Initial Activation Energy Research Articles

Thermal decomposition of a diazido ester: Pyrolysis GC–MS and DFT study

Azides are versatile compounds which find applications in organic synthetic reactions, biological methods as well as in propellants. The basic understanding of thermal decomposition mechanism of azides not only aid in assessing their suitability for use in these areas but also are also critical for hazard analysis and for developing suitable models for the risk analysis during their synthesis, handling and application. In the present paper, the thermal decomposition of a diazido ester 1,6-bis (azidoacetoyloxy) hexane (HDBAA) was investigated by thermogravimetric-differential scanning calorimetric studies. The mechanism of decomposition was elucidated using pyrolysis gas chromatography–mass spectrometric technique. At 230°C, HDBAA, preferentially form the corresponding diimine by elimination of N2. The decomposition of the diazido ester was complete, at 500°C yielding N2, CO, CH2NH and HCN with concurrent formation of diols and dienes. The experimental findings were rationalized through density functional theory (DFT) based computational analysis. DFT studies revealed that an initial activation energy of 155.1kJ/mol is required for the elimination of the first N2 from HDBAA leading to the formation of an imine through 1,2-hydrogen shift. The elimination of the first N2 is a highly exothermic reaction which leads to spontaneous elimination of the second N2 to form 1,6-bis (iminoacetoyloxy) hexane (HDBIA). All other pyrolytic products were formed from HDBIA and possess higher computed activation energy as evidenced from their presence in the pyrogram at elevated temperature of 500°C.

Cyclic peroxides and related initiating systems for radical polymerization of methyl methacrylate

Cyclic peroxides as initiators for the radical polymerization of methyl methacrylate were proposed. The initial rates, initiation rates, and effective activation energies of polymerization initiated by cyclic peroxides and cyclic peroxide-1-pyridyl-2-ferrocene systems were determined. The radical yields to the volume upon the thermal decomposition of cyclic peroxides and their catalytic decomposition in the presence of 1-pyridyl-2-ferrocene were determined. In combination with 1-pyridyl-2-ferrocene cyclic peroxides form efficient initiating systems favoring an increase in the polymerization rate, a decrease in the molecular weights, and an increase in syndiotacticity of the synthesized poly(methyl methacrylate).

Thermolysis parameter and kinetic research in copolyamide 66 containing triaryl phosphine oxide

Flame-retardant polyamide 66 (FR-PA66) was fabricated with adipic acid hexamethylene salt and bis(4-carboxyphenyl)phenyl phosphine oxide as raw materials. Thermogravimetric (TG) data of flame-retardant FR-PA66 at different heating rates were measured by employing TG analyzer, and analyzed with Flynn-Wall-Ozawa and Coast–Redfer method, respectively. The results show that the flame-retardant properties of triaryl phosphine oxide on FR-PA66 come from the first cleavage of P–C bond and forming of carbonized protective layer. The former reduces the initial thermolysis activation energy of FR-PA66 to 75 kJ/mol. The latter improves the middle and late thermolysis activation energy of FR-PA66 to 190 kJ/mol and 195 kJ/mol, which is higher than that of PA66 for 50 kJ/mol and 46 kJ/mol, respectively. The most probable thermolysis kinetic mechanism function ( f( α)) of FR-PA66 in three different stages are showed as following: when the rate of decomposition ( α) is lower than 0.1, [Formula: see text]; when α is between 0.1 and 0.7, [Formula: see text]; and when α is beyond 0.7, [Formula: see text].

Study on the Thermal Stability of Polyphenylene Sulfide Filter Media by Non-Isothermal Thermogravimetry

In order to study the thermal stability of PPS (polyphenylene sulfide) filter media, by means of non- isothermal thermogravimetry, thermal degradation kinetics behavior of two kinds of PPS filter media were analyzed. The kinetic parameters of PPS filter media were obtained according to Friedman method. Thermal stability of PPS filter media was discussed. It was found that the initial decomposition temperature and activation energy of N3 sample are all higher than B1 sample, the thermal stability of N3 sample is better than B1 sample, and kinetic analysis can be used as an important method to evaluate the thermal stability of filter media.

