Toughness Of Epoxy Resin Research Articles

Thin films of epoxy adhesives containing recycled polymers and graphene oxide nanoflakes for metal/polymer composite interface

Epoxy adhesives based on recycled poly(ethylene terephthalate) (PET), ground rubber tire (GTR), and graphene oxide (GO) nanoflakes were designed and their thermal and mechanical properties were discussed. By changing the amounts of the aforementioned components (recycled polymers and GO nanosheets), adhesive formulations were tested for tensile and single-lap shear strength applied at the interface between epoxy/carbon fiber and stainless steel. The best and the worst samples in regard to mechanical strength were specified and selected for thermal degradation analyses base on thermogravimetric analysis (TGA). The dispersion state of PET and GTR were also studied by the use of field-emission scanning electron microscopy (FE-SEM). It was found that addition of 10 phr of 75/25 (w/w) PET/GTR mixture to 100 parts by weight of epoxy together with 0.1 phr of GO could surprisingly enhance ca. 29, 260 and 585% the Young’s modulus, tensile strength, and the toughness of epoxy, respectively. It was also proved that introduction of GO to the adhesive enhanced thermal stability of epoxy/(PET/GTR).

Improving fracture toughness of epoxy resin composites by magnetic particles modified short glass fiber

In this paper, magnetic nanoparticles were loaded on the surface of short glass fibers by solvent thermal method to prepare magnetic short glass fibers (MSGF) that has orientation response to a weak magnetic field (0.12T), and further MSGF/epoxy resin (EP) composites were prepared. Scanning electron microscope, X-ray diffractometer, infrared spectroscopy and vibration sample magnetometer were used to characterize the samples before and after loading magnetic nanoparticles on the surface of SCF. The effects of MSGF particle content and magnetic field on the fracture toughness of MSGF/EP composites and the toughening mechanism were investigated. The results show that γ-Fe2O3 nanoparticles surface loaded MSGF are successfully achieved using solvothermal synthesis method under the 240 °C with ferric acetylacetonate as iron source and ethanol as solvent. With the optimum MSGF content of 3wt%, when MSGF are oriented along the direction perpendicular to the crack growth under magnetic field, compared to that of pure epoxy resin, the fracture toughness Kic and Gic of the composite materials with magnetic orientation are increased by 54.4% and 138.5%, respectively, and increased by 20% and 43.9% than that of MSGF/EP composites without magnetic orientation, respectively. The main mechanisms of toughening epoxy resin by MSGF include debonding, pulling-out, bridging and deflecting crack.

Epoxy nanocomposites significantly toughened by both poly(sulfone) and graphene oxide

Abstract Toughening of brittle epoxy (EP) resins is important to widen their applications. In this work, both polysulfone (PSF) as thermoplastic toughening agent and graphene oxide (GO) as nanofiller toughening agent are employed to toughen diglycidyl ether of bisphenol-A (DEGBA) epoxy resin. PSF and GO are added to EP via melt blending and solvent mixing method, respectively. Pure epoxy resin is brittle with a fracture toughness ( K I C ) of ca. 0.99 MPa . m 0.5 . Dual toughening by the simultaneous addition of PSF and GO significantly enhances the fracture toughness of the epoxy resin. The GO/PSF/EP ternary nanocomposite with 5 phr PSF and 0.2 phr GO shows the maximum value of ca. 1.88 MPa . m 0.5 with an increase of 89.90% in K I C compared to that of neat epoxy. Meanwhile, the elongation at break is also greatly enhanced by the addition of PSF and GO. Moreover, the tensile strength , Young's modulus and thermal stability are slightly enhanced and glass transition temperature is maintained after PSF and GO are introduced into EP resin. The current strategy of using both PSF and GO as dual toughening agents is promising for effectively toughening epoxy resins without sacrificing tensile and thermal properties.

