Kinetics modeling of a modified epoxy–amine formulation cured by thermal and microwave energy

The reaction kinetics of a rubber-modified epoxy formulation cured by microwave or thermal energy were investigated. Two phenomenological models were developed to predict the time and temperature dependence of the conversion for the neat and the modified systems. Good agreement was observed between the kinetic models and experimental results generated by chromatographic and calorimetric techniques. The same kinetic behavior was observed whatever the curing process (conventional or microwave heating). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 543–552, 1998     

Preparation,characterization, and thermal properties of controllable metal–imidazole complex curing agents for epoxy resins

A series of complexes incorporating the epoxy–imidazole adduct of phenyl glycidyl ether with 2‐ethyl‐4‐methylimidazole (PGE‐EMI), has been prepared with the acetato and chloro transition metal salts of Mn, Co, Ni, Cu, Zn, and Ag. These complexes have been characterized using spectroscopic methods (IR, UV‐Vis, ¹H‐ and ¹³C‐NMR, where appropriate) and their thermal stabilities have been determined using elevated temperature NMR techniques. These high‐temperature NMR results indicated that the chloro complexes studied (of Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) exist in equilibrium (i.e., they dissociate reversibly in a solution of dimethylsulphoxide, DMSO, at elevated temperatures), while the corresponding acetato complexes dissociate irreversibly. For the silver complexes, thermogravimetric analysis (TGA) was used to monitor the dissociation, showing that the weight loss recorded was consistent with the dissociation of the metal salt to liberate the PGE–imidazole ligand. The thermal stabilities of the metal complexes were influenced by changing both the transition metal (e.g., from Mn to Zn) and varying the anion (e.g., from acetate to chloride). From ¹H‐NMR analysis, a decrease of ca. 10°C was observed in the thermal dissociation of the acetato complexes when compared with the chloro complexes, showing that the series of PGE‐EMI complexes with acetate anions is less thermally stable than the corresponding chlorides. This finding suggests that these PGE‐EMI complexes may be modified to accommodate their use in a variety of different curing schedules when used to cure epoxy resins. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 201–217, 2000     

Determining the gel point of an epoxy–hexaanhydro‐4‐methylphthalic anhydride (MHHPA) system

The DEBGA–MHHPA epoxy system has found increasing applications in microelectronics packaging for which the ability to understand and model the cure kinetics mechanism accurately is crucial. The present article reports on the work done to elucidate accurate knowledge of the gel point by rheological methods. To determine the gel point using the G′–G″ crossover method was found not to be accurate, and the gel point obtained by this method was found to be frequency‐dependent. Using the point where tgδ was found independent of the frequency can accurately define the gel point at different temperatures. At the gel point determined by this method, G′ and G″ were found to follow the same power law, demonstrating the accuracy of the method in determining the gel point. The scaling exponent obtained was 0.75–0.79. The activation energy for the cure reaction of the system was determined to be 75.1 kJ/mol by the obtained gel times at different temperatures. The steady‐shear rheology test was also used to observe the viscosity change at the gel point. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1248–1256, 2000     

Curing kinetics and thermal property characterization of a bisphenol‐S epoxy resin and DDS system

The kinetics of the cure reaction for a system of bisphenol‐S epoxy resin (BPSER), with 4,4′‐diaminodiphenyl sulfone (DDS) as a curing agent was investigated with a differential scanning calorimeter (DSC). Autocatalytic behaviour was observed in the first stages of the cure which can well be described by the model proposed by Kamal, using two rate constants, k₁ and k₂, and two reaction orders, m and n. The overall reaction order, m + n, is in the range 2∼2.5, and the activation energy for k₁ and k₂ was 86.26 and 65.13 kJ mol⁻¹, respectively. In the later stages, a crosslinked network was formed and diffusion control was incorporated to describe the cure. The glass transition temperature (T_g) of the BPSER/DDS samples partially cured isothermally was determined by means of torsional braid analysis (TBA) and the results showed that the reaction rate increased with increasing T_g, in terms of rate constant, but decreased with increasing conversion. It was also found that the  SO₂ group both in the epoxy resin and in the hardener increases the T_g values of the cured materials compared with that of BPAER. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of BPSER/DDS has nth order reaction kinetics. © 2000 Society of Chemical Industry     

