The invention relates to the field of calcium carbonate-based materials and in particular to their use as a filler for plastic polymer materials. The invention provides a method of reducing the hygroscopicity of a material (M) comprising calcium carbonate by treatment with at least one homopolymer to aid grinding (P) which is neutralized in a particular way. The invention also relates to a method of conditioning this material (M) then having reduced hygroscopicity.

In the field of plastic polymer materials, and in particular polyolefin resins, it is important to be able to have available alternative preparation methods, in particular methods making it possible to reduce the quantities of polymers used. Thus, it is possible to substitute a portion of these polymers with filler materials during the preparation of plastic polymer materials.

These filler materials must have specific properties in order to be able to be used for these preparation methods. In particular, these filler materials must have a high compatibility with the polymers with which they are associated. These filler materials must not lead to a degradation of the properties of the plastic polymer materials in which they are integrated, for example a degradation of the mechanical or optical properties of these materials. These filler materials must not interfere with the preparation methods of the plastic polymer materials in which they are incorporated.

In particular, these filler materials should have improved properties in the presence of moisture. They must in particular have improved hygroscopicity, in particular reduced hygroscopicity. Thus, these materials must have a reduced capacity to absorb the humidity present in their environment, in particular during their preparation or else during their use for the preparation of plastic polymer materials, in particular during their storage or their use for the preparation. preparation of polyolefin resins.

Generally, these filler materials are materials of mineral origin. They can in particular be chosen from materials comprising calcium carbonate.

These materials comprising calcium carbonate are used in the form of particles which are prepared chemically or else by grinding and dispersing mineral materials, in particular by wet grinding. The methods of preparing these filler materials must therefore also be improved in order to be implemented at a high concentration of solid matter while making it possible to obtain filler materials having improved final properties. The control of the viscosity during the various stages of preparation of these filler materials is also a sought-after property. In carrying out these methods of preparing filler materials, grinding aids or dispersing agents are usually used.

However, the methods of the state of the art, and in particular the grinding aid agents or the dispersing agents which are used, continue to pose problems.

It is therefore important to have available improved methods and means for the preparation and use of these filler materials for plastic polymer materials.

Document WO 2014/049252 describes a process for preparing a polymer of (meth) acrylic acid having a molecular mass of less than 8,000 g / mol in the presence of a combination of a disulfide compound and a system polymerization initiator. Document WO 02/49765 discloses the use of homopolymers or copolymers of (meth) acrylic acid and of one or more acrylic, vinyl or allylic monomers as a dispersing agent or as an agent to aid in the grinding of mineral matter in aqueous suspension. Document WO 2018/109400 also relates to the grinding in the presence of water of a mineral material in the presence of at least one (meth) acrylic acid polymer prepared in the presence of sodium hypophosphite and disodium trithiocarbonate dipropionate.

The invention relates to a method of treating a material which makes it possible to provide a solution to all or part of the problems of the methods of the state of the art.

Thus, the invention provides a method of reducing the hygroscopicity of a material (M) comprising calcium carbonate and intended for use in a polymeric material, comprising the treatment of the material (M), by means of minus an aid homopolymer

grinding (P)

- prepared by a polymerization reaction of a compound chosen from acrylic acid, a salt of acrylic acid, methacrylic acid and a salt of methacrylic acid, and including:

- the molecular mass Mw (measured by CES) ranges from 3,000 to 5,000 g / mol,

- whose polymolecularity index (Ip) ranges from 1.5 to 2.9, and

- the carboxylic acid groups are partially or totally neutralized by:

* 70 mol% of Na + and

* from 10 to 30 mol% by at least one cation chosen from Na + , K + , Li + and their combinations.

Preferably, the method according to the invention comprises:

A. the preparation of an aqueous suspension of the material (M) comprising:

Al. Of water,

A2. at least one material (M),

A3 at least one homopolymer (P),

B. wet grinding of the material (M) in the aqueous suspension,

C. partial separation of water from the aqueous suspension comprising the ground material (M).

According to the invention, during the preparation (A) of the aqueous suspension of the material (M), different procedures can be implemented separately or in combination.

