Tearing energies for in-situ reinforced poly(dimethylsiloxane) networks

Tetraethoxysilane was used to end-link functionally-terminated poly(dimethyl-siloxane) chains, and then to serve as the source of reinforcing silica particles upon its hydrolysis and condensation within the elastomeric networks. These in-situ filled elastomers were characterized using transmission electron microscopy, thermogravimetric analysis, and tearing energy measurements. The electron micrographs showed the presence of well-dispersed, unagglomerated silica particles with average diameters rather narrowly distributed over the range 150–250 Å. These reinforcing particles were found to improve the thermal properties of the networks. Specifically, the larger the amount of filler thus incorporated, the higher the onset degradation temperature, and the larger the weight residue at 800°C. Effects were also found with regard to the tearing measurements, with the filled materials showing unstable tearing (stick-slip tearing), particularly at higher tearing rates. In contrast, the unfilled materials showed steady tearing. The tearing energies of the filled materials were significantly larger than those of the unfilled material. A marked increase in the tear strength occurred upon increasing the silica content up to 10 wt.%, followed by smaller improvements with additional increases in silica content.