Enhancing dielectric and mechanical behaviors of hybrid polymer nanocomposites based on polystyrene,polyaniline and carbon nanotubes coated with polyaniline

The dielectric and mechanical properties of hybrid polymer nanocomposites of polystyrene/polyaniline/carbon nanotubes coated with polyaniline(PCNTs) have been investigated using impedance analyzer and extensometer. The blends of PS/PANI formed the heterogeneous phase separated morphology in which PCNTs are dispersed uniformly. The incorporation of a small amount of PCNTs into the blend of PS/PANI has remarkably increased the dielectric properties. Similarly, the AC conductivity of PS/PANI is also increased five orders of magnitude from 1.6 × 10~(-10) to 2.0 × 10~(-5) S·cm~(-1) in the hybrid nanocomposites. Such behavior of hybrid nanocomposites is owing to the interfacial polarization occurring due to the presence of multicomponent domains with varying conductivity character of the phases from insulative PS to poor conductor PANI to highly conductive CNTs. Meanwhile, the tensile modulus and tensile strength are also enhanced significantly up to 55% and 160%, respectively, without much loss of ductility for three phase hybrid nanocomposites as compared to the neat PS. Thereby, the hybrid nanocomposites of PS/PANI/_P CNTs become stiffer, stronger and tougher as compared to the neat systems.     

Effect of dissolution-based recycling on the degradation and the mechanical properties of acrylonitrile-butadiene-styrene copolymer

A dissolution-based recycling technique for acrylonitrile-butadiene-styrene copolymer (ABS) is proposed, and the effects of repeated recycling cycles are studied measuring changes in chemical structure, melt viscosity, and tensile and impact properties. Acetone as solvent, 0.25 g/ml concentration, room temperature and 40 min for dissolution have been found to be the most reliable recycling parameters. FTIR, DSC and MFI results have shown that the dissolution-based recycling itself does not degrade the ABS. However, TGA analysis suggests that during the dissolution some stabilizers are probably eliminated, and consequently degradation takes place in the following injection moulding step. Darkening of recycled ABS is attributed to the butadiene degradation, pointed out by FTIR results. Otherwise, the chemical structure of the SAN matrix has not been modified, but its molecular weight has been reduced. The modulus of elasticity is not affected even after four recycling cycles. However, yield stress and impact strength decrease after the first recycling cycle, and remain constant in the following steps.     

The study of sorption and transport properties of membranes containing polyaniline

The transport properties of membranes based on polyimide-polyaniline composites are studied in the pervaporation separation of a methanol-toluene binary azeotropic mixture. The morphology of the membranes is investigated by electronic microscopy, and the wettability of their surface is analyzed by contact-angle measurements. Special attention is given to the study of sorption and diffusion characteristics of membranes affecting the selectivity and rate of membrane separation. It is found that the incorporation of polyaniline into the matrix of the aromatic polyimide facilitates a reduction in the density of the composites relative to that of the nonmodified polyimide. It is shown that the membranes based on the polyimide-polyaniline composites are more selective with respect to methanol and show lower permeability during pervaporation of the methanol-toluene mixture than polyimide membranes.     

The combined effect of photodegradation and stress cracking in polystyrene

This work aims to analyze the effects of photodegradation on the stress cracking resistance of polystyrene. Injection moulded samples were exposed to the ultraviolet light for various times in the laboratory prior to solvent contact. The bars were then stressed in a tensile testing machine under the presence of butanol. During this period the stress relaxation was monitored and the ultimate properties were evaluated after selected periods of stress cracking. Complementary tests were done by size exclusion chromatography and by scanning electron microscopy. The results indicated that butanol causes significant modification in polystyrene, with extensive surface crazing as well as reduction in mechanical properties. This is intensified under higher mechanical stress. The previous degraded samples showed a higher level of stress relaxation and a greater loss in tensile strength in comparison to the undegraded ones. The synergist action of photodegradation and stress cracking in polystyrene may be a consequence of the chemical changes caused by oxidation like the formation of polar chemical groups and the reduction in molecular weight.     

