A METHOD AND DEVICE FOR MEASURING FORMALDEHYDE EMISSION FROM SURFACES

Abstract: A method for measuring formaldehyde emission from surfaces is described in which a test chamber in the form of an open reservoir of a gas-tight and waterproof material with a gel layer containing a reagent for formaldehyde applied on the inner bottom surface, is placed on the plain test surface with its opening facing the test surface, which reagent when reacting with formaldehyde emitted from the test surface generates a colour change of the gel substance, by means of which the amount of formaldehyde absorbed in the gel substance can be determined. A device for carrying out said method is also described, which comprises a test chamber, which consists of a reservoir, which can be a dish or similar container, the opening of the reservoir being considerably larger than the height of the reservoir, and wherein a gel layer containing a reagent for formaldehyde is applied over the whole inner bottom surface and wherein the opening of the reservoir is closable with a gas-tight and waterproof cap.

Description: METHOD AND DEVICE FOR MEASURING FORMALDEHYDE EMISSION FROM SURFACES The present, invention relates to a method and a device for measuring formaldehyde emission from surfaces, preferably plane surfaces of surface treated or untreated materials, such as particle boards, fibre boards, plywood etc. Mesurement. of emission of formaldehyde from objects where this is a component of the material, as for example in the form of glue or paint, is in many different contexts necessary because of the environmentally dangerous and unhealthy properties of formaldehyde and the need of determining the level thereof in the atmosphere, for example in workrooms and residences. The known methods for measuring formaldehyde emission can be divided into indestructing and destructing testing. The so called chamber method belongs to the first group, and is described in for example DIN/frt/klg/001-8 Deutsche Norm: Prufung von Formaldehydeemittierenden erkstoffen, according to which the tested object is placed in a closed chamber, through which air is streaming under constant, temperature and speed. After that air is passed through an absorption drum where the formaldehyde that has been carried from the test chamber is dissolved in water and then the formaldehyde quantity is photometrically determined after a certain period of time by adding a reagent, acetylacetone, that reacts with formaldehyde in the presence of acetic acid and an ammonium salt of diacetyldihydrolutidine (Hantzsch-reactioπ) . However, the method that can be considered as serving as a standard for measuring of formaldehyde emission, is time consuming and requires a lot of space. If bigger objects are to be tested, for example a pane of a bookshelf, a corresponding size of the test chamber is required. The test time which is governed by the 'fact how soon a state of equilibrium between the formaldehyde emission and the air flowing through is attained in the test chamber, can be considerable, several hours. According to another known method that is described by Berge et al in Forest Products Journal Vol 29, No 1, p 21, Jan 1979, the chamber has been replaced by a clock that has been placed on the test surface which will be the bottom of the clock. Even if this equipment requires less space than the chamber method this method nevertheless is time consuming and lengthy. According to a similar method that is described by Mattews et al in Analytical Chem. Vol 56, No 3, p 448, March 1984, a so called Formaldehyde Surface Emission Monitor (FSEM) is used, where the emitted formaldehyde is stored in a molecular sieve placed inside an open chamber that is put on the test surface. Before the quantitative determination of the emitted formaldehyde this must be extracted from the molecular sieve with water. Also this method is time consuming and lengthy. An object according to the present invention is to provide a method for measuring of formaldehyde emission from surfaces, preferably plane surfaces, which method is rapid and simple and which enables indestructing determinations of formaldehyde and does not requires space and is well correlated to measurements made according to the chamber method. Another object according to the invention is to provide a cheap and simple device that will make possible measuring formaldehyde emission from surfaces, preferably plane surfaces, which device is storable in darkness at room temperature. In the method according to the invention for measuring formaldehyde emission from a plane surface, one or several test chambers in the form of small open reservoirs are placed on the plane surface with the opening facing the test surface. In the bottom of the reservoir that, can be dish, for example a petri-dish or a similar type of a dish, made of glass, plastic or another gas-tight and waterproof material, a layer contain¬ ing a reagent for formaldehyde, for example acetylacetone, is applied, which reagent is dissolved in a ' gel substance made of for example gelatine, polyacrylamide, polyvinylalcohol, poly- vinylpyrrolidone or starch, and water. This substance can be modified by adding a consistency former, for example gum arabic, and/or by adding a liquid binding agent, for example salts. The formaldehyde emitted from the test surface is absorbed in the gelatine layer in the bottom of the reservoir which is positioned a short distance from the test surface and reacts with the reagent, for example with acetylacetone to a yellowish compound, diacetyldihydrolutidine (DDL) with an absorption maximum of 412 nm. After a certain, not too long, period of time, about. 