WO2025041050A1

WO2025041050A1 - An accelerated method of impregnation of at least one wooden element

Info

Publication number: WO2025041050A1
Application number: PCT/IB2024/058111
Authority: WO
Inventors: Evgeny BOROVIN; Alessandro Bozzoli; Andrea GAIARDO; Manlio Nicola Innocenzo MAUGERI; Pietro MIRANDOLA; David Novel; Andrea PEDRIELLI; Matteo VALT
Original assignee: X Lam Dolomiti SpA
Current assignee: X Lam Dolomiti SpA
Priority date: 2023-08-22
Filing date: 2024-08-21
Publication date: 2025-02-27
Anticipated expiration: 2026-02-22

Abstract

An accelerated method of impregnation of at least one wooden element comprising at least one mechanical treatment (4) carried out so as to increase the chemical penetration and impregnation; the mechanical treatment (4) comprising at least one heating at a predetermined temperature and at least one compression at a predetermined pressure of the wooden element. Furthermore, the method of the invention also comprises at least one impregnation step (5) in which at least one impregnating solution is applied to the compressed wooden element so as to allow the impregnating solution to at least partially penetrate into the wooden element subsequent to the mechanical treatment (4).

Description

AN ACCELERATED METHOD OF IMPREGNATION OF AT LEAST ONE WOODEN ELEMENT

D E S C R I P T I O N

Field of application

The present invention is generally applicable to the technical field of timber and, in particular, relates to an accelerated method of impregnation of at least one wooden element.

Prior art

In the field of construction, for many centuries wood has been the most used material, however, natural wood has several limits in potential application fields since it is subject to the attack of atmospheric agents (for example: humidity, water, acid rain, snow/ice, solar radiation, temperature, fire, wind, sand) and to the attack of biological agents (for example: fungi, insects, marine organisms).

Such attacks can cause various alterations of the wood, starting with purely aesthetic transformations up to compromising the structural integrity thereof.

To obviate such drawbacks, i.e., to prevent, reduce or slow down such attack processes, there are numerous techniques in the prior arts suitable for the penetration of chemicals inside the wood and/or the impregnation thereof.

However, the known wood treatments involve significant costs and the execution of additional processes which typically require dedicated industrial systems.

The known treatments which precede the installation of wood comprise, for example, vacuum temperature treatments (e.g., Vacwood), supercritical CO2 treatments to increase the permeability of the wood, autoclave impregnation treatments (e.g., Acetylated wood).

Among these methods, the impregnation of wood and/or the penetration of chemicals therein thus represents one of the main strategies for the application of wood in environments in which the atmospheric and biological agents constitute a problem.

Generally, the chemicals comprise several product categories, each with specific advantages. An indicative and non-exhaustive list comprises:

• water-based wood hardeners: reinforce and consolidate deteriorated or damaged wood (for example: polyvinyl acetate, sodium silicate, formaldehyde solution, water-based polyurethane, water-based epoxy resins);

• water-based flame retardants: improve the fire resistance of wood (for example: ammonium phosphate-based or boron-based or ammonium sulphate-based);

• water-based antifungal and antimicrobial agents: prevent the growth of fungi and microorganisms in wood (for example: copper-based fungicides, borates, propiconazole, tebuconazole, IPBC (3-lodo-2- Propynyl Butylcarbamate), thiabendazole, thiocyanomethylthiobenzothiazole (TCMTB));

• quaternary ammonium compounds: protect wood from decomposition, rot and insect infestation (for example: didecyldimethylammonium chloride, benzalkonium chloride, N-(3- Aminopropyl) -N-dodecylpropan-1 -ammonium chloride, N-Dodecyl- N, N-dimethylbenzylammoniumchloride- N-Nitroso-N-methylurea chloride);

• water-based dyes and colourants: colour and improve the appearance of wood;

• water-based tannins: improve the natural colour and resistance of wood;

• penetrating water-based oils: penetrate deeply and nourish the wood fibres.

