Influence of thermally induced,dehydroxylated nanoclay on polymer nanocomposites

This work reports a novel approach towards a chemical-free treatment of nanoclay through extensive thermal exposure. Dehydroxylation at high temperature was utilized to enhance the influence of nanoclay on the properties of polymer. The effect of this treatment of nanoclay, on the polymer properties, with reference to Polypropylene (PP) has been investigated. The FTIR spectra revealed the successful removal of water from the intergallery spacing of the nanoclay. The maintained structural configuration of the clay was confirmed using WAXD pattern. The uniform dispersion and exfoliation of thermally treated clay layers inside the polymer matrix was confirmed through enhanced mechanical properties. Improved crystallization properties, thermal stability and flame retardant characteristic were also noticed in the nanocomposites reinforced with thermally dehydroxylated clay. This study revealed that the dehydroxylation approach of modification of nanoclay may provide much enhanced properties of polymer, without involvement of any chemical for modification.     

Network model for the viscoelastic behavior of polymer nanocomposites

A theoretical network model reproducing some significant features of the viscoelastic behavior of unentangled polymer melts reinforced with well dispersed non-agglomerated nanoparticles is presented. Nanocomposites with low filler volume fraction (∼10%) and strong polymer-filler interactions are considered. The model is calibrated based on results obtained from discrete simulations of the equilibrium molecular structure of the material. This analysis provides the statistics of the network of chains connecting fillers, of dangling strands having one end adsorbed onto fillers, and that of the population of loops surrounding each nanoparticle. The network kinetics depends on the attachment-detachment dynamics of grafted chains of various types and is modeled by using a set of convection equations for the probability distribution functions. The overall viscoelastic response depends strongly on the lifetime of the polymer-filler junctions. The largest reinforcement is observed at low strain rates and low frequency oscillations. A solid like behavior is predicted for systems in which the polymer molecules interact strongly with the nanoparticles, effect which is associated with the behavior of the network of bridging segments.     

Thermal behavior of thermoplastic polymer nanocomposites containing graphene nanoplatelets

Polypropylene (PP), acrylonitrile butadiene styrene (ABS), and thermoplastic polyurethane (TPU) nanocomposites filled with 5 wt % of two different kinds of commercially available graphene nanoplatelets (GNPs) were prepared. Composites materials were characterized in terms of thermal properties (thermal conductivity and thermal stability) in order to study the effect of different fillers within different thermoplastic matrices. The exfoliation process and the mechanical properties were also investigated. We chose three different thermoplastic polymers (polyolefin, copolymer and elastomer) to cover a wide range of thermoplastic materials and identify a guideline in the use of GNPs for nanocomposite materials. No drastic differences were observed in terms of mechanical properties when the same matrices were filled with different GNPs. Concerning thermal conductivity, it was observed that the GNPs plane dimensions play a crucial role in the increase of conductive properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44814.     

Influence of polymer solubilization on latex behavior

The effect of solubilization of latex polymers was investigated in various anionic surfactant solutions. The process of solubilization was studied by measuring the increase in light transmission and viscosity of the latexes. It was found that anionic surfactants differ widely in their ability to solubilize a given polymer, and susceptibility to solubilization is significantly affected by comonomer content of the polymer. If, for example, a poly(vinyl acetate) latex is stabilized exclusivdly by a strongly solubilizing sodium dodecyl benzene sulfonate, it is less stable and hydrolyzes faster than a similar latex made with a polyoxyethylene derivative, which has only a slight solubilizing action. Dibutyl mateate copolymers of vinyl acetate are less susceptible to solubilization than hompolymers of vinyl acetate.     

Anomalous first normal stress difference behavior of polymer nanocomposites and liquid crystalline polymer composites

