Electrical, mechanical and adhesive properties of ethylene-vinylacetate copolymer (EVA) filled with wollastonite fibers coated by silver

New type of electrically conductive polymeric composites was prepared using ethylene-vinylacetate (EVA) matrix filled with silver-coated wollastonite (W-Ag) fibers. The electrical, mechanical and adhesive properties of the composites are reported in this paper. The electrical percolation threshold was found about 8 vol.% and the highly electrical conductivity value (1.8 × 10⁵ S m⁻¹) is reached for 29 vol.% of filler fraction. The mechanical and adhesive properties of these composites were also discussed and correlated with some models.     

Electrically conductive composites of polyethylene filled with polyamide particles coated with silver

New types of electrically conductive polymeric composites were prepared on a base of high-density polyethylene (HDPE) matrix filled with silver-coated polyamide (PA) particles. The electrical, mechanical and adhesive properties of those composites are reported in this paper. The percolation concentration of the filler within a matrix was found to be 4 vol.%. Composites filled with high filler content were highly electrically conductive; their electrical conductivity reached the value of 6.8 × 10² S cm⁻¹. Mechanical properties and rheology of these composites were discussed. The adhesive properties of the composites to metal sharply increased with an increase in the filler content.     

Fluorene-containing block sulfonated poly(ether ether ketone) as proton-exchange membrane for PEM fuel cell application

A series of sulfonated block poly(ether ether ketone)s with different sulfonic acid group clusters were successfully synthesized by nucleophilic displacement condensation. Membranes were accordingly cast from their DMSO solutions, and fully characterized by determining the ion-exchange capacity, water uptake, proton conductivity, dimensional stabilities and mechanical properties. The experimental results showed that the main properties of the membrane can be tailored by changing the cluster size of sulfonic acid groups. The membrane of block-7c(40) has good mechanical, oxidative and dimensional stabilities together with high proton conductivity (5.09 × 10⁻² S cm⁻¹) at 80 °C under 100% relative humidity. The membranes also possess excellent thermal and dimensional stabilities. These polymers are potential and promising proton conducting membrane material for PEM full cell applications.     

Nanostructured carbon black filled polypropylene/polystyrene blends containing styrene-butadiene-styrene copolymer: Influence of morphology on electrical resistivity

This paper is part of a comprehensive study on using selective localization of carbon black (CB) at the interface of immiscible polymer blends in order to reduce the percolation threshold concentration and enhance the conductivity of the blends. CB was successfully localized at the interface of polypropylene/polystyrene (PP/PS) blend by introducing styrene-butadiene-styrene (SBS) tri-block copolymer to the blend. In CB-PP/PS/SBS blends, CB has higher affinity for the polybutadiene (PBD) section of the SBS copolymer, whereas in CB-PP/PS blends, CB prefers the PS phase. PP/PS interface is one of the preferred locations for the SBS copolymer in the (PP/PS) blend; at which the PBD section of the SBS copolymer forms a few nanometers thick layer able to accommodate the CB nano-particles. The influence of SBS addition on the morphology and electrical properties of various PP/PS blends filled with 1 vol% CB were studied. SBS influence on the conductivity of PP/PS blends was found to be a function of the PP/PS volume ratio and SBS loading. The most dramatic increase in conductivity was found in the (60/40) and (70/30) PP/PS blends upon the addition of 5 vol% SBS. 5 vol% SBS was found to be the optimum loading for most blends. Using 10 vol% of SBS was reported to deteriorate electrical conductivity of the conductive co-continuous PP/PS blends. For all blends studied, SBS addition was found to compatibilize the blends. Finer morphologies were obtained by increasing SBS loading.     

Highly conductive PEDOT/PSS microfibers fabricated by wet-spinning and dip-treatment in ethylene glycol

Highly conductive microfibers made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) were fabricated by wet-spinning and subsequent dip-treatment in ethylene glycol. The electrical conductivity of the PEDOT/PSS microfibers with a diameter of ca. 5 μm was significantly increased from 74 S cm⁻¹ to 467 S cm⁻¹ by the dip-treatment in 3 min. The result was explained by removal of insulating PSS from the surface of the PEDOT/PSS grains and crystallization of PEDOT, which led to the formation of large numbers of higher conductive grains that enhanced the transport of charge carriers in the microfiber. The mechanical properties of the microfibers were also improved by the dip-treatment where Young’s modulus and tensile strength increased from 3.2 GPa and 94 MPa to 4.0 GPa and 130 MPa, respectively.     

