Thermal compatibility between hydroquinone and retinoic acid in pharmaceutical formulations

Thermogravimetry (TG) and differential scanning calorimetry (DSC) are used in pharmaceutical studies for characterization of drugs, purity, compatibility of formulations, identification of polymorphism, evaluation of stability, and thermal decomposition of drugs and pharmaceutical formulations. Hydroquinone (HQ) and products containing HQ have been widely used as depigmentation agents for lightening the skin. Retinoids are compounds that have the basic core structure of vitamin A and its oxidized metabolites, or synthetic compounds that share similar mechanisms of action as naturally occurring retinoids. Depigmentants and excipients were analyzed by TG and DSC. The dynamic thermogravimetric curves were obtained on a SHIMADZU thermobalance, model DTG-60, using an alumina crucible, at the heating rate of 10 °C min^?1, in the temperature range of 25–900 °C, under an atmosphere of nitrogen at 50 mL min^?1. The sample's mass was 10 ± 0.05 mg. The DSC curves were obtained using Shimadzu calorimeter, model DSC-60, using aluminum crucible, at the heating rate of 10 °C min^?1, in the temperature range of 25–400 °C. The thermogravimetric and calorimetric curves were analyzed using TASYS software SHIMADZU. In this study were found the interaction between retinoic acid (RA) and the following excipients: cetyl alcohol(CA), cetostearyl alcohol (CTA), glycerin(GLY), and dipropylene glycol (DPG), and that between HQ and the excipient, DPG. Therefore, additional studies are necessary to evaluate final formulations. Thermal analysis is an effective and reliable technique that can be used in the control of raw materials and pharmaceutical products, and for evaluating their employment potential in the development and characterization of products.     

Thermal behavior of cashew gum by simultaneous TG/DTG/DSC-FT-IR and EDXRF

Cashew gum, an exudate polysaccharide from Anacardium occidentale L., was purified by alcohol precipitation. Thermal behavior of this polysaccharide was investigated by simultaneous TG/DTG/DSC-FT-IR analysis performed under nitrogen and air atmospheres and heating rate of 10 K min^?1. TG/DTG curves under oxidative atmosphere were similar to the curves under N₂ atmosphere until 340 °C, however, it was observed a profile difference due to the presence of two DTG peaks at 430 and 460 °C. DSC results showed endothermic and exothermic events corroborating with TG/DTG curves. The Simultaneous TG/DSC-FTIR analysis revealed that evolved gases from the decomposition of cashew gum sample were CO₂, CO, and groups: O–H, C–H, C=O, C–C, and C–O, in nitrogen and air atmospheres. Energy dispersive X-ray fluorescence analysis from the ash showed that the elements in larger amounts are CaO, MgO, and K₂O.     

Studies on the thermal behavior and decomposition kinetic of drugs cetirizine and simvastatin

Understanding the response of drugs and their formulations to thermal stresses is an integral part of the development of stable medicinal products. In the present study, the thermal degradation of two drug samples (cetirizine and simvastatin) was determined by differential scanning calorimetery (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the cetirizine occurs during two temperature ranges of 165–227 and 247–402 °C. The TG/DTA analysis of simvastatin indicates that this drug melts (at about 143 °C) before it decomposes. The main thermal degradation for the simvastatin occurs during two endothermic behaviors in the temperature ranges of 238–308 and 308–414 °C. The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of both the drug samples was verified. The results showed that as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the values of activation energy obtained by ASTM E696 method, the values of activation energy for cetirizine and simvastatin were 120.8 and 170.9 kJ mol^?1, respectively. Finally, the values of ΔS ^#, ΔH ^#, and ΔG ^# of their decomposition reaction were calculated.     

Thermal properties and kinetics of new-generation posterior bulk fill composite cured light-emitting diodes

In this study, the thermal behavior in terms of glass transition (T _g), degradation, and thermal stability of four commercial new-generation posterior bulk fill composites (Surefill SDR, Dentsply; Quixfill, Dentsply; Xtrabase, Voco; and Xtrafill, Voco) activated by light-emitting diodes (LEDs) was analyzed by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The activation energies (E _a) for the decomposition of the dental resins were calculated based on the Kissinger and Doyle kinetic models from the peaks of the endothermic curves obtained when the specimens were heated at four different temperatures (5, 10, 15, and 20 °C min^?1) during DSC. The results show that the Xtrabase composite displayed the highest T _g (120 °C at a 5 °C min^?1 heating rate) and E _a (157.64 kJ mol^?1) values associated with thermal degradation from the main chain of the polymer.     

