Chemical synthesis,characterization, and direct‐current conductivity studies of polypyrrole/γ‐Fe2O3 composites

The in situ polymerization of pyrrole was carried out in the presence of γ‐Fe₂O₃ to synthesize polypyrrole/γ‐Fe₂O₃ composites by a chemical oxidation method. The polypyrrole/γ‐Fe₂O₃ composites were synthesized with various compositions, including 10, 20, 30, 40, and 50 wt % γ‐Fe₂O₃ in pyrrole. The polypyrrole/γ‐Fe₂O₃ composites were characterized with X‐ray diffractometry and infrared spectroscopy. The surface morphology of these composites was studied with scanning electron microscopy. The direct‐current conductivity was studied from 40 to 200°C. The dimensions of the γ‐Fe₂O₃ particles in the matrix had a greater influence on the conductivity values. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2797–2801, 2007     

Synthesis and properties of conducting polypyrrole,polyalkylanilines, and composites of polypyrrole and poly(2‐ethylaniline)

Conducting polymers of alkylanilines, pyrrole, and their conducting composites were synthesized by oxidation polymerization. The oxidants used were KIO₃ and FeCl₃ for the polyalkylanilines and polypyrrole (PPy), respectively. Among the polyalkylanilines synthesized with KIO₃ salt, the highest conductivity was obtained with poly(2‐ethylaniline) (P2EAn) with a value of 4.10 × 10^?5 S/cm. The highest yield was obtained with poly(N‐methylaniline) with a value of 87%. We prepared the conducting composites (PPy/P2EAn and P2EAn/PPy) by changing synthesis order of P2EAn and PPy. The electrically conducting polymers were characterized by IR spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, and X‐ray diffraction spectroscopy. From the results, we determined that the properties of the composites were dependent on the synthesis order of the polymers. The thermal degradation temperature of PPy was observed to be higher than that of the other polymers and composites. We determined from X‐ray results that the structures of the homopolymers and composites had amorphous regions (88–95%) and crystal regions (5–12%). From the Gouy balance magnetic measurements, we found that the polymers and composites were bipolaron conducting mechanisms. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 241–249, 2006     

Electrically conductive composites based on epoxy resin containing polyaniline–DBSA‐ and polyaniline–DBSA‐coated glass fibers

Four kinds of polyaniline (PANI)‐coated glass fibers (GF–PANI) combined with bulk PANI particles were synthesized. GF–PANI fillers containing different PANI contents were incorporated into an epoxy–anhydride system. The best conductivity behavior of the epoxy/GF–PANI composites was obtained with a GF–PANI filler containing 80% PANI. Such a composite shows the lowest percolation threshold at about 20% GF–PANI or 16% PANI (glass fiber‐free basis). The PANI‐coated glass fibers act as conductive bridges, interconnecting PANI particles in the epoxy matrix, thus contributing to the improvement of the conductivity of the composite and the lower percolation threshold, compared with that of a epoxy/PANI–powder composite. Particularly, the presence of glass fibers significantly improves the mechanical properties, for example, the modulus and strength of the conductive epoxy composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1329–1334, 2004     

Effect of Blend Preparation on Electrical,Dielectric, and Dynamical‐Mechanical Properties of Conducting Polymer Blend: SBS Triblock Copolymer/Polyaniline

Conducting polymer blends based on styrene–butadiene–styrene (SBS) triblock copolymer and polyaniline doped with dodecylbenzene sulfonic acid (Pani.DBSA) were prepared by different procedures: mechanical mixing (MM) and ‘in situ’ polymerization (ISP) methods. The ISP blends exhibited higher levels of electrical conductivity, as compared to MM blends. The scanning electron micrographs of the ISP blend were characterized by the presence of microtubules, which favored the formation of the conducting pathways inside the SBS matrix. From dynamic mechanical and dielectric analysis, it was possible to suggest a higher interaction degree of the polyaniline with the polystyrene phase of the block copolymer. Blends prepared by ISP method displayed also higher dielectric constant and higher dielectric loss factor than blends prepared by MM method.

