Curing Reaction Of Epoxy Resin Research Articles

Tribological behavior of epoxy composites containing reactive SiC nanoparticles

AbstractThe present article evaluated the sliding wear behaviors of epoxy and its composites filled with SiC nanoparticles. Polyglycidyl methacrylate (PGMA) and a copolymer of glycidyl methacrylate and styrene were grafted onto the nanoparticles as a measure of surface pretreatment, respectively. The grafted polymers were selected because the epoxide groups on PGMA would take part in the curing reaction of epoxy resin and covalently connect the nanoparticles with the matrix, while styrene acted as a copolymerized monomer to adjust the amount of the reactive groups of the grafted macromolecular chains, and hence the compatibility between the grafted polymers and the matrix. In comparison to the composites filled with untreated nano‐SiC particles, the composites with the grafted nano‐SiC exhibit improved sliding wear resistance and reduced frictional coefficient owing to the chemical bonding at the filler/matrix interface. The results were analyzed in terms of structure‐properties relationship of the composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2608–2619, 2007

Miscibility and mechanical properties of an amine‐cured epoxy resin blended with poly(ethylene oxide)

AbstractBlends composed of diaminodiphenylmethane bisphenol‐A epoxy resin and poly(ethylene oxide) (PEO) were prepared via in situ curing reaction of epoxy in the presence of PEO. The miscibility of the blends before and after curing was established by thermal (differential scanning calorimetry, DSC), microstructural (atomic force microscopy) and dynamic mechanical analysis. Fourier transform infrared spectroscopy indicated that the OH groups developed through cure reactions interact by hydrogen bonding with PEO. After crystallinity analysis by DSC, the interaction parameter was determined through the depression of the equilibrium melting temperature. Mechanical properties of the miscible blends do not show any significant change, although improvement of fracture toughness has been observed with respect to the matrix properties. Copyright © 2006 Society of Chemical Industry

Multivariate Curve Resolution—Alternating Least Squares and Kinetic Modeling Applied to Near-Infrared Data from Curing Reactions of Epoxy Resins: Mechanistic Approach and Estimation of Kinetic Rate Constants

This study describes the combination of multivariate curve resolution-alternating least squares with a kinetic modeling strategy for obtaining the kinetic rate constants of a curing reaction of epoxy resins. The reaction between phenyl glycidyl ether and aniline is monitored by near-infrared spectroscopy under isothermal conditions for several initial molar ratios of the reagents. The data for all experiments, arranged in a column-wise augmented data matrix, are analyzed using multivariate curve resolution-alternating least squares. The concentration profiles recovered are fitted to a chemical model proposed for the reaction. The selection of the kinetic model is assisted by the information contained in the recovered concentration profiles. The nonlinear fitting provides the kinetic rate constants. The optimized rate constants are in agreement with values reported in the literature.

Miscibility and intermolecular specific interactions in thermosetting blends of bisphenol S epoxy resin with poly(ethylene oxide)

AbstractThermosetting blends composed of phloroglucinol‐cured bisphenol S epoxy resin and poly(ethylene oxide) (PEO) were prepared via the in situ curing reaction of epoxy in the presence of PEO, which started from initially homogeneous mixtures of diglycidyl ether of bisphenol S, phloroglucinol, and PEO. The miscibility of the blends after and before the curing reaction was established on the basis of thermal analysis (differential scanning calorimetry). Single and composition‐dependent glass‐transition temperatures (Tg's) were observed for all the blend compositions after and before curing. The experimental Tg's could be explained well by the Gordon–Taylor equation. Fourier transform infrared spectroscopy indicated that there were competitive hydrogen‐bonding interactions in the binary thermosetting blends upon the addition of PEO to the system, which was involved with the intramolecular and intermolecular hydrogen‐bonding interactions, that is, OH···OS, OH···OH, and OH, versus ether oxygen atoms of PEO between crosslinked epoxy and PEO. On the basis of infrared spectroscopy results, it was judged that from weak to strong the strength of the hydrogen‐bonding interactions was in the following order: OH···OS, OH···OH, and OH versus ether oxygen atoms of PEO. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 359–367, 2005

Formaldehyde Resins Bearing Diaminodiphenylmethane Groups: Synthesis, Characterization and Properties

