LIGNIN-CONTAINING POLYURETHANES

Abstract

The present invention relates to generally relates to polyurethanes containing at least one lignin compound. In particular, the invention relates to a reactive polyurethane system comprising at least one polyol, at least one polyisocyanate and at least one lignin compound. In further aspects, the invention relates to a process for producing a polyurethane from a reactive system as disclosed, a polyurethane obtainable by such process, polyurethane adhesives, articles comprising cured polyurethane adhesives and a method for adhesive bonding.

Claims

1. A reactive polyurethane-system comprising: (i) at least one polyol, (ii) at least one polyisocyanate, and (iii) at least one lignin compound.

2. The reactive polyurethane-system according to claim 1, wherein the at least one polyol is a hydrophobic polyol.

3. The reactive polyurethane-system according to claim 1, wherein the at least one polyol comprises at least 12 consecutive carbon atoms per molecule, wherein the ratio of carbon atoms to oxygen atoms per molecule is at least about 4.

4. The reactive polyurethane-system according to claim 1, further comprising (iv) at least one additive.

5. The reactive polyurethane-system according to claim 4, wherein the at least one additive is selected from the group consisting of polyether polyol, filler, foaming agent, abrasion reducer, amine catalyst, molecular sieve, antioxidant, flame retardant, antistatic agent, cell opener, dye, crosslinker, surfactant, softening agent, polyamine, and any combination thereof.

6. The reactive polyurethane-system according to claim 1, wherein the at least one polyisocyanate is selected from the group consisting of an aromatic and aliphatic polyisocyanate.

7. The reactive polyurethane-system according to claim 1, wherein an NCO content of component (ii) is 30-35%.

8. The reactive polyurethane-system according to claim 1, wherein the at least one lignin compound is a lignin, modified lignin, or lignin degradation product.

9. The reactive polyurethane-system according to claim 8, wherein the at least one lignin compound is a lignin derivative selected from a lignin modified by a reaction of at least a part of the lignin's hydroxyl groups with activated carboxylic acids, isocyanate or isocyanate prepolymers, or by a reaction of at least a part of the lignin's carboxyl groups with activated amines or alcohols.

10. The reactive polyurethane-system according to claim 8, wherein the lignin degradation product is selected from lignin monomers comprising guaiacol, syringol, or catechol, or from base-catalyzed degradation lignin oligomers, each of which is optionally organically modified.

11-16. (canceled)

17. The reactive polyurethane-system according to claim 1, wherein the at least one lignin compound is a lignin present in a powder form.

18. The reactive polyurethane-system according to claim 1, wherein the solubility of component (iii) in component (i) is characterized by the Hansen Solubility Parameters (HSP) and wherein a distance (R.sub.AB) in Hansen space between component (i) and component (iii) is being greater than the interaction radius (R.sub.0) of component (iii).

19. The reactive polyurethane-system according to claim 1, wherein a ratio of isocyanate reactive hydrogen atoms to isocyanate groups is from 100% to 115%, or from 105% to 110%.

20. A process for producing a polyurethane (PU) from the reactive polyurethane-system according to claim 1, comprising the steps of (1) dispersing component (iii) and optionally component (iv) in component (i), (2) mixing component (ii) with a dispersion obtained in step (1), (3) optionally loading a mixture obtained in step (2) with gas; (4) pouring the mixture obtained in step (2) or (3) onto a surface, optionally at elevated temperature, (5) optionally postcuring a mixture obtained in step (4), and (6) optionally shaping a product obtained after step (4) or (5) into the desired dimensions.

21. A polyurethane obtained by the process according to claim 20.

22. The polyurethane according to claim 21, wherein the polyurethane is a foam, a casting material, a coating, or an adhesive.

23. A two-component polyurethane adhesive, comprising: a first component comprising components (i), (iii) and optionally (iv) as defined in claim 1, and a second component comprising component (ii) as defined in claim 1, wherein a ratio of isocyanate reactive hydrogen atoms to isocyanate groups is from 100% to 115%.

24. An article comprising at least two substrates bonded together by cured reaction products of the two-component polyurethane adhesive according to claim 23.

