Showing papers on "Epoxy published in 2012"
TL;DR: An alternative method for improving the interfacial and tensile properties of carbon fiber composites by controlling the fiber-matrix interface was developed and such multiscale reinforced composites show great potential with their improved mechanical performance to be likely applied in the aerospace and automotive industries.
Abstract: The performance of carbon fiber-reinforced composites is dependent to a great extent on the properties of fiber–matrix interface. To improve the interfacial properties in carbon fiber/epoxy composites, we directly introduced graphene oxide (GO) sheets dispersed in the fiber sizing onto the surface of individual carbon fibers. The applied graphite oxide, which could be exfoliated to single-layer GO sheets, was verified by atomic force microscope (AFM). The surface topography of modified carbon fibers and the distribution of GO sheets in the interfacial region of carbon fibers were detected by scanning electron microscopy (SEM). The interfacial properties between carbon fiber and matrix were investigated by microbond test and three-point short beam shear test. The tensile properties of unidirectional (UD) composites were investigated in accordance with ASTM standards. The results of the tests reveal an improved interfacial and tensile properties in GO-modified carbon fiber composites. Furthermore, significa...
561 citations
TL;DR: In this article, two different dimensions of graphene nanoplatelets were used with flake sizes of 5 mu m and 25 mu m to investigate the influence of nanofiller size on composite properties.
556 citations
TL;DR: In this article, the authors report enhancements of 28-111% in mode I fracture toughness and up to 1580% in uniaxial tensile fatigue life through the addition of small amounts (≤1 wt %) of graphene oxide to an epoxy system.
Abstract: Epoxy systems have proven popular having important applications in aerospace and wind energy, but fracture and fatigue resistance of this polymer remain less than desired. Graphene oxide, a form of atomically thin carbon, possessing impressive multifunctional properties and an ideal interface for interacting with polymer matrices, has emerged as a viable reinforcement candidate. In this work, we report enhancements of 28–111% in mode I fracture toughness and up to 1580% in uniaxial tensile fatigue life through the addition of small amounts (≤1 wt %) of graphene oxide to an epoxy system. Graphene oxide was uniquely synthesized by unraveling and splaying open helical-ribbon carbon nanofibers. The resulting oxygenated basal planes and edges of the graphene oxide sheets were observed to promote onset of the cross-linking reaction and led to an increase in total heat of reaction effecting slightly higher glass transition temperatures of the cured composites. Measured improvements were also detected in quasi-st...
434 citations
TL;DR: In this article, the authors report on a systematic study of the effects of interface on the thermal conductivity of highly filled epoxy composites, where six kinds of surface treated and as received AlN particles are used as fillers.
Abstract: The interface between filler and matrix has long been a critical problem that affects the thermal conductivity of polymer composites. The effects of the interface on the thermal conductivity of the composite with low filler loading are well documented, whereas the role of the interface in highly filled polymer composites is not clear. Here we report on a systematic study of the effects of interface on the thermal conductivity of highly filled epoxy composites. Six kinds of surface treated and as received AlN particles are used as fillers. Three kinds of treated AlN are functionalized by silanes, i.e., amino, epoxy, and mercapto group terminated silanes. Others are functionalized by three kinds of materials, i.e., polyhedral oligomeric silsesquioxane (POSS), hyperbranched polymer, and graphene oxide (GO). An intensive study was made to clarify how the variation of the modifier would affect the microstructure, density, interfacial adhesion, and thus the final thermal conductivity of the composites. It was f...
390 citations
359 citations
TL;DR: In this paper, a simple covalent functionalization with 3-aminopropyl triethoxysilane was used to synthesize functionalized graphene nanosheets (f-GNSs).
356 citations
25 Apr 2012
TL;DR: In this paper, the authors describe 3D polymer networks formed by the chemical reaction between monomers (curing), which determines the properties of thermosetting polymers: unlike thermoplastics, this kind of polymers does not melt, and once the network has been formed the material cannot be reprocessed.
