Abstract Epoxy Research Articles

Curing Study of a Toughened Epoxy System Using the Dynamic Torsional Vibration Method

Epoxy resins are widely used as adhesives or as the matrix of high-performance composites and the monitoring for quality of their cure process is of great interest. In this paper, the cure kinetics of an epoxy/polyamide system was successfully studied using the dynamic torsional vibration method (DTVM) by measuring the change in mechanical properties (torque) during the cure. The experimental data were analyzed by the non-equilibrium thermodynamic fluctuation theory and the Avrami method. The results from dynamic mechanical thermal analysis (DMTA) reveal that the fully cured specimens of epoxy resin/polyamide exist in the rubbery plateau state at the applied cure temperature. With increasing cure temperature, the equilibrium torque drops, the gel time decreases and the cure reaction takes less time to complete. After the gel point, the same curing mechanism occurs at various cure temperatures. The effect of increasing hardener concentration on the rate of cross-linking at a given cure temperature was also examined. Excess polyamide increases the number of cross-linking points, and hence enlarges the Avrami exponent n.

Chain-extended epoxy-functionalised poly-(2-ethylhexylacrylate) as impact and adhesive modifier for epoxy resin

Epoxy resin is widely used for coatings, adhesives, casting, electrical insulation materials and other applications. However, unsolved problems still remain in its applications. The main problem is low toughness: cured epoxy resin is rather brittle with poor resistance to the propagation of cracks, derived from the internal stress generated by shrinkage in the cooling process from cure temperature to room temperature. The objective of this study was to improve the flexibility of diglycidyl ether of bisphenol-A based epoxy resin by using a liquid rubber. For this purpose, epoxy functionalised poly-(2-ethylhexylacrylate) (EFPEHA) and chain extended poly-(2-ethylhexylacrylate) (CEEFPEHA) based on the EFPEHA and Tris-2,4,6-(N,N-dimethyl amino methyl) phenol have been synthesised. The products were characterised by IR spectroscopy, non-aqueous titration, viscosity measurement and solubility characteristics. The developed CEEFPEHA was incorporated as a modifier into the epoxy matrix and its effect was studied by impact and adhesive strength measurements. Fractographic examinations under scanning electron microscope indicated the formation of rubber domains in the epoxy matrix.

Characterization in the Toughening Process of CTBN Modified Epoxy Resins Induced by Electron Beam Radiation

Epoxy resins are widely utilized as high performance thermosetting resins for many industrial applications but characterized by a relatively low toughness. Electron beam (EB) curing of polymer resins has a number of advantages over conventional thermal curing, such as shorter curing time, low energy consumption, low cure temperature, dimensional stability, reduced manufacturing cost. In the present work liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymers containing 8% acrylonitrile is added at different contents to improve the toughness of diglycidyl ether of bisphenol A (DGEBA) epoxy resins using triarylsulfonium hexafluoroanimonate as a photointiator. The EB irradiation was conducted 5 kGy to 250 kGy in nitrogen. The physics properties of CTBN modified epoxy resins were examined by determine gel content, DMA (dynamic mechanical analysis), UTM (Instron model 4443), SEM (scanning electron microscopy).

Preparation and mechanical behavior of modified epoxy resin with grafted silicon rubber

Epoxy resin (EP) was modified by grafted silicon rubbers (g-SRs) prepared by co-polymerization of methyl vinyl silicon rubber with vinyl acetate. The branched structure of the g-SRs has been identified by infrared spectrum. The mechanical properties of modified EP were examined and the related fracture surfaces were observed by a scanning electron microscope. The results indicated that the EPs have been reinforced and toughened obviously by the addition of g-SRs. The mechanical properties of modified EPs depended not only on synthesis processes of co-polymerization, but also on the amount of the g-SRs added. The best combination of tensile and impact strengths for the cured modified EPs have been reached by that modified with 15 phr g-SRs. The morphology of modified EP is remarkably different from that of the pure cured EP.

Zero-emission Process for Nd-Fe-B Melt-Spun Powder Used in Epoxy Resin Bonded Magnets.

