Thermal stability of pentoxifylline: active substance and tablets

Thermal analysis is a routine method in the solution of pharmaceuticals problems such as the control of raw materials, to the determination of purity, to the qualitative and quantitative analysis of drug formulation, tests of thermal stability and compatibility, the determination of kinetic parameters, etc. The evaluation of thermal stability in the solid state is mostly made by analyzing their decomposition under isothermal and non-isothermal conditions. The present work reports the study on the thermal behavior of pentoxifylline—active substance and tablets, respectively, the determination of the kinetic parameters for the decomposition process under non-isothermal conditions and in a nitrogen atmosphere at five heating rates: 2.5, 5, 7.5, 10 and 15 °C min^?1. For the determination of kinetic parameters from the TG/DTG curves, the following differential methods were utilized: Friedman isoconversional and Chang, respectively, integral methods: Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Li–Tang, and Starink. Thermoanalytical curves showed that the active substance is thermally more stable than the tablets. The decrease in stability was attributed to the presence of excipients.     

Thermal stability of ketoprofen��active substance and tablets

Simultaneous thermoanalytical techniques were used for the characterization of the thermal decomposition of ketoprofen??active substance and tablets. DTA and DSC curves showed that ketoprofen melts before the decomposition. A kinetic study regarding the ketoprofen??active substance??s thermal decomposition was performed under non-isothermal conditions and in a nitrogen atmosphere at five heating rates: 2.5, 5, 7.5, 10 and 15 °C min^?1. The kinetic parameters of thermal decomposition process were obtained from TG/DTG curves using the following differential methods: Friedman isoconversional, Chang, respectively, integral methods: Flynn?CWall?COzawa, Kissinger?CAkahira?CSunose, Coats?CRedfern and Madhusudanan. The careful treatment of the kinetic parameters obtained in certain thermal conditions was confirmed to be necessary as well as a different strategy of experimental data processing.     

Thermal behaviour studies of procaine and benzocaine

The analysed substances, procaine and benzocaine, are two anaesthetic agents currently being administered in tablet form, also in the topical (cream, gel, balm) and injectable dosage forms. The TG/DTG/DTA curves were obtained in air at different heating rates. For determination of the heat effects, the DTA curves (in μV) were changed with the heat flow curves (in mW), so that the peak area corresponds to an energy in J g^?1 or kJ mol^?1. The non-isothermal experiments are preformed to investigate the thermal degradation process of these active substances, both as a solid and are performed in a dynamic atmosphere of air at different heating rates, by heating from room temperature to 500 °C. The kinetic analysis was performed using the TG data in air for the first step of substance’s decomposition at four heating rates: 7, 10, 12 and 15 °C min^?1. The data were processed according to an appropriate strategy to the following kinetic methods: Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, Friedman and NPK, to obtain realistic kinetic parameters, even if the decomposition process is a complex one. Thermal analysis was supplemented using Fourier Transform infrared spectroscopy coupled with the TG device to identify the anaesthetics with any products which may have formed (EGA—the evolved gas analysis).     

Thermal behaviour and kinetic study of some triazoles as potential anti-inflammatory agents

Thermogravimetric (TG), differential thermogravimetric analysis and differential scanning calorimetry had been used to characterize the thermal stability of four new heterocyclic compounds with triazolic structure. The four analysed compounds have similar thermal behaviours, namely the thermal mal curves of these new compounds show three thermal events. These compounds were thermally stable up to 110 °C. Above this temperature, the evolution of hydrochloric acid took place as observed by EGA. Identification and the monitoring of gaseous species released during thermal decomposition of pure triazoles in air atmosphere have been carried out by coupled TG–FTIR. Between 110 and 220 °C the main gaseous product is HCl which was identified on the basis of these FTIR spectra. Arguments for a rapid thermooxidation of the four molecules were brought by EGA by identifying the substances which arise from both the destruction of side chains and of triazolic ring. The kinetic analysis of the destruction process of triazolic structure was investigated using the TG data in air for the substance’s decomposition in non-isothermal conditions. The isoconversional methods, Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa and Friedman, were applied to determine the activation energy from the analysis of four curves measured at different heating rates. In order to obtain realistic kinetic parameters, even if the decomposition process is a complex one, the non-parametric kinetics method was also used. A good agreement between the data obtained from the four applied methods was found.     

