Method for preparing a viscosity-controlled lignin-phenol-formaldehyde resin

Abstract

The present invention relates to a method for solubilizing a lignin material, controlling its molecular weight to prevent a potential decrease in its reactivity, and thereby controlling the viscosities of both the lignin material and the resulting condensate. This method comprises the step of dissolving lignin under acidic conditions using a phenol first fraction for producing a final resin product, and the step of performing condensation and crosslinking in parallel with the methylolation under alkaline conditions.

Description

Technical Field

[0001] The present invention relates to a method for producing a lignin-phenol-formaldehyde resin having a controlled viscosity. Further, the present invention relates to a resin produced in this way.

Background Art

[0002] Phenol-formaldehyde resins (or PF resins) are widely used as a group of adhesives derived from petroleum and natural gas and are suitable for a wide range of reconstituted wood products such as plywood, laminated veneer lumber, fiberboard, particle board, as well as decorative boards and molding compounds. There is a wide interest in replacing some of the phenol in the resin formulation in order to provide more sustainable alternatives.

[0003] Since lignin is a phenol-based natural compound, the use of lignin is a preferred alternative for replacing phenol in such resins, thereby producing lignin-phenol-formaldehyde resins (LPF resins). Generally, lignin is solubilized before use in resin production and may in some cases be further activated by, for example, phenolysis or depolymerization. It is important to select suitable conditions for these processes in order to affect the reactivity between lignin and the other components of the resin.

[0004] The solubility of lignin can be improved in various ways. For example, lignin can be solubilized in an organic solvent such as an alkali or methanol. In Patent Document 1 (US 20190048192 A1), lignin was dissolved in methanol under alkaline conditions. However, methanol should be avoided in such industrial processes, among other reasons, because of its flammability.

[0005] Lignin has been activated towards formaldehyde by phenolation in the past. Patent Document 2 (WO 2015079106 A1) describes a method of reacting lignin with phenol under neutral or alkaline conditions. The option of mixing the reactants at pH < 8 has also been discussed, but since an alkali is added, the pH does not reach acidic levels. However, neutral or alkaline conditions are not suitable for the use of all types of lignin, and especially due to the condensation of lignin and / or the formation of poorly soluble aggregates, it can result in a resin with high viscosity. As a result, the reactivity of lignin towards formaldehyde deteriorates and the resin viscosity increases.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The inventors have surprisingly found that by changing the conditions for lignin solubilization so that the reactivity of lignin in the subsequent reaction with formaldehyde is not impaired by harmful self - condensation reactions, the viscosity of the resin is controlled, resulting in a remarkable improvement in the properties of the resin and enabling the provision of a wider range of suitable lignin types.

Means for Solving the Problems

[0008] The present invention is defined by the features of the independent claims. Some specific embodiments are defined by the dependent claims.

[0009] According to a first aspect of the present invention, there is provided a method for solubilizing a lignin material, preventing a potential decrease in its reactivity, and as a result, maintaining its suitability for use in the production of resins.

[0010] According to a second aspect of the present invention, there is provided a method for producing a lignin-phenol-formaldehyde resin using the solubilized lignin material.

[0011] According to a third aspect of the present invention, there is provided a method for producing a lignin-phenol-formaldehyde resin using a wide range of suitable lignin starting materials derived from different types of biomass and fractionation processes.

[0012] According to a further aspect of the present invention, there is provided a novel lignin-phenol-formaldehyde resin having advantageous properties.

[0013] Thus, the present invention is based on preparing a solubilized lignin material and using it as a partial replacement of the phenol in a phenol-formaldehyde resin. Typically, the aim is to replace 30 - 50% of the phenol in such a resin.

[0014] The solubilization aims to prevent the self-condensation of lignin, which would increase the molecular weight of lignin, decrease its reactivity towards formaldehyde, and cause the resin viscosity to rise to an undesirable level.

