Contact angle, critical surface tension and glue-joint strength of corona treated Japanese pine (Pinus thunbergii Parl) containing 6.3 percent of alcohol-benzene extractives were measured.
The cosine contact angle with distilled water on the wood surface increased.
But the slopes of lines obtained by plots of cosine contact angle vs. extractives content did not change by this treatment.
Critical surface tension for less extractives content specimens decreased by the corona treatment a little, but increased for much extractives content specimens.
Joint strength of specimens, which contained more than 15 percent extractives content, glued with urea formaldehyde resin increased by the treatment. But, when extractves content was lower than 5 percent, the glue-joint strength did not change.
The slopes of lines obtained by plots of glue-joint strength vs. cosine contact angle increased by the treatment.
Relationship between the glue-joint strength and the critical surface tension was linear, since the critical surface tension was better than the cosine contact angle with distilled water as the surface activity parameter of corona treated specimens.
It is concluded that the surface energy of the wood skeleton which did not include extractives decreased a little and that the surface energy of extractives increased by this treatment.