CURING KINETICS AND THERMAL PROPERTY CHARACTERIZATION OF BISPHENOL-F EPOXY RESIN AND DDS SYSTEM

The curing kinetics of bisphenol-F epoxy resin (BPFER)/4,4′-diaminodiphenyl sulfone (DDS) system were studied by isothermal experiments using a differential scanning calorimeter (DSC). Autocatalytic behavior was shown in the first stages of the cure for the system, which could be well described by the model proposed by Kamal that includes two rate constants, k ₁ and k ₂, and two reaction orders, m and n. The curing reaction at the later stages was practically diffusion-controlled due to the onset of gelation and vitrification. To consider the diffusion effect more precisely, diffusion factor, f(α), was introduced into Kamal's equation. Thus, the curing kinetics could be predicted well over the whole range of conversion covering both pre- and postvitrification stages. The glass transition temperatures (T_gs) of the BPFER/DDS system isothermally cured partially were determined by means of torsional braid analysis (TBA), and the results showed that T_gs increased with conversion up to a constant value. The highest T_g was 406.2 K. The thermal degradation kinetics of cured BPFER were investigated by thermogravimetric analysis (TGA), revealing two decomposition steps.     

Cure Kinetics and Thermal Property of Bisphenol-S Epoxy Resin and Phthalic Anhydride

Abstract

The cure kinetics of bisphenol-S epoxy resin (BPSER) and curing agent phthalic anhydride, with N,N-dimethyl phenzylamine as an accelerator, were studied by means of differential scanning calorimetry (DSC). Analysis of DSC data indicated that an autocatalytic behavior showed in the first stages of the cure. The autocatalytic behavior was well described by the model proposed by Kamal including two rate constants, k1 and k2, and two reaction orders, m and n. The overall reaction order, m + n, is in the range 2～3. The activation energies for k1 and k2 were 111.69 and 80.47 KJ/mol, respectively. Diffusion control was incorporated to describe the cure in the latter stages. The glass transition temperatures (T_gS) of the BPSER/anhydride samples isothermally cured partially were determined by means of torsional braid analysis (TBA). and the results showed that the reaction rate increased with increasing T_g in terms of the rate constant, but decreased with increasing conversion. The T_g of completely cured BPSER/anhydride system is about 40 K higher than that of BPAER. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of the BPSER/phthalic anhydride has n-order reaction kinetics.     

Curing kinetics and thermal property characterization of a bisphenol‐F epoxy resin and DDO system

The curing kinetics of a bisphenol‐F epoxy resin (BPFER)/4,4′‐diaminodiphenyl oxide (DDO) system were studied with isothermal experiments via differential scanning calorimetry. Autocatalytic behavior was shown in the first stages of the cure for the system, which was well described by the model proposed by Kamal that includes two rate constants, k₁ and k₂, and two reaction orders, m and n. The curing reaction at the later stages was practically diffusion‐controlled because of the onset of gelation and vitrification. For a more precise consideration of the diffusion effect, a diffusion factor, f(α), was introduced into Kamal's equation. In this way, the curing kinetics were predicted well over the entire range of conversion, covering both previtrification and postvitrification stages. The glass‐transition temperatures (T_g's) of the BPFER/DDO system partially isothermally cured were determined by means of torsional braid analysis, and the results showed that T_g's increased with conversion up to a constant value. The highest T_g was 376.3 K. The thermal degradation kinetics of cured BPFER were investigated with thermogravimetric analysis, which revealed two decomposition steps. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1586–1595, 2002     

Cure and glass transition temperature of the bisphenol S epoxy resin with 4,4′‐diaminodiphenylmethane

The curing reaction of bisphenol S epoxy resin (BPSER) with 4,4′‐diaminodiphenylmethane (DDM) was studied by means of torsional braid analysis (TBA) in the temperature range of 393–433 K. The glass transition temperature (T_g) of the BPSER/DDM system is determined, and the results show that the reaction rate increases with increasing the T_g in terms of the rate constant, but decreases with increasing conversion. 1 The T_g of BPSER/DDM is about 40 K higher than BPAER/DDM. The gelation and vitrification time were assigned by the isothermal TBA under 373 K; in addition, an FTIR spectrum was carried out to describe the change of the molecular structure. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of the BPSER/DDM has n‐order reaction kinetics. 2 © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 794–799, 2000     

