Showing papers on "Epoxy published in 2003"

Improving the Dispersion and Integration of Single-Walled Carbon Nanotubes in Epoxy Composites through Functionalization

Abstract: Considerable improvement in the dispersion of purified single-walled carbon nanotubes (SWNTs) in an epoxy composite was obtained through functionalization of the SWNTs by using an optimized H2SO4/70% HNO3 acid treatment and subsequent fluorination. Epoxy composites containing 1 wt % nanotubes were processed by dissolving the functionalized SWNTs in dimethylformamide and mixing with the epoxy resin thereafter. The functionalized nanotubes were observed to be highly dispersed and well integrated in the epoxy composites. The enhancement of mechanical properties of the latter was indicated by a 30% increase in modulus and 18% increase in tensile strength. This work demonstrates the practical use of combining acid treatment and fluorination to achieve functionalization and unroping of SWNTs. The functionalized SWNTs can be integrated into epoxy composites through the formation of strong covalent bonds in the course of epoxy ring-opening esterification and curing chemical reactions.

Effectiveness of surface coatings in improving concrete durability

Abstract: This paper reports results of a study conducted to evaluate the durability of concrete coated with concrete surface coatings representing five generic types. The durability of the uncoated and coated concrete specimens was evaluated by assessing water absorption, chloride permeability and chloride diffusion. The chemical resistance was evaluated by immersing the uncoated and coated mortar specimens in 2.5% sulfuric acid. The results indicated that epoxy and polyurethane coatings performed better than acrylic, polymer and chlorinated rubber coatings. However, noticeable variation in the performance of the same generic type procured from different manufacturers was noted. Therefore, the selection of coatings should be done after conducting trial tests rather than basing it solely on the generic type.

ABC Triblock Copolymers/Epoxy−Diamine Blends. 2. Parameters Controlling the Morphologies and Properties

Abstract: The effect of composition and concentration of polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) copolymer triblock on final morphologies and properties of modified epoxy networks has been investigated. The DGEBA−MCDEA epoxy system, which ensures the miscibility of most of the PMMA blocks until the end of the reaction and thus the generation of a nanostructurated material, has been chosen. For low copolymer concentration (10 wt %), the network structure is found to be independent of the composition and micelles of PS and PB blocks can be undifferently observed. However, increasing copolymer amounts from 10 to 50 wt % induces a morphology change to either “spheres on spheres” or “core−shell” structure depending on the PB content in the triblock. For copolymer concentration higher than 50 wt %, the morphology strongly depends on the processing technique used, and only films prepared by solvent casting show an organization with long-range order similar to the neat block copolymer. The tou...

Strengthening of Steel-Concrete Composite Girders using Carbon Fiber Reinforced Polymers Sheets

Abstract: The use of advanced composite materials for rehabilitation of deteriorating infrastructure has been embraced worldwide. The conventional techniques for strengthening of substandard bridges are costly, time consuming, and labor intensive. Many new techniques have used the lightweight, high strength, and the corrosion resistance of fiber reinforced polymers ~FRP! laminates for repair and retrofit applications. The load-carrying capacity of a steel-concrete composite girder can be improved significantly by epoxy bonding carbon fiber reinforced polymers ~CFRP! laminates to its tension flange. This paper presents the results of a study on the behavior of steel-concrete composite girders strengthened with CFRP sheets under static loading. A total of three large-scale composite girders made of W355313.6 A36 steel beam and 75-mm thick by 910-mm wide concrete slab were prepared and tested. The thickness of the CFRP sheet was constant and a different number of layers of 1, 3, and 5 were used in the specimens. The test results showed that epoxy-bonded CFRP sheet increased the ultimate load-carrying capacity of steel-concrete composite girders and the behavior can be conservatively predicted by traditional methods.

Use of epoxy/multiwalled carbon nanotubes as adhesives to join graphite fibre reinforced polymer composites

Abstract: In this study, different weight fractions of multiwalled carbon nanotubes were dispersed in epoxy to produce toughened adhesives. The reinforced adhesives were used to bond the graphite fibre/epoxy composite adherends. Single lap joint samples were prepared and the average shear strengths were experimentally measured. Significant enhancement of the bonding performance was observed as the weight fraction of carbon nanotubes was increased.

Layered Silicate Nanocomposites Based on Various High-Functionality Epoxy Resins: The Influence of Cure Temperature on Morphology, Mechanical Properties, and Free Volume

Abstract: This paper investigates the relationship between cure temperature, morphology, and mechanical properties of di-, tri-, and tetrafunctional high-performance, epoxy layered-silicate nanocomposites. Wide-angle X-ray analysis (XRD) was carried out at different stages of cure to monitor organoclay exfoliation kinetics. It was found that some (small) degree of conversion was required to obtain significant intercalation. The nanocomposite morphology was also probed using transmission electron microscopy, XRD, and positron annihilation lifetime spectroscopy. The bifunctional DGEBA resin gave better exfoliation than the resins of higher functionalities. This is attributed to better catalysis of the intragallery reaction by the organo-ions which reside within the galleries. Higher cure temperatures were also found to improve clay delamination and simultaneously increased toughness and modulus in case of the DGEBA- and TGAP-based materials. Free volume properties did not vary significantly between resins or with cur...