聚酰亚胺-环氧树脂胶黏剂的固化动力学研究

以2,2-双[4-(4-氨基苯氧基)苯基1丙烷(BAPOPP)和2,2-双[4-(3,4-二羧基苯氧基)苯基]丙烷二酐(BPADA)为原料在室温下于DMAe溶剂中合成了一种新型聚酰亚胺,并用其改性环氧树脂体系获得聚酰亚胺-环氧体系胶黏剂.利用差示扫描量热计(DSC),以不同的升温速率对聚酰亚胺-环氧树脂胶黏剂进行DSC...     

Chemorheology and ultimate behavior of epoxy‐amine mixtures modified with a liquid oligomer

Rubber toughening of epoxy resins has been actively studied since the 1960s with clear progress in understanding of the ultimate properties: microstructure relationships. The morphology, obtained after curing of the modified thermosetting matrix, is a function of the process conditions as well as of the materials used because both influence the thermodynamics and the kinetics of phase separation. In this work several amounts of poly(oxypropylentriamine) (POPTA), have been added as modifier to a diglycidyl ether of bisphenol‐A (DGEBA)‐based epoxy matrix cured with a cycloaliphatic amine. Molecular weight of the neat resin and amine/epoxy stoichiometric ratio have also been used as variables. This investigation has focused upon the importance of cure chemorheology for microstructure formation by using both physicochemical (isothermal and dynamic calorimetry) and rheological techniques. In the second part of this study, the influence of the molecular weight of the epoxy resin in the ultimate properties of 15 wt % POPTA‐modified epoxy matrices is also analyzed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1269–1279, 2000     

Relationships between thermally induced residual stresses and architecture of epoxy‐amine model networks

The capability of epoxy‐amine resins to develop residual stresses was studied as a function of temperature and network architecture. These residual stresses were induced while cooling epoxy‐glass bilayers from temperatures higher than the network glass transition temperature, T_g. This behavior was the result of the marked differences (α_r − α_g), in linear thermal expansion coefficient of the two components, as evidenced by the measurement of α_r for the epoxy networks under study. Various network architectures were selected, resulting from variation of (1) the chemical nature of both epoxide and curing agent, (2) the nature and relative amount of the chain‐extensor agent, and (3) the stoichiometric ratio. Three ranges of cooling temperature were observed systematically: first, the range of temperatures above T_g, where no stress has been detected, then an intermediate temperature range (from T_g to T*), where stresses develop quite slowly, and finally, the low temperature range (T < T*), where a linear increase in stress accompanies the decrease of temperature. The two latter regimes were quantitatively characterized by the extent, T_g − T*, of the first one and by the slope, SDR, of the second one. T_g − T* values were shown to be governed by the T_g of the network: the higher the T_g, the larger the gap between T_g and T*. This result was interpreted by accounting for the variation of relaxation rate at T_g from one network to the other. It was also shown that a semiempirical relationship holds between SDR and T_g: SDR decreases monotonically as T_g increases. By inspecting the effects of network architecture in more details, it turned out that SDR is governed by the Young's moduli, E_r(T − T_g), of the epoxy resins in the glassy state: the lower E_r(T − T_g), the lower SDR in a series of homologous networks. As E_r(T − T_g) values are known to be related to the characteristics of the secondary relaxation β, which depends, in turn, on crosslink density, SDR values were finally connected to the amplitude of the β relaxation processes. This finding was corroborated by the measurements on an antiplasticized dense network. Finally, data relative to thermoplastic‐filled networks showed that the addition of thermoplastic reduces the development of residual stresses, whatever the system, is homogeneous or biphasic. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 638–650, 2000     

Morphology of a linear polymer‐modified epoxy‐amine formulation cured by microwave energy at different heating rates

