FIELD OF THE INVENTION

The invention relates to a method for produc ing a binder composition. Further, the invention re lates to a binder composition, to an adhesive composi tion, and to uses.

BACKGROUND OF THE INVENTION

Tannin and lignin are natural components, which can be extracted from e.g. bark and wood. For example the tannin content of Nordic softwood species, such as pine and spruce, is about 5 - 20 %.

As tannin and lignin are biological compo nents their use in e.g. glues instead of synthetic ma terials has been investigated in order to come up with a more environmentally friendly adhesive composition. Especially, the ability to replace synthetic phenol, derived from fossil sources, in final phenolic resins, such as phenol formaldehyde resin, has been the object of prior art.

However, the inventor has recognized the need for a method, which would result in a phenol free binder composition for further applications.

SUMMARY

A method for producing a binder composition without using a compound selected from the class of phenols is disclosed. The method may comprise:

(i) heating an aqueous composition comprising lignin in the presence of a catalyst at a temperature of 50 - 95 °C for 0.25 - 5 hours;

(ii) mixing a crosslinking agent with the aqueous composition from (i) and heating the same at a temperature of 60 - 95 °C for pre-polymerizing lignin and crosslinking agent; (iii) mixing tannin with the aqueous composi tion from (ii) until a binder composition with a pre determined viscosity value is formed; wherein the molar ratio of crosslinking agent to lignin and tannin is 0.5 - 1.7.

Further is disclosed a binder composition ob tainable by the method as defined in the current spec ification.

Further is disclosed an adhesive composition comprising the binder composition.

Further is disclosed the use of the binder composition in an impregnation application, for gluing a wood product or layered wood product or wood panel, for producing a laminate, shuttering film, mineral wool, nonwoven fiber product, molded fiber product, or extruded fiber product.

DETAILED DESCRIPTION OF THE INVENTION

A method for producing a binder composition without using a compound selected from the class of phenols is disclosed. The method may comprise:

(i) heating an aqueous composition comprising lignin in the presence of a catalyst at a temperature of 50 - 95 °C for 0.25 - 5 hours;

(ii) mixing a crosslinking agent with the aqueous composition from (i) and heating the same at a temperature of 60 - 95 °C for pre-polymerizing lignin and crosslinking agent;

(iii) mixing tannin with the aqueous composi tion from (ii) for polymerizing tannin with the pre polymerized lignin and crosslinking agent until a binder composition with a predetermined viscosity val ue is formed; wherein the molar ratio of crosslinking agent to lignin and tannin is 0.5 - 1.7. Further is disclosed a binder composition ob tainable by the method as defined in the current spec ification.

In one embodiment, the amount of free cross- linking agent, e.g. free formaldehyde monomers of the binder composition is at most 1 weight-%, or at most 0.5 weight-%, or at most 0.3 weight-%, or at most 0.1 weight-%, or at most 0.06 weight-%. The amount of free crosslinking agent, e.g. free formaldehyde, may be de termined in accordance with standard EN-ISO 11402 and hydroxylamine hydrochloride procedure with the excep tion that the sample is diluted in 20 ml of distilled water and 70 ml of 94 % ethanol.

In one embodiment, the amount of free phenol of the binder composition is below 0.01 weight-% when determined by gas chromatography-flame ionization de tector (GC-FID) method in accordance with standard SFS-EN ISO 8974:2002 with the exception that the alka line sample solution is diluted before neutralization.

In one embodiment, the water miscibility (tolerance) of the binder composition is above 500 %, or above 700 %, or above 900 %, or infinite, when de termined in accordance with the standard EN ISO 8989.

In one embodiment, the viscosity value of the binder composition increases at most 400 cP/7 days, or at most 300 cP/7 days, or at most 200 cP/7 days, or at most 100 cP/7 days, when stored at 25 °C after its production. The binder composition as disclosed in the current specification has the added utility of showing a good storage stability.

The inventor surprisingly found out that the specified amount of crosslinking agent as well as the molar ratio of crosslinking agent to the polymerizing components, i.e. lignin and tannin, affects the prop erties of the produced binder composition such that a binder composition with the above properties may be prepared. Further is disclosed an adhesive composition comprising the binder composition.

