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Title: Nanoindentation of Unembedded Wood Cell Walls

Source: In: 9th International Conference on Wood & Biofiber Plastic Composites, May 21-23, 2007; pp. 423

Author(s)Jakes; Frihart; Moon; Beecher; Stone

Publication Year: 2007  View PDF »

Category: Journal Articles

Abstract: In-situ testing of cell wall material using nanoindentation is a valuable tool for revealing the effects of chemical modification on the material properties of wood at the cell wall level. Current practice in this field involves embedding the wood in an epoxy matrix, then analyzing the nanoindentation data by tacitly assuming that the surface is homogeneous and infinite in size compared to the size of the indent. The problems with these procedures are that the embedment process may alter the mechanical properties of the cell wall and that the meso-structure of the wood may influence the nanoindentation measurement. We developed a method for preparing specimens with no embedment. The primary features of the resulting surface are cell walls (~5 µm wide) and empty lumens (~20 µm across). This is not the ideal surface assumed by standard nanoindentation methods. Indents performed in the cell wall material will be affected by the close proximity of the edge and by the open cellular structure which comprises the wood. We propose a nanoindentation method which accounts for edge effects and the structural compliance resulting from this cellular structure. To prove the efficacy of our method to account for edge effects, we placed indents near the edge of a standard fused silica specimen. Then, to demonstrate the capability of the method to account for structural compliances, we placed indents over the unsupported region of a silicon bridge structure. The literature values of hardness and Young’s modulus were obtained from indents placed at the edge of the fused silica and over the unsupported region of silicon. Finally, we applied the methods to our wood specimens and found that we can separate the effects of edges and compliant cell structure from the intrinsic properties of the cell wall material.

Keywords: nanoindentation; wood-plastic composites; cell wall; edge effects; structural compliance

File size: 92 kb(s)

Date posted: 06/18/2009
Current FPL Scientists associated with this product (listed alphabetically)
Frihart, Charles R.
Research Chemist
Jakes, Joseph
Research Materials Engineer
Moon, Robert J.
Materials Research Engineer

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