WO1994009062A1

WO1994009062A1 - A method for reducing the emission of formaldehyde from a foam material based on phenol-formaldehyde resin

Info

Publication number: WO1994009062A1
Application number: PCT/SE1993/000799
Authority: WO
Inventors: Jan Olof Andersson
Original assignee: Casco Nobel AB
Current assignee: Casco Adhesives AB
Priority date: 1992-10-08
Filing date: 1993-10-04
Publication date: 1994-04-28
Anticipated expiration: 1995-04-08
Also published as: SE9202958L; AU5288693A; EE9400214A; SE9202958D0

Abstract

A method for reducing the emission of formaldehyde from a foam material based on phenol-formaldehyde resin, in which process the foam material is treated with a solution of urea and thermally decomposable ammonium salt which ammonium salt gives off ammonia in substantial amounts in a temperature range of 15-90 °C. The solution contains 0.1-30 % by weight of urea and 0.1-25 % by weight of ammonium salt, the balance being water. The ammonium salt consists of ammonium carbonate or ammonium hydrogen carbonate or mixtures thereof.

Description

A METHOD FOR REDUCING THE EMISSION OF FORMALDEHYDE FROM A FOAM MATERIAL BASED ON PHENOL-FORMALDEHYDE RESIN

This invention relates to a method for reducing the emission of formaldehyde from a foam material based on phenol- formaldehyde resin. More specifically, the invention concerns a method in which the foam material is treated with a solution of urea and thermally decomposable ammonium salt. The treated foam material is especially suitable for floral decorations. It is known in the art to use foam materials of phenol- formaldehyde resins for heat and sound insulation. The foams are inexpensive to make, dimensionally stable as well as highly flame-resistant. Being of hydrophilic nature, phenolic resin foams absorb moisture, which has come out useful to florists. Thus, blocks of phenolic resin are used in the preparation of various floral decorations and arrangements. The blocks are able to absorb enough water for the flowers placed therein.

A well-known problem associated with formaldehyd -based resins resides in the emission of formaldehyde from the finished products. Naturally, this is especially serious for products used indoors. The trend goes towards the authorities tightening up the regulations on the emission of formaldehyde from different materials. Accordingly, the emission of formaldehyde from the hydrophilic foams used by florists has to be considerably reduced.

There are many ways of reducing the emission of formal¬ dehyde from formaldehyde-based resins. Thus, compounds binding formaldehyde can be added to the resin or the finished products. In the production of particle board, urea and a number of other compounds may be added as formaldehyde binders to the resin as well as the wood particles. Also, the finished particle boards may be treated with ammonia which can also be used for indoor decontamination. In the case of phenolic resin foams, it has been essential to obtain a method reducing the emission of formaldehyde to very low levels without affecting the water-absorbing capacity of the foam.

One object of the invention is, therefore, to provide a method for reducing the emission of formaldehyde from phenolic resin foam to extremely low levels. Another object of the invention is to provide a method that does not reduce the hydrophilicity of the foam. A further object of the invention is to provide a method that is both simple and effective. As appears from the appended claims, these objects are achieved by a method for reducing the emission of formaldehyde from foam material based on phenol-formaldehyde resin, in which the foam material is treated with a solution of urea and thermally decomposable ammonium salt which ammonium salt gives off ammonia in substantial amounts in a temperature range of 15-90°C.

It has surprisingly been found that the treatment with the solution of urea and ammonium salt gives a more than 95% reduction of the emission of formaldehyde, as compared with the initial content. Contents below 0.01 ppm (measured according to the 1 m³ chamber method) are easily obtained. The method is easily implemented and has no adverse effects on the other properties of the foam. Compared e.g. with treatment with pure ammonia gas, the method according to the invention has the advantages of being highly efficient, improving the working environment and involving harmless chemicals.

The method can be applied to all sorts of phenolic resin foams. Usually, phenolic resin foam is prepared from commercial resols with acid catalysts, but may also be produced from novolaks. A typical initial solution used when preparing phenolic resin foam consists of liquid phenolic resin, expanding agent, catalyst, surfactant and modifier. The formulations can be varied to enhance and alter such prop¬ erties as foam structure, combustibility and hydrophilicity. There are several known processes of preparation, and the foams are usually made in blocks which are cut to final size after intermediate storage.

Conveniently, the solution with which the foam material is treated contains 0.1-30% by weight of urea and 0.1-25% by weight of ammonium salt, the balance being water. Additio¬ nally, the solution may contain 0.1-20% by weight of aqueous ammonia with a concentration of 25% by weight of ammonia. Preferably, the solution contains 1-15% by weight of urea, 1-20% by weight of ammonium salt and 1-10% by weight of aqueous ammonia. The ammonium salts used should be thermally decomposable and give off ammonia gas in a temperature range of 15-90°C. Use is preferably made of ammonium carbonate, ammonium hydrogen carbonate, or mixtures thereof. The ammonium carbonate can optionally be prepared by mixing ammonium hydrogen carbonate or an aqueous solution thereof and aqueous ammonia.

