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1.
Two thermoset systems based on maleimides and diglycidyl ether of bisphenol A (DGEBA) cured with p-aminobenzoic acid were characterized in terms of thermal and electrical behavior. Thermal characterization has been undertaken by means of thermogravimetric analysis in nitrogen atmosphere up to 600°C using simultaneous thermogravimetric/Fourier transform infrared/mass spectrometry (TG/FT-IR/MS) analysis. In the first stage of thermal degradation, the global kinetic parameters [activation energy (Ea) and preexponential factor (log A1 (s−1))] were calculated using the isoconversional method of Friedman. The energies variation as well as the shape of the differential thermal analysis curves suggests that the thermal decomposition process occurred in multiple stages. The evolved gases analysis was conducted by simultaneous TG/FT-IR/MS coupled techniques. Dielectric relaxation spectroscopy characterization was also made. 相似文献
2.
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. 相似文献
3.
S. F. Santos M. C. de Andrade J. A. Sampaio A. B. da Luz T. Ogasawara 《Journal of Thermal Analysis and Calorimetry》2007,87(3):743-746
TiO2–CeO2 oxides
for application as ceramic pigments were synthesized by the Pechini method.
In the present work the polymeric network of the pigment precursor was studied
using thermal analysis. Results obtained using TG and DTA showed the occurrence
of three main mass loss stages and profiles associated to the decomposition
of the organic matter and crystallization. The kinetics of the degradation
was evaluated by means of TG applying different heating rates. The activation
energies (E
a) and
reaction order (n) for each stage were
determined using Horowitz–Metzger, Coats–Redfern, Kissinger and
Broido methods. Values of E
a
varying between 257–267 kJ mol–1 and n=0–1 were found. According to the kinetic
analysis the decomposition reactions were diffusion controlled. 相似文献
4.
Seiji Takahashi Masamichi Tsukagoshi Toshiya Sato Yuki Kitahara Toshihiro Fujii 《Journal of Thermal Analysis and Calorimetry》2013,111(1):685-688
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. 相似文献
5.
P. Budrugeac 《Journal of Thermal Analysis and Calorimetry》2009,97(2):443-451
The thermo-oxidative degradation of a parchment recent manufactured from a goat skin has been investigated by TG/DTG, DSC
simultaneous analysis performed in static air atmosphere, at six heating rates in the range 3–15 K min−1. At the progressive heating in air atmosphere, the investigated material exhibits three main successive processes occurring
with formation of volatile products, namely the dehydration followed by two thermo-oxidative processes. The processing of
the non-isothermal data corresponding to the first process of thermo-oxidation was performed by using Netzsch Thermokinetics—a
Software Module for Kinetic Analysis. The dependence of activation energy, evaluated by isoconversional methods suggested
by Friedman, and Ozawa, Flynn and Wall, on the conversion degree and the relative high standard deviations of this quantity
show that the investigated process is a complex one. The mechanism and the corresponding kinetic parameters were determined
by Multivariate Non-linear Regression program. Three mechanisms, one consisting in four successive steps and two others in
five successive steps, exhibit the best F-test Fit Quality for TG curves. It was also used the previously suggested criterion, according to which the most probable
process mechanism correspond to the best agreement between E
FR
= E
FR
(α) (E
FR
is the activation energy evaluated by isoconversional method suggested by Friedman; α is the conversion degree) obtained
from non-isothermal experimental data and activation energy values, E
iso
, obtained by applying the differential method to isothermal data simulated using non-isothermal kinetic parameters. According
to this last criterion, the most probable mechanism of parchment oxidation consists in four successive steps. The contribution
of the thermo-oxidation process in the parchment damage by natural aging is discussed. 相似文献
6.
P. Budrugeac Carmen Racles V. Cozan Maria Cazacu 《Journal of Thermal Analysis and Calorimetry》2008,92(1):263-269
Thermal and thermo-oxidative stability of some poly(siloxane-azomethine)s obtaining starting from bis(formyl-p-phenoxymethyl)tetramethyldisiloxane and different organic diamines have been investigated by TG+DTG+DSC simultaneous analyses
performed in argon flow and air static atmosphere, respectively. TG, DTG and DSC curves of each polymer showed three or four
successive degradation steps at different temperatures according to the composition of the sample and the gaseous atmosphere
in which the thermal analysis was performed. For each process, the following parameters were evaluated: total mass loss, temperature
corresponding to the maximum reaction rate, maximum reaction rate, temperature corresponding to certain mass loss. In order
to determine the thermal and thermo-oxidative stabilities of investigated polymers, the following values were determined:
T
x% — temperature corresponding to x% mass loss, and %Δm
T — mass loss at a given temperature T. The obtained orders of stability were correlated with the structure of investigated polymers. 相似文献
7.
