GB2618085A

GB2618085A - Method of making modified wood product, modified wood product and apparatus for making modified wood product

Info

Publication number: GB2618085A
Application number: GB2205997.6A
Authority: GB
Inventors: Mackie Andrew; Els Justin
Original assignee: Newood Tech Ltd
Current assignee: Newood Tech Ltd
Priority date: 2022-04-25
Filing date: 2022-04-25
Publication date: 2023-11-01
Also published as: GB202205997D0; WO2023209354A1

Abstract

Heating resin impregnated wood W to dry it without curing it; in a vessel 1001 capable of operating at a pressure less than 50kPa and more than 200kPa. The heating can be 65°C or cooler. Heating resin impregnated wood to curing it; in a vessel capable of operating at a pressure less than 50kPa and more than 200kPa. The heating can be 160°C or cooler at a pressure of 175kPa-200kPa. The resin can be phenol with a formaldehyde reagent. Heating resin impregnated wood to dry it without curing it at 100kPa or less. One chamber connected to a pressure reducing device and another chamber connected to a heater and a pressure reducing device. Resin with a density of 650kgm-3-750kgm-3 with 11% moisture content or less which is fire retardant. Multiple modified wood products where less than 1/10 are unsatisfactory.

Description

Method of making modified wood product, modified wood product and apparatus for making modified wood product

BACKGROUND OF THE INVENTION

[0001] The present invention concerns modified wood products. More particularly, but not exclusively, this invention concerns a method of making a modified wood product. The invention also concerns a modified wood product and an apparatus for making a modified wood product.

[0002] There is a need for wood products that may be used as building materials, particularly building materials that are fire resistant, strong and whose dimensions do not change significantly over time. Traditionally, hardwoods, such as oak and cedar, have been used as building materials. Such hardwoods are expensive, and are slow growing, which means that they are not sustainable. Many softwoods are sustainable, but they are typically not suitable for use as building materials. Softwoods may be impregnated with resins to form modified wood products that are suitable for use as building materials. The formation of modified wood products may comprise impregnating a wood product with a resin and curing the resin. Such processes can be time-consuming and are prone to reproducibility issues, with many products failing quality control tests.

100031 The present invention seeks to mitigate the above-mentioned problems. Alternatively, or additionally, the present invention seeks to provide an improved method of making a modified wood product.

SUMMARY OF THE INVENTION

[0004] In accordance with a first aspect of the present invention, there is provided a method of making a modified wood product, the method comprising a curing step comprising heating a resin-impregnated wood product, thereby curing the resin, in a variable pressure vessel chamber capable of operating at pressures less than 50kPa and capable of operating at pressures of at least 200kPa. -2 -

[0005] The applicant has discovered that curing the resin in a variable pressure vessel chamber is beneficial, because the same chamber may be used to dry the resin-impregnated wood product prior to curing. Reference herein to "cured" indicates that the product has been subjected to the curing step. The reference to "curing" indicates that the resin has been exposed to conditions that typically harden and/or toughen the resin. Curing typically involves a reaction between components of the resin, optionally to form a polymer.

100061 For the avoidance of doubt, and unless the context demands otherwise, the phrase "resin-impregnated wood product-refers to a wood product in which the resin is in an uncured form.

100071 The resin-impregnated wood product may have a moisture content of at least 2wt% prior to the heating that cures the resin, optionally at least 3wt%, optionally at least 4wV/0, optionally at least 5w0/0, optionally at least 6wt%, optionally at least 7wt%, optionally at least 8wt%, optionally at least 9wt% and optionally at least I Owt%.

100081 '[he resin-impregnated wood product may have a moisture content of no more than 20wt% prior to the heating that cures the resin, optionally no more than 18wt%, optionally no more than 17wt%, optionally no more than 15wt%, optionally no more than 14wt%, optionally no more than 13wt%, optionally no more than 12wt% and optionally no more than lOwt%.

[0009] The resin-impregnated wood product may have a moisture content of from 2 to 20wt% prior to the heating that cures the resin, optionally of from 5 to 18wt%, optionally of from 7 to I 7wt°/o and optionally of from 9 to I 4w0/0.

[0010] For the avoidance of doubt "moisture content" may be determined using one or more of the oven dry method, the electrical resistance method and the electrical capacitance method. Typically, moisture content may be determined using the oven dry method. The oven dry method is well-known to those skilled in the art, and is described in standards EN 15234, EN 14778 and EN ISO 52180. Essentially, the weight of the wood product is determined pre-drying and post-drying. The moisture content is defined by Equation 1: -6 Content = OTifli td weight of wood -Oven dry v..7eigitt, 0 ue n dry weight Equation I where original weight of wood is the pre-drying weight, and the oven dry weight is the weight after drying. For example, for a piece of 25mm thick board, a 25mm cube of board would be removed from the board and weighed. The cube would not be obtained from an end piece of the board because the end piece of the board is typically drier due to drying through the end grain. Typically, at least 230mm of the end of the board would be removed, and the sample not taken from that end portion of the board. Knotted portions are usually avoided. The cube would be heated to 103±2°C for two hours before being weighed again. This would be repeated until there is no further change in weight, at which point the wooden cube is moisture-free (and "oven dry"). Care is taken to ensure that all of the moisture has been removed from the wood, without destroying any of the wood itself Optionally, moisture content is determined for several samples, those samples having been obtained from pieces of wood located in different places in the chamber in which the wood samples were prepared.

[0011] As mentioned above, moisture content may be determined using electrical resistance or capacitance methods, typically using commercially-available moisture meters. Such moisture meters are typically capable of measuring moisture contents over a given range (for example, 10 to 30%).

[0012] The curing step may comprise heating the resin-impregnated wood product to produce a core temperature of at least 115°C, optionally at least 120°C, optionally at least 125°C, optionally at least 130°C, optionally at least 135°C, optionally at least 140°C, optionally at least 145°C and optionally at least 150°C.

[0013] The curing step may comprise heating the resin-impregnated wood product to produce a core temperature of no more than 200°C, optionally no more than 195°C, optionally no more than 190°C, optionally no more than 185°C, optionally no more than -4 - 180°C, optionally no more than 175°C, optionally no more than 170°C, optionally no more than 165°C and optionally no more than 160°C.

[0014] The curing step may comprise heating theresin-impregnated wood product to produce a core temperature of from 115 to 200°C, optionally of from 120 to 195°C, optionally of from 125 to I90°C, optionally of from 130 to 185°C and optionally of from 135 to 180°C.

[0015] The resin-impregnated wood product may be at the curing temperature for at least 10 minutes, optionally at least 15 minutes and optionally at least 20 minutes.

[0016] The resin-impregnated wood product may be at the curing temperature for no longer than 60 minutes, optionally no more than 45 minutes and optionally no more than 30 minutes. The temperature of the resin-impregnated wood product may be determined using one or more temperature probes and optionally using more than one temperature probe. Typically, a temperature probe is located in a bore made in a piece of the resin-impregnated wood product.

[0017] '[he variable pressure vessel chamber may be in fluid communication with a means for increasing the pressure in the variable pressure vessel chamber. The means for increasing the pressure in the variable pressure vessel chamber may be capable of increasing the pressure in the variable pressure vessel chamber above ambient pressure. Similarly, the variable pressure vessel chamber may be in fluid communication with a means for decreasing the pressure in the variable pressure vessel chamber. The means for decreasing the pressure in the variable pressure vessel chamber may be capable of decreasing the pressure below ambient pressure, such as a vacuum pump.

[0018] The pressure in the variable pressure vessel chamber during curing may be more than I 00kPa, optionally at least I 25kPa, optionally at least 150kPa, optionally at least 175kPa and optionally at least 200kPa.

100191 The pressure in the variable pressure vessel chamber during curing may be no more than 1000kPa, optionally no more than 800kPa, optionally no more than 600kPa, optionally no more than 400kPa and optionally no more than 200kPa.

100201 The pressure in the variable pressure vessel chamber during curing may be 100-800kPa, optionally 125-600kPa and optionally 150-400kPa. -5 -

[0021] The variable pressure vessel chamber may be capable of operating at pressures less than 25kPa, optionally less than 12IcPa, optionally less than 5kPa and optionally less than I kPa. The variable pressure vessel chamber may be capable of operating at pressures of at least 500kPa, optionally at least I 000kPa, optionally at least 5000kPa and optionally at least I 0,000kPa.

[0022] The curing step may take place in a variable pressure vessel comprising a variable pressure chamber for the location of one or more wood products, a heater for heating the contents of the variable pressure vessel chamber and a means for reducing the pressure in the variable pressure vessel chamber.

[0023] The method may comprise a drying step comprising heating the resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin. This drying of the resin-impregnated wood product precedes the curing step.

[0024] For the avoidance of doubt, the drying step does not remove all moisture from the resin-impregnated wood product. "The moisture content of the resin-impregnated wood product is merely reduced by the drying step. For the avoidance of doubt, and unless the context demands otherwise, "dried" indicates that the resin-impregnated wood product has been exposed to the drying step, but has not been exposed to a curing step. As mentioned above, the drying step reduces the moisture content of the resin-impregnated wood product, but does not cure the resin. As mentioned above, "curing" indicates that the resin has been exposed to conditions that harden and/or toughen the resin. Curing typically involves a reaction between components of the resin, optionally to form a polymer, such as a cross-linked polymer. Curing typically involves heating the dried, resin-impregnated wood product to a higher temperature than is used for the drying step. For example, a drying step may comprise heating the resin-impregnated wood product to a temperature of no more than 65°C, whereas a curing step may comprise heating the dried, resin-impregnated wood product to be temperature of about 130-150°C. If the temperature of the wood product is too high during the drying step, then there is a risk that some curing of the resin will occur. This may manifest itself, for example, by -6 -undesirable water retention. It is believed that such curing inhibits proper drying of the wood product, inhibiting egress of water from the wood product.

