Role of Wood Composition in the Carbonization of Transient Plastic Phase Biochar

Transient plastic phase biochars (TPPB) produced from different woody feedstocks (birch, spruce, and eucalyptus) were investigated to understand underlying factors responsible for differences in mechanical performance of biocarbon produced from these materials. All TPPB materials were produced under identical constant pressure (12.4 MPa) using wet 1–2 mm particles (75 wt % H2O addition) and reacted for 30 min at 320 °C under nitrogen gas. TPPB materials were analyzed using proximate analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), FTIR, quantitative 13C NMR and GC-MS of solvent extracts. While the general properties of the TPPB chars were overall quite similar, several key differences provide insights into the different mechanical performance after conversion to biocarbon. Specifically, the TPPB from birch contained a high concentration of triterpenoid-rich extractives and their carbonization products, which are not present in the TPPB from either eucalyptus- or spruce-derived TPPB. Differences in the 13C NMR spectra and TGA thermograms reflect this additional component. Results from this study suggests that the superior mechanical performance of biocarbon produced from birch TPPB likely results from the triterpenoid-derived components acting as a plasticizing agent that alters the glass transition temperature of the material. This results in more interparticle bonding during calcination, increasing the mechanical strength of the resulting biocarbon.