Nano-modified Epoxy Research Articles

Damage behaviour of nano-modified epoxy adhesives subject to high stress constraint

ABSTRACTThis paper presents a combined experimental and numerical study on the damage behaviour of core–shell rubber (CSR)-modified epoxy adhesives subject to high stress constraints. The test method consists of a notched axisymmetric adhesive layer loaded in tension. The stress–displacement curves of the rubber-modified adhesives have been found to exhibit a sudden reduction in stiffness after an initial linear loading region. It has been demonstrated that this corresponds to the cavitation of the rubber particles. The stress of rubber cavitation remained essentially constant at a critical hydrostatic stress of approximately 21 MPa over different rubber contents and different stress constraints. It is important to note that the rubber cavitation stress is also dependent on the size of the rubber particles, and the diameter of the rubber core is approximately 170 nm in current work. The stress constraint had negligible effect on the failure strength of the adhesive joints for the studied systems.

Influence of carbon nanoparticles/epoxy matrix interaction on mechanical, electrical and transport properties of structural advanced materials

The focus of this study is to design new nano-modified epoxy formulations using carbon nanofillers, such as carbon nanotubes, carbon nanofibers and graphene-based nanoparticles (CpEG), that reduce the moisture content and provide additional functional performance. The chemical structure of epoxy mixture, using a non-stoichiometric amount of hardener, exhibits unique properties in regard to the water sorption for which the equilibrium concentration of water (Ceq) is reduced up to a maximum of 30%. This result, which is very relevant for several industrial applications (aeronautical, shipbuilding industries, wind turbine blades, etc), is due to a strong reduction of the polar groups and/or sites responsible to bond water molecules. All nanofillers are responsible of a second phase at lower glass transition temperature (Tg). Compared with other carbon nanofillers, functionalized graphene-based nanoparticles exhibit the best performance in the multifunctionality. The lowest moisture content, the high performance in the mechanical properties, the low electrical percolation threshold (EPT) have been all ascribed to particular arrangements of the functionalized graphene sheets embedded in the polymeric matrix. Exfoliation degree and edge carboxylated groups are responsible of self-assembled architectures which entrap part of the resin fraction hindering the interaction of water molecules with the polar sites of the resin, also favouring the EPT paths and the attractive/covalent interactions with the matrix.

Experimental Study of Retrofitted Cracked Concrete with FRP and Nanomodified Epoxy Resin

AbstractNanosilica powder was added to modify the properties of epoxy binder. Two types of modified epoxy resin binder [crack glue and fiber-reinforced plastic (FRP) glue] are developed to repair c...

Experimental investigations of mechanical and electrical characteristics of a nanomodified epoxy resin DER-330

Technique preparation of a composite material based on epoxy resin DER-330 and 5 different nanopowders has been developed. The modifiers exert a positive effect on the elastic modulus, flexural strength, and dielectric permittivity of the epoxy-anhydride polymers. Weight content of nanoadditives in the matrix ranged from 0% to 4%. Dependences between mechanical properties of epoxy composites and concentration and nature of the filler were investigated in a three-point bending. Morphology of the fracture surface was studied. The complex analysis of nanofillers allowed us optimum fillers and concentrations when a significant increase of elastic and strength characteristics is achieved. It was showed that addition of silica fume nanoparticles A-380 to the matrix increases fracture stress on 30%. Composites with nanoparticles of aluminum nitride showed the best mechanical values in case of jointly investigated parameters. Growth of the elastic modulus is 12% and increase of the fracture stress is 7%. Adding alumina nanoparticles and nanofibers in the range of investigated concentration does not lead to significant changes in the mechanical characteristics of the composite

Bond properties of FRP-concrete interface with nano-modified epoxy resin under wet-dry cycles

The interface bonding properties of FRP-reinforced concrete under wet/dry conditions are studied by performing the interface bond test. The effects of the number of wet/dry cycles and FRP layers, and FRP reinforcing sequence on the efficiency of reinforcement are studied. The microstructure of FRP-concrete interface is observed by SEM. The variations in bond properties of FRP-concrete interface under extreme conditions under tension are investigated. Experimental results show at the early stage of wet/dry cycles, the strengths of concrete and epoxy resin increase, and further interface bond strength enhances. As wet/dry cycles forward, defects and loose microstructure form in both FRP and concrete, and the interface bond strength decreases. Under identical conditions, the interface bond strength of sample strengthened by FRP after wet-dry cycles is higher than that of sample strengthened before wet-dry cycles. FRP-concrete bond strength is related to the number of wet-dry cycles.