25. The reactive polyurethane system of claim 8, wherein the at least one lignin compound is an adhesion promoter or an anti-sedimentation agent.

26. The reactive polyurethane-system according to claim 1, wherein the reactive polyurethane system is an adhesive.

27. A method for adhesive bonding of a substrate S1 to a substrate S2, comprising the steps of: (1) applying the reactive polyurethane system according to claim 1 or the two-component polyurethane adhesive according to claim 23 to the substrate S1; (2) contacting the applied reactive polyurethane system or adhesive with the substrate S2 within an open time of the reactive polyurethane system or adhesive; or (1′) applying the reactive polyurethane system according to claim 1 or the two-component polyurethane adhesive according to claim 23 to the substrate S1 and to the substrate S2; (2′) contacting the applied reactive polyurethane system or adhesive with one another within an open time of the reactive polyurethane system or adhesive; wherein the substrates S1 and S2 are independently selected from metal, plastic, wood, concrete, or foam and a fiber composite.

Description

LEGENDS TO THE FIGURES

[0156] FIG. 1: Fracture pattern of wood (beech). Exemplary and reference adhesive was applied to test specimens. The adhesive was allowed to cure for 7 days at room temperature. Subsequently, the test specimens were stored in water for 9 days at room temperature. Then, a tensile test was performed as described below. Top panel: reference adhesive. Bottom panel: lignin containing adhesive.

[0157] FIG. 2: Fracture pattern of metal (galvanized steel), no treatment prior to application of the exemplary and reference adhesive. The adhesive was allowed to cure at room temperature. After a rest period of 20 days, a tensile test was performed as described below. Top panel: reference adhesive. Bottom panel: lignin containing adhesive.

[0158] FIG. 3: Fracture pattern of metal (stainless steel), no treatment prior to application of the exemplary and reference adhesive. The adhesive was allowed to cure at room temperature. After a rest period of 20 days, a tensile test was performed as described below. Top panel: reference adhesive. Bottom panel: lignin containing adhesive.

[0159] FIG. 4: Fracture pattern of metal (aluminium alloy AlMg3), no treatment prior to application of the exemplary and reference adhesive. The adhesive was allowed to cure at room temperature. After a rest period of 20 days, a tensile test was performed as described below. Top panel: reference adhesive. Bottom panel: lignin containing adhesive.

[0160] FIG. 5: Fracture pattern of concrete. Exemplary and reference adhesive was applied to test specimens. The adhesive was allowed to cure for 7 days at room temperature. Subsequently, the test specimens were stored in water for 9 days at room temperature. Then, the bonded specimens were separated using a chisel. Top panel: reference adhesive. Bottom panel: lignin containing adhesive.

EXAMPLES

Example 1: Two Component Adhesive

a) Preparation

[0161] Two component adhesive formulations with (Example) and without lignin (Comparison) have been prepared as follows.

TABLE-US-00001 TABLE 1 Component A: hydroxyl Example; Comparison; Compound value in wt % in wt % Arcol ® 1030 Polyol (polyether 400 10 10 polyol; e.g. Covestro) castor oil 1.sup.st pressing 166 24.90 24.90 molecular sieve A3 5.00 5.00 triethylene diamine 560 0.10 0.10 kraft-lignin (Sigma Aldrich) 20.00 0 calcit MX 30 40.00 60.00 total 100.00 100.00 total hydroxyl value 81.9 81.9

[0162] It is noted that lignin has free hydroxyl groups and thus, a hydroxyl value may be determined. However, in the context of the invention, it has been proven advantageous not taking into account a hydroxyl value of lignin for calculating the required amount of isocyanate. This approach may be explained by the fact that lignin hydroxyl groups are sterically hindered.

Component B:

[0163] Desmodur® 44V20LF (polymeric isocyanate based on MDI; e.g. Covestro) with 31 wt % NCO for both Example and Comparison.

[0164] Ratio of isocyanate reactive hydrogen atoms to isocyanate groups: 106% (corresponds to a mixing ratio of Component A to Component B of 100:21).

b) Results at 20° C.

