EP3323575B1 - Process of manufacturing of acetylated lignocellulose material with autoadhesive properties - Google Patents

Description

Wood-based materials are materials that are produced by crushing wood and then joining the structural elements together. The size and shape of the shredded wood determine the type of wood-based material and its properties. The structural elements are, for example, lumber (e.g., boards or veneers), wood shavings, wood fibers or wood wool. Instead of wood or in addition to wood, other lignocellulosic materials can be used as material materials.

Exemplary wood-based materials are solid wood materials, veneer materials, wood chip materials and wood fiber materials. Particle boards in particular are of great commercial importance. Particleboard accounts for more than 50% of total European and German wood-based panel production.

Binders usually play a central role in assembling the structural elements. For example, in all common chipboard production processes, the wood particles are mixed with predominantly synthetic adhesives and pressed under heat. The adhesives are used with up to 12% by weight and are usually based on petrochemical raw materials. In addition, 90% of adhesives used contain formaldehyde, whose indoor air limit has been 0.1 ppm since 1977 and since 2016 has been classified by the European Commission as a mutagenic and carcinogenic substance.

Against this background, it is known that the aim is to use only extremely low-formaldehyde or even formaldehyde-free adhesives for the production of wood-based materials, for example adhesives based on renewable materials Raw materials. For example, describe Dongre et al., Energies, 2015, 8, pp. 7897-7914 , Formaldehyde-free adhesives based on lignin-furfural polymers.

Another approach currently being pursued is the treatment of wood to form auto-adhesive properties. Such an auto-adhesive or "self-adhesive" wood could be processed with significantly less amount of external adhesive or even adhesive-free to a wood material. Known are, for example, the oxidizing treatment of wood with Fenton's reagent (a mixture of hydrogen peroxide and iron (II) salts) or with suitable enzymes. Also, a "steam explosion" treatment and hot pressing of the wood for adhesive-free bonding are known. Give an overview of these processes for the production of auto-adhesive or "self-adhesive" wood D. Zhang et al. in Wood Science and Technology, 2015, Volume 49, pp. 661-679 ,

To improve certain properties of the wood, in particular the resistance to wood-destroying fungi and insects and the dimensional stability, it is known to subject wood to a chemical modification. An already commercially implemented chemical wood modification process is acetylation.

For the preparation of acetylated wood, the starting material is treated with a suitable acetylating agent such as acetic anhydride. Excess acetic acid can be removed from the acetylated wood by an appropriate post-treatment (for example, with steam) to avoid unnecessary odor nuisance. The production of acetylated lignocellulose material is in EP 0 213 252 A1 . EP 0 680 810 A1 and DE 102009027635 A1 described. An up-to-date overview of the production and use of acetylated wood is given C. May in Wood Technology, 2010, No. 5, pp. 21-26 ,

JP 2007-084769 A describes a process in which ground wood is subjected to treatment with water at high temperature and high pressure to obtain a hemicellulose-liberated material, and then this material is subjected to acetylation.

EP 0 746 570 B1 describes a process in which a lignocellulosic material is acetylated in step (a) and this acetylated material is then contacted in step (b) at a temperature above 140 ° C with a heated, under the reaction conditions inert gas, so that the acetic or acetic anhydride content of the acetylated lignocellulose-containing material is reduced by stripping to below 10% by weight.

Y. Kurimoto et al., Journal of Wood Science, 59, 2013, pp. 209-215 describe a composite material made of acetylated wood and polypropylene. The acetylated wood is produced by a mechanochemical process.

It is an object of the present invention to produce a lignocellulosic material with auto-adhesive properties by a process which is as simple and efficient as possible and which enables the production of environmentally friendly, in particular low-formaldehyde or formaldehyde-free wood-based materials.

