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The influence of didecyldimethylammonium chloride (DDAC) treatment on wood weathering

University of British Columbia

The potential of alkylammonium compound (AACs) as wood preservatives, was recognized during the 1970s. Two of the problems associated with AAC-treated wood, particularly treated with didecyldimethylammonium chloride (DDAC), are severe surface degradation and discoloration compared to ammoniacal copper quaternary ammonium compound (ACQ) and chromated copper arsenate (CCA) treated wood. The key objective of this study was to identify the mechanistic pathways by which DDAC affects wood weathering. An FTIR technique was developed and employed to study the photodegradation of wood. The compositional changes in wood sections of various thickness following DDAC and ACQ treatment, and either natural weathering or UV irradiation were examined using FTIR spectroscopy. The studies on DDAC and ACQ fixation suggested that interaction between the preservative and lignin had taken place and that these preservatives favored fixation to lignin over cellulose. The natural weathering and artificial UV irradiation studies showed that DDAC accelerated wood weathering via enhancing wood photodegradation (mainly delignification), and that ACQ slowed wood photodegradation as demonstrated by inhibiting the formation of carbonyl groups and delignification. The effect of DDAC, ACQ, and CCA treatments and their retention on wood photodegradation during weathering was investigated using FTIR and Ultraviolet-Visible reflectance spectroscopy. Delignification, demethoxylation, and cellulose degradation were accelerated by DDAC treatment, but slowed by both ACQ and CCA treatments. ACQ treatment also inhibited carbonyl formation. Those effects were enhanced by higher preservative retentions. Weight loss of the weathered samples corroborated the FTIR and UV-Vis results. The comparison of the photodegradation of methylated and unmethylated wood demonstrated that both fixed and adsorbed DDAC must be involved in the photodegradation mechanism and that the fixation reaction of DDAC to lignin was one of the principal factors affecting wood photodegradation. The studies using lignin model compounds in solution revealed that DDAC had no influence on the major photoreactions taking place in the solvent employed. The lack of significant DDAC-lignin interaction in solution most likely explains why the solution photochemistry failed to provide useful evidence of the pathway. The ESR studies on the free radical formation and decay in wood revealed that DDAC functioned as photosensitizer. The fixed DDAC was essential for sensitization to occur while the adsorbed DDAC accelerated this process.

Thesis/Dissertation

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2009-04-02

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http://hdl.handle.net/2429/6752

Forestry

University of British Columbia

UBCV

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