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 treatment and, in particular, relates to a production method of a densified wood.

State of the art

Timber is widely used in numerous fields and, above all, in the field of construction. In fact, by means of suitable chemical and/or mechanical treatments, products with very high strengths can be obtained which can be used in structures such as multilayer structures (of the CLT/Glulam type) where the structural component consists of timber.

In the prior art there are numerous techniques for improving the physical and mechanical features of natural wood. In particular, thermo-compression has long been recognized as a method for improving the dimensional stability of wood. Such a process, combined with delignification, can also be applied to increase the mechanical properties of the wood.

As far as delignification is concerned, various methods are known for its execution, such as immersion in alkaline chemical pulping solutions or the use of hydrogen peroxide. In particular, the process of delignification by NaOH + Na2SOs (or other) is universally effective on various wood species.

The advantages of chemically delignified and thermo-compressed wood are related to the greater mechanical properties and dimensional stability of the resulting wooden products.

For example, WO 2018/191181 A1 is known which describes a densified, super strong and tough wood structure, formed by subjecting a cellulose-based natural wood material first to a chemical treatment to partially remove the lignin and, subsequently, to pressing.

However, the duration of the delignification process is high and it further increases for woods which are poorly permeable to the chemicals used for delignification. Furthermore, it has been seen how the current delignification processes lead to a damage of the cellulose and hemicellulose structure.

Moreover, the coupling of the two methods, delignification and thermocompression, within various known processes is related to various wood species and not related to the peculiarities of the various natural woods. In fact, recent developments in the field of coupling between delignification and thermocompression have been general and not targeted at specific species.

In addition, the recent crisis in raw materials has also involved the timber market with the consequent difficulties in finding natural wood to be treated and a sharp increase in prices. Moreover, such difficulties have made the known methods substantially outdated as the types of wood to which they are adapted suitable are now difficult to trace on the market.

Presentation of the invention

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

In particular, an object of the present invention is to provide a production method which allows to make a densified wood, i.e., a wood having improved physical and mechanical features with respect to a natural wood.

Another object of the present invention is to provide a production method capable of adapting to the various types of natural wood in an improved manner with respect to the known densification processes.

A further object of the present invention is to provide a production method which allows to improve the features of rigidity, specific rigidity and strength of the wooden products with respect the equivalent methods present in the prior art.

Said objects, as well as others which will become clearer in the following description, are achieved by a production method of at least one wood having a predetermined densification profile in accordance with the claims which follow, which are to be considered an integral part of the present patent.

According to an aspect of the invention, such a production method comprises a step of delignifying a piece of natural wood so as to at least partially remove the lignin therein.

According to another aspect of the invention, the method also comprises a step of thermo-compressing the delignified wood to obtain the densified wood. In particular, the step of thermo-compressing the delignified wood comprises a plurality of steps in which the delignified wood is subjected to a predetermined heating temperature and a predetermined pressure.

Furthermore, according to a further aspect of the invention, the predetermined heating temperature and the predetermined pressure vary so as to make the thermo-compression step variable.

In other words, the production method of the invention envisages first delignifying the natural wood, at least partially eliminating the lignin contained therein, and lastly performing a variable thermo-compression to obtain the predetermined densified wood.

Thus, advantageously, the method of the invention allows to make a densified wood starting from a piece of natural wood.

Still advantageously, the obtained densified wood will have improved physical/mechanical features with respect to the starting natural wood.

In addition, the method of the invention still advantageously allows to control the thermo-compression step by adjusting the temperature and pressure of each sub-step. This allows, still advantageously, to adapt the production method of the invention to any type of wood product in an improved manner with respect to the known densification processes.

Furthermore, still advantageously, the control of the temperature and pressure of each sub-step is also performed based on the features of the densified wood to be obtained.

On closer inspection, still advantageously, the presence of a plurality of thermo-compression steps allows to improve the stiffness and strength features of the wooden products with respect to the equivalent methods present in the prior art.

