Effect of the crosslinking degree on curing kinetics of an epoxy–anhydride styrene copolymer system

The cure kinetics of a high molecular weight acid copolymer used as a hardener for a commercial epoxy resin (DGEBA) was studied by DSC. The systems were uncured and partially cured epoxy poly(maleic anhydride-alt-styrene) (PAMS) at different periods of time. The state of cure was assessed as the residual heat of reaction and was varied by controlling both the time and temperature of cure. The conversion degree of crosslinking increased with time and temperature. Additionally, the activation energy and reaction order were calculated by the Freeman–Carrol relation and showed a dependence on the conversion degree of crosslinking. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2089–2094, 1999     

Effect of the crosslinking degree on curing kinetics of an epoxy–acid copolymer system

The hardening of a commercial epoxy resin (DGEBA) with the cure of high molecular weight acid copolymers was studied using differential scanning calorimetry (DSC). The systems were uncured and partially cured epoxy/poly(acrylic acid–styrene) (SAAS), at different contents of styrene. The conversion degree of the crosslinking of the systems, examined versus time, temperature of hardening, and styrene contents in the copolymers, were determined. The activation energies of the crosslinking reactions were calculated by the Freeman–Carrol relation and showed a dependence on the state of hardening. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2834–2839, 2003     

The effect of epoxy excess on the kinetics of an epoxy–anhydride system

The uncatalyzed cure of a commercial tetrafunctional epoxy monomer TGDDM (N,N,N′,N′‐tetraglycidyl‐4,4′‐diaminodiphenylmethane) with hexahydrophthalic anhydride (HHPA), using variable stoichiometric ratios is reported. The reaction was followed by differential scanning calorimetry (DSC). Two kinds of experiments were performed: (1) fresh samples were run at several heating rates, and (2) samples, precured a certain time in an oil bath at constant temperature (i.e., 80 to 120°C), were run at 10°C/min. Two peaks were observed in the case of the epoxy excess but only one for the stoichiometric formulation: the peak at low temperature was attributed to the epoxy copolymerization with the anhydride while the peak at high temperature was attributed to the epoxy homopolymerization. The catalytic effect of the OH groups present in the epoxy monomer on the copolymerization reaction was demonstrated by the decrease in the activation energy of the propagation step when increasing the epoxy excess. There is a catalytic effect of the copolymerization product on the homopolymerization reaction. Our simplest model, proposed previously for a catalyzed epoxy/anhydride system [J. Polym. Sci. Part B: Polym. Phys. Ed., 37, 2799 (1999)], can be used to fit both isothermal and dynamical kinetic data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2342–2349, 2002     

Rheological study of the curing kinetics of epoxy–phenol novolac resin

The curing reaction of an epoxy–phenolic resin under different conditions was monitored using rheological measurements. The evolution of viscoelastic properties, such as storage modulus, G′, and loss modulus, G″, was recorded. Several experiments were performed to confidently compare the rheological data obtained under varied curing conditions of temperature, catalyst concentration, and reactive ratios. The values of G′ measured at the end of the reactions (at maximum conversion) were independent of the frequency and temperature of the tests in the range of high temperatures investigated. The overall curing process was described by a second‐order phenomenological rheokinetic equation based on the model of Kamal. The effects of the epoxy‐to‐phenolic ratio as well as the curing temperature and the catalyst concentration were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4430–4439, 2006     

The effect of bismaleimide resin on curing kinetics of epoxy–amine thermosets

An analysis of the cure kinetics of several formulations composed of diglycidyl ether of bisphenol-A (DGEBPA) and aromatic diamines, methylenedianiline (MDA) and diaminodiphenyl sulfone (DDS), in the absence and presence of 4,4′-bismaleimidodiphenylmethane (BM) was performed. The dynamic differential scanning calorimetry (DSC) thermograms were analyzed with the help of ASTM kinetic software to determine the kinetic parameters of the curing reactions, including the activation energy, preexponential factor, rate constant, and 60 min ½ life temperature. The effects of substitution of one curing agent for another, their concentration, and the absence and presence of BM resin and its concentration on curing behavior, ethalpy, and kinetic parameters are discussed. © 1996 John Wiley & Sons, Inc.     

