Epoxy Matrix System Research Articles

Relationship between surface characteristics and interlaminar shear strength of oxyfluorinated carbon fibers in a composite system

In this work, a direct oxyfluorination method was used to study the effect of oxygen content on surface and mechanical interfacial characteristics of oxyfluorinated carbon fibers in an epoxy matrix system. The changes of surface functional groups, chemical compositions, and structures of the carbon fibers were characterized by Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, and X-ray diffraction measurements. Also, the mechanical interfacial properties of the composites were evaluated by means of interlaminar shear strength tests. The results indicated that graphitic carbon was the major carbon functional component on the carbon fiber surfaces and other functional groups were also present, such as CO, CO, HOCO, CF x , after oxyfluorination of carbon fibers. No large changes of structure were found with the content of oxygen. Consequently, these introductions of oxygen functional groups onto the carbon fiber surfaces led to an improvement of the ILSS of the composites.

Preparation and characterization of bismaleimide/1,3-dicyanatobenzene modified epoxy intercrosslinked matrices

An intercrosslinked network of cyanate ester (CE)–bismaleimide (BMI) modified epoxy matrix system was made by using epoxy resin, 1,3-dicyanatobenzene and bismaleimide (N,N ′-bismaleimido-4,4 ′-diphenyl methane) with diaminodiphenylmethane as curing agent. BMI–CE–epoxy matrices were characterised using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. The matrices, in the form of castings, were characterised for their mechanical properties such as tensile strength, flexural strength and unnotched Izod impact test as per ASTM methods. Mechanical studies indicated that the introduction of cyanate ester into epoxy resin improves the toughness and flexural strength with reduction in tensile strength and glass transition temperature, whereas the incorporation of bismaleimide into epoxy resin influences the mechanical and thermal properties according to its percentage content. DSC thermograms of cyanate ester as well as BMI modified epoxy resin show an unimodal reaction exotherm. Electrical properties were studied as per ASTM method and the morphology of the BMI modified epoxy and CE–epoxy systems were studied by scanning electron microscope.

Studies on thermal and morphological properties of 1,1‐bis(3‐methyl‐4‐cyanatophenyl)cyclohexane‐epoxy‐bismaleimide matrices

AbstractA new cyanate ester monomer, 1,1‐bis(3‐methyl‐4‐cyanatophenyl)cyclohexane has been synthesized and characterized. Epoxy modified with 4, 8 and 12% (by weight) of cyanate ester were made using epoxy resin and 1,1‐bis(3‐methyl‐4‐cyanatophenyl)cyclohexane and cured by using diaminodiphenylmethane. The cyanate ester modified epoxy matrix systems were further modified with 4, 8 and 12% (by weight) of bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenylmethane). The formation of oxazolidinone and isocyanurate during cure reaction of epoxy and cyanate ester blend was confirmed by IR spectral studies. Bismaleimide‐cyanate ester‐epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. Thermal studies indicate that the introduction of cyanate ester into epoxy resin improves the thermal degradation studies at the expense of glass transition temperature. Whereas the incorporation of bismaleimide into epoxy resin enhances the thermal properties according to its percentage content. However, the introduction of both cyanate ester and bismaleimide influences the thermal properties according to their percentage content. DSC thermogram of cyanate ester modified epoxy and bismaleimide modified epoxy show unimodel reaction exotherms. The thermal degradation temperature and heat distortion temperature of the cured bismaleimide modified epoxy and cyanate ester‐epoxy systems increased with increasing bismaleimide content. The morphology of the bismaleimide modified epoxy and cyanate ester‐epoxy systems were also studied by scanning electron microscopy. Copyright © 2003 John Wiley & Sons, Ltd.

Thermal and Morphological Properties of Bisphenol Dicyanate–Epoxy–Bismaleimide Intercrosslinked Matrix Materials

