Abstract
Untreated fibers and acetylated fibers were ozonized and used to make fiberboards. The effect of ozonization on the durability of the boards bonded with poly-methylene diphenyl diisocyanate (PMDI) and phenol formaldehyde resin was investigated. In order to study durability, the ASTM 6-cycle accelerated aging test was conducted. The internal bond strength (IB) after the accelerated aging test of the boards bonded with PMDI was decreased greatly by excessive ozonization. The great decrease suggests that the possibility of chemical bonding between the hydroxyl group of the wood and the carboxyl group of the PMDI was low. The carboxyl group introduced by ozonization instead reacts with the isocyanate group of the PMDI, resulting in obstruction of PMDI curing. On the other hand, suitable ozonization improved the IB of the acetylated boards bonded with phenol formaldehyde resin, and termite resistance was also improved. In addition, it was found that phenol formaldehyde resin was highly resistant to decay, and the combination of phenol formaldehyde resin, acetylation and ozonization was effective in enhancing resistance to both decay and termites.
