Micromechanical properties of wood cell wall and interface compound middle lamella using quasi-static nanoindentation and dynamic modulus mapping

Micromechanical properties of individual phases within wood tissues are crucially important for the processing and utilization of this biomass material. The quasi-static nanoindentation and dynamic modulus mapping techniques were employed to study the micromechanical properties of wood cell walls and their interface regions. Nanoindentation results showed that the reduced modulus of secondary cell walls (18 GPa) was twice that of interface compound middle lamella (CML) (7 GPa). Modulus mapping, with advantages of high resolution and undamaged test over conventional nanoindentation, was able to analyse the subtle variations in micromechanical properties of individual phases within the whole wood tissues, especially interface layers. The variation tendency across adjacent cell walls was similar to that tested by nanoindentation, and the secondary cell walls exhibited maxima in the middle of the secondary wall and slightly reduction approaching to the S-1 and S-3 layers. Moreover, the storage modulus of interface region CML showed W distribution, which meant that the modulus first fell and then rose from the central area to edge regions.