Intercrosslinked network of cyanate ester–bismaleimide modified epoxy matrix systems was developed. Epoxy systems modified with 4%, 8%, and 12% (by wt.) of cyanate ester were made by using epoxy resin and cyanate ester with diaminodiphenylmethane as curing agent. The reaction between cyanate ester and epoxy resin during the cure process of cyanate ester modified epoxy systems was studied using FTIR. The cyanate ester toughened epoxy systems were further modified with 4%, 8%, and 12% (by wt.) of bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenylmethane). BMI–CE–epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and heat deflection temperature (HDT) analysis. The studies indicate that the thermal stability and resistant to water absorption behavior of epoxy resin has been enhanced by the introduction of cyanate ester. However, glass transition temperature and heat deflection temperature are found to decrease with increasing cyanate ester concentration, whereas, the incorporation of bismaleimide into epoxy resin enhanced the thermal properties according to its percentage content. However, the introduction of both cyanate ester and bismaleimide influences the thermal properties according to their percentage content. Differential scanning calorimetry thermogram of cyanate ester modified epoxy and BMI modified epoxy during cure show an unimodel reaction exotherms. The fractured surface of cyanate ester modified epoxy systems reveals the presence of homogeneous morphology, and a smooth fractured surface is observed with increasing bismaleimide content.

Preparation and characterization of bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenyl methane)–unsaturated polyester modified epoxy intercrosslinked matrices

AbstractAn intercrosslinked network of unsaturated polyester–bismaleimide modified epoxy matrix systems was developed. Epoxy systems modified with 10, 20, and 30% (by weight) of unsaturated polyester were made by using epoxy resin and unsaturated polyester with benzoyl peroxide and diaminodiphenylmethane as curing agents. The reaction between unsaturated polyester and epoxy resin was confirmed by IR spectral studies. The unsaturated polyester toughened epoxy systems were further modified with 5, 10, and 15% (by weightt) of bismaleimide (BMI). The matrices, in the form of castings, were characterized for their mechanical properties. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of the matrix samples were performed to determine the glass transition temperature (Tg) and thermal degradation temperature of the systems, respectively. Mechanical properties, viz: tensile strength, flexural strength, and plain strain fracture toughness of intercrosslinked epoxy systems, were studied by ASTM methods. Data obtained from mechanical and thermal studies indicated that the introduction of unsaturated polyester into epoxy resin improves toughness but with a reduction in glass transition, whereas the incorporation of bismaleimide into epoxy resin improved both mechanical strength and thermal behavior of epoxy resin. The introduction of bismaleimide into unsaturated polyester‐modified epoxy resin altered thermomechanical properties according to their percentage concentration. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2853–2861, 2002

Preparation and characterization of siliconized epoxy/bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenyl methane) intercrosslinked matrices for engineering applications

AbstractNovel hybrid intercrosslinked networks of hydroxyl‐terminated polydimethylsiloxane‐modified epoxy and bismaleimide matrix systems have been developed. Epoxy systems modified with 5, 10, and 15 wt % of hydroxyl‐terminated polydimethylsiloxane (HTPDMS) were developed by using epoxy resin and hydroxyl‐terminated polydimethylsiloxane with γ‐aminopropyltriethoxysilane (γ‐APS) as compatibilizer and dibutyltindilaurate as catalyst. The reaction between hydroxyl‐terminated polydimethylsiloxane and epoxy resin was confirmed by IR spectral studies. The siliconized epoxy systems were further modified with 5, 10, and 15 wt % of bismaleimide (BMI). The matrices, in the form of castings, were characterized for their mechanical properties. Differential scanning calorimetry and thermogravimetric analysis of the matrix samples were also performed to determine the glass‐transition temperature and thermal‐degradation temperature of the systems. Data obtained from mechanical studies and thermal characterization indicate that the introduction of siloxane into epoxy improves the toughness and thermal stability of epoxy resin with reduction in strength and modulus values. Similarly the incorporation of bismaleimde into epoxy resin improved both tensile strength and thermal behavior of epoxy resin. However, the introduction of siloxane and bismaleimide into epoxy enhances both the mechanical and thermal properties according to their percentage content. Among the siliconized epoxy/bismaleimide intercrosslinked matrices, the epoxy matrix having 5% siloxane and 15% bismaleimide exhibited better mechanical and thermal properties than did matrices having other combinations. The resulting siliconized (5%) epoxy bismaleimide (15%) matrix can be used in the place of unmodified epoxy for the fabrication of aerospace and engineering composite components for better performance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 38–46, 2001

Roles of difunctional epoxy in the tetrafunctional epoxy matrix system

Roles of difunctional epoxy in the tetrafunctional epoxy matrix system

Mechanical properties of E‐glass fiber reinforced siliconized epoxy polymer composites

