Silica-reinforced natural rubber for low rolling resistance, energy-saving tires: aspects of mixing, formulation and compatibilization

Natural rubber (NR) is a renewable material, which combines excellent mechanical and dynamic properties. It has been and still is in use in a variety of applications, mostly in the form of filled vulcanizates. Silica filler technology used for rubber is relatively new, since silica can reinforce rubber and gives high performance of articles, particularly in tires. The major problem of this combination is that silica has a relatively high polarity by nature and can not easily be mixed with NR which is a non-polar material. In addition, NR is rather susceptible to degradation under excessive mixing conditions, compared to its synthetic counterparts. Bifunctional organosilane coupling agents effectively solve the incompatibility drawback as they are able to hydrophobize silica to become more compatible with hydrocarbon rubber and to additionally strengthen the interaction between silica and rubber. Bis-(triethyxysilypropyl) tetrasulfide (TESPT) is the most commonly silane coupling agent in the rubber industry nowadays. However, silane chemistry of rather complicated because of the necessary in-situ reactions during rubber processing. The mixing temperature necessary for silica/silane filled rubber requires a high energy input. In the presented project, the mixing conditions and formulation for the silica/silane/NR system are optimized ad subsequently a search for alternative routes for improving processability and utility of silica-rubber mixes is carried out. Polar-modified natural rubber is of interest in this contex because it may lead to a reduction or a possible replacement of conventional silane coupling agents.