Fire resistance of wood treated with potassium carbonate and silanes

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1 Proceedings IRG Annual Meeting (ISSN ) 2014 The International Research Group on Wood Protection IRG/WP THE INTERNATIONAL RESEARCH GROUP ON WOOD PROTECTION Section 3 Wood protecting chemicals Fire resistance of wood treated with potassium carbonate and silanes Bartłomiej Mazela 1, Magdalena Broda 1, Waldemar Perdoch 1 1 Poznan University of Life Sciences, Institute of Wood Chemical Technology, Wojska Polskiego 38/42, Pl Poznan, Poland bartsimp@up.poznan.pl Paper prepared for the 45 th IRG Annual Meeting St George, Utah, USA May 2014 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 Stockholm Sweden

2 Fire resistance of wood treated with potassium carbonate and silanes Bartłomiej Mazela 1, Magdalena Broda 1, Waldemar Perdoch 1 1 Poznan University of Life Sciences, Institute of Wood Chemical Technology, Wojska Polskiego 28, Pl Poznan, Poland bartsimp@up.poznan.pl ABSTRACT This paper reports on the effect that organosilicon compounds and potassium carbonate and urea (PCU) have on wood flammability. The study focus on reducing wood flammability by promoting char formation through manipulation of the condensed phase decomposition chemistry. Potassium carbonate is known as an effective fire retardant, however it is easily leached out from wood and increases its hygroscopicity. The aim of the research was to assess the ability of selected organosilicon compounds to reduce potassium carbonate leachability from the treated wood. The study was performed through the mini fire tube (MFT) method, where fireproofing properties of the treated wood were evaluated. Pine sapwood treated with PCU at the retention of ca. 160kg/m 3 showed 6% of wood mass loss as a result of combustion in MFT. The fireproofness effect has been reduced due to the ageing procedure and displayed 60% of wood mass loss. It has been shown that some selected silanes or their blends with siloxanes, superficialy applied on treated wood, allowed to retain PCU in wood and maintain its fireproofness. Wood mass loss resulting from sample s combustion was significantly reduced (ML<10%). AEAPTMOS, VTMOS and a mixture of alkylalkoxysilanes turned out to be most effective agents limiting potassium carbonate leachability and maintaining wood fireproofness. Keywords: fire resistance, fire retardant, wood treatment, fireproofing agents, potassium carbonate, organosilicon compounds, silane, leaching 1. INTRODUCTION There are several ways of producing a combined fire retardant and wood preservative treatment system. One method is modification of an existing preservative suitable for in-door or out-door applications by the addition of a fire retardant. Sometimes it is fixing into wood of conventional preservatives that demonstrate good fire retardancy. Another method is inorganic modification of wood to form wood-inorganic composites (Miyafuji and Saka 2001). White and Sweet (1992) produced an extensive literature review covering the period This review paper covered approaches used to produce a combined fire retardant-preservative treatment for wood. They found that the most promising approaches were in situ deposition of insoluble inorganic compounds and organic polymers that included nitrogen and phosphorus in the polymer chain. Since 1992 further studies have been carried out (Marney and Russell 2008). Intumescent coatings make the most efficient way of fire retarding of flammable materials. The coatings swell under the influence of heat and form a thick porous charred layer. The latter perfectly insulates a substrate against excessive increase of temperature and oxygen access. In order to make intumescent coatings more effective, a proper selection of essential 2

