Polymerizable solution for obtaining furan polymer impregnating material

Abstract

The present invention relates to a polymerizable solution for impregnating wood, a method for impregnating wood with the solution, and impregnated wood impregnated with the solution. The polymerizable solution contains furfuryl alcohol in the range of 25-75% by weight based on the total weight of the solution, a carboxylic acid in the range of 0.01-0.15 mol / kg based on the total weight of the solution, maleic anhydride in the range of 0.25-4% by weight based on the total weight of the solution, condensate from a previous wood hardening process in the range of 24-74% by weight based on the total weight of the solution, and a water-soluble alkali salt in an amount to obtain a pH in the range of 3-5 at the time the solution is made.

Description

[Technical field]

[0001] The present invention relates to a polymerizable solution for obtaining furan polymer impregnated materials such as wood. In particular, the present invention relates to reusing condensate from a preceding drying and curing process as a carrier in a polymerizable solution. [Background technology]

[0002] Furan polymer impregnated wood is known in the art and is generally produced by applying / impregnating wood with an appropriate amount of a polymerizable solution / liquid, and then heating and curing the wood so that the polymerizable compounds of the polymerizable solution are polymerized / cured into furan polymers within the wood cells.

[0003] The polymerizable solution generally contains a low molecular weight furan derivative, for example, furfural, furfuryl alcohol, bishydroxymethylfuran, or combinations thereof, and optionally contains catalysts, initiators, and stabilizers.

[0004] Furfuryl alcohol polymerizes (resinifies) in an acidic medium, where the acid initiates and accelerates the polymerization reaction. The presence of a strong acid is undesirable, since it can lead to a violent self-condensation polymerization of furfuryl alcohol, which is difficult to control. It is therefore desirable to use a weak acid, e.g. an organic acid, in the polymerizable solution, which does not separate from the furfuryl alcohol during impregnation and polymerization / curing. It is useful to select a weak acid that also has a chemical affinity with the material to be impregnated, e.g. wood. Non-separating mixtures with enhanced affinity for wood are known from US Pat. No. 5,399,323.

[0005] For some applications, it is desirable to impregnate porous materials such as wood with a more dilute starting furfuryl alcohol solution to provide better control and economy than disclosed in U.S. Patent No. 5,399,663. Lower concentrations of furfuryl alcohol polymer (also called furan polymer or furan resin) in the wood have been found to provide useful properties at lower cost and with less change in appearance. Wood prepared according to U.S. Patent No. 5,399,663 is very dark in color. At lower concentrations of furfuryl alcohol, colors ranging from light brown to dark brown are possible.

[0006] Control of the concentration of the furan polymer in the final cured product is obtained by using a liquid carrier for the furfuryl alcohol in the polymerizable solution. The carrier and furfuryl alcohol are added together in the product before the polymerization process begins.

[0007] Several carriers are known from the prior art, such as water or water and alcohol. Since furfuryl alcohol is soluble in water, water can be used as a carrier for the diluted uninitiated furfuryl alcohol. Water is an environmentally friendly, inexpensive material and is therefore often the preferred carrier.

[0008] As mentioned above, the polymerizable solution contains an initiator to start the polymerization reaction. When an organic acid initiator is mixed with furfuryl alcohol and water (water is the carrier), the solution becomes very reactive, causing the polymerization of furfuryl alcohol. Therefore, a stabilizer is required to provide a stable solution suitable for storage or at least impregnation prior to polymerization, which is the basis of US Pat. No. 5,399,633.

[0009] The first useful chemical stabilizers discovered were borax and the sodium salt of lignosulfonic acid. However, the sodium salt of lignosulfonic acid exhibits low solubility, is expensive, and is difficult to handle, and is therefore a less preferred stabilizer. Borax can be used to form a buffer and is also a biocide that increases protection from biological degradation for the final furan polymer impregnated product. However, borax, being a biocide, is undesirable for environmental reasons, as borax is easily washed off the final impregnated material and deposited in the environment.

[0010] Efforts have been made to produce stable polymerizable solutions without the use of the above-mentioned stabilizers. Such stable polymerizable solutions must remain in a certain pH range during storage, because an excessively acidic polymerizable solution will polymerize rapidly, resulting in phase separation and destroying the solution, since such a reaction is irreversible. On the other hand, an excessively basic polymerizable solution will retard or hinder the polymerization reaction of the polymerizable solution during use, and therefore will not be able to provide the required reactivity and target properties of the final impregnated product.