AbstractSiliconized epoxy‐matrix systems have been developed by an interpenetrating mechanism using epoxy resins GY 250 and LY 556 (Ciba‐Geigy) and hydroxyl terminated polydimethylsiloxane with γ‐aminopropyltriethoxysilane as crosslinker in the presence of dibutyltindilaurate catalyst. Aliphatic amine (HY 951, Ciba‐Geigy), aromatic amine (HT 972, Ciba‐Geigy) and polyamidoamine (HY 840, Ciba‐Geigy) are used as curing agents for epoxy resins. The tentative level of 10% siloxane introduction into epoxy resin has been ascertained from experimental studies to obtain reasonable improvements in the impact behavior without compromising other mechanical properties. The impact behavior of E‐glass reinforced composites made from the siliconized epoxy resin is enhanced to 2–4 times over that measured on the composites made from a pure epoxy resin. Composites cured with aromatic amine impart better mechanical properties than those cured with aliphatic amine and polyamidoamine.

Studies on thermal and morphological characteristics of E-glass/Kevlar 49 reinforced siliconized epoxy composites

Two different types of siliconized epoxy matrix systems are developed by interpenetrating technique using epoxy resins GY 250 and LY 556 (Ciba-Geigy) and hydroxyl terminated polydimethylsiloxane with γ-aminopropyltriethoxysilane as cross-linker with dibutyltindilaurate catalyst and cured by aliphatic amine (HY 951, Ciba-Geigy), aromatic amine (HT 972, Ciba-Geigy) and polyamidoamine (HY 840, Ciba-Geigy). Electrical resistant glass (E-glass) and Kevlar 49 reinforced composites are fabricated by hand-lay-up technique using siliconized epoxy matrix systems. The effect of curatives and the percentage of siloxanes on the thermal and morphological characteristics of the siliconized epoxy polymer composites are studied. The siloxane incorporation enhances the thermal stability due to the ablative behaviour of siloxane moiety. E-glass fibre reinforcement shows better intermolecular adhesion to epoxy resin than Kevlar-49 reinforcement due to the presence of ionic sites. The siloxane introduction into epoxy resin improves the service temperature of the matrix systems.

Influence of Aggregate Structure on Mode-III Interfacial Fracture between Concrete and CFRP

One of the crucial issues in the use of fiber reinforced polymers for civil engineering applications is the interfacial bonding between the different materials used. As a load transfer from the concrete to the composite components occurs via shear stresses in the interfacial region, studies of the interfacial bond quality should concentrate on load situations in which primarily shear stresses are induced. In this study, a 3-Point Bending Test was modified to initiate shear failure under Mode-III conditions in the interface between a composite and a concrete component. In particular it was the objective to study the interfacial shear strength between three different concretes and an unidirectional carbon fiber reinforced epoxy matrix system. The three concretes had the same compressive strength (B35 KP, German Standard), but differed in the type of filler material: (a) “heavy” concrete, filled with granite (Diorit) particles, (b) “normal” concrete, filled with gravel grains (Pyrite), and (c) “light weight” concrete, filled with vopourtone (Liapur). The mechanical test results showed that both the type of filler exposed to the joint surface as well as the type of adhesive used clearly influence the interfacial shear strength. Best values were achieved with Diorit-fillers, and the Sikadur-adhesive was in all cases superior to the Dywipox-adhesive. Reasons for these differences were demonstrated by light optical and scanning electron micrographs of the fractured surfaces.

Métodos de estudo da cinética de cura de resinas epóxi

Nas últimas décadas tem-se estudado a cinética da reação de cura de resinas epóxi por meio de técnicas analíticas como por exemplo a calorimetria exploratória diferencial. O uso desta técnica permite utilizar vários métodos de estudo da cinética de cura, divididos em: métodos dinâmicos e isotérmicos, e cada pesquisador escolhe o que melhor se adapta às suas necessidades. O presente trabalho tem como objetivo orientar na escolha de qual método deve ser utilizado, em função dos sistemas poliméricos em estudo, bem como sumarizar os principais métodos utilizados, auxiliando, dessa forma, no estudo da cinética de cura de resinas epóxi.

Low velocity impact behavior of glass/epoxy cross‐ply laminates with different fiber treatments

AbstractThis paper deals with the influence of the fiber/matrix adhesion quality on the impact behavior of cross‐ply glass/epoxy laminates. Glass fibers with two different treatments (one to promote and one to prevent adhesion to the matrix) were embedded in epoxy matrix systems and subjected to low velocity impacts at energies below perforation energy. It will be shown that the laminates with good fiber/matrix adhesion are significantely more damage resistant than the plates with poor adhesion. It will be pointed out that the composites with the more brittle matrix system show the lower damage resistance. For all materials, the absorbed energy correlates well with the amount of impact induced damage. Furthermore, an experimental/mathematical model is introduced that gives the possibility of predicting the maximum deflection and maximum force for any given impact energy. Only one experiment is needed for each material to identify the model parameters. These parameters describe the real material behavior and can be used as characteristic values to classify materials with respect to their impact stiffness and damage resistance.

