DE102019105822A1 - Chemically modified lignin and process for its production - Google Patents

Abstract

The present invention relates to a method for chemically modifying lignin. The invention also relates to chemically modified lignin which can be obtained by the process according to the invention, as well as molded articles obtainable by pressing and a method for producing such molded articles. The invention also relates to the use of a shaped body according to the invention, in particular in the production of vehicles, furniture, laminate floors and / or buildings.

Description

The present invention relates to a method for chemically modifying lignin. The invention also relates to chemically modified lignin which can be obtained by the process according to the invention, as well as molded articles obtainable by pressing and a method for producing such molded articles. The invention also relates to the use of a shaped body according to the invention, in particular in the production of vehicles, furniture, laminate floors and / or buildings.

Wood-based panels such as medium-density fiberboard (MDF), high-density fiberboard (HDF) or coarse chipboard (OSB) are known from the prior art. However, such panels have various disadvantages. For example, they have a high swellability on contact with water. In addition, toxic formaldehyde can be emitted. Apart from this, the complete or partial substitution of high-quality wood fibers by other materials is also advantageous from an economic and ecological point of view.

It would be particularly advantageous if lignin could be used as a substitute for wood fibers, since it is a by-product in the multi-digit megaton scale in the paper industry alone and is now used almost exclusively for energy. If lignin is nevertheless used for composite materials, it has so far typically been incorporated into a prepolymer matrix, with a significant reduction in mechanical stability being observed from a weight fraction of more than 30% lignin. This phenomenon is presumably due to various causes, among which the very strong increase in the viscosity of the reaction mixture by adding the lignin could play an important role.

The previously known chemical modification of lignin is carried out on molecularly dissolved lignin. This has several disadvantages. On the one hand, the purification is relatively complex, with large amounts of precipitant being required. On the other hand, the yield is relatively low, since a not insignificant proportion of the product remains in the solvent phase.

It is therefore an object of the present invention to overcome the disadvantages of the prior art. In particular, a method for the production of chemically modified lignin is to be provided, which enables simple purification, is resource-saving and has a high yield. In addition, the chemically modified lignin should be able to be used for the production of molded bodies, good mechanical properties being obtained despite a high lignin content.

1. a) Bereitstellen von Lignin, wobei das Lignin OH-Gruppen aufweist,
2. b) Zugabe einer Diisocyanat-Komponente zum Lignin zum Erhalt eines Reaktionsgemisches, wobei das Verhältnis des Stoffmengenanteils der Diisocyanat-Komponente zum Stoffmengenanteil der Lignin-basierten OH-Gruppen in dem Reaktionsgemisch weniger als 1 beträgt,
3. c) Halten des Reaktionsgemisches bei einer Temperatur von mindestens 50°C für einen Zeitraum von mindestens 10 Minuten,
4. d) Isolieren des chemisch modifizierten Lignins aus dem Reaktionsgemisch.

The object is achieved by the subject matter of the claims. The object is achieved in particular by a method for the production of chemically modified lignin comprising the following steps:

1. a) providing lignin, the lignin having OH groups,
2. b) adding a diisocyanate component to the lignin to obtain a reaction mixture, the ratio of the mole fraction of the diisocyanate component to the mole fraction of the lignin-based OH groups in the reaction mixture being less than 1,
3. c) keeping the reaction mixture at a temperature of at least 50 ° C for a period of at least 10 minutes,
4. d) isolating the chemically modified lignin from the reaction mixture.

In certain embodiments of the invention, the method consists of the steps mentioned.

The chemically modified lignin preferably contains free (and therefore reactive) isocyanate groups. Such free isocyanate groups are particularly advantageous in order to form a connection between the chemically modified lignin and a fiber component or a connection between two lignin polymers. Such compounds are particularly advantageous in the production of a shaped body from the chemically modified lignin or from a mixture of the chemically modified lignin with a fiber component. Connections between the chemically modified lignin and a fiber component are very particularly preferred.

In step a) the lignin can be provided in the form of a solid.

However, a lignin suspension is preferably provided in step a). The suspension preferably contains lignin particles in a suspension liquid.

The lignin is therefore preferably not in dissolved form, but in the form of a suspension which contains lignin particles. Preferably less than 5% by weight, more preferably less than 2% by weight, more preferably less than 1% by weight, more preferably less than 0.1% by weight of the lignin in the lignin suspension is in dissolved form Shape before.

Since a lignin suspension is preferably used, the lignin does not have to be soluble in order to carry out the method according to the invention. Therefore, lignins of different origins and from different digestion processes can be used. The process is very variable based on the raw material. The lignin is preferably selected from the group consisting of Kraft lignin, lignin from alkali digestion, lignin from sulfate digestion, lignin from Organosolv process. Kraft lignin, in particular dried Kraft lignin, is particularly preferred.

