Comparison of microwave and thermal cure of epoxy–anhydride resins: Mechanical properties and dynamic characteristics

The objective of this work was to compare the mechanical properties of epoxy resins cured by thermal heating and microwave heating. Epoxy–anhydride (100:80) resins were cured in a domestic microwave oven and in a thermal oven. The hardening agents included methyl tetrahydrophthalic anhydride and methyl hexahydrophthalic anhydride. Three types of accelerators were employed. Thermal curing was performed at 150°C for 20 and 14 min for resins containing 1 and 4% accelerator, respectively. Microwave curing was carried out at a low power (207 or 276 W) for 10, 14, and 20 min. All cured resins were investigated with respect to their tensile properties, notched Izod impact resistance, and flexural properties (three‐point bending) according to ASTM standards. The tan δ and activation energy values were investigated with dynamic mechanical thermal analysis, and the extent of conversion was determined with differential scanning calorimetry. The differences in the mechanical properties of the thermally cured and microwave‐cured samples depended on the resin formulation and properties. Equivalent or better mechanical properties were obtained by microwave curing, in comparison with those obtained by thermal curing. Microwave curing also provided a shorter cure time and an equivalent degree of conversion. The glass‐transition temperatures (tan δ) of the thermally and microwave‐cured resins were comparable, and their activation energies were in the range of 327–521 kJ/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1442–1461, 2005     

Investigation of cure in epoxy acrylate resins using rheological and dielectric measurements

Dielectric and rheological measurements are reported for the cure in a series of mixtures of an epoxy-acrylate with n-butyl methacrylate. The level of the initiator and properties of the epoxy acrylate and n-butyl methacrylate influence the cure characteristics and morphology of the film formed. Analysis of the rheological data indicates that during the curing process, microphase separation occurs within the mixture. The changes in the dielectric relaxation behavior with composition of the completely cured material is also consistent with microphase separation occurring in these resins while they are cured.     

Polyurethane acrylate/epoxy–amine acrylate hybrid polymer networks

New classes of hybrid polymer networks (HPNs), having variable polyurethane acrylate (PUA) and epoxy–amine acrylate (EAA) compositions, were prepared using initially miscible systems in methyl methacrylate (MMA). The initial systems were based on PUA prepolymer and EAA monomer solutions in MMA. HPNs were a result of epoxy–amine and radical polymerization competition. Phase separation occurred during the course of HPN formation. Mechanical dynamic analysis of the prepared HPNs showed good affinity between the PUA and PMMA phases and lower affinity between the EAA and PMMA phases. Mechanical property evolution and transmission electronic microscopy showed that, for all the composition ranges used in this study (PUA/EAA/PMMA 15/45/40–45/15/40 wt %), the PUA‐rich phase was the continuous phase. EAA‐rich phases, 20–50 nm, in the PUA‐rich matrix were obtained for HPNs containing up to 30 wt % EAA. For higher EAA concentration (45 wt %), 2 μm EAA‐rich phases were obtained in the PUA‐rich matrix. A substructure was also observed in each phase. PUA/EAA copolymers were prepared and used successfully for the compatibilization of the different phases of the HPNs. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2711–2717, 2000     

Characterization of imidazole-cured epoxy–phenol resins

The physical and chemical properties of the diglycidyl ether of bisphenol A (DGEBA) cured with different concentrations of bisphenol A (BPA) and 2-ethyl-4-methylimidazole (EMI-24) were examined using Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical and dielectric analyses, and solvent extraction studies. The effects of the phenol-epoxide and the secondary hydroxyl (R-OH)-epoxide reactions on the network formation process were analyzed using a recursive modeling technique to obtain expressions for the weight-averaged molecular weight, the weight fraction solubles, and the gel point as a function of the extent of cure and the epoxide-phenol reactant ratio. The sol fraction and the gel point predictions from recursive modeling studies of the network formation process agreed with the results obtained from the extraction studies. The results from the network modeling studies were also related to the thermal and rheological properties of the resin during cure.     

Film performance and UV curing of epoxy acrylate resins

Radiation curing technology has encountered increased applications in recent years. The Asian geographical vicinity has and will be an expensive territory for years to succeed. There has been heightened governmental obligation to progress towards diminishing solvent practice to preserve the environment.

In the present study, the novolac as well as bisphenol-A based epoxy acrylates (or vinyl ester resins, VERs) were synthesised and extent of reaction and polymerisation was studied. It was observed that the above prepared oligomer when used with monofunctional/polyfunctional diluents can be cured in seconds time. Evaluation of film performance was also carried out.     

