ISO 7781:2008 specifies methods for the determination of the soap and organic-acid content of raw styrene-butadiene rubber (SBR). Method A is the titration method using indicator reagent. Method B is the titration method using an autotitrator or pH-meter.
The methods depend on the extraction of the organic acids and soaps from the rubber by means of a specified solvent. In practice, therefore, it is convenient to determine both organic-acid and soap contents on separate portions of the same solvent extract. Since the soaps and organic acids present in the rubber are not single chemical compounds, the method gives only an approximate value for the soap and organic-acid content.