WO2015103713A1

WO2015103713A1 - Modified wood

Info

Publication number: WO2015103713A1
Application number: PCT/CH2014/000004
Authority: WO
Inventors: Etienne CABANE; Ingo BURGERT; Tobias KEPLINGER
Original assignee: Empa Eidgenössische Materialprüfungs- Und Forschungsanstalt; Eth Zurich
Priority date: 2014-01-10
Filing date: 2014-01-10
Publication date: 2015-07-16

Abstract

The present invention relates to a modified wood product comprising a species of wood and polymerized monomer as defined in claim 1; to methods of manufacturing such wood product; to the use of such wood product.

Description

- I -

Modified Wood

The present invention relates to a modified wood product comprising a species of wood and polymerized monomer; to methods of manufacturing such wood product and to the use of such wood product.

It is well known that wood is one of the most widely used materials in construction, with the potential to become a key engineering material. Intrinsic drawbacks of wood, such as low dimensional stability, poor resistance to decay and weathering are also known. To address these drawbacks, chemical modification of wood is an accepted approach .

Cabane et al (ACS, Sept.9, 2013) suggests in general terms to perform in-situ polymerizations in wood, using hydroxyl groups as anchoring sites for the covalent attachment of poly styrene chains to the cell wall. This method is considered advantageous, as the cell lumen is only marginally affected by such modification. The document fails to disclose how such covalent linkage may be achieved . Shingero et al ( JPH0215560 ) , Schneider (WO01/53050) and Berejka ( O2005/042175 ) suggest wood modification via treatment with reactive monomers. The modified wood obtained according to these documents does not contain covalent bonding between polymer and cell walls. Further, the cell lumen is affected resulting in densification of wood.

Thus, it is an object of the present invention to mitigate at least some of these drawbacks of the state of the art. In particular, it is an aim of the present invention to provide a modified wood product having improved properties with regards to weight percent gain, water uptake and / or anti-swelling efficiency.

These objectives are achieved by a modified wood product as defined in claim 1 and by a method as defined in claim 10. Further aspects of the invention are disclosed in the specification and independent claims, preferred embodiments are disclosed in the specification and the dependent claims.

The present invention will be described in more detail below. It is understood that the various embodiments, preferences and ranges as provided / disclosed in this specification may be combined at will. Further, depending of the specific embodiment, selected definitions, embodiments or ranges may not apply.

Unless otherwise stated, the following definitions shall apply in this specification:

As used herein, the terms "a", "an", "the" and similar terms used in the context of the present invention (especially in the context of the claims) are to be construed to cover both the singular and plural unless otherwise indicated herein or clearly contradicted by the context .

As used herein, the terms "including", "containing" and "comprising" are used herein in their open, non-limiting sense. The term "containing" includes the meanings "comprising", "essentially consisting of" and "consisting of".

The present invention will be better understood by reference to the figures. Figure 1 shows Raman images of latewood (L ) and earlywood (EW) showing the distribution of natural cell wall polymers (cellulose and lignin) , and polystyrene; prepared according to ex. 1.

Figure 2 shows SEM micrographs of modified spruce showing polymer thin film (PSt) , coating the inner cell wall surface (lumen of cells); prepared according to ex. 1. Figure 3 shows water sorption on the surface of modified wood (left) and water sorption on the surface of untreated wood (right) . Modified wood being prepared according to ex . 1. Figure 4 shows Raman images of modified wood. The images show the distribution of natural cell wall polymers (cellulose and lignin) , and polystyrene; prepared according to ex. 2. Figure 5 shows SEM micrographs of modified spruce. The micrographs show free lumen and no cell wall damage; prepared according to ex. 2.

Figure 6 shows water uptake of untreated wood cubes (squares), and modified wood according to ex. 2. y-axis: water uptake (%); x-axis : time (h) .

Figure 7 shows swelling of untreated wood cubes (squares), and modified wood according to ex. 2. y-axis: swelling (%) ; x-axis: time (h) .

Figure 8 shows water droplets on the surface of untreated wood (left) and modified wood according to ex. 2 (2^nd, 4^th, 6^th photograph after first step and 3^rd, 5^th, 7^th photograph after second step) . Figure 9 shows a reaction scheme for manufacturing the inventive modified wood products.