[0011] One method of providing such a stable polymerizable solution involves using a stabilizing co-solvent as disclosed in US Pat. No. 5,399,633. Such co-solvents can be methanol, ethanol, acetone or other volatile solvents. These co-solvents are both good solvents for furfuryl alcohol and good swelling agents for wood. The co-solvents dilute the acid concentration during storage and impregnation, thereby extending the shelf life of the polymerizable solution. When the co-solvent is removed from the wood after impregnation, i.e. before curing, the reactivity of the solution increases (pH decreases) as the co-solvent evaporates from the wood. An effective co-solvent removal step must be added to the treatment process. This removal step is preferably a vacuum drying process with a system for recovering the co-solvent, so that the co-solvent can be reused. By using such a stabilizing co-solvent, no additional stabilizer is needed and the initiator:furfuryl alcohol ratio can be reduced. This leads to a lower amount of leachable substances in the final impregnated wood product, which is preferable. Furthermore, experiments have shown that the stabilizing co-solvents maintained the pH in the polymerizable solution until after the wood has been impregnated. The pH was then decreased (became more acidic) and hardening was accelerated.

[0012] However, the use of such co-solvents is more expensive and places more demands on safety and process equipment than the use of water, and is therefore less preferred. These co-solvents are also considered to be volatile, difficult to recover, and flammable. The use of such flammable co-solvents, typically in closed volumes for process equipment, can lead to the formation of explosive atmospheres when containing oxidizing agents such as oxygen in air.

[0013] A conventional polymerization process for obtaining impregnated wood products is known, inter alia, from US Pat. No. 5,399,363, which is incorporated herein by reference. This process involves, inter alia, the use of an apparatus for combined drying and curing, i.e. a drying and curing chamber. This process involves adding a polymerizable solution to the material to be impregnated, e.g. wood, before the wood is introduced into the apparatus. The apparatus typically includes a drain that allows the so-called "bottom condensate" to be pumped out of the apparatus during the heating stage and, to a lesser extent, during the subsequent curing stage. The bottom condensate is realized by compounds from the polymerizable solution and from the wood, such as water, furfuryl alcohol, organic compounds, polymers and resins. Furthermore, the main mechanism for the removal of water and other chemicals, the so-called "top condensate", is by a condenser integrated into the drying and curing chamber towards its upper surface. Such top condensate is realized mainly by recondensing evaporated water, furfuryl alcohol and volatile organic compounds (VOCs) from the polymerizable solution and from the wood. The top condensate is then sent to a condensate tank for reuse. The bottom condensate is sent to a separation tank which separates the reusable portion of the condensate from the unusable high density polymer, which is then transferred to the condensate tank for reuse. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] WO 02 / 30638 [Patent Document 2] WO 02 / 060660 [Patent Document 3] International Publication No. 2004 / 011216 [Patent Document 4] European Patent Application Publication No. 2435223 Summary of the Invention [Problem to be solved by the invention]

[0015] However, the reuse of such condensates, i.e. the reusable parts of the top and bottom condensates, as carriers to provide a stable polymerizable solution suitable for obtaining the final impregnated wood product is a challenge. One of the reasons is that with increasing degree of polymerization during curing, the resinified and oligomerized components in the condensate originating from the polymerizable solution become increasingly non-polar. Since such components are soluble in furfuryl alcohol, their presence in the condensate when used as a carrier will reduce the solubility of the organic furfuryl alcohol phase in water. This reduction in solubility is manifested as an increase in the cloud point temperature, which is undesirable since the cloud point temperature of the initial polymerizable solution must be below the storage temperature of the solution to avoid phase separation. The condensate also has a low pH due to acidic by-products generated during the polymerization reaction. The low pH accelerates the polymerization reaction and therefore reduces the storage life of the polymerizable solution.

[0016] Furthermore, impregnation of wood, especially with the presence of organic solvents in the condensate as carriers, can extract non-polar components such as terpenes (e.g., α-pinene), which also affect the water solubility and thereby increase the cloud point temperature as the concentration increases.

[0017] It is therefore a first object of the present invention to provide a polymerizable solution for impregnating materials such as wood that overcomes the drawbacks of the prior art.