Water‐borne melamine–formaldehyde‐cured epoxy–acrylate corrosion resistant coatings

Organic protective coatings are widely used in corrosion control. However, environmental standards establish that the volatile organic compounds either must be removed or controlled at the lowest possible levels. The carcinogenic environmental impact of volatile organic compounds has led to the substitution of solvent‐borne coatings by water‐borne coating systems. Among recently developed water‐borne coatings, epoxy‐ and acrylic‐based coatings have a special significance over other reported water‐borne systems. Keeping in mind, the importance of water‐borne coatings in the present work, we report the synthesis of water‐borne epoxy–acrylate (EpAc) and melamine–formaldehyde (MF) as well as formulation of their anticorrosive coatings. The structural elucidation of MF‐cured EpAc was carried out by FTIR, ¹H NMR, and ¹³C NMR spectroscopic techniques. The coatings of EpAc‐MF were applied on mild steel strips and were evaluated for physicochemical, physicomechanical characterization, and the anticorrosive performance under different environmental conditions. The present coating system EpAc coatings exhibited superior performance as compared to the reported water‐borne epoxy–acrylatecoatings. The presence of melamine–formaldehyde in the resin increases the scratch hardness, impact resistance, alkali resistance, and thermal stability of these coatings. EpAc‐MF‐1 was found to cure at ambient temperature and exhibit good physicomechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dynamic mechanical properties of epoxy–rubber polyblends

The dynamic mechanical properties of the epoxy resin of the diglycidyl ether of bisphenol A cured with varying amounts of a carboxyl-terminated butadiene–acrylonitrile copolymer were determined. Isochronal measurements were made between ?90° to 170°C for eight compositions. Mechanical relaxations indicate the degree of interaction and the state of mixing of the two-phase system. Phase reversal occurs at a volume fraction of 0.5, where an intermediate compound is formed. In the low concentration range of the elastomeric phase, the impact strength improvement correlates well with an increase in the energy absorption of the relaxation. The known morphology of the system at this composition range allowed testing of various phenomenological mechanics models proposed to calculate the tensile properties of composite systems.     

Structure–properties relations of thermally cured epoxy–lignin polyblends

A bisphenol A based epoxy adhesive (EP) was modified by polyblending with Kraft Lignin (L). A systematic investigation of the thermally cured EP-L polyblends with up to 40% by weight L was undertaken. Adhesive shear tests, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and solid-state CP-MAS NMR spectroscopy were performed to establish the effect of L on the mechanical properties of the polyblends and on the morphology of these crosslinked structures. The possibility of an enhanced degree of bonding between L and the EP network is discussed. This bonding can arise from a chemical reaction between L and some unreacted amine groups present in the hardener.     

Epoxy resins. I. The stability of the epoxy–trimethoxyboroxine system

The useful life of a material depends on its environmental exposure. The diglycidyl ether of bisphenol A (DGEBA) cured with trimethoxyboroxine (TMB) was evaluated under various aging conditions. For isothermal aging, the main factor controlling weight loss appeared to be related to the diffusion of the degradation products (E_act = 22.1 kcal/mole). Chemical decomposition kinetic parameters were obtained using vacuum thermogravimetric analysis (TGA) on powder samples. The thermal decomposition activation energy and the reaction order of cured DGEBA were 37.5 kcal/mole and 1.05, respectively. The hydrolytic aging of this material was also kinetically analyzed, and it was concluded that the weight change was controlled by both water diffusion into the sample and diffusion of hydrolysis products from the sample. During hydrolytic aging below the glass transition temperature, the specimens gained weight up to 0.05 g based on 1-g unaged cured resin and then leveled off. At higher temperatures, the specimens initially gained weight and then began to lose weight, reaching a constant weight gain. The activation energies for water diffusion into the cured resin are 19.5 kcal/mole at temperatures above T_g and 21.5 kcal/mole at temperatures below T_g. The main hydrolysis product was boric acid from reaction of the boroxine ring with water. The time-temperature superposition principle was used for the weight loss study on isothermal and isothermal hydrolytic aging. The scale factor in this approach was found to be the ratio of the diffusion coefficient at the temperature of interest to that at a reference temperature.     

Effects of UV curable urethane acrylate resins treatments on the physical properties of medium‐ and small‐diameter softwoods