Curing kinetics and thermal property characterization of the bisphenol‐F epoxy resin and phthalic anhydride system

The curing kinetics of bisphenol‐F epoxy resin (BPFER) and curing agent phthalic anhydride, with N,N‐dimethylbenzylamine as an accelerator, were studied by differential scanning calorimetry (DSC). Analysis of DSC data indicated autocatalytic behaviour in the first stages of the cure for the system, and that this, could be well described by the model proposed by Kamal, which includes two rate constants, k₁ and k₂, and two reaction orders, m and n. The curing reaction in the later stages was practically diffusion‐controlled. To consider the diffusion effect more precisely, a diffusion factor, ??(α), was introduced into Kamal's equation. The glass transition temperatures (T_gs) of the BPFER/phthalic anhydride samples were determined by means of torsional braid analysis. The thermal degradation kinetics of cured BPFER were investigated by thermogravimetric analysis. © 2002 Society of Chemical Industry     

Kinetics of 4,4′-diaminodiphenylmethane curing of bisphenol-S epoxy resin

The kinetics of the cure reaction for a system of bisphenol-S epoxy resin (BPSER), with 4,4′-diaminodiphenylmethane (DDM) as a curing agent, were studied by means of differential scanning calorimetry (DSC). Analysis of DSC data indicated that an autocatalytic behavior showed in the first stages of the cure, with the model proposed by Kamal, which includes two rate constants, k₁ and k₂, and two reaction orders, m and n. Rate constants k₁ and k₂ were observed to be greater when curing temperature increased. The over-all reaction order, m + n, is in the range of 2.5 ∼ 3. The activation energies for k₁ and k₂ were 55 kJ/mol and 57 kJ/mol, respectively. Diffusion control is incorporated to describe the cure in the latter stages. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1799–1803, 1999     

Curing behavior and thermal property of epoxy resin with boron‐containing phenol‐formaldehyde resin

The curing reaction of bisphenol‐A epoxy resin (BPAER) with boron‐containing phenol–formaldehyde resin (BPFR) was studied by isothermal and dynamic differential scanning calorimetry (DSC). The kinetic reaction mechanism in the isothermal reaction of BPAER‐BPFR was shown to follow autocatalytic kinetics. The activation energy in the dynamic cure reaction was derived. The influence of the composition of BPAER and BPFR on the reaction was evaluated. In addition, the glass transition temperatures (T_gs) were measured for the BPAER‐BPFR samples cured partially at isothermal temperatures. With the curing conditions varying, different glass transition behaviors were observed. By monitoring the variation in these T_gs, the curing process and the thermal property of BPAER–BPFR are clearly illustrated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1054–1061, 2000     

Cure kinetics and morphology of blends of epoxy resin with poly (ether ether ketone) containing pendant tertiary butyl groups

The cure kinetics and morphology of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin modified with a poly (ether ether ketone) based on tertiary butyl hydroquinone (PEEK-T) cured with diamino diphenyl sulphone (DDS) were investigated using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and dynamic mechanical thermal analysis (DMTA). The results obtained from DSC were applied to autocatalytic and diffusion controlled kinetic models. The reaction mechanism broadly showed autocatalytic behaviour regardless of the presence of PEEK-T. At higher PEEK-T concentration, more diffusion controlled mechanism was observed. The rate of curing reaction decreased with increase in thermoplastic content and also with the lowering of curing temperature. The activation energies of the blends are higher than that of the neat resin. The blends showed a phase separated morphology. The dispersed phase showed a homogeneous particle size distribution. The T_g of the neat resin decreased with the decrease in cure temperature. Two T_g's corresponding to the epoxy rich and thermoplastic rich phases were observed in the dynamic mechanical spectrum. The storage modulus of 10 and 20 phr PEEK-T blends are found to be greater than the neat resin.     

