Plasma Polymerization of Monomers onto Fillers, to Tailor their Surface Properties in Tire Compounds

Rubber reinforcement by fillers is primarily based on filler structure and surface properties. A chemical change of the surface properties while maintaining the structure allows tailoring filler properties for improved filler–polymer compatibility, resulting in improved morphological, dynamic, and mechanical properties of straight rubbers as well as elastomer blends. Plasma polymerization based on acetylene, pyrrole, and thiophene as monomers are applied to silica in order to change surface polarity and chemistry, with untreated and silane-treated silica as references. Generally spoken, the plasma coating results in reduced filler–filler interaction, improved dispersion, and increased bound rubber content in straight SBR as well as in SBR/EPDM blends. In terms of stress-strain properties, the plasma treatment results in higher moduli compared to the untreated filler. The most prominent effect was found in the stress-strain properties of straight SBR: Polythiophene-coated silica results in significantly higher moduli and tensile strength values, even higher than the silane-treated material. In the case of the polymer blend, the plasma treatment results in higher tensile strength and elongation at break values. It is important to note that no unambiguous correlation was found between filler–filler interaction and filler–polymer interaction: A lower Payne-effect does not necessarily result in a higher bound rubber content.