Value to Wood No. FPI-113E Reduction of volatile organic

Reduction of volatile organic compound emissions (VOC, odours) for indoor wood products

Project No. 201001000

Value to Wood No. FPI-113E

Final Report 2009-2010

by

Alpha Barry Scientist, Group Leader

Wood Composites

March 2010

Alpha Barry Project Leader

Ayse Alemdar Reviewer

Gérald Beaulieu Department Manager


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AbstractNanoparticles including four metal oxides and two nanoclays were used in a water based coating to compare their effectiveness as emission barriers for formaldehyde and VOCs. Initially five nanoclays (Cloisite 30B, Cloisite Na+, Nanocor 1.30E, Nanocor 1.33M, and nanocor 1.34TCN) were investigated, and based on the quality of their dispersion in water, two of them (Cloisite Na+, and Nanocor 1.30E) were selected. In addition to these two nanoclays, four nanoparticles (Al2O3, Alumina Ceramic (BYK, LPX 2193), nanosilica (Fumed silica Aerosil R7200) and titanium dioxide (Aeroxide P25)) were selected for their VOC off gassing barrier efficiency from particleboard products. Because the coating was water based, the particleboard samples were veneer finished to avoid samples swelling. To glue the veneers a in house UF resin formulated with high U/F ratio to reduce the veneer barrier efficiency as already reported in previous studies. Three loading ratios, 1%, 3% and 5%, of the nanoparticles were investigated but only the two extremes were reported. The transmission electron microscopy (TEM) results showed that the nanoparticles, including Al2O3, AlCeramic, and TiO2 were well distributed in the coating for both 1wt% and 5 wt% loading ratios. In these formulations, small aggregates were observed with a diameter of about 100-150 nm. It was smaller by about 50nm for the AlCeramic (1%). The Nanosilica and the two nanoclay samples did not disperse well in the coating; they showed larger aggregates with a diameter of about several microns. In terms of formaldehyde and other carbonyls compounds barrier efficiency, the coating containing the Cloisite Na+ performed the best followed by the samples finished with the nanosilica both at 5% loading. A decrease of these carbonyl compounds emission varied from 60% to almost 70% when 5% of Cloisite Na+ was used in the coating formulation after 7 days samples conditioning. An overall TVOC emission reduction up to 82% was observed when Cloisite Na+ was added to the coating compared to the veneered and uncoated particleboard sample. This barrier efficiency result is very encouraging for the coating industry and could be considered for technology transfer where optimum conditions for the mixing of nanoparticles with the coating as well as the coating application and curing could be achieved with automated and performing equipments. The technology transfer based on results obtained from this project is highly recommended due to its anticipated lifting the VOC emission barriers from some countries regulations such as CARB for the formaldehyde emission limits and a new legislation for formaldehyde, some particular VOCs and TVOC recently released as DRAFT Regulation, in France.


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AcknowledgementsFPInnovations – Forintek Division expresses it’s thanks to Natural Resources Canada – Canadian Forest Service for their financial support for this research project.


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© 2010 FPInnovations – Forintek Division. All rights reserved.

Table of Contents Abstract.......................................................................................................................................................................... ii Acknowledgements ....................................................................................................................................................... iii List of Tables..................................................................................................................................................................v List of Figures ................................................................................................................................................................v 1 Objectives ...............................................................................................................................................................1 2 Introduction .............................................................................................................................................................1 3 Background and Literature Review.........................................................................................................................1

3.1 Gas barrier ...................................................................................................................................................2 3.2 VOC photodegradation catalyst ...................................................................................................................3 3.3 Adsorbents ...................................................................................................................................................6 3.4 Hybrid Technologies ....................................................................................................................................7

4 Staff ........................................................................................................................................................................8 5 Materials and Methods............................................................................................................................................8

5.1 Preparation and characterization of the coating formulations ......................................................................8 5.2 Transmission electron microscopy (TEM) ....................................................................................................8 5.3 Preparation of the sample panels with the coating material .........................................................................9 5.4 Formaldehyde and VOC emission testing procedures...............................................................................10 5.5 Quantification of formaldehyde and other carbonyls compounds...............................................................11 5.6 Quantification of the TVOC ........................................................................................................................12

6 Results and Discussion.........................................................................................................................................13 6.1 Coatings formulations ................................................................................................................................13 6.2 Formulated coatings application on the veneered particleboard samples..................................................15 6.3 Impact of the nanoparticles on Formaldehyde and carbonyl compounds off gassing................................15

6.3.1 Impact of seven days conditioning of some finished samples on formaldehyde off gassing........17 6.4 Impact of the nanoparticles modified coatings on VOCs off gassing .........................................................18

7 Benefits .................................................................................................................................................................20 8 Conclusions ..........................................................................................................................................................20 9 Recommendations ................................................................................................................................................21 10 References ...........................................................................................................................................................21


v

List of Tables Table 1 Classes of VOCs and their possible emission sources [27]......................................................................2 Table 2 Comparison of catalyst system for VOCs degradation under UV-light .....................................................5 Table 3 Comparison of catalytic activity of various catalysts under visible light ....................................................6 Table 4 Summary of the testing conditions..........................................................................................................10 Table 5 GC/MS and HPLC operating conditions .................................................................................................12 Table 6 Coatings Grind Gauge observations.......................................................................................................14 Table 7 Formaldehyde and Carbonyl compounds emissions as a function of coating formulations....................16 Table 8 Carbonyl compounds off gassing reduction as function of conditioning period ......................................17 Table 9 VOCs emissions as a function of the coating formulations.....................................................................19

List of Figures Figure 1 A view of a Transmission electron microscopy (TEM) ..............................................................................9 Figure 2 View of the small environmental chambers ............................................................................................11 Figure 3 TEM images of the nanoparticles in the coating (a) Al2O3 (5%), (b) TiO2 (1%), (c) AlCeramic (1%),

Cloisite Na (5%)......................................................................................................................................15 Figure 4 Coating with 5% nanoparticles loading formaldehyde and other carbonyl off gassing barrier

efficiency.................................................................................................................................................16 Figure 5 Effect of seven days samples conditioning on carbonyl compounds emissions .....................................18 Figure 6 Impact of different nanoparticles modified coating on few VOCs off gassing .........................................20