[0165]

TABLE-US-00002 TABLE 2 Results at 20° C. Example Comparison Sample size (A) 100  100  pot life 30′-35′ 18′-20′ Shore D overnight 81 Shore D 70° C. 71 final hardness Shore D 81 84

Example 2: Improvement of Adhesive Properties

[0166] Adhesive formulations (Example and Comparison) were prepared as in Example 1.

[0167] Thereafter, the adhesive was applied to different substrates (metal, wood, concrete, plastics). After curing of the adhesive, tensile shear strength was determined and fracture patterns analyzed.

[0168] Tensile shear strength was determined having regard to DIN EN 1465. Briefly, tensile shear strength of overlap adhesions was determined via applying a shear stress to an overlap splice in single-shear between rigid adherends. The tensile force acts in parallel to the adhesive surface and the main axis of the test specimen. For the experiments, a universal test machine (Zwick Z 020; Zwick GmbH & Co. KG, Ulm, Germany) was used. For joining the specimens, the freshly prepared adhesive was applied to one test specimen. A further test specimen was then laid onto the test specimen with applied adhesive, ensuring proper alignment. The specimens must not be moved until they reach handling stability. Testing is carried out at 23° C., and all test specimens were stored at this temperature at least 24 hours prior to testing. Test speed is selected such that the adhesion is destroyed within 65±20 seconds. The test specimen is aligned in line with the applied force. As results, the tensile shear strength (in MPa=N/mm.sup.2) and the average fracture pattern are recorded.

[0169] It resulted that the exemplary adhesive composition containing lignin is universally applicable to all substrates. The best results were obtained with metallic substrates and wood. Two things were particularly striking. First, the fracture patterns of the lignin containing adhesive was significantly better than those of the reference adhesive without lignin. Specifically, the lignin containing adhesive very often showed a completely cohesive fracture pattern or fracture pattern with a high proportion of cohesive fracture, whereas in the reference adhesive, cohesive fracture patterns rarely occurred (Tables and FIGS. 1-5).

Example 2.1 Metal Substrates

[0170] Experiments were carried out with test specimens where both adherends consisted of the same metal. The specimens were subjected to the above-described procedure, once using the lignin containing adhesive and once the reference adhesive (both according to Example 1). The specimens were pretreated by purification with isopropanol before applying the adhesive and had been stored at room temperature for two weeks. Results are shown in the following Table 3 (see also FIGS. 2, 3 and 4).

TABLE-US-00003 TABLE 3 Tensile shear strength and fracture pattern - metal substrates purified with isopropanol before application of the adhesive tensile shear average tensile shear average strength fracture strength fracture (MPa) pattern* (MPa) pattern* Substrate lignin containing adhesive reference adhesive copper 6.5 15% K 2.5 100% A stainless steel 15.6 50% K 13.9  17% K AlMg3 15 71% K 10.8 100% A galvanized steel 18.8 100% K  18.6  20% K *average fracture pattern classified as follows: K = cohesive fracture in %; A = adhesive fracture in %

[0171] For AlMg3, a further test was carried out with samples pretreated by sandblasting instead of isopropanol purification. There, a tensile shear strength of 15.1 MPa and a 100% K fracture was observed with the lignin containing adhesive, whereas with the reference adhesive, a tensile shear strength of 17.5 MPa and a 20% K fracture was observed.

[0172] In a further set of experiments, the same types of metal test specimens were used, but without any pre-treatment prior to application of the adhesive. Results are shown in the following Table 4.

TABLE-US-00004 TABLE 4 Tensile shear strength and fracture pattern - metal substrates purified with isopropanol before application of the adhesive tensile shear average tensile shear average strength fracture strength fracture (MPa) pattern* (MPa) pattern* Substrate lignin containing adhesive reference adhesive copper 12.3 35% K 2.38 100% A stainless steel 16.9 62% K 13.3 100% A AlMg3 13.9 35% K 10.8 100% A galvanized steel 17.8 44% K 18.6 100% A *average fracture pattern classified as follows: K = cohesive fracture in %; A = adhesive fracture in %

[0173] As can be seen from Tables 3 and 4, whether or not test specimens had been purified with isopropanol, the lignin containing adhesive not only showed a better fracture pattern, but also a higher absolute value in tensile shear strength.

