Thermal and photochemical ageing of epoxy resin - Influence of curing agents

The thermal and photochemical ageing of epoxy resin was studied using photoacoustic-FTIR spectroscopy. This technique was satisfactory for both unfilled resin and glass fibre filled epoxy composite. The influence of the curing agent (anhydride or amine) was significant for ageing. The durability of anhydride-epoxy system was the best for both thermal and photoageing.     

用FTIR定量研究环氧树脂固化反应动力学制样方法的确定

利用FTIR进行环氧树脂固化反应的动力学研究需要精确的样品制备方法,摸索到一套合适的样品制备方法。将KBr研成细粉,通过孔径为0.074mm筛子使粒子均匀,在120~150℃下加热24h后,取0.25g,放入红外压片模具,在压力为800MPa条件下加压时间5~10min,压制成厚度为0.08mm的透明均匀KBr盐片。将环氧树脂均匀涂在这种KBr盐片上,放入微型反应器中反应,之后一同放入FTIR仪中进行扫描,实验证明这种制样方法可以保证红外定量分析的可靠性。     

The curing kinetics and mechanical properties of epoxy resin composites reinforced by PEEK microparticles

In this paper, a polyether-ether-ketone (PEEK)/epoxy composite was prepared by using PEEK microparticles as the reinforcement. The nonisothermal differential scanning calorimetry (DSC) test was used to evaluate the curing reaction of PEEK/epoxy resin system. The curing kinetics of this system were examined utilizing nonisothermal kinetic analyses (Kissinger and Ozawa), isoconversional methods (Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose) and an autocatalytic reaction model. During these analyses, the kinetic parameters and models were obtained, the curing behavior of PEEK/epoxy resin system under dynamic conditions was predicted. The results show that isoconversional methods can adequately interpret the curing behavior of PEEK/epoxy resin system and that the theoretical DSC curves calculated by the autocatalytic reaction model are in good agreement with experimental data. Furthermore, the tensile elongation at break, tensile strength, flexural strength, compression strength and compression modulus increased by 81.6%, 33.66%, 36.53%, 10.98% and 15.14%, respectively, when PEEK microparticles were added in epoxy resin composites.     

Curing characteristics of carboxyl functionalized glucose resin and epoxy resin

The curing characteristics of carboxylic functionalized glucose resin (glucose maleic acid ester vinyl resin: GMAEV) and epoxy resin have been studied using DSC and FTIR methods. Exothermic reactions attributed to esterification and etherification reactions of the hydroxyl and carboxyl functionalities of GMAEV with the epoxy groups were identified. Exothermic reactions showed very different patterns according to the degree of carboxyl group substituent of GMAEV. The results showed that esterification reaction occurs in the early stage of cure and then etherification followed after completion of the esterification. A cured matrix containing epoxy resin and 50 wt.% of GMAEV was prepared and characterized. The cured matrix showed thermal stability up to 300 °C. The average glass transition temperature and storage modulus of the matrix were as high as 95 °C and 2700 MPa, respectively. The cured matrix of epoxy resin and GMAEV with higher degree of carboxyl group was found to have a lower density due to the formation of bulky groups in the crosslinks.     

Studies on the effect of different levels of toughener and flame retardants on thermal stability of epoxy resin

A thermoplastic toughener, polyether sulphone (PES) and a number of different types of flame retardants were blended in different ratios with a commercial epoxy resin triglycidyl-p-aminophenol (TGAP) and 4,4-diamino diphenyl sulphone (DDS) a curing agent. The effect of type and levels of flame retardants (FR) and the toughening agent on the curing, thermal decomposition and char oxidation behaviour of the epoxy resin was studied by the simultaneous differential thermal analysis and thermogravimetric techniques. It was observed that the toughener slightly increases the curing temperature (by up to 20 °C) but had minimal effect on the decomposition temperature of the resin. Flame retardants, however affected all stages depending upon the type of flame retardant used. The curing peak for samples containing tougher and flame retardants although slightly changed depending upon the type of FR, was not more than ± 20 °C compared to that of samples containing toughener only. All flame retardants lowered the decomposition temperature of the epoxy resin. Phosphorus- and nitrogen-containing flame retardants reduced the char oxidation leading to more residual char, whereas halogen- containing flame retardants had less effect on this stage.     