     

Silicone membranes to inhibit water uptake into thermoset polyurethane shape‐memory polymer conductive composites

Electroactive shape memory polymer (SMP) composites capable of shape actuation via resistive heating are of interest for various biomedical applications. However, water uptake into SMPs will produce a depression of the glass transition temperature (T_g) resulting in shape recovery in vivo. While water actuated shape recovery may be useful, it is foreseen to be undesirable during early periods of surgical placement into the body. Silicone membranes have been previously reported to prevent release of conductive filler from an electroactive polymer composite in vivo. In this study, a silicone membrane was used to inhibit water uptake into a thermoset SMP composite containing conductive filler. Thermoset polyurethane SMPs were loaded with either 5 wt % carbon black or 5 wt % carbon nanotubes, and subsequently coated with either an Al₂O₃‐ or silica‐filled silicone membrane. It was observed that the silicone membranes, particularly the silica‐filled membrane, reduced the rate of water absorption (37°C) and subsequent T_g depression versus uncoated composites. In turn, this led to a reduction in the rate of recovery of the permanent shape when exposed to water at 37°C. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41226.     

End‐Grained Wood‐Polyurethane Composites, 1

Summary: In order to improve the dimensional stability of end‐grained wood upon environmental humidity variations, a two‐step procedure was thoroughly studied which involved the osmotic impregnation of native poplar wood by PEG, followed by the reactive impregnation with HMDI, leading to polymer chain extension and polyurethane formation. It came out that the efficiency of PEG and/or polyurethane grafting within ligno‐cellulosic cell walls was intimately related to parameters such as concentration of the PEG impregnation bath, PEG molar mass, time and temperature of impregnation steps. Based on the different sample characterizations, Soxhlet extraction and density measurements, it came out that adequate experimental conditions are to carry out osmotic impregnation at 20 °C for 24 h starting from an aqueous solution of PEG ([PEG] = 0.5 mol · L^?1 and = 400 or 1 000) and reactive impregnation in bulk with a large excess of HMDI at 20 °C for 2 h. Combining scanning electron microscopy and mercury porosimetry demonstrated the selective impregnation of cell wall and wood rays which were collapsed in native wood and expanded in wood polyurethane composites.

SEM of an end‐grained wood transversal cross‐section after Soxhlet extractions successively with water and THF.     

Investigation of the electroactivity,conductivity, and morphology of poly(pyrrole‐co‐N‐alkyl pyrrole) prepared via electrochemical nanopolymerization and chemical polymerization

The copolymerization of pyrrole (Py) with N‐ethyl pyrrole, N‐butyl pyrrole, and N‐octyl pyrrole (NOPy) was carried out by electrochemical and chemical oxidation. In the electrochemical method, copolymer thin films with different feed ratios of monomers were synthesized by the cyclic voltammetry method in a lithium perchlorate (LiClO₄)/acetonitrile (CH₃CN) electrolyte on the surface of a glassy carbon working electrode. The deposition conditions on the glassy carbon, the influence of the molar ratios of the monomers on the formation of the copolymers, and the electroactivity of the copolymers were investigated with cyclic voltammetry. Nanoparticles made of a conjugate of the copolymers with different feed ratios of monomers were prepared by chemical polymerization (conventional and interfacial methods) in the presence of iron(III) chloride hexahydrate (FeCl₃·6H₂O) as the oxidant. Nanostructural copolymers with higher conductivities were synthesized by simple tuning of the preparation conditions in a two‐phase medium. Fourier transform infrared spectroscopy, scanning electron microscopy, and four‐probe conductivity measurement techniques were applied for the characterization of the obtained copolymers. The conductivity of the obtained copolymer by an interfacial method with chloroform as the organic phase was 20 times higher than the copolymer obtained via an interfacial method with toluene as the organic phase and 700 times higher than the copolymer prepared by the conventional method (for a molar ratio of 70 : 30 Py : NOPy). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Silicone‐Organic Resin Hybrid Matrix Composites

