Effect of nano-fillers on conductivity of polyethylene/low melting point metal alloy composites

A novel method for preparing conductive polyethylene(PE) composites has been developed. In the method, the powder of low melting point metal alloy(LMPA) is filled into the PE matrix by using twin screw extruder at a temperature below the melting point of the LMPA, and followed by a die drawing process at a temperature around the melting point of the metal alloy. It has been found that die drawing process, repeating the die drawing process and adding nano-fillers, such as montmorillonite(MMT) and multi-wall carbon nanotubes(MWCNTs), all help reduce the metal particle size in the PE matrix, thus improve the conductivity of the composite. The conductivity improvement is attributed to an increased number of the smaller metal particles. Therefore, conductive composites of polymer/metal alloy/nano-filler with high conductivity are possible to be prepared by using the new method.     

The complexes of macromolecules and metal nanoparticles: pseudo-template synthesis and behavior

Metal sols composed of metal nanoparticles (1 - 10 nm in diameter) protected with polymer molecules may be regarded as dispersions of polymer-metal complexes formed due to cooperative non-covalent (e.g., hydrophobic, coulombic) interaction of polymer chains with the surface of metal nanoparticles. The sols are commonly prepared by reducing of metal ions in solutions of appropriate polymers. The interactions between macromolecules and nanoparticles are reversible. In the case of long polymer chains and minute particles, the equilibrium constant of the reaction exponentially depends on the surface area of the particle. The probability of mutual “recognition” (complex formation) of growing particle and a macromolecule rapidly increases from practically zero to practically unity in narrow interval of the particle's diameters. The recognition is followed with the shadowing of the particles and the stop of their growths. Such kind of processes was termed “pseudo-template”. In frame of the concept of pseudo-template processes can be estimated: (1) the conditions at which sol particles of desirable size can be prepared, (2) the influence of temperature, polymer concentration, nanoparticles size, and other conditions on the stability of polymer - particle complex having been prepared, and (3) the conditions at which stable sol does not exist and can not be prepared at all. The interactions between metal nanoparticles and macromolecules are highly selective regard to the structure of polymer chains. The property can be effectively used for the control the size characteristics of metal nanoparticles (in course of their formation) and the stability of metal sols. The selectivity provides high conversions in catalytic chemical modification reactions in which a macromolecule is the substrate and a component of the catalyst in the same time. As an example, the hydrolysis of lactame groups in monomer unites of poly(N-vinyl pyrrolidone) catalyzed with copper sols is discussed.     

Preparation and Optical Properties of New Metal/Macromolecule Architectures

Polymer nanocomposite films with unusual and anisotropic optical properties were obtained by the controlled in-situ generation of noble metal nanoparticles (NPs). Poly(vinyl alcohol) (PVA) and poly(ethylene-co-vinylalcohol) (EVAl) nanocomposites containing gold and silver NPs were efficiently produced by a photo-reduction or thermal process both operating directly in the solid state and resulted efficiently stabilized by the presence of polymer hydroxyl groups, which prevent particles agglomeration. Uniaxial drawing of the NPs/polymer composites promoted anisotropic packing of the embedded particles along the stretching direction of the film, resulting in a shift of the surface plasmon resonance well above 40 nm and thus producing a well-defined polarization-dependent colour change. Such nanostructured materials when are obtained in the form of thin films can be applied to several fields, from sensor to photonics (i.e., macromolecular strain sensor, linear absorbing polarizer).     

Metal particle adsorption and diffusion in a model polymer/metal composite system

We have developed a model polymer/metal composite system based on the adsorption of colloidal gold particles from a dilute aqueous suspension to the surface of poly(2-vinylpyr-idine) (PVP). Particle coverages and tracer diffusion coefficients for the particles within a PVP matrix phase were measured by Rutherford backscattering spectrometry. The adsorption process is quantitatively described by a diffusion-limited mechanism where gold particles irreversibly adsorb to the surface of the polymer film. Model dispersions produced in this way are excellent model systems for studying the fundamental properties of metal particle dispersions, since the particle size and the areal density of particles on the surface are well-controlled. Diffusion coefficients for the gold particles within PVP were also measured. The diffusion of the gold particles was found to be coupled to the bulk viscosity of the polymer, even though the size of the gold particles was only slightly larger than the mesh size of the entanglement network for PVP. © 1995 John Wiley & Sons, Inc.     

