FORMALDEHYDE EMISSION A COMPARISON OF DIFFERENT STANDARD METHODS

Transcription

1 FORMALDEHYDE EMISSION A COMPARISON OF DIFFERENT STANDARD METHODS M Risholm-Sundman 1*, A Larsen 2, E Vestin 1 and A Weibull 1 1 Casco Adhesives AB, Stockholm, Sweden, 2 IKEA of Sweden AB, Älmhult, Sweden ABSTRACT This technical bulletin gives a comparison between European test methods e.g. chamber (EN 717-1), gas analysis (EN 717-2), flask (EN 717-3) and perforator method (EN 120) with Japanese test methods e.g. desiccator (JIS A 1460 and JAS 233) and small chamber method (JIS A 1901) for solid wood, particleboard, plywood and medium density fibreboard. The variations between the results from different methods are explained by specific differences in test conditions. The need for harmonisation is obvious, and use of e.g. the standardisation within ISO to work for such an international harmonisation should be encouraged. INDEX TERMS Formaldehyde emission, standard test method, correlation between methods, building material INTRODUCTION The emission of formaldehyde is an important factor in the evaluation of the environmental and health effects of woodbased board materials. Different test methods are used in different countries. In a global market it is of vital importance that it is possible to compare products with formaldehyde emission classes like European E1 with Japanese F*** and F**** based on different test methods. It is also important that interlaboratory tests are performed to make it possible to compare results, and to evaluate the spread that can be expected in the results obtained by different laboratories. Table 1. Comparison of standard methods for the determination of formaldehyde emission. Method Reproducibility Edge sealing Conditioning Test conditions Coefficient of (m open edge/m 2 Temp/RH Temp/RH variation surface area) In-lab Inter-lab EN Partly 0.225, 1 or 23 C/45* 23 C/45 40 m 3 (1.5 m/m 2 ) chamber Europe EN Gas analysis Not stated 60 C/ 3 Yes l chamber EN No Not stated 40 C/~ ml Flask (80 m/m 2 ) JIS A l 1 m 3 chamber 28 C/50 28 C/50 Yes Japan JIS A C/ l desiccator 20 C/ No JAS ** (27 m/m 2 ) No*** 9-11 l desiccator Global ISO/CD Partly 1 m 3 23 C/50* 23 C/50 chamber (1.5 m/m 2 ) * Conditioning in the chamber, ** See Figure 4, *** Stored at 20 C for 1 day wrapped in plastic before testing. * Corresponding author mars@nacka.casco.se 1925

2 There are quite large differences between European test methods e.g. chamber (EN 717-1), gas analysis (EN 717-2), flask (EN 717-3) and perforator method (EN 120) and Japanese test methods e.g. desiccator (JIS A 1460 and JAS 233) and small chamber method (JIS A 1901). Test conditions like temperature and relative humidity (RH) vary substantially, see Table 1. Another important factor for differences in the emission results is the variation in sample treatment like 1) sealing of the edges, 2) sealing or not sealing the back and 3) the requirements for conditioning before the measurement. In the Japanese desiccator methods and the European flask method, the edges are not sealed even though they constitute a large part of the total area. Since the emission in most cases is highest from the edges, this will have great impact on the results from these methods. Also, the conditioning differs; the gas analysis and JAS desiccator methods are run directly after removal of the plastic wrapping, while the other methods give values after conditioning. In this technical bulletin the impact of different test conditions like humidity, temperature and reproducibility of the test method are discussed. Comparison of formaldehyde emissions measured with different test methods are also presented. METHODS Interlaboratory tests Samples were sent to different laboratories for formaldehyde emission tests. Chamber test according to EN Particleboards of E2 quality, 10, 16 and 28 mm thick, were used. Samples packed in plastic were sent to six laboratories in Europe and the tests were made in both 225 l and 1 m 3 chambers. Gas analysis test according to EN Particleboard of E2 quality, 19 mm thick and MDF of E1 quality, 10 and 22 mm thick, were used. Samples cut to size and packed in plastic were sent to fifteen laboratories in Europe and Asia. The samples were analysed directly after opening the plastic and sealing the edges. Desiccator test according to JIS A 1460 Two different particleboards, 12 mm thick, and one MDF, 12 mm thick, all of E1 quality, were used. Samples were cut to size, packed in plastic and sent to eight laboratories in Europe and Asia. The samples were analysed after one week open conditioning at 20 C, 65 RH. Intralaboratory tests For the determination of the reproducibility within one lab, we made the following measurements for the different test methods: Chamber test, EN Two MDF samples, which both gave constant concentrations in the chamber (mean values 0.19 and 0.15 mg/m 3 resp), were measured 9 and 12 times resp. during a period of 14 days. A combined coefficient of variance (CV) was calculated. Gas analysis test, EN Twelve test pieces were cut from a 12 mm MDF board and then wrapped in plastic. At six occasions during July 2004 Jan 2005, two of the pieces were run. A pooled standard deviation was calculated from these 6 duplicate results. Desiccator test, JIS A 1460 From a 12 mm MDF board 99 test pieces were cut and stored at 20 C, 65 RH for 4 weeks. Nine pieces were put in each of 11 desiccators and the formaldehyde emission was measured. After measurement, the pieces were stored open at 20 C, 65 RH for another 4 weeks and then measured again. The tests were made four times and a combined CV was calculated. Desiccator relative humidity The relative humidity was measured during the 24 h desiccator test using a humidity sensor, placed at the level of 1926

