Low‐temperature sintering and enhanced piezoelectric properties of random and textured PIN–PMN–PT ceramics with Li2CO3

Low‐temperature sintered random and textured 36PIN–30PMN–34PT piezoelectric ceramics were successfully synthesized at a temperature as low as 950°C using Li₂CO₃ as sintering aids. The effects of Li₂CO₃ addition on microstructure, dielectric, ferroelectric, and piezoelectric properties in 36PIN–30PMN–34PT ternary system were systematically investigated. The results showed that the grain size of the specimens increased with the addition of sintering aids. The optimum properties for the random samples were obtained at 0.5 wt% Li₂CO₃ addition, with piezoelectric constant d₃₃ of 450 pC/N, planar electromechanical coupling coefficient k_p of 49%, peak permittivity ε_max of 25 612, remanent polarization P_r of 36.3 μC/cm². Moreover, the low‐temperature‐sintered textured samples at 0.5 wt% Li₂CO₃ addition exhibited a higher piezoelectric constant d₃₃ of 560 pC/N. These results indicated that the low‐temperature‐sintered 36PIN–30PMN–34PT piezoelectric ceramics were very promising candidates for the multilayer piezoelectric applications.     

Preparation and properties of acrylonitrile–butadiene rubber–graphene nanocomposites

The graphene oxide (GO) was prepared by sonication‐induced exfoliation from graphite oxide, which was produced by oxidation from graphite flakes with a modified Hummer's method. The GO was then treated by hydrazine to obtain reduced graphene oxide (rGO). On the basis of the characterization results, the GO was successfully reduced to rGO. Acrylonitrile–butadiene rubber (NBR)–GO and NBR–rGO composites were prepared via a solution‐mixing method, and their various physical properties were investigated. The NBR–rGO nanocomposite demonstrated a higher curing efficiency and a change in torque compared to the gum and NBR–GO compounds. This agreed well with the crosslinking density measured by swelling. The results manifested in the high hardness (Shore A) and high tensile modulus of the NBR–rGO compounds. For instance, the tensile modulus at a 0.1‐phr rGO loading greatly increased above 83, 114, and 116% at strain levels of 50, 100, and 200%, respectively, compared to the 0.1‐phr GO loaded sample. The observed enhancement was highly attributed to a homogeneous dispersion of rGO within the NBR matrix; this was confirmed by scanning electron microscopy and transmission electron microscopy analysis. However, in view of the high ultimate tensile strength, the NBR–GO compounds exhibited an advantage; this was presumably due to strong hydrogen bonding or polar–polar interactions between the NBR and GO sheets. This interfacial interaction between GO and NBR was supported by the marginal increase in the glass‐transition temperatures of the NBR compounds containing fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42457.     

Processing–morphology–property relationships of polypropylene–graphene nanoplatelets nanocomposites

Polypropylene (PP) nanocomposites reinforced with graphene nanoplatelets (GNPs) were prepared via melt extrusion. A special sheet die containing with two shunt plates was designed. The relationships among the flow field of the special die, exfoliation, and dispersion morphology of the GNPs in PP and the macroscopic properties of the nanocomposites were analyzed. Flow field simulation results show that the die with shunt plates provided a high shear stress, high pressure, and high velocity. The differential scanning calorimetry, X‐ray scattering, and electron microscopy results reveal that the nanocomposites prepared by the die with the shunt plates had higher crystallinity values and higher exfoliation degrees of GNPs. The orientation of the GNPs parallel with the extrusion direction was also observed. The nanocomposites prepared by the die with shunt plates showed a higher electrical volume conductivity, thermal conductivity, and tensile properties. This indicated that the high shear stress exfoliated the GNPs effectively to a thinner layer and then enhanced the electrical, thermal, and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44486.     

Crystallization of polycaprolactone–clay nanocomposites

The isothermal crystallization process of polycaprolactone/clay nanocomposites was studied at several temperatures. The effects of the clay type (modified and unmodified) and clay content were analyzed. Bulk crystallization was studied with differential scanning calorimetry and modeled with Avrami's equation. The reinforcement phase lowered the time at which the first crystal nucleus appeared (i.e., the induction time) and fastened the global crystallization rate in comparison with that of neat polycaprolactone. The spherulitic growth was analyzed by optical microscopy with polarized light. The presence of the clay produced more and bigger spherulites in the same time and with the same undercooling degree. All these properties were strongly dependent on the polycaprolactone/clay compatibility and hence the dispersion degree achieved in the nanocomposites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

The photoinduced charge transfer mechanism in aligned and unaligned carbon nanotubes

Using time-resolved reflectivity measurements on unaligned and aligned bundled single-wall carbon nanotubes with a pump energy of 1.55 eV, quasi-resonant with the second Van Hove singularity of semiconducting tubes, a positive sign of the transient reflectivity is detected in unaligned nanotubes. In contrast a negative sign is detected in aligned nanotubes. This discovery addresses a long-standing question showing that in unaligned nanotubes the stronger intertube interactions favor the formation of short-lived free charge carriers in semiconducting tubes. A detailed analysis of the transient reflectivity spectral response shows that the free carriers in the photo-excited state of semiconducting tubes move towards metallic tubes in about 400 fs.     