Fast-scan vs conventional differential scanning calorimetry (DSC) techniques in detection of crystallization events of tolbutamide–polyethylene glycol composite

This study investigated the capacity of fast-scan (400 °C min^?1) against conventional (10 °C min^?1) differential scanning calorimetry (DSC) techniques to track crystallization phenomenon in tolbutamide–polyethylene glycol 3000 composites prepared by hot melt method (mass ratios 1:1, 1:5, and 1:9) and stored at 25 and 75 % relative humidities. Drug crystallization in composites was indicated by X-ray diffractometry (XRD) and scanning electron microscopy characterization over 40 days storage. With reference to XRD as gold measurement standard, fast-scan DSC could not map the crystallization events of composites (Pearson correlation: fast-scan DSC peak temperature and enthalpy versus XRD peak intensity and area, p > 0.05). Conventional DSC was able to indicate marked drug crystallization through an increase in endothermic enthalpy value of peaks at high temperature regimes between 250 and 360 °C due to formation of high melting point crystal form.     

Thermal analysis of sulfurization of polyacrylonitrile with elemental sulfur

Thermal analysis of sulfurization of polyacrylonitrile (PAN) with elemental sulfur was investigated by thermogravimetry and differential thermal analysis of the mixture of polyacrylonitrile and elemental sulfur up to 600°C. Due to the volatilization of sulfur, the different heating rate (10 and 20 K min⁻¹) and different mixture proportion of polyacrylonitrile and elemental sulfur were adopted to run the analysis. The different heating rates make the DSC curves of sulfur different, but make the DSC curves of PAN similar. In the DSC curve of sulfur for the heating rate of 20 K min⁻¹ around 400°C, a small exothermic peak occurs at 400°C in the wide endothermic peak around 380∼420°C, indicative of that there is an exothermic reaction around 400°C. In the DSC curves of the mixture, the peaks around 320°C are exothermic as the content of sulfur is below 3.5:1 and endothermic as the content of sulfur is over 4:1, indicating that one of the reactions between PAN and sulfur takes place around 320°C. In the TG curves of the mixture, the mass losses begin at 220°C, and sharply drop down from 280°C. The curves for the low sulfur content obviously show two steps of mass loss, and curves for the high sulfur content show only one step of mass loss, indicative of more sulfur is benefit for the complete sulfurization of PAN. This study demonstrates that the TG/DSC analysis can give the parameter for the sulfurization, even if the starting mixture contains the volatile sulfur.     

Fast detection of sildenafil in adulterated commercial products using differential scanning calorimetry

Adulteration of drugs is a serious issue and can have a great impact on human health. It is mainly done with the intention of boosting the effects of products. For many years, the enforcement officers in Malaysia have had difficulty deciding whether some products should be confiscated as they have not been able to produce fast reliable evidence of adulteration. For that reason, we explored the use of differential scanning calorimetry (DSC) as a potential fast detection method of commercial products marketed in Malaysia that may be adulterated. We confirmed the outcomes qualitatively with high pressure liquid chromatography. DSC was set at a heating rate of 10 °C min^?1 and within a temperature range of 100–250 °C with nitrogen as a purge gas at a flow rate of 20 mL min^?1 to analyse a sildenafil reference standard (RS), sildenafil tablets and sildenafil adulterated commercial products. Four sildenafil adulterated commercial products were analysed. Since the melting point of sildenafil in the mixture tended to shift, the presence of sildenafil in three of these adulterated commercial products was confirmed using the spiking method and was re-analysed using DSC. The re-analysed results indicated that the enthalphy of fusion (?H) and the resolution peak of sildenafil increased accordingly depending upon the amount of spiked sildenafil RS. Apart from these results, the DSC curves also showed different patterns for sildenafil RS and the mixtures. Therefore, we concluded that DSC can potentially be used to detect sildenafil in adulterated commercial products.     

