Mechanical and fracture properties of halloysite nanotube reinforced vinyl‐ester nanocomposites

The mechanical and fracture properties of vinyl‐ester composites reinforced with halloysite nanotubes have been investigated. Enhancements in toughness are attributed to crack bridging, deflection, and localized plastic deformation, while strength improvements can be attributed to the large aspect ratio of fillers, favorable interfacial adhesion and dispersion, and inter‐tubular interaction. Comparisons of experimental data on elastic modulus and mathematical models for predicting particulate polymer composites have verified the models of Paul and Guth. The aspect ratio of fillers and the degree of interfacial adhesion are crucial factors in the prediction of elastic modulus in these polymer nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1716–1725, 2013     

In situ polymerization of bio‐based thermosetting polyurethane/graphene oxide nanocomposites

Novel bio‐based polyurethane/graphene oxide (GO) nanocomposites have been successfully synthesized from biorenewable epoxidized soybean‐castor oil fatty acid‐based polyols with considerable improvement in mechanical and thermal properties. The GO was synthesized via a modified pressurized oxidation method, and was investigated using Raman spectra, AFM and XPS, respectively. The toughening mechanism of GO in the bio‐based polyurethane matrix was explored. The elongation at break and toughness of polyurethane were increased by 1.3 and 0.8 times with incorporation of 0.4 wt % GO, respectively. However, insignificant changes in both mechanical strength and modulus were observed by adding GO. The results from thermal analysis indicated that the GO acts as new secondary soft segments in the polyurethane which lead to a considerable decrease in the glass transition temperature and crosslink density. The SEM morphology of the fracture surface after tensile testing showed a considerable aggregation of graphene oxide at concentrations above 0.4 wt %. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41751.     

Enhanced mechanical and electrical properties of nylon‐6 composite by using carbon fiber/graphene multiscale structure as additive

In order to improve the mechanical properties and electrical conductivity of nylon‐6 (PA6) composites, a highly effective multiscale structure filler comprising poly(diallyldimethylammonium chloride) (PDDA)‐modified graphene and negatively surface‐charged carbon fiber was synthesized in this study. For this, the graphene used a top‐down method for synthesis by exfoliating graphite oxide (GO) through focused solar radiation on it and then modified its surface by using a polyelectrolyte. The carbon fiber (CF) surface was functionalized by an acid oxidation method. The multiscale structure was manufactured via the electrostatic interaction between the positively charged solar graphene (SG) and oppositely charged CF by homogeneous mixing. Scanning electron microscopy (SEM) images of the fracture surface of the PA6 composites exhibited that the carbon fiber/graphene multiscale structure possessed better dispersion and compatibility than those of individual CF and SG did. Thus, the impact strength, bending properties, and electrical conductivity of the PA6 composites were enhanced. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41968.     

Decoration of graphene oxide nanosheets with amino silane‐functionalized silica nanoparticles for enhancing thermal and mechanical properties of polypropylene nanocomposites

Graphene oxide nanosheets were decorated by amino‐silane modified silica nanoparticles. An electrostatic interaction between the negative charge of oxygen‐containing groups of graphene oxide and the positive charge of amino‐silane functional groups on the surface of silica nanoparticles plays a major role for the interfacial interaction of these two materials. The hybrid material was then used as a reinforcement in polypropylene (PP) composite. The increasing tensile strength at yield, tensile, and flexural modulus of the PP composite at a graphene oxide‐ amino‐silane silica loading content of 20 wt % are about 24.81, 55.52, and 30.35%, respectively, when compared with those of PP. It is believed that GO assists the dispersion of SiO₂ nanoparticles to the polymer matrix because of its unique structure having hydrophilicity due to its oxygen functional groups and hydrophobicity owing to its backbone graphitic carbon structure. This hybrid material may also be used as the reinforcement in other polyolefins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44382.     

Influence of processing condition and carbon nanotube on mechanical properties of injection molded multi‐walled carbon nanotube/poly(methyl methacrylate) nanocomposites

In this work, multi‐walled carbon nanotubes (MWCNT) and poly(methyl methacrylate) (PMMA) pellets were compounded via corotating twin‐screw extruder. The produced MWCNT/PMMA nanocomposite pellets were injection molded. The effect of MWCNT concentration, injection melt temperature and holding pressure on mechanical properties of the nanocomposites were investigated. To examine the mechanical properties of the MWCNT/PMMA nanocomposites, tensile test, charpy impact test, and Rockwell hardness are considered as the outputs. Design of experiments (DoE) is done by full factorial method. The morphology of the nanocomposites was performed using scanning electron microscopy (SEM). The results revealed when MWCNT concentration are increased from 0 to 1.5 wt %, tensile strength and elongation at break were reduced about 30 and 40%, respectively, but a slight increase in hardness was observed. In addition, highest impact strength belongs to the nanocomposite with 1 wt % MWCNT. This study also shows that processing condition significantly influence on mechanical behavior of the injection molded nanocomposite. In maximum holding pressure (100 bar), the nanocomposites show highest tensile strength, elongation, impact strength and hardness. According to findings, melt temperature has a trifle effect on elongation, but it has a remarkable influence on tensile strength. In the case of impact strength, higher melt temperature is favorable. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43738.     

