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1.
Vitamin PP includes two vitamers, niacin and niacinamide which are essential for energy production. Vitamins are sensitive
and losses can occur during shelf life and heating processes. Thermal analysis can provide information about thermal behavior
of each vitamer relating them with time and/or temperature exposure. The vitamers thermal behavior were studied by TG/DTG
and DSC under air and nitrogen atmosphere and the results showed that niacin is more stable than the niacinamide and the decomposition
happens by volatilization at 238 °C while niacinamide melts at 129 °C and volatilize at 254 °C when there is the total mass
loss in the TG/DTG curves. 相似文献
2.
Data on the thermal stability of drugs was required to obtain information for handling, storage, shelf life and usage. In
this study, the thermal stability of two nonsteroidal anti-inflammatory drugs (NSAIDs) was determined by differential scanning
calorimetry (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG
analysis revealed that the main thermal degradation for the naproxen and celecoxib occurs in the temperature ranges of 196–300
and 245–359 °C, respectively. The TG/DTA analysis of compounds indicates that naproxen melts (at about 158.1 °C) before it
decomposes. However, the thermal decomposition of the celecoxib started about 185 °C after its melting. The influence of the
heating rate (5, 10, 15, and 20 °C min −1) on the DSC behavior of the both 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 various methods, the following order for the thermal stability was noticed: naproxen
> celecoxib. Finally, the values of Δ S
#, Δ H
#, and Δ G
# of their decomposition reaction were calculated. 相似文献
3.
In this paper, a novel form-stable phase change material (FS PCM) was prepared by incorporating the eutectic mixture of tetradecanol (TD) and myristic acid (MA) into the hydroxylpropyl methyl cellulose (HPMC). HPMC is used as support material, and the eutectic mixture is used as phase change material. The Fourier-transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD) and scanning electron microscopy (SEM) were used to study the chemical structure, crystallization behavior and morphology of the FS PCM, respectively. FT-IR, XRD and SEM showed that the TD–MA was distributed uniformly in HPMC by physical interaction. Specific surface area (BET) and pore size analysis determined the pore characteristics of the composite, and the results showed the porosity of HPMC. The thermal properties, thermal stability and thermal reliability were detected by differential scanning calorimetry (DSC), thermogravimetric analysis (TG), thermal cycling test and leakage test. The TG, DSC and leakage analysis results revealed that the absorption of eutectic mixture into HPMC is nearly 50% and without seepage from the composite. The peak temperatures of melting and solidifying were 34.61 and 31.09 °C, and latent heat was 102.11/84.58 J g ?1 by DSC. TG and cycling experiment detected that the FS PCM showed good thermal stability and reliability performance. 相似文献
4.
Resol resins are used in many industrial applications as adhesives and coatings, but few studies have examined their thermal
degradation. In this work, the thermal stability and thermal degradation kinetics of phenol–formaldehyde (PF) and lignin–phenol–formaldehyde
(LPF) resol resins were studied using thermogravimetric analysis (TG) in air and nitrogen atmospheres in order to understand
the steps of degradation and to improve their stabilities in industrial applications. The thermal stability of samples was
estimated by measuring the degradation temperature ( T
d), which was calculated according to the maximum reaction rate criterion. In addition, the ash content was determined at 800 °C
in order to compare the thermal stability of the resol resin samples. The results indicate that 30 wt% ammonium lignin sulfonate
(lignin derivative) as filler in the formulation of LPF resin improves the thermal stability in comparison with PF commercial
resin. The activation energies of degradation of two resol resins show a difference in dependence on mass loss, which allows
these resins to be distinguished. In addition, the structural changes of both resins during thermal degradation were studied
by Fourier transform infrared spectroscopy (FTIR), with the results indicating that PF resin collapses at 300 °C whereas the
LPF resin collapses at 500 °C. 相似文献
5.
Abstract Novel cyclotriphosphazenes containing cyanato group (PZCN) derivatives were synthesized by a substitution reaction of 4-hydroxyphenoxycyclotriphosphazenes and cyanogen bromide (BrCN) in the presence of triethylamine (TEA). The PZCNs were characterized by FT-IR, liquid chromatography–mass spectrometry (LC-MS), 1H NMR, 13C NMR, and 31P NMR spectroscopy. Curing reactions of the PZCNs were evaluated by FT-IR spectroscopy, thermogravimetry/differential thermal analysis (TG/DTA), and differential scanning, calorimetry (DSC). The PZCNs exhibited an exothermic peak due to curing within the temperature range of 140–300°C by DSC. The PZCNs were completely cured at 220°C. The cured PZCNs exhibited high thermal stability up to 350°C, a high char-forming capability, and electrical properties, such as dielectric constants (Dks) between 2.68 and 2.87, and dissipation factors (Dfs) between 0.008 and 0.013 at 1 MHz. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献
6.