Further is disclosed the use of the binder composition in an impregnation application, for gluing a wood product or layered wood product or wood panel, for producing a laminate, shuttering film, mineral wool, nonwoven fiber product, molded fiber product, or extruded fiber product.

The product produced by using the binder com position as disclosed in the current specification may have one or more of the following properties:

- the amount of formaldehyde emissions being 0.01 - 0.5 mg/1, or 0.1 - 0.35 mg/1 when measured by desiccator EN ISO 12460-4;

- the amount of formaldehyde emissions being 0.01 - 0.40 mg/m ² *h, or 0.05 - 0.30 mg/m ² *h, or 0.1 - 0.2 mg/m ² *h when measured by gas analysis method EN ISO 12460-3;

- fulfilling the minimum bonding class 1-4, or 2-4, or 3-4, or when measured by bonding quality test method EN 314-1 & EN 314-2.

The inventor surprisingly found out that by the method as disclosed in the current specification, one is able to produce a binder composition without using any compound selected from the class of phenols.

In this specification, unless otherwise stat ed, the term "compound selected from the class of phe nols" should be understood as meaning a fossil-based compound of phenols. I.e. phenols are compounds con sisting of a single aromatic ring where to one or more hydroxyls (—OH) are bonded.

Such a compound selected from the class of phenols may be e.g. phenol, cresol, or resorcinol. Such phenols are toxic compounds. In one embodiment, the method comprises the proviso that no compound se lected from the class of phenols is used for producing the binder composition. The method as disclosed in the current specification has the added utility of provid ing a manner to produce a binder composition free of materials of fossil origin. The binder composition produced may thus be free of fossil-based phenol com pound. Especially the polymerizable substances used in the method, i.e. lignin and tannin, are of biomass or biological origin. The binder composition as disclosed in the current specification may thus prepared as a non-toxic binder composition. I.e. a binder composi tion with reduced share of toxic or hazardous com pounds may be prepared. The binder composition as dis closed in the current specification may be prepared as 100 % biological binder composition.

The total amount of crosslinking agent used for producing the binder composition may be 3 - 7 weight-%, or 3 - 6 weight-%, or 4 - 5 weight-%, based on the total weight of the binder composition. The method as disclosed in the current specification has the added utility of allowing a reduced or low amount of crosslinking agent, such as formaldehyde, to be used without affecting the properties of the binder composition in a harmful manner.

The crosslinking agent may be an aldehyde, such as formaldehyde or paraformaldehyde. In one em bodiment, the aldehyde is prepared from bio-methanol. The aldehyde may thus be of biobased origin. The alde hyde may alternatively be of fossil origin. I.e. pro duced from a fossil material. In one embodiment, the aldehyde is prepared from methanol.

The "total weight" should in this specifica tion be understood, unless otherwise stated, as the weight of both the dry matter and the liquid part, e.g. water, of the binder composition.

The molar ratio of crosslinking agent to lig nin and tannin may be 0.9 - 1.7, or 1.0 - 1.6, or 1.1 - 1.7, or 1.2 - 1.6. In the current specification, the molar ratio (MR) is calculated as follows: MR = n(Fa)/(n(T)+n(L)) wherein n = the amount of substance in moles Fa = crosslinking agent T = tannin L = lignin

The amount of substance in moles are calculated as follows: n = M/m wherein

M = the molar mass of substance in g/mol m = the mass of substance in grams The following values are used for the above calcula tions in this specification:

M(tannin) = 320 g/mol (estimate based on literature and assumed chemical structure) M(lignin) = 180 g/mol (estimate based on literature and assumed chemical structure)

The weight ratio of tannin to lignin may be 0.05 - 1.0, or 0.1 - 0.43, or 0.15 - 0.33. The weight ratio of catalyst to lignin and tannin may be 0.20 - 0.37, or 0.22 - 0.35, or 0.26 - 0.33. The molar ratio of catalyst to lignin and tan nin may be 1.0 - 1.3, or 1.1 - 1.7, or 1.2 - 1.6. The amount of catalyst may beneficially affect the properties of the produced binder composition.