[0015] Thus, the present invention involves the dissolution of lignin under acidic conditions using phenol, preventing the condensation of lignin molecules or the formation of insoluble aggregates having a high molecular weight. The dissolution by this method results in lignin having sufficient reactivity towards formaldehyde, regardless of the type of lignin used. At least kraft lignin, soda pulp lignin, lignosulfonate, organosolv lignin, and ethanol process lignin are suitable for use in the method of the present invention.

[0016] Fenolation has been described in the past as a method of activating lignin, but the present invention is based on an alternative procedure using phenol to provide dissolution of lignin and prevent a potentially detrimental increase in the molecular weight of lignin prior to reaction with formaldehyde.

[0017] The inventors have found that significant advantages are achieved by using the present invention when the dissolution of lignin is carried out under phenol-induced acidic conditions. In the dissolution step, no additional acid is required other than the components normally used in resin production. Under such phenol-induced acidic conditions, a decrease in the reactivity of lignin, such as self-condensation or aggregate formation, which has been shown to occur with some lignin raw materials under neutral or alkaline conditions, is prevented. As a result, an undesirable increase in the final resin viscosity due to an overly high molar mass of lignin is also prevented. Without wishing to be bound by a particular theory, it is hypothesized that in addition to acting as a solvent, phenol molecules may act as a physical barrier between lignin molecules that could otherwise condense into high molecular weight lignin structures with reduced reactivity towards formaldehyde and increased resin viscosity.

[0018] Based on investigations of isolated lignin, we further hypothesize, again without wishing to be bound by a particular theory, that acidic conditions also bring about beneficial changes to the lignin structure, such as cleavage of alkyl-aryl ether bonds between lignin units, generating new phenolic hydroxyl groups and reducing its molar mass, thereby increasing its reactivity towards formaldehyde, while non-essential elements of lignin, such as ester groups in organosolv lignin, are hydrolyzed and removed, leaving lignin with a higher phenolic unit content on a mass basis.

[0019] Formaldehyde reacts more efficiently, resulting in a final resin formulation with a low content of unreacted formaldehyde, which is suitable for all kinds of applications and also for applications where there are regulations regarding formaldehyde emissions.

[0020] The resulting resin formulation has a controlled viscosity, which is achieved preferably without using separately added viscosity-reducing solvents such as methanol that are to be avoided in industrial processes. Thus, the number of reagents and solvents added to the mixture in resin preparation is minimized, and the number of reagents and solvents that need to be separated from the mixture after the reaction is also minimized. Instead, phenol can be used to dissolve lignin, and since phenol is a component of the final resin, it is always added to the reaction mixture in at least one step of the resin preparation process.

[0021] In particular, the acidic solution enables better control of the viscosity of the final lignin-phenol-formaldehyde mixture and the final resin product. These advantages can be further emphasized by using preferred conditions such as temperature and pressure in the steps of the method.

[0022] Since the viscosity can be controlled, it is also possible to introduce a large amount of lignin into the final resin formulation without causing a decrease in reactivity or a decrease in resin performance. Also, the dry matter content of the final resin formulation can be increased.

[0023] These advantages are particularly emphasized in applications where a low viscosity is required, such as impregnated paper.

Brief Description of the Drawings

[0024]

Figure 1

Modes for Carrying Out the Invention

[0025] The present invention relates to a method for producing a lignin-phenol-formaldehyde resin, the method comprising the following steps, namely, · A step of dissolving a lignin material at a temperature raised to a first phenolic fraction with a pH of 0.5 to 3.9 to obtain a dissolved acidic lignin, which is achieved without potentially harmfully increasing the molar mass of the lignin, the step of dissolving the lignin material, · A step of preparing a lignin-phenol-formaldehyde mixture and raising the pH of the obtained lignin solution to >9 and administering a first fraction of formaldehyde to bring about a methylolation reaction, wherein the obtained mixture is also called a methylolated lignin-phenol mixture, the step of administering the first fraction of formaldehyde, · A step of forming a lignin-phenol-formaldehyde condensation mixture from the methylolated lignin-phenol mixture by adjusting the pH to ≧9.5 and stirring the mixture, optionally including the sub-steps of adding a second fraction of phenol, confirming that the pH is ≧9.5, stirring the mixture, and adding a second fraction of formaldehyde, the step of forming the lignin-phenol-formaldehyde condensation mixture, · A step of crosslinking the components of the condensation mixture to obtain a lignin-phenol-formaldehyde resin, Comprising, The first fraction of phenol is 25 to 100 w-% of the total amount of phenol used in the method, and the first fraction of formaldehyde is 50 to 100 w-% of the total amount of formaldehyde used in the method.

