Co-pyrolysis of low-value wood sawdust and non-recyclable plastics into char: effect of plastic loading on char yield and its properties

Abstract

Co-pyrolysis of biomass and plastics is essential to improve the quality and yield of pyrolytic products, optimise energy recovery, and mitigate plastic waste, providing a sustainable approach to waste valorisation. This study examined char production from the co-pyrolysis of biomass and plastic in a semi-batch reactor at 500 °C with a heating rate of 10 °C min⁻¹ and a nitrogen gas flow rate of 100 mL min⁻¹. JCT and NRPET were physically mixed at 30, 50%, and 80% wt%, respectively. The physicochemical properties of biomass and plastics confirmed their suitability as pyrolysis feedstocks. TGA-FTIR results confirmed that the addition of NRPET at 30, 50 and 80 wt% with JCT significantly increased the hydrocarbons and reduced the formation of CO₂, CO and oxygenated compounds. Results showed that blending of non-recyclable PET (NRPET) with Jungle Cork Tree (JCT) at 30%, 50%, and 80% reduced char yield by 5.27%, 9.07%, and 12.47%, respectively. Additionally, the blending of JCT and NRPET improved the properties of the char, such as carbon content (22.59%), heating value (6.17 MJ kg⁻¹), bulk density (200.11 kg m⁻³), and electrical conductivity. The blending process also led to a significant reduction in the oxygen content (18.05%) and surface area (30.78 m² g⁻¹) of the char. FTIR analysis showed a loss of undesirable functional groups, while Raman spectroscopy revealed an increased I_D/I_G ratio. Finally, SEM analysis indicated that the incorporation of plastics increased the hardness and reduced the roughness of the char, enhancing its suitability for energy storage or carbon-based material applications.