Thermal stability of styrene butadiene rubber (SBR) composites filled with kaolinite/silica hybrid filler

Styrene butadiene rubber (SBR) composites filled with fillers, such as modified kaolinite (MK), precipitated silica (PS), and the hybrid fillers containing MK and PS, were prepared by melt blending. The kaolinite sheets were finely dispersed in the SBR matrix around 20–80 nm in thickness and reached the nano-scale. The SBR composites with fillers exhibited excellent thermal stability compared to the pure SBR. The thermal stability of SBR composites was improved with the increasing of MK mass fraction. When MK hybridized with PS, kaolinite sheets were covered by the fine silica particles and the interface between filler particles and rubber matrix became more indistinct. SBR composite filled by hybrid fillers containing 40 phr MK and 10 phr PS became more difficult in decomposition and was better than that of 50 phr PS/SBR and 50 phr MK/SBR in thermal stability. Therefore, the hybridization of the fine silica particles with the kaolinite particles can effectively improve the thermal stability of SBR composites.     

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.     

Synthesis and properties of Fe0.83V1.17O4

Thermal properties of the organic–inorganic bicontinuous nanocomposites prepared via in situ two-stage polymerization of various silanes, epoxy, and amine monomers are investigated, and the impact of filler content and its organic compatibility on thermal stability of these nanocomposites is studied. Two series of epoxy–silica nanocomposites, namely, EpSi-A and EpSi-B containing 0–20 wt% silica, are synthesized. An epoxy–silane coupling agent is employed to improve the organic compatibility of silica in EpSi–B nanocomposites. The composites synthesized via two-stage polymerization are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. DSC and TG/differential thermogravimetric results reveal substantially high glass transition (T _g) and excellent thermal stability of the bicontinuous nanocomposites as compared with pristine epoxy polymer. Both T _g and thermal properties, however, considerably vary depending on the organic compatibility of the nanocomposites. Significantly higher decomposition temperatures are recorded in case of EpSi-B nanocomposites owing to the chemical links between the epoxy and silica phases. Kinetic studies also show relatively higher activation energies of pyrolysis for EpSi-B nanocomposites.     

Thermal stability and sensitivity of RDX-based aluminized explosives

The thermal decomposition characteristics and thermal sensitivity are key indicators for reflecting the thermal stability of explosives in storage and application. The thermal decompositions in different degrees are used to determine the dominant factor which controls the thermal stability of composite explosive. Four kinds of RDX-based aluminized explosives are marked as RA1, RA2, RA3, and RA4 with the Al content increasing from 10 to 40 mass%. The initial thermal decomposition behaviors were studied by DPTA and the complete thermal decompositions were studied by DSC and TG. The thermal sensitivities were characterized by 5-s explosion point. The effects of micron-sized Al particles and their contents on thermal decomposition were investigated. The evolved gas amount (V _i) from DPTA test follows RA3 < RA4 < RA2 < RA1, indicating that RA3 has the best thermal stability at ambient storage conditions. However, according to TG and DSC tests, the characteristic temperatures of thermal decomposition (T _p, T _b, and T _SADT), the thermodynamic parameters (?H _e, ?S ^≠, and ?H ^≠), the kinetic parameters (E _a and A), and the 5-s explosion points all follow RA4 < RA3 < RA2 < RA1. The results indicate that the Al particles play different roles in the different degrees of thermal decomposition. In the initial decomposition, the Al particles have not been activated and are considered as inert materials that hinder the decomposition of explosive. In the complete decomposition, the Al particles catalyze the thermal decomposition, and such catalysis becomes more obvious as the Al content increases to a certain degree.     

Bismaleimide/rice husk silica reinforced composites

Silica derived from the renewable resource rice husk is modified using stearic acid and N-[4-(chlorocarbonyl)phenyl]maleimide. These materials are used as fillers in the bismaleimide, 4,4′-bismaleimidodiphenylmethane (BMIM), and thermally cured. The thermogravimetric (TG) curves for polyBMIM/silica composites showed no pronounced changes compared to the TG curve for the pure polyBMIM. Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and Friedman methods are used to compute the activation energy (E _a) for degradation. Silica and surface-modified silica using stearic acid dispersed by ultrasonication increase the activation energy for degradation and show considerable influence on the thermal stability of cured BMIM. The long alkyl chain present in the stearic acid modified silica and the bulky spacer present in the chemically modified silica definitely alter the degradation process of cured BMIM. The SEM studies indicated uniform dispersion of the silica particles in the polyBMIM.     