[0018] A second object of the present invention is to provide a polymerizable solution which is cheaper and more environmentally friendly than known solutions.

[0019] A third object of the present invention is to provide a polymerizable solution which is stable for at least 7 days, preferably at least 10 days, more preferably at least 14 days, and even more preferably at least 21 days, when stored in a closed container at ambient temperature, which is typically 15-30°C.

[0020] A fourth object of the present invention is to provide furan polymer impregnated / chemically modified products, such as wood, with good or improved dimensional stability, mechanical strength, resistance to leaching, decay and weathering. [Means for solving the problem]

[0021] In a first aspect, a polymerizable solution for impregnating wood is provided, said polymerizable solution comprising: furfuryl alcohol in the range of 25 to 75% by weight based on the total weight of the solution; A carboxylic acid in the range of 0.01 to 0.15 mol / kg based on the total weight of the solution; Maleic anhydride in the range of 0.25 to 4% by weight based on the total weight of the solution; a water-soluble alkali salt in an amount such that the initial composition has a pH in the range of 3 to 5; condensate from a previous wood hardening process in the range of 24-74% by weight based on the total weight of the solution; The amount of water-soluble alkali salt is such that the solution has a pH in the range of 3 to 5 when made.

[0022] In one embodiment according to the first aspect, the water-soluble alkali salt is added to obtain a pH in the range of 3-4.5, more preferably 3.5-4.

[0023] In one embodiment according to the first aspect, the amount of furfuryl alcohol is in the range of 30-60% by weight, preferably 35-60% by weight.

[0024] In one embodiment according to the first aspect, the water-soluble alkali salt is selected from at least one of a metal hydroxide salt, a metal bicarbonate salt, and a metal carbonate salt.

[0025] In one embodiment according to the first aspect, the carboxylic acid is selected from at least one of citric acid, fumaric acid, malic acid, malonic acid, oxalic acid, tartaric acid, 2-furoic acid, benzoic acid, levulinic acid and salicylic acid, preferably citric acid.

[0026] In one embodiment according to the first aspect, the total amount of carboxylic acid and maleic anhydride is less than or equal to 4.5 wt.%.

[0027] In a second aspect, there is provided impregnated wood impregnated with a polymerizable solution according to the first aspect and any embodiment thereof.

[0028] In a third aspect, a method for preparing a polymerizable solution is provided, the method comprising: providing condensate from the curing process into a container; adding furfuryl alcohol into the container; adding into said vessel a carboxylic acid, maleic anhydride and a water-soluble alkali salt.

[0029] In one embodiment according to the third aspect, the amount of water-soluble alkaline salt is added to obtain a pH in the range of 3 to 5 when the solution is made.

[0030] In a fourth aspect, a polymerizable solution for impregnating wood is provided, said polymerizable solution comprising: furfuryl alcohol in the range of 25 to 75% by weight based on the total weight of the solution; A carboxylic acid in the range of 0.01 to 0.15 mol / kg based on the total weight of the solution; Maleic anhydride in the range of 0.25 to 4% by weight based on the total weight of the solution; 24-74% by weight of condensate from a previous wood hardening process, based on the total weight of the solution; and a water-soluble alkali salt in an amount to obtain a pH in the range of 3 to 5 when the solution is prepared; Said polymerizable solution is obtained by the method of the third aspect.

[0031] In a fifth aspect, there is provided the use of a polymerizable solution according to the first aspect and any embodiment thereof for impregnating wood. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0033] Unless otherwise defined herein, all technical and scientific terms used have the same meaning as commonly understood by one of ordinary skill in the art of polymer engineering and wood impregnation.

[0034] In particular, to alleviate environmental challenges regarding the disposal of condensates generated in the curing / polymerization process, the present invention provides a polymerizable solution for impregnating materials such as wood that reuses such condensates as carriers in the polymerizable solution.

[0035] Thus, the present invention provides an optimized furan polymerizable solution that is suitable for storage, inexpensive, and environmentally friendly, provides furan polymer-impregnated wood with good or improved dimensional stability, mechanical strength, leaching resistance, decay resistance, and weather resistance, and uniform color and density, and further provides the ability to utilize condensate as a carrier in the solution.