AbstractSummary: Novel formaldehyde resins bearing diaminodiphenylmethane groups were synthesized by the polymerization of a mixture of diaminodiphenylmethane (DDM), cyclohexanone (CHx) and o‐cresol (o‐Cz) with formaldehyde (FA) in the presence of an acid catalyst (HCl). The resins obtained were characterized by spectral, elemental and thermal analysis and used as a hardener for epoxy resins. The curing and temperature behavior of these epoxy resin/formaldehyde systems were investigated using differential scanning calorimetry and thermogravimetry techniques. The resins had good thermal stability and the activation energies of degradation reactions had values between 70–98 kJ · mol−1.The curing reaction of epoxy resins with the DDM/CHx/o‐Cz/formaldehyde resins.magnified imageThe curing reaction of epoxy resins with the DDM/CHx/o‐Cz/formaldehyde resins.

Processing and chemorheology of epoxy resins and their blends with dendritic hyperbranched polymers

AbstractToughened epoxy systems have found increasing applications in automotive, aerospace, and electronic packaging industries. The present article reported work done for elucidation of gelation and vitrification for various epoxy systems and their blends with dendritic hyperbranched polymers (HBPs) having epoxy and hydroxyl functionality. Gel time was found to increase with increasing functionality from diglycidyl ether of bisphenol A (DGEBA) to tetraglycidyl diaminodiphenyl methane (TGDDM). The vitrification point was clearly identified from rheological experiments for triglycidyl p‐amino phenol (TGAP) and TGDDM. In the case of DGEBA a clear display of vitrification was not observed. TGDDM underwent vitrification sooner than did TGAP. Hydroxyl‐functionalized HBP reduced the gel time of the blends because of the accelerating effect of –OH groups to the epoxy curing reaction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1604–1610, 2004

Kinetic study of epoxy curing in the glass fiber/epoxy interface using dansyl fluorescence

The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.

Effect of Plasticization of Epoxy Networks by Organic Modifier on Exfoliation of Nanoclay

Plasticization of cross-linked epoxy networks by hydrocarbon chains of quaternary ammonium ions and its effect on exfoliation behavior of nanoclay particles in mixtures of aromatic and aliphatic epoxies were investigated. It was found that quaternary ammonium ions, apart from catalyzing epoxy curing reactions, are capable of plasticizing cross-linked epoxy chains, the effect of which was observed in terms of large reduction in glass transition temperature and lowering of the values of storage modulus of cured epoxy networks. The effect of plasticization on storage modulus was found to be small for aromatic epoxy and large for aliphatic epoxy. As a consequence, the aromatic epoxy−clay system produced complete exfoliation of clay galleries, while the systems with mixtures of aliphatic and aromatic epoxy resulted in intercalated systems, even though the extent of curing of epoxy was the same in all cases.

Using diethylphosphites as thermally latent curing agents for epoxy compounds

AbstractDiethylphosphite (DEP) and its derivative exhibited thermally latent properties for epoxy curing reactions through the formation of phosphonic acid as an active species from a reaction of ethanol elimination, which was observed with 1H NMR and pyrolysis gas chromatography/mass spectrometry measurements. The thermally latent properties and curing reaction kinetics of the curing reaction of DEPs with diglycidyl ether of bisphenol A were studied with differential scanning calorimetry. The cured epoxy resins possessed a phosphorous element coming from the DEP derivatives, exhibiting improved flame retardancy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 432–440, 2003

Effect of hydroxypropyl cellulose in epoxy network formation

Studies on the curing reactions of epoxy systems were carried out in the presence of a cellulose derivative, hydroxypropyl cellulose (HPC). The technique of differential scanning calorimetry (DSC) was applied to characterize the curing reactions/thermal properties. Classical nonisothermal kinetic methods, such as the Kissinger and the Osawa methods (multiple scan) and the Barrett method (single scan) as well as the recently one proposed by Samios et al., were applied to study the reaction kinetics of the epoxy system of diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenylmethane (DDM) with HPC. The Barrett method gives additional information about the process of initiation, gelation, and vitrification. At the beginning of the epoxy curing reaction, HPC acts as a catalyst so that the energy of activation diminishes and the reaction occurs at lower temperatures. Above the minimum temperature Tmin, it was concluded that HPC behaves as an inhibitor of the reaction (Tmin is the temperature which corresponds to the minimum point showed by the exotermic peaks during the curing reaction of an epoxy resin measured by DSC). By analyzing the behavior of the kinetic parameters, Ea, k, and ln A, the molecular interactions were shown to be related to the catalyst–inhibitor characteristics of HPC. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 676–683, 2003