Radiation induced effects on particulate composites from epoxy resin and fly-ash

In this paper gamma-radiation damages and effects on an epoxide matrix and on its particulate composite with coal fly ash have been studied; the curing of both formulations was carried out at room temperature by means of tetraethylenepentamine and of a tailored polyalkylenepolyaminophenolic product. The change on mechanical properties following the irradiation in air at room temperature has been tested as a function of the total absorbed dose. The chemical modification induced by the ionizing radiation on the matrices have been investigated by means of infrared spectrophotometry and differential scanning calorimetry. The high radiation resistance of the matrix and above all of the particulate composite suggests its use for the confinment of low and medium activity radwastes (nuclear or medical).     

Determination of mechanical properties of silica compounds using a curing kinetic model

Curing is the final step in rubber goods production and the mechanical properties of the vulcanized items, strongly depend on the processing conditions. The objective of this research is to predict the mechanical properties of SBR silica compound using kinetic data obtained from curemeter measurements. The model proposed is based on two curing parameters and on mechanical properties measured in the cured and uncured state. Results showed that the model is able to accurately predict the mechanical properties of the isothermal cured compound and therefore has potential application in the non-isothermal curing cycle optimization.     

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.     

Mechanical properties and curing kinetics of epoxy resins cured by various amino-terminated polyethers

<正>A high performance thermosetting epoxy resin crosslinkable at room temperature was obtained via directly moulding diglycidyl ether of bisphenol A(DGEBA) and flexibleα,ω-bisamino(n-alkylene)phenyl terminated poly(ethylene glycol).The influences of the n-alkylene inserted in aminophenyl of flexible amino-terminated polythers(ATPE) on the mechanical properties,fractographs and curing kinetics of the ATPE-DGEBA cured products were studied.The results show that the insertion of n-alkylene group into the aminophenyl group of the ATPE,on one hand,can significantly increase the strain relaxation rate and decrease glass transition temperature of the ATPE-DGEBA cured products,resulting in slight decrease of the Young's modulus and tensile strength,and significant increase of the toughness and elongation of the ATPE-DGEBA cured products.On the other hand,it can remarkably enhance the reactivity of amine with epoxy,much accelerating the curing rate of the ATPE-DGEBA systems.The activation energy of DGEBA cured by BAPTPE,BAMPTPE and BAEPTPE was 53.1,28.5 and 25.4 kJ·mol~(-1),respectively.The as-obtained ATPE-DGEBA cured products are homogeneous, transparent,and show excellent mechanical properties including tensile strength and toughness.Thus they are promising to have important applications in structure adhesives,casting bulk materials,functional coatings,cryogenic engineering, damping and sound absorbing materials.     

Isothermal curing of an epoxy resin by alternating differential scanning calorimetry

The quasi-isothermal curing of a diepoxide resin with a triamine of polyoxypropylene was studied by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The complex heat capacity measurements allows to analyse the vitrification process at curing temperatures (T_c) below the maximum glass transition of the fully cured epoxy (T_g∞=85.8°C). Initially, the modulus of the complex heat capacity, |C^*_p|, increases until a maximum (conversion between 0.42 and 0.56) and then decreases. This step is followed by an abrupt decay of |C^*_p|, due to the vitrification of the system, which allows the determination of the vitrification time. This value agrees well with that determined by the partial curing method. The phase angle and out-of-phase heat capacity show an asymmetric wide peak during the vitrification process. The change in |C^*_p| at vitrification decreases with the increase of T_c becoming zero at temperature T_g∞. This epoxy-triamine system shows a delay of the vitrification process respect to other model epoxy systems probably due to the presence of polyoxypropylene chains in the network.

The decay of |C^*_p| during vitrification may be normalised between unity and zero by defining a mobility factor. This mobility factor has been used to simulate the reaction rate during the stage where the reaction is controlled by diffusion. The observed reaction rate is simulated by the product of the kinetic reaction rate, determined by the autocatalytic model, and the mobility factor.     