The first normal stress difference (N₁) behavior of polymer nanocomposites and liquid crystalline polymer (LCP) composites is a measure of elasticity and is affected by shear stress as a result of morphological alterations at the molecular and nanostructure levels. In this study, the steady shear rheological behaviors of polylactide (PLA) and nanographite platelet (NGP) bionanocomposites containing 1, 2, 3, and 5 wt% nanofiller were investigated. The shear rheological properties of glass fiber‐filled LCPs (filler aspect ratio > 100) were also examined. One of the objectives of this study was to obtain a correlation between N₁, filler contents, and shear stress/rate of the measurements. The results suggest that N₁ in PLA/NGP bionanocomposites is dependent on the level of filler loading as well as the shear rate beyond a critical value. For the LCP systems, N₁ is positive for the unfilled and negative for the glass fiber‐filled LCPs, respectively. A novel rectangular hyperbola model was successfully developed and utilized to fit the N₁ data of the neat PLA and PLA/NGP composites as well as the unfilled LCPs. The anomalous N₁ behavior of PLA/NGP and LCP composites was also thoroughly discussed in this study. POLYM. ENG. SCI., 54:1300–1312, 2014. © 2013 Society of Plastics Engineers     

Large deformation mechanical behavior of flexible nanofiber filled polymer nanocomposites

In the present work, the large deformation behavior of high aspect ratio flexible nanofiber reinforced polymer composites is investigated. Simple or successive tensile tests are performed at room temperature, i.e. in the rubbery state. By studying two different types of fibers, namely cellulose nanofibrils and carbon nanotubes, with two processing routes, the role of entanglements and of interactions existing between fibers—within the nanofiber network that can be formed in the material—on the composite properties is highlighted. For cellulosic nanofillers, strong hydrogen bonds between fibers lead to a spectacular reinforcement effect combined with a decrease of the composite ultimate strain and an irreversible damage of composite properties after first deformation (rigid network). When such strong interactions between fillers are limited (soft entangled network or simple contacts between non-entangled fibers) the resulted reinforcement is less important and no decrease of the deformation at break is observed. For carbon nanotube fillers, the evolution of the filler network during tensile test is finally highlighted by in situ electrical measurements.     

Size-dependent mechanical behavior of nanoscale polymer particles through coarse-grained molecular dynamics simulation

Anisotropic conductive adhesives (ACAs) are promising materials used for producing ultra-thin liquid-crystal displays. Because the mechanical response of polymer particles can have a significant impact in the performance of ACAs, understanding of this apparent size effect is of fundamental importance in the electronics industry. The objective of this research is to use a coarse-grained molecular dynamics model to verify and gain physical insight into the observed size dependence effect in polymer particles. In agreement with experimental studies, the results of this study clearly indicate that there is a strong size effect in spherical polymer particles with diameters approaching the nanometer length scale. The results of the simulations also clearly indicate that the source for the increases in modulus is the increase in relative surface energy for decreasing particle sizes. Finally, the actual contact conditions at the surface of the polymer nanoparticles are shown to be similar to those predicted using Hertz and perfectly plastic contact theory. As ACA thicknesses are reduced in response to reductions in polymer particle size, it is expected that the overall compressive stiffness of the ACA will increase, thus influencing the manufacturing process.     

Influence of shear flow on the preparation of polymer layered silicate nanocomposites

In this paper the influence of melt-processing on the final polymer/layered silicate nanocomposite morphology is discussed. In particular the role of shear forces on the transformation of the original large clay agglomerates is of interest. Several polymer nanocomposites were prepared by melt-extrusion, involving polycaprolactone, poly(ethylene oxide), polyamide-12 or polyamide-6 as the matrix polymer. The nanocomposite morphology was characterised by X-ray diffraction and transmission electron microscopy and the clay tactoid morphology with polarised optical microscopy and scanning electron microscopy. The development of the tactoid and nanocomposite morphology during melt-mixing under shear was studied time-resolved by optical microscopy in conjunction with a rheometer and synchrotron X-ray scattering together with a Couette type flow cell. The shear forces in the melt-preparation of polymer layered mineral nanocomposites facilitate the break-up of large-sized agglomerates, whereas the extent of further exfoliation of the mineral layers is determined by the compatibility between the polymer matrix and the mineral layers rather than by shear forces.     

The relationship between thermal degradation behavior of polymer and the fire retardancy of polymer/clay nanocomposites

The change in the degradation pathway of a polymer by incorporation of clay has a significant effect on the fire retardancy of polymer/clay nanocomposites. Since the clay layers act as a barrier to mass transport and lead to superheated conditions in the condensed phase, extensive random scission of the products formed by radical recombination is an additional degradation pathway of polymers in the presence of clay. The polymers that show good fire retardancy upon nanocomposite formation exhibit significant intermolecular reactions, such as inter-chain aminolysis/acidolysis, radical recombination and hydrogen abstraction. In the case of the polymers that degrade through a radical pathway, the relative stability of the radical is the most important factor for the prediction of the effect that nanocomposite formation has on the reduction in the peak heat release rate. The more stable is the radical produced by the polymer, the better is the fire retardancy, as measured by the reduction in the peak heat release rate, of the polymer/clay nanocomposite.     