The catalyst may comprise a salt or a hydrox ide of an alkali metal or alkali earth metal. In one embodiment, the catalyst is selected from a group con sisting of sodium hydroxide, potassium hydroxide, bar ium hydroxide, and their combinations. In one embodi ment, the catalyst is sodium hydroxide.

The aqueous composition in step (i) may com prise or consist of or consist essentially of the lig nin in the presence of a catalyst.

Step (i) may comprise heating the aqueous composition comprising lignin in the presence of a catalyst at a temperature of 50 - 95 °C, 55 - 95 °C, or or 60 - 95 °C, or 65 - 90 °C, or 70 - 85 °C. Step (i) may be continued for 0.25 - 5 hours, or 0.25 - 4 hours, or 0.25 - 3 hours, or 0.5 - 2 hours, or 0.75 - 1.5 hours. During step (i) the lignin used is dis solved into the aqueous composition.

The temperature can be controlled during the production of the binder composition by cooling and/or heating the aqueous composition.

The aqueous composition in step (ii) may com prise or consist of or consist essentially of the aqueous composition from (i) and the crosslinking agent.

Step (ii) may comprise heating at a tempera ture of 70 - 90 °C, or at 75 - 80 °C. The heating in step (ii) may be continued until the aqueous composi tion has a viscosity value of 100 - 1200 cp, or 200 - 1000 cp, or 300 - 800 cP, or 400 - 500 cP, or 100 - 500 cP, or 400 - 800 cP, as measured at a temperature of at 25 °C. The viscosity can be measured at a tem perature of 25 °C by using a rotary viscometer (Digi tal Brookfield viscometer LVDV-II+ Pro; cone spindle). In one embodiment, step (ii) is continued for 1 - 8 hours, or 2 - 6 hours, or 3 - 5 hours.

In one embodiment, in step (ii), the molar ratio of crosslinking agent to lignin is 1.2 - 1.9, or 1.4 - 1.8, or 1.5 - 1.7. In one embodiment, heating in step (ii) is continued until the amount of free crosslinking agent, e.g. free formaldehyde, is at most 1 weight-%, or at most 0.5 weight-%, or at most 0.2 weight-%, based on the total weight of the aqueous composition in step

(ii). The amount of free crosslinking agent, e.g. free formaldehyde may be determined in accordance with standard EN-ISO 11402 and hydroxylamine hydrochloride procedure with the exception that the sample is dilut- ed in 20 ml of distilled water and 70 ml of 94 % etha nol. I.e. tannin may not be added to the aqueous com position from step (ii) before the desired level of free crosslinking agent, such as formaldehyde, is achieved. Step (ii) may comprise adding catalyst in a stepwise manner. I.e. further amount of catalyst in addition to the what is used in step (i) may be added during step (ii). The addition of the catalyst in a stepwise manner as the added utility of allowing lig- nin and crosslinking agent to pre-polymerize in a con trolled manner. In one embodiment, step (ii) comprises adding catalyst in a stepwise manner and heating the formed aqueous composition for pre-polymerizing lignin and crosslinking agent in a controlled manner. In one embodiment, tannin is mixed with the aqueous composition in step (iii) while keeping the temperature of the composition at 15 - 90 °C, or 20 - 80 °C, or 40 - 60 °C. In one embodiment, tannin is mixed with the aqueous composition in step (iii) while keeping the temperature of the composition at 55 - 95 °C, or 60 - 90 °C, or 70 - 80 °C. In one embodiment, tannin is mixed with the aqueous composition in step

(iii) while keeping the temperature of the composition at 15 - 60 °C, or 20 - 40 °C, or 15 - 25 °C, or 30 - 60 °C. The temperature of the aqueous composition from step (ii) may thus be cooled if needed before tannin is mixed thereto. In one embodiment, mixing in step (iii) is continued until a binder composition with a viscosity value of 150 - 800 cP, or 200 - 600 cp, is formed. In one embodiment, mixing in step (iii) is continued un- til a binder composition with a viscosity value of 150 - 500 cP, or 200 - 500 cP, or 250 - 400 cp, or 300 - 350 cP, is formed. In one embodiment, mixing in step (iii) is continued until a binder composition with a viscosity value of 500 - 800 cP, or 550 - 750 cp, or 600 - 700 cP, is formed. In one embodiment, step (iii) is continued for 0.15 - 6 hours, or 0.25 - 5 hours, or 0.5 - 3.5 hours.

