Study of the physical aging of the epoxy system BADGE n = 0/ m -XDA/CaCO 3 (original) (raw)
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Journal of Applied Polymer Science, 2006
The physical aging of the epoxy network consisting of a diglycidyl ether of bisphenol A, m-xylylenediamine, and polyetherimide was studied by differential scanning calorimetry. The glass transition temperature and the variation of the specific heat capacities have been calculated using the method, based on the intersection of both enthalpy-temperature lines for glassy and liquid states. The apparent activation energy (E H) was calculated using a single method that involved separate temperature and excess enthalpy dependency. All calorimetric data were compared with those obtained for the epoxy network without thermoplastic.
Physical aging for an epoxy network diglycidyl ether of bisphenol A/m-xylylenediamine
Polymer, 2003
The physical aging of the epoxy network consisting of a diglycidyl ether of bisphenol A (BADGE n ¼ 0) and m-xylylenediamine (m-XDA) were studied by differential scanning calorimetry. The following aging temperatures have been used in this work: 60, 70, 80, 90, 100 and 110 8C. The glass transition temperature and the variation of the specific heat capacities have been calculated using the method based on the intersection of both enthalpy-temperature lines for glassy and liquid states. The endothermic aging peak, relaxation enthalpy and fictive temperature were also calculated for each aging temperature and aging time.
Journal of Applied Polymer Science, 2009
The influence of the presence of CaCO 3 on the cure reaction of the epoxy network diglycidyl ether of bisphenol A with isophorone diamine has been studied. The total enthalpy of reaction, the glass transition temperature and the partial enthalpies at different isothermal temperatures have been determined using differential scanning calorimetry (DSC) in dynamic and isothermal mode. A kinetic model accounting the influence of the dif-fusion of the reactive groups at high conversions was used. All the kinetic parameters have been compared with those of the system without filler (CaCO 3 ).
Journal of Applied Polymer Science, 2002
Lifetime of the epoxy system diglycidil ether of Bisphenol A (BADGE nϭ0)/ m-xylylenediamine (m-XDA) was calculated by thermogravimetric analysis. The Flynn-Wall-Ozawa method is used to determine the activation energy of the reaction. Experimental lifetimes in the range of 60-300°C vary from 1.41 10 9 (2682 years) to 3.35 10 Ϫ4 min. This isoconversional method is not appropiate to calculate lifetime prediction because of high errors. Scaling factors were determined using the ratio of two reaction rates.
Physical aging of linear and network epoxy resins
Polymer Engineering and Science, 1981
Network and linear epoxy resins principally based on the diglycidyl ether of bisphenol-A and its oligomers have been prepared and studied. Both diamine and anhydride crosslinking agents were utilized. In addition, some rubber modified epoxies and a carbon fiber reinforced composite was investigated. All of these materials display time-dependent changes in many of their properties when they are stored (following quenching) at temperatures below their glass transition temperature (sub-T,/ annealing). For example, the degree of stress relaxation for a given time period is observed to decrease in a linear fashion with the logarithm of time during sub-T, annealing. Young's modulus and yield stress were also found to increase in physical aging. Solvent sorption experiments initiated after different sub-T,) annealing times have demonstrated that the rate of solvent uptake can be indirectly related to the free volume of the epoxy resins. The effect of water on the physical aging of these epoxy resins was not found to be a significant variable, Residual thermal stresses were also found to have little effect on the physical aging process, although this variable was not studied in detail. Finally, the physical aging process also affected the sub-T, properties of uniaxial carbon fiber reinforced epoxy material and the effects were as expected. The importance of the recovery or physical aging phenomenon, which affects the durability of epoxy glasses, is considered in view of the widespread applications for these resins as structural materials.
J Appl Polym Sci, 2001
Master plots were used to corroborate R n-type mechanisms calculated in a previous study, using the method proposed by Criado et al. (Thermochim Acta 1989, 147, 377). Analysis of experimental data seems to belong to the family of decelerated curves (R n) in the range of conversion studied. The lifetime of the system diglycidil ether of bisphenol A (BADGE n ϭ 0)/m-xylylenediamine (m-XDA) for different decelerated mechanisms was calculated using thermogravimetric analysis. From the experimental data it was found that the optimum temperature range of use for this material is 60-100°C for all R n-type mechanisms, at which corresponding lifetimes range between 190 years and 1 year.
