Proceedings IRG Annual Meeting (ISSN 2000-8953) © 2012 The International Research Group on Wood Protection
IRG/WP 12-40595
THE INTERNATIONAL RESEARCH GROUP ON WOOD PROTECTION Section 4
Processes and properties
Effects of nano-wollastonite impregnation on fire resistance and dimensional stability of Poplar wood Ali Karimi1,2, Azar Haghighi Poshtir2, Hamid Reza Taghiyari3, Yahya Hamzeh2, Ali Akbar Enayati2 1
Institute of Tropical Forestry & Forest products (INTROP), Universiti Putra Malaysia (UPM), Sertdang, 43400 Selangor, Malaysia (
[email protected])
2
Dept. of Wood and Paper Sciences & Technology, Faculty of Natural Resources, University of Tehran, P.O.Box: 31585-4314 Karadj-Iran (
[email protected]) 3
Department of Wood Science and Technology, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, 021-22970021, Tehran, Iran (
[email protected])
Paper prepared for the 43rd Annual Meeting Kuala Lumpur, Malaysia 6-10 May 2012
Disclaimer The opinions expressed in this document are those of the author(s) and are not necessarily the opinions or policy of the IRG Organization.
IRG SECRETARIAT Box 5609 SE-114 86 Stockholm Sweden www.irg-wp.org
Effects of nano-wollastonite impregnation on fire resistance and dimensional stability of Poplar wood Ali Karimi1,2, Azar Haghighi Poshtir2, Hamid Reza Taghiyari3, Yahya Hamzeh2, Ali Akbar Enayati2 1
Institute of Tropical Forestry & Forest products (INTROP), Universiti Putra Malaysia (UPM), Sertdang, 43400 Selangor, Malaysia (
[email protected])
2
Dept. of Wood and Paper Sciences & Technology, Faculty of Natural Resources, University of Tehran, P.O.Box: 31585-4314 Karadj-Iran (
[email protected]) 3
Department of Wood Science and Technology, Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, 021-22970021, Tehran, Iran (
[email protected])
ABSTRACT The fire-retardant properties of Nano-Wollastonite (NW) in poplar wood (Populus nigra) were determined in this study. Some physical properties such as water absorption, volumetric swelling and Anti-Swelling Efficiency (ASE) were also measured. Specimens were prepared according to the ISO 11925 standard for the fire-retarding properties, and ASTM D4446-2002 standard for the physical properties. Impregnation of wood specimens with nano-wollastonite was carried out using the Ruping Method (empty-cell process) with a concentration of 10%. Three fire-retarding properties were measured; weight loss, ignition point and fire endurance. The results showed that fire-retarding properties increased in the NW-treated specimens. In addition, the NWimpregnated specimens gained higher dimensional stability. However, the water absorption also increased. Keywords: poplar wood, nano-wollastonite, empty-cell process, rire-retardant properties, water absorption, anti-swelling efficiency 1. INTRODUCTION Wood is nature's most wondrous gift to humanityand has been widely used both as structural and decorative materials in buildings and for other uses. However, one of its key disadvantages is its high flammability which is determined by its composition [1-2-3]. The low-flammability of wood and wood based materials will contribute greatly to their applications; therefore the study on flame-retardant treatment of wood and wood based materials aiming to improve the flameretardant properties has amassed considerable industrial and scientific interests in recent years [1-4-6-7-11-12]. The materials commonly used as flame retardants in wood include bromine, chlorine, phosphorous, antimony, boron, nitrogen, silicon, zinc, metal hydroxides, melamine, ammonium, or a combination of two or more of these elements. Some of these flame retardants are practically always used with another synergist. For example, antimony, boron, nitrogen, silicon, and zinc are often used with phosphorous or halogenated compounds based on chlorine and bromine, which are effective flame retardants, and ammonium polyphosphate that is known to intumesce [2-4-9-10]. These materials can improved fire resistance through the following mechanisms; 1) redirecting decomposition and combustion reactions regarding the evolution of non-combustible gases, or producing heavy gases that interfere with the interchange of combustion gases and air, 2) redirecting the combustion and decomposition reactions towards reducing the heat of combustion, 3) maintaining the physical entirety of the material, and 4) increasing the specific heat or thermal conductivity [2-8]. While there are environmental concerns regarding the use of these materials, some of them are still widely used in industrial applications [2]. Furthermore, because of their water solubility, wood treated with these 2