3 the sample. The humidity was measured in three desiccators 1) Without sample, 2) With a MDF sample conditioned according to JIS A 1460 at 20 C, 65 RH for a week. The moisture content (MC) was 5.9 before conditioning and 8.2 after and 3) With an interior plywood sample conditioned according to JAS 233 in plastic at 20 C for one day. The moisture content of the sample was 7.6. Chamber test temperature Four samples from the same MDF board were tested according to JIS A 1901, two at 23 and two at 28 C in order to compare results from the European and Japanese chamber tests. The emission was measured after both 7 and 14 days. Comparison of different methods The formaldehyde emissions from solid wood, particleboards, plywood and MDF have been measured with different methods. The Japanese desiccator method JIS A 1460 was compared with European methods perforator EN 120 and chamber EN Particleboards, thickness mm, mostly of F**** quality were used, 21 samples for the EN 120 comparison and 8 for the EN comparison. RESULTS AND DISCUSSION Reproducibility in inter- and intralaboratory tests The results from the interlaboratory tests on methods EN 717-1, EN and JIS A 1460 are given in Figure 1-3. The reproducibility both within our laboratory and in the interlaboratory tests is presented in Table 1. The coefficient of variation (CV) for the interlaboratory tests was calculated after using the Grubbs test to remove possible outliers. The results for each sample were first normalized against the average of the results from all laboratories for the respective sample. The CV for the interlaboratory tests is 2-3 times higher than the intralaboratory CV m m m l l l Chamber method EN Samples 10 mm PB, mean value 0.20 mg/m 3 16 mm PB, mean value 0.18 mg/m 3 28 mm PB, mean value 0.15 mg/m Gas analysis method EN Samples 19 mm PB, mean value 8.3 mg/m 2 xh 10 mm MDF, mean value 3.0 mg/m 2 xh 22 mm MDF, mean value 2.9 mg/m 2 xh Desiccator method JIS A 1460 Samples 12 mm PB, mean value 0.24 mg/l 12 mm PB, mean value 0.64 mg/l 12 mm MDF, mean value 0.59 mg/l Figure 1-3. Results from interlaboratory test, normalized against the average of the results from all laboratories for the respective sample. 1927

4 Desiccator relative humidity The results from the humidity measurement in the desiccator show that wood based samples will lower the RH from 100 to about 60-80, see Figure 4. RH () JIS A 1460, MDF MC=8.2 JAS 233, Plywood MC=7.6 Empty desiccator Hours Figure 4. The relative humidity in the desiccator with samples of different moisture content. Chamber test temperature The MDF sample was tested according to JIS A 1901 at both 23 and 28 C. The result obtained at 23 C, 43.0 µg/(m 2 xh), may be converted to 28 C by using the conversion equation, C=C 0 x e -9799(1/t-1/t0), according to ASTM D This gives a value of 75, which agrees very well with the measured value 74, given in Table 2. Comparison of different test methods The formaldehyde emission measured with the different methods may be compared to the limit values, see Table 2. If the results are normalized against the values for the E0 particleboard, the diagram in Figure 5 may be drawn. As can be seen, the other particleboard, E1, has approximately the same value (about 2) for each method. This shows, that for the same kind of material, the methods show similar results; sample E1 emits approximately twice as much as sample E0. Looking at the MDF sample, EN 717-1, EN 120 and JIS A 1460 show similar behaviour, this sample emits about three times as much as sample E0 according to all three methods. The gas analysis method, EN 717-2, on the other hand, gives a much more pronounced difference, while the flask method, EN 717-3, gives a value comparable to sample E1 (twice E0). The results for the plywood samples are similar for EN and EN 717-2, while gives a much higher value. This is probably at least partly explained by the huge difference in the ratio (open edge area)/(surface area) for the flask method compared to the other two. Solid wood gives low formaldehyde emission, close to the determination limit, for all methods. The result for the MDF sample, when tested in the European chamber according to EN at 23 C, was 0.10 mg/m 3. According to the conversion equation this corresponds to 170 µg/m 3 at 28 C. Since the loading factor and the air exchange rate both are 1, this gives an emission rate of 170 µg/(m 2 xh). The explanation for the substantially higher value obtained in the European chamber compared to the result in the Japanese chamber, 74 µg/(m 2 xh), must be that the sample is run with partly open edges (1.5 m open edge/m 2 ). It has been shown earlier (on parquet samples), that the emission from the edges is much higher than from the surface (Risholm-Sundman et al 1999) The effect of conditioning may be seen in Table 2, from the results on solid pine obtained with the desiccator tests. In JAS 233, when the sample is wrapped in plastic until the test starts, the emission was measured to 0.18 mg/l. The conditioning for 1 week in JIS A 1460 at 20 C 65 RH lowered the formaldehyde emission dramatically, to < 0.1 (0.05) mg/l.the difference in our result in the gas analysis of solid pine, 0.3 mg/(m 2 xh), and the value obtained by Meyer (1997), 0.09 mg/(m 2 xh) may also be an effect of different conditioning. 1928

