EP1940987A2

EP1940987A2 - Lignin-based glue

Info

Publication number: EP1940987A2
Application number: EP06806116A
Authority: EP
Inventors: Katrin U. Schwarz
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-10-25
Filing date: 2006-10-09
Publication date: 2008-07-09
Also published as: WO2007048494A2; WO2007048494A3; DE102005051350A1

Abstract

An environment-friendly glue recognised as safe for health, in particular a glue for wood and cellulose materials, is disclosed, as well as its preparation and use. The glue contains as components at least one polysaccharide, lignin sulfonate and an aqueous solvent, or at least one polysaccharide and a lignin sulfonate dissolved in an aqueous solvent. Unlike the known glues based on lignin sulfonate, the glue according to the invention is more resistant to water.

Description

Lignin-based adhesive

The invention relates to a classified as environmentally friendly and not harmful to health adhesive, especially for materials made of wood and cellulose, its manufacture and its use.

The synthetic binders or adhesives used today in wood products are of the highest quality in their mechanical and technical properties, especially in the areas of adhesive strength and resistance to water. The disadvantage, however, is that these synthetic binders or adhesives contain constituents which are resistant to adhesive, for example formaldehyde, which can cause health impairments or even illnesses. These undesirable adhesive constituents usually already occur during the preparation of the adhesive and during processing, but also during the entire period of use of the article treated with the adhesive. If these objects are used in the living or working area, for example, in interiors, the people staying in these areas are particularly vulnerable. It is also problematic that these objects at the end of their life cycle not harmless energy, for example, by combustion or composting, can be supplied. The contained polluting ingredients are then released in the form of toxic emissions.

Natural adhesives are known from the state of the art, which damage such harmful and undesirable adhesives. Avoid substance-like components, as they occur with synthetic adhesives. In particular, natural adhesives are known which are produced on the basis of lignin sulphonate. Lignosulfonate is a polymer with adhesive properties, which is extracted in the pulp industry in the production of pulp in the so-called sulfite process the wood and is included as an ingredient in the sulfite waste liquor, among other wood degradation products. In the sulfite process, the wood consisting of cellulose, hemicellulose and lignin is digested in a cooking chemical solution containing sulfites or hydrogen sulfites and the lignin is converted into a water-soluble form by the introduction of hydrophilic sulfur-containing groups (sulfonated). The sulfonated lignin is water-soluble and also explains the technologically disadvantageous water solubility of the adhesives based on lignosulfonate known from the prior art.

This significantly limits the scope of these adhesives for certain areas, such as wet rooms, outdoor areas of buildings, and generally in high humidity areas.

It is an object of the present invention to provide an adhesive or a binder which has a higher water resistance in addition to the above-described conventional natural adhesives in addition to the retention of the adhesive properties.

The invention achieves this object by an adhesive which contains as components at least one polysaccharide, lignin sulfonate and an aqueous solvent or at least one polysaccharide and a lignosulfonate dissolved in an aqueous solvent.

Although the invention has recognized that the lignosulfonates and the polysaccharides are in each case water-soluble, their combination with one another makes the resulting mixture, in addition to its adhesive properties, superior to Schenderweise also significantly water resistant. After curing of the prepared mixture, which can be done both with and without heat (hot or cold gluing) an adhesive bond is obtained, which withstands even direct water contact without reducing the adhesive strength.

Applicants believe that this unexpected effect could be due to the modification of the lignosulfonates by the polysaccharide component. This may result in a reaction that is a reversal of the pulp-making process described above. That is, the decomposition process of the wood into the components polysaccharide (cellulose), lignin sulfonate and monosaccharide (hemicellulose) is reversed, at least in part, by adding to the polysaccharides the lignosulfonate present in the waste liquor of the pulp process and optionally degraded hemicellular monosaccharide fragments.

First, some are used in the invention

Terms explained.

The term adhesive refers to any substance which is suitable for bonding, that is to say bonding between two identical or different materials or materials. Usually it is a permanent connection. Suitable materials for bonding with the adhesive according to the invention are, for example, metal, glass, stone and plastic, preferably wood and cellulosic materials.

The adhesive according to the invention has lignin sulfonate as an essential component of the invention. It is a biopolymer with a molecular weight M _w of 10-50,000, which may be present as a solution, or as a dried powder. The lignosulfonate may be present as a salt, preferably calcium, magnesium and ammonium salt, more preferably as the sodium salt. Of particular advantage is when the adhesive of the invention no, or only has a low content of hemicellulose, for example based on the total amount of adhesive of less than 15 wt .-%, preferably less than 10 wt .-%, particularly preferably less than 2 wt .-%. As a result, the adhesive strength of the adhesive according to the invention can be increased even further. However, this does not mean that the adhesive according to the invention does not have to contain any hemicellulose. According to a preferred embodiment of the invention, the amount of lignosulfonate, based on the total amount of adhesive, 0.5-60 wt .-% and is preferably as part of a Trockenensubstanzsulfitablauge, for example, with a proportion of lignosulfonate in the Trockenensubstanzsulfi- tablauge 50-99 wt .-%, provided.