Summary: Glass fabric reinforced hybrid matrix composites of a toughened silicone resin and a vinyl ester resin were fabricated and their properties investigated. The hybrid composites consisted of multi‐layers of fiber reinforced silicone resins and vinyl ester resins. The toughened silicone resin, a crosslinkable phenylsilsesquioxane resin with high thermal and thermal oxidation resistance but relatively low T_g, was chosen to be the outer layers. The vinyl ester resin, with better strength, toughness and a much higher T_g than the toughened silicone resin, was used as the inner layers. A co‐cure process proved to establish a strong interface between the two in a hybrid composite. The hybrid composites had better flammability properties and much lower short term moisture absorption than the vinyl ester composites. The strength and modulus retention of the hybrid composites at elevated temperatures was higher than the composites using any single resin as the matrix. For example, when tested at 150 °C the flexural modulus and strength values of a twelve layer composite, with eight inner vinyl ester resin layers and four silicone outer layers, were almost an order of magnitude higher than the composite using the silicone resin alone, and were significantly higher than the one using vinyl ester resin alone. The room temperature short beam shear strength of the hybrid composites was also higher. DMA revealed that the inter‐diffusion of reactive components between the two resins was probably responsible for this synergistic effect, resulting in an α transition temperature of 182 °C for the hybrid composite, higher than that of either the silicone resin (85 °C) or the vinyl ester resin (162 °C).

     

Conducting systems based on styrene–butadiene‐block–copolymers: Microstructural characterization

This work reports on the preparation and structural and electrical characterization of composites consisting of HSBR, polypropylene (PP), and carbon black (CB) blends, comparing the data obtained from more or less rich PP samples. Structural analysis provided evidence of the plasticizing or crosslinked effects on the properties of composites, when CB is present in the initial system, as well as of the excellent conducting properties of CB composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 646–653, 2002; DOI 10.1002/app.10360     

Mechanical properties of conducting H‐type polysiloxane–polypyrrole graft copolymers and polytetrahydrofuran–polypyrrole block copolymers

The mechanical properties of block copolymers of polypyrrole and pyrrolyl‐ended azobis‐polytetrahydrofuran (TPPy) and graft copolymers of pyrrolyl‐ended H‐type polydimethylsiloxane (SPPy) were investigated and compared with those of polypyrrole (PPy). Conducting films were prepared electrochemically at a constant potential and doped with p‐toluene sulfonate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1663–1666, 2002     

Comparison of the corrosion protection of mild steel by polypyrrole–phosphate and polypyrrole–tungstenate coatings

The electrodeposition of polypyrrole–phosphate (PPy–P) and polypyrrole–tungstenate (PPy–W) on mild steel (MS) were achieved in an oxalic acid medium with cyclic voltammetry techniques. Adherent and homogeneous PPy–P and PPy–W films were obtained. The corrosion behavior of mild steel with phosphate (PPy–P) and tungstenate (PPy–W) composite coatings in 3.5% NaCl solutions were investigated through a potentiodynamic polarization technique, open‐circuit potential–time curves, and electrochemical impedance spectroscopy (EIS). On the basis of a physical model for corrosion of mild steel composites, Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy–W coatings could provide much better protection than the PPy–P and polypyrrole coatings. The effects of the phosphate and tungstenate process parameters on the morphology and structure of the passive films were investigated by scanning electron microscopy and electron dispersion X‐ray analyses. The results reveal that the PPy–P and PPy–W coated electrodes offered a noticeable enhancement in protection against corrosion processes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Conducting polymer composites of zinc‐filled urea–formaldehyde

This article is concerned with the preparation and characterization of composite materials prepared by the compression molding of mixtures of zinc powder and urea–formaldehyde embedded in cellulose powder. The morphologies of the constituent, filler, and matrix were investigated by optical microscopy. The elaborated composites were characterized by density, which was compared with calculated values, and the porosity rate was deduced. Further, the hardness of samples remained almost constant with increasing metal concentration. The electrical conductivity of the composites was less than 10^?11 S/cm unless the metal content reached the percolation threshold at a volume fraction of 18.9%, beyond which the conductivity increased markedly, by as much as eight orders of magnitude. The obtained results interpreted well with the statistical percolation theory. The deduced critical parameters, such as the threshold of percolation, the critical exponent t, and the packing density coefficient were in good accord with earlier studies. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2011–2015, 2005     