However, the prior techniques have strong limitations in the application thereof. In fact, they require the use of dedicated systems, long times and a different pressure condition than ambient pressure. Furthermore, such techniques encounter difficulties in the scalability of the technique with respect to high dimensions of the treated pieces of wood.

In addition, the prior techniques for the penetration of chemicals into wood are only applicable to certain classes of wood or specific species.

Obviously, facilitating the insertion of solutions and chemicals into wood need not be limited to mitigating the effects of atmospheric and/or biological agents on the wood. In fact, the penetration in wood and the impregnation thereof with different chemical solutions represents a technological challenge which is crucial, even in different areas with respect to those mentioned above.

In fact, the penetration in wood and the impregnation thereof with specific chemical solutions can be, for example, aimed at the introduction of solutions which have the purpose of modifying the structure of wood itself, increasing the mechanical properties thereof, or modifying the optical and electrical properties thereof.

The penetration of chemicals in wood is applied, among others, in the field of wood densification, i.e., the partial or total removal of one or more wood components and the subsequent thermo-compression of the wood so as to increase the specific properties thereof, including mechanical properties.

Presentation of the invention

The object of the present invention is to provide an accelerated method of impregnation which allows to at least partially overcome the drawbacks highlighted above.

In particular, the object of the present invention is to provide an accelerated method for promoting the impregnation of wood and in which the penetration of chemicals is more effective, less expensive and faster with respect to the methods present in the prior art.

Another object of the present invention is to provide an accelerated method of impregnation adapted to be carried out on any type of wood.

A further object of the present invention is to provide an accelerated method which allows the penetration in wood and the impregnation thereof with chemicals also at ambient pressure and at low temperatures.

Said objects, as well as others which will become clearer below, are achieved by an accelerated method of impregnation of at least one wooden element in accordance with the following claims, which are to be considered an integral part of the present patent.

In particular, it comprises at least one mechanical treatment carried out on the wooden element so as to increase the penetration thereof in wood and the impregnation thereof with specific chemicals. Such a mechanical treatment comprises at least one heating at a predetermined temperature and at least one compression at a predetermined pressure of the wooden element. Such a mechanical treatment is aimed at obtaining a decrease in thickness which is stable over time, even after pressure release.

Furthermore, the method of the invention also comprises at least one impregnation step in which at least one impregnating solution is applied to the compressed wooden element with a decrease in thickness so as to allow the impregnating solution to penetrate at least partially therein.

Advantageously, the method of the invention allows to improve the impregnation and penetration of chemicals in an element comprising wooden material with respect to the equivalent prior techniques.

Furthermore, the method of the invention still advantageously allows to speed up the impregnation process with respect to the known methods. Consequently, the method of the invention is also less expensive.

Still advantageously, the method of the invention is suitable for any type of wood, be it natural wood (dry and/or green) or a wood derivative (for example: plywood, panels made of wood pulp and fibres, OSB, etc.).

Furthermore, the method of the invention does not require a controlled pressure or excessively high temperature environment in order to be carried out. Thus, still advantageously, the method allows to further simplify the impregnation and penetration process of the substances with respect to the known equivalent processes.

Brief description of the drawings

Further features and advantages of the invention will become more evident in light of the detailed description of a preferred but non-exclusive embodiment of an accelerated method of impregnation according to the invention, illustrated by way of non-limiting example with the aid of the accompanying drawings, in which FIG: 1 depicts a block diagram of the impregnation method according to the invention.

Detailed disclosure of an exemplary preferred embodiment

With reference to the aforementioned figure, an accelerated method of impregnation 1 of a wooden element according to the invention is disclosed. Such a method can be carried out indifferently on a portion of the wooden element, on the whole element or even on several elements simultaneously.

As far as the wooden element is concerned, in the disclosed embodiment, it consists of a natural wood (dry and/or green). Obviously, such an aspect must not be understood as limiting for different executive embodiment variants of the invention where, for example, the wooden element comprises wood derivatives such as: hardwood, solid wood, laminated wood, wood panels, plywood, MDF (Medium Density Fibreboard), OSB (Oriented Strand Board).

According to an aspect of the invention, the method comprises a mechanical treatment step 4 in which the wooden element is subjected to heating and compression to obtain a modified element having reduced thickness and stable over time, even after the pressure release. Such a mechanical treatment step 4 is functional to improve and speed up the penetration of specific chemicals in the wood during the subsequent impregnation step 5.

The mechanical treatment 4 can be performed by applying pressure evenly or unevenly, for example, using non-planar plates inclined in the longitudinal direction of the wooden element.

Obviously, the type and geometry of the press must not be understood as limiting for different embodiment variants of the invention where, for example, a press with concave plates or a roller press is used.

According to the embodiment of the invention disclosed, the compression is carried out within temperature ranges from 50 °C to 180 °C and, preferably, between 90 °C and 110 °C.

Typically, the heating of the wooden element is carried out inside a suitable furnace such as in a humid furnace, i.e. , a furnace in which it is possible to control the internal humidity, for example, by injecting controlled steam in terms of relative humidity (rH) and/or temperature.

Still advantageously, the furnace heating allows to heat several elements at the same time, optimizing times.

Furthermore, the use of the furnace to heat one or more wooden elements allows a uniform heat diffusion. Advantageously, the inclusion of a furnace heating step also allows to use, as raw material, elements consisting of green wood, not dried or which have an internal humidity greater than the equilibrium moisture content.

According to different embodiment variants of the invention, the above mentioned heating step can also be carried out by one or more of the following methods:

- applying a hot saturated steam;

- applying a superheated steam;

- applying microwaves;

- applying infrared radiation.

As mentioned, such methods for carrying out the heating step can be used alternately with each other or in any combination.

In any case, regardless of the technology used, the heating of the wooden element is carried out until the glass transition temperature of the viscoelastic components of the wood is exceeded, which depends on the level of internal humidity of the wooden element.

Advantageously, pressing the wooden element at a temperature above the aforesaid glass transition temperature allows to avoid structural damage and to fix the mechanical deformation following the compression step.

As regards the compression of the wooden element, as mentioned, it is carried out at a predetermined pressure, which is generally controlled by an electronic system which allows it to be varied discretely or continuously according to the compression needs envisaged for the wooden element. Obviously, the nature of the pressure control must not be understood as limiting for different embodiment variants of the invention where, for example, the press is set with a predetermined pressure value or if there is a control on the movement speed of the plates.

Such a step has the purpose of compressing the wooden element so as to obtain a modified element having a reduced thickness and stable over time, even after the pressure release.

According to another aspect of the invention, the mechanical treatment 4 comprises a plurality of sub-steps each characterized by a predetermined temperature and a predetermined pressure applied to the wooden element.

Advantageously, in the method of the invention the internal structure of the wooden element is maintained almost entirely intact without the introduction of cracks, even if the porous structure has been partially or totally compacted, exploiting the plurality of thermo-compression sub-steps in which both pressure and temperature can be controlled independently. According to a non-limiting example for the present invention, the plurality of heating and compression sub-steps are performed in the temperature ranges of 50-180 °C, or preferably between 90-110 °C, and pressure ranges of 2-30 MPa. The temperature and pressure ranges of the present method represent the extremes within which the integrity of the wood structure can be maintained.

Obviously, as is evident to the person skilled in the art, the optimal ranges for different woods can be different from each other, thus further determined and optimized. Furthermore, the temperature and pressure ranges can vary depending on the technologies used to carry out the method, for example, depending on whether the heating is conducted in a furnace or using a press with heated plates.

