Volume fractal and surface fractal analysis of the pore structure of natural and heat-treated spruce wood using the mercury intrusion porosimetry test

Abstract Fractal geometry describes the complex pore structure in natural and heat-treated wood and the relationship between pore structure and wood properties, such as strength, heat conductivity, and transport properties. However, the fractal types and the scale-dependent properties of natural and heat-treated wood remain unclear. In this study, comprehensive fractal analysis of the pore structure of natural and heat-treated spruce wood was carried out based on mercury intrusion porosimetry data. Both the volume fractal and surface fractal of natural and heat-treated wood were determined. The results showed that the two fractal types had different scale-dependent fractal properties. Four regions were identified in the pore structures. A volume fractal region was identified for pores in the region of 2–90 μm, while a surface fractal region was identified for pores in the region of 90 nm–7 μm. The pore structure in the region of 2–90 μm that corresponded to the large pore (the lumina in the cell) range showed strong volume fractal properties, and the fractal dimensions were 2.645–2.884. The pore structure in the region of 90 nm–7 μm that corresponded to the small pore (voids on or in cell walls) range showed strong surface fractal properties, and the fractal dimensions were 2.323–2.999. The range of fractal regions was hardly affected by the heat treatment atmospheres. These results showed that fractal geometry can be used to characterize the pore structures of natural and heat-treated wood. These findings are expected to explain the differences in properties between natural and heat-treated wood in the future.