ITMI20100101A1 - LIGNOCELLULOSIC BASE PANELS WITH LOW RELEASE OF FORMALDEHYDE (CLASS E1) - Google Patents

Description

DESCRIPTION

Attached to a patent application for INDUSTRIAL INVENTION entitled:

"LIGNOCELLULOSIC-BASED PANELS WITH LOW FORMALDEHYDE RELEASE (CLASS E1)"

Field of the invention

The present invention relates to panels based on lignocellulosic materials, in particular wood chips or fibers, with low formaldehyde emission.

State of the prior art

Urea-formaldehyde (UF) resins are widely used substances as binders (binders) for the production of wood-based panels and / or cellulosic fibers. The vast industrial use of these resins depends on the fact that they are inexpensive and are easily treatable: the curing process takes place quickly in the presence of suitable catalysts. The final product of the cure reaction is a cross-linked material which guarantees good mechanical characteristics to the manufactured articles.

A serious problem with materials consisting of a lignocellulosic component and UF binders is that they slowly emit formaldehyde, a substance classified as a carcinogen and which is now considered one of the most dangerous pollutants in domestic environments. For this reason there is an increasing need for new low formaldehyde emission binders.

The scientific and patent literature on low formaldehyde emission binders is very poor in Europe and in particular in Italy. On the other hand, there are numerous patents filed in the United States concerning the production of wood-based panels with low formaldehyde emissions.

In US patent 4395504 the use of binders that do not emit formaldehyde (formaldehyde-free) prepared by reaction of cyclic urea with glyoxal is discussed. However, this system has the drawback of a low speed of the curing process and requires low pH values of the solution containing the proposed binder.

In US patent 5059488 glutaraldehyde is considered as a possible substitute for glyoxal. In particular, the patent proposes the use of an ethylenurea glutaraldehyde system for the production of wood-based panels. An improvement in the kinetics of the curing process and an increase in the pH necessary for the reaction is described. However, this solution has not found industrial applications, probably due to the toxicity of the glutaraldehyde and the low cost of the proposed solution.

In US patent 4692478 a formaldehyde-free binder based on polysaccharides, mineral acids and ammonia is described. Although this system is inexpensive and involves the use of substances largely obtained from renewable sources, the reaction requires extremely low pH values (about 0.5) and high pressures, conditions that make the system practically inapplicable on an industrial scale.

Another system based on polysaccharides is described in US patent 6822042. This system provides for the use of isocyanates as crosslinking agents. On the other hand, isocyanates are extremely toxic substances and for this reason their use for the production of binders to be used for the manufacture of wood-based panels or cellulosic fibers has not obtained significant industrial results.

In US patent 6599455 a process is described for the preparation of chipboard panels through the use of thermoplastic polymers and copolymers capable of undergoing a crosslinking process by reaction with epoxy compounds, isocyanates, N-methylol and ethylene carbonate (crosslinking substances). Although these binder compositions have led to the production of panels with good mechanical properties and water resistance, they have not found significant industrial applications.

US patent 6348530 instead describes the composition of a formaldehyde-free binder based on a mixture of hydroxylated polyamide and polycarboxylic acids. In this case the preparation of the binder is rather complex and the costs are quite high, such as to preclude a possible industrial application.

In US patent 6730718 the use of a binder in aqueous dispersion is proposed for the production of porous panels, such as wood-based panels. The binder comprises a blend of a polyvinyl ester and a polymer such as polyvinyl alcohol. Multifunctional aldehyde derivatives, such as glyoxal or glutaraldehyde, are used as crosslinkers. Various substances are proposed as catalyst such as, for example, aluminum trichloride.

A similar system is proposed in US 2007167561, which describes a binder consisting of a polymer containing hydroxyl groups, a cross-linking agent and possibly a catalyst, useful for making chipboard and MDF panels. Even in the last two cases described, the complexity of the binders and the use of toxic substances (such as glyoxal or glutaraldehyde) have in fact prevented possible industrial applications.