Study on the catalytic behavior of metal acetylacetonates for epoxy curing reactions

AbstractMetal acetylacetonates are effective latent catalysts for epoxy/anhydride systems. A screen test on the catalytic behavior of metal acetylacetonate shows that this system offers a wide range of curing latency and material properties. It can be inferred that the curing behavior is closely related to the bonding strength of the metal ion to the ligand. Isothermal kinetic study on the catalytic behavior of metal chelates with first‐row transition metal ions is conducted and analyzed by using an autocatalytic model. It is found that the activation energy of the system containing the divalent metal chelates follows the Irving and Williams rule. The activation energies of the reaction obtained in the kinetic study are compared with the dissociation energies of the metal/ligand bond and the results are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1572–1579, 2002

Monitoring the Change of Viscosity during Cure Reaction of Epoxy Resins with Resin Position Sensor

It was required that the fundamental understanding of the resin’s rheological properties, such as viscosity, gel point and degree of cure are known during the processing of epoxy resin. In order to monitor these properties in-situ, a sensor system that can measure the viscosity changes during cure is needed. The resin position sensor (RPS) based on DC conductometry has been able to measure the ionic contents and electrical conductivity of most organic resins. Complex viscosity and electrical resistance were measured simultaneously during the cure of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin with polyamide by mounting the RPS on the upper plate of rotational rheometer. To correlate the viscosity with the resistance, the rheological model for the viscosity changes and the electrical model for the resistance changes were used. From the results, the interrelationship of viscosity and resistance of epoxy resin could be confirmed.

Preparation and properties of epoxy resins cured with silyl esters of phenol novolak and cresol novolak

The curing agents of epoxy resin, trimethylsilyl ethers of phenol novolak (TMSPN) and cresol novolak (TMSCN) were prepared by refluxing phenol novolak and cresol novolak respectively, with the mixture of hexamethyldisilazane and chlorotrimethylsilane in THF. The curing reaction of epoxy resin with these curing agents and the thermal properties of cured resins were examined. The Tg values of epoxy resins cured with TMSPN were a little higher than those cured with TMSCN. The maximum of Tg is 118°C for TMSPN-cured epoxy resin against 112°C for TMSPN-cured epoxy resin. The water absorption of hydrophobic epoxy resins cured with TMSPN was a little lower than those cured with TMSCN. The clear decrease of water absorption is attributed to the difficulty of the micro-void formation caused by the more tight primary structures of TMSPN. The water absorption at 25°C containing trimethylsilyl groups is about one-tenth of that of epoxy resins cured with conventional curing agents and even one-half of that of the epoxy resins cured with active esters. The low water absorption is attributed to the presence of trimethylsilyl groups, which are more hydrophobic than ester groups, and to the absence of hydroxyl groups of the cured resins.

Polyaniline as a Curing Agent for Epoxy Resin: Cure Kinetics by Differential Scanning Calorimetry

A poly(aniline sulfate) salt was prepared by an emulsion polymerization pathway. A mixture of epoxy resin and the poly(aniline sulfate) salt sample was prepared using chloroform as solvent, and studied using both dynamic and isothermal differential scanning calorimetry (DSC). DSC analysis was performed on samples with different polyaniline/epoxy resin ratios, in the temperature range between 40 and 350°C. A single exothermic peak was observed for the curing reaction of epoxy resin using polyaniline. The result indicates that, epoxy resin can be cured using polyaniline in a 1 : 1 ratio at a temperature of 180°C for 5 min. Dynamic kinetic parameters were calculated using the Kissinger and Ozawa methods. Isothermal kinetic parameters, including k1, k2, n and m were determined, based on an autocatalytic mechanism proposed by Kamal.

Polyaniline as a Curing Agent for Epoxy Resin: Cure Kinetics by Differential Scanning Calorimetry

A poly(aniline sulfate) salt was prepared by an emulsion polymerization pathway. A mixture of epoxy resin and the poly(aniline sulfate) salt sample was prepared using chloroform as solvent, and studied using both dynamic and isothermal differential scanning calorimetry (DSC). DSC analysis was performed on samples with different polyaniline/epoxy resin ratios, in the temperature range between 40 and 350°C. A single exothermic peak was observed for the curing reaction of epoxy resin using polyaniline. The result indicates that, epoxy resin can be cured using polyaniline in a 1 : 1 ratio at a temperature of 180°C for 5 min. Dynamic kinetic parameters were calculated using the Kissinger and Ozawa methods. Isothermal kinetic parameters, including k1, k2, n and m were determined, based on an autocatalytic mechanism proposed by Kamal.