Characterization, thermal stability, and thermal decomposition of alkaline earth metal mandelates, M(C 6H 5CH(OH)CO 2) 2, (M = Mg(II), Ca(II), Sr(II), and Ba(II)), were investigated employing simultaneous thermogravimetry and differential thermal analysis or differential scanning calorimetry, (TG–DTA or TG–DSC), infrared spectroscopy (FTIR), complexometry, and TG–DSC coupled to FTIR. All the compounds were obtained in the anhydrous state and the thermal decomposition occurs in three steps. The final residue up to 585 °C (Mg), 720 °C (Ca), and 945 °C (Sr) is the respective oxide MgO, CaO, and SrO. For the barium compound the final residue up to 580 °C is BaCO 3, which is stable until 950 °C and above this temperature the TG curve shows the beginning of the thermal decomposition of the barium carbonate. The results also provide information concerning the thermal behavior and identification of gaseous products evolved during the thermal decomposition of these compounds. 相似文献
7.
This work synthesized and characterized the NOR-RIB 1:1 (mol–mol) cocrystal. During a study of the reagents, Riboflavin (RIB) melted at 304 °C, which is different from the temperature previously reported in the literature (280–290 °C); therefore, this compound was characterized individually. Subsequently, the cocrystal was synthesized with the active pharmaceutical ingredient (API) norfloxacin (NOR) with the RIB coformer, and the mechanochemical synthesis route was adopted. NOR, RIB, and the cocrystal were characterized by thermogravimetry–differential thermal analysis (TG–DTA), differential scanning calorimetry (DSC), DSC coupled to a microscope (photo-DSC), mid-infrared spectroscopy (MIR), and powder X-ray diffraction. The results of thermal analysis showed that the RIB starts decomposition process (260 °C) and then melts (304 °C). The MIR found that beginning at 295 °C, the RIB passes into the form of a decomposition intermediate; therefore, the melting point observed in the DSC curve is related to this decomposition material. The cocrystal presented thermal stability (200 °C) lower than the API (235 °C) and the coformer (260 °C). The DSC curve did not contain a melting peak. The bands at 1726 cm?1 (C=O of the carboxylic acid) for the NOR, and the band at 3326 cm?1 (stretch O–H), among others, were not visible for the cocrystal in the MIR spectrum, indicating interactions in these regions. The X-ray diffractograms showed a new diffraction pattern, which proved the obtainment of a new phase and cocrystal formation. 相似文献
8.
The esterification of sodium lignosulfonate (LS) with maleic anhydride (MA), which is a by-product of the papermaking industry, was successfully carried out in water solution under mild conditions. The esterification percentage was influenced by many factors including the concentration of LS and the weight ratio of LS/MA, temperature, pH, and reaction time. Optimum conditions of the factors studied obtained after a series of single-factor experiments for lignosulfonate reacted with maleic anhydride were weight ratio of 1.2 to 1.0 under vigorous stirring at 55°C in alkaline solution for 4 h. The products were characterized by FT-IR, thermogravimetric (TG) analysis, and differential scanning calorimetry (DSC). The emergence of a 1717 cm ?1 peak of the FT-IR curves indicated that the esterification reaction was successfully carried out. Moreover, the TG results showed an increase in thermal stability of esterified lignosulfonate compared to unmodified lignosulfonate. 相似文献
9.
Thermal stability and decomposition kinetics for two energetic materials, potassium nitroform (KNF) and 5-Nitro-2,4-dihydro-3 H-1,2,4-triazol-3-one (NTO), were investigated to obtain information on their safety for handling, storage, and use. Differential scanning calorimetry (DSC) and simultaneous thermogravimetry-differential thermal analysis (TG-DTA) techniques have been used to study thermal behavior of these energetic compounds. The results of TG analysis revealed that the main thermal degradation for the KNF occurs during two temperature ranges of 270?C330 and 360?C430?°C. Meanwhile, NTO decomposes completely in temperature range of 250?C300 °C. TG-DTA analysis of KNF indicates that this energetic compound dehydrated (at about 108?°C) before its decomposition. However, NTO is thermally stable until its decomposition. The decomposition kinetic of energetic materials was studied by non-isothermal DSC under various heating rates. Kinetic parameters such as activation energy and frequency factor for thermal decomposition of energetic compounds were obtained via the methods proposed by ASTM E696 and Starink. Also, thermodynamic parameters correspond to the activation of thermal decomposition and critical ignition temperatures of the compounds were obtained. 相似文献
10.
