Dynamic mechanical properties of epoxy/novolac system modified with reactive liquid rubber and carbon filler

This paper reports on the work carried out to evaluate the frequency dependent viscoelastic properties of epoxy/novolac compositons modified with a liquid reactive rubber and carbon filler. For epoxy systems modified with elastomer, three typical transitions were observed: the α-relaxation deeply related to the glass transition of epoxy, the β-transition of epoxy, and the glass transition of rubber appeared near to the β-relaxation of epoxy resin. Considering an Arrhenius equation, the activation energies of β-relaxation were estimated. In the region of glass transition and rubbery state the temperature dependence of the shift factor (α_T) was determined through Williams-Landel-Ferry (WLF) equation.     

Modification of epoxy binders using cycloaliphatic epoxy imides

The influence of epoxy imide cycloaliphatic epoxy resin EPOX-01 on the rheological properties of the epoxy amine system was investigated. The effect of the amount of amine hardener for solidification process of modified system is evaluated. It is shown that the use of epoxy imide cycloaliphatic resin allows one to obtain materials with improved technological characteristics of film technology (RFI).     

Phase separation behavior of epoxy resin modified with crosslinked rubber

Low molecular weight liquid rubber (ATBN = amine terminated butadiene acrylonitrile copolymer or CTBN = carboxyl terminated butadiene acrylonitrile copolymer)–DGEBA (diglycidyl ether of bisphenol A) blends indicated upper critical solution temperature (UCST) behavior. The phase separation behavior of the neat and crosslinked rubber (ATBN, CTBN)–epoxy blends was analyzed by a laser light scattering experiment. Lauryl peroxide (LPO) was employed to crosslink the rubber during the initial annealing stage. The onset point of the phase separation in the crosslinked ATBN–epoxy system occurred later than in the case of the neat ATBN–epoxy system. However, the onset point of the phase separation process started earlier in the case of the crosslinked CTBN–epoxy system. The domain correlation length of the crosslinked rubber-added system was smaller than that of the neat rubber-added system.     

Curing of liquid epoxy resin in plasma discharge

Epoxy resins in the solid state, liquid state and during polymerisation were treated by microwave oxygen plasma and analysed by FTIR spectra. Curing, etching and oxidation kinetics of epoxy resin were observed. In the liquid resin and polymerising mixture the effect of structure modification was observed more intensively than in the case of solid sample due to a mixing process. A modification of bulk layers of liquid epoxy resin was observed under plasma action. The polymerisation reaction of epoxy resin with amine hardening agent can be released in plasma discharge at low pressure.     

The compatibilizing effect of epoxy resin (EP) on polypropylene (PP)/recycled acrylonitrile butadiene rubber (NBRr) blends

A new method was used to prepare thermoplastic elastomers based on polypropylene (PP)/recycled acrylonitrile butadiene rubber (NBRr) with improved mechanical properties. An epoxy resin (EP) was used as a compatibilizing agent. The effect of EP on mechanical properties, swelling percentage and morphological characteristics of the blends was investigated with different blend compositions. The results showed that the incorporation of EP has improved the tensile strength, Young's modulus and elongation at break of PP/NBRr-EP blends compared with PP/NBRr blends. The enhancement of tensile properties of PP/NBRr-EP blends is due to the better adhesion between the two phases with the incorporation of EP. This is quite evident by scanning electron microscopy of tensile fractured surfaces. PP/NBRr-EP blend exhibits lower stabilization torque and swelling percentage than PP/NBRr blends. The lower stabilization torque is an indication of better processing characteristics.     

Effects of reactive diluent diepoxidized cardanol and epoxy fortifier on curing kinetics of epoxy resin

Different formulations, composed of the diglycidyl ether of bisphenol-A, diepoxidized cardanol as reactive diluent, an anhydride as curing agent, and a tertiary amine as curing catalyst, with/without the use of an epoxy fortifier, were analysed. The effect of the fortifier on the diluent was also observed. The overall kinetics of curing was observed to follow a simple Arrhenius-type temperaturedependence, with an activation energy in the range 54–120 kJ/mol, with first-order kinetics up to 85% conversion. An increase in activation energy was observed with an increase of diluent content. The curing reaction was found to follow a three-step mechanism, involving a nucleophilic bimolecular displacement reaction, for which an explanation was offered. Incorporation of the fortifier lowers the curing temperature, but does not alter the final degree of reaction.

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Zusammenfassung Es wurden verschiedene Ausgangsgemische, bestehend aus dem Diglyzidyläther von Bisphenol A, diepoxydiertem Kardanol als reaktives Streckmittel, einem Anhydrid als Vernetzungsmittel und einem tertiären Amin als Vernetzungskatalysator mit bzw. ohne Anwendung eines Fortifyers untersucht. Der Einfluss des Fortifyers auf das Streckmittel wurde ebenfalls untersucht. Die Bruttokinetik der Vernetzung zeigt eine Temperaturabhängigkeit einfachen Arrhenius-Types mit einer Aktivierungsenergie im Bereich von 54–120 kJ/mol sowie einen Reaktionstyp erster Ordnung mit einer Konversionsrate von 85%. Ein steigender Streckmittelgehalt bewirkt ein Anwachsen der Aktivierungsenergie. Der Vernetzungsreaktion liegt ein Dreistufenmechanismus zu Grunde, der unter anderem auch eine nukleofile bimolekulare Substitutionsreaktion beinhaltet. Der Einsatz eines Fortifyers senkt zwar die Vernetzungstemperatur, verändert aber nicht die Endkonversionsrate.

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液晶环氧p-PEPB的合成及改性双酚-A环氧树脂的研究

本文以对羟基苯甲酸乙酯、丙烯溴、对苯二酚等为原料合成了双4-环氧丙基醚苯甲酸对苯二酚酯液晶环氧树脂(p-PEPB).用IR、1HNMR、DSC、POM和XRD的对其进行了表征,结果表明该化合物为向列型液晶,其熔点为180℃,清晰点为250 ℃.研究了 p-PEPB/双酚-A环氧(BPAER)/4,4,-二氨基二苯醚(DDE)体系的非等温固化过程,得到了固化温度参数、表观活化能Ea及p-PEPB含量对Tg的影响,结果表明p-PEPB为5%可使BPAER的Tg提高14 ℃,固化过程服从Ozawa模型.     

Dynamic mechanical properties of epoxy resin/epoxidized rubber blends: Effect of phase separated rubber

The dynamic mechanical properties of blends of diglycidyl ether of bisphenol-A-based epoxy resin and internally epoxidized polybutadiene rubber have been studied. It is shown that the influence of the composition of the continuous phase and of the dispersed phase can be studied not only from the variations of the glass transition temperature but also from the changes in the apparent enthalpy of activation associated with this transition. As the initial rubber content increases, the composition of the dispersed phase remains practically constant while more rubber is able to dissolve in the continuous phase. Analysis of the rubbery plateau region reveals that the shear modulus of the blends is not much affected by the presence of dissolved rubber in the continuous phase but strongly depends on the volume fraction of dispersed phase. This volume fraction can be obtained from the relative drop in shear modulus after modeling the results with the Kerner equation. The results compares well with independent measurements by scanning electron microscopy. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of liquid crystalline epoxy and co-polymerisation with a non-mesomorphic epoxy resin

A novel liquid crystalline epoxy resin based on the imine group was synthesised and structurally characterised by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. The mesogenic behaviour of the monomer was measured by differential scanning calorimetry (DSC) and polarised optical microscopy (POM), and presented various textures in the extensive temperature range. Methyl nadic anhydride (MNA) was employed to cure the liquid crystalline epoxy resin and the curing process was investigated using POM and wide-angle X-ray diffraction (WAXD). Information about distribution of liquid crystalline epoxy resin in the blending system resulted from the FT-IR Imaging System, indicating that molecules of liquid crystalline epoxy resin can agglomerate to form anisotropic domains. The improvement in mechanical properties of diglycidyl ether of biphenol A (DGEBA) modified with liquid crystalline epoxy was achieved. Scanning electronic microscopy (SEM) showed that an extremely rough and highly deformed fracture surface can be obtained. DGEBA modified with liquid crystalline epoxy resin was characterised by dynamic mechanical analysis (DMA) for its thermal properties. The results indicate that the presence of the liquid crystal phase influences glass transition temperature (Tg).     

