Rubber-modified Epoxy Research Articles

Plastic behavior of a film type of epoxy adhesive under a wide range of stress multiaxiality conditions

The yield stress of rubber-modified epoxy adhesives is affected by hydrostatic stress in the adhesive layer. It is necessary to clarify whether hydrostatic stress modeling is essential for highly toughened epoxy adhesives and how hydrostatic stress should be considered under high multiaxial stress conditions. The elastic–plastic stress–strain behavior of a film-type epoxy adhesive AF163-2U was examined using a bulk adhesive tension test and a thick adherend shear test (TAST). The exponent Drucker–Prager model with an appropriate hydrostatic-stress sensitivity parameter (λ-parameter = 1.639) fully described the stress–strain curves both for the bulk adhesive tension test and TAST. The Hill’48 model of hydrostatic-stress-independent plasticity also simulated the bulk adhesive tension test and TAST as a response by determining the appropriate anisotropic parameters. To examine the effect of extremely high hydrostatic stress, a butt-joint tensile test and a finite element (FE) simulation were conducted using the exponent Drucker–Prager and Hill’48 models. The Hill’48 model completely failed in the butt-joint tensile test simulation. The exponent Drucker–Prager model, where a higher λ-parameter (=2.1) was required; consequently, it was concluded that the hydrostatic-stress effect should be considered for the adhesive model and the λ-parameter is not a fixed value but increases with increasing hydrostatic stress.

Fatigue bond behavior of FRP-to-concrete joints with various bonding adhesives

Bond degradation due to cyclic or fatigue loading has significant negative impacts on the service life of fiber-reinforced polymer (FRP) strengthened concrete structures. Existing studies have shown that the debonding failure of FRP-to-concrete joints under fatigue loading mainly occurs in the adhesive layer or the adhesive-concrete interfacial layer, and the fatigue bond behavior varies significantly among specimens with different bonding adhesives. This study evaluates the fatigue behavior of FRP-to-concrete joints with various bonding adhesives through experimental tests and numerical simulations. First, fatigue testing was conducted on the FRP-to-concrete double-lap shear specimens with various bonding adhesives (including soft, normal, stiff, and liquid rubber-modified epoxy adhesives). According to the test results, specimens with soft adhesive exhibited higher interfacial fatigue lives and superior fatigue bond behaviors than their normal adhesive counterparts. In comparison, stiff adhesives resulted in much lower interfacial fatigue lives and unsatisfactory failure modes. The use of liquid rubber-modified epoxy contributed to enhancing the bond performance under fatigue loading. Then, a fatigue bond-slip model considering the degradation of bond-slip stiffness was proposed, and the corresponding interfacial fatigue damage was quantified. On this basis, a simplified finite element (FE) model was developed and verified by the test results. The influence of adhesive properties on the fatigue bond behavior of FRP-to-concrete joints was investigated further using FE modeling.

Study of mechanical properties of epoxy/graphene and epoxy/halloysite nanocomposites

Abstract This article aimed to compare various mechanical properties of epoxy/graphene and epoxy/halloysite nanocomposites. Graphene nanoplatelets (GnPs) and halloysite nanotubes (HNTs) were used as fillers at different concentrations. The studied fillers were dispersed in the epoxy resin matrices. Elastic–plastic mechanical behavior modulation was observed utilizing the fillers’ nanoparticles and carboxyl-terminated butadiene–acrylonitrile copolymer rubber-modified epoxy resin. The hypothesis of the possible preceding inter-particle gliding of the individual GnPs in the complex resin nanocomposite matrix during mechanical testings was also confirmed. Increased ductility (elongation at break increased from 0.33 mm [neat matrix] to 0.46 mm [1 wt% GnPs] [39% increase]) and plasticity of the GnP nanocomposite samples were observed. In contrast, the decreasing mechanical stiffness as reflected in the decreased Young’s modulus of elasticity (from 3.4 to 2.7 GPa [20% decrease]) was found for the epoxy/HNT nanocomposites. The obtained dynamic stiffness of the investigated nanocomposites confirmed the complexity of the mechanical response of the studied material systems as a combination of the ductile and brittle phenomena.

