Kinetic evaluation of non-isothermal crystallization of oxidized extra virgin olive oil

In this study, accelerated storage tests were carried out at 60 °C up to 20 weeks on three extra virgin olive oils (Evoos) with different total phenol contents and fatty acid compositions (named as EvooA, EvooB, and EvooC). Their oxidative statuses, evaluated by means of primary oxidation value and total phenolic content, were related to both the shapes of differential scanning calorimetry (DSC) cooling curves and thermal properties. DSC cooling curves were all deconvoluted as crystallization occurs in a quite narrow range, and the single steps are not well separated. The first deconvoluted DSC peak for the three samples tested, which occurs in the temperature interval between −45 °C and −30 °C, can probably be ascribable to the crystallization of tri-unsaturated triacylglycerols. A non-isothermal crystallization kinetic procedure, derived by the well-known isothermal Avrami equation, combined with the method of Ozawa, was applied to the first deconvoluted DSC peak only by processing the data related to this DSC peak. Results of the modified Avrami method were found in agreement with those of the Ozawa method. In particular, Avrami and Ozawa's exponents lie from 2 to 4 (being those of fresh samples always lower than those subjected to the accelerated oxidation test). Crystallization is relatively slow for fresh samples whereas after the first 4 weeks; it occurs faster in EvooB and EvooC.     

The Influence of some Chain-Breaking Antioxidants on Thermal-Oxidative Decomposition of Linolenic Acid

Thermoxidation of linolenic acid inhibited by addition of 2,6-di-t-butyl-4-methylphenol and 2,4,6-trimethylphenol at various concentrations was investigated. The measurements were carried out under non-isothermal conditions in an atmosphere of oxygen. DSC curves permitted the determination of onset point and maximum points of the peaks. The influence of inhibitor concentration on temperature of the start of oxidation was noticed. However, no significant changes in temperatures of the maximum heat flow was observed. Measurements and calculations described in this report prove that the assessment of the antioxidant activity of chain-breaking inhibitors can be performed only from the onset temperatures. Calculations of the activation energy of inhibited linolenic acid thermoxidation were performed in order to elucidate the antioxidant activity of the phenolic compounds. This revised version was published online in August 2006 with corrections to the Cover Date.     

PA13N的合成和非等温结晶动力学研究

采用DSC方法研究了PA13N在不同降温速率下的结晶过程,并利用Avrami方程研究了其非等温结晶动力学。在非等温结晶过程中,随着降温速率的增大,结晶温度向低温偏移。综合利用Avrami方程得到Avrami指数为1.35~1.88和结晶速率常数Zc≈1;并求得其结晶活化能为-58.42kJ/mol。结果表明,PA13N的结晶能力小于其他脂肪族尼龙。     

Thermokinetic parameters and thermal hazard evaluation for three organic peroxides by DSC and TAM III

The thermokinetic parameters were investigated for cumene hydroperoxide (CHP), di-tert-butyl peroxide (DTBP), and tert-butyl peroxybenzoate (TBPB) by non-isothermal kinetic model and isothermal kinetic model by differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III), respectively. The objective was to investigate the activation energy (E _a) of CHP, DTBP, and TBPB applied non-isothermal well-known kinetic equation to evaluate the thermokinetic parameters by DSC. We employed TAM III to assess the thermokinetic parameters of three liquid organic peroxides, obtained thermal runaway data, and then used the Arrhenius plot to obtain the E _a of liquid organic peroxides at various isothermal temperatures. In contrast, the results of non-isothermal kinetic algorithm and isothermal kinetic algorithm were acquired from a highly accurate procedure for receiving information on thermal decomposition characteristics and reaction hazard.     

