Method for impregnating wood with a solution comprising lignin or derivatives thereof

Abstract

The present invention relates to a method of impregnating wood, wherein the method comprises the following consecutive steps of impregnating optionally dried wood with a solution comprising between 15-65 wt% lignin or derivatives thereof and drying of the impregnated wood.

Description

[0001] Method for impregnating wood with a solution comprising lignin or derivatives thereof

[0002] Field of the invention

[0003] The present invention relates to a novel method of impregnating wood with a solution comprising lignin or derivatives thereof.

[0004] Background of the invention

[0005] Lignin impregnation of wood is important because it fills up the material structure of native wood with hydrophobic lignin, which thereby increases the overall hydrophilicity of the wood while also creating physical blockage of the pores of the wood structure. Thereby, the lignin impregnations helps to 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, especially for wood with low natural durability such as beech and pine sapwood.

[0006] These factors will extend the service life of wooden structures, reduce the need for maintenance, and ultimately save costs. Additionally, lignin impregnation can be an environmentally friendly alternative to traditional wood preservatives, which in most cases involves harmful chemicals. Lignin impregnation is made using a renewable resource originating from residual plant materials, such as wood or straw, making it a more sustainable option. Furthermore, the lignin impregnated wood do not contain toxins, heavy metals, or other environmentally harmful substances, thus lignin impregnated timber will not be prone to the waste handling issues known from traditionally impregnated timber. Overall, lignin impregnation of wood has the potential to benefit both the environment and the economy.

[0007] WO98 / 16357 discloses pressure and vacuum impregnation processes for treating solid wood, such as pine or beech so as to fixate thereto a substance, e.g. a 0.1-10 wt% lignin solution. The process disclosed in WO98 / 16357 comprises treating the wood in a liquid medium, comprising: e.g. the lignin solution, an effective amount of an enzyme, e.g. laccases or peroxidases and an effective amount of an oxidising agent.

[0008] US4.752.509 discloses a method for the impregnation of wood, preferably pine, comprising the steps of first impregnation of said wooden objects with an aqueous solution of water- soluble lignin under heat and vacuum, followed by a second impregnation of said object with a weakly acidic fixing solution of lignin-insolubilizing and fungi-static metal ions until a lignin-precipitating amount of said ions has been deposited therein. W02022 / 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 W02022 / 117391A1 is envisaged for use as a fuel, especially for use as fuel in a combustion engine of a ship.

[0009] US5.246.739 discloses methods of impregnating wood, comprising the steps of forming an aqueous solution consisting of ammonium salt of lignin and a metal ion ammonia complex; followed by impregnating wood with said aqueous solution under vacuum; followed by subjecting the wood to pressure and drying the impregnated wood for a sufficient length of time to substantially remove ammonia gas from the wood.

[0010] JP3572323B1 discloses a method of impregnating wood with a lignin solution where (1) the wood is placed under reduced pressure, such as 100 mmHg or less, to remove air and moisture, (2) providing a lignin product, which mainly is composed of lignin sulfonate, treated with at least one of various aldehydes, methylolmelamine, methylolurea, initial condensation products of phenol formalin resin, epoxy compounds and diisocyanates, in order to make the lignin product insoluble, (3) impregnating the wood with the lignin product under pressure, (4) air-drying the impregnated wood and (5) heat-treating the air-dried wood about 700 °C for about 3 minutes in order to oxidize and thermoset the lignin component in the wood tissue.

[0011] CN110802700B discloses a method of vacuum pressurized impregnation of fast-growing wood with lignin liquefied resin followed by vacuum and pressure drying, smoking and charring of the impregnated wood. Said liquefied resin is prepared by mixing molten phenol, low molecular weight polyethylene glycol, anhydrous ethanol, concentrated hydrochloric acid and lignin under heating followed by adding caustic soda and formaldehyde solution. The purpose of the impregnation method is to provide a product from fast-growing wood with strong dimensional stability, high waterproof, high anticorrosion properties and strong mechanical properties.

[0012] Costas C F et al. (Holzforschung ■ January 2017, Enzymatic grafting of Kraft lignin (part I)) discloses methods of impregnating wood at atmospheric pressure with aqueous solutions of up to 20 g / L concentration, i.e. 2 wt%, of Kraft lignin and laccase under shaking and heat followed by a drying step.

[0013] Chirkova J. et al. (Holzforschung, Vol. 65, pp. 497-502, 2011) discloses vacuum impregnation of pinewood with various aqueous lignin solutions of low concentration, i.e. 0.5-1.0 wt% lignin. The impregnation process of Chirkova J. et al. comprises the process steps of drying pinewood samples under vacuum and then impregnating said dried wood under vacuum with a water solution of a lignin. During impregnation, the vacuum was switched periodically by deaerating of the solution to ensure the impregnation of wood.

[0014] Sanson CSL. at al., (Industrial Crops & Products 177 (2022) 114540) discloses an impregnation method using water-soluble fractions, with a concentration of solids of 4-9 wt%, separated from the pyrolytic lignin of fast-pyrolysis as bio-oil impregnation agent for pine wood protection against physical and biological agents. Sanson et al. discloses a method in which pinewood samples were oven-dried, air removed from the wood samples through placement in a vacuum, then the wood samples were impregnated with the impregnation agent under vacuum, finally, the treated wood was oven dried.

[0015] Borrega M. (preprint under review at European Journal of Wood and Wood Products, "Impregnation of pinewood with softwood Kraft lignin" (2022)) discloses a method of impregnating scots pine wood under vacuum with an aqueous 60% acetone solution containing about 10% softwood Kraft lignin. The impregnation treatment incorporated 6- 8% of lignin (based on wood dry mass) to the wood samples.

[0016] In view of the impregnation methods of the prior art, there is a need in the art for a more effective penetration and retention of impregnated lignin in wood.

[0017] The method for impregnating wood with lignin or derivatives thereof according to the present invention resulted in a surprisingly high degree of penetration into the wood of the lignin solution (mass gains of 33-40% for beech, 77-99% for Grand fir, 79-88% for Scots pine sapwood, and 38-61% for a range of other hardwood and softwood species) as well as a surprisingly high degree of fixation in the wood of the lignin solution (mass gains after leaching in water of 27-34% for beech, 69-91% for Grand fir, 68-81% for Scots pine sapwood, 31-56% for a range of other hardwood and softwood species).

[0018] Summary of the invention

[0019] Thus, an object of the present invention relates to a method for impregnating wood with lignin or derivatives thereof for improved penetration into the wood of the lignin or derivatives thereof as well as improved fixation in the wood of the lignin or derivatives thereof.

[0020] Thus, one aspect of the invention relates to a method of impregnating wood, wherein the method comprises the following consecutive steps: (a) impregnating wood with a solution comprising between 15-65 wt% lignin or derivatives thereof and comprising a ratio of solid lignin or derivatives thereof to liquid of between 1: 1.5-1:5 (w / w); wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% ethanol or methanol or mixtures thereof, (ii) 0-60 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols and Civ) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%; (b) drying of the impregnated wood from step (a).

[0021] Brief description of the figures

[0022] Figure 1 shows the mass gain (%) from impregnation of lignin solutions (Lignin 1-Lignin 5, see Table 1 for details) in beech wood before (unleached) and after (leached) leaching in water.

[0023] Figure 2 shows the mass gain (%) from impregnation of lignin solutions (Lignin 6-Lignin 10, see Table 1 for details) in beech wood before (unleached) and after (leached) leaching in water.

[0024] Figure 3 shows the mass gain (%) from impregnation of other types of impregnation solutions (WO, TS, LS, see Table 1 for details) in beech wood before (unleached) and after (leached) leaching in water. WO = Wood Oil is a liquid fuel derived from wood by pyrolysis (TO = Tall Oil is a by-product of the paper and pulp industry, primarily composed of fatty acids and resin acids. LS = Lignosulfonic Acid solution (lignosulfonates) is a 10 wt% solution of lignosulfonic acid and water was prepared for wood impregnation by dissolving lignosulfonic acid in water).

[0025] Figure 4 shows the mass gain (%) from impregnation of lignin solutions (Lignin 1-Lignin 5, see Table 1 for details) in Grand fir wood before (unleached) and after (leached) leaching in water.

[0026] Figure 5 shows the mass gain (%) from impregnation of lignin solutions (Lignin 6-Lignin 10, see Table 1 for details) in Grand fir wood before (unleached) and after (leached) leaching in water.

[0027] Figure 6 shows the mass gain (%) from impregnation of other types of impregnation solutions (WO, TS, LS, see table 1 for details) in Grand fir wood before (unleached) and after (leached) leaching in water (WO = Wood Oil is a liquid fuel derived from wood by pyrolysis. TO = Tall Oil is a by-product of the paper and pulp industry, primarily composed of fatty acids and resin acids. LS = Lignosulfonic Acid solution (lignosulfonates) is a 10 wt% solution of lignosulfonic acid and water was prepared for wood impregnation by dissolving lignosulfonic acid in water).

[0028] Figure 7 shows untreated beech wood stained with Safranin O. Figure 8 shows beech wood impregnated with Lignin 3 (43 wt% lignin, see table 1 for details) which shows consistent lumen filling and substantial cell wall impregnation. Mass gain after leaching was 30%.

[0029] Figure 9 shows beech wood impregnated with Lignin 4 (65 wt% lignin, see table 1 for details) which shows consistent lumen filling but no substantial cell wall impregnation. Mass gain after leaching was 34%.

[0030] Figure 10 shows beech wood impregnated Lignin 5 (10 wt% lignin, see table 1 for details) which shows cell wall impregnation but no lumen filling. Mass gain after leaching was 4%.

[0031] Figure 11 shows samples of beech wood after decay test with brown-rot fungus Rhodonia placenta-. Impregnated wood (left) and untreated wood (right).

[0032] Figure 12 shows the mass loss (%) after decay test with brown-rot fungus Rhodonia placenta. The impregnated samples showed improved durability to brown-rot fungal degradation compared to untreated samples.

[0033] Figure 13 shows that beech wood impregnated with Lignin 2 exposed to brown-rot fungus Rhodonia placenta showed no substantial cell wall degradation after 9 weeks of laboratory incubation. The mass loss was 1.8%.

[0034] Figure 14 shows untreated beech wood exposed to brown-rot fungus Rhodonia placenta for 9 weeks, which showed a mass loss of 20.5%. A considerable increase in lignin concentration was observed within cell walls as a result of the removal of carbohydrates by the fungus.

[0035] Figure 15 shows the estimated moisture content (g / g) within cell walls of water-saturated wood for both untreated wood and wood impregnated by lignin solutions.

[0036] Figure 16 shows the estimated moisture content (g / g) outside cell walls of water-saturated wood for both untreated wood and wood impregnated by lignin solutions. In the latter, the lignin fills up voids and hereby reduces the available space for liquid water.

[0037] Figure 17 shows the low-field NMR relaxation time (s) of the cell wall water of water- saturated wood for both untreated wood and wood impregnated by lignin solutions. The cell wall water is affected by the lignin impregnation which indicates that the treatment penetrates the cell walls of the wood. Figure 18 shows examples of surface with low contact angle (left) and high contact angle (right).

[0038] Figure 19 shows sessile droplet on transverse section of Lignin 3 impregnated beech wood (left) and untreated beech wood (right).

[0039] Figure 20 shows sessile droplet on transverse section of Lignin 3 impregnated Grand fir wood (left) and untreated Grand fir wood (right).

[0040] Figure 21 shows lignin yield (%) and lignin concentration (wt%) in solutions with 10 wt% glycerol. The weight percentage of ethanol is (1 - glycerol - water)*100. Values of water above 35 wt% seems to negatively affect lignin yield of the solutions.

[0041] Figure 22 shows lignin yield (%) and lignin concentration (wt%) in solutions with 25 wt% glycerol. The weight percentage of ethanol is (1 - glycerol - water)*100. Values with high glycerol affect the density of the solution but not the lignin yield of the solutions.

[0042] Figure 23 shows the mass gain (%) of different wood species (beech, Scots pine, paulownia, ash, black alder, lime, Monterey pine, poplar) impregnated with lignin solution consisting of 40 wt% lignin : 56 wt% ethanol : 4 wt% water using the vacuum impregnation method according to the invention.

[0043] Figure 24 shows the mass gain (%) after impregnation of solutions with different types of lignin in beech wood before (unleached) and after (leached) leaching in water. Lignin : Ethanol : Water content for the different lignin solutions: Kraft (BioPivalOO) 40 wt% : 56 wt% : 4 wt%, Alkali (Sigma Aldrich) 10 wt% : 67 wt% : 23 wt%, Organosolv (Sigma- Aldrich) 33 wt% : 50 wt% : 17 wt%, Soda (Protobind 2600) 18 wt% : 62 wt% : 21 wt%, Biorefinery (MelioraBio) 8 wt% : 69 wt% : 23 wt%.

[0044] Figure 25 shows the mass gain (%) after impregnation of solutions with different types of lignin in Scots pine wood before (unleached) and after (leached) leaching in water. Lignin : Ethanol : Water content for the different lignin solutions: Kraft (BioPivalOO) 40 wt% : 56 wt% : 4 wt%, Alkali (Sigma Aldrich) 10 wt% : 67 wt% : 23 wt%, Organosolv (Sigma- Aldrich) 33 wt% : 50 wt% : 17 wt%, Soda (Protobind 2600) 18 wt% : 62 wt% : 21 wt%, Biorefinery (MelioraBio) 8 wt% : 69 wt% : 23 wt%.

[0045] Figure 26 shows the solubility (%) in pure water during 1 hour of mixing of the different types of lignin solutions from Figure 25. The higher leaching of alkali lignin in Figure 25 is seen to correlate with a higher water solubility of this particular lignin solution. Data is missing for the solution with biorefinery lignin.

[0046] Figure 27 shows the mass gain (%) after impregnation of lignin solutions containing nonvolatile alcohols in beech wood before (unleached) and after (leached) leaching in water (for details of "Soda" and "Kraftl-7" , see Example 9, method 1). Figure 27 indicates that it is possible to substitute part of the volatile alcohols (such as ethanol or methanol) used to solubilize commercial lignin products, such as "BioPiva 100, Kraft", with non-volatile alcohols like e.g. glycerol and 1,2-propanediol and even water.

[0047] Figure 28 shows the mass gain (%) after impregnation of lignin solutions containing nonvolatile alcohols in Scots pine wood before (unleached) and after (leached) leaching in water (for details of "Soda" and "Kraftl-7", see Example 9, method 1). Figure 28 indicates that it is possible to substitute part of the volatile alcohols (such as ethanol or methanol) used to solubilize commercial lignin products, such as "BioPiva 100, Kraft", with nonvolatile alcohols like e.g. glycerol and 1,2-propanediol and even water.

[0048] Figure 29 shows the mass gain (%) after impregnation of pure volatile and non-volatile alcohols in beech wood and Scots pine wood before (unleached) and after (leached) leaching in water. Figure 29 indicates that the alcohols contained in the lignin solutions either evaporates during drying after lignin impregnation or are leached out by water, thus not contributing to the final mass gain of the wood after leaching.

[0049] Figure 30 shows the correlation between lignin concentration in the impregnation solution and the final mass gain after leaching in wood of Scots pine and beech. Both solutions with and without non-volatile alcohols are included. Figure 30 indicates that leaching wood impregnated with solutions containing non-volatile alcohols removes these while retaining the impregnated lignin in the wood, and that higher lignin concentration will lead to a higher mass gain after leaching.

[0050] Figure 31 shows the mass loss (%) after decay test of beech wood after 4, 7, and 10 weeks of exposure to brown-rot fungus Fomitopsis pinicola. Numbers above the columns indicate the average mass loss of five replicate samples. For the impregnated samples 15 replicates were used to document the mass loss after 10 weeks of exposure. The impregnated samples showed improved durability to brown-rot fungal degradation compared to untreated samples. Beech wood was impregnated with Kraft lignin or Soda lignin solutions, both of which had a concentration of 31 wt% lignin : 52 wt% ethanol : 17 wt% water. The mass gain after leaching in water was 23.6% and 20.9% for the Kraft and Soda lignin impregnated wood, respectively. Figure 31 indicates that while the brown-rot fungus continues to degrade the untreated beech wood over time, the impregnated wood is highly protected from fungal degradation.

[0051] Figure 32 shows the mass loss (%) after decay test of Scots pine wood after 4, 7, and 10 weeks of exposure to brown-rot fungus Fomitopsis pinicola. Numbers above the columns indicate the average mass loss of five replicate samples. For the impregnated samples 15 replicates were used to document the mass loss after 10 weeks of exposure. The impregnated samples showed improved durability to brown-rot fungal degradation compared to untreated samples. Beech wood was impregnated with Kraft lignin or Soda lignin solutions, both of which had a concentration of 31 wt% lignin : 52 wt% ethanol : 17 wt% water. The mass gain after leaching in water was 66.1% and 66.7% for the Kraft and Soda lignin impregnated wood, respectively. Figure 32 indicates that while the brown-rot fungus continues to degrade the untreated Scots pine wood over time, the impregnated wood is highly protected from fungal degradation.

[0052] Figure 33 shows samples of untreated beech wood (upper row) and untreated Scots pine wood (lower row) before (left column) and after (right column) exposure to the brown-rot fungus Fomitopsis pinicola for 10 weeks. Mass losses are seen in Figure 31 and Figure 32. Figure 33 illustrates a marked shrinkage of the wood dimensions after fungal degradation and final drying of the wood.

[0053] Figure 34 shows samples of beech wood (upper row) and Scots pine wood (lower row) impregnated with Kraft lignin solution (concentration of 31 wt% lignin : 52 wt% ethanol : 17 wt% water) before (left column) and after (right column) exposure to the brown-rot fungus Fomitopsis pinicola for 10 weeks. Figure 34 illustrates that the brown-rot attack did not have any visible effects on the impregnated wood.

[0054] Figure 35 shows samples of beech wood (upper row) and Scots pine wood (lower row) impregnated with Soda lignin solution (concentration of 31 wt% lignin : 52 wt% ethanol : 17 wt% water) before (left column) and after (right column) exposure to the brown-rot fungus Fomitopsis pinicola for 10 weeks. Figure 35 illustrates that the brown-rot attack did not have any visible effects on the impregnated wood.

[0055] Figure 36 shows the mass loss (%) after decay test of various wood species after 10 weeks of exposure to brown-rot fungus Fomitopsis pinicola. Numbers above the columns indicate the average mass loss of three replicate samples. Samples are identical to those reported in Figure 23. Figure 36 indicates that the impregnated wood is highly protected from fungal degradation. Figure 37 shows the mass loss (%) after decay test of wood of beech and Scots pine impregnated with solutions of different types of lignin after 10 weeks of exposure to brown-rot fungus Fomitopsis pinicola. Numbers above the columns indicate the average mass loss of three replicate samples. Samples are identical to those reported in Figure 24 and Figure 25. Figure 37 indicates that the impregnated wood with the different types of lignin is highly protected from fungal degradation, even with a large variety in mass gain as seen in Figure 24 and Figure 25.

[0056] Figure 38 shows the mass loss (%) after decay test of wood of beech and Scots pine impregnated with lignin solutions containing various non-volatile alcohols after 10 weeks of exposure to brown-rot fungus Fomitopsis pinicola. Numbers above the columns indicate the average mass loss of three replicate samples. Samples are identical to those reported in Figure 27 and Figure 28. Figure 38 indicates that the impregnated wood with solutions containing various types of non-volatile alcohols is highly protected from fungal degradation.

[0057] Figure 39 shows the schematic design of the Micro-Combustion Calorimeter (MCC).

[0058] Figure 40 shows the heat release rate curves obtained with the Micro-Combustion Calorimeter (MCC) on beech wood both untreated and impregnated with Kraft lignin (BioPivalOO) or Soda lignin (Protobind 2600) to mass gains of 21.3% and 19.4%, respectively. Samples impregnated with Kraft lignin are identical to those reported in Figure 23, while samples impregnated with soda lignin are identical to those reported in Figure 24. Figure 40 indicates that impregnation with lignin solutions improved the fire technical properties of the wood by reducing the initial heat release (peak #1) of the material and promoting the formation of a stable char layer as illustrated by the higher combustion temperature of Peak #2.

[0059] Figure 41 shows the heat release rate curves obtained with Micro-Combustion Calorimeter (MCC) on Scots pine wood both untreated and impregnated with Kraft lignin (BioPivalOO) or Soda lignin (Protobind 2600) to mass gains of 81.7% and 68.7%, respectively. Samples impregnated with Kraft lignin are identical to those reported in Figure 23, while samples impregnated with soda lignin are identical to those reported in Figure 25. Figure 41 indicates that impregnation with lignin solutions improved the fire technical properties of the wood by reducing the initial heat release (peak #1) of the material and promoting the formation of a stable char layer as illustrated by the higher combustion temperature of Peak #2. Figure 42 shows the maximum heat release rates (W / g) for peak #1 and peak #2 in the curves obtained with the Micro-Combustion Calorimeter (MCC) for beech (in Figure 40) and Scots pine (in Figure 41). The maximum heat release rate values are based on duplicate measurements. Figure 42 shows that the initial maximum heat release rate (peak #1) is lower for the lignin impregnated wood than the untreated wood. The maximum heat release rate of char pyrolysis (peak #2) is not affected by the treatment.

[0060] Figure 43 shows the peak temperature of maximum heat release rates (W / g) for peak #1 and peak #2 in the curves obtained with the Micro-Combustion Calorimeter (MCC) for beech (in Figure 40) and Scots pine (in Figure 41). The temperature of maximum heat release rate values are based on duplicate measurements. Figure 43 shows that the temperature for the maximum heat release rate of char pyrolysis (peak #2) is higher for the lignin impregnated wood than the untreated wood. This indicates that the formed char of the lignin impregnated wood is more stable than that formed in untreated wood. The temperature for maximum heat release rate of the initial heat release (peak #1) is not affected by the treatment.

[0061] Figure 44 shows the infrared spectra obtained with an ATR-FTIR spectrometer on the unmodified and three types of modified lignin: 1) mechanical modification with ball-milling, 2) enzymatic modification with laccase enzymes, 3) chemical modification with hydrogen peroxide. The infrared spectra are average spectra based on triplicate measurements, and they have been baseline corrected and normalised with the signal intensity of the 1500 cm-1to allow comparison across the various types of lignin. The spectra have been vertically shifted for improved readability, and the dashed grey lines indicate the baseline of each spectrum. Figure 44 indicates the four selected peaks where the various types of lignin are affected by modification as expected from data in literature.

[0062] Figure 45 shows the normalised intensity of four selected peaks in the infrared spectra of unmodified and modified lignin. Error bars show the standard deviation based on triplicate measurements. Figure 45 shows that mechanical modification does not change the chemistry of the lignin, only the particle size, whereas enzymatic and chemical modification changes the lignin chemistry.

[0063] Figure 46 shows the mass gain (%) after impregnation of solutions with different types of modified lignin in beech wood before (unleached) and after (leached) leaching in water. Lignin : Ethanol : Water content for all four lignin solutions was 42 wt% lignin : 43 wt% ethanol : 15 wt% water. Figure 46 indicates that modification of the lignin does not negatively affect the mass gain after impregnation and leaching in water. Figure 47 shows the mass gain (%) after impregnation of solutions with different types of modified lignin in Scots pine wood before (unleached) and after (leached) leaching in water. Lignin : Ethanol : Water content for all four lignin solutions was 42 wt% lignin : 43 wt% ethanol : 15 wt% water. Figure 47 indicates that modification of the lignin does not negatively affect the mass gain after impregnation and leaching in water.

[0064] Figure 48 shows the mass gain (%) after pressure impregnation of wood of beech wood with different samples geometries before (unleached) and after (leached) leaching in water. Lignin : Ethanol : Water content the impregnated solution was 41.5 wt% lignin : 43.9 wt% ethanol : 14.6 wt% water. Figure 48 shows that there is a size effect, where larger samples achieve smaller average mass gains, but also exhibit smaller effect of leaching. Data is missing for the mass gain after leaching of the pressure impregnated "Smallest" sample batch.

[0065] Figure 49 shows the mass gain (%) after pressure impregnation of wood of Scots pine wood with different samples geometries before (unleached) and after (leached) leaching in water. Lignin : Ethanol : Water content the impregnated solution was 41.5 wt% lignin : 43.9 wt% ethanol : 14.6 wt% water. Figure 49 shows that there is a size effect, where larger samples achieve smaller average mass gains, but also exhibit smaller effect of leaching. Data is missing for the mass gain after leaching of the pressure impregnated "Smallest" sample batch.

[0066] The present invention will now be described in more detail in the following.

[0067] Detailed description of the invention

[0068] Definitions

[0069] Prior to discussing the present invention in further details, the following terms and conventions will first be defined:

[0070] "BioPiva 100" or"BioPiva 100, Kraft": When referred to herein "BioPiva 100" or"BioPiva 100, Kraft" refers to a type of 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 wood during the production of paper, contains a high content of phenolic compounds and relatively low sulfur content compared to e.g. lignosulfonates. 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.

[0071] 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 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.

[0072] 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.

[0073] 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 include e.g. glycerol (also referred to as glycerine) and 1,2-propanediol (also referred to as propylene glycol).

[0074] 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.

[0075] "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.

[0076] "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.

[0077] 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.

[0078] 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. 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).

[0079] Wood Oil (WO): When used herein, WO is a liquid derived from wood by pyrolysis or gasification. It has properties such as high energy content, high viscosity, and can be corrosive. The toxicity of WO can vary based on its composition and source. WO contains a complex mixture of oxygenated organic compounds and water. Phenolic compounds, originating from degraded lignin, can make up a considerable fraction of bio-oil, often ranging from 20% to 30%.

[0080] Tall Oil (TO) : When used herein, TO is a by-product of the paper and pulp industry, primarily composed of fatty acids and resin acids. Tall oil is considered to have low toxicity. Phenolic compounds in tall oil include phenolic acids and lignans, but are present in relatively small amounts (range from 0.1% to 3%).

[0081] Lignosulfonic acid: When used herein, Lignosulfonic acid (lignosulfonates) is a water-soluble anionic polyelectrolyte complex compound derived from lignin, obtained as a by-product from the sulfite pulping process in the paper and pulp industry. It has properties such as solubility in water, acidity, binding capabilities, and chelating properties. Lignosulfonic acid is abundantly available due to its association with pulp production.

[0082] Embodiments

[0083] In one embodiment of the present invention there is provided a method of impregnating wood, wherein the method comprises the following consecutive steps: (a) impregnating wood with a solution comprising between 15-65 wt% lignin or derivatives thereof and comprising a ratio of solid lignin or derivatives thereof to liquid of between 1: 1.5-1:5 (w / w); wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% ethanol or methanol or mixtures thereof, (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%; (b) drying of the impregnated wood from step (a).

[0084] In another embodiment of the present invention there is provided a method of impregnating wood which has been subjected to drying, wherein the method comprises the following consecutive steps: (a) impregnating wood with a solution comprising between 15-65 wt% lignin or derivatives thereof and comprising a ratio of solid lignin or derivatives thereof to liquid of between 1: 1.5-1:5 (w / w); wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% ethanol or methanol or mixtures thereof, (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%; (b) drying of the impregnated wood from step (a).

[0085] In still another embodiment of the present invention there is provided a method of impregnating wood, which optionally has been subjected to drying, wherein the method comprises the following consecutive steps: (a) impregnating wood with a solution comprising between 15-65 wt% lignin or derivatives thereof and comprising a ratio of solid lignin or derivatives thereof to liquid of between 1: 1.5-1:5 (w / w); wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% ethanol or methanol or mixtures thereof, (ii) 0-60 wt% water, (iii) 0-50 wt% of one or more non-volatile alcohols and Civ) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%; (b) drying of the impregnated wood from step (a); wherein the method further comprises a leaching step (c) following step (b).

[0086] In still another embodiment of the present invention there is provided a method of impregnating optionally dried wood from the group consisting of Scots pine sapwood (Pinus sylvestris L.), beech (Fagus sylvatica L.), paulownia (Paulownia tomentosa (Thunb.) Steud.), ash (Fraxinus excelsior L.), European black alder (Alnus glutinosa (L.) Gaertn.), lime (Tilia cordata Mill.), Monterey pine (Pinus radiate D.Don), poplar Populus ssp.) and Grand fir (Abies grandis (Douglas ex D. Don) Lindley) by the following consecutive steps: (a) impregnating wood with a solution comprising between 15-65 wt% lignin or derivatives thereof and comprising a ratio of solid lignin or derivatives thereof to liquid of between 1: 1.5-1:5 (w / w); wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% ethanol or methanol or mixtures thereof, (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%; (b) drying of the impregnated wood from step (a); wherein the method optionally comprises a leaching step (c) following step (b).

[0087] In still another embodiment of the present invention there is provided a method of impregnating the optionally dried wood by the following consecutive steps: (a) impregnating wood under vacuum for 15-60 minutes, such as 30 minutes, with a solution comprising between 15-65 wt% lignin or derivatives thereof, such as 40-52 wt% lignin or derivatives thereof, for 1-10 hours, such as 3 hours, wherein the solution comprises a ratio of solid lignin or derivatives thereof to liquid of between 1: 1.5-1:5 (w / w); wherein said lignin or derivatives thereof has / have been solubilised in (i) 10-100 wt% ethanol or methanol or mixtures thereof, (ii) 0-60 wt% water, (iii) 0-50 wt% of one or more nonvolatile alcohols and (iv) any suitable additives;; the sum of the constituents (i)-(iv) not exceeding 100 wt%.

[0088] In still another embodiment of the present invention there is provided a method of impregnating wood wherein the lignin or derivatives thereof in the impregnation step (a) is a lignin that has been solubilised in a solvent comprising of volatile alcohols (10-100 wt%) (such as ethanol or methanol), water (0-60 wt%), and potentially additives (0-50 wt%) (such as glycerol, ammonia, ethyl acetate, surfactants (such as PEG6000, Tween80, etc.), etc.); the sum of the constituents not exceeding 100 wt%.

[0089] In still another embodiment of the present invention there is provided a method of impregnating wood wherein the lignin or derivatives thereof in the impregnation step (a) is a lignin from an industrial process such as Kraft lignin (such as from a Kraft pulping process), soda lignin (such as from a soda pulping process), biorefinery lignin (such as from bioethanol production based on lignocellulose (such as straw, wood, sugarcane bagasse etc.), organosolv lignin, or lignosulfonates (such as from a sulfite pulping process).

[0090] In still another embodiment of the present invention there is provided a method of impregnating wood wherein the lignin or derivatives thereof in the impregnation step (a) is a lignin which has been modified prior to solubilization e.g. chemically (by e.g. epoxidation, oxidation, esterification, ozonification, etc.), enzymatically (with e.g. peroxidases, laccases, etc.), physically (milling, explosive decomposition, radiation, etc.), or thermally (e.g. by heating to 50-150 °C), or by any combinations hereof.

[0091] In still another embodiment of the present invention there is provided a method of impregnating wood, wherein the lignin solution in impregnation step (a) comprises between 15-65 wt% lignin or derivatives thereof, preferably 20-60 wt% lignin or derivatives thereof, more preferably 25-55 wt% lignin or derivatives thereof, even more preferably 30-50 wt% lignin or derivatives thereof, most preferably 35-45 wt% lignin or derivatives thereof.

[0092] In still another embodiment of the present invention there is provided a method of impregnating wood, wherein the lignin solution in impregnation step (a) comprises (i) 0-100 wt% ethanol or methanol or mixtures thereof, preferably 10-100 wt% ethanol or methanol or mixtures thereof preferably 20-95 wt% ethanol or methanol or mixtures thereof, more preferably 30-90 wt% ethanol or methanol or mixtures thereof, even more preferably 40-85 wt% ethanol or methanol or mixtures thereof, most preferably 50-80 wt% ethanol or methanol or mixtures thereof, (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%.

[0093] In still another embodiment of the present invention there is provided a method of impregnating wood, wherein the lignin solution in impregnation step (a) comprises said lignin or derivatives thereof that has / have been solubilised in (i) 0-100 wt% ethanol or methanol or mixtures thereof, (ii) 0-60 wt% water, (iii) 0-100 wt% of one or more non- volatile alcohols, preferably 10-80 wt% of one or more non-volatile alcohols, more preferably 15-60 wt% of one or more non-volatile alcohols, most preferably 20-40 wt% of one or more non-volatile alcohols and (iv) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%;

[0094] The invention will now be described in further details in the following non-limiting examples.

[0095] Examples

[0096] Example 1: Protocol for impregnation of lignin in wood

[0097] Materials 1: Wood

[0098] Wood samples of beech Fagus sylvatica L.) and Grand fir (Abies grandis (Douglas ex D. Don) Lindley) were cut into cuboids of dimensions of 5 mm x 10 mm x 10 mm (L x H x W). The samples were marked by cutting a different number of angles off each sample to facilitate recognition within each batch of triplicates. These were dried in a vacuum oven (60 °C, 0 mbar) for 18 hours, and their dry masses determined. The samples were allowed to cool down for 15 minutes in a dry climate within cups with zeolites and closed with parafilm on top, followed by rapid weighing. Subsequently, the samples were placed back in the cups with zeolites in a desiccator.

[0099] Materials 2: Lignin solutions

[0100] Lignin solutions were prepared for impregnation, and the blocks were impregnated using a vacuum impregnation equipment positioned under the fume hood. Oil baths and warming plates were prepared. Concentrated lignin solutions were prepared by fractionation of lignin (Kraft or technical) in ethanol or methanol with specific alcohol: water: glycerol ratio (wt%) and with a solid (dry lignin) to liquid ratio of 1:5 (Lignin 1 to 5) (w / w) or 1:3 (Lignin 6 to 10) (w / w) (Table 1). The lignin alcohol mixtures 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 or further processed.

[0101] The soluble fraction of some lignin solutions (Lignin 1 to 5) were up-concentrated by rotor evaporation, to increase the concentration of lignin in the solutions. These were produced by partly removing the alcohols from the soluble lignin fractions using Buchi Rotavapor R300 with a water bath set to 50 °C and the coolant at 10 °C. The pressure was set to 337 mbar and 175 mbar for methanol and ethanol, respectively. As the alcohols are more volatile than water, the addition of pure alcohols was necessary to maintain a water concentration as the initial one. Additionally, three other types of impregnation solutions (containing modified or degraded lignin) were used for impregnation:

[0102] Wood Oil (WO) is a liquid fuel derived from wood by pyrolysis. It has properties such as high energy content, higher viscosity compared to conventional fuels, and can be corrosive. The abundance of wood pyrolysis oil depends on the availability of wood as a feedstock, and its toxicity can vary based on its composition and source. Wood oil contains a complex mixture of oxygenated organic compounds and water. Phenolic compounds, originating from degraded lignin, can make up a considerable fraction of bio-oil, often ranging from 20% to 30%.

[0103] Tall Oil (TO) is a by-product of the paper and pulp industry, primarily composed of fatty acids and resin acids. The name originated as an Anglicization of the Swedish tallolja ('pine oil'). It finds applications in the chemical industry, surfactant production, resins, and animal feed. Tall oil is considered to have low toxicity. Phenolic compounds in tall oil include phenolic acids and lignans, but are present in relatively small amounts (range from 0.1% to 3%).

[0104] Lignosulfonic Acid solution (LS (lignosulfonates)) is a 10 wt% solution of lignosulfonic acid and water was prepared for wood impregnation by dissolving lignosulfonic acid in water. Lignosulfonic acid is a water-soluble anionic polyelectrolyte complex compound derived from lignin, obtained as a by-product in the paper and pulp industry (from the sulfite pulping process). It has properties such as solubility in water, acidity, binding capabilities, and chelating properties. Lignosulfonic acid is abundantly available due to its association with pulp production.

[0105] Table 1: Lignin solutions and other types of impregnation solutions used for impregnation.

[0106] * The lignin solution was prepared by fractionation of lignin (Kraft or technical) in ethanol with 50 wt% alcohol : 25 wt% water : 25 wt% glycerol ratio and with a solid (dry lignin) to liquid ratio of 1:3 (w / w). The solution was prepared and immediately used for impregnation, without stirring, centrifugation or cold processing. ** The lignin solutions were produced by natural separation of one lignin solution that happened overnight. The supernatant fraction showed a dry mass of roughly 10 wt% and while the pellet showed a gel-like insoluble fraction with roughly 65 wt%. High Pressure Liquid Chromatography indicated that the liquid part of the two fractions contain the same ratio of alcohol and water (75 wt% and 25 wt%, respectively).

[0107] Methods: Impregnation

[0108] The lignin solutions were impregnated into the wood samples by following the protocols A, B or C.

[0109] A : Wood samples of beech and Grand fir were placed in a reaction flask and were evacuated using a vacuum pump. The lignin solution were then injected through a rubber cork into the reaction flask, and atmospheric pressure was re-established after 5 minutes. The reaction flask with wood samples and lignin solution were then lowered into an oil bath at 50 °C and left overnight to impregnate.

[0110] B, C : Wood samples of beech and Grand fir were placed in a reaction flask containing an impregnation solution, the flasks were closed with a glass stopper and were then lowered into an oil bath at 50 °C (B) or 105 °C (C) and left overnight to impregnate (no vacuum was applied).

[0111] The impregnated blocks were then cleaned with paper towels and vacuum dried at 60 °C and 0 mbar for 12 hours. After removal from the vacuum oven, the cubes were quickly weighed using the aforementioned procedure to determine the (unleached) mass gain before leaching. Then the impregnated blocks underwent leaching in water, following the modified European standard EN 84, i.e. one week in water with daily water refreshing at ambient temperature. Afterwards, vacuum drying of the impregnated blocks was performed in a vacuum oven at 60 °C and 0 mbar for 12 hours or overnight. Finally, the cubes were weighed and their (leached) mass gain after leaching determined. The mass gain from impregnation, Rmod, in terms of gram per gram initial (dry) material was determined as:

[0112] Where mdry,o (g) and mdry(g) are the dry mass before and after impregnation, respectively. The mass gain in % is 100* / ?mod. The mass gain before (unleached) and after (leached) water leaching was determined from the dry mass mdryobtained by vacuum drying before and after leaching.

[0113] Results:

[0114] Table 2: Mass gain after impregnation and subsequent leaching in water for the various solutions. Mass gains shown in units of both (g / g) and (%).

[0115] The mass gain shows similar trend in beech and Grand fir for the same type of lignin solution and other impregnation solutions (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6). The Grand fir wood generally had a mass gain 2-3 times higher than beech. Lignin 1 produced a yellow, mud-like coatings on the samples. Lignin 6 to 10 were employed to show the possibility of reducing the ethanol concentration while still achieving a mass gain >20% (Figure 2, Figure 5). Lignin 10, in addition, was used to test the possibility of having a one-pot recipe, shortening the production effort and time. WO solution gave high mass gain but also significant leaching (Figure 3, Figure 6). TO solution also gave high mass gain, whereas LS did not produce any considerable mass gain (Figure 3, Figure 6).

[0116] Example 2: Penetration of lignin solutions in wood

[0117] Materials:

[0118] Wood impregnated with lignin solutions (Lignin 1-5) from Example 1.

[0119] Method: Microscopy

[0120] Slices of 30 micrometre thickness were produced with rotary microtome (Leica RM2255), stained with 2% Safranin O solution, which is known to label lignin substructures. The slices were immersed in the staining solution for 10 minutes, then dried with ultra-absorbent paper tissues, rinsed and dried for two times using distilled water and ultra-absorbent paper tissues, before finally being placed on a microscopy slide, immersed in a drop of distilled water, and covered with cover glass slides. Samples were imaged with Leica ICC50W widefield microscope camera and Leica HIPLAN air immersion objectives with 20x or 40x magnification.

[0121] Results:

[0122] The solution Lignin 3 was one of the best performers, together with Lignin 1 and Lignin 2, showing high mass gains of the wood material in Example 1. The microscopy images show the impregnation of the cell wall material as well as filling of lumina in several fibres and vessels (Figure 8). The penetration of the cell wall can be observed by the darkening (reddish colour) of the secondary cell wall compared to the untreated samples (Figure 7). The solution Lignin 4 was produced from the pellet deposited from the lignimethanol: water solution made with high percentage of water (25 wt% of the liquid fraction). The colour of the cell walls of the impregnated beech samples (Figure 9) are more similar to the ones of the untreated samples (Figure 7), suggesting that this solution impregnated the lumina but did not penetrate the cell wall of the wood as much as the solution Lignin 3 did.

[0123] The solution Lignin 5 was obtained as the supernatant part left from the solution obtained with a lignimethanol: water ratio containing high percentage of water (25 wt% of the liquid fraction). The solution is stable with low lignin concentration (10 wt%) and lead to a mass gain of 4%. Despite the low mass gain the lignin seems to penetrate mostly the cell wall while not filling the lumina.

[0124] The separation of the solution that leads to the solutions Lignin 4 and Lignin 5 might be due to size differences, among other factors. The adopted methodology show that by tuning the solvent ratio it is possible to obtain lignin solutions which can selectively impregnate the cell wall and / or fill the lumina.

[0125] Example 3: Decay resistance of lignin impregnated wood

[0126] Materials: Wood and fungus

[0127] Samples of untreated and lignin impregnated (Lignin 2) beech from Example 1 were used in the experiment. The test fungus used was Rhodonia placenta FPRL 280.

[0128] Methods: Decay test and microscopy

[0129] Prior to the experiment, all samples were dried in a conventional oven at 103 °C for 20-22 hours, cooled in a desiccator, and weighed to obtain the dry mass (m0). The samples were placed in glass containers and sterilized by autoclaving at 120 °C for 20 minutes. Plastic netting was also autoclaved and used as a spacer between the samples and the growth medium. Petri dishes (100x20 mm) from Sarstedt (article number 83.3902) were prepared with a 4% malt / agar medium consisting of 20 g Difco malt, 10 g WVR agar, and 500 mL deionized water, autoclaved at 120 °C for 20 minutes. A plug of a relatively fresh culture of Rhodonia placenta FPRL 280 was placed in the center of each petri dish. A sterile plastic netting and three samples (treated or untreated) were placed on top. The petri dishes were incubated in a climatic chamber at 70±5% relative humidity and 22±2 °C for the desired number of weeks (9 weeks) (Figure 11). At harvest, the mycelium was carefully removed from the samples, and the wet mass was recorded. The samples were then dried at 103 °C for 21 hours, cooled in a desiccator, and weighed again to obtain the final dry mass. The average mass loss, standard deviation, and moisture content of the samples at harvest were calculated. Results:

[0130] Mass loss from fungal decay was higher in untreated beech wood than in impregnated wood, and the low mass loss (1.8%) of Lignin 2 impregnated wood suggests a high resistance to fungal decay (Figure 12). Microscopy pictures highlight that the structure of impregnated wood is more sound (Figure 14) while untreated and degraded wood is less structurally sound (Figure 13).

[0131] Example 4: Available space for water within the wood structure

[0132] Materials:

[0133] Specimens of beech and Grand fir either untreated or impregnated with either Lignin 1, Lignin 2, or LS solutions from Example 1 were used after these specimens had been leached in water. All specimens were water-saturated by vacuum-impregnation with water. The saturation process involved placing the specimens in double-necked, round-bottom reaction flasks equipped with rubber injection septa. A vacuum of about IO-2mbar was maintained for 20 minutes. Then, MilliQ water was injected through the rubber septum, and the flasks were returned to atmospheric pressure.

[0134] Method : Low-field NMR relaxometrv

[0135] Low-field Nuclear Magnetic Resonance (LFNMR) relaxometry was used to study the influence of lignin impregnation on the interaction between wood and water. Before conducting LFNMR measurements, each specimen was wiped with a moist cloth (Wettex, Freudenberg Household Products, Norrkoping, Sweden) to remove free water from the surface without drying the specimen. Subsequently, the specimen was placed in a pre-weighed NMR tube with a Teflon rod, which sealed the tube and limited evaporation by filling the air space above the specimen. The mass of the tube with the specimen and rod was measured to determine the vacuum-saturated mass of the specimen. The sealed tube, along with the specimen and rod, was then placed in a LFNMR instrument (Bruker mq20-Minispec, Bruker, Billerica, MA, USA) with a 0.47 Tesla permanent magnet. The orientation of the specimen was kept consistent for all measurements. The LFNMR instrument maintained a temperature of 21±0.5 °C using a water-cooling system (Julabo GmbH, Seelbach, Germany). Each sample was allowed to equilibrate to the instrument temperature for 5 minutes before the measurement. The spin-spin relaxation time (T2) was determined using the Carr-Purcell- Meiboom-Gill (CPMG) pulse sequence, employing a pulse separation (s) of 0.1 ms, 16,000 echoes, 32 scans, and a recycle delay of 5 seconds. The gain was individually set between 77 and 83 dB for each specimen.

[0136] The analysis of the T2 decay curves involved multi-exponential decay analysis. This analysis fitted a large number of exponential decay functions to the experimentally obtained curve. Each decay function was characterized by a relaxation time (a characteristic time constant) and a pre-exponential coefficient. The cell wall moisture content was estimated as the fraction of the sum of pre-exponential coefficients related to the peak with shortest relaxation time multiplied with the total moisture content. The capillary water was estimated as the fraction of the sum of pre-exponential coefficients that were outside the peak with the shortest relaxation time.

[0137] Results:

[0138] The capillary moisture content are reduced in Lignin 1 and Lignin 2 impregnated wood (Figure 16) as a result of the filling of lumina within the wood structure, leaving less space for water outside cell walls. At the same time, the cell wall moisture content appears slightly increased compared with untreated wood (Figure 15). This effect is likely a result of the hydrophilicity of the lignin polymer itself. Thus, the lignin filling lumina can hold some water molecules which will appear in the LFNMR data as water interacting with the wood cell walls. Lignin molecules found within the cell walls will both interact with water molecules present there, but also take up space for water within cell walls.

[0139] The LFNMR results indicate that the cell wall water is found within smaller nanopores in lignin impregnated wood as seen from the relaxation time of cell wall water for these materials (Figure 17). Thus, the shorter relaxation indicates that the water is confined in smaller pore spaces in the wood impregnated with Lignin 1 and Lignin 2 solutions, even though there appears to be slightly more of this water after impregnation (Figure 15). This shows that the lignin impregnation penetrates the wood cell walls.

[0140] Example 5: Surface interaction with liquid water

[0141] Materials:

[0142] Wood samples of beech and Grand fir, either untreated or lignin impregnated (Lignin 3) from Example 1 were used. Samples had been leached in water.

[0143] Method: Contact anole analysis

[0144] Contact angle analysis is a valuable 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. Results:

[0145] Table 3: Contact angle and absorption time of water droplet with the sessile drop method.

[0146] The results show that the lignin impregnated wood had significantly higher contact angle with the water droplet than untreated wood. In the latter, the water droplet was absorbed into the wood within seconds, whereas it remained on the impregnated wood surfaces for several minutes. This illustrates that lignin impregnation increases the hydrophobicity of the wood surface.

[0147] Example 6: Lignin yields and lignin concentration in solution

[0148] Method:

[0149] A variety of lignin solutions were made at different ethanol:water:glycerol ratio, with the aim to explore lignin yields and concentrations of the solutions. Concentrated lignin solutions were prepared by fractionation of BioPiva 100 (Kraft lignin) in ethanol with specific alcohol: water: glycerol ratio and with a solid (dry lignin) to liquid ratio of or 1 :3 (w / w). The lignin alcohol mixtures were stirred for 1 hour and subsequently centrifuged at 1000G for 10 min. The mixtures were left in the fridge overnight, then were further centrifuged at 1000G for 10 minutes. The pellet and soluble fraction were separated and oven dried overnight at 105 °C for dry mass balance estimation.

[0150] Results

[0151] Table 4: Yields and concentrations of lignin in solution.

[0152] (D* = Density (g / cm3), H** = Hildebrand Solubility Parameter)

[0153] The lignin concentration was found to be unaffected of the water concentration in the liquid fraction at 25 wt% glycerol (Figure 21) and only slightly negatively affected in solution with 10 wt% glycerol (Figure 22). For the latter, the lignin yield was negatively affected when the water concentration was higher than 35 wt%, but was improved by a water concentration of 25 wt% compared with other concentrations (Figure 21). For lignin solutions with 25 wt% glycerol, the lignin yield was only slightly affected by the water concentration, in particular at 45 wt% water (Figure 22).

[0154] Example 7: Impregnation of various wood species

[0155] Materials 1: Wood

[0156] Wood samples of beech Fagus sylvatica L.), Scots pine sapwood Pinus sylvestris L.), paulownia Paulownia tomentosa (Thunb.) Steud.), ash (Fraxinus excelsior L.), black alder (Alnus glutinosa (L.) Gaertn.), lime (Tilia cordata Mill.), Monterey pine Pinus radiata D.Don), and poplar Populus ssp.) were cut into cuboids of dimensions 5 mm x 10 mm x 10 mm (L x H x W). The samples were marked by cutting a different numbers of corners (from zero to four) to facilitate recognition of each individual sample in each batch of five replicates. The samples were dried in a vacuum oven (60 °C, 0 mbar) for 18 hours, and their dry masses determined. The samples were kept in a dry climate using zeolites (molecular sieves 3&) to prevent moisture uptake.

[0157] Method:

[0158] A lignin solution was prepared with Kraft lignin (BioPiva 100) solubilized in a 75 wt% ethanol : 25 wt% water mixture following a similar protocol to that described in Example 1. The composition of the final lignin solution was 40 wt% lignin : 45 wt% ethanol : 15 wt% water.

[0159] Four 100 mL round-bottom reactions flasks were used. In each of these, 5 replicates of two wood species were placed, and the reaction flasks were evacuated using a vacuum pump. The lignin solution were then injected through a rubber cork into each reaction flask, and atmospheric pressure was re-established after 5 minutes. The reaction flasks with wood samples and lignin solution were then lowered into an oil bath at 50 °C and left overnight to impregnate for approximately 20 hours. The wood samples were hereafter put on paper tissue to evaporate slightly before being dried in a vacuum oven at 60 °C and 0 mbar overnight for determination of the impregnated (unleached) dry mass. Finally, the samples were leached in water for one week before being dried in vacuum oven and the final (leached) dry mass determined. Results:

[0160] The mass gain of the various wood species was in the range 28-89% before leaching and 21-82% after leaching in water (Figure 23). The beech wood had the lowest mass gain while the Scots pine had the highest. Leaching on average reduced the mass gain by 7%.

[0161] Example 8: Impregnation of various types of lignin

[0162] Materials 1: Wood

[0163] Wood samples of beech Fagus sylvatica L.) and Scots pine sapwood Pinus sylvestris L.) were cut into cuboids of dimensions 5 mm x 10 mm x 10 mm (L x H x W). The samples were marked by cutting a different numbers of corners (from zero to four) to facilitate recognition of each individual sample in each batch of five replicates. The samples were dried in a vacuum oven (60 °C, 0 mbar) for 18 hours, and their dry masses determined. The samples were kept in a dry climate using zeolites (molecular sieves 3&) to prevent moisture uptake.

[0164] Materials 2: Lignin and other chemicals

[0165] Kraft lignin, UPM BioPiva™ 100 lignin (dried to 96% dry matter, DM)

[0166] Alkali lignin, Sigma-Aldrich (Product number: 471003)

[0167] Organosolv lignin, Aldrich (Product number: L165)

[0168] Soda lignin, Protobind 2600 from PLT Innovations, Switzerland

[0169] Biorefinery lignin, produced in a process consisting of hydrothermal pretreatment, enzymatic saccharification, fermentation and distillation by MelioraBio, Denmark (dried to 98% dry matter, DM).

[0170] 96% ethanol

[0171] Demineralized water

[0172] Method 1: Preparation and impregnation of lignin solutions

[0173] Five different recipes of lignin solutions with different sources of lignin were prepared. Only the lignin type differed among them, as detailed above. The remaining procedure was as follows:

[0174] 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 100g DM (dry matter) of lignin solubilized in a 75 wt% ethanol : 25 wt% water solvent at 40 °C, at speed 8, for 15 minutes. The resulting lignin solutions were centrifuged for 10 minutes at 1000G, at 20 °C, and the supernatant of each solution was used as impregnation fluid.

[0175] Final composition of the five different lignin solutions:

[0176] Kraft (BioPiva 100) 40 wt% lignin : 45 wt% ethanol : 15 wt% water Alkali (Sigma Aldrich) 10 wt% lignin : 68 wt% ethanol : 23 wt% water

[0177] Organosolv (Sigma Aldrich) 33 wt% lignin : 50 wt% ethanol : 17 wt% water

[0178] Soda (Protobind 2600) 18 wt% lignin : 62 wt% ethanol : 21 wt% water

[0179] Biorefinery (MelioraBio) 8 wt% lignin : 69 wt% ethanol : 23 wt% water

[0180] Five 100 mL round-bottom reactions flasks were used. In each of these, 5 replicates of both beech and Scots pine were placed, and the reaction flasks were evacuated using a vacuum pump. About 20 mL of each lignin solution were then injected through a rubber cork into each reaction flask, and atmospheric pressure was re-established after 5 minutes. The reaction flasks with wood samples and lignin solution were then lowered into an oil bath at 50 °C and left overnight to impregnate for approximately 20 hours. The wood samples were hereafter put on paper tissue to evaporate slightly before being dried in a vacuum oven at 60 °C and 0 mbar overnight for determination of the impregnated (unleached) dry mass. Finally, the samples were leached in water for one week before being dried in a vacuum oven and their final (leached) dry masses determined.

[0181] Method 2: Water soluble fraction of lignin solutions

[0182] To investigate the difference in leaching of the different types of lignin, the water solubility of the five solutions was investigated. This was done by drying a small amount of each solution in a Falcon tube in a vacuum oven at 60 °C and 0 mbar overnight. The dried lignin was then mixed with demineralised water and Vortex-stirred for 10-15 seconds followed by 1 hour of rotation in a hybridization incubator at 30 °C. Finally, all Falcon tubes were centrifuged for 10 minutes at 1000G, at 20 °C. The supernatant was removed and the water insoluble fraction determined by drying the tubes in a vacuum oven at 60 °C and 0 mbar overnight followed by weighing. The water soluble fraction during 1 hour of mixing was determined as 100% minus the water insoluble fraction.

[0183] Results:

[0184] Mass gain after leaching in water was found in the range 19-22% and 68-76% for beech and Scots pine, respectively, except for the alkali and biorefinery lignin solutions that showed low mass gains (Figure 24, Figure 25). These two solutions also had the lowest concentration of lignin, which is correlated with the mass gain. Thus, the higher lignin concentration, the higher mass gain was obtained as seen in Figure 28 which compiles the results of Example 7, Example 8, and Example 9. The alkali lignin solution exhibited a high degree of leaching dissimilar from all other solutions. The reason for this is likely the higher solubility of this lignin in pure water compared with the other lignins (Figure 26).

[0185] Example 9: Impregnation of solutions containing non-volatile alcohols

[0186] Materials 1: Wood Wood samples of beech (Fagus sylvatica L.) and Scots pine sapwood (Pinus sylvestris L.) were cut into cuboids of dimensions 5 mm x 10 mm x 10 mm (L x H x W). The samples were marked by cutting a different numbers of corners (from zero to four) to facilitate recognition of each individual sample in each batch of five replicates. The samples were dried in a vacuum oven (60 °C, 0 mbar) for 18 hours, and their dry masses determined. The samples were kept in a dry climate using zeolites (molecular sieves 3&) to prevent moisture uptake.

[0187] Materials 2: Lignin and other chemicals

[0188] UPM BioPiva™ 100 lignin (dried to 96% dry matter) 96% ethanol

[0189] Demineralized water

[0190] Glycerol (product G9012 from Sigma-Aldrich)

[0191] 1,2-propanediol (product 82280 from Sigma-Aldrich)

[0192] Method 1: Preparation of lignin solutions

[0193] Three different recipes of lignin solutions with low volatility alcohols (glycerol and 1,2- propanediol) were prepared. Only the solvent composition differed among them, as detailed below. The remaining procedure was as follows:

[0194] 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 150 g DM (dry matter) of lignin mixed with its respective solvent at 40 °C, at speed 8, for 15 minutes. The resulting lignin solutions were centrifuged for 10 minutes at 1000G, at 20 °C, to determine yield. In all cases, no pellet (insoluble fraction) was formed, indicating a 100% solvation yield.

[0195] The solvent mixtures for the various solutions consisted of (parts given by weight):

[0196] Soda: 3 parts ethanol to 2 parts glycerol.

[0197] Kraftl: 3 parts ethanol to 2 parts glycerol.

[0198] Kraft2: 2 parts ethanol to 2 parts glycerol to 1 part water.

[0199] Kraft3: 2 parts ethanol to 3 parts glycerol.

[0200] Kraft4: 3 parts ethanol to 2 parts 1,2-propanediol.

[0201] Kraft5: 2 parts ethanol to 2 parts 1,2-propanediol to 1 part water.

[0202] Kraft6: Pure 1,2-propanediol.

[0203] Kraft7: 1 part ethanol to 3 parts 1,2-propanediol to 1 part water.

[0204] Method 2: Impregnation of lignin solutions

[0205] Five 100 mL round-bottom reactions flasks were used. In each of these, 5 replicates of both beech and Scots pine were placed, and the reaction flasks were evacuated using a vacuum pump. About 20 mL of each lignin solution were then injected through a rubber cork into each reaction flask, and atmospheric pressure was re-established after 5 minutes. The reaction flasks with wood samples and lignin solution were then lowered into an oil bath at 50 °C and left overnight to impregnate for approximately 20 hours. The wood samples were hereafter put on paper tissue to evaporate slightly before being dried in a vacuum oven at 60 °C and 0 mbar overnight for determination of the impregnated (unleached) dry mass. Finally, the samples were leached in water for one week before being dried in vacuum oven and the final (leached) dry mass determined. Furthermore, three batches of 5 replicates of both beech and Scots pine were impregnated with a pure solvent of either ethanol, glycerol, or 1,2-propanediol, following the same protocol as described above. This was done to compare the mass gains of lignin impregnated wood with those obtained from impregnating pure solvents before and after leaching in water.

[0206] Results:

[0207] The mass gains before leaching was found to be 34-58% and 79-138% for beech and Scots pine, respectively (Figure 27, Figure 28). However, after leaching in water for one week, the mass gains were considerably lower, falling in the ranges 7-22% and 32-62% for beech and Scots pine, respectively. This was expected since part of the mass gain before leaching derives from the mass of the non-volatile alcohol being impregnated into the wood. While the volatile components of the solutions, i.e. ethanol and water, evaporate during drying after impregnation, the non-volatile alcohol remains in the wood. This is seen from the impregnation of pure glycerol and pure 1,2-propanediol (both non-volatile alcohols), while impregnation of pure ethanol (volatile alcohol) does not affect the mass gain before or after leaching in water (Figure 29). The non-volatile alcohols are, however, soluble in water and therefore leaching in water for one week is expected to remove these from the wood (Figure 29). By compilation of the mass gains after leaching from Example 7, Example 8, and Example 9, it is clear that the mass gain after leaching in water is strongly correlated with the concentration of lignin in the solution (Figure 30). Therefore, the final mass gain after leaching does not depend on whether the lignin solution contains non-volatile alcohols or not, since these are leached out by the water whereas the lignin remains in the wood.

[0208] Example 10: Decay resistance of various types of lignin impregnated wood

[0209] Materials 1: Wood materials

[0210] Wood samples from Example 7, Example 8, and Example 9 were used. Also, further wood samples of beech Fagus sylvatica L.) and Scots pine sapwood Pinus sylvestris L.) of dimensions 5 mm x 10 mm x 10 mm (L x H x W) were impregnated following the method in Example 8 using two different lignin solutions (BioPiva 100 Kraft lignin, Protobind 2600 soda lignin) with the composition 31 wt% lignin : 52 wt% ethanol : 17 wt% water. The mass gains obtained in beech were 23.6% and 20.9% for the Kraft and Soda lignin impregnated wood, respectively, while in Scots pine the mass gains were 66.1% and 66.7% for the Kraft and Soda lignin impregnated wood, respectively.

[0211] Materials 2: Fungus

[0212] The brown-rot fungus Fomitopsis pinicola were used for the decay test. Fruitbodies of the fungus, two growing on a beech stem and two on a spruce stem, were harvested in Grib Skov, Denmark.

[0213] Method 1: Preparation of fungal mycelium

[0214] Isolations from the fungal fruitbodies were transferred to various types of media in petri dishes, including potato dextrose agar (PDA) and malt agar (MA). The isolates were monitored for growth and contaminations and after 10 days re-isolated on fresh MA in petri dishes. They were then incubated at room temperature in dark cupboard. After 9 days, the mycelium cultures were ready for the experiment. 4% MA medium was prepared using 20 g of Difco malt agar powder and 10 g WVR agar mixed with 500 mL of Mil HQ water and autoclaved for 20 minutes at 120 °C using LaboKlav type SHP-135M (SHP Steriltechnik AG, Germany), and then transferred onto 16 cm petri dishes. An autoclaved plastic net was put into the filled dishes. 23 dishes prepared this way were inoculated with the spruce isolate of the fungus using an 8 mm sized inoculation plug. After 12 days, following an assessment of mycelium growth, untreated and impregnated wood samples were autoclaved 20 minutes at 120 °C and added to the petri dishes.

[0215] Method 2: Decay test of beech and Scots pine

[0216] For the samples of beech and Scots pine impregnated as described in this Example, the leached samples were placed on each petri dish so these contained 5 beech and 5 Scots pine samples that underwent the same treatment (either impregnated with Kraft lignin or soda lignin or untreated controls). Incubation followed at ambient temperature in a dark cupboard. Samples were harvested after 4 weeks, 7 weeks and 10 weeks of incubation. At each harvest point, the fungal mycelium was carefully removed from samples by hand before the wet mass of the samples was measured. Later, after drying the samples overnight in a vacuum oven at 60 °C, 0 mbar the dry mass was measured and from this the mass loss determined. During week 4 and week 7 harvests, one plate per treatment was measured, during week 10 harvest three plates per treatment were measured.

[0217] Method 3: Decay tests of samples from Examples 7, 8, and 9

[0218] Leached samples from Example 7 along with untreated control samples of all wood species were placed on petri dishes inoculated with the fungus. Four wood species, each with three replicates were placed on each petri dish. Treated and untreated samples were placed in separate petri dishes. All samples were harvested after 10 weeks of exposure. Leached samples from Example 8 were placed on petri dishes inoculated with the fungus. For each wood species (beech, Scots pine), three replicates of each sample type were placed on one petri dish with those impregnated with Kraft, Alkali and Organosolv lignin solutions being placed together on one petri dish and those impregnated with soda and biorefinery lignin solutions being placed on another petri dish. All samples were harvested after 10 weeks of exposure.

[0219] Leached samples impregnated with Kraft2, Kraft3, Kraft4, and Kraft5 solutions from Example 9 were placed on petri dishes inoculated with the fungus. For each wood species (beech, Scots pine), three replicates of each sample type were placed on one petri dish. All samples were harvested after 10 weeks of exposure.

[0220] Results:

[0221] The mass loss from fungal degradation increased over time from week 4 to week 10 for untreated samples of beech (Figure 31) and Scots pine (Figure 32), which also affected the integrity and dimensions of the wood samples (Figure 33). Meanwhile, lignin impregnated samples did not exhibit any marked effect of the fungal attack over the same period of time, neither in mass loss (Figure 31, Figure 32) nor in integrity or dimensions of the samples (Figure 34, Figure 35). The high resistance to fungal degradation was consistently seen across the various wood species of Example 7 (Figure 36), the different types of lignin of Example 8 (Figure 37), and the wood impregnated with solutions containing nonvolatile alcohols (Figure 38). The only exception were the beech treated with alkali lignin (Figure 37) which also showed negligible mass gain after leaching in water (Figure 24).

[0222] Example 11: Combustion test of lignin impregnated wood

[0223] Materials: Wood

[0224] From the materials in Example 8, two leached samples of each wood species (beech, Scots pine) were selected: one impregnated with Kraft lignin (BioPiva 100) and one impregnated with soda lignin (Protobind 2600). The selected samples with Kraft lignin had mass gains after leaching of 21.3% and 81.7% for the beech and Scots pine sample, respectively. The selected samples with soda lignin had mass gains after leaching of 19.4% and 68.7% for the beech and Scots pine sample, respectively. Small pieces were cut out of these materials and placed in plastic bags with zeolites (molecular sieves 3&) to keep them dry. Furthermore, sample material of untreated wood of beech and Scots pine were cut out and placed in similar plastic bags with zeolites.

[0225] Method : A micro-combustion calorimeter (MCC) (Figure 39) was used to characterize the fire resistance following the ASTM D7309 Method B, i.e. combustion in an atmosphere containing 20% oxygen and 80% nitrogen. The MCC is an apparatus developed by the US Federal Aviation Administration (FAA) (Flecknoe-Brown & van Hees, Journal of Fire Sciences, 2018, vol. 36, pp. 453-471). The MCC fills a perceived gap in material flammability testing, as other common flammability tests require relatively large sample sizes in comparison, e.g. the cone calorimeter. The sample sizes required in the MCC are in the order of milligrams (approx. 1-10 mg), allowing efficient testing of newly synthesised materials. The MCC is based on the principles of pyrolysis and combustion analysis via oxygen consumption calorimetry employing so-called pyrolysis-combustion flow calorimetry that can separate the two governing processes observed in flaming combustion: 1) solid-phase pyrolysis (i.e. generation of fuel gases from the material), and 2) gas-phase combustion. This is achieved via the MCC's two-stage reactor: the first stage is the pyrolysis section of the chamber and the second stage is where combustion of the pyrolysis gases takes place. Each chamber may be individually controlled, allowing users to adjust various input conditions, for example, heating rate, pyrolysis atmosphere, or combustor temperature. The use of the MCC has been standardised under ASTM D 7309. In the aerobic mode (Method B in ASTM D 7309), oxygen is added to the pyrolysis chamber atmosphere and thus samples may also react with oxygen while being heated, allowing solid-phase reactions to take place. The evolved gases from the pyrolysis chamber are completely combusted with excess oxygen in the second-stage combustion chamber. The flows of gases into the MCC are controlled via mass flow meters, and concentrations of each gas can be designated with the associated apparatus software. Oxygen and nitrogen are fed in separately and are mixed in the pyrolyser.

[0226] For each wood sample material, about 5 mg was cut out and loaded in the calorimeter. After waiting 15 minutes to stabilize the oxygen level in the sample chamber at 20%, the temperature was ramped by 1 °C per second. With increasing temperature, thermal degradation of the wood produces volatile gases. These flow to the combustion chamber where the heat released from their combustion at 900 °C is determined.

[0227] Results:

[0228] All wood materials exhibited two peaks in the heat release rate curves (Figure 40, Figure 41). These peaks are typically interpreted as initial formation of volatile components and formation of char (Peak #1) followed by pyrolysis of the formed char (Peak #2). Lignin impregnated samples exhibited lower heat release rates during the initial phase of combustion (Figure 42), whereas the pyrolysis of the char was shifted to higher temperatures (Figure 43). This indicates that the impregnated lignin increased the formation of char which is associated with improved fire retardancy, since a char layer on wood reduces the migration of oxygen to the zone of active combustion. Moreover, the higher temperature of char pyrolysis in the impregnated samples indicates that the impregnated lignin results in a more stable formed char, which also is a sign of improved fire retardancy.

[0229] Example 12: Impregnation of solutions with lignin modified by various methods

[0230] Materials 1: Wood

[0231] Wood samples of beech Fagus sylvatica L.) and Scots pine sapwood Pinus sylvestris L.) were cut into cuboids of dimensions 5 mm x 10 mm x 10 mm (L x H x W). The samples were marked by cutting a different numbers of corners (from zero to four) to facilitate recognition of each individual sample in each batch of five replicates. The samples were dried in a vacuum oven (60 °C, 0 mbar) for 18 hours, and their dry masses determined. The samples were kept in a dry climate using zeolites (molecular sieves 3&) to prevent moisture uptake.

[0232] Materials 2: Lignin and other chemicals

[0233] UPM BioPiva™ 100 Kraft lignin (dried to 96% dry matter) 96% ethanol Demineralized water 30% hydrogen peroxide

[0234] Enzyme: Laccase from Trametes versicolor (product 38429, Sigma-Aldrich)

[0235] Mediator: ABTS (2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, product A1888 from Sigma-Aldrich) 5M NaOH solution in water

[0236] Method 1: Mechanically modified lignin

[0237] Mechanically Modified Lignin: 165 g UPM BioPiva™ 100 was ball-milled by adding 8 g lignin at a time to a 25 mL milling tube with two metal balls. Each batch was milled for 3 minutes at 30 sec1, repeated until the total weight was processed.

[0238] Method 2: Chemically modified lignin

[0239] Chemically Modified Lignin: 200 g lignin was mixed with 800 g hydrogen peroxide solution containing 3 wt% hydrogen peroxide. This solution was mixed in a BOJ MC-2000 Thermo Blender with a 2 L capacity for 1 hour at 40 °C, at speed 6 on a scale of 1 to 10. The lignin was then dried at 60 °C before further use.

[0240] Method 3: Enzymatically modified lignin

[0241] Enzymatically Modified Lignin: 200 g lignin was mixed with 500 mL demineralized water in a 2 L plastic bottle, and the pH was adjusted to 5.1 with 5M NaOH. Then, 0.137 g ABTS mediator (corresponding to 500pM) and 0.72 mg laccase enzyme (corresponding to 1 unit / L) were added. The enzyme reaction was incubated at 50 °C for 6 hours, mixed at 120 rpm. The lignin was then dried at 60 °C before further use.

[0242] Method 4: Solutions with variously modified lignin

[0243] Lignin solutions with mechanically modified lignin (from Method 1), chemically modified lignin (from Method 2), enzymatically modified lignin (from Method 3), and unmodified lignin (as control) 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: 1.5 w / w solid-to-solvent ratio, using a solvent composition of 3 parts ethanol to 1 part water (75 wt% ethanol : 25 %wt water). The recipe included 150 g DM (dry matter) of each lignin mixed with water and ethanol at 40 °C, at speed 6, for 10 minutes. The resulting lignin solutions were homogeneous and did not form a pellet (insoluble fraction) when centrifuged for 10 minutes at 1000G at 20 °C. Thus, they were considered to have a 100% lignin yield. The resulting dry matter content was 42 wt%. The composition of the four lignin solutions were therefore similar and had 42 wt% lignin : 43 wt% ethanol : 15 wt% water. The lignin solutions were stored in closed plastic containers at ambient temperature.

[0244] Method 5: Characterisation of lignin chemistry bv infrared spectroscopy

[0245] Chemical changes of the lignin from the various modifications were characterized by infrared spectroscopy using an ATR-FTIR instrument (Spectrum 3, Perkin Elmer, Shelton, CT, USA). The infrared spectra of the four types of lignin (unmodified, mechanically modified, chemically modified, enzymatically modified) were recorded in the wavenumber range 4000-400 cm1with a resolution of 4 cm1. The spectra were based on the average of 25 scans and three replicates were obtained for each type of lignin. All spectra were baseline corrected and normalized with the signal intensity of the 1500 cm1vibration.

[0246] Important peaks in the fingerprint region of lignin (900-1700 cm1) were selected based on literature and the average and standard deviation of their intensity calculated based on the three replicate spectra.

[0247] Method 6: Impregnation with modified lignin solutions

[0248] Five 100 mL round-bottom reactions flasks were used. In each of these, 5 replicates of both beech and Scots pine were placed, and the reaction flasks were evacuated using a vacuum pump. About 20 mL of each lignin solution were then injected through a rubber cork into each reaction flask, and atmospheric pressure was re-established after 5 minutes. The reaction flasks with wood samples and lignin solution were then lowered into an oil bath at 50 °C and left overnight to impregnate for approximately 20 hours. The wood samples were hereafter put on paper tissue to evaporate slightly before being dried in a vacuum oven at 60 °C and 0 mbar overnight for determination of the impregnated dry mass.

[0249] Results:

[0250] The various modifications of the Kraft lignin had different effects on the lignin chemistry as seen from the infrared spectra (Figure 44). These show that the mechanical modification did not change the chemistry appreciably compared with the unmodified lignin (Figure 44, Figure 45). This is in line with results in literature (Begali et al., Cellulose Chemistry and Technology, 2021, vol. 55, pp. 529-537) and is expected since the mechanical modification only reduces the particle size. The enzymatic modification of lignin shows changes in the spectrum (Figure 44, Figure 45), particularly around the 1125 and 1145 cm1peaks related to aromatic C-H vibrations (Ai et al., Journal of Microbiology and Biotechnology, 2015, vol. 25, pp. 1361-1370). The chemical modification affected all four selected peaks (Figure 45), which is in line with literature results for treatment of lignin with hydrogen peroxide (Admad et al., Molecules, 2020, vol. 25, article 2329). Thus, all the modifications of the lignin had an effect on the chemistry or physical structure (i.e. particle size) of the lignin, proving that the lignin was indeed modified by the various modification protocols.

[0251] Mass gain after impregnation was not affected by any of the modifications of the lignin (Figure 46, Figure 47). While the average mass gain in beech with the chemically modified lignin was higher, the material exhibited larger variation between samples. Therefore, the results show it is possible to modify the lignin in various ways, while still retaining the same mass gain after impregnation. Leaching removed slightly more of the enzymatically modified lignin compared with the other types of modified lignin (Figure 46, Figure 47).

[0252] Example 13: Pilot-scale pressure impregnation of lignin solutions

[0253] Materials 1: Wood

[0254] Wood samples of beech Fagus sylvatica L.) and Scots pine sapwood Pinus sylvestris L.) were cut into different sample geometries. For each wood species the following sample geometries were produced:

[0255] Large: Two samples of L x H x W: 400 mm x 50 mm x 25 mm.

[0256] Medium: Five samples of L x H x W: 100 mm x 100 mm x 25 mm.

[0257] Smalll: Ten samples of L x H x W: 100 mm x 10 mm x 25 mm.

[0258] Small2: Ten samples of L x H x W: 50 mm x 50 mm x 25 mm.

[0259] Smallest: Ten samples of L x H x W: 5 mm x 10 mm x 10 mm.

[0260] Before impregnation, samples were dried in a conventional oven overnight at 103 °C and weighed to determine the initial dry mass. However, the "Smallest" sample batches of Scots pine and beech were dried in a vacuum oven at 60 °C and 0 mbar over-night to allow comparison with mass gains from other Examples. Furthermore, half of the samples in this batch was vacuum impregnated on laboratory scale for comparison with results from the other Examples.

[0261] Materials 2: Lignin solution

[0262] UPM BioPiva™ 100 lignin (native dry matter content 65%, some dried to 96%) 96% ethanol

[0263] Method 1: Lignin solution

[0264] Lignin solution were prepared using a BOJ MC-2000 Thermo Blender with a 2 L capacity. The mixing speed was arbitrary, scaled from 1 to 10. The impregnation solution for pilot scale pressure impregnation was made with a 1: 1.5 w / w solid-to-solvent ratio, using a solvent composition of 3 parts ethanol to 1 part water (i.e. 75 wt% ethanol : 25 wt% water). The recipe included 600 g DM (dry matter) of BioPiva lignin (546 g native, undried and 252 g dried), 675 g ethanol (equivalent to 730 g 96% ethanol), and 225 g water (contained in the lignin and ethanol). These ingredients were mixed at 40 °C, at speed 6, for 10 minutes. The resulting lignin solution was homogeneous and did not form a pellet (insoluble fraction) when centrifuged for 10 minutes at 1000G, at 20 °C. Thus, it was considered to have a 100% lignin yield. The resulting dry matter content was 41.5%, meaning the solution had concentration composition of 41.5 wt% lignin : 43.9 wt% ethanol : 14.6 wt% water. This procedure was repeated until a total of ~21 L was achieved. The lignin solution was stored in closed plastic containers at ambient temperature.

[0265] Method 2: Impregnation of lignin solution

[0266] A pilot-scale pressure impregnation equipment (Wood Treatment Technology, production year 2006, ID# 21 1042) at the Danish Technological Institute, Taastrup, Denmark, was used. Wood samples were placed in two layers in a metal box of dimensions L x H x W = 500 mm x 240 mm x 320 mm, each layer separated from each other as well as from the bottom of the box by thin wooden spatulas. The metal box was inserted in the pressure vessel (autoclave). The metal box had a valve on the side which was connected to the outside of the pressure vessel by a hose with a valve. Before injection of the impregnation solution, the pressure vessel was decompressed to 0.1 bar pressure for 1 hour while keeping the temperature at 50 °C. Meanwhile, the lignin solution was heated to 50 °C in an oven. After 1 hour at 0.1 bar pressure, the lignin solution was let into the metal box inside the pressure vessel through the hose. Hereafter, the pressure was increase to first 7.5 bar using nitrogen and then topped up with compressed air to 10.5 bar. This pressure was held constant for 2 hours while the temperature set point was 50 °C. Finally, atmospheric pressure was re-established and the metal box pulled out of the pressure vessel. Excess solution on the surfaces of the samples were scraped off with a metal spatula before the samples were put in an oven to dry overnight at 103 °C to determine the mass gain from impregnation.

[0267] Furthermore, five replicates of the "Smallest" sample batch were vacuum impregnated with the same lignin solution on the lab-scale following the protocol of Example 9.

[0268] Results:

[0269] Mass gains in beech and Scots pine wood after impregnation show a size effect in that larger samples had a smaller average mass gain (Figure 48, Figure 49). This is expected since the impregnation solutions needs to penetrate deeper in a larger sample than a smaller one. At the same time, larger samples exhibited less effect of leaching, i.e. the change in mass gain before and after leaching was smaller in these samples (Figure 48, Figure 49). This is expected because of the lower surface area per sample mass of the larger sample geometries than the smaller ones. Pressure impregnation did not significantly change the mass gain of the smallest wood samples compared with laboratory vacuum impregnation. The Scots pine wood had smaller mass gains that the beech wood for similar sized samples, which is surprising given that the reverse is seen in Example 7, Example 8, and Example 9. The difference may be due to a more pronounced size effect in Scots pine than beech. It could also stem from sensitivity of the Scots pine to the drying protocol, although it is not clear from literature what effect the drying protocol (temperature, atmosphere, etc) has on the mass gain from impregnation (Tarmian et al., European Journal of Wood and Wood Products, 2020, vol. 78, pp. 635-660).

Claims

Claims1. A method of impregnating wood, wherein the method comprises the following consecutive steps:(a) impregnating wood with a solution comprising between 15-65 wt% lignin or derivatives thereof and comprising a ratio of solid lignin or derivatives thereof to liquid of between 1: 1.5-1:5 (w / w); wherein said lignin or derivatives thereof has / have been solubilised in(i) 10-100 wt% ethanol or methanol or mixtures thereof,(ii) 0-60 wt% water,(iii) 0-50 wt% of one or more non-volatile alcohols and Civ) any suitable additives; the sum of the constituents (i)-(iv) not exceeding 100 wt%;(b) drying of the impregnated wood from step (a).

2. The method according to claim 1, wherein the wood is subjected to a drying step prior to the impregnation step (a).

3. The method according to any of claims 1 or 2, wherein step (b) is followed by a leaching step (c).

4. The method according to any of claims 1-3, wherein the wood is selected from the group consisting of Scots pine sapwood (Pinus sylvestris L.), beech (Fagus sylvatica L.), paulownia (Paulownia tomentosa (Thunb.) Steud.), ash (Fraxinus excelsior L.), European black alder (Alnus glutinosa (L.) Gaertn.), lime (Tilia cordata Mill.), Monterey pine (Pinus radiate D.Don), poplar Populus ssp.) and Grand fir (Abies grandis (Douglas ex D. Don) Lindley).

5. The method according to any of claims 1-4, wherein the impregnation in step (a) is carried out by applying vacuum for 15-60 minutes, followed by introduction of the solution and soaking for 1-10 hours.

6. The method according to any of claims 1-4, wherein the impregnation in step (a) of claim 1 is carried out by applying vacuum for 15-60 minutes, followed by introduction of the solution at 5-95 °C under applied pressure of 10-14 bar, for 1-12 hours.

7. The method according to any of claims 1-6, wherein the one or more non-volatile alcohols are chosen from the group consisting of glycerol and 1,2-propanedioL8. The method according to any of claims 1-7, wherein the additives are selected from a group consisting of glycerol, ammonia, ethyl acetate, surfactants, such as PEG6000 and Tween80.

9. The method according to any of claims 1-8, wherein the lignin or derivatives thereof in step (a) is a lignin from an industrial process such as Kraft lignin, soda lignin, biorefinery lignin, organosolv lignin, or lignosulfonates.

10. The method according to any of claims 1-9, wherein the lignin has been chemically modified prior to solubilization, enzymatically modified prior to solubilization, physically modified prior to solubilization, thermally modified prior to solubilization by heating to 50- 150 °C, or by any combination thereof.

11. The method according to claim 10, wherein the chemical modification prior to solubilization is by epoxidation, oxidation, esterification or ozonification.

12. The method according to claim 10, wherein the enzymatically modification prior to solubilization is by peroxidases or laccases.

13. The method according to claim 10, wherein the physical modification prior to solubilization is by milling, explosive decomposition or radiation.

14. The method according to any of claims 1-13, wherein the solution in step (a) comprises between 40-52 wt% lignin or derivatives thereof.

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