Interfacially modified LDPE/GTR composites with non-polar elastomers: From microstructure to macro-behavior

This paper provides some new insights into the mechanism of interaction and modifications in thermoplastic composites based on low density polyethylene (LDPE), ground tire rubber (GTR) and non-polar elastomer. The composites were prepared using a co-rotating twin-screw extruder at variable LDPE/GTR ratio and constant elastomer content. Two types of commercial elastomer were applied: styrene-butadiene-styrene (SBS) block copolymers (Kraton^®) with different topologies (linear/branched) and partially cross-linked butyl rubbers (Kalar^®) with different Mooney viscosities. Processing characteristics, static mechanical properties (tensile strength, elongation at break, hardness), dynamic mechanical properties, thermal properties and morphology of the resulting thermoplastic composites were investigated. Microstructure analysis shows that modification of LDPE/GTR composites with non-polar elastomers caused encapsulation of GTR particles within the elastomer phase. This phenomenon has significant influence on macro-behavior of thermoplastic composites based on LDPE/GTR blends. The results indicate that SBS copolymer improves interfacial interactions between GTR and LDPE, which enhances mechanical and thermal properties of the composites. On the other hand, cross-linked butyl rubber showed partial compatibility with LDPE and low compatibility with GTR particles.     

Thermoelectric properties of polycrystalline La1−xSrxCoO3

Thermoelectric properties of polycrystalline La_1−xSr_xCoO₃, where Sr²⁺ is substituted in La³⁺ site in perovskite-type LaCoO₃, have been investigated. Sr-doping increases the electrical conductivity (σ) of La_1−xSr_xCoO₃, and also decreases the Seebeck coefficient (S) for 0.01?x?0.40. A Hall coefficient measurement reveals that the increase in electrical conductivity arises from increases in both carrier concentration and the Hall mobility. The decrease in the Seebeck coefficient is caused by a decrease in carrier effective mass as well as increase in carrier concentration. The highest power factor (σS²) is 3.7×10⁻⁴ W m⁻¹ K⁻² at 250 K for x=0.10. The thermal conductivity (κ) is about 2 W m⁻¹ K⁻¹ at 300 K for 0?x?0.04, and increases for x?0.05 because of an increase in heat transport by conductive carrier. The thermoelectric properties of La_1−xSr_xCoO₃ are improved by Sr-doping, and the figure of merit (Z=σS² κ⁻¹) reaches 1.6×10⁻⁴ K⁻¹ for x=0.06 at 300 K (ZT=0.048). For heavily Sr-doped samples, the thermoelectric properties diminish mainly because of the decrease in the Seebeck coefficient and the increase in thermal conductivity.     

Polyaniline/thermoplastic polyurethane blends: Preparation and evaluation of electrical conductivity

Conducting polymer blends whose undiluted components have different properties are promising materials for specific applications and have attracted interest in recent years. The aim of this study was to obtain and evaluate the electrical conductivity of polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA)/polyurethane thermoplastic (TPU) blends. The PAni.DBSA was synthesized from DBSA-aniline (DBSAn) salt through an emulsion polymerization in tetrahydrofurane (THF) or in the presence of polyurethane thermoplastic solution, resulting in pure PAni.DBSA or PAni.DBSA/TPU blends. Blends of PAni.DBSA/TPU were also prepared through casting, at room temperature, after dissolving both components in THF as a common solvent. The insulator-conductor transition was very sharp and the percolation threshold was lower than 2.7 wt% of PAni.DBSA. The electrical conductivity of PAni.DBSA/TPU blends, prepared by both methods, reached maximum values at a PAni.DBSA concentration of 40 wt%, close to the value observed for the undiluted conducting polymer. However, for a PAni.DBSA content lower than 30 wt%, the electrical conductivity was dependent on the blend preparation method. Blends were characterized by infrared spectroscopy, thermogravimetric analysis (TG) and optical microscopy. The electrical conducting characteristics of the PAni.DBSA/TPU blends prepared using different procedures indicate a high potential for their successful application in electrical processes.     

