Temperature-dependent pyrolytic product evolution profile for low-density polyethylene from gas chromatographic study

摘要

In this work, a product distribution study from thermal degradation of low-density polyethylene (LDPE) is presented. Thermal degradation of the polymer was investigated under dynamic condition in an inert environment using a thermo-gravimetric analyzer (TGA) coupled with evolved products' analysis using a gas chromatograph (GC). Fractions evolved at nine different temperatures from 200 to 600 ℃ were injected into GC for a detailed product analysis. The main objective of the present investigation is to highlight the species-specific evolution profiles of LDPE pyrolyzates (C5-C44) at different stages of its degradation under an inert environment. Pyrograms have been analyzed in terms of amount of different products evolved at various pyrolysis temperatures. Volatile pyrolyzates essentially remain low at low decomposition temperature (200-300 ℃) of the polymer, which gradually increase to attain a maximum at maximum decomposition temperature (470 ℃) and finally level off at 600 ℃. In the mechanistic approach adopted to understand the decomposition mechanism of LDPE, the following reaction types were considered: (a) main chain cleavage to form chain-terminus radicals; (b) intramolecular hydrogen transfer to generate internal radicals; (c) intermolecular hydrogen transfer to form both volatile products and radicals; and (d) β-scission to form both volatiles and terminally unsaturated polymer.