Studies on ignition and afterburning processes of KClO4/Mg pyrotechnics heated in air

Thermal behavior of KClO₄/Mg pyrotechnic mixtures heated in air was investigated by thermal analysis. Effects of oxygen balance and heating rates on the TG?CDSC curves of mixtures were examined. Results showed that DSC curves of the mixtures had two exothermic processes when heated from room temperature to 700?°C, and TG curve exhibited a slight mass gain followed by a two-stage mass fall and then a significant mass increase. The exothermic peak at lower temperature and higher temperature corresponded to the ignition process and afterburning process, respectively. Under the heating rate of 10?°C?min^?1, the peak temperatures for ignition and afterburning process of stoichiometric KClO₄/Mg (58.8/41.2) was 543 and 615?°C, respectively. When Mg content increased to 50%, the peak ignition temperature decreased to 530?°C, but the second exothermic peak changed little. Reaction kinetics of the two exothermic processes for the stoichiometric mixture was calculated using Kissinger method. Apparent activation energies for ignition and afterburning process were 153.6 and 289.5?kJ?mol^?1, respectively. A five-step reaction pathway was proposed for the ignition process in air, and activation energies for each step were also calculated. These results should provide reference for formula design and safety storage of KClO₄/Mg-containing pyrotechnics.     

Effects of various fire-extinguishing reagents for thermal hazard of triacetone triperoxide (TATP) by DSC/TG

Acetone, hydrogen peroxide (H₂O₂), and sulfuric acid (H₂SO₄) are easily to produce triacetone triperoxide (TATP), which is an organic peroxide and a hazardous material. The aim of this study was to analyze the thermal hazard of various fire-extinguishing reagents mixed with TATP. Various functions of fire-extinguishing reagents may have different extent of reactions with TATP. Differential scanning calorimetry (DSC) and thermogravimetric analyzer (TG) were used to detect the thermal hazard and to evaluate the effect of fire-extinguishing reagents mixed with TATP under fire condition. TATP decomposed rapidly and final decomposition was calculated before 200 °C. Therefore, heat of decomposition (ΔH _d) of TATP was evaluated to be 2,500 J g^?1 by DSC under 2 °C min^?1 of heating rate. H₂O₂, acetone, and H₂SO₄ should not be mixed in a wastewater drum. TATP decomposed at 50 °C by DSC using O₂ of reaction gas that is an exothermic reaction and can decompose a large amount of heat. Therefore, TATP was applied to assess thermal pyrolysis by DSC employing N₂ of reaction gas that can analyze an endothermic reaction. Mass loss percentage of TATP was evaluated to be 100 % when the ambient temperature exceeds 110 °C by TG using O₂ or N₂ of reaction gas.     

Thermoanalytical study on the oxidation of uranium dioxides derived from uranyl nitrate,uranyl acetate and ammonium diuranate

The oxidation of UO₂ was investigated by TG, DSC and X-ray diffraction . UO₂ samples were prepared by the reduction of UO₃ at P_H2 + P_N2 = 100 + 50 mm Hg and 5°C min^?1 up to 800°C. In order to obtain six UO₂ samples with different preparative histories, UNH, UAH and ADU were used as starting materials and their thermal decomposition was carried out at 450–625°C for 0–9 h at an air flow rate of 100 ml min^?1. α-UO₃, γ-UO₃, UO₃ - 2 H₂O, and their mixtures were obtained. The reduction of UO₃ gave β-UO_2+x with different x values from 0.030 to 0.055. The oxidation carried out at P_O2 = 150 mm Hg was found to consist of oxygen uptake at room temperature. UO₂ - U₃O₇ (Step I) and U₃O₇ → U₃O₈ (Step II). TG and DSC curves of the oxidation showed two plateaus and two exothermic peaks corresponding to Steps I and II. In the case of two of the samples, the DSC peak of Step II split into two substeps, which were assumed to be due to the different reactivities of U₃O- formed from α-CO₃ and that from other types of UO₃. The increase in O/U ratio due to the oxygen uptake at room temperature changed from 0.010 to 0.042 except for a sample prepared from ADU which showed an extraordinarily large value of 0.445. TG curves showed an increase in O/U from room temperature to near 250°C for Step I and the plateau at 250–350°C where O/U was about 2.42, and showed a sharp increase in O/U above 350°C for Step II and the plateau above 100°C where O/U was 2.72–2.75. It is thought that the prepared UO₂ had a defective structure with a large interstitial volume to accommodate the excess oxygen.     

Thermal decomposition of tetraalkylammonium iodides

A number of tetramethylammonium (TMA) iodides, including mono-, tri-, and pentaiodide, were synthesized. Thermal decomposition of samples was investigated by simultaneous TG–DSC analysis accompanied by gaseous IR- and mass-spectrometry analyses. Two different reaction pathways have been observed for TMA pentaiodide at different heating rates. At low heating rates (1–5 K min^?1), a gradual mass loss takes place and a stability plateau due to monoiodide formation exists on TG curve. At high heating rates (10, 15 and 7 K min^?1 as the in-between stage), there are only two peaks on DTG curve (instead of three for lower heating rates) and no monoiodide formation is observed as the sample decomposes completely before 350 °C.     

