Co-pyrolysis of polyethylene terephthalate and epoxy resin waste: Does mixing influence process efficiency and product distribution?

Polyethylene terephthalate (PET) and epoxy resin (ER) are commonly used polymers that are frequently combined in many applications, posing significant challenges for their separation and recycling. Pyrolysis is an effective technology for organic waste recycling by thermal processing, and the co-pyrolysis of composite materials or mixtures may offer potential advantages in improving pyrolysis efficiency and product values. The specific performance of PET-ER co-pyrolysis is not yet clear. This study aimed to elucidate this process through a comprehensive investigation of the pyrolysis process and product characteristics. Thermogravimetric-differential thermogravimetric analysis demonstrated an interaction between PET and ER during pyrolysis. For example, the residue yield and apparent activation energy of P8E2 (a mixture with PET-ER mass ratio of 8:2) decreased by 7.46% and 14.83 kJ·mol-1, respectively, compared to the theoretical values. Pyrolysis experiments identified the suitable operating conditions for P8E2 as pyrolysis temperature of 450°C and holding time of 30 minutes. Gas chromatography-mass spectrometry analysis identified benzoic acid and its derivatives as the primary components of the pyrolysis oil, which suggests a radical-mediated mechanism and confirms the synergistic interactions between PET and ER, and combustible gases (CO and CH4) were the main components in the gaseous product. The results of this study would provide valuable insights into the recycling of multicomponent plastic mixtures and contribute to the advancement of pyrolysis technology, offering practical implications for the treatment of complex organic solid waste.