According to the invention, the adhesive contains the lignosulfonate dissolved in an aqueous solvent or the lignosulfonate is already dissolved in this solvent, wherein the amount of the aqueous solvent, based on the total amount of adhesive, is preferably 20-65 wt .-%. In this case, the possibly contributed water amount of an aqueous lignosulfonate solution is already taken into account. Aqueous solvent according to the present invention may be an alkali, preferably sodium hydroxide, or an acid, preferably selected from the group consisting of: formic acid, acetic acid and citric acid.

As a further component essential to the invention, the adhesive contains a polysaccharide component, preferably in an amount of preferably 0.1-75% by weight, more preferably 5-70

Wt .-%, more preferably 10-50 wt .-%, particularly preferably 10-30 wt .-% based on the total amount of adhesive. Polysaccharides (glycans) in the context of the present invention are starch, cellulose, pectins or else chitin and derivatives thereof, the water-soluble polysaccharides being particularly preferred. In addition to the native starches, such as the vegetable starch amylose or the animal starch glycogen, are chemically modified starches, eg starches, starch fractions and hydrolysis products converted by etherification, esterification or selective oxidation. It should be emphasized that the plasticizers commonly used in the adhesives of the prior art can be completely or partially replaced by the polysaccharides.

In addition to the usual known from the prior art adhesive additives such as dyes, etc., the inventive adhesive according to preferred embodiments of the invention contains as further components monosaccharides and / or plasticizers for adjusting the adhesive properties of the adhesive final mixture.

The monosaccharides (for example glucose) may be one or more monosaccharides whose amount, based on the total amount of adhesive, is 0-15% by weight, preferably 0-10% by weight.

Plasticizers in the context of the present invention are substances which are added to other substances, for example resins and plastics, in order to make them more supple or elastic. The plasticizer which is contained as an optional component in the adhesive according to the invention preferably in an amount of up to 30% by weight, based on the total amount of adhesive, is preferably a polyol, in particular selected from the group consisting of: ethylene glycols, glycerol and sorbitol.

It is particularly advantageous if the inventive

Adhesive is adjusted to a pH of 3-12. Especially when used as a wood adhesive occur on the Holzverklebungssteilen no undesirable material impairments such as cracks or crevices.

An adhesive composition according to the invention may comprise, for example, the following constituents: A) 0.5-60 wt.% Ligninsulfonate or dry matter

Sulfite waste liquor with 50-99% fraction of sulfonated lignosulfonate,

B) 20-65% by weight of a water-based solvent with adjustment of the pH of the adhesive mixture between 3 to 12,

C) 0.1-75% by weight of one or more polysaccharides, and optionally

D) up to 15 parts by weight, based on 100 parts by weight of the sum of the components A) to C) of one or more monosaccharides and

E) up to 30 parts by weight, based on 100 parts by weight of the sum of the components A) to C) of one or more plasticizers.

The present invention furthermore relates to a process for producing the adhesive according to the invention, wherein in a first step at least one polysaccharide, lignin sulfonate and an aqueous solvent or at least one polysaccharide and a lignosulfonate dissolved in an aqueous solvent are provided, before in a second step the components in any order, but preferably first the polysaccharides are mixed with the aqueous solvent prior to mixing with the lignosulfonate component. Although the order in the mixing process does not affect the quality of the final product. Nevertheless, the solution only leads to carbohydrate-containing substance groups at shorter times during the homogenization of the substance batch.

The mixing of the components is preferably carried out at a temperature of at most 100 ⁰ C, preferably at 30-80 ⁰ C, more preferably 50-70 ⁰ C and using a stirrer. In order to avoid foaming during mixing, preferably a correspondingly low speed, which may vary depending on the mixing batch, for example, at the beginning of the mixing operation to 1000 U / min, further below 700 U / min, selected and the Mischvor- and the adhesive is used before it is in a non-workable, high polymer state.

The adhesive of the invention cures both at room temperature (2O ⁰ C), as well as at elevated temperatures and under pressing conditions, as described in the introduction to the prior art for particle board adhesive, from. It is suitable as both cold and hot glue.

The components of the adhesive of the invention may be provided as individual components of a kit. According to the invention, such a kit contains a polysaccharide-containing component, a lignosulfonate-containing component and optionally an aqueous solvent or a polysaccharide-containing component and a lignosulfonate component dissolved in an aqueous solvent.

The invention will be explained in more detail by way of examples.

example 1

To 15 g of sodium-based powdered lignosulfonate and 10 g of potato starch was added 40 g of solvent, here citric acid, adjusted to pH 3 and 3 g of glycerol added. The mixture is reduced to max. 100 ⁰ C heated and then immediately cooled down again.

Example 2

To 28 g of a Natriumligninsulfonatpulvers containing 10% red. Substances and 10 g of a potato starch were added to 40 g of solvent, here sodium hydroxide, adjustment of the mixture to a pH of 12, and 5 g of sorbitol. The mixture was stirred for about 15 min at 6O ⁰ C until an increase in viscosity is discernible. Example 3. (Comparative Example)

As a reference sample, an adhesive was prepared, which was prepared without Polysaccharidzusatz consisting of 25 parts by weight of a sodium lignosulfonate and 40 parts by weight of solvent, citric acid with a pH of the mixture to 3, and 10 parts by weight of glycerol.