Graphene nanoplatelet‐polyetherimide composites: Revealed morphology and relation to properties

In this research, a novel sample preparation technique was applied to reveal the morphology exfoliated graphene nanoplatelets [GNP, ～10 nm thick and ～5 µm in diameter)] and Polyetherimide (PEId) nanocomposite and study the relationship between processing and properties. The morphology of nanoscale fillers used to be hard to capture through conventional sample preparation. The polish‐plasma etching approach presented in this article successfully created contrast between filler and matrix. As a result, distribution and orientation of the fillers were obtained to study the effect of injection molding, compression molding and annealing. It was found that the orientation was significantly different depending on processing routes. The information obtained from morphology study also led to the modification of Tandon–Weng model, resulting in improved prediction of elastic modulus of the composite. The SEM images also clearly revealed change of filler orientation after annealing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4081–4089, 2013     

Preparation and properties of styrene‐butadiene rubber nanocomposites blended with carbon black‐graphene hybrid filler

Graphene has become an attractive reinforcing filler for rubber materials, but its dispersion in rubber is still a big challenge. In this work, a novel carbon black‐reduced graphene (CB‐RG) hybrid filler was fabricated and blended with styrene‐butadiene rubber (SBR) via simple two‐roll mill mixing. The prepared CB‐RG hybrids had a microstructure with small CB agglomerates adsorbed onto graphene surfaces. CB acted as a barrier preventing the RG sheets from restacking even after drying. Homogeneous dispersion of graphene sheets in SBR matrix was observed by the mechanical mixing method based on the application of the CB‐RG hybrid fillers. Dynamic mechanical analysis showed that Tg of the SBR/CB‐RG blend was higher than that of the SBR/CB blend indicating strong interfacial interactions between RG and SBR due to the high surface area of graphene and the π‐π interaction between SBR and graphene. The tensile properties of SBR/CB‐RG composites improved significantly and the volume resistivity decreased compared with the SBR/CB blends. The thermal stability of SBR composites filled with CB and CB‐RG showed slight difference. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41309.     

Effect of the nanotube aspect ratio and surface functionalization on the morphology and properties of multiwalled carbon nanotube polyamide‐based fibers

In this study, the effect of the carbon nanotube (CNT) aspect ratio and surface functionalization on the mechanical behavior and morphological changes of polyamide (PA)‐based fibers was investigated. Composites were prepared by the melt blending of CNTs with PA, and at a later time, the fibers were prepared by melt spinning and cold drawing. A reinforcement effect was noticed for all of the CNTs samples, and the increase in the mechanical properties and dimensional stability was more pronounced for highly oriented filaments. When the elongational flow was increased, the orientation of CNTs along the fiber direction was observed, but the nanotube alignment was much more difficult for CNTs with ultrathin outer diameters because of nanotube waviness and folding. Moreover, the presence of functional groups on the CNT surface hindered their orientation along the fiber direction because some interaction between the functional groups could occur. The morphological variations of the oriented, anisotropic fibers, as studied with transmission electron microscopy, scanning electron microscopy, small‐angle X‐ray scattering, and differential scanning calorimetry analysis, were correlated with changes in the mechanical behavior. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Multilayer coextrusion of graphene polymer nanocomposites with enhanced structural organization and properties

A potential advantage of platelet‐like nanofillers as nanocomposite reinforcements is the possibility of achieving two‐dimensional (2D) stiffening through planar orientation of the platelets. Forced assembly by multilayer coextrusion, which enables the in‐plane orientation of platelet‐like fillers in alternating layers, was used in this work to produce poly(lactic acid) (PLA)/graphene multilayer films. These films exhibited a multilayer structure made of alternating layers of neat PLA and PLA containing graphite nanoplatelets (GNPs). Electron microscopy revealed information on the orientation of the individual GNPs. X‐ray diffraction results indicated that the thickness of the individual GNPs was reduced during the multilayer coextrusion process. A significant reinforcement of 120% at an overall GNP loading of 1 wt % in PLA was achieved. This high effective reinforcement was attributed to the high degree of planar alignment, improved dispersion and exfoliation and increased aspect ratio of the GNPs in the composite layers after multilayer coextrusion. Improved water vapor barrier properties were also achieved as a result of the highly organized 2D nanofillers in the multilayer films. These industrial scalable multilayer nanocomposite films open up possibilities for lightweight and strong packaging materials for food and industrial applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46041.     

