METHOD FOR CHEMICALLY MODIFYING A WOOD PART

Abstract

A method for chemically modifying a wood part comprising hydroxyl groups comprising: a first step of covalently reacting all or part of the hydroxyl groups with at least one non-polymeric compound comprising at least one group capable of covalently reacting with a hydroxyl group, whereby the wood part is thus covalently linked to residues of the non-polymeric compound(s); after or simultaneously with the first step, a second step of covalently reacting all or part of the residues of the non-polymeric compound(s) with at least one second compound, the first step and the second step being performed in the presence of at least one supercritical fluid.

Claims

1.-17. (canceled)

18. A method for chemically modifying a wood part comprising hydroxyl groups comprising the following steps: a first step of covalently reacting all or part of said hydroxyl groups with at least one non-polymeric compound, called the first compound, comprising at least one group capable of covalently reacting with a hydroxyl group, whereby, at the end of this first reaction step, the wood part is thus covalently linked to residues of the non-polymeric compound(s); after or simultaneously with said first step, a second step of covalently reacting all or part of the residues of the non-polymeric compound(s) with at least one second compound, said first step and said second step being performed in the presence of at least one supercritical fluid.

19. The method according to claim 18, wherein the supercritical fluid is supercritical CO.sub.2.

20. The method according to claim 18, wherein the wood part is made of one or more wood species selected from hardwoods, softwoods and mixtures thereof.

21. The method according to claim 18, wherein the wood part is a part of softwood(s).

22. The method according to claim 18, wherein the non-polymeric compound(s) is (are) selected from epoxy compounds, anhydride compounds, acyl halide compounds, carboxylic acid compounds, silyl ether compounds, isocyanate compounds and mixtures thereof.

23. The method according to claim 18, wherein the non-polymeric compound(s) is (are) epoxy compounds.

24. The method according to claim 18, wherein the non-polymeric compound(s) is (are) epoxy compounds comprising at least one vinyl group.

25. The method according to claim 18, wherein the first reaction step is performed in the presence of at least one cosolvent.

26. The method according to claim 18, wherein the first reaction step includes the following operations: an operation of placing, in a reactor, the wood part, at least one non-polymeric compound, optionally at least one cosolvent and optionally at least one catalyst an operation of introducing CO.sub.2 into the reactor; an operation of pressurising and heating the reactor to a temperature higher than the critical temperature of the CO.sub.2 and to a pressure higher than the critical pressure of the CO.sub.2, this temperature and this pressure being maintained until the reaction is completed.

27. The method according to claim 18, wherein the residue(s) comprise(s), as group(s) capable of reacting with at least one group of the second compound(s), at least one vinyl group.

28. The method according to claim 18, wherein the second compound(s) comprise(s) at least one group capable of imparting a given property to the wood part or improving a given property of the wood part, called the functional group of interest.

29. The method according to claim 28, wherein the second compound(s) include, as a functional group of interest, at least one group comprising at least one phosphorus atom, such as a phosphate group or a phosphonate group.

30. The method according to claim 27, wherein the second compound(s) comprise(s) at least one vinyl group.

31. The method according to claim 18, comprising successively the following steps: as a first step, a first step of covalently reacting all or part of said hydroxyl groups of the wood part with at least one non-polymeric compound, called the first compound, comprising at least one group capable of covalently reacting with a hydroxyl group and comprising at least one vinyl group, whereby, at the end of this first reaction step, the wood part is thus covalently linked to residues of the non-polymeric compound(s); as a second step, from the vinyl groups of the residues of the non-polymeric compound(s), a step of polymerising a second compound comprising at least one vinyl group, said first step and said second step being performed in the presence of at least one supercritical fluid.

32. The method according to claim 31, wherein: the first covalent reaction step is a step of covalently reacting all or part of said hydroxyl groups with a first compound comprising at least one epoxy group and at least one vinyl group, in the presence of supercritical CO.sub.2, the epoxy groups covalently reacting with all or part of the hydroxyl groups, whereby, at the end of this first reaction step, the wood part is thus covalently linked to residues of the first compound; the second covalent reaction step is a step of polymerising a second compound comprising at least one vinyl group and at least one functional group of interest, such as a phosphate group, in the presence of supercritical CO.sub.2, the polymerisation being initiated from the vinyl groups of the residues of the first compound.

33. The method according to claim 18, which is a method capable of imparting or improving a given property of the wood part.

34. The method according to claim 18, which is a method for treating the wood part with fire retardant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] FIG. 1 illustrates a photograph of the slice of wood (point a) corresponding to the edge of the specimen, point c) to the core of the specimen and point b) to an interspace between the edge and the core) obtained in accordance with the example below.

[0086] FIG. 2 illustrates IR-ATR spectra of wood samples obtained in accordance with the example below.

[0087] FIG. 3 illustrates IR-ATR spectra of wood samples obtained in accordance with the example below.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Example

[0088] This example illustrates the implementation of a specific mode of the chemical modification method of the invention which comprises a chemical modification in two steps:

[0089] 1) a step of reacting spruce wood parts, which are spruce specimens, with glycidyl methacrylate (referred to below as GMA);

[0090] 2) a step of reacting the thus modified parts with a phosphorus compound: bis[2-(methacryloyloxy)ethyl]phosphate (referred to below as BMEP),

[0091] these two steps being performed under supercritical CO.sub.2 in a specific reactor.