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1 ObjectivesThe main objective of the project is to evaluate the effectiveness of different nanoparticles as emission barriers in the coatings. Different nanoparticles such as nanoclays, nanoparticles (TiO2, ZnO) and their modified counterparts will be used to compare their effectiveness as emission barriers for formaldehyde and VOCs

2 IntroductionIndoor air quality has become an important public concern due to the increased amount of personal time spent in indoor environment (residences and workplaces). Indoor air pollutants mainly include nitrogen oxides, carbon oxides, volatile organic compounds (VOCs) and particulates. Urea-formaldehyde (UF) adhesives have been used by both the particleboard and MDF industries due to their relatively low costs and good adhesion properties in the wood products. However, UF has been criticized for air quality deterioration. Coatings and laminates have been used as barriers to limit formaldehyde emissions from unfinished products (1).

3 Background and Literature Review Indoor air quality has become a significant issue in North America and other parts of the world since the 1990s. The presence of organic chemicals in the indoor environment is a subject of increasing concern for both residences and workplaces. Wood is a naturally occurring complex organic material—its natural emissions (including odours) are often valued by consumers. Wood composites, including secondary manufactured products (such as furniture, kitchen cabinet, office furniture), use adhesives and are sometimes heated during their manufacturing processes. Gaseous emissions from wood and wood composites generally cause suspicions in terms of the nature, volume and toxicity of the organic chemicals that are emitted. Formaldehyde and volatile organic compounds (VOCs) emissions are particularly highlighted as a health concern. A list of classes of VOCs, and their possible indoor emission sources are shown in Table 1. Prior researches have shown that the addition of coatings on wood composite products can effectively limit the amount of VOCs and formaldehyde released in the ambient air [1]. The use of nanotechnologies in the wood composite coatings might help us improve the VOC barrier performance of such coatings. In 1985 Professor A. Kelly authored an article in Composites Science and Technology titled ‘‘Composites in Context’’ [2]. It was stated that, ‘‘The large scale social changes which influence the development of new materials are reviewed and the new materials and processing methods being developed in response to these are described and contrasted with some recent advances in composite materials science.’’ At the time, the new technologies that were in development included in situ metal–matrix composites, carbon-fiber-reinforced thermoplastic composites, SiC-reinforced aluminum as well as toughening of ceramics through the use of fiber-reinforcement. “Tremendous developments have been made in many aspects of composites research and technology during the two decades since the publication of Kelly’s paper. Recent advances in producing nanostructured materials with novel material properties have stimulated research to create multi-functional macroscopic engineering materials by designing structures at the nanometer scale. Motivated by the recent enthusiasm in nanotechnology, development of nanocomposites is one of the rapidly evolving areas of composites research” [3]


VOC class Environment and sources Aliphatic and cyclic hydrocarbons 1, 2, 4, 5, 7, 9–11 Aromatic hydrocarbons 1–7, 9, 11, 12 Aldehydes 1–12 Terpenes 1–4, 7–10 Alcohols 1–9, 11 Esters 1, 2, 4, 7–9 Halocarbons 1, 2, 7, 11 Glycols/glycolethers/glycolesters 1–4, 7, 9 Ketones 1–4, 6–12 Siloxanes 11 Alkene 2, 7 Organic acids 2, 3, 7–9, 11 Ethers 9 Other VOCs 1, 2, 4, 7, 11

1: Established buildings, 2: new and renovated buildings, 3: school, 4: new car interiors, 5: carpets, 6: floor coverings, 7: wood-based panel and furniture, 8: solid woods, 9: paints, 10: cleaning products, 11: unflued gas heaters and electric ovens, 12: office equipment.

Nanotechnology can be broadly defined as, ‘‘The creation, processing, characterization, and utilization of materials, devices, and systems with dimensions on the order of 0.1–100 nm, exhibiting novel and significantly enhanced physical, chemical, and biological properties, functions, phenomena, and processes due to their nanoscale size’’ [4]. Nanoparticles have been incorporated in many composite materials, mainly to improve their mechanical and physical properties (strength, elasticity, electrical and thermal conductivity) [3, 5]. For example, addition of only a small amount of smectite clay nanoparticles to pure polymers improves many characteristics of the resultant polymer-clay nanocomposites (PCN): tensile strength and modulus, heat deflection temperature (HDT), smoothness and paint ability, transparency and gas barrier property; and thus, without affecting the recyclability of the materials [6]. There are three ways nanoparticles in wood composite coatings can help limit the emission of VOCs: as a gas barrier, as an adsorbent or as a VOC photodegradation catalyst. 3.1 Gas barrier Based on the literature, some nanoparticles (clays in particular) increase the barrier properties by creating a maze (or “tortuous path”) that slows down the progress of the gas molecules through the material [7, 8]. The relative permeability coefficient value can be predicted using the Nielsen theoretical expression [9]:

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(1) where and are the nanocomposite and pure polymer permeability coefficient and are the length and width of the filler particles is the volume fraction of the nanoparticles in the matrix.

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Equation (1) shows that the gas barrier properties of this kind of nanocomposites primarily depend on two factors: the dimension of the nanoparticles used in the composite material, and their volume in the matrix. “The presence of filler, spherical, plate, cylindrical, etc., introduces a tortuous path for a diffusing penetrant. The reduction of permeability arises from the longer diffusive path that the penetrants must travel in the presence of filler. A sheet-like morphology is particularly efficient at maximizing the path length due to the large length-to-width ratio, when compared to other filler shapes such as spheres or cubes [7].” To a lesser degree, other factors, such as the degree of dispersion of the filler in the matrix [10, 11, 12], the relative orientation [7] and the chemical interaction with the polymer [13, 14, 15] will have an impact on the permeability coefficient. To design better materials using nanocomposites, one will have to take into account the choice of particles, sheet length, concentration (usually between 2 and 6 wt.%), relative orientation and state of aggregation [5, 7]. Clay silicates, such as the montmorillonite kind [(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2· H2O], are often used for this purpose, because of their availability, relatively low cost and sheet morphology [16, 17]. But other products, such as metal oxides, are also used [18, 19]. Poly( -caprolactone)/clay nanocomposites have also been investigated [61]. The gas barrier properties of nanocomposite materials are used in different industries, such as food packaging. Little research has been made in the wood composite field, and it was mainly aimed at the water vapour protection [20, 21, 22]. No publication talks about a VOC or formaldehyde barrier using nanocomposite coatings.