Influence of carbon nanofibers reinforcement on thermal and electrical behavior of polysulfone nanocomposites

Carbon nanofiber (CNF) based polysulfone (PSU) nanocomposites have been developed successfully by a innovative solution mixing technique to explore the effect of state of dispersion and wt% loading of CNFs on different properties of PSU. In order to enhance the interfacial adhesion between CNFs and PSU, CNFs were functionalized by air oxidation. Thermal properties were characterized by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and it was seen that thermal stability of PSU was increased with increase in CNFs loading. The state of dispersion of CNFs throughout the PSU matrix and PSU–CNFs interaction were confirmed using field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) study. The electrical properties of nanocomposites were studied from direct current (DC) and alternating current (AC) resistivity measurement. DC resistivity registered a very low percolation threshold in‐between 0.5–1 wt% of CNFs loading. DC resistivity of PSU was decreased by nine orders of magnitude with the addition of 1 wt% CNFs loading. Dielectric constant and dissipation factor of nanocomposites were significantly increased with increase in CNFs content in nanocomposites. The enhancement in these properties suggests a great potential application of the resulting nanocomposites as multifunctional materials in various electronics industries. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Modelling of the chemo–rheological behavior of thermosetting polymer nanocomposites

Epoxy/amine/montmorillonite nanocomposite systems are studied in this article. Both a thermo−kinetic analysis (performed using a differential scanning calorimeter) and a chemorheological characterization were carried out. The comparison of DSC thermograms has shown that the addition the nanofiller does not change the mechanism of crosslinking from a qualitative standpoint, but the nanoreinforcement seemed to produce an evident hindrance on the molecular mobility, which in turn influences the cure reactions. As none of the kinetic models available in literature was able to describe the cure behavior of the aforementioned materials, a new phenomenological model is proposed in this work, which considers the activation energy of the networking process a function of the degree of cure (rising exponentially towards infinity when thesystem approaches vitrification). The effects of the presence of the clay on the chemorheology of the composites was resumed as follows: the viscosity of the nanocomposite was higher at any temperature, furthermore the composite viscosity showed an higher heating sensitivity before networking and gelation occurred at lower degrees of cure, thus determining a narrower shape of the chemoviscosity behavior. A modified version of the classical Williams–Landel–Ferry (WLF) equation that took into account the gelation and the effects of crosslinking was uses as chemorheological model. Once the characteristic parameters of both the neat resin and the nanocomposite were found, the chemoviscosity models were integrated using a numerical algorithm, to check their ability to foresee the behavior of the systems during a dynamic cure process. A very good correspondence between the results and the experimental data was obtained. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

掺水量对聚吡咯高分子膜电化学性能的影响

在0.1 mol/L吡咯+0.2 mol/L Na Cl O4的乙腈溶液中加入不同含量[0,3%,6%,9%(体积分数)]的水,采用循环伏安法制备了聚吡咯(PPy)高分子膜。利用扫描电子显微镜(SEM)对其表面形貌进行了观察,利用恒电流充放电曲线研究了其电化学性能。比较了不同电流密度下不锈钢/聚吡咯(SS/PPy)比电容和能量密度,当电流密度由1 m A/cm2增大到5 m A/cm2时,PPy(6%)电极的比电容下降幅度最小,下降了21.6%。     

掺水量对聚吡咯高分子膜电化学性能的影响

在0.1 mol/L吡咯+0.2 mol/L Na Cl O4的乙腈溶液中加入不同含量[0,3%,6%,9%(体积分数)]的水,采用循环伏安法制备了聚吡咯(PPy)高分子膜。利用扫描电子显微镜(SEM)对其表面形貌进行了观察,利用恒电流充放电曲线研究了其电化学性能。比较了不同电流密度下不锈钢/聚吡咯(SS/PPy)比电容和能量密度,当电流密度由1 m A/cm2增大到5 m A/cm2时,PPy(6%)电极的比电容下降幅度最小,下降了21.6%。     

