Strain‐induced crystallization behavior of phenolic resin crosslinked natural rubber/clay nanocomposites

Nanocomposites of natural rubber (NR) and unmodified clay were prepared by latex compounding method. Phenolic resin (PhOH) was used to crosslink NR. Crosslinked neat NR was also prepared for comparison. The structure–property relationship of uncrosslinked and crosslinked NR/clay nanocomposites was examined to verify the reinforcement mechanism. Microstructure of NR/clay nanocomposites was studied by using transmission electron microscopic (TEM), X‐ray diffraction (XRD), wide angle X‐ray diffraction (WAXD), and small angle X‐ray scattering (SAXS) analyses. The results showed the evidence of intercalated clay together with clay tactoids for the nanocomposite samples. The highest tensile strength was achieved for the crosslinked NR/clay nanocomposite. The onset strain of deformation induced the crystallization of NR for nanocomposites was found at almost the same strain, and furthermore their crystallization was developed at lower strain than that of the crosslinked neat NR because of the clay orientation and alignment. However, at high strain region, the collaborative crystallization process related to the clay dispersion and conventional crosslink points in the NR was responsible to considerably high tensile strength of the crosslinked NR/clay nanocomposite. Based on these analyses, a mechanistic model for the strain‐induced crystallization and orientational evolution of a network structure of PhOH‐crosslinked NR/clay nanocomposite was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42580.     

Curing behavior and structure of an epoxy/clay nanocomposite system

The curing behavior of an epoxy/clay nanocomposite system composed of a bifunctional epoxy resin with an aromatic amine curing agent and an organically modified clay was investigated. Differential scanning calorimetry (DSC) was used to investigate the curing behavior of the epoxy/clay nanocomposite system. The curing rate of the nanocomposite system increased with increasing clay content. A kinetic equation, considering an autocatalytic reaction mechanism, could describe fairly well the curing behavior of the epoxy/clay nanocomposite system. The reaction kinetic parameters of the kinetic equation were determined by fitting DSC conversion data to the kinetic equation, using a nonlinear numerical method. Dynamic mechanical analysis was used to investigate the thermomechanical properties of the epoxy/clay nanocomposite system. The glass transition temperature of the epoxy/clay nanocomposite system increased slightly with increasing clay content. The structure of the nanocomposite system was characterized by X‐ray diffraction analysis and transmission electron microscope imaging. The formation of intercalated structures was observed dominantly in the epoxy/clay nanocomposites, together with some exfoliated structures. POLYM. ENG. SCI., 46:1318–1325, 2006. © 2006 Society of Plastics Engineers     

聚氧化乙烯/改性层状粘土纳米复合材料

本文通过使用熔融挤出的方法制备聚氧化乙烯(PEO)/改性层状粘土纳米复合材料,采用小角度X射线衍射仪(SAXS)和透射电镜(TEM)对其微观形态特征进行表征,同时使用动态力学性能分析仪(DMA)对其动态力学性能进行研究。     

Characterization of latex-based isotactic polypropylene/clay nanocomposites

Polypropylene/clay nanocomposite (PCN) containing 1 wt% organo-modified clay was prepared by latex technology, previously successfully applied for preparation of carbon nanotubes (CNTs)/polymer composites. The level of dispersion of organoclay and the microstructure of the resulting PCNs were characterized by means of X-ray diffraction analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The obtained results have demonstrated that the latex technique represents a promising method for preparation of PP/clay nanocomposites with good dispersion of exfoliated nanoclay particles. The influence of clay nanoparticles on nonisothermal crystallization of PCN was investigated by DSC. The crystallization onset temperature of the matrix rises for about 5 °C when crystallizing from the quiescent melt. Improved thermal stability of PP/nanoclay was observed as evaluated by TGA. The dynamic mechanical analysis reveals an increase in storage modulus of PP matrix in the nanocomposites for 30% over a temperature range, indicating an increase in the stiffness of the material with the addition of organically modified clay.     