[0025] Drying may take place at a low pressure. It is preferred that the pressure is maintained at no more than 100kPa while drying takes place. The pressure may optionally be maintained at no more than 100kPa for at least 70% of the duration of the heating of the drying process, optionally for at least 75%, optionally for at least 80%, optionally for at least 85%, optionally for at least 90%, optionally for at least 95%, optionally for at least 97%, optionally for at least 98%, optionally for at least 99% and optionally for at least 99.5% of the duration of said heating.

[0026] The pressure may vary throughout the drying process.

100271 Optionally, the maximum pressure during the drying step may be no more than 95kPa, optionally no more than 90kPa, optionally no more than 85kPa and optionally no more than 80kPa.

[0028] Optionally, the maximum pressure during the drying step may be at least 30kPa, optionally at least 351cPa, optionally at least 40kPa, optionally at least 451cPa and optionally at least 50kPa.

100291 Optionally, the maximum pressure during the drying step may be from 30 to 100kPa, optionally from 35 to 95kPa, optionally from 40 to 90kPa, optionally from 45 to 85kPa and optionally from 50 to 80kPa.

[0030] Optionally, the minimum pressure during the drying step may be no more than 2kPa, optionally no more than 51(Pa, optionally no more than 7kPa, optionally no more than 10kPa, optionally no more than 12kPa, optionally no more than 15kPa, optionally no more than 20kPa, optionally no more than 25kPa and optionally no more than 30kPa. [0031] Optionally, the minimum pressure during the drying step may be at least I kPa, optionally at least 2kPa, optionally at least 5kPa, optionally at least 7kPa, optionally at least 10kPa, optionally at least 12kPa and optionally at least 15kPa.

100321 Optionally, the minimum pressure during the drying step may be from 1 to 30kPa, optionally from 2 to 25kPa, optionally from 3 to 20kPa and optionally from 5 to 15kPa. 100331 Optionally, the mean pressure during the drying step may be no more than 20kPa, optionally no more than 25kPa, optionally no more than 30kPa, optionally no more than 40kPa, optionally no more than 501(Pa, optionally no more than 60kPa, optionally no more than 70kPa, optionally no more than 80kPa and optionally no more than 90kPa.

[0034] Optionally, the mean pressure during the drying step may be at least 5kPa, optionally at least 10kPa, optionally at least 15kPa, optionally at least 20kPa, optionally at least 25kPa, optionally at least 30kPa and optionally at least 35kPa.

[0035] Optionally, the mean pressure during the drying step may be from 5 to 90kPa, optionally from 10 to 80kPa, optionally from 15 to 70kPa and optionally from 20 to 60kPa.

[0036] Optionally, the pressure during the drying step may vary, with local maxima and minima of pressure. In this connection, drying of the resin-impregnated wood product causes the release of water from the wood product, such water forming a gas. This leads to an increase in pressure. The gaseous water may then be removed (for example, using a vacuum pump), thereby causing a decrease in pressure, with the pressure being reduced until a desired pressure is reached. Once the desired pressure is reached, the vacuum pump is turned off. the pressure will then typically increase as more water evaporates from the wood product. Pressure may then be reduced once again by once again removing the gaseous water.

[0037] Typically, it is easier to remove water from the resin-impregnated wood product if the water content of the resin-impregnated wood product is higher (for example, at the start of the drying process). In this case, the time period over which the pressure is allowed to rise before being reduced may be smaller than when the water content of the resin-impregnated wood product is lower (for example, later in the drying process). Therefore, the time between a local minimum in pressure and an adjacent local maximum in pressure may be smaller earlier in the drying process. There may be, therefore, a first local maximum in pressure and an adjacent, first local maximum in pressure, and a second local maximum in pressure and an adjacent, second local maximum in pressure, said first local maximum occurring earlier in the drying process than the second local maximum, wherein the time difference between the first local maximum and the first local minimum is less than the time difference between the second local maximum and the second local minimum. The difference in pressure between the first local maximum -8 -and the first local minimum may be less than the difference in pressure between the second local maximum and the second local minimum. For the avoidance of doubt, reference to "first" does not mean that the local maximum is the first such maximum in pressure that is observed during the drying process. Similarly, reference to "second" does not mean that the local maximum is the second such maximum in pressure that is observed during the drying process. In this connection, the words "first" and "second" are merely used as identifiers.

100381 There may be, therefore, a first set of local minima and maxima in pressure, and a second set of local minima and maxima in pressure, the first set being earlier in the drying process than the second set. The mean time difference between a local maximum in the first set and an adjacent local minimum may be less than the mean time difference between a local maximum in the second set and an adjacent local minimum. In this connection, earlier in the drying process, the method may comprise increasing and reducing the pressure at shorter time intervals than later in the drying process. The difference in pressure between a local maximum in the first set and an adjacent local minimum may be smaller than the difference in pressure between a local maximum in the second set and an adjacent local minimum. The mean difference in pressure between the local maxima in the first set and the associated adjacent local minima may be smaller than the mean difference in pressure between the local maxima in the second set and the associated adjacent local minima.

[0039] The moisture-reduced resin-impregnated wood product may have a moisture content of at least 2wt%, optionally at least 3 wt%, optionally at least 4wt%, optionally at least 5wt%, optionally at least 6wt%, optionally at least 7we/o, optionally at least 8wt%, optionally at least 9wt% and optionally at least I Owt%.

[0040] The moisture-reduced resin-impregnated wood product may have a moisture content of no more than 20wt%, optionally no more than 18wt%, optionally no more than 17wt%, optionally no more than 15wt%, optionally no more than 13wt%, optionally no more than 12wt%, optionally no more than lOwt% and optionally no more than 9wt%. -9 -

[0041] The moisture-reduced resin-impregnated wood product may have a moisture content of 2-20wt%, optionally 3-18w0/0, optionally 5-15wt%, optionally 8-12wt% and optionally 10-12wt%.

[0042] The temperature of the core of the wood product may be controlled during the drying process, for example, using a feedback loop based on temperature measurements. As mentioned above, a temperature probe may be located in or on a piece of the wood product. For example, a temperature probe may be located in a bore formed in a piece of the wood product. Alternatively, a relatively constant amount of thermal energy may be applied to the wood product and its environs during the drying process. In such a case, the temperature of the core of the wood product is determined, inter alia, by the physics of the evaporation process and the pressure. For example, evaporation of water is associated with a decrease in temperature because energy is used in evaporating the water, as opposed to heating the wood product. Such evaporation is also associated with an increase in pressure. Reducing the pressure (for example, using a vacuum pump) may be associated with an increase in temperature of the core of the wood product. Once the reduction in pressure is stopped, evaporation of water recommences, causing a decrease in temperature and an increase in pressure. While this explanation is over-simplified, it goes someway to explain why the temperature may have local minima and maxima.

[0043] The diving step may comprise heating the resin-impregnated wood product to produce a maximum core temperature of at least 40°C, optionally at least 45°C, optionally at least 50°C, optionally at least 55°C and optionally at least 60°C.

[0044] The drying step may comprise heating the resin-impregnated wood product to produce a maximum core temperature of no more than 95°C, optionally no more than 90°C, optionally no more than 85°C, optionally no more than 80°C, optionally no more than 75°C, optionally no more than 70°C and optionally no more than 65°C.

100451 The drying step may comprise heating the resin-impregnated wood product to produce a maximum core temperature of from 40 to 95°C, optionally of from 50 to 85°C and optionally of from 60 to 70°C.

-10 - [0046] The diving step may comprise heating the resin-impregnated wood product to produce a minimum core temperature of at least 20°C, optionally at least 25°C and optionally at least 30°C.

[0047] The diving step may comprise heating the resin-impregnated wood product to produce a minimum core temperature of no more than 60°C, optionally no more than 50°C, optionally no more than 45°C, optionally no more than 40°C, optionally no more than 35°C and optionally no more than 30°C.

100481 The drying step may comprise heating theresin-impregnated wood product to produce a minimum core temperature of from 20 to 50°C, and optionally of from 25 to 40°C.

100491 The drying step may comprise heating the resin-impregnated wood product to produce a mean core temperature of at least 30°C, optionally at least 35°C, optionally at least 40°C, optionally at least 45°C and optionally at least 50°C.

[0050] The drying step may comprise heating the resin-impregnated wood product to produce a mean core temperature of no more than 70°C, optionally no more than 65°C, optionally no more than 60°C, optionally no more than 55°C, optionally no more than 50°C and optionally no more than 45°C.

[0051] The diving step may comprise heating the resin-impregnated wood product to produce a mean core temperature of from 30 to 70°C, optionally of from 40 to 60°C and optionally of from 50 to 60°C.

[0052] As mentioned above, the temperature may have local maxima and minima. The time between a local minimum in temperature and an adjacent local maximum in temperature may be smaller earlier in the drying process. There may be, therefore, a first local maximum in temperature and an adjacent, first local maximum in temperature, and a second local maximum in temperature and an adjacent, second local maximum in temperature, said first local maximum occurring earlier in the drying process than the second local maximum, wherein the time difference between the first local maximum and the first local minimum is less than the time difference between the second local maximum and the second local minimum. The difference in temperature between the first local maximum and the first local minimum may be less than the difference in temperature between the second local maximum and the second local minimum. For the avoidance of doubt, reference to "first" does not mean that the local maximum is the first such maximum in temperature to be observed during the drying process. Similarly, reference to "second" does not mean that the local maximum is the second such maximum in temperature to be observed during the drying process. In this connection, the words "first" and "second" are merely used as identifiers.

