Moisture absorption behavior of rubber‐modified epoxy resins

The moisture absorption behavior of diglycidyl ether of bisphenol A/ethylene diamine resins incorporating a carboxy‐terminated butadiene–acrylonitrile rubber was investigated and associated with their morphology of phase separation. Although the diffusion coefficient of moisture was increased with the rubber content, its activation energy and free volume for moisture diffusion were barely changed until phase inversion occurred. After phase inversion, the free volume was significantly increased, and the activation energy decreased. In addition, the moisture absorption also reduced the β‐transition temperature of the resins and slightly increased the glass‐transition temperature before phase inversion. However, the reverse was found after phase inversion. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3718–3724, 2002     

Scratch behavior of epoxy nanocomposites containing α‐zirconium phosphate and core‐shell rubber particles

The effects of nanoscale core‐shell rubber (CSR) particles and α‐zirconium phosphate (ZrP) nanoplatelet fillers on the scratch behavior of epoxy have been examined using a newly established ASTM scratch testing method. The critical load for onset of microcrack formation is utilized to determine scratch resistance of the epoxy nanocomposites. Optical microscopy and scanning electron microscopy were performed to determine failure and fracture patterns caused by the scratch. The findings of this study suggest that the introduction of nanoparticles or nanoplatelets does not necessarily enhance the scratch resistance of epoxy. This implies that increases in ductility and fracture toughness alone, i.e., the epoxy/CSR case, and enhancements in modulus and tensile strength alone, i.e., the epoxy/ZrP case, will not necessarily improve scratch resistance of epoxy matrix. A combination of material property attributes is needed to prepare scratch resistant polymers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Fabrication of core–shell nanocomposites with enhanced photocatalytic efficacy

The current study establishes the unprecedented involvement in the evolution and production of novel core–shell nanocomposites composed of nanosized titanium dioxide and aniline‐o‐phenylenediamine copolymer. TiO₂@copoly(aniline and o‐phenylenediamine) (TiO₂@PANI‐o‐PDA) core–shell nanocomposites were chemically synthesized in a molar ratio of 5:1 of the particular monomers and several weights of nano‐TiO₂ via oxidative copolymerization. The construction of the TiO₂@PANI‐o‐PDA core–shell nanocomposites was ascertained from Fourier transform IR spectroscopy, UV–visible spectroscopy and XRD. A reasonable thermal behavior for the original copolymer and the TiO₂@PANI‐o‐PDA core–shell nanocomposites was investigated. The bare PANI‐o‐PDA copolymer was thermally less stable than the TiO₂@PANI‐o‐PDA nanocomposites. The core–shell feature of the nanocomposites was found to have core and shell sizes of 17 nm and 19–26 nm, respectively. In addition, it was found that the addition of a high ratio of TiO₂ nanoparticles increases the electrical conductivity and consequently lowers the electrical resistivity of the TiO₂@PANI‐o‐PDA core–shell nanocomposites. The hybrid photocatalysts exhibit a dramatic photocatalytic efficacy of methylene blue degradation under solar light irradiation. A plausible interpretation of the photocatalytic degradation results of methylene blue is also demonstrated. Our setup introduces a facile, inexpensive, unique and efficient technique for developing new core–shell nanomaterials with various required functionalities and colloidal stabilities. © 2018 Society of Chemical Industry     

Preparation of organic–inorganic nanocomposites with core‐shell structure by inorganic powders

Organic–inorganic nanocomposites with core‐shell structure were prepared in two steps. In the first step, the latex particles in the semibatch emulsion polymerization of butyl methacrylate (BMA), in the presence of methacrylic acid (MAA), were prepared. Small amounts of acrylic acid incorporated into the latex to have better interaction between the surface of particles and inorganic phase. MAA also increased the latex stability and decreased the amount of coagulum. In the second step, the core‐shell structures were prepared by coating the latex particles with three types of inorganic powders. Pectin coated precipitated calcium carbonate, alumina, and silica. The examinations show that pectin‐coated calcium carbonate has the best response than other types of calcium carbonate. Alumina was the second type of inorganic powder that was used for coating the core particles. Silicagel and fumed silica (Aerosil) were used for coating by silica. Scanning electron microscopy and transmission electron microscopy showed the particle morphology and the core‐shell structure, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Fracture behavior of crumb rubber‐filled elastomers