3.2 VOC photodegradation catalyst A review written by Shaobin Wang et al. [23] summarizes well the actual state of research in the VOC photodegradation field: “Photodegradation usually occurs at room temperature and pressure for air purification and may be more cost-effective than other conventional techniques such as activated carbon adsorption and chemical scrubbers, because the semiconductor catalysts are inexpensive and capable of mineralising most organic compounds effectively. However, this technique is still in the development stage for VOCs removal from indoor air. In the past two decades, a lot of investigations have been conducted in photocatalytic oxidation of VOCs and several types of photocatalyst systems have been developed [24]. However, most investigations concentrated on the VOC destruction at higher concentrations of the parts per million (ppm) levels. While concentrations in the ppm range are typical for chemical stream concentration, sub-ppm levels or parts per billion (ppb) concentrations are commonly associated with indoor (buildings, trains, vehicles, planes, etc.) VOCs. Extrapolation of the oxidation data collected at concentrations much higher than the intended application may not be valid [25]. Several investigations have found that different inlet contaminant concentrations lead to different reaction rates [26]. In general, reaction rate is enhanced with the increasing of inlet concentration of pollutants. Thus it is necessary to investigate the catalytic performance of catalysts at low pollutant level. However, there are limited studies on the photodegradation of VOC pollutants at typical indoor levels. With the increasing concerns on the indoor air quality, more researches have focused on photocatalytic oxidation of VOCs at ppb level in recent years.” “A good photocatalyst is characterised by its capability to adsorb simultaneously two reactants, which can be reduced and oxidised by a photonic activation through an efficient absorption ( >Eg). Currently, for

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the photocatalytic reaction, TiO2 [59] is the most important and widely used catalyst. Other semiconductors such as ZnO, ZnS, CdS, Fe2O3, SnO2, are also commonly used catalysts.” Researches have also been made using fibrous MnO2 [60]. The first developments in the photocatalyst field were done using commercially available Degussa P25 TiO2. Because of its high photoactivity, excellent stability and low cost, it was a candidate of choice and soon became a comparison standard for other studies. Other than choosing the right catalyst, many factors have to be taken into account. Firstly, the VOCs that need to be degradated exhibit different degradation rates. Some examples can be found in Table 2. Zuo et al. also studied the photocatalytic degradation of different volatile organic compounds using diverse photocatalysts, showing that benzene and carbon tetrachloride were the hardest molecules to degrade [35]. It is also reported that competitive adsorption between water and trace contaminant of VOCs has a significant effect on the oxidation rate [25]. But the presence of a small quantity of water is also important for the degradation of some compounds. The presence (and the wavelength) of UV light is also a factor to consider [28, 36]. Based on the value of band gap of 3.2 eV, the requirement wavelength of light excitation for TiO2 is 388 nm, which is in the ultraviolet range [23]. The size and porosity of the photocatalyst are also important factors [58]. As an example, for the decomposition of 1-butene, under UV illumination, ultrasmall SnO2 with a diameter of 5 nm exhibited initial photoactivity as high as 3 times than that of P25 TiO2 (30 nm), whereas larger size particle SnO2 (22 nm) did not show photoactivity [37]. The crystal structure of the photocatalyst also has an important effect [38, 57]. In the case of TiO2, both crystal structures, anatase and rutile, are commonly used as photocatalysts, the anatase showing a greater photocatalytic activity [39, 40] for most reactions. It has been suggested that this increased photoreactivity is due to anatase’s slightly higher Fermi level, lower capacity to adsorb oxygen and higher degree of hydroxylation (i.e., number of hydroxy groups on the surface) [40-43]. Furthermore, there are also studies which claim that a mixture of anatase (70–75%) and rutile (30–25%) is more active than pure anatase [44, 45, 46]. The weakness of actual photocatalysts, such as anatase TiO2, is that they show no or minimal activity under visible light, making them less attractive for indoor applications. The main challenge for the future generation of photocatalytic materials will be to improve their efficiency under visible light.


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Catalyst VOC (nm)

Conc. (ppb)

Conversion (%) Reference

TiO2 (5%) Formaldehyde 356 15 80 [28] TiO2 (5%) Acetaldehyde 356 15 60 [28] TiO2 (5%) Acetone 356 15 100 [28] TiO2 (6.8%) Benzene 365 15 30 [29] TiO2 (6.8%) m-Xylene 365 40 50 [29] TiO2 (6.8%) p-Xylene 365 60 55 [29] TiO2 (6.8%) o-Xylene 365 20 50 [29] TiO2 (20%) Benzene 352 93 100 [30] TiO2 (20%) m-Xylene 352 78 100 [30] TiO2 (20%) p-Xylene 352 78 100 [30] TiO2 (20%) o-Xylene 352 45 100 [30] TiO2 (20%) Ethyl benzene 352 21 100 [30] TiO2 (5%) Benzene 365 20 70 [31] TiO2 (5%)/AC Benzene 365 20 80 [31] TiO2 (5%) Toluene 365 20 88 [31] TiO2 (5%)/AC Toluene 365 20 88 [31] TiO2 (20%) PCE 352 77 82 [32] TiO2 (20%) TCE 352 23 84 [32] TiO2 (1%) Benzene 355 88 5 [33] TiO2 (1%) Toluene 355 80 24 [33] TiO2 (1%) Ethyl benzene 355 65 48 [33] TiO2 (1%) o-Xylene 355 60 54 [33] TiO2 (5%) Benzene 365 23 4 [34] La (1.2%)/TiO2 (5%) Benzene 365 23 30 [34] Nd (1.2%)/TiO2 (5%) Benzene 365 23 22 [34]

Visible-light activation usually requires semiconductors with band gaps lower or equal to 3.0 eV (such as rutile TiO2), thus ruling out the sole use of the 3.2 eV band gap anatase TiO2 [56]. It was discovered that metal-ion implantation with various transition-metal ions such as V, Cr, Mn, Fe, and Ni accelerated by high voltage makes possible a large shift in the absorption band of the titanium oxide catalysts toward the visible-light region, with differing levels of effectiveness [47]. Another approach to produce visible-light activated TiO2 photocatalysts is by doping with anions, such as N3 , C4 , S4 or halides (F , Cl , Br , I ) [48]. Many investigations have described the visible-light photocatalytic activity of N-doped TiO2 (NTO), leading to the formation of ring-opening products and much higher activity than that of commercial P25 [49-54, 56]. See Table 3.