Epoxy resin based on 4,4′-dihydroxydiphenysulfone. I. Synthesis and reaction kinetics with 4,4′-diaminodiphenylmethane and 4,4′-diaminodiphenylsulfone

Epoxy resins based on 4,4′-dihydroxydiphenylsulfone (DGEBS) and diglycidyl ether of bisphenol A (DGEBA) were prepared by alkaline condensation of 4,4′-dihydroxydiphenylsulfone (bisphenol S) with epichlorohydrin and by recrystallization of liquid, commercial bisphenol A-type epoxy resin, respectively. Curing kinetics of the two epoxy compounds with 4,4′-diaminodiphenylmethane (DDM) and with 4,4′-diaminodiphenylsulfone (DDS) as well as T_g values of the cured materials were determined by the DSC method. It was found that the ? SO₂? group both in the epoxy resin and in the harener increases T_g values of the cured materials. DGEBS reacts with the used hardeners faster than does DGEBA and the curing reaction of DGEBS begins at lower temperature than does the curing reaction of DGEBA when the same amine is used. © 1994 John Wiley & Sons, Inc.     

Characterization of the cure of TGDDM/DDS epoxy resins by chemiluminescence I. Spectral and thermal analysis

The emission of weak visible chemiluminescence (CL) during the cure of a tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM)-based epoxy resin, with three different concentrations of 4,4′-diaminodiphenylsulfone (DDS) has been studied at 135°C. Spectral analysis indicates that the CL originates from trace oxidation of the TGDDM resin and the emission intensity is sensitive to the viscosity changes during cure. From thermal analysis data, sharp discontinuities in CL intensity are shown to occur at the gel point. The temperature dependence of CL from a cured resin also shows a sharp discontinuity at T_g. These results indicate that CL provides a sensitive monitor of both the kinetics of gelation and the network formation in this epoxy resin.     

Curing Kinetics and Thermal Properties Characterization of o-Cresol-formaldehyde Epoxy Resin and MeTHPA System

The kinetics of the cure reaction for a system of o-cresol-formaldehyde epoxy resin (o-CFER) with 3-methyl-tetrahydrophthalic anhydride (MeTHPA) as a curing agent and N,N-dimethyl-benzylamine as an accelerator was investigated by means of differential scanning calorimetry (DSC). Analysis of DSC data indicated that an autocatalytic behavior showed in the first stages of the cure for the system, which could be well described by the model proposed by Kamal, which includes two rate constants, k₁ and k₂, and two reaction orders, m and n. The activation energy E₁ and E₂ are 195.84 and 116.54 kJmol^?1, respectively. In the later stages, the reaction is mainly controlled by diffusion, and a diffusion, factor, f(α), was introduced into Kamal's equation. In this way, the curing kinetics were predicted well over the entire range of conversion. Molecular mechanism for the curing reaction was discussed. The glass transition temperature T_g was determined by means of torsional braid analysis (TBA). The results showed that T_gs increased with curing temperature and conversion up to a constant value about 367.1 K. The thermal degradation kinetics of the system was investigated by thermogravimetric analysis (TGA), which revealed two decomposition steps.     

Curing kinetics,thermal property,and stability of tetrabromo-bisphenol-A epoxy resin with 4,4′-diaminodiphenyl ether

The curing reaction of tetrabromo-bisphenol-A epoxy resin (TBBPAER) with 4,4′-diaminodiphenyl ether (DDE) was studied by isothermal differential scanning calorimetry (DSC) in the temperature range of 110–140°C. The results show that the isothermal cure reaction of TBBPAER–DDE in the kinetic control stage is autocatalytic in nature and does not follow simple nth-order kinetics. The autocatalytic behavior was well described by the Kamal equation. Kinetic parameters, including 2 rate constants, k₁ and k₂, and 2 reaction orders, m and n, were derived. The activation energies for these rate constants were 83.32 and 37.07 kJ/mol, respectively. The sum of the reaction orders is around 3. The glass transition temperatures (T_gs) were measured for the TBBPAER–DDE samples cured partially in isothermal temperature. With the degree of cure varies, different glass transition behaviors were observed. By monitoring the variation in these T_gs, it is illustrated that the network of the system is formed via different stages according to the sequence reactions of primary and second amines with epoxides. It is due to the presence of the 4 bromine atoms in the structure of TBBPAER that this curing process can be clearly observed in DSC curves. The thermal stability of this system studied by differential thermal analysis–thermogravimetric analysis illustrates that the TBBPAER–DDE material can automatically debrominate and takes the effect of flame retarding when the temperature reaches 238.5°C. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1991–2000, 1998     