Still advantageously, the thermo-compression sub-steps are determined according to the treated wood, so as to optimize not only the maintenance of the structure of the wood but also the subsequent impregnation and/or penetration of chemicals.

A non-limiting example of the indicative pressure ranges according to the type of wood treated is: from 2 MPa for wood with a density lower than 0.4g/cm³ (e.g., Paulownia); from 4 MPa for wood with a density between 0.4 g/cm³ and 0.7g/cm³ (e.g., Spruce); from 8 MPa for wood with a density higher than 0.7g/cm³ (e.g., Beech).

Clearly, still advantageously, the use of a plurality of thermo-compression sub-steps allows to limit the degradation of the wooden element which could occur from a thermo-compression carried out in a single step and/or at temperatures and pressures outside the ranges taught by the present invention.

In addition to this, also the direction of compression of the wooden element must not be understood as limiting for different embodiment variants of the invention where, for example, it is carried out along the radial, longitudinal or tangential axis.

Furthermore, according to different embodiment variants of the invention, depending on the result to be obtained by the impregnation method of the invention, it is possible to carry out a non-uniform and/or variable direction compression.

According to a further aspect of the invention, the accelerated method also comprises an impregnation step 5 in which an impregnating solution is applied to the wooden element having reduced thickness so as to allow it to penetrate, entirely or partially, inside the element itself. In other words, the wooden element to which a suitable impregnating solution is applied will tend to swell up to dimensions close to the original ones (prior to the compression step), similarly to when it occurs for a sponge, which after being crushed recovers the previous shape and dimensions.

Advantageously, the method of the invention allows to keep the structure of the wooden element intact both during the mechanical treatment 4 and during the application of the impregnating solution.

Still advantageously, the method 1 of the invention allows to improve the impregnation process 5 with respect to known equivalent methods. In fact, carrying out the mechanical treatment 4 allows to make the impregnation method 1 more effective, less expensive and faster with respect to the methods present in the prior art.

Still advantageously, the method 1 of the invention can be employed to treat any type of timber and/or wooden element.

As mentioned, an advantage of method 1 of the invention is being able to treat the wooden element at ambient pressure, avoiding the use of pressurized systems (such as autoclaves). Obviously, also such an aspect must not be considered limiting for different embodiment variants of the invention where, for example, it is carried out pressurized in an environment with predetermined pressure or vacuum.

In particular, in the impregnation step, the penetration is promoted and accelerated by the swelling of the previously compressed wooden material which occurs following the application of solutions based on solvents which are typically, but not necessarily, protic polars (such as water). In fact, the porous structure of the previously compressed wooden element will swell by interposition of the protic polar molecules within the structure of the wooden material, which will tend to return to the initial thickness.

According to a non-limiting example for the invention, the impregnation step 5 is carried out by means of liquids having a solid-liquid phase transition at low temperature, i.e. , liquids in which the transition temperature is higher than the ambient temperature and the transition itself is used to absorb heat and minimize temperature variations.

According to another aspect of the invention, the treatment method 1 also comprises a chemical pretreatment step 7 in which a liquid and/or vapour phase chemical solution is applied to the wooden element before subjecting the wooden element to the mechanical treatment 4.

Advantageously, the chemical pretreatment 7 promotes an increase in the wettability of the wooden element by exploiting the use of particular chemicals, concentrations and temperatures. Furthermore, the presence of particular chemicals can act as a plasticizer and lower the glass transition temperature of the viscoelastic components of the wood, such as lignin. Such a chemical pretreatment 7 therefore advantageously allows the treatments 4 and 5 to be carried out at lower temperatures or with shorter times.

Furthermore, still advantageously, carrying out the chemical pretreatment 7, which consists of applying the solution to the wooden element, allows the subsequent mechanical treatment 4 to be carried out at lower temperatures. In fact, the glass transition temperature is a function of the humidity of the wooden element and, therefore, by increasing the humidity thereof by means of the chemical pretreatment 7, it is possible to carry out the heating step of the mechanical treatment 4 at lower temperatures.

