查看更多>>摘要：A novel fire-retardant system containing of allylamine polyphosphate/pentaerythritol (AAPP/PER) was used to enhance fire safety of polypropylene (PP). A series of PP with AAPP and PER were mixed via melt blend. Afterwards PP-AAPP/PER system was treated by electron-beam irradiation to increase its thermal stability. The degradation and fire behavior of PP-AAPP/PER system was systematically investigated. The results showed that the LOI testing of PP with 20 wt%AAPP/PER was greatly increased and passed UL 94 vertical testing V-0 rating level. Moreover, the cone-calorimeter testing showed that heat release, smoke produce as well as toxic gasses production of PP-AAPP/PER system largely decreased. Incorporation of PER and AAPP was very efficient for enhancing the fire safety of PP composites due to relatively more compact of char residues. Moreover, the sustainable electron-beam irradiation without any use of thermal stabilizers was used to improve the thermal performance of PP-AAPP/PER system.
查看更多>>摘要：A sort of low density polyethylene (LDPE) was characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), thermal analysis methods (TG, DTG, DTA) in nitrogen flow at constant heating rates of 2.50, 5.00, 9.91, 14.98 and 19.92 K min(-1) and at other five temperature programs, coupled TG + FTIR analysis, and DSC analysis in nitrogen flow. The kinetic analysis of TG data has been performed using an algorithm consisting of the following three successive steps: (1) the application of model-free (isoconversional) methods for evaluation of apparent activation energy dependence on the conversion degree, (2) the processing of the TG data recorded at constant heating rates to assess the possible kinetic schemes and the corresponding kinetic parameters, and (3) the selection of the kinetic scheme characteristic of the thermal decomposition of LDPE by comparing the experimental TG curves with the reconstructed ones corresponding to the temperature programs used. It has been pointed out that the overall process of thermal decomposition of LDPE consists of four successive stages with the Avrami-Erofeev kinetic models (An) - reaction order (Fn) - reaction order (Fn) - three-dimensional diffusion (D3). This kinetic scheme and corresponding kinetic parameters is suitable for prediction of thermal behavior of LDPE in some temperature programs and can be used for the design of pyrolysis reactors necessary for the conversion of LDPE waste into low molecular mass chemicals, which can be used as raw materials for chemical and petrochemical industry.
查看更多>>摘要：CO2 is proposed as an oxidant in a two-step phosphogypsum decomposition process, to oxidize the intermediate product of CaS into CaO. Isothermal and non-isothermal tests are conducted at a thermogravimetric analyzer combined with a Fourier transform infrared spectroscopy to reveal the reaction mechanism of CaS oxidation with CO2. During the course of non-isothermal process, several side reactions have been observed at low temperatures with CaCO3 and CaSO4 formations. CaS cannot be fully converted into CaO owing to the liquid melt formed by the mixture of CaSO4 and CaS. Full conversion into CaO is observed in the isothermal tests. The reaction order model fits the description of CaS oxidation into CaO with CO2, which is validated by both isothermal and non-isothermal data. In comparison with pure CaS, the CaS prepared from PG has a relatively lower reaction temperature with CO2, indicating the presence of impurities may have a catalytic effect.
查看更多>>摘要：Sodium carbonate is a well-known material for being used as a good sorbent of carbon dioxide from the atmosphere, and as such has gained increasing importance in environmental protection. In order to enhance its sorption ability, mechanochemical activation of sodium carbonate was carried out in this study while the occurred changes after the activation and the relaxation time in a controlled environment were monitored. Activation was performed in a vibro-mill from 1 to 28 min. Based on the results of specific surface area, obtained by BET, the samples activated for 2 and 7 min were chosen and placed in a moist carbon dioxide atmosphere for 96 h, a period called the relaxation time. Differential thermal and thermogravimetric analyses were applied with the aim of determining the changes that occurred on the activated samples during the relaxation period. The decomposition temperature change of activated Na2CO3 samples, as well as mass loss and conversion level of Na2CO3 to NaHCO3 were monitored depending on activation and relaxation time periods. The conversion reactions of sodium carbonate to sodium bicarbonate under the specified environment of carbon dioxide and moisture were also studied, and the thermodynamic data such are changes in enthalpy, entropy, and Gibbs energy at the temperature range of 0-160 degrees C are given.
查看更多>>摘要：Kinetic studies of chemical reactions typically assume a constant fractional conversion of reactants to products, alpha, at a particular time, t, or temperature, T, during the reaction. This constant (iso) conversion approach cannot provide both E-a and A of the Arrhenius rate constant, k = A exp[-E-a/RT], without specifying an algebraic model or value for the reaction mechanism, f(alpha), or its integral F(alpha), which are rarely known a priori. A new isoconversion rate approach eliminates the reaction model from consideration by specifying f(alpha)=1 at the reaction onset, so that the rate of conversion, d alpha/dt = k, is the same in isothermal and nonisothermal experiments. This equal (iso) kinetic approach reduces the kinetic problem to the relationship between time and temperature at the reaction onset, and allows for the determination of E-a and A for the initial step of a potentially complex chemical reaction by measuring the change in the onset temperature T-onset with heating rate, beta = dT/dt, in nonisothermal experiments, or the change in onset time t(onset) with temperature in isothermal experiments. In a test of the new theory, oxidation onset times of the reaction of hydrocarbons with oxygen at constant temperature (t(onset)) were calculated for a wide range of materials and experimental conditions using isothermal and nonisothermal values for E-a and A, and found to be in quantitative agreement with experimental values of the oxidation induction (onset) time (OIT).
