• Co-mixing biomass with plastics markedly increased biochar calorific value, reaching 24.14 MJ kg⁻¹ for the BM:PE blend. • Plastic additives enhanced biochar quality, delivering high fixed carbon (70.98 %) and low ash (12.4 %) for co-firing use. • PE and HDPE promoted fuel-rich syngas formation, increasing H₂ (0.58–1.47 %) and CH₄ (6.50–6.74 %) contents. • Co-pyrolysis improved bio-oil composition, with higher hydrocarbons and reduced oxygenated compounds. The growing demand for sustainable energy solutions and effective waste valorisation has intensified interest in producing high-energy solid biofuels from heterogeneous waste streams. This study evaluates the feasibility of co-mixing lignocellulosic biomass with selected additive waste materials such as food waste, polypropylene-based disposable facemasks, high-density polyethylene, and polyethylene to enhance the fuel properties of biochar for coal co-firing applications. Slow pyrolysis was conducted under controlled inert conditions, and the resulting biochar, bio-oil, and gas products were systematically characterised. Results show that co-mixing biomass with plastic-derived additives significantly improves biochar fuel quality. The biomass-polyethylene blend achieved the highest calorific value (24.14 MJ kg⁻¹), exceeding both raw biomass and sub-bituminous coal, while also exhibiting high fixed carbon and low ash content. Plastic-enriched blends further enhanced hydrocarbon formation in bio-oil and increased the presence of detectable combustible gas components relative to biomass alone. Overall, the findings demonstrate that co-pyrolysis of biomass with selected waste plastics offers a practical pathway for producing energy-dense biochar suitable for coal substitution, supporting waste-to-energy integration within a circular economy framework.
Shahmi et al. (Sun,) studied this question.