Song-Dong Ding 《Polymer Degradation and Stability》2006,91(10):2465-2470
Thermal stability of poly(p-dioxanone) (PPDO) was investigated isothermally and non-isothermally under air atmosphere using thermogravimetry (TG). The addition of 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (PMBP) could enhance successfully the thermal stability of PPDO compared with those of as-prepared and purified PPDO at temperature below about 230 °C. The activation energies for thermal degradation (ΔEtd) were evaluated at different weight loss values from TG data using the procedure recommended by MacCallum et al. The ΔEtd values of as-prepared PPDO, purified PPDO and PPDO containing 1.0 wt% PMBP were in the ranges of 20-50, 35-60, and 56-88 kJ mol−1, respectively, when they were evaluated at weight loss values of 10-80%. The remaining weights increase with the amounts of PMBP added up to 1.5 wt%. The mechanism for the enhanced thermal stability of PPDO was discussed. 相似文献
8.
K. Chennakesavulu M. Raviathul Basariya G. Bhaskar Raju S. Prabhakar 《Journal of Thermal Analysis and Calorimetry》2011,103(3):853-862
Thermal decomposition kinetics of calix[6]arene (C6) and calix[8]arene (C8) were studied by Thermogravimetry analysis (TG)
and Differential thermal analysis (DTA). TG was done under static air atmosphere with dynamic heating rates of 1.0, 2.5, 5.0,
and 10.0 K min−1. Model-free methods such as Friedman and Ozawa–Flynn–Wall were used to evaluate the kinetic parameters such as activation
energy (E
a) and pre-exponential factors (ln A). Model-fitting method such as linear regression was used for the evaluation of optimum kinetic triplets. The kinetic parameters
obtained are comparable with both the model-free and model-fitting methods. Within the tested models, the thermal decomposition
of C6 and C8 are best described by a three dimensional Jander’s type diffusion. The antioxidant efficiency of C6 and C8 was
tested for the decomposition of polypropylene (PP). 相似文献
9.
Bharti U. N. Verma Kingsuk Mukhopadhyay 《Journal of Thermal Analysis and Calorimetry》2011,104(3):1071-1075
The ligand [2-(1,2,3,4-thiatriazole-5-yliminomethyl)-phenol] (L) is a schiff base derived from condensation reaction of 1,2,3,4-thiatriazole-5-ylamine
and Salicylaldehyde. Synthesis of the ligand (L) and the complex [Cu(II)(L)2]·2H2O have been studied in our previous work (Bharti et al., Asian J Chem 23(2):773–776, 2011). Thermal decomposition behavior
of synthesized Cu(II) complex has been investigated by thermo gravimetric (TG) analysis at heating rate of 10 °C min−1 under nitrogen atmosphere. The mechanism of decomposition of Cu(II) complex has been established from TG data. Kinetic parameters
such as order of reaction (n), activation energy (E
a), frequency factor (Z) and entropy of activation (∆S
≠) were calculated by using Freeman and Carroll (J Phys Chem 62:394–397, 1958) as well as Doyle’s methods as modified by Zsako
(J Phys Chem 72(7):2406–2411, 1968). 相似文献
10.
D.M. Fernandes 《Thermochimica Acta》2006,441(1):101-109
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 (Ea) 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 Ea values. PVA and blends showed intervals of up to 50% in decomposition degree with nearly constant Ea, and smaller intervals in which Ea varies drastically. The influences of samples irradiation and of surrounding gas in TG analysis on Ea are also shown. 相似文献
11.
Rocco J. A. F. F. Lima J. E. S. Frutuoso A. G. Iha K. Ionashiro M. Matos J. R. Suárez-Iha M. E. V 《Journal of Thermal Analysis and Calorimetry》2004,77(3):803-813
Thermal decomposition kinetics of solid rocket propellants based on hydroxyl-terminated polybutadiene-HTPB binder was studied
by applying the Arrhenius and Flynn-Wall-Ozawa's methods. The thermal decomposition data of the propellant samples were analyzed
by thermogravimetric analysis (TG/DTG) at different heating rates in the temperature range of 300-1200 K. TG curves showed
that the thermal degradation occurred in three main stages regardless of the plasticizer (DOA) raw material, the partial HTPB/IPDI
binder and the total ammonium perchlorate decompositions. The kinetic parameters E
a (activation energy) and A (pre-exponential factor) and the compensation parameter (S
p) were determined. The apparent activation energies obtained from different methods showed a very good agreement.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Copolymer networks based on 4-vinylpyridine (4VPy)/crotonic acid (CrA)/divinylbenzene (DVB) and their N-oxide derivatives have been investigated by thermogravimetric analysis (TG) to evaluate their thermal stability in nitrogen atmosphere at fixed heating rate. Thermal stability was determined from TG curves to investigate the influence of 4VPy content and introduction of N-oxide groups. The TG and DTG curves of unmodified copolymers clearly show two thermodegradation stage and the same kinetic pathway. The decomposition temperatures do not depend on the 4VPy content. The copolymers modified by oxidation present lower thermostability than unmodified showing that the introduction of N-oxide groups modifies their kinetic pathways. A kinetic model Ozawa was used to determine the kinetic parameters. The apparent thermal decomposition activation energies (ΔEd) of the unmodified copolymer under nitrogen was higher than that in modified copolymer. Also, the characterizations of copolymer networks were done by Fourier transform infrared spectroscopy (FTIR). 相似文献
13.