Francisco Alves, Jose LuizGomes da Silva, Jean ConstantinoMumbach, Guilherme DaviAlves, Ricardo Francisco...
11页
查看更多>>摘要：This work provides the first insights on the bioenergy potential of macauba endocarp (Acrocomia aculeate) based on the pyrolysis kinetics and thermodynamic parameters of activation. The kinetic triplet was obtained from non-isothermal thermogravimetric data by using four isoconversional methods, kinetic compensation effect, and master-plots method. The pyrolysis behavior of macauba endocarp was modeled with three independent parallel reactions, describing the devolatilization of pseudo-hemicellulose, pseudo-cellulose and pseudo-lignin, with average activation energies of 90.2 - 99.5, 113.6 - 123.9 and 153.0 - 167.3 kJ mol(-1), respectively. Based on the pre-exponential factors, the devolatilization of both pseudo-hemicellulose and pseudo-cellulose occurred through surface reactions (<= 10(9) min(-1)), while pseudo-lignin devolatilized through a simpler chemistry reaction (> 10(9) min(-1)). The master-plots method results showed that the devolatilization of pseudo-hemicellulose and pseudo-cellulose followed R-type models, while the devolatilization of pseudo-lignin followed an F-type model. The thermodynamic analysis indicated that macauba endocarp is a viable feedstock for bioenergy production. The summative kinetic expression proposed from the kinetic results was able to reproduce and predict with excellence the experimental behavior of macauba endocarp pyrolysis (R-2 > 0.99 and Fit > 95.50%). This work's insights provide a new reference for future applications of macauba endocarp as an attractive and environmentally friendly alternative for bioenergy production.
查看更多>>摘要：In this work, the thermal conductivity of a series of ethylene-vinyl acetate copolymers (EVAs) with different vinyl acetate (VAc) contents at different temperatures are measured by the transient hot line method. It is found that the thermal conductivity of a series of EVA samples with different VAc contents decreased smoothly with increasing temperature at temperatures from -20 to 80 degrees C. Meanwhile, the crystallinity and melting point of a series of EVA samples are determined by differential scanning calorimetry (DSC), and an empirical formula between the thermal conductivity of EVA and temperature and crystallinity is established by using a data-fitting method. The theoretical calculation of thermal conductivity obtained from this empirical formula is compared with the measured results, and the error is within 5%. Therefore, this empirical formula is for guidance for predicting the thermal conductivity of EVA samples with different VAc contents at different temperatures in the future.
Odiyi, D. C.Sharif, T.Choudhry, R. S.Mallik, S....
14页
查看更多>>摘要：This paper explains the cure reaction mechanisms of a novel bio-based glass/Polyfurfuryl prepreg using an experimental and numerical approach. It suggests optimized parameters of rapid curing for isothermal curing conditions. Dynamic scanning calorimetry (DSC) under non-isothermal conditions was used to determine parameters for the two model-free kinetic methods Friedman and Ozawa Flynn Wall. The average activation energy (88.9 +/- 4.9 kJ/mol) was found to be higher than that reported for neat resin in literature. The validated models were used to gain insight into reaction mechanisms and were used to predict the evolution of reaction time under isothermal conditions for the PFA prepreg. This suggested that the curing time can be reduced to half by rapidly heating and maintaining isothermal conditions at 160 degrees C, which provides faster curing using hot-press. In addition, dynamic mechanical analysis (DMA) was carried out to compare the manufacturer recommended cure cycle with the rapid cycle suggested.
查看更多>>摘要：Silicone oil is used as matrix material and five nano-materials after surface treatment are employed as additives for preparing high performance silicone based thermal paste. The effects of filler weight fraction, morphologies and sizes on the thermal conductivity of polymer composites are studied. Experiment results show that the composite filled with ball-shaped aluminum (Al) particles exhibits high thermal conductivity (1.55 W/(m K)) at 80 wt.% loading, which is 7.6 times greater than pure silicone oil. Rod-shaped filler is more easily to form heat conductive pathways than ball-, platelet- and other irregular-shaped fillers. The effective synergistic enhancement in phonon transport in composites is achieved and a further 63% improvement in the thermal conductivity is realized by adding 75 wt.% ball-shaped Al particles and 10 wt.% rod-shaped zinc oxide (ZnO). Finally, the obtained data are compared with the value calculated by the theoretical thermal conductivity prediction models.
查看更多>>摘要：Thermal hazards and initial decomposition mechanisms of di-tert-butyl peroxide (DTBP), tert-butyl cumyl peroxide (TBCP), tert-butyl peroxy benzoate (TBPB) and tert-butyl peroxy-2-ethylhexanoate (TBPEH) were comprehensively studied. Activation energies of the four tert-butyl organic peroxides (TBOPs) were obtained by differential scanning calorimetry (DSC) experiments and kinetic analysis methods. Adiabatic thermal decomposition characteristic parameters were obtained by accelerating rate calorimeter (ARC) and thermal risk was evaluated by matrix assessment. Thermal decomposition products were determined by gas chromatography-mass spectrometry (GC-MS) experiments and decomposition pathways were proposed according to the analytical results. The energy of each step of the proposed pathways was calculated by density functional theory (DFT) method. The results indicated that all of the four TBOPs were divided into class III unacceptable hazard. Acetone was the main decomposition product of the four TBOPs. The most likely decomposition step to generate acetone was that the tert-butane oxygen radical detached a methyl. The main pathway was determined by comparing the energy barrier of rate-determining step. This work provided helpful suggestions for the safe application of the four TBOPs in the practical chemical process.
NSTL
Elsevier