The lignin has OH groups. The proportion of OH groups in the lignin from step a) of the method according to the invention is preferably in a range from 0.5 mol / kg to 100 mol / kg, more preferably from 1 mol / kg to 50 mol / kg, more preferably from 2 mol / kg to 20 mol / kg, more preferably 3 mol / kg to 12 mol / kg.

The lignin suspension contains lignin particles in a suspension liquid. The suspension liquid is preferably chosen such that the solubility of lignin in the suspension liquid is very low, so that a lignin suspension and not a lignin solution is obtained. On the other hand, the solubility of the diisocyanate component added in step b) should be high in the suspension liquid, so that the diisocyanate component is predominantly in dissolved form in the reaction suspension obtained in step b). The suspension liquid is preferably selected from the group consisting of aromatic solvents (especially toluene), aliphatic solvents, ethers, esters, ketones, hydrogen halides and mixtures of two or more thereof. The suspension liquid particularly preferably comprises toluene. The suspension liquid is even more preferably toluene, in particular dried toluene. Dried toluene can be obtained, for example, by spinning off about 5% of the volume.

The lignin fraction in the lignin suspension is preferably in a range from 10 g / l to 5000 g / l, more preferably from 20 g / l to 2000 g / l, more preferably from 50 g / l to 1000 g / l , more preferably from 100 g / l to 500 g / l, more preferably from 200 g / l to 300 g / l.

According to step b) of the process according to the invention, a diisocyanate component is added to the lignin, in particular to the lignin suspension, to obtain a reaction mixture, in particular to obtain a reaction suspension. In addition to the diisocyanate component, a catalyst is preferably also added to the lignin, in particular to the lignin suspension. However, a catalytic converter is not absolutely necessary, but only provided as an option.

In addition to the components mentioned above, the reaction mixture (in particular the reaction suspension) preferably contains no further components, in particular no resin components (for example synthetic resins). The reaction mixture, in particular the reaction suspension, is particularly preferably free from unsaturated polyester resins.

If it is stated in the present description that the reaction mixture (in particular the reaction suspension) does not contain a component or is free of a component, this preferably means that the proportion of such components in the reaction mixture, in particular in the reaction suspension, is less than 0.1 wt %, more preferably less than 0.05% by weight, more preferably less than 0.01% by weight.

The catalyst is preferably selected from the group consisting of tin (II) salts and tin organyls, in particular dialkyltin (IV) compounds.

The tin organyls selected from the group consisting of dibutyltin (IV) compounds, dipentyltin (IV) compounds, dihexyltin (IV) compounds, diheptyltin (IV) compounds, and dioctyltin (IV) compounds are particularly preferred and mixtures of two or more thereof. Dimethyl, diethyl and dipropyltin (IV) compounds are less preferred because they have high toxicity. In particularly preferred embodiments, the catalyst is a dioctyltin (IV) compound, in particular selected from the group consisting of dioctyltin oxide, dioctyltin dichloride, dioctlytin dilaurate, Dioctyl tin maleate, dioctyl tin dithioglycolate, dioctyl tin diacetate, dioctyl tin carboxylate, and mixtures of two or more thereof. The catalyst is very particularly preferably a dioctyltin (IV) catalyst. In other preferred embodiments, the catalyst is a dibutyltin (IV) compound, in particular selected from the group consisting of dibutyltin oxide, dibutyltin dichloride, dioctlytin dilaurate, dibutyltin maleate, dibutyltin dithioglycolate, dibutyltin diacetate, dibutyltin carboxylate and mixtures thereof. The catalyst is very particularly preferably a dibutyltin (IV) catalyst.

Preferred tin (II) salts are selected from the group consisting of salts of inorganic or organic acids. The tin (II) salts are particularly preferably salts of carboxylic acids, in particular tin (II) ethylhexanoate or salts of other carboxylic acids such as salts of acetic acid, lauric acid or salicylic acid. The tin (II) salt is very particularly preferably tin (II) ethylhexanoate.

The ratio of the mole fraction of the diisocyanate component to the mole fraction of the catalyst in the reaction suspension is preferably in a range from 50: 1 to 2000: 1, more preferably from 100: 1 to 1000: 1, more preferably from 200: 1 to 600: 1 , more preferably from 300: 1 to 500: 1.

The diisocyanate component is preferably selected from the group consisting of hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), toluene-2,4-diisocyanate (TDI) and mixtures of two or more thereof. The diisocyanate component hexamethylene diisocyanate is also preferred.