In one embodiment, step (iii) comprises mix ing tannin with the aqueous composition from (ii) for polymerizing tannin with the pre-polymerized lignin and crosslinking agent until a binder composition with a predetermined viscosity value is formed. The tannin may thus be allowed to react or polymerize with the pre-polymerized lignin and crosslinking agent. In- creasing the temperature of the composition wherein tannin has been added enables the polymerization reac tions to proceed. Alternatively, the tannin may be simply mixed with aqueous composition comprising the pre-polymerized lignin and crosslinking agent. If mix- ing of tannin with the aqueous composition is conduct ed in step (iii) in lower temperature, e.g. in room temperature, tannin may not polymerize with the pre- polymerized lignin and crosslinking agent.

In the context of this specification, the term "lignin" may refer to lignin originating from any suitable lignin source. In one embodiment, the lignin is essentially pure lignin. By the expression "essentially pure lignin" should be understood as at least 70 % pure lignin, or at least 90 % pure lignin, or at least 95 % pure lignin, or at least 98 % pure lignin. The essentially pure lignin may comprise at most 30 %, or at most 10 %, or at most 5 %, or at most 2 %, of other components and/or impurities. Extractives and carbohydrates such as hemicelluloses can be mentioned as examples of such other components.

Further, in the context of this specification, the term "tannin" may refer to tannin originating from any suitable tannin source. In one embodiment, the tannin is essentially pure tannin. By the expression "essentially pure tannin" should be understood as at least 70 % pure tannin, or at least 90 % pure tannin, or at least 95 % pure tannin, or at least 98 % pure tannin. The essentially pure tannin may comprise at most 30 %, or at most 10 %, or at most 5 %, or at most 2 %, of other components and/or impurities.

The lignin may contain less than 30 weight-%, or less than 10 weight-%, or less than 5 weight-%, or less than 3 weight-%, or less than 2.5 weight-%, or less than 2 weight-% of carbohydrates. The tannin may contain less than 20 weight-%, or less than 15 weight- %, or less than 10 weight-% of carbohydrates. The amount of carbohydrates present in lignin or tannin can be measured by high performance anion exchange chromatography with pulsed amperometric detector (HPAE-PAD) in accordance with standard SCAN-CM 71.

The ash percentage of lignin may be less than 7.5 weight-%, or less than 5 weight-%, or less than 3 weight-%, or less than 1.5 weight-%. The ash percentage of tannin may be less than 10 weight-%, or less than 5 weight-%, or less than 3 weight-%. The ash content can be determined in the following manner: Dry solid content of the sample is determined first in an oven at 105°C for 3h. Ceramic crucibles are pre-heated to 700 °C for 1 hour and weight after cooling. A sample (1.5 g - 2.5 g) is weighted into a ceramic crucible. The crucible with a lip is put into a cold oven. Temperature of the oven is raised: 20-200 °C, 30 min => 200-600 °C, 60 min => 600-700 °C, 60 min. Burning is continued without the lid at 700 °C for 60 min. The crucible is let to cool in desiccator and few drops of hydrogen peroxide (H2O2, 30 %) is added to the sample followed by burning in the oven at 700 °C for 30 minutes. If there are still dark spots in the ash, the hydrogen peroxide treatment and burning is repeated. The crucible is cooled down and weighted. All weigh-in is done with a precision of 0.1 mg and after cooling in a desiccator.

Calculation of the results

Ash content % = (100 a x 100) / (b x c) wherein a = weight of the ash, g b = weight of the sample, g c = dry solids of the sample, %

Ash content of a sample refers to the mass that remains of the sample after burning and annealing, and it is presented as percentage of the sample's dry content.

In one embodiment, the lignin is technical lignin. In the context of this specification, the term "technical lignin" may refer to lignin that is derived from lignin in any biomass by any technical process. In one embodiment, technical lignin is lignin received from an industrial process.

