RU2366571C1 - Method to produce articles from wood that features low degree of chemicals evaporation - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: proposed method comprises gluing wooden shavings or fibers together. Note here that prior to gluing, wood is subjected to treatment by bisulphate in atmosphere saturated with steam, or in air saturated with steam for 3 to 8 minutes at 6 to 12 bar. In using formaldehyde-resin binders, articles with extremely lows evaporation of chemicals can be produced that feature relatively light colour.

EFFECT: reduced degree of evaporation.

8 cl, 1 tbl, 1 ex

Description

The invention relates to a method for manufacturing products from wood material with a low degree of release of chemicals, as well as to products from wood material that can be obtained in this way.

Products from wood material, for example wood-particle boards or wood-fiber boards, are obtained from wood chips of fibrous materials with the addition of glue. Typically, the adhesive is applied to the chopped wood (shavings) or to fibrous material during the manufacturing process of the product from wood material and after that the still wet products from the wood material are pressed at high temperatures (hot pressing), while the adhesive cures. For a long time, formaldehyde-containing resins were used in such adhesives as curing and / or binding agents.

Wood-based panels are often used indoors. Therefore, it is important that these boards do not emit irritating (e.g., with a strong odor) or even hazardous substances. Released components can be released from the wood itself or from glue.

When using formaldehyde-containing resins for the manufacture of wood products, the resulting products emit formaldehyde, therefore its amount is limited by legislative norms and voluntary restrictions in the industry to significantly low values.

It is known that various methods reduce the formaldehyde content, in particular the emission of formaldehyde from products made from wood materials. Some of them are as follows:

- modification of the adhesive by reducing the molar ratio of formaldehyde and other resin components;

- the addition of substances that bind formaldehyde, such as urea;

- mixing resins containing formaldehyde with other resins;

- increase in pressing time.

However, these methods reduce production efficiency (increase cost, reduce productivity due to increased pressing time) or have a negative effect on the physical or mechanical properties of the product (decrease in resin stability, decrease in the stability and stability of joints, etc.).

Therefore, the object of the invention is to propose an improved method for manufacturing products from wood materials, resulting in products that have, in particular, a reduced degree of release of chemicals.

This problem is solved by a method of manufacturing products from wood materials containing wood shavings or wood fibers glued together, in which the wood is treated with bisulfite before gluing.

It was unexpectedly discovered that in this way improved products can be made from wood materials that have a very low degree of release of chemicals or do not emit unwanted (volatile) chemicals that are present in wood raw materials. In addition, wood chips or wood fibers treated with bisulfite show a better interaction with the adhesive.

For the manufacture of wood products, wood of broadleaf and acicular species is usually treated either individually or in a mixture. First, the wood is barked and ground. Sawdust or wood chips can be added to the chopped wood. After that, the mixture is sieved and separated to remove unwanted components such as sand, unnecessary debris, stones or metals. After this, the mixture is washed to remove unwanted components such as sand or stones. In the next step, chopped wood is heated and dehydrated. This is preferably carried out by pressing. The crushed and treated wood is then treated under a pressure of 0.8-12 bar in an atmosphere saturated with water vapor. According to the invention, a bisulfite salt is added to an atmosphere saturated with water vapor. The bisulfite salts may be alkali metal and / or ammonium salts. Sodium and / or ammonium bisulfites are preferably used. Ammonium bisulfite is particularly preferred. The amount of bisulfite salt is from 3 to 30 kg, preferably from 3 to 12 kg per cubic meter of the resulting plate. The processing time is at least 1.5 minutes, preferably from 3 to 8 minutes. In this case, large amounts of bisulfite lead to an increase in processing time until completion of the reaction, which will allow bisulfite to penetrate into the fibers to ensure stable impregnation.

In one of the embodiments of the invention, the wood is treated with bisulfite to obtain chips or fibers, for example in a furnace to facilitate the implementation of the method. Subsequent treatment of wood fibers with paraffin will not adversely affect the implementation of the method according to the invention.

According to another embodiment of the invention, the chips or fibers are treated with bisulfite, for example in a refiner. In this case, the method is particularly effective.

Not wanting to be limited by any theory, the inventors believe that the processing of crushed wood with bisulfite is important for the binding of volatile substances in crushed wood and to limit the release of volatile substances. When treated with bisulfite, for example, adducts of bisulfite with aldehydes, methyl ketone or alpha-ketoesters can form. In addition, bisulfite exhibits its whitening properties and can react with pigments present in wood, so fairly light wood products can be obtained. The light color of wood is an important indicator of quality.

In addition, in the processing of wood with bisulfite, there is a weak acid impregnation of the fibers, which results in complete polycondensation of the resins and, therefore, complete absorption of free formaldehyde in the case of resins containing formaldehyde. Both of these effects make it possible to obtain products from wood materials that exhibit very low perforation rates and, consequently, extremely low formaldehyde emissions.