Example 2.2 Wood Substrates

[0174] Even humid wood test specimens showed ideal properties. It was tested whether bonding could be obtained with humid wood. This condition could be simulated by storing test specimens (beech wood) in water for several days (here: 9 days at room temperature) after applying the adhesive. Otherwise, the procedure was identical to Example 2.1 (no pretreatment with isopropanol). It was again observed that the fracture pattern of the lignin containing adhesive shows a very high cohesive fracture proportion (50% K), whereas the reference adhesive shows a clearly adhesive fracture pattern (100% A), see FIG. 1. Moreover, the absolute values in tensile shear strength are again higher than those of the reference adhesive (5.5 MPa with lignin containing adhesive versus 5.06 MPa with reference adhesive).

[0175] A similar effect can be seen with two humid concrete test specimens (stored in water for 9 days at room temperature), which showed 15% K fracture with the lignin containing adhesive versus 100% A fracture with reference adhesive (see FIG. 5). Here, no tensile shear strength could be measured, and the adhesion was destroyed with the help of a chisel.

[0176] In conclusion, the exemplary lignin containing adhesive, which had not even been optimized for adhesion properties, could be used on various substrates and showed excellent fracture behaviour. In particular, with metal bondings at room temperature, additional increased tensile shear strength was observed. Also, it could be shown that it is not necessary to degrease the tests specimens before applying the adhesive. Accordingly, time and labor intensive preparation or pretreatment of substrates is, particularly with regard to metal bondings, unnecessary when using lignin containing adhesives according to the invention.

Example 3: Hansen Solubility Parameters

[0177] In the following table, Hansen Solubility Parameters for lignin in comparison to various polyols are presented. All values are available from the literature (individual references indicated below the table). All δ values in (cal/cm.sup.3).sup.1/2. For R.sub.AB, the differences were calculated using equation (I).

TABLE-US-00005 TABLE 5 HSP for lignin and various polyols δ.sub.Diffusion δ.sub.Polar δ.sub.Hydrogen solubility of δ.sub.total (=δ.sub.d) (=δ.sub.p) (=δ.sub.h) δ.sub.a R.sub.0 R.sub.AB lignin lignin* 15.6 10.8 7.0 8.8 11.2 7.1 PEG high**** 9.4 2.0 4.8 7.0 dissolution PEG low**** 7.5 1.0 4.4 10.0 no dissolution soy bean oil 8.6 2.2 4.2 8.0 swelling polyol hydroxyl value 148***** castor oil 8.3 4.4 8.4 swelling (hydrogenated)** castor oil methyl 7.9 3.3 4.5 8.2 swelling ester*** DEG* 14.6 7.9 7.2 10.0 12.3 6.0 dissolution THF* 9.5 8.2 2.8 3.9 4.8 8.3 swelling hexane* 7.2 7.2 13.3 no dissolution *values from “The Three Dimensional Solubility Parameter and Solvent Diffusion Coefficient - Their Importance In Surface Coating Formulation” by Charles M. Hansen; Copenhagen; Danish Technical Press; 1967 **values from U.S. Pat. No. 6,326,012 B1 (original values 16.96(J/cm.sup.3).sup.1/2 und 9.01(J/cm.sup.3).sup.1/2 converted to (cal/cm.sup.3).sup.1/2 via division by 2.0455) ***values from Batista, Guirardello, and Krähenbühl; School of Chemical Engineering-UNICAMP, 13083-970 Campinas, S P, Brazil; Energy Fuels, 2013, 27 (12), pp. 97-7509; DOI: 10.1021/ef401690f ****values from “Solubility parameter components of some polyols” by Ryszard Mieczkowski; Institute of Chemistry, N. Copernicus University, 87-100 Toruń, Poland; European Polymer Journal, Volume 27, Issues 4-5, 1991, pp. 377-379 *****values from Zhang C and Kessler M R; ACS Sustainable Chemistry and Engineering 2015, vol. 3, pp. 743-749.

[0178] As can be seen from the last column of Table 5, the desired swelling of lignin in polyol is observed, when using vegetable oils or derivatives thereof. There, the ratio of R.sub.AB to R.sub.0 are in the range of R.sub.0<R.sub.AB<1.25 R.sub.0.