Investigation of Wear Properties of Toughened Epoxy Resin using Silane Terminated Urethane

Investigation of Wear Properties of Toughened Epoxy Resin using Silane Terminated Urethane

Imidazole-supported silica one-pot processed nanoparticles to enhance toughness of epoxy based nanocomposites

In this study, imidazole supported silica nanoparticle (ISS) was prepared from Tetraethyl orthosilicate (TEOS) precursor via co-condensation method. To warrant the chemical linkage of imidazole group to the silica surface, different spectroscopic characterization was performed. The microscopic investigation under TEM elucidates GMS/ISS particle size compared to as synthesized nanosilica (nS), which also endorses their surface modification. Further, ISS (0–3 wt %) was used to prepare epoxy nanocomposites. The ISS/EP enhances the tensile strength as well as the tensile modulus by ∼45% (84 MPa) and ∼36% (1.37 GPa) with respect to the neat epoxy (58 MPa and 1 GPa) respectively. Herein, the ISS nanoparticle uplifts the tensile performance of the epoxy nanocomposites at lower (1 wt %) filler content. To verify this result, further the dispersion study of ISS in epoxy system under TEM study was performed. A homogeneous distribution is observed at 1 wt % of ISS nanoparticles. In addition to that, Composites embedded with 1 wt % of ISS showed significant enhancement in toughness without sacrificing their stiffness properties. This noticeable improvement offered by ISS opens up the scope to use theses one-pot synthesized nanoparticles as toughness enhancer for highly brittle epoxy systems.

Toughening of Epoxy Resin: The Effect of Water Jet Milling on Worn Tire Rubber Particles.

In this work a cycloaliphatic amine-cured epoxy (EP) resin was modified by micron-scale rubber particles (RP). Nominal RP, in sizes of 200 and 600 µm respectively, were produced using worn truck tires and ultra-high-pressure water jet cutting. The RP were dispersed into the EP resin using different mixing techniques (mechanical, magnetic, and ultrasonic stirring) prior to the introduction of the amine hardener. The dispersion of the RP was studied using optical light microscopy. A longer mixing time reduced the mean size of the particles in the EP compounds. Static (tensile and flexural), dynamic (unnotched Charpy impact), and fracture mechanical (fracture toughness and strain-energy release rate) properties were determined. The incorporation of the RP decreased the stiffness and strength values of the modified EPs. In contrast, the irregular and rough surface of the RP resulted in improved toughness. The fracture toughness and strain-energy release rate were enhanced up to 18% owing to the incorporation of 1% by weight (wt%) RP. This was traced to the effects of crack pinning and crack deflection. Considerably higher improvement (i.e., up to 130%) was found for the unnotched Charpy impact energy. This was attributed to multiple cracking associated with RP-bridging prior to final fracture.

Low dielectric constant and high toughness epoxy resin based on hyperbranched polyester grafted by flexible chain modified

A new kind of hyperbranched polymers was designed and prepared with flexible chain blocking in this paper. Not only the flexible chain blocking hyperbranched polyester could be used for a toughening agent about epoxy resin and the impact strength reached 29.8 kJ/mm2, but also reduces greatly the dielectric constant and the dielectric loss of the epoxy resin, and the lowest dielectric constant was 2.73 (107 Hz), as well the lowest dielectric loss was 0.002 (107 Hz), compared with the epoxy resin system modified with the traditional hyperbranched polyester. The results indicated that the flexible chain blocking hyperbranched polyester had offered free volume structure and flexible chain with epoxy resins chain formed the interpenetrating polymer networks which made transformation accomplish. The resins which had better toughness, low Dk, low dielectric loss and excellent insulation performance could be applied in various research and development fields, such as high frequency and low dielectric copper clad laminate and translucent structural adhesives, etc.

Practical Technology of Toughening Epoxy Resin: Influence of Toughening Agents on Mechanical and Heat Properties

This research studies the effect of several toughening agents, such as carboxyl-terminated polyether (CTPE), carboxyl-terminated polytetrahydrofuran (CTPF), carboxyl-terminated liquid nitrile rubber (CTBN), random-base liquid nitrile-butadiene rubber (RBNR) and core-shell polymer (CSP) containing polybutadiene, on epoxy resin. These epoxy resin systems containing various toughening agents showed different viscosity, in which the viscosity of CTPE and CTPF systems nearly unchanged and the viscosity of CTBN, RNBR and CSP systems increased significantly. The impact resistance of modified epoxy systems had been improved significantly, especially the CTPF system raised by 257.2%. Meanwhile, the heat resistance of epoxy systems containing different toughening agents showed different results. Compared with the pure sample, the hardness of all toughened systems decreased. CTPE and CTBN systems decreased significantly, while CTPF and CSP remained fundamentally unchanged. Toughness modification resulted in reduction of tensile strength and the retention ratio was CSP > RNBR > CTPF > CTBN > CTPE. Toughness modification resulted in reduction of compression strength and the retention ratio was RNBR > CSP > CTPF > CTBN > CTPE. All of the toughening systems kept the shear strength basically unchanged. The shear strength of the CSP system was even improved. In terms of peel strength, all of toughening systems had improved.

