F. Fraga

Activation energies for the epoxy system BADGE n = 0/m‐XDA obtained using data from thermogravimetric analysis

In this article we study the kinetics of thermal degradation of the epoxy system BADGE n = 0/m-XDA using different kinetic methods with data from thermogravimetric analysis (TGA) in dynamic conditions. Activation energies obtained using different integral methods (Flynn-Wall-Ozawa and Coats-Redfern Methods) are in good agreement with the value obtained using the Kissinger method (204.44 kJ/mol). The solid-state decomposition mechanism followed by this epoxy system is a decelerated Rn type (phase boundary controlled reaction). We have also calculated activation energies using the Van Krevelen and the Horowitz-Metzger methods. These last methods corroborate the decelerated behavior.

Influence of water absorption on the mechanical properties of a DGEBA (n = 0)/1, 2 DCH epoxy system

The diffusive, calorimetric, and mechanical behavior of a system composed of a diglycidyl ether of bisphenol-A (DGEBA, n = 0) and 1, 2 diamine cyclohexane (1, 2 DCH) were investigated during water sorption at different temperatures (23, 47, 58, 77, and 100°C). Experimental results showed that the water absorption at these temperatures fitted well to Ficks law. The water moisture content at the equilibrium temperature and the water moisture content at the equilibrium-curing conditions dependences have been checked. The activation energy for diffusion was calculated obtaining a value 26.01 kJ/mol. Dynamic mechanical analysis of several samples immersed in water at 100°C during different periods of time showed no significant changes in the glass transition temperature, and a decrease in the storage modulus at 2% of water content was observed. Storage modulus remained essentialy constant above that water content. Values of glass transition temperature were corroborated by differential scanning calorimetric measurements.

Physical aging for an epoxy network diglycidyl ether of bisphenol A/m-xylylenediamine

Abstract The physical aging of the epoxy network consisting of a diglycidyl ether of bisphenol A (BADGE n=0) and m-xylylenediamine (m-XDA) were studied by differential scanning calorimetry. The following aging temperatures have been used in this work: 60, 70, 80, 90, 100 and 110 °C. The glass transition temperature and the variation of the specific heat capacities have been calculated using the method based on the intersection of both enthalpy–temperature lines for glassy and liquid states. The endothermic aging peak, relaxation enthalpy and fictive temperature were also calculated for each aging temperature and aging time.

Effects of diffusion on the kinetic study and TTT cure diagram for an epoxy/diamine system

The curing reactions of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n 5 0) and 1,2-diamine cyclohexane (DCH) were studied to determine a time-temperature-transformation (TTT) isothermal cure diagram for this system. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and a solubility test were used to obtain the different experimental data reported. Two models, one based solely on chemical kinetics and the other accounting for diffusion, were used and compared to the experimental data. The inclusion of a diffusion factor in the second model allowed for the cure kinetics to be predicted over the whole range of conversion covering both pre- and post-vitrification stages. The investigation was made in the temperature range 60 -100°C, which is considered optimum for the isothermal curing of the epoxy system studied.

Kinetic and thermodynamic studies of an epoxy system diglycidyl ether of bisphenol-A/1,2 diamine cyclohexane

The curing reaction of a system consisting of a purified diglycidyl ether of bisphenol-A (BADGE, n = 0) and 1,2 diamine cyclohexane (DCH) was studied with a differential scanning calorimeter. The objective of this article was twofold: a kinetic study from which parameters such as reaction orders, rate constants, and activation energies were determined; and a thermodynamic study where values of enthalpy (ΔH#), entropy (ΔS#), and Gibbs free energy (ΔG#) changes were calculated. This second study showed that an n-order path reaction mechanism was more favored than the autocatalyzed mechanism above 338 K. This fact was also checked when plotting rate constant ratio against temperature.

Kinetic and thermodynamic studies of an epoxy system diglycidyl ether of bisphenol A/1, 2 diamine cyclohexane/calcium carbonate filler

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0) and 1,2-diaminecyclohexane (DCH) with a calcium carbonate filler was studied by differential scanning calorimetry (DSC) and using a scanning electronic microscope (SEM). As a first stage, the optimum content of the filler determined was 20%. From a kinetic study, in which two models were used, parameters such as reaction orders, rate constants, and activation energies were determined. A thermodynamic study allowed calculation of enthalpy (ΔH#), entropy (ΔS#), and free-energy ((ΔG#) changes. The results were compared to those obtained for the same epoxy systems without the filler.

Effects of diffusion on the kinetic study of the system BADGE n = 0/m-xylylenediamine

The curing reactions of an epoxy system composed of a diglycidyl ether of bisphenol A (BADGE n = 0) and m-xylylenediamine (m-XDA) were studied. Two models, the first based solely on chemical kinetics and the second accounting for diffusion, were used and compared to the experimental data. The epoxy resin was used as received in a first series of experiments. In a second series of experiments, the resin was purified in vacuo (180°C and 1 mmHg). The inclusion of a diffusion factor in the second model allowed for the cure kinetics to be predicted over the whole range of conversion covering both pre- and postvitrification stages. The investigation was made in the temperature range 50-110°C, which is considered optimum for the isothermal curing of the epoxy system studied.

Lifetime prediction of the epoxy system badge n = 0/1,2 DCH by thermogravimetric analysis

Lifetime of the system diglycidyl ether of bisphenol A (BADGE n 5 0)/1,2- diamine cyclohexane (DCH) was predicted by thermogravimetric analysis. Lifetime was considered when either 5% weight loss or 5% conversion was reached. Experimental results were treated using two different methods: The first method was independent of the degradation mechanism and the second was based on the thermodegradation kinetic mechanism. The activation energy of the reaction, determined using the Flynn- Wall-Ozawa method, was 148.51 kJ/mol. This value is in a good agreement with that of 144.01 kJ/mol obtained using Kissinger9s method. From the experimental results, it was found that the optimum temperature of service for this material is in the range of 100 -140°C, at which the corresponding lifetime range is from 27 to 2633 years.

Effects of diffusion on the kinetic study of an epoxy system diglycidyl ether of bisphenol A/1,2-diamine cyclohexane/calcium carbonate filler

The curing reactions of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0), 1,2-diamine cyclohexane (DCH) with calcium carbonate filler, were studied to determine different kinetic parameters. Two models-one based solely on chemical kinetics and the other accounting for diffusion-were used and compared to experimental data both for systems with and without filler. It was found that 100°C is the optimum service temperature, and also that the presence of the filler has no influence on the optimal service temperature range (60-100°C) of the epoxy system.

Elastic Moduli and Activation Energies for an Epoxy/m-XDA System by DMA and DSC

The influence of the resin/diamine ratio on the properties of the system diglycidyl ether of bisphenol A (BADGE n=0/m-xylylenediamine) (m-XDA) was studied. Variation of this ratio resulted in significant effects on the cure kinetics and final dynamic mechanical properties of the product material.The study was made in terms of storage modulus (E′), vss modulus (E″) and molecular mass between cross-links (Mc) at different ratios. Two geometries (cylindrical and rectangular) were considered. The influence of temperature was studied through the activation energy (Ea>), which depends on the epoxy/amine ratio and the geometry of the samples. Glass transition temperatures (Tg>) and glass transition temperatures for thermosets with null degree of conversion (Tgo>) were determined by DSC. Tg> decreases when amounts of curing agent greatly in excess of the stoichiometric composition were used.