Investigation on the properties of epoxy asphalt mixture containing crumb rubber for bridge expansion joint

The purpose of this research is to propose epoxy asphalt materials for bridge expansion joints. Epoxy asphalt was modified by adding 0%, 20%, 30% and, 40% crumb rubber (CR). The viscosity, tensile properties, adhesion, high-temperature stability, moisture resistance, low-temperature, and stress relaxation properties of rubber-modified epoxy asphalt (REA) were investigated comparing with the commercial BJ200-red. Thermal stress of epoxy asphalt expansion joint was also simulated by the finite element analysis platform. The results indicated that with the increase of CR content, the viscosity and deformation of REA binder increase, while operation time, the tensile strength, and adhesive decreases. CR has a slight negative effect on the high-temperature performance of epoxy asphalt mixture, and has a positive effect on low temperature deformation. When the rubber powder content is 30%, epoxy asphalt mixture has excellent mechanical properties and its high-temperature stability is higher than BJ200 mixture, but the low-temperature performance of the two is equivalent. Thermal stress analysis shows that epoxy asphalt containing 30% CR cannot fracture above −15 ℃, so it can be recommended for bridge expansion joints.

Modelling of Phase Transitions and Residual Thermal Stress of CTBN Rubber Modified Epoxy Resins during a Pultrusion Process

Abstract The implicit finite difference and fourth order Runge-Kutta method are used both to solve the heat transfer problem in the pultrusion reaction and to calculate the temperature and conversion distributions within a thermoset composite profile. The aim of our work is to study the influence of a rubbery phase added to the epoxy matrix in production conditions. The results have shown that the rubber modified systems have a low exothermic temperature peak value, so that neither the amount of cured resin nor the final product properties are limited. First of all we will show that the phase transition (gelation and vitrification) zones within the die change as the amount of rubber varies in the resin. The relationship between the position and of these zones and the resin systems will be discussed. We calculate the residual thermal stresses for all the investigated fibre/resin systems, showing a reduction when the rubber amount increases in the epoxy blend.

Viscoelastic behavior of glass fiber reinforced rubber-modified epoxy

Abstract Epoxies as a thermoset polymer have got a great attention in different applications. To elaborate their employing and surmount their brittleness, many polymers were blended with them. The results confirm that the good mechanical properties are obtained when 6wt% of Polysulfide Rubber (PSR) is blended with epoxy and reinforced with fiber glass. The effect of rubber and glass fiber on the viscoelastic properties of epoxy were investigated using creep-recovery data under different stress levels (5, 10, 15 and 20 MPa) and temperatures (30, 50, 70 and 90°C). Polysulfide addition caused larger creep and creep recovery. In addition, the creep resistance of glass fiber reinforced blend was significantly enhanced.

Coated, Stabilized Enhanced-Efficiency Nitrogen Fertilizers: Preparation and Effects on Maize Growth and Nitrogen Utilization.

Coated, slow/controlled release, or stabilized enhanced-efficiency nitrogen fertilizers (EENFs) are effective in improving nitrogen utilization efficiency (NUE) and crop yield. Better performance is expected from coated, stabilized EENFs where urease and nitrification inhibitors are treated in coated fertilizers. Firstly, five coated EENFs with different mass proportions of nature rubber (NR) in coating were prepared: CU0, CU1, CU2, CU3, CU4, and CU5 (0, 10, 20, 30, 40, and 50% of NR in coating). The controlled release performance of CU was tested by hydrostatic release test and the microstructure of controlled release urea, so as to screen the optimal addition ratio of NR (ER: NR = 7:3, CU3). Secondly, two coated, stabilized EENFs, CSU1 and CSU2, were prepared with natural rubber-modified epoxy resin (ER: NR = 7:3) as coating material. Seven treatments of different N fertilization were set up: CK (no N fertilization), urea, CU3, SU1, and SU2 (urease and nitrification inhibitors-treated urea fertilizers), CSU1 and CSU2 (urease and nitrification inhibitors-treated natural rubber-modified epoxy resin-coated urea fertilizers). Ammonia volatilization experiment and column leaching experiment showed that compared with conventional urea, NH3 volatilization loss was reduced by 20% and inorganic N leaching loss was reduced by 26% from CSU2, respectively. In the pot experiment, maize grain yield of 162.92 and 206.96 g/pot was achieved by CSU1 and CSU2, respectively, 41 and 79%, respectively, higher than that achieved by conventional urea. SUs treatments were more effective than conventional urea treatment in improving maize grain yield and NUE, but lower than in CSUs. The NUE, nitrogen fertilizer apparent utilization efficiency, partial factor productivity of applied N, and nitrogen utilization efficiency were 46, 30, 46, and 32%, respectively, higher in CSU1 and 58, 62, 58, and 29%, respectively, higher in CSU2 than in the conventional urea treatment. Compared with CSU1, CSU2 had better agronomic effectiveness with a higher NUE. It is recommended that urease and nitrification inhibitors be sandwiched between urea prill and the coating for preparation of novel, environmentally friendly coated, stabilized EENFs with high agronomic effectiveness, high NUE, and low N loss.

R-curve behavior of adhesively bonded composite joints with highly toughened epoxy adhesive under mixed mode conditions

The fracture toughness of an adhesively bonded carbon fiber reinforced plastic joint under mixed mode (I and II) conditions was determined by means of the Fernlund–Spelt type double cantilever beam (DCB) test, where a rubber-modified epoxy adhesive was used. The R curves were determined by calculating the energy release rates, GI and GII, based on the beam theory, along with a finite element analysis. The total energy release rate GT (= GI + GII) strongly depended on the I–II mixed mode. This means that it remarkably increased with increasing mode-II component; furthermore, it varied with crack growth from GTC (at the onset of cracking) to GTS (at the steady crack-propagation region). The difference between GTC and GTS increased with the increase in the mode II component. Such R-curve characteristics were discussed based on observation of the fracture surfaces with a scanning electron microscope and the corresponding crack propagation-path behavior.

Fracture properties of epoxy polymers modified with cross-linked and core–shell rubber particles

To improve the toughness of epoxy polymers, cross-linked rubber (CLR) particles or core–shell rubber (CSR) particles can be blended into the epoxy matrix. Particle cavitation is thought to be the main toughening mechanism of rubber-modified epoxies. Although CLR-modified epoxies have not been studied in depth previously, it is expected that the toughening mechanism differs from that of CSR-modified epoxies because void formation is less likely to occur. We formed the CLR- and CSR-modified epoxy resins using nanosized acrylonitrile butadiene CLR particles, which showed good compatibility with the epoxy matrix and the CSR particles with a rubbery core surrounded by a glassy shell. The toughening mechanism was examined by comparing the fracture behavior, fracture surfaces, and process zones via tensile and fracture toughness testing, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and transmission optical microscopy (TOM). There was a difference in the characteristics of the R-curves between the CLR- and CSR-modified epoxies. In addition, the SEM and TEM observations indicated that there was a difference in the fracture mechanism.

Effect of liquid rubber modification on the bond behavior of externally bonded FRP laminate-concrete interface under dynamic loading

Interfacial debonding between fiber-reinforced polymer (FRP) laminate and concrete substrate is one of the critical issues in the externally bonded FRP strengthened concrete members. Existing studies have shown that the addition of liquid rubber into the bonding adhesives can increase debonding resistance of FRP laminate-concrete interface and consequently improve the comprehensive performance of FRP strengthened concrete members under quasi-static loading. The purpose of this study is to clarify the effect of liquid rubber modification on the bond behavior of FRP laminate-concrete interface under dynamic loading. Six groups of double-lap shear specimens with neat or rubber-modified epoxy were tested under static and two dynamic loading rates. The parameters of peak load, FRP strain distribution and interfacial bond stress-slip relationship are analyzed. Test results indicate that the liquid rubber modification can significantly improve the bond capacity of FRP laminate-concrete interface under dynamic loading. Further, the influence mechanism of liquid rubber modification on the dynamic bond behavior of FRP laminate-concrete interface is discussed. Finally, an empirical dynamic bond stress-slip model considering the effect of liquid rubber modification is proposed and validated.

A New Design of Recycled Ethylene Propylene Diene Monomer Rubber Modified Epoxy Based Composites Reinforced with Alumina Fiber: Fracture Behavior and Damage Analyses

This study proposes a new design of lightweight and cost-efficient composite materials for the automotive industry using recycled fresh scrap rubbers (EPDM (ethylene propylene diene monomer) rubbers), epoxy resin and alumina (Al2O3) fibers (AF). Three-point bending tests were conducted to investigate fundamental mechanical characteristics and then experimentally obtained moduli were compared with a modified Halpin–Tsai model. In addition, tests were carried out to study the fracture characteristics of the composites. Then, a practical numerical study was carried out to observe the evolution of the strain energy release rate along the crack front. Mechanical test results showed that the reinforcement with AF improved the fracture toughness of these novel composites for low rubber contents. Besides, increasing recycled EPDM rubber content degraded the mechanical resistance and strain at break of the composites. Moreover, numerical studies indicated that energy release rate showed some variations along the specimen thickness. Toughening mechanisms were evaluated by scanning electron microscope (SEM) fractography. Typical toughening mechanisms observed were fiber bridging and shear yielding. By considering the advantageous effects of AF on the novel composites and cost efficiency under favor of recycled rubbers, these composites are promising candidates to manufacture the various components in automotive industry.

Failure behavior of adhesively bonded joints with a rubber modified epoxy adhesive under tensile-shear combined cyclic loading

Rubber-modified epoxy adhesives are used widely as structural adhesive owing to their properties of high fracture toughness. In many cases, these adhesively bonded joints are exposed to cyclic loading. Generally, the rubber modification decreases the static and fatigue strength of bulk adhesive without flaw. Hence, it is necessary to investigate the effect of rubber-modification on the fatigue strength of adhesively bonded joints, where industrial adhesively bonded joints usually have combined stress condition of normal and shear stresses in the adhesive layer. Therefore, it is necessary to investigate the effect of rubber-modification on the fatigue strength under combined cyclic stress conditions. Adhesively bonded butt and scarf joints provide considerably uniform normal and shear stresses in the adhesive layer except in the vicinity of the free end, where normal to shear stress ratio of these joints can cover the stress combination ratio in the adhesive layers of most adhesively bonded joints in industrial applications.In this study, to investigate the effect of rubber modification on fatigue strength with various combined stress conditions in the adhesive layers, fatigue tests were conducted for adhesively bonded butt and scarf joints bonded with rubber modified and unmodified epoxy adhesives, wherein damage evolution in the adhesive layer was evaluated by monitoring strain the adhesive layer and the stress triaxiality parameter was used for evaluating combined stress conditions in the adhesive layer. The main experimental results are as follows: S–N characteristics of these joints showed that the maximum principal stress at the endurance limit indicated nearly constant values independent of combined stress conditions, furthermore the maximum principal stress at the endurance limit for the unmodified adhesive were nearly equal to that for the rubber modified adhesive. From the damage evolution behavior, it was observed that the initiation of the damage evolution shifted to early stage of the fatigue life with decreasing stress triaxiality in the adhesive layer, and the rubber modification accelerated the damage evolution under low stress triaxiality conditions in the adhesive layer.

A rubber-modified epoxy composite with very high toughness and heat resistance

A high performance epoxy composite with very high toughness and heat resistance had been designed and prepared. Epoxy resin TDE-85 with an impact strength of 10.2 kJ m−2, a heat distortion temperature (HDT) of 121°C, and a glass transition temperature of 127°C was chosen as the matrix of the composite, while carboxylic nitrile-butadiene elastomeric nanoparticles (CNB-ENPs) coated with triethanolamine on the surface with a diameter of about 100 nm was selected as the modifier. Surprisingly, the rubber-modified epoxy resin exhibited not only very high toughness but also very high heat resistance. The HDT of epoxy resin TDE-85 after modification increased 57°C, reaching 178°C, while the impact strength increased by 107%, increasing to 21.1 kJ m−2. The relationship between the microstructure and performance had been evaluated by transmission electron microscopy, mechanical testing, and dynamic mechanical analysis. The results showed that the CNB-ENP/TDE-85 composite resulted in large interface and a special morphology after modification.

Epoxy modified with urea-based ORMOSIL and isocyanate-functionalized polybutadiene: Viscoelastic and adhesion properties

Epoxy networks present good adhesion properties but are brittle in nature due to the high crosslink degree. The modification with silica particles and rubber can be a useful approach for improving adhesion properties without affecting the thermal properties and stiffness. This work present a new epoxy system modified by a combination of organically modified silica (ORMOSIL) containing phenyl ureasil groups and liquid polybutadiene terminally functionalized with isocyanate groups. The ORMOSILs were prepared by a sol-gel process involving TEOS and phenyl ureasil-silane in methanol or ethanol. The synthesis in methanol resulted in smaller particle size and a better incorporation of the functionalized silane. Both epoxy resin (ER) and the rubber-modified epoxy (ERPBNCO) presented superior adhesion properties by using ORMOSIL prepared in methanol as the solvent [ORMOSIL(M)]. The combination of ERPBNCO and ORMOSIL(M) provide adhesive with superior adhesion properties while keeping the stiffness and glass transition temperature of the matrix.

Mechanical and durability performance evaluation of crumb rubber-modified epoxy polymer concrete overlays

The epoxy-based polymer concrete has been widely used for concrete repairing and overlays due to good mechanical properties and durability. To reduce environmental landfill problems with the accumulation of tire rubbers, scrap tire rubbers were added to epoxy polymer concrete in this investigation. The crumb rubber (with mesh size #50, 0.279 mm) were introduced into epoxy concrete with two different contents of 5% and 10% based on the epoxy monomer weight. The mechanical properties including direct tensile strength, compressive strength, splitting tensile strength and interface bond strength. Thermal- and moisture-related durability performance of rubberized epoxy concrete were measured and compared with the control samples. The compressive strength and splitting tensile strength were improved with the added 5% solid rubbers, and slightly reduced with 10% content. With a specially-designed testing method, the interface tensile bonding strength between the epoxy concrete overlay and concrete slab were measured as higher than 250 psi for both control and rubberized samples. The thermal conductivity of polymer concrete was reduced with the increase of rubber contents. In addition, very low water absorption rates (<0.5%) were measured with all types of epoxy concrete samples. The interface microstructure with SEM also indicated the good bonds between rubber particles and epoxy resins. The overall test results showed the enhanced performance of rubber-modified epoxy concrete which can facilitate the tire rubber recycling into epoxy polymer concrete for protecting the exist concrete pavement structures.

The curing behaviour and thermo-mechanical properties of core–shell rubber-modified epoxy nanocomposites

This work investigates the effects of core–shell rubber (CSR) nanoparticles on the curing behaviour and thermo-mechanical properties of an epoxy using differential scanning calorimetry and dynamic mechanical thermal analysis approaches. Interaction between CSR nanoparticles and epoxy matrix is detected at a temperature of approximately 97°C in the curing process. This results in an increase in the glass transition temperature ( Tg) of the cured nanocomposites. Given the semi-dynamic curing schedule, the curing process of all the epoxy nanocomposites consists of an abrupt onset stage followed by a slow diffusion-controlled stage. Higher temperature is required to initiate the curing for the epoxy nanocomposites with higher loading of CSR nanoparticles. This is attributed to the physical changes caused by the addition of CSR nanoparticles, such as the increase in the viscosity and the reduction in the density of the reactive groups. The storage modulus of the epoxy decreases in the glassy region but remains constant in the rubbery region due to the incorporation of CSR nanoparticles.

Mechanical behavior of liquid nitrile rubber-modified epoxy resin: Experiments, constitutive model and application

Quasi-static and dynamic experiments were carried out to examine the influence of liquid nitrile rubber (LNBR) on the compressive behavior of epoxy resin. The quasi-static tests were performed on an electronic universal machine under strain rates of 10−4/s and 10−3/s, while a Split Hopkinson Pressure Bar (SHPB) system was adopted to conduct the dynamic tests for strain rates up to 5600/s. The standard Zhu-Wang-Tang (ZWT) nonlinear viscoelastic model was selected to predict the elastic behavior of LNBR/epoxy composites under a wide range of strain rates in this study. After several necessary derivations and data fittings, a set of ZWT model parameters for the tested materials were finally achieved. Meanwhile, the dynamic response of a typical high-overload measurement system encapsulated by LNBR/epoxy composites under impact loading was simulated by LS-DYNA, where the ZWT model was used to simulate the mechanical behavior of LNBR/epoxy composites with model parameters obtained from the experiments. It was concluded that both the resistance to failure and protective effect of epoxy resin could be enhanced by 10% LNBR additive. However, 25% LNBR additive would decrease the mechanical properties of the epoxy resin.

Morphological study and mechanical property of epoxy-foam adhesives based on epoxy composites for automotive applications

The challenge of developing epoxy-foam adhesives for automotive applications lies in the difficulties associated with finding the optimal composition ensuring both high expansion ratio and mechanical strength. Herein, epoxy-foam adhesives based on epoxy composites were prepared and evaluated for automotive applications. The curing behavior was studied by differential scanning calorimetry, and the morphology was characterized non-destructively by micro X-ray computed tomography. Increasing the content of rubber-modified epoxy (RME) retarded the curing reaction by increasing the expansion ratio and affected the lap shear strength. A high expansion ratio and suitable mechanical strength was observed for epoxy-foam adhesives containing 10 or 15 wt% RME.

Mechanical Behavior of Liquid Nitrile Rubber-Modified Epoxy Resin under Static and Dynamic Loadings: Experimental and Constitutive Analysis.

Quasi-static and dynamic compression experiments were performed to study the influence of liquid nitrile rubber (LNBR) on the mechanical properties of epoxy resin. The quasi-static experiments were conducted by an electronic universal machine under strain rates of 0.0001/s and 0.001/s, while a Split Hopkinson Pressure Bar (SHPB) system was adopted to perform the dynamic tests for strain rates up to 5600/s. The standard Zhu-Wang-Tang (ZWT) nonlinear viscoelastic model was chosen to predict the elastic behavior of LNBR/epoxy composites under a wide range of strain rates. After some necessary derivation and data fitting, a set of model parameters for the tested materials were finally obtained. Meanwhile, the incremented form of the ZWT nonlinear viscoelastic model were deduced and implemented into the user material program of LS-DYNA. A simulation-test contrast had been performed to verify the validity and feasibility of the algorithm. The results showed that the viscoelastic behavior of epoxy resin can be effectively simulated.

Morphology and micromechanics of liquid rubber toughened epoxies

Abstract In the present work, a diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin was modified with the help of a liquid rubber (LR) obtained from the pyrolysis of rubber. Tensile tests on samples of rubber modified epoxy resins (REs) containing varying rubber volume fractions (RVF) were conducted to obtain their tensile properties. Fractographic analysis of fractured samples using field emission scanning electron microscopy (FESEM) revealed the presence of phase separated rubber zones characterized by microvoids, distributed uniformly in the epoxy domain. Young’s modulus and yield strength of REs were observed to drop with RVF. A three-dimensional (3D) finite element model was employed to predict the elastic properties and stress distributions in REs. Various stress distributions and their dependence on the properties of rubber were examined in detail through the model. The effect of rubber properties on bulk elastic properties of the REs were also studied. Lastly, the effective stress-strain relationship was predicted with the help of an elastic-plastic analysis. Predicted results showed coherence with experimental results.