Biodegradable polymers by reactive blending trans-esterification of thermoplastic starch with poly(vinyl acetate) and poly(vinyl acetate-co-butyl acrylate)

Wheat starch was reacted with poly(vinyl acetate) and with poly(vinyl acetate-co-butyl acrylate) in an internal mixer at 150 °C in the absence of catalyst, and in the presence of sodium carbonate, zinc-acetate and titanium(IV) butoxide. The resulted blends were pressed into film and characterized by ¹H NMR-¹³C NMR spectroscopy, differential scanning calorimetry (DSC), mechanical testing, dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), and water absorption. Partial trans-esterification took place between wheat starch and the polymers. The blends appeared as homogenous, translucent films with one glass transition temperature range, between that of starch and of the polymer. The presence of wheat starch in the blends improved the mechanical strength of the polymers, although elongation at break severely decreased, which is disadvantageous for processability. Zinc-acetate improved the tensile strength of the blends of starch with PVAC, while all catalysts resulted in an increase in strength of the blends of starch with poly(vinyl acetate-co-butyl acrylate) compared to the strength of the blends without catalyst. Water absorption of wheat starch/copolymer blends was between 150% and 250%, higher than that of the blends with the homopolymer, which was between 100% and 150% after soaking in water. The onset temperature of thermal decomposition was between 290 and 300 °C for all the blends, although the presence of sodium carbonate resulted in a decrease in the onset temperature of thermal decomposition by about 60 °C.     

Conductive polymer blends: preparation,properties and applications

This article presents a brief review concerning the production of conductive polymer blends and composites which combine conducting and insulating polymers. Different strategies for preparing these mixtures are examined, with emphasis on several properties of the final mixtures, such as: electronic conductivity, mechanical behaviour and thermal stability. The advantages of using blends in some technological applications instead of pure conducting polymers are discussed.     

Synthesis of novel crosslinked sulfonated poly(ether sulfone)s using bisazide and their properties for fuel cell application

Novel crosslinked sulfonated poly(ether sulfone)s (PESs) were prepared by thermal irradiation of the allyl-terminated telechelic sulfone polymers using a bisazide. The sulfonated polymers in different comonomer compositions were fully characterized by ¹H NMR, and the crosslinked structure was also verified by FT-IR spectroscopic analyses. Having both the uniform distribution of the hydrophilic conductive sites and controlled hydrophobic nature by minimized crosslinking over the rigid rod poly(ether sulfone) backbone, the crosslinked polymer membrane (PES-60) offered excellent proton conductivity of 0.79 S cm⁻¹ at 100 °C together with hydrolytic and oxidative stability. In addition, only 17% of methanol permeability of the Nafion^® was observed for the crosslinked PES-60.     

Investigation of mechanical properties of polyvinyl chloride-polyethylene oxide (PVC-PEO) based polymer electrolytes for lithium polymer cells

Polymer electrolytes composed of a blend of polyvinyl chloride-polyethylene oxide (PVC-PEO) as a host polymer, lithium triflate (LiCF₃SO₃) as a salt, mixture of ethylene carbonate (EC) and dibuthyl phthalate (DBP) as plasticizers and silica (SiO₂) as the nanocomposite filler were studied. Results suggest that PVC-PEO blending exhibits improved mechanical strength compared to that of pure PEO. The introduction of LiCF₃SO₃ changes the mechanical properties of PVC-PEO blends from hard and brittle to soft and tough. In PVC-PEO:LiCF₃SO₃ (70:30) system, the Young’s modulus value decreases from 5.30 × 10⁻¹ MPa to 4.78 × 10⁻⁴ MPa and the elongation at peak value increases from 3.71 mm to 32.09 mm with the incorporation of DBP and EC. The deteriorated mechanical properties with the addition of plasticizers are overcome with the addition of SiO₂ as nanocomposite filler. In PVC-PEO-LiCF₃SO₃-DBP-EC system, the addition of 5% SiO₂ increases the Young’s modulus value from 4.78 × 10⁻⁴ MPa to 1.51 × 10⁻³ MPa. The improvement of the mechanical properties reveals greater dispersion of SiO₂ particles in PVC-PEO blend based polymer electrolytes. In practical lithium polymer cells, inorganic fillers are frequently added to improve the mechanical strength of the electrolyte films.     