[0036] Thus, in a first aspect, there is provided a polymerizable solution for impregnating wood, said polymerizable solution comprising: furfuryl alcohol in the range of 25 to 75% by weight based on the total weight of the solution; A carboxylic acid in the range of 0.01 to 0.15 mol / kg based on the total weight of the solution; Maleic anhydride in the range of 0.25 to 4% by weight based on the total weight of the solution; a water-soluble alkali salt in an amount such that the initial composition has a pH in the range of 3 to 5; condensate from a previous wood hardening process in the range of 24-74% by weight based on the total weight of the solution; The amount of water-soluble alkali salt is such that the solution has a pH in the range of 3 to 5 when made.

[0037] Also described herein is a polymerizable solution for impregnating materials such as wood, said polymerizable solution comprising: furfuryl alcohol in the range of 25 to 75% by weight based on the weight of the total composition of the polymerizable solution; A carboxylic acid in a range of 0.01 to 0.15 mol / kg based on the weight of the total composition of the polymerizable solution, Maleic anhydride in the range of 0.25 to 4% by weight based on the weight of the total composition of the polymerizable solution; a water-soluble alkali salt in an amount such that the initial composition has a pH in the range of 3 to 5; The polymerizable solution has a composition including 24 to 74% by weight of water and / or condensate based on the weight of the entire composition of the polymerizable solution.

[0038] Since the pH of the initial composition without the water-soluble alkali salt is always less than 3, a water-soluble alkali salt is always present in the polymerizable solution.

[0039] The polymerizable solution of the above composition is suitable for storage, meaning that the solution can be stored in a closed container without separation under ambient conditions for at least 7 days, preferably at least 10 days, more preferably at least 14 days, and even more preferably at least 21 days.

[0040] The condensate used as a carrier in the polymerizable solution is acidic and may have a pH less than 3, so that when added to a conventional furan polymerizable solution as a carrier instead of water, it accelerates the polymerization of the solution and therefore provides a solution that separates quickly. A solution that separates quickly, e.g., within 48 hours, is undesirable because coating / impregnation of the material must occur before such separation occurs. The composition of the polymerizable solution of the present invention mitigates this problem in that it includes an organic buffer provided by the presence of a carboxylic acid as a buffering agent and a controlled amount of a water-soluble alkali salt to adjust the pH of the initial polymerizable solution to within a target pH range of 3-5, more preferably within a pH range of 3-4.5, and even more preferably within a pH range of 3.5-4. This range provides the most stable polymerizable solution and also retains good reactivity when heated in the polymerization process.

[0041] The carboxylic acid added to the polymerizable solution of the present invention does not function as an initiator, but as a buffer to keep the pH as constant as possible during storage so that the acidity of the condensate does not affect the pH stability of the solution, providing a less sensitive and more stable polymerizable solution. Experiments have shown that the amount of carboxylic acid in the polymerizable solution should be in the range of 0.01 to 0.15 mol / kg, based on the weight of the total composition of the polymerizable solution.

[0042] An excessively acidic polymerizable solution, such as a solution with a pH of less than 3, will polymerize rapidly, resulting in phase separation and destroying the solution since such reactions are irreversible. On the other hand, an excessively basic polymerizable solution, such as a solution with a pH of more than 5, will reduce or hinder the polymerization reaction of the polymerizable solution during use, and therefore will not be able to provide the required reactivity and target properties of the final impregnated product. It is therefore important to provide a polymerizable solution in which the pH of the initial solution can be controlled to a pH value within the range of 3 to 5 that is considered neither too acidic nor too basic. Due to the acidic properties of the condensate in the polymerizable solution, the amount of water-soluble alkali salt added depends on its acidity and the buffering range and buffering capacity of the added acid.

[0043] The water-soluble alkali salts may advantageously be selected from at least one of metal hydroxide salts, metal bicarbonates, and metal carbonates, since for all practical purposes they do not introduce cations and OH groups into the polymerizable solution. - is added, which mainly affects the pH of the polymerizable solution. Preferably, the water-soluble alkaline salt is sodium carbonate (Na2CO3), which is environmentally friendly, readily available, and inexpensive.