Example 4

To test the adhesive strength, the following method is practiced, which explains the effect of the invention:

The adhesive mixtures prepared according to Examples 1 to 3 were pressed according to DIN 205 with beech veneers at room temperature for 24 h and at 13O ⁰ C for 10 min using small glue clamps. The cured samples were conditioned for 7 days in a climate chamber under normal conditions (20 ⁰ C / 65% RH).

For the evaluation of an adhesive aging conditions are applicable to the bonds, such as the test under different humidity conditions. The determined tensile shear strengths (N / mm ² ) of the examples given are summarized in the following table.

Tensile shear strengths [N / mm ² ] on selected examples

Claims

claims

1. adhesive, characterized in that it contains the following components:

at least one polysaccharide,

Lignosulfonate and

an aqueous solvent or

at least one polysaccharide and

a lignosulfonate dissolved in an aqueous solvent.

2. An adhesive according to claim 1, characterized in that the amount of lignosulfonate, based on the total amount of adhesive, 0.5-60 wt .-% is.

3. The adhesive according to claim 1 or 2, characterized marked, that the lignosulfonate is a component of a

Sulfite waste liquor is.

4. An adhesive according to claim 3, characterized in that the Trockenensubstanzsulfitablauge has a proportion of lignin sulfonate of 50-99 wt .-%.

5. An adhesive according to claim 1 or 2, characterized in that the lignosulfonate salt, preferably calcium, magnesium and ammonium salt, particularly preferably present as the sodium salt.

6. Adhesive according to one of claims 1 to 5, characterized in that the adhesive contains no hemicellulose or the amount of hemicellulose, based on the total amount of adhesive less than 15 wt .-%, preferably less than 10 wt .-%, more preferably less is 2% by weight.

7. An adhesive according to any one of claims 1 to β, characterized in that the amount of the aqueous solvent, based on the total amount of adhesive, is 20-65 wt .-%.

8. Adhesive according to one of claims 1 to 7, characterized in that the aqueous solvent is an alkali, preferably sodium hydroxide, or an acid, preferably selected from the group consisting of: formic acid, acetic acid and citric acid.

9. Adhesive according to one of claims 1 to 8, characterized in that the amount of polysaccharide, based on the total amount of adhesive, 0.1-75 wt .-%, preferably 5-70

Wt .-%, more preferably 10-50 wt .-%, particularly preferably 10-30 wt .-%, is.

10. Adhesive according to one of claims 1 to 9, characterized in that the polysaccharides are water-soluble.

11. An adhesive according to claim 10, characterized in that the water-soluble polysaccharides are starch and / or starch derivatives.

12. Adhesive according to one of claims 1 to 11, characterized in that at least one monosaccharide is contained as a further component.

13. An adhesive according to claim 12, characterized in that the amount of monosaccharide, based on the total amount of adhesive is at most 15 wt .-%, preferably at most 10 wt .-%, is.

14. An adhesive according to claim 13, characterized in that the monosaccharide is glucose.

15. Adhesive according to one of claims 1 to 14, characterized in that at least one plasticizer is contained as a further component.

16. An adhesive according to claim 15, characterized in that the amount of the plasticizer, based on the total amount of adhesive, 0-30 wt .-% is.

17. An adhesive according to claim 15 or 16, characterized in that the plasticizer is a polyol, preferably selected from the group consisting of: ethylene glycol, glycerol and sorbitol.

18. Adhesive according to one of claims 1 to 17, characterized in that the pH of the adhesive is 3-12.

19. Use of an adhesive according to one of claims 1 to 18 for bonding metal, glass, stone and plastic, preferably of wood and cellulosic materials.

20. A process for producing an adhesive according to any one of claims 1 to 18, comprising the following steps:

i) Provision of the following components:

at least one polysaccharide,

Lignosulfonate and

an aqueous solvent or

at least one polysaccharide and

a lignosulfonate dissolved in an aqueous solvent;

ii) mixing the components in any order.

21. The method according to claim 20, characterized in that in step ii) the polysaccharides with the aqueous before mixing with the lignin sulfonate component.

22. The method according to claim 20 or 21, characterized marked B records that in step ii), the mixture of the components at a temperature of at most 100 ⁰ C, preferably at 30-80 ⁰ C, more preferably 50-70 ⁰ C takes place.

0 23. The method according to any one of claims 20 to 22, characterized in that in step ii), the mixing takes place at a speed at which the mixture does not foam, preferably at the beginning of the mixing process at a speed 1000 U / min, in the course below 5,700 rpm.

24. The method according to any one of claims 20 to 23, characterized in that in step ii), the mixing process is completed before the adhesive is in a non-workable, high polymer state.

25. A kit comprising: a) a polysaccharide-containing component b) a lignosulfonate-containing component and, if appropriate, c) an aqueous solvent.

26. A kit comprising: a) a polysaccharide-containing component b) a lignosulfonate component dissolved in an aqueous solvent.