M. Zilberman

On the "curiosity" of electrically conductive melt processed doped-polyaniline/polymer blends versus carbon-black/polymer compounds

Carbon black/polymer conductive compounds have been known and commercially used for many years, and their scientific background is quite well established and documented. In contrast, polyaniline/polymer blends (PANI/polymer) processible via dry (solvent-free) melt-shaping methods are still relatively unknown, insufficiently understood, and only a single commercial PANI/polymer blend for dry melt processing is presently commercially available (PANI/PVC, Zipperling, Germany). In this communication, a mechanism of PANI structuring in dry melt-processed PANI/polymer systems is suggested. In addition, the differences between these two conductive “fillers” (carbon black and PANI) in melt blending and processing, and the rules governing their mode of dispersion in the solidified polymer matrix, which determines the blends conductivity levels, are discussed. In future papers, detailed experimental evidence, supported by molecular modeling calculations, for the PANI/polymer systems, will be presented to support the ideas expressed in the present communication further. Conducting carbon blacks (CB) often consist of elongated aggregates (low aspect ratios) composed of very small (nanometric) primary particles sintered together. Upon melt blending with a polymer and processing, the CB may undergo deagglomeration, aggregate erosion and fracturing, and reagglomeration, resulting in either a uniform or more often a nonuniform distribution of the black particles [1, 2]. The level of the particle distribution nonuniformity varies and, as a rule, higher nonuniformity levels result in higher conductivity levels owing to the formation of conducting paths [3, 4]. For example, nonuniform distributions are formed in semicrystalline polymers, where carbon black particles are selectively located within the amorphous regions, and in polymers having low affinity to the surface of the carbon black particles [5]. Thus, in semicrystalline polymers and particularly in relatively nonpolar and low surface tension polymers, represented, for example, by polyethylene and polypropylene (PP), the tiny carbon black particles tend to segregate and even percolate, by forming conducting networks at extremely low content of the CB particles, e.g. 3 wt% Ketjenblack EC in PP [6], as in Fig. 1(a). Other parameters, such as melt-blending conditions including shear level and shear history, are less important within the practical acceptable regions of blending regarding the CB structuring and conductivity levels obtained. More uniform distributions of carbon black particles are obtained in amorphous polar polymers having higher surface tensions, similar to that of CB (~50 dyne/cm). Thus, by dispersing carbon black (Ketjenblack EC) particles in a soft, amorphous and polar random co-polyamide 6/6.9 (=poly[HN– (CH2)5 – CO] – co – [HN – (CH2)6 – NH – CO – (CH2)7 – CO]) [7,8], percolation has not been realized up to the

Melt-processed electrically conductive polymer/polyaniline blends

Abstract In the present study, conductive polyaniline-p-toluene sulfonic acid (PANI-pTSA) blends with thermoplastic polymers were prepared by melt processing. The blends′ characterization focused on their morphology in light of the components′ interaction and the resulting electrical conductivity. The PANI-pTSA blends were compared with blends containing PANI-DBSA (dodecyl benzene sulfonic acid). Generally, the level of interaction between the doped polyaniline and the matrix polymer determines the blend morphology and the resulting electrical conductivity. Similar solubility parameters of the matrix polymer and doped PANI lead to high levels of PANI dispersion within the matrix and to formation of conducting paths at low PANI contents. The morphology of a conducting network is described by a primary structure of small dispersed PANI particles interconnected by a secondary, short-range, fine fibrillar structure. The doped PANI network locates within the amorphous regions of a semicrystalline matrix, leadi...

Structured electrically conductive polyaniline/polymer blends

This paper describes electrically conductive polymer blends consisting of polyaniline (PANI) dispersed in a polymer matrix. Melt blending of previously mixed, coagulated and dried aqueous dispersions of PANI and the polymer matrix lead to high conductivities at extremely low PANI concentrations (∼0.5 wt% PANI). In these blends the surface properties (surfactants used) of the PANI and the polymer particles play a major role in the structuring process, in addition to the very small size of the PANI particles. In another approach, i.e. conventional melt blending of PANI powder with a given polymer powder, the success of generating an efficient conductive network depends on the PANI/polymer interaction level. A high interaction level (for example, similar solubility parameters) leads under dynamic hot blending conditions to the formation of conductive networks, but still at relatively high PANI concentration (>10 wt% PANI). To further reduce the PANI conductivity threshold concentration, ternary PANI/polymer/polymer blends can be designed, in which PANI is selectively attracted to the minor polymer component, thus generating double-percolation structures. The threshold PANI concentration in the ternary blends may be reduced by a factor of ∼2 compared to the binary blends. Further reduction can be expected in special ternary blends designed so that the PANI particles will mostly locate at the interfaces, rather than within the dispersed minor polymer particles. The blending method of aqueous dispersions is limited to matrix polymers which can be synthesized by emulsion polymerization. Thus, the conventional melt blending procedure and also the formation of ternary blend systems are particularly beneficial for condensation-type polymers, whereas melt blending of PANI/polymer powders prepared by the aqueous dispersions method is beneficial for the addition-type polymers. Copyright