This study analyzed the effects of ultraviolet curable urethane acrylate resin (UV resin) treatments on surface homogeneity, dimensional stability, and change in colors of medium‐ and small‐ diameter softwoods produced in Taiwan. The UV resins were formulated with urethane acrylate oligomer/methyl methacrylate (MMA) monomer by the weight ratio of 50/50, 60/40, 70/30, 80/20, and 90/10, and 3% of photoinitiator (benzil dimethyl ketal) by the total weight of UV resins was added, respectively. Four kinds of softwoods, including Taiwanina, China fir, Taiwan incense cedar and Japanese fir with a diameter of 10–15 cm were obtained from Hui‐Sun Forest Station, Taiwan. Results show that the oligomer derived from 2‐hydroxyethyl methacrylate (2‐HEMA) and polymeric toluene diisocyanate (PTDI) by the molar ratio of NCO/OH = 1.0 could be readily synthesized and the prepared UV resin were also easily applied to the woods at room temperature and normal pressure. The surface hardness and moisture excluding efficiency (MEE) of woods were markedly enhanced and correlated with the increased in oligomer content of the UV resins as well as the homogeneity of softwood surfaces were also improved. According to the antiswelling efficiency (ASE), the increased in dimensional stability of woods were achieved; especially for the lower specific gravity China fir had the greatest improved efficiency of 60.68% at oligomer/MMA ratio of 80/20. In addition, a massive, colorful, and warm feeling in sense of sight on UV resin‐treated wood, which would appeal to most people, was also obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Reversible isomerization and cure monitoring of epoxy azobenzene resins

The photoresponsive behavior of the glycidyloxyazobenzene (GOAB) monomer, synthesized using an improved method, is examined by UV/Vis spectroscopy. The monomer is cured with diethylenetriamine (DETA), forming a new epoxy resin. Proton NMR spectroscopy is used to monitor the completion of the curing reactions. Kinetics for reversible trans and cis isomerization in the cured system and also in the epoxy monomer are identified by UV/Vis spectroscopy during in situ irradiation with appropriate wavelengths (290–320 nm for UV and 400–500 nm for visible). The rates of recovery of the monomer from cis to trans forms are also obtained by heating and storing in the dark. Furthermore, the reactivity of the monofunctional GOAB monomer with a common amine, DETA, as a curing agent, is investigated using isothermal and dynamic heating scans in a DSC pan and by simultaneously monitoring the near‐FTIR spectra. The modified epoxy azobenzene proved to be reactive enough with DETA to form a network that can sustain temperatures of up to 200°C. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40770.     

Synthesis and characterization of epoxy‐acrylate composite latex

A waterborne epoxy‐acrylate composite latex was synthesized. The effects of the concentration of the initiator, surfactant, and epoxy resin on the particle size, molecular weight, and grafting ratios of the composite latex were investigated. The increase of the concentration of the initiator and epoxy resin led to the decrease of the weight‐average molecular weight. The graft ratios increased with an increase in the initiator level and a decrease in the epoxy resin concentration whereas the variation of the concentration of the surfactant did not have much influence on the graft ratios. The increase in the initiator level caused the aggrandizement of the particle size, and the increase of the concentration of the surfactant and epoxy resin caused a decrease in the latex particle size. Fourier transform IR spectroscopy with attenuated total reflectance indicated that the epoxy resin molecules were enriched in the mold‐facing surface in the film from the composite latex. The differential scanning calorimetry analysis, dynamic mechanical analysis, and Instron test showed that the polymer films cast by the composite latex had lower tensile strength and glass transition than those by the blend latex. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1736–1743, 2002     

Time–temperature–transformation cure diagrams of phenol–formaldehyde and lignin–phenol–formaldehyde novolac resins

In this study, the time–temperature– transformation (TTT) cure diagrams of the curing processes of several novolac resins were determined. Each diagram corresponded to a mixture of commercial phenol–formaldehyde novolac, lignin–phenol–formaldehyde novolac, and methylolated lignin–phenol–formaldehyde novolac resins with hexamethylenetetramine as a curing agent. Thermomechanical analysis and differential scanning calorimetry techniques were applied to study the resin gelation and the kinetics of the curing process to obtain the isoconversional curves. The temperature at which the material gelled and vitrified [the glass‐transition temperature at the gel point (_gelT_g)], the glass‐transition temperature of the uncured material (without crosslinking; T_g0), and the glass‐transition temperature with full crosslinking were also obtained. On the basis of the measured of conversion degree at gelation, the approximate glass‐transition temperature/conversion relationship, and the thermokinetic results of the curing process of the resins, TTT cure diagrams of the novolac samples were constructed. The TTT diagrams showed that the lignin–novolac and methylolated lignin–novolac resins presented lower T_g0 and _gelT_g values than the commercial resin. The TTT diagram is a suitable tool for understanding novolac resin behavior during the isothermal curing process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal and dielectric properties of epoxy resins

Epoxy resins were prepared using various molar ratios of epichlorohydrin and bisphenol-A and then cured with four different hardeners: diaminodiphenyl methane (DADPM), dithioterephthalic acid (DTTPH), dimethylamino propylamine (DMAPA) and diethylene triamine (DT). The thermal behaviour of these epoxy resins was studied. From the energy of activation data it was observed that DADPM gives the highest thermal stability of all these curing agents. Dielectric constant measurements of uncured resins were made at 30°C and at a frequency of 2.5 × 10³ Hz. The higher activation energies of the resins are related to the polarity of the hydroxyl moiety in the epoxy resins.     