The effect of ferric ions on the conductivity of various types of polymer cation exchange membranes

Recently, rejuvenated interest to fuel cells has posed a number of problems regarding the polymer electrolyte membrane properties and their behaviour in different electrolyte solutions. This work was dedicated to study the conductivity of H⁺-, Fe³⁺- and mixed H⁺/Fe³⁺-forms of cation exchange membranes Neosepta CMS, Nafion 112, 115 and 117 and Selemion HSF under conditions similar to these in the Fe³⁺/Fe²⁺–H₂/H⁺ fuel cell in the range of current densities 0–90 mA/cm². It was found that the conductivities of these membranes in 1.09 M H₂SO₄ solution decrease in the following order: Selemion HSF › Nafion 117 ≈ Nafion 115 ≈ Neosepta CMS › Nafion 112. Conductivities of perfluorinated membranes were discussed in terms of Hsu and Gierke percolation theory [20]. The Fe³⁺-forms of Nafion membranes studied displayed a monotonous decline in the resistance when current increased, which is a manifestation of gradual conversion of the Fe³⁺-form into H⁺-form of these membranes. Unlike the Nafion membranes, the Fe³⁺-forms of Neosepta CMS and Selemion HSF membranes exhibited a sharp jump of resistance at relatively high current densities (more than 70 mA/cm²) that is most probably a result of concentration polarization.     

The co-pyrolysis of flame retarded high impact polystyrene and polyolefins

The co-pyrolysis of brominated high impact polystyrene (Br-HIPS) with polyolefins using a fixed bed reactor has been investigated, in particular, the effect that different types of brominated aryl compounds and antimony trioxide have on the pyrolysis products. The pyrolysis products were analysed using FT-IR, GC–FID, GC–MS, and GC–ECD. Liquid chromatography was used to separate the oils/waxes so that a more detailed analysis of the aliphatic, aromatic, and polar fractions could be carried out. It was found that interaction occurs between Br-HIPS and polyolefins during co-pyrolysis and that the presence of antimony trioxide influences the pyrolysis mass balance. Analysis of the Br-HIPS + polyolefin co-pyrolysis products showed that the presence of polyolefins led to an increase in the concentration of alkyl and vinyl mono-substituted benzene rings in the pyrolysis oil/wax resulting from Br-HIPS pyrolysis. The presence of Br-HIPS also had an impact on the oil/wax products of polyolefin pyrolysis, particularly on the polyethylene oil/wax composition which converted from being a mixture of 1-alkenes and n-alkanes to mostly n-alkanes. Antimony trioxide had very little impact on the polyolefin wax/oil composition but it did suppress the formation of styrene and alpha-methyl styrene and increase the formation of ethylbenzene and cumene during the pyrolysis of the Br-HIPS.     

The co-pyrolysis of flame retarded high impact polystyrene and polyolefins

The co-pyrolysis of brominated high impact polystyrene (Br-HIPS) with polyolefins using a fixed bed reactor has been investigated, in particular, the effect that different types of brominated aryl compounds and antimony trioxide have on the pyrolysis products. The pyrolysis products were analysed using FT-IR, GC–FID, GC–MS, and GC–ECD. Liquid chromatography was used to separate the oils/waxes so that a more detailed analysis of the aliphatic, aromatic, and polar fractions could be carried out. It was found that interaction occurs between Br-HIPS and polyolefins during co-pyrolysis and that the presence of antimony trioxide influences the pyrolysis mass balance. Analysis of the Br-HIPS + polyolefin co-pyrolysis products showed that the presence of polyolefins led to an increase in the concentration of alkyl and vinyl mono-substituted benzene rings in the pyrolysis oil/wax resulting from Br-HIPS pyrolysis. The presence of Br-HIPS also had an impact on the oil/wax products of polyolefin pyrolysis, particularly on the polyethylene oil/wax composition which converted from being a mixture of 1-alkenes and n-alkanes to mostly n-alkanes. Antimony trioxide had very little impact on the polyolefin wax/oil composition but it did suppress the formation of styrene and alpha-methyl styrene and increase the formation of ethylbenzene and cumene during the pyrolysis of the Br-HIPS.     

