Formaldehyde and TVOC emission behaviors according to finishing treatment with surface materials using 20 L chamber and FLEC
Introduction
Wood-based panels, such as particleboard (PB), medium density fiberboard (MDF) and veneer, are used widely in the manufacture of furniture, flooring, housing and other industrial products. These consumer products contain formaldehyde-based resins on account of the latter's superb bonding properties and low cost. However, wood-based panels bonded with urea-formaldehyde resin emit formaldehyde, which is toxic and is associated with possible health hazards, such as irritation of the eyes and the upper respiratory tract. This can act as an obstacle to their acceptance by the public, given the prevailing climate of environmental awareness and concern. As a result, the European and Northern American governments have imposed regulations limiting the emission of formaldehyde from building materials and from the materials used in the manufacture of furniture and fittings [1].
Building and furnishing materials may emit many volatile organic compounds (VOCs) into the indoor air. Due to their toxicity and adverse effect on human health, it is essential to use low level polluting materials instead. Indoor air pollutants mainly include nitrogen oxides (NOx) and VOCs, which can have adverse health impacts on the occupants [2]. Even though the carpet is made by wool, VOCs and carbonyl are emitted. Especially, 4-phenylcyclohexene and 2,2-butoxyethoxy-ethanol were the main VOCs emitted and aromatic compounds and carbonyls (formaldehyde, acetaldehyde, acetone and propanal) are found at lower concentrations which tend to substantially decrease during the 3 days exposure period [3].
VOCs are composed primarily of BTEX (benzene, toluene, ethylbenzene and xylene) and halogenated hydrocarbons [4]. Among the many VOC compounds, toluene, ethylbenzene, xylene and styrene were chosen for this study, because they are the major VOCs found in indoor environments in different countries [5]. Wolkoff [6] reported that it is important to know the nature of primary and secondary emissions from building products. The primary emissions are free (non-bound) VOCs with generally low molecular weight, such as solvent residues, additives and non-reacted raw products, e.g. monomers. Secondary emissions are chemically or physically bound VOCs. Several of these are emitted or formed by a variety of processes under special chemical or physical conditions. Many building products based on natural raw materials, as opposed to synthetic building products, behave as a secondary emission sources and generally emit VOCs continuously. These emission sources appear to be caused partly by oxidative degradation to lower molecular weight VOCs with low odor thresholds, such as (unsaturated) aldehydes and fatty acids from C1 to C10, and alcohols such as 2-ethylhexanol [7].
Before they can be used as furnishing materials, wood-based panels need to be treated to match the specific requirements of their final use. Therefore, finishing treatment methods that produce an over layer or coating, such as paints, prints, varnishes, veneers, laminates, impregnated papers, and finishing foils, are used to reduce the absorption of water and humidity, as well as eliminate the release of harmful gases [8]. These surface materials, such as decorative vinyl films and melamine impregnated paper, can reduce the emission of formaldehyde from wood-based panels [9]. Nemli [10] examined the effects of the coating materials process parameters on the technological properties of PB, and stated that the surface coating decreased the level of formaldehyde emission.
A variety of methods are used to measure the level of formaldehyde emission from wood-based panels, including perforator, flask, gas analysis, desiccator, and large-scale chamber methods [11]. The 20 L small chamber and Field and Laboratory Emission Cell methods were designed to measure the emission of formaldehyde and VOCs from planar surface building materials and paints [12], [13].
The Korean government began controlling the indoor air quality in 2004. The guidelines prepared by the Ministry of Environment regulate the use of building materials that emit pollutants. The regulations prohibit the use of materials with a Total VOC (TVOC) emission level >4.0 mg/m2 h (JIS A 1901, small chamber method) [14]. Therefore, a comparison of formaldehyde emissions from building finishing materials used in underfloor heating systems traditionally used in Korea was carried out [15]. In addition, environmental-friendly hybrid resins were developed for flooring materials [16], [17], and the level of VOC emission from building finishing materials was evaluated at various temperatures using a 20 L small chamber and VOC Analyzer [13].
This study examined the level of formaldehyde and TVOC emissions from wood-based panels overlaid with a surface material to confirm the ability of each surface material to reduce these emissions using a 20 L small chamber and FLEC.
Section snippets
Materials
The MDF materials used in this study were 3 mm-thick furniture materials obtained from Dongwha Enterprise Co., Ltd. The MDF raw materials were Korean pine (Pinus densiflora Siebold et Zucc.), and urea-formaldehyde resin was used as the adhesive. This study employed three types of lignocellulosic surface materials, oak decorative veneer, low pressure melamine (LPM) impregnated paper and high pressure melamine (HPM) impregnated paper. The decorative veneer was manufactured by dry pressing in an
Measurement of TVOC emission from surface materials using 20 L chamber and FLEC
Fig. 2 shows the TVOC emission factors from the lignocellulosic surface materials measured by 20 L chamber. Koontz and Hoag [25] reported that unfinished PB and MDF from North America emitted a large amount of VOCs in addition to formaldehyde, often at greater levels than that of formaldehyde. The MDF emitted 0.38 mg/m2 h of TVOC after 7 days. However, the TVOC emission factors from the MDF coated with lignocellulosic surface materials ranged from 0.09 to 0.15 mg/m2 h, which was lower than that of
Conclusion
The uncoated lignocellulosic surface materials showed reduced TVOC and formaldehyde emissions. HPM showed the lowest TVOC and formaldehyde emissions using the 20 L small chamber. In the case of the uncoated lignocellulosic surface materials, the veneer reduced the TVOC emissions, and LPM showed a lower formaldehyde factor than the others. The coated surface materials effectively reduced the level of formaldehyde emission from the MDF in the measurements using the 20 L small chamber. However, in
Acknowledgement
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2009-0063383).
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