Study of the epoxy system BADGE (n = 0)/1,2‐DCH/CaCO3 filler by DMA and DSC

The influence of an inorganic filler, CaCO₃, on the curing kinetics of an epoxy system composed of diglycidyl ether of bisphenol A [BADGE (n = 0)], 1,2‐diaminecyclohexane (1,2‐DCH), and CaCO₃ filler was studied by DMA and DSC. Different contents of filler in the range from 10 to 30%, referred to the total weight of the mixture, were tried. It was found that maximum reproducibility of the results and better performance correspond to a filler content of 20%. As usual, the T_g's obtained by DMA and DSC are different at 10–20°C. The results obtained from this study were compared with those corresponding to the system BADGE (n = 0)/1,2‐DCH without filler; the T_g for this last system is higher than that for the system with filler incorporated, whereas E′ and M_c (molecular weight between repetition units) are lower for the system without filler. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 366–370, 2002     

Influence of an epoxy reactive diluent on the thermal degradation process of the system DGEBA n = 0/1,2 DCH

The thermal degradation of two epoxy systems diglycidyl ether of bisphenol A (DGEBA n = 0)/1,2‐diamine cyclohexane (DCH) containing different concentrations of an epoxy reactive diluent, vinylcyclohexene dioxide (VCHD), was studied by thermogravimetric analysis to determine the reaction mechanism of the degradation process for these two systems. Values of the activation energy, necessary for this study, were calculated by using various integral and differential methods. Values obtained by using the different methods were compared to the value obtained by Kissinger's method, which does not require a knowledge of the reaction mechanism. All the experimental results were compared to master curves in the range of Doyle's approximation (20–35% of conversion). Analysis of the results suggests that the two reaction mechanisms are R_n and F_n deceleratory type in contrast with the sigmoidal A₂ type of the system with filler and the sigmoidal A₄ type of the system without additives. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1199–1207, 2004     

Lifetime prediction of the epoxy system DGEBA (n = 0)/1,2‐DCH modified with an epoxy reactive diluent by thermogravimetric analysis

Thermogravimetric analysis was used to predict the lifetime of two three‐component systems of diglycidyl ether of bisphenol A (n = 0)/1,2‐diamine cyclohexane [DGEBA (n = 0)/1,2‐DCH] modified with different concentrations of an epoxy reactive diluent, vinylcyclohexene dioxide (VCHD). Experimental results were treated using two methods. The first method was independent of the degradation mechanism, and the second was based on the thermodegradation kinetic mechanism. The activation energies of the reaction were determined using the Flynn–Wall–Ozawa method. These values were compared with those obtained using Kissinger's method. From experimental results it was found that the optimum temperature of service for these materials were different, so one or the other must be selected, depending on the application temperature considered. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3835–3839, 2003     

Effect of water sorption on the structure and mechanical properties of an epoxy resin system

The characteristics of sorption and diffusion of water in an amine‐cured epoxy system based on tetraglycidyl diaminodiphenylmethane and a novolac glycidyl ether resin were studied as a function both of the polymer microstructure, known from previous works, and the temperature. Water‐sorption experiments and dynamic mechanical analysis (DMA) were performed. Tensile stress–strain and Rockwell hardness tests were conducted to investigate the effects of absorbed water on the mechanical properties of the material. Competing effects of the sorption of water in the free volume and of strong interactions between water molecules and polar groups of the network were used to explain the diffusional behavior observed, which followed Fick's second law. DMA analysis seemed to be sensitive to the water effects and the viscoelastic behavior was related both to the water‐sorption processes and to the microstructure of the system. An important impact of water uptake on the tensile properties at break was also appreciated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 71–80, 2001     

Lifetime prediction of the epoxy system badge n = 0/1,2 DCH by thermogravimetric analysis

Lifetime of the system diglycidyl ether of bisphenol A (BADGE n = 0)/1,2‐diamine cyclohexane (DCH) was predicted by thermogravimetric analysis. Lifetime was considered when either 5% weight loss or 5% conversion was reached. Experimental results were treated using two different methods: The first method was independent of the degradation mechanism and the second was based on the thermodegradation kinetic mechanism. The activation energy of the reaction, determined using the Flynn–Wall–Ozawa method, was 148.51 kJ/mol. This value is in a good agreement with that of 144.01 kJ/mol obtained using Kissinger′s method. From the experimental results, it was found that the optimum temperature of service for this material is in the range of 100–140°C, at which the corresponding lifetime range is from 27 to 2633 years. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1239–1244, 2000     

Miscibility, morphology, thermal, and mechanical properties of a DGEBA based epoxy resin toughened with a liquid rubber

