METHOD FOR OBTAINING A PRECURSOR OF A HYBRID WOOD -I NORGANIC

MATERIAL AND METHOD FOR OBTAINING A HYBRID WOOD -I NORGANIC MATERIAL

Cross-reference to related patent applications

This patent application claims the priority of Italian patent application No. 102020000019033 filed on August 3, 2020, the content of which is incorporated herein by reference . Technical field

The present invention relates to a method for obtaining a hybrid wood-inorganic material precursor, a method for obtaining a hybrid wood-inorganic material, a product obtained by this method and uses thereof. State of the art

Wood is used to produce several objects and structures. For environmental and cost-effectiveness reasons, different materials have been developed having similar or improved features with respect to wood so as to advantageously replace this material.

Some of these materials are based on wood or its derivatives .

Different processing systems are known for wood, which are used in the paper industry and substantially transform the morphological features of the starting material.

Processes are also known, which lead to the formation of carbides by means of high temperature processing (> 500°C) and can maintain the structure of wood. These are based on siliceous materials. Processes are also known which attempt to mimic the silicification that takes place during the chemical metamorphosis processes during time periods equivalent to geological eras.

Each of these processes aims at rendering the internal structure of wood stable in time or mimic the same, so as to obtain a resistant and light material.

Silicification results very difficult to perform, because performing a millennial process is complicated in itself .

The formation of siliceous carbides leads to the formation of materials which are resistant but do not have a sufficiently solid structure (the formation of gas and vapours during the thermal treatment generates porosity in the material) .

Processes in the paper field lead to materials which are not comparable to the solidity of wood.

Another important problem is that, once wood is cut (or processing waste such as wood shavings and sawdust) , the only way to return the material to being stiff and resistant is mixing the components with binders or hardening agents.

There are therefore numerous problems related to materials and processes which are currently used. Technical problem

It is an object of the present invention to provide a method for obtaining a hybrid wood-inorganic material that works as a precursor in the silicification process, which is simpler and more cost-effective than previous ones, which uses lower temperatures than the previous methods and which allows to obtain a rigid, resistant and light final product .

This object is achieved by the present invention by means of the method according to claim 1.

A further object of the present invention is to provide a wooden material which is as resistant and light as wood, if not even more.

This object is achieved by the present invention by means of the product according to claim 12.

Definitions

By "wood waste based material" there is intended any material that comprises the non-processed products of the wood industry. Examples of this material are: wood shavings, sawdust, threads, etc.

By "precursor of a wood waste based material" there is intended a product derived from the wood industry, which has been subjected to chemical treatments which have modified the chemistry of natural wood.

By "phase 1" or similar terms, in the examples, there is intended a material based on wood waste, a hydroxide and/or an oxidizing/reducing agent and water treated as disclosed in the following in steps a) , b) and c) of the different embodiments of the method according to the present invention.

By "phase 2" there is intended a product obtained by kneading and mixing phase 1 with a mineral filler of different kinds.

Detailed description of the invention

The present invention relates to a method for obtaining a precursor of a hybrid wood-inorganic material comprising the following steps.

In a first step a) , the following are mixed: a wood waste based material, preferably wood shavings or sawdust,

- sodium hydroxide or potassium hydroxide,

- an oxidizing/reducing agent selected from the group consisting of sodium sulphite, potassium sulphite, sodium bisulphite, potassium bisulphite, sodium sulphide and a peroxide (preferably hydrogen peroxide or peracetic acid) , and water in an amount sufficient to cover the above said solid components; in relative weight percentages of material / hydroxide / oxidizing/reducing agent 40-45/35-42/15-25 % respectively .

In a second step b) the mixture is heated to a temperature from 60 to 120°C, preferably boiled, for a time from 60 to 150 minutes, preferably 60 minutes, adding water so as to maintain the same volume.

In a third step c) , the material obtained in step b) is rinsed with water at least once. Depending on the kind of wood waste material used in step a) , one or more rinsing steps (i.e. washing steps) will be necessary. For example, if the material contains more resin, a greater number of rinsing steps will be necessary. If less resin is present in the material, then less rinsing steps will be necessary.

In a fourth step d) , the material obtained in the previous step c) is kneaded with:

- a silicate,

- calcium hydroxide, and/or

- a mineral filler; in relative weight percentages of material obtained in step c) / silicate / calcium hydroxide / mineral filler of 35-100/0-40/0-40/0-40 % respectively for a time from 30 to

75 minutes.

In a preferred embodiment, the silicate, the calcium hydroxide, and the mineral filler are in weight percentages of material obtained in step c) / silicate and/or calcium hydroxide and/or mineral filler of 35-99/1-65 %.