Thermal behavior of BST//PVDF ceramic–polymer composites

In this paper, we report the results of a study of microstructure and thermal behavior of ceramic–polymer composites composed of barium strontium titanate Ba_0.6Sr_0.4TiO₃ (BST60/40) and polyvinylidene fluoride (PVDF). The Ba_0.6Sr_0.4TiO₃ ceramic powder was prepared by the sol–gel method. Thermal evolution of the dried gel as well as ceramic powder was studied by simultaneous thermal analysis. The composite BST60/40//PVDF was obtained by hot pressing method for volume fraction of BST60/40 ceramic powder c _v = 50 %. The morphology of BST60/40//PVDF composite powder was observed by transmission electron microscopy and the morphology of BST60/40//PVDF composite sample was observed by scanning electron microscopy. Temperature dependence of dielectric constant and dielectric loss factor of BST60/40//PVDF composites was measured in the frequency range of f = (10 × 10³–1 × 10⁶) Hz. Dynamic mechanical properties of BST60/40//PVDF composites were measured by dynamic mechanical thermal analysis DMTA.     

Thermal stability of several polyaniline/rare earth oxide composites III

Polyaniline/Nd₂O₃ (PANI/Nd₂O₃) composites were synthesized by in situ polymerization at the presence of sulfosalicylic acid (as dopant). The composites obtained were characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD). The thermal stability of the composites was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG). The electrochemical performance of the composites was investigated by cyclic voltammetry (CV). The results of FTIR, XRD, and CV show that the structure of composite has changed greatly when Nd₂O₃ content is ≥0.7 g and the PANI in the composite has transformed into pernigraniline base (non-conducting state) from emeraldine base (conducting state). TG–DTG analysis indicates that the thermal stability of PANI/Nd₂O₃ composites was higher than the pure PANI.     

Dehydration characteristics of struvite-K pertaining to magnesium potassium phosphate cement system in non-isothermal condition

Struvite-K (KMgPO₄·6H₂O) is the main hydration product of magnesium potassium phosphate cement. Its thermal stability is critical to the properties of magnesium potassium phosphate cement. Therefore, in this study, the dehydration behavior of struvite-K was investigated at N₂ atmosphere in non-isothermal condition. The process was conducted and controlled in a simultaneous TG/DTA analyzer, at heating rates of 2, 5, 10, 15, and 20 K min^?1. The residual mass was always around 58.5% of the initial one, regardless of the heating rate, which corresponds to the dehydration reaction through one step, KMgPO₄·6H₂O → KMgPO₄. The activation energy (E _a) corresponding to the dehydration of struvite-K was evaluated by non-isothermal kinetic analysis based on the application of isoconversional methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods). The calculated results show that Flynn–Wall–Ozawa has slightly higher values of activation energy (E _a) and correlation coefficients (R ²). Both methods have been proved to be suitable for analyzing dehydration behavior of struvite-K.     

Thermosetting polymers from epoxy resin and a Nickel catalyst of diethylenetriamine

The kinetics and mechanism of cure reaction of DGEBA using a chelate of Ni(II) with diethylenetriamine (dien), Ni(dien)₂I_2, as a curing agent was studied by DSC. TG curve of the complex curing agent showed mass loss in two region of temperature: 200–320 and 450–550 °C. Dynamic DSC measurements showed only one exothermic peak with a maximum about 250 °C depending on the heating rate. According to the methods of KAS and Ozawa–Flynn–Wall the values of E _a were 92.5 and 96.2 kJ/mol, respectively. The isoconversional kinetic analysis in whole range of conversion, α = 0.02–0.95, showed small changes in the E _a values in the region of α = 0.04–0.6 and most likely represent some average values (E _a = 110 kJ/mol) between the values of E _a of non-autocatalyzed and autocatalyzed reactions. Using the sole dependence of E _a on α, the time required to reach fully cured materials under isothermal conditions were also predicted and compared with the experimental results.     

Thermal analysis, decomposition kinetics, and molecular modeling of transition metal (Fe, Co) surfactant complexes

A detailed thermal analysis of iron and cobalt surfactant complexes of the type [M(CH₃COO)₄]^2?[C₁₂H₂₅NH₃ ⁺]₂ has been carried out using Thermogravimetric (TG) analysis at different heating rates (i.e., 5, 10, 15, and 20 °C min^?1). It has been observed that iron complex decomposes by a different mechanism compared to other transition metal complexes. Metal is the final product instead of metal oxide. Combining the results from our previous study, first row transition metal complexes exhibit an order of stability in agreement with the famous Irving Williams series, i.e., the apparent activation energy, E for thermal decomposition varies as: E _Fe > E _Co < E _Ni < E _Cu > E _Zn (exception being iron because of different decomposition mechanism). Thermal decomposition parameters have been measured and compared using the multiple heating rate method of Flynn–Wall–Ozawa. Further, molecular modeling calculations have been carried out to compare the experimental TG data with theoretical computations for the synthesized metal surfactant complexes. Minimum energy optimized structures for the complexes have been obtained using Gaussian software.     

