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

ɛ

′) and relative loss factor (ɛ′′) 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 energy effectively heats the acetic anhydride used for modification by acetylation and that the power penetration depth (d _p) of the microwaves is about 10 cm in acetic anhydride impregnated wood. The relative permittivity and the relative loss factor were found to decrease with increasing temperature, which indicates that the energy absorption will preferably be directed to less heated parts of the wood object. This will promote a more uniform heat distribution, and, accordingly, a more uniform acetylation of the wood.

d

_p) für das getränkte Holz etwa 10 cm beträgt. Dielektrizitätskonstante und Verlustfaktor nehmen mit steigender Temperatur ab; d.h. die Energieaufnahme wird vorzugsweise zu den weniger erhitzten Teilen des Holzes gelenkt. Das wiederum fördert eine gleichförmige Acetylierung des Holzes.