Thus, this suspension can be prepared by simultaneously mixing water, material (M) and homopolymer (P).

It is also possible to separately mix water and material (M) and then add G homopolymer (P).

It is also possible to separately mix water and the homopolymer (P) and then add the material (M).

Finally, it is also possible to separately mix the material (M) and the homopolymer (P) and then add water.

Preferably according to the invention, the method also comprises:

D. drying the suspension of the ground material (M) and possibly

E. treating the crushed and dried material (M) with at least one hydrophobicizing agent.

Thus, the implementation of the method according to the invention makes it possible to provide particular properties to the material (M) which are particularly useful when using the material (M) thus conditioned. The invention therefore also provides a method of conditioning a filler material (M) for plastic polymer, comprising calcium carbonate and having low sensitivity to humidity. The conditioning method according to the invention comprises the treatment of the material (M) by means of at least one homopolymer to aid grinding (P) prepared by a polymerization reaction of a compound chosen from acrylic acid, a salt of 'acrylic acid, methacrylic acid and a salt of methacrylic acid, and of which:

- the molecular mass Mw (measured by CES) ranges from 3,000 to 5,000 g / mol,

- the polymolecularity index (Ip) ranges from 1.5 to 2.9, and

- the carboxylic acid groups are partially or totally neutralized by:

* 70 mol% of Na + and

* from 10 to 30 mol% by at least one cation chosen from Na + , K + , Li + and their combinations.

The preferred, particular or advantageous characteristics of the method for reducing the hygroscopicity of a material (M) according to the invention define conditioning methods according to the invention which are also preferred, particular or advantageous.

Preferably according to the invention, the material (M) comprising calcium carbonate is chosen from marble, limestone, chalk, dolomite, their mixtures and their combinations. The calcium carbonate used according to the invention can therefore be of natural origin but also of synthetic origin. Preferably, the calcium carbonate of synthetic origin (PCC) is chosen from vaterite, calcite aragonite, their mixtures and their combinations.

Preferably according to the invention, the ground material (M) has a median particle diameter dso by weight (determined by sedimentation) of 0.1 to 3 μm, preferably 0.1 to 2.8 mih, more preferably from 0.4 to 2.6 µm, much more preferably from 0.6 to 2.5 µm. Also preferably according to the invention, the ground material (M) has a specific surface area measured according to the BET method according to the ISO 9277 (2010) standard ranging from 1 to 50 m 2 / g, preferably from 2 to 20 m 2 / g and more preferably from 3 to 10 m 2 / g.

Also preferably, the aqueous suspension of step (A) comprises from 40 to 78% by weight, preferably from 50 to 70% by weight, of material (M).

According to the invention, step (B) of grinding the suspension (M) prepared during step (A) is followed by step (C) of separation making it possible to increase the concentration by weight of material ( M) ground relative to the amount by weight of suspension.

Thus and also preferably, the aqueous suspension obtained after separation (C) comprises at least 74% by weight, preferably at least 76% by weight of ground material (M) relative to the quantity by weight of suspension. More preferably, the aqueous suspension obtained after separation (C) comprises at least 78% by weight, in particular from 74 to 83% by weight or from 76 to 83% by weight or even from 78 to 83% by weight, of material (M) ground relative to the amount by weight of suspension.

Essentially, the invention comprises the use of at least one homopolymer (P). Preferably, the carboxylic acid groups of the homopolymer (P) are partially neutralized. More preferably, the neutralization is carried out using Na + . Much more preferably, the carboxylic acid groups of the homopolymer (P) are partially neutralized to at least 80 mol% by Na + , much more preferably neutralized to at least 90 mol% by Na + or neutralized to 100 mol% by Na + . Also preferably, when the carboxylic acid groups of the copolymer (P) are partially neutralized with at least 80 mol% of Na +, the other carboxylic acid groups of the copolymer (P) are in free acid form or else are partially neutralized by at least one cation chosen from K + , Li + and their combinations.