Synthesis and properties of silica/polystyrene/polyaniline conductive composite particles

In this study, silica/polystyrene/polyaniline (SiO₂/PS/PANI) conductive composite particles were synthesized by four sequential reactions. The nanosized SiO₂ particles were synthesized from tetraethoxysilane (TEOS) by a sol–gel process with water as the solvent medium, followed by a surface modification with triethoxyvinylsilane; then the surface modified SiO₂ particles were used as seeds to synthesize SiO₂/PS composite particles with soapless seeded emulsion polymerization. Finally, the SiO₂/PS particles were used as seeds to synthesize the SiO₂/PS/PANI conductive composite particles. The sol–gel process of SiO₂, the effect of surface modification, and several other factors that influenced polymerization of styrene in the soapless seeded emulsion polymerization will be discussed. Either potassium persulfate (KPS) or 2,2′‐azobis(isobutyramidine) dihydrochloride (AIBA) was used as the initiator to synthesize the uniform SiO₂/PS particles successfully, and the cross‐section morphology of the SiO₂/PS particles was found to be of a core–shell structure, with SiO₂ as the core, and PS as the shell. The SiO₂/PS particles were well dispersed in many organic solvents. In the following step to synthesize SiO₂/PS/PANI conductive composite particles, sodium dodecyl sulfate (SDS) played an important role, specifically, to absorb aniline onto the surfaces of the SiO₂/PS particles to carry out the polymerization of aniline over the entire surface of the particles. The conductivity of the SiO₂/PS/PANI composite particles approached that of semiconductive materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 342–354, 2005     

Morphology influence on the permeation properties of styrene and polystyrene modified polyethylene membranes

Influence of the structure of styrene and polystyrene modified PE membranes on their permeation properties is presented. It is demonstrated that the temperature of styrene treatment (N membranes) and the presence of polystyrene (P membranes) results in high differentiation of the permeation properties. SALS studies have shown the structural reorganization depending on modification extent and diffusion of the penetrant. It is also shown that the morphology of the dried films remains unchanged. This work proves that the appropriate modification of PE films results in membranes with controlled permeation behavior.     

Spatial distribution of foulants on membranes during ultrafiltration of protein mixtures and the influence of spacers in the feed channel

Using matrix assisted laser desorption ionisation mass spectrum (MALDI-MS), this study reports the observations of the fouling distribution and composition along the membrane channel after the membranes were subjected to ultrafiltration of protein mixture solution in a crossflow module with and without spacer. In the fouling layer on a fully retentive membrane, the protein components with high molecular weight has higher presentation after 2 h of filtration and the presentation reduced to be lower than the smaller components after 6 h of filtration due to protein exchange and displacement phenomena in deposition layer caused by the differences in structure and diffusivity of different components. The protein exchange and replacement in the deposition layer was also observed on partial retentive membrane using a sequential fouling procedure. Fouling distribution along the membrane channel with spacer inserted in the module was more uniform and the flux was higher than that without spacer despite higher protein deposition observed in some cases.     

The effect of pH on the separation of manure nutrients with reverse osmosis membranes

This paper reports on the effect of pH on the retention of dry matter (DM), total ammonia-nitrogen (TAN), potassium, phosphorus and volatile fatty acids (VFAs) during the filtration of pretreated swine manure by three highly selective reverse osmosis (RO) membranes. The manure was pretreated using various combinations of biological and physical technologies, namely anaerobic digestion (AD), vacuum filtration through diatomaceous earth (DE), nanofiltration (NF), and a first stage RO filtration. The objective was to establish the level of acidification required to optimize permeate quality while minimizing chemical addition.     

The mycological effect on morphological,electrochemical and redox properties of the polyaniline surface

Biofilm formation with eight different microscopic fungi on the polyaniline surface and its effect on the morphological, electrochemical and redox properties have been studied. The investigations on selected Chrysosporium merdarium and Rhizomucor pusillus fungi behavior were performed. Conspicuous difference in the oxidation level, redox activity and oxalate impurities at the polymer surface layer treated with Chrysosporium merdarium and Rhizomucor pusillus was confirmed. The electrochemical behavior of the modified electrode was characterized using the cyclic voltammetry technique. The chemical composition of treated surface was determined by X‐ray photoelectron spectroscopy. For the estimation of conductive polymer morphology and roughness, the method of optical and scanning probe microscopy was applied, which showed that the polyaniline surfaces treated with Chrysosporium merdarium are homogenous and smoother than the polyaniline surfaces treated with Rhizomucor pusillus. Water contact angle measurements confirmed the effect of microbial growth on the properties of the polyaniline surface. Copyright © 2013 John Wiley & Sons, Ltd.     

