One‐component epoxy resin with imine as water‐initiated latent hardener: Improvement of the mechanical and adhesive properties by the addition of methacrylate copolymer

The effect of addition of methacrylate polymer into a one‐component epoxy resin, containing Epikote 828 and diimine as a water‐initiated hardener, was examined. Although the cured epoxy resin in the presence of methyl methacrylate–butyl acrylate (MMA–BA) copolymer was very brittle, the resin containing MMA–BA–[γ‐(methacryloxy)propyl]trimethoxysilane (TMSMA) copolymer showed good mechanical and adhesive properties. The adhesive strength of the cured epoxy resin containing MMA–BA–TMSMA copolymer was much higher than that without its polymer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1943–1949, 2005     

Synthesis,thermal properties,and flame retardance of phosphorus‐containing epoxy‐silica hybrid resins

A novel epoxy resin modifier, phosphorus‐containing epoxide siloxane (DPS) with cyclic phosphorus groups in the Si O network, was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with polyhedral‐oligomeric siloxanes, which was synthesized by the sol–gel reaction of 3‐glycidoxypropyltrimethoxysilane. DPS was confirmed by Fourier transform infrared and ²⁹Si NMR measurement, and then was employed to modify epoxy resin at various ratios, with 4,4‐diaminodiphenyl‐methane as a curing agent. In order to make a comparison, DOPO‐containing epoxy resins were also cured under the same conditions. The resulting organic–inorganic hybrid epoxy resins modified with DPS exhibited a high glass transition temperature (T_g), a good thermal stability, and a high limited oxygen index. In addition, the tensile strength of cured products was also rather desirable. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

One‐pot curing system of epoxy resin imines initiated with water

The curing and adhesive properties of one‐component epoxy resins containing Epikote 828 and diimines, derived from N,N′‐di(1‐ethylpropylidene)‐m‐xylylenediamine, N,N′‐di(1‐ethylpropylidene)‐1,3‐diaminomethylcyclohexane (2), and N,N′‐di(1,3‐dimethylbutylidene)‐m‐xylylenediamine, which were used as water‐initiated hardeners, were examined. Diethyl ketone‐based imines with a lower electron density on the C?N carbon were efficiently hydrolyzed and showed curing activity. 2, a novel diethyl ketone‐based diimine, served as an efficient latent hardener of the epoxy resin. A paste of the epoxy resin with 2 showed good storage stability at room temperature and good adhesive properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 878–882, 2003     

Ultraviolet/heat dual‐curable film adhesives with pendant‐acryloyl‐functional‐group‐modified epoxy resin

To facilitate the fabrication of a reliable semiconductor package, the UV/heat dual curing of film adhesives was investigated. The curing system of the epoxy resin affected the film adhesive properties. As the UV/heat dual‐curable epoxy resin, a modified o‐cresol novolak epoxy resin, in which half of the glycidyl groups were substituted by acryloyl groups (OCN‐AE), was applied to the film adhesive. The formulated film adhesive contained acrylic copolymer, OCN‐AE, phenolic aralkyl resin as a heat‐curing agent of the glycidyl groups, and 1‐hydroxycyclohexyl phenyl ketone as a photoinitiator of the acryloyl groups. The formulated reference film adhesive contained unmodified o‐cresol novolak epoxy resin (OCN‐E) in place of OCN‐AE. Formulated film adhesives containing a mixture of OCN‐E and o‐cresol novolak epoxy acrylate were also used as references. The morphology and the film adhesive properties were investigated. In these investigations, the film adhesive of OCN‐AE showed better adhesive properties, lower modulus, and a better stress‐relaxation ability than the referenced adhesives. As a result, a reliable film adhesive for semiconductor packages was successfully developed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of aliphatic amine epoxy hardener on the adhesive properties of blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with epoxy resin

The adhesive properties have been investigated in blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with diglycidyl ether of bisphenol A and three different aliphatic amine epoxy hardener. The adhesives properties are evaluated in steel alloy substrate using single‐lap shear test. The copolymers are initially miscible in the stoichiometric blends of epoxy resin and hardener at room temperature. Phase separation is noted in the course of the polymerization reaction. Different morphologies are obtained according to the amine epoxy hardener. The most effective adhesive for steel–steel joints in single‐lap shear test is the blends using 1‐(2‐aminoethyl)piperazine (AEP) as hardener. This system shows the biggest lap shear strength. However, the modified adhesives show a reduction in the mechanical resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis,characterization, and curing of {2,6–bis‐[2‐(bis‐oxiranylmethyl‐amino)‐methylbenzyl]‐phenyl}‐bis‐oxiranylmethylamine (BPBOMA)