Curing behavior of epoxy resin having hydroxymethyl group and different molecular weight distribution

o-Cresol novolac-type epoxy resins having hydroxymethyl group were synthesized. These epoxy resins were cured with a mixture of 4,4′-diaminodiphenylmethane and m-phenylenediamine (molar ratio, 6:4) as a hardener. Effects of molecular weight distribution of epoxy resins on curing behavior were studied. Curing behavior of epoxy resins with hardener were examined by differential scanning calorimetery (DSC), and cure reaction parameters were obtained. Viscoelastic properties of the cured epoxy resins were studied by dynamic mechanical analyzer. It was found that the lower the average molecular weight of the epoxy resin, that is, the higher the concentration of hydroxymethyl group, the shorter the onset time of exothermal reaction, the higher the rate constant (k), and the lower the activation energy (E_a) were. It was also found that glass transition temperature (T_g) of fully cured epoxy resins was higher than those of fully cured general novolac-type epoxy resins.     

Curing kinetics and reaction‐induced homogeneity in networks of poly(4‐vinyl phenol) and diglycidylether epoxide cured with amine

Mixtures of diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin with poly(4‐vinyl phenol) (PVPh) of various compositions were examined with a differential scanning calorimeter (DSC), using the curing agent 4,4′‐diaminodiphenylsulfone (DDS). The phase morphology of the cured epoxy blends and their curing mechanisms depended on the reactive additive, PVPh. Cured epoxy/PVPh blends exhibited network homogeneity based on a single glass transition temperature (T_g) over the whole composition range. Additionally, the morphology of these cured PVPh/epoxy blends exhibited a homogeneous network when observed by optical microscopy. Furthermore, the DDS‐cure of the epoxy blends with PVPh exhibited an autocatalytic mechanism. This was similar to the neat epoxy system, but the reaction rate of the epoxy/polymer blends exceeded that of neat epoxy. These results are mainly attributable to the chemical reactions between the epoxy and PVPh, and the regular reactions between DDS and epoxy. Polym. Eng. Sci. 45:1–10, 2005. © 2004 Society of Plastics Engineers.     

Reaction kinetics,thermal properties of tetramethyl biphenyl epoxy resin cured with aromatic diamine

Epoxy resins, 4, 4′‐diglycidyl (3, 3′, 5, 5′‐tetramethylbiphenyl) epoxy resin (TMBP) containing rigid rod structure as a class of high performance polymers has been researched. The investigation of cure kinetics of TMBP and diglycidyl ether of bisphenol‐A epoxy resin (DGEBA) cured with p‐phenylenediamine (PDA) was performed by differential scanning calorimeter using an isoconversional method with dynamic conditions. The effect of the molar ratios of TMBP to PDA on the cure reaction kinetics was studied. The results showed that the curing of epoxy resins contains different stages. The activation energy was dependent of the degree of conversion. At the early of curing stages, the activation energy showed the activation energy took as maximum value. The effects of rigid rod groups and molar ratios of TMBP to PDA for the thermal properties were investigated by the DSC, DMA and TGA. The cured 2/1 TMBP/PDA system with rigid rod groups and high crosslink density had shown highest T_g and thermal degradation temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Cure characterization of triglycidyl epoxy/aromatic amine systems

The curing of triglycidyl para-aminophenol (TGPAP) epoxy resin with three aromatic amine hardeners, diaminodiphenye sulphone (DDS), pyridinediamine (PDA), and toluenediamine (TDA), has been investigated. A series of iosthermal cures was conducted and analyzed by Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry (DSC). The chemical reactions occurring during cure were monitored at different temperatures by qualitative and quantitative estimation of different groups in the IR spectra, and the ratio of rate constants (k₂/k₁) were evaluated. Dynamic DSC analysis of TGPAP/TDA resulted in two exothermal peaks, indicating cure kinetics different from those of TGPAP/DDS and TGPAP/PDA systems, which gave a single exothermal peak. Various kinetic parameters such as total heat of reaction. ΔH′, activation energy E_a, Frequency factor z, and order of reaction n were evaluated for all the three systems. From the initial kick-off temperatures and activation energy values it was concluded that the rate of curing followed the order TDA > PDA > DDS. The reaction conversions during cure, evaluated from IR analysis, were exactly the same as those obtained from DSC Borchardt–Daniels kinetics. Using this model, the plots of time vs. temperature for different conversions were constructed for all the three systems; on the basis of these, the cure cycles can be fixed. © 1995 John Wiley & Sons, Inc.     

