Determination of the optimum epoxy/curing agent ratio: A study of different kinetic parameters (original) (raw)
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Cure kinetics of epoxy resins studied by non-isothermal DSC data
Thermochimica Acta, 2002
The curing kinetics of diglycidyl ether of bisphenol A (DGEBA) and diglycidyl ether of hydroquinone (DGEHQ) epoxy resins in presence of diglycidyl aniline as a reactive diluent and triethylenetetramine (TETA) as the curing agent was studied by non-isothermal differential scanning calorimetry (DSC) technique at different heating rates. The kinetic parameters of the curing process were determined by isoconversional method given by Ma Âlek for the kinetic analysis of the data obtained by the thermal treatment. A two-parameter (m, n) autocatalytic model (S Ï esta Âk±Berggren equation) was found to be the most adequate selected to describe the cure kinetics of the studied epoxy resins. Reactive diluent decreases both the activation energy and the cure kinetic parameters. Non-isothermal DSC curves obtained using the experimental data show a good agreement with that theoretically calculated. #
A thermoanalytical study of the cure characteristics of an epoxy resin system
1979
Rates and extents of cure at different times and temperatures are determined for a modified epoxy resin system and related to gel time measurements. An empirical equation based on time-temperature superposition determines cure time as a function of degree and temperature of cure. The dependence of glass transition temperature on degree of cure, and heat capacity measurements on the cured resin, are discussed.
Thermochimica Acta, 2001
Curing reaction of three tetrafunctional epoxy resins in the presence of tetraethylene tetramine was examined by differential scanning calorimetry at different heating rates. The kinetic parameters of the curing reaction were determined using various computational methods (Barrett, Borchardt±Daniels and Kissinger). The heating rate shows a great in¯uence on the curing process. The activation energy varied in the range 43±80 kJ/mol, and the order of the curing reaction is observed to be %1.0 with slight variations. #
Isothermal differential scanning calorimetry study of a glass/epoxy prepreg
Polym Advan Technol, 2009
Isothermal differential scanning calorimetry (DSC) was used to study the curing behavior of epoxy prepreg Hexply 1 1454 system, based on diglycidyl ether of bisphenol A (DEGBA)/dicyandiamid (DICY) reinforced by glass fiber. Cure kinetics of an autocatalytic-type reaction were analyzed by general form of conversion-dependent function. The characteristic feature of conversion-dependent function was determined using a reduced-plot method where the temperature-dependent reaction rate constant was analytically separated from the isothermal data. An autocatalytic kinetic model was used; it can predict the overall kinetic behavior in the whole studied cure temperature range (115-130-C). The activation energy and pre-exponential factor were determined as: E ¼ 94.8 kJ/mol and A ¼ 1.75 T 10 10 sec S1 and reaction order as 2.11 (m R n ¼ 0.65 R 1.46 ¼ 2.11). A kinetic model based on these values was developed by which the prediction is in good agreement with experimental values.
Journal of Applied Polymer Science, 1995
By employing differential scaning calorimetry, DSC, we have studied, under isothermal conditions, the kinetics of the cure reaction for a system containing a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcyclohexane (1,3-BAC) as a curing agent, over the temperature range of 60–110°C. We have determined the conversions reached at several cure temperatures and the reaction rates. The experimental data, showing an autocatalytic behavior, were compared with the model proposed by Kamal, which includes two rate constants, k1 and k2, and two reaction orders, m and n. This model gives a good description of cure kinetics up to the onset of vitrification. The activation energies for these rate constants were 44–57 kJ/mol. The reaction orders present a moderate change but their sum is in the range 2.5–3. Diffusion control is incorporated to describe the cure in the latter stages (postivitrification region). By combining the autocatalytic model and a diffusion factor, it was possible to predict the cure kinetics over the whole range of conversion. © 1995 John Wiley & Sons, Inc.
Journal of Thermal Analysis and Calorimetry, 2010
A new homologous series of curing agents (LCECAn) containing 4,4 0-biphenyl and n-methylene units (n = 2, 4, 6) were successfully synthesized. The curing behaviors of a commercial diglycidyl ether of bisphenol-A epoxy (E-51) and 4,4 0-bis(2,3-epoxypropoxy)biphenyl (LCE) by using LCECAn as the curing agent have been investigated by differential scanning calorimetry (DSC), respectively. The Ozawa equation was applied to the curing kinetics based upon the dynamic DSC data, and the isothermal DSC data were fitted using an autocatalytic curing model. The glass transition temperatures (T g) of the cured epoxy systems were determined by DSC upon the second heating, and the thermal decomposition temperatures (T d) were obtained by thermogravimetric (TG) analyses. The results show that the number of methylene units in LCECAn has little influence on the curing temperatures of E-51/LCECAn and LCE/LCECAn systems. In addition, the activation energies obtained by the dynamic method proved to be larger than those by the isothermal method. Furthermore, both the T g and T d of the cured E-51/LCECAn systems and LCE/LCECAn systems decreased with the increase in the number of methylene units in LCECAn.
