EP4619472A1 - Modified precipitated silica, its manufacture and use - Google Patents

Abstract

The invention concerns a modified precipitated silica (MPS) comprising precipitated silica particles, a polyethylene glycol and an antioxidant that is chosen among certain hydroxyfuranone or phenolic derivatives. The invention concerns also a process for the manufacture of the MPS, elastomeric compositions comprising the MPS and their use for the manufacture of semi-finished or finished articles such as tire parts.

Description

MODIFIED PRECIPITATED SILICA, ITS MANUFACTURE AND USE

Cross Reference to a Related Application

[0001] This application claims priority from European application No. 22207337.1 filed on 14 November 2022, the whole content of this application being incorporated herein by reference for all purposes.

Technical Field

[0002] The present invention relates to a modified precipitated silica and to a process for the preparation of a modified precipitated silica, to a use of the modified precipitated silica in a polymer composition suitable for the manufacture of tire parts.

Background Art

[0003] Precipitated silica has long been used as reinforcing filler in polymeric materials and, in particular, in elastomers. In the latter, it is known to use a polyethylene glycol polymer (CAS number 25322-68-3) to block the surface of silica to prevent adsorption of ingredients prior to reticulation. It is however unpractical to mix a polyethylene glycol with silica and other ingredients of the formulation and the same is true when silica is used in other polymeric compositions like in paint and lacquers.

[0004] CA2255456 aims at solving this problem by providing a precipitated silica that is coated with polyethylene glycol. In example 8 thereof, a polyethylene glycol having a molecular weight of 1000 is added to a filter cake of silica which has been liquefied. The Applicant has observed that a modified precipitated silica such as the one of CA2255456 exhibits an improved ability to disperse in elastomeric matrices and, probably as a result thereof, a globally improved balance of mechanical properties; in particular, the Applicant has found that tire rubber compositions filled with this precipitated silica achieve a better compromise between wear resistance and rolling resistance. Unfortunately, as also observed by the Applicant, such precipitated silicas modified with a polyethylene glycol and the rubber compositions incorporating them suffer from a poor thermal stability.

[0005] There is a need for a modified precipitated silica that has a substantially higher thermal stability than a polyethylene glycol-modified silica, such as the one of CA2255456, desirably as close as possible to the thermal stability of an unmodified precipitated silica, while retaining a good ability to disperse in elastomeric matrices and still allowing for the preparation of elastomeric compositions with a good balance of mechanical properties, as the polyethylene glycol-modified silica of CA2255456 does. In particular, there is a need for a modified precipitated silica which, when contained in a tire rubber composition, provides said tire rubber composition with a better compromise between wear resistance and rolling resistance than the one that can be obtained with an unmodified precipitated silica, while preserving a high thermal stability, substantially higher than the one that can be obtained with a precipitated silica modified with a polyethylene glycol.

Description of the invention [0006] These needs and still other ones are met with a modified precipitated silica in accordance with the present invention, namely a modified precipitated silica (MPS) comprising

- at least 70 wt%, based on the total weight of the MPS, of precipitated silica particles,

- at least 1 .0 wt%, based on the total weight of the MPS, of at least one polyethylene glycol, and

- at least 0.0010 wt%, based on the total weight of the MPS, of at least one antioxidant, wherein the antioxidant is:

(i) at least one hydroxyfuranone derivative selected from the group consisting of dehydroascorbic acid and its hydrates, hydroxyfuranone derivatives of formula (I) and hydroxyfuranone derivatives of formula (II) wherein

- R⁷ is hydrogen or Ci-C alkyl

- R⁸ is selected from the group consisting of hydroxy, Ci-C alkyl, Ci-C alkoxy, C₂-C₄ alkenyl and C₂-C₄ alkenyloxy

- R⁹ is selected from the group consisting of hydrogen, Ci-C alkyl, Ci-C and R^d, independently from each other, are selected from the group consisting of hydrogen and Ci-C alkyl, and

- R¹⁰ is hydrogen or Ci-C alkyl and/or

(ii) a phenolic derivative of formula (III) wherein

- R¹, R³ and R⁵, independently of each other, are hydrogen or C1-C4 alkyl

- R² is selected from the group consisting of hydroxy, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 hydroxyalkyl, C₂-C₄ alkenyl, C₂-C₄ alkenyloxy, C₂-C₄ hydroxyalkenyl, -C(=O)H, -COOH, -COOMe wherein Me is an alkali metal (in particular, Na or K), -COOR^fwherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl, -R^f-COOH wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl and -R^f-COOMe wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl and Me is an alkali metal (in particular, Na or K)