Epoxy resin is generally used as a binder for consolidating Nd-Fe-B melt-spun powder into a specific shape, because the usage of this binder enables us to obtain a density higher than that of other polymers. Reports concerning methods of recycling melt-spun powder included in epoxy resin bonded magnets, however are sparse. We newly therefore developed a technique for recycling Nd-Fe-B melt-spun powder, using liquid-phase pyrolysis of cured epoxy in solvent, and prepared Nd-Fe-B bonded magnets using the recycled powder. This paper reports the new technique for recycling Nd-Fe-B melt-spun powder and evaluates both magnetic properties of the bonded magnets prepared from recycled melt-spun powder and characteristics of a small motor using the recycled magnets.

Epoxy resin particles, 2. An efficient synthetic method of epoxy resin particles in organic solvent by the aid of modified polyolefins as dispersant

Epoxy resin particles were efficiently prepared by addition of Bisphenol A diglycidyl ether to a solution of polyamine hardener in organic solvents containing polyolefin dispersants modified with maleic anhydride and maleimide. Aliphatic hydrocarbons and their mixtures with aromatic hydrocarbons were used as the reaction solvents. The size and size distribution of the particles could be controlled by modulating the difference in solubility parameter between the solvent and the polymer and by changing the reaction temperature. Smaller particles were formed when combined with more highly reactive amine hardeners. The particles prepared by this method showed a rough surface probably because of the polymer deposition on the finally formed particles in the final reprecipitation process. The present synthesis can afford an efficient method for manufacturing the epoxy resin particles in large scale.

Curing of epoxy resin contaminated with water

Epoxy resins used for reinforcement of bridges and buildings are explored in the light of both curing rates and mechanical properties when resins are contaminated with water in outdoor construction. The developed resin is composed of a conventional resin of bisphenol A diglycidyl ether and a hardener with a polyoxipropyldiamine base. Curing rates were obtained by time variation of the near infrared absorbance of amine groups in the hardener at various water contents. They obeyed the second-order reaction law with respect to the hardener, of which the activation energy was 70 kJ mol−1. Water increased the reaction rate. Mechanical properties such as ultimate tensile strength, adhesive shear stress, and flexural strength were measured at various water contents for the developed epoxy resin and the commercially available low-temperature epoxy resin. The developed cured resin shows not only higher mechanical strengths but also much less deterioration by water than the conventional cured resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 214–220, 2001

Strain rate and temperature dependence of shear properties of epoxy resin with various molecular weight between cross-linkings

Epoxy resins with various molecular weights between cross-linkings were prepared. In order to examine the strain rate and temperature dependence of the shear yield strength and the shear strength, test specimens were subjected to shear deformation at various strain rates and temperatures. The shear yield strength and the shear strength increased almost linearly as the logarithm of the strain rate increased. The strain rate-temperature superposition held for these shear properties. In particular, an experimental equation of the strain rate-temperature superposition for the shear yield strength was found. The shift factor to obtain a master curve was given with the temperature dependence of an Arrhenius type. Furthermore, the strain rate-temperature-molecular weight between cross-linkings superposition held for the shear properties.

A study of epoxy resin-acrylated polyurethane semi-interpenetrating polymer networks

Epoxy resin–acrylated polyurethane semi-interpenetrating polymer networks (semi-IPNs) were synthesized containing various ratios of the diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin and an acrylated aliphatic urethane oligomer. The synthesis was carried out in the presence of a mixture of triarylsulfonium hexafluoroantimonate salts as a dual photoinitiator that initiates both the cationic polymerization of the epoxy resin and the free-radical polymerization of the acrylated urethane oligomer simultaneously, upon irradiation with ultraviolet light. The simultaneous photopolymerization, followed by isothermal differential scanning calorimetry measurements, gave rise to simultaneous semi-interpenetrating polymer networks (semi-SINs). During polymerization, partial inhibition of the cationic polymerization was noticed. This was investigated by determination of the gel content and the infrared spectroscopy of the soluble fraction, after extraction of the synthesized polymer films in a Soxhlet apparatus, and by determination of the network density of investigated systems with thermal mechanical analysis. The compatibility of the components in the semi-IPNs was investigated by dynamic mechanical thermal analysis. It was found that glass transition temperatures are shifted inwardly, which indicated that the epoxy resin–acrylated polyurethane semi-IPNs were compatible. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:111–119, 1998

Development of methods for the determination of bisphenol A in food simulants

Epoxy resins based on bisphenol A (BPA) have been used as components of food and beverage can coatings for more than 50 years. The recent interest in analysis of extractable BPA from these resins has made it necessary to develop validated methods with performance characteristics necessary for successful analyses in regulatory food simulants. The present study was conducted to develop analytical methodology so that suitably equipped laboratories could confidently perform these analyses. Two methods were developed and validated through round-robin sampling. A historical treatment of the method development challenges, round-robin studies, and results are described here.