From what has been said, it is evident that the objects described are also achieved by a densified wood element performed by means of the production method according to what is disclosed above.

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 a production method of a wood having a predetermined densification profile 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 production method according to the invention.

Detailed description of some preferred example embodiments

With reference to the aforementioned figure, a production method of a wood having a predetermined densification profile according to the invention is described. In particular, such a method comprises a delignification step, indicated in the figure with 2, and a subsequent thermo-compression step of the delignified wood, indicated in the figure with 3, to obtain the densified wood.

According to the embodiment of the invention which is described, the method further comprises a pretreatment step, not depicted in the figure, which is performed where it is desired to increase the permeability of natural wood to the chemicals used for delignification.

Advantageously, the pretreatment to increase the permeability of natural wood favours the reduction of the delignification treatment time and allows to reduce the damage of the cellulose and hemicellulose structure with respect to the equivalent methods present in the prior art.

According to the embodiment of the invention which is described, such a pretreatment optionally comprises a chemical pretreatment in which a liquid and/or vapour phase solution is applied to the wood.

Furthermore, the pretreatment comprises a mechanical pretreatment step in which the wood is subjected to heating, typically in the oven or by means of heated plates, and compression to increase the wettability thereof, i.e. , the ability of a solid surface to become wet if placed in contact with a liquid.

In particular, regardless of the technology used, the heating of the wooden element is performed until the typical glass transition temperature of the treated element is exceeded.

Advantageously, pressing the element comprising wooden material at a temperature above the glass transition temperature allows to avoid structural damage and to fix the mechanical deformation.

Such a step is intended to compress the wooden element so as to obtain a minimum thickness and thus improve the impregnability thereof.

In addition, the pretreatment further comprises an impregnation step in which an impregnating solution is applied to the compressed wood so as to allow it to penetrate, in whole or in part, inside the element itself during the return of the wooden element following the release of the pressure exerted previously.

In other words, an impregnating solution is applied to the compressed wood during its return 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.

Depending on the type of impregnating solution and the wooden product to be obtained, the application of the impregnating solution comprises wetting a portion of the element comprising wooden material or the immersing thereof in the solution.

According to an aspect of the invention, the delignification step 2, typically but not necessarily with a spatial lignin removal gradient, is performed on a piece of natural wood so as to remove, at least partially, the lignin thereof.

Furthermore, the aforesaid delignification 2 is typically, but not necessarily, performed by means of a chemical solution (not only alkaline). Obviously, such an aspect must not be considered limiting for different embodiments of the invention where, for example, the delignification is carried out using hydrogen peroxide.

Such a step allows, in addition to lignin, the at least partial removal of hemicellulose.

Furthermore, optionally the application of the chemical solution during the delignification 2 is alternated by one or more washes in aqueous solution, or buffered solution.

With regard to the thermo-compression step 3, it comprises a plurality of steps, not indicated in the figure, in which the delignified wood is subjected to a predetermined heating temperature and a predetermined compression which vary so as to make the thermo-compression step variable.

Advantageously, the method of the invention allows to obtain a piece of densified wood. In fact, it optionally envisages a pretreatment aimed at increasing the permeability of the piece of natural wood and, subsequently, delignifying the natural wood and, finally, applying a temperature and compression for a plurality of steps to obtain the predetermined densification profile.

Furthermore, still advantageously, the resulting densified wood will have improved physical/mechanical features than the natural wood subjected to the production method in question.

In particular, still advantageously, the thermo-compression 3 divided into several sub-steps allows to optimize the improvement of the stiffness, specific stiffness and strength features of the wooden products with respect to the equivalent methods present in the prior art.

On closer inspection, therefore, the production method of the invention allows, still advantageously, to prepare a treatment tailored to the specific application purposes.

In addition, the method of the invention also allows, still advantageously, to make densified wood which can then be used in any form (boards, slats, etc...) and for any application. In fact, the woody material is no longer assembled into multicomponent structural elements or used as such, but conceived for specific purposes.

