Effect of hydro-thermal carbonisation on the structural properties of bulk-type wood (Chamaecyparis obtusa) upon high-temperature heat treatment

Hydro-thermal carbonisation (HTC) is a method to convert biomorphic materials such as wood to carbon, with the advantage of enhancing their specific surface area to an extent greater than that by pyrolysis. In this study, wood samples underwent HTC at 250 °C, followed by a heat treatment at 600, 800 or 1000 °C. The cell walls of the HTC processed samples showed a structure made of alternating porous and dense carbon layers that changed as a function of the additional heat-treatment temperature. The specific surface area of the samples which underwent only a pyrolysis carbonisation drastically decreased at 80 °C, while that of the HTC samples was 473 m2/g, which enabled them to maintain a high-temperature stability. Compressive strength tests demonstrated plastic deformation and a different fracture mode for the HTC samples compared to the samples subjected to pyrolysis carbonisation only. Different values of mechanical strength in longitudinal and vertical directions were analysed.