Structure and Mechanical Properties of Melt Intercalated Po1lypropylene–Organomontmorillonite Nanocomposites

The preparation and properties of polymer nanocomposites, obtained by melt-compounding of polypropylene (PP) and organomontmorillonite (OMMT) modified by different alkyl ammonium salts, are described. A copolymer of maleic anhydride and PP was used as a compatibilizing additive. Nanocomposites with OMMT content of 1, 5 and 10 wt% were prepared and tested. The influence of OMMT content on the tensile stress–strain curves, elastic modulus, yield and tensile strength, and ultimate elongation of the nanocomposites is determined. The results of measuring the microhardness and impact strength of polymer nanocomposites are presented. Long-term creep tests were performed to predict the long-term deformation behavior of nanocomposites. The crystallinity of nanocomposites was analyzed by means of differential scanning calorimetry and optical microscopy, while the structural features were studied by X-ray diffraction and scanning electron microscopy methods.     

Valence band and core level X-ray photoelectron spectroscopy of lead sulfide nanoparticle-polymer composites

Valence band and core level X-ray photoelectron spectroscopy (XPS) were used to probe lead sulfide (PbS) nanoparticle-polymer nanocomposites. Composite materials were prepared by trapping commercially available monodisperse 3 and 10 nm PbS nanoparticles in two polymers, the non-conducting polymer, polystyrene, and the conjugated polymer, poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene (referred to below as MEH-PPV). The nanocomposites prepared from commercial nanoparticles underwent oxidation, mainly to form lead sulfate. However, the narrow size distributions of the commercial nanoparticles allowed observation of distinct changes in the valence band from the 3 to 10 nm nanoparticles. Nanocomposites of 2-5 and 4-7 nm PbS nanoparticles were synthesized by growing the particles in poly(vinyl alcohol) (referred to below as PVA) and MEH-PPV, respectively. These composites both indicated the formation of lead sulfide nanoparticles. Furthermore, the XP spectra for the PVA/PbS composite displayed bonding between the PbS nanoparticles and the polymer while MEH-PPV showed no PbS-polymer bonding. The nanoparticles synthesized in MEH-PPV did not undergo oxidation. The particle size distributions of the synthesized nanoparticles were too broad to display size-dependent changes in the valence band.     

Nanocomposites based on polymethylmethacrylate and silica

Nanocomposites based on polymethylmethacrylate and silica were synthesized by means of bulk polymerization. The morphology of the obtained polymer composites was studied by scanning electron microscopy. It was established that silica influences the mechanical and tribological properties of nanocomposites.     

Molecular dynamics of poly(ethylene terephthalate)/poly(phenylene sulfide) nanocomposites with barium titanate

The relaxation processes and the properties of polymer/ceramic nanocomposites have been studied by the ¹H nuclear magnetic resonance methods. Nanocomposites of poly(ethylene terephthalate) PET and poly(phenylene sulfide) PPS with 0.25, 2.5 and 5% wt. barium titanate BT were prepared using a twin screw extruder and injection moulding machine. The spin-lattice relaxation time T₁, second moment M₂ and the motional parameters as e.g. the activation energies in the nanocomposites were investigated.     

Photoluminescent zinc oxide polymer nanocomposites fabricated using picosecond laser ablation in an organic solvent

Nanocomposites made of ZnO nanoparticles dispersed in thermoplastic polyurethane were synthesized using picosecond laser ablation of zinc in a polymer-doped solution of tetrahydrofuran. The pre-added polymer stabilizes the ZnO nanoparticles in situ during laser ablation by forming a polymer shell around the nanoparticles. This close-contact polymer shell has a layer thickness up to 30 nm. Analysis of ZnO polyurethane nanocomposites using optical spectroscopy, high resolution transmission electron microscopy and X-ray diffraction revealed that oxidized and crystalline ZnO nanoparticles were produced. Those nanocomposites showed a green photoluminescence emission centred at 538 nm after excitation at 350 nm, which should be attributed to oxygen defects generated during the laser formation mechanism of the monocrystalline nanoparticles. Further, the influence of pulse energy and polymer concentration on the production rate, laser fluence and energy-specific mass productivity was investigated.     

Influence of Surfactant Functional Groups on Morphology and Rheology of Polypropylene/Organoclay Nanocomposites

Three surfactants, with the same long alkyl tail but varying in functional groups, were selected to modify two pristine clays with different cation exchange capacities (CEC). Each of the modified clays was melt-mixed with polypropylene (PP) to prepare nanocomposites. The microstructure of the resultant nanocomposites was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and rheological techniques. The results showed that the surfactant structure had remarkable effects on the morphology and shear rheology of the nanocomposites based on the high-CEC organoclay: use of benzyl functional groups led to the highest extent of intercalation and highest enhancement of shear properties, while use of 2-hydroxyethyl groups had the opposite effect. Nanocomposites based on low-CEC organoclay all exhibited poor dispersion and their shear behavior was changed only slightly in comparison to the polymer matrix. In the case of extensional rheology, strain hardening was observed only in the two nanocomposites containing surfactants with 2-hydroxyethyl groups, regardless of the dispersion state of the nanoparticles.     