Influences of inorganic fillers on curing reactions of epoxy resins initiated with a boron trifluoride amine complex

Inorganic fillers are widely used for epoxy resins to improve mechanical and thermal properties. However, inorganic fillers may unexpectedly affect the curing reactions of such epoxy resins. In our present study, influences of inorganic fillers on the curing reactions of phenol novolac epoxy resin (EPN) initiated with boron trifluoride ethylamine complex (BF3MEA) are detailed. The gel times of epoxy resins containing alumina (Al2O3) fillers were longer than those of corresponding unfilled epoxy resins, indicating that Al2O3 fillers delayed the curing reactions of epoxy resins. Mechanisms were proposed and influences of aluminum hydroxide (Al(OH)3), silica (SiO2), and aluminum fluoride (AlF3) fillers were also described.

Effects ofin situ esterification on the performance of carboxyl functionalized rubber-modified epoxy film adhesives

Epoxy-based film adhesive formulations were developed with 10 wt % solid carboxyl functional rubber. Due to the high rubber content and resulting viscosity restrictions, the rubber could not be prereacted with the epoxy before hot-melt filming. Therefore, an esterification catalyst was used to perform this reaction in situ before the epoxy curing reactions. The performance of this adhesive system is compared to that of one without the esterification catalyst. A significant difference in the flow characteristics was observed with incorporation of the esterification catalyst, but only small variations in mechanical performance were found. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 728–734, 2000

Toughened interpenetrating polymer network materials based on unsaturated polyester and epoxy

Simultaneous interpenetrating polymer networks (IPNs) based on epoxy (diglycidyl ether of bisphenol A) and unsaturated polyester (UP) were prepared by using m-xylenediamine and benzoyl peroxide as curing agents. A single glass transition temperature for each IPN was observed with differential scanning calorimetry, which suggests good compatibility of epoxy and UP. This compatibility was further confirmed by the single damping peak of the rheometric dynamic spectroscopy. Curing behaviors were studied with dynamic differential scanning calorimetry, and the curing rates were measured with a Brookfield RTV viscometer. It was noted that an interlock between the two growing networks did exist and led to a retarded viscosity increase. However, the hydroxyl end groups in UP catalyzed the curing reaction of epoxy; in some IPNs where the hydroxyl concentration was high enough, such catalytic effect predominated the network interlock effect, leading to fast viscosity increases. In addition, the entanglement of the two interlocked networks played an important role in cracking energy absorption and reflected in a toughness improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 585–592, 1999

Toughened interpenetrating polymer network materials based on unsaturated polyester and epoxy

Simultaneous interpenetrating polymer networks (IPNs) based on epoxy (diglycidyl ether of bisphenol A) and unsaturated polyester (UP) were prepared by using m-xylenediamine and benzoyl peroxide as curing agents. A single glass transition temperature for each IPN was observed with differential scanning calorimetry, which suggests good compatibility of epoxy and UP. This compatibility was further confirmed by the single damping peak of the rheometric dynamic spectroscopy. Curing behaviors were studied with dynamic differential scanning calorimetry, and the curing rates were measured with a Brookfield RTV viscometer. It was noted that an interlock between the two growing networks did exist and led to a retarded viscosity increase. However, the hydroxyl end groups in UP catalyzed the curing reaction of epoxy; in some IPNs where the hydroxyl concentration was high enough, such catalytic effect predominated the network interlock effect, leading to fast viscosity increases. In addition, the entanglement of the two interlocked networks played an important role in cracking energy absorption and reflected in a toughness improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 585–592, 1999

Kinetic approach for epoxy resins cured with diaminodiphenyl sulfone under non‐isothermal conditions

The curing reactions of epoxy resin basing on diglycidyl ether bisphenol A (DGEBA) with 4,4′-diaminodiphenyl sulfone (DDS) were investigated with a differential scanning calorimeter and gel permeation chromatography. Based on the generating function method and the Monte Carlo simulation procedure, kinetic models for both isothermal and nonisothermal curing conditions were proposed. The apparent activation energy of curing reactions was found to be 14.9 Kcal/mol by the thermal analysis. According to our kinetic models, gel points, the profiles of epoxy conversion, and the molecular weights of polymers were calculated. Good agreement is obtained between the model predictions and experimental data. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 721–728, 1999