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UBC Theses and Dissertations

Visualizing inorganics in wood and wood composites using X-ray micro-CT Feng, Dengcheng


Inorganic materials are a natural component of wood and can also be added to lumber and wood composites to improve their durability. Traditional methods of visualizing the distribution of inorganics in wood are limited to a two-dimensional space and thus are not ideal for studying the 3D distribution of inorganics. I hypothesize that X-ray micro-CT will be able to visualize and reveal novel information about spatial distribution of inorganics in wood. I first test this hypothesis by visualizing the distribution of silica particles in four siliceous Australian hardwood species. A number of novel findings arose from this research. I found that silica particles were associated with rays in the four hardwoods, but their distribution within rays varied. Silica particles were evenly distributed in rays in most species except in Endiandra palmerstonii where they were mainly found in the upright and square cells of rays. Silica particles were associated with growth rings in Lophostemon confertus. Dense materials other than silica particles were found in the vessels of Syncarpia glomulifera and Syncarpia hilli. X-ray fluorescence microscopy confirmed that these materials were inorganic silica and metal elements. Secondly, I tested my hypothesis by visualizing the distribution of zinc borate (ZB) in a wood-plastic-composite (WPC) and examined if a sodium iodide label could improve the contrast between wood and plastic in CT images of WPC. I found that ZB occurred mainly as discrete particles between wood flakes. Interfacial voids formed a network of cracks within the WPC. Impregnation with NaI improved visualization of wood and plastic and made it possible to quantify the levels of wood, plastic, void and zinc borate in the WPC and the geometry of wood particles. However, NaI impregnation swelled wood, closed interfacial voids, and partially dissolved ZB particles. In conclusion, X-ray micro-CT is an effective method for visualizing the spatial distribution of inorganics in solid wood and wood composites, but the intimate association of inorganics with the cell wall in solid wood, and the poor X-ray contrast between wood and polymers complicates the visualization of inorganics in wood and wood composites. Further research is required to address these issues.

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