Abstract
Studies into transient plastic phase biochar (TPPB) were conducted to compare how feedstock, moisture, acetic acid addition, and reaction time impacted the formation of TPPB and mechanical properties. Our results show that pyrolysis conditions sufficient for TPPB formation from birch wood do not lead to TPPB formation from spruce, cellulose (paper plates), or rice straw. However, TPPB formation was possible with spruce and rice straw with the addition of water to the initial material. Plasticized biochar and non-plasticized biochar (NTPPB) produced from spruce and rice straw were compared in terms of the charcoal yield, proximate analysis (fixed carbon content), and mechanical properties of pelletized particles. Despite observing only minimal differences in the charcoal yields and fixed carbon contents between TPPB and NTPPB, the tensile strengths of biochar and biocarbon pellets [calcined at 900 °C (N2)] were substantially improved with TPPB. Biocarbon pellets produced from spruce TPPB and rice straw TPPB were 5× and 1.5× stronger than the NTPPB counterparts. Adding 75 wt % H2O to birch (nominal 8% moisture content) resulted in biocarbon with nearly 10 times higher tensile strength, despite both biocarbon materials being produced from a birch TPPB precursor. Birch biochars produced with shorter reaction times produced biocarbon pellets with nearly 3× higher tensile strength. Lastly, measured tensile (39 MPa) and compressive (188 MPa) strength values obtained from finely ground birch TPPB samples constitute one of the strongest biocarbon materials reported to date and would have sufficient mechanical strength to serve as a direct substitute for petroleum carbon anodes without any binder. These results demonstrate that plasticized biochar can be produced from a variety of different feedstocks and increasing their water content along with reducing the reaction time improves the mechanical properties of the biocarbon formed from the plasticized biochar intermediate.