Torsional braid analysis of the aromatic amine cure of epoxy resins

The cure behavior of diglycidyl ether of bisphenol A (DGEBA) type of epoxy resins with three aromatic diamines, 4,4′-diaminodiphenyl methane (DDM), 4,4′-diaminodiphenyl sulfone (44DDS), and 3,3′-diaminodiphenyl sulfone (33DDS) was studied by torsional braid analysis. For each curing agent the stoichiometry of the resin mixtures was varied from a two to one excess of amino hydrogens per epoxy group to a two to one excess of epoxy groups per amino hydrogen. Isothermal cures of the resin mixtures were carried out from 70 to 210°C (range depending on epoxy—amine mixture), followed by a temperature scan to determine the glass transition temperature (T_g). The times to the isothermal liquid-to-rubber transition were shortest for the DDM mixtures and longest for the 44DDS mixtures. The liquid-to-rubber transition times were also shortest for the amine excess mixtures when stoichiometry was varied. A relatively rapid reaction to the liquid-to-rubber transition was observed for the epoxy excess mixtures, followed by an exceedingly slow reaction process at cure temperatures well above the T_g. This slow process was only observed for epoxy excess mixtures and eventually led to significant increases in T_g. Using time—temperature shifts of the glass transition temperature vs. logarithm of time, activation energies approximately 50% higher were derived for this process compared to those derived from the liquid-to-rubber transition. The rate of this reaction was virtually independent of curing agent and was attributed to etherification taking place in the epoxy excess mixtures. © 1994 John Wiley & Sons, Inc.     

Glass transition temperature (Tg) determination of partially cured thermosetting systems

Previous experiments have shown that T_g of a partially cured thermosetting system can be measured with conventional thermal scan methods only if no appreciable additional cure occurred during the scan. For high temperature performance systems, the partially cured T_g is often at a temperature where kinetics rate is very rapid, causing either an observation of a more advanced cured T_g, or only the completely cured system's T_g [T_g (∞)]. Two methods to interpolate the T_g information in spite of additional cure are presented and illustrated with an epoxy resin as a testing material. The Isocure State Curve method is demonstrated with a two-step curing experiment with the Torsion Impregnated Cloth Analysis (TICA) technique, which is a forced torsion measurement on the Rheometrics mechanical spectrometer, with the resin impregnated on a glass cloth specimen. The calibration method is demonstrated by the post cure experiments of TICA, using the time to loss modulus maximum, and the softening parameter R as the calibration parameters.     

Synthesis and properties of urethane elastomer-modified epoxy resin having hydroxymethyl group

Synthesis and properties of urethane elastomer-modified epoxy resins were studied. The urethane elastomer-modified epoxy resins were synthesized by the reaction of a 4-cresol type epoxy compound having hydroxymethyl groups (EPCDA) with isocyanate prepolymer. The structure was identified by IR, ¹H NMR and GPC. These epoxy resins (EPCDATDI) were mixed with a commercial epoxy resin (DGEBA) in various ratios. The mixed epoxy resins were cured with a mixture of 4,4′-diaminodiphenylmethane and 3-phenylenediamine (molar ratio 6:4) as a hardener. The curing behaviour of these epoxy resins was studied by DSC. The higher the concentration of EPCDATDI, the higher the onset temperature and the smaller the rate constant (k) of the exothermic cure reaction were. It was considered that the ratio of hydroxymethyl group to epoxide group was very small and the molecular weight of EPCDATDI was large. Therefore, the accelerating effect of the hydroxymethyl group on the epoxide–amine reaction was cancelled by the retardant effect of increased molecular weight and viscosity, and decreased molecular motion. Toughness was estimated by Izod impact strength and fracture toughness (K_1C). On addition of 10 wt% EPCDATDI with low molecular weight (M?_n 6710, estimated by GPC using polystyrene standard samples), Izod impact strength and K_1C increased by 70% and 60%, respectively, compared with unmodified epoxy resin. Glass transition temperatures (T_g) for the cured epoxy resins mixed with EPCDATDI measured by dynamic mechanical spectrometry were the same as those of unmodified epoxy resin. The storage modulus (E′) at room temperature decreased with increasing concentration of EPCDATDI. Toughness and dynamic mechnical behaviour of cured epoxy resin systems were studied based on the morphology.