Abstract: Epoxy resins are a family of thermosetting materials widely used as adhesives, coatings and matrices in polymer composites because of the low viscosity of the formulations, good insulating properties of the final material even at high temperatures and good chemical and thermal resistance (May, 1988). Epoxy thermosets can be described as 3D polymer networks formed by the chemical reaction between monomers (“curing”). This 3D covalent network structure determines the properties of thermosetting polymers: unlike thermoplastics, this kind of polymers does not melt, and once the network has been formed the material cannot be reprocessed. Maybe one of the main advantages of epoxy thermosets is that the starting monomers have low viscosity so that complex geometries can be easily shaped and fixed after curing the monomers. Thus the formation of the network via chemical reaction is a key aspect in this kind of materials.
343 citations
TL;DR: In this article, the effects of filler shape, surface modification and polarity of polymer matrix on the microstructure, dielectric constants and breakdown strength of polymer composites are investigated in detail.
Abstract: Flexible polymer composite films are prepared by a solution cast method with polar polyvinylidene fluoride (PVDF) or non-polar epoxy as the polymer matrix. BaTiO3 nanoparticles and BaTiO3 nanofibers with large aspect ratio are used as dielectric fillers after surface modification by polydopamine. The effects of filler shape, surface modification and polarity of polymer matrix on the microstructure, dielectric constants and breakdown strength of polymer composites are investigated in detail. Surface modification by polydopamine improves the compatibility between BaTiO3 and polymer as well as passivating the surfaces of BaTiO3. At the same volume fraction, composites filled with BaTiO3 nanofibers exhibit greater dielectric constants than the composites filled with BaTiO3 nanoparticles. The polydopamine layers on BaTiO3 nanofibers give rise to stronger interfaces between the fillers and polymer matrices. Improved breakdown strengths are achieved in both composites. This work may provide a general strategy for flexible polymer nanocomposites with greatly enhanced dielectric constants and breakdown strength.
338 citations
TL;DR: In this paper, Amine functionalized expanded graphene nanoplatelets (EGNPs) were dispersed within epoxy resins using high-pressure processor followed by three roll milling.
337 citations
TL;DR: In this article, three bio-composites, i.e., flax, linen and bamboo fabric reinforced epoxy resin, were manufactured using a vacuum bagging technique, and the influence of alkali treatment (with 5'wt% NaOH solution for 30'min) on tensile properties of single-strand yarns, surface morphology and mechanical properties of the composites were investigated.
Abstract: In this article, three bio-composites, i.e. flax, linen and bamboo fabric reinforced epoxy resin, were manufactured using a vacuum bagging technique. The influence of alkali treatment (with 5 wt% NaOH solution for 30 min) on tensile properties of flax, linen and bamboo single-strand yarns, surface morphology and mechanical properties (with respect to tensile and flexural properties) of the composites were investigated. It was found that the failure mechanism of single-strand fibres under tension consists of fibre breakage and slippage simultaneously. The alkali treatment had a negative effect on the tensile strength and modulus of the flax, linen and bamboo single-strand yarns. However, after the treatment, the tensile and flexural properties of all the composites increased, e.g. the tensile and flexural strength of the treated flax/epoxy composite increased 21.9% and 16.1%, compared to the untreated one. After the treatment in all the composites, the tensile fractured surfaces exhibited an improvement of...
317 citations
TL;DR: In this article, a dual-microcapsule epoxy-amine chemistry in thermoset epoxy was used for self-healing in a double-cantilever-beam (TDCB) fracture.
TL;DR: In this paper, the flexural properties of unidirectional long kenaf fiber reinforced epoxy (KFRE) composites are studied and the failure mechanism and damage features of the materials were categorized with the surface observation by scanning electron microscope (SEM).
TL;DR: A core-shell structured hybrid (SiO(2)-GO) was prepared and introduced into an epoxy polymer matrix as a new filler, which optimized the modulus, strength and fracture toughness of the composites simultaneously.
