Control of formaldehyde and TVOC emission from wood-based flooring composites at various manufacturing processes by surface finishing
Introduction
In renovated or completely new buildings, levels of indoor air pollutant emissions from construction and building materials, especially of VOCs, are often several orders of magnitude higher than the VOC levels in buildings under normal use [1], [2], [3], [4]. The use of small-scale environmental chambers with volumes ranging from a few liters to a few cubic meters has been increasing [5]. The weakness of these traditional chamber techniques is that they cannot be used to investigate emissions from existing real building structures. The emission of VOCs from a material in a real building structure is affected not only by the material but also by the environmental conditions and other surrounding materials [6]. Secondary emissions can develop under the influence of humidity, ozone, UV-light, etc. [7], [8]. Hydrolysis reactions in the floor structure (PVC/adhesive/casein containing leveling agents) can produce 2-ethylhexanol, butanol and ammonia [9]. Thus, the emission measured on site can differ considerably from the emission measured from a single material under laboratory conditions [10]. The impact of the increased consciousness about indoor environment has created a demand for low-emitting (healthy) building materials, and hence also for standardized methods to characterize and quantify the VOC emissions from building materials and consumer products. Furthermore, methods for easy source identification of potential VOC emission from building materials on site and for their quantification are required. Therefore, the field and laboratory emission cell (FLEC) has been proposed and has become a European standard for emission testing (prENV 13419-2, 1998). This is a kind of micro-emission cell featuring a high sensitivity due to the large loading ratio (surface area/volume). Nowadays, a large percentage of emission tests for various materials are performed with FLEC [11], [12], [13]. As a pre-test method for TVOC emission from building material, the VOC analyzer was successfully applied. There was a good correlation between TVOC emission concentration by the VOC analyzer and TVOC EF by the standardized 20 L small chamber method in the case of paints [14], [15].
Recently, there have been many concerns about human health and the environment. PVC flooring, laminated paper lacquered with bean oil, which was used in most Korean houses has been replaced by wood flooring materials, especially in new apartments [16]. There are three kind of flooring composites; engineered flooring, laminate flooring and parquet flooring used in Korea. Among these, parquet is made from thick veneer which is more expensive then the others for normal living rooms. Therefore, engineered flooring and laminate flooring are commonly used in new apartment interiors and in the remodeling market in Korea. Laminate flooring is a composite floor with either a chipboard or HDF core that is bonded to a film of wood effect veneer and covered with a laminated surface; overlay paper, deco paper and valance paper. Each paper is impregnated with melamine-papers pressed at about 200 °C. A clear cap sheet made of an aluminum oxide saturated film (overlay paper) and a balancing backing are also put on the top of deco paper and on the back of the panel, respectively. The main purpose of the aluminum oxide film is to protect the surface against any stain [17]. Finally, the product is processed on the sides and edge with the tenoner. In the case of engineered flooring, fancy veneer of 0.5 mm thickness; woods such as birch, oak, beach, cherry, or maple are glued on plywood of 7.2 mm thickness and pressed at about 160 °C. UV-curable coating is placed on this fancy veneer [18].
Before they can be used as furnishing materials, wood-based panels have to be treated to match the specific requirements of their final use. Therefore, finishing treatment methods which produce an overlay or coating, such as paints, prints, varnishes, veneers, laminates, impregnated papers, finishing foils, etc., are used to reduce the absorption of water and humidity, and eliminate the release of harmful gases [19]. Interior fitment and furniture manufacturers are using more surfacing materials for decorating fiberboard. This material is manufactured as uniform, flat panels that provide excellent surfaces for the application of coating materials [20], [21]. These surface materials, such as decorative vinyl film and melamine impregnated paper, can lower the formaldehyde emission concentration from wood-based panels [22]. Nemli examined the effects of the coating materials process parameters on the technological properties of particleboard and stated that the surface coating decreased the formaldehyde emission [23].
In this study, FLEC was used to measure formaldehyde and VOCs emission levels from engineered flooring and laminate flooring throughout the manufacturing steps and to compare the VOCs results with those obtained from the VOC analyzer. Especially, it was used to investigate the effect of various manufacturing steps of surface finishing treatment to TVOC/formaldehyde emission behaviors of each flooring.
Section snippets
Materials
Among the various floorings, we chose laminate flooring and engineered flooring. Currently, these are extensively used in new apartment interiors and in the remodeling market in Korea. Laminate flooring is composed of waterproof, high-density fiberboard (HDF) as the core material, with overlay paper, deco paper and valance paper. The wood fiber, for HDF, distributed from Dongwha Enterprise was made from Korean pine (Pinus densiflora) with a moisture content of 4%. Urea–melamine–formaldehyde
Results and discussion
Generally laminate flooring is manufactured to satisfy the E1 grade in Europe. The greatest influence on formaldehyde emission in laminate flooring is exerted by HDF, which is the core of laminate flooring. This grade of laminate flooring can be used for residences. E1 grade wooden flooring materials have been circulating in Korean flooring market [27]. The formaldehyde emission results obtained by FLEC for each flooring samples are shown in Fig. 3. When LPMs were applied on each side of the
Conclusion
Flooring is one of major formaldehyde and TVOC emission wood products. However, formaldehyde and TVOC emission can be reduced during the manufacturing process if the emission levels at each manufacturing steps are found. When LPM and UV coating were applied on HDF for laminate flooring and fancy veneer with plywood for engineered flooring, formaldehyde and TVOC emission decreased because these LPM and UV coatings functioned as a covering material. Although formaldehyde and TVOC emission
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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