The ratio of the mole fraction of the diisocyanate component to the mole fraction of the lignin-based OH groups in the reaction suspension is less than 1. The ratio of the mole fraction of the diisocyanate component to the mole fraction of the lignin-based OH groups in the reaction suspension is preferably in a range from 0.1 to 0.99, more preferably from 0.2 to 0.95, more preferably from 0.5 to 0.9, more preferably from 0.8 to 0.85. It is a particular advantage of the present invention that the diisocyanate component can be used in a stoichiometric deficit. This is extremely resource-saving. Only the surface of the lignin particles is preferably modified, which results in an advantageous low mass fraction of isocyanate and a high fraction of lignin. This is supported by the fact that a lignin suspension with lignin particles is used instead of a lignin solution.

The reaction suspension is preferably obtained by first adding the catalyst and only then adding the diisocyanate component to the lignin suspension. The diisocyanate component is preferably added using a dropping funnel. The diisocyanate component is preferably added with stirring. The diisocyanate component is preferably added at temperatures in a range from 15 ° C. to 30 ° C., more preferably from 20 ° C. to 25 ° C., in particular at room temperature.

According to step c), the reaction suspension is kept at a temperature of at least 50 ° C. for a period of at least 10 minutes. Step c) is preferably carried out with stirring of the reaction suspension. Step c) promotes the production of chemically modified lignin in the reaction suspension. The reaction suspension is preferred for a period of time from 20 minutes to 360 minutes, more preferably from 30 minutes to 300 minutes, more preferably from 60 minutes to 240 minutes, more preferably from 90 minutes to 180 minutes at a temperature in a range of 60.degree to 105 ° C, more preferably from 70 ° C to 100 ° C, more preferably from 80 ° C to 95 ° C.

According to step d) of the method according to the invention, the chemically modified lignin is isolated from the reaction suspension. It is a particular advantage of the method according to the invention that the chemically modified lignin is present as a solid in suspended form. This enables a particularly simple isolation of the chemically modified lignin from the reaction suspension. The chemically modified lignin is preferably isolated from the reaction suspension by centrifugation and / or filtration. Centrifugation is particularly preferred.

The process according to the invention is distinguished by a high yield. This is presumably at least partly due to the fact that, unlike in the prior art, no precipitation of the product from a solution is required, so that no product remains in a solvent phase. The ratio of the mass of the chemically modified lignin isolated in step d) to the mass of the lignin in the lignin suspension provided according to step a) is preferably at least 0.8, more preferably at least 0.85, more preferably at least 0.9 preferably at least 0.95, more preferably at least 1.0, more preferably at least 1.05. The fact that the mass ratio can be greater than 1.0 results from the fact that the chemically modified lignin has a greater molecular weight than the lignin in the lignin suspension provided according to step a) due to the chemical modification.

The method according to the invention can optionally contain the further step e) of washing the lignin isolated according to step d). Step e) can comprise one or more washing steps. At least two washing steps, more preferably at least three washing steps, more preferably at least four washing steps are preferably carried out. Each washing step preferably comprises the steps of adding washing liquid to the chemically modified lignin to obtain a washing suspension and isolating the lignin from the washing suspension. The chemically modified lignin is preferably isolated from the washing suspension by centrifugation and / or filtration. Centrifugation is particularly preferred. Different washing liquids can be used in different washing steps. In particularly preferred embodiments, washing is carried out twice with toluene and twice with diethyl ether, in particular first with toluene and then with diethyl ether.

The method according to the invention optionally comprises the further step f) of drying the isolated lignin. Step f) preferably follows step d) of isolating the chemically modified lignin from the reaction suspension and / or step e) of washing the isolated lignin. The drying step f) is preferably carried out at temperatures in a range from 40.degree. C. to 60.degree. C., more preferably from 45.degree. C. to 55.degree. The drying in step f) is preferably carried out in vacuo, in particular at a pressure of less than 1 hPa, more preferably less than 0.1 hPa. The drying step f) is preferably carried out for a period of 2 to 48 hours, more preferably 5 to 24 hours Hours, more preferably 10 to 16 hours.

The present invention also relates to chemically modified lignin, in particular such obtainable or obtained by the method according to at least one of the preceding claims, the chemically modified lignin isocyanate groups (-NCO) in a proportion of 0.1 mmol / g to 5 mmol / g, more preferably from 0.2 to 2 mmol / g, more preferably from 0.5 to 1 mmol / g. The chemically modified lignin is preferably present as lignin particles. Only the surface of the lignin particles is preferably modified, which results in an advantageously low proportion of isocyanate.