Other systems proposed for the production of formaldehyde-free binders are described in patents SI 648807 and US 5532330, in which the binder consists of a mixture of substances including some types of tannins. Other undoubtedly interesting systems proposed, such as the one described in patent DE 4331656, are instead based on the use of polyisocyanates in combination with substances containing amino or hydroxyl groups. Although these latter systems have also been the subject of great interest at an industrial level for the construction of binders to be used for the manufacture of lignocellulose-based panels, to date they have not found widespread use in the reference sector.

Solutions based on the use of phenol-formaldehyde (PF) based binders are finally described in some scientific papers. Although PF type binders are characterized by significantly lower formaldehyde emission values than those of UF binders, PF resins usually require more drastic process conditions than those used for curing more traditional UF resins. Given the premises, it is evident that there is still a strong demand, from the producers of lignocellulose-based panels, for new binders characterized by:

- a low emission of toxic substances before and during the treatment process;

a low emission of toxic substances such as formaldehyde downstream of the curing process;

- a relatively low cure temperature (lower than the degradation temperatures of the various lignocellulosic substances);

- a good speed of the treatment process.

The problem underlying the present invention is therefore that of providing panels based on lignocellulosic materials which emit low quantities of toxic substances, in particular formaldehyde, before, during and after the curing process.

This problem is solved by a panel based on lignocellulosic materials and by a process for its preparation as outlined in the attached claims.

Description of the invention

The present invention relates to a panel based on lignocellulosic materials, in particular wood chips or fibers, comprising a polymeric binder consisting of repeating units of an acrylic or methacrylic nature. The binder is characterized by a low volatility which avoids the emission of toxic and / or harmful substances during the polymerization reaction.

Furthermore, the binder is capable of undergoing a polymerization process in the presence of suitable reaction initiators and following thermal treatment.

In particular, the polymeric binder comprises repeating units deriving from the monomer of formula (I):

R 'and R' ', equal or different from each other, are H or a linear or branched alkyl group (C1-C4);

R is chosen from the group consisting of:

wherein R1 is H or an alkyl group

(C1-C4) linear or branched; R2 is a linear or branched (C1-C4) alkyl group; n is an integer between 1 and 20;

wherein R3 is H or a methyl group; R4

it is a linear or branched alkyl group (C1-C6); n is an integer between 1 and 20;

- is an oligomeric segment (C4-C20) containing urethane groups

in the main chain

- is an oligomeric segment (C3-C20) containing ester groups

m main chain

- a linear or branched alkylene segment (C2-C20);

an aromatic group (C6-C10);

a mixed aromatic-alkyl group (C7-C30);

where R4 and R7, the same or different

among themselves, they are H or a linear or branched alkyl group (C1-C4); m and n, equal to or different from each other, are integers between 1 and 20; R6 is a mixed aromatic-alkyl group (C7-C30), or is the group:

where: R8 and Rio are an aromatic group (C6-C10); R9 is a linear or branched alkyl group (C2-C6).

Preferably, R 'and R' ', the same or different from each other, are H or a methyl group; more preferably they are H.

In a preferred form, R1 and R2, the same or different from each other, are H or a methyl group. Preferably, n is an integer between 2 and 10.

In another embodiment, R3 is H; R4 is a methyl group; n is an integer from 2 to 10.

Advantageously, the alkylene segment is a linear (C2-C10) segment.

Preferably, the aromatic group is a C6 group. The mixed aromatic-alkyl group is advantageously a group:

where Rn is a linear or branched (C1-C6) alkyl group, preferably a branched C3 alkyl group.

In another embodiment, R5 and R7 are H; m and n, equal to or different from each other, are integers from 2 to 10.

In another form, Rsed Ri0 are a C6 aromatic group; said R9 is a branched C3 alkyl group.