Durability characteristics of concrete columns confined with advanced composite materials

The durability performance of concrete columns confined with fiber-reinforced polymer composite (FRPC) sheets was studied. Columns were wrapped around with four different types of FRP composite wraps: two carbon (C1 and C5) and two glass (GE1 and GE2). Two types of epoxy matrix systems, Type A and B, were used. The confined and unconfined specimens were subjected to two environmental conditions: room temperature, wet and dry cycling. For the wet and dry exposure, the specimens were placed in an environmental chamber in which they were subjected to 300 cycles of wetting and drying. Sea water was used for the wet cycles and hot air at 35 °C average for the dry cycles. After every 30 cycles, pulse velocity and weight changes were measured. At the end of 300 cycles the stress-strain behavior of the samples was obtained in order to evaluate their strength, stiffness, and ductility, which were compared to the performance of the unconditioned samples (room temperature exposure). Results show that both epoxy systems produce similar results in the unconditioned specimens, with respect to strength, ductility, and failure behavior. However, specimens wrapped with glass fiber-reinforced polymer (GFRP) using Type A epoxy experienced no reduction in strength or ductility due to wet/dry exposure, whereas samples using Type B epoxy experienced reduction in both strength and ductility. Specimens wrapped with carbon fiber-reinforced polymer (CFRP) using either epoxy Type A or Type B exhibited no reduction in strength nor in ductility due to exposure.

Roles of Unsaturated Polyester in the Epoxy Matrix System

A study of the interpenetrating polymer network (IPN) as a polymer blend matrix was carried out using different compositions of unsaturated polyester (UP) to epoxy (EP) resins. It was observed that 5 wt% UP in the blend provides maximum mechanical properties, particularly the impact strength for optimum casting. Fourier transform infrared (FT-IR) spectroscopy was used to investigate the intermolecular hydrogen bonding and functional group change. In this work, changes of physical property, e.g., viscosity and specific component of interfacial tension were evaluated before and after cure, respectively. Increase of the physical properties was observed in 5 wt% UP in the blend, probably due to the effects of hydrogen bonding, resulting in higher toughness properties of the casting specimens.

Synthesis and Characterization of High Performance Polymeric Hybrid Siliconized Epoxy Composites for Aerospace Applications

Two different types of hybridized siliconized epoxy matrix systems have been developed using two commercially available (CIBA-GEIGY) epoxy resins with hydroxyl terminated polydimethyl siloxane. The percentage siloxane content in the epoxy systems have been optimized based on the physico-chemical, electrical, mechanical and thermal properties. The matrix resins are cured using aliphatic amine (HY951), aromatic amine (HT972) and polyamidoamine (HY840) from CIBA-GEIGY and γ-aminopropyltriethoxysilane (A-186, Union Carbide). The optimized siliconized epoxy materials are filled with additives like fillers (SiO2, BaSO4 and TiO2), plasticizer (dioctylphthalate), flame retardant (tris (2-chloropropyl) phosphate) and reinforced with E-glass fiber and Kevlar-49 and their effect on electrical and mechanical properties are studied. Introduction of siloxane units (silicone) in to the epoxy systems enhances dielectric properties with little loss of mechanical properties. Additives alter the electrical and mechanical characteristics based on their nature and concentration. Reinforcements enhanced the electrical and mechanical behavior to an appreciable extent. Data resulted from the studies reveal that the siliconized epoxy matrix systems reinforced with E-glass fiber and Kevlar-49 can be used in the filament wound liquid pressure vessels in the field of aerospace and other high performance engineering applications.

