M. R. Núñez

Influence of water absorption on the mechanical properties of a DGEBA (n = 0)/1, 2 DCH epoxy system

The diffusive, calorimetric, and mechanical behavior of a system composed of a diglycidyl ether of bisphenol-A (DGEBA, n = 0) and 1, 2 diamine cyclohexane (1, 2 DCH) were investigated during water sorption at different temperatures (23, 47, 58, 77, and 100°C). Experimental results showed that the water absorption at these temperatures fitted well to Ficks law. The water moisture content at the equilibrium temperature and the water moisture content at the equilibrium-curing conditions dependences have been checked. The activation energy for diffusion was calculated obtaining a value 26.01 kJ/mol. Dynamic mechanical analysis of several samples immersed in water at 100°C during different periods of time showed no significant changes in the glass transition temperature, and a decrease in the storage modulus at 2% of water content was observed. Storage modulus remained essentialy constant above that water content. Values of glass transition temperature were corroborated by differential scanning calorimetric measurements.

Effects of diffusion on the kinetic study and TTT cure diagram for an epoxy/diamine system

The curing reactions of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n 5 0) and 1,2-diamine cyclohexane (DCH) were studied to determine a time-temperature-transformation (TTT) isothermal cure diagram for this system. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and a solubility test were used to obtain the different experimental data reported. Two models, one based solely on chemical kinetics and the other accounting for diffusion, were used and compared to the experimental data. The inclusion of a diffusion factor in the second model allowed for the cure kinetics to be predicted over the whole range of conversion covering both pre- and post-vitrification stages. The investigation was made in the temperature range 60 -100°C, which is considered optimum for the isothermal curing of the epoxy system studied.

Kinetic and thermodynamic studies of an epoxy system diglycidyl ether of bisphenol A/1, 2 diamine cyclohexane/calcium carbonate filler

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0) and 1,2-diaminecyclohexane (DCH) with a calcium carbonate filler was studied by differential scanning calorimetry (DSC) and using a scanning electronic microscope (SEM). As a first stage, the optimum content of the filler determined was 20%. From a kinetic study, in which two models were used, parameters such as reaction orders, rate constants, and activation energies were determined. A thermodynamic study allowed calculation of enthalpy (ΔH#), entropy (ΔS#), and free-energy ((ΔG#) changes. The results were compared to those obtained for the same epoxy systems without the filler.

Effects of diffusion on the kinetic study of the system BADGE n = 0/m-xylylenediamine

The curing reactions of an epoxy system composed of a diglycidyl ether of bisphenol A (BADGE n = 0) and m-xylylenediamine (m-XDA) were studied. Two models, the first based solely on chemical kinetics and the second accounting for diffusion, were used and compared to the experimental data. The epoxy resin was used as received in a first series of experiments. In a second series of experiments, the resin was purified in vacuo (180°C and 1 mmHg). The inclusion of a diffusion factor in the second model allowed for the cure kinetics to be predicted over the whole range of conversion covering both pre- and postvitrification stages. The investigation was made in the temperature range 50-110°C, which is considered optimum for the isothermal curing of the epoxy system studied.

Lifetime prediction of the epoxy system badge n = 0/1,2 DCH by thermogravimetric analysis

Lifetime of the system diglycidyl ether of bisphenol A (BADGE n 5 0)/1,2- diamine cyclohexane (DCH) was predicted by thermogravimetric analysis. Lifetime was considered when either 5% weight loss or 5% conversion was reached. Experimental results were treated using two different methods: The first method was independent of the degradation mechanism and the second was based on the thermodegradation kinetic mechanism. The activation energy of the reaction, determined using the Flynn- Wall-Ozawa method, was 148.51 kJ/mol. This value is in a good agreement with that of 144.01 kJ/mol obtained using Kissinger9s method. From the experimental results, it was found that the optimum temperature of service for this material is in the range of 100 -140°C, at which the corresponding lifetime range is from 27 to 2633 years.

Effects of diffusion on the kinetic study of an epoxy system diglycidyl ether of bisphenol A/1,2-diamine cyclohexane/calcium carbonate filler

The curing reactions of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0), 1,2-diamine cyclohexane (DCH) with calcium carbonate filler, were studied to determine different kinetic parameters. Two models-one based solely on chemical kinetics and the other accounting for diffusion-were used and compared to experimental data both for systems with and without filler. It was found that 100°C is the optimum service temperature, and also that the presence of the filler has no influence on the optimal service temperature range (60-100°C) of the epoxy system.

thermal stability of epoxy systems badge (n=0)/1,2-dch and badge (n=0)/ 1,2-dch/vinylcyclohexene dioxide

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-Ozawas 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 Doyles approximation (20-35% of conversion). Analysis of the results suggests that the reaction mechanism could be F2, F3, or A2 type.

Kinetic study of an epoxy system badge (n=0)/1, 2 dch modified with an epoxy reactive diluent

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.

TTT Cure Diagram

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 Tg and fractional conversion, a independent of cure temperature. As a consequence, Tg 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.

The influence of lixiviates on the thermal degradation of diglycidyl ether of bisphenol A n=0/1,2-diaminecyclohexane studied by dynamic mechanical analysis and thermogravimetry-Fourier transform infrared spectroscopy

The influence of the lixiviates 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 dynamic mechanical analysis. Storage modulus (E′), loss modulus (E″), and glass transition temperature were measured to make a comparative study between the samples before and after being exposed to the chemical compounds in the lixiviate agents. 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. Thermal stability of the system diglycidyl ether of bisphenol A/1,2-diaminecyclohexane exposed to the attack of lixiviates has also been studied by thermogravimetric analysis. A quantitative study of the gases originated during thermal degradation of the epoxy/diamine system made by infrared spectroscopy.