Authors:P. Melnikov, A. Guirardi, M. Secco, and E. Nogueira de Aguiar
Mechanisms of formation of polyphosphates MeIII(PO3)3, where MIII=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, Fe, Ga, Al and Cr has been simulated by thermal analysis technique.
MeIII oxides and ammonium dibasic phosphate (NH4)2HPO4 were used as starting materials. For MIII=La-Lu, Y and Fe three main stages were observed: 1. elimination of water and ammonia leading to the formation of ammonium
tripolyphosphate (NH4)5P3O10; 2. reaction of the latter with Me2IIIO3 and formation of acidic polyphosphates MeIIIH2P3O10 or their isomers MeIII(PO3)3·H2O; 3. final loss of water and formation of MeIII(PO3)3. For MeIII=Sc and Ga the second stage is prolonged and the polyphosphates form at higher temperatures. Aluminum and chromium polyphosphates
are unstable. It is suggested that thermal behavior of the compounds is determined by MeIII ionic radii.
Authors:L. Barral, J. Cano, A. López, P. Nogueira, and C. Ramírez
Using dynamic mechanical analysis (DMA) we have studied the variation with the frequency of the dynamic mechanical properties
(storages modulus,E'; loss modulus,E'' and loss tangent or tan σ) for a system containg a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcyclohexane
(1,3-BAC). These properties were measured both in the glass transition and β transition regions. An increase in frequency
caused a shift of tan σ peak positions in both regions toward higher temperature. Finally, we report the activation energies
of a DGEBA/1,3-BAC expoxy system for α and β transitions.
Authors:L. Barral, J. Cano, A. J. López, J. López, P. Nogueira, and C. Ramírez
The diffusive and dynamic mechanical behavior of the DGEBA/1,3-BAC epoxy resin system was studied during water absorption. The diffusion of water was investigated at 100% relative humidity, by immersion of specimens in water at 60, 80 and 100°C. In all absorption experiments, water diffusion followed Fick's law. Diffusion coefficients and saturated water concentrations are given for these temperatures. The activation energy for diffusion was determined from the relationship between the diffusion coefficient and the reciprocal of the absolute temperature. The value obtained was 31.2 kJ mol−1. Dynamic mechanical analysis of samples immersed in 100°C water and with various water contents showed both a shift of Tg, defined by thetanδ peak, to lower temperatures and a slight decrease in the dynamic modulus in the presence of water. These effects are probably a result of plasticization.
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, A. López, J. López, P. Nogueira, and C. Ramírez
Using dynamic mechanical analysis (DMA) we have studied thermal degradation for a system containing a diglycidyl ether of
bisphenol A (DGEBA) and 1,3-bisaminomethylcylohexane (1,3-BAC). The changes of dynamic mechanical properties during thermal
degradation indicated a shift of the glass transition temperature (Tg) to higher temperatures and a decrease in the peak value of the dynamic loss factor (tan δ) with an increasing of aging time.
The value of dynamic storage modulus (E′) at the rubbery state showed an increase with aging time, whiteE′ at the glassy state only underwent a moderate change with increased thermal degradation. From these results it can be argued
that thermal degradation during the stage prior to the onset of the severe degradation involves structural changes in the
epoxy system, as further crosslinking and loss of dangling chains in the crosslinked network.
Authors:L. Barral, J. Cano, J. López, I. López-Bueno, P. Nogueira, C. Ramírez, and M. Abad
A study of an epoxy-cycloaliphatic amine system has been realized using a thermogravimetric technique (TG). Isothermal and
non-isothermal (dynamic) methods were employed to determine the kinetic data of this system.
Five methods were used for determining the activation energies of this system in the dynamic heating experiments. In two of
them (Flynn-Wall-Ozawa, and Kissinger) it is not necessary to have a prior knowledge of the reaction mechanism of the degradation
behaviour for this system. In the other ones (Coats and Redfern, Horowitz and Metzger, and Van Krevelen et al.) it is necessary
to know this reaction mechanism, besides Criado et al. method was used for determining it.
The results have shown that good agreement between the activation energies obtained from all methods can be achieved if it
is assumed that the degradation behaviour of this system is of sigmoidal-rate type.
Authors:H. P. de Oliveira, J. Rieumont, C. Nogueiras, D. Souza, and R. Sánchez
The thermal degradation of an amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide)-carboxylic acid terminated (PE-b-80%PEO–CH2COOH) and its salt obtained as intermediary product from chemical oxidation of the end group of poly(ethylene)-b-poly(ethylene oxide) (PE-b-80%PEO) has been studied using a thermogravimetric mass spectrometry (TG/MS) coupled system. The isothermal fragmentation of PE-b-80%PEO–CH2COOH showed a more complex fragmentation pattern than PE-b-80%PEO owing to the simultaneous occurrence of the polyether block and the carboxylic end group fragmentations. This led to the appearance of four overlapping ion current peaks of fragments with m/z 44 and two peaks relative to m/z 18 at different times by acid-terminated copolymer. For the PE-b-80%PEO copolymer, two ion current peaks associated to m/z 44 and one large peak relative to m/z 18 fragments were detected. The intermediary product (PE-b-80%PEO–CH2COO− K+) showed differences related to the fragmentation behavior. It has more defined ion current signals and presented characteristic peaks attributed to m/z 43 fragment at the very beginning of the thermal degradation process, which it not detected in the acid copolymer.
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.