Showing papers on "Epoxy published in 2007"

Graphite Nanoplatelet−Epoxy Composite Thermal Interface Materials

Abstract: Natural graphite was intercalated, thermally exfoliated, and dispersed in acetone to prepare graphite nanoplatelets (GNPs, Gn) of controlled aspect ratio. Thermal conductivity measurements indicate that few graphene layer Gn, where n ∼ 4, with a thickness of ∼2 nm function as a very efficient filler for epoxy composites. When embedded in an epoxy matrix, the G4 GNPs provide a thermal conductivity enhancement of more than 3000% (loading of ∼25 vol %), and a thermal conductivity κ = 6.44 W/mK, which surpasses the performance of conventional fillers that require a loading of ∼70 vol % to achieve these values. We attribute the outstanding thermal properties of this material to a favorable combination of the high aspect ratio, two-dimensional geometry, stiffness, and low thermal interface resistance of the GNPs.

Multiscale carbon nanotube-carbon fiber reinforcement for advanced epoxy composites.

Abstract: We report an approach to the development of advanced structural composites based on engineered multiscale carbon nanotube−carbon fiber reinforcement. Electrophoresis was utilized for the selective deposition of multi- and single-walled carbon nanotubes (CNTs) on woven carbon fabric. The CNT-coated carbon fabric panels were subsequently infiltrated with epoxy resin using vacuum-assisted resin transfer molding (VARTM) to fabricate multiscale hybrid composites in which the nanotubes were completely integrated into the fiber bundles and reinforced the matrix-rich regions. The carbon nanotube/carbon fabric/epoxy composites showed ∼30% enhancement of the interlaminar shear strength as compared to that of carbon fiber/epoxy composites without carbon nanotubes and demonstrate significantly improved out-of-plane electrical conductivity.

A self-healing carbon fibre reinforced polymer for aerospace applications

Abstract: Self-healing is receiving increasing interest worldwide as a technology to autonomously address the effects of damage in composite materials. This paper describes the results of four point bend flexural testing (ASTM-D6272-02) of T300/914 carbon fibre reinforced epoxy with resin filled embedded hollow glass fibres (HGF) which provided a self-healing functionality. The study investigated the effect of the embedded HGF on the host CFRP mechanical properties and also the healing efficiency of the laminates after they were subjected to quasi-static impact. Specimens were tested in the undamaged, damaged and healed conditions using a commercial two-part epoxy healing agent (Cytec Cycom 823). Microscopic characterisation of the embedded HGF was also undertaken to characterise the effect on the host laminate fibre architecture.

Bioinspired self-healing of advanced composite structures using hollow glass fibres.

Abstract: Self-healing is receiving an increasing amount of worldwide interest as a method to autonomously address damage in materials. The incorporation of a self-healing capability within fibre-reinforced polymers has been investigated by a number of workers previously. The use of functional repair components stored inside hollow glass fibres (HGF) is one such bioinspired approach being considered. This paper considers the placement of self-healing HGF plies within both glass fibre/epoxy and carbon fibre/epoxy laminates to mitigate damage occurrence and restore mechanical strength. The study investigates the effect of embedded HGF on the host laminates mechanical properties and also the healing efficiency of the laminates after they were subjected to quasi-static impact damage. The results of flexural testing have shown that a significant fraction of flexural strength can be restored by the self-repairing effect of a healing resin stored within hollow fibres.

Stress-strain model for concrete confined by FRP composites

Abstract: In this paper, a stress–strain model for concrete confined by fiber reinforced polymer (FRP) composites is developed. The model is based on the results of a comprehensive experimental program including large-scale circular, square and rectangular short columns confined by carbon/epoxy and E-glass/epoxy jackets providing a wide range of confinement ratios. Ultimate stress, rupture strain, jacket parameters, and cross-sectional geometry were found to be significant factors affecting the stress–strain behavior of FRP-confined concrete. Such parameters were analyzed statistically based on the experimental data, and equations to theoretically predict these parameters are presented. Experimental results from this study were compared to the proposed semi-empirical model as well as others from the literature.