In a particularly preferred embodiment, the group R is selected from:

wherein R1, R2 and R5-R7 are as defined above. In this embodiment, more preferably R1 is H; more preferably R2 is Cl. In this embodiment more preferably R5 and R7 are H; more

preferably R6 is the group

In a particularly preferred form, the panel of the invention comprises repeating units deriving from the monomer:

The polymeric binder of the invention is obtained by radical polymerization of at least one monomer of formula (I) using a polymerization initiator containing at least one peroxidic bond.

The polymerization initiator is selected from the group consisting of benzoyl peroxide, cumyl peroxide, laureyl peroxide, di-tert-butyl peroxide, di-tert-amyl-peroxide, preferably benzoyl peroxide.

The monomer and the polymerization initiator containing a peroxide bond are used in a weight ratio ranging from 99.5: 0.5 to 90:10, preferably 97: 3.

In addition to the monomer and the polymerization initiator, other substances may be present in the mixture such as low quantities of solvents, plasticizers (for example dibutyl phthalate), substances that regulate the viscosity of the binder or substances that facilitate the dissolution of the reaction initiator , which do not significantly (positively or negatively) affect the characteristics of the binder.

The panel of the invention is prepared by a process comprising the steps of:

a) mixing at least one monomer of formula (I) with a polymerization initiator comprising at least one peroxidic bond and, optionally, a plasticizer;

b) apply the mixture of point a) to shavings or fibers made of lignocellulosic material in a quantity comprised between 2% and 20% by weight, preferably between 8% and 12% by weight, calculated as a solid quantity of polymer at the end of the process of polymerization / crosslinking;

c) polymerizing and crosslinking said monomer by heating the mixture of point b) at a temperature ≥ 90 ° C, preferably at a temperature> 120 ° C.

The mixtures of step a) are applied to the lignocellulosic materials, for example by spraying, in variable quantities depending on the type of final product to be made (chipboard panels, multilayer panels, MDF or HDF panels). After applying the binder, the material is heated to a temperature not lower than 90 ° C, preferably to a temperature above 120 ° C, to allow the curing process to take place. Typically the product is pressed during the cure. The pressure applied and the duration of the heat treatment depend on the type of lignocellulosic material used as a base for the panels and on the type of product to be made. At the end of the curing process, the panel made is cooled down to room temperature.

Benefits

The low formaldehyde emission lignocellulose-based panels made through the use of low toxicity binders with the method of the invention have the following advantages.

1. The process allows the production of lignocellulose-based panels with an extraordinarily low formaldehyde release compared to those currently on the market.

2.11 process allows the production of lignocellulose-based panels which, with the same type and density compared to those currently on the market, have mechanical characteristics that are comparable or superior to them.

3.1 panels of the invention, with the same type and density with respect to those currently on the market, have water absorption comparable or lower than them.

4.1 panels of the invention, with the same type and density with respect to those currently on the market, have thermal insulation characteristics that are comparable or superior to them.

5.11 process is compatible with the production technologies currently used at industrial level for the production of wood-based panels does not imply significant changes to current systems and machinery.

6.11 system does not require temperatures and pressures higher than those currently used for the production of lignocellulose-based panels.

7.11 process requires an amount of energy comparable to or less than the quantities currently used industrially for the production of wood-based panels

8.11 process is characterized by the absence of solvents and by the absence of emissions of volatile, toxic or harmful substances, during the production phase and throughout the life cycle of the products.

Experimental part

Example 1 - Preparation of chipboard panels using an acrylic binder and, by comparison, urea-formaldehyde and phenoloformaldehyde-based binders.

An acrylic binder sample was obtained by mixing a) Bisphenol A ethoxylate dimethacrylate with b) 5% by weight of a mixture of benzoyl peroxide and dibutyl phthalate (40% by weight in dibutyl phthalate).

For comparison, a sample of urea-formaldehyde binder was obtained by mixing the commercial resin Kaurit 350 (Basi) with 2.4% by weight of ammonium sulphate. For further comparison, a sample of phenoloformaldehyde binder was obtained by mixing the commercial Bakelite PF 1279 MH (Hexion Specialty Chemicals) resin with 6% by weight of potassium carbonate. Wood particles (Pinea abies) were dried in an oven at 60 ° C until they reached a moisture content between 2 and 4% by weight.