Cure Kinetics of DGEBA with Hyperbranched Poly （3-hydroxyphenyl） Phosphate as Curing Agent Studied by Non-isothermal DSC

IntroductionEpoxy resins are widely used in the fields of coa-tings,adhesives,insulating materials,etc..Diglycidylether of bisphenol A(DGEBA)is the most importantepoxy resin in industry because of its fluidity,physicaland mechanical properties after cure,…     

Hazard evaluation for oxidation of cyclic ethers

Ethers are widely used as a solvent for synthesis reactions, however, they are known as hazardous chemicals as they have low flash points and form peroxides under oxidative conditions. In this study, the oxidative reactivity of cyclic ethers was evaluated by thermal analysis. The accelerated test was performed in a pressure vessel under a high oxygen pressure (2 MPa), and DSC was used to detect the products of the reaction. Tetrahydrofuran (THF) and 1,3-dioxolane were used as a sample. The result of the DSC measurement of THF without any antioxidant showed that the DSC curve depended on the exposure time. It was found that this method can be used for the oxidation evaluation. The DSC measurement was also used for the detection of ether peroxides, and this method was faster and simpler than the potassium iodine titration.     

Measurement and modeling of peroxides half-life: A thermo-kinetic approach

Half-life values of organic peroxides at elevated temperature conditions are important in characterizing the reactivity and are often available in literature or through vendors. However, there is often lack of details/accuracy on methods used to obtain these values, as well as differences in methods across vendors and publications, thus resulting in discrepant reactivity profile. To address this, a method involving calorimetric experiment and thermo-kinetic modeling was developed. The current approach was applied on five peroxides samples to obtain kinetic parameters and estimate their half-life in the temperature range of interest. The measurements were performed by DSC under non-isothermal conditions on the dilute peroxide solutions (∼0.12 M in mineral oil) and the data were kinetically treated according to three model-based and one model-free kinetic equations. A very good agreement was found between the half-life calculated by all kinetic methods, but significant differences were noticed with the kinetic parameters reported in literature. Additionally, the obtained half-life results, based on non-isothermal measurements developed kinetic models, were validated through isothermal calorimetric testing. Given the accuracy and robustness of our results, the current method can be applied to estimate half-life of organic peroxides at elevated temperature conditions.     

Methods of non-isothermal kinetic analysis by DSC curves: An investigation on lattice reorganization in copper

Various analytical methods of non-isothermal kinetics have been applied to DSC curves to determine the kinetic parameters ruling the lattice reorganization (primary recrystallization) of prestrained pure copper.The techniques by Borchardt and Daniels, and Rogers and Smith have been modified to make them suitable for complex phenomena other than nth-order reactions.The results supplied by the new formulas are consistent with the data previously obtained under isothermal conditions. The same applies to the other methods tested, provided an accurate temperature calibration be made to correct the thermal lag of the calorimetric sensors.Such a calibration is of prime importance when DSC peak shifts are analyzed as a function of heating rate.     

Effect of Solvent Composition on DSC Exothermic Peak of Human Serum Albumin Suspended in Pyridine-n-Hexane Mixtures

Human serum albumin (HSA) immersed in pyridine-n-hexane mixtures was analyzed using differential scanning calorimetry (DSC). State of the solid HSA in organic solvent mixtures is the non-equilibrium state which is seen as the exothermic peak on the DSC curves. The enthalpy change corresponding to this exothermic peak approaches zero when going from pure pyridine to pure n-hexane. Dependence of the enthalpy change on the pyridine concentration is suggestive that the non-equilibrium state of the immersed HSA results from the HSA-pyridine interactions 'frozen' at the lower temperature. Most likely the temperature-initiated exothermic peak observed on the DSC curves reflects the swelling of HSA by pyridine. This revised version was published online in August 2006 with corrections to the Cover Date.     