• die Acetylierung eines Lignocellulose-Materials mit einem Acetylierungsmittel unter Erhalt eines acetylierten Lignocellulose-Materials, wobei die Acetylierung des Lignocellulose-Materials einen Acetylierungsgrad AG im Bereich von 1% bis 25% aufweist und der Acetylierungsgrad durch folgende Beziehung bestimmt wird: $$\mathrm{AG}=\left[\left(\mathrm{TM}2-\mathrm{TM}1\right)/\mathrm{TM}1\right]\times 100\%$$
  
  wobei
  • TM2: Trockenmasse des acetylierten Lignocellulose-Materials
  • TM1: Trockenmasse des Lignocellulose-Materials vor der Acetylierung,
  und
• die partielle Verseifung des acetylierten Lignocellulose-Materials,

wobei unter Verseifung die Spaltung einer Esterverbindung durch Hydrolyse verstanden wird und durch die partielle Verseifung ein Teil der im Acetylierungsschritt gebildeten Essigsäureesterverbindungen wieder gespalten wird, wobei die partielle Verseifung des acetylierten Lignocellulose-Materials einen Verseifungsgrad VG in % aufweist, der durch die folgende Beziehung bestimmt wird: $$\mathrm{VG}=\left[\left(\mathrm{TM}2-\mathrm{TM}3\right)/\mathrm{TM}2\right]\times 100\%$$

wobei

TM2:

Trockenmasse des acetylierten Lignocellulose-Materials

TM3:

Trockenmasse des nach der partiellen Verseifung erhaltenen Lignocellulose-Materials;

und der Verseifungsgrad VG und der Acetylierungsgrad AG der folgenden Bedingung genügen: $$\mathrm{VG}/\mathrm{AG}\le \mathrm{0,7.}$$

The object is achieved by a method for producing a chemically modified lignocellulosic material, comprising

• the acetylation of a lignocellulosic material with an acetylating agent to give an acetylated lignocellulosic material, wherein the acetylation of the lignocellulosic material has an acetylation degree AG in the range of 1% to 25% and the degree of acetylation is determined by the relationship: $$\mathrm{AG}=\left[\left(\mathrm{TM}2-\mathrm{TM}1\right)/\mathrm{TM}1\right]\times 100\%$$
  
  in which
  • TM2: dry matter of the acetylated lignocellulosic material
  • TM1: dry matter of lignocellulosic material before acetylation,
  and
• the partial saponification of the acetylated lignocellulosic material,

wherein saponification is understood to mean the cleavage of an ester compound by hydrolysis and partial saponification cleaves again a portion of the acetic acid ester compounds formed in the acetylation step, the partial saponification of the acetylated lignocellulosic material having a saponification degree VG% determined by the following relationship : $$\mathrm{VG}=\left[\left(\mathrm{TM}2-\mathrm{TM}3\right)/\mathrm{TM}2\right]\times 100\%$$

in which

TM2:

Dry matter of the acetylated lignocellulosic material

TM3:

Dry matter of the lignocellulosic material obtained after partial saponification;

and the saponification degree VG and the acetylation degree AG satisfy the following condition: $$\mathrm{VG}/\mathrm{AG}\le \mathrm{0.7.}$$

As mentioned in the introduction, the acetylation of a lignocellulosic material such as wood is already an established process in which OH groups are esterified. It has surprisingly been found within the scope of the present invention that a lignocellulosic material having autoadhesive properties is obtained when the ester groups introduced by the acetylation are partially hydrolyzed again (ie partial saponification of the acetylated lignocellulose material).

A preferred lignocellulosic material is wood. However, in the process of the present invention, other lignocellulosic materials such as e.g. Natural fiber plants, bamboo, annual plants, flax, hemp or sisal are used.

The wood to be acetylated may be in the form of solid wood (e.g., boards or rods), veneer (e.g., sheet thin wood materials), or finely divided wood (e.g., chips, fibers, wood chips, strands, chips, pellets, or wood wool).

Suitable acetylating agents for the acetylation of lignocellulosic materials are known to those skilled in the art. Acetic anhydride, acetic acid or ketene (ethenone CH ₂ = C =O) or a mixture of at least two of these compounds is preferably used as the acetylating agent.

Suitable process conditions for the acetylation of lignocellulosic materials are known to those skilled in the art. By way of example, the in EP 0 213 252 A1 (Acetic anhydride as acetylating agent), EP 0 680 810 A1 (Acetic anhydride as the acetylating agent) and DE 102009027635 A1 (Acetylene ketene acetylenic) described.

wobei

• m_w die Masse des in der Probe enthaltenen Wassers und
• m₀ die Trockenmasse ist.