Synthesis and characterization of polyaniline–organoclay nanocomposites

Polyaniline (PANI)–organoclay nanocomposites were prepared. Intercalation of aniline monomer into montmorillonite (MMT) modified by polyoxyalkylene was followed by subsequent oxidative polymerization of the aniline in the interlayer spacing. The organoclay was prepared by cation exchange process between sodium cation in MMT and onium ion in four different types of polyoxyalkylene diamine and triamine with different molecular weight. Infrared spectra confirm the electrostatic interaction between the positively charged onium group (NH₃⁺) and the negatively charged surface of MMT. X‐ray diffraction analysis provides a structural information. The absence of d₀₀₁ diffraction band in the nanocomposites was observed at certain types and contents of organoclay. Scanning electron microscopy and transmission electron microscopy were employed to determine the dispersion of the clay into PANI. The thermal degradation behavior of PANI in the nanocomposites has been investigated by thermogravimetric analysis. The weight loss suggests that the PANI chains in the nanocomposites are more thermally stable than pristine PANI. This improvement is attributed to the presence of nanolayers with high aspect ratio acting as barriers, thus shielding the diffusion of degraded PANI from the nanocomposites. The electrical conductivity of the nanocomposites was increased 30 times more than that of pure MMT at a certain concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of polyurethane–organoclay nanocomposites

Nanocomposite polyurethane (PU)–organoclay materials have been synthesized via in‐situ polymerization. The organoclay is first prepared by intercalation of tyramine into montmorillonite (MMT)‐clay through ion exchange process. The syntheses of polyurethane–organoclay hybrid films containing different ratios of clay were carried out by swelling the organoclay into diol and diamine followed by addition of diisocyanate and then cured. The nanocomposites with dispersed and exfoliated structure of MMT were obtained as evidenced by X‐ray diffraction and scanning electron microscope. X‐ray diffraction showed that there is no peak corresponding to d₀₀₁ spacing in organoclay with the ratios up to 20 wt%. SEM images confirmed the dispersion of nanometer silicate layers in the polyurethane matrix. Also, it was found that the presence of organoclay leads to improvement in the mechanical properties. The tensile strength was increased with increasing the organoclay contents to 20 wt% by 221% in comparision to the PU with 0% organoclay. POLYM. COMPOS. 28:108–115, 2007. © 2007 Society of Plastics Engineers     

Structure and properties of polyurethane–silica nanocomposites

Nanocomposites with different concentrations of nanofiller were prepared by adding nanosilica filler to the single‐phase polyurethane matrix. A control series was prepared with the same concentrations of micron‐size silica. The nanosilica filler was amorphous, giving composites with the polyurethane that were transparent at all concentrations. The nanocomposites displayed higher strength and elongation at break but lower density, modulus, and hardness than the corresponding micron‐size silica‐filled polyurethanes. Although the nanosilica showed a stronger interaction with the matrix, there were no dramatic differences in the dielectric behavior between the two series of composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 133–151, 2000     

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     

Synthesis and exfoliation of bismaleimide–organoclay nanocomposites

Bismaleimide-clay nanocomposites were synthesized by swelling two kinds of organophilic clays (OCLs) in allyl-compound modified bismaleimide (BMI) resins and subsequent thermal curing and characterized by DSC, Wide-angle X-ray diffraction (WAXD), Field emission SEM, TEM and Rheometer. The results indicated that the synthesis of modified BMI-clay nanocomposites was determined by the factors including the preparation methodology, curing conditions, and nature of OCLs. Exfoliation of clay can be promoted by homogeniser and ultrasonication. Allyl-compound played a key role for the exfoliation of OCLs in modified BMI matrix as the pre-intercalation agent. It seems that the exfoliation should be carried out before gelation in order to obtain fully exfoliated structure in modified BMI matrix. The good combination of compatibility and acceleration effect on the intragallery polymerization are the favorable conditions to obtain exfoliated nanocomposites based on modified BMI matrix. The exfoliated structure favored the improvement in impact strength.     