Investigation on the reaction of iron powder mixture as a portable heat source for thermoelectric power generators

This paper reports our investigation on the thermal behavior and ignition characteristics of iron powder and mixtures of iron with other materials such as activated carbon and sodium chloride in which iron is the main ingredient used as fuel. Thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetric analysis were used to characterize the materials and for further understanding of reaction kinetics of the pyrophoric iron mixtures. The experimental results demonstrated that iron micron particles react exothermically to the oxygen in atmosphere and produced iron oxide with ignition temperature of 427.87 °C and heat generation of 4,844 J g^?1. However, in this study, the pyrophoric iron mixture acts as a heat source for the thermoelectric power generators, the final mixture composition is determined to compose of iron powder, activated carbon, and sodium chloride with the mass ratio of approximately 5/1/1. The mixture generated two exothermic peaks DSC curves that showed ignition temperature of 431.53 and 554.85 °C and with a higher heat generation of 9,366 J g^?1 at higher temperature. The effects of test pan materials and heating rate on the ignition were also examined by DSC method. Kinetic data such as the activation energy (E _a), the entropy of activation (ΔS ^# ), enthalpy of activation (ΔH ^# ), and Gibbs energy of activation (ΔG ^# ) on the ignition processes was also derived from the DSC analysis. From the ignition temperature, heat generation, and kinetics test data, the mass ratio of 5/1/1 proved to generate the most amount of heat with high temperatures for the standalone thermoelectric power generators.     

Thermal characteristics of the combustion process of biomass and sewage sludge

The combustion of two kinds of biomass and sewage sludge was studied. The biomass fuels were wood biomass (pellets) and agriculture biomass (oat). The sewage sludge came from waste water treatment plant. The biomass and sludge percentage in blends with coal were 10 %. The studied materials were characterised in terms of their proximate and ultimate analysis and calorific value. The composition of the ash of the studied fuels was also carried out. The behaviour of studied fuels was investigated by thermogravimetric analysis (TG, DTG and DTA). The samples were heated from an ambient temperature up to 1,000 °C at a constant three rates: 10, 40 and 100 °C min^?1 in 40 mL min^?1 air flow. TG, DTG and DTA analysis showed differences between coal, biomass fuels and sewage sludge. 10 % addition of studied fuels to the mixture with coal changed its combustion profile in the case of sewage sludge addition. The combustion characteristics of fuel mixtures showed, respectively, qualitative summarise behaviour based on single fuels. Evolved gaseous products from the decomposition of studied samples were identified. This study showed that thermogravimetric analysis connected with mass spectrometry is useful techniques to investigate the combustion and co-combustion of biomass fuels, and sewage sludge, together with coal. Non-isothermal kinetic analysis was used to evaluate the Arrhenius activation energy and the pre-exponential factor. The kinetic parameters were calculated using Kissinger–Akahira–Sunose model.     

Thermal behaviour of cephalexin in different mixtures

The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate, starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min⁻¹. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min⁻¹. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears. These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates: 5, 7, 10 and 12 °C min⁻¹. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C).     

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.     

Thermogravimetric analysis of walnut shell as pyrolysis feedstock

Thermal degradation behavior and kinetics of a biomass waste material, namely walnut shell, were investigated by using a thermogravimetric analyzer. The desired final temperature of 800 °C was achieved at three different heating rates (2, 10, and 15 °C min^?1) under nitrogen flow (50 mL min^?1). The TG and DTG curves exhibited three distinct zones that can mainly be attributed to removal of water, decomposition of hemicellulose + cellulose, and decomposition of lignin, respectively. The kinetic parameters (activation energy, pre-exponential factor, and reaction order) of active pyrolysis zone were determined by applying Arrhenius, Coats?CRedfern, and Horowitz?CMetzger methods to TG results. The values of activation energies were found to be between 45.6 and 78.4 kJ mol^?1. There was a great agreement between the results of Arrhenius and Coats?CRedfern methods while Horowitz?CMetzger method yielded relatively higher results. The existence of kinetic compensation effect was evident.     