Immobilization of invertase in conducting polypyrrole/PMMA‐co‐PMTM graft copolymers

In this study, invertase was immobilized in copolymer electrodes constructed. Three different types of polymethyl methacrylate‐co‐polymethyl thienyl methacrylate matrices were used to obtain copolymers that were characterized by FT‐IR spectroscopy. Immobilization of enzymes was carried out by the entrapment of the enzyme in conducting polymer matrices during electrochemical polymerization of pyrrole through thiophene moieties of polymers. Immobilization of the enzyme was achieved by application of 1.0 V constant potential on a platinum electrode for 30 min in solution. The effects of temperature and pH on the activity of the enzyme electrodes were examined and operational stability studies were done. The changes in the maximum reaction rate and the variations in the Michaelis–Menten constant were studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 502–507, 2005     

Conducting epoxy networks modified with non‐covalently functionalized multi‐walled carbon nanotube with imidazolium‐based ionic liquid

Multi‐walled carbon nanotube (MWCNT) was non‐covalently functionalized with room‐temperature ionic liquid (IL), 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate and blended with epoxy pre‐polymer (ER) with the assistance of ultrasonication in the presence of acetone as a diluting medium. The ability of IL in improving the dispersion of MWCNT in epoxy pre‐polymer was evidenced by transmission optical microscopy. The corresponding epoxy/MWCNT networks cured with anhydride displayed an increase of the electrical conductivity of around three orders of magnitude with the addition of IL in a proportion of MWCNT/IL = 1:5 mass ratio. The effect of IL on dynamic mechanical properties and thermal conductivity was also evaluated. The improved thermal and electrical properties was attributed to the better dispersion of MWCNT within the epoxy matrix by IL, evidenced by transmission electron microscopy of the ER/MWCNT networks cured with anhydride. Raman spectroscopy was also used to confirm the interaction between MWCNT and IL. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43976.     

Preparation and characterization of cation‐exchange media based on flexible polyurethane foams

Continuous electrodeionization (CEDI) is used to deionize a solution to a level attained by mixed bed ion exchange without chemical regeneration. However, handling of ion‐exchange beads is laborious for a large‐scale CEDI system. In this study, a new type of ion‐exchange polyurethane foam containing sulfonic acid groups was synthesized by bulk condensation polymerization for use as a cation‐exchange medium. Polyurethanes are synthesized by the reaction between a diisocyanate and a polyol. Toluene diisocyanate 2,4‐80%, 2,6‐20% ( http://www.tciamerica.com/ ) was reacted with poly(propylene glycol) to synthesize a polyurethane prepolymer and then N,N‐bis(2‐hydroxylethyl)‐2‐aminoethanesulfonic acid (BES) was added to give a foam containing sulfonic acid groups. The functional polyurethane prepolymers were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR), Fourier transform infrared spectroscopy (FT‐IR), elemental analysis (EA), and gel permeation chromatography (GPC). The ion‐exchange capacity was measured as 2.5 meq/g, and the equiconductance point of the polyurethane foams were 14, 19, 29, and 33 μ/cm for BES molar ratios of 0.5, 0.7, 1.0, and 1.5, respectively. The porous plug model shows that the current flows dominantly through the solution phase of the polyurethane foam, which indicates the polyurethane foam is a suitable medium for use in a CEDI operation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1773–1781, 2002     

Humic acid/polypyrrole on a paraffin‐impregnated graphite electrode and its use in arsenic extraction