The method according to the invention also comprises the wet grinding of the material (M) in the aqueous suspension prepared beforehand. Preferably, the grinding (B) is carried out in the presence of 0.05 to 0.5% by weight of homopolymer (P) relative to the quantity by weight of material (M). Also preferably, the grinding (B) is carried out in the presence of 0.08 to 0.4% by weight of homopolymer (P) relative to the amount by weight of material (M). More preferably, the grinding (B) is carried out in the presence of from 0.1 to 0.3% by weight of homopolymer (P) relative to the quantity by weight of material (M).

Much more preferably, the grinding (B) is carried out in the presence of 0.12 to 0.2% by weight of homopolymer (P) relative to the quantity by weight of material (M).

Also preferably, the partial separation (C) of the water from the aqueous suspension is carried out by at least one means chosen from among mechanical means, thermal means; preferably by thermal means, optionally under vacuum or optionally combined with suction means. More preferably, the partial separation (C) of the water from the aqueous suspension is carried out by at least one thermal means.

Also preferably, the ground material (M) is dried by at least one means chosen from an atomization means, a freeze-drying means, a spraying means, a rotary oven, a heating strip, a jet heating means. , a fluidized bed, a fluidized lyophilization means and a nozzle drying means. More preferably, the ground material (M) is dried by at least one pulverization means.

According to the invention, the ground and dried material (M) is treated by means of at least one hydrophobicizing agent. Preferably, the hydrophobizing agent is chosen from a carboxylic acid, preferably an aliphatic carboxylic acid, in particular a C4-C24-aliphatic carboxylic acid. Particularly preferably, the hydrophobizing agent is an aliphatic monocarboxylic acid, in particular a C4-C24-aliphatic monocarboxylic acid. Stearic acid is the preferred hydrophobizing agent.

The hydrophobizing agent can also be chosen from a derivative of succinic acid anhydride monosubstituted by a linear, branched or cyclic C2-C30-alkyl group, and a reaction product of such a derivative.

The hydrophobizing agent can also be chosen from a mixture of phosphoric acid monoesters, phosphoric acid diesters or their reaction products or else chosen from a polyhydrogenosiloxane, an inert silicone compound, preferably an oil. inert silicone, in particular polydimethylsiloxane, and mixtures thereof or alternatively chosen from a C Ô -CU aliphatic aldehyde, preferably a C Ô aliphatic aldehyde-C 12, more preferably a C8-C9 aliphatic aldehyde, in particular hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodecanal, tridecanal, butadecanal and their mixtures. The hydrophobizing agent can also be chosen from butanoic acid, pentanoic acid, hexanoic acid, hetpanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachidic acid, heneicosylic acid, behenic acid, lignoceric acid and their combinations.

In particular, the invention makes it possible to obtain a material having improved properties. Preferably, the ground and dried material (M) comprises less than 0.5% by weight, preferably less than 0.4% by weight or less than 0.2% by weight, of moisture relative to the amount total of material (M).

Also preferably, the ground, dried and treated material (M) has a hygroscopicity less than or equal to 0.26 mg / m 2 , preferably less than or equal to 0.25 mg / m 2 , measured according to the method described in the examples.

More preferably, the material (M) crushed, dried and treated by means of at least one hydrophobizing agent has a hygroscopicity less than or equal to 0.26 mg / m 2 , preferably less than or equal to 0, 25 mg / m 2 , measured according to the method described in the examples.

The method according to the invention makes it possible to obtain a material (M) which has reduced hygroscopicity. The use as filler of plastic polymer materials of this treated material (M) is then particularly advantageous. In particular, the material (M) obtained according to the invention can be used as filler for plastic polymer materials chosen from polyolefins, polyamides, halogenated polymers and polyesters.

The examples which follow make it possible to illustrate the various aspects of the invention.

Examples

Methods of measuring properties

Measurement of the weight-average molecular mass (Mw) and of the polymolecularity (Ip) of the polymers according to the invention and for comparisons

According to the invention, the molecular weight of the copolymers is determined by Steric Exclusion Chromatography (CES) or in English “Gel Permeation Chromatography” (GPC). This technique uses a Waters brand liquid chromatography apparatus equipped with a detector. This detector is a Waters brand refractometric concentration detector. This liquid chromatography apparatus is fitted with a steric exclusion column in order to separate the different molecular weights of the copolymers studied. The liquid phase of elution is an aqueous phase adjusted to pH 9.00 by means of 1N sodium hydroxide containing 0.05 M of NaHCO 3 , 0.1 M of NaNO 3, 0.02 M of triethanolamine and 0.03% of NaN3.