The curing behavior of epoxy resin prepared by reacting epichlorohydrin with amine functional aniline acetaldehyde condensate (AFAAC) was investigated using AFAAC as a curing agent. The epoxy resin, {2,6‐bis‐[2‐(bis‐oxiranylmethyl‐amino)‐methylbenzyl]‐phenyl}‐bis‐oxiranylmethylamine (BPBOMA), was characterized by FTIR and ¹H‐NMR spectroscopy, viscosity measurement, and determination of epoxy content. Analysis of the curing reaction was followed by differential scanning calorimetry (DSC) analysis. To investigate the curing kinetic with AFAAC, dynamic DSC scans were made at heating rates of 5, 10, 15, and 20°C/min. The activation energy and frequency factor of the AFAAC formulation were evaluated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3168–3174, 2006     

Bonding properties of epoxy resins containing two mesogenic groups

Liquid‐crystalline epoxy resins, with introduced aliphatic chains between two mesogenic groups, were synthesized and their adhesive bonding properties were compared to those of the bisphenol‐A–type epoxy resin and the liquid‐crystalline epoxy resin, previously reported. The bonding strength of the former resin system was higher than that of the two later systems. We suggest that the high bonding strength of the twin mesogenic epoxy resins, cured with an aromatic amine, was attributable to the large plastic deformation of the adhesive layer in the fracturing process. We also investigated the effects of the aliphatic chain length in the twin mesogenic epoxy resin on their dynamic mechanical and bonding properties. The bonding strength of the cured twin mesogenic epoxy resins increased with an increase in the aliphatic chain length. We suggest that the high bonding strength of the system introduced by the long aliphatic chain was attributable to the large plastic deformation of the adhesive layer because of the higher network mobility. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3721–3729, 2004     

Preparation and characterization of modified‐clay‐reinforced and toughened epoxy‐resin nanocomposites

Epoxy–clay nanocomposites were prepared by the dispersion of an organically modified layered clay in an epoxy resin (diglycidyl ether of bisphenol A) and curing in the presence of methyl tetrahydro acid anhydride at 80–160°C. The nanometer‐scale dispersion of layered clay within the crosslinked epoxy‐resin matrix was confirmed by X‐ray diffraction and transmission electron microscopy, and the basal spacing of the silicate layer was greater than 100–150 Å. Experiments indicated that the hydroxyethyl groups of the alkyl ammonium ions, which were located in the galleries of organically modified clay, participated in the curing reaction and were directly linked to the epoxy‐resin matrix network. Experimental results showed that the properties of epoxy were improved, evidently because of the loading of organically modified clay. The impact strength and tensile strength of the nanocomposites increased by 87.8 and 20.9%, respectively, when 3 wt % organic clay was loaded, and this demonstrated that the composites were toughened and strengthened. The thermal‐decomposition and heat‐distortion temperatures were heightened in comparison with those of pure epoxy resin, and so were the dynamic mechanical properties, including the storage modulus and glass‐transition temperature. Moreover, experiments showed that most properties of the composites were ameliorated with low clay contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2649–2652, 2004     

Solid freeform fabrication of epoxidized soybean oil/epoxy composites with di‐, tri‐, and polyethylene amine curing agents

Soybean oil/epoxy‐based composites are prepared by solid freeform fabrication (SFF) methods. SFF methods built materials by the repetitive addition of thin layers. The mixture of epoxidized soybean oil and epoxy resin is modified with di‐, tri‐, or polyethylene amine gelling agent to solidify the materials until curing occurs. The high strength and stiffness composites are formed through fiber reinforcement. E‐glass, carbon, and mineral fibers are used in the formulations. The type of fiber affects the properties of the composites. It was found that a combination of two types of fibers could be used to achieve higher strength and stiffness parts than can be obtained from a single fiber type. In addition, the effects of curing temperature, curing time, and fiber concentration on mechanical properties of composites are studied and reported. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 356–363, 2004     

Adhesive Properties of Epoxy Resin with Chromic Hardener

Cohesive and adhesive properties have been compared of epoxy resins crosslinked either with chromic‐based hardener or with conventional amine‐type hardener. Higher cohesive parameters, such as yield strength, Young's modulus and impact resistance were observed for the material cured with chromic hardener. The adhesive strength of metal‐metal joints (steel‐aluminium) has been also found to be higher for chromic hardener containing epoxy compared to conventional curing systems. The time dependencies of adhesive strength after thermal treatment at 140°C of the joints showed a higher thermal resistance of the epoxy with chromic hardener when compared to the amine cured resin.     