[0053] There may be, therefore, a first set of local minima and maxima in temperature, and a second set of local minima and maxima in temperature, the first set being earlier in the drying process than the second set. The mean time difference between a local maximum in the first set and an adjacent local minimum may be less than the mean time difference between a local maximum in the second set and an adjacent local minimum. The difference in temperature between a local maximum in the first set and an adjacent local minimum may be smaller than the difference in temperature between a local maximum in the second set and an adjacent local minimum. The mean difference in temperature between the local maxima in the first set and the associated adjacent local minima may be smaller than the mean difference in temperature between the local maxima in the second set and the associated adjacent local minima.

[0054] The duration of the drying process will depend, for example, on the size and shape of the wood product, the number of pieces of wood product being dried, the drying temperature and the desired moisture content of the dried wood product.

[0055] Drying may take placed in the variable pressure vessel chamber capable of operating at pressures less than 50kPa and capable of operating at pressures of at least 200kPa i.e. in the same chamber used to cure the resin.

[0056] According to a second aspect of the present invention, there is provided a method of making a modified wood product, the method comprising a drying step comprising heating a resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, at a pressure of no more than 100kPa.

100571 The applicant has discovered that heating the resin-impregnated wood product at low pressure so as to reduce the moisture content of the resin-impregnated wood product -12 - (i.e., drying the resin-impregnated wood product) is beneficial in that the drying process may be relatively quick compared to the traditional kiln drying processes, and there may be relatively few samples discarded.

[0058] As mentioned above, this drying process takes place at a low pressure. It is preferred that the pressure is maintained at no more than 100kPa while drying takes place. The pressure may optionally be maintained at no more than 100kPa for at least 70% of the duration of the heating of the drying process, optionally for at least 75%, optionally for at least 80%, optionally for at least 85%, optionally for at least 90%, optionally for at least 95%, optionally for at least 97%, optionally for at least 98%, optionally for at least 99% and optionally for at least 99.5% of the duration of said heating.

100591 The pressure may vary throughout the drying process.

[0060] Optionally, the maximum pressure during the drying step may be no more than 95kPa, optionally no more than 90kPa, optionally no more than 85kPa and optionally no more than 80kPa.

[0061] Optionally, the maximum pressure during the drying step may be at least 30kPa, optionally at least 35kPa, optionally at least 40kPa, optionally at least 45kPa and optionally at least 50kPa.

[0062] Optionally, the maximum pressure during the drying step may be from 30 to 100kPa, optionally from 35 to 95kPa, optionally from 40 to 90kPa, optionally from 45 to 85kPa and optionally from 50 to 80kPa.

[0063] Optionally, the minimum pressure during the drying step may be no more than 2kPa, optionally no more than 5kPa, optionally no more than 7kPa, optionally no more than I OkPa, optionally no more than I 2kPa, optionally no more than I 5kPa, optionally no more than 20kPa, optionally no more than 25kPa and optionally no more than 30kPa. 100641 Optionally, the minimum pressure during the drying step may be at least 11(Pa, optionally at least 2kPa, optionally at least 5kPa, optionally at least 7kPa, optionally at least 10kPa, optionally at least 12kPa and optionally at least 15kPa.

100651 Optionally, the minimum pressure during the drying step may be from 1 to 30kPa, optionally from 2 to 251(Pa, optionally from 3 to 20kPa and optionally from 5 to 15kPa.

-13 - [0066] Optionally, the mean pressure during the drying step may be no more than 20kPa, optionally no more than 25kPa, optionally no more than 30kPa, optionally no more than 40kPa, optionally no more than 501(Pa, optionally no more than 60kPa, optionally no more than 70kPa, optionally no more than 80kPa and optionally no more than 90kPa.

[0067] Optionally, the mean pressure during the drying step may be at least 5kPa, optionally at least 10kPa, optionally at least 15kPa, optionally at least 20kPa, optionally at least 25kPa, optionally at least 30kPa and optionally at least 35kPa.

100681 Optionally, the mean pressure during the drying step may be from 5 to 90kPa, optionally from 10 to 80kPa, optionally from 15 to 70kPa and optionally from 20 to 60kPa.

100691 Optionally, the pressure during the drying step may vary, with local maxima and minima. In this connection, drying heating of the resin-impregnated wood product causes the release of water from the wood product, such water forming a gas. This leads to an increase in pressure. The gaseous water may then be removed (for example, using a vacuum pump), causing a decrease in pressure, with the pressure being reduced until a desired pressure is reached. Once the desired pressure is reached, the vacuum pump may be turned off The pressure will then typically increase as more water evaporates from the wood product. The pressure may then be reduced once again by once again removing the gaseous water.

[0070] Typically, it is easier to remove water from the resin-impregnated wood product if the water content of the resin-impregnated wood product is higher (for example, at the start of the drying process). In this case, the time period over which the pressure is allowed to rise before being reduced may be smaller than when the water content of the resin-impregnated wood product is lower (for example, late in the drying process). Therefore, the time between a local minimum in pressure and an adjacent local maximum in pressure may be smaller earlier in the drying process. There may be, therefore, a first local maximum in pressure and an adjacent, first local maximum in pressure, and a second local maximum in pressure and an adjacent, second local maximum in pressure, said first local maximum occurring earlier in the drying process than the second local maximum, wherein the time difference between the first local maximum and the first -14 -local minimum is less than the time difference between the second local maximum and the second local minimum. The difference in pressure between the first local maximum and the first local minimum may be less than the difference in pressure between the second local maximum and the second local minimum. For the avoidance of doubt, reference to "first-does not mean that the local maximum is the first such maximum in pressure that is observed during the drying process. Similarly, reference to "second" does not mean that the local maximum is the second such maximum in pressure that is observed during the drying process. In this connection, the words "first" and "second" are merely used as identifiers.

[0071] There may be, therefore, a first set of local minima and maxima in pressure, and a second set of local minima and maxima in pressure, the first set being earlier in the drying process than the second set. The mean time difference between a local maximum in the first set and an adjacent local minimum may be less than the mean time difference between a local maximum in the second set and an adjacent local minimum. In this connection, earlier in the drying process, the method may comprise increasing and reducing the pressure at shorter time intervals than later in the drying process. The difference in pressure between a local maximum in the first set and an adjacent local minimum may be smaller than the difference in pressure between a local maximum in the second set and an adjacent local minimum. The mean difference in pressure between the local maxima in the first set and the associated adjacent local minima may be smaller than the mean difference in pressure between the local maxima in the second set and the associated adjacent local minima.

[0072] The moisture-reduced resin-impregnated wood product may have a moisture content of at least 2wt%, optionally at least 3wt%, optionally at least 4wt%, optionally at least 5wt%, optionally at least 6wt%, optionally at least 7wt%, optionally at least 8wt%, optionally at least 9wt% and optionally at least lOwt%.

100731 The moisture-reduced resin-impregnated wood product may have a moisture content of no more than 20wt%, optionally no more than 18wt%, optionally no more than 17wt%, optionally no more than 15wt%, optionally no more than 13wt%, optionally no more than 12wt%, optionally no more than 1Owt% and optionally no more than 9wt%.

-15 - [0074] The moisture-reduced resin-impregnated wood product may have a moisture content of 2-20wt%, optionally 3-18wt%, optionally 54 5wt%, optionally 8-12wt% and optionally 9-10wt%.

[0075] The temperature of the core of the wood product may be controlled during the drying process, for example, using a feedback loop based on temperature measurements, for example, using a temperature probe as discussed above. Alternatively, a relatively constant amount of thermal energy may be applied to the wood product and its environs during the drying process. In such a case, the temperature of the core of the wood product is determined, inter al/a, by the physics of the evaporation process and the pressure. For example, evaporation of water is associated with a decrease in temperature because energy is used in evaporating the water, as opposed to heating the wood product. Such evaporation is also associated with an increase in pressure. Reducing the pressure (for example, using a vacuum pump) may be associated with an increase in temperature of the core of the wood product. Once the reduction in pressure is stopped, evaporation of water recommences, causing a decrease in temperature and an increase in pressure. While this explanation is over-simplified, it goes someway to explain why the temperature may have local minima and maxima.

[0076] The diving step may comprise heating the resin-impregnated wood product to produce a maximum core temperature of at least 40°C, optionally at least 45°C, optionally at least 50°C, optionally at least 55°C and optionally at least 60°C.

[0077] The diving step may comprise heating the resin-impregnated wood product to produce a maximum core temperature of no more than 95°C, optionally no more than 90°C, optionally no more than 85°C, optionally no more than 80°C, optionally no more than 75°C, optionally no more than 70°C and optionally no more than 65°C.

[0078] The drying step may comprise heating the resin-impregnated wood product to produce a maximum core temperature of from 40 to 95°C, optionally of from 50 to 85°C and optionally of from 60 to 70°C.

[0079] The diving step may comprise heating the resin-impregnated wood product to produce a minimum core temperature of at least 20°C, optionally at least 25°C and optionally at least 30°C.

-16 - [0080] The diving step may comprise heating the resin-impregnated wood product to produce a minimum core temperature of no more than 60°C, optionally no more than 50°C, optionally no more than 45°C, optionally no more than 40°C, optionally no more than 35°C and optionally no more than 30°C.

[0081] The drying step may comprise heating the resin-impregnated wood product to produce a minimum core temperature of from 20 to 50°C, and optionally of from 25 to 40°C.

100821 The drying step may comprise heating the resin-impregnated wood product to produce a mean core temperature of at least 30°C, optionally at least 35°C, optionally at least 40°C, optionally at least 45°C and optionally at least 50°C.

100831 The drying step may comprise heating the resin-impregnated wood product to produce a mean core temperature of no more than 70°C, optionally no more than 65°C, optionally no more than 60°C, optionally no more than 55°C, optionally no more than 50°C and optionally no more than 45°C.