[0026] The above addition of the second fraction of phenol and the second fraction of formaldehyde is optional when the first fraction of phenol and the first fraction of formaldehyde include 100% of the total amounts of phenol and formaldehyde used in the method. When the first fraction of phenol includes less than 100% of the total amount of phenol, the condensation mixture is formed at a stage including the addition of the second fraction of phenol. Similarly, when the first fraction of formaldehyde includes less than 100% of the total amount of formaldehyde, the condensation mixture is formed in a step including the addition of the second fraction of formaldehyde.

[0027] Figure 1 shows the main steps of the above method, where dissolution 1 is the above acid dissolution, dissolution 2 involves raising the pH to a level >9, the methylolation involves the next addition of formaldehyde to the lignin-phenol solution, and the condensation involves the final step of the above method.

[0028] The lignin material can be selected from any lignin, such as organosolv lignin, kraft lignin, soda pulp lignin, lignosulfonate, or enzymatic hydrolysis process lignin. Preferably, it is selected from technical softwood, hardwood, or non-wood lignin obtained from lignin-containing biomass such as wood sources and non-wood agricultural residues or perennial plants, and more preferably from organosolv lignin, ethanol lignin, or kraft process lignin extracted from these lignin-containing biomasses.

[0029] In one embodiment, the lignin material is selected from hardwood lignin. In another embodiment, the lignin material is selected from organosolv lignin. The lignins of these embodiments have the most advantageous initial molecular weights and are thus particularly suitable for use in the preparation of resins with low molecular weights and advantageous viscosities. Therefore, the lignin material is preferably selected from lignins having an initial molecular weight (before use in the dissolution step) of <6000 g / mol, more preferably <5000 g / mol, even more preferably 4500 g / mol or less, and most preferably 4300 g / mol or less.

[0030] Examples of lignin sources include common softwood species such as spruce and pine, common hardwood species such as eucalyptus and oak, and common non-wood species such as bagasse, bamboo, wheat straw, rye straw, barley straw, rice straw, and miscanthus (typically in the form of grass-type agricultural residues or perennial plants).

[0031] The phenol used in this method is typically unsubstituted phenol. Other phenolic compounds such as cresol and tannin are also suitable for use, but unsubstituted phenol is the most convenient to use as it is readily available.

[0032] As indicated above, the first phenol fraction is 25 to 100 w-% of the total amount of phenol used in the method. Preferably, the first phenol fraction is about 50 w-% of the total amount of phenol used in the method. Similarly, the first formaldehyde fraction is 50 to 100 w-% of the total amount of formaldehyde used in the method, preferably about 75 w-%.

[0033] In one embodiment of the invention, the dissolution of the lignin material using the first phenol fraction is preferably carried out in an aqueous solution having a water content of > 30 wt-%, more preferably 40 to 60 wt-%, thus avoiding the addition of an organic solvent that would require separation from the final resin mixture. The water in the solution prevents the phenolation of lignin during the dissolution step, which could lead to an undesirable increase in the viscosity of the material. Preferably, a lignin content of 20 to 85 wt-%, more preferably 25 to 80 wt-%, or 25 to 60 wt-%, most preferably 30 to 60 wt-% is used, based on the total weight of lignin and phenol in the final resin (thus representing the total amount of phenol substitution in the resin).

[0034] Typically, the dissolution is carried out at a total dry matter content of 40 to 60 w-%.

[0035] The pH of the reaction mixture during the phenol-based dissolution step is typically adjusted using the phenol dosage to bring the pH of the solution to the desired level. Optionally, a small amount of additional acid, preferably a mineral acid such as sulfuric acid, can be used. However, usually, the phenol alone provides sufficient acidity.

