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:L. Barral, J. Cano, J. López, I. López-Bueno, P. Nogueira, M. Abad, and C. Ramírez
The physical aging of a system containing tetraglycidyl-4-4′-diaminodiphenylmethane (TGDDM), with a multifunctional novolac
glycidyl ether resin hardened by 4,4′-diaminodiphenylsulphone (DDS) has been investigated by differential scanning calorimetry
(DSC) and dynamic mechanical analysis (DMA). Samples fully cured were aged at temperatures between 200 and 250C, during periods
of time from 1 to a maximum of 336 h. Furthermore, the dynamic mechanical relaxation behaviour annealed at temperature of
220C, was studied, aging during 24 and 168 h. The effect of the enthalpy relaxation during DSC heating scan is shown by the
presence of an endothermic peak whose position and intensity depends on the aging conditions, both temperature and time. DSC
studies suggest that enthalpy relaxation increases gradually with aging time to a limiting value for each temperature where
structural equilibrium is reached. DMA results show that the effect of aging is to cause chain stiffening and a decrease in
the height of the peak value of the loss factor.
Authors:L. Barral, J. Cano, J. López, I. López-Bueno, P. Nogueira, C. Ramírez, A. Torres, and M. Abad
Cure kinetics using a differential scanning calorimetry (DSC) technique were analyzed for a thermoplastic modified tetraglycidyl-4,4′-diaminodiphenylmethane
(TGDDM) epoxy resin cured with diaminodiphenylsulphone (DDS), an aromatic diamine. The neat resin and its blends with the
poly(styrene-co-acrylonitrile) (SAN) of various compositions were studied by applying a phenomenological model proposed by
Kamal. Kinetic parameters were determined by fitting experimental data. This model gives a good description of cure kinetics
up to the onset of vitrification. Diffusion control was incorporated to describe the cure in the latter stages of cure. The
results showed that the addition of SAN did not alter the nature of the reaction, but the reaction rates and final conversions
decreased when SAN contents increase, due to reduction of mobility of the reacting species.