Kinetic analysis for non-isothermal decomposition of un-irradiated and gamma-irradiated potassium bromate

The thermal decomposition of un-irradiated and gamma-irradiated potassium bromate (KBrO₃) was performed under non-isothermal conditions at different heating rates (5, 10, 15 and 20 K min^?1). The data was analysed using isoconversional and non-isoconversional methods. The kinetic parameters of thermal decomposition process were obtained by three model-free isoconversional methods: Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Friedman. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy decreases on irradiation. Kinetic analysis of data in view of various solid-state reaction models showed that the decomposition of un-irradiated and irradiated anhydrous KBrO₃ is best described by the Avrami–Erofeev model equation, [?ln(l?α)]^1/2 = kt.     

Thermal stability of piroxicam

The application of thermal method is of great importance regarding the pharmaceutical problems such as the control of raw materials, the determination of purity, the qualitative and quantitative analysis of drug formulation, tests of thermal stability and compatibility and the determination of kinetic parameters etc. The purpose of a kinetic investigation is to calculate the kinetic parameters and the determination of the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the piroxicam—active substance’s thermal decomposition was performed under isothermal conditions and nitrogen atmosphere, for the temperature steps: 200, 205, 210, 215 and 220 °C. The TG/DTG data were processed by three differential methods: isothermal—isoconversional, Friedman’s isothermal isoconversional and isothermal model-fitting. The obtained results are in good accord between them, as well as with those obtained under non-isothermal conditions from a previous work and confirm the necessity of the kinetic parameters determining in different thermal conditions, by the adequate calculation methods.     

Thermal stability of ketoprofen

The purpose of this investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the ketoprofen—involving active substance’s thermal decomposition—was performed under isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 260; 265; 270; 275; and 280 °C. The thermogravimetry/derivative thermogravimetry data were processed by three differential methods: isothermal–isoconversional, Friedman’s isothermal–isoconversional, and isothermal model-fittings. The obtained results are in good accordance with those obtained under non-isothermal conditions of a previous study, and confirm the necessity for the kinetic parameters to be determined, under different thermal conditions, by the adequate calculation methods.     

Thermal kinetic studies on the decompositions of cefuroxime lysine in different atmospheres and heating rates

The thermal decomposition of a new antibiotic agent, cefuroxime lysine, was investigated by thermogravimetry analysis/derivative thermogravimetry and differential scanning calorimetry (DSC) methods in anoxic and oxidative environments. The influence of heating rates (including 5, 10, 15, and 20 °C/min) on the thermal behavior of cefuroxime lysine was revealed. By the methods of Kissinger and Flynn–Wall–Ozawa, the thermal kinetic parameters of activation energy and pre-exponential factor for the exothermic processes under non-isothermal conditions were calculated using the analysis of corresponding DSC curves.     

Thermal decomposition and kinetics studies on the 2,2-dinitropropyl acrylate–styrene copolymer and 2,2-dinitropropyl acrylate–vinyl acetate copolymer

In the present work, kinetics of thermal decomposition of 2,2-dinitropropyl acrylate–styrene copolymer (DNPA/St) and 2,2-dinitropropyl acrylate–vinyl acetate copolymer (DNPA/VAc) was investigated by differential scanning calorimetry (DSC). The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of the copolymer was verified. The results showed that, as the heating rate was increased, decomposition temperature of the copolymer was increased. Also, the kinetic parameters such as activation energy and frequency factor of the copolymer were obtained from the DSC data by the isoconversional methods proposed by Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO). Average activation energy obtained by KAS and FWO methods for the thermal decomposition reaction of DNPA/St and DNPA/VAc are 157.38 ± 0.27 and 147.67 ± 0.57 kJ mol^?1, respectively. The rate constants for thermal decomposition calculated from the activation parameters showed the structural dependency. The relative stability of two copolymers under 50 °C was in this order: DNPA/St > DNPA/VAc. The results of thermogravimetry (TG) analysis revealed that the main mass changes for DNPA/St and DNPA/VAc occurred in the temperature ranges of 200–270 °C. The DSC-FTIR analysis of DNPA/St indicates that the band intensity of nitro and other groups increased haphazardly from 230 °C due to thermal decomposition.     