Study on preparation and fire-retardant mechanism analysis of intumescent flame-retardant coatings

Abstract: An intumescent flame-retardant coating was prepared by unsaturated polyester resin and epoxy resin as two-component matrix resins, ammonium polyphosphate (APP) as acid source, melamine (Mel) as the blowing agent and pentaerythritol (PER) as carbon agent, expandable graphite as synergistic agent, adding titanium dioxide (TiO2), solvent and other assistants. Results showed that such a coating had excellent physical–chemical properties. When the thickness of the coating on the wood matrix reached 2.0 mm, the limit of fire-endurance could get to 210 min. And the various component thermal characteristics, decompose processes and interactions of the flame-retardant coating system were investigated by DSC and TGA. The contribution of phosphorus to the formation of the final charring layer and their morphological structures was studied by SEM, XRD and FTIR. On the basis, the flame-retardant mechanism of the intumescent flame-retardant coating was systematically investigated.

Clay Assisted Dispersion of Carbon Nanotubes in Conductive Epoxy Nanocomposites

Abstract: Clay was introduced into single-walled carbon nanotube (SWNT)/epoxy composites to improve nanotube dispersion without harming electrical conductivity or mechanical performance. Unlike surfactant or polymer dispersants, clay is mechanically rigid and known to enhance the properties (e.g., modulus, gas barrier, and flame retardation) of polymer composites. Combining nanotubes and clay allows both electrical and mechanical behavior to be simultaneously enhanced. With just 0.05 wt % SWNT, electrical conductivity is increased by more than four orders of magnitude (from 10–9 to 10–5 S cm–1) with the addition of 0.2 wt % clay. Furthermore, the percolation threshold of these nanocomposites is reduced from 0.05 wt % SWNT to 0.01 wt % with the addition of clay. SWNTs appear to have an affinity for clay that causes them to become more exfoliated and better networked in these composites. This clay-nanotube synergy may make these composites better suited for a variety of packaging, sensing, and shielding applications.

Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nanoclay-filled epoxy matrix

Abstract: The mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading, and the improvement of flexural modulus was at the expense of a reduction in flexural strength. The quasi-static fracture toughness increased, whereas the impact fracture toughness dropped sharply with increasing the clay content. Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed the trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. Both the initiation and propagation values of mode I interlaminar fracture toughness of CFRP composites increased with increasing clay concentration. In particular, the propagation fracture toughness almost doubled with 7 wt% clay loading. A strong correlation was established between the fracture toughness of organoclay-modified epoxy matrix and the CFRP composite interlaminar fracture toughness.

Enhanced thermal conductivity of boron nitride epoxy‐matrix composite through multi‐modal particle size mixing

Abstract: Castable particulate-filled epoxy resins exhibiting excellent thermal conductivity have been prepared using hexagonal boron nitride (hBN) and cubic boron nitride (cBN) as fillers. The thermal conductivity of boron nitride filled epoxy matrix composites was enhanced up to 217% through silane surface treatment of fillers and multi-modal particle size mixing (two different hBN particle sizes and one cBN particle size) prior to fabricating the composite. The measurements and interpretation of the curing kinetics of anhydride cured epoxies as continuous matrix, loaded with BN having multi-modal particle size distribution, as heat conductive fillers, are highlighted. This study evidences the importance of surface engineering and multi-modal mixing distribution applied in inorganic fillered epoxy-matrix composite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Properties of halloysite nanotube–epoxy resin hybrids and the interfacial reactions in the systems

Abstract: A naturally occurred microtubullar silicate, halloysite nanotubes (HNTs), was co-cured with epoxy/cyanate ester resin to form organic–inorganic hybrids. The coefficient of thermal expansion (CTE) of the hybrids with low HNT concentration was found to be substantially lower than that of the plain cured resin. The moduli of the hybrids in the glassy state and rubbery state were significantly higher than those for the plain cured resin. The dispersion of HNTs in the resin matrix was very uniform as revealed by the transmission electron microscopy (TEM) results. The interfacial reactions between the HNTs and cyanate ester (CE) were revealed by the results of Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The substantially increased properties of the hybrids were attributed to the covalent bonding between the nanotubes and the matrix.

