DSC study of the cure kinetics during nanocomposite formation: Epoxy/poly(oxypropylene) diamine/organically modified montmorillonite system

The effect of an organically modified montmorillonite (OMMT) on the curing kinetics of a thermoset system based on a bisphenol A epoxy resin and a poly(oxypropylene)diamine curing agent were studied by means of differential scanning calorimetry (DSC) in isothermal and dynamic (constant heating rate) conditions. Montmorillonite and prepared composites were characterized by X‐ray diffraction analysis (XRD) and simultaneous differential scanning calorimetry–thermogravimetric analysis (DSC–TGA). Analysis of DSC data indicated that the presence of the filler has a very small effect on the kinetics of cure. A kinetic model, arising from an autocatalyzed reaction mechanism, was applied to the DSC data. Fairly good agreement between experimental and modeling data was obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 550–557, 2006     

Cure kinetics of epoxy resin used for advanced composites

The cure kinetics of an epoxy resin used for the preparation of advanced polymeric composite structures was studied by isothermal differential scanning calorimetry (DSC). A series of isothermal DSC runs provided information about the kinetics of cure over a wide temperature range. According to the heat evolution behavior during the curing process, several influencing factors of isothermal curing reactions were evaluated. The results showed that the isothermal kinetic reaction of this epoxy resin followed an autocatalytic kinetic mechanism. In the latter reaction stage, the curing reaction became controlled mainly by diffusion. Cure rate was then modeled using a modified Kamal autocatalytic model that accounts for the shift from a chemically controlled reaction to a diffusion‐controlled reaction. The model parameters were determined by a nonlinear multiple regression method. Copyright © 2004 Society of Chemical Industry     

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     

Cure kinetics modeling of epoxy resins using a non‐parametric numerical procedure

The paper presents the development of a novel non‐parametric procedure for modeling of the chemical cure kinetics of a commercial resin‐transfer‐molding epoxy resin, RTM6. The procedure is entirely numerical and involves interpolation between experimentally determined values of cure reaction rates. The base data are obtained by Differential Scanning Calorimetry (DSC). The newly developed procedure is set against a background overview of other cure kinetics modeling approaches. It is shown that the numerical procedure can achieve a satisfactory level of accuracy in describing the progress of cure in this resin system. The important advantage, compared with other techniques, is that no information on the chemical naturr of the process is required.     

Comparison of the curing kinetics of the RTM6 epoxy resin system using differential scanning calorimetry and a microwave‐heated calorimeter

The cure of a commercial epoxy resin system, RTM6, was investigated using a conventional differential scanning calorimeter and a microwave‐heated calorimeter. Two curing methods, dynamic and isothermal, were carried out and the degree of cure and the reaction rates were compared. Several kinetics models ranging from a simple nth order model to more complicated models comprising nth order and autocatalytic kinetics models were used to describe the curing processes. The results showed that the resin cured isothermally showed similar cure times and final degree of cure using both conventional and microwave heating methods, suggesting similar curing mechanisms using both heating methods. The dynamic curing data were, however, different using two heating methods, possibly suggesting different curing mechanisms. Near‐infrared spectroscopy showed that in the dynamic curing of RTM6 using microwave heating, the epoxy‐amine reaction proceeded more rapidly than did the epoxy‐hydroxyl reaction. This was not the case during conventional curing of this resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3658–3668, 2006     

Microdielectric analysis and curing kinetics of an epoxy resin system

Microdielectric analysis (DEA) was carried out to investigate the cure behavior of a bisphenol F epoxy/aromatic amine resin system using an online dielectric cure monitoring technique. Ionic conductivity measured by a microdielectric sensor under isothermal conditions was correlated to the degree of cure and glass‐transition temperature, which are determined by differential scanning calorimetry (DSC). Results obtained by isothermal DSC measurement were used to establish a cure kinetic model for the epoxy resin. Experimental results show that the ratio of the ion conductivity to the initial ion conductivity, Logσ/Logσ₀, has a linear relation with the glass‐transition temperature. Furthermore, correlations between ion conductivity and degree of cure and cure rate are established using the best fit of the measured data. Cure behavior of the epoxy resin obtained by DEA is compared with that predicted by the cure kinetics model. Good agreement was observed. POLYM. ENG. SCI., 47:150–158, 2007. © 2007 Society of Plastics Engineers     