Freeze‐thaw stability of epoxy resin emulsions

Epoxy resin emulsions are used in water‐based coatings for surface protection of concrete and metal. An unfortunate drawback for most emulsions is their poor freeze‐thaw stability. Epoxy emulsions are indeed unstable below 0°C, ‐5°C or ‐10°C, depending on the type of resin. In this study, other factors capable of influencing the freeze‐thaw behaviour were investigated: e.g. solids content, amount and type of emulsifiers, solvents, protective colloids. Discusses methods for testing the quality of thawed emulsions as well as the physics involved in their destabilization. Freeze‐thaw performance can be improved by different means but mostly not without sacrificing resistance properties of the coating. Therefore, avoiding temperatures below 0°C is still the best advice.

Image contrast in sections of epoxy resin-embedded biological material: maintenance of a proper anhydride-epoxy ratio during tissue impregnation.

Epoxy resins are mixtures of several components formulated in exact proportions to assure proper polymerization. It is necessary that this composition be maintained throughout the tissue being infiltrated to avoid embedding artifacts. Unfortunately, the separate resin components will not penetrate the tissue at the same rate unless they all have the same viscosity and molecular size. Failure to meet these criteria will result in component separation during tissue infiltration and may result in severe embedding defects. This and several ancillary problems such as low tissue contrast, damage to diamond knives, and poor postsection staining are explored in this brief discussion.

Synthesis and modification of trifunctional epoxy resin with amine terminated polydimethyl siloxanes for semiconductor encapsulation application

Epoxy resins based on the triglycidyl ether of tris(hydroxyphenyl)methane (TETM) possess a very high heat distortion temperature and superior thermal oxidative stability over other types of epoxy resins. The high performance trifunctional epoxy resin (TETM) was synthesized by the condensation of a hydroxybenzaldehyde with phenol followed by epoxidation with a halohydrin. The structure of the synthesized TETM was confirmed by infrared (IR), mass spectra (MS), and nuclear magnetic resonance (NMR) spectroscopy. Amine terminated polydimethylsiloxanes (ATPDMS) were used to reduce the stress of trifunctional epoxy resin cured with phenolic novolac resin for electronic encapsulation applications. The dispersed silicone rubbers effectively reduce the stress of cured epoxy resins by reducing the coefficient of thermal expansion (CTE) and flexural modulus, while the glass transition temperature (Tg) is depressed by only a small amount.

Effect of physico-chemical degradation of epoxy resin on partial discharge behavior

Epoxy resin coated electrode specimens were subjected to partial discharges (PD) in air at twice the discharge inception voltage for durations ranging to 5000 h. The PD behavior was characterized by a transition from initially large pulse type discharges (- 200 to 300 pC) to either small pulse (- 1 pC), pseudoglow, glow discharge, or a combination thereof. Although these different forms of discharges were capable of occurring simultaneously, each type tended to prevail over certain periods of the exposure time. The physical and chemical nature of the degradation products formed on the surfaces of the epoxy resin also varied accordingly, indicating that each discrete form of discharge exerts its particular effect on the overall degradation process. Droplet formation on the central portion of the epoxy surfaces typified the large pulse discharge regime, whilst crystals formed within the transition region over which small discharge pulses (- 1 pC) were usually superimposed upon a continuous glow (pseudoglow and true glow regime). The droplets were identified as being partially comprised of a mixture of acids, mainly formic, glycolic, glyoxalic and nitric acids, whilst the crystals consisted of hydrated oxalic acid. Since similar results were obtained with discharges in both air and nitrogen, the effects of gas phase reactions on the PD activity would appear to be only of secondary importance compared to the reactions taking place on the surface of the epoxy resin. Since the test cell design did not allow any pressure variation within the discharge gap, the observed discharge transition cannot be attributed to pressure changes such as may take place within occluded cavities. Nevertheless, the transition observed here is similar to what is found with actual stator bar type insulation, suggesting that pronounced chemical and physical modifications on the surface of the physical cavity inclusions in the bar insulation may account for the characteristic PD behavior observed as a function of time.