Morphology, dynamic mechanical and thermal studies on poly(styrene-co-acrylonitrile) modified epoxy resin/glass fibre composites

Abstract: Poly(styrene-co-acrylonitrile) (SAN) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRPs) in order to get improved mechanical and thermal properties. E-glass fibre was used as the fibre reinforcement. The morphology, dynamic mechanical and thermal characteristics of the systems were analyzed. Morphological analysis revealed heterogeneous dispersed morphology. There was good adhesion between the matrix polymer and the glass fibre. The dynamic moduli, mechanical loss and damping behaviour as a function of temperature of the systems were studied using dynamic mechanical analysis (DMA). DMA studies showed that DDS cured epoxy resin/SAN/glass fibre composite systems have two Tgs corresponding to epoxy rich and SAN rich phases. The effect of thermoplastic modification and fibre loading on the dynamic mechanical properties of the composites were also analyzed. Thermogravimetric analysis (TGA) revealed the superior thermal stability of composite system.

Functionalizing Carbon Nanotubes by Plasma Modification for the Preparation of Covalent-Integrated Epoxy Composites

Abstract: A novel method for preparing a fully integrated nanotube composite material through the use of functionalized multi-walled carbon nanotubes (MWNTs) is presented in this study. The functionalization of MWNTs was performed via plasma treatment; subsequently, maleic anhydride (MA) was grafted onto the MWNTs (CNTs-MA). Nanotube-reinforced epoxy polymer composites were prepared by first mixing the CNTs-MA and a diamine curing agent, followed by a further reaction with the epoxy matrix. In this hybrid nanocomposite system, the CNTs-MA were covalently integrated into the epoxy matrix and became part of the cross-linked structure rather than just a separate component. Fourier transform infrared (FT-IR) and high resolution X-ray photoelectron (XPS) spectroscopes were used to characterize the functional groups on the surface of the MWNTs after the plasma modification. In addition, observations of scanning electronic microscopy (SEM) and transmission electron microscopy (TEM) images showed that the functionalized na...

Dynamic mechanical analysis of carbon/epoxy composites for structural pipeline repair

Abstract: The viscoelastic behavior of a carbon fiber/epoxy matrix composite material system used for pipeline repair has been evaluated though dynamic mechanical analysis. The effects of the heating rate, frequency, and measurement method on the glass transition temperature ( T g ) were studied. The increase in T g with frequency was related to the activation energy of the glass transition relaxation. The activation energy can be used for prediction of long term performance. The measured tan delta peak T g ’s of room temperature cured and post-cured composite specimens ranged from 60 to 129 °C. Analysis of T g data at various cure states was used to determine use temperature limits for the composite repair system.

Experimental study on the thermal and mechanical properties of multi-walled carbon nanotube-reinforced epoxy

Abstract: In this study, multi-walled carbon nanotubes (CNTs) were infused into Epon 862 epoxy through a high intensity ultrasonic liquid processor and then mixed with EpiCure curing agent W using a high-speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and flexural tests were performed on unfilled, 0.1, 0.2, 0.3, and 0.4 wt% CNT-filled epoxy to identify the loading effect on the thermal and mechanical properties of composites. DMA studies revealed that filling the carbon nanotube into epoxy can produce a 90% enhancement in storage modulus and a 22 °C increase in Tg. However, due to the lower crosslink density of the nanophased systems, a 6 °C decrease in decomposition temperature was observed in the 0.4 wt% CNT/epoxy in the TGA test. The flexural results showed that modulus increased with higher CNT loading percentages and the 0.3 wt% CNT-infusion system showed the maximum strength enhancement. Based on the experiment's results, a nonlinear constitutive equation was established for neat and nanophased epoxy.