The lignin used for preparing the binder com position may be selected from a group consisting of kraft lignin, steam explosion lignin, biorefinery lig nin, supercritical separation lignin, hydrolysis lig nin, flash precipitated lignin, biomass originating lignin, lignin from alkaline pulping process, lignin from soda process, lignin from organosolv pulping, lignin from alkali process, lignin from enzymatic hy drolysis process, and any combination thereof. In one embodiment, the lignin is wood based lignin. The lig nin can originate from softwood, hardwood, annual plants or from any combination thereof.

By "kraft lignin" is to be understood in this specification, unless otherwise stated, lignin that originates from kraft black liquor. Black liquor is an alkaline aqueous solution of lignin residues, hemicel- lulose, and inorganic chemicals used in a kraft pulp ing process. The black liquor from the pulping process comprises components originating from different soft wood and hardwood species in various proportions. Lig nin can be separated from the black liquor by differ ent, techniques including e.g. precipitation and fil tration. Lignin usually begins precipitating at pH values below 11 - 12. Different pH values can be used in order to precipitate lignin fractions with differ ent properties. These lignin fractions differ from each other by molecular weight distribution, e.g. Mw and Mn, polydispersity, hemicellulose and extractive contents. The molar mass of lignin precipitated at a higher pH value is higher than the molar mass of lig nin precipitated at a lower pH value. Further, the mo lecular weight distribution of lignin fraction precip itated at a lower pH value is wider than of lignin fraction precipitated at a higher pH value. The pre cipitated lignin can be purified from inorganic impu rities, hemicellulose and wood extractives using acid ic washing steps. Further purification can be achieved by filtration.

The term "flash precipitated lignin" should be understood in this specification as lignin that has been precipitated from black liquor in a continuous process by decreasing the pH of a black liquor flow, under the influence of an over pressure of 200 - 1000 kPa, down to the precipitation level of lignin using a carbon dioxide based acidifying agent, preferably car bon dioxide, and by suddenly releasing the pressure for precipitating lignin. The method for producing flash precipitated lignin is disclosed in patent ap plication FI 20106073. The residence time in the above method is under 300 s. The flash precipitated lignin particles, having a particle diameter of less than 2 ym, form agglomerates, which can be separated from black liquor using e.g. filtration. The advantage of the flash precipitated lignin is its higher reactivity compared to normal kraft lignin. The flash precipitat- ed lignin can be purified and/or activated if needed for the further processing.

The lignin may be derived from an alkali pro cess. The alkali process can begin with liquidizing biomass with strong alkali followed by a neutraliza- tion process. After the alkali treatment, the lignin can be precipitated in a similar manner as presented above.

The lignin may be derived from steam explo sion. Steam explosion is a pulping and extraction technique that can be applied to wood and other fi brous organic material.

By "biorefinery lignin" is to be understood in this specification, unless otherwise stated, lignin that can be recovered from a refining facility or pro- cess where biomass is converted into fuel, chemicals and other materials.

By "supercritical separation lignin" is to be understood in this specification, unless otherwise stated, lignin that can be recovered from biomass us- ing supercritical fluid separation or extraction tech nique. Supercritical conditions correspond to the tem perature and pressure above the critical point for a given substance. In supercritical conditions, distinct liquid and gas phases do not exist. Supercritical wa- ter or liquid extraction is a method of decomposing and converting biomass into cellulosic sugar by em ploying water or liquid under supercritical condi- tions. The water or liquid, acting as a solvent, ex tracts sugars from cellulose plant matter and lignin remains as a solid particle.

The lignin may be derived from a hydrolysis process. The lignin derived from the hydrolysis pro cess can be recovered from paper-pulp or wood-chemical processes.

The lignin may originate from an organosolv process. Organosolv is a pulping technique that uses an organic solvent to solubilize lignin and hemicellu- lose.

In one embodiment, the lignin consists of softwood Kraft lignin. In one embodiment, the lignin is softwood Kraft lignin. In one embodiment, the lig nin is a combination of softwood lignin and hardwood lignin. In one embodiment, at most 30 weight-%, or at most 25 weight-%, or at most 10 weight-%, or at most 5 weight % of the lignin originates from hardwood.

The weight average molecular weight of the softwood Kraft lignin may be 2500 - 9000 Da, or 3000 - 8000 Da, or 3500 - 7000 Da. The lignin, e.g. the Kraft lignin, may have a polydispersity index of 2.9 - 6.0, or 3.0 - 5.0, or 3.2 - 4.5.