Effects of novel reactive toughening agent on thermal stability of epoxy resin

A reactive amino-ended toughener was blended with different commercial epoxy resins namely, diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl p-aminophenol and 1,5-naphthalenediamine as curing agent. The toughener was an aromatic amino-ended copolyethersulphone (coPES):poly(ether-sulphone)–poly(etherether-sulphone). The effect of the toughener on the thermal decomposition and char oxidation behaviour of the epoxy resins was studied by the simultaneous differential thermal analysis and thermogravimetric techniques. The glass transition temperature (T _g) as well as characteristic parameters of decomposition, initial decomposition temperature (T _i) and temperature at maximum degradation rate (T _m), in both inert and oxidative environments, were determined in order to verify the influence of toughener on the thermal degradation of the different epoxy systems. It was observed that the presence of coPES maintains the high level thermal stability of the resin and that the glass transition temperature increase with the toughener percentage.     

Effect of CTBN rubber inclusions on the curing kinetic of DGEBA-DGEBF epoxy resin

The curing kinetics of an epoxy resin matrix, based on diglycil ether of bisphenol A and F (DGEBA-DGEBF), associated with an anhydride hardener, at different carboxyl-terminated copolymer of butadiene and acrylonitrile liquid rubber (CTBN) concentration (0-10 phr) are studied using a differential scanning calorimetry (DSC) and a stress-controlled rheometer in isothermal and dynamic conditions. The aim of this work is to correlate the presence of the rubber phase with the transition phenomena that occur during the curing process. The CTBN rubber induces a catalytic effect on the polymerization of the pure resin clearly observed by a significant enhancement of the curing rate. Calorimetric and rheological analysis also evidences that gelation and vitrification times take place not punctually but in a wide range of time. Rheological data show that the presence of rubbery phase induces a higher rate of gel formation during the early stages of the reactions, confirming the calorimetric results. Finally the results are compared with theoretical models evidencing a good fitting between experimental and predictive data.     

Effect of substituents on the curing of liquid crystalline epoxy resin

The synthesis of an aromatic ester based liquid crystalline epoxy resin (LCE) with a substituent in the mesogenic central group is described. Chlorine and methyl groups were introduced as substituents. The curing behaviors of three epoxy resins were investigated using diaminodiphenyl ester as the curing agent. The curing rate and heat of curing of LCE were measured with dynamic and isothermal DSC. The chlorine substituent accelerated the curing of LCE, while the methyl substituent decelerated the curing of LCE. The heat of curing of substituted LCE was diminished compared to LCE with no substituent. Glass transition temperature and elastic modulus of LCE decreased with increasing the size of the substituent. Three liquid crystalline epoxy resins based on aromatic ester mesogenic groups formed a liquid crystalline phase after curing, and the liquid crystalline phase was stable up to the decomposition temperature. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 911–917, 1998     

Physical aging of poly(ether sulfone)-modified epoxy resin

The physical aging process of 4,4′-diaminodiphenylsulfone (DDS) cured diglycidyl ether bisphenol-A (DGEBA) blended with poly(ether sulfone) (PES) was studied by differential scanning calorimetry (DSC) at four aging temperatures between T_g-50°C and T_g-10°C. At aging temperatures between T_g-50 and T_g-30°C, the experimental results of epoxy resin blended with 20 wt% of PES showed two enthalpy relaxation processes. One relaxation process was due to the physical aging of PES, the other relaxation process was due to the physical aging of epoxy resin. The distribution of enthalpy relaxation process due to physical aging of epoxy resin in the blend was broader and the characteristic relaxation time shorter than those of pure epoxy resin at the above aging temperatures (between T_g-50 and T_g-30°C). At an aging temperature between T_g-30 and T_g-10°C, only one enthalpy relaxation process was found for the epoxy resin blended with PES, the relaxation process was similar to that of pure epoxy resin. The enthalpy relaxation process due to the physical aging of PES in the epoxy matrix was similar to that of pure PES at aging temperatures between T_g-50 and T_g-10°C. © 1997 John Wiley & Sons, Inc.     