[0092] The simplified reaction scheme for these two reactions can be as follows:

##STR00002## [0093] Wood-OH corresponding to the wood part, with only one —OH group represented for the sake of simplification and p corresponding to the number of repeats of the repeating unit in brackets.

[0094] The specific reactor mentioned above is a 600 mL stainless steel batch type reactor with an outer heating system. The reagents (GMA, BMEP), catalysts and solvents (acetone) are deposited in a 70 mL crystalliser placed at the bottom of the reactor. The wood specimens are placed on the edges of the crystalliser to ensure that there is no direct contact between the reagents, catalysts and solvent on the one hand and the wood on the other. The CO.sub.2 is introduced into the reactor, slightly preheated above 31° C., with a double piston pump whose heads are cooled to a temperature below 5° C. to have CO.sub.2 in the liquid phase in the tubes and avoid cavitation problems. In the reactor, however, the CO.sub.2 is never present in the liquid state.

[0095] The wood parts are spruce specimens with dimensions 65*20*24 cm, the wood grain being in the direction of the last dimension and weighing, once dried for 1 hour at 103° C., from 13 to 14 g.

[0096] 1) Step of Reacting Spruce Specimens with GMA

[0097] For this purpose, two spruce specimens previously dried for one hour at 103° C. and meeting the above-mentioned specificities were placed, as described above, in the reactor above the crystalliser containing 27 mL of GMA and 27 mL of acetone. The aim of the acetone added to the reaction medium is to prevent self-polymerisation of the GMA in the crystalliser. 2.7 mL of triethylamine was placed in a separate crystalliser in the reactor. CO.sub.2 was introduced and the reactor was then placed under 200 bar and 140° C. to form supercritical CO.sub.2, these conditions being maintained for 7 hours.

[0098] After depressurisation, the wood specimens were recovered and dried in a vacuum oven at 103° C. overnight. The weight percentage gain (WPG) of the specimens was 22.1 and 22.0% (relative to the dry mass before treatment), and the longitudinal swelling of the specimens after one day's immersion in water was reduced by 60.1 and 56.2% respectively.

[0099] One of the wood specimens was partially cut for analysis by attenuated total reflectance infrared spectroscopy (ATR-IR), the places where the spectroscopy was performed being represented in FIG. 1 which illustrates a photograph of the slice of wood (point a) corresponding to the edge of the specimen, point c) to the core of the specimen and point b) to an interspace between the edge and the core).

[0100] The IR-ATR spectra of unmodified wood (curve d)) and GMA-modified wood (curve a) for the edge, curve b) for the interspace and curve c) for the core) are illustrated in the appended FIG. 2, with the ordinate representing intensity I of the peaks and the abscissa the wave number N (in cm.sup.−1).

[0101] An increase in the intensity of the peak at 1710 cm.sup.−1 corresponding to C═O bonds (especially GMA ester) is observed with the modification by GMA and the depth of analysis in the wood (in the direction of the wood grain). The more the wood is modified, the higher the peak in comparison for example with the peak at 1620 cm′ which corresponds to the aromatic C═C bonds of the lignin (not affected by the modification). It is observed from these spectra that the modification has been carried out to the core of the wood and that a gradient of modification is observed between outside (which is more strongly modified) and the core.

[0102] 2) Step of Reacting the Thus Modified Specimens with BMEP

[0103] The specimens thus modified in the previous step were treated under supercritical CO.sub.2 with bis[2-(methacryloyloxy)ethyl] phosphate (BMEP) in the presence of a free radical initiator: α,α′-AzoBisobutyronitrile (AIBN).

[0104] For this purpose, 5 mL of BMEP and 20 mL of acetone are placed in the crystalliser of the reactor defined above. 0.2 mg of AIBN is deposited at the bottom of the reactor outside the crystalliser. The GMA-modified wood specimens are then placed above the crystalliser without contact with the liquid or the AIBN. The reactor is closed and CO.sub.2 is introduced and the treatment is applied in 2 phases with a first impregnation phase at 40° C., 100 bar for 5 hours followed by a reaction phase at 110° C. and 220 bar for 2 hours.

[0105] The specimens are then recovered and dried in a vacuum oven overnight.

[0106] One of the wood samples was subjected to an analysis of its edge by attenuated total reflectance infrared spectroscopy (IR-ATR), the IR-ATR spectra of the unmodified wood (curve a)), of the wood modified by GMA only (curve b) for the edge) and of the wood modified by GMA and BMEP (curve c)) are represented in the appended FIG. 3, the ordinate representing intensity I of the peaks and the abscissa the wave number N (in cm.sup.−1).

[0107] On curve c), the presence of BMEP clearly appears, especially with the increase in the intensity of the peaks at 983 cm′ (P—O—C bond) and at 1720 cm′ (C═O bond of the BMEP acrylate), thus validating the system described by the invention, which makes it possible to provide functionality via a pre-grafting of a vinyl compound.