Preparation and characterization of graphite nano-platelet (GNP)/epoxy nano-composite: Mechanical,electrical and thermal properties

Epoxy based polymer nano-composite was prepared by dispersing graphite nano-platelets (GNPs) using two different techniques: three-roll mill (3RM) and sonication combined with high speed shear mixing (Soni_hsm). The influence of addition of GNPs on the electrical and thermal conductivity, fracture toughness and storage modulus of the nano-composite was investigated. The GNP/epoxy prepared by 3RM technique showed a maximum electrical conductivity of 1.8 × 10⁻⁰³ S/m for 1.0 wt% which is 3 orders of magnitude higher than those prepared by Soni_hsm. The percentage of increase in thermal conductivity was only 11% for 1.0 wt% and 14% for 2.0 wt% filler loading. Dynamic mechanical analysis results showed 16% increase in storage modulus for 0.5 wt%, although the Tg did not show any significant increase. Single edge notch bending (SENB) fracture toughens (K_IC) measurements were carried out for different weight percentage of the filler content. The toughening effect of GNP was most significant at 1.0 wt% loading, where a 43% increase in K_IC was observed. Among the two different dispersion techniques, 3RM process gives the optimum dispersion where both electrical and mechanical properties are better.     

A novel gel polymer electrolyte based on poly ionic liquid 1-ethyl 3-(2-methacryloyloxy ethyl) imidazolium iodide

Poly ionic liquid 1-ethyl 3-(2-methacryloyloxy ethyl) imidazolium iodide (PEMEImI) as a single-ion conductor was designed and synthesized. When appropriate amount of suitable plasticizers, I₂ and polyacrylonitrile (PAN) were incorporated into it, the complex formed gel polymer electrolyte. Chemical structure, thermal behavior and ionic conductive properties of the gel polymer electrolyte were investigated by Raman spectra, UV-Vis spectra, differential scanning calorimetry (DSC), and complex impedance analysis, respectively. For the new gel polymer electrolyte, the ionic conductivity of about 1 × 10⁻³ S cm⁻¹ at room temperature was achieved.     

Electroactive polyimide with oligoaniline in the main chain via oxidative coupling polymerization

By oxidative coupling polymerization of the imidic macromonomer of oligoaniline and p-phenylenediamine we have prepared an electroactive polyimide, exhibiting exciting molecular structure, electrochemical properties and excellent thermal stability. The polymerization characteristics and structure of the electroactive polyimide were systematically studied by Fourier-transform infrared (FTIR) spectra and X-ray powder diffraction (XRD). Electrochemical activity of the polyimide was tested in 1.0 M H₂SO₄ aqueous solution and it shows two redox peaks, which is the same as that of polyaniline. Moreover, the thermal properties of the polyimide were evaluated by thermogravimetric analysis (TGA). Its electrical conductivity is about 8.87 × 10⁻⁶ S cm⁻¹ at room temperature upon preliminarily protonic-doped experiment.     

p-Type thermoelectric properties of the oxygen-deficient perovskite Ca2Fe2O5 in the brownmillerite structure

Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (direct current electrical conductivity σ, Seebeck coefficient α, thermal conductivity κ, thermal expansion α_L) were measured from 373 to 1050 K in air. Seebeck coefficient was positive over all temperatures indicating conduction by holes, and electrical properties were continuous through the Pnma-Imma phase transition. Based on the thermopower and conductivity activation energies as well as estimated mobility, polaron hopping conduction was found to dominate charge transport. The low electrical conductivity, <1 S/cm, limits the power factor (α²σ), and thus the figure of merit for thermoelectric applications. The thermal conductivity values of ∼2 W/mK and their similarity to Ruddlesden-Popper phase implies the potential of the alternating tetrahedral and octahedral layers to limit phonon propagation through brownmillerite structures. Bulk linear coefficient of thermal expansion (∼14×10⁻⁶ K⁻¹) was calculated from volume data based on high-temperature in situ X-ray powder diffraction, and shows the greatest expansion perpendicular to the alternating layers.     