Resistance of composite materials based on BaCeO3 against the corrosive effects of carbon dioxide and water vapour at intermediate fuel cell operating temperatures

The objective of this work is to analyse the chemical stability of BaCe_0.85Y_0.15O_3?δ –Ce_0.85Y_0.15O_2?δ (BCY15–YDC15) composite materials at 600 °C and to compare the aforementioned chemical stability with that of pure BCY15. The composite powders were obtained by mixing together powders of BCY15 and YDC15 in the following volume fractions: 90 % BCY15 + 10 % YDC15, 70 % BCY15 + 30 % YDC15, 30 % BCY15 + 70 % YDC15, 20 % BCY15 + 80 % YDC15 and 10 % BCY15 + 90 % YDC15. After that both powders and sintered samples of the BCY15 and the BCY15–YDC15 composites were saturated in two different atmospheres at 600 °C: CO₂/H₂O (3.1 mol% H₂O) and N₂/H₂O (46.8 mol% H₂O). The effects of the previously mentioned atmospheres on the physicochemical properties of the samples were investigated via differential thermal analysis (DTA) combined with thermogravimetric analysis (TG). Furthermore, mass spectrometry was used to analyse the chemical composition of the gases released from the samples during the DTA–TG heating process. The surface and cross-section morphology of the samples were examined by scanning electron microscopy. Moreover, the phase composition of each sample was studied via X-ray Diffraction. From the combined analysis, it can be concluded that the addition of YDC15 in the composite samples leads to an increase in resistance against the corrosive effects of CO₂. Furthermore, it was determined that all samples maintain stability in the presence of H₂O at 600 °C.     

The investigation of methyl phenyl silicone resin/epoxy resin using epoxy-polysiloxane as compatibilizer

Styrene–butadiene rubber was subjected to long-term thermal aging treatment at 80 °C with aging period up to 180 days. The degradation kinetics of the aged sample was analyzed by thermogravimetric analysis. Multiple heating rate experiments were carried out in nonisothermal conditions and three isoconversional model-free methods (Friedman; Kissinger–Akahira–Sunose; Li and Tang methods) were employed. The results showed that the temperature for 5 % mass loss increased, whereas the maximum mass loss temperature decreased after aging. Activation energies (E _a) derived from the three methods were found to be dependent on conversion degree (α). E _a increased with increasing α in the whole range of conversion for samples aged for 0, 60, and 120 days, while the aged samples displayed higher E _a values. However, samples aged for 180 days showed declining E _a versus α. The changes on the degradation kinetics were associated with the modification on the chemical structure after thermal aging.     

Evaluation of thermal stability and parameters of dissolution of nifedipine crystals

Nifedipine is a calcium channel blocker as well as a powerful vasodilator used to treat ischemic heart disease and hypertension. Its photosensitivity and very low solubility in water have been widely acknowledged as important properties deserving improvements. The main thrust of this study is to characterize the nature and the solid-state of nifedipine crystals obtained using different solvents as well as assess the stability by thermal methods (TG and DSC) and crystals structure by means of spectroscopic techniques (MID FTIR and XRD) and assess the dissolution parameters for such crystals. The calculated kinetic parameters activation energy (E _a = 123.3 kJ mol^?1 ± 0.1), the factor frequency (A = 25.93 ± 0.9 min^?1), and the reaction order (n = 0.2) of the main stage of thermal decomposition of nifedipine raw material were performed according to the Ozawa model. The data showed a zero-order kinetic behavior for all crystals despite the different values of E _a and A. The dissolution profiles were obtained for such crystals in three dissolution media with different pH values. After 1 h of dissolution, the higher amount of nifedipine dissolved was observed for crystals obtained in isopropyl alcohol (52.5 %, pH 4.5), followed by those in chloroform (48.1 %, pH 1.2) and subsequently in acetone (32.5 %, pH 6.8). Results showed different thermal stabilities and significant variations in the solubility of the crystals.     

Thermogravimetry of the thermal degradation of Japanese lacquer (urushi) films

The kinetics of the thermal degradation of Japanese lacquer (urushi) films in N₂ and in air were studied by means of thermogravimetry (TG). Thermogravimetric and derivative thermogravimetric curves indicated that the degradation occurred in three stages. The atmosphere influenced the apparent activation energies (E _a) of the three degradation stages. The activation energies (E _a) for the first stage in N₂ and air, obtained from the TG curve, were 19.12 and 10.19 kcal mol^?1, respectively, and the corresponding pre-exponential factors (A) were 6.18 × 10⁵ and 1.24 × 10² min^?1 for 1-year-old urushi films.     