Epoxy resin based on diglycidyl ether of bisphenol A and varying content of hydroxyl terminated polybutadiene were cured using an anhydride hardener. The ultimate aim of the study was to modify the brittle epoxy matrix by liquid rubber to improve the toughness characteristics. Chemorheological analysis of the modified network was performed to understand the physical transformations taking place during the cure polymerization reaction. The delay in gel time on inclusion of rubber can be explained by lower reactivity due to dilution and viscosity effect. Tensile, flexural, and fracture toughness behaviors of neat as well as modified networks have been studied to observe the effect of rubber modification. The morphological evolution of the toughened networks was examined by scanning electron microscope, and the observations were used effectively to explain the impact properties of the network having varying content of liquid rubber. Acoustic emission studies were performed on neat and certain modified systems. Based on acoustic emission results and morphological characteristics, toughening and failure mechanisms were discussed. The behavior of the relaxation peaks were evaluated by dynamic mechanical analysis and tried to explain the composition of networks. Thermal stabilities of the toughened epoxies were studied using thermogravimetric analysis (TGA). The activation energy for decomposition of neat and modified epoxies has been estimated and compared. The reduction in cross-linking density of the thermoset upon modification has been confirmed and explained.     

鳞片石墨对环氧涂层强度和吸水性能的影响

分别研究了含不同质量分数鳞片石墨的环氧涂层的剪切强度以及经冷热水循环浸泡后涂层的重量吸水率与浸泡时间、浸泡72h后涂层的体积变化率、密度和鳞片石墨质量分数的关系。结果表明,随着石墨含量的增加,涂层剪切强度急剧降低,在w(石墨)=10%处达最低值,之后逐渐升高。当w(石墨)=20%时,涂层剪切强度较大。涂层重量吸水率随浸泡时间的增加而增大,并呈现周期性变化(以每24h为周期)。同时,随着石墨含量的增大,涂层吸水率降低。不同石墨含量的涂层浸泡72h后其体积变化率随石墨含量的增加呈现双峰特征,当w(石墨)=20%时,其体积变化率较低,为2.8%。浸泡前和浸泡72h后,涂层密度随石墨含量的增加均呈现先下降后增大的趋势,而且,两者在石墨含量为5%处的密度几乎相等。解释了涂层中不同石墨含量对其强度和耐水性的影响。涂层中适宜的石墨含量为20%。     

Water absorption by an epoxy resin and its effect on the mechanical properties and infra-red spectra

A filled epoxy resin used as a structural adhesive and based on the diglycidyl ether of bisphenol A cured with dicyandiamide has been subjected, in its bulk form, to ageing at 40, 55 and 70°C and ca. 100% relative humidity. Gravimetric, viscoelastometric and FTi.r. studies have been effected after various times of exposure. Water absorption in the polymer is essentially Fickian, although closer inspection reveals the finer behaviour to be sigmoidal. The activation energy for diffusion is of the order of 80 kJ mol⁻¹, but there appears to be no clear relationship between equilibrium absorption values and temperature. Viscoelastometry has shown that T_g diminishes from ca. 115°C before ageing to ca. 90°C at saturation, 1% of water uptake corresponding to ca. 8°C reduction in T_g. Reductions in Young's modulus were observed both in the glassy and rubbery states after ageing and the latter is associated with molecular chain scission. FTi.r. analysis has shown several modifications occurring due to water absorption, the main one being an increase in intensity of the band at 1740 cm⁻¹. It is concluded that water absorption leads both to plasticization effects and chemical modification of the epoxy resin.     

Thermal degradation of the epoxy system BADGE n = 0/1,2‐DCH immersed in hydrochloric acid

The thermal degradation of an epoxy system consisting of diglycidyl ether of bisphenol‐A and 1,2‐diamine cyclohexane (BADGE n = 0/1,2‐DCH), immersed in hydrochloric acid for 30 days, was studied by thermogravimetric analysis, to determine the reaction mechanism of the degradation process. The results were compared with experimental data corresponding to the same epoxy system without exposure to the acid. It was found that the kinetic reaction mechanism changed with the immersion in HCl. The average activation energy of the solid‐state process was determined by using the Flynn‐Wall‐Ozawa method, resulting in 81 ± 2 kJ/mol. Different integral and differential methods and different reaction mechanisms reported in the literature were used and compared to this value. Analysis of experimental results suggests that in the conversion range studied, 5–20%, the reaction mechanism is somewhere between the different types of phase boundary controlled reaction and random nucleation with one nucleus on the individual particle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 371–375, 2002     

Influence of PP content on mechanical properties,water absorption,and morphology in PA6/PP blend

PA6/polypropylene (PP) blends are investigated for obtaining balanced strength and toughness. The focus of this study is to understand the effect of PP content on mechanical property, water absorption, impact strength, thermal behavior, and morphology of PP in the absence and presence of PP-g-maleic anhydride compatibilizer. In comparison to pure PA6, all blends have higher impact strength with 161 and 124% increase at 5 wt % PP content in uncompatibilized and compatibilized blends (UB and CB), respectively. Morphology of impact fractured samples shows brittle fracture in the case of CB. scanning electron microscope of cryogenically fractured samples show decrease in domain size and change in shape from ellipsoid to spherical, from UB to CB. Then, 75% reduction in water absorption is observed for 50 wt % PP content UB. Postwater absorption yield strength (YS) remains constant above 10 wt % PP in both UB and CB and decrease in YS is less at higher PP content in CB. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47690.     