Example 4: Lignin Containing Polyol Dispersions

[0179] The homogeneity of Component A of the two component adhesive according to the invention (see above, Example 1) can be examined via storage stability tests. Formulations that are not storage-stable separate over time. Often, the filler settles as a rigid layer, which cannot be re-dispersed. In the lignin containing formulation of Component A according to the invention, even after storage for three months at room temperature, no separation of constituents or settling of a rigid filler layer is observed. Only some polyol floats, but can easily be re-dispersed without any effect on the quality of the formulation.

Example 5: Lignin Degradation Product Containing Polyol

[0180] Wood chips (spruce) were incubated at 150° C. for 4 hours in a ionic liquid and in the presence of organic co-solvent and polyethylene glycol (PEG). After cooling down the mixture and removal of (solid) cellulose, a liquid, homogeneous reaction product of dark brown color was obtained. This reaction product is based on PEG, lignin (in solution) and hemicellulose (in solution) and can be used as a polyol component for the preparation of polyurethanes.

Example 6: Ester Polyols from Lignin Degradation Products

[0181] Guaiacol, obtained from degradation of lignin, was reacted with glycidol, either in the presence of amine catalyst in ethanol at 84° C., or in the presence of sodium hydroxide at 90° C.

[0182] The resulting guaiacol-glycerolether (G-Glyc) was reacted with adipic acid (Adip) alone or with diethylene glycol (DEG) and adipic acid (Adip). The following exemplary ester polyols were obtained (Table 6).

TABLE-US-00006 TABLE 6 Ester polyols from guaiacol hydroxyl viscosity acid polyol conc. value (mPa .Math. s at number batch monomers G-Glyc (mg KOH/g) 25° C.) (mg KOH/g) F5 G-Glyc/Adip 66% 97 25990 8.2 F8 G-Glyc/Adip 73% 205 10940 5.3 F7 G-Glyc/DEG/Adip 38% 563 1460 2.3 F10 G-Glyc/DEG/Adip 24% 404 379 2.3