materials are not suitable for exterior and underground construction, where the flame retardants leach easily [1-2-5]. Based on the above mentioned literature review, besides flammability, fire-retardant chemicals may be assessed by three main perspectiveswhich are the reduction in the strength of wood and corrosion on fasteners, increased hygroscopicity, and the amount of toxic and smoke gases produced. Although all these perspectives have been considered over the years and nearly all requirements are met in new fire-retardant formulations, fire-retarding properties of nanowollastonite should be studied as it does not contain any acidic chemicals. In the meantime, its nature as a mineral may be a barrier towards fire or heat transfer. In the meantime, wollastonite mines are abundant in Iran and could decrease the cost of preservation. Therefore, the possibility of using nano-wollastonite as a fire retardant in poplar wood is studied. 2. EXPERIMENTAL METHODS 2.1 Specimen Preparation Wood specimens were prepared according to the ISO 11925 standard with dimensions of 150 (length) × 100 (width) × 9 (thickness) mm. The length of the specimens was in the longitudinal and the width in the marginal direction of wood, for the fire-retarding properties. Tests for the physical properties were carried out using the ASTM D4446-2002 standard with the specimen sizes being 2 ×2×2 mm. Impregnation of wood specimens with nano-wollastonite was carried out using Ruping method (empty-cell process) at a concentration of 10% and a pressure of 3 atm for 2 hours. Specimens were kept in a conditioning chamber (20 ± 5 °C, and 25% relative humidity) for 2 months before tests were carried out on them. The moisture content of the specimens at the time of testing was 6.5%. Ten wood specimens were prepared for each treatment. All tests were carried out 2 months after the impregnation process with NW. For the fire-retardancy tests, an apparatus that was invented by the third author according to ISO 11925-3 standard was used (Iranian patent No. 67232). In this apparatus, the specimen was mounted vertically on a holder up-straight and exposed to a Bunsen-type burner held at 45 degrees to the surface of the specimen for 120 seconds in accordance with the ISO 11925-3 standard. The burner was fixed on a slidethat can be moved back and forth and equipped with an adjustable stop to keep the flame at a certain distance from the specimen. When the slide was away from the specimen, the burner was turned on and the slide wasthen pulled forward abruptly to expose the specimen to the flame. The time it takes for each specimen to catch an evident visible flame on the spot nearest to the Bunsen-type burner, and the time that the spot starts to glow were registered as ignition and glowing times respectively. After 120 seconds, the slide was pulled back to prevent over-exposure of the specimen to the flame. The length of time that the specimen keeps a visible fire after the removal of the burnerwas registered as the fire endurance time (the duration time of a visible flame). Once the flame was extinguished or the specimen was no longer burning, the carbonization areawas measured. The weight was also measured before and after the test to calculate the weight loss. The water absorption and volumetric swelling of each specimen were measured after the specimens were soaked in water for 2 and 24 hours. Then the ASE of the samples was also calculated to determine the effects of nano-wollastonite on the dimensional stability of treated specimens. The nano-wollastonite gel was procured from Vard Manufacturing Company of Mineral and Industrial Products, Iran. Wollastonite mines are abundant in Iran and therefore may decrease the preservation costs.
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2.2 Statistical Analysis Statistical analysis was conducted using the SPSS software program, version 16. One-way analysis of variance (ANOVA) was performed on the data to conclude significant differences at 95% level of confidence. 3. RESULTS AND DISCUSSION 3.1 Weight Loss The results showed that the percentage of weight loss in NW-treated specimens (Fig.1) was lower than non-treated specimens. This reduction was significant and it was about 1.5 times less in comparison to non-treated specimens (49.64%). 3.2 Ignition Point The longest ignition times were found in NW-treated specimens at 14.44 seconds, while the lowest was 9.65 secondsfor untreated specimens (Fig.2).
Figure 1. Weight loss in control and nanowollastonite impregnated specimens
Figure 2. Ignition point in control and nanowollastonite impregnated specimens
3.3 Fire Endurance The results showed a highly significant difference between NW-treated and untreated specimens. The duration of flame decreased by 77.17% in NW-treated specimens compared to non-treated specimens (Fig.3). 3.4 Water Absorption As shown in Figure 4, the water absorption of NW-treated specimens was higher than untreated specimens. The gain in NW-treated specimens in comparison to the untreated specimens was 28.88% and 37/62% after 2 and 24 hours respectively. This was an unexpected result because NW is less hygroscopic than wood and during the treatment process, it is expected that the NW would fill the pores in wood, thus lowering the water absorption. However, the opposite result was found and this could be due to a few reasons. The treatment process could have caused minute cracks in the specimens which might result in increased pore connectivity thus allowing more water to penetrate and fill pores that were previously isolated.
