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 of fillers while maintaining the filler structure allows tailoring filler properties for improved filler-polymer compatibility. The aim of this work is to increase filler-polymer interaction and reduce filler-filler interaction, resulting in improved morphological, dynamic and mechanical properties, especially for tire applications.

Plasma polymerization is applied to silica in order to change surface polarity and chemistry. Coatings based on acetylene, pyrrole and thiophene are applied, and the filler is tested in a SBR matrix; with untreated and silane-treated silica as references. The three plasma coatings result in a reduction of the Payne effect compared to untreated silica, showing the reduced filler-filler interaction. Bound rubber content can significantly be increased by the plasma-thiophene and -acetylene treatment, with filler-polymer interaction being significantly higher than in the case of silane-treated silica. It is important to note, that no unambiguous correlation was found between filler-filler interaction and filler-polymer interaction. The dispersion of the filler was improved by the plasma coating and reached the same level as silane-treated silica. The most prominent effect was found in the stress strain properties: Polythiophene-coated silica results in significantly higher moduli and tensile strength values, even higher than the silane-treated material.

Plasma-polymerization treatments of silica result in improvements of material properties, and different types of coatings have their own specific impact on the material properties.