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. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2285–2295, 2000     

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. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 291–305, 2000     

Time–temperature-transformation (TTT) diagram of the isothermal crosslinking of an epoxy/amine system: Curing kinetics and chemorheology

Rotational molding is a new process for thermosets, few research works have been done on this subject. The goal of this study is to determine the optimal conditions (time, temperature, viscosity, etc) of this process for an epoxy-amine system. The thermal and rheological analysis help us to investigate the vitrification and the gelation of the reactive system (DGEBA-DETDA) and to draw the TTT diagram. We have completed this diagram by adding the isoviscosity curves to determine the available domain for rotational molding. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Evolution of properties of an isocyanate/epoxy thermosetting system during cure: Continuous heating (CHT) and isothermal time—temperature—transformation (TTT) cure diagrams

The present article describes a methodology for examining the evolution of the properties vs. cure of a complex thermosetting isocyanate/epoxy reactive mixture which reacts through two consecutive but separable reaction regimes. The methodology is based on the use of the torsional braid analysis (TBA) technique and the continuous heating (CHT) and isothermal time—temperature—transformation (TTT) cure diagrams. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 15–25, 1997     

A study on the cure characteristics of epoxy/diaminodiphenylmethane system prepared at room temperature

The curing behavior and kinetics of epoxy resin with diaminodiphenylmethane (DDM) as the curing agent was studied by many researchers, however all of them prepared the system at a high‐temperature condition (i.e., T ≥ 80°C). In this study, a mixture of epoxy/DDM was prepared at ambient temperature and its curing characteristics were studied by using differential scanning calorimetry (DSC). The autocatalytic model was used to calculate the kinetic factors in the dynamic experiments. The kinetics of the curing reaction was also evaluated by two different isoconversional models; namely Friedman method and the Advanced Isoconversional method proposed by Vyazovkin to investigate the activation energy behavior during the curing reaction. The activation energy of the curing reaction was found to be in the range of 48 ± 2 kJ/mol and might be considered to be constant during the curing. In fact, our findings were different from the result reported by other researchers for the system which was prepared at elevated temperature. Therefore, it seems that the preparation temperature of the samples influenced considerably on the curing behavior of epoxy with DDM. Finally, a time–temperature–transformation (TTT) diagram was established to determine the cure process and glass transition properties of the system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Theoretical evaluation and the effect of thermal degradation on the Time–Temperature–Transformation (TTT) diagram of bisphenol A epoxies

A brief discussion about the Time–Temperature–Transformation (TTT) diagram is presented. Using diamino diphenylsulfone‐cured diglycidyl bisphenol A as a representative example, its TTT diagram is completed by including the thermal degradation. The theoretical diagram as obtained from the kinetics of curing and thermal degradation is compared with experimental data. The agreement is good, slight deviations are observed only in the time to vitrify above 150°C and the maximum available glass temperature, which is due to side reactions and onset of thermal degradation during curing. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3894–3896, 2003     

Modification of a two‐component system by introducing an epoxy‐reactive diluent: Construction of a time–temperature–transformation (TTT) diagram

Curing reactions of a three‐component system consisting of an epoxy resin diglycidyl ether of bisphenol A (DGEBA n = 0), 1,2‐diaminecyclohexane as curing agent, and vinylcyclohexene dioxide as a reactive diluent were studied to calculate a time–temperature–transformation isothermal cure diagram for this system. 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 α, 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 (58.5 ± 1.3 kJ/mol). This value was similar to the results obtained for other similar epoxy systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1190–1198, 2004     

Lignocellulosic substrates influence on TTT and CHT curing diagrams of polycondensation resins

Lignocellulosic substrates such as wood were found to have a marked modifying influence on a well‐defined region of CHT diagrams during hardening of phenol–formaldehyde (PF) and urea–formaldehyde (UF) polycondensates. This was ascribed to more complex resin phase transitions due to resin/substrate interactions peculiar to these substrates. The chemical and physical mechanisms of the interactions of the resin and substrate causing such CHT diagram modifications are presented and discussed. The Di Benedetto equation describing the glass transition temperature T_g of the system as a function of the resin degree of conversion p has been slightly modified to take into account the modified CHT diagram. The modified CHT diagram can be used to good effect to describe the behavior of polycondensation resins when used as wood adhesives during their curing directly into the wood joint. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 915–925, 1999     

Chemorheological study of DGEBA/IPD system for reactive rotational molding (RRM)

The identification of kinetic parameters controlling the crosslinking of Diglycidyl ether of bisphenol/isophorone diamine reactive system was achieved via optimization program (Inverse method) based on Fourier transform near infrared spectroscopy results. The reactivity ratio (k₂/k₁) was determined using a new method based on the variation of amine conversion ratio versus epoxy conversion ratio. Gelation and vitrification of the reactive system were also analyzed. Time, temperature, transformation diagram was established to assess the rotational molding of this reactive system. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical behavior of tetrafunctional/phenol novolac epoxy mixtures cured with a diamine

An amine‐cured epoxy system based on tetraglycidyldiaminodiphenylmethane and a novolac glycidyl ether resin was studied. Epoxies were prepared by varying the cure schedules and using the isothermal time–temperature–transformation diagram of the system. The materials were characterized using dynamic‐mechanical analysis (DMA), tensile stress–strain tests over a range of temperatures and testing speeds, impact, and hardness tests. Optical microscopy was used to study the fracture surfaces of the samples. Some interrelations between the behavior and the microstructure of the system are discussed. In addition, the effect of thermal aging on the mechanical properties has been studied. DMA analysis seemed to reveal a structure that tended to be less heterogeneous with increasing the crosslink density. The advance in the etherification reactions or the thermal aging has reduced the mechanical properties related with the consumption of energy to break. The optimal cure schedule according to the global properties has been established. The morphology of fractured surfaces by optical microscopy showed a clear correlation with the variation of the tensile properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2305–2313, 2000     