[0036] A suitable phenol dosage can be, for example, in the acidic lignin dissolution stage, such that the mass ratio of lignin to phenol is >1.0, preferably 1.8 - 2.5, more preferably about 2.0.

[0037] The pH during acidic dissolution is, as shown above, 0.5 - 3.9, the preferred pH range is 0.5 - 3.5, and the more preferred range is 2.0 - 3.0. When the pH stabilizes after the addition of phenol, it typically reaches a level of 2.5 - 2.8.

[0038] An elevated temperature showing a temperature above room temperature (25 °C) is typically used, preferably a temperature of 50 - 90 °C, more preferably 70 - 80 °C. Similarly, an appropriate residence time is selected such that the reaction is completed. For example, the residence time is 30 - 120 minutes, preferably 30 - 60 minutes.

[0039] Throughout this method, unless otherwise specified, the preferred pressure is atmospheric pressure.

[0040] In one embodiment of the present invention, the next step of the method preferably includes raising the pH of the dissolved acidic lignin solution to >9, particularly a pH of 9.5 - 10, using an alkali which can be, for example, sodium hydroxide. After the addition of the alkali, the first fraction of formaldehyde is preferably added slowly or over a period of 45 - 75 minutes, or about 60 minutes, preferably while raising the temperature, thus promoting the desired methylolation reaction. A suitable temperature can be 60 - 75 °C, preferably about 70 °C. The elevated temperature is maintained under constant stirring until the reaction is completed, for example, up to 30 minutes, but usually it is sufficient to maintain the temperature for 10 - 15 minutes.

[0041] The condensation mixture is prepared from the methylolated lignin - phenol mixture using method steps including at least pH adjustment and stirring of the mixture.

[0042] In one embodiment of the present invention, the condensation mixture is first prepared by adding a second fraction of phenol to the methylolated lignin - phenol mixture while stirring, such that the pH of the mixture is ≧ 9.5, preferably 9.5 - 10. Thereafter, the mixture is stirred and a second fraction of formaldehyde is added, usually at a slow pace or over a period of 45 - 70 minutes, or about 60 minutes, while maintaining the temperature, for example, at 60 - 75°C.

[0043] Preferably, a molar ratio of formaldehyde to phenol of 1 - 2, preferably 1.5 - 1.7, is used relative to the total amount of phenol and formaldehyde used in this method, and the amount of formaldehyde depends on the content of formaldehyde - reactive sites on the lignin used.

[0044] The final cross - linking step to form the resin from this condensation mixture can be achieved by raising the temperature of the reaction mixture to a temperature of preferably 75 - 95°C, more preferably 85 - 95°C, and maintaining the elevated temperature for 15 - 35 minutes, preferably 20 - 30 minutes.

[0045] In an exemplary embodiment, the resin is prepared using organic solvent lignin from straw. As a first step, lignin, water, and phenol (an amount corresponding to 50% of the total phenol content in the resulting resin) are mixed. If the pH is not adjusted, the pH settles to about 2.5. This dissolution mixture is mixed at 70 °C for about 1 hour. In the next step, an alkali is added to adjust the pH to 10, and the resulting alkali mixture is mixed again at 70 °C for about 1 hour. In the next methylolation step, formaldehyde is added over about 1 hour at a temperature of 70 °C (50% of the total formaldehyde content in the final resin). The mixture is then cooled, and mixing is continued for an additional 10 minutes. The final condensation step consists of the following consecutive steps: 1) adding the remaining phenol, 2) adjusting the pH to 9.5 - 10, 3) adding the remaining formaldehyde over about 1 hour at 70 °C, 4) raising the temperature to 90 °C and maintaining that temperature for about 1 hour, and 5) cooling the resulting product to room temperature.

[0046] Using the steps of the method described herein for producing a lignin - phenol - formaldehyde resin, particularly using the acidic dissolution step of lignin, and using the order of the steps described allows for high efficiency of the formaldehyde reaction and control of the viscosity of the condensation mixture, or the resin, typically both.