Research on starch‐g‐polyvinyl acetate and epoxy resin‐modified corn starch adhesive

A new corn starch adhesive modified by starch‐g‐polyvinyl acetate (starch‐g‐PVAc) and epoxy resin is described in this study. Starch‐g‐PVAc is used as high cohesive energy component to improve the dry shear strength of the starch adhesive. Although the epoxy resin, which can easily crosslink with the oxidized starch, is used as water‐resistant component to improve the wet shear strength. Because there is no chemical reaction happening between polyvinyl acetate and epoxy resin, both the dry shear strength and the wet shear strength of the corn starch adhesive are notably increased. Considering all the related factors, the optimum of the modification is achieved when the dosage of starch‐g‐PVAc and epoxy resin is 70% of the oxidized starch latex with m(Ep): m(starch‐g‐PVAc) = 1:2. That is, the epoxy resin is 23% in mass fraction and starch‐g‐PVAc 47% in mass fraction. The dry shear strength is 4.50 MPa, and the wet shear strength is 2.51 MPa. The modified corn starch has a broad prospect in the application of plywood industry. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Study of the isothermal curing of an epoxy prepreg by near‐infrared spectroscopy

The commercial epoxy prepreg SPX 8800, containing diglycidyl ether of bisphenol A, dicyanodiamide, diuron, and reinforcing glass fibers, was isothermally cured at different temperatures from 75 to 110°C and monitored via in situ near‐infrared Fourier transform spectroscopy. Two cure conditions were investigated: curing the epoxy prepreg directly (condition 1) and curing the epoxy prepreg between two glass plates (condition 2). Under both curing conditions, the epoxy group could not reach 100% conversion with curing at low temperatures (75–80°C) for 24 h. A comparison of the changes in the epoxy, primary amine, and hydroxyl groups during the curing showed that the samples cured under condition 2 had lower initial epoxy conversion rates than those cured under condition 1 and that more primary amine–epoxy addition occurred under condition 2. In addition, the activation energy under cure condition 2 (104–97 kJ/mol) was higher than that under condition 1 (93–86 kJ/mol), but a lower glass‐transition temperature of the cured samples was observed via differential scanning calorimetry. The moisture in the prepreg was assumed to account for the different reaction kinetics observed and to have led to different reaction mechanisms. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2295–2305, 2003     

A phosphorus‐containing diamine for flame‐retardant,high‐functionality epoxy resins. I. Synthesis,reactivity, and thermal degradation properties

A phosphorus‐containing amine, bis(4‐aminophenoxy)phenyl phosphine oxide (BAPP), suitable for curing epoxy resins with improved fire performance was synthesized and characterized with Fourier transform infrared spectroscopy and nuclear magnetic resonance. The reactivity of the amino group was evaluated by differential scanning calorimetry of the epoxy–amine mixture and by proton nuclear magnetic resonance of the amino unit. With BAPP as a curing agent, a range of high‐functionality, aerospace epoxy resins were cured, and the dynamic kinetic parameters calculated from Kissinger's and Ozawa's models were compared with those from the more widely used amines. The thermal degradation properties of the phosphorus‐containing epoxy resins were studied by thermogravimetric analysis, the degradation activation energy was calculated, and a multistep thermal degradation process was observed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2093–2100, 2004     

Heterocyclic‐based epoxy‐terminated structural adhesive. II. Curing,adhesive strength,and thermal stability

We studied the curing behavior of heterocyclic‐based epoxy‐terminated resins using diaminodiphenyl ether, diaminodiphenyl sulfone, benzophenone tetracarboxylicdianhydride, and the commercial hardener of Ciba‐Geigy's two‐pack Araldite as curing agents. The adhesive strength of the adhesives was measured by various ASTM methods such as lap‐shear, peel, and cohesive tests on metal–metal, wood–wood, and wood–metal interfaces. All of these results were compared with those of an epoxy resin prepared from bisphenol‐A and epichlorohydrin resin with an epoxy equivalent value of 0.519. The thermal stability of both the virgin resin and its cured form was also studied by thermogravimetric analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3520–3526, 2002     

Novel rapid‐cure adhesives for low temperature using thiirane compound

We investigated improvement of workability (viscosity), storage stability, and curing ability of thiirane resin for adhesive applications. The viscosity of bisphenol‐F thiirane resin was lower than that of bisphenol‐A thiirane resin, especially at low temperatures, thus improving ease of handling. Addition of diphenyl decyl phosphite improved its storage stability to a level similar to that of bisphenol‐A epoxy resin. The curing of bisphenol‐F thiirane resin increased three times faster by adding 2,4,6‐tris(dimethylaminomethyl)phenol (DMP‐30) as a tertiary amine. In applications of this new thiirane resin as civil and architectural adhesives, a superior curing ability at low temperature was attained. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2953–2957, 2001     

