DEVELOPMENT OF EMULSION AND IMPREGNATION TECHNOLOGY FOR WOOD BIOPROTECTION

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1 8th International DAAAM Baltic Conference "INDUSTRIAL ENGINEERING April 2012, Tallinn, Estonia DEVELOPMENT OF EMULSION AND IMPREGNATION TECHNOLOGY FOR WOOD BIOPROTECTION T. Kaps, R. Reiska, U. Kallavus, Ü. Luga & J. Kers Abstract: The timber used in impregnation and leachability experiments was vacuum dried pinewood (Pinus silvestris). Impregnating emulsion joins the benefits of both water solutions and oil. The new impregnation emulsion was tested against the emulsion prepared from widely used Tanalith E wood preservative. The obtained results demonstrated that a new penetration agent ensures effective protection against wood rotting fungi and discolouring fungi. Bio testing at Latvian State Institute of Wood Chemistry (EN113) revealed that a new penetration agent ensures effective protection against wood rotting fungi (mass loss less than 3%) and discolouring fungi (mould). Key words: Pine-wood, rapeseed oil-based wood preservatives, protection against wood rotting 1. INTRODUCTION Pinewood is most common material to be used in building and construction as well in furniture industry. For use in outdoor conditions it is important to protect pinewood against rotting fungi. When impregnated wood is exposed to surface water during its service life, toxic substances in wood preservatives like chromium and arsenic can leach and harm the environment [ 1 ]. After the use of chromium and arsenic containing preservatives (CCA) was restricted due to environmental concerns, other systems were introduced. Nonbiocidal techniques for wood protection have become more and more important in the last few years. One of the possible treatments to enhance wood durability is use of water repellents [ 2 ]. Former studies show that CCA bounds copper most effectively and the element is not that strongly bound in other preservatives [ 2-3 ]. Solutions of Wolmanit CX-8 and Tanalith were used for impregnation procedure [ 4 ]. Therefore copper consisting protecting agents are under observation as well. Some alternative preservative systems for pine wood are developed in papers [ 5 ]. In water environment inorganic constituent chemicals diffuse into wood cell wall regions and protect wood against aggressive decay. Drying vegetable oil in this case rapeseed oil forms on the internal surfaces of wood cell and inside microcapillaries hydrophobic polymerised film what decreases the washing-out of active ingredients. To compare the impregnation results of rapeseed oil and boron based emulsion, the commonly used copper consisting waterbased impregnation solutions Tanalith-E was used. Leaching is influenced by the conditions where the wood is placed into, water ph and flow, also by site, species and preservatives, extractive content in wood etc. [ 6-7 ]. The leaching of boron from spruce wood impregnated with preservative solutions based on boric acid can be significantly reduced [ 8 ]. The main objective of the current research work was to develop new environmentally friendly impregnation emulsion for effective protection of pine wood against rotting fungi. The new impregnation emulsion was tested against the emulsion 627

2 prepared from widely used Tanalith E wood preservative. 2. EXPERIMENTAL STUDY 2.1 Material The round wood and sawn timber of Scots pine (Pinus silvestris) were selected for impregnation experiments. The samples of pine roundwood stem were with outside dimensions 1000mm in length and about 200 mm of diameter The density of used Estonian pinewood was in the range of kg/m 3 and about 5 8 rings per 1cm. To prevent the liquid flow in the longitudinal direction, cross sections of the samples were sealed with nitrolaquer. To ensure the more effective penetration of impregnation agent the vacuum drying process was used. After vacuum drying the resin canals in pinewood are easier permeable compared to other drying methods. 2.3 Impregnation technology For wood impregnation two main types of technological processes are in use non-pressure and pressure based processes. In nonpressure based passive-impregnation methods the preservatives are applied by means of brushing or spraying, dipping, soaking, steeping or by means of hot and cold bath [8]. The most common wood protection processes are based on treatments in closed cylindrical vessels, where deeper and more uniform penetration and a higher absorption of preservative can be achieved by applied vacuum or pressure conditions [9]. To perform the impregnation tests with rapeseed oil based emulsion and Tanalith E new autoclave with 1m 3 capacity and 16 bar maximum pressure was designed and built in laboratory of TUT Woodworking Chair (see Fig. 3). 2.2 Development of emulsion The developed impregnating emulsion is based on rapeseed oil in water emulsion. The optimal concentration of rapeseed oil in water emulsion was determined experimentally. Active ingredients for emulsion were chosen among Boron compounds borax, boric acid and quaternary ammonium salts QUATS (here dioctylmethyl ammonium chloride). Boron compounds ensure the potential bio protection against wood rotting fungi and QUATS against discolouring fungi. To stabilize the emulsion oleic acid and the by-product of the rapeseed oil production (partially de-esterificated rapeseed oil, socalled acid oil) was used. Emulsification was carried out in a TUT developed specific pulsating emulsifier apparatus. During the emulsion preparation experiments two pulse frequencies of 900 and 1800 Hz were used. The viscosity and stability of emulsions were analysed. Fig. 3. Autoclave used in pinewood impregnation process In impregnation experiments the water-based pressure impregnation treatment in pressure autoclave was used. 2.4 Leaching test To assess leachability of emulsions two methods were worked out M1 and M2. Method M1 is based on analyzing copper and boron content after 24h leaching in C water. Firstly, the specimens were cut from impregnated roundwood in radial direction with dimensions 40x25x25 mm. Then the specimens were dried and all 628