A renewable tung oil-derived nitrile rubber and its potential use in epoxy-toughening modifiers.

In this study, a modifier (CTMA) prepared by emulsion copolymerization of tung oil fatty acid, methyl esters of tung oil fatty acid and acrylonitrile was used to toughen epoxy resins. The structural characterization of the copolymer was carried out by Fourier transform infrared spectroscopy, 1H NMR spectroscopy and high-temperature gel permeation chromatography. Mechanical testing, thermal characterization and scanning electron microscopy were conducted to investigate the properties of epoxy resin modified by the copolymer and further reveal its toughening mechanism. The results indicated that the newly synthesized copolymer effectively toughened the epoxy resin because the elongation-at-break was increased to 89.48%, the maximum toughness calculated by work before break was nearly 4.6 times that of the neat epoxy resin, and apparent shear yields and plastic deformations were observed in the morphology of the fractured surfaces. CTMA, which acts as a flexible cross-linker in the epoxy thermoset, may decrease the cross-linking density.

Influence of material and manufacturing technology on the failure behavior of composite laminate bonded joints

The purpose of this work is to evaluate the influence of co-lamination vs. co-bonding on the failure behavior, and namely the fracture toughness, of carbon fibre reinforced (CFR) composite laminate joints in order to assess comparatively their performance. Since the strength of the laminate and ply texture are parameters affecting the strength of the joint, the comparison is extended to two different types of CFR pre-preg fibers, a satin T1100 with 2573 Nanoalloy® epoxy resin supplied by Toray and a twill T700 with ER450 toughened epoxy resin supplied by CIT, Toray group, representative of two different fields of application, racing and automotive, respectively.

Experimental Characterization of CFRP by NOL Ring Test

Abstract Carbon fiber composites are widely used in aerospace applications such as rocket motor casings, electronic packaging etc., to gainfully exploit their higher specific strength properties. Commercial availability of carbon fibers like T 700 with superior strength needs an epoxy matrix with higher ductility. In this paper, elaborate experimental results obtained on composite specimens made with T 700 carbon fibers in a special toughened epoxy matrix are presented. Tests in accordance with the relevant ASTM specifications were conducted on standard unidirectional tensile test specimens as well as National Ordnance laboratories (NOL) ring test. It was observed from the experimental results that the strength measured by NOL-Ring test is more reliable than the results of unidirectional tensile test. It was also found that the maximum frequency of repetition of failure stress is in between 1675-1725 M Pa. These results are very useful as reliable design inputs for aerospace and automobile applications.

Improved fracture toughness of epoxy resin reinforced with polyamide 6/graphene oxide nanocomposites prepared via in situ polymerization

In this work, a facile in situ polymerization method was developed for the preparation of polyamide 6 (PA6) chains grafted graphene oxides (GO). Based on ethanolic solution precipitation method, the powders of PA6, PA6/GO-0.5 and PA6/GO-1.0 were fabricated and dispersed uniformly into epoxy resins at varying loadings. The surface modification of GO and mechanical properties of epoxy composites were investigated systematically. The mechanical tests indicate that, without impairing tensile properties and glass transition temperature, the fracture toughness of PA6/GO-1.0 particles reinforced epoxy composites exhibits a 52.6% increase compared with neat epoxy at 1.5 wt% loading. Based on adequate fractographic study, the excellent toughening effect of PA6/GO-1.0 can be attributed to the better particle/matrix interface, rougher interface with small convex structures and more energy consumption of particle fracturing, which are resulted from the existence of PA6 chains grafted GO nanosheets. Moreover, the addition of GO and PA6 is 0.015 and 1.5 wt% respectively for the maximum fracture toughness value in this work. The dosage is very small compared with epoxy reinforced with GO or PA6 separately, giving an economically feasible method for the toughening of epoxy resin.