[0047] Accordingly, the present invention also relates to a lignin - phenol - formaldehyde resin produced using the method described herein. Such a resin typically has a viscosity of <550 cP, preferably <350 cP, most preferably <200 cP when measured at 20 °C.

[0048] The embodiments of the present invention disclosed are not limited to the specific structures, process steps, or materials disclosed herein, but are to be extended to their equivalents that would be recognized by those of ordinary skill in the relevant art. It should also be understood that the terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting.

[0049] Throughout this specification, reference to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. For example, when referring to a numerical value using terms such as about or substantially, the exact numerical value is also disclosed.

[0050] As used herein, multiple items, structural elements, components, and / or materials may sometimes be presented for convenience in a common list. However, these lists should be construed as if each member of the list were individually identified as a separate and distinct member. Further, various embodiments and examples of the present invention may be referred to herein along with alternatives for the various components thereof. Such embodiments, examples, and alternatives should not be construed as factual equivalents of one another, but rather as separate and autonomous representations of the present invention.

[0051] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In this specification, numerous specific details are provided to provide a thorough understanding of the embodiments of the present invention. However, those of ordinary skill in the relevant art will recognize that the present invention may be practiced without one or more of the specific details.

[0052] The above embodiments illustrate the principles of the present invention in one or more specific applications. However, it will be apparent to those skilled in the art that numerous changes in form, usage, and details of implementation can be made without departing from the principles and concepts of the present invention and without exercising inventive faculty. Therefore, the present invention is not intended to be limited except as defined by the claims set forth below.

[0053] The following non-limiting examples are intended merely to illustrate the advantages obtainable with embodiments of the present invention.

Example

[0054] (Example 1) Preparation of the resin of the present invention Lignin-phenol-formaldehyde resins (LPF resins) were prepared using organic solvent lignin from wheat straw according to four different recipes (LPF1-LPF4). LPF1 and LPF2 were prepared according to the present invention, with the first stage of preparation being dissolution under acidic conditions, and LPF3 and LPF4 were reference resins prepared by carrying out dissolution 1 under alkaline conditions.

[0055] LPF1 differs from LPF2 particularly in the pH level used for acidic dissolution. LPF1 was prepared by adding a mineral acid, and thus, a lower pH is obtained after dissolution 1 than when adding phenol to LPF2. What particularly differentiates LPF3 from LPF4 is that LPF4 was prepared without adding phenol during the dissolution stage. The main steps of the recipes are shown in FIG. 1 and the details are shown in Table 1.

[0056] Table 1 Preparation of resins LPF1 and LPF2 according to the present invention and reference resins LPF3 and LPF4

Table 1

[0057] (Example 2) Evaluation of the molecular weight and viscosity of the reaction mixture and the resin The dissolved mixture obtained after stage 2 of Table 1 above and the finished resin obtained after stage 4 were further analyzed. In particular, the molecular weight of the dissolved mixture and the resin viscosity were measured. The results are shown in Table 2 below.

[0058] Table 2 Influence of Dissolution Conditions on the Molecular Weight of Dissolved Lignin and the Viscosity of LPF Resin

Table 2

[0059] As the results show, the presence of phenol in dissolution 1 at the same pH level as dissolution 1 affects both the molecular weight of the lignin after dissolution and the viscosity of the final resin.

[0060] As described above, these results suggest a hypothesis that, in addition to the phenol molecules acting as a solvent, they also act as a physical barrier between lignin molecules that could otherwise reduce the reactivity towards formaldehyde and condense into higher molecular weight lignin structures giving a higher resin viscosity.

[0061] Furthermore, acidic conditions bring about beneficial changes to the lignin structure such as cleavage of the alkyl-aryl ether bonds between lignin units, reducing the molar mass and increasing the content of phenolic hydroxyl groups, thereby increasing the reactivity of the lignin towards formaldehyde.

