Effects of chemical modification reagents on acoustic properties of wood

The acoustic properties of several chemically modified Sitka spruce samples (Picea sitchensis Carr.) were evaluated in the longitudinal direction of wood specimens. Sit;a spruce treated with glyoxal and carboxymethyl cellulose (CMC) displayed superior acoustic properties to those obtained by the other treatments. The acoustic converting efficiency (ACE) of the glyoxal-CMC treated Sitka spruce was 1.84 times of that of the untreated specimen and the specific dynamic Young's modulus (E'/r) was retained without decrement after such treatment. Changes in the tan delta of Sitka spruce treated with glyoxal and different concentrations of 1,4-butanediol were opposite. With a low concentration of 1,4-butanediol (10 %,), the tan delta of the treated specimen decreased as a result of the formation of crosslinked cyclic structures. The potential presence of more alkyl hydroxyl groups in the Sitka spruce, after bring treated with glyoxal and a high concentration of 1,4-butanediol (20 %), resulted in the increment of tan delta and the decrement of ACE. The impairment of the acoustic properties of Sitka spruce was caused by the introduction of free chains with endwise carboxylic acid groups into cell walls after the succinic anhydride treatment. Slight improvement on the ACE of Sitka spruce was achieved by the reaction with acetic anhydride and the decrease in the tan delta was about 15 %, which was attributed to the partial Formation of crosslinked matrix. These results revealed the improvement of the acoustic proper ties of chemically modified wood that was probably achieved only by the formation of network structures between wood components and reagents.