DSC Analysis of the Induction Period in the Vulcanisation of Rubber Compounds

Vulcanisation of rubber compounds was studied by DSC under isothermal and non-isothermal conditions. The parameters of an Arrhenius-like equation describing the temperature dependence of induction period have been obtained both from isothermal and non-isothermal measurements. A new method for obtaining the kinetic parameters from non-isothermal measurements, based on the dependence of onset temperature of vulcanisation peak on heating rate, is presented. Also, a procedure for the evaluation of temperature difference between the furnace and sample is proposed. It has been shown that the treatment of non-isothermal DSC measurements gives the kinetic parameters free of systematic errors. The new method can also be used for studying other reactions exhibiting the induction period. This revised version was published online in August 2006 with corrections to the Cover Date.     

Oxidation of Saturated Fatty Acids Esters DSC investigations

Oxidation of saturated fatty acids ethyl esters: laurate, myristate, palmitate and stearate was investigated by means of DSC techniques under isothermal and non-isothermal conditions. The activation energies of isothermal oxidation were similar to each other (112–123 kJ mol⁻¹) and no influence of carbon length on the rate of oxidative decomposition was observed. Results obtained from non-isothermal experiments were similar only for the first stage of oxidation. This revised version was published online in August 2006 with corrections to the Cover Date.     

溴化轻稀土丙氨酸配合物的热分解动力学

溴化轻稀土丙氨酸配合物的热分解动力学;溴化轻稀土丙氨酸配合物;差示扫描量热法;热分解动力学;分解机理     

Crystallization kinetics of polyethylene/paraffin oil blend sheets formed by thermally induced phase separation with different molecular weights of polyethylene

Polyethylene/paraffin oil blend sheets with different molecular weights of polyethylene were prepared by thermally induced phase separation. Isothermal and non-isothermal crystallization behaviors of blend sheets were investigated by differential scanning calorimetry (DSC). Isothermal DSC curves were analyzed by Avrami equation, whereas non-isothermal DSC curves were analyzed by Jeziorny method and Mo method. Effective activation energy (ΔE) of isothermal and non-isothermal crystallization was calculated by Friedman method. Under isothermal condition, value of n in Avrami equation hovered at 2.1, and lgZ increased with the decrease of crystallization temperature. lgZ and ΔE of blend sheets with a larger molecular weight of polyethylene was smaller than that of blend sheets with smaller molecular weight. Under non-isothermal condition, value of n obtained by Jeziorny method hovered at 2.4, close to n of isothermal condition. lgZ _c increased with the increase of cooling rate and decrease of molecular weight of polyethylene. ΔE of different blend sheets were close to each other. Crystal structures of blend sheets formed under non-isothermal condition were analyzed by X-ray diffraction (XRD) analysis. XRD analysis showed that molecular weight of polyethylene and cooling rate had slight influence on crystal structure and crystallinity of polyethylene/paraffin oil blend sheet.     

热分析法研究聚全氟乙丙烯非等温裂解反应动力学

本文从非等温差示扫描量热(DSC)曲线研究聚(?)氟乙丙烯(FEP)在空气中热裂解过程分为两个阶段的机制及其微分动力学方程。利用峰形指数确定的两个阶段的裂解反应级数,用多项式回归了相应的裂解活化能,指前因子随裂解率变化的规律及其补偿效应。     

尼龙-1010非等温结晶动力学

<正> 尼龙-1010是我国独创的工程塑料品种,已被较广泛地应用于精密机械零件、仪表制造、家用电器、航空等方面。有关尼龙-1010的基础研究大多在我国学者中间进行,由于在实际加工生产过程中,如通常的融熔纺丝、注射、模压等工艺均是在非等温条件下进行,有关它的非等温结晶动力学尚未见报道,本文用几种理论方法对尼龙-1010的非等温结晶动力学过程进行研究。     

Estimation of the curing rate of acrylamide used as a consolidant in heritage sandstone conservation

