Determination of carbon black in vulcanized rubber by pyrolysis technique

An analytical method to determine the carbon black content in vulcanized rubber was investigated by means of pyrolysis technique. This method is based on the evolution of organic compound in a vulcanized rubber on the pyrolysis in a nitrogen (N2) gas and on the combustion of the carbon black to carbon dioxide in an air. Pyrolysis of the sample in N2 gas was carried out by using a commercial differential thermal analyser (Rigaku Denki Co., Ltd.)and them the combustion of the residue was performed by an electric furnace in an air. The pyrolysis temperature in N2 gas was first programmed at maximum heating rate of 20°C/min. from room temperature to the fixed pyrolysis temperature (between 500 and 750°C), and then kept for 10 minutes isothermally at the desired pyrolysis temperature. After reweighing, subsequent combustion of sample in an air was performed in an electric furnace at 700 °C. The percentage of carbon black in vulcanized rubber was calculated as follows: Carbon black content (wt%) =B-C/A×100 Where A=grams of specimen used, B=grams of pyrolysis residue in N2 gas, C=grams of combustion residue in air. Carbon black content determined between 500 and 750°C was independent of the pyrolysis temperature. For this reason, the optimum pyrolysis temperature of 600°C was experimentally decided.Under these experimental condition, this method is satisfactory for the determination of carbon black in a vulcanized rubber. The observed values of such hydrocarbonic vulcanized rubber as styrene-butadie necopolymer (SBR), natural rubber (NR), isobutylene isoprene copolymer (IIR) and ethylene-propylene terpolymer (EPDM) were in fairly good agreement withthe theoretical values calculated from the vulcanization recipe. While the observed values of polychloroprene rubber (CR) and acrylonitrile-butadiene copolymer vulcanized rubber (NBR) were in poor agreement with the theoretical values because of carbonaceous residue on pyrolysis in N2 gas in addition to raw carbon black.Therefore, carbon black content of the former vulcanized rubber was determined directly from the experimental results, while the case of latter were determined successfully from the calibration curves by experimental correction. By using of calibration curves, EPDM which is representitative hydrocarbonic polymer, NBR and CR would be determined with 0.4, 1.0 and 0.5 wt% of mean absolute deviation, respectively, at the pyrolysis temperature of 600°C. This technique is very simple and rapid, and is applica