To obtain an oil-displacement polymer with good thermal stability and solution properties, self-assembling acrylamide (AM)/4-butylstyrene
(BST) copolymers (PSA) were synthesized by the micellar copolymerization technique. The resulting polymer was characterized
by elemental analysis and UV and FT-IR spectroscopy. Conventional DSC measurement was used successfully to characterize the
hydrophobic microblock structure of PSA, and two glass transition temperatures were found in the polymer: at 203 °C for the
AM segments and at 106 °C for the hydrophobic BST segments. The initial decomposition temperature (234 °C) of the polymer
is higher than that of polyacrylamide (210 °C). The DSC and TG results suggest that incorporation of BST into PSA enhances
the molecular rigidity and thermal stability of the polymer. The apparent viscosity of a PSA solution greatly depends on the
amount of BST in the polymer, and the polymer exhibits salt-thickening, temperature-thickening, thixotropy, pseudo-plastic
behavior, anti shearing, and good anti-aging properties at 80 °C. In addition, the apparent viscosities of PSA solutions are
increased remarkably by the addition of a small amount of surfactant. AFM measurements show that large block-like aggregates
and small compact aggregates are formed in aqueous solutions of 0.4 g⋅dL −1 PSA because of strong intermolecular hydrophobic associations, despite the low molecular weight, and their sizes increase
upon addition of a small amount of salt. 相似文献
11.
The thermal behavior of kaolinite?Cdimethylsulfoxide intercalation complex was investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) analysis, and Fourier-transform infrared (FT-IR) spectroscopic analysis. The samples gradually heated up to different temperatures were studied by XRD and FT-IR. The kaolinite?Cdimethylsulfoxide intercalation complex is stable below 130?°C. With the rise in the temperature, the relative intensity of the 1.124-nm peak gradually decreased and disappeared at 200?°C, however, the intensity of the 0.714?nm peak increased in the XRD patterns. In the infrared spectra, the appearance of methyl bands at 3018, 2934, 1428, and 1318?cm ?1 indicates the presence of intercalated dimethylsulfoxide, the intensities of these bands decreased with the temperature rising and remained until around 175?°C, which agree with the XRD and TG?CDSC data. 相似文献
12.
The aim of this study was the synthesis of three different epoxy compounds based on naphthalene-2,7-diol (2,7-NAF.EP, 2,7-NAF.WEP, 2,7-NAF.P.EP) and then their cross-linking by triethylenetetramine (TETA). All epoxides were prepared by the reaction of naphthalene-2,7-diol with epichlorohydrin but under different conditions and with other catalysts. The structures of the obtained compounds before and after the cross-linking reactions were confirmed by the attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR). The ATR/FT-IR spectra of cross-linked compounds show disappearance of the C–O–C bands (about 915 cm?1) derived from the epoxy groups. DSC and TG/DTG measurements indicated that the obtained materials possess good thermal resistance; they are stable up to about 250 °C. The hardness of the cross-linked products was determined using the Shore D method. The highest value of hardness was obtained for the 2,7-NAF.EP-POL. Additionally, the UV–Vis absorption spectra of the obtained polymers were registered and evaluated. 相似文献
13.
Norfloxacin was studied by thermal methods (TG and DSC), X-ray powder diffraction, and by FT-IR, UV-VIS and NMR spectroscopy.
The drug substance can be prepared in two different crystalline forms and in amorphous state, depending on the experimental
conditions of preparation. DSC examinations were carried out at various heating rates and by cycling the samples in the temperature
range 50°–250°C. The unstable crystalline form undergoes two irreversible solid-solid phase transitions at 176.5° and 197.6°C.
The polymorph melts in the temperature range 218.5°–220.0°C.