[0183] The invention is further characterized by the following items. [0184] Item 1. Reactive polyurethane-system comprising [0185] (i) at least one polyol (A), [0186] (ii) at least one polyisocyanate (B), and [0187] (iii) at least one lignin compound (C). [0188] Item 2. Reactive polyurethane-system according to item 1, wherein the at least one polyol (A) is a hydrophobic polyol. [0189] Item 3. Reactive polyurethane-system according to item 1 or 2, wherein the at least one polyol (A) is a polyester-based polyol, particularly a hydrophobic polyester-based polyol. [0190] Item 4. Reactive polyurethane-system according to item 1 or 2, wherein the at least one polyol (A) is an oil, particularly a natural oil, more particularly a vegetable oil, or a derivative of an oil, particularly a derivative of a vegetable oil. [0191] Item 5. Reactive polyurethane-system according to item 4, wherein the oil is an animal oil, e.g. fish oil, or a vegetable oil selected from the group consisting of castor oil, soybean oil, safflower oil, peanut oil, rapeseed oil, sunflower oil, palm oil, linseed oil, olive oil, tung oil, corn oil, canola oil, sesame oil and cottonseed oil, or a blend of at least two oils. [0192] Item 6. Reactive polyurethane-system according to item 4 or 5, wherein the derivative of an oil is a reaction product obtainable by subjecting an oil, particularly a vegetable oil, to [0193] (i) transesterification, such as a reaction product with any one of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, glycerol, pentaerythriol, di-pentaerythriol, tri-pentaerythriol, trimethyolpropane (TMP), sorbitol, isosorbide, cyclohexanediol, fatty dialcohols, propanediols, butanediols, pentanediols, hexanediols, cyclohexanediols, di- and polyamines like ethylene diamine, neopentylamine, diaminohexane, diethylene triamine, triethylene tetramine, aminoalcohols like ethanolamine, diethanolamine, triethanolamine, [0194] (ii) epoxidation and subsequent ring opening, [0195] (iii) amidation, [0196] (iv) hydroformylation and subsequent reduction, [0197] (v) ozonolysis and subsequent reduction, [0198] (vi) thiol-ene addition, [0199] (vii) epoxides hydrogenation, [0200] (viii) ester reduction, [0201] (ix) diels alder cyclization, [0202] (x) double bonds oxidation to peroxides and reduction to alcohols, [0203] (xi) electrophilic additions of formaldehyde, metathesis and reduction, [0204] (xii) or a combination of two or more of the above. [0205] Item 7. Reactive polyurethane-system according to any one of the preceding items, wherein the at least one polyol (A) comprises at least 12 consecutive carbon atoms per molecule, wherein the ratio of carbon atoms to oxygen atoms per molecule is at least about 4, e.g. about 6, preferably 4-8. [0206] Item 8. Reactive polyurethane-system according to any one of the preceding items, wherein the at least one polyol (A) is selected from the group consisting of castor oil, preferably castor oil from first pressing, castor oil with low water content, castor oil with low acid value, pharmaceutical grade castor oil, blown castor oil, partially dehydrated castor oil, partially hydrogenated castor oil, castor oil esters, e.g. castor oil esters with C.sub.1-6 alkanols, such as methanol and ethanol, and ricinoleic acid esters with C.sub.1-6 alkanols or typical diols, such as 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, ethylene glycol, diethylene glycol, triethylene glycol, pentanediols, hexanediols or diols with even higher molecular weight. [0207] Item 9. Reactive polyurethane-system according to any one of the preceding items, further comprising [0208] (iv) at least one additive (D). [0209] Item 10. Reactive polyurethane-system according to item 9, wherein the at least one additive (D) is selected from polyether polyol, filler, foaming agent, abrasion reducer, amine catalyst, molecular sieve, antioxidant, flame retardant, antistatic agent, cell opener, dye, crosslinker, surfactant, softening agent, polyamine, or any combination thereof. [0210] Item 11. Reactive polyurethane-system according to any one of the preceding items, wherein the at least one