Evaluation of mechanical properties of epoxy–guar gum composites

Guar gum (GG) and hydroxypropyl guar gum (HPG) are widely used in a variety of applications ranging from foods, pharmaceutics to mining and explosives. However, there have been very few studies conducted investigating the use of these materials as fillers in polymer composites. GG and HPG were incorporated in an epoxy matrix and the mechanical properties of the resultant composites were determined. The tensile strength, flexural strength, and impact strength of the composites indicate that they provide reinforcement to the composites upto 5–7.5 phr after which there is a rapid decrease in the respective properties. HPG with higher propoxy content was found to provide greater reinforcement due to its increased hydrophobic nature leading to greater polymer–filler interaction. The nature of the filler required that the water absorption and related tests be carried out. The composites showed increased water absorption and also weight loss on exposure to acid and alkali environments, with HPGs showing greater variations when compared with GG, making the composites susceptible to moisture. The study shows that these fillers make an inexpensive, eco‐friendly, and renewable addition to conventional organic and inorganic fillers where the composites do not come into immediate contact with water. POLYM. ENG. SCI., 48:124–132, 2008. © 2007 Society of Plastics Engineers     

Master curve and time–temperature–transformation cure diagram of lignin–phenolic and phenolic resol resins

The aim of this work is to generate both a master curve of resol resins based on the time–temperature superposition principle and their TTT cure diagrams. The samples used for this purpose were lignin–phenolic and phenol–formaldehyde resol resins. A TMA technique was employed to study the gelation of resol resins. In addition, a DSC technique was employed to determine the kinetic parameters through the Ozawa method, which allowed us to obtain isoconversional curves from the data fit to the Arrhenius expression. Establishing the relationship between the glass‐transition temperature and curing degree allowed the determination of the vitrification lines of the resol resins. Thus, using the experimental data obtained by TMA and DSC, we generated a TTT cure diagram for each of resins studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3362–3369, 2007     

New epoxy resins. I. The stability of epoxy–trialkoxyboroxines triaryloxyboroxine system

A polymer with high aromaticity and/or cyclic ring structures chain backbone usually has high heat, thermal, and flame resistance. Two diglycidyl ethers of bisphenols were prepared from 4,4′ isopropylidenediphenol (DGEBA) and 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) for evaluation. Four boroxines—trimethoxyboroxine (TMB), triethoxyboroxine (TEB), triisopropoxyboroxine (TIPB) and triphenoxyboroxine (TPB)—were used as the curing agents. DGEBA and DGEBF cured with various boroxines indicate that the trend for their respective glass transition temperature (T_g's), degradation temperatures (T_d's), and gel fractions are TMB-cured epoxy ≈ TEB-cured epoxy < TIPB cured epoxy < TPB cured epoxy. The DGEBF system usually has a higher T_g, T_d, gel fraction, oxygen index (OI), and char yield than the related DGEBA system. DGEBF/DGEBA (80/20 mol ratio) shows a synergistic effect in regard to char formation. This effect exists not only in the copolymer system but also in blended homopolymers of the separately cured resins. A modified mechanism for the polymerization of phenyl glycidyl ether (PGE) with TMB has been proposed.     

Antibacterial materials: structure–bioactivity relationship of epoxy–amine resins containing quaternary ammonium compounds covalently attached

Bifunctional aminoalkyldimethylpropylammonium salts (N‐(3‐aminopropyl)‐N,N‐dimethylpentylammonium chloride, N‐(3‐aminopropyl)‐N,N‐dimethyloctylammonium chloride, N‐(3‐aminopropyl)‐N,N‐dimethyldecylammonium chloride, N‐(3‐aminopropyl)‐N,N‐dimethyldodecylammonium chloride) are synthesized and their structure‐dependent antibacterial effect against Gram‐negative Escherichia coli and Gram‐positive Lactococcus lactis is investigated. To this end, resins prepared from bisphenol A diglycidyl ether (2,2‐bis[4‐(glycidyloxy)phenyl]propane) and diethylenetriamine (2,2′‐diaminodiethylamine) as matrix and the bifunctional aminoalkyldimethylpropylammonium salts in a ratio of 6 mol% compared to epoxy components are used. A dependence of antibacterial effect on alkyl chain length of the quaternary ammonium compounds is observed for both species. Furthermore, resins with N‐(3‐aminopropyl)‐N,N‐dimethyldecylammonium chloride in varying concentrations up to 16 mol% for both organisms show a concentration‐dependent antibacterial effect of the quaternary ammonium salt. The antibacterial materials are characterized by differential scanning calorimetry, infrared spectroscopy and rheological studies. © 2013 Society of Chemical Industry