WO2010046542A1

WO2010046542A1 - Method for preparing modified fiber products

Info

Publication number: WO2010046542A1
Application number: PCT/FI2009/050858
Authority: WO
Inventors: Jaakko Hiltunen; Terhi Hakala; Tiina Pursula
Original assignee: Oy Keskuslaboratorio - Centrallaboratorium Ab
Priority date: 2008-10-24
Filing date: 2009-10-26
Publication date: 2010-04-29
Also published as: FI20086013L; FI20086013A0

Abstract

The present invention relates to a method for modifying lignocellulosic material having phenolic groups or derivatives of phenolic groups. The method comprises the steps of oxidizing the phenolic groups or the phenoxy derivative groups of the lignocellulosic material to quinines, quinone derivatives or other carbonyl groups, and contacting the oxidized fibre material with a biochemical agent comprising a reactive nucleophilic group, said biochemical agent forming a covalent bond with the lignocellulosic material. The invention relates also to modified lignocellulosic products.

Description

METHOD FOR PREPARING MODIFIED FIBER PRODUCTS

Background of the Invention

Field of the Invention

The present invention relates to a method for preparing novel modified fibre products. In particular the present invention relates to a method for grafting lignocellulosic fibre products with biochemical compounds. The invention relates also to the modified products.

Description of Related Art

Fiber modification is a potential technology for tailoring fibers for different use. Enzymatic technologies have developed substantially to a point where cost-effective highly selective fiber modification applications are becoming a reality. These technologies could also enable new products.

Laccase-based fiber grafting for creating novel fiber properties has been studied in many applications. Functionalities such as acidity, conductivity, hydrophobicity, charge, antibacterial properties, hydrophilicity, UV-resistance and barrier properties have been targeted with laccase-aided grafting of fibers, for example WO 2005/060332 and Buchert et al. 2005. Laccase immobilization on fibers to produce active paper has also been suggested (Viikari et al. 2007). It is not based on grafting of any radicalized compounds, but attaching the enzyme on paper surfaces.

The existing grafting method is based on a radical coupling between the oxidized lignin structures and the chemicals that are reactive with laccase e.g. are substrates of laccase (Buchert et al. 2005).

However, the existing methods are not yet in commercial use. Since the prior art grafting chemicals must be reactive with laccase, the amount of suitable compounds is limited. These chemicals are also quite expensive. Furthermore, radical coupling may occur more between the chemicals than between the chemical and the fiber, which results in low yields. Further drawback is that grafted compounds can be removed by laccase via further oxidations.

There is thus still a need for novel methods of introducing new properties directly to fibres. Such properties include, for example, conductivity, charge, hydrophobicity and color.

Summary of the Invention

It is an aim of the present invention to eliminate at least some problems of the prior art and to provide a novel method of functionalizing fibres, in particular lignocellulosic fibres derived from plant materials.

It is a particular aim of the present invention to prepare lignocellulosic fibres with novel functional properties.

The invention is based on the idea of producing modified fibrous products with novel properties. The lignocellulosic material is allowed to react with an oxidizing agent capable of oxidizing phenolic groups or derivatives of phenolic groups to quinines, quinone derivatives or other carbonyl groups. The oxidation can be carried out either enzymatically or chemically. The oxidized lignocellulosic material is then allowed to react with biochemical compounds having a reactive, preferably strong nucleophilic group, such as amine group or thiol group. Furthermore the biochemical compounds having a reactive, preferably strong nucleophilic group can be linked to other chemical or biochemical compounds useful for modifying the properties of fibres.

More specifically, the method of the present invention is mainly characterized by what is stated in the characterizing part of claim 1

The product of the present invention is mainly characterized by what is stated in the characterizing part of claim 14.

Significant advances are achieved with the present invention. The present invention can be used for preparing novel board products, magazine papers, newsprint, chemical pulps and completely novel fibre products.

Water removal and bulk are important factors especially for the board middle layer. The method of the present invention can be a novel way to improve these properties. In addition to this, other properties can also be obtained with different chemical selection.

The present invention can also be used for adding functionalities into mechanical pulps, for example in magazine paper furnishes or in newsprint furnishes.

The present invention is also applicable for the unbleached chemical pulps. For example fiber rigidity may be improved by grafting proper chemicals onto the fiber lignin. The modified fibers can then replace mechanical fibers in some applications.