According to the above, the sub-steps of the production method of the invention allow, still advantageously, to adapt the temperature and the degree of compression according to the densification profile to be obtained and to the features of the starting natural wood. This allows, still advantageously, to adapt the production method of the invention to any type of timber/wooden product in an improved matter with respect to the known densification processes.

Moreover, the method of the invention allows to subject also wet delignified wood to thermo-compression 3. This allows, still advantageously, to avoid the drying process with the consequent savings in terms of costs and production times.

Furthermore, still advantageously, performing the thermo-compression step 3 on a wood which has not been dried allows to improve the final stability of the densified wood.

According to the embodiment described, the thermo-compression step varies progressively, modifying, for example, the release of the load between the various sub-steps. Obviously, such an aspect must not be considered limiting for different embodiments of the invention where, for example, temperature and degree of compression vary exponentially or are determined according to the state of the wood in the previous sub-step so as to further improve the adaptation of the method to the delignified wood.

Furthermore, even the direction of application must not be considered as limiting for different embodiments of the invention, in fact, the compression can be applied in any direction.

According to the embodiment described, the production method is particularly suitable for natural woods having a density less than 480 kg/m ³ , such as wood selected from the species Eucalyptus and Paulownia.

Advantageously, the production method of the invention allows to obtain densified wood also starting from wood considered tender and, therefore, unsuitable for densification and, consequently, for structural applications.

Obviously, the density and spices of natural wood must not be considered limiting for different embodiments of the invention.

According to another aspect of the invention, said thermo-compression step 3 is carried out by means of a press, not depicted in the figure, having a pair of plates.

According to the embodiment of the invention which is described, the method also comprises a preheating step of the thermo-compression equipment, not indicated in the figure, which is operatively interposed between the delignification and the thermo-compression. Such a preheating step envisages preheating the press plates up to a first predetermined temperature before they come into contact with the delignified wood.

In particular, again according to the embodiment of the invention being described, such a first temperature is higher than the target temperature to which the wood is to be brought and, therefore, the temperature of the plates will be decreased after contact with the wood itself.

Advantageously, this allows to speed up the achievement of the target temperature to which the delignified wood is to be brought during the thermo- compression step 3 and, consequently, allows to increase the productivity of the plant.

Differently, according to an embodiment variant of the invention, said first temperature is less than or equal to the aforesaid target temperature and the plates are heated after their contact with the wood.

Advantageously, having a lower or equal temperature in the preheating step allows to obtain a gradual release/evaporation of the liquids present in the delignified wood.

Obviously, also the use of a press must not be considered limiting for different embodiments of the invention where, for example, the thermocompression is carried out by means of a series of reheatable rollers.

According to a further aspect of the invention, the production method also comprises a variable release step, also not indicated in the figure, comprising a plurality of sub-steps in which the heating temperature of the densified wood and the compression exerted vary independently.

Furthermore, according to the embodiment of the invention which is described, in such a release step the densified wood is cooled by applying a compression such as to limit the elastic release of the wood itself. Obviously, also such an aspect must not be considered limiting for different embodiments of the invention where, for example, the cooling step occurs without applying a compression.

From the above, it is evident that the object of the invention is also a piece of densified wood, not depicted in the figure, made according to the production method according to what has been disclosed so far.

A complete description of the piece of densified wood of the invention is omitted here, since it would replicate what is already written about the same during the description of the production method. What is observed is that it achieves all the aforementioned advantages.

In light of the foregoing, it is understood that the production method and the piece of densified wood of the invention achieve all the intended objects.

In particular, the production method of the invention allows to delignify and thermo-compress a piece of wood so as to obtain a wood having a predetermined densification profile.

Furthermore, since the thermo-compression step is divided into several substeps, the method of the invention adapts to any type of timber/wooden product in an improved manner with respect to the known densification processes. In addition, the production method of the invention allows to obtain densified woods, in particular for low density woods, having better stiffness, specific stiffness and strength features with respect to the equivalent methods present in the prior art.

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