The physical aging of a n epoxy resin based on diglycidyl ether of bisphenol-A cured by a hardener derived from phthalic anhydride has been studied by differential scanning calorimetry. The isothermal curing of the epoxy resin was carried out in one step a t 130°C for 8 h, obtaining a fully cured resin whose glass transition was at 98.9"C. Samples were aged a t temperatures between 50 and 100°C for periods of time from 15 min to a maximum of 1680 h. The extent of physical aging has been measured by the area of the endothermic peak which appears below and within the glass transition region. The enthalpy relaxation was found to increase gradually with aging time to a limiting value where structural equilibrium is reached. However, this structural equilibrium was reached experimentally only a t an aging temperature of Tg -10°C. The kinetics of enthalpy relaxation was analysed in terms of the effective relaxation time 7,ff. The rate of relaxation of the system given by 1 / T ,~ decreases as the system approaches equilibrium, as the enthalpy relaxation tends to its limiting value. Single phenomenological approaches were applied to enthalpy relaxation data. Assuming a separate dependence of temperature and structure on 7, three characteristic parameters of the enthalpic relaxation process were obtained (In A = -333, EH = 1020 kJ/ mol, C = 2.1 g/ J ) . Comparisons with experimental data show some discrepancies at aging temperatures of 50 and 60"C, where sub-T, peaks appears. These discrepancies probably arise from the fact that the model assumes a single relaxation time. A better fit to aging data was obtained when a Williams-Watts function was applied. The values of the nonexponential parameter p were slightly dependent on temperature, and the characteristic time was found to decrease with temperature.
Isothermal differential scanning calorimetry study of a glass/epoxy prepreg
Polym Advan Technol, 2009
Isothermal differential scanning calorimetry (DSC) was used to study the curing behavior of epoxy prepreg Hexply 1 1454 system, based on diglycidyl ether of bisphenol A (DEGBA)/dicyandiamid (DICY) reinforced by glass fiber. Cure kinetics of an autocatalytic-type reaction were analyzed by general form of conversion-dependent function. The characteristic feature of conversion-dependent function was determined using a reduced-plot method where the temperature-dependent reaction rate constant was analytically separated from the isothermal data. An autocatalytic kinetic model was used; it can predict the overall kinetic behavior in the whole studied cure temperature range (115-130-C). The activation energy and pre-exponential factor were determined as: E ¼ 94.8 kJ/mol and A ¼ 1.75 T 10 10 sec S1 and reaction order as 2.11 (m R n ¼ 0.65 R 1.46 ¼ 2.11). A kinetic model based on these values was developed by which the prediction is in good agreement with experimental values.
Polymer, 2001
Curing reactions of the epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n 0; 1,2 diaminecyclohexane (DCH); and calcium carbonate ®ller were studied to calculate a time±temperature-transformation (TTT) isothermal cure diagram for this system. Gel times were measured as a function of temperature using two experimental methods: solubility test and dynamic mechanical analysis (DMA). The results obtained are in fair agreement with that obtained for the two component system BADGE n 0=1; 2 DCH. Vitri®cation times for the three component system was higher than those obtained for the system BADGE n 0=1; 2 DCH and the conversions achieved were very close to maximum values. The activation energy for the overall polymerization reaction was calculated from the gel times obtained using the two above mentioned methods: solubility test (57.12 kJ/mol) and DMA (54.12 kJ/mol). These values are of the same order than those obtained for the two component epoxy system. It was established that the addition of calcium carbonate ®ller avoids the appearance of physical aging, thus making easier both the determination of glass transition temperatures, and the calculation of the TTT diagram.
Thermo-oxidative aging of epoxy coating systems
Progress in Organic Coatings, 2014
The thermo-oxidative behavior of unformulated (unfilled) samples of epoxy coatings has been studied at five temperatures ranging from 70 • C to 150 • C. Two epoxy networks based on diglycidyl ether of bisphenol A (DGEBA), respectively, cured by jeffamine (POPA) or polyamidoamine (PAA) were compared. Infrared spectrophotometry (IR), differential scanning (DSC) and sol-gel analysis (SGA) were used to monitor structural changes. Thermal oxidation leads to carbonyl and amide formation in both systems. POPA systems appear more sensitive to oxidation than PAA ones. Thermal oxidation leads to predominant chain scission as evidenced by the decrease of glass transition temperatures (T g) and increase of sol fraction.