1. i) Optionales Mischen des chemisch modifizierten Lignins der Erfindung mit einer Faserkomponente,
2. ii) Pressen des chemisch modifizierten Lignins der Erfindung oder der Mischung aus Schritt i) bei einer Temperatur von mindestens 90°C und einem Druck von mindestens 50 bar zum Erhalt des Formkörpers.

The present invention also relates to a method for producing a shaped body comprising the following steps:

1. i) Optionally mixing the chemically modified lignin of the invention with a fiber component,
2. ii) pressing the chemically modified lignin of the invention or the mixture from step i) at a temperature of at least 90 ° C. and a pressure of at least 50 bar to obtain the shaped body.

The pressing is preferably carried out at a temperature in a range from 100 ° C to 200 ° C, more preferably 125 ° C to 175 ° C, more preferably 130 ° C to 150 ° C. The pressing is preferably carried out at a pressure in a range from 100 bar to 500 bar, more preferably 150 bar to 400 bar, more preferably 200 bar to 375 bar. The pressing is preferably carried out for a period of 1 to 20 minutes, more preferably 2 to 15 minutes, more preferably 5 to 10 minutes. The pressing is preferably carried out in a mold, in particular in a metal mold.

According to the method of the invention, molded articles can be obtained by pressing the chemically modified lignin of the invention. Optionally, the chemically modified lignin of the invention can be mixed with a fiber component prior to pressing. The fiber component is preferably a natural fiber. The fiber component is particularly preferably selected from the group consisting of wood fibers, wood chips, wood flour, cellulose fibers, cellulose fibers and mixtures of two or more thereof. In particular by adding the fiber component to the chemically modified lignin, the mechanical and / or chemical properties of the molded bodies obtained can be influenced.

Before pressing, the chemically modified lignin or the mixture obtained according to step i) is preferably in the form of a powder.

The mixture obtained according to step i) preferably contains chemically modified lignin in a proportion of 30 to 60% by weight, more preferably 40 to 50% by weight, and the fiber component in a proportion of 30 to 70% by weight preferably 40 to 60% by weight. An isocyanate component can optionally be present in a proportion of 0 to 20% by weight, more preferably 5 to 15% by weight. Mixtures of 50 wt.% Lignin and 50 wt.% Fiber component or mixtures of 50 wt.% Fiber component, 40 wt.% Lignin and 10 wt.% Isocyanate component are particularly preferred. In particularly preferred embodiments, the mixture obtained according to step i) consists of the chemically modified lignin of the invention and the fiber component.

The ratio of the proportion by weight of the fiber component to the proportion by weight of the chemically modified lignin in the mixture is preferably in a range from 0.2 to 10, more preferably from 0.5 to 5, more preferably from 1 to 3. The proportion of chemically modified lignin is preferred Lignin in the mixture in a range from 5 to 90% by weight, more preferably more preferably 10 to 80% by weight, more preferably 20 to 70% by weight, more preferably 30 to 60% by weight, more preferably 40 to 50% by weight.

The present invention also relates to a shaped body which is obtainable or is obtained by the process of the invention. The molded body preferably has a flexural strength in a range from 10 MPa to 100 MPa, more preferably from 15 MPa to 60 MPa, more preferably from 20 MPa to 50 MPa, more preferably from 25 MPa to 30 MPa. The flexural strength is preferred according to DIN EN 310: 1993-08 certainly. The shaped body is preferably a plate.

The shaped body of the invention preferably has a low swellability on contact with water. This preferably corresponds to the requirements DIN EN 622-3: 2004-07-00 . In particular, the thickness swelling is preferably less than 25% based on the thickness of the dry molded body. The thickness swelling indicates the increase in the thickness of the wet sample in relation to the thickness of the dry sample. The thickness swelling is preferably determined by determining the thickness of a sample, then storing it completely in water for 24 hours and then determining the thickness swelling of the sample as the ratio of the thickness of the wet samples to the thickness of the dry sample. The swellability (thickness swelling) is preferably determined in accordance with DIN EN 317: 1993-08-00 .

The shaped body is preferably free from formaldehyde, particularly preferably free from formaldehyde and potentially formaldehyde-generating compounds. In this way, the emission of formaldehyde from the molding can be avoided, which is advantageous because of the toxicity of formaldehyde.

The present invention also relates to the use of a molded body of the invention, in particular in the manufacture of vehicles, furniture and / or buildings. Compared to known moldings, the moldings of the present invention, which can be obtained using the chemically modified lignin according to the invention, have many advantages, especially for the uses mentioned, such as reduced swellability on contact with water, avoidance of formaldehyde emissions and economic advantages Replacement of wood components by the cheaper lignin. In addition, lower flammability and better stability against microorganisms can be achieved.