A method in which the composition is prepared without inorganic additives can be implemented. However, in the above preferred embodiment a defined percentage of inorganic additives is provided. If only one inorganic additive is to be used, then the preferred additive is silicate .

Experimental tests have been performed, in which no inorganic additives have been added to the processed and rinsed organic part. Articles with better mechanical characteristics have been obtained with respect to those made according to the prior art. However, the addition of inorganic additives further improved these characteristics.

In a preferred embodiment, in step d) :

- the material obtained in step c) is first kneaded with the silicate, preferably the sodium silicate, for 5 to 15 minutes, preferably 10 minutes;

- calcium hydroxide is then added and the resulting mixture kneaded for 5 to 15 minutes, preferably 10 minutes; and

- the mineral filler is then added, and the resulting mixture kneaded for 5 to 15 minutes, preferably 10 minutes.

In this embodiment, the mineral filler is preferably kaolin .

In an alternative embodiment, in step d) :

- a first part of the material obtained in step c) is kneaded with the silicate, preferably sodium silicate, in a first container for 5 to 15 minutes (preferably 10 minutes) so as to obtain a first slurry;

- a second part of the material obtained in step c) is kneaded with the calcium hydroxide in a second container for 5 to 15 minutes (preferably 10 minutes) so as to obtain a second slurry;

- a third part of the material obtained in step c) is kneaded with the mineral filler in a third container for 5 to 15 minutes (preferably 10 minutes) so as to obtain a third slurry; the first, second and third slurries are then kneaded for additional 5 to 15 minutes (preferably 10 minutes) .

In this embodiment, the mineral filler is preferably a phyllosilicate, preferably bentonite, talc or kaolin.

In an alternative embodiment, the method for obtaining the precursor of a hybrid wood-inorganic material comprises the following steps.

In a first step a) , the following are mixed: a wood waste based material, preferably wood shavings or sawdust, - sodium hydroxide or potassium hydroxide,

- an oxidi zing/reducing agent selected from the group consisting of sodium sulphite, potassium sulphite, sodium bisulphite, potassium bisulphite, sodium sulphide and a peroxide (preferably hydrogen peroxide or peracetic acid) , and

- water in an amount sufficient to cover the above said solid components; in relative weight percentages of material / hydroxide / oxidizing/reducing agent 40-45/35-42/15-25 % respectively;

In a second step b) the mixture is heated to a temperature from 60 to 120°C, preferably boiled, for a time from 60 to 150 minutes, preferably 60 minutes, adding water so as to maintain the same volume.

In a third step c) , the material obtained in step b) is rinsed with water at least once. As already mentioned, depending on the kind of wood waste material used in step a) , one or more rinsing steps (i.e. washing steps) will be necessary .

In a fourth step d) , the material obtained in the previous step c) is kneaded with:

- a silicate, at least one calcium salt, hydroxide or oxide, at least one magnesium salt, hydroxide or oxide and/or

- at least one aluminium salt, hydroxide or oxide, in relative weight percentages of material obtained in step c) / silicate / calcium salt, hydroxide or oxide / magnesium salt, hydroxide or oxide / aluminium salt, hydroxide or oxide of 35-100/0-40/0-40/0-40/0-40 % respectively for a total time from 40 to 60 minutes.

In a preferred embodiment, the material obtained in step c) , the silicate, the at least one calcium salt, hydroxide or oxide, the at least one magnesium salt, hydroxide or oxide, and/or the at least one aluminium salt, hydroxide or oxide are in relative weight percentages of material obtained in step c) / silicate and/or calcium salt, hydroxide or oxide, and/or magnesium salt, hydroxide or oxide, and/or aluminium salt, hydroxide or oxide of 35- 99/1-65 %.

A method in which the composition is prepared without inorganic additives can be implemented. However, in the above preferred embodiment a defined percentage of inorganic additives is provided. If only one inorganic additive is to be used, then the preferred additive is aluminium .

Experimental tests have been performed, in which no inorganic additives have been added to the processed and rinsed organic part. Articles with better mechanical characteristics have been obtained with respect to those made according to the prior art. However, the addition of inorganic additives further improved these characteristics.

In this latter embodiment, in step d) :

- a first part of the material obtained in step c) is kneaded with the silicate, preferably sodium silicate, in a first container for 5 to 15 minutes (preferably 10 minutes) so as to obtain a first slurry;

- a second part of the material obtained in step c) is kneaded with the calcium salt, hydroxide or oxide in a second container for 5 to 15 minutes (preferably 10 minutes) so as to obtain a second slurry;

- a third part of the material obtained in step c) is kneaded with the magnesium salt, hydroxide or oxide in a third container for 5 to 15 minutes (preferably 10 minutes) so as to obtain a third slurry;

- a fourth part of the material obtained in step c) is kneaded with the at least one aluminium salt, hydroxide or oxide in a fourth container for 5 to 15 minutes (preferably 10 minutes) so as to obtain a fourth slurry;

- the first, second, third and fourth slurries are then kneaded for additional 5 to 15 minutes (preferably 10 minutes) .