Preparation and properties of polylactide–silica nanocomposites

Poly(lactic acid) (PLA)/SiO₂ nanocomposites were prepared via melt mixing with a Haake mixing method. To improve the dispersion of nanoparticles and endow compatibility between the polymer matrix and nanosilica, SiO₂ was surface‐modified with oleic acid (OA). The interfacial adhesion of the PLA nanocomposites was characterized by field‐emission scanning electron microscopy. The storage modulus and glass‐transition temperature values of the prepared nanocomposites were measured by dynamic mechanical thermal analysis. The linear and nonlinear dynamic rheological properties of the PLA nanocomposites were measured with a parallel‐plate rheometer. The effects of the filling content on the dispersability of the OA–SiO₂ nanoparticles in the PLA matrix, the interface adhesion, the thermomechanical properties, the rheological properties, and the mechanical properties were investigated. Moreover, the proper representation of the oscillatory viscometry results provided an alternative sensitive method to detect whether aggregation formed in the polymeric nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and properties of ethylene–propylene–diene rubber/organomontmorillonite nanocomposites

Ethylene–propylene–diene rubber (EPDM)/organomontmorillonite (OMMT) nanocomposites were prepared with a maleic anhydride grafted EPDM oligomer as a compatibilizer via melt intercalation. X‐ray diffraction and transmission electron microscopy indicated that the silicate layers of OMMT were exfoliated and dispersed uniformly as a few monolayers in nanocomposites. The change in the crystallization behavior of the nanocomposites was examined. The nanocomposites exhibited great improvements in the tensile strength and tensile modulus. The incorporation of OMMT gave rise to a considerable reduction of tan δ and an increase in the storage modulus. Moreover, the solvent resistance of the nanocomposites increased remarkably. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 440–445, 2004     

Fire behaviour of polyester–clay nanocomposites

The aim of this study was on the one hand, to compare the fire behaviour of polyester/clay nanocomposites with that of the neat polymers added with the conventional flame retardant melamine isocyanurate (MIC) and on the other hand, to study the effect of the flame retardant added to the nanocomposites. Polyester/clay nanocomposites were prepared by using polybutylene terephthalate (PBT) and a co‐polyester elastomer as polymeric matrices and a commercial organoclay as filler. As verified by X‐ray diffractometry (XRD) and transmission electron microscopy (TEM) intercalated structures were obtained by mixing the molten polymer with the layered silicate in a corotating twin screw extruder. The fire behaviour of these materials was investigated by means of an oxygen consumption calorimetry (Cone Calorimeter). Peak heat release rate of 3‐mm thick samples measured at 50 kW/m² external heat flux was reduced by a factor of 2–3 by the addition of organically modified montmorillonite to the polymers. The further addition of MIC did not give a significant improvement in the behaviour of the materials. Copyright © 2005 John Wiley & Sons, Ltd.     

Formation and structure of polyacrylamide–silica nanocomposites by sol–gel process

The formation of nanocomposites by the sol–gel reaction of tetraethoxysilane (TEOS) in polyacrylamide (PAAm) is studied. The nanocomposites are prepared in aqueous solution. Fourier transform IR spectroscopy shows that substantial hydrogen bonding occurs in the nanocomposites. The fracture surfaces of the nanocomposites are observed by atomic force microscopy (AFM) as a function of the TEOS content. The AFM images reveal that the PAAm–silica nanocomposite exhibits particle–matrix morphology. It is also found that aggregate formation is more dominant than the particle growth with the TEOS contents. The solution of composite precursor is also applied to spin coating. Furthermore, during the calcination there is an observable change in the silica networks, and then a microinterconnected structure is generated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1817–1823, 2002     

Photooxidative behavior of polystyrene–montmorillonite nanocomposites

The weathering behavior of polystyrene and polystyrene–montmorillonite composites containing 2.5, 5.0, and 7.5 wt% of montmorillonite (MMT) was investigated. Samples were exposed to UV radiation for periods of up to ～12 weeks and their molecular weight, chemical changes, and mechanical properties were monitored as a function of time. The addition of MMT was shown to improve the photostability of all composites investigated, probably because of a screen effect against UV radiation and barrier effect against diffusion of oxygen promoted by the silicate layers of MMT. Scanning electron microscopy of fracture surfaces of degraded samples showed that there is a degraded layer near the surface that provided a recovery of tensile strength of the samples. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Rheology and curing characteristics of epoxy–clay nanocomposites