- R⁴ is selected from the group consisting of hydrogen, hydroxy, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 hydroxyalkyl, C₂-C₄ alkenyl, C₂-C₄ alkenyloxy, C₂-C₄ hydroxyalkenyl, -C(=O)H, -COOH, -COOMe wherein Me is an alkali metal (in particular, Na or K), -COOR^fwherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl, -R^f-COOH wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl, -R^f-COOMe wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl and Me is an alkali metal (in particular, Na or K), and -SO₃Me wherein Me is an alkali metal (in particular, Na or K),

- R⁶ is hydrogen, hydroxy, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 hydroxyalkyl, C₂-C₄ alkenyl and -SO₃Me wherein Me is an alkali metal (in particular Na or K).

[0007] The terms “precipitated silica particles” are used herein to refer to synthetic amorphous silica (silicon dioxide, SiO₂) particles obtained by a process wherein a silicate is reacted with an acid causing the precipitation of SiO₂.

[0008] For the avoidance of doubt, the weight amount of the precipitated silica particles contained in the MPS, as herein provided, does not include the weight amount of by-products and other impurities that may result from the precipitation process to form said precipitated silica particles; otherwise said, the weight amount of the precipitated silica particles represents a weight of silica and only silica.

[0009] The precipitated silica particles are comprised in the MPS in an amount which is preferably of at least 75 wt%, more preferably of at least 80 wt% and still more preferably of at least 82 wt%, based on the total weight of the MPS. Besides, they are comprised in the MPS in an amount that is generally of at most 95 wt%, preferably at most 90 wt% and more preferably of at most 88 wt%, based on the total weight of the MPS.

[0010] The MPS can be characterized by a CTAB surface area and a BET surface area, which typically reflect respectively the CTAB surface area and the BET surface area of the precipitated silica particles contained therein, as the MPS is generally free of any particles other than the precipitated silica particles.

[0011] The CTAB surface area is a measure of the external specific surface area of the precipitated silica particles as determined by measuring the quantity of N- hexadecyl-N,N,N-trimethylammonium bromide adsorbed on the silica surface at a given pH. The CTAB surface area can be determined according to the standard NF ISO 5794-1 , Appendix G (June 2010). The CTAB surface area of the MPS and the CTAB surface area of the precipitated silica particles range generally from 50 to 350 m²/g, very often from 70 to 300 m²/g, often from 100 to 250 m²/g. Sometimes, they range from 150 up to less than 200 m²/g, and some other times, they range from 200 to 250 m²/g. [0012] The BET surface area of the MPS and the BET surface area of the precipitated silica particles range generally from 40 to 450 m²/g, very often from 60 to 350 m²/g, often from 80 to 300 m²/g. Sometimes, they range from 80 up to less than 150 m²/g, or from 150 up to less than 200 m²/g, or from 200 up to less than 250 m²/g or from 250 up to 300 m²/g. The BET surface area is determined according to the Brunauer - Emmett - Teller method described in The Journal of the American Chemical Society, Vol. 60, page 309, February 1938, and corresponding to the standard NF ISO 5794-1 , Appendix D (June 2010).

[0013] The polyethylene glycol is comprised in the MPS in an amount which is preferably of at least 2.0 wt%, more preferably of at least 4.0 wt% and still more preferably of at least 6.0 wt%, based on the total weight of the MPS. Besides, it is comprised in the MPS in an amount that is generally of at most 20 wt%, preferably at most 15 wt% and more preferably of at most 10 wt%, based on the total weight of the MPS.

[0014] In a similar manner, the weight amount of the polyethylene glycol can be expressed with respect to the weight amount of the precipitated silica particles. The weight amount of the polyethylene glycol, based on the weight amount of the precipitated silica particles, ranges advantageously from 1 .0 wt% to 20 wt%. It is preferably of at least 2.0 wt%, more preferably of at least 4.0 wt% and still more preferably of at least 6.0 wt%, based on the weight amount of the precipitated silica particles. Besides, it is preferably at most 15 wt% and more preferably of at most 10 wt%, based on the weight amount of the precipitated silica particles.

[0015] Advantageously, at least part of, preferably more than half of the weight amount, still more preferably essentially the whole amount of the polyethylene glycol comprised in the MPS forms a coating and/or is adsorbed on the surface of the precipitated silica particles.

