Wood modification by catalytic conversion of hemicelluloses

Abstract

Disclosed is a wood modification method that avoids the reported mechanical degradation of wood effected by thermal modification. By substituting heat with high pressure, mechanical degradation of wood is avoided and its applications as a building material improved.

Description

[0001] Wood Modification by Catalytic Conversion of Hemicelluloses

[0002] Field of the Invention

[0003] The present invention relates to a novel and inventive method of wood modification by means of water and high pressure according to the principles of catalytic conversion and high-pressure organic chemistry.

[0004] Background of the Invention

[0005] Commercially, the most important property enhancement of wood for outdoor applications is improved resistance to biological attack. This has traditionally been achieved by means of treatment with biocides. However, the use of biocides is increasingly perceived as being problematic by institutions and markets, and this is why wood modification aims at achieving improved resistance to biological attack by non- biocidal modes of action.

[0006] In the art there has been suggested various methods for thermo treatment of wood as will be explained below. The purpose of subjecting wood to a thermo treatment is that it has for a long time been known that by treating wood under a certain temperature regime, increasing the temperature for a period, and thereafter reducing the temperature back to ambient temperature, the wood attains some improved qualities. For example, the durability as well as the insulating properties of the timber are improved.

[0007] Wood mainly consists of three different components, namely hemicelluloses, celluloses and lignin. These materials have different characteristics and as such they modify differently during the heat treatment. Accessible OH groups, causing wood to be hydrophilic because they readily bind water molecules chemically, are primarily situated in the hemicelluloses. Hemicelluloses is unstable when subjected to heat, and the mode of action of thermal modification is to remove accessible OH groups by breaking down hemicelluloses by means of heat. However, heat will also degrade celluloses and lignin in the cell wall structure, causing considerable mechanical deterioration. This is a problem when wood is used as a building material. Hill (2006) defines wood modification to involve the “action of a chemical, biological or physical reagent upon the material, resulting in a desired property enhancement during the service life of the modified wood. The modified wood itself should be nontoxic under service conditions, and furthermore, there should be no release of any toxic substances during service, or at end of life, following disposal or recycling of the modified wood. If the modification is intended for improved resistance to biological attack, then the mode of action should be non-biocidal” (21 p.p.).

[0008] Hill (see also Jones & Sandberg (2020)) continues to identify different classes of wood modification, including “Cross-Linking”, “Bulking” and “Thermal”.

[0009] The common factor for the above-mentioned wood modification techniques is the goal of reducing accessible OH (hydroxyl) groups within the wood. Reduction of OH groups reduces the wood’s affinity to water, reducing its moisture content. This, in turn, improves resistance to fungal attack and dimensional stability.

[0010] Thus, existing arts can all be classified by belonging to one of the classes identified by Hill (2006), categorized by their mode of action to reduce OH group content in the wood cell wall.

[0011] Hill continues to define thermal modification of wood “as the application of heat to wood in order to bring about a desired improvement in the performance of the material” (2006: 22).

[0012] Sandberg et al. (2021 : 216) categorize thermal modification in three different systems:

[0013] - Vacuum systems, that thermally modify wood at sub-atmospheric pressure at 225 °C and above.

[0014] - Open systems, that thermally modify wood at atmospheric pressure at 225 °C and above.

[0015] - Closed systems, that thermally modify wood in a pressurized atmosphere between 8 and 16 bar at 175 °C and above.

[0016] These three different system types are summarized in Table 1 below, together with the present invention. As demonstrated in Table 1, the significant difference of the present invention and prior state of the art, is the use of high pressure to promote the modification process.

[0017] Table 1: Vacuum, Open, Closed Thermal and Catalytic wood modification (modified after Sandberg et al 2021).

[0018] In a recent comprehensive review of wood modification technologies, Zelinka et al. elaborates that “.. .thermal modification relies on the effect of heat and does not require any chemical additives. The treatment in an environment with low oxygen content at 160 - 240°C partially degrades the wood, which causes changes in the chemical composition. ... A higher mass loss is observed with increased treatment temperatures and / or longer durations.” (2022: 15)

[0019] Thus, a major drawback from thermal modification is loss of density and mechanical strength, as well as fire resistance. As wood cell wall components are broken down from the effects of heat, the structural integrity of the cell wall is diminished significantly. For modification levels sufficient to ensure high resistance to fungal attack, density and strength losses of 30 - 50 % are often reported in literature. This is a significant drawback in outdoor building material applications.

[0020] Sandberg et al. (2017) report the undesirable property changes of thermally modified wood as:

[0021] - Decreased modulus of rupture and to some extent modulus of elasticity.

[0022] - Decreased impact strength.

[0023] - Increased brittleness.

[0024] - Decreased hardness. Accordingly, there is a need for a modification method for hemicellulose-based materials such as wood and / or engineered wood, that produces wood and / or engineered wood demonstrating high resistance to fungal attack, without the negative effects of heat reported above.

[0025] To solve this problem, the present invention provides a modification method for hemicellulose-based material such as wood and / or engineered wood, which does not rely entirely on the effect of heat, and therefore providing a wood modification method wherein the heat applied during the modification of wood can be lowered preferably lowered considerably. This is achieved by utilizing the principles of catalytic conversion and high-pressure organic chemistry. Catalytic conversion is a process for converting heavy (longer chained) hydrocarbons to light (short chained) hydrocarbons through the use of catalysts.

[0026] Object of the Invention

[0027] It is an objective of the present invention to provide a method of generally modifying hemicellulose-based material, in particular wood and engineered wood.

[0028] In particular, it is an objective of the present invention to provide a wood modification method, which does not rely entirely on the effect of heat and therefore avoids the reported mechanical degradation of wood that arises from the utilization of thermal modification at temperatures higher than 225°C. Instead, the invention applies principles of catalytic conversion and high-pressure organic chemistry for the conversion of wood cell wall hemicelluloses, at much higher pressure than previously applied, resulting in a superior wood modification method that utilizes temperatures below 180°C and pressure above 25 bar, preferably above 30 bar. of the Invention

[0029] One aspect of the present invention is to provide a method of modifying hemicellulosebased material, in particular wood and engineered wood, comprising the steps of: a) Selecting hemicellulose-based material, such as wood and / or engineered wood with a moisture content between 6 and 20% b) Placing the hemicellulose-based material such as wood and / or engineered wood in a modification chamber; c) Exchanging the atmosphere inside the modification chamber by evacuating the air, replacing the evacuated air by an inert gas, at a pressure between 25 to 2000 bar, preferably between 30 to 2000 bar; e) Heating the inert gas in the modification chamber to a temperature up to 180° C; f) Maintaining the pressure from step c and the temperature from step e in the modification chamber for a holding phase lasting between 30 to 240 minutes; g) Cooling the inert gas in the modification chamber to a temperature between 20 to 35° C; h) Reduce the pressure of the inert gas in the modification chamber down to atmospheric pressure; and i) Retrieving the modified hemicellulose-based material, such as wood and / or engineered wood from the modification chamber.

[0030] Alternatively, the method step c may be replaced by two steps c and d: c) Exchanging the air inside the modification chamber by evacuating the air and replacing the evacuated air by an inert gas; d) Increasing the pressure in the modification chamber up to a pressure between 25 to 2000 bar;

[0031] In one aspect of the invention, steps c), d) and e) may preferably be performed at a pressure between 30 to 2000 bar and at temperature up to 165° C, respectively.

[0032] Detailed Description of the Invention

[0033] Wood cell hemicelluloses are different configurations of polysaccharides, built from penta- and hexavalent monosaccharides (e.g. Arabinose, Xylose and Mannose, Glucose, Galactose, respectively). The hemicelluloses’ content and structure are different across species as well as between heart- and sapwood within the same species. Since hemicelluloses contain accessible hydroxyl (OH) groups making wood hydrophilic, the variation in hemicelluloses content mirror variation in moisture behavior and durability.

[0034] Expression (1): catalytic conversion of hemicellulose

[0035] In expression (1) above, the first (left) expression denotes a hemicelluloses polysaccharide built from pentavalent simple sugars. Catalyzed by water, present in the cell wall, the hemicelluloses are decomposed into its constituent simple sugars, in a reversible process. The presence of water in the cell wall is critical to the catalytic conversion of hemicelluloses, and the minimum required moisture content is 6-8%.

[0036] In a second step, catalyzed by acid, the simple sugars are further decomposed into a number of volatile organic compounds (VOCs) and non-volatile residual components, mainly acetic acid and furans. The second step is non-reversible. To ensure that the finished product retains its improved characteristics such as reduced moisture content and improved decay resistance, it is important that the modification process has been fully completed and no residual intermediate simple sugars are left in the cell wall.

[0037] As the term indicates, catalytic conversion involves one or more catalysts. A catalyst is a substance or a process parameter which increases the rate of a chemical reaction without being part of the chemistry itself. Typical catalysts are heat, pressure, reaction surfaces, metals and acids.

[0038] The process in expression (1) above may also be performed by other means than by heat. In industrial biomass conversion, the most common type of catalysts are metals (for a review see Suib (2013)).

[0039] In the present invention, instead of heat, high pressure is used as catalyst, utilizing catalytic conversion and high-pressure organic chemistry principles for the conversion of wood cell wall hemicelluloses at low temperatures below 180°C, preferably below 165°C. Catalytic conversion is a process applied for converting the three main components of biomass, i.e., cellulose, hemicellulose and lignin, into various compounds. Celluloses and hemicelluloses are hydrolysed into sugars and upgraded into oxygen-containing chemicals such as 5-HMF, furfural, polyols, and organic acids, or even nitrogencontaining chemicals such as amino acids. On the other hand, lignin is first depolymerized into phenols, catechols, guaiacols, aldehydes and ketones, and then further transformed into hydrocarbon fuels, bioplastic precursors and bioactive compounds. These processes are typically performed at atmospheric pressure and low temperatures of 80 - 100 °C with the use of acids and metallic compounds as catalysts.

[0040] With catalytic conversion of wood cell wall hemicelluloses at temperatures below those of thermal modification, significant mechanical degradation of the wood can be avoided.

[0041] High pressure is being applied in organic chemistry as a catalyst to increase the rate and extent of reaction by affecting the process kinetics. It can also allow for isolation of intermediates that would not be stable under conditions necessary for reaction at atmospheric or lower pressure below 20 bar. In the present invention, both catalytic effects of increase of reaction rate and isolation of intermediates are utilised to substitute the use of heat. This is explained in the following.

[0042] The rate of reaction in the conversion of hemicelluloses is increased due to a reduction in molecular volumes, expressed as a negative initial volume or formally AV *< 0. Ana Vidis et al (2006) showed how the application of high pressure increased the kinetic sensitivity in a Dies-Alder reaction by (i) accelerating the rate of reaction, (ii) increasing the selectivity of process intermediates and (iii) causing changes to the equilibrium. Applied to the present invention, these kinetics are obtained by the increased molecular density of the highly pressurized gas in the treatment chamber.

[0043] The selectivity of the hemicelluloses’ conversion process is increased. Returning to expression (1) above and as already discussed, the conversion of process intermediate simple sugars is strongly catalysed by organic acids, as indicated in the second arrow from the right in the expression. However, the boiling point of acetic acid is 118°C, which means that the residual acetic acid will increasingly evaporate and boil away from the cell wall as temperature is increased during the thermal modification at normal process conditions. This can be avoided by increasing pressure in the modification chamber. This is utilized to some extent in the pressurized, closed system type of processes discussed in Table 1 above. By applying very high pressures above 25 bar, preferably above 30 bar, the selective catalytic effect from acetic acid on the decomposition of intermediate simple sugars is maximized.

[0044] The inventor of the present invention has surprisingly discovered that by increasing the pressure, the selective catalytic effect from acetic acid on the decomposition of intermediate simple sugars is also increased, thus resulting in an effective method for treatment of wood, wherein the wood is treated at a lower temperature. Without being bound by theory, it is believed that this escalation of the positive catalytic effect from the acetic acid on the decomposition of intermediate simple sugars will continue with even higher pressure, such as over 30 bar or over 35 bar or even higher, such as over 40 or 50 bar. Without being bound by theory, it is further believed that there is a linear symmetry or equilibrium between the applied temperature and the applied pressure, such that at even higher pressure, such as above 40-50 bar, the temperature needed can be lowered accordingly, even as low as below 160 °C or below 150 °C or even below 140 °C.

[0045] Thus, the present invention provides an effective method for treatment of wood, wherein there is a equilibrium between the applied temperature and the applied pressure, such that the same or even more positive results will be gained when the temperature applied is decreased and the pressure applied is increased. Process residual yield is increased by pushing the process equilibrium towards the right. This is particularly critical for the effectiveness of removing accessible hydroxyl groups in wood cell modification; these OH groups, present in the wood cell hemicelluloses, continue to be present in the simple sugar process intermediates from the decomposition of Hemicelluloses according to expression (1). To remove the OH groups therefore require the further decomposition of the simple sugars into the process residuals, i.e. pushing the process equilibrium as far to the right as possible for maximum OH removal effectiveness. Based on these effects from high pressure on wood cell OH group conversion, the present invention seeks to substitute the effects from using heat on wood cell OH group conversion, with the effects from using high pressure. Further below, initial empirical data are reported which supports the effectiveness of such substitution.

[0046] In conclusion, applying high pressures above 25 bar, preferably above 30 bar to the process illustrated in expression (1) will compensate for the reduced rates of reaction by not using heat in the following way:

[0047] (i) increase the rate of reaction of expression (1) (which is slowed down by running at low temperature negating the process effects from heat).

[0048] (ii) increase selectivity by maximizing the volume of organic acids in liquid state and thereby its catalytic effects on the process.

[0049] (iii) increase the efficiency of the process by pushing the process equilibrium towards its residuals, i.e. towards the right in expression (1) above.

[0050] As a possible complimentary effect, reactions with AV *< 0 may also be accelerated in water (A. Lubineau (1986)). He postulated that a kinetically controlled reaction between two non-polar molecules for which AV * is negative, must be accelerated in water. This would include hydrolytic processes of the type shown in expression (1) above. Carbohydrates are soluble in water, and the acceleration effect described by Lubineau may be further increased when using high pressure, for the same reasons as discussed above.

[0051] One aspect of the present invention provides a method for modifying hemicellulosebased material, in particular wood and engineered wood, comprising the steps of: a) Selecting hemicellulose-based material, such as wood and / or engineered wood with a moisture content between 6 and 20%; b) Placing the hemicellulose-based material, such as wood and / or engineered wood in a modification chamber; c) Exchanging the atmosphere inside the modification chamber by evacuating the air, replacing the evacuated air by an inert gas atmosphere; d) Increasing the pressure in the modification chamber up to a pressure between 25 to 2000 bar, preferably between 30 to 2000 bar; e) Heating the inert gas atmosphere in the modification chamber to a temperature up to 180 °C; f) Maintaining the pressure from step d) and the temperature from step e) in the modification chamber for a holding phase lasting between 30 to 240 minutes; g) Cooling the inert gas atmosphere in the modification chamber down to a temperature between 20 to 35°C; h) Reduce the pressure of the inert gas atmosphere in the modification chamber down to atmospheric pressure; and i) Retrieving the modified hemicellulose-based material, such as wood and / or engineered wood from the modification chamber.

[0052] In step a), the hemicellulose-based material, such as wood and / or engineered wood, that is to be treated by the method provided by the present invention is chosen. As explained above, the presence of water in the cell wall is critical to the catalytic conversion of hemicelluloses, where the minimum required moisture content for successful catalytic conversion is between 6-8%. Wood and / or engineered wood with moisture content ranging from 6% up to 20%, can be modified by the method provided by the present invention, such as wood and / or engineered wood with moisture content between 6-10%, 6-15%, 8-10%, 8-15% or such as between 8-20%, 10-15%, 11-13%, around 12% or between 11-15% moisture content. The moisture content of the wood to be treated will vary between wood species, and the inventor of the present invention has discovered that the method of treating wood provided by the invention is surprisingly effective on wide range of moisture content, with even the most positive results if the moisture content is above 10% and below 20%, such as between 11-19% or between 11-15% moisture content.

[0053] In the context of the present application, when referred to the moisture content of a hemicellulose-based material in percents (%), it refers to weight by weight or w / w, that is the weight of water divided by the weight of the dry weight of the hemicellulosematerial.

[0054] Step b). In step b) the hemicellulose-based material, such as wood and / or engineered wood, that was chosen in step a) and is to be treated by the method provided by the present invention is placed in a suitable modification chamber. A suitable modification chamber is any chamber that can be heated, cooled, pressurized and depressurized in a controlled manner including maintaining the chosen temperature and / or pressure over a predetermined amount of time. A suitable modification chamber will further be capable of evacuating and / or exchanging the air / any preferred gas sort within the chamber.

[0055] After the hemicellulose-based material such as wood and / or engineered wood, has been placed in the modification chamber, the modification chamber is airtightly closed. In step c) the modification chamber is activated and the air within the closed modification chamber is evacuated and replaced with an inert gas at a pressure of between 25 to 2000 bar, preferably between 30 to 2000 bar.

[0056] It is to be understood that the step of evacuating the air and replacing it with inert gas at a pressure between 25-2000 bar or preferably between 30 to 2000 bar, is not limited to a process comprising two separate steps of first evacuating the air from the modification chamber and then filling the modification chamber with inert gas at a pressure of between 25-2000 bar or preferably between 30 to 2000 bar. The process of replacing gas (such as air) in an airtight chamber with inert gas (or any other gas) at a pressure over atmospheric pressure, is known in the art, and will depend on the type of modification chamber utilized.

[0057] In one embodiment of the present invention, step c) is a simultaneous process, where the inert gas is pumped or filled into the modification chamber at a high pressure, whereafter the pressure of the inert gas within the modification chamber can be adjusted to the predetermined value between 25-2000 bar or preferably between 30 to 2000 bar. In another embodiment of the present invention, step c) is a two-step process, where the air is first removed / evacuated from the modification chamber, followed by filling the modification chamber with inert gas at a pressure of between 25-2000 bar or preferably between 30 to 2000 bar. In yet another embodiment of the present invention, a method of modification is provided, where step c) is a multistep process, where the two steps of removing the existing gas (air) from the chamber and adding inert gas under pressure are repeated, thereby resulting in a modification chamber that is filled with inert gas at a pressure of between 25-2000 bar or preferably between 30 to 2000 bar.

[0058] In one embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood is provided where the inert gas within the modification chamber has a pressure over 25 bar, such as over 26 bar, such as over 27 bar, such as over 28 bar, such as over 29 bar, such as over 30 bar, such as over 31 bar, such as over 32 bar, such as over 33 bar, such as over 34 bar or such as over 35 bar. In another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood is provided where the inert gas within the modification chamber has a pressure above 37 bar, such as above 40 bar, such as above 45 bare or above 50 bar. In another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood is provided where the inert gas within the modification chamber has pressure between 25 to 100 bar, such as between 25 to 50 bar, such as between 25 to 35 bar, such as between 25 to 30 bar, such as between 25 to 30 bar, or the pressure of the inert gas within the modification chamber is between 25 to 30 bar. In another embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood is provided where the inert gas within the modification chamber has a pressure between 30 to 100 bar, such as between 30 to 50 bar, such as between 30 to 40 bar, such as between 30 to 35 bar, such as between 35 to 40 bar, such as between 35 to 50 bar, such as between 35 to 70 bar, such as between 35 to 100 bar or such as between 30 to 70 bar. In yet another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood is provided where the inert gas within the modification chamber has pressure of 25.1 bar, or 26 bar, or 27 bar, or 28 bar, or 29 bar, or 30 bar, or 31 bar, or 32 bar, or 33 bar, or 34 bar, or 35 bar, or 36 bar, or 37 bar, or 38 bar, or 39 bar, or 40 bar, or 45 bar or 50 bar or 55 bar or over 50 bar.

[0059] In the context of the present application, the phrase “air” means the atmospheric air surrounding the chamber, that has flown into the chamber during the placement of the hemicellulose-material within the chamber and is trapped within the airtight chamber. In the context of the present application, the phrases “inert air” and “inert gas” and “inert gas atmospheric” are used interchangeably and is to be understood as referring to any type of inert gas, preferably nitrogen. In this context inert gas is to be understood as any gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds.

[0060] After the air within the modification chamber has been replaced with inert gas at a pressure of between 25 to 2000 bar or preferably between 30 to 2000 bar, the temperature of the inert gas within the modification chamber is increased to a temperature of up to 180 degrees Celsius.

[0061] It is to be understood, that the sequence or order of the process step c) - the replacement of the air within the modification chamber with inert gas at a pressure of between 25- 2000 bar, or preferably between 30 to 2000 bar, and process step e) - the heating of the inert gas within the modification chamber to a temperature up to 180 degrees Celsius can differ, as the process of replacing gas (such as air) in an airtight chamber with inert gas (or any other gas) at a pressure over atmospheric pressure and at a temperature over room temperature, is known in the art, and will depend on the type of modification chamber utilized.

[0062] In one aspect of the invention, steps c), d) and e) may preferably be performed at a pressure between 30 to 2000 bar and at temperature up to 165° C, respectively.

[0063] In one aspect of the invention, steps c), d) and e) may preferably be performed at a pressure between 30 to 2000 bar, and at temperatures up to 170° C, respectively.

[0064] In one aspect of the invention, steps c), d) and e) may preferably be performed at a pressure between 30 to 2000 bar, and at temperatures up to 175° C, respectively. In one embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood, is provided wherein the air within the modification chamber is replaced by inert gas at a pressure between 25 to 200 bar, or preferably at a pressure between 30 to 2000 bar, first (step c) whereafter the pressurized inert gas is heated up to a temperature up to 180 degrees Celsius. In another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood, is provided wherein the air within the modification chamber is replaced by hot inert gas at a pressure between 25 to 200 bar first (step c) , or preferably at a pressure between 30 to 2000 bar, whereafter the temperature of the pressurized inert gas is adjusted to a predetermined value of up to 180 degrees Celsius. In yet another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood, is provided wherein step c) and step d) happen simultaneously and / or by multiple iterations, wherein the air within the modification chamber is replaced by heated and pressurized inert gas, whereafter both the pressure and the temperature of the inert gas within the modification chamber is adjusted simultaneously, or in multiple responding adjusting iterations of both temperature and pressure, as result in a modification chamber with inert gas at a predetermined pressure between 25 to 200 bar, or preferably at a pressure between 30 to 2000 bar and a temperature of up to 180 degrees Celsius.

[0065] In one embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood, is provided wherein the air within the modification chamber is replaced by inert gas at a pressure between 30 to 2000 bar, first (step c) whereafter the pressurized inert gas is heated up to a temperature up to 175 degrees Celsius. In another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood, is provided wherein the air within the modification chamber is replaced by hot inert gas at a pressure between 30 to 2000 bar, whereafter the temperature of the pressurized inert gas is adjusted to a predetermined value of up to 175 degrees Celsius. In yet another embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood, is provided wherein step c) and step d) happen simultaneously and / or by multiple iterations, wherein the air within the modification chamber is replaced by heated and pressurized inert gas, whereafter both the pressure and the temperature of the inert gas within the modification chamber is adjusted simultaneously, or in multiple responding adjusting iterations of both temperature and pressure, as result in a modification chamber with inert gas at a predetermined pressure between 30 to 2000 bar and a temperature of up to 150 degrees Celsius.

[0066] In one aspect of the above-mentioned embodiments the method may preferably be performed at a pressure between 30 to 2000 bar and at a temperature up to 165°C, respectively. In another aspect of the above-mentioned embodiments the method may preferably be performed at a pressure between 30 to 2000 bar and at a temperature up to 175°C, respectively, and in yet another aspect of the above-mentioned embodiments the method may preferably be performed at a pressure between 30 to 2000 bar and at a temperature up to 160°C, respectively.

[0067] In one aspect of the above-mentioned embodiments the method may preferably be performed at a pressure above 30 bar and wherein the temperature applied is as low as below 1600Celsius. In another aspect of the above-mentioned embodiments the method may preferably be performed at a pressure above 35 bar and wherein the temperature applied is below 1600Celsius. In yet another aspect of the above-mentioned embodiments the method may preferably be performed at a pressure between 30-50 bar and wherein the temperature applied is below 1600Celsius.

[0068] In one aspect of the above-mentioned embodiments the method may preferably be performed at a pressure above 30 bar and wherein the temperature applied is as low as below 165 degrees Celsius. In another aspect of the above-mentioned embodiments the method may preferably be performed at a pressure above 35 bar and wherein the temperature applied is below 165 degrees Celsius. In yet another aspect of the above- mentioned embodiments the method may preferably be performed at a pressure between 30-50 bar and wherein the temperature applied is below 165 degrees Celsius. In one aspect of the above-mentioned embodiments the method may preferably be performed at a pressure above 30 bar and wherein the temperature applied is as low as below 170 degrees Celsius. In another aspect of the above-mentioned embodiments the method may preferably be performed at a pressure above 35 bar and wherein the temperature applied is below 170 degrees Celsius. In yet another aspect of the above- mentioned embodiments the method may preferably be performed at a pressure between 30-50 bar and wherein the temperature applied is below 170 degrees Celsius.

[0069] In one aspect of the above-mentioned embodiments the method may preferably be performed at a pressure above 30 bar and wherein the temperature applied is as low as below 175 degrees Celsius. In another aspect of the above-mentioned embodiments the method may preferably be performed at a pressure above 35 bar and wherein the temperature applied is below 175 degrees Celsius. In yet another aspect of the above- mentioned embodiments the method may preferably be performed at a pressure between 30-50 bar and wherein the temperature applied is below 175 degrees Celsius. In one embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood, is provided wherein the inert gas within the modification chamber has a temperature up to 165 degrees Celsius, such as a temperature between 150-165 degrees Celsius or a temperature between 150-164 degrees Celsius, or between 150-159 degrees Celsius or a temperature between 150-158 degrees Celsius or a temperature between 150-157 degrees Celsius. In another embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood, is provided wherein the inert gas within the modification chamber has a temperature of 165 degrees Celsius, or 164 degrees Celsius, or 159 degrees Celsius, or 158 degrees Celsius, or 157 degrees Celsius or 156 degrees Celsius or 155 degrees Celsius.

[0070] In another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood, is provided wherein the inert gas within the modification chamber has a temperature up to 170 degrees Celsius, such as a temperature between 150-170 degrees Celsius or a temperature between 150- 170 degrees Celsius, or between 150-175 degrees Celsius or a temperature between ISO- 178 degrees Celsius or a temperature between 150-179 degrees Celsius. In another embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood, is provided wherein the inert gas within the modification chamber has a temperature of 179 degrees Celsius, or 178 degrees Celsius, or 177 degrees Celsius, or 176 degrees Celsius, or 175 degrees Celsius or 174 degrees Celsius or 173 degrees Celsius, such as 172 degrees Celsius, or 171 degrees Celsius or 170 degrees Celsius.

[0071] After the air within the modification chamber has been replaced with inert gas at a predetermined pressure of between 25 to 2000 bar and with a predetermined temperature up to 180 degrees Celsius, both the pressure and temperature are kept at the predetermined value for a holding phase lasting between 30 to 240 minutes.

[0072] Alternatively, after the air within the modification chamber has been replaced with inert gas at a predetermined pressure of between 30 to 2000 bar, or preferably at a pressure between 30 to 2000 bar and with a predetermined temperature up to 165 degrees Celsius, both the pressure and temperature are kept at the predetermined value for a holding phase lasting between 30 to 240 minutes.

[0073] As explained above, it is important to ensure that the modification process has been fully completed and no residual intermediate simple sugars are left in the cell wall. The holding phase is needed for ensuring completed conversion of the hemicellulose within the hemicellulose-based material, such as wood and / or engineered wood.

[0074] In one embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood, is provided wherein the holding phase is between 20 to 240 minutes, such as between 100 and 140 minutes, such as between 110 and 130 minutes, or such as between 115 and 125 minutes, or between 110 and 120 minutes or between 120 and 130 minutes. In another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood, is provided wherein the holding phase is 110 minutes, or 115 minutes, or 116 or 117 or 118 or 119 or 120 minutes or 121 or 122 or 123 or 124 or 125 minutes.

[0075] After the holding phase, the temperature of the inert gas within the modification chamber is lowered down to a room temperature or the surrounding temperature or a temperature of between 20 to 35 degrees Celsius (step f) and the pressure of the inert gas within the modification chamber is lowered down to atmospheric pressure (step g).

[0076] It is to be understood, that just as with method steps c) and d), the sequence or order of the process steps f) - the cooling of the inert gas within the modification chamber and process step g) - the lowering of the pressure of the inert gas within the modification chamber; c) is not important and can differ, as the process of lowering the pressure of inert gas within a pressurized chamber to atmospheric pressure, and the process lowering the temperature of hot inert gas within a modification chamber to room temperature, is known in the art, and will depend on the type of modification chamber utilized.

[0077] In one embodiment of the present invention, a method of modification of hemicellulosematerial such as wood and / or engineered wood, is provided wherein the pressure of the inert gas is lowered first to an atmospheric pressure (step g), whereafter the temperature of the inert gas is lowered down to a room temperature or temperature between 20 to 35 degrees Celsius (step f). In another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood, is provided wherein the temperature of the pressurized inert gas within the modification chamber is lowered to a room temperature or temperature between 20 to 35 degrees Celsius (step f), whereinafter the pressure of the inert gas is lowered to an atmospheric pressure (step g).

[0078] In yet another embodiment of the present invention, a method of modification of hemicellulose-material such as wood and / or engineered wood, is provided wherein step f) and step g) happen simultaneously and / or by multiple iterations, wherein both the temperature and the pressure of the heated and pressurized inert gas within the modification chamber is lowered simultaneously, or in multiple responding adjusting iterations of both temperature and pressure, resulting in a modification chamber with inert gas at atmospheric pressure and at room temperature or temperature between 20 to 35 degrees. After the temperature of the modification chamber has been lowered down to room temperature or temperature between 20 to 35 degrees and the pressure has been lowered down to atmospheric temperature, the airtight modification chamber is opened and the modified hemicellulose-based material, such as wood and / or engineered wood is removed from the chamber.

[0079] As explained above (see table 1), the present invention provides a wood modification method that utilizes much higher pressure than prior art wood modification methods, that have mainly relied on temperature for receiving the desired modification of the wood. The present invention provides a wood modification method, that utilizes catalytic conversion and high-pressure organic chemistry for the conversion of wood cell wall hemicelluloses, thereby allowing for high quality modification of wood at a temperature of 180 degrees Celsius or lower, preferably 178 degrees Celsius or lower, such as 165 degrees Celsius or lower. Even though prior art wood modification methods have reported being capable of providing sufficient effect at temperatures as low as 160 degrees Celsius, in reality higher temperatures have been applied, as the results gained at 160-170 degrees Celsius or from 170-180 degrees Celsius have been unsatisfactory, in particular for softwoods which are commercially the most important types of wood. Typically, softwood species such as Pine and Spruce, temperatures above 180 degrees Celsius are necessary to obtain the required improvement in durability performance.

[0080] It should further be noted that the temperature applied will depend on the wood being modified. Broadly stated, conifer wood species, such as cedar or pine require higher temperature during modification, having commonly been modified at temperature over 180 degrees Celsius, while hardwood species, such as ash and oak have commonly been modified at a lower temperature of down to between 175 to 180 degrees Celsius. Typically, however, temperatures above 180 degrees Celsius are necessary to obtain the required improvement in durability performance.

[0081] By altering both the temperature and the pressure, the present invention provides a wood modification method that lowers the temperature applied with around 20 degrees Celsius, depending on the type of wood being modified, compared to previous wood modification methods. As an example, for modification of ash, the closed modification method disclosed in Table 1 above, would commonly have applied temperature at the lowest between 175-180 degrees Celsius and a pressure around 10 bar. The current application provides a wood modification method utilizing higher pressure and a temperature below 180 degrees, such as between 165-175 or between 160-170, or between 160-175 or even blown 160 degrees Celsius at a pressure of at least 30 bar for modification of ash.

[0082] Substituting temperature for pressure has a number of advantages. Modification at lower temperatures reduces overall heating and energy costs, enabling process cost savings and, importantly, carbon footprint reductions. It also reduces stress and mechanical degradation of the wood. It is well known that thermal modification causes mechanical degradation and strength loss as an increasing function of temperature and process time; reducing modification temperature and process time by increasing modification pressure thus improves the mechanical qualities of the modified end product.

[0083] In one embodiment of the present invention, a wood modification method is provided wherein the process parameters of temperature and pressure for different species of wood are altered in comparison to the closed modification method disclosed in Table 1 above, such that the temperature is lowered with at least 10 degrees Celsius while the pressure is increased with at least 10 bar. In another embodiment of the present invention, a wood modification method is provided wherein the process parameters of temperature and pressure for different species of wood are altered in comparison to the closed modification method disclosed in Table 1 above, such that the temperature is lowered with at least 15 or 20 degrees Celsius while the pressure is at least doubled. Therefore, previous methods, where the temperature applied was above 225 degrees Celsius while the pressure applied commonly was between 2-10 bar, can be altered according to the present invention, receiving the same or even better results.

[0084] Without being bound to theory, it is thus believed that a prior art method of treating wood utilizing a pressure of 5 bar and a temperature of 225 degrees Celsius, can be amended symmetrically, by 3 times doubling the pressure to 40 bar, the temperature can be lowered accordingly with at least 3 times 20 degrees, or below 165 degrees Celsius. As explained above, without being bound to theory, it is believed that by applying even higher pressure than 25 or 30 bar, the temperature can be lowered accordingly and still provide the same surprisingly effective wood treatment with positive results.

[0085] Experiments

[0086] Currently, there is a lack of research validating the effectiveness of the present invention. From an empirical perspective, a validation of present invention effectiveness (proof of concept) would require data showing increased process effectiveness with increasing pressure above 25 bar, all other things being equal.

[0087] For this purpose, a simple initial laboratory test was performed in April 2024.

[0088] The standard proxy of hemicelluloses rate of conversion in wood modification is Equilibrium Moisture Content (EMC) (for a review see Thybring (2013)). As discussed above, the majority of accessible OH groups are situated in the hemicelluloses part of the cell wall structure. EMC is a measure of wood cell wall capacity to bind water and thus the conversion of hemicelluloses is directly related to the rate of reduction in EMC. To validate the theory of high pressure causing increased conversion effectiveness, the data must show decrease in EMC when pressure is increased, all other things being equal.

[0089] Table 2 below presents the results of the laboratory test. The test was performed at two levels of pressure, 25 and 30 bar, at two different temperatures of 150°C and 160°C, with all other process parameters being the same. The holding time (that is, the time each batch was held at the designated temperature and pressure) was two hours.

[0090] Table 2: EMC values (%) as function of pressure

[0091] The data shown in Table 2 clearly supports the theory behind the present invention. At 150°C, a 5 bar increase in pressure from 25 to 30 bar causes an Equilibrium Moisture Content reduction of 0.76% or an 8.5% increase in conversion effectiveness. Similarly, at 160°C, the EMC reduction is 0.39% or 4.9% conversion effectiveness increase.

[0092] Comparing the increase in conversion effectiveness from increasing heat temperature from 150°C to 160°C, at 25 bar the reduction in EMC is 0.9% and at 30 bar it is 0.53. These numbers are very close to those resulting from a 5 bar pressure increase and indicate that pressure is a powerful and efficient catalysator, at par with heat. In other words, present invention wood cell modification by catalytic conversion is an effective alternative to existing thermal modification technologies - without mechanical degradation effected by heat.

[0093] Literature

[0094] Hill, C. (2006): “Wood Modification - Chemical, Thermal and Other Processes”. Wiley & Sons Ltd., West Sussex.

[0095] Jones & Sandberg (2020): “A review of Wood Modification Globally - Updated Findings from COST FP1407. Interdisciplinary Perspectives on the Built Environment. Lubineau, A., Journal of Organic Chemistry, 1986 (51), 2142.

[0096] Thybring, E. (2013): “Review: The decay resistance of modified wood influenced by moisture exclusion and swelling reduction”. International Biodeterioration & Biodegradation 82:87-95.

[0097] Sandberg, D., Kuntnar, A. and Mantanis, G.: “Wood modification technologies - A review”. Forest 10: 895-908 (2017).

[0098] Sandberg, D., Kutnar, A., Karlsson, O. and Jones, D. : “Wood modification technologies - principles, sustainability and the need for innovation”. CRC Press, Boca Raton, 2021. Suib, S.: “New and future developments in catalysis”. Elsevier, Amsterdam, 2013.

[0099] Zelinka, S., Altgen, M., Emmerich, L., Guigo, N., Keplinger, T., Kymalainen, M., Thybring, e., and Thygesen, L.: “Review og Wood Modification and Wood Functionalization Technologies. Forests (2022), 13, 1004.

Claims

Claims1. A method of modifying wood and / or engineered wood, the method comprising the steps of: a) Selecting wood and / or engineered wood with a moisture content between 6 and 20%; b) Placing the wood and / or engineered wood in a modification chamber; c) Exchanging the air inside the modification chamber by evacuating the air and replacing the evacuated air by an inert gas; d) Increasing the pressure in the modification chamber up to a pressure between 30 to 2000 bar; e) Heating the inert gas in the modification chamber to a temperature of up to 180°C; f) Maintaining the pressure from step d) and the temperature from step e) in the modification chamber for a holding phase lasting between 30 to 240 minutes; g) Cooling the inert gas in the modification chamber down to a temperature between 20 to 35°C; h) Reduce the pressure of the inert gas in the modification chamber down to atmospheric pressure; and i) Retrieving the modified wood and / or engineered wood from the modification chamber.

2. The method of modifying wood, according to claim 1, wherein the preferred temperature in step e) of the modification chamber is 178 degrees Celsius or lower.

3. The method of modifying wood, according to claim 1 or 2, wherein the preferred temperature in step e) of the modification chamber is 175 degrees Celsius or lower.

4. The method of modifying wood, according to any of the preceding claims, wherein the preferred pressure in the modification chamber in step d) is 35 to 2000 bar.

5. A method of modifying wood, according to any of the preceding claims, wherein the preferred temperature of the modification chamber is between 150-178 degrees Celsius.

6. A method of modifying wood, according to any of the preceding claims, wherein the preferred temperature of the modification chamber is between 155-175 degrees Celsius.

7. A method of modifying wood, according to any of the preceding claims, wherein the preferred temperature of the modification chamber is between 165-178 degrees Celsius.

8. A method of modifying wood, according to any of the preceding claims, wherein step c) and d) are performed simultaneously.

9. A method of modifying wood, according to any of the preceding claims, wherein step c), d) and e) are performed simultaneously.

10. A method of modifying wood, according to any of claims 1-7, wherein step e) is performed before step d).

11. A method of modifying wood, according to any of the preceding claims, wherein step g) and h) are performed simultaneously.

12. A method of modifying wood, according to any of claims 1-10, wherein step h) is performed before step g).

13. Use of the method according to any one of the claims 1-12 for the modification of wood.

14. Modified wood or engineered wood, that has been modified by the method of any one of the claims 1-12.

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