Objective  This work was conducted to investigate the changing tendency and mechanism of pore structure in wood cell wall induced by water, so as to provide theoretical guidance for heat and mass transfer within wood, wood permeability and wood modification.

  Method  Poplar wood and fir wood were prepared into wood slices of 5 mm (R) × 5 mm (T) × 1 mm (L) . Based on nitrogen sorption method and differential scanning thermoporosimetry, the characteristic parameters of pore size distribution, specific surface area, pore volume were investigated at four typical moisture content states including oven-dry state, air-dry state, fiber saturation state and saturated state. The pore structure differences between different states and different tree species were compared.

  Result  The pore size of wood cell wall was mostly less than 10 nm, especially below 4 nm, with relatively few pores above 10 nm. With the increase of moisture content, the pore size distribution curve of wood cell wall rose significantly. From air-dry state to fiber saturation state, the maximum pore size distribution of poplar wood and fir wood increased by 52.73% and 58.62%, respectively, furtherly from fiber saturation state to saturated state, those values increased by 435.24% and 470.43%, respectively.

  Conclusion  As the wood gradually changes from oven-dry state to saturated state, the pore volume of wood cell wall becomes higher obviously. When the wood reaches saturated state, the volume of cell wall pores reaches the maximum. However, due to the signal interference from a large amount of free water, the detecting range of pore size distribution measured by the differential scanning thermoporosimetry is limited. There is no obvious difference in pore distribution among different tree species in this study.