Experimental characterization of a curing thermoset epoxy‐anhydride system—Isothermal and nonisothermal cure kinetics

This work describes in detail the kinetic model for the cure of an epoxy‐anhydride thermoset matrix resin system. The cure kinetics in both nonisothermal and isothermal modes has been characterized using differential scanning calorimetry. The Sestak–Berggren two‐parameter autocatalytic model was used to describe the nonisothermal cure behavior of the resin satisfactorily. The isothermal cure data was fitted with Kamal's four‐parameter autocatalytic model, coupled with a diffusion factor. These characterization data will form material property inputs for a multiscale modeling framework for the estimation of cure‐induced residual stresses in thick thermoset matrix composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the crosslinking density and programming temperature on the shape fixity and shape recovery in epoxy–anhydride shape‐memory polymers

In addition to the fabrication of thermoset epoxy–anhydride shape‐memory polymers (SMPs), a systematic experimental investigation was conducted to characterize the crosslinking density, micromorphology, thermal properties, mechanical properties, and shape‐memory effects in the epoxy SMP system, with a focus on the influence of the crosslinking density and programming temperature on the shape‐fixity and shape‐recovery behaviors of the polymers. On the basis of the crosslinking density information determined by NMR technology, we concluded that the effect of the crosslinking density on the shape‐fixity behaviors was dependent on the programming temperature. The advantage of a nice combination of crosslinking density and programming temperature provided an effective approach to tailor the actual shape recovery within a wide range. The increasing crosslinking density significantly improved the shape‐recovery ratio, which could be further improved through a decrease in the programming, whereas the crosslinking density was more fundamental. This exploration should play an important role in the fabrication and applications of SMP materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40559.     

Influence of diaminobenzoyl‐functionalized multiwalled carbon nanotubes on the nonisothermal curing kinetics,dynamic mechanical properties,and thermal conductivity of epoxy–anhydride composites

To obtain advanced materials with a high thermal dissipation, the addition of multiwalled carbon nanotubes containing diverse functionality groups, that is, as‐received multiwalled carbon nanotubes (AS‐MWCNTs) and diaminobenzoyl multiwalled carbon nanotubes (DA‐MWCNTs), to epoxy–anhydride composites was accomplished. According to nonisothermal differential scanning calorimetry analysis, the reactive functional groups present on the surfaces of the AS‐MWCNTs and DA‐MWCNTs accelerated the nucleophilic addition reaction of epoxy composites. Because of the difference in the reactivities of these functional groups toward epoxy groups, the distinction of fractional conversion and the reaction rate of the curing process were remarkably evident at the early stage. A suitable kinetic model was effectively elucidated with the Málek approach. The curing kinetics could best be described by a two‐parameter autocatalytic model as a truncated ?esták–Berggren model. The DA‐MWCNTs achieved effective load transfer and active heat conductive pathways; this resulted in good dynamic mechanical and thermal properties. As a result, the diglycidyl ether of bisphenol A/DA‐MWCNTs constituted an effective system with enhanced heat dissipation of materials for electronic applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43567.     

聚酰亚胺改性环氧树脂/酸酐体系固化动力学研究

采用非等温差示扫描量热(DSC)法研究了聚酰亚胺(PI)改性环氧树脂(EP)/酸酐体系的固化反应动力学及其固化工艺。通过Kissinger法、Ozawa法和Crane法计算出该体系的动力学参数。结果表明:该固化体系具有较高的活性,其固化工艺条件为"80℃/2 h→120℃/2 h",后处理工艺为150℃/2 h;采用Kissinger法和Ozawa法计算出该体系的平均表观活化能为8.24 kJ/mol;结合Crane方程计算出该体系的反应级数为0.95,近似一级反应。     

Glass‐transition temperature–conversion relationship for an epoxy–hexahydro‐4‐methylphthalic anhydride system