Preferably, the inventive method is used for treating highly hydrophilic phenolic resin foams of low density. These foams have a density of about 10-100 kg/m³, preferably 15-25 kg/m³. "Highly hydrophilic foams" means foams which are able to bind as much as 900 1 of water or more per m³. Such a foam, intended for floristic use, is manufactured by the company Oasis. It is also essential that the pH of the foams is acid, thereby to prevent unwanted growth in the foam.

Conveniently, the foam is treated in the form of sheets, rods or the like having their final thickness. The solution can be applied with the aid of known technique, but is preferably sprayed onto the blocks or sheets. The amount of solution to be applied depends on the concentration of the solution and the initial content of formaldehyde in the foam. Although this amount is easily established by a person skilled in the art, it may be mentioned, for guiding purposes, that 1- 5 1 of a saturated solution may conveniently be applied per m³. After the treatment, the sheets are suitably stored to prevent or minimise evaporation. Thus, they may be stored in e.g. sealed packages for at least 24 hours so that as much as possible of the formaldehyde will have reacted.

The invention will now be illustrated by the following Example, in which the figures in parts and per cent are all by weight, unless otherwise stated.

Example

Six sheets (80x500x1000 mm) of a phenolic resin foam were treated with different solutions. Thus, each sheet was conveyed on a roller conveyor at about 60 m/min below an array of spray nozzles providing an evenly distributed curtain of the solution. First, each sheet was treated on one side, to be immediately treated on the other side. Then, each sheet was at once put in a bag of polyethylene. The bags were stacked, and a heavy sheet was put on top. After three days' storage at room temperature, the sheets were removed, and their smell and appearance were evaluated and samples were taken for measuring the emission according to the REM method. After another three days, samples were taken for a more accurate measurement of the emission according to the 1 m³ chamber method. After the chamber measurement had been completed, the pH and the water absorption were determined. Three different solutions were prepared as follows.

The balance up to 100% of the three solutions consisted of water. Then, 1 1 and 2 1 of each solution were applied per m³ of the foam sheets. The results are given below, where A, B, C stand for the respective solutions and 1 and 2 indicate that 1 1 and 2 1, respectively, of the solutions have been applied.

The sheets changed colour slightly (from greyish green to brighter green) . Immediately after the treatment, there was a faint smell of ammonia from the sheets. However, after three days, the treated sheets were completely odourless, whereas the blank smelled faintly of something undefinable. As appears from the above results, the emission of formaldehyde was considerably reduced for the treated sheets, and pH remained acceptable and the water absorption was largely the same. The different testing methods were performed as follows. REM: A cylinder (d:25, 1:80 mm) was suspended under the lid of a 500 ml polyethylene jar. Then, 100 ml of water was poured on the bottom, and the lid was put on. The jar was stored for 3 hours at 40°C. Thereafter, the formaldehyde content of the water was analysed, and the results were given in mg HCHO/1 water.

Chamber method: A sheet (80x500x1000 mm) was placed in a non- corrosive sheet-metal chamber with a volume of 1 m³. Then, 1 m³ of clean air (23°C, 50% R.H.) was drawn through the chamber per hour. When a state of equilibrium had been attained (after 3-5 days) , the formaldehyde content of the drawn-out air was determined, and the results were indicated in mg HCHO/m³. pH: A block (80x80x110 mm) was saturated with distilled water. Then, the pH of water pressed out of the block was estab- lished.

Water absorption: The absorption of water was measured by weighing the block before and after water had been absorbed in view of establishing the pH. The water absorption was indi¬ cated in g water per g dry foam.

Claims

1. A method for reducing the emission of formaldehyde from a foam material based on phenol-formaldehyde resin, c h a r a c t e r i z e d in that the foam material is treated with a solution of urea and thermally decomposable ammonium salt which ammonium salt gives off ammonia in substantial amounts in a temperature range of 15-90°C.

2. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the solution contains 0.1-30% by weight of urea and 0.1-25% by weight of ammonium salt, the balance being water.

3. A method according to claim 2, c h a r a c t e r ¬ i z e d in that the solution further contains 0.1-20% by weight of aqueous ammonia with a concentration of 25% by weight of ammonia.

4. A method according to claims 1 - 3, c h a r a c ¬ t e r i z e d in that the ammonium salt consists of ammonium carbonate or ammonium hydrogencarbonate or mixtures thereof.

5. A method according to claim 1, c h a r a c t e r - i z e d in that sheets, rods or the like made of the foam material and having their final thickness are treated with the solution.

6. A method according to claim 5, c h a r a c t e r ¬ i z e d in that the sheets or rods after the treatment are stored, e.g. in sealed packages, to prevent or minimise evaporation.

7. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the foam material is highly hydrophilic.

8. A method according to claim 1, c h a r a c t e r - i z e d in that the foam material has a density in the range of 10-100 kg/m³.

9. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the foam material is treated with the solution until it has a formaldehyde emission, according to lm³ chamber method , below 0.01 ppm.