Thermal, mechanical and electrical properties on the styrene-grafted and subsequently sulfonated FEP film induced by electron beam

This paper examined the mechanical and electrical properties of poly(tetrafluoroethylene-co-hexafluoropropylene: FEP) film modified by electron beam (EB). The simultaneous irradiation method with EB was adopted for the grafting of styrene and subsequent sulfonation onto FEP film. The thermal and mechanical characteristics of the irradiated FEP film, and also those of the grafted and sulfonated FEP films, were investigated by TGA, FT-IR spectrometer, and Instron. The simultaneous irradiation with EB facilitated the homogeneous grafting, as well as a high degree of grafting with a maximum value of around 60%, thereby allowing accurate control of the degree of grafting at doses ranging from 10 to 100 kGy.The grafting or sulfonation decreased the thermal stability of FEP, whereas it considerably increased its mechanical properties. The high radiation resistance of virgin FEP up to a dose of 100 kGy enabled the sulfonation of FEP film to considerably reinforce its polymeric structures except of 10 kGy, thereby increasing its tensile strength at 30 kGy by two-fold compared to that of the virgin FEP film. The ion conductivity (IC) and ion-exchange capacity (IEC) values of the FEP membrane (125 μm thick), which were dependant on the degree of grafting, were 0.25 S cm⁻¹ and 2.4 mmol/g, respectively, at 59.2% of the degree of grafting and were superior to those of the commercialized Nafion membrane (IC, 0.12 S cm⁻¹; IEC, 0.9-1.0 mmol/g).     

A study of linear versus angled rigid rod polymers for proton conducting membranes using sulfonated polyimides

Linear and angled monomers were incorporated into the main chain of a polyimide in order to investigate the effect of kinked versus linear polymers on membrane properties such as water uptake and proton conductivity. Polymers prepared using linear 4,4′-sulfonyldianiline, SPI1, and using angled 3,4′-sulfonyldianiline, SPI2, were cast into membranes possessing ion exchange capacities that varied from 0.79 to 2.75 meq g⁻¹. Membranes are thermally stable up to 300 °C under air. Proton conductivity of both membranes increases with temperature to values of 0.1-0.2 S cm⁻¹. The conductivity of angled, SPI2 membranes is greater than those prepared from SPI1 for a given IEC but water uptakes are lower. These differences are attributed to increased entanglements of the angled polymers, which limits the degree of swelling and increases the proton concentration. These results may be important in the design of proton conducting membranes from other rigid polyarylenes.     

Diaminobisbenzothiazole chain extended polyurethanes as a novel class of thermoplastic polyurethane elastomers with improved thermal stability and electrical insulation properties

This work was devoted to the development of a new class of modified polyurethane as an electrical insulating material. For this purpose, NCO‐terminated urethane prepolymers at different NCO contents were prepared and chain extended by 6,6′‐oxybis(2‐aminobenzothiazole) (ABT) to produce thermoplastic polyurethane elastomers. All of the polymers were characterized by FTIR and ¹HNMR spectroscopies and examined for their thermal, mechanical, and electrical properties. The dynamic mechanical measurements results showed two glass transitions indicating phase separation. A considerable improvement in the thermal and electrical properties in comparison to common polyurethanes was detected for these polymers. The level of enhancement in the measured properties was related to the polyol molecular weight, hard segment content, and consequently the amount of the introduced urea and benzothiazole moieties. These findings indicated the improved high service temperature performance of these materials as electrical insulator for metallic surfaces. Copyright © 2008 John Wiley & Sons, Ltd.     

Novel fluoroacrylated copolymers: synthesis, characterization and properties

The development of polymer waveguides leads to synthesis of fluorinated amorphous polymers with high transmission capacity, potential to tune their optical properties by tailoring the molecular structure, together with good processability, easy handling, good flexibility and low cost.In this work we have investigated new thermoplastic fluoroacrylated copolymers, synthesized by radical copolymerization of fluoroalkene(s) with five-membered cyclic carbonate and a third monomer or transfer agent, both containing OH group susceptible to be used for grafting of photocrosslinkable groups. The reaction of hydroxy functionalized copolymers with different acrylating agents results in fluoroacrylated resins with molecular weight in the range of 2000-3000 g mol⁻¹, yield >75% and good solubility in reactive diluents. In the presence of photoinitiator(s), they were crosslinked under UV-radiation in order to obtain optical waveguides.The copolymers synthesized were characterized by ¹H, ¹⁹F and ¹³C NMR as well as FT-IR spectroscopies and have good thermal stability (T_d > 200 °C). The refractive indeces of hydroxy functionalized fluorooligomers and acrylated resins were found to range from 1.44 to 1.45 at 23 °C and the T_gs (by DSC) varied from 40 to 110 °C depending on the content of the cyclic monomer. The optical characteristics of these thermoplastic fluoroacrylated copolymers are under progress.