Mechanical properties of pyrolysed wood – a nanoindentation study

Gerald Zickler (1) , Thomas Schöberl (2) , Oskar Paris (1)

1 Department of Biomaterials [Potsdam]
2 ESI - Erich Schmid Institute of Materials Science

The present work is focused on changes of mechanical properties in pyrolysed spruce wood as a function of temperature up to 2400°C. Nanoindentation tests are used for the determination of mechanical properties at the scale of single wood cell walls. Hardness, indentation modulus and elasto-plastic/brittle behaviour of the carbonaceous residues are derived as function of pyrolysis temperature. Hardness values increase continuously by more than one order of magnitude to 4.5 GPa at 700°C. The indentation modulus shows complex changes with a minimum of 5 GPa around 400°C, and a maximum of 40 GPa around 1000°C. The deformation induced by the indenter is largely (visco-) plastic in native wood, but it is almost purely elastic in the carbonaceous residue with particular low values of the indentation ductility index around 700°C. A low density, strongly cross-linked carbon structure may explain the mechanical behaviour at these intermediate temperatures. A final decrease of the modulus and a slight recovery of ductility for temperatures above 2000°C can be attributed to a continuous structural transition of the material towards graphite-like stacking of carbon sheets and to preferred carbon orientation along the wood cell axis.

Mots clés: Physical Sciences

Gerald Zickler, Thomas Schöberl, Oskar Paris. Mechanical properties of pyrolysed wood – a nanoindentation study. Philosophical Magazine, 2006, 86 (10), pp.1373-1386. ⟨10.1080/14786430500431390⟩. ⟨hal-00513635⟩