Before acetylation, the lignocellulosic material may optionally be subjected to drying. Preferably, the moisture (wood moisture in the case of wood) of the lignocellulosic material prior to acetylation is at most 12%, more preferably at most 5%, eg 0.1% to 12%, more preferably 0.5% to 5%. The moisture F of the lignocellulosic material (in the case of wood the wood moisture) is determined by the following relationship: $$\mathrm{F}\left(\mathrm{in}\%\right)=\left[\left({\mathrm{m}}_{\mathrm{w}}/{\mathrm{m}}_0\right)\right]\times 100\%$$

in which

• m _{w is} the mass of the water contained in the sample and
• m _{0 is} the dry matter.

The dry matter is determined by drying at 103 ° C to constant weight.

For the acetylation, the acetylating agent (preferably acetic anhydride) and the lignocellulosic material may be brought into contact at room temperature or under slight heating (eg a temperature of 15-60 ° C) or also at elevated temperature (eg 60 ° C-200 ° C) become.

For example, the lignocellulosic material may first be impregnated with the acetylating agent at a relatively low temperature (e.g., 15-60 ° C), and then the temperature is raised to, for example, 60-200 ° C to carry out the acetylation. Alternatively, it is also possible to bring the lignocellulosic material in contact with a suitably preheated acetylating agent.

The acetylation can take place under vacuum, atmospheric pressure or under elevated pressure.

Depending on the type of lignocellulosic material to be acetylated (e.g., solid wood or finely divided wood), the duration of acetylation may vary within a wide range, e.g. 1 hour to 48 hours, more preferably 1 hour to 24 hours.

In principle, the acetylation can be carried out in the presence of a catalyst. Preferably, however, the acetylation is carried out without a catalyst.

wobei

TM2:

Trockenmasse des acetylierten Lignocellulose-Materials

TM1:

Trockenmasse des Lignocellulose-Materials vor der Acetylierung

Die Trockenmasse wird bestimmt durch Trocknung bei 103°C bis zur Gewichtskonstanz.In the production of acetylated lignocellulosic material, the degree of acetylation AG (in%) is expressed by the relative weight gain in the acetylation by the following relationship: $$\mathrm{AG}=\left[\left(\mathrm{TM}2-\mathrm{TM}1\right)/\mathrm{TM}1\right]\times 100\%$$

in which

TM2:

Dry matter of the acetylated lignocellulosic material

TM1:

Dry matter of lignocellulosic material before acetylation

The dry matter is determined by drying at 103 ° C to constant weight.

In the context of the present invention, the degree of acetylation is in the range of 1% to 25%, more preferably 3% to 15%.

The amount of acetylating agent to be used to achieve a certain degree of acetylation can be readily determined by one skilled in the art.

After acetylation of the lignocellulosic material, excess acetylating agent and possible undesirable by-products (such as acetic acid using acetic anhydride) may be separated from the acetylated wood. Suitable methods for their separation are known in the art. For example, the acetylated wood may be treated with water or steam prior to the partial saponification step, exposed to a vacuum, and / or thermally treated. Alternatively, it is also possible to subject the acetylated wood after the acetylation without further intermediate treatment of the partial saponification.

Saponification in the context of the present invention is understood to mean the cleavage of an ester compound by hydrolysis. The saponification can take place at an acidic pH, an alkaline pH or even at a neutral pH.

Partial saponification re-cleaves some of the acetic ester bonds formed in the acetylation step (i.e., the degree of acetylation is reduced by saponification).

Preferably, the partial saponification of the acetylated wood takes place at acidic pH. For this purpose, the acetylated wood is treated with an acid-containing aqueous medium. The acid present in the aqueous medium which acts as a catalyst for the saponification may be, for example, a mineral acid, in particular sulfuric acid. One or more additional acids may also be present in the aqueous solution, for example acetic acid. For example, partial saponification is accomplished by mixing the acetylated lignocellulosic material with concentrated acetic acid (e.g., 30-80% acetic acid (% by weight) containing a mineral acid, e.g. Sulfuric acid, as catalyst contains, is treated.