3 components, i.e. carbonizing, foam-producing and dehydrating materials, is necessary. The choice of components for an intumescent fire retardant composition has an essential effect on the rate of charred mass formation and its structure (Wladyka-Przybylak 2000). The predominant approach is still one of formation of wood-inorganic composites, often using boron-based compounds to utilize its ability to act as both a wood preservative and a fire retardant. The leaching issues associated with boron compounds is often overcome by use of a fixing process, rendering the boron inaccessible to water during the useful life of the timber. Often the means of controlling the leaching of boron is by forming a water insoluble organic polymer around the boron (Ratajczak and Mazela 2007). The exception to this is the work by Lewin (1997) where bromine is used to modify the wood. Another creative approach is to synthesize a ceramic or glass type material by impregnating pre-ceramic compounds, such as silicic acid or silanes along with a source of phosphorus and boron, into the timber in a sol gel type process and then complete the process by control of solution ph or by changing temperature conditions and subsequent drying at slightly elevated temperatures. An alternative to the use of halogenated fire retardants, which control flammability by changing the chemistry in the flame, is to control wood flammability by manipulating the condensed phase chemistry. Additives that increase the amount of charcoal-like residue or carbonaceous char that forms during wood combustion are very effective fire retardants (Gilman et al. 1996). The following study focus on reducing wood flammability by promoting char formation through manipulation of the condensed phase decomposition chemistry. This paper reports on the effect that organosilicon compounds and potassium carbonate and urea have on wood flammability. The aim of the study was to evaluate experimentally under laboratory conditions the effectiveness of pine wood fire protection with the use of compounds based on potassium carbonate and measuring the effect of the stability of organosilicon compounds on potassium carbonate as the main ingredient of this fire retardant. Potassium carbonate (K 2 CO 3 ) is known as an effective fire retardant and its most important advantage is its high solubility in water, fungicidal properties, low corrosivity of iron and the lack of harmful effects on humans and animals both in solution and combustion products (Grześkowiak 2012). Furthermore, potassium carbonate is capable of forming a foam layer under high temperature, which reduces the heat transfer into the material. Unfortunately, this compound is easily leached out from the wood, it increases its hygroscopicity and water absorption. In order to reduce potassium carbonate leachability and limit the hygroscopicity of the treated wood, organosilicon compounds were used in the following study. The aim of the research was to assess the ability of selected organosilicon compounds to reduce potassium carbonate leachability from the treated wood. The study was performed through the mini fire tube (MFT) method, where fireproofing properties of the treated wood were evaluated. 2. EXPERIMENTAL METHODS 2.1. Materials and treatment method Pine sapwood (Pinus sylvestris L.) in the form of samples with dimensions 5x10x100mm (the last dimension along the fibers) were used in the study. Oven-dried wood samples had average density of 480kg/m 3. The fireproofing agent was the potassium carbonate and urea in a weight ratio of 3:1 (PCU). The treatment formulation was 20% water-based solution of PCU. Wood samples were vacuum treated under the following conditions: 0.1MPa for 30min, and next under atmospheric pressure for 120min. The PCU retention in wood was approximately 160kg/m3. After 7 days of conditioning, samples treated with PCU were coated with organosilicon compounds (Table 1). 3

4 Table 1. Composition of fireproofing agents. Silane Silane Code Silane name Composition Formulation code - - Potassium carbonate 15% PCU - reference Urea 5% system TEOS Triethoxy(octyl)silane Triethoxy(octyl)silane PCU/TEOS VTMOS Vinyltrimethoxysilane Vinyltrimethoxysilane VTMOS BLEND1 Mixture of Alkoxysilanes Tetraethoxysilane 85,0 100,0% PCU/BLEND1 Ethanol <1,0% Triethoxymethylsilane <1,0% BLEND2 Mixture of Alkoxysilanes Trimethoxymethylsilane 7,0-13,0% PCU/BLEND2 Triethoxy(octyl)silane 5,0-10,0% Tetra butyl titanate 1,0-5,0% Octamethylcyclotetrasiloxane 1,0-5,0% Methanol 1,0% BLEND3 Triethoxy(octyl)silane Triethoxy(octyl)silane 98,0% PCU/BLEND3 branched Octyltriethoxysilanes 2,0% AEAPTMOS Aminethyl-aminpropyl Aminethyl-aminpropyl trimethoxysilane PCU/AEAPTMOS trimethoxysilane >60,0% Methoxysilane 15,0-40% Methanol <1,0% MTMOS Methyltrimethoxysilane Methyltrimethoxysilane >99,5% PCU/MTMOS GPTEOS (3- Glycidyloxypropyl)trieth oxysilane (3-Glycidyloxypropyl)triethoxysilane 99,0% Methanol 1,0% BLEND4 Methyltrimethoxysilane Methyltrimethoxysilane 90,0-98,0% Methanol 1,0-5,0% Methyldimethoxysilane 1,0-5,0% BLEND5 PRT Mixture of Alkyl alkoxysilanes Protectosil SC CONCENTRATE Metanol 50,0% Octadecyldimethyl [3(trimethoxysilyl)propyl] ammonium chloride 42% 3-Chloropropyltrimethoxysilane 8% 3-(trimethoxysilyl)propyl Hexadecyldimethyl ammonium chloride >0,1 PCU/GPTEOS PCU/BLEND4 PCU/BLEND5 - PCU/PRT 2.2. Artificial ageing cycle Treated samples (acc. to Table 1) have undergone a process of artificial ageing including 4 identical cycles. Each cycle was as follows: a) Heating at 70 C for 12h; b) Leaching (5 parts of water volume to 1 part of wood volume) for 12h; c) Freezing at -25 C for 12h; d) Leaching (5 parts of water volume to 1 part of wood volume) for 12h. 2.3 Combustibility test All samples were oven-dried before the combustion and their mass was recorded. Assessment of fireproofing efficiency was performed through the MFT. The measurement was based on an analysis of mass loss (ML) of samples and the temperature changes (T) as a result of fire action. The central part of the device was a fire tube made of aluminum. Inside the fire tube a wood sample was placed vertically, just above the flame. The source of fire was a gas burner, and the flame height was approximately 20mm. The flame was maintained for a period of 6 4