In more general terms, in a first aspect, the invention relates to a modified wood product. According to this invention, a wood product is provided which comprises a species of wood and a polymerized monomer (i.e. a polymer) , said polymerized monomer and said wood being covalently bond by a linker.

Accordingly, the invention provides for a wood product comprising bulk wood of various species and a polymerized monomer, characterized in that said polymerized monomer (polymer) is covalently bonded, in and at the cell walls of said wood, by an initiator for a modular in-situ polymerization. This wood product may possess different material profiles and functionalities, depending on the choice of monomer. When using styrene as monomer, 10% to 30% weight percent gain may be obtained; at least 50% decrease of water uptake may be obtained and/or up to 40 % anti-swelling efficiency may be obtained.

This aspect of the invention shall be explained in further- detail below:

Species of Wood: The species of wood to be used in this invention is not critical. Basically, any naturally occurring species of wood is suitable for use in this inventio .

The term wood is known in the field and denotes in its broadest sense lignified plant tissue. More precisely, the term includes the hard, fibrous structural tissue found in the stems and roots of trees and other woody plants, containing cell walls made up of cellulose fibrils embedded in a matrix of hemicelluloses and lignin.

The use of wood as construction material is known for thousands of years. It is an advantage of the present invention, that bulk wood may be used. This is important, as known methods relate to the modification of isolated lignin or to the modification of chemically extracted cellulosic fibers and their surfaces only. Accordingly, in one embodiment of the invention, the wood is bulk wood. The term "bulk wood" is used to distinguish the inventive material from wood surface treatments, from disintegrated wood structures and from treatment of chemical components derived from wood.

Polymerized monomer: A wide variety of monomers may be used according to this invention. Suitable monomers are susceptible to radical polymerisation (particularly free radical polymerisation and ATRP) and include acrylonitrile, styrene derivatives ( "styrenics , la) , acrylate derivatives ( "acrylates" , lb) , acrylamide derivatives ( "acrylamides" , Ic) ,

R² represents unsubstituted or substituted C6-10 aryl, unsubstituted or substituted heteroaryl having 5-10 ring members and 1-3 heteroatoms independently selected from N, 0, S, and the substituents being selected from C1-4 alkyl,

(Tri-Ci-4-alkylammonium) -Ci-4 alkyl, B(OH)₂. R² preferably represents phenyl, p- (Trimethyl-ammonium-methyl ) phenyl, p-

(boronic) phenyl , p-pyridyl .

R³ represents hydrogen, C1-4 alkyl. R³ preferably represents hydrogen or methyl .

R⁴ represents vinyl, C1-4 alkyl; ( Di-Ci-4-alkylamino) -C1-4 alkyl, (Tri-Ci-4-alkoxysilyl) -C1-4 alkyl, (Cyclopropox ) -C1-4 alkyl, (meth)acryl, mono- to pentaethylenglycol . R⁴ preferably represents vinyl, methyl, ethyl, iso-propyl tert. butyl, ( Dimethylamino ) etyhl , (Trimethoxysilyl ) - propyl, (Cyclopropoxy ) methyl , methacryl, hydroxyethyl .

R⁵ represents C1-4 alkyl; (hydroxy) -C1- 4 alkyl, (acrylamino) Ci-4 alkyl. R⁵ preferably represents methyl, ethyl, iso- propyl, tert. butyl, (hydroxy) -propyl, acrylamino-methyl .

Preferred monomers, suitable to produce the polymerized monomers ("polymers") are acrylonitrile and the monomers shown

A particularly preferred monomer is styrene. After reaction is completed, the monomers are polymerized and termed "polymerized monomers", or synonymously "polymers" .

Linker: A wide variety of linkers may be used in this invention. Suitable linkers include compounds of formula (II) and of formula (III) .

In one embodiment, the invention relates to linkers of formula (II) ,

0 «

R' ( I D

X¹ represents halogen. X¹ preferably represents bromo.

X² represents halogen, substituted C1-4 alkoxy, the substituents being selected from the group consisting of cyclopropxoy, (Tri-Ci 4-alkxylsilyl ) , (Tri-Ci-4 - alkoxysilyl) , (Tri-halogensilyl . X² preferably represents bromo .

R⁶ represents C1- 4 alkyl. ^{d6 p}referably represents methyl

R⁷ represents hydrogen, C1-4 alkyl. R⁷ preferably represents methyl .