As already mentioned above, the partial saponification of the acetylated wood can also take place at alkaline or neutral pH. Suitable alkaline media for the alkaline saponification of esters are known in the art.

Depending on the degree of acetylation achieved in the acetylation, the duration of partial saponification may vary within a wide range, e.g. 1 hour to 48 hours, more preferably 1 hour to 24 hours.

The partial saponification of the acetylated lignocellulosic material may take place at room temperature or with slight heating (e.g., a temperature of 15-60 ° C) or even at elevated temperature (e.g., 60 ° C-200 ° C).

For example, the acetylated lignocellulosic material may first be impregnated with the saponifying agent at a relatively low temperature (eg, 15-60 ° C), and then the temperature is raised to, for example, 60-200 ° C to carry out the partial saponification. Alternatively, it is also possible to acetylate To bring lignocellulosic material in contact with a suitably preheated saponification agent.

wobei

TM2:

Trockenmasse des acetylierten Lignocellulose-Materials

TM3:

Trockenmasse des nach der partiellen Verseifung erhaltenen Lignocellulose-Materials

Die Trockenmasse wird bestimmt durch Trocknung bei 103°C bis zur Gewichtskonstanz.In the partial saponification of the acetylated lignocellulosic material, the saponification degree VG (in%) is expressed by the relative weight loss by the following relationship: $$\mathrm{VG}=\left[\left(\mathrm{TM}2-\mathrm{TM}3\right)/\mathrm{TM}2\right]\times 100\%$$

in which

TM2:

Dry matter of the acetylated lignocellulosic material

TM3:

Dry matter of the lignocellulosic material obtained after partial saponification

The dry matter is determined by drying at 103 ° C to constant weight.

• Bevorzugt gilt: VG / AG ≤ 0,6;
• noch bevorzugter gilt: VG / AG ≤ 0,5.

The saponification degree VG and the degree of acetylation AG satisfy the following condition: $$\mathrm{VG}/\mathrm{AG}\le 0.7$$

• Preferably: VG / AG ≤ 0.6;
• more preferably: VG / AG ≤ 0.5.

noch bevorzugter gilt: $$\mathrm{0,1}\le \mathrm{VG}/\mathrm{AG}\le \mathrm{0,6};$$

noch bevorzugter gilt: $$\mathrm{0,2}\le \mathrm{VG}/\mathrm{AG}\le \mathrm{0,5.}$$

In a preferred embodiment: $$0.05\le \mathrm{VG}/\mathrm{AG}\le 0.7;$$

even more preferably: $$0.1\le \mathrm{VG}/\mathrm{AG}\le 0.6;$$

even more preferably: $$0.2\le \mathrm{VG}/\mathrm{AG}\le \mathrm{0.5.}$$

The lignocellulosic material obtained after the partial saponification may optionally be subjected to an aftertreatment. The preferred by the Ester cleavage liberated acetic acid removed. For this purpose, the lignocellulosic material can be treated after the partial saponification, for example, with water or steam. Optionally, this post-treatment can take place in vacuo and / or at elevated temperature.

As described in more detail below, the lignocellulosic material obtained via the process described above has auto-adhesive properties. By heating the lignocellulosic material to a sufficiently high temperature, for example in the range of 100 ° C to 210 ° C, optionally supplemented by pressure, the surface of the material behaves autoadhesive (ie has a self-tackiness) and thus allows a joining of structural elements from this material with reduced amount of external adhesive or even without external adhesive.

• die Herstellung eines chemisch modifizierten Lignocellulose-Materials durch das oben beschriebene Verfahren,
• Erwärmen des chemisch modifizierten Lignocellulose-Materials und Zusammenfügen zu einem Werkstoff.

Furthermore, the present invention relates to a method for producing a lignocellulosic material, comprising

• the preparation of a chemically modified lignocellulosic material by the method described above,
• Heating the chemically modified lignocellulosic material and joining it to a material.