Abstract: Controlling the interface interaction of polymer/filler is essential for the fabrication of high-performance polymer composites. In this work, a core–shell structured hybrid (SiO2–GO) was prepared and introduced into an epoxy polymer matrix as a new filler. The incorporation of the hybrid optimized the modulus, strength and fracture toughness of the composites simultaneously. The ultrathin GO shells coated on silica surfaces were regarded as the main reason for the enhancement. Located at the silica-epoxy interface, GO served as an unconventional coupling agent of the silica filler, which effectively enhanced the interfacial interaction of the epoxy/SiO2–GO composites, and thus greatly improved the mechanical properties of the epoxy resin. We believe this new and effective approach that using GO as a novel fillers surface modifier may open a novel interface design strategy for developing high performance composites.
TL;DR: In this article, the effect of the dispersion conditions has been thoroughly investigated with regard to the CNT content, the sonication time and the total sonication energy input with respect to the resulting nanocomposites.
Abstract: In this work, multi wall carbon nanotubes (MWCNTs) dispersed in a polymer matrix have been used to enhance the thermo-mechanical and toughness properties of the resulting nanocomposites. Dynamic mechanical analysis (DMA), tensile tests and single edge notch 3-point bending tests were performed on unfilled, 0.5 and 1 wt.% carbon nanotube (CNT)-filled epoxy to identify the effect of loading on the aforementioned properties. The effect of the dispersion conditions has been thoroughly investigated with regard to the CNT content, the sonication time and the total sonication energy input. The CNT dispersion conditions were of key importance for both the thermo-mechanical and toughness properties of the modified systems. Sonication duration of 1 h was the most effective for the storage modulus and glass transition temperature (Tg) enhancement for both 0.5 and 1 wt.% CNT loadings. The significant increase of the storage modulus and Tg under specific sonication conditions was associated with the improved dispersion and interfacial bonding between the CNTs and the epoxy matrix. Sonication energy was the influencing parameter for the toughness properties. Best results were obtained for 2 h of sonication and 50% sonication amplitude. It was suggested that this level of sonication allowed appropriate dispersion of the CNTs to the epoxy matrices without destroying the CNT’s structure.
TL;DR: In this article, the results of several static and fatigue tests are described and two polymeric matrices are taken into account, vinylester and epoxy, to assess their influence on the evaluated parameters, and the thermal answer of the specimens to mechanical loads is evaluated by means of thermography.
TL;DR: In this paper, the effect of silica nanoparticles and particle size on glass transition temperature (T g ), coefficient of thermal expansion (CTE), Young's modulus (E ), yield stress ( σ ), fracture energy (G IC ), and fracture toughness (K IC ), were investigated.
Patent•
02 Nov 2012
TL;DR: In this article, an epoxy resin composition for encapsulating semiconductors is presented, which contains a phenolic resin, a curing accelerator, an inorganic filler and a phosphazene compound as essential components.
Abstract: The present invention provides an epoxy resin composition for encapsulation of semiconductors which contains substantially neither halogen-based flame retarding agents nor antimony compounds and is excellent in moldability, flame retardance, high-temperature storage characteristics, reliability for moisture resistance, and solder cracking resistance. That is, the present invention is an epoxy resin composition for encapsulating semiconductors which contains (A) an epoxy resin, (B) a phenolic resin, (C) a curing accelerator, (D) an inorganic filler and (E) a phosphazene compound as essential components, the total weight of phosphate ion and phosphite ion contained in the phosphazene compound being not more than 500 ppm. Further, the epoxy resin composition may optionally contain a flame-retarding assistant or an ion scavenger.
TL;DR: Carbon nanotubes (CNTs) have been deposited onto carbon-fiber fabric using electrophoretic deposition (EPD) prior to the infusion of epoxy resin for the production of carbon/epoxy composites.
TL;DR: In this article, a simple refluxing of GO with octa-aminophenyl polyhedral oligomeric silsesquioxanes (OapPOSS) without the use of any reducing agents was realized by simple reduction and surface functionalization of graphene oxide.