Carbon nanotube integrated multifunctional multiscale composites

Abstract: Carbon nanotubes (CNTs) demonstrate extraordinary properties and show great promise in enhancing out-of-plane properties of traditional polymer composites and enabling functionality, but current manufacturing challenges hinder the realization of their potential. This paper presents a method to fabricate multifunctional multiscale composites through an effective infiltration-based vacuum-assisted resin transfer moulding (VARTM) process. Multi-walled carbon nanotubes (MWNTs) were infused through and between glass-fibre tows along the through-thickness direction. Both pristine and functionalized MWNTs were used in fabricating multiscale glass-fibre-reinforced epoxy composites. It was demonstrated that the mechanical properties of multiscale composites were remarkably enhanced, especially in the functionalized MWNT multiscale composites. With only 1?wt% loading of functionalized MWNTs, tensile strength was increased by 14% and Young's modulus by 20%, in comparison with conventional fibre-reinforced composites. Moreover, the shear strength and short-beam modulus were increased by 5% and 8%, respectively, indicating the improved inter-laminar properties. The strain?stress tests also suggested noticeable enhancement in toughness. Scanning electron microscopy (SEM) characterization confirmed an enhanced interfacial bonding when functionalized MWNTs were integrated into epoxy/glass-fibre composites. The coefficient thermal expansion (CTE) of functionalized nanocomposites indicated a reduction of 25.2% compared with epoxy/glass-fibre composites. The desired improvement of electrical conductivities was also achieved. The multiscale composites indicated a way to leverage the benefits of CNTs and opened up new opportunities for high-performance multifunctional multiscale composites.

Thermo-physical properties of epoxy nanocomposites reinforced with amino-functionalized multi-walled carbon nanotubes

Abstract: The modification of multi-walled carbon nanotubes (MWNTs) with amine groups was investigated by FTIR, Raman spectroscopy and XPS after such steps as carboxylation, acylation and amidation. Nanotube-reinforced epoxy polymer composites were prepared by mixing amino-functionalized MWNTs with epoxy resin and curing agent. DSC, TGA, SEM and flexural test were used to investigate the thermal and mechanical properties of the composites. The results showed that amino-functionalized MWNTs could enhance the interfacial adhesion between the nanotubes and the matrix, thus greatly improve the thermal and mechanical properties of the resin epoxy bulk material.

Pyrolysis of epoxy resins and fire behavior of epoxy resin composites flame‐retarded with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide additives

Abstract: The pyrolysis of an epoxy resin and the fire behavior of corresponding carbon fiber-reinforced composites, both flame-retarded with either 10-ethyl-9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide or 1,3,5-tris[2-(9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide-10-)ethyl]1, 3,5-triazine-2,4,6(1H,3H,5H)-trione, are investigated The different fire retardancy mechanisms are discussed, and their influence on the fire properties assessed, in particular for flammability (limiting oxygen index, UL 94) and developing fires (cone calorimeter with different external heat fluxes of 35, 50, and 70 kW m−2) Adding the flame retardants containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide affects the fire behavior by both condensed phase and gas phase mechanisms Interactions between the additives and the epoxy resin result in a change in the decomposition pathways and an increased char formation The release of phosphorous products results in significant flame inhibition The fire properties achieved are thus interesting with respect to industrial exploration © 2007 Wiley Periodicals, Inc J Appl Polym Sci 104: 2260–2269, 2007

Mechanical properties of CFRP laminates manufactured from unidirectional prepregs using CSCNT-dispersed epoxy

Abstract: This study presents the experimental results of the mechanical properties of three-phase CFRP laminates consisting of traditional carbon fibers and epoxy matrix modified using cup-stacked carbon nanotubes (CSCNTs) in comparison to those of CFRP laminates without CSCNTs. The prepreg system of carbon fibers impregnated with CSCNT-dispersed epoxy is developed, and successful fabrication of three-phase CFRP laminates is achieved using an autoclave. Basic mechanical properties of unidirectional laminates (stiffness, strength, fracture toughness, etc.) are summarized. Next, quasi-isotropic laminates are subjected to tension, compression, flexural, and compression after impact (CAI) tests. Improvement of stiffness and strength and no adverse effects on mechanical properties due to CSCNT dispersion are experimentally verified.