[0044] It is commonly known that a buffer has the ability to resist the change in pH that accompanies a change in the concentration of an acid or alkali. Buffer capacity (β) is a quantitative measure of this and can be expressed for a solution of a simple carboxylic acid as follows:

[0045]

number

[0046] The above equation shows that the buffer capacity of such a solution depends mainly on the carboxylic acid concentration. For monocarboxylic acids, the buffer capacity is given by pH = pK a It is maximum when pH=pK a ±1, the pH value drops to 33% of the maximum value, and pH=pK a ±1.5, it decreases to 12% of the maximum value, pH=pK a The pK of dicarboxylic acids is 2, and the difference is 4%. a The value is pK a1 +1=pH=pK a2 -1, while providing a total buffering capacity of 66% at pK aThe value would result in a buffer capacity of 24% at the midpoint.

[0047] Therefore, the pK of the carboxylic acid in the polymerizable solution a value, or at least one pK a The value may preferably be within ±1.5 of the target pH or within ±1.5 of one of the endpoints of the target pH range (buffer region). a value, or at least one pK a The value may preferably be within ±1 of the target pH or within ±1 of one of the endpoints of the target pH range.

[0048] In addition, there are several pKs separated by ≤3, i.e., Δ≤3. a Polycarboxylic acids having such a value have an increased buffering capacity which is advantageous and therefore preferred.

[0049] Carboxylic acids suitable as buffering agents include, but are not limited to, monocarboxylic acids such as acetic acid, propionic acid, and butyric acid; unsaturated carboxylic acids such as crotonic acid and sorbic acid; hydroxycarboxylic acids such as glycolic acid and lactic acid; ketocarboxylic acids such as pyruvic acid and levulinic acid; heterocyclic aromatic carboxylic acids such as 2-furoic acid; phenylcarboxylic acids such as benzoic acid, salicylic acid, and gallic acid; dicarboxylic acids such as oxalic acid, malonic acid, and succinic acid; unsaturated dicarboxylic acids such as fumaric acid; hydroxydicarboxylic acids such as malic acid and tartaric acid; and tricarboxylic acids such as propane-1,2,3-tricarboxylic acid, aconitic acid, and citric acid.

[0050] The carboxylic acid of the polymerizable solution of the present invention may preferably be selected from at least one of citric acid, fumaric acid, malic acid, malonic acid, oxalic acid, tartaric acid, 2-furoic acid, levulinic acid, benzoic acid and salicylic acid.

[0051] The total amount of carboxylic acids added to the total composition is in the range of 0.01-0.15 mol / kg based on the total composition of the polymerizable solution, as described above. This amount corresponds to about 0.25-3 wt% citric acid, about 0.15-1.8 wt% fumaric acid, about 0.17-2.1 wt% malic acid, about 0.14-1.6 wt% malonic acid, about 0.12-1.4 wt% oxalic acid, about 0.20-2.3 wt% tartaric acid, about 0.15-1.8 wt% 2-furoic acid, about 0.15-1.8 wt% levulinic acid, about 0.18-2.2 wt% salicylic acid, and about 0.16-1.9 wt% benzoic acid, all based on the weight of the total composition of the polymerizable solution, as known to those skilled in the art.

[0052] Non-carboxylic acids, such as phosphoric acid and sulfuric acid, are not suitable as buffers because such solutions rapidly separate. Phosphoric acid has pK values ​​of 2.1, 7.2, and 12. a value and therefore has a Δ>3, which makes phosphoric acid much less suitable than, for example, citric acid, which meets this criterion. Sulfuric acid is not suitable because it is not a weak acid and therefore accelerates the polymerization process.

[0053] Other advantageous properties of carboxylic acids that may affect the polymerizable solution in comparison to non-carboxylic acids are the partition coefficient (logP), dipole moment

number

[0054] Citric acid is highly soluble in both water and furfuryl alcohol, and furthermore has a pK value that allows the pH of the polymerizable solution to be stable within the ranges mentioned above, thus allowing for greater buffering capacity. a Furthermore, citric acid is inexpensive and is considered environmentally friendly when released into the environment.

[0055] Experiments have shown that the amount of carboxylic acid must be limited, i.e., not exceed 0.15 mol / kg of the total composition, since too much reduces the storage time of the polymerizable solution, i.e., the time until phase separation, and thus the carboxylic acid acts as an initiator rather than a buffer, thus providing a more unstable polymerizable solution that is not suitable for storage.

[0056] Therefore, maleic anhydride is added to the solution to act as an initiator in the polymerizable solution. Maleic anhydride is a well-known initiator with great initiation properties and wood affinity, and is more environmentally friendly than other initiators known from the prior art, such as phthalic anhydride.