Effects of diffusion on the kinetic study of the system BADGE n = 0/m‐xylylenediamine

The curing reactions of an epoxy system composed of a diglycidyl ether of bisphenol A (BADGE n=0) and m‐xylylenediamine (m‐XDA) were studied. Two models, the first based solely on chemical kinetics and the second accounting for diffusion, were used and compared to the experimental data. The epoxy resin was used as received in a first series of experiments. In a second series of experiments, the resin was purified in vacuo (180°C and 1 mmHg). The inclusion of a diffusion factor in the second model allowed for the cure kinetics to be predicted over the whole range of conversion covering both pre‐ and postvitrification stages. The investigation was made in the temperature range 50–110°C, which is considered optimum for the isothermal curing of the epoxy system studied. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2997–3005, 1999     

Cure kinetics of a diglycidyl ether of bisphenol a epoxy network (n = 0) with isophorone diamine

The study of the cure reaction of a diglycidyl ether of bisphenol A epoxy network with isophorone diamine is interesting for evaluating the industrial behavior of this material. The total enthalpy of reaction, the glass‐transition temperature, and the partial enthalpies at different curing temperatures have been determined with differential scanning calorimetry in dynamic and isothermal modes. With these experimental data, the degree of conversion and the reaction rate have been obtained. A kinetic model introduces the mechanisms occurring during an epoxy chemical cure reaction. A modification of the kinetic model accounting for the influence of the diffusion of the reactive groups at high conversions is used. A thermodynamic study has allowed the calculation of the enthalpy, entropy, and Gibbs free energy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effects of curing program on mechanical behavior and water absorption of DGEBA/TETa epoxy network

Water uptake in organic coatings remains an interesting challenge for fundamental and applied researches because chemical, physical, and mechanical properties are concerned. The polymer network, which is affected by the curing program, is a key factor for water absorption. In this work, an epoxy network based on diglycidyl ether of bisphenol A and a hardener triethylentetramine was cured at different temperatures: below T_g (protocol 1) and above T_g (protocol 2). DMA, Differential Scanning Calorimetry (DSC), and FT‐IR measurements showed that both protocols allow to obtain totally cured networks. However, DSC and DMA results revealed that both cured networks present different levels of homogeneity, depending on the different curing conditions, which affect the free volume and the activation volume associated with visco‐elastic properties. The mechanical properties of free films and water sorption behaviors were investigated as function of cured conditions. It was found that protocol 1‐cured networks present higher mechanical properties and was less affected by water ingress than protocol 2‐cured systems, leading to better barrier properties. These results highlight the influence of the curing program onto the heterogeneous distribution of the epoxy network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Development of an epoxy system characterized by low water absorption and high thermomechanical performances

Water absorption and thermomechanical properties of epoxy systems based on multifunctional dicyclopentadiene epoxy novolac resin Tactix556 cured with 4,4′ diaminodiphenilsulfone (4,4′DDS) as curing agent has been studied. The base system was modified by the addition of a novel 40 : 60 PES : PEES (Polyethersulphone : Polyetheretheresulphone) amine‐ended copolymer to improve toughness properties. The effect of thermoplastic addition on water adsorption was studied by gravimetric experiments. The viscoelastic properties of the resulting blend were analyzed by means of dynamic mechanical thermal analysis. The formulated systems were compared with a system based on tetraglycidyl‐4,4′diaminodiphenylmethane resin (MY721) cured with 4,4′ diaminodiphenilsulfone. The use of Tactix556 resin showed that water uptake values were minimized while retaining high glass transition temperatures, and toughness values were found in the same range of standard toughened matrices used for aerospace composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4880–4887, 2006     