The fracture behavior of a crumb rubber‐filled elastomer was observed in optical micrographs. It was found that the failure started from the surface of the unfilled samples. The failure, however, started from a cavity around a crumb in the crumb‐filled samples. This paper suggests that the failure mechanism in the crumb‐filled elastomers (NR, NBR) was based on the microscopic observation of highly strained samples. This paper also considers the failure behavior of two‐component systems: NR/NBR, SBR/NR, and NR/SBR. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3137–3144, 1999     

Evaluation and modeling of the mechanical behavior of carbon nanoparticle/rubber‐modified polyethylene nanocomposites

Recently, the production of polymers loaded with inorganic nanomaterials has been one of the most economical techniques playing a special role in improving the physical and mechanical properties of nanocomposites. Rubbers loaded with different concentrations of carbon nanoparticles (CNPs) were synthesized. The mechanical properties were tested according to standard methods. It was found that the properties of the investigated nanocomposites were improved, depending on the concentration of CNPs in the investigated composite. The optimum concentration was found to be 1.3 vol %. Affine deformation based on the Mooney–Rivilin model was used to visualize the effect of CNPs on the rubber. When polyethylene (PE) was added to rubber/CNPs at the optimum concentration (12.4 vol %), the modulus, tear resistance, and fatigue life were increased, whereas the tensile strength decreased, and the strain at rupture remained almost same. A crosslink model was used to explain the influence of PE on the rubber/CNP nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Microstructural and microwave shielding characteristics of water‐soluble polypyrrole–polyvinyl alcohol–graphite oxide core–shell nanocomposites

This article reports on a facile route for the preparation of polypyrrole–polyvinyl alcohol–graphite oxide nanocomposites through the polymerization of pyrrole with different concentration (wt%) of graphite oxide using ammonium persulfate as an oxidant. The synthesized nanocomposites were characterized by Fourier transform infrared spectroscopy, and their surface morphologies were studied by scanning electron microscopy and transmission electron microscopy. Their solubility in water, DC conductivity in solution, and the current–voltage characteristics of the nanocomposites were studied. Furthermore, the microwave absorption at 1.0–10.0 MHz and the effects of sample thickness on the microwave absorption were investigated. The composites including higher concentration of graphite oxide showed increased solubility and electrical conductivity, and high electromagnetic shielding effectiveness. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers     

Fracture behavior of styrene‐ethylene‐propylene rubber‐toughened polypropylene

The morphology and fracture behavior of isotactic polypropylene toughened by styrene‐ethylene‐propylene (PP/SEP) were investigated. The SEP rubber, having an average particle size of 0.2 µm, is found to be well dispersed in the PP matrix. The fracture toughness of SEP‐modified PP is greatly improved. The toughening mechanism investigation shows that a widespread crazing zone is generated in the crack tip damage zone. An intense narrow damage band in the center of crazed zone is formed. Crazing and shear yielding are found to be the dominant toughening mechanisms in PP/SEP. The crazes are initiated only by large SEP particles in the blend. The small SEP particles (< 0.3 µm) can neither cavitate nor trigger crazing. As a result, large scale shear deformation is suppressed in this blend. These findings are consistent with the notion that the crack tip plane strain constraint has to be relieved in magnitude in order for the deviatoric stress to reach a critical value for widespread shear banding.     

Self‐healing and interfacially toughened carbon fibre‐epoxy composites based on electrospun core–shell nanofibres

Dual components of a self‐healing epoxy system comprising a low viscosity epoxy resin, along with its amine based curing agent, were separately encapsulated in a polyacrylonitrile shell via coaxial electrospinning. These nanofiber layers were then incorporated between sheets of carbon fiber fabric during the wet layup process followed by vacuum‐assisted resin transfer molding to fabricate self‐healing carbon fiber composites. Mechanical analysis of the nanofiber toughened composites demonstrated an 11% improvement in tensile strength, 19% increase in short beam shear strength, 14% greater flexural strength, and a 4% gain in impact energy absorption compared to the control composite without nanofibers. Three point bending tests affirmed the spontaneous, room temperature healing characteristics of the nanofiber containing composites, with a 96% recovery in flexural strength observed 24 h after the initial bending fracture, and a 102% recovery recorded 24 h after the successive bending fracture. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44956.     

