Wood acetylation represents a chemical modification that increases the hydrophobicity of wood. The level of acetylation in the wood structure determines the extent of hydrophocity with higher levels providing reduced moisture affinity. Due to the reduced hygroscopic nature of acetylated wood, performance features such as dimensional stability, resistance to termites, and resistance to rot and decay fungi are significantly improved. The fiber saturation point (FSP) represents the theoretical moisture content at which wood cell walls are completely saturated with water and no additional water can be absorbed into the wall structure as bound water. The fiber saturation point of acetylated wood is reduced as compared to unacetylated wood also due to its increased hydrophobicity. In this work, the fiber saturation point of a series of 30.5 cm x 14 cm x 2.54 cm acetylated Southern Pine radius edged deck boards with varied levels of acetyl was determined by measuring the width as a function of moisture content. It was found that the fiber saturation point of acetylated wood correlates with the level of acetyl in the wood substrate. A linear relationship is found between these two factors with increasing levels of acetyl providing a reduction in fiber saturation point. The method used to determine the fiber saturation point in this work provides consistent results with that previously determined via an alternate technique. Unacetylated Southern Pine deck boards were also studied in this work and revealed fiber saturation points consistent with prior determinations in the literature and fitted the relationship between acetyl level and fiber saturation point.

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