[0084] '[he diving step may comprise heating the resin-impregnated wood product to produce a mean core temperature of from 30 to 70°C, optionally of from 40 to 60°C and optionally of from 50 to 60°C.

[0085] As mentioned above, the temperature may have local maxima and minima, The time between a local minimum in temperature and an adjacent local maximum in temperature may be smaller earlier in the drying process. There may be, therefore, a first local maximum in temperature and an adjacent, first local maximum in temperature, and a second local maximum in temperature and an adjacent, second local maximum in temperature, said first local maximum occurring earlier in the drying process than the second local maximum, wherein the time difference between the first local maximum and the first local minimum is less than the time difference between the second local maximum and the second local minimum. The difference in temperature between the first local maximum and the first local minimum may be less than the difference in temperature between the second local maximum and the second local minimum. For the avoidance of doubt, reference to "first" does not mean that the local maximum is the first such maximum in temperature observed during the drying process. Similarly, reference to -17 - "second" does not mean that the local maximum is the second such maximum in temperature observed during the drying process. In this connection, the words "first" and "second" are merely used as identifiers.

[0086] There may be, therefore, a first set of local minima and maxima in temperature, and a second set of local minima and maxima in temperature, the first set being earlier in the drying process than the second set. The mean time difference between a local maximum in the first set and an adjacent local minimum may be less than the mean time difference between a local maximum in the second set and an adjacent local minimum. The difference in temperature between a local maximum in the first set and an adjacent local minimum may be lower than the difference in temperature between a local maximum in the second set and an adjacent local minimum. The mean difference in temperature between the local maxima in the first set and the associated adjacent local minima may be lower than the mean difference in temperature between the local maxima in the second set and the associated adjacent local minima.

[0087] "[he method of the second aspect of the present invention may comprise a curing step comprising heating the dried resin-impregnated wood product, thereby curing the resin. The curing step may comprise the features described above in relation to the method of the first aspect of the present invention.

[0088] The curing step may comprise heating the resin-impregnated wood product to produce a core temperature of at least 115°C, optionally at least 120°C, optionally at least 125°C, optionally at least 130°C, optionally at least 135°C, optionally at least 140°C, optionally at least 145°C and optionally at least 150°C.

[0089] The curing step may comprise heating the resin-impregnated wood product to produce a core temperature of no more than 200°C, optionally no more than I95°C, optionally no more than 190°C, optionally no more than 185°C, optionally no more than 180°C, optionally no more than 175°C, optionally no more than 170°C, optionally no more than 165°C and optionally no more than 160°C.

[0090] The curing step may comprise heating theresin-impregnated wood product to produce a core temperature of from 115 to 200°C, optionally of from 120 to 195°C, -18 -optionally of from 125 to 190°C, optionally of from 130 to 185°C and optionally of from 135 to 180°C.

[0091] Drying (and optionally curing) may take place in a variable pressure vessel chamber for the location of one or more wood products. The variable pressure vessel chamber may have the features described above in relation to the method of the first aspect of the present invention. The variable pressure vessel chamber may be part of a variable pressure vessel, which variable pressure vessel comprises the variable pressure vessel chamber, optionally a heater for heating the contents of the variable pressure vessel chamber, optionally a means for reducing the pressure in the variable pressure vessel chamber and optionally a means for increasing the pressure in the variable pressure vessel chamber. Drying may take place in a variable pressure vessel chamber capable of operating at pressures less than 501(Pa and capable of operating at pressures of at least 200kPa. Curing may also take place in the same variable pressure vessel chamber.

[0092] According to a third aspect of the present invention, there is provided a method of making a modified wood product, the method comprising a drying step comprising heating a resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, in a variable pressure vessel chamber capable of operating at pressures less than 50kPa and capable of operating at pressures of at least 200kPa.

[0093] The method of the third aspect of the present invention facilitates the drying and curing of a resin-impregnated wood product in the same heating unit chamber.

[0094] The method of the third aspect of the present invention may comprise one or more of the features of the method of the second aspect of the present invention.

[0095] The drying step may comprise heating the resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, at a pressure of no more than 100kPa.

100961 The method may comprise reducing the pressure in the variable pressure vessel prior to and/or during the drying step. The applicant has discovered that it is beneficial for at least part of the drying step to take place at a pressure less than ambient pressure.

-19 - [0097] The method of the third aspect of the present invention may comprise a curing step comprising heating the dried resin-impregnated wood product so as to cure the resin. Heating of the dried resin-impregnated wood product so as to cure the resin may take place in the variable pressure vessel chamber capable of operating at pressures less than 50kPa and capable of operating at pressures of at least 200kPa. The curing step may comprise one or more of the features described in relation to the methods of the first and/or second aspects of the present invention.

100981 For the avoidance of doubt, the statements below pertain to the methods of the first, second and third aspects of the present invention.

[0099] The method may comprise providing a source wood product. The source wood product is permeable to liquids. The source wood product may have Class 1 treatability (formerly classed as "permeable") in accordance with EN350:2016 ("Durability of wood and wood-based products -Testing and classification of the durability to biological agents of wood and wood-based materials"). Such a treatability may facilitate penetration of resin into the source wood product.

[00100] The source wood product may comprise a softwood or a hardwood. The source wood product may comprise one or more of Monterey Pine (Pinus radiata), Western Hemlock (Tsuga heterophylla), Eastern White Pine Tree (Pin 1ff strobus), Sugar Pine Tree (Pinus lambertictna), Red Pine Tree (Pinus resinosa), Gray Pine Tree (Pinus sabiniana), Pitch Pine Tree (Pinus rigida), Jack Pine Tree (Pinus banksiana), Scots Pine (Pinus sylvestris), Longleaf Pine (Pinto' pahtstris), Shortleaf Pine (Pinus echinatct), Loblolly pine (Pinus taeda), Slash pine (Pintts Virginia pine (Pinta virginiana), Lodgepole pine (Pilaus contorta), Common Beech (Fagus sylvatica) and Tulipwood sapwood (Tiriodendron ittlipifera). Monterey Pine, Western Hemlock, Loblolly Pine, Slash Pine and Common Beech are preferred from the viewpoint of excellent take-up of impregnating resin.

1001011 The source wood product need not comprise a contiguous piece of wood.

For example, the source wood product may comprise particulate. For example, the source wood product may comprise particulate formed into a source wood product.

-20 - [00102] The source wood product may be substantially devoid of knots, for

example.

[00103] The source wood product may be generally rectilinear in shape. The source wood product may be in the form of one more timber. The source wood product may have a length of from 1000 to 3000mm. The source wood product may have a width of from 30 to 600mm. The source wood product may have a thickness of from 15 to 150mm Typically, a plurality of source wood products may be treated at any one time.

1001041 The method may optionally comprise reducing the moisture content of a source wood product. Such reducing the moisture content of a source wood product optionally takes place prior to impregnating a source wood product with resin to form a resin-impregnated source wood product. Whether or not it is desirable to reduce the moisture content of a source wood product depends on the original moisture of the source wood product and the desired moisture content.

[00105] This drying of the source wood product may take place at elevated temperature and/or reduced pressure, -elevated" and -reduced" being determined raised relative to ambient conditions.

1001061 This drying of the source wood product may take place in a variable pressure vessel comprising a variable pressure vessel chamber for the location of one or more wood products, optionally a heater for heating the contents of the chamber optionally and a means for reducing the pressure in the variable pressure vessel chamber.

[00107] The moisture content of the dried source wood product may be at least 5wV/0, optionally at least 7wt%, optionally at least 9wt%, optionally at least Ilwt%, optionally at least 13wt% and optionally at least 15wt%.

[00108] The moisture content of the dried source wood product may be no more than 25wt%, optionally no more than 23wt%, optionally no more than 2Iwt%, optionally no more than 19wt%, optionally no more than 18wt%, optionally no more than 17wt%, optionally no more than 15wt% and optionally no more than 13wt%.

[00109] The moisture content of the dried source wood product may be from 5 to 25wt%, optionally from 7 to 21wt% and optionally from 11 to 19wt%.

-21 - [00110] The method may comprise impregnating the source wood product with a resin to provide a resin-impregnated wood product [00111] The resin may comprise an aqueous resin (i.e. a resin comprising water).

[00112] The resin may comprise a two-part resin i.e. a resin comprising two components or moieties that react when the resin is cured, optionally to form a polymer, optionally to form a water-insoluble polymer, optionally to form a cross-linked polymer.

[00113] The resin may comprise phenol. The resin may comprise formaldehyde or other reagent capable or reacting with phenol to form a molecule comprising multiple hydroxyl groups. The resin may comprise a diamine, such as urea.

[00114] The method may comprise an impregnation step comprising impregnating the source wood product with a resin composition. The resin composition may, for example, comprise a solution and/or suspension of a resin.

[00115] The resin content of the resin composition may optionally be at least 10%wt/vol., optionally at least 15%wt../vol., optionally at least 20%wt./vol., optionally at least 25%wt./vol, and optionally at least 25%wtivol.

[00116] The resin content of the resin composition may optionally be no more than 60%wtivol., optionally no more than 55%wt./vol., optionally no more than 50%wtivol., optionally no more than 48%wtivol., optionally no more than 45%wtivol. and optionally no more than 40%wtivol..

[00117] The resin content of the resin composition may be from 10 to 60%wtivol., optionally from 15 to 55%wt./vol., optionally from 20 to 50%wtivol., optionally from 25 to 50%wtivol. and optionally from 25 to 48%wtivol..

[00118] The method may optionally comprise adjusting the resin content of a resin precursor composition to form the resin composition. For example, the method may comprise diluting the resin precursor composition to form the resin composition.