The DGEBA–MHHPA epoxy system has found increasing applications in microelectronics packaging, making crucial the ability to understand and model the cure kinetics mechanism accurately. The present article reports on work done to elucidate an appropriate model, modified from the empirical DiBenedetto's equation, to relate the glass‐transition temperature (T_g) to the degree of conversion for a DGEBA–MHHPA epoxy system. This model employs the ratio of segmental mobility for crosslinked and uncrosslinked polymers, λ, to fit the model curve to the data obtained. A higher ratio value was shown to indicate a more consistent rate of increase of T_g in relation to the degree of conversion, while a lower value indicated that the rate of T_g increase was disproportionately higher at higher degrees of conversion. The best fit value of λ determined by regression analysis for the DGEBA–MHHPA epoxy system was 0.64, which appeared to be higher than for those previously obtained for other epoxy systems, which ranged from 0.43–0.58. The highest T_g value obtained experimentally, T_{g max}, was 146°C, which is significantly below the derived theoretical maximum T_g∞ value of 170. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 511–516, 2000     

Rheology and curing characteristics of epoxy–clay nanocomposites

Diglycidyl ethers of bisphenol‐A (DGEBA) epoxy resin, filled separately with organoclay (OC) and unmodified clay (UC), were synthesized at room temperature and at high temperature (80 °C) by mechanical shear mixing. The room temperature curing (RTC) and high temperature curing (HTC) were carried out with the addition of triethylene tetramine (TETA) and diaminodiphenylmethane (DDM) curing agents respectively. The OC used was alkyl ammonium modified montmorillonite (MMT) and the UC was Na⁺‐MMT. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) were used to study the structure and morphology of the nanocomposites. The influence of OC and UC particles on rheology and curing characteristics was studied. The rate of increase in viscosity was higher for OC‐filled resin than that of the UC‐filled resin. The curing study showed that the amine ions of the OC aided the polymerization process and favoured the curing at low temperature over the curing of unfilled epoxy resin. The tensile properties were enhanced for epoxy filled with OC particles rather than those filled with UC particles. Copyright © 2005 Society of Chemical Industry     

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     

Viscoelastic changes of epoxy resin–acid anhydride system during curing

The changed viscoelastic properties of the epoxy resin-acid anhydride system, Epikote 834-HHPA, are followed to the gel point at 130, 140, and 150°C with a dynamic viscoelastometer. The viscosity increases with curing time through two inflections designated A and B. The point A is interpreted (from the reference to the chemical changes reported in the previous paper) as the termination of the initial stage of this curring reaction, and point B coincides with the gel point determined by the torsion method. The resonance frequency remains constant value up to the point B, followed by a rapid increase. The extents of reaction for epoxide, anhydride, and initial OH are 15, 45.8, and 100% at the point A; 27.8, 63.7, and 100% at the point B, respectively. The apparent activation energies for viscosity are 7.5 kcal/mole for the resin mixture before curing, 10.5 kcal/mole for point A, 48.8 kcal/mole for point B (gel point). The overall apparent activation energies of this curing reaction are obtained from the Arrhenius plots for the curing time required for the resin mixture to reach the state of the points A and B; these values were 8.9 kcal/mole for point A and 16.2 kcal/mole for point B.     

Use of temperature‐modulated DSC in kinetic analysis of a catalysed epoxy–anhydride system

The curing kinetics of a catalysed epoxy‐anhydride system was studied by temperature‐modulated differential scanning calorimetry. The chemical‐controlled regime was analysed by empirical kinetic equations. The diffusion‐controlled regime was detected by the diffusion factor, DF(α,T), which was calculated from the ratio of the experimental rate to the chemical reaction rate. DF(α,T) was compared with a mobility factor, MF(α,T), which was obtained by measuring the modulus of the complex heat capacity |C_p*|. The equivalence of the two factors allowed the diffusion‐controlled regime to be studied using the |C_p*| signal. However, the results obtained in the epoxy–anhydride system showed a limitation to the method, and this is discussed in terms of the modulation period necessary for the variation in MF(α,T) to occur in the same conversion interval as does DF(α,T). Copyright © 2004 Society of Chemical Industry     

Comparative study on the curing kinetics and mechanism of a lignin-based-epoxy/anhydride resin system