The Effect of Styrene on Epoxy Resin Formulations for Filament Winding

Abstract The effect of styrene on epoxy resin formulations for filament winding were studied from the viewpoints of processing, mechanical, and thermal properties. Five epoxy blends with different compositions of epoxy resin, hardener, and styrene were made and evaluated. The addition of a small amount (maximum 10%) of styrene to the epoxy formulations decreased the resin viscosity from 605 to 160 cP and increased the pot life of the mixed resin system. The tensile and flexural properties were found to be similar, regardless of styrene content. The thermal properties (heat deflection temperature, glass transition temperature, etc.) of the resulting thermoset blends decreased as the styrene content increased. From the viewpoints of resin viscosity, pot life, and mechanical and thermal properties, it was found that the addition of a small amount (5–10%) of styrene to an epoxy resin was adequate for an epoxy matrix system used for filament winding.

Role of polyester resin on the epoxy matrix system

AbstractInterpenetrating polymer network (IPN) as a polymer blend matrix was prepared using different ratios of polyester (PE) to epoxy (E) resins. It was observed that 11.33 wt % PE in the blend provides maximum mechanical properties, particularly the modulus for the casting, and such a blend is referred to as “optimum casting” (OC). The density of the blends containing up to 11.33% PE, especially of OC, was found to have increased by the presence of PE in the E network significantly more than would have been estimated from the calculation based on the rule of additivity. The thermal expansion coefficient parameter (Δαi) of the OC was found to be 2.68 × 10−4K−1. The scanning electron micrograph (SEM) of the fracture surface of OC only showed a glass‐like smooth surface. The change in the mechanical properties due to the varying proportions of PE in the blend was studied critically on the basis of failure mechanisms and morphological features. The differential thermogravimetric analysis (DTGA) of OC indicated only one peak in spite of the presence of two resin constituents, whereas castings with an excess of PE in the blend showed multiple peaks. Interestingly, as far as the DTGA is concerned, a domain of seemingly OC origin was found to remain, even in the blends containing PE resin above its optimum level (> 11.33 wt %). ©1995 John Wiley & Sons, Inc.

Toughening studies on an ABS/PC blend-modified epoxy resin system

Studies were carried out on the toughening of a bifunctional epoxy (diglycidyl ether of bisphenol-A) matrix system with an ABS/PC thermoplastic blend. The thermoplastic blend was incorporated into the epoxy matrix by particle dispersion and melt-mix methods. The unmodified and modified epoxy resin systems were cured with a stoichiometric quantity of diamino diphenyl methane (DDM). The cured castings were characterized by measurement of glass transition temperature (Tg) by DsC, evaluation of plane strain fracture toughness (Klc) by three-point bending tests and SEM analysis of non-etched and base/acid etched fracture surfaces. In genera] ABS/PC-modified (15% w/w) epoxy-resin-cured systems showed enhanced fracture toughness without lowering the glass transition temperature. The melt-mix method yielded higher fracture toughness than the particle dispersion method; this conclusion was also supported by scanning electron micrographs.

Compression Fatigue Response for Carbon Fiber With Conventional and Toughened Epoxy Matrices With Damage

This paper compares the open hole compression, compression after impact, compression fatigue of open hole specimens, and compression fatigue after impact response of quasi-isotropic laminates with IM7 carbon fiber and 3501-6 and 8551-7 epoxy matrices. These matrices can be considered to be a relatively brittle and a high-toughness resin, respectively. The objective was to establish whether the improved compression after impact response associated with high toughness matrices also held after fatigue loading. The results of impact and compression fatigue tests show that residual strengths of the toughened epoxy matrix system were approximately twice that of the brittle matrix system, and that fatigue resistance after impact and of open hole specimens was generally improved.

Processing-structure relationships for multiphase epoxy matrix systems

A styrene-modified diglycidyl ether of bisphenol-A (DGEBA) epoxy system cured with trimellitic anhydride (TMA) has been investigated to explore processing and structure relationships. During cure, the reactive styrene precipitated with polymerization into phase domains separate from the epoxy phase. Dynamic mechanical analysis and microscopy studies were performed to gain insight to matrix structure. The DMA studies showed that the styrenemodified epoxy system after cure exhibited two partially overlapped but distinct relaxation peaks, which are associated with the T gs of the polystyrene and epoxy phases. The glass transition of the polystyrene phase was shown to be broadened and the T g to depend strongly on processing temperature profiles. While the T g of the epoxy phase increases with curing agent concentrations, the T g of the polystyrene phase does not. Microscopic studies showed that the styrene-modified system exhibited a rougher fracture surface but did not reveal well defined phase domains in which the precipitated polystyrene component was aggregated. Overall, the study has demonstrated correlations of the kinetic factors in controlling the morphology in reactive modifier-epoxy systems.