5 Material Solid wood Particle Board Plywood MDF Table 2. Formaldehyde emission measured according to different standard methods. Thickness analysis r Gas Perforato Chamber Flask Chamber Desiccator mm JIS A JIS A EN EN EN EN 120 mg/m 3 mg/(m 2 xh) mg/kg mg/100 g Oak MC=8 Pine MC=8 E0 MC=6.8 E1 MC=6.0 Interior MC=8.6 Exterior MC=6.2 MC= µg/(m 2 xh) 1460 mg/l ) ) ) ) < 0.1 (0.00)** ) 0.3* ) ) ) < 0.1 (0.05)** (43 at 23 C) 0.6 JAS 233 mg/l < 0.1 (0.03)** Limit E F**** F*** ) Value from Meyer et al 1997, * No conditioning, **Analysed value, below the determination limit of 0.1 mg/l 0.18 Normalised value Value 16 Methods EN EN EN EN 120 JIS A Solid oak Solid pine PB E0 PB E1 Plywood int Plywood ext MDF Figure 5. Comparison of the results from different test methods on different samples. The results have been normalized against the particleboard (PB) E0 value. The correlation between the Japanese desiccator method JIS A 1460 and the European methods EN (chamber) and EN 120 (perforator) was not convincing, the R 2 values obtained were 0.66 and 0.73, see Figures 6 and 7. The values for the European methods that correspond to F ****, 0.3 mg/l, are given in Table 3. These values agree quite well with values reported earlier (Bulian et al 2004) for particleboards in the range mg/m 3 (also including boards with higher formaldehyde emission). 1929

6 Figure 6. Correlation between JIS A 1460 and EN for particleboards Figure 7. Correlation between JIS A 1460 and EN 120 for particleboards Table 3. Correlation between JIS A 1460 and EN and EN 120 resp. Result corresponding to F**** limit Literature result (Bulian et al, 2004) EN (mg/m 3 ) EN 120 (mg/100 g) CONCLUSION Comparisons of different formaldehyde emission methods show that: The variation can be explained by differences in the test conditions. Factors like edge sealing, conditioning of the sample before the test and test temperature have a large effect on the final emission result. The limit for F**** particleboard is equivalent to 0.04 mg/m 3 in European chamber test EN and 2.8 mg/100g in perforator test EN 120. The correlation between the desiccator JIS A 1460 and the chamber and perforator methods resp. is not convincing (R 2 = 0.7). The variations in interlaboratory tests of chamber method EN (CV=11), gas analysis EN (CV= 10) and desiccator JIS A 1460 (CV=15) are 2-3 times higher than in intralaboratory tests. Different standards in different countries make it difficult for the manufacturer of woodbased board materials to be able to comply with regulations in different countries. There is a need for harmonisation and use of e.g. the standardisation within ISO to work for such an international harmonisation should be encouraged. REFERENCES ASTM D Standard test method for determining formaldehyde concentration in air from wood products using small scale chamber Bulian et al. Formaldehyde Testing of Wood-based Panels: Correlations between European and Japanese Test Methoids, Wood based Panel Symposium in Hannover Sept Meyer B. and Boehme C Formaldehyde emission from solid wood, Forest Products Journal, vol 47, no 5, p Risholm Sundman M. and Wallin N Comparison of different laboratory methods for determining the formaldehyde emission from three-layer parquet floors, Holz als Roh- und Werkstoff 57: Winter Funch L. Danish Technological Institute. Report RRT on pren 717-1,