Photoprotection of Wood Surfaces by Wood-Ion Complexes

Mechanisms for protection of wood surfaces against weathering imparted by metal ions of inorganic salts, namely ferric ions and chromium ions, were elucidated. The lignin model compounds study revealed that the effectiveness of weathering protection is likely due to formation of complex between wood components and ferric chloride as well as chromium trioxide, which induced energy transfer to provide protection. The complex formation between lignin model compounds and metal ions was confirmed by the analyses of their infrared spectra, ultraviolet-visible spectra, and nuclear magnetic resonance spectra. These findings revealed that guaiacol and catechol reacted with metal ions to form water-insoluble complexes. Although cellobiose-ion complex was not isolated, it was evident by IR study that cellobiose participated in complex formation and accelerated the rate of complex formation. Like model compounds, it is plausible that wood-ion complexes being formed at the wood surfaces effectively blocked the free phenolic hydroxy groups, which are the reactive centers to initiate photochemical reactions, and thereby provided photoresistance to wood surfaces. It is likely that the complex systems are capable of minimizing photochemical reactions by energy transfer from wood to wood complexes, to emit effective energy harmlessly from wood surfaces. In addition, it is possible that wood-ion complexes might decompose peroxide impurities formed at wood surfaces to avoid photodegradation chain reactions