Research on Thermal Degradation Kinetics of Polyphenylene Sulfide Filter Media

In order to study the thermal stability of PPS (polyphenylene sulfide) filter media, by means of thermogravimetry(TG), thermal degradation kinetics behavior of two kinds of PPS filter media were analyzed. The kinetic parameters of PPS filter media were obtained according to Flynn-Wall-Ozawa method. Thermal stability of PPS filter media was discussed. It was found that the initial decomposition temperature and activation energy of N3 sample are all higher than B1 sample, the thermal stability of N3 sample is better than B1 sample, and kinetic analysis can be used as an important method to evaluate the thermal stability of filter media.

Random spin freezing in single crystalline Ce2CuSi3

We present the results of ac and dc susceptibility, magnetization and magnetic relaxation measurements performed on single crystalline Ce2CuSi3, a hexagonal AlB2-type nonmagnetic atom disorder compound, with the magnetic field applied along two typical crystallographic directions, i.e. H⊥c-axis and H//c-axis. For both the directions, spin-glass state is confirmed to form at low temperature with almost the same spin freezing temperature Tf (∼2.07K), initial frequency shift δTf (∼0.015) and activation energy Ea/kB (∼10.04 K) in zero dc field. Strong magnetic anisotropy is also found to be a significant feature of this compound. The experimental results and the dynamical analyses suggest that spin-glass behavior is intrinsic to the title compound.

The effect of crystal structure on the thermal reactivity of CL-20 and its C4 bonded explosives (I): thermodynamic properties and decomposition kinetics

The crystal structure, thermal behavior, and decomposition kinetics of e-CL-20, RS-e-CL-20, α-CL-20, e-CL-20/C4, and RS-e-CL-20/C4 were investigated by nonisothermal FTIR, TG, and DSC techniques. It was found that the thermal decomposition of α-CL-20, e-CL-20/C4, and RS-e-CL-20/C4 could be considered as a two-step process and the initial step is partly controlled by crystal structure. However, the crystal structure could only affect the initial step of decomposition and the total heat release, and the heat release of RS-e-CL-20 is the highest compared with α- and normal e-CL-20. In addition, the activation energy of studied materials was calculated by Kissinger method and modified KAS method, which was compared with the results obtained by other researchers. It was indicated that the obtained activation energy of e-CL-20 by Kissinger method is about 176.0 kJ mol−1, which is almost the same with the results from the literatures by STABIL and Noniso-TG methods. It was noticed that the crystal structure has significant effect on the initial activation energy distribution of CL-20, while in case of second stage (α = 0.30–0.85) this effect is relatively small, resulting in identical decomposition mechanism. Moreover, the kinetic compensation effects show that the studied materials could be divided into two groups, one including e-CL-20, RS-e-CL-20, α-CL-20, and e-CL-20/C4 which decompose at solid state and another including e-CL-20/Formex and RS-e-CL-20/C4 which decompose at partial liquid state, resulting in different kinetic compensation effects. It reveals that the C4 base could affect the distribution of activation energy of e-CL-20 and RS-e-CL-20 in a totally different way.

Influence of Mg/Si ratio on the clustering kinetics in Al–Mg–Si alloys

Abstract The clustering kinetics of Al–Mg–Si alloys are studied by means of differential scanning calorimetry. Five alloys with different Mg and Si contents from 0.4 to 1.1 at.% are used. Two overlapping cluster peaks are observed in the heat flow curves; Cluster 1 (C1) situated at ≈50°C and Cluster 2 (C2) situated at around ≈80°C when heating at 10 K min−1. It was found that the heat effect of clustering is largest in alloys with Mg/Si close to 1, while the C1/C2 heat effect ratio depends on the Si content. Activation energies for the two clustering processes C1 and C2 are obtained by applying different evaluation methods. The alloy having an Mg/Si ratio close to 1 has the smallest initial activation energies for C1, while samples with higher Mg content have lower initial activation energies for C2, inferring that C1 is Si-related, whereas C2 is Mg-related. However, the entire clustering process requires both Mg and Si to proceed.

