Methods of improving the preservative treatment of radiata pine and eucalyptus with emphasis on the use of novel boron compounds

© 1998 Dr. Francisco Javier Romero AmayaThis thesis identifies the effect of raw materials and processing parameters on the application of TMB on wood and wood products. It also describes the effect of TMB on the properties of wood and wood products. This work proposes the application of TMB by momentary immersion following by storage in a close container. The effect of wood moisture content, temperature and time were studied. Low wood moisture content (3%) is required to produce high penetration of the TMB in radiata pine (Pinus radiata D. Don) sapwood. High temperatures (40°C) during storing stage can result in adequate penetration. The storage stage is described in two phases, the emission of chemicals from the wood and the diffusion of the chemical from the head space of the container into the wood. Parameters affecting the process include temperature, wood moisture content and time. Wood moisture contents as low as 3% were found necessary to achieve high penetration of chemicals into wood. During the storage of treated timber, high temperatures reduced the emission and vapour diffusion phases. The levels of TMB and methanol in the headspace of the container were lower at high temperatures. The concentration of TMB and methanol in the head space of the desiccator achieved an equilibrium concentration at 100 hrs for samples stored at 40°C and 200 hrs for samples stored at 20°C. Methanol emission produced by the interaction between water in the wood and TMB was found in low levels. Samples of radiata pine were preconditioned to 3% wood moisture content, treated by momentary immersion in TMB and then stored at 20°C. After vapour diffusion the samples were submitted to an airflow of 0.25 L/min for 24 hrs. Emissions were collected in a water trap. For samples treated at 3% moisture content and stored at 20°C, the analysis showed that only 9.6% of the total production of methanol was found in the emissions. For radiata pine this equals to 28 g/m3/hr. Methanol in the wood is removed easily by water. However a strong bond between wood and methanol is formed. Samples of different species were saturated with methanol and then dried at 105°C for 24 hrs. Twenty nine grams of methanol was found in radiata pine after this process. Pre-conditioning of wood prior to momentary immersion improves the penetration and retention of TMB. Several pre-conditioning processes were studied. Steaming reported better absorption and penetration than microwaving, high temperature and air drying. TMB penetration and a retention of 2.48L/m3 was achieved when steamed radiata pine samples were immersed in TMB for 30 secs. These values were statistically different from values obtained with other processes. Momentary immersion of particleboards in TMB following by a storing stage in a close container was studied. Wood moisture content required to achieve total penetration was 8% for particleboards of thickness 12 and 18 mm. Thicker panels required lower moisture contents. Stiffness (MOE) and strength (MOR) was reduced as maximum as 13 and 17% respectively. Momentary immersion in TMB following by vapour diffusion in a close container was successfully trialed in sapwood of radiata pine, messmate (Eucalyptus obliqua L'Herit), jarrah (Eucalyptus marginata Donn. Ex Sm) and blue gum (Eucalyptus globulus Labill). The effect of non-polar solvents as carriers upon vacuum-pressure impregnation of timber with TMB was studied. Total penetration in sapwood of radiata pine was achieved at wood moisture contents below 14%. The rate of hydrolysis of TMB in non- polar systems was measured and compared with other systems. Non-polar systems have a rate of hydrolysis 26 times slower that polar systems. This allows TMB to penetrate deeper into the timber before hydrolysis begins. Different polymers of trymethylborates were also tested in these systems. Methylpolyborates, a polymer of TMB, were used in the manufacture of pastes and rods for remedial treatments of wood. Methylpolyborates in combination with copper and fluoride compounds were used as active in the manufacture of pastes and rods. Diffusion in stubs of red gum (Eucalyptus camaldulensis Dehnh.) after 60 days demonstrate the feasibility of these TMB polymers as diffusible wood preservatives