Showing papers on "Polymer nanocomposite published in 2009"

New prospects in flame retardant polymer materials: From fundamentals to nanocomposites

Abstract: The objective of this review is to make the field of “flame retardants for polymer materials” more accessible to the materials science community, i.e. chemists, physicists and engineers. We present the fundamentals of polymer combustion theory, the main flame retardant properties and tests used to describe fire behavior, together with the nature and modes of action of the most representative flame retardants and the synergistic effects that can be achieved by combining them. We particularly focus on polymer nanocomposites, i.e. polymer matrices filled with specific, finely dispersed nanofillers, which will undoubtedly pave the way for future materials combining physicochemical and thermo-mechanical performances with enhanced flame retardant behavior.

Anisotropic self-assembly of spherical polymer-grafted nanoparticles

Abstract: It is easy to understand the self-assembly of particles with anisotropic shapes or interactions (for example, cobalt nanoparticles or proteins) into highly extended structures. However, there is no experimentally established strategy for creating a range of anisotropic structures from common spherical nanoparticles. We demonstrate that spherical nanoparticles uniformly grafted with macromolecules ('nanoparticle amphiphiles') robustly self-assemble into a variety of anisotropic superstructures when they are dispersed in the corresponding homopolymer matrix. Theory and simulations suggest that this self-assembly reflects a balance between the energy gain when particle cores approach and the entropy of distorting the grafted polymers. The effectively directional nature of the particle interactions is thus a many-body emergent property. Our experiments demonstrate that this approach to nanoparticle self-assembly enables considerable control for the creation of polymer nanocomposites with enhanced mechanical properties. Grafted nanoparticles are thus versatile building blocks for creating tunable and functional particle superstructures with significant practical applications.

Functionalized Graphenes and Thermoplastic Nanocomposites Based upon Expanded Graphite Oxide

Abstract: Exfoliation of expanded GO represents an attractive route to functionalized graphenes as versatile 2D carbon nanomaterials and components of a wide variety of polymer nanocomposites. Thermally reduced graphite oxides (TrGO) with specific surface areas of 600 to 950 m2 · g−1 were obtained by oxidation of graphite followed by thermal expansion at 600 °C. Thermal post treatment at 700 °C and 1 000 °C increased carbon content (81 to 97 wt.-%) and lowered resistivity (1 600 to 50 Ω · cm). During melt extrusion with PC, iPP, SAN and PA6, exfoliation afforded uniformly dispersed graphenes with aspect ratio > 200. In comparison to conventional 0D and 1D carbon nanoparticles, TrGO afforded nanocomposites with improved stiffness and lower percolation threshold. Recent progress and new strategies in development of functionalized graphenes and graphene-based nanocomposites are highlighted.

Electrorheology of polymers and nanocomposites

Abstract: This highlight aims to report electrorheological (ER) materials in state-of-the art polymeric particles and their various nanocomposites with clay, mesoporous inorganics and carbon nanotubes along with their potential application. ER fluids, suspensions of these particles having higher dielectric constant or electrical conductivity than the low-viscosity fluids in which they are suspended, are currently regarded as a smart/intelligent material, because their structural and rheological properties can be systematically tuned by controlling electric field strengths. In this highlight, various conducting polymers, including polyaniline, polypyrrole, poly(p-phenylene), poly(naphthalene quinone) and copolyaniline, are introduced and different types of polymer nanocomposites are emphasized. Flow curves for shear stress of the ER fluids are also examined.

Fundamental aspects and recent progress on wear/scratch damage in polymer nanocomposites

Abstract: It is realized that the addition of a small percentage of rigid nanoparticles to polymers significantly improves many of their mechanical properties, especially stiffness and strength. Such improvements are often attributed to the availability of large numbers of nanoparticles with huge interfacial areas compared to their macro- and micro-scale counterparts. In particular, from the tribological viewpoint, the small size of nanoparticles with homogenous dispersion in the matrix and good interfacial adhesion between nanoparticles and matrix are thought to be necessary requirements for a polymer nanocomposite. Material removal will be less since the nano-additives have similar sizes to the segments of surrounding polymer chains. Despite these positive effects due to the addition of nanoparticles, there are still some critical questions that are unanswered. Here, we review the fundamentals, recent progress and advances that have been made on the tribological aspects of polymer nanocomposites, particularly focusing on their wear (in dry sliding and unlubricated conditions) and scratch damage. The review shows that (a) it is not valid to assume that nano-fillers always improve wear/scratch (and friction) properties; and (b) material properties like modulus, hardness, fracture toughness or extent of wear rate or scratch penetration depth are not the sole indicators to compare and/or rank candidate materials. Several facets of wear/scratching or material response to the sliding processes require thorough understanding in order to determine parameters that control the surface integrity and material removal from polymer nanocomposites. This review also shows the apparent contradictions and false impressions on several material systems in many studies owing to poor characterizations of polymer nanocomposites and lack of quantitative descriptions of the observed phenomena.

