Effects Of Post-treatments On Leaching And Fixation Mechanism Of ACQ-D Treated Wood

In order to improve the leaching resistance of the active ingredient of copper in alkaline copper quat-type D (ACQ-D) wood preservative, hot air, hot water, microwave and steaming post treatments were performed in this study to accelerate the fixation process of copper in ACQ-D treated Chinese fir, and investigate the different factors on copper leaching, the compression strength parallel to grain and the valence conversion of copper in treated wood during different post-treatments. The fixation mechanism of ACQ constituents in treated wood was determined with the help of FTIR analysis and tensile stress relaxation analysis. Furthermore, the effects of post-treatments on ACQ-D treated Chinese fir (Cunninghamia lanceolata Hook.) and Mongolian Scots pine (Pinus sylvestris Linn. var. mongolica Litv.) were evaluated by field test. The purpose of this study is to provide some useful information for the widely use of plantation-grown wood Chinese fir in the wood preservation market.The results of this study were summarized as follows:1. During hot air post-treatments, the important factors on copper leaching from treated wood include temperature, treatment duration, relative humidity, copper retention, the oxygen concentration and air velocity in air ventilation condition. Hot air post-treatments with higher temperature and relative humidity could improve the leaching resistance of copper in ACQ-D treated Chinese fir effectively, and part of cupic copper could convert to cuprous forms during this process. The percentage of copper conversion would increase as the temperature increased. The effects of air ventilation on copper leaching are associated with the oxygen concentration and air velocity, and more copper would be leached out as the oxygen concentration decreased. With sufficient oxygen concentration, air velocity would promote the heat transfer to accelerate the fixation process of copper, but it would also result in the fast evaporation of water from the treated wood and decrease the fixation temperature, which is a adverse effect on copper fixation.2. Hot water post-treatments could also accelerate the fixation process of copper in ACQ-D treated Chinese fir effectively, and the percentage of copper conversion would increase as the temperature and treatment duration increased. The lower copper leaching is corresponded with the higher copper valence conversion. Copper leaching from the treated wood could be reduced significantly after a short duration of microwave or steaming post-treatments, but could not be reduced effectively. The copper leaching resistance in the treated wood could be improved as the microwave power and treatment duration increased and also for the samples wrapped. The effects of steaming temperature and treatment duration on copper leaching are negligible in this study.The valence conversion of copper changed slightly during microwave and steaming post-treatments, which results in no strong correlation between the percentage of copper leaching and valence conversion of copper in treated wood. In this study, except for steaming post-treatment, the other three post-treatments could not reduce the compression strength parallel to grain of ACQ-D treated Chinese fir significantly.3. From FTIR spectra analysis, lignin and hemicellulose are the major fixation sites in ACQ-D treated wood. The stress relaxation curves obtained from treated wood impregnated in different ACQ solutions with different constituents and temperatures showed that the complex interactions between the components of ACQ solutions and wood matrix:in rapid phaseâ… , the splitting of the easily accessible hydrogen bonds (mainly in the matrix) are prevalent by interaction with components of ACQ solution; (2) in slow phaseâ…¡, Cu penetrates deeper in less accessible regions (e.g., in paracrystalline regions of cellulose) and renders possible further relaxation. The results of range and variance analysis reveal that the formation of complexes with Cu is still the major reaction in wood although the competitions among ACQ constituents for reaction sites exist.4. From the field test results of ACQ-D treated Mongolian Scots pine and Chinese fir after air drying (AD), high temperature drying (DO), high humidity and temperature condition (HC) and hot water (HW) post-treatments, it was found that the natural durability of Chinese fir is better than Mongolian Scots pine, and the effects of post-treatments would be affected by wood species, test site and the exposure locations of the treated wood. However, in these two test sites, both ACQ-D treated Mongolian Scots pine and Chinese fir displayed excellent decay and termite resistance performance after HC post-treatment. More copper has been leached out from the treated wood in-ground than from the samples above-ground and the serious copper leaching and poor biological performance were found in Guangzhou test site, which are due to its climate conditions and soil type. Additionally, after comparation of the compression strength parallel to grain after 20 months outdoor exposure, slight reduction was found in treated wood after HC and HW post-treatments, while the obvious reduction was found in treated wood after AD and DO post-treatments, especially for Mongolian Scots pine. Therefore, compare to Mongolian Scots pine, Chinese fir has better performance in field test.