In situ silica reinforcement of radiation prevulcanized natural rubber latex

Abstract

A method to prepare radiation-vulcanized NR sheets containing in situ generated silica was reported. The NR latex having 50% dry rubber content was irradiated under gamma rays with a total radiation dose of 15 kGy. The prevulcanized latex was then mixed with alkoxysilanes, precursors of silica. The latex misture was heated at 50 [degree celcius] for 48 hours in order to initiate the sol-gel process of the silane to form silica particles inside the rubber matrix. Three types of alkoxysilanes were studied-tetraethoxysilane (TEOS), vinyltriethoxysilace (VTOS), and ethyltriethoxysilane (ETOS). The percentage of conversion from silanes to silica were in the order of TEOS (80%)>VTOS (60%)>ETOS (10%), reflecting the bulkiness and polarity of the vinyl and ethyl substituent of the silane. The silica particles obtained from all silanes dispersed evenly in the rubber matrix as observed by SEM. The silica particles generated from TEOS formed various aggregate sizes of about 1 [micro]m. The sizes of silica particles generated from either VTOS or ETOS were found to be about 0.1 [micro]m and aggregation was not found. Swelling behavior in toluene and water, physical properties and thermal properties of the in situ silica/radiation vulcanized natural rubber composites were also investigated as a function of type and amount of alkoxysilanes used.