Temperature dependence of liquid epoxy resin impregnation through polyester non-woven fabric

The temperature dependence of liquid epoxy resin impregnation under atmospheric pressure was measured under the condition that the impregnation was through polyester non-woven fabric sheets, sandwiched between two circular glass plates. It was expected that impregnation would take place to a small extent, because the pressure in the sheet increases to more than atmospheric pressure in the course of impregnation from the perimeter of the circular sheet toward its center, but the liquid resin impregnates to a great extent and impregnating velocity increases with a rise in temperature. This phenomenon can be analyzed by the Kozeny-Carman equation improved by the introduction of the theoretically calculated capillary force in the modeled fiber bed structure and a parameter to postulate gas solubility and diffusion into the liquid resin. An increase in the impregnating velocity with the temperature rise is caused by decrease in the resin viscosity, by increase of the capillary force pressure and by decrease in the gas pressure corrected by a parameter.     

Synthesis and curing behavior of a novel liquid crystalline epoxy resin

This article described the synthesis and mesomorphic behavior transition of a novel liquid crystalline (LC) epoxy resin 4-(2,3-epoxypropoxy)biphenyl,4″-(2,3-epoxypropoxy)phenyl-4′carboxylate (EBEPC), which combined a hydroxyl benzoic aromatic ester and biphenol rigid-rod group. EBEPC showed a clear nematic schlieren texture under curtain conditions. The reaction kinetics of EBEPC cured by 4,4′-diaminodiphenyl-methane (DDM) was studied by using an isoconversional method under isothermal conditions with differential scanning calorimetry (DSC). The isothermal DSC data can be fitted reasonably by an autocatalytic curing model. Smectic phases had been observed in the EBEPC/DDM curing system. The results of DSC showed that the formation of the LC phase had pronounced influence on the curing reaction.     

Modification of epoxy novolak resin with polyamic acid,investigation of cocuring mechanism

The processes of thermal curing in the epoxy novolak resin-polyamic acid system were investigated by means of high-temperature FTIR spectroscopy. It was shown that, under the conditions studied, the formation of copolymer took place, and the mechanism of cocuring changed depending on the concentration of modifying agent.     

Phase behavior and morphology in epoxy resin/poly(L-lactide) blends. Comparison with epoxy resin/poly(L,D-lactide) blends

Thermoset/thermoplastic blends were prepared with epoxy–aromatic diamine mixtures and poly(L-lactide) (PLLA), as semicrystalline thermoplastic, in concentrations ranging from 4 to 25 wt.%. In some cases, poly(L,D-lactide) (PDLLA), an amorphous thermoplastic, was used instead for comparative purposes. Diglycidyl ether of bisphenol-A (DGEBA) was employed as epoxy resin and 4,4′-diaminodiphenylmethane (DDM) as curing agent. Phase behavior and morphology were studied during curing at 140 °C. Initially, all blends were homogeneous; however, the curing reaction of the epoxy resin caused a liquid–liquid phase separation. A co-continuous morphology was formed at the beginning of the phase separation in all the considered blend compositions. Blends evolved to a particle/matrix structure or to a phase-inverted structure depending on the initial blend composition. At 140 °C, crystallization only occurred in blends with 16 and 25 wt.% PLLA. This crystallization originates changes in the surface of the epoxy-rich droplets developed with the phase separation.     

Modification of epoxy resins with liquid polysulfide and carboxylated butadiene rubbers

In this work, we present the results of studying the effect of liquid carboxylated butadiene and polysulfide rubbers on the physicomechanical and adhesive properties of epoxy adhesive compositions with curing agents of different chemical nature—diethylene triamine and polyoxypropylene triamine. It is found that carboxylated butadiene rubbers are more effective modifiers than polysulfide rubbers because they yield a higher complex of properties. It is also shown that the change in the chemical nature of a curing agent has no significant effect on the properties of epoxy-rubber adhesive compositions, which allows one to control their key technological parameters without fear of losing strength characteristics.     

Reaction pathway of liquid crystalline epoxy resin/aromatic diamine curing system

The reaction pathway of a monotropic liquid crystalline epoxy resin (HQEP2) was studied using FT‐IR and DSC. The reaction mechanism was correlated with the amine to epoxy ratio, curing temperature and morphology of the curing system. Experimental results showed that the linearly growing molecules lead to a nematogen but branching intermediates induced an isotropic texture.