Functionalized aramid nanofibers prepared by polymerization induced self-assembly for simultaneously reinforcing and toughening of epoxy and carbon fiber/epoxy multiscale composite

Aramid nanofibers (ANFs) are polymeric nanofibers that have been drawing tremendous attention as new nanoscale building blocks of advanced composites. Herein, we report a new strategy to rapidly synthesize functionalized ANFs (fANFs) through polymerization-induced self-assembly of poly(phenylene terephthalamide) (PPTA) using soluble sulfonated PPTA to tailor the size of fANTs, and the extraordinary reinforcing and toughening effect of fANFs on epoxy (EP) resin and multiscale carbon fiber (CF)/EP composites. With a diameter of ∼30 nm, and reactive sulfonic acid groups on the surfaces, the branched fANFs can be easily dispersed in EP and are reactive with the matrix, therefore, remarkably improve the interfacial interaction and mechanical properties (including both strength and toughness) of EP at low fANF contents. The tensile strength, Young's modulus, toughness and elongation at break of fANFs/EP nanocomposites are increased by ∼59%, ∼19%, ∼112% and ∼36%, respectively. The flexural strength, interlaminar shear strength, total energy dissipation and flexural strain at break of fANFs/CF/EP multi-scale composite are increased by ∼57%, ∼38%, ∼65% and ∼71%, respectively. To the best of our knowledge, the enhancement in the strengths is comparative with those provided by graphene oxide, and the total fracture energy and flexural strain at break are more significantly increased by fANFs than almost all of the nanofillers ever reported.

Polyether Sulfone-Based Epoxy Toughening: From Micro- to Nano-Phase Separation via PES End-Chain Modification and Process Engineering.

The toughness of a high-performance thermosetting epoxy network can be greatly improved by generating polyether sulfone−based macro- to nano-scale morphologies. Two polyethersulfones (PES) which only differ by their chain-end nature have been successively investigated as potential tougheners of a high-Tg thermoset matrix based on a mixture of trifunctional and difunctional aromatic epoxies and an aromatic diamine. For a given PES content, morphologies and toughness of the resulting matrices have been tuned by changing curing conditions and put into perspective with PES chain-end nature.

Cardanol derived benzoxazine in combination with boron-doped graphene toward simultaneously improved toughening and flame retardant epoxy composites

A bio-based phosphorus-containing benzoxazine monomer (CBz) was successfully synthesized through the reaction between cardanol and DOPO-based diamine. In order to simultaneously improve the toughness and flame retardancy of epoxy resin (EP), various contents of CBz in combination with boron-doped graphene (BG) nanosheets were incorporated into EP to obtain boron-doped graphene/cardanol derived benzoxazine-epoxy composites (EP/CBz/BG). By comparison, cardanol derived benzoxazine-epoxy co-polymers (EP/CBz) were also fabricated. Results show that the addition of the as-prepared CBz into EP not only endowed EP with excellent flame retardancy, but also improved the glass transition temperature and impact strength. Specifically, the peak heat release rate of EP composite with 13 wt% CBz and 2 wt% BG decreased by 48% compared to that of neat EP, accompanying with an increase of impact strength by 22%. These favorable features of EP/CBz/BG composites are attributed to the unique structure of CBz and high resistance to thermal decomposition of BG.

Low viscosity and high toughness epoxy resin modified by in situ radical polymerization method for improving mechanical properties of carbon fiber reinforced plastics

In situ radical polymerization method, which is a method for toughening thermosetting resins by modifier polymers radically generated in the curing system of the resins, was applied to epoxy resin for the matrix of carbon fiber reinforced plastic (CFRP) to achieve both high fracture toughness of the cured resin and low viscosity of the resin composition. Benzyl methacrylate (BzMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) were selected as the modifier monomers, and the resulting cured epoxy resin having co-continuous phase separation with the polymerized modifier at a nanometer level showed 2.1 times higher fracture toughness (KIC) than the unmodified cured resin. The modified epoxy resin system was then successfully applied to the fabrication of CFRP by resin transfer molding (RTM) due to its low viscosity in the uncured state. The resultant CFRP system showed 30% increase of the interlaminar fracture toughness (GIC) from the unmodified system.