A predetermined amount of acrylic binder was then sprayed onto the particles. The same procedure was repeated by applying, from time to time, the urea-formaldehyde-based binder and the phenol-formaldehyde-based one. For all resins, the quantity of binder applied was equal to 10% by weight (value calculated as the quantity of solid resin, at the end of the curing process) with respect to the weight of the wood particles.

The wood particles treated with the different binders were then placed in a 300 mm x 300 mm mold. A heated plate press was used for the preparation of the chipboard panels. For all the samples the temperature used was 170 ° C and the cure time was 10 minutes.

For each type of binder, 4 target density values for chipboard were selected: 0.50, 0.63, 0.76 and 0.89 g cm <"3>. For each target density value the chipboard samples were prepared by varying the final distance between the press plates (and consequently the thickness of the samples).

For each selected binder and for each target density value 2 panels were prepared, for a total of 24 panels. The panels were conditioned for one week at 60% relative humidity. A density measurement was then carried out on each panel. The results of these experiments, expressed as the average of 2 measurements (one for each panel) are shown below, together with the target density values (d [target]).

Panels 1-2 (acrylic binder) d [target] = 0.50 g cm-3 density = 0.495 ± 0.020 g cm <'3>

Panels 3-4 (acrylic binder) d [target] = 0.63 g cm density = 0.610 + 0.010 g cm <"3>

Panels 5-6 (acrylic binder) d [target] = 0.76 g cm density = 0.755 ± 0.010 g cm <"3>

Panels 7-8 (acrylic binder) d [target] = 0.89 g cm-3 density = 0.890 ± 0.040 g cm-3

Panels 9-10 (binder UF) d [target] = 0.50 g cm <"3> density = 0.495 + 0 .010 g cm <" 3>

Panels 11-12 (binder UF) d [target] = 0.63 cm density = 0.620 + 0.020 g cm <"3>

Panels 13-14 (binder UF) d [target] 0 .76 cm 3 density = 0.770 + 0.020 g cm <"3>

Panels 15-16 (binder UF) d [target] = 0.89 cm-3 density = 0.910 + 0.020 g cm <"3>

Panels 17-18 (binder PF) d [target] 0 .50 cm density = 0.500 + 0.010 g cm <"3>

Panels 19-20 (binder PF) d [target] = 0.63 cm-3 density = 0.620 + 0.010 g cm <"3>

Panels 21-22 (binder PF) d [target] 0 .76 cm 3 density = 0.775 + 0.030 g cm <"3>

Panels 23-24 (binder PF) d [target] 0 .89 cm density = 0.915 + 0.010 g cm <"3>.

This example demonstrates that it is possible to prepare particleboard using an acrylic binder under the same operating conditions that are used for panels made with commercial binders (based on urea-formaldehyde or phenoloformaldehyde).

Example 2 - Evaluation of formaldehyde release from panels prepared with acrylic-based binder as per example 1.

From the panels with target density 0.63 and 0.76 g cm <"3> prepared as described in example 1 and made with the acrylic binder (panels 3-4 and 5-6, respectively), samples of 200 x 280 size were taken mm. A measurement of formaldehyde release was carried out on these samples using the specifications described in the UNI EN 717-1: 2004 standard. The results, shown below, represent the averages of the measurements made on 2 samples analyzed for each type of panel .

