Abstract:

Objective: Potassium iodide was catalyzed by laccase and the iodine free radicals produced from the reaction could be fixed on bamboo, which was expected to improve the leaching resistance as well as the decay resistance. In this paper, enzymatic catalyzation was applied to fix antifungal agents on bamboo, which would provide an ecological and effective method for the protection and modification of wood and bamboo. Method: Using ABTS as mediator, bamboo blocks were iodized in different activities of laccase and potassium iodide(KI) combinations. The decay resistance of treated bamboo before and after 14 days was tested. The morphology and components of treated bamboo were characterized by means of scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). Result: Bamboo treated with KI alone showed limited decay resistances with a mass loss rate(ML) above 10%, while the ML of laccase catalyzed iodization of bamboo revealed better decay resistances comparing with KI alone treated ones. The best performance for bamboo protection was laccase activity at 0.60 U·mL^-1 (0.60LAK). The mass loss rate of bamboo iodized by 0.60 U·mL^-1 laccase(0.60LAK) was 7.92 % when exposed to Trametes versicolor after 3 months. After leaching, the mass loss rate increased to 9.85%, still belonged to Ⅰ decay resistance. Gloeophyllum trabeum degraded bamboo more vigorously than white rot fungi T. versicolor, causing about 24.95% mass loss rate for the untreated bamboo. The mass loss rate of 0.60 U·mL^-1 laccase iodized bamboo was 9.44%, after leaching the ML increased by 0.91%. The mass loss rate of KI alone treated one increased from 14.30% to 15.34%. Accordingly, laccase catalyzed iodination of bamboo was an effective method for bamboo against decay fungi. SEM presented clear grooves and serious damage in the structure of untreated bamboo after leaching, especially G. trabeum. Some pits were enlarged even connected together, and the integrity of cell was much destroyed. However, 0.60 U·mL^-1 laccase iodized bamboo showed a less destruction and no obvious mycelia existed. XPS analyses showed that the leached 0.60LAK samples were slightly oxidized by T. versicolor and G. trabeum. The results indicated that bamboo treated with KI-laccase could inhibit the cell wall degradation caused by T. versicolor and G. trabeum, which also had a good leaching resistance. Conclusion: The treatment of bamboo with the KI-laccase mediator systems could improve both the fixation of iodine and decay resistance, the decay resistance of laccase catalyzed iodization of bamboo was higher than that of KI alone treated. Thus, the KI-laccase mediator system might be an effective and ecological way to protect bamboo against decay fungi.

Key words: bamboo, laccase, iodide, leaching treatment, decay resistance