Nanoindentation, compression and fractural characterization of highly dispersed epoxy silica nanocomposites

Uniaxial compression tests were conducted in this study in order to investigate the compressive properties of the unmodified and nanomodified epoxy with silica nanoparticles. An instrumented nanoindentation technique was also used to investigate its applicability for measuring mechanical properties for such nanocomposite systems. Additionally, the fracture toughness of the unmodified and nanomodified epoxy was measured with single-edge-notch bending tests. The Young’s modulus was found to significantly improve with addition of silica nanoparticles and increase with increasing filler content when measured with both compression and nanoindentation tests. The modulus obtained from the nanoindentation testing was 4–8% higher than the one obtained from the compression tests. As expected, the addition of silica nanoparticles had a significant impact on the fracture toughness and fracture energy and increased with increasing filler content, while observation of the fracture surfaces using SEM suggested that the nanoparticles affected the fracture behavior of such epoxy systems. Implementation of an analytical model in the current nanomodified epoxy network as compared with the experimental fracture energy results showed that the 15% matrix void growth, from debonded nanoparticles, as well as the matrix shear banding are the governing mechanisms of energy absorption.

Thermal protection with a nanomodified epoxy matrix

The results of investigations on the creation of a composite structured by Al2O3 nanopowder operating by the ablation principle for thermal protection of aircraft instead of TZMKT-8 or as an external layer of double-layer heat-resistant coating are presented.

Monitoring the Mechanical Behaviour of Electrically Conductive Polymer Nanocomposites Under Ramp and Creep Conditions

Various amounts of carbon black (CB) and carbon nanofibres (CNF) were dispersed in an epoxy resin to prepare nanocomposites whose mechanical behaviour, under ramp and creep conditions, was monitored by electrical measurements. The electrical resistivity of the epoxy resin was dramatically reduced by both nanofillers after the percolation threshold (1 wt% for CB and 0.5 wt% for CNF), reaching values in the range of 10(3)-10(4) omega . cm for filler loadings higher than 2 wt%. Due to the synergistic effects between the nanofillers, an epoxy system containing a total nanofiller amount of 2 wt%, with a relative CB/CNF ratio of 90/10 was selected for the specific applications. A direct correlation between the tensile strain and the increase of the electrical resistance was observed over the whole experimental range, and also the final failure of the samples was clearly detected. Creep tests confirmed the possibility to monitor the various deformational stages under constant loads, with a strong dependency from the temperature and the applied stress. The obtained results are encouraging for a possible application of nanomodified epoxy resin as a matrix for the preparation of structural composites with sensing (i.e., damage-monitoring) capabilities.

Monitoring the mechanical behavior under ramp and creep conditions of electrically conductive polymer composites

In this work a nanomodified epoxy matrix was used to prepare glass fibers reinforced laminates to be tested under ramp and creep conditions, with a continuous monitoring of their deformational and damage behavior through electrical measurements. A combination of carbon black (CB) and carbon nanofibers (CNFs), with a relative CB/CNF ratio of 90/10 and a total filler amount of 2wt.%, was selected to prepare nanomodified composite laminates by a hand lay-up technique. Tensile tests under ramp and creep conditions highlighted a remarkable strain and damage monitoring capability of the prepared composites, with a strong dependency of the response on the testing temperature and on the load level.

Tensile Properties of Nanosilica/Epoxy Nanocomposites

The effect of nanosilica on the tensile stress-strain response of Epikote 828 epoxy polymer was studied. A 40 wt% nanosilica/epoxy masterbatch was used to prepare a series of nanocomposites with 5–25 wt% nanosilica content. Static uniaxial tensile tests were conducted to investigate the tensile stress–strain response and tensile properties of unmodified and nanomodified epoxy polymers. In addition, the degree of dispersion of the silica nanosphere particle in the epoxy matrix was investigated using transmission electron microscopy. It was found that the incorporation of a well-disperse nanosilica improved the tensile properties of the polymer. The addition of 25 wt% nanosilica enhanced the tensile modulus and strength of about 38% and 24%, respectively, compared to the neat polymer without sacrificing the failure strain.

Compatibility and Anti-oxidation Properties of Study on Liquid Oxygen Compatibility with Nano-modified Epoxy Composites

Nano-sized silica particles were synthesized by sol-gel reaction. Epoxy resin/nano-silica composites were prepared by high-speed mixing after ultrasonic dispersion. By using electron microscopy and scanning electron microscope (SEM) techniques, the particle dispersion in the epoxy resin/nano-silica composites is studied. Anti-oxidation properties of the materials were investigated by thermogravimetric analysis (TGA) in the oxygen. The compatibility of the nano-composites with liquid oxygen was ranked according to the liquid oxygen sensitivity impact test results by the ASTM D2512 liquid oxygen (LOX) impact test. The results showed that the nano-modification method can significantly improve the liquid oxygen compatibility of epoxy composites.