5 minutes and so was the whole experiment. The fire tube was placed on an analytical balance. A thermocouple was located at the exhaust outlet of the mini tube. The analytical balance and heat detector were linked to a computer. The computer recorded wood mass loss and temperature changes during the entire measurement with intervals of 2 seconds. 3. RESULTS AND DISCUSSION The wood treated with PCU system as a result of sample combustion showed a mass loss of about 6.5%. This fact proves a high efficiency of the fireproofing agent. As a result of artificial ageing, the fireproofing properties of wood treated with PCU were reduced and mass loss was about 60%. With the increase of mass loss of aged wood, the increase of temperature during combustion was observed. After the period of 154 seconds, of exposure to fire, the mass loss of wood subjected to leaching was the most intense and the temperature reached 240 C. The maximum combustion temperature of unaged wood was 71 C. The details of the mass loss and the combustion temperature are shown in figure 1. The obtained results confirm a need for stabilizing fire retardant in wood. Figure 1. Mass loss (A) and temperature (B) due to combustion time of wood treated with PCU before and after leaching (L). Table 2 summarizes the results of wood absorption of PCU containing formulations and secondary treated with organosilicon compounds. The results of mass loss after the artificial ageing process and after combustion are also presented. Table 2. Retention of fireproofing agents and mass loss after combustion of wood samples. Formulation code PCU retention [kg/m 3 ] Silane retention [g/m 2 ] Mass loss after ageing test [%] Mass loss after combustion [%] PCU ,6 59,3 PCU/TEOS ,0 12,2 VTMOS ,9 19,6 PCU/BLEND ,1 93,5 PCU/BLEND ,0 8,6 PCU/BLEND ,8 9,9 PCU/AEAPTMOS ,8 9,6 PCU/MTMOS ,9 9,0 PCU/GPTEOS ,2 22,4 PCU/BLEND ,7 53,5 PCU/BLEND ,6 11,1 PCU/PRT ,7 42,0 5

6 The secondary treatment with organosilicon compounds formed a coating effect on a wood surface. The absorption was ranging from 65 to 265g/m 2 depending on the type of silane. The wood mass loss caused by leaching due to the artificial aging trials was also related to the types of silane coatings and ranged from 23% to 29%. Based on the obtained data, a direct relationship between mass loss due to aging and an application rate of the coating cannot be estimated. All of the used organosilicon compounds (with the exception of BLEND1) increased fireproofness of PCU-treated wood. Satisfactory results were obtained for the following agents: AEAPTMS, MTMOS, BLEND2, BLEND3. Wood mass loss due to combustion of samples coated with above mentioned agents did not exceed 10%. The results did not show a clear relationship between wood mass loss as a result of aging trials and a mass loss as an effect of combustion. The course of mass loss due to combustion is presented in figure 2. Figure 2. Wood samples mass loss during the combustion process. The temperature measured at the end of furnace tube during combustion depends on the speed and the percentage of mass loss. The highest value of the temperature corresponds to the most intense mass loss. Table 3 shows the maximum value of temperature recorded for all tested fireproofing agents. Table 3. Schedule of mass loss and temperature courses during combustion of PCU-silane treated wood samples. System code Maximum temperature [ C] Time to get maximum temperature [sec] Temperature at the end of experiment [ C] Final mass loss [%] PCU 240, ,8 59,3 PCU/TEOS 112, ,0 12,2 PCU/VTMOS ,7 19,6 PCU/BLEND1 459, ,6 93,5 PCU/ BLEND2 96, ,9 8,6 PCU/ BLEND3 91, ,4 9,9 PCU/AEAPTMOS 88, ,2 9,6 PCU/MTMOS 90, ,2 9,0 PCU/GPTEOS 147, ,8 22,4 PCU/BLEND4 287, ,5 53,5 PCU/ BLEND5 92, ,5 11,1 PCU/PRT 256, ,6 42,0 6