A preferred linker of formula (II) is selected from the

MeO ci A particularly preferred linker of formula (II) is "BiBi

Linkers of formula (II) are particularly suitable for atom transfer radical polymerization reactions (ATRP) . This type of polymerization reaction is well known in the field and requires presence of a further catalyst. Suitable are transition metal catalysts, such as copper complexes. Such catalysts and appropriate reaction conditions are known.

In one alternative embodiment, the invention relates to linkers of formula (III) ,

X³ represents halogen or hydroxyl. X³ preferably represents chloro.

R⁸ represents Ci-Cs alkandiyl optionally substituted by CN . R⁸ preferably represents n-propyl substituted by methyl (preferably in alpha position to the diazo-group) and substituted by methyl (preferably in alpha position to the diazo-group) .

A preferred linker of formula (III) is "ACVAC1",

The modified wood product as described herein as a number of beneficial properties; particularly relevant parameters are outlined below. Structural and chemical characterization: In the wood product according to the invention, the polymer is present in and at the cell wall and forms a thin coating on the cell wall surface at the lumen side. It is considered particularly beneficial that the lumen of the cell, apart from a few cells and the cell wall cover, is essentially free of polymers. This avoids unwanted densification of the wood treated and also avoids excess use of polymer. This finding is confirmed by Raman analysis and SE data; see figs. 1 & 2.

In the wood product according to the invention, the polymer is chemically bond to the cell. This finding is confirmed by the above analysis and the fact that the wood product shows no, or essentially no, leaching.

In a further embodiment the invention thus provides for a wood product as described herein characterized in that at least 10 wt%, preferably at least 30 wt% of said polymerized monomer is located within the cell wall of said wood. It was found that linkers of formula (II) can result in very high amounts, up to 90 wt%, while linkers of formula (III) may result in amounts of up to 50 wt%. It is considered particularly beneficial that a significant amount of polymer bulks the cell wall structure. This results in intrinsic alteration of the wood structure and conveys superior modification of the wood properties, as opposed to surface treatments. This finding is confirmed by Raman analysis data; see figs. 1 & 4, Water uptake (WU) : The wood product according to the invention shows a decrease in water uptake, after five days soaking in water, by a factor of -3 when compared to untreated wood. WU is defined as:

Where W_w = wet weight and Wd = oven dry weight of modified wood. A typical WU value for wood treated according to this invention is comprised between 60 and 75%, while untreated wood has a WU comprised between 180 and 220%. In a further embodiment the invention thus provides for a wood product as described herein characterized in that it has a water uptake of 60-75%. Anti-Swelling Efficiency (ASE) : The wood product according to the invention shows an improvement in ASE. ASE is defined as:

ASE (%) = 100 · (Su-Sm) /Su

With Sm = swelling coefficient of modified wood

Su = swelling coefficient of the untreated wood.

Cubes of the inventive wood product show an ASE between 5 and 45 %.

In a further embodiment the invention thus provides for a wood product as described herein characterized in that it has an anti-swelling efficiency of 5-45%.

Weight Percent Gain (WPG) : The wood product according to the invention has a weight percent gain of at least 10%, and up to 35%. An ideal WPG is in the range of 30%.

WPG is defined as:

WPG (%) = 100 · (Wm-Wu) /W_u

Where W_m = oven dry weight of modified wood and W_u = oven dry weight of untreated wood.

In a further embodiment the invention thus provides for a wood product as described herein characterized in that it has a weight percent gain of not more than 10-30 %.

Surface properties: Surface properties of the inventive wood product are also affected when compared to untreated wood. The inventive wood is hydrophobic, see e.g. fig. 3.

Without being bound to theory, it is believed that the thin film of polymer grafted onto the cell wall at the lumen side, changes the overall surface properties of wood. This polymer film was characterized with both SEM and Raman, as discussed above.

In a second aspect, the invention relates to a process for manufacturing a modified wood product as described herein. This aspect of the invention shall be explained in further detail below. As already discussed, and outlined in further detail below, the manufacturing comprises two essential steps. The first step comprises covalently binding ("anchoring") a linker of formula (II) or (III) to functional groups of the cell wall, preferably to hydroxyl groups. The second step comprises radical chain polymerisation of monomers of formula (I) onto said linker. While the reaction mechanisms differ, the process steps are essentially the same and are schematically depicted in fig. 10. Polymerisation from linker (II) proceeds via ATRP, polymerisation from linker (III) proceeds via free-radical chain polymerisation.