Abstract: Simultaneous reduction and surface functionalization of graphene oxide (GO) was realized by simple refluxing of GO with octa-aminophenyl polyhedral oligomeric silsesquioxanes (OapPOSS) without the use of any reducing agents. The presence of OapPOSS made the hydrophilic GO hydrophobic, as evidenced by the good dispersion of the OapPOSS-reduced GO (OapPOSS-rGO) in tetrahydrofuran solvent. The structure of OapPOSS-rGO was confirmed by XPS, FTIR and TEM. A morphological study showed that, due to the good interfacial interaction between the functionalized graphene and epoxy, OapPOSS-rGO was dispersed well in the matrix. With the incorporation of 2.0 wt% of OapPOSS-rGO, the onset thermal degradation temperature of the epoxy composite was significantly increased by 43 °C. Moreover, the peak heat release rate, total heat release and CO production rate values of OapPOSS-rGO/EP were significantly reduced by 49%, 37% and 58%, respectively, compared to those of neat epoxy. This dramatically reduced fire hazards was mainly attributed to the synergestic effect of OapPOSS-rGO: the adsorption and barrier effect of reduced graphene oxide inhibited the heat and gas release and promoted the formation of graphitized carbons, while OapPOSS improved the thermal oxidative resistance of the char layer.
TL;DR: In this article, the effect of water absorption on the mechanical and physical properties of reinforced cellulose fiber reinforced epoxy composites was investigated and the results showed that flexural strength, flexural modulus, fracture toughness and impact strength increased as the fibre content increased.
TL;DR: In this paper, the thermal conductivity coefficient of the composites with 60% mass fraction of modified BN is 1.052 W/mK, five times higher than that of native EP.
Abstract: Boron nitride (BN) micro particles modified by silane coupling agent, γ-aminopropyl triethoxy silane (KH550), are employed to prepare BN/epoxy resin (EP) thermal conductivity composites. The thermal conductivity coefficient of the composites with 60% mass fraction of modified BN is 1.052 W/mK, five times higher than that of native EP (0.202 W/mK). The mechanical properties of the composites are optimal with 10 wt% BN. The thermal decomposition temperature, dielectric constant, and dielectric loss increase with the addition of BN. For a given BN loading, the surface modification of BN by KH550 exhibits a positive effect on the thermal conductivity and mechanical properties of the BN/EP composites. Copyright © 2011 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors investigated the effect of water absorption on the mechanical properties of nano-filler reinforced epoxy nanocomposites as well as to study the influence of different types of nanofillers such as nano-clay platelets, halloysite nanotubes (HNTs) and nano-silicon carbide (n-SiC) particles on the water absorption behavior of epoxy based nanocom composites.
TL;DR: In this article, an interactive crosslinking-relaxation methodology is developed to construct the simulation cell, which allows the construction of highly crosslinked polymer network from a given set of monomers.
TL;DR: A potential trend is pointed out where GnPs would replace carbon nanotubes and silicate layers for many applications of polymer nanocomposites due to its exceptionally high mechanical performance and electrical and thermal conductivity.
Abstract: In spite of extensive studies conducted on carbon nanotubes and silicate layers for their polymer-based nanocomposites, the rise of graphene now provides a more promising candidate due to its exceptionally high mechanical performance and electrical and thermal conductivities. The present study developed a facile approach to fabricate epoxy–graphene nanocomposites by thermally expanding a commercial product followed by ultrasonication and solution-compounding with epoxy, and investigated their morphologies, mechanical properties, electrical conductivity and thermal mechanical behaviour. Graphene platelets (GnPs) of 3.57 ± 0.50 nm in thickness were created after the expanded product was dispersed in tetrahydrofuran using 60 min ultrasonication. Since epoxy resins cured by various hardeners are widely used in industries, we chose two common hardeners: polyoxypropylene (J230) and 4,4′-diaminodiphenylsulfone (DDS). DDS-cured nanocomposites showed a better dispersion and exfoliation of GnPs, a higher improvement (573%) in fracture energy release rate and a lower percolation threshold (0.612 vol%) for electrical conductivity, because DDS contains benzene groups which create π–π interactions with GnPs promoting a higher degree of dispersion and exfoliation of GnPs during curing. This research pointed out a potential trend where GnPs would replace carbon nanotubes and silicate layers for many applications of polymer nanocomposites.