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Catalyst VOC (nm)

Conc. (ppm)

Conversion (%)

Reference

TiO2 n-Butanol 380 145 95 [55] TiO2 n-Butanol 380 580 100 [55] TiO2 Acetaldehyde 436 485 85 [49] TiO2–N Acetaldehyde 436 485 49 [49] TiO2–N Acetone 470 21 100 [51] TiO2–N Ethylene 450 227 35 [54] TiO2–N/ZrO2 Ethylene 450 227 52 [54] TiO2–N Toluene 420 20 100 [52] TiO2–N Acetaldehyde 420 930 32 [53] TiO2–N Tricholoroethylene 420 943 18 [53] TiO2–N–F Acetaldehyde 420 930 65 [53] TiO2–N–F Tricholoroethylene 420 943 37 [53]

A strongly beneficial effect have been observed when adding a low amount of WO3 (4 wt.%) to rutile TiO2. The WO3 semiconductor displayed a 2.8–3.0 eV band gap; therefore, is activated by visible light irradiation, together with rutile TiO2 [62]. Most of the research made in that field so far concerned high VOCs emission, industrial sream (emission in the order of ppm). For low emission, indoor sources, studies were mainly aimed at the development of reactor or filter technologies. Very few articles listed coatings or paints with photodegradation properties under visible light [63, 64]. Finally, note that if a photocatalyst is really efficient in the degradation of organic compounds, it also means that it will have the capability to slowly destroy the organic matrix in which it is dispersed, affecting the long term stability of the product. 3.3 Adsorbents Three common adsorbents for VOC removal are activated carbon, silica gel and zeolites. Two of them are generally used for indoor applications. Activated carbon is predominantly used to remove hydrocarbons and non-polar gases, and zeolites are used to adsorb polar gases and vapours. The main characteristics of adsorbents are their micro- or mesoporous structure and their very large surface area that allows them to trap and retain VOCs. Activated carbon is processed so it becomes very porous. A typical activated carbon has a large surface area (500-3000 m2/g) and a modest density (0.55 g/cm3). It is used to retain VOCs with molecular weights over 45 and boiling points above 0°C, and is easily regenerated thermally [25, 69]. Nanoporous activated carbon nanoparticles have been used for the removal of organic contaminants, in water and air [68, 69]. A fibrous form, active carbon fibers, has been developed by carbonization and activation of organic fibers [69, 70]. Cited advantages are smaller fiber diameter, narrow pore size distribution and excellent adsorption capacity at low concentration compared to powdered activated carbon [69]. But no paper related to the use of nano-activated carbon in VOC removal coating applications has been found in the literature.


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“Silica gel is a chemically inert, nontoxic, polar and dimensionally stable (< 400 °C) amorphous form of SiO2. It is prepared by the reaction between sodium silicate and sulfuric acid followed by a series of after-treatment processes such as aging, pickling, etc. These after treatment methods resulted in various pore size distributions. Silica is used for drying in process air (e.g. oxygen, natural gas) and for adsorption of heavy (polar) hydrocarbons from natural gas” [67]. A technique has also been developed to prepare mesoporous silica fiber matrix using the paper making technologies [71]. These mesoporous materials can be prepared as sheet form to remove VOCs in atmosphere. Mesostructured materials belonging to a new class of solid acids known as porous clay heterostructures (PCHs) have been prepared by chemical modification of natural clay” [72]. The synthesized hydrophopic organo-silica materials were very effective as adsorbents of VOCs according to tests conducted with methanol, methyl ethyl ketone, toluene and trichloroethylene. No coating application has been found using silica material as a VOC removal agent. Zeolites are crystalline, highly porous materials, which belong to the class of aluminosilicates. They usually show selective adsorption due to the uniform pore size of their structure and have a high adsorption capacity for polar substances at low concentrations [65]. Zeolites have been shown to remove benzene, -hexane, and formaldehyde from indoor air [66]. Also, Y and ZSM-5 zeolites loaded with 3.0-3.5 wt% of copper have been shown to effectively remove phosphine (PH3) from air at high concentrations [73]. But once again, no paper has been published concerning VOC removal from coatings doped with zeolites. Other products have been synthesized with VOC adsorbing capabilities. A Japanese research group developed microporous layered organic-inorganic nanocomposites by alkoxysilyation of ilerite with biphenylene-bridged alkoxysilanes [74]. BESB-ilerites gave better results than other porous silica materials. In another project, the use of nanosized particles of hydroxyapatite deposited on a polyamide film allowed better adsorption of formaldehyde than the commercially available powder [75]. Nanocomposite membranes of mesoporous alumina have been modified by chemically and physically attaching small organic molecules (Octadecyltrichlorosilane, phenyltrichlorosilane and a triazine-based hyperbranched molecule) to the surface [76]. One membrane exhibited separation factors comparable to currently employed PDMS membrane technology but at significantly higher permeances.

3.4 Hybrid Technologies There has been some work on developing new technologies by using a combination of two methods to limit VOCs emissions. For example, a nano-TiO2/activated carbon composite has been prepared [77], but the product hasn’t yet been tested specifically in VOC removal applications. 12 hybrid photocatalysts consisting of TiO2 and an adsorbent were investigated for the photocatalytic decomposition of toluene [78]. The highest decomposition rate was obtained with the use of mordenite and silicon dioxide (SiO2) as additives to TiO2. The reaction areas of two hybrid photocatalysts were 1.52 and 1.64 times larger than that of P25 TiO2. The efficiency of clay-TiO2 nanocomposites on the photocatalytic elimination of toluene has been studied [79]. Clay materials combining high surface area and porosity (such as hectorite) with relatively less hydrophilic surfaces (such as kaolinite) should be a more effective photocatalyst for the elimination of hydrophobic VOCs than pure TiO2.


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Lastly, a dual functional adsorbent/catalyst system (an Ag loaded/hydrophobic HY zeolite catalyst) with both adsorption and catalytic function was suggested as an effective control method for the removal of low concentration VOC [80]. Ag/HY catalyst showed the lowest conversion temperature for both toluene and MEK oxidation among all the M/HY catalysts tested. Its catalytic activity was enhanced by increasing the Ag loading.

4 StaffAlpha Barry, Group Leader Ayse Alemdar, Research Scientist Frédéric de Champlain, Research Scientist Mathieu Gosselin, Technician Diane Corneau, Technician

5 Materials and Methods All measurements were done in general agreement with the specified standards and protocols. The precision levels were in accordance with the technical requirements. 5.1 Preparation and characterization of the coating formulations Two nanoclays (Cloisite Na, a natural montmorillonite nanoclay and a nanomer 1.30E an anion modified montmorillonite nanoclay) and four nanopartilces Al2O3, Alumina Ceramic (BYK, LPX 2193), nanosilica (Fumed silica Aerosil R7200) and Titanium dioxide (Aeroxide P25) were selected for the coating formulation. The water based coating commercially named Canlak 301-001 Maxixure was used as base coat. Three different loadings 1%, 3% and 5% based on the solid content of the coating have been investigated. The mixtures were prepared at optimum conditions of 1050 RPM mixing speed for 15 minutes after multiples mixing conditions trials. The pH of the coating before and after the addition of the nanoparticles were measured and found as 7.1 and between 7.3 and 7.5, respectively for all formulated coatings. This value is close to the required pH conditions (7.5 to 8.5) in most coating applications. The dispersion quality of the nanoparticles, whether there are aggregates of the nanoparticles, in the coating was characterized with both the Ground Gage and the transmission electron microscopy (TEM) methods. The quality of the formulation was based on the presence or absence of aggregates which can be seen by eyes when possible or with the TEM. 5.2 Transmission electron microscopy (TEM) Transmission electron microscopy (TEM) is a microscopy technique where a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through the specimen such as a thin film of a polymeric material. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen or on a layer of photographic film, etc. TEM is capable of imaging at a significantly higher resolution than light microscopes; it forms a major analysis method in a range of scientific fields, in both physical and biological sciences. TEM finds application in cancer research, virology, materials science as well as pollution and semiconductor research. For the purpose of evaluating the quality of the nanoparticles distribution in the coating, JEOL 1230 model TEM was used at an accelerated voltage of 80 kV. The coating with nanomaterials was dried on glass substrates. Small piece


of the material was embedded in epoxy and cured. The transparent foils of the materials were microtomed and placed on the TEM grids (Figure 1)

NB: The electron source of the TEM is at the top, where the lensing system (4,7 and 8) focuses the beam on the specimen and then projects it onto the viewing screen (10). The beam control is on the right (13 and 14) 5.3 Preparation of the sample panels with the coating material To investigate the impact of the different formulations, we selected particleboard panels with an initial formaldehyde and VOC emissions relatively high. The measured initial formaldehyde emission from the panel was 0.12ppm and initial VOCs 376.3 μg/m³. Because the coating is water based coating, we have decided to apply a veneer on the particleboard sample to avoid its disintegration after the coating application. Because the veneer can act as a physical formaldehyde and VOC barrier, based on previous

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study [1], we used a high free formaldehyde UF resin to apply the veneer on the reference particleboard sample before applying the coatings. A glass substrate coated with the Canlak coating was also used as background in order to evaluate the coating formaldehyde and VOCs off gassing and to be used for estimating the effectiveness of the nanoparticles barriers impact if any. 5.4 Formaldehyde and VOC emission testing procedures ASTM D6007 and ASTM D5116 standard methods were used for the testing of formaldehyde and VOCs from the finished panels, respectively. Prior the testing, the test samples were cut into the dimensions of 10.5 cm x 10.5 cm from the trimmed and conditioned panels. Formaldehyde samples of 10.5 cm x 10.5 cm were edge-sealed with aluminum tape and conditioned at 23°C ± 0.5°C and 50% ± 5% relative humidity for 1 day before analysis. For both VOC and formaldehyde testing, the loading ratio was set at 0.41m²/m³. VOC samples of the same sizes were also conditioned for 7 days at 23°C±0.5°C and 50% ± 5%. In the case of this study, we used the same sample for both formaldehyde and VOCs and thus conditioning edge sealing and air change rate were kept similar. Because we conditioned samples for only 24 hours, samples were edge sealed for 24 hours conditioning before being installed in the small chamber set at 0.5.0±0.05air change/hour. Table 4 summarizes the testing conditions for both formaldehyde and VOCs.

Parameters Symbols Units Forintek Formaldehyde

ASTM D 6007 VOCs

ASTM D 5116 Sample conditioning time days 1 1 Product exposed area A m² 0.022

(two faces of 0.0105 m by 0.0105 m)

0.022 (two faces of 0.0105 m by 0.0105 m)

Chamber volume V m³ 0.053 0.053 Loading Ratio N m²/m³ 0.41 0.41 Air Exchange Rate AER h-1 0.5 0.5 Temperature T °C 23±0.5 23±0.5 Relative Humidity RH % 50±5 50±5

A constant and adjustable airflow, conditioned for relative humidity, was fed through small environmental chambers shown in Figure 3. The VOC sampling procedures excluding formaldehyde were similar to those described in the ASTM guide D 5116-97. The material used in the construction of the chambers was stainless steel. The chambers were equipped with suitable accessories such as inlet and outlet ports for airflow and an inlet port for temperature/humidity measurements. The air sampling was accomplished from the airflow outlet port. The small chambers were placed inside a controlled temperature room. The humidity of the air flowing through the chambers was controlled by adding de-ionized water to the air stream for each line. For collection of the emissions, sorbent cartridge tubes constructed of Pyrex glass (11.5cmx6mm OD with 4 mm ID) were used. The tubes were packed with three layers of: Carbotrap C (300 mg), Carbotrap B (200 mg) and Carbosieve S-III (30 mg). Prior to use, thermal tubes were conditioned at