Radical homopolymerization of tetrafluoroethylene initiated by perfluorodiacyl peroxide in supercritical carbon dioxide: Reaction mechanism and initiation kinetics

Radical homopolymerizations of tetrafluoroethylene (TFE) in supercritical carbon dioxide (sc-CO2) initiated by bis(perfluoro-2-n-propoxypropionyl) peroxide (BPPP) were conducted. Low molecular weight polytetrafluoroethylenes (PTFEs) which are widely used in diverse fields with stable end groups were successfully obtained. PTFEs were characterized by solid-state 19F NMR and FT-IR spectroscopy. From rational assignment of the characteristic signals, an overall reaction mechanism explaining the homopolymerization processes is proposed. The carboxyl radicals resulted from thermal decomposition of BPPP were completely decarboxylated to n-C3F7OCF(CF3) before reacting with TFE. Additionally, a small amount of n-C3F7OCF(CF3) rearranged into n-C3F7 with decreased rearrangement fraction from 0.11 to 0.04 when the reaction temperature was lowered from 35 to 5°C. Initiation rate constants (kd) were slightly increased with elevated pressure. The initiation activation energy derived from kd is 90.3kJmol−1, which is much lower than those of the other systems where nonfluorinated diacyl peroxides are used. Such mechanism and kinetics insights into the homopolymerizations of TFE in sc-CO2 will be instructive for the syntheses of fluoropolymers with desired properties in future.

Effects of phenyl-s-triazine moieties on thermal stability and degradation behavior of aromatic polyether sulfones

The effect of the incorporation of phenyl-s-triazine units into the main chain of phthalazinone-based polyether sulfones on initial decomposition temperature, activation energy, thermal-mechanical property and possible degradation mechanism has been investigated. To this purpose, decomposition of poly(phthalazinone ether sulfone phenyl-s-triazine) copolymers (PPESPs) of different monomer compositions have been studied by utilizing thermogravimetry and differential scanning calorimetry. Non-isothermal experiments under nitrogen were performed, and the apparent activation energy (E a) was calculated by isoconversional and conversional methods including the methods of Flynn-Wall-Ozawa, Friedman and Kissinger. In the conversion range (5–30%) studied, solid-state decomposition process of PPESPs is found to be a mechanism involving phase boundary controlled reaction (E a: 189–201 kJ mol−1) except that phenyl-s-triazine-rich copolymers exhibit a mechanism involving three-dimensional diffusion (E a: 196–225 kJ mol−1) in terms of Coats–Redfern method. The phenyl-s-triazine-rich copolymers display much higher E a and slighter mechanical property-change compared to sulfone-rich copolymers and generic aromatic polyether sulfone, suggesting strong stabilizing effect of the phenyl-s-triazine moieties.

The rheological, thermostable, and mechanical properties of polypropylene/fullerene C60 nanocomposites with improved interfacial interaction

AbstractPolypropylene (PP)/C60 nanocomposites with improved interfacial interaction were prepared via in situ melt radical reaction. It was found that the relaxation time of PP/C60 nanocomposites containing peroxide increased due to the reaction between C60 and PP macroradicals and the formation of long chain branched or crosslinking structure. Thermogravimetric analysis (TGA) results showed that the thermal stability of PP/C60 nanocomposites was enhanced. The initial decomposition temperatures and activation energy of PP/C60 nancomposites were strongly influenced by the content of unreacted C60. Because of the improved interfacial interaction, PP/C60 nanocomposites containing peroxide showed obvious increase in tensile strength, Young' modulus, flexural strength, flexural modulus, and impact strength, compared to PP/C60 nanocomposites (without peroxide) containing the same content of C60. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Mechanical and aging resistance performance of acrylic sheets containing EPDM-graft-poly(styrene-co-methyl methacrylate)