Degradation of commercial polysulfones (PSF) was investigated in air and in inert atmosphere (nitrogen) using thermogravimetric (TG) method. It has been found that the degradation of Udel P-1800 PSF is initiated about 400°C, both in air and in nitrogen. The activation energy of degradation of PSF, (E a), has been calculated by the Kissinger and Ozawa methods. The value ofE a about 200 kJ·mol?1 has been found for both air and nitrogen atmosphere. Experimental results concerning thermal properties of PSF (T g andT d,1/2) were compared with those obtained by the computer modeling technique, and a good agreement has been found. 相似文献
14.
Five bis(ethylenediamine)metal perchlorate (BEMP) complexes like [M(en)2](ClO4)2 (where M=Mn, Co, Ni, Cu, Zn and en=ethylenediamine) have been prepared and characterized by gravimetric methods, infrared spectroscopy (IR) and elemental analysis. Thermal decomposition studies have been undertaken using simultaneous thermogravimetry (TG) and differential thermal analysis (DTA) in nitrogen atmosphere. Non-isothermal TG and DTA studies have also been carried out separately in air to examine the effect of atmosphere on thermolysis of these complexes. Thermal stability of the complexes was found to decrease in the order: [Zn(en)2](ClO4)2>[Mn(en)2](ClO4)2>[Ni(en)2](ClO4)2>[Cu(en)2](ClO4)2>[Co(en)2](ClO4)2.Isothermal TG over the temperature range of decomposition of all these complexes, has been done to evaluate the kinetics of decomposition. Both model fitting and model free isoconversional methods have been used to analyse the kinetics. Isoconversional method has been found to be superior over the conventional model fitting method and is able to describe the complex decomposition of these complexes. It indicates that the values of activation energy vary with the extent of conversion (α) while model fitting method results in a single value of E for overall decomposition process which cannot be attributed to any process under such a complex decomposition reaction. Explosion delay (DE) measurement has been carried out to investigate the response of these complexes under the condition of rapid heating. 相似文献
15.
Hélio Salvio Neto Jivaldo do Rosário Matos 《Journal of Thermal Analysis and Calorimetry》2011,103(1):393-399
In this work, TG/DTG and DSC techniques were used to the determination of thermal behavior of prednicarbate alone and associated
with glyceryl stearate excipient (1:1 physical mixture). TG/DTG curves obtained for the binary mixture showed a reduction
of approximately 37 °C to the thermal stability of drug (
T\textdm/\textdt = 0 \textDTG\textMax T_{{{\text{d}}m/{\text{d}}t = 0\,{\text{DTG}}}}^{\text{Max}} ). The disappearance of stretching band at 1280 cm−1 (νas C–O, carbonate group) and the presence of streching band with less intensity at 1750 cm−1 (νs C–O, ester group) in IR spectrum obtained to the binary mixture submitted at 220 °C, when compared with IR spectrum of drug
submitted to the same temperature, confirmed the chemical interaction between these substances due to heating. Kinetics parameters
of decomposition reaction of prednicarbate were obtained using isothermal (Arrhenius equation) and non-isothermal (Ozawa)
methods. The reduction of approximately 45% of activation energy value (E
a) to the first step of thermal decomposition reaction of drug in the 1:1 (mass/mass) physical mixture was observed by both
kinetics methods. 相似文献
16.