As mentioned above, when wood is used as the lignocellulosic starting material, it can be used as solid wood (eg boards or rods), wood veneer (eg flat thin wood materials) or as finely divided wood (eg shavings, fibers, wood chips, strands, chips, Pellets or wood wool). This form of wood is preserved during acetylation and subsequent partial saponification. Thus, the chemically modified wood produced by the process according to the invention is usually present as solid wood, plywood or finely divided wood.

By heating to a sufficiently high temperature, usually at least 100 ° C (eg 100-210 ° C), the surface of the chemically modified lignocellulosic material according to the invention has sufficient self-tackiness to be joined to a material (eg fiber material, chip material , in particular chipboard, solid wood material, veneer material, composite material). In addition to the chemically modified lignocellulosic material according to the present invention, the material may also comprise other lignocellulosic materials and / or non-wood materials, e.g. Metal, ceramic or plastic included. Wood-plastic composite materials or composites are also referred to as "WPCs".

The heating of the chemically modified lignocellulosic material can be carried out in a known manner via an external heat source, a microwave heating or a high-frequency heating. Alternatively or additionally, the heating of the chemically modified lignocellulosic material may also be effected by friction, for example a friction between the surface of the chemically modified lignocellulosic material and another material to be combined with the chemically modified lignocellulosic material to form the material. The friction can be achieved, for example, by pressing the surfaces of the materials together and then moving them against each other.

The assembly of the chemically modified lignocellulosic material, optionally together with one or more additional materials, e.g. other lignocellulosic materials and / or non-wood materials such as metal, ceramic or plastic, to a material is preferably by compression (i.e., at elevated pressure).

The present invention will be described in more detail by the following examples.

Examples

In Examples IE1 and IE2 according to the invention, spruce chips were subjected to acetylation and then to partial saponification. Due to their self-adhesive properties, these spruce shavings could be processed into a wood material without the use of an external adhesive. In a comparative experiment CE1, the spruce shives were subjected only to acetylation (under the same conditions as in the examples according to the invention), but no partial saponification.

The acetylation in IE1, IE2 and CE1 was carried out as follows:
The spruce chips were dried. Taking into account the moisture content of wood, the corresponding mass of chips (350 g (atro)) was weighed into a stainless steel mixing bowl and mixed with an appropriate volume of acetic anhydride while stirring. The chips were transferred to a stainless steel bowl. The covered bowl was then placed in a preheated oven. After 4 hours, the chips were removed and washed five times with tap water. The washed chips were dried. Subsequently, the wood moisture and mass increase were determined.

The partial saponification of the acetylated samples of Examples IE1 and IE2 was carried out as follows:
The previously acetylated spruce chips were dried. Taking into account the moisture content, the corresponding mass of chips (175 g (atro)) was weighed into a stainless steel bowl. Subsequently, according to the experiment, a mixture consisting of acetic acid (60%) and concentrated sulfuric acid (0.005 (v / v)) added to the chips. The mixture was previously heated to 15 ° C below the target temperature (ie saponification reaction temperature). The reaction mixture was covered and placed in the oven preheated to the intended temperature. After 4 hours, the chips were removed, washed five times with tap water and dried. Subsequently, the wood moisture content and the reduction in mass were determined in relation to the mass of the acetylated chips used.

Table 1 below summarizes the process conditions. Table 1: Process conditions of examples IE1, IE2 and CE1 example Volume of acetic anhydride [mL] Reaction temperature of acetylation [° C] Volume of 60% acetic acid [L] Reaction temperature of saponification [° C] IE1 350 120 1.75 80 IE2 350 100 2.10 80 CE1 350 100 - -

From the spruce chips obtained in Examples IE1, IE2 and CE1, a wood material was prepared as follows:
For the production of chipboard (edge length 220 mm, thickness 4-4.3 mm), frames were first made of wood fibers, into which the chips (about 160 g) were then manually interspersed. Then they were placed on a metal plate, covered with paper and another metal plate and pressed in the hydraulic press for 480 s at 200 ° C to test specimens. The frames then remained in the press for 600 seconds so that they cooled to about 100 ° C. Afterwards, they cooled to room temperature outside the press.

