Dimensional changes in Corsican pine (Pinus nigra Arnold) modified with acetic anhydride measured using a helium pycnometer

Helium pycnometry was used to determine the changes in volume of wood samples of Corsican pine following modification with acetic anhydride. Results were compared with changes in volume determined from external dimensions only. Percentage change in volume, as determined from external dimensions of the sample, showed a non-linear relationship with weight percentage gain as a result of acetylation; whereas percentage volume change determined by helium pycnometry showed a linear relationship. The difference in volume as determined by the two methods is explained by considering volume change of the lumens as level of cell wall substitution increases. Results obtained in this study show that volume increases due to chemical modification, when determined by measurement of external dimensions, should not be used to evaluate changes in cell wall volume.