Evolution of nanoporosity and electrochemical behavior in organosilicon polymer derived carbon hybrids

Nanoporous carbon hybrids with high specific surface area and pore volume have been prepared from inexpensive commercial precursors, such as nanocarbon and organosilicon polymers. The synthesized carbon hybrids were found to possess specific surface area from 916 to 1798 m² g^?1, pore volume in the range of 0.5–1.2 cc g^?1, and micropore volume up to 0.804 cc g^?1. Cyclic voltammetry in aqueous electrolyte indicated ideal supercapacitive behavior for certain samples. Specific capacitance in the range of 176–333 F g^?1for a moderate voltage scan rate of 20 mV s^?1 was observed for the carbon hybrids. The article explores a simple method for the fabrication of novel carbon hybrids with excellent porosity control and pore volume. The process can open new avenues for the fabrication of a series of novel carbon hybrids, where pore dimensions and specific surface area can be engineered with the careful selection of organosilicon polymers and process conditions.     

PVC polymer/ZnO/NiO/Co3O4 nanocomposites: Toward improved optical properties

Undoped and doped polyvinyl chloride (PVC) with zinc, nickel and cobalt oxides, ZnO/[(1 − x)NiO/xCo₃O₄], composites were fabricated using co-precipitation and casting techniques. The different phases present in the nanofiller ZnO/[(1 − x)NiO-xCo₃O₄] mixed oxides were determined using synchrotron x-ray diffraction technique. X-ray diffraction, scanning electron microscopy (SEM) images and energy dispersive spectroscopy (EDS) analysis techniques were used to investigate the structure, composition, and morphology of pure and loaded PVC with nanofiller oxides. In general, compared with pure PVC, the absorbance was greatly enhanced, especially in the UV region, upon loading ZnO/[(1−x)NiO-xCo₃O₄], but it changed irregularly with the cobalt oxide (Co₃O₄) content (x). The direct and indirect optical band gaps of pristine PVC (4.14, 4.12 eV) reduced irregularly to minimum values 3.97 and 3.23 eV respectively for the polymer doped with ZnO/[0.3NiO/0.7Co₃O₄]. The refractive index was enhanced in the visible and IR regions and attained its highest value for PVC doped with zinc oxide/nickel oxide (ZnO/NiO) only (x = 0.0). NiO and Co₃O₄ ratios affect the linear and nonlinear optical parameters. The emitted spectra from pure and doped PVC polymers with the composite oxides [ZnO/[(1−x)NiO-xCo₃O₄] under different excitation wavelengths were also explored. The FL intensity enhanced for the excitation wavelengths (λ_exc) = 380 and 434 nm but quenched for λ_exc = 317 nm. The loaded polymers absorb UVA, UVB, and UVC rays and are good candidates for solar cell applications.     

Influence of surface roughness on the electrochemical behavior of carbon steel

The effect of the surface roughness of carbon steel on corrosion properties was investigated using electrochemical tests, and surface and Kelvin probe force microscopy (KPFM) analyses. The results of electrochemical tests show that the corrosion rate of carbon steel is increased as the surface roughness increases. It was estimated using KPFM measurement that the difference in the Volta potential between the peak and the valley increased with increasing surface roughness. As the peak has a lower potential than that of the valley, the peak acts as an anode. The surface roughness affects the Volta potential, and the Volta potential difference is inversely proportional to electron work function (EWF). The larger difference in Volta potential between the peak and valley on the rougher surface and the smaller EWF accelerated the micro-galvanic corrosion between them. The surface analyses reveal that corrosion initiated along the peak lines. The results from this study suggest that an increase of surface roughness leads to a decrease of the corrosion resistance.     

