Isoconversional kinetic study of alachlor and metolachlor vaporization by thermal analysis

The vaporization kinetics of two acetamide pesticides, namely alachlor and metolachlor, was studied by thermogravimetric analysis under nonisothermal conditions (using heating rates between 1.0 and 10 K min^?1). A model‐free isoconversional method of kinetic analysis was proposed, and activation energy dependences on the extent of conversion α for nonisothermal experiments were given. An increase in activation energy is shown for alachlor from 50 to 60 kJ mol^?1, while E values do not significantly vary in the range α > 0.1: 63 kJ mol^?1 for metolachlor while 60 kJ mol^?1 for alachlor. At the end of vaporization (0.9 < α < 1.0), the activation energies are in close agreement with the enthalpies of vaporization calculated from DSC measurements. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 74–80, 2005     

Polymerization kinetic pathways of epoxidized linseed oil with aliphatic bio-based dicarboxylic acids

The curing of epoxidized linseed oil (ELO) with three different bio-based dicarboxylic acids (sebacic acid, suberic acid, and succinic acid) has been investigated. No accelerators or catalysts were used and the resulting thermosets are 100% bio-based. Structural investigations of the three crosslinked ELO resins were made using FTIR spectroscopy and TMA, that is, tensile tests, TGA, and DMA. As evidenced by FTIR measurements ELO and dicarboxylic acids reacts but no major differences can be distinguished between the dicarboxylic acids. Non-isothermal curing has been conducted by rheological and DSC measurements. Advanced isoconversional analysis applied to DSC data in association with the complex viscosity variations gives new insights into the polymerization mechanism. The length of dicarboxylic acid carbon chain modifies the reaction rate. Then, a correlation between reaction rate, activation energy, pre-exponential factors, polymerization mechanism, and change in rate-limiting step was shown. DMA and tensile tests highlight the relationship between the carbon chain length, reactivity, and thermomechanical properties. The use of succinic acid allows reaching a higher T_g and thermal stability.     

Kinetics of Epoxy–Amine Curing Accompanied by the Formation of Liquid Crystalline Structure

The curing of a mesomorphic epoxy has been studied by polarized light microscopy (PLM) and differential scanning calorimetry. PLM in combination with wide‐angle X‐ray diffraction proves the formation of a liquid crystalline (LC) structure. An advanced isoconversional method reveals that the formation of the LC structure is accompanied by a dramatic decrease in the effective activation from ∼60 to ∼10 kJ · mol⁻¹. A kinetic model of the phenomenon has been discussed.

The dependence of the activation energy on the extent of conversion for isothermal curing of the diglycidyl ether of 4,4′‐dihydroxybiphenyl/2,6‐diaminopyridine (diamonds) and DGEBA/2,6‐diaminopyridine (circles) systems.     

Kinetic analysis of isothermal cures performed below the limiting glass transition temperature

The paper addresses the problem of the application of isoconversional kinetic analysis to incomplete cures. Contrary to the expectations, a theoretical analysis suggests that correct estimates of the activation energy can be obtained if one uses the relative extents of cure instead of the absolute values. This conclusion is illustrated by simulated data for a hypothetical process and experimental data for epoxy‐novolac cure.     

Application of DSC as a tool for honey floral species characterization and adulteration detection

The thermal behaviour of authentic honeys and sugar syrups (industrial and homemade) was investigated by DSC. To confirm the first previous results concerning the effect of adulteration on the thermal behaviour of authentic honeys, 30 honey samples (Robinia, Lavender, Chestnut and Fir) were analyzed by DSC and their T _g were measured following a suited experimental protocol. The results indicated that this parameter was useful to characterize and to distinguish significantly these varieties between them. Applied to honey samples artificially adulterated with different industrial syrups, DSC showed a detection level of 5–10% depending on the type of syrup. An endothermic phenomenon occurring between 40–90°C during the heating was studied by TMDSC and a new thermal transition similar to a glass-transition was highlighted.This revised version was published online in November 2005 with corrections to the Cover Date.     

