Photo-resistance of alkylammonium compound treated wood
Creators: name: Zhang, Xueyuan
Publisher: name: University of British Columbia
Year: 2009

description: The potential of alkylammonium compounds (AACs) as wood preservatives, was recognized during the 1970s. The problems associated with AAC-treated wood, particularly treated with didecyldimethylammonium chloride (DDAC), are severe surface degradation and discoloration compared to untreated wood. The aims of this study were to assess the performance of AAC based chemically treated wood to ultraviolet (UV) irradiation and also determine photo-resistance of wood treated with a combination of selected additives plus DDAC, during UV irradiation. Southern pine sapwood thin sections were treated with the new biocides and then exposed to artificial UV light. The compositional changes in the treated and untreated wood sections were examined using Fourier transformed infrared spectroscopy (FTIR), which provides a rapid and nondestructive analysis of the wood during UV irradiation. The relative lignin degradation and the formation of carbonyl groups were quantitatively analyzed based on the peaks at 1510 and 1730 cm⁻¹ in the FTIR spectra. The studies showed that only the new biocides containing the cobiocide copper, slowed wood photodegradation by inhibiting the formation of carbonyl groups and delignification compared to the untreated wood and wood treated with only organic biocide formulations. DDAC treatment accelerates delignification and demethoxylation via the formation of free radicals. In order to increase the photo-resistance of DDAC treated wood, additives including butylated hydroxytoluene (BHT), lignosulfonic acid (LSA), tannic acid and wood extractives, isolated from Douglas-fir (Pseudotsuga menziesii), western red cedar (Thuja plicata) and Scots pine (Pinus sylvestris) heartwood, were used with DDAC. FTIR was used to examine the effectiveness of the additives in slowing the photodegradation of DDAC treated wood during U V irradiation. The FTIR spectra showed that tannic acid and Douglas-fir extractives greatly improved the photo-resistance of DDAC treated wood based on the changes to the peak at 1510 cm⁻¹ which presents aromatic skeletal vibrations in lignin. A quantitative analysis of the FTIR spectra was used to assess the lignin degradation and the formation of carbonyl groups. The results showed that the addition of Douglas-fir extractives, and tannic acid to DDAC reduced lignin degradation. Douglas-fir and cedar extractives also reduced the formation of carbonyl groups of the wood to some degree. Douglas-fir extractives and tannic acid contain polyphenolic components, which have antioxidant potential. The results suggested that the antioxidant properties of the additives slowed the oxidation process of lignin in the wood during UV exposure by terminating the formation of free radicals from lignin, generated by UV light. A washing study showed that the action of washing might wash off the additives and DDAC in the wood sections, because their FTIR spectra showed no clear difference on the peak intensity after 6 days of UV exposure. The color changes in photoexposed samples were examined by a Minolta CM-2600d spectrophotometer for the wood sections treated with additives plus DDAC during UV irradiation. It was found that the color change was greatly retarded in the wood treated with Douglas-fir or cedar extractives. Douglas-fir and cedar extractives effectively resisted color change and also provided an excellent brightness stability when combined with up to 5% DDAC treated wood. The discoloration study of wood sections treated with additives plus DDAC by UV irradiation and washing showed that the action of washing may wash out some of the additives in the wood, but Douglas-fir and cedar extractives still resisted color change to some degree and provided brightness stability for DDAC treated wood.