Treatment with bisulfite for at least 1.5 minutes ensures that the disintegration of the wood is almost complete and, therefore, subsequent treatment with an impregnating agent against swelling of the wood in the presence of moisture will be effective.

After that, the impregnated wood raw materials are further crushed to shavings or fibers, glued, dried and pressed. This is carried out by known methods.

The adhesive that is used for bonding chips or fibers is preferably an aminoplast. It is especially preferred to use a formaldehyde-containing resin. It is preferably selected from the group consisting of urea-formaldehyde resin, melamine-formaldehyde resin, urea-melamine-formaldehyde resin and melamine urea-phenol-formaldehyde resin. Suitable resins are commercially available as solutions or powders, and the manufacture and use of suitable resins is described in the art. For the method according to the invention, urea-formaldehyde resin and melamine-formaldehyde resin, which are used in conventional amounts, are preferred.

It is particularly preferable to use resins with a low formaldehyde content, with a low ratio of formaldehyde to urea. A preferred molar ratio of formaldehyde to urea is from 0.8: 1 to 1.05: 1.

However, when using crushed wood with bisulfite, glues with a higher molar ratio of formaldehyde to urea can also be used. Also, wood products obtained in this way show extremely low perforation values that satisfy existing standards. With such resins, which are more reactive and cheaper than resins with a low formaldehyde content, you can even get class E1 boards. The method according to the invention has the advantage that conventional resins without additional formaldehyde binding agents can be used in adhesives without adversely affecting the mechanical or physical properties of the final product. However, if desired, an adhesive may be used that additionally contains formaldehyde binding agents.

In addition to the aminoplast, the adhesive may contain additives such as crosslinking agents to accelerate curing, hydrophobic agents, inert salts, pH maintenance agents, fungicides or biocides.

Bonding is preferably carried out by pressing the finely chopped wood into which the adhesive is added at temperatures from 120 to 250 ° C. Under such conditions, the aminoplast cures quite quickly and produce products from wood materials with good mechanical properties, which are largely immune to moisture.

Example

Two wood-fiber boards S1 and V1 were prepared as described above using formaldehyde urea resin with a molar ratio of formaldehyde to urea equal to 1: 1.08, with the difference that chopped wood was not treated with bisulfite before the impregnation process to produce plate V1. The crushed wood was treated with bisulfite under a pressure of 8.5 bar for 3.5 minutes, the amount of bisulfite was 3 kg per 1 m ^{3 of} crushed wood. After pretreatment of the wood, moistening with a non-impregnating agent was carried out and then pressing.

Table 1 shows the values of formaldehyde content determined by extraction using a punch (according to DIN EN 120 - wood materials - determination of formaldehyde content) of both wood-fiber boards S1 and V1.

Table 1 Wood fiber board Formaldehyde content in mg HCNO / 100 g S1 2.5 V1 6.5

The values in the table show that the processing of crushed wood with bisulfite allows you to get products from wood materials, showing an extremely low degree of release of chemicals. In addition, S1 fiberboard produced extremely small amounts of other chemicals and was significantly lighter than V1 fiberboard.

Claims (9)

1. A method of manufacturing a product from wood material, comprising bonding together wood chips or wood fibers, in which before the bonding process the wood is treated with bisulfite in an atmosphere saturated with water vapor, or in air saturated with water vapor, for 3 to 8 minutes under pressure from 6 to 12 bar. 2. The method according to claim 1, characterized in that the wood is treated with bisulfite before preparing wood chips or wood fibers, for example, in a furnace. 3. The method according to claim 1, characterized in that the wood chips or wood fibers are treated with bisulfite, for example, in a refiner. 4. The method according to claim 1, characterized in that the bisulfite is added in an amount of from 1 to 30 kg per 1 m ^{3 of} wood, preferably in an amount of from 3 to 12 kg per 1 m ^{3 of} wood. 5. The method according to claim 1, characterized in that the bisulfite is added in an amount of from 1 to 30 kg per 1 m ^{3 of} wood, preferably in an amount of from 3 to 12 kg per 1 m ^{3 of} wood, and the bisulfite is selected from the group comprising sodium bisulfite and ammonium bisulfite. 6. The method according to claim 1, characterized in that the bisulfite is selected from the group comprising sodium bisulfite and ammonium bisulfite. 7. The method according to claim 1, characterized in that the wood treated with bisulfite is converted into wood shavings or wood fibers, which are then glued with an aminoplast. 8. The method according to claim 1, characterized in that the wood shavings or wood fibers are glued using an aminoplast selected from the group consisting of urea-formaldehyde resin, melamine-formaldehyde resin, urea-melamine-formaldehyde resin and melamine urea-phenol-formaldehyde resin. 9. A product made of wood material, consisting of wood chips or wood fibers glued together, where before gluing the wood is treated with bisulfite in an atmosphere saturated with water vapor or in air saturated with water vapor for 3 to 8 minutes under pressure from 6 to 12 bar.