Catalytic and Optical Behavior of Polymer Embedded Metal Nanoparticles

Very small metal aggregates (nanoaggregates) embedded in an inert polymer matrix, which simply stabilizes the nanodispersion, show unique catalytic and optical behaviour. Indeed Ru-nanoparticles in vinyl-aromatic polymers or polyphosphazenes display an enhanced reactivity for hydrogenation of different groups, such as aromatic rings, keto and nitro groups, oximes and nitriles which are converted into the corresponding saturated derivatives under mild conditions. The optical properties of terthiophenethiol-coated gold nanoparticles in UHMWPE (concentration lower than 4 wt.%) are characterized by poor dichroism due to their centrosymmetric structure. High dichroism (R = 30 at 400 nm, DR = 30) is on the contrary recorded for the terthiophene band showing the chromophores to be sensitive to mechanical orientation also when complexed with gold. On the other hand, nanocomposites based on polymers containing vinyl alcohol units and dispersed gold nanoparticles with average diameter ranging from 3 to 20 nm have been efficiently prepared by an UV photo-reduction process. Uniaxial drawing of the irradiated Au/polymer nanocomposites favours the anisotropic distribution of packed assemblies of gold particles, providing oriented films with polarization-dependent tunable optical properties.     

高分散性SiO_2/PMMA复合材料的制备与表征——稀释分散性

以高无机含量SiO2/聚甲基丙烯酸甲酯(PMMA)接枝复合材料为预分散母料,与PMMA树脂进行熔融共混,制得低无机含量的SiO2/PMMA复合材料.通过切片透射电镜(TEM)观察熔融共混过程中预分散母料内堆积SiO2粒子分散状态的演化.发现预分散母料接枝状态对其影响最为显著,不经接枝修饰的SiO2粒子经熔融共混后,不可避免地会在熔体中产生大量亚微米级的立体团聚体;复杂接枝预分散母料内构成以SiO2粒子为交联点的立体交联结构,其中的堆积SiO2粒子不能在剪切场中得到有效解离和释放;只有在使用简单接枝预分散母料时,基体高分子链才能不断地渗透扩散进入预分散母料内,而预分散母料可被不断地溶胀和撕裂,因而其中的堆积SiO2才可不断地向基体相迁移和扩散,并最终在整个复合材料内实现初级粒子形式的高度均匀稳定分散.     

碳纳米管改性聚苯硫醚熔纺纤维的结构与性能研究

将多壁碳纳米管(MWCNTs)和聚苯硫醚(PPS)经过熔融挤出后制备成复合材料切片,并采用熔融纺丝法制得碳纳米管改性聚苯硫醚复合纤维.采用扫描电镜(SEM)、拉曼光谱、示差扫描量热分析(DSC)、动态机械分析(DMA)以及力学性能测试等表征手段研究了复合纤维中碳管的分散状态,与基体的界面作用,复合纤维的结晶性能以及力学性能,从而探讨了聚苯硫醚/碳纳米管复合纤维体系的微观结构与宏观性能之间的关系.研究表明,聚苯硫醚分子结构与碳纳米管之间具有的π-π共轭作用使碳管较为均匀的分散在基体中,界面结合较为紧密.同时熔融纺丝过程中的拉伸作用使碳管进一步解缠并使碳管沿纤维拉伸方向取向.另一方面,拉曼光谱显示拉伸作用有效地增强了界面作用,有利于外界应力的传递.碳管的良好分散以及强的界面作用使复合纤维力学性能得到大幅度的提高,当碳管含量达到5 wt%时,复合纤维的模量有了明显的提高,拉伸强度较纯PPS纤维提高了近220%.     