Electrical properties of nanocomposites subjected to deformation

The electrophysical properties of a new type of nanocomposites are considered. In these materials, the metallic granules are distributed in a rubberlike matrix. Nanocomposites exhibit either metallic or hopping conduction, depending on the bulk concentration of the metallic granules. The effect of pressure (for hydrostatic compression and for uniaxial deformation) upon the resistance of such composites is studied in both conduction regimes. The practically important extremely strong dependence of their resistance upon pressure in the hopping conduction regime is a consequence of the exponentially strong dependence of the probability of intergranule electron tunneling on the distance between the granules.     

Optical properties of conjugated polymer-ZnSe nanocrystal nanocomposites

Nanocomposites of poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene]-zinc selenide (MOPPV-ZnSe) are synthesized by mixing the polymerization of 1,4-bis (chloromethyl)-2-methoxy-5-octoxy-benzene in the presence of ZnSe quantum dots. The resulting MOPPV-ZnSe nanocomposites possess a well-defined interfacial contact, thus significantly promoting the dispersion of ZnSe within the MOPPV matrix and facilitating the electronic interaction between these two components. Raman and UV--visible absorption spectra are influenced by the incorporation of ZnSe nanocrystals. High-resolution transmission electron microscopic and tapping-mode atomic force microscopic results show clearly the evidence for phase-segregated networks of ZnSe nanocrystals, which provide a large area of interface for charge separation to occur. Steady-state spectra of MOPPV-ZnSe nanocomposites are markedly quenched by the introduction of intimate polymer/ZnSe junctions. Time-resolved photoluminescence measurements show that the lifetime decays quickly, which further confirms the occurrence of charge transfer in MOPPV-ZnSe nanocomposites.     

Resonant infrared laser deposition of polymer-nanocomposite materials for optoelectronic applications

Polymers find a number of potentially useful applications in optoelectronic devices. These include both active layers, such as light-emitting polymers and hole-transport layers, and passive layers, such as polymer barrier coatings and light-management films. This paper reports the experimental results for polymer films deposited by resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) and resonant infrared pulsed laser deposition (RIR-PLD) for commercial optoelectronic device applications. In particular, light-management films, such as anti-reflection coatings, require refractive-index engineering of a material. However, refractive indices of polymers fall within a relatively narrow range, leading to major efforts to develop both low- and high-refractive-index polymers. Polymer nanocomposites can expand the range of refractive indices by incorporating low- or high-refractive-index nanoscale materials. RIR-MAPLE is an excellent technique for depositing polymer-nanocomposite films in multilayer structures, which are essential to light-management coatings. In this paper, we report our efforts to engineer the refractive index of a barrier polymer by combining RIR-MAPLE of nanomaterials (for example, high refractive-index TiO₂ nanoparticles) and RIR-PLD of host polymer. In addition, we report on the properties of organic and polymer films deposited by RIR-MAPLE and/or RIR-PLD, such as Alq₃ [tris(8-hydroxyquinoline) aluminum] and PEDOT:PSS [poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)]. Finally, the challenges and potential for commercializing RIR-MAPLE/PLD, such as industrial scale-up issues, are discussed.     

Study on Steady Shear,Morphology and Mechanical Behavior of Nanocomposites based on Polyamide 6

Nanocomposites of two different grades of polyamide 6 (PA6) with organically modified nanoclay were prepared via melt compounding in a twin‐screw extruder. The rheological behavior, morphology and mechanical properties of the nanocomposites were studied using a capillary rheometer, x‐ray diffraction (XRD), tapping‐mode atomic force microscopy (AFM), and tensile and flexural tests. XRD patterns indicate that the organically modified layered silicate was well dispersed in the PA6 matrix. From the AFM images the surface roughness of PA6 slightly increases with addition of organoclay. The rheological studies showed that the prepared nanocomposites have shear thinning behavior, obeying the power law equation. Addition of organoclay increases the shear stress and shear viscosity. At high rate of shear deformation the viscosity of nanocomposites are comparable to those of the pure polyamides. The activation energy of flow decreases with increasing nanoclay content. For most of the prepared nanocomposites the activation energy values increase with increasing shear rate. The tensile strength and flexural modulus and strength of the nanocomposites increase with increase of nanoclay content, but the extension at yield decreases with increasing clay loading.     