Well-Dispersed Fractal Aggregates as Filler in Polymer−Silica Nanocomposites: Long-Range Effects in Rheology

Abstract: We are presenting a new method of processing polystyrene−silica nanocomposites, which results in a very well-defined dispersion of small primary aggregates (assembly of 15 nanoparticles of 10 nm diameter) in the matrix. The process is based on the use of a high boiling point solvent, in which the nanoparticles are well dispersed, and a controlled evaporation procedure. The filler’s fine network structure is determined over a wide range of sizes, using a combination of small-angle neutron scattering (SANS) and transmission electronic microscopy (TEM) experiments. The mechanical response of the nanocomposite material has been investigated for both small (ARES oscillatory shear and dynamical mechanical analysis) and large deformations (uniaxial traction) as a function of the concentration of the particles in the matrix. Our findings show that with a simple tuning parameter, the silica filler volume fraction, we can investigate in the same way the structure−property correlations related to the two main reinfo...

Graphite Oxide Flame-Retardant Polymer Nanocomposites

Abstract: Graphite oxide (GO) polymer nanocomposites were developed at 1, 5, and 10 wt % GO with polycarbonate (PC), acrylonitrile butadiene styrene, and high-impact polystyrene for the purpose of evaluating the flammability reduction and material properties of the resulting systems. The overall morphology and dispersion of GO within the polymer nanocomposites were studied by scanning electron microscopy and optical microscopy; GO was found to be well-dispersed throughout the matrix without the formation of large aggregates. Mechanical testing was performed using dynamic mechanical analysis to measure the storage modulus, which increased for all polymer systems with increased GO loading. Microscale oxygen consumption calorimetry revealed that the addition of GO reduced the total heat release and peak heat release rates in all systems, and GO−PC composites demonstrated very fast self-extinguishing times in vertical open flame tests, which are important to some regulatory fire safety applications.

Morphological and physical properties of a thermoplastic polyurethane reinforced with functionalized graphene sheet

Abstract: BACKGROUND: Functionalized graphene sheet (FGS) was recently introduced as a new nano-sized conductive filler, but little work has yet examined the possibility of using FGS as a nanofiller in the preparation of polymer nanocomposites. In particular, there are currently no published papers that evaluate polyurethane/FGS nanocomposites. The purpose of this study was to prepare a polyurethane/FGS nanocomposite and examine the morphological and physical properties of the material. RESULTS: A cast nanocomposite film was prepared from a mixture of thermoplastic polyurethane (TPU) solution and FGS suspended in methyl ethyl ketone. The FGS dispersed on the nanoscale throughout the TPU matrix and effectively enhanced the conductivity. A nanocomposite containing 2 parts of FGS per 100 parts of TPU had an electrical conductivity of 10−4 S cm−1, a 107 times increase over that of pristine TPU. The dynamic mechanical properties showed that the FGS efficiently reinforced the TPU matrix, particularly in the temperature region above the soft segment melt. CONCLUSION: Our results show that FGS has a high affinity for TPU, and it could therefore be used effectively in the preparation of TPU/FGS nanocomposites without any further chemical surface treatment. This indicates that FGS is an effective and convenient new material that could be used for the modification of polyurethane. It could also be used in place of other nano-sized conductive fillers, such as carbon nanotubes. Copyright © 2009 Society of Chemical Industry

Ferroelectric polymer/silver nanocomposites with high dielectric constant and high thermal conductivity

Abstract: Ferroelectric polymer nanocomposites with silver (Ag) nanoparticles as inclusions were prepared and the dielectric properties and thermal conductivity were studied. The results showed that the nanocomposites have high dielectric constant and high thermal conductivity. When the loading level of Ag nanoparticles is 20.0 vol %, the dielectric constant and thermal conductivity of the nanocomposites were 120 at 103 Hz and 6.5 W/mK, respectively. Our results also showed that there is no percolation in the nanocomposites when Ag loading range is within 20.0%.

Developments of polyhedral oligomeric silsesquioxanes (POSS), POSSnanocomposites and their applications: A review

Abstract: This review presents a brief account of recent developments in synthesis and properties of organic-inorganic hybrids using polyhedral oligomeric silsesquioxanes (POSS) nanoparticIe, and applications of POSS monomers and nanocomposites. Therma], rheology and mechanical properties of polyimides, epoxy polymers, polymethymethacrylate, polyurethanes, and various other polymer nanocomposites are discussed.

