Co-pyrolysis and synergistic effect analysis of biomass sawdust and polystyrene mixtures for production of high-quality bio-oils

•Waste plastic disposal represents serious environmental issue.•Co-pyrolysis of biomass sawdust and PS enhance bio-oil properties.•Synergistic effect is most evident for lower share of plastic content.•PS yields high amount of valuable aromatic hydrocarbons as well as toxic PAHs.•Optimal plastic content in fuel mixture is between 20–40 % for high quality bio-oils. Usage of traditional biomass raises serious concerns regarding its sustainability due to the inefficient combustion in household stoves and potential over-usage if the intention is to replace fossil fuels in power plants. Co-pyrolysis of biomass feedstock with different waste materials, especially plastics, might be a promising alternative for sustainable usage of enhanced biofuels. Even more, co-pyrolysis can help to integrate waste management schemes into the power production sector. Plastics materials have properties similar to those of fossil fuels in terms of heating value and the absence of oxygenated compounds; therefore, they could significantly improve the properties of biomass products, especially bio-oils. Especially interesting for this method is polystyrene (PS) since it yields a high share of liquid fraction, which is the most valuable pyrolytic product. In this work, co-pyrolysis was performed for a mixture of waste biomass sawdust (oak, poplar and fir wood) and waste polystyrene from dairy product packaging. Pyrolysis was carried out for sawdust and polystyrene alone, and their respective fuel blends (PS/SD 25−75%, PS/SD 50−50%, PS/SD 75−25%) from room temperature to 600°C with a retention time of half an hour. The highest yield of liquid fraction was noticed for mixtures with 75 % of PS, while the lowest one was for blends with 25 % of PS, with a yield of 83.86 % and 62.33 %, respectively. Additionally, the mass spectrometric analysis was carried out to determine the chemical composition of the obtained oil.