Microwave energy was used to cure a bisphenol A diglycidyl ether‐based epoxy resin with an aromatic diamine curing agent (4,4′‐diaminodiphenylsulfone) in the presence of a rubber (epoxy‐terminated butadiene–acrylonitrile copolymer) or a thermoplastic (polyetherimide). Because microwaves allow high flexibility in the choice of the cure schedule, samples were cured at different heating rates between 3 and 110°C/min. The morphologies of the systems were studied as a function of the cure schedule. Scanning and transmission electron microscopy and differential scanning calorimetry were used to characterize the generated morphologies. The influence of the heating rate on the particle size distribution, the volume fraction of the dispersed phase, and the composition of both phases are discussed. The generated morphologies were found to be conditioned by the time–temperature profile, no matter what kind of heating was used. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1118–1128, 2001     

环氧树脂固化动力学的非等温DSC研究

用非等温DSC对环氧树脂在动态升温过程中的固化动力学进行了研究,采用Kissinger方程对固化动力学模型参数中固化反应活化能、反应级数和指前因子进行了计算,并用Ozawa法对固化反应活化能进行了验证,计算结果表明,EP/DDS固化反应符合n阶固化动力学模型,结合不同升温速率下的特征温度,对环氧树脂的固化条件进行了优化。     

Thermal analysis of curing process of epoxy prepreg

The curing process of epoxy prepreg was studied by means of differential scanning calorimetry analysis. The dynamic, isothermal, and combinations of dynamic and isothermal measurements were done over selected temperature ranges and isothermal cure temperatures. The heats of reaction for dynamic and isothermal cure were determined. The results show that the heat of the isothermal‐cure reaction increased with the increment of temperature. The degree of cure was calculated from the heat of the isothermal‐cure reaction. The complete cure reaction could be achieved at 220°C within a very short cure time. The changes of cure rate with time were given for the studied isothermal cure temperatures. To simulate the relationship between the cure rate and degree of cure, the autocatalytic model was used and the four parameters were calculated. Except in the late stage of the cure reaction, the model agrees well with the experimental data, especially at high temperatures. To account for the effect of diffusion on the cure rate, a diffusion factor was introduced into the model. The modified model greatly improved the predicted data at the late stage of cure reaction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1074–1083, 2002     

Etherification versus amine addition during epoxy resin/amine cure: An in situ study using near-infrared spectroscopy

The reactions between a multifunctional epoxy resin, tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) and a monofunctional amine, methylaniline (mAnil) are studied. Due to the existence of a tertiary amine catalytic center within the TGDDM molecule, the etherification reaction during cure of TGDDM is usually more significant than in other epoxide systems. The importance of this reaction relative to the amine addition reactions is investigated. In situ near-infrared spectroscopy is used to obtain kinetic data during the cure reactions. The reaction rate constants are calculated from linear regression analysis for both amine addition and etherification reactions based on the reaction mechanisms proposed. Arrhenius relationships are observed for all the reaction rate constants involved. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:895–901, 1998     

Cure properties of epoxies with varying chain length as studied by DSC

The cure of diglycidyl ether of bisphenol A (DGEBA) and a homologous series of poly(ethylene oxide) diglycidyl ether (PEODE) epoxy resins with 4,4′‐diaminodiphenyl sulfone (DDS) was studied by scanning and isothermal differential scanning calorimetry (DSC). The heat of polymerization was relatively independent of monomer structure and chain length when determined by isothermal DSC. Variations in the heats of polymerization determined by the scanning method were attributed to degradative reactions at higher temperatures during the scan. The activation energies determined by scanning DSC experiments were relatively constant at 61 ± 3 kJ/mol. However, using an isothermal cure method, the activation energies were found to vary with monomer structure and extent of cure. The isothermal kinetics were analyzed in terms of the autocatalytic model on the basis of competing reaction paths involving catalysis by either initial impurities or hydroxyl groups produced in situ. The activation energies of both reaction paths were found to vary with monomer structure and degree of conversion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1479–1488, 1999     

差示扫描量热法环氧胶膜固化动力学研究

以差示扫描量热法研究中温固化环氧胶膜的非等温固化动力学。得出 SY-24中温胶膜的固化为放热反应,测得固化始点温度,求得固化反应热、固化反应级数和固化反应表观活化能。固化反应速度常数的对数与固化反应绝对温度的倒数成线性关系的结论。     