Study on aluminium-based single films

In the present paper the authors studied isolated metallic films made from the same material used for making metallic foams, and then characterised their properties. Metal films were made from a liquid aluminium alloy reinforced with ceramic particles of known concentration. Melts without such particles were also investigated. It is shown that stable films could not be made from Al-Si alloy having no particles, and just extremely thin and fragile films could be made from commercially-pure Al. In contrast, aluminium alloys containing particles such as SiC and TiB(2) allowed pulling thin, stable films, which did not rupture. Significant thinning of films was observed when the particle concentration in the melt decreased. By in situ X-ray monitoring of liquid films during pulling, film thickness and drainage effects within the liquid film could be studied. The morphology and microstructure of films was characterised after solidification. Our work shows that the question of how foams are stabilised can be studied using a simplified system such as a film, instead of having to deal with the multitude of different structural elements present in a foam.     

基体分子运动对聚偏氟乙烯/碳纤维复合材料的聚合物基正温度系数性能的影响

聚合物基正温度系数(PTC)材料中,基体分子在熔体状态下的运动能力可显著影响填料分布、PTC强度及稳定重复性等,明确其机理有利于高灵敏性且稳定可重复的PTC复合材料的设计与制备.通过探究基体熔体黏度不同的聚偏氟乙烯(PVDF)/碳纤维(CF)的电阻-温度响应行为,可以发现复合材料PTC转变温度区间仅取决于基体化学结构与结晶性,而PTC循环稳定性却受到基体分子运动能力的显著影响.当基体分子运动能力较强时,分子链极易黏附填料在CF表面形成包覆层,导致局部填料间距增大到隧穿距离以上,不利于复合材料导电网络的重建,导致随热循环次数增加,复合材料的室温电阻率有所升高,PTC可重复性略微降低.而对基体分子链缠结明显的PVDF/CF复合材料中,运动能力较弱的分子链不会包覆CF粒子,在多次升温-降温循环后导电通路能恢复到初始状态,复合材料呈现良好的PTC可重复性,将其应用于电路过热保护装置时,复合材料表现出灵敏的温度响应特性及可多次循环的开关特性.     

Decomposition of isopropanol: A sensitive probe reaction to reveal the influence of zeolite on the catalytic function of supported Pt

A Si-Al-Y Zeolite matrix was used as base support for Cu, Co and Cd catalysts. The matrix was prepared by an inorganic-based sol-gel method. Metal incorporation into the matrix is a function of the metal loading and the metal itself. Incorporation follows the order Co>Cu≫Cd.     

Influence of the morphology of barium sulfate nanofibers and nanospheres on the physical properties of polyurethane nanocomposites

Barium sulfate spherical agglomerates and fibers in the nanometric size range were used to prepare polyurethane (PU) nanocomposites (with 1 wt.% concentration) via melt extrusion. A detailed analysis on the effect of the morphology of the barium sulfate phase upon the mechanical, rheological and optical properties was carried out. Results show that the inclusion of the dispersed phase (with various morphologies and sizes) in the polymer matrix does not decrease the polymer mechanical properties, as is observed when particles in the micrometric size range are included. Rheological studies show that the nanocomposite containing spherical particles presents a slightly higher shear viscosity than that of the polymer matrix, in contrast to the nano-fibers viscosity which presents lower values. This is reflected in the effect of the particle morphology on the processability of the material; in contrast, the morphology has no effect on the radio-opacity of the samples. The structure and dispersion of the particles were analyzed using scanning and transmission electron microscopy. The sample with 1 wt.% nanofibers presents better processability than the system with spherical agglomerates maintaining the X-ray opacity properties.     

Nanocomposites of polymers and metals or semiconductors: Historical background and optical properties

Upon transmission of visible light through composites comprising of a transparent polymer matrix with embedded particles, the intensity loss by scattering is substantially reduced for particle diameters below 50–100 nm (nanoparticles, nanosized particles). As a consequence, related materials (nanocomposites) have found particular interest in optical studies. The first part of this article deals with a historical survey on nanoparticles and nanocomposites and the importance of small particle sizes on their optical properties. The second part focuses on results from our laboratory concerning nanocomposites with extremely high or low refractive indices and dichroic nanocomposites and their application in bicolored liquid crystal displays (LCD). The inorganic colloids required for these studies (lead sulfide, iron sulfides, gold, and silver) were prepared in situ in presence of a polymer or isolated as redispersable metal colloids modified at the surface with a self‐assembled monolayer (SAM) of an alkanethiol. The nanocomposites themselves were finally obtained by coprecipitation, spin coating, solvent casting or melt extrusion, with poly(ethylene oxide), gelatin, poly(vinyl alcohol) and polyethylene as matrix polymers.     

