Effects of cellulose contamination on polystyrene recycling to styrene monomer via microwave pyrolysis

The increasing population and by extension the plastic waste increasing rate requires innovative waste management mitigation solutions, especially for a challenging polymer such as polystyrene. However, the presence of a broad range of contaminants in its waste stream, cellulose-based contaminants being one of the most prevalent, hinders polystyrene recycling. Herein, a microwave co-pyrolysis of polystyrene and cellulose was carried out to recycle styrene as monomer and to investigate the synergy between both reactants at 500°C. Polystyrene pyrolysis presented a high styrene yield of 0.355g styrene/g polystyrene; while as the cellulose content increased, higher amounts of hydrogen are produced, leading to the hydrogenation of styrene into ethylbenzene and other styrenic derivatives such as 1,4-Diphenyl-2-butene and 1,3-Diphenyl-1-butene. A noticeable 29% decrease in styrene yield was observed for an equal amount of polystyrene and cellulose. At the same conditions, the detrimental effect of the co-pyrolysis also involved the reduction of the oil yield, from 58.9%, polystyrene pyrolysis, to 30.2%. The negative synergy between cellulose and polystyrene co-pyrolysis for the recycling of styrene monomer indicates that polystyrene waste streams must be handled thoroughly prior to being recycled. •Synergy between cellulose and polystyrene was found during their microwave pyrolysis.•Addition of cellulose decreases styrene mass fraction in the pyrolytic oil.•Addition of cellulose increases ethylbenzene mass fraction in the pyrolytic oil.•A polystyrene depolymerization mechanism scheme was proposed.•Excess H2 from cellulose pyrolysis explains the changes in the pyrolytic oil.