Sensors for chemicals based on electrically conductive immiscible HIPS/TPU blends containing carbon black

Carbon Black (CB)-containing immiscible polymer blends based on high-impact polystyrene/thermoplastic polyurethane (HIPS/TPU) were studied as sensing materials for an homologous series of alcohols, including, methanol, ethanol and 1-propanol. The studied immiscible blend was designed to exhibit a double-continuity structure i.e., the CB particles form chain-like network structures within the TPU phase, which forms a continuous phase within the HIPS matrix. Extruded HIPS/TPU/CB filaments produced by a capillary rheometer process at various shear rate levels were used for the sensing experiments. All filaments displayed a selective resistance changes upon exposure to the various alcohols combined with reproducibility and recovery behaviour. An attempt is made to identify the dominant mechanisms controlling the sensing process in a CB-containing immiscible polymer blend characterized by a double-continuity structure. The distinct structure and composition of the HIPS/TPU interphase region were found to have a crucial role in the sensing mechanism, determining the selectivity of the filaments toward the studied alcohols. Additionally, the sensing performance of HIPS/TPU/CB system is compared to recent results for TPU/CB compounds, polypropylene/TPU/CB and HIPS/ethylene vinyl acetate/CB immiscible polymer blends.     

The sol/gel contribution to the behavior of γ-irradiated poly(vinylidene fluoride)

Poly(vinylidene fluoride) films were γ-irradiated in the dose range of 1–20 Mrad, resulting in up to 74% gel. The irradiated polymer undergoes both crosslinking and chain scission, about 5 : 3 events, respectively. Swelling measurements indicate an increasing crosslink density with the gel content, already at the lower doses. Thermal analysis of the gel fraction and the unextracted irradiated samples shows that although crosslinking affects the crystallization, degree of crystallinity, and the melting characteristics, the behavior of the crosslinked material is predominantly controlled by the extractable sol fraction which consists of the more mobile original chains, branched chains, and degraded ones. The crosslinks, already at low density, retard the development of ordinary crystalline polymer morphology.     

Precipitation from glassy polymer solutions

Solid solutions of general-purpose polystyrene containing crystalline tetrabromoxylene, tetrachloroxylene, or tetrachlorobenzene were prepared. The effects of the low molecular weight crystalline additive concentration and the thermal history on the thermal properties of the system have been studied. The system solubility, rejection of solute, etc., were characterized by such techniques as rheology, thermal analysis (DSC), and Vicat softening point.     

Crystallization of crystalline/crystalline blends: Polypropylene/polybutene-1

The crystallization, from molten blends, of polypropylene (PP) and polybutene-1 (PB), two highly crystallizable, polymers, their interaction in the amorphous phase, and the resulting tensile mechanical properties were studied. The crystallization was followed by DSC, showing two separate PP and PB crystallization processes which are affected each by the presence of the other component. The crystallization temperature of PP is significantly affected only in PB rich blends whereas that of PB is affected in the whole composition range. The PP crystalline phase, acting as a nucleating agent, increases the PB crystallization temperature whereas the PP amorphous phase, acting as a high viscosity polymeric diluent, reduces the PB crystallization temperature. The first effect is dominant at low PP content, and the second one becomes increasingly effective with increasing PP content in the blend. The interaction between the two polymers in the amorphous phase was studied by applying dynamic mechanical analysis, in which a single glass transition was observed for the blends and its temperature was found to vary with the blends' composition. Tensile mechanical properties of blends were found to be more sensitive to thermal treatments, such as isothermal crystallization or annealing at elevated temperatures, than single component systems. Such thermal treatments enable better structured blends to be formed, resulting in mechanical properties with no abrupt changes in the whole composition range.     

Effect of particulate reinforcement on creep behavior of polyurethane foams

The compressive creep behavior of rigid unreinforced and particulate reinforced polyurethane foams at different densities, filler contents, temperatures, and loads was investigated. The creep behavior could be described by a power function of time and its temperature dependence by an Arrhenius type relation. The addition of particulate rigid fillers enhances the creep resistance as well as the foam elastic modulus. Particulate reinforcement of polyurethane foams was found to be efficient for the higher foam densities, especially for higher filler levels.     

Immiscible ethylene vinyl acetate and nylon blends processed below nylon melting temperature

This article focuses on unique compounding and processing conditions at a temperature slightly below the melting temperature of the dispersed phase and well above the melting peak temperature of the matrix. Compounding and processing were carried out at the same temperature. Fibrillar morphologies were obtained by blending ethylene vinyl acetate (EVA) copolymer with nylon 6 (N6) and compounding and processing them slightly below the N6 melting temperature. A hot, soft-solid particle drawing mechanism that operates in such processing conditions caused fibrillation of the N6 particles and formation of highly oriented fibril-filled composites throughout the entire volume. Morphological observations were made in the core region. Enhancement of some mechanical properties and interesting morphological structures were found in some of the blends. The melt elasticity, which was measured by the die swell of the filaments, was maximum at a temperature slightly below the N6 melting temperature, which supported the concept of fibrillation by processing it slightly below the melting temperature of the dispersed phase. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 661–671, 2001     

Electrical properties of hybrid carbon black/carbon fiber polypropylene composites

The electrical conductivity and morphology of injection molded polypropylene based composites containing two conductive fillers, carbon black (CB) and carbon fibers (CF) were studied. Injection moldings containing both, CB and CF, where the content of each filler was above its own percolation threshold, resulted in similar or lower values of overall composite volume resistivity compared with the resistivity of systems filled only with CB at the corresponding content. However, the resistivity of two-filler systems is always higher than the resistivity of systems filled only with CF at the corresponding content. The morphology and fiber length analysis of the injection molded composites are quite intriguing. Fiber orientation in the injection molded two-filler systems was found to be almost perpendicular to the melt flow direction, with no significant skin-core fiber orientation patterns, contrary to the typically observed fiber orientation in injection molded fiber filled composites. Moreover, the CF breakage in the presence of the CB was found more intense than when just CF is used, resulting in shorter fibers with narrower length distributions. This unexpected fiber behavior is responsible for the unexpected electrical behavior. However, the coexistence of CB and CF electrically conductive networks, supporting each other, was confirmed, in spite of the mechanical disturbances caused by the presence of fibrilar and particulate fillers.     

In situ acoustic emission monitoring and mechanical testing in the scanning electron microscope

On sabbatical leave from: Department of Materials Engineering, Technion, Haifa, Israel.     

Tensile behaviour of multilayer thermoplastic composites

Multilayer thermoplastic composite sheets consisting of alternating layers of two materials mainly differing in their ductility were laminated. The mechanical behaviour, irreversible deformation mechanism and fracture of two systems made up of (I) polystyrene (PS)/Noryl and (II) rigid PVC/PVC-EVA blend were studied. In System I the tensile properties change with composition up to 40 to 60 vol % PS while at higher PS content the latter dictates the behaviour of the system. Upon stretching, crazes and cracks were formed in the PS layer. Their propagation was retarded by the Noryl Layers. Subsequently the PS was deformed to rather high strains, otherwise not attainable, and shear bands, which were initiated at the crack tips, developed in the Noryl layers. The interaction between cracks and shear zones resulted in delocalized deformation and fracture delay. In System II the low strain properties linearly change with composition, identical to the behaviour of blends of similar compositions. However the ultimate elongation of three layers sheets and PVC/EVA blends attain maximum values which are higher than those of the components themselves, while that of five layer sheets changes gradually with composition. The good interlayer adhesion in all the systems studied enables cooperative irreversible deformation processes reflected by the mechanical behaviour and the fracture surface morphology of the composite sheets.