Effect of clay content on the ultraviolet-curing and physical properties of urethane-acrylate/clay nanocomposites

The effect of clay content on the ultraviolet (UV)-curing behavior and physical properties of a urethane-acrylate/clay nanocomposite system was studied. The UV-curing behavior of the nanocomposite system was investigated by monitoring the change of a characteristic IR absorption peak for acrylate groups. The UV-curing rate and final conversion of the nanocomposite system increased with increasing clay content and affected the physical properties of the nanocomposites. The thermal, mechanical and optical properties of the nanocomposites were affected by clay content. The X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) image showed that the nanocomposites had an intercalated structure. POLYM. COMPOS., 28:325–330, 2007. © 2007 Society of Plastics Engineers     

Polymerization kinetics and thermal properties of dicyanate/clay nanocomposites

The polymerization kinetics and thermal properties of dicyanate/clay nanocomposites were investigated. A type of organically modified clay was used as nanometer‐size fillers for the thermosetting dicyanate resin. Differential scanning calorimetry (DSC) was used to study the curing behavior of the dicyanate/clay nanocomposite systems. The polymerization rate of the nanocomposite systems increased with increasing clay content. An autocatalytic reaction mechanism could adequately describe the polymerization kinetics of the dicyanate/clay nanocomposite systems. The polymerization kinetic parameters were determined by fitting the DSC conversion data to the proposed kinetic equation. The glass‐transition temperature of the dicyanate/clay nanocomposites increased with increasing clay content. The thermal decomposition behavior of the dicyanate/clay nanocomposites was investigated by thermogravimetric analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1955–1960, 2004     

Constitutive modeling of HDPE polymer/clay nanocomposite foams

A constitutive model for tensile behavior of high density polyethylene (HDPE)/clay nanocomposite foams was proposed. The elastic modulus of HDPE/clay nanocomposite was developed using micromechanics theory, and the modulus for foams was obtained by using representative volume element (RVE) concept. In order to describe the tensile behavior of the foams, a constitutive equation obtained from a viscoelastic model was proposed. The constitutive model was expressed in terms of microstructural properties of polymer, and physical properties of the foams. The effects of the material parameters and processing conditions on the foam morphologies and mechanical properties of HDPE/clay nanocomposite foams were investigated. Microcellular closed-cell nanocomposite foams were manufactured with HDPE, where the nanoclay loadings of 0.5, 1.0, and 2.0 wt% were used. The effect of clay loading and foaming conditions on the volume expansion ratio, elastic modulus, tensile strength, and elongation at break was investigated. Except for the elongation at break, the mechanical properties were improved with nanoclay loading. The tensile experimental data of the foams were compared with the prediction by the theoretical model. It was demonstrated that the tensile behaviors of HDPE/clay nanocomposite foams were well described by the constitutive model.     

Unique clay orientation in the injection-molded bar of isotactic polypropylene/clay nanocomposite

In this article, the injection-molded bars of isotactic polypropylene/organoclay nanocomposite with different clay contents have been obtained via dynamic packing injection molding (DPIM). The oriented microstructure including layered nanoparticles and PP lamellae has been inspected through 2D-WAXS analyses along the sample thickness of the molded bars. Depending on the clay content and sample thickness, various oriented clay structures with nanoparticles uniplanar-axially oriented parallel to the surface of molded bar, or partially tumbled around the flow axis of the molded bar, or even a random orientation, could be observed. The observed orientation behavior of nanoparticles could be temporarily elucidated as the results of the sensitive response of layered nanoparticles to shear deformation and the structural recovery of clay network assisted by the electrostatic attraction existing between adjacent nanoplatelets.     

Effect of interfacial attraction on intercalation in polymer/clay nanocomposites

In order to examine the adhesive behavior of a polar polymer between hydrophilic clay layers, the so‐called glue effect, a clay intercalation by an ethylene–vinyl alcohol (EVOH) copolymer, which was capable of strong hydrogen bonding with the silicate surface of clay, was prepared by the melt intercalation technique and compared with a clay nanocomposite containing styrene–acrylonitrile (SAN) copolymer of less polar interaction energy in terms of the morphology and mechanical properties. Although initial penetration of the guest polymer into the gallery of the host clay occurred more rapidly for EVOH because of its strong hydrophilic nature, the dissociation of clay nanoplatelets was better developed for SAN with less polar interaction with clay, well evidencing the fact that the glue effect effectively affects the intercalation behavior of polymer/clay nanocomposites. However, the mechanical properties of the EVOH/clay nanocomposite were superior to those of SAN/clay nanocomposites. Although dissociation of respective silicate layers was poor for EVOH/clay nanocomposites, strong attractive energy stabilizes the interface between inorganic nanoparticles and the polymer matrix much more effectively, resulting in higher mechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2749–2753, 2006     

Improving toughness of ultra-high molecular weight polyethylene with ionic liquid modified carbon nanofiber

Ionic liquids (ILs) with long alkyl substituted groups, including 1-docosanyl-3-methylimidazolium bromide (IL-1) and 1-docosanyl-3-methylimidazolium hexafluorophosphate (IL-2), were synthesized and used to modify the surface of carbon nanofibers (CNF). The nanocomposite film prepared by solution-blending of ionic liquid modified CNF (i-CNF) and ultrahigh molecular weight polyethylene (UHMWPE) displayed better toughness when compared with pure UHMWPE even at very low concentrations (e.g. 0.4 wt%). The effect of ionic liquids on the elongation-to-break ratio of this nanocomposite system was investigated. The ionic liquid with hexafluorophosphate as the anion was more efficient to increase the toughness of UHMWPE due to the improved compatibility of IL with UHMWPE in the polymer matrix than that of the bromide. The rheological behavior of molten nanocomposites revealed that the storage modulus and the complex viscosity decreased with increasing ionic liquid content in the high frequency region. However, a reverse trend was observed when the frequency was less than 0.05 s⁻¹. In-situ monitoring in the change of crystallinity of the nanocomposite during tensile deformation suggested a mechanism of sliding between UHMWPE crystal regions and the surface of carbon nanofibers.     

Intercalated clay structures and amorphous behavior of solution cast and melt pressed poly(ethylene oxide)–clay nanocomposites

The polymer nanocomposite (PNC) films consisted of poly(ethylene oxide) (PEO) and sodium cations montmorillonite (MMT) clay were prepared by aqueous solution casting and direct melt press compounding techniques, whereas the films of PEO with trimethyl octadecyl ammonium cations organo‐modified montmorillonite (OMMT) clay were formed by melt pressed technique. The clay concentrations in the nanocomposites used are 1, 2, 3, 5, 10, and 20 wt % of the PEO weight. The X‐ray diffraction patterns of these nanocomposites were measured in the angular range (2θ) of 3.8–30°. The values of basal spacing d₀₀₁ of MMT/OMMT, clay gallery width W_cg, d‐spacings of PEO crystal reflections d₁₂₀ and d₁₁₂, and their corresponding crystallite size L, and the peaks intensity I (counts) were determined for these nanocomposites. Results reveal that the nanocomposites have intercalated clay structures and the amount of intercalation increases with the increase of clay concentration. As compared to melt pressed PEO–MMT nanocomposites, the amount of clay intercalation is higher in aqueous solution cast nanocomposites. At 20 wt % MMT dispersion in PEO matrix, the solution cast PEO–MMT nanocomposite almost changes into amorphous phase. The melt press compounded PEO–OMMT films show more intercalation as compared to the PEO–MMT nanocomposites prepared by same technique. In melt pressed nanocomposites, the PEO crystalline phase significantly reduces when clay concentration exceeds 3 wt %, which is evidenced by the decrease in relative intensity of PEO principal crystalline peaks. The effect of interactions between the functional group (ethylene oxide) of PEO and layered sheets of clay on both the main crystalline peaks of PEO was separately analyzed using their XRD parameters in relation to structural conformations of these nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39898.     

Wear properties of 3‐aminopropyltriethoxysilane‐functionalized carbon nanotubes reinforced ultra high molecular weight polyethylene nanocomposites

Ultra high molecular weight polyethylene (UHMWPE) is extensively used as a material in various high‐end applications with superior mechanical properties. Carbon nanotubes (CNTs) reinforced UHMWPE (CNT/UHMWPE) nanocomposite is a promising material that can compensate for the weak durability of UHMWPE. In this study, multiwalled carbon nanotubes were oxidized and silanized using acid mixture and 3‐aminopropyltriethoxysilane, respectively, to improve the interfacial strength between CNTs and UHMWPE. The CNT/UHMWPE nanocomposite was fabricated using these oxidized and silanized CNTs. The treatment effect of CNTs on the wear behavior of the CNT/UHMWPE nanocomposites was investigated through wear tests. The oxidization and silanization of CNTs were confirmed by infrared spectroscopy. Scanning electron microscope analysis showed that the silane‐treated CNT/UHMWPE nanocomposites showed better dispersion and interfacial adhesion between UHMWPE and CNTs becaue of the newly formed functional groups on the CNTs. The friction coefficient and wear rate of silanized CNT/UHMWPE nanocomposite were also found to be lower than those of raw UHMWPE and oxidized CNT/UHMWPE nanocomposite. CNTs were functionalized using oxidation and silanization methods to improve the interfacial adhesion between CNTs and UHMWPE. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Structure and properties of UHMWPE fiber/carbon fiber hybrid composites

Ultrahigh molecular weight polyethylene (UHMWPE) fiber/carbon fiber hybrid composites were prepared by inner‐laminar and interlaminar hybrid way. The mechanical properties, dynamic mechanical analysis (DMA), and morphologies of the composites were investigated and compared with each other. The results show that the hybrid way was the major factor to affect mechanical and thermal properties of hybrid composites. The resultant properties of inner‐laminar hybrid composite were better than that of interlaminar hybrid composite. The bending strength, compressive strength, and interlaminar shear strength of hybrid composites increased with an increase in carbon fiber content. The impact strength of inner‐laminar hybrid composite was the largest (423.3 kJ/m²) for the UHMWPE fiber content at 43 wt % to carbon fiber. The results show that the storage modulus (E′), dissipation factor (tan δ), and loss modulus (E″) of the inner‐laminar hybrid composite shift toward high temperature remarkably. The results also indicate that the high‐performance composite with high strength and heat resistance may be prepared by fibers' hybrid. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1880–1884, 2006     

In Situ preparation of resol/clay nanocomposites

In this study, in situ modified phenol formaldehyde resins were prepared from hydroxyl terminated polydimethyl siloxane (DH.PDMS), clay (montmorillonite) in the presence of base catalyst. Different clay contents (0.5, 1, 3, 5 wt %) were used to produce DH.PDMS modified resol/clay nanocomposite resins (DH.PDMS‐LC‐PFRs). DH.PDMS‐LC‐PFRs were partially cured by heat, and the effects of the curing process and the clay content in the resol resin were determined on the spectroscopic, thermal, mechanical and microscopic properties of the final products. Furthermore, the effects of the reaction time on the polymerization and on the morphology of the materials were investigated. The structures of the specimens were characterized by means of Fourier Transform Infrared (FTIR‐ATR) spectroscopy. Thermal properties of the samples were determined with Differential Scanning Calorimeter (DSC) and Thermogravimetric Analyzer (TGA). Mechanical properties of the specimens were determined by Dynamic Mechanical Analyzer (DMA). The obtained samples were also characterized morphologically by Scanning Electron Microscope (SEM). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Reaction kinetics and characteristics of polyurethane/clay nanocomposites

The reaction behavior and physical properties of polyurethane (PU)/clay nanocomposite systems were investigated. Organically modified clay was used as nanofillers to formulate the nanocomposites. Differential scanning calorimetry was used to study the reaction behavior of the PU/clay nanocomposite systems. The reaction rate of the nanocomposite systems increased with increasing clay content. The reaction kinetic parameters of proposed kinetic equations were determined by numerical methods. The glass transition temperatures of the PU/clay nanocomposite systems increased with increasing clay content. The thermal decomposition behavior of the PU/clay nanocomposites was measured by using thermogravimetric analysis. X‐ray diffractometer and transmission electronic microscope data showed the intercalation of PU resin between the silicate layers of the clay in the PU/clay nanocomposites. A universal testing machine was used to investigate the tensile properties of the PU/clay nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1641–1647, 2005     

Functional Copolymer/Organo-MMT Nanoarchitectures: XXVI. Fabrication and Characterization of Electrospun Nanofibers from PCL/ODA-MMT and Copolymer-g-PLA/ Ag-MMT Blends

We synthesized poly(?-caprolactone)/octadecyl amine-montmorillonite clay nanocomposite as a matrix polymer by solution intercalative method and new amphiphilic poly(maleic anhydrde-alt-1-octadecene)-g-poly(L-lactic acid)/Ag⁺-montmorillonite clay nanocomposite as a partner polymer by interlamellar graft copolymerization of lactic acid onto anhydride copolymer in the presence of silver salt of montmorillonite clay as catalyst-nanofiller. Novel polymer nanofibers were fabricated by electrospinning of matrix/partner blends with different volume ratios. The nanocomposites and nanofibers were investigated by Fourier transform infrared spectroscopy, thermal gravimetric analysis–differential scanning calorimetry, and scanning electron microscope–transmission electron microscope methods. The diameters, morphologies, and thermal behavior of fibers were strongly depended on the partner-polymer nanocomposites loadings. The fabricated biocompatible and biodegradable nanofibers can be utilized for biomedical and filtration applications.     

Synthesis and characterization of nylon 1012/clay nanocomposite

A nylon 1012/clay nanocomposite was prepared by melt polycondensation polymerization of diamine and diacid in the presence of organoclay. The nylon 1012 and nanocomposite were characterized by Fourier transform IR spectroscopy with attenuated total reflection, and a shift of the Si? O? Si band toward a lower wavenumber was found as the result of the strong interaction of nylon 1012 with the organoclay. The X‐ray diffraction analysis and transmission electron microscopy observation showed that the clay minerals were exfoliated. Clay platelets increased the crystallization rate but decreased the crystallinity. Differential scanning calorimetry and dynamic mechanical thermal analysis measurements showed that the glass‐transition temperature of the nylon 1012/clay nanocomposite decreased to some degree as compared to nylon 1012 because of the combined effect of confinement and the reduction of the physical crosslink density. The mechanical properties of the nanocomposite such as the tensile strength and tensile modulus are higher than those of nylon 1012, and the water absorption is reduced because of the improvement in the barrier property of the nanocomposite. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2403–2410, 2002     

NR/SBR/organoclay nanocomposites: Effects of molecular interactions upon the clay microstructure and mechano‐dynamic properties

Nanocomposites based on (70/30) blends of natural rubber (NR), styrene‐butadiene rubber (SBR), and organoclay (OC) have been prepared successfully via melt‐mixing process. Effects of the extent of polymers/clay interactions upon the developed microstructure, fatigue life, and dynamic energy loss by the nanocomposites have been investigated. Maleated EPDM (EPDM‐g‐MAH) and epoxidized NR (ENR50) were employed as compatibilizer. Nanocomposites were characterized by means of X‐ray diffractometer (XRD), transmission electron microscope (TEM), scanning electron microscope, atomic force microscopy, root mean square, and dynamic mechanical thermal analysis. EPDM‐g‐MAH showed more potential in enhancing dispersion of the clay nanolayers and their interaction with rubber phases. More potential for separating and dispersing the clay nanoplatelets with better interface enhancement was exhibited by EPDM‐g‐MAH as compatibilizer. This was consistent with higher resistance towards large strain cyclic deformations along with more heat build‐up characteristics showed by EPDM‐g‐MAH based nanocomposites especially at compatibilizer/organoclay ratio of 3. Pronounced non‐terminal behavior within low frequency region was also observed for melt storage modulus of this nanocomposite, indicating higher extent of intercalation/exfoliation microstructure with reinforced interfaces than the nanocomposite generated by ENR50. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Phenolic resin‐crosslinked natural rubber/clay nanocomposites: Influence of clay loading and interfacial adhesion on strain‐induced crystallization behavior

Nanocomposites of natural rubber (NR) and pristine clay (clay) were prepared by latex mixing, then crosslinked with phenolic resin (PhOH). For comparative study, the PhOH‐crosslinked neat NR was also prepared. Influence of clay loading (i.e., 1, 3, 5, and 10 phr) on mechanical properties and structural change of PhOH‐crosslinked NR/clay nanocomposites was studied through X‐ray diffraction (XRD), transmission electron microscopic (TEM), wide‐angle X‐ray diffraction (WAXD), tensile property measurement, and Fourier transform infrared spectroscopy (FTIR). XRD and TEM showed that the clay was partly intercalated and aggregated, and that the dispersion state of clay was non‐uniform at higher clay loading (>5 phr). From tensile test measurement, it was found that the pronounced upturn of tensile stress was observed when the clay loading was increased and a maximum tensile strength of the PhOH‐crosslinked NR/clay nanocomposites was obtained at 5 phr clay. WAXD observations showed that an increased addition of clay induced more orientation and alignment of NR chains, thereby lowering onset strain of strain‐induced crystallization and promoting crystallinity of the NR matrix during tensile deformation. FTIR investigation indicated a strong interfacial adhesion between NR matrix and clay filler through a phenolic resin bridge. This suggested that the PhOH did not only act as curative agent for crosslinking of NR, but it also worked as coupling agent for promoting interfacial reaction between NR and clay. The presence of strong interfacial adhesion was found to play an important role in the crystallization process, leading to promotion of mechanical properties of the PhOH‐crosslinked NR/clay nanocomposites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43214.     

A short review on rubber/clay nanocomposites with emphasis on mechanical properties

The invention of Nylon‐6/clay nanocomposites by the Toyota Research Group of Japan heralded a new chapter in the field of polymer composites. This article highlights the work done in the field of rubber/clay nanocomposites. The preparations of rubber/clay nanocomposites by solution blending, latex compounding, and melt intercalation are covered and a thorough discussion of the mechanical properties of the various rubber/clay nanocomposite systems is presented. Other properties such as barrier, dynamic mechanical behavior, and thermal properties are also discussed. Finally, the future trends in the rubber/clay nanocomposites are mentioned. POLYM. ENG. SCI., 47:1956–1974, 2007. © 2007 Society of Plastics Engineers