[0057] Advantageously, in order to limit the acceleration of the polymerization of the polymerizable solution, the total amount of carboxylic acid and maleic anhydride in the polymerizable solution is equal to or less than 4.5% by weight, even more preferably less than 4% by weight.

[0058] Another problem with the reuse of condensates in conventional furan polymerizable solutions is related to the presence of oligomers and / or other compounds in the condensates that are insoluble in water, which must be dissolved in the polymerizable solution prior to storage and impregnation to ensure uniform density and flat surface structure of the final impregnated product to provide better weather resistance, mechanical strength properties, etc.

[0059] The polymerizable solution of the present invention dissolves such compounds by having a sufficient amount of furfuryl alcohol in the polymerizable solution.

[0060] In general, for any polymerizable solution suitable for storage, it is also important that the cloud point temperature (Cp) of the initial polymerizable solution is below the storage temperature of the solution. The cloud point temperature is defined as the temperature at which the onset of phase separation can be visually observed as clouding of the solution. The presence of oligomers in the solution contributes to increasing the cloud point temperature of the polymerizable solution, while the increased presence of furfuryl alcohol decreases the cloud point temperature.

[0061] Thus, in addition to being an essential component for the polymerization of the polymerizable solution, the amount of furfuryl alcohol is important for providing a stable polymerizable solution suitable for storage.

[0062] The amount of furfuryl alcohol must be at least 25% by weight of the total composition of the polymerizable solution to provide such properties.

[0063] The most stable polymerizable solutions for storage have furfuryl alcohol in an amount ranging from 25 to 75% by weight, preferably ranging from 30 to 60% by weight, and even more preferably ranging from 35 to 60% by weight of the total composition of the polymerizable solution.

[0064] Although wood and wood-based materials are the primary products that are impregnated and polymerized with the polymerizable solutions of the present invention, other porous materials such as brick, Portland cement, concrete and stone may be impregnated as well.

[0065] In a third aspect, there is provided impregnated wood impregnated with a polymerizable solution according to the first aspect and embodiments thereof.

[0066] A fourth aspect of the present invention provides a method for preparing a polymerizable solution according to the first aspect.

[0067] This method is providing condensate from the curing process into a container; adding furfuryl alcohol into the vessel containing the condensate; adding a carboxylic acid, maleic anhydride and a water-soluble alkali salt to the vessel containing the furfuryl alcohol and condensate.

[0068] In other words, the method may include adding the carrier in the form of a condensate to a vessel. Then, furfuryl alcohol may be added to the same vessel, preferably with stirring. Then, the carboxylic acid, maleic anhydride, and water-soluble alkali salt may be added simultaneously or nearly simultaneously while measuring the pH of the initial polymerizable solution.

[0069] In one embodiment, a water-soluble alkali salt is added in an amount to obtain a pH in the range of 3-5 once the solution is made.

[0070] The pH of the initial polymerizable solution may be measured by any conventional method known in the art.

[0071] The method may further include stirring or mixing during and / or between each step.

[0072] Depending on the process equipment, the entire process may take from about 5 minutes to several hours.

[0073] If the container is stored under non-ambient temperatures, it is preferred that the container be made from a material that allows the contents therein to not be affected by the surroundings.

[0074] In a fourth aspect, a polymerizable solution for impregnating wood is provided, said polymerizable solution comprising: furfuryl alcohol in the range of 25 to 75% by weight based on the total weight of the solution; A carboxylic acid in the range of 0.01 to 0.15 mol / kg based on the total weight of the solution; Maleic anhydride in the range of 0.25 to 4% by weight based on the total weight of the solution; 24-74% by weight of condensate from a previous wood hardening process, based on the total weight of the solution; and a water-soluble alkali salt in an amount to obtain a pH in the range of 3 to 5 when the solution is prepared; The polymerizable solution is obtained by the method according to the third aspect.

[0075] There is also provided a polymerizable solution for impregnating materials such as wood, said solution comprising: furfuryl alcohol in the range of 25 to 75% by weight based on the weight of the total composition of the polymerizable solution; A carboxylic acid in a range of 0.01 to 0.15 mol / kg based on the weight of the total composition of the polymerizable solution, Maleic anhydride in the range of 0.25 to 4% by weight based on the weight of the total composition of the polymerizable solution; a water-soluble alkali salt in an amount such that the initial composition has a pH in the range of 3 to 5; A condensate in the range of 24 to 74% by weight based on the weight of the total composition of the polymerizable solution; The polymerizable solution is obtained by the method described above.