Pre-fibrillation of pulps to manufacture cellulose nanofiber-reinforced high-density polyethylene using the dry pulp direct kneading method

The dry pulp direct kneading method is an industrially viable, low-energy process for manufacturing cellulose nanofiber (CNF)-reinforced polymer composites, where the chemically modified pulps are nanofibrillated and uniformly dispersed in the polymer matrix during melt compounding. In the present study, cellulose fibers of various sizes ranging from surface-fibrillated pulps (20 μm in width) to fine CNFs (20 nm in width) were prepared from softwood bleached kraft pulps using a refiner and a high-pressure homogenizer. These cellulose fibers were modified with alkenyl succinic anhydride and dried. The dried fibers were used as a feed material for melt compounding in the dry pulp direct kneading method to fabricate CNF-reinforced high-density polyethylene (HDPE). When surface-fibrillated pulps were employed as a feed material, the pulps were nanofibrillated and dispersed uniformly in the HDPE matrix during melt compounding. The resulting composites had much better properties—i.e., much higher tensile modulus and strength values, and much lower coefficient of thermal expansion values—than the composites produced using pulps without pre-fibrillation. However, when CNFs were used as a feed material, they were shortened and agglomerated during melt compounding, and the properties of the composites consequently deteriorated. The study concludes that surface-fibrillated pulp, which can be produced cost-effectively using a refiner on an industrial scale, is more suitable as a feed material than CNFs for melt compounding in the dry pulp direct kneading method. This finding enables the elimination of a preliminary step in the preparation of CNFs from pulps, which is a time-consuming and energy-intensive process.

Graphical abstract

     

Use of supercritical CO2‐aided and conventional melt extrusion for enhancing the dissolution rate of an active pharmaceutical ingredient

Dispersing at the molecular level a drug in a polymer matrix is a major challenge to be addressed by the pharmaceutical industry to enhance its bioavailability or to control its release. Melt extrusion and supercritical CO₂‐aided melt extrusion of solid pharmaceutical formulations were performed to enhance the dissolution rate of carvedilol, taken as a model of poorly soluble drug. The presence of the drug improved the processability of the polyacrylate matrix (Eudragit E) through its plasticizing effect. The supercritical method was found gentle compared with melt extrusion owing to the shorter residence time and lower processing temperature and melt viscosity. No traces of decomposition of the drug could be detected after the supercritical extrusion process based on capillary electrophoresis results. This extrusion process resulted in effective homogenization of the components and amorphization of the drug according to Raman mapping, Fourier transform infrared spectrometry, X‐ray diffraction, and polarized light microscopy. The kinetics of dissolution can be dramatically improved. Copyright © 2011 John Wiley & Sons, Ltd.     

Environmentally sensitive silver nanoparticles of controlled size synthesized with PNIPAM as a nucleating and capping agent

Metal nanoparticles combined with environmentally sensitive polymers can lead to enhanced nanometer-sized switches. We present a silver nanoparticle synthesis method that uses poly(N-isopropylacrylamide) (PNIPAM) as the nucleating, capping, and stabilizing agent. The synthesis is performed at room temperature by sodium borohydride-mediated reduction of silver nitrate in the presence of a fully hydrated polymer. The resulting metal nanoparticles have a narrow size distribution comparable to or better than those achieved with other synthesis methods. The silver particles can be thermally precipitated by the collapse of the PNIPAM shell and resolubilized with fast response times, as shown by surface plasmon spectroscopy. The silver-PNIPAM composite allows for combined surface plasmon and thermal switching applications.     

