In-Plane Permeability of Oriented Strand Lumber. Part II: Microscopic Investigation of Void Structure During Compression
Keywords:Strands, wood composites, microscopic, voids, compression, vessel, fiber
AbstractThis study investigated the changes of void structure in oriented strand lumber samples pressed to different densities using microscopic techniques. Specimens of five densities, 450, 550, 625, 700, and 800 kg/m3, were examined. A method for preparing a large sectional area of wood composites for examination in a light microscope was developed. It was able to retain the original void structure and to provide high-quality images for further investigation. Microscope slides mounted with thin cross-sections for each density were prepared and then examined using fluorescence microscopy. The size and quantity of interstrand voids decreased dramatically with increasing board density. The forming and deformation of interstrand and intrastrand (ie cell lumens) voids, including failure of cell walls and nonhomogeneous collapse of cells, were observed. Generally the vessels were compressed before fibers as a result of their difference in diameter and cell wall thickness. The variability of deformation between regions within a strand and between strands within a mat was high, due to differences in strand cutting orientation, heterogeneity of mat structure, and strand property variation created by its source in different positions on a tree stem and between trees.
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