polyisocyanate (B) is selected from the group consisting of an aromatic or aliphatic polyisocyanates. [0211] Item 12. Reactive polyurethane-system according to any one of the preceding items, wherein the at least one polyisocyanate (B) is an aromatic polyisocyanate selected from monomeric methylenedi(phenylisocyanate) (MDI), polymeric MDI and toluylene diisocyanate (TDI), preferably polymeric MDI. [0212] Item 13. Reactive polyurethane-system according to any one of items 1-11, wherein the at least one polyisocyanate (B) is an aliphatic polyisocyanate selected from methylenedi(cyclohexyl isocyanate) (HMDI), isophorone diisocyanate (IPDI), pentamethylene diisocyanate (PDI) and hexamethylene diisocyanate (HDI). [0213] Item 14. Reactive polyurethane-system according to any one of the preceding items, wherein the NCO content of component (ii) is 30-35%, preferably 30-33%, more preferably 30.5-31.5%. [0214] Item 15. Reactive polyurethane-system according to any one of the preceding items, wherein component (ii) is polymeric MDI, preferably polymeric MDI with an NCO content of about 31%. [0215] Item 16. Reactive polyurethane-system according to any one of the preceding items, wherein the at least one lignin compound (C) is a lignin or a lignin derivative. [0216] Item 17. Reactive polyurethane-system according to any one of the preceding items, wherein the at least one lignin compound (C) is a lignin derivative selected from modified lignin and a lignin degradation product. [0217] Item 18. Reactive polyurethane-system according to item 17, wherein the modified lignin is an organically modified lignin, particularly lignin modified by reaction of at least a part of its hydroxyl groups with activated carboxylic acids, isocyanate or isocyanate prepolymers, or by reaction of at least a part of its carboxyl groups with activated amines or alcohols. [0218] Item 19. Reactive polyurethane-system according to item 17, wherein the lignin degradation product is selected from lignin monomers, e.g. guaiacol, syringol, catechol, and base-catalyzed degradation (BCD) lignin oligomers, each of which is optionally organically modified, e.g. by epoxidation/ring opening. [0219] Item 20. Reactive polyurethane-system according to item 19, wherein the organically modified lignin degradation product is a 3-aryloxy-1,2-propane-diol, wherein aryl is phenyl which is optionally independently substituted with 1, 2 or 3 C.sub.1-C.sub.3 alkyl, C.sub.1-C.sub.3 alkoxy, C.sub.2-C.sub.3 alkenyl or hydroxyl groups. [0220] Item 21. Reactive polyurethane-system according to any one of items 1-16, wherein the at least one lignin compound (C) is a lignin present in powder form. [0221] Item 22. Reactive polyurethane-system according to item 21, wherein the lignin has a maximum humidity of 10%, preferably 5% or less by weight with regard to the total weight of the at least one lignin compound (C). [0222] Item 23. Reactive polyurethane-system according to item 21 or 22, wherein the lignin has a mean particle size (D50) of ≤300 μm, preferably ≤50 μm, more preferably ≤10 μm. [0223] Item 24. Reactive polyurethane-system according to any one of items 21-23, wherein the lignin is selected from the group consisting of kraft-lignin, organosolv-lignin, hydrolysis lignin and IL-lignin, or any combination thereof. [0224] Item 25. Reactive polyurethane-system according to any one of the preceding items, wherein the lignin compound (C) has not been subjected to chemical pretreatment, e.g. with isocyanate. [0225] Item 26. Reactive polyurethane-system according to any one of the preceding items, wherein the solubility of component (iii) in component (i) is characterized by the Hansen Solubility Parameters (HSP) distance (R.sub.AB) in Hansen space between component (i) and component (iii) being greater than the interaction radius (R.sub.0) of component (iii). [0226] Item 27. Reactive polyurethane-system according to item 26, wherein R.sub.0<R.sub.AB<1.4.Math.R.sub.0, preferably R.sub.0<R.sub.AB<1.25.Math.R.sub.0. [0227] Item 28. Reactive polyurethane-system according to item 26 or 27, wherein R.sub.AB is determined according to equation (I)