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     

Synthesis of epoxy resins from alcohol‐liquefied wood and the mechanical properties of the cured resins

New wood‐based epoxy resins were synthesized from alcohol‐liquefied wood. Wood was first liquefied by the reaction with polyethylene glycol and glycerin. The alcohol‐liquefied wood with plenty of hydroxyl groups were precursors for synthesizing the wood‐based epoxy resins. Namely, the alcoholic OH groups of the liquefied wood reacted with epichlorohydrin under alkali condition with a phase transfer catalyst, so that the epoxy groups were put in the liquefied wood. The wood‐based epoxy resins and the alcohol‐based epoxy resins as reference materials were cured with polyamide amine. The glass transition temperature (Tg), the tensile strength, and the modulus of elasticity of the wood‐based epoxy resin were higher than those of the alcohol‐based epoxy resin. Also, the shear adhesive strength of the wood‐based epoxy resin to steel plates was higher than those of the alcohol‐based epoxy resins, which was equivalent to the level of petroleum‐based bisphenol‐A type epoxy resins. The higher Tg of the wood‐based epoxy resin than that of the alcohol‐based epoxy resin is one of the evidences that the wood‐derived molecules were chemically incorporated into the network structures. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Curing kinetics and viscosity change of a two‐part epoxy resin during mold filling in resin‐transfer molding process

The curing kinetics and the resulting viscosity change of a two‐part epoxy/amine resin during the mold‐filling process of resin‐transfer molding (RTM) of composites was investigated. The curing kinetics of the epoxy/amine resin was analyzed in both the dynamic and the isothermal modes with differential scanning calorimetry (DSC). The dynamic viscosity of the resin at the same temperature as in the mold‐filling process was measured. The curing kinetics of the resin was described by a modified Kamal kinetic model, accounting for the autocatalytic and the diffusion‐control effect. An empirical model correlated the resin viscosity with temperature and the degree of cure was obtained. Predictions of the rate of reaction and the resulting viscosity change by the modified Kamal model and by the empirical model agreed well with the experimental data, respectively, over the temperature range 50–80°C and up to the degree of cure α = 0.4, which are suitable for the mold‐filling stage in the RTM process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2139–2148, 2000     

Accelerated-curing epoxy structural film adhesive for bonding lightweight honeycomb sandwich structures

Accelerating the curing of epoxy/aromatic amine adhesives and improving their toughness are challenges in heat-resistant epoxy structural adhesives. Herein, we report an epoxy/aromatic amine adhesive accelerated curing system with an oxo-centered trinuclear (chromium III) complex, which is toughened using a thermoplastic block copolymer (TPBC). The reaction characteristics, heat resistance, microstructure, and bonding properties of the accelerated epoxy adhesives were analyzed. The reaction peak temperature of the epoxy with 3% catalyst was 113.1°C, which was 113.6°C lower than that of epoxy without catalyst, and the modified epoxy resin demonstrated a potential for rapid curing at medium temperature. The glass transition temperature of the TPBC-toughened epoxy adhesive was 125°C after curing, indicating excellent thermal stability after medium temperature curing. The introduction of the TPBC increased the single-lap shear strength of the epoxy adhesive without reducing its heat resistance. The shear strength at room temperature and 120°C of the modified epoxy adhesive with 50 phr of TPBC was 25.2 and 10.9 MPa, respectively. Moreover, the epoxy film adhesive exhibited outstanding bonding properties when used in the bonding of lightweight honeycomb sandwich structures.     

Adhesive properties of epoxy resin modified by end‐functionalized liquid polybutadiene

Adhesive properties of epoxy resin networks modified with different functionalized liquid polybutadiene were evaluated by using aluminum adherent. The end‐functionalized polybutadiene rubbers were hydroxyl‐ (HTPB), carboxyl‐ (CTPB), and isocyanate‐terminated polybutadiene (NCOTPB). The adhesive properties depend upon the morphology and the degree of interaction between the rubber–epoxy system. The most effective adhesive for Al–Al joint in both butt and single‐lap shear testing was epoxy resin–NCOTPB system. This system presents stronger rubber–epoxy interactions and a higher degree of rubber particle dispersion with particle size diameter in the nanoscale range. These characteristics were not important for improving the toughness of the bulk network but are fundamental for the improvement of adhesive strength. The effect of the pretreatment of the aluminum surface on the roughness was also evaluated by using profilometry analysis. The type of failure was also investigated by analyzing the adhered surfaces after fracture by scanning electron microscopy and profilometry. A proportion of cohesion failure higher than 90% was observed in all systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2370–2378, 2004