R. Tchoudakov

Sensors for liquids based on conductive immiscible polymer blends

Abstract The present paper discusses the application of conductive immiscible polymer blends as sensor materials for detection of organic liquid solvents and of their vapors. Immiscible polymer blends of high impact polystyrene (HIPS), ethylene vinyl acetate copolymer (EVA) and carbon black (CB), and compounds of EVA/CB have been used to produce a series of electrically conductive filaments by a capillary rheometer process. In these immiscible blends, HIPS serves as a matrix and EVA as the semi-crystalline dispersed phase. The enhancement of conductivity in these blends is due to the attraction of CB to EVA, giving rise to conductive networks. The dc electrical resistivity of extruded filaments, produced at different shear levels, is found to be sensitive to various organic liquid solvents. The shear rate, at which the filaments are produced, has an important effect on the HIPS/EVA/CB filaments sensitivity. The compositions studied were close to the double-percolation structure believed to perform best as sensor materials. The HIPS/EVA interface seems to play an important role in the sensing process. In some cases, liquid contact/drying cycling of filaments indicates stabilization of the sensitivity change, making the sensing process reversible. Liquid transport principles are an important basis for interpretation of the sensing behavior of immiscible blend-based filaments in contact with liquids.

Electrically conductive composites based on epoxy resin with polyaniline-DBSA fillers

A conductive epoxy-anhydride system containing polyaniline (PANI)-dodecylbenzenesulfonic acid (DBSA) has been developed and characterized. Two forms of PANI-DBSA, powder and paste (containing excess DBSA), have shown that excess DBSA in the paste contributes to improved dispersion of PANI-DBSA in the resin, and thus a lower percolation threshold is found. Excess DBSA, however, retards the curing reaction of epoxy/hardener system, but this deficiency can be remedied by using higher accelerator concentrations. Similar trends were found by incorporation of PANI-DBSA coated mica particles, however, the PANI-DBSA engulfed mica particles result in a much lower percolation threshold compared to the PANI-DBSA powder or paste. SEM observation provides useful information for understanding the conductivity behavior of the conductive epoxy systems. Significantly different morphologies are observed for the PANI-DBSA powder and paste dispersed in the epoxy matrix.

Segregated structures in carbon black-containing immiscible polymer blends: HIPS/LLDPE systems

The structure/electrical resistivity relationship in CB-loaded immiscible HIPS/LLDPE blends was studied. Effects of CB content and location, dispersed polymer phase size and shape, dispersed phase viscosity, and processing procedures were examined. The elongated dispersed phase in CB-containing blends is essential for promoting conductivity in formulations prepared by melt mixing and compression molding. However, the same formulations proved highly resistive when injection-molded, due to orientation and excessive shearing.

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.

Physical and chemical interactions in melt mixed nylon-6/EVOH blends

Abstract Nylon‐6 (Ny‐6) and ethylene‐vinyl alcohol copolymer (EVOH) binary blends were prepared in various compositions via dynamic melt blending. In addition, 50/50 blends of EVOH with nylon‐6/6.9 (Ny6/6.9) and nylon‐11 (Ny‐11) were prepared to study the effect of nylon type on the structuring process under melt mixing. The phase morphology and the crystallization behavior of the blends were investigated using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The insoluble content was studied by solvent extraction. The mixing torque was found to increase with mixing time for intermediate Ny‐6 contents, indicating chemical reactions and hydrogen bonds formation between the polymers. Based on FT‐Raman spectroscopy chain extension is suggested to be the main chemical reaction between EVOH and Ny‐6. The different interaction levels obtained for the Ny‐6/EVOH blends affect their properties. The melting temperature of one component decreases as the content of the other component is increased. EVOH has lower crystallization degree when its content is lower; conversely, Ny‐6 crystallinity increases for some compositions compared to the neat polymer. Storage modulus and glass transition temperature values of the blends are between those of the neat polymers according to composition. However, positive deviation was obtained for the 50/50 Ny‐6/EVOH blend owing to the chemical reaction between the polymers. SEM micrographs of fractured surfaces exhibit quite uniform, almost as a single‐phase morphology, indicating high interaction level between the polymers. SEM/EDS of etched samples revealed that the dispersed particles in the blends are on a submicron scale.

MULTI‐COMPONENT POLYMER SYSTEMS PROCESSED WITHIN A NARROW TEMPERATURE WINDOW

The present study deals with model systems based on two immiscible polymers, polypropylene (PP) and copolyamide (PA), containing nano‐size inorganic TiO2, processed in a narrow temperature window, just below the melting temperature of the dispersed copolyamide phase. The blends were compounded using a twin‐screw intermeshing extruder followed by injection molding. The effect of processing temperature and blend composition on morphology, mechanical, rheological and thermal properties of the model systems containing nano‐sized TiO2 and their references were explored. It was found that in‐situ fibrillation of the PA phase occurred in the blends based on PP of a relatively high melt flow index, MFI = 12 g/10 min and higher. The nano‐sized TiO2 particles were located upon and within the PA phase and have slightly influenced the shape of the PA fibrils. A correlation between the processing temperature, morphology and properties of the composites is presented.

Rheology/Resistivity Correlation in Carbon Black-Containing Immiscible Polymer Blends

Immiscible polymer blends are interesting host multiphase systems for the incorporation of low concentrations of fine electrically conductive fillers, such as carbon black (CB). The filler tends to accumulate preferentially in certain regions within the multi-phase matrix, inducing the formation of segregated structures whereupon CB may form a conductive network [Gubbels et al, 1995; Breuer et al., 1997]. Thus, the electrical conductivity is enhanced, and the critical CB content essential for percolation is significantly reduced. The low filler content is of practical advantage due to the tendency of high CB contents to complicate polymer compounding and processing and to diminish mechanical properties.