Obviously, the nature of the components of the chemical solution must not be understood as limiting for different embodiment variants of the invention where, it is in liquid and/or vapour phase.

According to the embodiment of the invention disclosed, the solution applied during the chemical pretreatment 7 comprises polar chemical solvents.

In particular, solutions based on polar chemical solvents, especially protic (such as water, alcohols, carboxylic acids, etc.), are an excellent means for wetting cellulose, hemicellulose and lignin fibres, establishing hydrogen bridge bonds therewith and effectively impregnating the wooden element.

Furthermore, the addition in the solution of organic compounds (for example dimethylsulfoxide, etc.), or of organic or inorganic acids and/or bases (for example peracetic acid, tetramethylammonium hydroxide, hydrochloric acid, sodium hydroxide, etc.), can lead to an increase in surface wettability thanks to the chemical modifications to the components of the wooden element. The increase in wettability results in an improvement in the penetration and impregnation of the treated element.

Obviously, such an aspect must not be considered limiting for different embodiment variants of the invention where, for example, the solution comprises apolar liquids.

In addition, according to an embodiment variant of the invention not depicted in the figures, the accelerated method of impregnation also comprises a step operatively interposed between the mechanical treatment 4 and the impregnation step 5 in which the wooden element is left to cool, or cooling is induced. Advantageously, the cooling step is applied to limit or eliminate the undesirable effects given by the dimensional recovery due to the residual internal humidity (known as set-recovery) of the wooden element at the end of the mechanical treatment 4. For example, if the wooden element at the end of the plurality of sub-steps of the mechanical treatment 4 turns out to have a residual internal humidity higher than its equilibrium humidity and the final temperature of the plurality of sub-steps of 4 is higher than 70°C, it is advantageous to apply a cooling step.

According to a further aspect of the invention, a constraint is applied to the compressed wooden element due to the mechanical treatment 4, in the direction of the compression and/or laterally, shaped to prevent the dimensional return thereof, i.e., the return to pre-com pression dimensions.

Such a constraint allows the wooden element to be kept compressed during storage and/or the cooling thereof or even during the impregnation step 5, so as to limit the return thereof in terms of thickness.

In particular, the constraint applied in the impregnation step 5 is used to impart any predetermined shape to the treated wooden element. Advantageously, by applying the constraint during the impregnation step 5, it is possible to model the shape of the element during the swelling thereof. In other words, the constraint will prevent the free swelling of the wooden element, giving it the desired shape. By way of non-limiting example for the invention, to demonstrate the effectiveness of the method, the absorption data are reported of demineralized water at 25°C, under full immersion conditions, over time on different elements. The samples comprise four red spruce elements with dimensions of 125 mm, 80 mm, 25 mm (respectively for wood growth directions L,T,R) which have been used to follow the test disclosed. No mechanical treatment was applied to the first reference element. On the other three elements, a maximum pressure of 5 MPa was applied (on the T, R plane of the samples, i.e., on the 125x80 mm surface). The pressure of 5 MPa was reached by means of 10 steps with 0.5 MPa increments each lasting 1 minute, for a total mechanical treatment time of 10 minutes.

Three different temperatures (25 °C, 50 °C, 105 °C) were tested for the three elements.

The percentage weight increases for the four elements are shown below:

The effectiveness, understood as the greater absorption by weight of water over time, of the proposed method is evident. In particular, it is noted that the efficacy increases with the treatment temperature and the method can also be carried out for samples whose treatment involves temperatures above the typical glass transition temperature of the treated element (e.g., sample 3).

