The influence of the recycling stress history on LDPE waste pyrolysis

Abstract

It is elementary to recognize the benefits and the negative impacts of the use of plastic materials on modern societies. Polyethylene (PE) is the major plastic component present in the municipal solid waste. In this paper, two types of low-density PE (LDPE) waste with different mechanical recycling stress histories were used to investigate the influence of recycling cycles on pyrolysis. The kinetic triplet and thermal degradation study were obtained using TGA data.To determine the sample composition and hydrocarbon arrangements, ultimate, proximate and X-ray diffraction analyses were carried out. Taking advantage of these analyses and combining them with differential scanning calorimetry (DSC) data, a series–parallel pyrolysis pathway was formulated. The waste of recycled polyethylene presented low enthalpy of pyrolysis, at about 205 J/g against 299 J/g for a virgin PE. The DSC analyses evidenced a multi-step reaction behavior of the pyrolysis, confirmed by the kinetic study using different isoconversional methods: the waste of recycled polyethylene presented a higher variation of activation energies as a function of the fraction reacted. The main conclusion is that the results suggest that the recycling stress history promotes the increase of long carbon chains while weakening the boundary among the compounds. This explains the fact that recycled waste needs less activation energy than other samples to degrade thermally. Finally, different categories of low-density polyethylene wastes must be considered when dealing with either kinetics or modeling of the product recovery process.