The addition of ethylene-propylene-diene rubber (EPDM) into acrylic sheets was expected to enhance their thermal and UV aging resistance for outdoor applications. According to the dissimilar polarity of EPDM and styrene (ST)/methyl methacrylate (MMA) monomer mixture (20/80% (w/w)) used for preparation of acrylic sheets, this research aimed to modify EPDM via graft copolymerization with ST and MMA to increase its compatibility. The graft copolymerization of ST and MMA at a ST/MMA ratio of 25/75% (w/w) onto EPDM was carried out in the solution polymerization initiated by benzoyl peroxide at 90 °C for 16 h, resulting in 88.1% grafting efficiency. The addition of 1.0–3.0% (w/w) of graft EPDM (GEPDM) into the acrylic sheets increased their impact strength (~ 17–22%), but decreased their flexural strength (~ 12–36%). However, their mechanical properties were improved after thermal and UV aging. Scanning electron microscopy (SEM) based analysis of the modified acrylic sheets revealed that the fracture surface shifted from brittle to ductile failure characteristics after modification. The thermogravimetric analysis results also exhibited that the addition of GEPDM improved the thermal and UV resistance of the modified acrylic sheets by increasing their initial decomposition temperature and activation energy of thermal decomposition.

Characterization of depolymerized residues from extremely low acid hydrolysis (ELA) of sugarcane bagasse cellulose: Effects of degree of polymerization, crystallinity and crystallite size on thermal decomposition

Sugarcane bagasse cellulose was subjected to the extremely low acid (ELA) hydrolysis in 0.07% H2SO4 at 190, 210 and 225°C for various times. The cellulose residues from this process were characterized by TGA, XRD, GPC, FTIR and SEM. A kinetic study of thermal decomposition of the residues was also carried out, using the ASTM and Kissinger methods. The thermal studies revealed that residues of cellulose hydrolyzed at 190, 210 and 225°C for 80, 40 and 8min have initial decomposition temperature and activation energy for the main decomposition step similar to those of Avicel PH-101. XRD studies confirmed this finding by showing that these cellulose residues are similar to Avicel in crystallinity index and crystallite size in relation to the 110 and 200 planes. FTIR spectra revealed no significant changes in the cellulose chemical structure and analysis of SEM micrographs demonstrated that the particle size of the cellulose residues hydrolyzed at 190 and 210°C were similar to that of Avicel.

Study on Curing Characteristics of Low-Toxicity Urea-Formaldehyde Resin

Curing characteristics of low-toxicity urea-formaldehyde (UF) resin in different curing system were studied by differential scanning carlorimetry (DSC). Test results showed that the initial orterminal temperature and activation energy needed of curing reaction for low-toxicity UF resin were different in different curing system. The initial temperature of curing reaction for low-toxicity UF resin and activation energy were the lowest, and exotherm was most under curing system C, which showed the acceleration of curing system C on low-toxicity UF resin was best. The appropriate curing system can be optimized and applied for hot-press process in practical production by means of DSC to investigate curing characteristics of low-toxicity UF resin.

Crack Propagation During Sustained-Load Cracking of Al-Zn-Mg-Cu Aluminum Alloys Exposed to Moist Air or Distilled Water