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     

Curing of an epoxy resin modified with poly(methylmethacrylate) monitored by simultaneous dielectric/near infrared spectroscopies

Simultaneous dielectric and near infrared measurements have been performed in “real-time” to follow polymerisation reactions on blends of a diglycidyl ether of bisphenol-A epoxy resin with 4,4^′-diaminodiphenylmethane hardener and different amounts of poly(methylmethacrylate) as modifier. The effect of the modifier amount on the polymerisation reactions has been studied, as well as that of the curing temperature. Epoxy and amine conversions have been followed by near infrared spectroscopy (NIR), while changes in molecular mobility in the reaction mixture have been analysed by dielectric relaxation spectroscopy (DRS). Evolutions of ionic conductivity and α-relaxation have been analysed and vitrification times have been obtained. The relaxational behaviour has been analysed through curing in the frequency domain, being the change of the main relaxation indicative of the cure reaction advancement. DRS data are also presented as complex impedance Z(ω). Vitrification times, obtained by dielectrometry have been compared with those obtained by rheological measurements and gelation times obtained by NIR have been compared with those obtained by solvent extraction.     

Synthesis of an epoxy functionalized spiroorthocarbonate used as low shrinkage additive in cationic UV curing of an epoxy resin

The synthesis of an epoxy functionalized spiroorthocarbonate (SOC) is reported. The obtained monomer has been used a slow shrinkable additive in cationic UV curing of a commercially available dicycloepoxy resin. A polymer network flexibilization was evidenced by increasing the SOC content in the photocurable formulation. It has been demonstrated that SOC acts as shrinkage reduction additive reaching expansion on volume after polymerization in the presence of 10 wt% of the functionalized spiroorthocarbonate.     

Study on curing of novolac epoxy resin

The optimization of proportions of novolac epoxy resin, Dobeckot E4 and polyamide hardener, EH411 has been established by DSC and the data indicates that resin-polyamide, 100∶40 and 100∶50, appear to be optimum where ‘extent of cure’ is maximum. The kinetic parameters for these formulations have been evaluated using isothermal and dynamic modes by employing DSC. The rate constants have been evaluated for curing process of these formulations using isothermal DSC mode in the temperature range of 70°–90°C. These have also been predicted at 20°±1°C (room temperature) by extrapolating the data obtained at elevated temperatures. A comparison of the predicted values with the experimental values shows that there is a good agreement between them.     

The effect of zeolite on the curing of epoxy resin by polyaniline: a kinetic study

Polyaniline sulfate‐zeolite composite was prepared by emulsion polymerization. Epoxy resin was cured using polyaniline‐sulfate salt and various amounts of polyaniline sulfate‐zeolite composite. The kinetics of the cure reaction for an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) with polyaniline‐sulfate and polyaniline sulfate‐zeolite composite have been studied using differential scanning calorimetry (DSC) under isothermal and dynamic conditions. Isothermal kinetics analysis was performed using the phenomenological model of Kamal. Dynamic kinetic analysis was performed using Kissinger's method. Copyright © 2002 John Wiley & Sons, Ltd.     

Curing behavior and properties of high biosourced epoxy resin blends based on a triepoxy monomer and a tricarboxylic acid hardener from 10-undecenoic acid

Renewable propane-1,2,3-triyl tris(9-(oxiran-2-yl) nonanoate) (EGU, 100 wt% biogenic) and a tricarboxylic acid triglyceride (CGTU) hardener (85.7 wt% biogenic) were synthesized from 10-undecenoic acid (10-UDA) and used to produce epoxy resins with 52–92 wt% biobased carbon. CGTU was prepared by thermally activated thiol-ene coupling of thioglycolic acid onto propane-1,2,3-triyl tris(undec-10-enoate), (GUD) in the absence of solvent. The characterized CGTU was used as a green hardener of blends based on EGU and a conventional bisphenol A-based epoxy pre-polymer (DGEBA) at various mass percentages (0–100 wt%) with an stoichiometric epoxy/acid equivalent ratio. Calorimetric studies revealed higher peak temperature, lower reaction heats, and longer gelation times in resins with high EGU proportion, evidencing the lower reactivity of aliphatic EGU compared with aromatic DGEBA. Cured resins were yellowish transparent rubber-like materials with glass transition temperatures (Tg) varying from −14 °C to −42 °C and tensile strength in the range of 1750 kPa–790 kPa, for 0 and 100 wt % EGU, respectively. The soluble fraction of all resins was less than 4.3%, reflecting a high level of crosslinking. Thermosets with high biobased content showed both UV-light protection and visible light transparency.     

