Authors:M. Villanueva, J. Martín-Iglesias, J. Rodríguez-Añón, and J. Proupín-Castiñeiras
The thermal degradation of the epoxy system diglycidyl ether of bisphenol A (DGEBA n=0) and m-xylylenediamine (mXDA) containing different concentrations of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles was studied by thermogravimetric
analysis in order to determine the influence of both, the POSS concentration and the curing cycle on the degradation process
and to compare it with the results for the non modified system.
Glass transition temperatures for the same systems were also determined by differential scanning calorimetry. Different behaviors
have been observed, depending on the POSS concentration and on the curing selection.
Authors:Lisardo Núñez, M. Villaneuva, B Rial, M. Núñez, and L. Fraga
The thermal degradation of the epoxy system diglycidyl ether of bisphenol A (BADGE n=0)/1,2-diamine cyclohexane (DCH) containing different concentrations of an epoxy reactive diluent was studied by thermogravimetric
analysis in order to determine the reaction mechanism of the degradation process and to compare it with the results for the
same system without diluent. The value of the activation energy, necessary for this study, was calculated using various integral
and differential methods. Values obtained using the different methods were compared to the value obtained by the Flynn-Wall-Ozawa"s
method (between 193-240 kJ mol-1 depending on the diluent concentration) with does not require a knowledge of the nth order reaction mechanism. All the experimental
results were compared to master curves in the range of Doyle"s approximation (20-35% of conversion). Analysis of the results
suggests that the reaction mechanism could be F2, F3, or A2 type.
Authors:M. Núñez, M. Villanueva, B. Rial, and L. Núñez-Regueira
The thermal degradation of the epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) and diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diaminecyclohexane (DCH) containing calcium carbonate filler immersed and not immersed in hydrochloric acid have
been studied by thermogravimetric analysis in order to compare their decomposition processes and to determine the reaction
mechanism of the degradation processes. The value of the activation energies, necessary for this study, were calculated using
various integral and differential methods. Analysis of the results suggests that hydrochloric acid does not affect the decomposition
of the epoxy network and that the reaction mechanisms produce sigmoidal-type curves for the systems not immersed in HCl and
deceleration curves for the same systems immersed.
Authors:L. Barral, J. Cano, J. López, P. Nogueira, M. Abad, and C. Ramírez
Differential scanning calorimetry (DSC) was applied to study the cure kinetics of an epoxy system containing both tetraglycidyl
4,4′-diaminodiphenylmethane (TGDDM) and a multifunctional Novolac glycidyl ether resin, cured with 4,4′-diaminodiphenylsulfone
(DDS). The experimental data were analyzed in terms of a mechanistic model proposed by Cole, which includes the etherification
reaction. The kinetics can be completely described in terms of three rate constants, which obey the Arrhenius relationship.
This model gives a good description of the cure kinetics up to the onset of vitrification. The effect of diffusion control
was incorporated to describe the cure in the later stages. By combining the model and a diffusion factor, it was possible
to predict the cure kinetics over the whole range of conversion, including an analysis of the evolution of different chemical
species during the curing process. Good agreement with the experimental DSC data was achieved with this mechanistic model
over the whole range of cure when the etherification reaction was assumed to be of first order with respect to the concentrations
of epoxide groups, hydroxy groups, and the tertiary amine groups formed in the epoxide amine reaction.
Authors:G. Liu, L. Zhang, X. Qu, Y. Li, J. Gao, and L. Yang
A new model has been deduced by assumed autocatalytic reactions. It includes two rate constants, k1 and k2, two reaction orders, m and n, and the initial concentration of [OH]. The model proposed has been applied to the curing reaction of a system of bisphenol-S
epoxy resin (BPSER), with4,4'-diaminodiphenylmethane (DDM) as a curing agent. The curing reactions were studied by means of
differential scanning calorimetry (DSC). Analysis of DSC data indicated that an autocatalytic behavior showed in the curing
reaction. The new model was found to fit to the experimental data exactly. Rate constants, k1 and k2 were observed to be greater when curing temperature increased. The activation energies for k1 and k2 were 95.28 and 39.69 kJ mol–1, respectively. Diffusion control was incorporated to describe the cure in the latter stages.
Authors:D. Chinn, Sang -Beom Shim, and J. C. Seferis
Five epoxy resins of different chemistry and functionality were cured with DDS (4,4′-diaminodiphenyl sulfone) using 2, 8 and 14 h curecycles. Both Differential Scanning Calorimetry (DSC) and Thermomechanical Analysis (TMA) were used to characterize reaction behavior and cured properties of the resin systems. In addition, static mechanical tests and density measurements were integrated with the thermal characterization methods to correlate resin properties with process time. Flexural three-point bending experiments showed that the resins tended to have higher yield stress and toughness values at extended cure times. The improved mechanical properties could be attributed to the full development of the epoxy molecular structure, in the form of cross-linked networks and molecular rearrangement. These results suggest that extended cure times or high temperature post-curing may be required to obtain the resin's ultimate mechanical properties for high performance composites.
Authors:L. Núńez-Regueira, S. Gómez-Barreiro, and C. A. Gracia-Fernández
Modulated differential scanning calorimetry (MDSC) and dielectric analysis (DEA) have been used to characterize the cure process
of the system diglycidyl ether of bisphenol A (DGEBA(n=0)/1,2 diaminocyclohexane (1,2 DCH). The trans isomer and a mixture cis/trans(30-70% respectively) of 1,2 DCH were used to find their different behaviour. The study allowed to check the influence of
the cisisomer on the thermoset curing process. Gelation times were obtained through the equation proposed by Johari and vitrification
times from the point of inflection of the complex calorific capacity modulus.
Authors:I. Blanco, L. Oliveri, G. Cicala, and A. Recca
loosely used to include cured epoxysystems [ 2 ]. It should be noted that very high molecular weight epoxy resins and cured epoxy resins contain very little or no epoxide groups. The vast majority of industrially important epoxy resins are bi- or