Melt-Processed, Electrically Conductive Ternary Polymer Blends Containing Polyaniline

Conductive binary and ternary blends containing polyaniline (PANI) were developed through melt blending. The investigation of the binary blends focused on their morphology in light of the interactions between their components and on the resulting electrical conductivity. Similar solubility parameters of PANI and a constituting polymer lead to a fine PANI particle segregated dispersion within that polymer and to the formation of conducting paths at low PANI contents. In ternary blends consisting of PANI and two immiscible polymers, the PANI preferentially locates in one of the phases due to increased interactions between PANI and the preferred polymer. This concentration magnification effect leads to increased electrical conductivity at lower PANI nominal contents. The electrical conductivity of a ternary blend is mainly determined by the effective PANI content in the preferred phase, by the level of PANI fracturing in this phase, and by the details of the conductive network structure created in the co-continuous structure blend.

The glass transition temperature of 6/6.9 random copolyamides

Abstract The glass transition temperatures ( T g ) of a 6/6.9 random copolyamide series have been investigated as a function of copolymer composition. The analysis was carried out using the technique of differential scanning calorimetry, and the degree of crystallinity was determined by wide angle X-ray diffraction. It was found that conventional models for determining T g values do not fit the copolymers of this study. An appropriate description is achieved by considering a model that accounts for molecular interactions. Both hydrogen bond content and degree of crystallinity lead to the observed deviation in T g from the values predicted by conventional models.

Structure and properties of 6/6.9 copolyamide series. I. Amorphous phase

The amorphous phase of a series of random 6/6.9 copolyamides was investigated. It was characterized by the glass transition temperature (Tg) and the hydrogen bond content, as a function of the copolymer composition, compared to the corresponding homopolymers, polyamide 6 and polyamide 6.9. The hydrogen bonds in the amorphous phase have a major influence on the copolymer properties. The glass transition temperature decreases as either comonomer content increases, attaining a minimum value at about 1 : 1 molar composition. This is due to the decreased content of hydrogen bonds, their broader strength distribution, and the decreased degree of crystallinity. In addition to the usual effects, quenching in the present system causes the formation of a less dense and less regular hydrogen bonds network, reducing the Tg. Following room temperature aging, the usual hydrogen bond content is restored.

Electrically conductive extruded filaments of polyaniline/polymer blends

Blends of plasticized polystyrene and conductive polyaniline (PANI) were prepared by melt processing, and extruded filaments were obtained by using a capillary rheometer. The effect of flow conditions, including temperature and shear rate, on the morphology of the blends and on the resulting electrical conductivity were investigated. Under a combination of specific processing and given blend compositions, the electrical conductivity was found to be independent of shear level over a wide range of shear rates. Thus, conductive melt processible PANI-based blends can be designed, however relatively high PANI concentrations (well above percolation) are required. Blend systems can be developed to further reduce the PANI concentration in ternary component blends.

Computer-aided selection of a polymer matrix for polyaniline conductive blends

The selection of a polymer matrix for a conductive blend with polyaniline and para-toluene sulfonic acid (PANI-pTSA) was performed using molecular simulation techniques, both a fast quantitative structure–properties relationship method as a first screening phase followed by atomistic simulation. Using the atomistic simulation method, the solubility parameters and the heat of mixing of each blend were calculated to enable the determination of compatible matrices in blends with PANI-pTSA, which was validated by experimental scanning electron microscopy fractographs. Based on such calculations, polycaprolactone (PCL)/PANI-pTSA phase diagrams were estimated, showing slight miscibility of polydispersed PANI in PCL, particularly the short chains fraction, at the elevated melt processing temperature. It was suggested that this partial miscibility at the elevated temperature might lead to a conductive network morphology of PANI in PCL at room temperature, because of phase separation and precipitation of soluble PANI molecules, upon cooling and solidification of the melt.

Structure and properties of 6/6.9 copolyamide series. II. The crystalline phase

Abstract The crystalline phase of a series of random 6/6.9 copolyamides was studied. The crystallization and fusion behavior, crystallography, and morphology were investigated. A decrease in melt crystallization temperature and rate, and an increase in cold crystallization temperature are caused by increasing either monomer content. The hydrogen bonding formation is interrupted by the comonomers, reducing the degree of crystallinity (17–41%). Melting temperature depression caused by the increase in comonomer 6.9 content is accompanied by a decrease in crystal size. The measured melting temperatures are lower than the predicted ones (according to Flory), due to comonomer incorporation in the crystal lattice. The copolyamides consist of α-form and 63–89% γ-form crystals. The γ crystal content increases with an increase in the comonomer 6.9 content. Polyamide 6 and the copolyamides rich in caprolactam exhibit sheaflike spherulites which become less perfect with an increase in the comonomer 6.9 content. The o...