Cure kinetics of aqueous phenol–formaldehyde resins used for oriented strandboard manufacturing: Analytical technique

The cure kinetics of commercial phenol–formaldehyde (PF), used as oriented strandboard face and core resins, were studied using isothermal and dynamic differential scanning calorimetry (DSC). The cure of the face resin completely followed an nth‐order reaction mechanism. The reaction order was nearly 1 with activation energy of 79.29 kJ mol^?1. The core resin showed a more complicated cure mechanism, including both nth‐order and autocatalytic reactions. The nth‐order part, with reaction order of 2.38, began at lower temperatures, but the reaction rate of the autocatalytic part increased much faster with increase in curing temperature. The total reaction order for the autocatalytic part was about 5. Cure kinetic models, for both face and core resins, were developed. It is shown that the models fitted experimental data well, and that the isothermal DSC was much more reliable than the dynamic DSC in studying the cure kinetics. Furthermore, the relationships among cure reaction conversion (curing degree), cure temperature, and cure time were predicted for both resin systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1642–1650, 2006     

Effect of curing order on the curing kinetics and morphology of bisGMA/DGEBA interpenetrating polymer networks

The curing kinetics and morphology of an interpenetrating polymer network (IPN) formed from an epoxy resin (DGEBA) cured by an imidazole (1‐MeI) and a dimethacrylate resin (bisGMA), cured by low‐ and high‐temperature peroxide initiators (TBPEH and DHPB, respectively) have been studied by temperature‐ramping DSC, isothermal near‐infrared (NIR), DMTA and small‐angle neutron scattering (SANS). bisGMA and DGEBA are polar and chemically similar thermosetting resins which should enhance the miscibility of their IPNs. The phase structure was controlled by varying the curing procedure: the order of gelation of the components is dependent on the choice of low‐ and high‐temperature initiators for bisGMA and this affects the morphology formation. In the cure of the bisGMA/TBPEH:DGEBA/1‐MeI system, the dimethacrylate cures first. For isothermal cure studies at 80 °C, the final conversion of the epoxy is reduced by high crosslinking of the methacrylate groups in the IPN causing vitrification before full cure. The dimethacrylate conversion is enhanced due to plasticisation with unreacted DGEBA, and its cure rate is increased due to accelerated decomposition of TBPEH initiator by 1‐MeI. SANS revealed that phase separation occurs in these IPNs with domains on the scale of 6–7 nm. In the cure of the bisGMA/DHBP:DGEBA/1‐MeI system, the epoxy cures at a similar rate to that of the methacrylate groups. For isothermal cure studies at 80 °C, similar final conversions of the epoxy have been observed except for the 75:25 IPN. The cure rate of the methacrylate groups in the IPN is increased also due to accelerated decomposition of DHBP initiator by 1‐MeI, and the extent of accelerated decomposition for DHBP is stronger than that in the TBPEH‐based systems. SANS studies revealed that this system is more homogeneous due to the rapid formation of the dimethacrylate gel in the presence of the preformed epoxy network which interlocks the networks at low degrees of methacrylate conversion. Copyright © 2006 Society of Chemical Industry     

Comparison of the curing kinetic behavior for two epoxy resin systems containing EPIKOTE 828–EPIKURE 3090 and DURATEK KLM 606A–DURATEK KLM 606B

The aim of the study is to determine the optimum cure temperatures and kinetics for two different epoxy resin systems without using solvent. Two resin systems consist of EPIKOTE 828® epoxy resin–EPIKURE® 3090 polyamidoamine curing agent and DURATEK® KLM 606A epoxy resin–DURATEK® KLM 606B polyamide curing agent. The ratio of resin to curing agent was kept as 1:1 for both the systems. Curing temperatures of both the systems were determined and kinetic parameters were calculated with respect to the experimental results following nth‐order kinetics. Then, a series of isothermal temperatures was applied to the resin systems in order to assess the cure process in terms of conversion, time, and temperature by using differential scanning calorimeter (DSC). The test results of both systems show that the rate of degree of cure for EPIKOTE 828® epoxy resin–EPIKURE® 3090 polyamidoamine curing agent system is approximately 10 times higher than that of DURATEK® KLM 606A epoxy resin–DURATEK® KLM 606B polyamide curing agent system at 230°C. POLYM. COMPOS., 28:762–770, 2007. © 2007 Society of Plastics Engineers     

Cure kinetics,glass transition temperature development,and dielectric spectroscopy of a low temperature cure epoxy/amine system