3 sections were covered with polyvinyl acetate glue, only outside tangential surface was not covered. Then the specimens were soaked in C water about 24 hours. Leaching method M2 was based on imitation of rainy conditions to the impregnated wood. The specimens were cut from impregnated roundwood in stem direction with dimensions 60x30x30 mm. Then the specimens were dried and all sections were covered with polyvinyl acetate glue, only outside tangential surface was not covered. Then the specimens were tested under burette with 100ml water and test speed was about 8-12 drops per minute. The content of copper and boron was analyzed in collected leaching water. The copper content in leaching water was analyzed by atomic absorption spectroscopy (AAS). The boron content in leached-out water was analysed via ICP (Inductively Coupled Plasma) technique. emulsion it is advisable to use emulsion during first 8 hours. Working emulsion is reusable in impregnation process. Emulsification technology Pulsation frequency, Emulsion mark Properties of emulsion Particles size, m Visco -sity, s Hz T T U Table 1. Properties of emulsions 2.5 Decay test Bio testing was performed in Latvian State Institute of Wood Chemistry according to standard EN 113. Scots pine (Pinus sylvestris L.) sapwood blocks ( mm) were cut out from impregnated sapwood. Wood specimens were sterilized and conditioned. The specimens were exposed to fungi according to the EN113 (1996) using brown-rot fungies Coniophora puteana, Gleophyllum trabeum, Poria Placenta. Fig. 1. Emulsion U25 2%, Boroncompounds, Rapeseed oil 3%, Acid oil 3% 3. RESULTS AND DISCUSSION 3.1 Developed emulsion Emulsification technology tests were made with pulsating emulsifier with two different frequencies 900, 1800 Hz (see Table 1). Change of pulsating frequencies did not change the viscosity remarkably and after repetition of emulsification experiments particles size was still in the same range and emulsion stability was good (see Figs 1 and 2). Obtained emulsion is stable for 24 hours but for the assurance of higher dispersion rate of the Fig. 2. Emulsion T27: Tanalith E 2%, Rapeseed oil 3%, Acid oil 3%. 629

4 3.2 Developed impregnation technology The impregnating agent was carried in the wood in one technological step. The developed technological regime for the penetration was as following: preliminary vacuum treatment at 100 mbar for 0.5 hours; pressure impregnation at 12.5 bar for 1 hour; final vacuum treatment was executed 100 mbar for 0.5 hours. To evaluate the penetration efficiency absorption rate of the agent (standard load 200 kg/m 3 ), average depth of penetration, leaching-out of active components and bio resistivity was carried out. After the impregnation tests the colour characteristics of a wood impregnated with new agent are similar to those of untreated wood (see Figs 4-5). To compare the leaching test results with aqueous solutions and emulsions, the leach ability of active agent reduced for Tanalith E based emulsions about 2.3 times and for emulsion with rapeseed oil and boroncompounds about 1.7 times. Washing out of active components in the rapeseed oil based penetration agent with minimal oil content (2%) is 1.5 times less than with water solutions (see Table 2). The absorption of emulsion in pine sapwood was in similar range with oil based and water based emulsions. Emulsion marking Density kg/m 3 Wood properties Rings no/cm Humidity % Absorbtion of emulsion kg/m 3 Impregnation test results Average impreg - Stat. Leach ability. Cu or B *, mg nation deviation M1 M2 depth mm mm T T TVL U * 28 * UVL * 47 * Table 2. Results of the impregnation tests Fig. 4. Results of impregnation tests of pine roundwood with Tanalith-E agent 630 Fig. 5. Results of impregnation tests of pine roundwood with Rape-seed oil based emulsion