370°C for 45 min. During the tube conditioning an ultra-high-purity helium flow was maintained through the tubes at 45 ml/min. The collection of VOCs on an appropriate adsorbent medium is required to avoid overloading of the analytical equipment. In order to maintain integrity of the airflow in the small chambers (0.5 air exchange per hour for TVOC as well for formaldehyde were selected because in this case we used the same sample for both samplings), the sampling flow rate was 100 ml/min for a sampling period of 100 minutes for VOC sampling. The formaldehyde sampling rate was set at 250 mL/min and for two hours for a total of 30L. The analysis was accomplished according to ASTM D 6007-96 with the same small chamber used to collect the VOC emission from the unfinished panel product. In some cases the DNPH method was used to analyze formaldehyde off gassing, particularly when low emission levels were expected.

5.5 Quantification of formaldehyde and other carbonyls compounds Formaldehyde emissions were quantified according to the modified National Institute of Occupational Safety and Health (NIOSH) Test Method 3500. The method can be summarized as follows: 4 mL of the scrubber’s content and 0.1 mL of 1.0 % chromotropic acid are poured in a 50-mL Pyrex® test tube with a screw top cap. Six mL of concentrated sulphuric acid (96%) are slowly added and agitated for 2 minutes, then heated for 30 minutes at 100°C and cooled and tested in triplicate. Solution absorbencies were read through a UV-visible spectrophotometer set at 580 nM. Distilled water was run as a blank, and with a formaldehyde solution calibration curve, each absorbency reading was converted into μg/mL of formaldehyde. When the condensate samples were too concentrated to yield absorbencies in the linear range of the calibration curve, aliquots of these samples were diluted with distilled water to a level within the linear range of the calibration curve. The concentration obtained from this dilution was back-

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calculated to the original concentration and presented as micrograms of formaldehyde per litre, which is then converted in parts per million (ppm). Formaldehyde and acetaldehyde tubes were desorbed with acetonitrile solvent and injected into a high performance liquid chromatograph (HPLC). Table 5 summarises the GC/MS and the HPLC operating conditions.

Thermal desorption unit (Type ACM 900) Desorption temperature 250ºC Desorption time 6 min. Cryofocus unit model 951 Cooling Temperature -50ºC Time 4 min. Desorption Temperature 150ºC Desorption time 15 min. GC/MS : Agilent 5890 series II Plus Carrier gas He, 43.2 cm/sec Column J&W Scientific DB-1 30m x 0.25mmID, 1.0μm Injection type Split : 22 :1 at 230ºC Oven Heating program 10 min. at 70ºC 8ºC /min. to 200ºC 3 min. at 200ºC Detector MSD, transfer line temp. 280ºC HPLC type: Agilent series 1100 Column Zorbax Eclipse XDB-C18 Analytical 4.6 x 150mm, 5 microns Phase Mobile 70%ACN :30% water Flow Rate 1.0 ml/min. Total injected Volume 25μL Column Temperature 20ºC Detector DAD 360 nm

5.6 Quantification of the TVOC VOC measurements from panel samples were conducted in accordance to the ASTM D 5116-97 guide and described in great detail in a previous paper (Barry [61]). Without going into detail in the description of the method, one can summarize some key points: the small chamber, maintained at 23±0.5°C and 50±5% relative humidity, has a volume of 50 L and its interior surfaces are electro polished to minimize the sink effect; the loading ratio is fixed at 0.41 m²/m³ with half air exchange per hour (0.5±0.05). A Thermal Desorber/Gas Chromatograph/Mass Spectrometer (TDU/GC/MS) system was utilized to desorb and quantify the total volatile organic compounds (TVOC). A “cryo-trap” device was connected to the GC column in order to “cryofocus” the thermally desorbed chemicals prior to their injection into the GC. The GC oven was programmed for 10 min at 70°C, followed by ramping up the heat to 200°C at a rate of 8°C/min, and held for 10 minutes. The mass scan ranged from 29 to 550 atomic mass units (amu). Quantitative evaluation was achieved by comparing the chromatogram peak area of each compound to the corresponding peak area of a standard.


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6 Results and Discussion The coating mixture with the nanoparticles was first optimized before their application onto the veneered particleboard samples. The selected coating name and description is as follow: Identification: Canlak 301-001 Maxixure Tiecoat UV water base Physical state: Liquid Color: Milky white Relative density: 1.0339 gram/ml Volatility: 76.12% (v/v), 75.46% (wt/wt) VOC: 17.6 (g/l) Solid content: 45.5% As one can see the VOC content of the coating was less than 2% as specified by the manufacturer even if the solid content was less than 50%. Of the five nanoclays tested (Cloisite 30B, Cloisite Na+, Nanocor 1.30E, Nanocor 1.33M, and nanocor 1.34TCN), two nanoclays (Cloisite Na+, and Nanocor 1.30E) were selected for the coating formulations based on the quality of their dispersion in water as prepared by IKA T25 Digital Ultra Turrax mixer. The dispersion test was conducted in water because the coating was a water base. The Ragogna High Shear tester was used to optimize the coating formulation at different speed and time. Optimum mixing was set at 1050 RPM for 15 minutes. 6.1 Coatings formulations In addition to the two nanoclays selected in the previous section, four nanoparticles (Al2O3, Alumina ceramic, Nanosilica, and TiO2) were selected for coatings formulations and the optimum conditions (1050 RPM, 15 minutes) were applied. The dispersion quality of the nanoparticles at different loadings in the coating was determined using the Grind Gauge observations and transmission electron microscopy. The Grind Gauge method only shows the existence of aggregates at micrometer levels. The results obtained by this method are summarized in Table 6. This method was not accurate for the observation of the smaller aggregates. The TEM results showed that the nanoparticles, including Al2O3, AlCeramic, and TiO2 were well distributed in the coating for both 1wt% and 5 wt% loading ratios (Fig 4). In these formulations, small aggregates were observed with a diameter of about 100-150 nm. It was smaller, about 50nm, for the AlCeramic (1 wt%). The Nanosilica and the two clay samples showed larger aggregates with a diameter of about several microns at higher concentrations.