This article reports a study of the chemical cure kinetics and the development of glass transition temperature of a low temperature (40°C) curing epoxy system (MY 750/HY 5922). Differential scanning calorimetry, temperature modulated differential scanning calorimetry, and dielectric spectroscopy were utilized to characterize the curing reaction and the development of the cross‐linking network. A phenomenological model based on a double autocatalytic chemical kinetics expression was developed to simulate the cure kinetics behavior of the system, while the dependence of the glass transition temperature on the degree of cure was found to be described adequately by the Di Benedetto equation. The resulting cure kinetics showed good agreement with the experimental data under both dynamic and isothermal heating conditions with an average error in reaction rate of less than 2 × 10^?3 min^?1. A comparison of the dielectric response of the resin with cure kinetics showed a close correspondence between the imaginary impedance maximum and the calorimetric progress of reaction. Thus, it is demonstrated that cure kinetics modeling and monitoring procedures developed for aerospace grade epoxies are fully applicable to the study of low temperature curing epoxy resins. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Curing kinetics of epoxy resin–imidazole–organic montmorillonite nanocomposites determined by differential scanning calorimetry

The curing kinetics of epoxy resin–imidazole–organic montmorillonite nanocomposites were investigated by differential scanning calorimetry (DSC) in the isothermal mode. X‐ray diffraction (XRD) analysis indicated the formation of a layered silicate–epoxy nanocomposite. The cure rates for the epoxy resin–imidazole–organic montmorillonite nanocomposite were lower than the values for the neat system at higher temperature (120 and 130°C), as indicated by the relation between the cure conversion and time. These results revealed that the autocatalytic model and the modified Avrami equation are both valid for describing the cure behaviors of epoxy resin–imidazole–organic montmorillonite systems. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2932–2941, 2003     

Novel nitrogen‐containing epoxy resin. II. Cure kinetics by differential scanning calorimetry

The isothermal and nonisothermal cure behaviors of a novel nitrogen‐containing epoxy resin (XT resin) were studied by differential scanning calorimetry (DSC). Various kinetic parameters and details of cure process were obtained based on the Avrami theory. The results indicated that Avrami method is suitable for calculating the kinetic parameters up to the gel point at least. The apparent activation energy (E_a) for isothermal cure process was in agreement with that for nonisothermal cure process. E_a value in the early stage (78.5–81.0 KJ mol^?1) was about three times than that in the later stage (23.3–26.5 KJ mol^?1). The kinetic results from Avrami theory may present a combined effect of all factors, and which is helpful to understand the cure technique for XT–DDS system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3483–3489, 2006     

Equivalent processing time analysis of glass transition development in epoxy/carbon fiber composite systems

The cure kinetics and glass transition development of a commercially available epoxy/carbon fiber prepreg system, DMS 2224 (Hexel F584), was investigated by isothermal and dynamic‐heating experiments. The curing kinetics of the model prepreg system exhibited a limited degree of cure as a function of isothermal curing temperatures seemingly due to the rate‐determining diffusion of growing polymer chains. Incorporating the obtained maximum degree of cure to the kinetic model development, the developed kinetic equation accurately described both isothermal and dynamic‐heating behavior of the model prepreg system. The glass transition temperature was also described by a modified DiBeneditto equation as a function of degree of cure. Finally, the equivalent processing time (EPT) was used to investigate the development of glass transition temperature for various curing conditions envisioning the internal stress buildup during curing and cooling stages of epoxy‐based composite processing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 144–154, 2002; DOI 10.1002/app.10282     

New model for characterising resin cure by dynamic differential scanning calorimetry

Abstract

In general, mould filling and resin cure are essential parts of thermoset composite manufacturing processes. While resin viscosity is a crucial property required in modelling and designing mould filling, resin cure or chemical reaction plays a key role in consolidating a composite. For a given cure cycle, resin cure is predicted by calculating the degree of cure using a cure kinetics model. Normally, cure kinetics is modelled by quantifying the extent of chemical reaction. There are many other methods for quantifying the chemical reaction and released heat was used in this study. A new model for determining cure kinetics with dynamic differential scanning calorimetry has been developed. The new method was applied to an epoxy resin system and was verified by comparison of measurement with prediction.     