Zusammenfassung Norfloxacin wurde mittels thermischer Methoden (TG und DSC), weiterhin mittels der Debye-Scherrer-Methode und FTIR-, UV-VIS-und
NMR-Spektroskopie untersucht. Je nach den experimentellen Bedingungen bei der Herstellung kann die Wirkstoffsubstanz in zwei
verschiedenen kristallinen und in einer amorphen Form hergestellt werden. Die DSC-Untersuchungen wurden bei zahlreichen Aufheizgeschwindigkeiten
und durch abwechselnden Temperaturwechsel zwischen Raum- und Schmelztemperatur durchgeführt. Die unstabile kristalline Form
unterliegt zwei irreversiblen Feststoff-Feststoff-Umwandlungen bei 176.5° und bei 195.6°C. Das polymorphe Material schmilzt
im Temperaturbereich 218.5°–220.0°C.
相似文献
14.
The thermal stability of HMT under dynamic, isothermal and adiabatic conditions was investigated using differential scanning calorimeter (DSC) and accelerating rate calorimeter (ARC), respectively. It is found from the dynamic DSC results that the exothermic decomposition reaction appears immediately after endothermic peak, a coupling phenomenon of heat absorption and generation, and the endothermic peak and exothermic peak were indentified at about 277–289 and 279–296 °C (Tpeak) with the heating rates 1, 2, 4 and 8 °C min−1. The ARC results reveal that the initial decomposition temperature of HMT is about 236.55 °C, and the total gas production in decomposition process is 6.9 mol kg−1. Based on the isothermal DSC and ARC data, some kinetic parameters have been determined using thermal safety software. The simulation results show that the exothermic decomposition process of HMT can be expressed by an autocatalytic reaction mechanism. There is also a good agreement between the kinetic model and kinetic parameters simulated based on the isothermal DSC and ARC data. Thermal hazards of HMT can be evaluated by carrying out thermal explosion simulations, which were based on kinetic models (Isothermal DSC and ARC) to predict several thermal hazard indicators, such as TD24, TD8, TCL, SADT, ET and CT so that we can optimize the conditions of transportation and storage for chemical, also minimizing industrial disasters. 相似文献
15.
Thermogravimetric (TG) techniques and differential scanning calorimetry (DSC) used for the study of pre-formulation or drug–adjuvant compatibility have been gaining importance in Brazil. These techniques are being used for the verification of possible interactions between drugs and adjuvants. Aiming at studying the behavior of a plant extract and its mixture with adjuvants, using these thermoanalytical techniques the plant species Heliotropium indicum L. was used. This plant which is originally from India and has been well acclimatized in Brazil has healing and anti-inflammatory properties. The methodology for obtaining the extract followed the Brazilian Pharmacopoeia methodology. And the incorporation of the extract with adjuvants was through binary mixtures (1:1 w/w). The TG and DSC curves were obtained under nitrogen atmosphere (25 mL min ?1) at a heating rate of 5 °C min ?1; TG tests were analyzed within a temperature range from 25 to 600 °C and DSC from 25 to 300 °C. The TG curves show good thermal stability of the extract and its mixtures with adjuvants up to 150 °C, except the propylene glycol (PLG). The DSC curves revealed an incompatibility of the extract with methylparaben and PLG mixture. 相似文献
16.
The pyrolysis behavior of bitumen was investigated using a thermogravimetric analyzer–mass spectrometer system (TG–MS) and
a differential scanning calorimeter (DSC) as well as a pyrolysis-gas chromatograph/mass spectrometer system (Py-GC/MS). TG
results showed that there were three stages of weight loss during pyrolysis—less than 110, 110–380, and 380–600 °C. Using
distributed activation energy model, the average activation energy of the thermal decomposition of bitumen was calculated
at 79 kJ mol −1. The evolved gas from the pyrolysis showed that organic species, such as alkane and alkene fragments had a peak maximum temperature
of 130 and 480 °C, respectively. Benzene, toluene, and styrene released at 100 and 420 °C. Most of the inorganic compounds,
such as H 2, H 2S, COS, and SO 2, released at about 380 °C while the CO 2 had the maximum temperature peaks at 400 and 540 °C, respectively. FTIR spectra were taken of the residues of the different
stages, and the results showed that the C–H bond intensity decreased dramatically at 380 °C. Py-GC/MS confirmed the composition
of the evolved gas. The DSC revealed the endothermic nature of the bitumen pyrolysis. 相似文献
17.