1001191 The impregnation step may comprise heating the source wood product to elevated temperature, optionally at elevated pressure, "elevated" meaning higher than ambient. The impregnation step may comprise contacting the source wood product with, or immersing the source wood product in, a resin composition. The method may comprise applying an elevated pressure to the resin composition while the source wood product is -22 -in contact with, or immersed in, the resin composition. The elevated pressure may optionally be at least 5001cPa, optionally at least 600kPa, optionally at least 700kPa, optionally at least 800kPa, optionally at least 900IcPa and optionally at least 1000kPa.

[00120] The method may comprise subsequently reducing the pressure to remove excess resin composition.

[00121] The impregnation step may take place in an impregnation unit for impregnating a source wood product with a resin, the impregnation unit comprising an impregnation chamber for the location of a source wood product, optionally a means for increasing the pressure in the impregnation chamber, and optionally a heater for heating the contents of the impregnation chamber. The impregnation unite may comprise an autoclave.

1001221 The durat on of the impregnation step may be at least 1 hour, optionally at least 2 hours, optionally at least 3 hours, optionally at least 5 hours, optionally at least 8 hours, optionally at least 10 hours, optionally at least 12 hours, optionally at least 14 hours, optionally at least 16 hours, optionally at least 18 hours and optionally at least 20 hours.

1001231 The duration of the impregnation step may be no more than 60 hours, optionally no more than 55 hours, optionally no more than 50 hours, optionally no more than 45 hours, optionally no more than 40 hours, optionally no more than 35 hours and optionally no more than 30 hours, optionally no more than 25 hours, optionally no more than 20 hours, and optionally no more than 15 hours.

[00124] The duration of the impregnation step may be from I to 60 hours, optionally from 2 to 30 hours, optionally from 2 to 25 hours, and optionally from 3 to 20 hours.

1001251 The duration of the impregnation step may depend on the thickness of the wood to be impregnated. For example, the duration of the impregnation step for wood having a thickness of 12mm-18mm may be 3-4 hours). A duration of 4-6 hours may be used for wood of 25-32mm thickness. Wood having a thickness of 38-42mm may have an impregnation step of 5-6 hours duration. For wood of 50-75mm thickness, a 6-8 hour impregnation step may be used. A 7-9 hour impregnation step may be used for wood of -23 - 80-100mm thickness. An impregnation step of 10-18 hours may be used for wood having a thickness of 100-150mm.

[00126] The method may comprise a storage step comprising storing resin-impregnated wood product, optionally in conditions in which the moisture content of the resin-impregnated product is not significantly changed. Such storing permits a more even distribution of the resin throughout the wood product. Such a storage step is often referred to in the art as "diffusion" because it allows the resin to diffuse throughout the wood product. Such a storage step may also be referred to in the art as "drip drying", although typically no significant drying of the resin-impregnated takes place. The storage step optionally takes place before drying of the resin-impregnated wood product.

1001271 Storing may optionally take place for at least 10 hours, optionally at least 14 hours, optionally at least 18 hours, optionally at least 22 hours, optionally at least 24 hours and optionally at least 26 hours.

[00128] Storing may optionally take place for no more than 48 hours, optionally no more than 44 hours, optionally no more than 40 hours, optionally no more than 36 hours, optionally no more than 32 hours, optionally no more than 28 hours and optionally no more than 24 hours.

[00129] Storing may optionally take from 10 to 48 hours, optionally from 18 to 40 hours and from 22 to 32 hours.

[00130] Storing may take place at a temperature of at least 5°C, optionally at least 10°C and optionally at least 15°C.

[00131] Storing may take place at a temperature of no more than 30°C, optionally no more than 25°C and optionally no more than 20°C.

[00132] The method may comprise more than one impregnation step. For example, the method may comprise a first impregnation step comprising impregnating the source wood product with a resin to provide a resin-impregnated wood product, storing resin-impregnated wood product, optionally in conditions in which the moisture content of the resin-impregnated product is not significantly changed, and a second impregnation step comprising impregnating the resin-impregnated wood product with more resin.

-24 - [00133] The method may optionally comprise a pre-drying step after the impregnation step and before the drying step, optionally at a pressure of no more than 100kPa, to produce a moisture-reduced resin-impregnated wood product. The pre-drying step may comprise heating the resin-impregnated wood product, optionally at ambient pressure, to a temperature of at least 30°C, optionally at least 35°C, optionally at least 40°C, optionally at least 45°C and optionally at least 50°C. Pre-drying may comprise heating the resin-impregnated wood product at ambient pressure to a temperature of no more than 80°C, optionally no more than 70°C, optionally no more than 60°C and optionally no more than 50°C. Pre-drying may comprise heating the resin-impregnated wood product at ambient pressure to a temperature of 30-70°C, optionally 40-60°C and optionally 50-60°C.

1001341 If the method comprises a storage step or diffusion", the pre-drying step may take place before or after the storage step.

[00135] The moisture content of the resin-impregnated wood product before the drying step may optionally be at least 40%, optionally at least 45%, optionally at least 50%, optionally at least 55%, optionally at least 60%, optionally at least 65%, optionally at least 70% and optionally at least 75%.

[00136] The moisture content of the resin-impregnated wood product before the drying step may optionally be no more than 95%, optionally no more than 90%, optionally no more than 85%, optionally no more than 80%, optionally no more than 75%, optionally no more than 70% and optionally no more than 65%.

[00137] The moisture content of the resin-impregnated wood product before the drying step may optionally be 50-90%, optionally 60-90%, optionally 70-90%, optionally 80-90% and optionally 60-70%. Pre-drying has been found to reduce the moisture content of resin-impregnated wood product after it has been dried, optionally to 60-70%. In the absence of pre-drying, the moisture content of the resin-impregnated wood product may, for example, be 80-90%.

[00138] The method may optionally comprise a conditioning step comprising conditioning the cured, resin-impregnated wood product, optionally by contacting the cured, resin-impregnated wood product with steam at an elevated temperature. The -25 -elevated temperature may be at least 80°C, optionally at least 90°C, optionally at least 100°C and optionally at least 110°C. The elevated temperature may be no more than 150°C, optionally no more than 140°C, optionally no more than 130°C and optionally no more than 120°C. The elevated temperature may be 80-150°C, optionally 90-140°C, optionally 100-130°C and optionally I10-120°C. The steam may be contacted with the cured, resin-impregnated wood product at a pressure of no more than 350kPa, optionally no more than 300kPa, optionally no more than 250kPa and optionally no more than 200kPa. The steam may be contacted with the cured, resin-impregnated wood product at a pressure of at least 50kPa, optionally at least I 00kPa and optionally at least I 50kPa.

[00139] The drying and curing steps may optionally take place in a variable pressure vessel comprising a variable pressure vessel chamber for the location of one or more wood products, optionally a heater for heating the contents of the chamber and optionally a means for reducing the pressure in the variable pressure vessel chamber. The variable pressure vessel may be capable of producing elevated pressure (more than ambient pressure) in the variable pressure vessel chamber. 'This has the advantage that the drying and curing of the resin-impregnated wood product may take place in the same chamber.

[00140] The method of the first and second aspects of the present invention may therefore comprise: optionally reducing the moisture content of a sourcewood; impregnating the source wood with a resin to produce a resin-impregnated wood produce; optionally storing the resin-impregnated wood product; heating the resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, optionally at a pressure of no more than 100kPa, to produce a moisture-reduced resin-impregnated wood product; and heating the moisture-reduced es n-mpregnated wood product, thereby curing the resin.

-26 - [00141] The method may optionally comprise conditioning the cured, resin-impregnated wood product, optionally by contacting the cured, resin-impregnated wood product with steam at an elevated temperature. Conditioning may comprise those features described above.

[00142] The method may optionally comprise pre-drying the resin-impregnated wood product, after (i) impregnating the source wood with a resin to produce a resin-impregnated wood produce, and before (ii) heating the resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, optionally at a pressure of no more than 100kPa, to produce a moisture-reduced resin-impregnated wood product. Pre-drying may comprise those features described above.

1001431 According to a fourth aspect of the present invention, there is provided an apparatus for making a modified wood product, the apparatus comprising: an impregnation unit for impregnating a source wood product with a resin, the impregnation unit comprising an impregnation chamber for the location of a source wood product, and a means for increasing the pressure in the impregnation chamber; and a variable pressure vessel comprising a variable pressure vessel chamber for the location of one or more wood products, a heater for heating the contents of the chamber and a means for reducing the pressure in the variable pressure vessel chamber.

1001441 The apparatus may comprise one or more of the features described above in relation to the methods of the first, second and third aspects of the present invention.

1001451 According to a fifth aspect of the present invention, there is provided a modified wood product, the modified wood product comprising a resin, having a density of from 650kgm-3 to 750kgm-3, having a moisture content of no more than 11% and being fire-retardant in accordance with ASTM E84-20 Class A 30 minutes.

[00146] The modified wood product may be durable. The modified wood product may show durability to Class 1 when tested to standard EN113, using the American Wood Protection Association El0 method.

-27 - [00147] The modified woof product may be resistant to attack by subterranean termites. For example, the modified wood product may pass the American Wood Protection Association El -17 test.

[00148] The modified wood product may exhibit a pH of 7.0-8.5 in a pH test.

[00149] The modified wood product may pass an emissions test, for example, BSEN120 or HS1460.

[00150] The modified wood product may optionally pass a slip resistance test, such as BS7976-2.

[00151] The modified wood product may have a hardness (as determined by BS373) of at least 4000N (radially) and/or at least 4000N (tangentially), optionally at least 4500N (radially) and/or at least 4500N (tangentially), and optionally at least 5000N (radially) and/or at least 5000N (tangentially).

[00152] The modified wood product may have a strength and/or a stiffness as determined by ASTM 143 of 80-150% of that of teak.