A facile approach to obtaining PVDF/graphene fibers and the effect of nanoadditive on the structure and properties of nanocomposites

The key factors in the design of nanocomposites include obtaining a good adhesion between components and homogeneous dispersion of the nanoadditive in the polymer matrix. Direct mixing of graphene with polymers which are then processed by melt compounding method results in strong tendency of nanoadditive to agglomerate. The article presents a new approach to obtaining poly(vinylidene fluoride)/graphene (PVDF/rGO) nanocomposites in the form of fibers. This method is characterized by the use of graphene oxide (GO) dispersed in the plasticizer instead of graphene. The combination of the fibers forming process with simultaneous reduction of GO to rGO allowed the authors to obtain nanocomposites with graphene homogeneously dispersed in the polymer matrix. Moreover, addition of graphene resulted in formation of β-phase in the nanocomposites, which is characteristic for PVDF and responsible for pyroelectric and piezoelectric properties of this polymer.     

Transformation of methane to synthesis gas over metal oxides without using catalyst

This article reviews a new developing method in the field of metal oxide reduction in chemical and metallurgical processes, which uses methane as a reducing agent. Commonly, coal is used as the reducing agent in the reduction of metal oxide and other inorganic materials; Metal producing factories are among the most intensive and concentrated source of greenhouse gases and other pollutants such as heavy metals, sulfur dioxide and fly ash. Thermodynamically, methane has a great reducing capability and can be activated to produce synthesis gas over a metal oxide as an oxygen donor. Metal oxide reduction and methane activation, two concurrent thermochemical processes, can be combined as an efficient and energy-saving process; nowadays this kind of technologies is of great importance. This new reduction process could improve energy efficiencies and significantly decrease greenhouse gas emission compared to the conventional process; furthermore, the produced gases are synthesis gas that is more valuable than methane. In this paper, thermodynamic studies and advantages of this promising method were discussed. The major aim of this article is to introduce methane as a best and environmentally friendly reducing agent at low temperature.     

Controllable porous polymer particles generated by electrospraying

In this paper, an electrospraying technique was applied to prepare polycaprolactone (PCL) polymer particles with a different microstructure. The PCL particles can be controlled to have a porous microstructure by tailoring the evaporation of solvents during the electrospraying process. The effect of various concentrations on the morphology and microstructure of PCL particles was investigated. The experiment has demonstrated the versatile capability of the electrohydrodynamic atomization process for preparing polymer PCL porous particles and fibers. The thermally induced and evaporation-induced phase separations are proposed as the main mechanisms for the porous microstructure formation. The results demonstrate that the electrospraying method is a simple, innovative and cost-effective method for preparing polymer particles with controllable microstructures.     

Forces between nanorods with end-adsorbed chains in a homopolymer melt

Adsorbed or grafted polymers are often used to provide steric stabilization of colloidal particles. When the particle size approaches the nanoscale, the curvature of the particles becomes relevant. To investigate this effect for the case of cylindrical symmetry, I use a classical fluids density functional theory applied to a coarse-grained model to study the polymer-mediated interactions between two nanorods. The rods are coated with end-adsorbing chains and immersed in a polymer melt of chemically identical, nonadsorbing chains. The force between the nanorods is found to be nonmonotonic, with an attractive well when the two brushes come into contact with each other, followed by a steep repulsion at shorter distances. The attraction is due to the entropic phenomenon of autophobic dewetting, in which there is a surface tension between the brush and the matrix chains. These results are similar to previous results for planar and spherical polymer brushes in melts of the same polymer. The depth of the attractive well increases with matrix chain molecular weight and with the surface coverage. The attraction is very weak when the matrix chain molecular weight is similar to or smaller than the brush molecular weight, but for longer matrix chains the magnitude of the attraction can become large enough to cause aggregation of the nanorods.     

相变过程对等规聚丙烯/炭黑复合材料中填料网络的影响

采用柔和混合方法制备出炭黑(CB)填充等规聚丙烯(iPP)复合材料,CB在iPP熔体中可以进行团聚而形成填料网络,采用动态流变-电阻同步测试的方法,研究原位结晶-熔融过程对所形成网络的影响.实验结果表明,经历原位结晶-熔融后复合材料中可以被动态流变实验检测到的填料网络消失,这是由于结晶和熔融过程中都会影响填料网络结构,而熔融过程中网络的破坏更为显著.相变后网络的重建过程说明,相变过程不能完全破坏熔体中形成的团聚结构,填料网络容易重新形成.