Influence of stoichiometric ratio on water absorption in epoxy resins

Dielectric, gravimetric, dynamic mechanical, and infrared measurements are reported on the effect of different stoichiometric ratios on the water absorption of diglycidyl ether of bisphenol A (DGEBA), MY720 (Ciba Geigy) cured with stoichiometric variations of triethylenetetramine (TETA), (BDH). Resin samples were prepared with stoichiometric ratios of epoxy:amine from 3 : 1 through 1 : 1 to 1 : 3. Analysis of the water absorption characteristics of these materials showed the existence of water in two different environments; molecules bound to specific sites in the matrix and clustered in microvoids as “free water.” Diffusion coefficients and equilibrium water uptake were shown to markedly increase with an increase in the amine ratio. An anomaly observed in dielectric results is attributed to a high rate of diffusion in the high amine ratio materials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2369–2376, 1998     

Desiccant films made of low-density polyethylene with dispersed calcium oxide: Water vapor absorption,permeation and mechanical properties

Polymers with dispersed desiccants are relevant for various packaging applications to protect packaged goods from water vapor. The intention of this study was to analyze and to describe a relevant system. Therefore, films with calcium oxide (CaO) were investigated, because such materials are hardly described in scientific literature. Monolayer films with 0.14 to 0.51 g dispersed CaO per 1 g film (PE-LD) were prepared and they absorbed up to 0.2 g water vapor per 1 g of film. The water vapor absorption was described by effective diffusion coefficients. By the use of effective diffusion coefficients and the absorption capacity, the absorption behavior of layers with various thicknesses can be estimated. The steady state (effective) water vapor permeation coefficients of the films with dispersed CaO were a factor of 2 to 24 (8.4 to 101.5 mg cm [cm² s Pa]^–1 × 10¹², at 23 °C) higher than for pure PE-LD films (4.26 mg cm [cm² s Pa]⁻¹ × 10¹², 23 °C). The tensile stress changed only slightly (pure PE-LD: 9.5 N mm⁻²; PE-LD with 0.14 g dispersed CaO per 1 g film: 8.1 N mm⁻²; PE-LD with 0.51 g dispersed CaO per 1 g film: 10.5 N mm⁻²), while the tensile strain at break was reduced with higher CaO concentration from 318% (pure PE-LD) to 10% (PE-LD with 0.51 g dispersed CaO per 1 g film). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47460.     

Influence of amine-terminated additives on thermal and mechanical properties of diglycidyl ether of bisphenol A (DGEBA) cured epoxy

The present work accounts for the influence of aromatic amide oligomers on the inherent brittleness of cured epoxy. Aromatic and aliphatic amine-terminated amide oligomers have been prepared by condensation polymerization using isophthaloyl dichloride and two different amines. The oligomers have been characterized using Fourier transform infrared spectroscopy and wide angle X-ray diffraction analysis. Diglycidyl ether of bisphenol A (DGEBA) is cured with a diamine (4,4′-oxydianiline) by using different weight ratio of oligomers. The FTIR of cured epoxy shows ring opening by the disappearance of oxirane ring peak at 913 cm⁻¹, whereas X-ray diffraction shows its amorphous phase in the cured state. The thermogravimetric analysis of the resultant composites shows that the thermal stability slightly decreases (467–454 °C) with increasing the oligomer content from 5 to 25 wt %, whereas the mechanical parameters (Young's modulus, tensile strength, impact strength, and elongation at break) increase with increase in the oligomer content. DMA shows lower tanδ values for aliphatic amine-terminated oligomers for cured epoxy. Two-phase surface morphology is observed through scanning electron microscopy. Owing to their high mechanical and thermal properties, aromatic amides have observed to greatly influence the mechanical properties of cured epoxy, particularly its brittleness. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48404.     

Determining the mechanical properties of epoxy resin (DGEBA) composites by ultrasonic velocity measurement

In this study, the composites of diglycidyl ether of bisphenol A (DGEBA) epoxy resin that have been formed by mixing epoxy resin with allyl glycidyl ether (AGE) and 2,3‐epoxypropyl methacrylate [glycidyl methacrylate (GMA)] were prepared in weight % ratios of 90 : 10, 80 : 20, and 70 : 30. A computer controlled analyzer with 35 MHz and a digital oscilloscope with 60 MHz were used for measuring the velocities of ultrasonic wave. The measurement of ultrasonic velocity carried out by pulse echo method at frequencies of 2.25 and 3.5 MHz at room temperature. The values of acoustic impedance (Z), Poisson ratio (μ), and coefficients of elasticity (L, G, K, E) of composites were calculated by values of densities and velocities that obtained. Thus, the effect of modificating epoxy resin (DGEBA) by AGE and GMA on mechanical properties of DGEBA was investigated using the ultrasonic method. Atomic force microscopy has been used for determining the microstructure of composites. By the results obtained from the investigation, it have been established that the longitudinal and shear ultrasonic wave velocities, and the values of all the elasticity constants of DGEBA were increased by modification with AGE and GMA. Also the most suitable combination ratio for the compound of DGEBA : AGE and DGEBA : GMA has been found as 80 : 20. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013