Electrically conductive polycarbonate/ethylene‐propylene copolymer/multi‐walled carbon nanotubes nanocomposites with improved mechanical properties

In this article, the effect of Multi‐walled carbon nanotubes (MWCNTs) on the electrical conductivity and mechanical properties of polycarbonate (PC) toughened with cross‐linked ethylene‐propylene copolymer (EPC) was investigated. The solubility parameters of the PC and EPC were calculated using Hoy methods to clarify the miscibility of the polymer blends. It could be concluded that in the cooled state, the blends form a heterogeneous structure with two separate phases. The tensile, flexural, impact toughness properties of the PC/EPC blend and PC/EPC/MWCNT nanocomposites were carried out to illuminate the optimum concentration of polymer blends and MWCNTs. The 335% increment for the impact strength results appeared with combination of 10% EPC in the PC matrix. The flexural modulus and strength of PC/EPC blend increased by 75.1% and 59.1%, respectively. The Nielsen model was performed to fit the best curve of theoretical simulation to experimental results for elastomeric dispersed in the plastic matrix. Halpin‐Tsai model was applied to estimate the stiffness of nanocomposites blends with different volume fraction and aspect ratio of MWCNTs in the PC/EPC blends. Finally, in the presence of MWCNTs, all nanocomposite samples were semi‐conducting and the percolation threshold of the PC/EPC (10%) blends was between 0.5% and 1.0% MWCNTs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44661.     

Effect of tungsten disulfide nanotubes on the thermomechanical properties of polypropylene‐graft‐maleic anhydride nanocomposites

In this work, the influence of tungsten disulfide nanotubes (INT‐WS₂) on the mechanical, thermal, structural, and morphological characteristics of Polypropylene‐graft‐maleic anhydride (PPGMA) nanocomposites is investigated. The addition of 5% INT‐WS₂ increases the Young's Modulus by 28.5% and the storage modulus by 196.5% (in the rubbery state). Furthermore, the nanocomposites' thermal stability increases (up to 10 °C) with the addition of INT‐WS₂. Transmission electron microscopy observations of the nanocomposites revealed that nanotubes' length is significantly reduced during processing and that nanotubes are well‐dispersed inside the PPGMA matrix. DSC results indicated that INT‐WS₂ serve as nucleating agents in PPGMA. Moreover, AFM observations (coupled with DSC results) suggested the formation of fibrillar crystallites in the nanocomposites. This interfacial crystalline structure seems to interpose between the PPGMA and INT‐WS₂. Thus, it plays a crucial role in the load transfer from the amorphous part of the polymer to the rather stiff INT‐WS₂. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43887.     

Thermal,electrical, and mechanical properties of polyethylene–graphene nanocomposites obtained by in situ polymerization

In this study, we investigated the thermal, dynamic mechanical, mechanical, and electrical properties of polyethylene (PE)–graphene nanosheet (GNS) nanocomposites, with GNS amounts from 0 to 20 wt %, prepared by in situ polymerization. The thermal stability was evaluated by thermogravimetric analysis (TGA) and showed that the addition of GNSs to the polyolefin matrix increased the onset degradation temperature by 30°C. The electrical conductivity, measured by the impedance technique, presented a critical percolation threshold of 3.8 vol % (8.4 wt %) of GNS. A slight decrease in the tensile strength was found. On the other hand, dynamic mechanical analysis showed an increase in the storage modulus of the nanocomposites compared with that of neat PE. The glass‐transition temperature value increased from ?111°C (neat PE) to ?106°C (PE/6.6 wt % GNS). All of these results show that PE became stiffer and thermally more stable and could be transformed from an insulator to a semiconductor material in the presence of GNSs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Epoxy/p‐phenylenediamine functionalized graphene oxide composites and evaluation of their fracture toughness and tensile properties

In an attempt to enhance the mechanical properties of epoxy/graphene‐based composites, the interface was engineered through the functionalization of graphene oxide (GO) sheets with p‐phenylenediamine; this resulted in p‐phenylenediamine functionalized graphene oxide (GO–pPDA). The morphology and chemical structure of the GO–pPDA sheets were studied by spectroscopic methods, thermal analysis, X‐ray diffraction, and transmission electron microscopy. The characterization results show the successful covalent functionalization of GO sheets through the formation of amide bonds. In addition, p‐phenylenediamine were polymerized on graphene sheets to form crystalline nanospheres; this resulted in a GO/poly(p‐phenylenediamine) hybrid. The mechanical properties of the epoxy/GO–pPDA composite were assessed. Although the Young's modulus showed improvement, more significant improvements were observed in the strength, fracture strain, and plane‐strain fracture toughness. These improvements were attributed to the unique microstructure and strong interface between GO–pPDA and the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43821.     