This work was aimed at the study of cure kinetics of two commercial thermosetting epoxy systems, Epikote resin 816 LV/Epikure F205 and Epikote resin 240/Epikure F205, by Fourier Tranform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). The studied systems consist of a resin (A), based on a diglycidyl ether of bisphenol A and a hardener (B) based on the Isophorodiamine (IPDA) a cycloaliphatic diamine. These systems are used for the building and civil engineering industries, e.g. flooring compounds, adhesives, mortars and grouts. FTIR spectroscopy was employed to investigate the isothermal curing kinetics at 30, 50 or 70 • C and DSC analysis to study the non-isothermal curing kinetics at different heating rates 2.5, 5, 10 and 20 • C/min, from 20 to 300 • C. A kinetic model was employed to simulate the FTIR isothermal experimental data using two kinetic rate constants and incorporating also diffusion control at high degrees of conversion. Finally, the variation of the effective activation energy with the extent of curing was estimated using isoconversional analysis of non-isothermal DSC data.
Cure kinetics of a diglycidyl ether of bisphenol a epoxy network ( n = 0) with isophorone diamine
Journal of Applied Polymer Science, 2007
The study of the cure reaction of a diglycidyl ether of bisphenol A epoxy network with isophorone diamine is interesting for evaluating the industrial behavior of this material. The total enthalpy of reaction, the glass-transition temperature, and the partial enthalpies at different curing temperatures have been determined with differential scanning calorimetry in dynamic and isothermal modes. With these experimental data, the degree of conversion and the reaction rate have been obtained. A kinetic model introduces the mechanisms occurring during an epoxy chemical cure reaction. A modification of the kinetic model accounting for the influence of the diffusion of the reactive groups at high conversions is used. A thermodynamic study has allowed the calculation of the enthalpy, entropy, and Gibbs free energy.
Journal of Applied Polymer Science, 2019
Fast curing epoxy resins were prepared by the reactions of diglycidyl ether of bisphenol A with isophorone diamine (IPD) and N-(3-aminopropyl)-imidazole (API), and their curing kinetics and mechanical properties influenced by IPD content were also investigated. The analysis of curing kinetics was based on the nonisothermal differential scanning calorimetry (DSC) data with the typical Kissinger, Ozawa, and Flynn-Wall-Ozawa models, respectively. The glass-transition temperature was also measured by the same technique. Additionally, the mechanical properties including flexural, impact, and tensile performances were tested, and the curing time was estimated by isothermal DSC. The degree of cure (α) dependency of activation energy (E a) revealed the complexity of curing reaction. Detailed analysis of the curing kinetics at the molecular level indicated that the dependence of E a on the α was a combined effect of addition reaction, autocatalytic reaction, viscosity, and steric hindrance. From the nonisothermal curves, the curing reaction mechanism could be proposed according to the increasingly obvious low temperature peaks generated by the addition reaction of epoxy group with the primary amines in API and IPD molecules. Using the preferred resin formulation, the resin system could be cured within 10 min at 120 C with a relatively good mechanical performance.
Cure kinetics of a liquid-crystalline epoxy resin studied by non-isothermal data
Polymer Testing, 2004
The curing kinetics of diglycidyl ether of 4,4Ј-bisphenol (DGEBP) epoxy mesogenic resin in the presence of sulphanilamide (SAA) was studied by non-isothermal differential scanning calorimetry (DSC) at different heating rates. At low heating rates (2-5°C min Ϫ1 ), the curing reaction takes place by two processes evidenced by the presence of a double peak on the DSC thermograms. The first process is due to the reaction of primary amine with epoxy, while the second one corresponds to the formation of the crosslinked network with liquid crystalline (LC) properties by the attack of the secondary amine previously formed onto the epoxide groups unreacted in the first stage of the reaction. An activation energy (E a = 59 kJ mol Ϫ1 ) was evaluated for the second process and an autocatalytic kinetic model (Š esták-Berggren equation) was proposed to better describe the cure kinetics of the studied system. The theoretical DSC curves calculated using the kinetic parameters determined in non-isothermal conditions show good agreement with those experimentally determined.