Study on the Stable State Formaldehyde Emission at 60 C for Plywood by A Modified Flask Method

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1 Study on the Stable State Formaldehyde Emission at 60 C for Plywood by A Modified Flask Method Loredana Anne Marie Badescu, Valeriu Petrovici, Simona Urdea, Iudith Kinga David Faculty of Wood Industry, Wood Technology Department Transilvania University of Brasov B-dul Eroilor nr.29, , Brasov ROMANIA loredana@unitbv.ro; petrovic@unitbv.ro; Abstract: - Although European standards were developed to determine the stable state formaldehyde emission, they are rather costly and time consuming. This paper presents a new proposal regarding the study of the stable state formaldehyde emission for plywood by a modified flask method, which has the advantage of being rapid and cheap. Tests were conducted at a temperature of 60 º C in order to speed the formaldehyde emission, value which was inspired from the gas analysis method in SR EN 717-2:1995. The methodology from the flask method was adapted for cycling testing with a cumulated length of time of maximum 172 hours found sufficient to reach a stable state formaldehyde emission. For the specimens, there were used not only the type recommended in EN 717-3: 1996, but also a new configuration, VA, proposed by the authors, which enhances the formaldehyde release through all specimen faces and edges. Experimental research was performed on 4, 8 and 12 mm beech plywood for interior use in dry condition, glued with urea-melamine-formaldehyde resin. Based on the experimental results it was established a general theoretical equation of the formaldehyde emission with time. To check the stable state it was used a threshold condition from the chamber method in SR EN 717-1:2005 [9]. The reliability of the method was tested and worked well for various plywood thicknesses. The methodology proposed may be regarded as a challenge in this field, because invites to further improvement of existing standard methods or development of new ones. Key-Words: - Formaldehyde emission, Stable state, Flask method, Plywood 1. Introduction Since its discovery in the last half of the nineteenth century, formaldehyde has become an industrial chemical of outstanding importance since it is one of the substances most used by various economic sectors [15]. In consequence, the formaldehyde emission is today one of the key issues in the chemical industry, by its synthesis or by the synthesis of its derivatives (synthetic resins, plastics, medicines, coloring agents), in the wood industry, the textile industry, etc [4], [14]. Some information about the possible implications of this substance as an industrial toxic in the manufacturing of wood particleboards was available since 1962, while the first regulations in this domain regarding the formaldehyde emission are dating back to 1980 [5]. Since many years, this has been a reason of concern and an important subject for discussion regarding the approximately 17 construction materials that emanate formaldehyde, half of which representing wooden products and corresponding technological materials: plywood, wooden flooring, glue laminated timber, MDF, particleboard, urea and phenolic resins, adhesives, finishing materials, paints, etc. The present importance of such problematic results from the fact that formaldehyde is the first among the 6 chemical substances considered as industrial hazards in this domain being followed by toluene, xylene, wood preservatives, termite chemicals and plasticizers [12]. Given the above motivation, this topic represents the basis of numerous regulations advanced by some governmental organizations, such as: ministries of health and work safety, ministries of economy and commerce, of science and technology, of agriculture, of education and culture, specialized agencies and even regional organisms such as the European Confederation of Woodworking Industries (CEI- Bois), which held 28 national organizations in the woodworking domain from Europe [16]. In the same framework, national organizations of research, evaluation and certification are intensively acting today, among which can be cited: the Japan Testing Center for Construction Materials, Japan Plywood Inspection, Japan Housing and Wood ISSN: ISBN:

2 Technology Center, in Japan [12], the Engineering Wood Association-APA in North America [17], Hardwood Plywood and Veneer Association-HPVA in America, Professional Services Incorporated-PSI in South America, China Certification and Inspection Company-CCIC in China [1], SP Sveriges Tekniska Forskninginstitut in Sweden, Wood Research Wilhelm Klauditz Institute-WKI in Germany [5], etc. It can be remarked that a series of other regional or international organizations have elaborated standards and specific methods regarding the formaldehyde contained in the wood based products, such as: ASTM (North America), CEN (Europe), GB (China), JIS/JAS (Japan), JANZ (Australia) and ISO (international). Being a toxic substance, for human exposure in such environment and especially in the workplace atmosphere, the formaldehyde in itself or as emission from the wood based products represents a major concern for some national organizations which have developed specific environmental regulations, such as: California Air Resources Board CARB (California), Occupational Safety and Health Administration-OSHA, Federal Emergency Management Agency-FEMA (USA), etc [7]. The noxious effect of this substance has become worrying by its severe consequences not only as eye and breath system irritative at humans, but mostly as a local nasal carcinogen and nasopharyngeal or as systemic inducing leukemia to humans and animals. As a result, [3] reported that the International Agency for Research on Cancer (IARC) decided in June 2008, based on some epidemiologic data, the update of this substance from Group 2A (probably carcinogenic to humans) to Group 1 (carcinogenic to humans). Given the above, it is necessary from technical reasons to emphasize the differences between the formaldehyde emission and the content of formaldehyde. The formaldehyde content or the Perforator value, expressed in mg/kg board absolutely dried (a.d.), determined according to SR EN 120:1995 [8], refers to the amount of formaldehyde which really exists in the internal structure of a wood based board at a time. This can be in a free state, in the board itself, or as a result of some physical, chemical and heating processes to which adhesives are subjected during the mat pressing. The formaldehyde emission refers to the quantity of formaldehyde that is freely released by a wooden board through all its faces and edges in the air of a room, under normal or accelerated well determined conditions. In this case, formaldehyde is an effective pollutant agent of the atmosphere in working and living spaces, practically being possible to be determined by using one of the three European current standards, like: the chamber method, according to SR EN 717-1:2005 [9], expressed in mg/m 3 air; the gas analysis method, according to SR EN 717-2:1995 [10] expressed in mg/m 2 h absolutely dried (a.d.) board the flask method according to SR EN 717-3:1996 [11] expressed in mg/kg a.d. board The formaldehyde emission from a wooden based board is a complex phenomenon, since it is influenced by many factors, such as: manufacturing technology, storing conditions, the period of time past from the manufacturing, the determination method etc. In Romania, the formaldehyde emission from particleboards is determined only by the gas analysis method, the other two methods are not yet effectively implemented in the production control. Anyway the costs are quite high, being necessary to offer a more accessible alternative to the chamber and gas analysis methods. Following this fact, in approaching the present research topic, the start point was the premise that the determination of the formaldehyde emission by the flask method could be a more accessible mean for the internal and external control of the plywood manufacturing in companies, especially in case of small and medium ones. Preliminary research has shown that the determination of the formaldehyde emission for plywood by the flask method is influenced by the samples configuration. In this context, a correlation between the pack configuration and the structure, thickness and density of plywood has already been established [6]. In a previous published work [14] were established the appropriate methodology, specimen configuration and algorithm that can define and check the formaldehyde emission from plywood at a stable state, by using a modified flask method at temperatures of 23 C and respectively, 40 C. These temperatures were chosen based on the fact that the first represents the value foreseen in the standard SR EN 717-1:2005 [9] to determine the emission by the chamber method, whereas the latter is recommended for determining the formaldehyde emission by the flask method in the related standard SR EN 717-3:1996 [14]. The objective of this paper is to establish the appropriate methodology and algorithm that can define and check the formaldehyde emission from plywood at a stable state for a temperature of 60 C by using a modified flask method. This temperature ISSN: ISBN:

3 was inspired and chosen based on the fact that this is the value foreseen in the standard SR EN 717-2:1995 [10] for determining the formaldehyde emission by gas analysis. 2. Problem Formulation In order to determine the stable state of the formaldehyde emission for a temperature of 60 C it was developed a methodology based on the flask method, but modified by an increased temperature to speed the emission and with a length of time sufficient to reach a stable state. The determination of formaldehyde emission was performed on beech plywood of 4, 8, 12 mm thicknesses, for interior applications by using the flask model type 2, presented in Fig. 1speed the emission and with a length of time sufficient to reach a stable state. The determination of formaldehyde emission was performed on beech plywood of 4, 8, 12 mm thicknesses, for interior applications by using the flask model type 2, presented in Fig. 1. Some of our previous research allowed us to observe that the present V-type configuration of the sample pack as stipulated by SR EN 717-3:1996 [11], may give some analysis errors, mainly generated by the uneven griping with the elastic strap. Fig. 1: Equipment type 2 for determination of formaldehyde emission by the flask method: 1-flask; 2-hook; 3-rubber strip; 4-water level in the flask For this reason, but especially in order to obtain the maximum possible formaldehyde emission of all samples in the pack, it was adopted a new configuration VA-type as is presented in Table 1, where the samples are spaced by 1 mm pins. Table 1: Codified representation of the samples configurations in the pack used for experimental tests No. crt Type of the working variant 1. Standard variant V (according to SR EN 713-3:1996) 2. VA-type modified variant Pack configuration The emission code FV FVA Detailed description of the pack configuration The pack freely emits through all its edges and through the upper and lower faces. Samples in the pack are equidistantly 1 mm spaced. The pack freely emits through all the edges and faces of all its components. Observations Practical situation corresponding to compact stacking of plywood on pallets. The real case of maximum possible emission of all samples in the pack. Samples with areas of 25 x 25 (mm 2 ) were cut from the plywood board conditioned according to standard specifications. Packs were prepared by overlaying above samples as V and VA-type configurations, having 20g/pack, and were then gripped by an elastic strap. Each pack was then suspended in a flask, with the bottom face distanced 40 mm from the level of 50 ml distilled water. For each analysis three parallel tests were made, corresponding to each configuration and plywood thickness. The packs were maintained at 60 C and after 4 hours, they were removed from the flasks. From each flask 10 ml solution was extracted, in order to determine the formaldehyde concentration by using the photo colorimetric method with acetyl acetone and ammonium acetate at 412 nm. In the same flasks, 50 ml distilled water was introduced again and the packs were re-suspended and were maintained in the oven at 60 C for 20 hours. ISSN: ISBN:

4 After this interval, the packs were removed from the flasks and the formaldehyde solutions freshly resulted were removed. In the flasks, other 50 ml of fresh distilled water was introduced and the cycle continued for another 4 hours at the same temperature mentioned above. From the newly resulted solution, 10 ml was again sampled to determine the formaldehyde concentration. All these cyclic operations were identically repeated for 172 hours, after which the determination was no more possible, as the samples started to deteriorate. Formaldehyde emission, by the modified flask method, for FV and FVA configurations was assessed for each cycle of analysis based on the equation specified in SR EN 717-3:1996 [11]. After experimental data was obtained, the following stages follow as in the previous work of [14]: Search of a representative theoretical function based on the experimental data by checking the functions provided by DataFit program Determination of the stable state of the formaldehyde emission based on the theoretical function and checked with a condition given in SR EN 717-1:2005 [9]. 3. Problem Solution In Table 2 are presented the experimental values obtained for the formaldehyde emission determined by the modified flask method after 172 hours, by following the above procedure at 60 C for each plywood thickness and pack configuration. Table 2 Formaldehyde emission determined experimentally by the modified flask method at a temperature of 60 C for plywood 4, 8 and 12 mm thick No. Time, hours Formaldehyde emission, FV and FVA, experimentally determined as mg/kg a.d.board Standard pack configuration, V type Adopted pack configuration, VA type Plywood thickness, mm As it results from the data presented in Table 2 and Fig. 2, the formaldehyde emission from plywood determined in absolute values by the modified flask method at 60 C is progressively increasing with time for each board thickness and configuration having then a trend to stabilize. This fact is in disagreement with findings in a previous work for the