Patent•
25 Jul 2012TL;DR: In this article, a prepreg is used to cure the prepeg of a perforated plate in a wet-heat environment to achieve improved interlaminar strength and lower water absorption.
Abstract: A prepreg giving a cured product exhibiting a lowered water adsorption comprising reinforcing fibers and a matrix resin comprising an epoxy resin of a specific composition, a curing agent of a specific structure, and a highly heat-resistant thermoplastic resin; a prepreg improved in interlaminar strength comprising reinforcing fibers and a matrix resin comprising an epoxy resin of a specific composition, a curing agent of a specific structure, and a highly heat-resistant thermoplastic resin; a prepreg improved in interlaminar strength and giving a cured product exhibiting a lowered water absorption, comprising reinforcing fibers and a matrix resin comprising an epoxy resin of a specific composition, a curing agent of a specific structure, and a highly heat-resistant thermoplastic resin; and a product prepared by curing the prepeg which is satisfactory in both impact resistance (residual compressive strength after impacting) and characteristics in a wet-heat atmosphere (compressive strength of perforated plate under the circumstances of high temperature and humidity), both properties having been conflicting with each other in the prior art.
TL;DR: In this article, the authors adopted the acoustic emission technique to study the failure mechanisms and damage evolution of carbon fiber/epoxy composite laminates, and studied the effects of different lay-up patterns and hole sizes on the acoustic response.
TL;DR: In this paper, high modulus carbon fibres were used to prepare single fiber model composites based on an epoxy resins and their moisture uptake behavior was monitored, and the equilibrium moisture content and diffusion coefficients for the samples were determined.
TL;DR: In this article, the authors proposed that by proper functionalization and mixing strategy of graphene its dispersion, and bonding to the polymeric matrix can be improved, and they then applied this strategy to graphene-epoxy system by amino functionalization of graphene oxide (GO).
Abstract: Dispersion of nanomaterials in polymeric matrices plays an important role in determining the final properties of the composites. Dispersion in nano scale, and especially in single layers, provides best opportunity for bonding. In this study, we propose that by proper functionalization and mixing strategy of graphene its dispersion, and bonding to the polymeric matrix can be improved. We then apply this strategy to graphene-epoxy system by amino functionalization of graphene oxide (GO). The process included two phase extraction, and resulted in better dispersion and higher loading of graphene in epoxy matrix. Rheological evaluation of different graphene-epoxy dispersions showed a rheological percolation threshold of 0.2 vol% which is an indication of highly dispersed nanosheets. Observation of the samples by optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM), showed dispersion homogeneity of the sheets at micro and nano scales. Study of graphene-epoxy composites showed good bonding between graphene and epoxy. Mechanical properties of the samples were consistent with theoretical predictions for ideal composites indicating molecular level dispersion and good bonding between nanosheets and epoxy matrix.
TL;DR: In this article, two different fillers, cork powder and nanoclays Cloisite 30B, were used in order to improve the impact response of these laminates.
TL;DR: In this article, remarkable synergetic efficiency was realized in graphene nanoplatelet (GNP) and multiwalled carbon nanotube (CNT) highly loaded epoxy composites through a well-designed fabrication method.
Abstract: Utilizing synergetic effects of different fillers is an important strategy to design and develop high-performance nanocomposites. However, owing to the well-known problems such as dispersion, solution viscosity control, and so on, synergetic enhancement effects are usually offset by the defects induced by fillers in highly loaded nanocomposites. In this work, remarkable synergetic efficiency was realized in graphene nanoplatelet (GNP) and multiwalled carbon nanotube (CNT) highly loaded epoxy composites through a well-designed fabrication method. Dramatic thermal conductivity enhancement was observed in the epoxy composites with 10–50 vol% nanocarbon filler due to synergetic effects. For example, the composite with 20 vol% CNTs and 20 vol% GNPs possess a thermal conductivity up to 6.31 W/mK. This is even much higher than that of the composites with individual 50 vol % CNTs or 50 vol% GNPs. A maximum thermal conductivity 7.30 W/mK was obtained, which is 38-fold of that of the pure epoxy resin. Thermal trans...