Effect of heating rate and feedstock nature on electrical conductivity of biochar and biochar-based composites

Cost-effective strategies for integrating bio-oil production with biochar utilization in new sustainable platforms are needed to improve the economic viability of pyrolysis for energy applications. Recently, the use of biochar as filler in the preparation of polymer based composites received a great attention due to its ability to improve polymers mechanical, electrical and thermal properties. This work aims to expand knowledge on the effect of the heating rate and feedstock chemical composition on the on the biochar structural and chemical characteristics affecting electrical properties of the biochar at different pyrolysis temperatures. Biochars were produced from three feedstocks, namely walnut shells (WS), the lignin rich residue from bio-ethanol production (LRR) and sewage sludge (SS), under slow and fast heating rate at 500, 600 and 700 degrees C. The three feedstock differ for both the organic components (i.e. high lignin content in WS and LRR and presence of proteins in SS) and ash content which is highest in SS.The produced biochars were characterized and the observed differences in their chemical and structural properties were discussed in relation to their effect on the measured electrical conductivity.The severity of the pyrolysis treatment improved biochars electrical conductivity. Heating rate and feedstock type affected the electrical conductivity only marginally at 500 and 600 degrees C, whereas at 700 degrees C any relevant effect was observed. WS biochars produced at 500 and 600 degrees C exhibited the lowest electrical conductivity regardless of the heating rate of the production process.The biochars produced at 700 degrees C were used to prepare epoxy resins composites. Despite their comparable conductive performance, the biochars lent different electrical conductivity to the composites depending on the biomass type and the heating rate experienced by the biomass samples during the pyrolytic treatment. The composite prepared with WS biochar produced under fast heating rate exhibited the highest electrical conductivity.