Thermal hazard evaluation of tert-butyl hydroperoxide mixed with four acids using calorimetric approaches

Possessing thermal instability inherently, organic peroxides have caused many severe accidents in chemical industries all over the world. tert-Butyl hydroperoxide (TBHP) is usually used as initiator or oxidant because of its strong oxidizing ability in the chemical process. In this study, the thermal hazard analysis of TBHP mixed with various acids was investigated. Differential scanning calorimetry (DSC) and vent sizing package 2 were used to figure out the thermal runaway behaviors of TBHP. Thermokinetic parameters, such as exothermic onset temperature (T ₀), maximum temperature (T _max), and enthalpy (ΔH), were obtained from thermal curves. In addition, the activation energy (E _a) and rate constant (k) were calculated by the Arrhenius equation. Therefore, the T ₀ was determined to be 91.6 °C for exothermic reaction using DSC under 4 °C min^?1 of heating rate. The E _a for exothermic reaction was calculated to be 92.38 kJ mol^?1 by DSC in this study. As far as loss prevention is concerned, thermokinetic parameters are crucial to the relevant processes in the chemical industries, particularly under process upsets.     

Pyrolysis and combustion model of oil sands from non-isothermal thermogravimetric analysis data

Thermogravimetric (TG) data of oil sand obtained at Engineering Research Center of Oil Shale Comprehensive Utilization were studied to evaluate the kinetic parameters for Indonesian oil sand samples. Experiments were carried out at heating rates of 5, 15, and 25 °C min^?1 in nitrogen, 10, 20, and 50 °C min^?1 in oxygen atmosphere, respectively. The extent of char combustion was found out by relating TG data for pyrolysis and combustion with the ultimate analysis. Due to distinct behavior of oil shale during pyrolysis, TG curves were divided into three separate events: moisture release, devolatilization, and evolution of fixed carbon/char, where for each event, kinetic parameters, based on Arrhenius theory, were calculated. Coats–Redfern method, Flynn–Wall–Ozawa method, and distributed activation energy model method have been used to determine the activation energies of degradation. The methods are compared with regard to their characteristics and the ease of interpretation of the thermal kinetics. Activation energies of the samples were determined by three different methods and the results are discussed.     

Slow molecular mobility in the amorphous thermoplastic polysulfone

The thermally stimulated depolarization current (TSDC) technique has been used to study the slow molecular mobility of polysulfone in the glassy state and in the glass transformation region, i.e., in the temperature ranging from ?155 to 183 °C. Since the polysulfone is a rigid polymer without polar side-groups, a broad and low-intensity secondary relaxation was detected in the temperature region from ?120 °C up to the glass transition; the activation energy of the motional modes of this secondary relaxation is in the range between 35 and 100 kJ mol^?1. The glass transition temperature of polysulfone provided by the TSDC technique is T _M = T _g = 176 °C (at 4 °C min^?1). The relaxation time at this temperature is τ(T _g) = 33 s and the fragility index was found to be m = 91. Our results are compared with literature values obtained by dynamic mechanical analysis and by dielectric relaxation spectroscopy. The amorphous polysulfone was also characterized by DSC; a glass transition signal with an onset at T _on = 185.5 ± 0.3 °C (heating rate 10 °C min^?1) was detected, with ΔC _p = 0.21 ± 0.01 J g^?1 °C^?1.     

Thermal behavior and solid fraction dependent gel strength model of waxy oils

Thermal behavior of waxy oils is investigated using the techniques of thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Model waxy oils and real waxy crude oils are utilized. Decomposition temperatures of waxy oils are obtained using TG analysis. The effects of thermal history, wax content, and additive on the gelation process of waxy oils are investigated using DSC. The DSC method provides a measure of wax solubility as well as solid fraction. An integration method and a computation method are utilized to predict solid fraction. In addition, wax crystallization onset points are obtained at the cooling rates ranging from 1 to 20 °C min^?1. Similarly, wax dissolution endset points are obtained at heating rates ranging from 1 to 20 °C min^?1. Extrapolated onset and endset points yield wax precipitation temperature and wax dissolution temperature, respectively. Subsequently, wax solubility curves are obtained using thermodynamic computations. A wax precipitation temperature method and a wax dissolution temperature method combine thermodynamic phase behavior with onset/endset points to predict solid fraction. Both the wax precipitation temperature method and the wax dissolution temperature method can predict solid fraction of waxy oil samples. The wax precipitation temperature method and the wax dissolution temperature method are accurate when the temperature is close to the wax appearance temperature. A heat-integration method provides accurate values of the solid fraction at temperatures significantly below the wax appearance temperature. Therefore, integration method and wax precipitation temperature/wax dissolution temperature method are combined to predict solid fraction. The effect of solid fraction on yield stress is also investigated using differential scanning calorimetry and rheometry. Finally, a new solid fraction dependent gel strength model is obtained for shut in and restart of waxy crude oil pipelines.