This method is applicable for numerous different chemicals. Different properties like conductivity, charge, hydrophobicity and color can be introduced to the fiber lignin, depending on the nature of a grafted chemical. This provides possibilities to develop novel fiber-based products.

The invention will be examined more closely with the aid of a detailed description and a number of working examples.

Figure 1 depicts arginine dissociation with the carboxylic acids. Figure 2 depicts how arginine linoleate (last column) distinctively decreased WRV. Figure 3 depicts the increase of freeness.

Figure 4 depicts the increase of bulk with arginine linoleate (last column).

Figure 5 depicts the decrease of tensile strength with arginine linoleate.

Figure 6 depicts the increase of Scott-Bondwith both arginine and laccase.

Figure 7 depicts the increase of bending stiffness with laccase and arginine treatment Figure 8depicts the increase of Light- Scattering coefficient with arginine linoleate (last column).

Figure 9 depicts the increase of brightness of arginine linoleate.

Figure 10 depicts the increase of opacity in all the treatments. Detailed description of the invention

By "lignocellulosic material" is meant here fibre made from plants, in particular from wooden plants by using mechanical, chemical or chemomechanical pulping. In industrial processes woody raw-material is refined into fine fibre in processes, which separate the individual fibres from each other. The fibre materials typically are at least partly covered with lignin or lignin compounds having phenolic groups or derivatives of phenolic groups. Lignocellulosic material comprises for example thermomechanical pulp, TMP, groundwood pulp, GW, pressurized groundwood pulp , PGW, chemithermomechanical pulp, CTMP, refiner mechanical pulp, RMP and pressurized refiner mechanical pulp , RPMP.

"Phenolic groups" mean -OH groups and derivatives of phenolic groups mean derivatives of OH groups, such as -OCH3. Generally, the concentration of lignin in the lignocellulosic material should be at least 0.1 wt-%, preferably at least about 1.0 wt-% to give at least a minimum amount of phenolic groups necessary for providing binding sites for the reactive nucleophilic groups of the biochemical compounds.

By "oxidation reaction" is meant chemical or enzymatic oxidation reaction.

The chemical oxidizing agent may be a free radical forming substance such as hydrogen peroxide, Fenton reagent, organic peroxidase, potassium permanganate, ozone and chloride dioxide. Examples of suitable salts are inorganic transition metal salts, specifically salts of sulphuric acid, nitric acid and hydrochloric acid. Ferric chloride is an example of suitable salts. Strong chemical oxidants such as alkali metal- and ammoniumpersulphates and organic and in-organic peroxides can be used as oxidising agents. In general, suitable oxidizing agents are for example CAN, persulphates, periodates, selenedioxide, kaliumferrocyanide, salcomine.

According to an embodiment of the invention, the chemical oxidants capable of oxidation of phenolic groups are selected from the group of compounds reacting by radical mechanism. According to another embodiment, the lignocellulosic material can be reacted with a radical forming radiation capable of catalyzing the oxidation of phenolic or similar structural groups to provide an oxidized lignocellulosic material.

According to one further embodiment of the invention oxidizing agent is an enzyme and the enzymatic reaction is carried out by contacting the lignocellulosic material with an oxidizing agent, which is capable - in the presence of the enzyme - of oxidizing the phenolic or similar structural groups to provide an oxidized fibre material. Such oxidizing agents are selected from the group of oxygen and oxygen-containing gases, such as air, and hydrogen peroxide. Oxygen can be supplied by various means, such as efficient mixing, foaming, air enriched with oxygen or oxygen supplied by enzymatic or chemical means, such as peroxides to the solution. Peroxides, such as hydrogen peroxide can be added in situ. Although any oxygen-containing gas can be used, it is preferred to use ambient air, oxygen enriched air, oxygen gas, pressurized systems of these or oxygen releasing chemicals.

