4.2.1. The hydrocarbon cracking mechanism
4.2.1.1. Mechanism of thermal degradation. As a rule, the plastic
pyrolysis follows complex routes that cannot be described by one
or more chemical reactions, but still rather imperfectly by either
empirical formulas featuring fractional stoichiometric coefficients
or compressive systems of elementary reaction, i.e. reaction that
really occurs as written [77].
A detail study on the mechanism for the thermal decomposition
of polymers is proposed by Cullis and Hirschler [78]. The four
different mechanisms proposed are: (1) End-chain scission or
unzipping, (2) Random-chain scission/fragmentation, (3) Chainstripping/elimination
of side chain, (4) Cross-linking. The decomposition
mode mainly depends on the type of polymer (the
molecular structure).The following Table 3 describes the reaction
pattern of different thermoplastics where first three types of
mechanism is being followed [77]. This has been shown as below