Sekine and Fujimoto [86] have proposed a free radical
mechanism for the catalytic degradation of PP using Fe/activated
carbon catalyst. During degradation, methyl, primary and secondary
alkyl radicals are formed, and by hydrogen abstractions and
recombination of radical units, methane, olefins and monomers are
produced [47]. The various steps in catalytic degradation are
shown below. In initiation step, random breakage of the C–C bond
of the main chain occurs with heat to produce hydrocarbon
radicals. In propagation, the hydrocarbon radical decomposes to
produce lower hydrocarbons such as propylene, followed by bscission
and abstraction of H radicals from other hydrocarbons to
produce a new hydrocarbon radical. Disproportionation or
recombination of two radicals is termination reaction. During
catalytic degradation with Fe/activated charcoal in a H2 atmosphere,
hydrogenation of hydrocarbon radical (olefin) and the
abstraction of the H radical from hydrocarbon or hydrocarbon
radical generate radicals, enhancing degradation rate. In a reaction
temperature lower than 400 8C or a reaction time shorter than
1.0 h, many macromolecular hydrocarbon radicals exist in the
reactor, and recombination occurs readily because these radicals
cannot move fast. However, with Fe/Activated Carbon in a H2
atmosphere, these radicals are hydrogenated and therefore
recombination may be suppressed. Consequently, it seems as if
the decomposition of the solid product is promoted, including low
polymers whose molecular diameter is larger than the pore size of
the catalysts