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(a) (b)

(c) d)

6.2 Formulated coatings application on the veneered particleboard samples The formulations were applied on the veneered particle board samples with a 4 mils thickness applicator. A total of 4 layers of 4 mils per layer were applied. The process for each layer consists of layer application, air-drying for one hour followed by a UV curing for 25secondes, and slight sanding with a sand paper of 320 grains; the last layer was not sanded. All the samples were then air-dry overnight, wrapped in aluminum paper, double wrapped in plastic bags and store at 4°C till emissions analysis. 6.3 Impact of the nanoparticles on Formaldehyde and carbonyl compounds off gassingTable 7 summarizes formaldehyde, acetaldehyde and acetone emissions from the veneered particleboard samples as a function of the nanoparticles types and loading ratios. In Table 7, the results were collected from samples conditioned for only 24 hours and the maximum decrease of all three compounds (22% for formaldehyde, 47% and 48% for acetaldehyde and acetone, respectively) was observed with samples finished with the coating containing the Cloisite Na+ at a loading ratio of 5% followed by the samples finished with the nanosilica at 5% loading. Figure 5 illustrates the 24 hours samples conditioning carbonyl compounds results for a quick view and easy comparison of the different formulations off

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gassing barrier efficiency. These results are excellent and it is important to obtain the results with samples conditioned for a week or a month because, usually, finished products reach the client only after a month or later.

1% 5% 1% 5% 1% 5% 1% 5% 1% 5% 1% 5%

Formaldehyde 86,5 41,1 38,6 32,2 42,0 25,2 37,7 33,2 41,7 37,4 36,5 25,7 36,8 45,3

Acetaldehyde 16,9 19,2 15,7 10,1 23,0 18,6 18,8 17,8 16,6 16,9 18,5 14,6 15,5 18,8

Acetone 61,7 95,1 75,6 49,3 115,0 107,8 90,6 87,5 76,2 78,1 90,0 79,0 56,8 53,1

Formaldehyde Emission Reduction/Increase(+)

NA NA -6 -22 2 -39 -8 -19 1 -9 -11 -38 -10 10

Acetaldehyde Emission Reduction/Increase(+)

NA NA -18 -47 20 -3 -2 -8 -14 -12 -4 -24 -20 -2

Acetone Emission Reduction/Increase(+) NA NA -20 -48 21 13 -5 -8 -20 -18 -5 -17 -40 -44

Concentration in ppb

PB Veneer+Coating

Formaldehyde and Other Carbonyl Compounds

PB Veneer

PB Veneer + Coating

Nanoparticules Type

Cloisite Na + Nanocor 1.30E Aluminium Oxide Alumina Ceramic Nanosilica Titanium Dioxide

0

20

40

60

80

100

120

PB V

enee

r (Refe

rence

)

Pb V

enee

r+Coa

ting

Cloisit

e Na +

Nanoc

or 1.3

0E

Alumini

um O

xide

Alumina

Cera

mic

Nanos

ilica

Titaniu

m Diox

ide

Emis

sion

s (pp

b)

Formaldehyde Acetaldehyde Acetone

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6.3.1 Impact of seven days conditioning of some finished samples on formaldehyde off gassing

Due to the limited budget, only few samples were tested after one week conditioning. Table 8 shows the results from the samples conditioned seven days (in agreement with the ASMT D 5116 method). The reduction of the carbonyl compounds off gassing was very clear with a decrease ranging from 60 to almost 70% when 5% of Cloisite Na+ was used in the coating formulation. Figure 6 illustrates the same results and quickly illustrates the positive effect of conditioning samples for 7 days instead of 1 day. One could expect that aging the finished samples could improve the formulations efficiency in terms of off gassing barrier as already observed in previous studies.

1day 1day 7 days 1day 7 days 1day 7 days

Formaldehyde 41,1 32,2 15,6 25,2 16,2 25,7 27,7

Acetaldehyde 19,2 10,1 7,6 18,6 13,1 14,6 18,1

Acetone 95,1 49,3 29,0 107,8 61,8 79,0 75,7

Formaldehyde Emission Reduction/Increase(+) -22 -62 -39 -61 -38 -33

Acetaldehyde Emission Reduction/Increase(+) -47 -60 -3 -32 -24 -6

Acetone Emission Reduction/Increase(+) -48 -69 13 -35 -17 -20

5% Cloisite Na+ 5% Nanocor 1.30E 5% NanosilicaFormaldehyde and Other Carbonyl Compounds

PB Veneer + CoatingNanoparticules Type

Concentration in ppb

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0

20

40

60

80

100

120

1day

1day

7 day

s1d

ay7 d

ays

1day

7 day

s

PB Veneer+ Coating

5% Cloisite Na+ 5% Nanocor 1.30E 5% Nanosilica

Emis

sion

s (pp

b)

Formaldehyde Acetaldehyde Acetone

6.4 Impact of the nanoparticles modified coatings on VOCs off gassing Table 9 summarizes the VOCs emissions from the veneered particleboard samples finished with the different coating formulations and Figure 7 illustrates the impact of the finishing on the most emitted VOCs as a function of the coating formulations. In Table 9, the last two rows summarize the TVOC emission decrease as a function of the different nanoparticles in the coating formulations in comparison to the unmodified coating and to only veneered particleboard sample, respectively. The coating application reduced the TVOC by 58% compared to the uncoated veneered particleboard sample and this emission decrease was accentuated with the incorporation of most nanoparticles investigated except the nanocore 1.30E with a surprising increase of the TVOC at 1% loading. After some internal discussions, it was concluded that this increase could be due to a non uniform coating application on the sample. As with the carbonyl compounds, which includes the formaldehyde, the Nanocloisite Na+ was more efficient as a barrier to VOC off gassing from the finished panel samples. The sample with 5% loading performed better than the 1%. With aluminum oxide, alumina ceramic and Ti2O3, the 1% loading was more efficient than the 5% level. Overall, the nano Cloisite Na+ at 5% loading was more efficient barrier for both the carbonyl compounds and the other VOCs than the remaining nanoparticles investigated in this study. The last line in table 9 indicates the TVOC emission reduction as a result of both the coating application and the effect of the presence of the nanoparticles in the coating. An overall TVOC emission reduction up to 82% was observed when nanocloisite Na+ was added to the coating as compared to the veneered and uncoated particleboard sample. The Titanium dioxide nanoparticles performed the best after the nanocloisite with a 78% reduction of the TVOC compared to the unfinished samples. This barrier