[0062] (Example 3) Evaluation of the Molecular Weight and Viscosity of Reaction Mixtures and Resins Prepared from Various Raw Materials Lignin-phenol-formaldehyde resin (LPF resin) was prepared using lignin raw materials according to the LPF2 recipe described in Table 1 of Example 1, and the pH in the first stage (S1) was 2.5 - 3.7 for all lignins.

[0063] The molecular weight was measured for both the starting lignin and the stage 4 product. Similarly, the viscosity was also measured for the stage 4 (S4) product. The results are shown in Table 3 below.

[0064] Table 3 Molecular weights of lignin and LPF resin and resin viscosity

Table 3

[0065] As shown by these results, the method for producing the LPF resin of the present invention is very suitable for use with various lignins and can provide a resin with low viscosity while controlling the molecular weights of the lignin component and the condensation product.

[0066] In order to provide a low-viscosity lignin-phenol-formaldehyde resin, it has been found advantageous to use in the method reagents (lignin, phenol and formaldehyde) having low molecular weights and reacting with condensation products having low molecular weights. This was achieved using the reaction conditions of the LPF2 recipe described above.

[0067] By using the above-mentioned reagents and the reaction conditions of the present invention, there is also a tendency to obtain an LPF resin containing a phenol component composed of 10 - 25% by mass of phenol (MW 94 Da) and low molecular weight methylolated and condensed products of phenol and formaldehyde (MW < 400 Da).

[0068] These aforementioned low Mw methylolated and condensed products typically consist of one or more of the following: 2-hydroxymethylphenol, 4-hydroxymethylphenol, 2,4,6-tris(hydroxymethyl)phenol; 2,6-bis(hydroxymethyl)phenol, 2,4-bis(hydroxymethyl)phenol, 4,4'-bis(hydroxyphenyl)methane, 2-(hydroxymethyl)phenol hemiformal, 4-(hydroxymethyl)phenol hemiformal, 3,3'-bis(hydroxymethyl)-4,4'-bis(hydroxyphenyl)methane, 3,5-bis(hydroxymethyl)-4,4'-bis(hydroxyphenyl)methane, 3,5'-bis(hydroxymethyl)-2,2'-bis(hydroxyphenyl)methane, 3,5-bis(hydroxymethyl)-2,2'-bis(hydroxyphenyl)methane, 3-hydroxymethyl-2,2'-bis(hydroxyphenyl)methane, 3-hydroxymethyl-4,4'-bis(hydroxyphenyl)methane, 2,6-bis(hydroxymethyl)phenol (mono) hemiformal, 2,4-bis(hydroxymethyl)phenol (mono) hemiformal, 2,4-bis(hydroxymethyl)phenol (di) hemiformal, 2,4,6-tris(hydroxymethyl)phenol (mono) hemiformal, 2,4,6-tris(hydroxymethyl)phenol (di) hemiformal, 2,4,6-tris(hydroxymethyl)phenol (tri) hemiformal, 3,3',5,5'-tetrakis(hydroxymethyl)-4,4'-bis(hydroxyphenyl)methane, 3,3',5,5'-tetrakis(hydroxymethyl)-2,2'-bis(hydroxyphenyl)methane, tris(hydroxymethyl)-bis(hydroxyphenyl)methane.

[0069] Referring to Table 3, it can be seen that more than 50% of the molecules in such a resin product mixture have a molecular weight of 2500 Da or less in this way.

Industrial Applicability

[0070] The method of the present invention for manufacturing lignin - phenol - formaldehyde resins provides a resin with a controlled viscosity in which part of the phenol is replaced by lignin in order to provide a more sustainable alternative. Thus, in the method of the present invention, a larger amount of lignin can be introduced into the final resin formulation compared to resins existing on the market without causing a decrease in reactivity or resin performance.

[0071] In particular, the formaldehyde component of the lignin - phenol - formaldehyde resin reacts efficiently with the solubilizing mixture and leaves no free formaldehyde in the final resin formulation. Such resins with a low content of unreacted formaldehyde are particularly suitable for applications where there are regulations regarding formaldehyde emissions.

[0072] Due to the advantageous viscosity achieved, the resins produced as described herein are particularly suitable for applications such as those where a low viscosity resin is required for impregnating paper.