Curing kinetics and mechanism of liquid lignin based epoxy resin (LEPL)–maleic anhydride (MA) system accelerated with benzyldimethylamine (BDMA) were studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). In order to investigate the difference in the curing process, heating FTIR was used to study the change of the functional group. Complete consumption of the epoxides has been observed after the heating temperature was higher than 110 °C. E constant method and E variable method, to study the dynamic DSC curves, were deduced by assuming a constant and a variable activation energy, respectively. With E constant method, the cure reaction activation energy E, the frequency factor A and overall order of reaction n + m are calculated to be 59.68 kJ mol⁻¹, e^20.6 and 1.462, respectively. With E variable method, E is proved to decrease initially, and then increases as the cure reaction proceeds. The value of E spans from 60.16 to 87.80 kJ mol⁻¹. With the E constant method, E variable method and heating FTIR spectra used together, we can have a comprehensive and profound understanding of the cure reactions of the LEPL–MA system.     

Analysis of the crosslinking process of epoxy–phenolic mixtures by thermal scanning rheometry

The curing reaction of different mixtures of an epoxy resin (diglycidyl ether of bisphenol A type) and a phenolic resin (resole type) cured with different amine concentrations (triethylene tetramine) was studied with thermal scanning rheometry under isothermal conditions from 30 to 95°C. The gel time, defined by several criteria, was used to determine the apparent activation energy of the process. Moreover, with an empirical model used to predict the change in the complex viscosity versus time until the gel time was reached, and under the assumption of first‐order kinetics, the apparent rate constant and the apparent activation energy for the curing process were calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 818–824, 2005     

Study of the exfoliation process of epoxy–clay nanocomposites by different curing agents

Epoxy–clay nanocomposites were synthesized using two organoclays cured with different chemicals at different temperatures. Interlayer distance of the clay layers and curing process were investigated by X‐ray diffraction and infrared spectra. The clay treated with facilitated curing agent, 2,4,6‐tris[(dimethylamino)methyl]phenol, can exfoliate at all curing conditions, but for the other clay treated with low‐speed curing agent, p,p′‐diaminodiphenylmethane, exfoliation of the clay layers does not occur. It was found that the relative curing speed between the interlayer and extralayer was the most important factor determining clay exfoliation. Exfoliated epoxy–clay nanocomposites can be prepared if the curing speed of the interlayer is higher than that of the extralayer, irrespective of the curing agent and temperature used. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 511–517, 2003     

桐马酸酐与环氧树脂的非等温固化反应动力学

采用Málek法对桐马酸酐与双酚A环氧树脂E-51体系(含有1%质量分数的DMP-30)的非等温固化反应动力学进行了研究。通过机理函数esták-Berggren方程很好地模拟了真实的固化反应过程。等转化率法求得反应活化能为69.78 kJ/mol。指前因子A的值为4.567×108 min-1,n和m的值分别为1.082和0.456。根据得到的固化动力学方程计算可知,在固化温度为137.05℃时达到98%固化度的固化时间为115 min。     

Curing of epoxy–urethane copolymers in a heated mold: Effect of the curing conditions on the phase‐separation process

The curing process of an epoxy–urethane copolymer in a heated mold was studied. The epoxy resin (DGEBA, Araldyt GY9527; Ciba Geigy), was coreacted with a urethane prepolymer (PU, Desmocap 12; Bayer) through an amine that acted as crosslinking agent (mixture of cycloaliphatic amines; Distraltec). The study focused on the effect of the curing condition and PU concentration on time–temperature profiles measured in the mold and the consequent final morphologies obtained. As the PU concentration increases, the maximum temperature reached in the mold decreases as a result of the dilution effect of the elastomer on reaction heat, whereas the T_g of the piece also decreases. Phase separation is a function of conversion and temperature reached in the curing part and was analyzed using experimental data and a mathematical model that predicts temperature and conversion throughout the thickness of the mold. Scanning electron microscopy and atomic force microscopy were used to determine the characteristics of the dispersed phase for the different formulations and conditions of curing. It was shown that the size of the dispersed phase increased with the initial PU concentration, whereas there were practically no differences in the separated phase as a function of position or temperature of curing (in the range of 70 to 100°C studied). The superposition of the phase diagrams with the conversion–temperature trajectories during cure provided an explanation of the morphologies generated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 889–900, 2001