This method consists,
in a first step, in dissolving in toluene the NR as received with the aim
of removing the impurities by precipitation,
then the purified solution was extracted and the solvent was evaporated at room temperature during two days to get a film
of purified NR.
To prepare the compounds the relations
of elastomer to solvent were 18 g/dm3 and 20 g/dm3
for NR (purified) and SBR,respectively.
The viscosities
of these solutions, measured at room temperature with a Brookfield viscometer, were 55 cP
for the NR/toluene and 9.8 cP
for SBR/toluene solutions.
To prepare each blend,
both solutions were mixed with the chosen proportions
of each elastomer and the required chemicals according to the recipe.
The mixture was further homogenized by mechanical stirring and by ultrasonic treatment in a bath.
Finally,
the solvent was evaporated at room temperature
for 3 days until obtaining a constant weight.