The method for obtaining a hybrid wood-inorganic material according to the present invention comprises steps from a) to d) according to the previously disclosed embodiments and the following steps. In a step e) the material obtained in step d) is formed using a mould with the negative of the desired shape, placing the material under a pressure from 0 to 40 MPa and at a temperature from 100 °C to 250 °C.

The resulting product has particular and very advantageous structural features. Wood has a tubular structure, which is reinforced and stiffened by lignin, in the presence of additional substances such as fats, resins, etc. By emptying the spaces occupied by these substances, even partially, by mechanical or chemical processes, it is possible to maintain this structure and subsequently fill it with fillers such as silicates. The use of soluble silicates to fill the wood structure makes subsequent cross-linking necessary to generate a stable structure. Therefore, for the structure to be stable, these fillers need to be cross-linked. The method according to the invention leads to this result. The resulting product therefore has a particularly resistant structure.

The resulting product may be used for producing kitchenware, construction materials, technical materials, furniture, insulating fillers, insulating materials, packaging materials, or prestressed materials.

Examples Example 1

Formulation of phase 1

Wood chips, water, NaOH flakes and Na2SOs are placed in a container.

The mixture is heated so that it boils and is kept at boiling point for 60 minutes, topping up with water the amount that has been lost during boiling.

At the end of the reaction, the mixture is rinsed with water .

Below is a table showing some of the experiments carried out.

Example 2

Formulation of phase 2

Phase 1 is mixed with sodium silicate in a container. This is mixed for about 10 minutes.

Lime is added to this mixture and mixed for a further 10 minutes.

At the end of this mixture, the mineral filler is added and mixed for additional 10 minutes.

Below is a table showing some of the experiments carried out .

Example 3

Formulation of phase 2

Phase 1 is mixed with sodium silicate in a container. This is mixed for about 10 minutes.

Phase 1 is mixed with calcium hydroxide in a second container. This is mixed for about 10 minutes.

Phase 1 is mixed with phyllosilicate in a third container. This is mixed for about 10 minutes. This is mixed for about 10 minutes in a fourth container .

Example 4

Formulation of phase 2

Phase 1 is mixed with sodium silicate in a container. This is mixed for about 10 minutes.

Phase 1 is mixed with calcium salts or oxides in a second container. This is mixed for about 10 minutes.

Phase 1 is mixed with magnesium salts in a third container. This is mixed for about 10 minutes. Phase 1 is mixed with aluminium salts in a fourth container. This is mixed for about 10 minutes.

This is mixed for about 10 minutes in a fifth container .

Below is a table showing the main experiments carried out. The amount of phase 1 indicated must be equally divided among the components. Example 5

Production of the final product

The product obtained from phase 2 is introduced as it is into a defined mould, which bears the negative of the element to be produced.

After this operation, the mould is mechanically pressed and at the same time subjected to heating with a temperature and for a time that depend on the characteristics of the finished product. Example 6

The density and flexural elastic modulus of an article obtained as sample XIV of Example 2 without the treatment according to Example 1 (material from organic phase only without the treatment according to steps a) -d) of the method of the invention) and the density and flexural elastic modulus of sample XIV of Example 2 treated according to the method of the invention were tested. Density and flexural elastic modulus are two quantities which represent well the stiffness and thus the cohesion of the different chemical species.

As can be seen from the results shown in the table below, the treatment according to the method of the invention leads to an improvement of about 25% in the flexural elastic modulus.

Example 7

The density and flexural elastic modulus of specimens other than the previous examples were also tested. From these tests, the advantages in terms of improved stiffness are evident .

Advantages

While the traditional wood treatment processes currently known lead to the almost compulsory passage from paper-type products (e.g. cellulose fibres, pulp, etc. ) , the method according to the invention allows to obtain a product derived from wood without losing the structural part itself, arriving at the paper-type product, but leaving the structural part available which is then partially "filled" with silicate elements (e.g. silicate 48/50) and joining together the wood tubulars filled with silicates by means of minerals or inorganic salts.

Furthermore, the traditional processes display considerable problems: various materials that attempt to mimic this structural concept, moving from paper-like elements, owe their structure exclusively to inorganic elements. In the method according to the invention, on the other hand, the structure is provided by the wood, while the inorganic part serves as a filler that strengthens the structure and enables it to be expanded.