• Querzugfestigkeit (DIN EN 319:1993-08)
• Biegefestigkeit sowie Biege-Elastizitätsmodul (Biege-E-Modul) (DIN EN 310:1993-08)
• Dickenquellung nach 24 Stunden Wasserlagerung (DIN EN 317:1993-08)

The following properties were determined for the wood-based materials:

• Transverse tensile strength (DIN EN 319: 1993-08)
• Bending strength and flexural modulus of elasticity (bending modulus of elasticity) (DIN EN 310: 1993-08)
• Thickness swelling after 24 hours of water storage (DIN EN 317: 1993-08)

The results are summarized in Table 2 below. Table 2: Properties of the wood-based materials example Transverse tensile strength [N / mm2] Bending strength [N / mm2] Bending modulus [N / mm2] Swelling 24 h [%] IE1 0.24 6.1 2150 19 IE2 0.17 4.9 1732 20 CE1 0.03 2.0 681 158

Due to their self-adhesive properties, spruce shavings according to the invention could also be processed to a wood material with good mechanical properties without the use of an external adhesive.

In contrast, the wood chips, which were only acetylated, but not partially saponified, no significant auto-adhesive properties. Therefore, the mechanical properties of the material according to CE1 compared to those of the inventive materials of Examples IE1 and IE2 are significantly worse.

Claims (10)

1. Process for producing a chemically modified lignocellulose material, comprising

   - the acetylation of a lignocellulose material with an acetylating agent to give an acetylated lignocellulose material, where the acetylation of the lignocellulose material exhibits a degree of acetylation DA in the range from 1% to 25% and the degree of acetylation is defined by the following relation: $$\mathrm{DA}=\left[\left(\mathrm{DM}2-\mathrm{DM}1\right)/\mathrm{DM}1\right]\times 100\%$$

   

   where

   DM2: dry mass of the acetylated lignocellulose material

   DM1: dry mass of the lignocellulose material before the acetylation

   and

   - the partial saponification of the acetylated lignocellulose material,

   where saponification refers to the cleaving of an ester compound by hydrolysis and through the partial saponification a part of the acetic ester compounds formed in the acetylation step is cleaved again, where the partial saponification of the acetylated lignocellulose material features a degree of saponification DS in % which is defined by the following relation: $$\mathrm{DS}=\left[\left(\mathrm{DM}2-\mathrm{DM}3\right)/\mathrm{DM}2\right]\times 100\%$$

   

   where

   DM2: dry mass of the acetylated lignocellulose material

   DM3: dry mass of the lignocellulose material obtained after the partial saponification;

   and the degree of saponification DS and the degree of acetylation DA satisfy the following condition: $$\mathrm{DS}/\mathrm{DA}\le \mathrm{0.7.}$$

   
2. Process according to Claim 1, where the lignocellulose material is wood, a natural fibre plant, bamboo, an annual plant, flax, hemp or sisal.
3. Process according to Claim 1 or 2 where the wood is a finely divided wood, more particularly in the form of wood shavings, fibres, shreds, strands, chips, pellets or wood wool, a solid wood or a veneer wood.
4. Process according to any of the preceding claims, where the acetylating agent is acetic acid, acetic anhydride or ketene or a mixture of at least two of these compounds.
5. Process according to any of the preceding claims, where the partial saponification of the acetylated lignocellulose material takes place at acidic, alkaline or neutral pH.
6. Process according to Claim 5, where the acetylated lignocellulose material is treated with an aqueous medium which comprises a mineral acid and optionally acetic acid.
7. Process for producing a lignocellulose material, comprising

   - the production of a chemically modified lignocellulose material by the process according to any of Claims 1-6,

   - heating of the chemically modified lignocellulose material and assembly to form a material.
8. Process according to Claim 7, where the heating of the chemically modified lignocellulose material takes place via an external heat source, microwave heating, high-frequency heating and/or by friction.
9. Process according to Claim 7 or 8, where the material is a particle material, more particularly a particle board, a fibre material, a solid wood material, a veneer material or a composite material.
10. Process according to any of Claims 7-9, where the assembly to form the material takes place by pressing.