An investigation of the curing (polymerisation) rate of acrylamide was carried out using isothermal and non-isothermal DSC in order to estimate the time for complete conversion of monomer at ambient temperatures. The non-isothermal data were used to model the rate using integral isoconversional and incremental isoconversional kinetic methods. Applying the equations for integral isoconversional methods and extrapolating to ambient temperatures resulted in non-sensical conversion–time curves, where the time estimated decreased for increasing degree of conversion to be reached. This odd behaviour was attributed to the incorrectness of the integration where the kinetic parameters (e.g. the activation energy) are a function of conversion. The problem was addressed by applying incremental methods which provided more reasonable results as the integration is carried out over small conversion increments where the kinetic parameters are assumed to be constant. Estimates of the conversion were compared to isothermal measurements and, although isothermal DSC produced significant variability in the data, extrapolated estimates from non-isothermal kinetic analysis produced, at best, an upper boundary for the estimation of the time to reach a fixed degree of conversion.     

Determination of oxidation parameters of fatliquored leather by DSC

The oxidation of a number of fatliquoring formulations, of different iodine index, derived from fish oil, rapeseed oil, neatsfoot oil, lecithin, paraffin, sulphited and sulphated variants was studied. The formulations included dispersing agents, stabilizers and/or anti-oxidants. Sheepskins were treated with fatliquoring agents at 5% of fatty matter. The oxidation of the fatliquoring formulations and the fatliquored skins was studied by non-isothermal differential scanning calorimetry (DSC). The onset thermoxidation temperature and the enthalpy of the thermoxidation peak located between 195 and 265 °C were determined and then related to the different fatliquoring standard formulations. The skins were subjected to ageing treatments using UV radiation and temperature. The fall in the denaturation temperature of the skin due to ageing was related to the oxidability of the fatliquoring agent.     

Thermal Decomposition Kinetics of Lead 2,4,6-Trinitroresorcinate Monohydrate

IntroductionLead 2 ,4,6- trinitroresorcinate monohydrate,Pb( TNR)· H2 O,has good detonating propertiesand is sensitive to flame.It can be used as initiat-ing agent,igniter powder or delay powder.Itspreparation,properties,crystal structure[1] andthermal behavior[2 ] have been reported.In the pre-sent paper,we will report its kinetic parametersand mechanism of thermal decomposition reactionstudied with TG- DTA,IR and DSC.This is quiteuseful in the evaluation of its thermal stability un-d…     

Simulation of isothermal cure of A powder coating

The curing of a thermosetting powder coating was studied by means of differential scanning calorimetry (DSC). The isothermal cure was simulated by non-isothermal experiments. The results of the simulation were compared with experimental isothermal data. From non-isothermal isoconversional procedures (free model), it was concluded that these permit simulation of the isothermal cure but do not enable us to determine the complete kinetic triplet (A preexponential factor, E activation energy, f(a) and/or g(a) function of conversion). Non-isothermal procedures based on a single heating rate or on master curves present difficulties for determination of all the kinetic parameters, due to the compensation effect between preexponential factor and activation energy. The kinetic triplet can be determined by a combination of various non-isothermal methods or by using experimental isothermal data in addition to non-isothermal data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal runaway hazards of <Emphasis Type="Italic">tert</Emphasis>-butyl hydroperoxide by calorimetric studies

Thermal runaway reactions associated with exothermic behaviors of tert-butyl hydroperoxide (TBHP) solutions and TBHP reacting with alkaline contaminants were studied. A differential scanning calorimetry (DSC) was used to characterize these inherent behaviors of TBHP solutions with KOH, NaOH, LiOH and NH₄OH. The exothermic peak in thermal curves of TBHP solutions with different alkali were detected by DSC thermal analysis. By thermal analysis, we compared various heats of decomposition of TBHP solutions with alkaline impurities, and determined the incompatible hazards of various TBHP solutions with alkaline contaminants. Comparing with TBHP in various diluents, the adiabatic runaway reaction via vent sizing package 2 (VSP2) indicated that aqueous TBHP intrinsically possesses the phenomena of thermal explosion with dramatic self-reactive rate and pressure rise under adiabatic conditions. Many commercial organic peroxides may have different hazard behaviors. Therefore, using thermal method to classify the hazards is an important subject.