A novel and simple electrode with rapid preparation was developed with humic acid (HA) and polypyrrole (PPy) films. The method for modified electrode preparation embraced the abrasive transfer technique on a paraffin‐impregnated graphite electrode (PIGE) followed by the electrochemical incorporation of a PPy polymeric film upon bare PIGE and PIGE/HA electrodes. Cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry were used for the study of the modified electrodes. Morphological characterization was performed by scanning electron microscopy. The obtained results demonstrated that the presence of HA did not affect the electrical properties of the system but indeed provoked changes in the polymer morphology, turning it more granular. Next, PIGE/HA/PPy was tested in arsenic solutions [As(V)] because arsenic contamination of water is an important worldwide environmental issue because of the sources of arsenic contamination of water come from both natural processes and anthropogenic activities. The modified electrode displayed good and reversible extraction properties toward the analyte in acid medium and was 18% more efficient than a previously reported PPy‐modified electrode (PIGE/PPy). From an environmental standpoint, this novel application of conductive polymer properties with the chelating capacity of humic substances constitutes a first step in the development of more efficient technologies for the removal of contaminants present in soil–water media. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation,characterization, thermooxidative degradation,and stability of polyaniline/polyacrylonitrile composites in terms of direct‐current electrical conductivity retention

Electrically conducting composites based on polyaniline and polyacrylonitrile were prepared by two slightly different techniques and were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The thermooxidative degradation of the composites was studied by simultaneous thermogravimetric analysis and differential thermal analysis techniques. The stability of the composites in terms of direct‐current electrical conductivity retention was studied in an oxidative environment by isothermal and cyclic techniques. The composites were thermally stable under ambient environmental conditions; however, their properties were dependent on the method of preparation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 437–448, 2006     

End‐Grained Wood/Polyurethane Composites, 3 – Isocyanate‐Free Route

End‐grained wood/polyurethane composites were obtained by a water‐based one‐pot process free of diisocyanates. Wood was impregnated with both PEG and CBC‐functionalized PEG as a coupling agent. A thorough study of the CBC‐mediated end‐groups conversion of PEG was achieved. It came out that functionalization conditions strongly affected the polyurethane chain extension and its grafting onto the wood structure. Antiswelling efficiency measurements showed that the one‐pot procedure allowed to reach comparable dimensional stabilization than the diisocyanate‐based process previously described. Morphological analysis demonstrated that such an improvement was attributable to the formation of cell wall‐bulked WPCs.

     

Electrical and Optical Properties of Conducting Poly(3-hexylthiophene)/Multi-walled Carbon Nanotube System

Polymer multi-wall carbon nanotube (MWNT) composites were prepared and characterized as part of an effort to develop polymeric materials with improved combinations of properties for potential use in solar cell applications. Multi-walled carbon nanotube (MWNT) poly(3-hexylthiophene) nanocomposites were synthesized by in situ polymerization of monomers in the presence of different amounts of MWNTs. A process is reported to efficiently disperse multi-walled carbon nanotube (MWNT) bundles in a semiconducting polymer matrix. A uniform dispersion of the nanotubes in the polymer matrix was obtained. Characterization of the nanocomposites and the effects of MWNT concentration and dispersion on the structural, optical and electrical properties were discussed. FTIR and Raman spectroscopic investigations of nanocomposites indicate that the polymer is wrapped on the nanotubes, taking up a rigid orientation through π-π stacking. The Hall voltage measurement is followed to monitor carrier concentrations and mobilities, instead of the device fabrication and hole mobility measurements.     

Potassium persulfate-mediated preparation of conducting polypyrrole/polyacrylonitrile composite fibers: Humidity and temperature-sensing properties

Conducting polypyrrole (PPy)/polyacrylonitrile (PAN) composite fibers were prepared by the polymerization of pyrrole in the presence of PAN fibers with potassium persulfate in an acidic aqueous solution. We obtained composite fibers containing concentrations of PPy as high as 1.14% and having surface resistivities as low as 0.6 kΩ/cm² by changing the polymerization parameters, including the temperature and concentrations of pyrrole and oxidant. The tensile strength of 10.02 N/m² and breaking elongation of 32.68% for the pure PAN fiber increased up to 10.45 N/m² and 33.23%, respectively, for the composite fiber containing 0.13% PPy. The change in the resistivity of the PPy/PAN composite fiber during heating–cooling cycles in the temperature range of +5 to 120°C was examined. Scanning electron microscopy and optical microscopy images of the composite fibers showed that the PPy coating was restricted to the surfaces of the PAN fibers. Surface resistivity measurements, Fourier transform infrared spectroscopy, and thermogravimetric analysis techniques were also used to characterize the composite fibers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012