In this paper, two types of PE wastes with different degrees of recycling were used to investigate the influence of recycling stress history on the pyrolysis. The main results suggest that the thermal and mechanical stress promotes the increase of long carbon chains while weakening the boundaries among the compounds. This might explain the fact that recycled waste needs less activation energy than recycled samples to degrade thermally. The waste of recycled polyethylene presented the lowest enthalpy of pyrolysis, at about 205 J/g.

The DSC trials evidenced a multi-step reaction behavior. This behavior was confirmed by using different isoconversional methods for the kinetic study. Large variations around the average activation energy values were observed. The waste of recycled polyethylene presented a higher variation of about 66% in the range of 185.5 ± 61.6 kJ/mol. Also, it needs less activation energy than VPE and WVPE to degrade thermally. The degradation of all samples can follow Avrami–Erofeev (A, A, and A) and first-order () models, also, the recycled can be described by contracting geometry (R) and three-dimensional diffusion (D) models.

The pyrolysis pathway is a series–parallel phenomenon dominated mainly by the competition of evaporation and pyrolysis reactions.

We recommend that the physical stress history between different categories of polyethylene waste should be considered for kinetics purposes, as well as, for the modeling of the product recovery process.

Research submitted by
a
Federal Institute of Education, Science and Technology of Espírito Santo, Serra, 29173-087, Brazil
b
Laboratory of Combustion and Combustible Matter (LCC), PPGEM, Federal University of Espírito Santo, Vitória, 29075-910, Brazil
c
Institut de Mécanique des Fluides de Toulouse (IMFT) - Université de Toulouse, CNRS-INPT-UPS, Toulouse, 31400, France
d
Federal University of Espírito Santo, Vitória, 29075-910, Brazil