APPLICATION OF MICROWAVE-HEATING TO THE DETERMINATION OF FREE, COMBINED AND TOTAL SULFUR IN RUBBER

An atomic absorption spectrometry (AAS) method for the determination o f total and combined sulphur in rubber and a catalytic method for the determination of Free sulphur in rubber are described. The catalytic m ethod is based on the iodine-azide reaction and is followed by an extr action of free sulphur with benzene, toluene or acetone. The catalytic determination, with the aid of gas chromatography, was performed in N ,N-dimethylformamide after expelling the more volatile solvents used i n the extraction. The calibration is linear over the range 2 x 10(-6)- 3 x 10(-4) M. Before the determination of total and combined sulphur, the rubber samples were decomposed by microwave assisted heating (5 mi n, 110 W) in a Teflon closed vessel. After microwave heating the solut ion was clear and homogenous and all sulphur compounds contained in th e rubber were quantitatively oxidized to sulphate. The sulphates were then precipitated as BaSO4 and an excess of barium was determined by A AS. From the difference in the results of the determinations of total and free sulphur the amount of combined sulphur can be calculated, and from the difference in the determinations of total and combined sulph ur the amount of free sulphur can be calculated. In the latter case th e catalytic analysis is not needed.