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3.5 Volumetric Swelling The volumetric swelling of NW-treated specimens was significantly less in comparison to untreated specimens. The NW-treated specimens had 28.94% and 30.02% less swelling than untreated specimens after 2 and 24 hours respectively (Fig.5). This result was expected because the NW covers the surface of wood in the specimens thus lowering the bound water absorption and this in turn would reduce the swelling of the specimens.
Figure 3. Fire Endurance in control and nano-wollastonite impregnated specimens
Figure 4. Water absorption in control and nano-wollastonite impregnated specimens
3.6 Anti-Swelling Efficiency (ASE) The results showed that NW-impregnation significantly increased the dimensional stability of the treated specimens (Fig.6).
Figure 5. Volumetric swelling in control and nano-wollastonite impregnated specimens
Figure 6. Anti-Swelling Efficiency in control and nano-wollastonite impregnated specimens
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4. CONCLUSIONS Based on the obtained results and analysis, it may be concluded that impregnated wood species with nano-wollastonite significantly improved its fire resistant properties. Furthermore, the treated wood specimens showed higher dimensional stability but the water absorption was higher than untreated specimens. ACKNOWLEDGMENTS The authors are grateful to Mr. Mohammad Hossein Vardi, the managing director of Vard Manufacturing Company of Mineral and Industrial Products, for providing the Nanowollastonite gel. 5. REFERENCES 1. Hongqiang, Qu., Weihong, Wu., Yunhong, Jiao., Jixing, Xie. and Jianzhong, Xu. (2011). Investigation on the thermal decomposition and flame retardancy of wood treated with a series of molybdates by TG–MS. J Therm Anal Calorim 105: 269–277. 2. Stark, Nicole M., White, Robert H., Mueller, Scott A. and Osswald, Tim A. (2010). Evaluation of various fire retardants for use in wood flour–polyethylene composites. Polymer Degradation and Stability 95: 1903–1910. 3. Sain , M., Park, S.H., Suhara, F., Law, S. (2004). Flame retardant and mechanical properties of natural fibre–PP composites containing magnesium hydroxide. Polymer Degradation and Stability 83: 363–367. 4. Taghiyari, H. R., Rassam, Gh., Lotfinejad Sani Y, and Karimi, A. (2012). Effects of nano-silver impregnation on some mechanical properties of ice-blasted specimens prepared from two native species. Journal of Tropical Forest Science, in press: JTFS Jan. 2012. 5. Taghiyari, H. R. (2011). Fire-Retarding Properties of Nano-Silver in Solid Woods. Wood Science and Technology, Accepted Oct. 2011. 6. Baysal, E., Altinok, M., Colak, M., Ozaki, K., Toker, H. (2007). Fire resistance of Douglas fir (Pseudotsuga menzieesi) treated with borates and natural extractives. Bioresource Technology, 98, 1101–1105. 7. Luyt, A.S., Dramicanin, M.D., Antic, Z., Djokovic, V. (2009). Morphology, mechanical and thermal properties of composites of polypropylene and nanostructured wollastonite filler. Polymer testing 28, 348-356. 8. Ransinchung, G.D., Kumar, B., Kumar, V. (2009). Assessment of water absorption and chloride ion penetration of pavement quality concrete admixed with wollastonite and microsilica. Construction and Building Materials 23, 1168-1177.
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9. Hamid Reza Taghiyari, Bahman Moradi Malek, Ali Karimi (2011). Effects of nano-silver on brittleness of heat-treated solid woods. Proceeding IRG Annual Meeting, IRG/WP 1140572. 10. Hamid Reza Taghiyari, Aisona Talaei, Ali Karimi (2011). Effects of Heat-Treatment in Hot Water and Steam Mediums on Gas Permeability of Beech Wood. Proceeding IRG Annual Meeting, IRG/WP 11-40557. 11. Perré P., Karimi A. (2002). Fluid Migration In Two Species of Beech (Fagus silvatica and Fagus orientalis): A Percolation Model Able to Account for Macroscopic Measurements and Anatomical Observations. Maderas, 2002, 4(1). 12. Karimi A.N., Perre P. (2005). Investigation of transport process in macro and microscopic scale in Beech wood, interpretation with the aid of a percolation model. 9th IUFRO Wood Drying Conference, 21-26 August 2005, China.
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