Toughening structural adhesives via nano- and micro-phase inclusions

Abstract: It has been clearly demonstrated that the addition of low concentrations of nanosilica particles to a typical rubber-toughened adhesive, based upon a two-part epoxy formulation, leads to very signi...

Clay‐reinforced epoxy nanocomposites

Abstract: Epoxy/clay nanocomposites were prepared using a conventional diglycidyl ether of bisphenol A (DGEBA) epoxy, cured with diethyltoluene diamine (DETDA). The nanocomposites were characterized by dynamic mechanical analysis. A modest increase in glass transition temperature and significant increase in storage modulus were achieved as a result of incorporation of clay. The formation of nanocomposite was confirmed by wide-angle X-ray analysis. The higher impact strength of the nanocomposite compared the DGEBA matrix was explained in terms of with the morphology observed by SEM. © 2003 Society of Chemical Industry

Formation of silica/epoxy hybrid network polymers

Abstract: Epoxy-based inorganic–organic hybrid polymers, for use as a matrix in coatings, have been prepared from 3glycidoxypropyltrimethoxysilane by a sol–gel process. The precursor molecule possesses both epoxy and silicon alkoxide functionality and so interlinked inorganic–organic networks can be formed. Diethylenetriamine was used to open the epoxy rings and form the organic network to an extent determined by the initial ratio of amine to epoxy groups. The materials were cured either at room temperature or with an additional heat treatment at 150 C. Structural characterisation of the cured hybrid materials was performed using a combination of Raman, and 29 Si and 13 C MAS NMR spectroscopies. These show that the formation of the two networks does not occur independently and the rate or extent of organic cross-linking has a direct effect on the extent of the inorganic network formation, and vice-versa. 2003 Elsevier Science B.V. All rights reserved.

Toughening Epoxy Adhesives to Meet Today's Challenges

Abstract: There are many advantages that polymeric adhesives can offer compared with the more traditional methods of structural joining such as bolting, brazing, welding, and mechanical fastening, and epoxy adhesives represent the most common type of structural adhesive. When polymerized, epoxy adhesives are amorphous and highly cross-linked materials, and this microstructure results in many useful properties for structural engineering applications, such as a high modulus and failure strength, low creep, and, by careful formulation, good performance at elevated temperatures. However, the structure of such thermosetting adhesives also generally leads to one highly undesirable property: they are relatively brittle materials, with poor resistance to crack initiation and growth. Nevertheless, the incorporation of a second phase of dispersed rubbery particles into the epoxy polymer can greatly increase their toughness without significantly impairing their other desirable engineering properties. Thus, rubber-toughened epoxy adhesives can be used, for example, in applications where very high impact resistance is required for the bonded joint.

Study of high thermal conductive epoxy resins containing controlled high-order structures

Abstract: Heat is transported by phonons through dielectric solids such as ceramics and organic insulating resins. Especially in organic insulating resins, phonons scatter intensely mainly by their amorphous structure, which affects their thermal conductivities, usually 1 to 3 orders lower than those of ceramics and metals. Here, we show that by the thermosetting resin system with a crystal-like structure that is microscopic anisotropy, the thermal conductivities of the resin themselves can be improved while keeping their macroscopic isotropy. We studied four kinds of diepoxy monomers with a biphenyl group or two phenyl benzoate groups as mesogens, and cured them thermally with an aromatic diamine curing agent. These thermal conductivities were maximally 5 times higher than that of conventional epoxy resins because mesogens were highly ordered to form crystal-like structures to suppress phonon scattering. We also succeeded in the direct confirmation of the existence of crystal-like structures in the epoxy resins by TEM observation. These results suggest a novel strategy to improve thermal conductivities of insulating resins themselves by controlling the high-order structures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2464–2467, 2003

Effect of Palmitic Acid on the Electrical Conductivity of Carbon Nanotubes−Epoxy Resin Composites

Abstract: We found that the palmitic acid allows an efficient dispersion of carbon nanotubes in the epoxy matrix. We have set up an experimental protocol in order to enhance the CNTs dispersion in epoxy resin. Electrical conductivity is optimal using a 1:1 CNTs to palmitic acid weight ratio. The associated percolation threshold is found between 0.05 and 0.1 wt % CNTs, i.e., between 0.03 and 0.06 vol %. The SEM image shows essentially individual CNTs which is inagreement with conductivity measurements. In comparison with composites without palmitic acid, the use of palmitic acid improves the electrical properties of CNTs-epoxy resin composites.

Preparation, thermal properties, and flame retardance of epoxy–silica hybrid resins

Abstract: A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′-diaminodiphenylmethane with the sol–gel reaction of a phosphorus-containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with 3-glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, 1H and 31P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass-transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003