A Micromechanics Model for the Electrical Conductivity of Nanotube-Polymer Nanocomposites

Abstract: The introduction of carbon nanotubes (CNTs) into nonconducting polymers has been observed to yield orders of magnitude increases in conductivity at very low concentrations of CNTs. These low percolation concentrations have been attributed to both the formation of conductive networks of CNTs within the polymer and to a nanoscale effect associated with the ability of electrons to transfer from one CNT to another known as electron hopping. In the present work, a micromechanics model is developed to assess the impact of the effects of electron hopping and the formation of conductive networks on the electrical conductivity of CNT-polymer nanocomposites. The micromechanics model uses the composite cylinders model as a nanoscale representative volume element where the effects of electron hopping are introduced in the form of a continuum interphase layer, resulting in a distinct percolation concentration associated with electron hopping. Changes in the aspect ratio of the nanoscale representative volume element are used to reflect the changes in nanocomposite conductivity associated with the formation of conductive networks due to the formation of nanotube bundles. The model results are compared with experimental data in the literature for both single- and multi-walled CNT nanocomposites where it is observed that the model developed is able to qualitatively explain the relative impact of electron hopping and nanotube bundling on the nanocomposite conductivity and percolation concentrations.

Polymer Nanocomposites Handbook

Abstract: Overview of Challenges and Opportunities, RK Gupta, EB Kennel, and K-J Kim History of Carbon Nanomaterials, A Oberlin and GG Tibbetts The Incorporation of Nanomaterials into Polymer Media, HC Ashton Mixing Terminology, Nanoparticle Dispersion and Reinforcement by Surface Modification with Additives, K-J Kim and JL White Surface Modification of Carbon Nanofibers, ML Lake, DG Glasgow, GG Tibbetts, and DJ Burton Compounding Layered Silicate Nanocomposites, P Andersen Dispersion of Agglomerated Nanoparticles in Rubber Processing, K-J Kim and JL White The Rheology of Polymeric Nanocomposites, S Bhattacharya, RK Gupta, and S Bhattacharya Fundamentals of Carbon-Based Nanocomposites, EV Barrera, E Corral, M Shofner, and D Simeon Polymer Nanocomposites Containing Vapor-Grown Carbon Fibers Aligned by Magnetic or Electric Field Processing, T Takahashi and K Yonetake Utility of Carbonaceous Nanofillers in Elastomers and Thermoplastic Elastomeric Gels, JK Kim, M Pagalicawan, and V Sridhar Nanocomposites of Liquid Crystalline Polymers Dispersed in Polyester Matrices, CH Song and AI Isayev Transmission Electron Microscopy and Related Techniques in the Structure Characterization of Polymer Nanocomposites, VK Berry Mechanical Properties of Clay-Containing Polymeric Nanocomposites, LA Utracki Appendices, Mass Transport through Polymer Nanocomposites, D De Kee and KJ Frederic Flammability Properties of Polymer Nanocomposites, J Zhu and CA Wilkie Electrical Properties of Nanoparticle-Filled Polymers, EB Kennel Thermal Conductivity of Polymer Nanocomposites, S Agarwal and RK Gupta Bio-Based Nanocomposites from Functionalized Plant Oils, C-K Hong, J Lu, and RP Wool

Fabrication and characterization of iron oxide nanoparticles filled polypyrrole nanocomposites

Abstract: 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.

Study of Glass Transition and Reinforcement Mechanism in Polymer/Layered Silicate Nanocomposites

Abstract: The structure−property relationship of polymer/layered silicate nanocomposites was investigated in this study. Polymer nanocomposites based on completely amorphous poly(hexamethylene isophthalamide) with exfoliated, intercalated, or agglomerated nanoclay morphology were produced and analyzed by X-ray diffraction and transmission electron microscopy. Differential scanning calorimetry measurements were used to characterize the glass-transition behavior. Dynamic mechanical analysis was performed to investigate the nature of the constrained region as the reinforcement mechanism. The modulus enhancement of the organoclay nanocomposites was found to have good linear correlation with the volume of the constrained region. The type of polymer−nanofiller interaction strongly influences the amount and modulus of the constrained region, and both of the latter contribute to the enhancement in the storage modulus of the polymer nanocomposite. The mechanical properties of the constrained region are temperature-dependent...

Electrochemically controlled swelling and mechanical properties of a polymer nanocomposite.

Abstract: We present the layer-by-layer assembly of an electroactive polymer nanocomposite thin film containing cationic linear poly(ethyleneimine) (LPEI) and 68 vol % anionic Prussian Blue (PB) nanoparticles, which allow for electrochemical control over film thickness and mechanical properties. Electrochemical reduction of the PB doubles the negative charge on the particles, causing an influx of water and ions from solution to maintain electroneutrality in the film; concomitant swelling and increased elastic compliance of the film result. Reversible swelling upon reduction is on the order of 2−10%, as measured via spectroscopic ellipsometry and electrochemical atomic force microscopy. Reversible changes in the Young’s elastic modulus of the hydrated composite film upon reduction are on the order of 50% (from 3.40 to 1.75 GPa) as measured with in situ nanoindentation, and a qualitative increase in viscous contributions to energy dissipation upon redox is indicated by electrochemical quartz crystal microbalance. Ele...