The ornidazole drug substance presents melt at approximately 90 °C (∆T = 85–98 °C), which is critical for its use on pharmaceutical manufacturing process. This work aimed the thermal characterization
of ornidazole raw-material synthesized by three different manufacturers from India, China, and Italy, using the thermoanalytical
techniques of DTA, DSC, and TG, besides the verification of its stability and compatibility as a solid pharmaceutical product
by the analysis of its binary mixtures (BM) with excipients and a tablet formulation. The characterization includes the thermal
decomposition kinetic investigation by Ozawa model using Arrhenius equation and drug purity determination by Van’t Hoff equation.
The DSC purity determination and precision were compared with results from UV–Vis spectrophotometric and liquid chromatography,
showing an adequate correlation before being recommended as a general method for purity assay. The drug raw-materials presented
similar quality and zero-order kinetic behavior, besides showing differences on thermal stability. The drug presented compatibility
with the tested excipients since the BM studied presented melting at the same temperature range as the drug and a decomposition
temperature similar to the drug for two of the BM, and at a higher temperature for the others three of the BM evaluated, which
presented excipients with higher molecular structure, capable of spatial coating on the small drug molecule promoting a physical
interaction pharmaceutical acceptable. The tablet was processed by wet granulation and compressed under normal conditions
of pressure and temperature, maintaining the physical properties of solid drug approving the manufacturing process used. In
this study, the thermal analysis was used with success as an alternative method to characterize, quantify, and perform a preformulation
study. 相似文献
18.
Thermal treatment is one of environmental friendly wood modification processes, developed in order to improve wood’s natural
durability and dimensional stability. Beside wood species, mainly isothermal temperature of heat-treatment and process duration
affect these properties, which also correlate with the mass losses caused by the treatment. However, there is a lack of suitable
external quality control methods. In this work thermogravimetry as a potential method for determining the degree of thermal
modification is presented. Several calibration curves, representing the mass losses in a certain temperature range (the values
obtained from the TG curves) compared to weight losses caused by previous heat-treatment (known values), were established
for spruce wood samples modified at different isothermal temperatures (from 170 to 220 °C). Linear plot and good correlation
factors ( R
2 = 0.95 and 0.96) were obtained for the TG mass losses from 130 to 280 °C and from 130 to 300 °C, both under nitrogen atmosphere.
The predominant cause of mass loss in this temperature region was depolymerisation and thermal decomposition of hemicelluloses
residues. Lower correlation factors were obtained under the air atmosphere and in the wider temperature range, respectively. 相似文献
19.
Thermal behavior of its components such as separator, electrolyte, cathode, anode, and each binder were investigated by differential scanning calorimetry and thermal gravimetric (DSC/TG) to explain thermal runaway mechanism of Li‐ion battery under overcharged test. DSC results indicated the decomposition reaction temperature of SEI (solid electrolyte interface) layer in anode was at about 126°C. It was found that heat generation in anode under normal charged state increased obviously with the increasing of charged voltage. When the battery was overcharged to 4.6 V or 5.0 V, the onset temperature and heat generation of thermal reaction in anode changed a little, while those in cathode had large increase. It was proposed that thermal behavior in cathode mainly caused by the reaction of electrolyte with evolutional oxygen played a key role to thermal runaway for the studied Li‐ion battery under overcharged test. 相似文献
20.
In sedimentary environments or clay-rich rocks, clay minerals are usually combined with organic matter; however, little research has focused on the effects of combinations of organic matter and clay minerals on the thermal degradation of organics and on subsequent hydrocarbon generation. In this study, the long-chain fatty acid octadecanoic acid (OA) and its derivative octadecy trimethyl ammonium bromide (OTAB) were selected as model organics. The organics were prepared for clay–organic associations with Na-based montmorillonite (Mt(Na)). The thermal decomposition behaviors of these associations were studied via thermogravimetric (TG/DTG) analysis. In the presence of Mt(Na), OA decomposed at 275.2 °C, decomposing sooner than pure OA. The thermal decomposition behavior of OTAB is nearly consistent with that of pure OTAB, but for interlayer OTAB, the decomposition temperature increased to higher than 300 °C. The results indicate that Mt(Na) plays a dual role in the thermal decomposition of fatty acid. Mt(Na) may accelerate the thermal decomposition of OA, and inherent solid acidity levels may be the key factor. In addition, the interlayer structure of Mt(Na) can increase the thermal stability of OA and OTAB. The above results further demonstrate that the thermal decomposition behavior of a given organic material may also depend on its structure and composition. In the presence of Mt(Na), organics with amino and amine structures are more stable than those with carboxyl groups. 相似文献
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