Thermal decomposition kinetics of potassium iodate

The effect of gamma ray irradiation on the rate and kinetics of thermal decomposition of potassium iodate (KIO₃) has been studied by thermogravimetry (TG) under non-isothermal conditions at different heating rates (3, 5, 7, and 10 K min^?1). The thermal decomposition data were analyzed using isoconversional methods of Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman. Irradiation with gamma rays increases the rate of the decomposition and is dependent on the irradiation dose. The activation energy decreases on irradiation. The enhancement of the rate of the thermal decomposition of KIO₃ upon irradiation is due to the combined effect of the production of displacements and extended lattice defects and chemical damage in KIO₃. Non-isothermal model fitting method of analysis showed that the thermal decomposition of irradiated KIO₃ is best described by the contracting sphere model equation, with an activation energy value of ~340 kJ mol^?1.     

Thermal degradation kinetics study and thermal cracking of waste cooking oil for biofuel production

Thermal cracking of waste cooking oil (WCO) for production of liquid fuel has gained special interest due to the growing demand of renewable fuel, depleting fossil fuel reserves and environmental issues. In the present work, thermal cracking of WCO to produce liquid hydrocarbon fuels without any preprocessing has been studied. Moreover, non-isothermal kinetics of WCO using thermogravimetric analysis (TGA) has been studied under an inert atmosphere at various heating rates. According to TGA result, active thermal decomposition of WCO was found to be between 318 and 500 °C. Furthermore, the temperature at which the maximum mass loss rate attained was shifted to higher values as the heating rates increased from 10 to 50 °C min^?1 and the values were found to be approximately similar to that of R ₅₀. Besides, model-free iso-conversion kinetic methods such as Friedman (FM), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) were used to determine the activation energies of WCO degradation. The average activation energy for the thermal degradation of WCO was found to be 243.7, 211.23 and 222 kJ mol^?1 for FM, KAS and FWO kinetic methods, respectively. Additionally, the cracking of WCO was studied in a semi-batch reactor under an inert atmosphere and the influences of cracking temperature, time and heating rates on product distribution were investigated. From the reaction, an optimum yield of 72 mass% was obtained at a temperature of 475 °C, time of 180 min and a heating rate of 10 °C min^?1. The physicochemical properties studied were in accordance with ASTM standards.     

Thermal analysis applied for the removal of surfactant from mesoporous molecular sieves MCM-41 synthesized from gold mine tailings slurry

The aim of the current study is to obtain the thermal behavior and kinetic analyses of the removal of surfactant from MCM-41 synthesized from tailings slurry at different heating rates. X-ray diffraction and thermogravimetric analyses were carried out to determine the characterization of the synthesized samples. Kissinger–Akahira–Sunose and Friedman isoconversional kinetic methods were applied for the purpose of determining the kinetic analysis parameters of the decomposition of surfactant from the mesoporous molecular sieves MCM-41 under non-isothermal conditions. For the comparison of these results, MCM-41 was synthesized from a pure silica source. The thermal behaviors of MCM-41 synthesized from tailings slurry do not differ from samples synthesized from pure silica during the decomposition reactions. The kinetic analysis’ results indicate that the decomposition reactions of the synthesized MCM-41 samples had complex reaction mechanisms.     