Effect of new nonionic curing agent on curing kinetics and mechanical properties of epoxy resin

The current research work presents a novel nonionic curing agent (AEDA) synthesized by utilizing ethylene glycol diglycidyl ether (EGDE), 3,4-dimethoxyaniline (DI), and triethylenetetramine (TETA). Infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to characterize the structure of AEDA curing agent. Non-isothermal scanning calorimetry was used to determine the activation energy and curing conditions of epoxy resin in the curing process. An impact testing machine, a tensile testing machine and a scanning electron microscope (SEM) were used to analyze the impact strength, tensile strength, bending strength, and micromorphology of the AEDA/E-51 system with different mass ratios. The results show that AEDA is an effective high-temperature curing agent. For the AEDA/E-51 system with the optimal mass ratio of 10:100, the best curing temperature is 92.15°C, and the post-curing temperature is 135.65°C. Furthermore, the apparent activation energy (E_a) of 1670 J/mol, the pre-exponential factor (A) of 3.7 × 10^?4, and the reaction series (n) value of 0.76 are obtained for the AEDA/E-51 system. The impact strength of AEDA/E-51 epoxy resin polymer is 7.82 kJ/m², tensile strength is 14.2 MPa, and bending strength is 18.92 MPa. The micromorphological results of the AEDA/E-51 system are consistent with the results of DSC test and mechanical properties test. Hence, this study provides theoretical support for the practical applications of AEDA as curing agent.     

Effect of nanosilica on the kinetics of cure reaction and thermal degradation of epoxy resin

Nanocomposites from nanoscale silica particles(NS),diglycidylether of bisphenol-A based epoxy(DGEBA),and 3,5-diamino-N-(4-(quinolin-8-yloxy) phenyl) benzamide(DQPB) as curing agent were obtained from direct blending of these materials.The effect of nanosilica(NS) particles as catalyst on the cure reaction of DGEBA/DQPB system was studied by using non-isothermal DSC technique.The activation energy(E_a) was obtained by using Kissinger and Ozawa equations. The E_a value of curing of DGEBA/DQPB/10%NS system showed a decrease of about 10 kJ/mol indicating the catalytic effect of NS particles on the cure reaction.The E_a values of thermal degradation of the cured samples of both systems were 148 kJ/mol and 160 kJ/mol,respectively.The addition of 10%of NS to the curing mixture did not have much effect on the initial decomposition temperature(T_i) but increased the char residues from 20%to 28%at 650℃.     

Techniques used for determining cure kinetics of rubber compounds

Controlling and assuring the quality of the manufacture of high precision engineering rubber components has led to the need to simulate fundamental industrial processes such as compression molding and injection molding using CAE tools. Both compression and injection molding techniques for the fabrication of rubber products involve crosslinking or vulcanization which is invariably assisted by temperature and pressure. Vulcanization is a chemical process and therefore its simulation necessarily involves characterization of kinetic parameters. The kinetics of curing or vulcanization is somewhat complex as it depends upon the compound formulation, temperature and in some cases pressure. The present paper reports and discusses the application and utility of different techniques for characterizing the cure behavior of rubber compounds. Kinetic data has been fitted to various mathematical models in order to see which of the models can best represent the crosslinking behavior of selected rubber compounds. Finally, the kinetic data is used to simulate the injection molding process for relatively simple geometries.     

Factors influencing EB curing of epoxy matrix

The effectiveness of electron beam (EB) curing of epoxy resins was found to be influenced by catalyst. In the presence of iodonium salt (diaryl iodonium hexafluoroantimonate, C3), the EB curing of epoxy resin is easier than in the presence of triaryl sulfonium hexafluoroantimonate (C1), or triaryl sulfonium hexafluorophosphate (C2), or iron arene containing cationic catalyst (Irgacure 261). The epoxy 616 (diglycidyl ether of bisphenol A) and 648 (diglycidyl ether of phenolic novolacs) can be cured by the above onium salts catalysts C1–C3. The epoxy with glycidyl amino epoxide group (such as AG 80; AFG 90) could not be cured by onium salts catalyst. The influence of irradiation dose, temperature and the effect of impurities on curing reaction were investigated.