Intergranular sustained-load cracking of Al-Zn-Mg-Cu (AA7xxx series) aluminum alloys exposed to moist air or distilled water at temperatures in the range 283 K to 353 K (10 °C to 80 °C) has been reviewed in detail, paying particular attention to local processes occurring in the crack-tip region during crack propagation. Distinct crack-arrest markings formed on intergranular fracture faces generated under fixed-displacement loading conditions are not generated under monotonic rising-load conditions, but can form under cyclic-loading conditions if loading frequencies are sufficiently low. The observed crack-arrest markings are insensitive to applied stress intensity factor, alloy copper content and temper, but are temperature sensitive, increasing from ~150 nm at room temperature to ~400 nm at 313 K (40 °C). A re-evaluation of published data reveals the apparent activation energy, E a for crack propagation in Al-Zn-Mg(-Cu) alloys is consistently ~35 kJ/mol for temperatures above ~313 K (40 °C), independent of copper content or the applied stress intensity factor, unless the alloy contains a significant volume fraction of S-phase, Al2CuMg where E a is ~80 kJ/mol. For temperatures below ~313 K (40 °C) E a is independent of copper content for stress intensity factors below ~14 MNm−3/2, with a value ~80 kJ/mol but is sensitive to copper content for stress intensity factors above ~14 MNm−3/2, with E a , ranging from ~35 kJ/mol for copper-free alloys to ~80 kJ/mol for alloys containing 1.5 pct Cu. The apparent activation energy for intergranular sustained-load crack initiation is consistently ~110 kJ/mol for both notched and un-notched samples. Mechanistic implications are discussed and processes controlling crack growth, as a function of temperature, alloy copper content, and loading conditions are proposed that are consistent with the calculated apparent activation energies and known characteristics of intergranular sustained-load cracking. It is suggested, depending on the circumstances, that intergranular crack propagation in humid air and distilled water can be enhanced by the generation of aluminum hydride, AlH3, ahead of a propagating crack and/or its decomposition after formation within the confines of the nanoscale volumes available after increments of crack growth, defined by the crack arrest markings on intergranular fracture surfaces.

Influence of fungal pretreatment on thermogravimetric characteristics and fast pyrolysis vapors of corn stover

White rot fungi with different degradation patterns may have different effects on the thermal characteristics and pyrolysis products of biomass. Therefore, the influences of two fungal pretreatments with different degradation effects on thermal characteristics and pyrolysis products of corn stover were investigated. Auricularia polytricha AP degraded lignin, cellulose and hemicellulose with lignocellulolytic enzymes. Stereum hirsutum ZT had no ability to degrade hemicellulose and lignin, despite its higher xylanase activity. Thermogravimetry and kinetic parameter analysis demonstrated that the initial pyrolysis temperature and activation energies of corn stover treated by fungi were lower than that of untreated corn stover. Pyrolysis-gas chromatography–mass spectroscopy analysis suggested that differences within pyrolysis vapors could be observed between biopretreated and untreated corn stover, and that the degradation pattern of fungi made a difference to the pyrolysis products.

The Effect of CTBN Concentrations on the Kinetic Parameters of Decomposition of Blends of Epoxy Resins Modified with Carboxyl-Terminated Liquid Copolymer

Diglycidyl ether of bisphenol—A (DGEBA)—based epoxy resin was blended in the ratio of 3:1 (weight basis) with cycloaliphatic epoxy (CAE) resin. The prepared blend sample was further blended with different weight percentages of carboxyl-terminated butadiene acrylonitrile copolymer (CTBN) ranging between 0 and 25 wt% with an interval of 5 wt% and cured with stiochiometric amounts of 4, 4’- diamino diphenyl sulphone (DDS) cure agent. Structural changes during blending were studied by Fourier-transform infra-red (FTIR) spectroscopic analysis. The kinetic parameters, viz., order of decomposition reaction (n), activation energy (E), pre-exponential factor (Z) and rate decomposition constant (k), for the decomposition of the samples were calculated by applying Coats-Redfern equation over thermogravimetric (TG) data. The degradation of each sample followed second-order degradation kinetics, which was calculated by Coats-Redfern equation using best-fit analysis. This was further confirmed by linear regression analysis. The validity of data was checked by t-test statistical analysis. Further, the blend sample had higher initial degradation temperature and activation energy than its respective pure epoxy resin indicating that the CTBN acted as thermal stabilizer for epoxy resin which improved the thermal stability.

