This part of GB/T 4497 specifies an oxygen combustion flask method for the determination of the total sulfur content of rubber.
The method is applicable for the determination of all the sulfur present in various rubber or rubber product, except that contained in barium sulfate. It is applicable to NR, CR, SBR, BR, IR, MR, EPDM, NBR and ebonite as well as the combination product of above rubbers.
This method gives unreliable (usually low) results in the presence of lead, antimony, zinc, barium and calcium compounds. If calcium carbonate is the only calcium compound present, good results can be obtained by modifying the absorbing solution.
2 Principle
A test sample is ignited in an atmosphere of oxygen in an oxygen combustion flask containing hydrogen peroxide, the carbon and hydrogen of the organic matter being oxidized and the sulfur being converted to sulfuric acid. If necessary, the resulting solution is passed through a cation-exchange column to remove interfering cations. The absorbing solution is titrated with barium perchlorate using thorin indicator or thorin and methylene blue indicator.