Kinetics of Curing and Thermal Degradation of POSS Epoxy Resin/DDS System

Polyhedral oligomeric silsesquioxanes epoxy resin (POSSER) was prepared from 3-glycidypropyl-trimethoxysilane (GTMS) and tetramethylammonium hydroxide (TMAH) by hydrolytic condensation. POSSER was characterized using Fourier-transformed infrared spectroscopy (FTIR), ¹H-NMR, and liquid chromagraphy/mass spectrometry (LC/MS). The epoxy value of POSSER is 0.50 mol/100 g. The LC/MS analysis indicated that T₁₀ is the majority and contain some amount of T₈, besides, a trace T₉ also exists. The curing kinetics of POSSER with 4,4′-diaminodipheny sulfone (DDS) as a curing agent was investigated by means of differential scanning calorimetry (DSC). The curing reaction order n is 0.8841 and the activation energy Ea is 61.06 kJ/mol from dynamic DSC analysis. Thermal stability and kinetics of thermal degradation were also studied by thermal gravimetric analysis (TGA). TGA results indicated that the temperature of POSSE/DDS system 5% weight loss is approximately 377.0°C, which is higher by 12.6°C than that of pure POSSER, and the primary degradation reaction (300–465°C) followed first order kinetics; the activation energy of degradation reaction is 75.81 kJ/mol.     

Non-isothermal cure kinetics of aerogel/epoxy composites using differential scanning calorimetry

ABSTRACT

The present work determines the non-isothermal cure parameters of aerogel/epoxy samples along with the effect of a wetting agent. The cure parameters were calculated using Kissinger and isoconversional methods after which the reaction was modeled with the Sestak–Berggren equation. It is seen that the composites had higher activation energy and frequency factor values compared to the pure resin, and similarities in cure parameters between the aerogel/epoxy composites with and without the wetting agent were seen. Hence, the former’s use is advocated due to its positive influence on the resin–aerogel interface without sacrificing the cure parameters.     

Emulsion polymerization of an epoxy‐acrylate emulsion stabilized with polyacrylate. i. influence of salt,initiator, neutralizing amine,and stirring speed

The past decade has seen the development of high‐performance epoxy‐acrylate coatings. Some of these coatings are used exclusively as can coatings. To improve chemical resistance, emulsion polymerization in the presence of the dispersed epoxy resin can be conducted. Replicated factorial designs were designed to investigate some of the factors that contribute to the performance and stability of the epoxy‐acrylate coating. The factors investigated in this study were: the type and amount of neutralizing amine, the type of initiator, the presence or absence of salt, and the stirring speed of the impeller. The measured responses for the experimental design were particle size, particle size distribution, and conversion. It has been shown in this study that the type of amine used to neutralize the polyacrylic stabilizer significantly influenced the observed responses probably by acting as chain transfer agent during polymerization. The addition of salt significantly affected the observed responses by shielding the surface charges on the particle surface that impart stability to the latex through electrostatic repulsion. Stirring speed of the impeller and the type of initiator as factors in the range investigated do not influence the kinetics or the particle size and polydispersity to any great extent either on their own or in combination with other factors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1347–1360, 1999     

Curing kinetics and viscosity change of a two‐part epoxy resin during mold filling in resin‐transfer molding process

The curing kinetics and the resulting viscosity change of a two‐part epoxy/amine resin during the mold‐filling process of resin‐transfer molding (RTM) of composites was investigated. The curing kinetics of the epoxy/amine resin was analyzed in both the dynamic and the isothermal modes with differential scanning calorimetry (DSC). The dynamic viscosity of the resin at the same temperature as in the mold‐filling process was measured. The curing kinetics of the resin was described by a modified Kamal kinetic model, accounting for the autocatalytic and the diffusion‐control effect. An empirical model correlated the resin viscosity with temperature and the degree of cure was obtained. Predictions of the rate of reaction and the resulting viscosity change by the modified Kamal model and by the empirical model agreed well with the experimental data, respectively, over the temperature range 50–80°C and up to the degree of cure α = 0.4, which are suitable for the mold‐filling stage in the RTM process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2139–2148, 2000