(R.sub.AB).sup.2=4(δ.sub.d2−δ.sub.d1).sup.2+(δ.sub.p2−δ.sub.p1).sup.2+(δ.sub.h2−δ.sub.h1).sup.2  (I)

wherein δ.sub.d represents the effects of the dispersion forces (d),
δ.sub.p represents the effects of the polar forces (p), and
δ.sub.h represents the effects of the hydrogen bonding forces (h), and wherein
δ.sub.x2 with x=d, p or h is the respective solvent coordinate and δ.sub.x1 with x=d, p or h is the respective center point of the solute sphere. [0228] Item 29. Reactive polyurethane-system according to any one of the preceding items, wherein component (i) is present in an amount of 15-35 wt %, preferably 20-30 wt %, more preferably about 25 wt %, based on the total weight of components (i), (iii) and (iv). [0229] Item 30. Reactive polyurethane-system according to any one of the preceding items, wherein component (iv) is present in an amount of 40-70 wt %, preferably about 55 wt %, based on the total weight of components (i), (iii) and (iv). [0230] Item 31. Reactive polyurethane-system according to any one of the preceding items, wherein the component (iv) comprises a polyether polyol, e.g. in an amount of 5-15 wt %, preferably about 10 wt %, a filler, e.g. in an amount of 30-50 wt %, preferably about 40 wt %, a molecular sieve, e.g. in an amount of 3-8 wt %, preferably about 5 wt %, and/or an amine catalyst, e.g. in an amount of 0.05-0.5 wt %, preferably about 0.1 wt %, each based on the total weight of components (i), (iii) and (iv). [0231] Item 32. Reactive polyurethane-system according to any one of the preceding items, wherein the ratio of isocyanate reactive hydrogen atoms to isocyanate groups is from 100% to 115%, preferably from 105% to 110%. [0232] Item 33. Process for producing a polyurethane (PU) from a reactive polyurethane-system according to any of items 1-32, comprising the steps of [0233] (1) dispersing component (iii) and optionally component (iv) in component (i), [0234] (2) mixing component (ii) with the dispersion obtained in step (1), [0235] (3) optionally loading the mixture obtained in step (2) with gas, such as air, [0236] (4) pouring the mixture obtained in step (2) or (3) onto a surface, optionally at elevated temperature, [0237] (5) optionally postcuring the mixture obtained in step (4), and [0238] (6) optionally shaping the product obtained after step (4) or (5) into the desired dimensions. [0239] Item 34. Process according to item 33, wherein only steps (1), (2) and (4) are performed. [0240] Item 35. Process according to items 33 or 34, wherein component (iii) is a lignin, wherein the mean particle size (D50) after dispersing component (iii) in component (i) is between 1 and 200 μm. [0241] Item 36. Polyurethane (PU) obtainable by a process according to any one of items 33-35. [0242] Item 37. Polyurethane (PU) according to item 36, which is a foam, particularly an open or closed cell foam, particularly a closed cell foam, or a casting material. [0243] Item 38. Polyurethane (PU) according to item 36, which is a coating. [0244] Item 39. Polyurethane (PU) according to item 36, which is an adhesive. [0245] Item 40. Two-component polyurethane adhesive, comprising a first component comprising [0246] components (i), (iii) and optionally (iv) as defined in any one of items 1-10 and 16-31 and a second component comprising component (ii) as defined in any one of items 1 and 11-15, wherein the ratio of isocyanate reactive hydrogen atoms to isocyanate groups is as defined in item 32. [0247] Item 41. Article comprising at least two substrates, particularly two substrates, bonded together by cured reaction products of the two-component polyurethane adhesive according to item 40. [0248] Item 42. Article according to item 41, wherein each substrate is independently selected from metal, plastic, wood, concrete, foam and a fiber composite, particularly from wood and metal. [0249] Item 43. Article according to item 41 or 42, wherein all substrates are of the same material. [0250] Item 44. Article according to any one of items 41-43 comprising two substrates, wherein both substrates are metal substrates selected from stainless steel, galvanized steel, copper and aluminum alloys such as AlMg3. [0251] Item 45. Use of a lignin compound (C) as defined in any one of items 16-25, particularly as defined in any one of items 21-25, as an adhesion promoter in a reactive polyurethane system comprising at least one polyol (A) and at least one isocyanate (B). [0252] Item 46. Use of a lignin compound (C) as defined in any one of items 16-25, particularly as defined in any one of items 21-25, as an anti-sedimentation agent in a reactive polyurethane system comprising at least one polyol (A) and at least one isocyanate (B). [0253] Item 47. Use of a lignin compound (C) according to item 45 or 46, wherein the at least one polyol (A) is defined as in any one of items 2-8, and the at least one polyisocyanate (B) is defined as in any one of items 11-13. [0254] Item 48. Use of a reactive polyurethane-system according to any of items 1-32 as an adhesive. [0255] Item 49. Use of a reactive polyurethane-system according to any of items 1-32 or a two-component polyurethane adhesive according to item 40 in a method of adhesive bonding. [0256] Item 50. Method for adhesive bonding of a substrate S1 to a substrate S2, comprising the steps of: [0257] (1) applying a reactive polyurethane system according to any one of items 1-32 or a two-component polyurethane adhesive according to item 40 to a substrate S1; [0258] (2) contacting the applied reactive polyurethane system or adhesive with a substrate S2 within the open time of the reactive polyurethane system or adhesive; [0259] or [0260] (1′) applying a reactive polyurethane system according to any one of items 1-32 or a two-component polyurethane adhesive according to item 40 to a substrate S1 and to a substrate S2; [0261] (2′) contacting the applied reactive polyurethane system or adhesive with one another within the open time of the of the reactive polyurethane system or adhesive; [0262] wherein the substrates S1 and S2 are preferably independently selected from metal, plastic, wood, concrete, foam and a fiber composite, particularly from wood and metal. [0263] Item 51. Method according to item 50, wherein the surfaces of substrates S1 and S2 are not pretreated before applying the reactive polyurethane system or adhesive. [0264] Item 52. Method according to item 50 or 51, wherein the substrates S1 and S2 both made of the same material and are selected from wood and concrete, and wherein the substrates S1 and S2 are stored in water prior to applying the reactive polyurethane system or adhesive.