[0016] In some embodiments, it can be useful to express the weight amount of the polyethylene glycol with respect to the CTAB surface area of the MPS or of the precipitated silica particles. The weight amount of the polyethylene glycol, based on the CTAB surface area of the MPS or of the precipitated silica particles, ranges advantageously from 0.030 to 5.0 mg/m². It is preferably of at least 0.075, more preferably of at least 0.15 mg/m² and still more preferably of at least 0.30 mg/m², based on the CTAB surface area of the MPS or of the precipitated silica particles. Besides, it is preferably at most 3.0 mg/m², more preferably of at most 1.5 mg/m² and still more preferably of at most 0.70 mg/m², based on the CTAB surface area of the MPS or of the precipitated silica particles. Good results were obtained with a weight amount of the polyethylene glycol, based on the CTAB surface area of the MPS or of the precipitated silica particles, ranging from 0.20 to 1 .00 mg/m², especially from 0.30 to 0.70 mg/m².

[0017] The weight average molecular weight Mw of the polyethylene glycol, as measured by Gel Permeation Chromatography (GPC)ZSize Exclusion Chromatography (SEC) using polystyrene calibration standards, is generally in the range from 100 to 10000 g/mol. It is preferably of at least 200 g/mol, more preferably of at least 300 g/mol and still more preferably of at least 400 g/mol. Besides, it is preferably of at most 5000 g/mol, more preferably at most 2000 g/mol, still more preferably of at most 1000 g/mol and even more preferably of at most 800 g/mol. Good results were obtained with a polyethylene glycol having a weight average molecular weight Mw in the range of from 400 to 800 g/mol, especially from 500 to 700 g/mol.

[0018] The melting point of the polyethylene glycol depends to a significant extent on the molecular weight. It ranges usually from -60 °C to +60 °C. It is preferably greater than 0 °C, more preferably of at least 10 °C and still more preferably of at least 15°C. Besides, it is preferably of at most 50°C, more preferably of at most 40°C and still more preferably of at most 30°C. Good results were obtained with a polyethylene glycol having a melting point from 15 °C to 30 °C, in particular from 20 °C to 25 °C.

[0019] Exemplary polyethylene glycols in accordance with the present invention are PEG 400 (wherein PEG stands for “polyethylene glycol” with a M_w of about 400, having generally a melting point of from 2 to 10 °C, often from 4 to 8 °C), PEG 600 (with a M_w of about 600, having generally a melting point of from 17 to 25 °C, often from 19 to 24 °C), PEG 1000 (having generally a melting point of from 32 to 40 °C) and PEG 1500 (having generally a melting point of from 42 to 50 °C, often from 44 to 48 °C).

[0020] The antioxidant is comprised in the MPS in an amount which is preferably of at least 0.0030 wt%, more preferably of at least 0.010 wt%, still more preferably of at least 0.030 wt% and even more preferably of at least 0.050 wt%, based on the total weight of the MPS. Besides, it is comprised in the MPS in an amount which is generally of at most 3.0 wt%, preferably of at most 1 .0 wt%, more preferably of at most 0.30 wt% and more preferably of at most 0.10 wt%, based on the total weight of the MPS.

[0021] Advantageously, at least part of, preferably more than half of the weight amount, still more preferably essentially the whole amount of the antioxidant comprised in the MPS is homogeneously dispersed or at least substantially homogeneously dispersed in a coating formed by the polyethylene glycol at the surface of the precipitated silica particles and/or throughout the polyethylene glycol adsorbed at the surface of said precipitated silica particles.

[0022] In some embodiments, it can be useful to express the weight amount of the antioxidant with respect to the weight amount of the polyethylene glycol. The weight amount of the antioxidant, based on the weight amount of the polyethylene glycol, ranges generally from 0.10 wt% to 10.0 wt%. It is preferably of at least 0.25 wt%, more preferably of at least 0.50 wt% and still more preferably of at least 0.75 wt%. Besides, it is preferably of at most 5.0 wt%, more preferably of at most 2.5 wt% and still more preferably of at most 1 .5 wt%. Good results were obtained with a weight amount of the antioxidant, based on the weight amount of the polyethylene glycol, ranging from 0.75 wt% to 1 .5 wt%.

[0023] In many embodiments, the antioxidant is a solid under standard ambient temperature and pressure conditions (25°C = 298.15 K and 1 atm = 101.325 kPa, hereinafter “SATP”).