5 In impregnation tests two additional emulsions (TVL Tanalith E aqueous solution and UVL Aqueous solution of boron compounds) were compared with developed oil in water emulsions. The best absorption results gave oil in water emulsion where the maximum concentration of the rapeseed oil concentration was 4 % of the emulsion. In the case of higher concentrations of oil the permeability of the sapwood decreased even when the effect of hydrophobisation was increased. The results of impregnation process showed that the sawn timber of pinewood could be penetrated more effectively than that of pine roundwood. This effect is explained with the greater specific surface area of sawn timber. Used impregnation regime allows penetrating sapwood up to % The obtained results demonstrated that the new penetration emulsion ensures effective protection against wood rotting fungi and discolouring fungi (see Fig. 6). The most effective emulsion against wood rotting fungi penetration agent had the composition of 3.5% boron compounds, 2% rapeseed oil, 2% acid oil. Mass-loss caused by fungal decay was after leaching less than 3% (according to EN113). On the basis of this scientific research an utility model Method of preservation of pinewood has been received (EE ). 5. ACKNOWLEDGEMENTS This research work was supported by Enterprise Estonia Research and Development programme project Improved impregnating technology for pinewood protection. ERDF project code EU REFERENCES Fig. 6. Mass loss of different treated and untreated wood samples 4. CONCLUSION Effective rapeseed oil and boroncompounds based emulsion was worked out. Leachability of active components in the penetration agent with minimal oil content (2%) is 1.5 times less than with only water based solutions. With increasing the oil content in emulsion composition it can be presumed that leachability of wood preservatives decreases even more. 1. Sierra-Alvarez, R., Removal of Copper, Chromium and Arsenic from Preservative-Treated Wood by Chemical Extraction-Fungal Bioleaching, Waste Management, Vol. 29, 6, 2009, pp Lesar, B., Straze, A., Humar, M., Sorption Properties of Wood Impregnated with Aqueous Solution of Boric Acid and Montan Wax Emulsion, Journal of Applied Polymer Science, Vol. 120, 3, 2011, pp Temiz, A., Yildiz, Umit C. & Nilsson, T Comparison of Copper Emission Rates from Wood Treated with Different Preservatives to the Environment. Building and Environment 41, 7, 2012, pp Kängsepp, K., Larnøy, E., 2, Meier, P., The Influence of Sample Origin on the Leachability of Wood Preservatives, 631

6 Materials science, 17, 3, 2011, pp Liibert, L.; Treu, A.; Meier, P., The Fixation of New Alternative Wood Protection Systems by Means of Oil Treatment, Materials Science,17, 4, 2011, pp Freeman, M. H., McIntyre, C. R A Comprehensive Review of Copper- Based Wood Preservatives. Forest Products Journal, 58(11): Dickey, P Guideline for Selecting Wood Preservatives. For the San Francisco Department of the Environment 8. Islam, MN, Ando, K., Yamauchi, H., Kobayashi, Y., Hattori, N., Comparative Study between Full Cell and Passive Impregnation Method of Wood Preservation for Laser Incised Douglas Fir Lumber, Wood Science and Technology, Vol. 42, 4, 2008 pp Winfield, PH., Becerra, N., Kaczmar, P.,Investigation of Primer/Preservative Basecoats for Timber Using Vacuum Impregnation, International Journal of Adhesion and Adhesives, Vol. 29, 7, 2009, pp ADDITIONAL DATA ABOUT AUTHORS Tiit Kaps, PhD. Professor Emeritus Chair of Woodworking Department of Polymer Materials Tallinn University of Technology Teaduspargi 5, 12618, Tallinn, Estonia Phone: tiit.kaps@ttu.ee 632