The influence of carbon spheres on thermal and mechanical properties of epoxy composites

In order to improve the properties of epoxy resion, a reinforcement addictive of carbon spheres (CSs) was successfully synthesized by hydrothermal methods and CSs/Epoxy composite was prepared using in-situ polymerization technique. The morphology and structure of CSs and CSs/Epoxy composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that CSs distributed homogeneously in epoxy matrix and the integrating state of interface between CSs and epoxy is good. TGA and DMA analysis showed that the thermal stability of CSs/Epoxy composite in air and the glass transition temperature (Tg) increased with the addition of CSs. DMA results show that the creep recovery property also improved. Additionally. The impact fracture strength of EP composites increased after the addition of CSs compared to pure EP, it means the toughness of epoxy improved effectively, which attribute to the effective dissipation of the crash energy. Finally, the mechanism for the improvement of mechanical properties by the CSs is also discussed.

High Toughness Induced by Wormlike-Nanostructure in Epoxy Thermoset Containing Amphiphilic PDMS–PCL Block Copolymers

The modification of epoxy composites through the construction of nanostructures via self-organization of block copolymers has become a hot topic. In this research, high toughness epoxy thermoset was prepared through constructing wormlike-nanostructure by incorporating amphiphilic polydimethylsiloxane-block-poly(e-caprolactone) block copolymer. The fracture toughness of subsequent epoxy thermosets increased nearly 355% comparing with neat epoxy with the addition of 40 wt % wormlike nanostructure, which was higher than that of thermosets with spherical nanostructure (142%). There was obviously plastic deformation in fractured surfaces of thermosets with wormlike nanostructure, it is believed that a combination of several toughening mechanisms leads to the improvement in fracture toughness. The morphologies transition, dynamic mechanical properties and wetting behavior of the thermoset containing spherical/wormlike nanostructures are also reported.

Reactive block copolymers for the toughening of epoxies: Effect of nanostructured morphology and reactivity

ABSTRACTBlock copolymers (BCPs) have stimulated widespread research interest due to their applications as facile templates in the fabrication of optimized thermosets with micro– or nanostructured morphologies. In the present work, a novel block copolymer was obtained from a commercial poly(styrene-block-butadiene-block-styrene) (SBS) triblock copolymer precursor by a two-step process including reaction with hydrogen peroxide in a water/dichloroethane biphasic system to achieve an epoxidized derivative with a 46 mol% degree of epoxidation (thus denoted as eSBS46), which was then followed by reaction with 1-(2-aminoethyl)piperazine (AEP, thus yielding eSBS46-AEP) as a reactive functional group that was incorporated to prepare nanostructured epoxy thermosetting blends. As a result of the oxirane ring-opening achieved (to a conversion degree of 10 mol%) by reaction with AEP, the nanostructured morphology was converted from spherical micelles in the case of eSBS46 to branched wormlike micelles for eSBS46-AEP. At 5 wt% loading of this BCP material, the fracture toughness was improved by 51% over the neat epoxy. These findings were compared with data obtained from the same epoxy thermoset formulation containing the eSBS46. Various measurements including transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and measuring stress field factor (KIC) analysis were employed to investigate the morphology, fracture graph, storage modulus, glass transition temperature (Tg), and fracture toughness of the epoxy thermosets containing these BCPs. The specific side-groups of eSBS46-AEP containing secondary amines and ternary amines increased the reactivity to epoxy matrices. A combination of fracture mechanisms including shear deformation, crack tip blunting, and matrix ductility enhancement contributed toward helped enhance the toughness. These results demonstrate that the role of modulating the reactivity of BCP has a significant effect on the final morphology and properties of the epoxy composites.

Toughening of Epoxy Polysulfide Binary Blend Composite

In a composite structure, it is anticipated that high toughening can be achieved by taking advantage of mixing rubber with epoxy. The purpose of this paper is to investigate the toughness characteristics of Polymeric Composites containing Polysulfide Rubber (PSR) as a toughener to a brittle base epoxy resin. Through comparing with neat resin specimens (epoxy, epoxy +PSR), the results showed that the addition of PSR into polymeric resin enhance toughness of epoxy. Similarly experiment showed that the maximum value of mixing ration is 6% PSR, which cause a noticeable enhancement in composite strain, but a reduction in tensile strength and modulus of elasticity at fracture.