Synthesis,characterization, conductivity and sensor application study of polypyrrole/silver doped nickel oxide nanocomposites

Conducting polymer composites of polypyrrole (PPy) and silver doped nickel oxide (Ag-NiO) nanocomposites were synthesised by in situ polymerisation of pyrrole with different contents of Ag-NiO nanoparticles. The formation of nanocomposites were studied by Fourier transform infrared (FTIR) and UV–vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and AC and DC conductivity measurements. The sensitivity of ammonia gas through the nanocomposite was analysed with respect to different contents of nanoparticles. Spectroscopic studies showed the shift in the absorption bands of polymer nanocomposite than that of pure PPy indicating the strong interaction between the nanoparticles and polymer chain. FESEM revealed the uniform dispersion of nanoparticles with spherically shaped metal oxide particles in PPy matrix. The XRD pattern indicated a decrease in amorphous domain of PPy with increase in loading of nanoparticles. The higher thermal stability and glass transition temperature of polymer nanocomposites than that of pure PPy were revealed from the TGA and DSC respectively. The dielectric properties, DC and AC conductivity of nanocomposites were much higher than PPy and these electrical properties increases with the loading of nanoparticles. The nanocomposites showed an enhancement in sensitivity towards ammonia gas detection than PPy.     

Fabrication and Physical Characterization of Biodegradable Poly(butylene succinate)/Carbon Nanofiber Nanocomposite Foams

Nanocomposites of biodegradable poly(butylene succinate) (PBS) and carbon nanofibers (CNFs) were prepared by three different methods, that is, solution blending, melt compounding, and solution and subsequent melt blending (SOAM) method, among which the SOAM method, where nano-scale fillers and polymer matrix are solution-blended and subsequently melt-mixed in a torque rheometer, is a two-step process for obtaining polymer nanocomposite. Dispersion of CNFs in the PBS matrix was characterized by FE-SEM, while thermal and mechanical properties were analyzed by thermogravimetric ananlysis (TGA) and universal test machine (UTM), respectively. The PBS/CNF nanocomposites were then converted to foams by employing a chemical blowing agent (CBA) in the melt. The presence of CNFs increased the melt viscosity of PBS so that the PBS/CNF nanocomposite foams were produced without modifying the chemical structure of the PBS. Nanocomposite foams prepared by the SOAM method showed higher physical properties compared with those prepared by the solution blending and the melt mixing. Cell size and blowing ratio increased with the increase in the CBA content, blowing temperature and time. Cell morphology of the nanocomposite foams was examined by optical microscopy, and the cell size distribution was also investigated.     

Synthesis and characterization of PMMA/silylated MMTs

Commercially available Sodium clay (Dellite HPS) and organo-clay (Dellite 72T) are modified via a silylation reaction. These silylated clays are characterized by IR, XRD, thermogravimetric analyses, and their equilibrium contact angles are measured. They are used to prepare nanocomposites at different loading percentage (1, 3, 5% wt) by in situ intercalative polymerization of Methyl methacrylate and morphology and thermal properties of nanocomposites are examined. SEM images of nanocomposites fractured surface show the absence of clays aggregates, confirming a good dispersion and distribution of montmorillonites in the polymer matrix. The effects of modified clays on the thermal properties of nanocomposites are analyzed by differential scanning calorimetry and thermogravimetric analyses showing an increase of glass and decomposition temperatures of all nanocomposites respect to homopolymer ones. The best results are obtained in the presence of silylated montmorillonites, clearly the organosilane improves the compatibility between polymer matrix and clay and as effect the properties of nanocomposites.     

Nanoclay and Cu Nanoparticles Loaded Polyethylene Nanocomposites for Natural Gas Transfer Applications

High density polyethylene nanocomposites loaded with a reinforcing filler (Cloisite 20A as a modified nanoclay) and an electrically conductive filler (Cu nanoparticles) were prepared by a melt blending method. The morphological, mechanical, thermal, and electrical properties of the prepared nanocomposites were investigated to evaluate their performances as appropriate materials for production of reinforced conductive polymeric pipes to be used in natural gas distribution and transportation pipelines. A random and uniform dispersion of both nanoparticles in the polyethylene matrix, with a nanoclay intercalated morphology, was observed by scanning electron microscopy and X-ray diffraction techniques. The results revealed ca. 117, 13 and 21% increases in the Young’s modulus, tensile strength and yield stress of the polyethylene matrix by adding 3 wt.% of Cloisite 20A into it. For the similar conditions, however, more than a 71% decrease was observed for the elongation at break. Thermal analysis demonstrated that the melting points of the nanocomposites were increased by incorporating both fillers and the crystallinity of polyethylene chains was decreased by incorporating Cloisite 20A and then slightly increased by adding Cu nanoparticles. Moreover, the results revealed the creation of conductivity inside the non-conductive polyethylene matrix due to the presence of the conductive Cu nanoparticles.     

