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Abstract  

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.

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Journal of Thermal Analysis and Calorimetry
Authors: C. Ramírez, M. Rico, J. M. L. Vilariño, L. Barral, M. Ladra, and B. Montero

Summary Cubic silsesquioxanes offer access to organic/inorganic hybrids. A system formed by a polyhedral oligomeric silsesquioxane (POSS) with eight epoxy reactive groups per molecule, octaepoxycyclohexyldimethylsilyl-POSS, cured with an aliphatic diamine (bisaniline) was studied in different ratios. The characterization of the POSS was carried out by differential scanning calorimetry (DSC) and thermogravimetry (TG). The distribution of species in the reaction of the mixtures POSS/diamine was followed by gel permeation chromatography (GPC). The degradation was studied by thermogravimetric analysis.

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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.

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Abstract  

Isothermal crystallization and melting of isotactic polypropylene in binary polypropylene-wood flour composites has been studied by DSC, and the influence of an ethylene-methacrylic acid copolymer interfacial agent analyzed. Wood flour induces a slight nucleating effect, reducing the basal interfacial free energy of nucleation and increasing the overall crystallization rate. The interfacial agent generates a compatibilization phenomenon and an increase in the basal interfacial free energies with respect to the binary composites. In both binary and ternary systems the melting behaviour is a function of undercooling and is unaltered by the presence of either wood flour or the interfacial agent.

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Abstract  

Using differential scanning calorimetry (DSC) we have studied the physical aging of an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) modified by two different contents of an acrylonitrile-butadiene-styrene (ABS) and cured with 1,3-bisaminomethylcyclohexane (1,3-BAC). Samples fully cured were annealed at temperature of 125C for periods of time of 72 and 120 h, to determine the process of physical aging. The apparent activation energy for the enthalpy relaxation, Dh*, is determined as the sample is heated at 10C min-1 following cooling at various rates through the glass transition region. DSC studies suggested that the presence of thermoplastic inhibits the process of relaxation.

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Abstract  

The thermal behaviour of an epoxy resin cured with an amine-POSS was studied using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The kinetic of polymerization reaction and the thermal degradation have been analyzed based on an iso-conversional model. The obtained results showed that the activation energies of both processes depend on the degree of conversion.

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Abstract  

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.

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