Enhanced interfacial interaction of epoxy nanocomposites with activated graphene nanosheets

The interfacial properties of epoxy nanocomposites reinforced by thermally exfoliated graphene nanosheets (TEG) and activated thermally exfoliated graphene nanosheets (a‐TEG) were compared. The specific surface area (SSA) of a‐TEG with well‐defined micro‐mesopore size distribution was 1000 m²/g, which was much higher that of TEG (550 m²/g). The interfacial interaction between a‐TEG and epoxy was stronger than that of TEG/epoxy owing to their higher SSA and pore size which was proved by dynamic mechanical analysis. As a result, the tensile strength of a‐TEG/epoxy was increased compared with that of TEG/epoxy for all concentrations. In particular, the tensile and flexural strength of a‐TEG/epoxy was increased up to 20 and 50% in comparison to that of TEG/epoxy at 0.05 wt % graphene, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41164.     

Effect of MWNTs concentration and cooling rate on the morphological,structural, and electrical properties of non‐isothermally crystallized PEN/MWNT nanocomposites

The effect of multiwall carbon nanotubes (MWNT) concentration and cooling rate on the morphological, structural and electrical properties of non‐isothermally crystallized Poly(ethylene naphthalate) nanocomposites (PEN/MWNT) was studied. PEN/MWNT nanocomposites containing 1 and 2 wt % of nanotubes were prepared by melt blending in a mini twin screw extruder. Nanocomposite samples with different degree of crystallinity (X_c) were obtained via non‐isothermally crystallization at cooling rates of 2, 10, 20, and 300°C min^?1. In this study it was demonstrated that carbon nanotubes and cooling rate strongly influence morphological and structural characteristics of PEN. Calorimetric results showed that the peak crystallization temperature (T_c) of PEN nanocomposites was increased ～9° through heterogeneous nucleation with respect to pure PEN. X‐ray diffraction revealed that carbon nanotubes modify the crystalline structure of PEN favoring the formation of β‐crystals, and this effect increases with the nanotubes content. On the basis of X‐ray scattering analysis, the variation of lamellar thickness revealed that nanotubes promote the formation of lamellar crystals with average thickness of 20 nm at different cooling rates. These structural and morphological changes play an important role on the electrical properties of nanocomposites. It was found that higher concentration of nanotubes and crystallinity promotes electrical conductivity of nanocomposites in the order of semiconductors (until 1 × 10^?4 S cm^?1) as well as permittivity of 20 at different tested frequencies. This may due to the interconnected networks of nanotubes throughout the crystalline structure formed in PEN nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41765.     

Functionalization of carbon nanotubes with (3‐glycidyloxypropyl)‐trimethoxysilane: Effect of wrapping on epoxy matrix nanocomposites

In this work, multiwalled carbon nanotubes (MWCNT), after previous oxidation, are functionalized with excess (3‐glycidyloxypropyl)trimethoxysilane (GLYMO) and used as reinforcement in epoxy matrix nanocomposites. Infrared, Raman, and energy‐dispersive X‐ray spectroscopies confirm the silanization of the MWCNT, while transmission electron microscopy images show that oxidized nanotubes presented less entanglement than pristine and silanized MWCNT. Thickening of the nanotubes is also observed after silanization, suggesting that the MWCNT are wrapped by siloxane chains. Field‐emission scanning electron microscopy reveals that oxidized nanotubes are better dispersed in the matrix, providing nanocomposites with better mechanical properties than those reinforced with pristine and silanized MWCNT. On the other hand, the glass transition temperature of the nanocomposite with 0.05 wt % MWCNT‐GLYMO increased by 14 °C compared to the neat epoxy resin, suggesting a strong matrix–nanotube adhesion. The functionalization of nanotubes using an excess amount of silane can thus favor the formation of an organosiloxane coating on the MWCNT, preventing its dispersion and contributing to poor mechanical properties of epoxy nanocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44245.     