General Procedure

The invention provides for a method for manufacturing a wood product as described herein comprising the steps of:

^■ Providing a species of dry wood (1.1) .

^■ Impregnating said species with a first solution

comprising a linker of formula (II) or (III) (1.2).

^■ Reacting the linker with said dry wood at room

temperature. By this step, activated wood, i.e. wood having a covalent bond to said linker, is obtained. It is assumed that hydroxyl groups of wood react with the linker to form a covalent bond (1.3).

^■ Optionally removing excess linker (1.4).

^■ Impregnating said activated wood with a second

solution comprising monomers as defined above (2.1) .

^■ Polymerizing said monomers. By this step, a wood

product having covalent bond between polymer chains and cell walls is obtained (2.2) .

^■ Optionally post-treatment. By this step, the final

wood product is obtained (2.3) . ATRP Polymerisaton Step 1.1) Providing starting materials, particularly a sample of dry wood, solution containing the linker (II), solution containing the monomers of formula (I) Step 1.2) Impregnation of dry wood with a solution of linker (II), e.g. a-Bromoisobutyryl bromide (BiBB) of formula (II~), in a suitable anhydrous solvent. Preferred solvents are aprotic, polar, with a high wood swelling capability, e.g. pyridine or dimethylformamide / triethylamine . The concentration of the linker in solution is typically between 1 and 10 % by weight and the number of moles engaged in the reaction is calculated as 0.1 to 1 equivalent, with MW(wood) = 162 g/mol (equivalent of glucopyranose units).

Impregnation of solution into wood may be facilitated with the use of vacuum or vacuum-pressure cycles. If vacuum is used, dry wood is placed in impregnation apparatus, then vacuum is applied (e.g. 10 to 100 mbars) for a sufficient amount of time (e.g. 15 minutes or more), then solution is injected and vacuum is slowly released to reach atmospheric pressure. If vacuum-pressure cycles are used, a slight overpressure is applied (2 or 3 bars) after vacuum.

The system should be water free (or close to water-free conditions), in order to avoid side reactions, such as conversion of acyl bromide to the less reactive carboxylic acid .

Step 1.3), Anchoring step: Reaction of linker solution (e.g. BiBB solution) with wood may take place at room temperature for a given amount of time. The reaction times may vary over a broad range, typically from 2 to 24h, depending on the geometry of the wood samples (cutting directions), the wood species, and the degree of functionalization targeted (e.g. from 5 to 20% weight gain) . Suitable reaction times may be determined by routine experiments. Step 1.4), Rinsing step: The thus obtained wood products are rinsed several (e.g. once, twice or three times) with the solvent used in the following step 2 or other suitable solvents, such as methanol or acetone. By such solvent exchange, unreacted species are removed. Suitable rinsing conditions may be determined by routine experiments.

Step 2.1) Impregnation: The activated wood product of step 1 (e.g. wood-BiBB) is impregnated with a solution of a polymerizable monomer (compounds of formula (I)) and catalyst in a suitable solvent; or with a polymerizable monomer and catalyst in the absence of solvent.

The monomer used must be polymerizable via ATRP, and can be chosen within a large range of molecules as defined above. When using hydrophobic monomers (such as styrene (St) or methylmethacrylate (MMA) ) , a proper solvent with affinity to wood and the monomer is chosen, such as DMF or DMSO. When using hydrophilic compounds (such as Hydroxyethylmethacrylate (HEMA) or (Dimethylamino) ethyl methacrylate (DMAEMA) ) , alcohols or water may be used as solvent, or no solvent is used. The monomer concentration is typically from 10 to 100 % by weight, depending on its solubility and the degree of polymerization desired. The catalyst for ATRP (transition metal catalyst) is typically formed in situ. Suitable catalysts are based on copper bromide (CuBr) or copper chloride (CuCl) and associated ligands , including for example 2,2' -bipyridine (bpy) , Ν,Ν,Ν' ,Ν* ,Ν' ' -Pentamethyldiethylenetriamine (PMDETA), or 1, 1, 4, 7, 10, 10-Hexamethyltriethylenetetramine (HMTETA) .