The weight average molecular weight may be determined by using gel permeation chromatography (GPC) equipped with UV detector (280nm) in the follow ing manner: A sample is dissolved into 0.1 M NaOH. The sample solution is filtered with 0.45 micron PTFE fil ter. The measurement is performed in 0.1 M NaOH eluent (0.5 ml/min, T = 30 °C) using PSS MCX precolumn, 1000 A and 100 000 A columns, with sulfonated styrene- divinylbenzene copolymer matrix. The molecular weight distribution of the sample is calculated in relation to Na-polystyrene sulfonate standards (6 pieces) Mw 891 - 65400. Values Mw (weight average molecular weight) and Mn (number average molecular weight), pol- ydispersity index (PDI, Mw/Mn) are reported based on two parallel measurements.

The amount of alkali insoluble matter of the softwood Kraft lignin may be below 10 %, or below 5 %, or below 0.5 %. The amount of alkali insoluble matter may be determined in the following manner: Dry solid content of the sample is determined first in an oven at 105°C for 3h. 100 g of sample is dissolved into 277 g NaOH-water solution (pH 12 - 13) at mixed at 50 - 60 °C for 30 min. Solution is filtrated with a Buchner funnel through a glass filter. The residue on the fil ter is washed with 0.1M NaOH and finally with water. The filter with the residue is dried in an oven and then weighted. The amount of alkali insoluble matter is then calculated as follows:

Alkali insoluble matter, % = [weight of the filter with residue (dryed)(g)- weight of the filter] /

[weight of the sample (g) * dry solid content of the samples (%)]

The amount of condensed and syringul groups of softwood Kraft lignin may be below 3.0 mmol/g, or be low 2.5 mmol/g, or below 2.0 mmol/g when determined with 31P NMR. The amount of aliphatic OH groups of softwood Kraft lignin may be below 3,0 mmol/g, or be low 2.5 mmol/g when determined with 31P NMR. The amount of Guaiacyl OH of softwood Kraft lignin may be at least 1.5 mmol/g when determined with 31P NMR.

The measurements conducted with 31P NMR spec troscopy after phosphitylation can be used for quanti tative determination of functional groups (aliphatic and phenolic hydroxyl groups, and carboxylic acid groups). Sample preparation and measurement are per formed according to method by Granata and Argyropoulos (Granata, A., Argyropoulos, D., J. Agric. Food Chem. 1995, 43:1538-1544). Accurately weighted sample (~25 mg) is dissolved in N,N-dimethylformamide, and mixed with pyridine and internal standard solution (ISTD) endo-N-Hydroxy-5-norbornene-2 ,3-dicarboximide (e- HNDI). Phosphitylation reagent (200 mΐ) 2-chloro- 4,4,5,5-tetramethyl-l,3,2-dioxaphopholane is added slowly, and finally a 300 mΐ CDCI ₃ is added. NMR meas urements are performed immediately after addition of the reagent. Spectra are measured with spectrometer, equipped with a broadband detection optimized probe- head.

In one embodiment, the tannin used originates from any wood species. Tannin may originate from e.g. bark or heartwood. Quebracho tree, beech tree, oak tree, chestnut, pine, spruce, and acacia tree species are presented as examples of possible sources of tan nin.

In one embodiment, the tannin used originates from softwood bark. The tannin may be separated from softwood bark of debarking units in sawmills or pulp mills. The separation process can be combined with an ethanol extraction process, a hot water extraction process, a hot steam extraction process or a water- ethanol extraction process of softwood bark.

In one embodiment, the tannin is condensed tannin. Condensed tannin has a high dry content and is therefore suitable to be used in the method as dis closed in the current specification. The dry matter content of condensed tannin may vary between 40 - 100 % and is suitably between 60 - 90 % or between 70 - 80 %. Tannin with such dry matter content can easily be dispersed, whereby a good reactivity with the other reactant components is achieved. The tannin may also be hydrolysable tannin.

