médio encontrado foi 137 e 144 kJ mol -1 , respectivamente, para a forma I e forma II.

Thermal kinetics and thermo‐mechanical properties of graphene integrated fluoroelastomer

“…The peak temperature of the DTG was identified as the highest weight loss temperature. By using the Ozawa method, the activation energy for the decomposition (Eap) was determined which represents the thermal stability of the rubber . The crosslink density of the GO/FKM and RGO/FKM was investigated by the equilibrium swelling test according to ASTM D6814.…”

Determination of the imatinib mesylate purity by differential scanning calorimetry

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Development of novel chitosan based ketorolac implant controlled release formulation for subcutaneous drug delivery

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