According to a further non-limiting example for the invention, to demonstrate the effectiveness of the method, the absorption data are reported of demineralized water at 25°C, under full immersion conditions, over time on different elements. The samples comprise four paulownia elements with dimensions of 125 mm, 80 mm, 25 mm (respectively for wood growth directions L,T,R) which have been used to follow the test disclosed. No mechanical treatment was applied to the first reference element. On the other three elements, a maximum pressure of 5 MPa was applied (on the T, R plane of the samples, i.e. , on the 125x80 mm surface). The pressure of 5 MPa was reached by means of 10 steps with 0.5 MPa increments each lasting 1 minute, for a total mechanical treatment time of 10 minutes.

The percentage weight increases for the four elements are shown below:

From the above, it is evident that the object of the invention is also a product comprising a wooden element, not depicted in the figures, treated in accordance with the accelerated method of impregnation reported above.

A complete description of the product comprising a wooden element of the invention is omitted here, since it would replicate what is already written about the same during the disclosure of the impregnation method. What is observed is that it achieves all the aforementioned advantages.

In light of the foregoing, it is understood that the accelerated method of impregnation of the invention achieves all the preset objects.

In particular, the method of the invention allows to promote the penetration of chemicals and the impregnation of wood in a more effective, less expensive and faster manner with respect to the methods present in the prior art. Furthermore, the impregnation method is adapted to be carried out on any type of wood.

Finally, it allows the increase of chemical penetration and impregnation of wood even at ambient pressure and at low temperatures.

The invention is subject to numerous modifications and variations, all falling within the appended claims. All the details and steps can be replaced by other technically equivalent elements, and the materials can be different depending on the needs, without departing from the scope of protection of the invention defined by the attached claims.

Claims

C L A I M S

1. An accelerated method of impregnation of at least one wooden element characterized in that it comprises at least the following steps: at least one mechanical treatment (4) carried out on said at least one wooden element so as to increase the chemical penetration and impregnation of said at least one wooden element, said at least one mechanical treatment (4) comprising at least one heating at a predetermined temperature of said at least one wooden member and at least one compression at a predetermined pressure of said at least one wooden element; at least one impregnation step (5) in which at least one impregnating solution is applied to said at least one compressed wooden element so as to allow said at least one impregnating solution to at least partially penetrate into said at least one wooden element subsequent to said at least one mechanical treatment (4).

2. Accelerated method of impregnation according to claim 1 , wherein said at least one mechanical treatment (4) comprises a plurality of sub-steps, each of said plurality of sub-steps being characterized by a predetermined heating temperature of said at least one wooden element and/or a predetermined pressure exerted on said at least one wooden element.

3. Accelerated method of impregnation according to claim 1 or 2, wherein said at least one heating of said at least one wooden element envisages heating said at least one wooden element at a temperature higher than the glass transition temperature of said at least one wooden element.

4. Accelerated method of impregnation according to one or more of the preceding claims, wherein said at least one heating of said at least one wooden element is carried out in at least one furnace.

5. Accelerated method of impregnation according to one or more of claims 1 to 3, wherein said at least one heating of said at least one wooden element is carried out by means of at least one heated plate of at least one press.

6. Accelerated method of impregnation according to one or more of the preceding claims, comprising at least one chemical pretreatment step (7) wherein at least one chemical solution in liquid and/or vapour phase is applied to said at least one wooden element, said at least one chemical pretreatment (7) being carried out prior to said at least one mechanical treatment (4).

7. Accelerated method of impregnation according to claim 6, wherein said at least one liquid and/or vapour phase chemical solution comprises polar chemical solvents.

8. Accelerated method of impregnation according to one or more of the preceding claims, wherein in said at least one impregnation step at least one constraint is applied to said at least one wooden element so as to prevent the dimensional return of said at least one wooden element.

9. Accelerated method of impregnation according to one or more of the preceding claims, comprising at least one cooling step of said at least one wooden element, said at least one cooling step being operatively carried out between said at least one mechanical treatment (4) and said at least one impregnation (5).

10. Product comprising at least one wooden element characterized in that it is treated according to an accelerated method of impregnation according to one or more of the preceding claims.