Influence of octakis-functionalized polyhedral oligomeric silsesquioxanes on the physical properties of their polymer nanocomposites

We synthesized the polyhedral oligomeric silsesquioxane (POSS) derivatives octakis[dimethyl(phenethyl)siloxy]silsesquioxane (OS-POSS), octakis[dimethyl(4-acetoxy phenethyl)siloxy]silsesquioxane (OA-POSS), and octakis[dimethyl(4-hydroxyphenethyl)siloxy] silsesquioxane (OP-POSS) through hydrosilylation with octakis(dimethylsiloxy)silsesquioxane (Q₈M₈^H). To investigate the influence of these octuply functionalized POSS derivatives in polymer nanocomposites, we blended OP-POSS, OA-POSS, and OP-POSS with the homopolymer poly(ethylene oxide) (PEO) and characterized its resulting intermolecular interactions (e.g., hydroxyl-ether and carbonyl-ethylene oxide) using FTIR spectroscopy. The thermal properties of these blend systems were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The crystallization kinetics in the miscible binary blends of the crystalline polymer and these inorganic nanoparticles were also determined through DSC and optical microscopy (OM) analyses. Herein, we emphasize the effects of the functional groups on POSS nanocomposites on the crystallization kinetics of PEO. We found that OP-POSS/PEO blend had the highest thermal stability and lowest crystallization rate because its hydrogen bonding interactions (between its hydroxyl and ether units) were stronger than those (between carbonyl and methylene groups) in OA-POSS/PEO.     

Thermomechanical behavior of polymer/layered silicate clay nanocomposites based on unmodified low density polyethylene

The purpose of this study was to investigate the effect of filler content and aspect ratio on the thermomechanical behavior of unmodified low density polyethylene (LDPE)‐based layered silicate clay nanocomposites. LDPE‐based nanocomposites, without any polymer modification and with two kinds of clays, one with low aspect ratio (i.e., synthetic laponite ‐Lp) and another with high aspect ratio (i.e., montmorillonite) were prepared and characterized using dynamic mechanical analysis (DMA). Organosilicates were added at 2, 5 and 10 wt%, respectively. X‐ray diffraction (XRD) analysis was performed on composites obtained by dispersing the organosilicates in unmodified LDPE. The LPDE reinforced with organo‐montmorillonite (OMt) had better performance in the whole temperature range than those with organo‐laponite (OLp). It was concluded that the relatively high aspect ratio OMt can induce superior dynamic mechanical properties to the LDPE polymer compared to lower aspect ratio OLp. This was linked to the higher active surface area and preferential orientation of longer platelets resulting in higher mechanical enhancement. This behavior was more pronounced up to filler contents of 5 wt%. Further increase of the filler content led to more conventional composites, which hindered the reinforcing ability of the silicates. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Effective electrical conductivity of nanocomposites. Influence of image forces on contact conductivity of metal‐filled polymer nanocomposites

The generalized effective conductivity of a heterogeneous medium with chaotic structure is defined based on the ideas of the renormalization group transformation method and the theory of fractals. The fractal sets obtained from rectangular lattices have been used to construct the structure of a nanocomposite with random distribution of components (phases). A model for the calculation of effective electrical conductivity of filled polymer nanocomposites is developed. It is based on conductivity between two filler particles separated by matrix polymer as an elementary conductivity event and the application of an iterative averaging method. The comparison of the calculation and experimental data of different filled polymer systems shows good agreement. PACS: 72.80 Tm; 72.60+ g; and 84.32 Ff. POLYM. COMPOS., 31:1541–1553, 2010. © 2009 Society of Plastics Engineers     

Influence of multi-walled carbon nanotubes on the electrochemical performance of graphene nanocomposites for supercapacitor electrodes

In this work, multi-walled carbon nanotube (MWNT) bonded graphene (M-GR) composites were prepared using the chemical reduction of graphite oxide (GO) and acid treated MWNTs with different ratios. The M-GR/polyaniline (PANI) nanocomposites (M-GR/PANI) were prepared using oxidation polymerization. The effect of the M-GR ratio on the electrochemical performances of the M-GR/PANI was investigated. It was found that the substrate 2D graphene was coated with 1D MWNTs by chemical reduction and the M-GR was further coated with PANI, leading to increased electrical properties by the π–π interaction between the M-GR and PANI. In addition, the electrochemical performances, such as the current density, charge–discharge, and specific capacitance of the M-GR/PANI were higher than those of graphene/PANI and the highest specific capacitance (1118 F/g) of the composites was obtained at a scan rate of 0.1 A/g for the PANI containing a 0.5 M-GR ratio compared to 191 F/g for the graphene/PANI. The dispersion of the MWNTs onto the graphene surface and the ratio of M-GR had a pronounced effect on the electrochemical performance of the PANI-based composites, which was attributed to the highly conductive pathway created by the M-GR incorporated in the PANI-based composites and the synergistic effect between M-GR and PANI.