The effects of fillers on the chemorheology of highly filled epoxy resins: I. Effects on cure transitions and kinetics

This work examines the effects of level of silica filler (at 0, 10, 30, 50 wt%) on the gelation and vitrification of a model silica‐filled diglycidyl ether of bisphenol F (DGEBF)/methylenedianiline (MDA) system. An increased filler level is shown to decrease the gelation and vitrification times at low temperatures (below 80 °C). FTIR cure kinetics show that the reaction rates are increased and the activation energies of gelation are reduced at these temperatures, indicating that network formation is made easier. Entropic and catalytic reasons for this phenomenon are discussed. © 2003 Society of Chemical Industry     

TTT isothermal cure diagram of a dyglicidyl ether of bisphenol A/1,3-bisaminomethylcyclohexane (DGEBA/1,3-BAC) epoxy resin system

The isothermal cure of an epoxy-cycloaliphatic amine system has been studied following the evolution of both glass transition temperature and conversion. A functional relationship between T_g and conversion is established. The cure reaction is satisfactorily described by a phenomenological model with parameters determined from DSC experiments. By applying the kinetic model, gelation and vitrification curves are calculated and compared with experimental times to gelation and times to vitrification determined at temperatures between 50 and 100°C. The isothermal time-temperature-transformation (TTT) curing diagram including iso-T_g contours has been established. © 1996 John Wiley & Sons, Inc.     

环氧固化剂改性甲基环戊二胺的合成与性能研究

采用胺甲基化法对甲基环戊二胺(TAC)进行加成改性,合成了一种新型脂环胺类环氧固化剂,研究了反应温度与时间对固化剂性能的影响,并对TAC改性前后其固化物的物理力学性能进行了测试。结果表明:TAC改性后,其固化物耐冲击性及粘接性能均有明显提高,冲击强度提高159%,ABS剪切强度提高35.6%,Al片剪切强度提高47.5%。     

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. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2997–3005, 1999     

Isothermal and nonisothermal cure kinetics of an epoxy/poly(oxypropylene)diamine/octadecylammonium modified montmorillonite system

The effect of an octadecylammonium‐exchanged montmorillonite on the curing kinetics of a thermoset system based on a bisphenol A epoxy resin and a poly(oxypropylene)diamine curing agent were studied with differential scanning calorimetry (DSC) in isothermal and dynamic (constant‐heating‐rate) conditions. Montmorillonite and the prepared composites were characterized by X‐ray diffraction analysis and simultaneous DSC and thermogravimetric analysis. The analysis of the DSC data indicated that the intercalated octadecylammonium cations catalyzed the epoxy–amine polymerization. A kinetic model, arising from an autocatalyzed reaction mechanism, was applied to the DSC data. Fairly good agreement between the experimental data and the modeling data was obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1765–1771, 2006     

Curing kinetics of epoxy‐urethane copolymers

The cure of the epoxy resin diglycidyl ether of bisphenol A (Araldyt GY9527) with a mixture of cycloaliphatic amines (Distraltec) was studied, and the focus was on the effect of the copolymerization with a commercial polyurethane (PU) elastomer (Desmocap 12). A simplified phenomenological model was proposed to represent the copolymerization reaction. It considered the effect of the temperature and the concentration of the elastomer on the reaction rate, and it was simple enough to be included in models of processing conditions. A nonlinear regression analysis of the experimental conversion data obtained from differential scanning calorimetry was utilized to find the best fitting parameters to Kamal's equation for the chemically controlled part of the reaction (short times) under isothermal and constant heating‐rate conditions. The Rabinowitch approach together with the Addam–Gibbs theory was utilized to introduce the effect of diffusion control at the end of the reaction on the overall constant for the reaction rate. The Di Benedetto equation was used to predict the conversion at which vitrification takes place for each run. Experimental results for conversions higher than this critical conversion were utilized to obtain information about the diffusion kinetic constant using a nonlinear regression analysis as previously. The overall model obtained was used to calculate a calorimetric conversion and reaction rate as functions of time, which was in excellent agreement with the experimental results. The addition of PU elastomers affected the values of the activation energies of the chemically and diffusion controlled parts of the reaction, as well as the final conversion reached by the epoxy–amine system. The proposed model allowed prediction of all the observed features using parameters that were independent of the temperature of the curing reaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1771–1779, 2001     

Master curve and time–temperature–transformation cure diagram of lignin–phenolic and phenolic resol resins

The aim of this work is to generate both a master curve of resol resins based on the time–temperature superposition principle and their TTT cure diagrams. The samples used for this purpose were lignin–phenolic and phenol–formaldehyde resol resins. A TMA technique was employed to study the gelation of resol resins. In addition, a DSC technique was employed to determine the kinetic parameters through the Ozawa method, which allowed us to obtain isoconversional curves from the data fit to the Arrhenius expression. Establishing the relationship between the glass‐transition temperature and curing degree allowed the determination of the vitrification lines of the resol resins. Thus, using the experimental data obtained by TMA and DSC, we generated a TTT cure diagram for each of resins studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3362–3369, 2007