7 The reference sample (PCU) and samples treated with PCU/BLEND1 showed a maximum wood mass loss (the value of ML exceeded 50%). The maximum temperature reached 240 and 450 o C respectively. The course of temperature due to combustion of wood treated with PCU, PCU/AEAPTMOS and PCU/GPTEOS was presented on figure 3. PCU and PCU/AEAPTMOS showed an extreme readings of the maximum temperature during the combustion (240 and 89 o C respectively). The value of final wood mass loss for these two agents was also divergent (59,3 and 9,6% respectively). Figure 3. The temperature course during combustion of wood treated with PCU, PCU/AEAPTMOS and PCU/GPTMOS. 4. CONCLUSIONS Fireproofing agent based on PCU effectively reduced wood flammability. Pine sapwood treated with PCU at the retention of ca. 160kg/m 3 showed 6% of wood mass loss as a result of combustion in MFT. However, PCU fireproofness was not durable in wood exposed to ageing procedure. The same sample treated at the above mentioned conditions, subjected to ageing procedure and then burned in MFT, showed c.a. 60% of mass loss. Due to the PCU water solubility and its high leachability, the fireproofness of aged wood samples decreased. It has been shown that the following organosilicon compounds: AEAPTMOS, BLEND2, BLEND3 and MTMOS, superficialy applied on treated wood allowed to retain PCU in wood and maintained its fireproofness (ML<10%). AEAPTMOS, VTMOS and BLEND5 turned out to be most effective agents limiting potassium carbonate leachability and maintaining its fireproofness. Acknowledgment This work was partially supported by the National Centre for Research and Development of Poland supported by Norway Grants as a part of Polish-Norwegian Research Programme as the DURAWOOD project Pol-Nor/203119/32. 7

8 5. REFERENCES Gilman J.W., Kashiwagi T., Lomakin S.M. (1996): Environmentally safe fire retardants for polymeric materials I. Silica gel potassium carboanate additive. 41 st International SAMPE Symposium, March Grześkowiak, W (2012): Evaluation of the effectiveness of the fire retardant mixture containing potassium carbonate using a cone calorimeter. FIRE AND MATERIALS, Fire Mater. 2012; 36: Lewin M. (1997): Flame Retarding Wood by Chemical Modification with Bromate-bromide Solutions, Journal of Fire Science, vol. 15, 1997, pp Marney D.C.O., Russell L.J. (2008): Combined Fire Retardant and Wood Preservative Treatments for Outdoor Wood Applications A Review of the Literature. Fire Technology. March 2008, Volume 44, Issue 1, pp 1-14 Miyafuji H., Saka S. (2001): Na20-Si02 wood-inorganic composites prepared by the sol-gel process and their fire-resistant properties. Journal of Wood Science, 47: Ratajczak I., Mazela B. (2007): The boron fixation to the cellulose, lignin and wood matrix through its reaction with protein. Holz als Roh- und Werkstoff 65: White, R. H. and Sweet, M. S. (1992): Flame Retardancy of Wood: Present Status, Recent Problems and Future Fields. Recent Advances in Flame Retardancy of Polymeric Materials. Proceedings of 3rd Annual BCC Conference on Flame Retardance, Stamford, CT. Wladyka-Przybylak M. (2000): Combustion Characteristics of Wood Protected by Intumescent Coatings and the Influence of Different Additives on Fire Retardant Effectiveness of the Coatings, Molecular Crystals and Liquid Crystals, 354: 1,

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