Epoxy Resin as Inhibitor for Nitramine Containing Composite Modified Double Base (CMDB) Propellants

Abstract Epoxy resin was investigated as inhibitor for nitramine containing Composite modified double base (CMDB) propellants. Inhibited CMDB propellants were statically (rocket firing under static condition) evaluated at ambient, hot (+60°C) and cold (-30°C) temperatures. Incompatibility problem between epoxy resin and CMDB propellants were overcome by use of barrier layers of fast-setting isophthalic acid based polyester resin (Acrolite-471). Storage ageing trials at ambient and hot (+60°C) temperatures were also studied for propellant-inhibitor bond failure at above mentioned temperatures.

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

AbstractEpoxy 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 Tg 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 Tg 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.

The performance of specialized collections of bisphenol A epoxy resin system components in the evaluation of workers in an occupational health clinic population.

Epoxy resin of the bisphenol A type (ERBA) is a common cause of occupational contact dermatitis. 167 patients with a history of potential exposure were patch tested with epoxy resin (molecular weight 340) (ERBAM) 1% in pet. and with a number of other ingredients in ERBA systems. 18% of the test patients exhibited a positive response to ERBAM. Phenyl glycidyl ether was the most frequent system component other than ERBAM itself to elicit a positive response (6.1%). Approximately 80% of those tested were unresponsive to ERBAM or any other of the system components, while 20% exhibited a positive response to one or more of the test materials. Only a small % were positive to system materials, but negative to ERBAM, in keeping with previous studies. The study suggests that there is a marginal benefit to testing with other than ERBAM 1%, except in instances where there is known exposure to another ERBA system ingredient, in which event, the patient should also be tested with the specific material to which they have been exposed if there is no response to ERBAM.

Alternatives to traditional epoxy embedding “kits”: Novel choices

Epoxy resin embedding “kits” invariably are offered as one epoxy resin coupled with the hardners dodecynyl succinic anhydride (DDSA), nadic methyl anhydride (NMA) and the amine catalyst 2,4,6-Tri(dimethylaminomethyl)phenol (DMP-30). This well-known mixture has been used widely for many years, perhaps in part because it is offered in the form of a convenient kit. Microscopists should be aware that packaged kits, eventhough they produce successful results, possess a never-changing high viscous character that could compromise optimum infiltration or damage delicate specimens. Past studies have shown clearly that the kit compnents DDSA and DMP-30 are particularly viscous compounds. Replacing DDSA with the less viscous nonenyl succinic anhydride (NSA), and substituting either dimethylaminoethanol (DMAE) or benzyldimethylamine (BDMA) as the catalyst of choice in place of DMP-30 will significantly reduce the viscosity of the overall mixture while producing easily manageable media that maintain fluidity longer, insure optimum infiltration, and ultimately produce results equal to those obtained with traditional kits.

Speciality epoxy resins derived from heterocyclic compounds

Epoxy resins are compounds which contain in their molecule more than one 1,2 epoxy group capable of undergoing polyreactions, referred to as curing reactions. The presence of epoxy groups may be either internal, terminal or on cyclic structures. Polyreactions take place at varying temperatures from low room temperature cure to high temperature cure systems upon addition of curing agents such as amines, amides or carboxylic acid anhydrides. The uncured resins which range from low viscosity liquids to high melting solids, soluble in organic solvents, become insoluble, infusible hard materials on curing due to crosslinked structure of the cured products.

Preparation and Properties of Epoxy Resins Containing Quinazolone Rings

Abstract Epoxy resins containing quinazolone rings were synthesized and characterized. Epoxy resins were made by reacting bisquinazolone phenol or bisquinazoline with epichlorohydrin or the diglycidyl ether of Bisphenol A. These resins were analyzed by DSC, GPC, IR, and NMR. The electrical and mechanical properties of the cured resins were evaluated. They have glass transition temperature above 200°C and excellent thermal stability, and Tg increases in the order of o-, m-, p-substituted phenol groups.