Investigation of thermal decomposition kinetics of taurine

The non-isothermal thermal decomposition of taurine was investigated by means of thermogravimetric analysis (TG) and differential thermal analysis (DTA). The experimental data were treated using Flynn–Wall–Ozawa, Doyle, Kissinger, and ?atava–?esták methods, respectively. The results show that the non-isothermal thermal decomposition mechanism of taurine is classified as phase boundary reaction, and the mechanism function is the Mampel Power law with n = 1. The forms of both integral and differential for the mechanism function are $ G(\alpha ) = \alpha $ and $ f(\alpha ) = 1 $ , respectively. The activation energy and the pre-exponential factor are 167.88 kJ mol^?1 and 1.82 × 10¹³min^?1, respectively.     

Thermal behavior and kinetic modeling of (NH4)4UO2(CO3)3 decomposition under non-isothermal conditions

The thermal behavior and kinetic analysis of ammonium uranyl carbonate decomposition has been studied in inert gas, O₂, and 90%Ar–10%H₂ atmospheres under non-isothermal conditions. The results showed a dependence on specific surface area with the decomposition temperature of ammonium uranyl tri-carbonate (AUC). Specific surface area increases and reaches a maximum between 300 and 400 °C and decreases at T > 400 °C. The reaction paths of AUC decomposition under the three atmospheres were proposed. The integral methods Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) were used for the kinetic analysis. The activation energy averages are 58.01 and 56.19 kJ/mol by KAS and FWO methods, respectively.

     

A facile synthesis of boron nanostructures and investigation of their catalytic activity for thermal decomposition of ammonium perchlorate particles

In this research, ultrasound irradiation as a simple method was used to produce boron nanostructures. Reaction conditions such as boron concentration and sonication time show important roles in the size, morphology and growth process of the final products. The boron nanostructures (nanoparticles and nanorods) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, small-angle X-ray scattering and inductively coupled plasma atomic emission spectroscopy techniques. Primary evaluation of results showed that nanoparticles and nanorods of boron successfully have been prepared with 25–40 and 50–100 nm average particle size, respectively. These nanostructures (nanoparticles and nanorods) were studied as an additive for promoting the thermal decomposition of ammonium perchlorate (AP) particles. Thermochemical decomposition behaviors of treated samples were characterized by thermal gravimetric analysis and differential scanning calorimetry techniques. Also, the kinetic parameters of thermal decomposition processes of pure and treated samples were obtained by nonisothermal methods proposed by Kissinger and Ozawa. However, boron nanoparticles with the smallest average particle size (25–40 nm) have the most significant catalytic effect including the decrease in decomposition temperature of AP + B nanocomposite by 100 °C, increase in the heat of decomposition from 580 to 1354 J g^?1 and decrease in activation energy from 207 to 110 kJ mol^?1.     

The thermal behavior of powder emulsion explosives

The determination of the most probable mechanism function and the calculation of kinetic parameters of thermal decomposition of powder emulsion explosives have been achieved by different kinetic equations and different kinetic methods from data non-isothermal SC-DSC curves, DSC curves, and thermal explosion delay curve. The courses which the reaction would follow under adiabatic conditions are predicted.

---

Zusammenfassung Mittels verschiedener kinetischer Gleichungen und verschiedener kinetischer Methoden wurde anhand der Angaben aus nichtisothermen SC-DSC-Kurven, DSC-Kurven und thermischer Explosionsverzugskurven die wahrscheinlichste Mechanismusfunktion der thermischen Zersetzung von Pulveremulsions-Sprengstoffen ermittelt und die diesbezüglichen kinetischen Parameter berechnet. Der Reaktionsweg unter adiabatischen Bedingungen wird vorausgesagt.

     

过氧化二异丙苯的热分解动力学研究

过氧化二异丙苯(DCP)是一种有广泛用途的过氧化物交联剂,具有高的交联效率和优良的交联性能.其分解温度较低,热分解速度较快,即使没有外界能量的作用,在自然储存的条件下也会发生化学反应,放出热量[1,2].     

Comparative kinetic study of decomposition of some diazepine derivatives under isothermal and non-isothermal conditions

Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances. TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability, compatibility, polymorphism, kinetic analysis, phase transitions etc.). The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric kinetics. In the model-fitting methods the kinetic triplets (f(α), A and E _a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous work. The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as well as a different strategy of experimental data processing.