Polymer blends with ordered distribution of conductive filler

This review highlight approaches to the formation of an ordered distribution of conductive filler in polymer blends. This distribution leads to a significant decrease of the percolation threshold in the polymer mixture, i.e. to a decrease in the critical concentration of the filler, at which the transition of the system from a non-conductive to a conductive state occurs. This improves the mechanical properties of the composition and its processability. It is shown that the ordered structure of the filler is formed in the polymer blend upon mixing the components in the melt under the action of three factors - thermodynamic (the ratio between the values of the interfacial tension of the filler-polymer A and filler-polymer B, as well as between polymers A and B), kinetic (the ratio between viscosities of polymer components A and B) and technological (the intensity and temperature of processing, as well as the order of introduction of a filler into a heterogeneous polymer matrix, which can enhance or suppress the effect of thermodynamic or kinetic factors). On the example of the works performed by the author on mixtures of thermoplastics filled with electrically conductive carbon fillers such as carbon black and carbon nanotubes, as well as a metal filler - dispersed iron, with the involvement of literature data on filled polymer blends, the influence of each of the factors on the formation of an ordered structure of the conducting phase in polymer blends is shown.

Simple Fabrication and Carrier Type Modification of Semi-Conductive C/Al2O3 Composites by Powder Mixtures and Pulsed Electric Current Sintering

Semi-conductive C/Al2O3 ceramic composites were successfully fabricated by a pretty simple approach, combining a powder mixture process and pulsed electric current sintering. In order to obtain homogeneous distribution of carbon contents, popular polymers were used as carbon fillers to mix with Al2O3 powder by a wet ball milling step. The sintering was conducted by pulsed electric current sintering without any special requirement of the reductive environment like in conventional sintering. Density of bulk bodies, states of carbon contents after sintering and the electrical properties were analyzed in this study. Although the density of sintered bodies and their electrical properties were not superior, those characteristics of C/Al2O3 ceramic composites in this study were still comparatively high among semi-conductive ceramics. Especially, the carrier type of semi-conductive C/Al2O3 composites could be modified easily by adding polycarboxylic acid (PCA) in the powder mixture as a dispersant.

Effects of Basalt and Carbon Fillers on Fire Hazard, Thermal, and Mechanical Properties of EPDM Rubber Composites

Due to growing restrictions on the use of halogenated flame retardant compounds, there is great research interest in the development of fillers that do not emit toxic compounds during thermal decomposition. Polymeric composite materials with reduced flammability are increasingly in demand. Here, we demonstrate that unmodified graphene and carbon nanotubes as well as basalt fibers or flakes can act as effective flame retardants in polymer composites. We also investigate the effects of mixtures of these carbon and mineral fillers on the thermal, mechanical, and rheological properties of EPDM rubber composites. The thermal properties of the EPDM vulcanizates were analyzed using the thermogravimetric method. Flammability was determined by pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry.

Mechanical, Thermal, Electrical Characteristics and EMI Absorption Shielding Effectiveness of Rubber Composites Based on Ferrite and Carbon Fillers

In this work, rubber composites were fabricated by incorporation of manganese-zinc ferrite alone and in combination with carbon-based fillers into acrylonitrile-butadiene rubber. Electromagnetic parameters and electromagnetic interference (EMI) absorption shielding effectiveness of composite materials were examined in the frequency range 1 MHz–3 GHz. The influence of ferrite and fillers combination on thermal characteristics and mechanical properties of composites was investigated as well. The results revealed that ferrite imparts absorption shielding efficiency to the composites in tested frequency range. The absorption shielding effectiveness and absorption maxima of ferrite filled composites shifted to lower frequencies with increasing content of magnetic filler. The combination of carbon black and ferrite also resulted in the fabrication of efficient EMI shields. However, the EMI absorption shielding effectiveness was lower, which can be ascribed to higher electrical conductivity and higher permittivity of those materials. The highest conductivity and permittivity of composites filled with combination of carbon nanotubes and ferrite was responsible for the lowest absorption shielding effectiveness within the examined frequency range. The results also demonstrated that combination of ferrite with carbon-based fillers resulted in the enhancement of thermal conductivity and improvement of mechanical properties.

Comparison of Three Interfacial Conductive Networks Formed in Carbon Black-Filled PA6/PBT Blends

Interfacial localization of carbon fillers in cocontinuous-structured polymer blends is well-known as a high-efficiency strategy for conductive network formation. However, a comparison with interfacial localization of carbon fillers in sea-island-structured polymer blends is lacking. Here, three types of highly efficient conductive networks formed on the basis of interfacial localization of carbon black (CB) in polyamide 6 (PA6)/poly(butylene terephthalate) (PBT) blends with different blend compositions (80/20, 50/50 and 20/80 vol/vol) were investigated and compared in terms of electrical resistivity, morphology as well as rheological and mechanical properties. The order of the electrical percolation threshold of CB in the three blends is 50/50 < 20/80 < 80/20, which can be attributed to different network structures. The rheological percolation thresholds are close to the electrical ones, confirming the formation of CB networks. The formation mechanisms for the three types of CB network structures are analyzed. All the three types of PA6/PBT-6 vol% CB composites showed improved tensile strength compared with PA6/PBT blends, being in favor for practical applications.