Thermal–oxidative degradation and accelerated aging behavior of polyamide 6/epoxy resin‐modified montmorillonite nanocomposites

Polyamide 6 (PA6) nanocomposites based on epoxy resin‐modified montmorillonite (EP‐MMT) were prepared by melt processing using a typical twin‐screw extruder. X‐ray diffraction combined with transmission electron microscopy was applied to elucidate the structure and morphology of PA6/EP‐MMT nanocomposites, suggesting a nearly exfoliated structure in the nanocomposite with 2 wt % EP‐MMT (PA6/2EP‐MMT) and a partial exfoliated‐partial intercalated structure in PA6/4 wt %EP‐MMT nanocomposite (PA6/4EP‐MMT). The thermogravimetric analysis under air atmosphere was conducted to characterize the thermal–oxidative degradation behavior of the material, and the result indicated that the presence of EP‐MMT could inhibit the thermal‐oxidative degradation of PA6 effectively. Accelerated heat aging in an air circulating oven at 150°C was applied to assess the thermal–oxidative stability of PA6 nanocomposites through investigation of reduced viscosity, tensile properties, and chemical structure at various time intervals. The results indicated that the incorporation of EP‐MMT effectively enhanced the thermal–oxidative stability of PA6, resulting in the high retention of reduced viscosity and tensile strength, and the low ratio of terminal carboxyl group to amino group. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40825.     

Core–shell particles to toughen epoxy resins. I. Preparation and characterization of core–shell particles

A two-stage, multistep soapless emulsion polymerization was employed to prepare various sizes of reactive core–shell particles (CSPs) with butyl acrylate (BA) as the core and methyl methacrylate (MMA) copolymerizing with various concentrations of glycidyl methacrylate (GMA) as the shell. Ethylene glycol dimethacrylate (EGDMA) was used to crosslink either the core or shell. The number of epoxy groups in a particle of the prepared CSP measured by chemical titration was close to the calculated value based on the assumption that the added GMA participated in the entire polymerization unless it was higher than 29 mol %. Similar results were also found for their solid-state ^13C-NMR spectroscopy. The MMA/GMA copolymerized and EGDMA-crosslinked shell of the CSP had a maximum glass transition temperature (T_g) of 140°C, which was decreased with the content of GMA at a rate of −1°C/mol %. However, the shell without crosslinking had a maximum T_g of 127°C, which decreased at a rate of −0.83°C/mol %. The T_g of the interphasial region between the core and shell was 65°C, which was invariant with the design variables. The T_g of the BA core was −43°C, but it could be increased to −35°C by crosslinking with EGDMA. The T_g values of the core and shell were also invariant with the size of the CSP. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2069–2078, 1998     

Polymerization‐induced bimodal phase separation in a rubber‐modified epoxy system

The bimodal phase separation process of a rubber‐modified epoxy system, consisting of diglycidyl ether of bisphenol A (DGEBA), and a hydroxyl‐terminated butadiene–acrylonitrile random copolymer (HTBN), during curing with tetrahydro‐phthalic anhydride was studied by time‐resolved small‐angle light scattering (TRSALS), differential scanning calorimetry (DSC), and digital image analysis (DIA). The HTBN/DGEBA mixture reveals an upper critical solution temperature (UCST). At higher curing temperatures, double‐peak structure from the matrix was investigated by TRSALS and confirmed by DIA. The special two characteristic size distribution behavior was explained qualitatively by nucleation growth coupled with spinodal decomposition (NGCSD) and the competition between phase separation and polymerization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 59–67, 1999     

Toughening of PA6 nanocomposites by reactive acrylonitrile–butadiene–styrene core–shell rubber particles