[00153] The modified wood product may have a high dimensional stability, demonstrating a low shrinkage (no more than 3%) when assessed in accordance with the 1982 BRE Technical Note. Shrinkage is measured in tangential and radial directions when wood conditioned at 90% relative humidity and 25°C is re-conditioned to 60% relative humidity and 25°C. Total shrinkage is calculated by adding radial and longitudinal shrinkages. Total shrinkage is optionally no more than 3%, optionally no more than 2.5% and optionally no more than 2.0%.

[00154] The modulus of rupture of the modified wood product is optionally 80- 120%, and optionally 90-110% of the modulus of rupture of the source wood product.

[00155] The modulus of elasticity of the modified wood product is optionally I 00- 150%, and optionally I 10-I 30% of the modulus of elasticity of the source wood product.

1001561 The hardness of the modified wood product is optionally 120-180% of that of the source wood product.

[00157] The modified wood product may be classed as very durable (DC1) to attack by basidiomycete fungi.

-28 - [00158] The durability of the modified wood product to soft rot fungi may be comparable to teak, for example, may be 80-120% of the durability of teak.

[00159] The modified wood product may comprise residue of a source wood product having the properties described above in relation to the methods of the first, second and third aspects of the present invention. The modified wood product of the fifth aspect of the present invention may be makeable, or made, by a method in accordance with the method of the first, second and/or third aspect of the present invention.

1001601 According to a sixth aspect of the present invention, there is provided a plurality of modified wood products, the plurality of modified wood products comprising a first set of satisfactory modified wood products and a second set of unsatisfactory modified wood products, the number of the satisfactory modified wood products in the first set being at least ten times the number of unsatisfactory modified wood products in the second set.

[00161] The applicant has discovered that it is possible to use the methods of the first, second and third aspects of the present invention to make modified wood products in a far more reproducible manner.

1001621 The plurality of modified wood products are optionally made using the method of the first, second and/or third aspects of the present invention.

[00163] Whether or not a product is satisfactory or unsatisfactory may be determined by one of more of the following tests: moisture content as determined by oven dry method of no more than 11%, anti-shrinking efficiency of +30%, acceptable warp, acceptable number of resin pockets and acceptable number of knots. The number of the satisfactory modified wood products in the first set is optionally at least twelve times the number of unsatisfactory wood products in the second set, optionally at least fourteen times, optionally at least sixteen times, optionally at least eighteen times and optionally at least twenty times the number of unsatisfactory wood products in the second set.

1001641 It will, of course, be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

-29 -

DESCRIPTION OF THE DRAWINGS

[00165] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: 1001661 Figure 1 shows a schematic representation of a method of making a modified wood product according to a first embodiment of the invention; [00167] Figure 2 shows the variation of pressure and temperature with time inside a vacuum heating apparatus during the drying step of the method shown in Figure 1; 1001681 Figure 3 shows a schematic representation of a vacuum heating apparatus that is used to perform the drying and curing steps of the method shown in Figure 1; [00169] Figure 4 shows a schematic representation of an apparatus for making a modified wood product according to another embodiment of the invention; 1001701 Figure 5 shows the variation of pressure and temperature with time inside a vacuum heating apparatus during the curing step of the method shown in Figure 1; [00171] Figure 6 shows a schematic representation of how pieces of wood product are arranged during a drying step of a method of making a modified wood product according to yet another embodiment of the invention; [00172] Figure 7 shows the percentage loss of mass for various wood products when exposed to subterranean termites; 1001731 Figure 8 shows photographic images of various wood products after exposure to subterranean termites (C, formosanus); and 1001741 Figure 9 shows the number of bacteria as a function of time on a variety of substrates, including an example of a wood product in accordance with the present invention.

DETAILED DESCRIPTION

1001751 A method in accordance with an embodiment of the first and second aspects of the present invention will now be described by way of example only with reference to Fig. 1. The method of making a modified wood product is denoted generally by reference numeral 1. The method 1 comprises heating 500 a resin-impregnated wood -30 -product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, at a pressure of no more than 100kPa. The resin-impregnated wood product is heated in a variable pressure vessel chamber, which is discussed in more detail below. The method 1 also comprises heating 600 the dried resin-impregnated wood product, thereby curing the resin, in the variable pressure vessel chamber. The variable pressure vessel chamber is capable of operating at pressures less than 50kPa and capable of operating at pressures at least 200kPa. The applicant has determined that it is beneficial to both dry and cure the wood product in the same chamber. This means that it is not necessary to move the wood product between the drying and the curing process. Furthermore, the applicant has determined that it is beneficial to dry the resin-impregnated wood product at a low pressure. This has been found to be effective, takes less time than traditional kiln drying processes and may help reduce the risk of samples splitting or becoming distorted as a result of the drying process.

[00176] Other steps of the exemplary method I will now be briefly discussed. A suitable source wood product is selected. 'The method 1 comprises optionally reducing 100 the moisture content of the source wood product to provide a dried source wood product, if the moisture content of the source wood product is higher than desired. Those skilled in the art will realise that "dried" does not indicate that the moisture content of the source wood product is nil. A typical moisture content of the dried source wood product may, for example, be lOwt%. The dried source wood product is then impregnated 200 with a resin to form a resin-impregnated wood product. The resin-impregnated wood product is then subjected 300 to a pre-drying process by heating the resin-impregnated wood product to about 50°C.The resin-impregnated wood product is then stored 400 in conditions that typically do not alter the moisture content of the resin-impregnated wood product. The pre-dried resin-impregnated wood product is then heated 500, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, at a pressure of no more than 100kPa. The dried resin-impregnated wood product is then heated 600 to cure the resin. The method also comprises conditioning 700 the cured, resin-impregnated wood product by contacting the cured, resin-impregnated wood product with steam.

-31 - [00177] Each of the steps above will now be discussed in more detail, with particular attention to drying 500 and curing 600 of the resin-impregnated wood products.

[00178] The source wood treated using the embodiment of the method of the present invention in this example is Pinta radiate/. Those skilled in the art will realise that any suitable source wood may be used. Such source wood should preferably have Class I treatability (formerly classed as "permeable") in accordance with EN350:2016 ("Durability of wood and wood-based products -Testing and classification of the durability to biological agents of wood and wood-based materials"). Such a treatability facilitates penetration of resin into the source wood product. The source wood is in the form of rectilinear planks having a length of 1.5 or 3m, a width of 25cm and a depth of 25mm.

1001791 The moisture content of the source wood product is assessed using the oven-drying method. If the moisture content is more than 1 5wt%, the source wood is dried 100, by heating the source wood in a kiln until the desired moisture content is achieved. Alternatively, a moisture content meter may be used.

[00180] Once the moisture content of the source wood product has been reduced to a suitable value (typically 9-15wt%), the source wood product is then impregnated 200 with resin. In the present case, the resin is PUF P3026 (a phenol urea formaldehyde ("PUP') resin obtained from Hexion). Alternative sources of the resin (e.g Prefere) are available. An aqueous formulation having a solids content of 30%wt/vol, is used. Typically, the resin is supplied as a precursor formulation with a solids content of about 40-50%wtkol., so it is often necessary to dilute the precursor formulation to form a formulation suitable for impregnation. Those skilled in the art will realise that different resins may be used, for example, phenol urea resorcinol formaldehyde ("PURF") resins.

[001811 A stack of source wood product having the desired moisture content is placed into an autoclave or other vessel suitable for operation at elevated pressure. Resin formulation is then introduced into the autoclave so that that source wood product is immersed in resin formulation. This is typically done by reducing the pressure in the autoclave. The pressure in the autoclave is then increased to about 1200kPa to facilitate impregnation of the source wood product with resin formulation. A pressure of about -32 - 1200KPa is maintained for about 3 hours. The pressure in the autoclave is then reduced to about 20kPa for about 30 minutes to remove excess resin formulation from the resin-impregnated wood product and to facilitate movement of the resin formulation throughout the resin-impregnated wood product. Impregnation typically takes place at ambient temperature, for example, 15°C. It is desirable that impregnation does not take place at an elevated temperature.

[00182] The resin-impregnated wood product may be subjected to a pre-drying 300 process in which the resin-impregnated wood product is maintained at a temperature of 50°C for several hours in the autoclave.

[00183] The resin-impregnated wood is then stored 400. Storing 400 resin-impregnated wood product for a diffusion period of typically no less than 24 hours (also known as "drip drying") gives the wood product time to relax and extricate excessive resin and help with resin reaching the desired position in the wood. Storing 400 takes place in a no-drying environment. Typically, the resin-impregnated wood product is stored 300 for a maximum of 2 days.

[00184] The resin-impregnated wood product is then heated 500, thereby reducing the moisture content of the resin-impregnated wood product, but not curing, said resin. This drying heating 500 takes place in a variable pressure vessel shown schematically in Fig. 3. The planks of resin-impregnated wood product W are stacked as shown in Fig. 3 in a variable pressure vessel chamber 1002. Spacers are provided to ensure that there is space around each plank, as is well-known to those skilled in the art. The variable pressure vessel 1001 is configured to operate at both positive and negative pressures (compared to ambient). In this connection, the variable pressure vessel 1001 is provided with a vacuum pump 1003 for reducing the pressure in the variable pressure vessel chamber below ambient pressure. The variable pressure vessel is also provided with a pump 1004 for increasing the pressure in the variable pressure vessel chamber to above ambient pressure. Heaters 1005 are provided for heating the contents of the variable pressure vessel chamber. Turbulence plates 1006 are provided to generate turbulent air flow between the planks of wood product. Condensers 1007 are provided to condense liquid present in the variable pressure vessel chamber 1002.

