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1.
Núñez Lisardo Villaneuva M. Rial B Núñez M. R. Fraga L. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):75-84
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.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Núñez Lisardo Fraga L. Núñez M. R. Villanueva M. Rial B. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):9-17
Curing reactions of the epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n=0) and m-xylylenediamine (m-XDA) were studied to calculate time-temperature-transformation (TTT) isothermal cure diagram for this system. Gel times were
measured as a function of temperature using solubility test. Differential scanning calorimetry (DSC) was used to calculate
the vitrification times. DSC data show a one-to-one relationship between T
g and fractional conversion, a independent of cure temperature. As a consequence, T
g can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from
the gel times obtained using the solubility test (41.5 kJ mol-1). This value is similar to the results obtained for other similar epoxy systems. Isoconversion contours were calculated by
numerical integration of the best fitting kinetic model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Lisardo Núñez F. Fraga A. Castro L. Fraga 《Journal of Thermal Analysis and Calorimetry》1998,52(3):1013-1022
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.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Lisardo Núñez-Regueira M. Villanueva I. Fraga C. A. Gracia-Fernández S. Gómez-Barreiro 《Journal of Thermal Analysis and Calorimetry》2006,86(1):235-241
The thermal degradation
of an epoxy system consisting of a diglycidyl ether of bisphenol A (DGEBA, n=0) and m-xylylenediamine (m-XDA)
was studied by both thermogravimetric analysis (TG) and dielectric analysis
(DEA). It has been checked a deviation of the typical behaviour in the Arrhenius
plot expected for this kind of systems, owing to the thermal degradation.
Both, structural relaxation time and conductivity values, were represented
as a function of the mass loss, that allow a relationship to be obtained between
characteristic relaxation time and the degree of degradation at the beginning
of the degradation process. 相似文献
5.
Villaneuva M. Núñez Lisardo Núñez M. R. Rial B. Fraga L. Monsterrat S 《Journal of Thermal Analysis and Calorimetry》2002,70(1):45-56
The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (n=0) and 1, 2 diaminecyclohexane (DCH) with an epoxy reactive diluent vinylcyclohexane dioxide was studied by temperature modulated
differential scanning calorimetry (TMDSC). The models proposed by Kamal and by Horie et al. were employed in the kinetic study.
From these studies reaction orders, rate constants, and activation energies were determined. The technique of TMDSC allows
to include in the kinetic study the effect of diffusion by means of the mobility factor, calculated from the curves of the
complex heat capacity registered during the curing isothermal experiments. The results were compared to those obtained for
the same system employing the reaction rate data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Lisardo Núñez Silvia Gómez-Barreiro Carlos Alberto Gracia-Fernández 《Rheologica Acta》2005,45(2):184-191
Rheology was used to characterise the curing process of the epoxy system consisting of a diglycidyl ether of bisphenol A [DGEBA(n=0)] and one, or a mixture of the two isomers of the curing agent 1,2-diaminocyclohexane (1,2-DCH). The trans isomer and a mixture cis–trans (30–70% respectively) of 1,2-DCH were used to investigate their different behaviour. In a previous article (L. Núñez et al., Therm Anal Calorim, 2005), it was reported that the values of gel time measured by dielectric analysis for the systems DGEBA(n=0)/trans-1,2-DCH and DGEBA(n=0)/cis–trans −1,2-DCH were very similar, while times to vitrification, as measured by modulated scanning calorimetry differed widely. In the present study, rheometry was used to corroborate the results obtained in the previous article for gel time and activation energy and also to analyse differences in the cure of the two epoxy systems studied by comparing the results reported here with those previously measured by DEA and DSC. 相似文献
7.
Lisardo Núñez-Regueira J. Proupín-Castiñeiras J. A. Rodríguez-Añón Maria Villanueva-López O. Núñez-Fernández 《Journal of Thermal Analysis and Calorimetry》2006,85(2):271-277
The design of a rigorous experimental procedure is
the basis for any environmental study. In this work, the basic criteria are
established for determination of soil health using microcalorimetry as the
main technique complemented by the study of physical (temperature, moisture,
porosity, hydraulic conductivity, density and plasticity), chemical (pH and
C to N ratio) and biological features (most probable number of microorganisms
and organic matter content), and also environmental properties in the form
of bioclimatic diagrams. The design was elaborated using as a reference a
humic eutrophic-Cambisol subjected to afforestation with P.
pinaster Aiton situated in Viveiro (Galicia, NW Spain). Main results
of this study refer to total heat evolved during the processes (2.65 to 3.81
J g–1), time to reach the maximum of the
peak from 16.17 to 19.29 h, and microbial growth rate constant from 0.0732
to 0.1043 h–1. These results change over
the year as they are influenced by the action of environmental parameters
over soil microbial activity. The results are in close agreement with some
others previously reported using different experimental techniques. 相似文献
8.
Summary Polymers have a great interest for the study and design of new materials. Among these materials are epoxy resins, that have good properties, such as low shrinkage during cure, good adhesion, high water and chemical resistance, etc. They have also fast and easy cure in a broad range of temperatures. TTT diagrams are very helpful to design new epoxy materials as they allow the search for very important final properties, such as thermal stability, conversion or glass transition temperature of a material cured through a selected curing cycle. In this work the dependence of the thermal stability on the selected curing cycle for a DGEBA/1,2 DCH system was studied. 相似文献
9.
Núñez Regueira Lisardo Núñez M. R. Villanueva M. Rial B. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):29-35
The influence of agents originated in a municipal landfill on the thermal degradation of a polymeric system composed of a
diglycidyl ether of bisphenol A (n=0) and 1,2-diaminecyclohexane was studied by thermogravimetric analysis (TG) in order to obtain the lifetime of this material
before and after being attacked. The different data obtained were analyzed to check the resistance of these materials to chemical
attack and the possibility of their use as coating materials in plants where those reagents were present. At the optimum temperature
of service for this material, 373.16 K, the lifetimes obtained from the experimental results were 2633 years and 2135 years,
respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Lisardo Núñez F. Fraga López L. Fraga Grueiro J. A. Rodriguez Añón 《Journal of Thermal Analysis and Calorimetry》1996,47(3):743-750
From the peak reaction temperatures as a function of heating rate, the activation energies were obtained for a system consisting of an epoxy resin (Badgen=0) and a curing agent (isophorone diamine), using a Perkin Elmer DSC7 operated in the dynamic mode. At the same time, the Arrhenius law was used to calculate rate constants. 相似文献