Influence of the co-fungal treatment with two white rot fungi on the lignocellulosic degradation and thermogravimetry of corn stover

This work investigated the effect of the co-culture of Auricularia polytricha AP with Irpex lacteus CD2 on the lignocellulolytic enzymes activities, lignocellulosic degradation and pyrolysis characteristics of corn stover. The results showed that the lignocellulolytic enzyme activities of the co-culture exceeded that of the monoculture. Although no lignolytic activity was detected, I. lacteus CD2 could significantly degrade lignin. The co-culture lignin degradation ratio was between that of A. polytricha AP and I. lacteus CD2 and increased quickly during the first 20 days, then trended to exceed that of I. lacteus CD2 after 20 days. Co-culture degradation ratios of cellulose and hemicellulose exceeded that of both monocultures. Thermogravimetry and kinetic parameter analysis showed that the initial pyrolysis temperature and activation energies of biotreated samples were lower than that of the control. Biopretreatment decreases the onset pyrolysis temperature and activation energy thus enhancing the thermal decomposition reaction. However, there were not significant differences between the co-culture and I. lacteus CD2.

Electrochemical characterization of PEDOT–PSS–Sorbitol electrodes. Sorbitol changes cation to anion interchange during reactions

Oxidation/reduction reactions of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulfonate) (PSS) and Sorbitol free-standing films were studied in LiClO 4 aqueous solution by cyclic voltammetry and chronoamperometry. The oxidation by potential steps follows reaction kinetics having induction times. Taking slopes from the oxidation kinetics attained at different concentrations of the reactants or different temperatures as initial reaction rates, kinetic constants, reaction orders and activation energies were obtained for the oxidation reaction. Oxidation kinetics having induction times, anodic chronoamperograms showing a large maximum, and increasing activation energies for initial states obtained after reduction at rising cathodic overpotentials suggest that the material shrinks and compact by reduction, with prevalent expulsion of anions towards the electrolyte during reduction and swells during oxidation with anion’s entrance. Energy-Dispersive X-ray spectroscopy (EDX) analysis proved this interchange. The presence of a non-charged guest, as sorbitol, transforms PEDOT–PSS, which interchanges cations during electrochemical reactions, to new PEDOT–PSS–Sorbitol material interchanging anions.

저급탄의 열분해 및 촤-CO2가스화 반응의 속도론적 연구

인도네시아 아역청탄인 ABK탄과 중국 갈탄(lignite)과 같은 저급탄에 대한 열분해와 촤-<TEX>$CO_2$</TEX> 가스화반응에 대한 실험을 비등온의 승온 조건에서 열중량분석기(Thermogravimetric analysis, TGA)를 이용하여 수행하였다. 열분해 속도는 2단계, 1차의 열분해 모델(Kissinger 법의 변형)에 의해 잘 모사되었다. 촤의 <TEX>$CO_2$</TEX> 가스화반응은 수축 핵 모델에 적용하여 초기의 활성화 에너지가 ABK탄은 189.1 kJ/mol, lignite는 260.5 kJ/mol의 값을 얻었으며, 수축 핵 모델에 의해 잘 모사되었다. 특히, 촤의 <TEX>$CO_2$</TEX> 가스화반응에서 활성화 에너지는 무연탄의 결과와 유사하였으며, 다른 모델이나 석탄의 종류에 따라 큰 차이를 보였다. Thermogravimetric analysis(TGA) was carried out for pyrolysis and char-<TEX>$CO_2$</TEX> gasification of low rank Indonesian ABK coal and China lignite. The pyrolysis rate was successfully described by a two-step model adopting the modified Kissinger method. The shrinking core model, when applied to char-<TEX>$CO_2$</TEX> gasification gave initial activation energy of 189.1 kJ/mol and 260.5 kJ/mol for the ABK coal and China lignite, respectively. Thus, the char-<TEX>$CO_2$</TEX> gasification has been successfully simulated by the shrinking core model. In particular, the activation energy of char-<TEX>$CO_2$</TEX> gasification calculated in this work is similar to the results on the anthracite coal, but considerable difference exists when other models or coal types are used.