Examples

Manufacture of chemically modified lignin

A modification of Kraft lignin with the aliphatic diisocyanate HDI (hexamethylene diisocyanate) was carried out according to the following reaction scheme:

The following approach was used to carry out the modification of the lignin: substance Molar mass [g / mol] Amount [mol] Mass [g] Equivalents Domtar Kraft lignin approx. 1.5 mol OH groups 250 1 Hexamethylene diisocyanate 168.2 1.25 210.25 0.83 equivalents per OH group Tin (II) -2-ethylhexanoate 405 0.005 2.1 0.003 equivalents based on the OH groups of the lignin

The reaction was carried out as described below:

Dried DKL (Domtar Kraft-Lignin) was suspended in dried toluene (1000 ml). The toluene was dried by evaporating about 5% of the volume. After adding the catalyst, HDI was slowly added using a dropping funnel. It was stirred at room temperature until all of the HDI had been added. Thereafter, the oil bath in which the glass round bottom flask containing the mixture was immersed was heated to 90 ° C. As soon as the temperature of 90 ° C. was reached, the mixture was stirred at 90 ° C. for 2 hours. Overall, the addition of the reactants, the heating to 90 ° C. and the stirring at 90 ° C. resulted in a total duration of 3 hours, as also indicated in the above reaction scheme.

The chemically modified lignin, which was present as a solid, was separated off by centrifugation. This was followed by washing twice with toluene and twice with diethyl ether. The chemically modified lignin was then dried overnight at 50 ° C. in a vacuum.

The yield was 272 g.

Production of moldings

1. a) Moldings made from mixtures of lignin and fibers The chemically modified lignin from Example 1 was mixed with natural fibers (wood fibers (so-called refiner fibers from Egger), wood flour, cellulose fibers (Rettenmeier)) in a weight ratio of 1: 1, filled into a metal mold and then at 150 ° C. for 10 min pressed at 360 bar, so that rod-shaped moldings were obtained. The moldings were examined mechanically for flexural strength. This resulted in flexural strengths of up to 35 MPa for cellulose fibers and flexural strengths of up to 55 MPa for refiner fibers from Egger.
2. b) Moldings made from mixtures of lignin, fibers and isocyanate A mixture was provided which contained 50% by weight of wood chips, 40% by weight of chemically modified lignin from Example 1 and 10% by weight of isocyanate. A molding was produced from the mixture using the compression molding process described in Example 2. A mechanical analysis showed flexural strength values of around 27 MPa, which is in the range of typical medium-density fibreboard (MDF).

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Non-patent literature cited

• DIN EN 310: 1993-08 [0038]
• DIN EN 622-3: 2004-07-00 [0039]
• DIN EN 317: 1993-08-00 [0039]

Claims (10)

A method for the production of chemically modified lignin comprising the following steps: a) providing lignin, the lignin having OH groups, b) adding a diisocyanate component to the lignin to obtain a reaction mixture, the ratio of the mole fraction of the diisocyanate component to the mole fraction of the lignin-based OH groups in the reaction mixture being less than 1, c) keeping the reaction mixture at a temperature of at least 50 ° C for a period of at least 10 minutes, d) isolating the chemically modified lignin from the reaction mixture. Procedure according to Claim 1 comprising the further step: e) washing the isolated lignin. Method according to at least one of the Claims 1 or 2 comprising the further step: f) drying the isolated lignin. Method according to at least one of the preceding claims, wherein according to step a) a lignin suspension is provided which contains lignin particles in a suspension liquid. Process according to at least one of the preceding claims, wherein in order to obtain the reaction mixture in step b) a catalyst is added to the lignin in addition to the diisocyanate component. Method according to at least one of the preceding claims, wherein the ratio of the mass of the chemically modified lignin isolated in step d) to the mass of the lignin in the lignin suspension provided according to step a) is at least 0.8. Chemically modified lignin obtainable by the process according to at least one of the preceding claims, wherein the modified lignin contains isocyanate groups (-NCO) in a proportion of 0.1 mmol / g to 5 mmol / g. A process for the production of a molded body comprising the following steps: i) Optional post-mixing of the chemically modified lignin Claim 7 with a fiber component, ii) pressing the chemically modified lignin after Claim 7 or the mixture from step i) at a temperature of at least 90 ° C. and a pressure of at least 50 bar to obtain the molded body. Moldings obtainable by the process according to Claim 8 . Use of the molding after Claim 8 in the manufacture of vehicles, furniture, laminate floors and / or structures.