Impregnation conditions are similar to step 1.2. Accordingly, vacuum and pressure may be applied to achieve sufficient impregnation. Step 2.2) Polymerization of impregnated monomers within wood: The polymerization is initiated by heat. Suitable temperatures are 65-85°C; such temperatures allow acceptable reaction rates but prevent considerable wood damages. The reaction times may vary over a broad range, typically from 2 to 24h, depending on the geometry of the wood samples (cutting directions), the wood species, and the degree of polymerisation targeted. The polymerization is conducted in oxygen free environment.

Step 2.3) Cleaning. After polymerization, modified wood samples are removed from the solution, rinsed with a solvent (e.g. acetone or another suitable solvent) and optionally dried in at elevated temperatures (e.g. in an oven at 65°C for 24h or until constant weight) . This cleaning step aims at eliminating unbound polymer chains, and non-reacted starting materials and provides the modified wood product as described in the first aspect of the invention.

An advantage of ATRP is uniform polymerization essentially without the presence of unbound polymer. It is believed that this effect is attributed to the presence of the copper catalyst. In free-radical polymerization, radicals are present in solution and addition of new monomers occurs continuously. In ATRP, there is an equilibrium between radicals and "dormant species". At a given time, the radical concentration in solution is extremely low.

Free-radical Radical chain Polymerisation

Step 1.1) Providing starting materials, particularly a sample of dry wood, solution containing the linker (III), solution containing the monomers of formula (I) .

Step 1.2) Impregnation: Dry wood is impregnated with a solution containing the linker of formula (III), e.g. ACVAC1 of formula (III^"), in a suitable anhydrous solvent. Preferred anhydrous solvents are aprotic, polar, with a high wood swelling capability, e.g. pyridine or dimethylformamide / triethylamine . The concentration of the linker in solution is typically between 1 and 10 % by weight and the number of moles engaged in the reaction is calculated as 0.1 to 1 equivalent, with M (wood) = 162 g/mol (equivalent of glucopyranose units) .

Impregnation of solution into wood may be performed using conventional processes. Impregnation is facilitated with the use of vacuum or vacuum-pressure cycles. If vacuum is used, dry wood is placed in impregnation apparatus, then vacuum is applied (e.g. 10 to 100 mbars) for a sufficient amount of time (e.g. 15 minutes or more), then solution is injected and vacuum is slowly released to reach atmospheric pressure. If vacuum-pressure cycles are used, a slight overpressure is applied (e.g. 2 or 3 bars) after vacuum.

Impregnation is preferably done in the absence of water. The system should be under water-free conditions, or close to water-free conditions, for avoid loss of linker (e.g. by conversion of acyl chlorides of formula (III) to the corresponding carboxylic acid derivatives).

Step 1.3) Anchoring step: Reaction of linker solution (e.g. ACVAC1 solution) with wood may take place at room temperature for a given amount of time. The reaction times may vary over a broad range, typically from 2 to 24h, depending on the geometry of the wood samples (cutting directions), the wood species, and the degree of functionalization targeted. Suitable reaction times may be determined by routine experiments.

Step 1.4) Rinsing step: The thus obtained wood products are rinsed several (e.g. once, twice or three times) with the solvent used in the following step 2. By such solvent exchange, unreacted species are removed. Suitable rinsing conditions may be determined by routine experiments. Step 2.1) Impregnation: The activated wood product of step 1 (e.g. ood-ACVACl) is impregnated with a solution of a polymerizable compound (compounds of formula (I)) in a suitable solvent; or with polymerizable compound in the absence of solvent.

Suitable solvents may be selected by the skilled person. When using hydrophobic monomers of formula (I), such as styrene (St) or methylmethacrylate ( MA) , a proper solvent with affinity to wood and the monomer is chosen, such as DMF or D SO. When using hydrophilic monomers (such as HEMA) or (DMAEMA) ) , alcohols or water may be used as solvent, or no solvent is used. The monomer concent ation is typically from 10 to 100 % by weight, depending on its solubility and the degree of polymerization desired.

Impregnation conditions are similar to step 1.2. Accordingly, vacuum and pressure may be applied to achieve sufficient impregnation.

Step 2.2) Polymerization of impregnated monomers within wood: The polymerization is initiated by heat. Suitable temperatures are 65-85°C. Such temperatures allow acceptable reaction rates but prevent considerable wood damages. The reaction times may vary over a broad range, typically from 2 to 24h, depending on the geometry of the wood samples (cutting directions), the wood species, and the degree of polymerisation targeted.