[0076] In a fifth aspect, the present invention discloses the use of a polymerizable solution of the first aspect and its embodiments for impregnating wood to obtain a final impregnated wood product.

[0077] The term "initial composition / initial polymerizable solution" should be interpreted as the starting composition of the polymerizable solution before storage. It is therefore the composition of the polymerizable solution immediately after all components have been added and mixed.

[0078] The term "impregnating / impregnating" should be interpreted as the action of adding a polymerizable solution to a material (eg wood) in the process to obtain an impregnated product (eg impregnated wood).

[0079] The "final furan polymer impregnated product / impregnated product" should be interpreted as the product / material obtained after the material has been subjected to impregnation and curing / polymerization, and thus is a material comprising a furan polymer, such as furan polymer impregnated wood.

[0080] The term "condensate" should be interpreted as the solution obtained during the process of drying and hardening impregnated wood with the polymerizable solution of the present invention, including the so-called "top condensate" and the reusable part of the so-called "bottom condensate". The condensate therefore mainly contains water, furfuryl alcohol, residues of organic compounds and acids obtained from the previous wood hardening process with the polymerizable solution according to the present invention.

[0081] The term "stable solution" should be interpreted as a polymerizable solution in which no phase separation occurs. Thus, a stable solution can be stored at ambient temperature and pressure for at least 7 days, preferably 10 days, more preferably 14 days, and even more preferably 21 days, without the occurrence of phase separation.

[0082] The ranges set forth herein should be interpreted as inclusive of the endpoints.

[0083] Ambient temperature should be interpreted as a temperature between 15 and 30° C. Ambient pressure should be interpreted as atmospheric pressure. The term "ambient conditions" should be interpreted as conditions where the temperature is between 15 and 30° C. and the pressure is atmospheric pressure.

[0084] In the first experiment below, the polymerizable solutions were made with water as the carrier because different amounts of components in the polymerizable solutions were compared. As already mentioned, the composition of the condensate will vary because each polymerization process produces a condensate of different composition.

[0085] Therefore, experiments were carried out using polymerizable solutions with different compositions, as shown in Table 1.

[0086] [Table 1]

[0087] In the experiments, furfuryl alcohol (FA), maleic anhydride (MA), a carboxylic acid buffer (represented by citric acid (CA)), a water-soluble alkali salt (represented by anhydrous sodium carbonate (SC)) and water were mixed together and stored at 27°C and ambient pressure for 21 days. The amounts of FA, MA, CA and SC in the solutions are given in weight percent (wt%), the remaining component is water, and the amounts of all components add up to 100 wt%, which is the total composition of the polymerizable solution.

[0088] Table 1 shows that the initial pH of the polymerizable solution is approximately 3.8 to 3.9. This is the pH of the solution after all of the components have been added together and stirred until a homogenous solution is obtained, and therefore the pH of the solution when it is first placed for storage.

[0089] Table 1 further shows the results after 1 day (d1) storage and after 14 days (d 14 ) pH after storage and on the day of storage (d0) and for 14 days (d 14 ) pH difference after storage ΔpH(d1-d 14 ) is shown.

[0090] 1 day (d1) and 14 days (d 14 ) After the solutions were stored, the cloud point temperatures (Cp) were also measured.

[0091] The last column of the table shows the time periods for 1 day (d1), 7 days (d7), and 14 days (d 14 ) and 21 days (d 21 ) indicates whether phase separation occurred after the solution was stored, with "N" indicating that phase separation did not occur and "Y" indicating that phase separation did occur.

[0092] Experiments No. 1-6, 10, and 11 were performed during the first 14 days (d 14 ) no phase separation occurred, and therefore these solutions are considered stable.

[0093] Additionally, the table shows that adding excess carboxylic acid initiator to the composition, such as 4% by weight or more, provides a more unstable solution that causes phase separation during 14 days of storage, as shown in Runs 7, 12, and 13. Therefore, it is important to control the total amount of acid added to avoid premature initiation of the polymerization process.