According to a first step, the copolymer solution is diluted to 0.9% dryness in the solvent for solubilizing the CES, which corresponds to the liquid phase for eluting the CES to which 0.04% of dimethylformamide is added, which plays a role. the role of flow marker or internal standard. Then, it is filtered at 0.2 µm. 100 μL are then injected into the chromatography apparatus (eluent: an aqueous phase adjusted to pH 9.00 with IN sodium hydroxide containing 0.05 M of NaHCO 3 , 0.1 M of NaNCh, 0.02 M of trietanolamine and 0.03% NaN 3 ).

The liquid chromatography apparatus contains an isocratic pump (Waters 515) whose flow rate is set at 0.8 mL / min. The chromatography apparatus also comprises an oven which itself comprises the following column system as standard: a Guard Column Ultrahydrogel Waters type precolumn 6 cm in length and 40 mm in internal diameter and a Waters Ultrahydrogel type linear column of 30cm in length and 7.8mm inside diameter. The detection system consists of an RI Waters 410 type refractometric detector. The oven is brought to a temperature of 60 ° C and the refractometer is brought to a temperature of 45 ° C.

The chromatography apparatus is calibrated using standards of sodium polyacrylate powder of different molecular masses certified by the supplier: Polymer Standards Service or American Polymers Standards Corporation (molecular mass ranging from 900 to 2.25.10 6 g / mol and polymolecularity index ranging from 1.4 to 1.8).

PH measurement

The pH is measured at 25 ° C using a Mettler Toledo Seven Easy pH meter and a Mettler Toledo InLab Expert Pro pH electrode. A three-point calibration (using the segment method) of the instrument was first performed using commercially available buffer solutions showing pH values ​​of 4.7 and 10 at 25 ° C. (Aldrich). The reported pH values ​​were the final values ​​detected by the instrument (the signal differs by less than 0.1 mV from the mean in the last 6 seconds).

Conductivity measurement of mineral material suspensions

The conductivity of the suspensions is measured at 25 ° C with a Mettler Toledo Seven Multi device equipped with a corresponding Mettler Toledo extension and a Mettler Toledo InLab 731 conductivity probe, directly after preparation of the suspension with stirring at 1,500 rpm. min with a Pendraulik tine agitator. The instrument was calibrated within the appropriate conductivity range using commercial conductivity calibration solutions (Mettler Toledo). The influence of temperature on the conductivity is corrected automatically by the linear correction mode. The measured conductivities are reported for the reference temperature of 20 ° C. The reported conductivity values ​​are the end point values ​​detected by the instrument, when the measured conductivity differs by less than 0,

Particle size distribution and median diameter by weight of the particles of mineral material

The particle size distribution (% by mass of particles with a diameter less than a fixed value) and the median diameter by weight (dso) of the material particles were determined by a known sedimentation method. This is an analysis of the behavior of sedimentation in a gravity field. The measurement was carried out at 25 ° C. by means of a Sedigraph 5100 apparatus. The measurement was carried out in an aqueous solution of 0.1% by weight of Na 4 P 2 0 7 . The samples particles of mineral material are dispersed using a high speed and ultrasonic stirrer.

Measurement of the viscosity of mineral material suspensions

The Brookfield viscosity was measured at 25 ° C. and at a rotational speed of 100 rev / min, using a Brookfield model RVT viscometer equipped with a suitable 2, 3 or 4 disc axis.

Measurement of the specific surface of the crushed mineral material

The specific surface (m 2 / g) was determined using the BET method (with nitrogen as adsorbent gas) in accordance with ISO 9277 (2010). The total area (m 2 ) of the filling material was then obtained by multiplying the area and the mass (g) of the corresponding sample.