Step 2.3) Cleaning : After polymerization, modified wood samples are removed from the solution, rinsed with a solvent (e.g. acetone or another suitable solvent) and optionally dried in at elevated temperatures (e.g. in an oven at 65°C for 24h or until constant weight) . This cleaning step aims at eliminating unbound polymer chains, and non-reacted starting materials and provides the modified wood product as described in the first aspect of the invention. Free-radical polymerisation results in a certain amount of non-covalently bound polymers. It is believed that this effect is attributed to the "symmetrical" linker of formula (III): homolythic cleavage of the molecule (III) yields one radical species attached to cell wall and one free in solution. This potential disadvantage is balanced by the fact that no catalytic active substances have to be added . In a third aspect, the invention relates to the use of a modified wood product, as described herein. This aspect of the invention shall be explained in further detail below;

Wood materials obtained according to this invention can compete with other wood modification techniques and tropical wood species of high ecological importance and high value. Due to the versatility of the two-step treatment, novel properties can potentially be provided to wood products, and dimensional stability, fire resistance, durability, and / or UV resistance can be improved in a variety of applications including furniture, building elements for indoor and outdoor uses. The invention thus provides for the use of modified wood products as described herein in applications where dimensional stability, fire resistance, durability, and / or UV resistance are important. The invention further provides for the use of the modified wood products as described herein as construction material in indoor and outdoor applications .

To further illustrate the invention, the following examples are provided. These examples are provided with no intend to limit the scope of the invention. Example 1: free-radical polymerisation

Preparation of modified wood Step 1: Spruce wood blocks (RxTxL: 10x10x5 mm3) are oven dried at 65°C for 24h. The cubes (3.2 g, 19.7mmol OH) are placed in anhydrous pyridine for 24h, in order to reach the swollen state of wood. A solution of ACVAC1 in pyridine (0.69g, 2.2mmol, 0.11 equivalent) is then added and the blocks are gently stirred in solution for 16h. After reaction, the cubes are removed from solution, blotted with paper (to remove excess solvent), and washed with several volumes of DMF (to remove all unreacted linker) .

Step 2: After the rinsing step, the functionalized cubes are placed in a solution of styrene in DMF (50:50 w/w) for 16h under nitrogen atmosphere. Then the temperature of the solution is raised to 75°C, to initiate the reaction. Polymerization is terminated after 16h. After reaction completion, the blocks are retrieved from solution, washed with acetone and water, and oven-dried for 24h at 65 °C to obtain inventive modified wood samples. Characteristics of modified wood

1) Structural and chemical characterization: According to Raman analysis and SEM data, the polymer is present in cell wall and also forms a thin coating on the cell wall surface at the lumen side; see figs. 1 & 2.

2) Surface properties: The obtained wood is hydrophobic; see fig. 3.

3) Water uptake (WU) of the samples is determined (see following Table)

4) ASE of the samples is determined (see following Table).

Sample Water uptake (%) ASE (%)

Reference (untreated wood) 211 /

Controls 216 -1.5

Wood modified with PSt 64 34 5) WPG of the samples is determined to 30%.

The above results convincingly show the effect of the modification according to this invention.

Example 2 : ATRP polymerisation Preparation of modified wood

Step 1: Spruce wood blocks (RxTxL: 10x10x5 mm3) are oven dried at 65°C for 24h. The cubes (6.0 g, 37.0 mmol OH) are placed in a flask under vacuum for 30 minutes. In a second flask cooled in an ice bath, a-Bromoisobutyryl bromide (4.2 g, 18.5 mmol) is slowly added to anhydrous pyridine. After addition and if needed, precipitate is filtered off. Then the solution is added to the first flask, and the blocks are gently stirred in solution for 5h. After reaction, the cubes are removed from solution, blotted with paper to remove excess solvent, and washed with several volumes of acetone to remove all unreacted linker. After the rinsing step, the functionalized cubes are placed in the oven for drying (65°C, 24h) .

Step 2: the cubes are placed under vacuum for 30 minutes. In a second flask, the reaction media is prepared: CuBr (73 mg, 51 pmol), PMDETA (88 mg, 51 pmol), styrene in D F (50:50 w/w) are mixed together. The flask is degassed and three freeze-pump-thaw cycles are performed in order to get rid of oxygen. The solution is transferred to the first flask using a steel cannula, then the temperature of the solution is raised to 75°C to initiate the reaction, and the polymerization is terminated after 5h. The blocks are retrieved from solution, washed with acetone and water, and oven-dried for 24h at 65°C.