Influence of epoxy sizing of carbon‐fiber on the properties of carbon fiber/cyanate ester composites

The high modulus carbon fiber (M40J) sized by epoxy resin E51 and E20 reinforced bisphenol A dicyanate (2,2′‐bis(4‐cyanatophenyl) isopropylidene resin composite was prepared in order to investigate the influence of epoxy sizing of the fiber on the properties of the composite. Differential scanning calorimetry (DSC) and fourier transforms infrared (FTIR) analysis showed that epoxy resin have catalytic effect on cure reaction of cyanate ester. Mechanical properties of the composite revealed that M40J fiber sized by epoxy resin could improve the flexural strength and interlaminar shear strength of M40J/bisphenol A dicyanate composites. The micro‐morphology of the composite fractures was studied by means of scanning electron microscopy (SEM). Reduced flaws were observed in the M40J‐bisphenol A dicyanate interface when the sized fiber was used. Water absorption of the composites was also investigated. It was found that the water absorption descended at the initial boiling stage (12 h). POLYM. COMPOS, 27: 591–598, 2006. © 2006 Society of Plastics Engineers     

Resin transfer molding (RTM) process of a high performance epoxy resin. I: Kinetic studies of cure reaction

The cure kinetics of a high performance PR500 epoxy resin in the temperature range of 160–197°C for the resin transfer molding (RTM) process have been investigated. The thermal analysis of the curing kinetics of PR500 resin was carried out by differential scanning calorimetry (DSC), with the ultimate heat of reaction measured in the dynamic mode and the rate of cure reaction and the degree of cure being determined under isothermal conditions. A modified Kamal's kinetic model was adapted to describe the autocatalytic and diffusion‐controlled curing behavior of the resin. A reasonable agreement between the experimental data and the kinetic model has been obtained over the whole processing temperature range, including the mold filling and the final curing stages of the RTM process.     

Investigation of the effect of double‐walled carbon nanotubes on the curing reaction kinetics and shear flow of an epoxy resin

In this article, the effect of combined temperature‐concentration and shear rate conditions on the rheology of double‐walled carbon nanotubes (DWCNTs)/RTM6‐Epoxy suspension was investigated to determine the optimum processing conditions. The rheological behavior and cure kinetics of this nanocomposite are presented. Cure kinetics analysis of the epoxy resin and the epoxy resin filled with DWCNTs was performed using Differential Scanning Calorimeter (DSC) and parameters of the kinetics model were compared. The DWCNTs have an acceleration effect on the reaction rate of the epoxy resin but no significant effect is noted on the glass transition temperature of the epoxy resin. This study reveals that the effect of shear‐thinning is more pronounced at high temperatures when DWCNTs content is increased. In addition, the steady shear flow exhibits a thermally activated property above 60°C whereas the polymer fluid viscosity is influenced by the free volume and cooperative effects when the temperature is below 60°C. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Relationship between isothermal and dynamic cure of thermosets via the isoconversion representation

This study deals with the cure of thermoset resins used in the pultrusion of fiber reinforced composites. The objective was to predict the degree of cure under non‐uniform time‐temperature profiles. A simple procedure using differential scanning calorimetry results was developed for predicting the degree of cure vs. time under isothermal conditions from dynamic DSC tests and vice versa. The principal feature of the procedure is the transformation of the degree of cure vs. time curves obtained under isothermal or dynamic DSC conditions into isoconversion curves as time vs. temperature or time vs. heating rate diagrams. The proposed procedure is validated with isothermal and dynamic DSC results from epoxy and polyester resin formulations used in the pultrusion of fiber reinforced composites. The agreement between predictions and experiments was very good and the extension of the procedure for predicting the cure under non‐uniform temperature profiles as in pultrusion seems to be feasible.     

Effect of polyaniline surface modification of carbon nanofibers on cure kinetics of epoxy resin

Polyaniline (PANI) “nanograss” was grown on carbon nanofibers (CNFs). The cure behavior of an epoxy resin with and without unmodified CNFs or PANI modified CNFs was studied by means of non‐isothermal and isothermal differential scanning calorimetry (DSC). CNFs accelerated the reaction of epoxy and diamine. PANI surface modification further increased the reaction rate and the extent of reaction. An autocatalytic cure kinetic model was used to fit the reaction curves. It was found that activation energies of the epoxy reaction decreased in the presence of CNFs and PANI modified CNFs. The observed catalytic effect of CNF and PANI surface coating can be very useful for low temperature cure of large epoxy composite products. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010