Verification of Interactions between Silica and Epoxidized Squalene as a Model for Epoxidized Natural Rubber

Unmodified squalene (Sq) and epoxidised squalene (ESq), as models for natural rubber and epoxidised natural rubber, were mixed with silica in a reactor at 140 – 145ºC, which corresponds to the optimal mixing dump temperature of silica-filled natural rubber or epoxidised natural rubber compounds. The mixtures were prepared with and without bis-(triethoxysilylpropyl) tetrasulphide (TESPT) silane coupling agent. The bound silica in the mixtures was extracted and checked for its composition by using Fourier-transform infrared (FTIR) spectroscopy. The results indicate that Sq and ESq with the help of TESPT can chemically link to the silica surface, as the FTIR spectra of purified bound silicas show absorption peaks of hydrocarbon structures. The epoxidised squalene also produces chemical interaction with silica in the absence of TESPT, but to a lesser extent compared to the one with TESPT, as indicated by the absorption intensity. On the other hand, the silica in the Sq mixture without TESPT shows no trace of hydrocarbon, indicating that there is no noticeable chemical interaction involve

Rezepturoptimierung für kieselsäureverstärkte Naturkautschukmischungen

The rubber formulation plays a significant role in the properties of NR compounds filled with silica. In this work, the influences of various silicas, silane coupling agents and diphenylguanidine (DPG) on the properties of compounds and vulcanizates, i. e. cure characteristics, Mooney viscosity, flocculation kinetics, bound rubber content, Payne effect, tan δ at 60 °C, tensile and tear properties are investigated. The results demonstrate that compound viscosity and curing behavior, as well as vulcanizate properties of the silica-filled NR are much improved by incorporating silane coupling agents. Bis-triethoxysilylpropyltetrasulfide (TESPT) clearly gives better overall properties than the disulfide-based silane (TESPD), except for scorch safety. DPG acts as a synergist to sulfenamide primary accelerators, as well as activator for the silanization reaction. Highly dispersible (HD) silicas can significantly enhance the degree of dispersion, and so lead to higher filler-rubber interaction. As a consequence, the HD silicas provide better dynamic and mechanical properties for filled NR vulcanizates compared to conventional (CV) counterparts. The optimal quantities of both, silane coupling agent and DPG, required in the formulation are correlated to the cetyl trimethylammonium bromide (CTAB) specific surface area of the silicas. Furthermore, the results reveal that the silica structure as characterized by the dibutylphthalate (DBP) adsorption also strongly influences the reinforcing efficienc