Solid-plastic transitions kinetics by DSC

The kinetic parameters of solid-plastic transitions on alcohols derived from neopentane were determined using differential scanning calorimetry (DSC) by a single or multiple scan analysis. The methods studied (Borchard-Daniels, Ellerstein, Multilinear law, Freeman-Carroll, Ozawa, Kissinger), never used before for that kind of transition, imply a single Arrhenius behaviour. These methods werre applied to 2,2-dimethyl 1-propanol (DP), 2,2-dimethyl 1,3-propanediol or neopentylglycol (NPG), 2-hydroxymethyl 2-methyl 1,3-propanediol or pentaglycerine (PG), and 2,2-dihydroxymethyl 1,3-propanediol or pentaerythritol (PE). A simple isothermal test is recommended to check the validity of activation energies experimentally obtained and Arrhenius frequency factors. Taking some restrictions on the heating rate for the heat evolution methods, the results are in agreement with the data obtained by isothermal tests. We have noted a linear dependence of the activation energy values on the number of hydroxyl groups with the exception of pentaerythritol. Isothermal simulations of the solid-plastic transition are an example of industrial applications.

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Zusammenfassung Mittels DSC wurden in einem Single-bzw. Multiscananalyse die kinetischen Parameter der fest-plastischen Umwandlung einiger von Neopentan abgeleiteten Alkohole bestimmt. Die untersuchten Verfahren (Borchard-Daniels, Eilerstein, Multilineares Gesetz, Freeman-Carroll, Ozawa, Kissinger), die noch nie für diese Umwandlung angewendet wurden, lassen auf ein einfaches Arrheniussches Verhalten schließen. Diese Verfahren wurden bei 2,2-Dimethyl-1-propanol (DP), 2,2-Dimethyl-1,3-propandiol oder Neopentylglykol (NPG), 2-Hydroxymethyl-2-methyl-1,3-propandiol oder Pantaglycerin (PG) sowie bei 2,2-Dihydroxymethyl-1,3-propandiol oder Pentaerythrit (PE) angewendet. Es wird ein einfacher isothermer Test vorgeschlagen, um die Gültigkeit der experimentell ermittelten Aktivierungsenergien und der Arrheniusschen Frequenzfaktoren zu überprüfen. Unter einer gewissen Einschränkung der Aufheizgeschwindigkeit stimmen die Ergebnisse mit denen des isothermen Testes überein. Mit Ausnahme von Pentaerythrit konnten wir einen linearen Zusammenhang zwischen den Werten für die Aktivierungsenergie und der Anzahl der Hydroxylgruppen feststellen. Die isothermen Simulierungen von fest-plastischen Umwandlungen sind Beispiele für industrielle Anwendungen.

     

Gelation on Heating of Supercooled Gelatin Solutions

Diluted (1.0–1.5 wt%) aqueous gelatin solutions have been cooled to –10 °C at a cooling rate 20 °C min⁻¹ without freezing and detectable gelation. When heated at a constant heating rate (0.5 –2 °C min⁻¹), the obtained supercooled solutions demonstrate an atypical process of gelation that has been characterized by regular and stochastically modulated differential scanning calorimetry (DSC) as well as by isoconversional kinetic analysis. The process is detectable as an exothermic peak in the total heat flow of regular DSC and in the nonreversing heat flow of stochastically modulated DSC. Isoconversional kinetic analysis applied to DSC data reveals that the effective activation energy of the process increases from approximately 75 to 200 kJ mol⁻¹ as a supercooled solution transforms to gel on continuous h eating.     

Variation of the Effective Activation Energy Throughout the Glass Transition

Summary: An advanced isoconversional method has been applied to determine the effective activation energies (E) for the glass transition in polystyrene (PS), poly(ethylene terephthalate) (PET), and boron oxide (B₂O₃). The values of E decrease from 280 to 120 kJ · mol⁻¹ in PS, from 1 270 to 550 kJ mol⁻¹ in PET, and from 290 to 200 kJ mol⁻¹ in B₂O₃. It is suggested that a significant variation in E should be observed for the fragile glasses that typically include polymers.

Variation in the effective activation energy of PS, PET, and B₂O₃ with temperature.