Method for surface treating wood with a solution comprising lignin or derivatives thereof

Abstract

The present invention relates to a novel method of surface treating wood containing a high concentration of lignin and can be applied to wood substrates without additional need for curing at elevated temperature. Said method comprises the following consecutive steps: (a) applying the wood with a solution comprising a concentration between 15-75 wt% of lignin or derivates thereof; wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% alcohol, (ii) 0-60 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%.

Description

[0001] (85627EP01)

[0002] 1

[0003] Method for surface treating wood with a solution comprising lignin or derivatives thereof

[0004] Field of the invention

[0005] The present invention relates to a novel method for surface treatment of wood with a solution comprising lignin or derivatives thereof.

[0006] Background of the invention

[0007] Surface treatment of wood with lignin solution is important because it fills up the surface structure of native wood with hydrophobic lignin, which thereby increases the overall hydrophobicity of the wood while also creating physical blockage of the pores in the surface of the wood structure. Thereby, surface treatment of wood with lignin solutions helps protect the wood from various harmful elements such as moisture, insects, fire, and decay. In turn, this will increase the service life of wood products, reduce the need for maintenance, and ultimately save costs, especially for wood with low natural durability such as pine sapwood.

[0008] Currently, surface treatment of wood is predominantly based on petrochemical chemicals such as synthetic polymers. Therefore, there is a need for new, biobased surface treatments for wood made from renewable resources. Lignin is a natural polymer of wood which is highly resistant to fungal digestion, thereby improving wood durability.

[0009] Furthermore, lignin can act as a fire retardant by promoting surface charring during fire which limits oxygen supply to the actively burning layers beneath. Lignin is also abundantly available as a cheap waste-stream from the paper industry, making it a sustainable resource for surface treatments for wood. Industry and academia have put in a sustained effort to valorize lignin waste streams into useful materials and chemicals, including coatings for various substrates. An important first step in many coating production processes is the solubilization of lignin in a solvent or solvent mixture.

[0010] WO1993 / 023477 discloses a method for getting non-sulfonated Kraft lignin in aqueous solution by increasing the pH above 8 and then lowering it below pH 7. The final concentration of lignin in solution after such treatment is from 3.8 wt% to 11.3 wt%.

[0011] WO2022 / 117391A1 discloses methods of producing Cold processed Ethanol Lignin Oil (CLEO) and Cold processed Methanol Lignin Oil (CLiMO) having a dry matter content of at least 30 wt%. The CLEO and CLiMO of WO2022 / 117391A1 is envisaged for use as a fuel, especially for use as fuel in a combustion engine of a ship.(85627EP01)

[0012] 2

[0013] WO2023 / 097359A1 discloses methods for producing a biodegradable coating by dissolving lignin in up to 32 wt% concentration in an acidic or alkaline solution together with cellulose and / or latex. Subsequently, the coating is cured after application to a substrate by heating or acid treatment.

[0014] US 2022 / 0290006A1 discloses a method for producing a lignin-based, microporous coating for water-soluble granules. In one embodiment, the coating was based on 100% lignin solubilized in acetone to concentration of 6 wt% lignin, whereas in another embodiment the coating composition comprised a polymer blend of organosolv lignin and cellulose acetate mixed in acetone with a lignin concentration of 2.5 wt%.

[0015] US 6072015A discloses a method for producing a surface treatment for wood containing water-soluble lignosulphonates, phenol oxidative enzymes and a dye or pigment in an aqueous solution. The concentration of the lignosulphonates ranges from 1 wt% to 60 wt% in the solution. Phenol oxidate enzymes are used to chemically modify the lignosulphonates and cause polymerization of these.

[0016] Hult et al. 2013 (https: / / doi.Org / 10.1016 / j.indcrop.2013.08.013) describes a method for making a lignin-based coating for paper and cardboard by functionalizing lignin with tall oil fatty acid. This lignin is then dissolved to 17 wt% concentration in acetone before being applied to the substrate.

[0017] WO2017 / 188874 discloses a method for producing lignin-based coatings for the automotive industry comprising of lignin of 10-50 wt%, liquid C2-C4 polyol (ethylene glycol, propylene glycol, 1,2-butanediol, 1,4-butanediol, glycerol) of 10-50 wt%, and acrylic resin of 10-50 wt%. These ingredients are mixed into a viscous paste than may be thinned by solvents. After application to intended objects the coating needs curing at 100-120 °C.

[0018] W02014 / 095800 discloses coating compositions of lignin, a solvent and a crosslinker such as polymeric epoxies are cured at elevated temperatures in the range 120-200 °C.

[0019] In view of the drawbacks of the surface treatments of wood with lignin in the prior art, there is a need in the art for a coating composition that contains a high concentration of lignin and can be applied to wood substrates without additional need for curing at elevated temperature.(85627EP01)

[0020] 3

[0021] Summary of the invention

[0022] Thus, an object of the present invention relates to a novel method of surface treating wood containing a high concentration of lignin and can be applied to wood substrates without additional need for curing at elevated temperature.

[0023] The treated wood exhibits enhanced water-repellency, UV-stable colour, and increased resistance to fungal decay, providing a durable and sustainable alternative to conventional surface treatments.

[0024] The method according to the invention comprises the following consecutive steps: (a) applying the wood with a solution comprising a concentration between 15-75 wt% of lignin or derivatives thereof; wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% alcohol, (ii) 0-60 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%.

[0025] From previous work, the inventors have shown how to solubilize lignin with high yield and high concentration in simple solvent systems containing water, ethanol, and other alcohols. This allowed the inventors to process solubilized lignin and use it in a range of applications. The present invention covers a method of using lignin solutions as a surface treatment for wood, providing a moisture barrier, improved resistance to fungal decay, and enhanced UV stability of the surface. The inventors have coated wood boards of various species with lignin solutions of different combinations of alcohols and water and have characterized the liquid water uptake through coated side grain, the contact angle with water, and the depth of penetration using light microscopy.

[0026] Experimental observations have demonstrated that certain lignin formulations create a hydrophobic surface with minimal water absorption, as evidenced by stable and high contact angles over time. Furthermore, microscopy analysis indicates that deeper penetration of specific lignin solutions correlates with stronger adhesion and reduced delamination under prolonged water exposure. These findings indicate that the invention provides a biobased alternative to conventional coatings, enhancing the durability of wood under varying environmental conditions.

[0027] Brief description of the figures

[0028] Figure 1 shows the penetration of different lignin solutions in Scots pine seen by light microscopy on radial sections. Arrows indicate the frontier of the various solutions into the(85627EP01)

[0029] 4

[0030] wood tissue. Arrows in brackets indicate vague frontiers, i.e. low presence of lignin solution. Numbers on the images indicate the ID of lignin solutions detailed in Table 1.

[0031] Figure 2 illustrates the principle of contact angle analysis on images of a water droplet on untreated wood acquired after 5 seconds and 60 seconds. A larger contact angle indicates a more hydrophobic wood surface. As the water wets the surface of the untreated wood the contact angle decreases as seen in the lower image.

[0032] Figure 3 depicts the change in contact angle of a water droplet over 60 seconds for wood treated with lignin solutions 1-3 of Table 1 compared with untreated wood (dotted line). Error bars indicate standard deviation calculated based on triplicate measurements. As can be seen, the contact angles of lignin solutions 1 and 2 remain relatively constant around 50° and 30°, respectively, over 60 seconds compared to untreated wood for which the contact angle decreases from around 60° to around 30° over 60 seconds. This indicates that the surfaces treated with lignin solutions 1 and 2 are not wetted by the water droplet like the untreated wood where the contact angle decreases.

[0033] Figure 4 shows the change in contact angle of a water droplet over 60 seconds for wood treated with lignin solutions 4-7 of Table 1 compared with untreated wood (dotted line). Error bars indicate standard deviation calculated based on triplicate measurements. As can be seen, the contact angles of lignin solutions 4-7 remain relatively constant between around 70° and 90° over 60 seconds compared to untreated wood for which the contact angle decreases from around 60° to around 30° over 60 seconds. This indicates that the surfaces treated with lignin solutions 4-7 are hydrophobic and are not wetted by the water droplet like the untreated wood where the contact angle decreases.

[0034] Figure 5 illustrates the change in contact angle a water droplet over 60 seconds for wood treated with lignin solutions 8-11 of Table 1 compared with untreated wood (dotted line). Error bars indicate standard deviation calculated based on triplicate measurements. As can be seen, the contact angles of lignin solutions 8, 9, and 11 remain relatively constant between around 70° and 90° over 60 seconds compared to untreated wood for which the contact angle decreases from around 60° to around 30° over 60 seconds. This indicates that the surfaces treated with lignin solutions 8, 9, and 11 are hydrophobic and are not wetted by the water droplet like the untreated wood where the contact angle decreases.

[0035] Figure 6 depicts the change in contact angle a water droplet over 60 seconds for wood treated with lignin solutions 12-14 of Table 1 compared with untreated wood (dotted line). Error bars indicate standard deviation calculated based on triplicate measurements. As can be seen, the contact angles of lignin solutions 12-14 remain relatively constant between(85627EP01)

[0036] 5

[0037] around 60° and 80° over 60 seconds compared to untreated wood for which the contact angle decreases from around 60° to around 30° over 60 seconds. This indicates that the surfaces treated with lignin solutions 12-14 are hydrophobic and are not wetted by the water droplet like the untreated wood where the contact angle decreases.

[0038] Figure 7 shows the initial contact angle of the water droplet 5 seconds after it touched the surface of the untreated wood and wood treated with lignin solutions 1-14 of Table 1. Error bars indicate standard deviation calculated based on triplicate measurements. As can be seen the initial contact angle is similar or higher for lignin solutions 4-9 and 11-14.

[0039] Figure 8 shows the reduction in contact angle of the water droplet between measurements after 5 seconds and 60 seconds on the untreated wood and wood treated with lignin solutions 1-14 of Table 1. Error bars indicate standard deviation calculated based on triplicate measurements. As can be seen the reduction in contact angle of all lignin solution is lower than that observed for untreated wood, where the water droplet wets the surface and the contact angle decreases markedly.

[0040] Figure 9 illustrates the effect on the surface appearance of wood samples treated with lignin solutions 1-14 of Table 1. The treated surface of the samples were exposed to liquid water for 6 hours with regular wiping of the surface. Numbers on the images indicate the ID of lignin solutions detailed in Table 1. Arrows indicate cracks in the surface or delamination. As can be seen surfaces treated with lignin solutions 4, 5, 7, 9, 11, and 14 did not delaminate or show signs of cracking after the test.

[0041] Figure 10 illustrates the principle of the floating test where a test sample with sealed edges is placed with the treated surface facing downwards onto a liquid water surface. Images depict a sidegrain sample of dimensions 15x120x120 mm.

[0042] Figure 11 shows the water uptake over 24 hours in sidegrain samples treated with lignin solutions 15-17 of Table 3 compared with untreated wood. Error bars indicate standard deviation calculated based on five replicate measurements. This clearly shows that surface treated samples had a lower water uptake through the lignin treated surface than untreated wood. Thus, the lignin treatment presents a moisture barrier.

[0043] Figure 12 illustrates the water uptake over 24 hours in sidegrain samples treated with lignin solutions 18-20 compared with untreated wood. Error bars indicate standard deviation calculated based on five replicate measurements. This clearly shows that surface treated samples had a lower water uptake through the lignin treated surface than untreated wood. Thus, the lignin treatment presents a moisture barrier.(85627EP01)

[0044] 6

[0045] Figure 13 depicts the water uptake over 24 hours in sidegrain samples treated with lignin solutions 21 and 23 compared with untreated wood. Error bars indicate standard deviation calculated based on five replicate measurements. This indicates that surface treated samples had a slightly lower water uptake through the lignin treated surface than untreated wood. Thus, the lignin treatment presents a moisture barrier.

[0046] Figure 14 shows the water uptake over 24 hours in sidegrain samples treated with lignin solutions 24-26 compared with untreated wood. Error bars indicate standard deviation calculated based on five replicate measurements. This indicates that surface treated samples had a slightly lower water uptake through the lignin treated surface than untreated wood. Thus, the lignin treatment presents a moisture barrier.

[0047] Figure 15 illustrates the initial contact angle of the water droplet 5 seconds after it touched the sidegrain surface of the untreated wood and wood treated with lignin solutions of Table 3. Error bars indicate standard deviation calculated based on 30 replicate measurements for untreated wood and 15 replicate measurements for each surface treatment. As can be seen the initial contact angle is similar for sidegrain surfaces treated with lignin solutions 17 and 20 as for untreated wood. These two solutions contain the acetone soluble lignin fraction of the soda lignin.

[0048] Figure 16 shows the final contact angle of the water droplet 60 seconds after it touched the sidegrain surface of the untreated wood and wood treated with lignin solutions of Table 3. Error bars indicate standard deviation calculated based on 30 replicate measurements for untreated wood and 15 replicate measurements for each surface treatment. As can be seen the final contact angle is higher for sidegrain surfaces treated with lignin solutions 17 and 20 than for untreated wood. These two solutions contain the acetone soluble lignin fraction of the soda lignin.

[0049] Figure 17 depicts the reduction in contact angle between the first and last measurement over the 60 seconds on sidegrain samples of untreated wood and wood treated with lignin solutions of Table 3. Error bars indicate standard deviation calculated based on 30 replicate measurements for untreated wood and 15 replicate measurements for each surface treatment. It is clear that the contact angle for sidegrain surfaces treated with lignin solutions 17 and 20 is very stable and hardly changes at all. These two solutions contain the acetone soluble lignin fraction of the soda lignin.

[0050] Figure 18 illustrates the initial contact angle of the water droplet 5 seconds after it touched the endgrain surface of the untreated wood and wood treated with lignin solutions of Table(85627EP01)

[0051] 7

[0052] 3. Error bars indicate standard deviation calculated based on 30 replicate measurements for untreated wood and 15 replicate measurements for each surface treatment. As can be seen the initial contact angle is similar for endgrain surfaces treated with lignin solutions 17 and 20 as for untreated wood. These two solutions contain the acetone soluble lignin fraction of the soda lignin.

[0053] Figure 19 shows the final contact angle of the water droplet 60 seconds after it touched the endgrain surface of the untreated wood and wood treated with lignin solutions of Table 3. Error bars indicate standard deviation calculated based on 30 replicate measurements for untreated wood and 15 replicate measurements for each surface treatment. As can be seen the final contact angle is higher for endgrain surfaces treated with lignin solutions 17, 20, 23, and 26 than for untreated wood. These four solutions contain the acetone soluble lignin fraction of soda lignin (17, 20) and Kraft lignin (23, 26).

[0054] Figure 20 depicts the reduction in contact angle between the first and last measurement over the 60 seconds on endgrain samples of untreated wood and wood treated with lignin solutions of Table 3. Error bars indicate standard deviation calculated based on 30 replicate measurements for untreated wood and 15 replicate measurements for each surface treatment. It is clear that the contact angle for endgrain surfaces treated with lignin solutions 17, 20, 23, and 26 is very stable and changes very little. These four solutions contain the acetone soluble lignin fraction of soda lignin (17, 20) and Kraft lignin (23, 26).

[0055] Figure 21 shows microscopy images (lOx magnification) of wood surfaces treated with the lignin solutions of Table 7 with different concentrations of lignin. At low lignin concentration a smooth surface is observed, while microcracks are visible at high lignin concentrations. It is clear that a smooth surface can be achieved at relatively high lignin concentration, whereas a branched network of cracks appears at the two highest concentrations.

[0056] Scale bar = 1 mm.

[0057] Figure 22 shows microscopy images (lOx magnification) of wood surfaces treated with the lignin solutions of Table 8 with different types of additives. A smooth surface is observed for the solution with PEG while few microcracks are visible for the solution with Tween80 and more for the rest of the solutions. It is clear that the additives all have a positive effect on the surface quality, since the cracking is considerably reduced compared with wood treated with solution 36 in Figure 21. Scale bar = 1 mm.

[0058] Figure 23 illustrates the initial contact angle of the water droplet 5 seconds after it touched the surface of various wood species and modified wood products. These wood surfaces were either untreated or surface treated by brushing with solution 23 of Table 6. Error bars(85627EP01)

[0059] 8

[0060] indicate standard deviation calculated based on triplicate measurements. It is clear that the treated surfaces had closely similar contact angle, whereas the untreated surfaces exhibited a high variability among species and products as expected.

[0061] Figure 24 depicts the final contact angle of the water droplet 60 seconds after it touched the surface of various wood species and modified wood products. These wood surfaces were either untreated or surface treated by brushing with solution 23 of Table 6. Error bars indicate standard deviation calculated based on triplicate measurements. It is clear that the contact angle of water droplets on treated surfaces is quite similar and close to the initial values of Figure 23, whereas the untreated surfaces exhibit much lower contact angles with water. This is expected as the untreated surfaces are wetted by the water droplet, whereas the surface treatment with lignin presents a barrier to liquid water.

[0062] Figure 25 shows the reduction in contact angle between the first and last measurement over the 60 seconds after it touched the surface of various wood species and modified wood products. These wood surfaces were either untreated or surface treated by brushing with solution 23 of Table 6. Error bars indicate standard deviation calculated based on triplicate measurements. It is clear that untreated wood surfaces exhibit a dramatic reduction in contact angle as a result of the droplet wetting the surfaces. On the contrary, the lignin treated surfaces show remarkable stable droplets as seen from the only slight reduction in contact angle. This is expected as the lignin surface treatment presents a barrier to liquid water.

[0063] Figure 26 illustrates the initial contact angle of the water droplet 5 seconds after it touched the surface of untreated wood and wood treated with the lignin solutions of Table 7 with different concentrations of lignin. Error bars indicate standard deviation calculated based on triplicate measurements. The contact angle is seen to be closely similar for lignin concentrations of 15-35 wt% and lower than for the untreated wood.

[0064] Figure 27 depicts the final contact angle of the water droplet 60 seconds after it touched the surface of untreated wood and wood treated with the lignin solutions of Table 7 with different concentrations of lignin. Error bars indicate standard deviation calculated based on triplicate measurements. The contact angle is seen to be closely similar for all surfaces.

[0065] Figure 28 shows the reduction in contact angle between the first and last measurement over the 60 seconds after it touched the surface of untreated wood and wood treated with the lignin solutions of Table 7 with different concentrations of lignin. Error bars indicate standard deviation calculated based on triplicate measurements. It is seen that the reduction in contact angle decreases with increasing lignin concentration up to 25 wt% and(85627EP01)

[0066] 9

[0067] then rises again. This corresponds well with the images of Figure 21, where microcracks are visible at high lignin concentrations (30 and 35 wt%). Up to 25 wt% a higher lignin concentration leads to more lignin being applied to the surfaces which leads to better barrier properties against liquid water. As microcracks become visible at the highest concentrations, the barrier properties decrease again. Nonetheless, the untreated wood surface still shows the largest reduction in contact angle as a result of the water droplet wetting the surface.

[0068] Figure 29 illustrates the initial contact angle of the water droplet 5 seconds after it touched the surface of untreated wood and wood treated with the lignin solutions of Table 8 with different types of additives. Error bars indicate standard deviation calculated based on triplicate measurements. The contact angle is seen to be closely similar for lignin concentrations and lower than for the untreated wood.

[0069] Figure 30 depicts the final contact angle of the water droplet 60 seconds after it touched the surface of untreated wood and wood treated with the lignin solutions of Table 8 with different types of additives. Error bars indicate standard deviation calculated based on triplicate measurements. The contact angle is seen to be closely similar for all wood surfaces, indicating that the contact angle for untreated wood has reduced markedly more than for treated surfaces as a result of wetting.

[0070] Figure 31 shows the reduction in contact angle between the first and last measurement over the 60 seconds after it touched the surface of untreated wood and wood treated with the lignin solutions of Table 8 with different types of additives. Error bars indicate standard deviation calculated based on triplicate measurements. Untreated wood is seen to have a markedly higher reduction in contact angle from wetting of the surface by the water droplet, whereas the lignin treatment presents a barrier to liquid water.

[0071] Figure 32 depicts microscopy images (lOx magnification) of wood surfaces treated with lignin solution 30 of Table 7. Small dots from air bubbles are seen on dipped surfaces (middle column), similar to observations for brushed surfaces in Figure 21. The dots are absent from sprayed surfaces (left column) which on the other hand show more visible microcracks. The roller treated surfaces (right column) have a similar appearance as the dipped surfaces, even though the lignin concentration was remarkably higher. It is clear that treating wood surfaces by spraying, dipping, and rolling yields as smooth surfaces as brushing (Figure 21), demonstrating the broad applicability of lignin solutions for treating wood with different application methods.

[0072] The present invention will now be described in more detail in the following.(85627EP01)

[0073] 10

[0074] Detailed description of the invention

[0075] Definitions

[0076] Prior to discussing the present invention in further details, the following terms and conventions will first be defined:

[0077] "BioPiva 100" or "BioPiva 100, Kraft" or "UPM BioPiva 100": When used herein "BioPiva 100" or "BioPiva 100, Kraft" or "UPM BioPiva 100" refers to a type of a softwood Kraft lignin product in form of dry powder. Kraft lignin is a byproduct of the Kraft pulping process, which is widely used in the paper and pulp industry. Specifically, "BioPiva 100, Kraft", which is derived from the Kraft pulping process, where lignin is separated from softwood during the production of paper, contains a high guaiacyl content, and relatively low sulfur content compared to lignosulfonates.

[0078] Kraft process: When used herein, "Kraft process" (or Kraft lignin produced from a Kraft process, or similar) refers to an industrial way of producing lignin. The Kraft process, currently being the biggest source of producing industrial lignin, is based on the usage of a mixture of sodium hydroxide and sodium sulfide at a high temperature, which delignifies the lignocellulosic biomass, producing a mixture of degraded lignin, oxidized inorganic compounds and other organic materials called black liquor - from which the lignin is isolated by acidification.

[0079] Lignin: When used herein, "lignin" refers to a heterogeneous cross-linked biopolymer composed of phenolic subunits, which is a structural material in many plants, and any lignin-containing plant may be used to provide the lignin-containing material for use in the present invention. Lignin-containing biomass may be derived from trees, such as trees commonly used for pulp and paper production and lumber or timber, including waste from forestry, e.g. softwood or hardwood. Lignin is formed primarily from p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) units, which are derivatives of respectively p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, known as monolignols. In hardwood, lignin is mostly made of G and S units, with low amounts of H units, while softwood lignin is primarily made of G units with traces of H units, while grasses have similar levels of all three units. Lignin is the most abundant, and renewable source of aromatic polymers in the world. In order to use lignin as a product, it has to be isolated from lignocellulosic biomass and processed. There are numerous ways to do that, however they are all based on degrading lignin into smaller fragments while modifying their functional groups, what allows for its dissolution. The main industrial ways of creating lignin products are the Kraft(85627EP01)

[0080] 11

[0081] process, soda process, sulfite process and organosolv process, in which production of lignin is a side stream from biorefinery production of pulp. Hence, when used herein, "lignin" may also refer to lignin derived from second generation bioethanol fermentation, pulp and paper manufacture, processing of wood and other lignocellulosic materials and other sources. The lignin used in accordance to the invention may be selected from native lignins as well as processed lignins, such as chemically processed (such as via the Kraft process which generally provides a depolymerised lignin which may have a higher water-solubility than other lignin types), enzymatically processed (e.g. using cellulases and / or hemicellulases, to convert non-soluble carbohydrates, e.g. cellulose and hemicellulose, to fermentable, and soluble, sugars) or physically modified lignins, compositions comprising lignin, and combinations thereof.

[0082] Lignin derivative: When used herein, "lignin derivative" refers to the various chemicals and materials obtained through the processing and modification of lignin. Lignosulfonates, also referred to as "Lignosulfonic acid" (produced by the sulfite pulping process where lignin is sulfonated), Kraft lignin (being derived from the kraft pulping process, where lignin is separated from cellulose using sodium hydroxide and sodium sulfide) and organosolv lignin (obtained through the organosolv pulping process, which uses organic solvents to solubilize lignin) are examples of lignin derivatives according to the present invention.

[0083] Non-volatile alcohol: When used herein "non-volatile alcohols" refers to alcohols that have low vapor pressures and do not easily evaporate at room temperature and are characterized by having low vapor pressure, higher boiling points compared to volatile alcohols. Examples of non-volatile alcohols are glycol ethers, including glycerol (also referred to as glycerine), 1,2-propanediol (also referred to as propylene glycol), 4-oxa-2,6-heptanediol (also referred to as dipropylene glycol), and l-methoxy-2-propanol (also referred to as propylene glycol monomethyl ether).

[0084] "Organosolv - Aldrich": When used herein "Organosolv - Aldrich" refers to lignin produced by organosolv processes utilizing organic solvents such as methanol, ethanol and acetone at increased temperature and pressure to solubilize lignin, which is later precipitated.

[0085] Organosolv lignin: When used herein "organosolv lignin" refers to lignin produced by organosolv processes utilizing organic solvents such as methanol, ethanol and acetone at increased temperature and pressure to solubilize lignin, which is later precipitated. These processes create lignin of high purity, high solubility in organic solvents and very high hydrophobic properties.(85627EP01)

[0086] 12

[0087] "Protobind 1000, Technical" or "Protobind 1000": When used herein, "Protobind 1000, Technical" or "Protobind 1000" refers to a commercially available technical-grade dry soda lignin derivative, which contains a high percentage of lignin with minimal impurities.

[0088] "Protobind 2600, Technical" or "Protobind 2600": When used herein, "Protobind 2600, Technical" or "Protobind 2600" refers to a commercially available technical-grade dry soda lignin derivative, which contains a high percentage of lignin with minimal impurities.

[0089] "Repapp / AICell": when used herein "Repapp / AICell" refers to lignin produced by the AlCell process, an ethanol-based organosolv pulping method, which utilizes a mixture of ethanol and water at elevated temperature and pressure to solubilize lignin from lignocellulosic biomass, which is subsequently precipitated. AlCell lignin is characterized by high purity and good solubility in organic solvents.

[0090] Soda lignin: When used herein, "soda lignin" refers to a type of lignin (dry powder or granules) obtained as a by-product of the soda pulping process, which is used to produce paper pulp from non-wood plant materials, which involves cooking said plant materials with sodium hydroxide (NaOH) to separate lignin from cellulose fibers. Soda lignin contains relatively low sulfur content compared to e.g. Kraft lignin.

[0091] Solid-to-liquid ratios: When used herein, solid-to-liquid ratios refer to weight (w / w) ratios of the solid fraction and the liquid fraction, unless otherwise specified.

[0092] "Sekab BioRefinery": when used herein "Sekab BioRefinery" refers to lignin obtained from a biorefinery operated by Sekab, which processes lignocellulosic biomass, primarily spruce, using a fractionation process to separate lignin from cellulose and hemicellulose.

[0093] Surface treatment: When used herein, surface treatment refers to the application of a liquid solution on the bulk surface of wood by brushing, rolling, spraying, or dipping the wood. The applied liquid solution may penetrate up to 5 mm into the porous wood structure or remain on the bulk surface of the wood.

[0094] Surface treated: When used herein, surface treated refers to wood which has been subjected to surface treatment with a liquid solution.

[0095] Thermally modified wood: When used herein, thermally modified wood refers to wood products heated at temperatures between 150 and 240 °C, which results in a material that is darker in colour, has improved dimensional stability and microbial resistance compared to unmodified wood. Thermal modification can be divided into 'dry' and 'wet' modification(85627EP01)

[0096] 13

[0097] processes. Initial stages of dry thermal modification involve an increase in temperature (ramp) during which the wood loses sorbed water. Alternatively, the heating can take place under conditions designed to keep the water in the wood cell wall, in a wet process. Wet conditions are herein defined as being thermal modification where the cell wall of the wood still contains moisture during the process, whereas dry conditions are defined as those in which the wood has been dried to close to zero moisture content before the thermal modification process. In dry processes, the timber can be heated under an inert gas blanket of nitrogen, in a vacuum, under superheated steam or in ambient air. The types of thermal modification process differ, depending on time and temperature of treatment (including ramp-up, hold and ramp-down stages), treatment atmosphere (inert gas, air, vacuum), open or closed systems, wood species, and 'wet' or 'dry' systems. Wet conditions can be formally divided into processes which use saturated steam as the heating medium and those in which the wood is completely immersed in water during the process.

[0098] "UPM Uruguay": when used herein "UPM Uruguay" refers to hardwood Kraft lignin obtained as a byproduct of the Kraft pulping process at UPM's pulp mills in Uruguay, using primarily eucalyptus as feedstock. Hardwood Kraft lignin is characterized by a high syringyl-to-guaiacyl ratio, distinguishing it from softwood Kraft lignins.

[0099] wt%: When used herein, "wt%" refers to mass fraction expressed with a denominator of 100, i.e. as percentage by weight, wt% (also referred to as "w / w%", "% by weight" or similar).

[0100] Embodiments

[0101] In one embodiment of the present invention there is provided a method of surface treating wood, wherein the method comprises the following consecutive steps: (a) applying the wood with a solution comprising a concentration between 15-75 wt% of lignin or derivates thereof; wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% alcohol, (ii) 0-60 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%.

[0102] Another embodiment of the invention relates to a method of surface treating wood, such as a softwood species (e.g. Scots pine {Pinus sylvestris L.), Norway spruce (Picea abies L.), larch (Larix spp.)~, Grand fir {Abies grandis (Douglas ex D. Don) Lindley)) or a hardwood species (e.g. European beech (Fagus sylvatica L.), ash (Fraxinus excelsior L.), European oak (Quercus robur)) or thermally modified wood, wherein the method comprises the following consecutive steps: (a) applying said wood with a solution comprising a concentration between 15-75 wt% of lignin or derivates thereof, preferably between 15-60(85627EP01)

[0103] 14

[0104] wt% of lignin or derivates thereof, more preferably between 15-50 wt% of lignin or derivates thereof, most preferably between 15-45 wt% of lignin or derivates thereof, wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% alcohol, (ii) 0-60 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%.

[0105] Still another embodiment of the invention relates to a method of surface treating wood, wherein the method comprises the following consecutive steps: (a) applying said wood with a solution comprising a concentration between 15-75 wt% of lignin or derivates thereof, wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% alcohol, preferably 20-90 wt% alcohol, more preferably 30-80 wt% alcohol, most preferably between 40-80 wt% alcohol, (ii) 0-60 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%; and wherein said alcohol is chosen from the group consisting of ethanol, isopropanol or n-butanol or any combinations thereof.

[0106] Still another embodiment of the invention relates to a method of surface treating wood, wherein the method comprises the following consecutive steps: (a) applying said wood with a solution comprising a concentration between 15-75 wt% of lignin or derivates thereof, wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% alcohol, preferably 20-90 wt% alcohol, more preferably 30-80 wt% alcohol, most preferably between 40-80 wt% alcohol, (ii) 0-60 wt% water, preferably 10-50 wt% water, more preferably 15-35 wt% water, most preferably between 20-25 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols, preferably between 10-45 wt% of one or more non-volatile alcohols, most preferably 40 wt% of one or more non-volatile alcohols, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%; and wherein said alcohol is chosen from the group consisting of ethanol, isopropanol or n-butanol or any combinations thereof.

[0107] Still another embodiment of the invention relates to a method of surface treating wood, wherein the method comprises the following consecutive steps: (a) applying said wood with a solution comprising a concentration between 15-75 wt% of lignin or derivates thereof, wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% alcohol, preferably 20-90 wt% alcohol, more preferably 30-80 wt% alcohol, most preferably between 40-80 wt% alcohol, (ii) 0-60 wt% water, preferably 10-50 wt% water, more preferably 15-35 wt% water, most preferably between 20-25 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols, preferably between 10-45 wt% of one or more non-volatile alcohols, most preferably 40 wt% of one or more non-volatile alcohols, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%;(85627EP01)

[0108] 15

[0109] and wherein said alcohol is chosen from the group consisting of ethanol, isopropanol or n-butanol or any combinations thereof and; and wherein the one or more non-volatile alcohols in step (a)(iii) are chosen from the group consisting of glycol ethers, such as glycerol, 1,2-propanediol, 4-oxa-2,6-heptanediol, and l-methoxy-2-propanol or any combinations thereof.

[0110] Still another embodiment of the invention relates to a method of surface treating a softwood species, such as Scots pine (Pinus sylvestris L.), wherein the method comprises the following consecutive steps: (a) applying the softwood species with a solution comprising a concentration between 15-45 wt% of lignin or derivates thereof; wherein said lignin or derivatives thereof has / have been solubilised in (i) 40-80 wt% alcohol selected from group consisting of ethanol, isopropanol or n-butanol or any combinations thereof, (ii) 20-25 wt% water, (iii) 40 wt% of one or more non-volatile alcohols selected from the group consisting of glycol ethers, such as glycerol, 1,2-propanediol, 4-oxa-2,6-heptanediol, and l-methoxy-2-propanol or any combinations thereof, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%.

[0111] Still another embodiment of the invention relates to a method of surface treating a softwood species, such as Scots pine (Pinus sylvestris L.), wherein the method comprises the following consecutive steps: (a) applying the softwood species with a solution comprising a concentration between 15-45 wt% of lignin or derivates thereof; wherein said lignin or derivatives thereof has / have been solubilised in (i) 40-80 wt% ethanol, isopropanol or n-butanol or any combinations thereof, (ii) 20-25 wt% water, (iii) 40 wt% glycol ethers, such as glycerol, 1,2-propanediol, 4-oxa-2,6-heptanediol, and l-methoxy-2-propanol or any combinations thereof, and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%.

[0112] In still another embodiment of surface treating wood according to the invention, the treated wood is either a softwood species, e.g. Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.), larch (Larix spp.)~, Grand fir {Abies grandis (Douglas ex D. Don) Lindley), or a hardwood species, e.g. European beech (Fagus sylvatica L.), ash (Fraxinus excelsior L.), European oak (Quercus robur).

[0113] In still another embodiment of surface treating wood according to the invention, the treated wood is thermally modified.

[0114] In still another embodiment of surface treating wood according to the invention, the concentration of lignin or derivates thereof in the lignin solution is between 15-45 wt%.(85627EP01)

[0115] 16

[0116] In still another embodiment of surface treating wood according to the invention, the ratio of solid lignin or derivatives thereof to liquid of between 1:5.7-1:0.33 (w / w).

[0117] In still another embodiment of surface treating wood according to the invention, the concentration of alcohol in step (a)(i) is between 40-80 wt%.

[0118] In still another embodiment of surface treating wood according to the invention, the concentration of water in step (a)(ii) is between 20-25 wt%.

[0119] In still another embodiment of surface treating wood according to the invention, the concentration of one or more non-volatile alcohols in step (a) (iii) is 40 wt%.

[0120] In still another embodiment of surface treating wood according to the invention, the alcohol in step (a) (i) is chosen from the group consisting of ethanol, isopropanol or n-butanol or any combinations thereof.

[0121] In still another embodiment of surface treating wood according to the invention, the one or more non-volatile alcohols in step (a) (iii) are chosen from the group consisting of glycol ethers, such as glycerol, 1,2-propanediol, 4-oxa-2,6-heptanediol, and l-methoxy-2-propanol or any combinations thereof.

[0122] In still another embodiment of surface treating wood according to the invention, the additives in step (a)(iv) are selected from a group consisting of polyethylene glycols (PEG), micro-crystalline cellulose, methylated cellulose, starch such as amylodextrin, Polysorbate 80, tetraethoxysilane (TEOF), glycerol, and xanthan gum.

[0123] In still another embodiment of surface treating wood according to the invention, the lignin or derivatives thereof in step (a) is a lignin from an industrial process such as Kraft lignin, soda lignin, biorefinery lignin, or organosolv lignin or any combinations thereof.

[0124] In still another embodiment of surface treating wood according to the invention, the ligninsolution is applied to the wood surface by brushing, spraying, rolling, or dipping the wood.

[0125] The invention will now be described in further details in the following non-limiting examples.

[0126] Examples(85627EP01)

[0127] 17

[0128] Example 1: Lignin solutions and surface treatment of wood

[0129] Materials 1: Wood

[0130] Wood samples of Scots pine (Pinus sylvestris L.) boards with dimensions of 22x50x75 mm where the 50x75 mm area describes the tangential face of the wood.

[0131] Materials 2: Lignin solutions

[0132] Kraft lignin, softwood, UPM BioPiva™ 100 lignin

[0133] Kraft lignin, hardwood, UPM Uruguay lignin

[0134] Organosolv lignin, hardwood, Repapp / AICell

[0135] Organosolv lignin, Aldrich (Product number: L165)

[0136] Soda Lignin, Protobind 2600 from PLT Innovations, Switzerland

[0137] Biorefinery lignin, spruce, Sekab

[0138] Concentrated lignin solutions were prepared by solvation of the various types of lignin in different solvent systems of various composition (Table 1), containing two or more of the following solvents: ethanol (EtOH), water, glycerol, 1,2-propanedioL The mixtures of lignin and solvent were stirred for 1 hour and subsequently centrifuged at 1000G for 10 min. The pellet was defined as the insoluble fraction while the pooled supernatant was defined as the soluble fraction. The pellet was discarded while the soluble fraction was used as it is.

[0139] Table 1 : Lignin solutions used for surface treatment in Example 1.

[0140]

[0141] (85627EP01)

[0142] 18

[0143]

[0144] Methods: Surface treatment

[0145] Concentrated lignin solutions were applied with a brush on the wood samples once on one of their tangential faces. After treatment, the samples were left to airdry overnight. The samples were weighed immediately before and after treatment to determine the mass gain from the treatment.

[0146] Results:

[0147] The amount of applied lignin solution on the wood samples varied in the range ~150-300 grams (wet mass) per square metre (Table 2).

[0148] Table 2: Applied amount (wet mass) of concentrated lignin solution to wood samples.

[0149]

[0150] (85627EP01)

[0151] 19

[0152] Example 2: Penetration of lignin solutions in wood

[0153] Materials:

[0154] Surface treated wood samples from Example 1.

[0155] Method: Microscopy

[0156] The samples were split and cut into cubes of 10x10x10 mm. The penetration of the lignin treatment was evaluated by light microscopy on radial sections and cross-sections. These sections were cut with a microtome to achieve a smooth surface suitable for microscopy. Samples were imaged with a Photomakroskop M400 light microscope (Wild, Switzerland) with objectives of lOx or 25x magnification and a MC170 HD microscope camera (Leica, Germany).

[0157] Results:

[0158] It was easier to evaluate the penetration into the wood structure on radial sections (Fig. 1) than the cross-sections (images not shown). The samples with Kraft lignin, BioPiva 100 in ethanokwater solvent systems (solution 4-7 in Table 1) did not penetrate appreciably into the wood structure but was only found on top of the wood surface. However, a slight penetration was observed for that kind of solution 6 (Table 1) with chemically modified Kraft lignin, BioPiva 100 (Fig. 1).

[0159] Penetration depths were in the 100-400 pm range for solutions 8-14 (Table 1, Fig. 1). Solution 8-11 contained non-volatile alcohol (glycerol or 1,2-propanediol) in the solvent system, whereas solutions 12-13 were made with organosolv and soda lignin, respectively. Solution 14 was similar to solution 4 that had poor penetration, but the lignin concentration in the previous was only 23 wt%, whereas solution 4 had 42 wt% lignin. Therefore, it appears that non-volatile alcohols at concentrations around 23 wt% is needed for good penetration of solutions with softwood Kraft lignin, BioPiva 100.

[0160] Interestingly, solutions 1-2 (Table 1) were made with an ethanokglycerol solvent system and had a high lignin concentration around 45 wt%, but they did not penetrate the wood structure. Solution 3 had a very low lignin concentration of 5 wt% and the lignin could not be reliably detected in the microscope images.

[0161] Example 3: Surface interaction with liquid water

[0162] Materials:

[0163] Surface treated wood samples from Example 1 as well as untreated wood samples cut out of the same boards as controls.(85627EP01)

[0164] 20

[0165] Method: Contact anqle analysis

[0166] Contact angle analysis is a technique used to assess the surface wettability of materials. In this study, it was used to explore the wettability of the transverse section of wood after it has been treated or left untreated. By measuring the angle formed between a liquid water droplet and the wood surface, contact angle analysis provides insights into how well the liquid spreads or beads up on the surface. This analysis helps determine the extent to which the wood surface is hydrophilic (attracts water) or hydrophobic (repels water), which is crucial for understanding its performance and potential applications. By examining the contact angle, researchers can gain valuable information about the surface properties of wood in a non-destructive and quantitative manner.

[0167] Contact angle analysis was performed with an OCA 25 all-purpose measuring device (DataPhysics Instruments, Germany). A water droplet of 24 pL was dispensed by a ImL needle at a rate of 7 pL / second. After the water droplet touched the wood sample surface, the water droplet was images every 5 seconds for 60 seconds and the contact angle determined from the acquired images (Fig. 2).

[0168] Results:

[0169] The contact angle differed between the various solutions (Figs. 3-6). In general, the contact angle of surface treated wood was higher than for untreated wood, except for solutions 1, 2, 3, and 10. Even though the initial contact angle after 5 seconds was high for untreated wood and comparable to that of surface treated wood (Fig. 7), the contact angle of water on untreated wood quickly decreased as the surface was wetted by the water (Figs. 3-6). Thus, the stability of the water droplet on treated surfaces was much better than for untreated wood as seen from the only slight reduction in contact angle over the measurement time (Fig. 8). This shows that the treatments with most of the solutions created a stable, moisture-repellent surface.

[0170] Example 4: Delamination of surface treatments after water exposure Materials:

[0171] Surface treated wood samples from Example 1.

[0172] Methods:

[0173] To investigate whether the lignin treatments adhered well or delaminated from the wood surface, specimens were exposed to liquid water over 6 hours. These specimens were cut out from the surface treated wood samples of Example 1. The specimens were cut with(85627EP01)

[0174] 21

[0175] dimensions of 25x25 mm of the treated face. Sides adjacent to this face were sealed with a two-component epoxy adhesive (Casco Strong Epoxy Professional).

[0176] The treated surface was placed downwards on top of a liquid water surface for 6 hours during which the treated surface was dabbed with a cloth five times. How well the lignin treatments adhered to the wood was visually evaluated after air-drying the specimens at the end of the test.

[0177] Results:

[0178] Exposure to liquid water and regular removing of the surface water with a cloth showed extensive damage to several of the treated surfaces (Fig. 9). Thus, surface treated with solutions 1, 2, 6, 8, 12, and 13 had surface cracks that for some coincided with latewood, i.e. denser and less porous tissue. For the surface treated with solution 3 no treatment could be detected, similar to the microscope investigations of Example 2, presumably because of the low lignin concentration in the solution (Table 1). For the surface treated with solution 10, not much of the treatment remained on the surface after the test. This explains the poor performance of this treatment when measuring the contact angle in Example 3.

[0179] All the solutions containing glycerol (solutions 1, 2, 3, 8, and 10) did not adhere well to the surface. This indicates that glycerol with a 40 wt% concentration in the solvent system has a negative effect on performance. On the contrary, solutions with 1,2-propanediol (solution 9 and 11) both worked very well, adhering to the surface and providing it with a rich red-brown colour. Furthermore, the microscope investigations of Example 2 showed good penetration of these solutions.

[0180] Solutions 4 and 14 had similar ethanokwater solvent systems and similar lignin types, but differed in their lignin concentration. The surface treated with solution 4 (lignin concentration: 42 wt%) had a dark brown colour but slight indications of cracking whereas the surface with solution 10 (lignin concentration: 23 wt%) had a lighter colour and no apparent cracking. This indicates that lignin concentration is an important factor for achieving a good performing treatment of the wood surface.

[0181] Example 5: Surface treatment of wood with solutions of fractionated lignin Materials 1: Wood

[0182] Wood samples of Scots pine (Pinus sylvestris L.) boards were prepared into samples of two different geometries:(85627EP01)

[0183] 22

[0184] (i) Sidegrain samples with dimensions of 15x120x120 mm, where the longitudinal direction was along one of the 120 mm lengths. The shortest dimension was predominantly in the radial direction of the wood, meaning that the 120x120 mm area was the tangential face of the wood. All sides adjacent to this face were sealed with a two-component epoxy adhesive (Casco Strong Epoxy Professional).

[0185] (ii) Endgrain samples with dimensions of 15x120x16 mm, where the longitudinal direction was along the 16 mm length. The 15x120 mm area was the cross-sectional face of the wood. All sides adjacent to this face were sealed with a two-component epoxy adhesive (Casco Strong Epoxy Professional).

[0186] All samples were moisture conditioned in a desiccator over a saturated salt solution of sodium bromide that yields a relative humidity of ~58%.

[0187] Materials 2: Chemicals

[0188] Kraft lignin, UPM BioPiva 100 lignin

[0189] Soda lignin, Protobind 1000 lignin from PLT Innovations, Switzerland

[0190] Acetone

[0191] Ethanol 96%

[0192] 1,2-propanediol

[0193] Demineralized water

[0194] Methods 1: Acetone fractionation of lignin

[0195] The following procedure for fractionation of lignin with acetone was performed on both types of lignin (Kraft, soda) separately. Dried lignin powder (~95-96% dry matter) were put in 180 mL centrifuge tubes in batches of 13 gram powder, and 130 mL acetone was added to each tube. After vortex mixing the tube for 10 seconds, the liquid in each tube was stirred at 300 RPM for 90 minutes at ambient temperature. Hereafter, the tubes were centrifuged at 1000G for 10 minutes and the supernatants collected, which was therefore the acetone soluble fraction. The remaining pellet in the tube was washed with 100 mL acetone, mixed for 10 seconds on a vortex mixer and shaken vigorously before it was centrifuged again at 1000G for 10 minutes.

[0196] The supernatants collected after the second washing was pooled with those of the first. The remaining pellet after second washing was the acetone insoluble fraction. For the acetone soluble fraction, the major part of the acetone was evaporated using a rotavapor at 385 mPa and 50 °C. The collected, distilled acetone was reused in subsequent fractionations. Hereafter, the soluble and insoluble fractions were dried in a vacuum oven overnight at 50°C.(85627EP01)

[0197] 23

[0198] Methods 2: Lignin solutions

[0199] Concentrated lignin solutions were prepared using a BOJ MC-2000 Thermo Blender with a 2 L capacity. The mixing speed was arbitrary, scaled from 1 to 10. Each impregnation solution was made with a 1:2 solid-to-solvent ratio. The recipe included ~100 g DM (dry matter) of lignin mixed, at speed 8 for 15 minutes, with its respective solvent that was preheated beforehand at 50 °C. The prepared solutions were poured into bottles and used within a few days for the surface treatment.

[0200] Table 3: Lignin solutions used for surface treatment in Example 5.

[0201]

[0202] Methods 3: Surface treatment of wood

[0203] Concentrated lignin solutions were applied with a brush to both sidegrain and endgrain samples. For each solution, 5 replicate sidegrain samples were treated once on the tangential face which faced the pith of the tree, i.e. the annual rings curved towards the treated surface. 3 replicate endgrain samples were treated once one of their cross-sectional faces. After treatment, the samples were left to airdry overnight before being reconditioned at ~58% RH above saturated salt solution of sodium bromide.

[0204] Results:

[0205] Mass gains for endgrain samples were markedly higher than sidegrain samples as seen for both the applied wet solution mass (Table 4) and applied dry mass after solvent(85627EP01)

[0206] 24

[0207] evaporation (Table 5). This is natural given the easier penetration of liquids in the longitudinal direction of wood. The difference in mass gain between sidegrain and endgrain samples were highest for the solutions with acetone soluble lignin that gained about 5-6 times more in endgrain samples, whereas solutions with acetone insoluble lignin only gained about twice as much in endgrain samples. This indicates a much better penetration of solutions with acetone soluble lignin, presumably related to the much more low-viscosity character of these solutions.

[0208] Acetone insoluble Kraft lignin could not be processed into a solution but showed clear signs of phase separation with a very hard and tough solid phase. Therefore, no data for the applied mass of acetone insoluble Kraft lignin were acquired (Table 4 and Table 5).

[0209] Table 4: Applied amount (wet mass) of concentrated lignin solution to sidegrain and endgrain samples. The values indicate averages while the standard deviation is given in parentheses. For solutions of unfractionated lignin only sidegrain samples were treated.

[0210]

[0211] Table 5: Applied amount dry mass of concentrated lignin solution to sidegrain and endgrain samples after solvent evaporation. The values indicate averages while the standard deviation(85627EP01)

[0212] 25

[0213] is given in parentheses. For solutions of unfractionated lignin only sidegrain samples were treated.

[0214]

[0215] Example 6: Water uptake through wood surface treated with lignin solution Materials:

[0216] Surface treated sidegrain wood samples from Example 5 as well as untreated, edge-sealed wood samples of similar geometries as controls, with 5 replicates of each batch.

[0217] Aluminium foil trays (volume 542 mL) of dimensions 153x153x24 mm

[0218] Demineralised water

[0219] Methods: Floating test

[0220] The floating test is a good, simple method for evaluating the moisture transport into a surface treated sample upon exposure to liquid water. The method imitates the exposure of surface to liquid water contact, e.g. rainwater on a decking material. The floating test was conducted using individual aluminium foil tray for each sample, in order to avoid contamination of the water between sample types with potential leachable compounds.

[0221] Before the floating test, all samples were weighed to determine their initial mass.

[0222] Thereafter, demineralised water was poured into the aluminium foil trays and the surface(85627EP01)

[0223] 26

[0224] treated face of each wood sample from Example 5 was placed on top of the liquid water surface (Fig. 10). In a similar way, the untreated controls were placed in a tray with demineralised water. Each sample had its own tray.

[0225] All trays were placed inside a cupboard with a saturated salt solution of sodium bromide and a fan to ensure air circulation. Samples were taken out of the tray periodically for weighing to determine the mass gain from water uptake. The mass was determined after 0.5, 1, 2, 4, and 24 hours of exposure to liquid water. After taking out a sample from the water-filled tray, excess water on the sample was dabbed off with paper tissue before weighing.

[0226] Results:

[0227] The water uptake in wood treated with liquid solutions is reduced compared with untreated wood (Fig. 11-14). This is because the applied lignin forms a moisture barrier on the surface of the wood that slows the ingress of water into the wood substrate. The wood treated with acetone soluble lignin solutions (solutions 17, 20, 23, and 26) had a similar or lower water uptake than wood treated with other solutions. This is important given that treatments with acetone soluble lignin solution had lower mass gains (Table 4, Table 5). Thus, acetone soluble lignin performed equally well or better as moisture barrier than unfractionated and acetone insoluble lignin, even though treatment with these solutions yielded 1.5-3 times higher mass gains (Table 4, Table 5). This demonstrates the advantage of solvent fractionation to provide better-performing lignin fractions for coating applications.

[0228] Example 7: Contact angle analysis on sidegrain wood samples treated with solutions of fractionated lignin

[0229] Materials:

[0230] Surface treated wood sidegrain samples and untreated wood sidegrain samples from Example 5 after the floating test of Example 6 were used. The middle part of approximately 100x100 mm was cut of out each sample and saved for other measurements. One of the thin strips (dimensions approximately 10x15x120 mm) cut off each sample was used for contact angle analysis. Specifically, one of the two strips of length 120 mm cut across the grain of each sample was used.

[0231] Method: Contact angle analysis

[0232] The same protocol as in Example 3 was used. For surface treated samples, 5 replicates were used whereas 10 replicates were used for untreated samples. For each individual sample, contact angle analysis was performed in three locations (middle and close to each end), i.e.(85627EP01)

[0233] 27

[0234] the total number of measurements for each type of surface treatment was 15 and for untreated samples 30 measurements were collected.

[0235] Results:

[0236] The initial contact angle of the water droplet 5 seconds after it touched the surface was similar for untreated wood and surfaces treated with lignin solutions 17 and 20 (Fig. 15). These two solutions contain the acetone soluble lignin fraction of the soda lignin. The contact angle decreased over time for all samples, both surface treated and untreated, except for surfaces treated with these two solutions (Fig. 16). Thus, whereas the contact angle reduction of all other samples except these two were similar (Fig. 17), the surfaces with lignin solution 17 and 20 hardly decreased at all between the first and last measurement but stayed hydrophobic over time and were not wetted by the water droplet. Notably, the water droplet was kept on samples after contact angle analysis, and it was visually observed that untreated samples had completely absorbed the droplet within 5-10 minutes, while drops on surface treated samples remained on the surface after that time. This indicates that certain lignin solutions are more effective than others in making the wood surface hydrophobic, but that all surface treatments with lignin solutions present a barrier to liquid water.

[0237] Example 8: Contact angle analysis on endgrain wood samples treated with solutions of fractionated lignin

[0238] Materials:

[0239] Surface treated wood endgrain samples and untreated wood endgrain samples from Example 5 were used.

[0240] Method: Contact angle analysis

[0241] The same protocol as in Example 3 was used. For all samples, 3 replicates were used and contact angle analysis was performed in three locations (middle and close to each end).

[0242] Results:

[0243] The initial contact angle of the water droplet 5 seconds after it touched the surface was similar for untreated wood and surfaces treated with lignin solutions 17 and 20 (Fig. 18); similar to the results of Example 7. The contact angle decreased over time for all samples, both surface treated and untreated (Fig. 19). However, the reduction in contact angle was significantly higher for untreated wood and wood surface treated with lignin solutions 16 and 19. The other surfaces treated with lignin solutions 17, 20, 23, and 26 hardly decreased at all between the first and last measurement but stayed hydrophobic over time and were not wetted by the water droplet. This indicates that certain lignin solutions are(85627EP01)

[0244] 28

[0245] more effective than others in making the wood surface hydrophobic, but that all surface treatments with lignin solutions present a barrier to liquid water.

[0246] Example 9: Penetration of solutions with fractionated lignin into wood Materials:

[0247] Surface treated wood sidegrain samples and untreated wood sidegrain samples from Example 5 after the floating test of Example 6 were used.

[0248] The middle part of approximately 100x100 mm was cut of out each sample and saved for other measurements. One of the thin strips cut off each sidegrain sample was used for microscopy. Specifically, one of the two strips of length 100 mm cut along the grain of each sidegrain sample was used.

[0249] Method: Microscopy

[0250] The same protocol as in Example 2 was used.

[0251] Results:

[0252] The results show generally deeper penetration of the solutions with ethanol:l,2-propanediol solvent systems than the ethanokwater systems for both soda and Kraft lignins (Table 6). Surprisingly, the solution with the deepest penetration was solution 20 with acetone-insoluble soda lignin. This does not imply, however, that all parts of the solution penetrated evenly deep. Thus, dark streaks in the latewood extended further into the wood structure than was generally observed. The general deeper penetration of the solutions with ethanol:l,2-propanediol could be a result of lower solvent evaporation or solvent uptake into wood cell walls after application of the surface treatment. Overall, all tested solutions showed a penetration into the wood structure, i.e. they extended into the wood instead of just residing on the top surface. This demonstrates the use of lignin solutions as a primer or other part of a wood coating system, as well as a penetrating wood treatment.

[0253] Table 6: Penetration of lignin solutions in sidegrain samples of Example 5 evaluated by light microscopy.

[0254]

[0255] (85627EP01)

[0256] 29

[0257]

[0258] Example 10: Stability of lignin solutions with different lignin concentrations and surface treatment of wood with these

[0259] Materials:

[0260] Wood boards of Scots pine Pinus sylvestris L.)

[0261] Kraft lignin, softwood, UPM BioPiva™ 100 lignin

[0262] Ethanol

[0263] Demineralized water

[0264] Method 1:

[0265] Lignin solutions with different concentrations of lignin were prepared in 100 mL bluecap bottles. In each bottle, 100 g of liquid was produced by loading appropriate amounts of dried lignin, ethanol and water, and subsequently mixing with an Ultra-Turrax high-shear dispension mixer running at 10,000 rpm for 3 minutes.

[0266] The stability of the solutions understood as the lack of sedimentation was observed after 1 hour and after 2 days, while the solutions were kept in their respectively bottles at ambient temperature. By turning the bottle upside down, the amount of sediment was visually assessed and potential sediment was sought re-solubilised by Vortex mixing vigorously for 15 seconds. Hereafter, the bottle was visually inspected again for potential sedimentation.(85627EP01)

[0267] 30

[0268] Method 2: Surface treatment of wood

[0269] The concentrated lignin solutions were applied with a brush on the wood samples once on a sidegrain faces. After treatment, the samples were left to airdry overnight.

[0270] Method 3: Microscopy

[0271] The film-forming ability of the solutions was assessed by visually inspecting the treated wood surfaces with light microscopy.

[0272] Results:

[0273] The stability of the produced lignin solutions differed, with the those with the highest concentration of lignin exhibiting the highest degree of stability after 1 hour and 2 days in the bottle (Table 7). Thus, the final concentration of lignin in the solution were considerably lower in solutions 27-30, whereas the highly concentrated lignin solutions 31 and 32 did not exhibit any appreciable sedimentation in the bottles.

[0274] Table 7: Lignin solutions with different concentrations of lignin. The stability was observed after 1 hours and 2 days under laboratory conditions. The dry matter (DM) content of the solution was determined and the final composition of the lignin solutions determined.

[0275]

[0276] X = visible precipitate in the bottle; little change after 15 seconds of vortexing

[0277] XV = slight precipitate visible after 15 seconds of vortexing

[0278] V = no precipitate left after 15 seconds of vortexing

[0279] W = no precipitate, even before vortexing

[0280] Investigation of the surface quality by light microscopy showed smooth surfaces at lower lignin concentrations (10-25 wt° / o) and visible microcracks at the two highest lignin concentrations (Figure 21). Thus, it is dear that a smooth surface was achieved at a(85627EP01)

[0281] 31

[0282] relatively high lignin concentration of 25 wt° / o without additives, whereas a branched network of microcracks appeared at higher concentrations.

[0283] Example 11: Stability of lignin solutions with different additives and surface treatment of wood with these

[0284] Materials:

[0285] Wood boards of Scots pine Pinus sylvestris L.)

[0286] Kraft lignin, softwood, UPM BioPiva™ 100 lignin

[0287] Ethanol

[0288] Demineralised water

[0289] Tetraethoxysilane (TEOS)

[0290] Glycerol

[0291] Polyethylene glycol (PEG)

[0292] SigmaCell cellulose

[0293] Methylcellulose

[0294] Polysorbate 80 (Tween 80)

[0295] Xanthan gum

[0296] Starch (amylodextrin)

[0297] Method 1: Lignin solutions and their stability

[0298] Initially, a larger batch of concentrated lignin solution was prepared according to Method 2 of Example 5. The solution had a chemical composition of lignin : ethanol : water of 40 : 48 : 12 wt%. This batch was distributed into eight bluecap bottles (100 mL capacity) with 100 g solution in each. To each bottle, 5 gram additive was added and the solution was mixed using an UltraTurrax dispersion mixer for 3 minutes at 10,000 rpm. The additives used were TEOS, glycerol, PEG, SigmaCell cellulose, methylcellulose, Tween 80, xanthan gum, and starch, and one solution was made for each of these. All solutions had a final chemical composition of lignin : ethanol : water : additive (wt%) = 38 : 46 : 11: 5.

[0299] The stability of the solutions understood as the lack of sedimentation was observed after 1 hour and after 1 week, while the solutions were kept in their respectively bottles. By turning the bottle upside down, the amount of sediment was visually assessed and potential sediment was sought re-solubilised by Vortex mixing vigorously for 15 seconds. Hereafter, the bottle was visually inspected again for potential sedimentation.

[0300] Method 2: Surface treatment of wood and microscopy

[0301] The concentrated lignin solutions were applied with a brush on the wood samples once on a sidegrain faces. After treatment, the samples were left to airdry overnight. Thereafter,(85627EP01)

[0302] 32

[0303] the film-forming ability of the solutions was assessed by visually inspecting the treated wood surfaces with light microscopy.

[0304] Results:

[0305] The stability of the produced lignin solutions with different additives was high in that no or only slight sedimentation was observed after 1 hour or 1 week (Table 8). The only exception was solution 37 with methylcellulose that turned into a sticky lump immediately upon mixing.

[0306] Table 8: Lignin solutions with different additives. The stability was observed after 1 hour and 1 week under laboratory conditions. Assessment grades are shown below the table.

[0307]

[0308] X = visible precipitate in the bottle; little change after 15 seconds of vortexing

[0309] XV = slight precipitate after 15 seconds of vortexing

[0310] V = no precipitate left after 15 seconds of vortexing

[0311] VV = no precipitate, even before vortexing

[0312] Investigation of the surface quality by light microscopy showed a smooth surface for solution 35 containing PEG (Figure 22). Few microcracks were visible for surfaces treated with solution 38 containing Tween 80, and more microcracks for the rest of the solutions. However, the lignin concentration in the solutions was even higher than the highest concentration in Example 10. Thus, this clearly illustrates that the various additives all had a positive effect on the surface quality, since the cracking was considerably reduced compared with wood treated with solution 36 in Figure 21.(85627EP01)

[0313] 33

[0314] Example 12: Surface treatment of various wood species and wood products with solution of fractionated lignin

[0315] Materials:

[0316] Wood boards of various softwood species: Grand fir {Abies grandis (Douglas ex D. Don) LindL), European larch (Larix decidua Mill.), Norway spruce (Picea abies L.)

[0317] Wood boards of various hardwood species: European ash (Fraxinus excelsior L.), European beech (Fagus sylvatica L.), European oak (Quercus robur L.)

[0318] Wood boards of commercially available thermally modified wood of Scots pine (Pinus sylvestris L.) and European ash {Fraxinus excelsior L.)

[0319] Lignin solution 23 from Example 5.

[0320] Methods:

[0321] A concentrated lignin solution 23 of Example 5 was applied with a brush to one sidegrain surface. After treatment, the samples were left to airdry overnight. The surface interaction with water was investigated with contact angle analysis using the protocol of Example 3. Triplicate water droplets were placed on both untreated and treated surfaces of each board and the contact angle determined over 60 seconds.

[0322] Results:

[0323] The initial contact angle of the water droplet 5 seconds after it touched the surface was closely similar for all surfaces treated with lignin solution 23 of Example 5 (Figure 23). However, the initial contact angle varied significantly between wood species and thermall modified wood products. This was to be expected from the wide natural variability between wood species and thermally modified wood products. However, after 60 seconds the contact angle was significantly lower for a range of untreated wood surfaces (Figure 24) due to the fact that the water droplet wetted the untreated wood. This was also seen from the large reduction in contact angle over time (Figure 25). On the other hand, all wood surfaces treated with lignin solution were wetted to a much lower extent as seen from the remarkably stable contact angle for surface treated wood (Figure 25). This clearly demonstrates that the surface treatment with lignin solution is effective in making wood surfaces across wood species and modified wood products hydrophobic, and that the surface treatment presents a barrier to liquid water.

[0324] Example 13: Contact angle analysis on wood samples treated with solutions with different lignin concentration or with different additives

[0325] Materials:

[0326] Wood samples from Examples 10 and 11 were used.(85627EP01)

[0327] 34

[0328] Methods:

[0329] The same protocol as in Example 3 was used. Triplicate water droplets were placed on both untreated and treated surfaces of each sample and the contact angle determined over 60 seconds.

[0330] Results:

[0331] For wood surfaces treated with lignin solutions of different lignin concentration, the initial contact angle of the water droplet 5 seconds after it touched the surface was similar for untreated wood and surfaces treated with lignin solution 27 of 10 wt% (Figure 26), but lower for wood treated with lignin solutions 28-32. However, after 60 seconds the contact angle was similar for untreated wood and surface treated wood (Figure 27) due to the fact that the water droplet wetted the untreated wood, whereas the surfaces treated with solutions 28-32 were wetted to a much lower extent by the water droplets, and therefore the contact angle was remarkably stable (Figure 28), especially for solutions 30-32, i.e. with lignin concentrations of 25-35 wt%. This indicates that high concentration lignin solutions are more effective in making the wood surface hydrophobic, even though microcracks are visible (Figure 21) at these concentrations. The surface treated with solution 30 with 25 wt% lignin exhibited the smallest reduction in contact angle. This corresponds well with the images of Figure 21, where microcracks are visible at high lignin concentrations (30 and 35 wt%). Up to 25 wt% a higher lignin concentration led to more lignin being applied to the surfaces which gave better barrier properties against liquid water. As microcracks became visible at the highest concentrations, the barrier properties decreased again. Nonetheless, the untreated wood surface still showed the largest reduction in contact angle as a result of the water droplet wetting the surface. This indicates that all surface treatments with lignin solutions of different lignin concentrations present a barrier to liquid water.

[0332] For wood surfaces treated with lignin solutions with different additives, the initial contact angle of the water droplet 5 seconds after it touched the surface was higher for untreated wood than for the surface treated wood (Figure 29). However, after 60 seconds the contact angle was similar for untreated wood and surface treated wood (Figure 30) due to the fact that the water droplet wetted the untreated wood, whereas the surfaces treated with solutions 33-36, 38, and 40 were wetted to a much lower extent by the water droplets, and therefore the contact angle was remarkably stable (Figure 31) and was only slightly reduced, even though microcracks were visible for some of the treated surfaces (Figure 22). This indicates that all surface treatments with lignin solutions of different additives present a barrier to liquid water.(85627EP01)

[0333] 35

[0334] Example 14: Surface treatment of wood with lignin solution using different methods of application

[0335] Materials:

[0336] Wood specimens of Scots pine (Pinus sylvestris L.), European beech {Fagus sylvatica L.), and Grand fir {Abies grandis (Douglas Ex D. Don) LindL) of dimensions 25 x 25 x 100 mm Lignin solution 30 of Example 10

[0337] Base lignin solution without additives of Example 11

[0338] Methods:

[0339] Surfaces of the wood boards were treated with the lignin solution by three methods of application: spraying, dipping, and rolling. Spraying was performed with a hand-operated pump with a nozzle and container for the solution. Dipping was performance by submerging the wood slightly into the solution for 8 seconds by hand. Both spraying and dipping was performed with lignin solution 30 with a chemical composition of lignin : ethanol : water = 21 : 63 : 16 wt%. Application of a lignin solution to the wood surfaces by rolling was done with a commercially available paint roller, using the base lignin solution without additives of Example 11 having a chemical composition of lignin : ethanol : water = 40 : 48 : 12 wt%. After drying of all treated surfaces under laboratory conditions, the surfaces were visually inspecting with light microscopy.

[0340] Results:

[0341] All application methods were easy to use and produced nice, smooth surfaces after treatment. Investigation of the surface quality by light microscopy showed differences between application methods. Small dots from air bubbles are seen on dipped surfaces (Figure 32, middle column), similar to observations for brushed surfaces in Figure 21. The dots were absent from sprayed surfaces (Figure 32, left column) which on the other hand showed more visible microcracks. The roller treated surfaces had a similar appearance as the dipped surfaces, even though the lignin concentration was remarkably higher. Also, compared with the brushed surfaces with high lignin concentration (Figure 21, bottom), the roller treated surfaces had much fewer visible microcracks (Figure 32, right column). These results demonstrate that treating wood surfaces by spraying, dipping, and rolling yields as smooth surfaces as brushing. This demonstrates the broad applicability of lignin solutions for treating wood with different application methods.

Claims

1. (85627EP01)36Claims1. A method of surface treating wood, wherein the method comprises the following consecutive steps:(a) applying the wood with a solution comprising a concentration between 15-75 wt% of lignin or derivates thereof;wherein said lignin or derivatives thereof has / have been solubilised in(i) 10-100 wt% alcohol,(ii) 0-60 wt% water,(iii) 0-50 wt% of one or more non-volatile alcohols, and (iv) any suitable additives;the sum of the constituents (i)-(iv) not exceeding 100 wt%.

2. The method according to claim 1, wherein the wood is either a softwood species, e.g. Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.), larch (Larix spp.)~, Grand fir {Abies grandis (Douglas ex D. Don) Lindley), or a hardwood species, e.g. European beech (Fagus sylvatica L.), ash (Fraxinus excelsior L.), European oak (Quercus robur).

3. The method according to any of claims 1-2, wherein the wood is thermally modified.

4. The method according to any of claims 1-3, wherein the concentration of lignin or derivates thereof in the solution is 15-45 wt%.

5. The method according to any of claims 1-4, wherein the ratio of solid lignin or derivatives thereof to liquid of between 1:5.7-1:0.33 (w / w).

6. The method according to any of claims 1-5, wherein the concentration of alcohol in step (a)(i) is between 40-80 wt%.

7. The method according to any of claims 1-6, wherein the concentration of water in step (a)(ii) is between 20-25 wt%.

8. The method according to any of claims 1-7, wherein the concentration of one or more non-volatile alcohols in step (a)(iii) is 40 wt%.

9. The method according to any of claims 1-8, wherein the alcohol in step (a) (i) is chosen from the group consisting of ethanol, isopropanol or n-butanol or any combinations thereof.(85627EP01)3710. The method according to any of claims 1-9, wherein the one or more non-volatile alcohols in step (a)(iii) are chosen from the group consisting of glycol ethers, such as glycerol, 1,2-propanediol, 4-oxa-2,6-heptanediol, and l-methoxy-2-propanol or any combinations thereof.

11. The method according to any of claims 1-10, wherein the additives in step (a)(iv) are selected from a group consisting of, polyethylene glycols (PEG), micro-crystalline cellulose, methylated cellulose, starch such as amylodextrin, Polysorbate 80, tetraethoxysilane (TEOS), glycerol, and xanthan gum.

12. The method according to any of claims 1-11, wherein the lignin or derivatives thereof in step (a) is a lignin from an industrial process such as Kraft lignin, soda lignin, biorefinery lignin, or organosolv lignin or any combinations thereof.

13. The method according to any of claims 1-12, wherein the lignin-solution is applied to the wood surface by brushing, spraying, rolling, or dipping the wood.

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