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efficiency result is very encouraging for the coating industry and could be considered for industry transfer where optimum conditions for the mixing of nanoparticles with the coating as well as the coating application and curing for a better finishing could be achieved with automated and performing equipments.

PB Veneer+Coating

1% 5% 1% 5% 1% 5% 1% 5% 1% 5% 1% 5%

Acetic acid 15,9 nd nd nd nd nd 2,5 nd < 2,0 nd < 2,0 nd < 2,0 nd

Pentanal 13,7 6,8 6,2 3,4 10,8 7,2 6,2 6,1 4,0 6,6 7,3 3,0 4,3 7,3

Hexanal 57,7 27,3 22,1 11,1 49,9 23,8 24,4 29,8 21,0 23,1 30,3 19,3 17,1 29,7

alpha-Pinene 47,7 27,6 22,3 15,3 50,4 26,6 15,1 38,7 25,5 34,0 36,5 21,5 14,6 28,6

beta-Pinene 9,2 nd 3,4 nd 5,9 2,9 2,3 4,1 2,9 2,3 2,6 nd < 2,0 3,1

Octanal 2,5 nd nd nd nd nd nd nd nd nd nd nd nd nd

3-Carene 2,8 2,2 < 2,0 nd < 2,0 < 2,0 nd 4,5 < 2,0 nd < 2,0 nd < 2,0 < 2,0

p-Cymene 4,3 3,6 nd < 2,0 2,1 < 2,0 nd nd < 2,0 nd < 2,0 nd < 2,0 nd

Limonene 3,3 < 2,0 < 2,0 nd nd < 2,0 nd nd < 2,0 nd < 2,0 nd < 2,0 < 2,0

Nonanal 2,4 < 2,0 nd < 2,0 < 2,0 < 2,0 nd < 2,0 nd nd < 2,0 nd nd < 2,0

Unknown compounds 3,3 nd nd nd nd nd nd nd nd nd nd nd nd nd

TVOC 162,7 67,5 53,9 29,8 119,2 60,5 50,4 83,1 53,4 66,1 76,7 43,8 36,0 68,7

VOC Emission Reduction/Increase(+) NA -20 -56 76 -10 -25 23 -21 -2 14 -35 -47 2

-58 -67 -82 -27 -63 -69 -49 -67 -59 -53 -73 -78 -58

Concentration expressed as alpha-Pinene in μg/m³

Cloisite Na + Nanocor 1.30E Aluminium Oxide Alumina Ceramic

Combined effect of coating and nanoparticles on VOC

emissions

Volatile Organic Compounds detected

PB Veneer

PB Veneer + CoatingNanoparticules Type

Nanosilica Titanium Dioxide

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0

20

40

60

80

100

120

140

160

180

PB Ven

eer (R

eferen

ce)

Pb Ven

eer+Coa

ting

Cloisit

e Na +

Nanoc

or 1.3

0E

Alumini

um O

xide

Alumina

Ceramic

Nanosi

lica

Titaniu

m Diox

ide

Emis

sion

s (μg

/m³)a

lpha

-Pin

ene

Acetic acid Pentanal Hexanal alpha-Pinene TVOC

7 BenefitsAs it has been indicated in the project statement on potential benefits to the industry, the technology transfer of the findings of this project could help keep market share and eventually get access to new markets where new regulations on indoor air quality are reinforced or implemented. The 2007 flooring market in the US projected for 2010 was around 4 billion dollars and Canada exportation to US and over seas (75% of the production) corresponds to $330 million of that market. 1% increase of the market because of the project could lead to a market gain of approximately $3 million, which excludes the interior consumption.

8 ConclusionsFive different nanoparticles have been investigated in this study in order to determine their barrier effectiveness of formaldehyde and VOCs off gassing from veneered particleboard samples. The selected coating showed that it contains its own VOCs even after curing but we concentrated the study on common VOCs off gassing from the particleboard sample originating from the wood furnish and the resin used. Results showed that finishing the veneered particleboard sample with the coating, which has nanoparticles, resulted in a decrease of both formaldehyde and VOC emissions. The increase of the nanoparticles loading also resulted in an increase of the coating barrier efficiency. The nanocloisite Na+

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performed better than any other nanoparticles investigated with a decrease of carbonyl compounds including formaldehyde up to 70% for acetone after one week samples conditioning as required in the standard method. For VOCs, the addition of the nanocloisite Na+ resulted even with much higher emission reduction; up to 82% reduction of TVOC emission compared to the veneered and uncoated particleboard samples at 5% nanocloisite loading. The barrier efficiencies obtained from this project could assist the wood industry, particularly the furniture industry, easily meets indoor air regulations (formaldehyde, individual VOCs, and TVOC) in force in many countries and the states such as California with its CARB formaldehyde legislation, Japan with its more indoor air stringent regulation, France with its very new DRAFT REGULATIONS on construction products VOCs, formaldehyde and TVOC, etc.

9 RecommendationsThe results from this study showed that the use of nanoparticles in the coating drastically effect on the barrier efficiency of the coating for formaldehyde and VOCs. The results suggest that a mill trial could be an excellent option for technology transfer. If the nanoparticles and the coating mixing is conducted at the mill were excellent mixing conditions exist along with excellent curing conditions could result in better performance of the finish in terms of barrier efficiency.

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Value to Wood No. FPI-113E Reduction of volatile organic