The tannin may have a weight average molecu lar weight (Mw) of 1500 - 5000 Da, or 2000 - 4500 Da, or 2500 - 4000 Da. The tannin may have a polydispersi- ty index of 2.8 - 1.0, or 2.6 - 1.3, or 2.4 1.5. In one embodiment, the method comprises dis persing tannin before mixing it with the aqueous com position. Tannin may be dispersed in an aqueous solu tion or an aqueous alkali solution before mixing the same with the aqueous composition. The alkali solution may be the same as used as the catalyst. The pH of the formed dispersion may be 4 - 10, or 7 - 9. The concen tration of tannin in the dispersion may be 30 - 50 %.

Tannin is rather reactive and thus may react rapidly with the crosslinking agent, such as formalde hyde, to form crosslinked polymeric structure. The in ventor surprisingly found out that the polymerization reaction may be controlled by adjusting the tempera ture of step (iii) and/or by simply adding tannin to the aqueous composition after lignin and crosslinking agent have been pre-polymerized in step (ii).

The precise order of combining and/or adding the components needed for the binder composition pro duction may vary depending e.g. on the required prop- erties of the formed binder composition. The choice of the sequence of combining and/or adding the required components is within the knowledge of the skilled per son based on this specification. The precise amount of the components used for producing the binder composi- tion may vary and the choice of the amounts of the different components is within the knowledge of the skilled person based on this specification.

When determining the order of mixing and com bining together the components to be used in the pro- duction of the binder composition, it is be taken into consideration that tannin is a more reactive component than lignin. Therefore, lignin is mixed and heated in the aqueous composition with the crosslinking agent before tannin is added. In this way it is ensured that lignin has sufficiently time to react with the cross- linking agent, e.g. the aldehyde. Further is disclosed an adhesive composition comprising the binder composition as disclosed in the current specification. The adhesive composition can, in addition to the binder composition, comprise one or more adhesive components selected from a group con sisting of other binders, extenders, additives, cata lysts and fillers. A binder is a substance, which is mainly responsible for creating the growing and cross- linking of polymer and thus assists in the curing of polymer systems. The binder may also provide adhesion properties to the binder composition. An extender is a substance, which assists the binder by adjusting phys ical properties for example by binding moisture. The additive can be a polymer or an inorganic compound, which assists in properties like filling, softening, reducing costs, adjusting moisture, increasing stiff ness and increasing flexibility. The catalyst is a substance, which usually boosts and adjusts the curing speed. By "substance" is herein to be understood as including a compound or a composition. The binder com position may serve as a binder, an extender, an addi tive, a catalyst and/or a filler in the adhesive com position.

The binder composition as well as the adhe sive composition may be used for gluing a wood prod uct. In one embodiment, the wood product is selected from a group consisting of a wood board, a wood ve neer, and a wood bar.

The method as disclosed in the current speci fication has the added utility of enabling the produc tion of a binder composition without the use of e.g. phenol, or any other compound selected from the class of phenols. The method as disclosed in the current specification has the added utility of enabling the production of a phenol-free binder composition having suitable properties, such a weight average molecular weight and viscosity, for industrial applications. Further, the binder composition as disclosed in the current specification has the added utility of provid ing water resistant, stabile adhesion and/or low for maldehyde emissions for the end product produced by using said binder composition.

EXAMPLES

Reference will now be made in detail to various embodiments. The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the embodiments based on the disclosure. Not all steps or features of the embodiments are discussed in detail, as many of the steps or features will be obvious for the person skilled in the art based on this specification.

EXAMPLE 1 - Preparing a binder composition In this example a lignin-tannin-formaldehyde binder composition was produced.

The following components and their amounts were used: water 100 % 1362kg

NaOH (I part) 50 % 420 kg kraft lignin 74 % 1460 kg

NaOH (II part) 50 % 320 kg formaldehyde 37.5 % 893 kg tannin 40 % (in alkaline solution) 545 kg

The percentages of the components (based on total weight) used in this example were the following:

NaOH about 8.1 % kraft lignin about 21.6 % tannin about 3.8 % formaldehyde about 6.70 %

The molar ratio of NaOH to lignin and tannin was 1.5. The molar ratio of formaldehyde to lignin and tannin was 1.70.