-33 - [00185] The drying of the resin-impregnated wood product will now be discussed with reference to Fig. 2. The pressure in the variable pressure vessel chamber 1002 is initially about 3 psi (point A on Fig. 2), and the temperature in the variable pressure vessel chamber is about 65°C. At a pressure of about 3 psi, the boiling point of water is about 60°C. Water in the wood product evaporates, leading to an increase in pressure to a local maximum of about 5.5 psi (point B). The temperature decreases as thermal energy is used to evaporate the water. It should be noted that the variable pressure vessel chamber is provided with a constant thermal power, and is not therefore maintained at a constant temperature. The pressure is then reduced by activating the vacuum pump to achieve a further local pressure minimum of about 3 psi (point C). The vacuum pump is then deactivated, and the pressure rises again as water evaporates from the wood product, rising to a pressure of about 6.5 psi (point D). The amount of time between adjacent local minima and maxima in this region of the heating process is about 3-4 minutes. This relatively rapid cycling of pressure takes place for about an hour. In this period, liberation of water from the wood product is relatively rapid and therefore relatively rapid cycling of pressure is adequate to liberate water from the wood product. It should be noted that the temperature changed as the pressure changed, with the temperature periodically changing between about 48°C and about 63°C.

[00186] After about an hour, a different pressure change regime was used. The pressure at point E was about 3 psi. Pressure was allowed to increase over a period of about 10 minutes to a local maximum of about 10 psi (point F). The vacuum pump was then used to reduce pressure over a period of about 10 minutes to a local minimum at about 3 psi (point G). This pressure change regime with longer periods of increasing and decreasing pressure was found to be beneficial later in the drying process, because drying becomes slower as the resin-impregnated wood product becomes drier. This regime of bigger pressure changes over a longer period of time was maintained for the remainder of the drying process. It should be noted that the temperature changed as the pressure changed, with the temperature periodically changing between about 33°C and about 67°C.

1001871 This regime of "cycling" the pressure between relatively low and high values by causing a decrease in pressure using the vacuum pump and allowing the -34 -pressure to increase as the wood product dries has been found to be a particularly effective way of drying a resin-impregnated wood product without damaging the wood product. Furthermore, this method of drying the resin-impregnated wood product is far quicker than the traditional kiln-drying process.

[00188] Once the resin-impregnated wood product has been dried, it has to be cured 600. Curing 600 also takes place in the variable pressure vessel chamber 1002. Curing essentially comprises heating the wood product so that the resin in the wood product cures. Referring to Fig. 5, the resin is cured in the region labelled X by heating the resin-impregnated wood product to a temperature of about 130-150°C. The pressure in the variable pressure vessel chamber is about 25-28 psi during the curing process. After curing, pressure is slowly lowered and the temperature reduced.

1001891 Once the resin has been cured, the wood product is conditioned 700 by contacting the wood product with steam at a temperature of about 115-120°C at a pressure of about 20-25 psi.

[00190] After conditioning, the temperature and pressure may be reduced to facilitate removal of the modified wood product.

1001911 An embodiment of an apparatus for making a modified wood product in accordance with the invention will now be described with reference to Figs. 3 and 4. The apparatus is denoted generally by reference numeral 3001 and comprises an impregnation unit 2001 for impregnating a source wood product with a resin, the impregnation unit comprising an impregnation chamber 2002 for the location of a source wood product and means 2003 for increasing the pressure in the impregnation chamber; and a variable pressure vessel 1001 comprising a variable pressure vessel chamber 1002 for the location of one or more wood products, a heater 1004 for heating the contents of the chamber and a means 1003 for reducing the pressure in the variable pressure vessel chamber.

[00192] The means 2003 for increasing the pressure in the impregnation chamber is a means for increasing the pressure in the impregnation chamber to a pressure above -35 -ambient pressure, such as a pump. The means 1003 for reducing the pressure in the variable pressure vessel chamber is a means for reducing the pressure in the variable pressure vessel chamber below ambient pressure, such as a vacuum pump.

[00193] Examples of further embodiments of methods in accordance with the present invention will now be described Example Set A -25mm thick, 1500mm or 3000mm long pieces of Pinus radiata [00194] 25mm thick (either 1500mm or 3000mm long) pieces of pine from three different packs were impregnated with Prefere 925202S resin at 30%wtIvol, solids content, using an autoclave (I hour at 0.1bar, followed by 1 hour at 12 bar). The results are shown in Table 1.

Pack number Ave %MC prior to impregnation Wood density kgAM Uptake of resin kg/m' 1484 12.9 421 841 1485 13.2 414 870 1486 12.8 423 884 Table 1 -impregnation conditions for 25mm thick Pinus radiate: 1001951 One of the three packs was heated for 24 hours in the autoclave at 50°C, ambient pressure to investigate the effect of pre-drying prior to drying at low pressure.

[00196] The packs were then stored (or "diffused") for 3 days.

[00197] The samples were loaded into a vacuum chamber as shown in Fig. 6, and then dried in the vacuum chamber at a temperature of 45°C and a pressure of 125mBar for 8.5 days. Drying was stopped periodically to remove water from the chamber and take samples for moisture content determinations. The moisture content of the dried, resin-impregnated wood product was determined for various samples located in the core of the stack of samples and for various samples located in the edge of the stack of samples. Referring to Fig. 6, the core is the smaller, differently-shaded region at the centre of the stack. The edge is the outer region around the core. Table 2 demonstrates the effect of low pressure drying on the moisture content of the resin-impregnated wood product.

-36 -Pack Code Initial %MC (before drying) Average pack post Average pack edge Average pack core MC% %MC post drying %MC post drying drying I.5m long, 86.8+5.4 21 2+5 9 12.7+7.0 21 0+3 4 no pre-dry I.5m, pre- 66.1+8.3 12.4+2.5 11.7+1.7 14.2+3.6 dry 3.0m long, 83.3+6.5 36±11 37±13 37.3+5.1 no pre-dry Table 2 -effect of low pressure drying on moisture content (%MC) [00198] It is clear from the data of Table 2 that pre-drying is beneficial in that the moisture content of the pre-dried pack was reduced after drying compared to packs that were not subject to the pre-drying process. Furthermore, there was less variation in moisture content within the pack of wood product when the pack was pre-dried.

[00199] The dried resin-impregnated wood products were inspected for defects, and the defects were found as indicated in Table 3 Defect % Defect (3 long, % Defect (1.5m % Defect Pack long, no pre-dry) long, no pre-diy) (1.5m long, pre-Warp Warp 0 0 0 Splits 11 9 3 Checks 4 16 1 Cell collapse 14 38 21 Table 3 -percentage of samples having a particular defect [00200] The data from Table 3 illustrate that pre-drying reduces the number of splits, checks and cell collapses. It is expected that the use of a higher drying temperature (such as 60°C, as used for the 50mm thick samples) will improve the drying of 25mm thick samples.

Example Set B -50mm thick, 1500mm long pieces of Pin us radiata -37 - [00201] 50mm thick, 1500mm long pieces of pine from three different packs were impregnated with Prefere 925202S resin at 30%wt/vol, solids content, using an autoclave (2 hours at 0.1bar, followed by 3 hour at 12 bar). The results are shown in Table 4.

Pack number Ave 9'iNIC prior to Wood density kg/m3 Uptake of resin kg/m' impregnation 1654 12.6 430 930 1659 12.4 504 743 1660 13.4 496 738 Table 4 -mpregnation conditions for 50mm thick Punts radiate! [00202] One of the three packs was heated for 24 hours in the autoclave at 50°C, ambient pressure to investigate the effect of pre-drying prior to drying at low pressure.

[00203] The packs were then stored (or "diffused") for 7 days.

[00204] The samples were loaded into a vacuum chamber as shown in Fig. 6, and then dried in the vacuum chamber at a temperature of 60°C and a pressure of 125mBar for 10.4 days. Drying was stopped periodically to remove water from the chamber and take samples for moisture content determinations. After 10.4 days of drying the moisture content of all pieces was below 10%. The moisture content of the dried, resin-impregnated wood product was determined for various samples located in the core of the stack of samples and for various samples located in the edge of the stack of samples. Referring to Fig. 6, the core is the smaller, differently-shaded region at the centre of the stack. The edge is the outer region around the core. Table 5 demonstrates the effect of low pressure drying on the moisture content of the resin-impregnated wood product.

-38 -Pack Code Initial % MC Average pack Average pack Average pack (before drying) MC% post drying edge %MC post drying core %MC post drying 1.5m long, no 86.74.8 6.7+0.6 6.7+0.5 6.8+0.8 pre-dry I.5m long, pre-dried 774+5.6 5.5+0.1 5.5+0.2 5.1+1.1 3.0m long, no 85.5+1.0 7.1+0.4 7.0+0.2 7.1+0.5 pre-dry Table 5 -effect of low pressure drying on moisture content (%MC) [00205] Table 5 shows that drying using low pressure can produce resin-impregnated wood product with low moisture content, and with low variation in moisture content throughout a stack of wood products. It is clear from the data of Table 5 that pre-drying is beneficial in that the moisture content of the pre-dried pack was reduced after drying compared to packs that were not subject to the pre-drying process. Furthermore, there was less variation within the pack of wood product when the pack was pre-dried.

[00206] The dried resin-impregnated wood products were inspected for defects. No checking, splitting or warping was found in any of the 50mm thick samples.

[00207] The applicant has demonstrated that low pressure drying of resin-impregnated samples can be successful. Furthermore, low pressure drying is significantly faster than conventional kiln drying (about 85% faster).