The effect of addition of organoclay and the reactive ABS‐g‐MA core‐shell particles on the mechanical properties and morphology of blends of polyamide (PA6) were reported. The reactive rubber particles with core‐shell structure were selected as modifier instead of conventional reactive bulk rubber. The microstructure of the ternary nanocomposites was characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Impact strength and stress–strain behavior of blends were measured as a function of organoclay content and core/shell ratio of ABS‐g‐MA. The organoclay plates affected the interfacial adhesion between polyamide and the core‐shell particles because of a shielding effect of organclay on the interacting of amine end groups of PA6 with the MA groups of ABS‐g‐MA. The poor dispersion behavior of ternary nanocomposites was observed when the core/shell ratio is 80/20, and with an increase of organoclay content, the core/shell dispersed phase size increased. Blends based on the maleated elastomer with the core/shell ratio 60/40 gave a more beneficial balance of toughness versus stiffness. POLYM. COMPOS., 35:864–871, 2014. © 2013 Society of Plastics Engineers     

Morphology and rheology relationships of epoxy/core‐shell particle blends

The morphological and rheological behaviors of toughened epoxy resins modified with core‐shell rubber particles (CSR) were studied. These rubber particles were based on a poly (butadiene‐co‐styrene) core and a crosslinked poly (methyl methacrylate) shell. The effect of functionalized groups was performed on two types of CSR particles: first, those containing carboxyl‐functionalized groups (CSf), and second, particles containing no carboxyl‐functionalized groups (CSnf) in the PMMA‐shell. For these blends, the correlations between the morphology, particle dispersion state and their rheological behaviors before curing were investigated. Preliminary work using TEM micrographs indicated that the blends modified with CSf and CSnf exhibited the same particle size but differed with respect to the dispersion state. Rheological behavior of these blends was assessed in steady shear flow and dynamic viscoelastic experiments. Yield viscosity near‐zero shear rate occurred in the DGEBA/CSf blend presenting non‐Newtonian behavior at the particle volume fraction of 20% vol. The rheological behavior was clearly related to the state of particle dispersion and analyzed taking into account interactions between the particles‐particles and the particles‐matrix. The Williams‐Landel‐Ferry (WLF) shift procedure was used to construct modulus master curves G′ and G″ from the elastic solid state to molten polymers. A secondary plateau existed at low frequencies and was related to the presence of interactions leading to a physical network‐type structure. The deviation between theoretical G′ (Paleirne's model) and experimental G′ values was evaluated and exhibited high elasticity at the terminal zone, which correlated well with available literature.     

Cloisite clay‐infused phenolic foam nanocomposites

A sonochemical technique was developed to infuse Cloisite clay nanoparticles into phenolic foam materials. Phenolic resin solution (Part A) was mixed with clay particles, and irradiated using a high intensity ultrasonic liquid processor. In the next step, the modified phenolic resin solution containing clay particles was mixed with Part B (containing phenol sulfonic acid, catalyst) through a high‐speed mechanical stirrer. The reaction mixture was then cast into rectangular molds to make nanophased foam panels. Test coupons were cut precisely from the panels to carry out thermal, morphological, and mechanical characterizations. The as‐prepared foam samples were characterized by scanning electron microscopy (SEM), X‐ray diffraction, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The SEM studies have shown that the particles are well dispersed over the entire volume of the matrix with minimal agglomeration. The foam cells structures are well‐ordered and uniform in size and shape. The TGA and DSC analyses show that the nanophased foams are thermally more stable than the corresponding neat system. Quasistatic compression tests have been carried out for both nanophased and neat foams systems. The test results show that there is a significant increase (approximately in the range of 150–180%) in the compressive strength and modulus of the nanophased foams over the neat system. This improvement in compressive properties has been noted repeatedly for multiple batches and with a minimum of three specimens tested from each batch. Details of the synthesis, thermal and mechanical characterization are presented in this paper. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 308‐314, 2007     

Preparation and characterization of rubber–clay nanocomposites

Rubber–clay nanocomposites were prepared by two different methods and characterized with TEM and XRD. The TEM showed clay had been dispersed to one or several layers. The XRD showed that the basal spacing in the clay was increased. It was evident that some macromolecules intercalated to the clay layer galleries. The clay layer could be uniformly dispersed in the rubber matrix on the nanometer level. The mechanical tests showed that the nanocomposites had good mechanical properties. Some properties exceeded those of rubber reinforced with carbon black, so the clay layers could be used as an important reinforcing agent as the carbon black was. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1879–1883, 2000     

Effects of rubber‐rich domains and the rubber‐plasticized matrix on the fracture behavior of liquid rubber‐modified araldite‐F epoxies

