The chemical modification of wood via acetylation with acetic anhydride has been a well investigated technology and is of current commercial interest due to improved properties such as dimensional stability as well as resistance to termites and resistance to rot and decay fungi. Despite this, the acetylation of a board substrate requires further investigation in order to assess board properties as they relate to acetylation process variables. Based on these interests, Radiata pine and Southern pine boards with varied densities and moisture contents were studied in a laboratory glass acetylation reactor to assess acetic anhydride impregnation, board characteristics during acetylation, and final board acetyl content. Board density is found to have a significant impact on the level of acetic anhydride that can be delivered into the board substrate prior to acetylation. This feature and the board moisture content are found to have a significant impact on the ultimate wood acetyl content. Further, it is well known that wood acetylation serves to leave the wood in a swollen state; however actual expansion of the board during acetylation is much greater than the ultimate swollen state upon final drying. The capability of the laboratory glass reactor has allowed for the measurement and observation of boards during their width expansion in the laboratory acetylation process. The expansion of both Radiata pine and Southern pine boards occurs simultaneously with the rapid temperature increase of the boards during the exothermic acetylation reaction, due to the generation of hot acetic acid by-product. Time lapse photography has revealed varied rates of board expansion based on varied starting moisture contents. Nevertheless, even with differing initial moisture contents as well as varied levels of combined acetyl achieved as a function of starting moisture content, similar boards expand to the same degree during the acetylation phase of the laboratory process to produce acetylated boards.

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