3 minutes to 1 hour, depending on what the magnitude of formaldehyde emission is, the reservoir is removed from the test surface and is closed. Then the reservoir is heated up and is held - when using acetylacetone as a reagent - at about 60°C for about 10 minutes. By this procedure the gelatine substance is brought into liquid state and the absorbed formaldehyde is brought to react completely with the reagent. Then the liquid substance can either be transferred to a measuring cuvette for determin¬ ing the light absorption in a photometer at the wavelength of 412 nm or the test chamber itself can be turned edgeways and can serve as a measuring cuvette (see Fig. 2). According to another simplified procedure for facilitating the determina¬ tion the reservoir can be equipped with a comparison scale of different tints that correspond to different absorbency values for the gelatine substance, compare with Fig. 2. By comparison with determinations of formaldehyde emissions made according to the chamber method and correlations with these as is described in example 2 the quantity of emitted formaldehyde during a certain period of time and from a given surface can easily be determined by comparising the colour of the gelatine substance with the colour scale by means of which it can be controlled if the emitted quantity of formaldehyde is below or above an allowed limit value. A suitable device according to the invention for performing the method according to the invention is a test chamber of the following construction, compare with Fig. 1: The test chamber consists of a reservoir (A) that can be in the form of a dish, for example a petri-dish or a similar one, made of glass, plastic or another gas-tight and waterproof material. The shape of the dish is, but. not necessarily, cylindrical, the diameter being considerably larger than the height and has a value within in the area 1-20 cm, principally 2-10 cm, while the most suitable height is within the area 0.2-10 cm. A layer (B) containing a reagent for formaldehyde, for example acetylacetone, is applied over the whole inner bottom surface of the reservoir, which reagent is dissolved in a gel of for example gelatine or water. The thickness of the mentioned layer is 0.2-10 mm, preferably 0.5-2 mm. The opening of the reservoir is closed with a gas-tight cap that can be a gas-tight plastic cap or a peelable plastic foil or another material that easily can be removed when the reservoir is to be used. Alternatively two reservoirs can be closed against each other, for example with mechanical means or with an adhesive, see Fig. 3. • > .'- In the determination of the formaldehyde emisrion from a plane surface the cap of the reservoir is removed and the reservoir is placed with its opening down on the test surface. After the end of the test period the reservoir is removed from the test surface area and is again closed with the cap. For determin¬ ation of the light absorption in the manner mentioned above the gel layer is brought into liwuid state by heating the reservoir and the light absorption is determined as mentioned above. The reservoir itself can be used as a measuring cuvette or the gel substance, can be transferred to a separate measuring cuvette. Furthermore, the reservoir can be equipped with a graduated colour scale by means of which the tinting of the gel substance can be directly compared to a colour scale directly related to values for formaldehyde emission whereby it easily can be determined if the formaldehyde emission is above or below a certain stipulated limit. Example 1 Making a test chamber: An acetylacetone-gelatine solution is made as follows: 1.7 g gelatine 7.7 g ammoniumacetate 0.1 ml acetylacetone 0.15 ml acetic acid 100% g.s. water 100 ml are dissolved while stirring at about 45°C. 2 ml of the heated solution is poured into a cylindrical Petri-dish made of clear polystyrene plastic with an inner diameter of 49 mm and an inner height of 7 mm and is evenly distributed over the bottom of the chamber. The chamber with its content is closed with a plastic cap and is then placed on a horizontal support in order to get cool by means of which procedure the solution solidifies to a gel. The gel layer has a thickness of about 1 mm. This device is storable in darkness at room temperature. Example 2 Comparative measurements with the chamber method according to DIN. Testing time: 30 minutes with test chamber according to example 1. Test surface in determination according to DIN: 0.06 m 2 . Chamber volume: 20 litres. Air quantity: 1.16 litres/minute. Samples: Acid hardening alkyd/amine resin paints applied on glass. • Test results are shown in the diagram in Fig. 4 in which the correlation according to a statistical correlation analysis is represented by a straight line with the equation: y = 0.4S06x - 0.0121, where the y absorbency at 412 nm and x = the chamber value in mg/m 3 . The correlation shown is statistically significant. Example 3 Examination of the distribution of the test results with the new method. Experimental panel: Glass panel 25 x 25 cm covered with an acid hardening alkyd/amine lacquer. Samples: 20 test chambers according to example 1 and placed on the experimental panel according to Fig. 5. Testing time: 30 minutes. The test results are shown in Fig. 5 in which the reported values refer to the absorbency multiplied with a factor of 1000. The average value is 0.0297. The corresponding test result when measuring with the chamber method is 0.073 mg/m 3 which result well corresponds with the correlation shown according to example 2.

Claims: CLAIMS '' 1. Method for measuring formaldehyde emission from surfaces, preferably plane surfaces of surface treated or untreated materials, c h a r a c t e r i z e d in that on the surface to be examined one or several test chambers formed as open reservoirs are placed on the plane surface with their openings facing the area to be examined / wherein a gel layer containing a reagent for formaldehyde is applied on the inner bottom surface of the reservoir which is made of glass, plastic or another gas-tight and waterproof material and which reagent when reacting with formaldehyde generates a coloured reaction product, the formaldehyde emitted from the test surface being absorbed in the gel substance in the bottom of the reservoir, which bottom is positioned a short distance above the test surface, and there reacts with the reagent generating a change of the colour of the gel substance, and then the reservoir after a short period of time, of from about 3 minutes to 1 hour is removed from the test surface and is closed and then the gel substance is brought to a liquid state by heating the reservoir and thereafter the quantity of formaldehyde absorbed in the gel substance, which quantity is directly related to the quantity of formaldehyde emitted from the test surface, is determined by means of the colour change of the gel substance. 2. Method according to claim 1, c h a r a c t e r i z e d in that the reagent for formaldehyde is acetylacetone and that the gel substance is made of gelatine and water 3. Method according to claim 1 or 2, c h a r a c t e r i z e d in that the quantity of absorbed formaldehyde is determined by measuring the light absorption by a photometer in a measuring cuvette. 4. Method according to claim 3, c h a r a c t e r i z e d in that the test chamber itself is used as a measuring cuvette. 5. Method according to claim 1 or 2, c h a r a c t e r i z e d in that the quantity of absorbed formaldehyde is determined by comparing the tint generated in the gel substance with a colour scale according to which the quantity of absorbed formaldehyde is directly proportional to the colour intensity of the colour scale. 6. A device for measuring formaldehyde emission from surfaces of treated or untreated materials by absorption of formaldehyde emitted from the said surfaces in a test chamber, c h a r a t e r i z e d in that, the test chamber consists of a reservoir (A) which can be a dish or similar, made of glass, plastic or another gas-tight and waterproof material, the shape of the reservoir suitably being cylindrical, the opening being considerably larger than the height of the reservoir and where the surface of the opening is within the area 0.8-300 cm 2 , preferably 3-150 cm 2 , and where a layer (B) containing a reagent for formaldehyde is applied over the whole inner bottom surface of the reservoir and where the opening of the reservoir is closed with a gas-tight and waterproof cap. 7. A device according to claim 6, c h a r a c t e r i z e d in that the reservoir (A) is cylindrical with a circular opening. 8. A device according to claim 6 or 7, c h a r a c t e r i z e d in that the reagent for formaldehyde is acetylacetone and the gel substance is made of gelatine and water. 9-. A device according to claims 6-8, c h a r a c t e r i z e d in that the thickness of the gel substance is 0.2-10 mm, preferably 0.5-2 mm. 10. A device according to any of claims 6-9, c h a r a c t e r i z e d in that the gas-tight and waterproof cap consists of an identical reservoir the two reservoirs being closed with each other. 11. A device according to any of claims 6-10, c h a r a c t e r i z e d in that the reservoir also is a measuring cuvette for measuring absorbency in a photometer. 12. A device according to any of claims 6-11, c h a r a c t e r i z e d in that the reservoir is provided with a colour scale that indicates the quantity of absorbed formaldehyde as a function of colour intensity.

Inventors: FORSSMAN JOAKIM, FORSSMAN, JOAKIM
Applicants: BECKER WILHELM AB, AB WILH BECKER
Application year: 1989
Main classification: G01N21
IPC codes: G01N21, G01N31