Diglycidyl ethers of bisphenol‐A (DGEBA) epoxy resin, filled separately with organoclay (OC) and unmodified clay (UC), were synthesized at room temperature and at high temperature (80 °C) by mechanical shear mixing. The room temperature curing (RTC) and high temperature curing (HTC) were carried out with the addition of triethylene tetramine (TETA) and diaminodiphenylmethane (DDM) curing agents respectively. The OC used was alkyl ammonium modified montmorillonite (MMT) and the UC was Na⁺‐MMT. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) were used to study the structure and morphology of the nanocomposites. The influence of OC and UC particles on rheology and curing characteristics was studied. The rate of increase in viscosity was higher for OC‐filled resin than that of the UC‐filled resin. The curing study showed that the amine ions of the OC aided the polymerization process and favoured the curing at low temperature over the curing of unfilled epoxy resin. The tensile properties were enhanced for epoxy filled with OC particles rather than those filled with UC particles. Copyright © 2005 Society of Chemical Industry     

Preparation and thermal analysis of cotton–clay nanocomposites

Nanocomposites were produced from cotton with montmorillonite clay used as the nanofiller material. Three exfoliation and intercalation methods with different solvents and clay pretreatment techniques were tested for the production of these organic–inorganic hybrids. The method that resulted in superior clay–cotton nanocomposites used a clay pretreatment with 4‐methylmorpholine‐N‐oxide as the cotton solvent. The nanocomposites showed significant improvements in the thermal properties in comparison with unbleached cotton and cotton processed under the conditions for nanocomposite preparation. The degradation temperature of the nanocomposites increased by 45°C, and the char yields for some compositions were twice those of unbleached cotton. The crystalline melt of the materials decreased by 15°C. Future research will include the development of textiles based on these cotton–clay materials and testing for flame‐retardant properties and product strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2125–2131, 2004     

Preparation and characterisation of polyamide–polyimide organoclay nanocomposites

BACKGROUND: Ternary nanocomposites containing an organomodified layered silicate polyimide additive within a polyamide matrix have been investigated to gain greater insight into structure–property relationships and potential high‐temperature automotive applications. RESULTS: Polyamide nanocomposite blends, containing 3 wt% of organoclay, were prepared and compared with organoclay‐reinforced polyamide and neat polyamide. Nanoclay addition significantly increased heat distortion temperature, as well as both the tensile and flexural moduli and strength. The addition of polyimide demonstrated further increases in heat distortion temperature, glass transition temperature and the flexural and tensile moduli by about 17, 21 and 40%, respectively. The tensile and flexural strengths were either unaffected or decreased modestly, although the strain‐to‐failure decreased substantially. Morphological studies using transmission electron microscopy (TEM) and X‐ray diffraction showed that the nanoclay was dispersed within the ternary blends forming highly intercalated nanocomposites, regardless of the presence and level of polyimide. However, TEM revealed clay agglomeration at the polyamide–polyimide interface which degraded the mechanical properties. CONCLUSIONS: A range of improvements in mechanical properties have been achieved through the addition of a polyimide additive to a polyamide nanocomposite. The decrease in ductility, arising from the poor polyamide–polyimide interface and nanoclay clustering, clearly requires improving for this deficiency to be overcome. Copyright © 2008 Society of Chemical Industry     

Mechanical properties and structures of dicyanate–clay nanocomposites

Dicyanate–clay nanocomposites comprising a dicyanate resin and a type of organically modified clay were prepared and characterized, and their thermomechanical properties were investigated. The organically modified clay had silicate layers of nanometer size intercalated with an organic modifier, which improved the compatibility between the clay and organic materials, such as dicyanate resins. Dynamic mechanical analysis was performed to investigate the thermomechanical properties of the dicyanate–clay nanocomposites containing various amounts of the clay. The storage modulus of the nanocomposites below their glass‐transition temperatures slightly increased with increasing clay content. The glass‐transition temperature of the dicyanate–clay nanocomposites increased with increasing clay content. The nanostructures of the dicyanate–clay nanocomposites were characterized by transmission electron microscopy and X‐ray diffraction analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2629–2633, 2003     

Synthesis and characterization of polymer–nanoclay conductive nanocomposites

Polymer–clay nanocomposites based on poly(3,4‐ethylenedioxythiophene)/polystyrene sulfonate (PEDOT) : PSS and nanoclay montmorillonite were synthesized and characterized. The doping of PEDOT with polystyrene sulfonate made it water dispersible (PEDOT–PSS). Sodium dodecyl benzene sulfonate (SDBS) and ionic liquid were used to increase the interlayer spacing and the conductivity of the nanocomposites, respectively. The nanocomposite was characterized by various techniques, such as X‐ray diffraction (XRD), TEM, surface resistivity, and thermogravimetric measurement analysis. Interlayer spacing increased as a result of the addition of SDBS, and this was confirmed by the 2θ shift observed via XRD analysis. The surface morphology of the conductive coated clay was examined by TEM analysis. Good electrical surface conductivity, interlayer spacing, and polymer coating were observed for the material prepared using the surfactant and conductive ionic liquid. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010