The effect of carbon black on the thermal decomposition of vinyl polymers

The effect of carbon black on the thermal decomposition of various polymers has been studied in an inert atmosphere by thermogravimetry/mass spectrometry and pyrolysis-gas chromatography/mass spectrometry. It has been established that the nature of substituents on the hydrocarbon chain of the polymers affects the thermal behavior of the mixtures with carbon black. Carbon black exhibits no influence on the decomposition of poly(methyl methacrylate) (PMMA) which has quaternary carbon atoms in the polymer chain and decomposes by depolymerization. The decomposition of polypropylene (PP) is promoted, whereas, that of polyethylene (PE), polystyrene (PS) and polyacrylonitrile (PAN) is hindered in the presence of carbon black. The char yield of PAN is increased significantly, however, carbon black has no impact on the amount of residue of non-char-forming polymers. Analysis of the pyrolysis products indicates that carbon black has influence through the chain cleavage and H-transfer reactions. The promotion of the chain scission reactions in PP is indicated by the lower decomposition temperature and the increased formation of products originating from the primary macroradicals. It appears that carbon black participates in the termination of the chain reactions, too, thus. the yield of oligomers is significantly reduced from the vinyl polymers. The increased yield of hydrogenated products also confirms that carbon black participates in the H-transfer reactions. (C) 2002 Elsevier Science B.V. All rights reserved.