Reinforced Elastomers: Interphase Modification and Compatibilization in Rubber-Based Nanocomposites

Abstract

An extended review is presented on the structure and properties of filler-matrix interface in reinforced elastomeric materials, since the above characteristics are critical for the overall performance of the related products. The current trends for interphase modification in rubber systems containing various fillers, such as Carbon black, Silica, Calcium Carbonate, Clays with emphasis on clay nanofillers, as well as Graphene is discussed. The use of fibrilar reinforcements is also reported, including traditional materials, such as Natural fibres, as well as Aramids and Carbon Nanotubes. On the other hand, the concept of hybrid composites, i.e., those composed of a mixture of matrices or reinforcements, further enhances the versatility of those materials, since it provides new possibilities of extending the area of rubber applications. In fact, the above products combine the property improvement attributed to each one of the system’s components and, moreover, they can usually take advantage of their synergistic action. In the same context the role of some other additives, necessary to adjust mechanical properties (e.g. plasticizers) or to promote phase miscibility in complex systems, such as compatibilizers, was investigated. The vulcanization of elastomeric materials is a critical step, with high impact on the properties of final products. In fact, the extent of this reaction, the cross-links density along with the other network parameters, are some important factors controlling the overall behavior of the vulcanized rubber and, therefore, monitoring, control, and modeling of rubber vulcanization are also examined in this work. The above review showed that the main reason for reinforcing rubbers is to improve their mechanical and thermal properties, as well as to reduce cost and sometimes the weight of a construction. It seemed that recent advances in nanoparticles have attracted much attention in manufacturing of rubber nanocomposites, because of the small size of filler and the corresponding increase in the surface area, which leads to the required mechanical properties at low filler loading. Carbon nanotubes and graphene nanoparticles are promising materials, offering good electrical properties. Surface treatment of the filler particles with the appropriate coupling agents is often vital, in order to promote proper dispersion and adequate filler/matrix interactions. Also, efficient dispersion of the reinforcement into rubber matrices usually needs the assistance of functionalized polymers, i.e., compatibilizers. Among the different modifying agents, maleic anhydride is the most commonly used and seems to ensure best results at relatively low cost. Finally, the cross-linking parameters must be controlled for an optimal network formation. The newly developed polyblends, based on mixtures of rubbers with polyolefins, require the suitable compatibilization in order to reveal their unique properties. Nanoparticles, being very efficient reinforcing agents even at low concentrations, were also found to play the role of compatibilizer for these mixtures of immiscible polymers.