Special wetting behavior of a graphitic nanofiber-modified epoxy generalized for rough textured fabric surfaces

Wetting behavior of a polymer resin used as matrix on fabric surfaces is one of the key attributes for making high quality structural composites. Though incorporation of various functionalized nanoparticles can stimulate improvements to many properties of epoxy resins, there has not been any report on wettability of any nano-modified epoxy on rough inclined fabric surfaces. In this research work, wetting behavior of a previously developed nano-epoxy resin modified by a type of reactive graphitic nanofibers (r-GNFs) was investigated. The observation results revealed that a unique wetting behavior was discovered from the nano-epoxy on rough fabric surfaces due to the contribution of the r-GNFs. Based on this dramatically improved wettability of the epoxy, a concept of dry–wet contact model was proposed to interpret the different wetting phenomenon observed from the nano-epoxy and that of the pure epoxy. The improved wetting characteristics of the nano-epoxy system will be essential for enabling future energy efficient infusion processing for manufacturing high quality and high-performance structural composite applications.

Wetting characteristics of epoxy resins modified by graphitic nanofibers with different functional groups

Resin wettability and flowability are critically important for manufacturing structural composites. Various nano-modified epoxy resins have shown great potential for improving composite performance. However, the effects of the nanofillers with different functional groups on wetting behaviors of epoxy resins have not been reported. In this work, wetting characteristics of epoxy resins modified by as-received graphitic nanofibers (GNFs), oxidized GNFs and reactive GNFs (re-GNFs) that we previously developed were studied. To quantitatively evaluate effects of the matrix modification on the wetting behavior, the measuring techniques of dynamic contact angle, Du Nouy ring, and droplet spreading rate tests were taken to characterize dynamic wetting behaviors of the nano-modified epoxy matrices. The study results showed that GNFs with different functional groups led to different effects on surface tension, advancing contact angle, spreading rate of epoxy resin. In particular, the re-GNF modified epoxy showed remarkably improved wettability that was observed from the special wetting phenomenon on a fabric surface. This nano-modified epoxy system will be significant for enabling energy efficient infusion processing for manufacturing high quality and high performance structural composite application.

Effect of silica nanoparticles on compressive properties of an epoxy polymer

The effect of nanosilica on compressive properties of an Epikote 828 epoxy at room temperature was studied. A 40 wt% nanosilica/epoxy masterbatch (nanopox F400) was used to prepare a series of epoxy based nanocomposites with 5–25 wt% nanosilica content. Static uniaxial compression tests were conducted on cubic and cylindrical specimens to study the compressive stress–strain response, failure mechanisms and damage characteristics of the pure and nanomodified epoxy. It was found that the compressive stiffness and strength were improved with increasing nanosilica content without significant reduction in failure strain. The presence of nanosilica improved ductility and promoted higher plastic hardening behaviour after yielding in comparison with the unmodified resin system. This result suggested that nanoparticles introduced additional mechanisms of energy absorption to enhance the compressive properties without reducing the deformation to failure.

Nano-structured sandwich composites response to low-velocity impact

Abstract This paper investigates the influence of exfoliated nano-structures on sandwich composites under impact loadings. A set of sandwich composites plates made of fiberglass/nano-modified epoxy face sheets and polystyrene foams was prepared. The core was 25 mm thick and the face sheets were made of eight layers of woven fabric glass fibers and nano-modified epoxy (≈0.8 mm of thickness). The epoxy system was bisphenol A resin and an amine hardener. The fiber volume fraction used was around 65%, while the nanoclay content varied from 0 wt.% to 10 wt.%. The nanoclay used was Cloisite 30B from Southern Clay. The sandwich panels were submitted to low-velocity impact tests with energies from 5 J to 75 J. Two sets of experiments were performed, i.e. high velocity + low mass and low velocity + high mass. Damage caused by the two groups of experiments and peak forces measured were dissimilar. The results show that the addition of 5 wt.% of nanoclay lead to a more efficient energy absorption. The failure modes were also analyzed, and they seems to be affected by the nanoclay addition to face sheets.

Fracture Behavior of GFRP Laminates with Nanocomposite Epoxy Resin Matrix

Nano-sized, functionalized organo-silicate fillers dispersed in the epoxy matrix are one approach that is investigated for improving the delamination resistance of fiber-reinforced composites. The variety of nano-silicate fillers available on the market, of processing conditions and the related characterization effort make it desirable to have a simple, easily analyzed screening method for both, nano-modified resins and laminates. An impact test using hail simulation equipment and visual assessment on glass-fiber laminates with nano-modified epoxy matrix yields rough indications of the effect of nano-modification on the fracture behavior of the specimens that correlate with more sophisticated macroscopic and microscopic characterization.

The influence of silicate-based nano-filler on the fracture toughness of epoxy resin

Dispersion of nano-sized, silicate-based filler in epoxy resin is expected to yield improved materials properties in several areas. Various mechanical properties, specifically improved fracture toughness, as well as improved flame-retardant effects are of interest. The final objective of the research is investigating whether a nano-modified epoxy matrix yields improved delamination resistance in a fiber-reinforced laminate compared to a laminate with neat epoxy as matrix material. As a first step towards this goal, the fracture toughness of nano-modified epoxy resin is compared with that of the neat resin. Fracture toughness improvement up to about 50% and energy release rates increased by about 20% are observed for addition of 10 wt.% of organosilicate clay.