According to an embodiment of the invention, the oxidative enzymes capable of catalyzing oxidation of phenolic groups, are selected from, e.g. the group of phenoloxidases

(E. C.1.10.3.2 benzenediol: oxygen oxidoreductase) and catalyzing the oxidation of o- and p-substituted phenolic hydroxyl and amino/amine groups in monomeric and polymeric aromatic compounds or carbohydrate oxidases (e.g. galactose oxidase, hexose oxidase) catalyzing the oxidation Of C₂, C3 or C₆ in the sample. The oxidative reaction of lignin with the phenoloxidases leads to the formation of phenoxy radicals. Other groups of enzymes comprise the peroxidases and other oxidases. "Peroxidases" are enzymes, which catalyze oxidative reaction using hydrogen peroxide as their electron acceptor, whereas "oxidases" are enzymes, which catalyze oxidative reactions using molecular oxygen as their electron acceptor. The oxidable substrate of these enzymes can be any structural compound of lignocellulosic fibres, preferably lignin or hemicellulose.

In the method of the present invention, the enzyme used may be for example laccase, tyrosinase, peroxidase or oxidase, in particular, the enzyme is selected the group of laccases (EC 1.10.3.2), catechol oxidases (EC 1.10.3.1), tyrosinases (EC 1.14.18.1), bilirubin oxidases (EC 1.3.3.5), horseradish peroxidase (EC 1.11.1.7), manganase peroxidase (ECl.11.1.13), lignin peroxidase (EC 1.11.1.14), galactose oxidase (EC 1.1.3.9) and lipoxygenase (EC 1.13.11.12), hexose oxidase (EC 1.1.3.5) and other carbohydrate oxidases.

The amount of the enzyme is selected depending on the activity of the individual enzyme and the desired effect on the fibre. Advantageously, the enzyme is employed in an amount of 0.0001 to 10 mg protein/g of dry matter.

Different enzyme dosages can be used, but advantageously about 0,01 to 100 U/g, typically 1 to 50 U/g.

The activation treatment is carried out in a liquid medium, preferably in an aqueous medium, such as in water or an aqueous solution, at a temperature of 5 to 100 ⁰C, typically about 10 to 85 ⁰C. Normally, ambient temperature (room temperature) or a slightly elevated temperature (20 to 80 ⁰C) is preferred. Normally, ambient temperature (room temperature) or a slightly elevated temperature (25 to35 ⁰C) is preferred. The consistency of the pulp is, generally, 0.5 to 95 % by weight, typically about 1 to 50 % by weight, in particular about 2 to 40 % by weight. The pH of the medium is preferably slightly acidic, in particular the pH is about 2 to 10, in the case of phenoloxidases. Peroxidases are typically employed at a wide pH range, pH of about 3 to 12. The reaction mixture is stirred during oxidation. Other enzymes can be used under similar conditions, preferably at pH 2- 10.

Biochemical agent comprising a reactive nucleophilic group can be a natural or synthetic or partly synthetic amino acid or protein or other amine compound, such as nucleic acid. The biochemical agent may also be an inorganic or synthetic or partly synthetic nucleophile, such as polyamine.

Biochemical agent comprising a reactive nucleophilic group may be selected from the group of the most common amino acids comprising alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, iso leucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine. Preferably the reactive nucleophilic group is selected from the group comprising thiol, amine, guanidine, imidazoline, indole and pyrroline groups. Most preferably the nucleophilic group is amine or thiol group.

Preferably the amino acid or protein or other amine compound comprising a reactive nucleophilic group comprises also nucleophilic side groups, such as thiol, amine, guanidine, imidazoline, indole or pyrroline groups.

The lignocellulosic material with the covalently bound biochemical agent is contacted with an acid in an aqueous solution allowing the biochemical agent to form a ionic bond with the acid.

The acid may be a hydrophobic or hydrophilic acid. The acid may or may not be a substrate for laccase. The acid may be an organic or inorganic acid. The acid may be for example a fatty acid.

According to one preferred embodiment of the invention the method of the present invention comprises that

- the phenolic groups or the derivatives of phenolic groups of the lignocellulosic material are oxidized to quinines, quinone derivatives or other carbonyl groups, and

- the oxidized fibre material is contacted with a biochemical agent comprising a reactive nucleophilic group, said biochemical agent forming a covalent bond with the lignocellulosic material.

According to one other preferred embodiment of the invention the method further comprises that a desired chemical or biochemical compound is ionically bound to the biochemical agent comprising a reactive nucleophilic group.