Characteristics of wood modified

1) Structural and chemical characterization: According to Raman analysis and SEM data, the polymer is present in cell wall only; see figs. 4 and 5. 2) Surface properties: The modified wood has s hydrophobic surfaces, as shown in figure 8. It should be noted that the first step of the treatment (reaction of -OH groups with the linker ( ood-BiBB) , already provides significant hydrophobic properties.

3) Water uptake (WU) : The water uptake of modified wood (after five days soaking in water) , is decreased by a factor of ~ 2 when compared to untreated wood. A typical WU value for wood treated according to this invention is comprised between 60 and 75%, while untreated wood has a WU comprised between 180 and 210%, see fig. 6.

4) Modified wood cubes show reduced swelling upon immersion in water when compared to untreated wood; see fig . 7.

5) WPG of the samples is determined to 18%.

Claims

Claims :

1. A wood product comprising a species of wood and a

polymerized monomer, characterized in that said species of wood is a bulk wood; said polymerized monomer is selected from the group consisting of acrylonitrile, styrenics, acrylates, acrylamides ; said polymerized monomer is covalently bond to said of formula (II) or (III)

wherein

X¹ represents halogen;

X² represents halogen, substituted Ci-4 alkoxy, the substituents being selected from the group consisting of cyclopropxoy , (Tri-Ci-4-alkxylsilyl ) , (Tri-Ci- 4-alkoxysilyl) , (tri-halogensilyl;

R⁶ represents Ci-4 alkyl;

R⁷ represents hydrogen, C₁-4 alkyl;

X³ represents halogen or hydroxy;

R⁸ represents Ci-Ca alkandiyl optionally substituted

2. The wood product according to claim 1, characterized in that said polymerized monomer is selected from the group of acrylonitrile, styrenics of formula (la), acrylates of formula (lb), acrylamides of formula (Ic) ,

wherein

R² represents unsubstituted or substituted C6-10 aryl, unsubstituted or substituted heteroaryl having 5- 10 ring members and 1-3 heteroatoms independently selected from N, 0, S, and the substituents being selected from Ci-4 alkyl, (Tri-Ci-4-alkylammonium) - Ci-4 alkyl, B(OH)₂;

R³ represents hydrogen, Ci-₄ alkyl;

R⁴ represents vinyl, C1-4 alkyl; (di-Ci-4-alkylamino) - Ci-4 alkyl, (tri-Ci-₄-alkoxysilyl) -C1-4 alkyl, (Cycloporpoxy) -Ci-4 alkyl, (meth) acryl, mono- to penta-ethylenglycol;

R⁵ represents C1-4 alkyl; (hydroxy) -C1-4 alkyl,

acrylamino) C1-4 alkyl.

The wood product according to any of the preceding claims, characterized in that said polymerized monomer is selected from styrene.

The wood product according any of the preceding claims, characterized in that said linker of formula (II) is

or said linker of formula (III) is

5. The wood product according to any of the preceding

claims characterized in that at least 10 wt% of said polymerized monomer is located within the cell wall of said wood. The wood product according to any of the preceding claims characterized in that

^■ it has a weight percent gain of 10-30%; and / or

^■ it has a water uptake of 60-75%; and / or

^■ it has an anti-swelling efficiency of 5-45%.

A shaped article, particularly selected from the group consisting of building elements, furnitures, chips, comprising a wood product according to any of the preceding claims.

Use of a compound according to formula (II) or (III), as defined in claims 1 and 5, for the treatment of wood .

Use of a wood product according to claim 1-6 or a shaped article according to claim 7 as a building element or as a veneer.

A method for manufacturing a wood product according to any of claims 1 - 6 comprising the steps of

^■ providing a species of dry wood;

^■ impregnating said species with a first solution comprising a linker of formula (II) or (III);

^■ reacting the linker with hydroxy groups of said dry wood at room temperature to obtain activated wood;

* optionally removing excess linker;

^■ impregnating said activated wood with a second

solution comprising monomers selected from the group consisting of acrylonitrile, styrenics, acrylates, acrylamides;

^■ polymerizing said monomers, preferably by free

radical polymerisation or by ATRP;

^■ optionally post-treatment.