[00208] Modified wood products made using methods in accordance with embodiments of the present invention were tested. Samples of the modified wood product were subjected to termite testing in accordance with AWPA E1-17. Fig. 7 shows the % average mass loss for modified wood products in accordance with embodiments of the invention. Embodiments of modified wood products in accordance with the present invention are labelled EX I, EX2, EX3. Comparative examples are CEX I (Scots pine), CEX2 (Beech), CEX3 (Western red cedar heartwood), CEX4 (teak heartwood) and CEX5 (Irok° heartwood). Fig. 7 shows that % mass loss to termites was very low and comparable to teak. Fig. 8 shows images of pieces of wood that had been exposed to 400 -39 -C. formosanus (subterranean termites) for 28 days. Row A is pine, Row B is radiata pine, Row C is alkaline copper quaternary-treated pine, Row D is modified wood product in accordance with an embodiment of the present invention and Row E is southern pine. Fig. 8 shows that the modified wood product according to an embodiment of the invention is resistant to termite attack, far more resistant than the untreated products of Rows A, B and E, and comparable in resistance to alkaline quaternary copper-treated pine. AQC treatment is a standard wood treatment 1002091 Further properties of the modified wood products of embodiments of the present invention were studied. They had a density of from 650 to 750kgm3, and had a moisture content of less than 11%. They had a Class I durability as assessed using EN113, AWPA El 0 method. They gave few emissions, testing EXCELLENT PASS under BSEN120 and J1S1460. The products were EXCELLENT PASS for slip resistance under BS79976-2. Hardness values of 5355N (radial) and 5 I 36N (tangential) were obtained using BS373. The dimensional stability of the modified wood product was assessed using methods set out in BRE Technical Note (1982, Anon.). this measures shrinkage in radial and tangential planes when wood conditioned at 90%RH and 25°C is re-conditioned to 60% relative humidity (RH) and 25°C. The equilibrium moisture contents of EXIMUIS samples under these environmental conditions were also measured. Percentage radial and tangential shrinkage for EXEMUIS and radiata pine are presented in Table 6, along with values published in BRE Technical Note for other species.

Timber EMC at 90%RH EMC at Corresponding tangential movement % Corresponding radial movement % 60%RH Present invention 17.6 6.5 1.15 0.7 Radiata pine 21.3 12.5 2.06 1.23 Ekki* 20 13 2.8 2.3 Iroko* 15 11 1 0.5 Radiata pine* 21.3 12.5 2.06 1.23 Scots pine* 20 12.5 2.1 0.9 Teak* 15 10 1.2 0.7 Table 6 -dimensional stabili y of modified wood product vs. othe wood products -40 - [00210] The sum of radial and tangential shrinkage is used to assign timber species to movement classes. Large movement class timbers have shrinkage >4.5% (e.g., beech and ekki), medium class timbers have shrinkage 3.0-4.5% (e.g., and radiata pine and Scot's pine) and small movement timbers have shrinkage <3% (e.g. iroko and teak). Embodiments of the modified wood product of the present invention show small movement.

[00211] Figure 9 demonstrates how an example of an embodiment of a wood product in accordance with the present invention, EX4, is effective when contaminated with bacteria. Surfaces of EX4 and other substrates were coated with bacteria. The concentration of bacteria on those surfaces were monitored as a function of time. Somewhat surprisingly, bacteria were retained less on the surface of EX4 and other wood products when compared to plastic and stainless steel.

1002121 Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[00213] The examples above describe a method of treating wood in accordance with the first and second aspects of the present invention. Those skilled in the art will realise that it is not essential for the method to comprise both the methods of the first and second aspects of the invention.

[00214] The examples above describe the treatment of contiguous pieces of wood.

Those skilled in the art will realise that the methods of the present invention may be used to treated source wood products comprising particulate.

[00215] The examples above describe the treatment of Monterey pine (Pinu.s-radiata). Those skilled in the art will realise that different types of source wood products may be used, such as Western Hemlock, Loblolly Pine, Slash Pine and Common Beech.

-41 - [00216] The examples above describe the use of a phenolic resin. Those skilled in the art will realise that other resins may be used.

[00217] The examples above disclose that the same variable pressure vessel may be used for both the drying and curing steps. Those skilled in the art will realise that this need not be the case. Different apparatus may be used for the drying and curing steps.

[00218] The examples above describe the drying and curing of rectilinear pieces of source wood product of length I.5m or 3.0m, with a thickness of 25mm or 50mm. those skilled in the art will realise that other sizes and shapes of source wood product may be used.

[00219] The examples above describe a drying process in which there is periodic reduction in pressure. Those skilled in the art will realise that different drying regimes may be used [00220] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

-42 -CLAIMSI A method of making a modified wood product, the method comprising a drying step comprising heating a resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, in a variable pressure vessel chamber capable of operating at pressures less than 501(Pa and capable of operating at pressures of at least 200kPa.
2 The method according to claim 1 comprising a curing step comprising heating the dried resin-impregnated wood product so as to cure the resin, the curing step taking place in said variable pressure vessel chamber capable of operating at pressures less than 50kPa and capable of operating at pressures of at least 200kPa.
3 The method according to claim 1 or claim 2, wherein the drying step comprises heating the resin-impregnated wood product to produce a maximum core temperature of no more than 65°C.
4 The method according to claim 2 and claim 3 when dependent on claim 2, wherein the curing step comprises heating the resin-impregnated wood product to a product a maximum core temperature of no more than 160°C.
The method according to any preceding claim, wherein the drying step takes place at a pressure of no more than I 00kPa.
6 The method according to any preceding claim, comprising reducing the pressure in the variable pressure vessel prior to, and/or during, the drying step.
7 The method according to claim 2 and any of claims 3 to 6 when dependent on claim 3, wherein the pressure in the variable pressure vessel chamber during curing is at least 125kPa.
8 The method of claim 7, wherein the pressure in the variable pressure vessel chamber during curing is at least 175kPa.
9 The method of any preceding claim comprising, prior to the drying step, an impregnation step comprising impregnating a source wood product with a resin composition.
-43 - 10. The method of claim 9, wherein the source wood product has Class 1 treatability (formerly classed as "permeable") in accordance with EN350:2016 ("Durability of wood and wood-based products -Testing and classification of the durability to biological agents of wood and wood-based materials").
11 The method according to claim 9 or claim 10, the resin composition comprising phenol, and formaldehyde or other reagent capable of reacting with phenol to form a molecule comprising multiple hydroxyl groups.
12. The method according to any of claims 9 to 11, wherein impregnating the source wood product comprises contacting the source wood product with, optionally by immersing the source wood product in, a resin composition, and applying an elevated pressure to the resin composition while the source wood product is in contact with, or immersed in, the resin composition.
13. The method according to any of claims 9 to 12, comprising a storage step comprising storing resin-impregnated wood product, optionally in conditions in which the moisture content of the resin-impregnated product is not significantly changed, after the impregnation step and before the drying step.
14. The method according to any of claims 9 to 13, comprising a pre-drying step after the impregnation step and before the drying step in which the moisture content of the resin-impregnated product is reduced.
The method according to claim 2 or any of claims 3 to 14 when dependent on claim 2, comprising, after the curing step, a conditioning step comprising conditioning the cured, resin-impregnated wood product, optionally by contacting the cured, resin-impregnated wood product with steam at an elevated temperature.
16. A method of making a modified wood product, the method comprising a curing step comprising heating a resin-impregnated wood product, thereby curing the resin, in a variable pressure vessel chamber capable of operating at pressures less than 50kPa and capable of operating at pressures of at least 2001(Pa.
17. The method of claim 16, wherein the curing step comprising heating the resin-impregnated wood product to a temperature of 130 to 180°C.
-44 - 18. The method of claim 16 or claim 17, wherein the pressure in the variable pressure vessel chamber during curing is at least 150kPa and is no more than 400kPa and optionally no more than 200kPa.
19. The method of any of claims 16 to 18, comprising a drying step comprising heating the resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, optionally at a pressure of no more than I 00kPa while drying takes place.
20. A method of making a modified wood product, the method comprising a drying step comprising heating a resin-impregnated wood product, thereby reducing the moisture content of the resin-impregnated wood product but not curing said resin, at a pressure of no more than I 00kPa,
21 An apparatus for making a modified wood product, the apparatus comprising: an impregnation unit for impregnating a source wood product with a resin, the impregnation unit comprising an impregnation chamber for the location of a source wood product and means for increasing the pressure in the impregnation chamber; and a variable pressure vessel comprising a variable pressure vessel chamber for the location of one or more wood products, a heater for heating the contents of the chamber and a means for reducing the pressure in the variable pressure vessel chamber.
22. A modified wood product, the modified wood product comprising a resin, having a density of from 650kgm3 to 750kgm3, having a moisture content of no more than 11% and being fire-retardant in accordance with ASTM E84-20 Class A 30 minutes, and optionally one or more of the following features: -45 - (i) durability to Class 1 when tested to standard EN113, using the American Wood Protection Association BID method; (ii) resistance to attack by subterranean termites as defined in American Wood Protection Association E1-17 test; (iii) a pH of 7.0-8.5 (iv) pass an emissions test in accordance with BSEN120 or HS1460; (v) pass a slip resistance test in accordance with BS7976-2; (vi) a hardness (as determined by BS373) of at least 4000N (radially) and/or at least 4000N (tangentially); (vii) a strength and/or a stiffness as determined by ASTM 143 of 80150% of that of teak; (viii) a high dimensional stability, demonstrating a low shrinkage (no more than 3%) when assessed in accordance with the 1982 BRE Technical Note; (ix) a modulus of rupture that is 80-120% of that of the source wood product; (x) a modulus of elasticity that is 100-150% of that of the source wood product; (xi) a hardness that is 120-180% of that of the source wood product; (xii) very durable (DC1) to attack by basidiomycete fungi; or (xiii) a durability to soft rot fungi comparable to teak;
23. A plurality of modified wood products, the plurality of modified wood products comprising a first set of satisfactory modified wood products and a second set of unsatisfactory modified wood products, the number of the satisfactory modified wood products in the first set being at least ten times the number of unsatisfactory modified wood products in the second set.