The invention provides a modified lignocellulosic product, wherein a biochemical agent comprising a reactive nucleophilic group is bound covalently to quinines, quinone derivatives or other carbonyl groups of the lignocellulosic fibre material. The invention provides further a modified lignocellulosic product, where a biochemical agent comprising a reactive nucleophilic group, such as an amine group is bound covalently to quinines, quinone derivatives or other carbonyl groups of the lignocellulosic fibre material and a desired chemical or biochemical compound is bound ionically to the biochemical agent comprising a reactive nucleophilic group.

The present invention provides a novel method for modification of lignin-containing fibers. The method utilizes oxidation agents and sustainable chemistry to add novel properties into fiber surfaces. The problems of the existing laccase grafting methods, cross-reactions between chemicals and high price of the grafted chemicals, can be eliminated by using amino acid or protein or other amine compound mediated indirect grafting. The results indicate that bulk can be increased and dewatering improved.

By using the present invention it is possible to graft lignocellulosic material by various amino acids, proteins or other amine compounds. The reactive nucleophilic groups, such as amine groups can be further bound ionically to acids, for example shorter or longer chains of fatty acids. Preferably, fatty acids derived from the triglycerides from wood origin are used. First the fatty acids should be degraded with lipase and then grafted onto fiber lignin with the system of the present invention. This is especially beneficial for pine pulp, having high resin content. The present invention can be used also to decrease or prevent hexanal formation.

Further advantageous applications are grafting of proteins on fibers since larger molecules may produce more pronounced effects. Another interesting approach is modification of fines to generate novel paper and board making raw materials, mixing of modified fibers with untreated pulp and testing of the developed method with unbleached Kraft pulp which could enable replacement of mechanical pulp with modified unbleached Kraft pulp in some applications.

By enzyme-aided, specifically laccase-aided grafting of biochemicals, in particular amino acids and fatty acids, major changes for pulp and paper properties can be achieved. According to the present invention up to 19% increase in bulk with the 15% decrease in WRV can be obtained. This application is novel approach compared to the existing laccase-based grafting methods since it is not limited to laccase subtrates. The efficiency in this invention is demonstrated in improvement of bulk and WRV of mechanical pulps, but also other properties can be introduced to fibers depending on the used grafting chemicals. In addition to TMP other lignin-based pulps, such as unbleached Kraft pulp or ground wood can be used as raw material.

According to one preferred embodiment only part, for example 50 % or only 30 % of the pulp is treated by the process of the present invention. If only part of the pulp is treated, the process will be more complicated, but economically more feasible.

According to another preferred embodiment of the invention ungrafted chemicals and oxidating enzymes may be recycled. This may also reduce the chemical costs.

This technology can be regarded as sustainable, since it is based on the use of biochemicals and totally lacks harsh chemistry. Therefore no major environmental impacts are expected. Increased bulk of the board products may increase the efficiency of raw material usage, reduce the need of transportations and increase the competitiveness of the forest industry.

Examples

Example 1

In the experiments were used the following materials:

- Unbleached spruce TMP, CSF 80

- Arginine (>98,5 %, FCC Aldrich) - Linoleic acid (technical, 60-75 % Fluka)

- Acetic acid (puriss. >99,5 %, Fluka)

- Gallic acid (>98,0% Fluka)

- SO₂ -water (for pH adjustment)

- Laccase (Novozymes 51003) - Magnesium sulfate (for fixing of conductivity)

With arginine were used linoleic acid, gallic acid and acetic acids. Linoleic acid was selected, because it is very hydrophobic and was thus expected to improve both bulk and dewatering. Gallic acid is a laccase substrate and also represents the reference for prior art grafting method based on radical coupling. Acetic acid is small and demonstrates the effect of carbon chain length when compared to linoleic acid.

Grafting experiments were performed with the plain arginine and its different salt compounds as presented in Fig. 1. The plain arginine dissociates in neutral water forming a hydroxide salt. The organic salts are formed simply by mixing equal molar amounts of acid and arginine.

Arginine linoleate and acetate react mainly via arginine amino groups. These compounds are not substrates for laccase. Arginine gallate instead is known to be a laccase substrate (Chandra et al. 2004) and therefore also reacts via radical coupling (the conventional approach in laccase-based grafting processes).

The experiments were performed in a Zirco-reactor (5% TMP pulp consistency) at 50 ⁰C under 8 bar oxygen pressure. TMP 500 g was first reacted with laccase 1 U/g for 1 hour (at pH 5.5), and after that other chemicals were added. The total reaction time was 2 h. The chemicals were dispensed automatically. The dose of the grafting chemicals was total 20 % (arginine + acid in molar ratio 1 :1) of the weight of the TMP pulp. The pulp was washed and the pH adjusted to pH 5.2.

After grafting, the pulps were diluted to 1% consistency and hand sheets (60 g/m²) with white water circulation were prepared. The test points are shown in Table 1.

Table 1. Test points.

The effects of different arginine compounds on pulp and fiber properties were studied. The results are mainly presented as the relative changes from the reference. The most important properties are discussed below.

Analysis of fibers and pulp

Z-potential and charge measurements also showed some differences between the samples (Table 2.). Arginine linoleate seemed to increase the fiber charge more than the other treatments. This might indicate that the fiber surfaces contain negatively charged linoleate anions, which are ionically bounded to arginine.

Table 2. Pulp and fiber charge and Z-potential of samples.

Sample Water Pulp Fibers Z- potential

Reference -6.0 -850 -45 -46

Arginine (Arg.) -10.3 -800 -50 -71

Laccase (Lace.) -4.6 -630 -43 -50

Lace. + Arg. -10.7 -900 -50 -51

Lace. + Arg. + Gallic acid -7.0 -890 -42 -105

Lace. + Arg. + Acetic acid -11.5 -710 -54 -56

Lace. + Arg. + Linoleic acid -20.4 -940 -75 -64 Dewatering and bulk

Freeness was used to illustrate the drainability in the wire section and WRV in the press section.

The changes in WRV were small excluding the arginine linoleate treatment (Fig. 2 last column). Here the decrease was about 15 %, which is very significant. This observation also correlates with the hypothesis that long carbon chains on fiber surface may improve dewatering.

Similar phenomenon could not be seen in Freeness (drainability), where the changes in all cases were relatively small (Fig. 3. The plausible explanation is that freeness is mainly dependent on the fines content, which was here invariable, whereas WRV is also dependent on the structure and chemistry of fibers and fines.

Laccase with arginine linoleate had also significant effect on bulk (Fig. 4) Almost 20 % increase is very significant. For the other treatments, the changes in bulk were relatively small.

Arginine linoleate clearly increased bulk and decreased water retention value indicating also improved dewatering. Long and bulky carbon chain on the fiber surface seems thus to improve both bulk and dewatering.

Physical properties

Figure 5 shows that arginine linoleate had a negative effect on tensile index. This is typical for the hydrophobic compounds, because they tend to block the hydrogen bonding of fibers. For the other treatments the changes were relatively small; the best results were obtained with plain laccase. The increasing effect of laccase on tensile strength has been observed earlier (Lund et al. 2003).

Similar to tensile strength, arginine linoleate caused a major decrease in internal bonding strength (Scott-Bond), whereas laccase and especially plain arginine had an opposite effect (Fig. 6). Bulk reduction may partly explain this result (Fig. 4). Bending stiffness of the treated pulps was not in line with bulk (Fig. 7). The normal correlation could not be observed:

- laccase + arginine: increased bending stiffness and decreased bulk

- laccase +arginine linoleate: decreased bending stiffness and increased bulk

In the case of arginine linoleate (and arginine acetate) the decreased bending resistance may result from the lowered friction between the fibers, which enables their sliding under tension leading to decreased bending resistance.

Optical properties

Light-scattering coefficient increased with all arginine salt compounds, but the change was exceptionally high with arginine linoleate (Fig. 8).

This result correlated well with the increased brightness of arginine linoleate treated fibers (Fig. 9). In all the other treatments the brightness decrease was very distinct. This was expected due to the literature (Modica et al. 2001). The formation of chromophores also indicated that arginine might have covalently reacted with lignin (enzymatic browning). Figure 9 shows that arginine linoleate increased brightness whereas all other treatments had a detrimental effect.

Pulp opacity increased in all the treatments (Figure 10). The results are somewhat inversely proportional to ISO brightness, and due to the opacifying effect of the chromophores any correlation with the bulk could not be observed.

The only exception is arginine linoleate, which increased all optical properties. The plausible explanation might be the very high light-scattering coefficient, masking the effect of arginine- lignin chromophores.

The results of this study proved that bulk can be increased and dewatering improved by grafting arginine linoleate on TMP lignin. The other treatments were less effective. Table 3 summarizes the main results of laccase and arginine linoleate treatment: Table 3. The main results of laccase and arginine linoleate treatment of TMP fibers.

Property Effect, % imm Trø n&nnu*

WRV

Opacity

Light-scattering coefficient

ISO Brightness

Bulk

In these experiments can be observed the occurrence of reactions between arginine and laccase-oxidized lignin due to formation of colored compounds. Only minor effects were obtained with arginine gallate (except optical properties), which represents the prior art grafting method . From these experiments can be concluded that the size of the fatty acid is very important in creating novel fiber properties. The long carbon chain linoleic acid was much more effective than the short carbon chain acetic acid. Plain arginine seems to cause strong internal fibrillation on fibers, but it is prevented by the laccase pre-treatment.

References

Buchert, J., Grόnqvist, S., Mikkonen, H., Oksanen, T., Peltonen, S., Suurnάkki, A. Viikari, L. Process for procuding a fibrous product. (2005) WO2005/061790A1.

Viikari, L., Koivula, A., Smolander, M., Boer., H., Valkiainen, M., Immonen, K., Qvintus- Leino, P., Kaukoniemi, O. -V. Printed fuel cells with laccases as cathodic biocatalyst. In: 10^th International congress on the biotechnology in the pulp and paper industry, 10- 15.6.2007, Book of abstracts p. 62.

Chandra, R., Lehtonen, L. Ragauskas, A. Modification of lignin content kraft pulps with laccase to improve paper strength properties. 1. Laccase treatment in the presence of gallic acid. Biotechnol. Prog. 20 (2004)1, pp 255-261.

Lund, M., Felby, C. .Process for treating pulp with laccase and a mediator to increase paper wet strength (2003) US6610172B2. Modica, E., Zanaletti, R., Freccero, M., Mella, M. Alkylation of amino acids and glutathione in water by a-quinone-methide; reactivity and selectivity, J. Org. Chem., 66 (2001)1, pp 41-52.

Claims

1. A method for modifying lignocellulosic material having phenolic groups or derivatives of phenolic groups, wherein the method comprises the steps of - oxidizing the phenolic groups or the phenoxy derivative groups of the lignocellulosic material to quinines, quinone derivatives or other carbonyl groups, and

- contacting the oxidized fibre material with a biochemical agent comprising a reactive nucleophilic group, said biochemical agent forming a covalent bond with the lignocellulosic material.

2. The method according to claim 1, wherein the nucleophilic group is selected from the group comprising thiol, amine, guanidine, imidazoline, indole and pyrroline groups, preferably from the group comprising amine or thiol group.

3. The method according to claim 1 or 2, wherein the oxidation reaction is enzymatic or chemical.

4. The method according to any one of claims 1 to 3, wherein the oxidation reaction is catalyzed by peroxidases or oxidases.

5. The method according to any one of the preceding claims, wherein the oxidation is carried out by using laccase (EC 1.10.3.2).

6. The method according to any one of the preceding claims, wherein the biochemical agent comprising a nucleophilic group is not a substrate for the enzyme catalysing the oxidation.

7. The method according to any one of the preceding claims, wherein the biochemical agent comprising a nucleophilic group is a natural or synthetic or partly synthetic amino acid, or protein, or other amine compounds, such as nucleic acid, or inorganic or synthetic nucleophile, such as polyamine.

8. The method according to any one of the preceding claims, wherein the biochemical agent is selected from the group comprising alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine.

9. The method according to claim 5 or 6, wherein the amino acid or protein or other amine compound comprises nucleophilic side groups.

10. The method according to any one of claims 1 to 9, wherein the lignocellulosic material with the covalently bound biochemical agent is contacted with an acid in an aqueous solution allowing the biochemical agent to form an ionic bond with the acid.

1 l.The method according to claim 10, wherein the acid is a hydrophobic acid.

12. The method according to claim 10, wherein the acid is a substrate for laccase.

13. The method according to any one of claims 10 to 12, wherein the acid is an organic acid.

14. A modified lignocellulosic product having phenolic groups or derivatives of phenolic groups, characterized in that a biochemical agent comprising a reactive nucleophilic group is covalently bound to the phenolic groups or derivatives of phenolic groups of the lignocellulosic material.

15. The modified lignocellulosic product according to claim 14, wherein the covalently bound biochemical agent is ionically bound to an acid.