Panels 3-4 (acrylic binder) formaldehyde release = 0.011 ± 0.002 ppm

Panels 5-6 (acrylic binder) formaldehyde release = 0.008 ± 0.001 ppm

This example demonstrates that panels prepared with acrylic binder show extremely low formaldehyde release values, such as to classify them panels E1 (UNI EN 13986: 2005) or even F *, according to the classification provided in Japan (JIS A 5908) . Example 3 - Evaluation of the moisture content of the panels prepared as per example 1: comparison between panels prepared using acrylic binders and panels prepared using urea-formaldehyde and phenol-formaldehyde-based binders. From the panels prepared and conditioned as described in example 1, 2 samples of each type (one for each panel) of dimensions 100 mm x 100 mm were taken. A measurement of the moisture content (MC) was carried out on these samples, using the equation: ;; ;; where Wa is the weight of the sample after conditioning and W0 is the weight of the sample dried in an oven at 90 ° C for 24 hours. ; For each type of panel the results, shown below, represent the average of the two measures. ; Panels I-2 (acrylic binder) MC = 3.7 ± 0.1 Panels 3-4 (acrylic binder) MC = 3.5 ± 0.1 Panels 5-6 (acrylic binder) MC = 3.7 ± 0.2 Panels 7-8 (acrylic binder) MC = 3.4 ± 0.1 Panels 9-10 (binder UF) MC = 5.1 ± 0.2 Panels II-12 (binder UF) MC = 5.3 ± 0.2 Panels 13-14 (binder UF) MC = 5.1 ± 0.1 Panels 15-16 (binder UF) MC = 5.1 ± 0.2 Panels 17-18 (binder PF) MC = 4.2 ± 0.1 Panels 19-20 (binder PF) MC = 4.1 ± 0.1 Panels 21-22 (binder PF) MC = 4.1 ± 0.1 Panels 23-24 (binder PF) MC = 4.2 0.1 This example demonstrates that the panels prepared with the acrylic binder show lower moisture content values than those shown by the panels prepared using the UF or PF binders. Example 4 - Analysis of the mechanical properties of the panels prepared as in example 1: comparison between panels prepared using acrylic binders and panels prepared using urea-formaldehyde and phenol-formaldehyde-based binders. ; Mechanical tests were carried out on samples taken from panels prepared and conditioned as described in example 1 to determine the following properties:; Modulus of elasticity (MOE); Flexural strength (Modulus of rupture, MOR) ; On samples taken from panels with target density 0.63 and 0.76 g cm <"3> (panels 3-4, 5-6, 11-12, 13-14, 1920, 21-22) mechanical tests were also carried out to determine the tensile strength perpendicular to the faces (Internai bonding, IB).; For the determination of the MOE and the MOR 6 samples (dimensions 40 mm x 300 mm) were used for each type of panel. For the determination of the IB they were 6 samples (dimensions 40 mm x 40 mm) used for each type of panel selected. The tests were performed using the specifications indicated in the UNI EN 310: 1994 and UNI EN 319: 1994 standards. The results of the tests, shown below, represent an average of the 6 measurements made for each type of panel. ; Panels 1-2 (acrylic binder):; MOE = 875 ± 100 MPa MOR = 8.9 ± 0.8 MPa; Panels 3-4 (acrylic binder):; MOE = 1555 ± 120 MPa MOR = 15.2 ± 1.3 MPa IB = 0.47 ± 0.2 MPa; Panels 5-6 (acrylic binder):; MOE = 2420 ± 100 MPa MOR = 22.9 ± 1.3 MPa IB = 0.56 ± 0.3 MPa; Panels 7-8 (acrylic binder):; MOE = 3480 ± 140 MPa MOR = 33.0 ± 1.5 MPa; Panels 9-10 (binder UF):; MOE = 480 ± 60 MPa MOR = 4.9 ± 0.5 MPa; Panels 11-12 (binder UF):; MOE = 1070 ± 60 MPa MOR = 10.0 ± 0.7 MPa IB = 0.36 ± 0.2 MPa; Panels 13-14 (binder UF):; MOE = 2160 ± 130 MPa MOR = 19.2 ± 1.4 MPa IB = 0.43 ± 0.3; MPa; Panels 15-16 (binder UF):; MOE = 3270 ± 90 MPa MOR = 32.0 ± 2.1 MPa; Panels 17-18 (binder PF):; MOE = 330 ± 70 MPa MOR = 2.9 0.4 MPa; Panels 19-20 (binder PF):; MOE = 900 ± 80 MPa MOR = 7.2 ± 0.8 MPa IB = 0.30 ± 0.2 MPa; Panels 21-22 (binder PF):; MOE = 1970 ± 110 MPa MOR = 19.2 ± 1.4 MPa IB = 0.39 ± 0.2 MPa; Panels 23-24 (binder PF):; MOE = 2880 ± 180 MPa MOR = 29.9 ± 1.7 MPa; This example demonstrates that, with the same density, the panels prepared with the acrylic binder show higher mechanical property values (MOE, MOR, IB) than those shown by the panels made using UF or PF binders. Example 5 - Evaluation of the water absorption by immersion of the panels prepared as in example 1: comparison between panels prepared using acrylic binders and panels made using urea-formaldehyde and phenol-formaldehyde-based binders. ; From panels with target density 0.63 and 0.76 g cm-3 (panels 3-4, 5-6, 11-12, 13-14, 19-20, 21-22), prepared as described in example 1, were 4 samples of each type were taken (two for each panel) with dimensions of 30 mm x 30 mm. All the samples were then dried in an oven at 90 ° C for 24 hours. A water absorption (WA) measurement was carried out on these samples after immersion for 24 h. The WA values were obtained using the equation: ;; ;; where W24 is the weight of the sample after 24 hours of immersion in water and W0 is the weight of the dry sample. ; The water absorption results, shown below, represent an average of the 4 measurements made for each type of panel. ; Panels 3-4 (acrylic binder) WA = 78.1 ± 4.5%; Panels 5-6 (acrylic binder) WA = 64.3 ± 3.4%; Panels 11-12 (UF binder) WA = 126.2 ± 11.4; Panels 13-14 ( binder UF) WA = 92.1 ± 6.3%; Panels 19-20 (binder PF) WA = 95.4 ± 7.0%; Panels 21-22 (binder PF) WA = 80.7 6.2%; This example shows that, with the same density, the panels prepared with the acrylic binder show values of water absorption by immersion lower than the values shown by panels made using UF or PF binders. Example 6 - Evaluation of the thermal conductivity of the panels prepared as in example 1: comparison between panels prepared using acrylic binders and panels prepared using urea-formaldehyde and phenol-formaldehyde-based binders. ; On samples of dimensions 40 mm x 40 mm, taken from the panels made as described in example 1 and conditioned at 65% relative humidity for 1 week, thermal conductivity measurements (λ25 ° C) were carried out in a direction perpendicular to the surface , in order to determine the possible influence of the type of binder on the thermal insulation capacity of the panels. The measurements were performed using an ISOMET (Applied Precision) system. The values of À25 ° C shown below represent the average of 4 measurements made on each sample. ; Panels 1-2 (acrylic binder) λ25 ° 0 0, 121 0, 003 W ra-1 K-l; Panels 3-4 (acrylic binder) λ25 ° 0 0.158 0, 002 W m-1 K-l; Panels 5-6 ( acrylic binder) λ25 ° 0 0.195 ± 0, 010 W m-1 K-l; Panels 7-8 (acrylic binder) λ25 ° C 0.231 0, 010 W m-1 K-l; Panels 9-10 (UF binder) λ25 ° C 0.119 ± 0, 002 W m-1 K-l; Panels 11-12 (binder UF) λ25 ° C 0, 148 0, 002 W m-1 K-l; Panels 13-14 (binder UF) λ25 ° 0 0.180 ± 0, 010 W m-1 K-l; Panels 15-16 (binder UF) λ25 ° 0 0, 240 ± 0, 014 W m-1 K-l; Panels 17-18 (binder PF) λ25 ° C 0.116 ± 0, 004 W m-1 K-l ; Panels 19-20 (binder PF) λ25 ° C 0,159 0, 006 W m-1 K-l; Panels 21-22 (binder PF) λ25 ° 0 0,179 ± 0, 001 W m-1 K-l; Panels 23-24 (binder PF) λ25 ° C 0.234 0, 015 W m-1 K-l; This example demonstrates that, with the same density, there is no significant influence of the type of binder on the thermal conductivity of the panels in the direction perpendicular to the surface. *