Measurement of the level of solid matter, or dry extract, of suspensions of mineral material

The dry extract (% by weight) is determined by dividing the mass of the solid material by the total mass of the aqueous suspension. The dry extract in solid material is determined by weighing the quantity of solid material after evaporation of the aqueous phase of the suspension and then drying the material obtained until a constant mass is obtained.

Measurement of the hygroscopicity of materials (M) obtained according to the invention or comparative

After exposure to an atmosphere of 10% relative humidity, for 2.5 hours and at a temperature of 23 ± 2 ° C, the mass of a sample of material (M) obtained according to the invention by means of a GraviTest 6300 device (Gintronic).

Then, the humidity of the atmosphere is changed to reach 85% relative humidity and the sample of material (M) is exposed to this atmosphere for 2.5 hours and at a temperature of 23 ± 2 ° C. The mass of the material sample (M) is then measured again.

The variation in mass (mg / g of sample) is then calculated to determine the hygroscopicity of the material (M).

Similarly, the hygroscopicity of a comparative material (M) obtained by means of a comparative polymer is determined.

Measurement of the moisture content of materials (M) obtained according to the invention or comparative

A sample of material (M) obtained according to the invention (10 g) is heated to 150 ° C. in an oven until its mass is constant for 20 minutes. The mass loss is determined by gravimetry and is expressed in% by weight from the initial mass of the sample. This variation in mass makes it possible to determine the moisture content of the sample.

In an analogous manner, the variation in mass of a comparative material (M) obtained by means of a comparative polymer is determined.

Preparation of homopolymers (P) according to the invention and of comparative polymers Polymer (PI) according to the invention

In a synthesis reactor equipped with a mechanical stirring system and an oil bath type heating system, are introduced:

- water: 654 g,

- sodium hypophosphite monohydrate: 8 g.

The medium is heated to 95 ° C, then added simultaneously and continuously, for 2 hours using 3 pumps:

- an aqueous solution consisting of 8.4 g of sodium persulfate and 150 g of water,

- an aqueous solution consisting of 71 g of sodium hypophosphite monohydrate and 150 g of water,

- 1 017 g of acrylic acid.

Heating is continued for 1 hour at 95 ° C.

The polymer is then neutralized with 50% by weight sodium hydroxide in water to a pH of 8.4. The polymer is diluted with water to reach a concentration of 42% by dry weight.

A polymer is obtained having a molecular mass Mw of 3630 g / mole and 2.0 of polymolecularity index.

Polymer (P2) according to the invention

In a synthesis reactor equipped with a mechanical stirring system and an oil bath type heating system, are introduced:

- water: 654 g,

- sodium hypophosphite monohydrate: 8 g.

The medium is heated to 95 ° C, then added simultaneously and continuously, for 2 hours using 3 pumps:

- an aqueous solution consisting of 8.4 g of sodium persulfate and 150 g of water,

- an aqueous solution consisting of 71 g of sodium hypophosphite monohydrate and

150 g of water,

- 1 017 g of acrylic acid.

Heating is continued for 1 hour at 95 ° C.

The polymer is then treated with sodium hydroxide at 50% by weight in water to neutralize 90 mol% of the carboxylic groups. A polymer solution at pH 5.8 is obtained.

The polymer is diluted with water to reach a concentration of 42% by dry weight.

A polymer is obtained having a molecular mass Mw of 3630 g / mole and 2.0 of polymolecularity index.

Comparative Polymer (PCI)

In a synthesis reactor equipped with a mechanical stirring system and an oil bath type heating system, are introduced:

- water: 241 g,

- copper sulphate pentahydrate: 0.32 g,

- ferrous sulfate heptahydrate: 0.276 g.

The medium is heated to 95 ° C, then added simultaneously and continuously, for 2 hours:

- an aqueous solution of 3.5 g at 20.9% by weight by weight in water of the sodium salt of DPTTC (CAS number 86470-33-2) diluted in 31 g of water,

- 35.3 g of 130 V hydrogen peroxide diluted in 9.4 g of water and

- 279.9 g of acrylic acid diluted in 31 g of water.