formaldehyde emission determined from the same plywood boards and configurations with an identical methodology, but at different temperatures of 23 C and 40 C, where, the formaldehyde decreased in time before reaching a stable state [14]. In this sense, it is possible that at a temperature of 60 C beside the actual emission of free formaldehyde a supplementary emission of formic aldehyde takes place as a consequence of a hydrolytic decomposition of the ureic adhesive being in a resite stage and breakage of methylenic or/and methylen-etheric bonds. This process could be simultaneously accompanied by the emission of other aldehydes and/or of some organic compounds easily volatile, which also contain the organic function of aldehyde type and being characterized by boiling temperatures of up to 60 C. Therefore, it wasn t possible to draw a diagram of the formaldehyde emission as function of time simply by applying the equation specified in SR EN 717-1:2005 [9] and to determine in this way the stable state of the process according to this method. As a consequence, it was decided to use the DataFit Program from which about 45 regression equations ISSN: ISBN:

5 for each thickness and pack configuration were applied to the experimental data of formaldehyde emissions contained in Table 2. Formaldehide emission, mg/kg mm, FV 4mm, FVA 8mm, FV 8mm, FVA 12mm, FV 12mm, FVA Time, h Fig. 2 The formaldehyde emission with time for plywood of 4, 8 and 12 mm thickness, configurations V and VA at a temperature of 60 C Out of these equations one was chosen, a power function, which proved to have the coefficient of multiple determination R 2 the closest to 1 and positive b and c coefficients ( 1): x c y= a b x ( 1) where: y - Formaldehyde emission calculated in mg/kg a.d. board a value of the formaldehyde emission determined experimentally at a temperature of 60 C by the flask method after 4 hours in the first day of analysis, in mg/kg a.d. board b,c coefficients calculated by DataFit for each selected equation x Time for determination of the formaldehyde emission after each cycle analysis, in hours In a different work stage, were drawn the theoretic curves corresponding to the power function from equation ( 1) applied to the same experimental data, but by increasing the values of a with 10, 20 and respectively 30% as instructed by SR EN 717-1:2005 [9] for determination of the stable state formaldehyde emission for wood based panels by the chamber method. By centralizing the new theoretical values a of the formaldehyde concentrations, as well as the coefficients b and c provided by DataFit for a confidence interval of 99% it was found that they also had only positive values. For all plywood thicknesses and pack configurations, when a takes values between mg/kg a.d. board, the coefficient b can vary between , c between , while the coefficient of multiple determination R 2 has values between In the same context, by processing the experimental data for all thicknesses and pack configurations was verified the stable state formaldehyde emission by using the inequation ( 2) specified in the same standard above, but by modifying the lengths of time, respectively: [( c ) c ] δ c ( 2) t t+ 24 / t+ 24 where: c t, c t+24 formaldehyde concentrations calculated with equation ( 1) at t and t + 24 h, in mg/kg a.d.board. t the period of time used to assess ( 2) in a recursive manner (4, 28, 52, 76, 100, 124 and 148h) δ - coefficient, with a value of 0.05 as recommended in SR EN 717-1:2005 [9]. In this sense, experimental data containing the length of time and corresponding formaldehyde emissions was introduced in Excel. Then, for all thicknesses and pack configurations was drawn the theoretical regression curve according to ( 1), in which was introduced the experimental value of a as such or increased with 10%-30%, and for the coefficients b and c, the values were randomly chosen from the value intervals previously established with DataFit program and presented above. For each theoretic curve was checked the moment for the occurrence of a stable state formaldehyde emission by testing the condition in ( 2), in which were gradually introduced the values of formaldehyde concentrations corresponding to durations t and t+24. Therefore, it was found that the stable state formaldehyde emission for an imposed condition ( 2) can be achieved according to the plywood thickness and pack configuration after hours. In order to check the reproducibility of this new methodology a similar case study was performed by using another plywood board of the same type, but with a thickness of 5 mm. By introducing the new experimental data of the formaldehyde emission and corresponding lengths of time in Excel and by following a similar procedure as described above it was found that the stable state of the formaldehyde emission was reached after 100 hours, result which is similar to the previous findings. 4. Conclusion Determination of the stable state formaldehyde emission is at present regulated by generally accepted standards. However, the need to speed the duration of analysis and to allow for accessible simple tests in terms of equipment, have motivated the authors to ISSN: ISBN:

6 develop a new methodology based on a modified flask method. A new specimen configuration is suggested, based on the standard method, which leaves free all surfaces of the specimens and enhances the formaldehyde release, eliminating in this way the possible errors given by an uneven gripping with the elastic strap. In order to speed the emission, the standard temperature of 40 C was modified to 60 C, which is inspired from the gas analysis method. Based on the experimental data measured for plywood of various thicknesses, it was established a theoretic power type function that can be used to assess the formaldehyde emission in time. To check the stable state formaldehyde emission the authors suggest an inequation from the chamber method in SR EN 717-1:2005 [9], but using modified lengths of time. It was found that the stable state formaldehyde emission is reached at a moment, after at least 4 consecutive days and maximum 172 hours, when the ratio of the concentration increment to the current concentration value becomes equal or less than 0.05, which is a value recommended in the above standard. The modified flask method is easier and cheaper, but as efficient alternative to the chamber method in assessing the formaldehyde stable state emission. Furthermore it takes maximum 172 hours compared to approximately 28 days of the chamber method. The method that proved to be repeatable for all plywood thicknesses tested, could be implemented on the Romanian market, but also could invite to a larger European collaboration in a common project that would develop new related standards or improve the existing ones. References: [1] Aguila, J., An Implementation Update on California s Composite Wood Products ATCM, Technical Formaldehyde Conference, Hanover, Germany, March, [2] David, K.I., Zeleniuc, O., Petrovici, V., Sângeorzan, L., Study on the Formaldehyde Emission Stable State for Particleboards by the Flask Method, Proc. of the International Panel Products Symposium, ESPOO, Finland, September, 2008, pp [3] Gelbke, H.P., Formaldehyde: The Toxicological Profile and Regulatory Issues, Technical Formaldehyde Conference, Hanover, Germany, March, [4] Liga, A., Ciubotaru, M., Caranfil, A., NuŃǎ, V., Diminuarea degajarii de formaldehida din placi aglomerate din lemn. Industria Lemnului 1, [5] Marutzky, R., Technical Formaldehyde Conference-Opening and Thematic Introduction, Technical Formaldehyde Conference, Hanover, Germany, Hanover, Germany, March, [6] Petrovici, V., Urdea, S.N., David, K.I., PîrnuŃǎ, O., Research Studies Concerning the Formaldehyde Emission of Plywood Using the Flask Method. Proc. of the 3rd International Conference on Environmental Engineering and Management, ICEEM/03, Iasi, Romania, September, [7] Schutfort, E., US Test Methods and Practical Experiences, Technical Formaldehyde Conference, Hanover, Germany, March, [8] SR EN 120: Romanian Norm: Wood-Based Panels. Determination of Formaldehyde Content- Extraction Method Called the Perforator Method. [9] SR EN 717-1: Romanian Norm: Wood- Based Panels. Determination of Formaldehyde Release. Part I: Formaldehyde Emission by the Chamber Method. [10] SR EN 717-2: Romanian Norm. Wood- Based Panels. Determination of Formaldehyde Release. Part II: Formaldehyde Release by the Gas Analysis. [11] SR EN 717-3: Romanian Norm. Wood- Based Panels. Determination of Formaldehyde Release. Part III: Formaldehyde Release by the Flask Method. [12] Tanabe, S., Japanese Formaldehyde Regulations: Actual Situation and Future Developments, Technical Formaldehyde Conference, Hanover, Germany, March, [13] Urdea, S., Raport privind stadiul actual al cercetarii in domeniul emisiei de formaldehida la placi stratificate din lemn. Şcoala Doctoralǎ, Universitatea Transilvania din Brasov, Romania, [14] Urdea, S.N., Zeleniuc, O., Petrovici, V., Sângeorzan, L., Study on the Stable State Formaldehyde Emission for Plywood by Flask Method, Proc. of the 3 rd International Conference on Environmentally Compatible Forest Products, Porto, Portugal, September 2008, pp [15] Walker, J.F., Formaldehyde. Third Edition, American Chemical Society, New York, Reinhold Publishing Corporation, [16] Wignendaele, K., European Formaldehyde Regulation and Impact on the Wood-Based Panels Industries Technical Formaldehyde Conference, Hanover, Germany, March, [17] Zylkowski, S., Wood Products in North America-What about Formaldehyde? Technical Formaldehyde Conference, Hanover, Germany, March, ISSN: ISBN: