FR2800082A1 - Wood particle modification, comprises mixing with a copolymer of monomers reacting with wood cellulose hydroxyl groups, ensuring chemical compatability and regulating surface properties - Google Patents

Abstract

Modification of the surface properties of wood particles comprises forming a copolymer by radical polymerization of a monomer(s) (M1) reacting with the hydroxyl groups of wood cellulose, a second monomer(s) (M2) ensuring chemical compatibility with a polymer matrix and a third monomer(s) (M3) regulating the surface properties of the copolymer. Modification of the surface properties of wood particles comprises forming a copolymer by radical polymerization of a monomer(s) (M1) reacting with the hydroxyl groups of wood cellulose, a second monomer(s) (M2) ensuring chemical compatibility with a polymer matrix and a third monomer(s) (M3) regulating the surface properties of the copolymer, this copolymer or a reactive latex having chemical functional groups, mixing with wood particles and cooling. An Independent claim is included for the obtained treated wood particles.

Description

The present invention relates to a method for modifying the surface of the wood particles to improve their properties, with a view to their use in particular for the manufacture of composite materials based on synthetic polymers, as well as the products obtained.

It consists in transforming wood particles by fixing a reactive latex (specially synthesized) to give them special properties such as compatibility with thermoplastic matrices such as polyolefins, polystyrene, polyvinyl chloride or thermoset sands such as resins epoxy, polyesters.

<B> It is known that the addition of a filler such as talc, mica, fiberglass or carbon, etc. in a polymer matrix makes it possible to improve the mechanical properties of the material, in particular its rigidity and strength. .

Wood particles (sawdust or flour) used as filler in thermoplastic or thermosetting dies have many advantages such as the possibility of giving composites a natural appearance, their low cost, their low density, their ease of supply and their biodegradability. but also many drawbacks such as poor adhesion between the particles and the plastic matrix, moisture uptake, dimensional instability, poor resistance to biological degradation agents, poor fire resistance, hydrophilicity rendering wood particles incompatible with most polymers. As a result, the use of wood particles as a filler in plastic matrix generates brittle materials.

Three ways are possible to control parameters # 1) Add a compatibilizer.

 # 2) Chemical modification of the polymer matrix. # 3) Chemical modification of wood particles.

From an economic point of view, it is not interesting to introduce a compatibilizing agent or to chemically modify a polymer matrix generally consisting of mixed plastic waste not compatible with each other. Hence the interest of chemically modifying the wood particles before incorporating them into the polymer matrix.

Work has already been done to improve the intrinsic properties of wood The method of wood rectification, described for example in the following patents: FR 2 591 611 (ARMINES), FR 2 609 927 (ARMINES) and FR 2 751 580 (NEW OPTION WOOD), involves subjecting the wood to a controlled heat treatment under an inert or reducing atmosphere which leads to the thermo-condensation of lignocellulosic wood compounds. The wood is usually treated at a temperature below 250 C in order to maintain sufficient mechanical properties. This process reduces the hydrophilic nature of wood and improves its properties such as resistance to microorganisms, dimensional stability and temperature resistance. In addition, the porosity of the wood is increased, and the surface characteristics and mechanical properties are modified.

However, it is necessary to note a dark coloration due to the combustion of a part of the wood polymers such as hemicellulose, lignin and cellulose. In addition, the retification does not give the wood particles a proper adhesion with the polymer matrix.

The method according to the present invention aims to remedy this state of affairs. In fact, it not only makes it possible to significantly improve the adhesion of the wood-polymer interface, but also to limit the thermal degradation of the wood particles at the processing temperature of the composites, to reduce the hydrophilic nature of the composition. wood, to improve its dimensional stability, to increase its resistance to biological degradation agents, to preserve its physico-mechanical properties, to improve its resistance to fire and to preserve its color.

The method also has the advantage of making it possible to prepare the composites from polar or apolar matrices.

This process is characterized by the radical preparation, optionally in emulsion, of a copolymer formed of at least one component reacting with the hydroxyl (OH) groups of the wood cellulose, of at least one component ensuring compatibility with the matrix. polymer, and at least one component to regulate properties such as hydrophobicity and resistance to bacteria, this copolymer, also called reactive latex, being then mixed wood particles, which can be activated or not, for the purpose of chemically modify their surface, the mixture being finally dried while hot.

In the accompanying drawing, given by way of non-limiting example of an embodiment of the object of the invention, Figure 1 is a symbolic diagram of the essential phases of the claimed process.

The basic formulation of the reactive latex includes three essential chemical components - one or more monomers (M1) to ensure the chemical reaction with the hydroxyl groups of the wood cellulose, - one or more monomers (M2) to be compatible or react with the polymeric matrices, - one or more monomers (M3) for regulating surface properties such as hydrophobicity and for improving bacterial resistance.

The latex may contain in addition various additives intended to impart to the wood particles (P) specific properties and whose presence the concentration will depend on the desired objectives. These are, for example, flame retardants of the phosphorus acrylate type.

The monomers (M1) intended to ensure the chemical reaction with the hydroxyl (OH) groups of the cellulose may be, for example, vinyl dimethyl azlactone of formula CH2 = CH CNC (CH3) 2CO2 - m-isopropenyl, dimethyl benzyl isocyanate ( TMI) of formula H 2 C = C (CH 3) C 6 HCl <B> (CHI) NCO, - isocyanate methacryloyl (MAI) of formula H 2 C = C (CH 3) CONCO - adduct obtained from acrylate hydroxyethyl of formula H 2 C = CHCO 2 <B> (CHI </ B> OH) and pure toluene 2,4-diisocyanate (TDI) of formula H3CCIH3 (NCO) 2 - maleic anhydride - derivatives of acrylamide, for example N. (hydroxymethyl) acrylamide of formula H 2 C = CHCONHCH 2 OH The chemical reactions between the reactive groups present in the latex and the hydroxyl groups of the cellulose occur during the mixing and drying steps.

Cette molécule présente les particularités suivantes - structure acrylique et non vinylique, car composés acryliques sont plus réactifs que les composés vinyliques en polymérisation radicalaire. There will be, for example, formation of a stable amido ester between the OH and azlactone groups, urethanes between the OH and isocyanate groups, and ethers between the OH groups and the acrylamide derivatives. Monomers (M2) for compatibility or reaction with a polymer matrix have the following chemical structure

This molecule has the following particularities - acrylic and non-vinyl structure, because acrylic compounds are more reactive than vinyl compounds in radical polymerization.

- presence of an alkyl chain R2 = CyH2y + 1 making it possible to ensure compatibility with a polymer matrix made of polyvinyl chloride when y = 1 or with a polyolefin-type polymer matrix when y = 8 or 12. In the case where y = 8, the chemical compounds used are of the fatty-chain acrylate type.

<U> Special cases </ U> # Monomer used to react with an epoxy resin type matrix: Glycidyl methacrylate.

 # Monomer used to ensure compatibility with a matrix type polyester: Styrene - Monomer used to ensure the reaction with polyurethanes hydroxyethyl acrylate.

Monomers (M3) intended to regulate surface properties such as hydrophobicity are of the fatty-chain acrylate type, for example lauryl acrylate or fluorinated acrylates, and the monomers intended to improve the resistance to bacteria are of acrylate type carrying a quaternary ammonium or quaternary phosphorus function.

The synthesis of the latex (L) is preferably obtained by radical polymerization in emulsion according to the known procedures. The emulsion comprises a hydrophilic solvent such as water or optionally a mixture of water and water-miscible solvent, for example alcohol.

The reactive latex obtained by radical emulsion polymerization is synthesized from a fatty-chain acrylate type monomer, a vinyl dimethyl azlactone or N- (hydroxymethyl) acrylamide type reactive monomer, or of the m-isopropenyl type, dimethyl benzyl isocyanate (TMI) or methacryloyl isocyanate (MAI) or adduct of hydroxyethyl acrylate and toluene 2,4 - diisocyanate in which the N = C = O functions are blocked by ε-caprolactam or a tert- butyl phenol and an acrylate monomer bearing a quaternary ammonium or phosphorus function.

If it is preferred to use the reactive monomers of the m-isopropenyl, dimethyl benzyl isocyanate (TMI) or methacryloyl isocyanate (MAI) type or adduct of hydroxyethyl acrylate and toluene 2,4-diisocyanate without blocking the functions N = C = O or alternatively maleic anhydride, conventional radical polymerization in solution will be used instead of the emulsion polymerization.

The wood particles (P) will consist of sawdust or wood flour.

The size of these particles is generally between 350 and 4000 pm. Regarding the flour, the size is less than pm.

The wood particles can advantageously come from trees such as spruce or beech and have the following characteristics: - Granulometry of 350 to 2000 μm, preferably 530 to 750 μm. Density of 0.12 to 0.19 g / cm 3, preferably 0.14 to 0.19 g / cm 3. - sieved and dusted.

- No dyes, insecticides, fungicides or chemicals. - Thermal stability 200 C.

Flour: - Particle size less than 500 μm. - Density 0.10 to 0.17 gr / cm3.

To facilitate the reaction of the particles with the latex, it is possible to carry out a prior activation (Pa) of the surface of the particles. The process consists in dry ozonizing sawdust or wood flour in a reactor at room temperature for 30 to 120 minutes, with a constant flow of an air-ozone mixture (03) and an ozone concentration of between 5 and 10-3 g / l, with stirring to ensure good contact.

During this ozonization reaction, there is a partial destruction of the wood fibers. Ozone degrades lignin, which no longer plays its role as a binder between cellulose fibers and makes the hydroxyl functions of cellulose more accessible.

This activation will be used mainly in cases where the particles contain a lot of lignin. Ozonation also leads to the formation of reactive groups such as peroxides or hydroperoxides which make it easier to fix the latex on the surface of the wood particles during drying. The wood particles, activated or not, are mixed (M) with the reactive latex in a reactor at room temperature by mechanical stirring.

The drying (S) of the suspension thus obtained will be a temperature of between 100 and 120 ° C. When the latex is synthesized from monomers in which the functions N = C = O are blocked by ε-caprolactam, drying will take place at 160 C.

The drying time is controlled by the moisture content of the wood particles which should be less than 5%, preferably less than 5%. When the drying is carried out in a rotary thermostatic oven, it is desirable to provide a ventilation so as to allow evaporation of the solvents and the water of the latex. In this context, it is also possible to dry by infrared radiation or by microwaves, always respecting the temperature ranges indicated above.

The purpose of hot drying is to remove solvents from the water and initiate chemical reactions between the latex and the wood. During this step, the reactive groups present in the latex will react with the hydroxyl groups of the cellulose. The end result is to obtain modified wood particles (PM) with surface properties that have not been obtained to our knowledge by other known methods.

The positioning of the various constituent elements gives the object of the invention a maximum of useful effects which had not been obtained so far by similar methods. The following two examples of application of the method are given for information only.

EXAMPLE 1 1. Synthesis of the Copolymer: Acrylate Bearing a Quaternary Ammonium Function / Lauryl Acrylate / Vinyl Dimethyl Azlactone in Emulsion

The emulsion copolymerization of the system: Acrylate bearing a quaternary ammonium function / laurylelvinyl dimethyl azlactone acrylate takes place at 75 ° C. according to the process described below. The monomers, the surfactant and the initiator are used in the receiving state without further purification because the high polymerization temperature (75 ° C.) prevents the presence of an inhibition period at the beginning of the polymerization. The reaction is carried out under an inert atmosphere. In a reactor equipped with a condenser and a mechanical stirrer, 70 g of distilled water and a solution composed of the 3 monomers (20 g) and the surfactant (sodium dodecyl sulphate) are introduced. Then, the initiating solution is introduced dropwise, that is to say 0.1 g of initiator (potassium persulfate) with 10 g of distilled water. The mixture is kept under mechanical stirring at 75 ° C. for 24 hours. A fraction of the product, taken from the reactor, is purified dried under vacuum before being analyzed by proton NMR.

2. Modification of wood particles.

The reactor containing the reactive latex g is charged with non-activated wood particles. The whole is kept under mechanical stirring for 4 hours at room temperature. Then the drying is carried out to remove water and solvents and to promote chemical reactions between the wood particles and the reactive latex. The drying takes place at 110 ° C. in a ventilated and rotary dryer to obtain a product having a moisture content of less than 2% by weight.

<U> Example 2 </ U> 1. Synthesis of the copolymer: Acrylate carrying a quaternary ammonium function / lauryl acrylate / m-isopropenyl, dimethyl benzyl isocyanate by radical polymerization in solution.

In a reactor equipped with a mechanical stirrer, g monomers (acrylate bearing a quaternary ammonium function, lauryl acrylate and m-isopropenyl, dimethyl benzyl isocyanate), 0.14 g of AIBN and 200 cc tetrahydrofuran (THF) are introduced. ). After degassing, the mixture is brought to overnight. A fraction of the product, taken from the reactor, is purified dried under vacuum before being analyzed by proton NMR. The radical polymerization reaction is also carried out under an inert atmosphere.

2. Modification of wood particles.

The copolymer-containing reactor is then charged with a few drops of tin dibutylaureate (DBTL) and then with unactivated wood particles. The whole is kept under mechanical stirring for 4 hours at room temperature. Then, the product is dried to remove the solvents and promote chemical reactions between wood particles and the copolymer. The drying takes place at 110 ° C. in a rotary dryer and ventilated until a moisture content of less than 2% by weight is obtained.

3. Characterization.

The modified wood is characterized by Fourier-transformed infrared. On the infrared spectra, the disappearance of characteristic peaks of the OH functions at 3400 cm -1 and N = C = O at 2270 cm -1 is observed. The appearance of a peak at 3340 cm -1 from the NH groups.

Claims (12)

<B> <U> CLAIMS </ U> </ B> 1. Process for modifying the surface properties of wood particles with a view to their use, in particular for the manufacture of composite materials based on synthetic polymers, whose objective is the transformation of wood particles by fixing a reactive latex to make this material compatible with thermoplastic or thermosetting dies. characterized by the radical synthesis (L) of a copolymer formed of at least one monomer (M1) reacting with the hydroxyl (OH) groups of the wood cellulose, at least one monomer (M2) ensuring the compatibility or chemical reaction with the polymer matrix and at least one monomer (M3) which regains surface properties such as hydrophobicity and resistance to bacteria, this copolymer, or reactive latex, carrying chemical entities with well-defined functions and specific to the properties that one wishes to impart to the wood particles and then mixed (M) with the wood particles (P), and the hot-dried mixture (S). 2. Process according to Claim 1, characterized in that the monomer (s) (M1) carrying out the chemical reaction with hydroxyl groups (OH) of the cellulose is (are) composed of vinyl dimethyl azlactone or m-isopropenyl, dimethyl benzyl isocyanate (TMI) or methacryloyl isocyanate (MAI) or adduct of hydroxyethyl acrylate and toluene 2,4 diisocyanate or maleic anhydride or N- (hydroxymethyl) acrylamide, the chemical reactions between the reactive groups present in the latex and the hydroxyl groups of the cellulose occurring during the mixing and drying steps. 3. Process according to any one of the preceding claims, characterized in that the reactive latex is synthesized by radical emulsion polymerization from a fatty-chain acrylate monomer, a vinyl-type reactive monomer. dimethyl azlactone or N- (hydroxymethyl) acrylamide or m-isopropenyl, dimethyl benzyl isocyanate (TMI) or methacryloyl isocyanate (MAI) or adduct of hydroxyethyl acrylate and toluene 2,4 diisocyanate in which the N functions C = O are blocked by -caprolactam or tert-butyl phenol and an acrylate-type monomer carrying a quaternary ammonium or phosphorus function. 4. Process according to any one of claims 1 and 2, characterized in that the reactive copolymer is synthesized by solution radical polymerization from a fatty-chain acrylate monomer, a reactive monomer where N = C functions. = O are not blocked of m-isopropenyl, dimethyl benzyl isocyanate (TMI) or methacryloyl isocyanate (MAI) or adduct of hydroxyethyl acrylate and toluene 2,4 diisocyanate or else maleic anhydride and a monomer carrying a quaternary ammonium or phosphorus function.   5. Process according to any one of the preceding claims, characterized in that the monomer (s) (M2) conferring on the wood particles (P) their particular properties is (are) constituted of ) monomer (s) of acrylic structure ensuring compatibility or chemical reactions with a polymer matrix and having the following chemical structure:

    with y = 1 when the polymer matrix consists of polyvinyl chloride and y = 8 or 12 when the polymer matrix consists of polyolefins. 6. Process according to any one of Claims 1 to 4, characterized in that the reactive latex is synthesized with glycidyl methacrylate so as to ensure compatibility of the wood particles (P) with an epoxy resin matrix. 7. Process according to any one of Claims 1 to 4, characterized in that the reactive latex is synthesized with styrene so as to ensure the compatibility of wood particles (P) with a polyester-type matrix. 8. Process according to any one of the preceding claims, characterized in that the wood particles consist of sawdust or sifted and dusted wood flour, without dye, insecticide, fungicide or chemical products, having a stability 200 C thermal and having the following characteristics sawdust: - Granulometry of at 2000 pm, preferably 530 to 750 pm - Density of 0.12 to 0 gr / cm3, preferably 0.14 to 0.19 gr / cm3 flour: - Particle size less than 500 μm - Density 0.10 to 0.17 gr / cm3. 9. Process according to any one of the preceding claims, characterized in that the drying (S) of the reactive latex mixture and of wood particles is carried out at a temperature of between 100 and 120 ° C. or close to 160 ° C. when latex is synthesized from monomers where the functions N = C = O are blocked by .caprolactam, the drying time being controlled by the moisture content of the wood particles which should be less than 5%, preferably lower than at 2%. 10. Process according to Claim 9, characterized in that the drying is carried out in a thermostatically controlled oven with ventilation so as to allow the evaporation of the solvents and the water of the latex. 11. Process according to any one of the preceding claims, characterized in that the wood particles (P) are subjected to a prior activation (Pa) of their surface by dry ozonisation of sawdust or wood meal in a reactor at room temperature for 30 to 120 minutes, with a constant flow of an air-ozone mixture (03) and an ozone concentration of between 5 and 8 103 g / l, with mechanical stirring to ensure good contact. 12. Processed wood particles, in particular for the production of composite materials based on synthetic polymers, characterized in that the properties of their surface are modified the fixing of a reactive latex having, on the one hand, a well-defined and specific function capable of making the material thus obtained compatible with thermoplastic or thermosetting matrices, but also ensuring the regulation of surface properties such as hydrophobicity and resistance to bacteria.