SURFACE ENERGY OF COMMERCIAL AND PYROLYTIC CARBON BLACKS BY INVERSE GAS CHROMATOGRAPHY HANS DARMSTADT AND CHRISTIAN ROY* Université Laval, Département de génie chimique, Ste-Foy (P. Québec) G1K 7P4 Canada and Institut Pyrovac Inc., Parc technologique du Québec métropolitain, 333 rue Franquet, Sainte-Foy (Québec) G1P 4C7 Canada AND SERGE KALIAGUINE Université Laval, Département de génie chimique, Ste-Foy (P. Québec) G1K 7P4 Canada AND HELGA CORMIER Institut Pyrovac Inc., Parc technologique du Québec métropolitain, 333 rue Franquet, Sainte-Foy (Québec) G1P 4C7 Canada ABSTRACT The surface properties of carbon blacks obtained by vacuum pyrolysis of different used rubbers (CBP) and of commercial carbon blacks were measured by inverse gas chromatography (IGC). The dispersive component of the surface energy (γs d ) and the specific interaction (Isp) of the recovered CBP were lower than γs d and Isp of the virgin carbon black initially present in the rubber. However, γs d and Isp of recovered medium surface area carbon black and of virgin low-surface-area carbon black were comparable. During the pyrolysis carbonaceous deposits are formed on the CBP surface. A correlation between γs d and Isp and the amount of the carbonaceous deposits, measured by ESCA, was found, suggesting that the formation of these deposits is responsible for the decrease of γs d and Isp. INTRODUCTION Inverse gas chromatography (IGC) has been used by different groups to investigate surface properties, such as surface energies and adsorption enthalpies, of commercial carbon blacks 1-3 and other reinforcing fillers for elastomers. 4-6 If suitable model compounds for elastomers are used as probes, interactions between the filler and elastomers can be estimated using IGC. A good correlation between the adsorption enthalpies of probe molecules and rheological properties of carbon black reinforced elastomers has been found. 1 Therefore, IGC can be used as an important factor in predicting the reinforcing potential of carbon blacks. In this laboratory, pyrolytic carbon blacks (CB P ) are obtained by vacuum pyrolysis of different rubber wastes, such as used tires 7,8 , cable wastes 9 and polyisoprene rubber. 10 The vacuum pyrolysis Pyrocycling TM process of rubber waste (e.g. used tires) is a technology protected by several patents. 11 The process is commercialised by Pyrovac International Inc. (Québec, Canada). In the pyrolysis reactor the elastomers composing the feedstock are cracked to vapours which are recovered as condensable pyrolytic oils. The remaining solid phase consists of the recovered carbon black filler and some inorganic components (e.g. ZnS and ZnO). 12 The waste rubber feedstocks often contain a variety of different carbon black grades. In tire compounding, for example, carbon blacks from the N100 to the N700 series are added as fillers. High-surface area carbon blacks are used for the tire tread, whereas low-surface grades are found in the sidewall. 13 The quality of the recovered CB P will of course depend on the quality of the carbon black filler in the rubber feedstock. It has been shown by surface spectroscopic methods such as ESCA and static SIMS that carbonaceous deposits are formed on the CB P surface during the pyrolysis reactions. 14-16 The relative amount of carbonaceous * Author to whom correspondence should be addressed.