ABSTRACT
214Use of active carbon as functional fillers in elastomer composites, designed to absorb electromagnetic waves, is evoked by its porous structure (its content of micro- and mesopores). This structure, particularly the size of pores, provides a significant inner surface and allows modification. The properties of activated charcoals can be controlled by the choice of initial material, selected method of activation, conditions of treatment and so on. On the other hand, the well-developed outer surface of the activated carbon, which contains a significant number of oxygen-containing groups, determines the presence of isoelectric points (IEPs). Those are a prerequisite for initiating an interaction between the elastomer macromolecules and functional filler. Last but not least, it is the specific porous structure of activated charcoal, which implies a significant uptake of insignificant reflection of electromagnetic waves
Six types of hybrid fillers have been used in our investigation. The adsorption-texture characteristics of the fillers have been determined by various methods. They have been used as functional fillers for natural rubber (NR)- and SBR-based composites. The dielectric (dielectric constant and dielectric loss angle tangent) and microwave (reflection coefficient attenuation coefficient and shielding effectiveness) properties of the vulcanizates thus obtained have been studied.
Hybrid dual-phase fillers based on activated carbon, and nano-sized magnetite, prepared in situ were obtained for the first time. The fillers have been characterized by X-ray diffraction and photoelectron spectroscopy. The influence of magnetite content in the hybrid filler on a number of properties of the resulting NR-based composites has been investigated. The vulcanization, mechanical and dynamic properties, electrical and thermal conductivity, dielectric and microwave properties of the new materials have been determined.
First, the observed effects could be explained by the impact that deposited magnetite has on the structure and properties of the very dual-phase filler (texture characteristics and adsorption activity) as well as by the change in the intensity of elastomer-filler interactions. It has been found that the total shielding effectiveness of the composite materials filled with activated carbon, modified with magnetite, exists mainly because of the mechanism of reflection of electromagnetic power (reflective shielding effectiveness). However, in the 5-6 GHz range, it is the mechanism of absorption (absorptive shielding effectiveness) that has a crucial role for all studied composites.
Another part of our study is focused on the modification of activated carbon to improve the absorption properties as a functional filler in 215elastomeric composites intended for microwave absorbers. Impregnation method has been used as the most popular among other procedures for depositing various phases over the support (in the production of catalysts) or to surface and texture modification of adsorbents. The method allows controlled deposition of a modifying agent in the macro- and the mesopores of the activated carbon. The chosen modifying agent is ZnO.
The fillers obtained have been characterized by Auger electron spectroscopy (AES) and have been used to prepare the SBR-based elastomer composites. It has been found that the modified fillers improve several important operational characteristics of the vulcanizates containing them.