Thermal Decomposition of Some Chemical Compounds Used As Food Preservatives and Kinetic Parameters of This Process 总被引:1,自引:0,他引:1
Thermal decomposition processes of selected chemicals used as food preservatives such as sodium formate, sodium propionate,
sodium nitrates(V and III) and sodium sulphate(IV) were examined by the derivatographic method. Based on the curves obtained,
the number of decomposition stages and characteristic temperatures of these compounds have been found. Mass decrements calculated
from TG curves ranged from 28.9% for sodium formate to 77.8% for sodium nitrate(V), while sodium sulphate showed a mass increment
of 5.6%. Kinetic parameters such as activation energy (E
a ), frequency factor (A ) and reaction order (n ) were calculated from TG, DTG and T curves. Sodium formate shows the highest values of E
a and A which amount to 171.7 kJ mol–1 and 5.8⋅1014 s–1 , respectively, while the lowest ones, E
a =28.2 kJ mol–1 and A =3.65⋅102 s–1 belong to sodium nitrate(V).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
A new polyoxometalate (CPFX·HCl)3H4SiW12O40·10H2O was prepared from ciprofloxacin hydrochloride and H4SiW12O40·nH2O in aqueous solution, and characterized by elemental analysis, IR spectra and DTA-TG-DTG techniques. The IR spectrum confirmed the presence of Keggin structure and the characteristic functional group for ciprofloxacin in the compound. The TG-DTA-DTG curves showed that its thermal decomposition was a four-step process consisting of simultaneous collapse of Keggin type structure. The residue of decomposition was the mixture of WO3 and SiO2, confirmed by X-ray diffraction and IR spectroscopy. The decomposition mechanism and nonisothermal kinetic parameters of the polyoxometalate were obtained from an analysis to the TG-DTG curves by the single scanning methods (the Achar method and Coats-Redfern method) and the multiple scanning methods (the Kissinger method, Flynn-Wall-Ozawa method and Starink method). The results indicate that the kinetic equationswith parameters describing the thermal decomposition reaction are dα/dt=6.65×10^6[3(1-α)^2/3]e^-10495.5/T with E=87.26 kJ/mol and A=6.65×10^6 s^-1 for the second step,dα/dt=7.01×10^9(1-α)e^-18770.7/T with E=156.06 kJ/mol and A=7.01×10^9 s^-1 for the third step,dα/dt=9.77×10^43[(1-α)^2]e^-88980.0/T with E=739.78 kJ/mol and A=9.77×10^43 s^-1 for the fourth step. 相似文献
18.
Abate L: Blanco A: Pollicino A. Recca A. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):63-73
The isothermal degradation of three aromatic polyetherketones was studied in an inert environment at various temperatures
in the range 683-803 K. In the first degradation stage (mass loss D£20%) a linear increase of D as a function of heating time (t) was observed and the corresponding kinetic D=D
o+bt equations at various temperatures were directly drawn by smoothing the experimental TG data. The b values, which represent
the mass loss rates during degradation, increased as a function of temperature according to Arrhenius-type equations, from
which degradation E
a values were determined, which appear in agreement with those from literature methods. Some differences observed were discussed
and interpreted.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Through addition reaction of Schiff‐base terephthalylidene‐bis‐(p‐aminophenol) ( DP‐1 ) and diethyl phosphite (DEP), a novel phosphorus‐modified epoxy, 4,4'‐diglycidyl‐(terephthalylidene‐bis‐(p‐aminophenol))diphosphonate ether ( EP‐2 ), was obtained. An modification reaction between EP‐2 and DP‐1 resulted in an epoxy compound, EP‐3 , possessing both phosphonate groups and C?N imine groups. The structure of EP‐2 was characterized by Fourier transform infrared (FTIR), elemental analysis (EA), 1H, 13C, and 31P NMR analyses. The thermal properties of phosphorus‐modified epoxies cured with 4,4'‐diaminodiphenylmethane (MDA) and 4,4'‐diaminodiphenyl ether (DDE) were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The activation energies of dynamic thermal degradation (Ed) were calculated using Kissinger and Ozawa's methods. The thermal degradation mechanism was characterized using thermogravimetric analysis/infrared spectrometry (TG‐IR). In addition, the flame retardancy of phosphorus‐modified epoxy thermosets was evaluated using limiting oxygen index (LOI) and UL‐94 vertical test methods. Via an ingenious design, phosphonate groups were successfully introduced into the backbone of the epoxies; the flame retardancy of phosphorus‐modified epoxy thermosets was distinctly improved. Due to incorporation of C?N imine group, the phosphorus‐modified epoxy thermosets exhibited high thermal stabilities; the values of glass‐transition temperatures (Tgs) were about 201–210°C, the values of Ed were about 220–490 kJ/mol and char yields at 700°C were 49–53% in nitrogen and 45–50% in air. These results showed an improvement in the thermal properties of phosphorus‐modified epoxy by the incorporation of C?N imine groups. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
20.
Graft copolymerization of methyl methacrylate on potato starch was carried out in methanol-water medium at 35°C in the dark using potassium trioxalatomanganate, K3[Mn(C2O4)3], as initiator. The effect of different methanol-water ratios (v/v), the temperature of polymerization, the initiator concentration, the monomer concentration, the starch content, and the time of polymerization were studied. Percent total conversion, % grafting, and grafting efficiency (%) under different conditions were evaluated and compared. High grafting efficiency (~80%), high % total conversion (~85%), and high % grafting (-95%) were readily obtained. The reaction mechanism for graft copolymer formation is discussed. 相似文献