The effect of the polyaniline morphology on the performance of polyaniline supercapacitors

The polyaniline (PANI) prepared by the pulse galvanostatic method (PGM) or the galvanostatic method on a stainless steel substrate from an aqueous solution of 0.5 mol/l H₂SO₄ with 0.2 mol/l aniline has been studied as an electroactive material in supercapacitors. The electrochemical performance of the PANI supercapacitor is characterized by cyclic voltammetry, a galvanostatic charge–discharge test and electrochemical impedance spectroscopy in NaClO₄ and HClO₄ mixed electrolyte. The results show that PANI films with different morphology and hence different capacitance are synthesized by controlling the synthesis methods and conditions. Owing to the double-layer capacitance and pseudocapacitance increase with increasing real surface area of PANI, the capacitive performances of PANI were enhanced with increasing real surface area of PANI. The highest capacitance is obtained for the PANI film with nanofibrous morphology. From charge–discharge studies of a nanofibrous PANI capacitor, a specific capacitance of 609 F/g and a specific energy density of 26.8 Wh/kg have been obtained at a discharge current density of 1.5 mA/cm². The PANI capacitor also shows little degradation of capacitance after 1,000 cycles. The effects of discharge current density and deposited charge of PANI on capacitance are investigated. The results indicate that the nanofibrous PANI prepared by the PGM is promising for supercapacitors.     

Molecular elucidation of morphology and mechanical properties of PVDF hollow fiber membranes from aspects of phase inversion, crystallization and rheology

This study explores the fundamental science of fabricating poly(vinylidene fluoride) (PVDF) hollow fiber membranes as well as elucidates the correlation among membrane morphology, crystallinity and mechanical properties as functions of non-solvent additives and dope rheology in the phase inversion process. A series of non-solvents (i.e. water, methanol, ethanol, isopropanol) are used either as non-solvent additives in the dope or as a component in the external coagulant. Depending on the strength of the non-solvent, the phase inversion of semi-crystalline PVDF membranes is dominated by liquid–liquid demixing or solid–liquid demixing accompanying crystallization. As a result, the membrane morphology transforms from an interconnected-cellular type to an interconnected-globule transition type with lower mechanical strengths when adding water, methanol, ethanol, or isopropanol into the spinning dopes or into the coagulation bath. The crystallinity and size of spherulitic globules in the morphology are controlled by the amounts of non-solvents presented in the systems. The rheological behavior of dope solutions is explored and the relationship between elongation viscosity and mechanical properties has been elaborated. Analytical methods and molecular dynamics simulations are employed to provide insights mechanisms from the views of thermodynamic and kinetic aspects as well as the state of polymer chains involved in the phase inversion process.     

The effect of a polypyrrole coating on the thermal stability of microporous polyethylene membranes

Microporous polyethylene (PE) membranes were coated on both sides with a polypyrrole (PPy) overlayer. PPy was deposited also on the walls of pores. Thermodeformation measurements indicate that the hard framework produced by rigid-chain PPy controls the mechanical properties of composite membranes. FTIR spectroscopy was used to detect oxidative processes in both polymer components above 200 °C. Elemental analysis showed that the nitrogen content remains at high level, even after the treatment of membranes in air at 300 °C, indicating that the decomposition involved mainly PE while PPy was much more stable. The changes in surface relief after annealing were assessed with electron microscopy. No oxidative processes were identified in the FTIR spectra of composites after annealing in vacuum, even after treatment at 300 °C.     