[0073] [List of cited references] ·US 20190048192 A1 ·WO 2015079106 A1

Claims

1. A method for producing a lignin-phenol-formaldehyde resin, comprising: dissolving the lignin material in a phenolic first fraction at a pH of 0.5 to 3.9 at elevated temperature to obtain dissolved acidic lignin; - providing a lignin-formaldehyde mixture and increasing the pH of the resulting lignin solution to >9 and dosing with a first fraction of formaldehyde to effect a methylolation reaction; forming a lignin-phenol-formaldehyde condensation mixture from the methylolated lignin-phenol-formaldehyde mixture by adjusting the pH to ≧9.5 and stirring the mixture, optionally comprising the substeps of adding a second fraction of phenol, ensuring the pH is ≧9.5, stirring the mixture, and adding a second fraction of formaldehyde; - cross-linking the components of the condensation mixture to obtain a lignin-phenol-formaldehyde resin; Equipped with wherein the phenol first fraction is 25 to 100 wt. % of the total amount of phenol used in the process and the formaldehyde first fraction is 50 to 100 wt. % of the total amount of formaldehyde used in the process.

2. 10. The method of claim 1, wherein the lignin material is selected from technical softwood, hardwood, or non-wood lignins obtained from lignin-containing biomass such as wood sources, agricultural residues, e.g., straw, or perennial plants, and preferably selected from kraft, ethanol, or organic solvent lignins.

3. 2. The method of claim 1, wherein the lignin material is dissolved in the phenolic first fraction in an aqueous solution, using a lignin content of 20-85 wt%, preferably 25-80 wt%, or 25-60 wt%, most preferably 30-60 wt%.

4. 10. The method of claim 1, wherein the first fraction of phenol is about 50 wt. % of the total amount of phenol used in the method.

5. 10. The method of claim 1, wherein the first fraction of formaldehyde is about 75 wt. % of the total amount of formaldehyde used in the method.

6. 10. The method of claim 1, wherein the lignin material is dissolved in a dose of phenol to bring the pH of the solution to the desired level, preferably with a lignin to phenol mass ratio of >1.5, more preferably between 1.8 and 2.5, and most preferably about 2.

0.

7. 10. The method of claim 1, wherein the step of dissolving the lignin material in phenol is carried out at a pH of 2 to 3.

8. 2. The method of claim 1, wherein the step of dissolving the lignin material in phenol is carried out at a temperature of from 50 to 90°C, more preferably from 70 to 80°C, with a residence time typically of from 30 to 120 minutes, preferably from 30 to 60 minutes.

9. 2. The method of claim 1, wherein the pH of the solution of dissolved acidic lignin is raised to pH > 9, most preferably pH 9.5-10, using alkali, preferably sodium hydroxide.

10. 2. The method of claim 1, wherein the step of reacting the alkaline lignin solution with the first fraction of formaldehyde is carried out by adding formaldehyde to a solution having a pH > 9, then raising the temperature, preferably to a temperature of 60-75°C, and maintaining the temperature for up to 30 minutes, preferably 10-15 minutes.

11. 2. The method of claim 1, wherein a molar ratio of formaldehyde to phenol of 1 to 2, preferably 1.5 to 1.7, more preferably about 1.6, is used relative to the total amount of phenol and formaldehyde used.

12. 2. The method of claim 1, wherein the condensation mixture is obtained by first adding the second fraction of phenol to a lignin-formaldehyde mixture until the pH of the mixture is ≧9.5, preferably 9.5-10, and then adding the second fraction of formaldehyde while typically maintaining the temperature of the mixture at 60-75°C.

13. 2. The method of claim 1, wherein the crosslinking is achieved by raising the temperature of the reaction mixture, preferably to a temperature of 75-95°C, and maintaining the elevated temperature for 15-35 minutes, preferably 20-30 minutes.

14. A lignin-phenol-formaldehyde resin produced using the method of any one of claims 1 to 13.

15. 15. The resin of claim 14 having a viscosity of <550 cP when measured at 20°C.

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