The fracture behavior of a bisphenol A diglycidylether (DGEBA) epoxy, Araldite F, modified using carboxyl‐terminated copolymer of butadiene and acrylonitrile (CTBN) rubber up to 30 wt%, is studied at various crosshead rates. Fracture toughness, K_IC, measured using compact tension (CT) specimens, is significantly improved by adding rubber to the pure epoxy. Dynamic mechanical analysis (DMA) was applied to analyze dissolution behavior of the epoxy resin and rubber, and their effects on the fracture toughness and toughening mechanisms of the modified epoxies were investigated. Scanning electron microscopy (SEM) observation and DMA results show that epoxy resides in rubber‐rich domains and the structure of the rubber‐rich domains changes with variation of the rubber content. Existence of an optimum rubber content for toughening the epoxy resin is ascribed to coherent contributions from the epoxy‐residing dispersed rubber phase and the rubber‐dissolved epoxy continuous phase. No rubber cavitation in the fracture process is found, the absence of which is explained as a result of dissolution of the epoxy resin into the rubber phase domains, which has a negative effect on the improvement of fracture toughness of the materials. Plastic deformation banding at the front of precrack tip, formed as a result of stable crack propagation, is identified as the major toughening process.     

Failure of elastic‐plastic core–shell microcapsules under compression

Characterization of the failure behavior of microcapsules is extremely important to control the release of their core actives by mechanical forces. The strain and stress of elastic‐plastic uninflated core–shell microcapsules at failure (rupture or bursting) has been determined using finite element modeling (FEM) and micromanipulation compression experiments. The ductile failure of polymeric microcapsules at high deformations is considered to occur when the maximum strain in the shell exceeds a critical strain, resulting in their rupture. FEM has been used to determine the maximum strains present in the capsule wall at different deformations for three types of shell material: elastic, elastic—perfectly plastic and elastic—perfectly plastic with strain hardening at large strains. The results obtained were used to determine the failure strain and stress of melamine‐formaldehyde microcapsules, with average population values of ～0.48 and ～350 MPa, respectively. Thus, the elastic‐plastic stress–strain relationship has been determined for the core–shell microcapsules tested. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Thermal decomposition kinetics of an epoxy resin with rubber‐modified curing agent

Thermal decomposition kinetics of diglycidyl ether of bisphenol A (DGEBA)/4,4′‐methylene dianiline (MDA) system with rubber‐modified MDA was studied by the methods of Ozawa, Kissinger, and Friedman, and the kinetic parameters were compared. The thermal decomposition data of the cured epoxy resin were analyzed by thermogravimetric analysis (TGA) at different heating rates. TG curves showed that the thermal decomposition of the epoxy system occurred in one stage regardless of rubber‐modified MDA content. The apparent activation energies for the DGEBA/MDA system with 10 phr of rubber‐modified MDA, as determined by the Ozawa, Kissinger, and Friedman methods, are 184, 182, and 222 kJ/mol, respectively. The thermal stability of the epoxy system increased with the increasing content of rubber‐modified MDA, which has four benzene rings with high thermal resistance due to the resonance structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 479–485, 2001     

TiO2‐Oligoaldaramide nanocomposites as efficient core‐shell systems for wood preservation

Homogeneous core‐shell systems were obtained with a growth, in controlled steps, of several oligoamides on TiO₂ nanoparticles. Derivatives of natural compounds, such as l ‐tartaric acid and α,α′‐trehalose, were used as diesters in the polycondensation reactions with ethylenediamine. TiO₂ anatase was chosen because of its high photo‐activity and its antimicrobial activity. The TiO₂ nanoparticles had been previously activated then functionalized using two different coupling agents, and finally, the TiO₂‐oligoamide nanocomposites were synthesized using two synthetic pathways. The final products were characterized by ¹H NMR, ¹³C NMR, FT‐IR, and transmission electron microscope. These nanocomposites can show improved properties in comparison with the single components (TiO₂ nanoparticles or oligoamides), which are useful in many fields, such as antimicrobial coatings for surfaces in cultural heritage conservation. A nanocomposite (TiO₂‐polyethylenetartaramide) was used for applicative studies, and it has shown a good efficacy against fungal attack by Trametes versicolor on wood specimens (Fagus sylvatica). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42047.