The effect of gel layer thickness on the salt rejection performance of polyelectrolyte gel-filled nanofiltration membranes

The effect of gel layer thickness on salt separation of positively charged pore-filled nanofiltration membranes has been examined both theoretically and experimentally. The extended Nernst-Planck (ENP) equation coupled with the Teorell-Meyer-Sievers (TMS) model were used to calculate the pressure-driven sodium chloride rejections for membranes having gel densities in the range typically used in nanofiltration applications. It was found that salt rejection was dependent on membrane (gel-layer) thickness with salt rejections increasing rapidly with thickness up to 50–75 μm. Further increases in thickness beyond this point had a much smaller effect on salt rejection. The theoretical predictions were examined experimentally by preparing a series of membranes with cross-linked poly(3-acrylamidopropyl)-trimethylammonium chloride (PAPTAC) gels with varying densities within the pores of a thin microporous polyethylene (PE) support. The membranes were characterized by their polymer volume fractions (gel concentration), thicknesses and effective charge densities. The effect of membrane thickness was examined by using single and stacks of two membranes. The pure water fluxes and salt rejections of the membranes and membrane stacks were determined in the pressure range 50–550 kPa. The single salt rejections of the membranes which were very dependent on the thickness of the membrane or membrane stack, were fully in accord with the calculated salt rejections of the membranes.     

The effect of Ce3+ cations on polyaniline morphology and electric properties

Polyaniline (PANI) is synthesized in the potentiostatic pulse mode from an electrolyte containing Ce₂(SO₄)₃. Cations Ce³⁺ are incorporated into the polymer composition during PANI redox transformations. It is shown that PANI in its conducting and dielectric forms contains different amounts of Ce³⁺ cations. Starting with the beginning of polymerization, the Ce³⁺ cations actively form the special polymer morphology as demonstrated by SEM images. The chief consequence of the formation of so well-developed uniform nanostructure is that the latter allows the dopant anions, cations, and protons to easily enter and leave it. This, in turn, results in the high electrochemical activity of this polymer and enhances the conductivity of PANI samples doped with Ce³⁺ cations as compared with those doped with only protons.     

The effect of acrylic acid amount on the colloidal properties of polystyrene latex

Poly(styrene-co-acrylic acid) (St/AA) latices were prepared by using a batch soap-free emulsion copolymerisation in non-buffered medium. Polymerisation kinetics, followed by gravimetric method, revealed that increasing AA comonomer concentration was directly proportional to the copolymerisation rate, while adding AA comonomer caused a strong decrease of particle size of final St/AA latex particle without affecting the size distribution. Transmission electron microscopy indicated that the particles were monodispersed and spherical in shape irrespective of AA amount used in the investigated range. The colloidal stability of the latices was increased upon increasing the AA concentration; owing to the electrosteric stabilisation originated from AA-rich layer on the particle surface. In addition, electrophoretic mobility of formed particles versus polymerisation conversion exhibited the constancy of the surface charge density during the polymerisation process and was inferred for discussion of the polymerisation mechanism of this system.     

The effect of thiolation on the mechanical and protein adsorption properties of polyurethanes

Segmented polyurethanes are important polymers for a number of industrial and technological applications. The purpose of this work was to synthesize polybutadiene-based polyurethanes and subsequently graft carboxylate and sulfonate side chains via thiol-ene reaction. Spectroscopic investigations showed that grafting yielded good conversion for the vinyl unsaturation of the polybutadiene soft segment. DSC and tensile testing revealed that grafted polyurethanes had a better segmental compatibility and superior mechanical properties than the control polyurethane without grafting. The carboxylic side chains of the soft segment were responsible for the observed improved mechanical properties. Initial protein adsorption tests on these polymers were found to be higher than the control surface. The polyurethanes of the current study could be used for biomedical applications where protein attachment to the surface is needed for specific cell adhesion and tissue repair.     

Study of the interaction between cyclodextrins and liposome membranes: effect on the permeability of liposomes

We wanted to compare and understand the effect of the most currently used cyclodextrins on a model membrane. We studied the influence of most currently used cyclodextrins on the release of a fluorescent marker encapsulated in the inner cavity of SUV liposomes. It was shown that the observed effect on calcein release can be directly related to the affinity of cyclodextrins for both lipid components of liposomes, cholesterol and phosphatidylcholine. From this relationship, we were able to determine, for each cyclodextrin, a theoretical concentration giving rise to 50% or 100% calcein release. This theoretical concentration was confirmed experimentally.