[0094] Furthermore, the experiments show that less than 20 wt% furfuryl alcohol in the solution (Experiments No. 8 and 9) also caused phase separation during 14 days of storage. This is caused by the lower amount of furfuryl alcohol being less tolerant to the presence of oligomers and polymers that increase over time before phase separation occurs, thus resulting in a more rapid increase in cloud point (Cp) than a similar solution with more FA. Therefore, the polymerizable solution should contain at least 25 wt% furfuryl alcohol to provide a stable polymerizable solution.

[0095] In addition, experiments were carried out to compare the initial cloud point temperatures of polymerizable solutions using water or condensate as carriers without the addition of carboxylic acid as a buffer. The experimental polymerizable solutions contained 35% by weight of furfuryl alcohol, 1% by weight of maleic anhydride (MA) and a water-soluble alkali salt (represented by anhydrous sodium carbonate (SC)) to adjust the initial pH for comparative reasons. See Table 2 below.

[0096] [Table 2]

[0097] As shown in Table 2, the initial cloud point when using water as a carrier is much lower than that of the condensate. Thus, using water as a carrier would provide a more stable polymerizable solution than the use of the condensate under the same conditions. Thus, Table 2 illustrates the challenges associated with providing a stable polymerizable solution when using a condensate as a carrier.

[0098] Table 3 below lists the pK values ​​within ±1 of the target pH or within ±1 of one of the endpoints of the target pH range (buffer region). a pK value or at least one if more than one a Examples of preferred carboxylic acids having the following values ​​are given below.

[0099] Additionally, preferred polycarboxylic acids have pK a It has a value.

[0100] [Table 3]

Claims

1. A polymerizable solution for impregnating wood, said solution comprising: furfuryl alcohol in the range of 25 to 75 wt. % based on the total weight of the solution; a carboxylic acid in the range of 0.01 to 0.15 mol / kg based on the total weight of the solution; maleic anhydride in the range of 0.25 to 4 wt. % based on the total weight of the solution; a water-soluble alkali salt in an amount such that the initial composition has a pH in the range of 3 to 5; condensate from a previous wood curing process in the range of 24 to 74 wt. %, based on the total weight of the solution; The amount of water-soluble alkali salt is to obtain a pH in the range of 3 to 5 when said solution is made.

2. 10. The polymerizable solution of claim 1, wherein the water-soluble alkali salt is added to obtain a pH in the range of 3 to 4.

5.

3. The polymerizable solution described in Claim 2, wherein the water-soluble alkaline salt is added to obtain a pH in the range of 3.5 to 4.

4. The polymerizable solution according to any one of claims 1 to 3, wherein the amount of furfuryl alcohol is in the range of 30 to 60% by weight.

5. The polymerizable solution of claim 4, wherein the amount of furfuryl alcohol is in the range of 35 to 60% by weight.

6. 4. The polymerizable solution of claim 1, wherein the water-soluble alkali salt is selected from at least one of a metal hydroxide salt, a metal bicarbonate salt, and a metal carbonate salt.

7. 4. The polymerizable solution according to claim 1, wherein the carboxylic acid is selected from at least one of citric acid, fumaric acid, malic acid, malonic acid, oxalic acid, tartaric acid, 2-furoic acid, benzoic acid, levulinic acid, and salicylic acid.

8. The polymerizable solution of claim 7, wherein the carboxylic acid is citric acid.

9. 4. The polymerizable solution according to claim 1, wherein the total amount of the carboxylic acid and maleic anhydride is 4.5% by weight or less.

10. 4. Impregnated wood impregnated with the polymerizable solution according to claim 1.

11. A method for preparing the polymerizable solution according to any one of claims 1 to 3, comprising the steps of: providing condensate from the curing process into a container; adding furfuryl alcohol to the container; adding into said vessel a carboxylic acid, maleic anhydride and a water-soluble alkali salt.

12. A polymerizable solution for impregnating wood, comprising: furfuryl alcohol in the range of 25 to 75 wt. % based on the total weight of the solution; a carboxylic acid in the range of 0.01 to 0.15 mol / kg based on the total weight of the solution; maleic anhydride in the range of 0.25 to 4 wt. % based on the total weight of the solution; condensate from a previous wood curing process in the range of 24 to 74 wt. %, based on the total weight of the solution; a water-soluble alkali salt in an amount to obtain a pH in the range of 3 to 5 when the solution is made; The polymerizable solution is obtainable by the method of claim 11 .

13. Use of the polymerizable solution according to any one of claims 1 to 3 for impregnating wood.