Ionic transport studies in hyperbranched polyurethane/clay nanocomposite gel polymer electrolytes

In the present work, we report a novel nanocomposite gel electrolytes based on intercalation of hyperbranched polyurethane (HBPU) into organically modified montmorillonite for application in Li-ion batteries. The nanocomposites have been prepared by solution intercalation technique with varying clay loading. The formation of partially exfoliated nanocomposites has been confirmed by X-ray diffraction. Nanocomposites were soaked with 1 M LiCO₄ in 1:1 (v/v) solution of propylene carbonate and diethyl carbonate to get the required gel electrolytes. AC impedance analysis shows that ionic conductivity increases with the increase of clay loading and attains the highest value of 8.3?×?10^?3 S/cm for 5 wt.% clay concentration. Surface morphology of the nanocomposite electrolytes has been examined by SEM analysis. Improvement of electrochemical properties, viz., electrochemical potential window and interfacial stability, is also observed in the clay-loaded HBPU samples.     

Material characterization of a nanocrystal based photovoltaic device

Nanocomposites have shown promise as the active layer for photovoltaic energy conversion. One example is the CdSe nanocrystal \polymer composite demonstrated by Hyunh and Greenham [#!Ref1!#,#!Ref2!#]. In this paper we investigate the baseline properties of the materials used in such a device. We present surface chemical information for CdSe nanocrystals and chemical analysis for poly-(3-hexylthiophene) (P3HT) polymer. Received 30 November 2000     

Fabrication and characterization of iron oxide nanoparticles filled polypyrrole nanocomposites

The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated. In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis (TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication.     

Steady Shear Rheological Behavior,Mechanical Properties,and Morphology of the Polypropylene/Carbon Nanotube Nanocomposites

Nanocomposites based on polypropylene (PP) and multiwall carbon nanotubes (MWNT) have been prepared through melt blending. Scanning electron microscopy (SEM) observations indicate that nanotubes were dispersed almost homogeneously throughout the matrix; however, some aggregates were also observed at high nanotubes loading. Rheological studies showed that at low shear rates, there is an increase in steady shear viscosity and shear stress of samples with increasing of nanotubes concentration. However, at high shear rates nanocomposites behave like pure PP. The activation energy of flow showed an increasing trend and has a maximum at 1wt% MWNT content. It was found that incorporation of nanotubes causes a remarkable decrease in surface and volume resistivity values of the polymeric matrix. The presence of CNTs improved the tensile and flexural properties of the polymeric matrix.     

Structure and Mechanical Properties of 50/50 NR/SBR Blend/Pristine Clay Nanocomposites

A blend/clay nanocomposites of 50/50 (wt%) NR/SBR was prepared via mixing the latex of a 50/50 NR/SBR blend with an aqueous clay dispersion and co‐coagulating the mixture. The structure of the nanocomposite was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Nanocomposites containing less than 10 phr clay showed a fully exfoliated structure. After increasing the clay content to 10 phr, both nonexfoliated (stacked layers) and exfoliated structures were observed in the nanocomposites. The results of mechanical tests showed that the nanocomposites presented better mechanical properties than clay‐free NR/SBR blend vulcanizate. Furthermore, tensile strength, tensile strain at break, and hardness (shore A) increased with increasing clay content, up to 6 phr, and then remained almost constant.     

Conductive plastics: comparing alternative nanotechnologies by performance and life cycle release probability

Nanocomposites can be considered safe during their life cycle as long as the nanofillers remain embedded in the matrix. Therefore, a possible release of nanofillers has to be assessed before commercialization. This report addresses possible life cycle release scenarios for carbon nanotubes (CNT), graphene, and carbon black (CB) from a thermoplastic polyurethane (TPU) matrix. The content of each nanofiller was adjusted to achieve the same conductivity level. The nanofillers reduced the rate of nanoscale releases during mechanical processing with decreasing release in the order neat TPU, TPU-CNT, TPU-graphene, and TPU-CB. Released fragments were dominated by the polymer matrix with embedded or surface-protruding nanofillers. During electron microscopy analysis, free CB was observed, however, there was no free CNT or graphene. Quantitatively, the presence of free nanofillers remained below the detection limit of <0.01% of generated dust. Further, both the production process and type of mechanical processing showed a significant impact with higher release rates for injection-molded compared to extruded and sanded compared to drilled materials. Due to its optimal performance for further development, extruded TPU-CNT was investigated in a combined, stepwise worst case scenario (mechanical processing after weathering). After weathering by simulated sunlight and rain, CNT were visible at the surface of the nanocomposite; after additional sanding, fragments showed protruding CNT, but free CNT were not detected. In summary, this preliminary exposure assessment showed no indication that recommended occupational exposure limits for carbonaceous nanomaterials can be exceeded during the life cycle of the specific TPU nanocomposites and conditions investigated in this study.