Acetylation of solid wood using microwave heating Part 1: Studies of dielectric properties

The possibility of using microwave energy as the source of heat for the mod ification of wood by means of acetylation with acetic anhydride was investi gated, with the aims of reducing reaction time, achieving an efficient remo val of excess chemicals after reaction, and obtaining a uniform distributio n of acetyl groups within the acetylated wood. When using microwave heating in the acetylation process, the heat is instantly generated within the who le wood object and the absorbed microwave energy depends on the polarizabil ity of the chemicals. The parameters, relative permittivity (epsilon') and relative loss factor (epsilon") give information on how the microwaves can penetrate into the wood object and of possible thermal gradient effects on the wood during modification. This investigation shows that microwave energ y effectively heats the acetic anhydride used for modification by acetylati on and that the power penetration depth (d(p)) of the microwaves is about 1 0 cm in acetic anhydride impregnated wood. The relative permittivity and th e relative loss factor were found to decrease with increasing temperature, which indicates that the energy absorption will preferably be directed to l ess heated parts of the wood object. This will promote a more uniform heat distribution, and, accordingly, a more uniform acetylation of the wood.