Wood has several levels of hierarchical structure, spanning from the configuration of growth-rings down to the configuration of the base polymers (cellulose, hemicellulose, and lignin). The bulk properties of wood result from the culmination of interactions over all length scales. Gaps presently exist in the fundamental knowledge relating the contribution of wood properties at each structural level to the resulting bulk properties. The advent of nanoindentation has facilitated mechanical property measurement at the cell wall layer; however, there is limited understanding of how and to what extent the properties at the cell wall level influence the bulk properties. This paper summarizes some preliminary work relating hardness measurement by nanoindentation to macroindentation. Nanoindentation was used to measure hardness within the cell wall S2 layer of radiata pine (Pinus radiata) latewood (LW) cells, whereas macroindentation was used to indent the same LW band from which the nanoindentation specimens were obtained. Meyer hardness measured via nanoindentation was found to be ~5 times larger than that measured by macroindentation. The differences in measured hardness between the two scales of indentation has been consider to result from differences in woody material volume fraction and the structure of the material being deformed. Additionally, the effects of a wood chemical modification treatment on the measured hardness for nanoindentation and macroindentation hardness demonstrated how changes in cell wall latewood properties propagate though to bulk hardness measurements of latewood.
Moon, Robert J.; Jakes, Joseph E.; Beecher, Jim F.; Frihart, Charles R.; Stone, Donald S. 2009. Relating nanoindentation to macroindentation of wood. Advanced biomass science and technology for bio-based products. [S.l.] : Chinese Academy of Forestry, c2009: p. 145-157.