Study of thermal behaviour of some edible mushrooms

This paper is aimed to analyse the thermal behaviour in air of edible mushrooms through nonisothermal (TG, DTG, DTA) and calorimetric (Berthelot calorimeter) methods. The studied mushrooms were Pleurotus ostreatus spontaneously grown and from culture and Agaricus bisporus from culture, currently used in alimentation but insufficiently investigated from this point of view. The analysis of TG–DTG–DTA curves has indicated that the degradation mechanism is complex and characteristic to every species and major differences between the cap and the stipe of investigated mushrooms have not been recorded. These species are thermally stable in the range of 30–160 °C. The thermal stability in terms of initial degradation temperature (T _i °C) and the temperature corresponding to the conversion grade (T _α=0.03 °C) indicate that the stipe has a thermal stability close to the cap one and that the cultivated mushrooms are more thermally stable than those spontaneously grown. The obtained results concerning the combustion of the sample using Berthelot calorimeter are in accordance with the TG–DTG–DTA analysis. The residue obtained is a measure of the mineral content and is quantitatively close.     

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and characterization of sulfonated polyimide/TiO2 composite membrane for vanadium redox flow battery

A sulfonated polyimide (SPI)/TiO₂ composite membrane was fabricated by a blend way to improve its performance in vanadium redox flow battery (VRB). Both EDS and XRD results verify the successful preparation of the SPI/TiO₂ composite membrane. The surface SEM image shows its homogeneous structure. TG analysis identifies its thermal stability. The SPI/TiO₂ composite membrane possesses much lower permeability of VO²⁺ ions (2.02?×?10^?7 cm² min^?1) and favorable proton conductivity (3.12?×?10^?2 S cm^?1). The VRB single cell with SPI/TiO₂ composite membrane shows higher coulombic efficiency (93.80–98.00 %) and energy efficiency (83.20–67.61 %) at the current density ranged from 20 to 80 mA cm^?2 compared with that with Nafion 117 membrane. And the operational stability of the as-prepared composite membrane is good after 50 times of cycling tests. Therefore, the low-cost SPI/TiO₂ composite membrane with excellent battery performance exhibits a great potential for application in VRB.     

Thermal conductivity behavior of SiC–Nylon 6,6 and hBN–Nylon 6,6 composites

A study was performed to determine the effect of the content and orientation of fillers on the thermal conductivity of a polymeric composite packed with hexagonal boron nitride (hBN) and silicon carbide (SiC) fillers. The thermal conductivity behavior of SiC–Nylon 6,6 and hBN–Nylon 6,6 composites was more dependent on the orientation and shape of the filler than on its thermal conductivity. The thermal conductivity of SiC–Nylon 6,6 composites with 59 % (v/v) isotropic SiC fillers increased from 0.25 to 3.83 W/m K. That of hBN–Nylon 6,6 composites with 62 % (v/v) anisotropic hBN fillers increased from 0.25 to 2.16 W/m K in the perpendicular direction whereas in the parallel direction it increased rapidly to 8.55 W/m K .     

Kinetic study of the thermal decomposition of poly(vinyl alcohol)/kraft lignin derivative blends

A kraft lignin derivative (KLD) obtained by reaction with p-aminobenzoic acid/phthalic anhydride, was blended with poly(vinyl alcohol) (PVA) by solution casting from DMSO. PVA and PVA/KLD films were exposed to ultraviolet radiation (Hg lamp, 96 h) and analyzed by thermogravimetry (TG) in inert and oxidative atmosphere. Typical multi-step decomposition profiles were obtained. The apparent activation energy (E_a) of the thermal degradation of the samples was computed by the Vyazovkin method. The KLD degradation presented only small intervals of decomposition degree with constant E_a values. PVA and blends showed intervals of up to 50% in decomposition degree with nearly constant E_a, and smaller intervals in which E_a varies drastically. The influences of samples irradiation and of surrounding gas in TG analysis on E_a are also shown.     

Synthesis,thermal decomposition and dielectric behavior of bis(thiourea)silver(I)nitrate

New semi-organic bis(thiourea)silver(I)nitrate (TuAgN) single crystals have been grown from slow evaporation solution growth technique. Single crystal X-ray diffraction study reveals that the crystal belongs to orthorhombic system with the non-centrosymmetric space group C2221 and the calculated cell parameters are a = 33.3455 (6) Å, b = 45.2957 (7) Å, c = 20.3209 (5) Å, α = β = γ = 90°, and V = 30692.8 (10) Å ³. The thermal stability and decomposition behavior of TuAgN compound have been studied by thermogravimetric analysis at three different heating rates 5, 10, and 15 °C min^?1. The effective activation energy (E _a) and pre-exponential factor (ln A) of thermal decomposition of thiourea from TuAgN compound at three different heating rates are estimated by model free methods: Arrhenius, Flynn–Wall, Kissinger, and Kim–Park. The calculated effective activation energies were found to vary with the fraction (α) reacted. The compensation effect between the (ln A) and (E _a) has also been studied. Dielectric properties of TuAgN crystal have been studied in a wide range of frequencies and temperatures. AC conductivity has also been carried out.