Claims (17)

CLAIMS 1. Panel based on lignocellulosic materials comprising wood chips or fibers and a binder, wherein said polymeric binder comprises repeating units deriving from the monomer of formula (I): where is it : R 'and R' ', equal or different from each other, are I or a linear or branched alkyl group (C1-C4); R is selected from the group consisting of: where R 1 is H or an alkyl group (C1-C4) linear or branched; R2 is a linear or branched (C1-C4) alkyl group; n is an integer between 1 and 20; wherein R3 is H or a methyl group; R4 it is a linear or branched alkyl group (C1-C6); n is an integer between 1 and 20; - is an oligomeric segment (C4-C20) containing urethane groups in the main chain - is an oligomeric segment (C3-C20) containing ester groups in the main chain - a linear or branched alkylene segment (C2-C20); an aromatic group (C6-C10); a mixed aromatic-alkyl group (C7-C30); where R4 and R7, the same or different among themselves, they are H or a linear or branched alkyl group (C1-C4); m and n, equal to or different from each other, are integers between 1 and 20; R6 is a mixed aromatic-alkyl group (C7-C30), or is the group: where: R8 and Rio are an aromatic group (C6-C10); Rg is a linear or branched alkyl group (C2-C6). 2. Panel according to claim 1, wherein said R is selected from: wherein R1, R R5-R are as defined in the claim 3. Panel according to claim 1 or 2, wherein said R 'and R' ', equal or different from each other, are H or a methyl group. 4. Panel according to claim 3, wherein said R 'and R' 'are H. 5. Panel according to any one of claims 1 to 4, wherein said R1 is H or a methyl group. 6. Panel according to any one of claims 1 to 5, wherein said n is an integer between 2 and 10. Panel according to any one of claims 1 to 6, wherein said alkylene segment is a linear (C2-C10) segment. 8. Panel according to any one of claims 1 to 7, wherein said aromatic group is a C6 group. 9. Panel according to any one of claims 1 to 8, wherein said mixed aromatic-alkyl group is a group: where Rn is a linear or branched alkyl group (C1-C6). 10. Panel according to any one of claims 1 to 9, wherein said Rs and Rs are H; m and n, equal to or different from each other, are integers from 2 to 10. 11. Panel according to any one of claims 1 to 10, wherein said R8 and Rio are a C6 aromatic group; said R9 is a branched C3 alkyl group. Panel according to any one of claims 1 to 11, wherein said R1 is H and said R1 is Cl. 13. Panel according to any one of claims 1 to 12, wherein said R5 and R7 are H and said R6 is the group 14. Panel according to any one of claims 1 to 13, wherein said monomer of formula (I) is: Panel according to any one of claims 1 to 14, wherein said polymeric binder is obtained by radical polymerization of at least one monomer of formula (I) using a polymerization initiator containing at least one peroxide bond. 16. A panel according to claim 15, wherein said polymerization initiator is selected from the group consisting of benzoyl peroxide, cumyl peroxide, lauroyl peroxide, ditert-butyl peroxide, di-tert-amyl-peroxide. 17. Process for the preparation of a panel according to any one of claims 1 to 16, comprising the steps of: a) mixing at least one monomer of formula (I) with a polymerization initiator comprising at least one peroxide bond and, optionally, a plasticizer, -b) applying the mixture of point a) to shavings or fibers made of lignocellulosic material in quantities ranging from 2% and 20% by weight, preferably between 8% and 12% by weight, calculated as a solid amount of polymer at the end of the polymerization / crosslinking process; c) polymerizing and crosslinking said monomer by heating the mixture of point b) at a temperature> 90 ° C, preferably at a temperature ≥ 120 ° C.