High-performance epoxy nanocomposites via constructing rigid structured interphase with epoxy-rich graphene oxide

Epoxy resins, as the most important thermosetting matrix of carbon fiber reinforced polymer (CFRP) composites, are widely used in the structural field, but the highly intrinsic brittleness of epoxy resins greatly limits their application. Therefore, it is urgent to develop new method to prepare high-performance epoxy composites. In this research, GO riched with rigid short-chain structure epoxy group on its surface was synthesized by chemically grafting dopamine, hexachlorocyclotriphosphazene and glycidol successively. Then the modified nanofillers were incorporated into the epoxy matrix to prepare high-performance nanocomposites. The effect of epoxy-rich GO nanosheets as fillers on mechanical properties of aerospace grade epoxy was studied. The results revealed that the epoxy-rich GO could effectively optimize the performance of epoxy resins owing to forming the rigid structured interphase. The tensile strength and elongation at break of the nanocomposites were up to 113 MPa and 7.6% with 0.075 wt% additives, respectively, which greatly surpassed the value reported by the limited researches on strengthening epoxy with GO and its derivate nanofillers. Therefore, instructive idea and effective method were provided to obtain high-performance polymer nanocomposite matrix in this study.     

Studies of nanocomposites based on carbon nanomaterials and RTV silicone rubber

The mechanical and electrical properties were investigated for nanocomposites based on carbon nanotubes (CNTs) and conductive carbon black (CB). Solution room‐temperature‐vulcanized silicone rubber was used as a matrix. Vulcanizates based on CNTs and CB was prepared by solution mixing. With the addition of 2 phr of CNTs to the rubber matrix, the Young's modulus increased by 272% and reached as high as ～706% at 8 phr, whereas the modulus increased only 125% for CB specimens at 10 phr. Similarly, the electrical properties at 5 phr content of CNT were ～0.7 kΩ against ～0.9 kΩ at 20 phr CB. The Kraus plot from equilibrium swelling tests shows that the high properties for CNT specimens are due to high polymer–filler interfacial interactions, the small particle size that improves the distribution of the filler in a highly exfoliated state, and high electrical connective networks among the filler particles. These improvements can especially influence medical products such as feeding tubes, seals and gaskets, catheters, respiratory masks and artificial muscles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44407.     

Enhanced thermoelectric performance by alcoholic solvents effects in highly conductive benzenesulfonate‐doped poly(3,4‐ethylenedioxythiophene)/graphene composites

Benzenesulfonate‐doped poly(3,4‐ethylenedioxythiophene) (PEDOT‐Bzs)/graphene thermoelectric (TE) composites with various graphene filler contents were synthesized in five different kinds of solvents. Dodecylbenzenesulfonic acid (DBSA) was used to achieve good dispersion of graphene into the PEDOT matrix. Among the synthesized PEDOT materials, the one synthesized in methanol (PEDOT‐MeOH) had the highest electrical conductivity. X‐ray photoelectron spectroscopy (XPS) analysis showed almost the same charge carrier concentration for all PEDOT materials. However, the X‐ray diffraction (XRD) analysis highlighted the enhancement of PEDOT chain stacking by shorter‐chain alcoholic solvents, as a result of which the carrier mobility and electrical conductivity were increased. The electrical conductivity and the Seebeck coefficient of the PEDOT/graphene composites were significantly improved with increasing the graphene content, which strongly depended on increased carrier mobility. The thermal conductivity of the composites exhibited relatively small changes, attributed to phonon scattering effects. The maximum TE efficiency of the PEDOT‐MeOH/graphene composite with 75 wt % graphene showed a substantially improved value of 1.9 × 10^?2, higher than that of the other PEDOT/graphene composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42107.     

In situ fast polymerization of graphene nanosheets‐filled poly(methyl methacrylate) nanocomposites

A series of graphene nanosheets‐filled poly(methyl methacrylate) nanocomposites (GNS/PMMA) is successfully prepared by an in situ fast polymerization method with graphene weight fractions from 0.1 to 2.0 wt %. In situ polymerization is effective in well dispersing of GNS in matrixes and suitable for both low and high content of GNS. The synthesis processes of polymer composites could be simplified and fast by using industrial grade graphene. The GNS fillers are found to disperse homogeneously in the PMMA matrix. The maximum electrical conductivity of the composites achieves 0.57 S m^?1, with an extremely low percolation threshold of 0.3 wt %. The electrical conductivities are further predicted by percolation theory and found to agree well with the experimental results. The results indicate that the microstructures, thermal, electrical, and mechanical properties of PMMA polymer are significantly improved by adding a low amount of graphene nanosheets. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43423.