Colored acetylated wood

Abstract

A colored acetylated wood of the Pinus taeda species, which has been found to yield advantageous coloring properties, is disclosed. A method for producing colored acetylated wood is also disclosed. Here, the wood is subjected to a wood acetylation treatment and a wood coloring treatment. The wood coloring treatment includes impregnating the wood with a liquid containing a coloring agent to obtain impregnated wood, and removing the liquid from the wood by evaporation or the like.

Description

Technical Field

[0001] The present invention relates to a process for the acetylation of wood, which wood is subjected to coloring. The present invention also relates to acetylated wood provided with a colorant.

Background Art

[0002] The acetylation of wood has long been recognized as a way to improve the durability of otherwise non-durable softwood species. It is also known as a method for improving properties of wood such as hardness, durability, and dimensional stability.

[0003] Over the decades since 1928, various processes for the acetylation of wood have been proposed. A background reference regarding a particularly suitable process is International Publication No. 2009 / 095687. Other references include European Patent No. 0650998, European Patent No. 0799272, and International Publication No. 2010 / 151320. The various acetylation processes have been disclosed in relation to various wood species such as radiata pine, beech, poplar, southern yellow pine, and spruce.

[0004] Following decades of research and the availability of a wide variety of wood species, commercial development has so far been limited to a few species, particularly pine such as southern yellow pine and radiata pine. The latter is known under the trade name Accoya® and is today recognized as the gold standard in the art.

[0005] A major advantage of acetylated solid wood is that it generally allows outdoor use without significant protection means such as coatings. The latter advantage clearly applies to acetylated wood when used as such. In fact, the natural color of the wood is generally evaluated for acetylated wood. As the interest in acetylated wood for various applications such as outdoor furniture, decks, doors, windows, etc. increases, the interest in the availability of acetylated wood in various colors is also increasing.

[0006] However, painting acetylated wood for protective purposes contradicts one of its main advantages, namely its ability to be used outdoors without coating. Considering this, it has been proposed in the art to provide colored acetylated wood by impregnating it with a colorant. This results in a wood material that provides the appearance and feel of natural wood, but with the desired color and without the need for coating. This also has the added advantage of avoiding the typical polymer components of paints that have adverse environmental impacts on related wood products.

[0007] Background references regarding the coloring of acetylated wood include International Publication Nos. 2018 / 106923 and International Publication Nos. 2018 / 106925. These publications describe a method for coloring acetylated wood by impregnating it with a coloring medium in a chamber and then heating it.

[0008] A suitable example of acetylated wood products, colored by supplying stains to wood, is commercially available as Accoya® Color. However, the production of such colored acetylated wood involves considerable challenges associated with the impregnation process. Specific problems include color uniformity (within a board) and color distribution (between boards). Poor color uniformity is typically observed by wide-ranging color variations between samples of colored acetylated wood products, such as beams or boards. Poor color uniformity and distribution manifest as a lack of or insufficient coloring in various places on the wood product, which may be visible as white or pale patches.

[0009] The aforementioned problems result in a relatively high rejection rate during the production of colored acetylated wood. This negatively impacts the efficiency of the coloring process, the costs involved, and leads to an undesirably large amount of waste wood product. Therefore, it is desirable to find a method for producing colored acetylated wood that has better color uniformity, better color distribution, or both. [Overview of the project]

[0010] To adequately address one or more of the above-mentioned requirements, the present invention provides, in one embodiment, an acetylated wood product comprising at least one coloring agent in wood, wherein the wood is of the Pinus taeda species.

[0011] In another embodiment, the present invention provides a process for producing colored acetylated wood, comprising preparing wood and subjecting the wood to a wood acetylation treatment and a wood coloring treatment, wherein the wood coloring treatment includes impregnating the wood with a liquid containing a coloring agent to provide impregnated wood, optionally followed by heating and removing the liquid from the wood by evaporation or the like, wherein the wood is of the Pinus taeda species.

[0012] In yet another embodiment, the present invention provides a process for producing colored acetylated wood, comprising preparing acetylated wood, impregnating the wood with a liquid containing a coloring agent to provide impregnated wood, and removing the liquid from the wood by evaporation or the like, wherein the wood is of the Pinus taeda species, and in particular by coloring the acetylated wood.

[0013] In a further embodiment, the present invention relates to the use of Pinus taeda wood for producing colored acetylated wood.

[0014] In another aspect, the present invention provides the use of Pinus taeda wood by acetylating the wood for the purpose of producing acetylated wood that is colored by impregnating it with a pigment dispersion, preferably an aqueous pigment dispersion. [Modes for carrying out the invention]

[0015] This invention is based on the insightful selection of Pinus taeda species wood for producing acetylated wood with properties suitable for impregnation with colorants. In particular, Pinus taeda species wood, commonly known as Lobbrolli pine or Taeda pine, exhibits better coloring properties than Radiata pine. This is unexpected, considering the fact that Radiata pine and Lobbrolli pine exhibit similar properties with respect to their ability to be acetylated.

[0016] This invention is defined in relation to acetylated wood products comprising at least one colorant in wood. The presence of a colorant in the wood helps to distinguish the colorants applicable to this invention from any colorants present in a coating or paint, or otherwise applied externally. The wood of this invention is colored by impregnation with a colorant. The colorant can generally be any colorant, in particular dyes or pigments. Dyes are generally soluble colorants, while pigments are generally colorants that are completely or nearly insoluble in water or a solvent, and are thus provided as dispersions. In most cases, dyes are organic compounds. Dyes include acidic colorants. Pigments can be inorganic or organic compounds, but often pigments are inorganic compounds. Pigments can be ionic or neutral compounds.

[0017] Since the colorants are applied by impregnation, they are provided in a suitable liquid carrier, preferably an aqueous liquid, more preferably water containing a co-solvent, and more preferably water containing 0% w / w to 10% w / w of a co-solvent. Dyes are generally water-soluble and are applied in the form of aqueous solutions. Pigments are applied by impregnating the wood with an aqueous dispersion or solvent-based dispersion. Preferably, the colorants are provided in the form of an aqueous dispersion of the pigment. Preferably, such dispersions have a pigment concentration of 0.1% w / w to 10% w / w, more preferably 0.2% w / w to 8% w / w.

[0018] Preferably, the liquid carrier used is mostly aqueous, and the colorant used is essentially insoluble in this liquid medium, so the resulting colorant medium is in the form of a particulate dispersion of the colorant in the selected liquid medium. In this embodiment, the colorant is selected from the classes of colorants defined by Colour Index International as pigments (including organic pigments, inorganic pigments and lakes), disperse dyes, vat dyes and sulfur dyes, and a single or more colorants within the same Colour Index class, or a single or more colorants from two or more different Colour Index classes can be used. Appropriate colorant selection includes, but is not limited to, the following: [CI Yellow Pigments 1, 3, 34, 35, 42, 53, 73, 74, 83, 93, 97, 109, 110, 120, 128, 135, 150, 151, 154, 138, 155, 139, 170, 175, 180, 181, 183, 184, 191, 194, 213], [CI Orange Pigments 20, 36, 38, 43, 62, 64, 66, 71, 72, 73, 78, 82], [CI red pigments 31, 48, 48.1, 48.2, 48.3, 48.4, 101, 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 170, 175, 176, 177, 178, 179, 184, 185, 187, 18 8, 190, 202, 208, 224, 242, 254, 255, 264, 265, 266, 268, 269, 275], [CI purple pigment 19, 23, 28, 32], [CI blue pigment 15.1, 15.2, 15.3, 15.4, 15.5, 15.6, 36, 60], [CI green pigment 7, 8, 17, 36, 50], [CI brown pigment 23, 25, 3 8], [CI Black Pigments 7, 11, 26, 28], [CI Yellow Disperse Dyes 23, 42, 54, 64, 82, 114, 211], [CI Orange Disperse Dyes 25, 29, 30, 44, 61, 73, 76], [CI Red Disperse Dyes 50, 53, 55, 59, 60, 73, 74, 82, 91, 146, 153, 167, 179, 190, 343, 364], [CI[CI Violet Disperse Dyes 26, 28, 31, 33, 63, 73, 77, 93], [CI Blue Disperse Dyes 56, 60, 72, 73, 77, 79, 87, 143, 148, 165, 183.1, 257, 359, 360, 367], [CI Brown Disperse Dyes 1, 1.1, 19, 27], [CI Bat Yellow 1, 33], [CI Bat Orange 1, 2, 3, 9], [CI Bat Red 1, 10, 13, 14, 15, 29, 31, 54], [CI Bat Violet 1], [CI Bat Blue 4, 6, 13, 14, 15, 18, 20, 43], [CI Bat Gri [CI Sulfur Yellow 1, 3, 8, 9, 13], [CI Bat Brown 1, 3, 68, 72], [CI Bat Black 8, 9, 25, 27, 29, 38], [Yellow Solvent 16, 163, 193, 232], [Red Solvent 242], [Purple Solvent 11], [Blue Solvent 36, 63, 78, 97, 102], [Green Solvent 3], [CI Sulfur Yellow 2, 9], [CI Sulfur Orange 1], [CI Sulfur Red 6], [CI Sulfur Blue 5, 7, 13, 15], [CI Black 1, 6], [CI Sulfur Green 6], [CI Sulfur Brown 10].

[0019] A preferred colorant is an aqueous carbon black pigment dispersion, such as EFI / Rialco AWC1 gray pigment dispersion.

[0020] The final pigment or dye content of colored wood typically depends on the extinction coefficient and concentration of the pigment / dye. A preferred range for the pigment content of wood is 0.05% w / w to 10% w / w, more preferably 0.05% w / w to 5% w / w.

[0021] Impregnation can be carried out by impregnation methods known to those skilled in the art of wood impregnation, such as the Lowry process or the Bethel process. Generally, the pigment concentration is selected in a high range, in the case of the Lowry process, which involves injecting the impregnation fluid into the wood under pressure. Similarly, the Rueping process can also be used.

[0022] Typical impregnation conditions for a Tanker-type process (preferably at room temperature) include, continuously, fluid filling at atmospheric pressure, impregnation pressure of 12.0 bar (absolute pressure) for 15 to 30 minutes (also denoted as Bara), liquid removal, and a final vacuum of 0.13 bar (absolute pressure) for 20 to 25 minutes.

[0023] Typical impregnation conditions for a vessel-type process (preferably at room temperature) include, continuously, a pre-vacuum of 0.15 bar (absolute pressure) for 7 to 15 minutes, fluid filling while applying vacuum, an impregnation pressure of 12.0 bar (absolute pressure) for 15 to 30 minutes, liquid removal, and a final vacuum of 0.13 bar (absolute pressure) for 20 to 25 minutes.

[0024] The impregnation process is preferably designed to satisfy the following results: 1 m of wood 3 Fluid intake of 250 to 700 liters per unit (depending on the selected process), penetration of the pigment dispersion into the entire wood product, and uniform penetration and retention throughout the height, width, and length of the stack. This can be achieved more easily with Pinus taeda wood than with radiata pine.

[0025] In generally preferred embodiments, impregnation includes placing wood in a vacuum chamber, optionally applying a pre-vacuum to remove air from the wood, adding a liquid containing a coloring agent to the chamber, optionally holding the wood in the chamber under vacuum to fill the chamber with the liquid, raising the pressure of the liquid-filled chamber above atmospheric pressure for 1 to 180 minutes, reducing the pressure to provide impregnated wood, and finally removing excess liquid from the chamber and optionally applying a final vacuum.

[0026] After the coloring and impregnation process, the resulting product is typically (but not limited to) kiln-dried at 60°C to 80°C to remove the water used during the coloring process, preferably until the moisture content is 8% or less, but this is not mandatory. This generally takes 3 to 18 days, depending on the kiln load capacity, liquid intake, kiln configuration, and wood size.

[0027] In the field of wood acetylation, generally two types of substrates for acetylation are distinguished, namely, solid wood and wood elements. The latter generally refers to smaller wood pieces ranging from larger elements such as chips or strands to smaller elements such as fibers. The term "solid wood" is generally used to denote relatively large wood forms such as beams or boards. Another typical relatively large wood form is the veneer wood form. Although one dimension (thickness) is essentially thin, the veneer has relatively large dimensions in terms of length and possibly width.

[0028] The Pinus taeda wood products disclosed herein are typically solid wood products or veneers. Apart from practical considerations known to those skilled in the art, such as the availability of sufficiently large equipment, the wood may have any size. The solid wood (e.g., boards / planks) or wood veneers of the present invention preferably have a length or width of at least 8 cm. The thickness is preferably at least 1 mm. In some embodiments, the wood has a width of 2 cm to 30 cm, a thickness of 1 cm to 16 cm, and a length of 0.5 m to 6.0 m. In other embodiments, the wood has a thickness of at least 1 mm, a width of 10 cm to 25 cm, and a length of 1 m to 6 m.

[0029] The wood acetylation process for acetylating Pinus taeda wood can be a batch process, a semi - continuous process (such as a process combining batch - type feeding and continuous acetylation), or a continuous process. The acetylation of the wood of the present invention is generally carried out according to an optimized acetylation process known in the art. Preferred processes include the following steps: Preparing the wood (solid wood or wood veneer); Controlling and optionally adjusting the moisture content of the solid wood or wood elements; Impregnating the solid wood or wood veneer with an acetylation fluid; Subjecting the impregnated solid wood or wood veneer to one or more heating steps to achieve acetylation of the solid wood or wood elements; Separating the acetylated solid wood or wood veneer from the excess acetylation fluid.

[0030] The acetylation process itself can be carried out using liquid and / or gaseous acetylation fluids, as is known in the art. Typical acetylation fluids are acetic acid, acetic anhydride, and mixtures thereof. Preferably, the initial acetylation fluid used is acetic anhydride, more preferably in small amounts, generally 2 wt.% to 20 wt.%, for example, 5 wt.% to 10 wt.% of acetic acid. The composition of the acetylation fluid changes during the process, as acetic acid is formed thereby as a result of the acetylation reaction.

[0031] In an interesting embodiment, acetylation is carried out according to any one of the acetylation processes described in International Publication No. 2009 / 095687, International Publication No. 2011 / 95824, International Publication No. 2013 / 117641, International Publication No. 2013 / 139937, or International Publication No. 2016 / 008995, the disclosures thereof incorporated herein by reference.

[0032] A preferred process is described in International Publication No. 2009 / 095687. This specification describes a process for acetylating wood, the method comprising the steps of immersing wood in an acetylation solution in a reaction pressure vessel, performing an impregnation procedure, removing excess acetylation fluid, introducing an inert fluid (typically nitrogen gas, the inert fluid optionally containing non-inert acetic anhydride and / or acetic acid) into the vessel, circulating and heating the inert fluid according to a heating regime to bring about proper acetylation of the wood, and removing the circulating fluid and cooling the acetylated wood.

[0033] Another preferred process is the one described in International Publication No. 2013 / 117641, which discloses an acetylation method suitable for achieving high acetyl content in high-density wood species such as Pinus taeda (Robloly pine / Taeda pine) and other Southern Yellow pine species. Here, the moisture content of the wood to be acetylated is controlled to be less than 5 wt.%, preferably at a level of 1 wt.% to 4 wt.%.

[0034] The acetylated wood obtained by the above method has a high degree of acetylation. In particular, it has an acetyl content of more than 20% by weight at its geometric center. Preferably, the acetyl content is more than 21% by weight at its geometric center, more preferably more than 22% by weight, and even more preferably more than 23% by weight. In a preferred embodiment, the acetyl content of the acetylated wood is 21 wt.% to 26 wt.% at its geometric center.

[0035] To determine the acetyl content of wood, samples are ground into wood particles. From these samples, residual trace amounts of acetic acid and / or acetic anhydride are removed by washing with water and then drying at 103±2°C for 14–24 hours. After weighing these dried samples, acetyl groups are released from the wood in the form of acetate ions by saponification with a sodium hydroxide solution at high temperature. This saponification reaction is carried out for 4 hours, stirring every 15 minutes. Acetate ions are quantified by high-pressure liquid chromatography (HPLC), calibrated with a standard acetate solution and using sodium butyrate as an internal reference. This provides a more direct measure of acetyl content than the common weight gain rate (WPG) frequently used in other studies.

[0036] The present invention also relates to a process for producing colored acetylated wood, wherein the wood is of the Pinus taeda species.

[0037] This process involves providing wood of the Pinus taeda species and subjecting the wood to wood acetylation and wood staining treatments. This process may include first subjecting the wood to a staining treatment, and then subjecting the resulting stained wood to wood acetylation treatment. Alternatively, this process may include subjecting the staining treatment and acetylation treatment in parallel. Preferably, the wood is first subjected to acetylation treatment, and the resulting acetylated wood is then subjected to wood staining treatment.

[0038] In all of these embodiments, the wood staining treatment includes impregnating Pinus taeda wood with a liquid containing a staining agent to obtain impregnated wood, optionally followed by heating, and removing the liquid from the wood by evaporation or the like. In all of these embodiments, the acetylation treatment is preferably carried out by the wood acetylation process described above.

[0039] The wood staining treatment itself can be carried out according to the processes disclosed, for example, in International Publication Nos. 2018 / 106923 and International Publication Nos. 2018 / 106925, which are incorporated herein by reference. In preferred embodiments, the liquid, i.e., the liquid carrier for one or more coloring substances, is subjected to heating before, during, or after impregnation. This is thought to help fix the one or more coloring substances to the surface and areas (external or internal) of the acetylated wood product impregnated with the liquid carrier. The heating temperature is generally from 50°C to the boiling point of the liquid, preferably water. It will be understood that temperatures above the atmospheric pressure boiling point can be achieved at appropriately higher pressures. Thus, with water as the preferred liquid, the heating is preferably in the range of 50°C to 160°C, preferably 50°C to 140°C, more preferably 60°C to 120°C, and most preferably 60°C to 100°C.

[0040] In a preferred embodiment in which coloring is performed after acetylation, the process includes preparing acetylated wood. The wood is then impregnated with a liquid containing a colorant to provide impregnated wood. Preferably, the liquid is water, and more preferably, the liquid containing the colorant is preferably an aqueous dispersion of the pigment described above. The impregnated wood is an intermediate product, and it will be understood that the colored wood is finally obtained after at least a portion of the liquid carrier has been removed from the wood in such a manner that the colorant remains. Typically, such removal is by evaporation. When water is the liquid, evaporation typically includes drying, preferably kiln drying.

[0041] In a different embodiment, the present invention presents a novel use of Pinus taeda wood, namely, the production of colored acetylated wood. Hereinafter, Pinus taeda wood is used in the production of acetylated wood by acetylating the wood for the purpose of producing colored acetylated wood by impregnating it with a liquid containing a colorant, such as a dye solution or pigment dispersion, preferably an aqueous pigment dispersion. Any embodiments described for the products and processes of the present invention are also applicable to the uses of the present invention.

[0042] The colored acetylated wood of the present invention can be used in many applications, preferably outdoors, in order to benefit from the properties of acetylated wood. Typical applications include joinery, decking, and exterior materials. Regarding the coloring of the wood, applications that may have design requirements, such as decking or outdoor furniture, are preferred.

[0043] After the coloring process, the product (colored acetylated pinus taeda) is planed to evaluate the quality / uniformity of the through-and-through coloring process. Typically, 0.5mm to 2mm of the product is planed off.

[0044] In summary, colored wood of the Pinus taeda species is disclosed, which is found to provide advantageous coloring properties. A method for producing colored acetylated wood is also disclosed. Here, the wood is subjected to wood acetylation treatment and wood coloring treatment. The wood coloring treatment includes impregnating the wood with a liquid containing a coloring agent to obtain impregnated wood, and removing the liquid from the wood by evaporation or the like.

[0045] Example 1 - Coloring of acetylated Pinus taeda: 25 x 250 x 2400 mm Pinus Taeda boards supplied from Uruguay were acetylated in accordance with International Publication No. 2013 / 117641. The coloring process was carried out in a typical pressure impregnation vessel. Before treatment with the coloring agent, the acetylated Pinus Taeda boards were stacked into bundles (packs), with untreated softwood battens or equivalent used to space the boards apart to ensure that the liquid or gas could be evenly distributed throughout the entire bundle of wood.

[0046] Next, the acetylated wood is pressure-treated with EFI / Rialco AWC1 gray stain in a standard high-pressure wood treatment plant. The AWC1 working solution is prepared by mixing the AWC1 concentrate with water to a concentration of 6.5% w / w of AWC1 concentrate in water. The solution concentration can be measured on-site using a spectrophotometer, and this should be done after each mixing. Impregnation is carried out at a pressure of 12 bar (absolute pressure) for 30 minutes.

[0047] The impregnation process is designed to yield the following deliverables: ·Wood 1m 3 Intake of 250 to 350 liters of fluid per unit • Complete penetration throughout the entire board • Uniform penetration and retention throughout the entire height of the pack

[0048] After this color treatment, the product is kiln-dried at 70°C for 10 days, and the water used during the treatment process is removed to a moisture content of 8% or less while monitoring the moisture content.

[0049] For the kiln drying process, battens with a minimum thickness of 19 mm were used to allow sufficient airflow through the bundles (packs).

[0050] In the final stage, the kiln-dried products are planed to visualize the difference between uniform and uneven coloring. Typically, planing is done to remove the top 0.5 mm to 1.5 mm of the wood surface. The product demonstrated good color uniformity when visually evaluated.

[0051] Comparative example - Coloration of acetylated pine radiata. The conditions of the example are used, but acetylated New Zealand radiata pine is used as the wood source. The product exhibited insufficient color uniformity upon visual evaluation. This resulted in significantly higher localized variations in color intensity within and between boards compared to Pinus Taeda-based colored products.

[0052] Example 2 After acetylation, 28 boards of acetylated pine (TP), measuring 25 x 250 mm / 1.8 m, were colored by impregnating the wood with a liquid containing a wood stain and EFI / Rialco AWC1 gray pigment. As a reference, a 25 x 200 mm board of Accoya® Radiata Pine (RP) was similarly colored. The coloring involved impregnation using either the Laurie process or the Vessel process.

[0053] After coloring, the boards were planed and evaluated for color unevenness. Four boards were randomly selected from both wood species. Photographs were taken with an iPhone® Xs. The boards were cut to a length suitable for a scanner; Konica Minolta Bizhub C3351. The heartwood and bark sides of each sample were scanned as jpg files (300 x 300 pixels resolution). The scans were then cropped and evaluated in grayscale using a software program called "ImageJ". A grayscale histogram (ranging from 0 to 255) of the images was created for each sample. Average color and color variation (based on the 5th to 95th percentiles) were calculated for each sample.

[0054] Table 1 summarizes the evaluation results per sample (on the bark side) regarding the mean, median, and variability (based on the 5th to 95th percentiles) of the grayscale.

[0055] [Table 1]

[0056] Analysis of the results: For both wood species, the darkness is slightly higher with the Bethel process compared to the Laurie process. In the case of ACO Taeda, the average grayscale value for the Bethel process is 95-97, while for the Laurie process it is 102-105. The darkest and most uniform color is seen in ACO NZ RP (plate 18) using the bezel process. The difference in grayscale mean values ​​and the maximum variation (scatter) are observed in ACO NZ RP boards produced by the Vessel process. Based on these four boards, the minimum difference in grayscale mean values ​​and the minimum variation within the board (5th percentile to 95th percentile) were found for ACO TP boards processed by the Vessel process, followed by ACO TP boards processed by the Laurie process. Generally, objective evaluations have demonstrated that ACO TP exhibits more uniform inter- and intra-board coloring compared to ACO NZ RP results, for both the Vessel and Laurie processes.

[0057] [Table 2]

Claims

1. An acetylated wood product comprising at least one coloring agent in wood, wherein the wood is of the Pinus taeda species.

2. The acetylated wood product according to claim 1, wherein the coloring agent is a pigment or a dye.

3. The acetylated wood product according to claim 2, wherein the coloring agent is a pigment selected from the group consisting of organic pigments, inorganic pigments, and combinations thereof.

4. The acetylated wood product according to claim 3, wherein the pigment is a carbon black pigment such as EFI / Rialco AWC1 gray pigment.

5. The process includes preparing wood, subjecting the wood to wood acetylation treatment and wood staining treatment, wherein the wood staining treatment includes subjecting the wood to impregnation with a liquid containing a coloring agent to provide impregnated wood, and removing the liquid from the wood by evaporation or the like. A process for producing colored acetylated wood, wherein the wood is of the Pinus taeda species.

6. The process according to claim 5, wherein the impregnated wood is heated during or after impregnation.

7. The process according to claim 5 or 6, wherein the wood coloring treatment is performed before or during the wood acetylation treatment.

8. The process according to claim 5 or 6, wherein the wood coloring treatment is performed after the wood acetylation treatment.

9. A process for producing colored acetylated wood, comprising: preparing acetylated wood; impregnating the wood with a liquid containing a coloring agent to provide impregnated wood; and removing the liquid from the wood by evaporation or the like, wherein the wood is of the Pinus taeda species.

10. The process according to any one of claims 5 to 9, wherein the liquid is water or a mixture of water and an organic cosolvent.

11. The process according to any one of claims 5 to 10, wherein the liquid containing the coloring agent is a dispersion of pigment in water or a dispersion of pigment in a mixture of water and an organic cosolvent.

12. The process according to claim 11, wherein the pigment is a carbon black pigment such as EFI / Rialco AWC1 gray pigment.

13. The process according to any one of claims 6 to 12, wherein the liquid is removed from the impregnated wood by kiln drying.

14. The impregnation process according to any one of claims 6 to 12, comprising: placing the wood in a vacuum chamber; optionally applying a pre-vacuum to remove air from the wood; adding the liquid containing the coloring agent to the chamber; optionally holding the wood in the chamber under vacuum to fill the chamber with the liquid; raising the pressure of the liquid-filled chamber above atmospheric pressure for 1 to 180 minutes; reducing the pressure to provide impregnated wood; and finally removing excess liquid from the chamber and optionally applying a final vacuum.

15. The use of Pinus taeda wood in producing acetylated wood by acetylating the wood, for the purpose of producing acetylated wood that is colored by impregnating it with a pigment dispersion, preferably an aqueous pigment dispersion.

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