Heating is continued for 1.5 hours at 95 ° C.

A polyacrylic acid solution is obtained having a molecular mass Mw of 6000 g / mol and of 2.6 of polymolecularity index.

The polyacrylic acid solution is treated with a 50% sodium hydroxide solution in water (212 g) and Ca (OH) 2 (42.5g) and water up to pH 8.7 and a concentration of 38% by dry weight.

Preparation, treatment and evaluation of the properties of materials (M) according to the invention and of comparative materials

An aqueous suspension is prepared from a material (M) (natural marble from Avenza, Italy) whose measured particle size is characterized by a dg value of 50 mih, a dso value of 10 mih and a ho value. of 2 mhi. The dry extract of the suspension is approximately 71% by weight.

With stirring by means of a Y stral Dispermix mixer, a polymer according to the invention or a comparative polymer is introduced into the suspension in a quantity by dry weight of 1500 ppm.

Then, the material (M) present in the suspension is wet ground in the presence of the polymer introduced previously. Grinding is carried out by means of a 200 liter vertical attritor mill using zirconium silicate beads with a diameter of 0.6 to 1.0 mm. The temperature of the suspension at the inlet of the mill is 20 ° C and 50 to 70 ° C at its outlet. The parameters of the mill are adjusted in order to achieve a particle size distribution of at least 46% of particles smaller than 2 µm in size. The polymers used and the characteristics of the suspensions are presented in Table 1.

[Table 1]

It is noted that for very high solids values ​​(greater than 71%), the suspensions according to the invention have viscosities much lower than the viscosity of the comparative suspension not comprising a particular polymer selected according to the invention.

Then, part of the water is separated from the suspensions at a suspension temperature of 95 ° C. by means of an Epcon thermally controlled evaporator. The suspensions are allowed to cool and the dry extract, the viscosity at 25 ° C. and the specific surface area of ​​the ground material are measured. The results are shown in Table 2.

[Table 2]

It is again noted that for even higher solids values ​​(greater than 74.5%), the suspensions according to the invention have viscosities much lower than the viscosity of the comparative suspension not comprising a particular polymer selected according to invention.

The suspensions are then spray dried using a Niro dryer (GEA) operating at a spray speed of 16,680 rpm. The burner temperature is 400 ° C. The temperature of the drying tower is 130 ° C.

The ground and dried material (M) obtained is then treated with stearic acid as a hydrophobizing agent in an amount of 1.2% by weight of stearic acid relative to the dry weight of material (M), using a Somakon MP-LB mixer (Somakon Verfahrenstechnik). The material (M) is first stirred at 2000 rpm and heated to 120 ° C. then stearic acid is added over a period of 10 min while maintaining heating and stirring. The hygroscopicity is then determined for the different materials (M) according to the invention and for comparison. The results are shown in Table 3.

[Table 3]

It is observed that the use of a particular polymer selected according to the invention confers an improved hygroscopicity compared to the material (M) after drying and treatment by means of a hydrophobizing agent compared to a material (M) ground in the presence of 'a comparative polymer.

CLAIMS

1. Method of reducing the hygroscopicity of a material (M) comprising calcium carbonate and intended for use in a polymeric material, comprising the treatment of the material (M) by means of at least one homopolymer of grinding aid (P)

- prepared by a polymerization reaction of a compound chosen from acrylic acid, a salt of acrylic acid, methacrylic acid and a salt of methacrylic acid, and of which

- the molecular mass Mw (measured by CES) ranges from 3,000 to 5,000 g / mol,

- whose polymolecularity index (Ip) ranges from 1.5 to 2.9, and

- the carboxylic acid groups are partially or totally neutralized by:

* 70 mol% of Na + and

* from 10 to 30 mol% by at least one cation chosen from Na + , K + , Li + and their combinations.

2. Method according to claim 1 comprising:

A. the preparation of an aqueous suspension of the material (M) comprising:

Al. Of water,

A2. at least one material (M),

A3 at least one homopolymer (P),

B. wet grinding of the material (M) in the aqueous suspension,

C. partial separation of water from the aqueous suspension comprising the ground material (M).

3. Method according to claim 2 also comprising:

D. drying the suspension of the ground material (M) and possibly

E. treating the crushed and dried material (M) with at least one hydrophobicizing agent.

4. Method according to one of claims 2 or 3 for which:

- the ground material (M) has a median particle diameter dso by weight (determined by sedimentation) of 0.1 to 3 μm, preferably from 0.1 to 2.8 μm, more preferably from 0.4 to 2, 6 µm, much more preferably 0.6 to 2.5 µm;

- the ground material (M) has a specific surface area measured according to the BET method according to standard IS09277 (2010) ranging from 1 to 50 m 2 / g, preferably from 2 to 20 m 2 / g and more preferably from 3 to 10 m 2 / g; Where

- the material (M) is chosen from among marble, limestone, chalk, dolomite, their mixtures and their combinations or is of natural or synthetic origin, for example vaterite, calcite aragonite, their mixtures and their combinations.

5. Method according to one of claims 2 to 4 for which the aqueous suspension of step (A) comprises from 40 to 78% by weight, preferably from 50 to 70% by weight, of material (M).

6. Method according to one of claims 2 to 5 for which the aqueous suspension obtained after separation (C) comprises at least 74% by weight, preferably at least 76% by weight, more preferably at least 78% by weight, in particular from 74 to 83% by weight or from 76 to 83% by weight or else from 78 to 83% by weight, of material (M) ground relative to the quantity by weight of suspension.

7. Method according to one of claims 1 to 6 for which the carboxylic acid groups of the homopolymer (P) are partially neutralized, preferably by Na + , more preferably neutralized to at least 80 mol% by Na + , much more preferably neutralized to at least 90 mol% with Na + or neutralized to 100 mol% with Na + .

8. Method according to one of claims 2 to 7 for which the grinding (B) is carried out in the presence of 0.05 to 0.5% by weight, preferably from 0.08 to 0.4% by weight, more preferably from 0.1 to 0.3% by weight, even more preferably from 0.12 to 0.2% by weight, of homopolymer (P) relative to the amount by weight of material (M).

9. Method according to one of claims 2 to 8 for which the partial separation (C) of the water from the aqueous suspension is carried out by at least one means chosen from among mechanical means, thermal means; preferably by thermal means, optionally under vacuum or optionally combined with suction means.

10. Method according to one of claims 3 to 9 for which the ground material (M) is dried by at least one means chosen from an atomization means, a freeze-drying means, a spraying means, a rotary kiln, a heating strip, jet heating means, fluidized bed, fluidized lyophilization means and nozzle drying means; preferably by spraying means.

11. Method according to one of claims 3 to 10 for which the hydrophobizing agent is chosen from:

a carboxylic acid, preferably an aliphatic carboxylic acid, in particular a C4-C24-aliphatic carboxylic acid, more preferably an aliphatic monocarboxylic acid, in particular a C4-C24-aliphatic monocarboxylic acid, in particular stearic acid;

a derivative of succinic acid anhydride monosubstituted by a linear, branched or cyclic C2-C3o-alkyl group or a reaction product of such a derivative;

- a mixture of phosphoric acid mono-esters, of phosphoric acid diesters or of their reaction products;

- a polyhydrogenosiloxane, an inert silicone compound, preferably an inert silicone oil, in particular polydimethylsiloxane, and mixtures thereof;

- a C Ô -CU aliphatic aldehyde, preferably a C6-C12 aliphatic aldehyde, more preferably a C8-C9 aliphatic aldehyde, in particular hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodecanal, tradidecanal and, their mixtures.

12. Method according to one of claims 3 to 11 for which the crushed and dried material (M) comprises less than 0.5% by weight, preferably less than 0.4% by weight or less than 0.2% by weight. weight, moisture in relation to the total amount of material (M).

13. Method according to one of claims 1 to 12 for which the material (M) crushed, dried and treated, optionally by means of at least one hydrophobicizing agent, has a hygroscopicity less than or equal to 0.26 mg / m 2 , preferably less than or equal to 0.25 mg / m 2 , measured according to the method described in the examples.