Firstly, water and the first part of NaOH were mixed at room temperature and heating of the same was started. When the temperature reached 72 °C, lig nin was added to the aqueous composition and the heat- ing and mixing of the same was continued for 30 minutes while keeping the temperature at about 80 - 90 °C. Then the temperature of the aqueous composition was allowed to cool to 65 °C, and the formaldehyde were added. Mixing and heating of the formed aqueous com position was continued for 1 hour, the second part of the NaOH was added in two portions and again mixing and heating was continued until the viscosity of the formed composition was 770 cP (as measured at 25 °C). Then the aqueous composition was cooled to a temperature of about 35 °C and tannin was added there to and the formed aqueous composition was mixed for about 45 minutes.

The formed binder composition had the follow- ing measured properties:

Solids, % 37,1 (3 hours at 105 C) pH 12.8

Viscosity, cp 420 (at 25 °C) Alkalinity, % 5.4

Free formaldehyde, % 0.13

EXAMPLE 2 - Preparing a binder composition

In this example a lignin-tannin-formaldehyde binder composition was produced. The following components and their amounts were used: water 100 % 1241 kg NaOH (I part) 50 % 470 kg kraft lignin 65 % 1592 kg

NaOH (II part) 50 % 170kg formaldehyde 40.57 % 604 kg

NaOH (III part) 50 % 60kg tannin 40 % (in alkaline solution) 922 kg

The percentages of the components (based on total weight) used in this example were the following:

NaOH about 7.0 % kraft lignin about 20.7 % tannin about 6.9 % formaldehyde about 4.9 %

The molar ratio of NaOH to lignin and tannin was 1.3. The molar ratio of formaldehyde to lignin and tannin was 1.2.

Firstly, water and the first part of NaOH were mixed at room temperature and heating of the same was started. When the temperature reached 70 °C, lig nin was added to the aqueous composition and the mix ing and the heating of the same were continued for 30 minutes while keeping the temperature at about 90 °C. Then the temperature of the aqueous composition was allowed to cool to 60 °C, and formaldehyde was added.

Mixing and heating of the formed aqueous com position was continued for 44 minutes at a temperature of about 70 - 76 °C. Then part of the NaOH II was add ed, mixing and heating continued at a temperature of about 75 - 80 °C for 70 minutes. Then the second part of the NaOH II was added and mixing and heating was continued for 2 hours 14 minutes at a temperature of about 70 - 75 °C. The viscosity of the formed composi tion reached about 500 cp (as measured at 25 °C) after which tannin was added. Mixing of the aqueous composi tion was continued and the temperature was raised from about 75 °C to about 90 °C until the viscosity was about 290 cP. Then the composition was cooled to 30 °C.

The formed binder composition had the following meas ured properties:

Solids, % 35.3 (3 hours at 105 °C) pH 13.1

Viscosity, cp 280 (at 25 °C) Alkalinity, % 5.1

Free formaldehyde, % 0.03 phenols, GC weight-% <0.010 water tolerance 900%

Example 3 - Producing a plywood product

The binder composition produced in example 2 was used to produce an adhesive composition. The adhe sive composition was formed by mixing binder composi tion with wheat flour and limestone (1:1) to arrive to the target viscosity of 70-100 second FC 6mm at 25 °C. In the adhesive composition 3 % of sodium carbonate was used a hardener.

The formed adhesive composition was then used to produce a plywood product of wood veneers. The wood veneers having the thickness of 1.5 mm were joined to gether by the adhesive composition for forming 4.5 mm thick plywood panels. The dry matter content of the adhesive composition was between 35 and 50 %. The wood veneers with the adhesive composition were pressed by hot-pressing technique at a temperature between 130 - 170 °C. The adhesive composition was simultaneously cured. The adhesive composition was found suitable for gluing wood veneers together and thus for manufactur ing plywood. Results showed that the gluing effect of the adhesive composition was sufficiently good for gluing wood veneers fulfilling the requirements of Bonding class 3 according to EN 314-1 and EN 314-2 standards and formaldehyde emission class- El measured according to EN ISO 12460-3. 0 Table 1. Measurements results

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea may be implemented in various ways. The embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims. 0 The embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A method, a binder composition, an adhesive composition, or the uses, disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or 0 all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of those items. The term "comprising is used in this specification to mean including the feature(s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts.