EP-4735220-A1 - 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.

Inventors

• KLAAS, Johann Peter

Assignees

• WTT Innovation ApS

Dates

Publication Date

20260506

Application Date

20250919

Claims (14)

1. 1. 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. 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. 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. 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. 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. 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. 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. 8. A method of modifying wood, according to any of the preceding claims, wherein step c) and d) are performed simultaneously.
9. 9. A method of modifying wood, according to any of the preceding claims, wherein step c), d) and e) are performed simultaneously.
10. 10. A method of modifying wood, according to any of claims 1-7, wherein step e) is performed before step d).
11. 11. A method of modifying wood, according to any of the preceding claims, wherein step g) and h) are performed simultaneously.
12. 12. A method of modifying wood, according to any of claims 1-10, wherein step h) is performed before step g).
13. 13. Use of the method according to any one of the claims 1-12 for the modification of wood.
14. 14. Modified wood or engineered wood, that has been modified by the method of any one of the claims 1-12.

Description

Wood Modification by Catalytic Conversion of Hemicelluloses Field of the Invention 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. Background of the Invention 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. 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. 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.). Hill (see also Jones & Sandberg (2020)) continues to identify different classes of wood modification, including “Cross-Linking”, “Bulking” and “Thermal”. 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. 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. 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). Sandberg et al. (2021 : 216) categorize thermal modification in three different systems: - Vacuum systems, that thermally modify wood at sub-atmospheric pressure at 225 °C and above. - Open systems, that thermally modify wood at atmospheric pressure at 225 °C and above. - Closed systems, that thermally modify wood in a pressurized atmosphere between 8 and 16 bar at 175 °C and above. 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. Table 1: Vacuum, Open, Closed Thermal and Catalytic wood modification (modified after Sandberg et al 2021). 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) 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, den