[0024] In some embodiments, the antioxidant is a solid at temperature T_s and atmospheric pressure (1 atm = 101.325 kPa), wherein T_s is equal to the temperature of the melting point of the polyethylene glycol plus 30 °C. In these embodiments, the weight amount of the antioxidant, based on the weight amount of the polyethylene glycol, is advantageously below the solubility limit of the antioxidant in the polyethylene glycol as determined at temperature T_s and atmospheric pressure, wherein the weight amount of the antioxidant based on the weight amount of the polyethylene glycol and the solubility limit of the antioxidant in the polyethylene glycol are expressed in the same unit, e.g. wt% (grams of antioxidant per 100 grams of polyethylene glycol). The solubility limit of the antioxidant can be determined by adding an amount of the antioxidant to the polyethylene glycol under agitation and waiting for a sufficient time until a homogeneous solution is obtained, and repeating the same until no more homogeneous solution can be obtained at equilibrium (because the antioxidant cannot dissolve any more in the polyethylene glycol). The determination of the solubility limit can be made visually and/or with the assistance of a turbidimeter, a UV-visible spectrophotometer, a Dynamic Light Scattering equipment or the like. The weight amount of the antioxidant based on the weight amount of the polyethylene glycol may be at least twice, at least 5 times, at least 10 times, at least 20 times, at least 50 times, at least 100 times lower than the solubility limit of the antioxidant in the polyethylene glycol as determined at temperature T_s and atmospheric pressure.

[0025] In some other embodiments, the antioxidant is a liquid at temperature T_s and atmospheric pressure (1 atm = 101.325 kPa), wherein T_s is equal to the temperature of the melting point of the polyethylene glycol plus 30 °C. In these embodiments, the weight amount of the antioxidant and the weight amount of the polyethylene glycol contained in the MPS are such that, when the antioxidant and the polyethylene glycol are combined at temperature T_s and atmospheric pressure in such weight amounts to form a binary liquid mixture consisting of the antioxidant and the polyethylene glycol, the binary liquid mixture resulting from such a combination is a homogeneous solution (otherwise said, it is a one-phase binary mixture, wherein the antioxidant and the polyethylene glycol are miscible with each other). In these embodiments, the antioxidant is preferably either fully miscible (i.e. in any proportions) with the polyethylene glycol at temperature T_s and atmospheric pressure, or it is only partially miscible with the polyethylene glycol at temperature T_s and atmospheric pressure but up to a weight amount, based on the weight of the polyethylene glycol that is contained in the MPS, that is at least twice, preferably at least 5 times, at least 10 times, at least 20 times, at least 50 times or even at least 100 times higher than the weight amount of the antioxidant, based on the amount of the polyethylene glycol, that is effectively contained in the MPS. The assessment of the miscibility of liquid antioxidants in the polyethylene glycol can be likewise made by adding an amount of the antioxidant to the polyethylene glycol under agitation and waiting for a sufficient time until a homogeneous solution is obtained, and repeating thus until no more homogeneous solution can be obtained at equilibrium (because the antioxidant and the polyethylene glycol for a two-phase liquid binary mixture).

[0026] In a first embodiment, the antioxidant is a hydroxyfuranone derivative as above detailed.

[0027] The hydroxyfuranone derivative can be dehydroascorbic acid of formula (IV) or a hydrate thereof; hydrates of the dehydroascorbic acid are compounds formulae (IVa) and (IVb)

[0028] The hydroxyfuranone derivative can be of formula (I).

[0029] In formula (I), R⁷ is preferably hydrogen or methyl; more preferably, R⁷ is hydrogen.

[0030] Besides, in formula (I), R⁸ is preferably selected from the group consisting of hydroxy, Ci-C alkoxy and C₂-C₄ alkenyloxy (e.g. allyloxy); more preferably, R⁸ is hydroxy or methoxy, and, still more preferably, R⁸ is hydroxy.

[0031] Besides, in formula (I), R⁹ is preferably selected from the group consisting of Ci-

C₄ alkyl, Ci-C dihydroxyalkyl, wherein R^c and R^d, independently from each other, are selected from the group consisting of hydrogen and Ci-C alkyl and wherein preferably at least one, more preferably both, of R^cand R^d is (are) Ci-C alkyl, especially methyl; still more preferably, R⁹ is -CHOH-CH2OH.

[0032] Non limitative examples of hydroxyfuranone derivatives of formula (I) are: [0033] - 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone, commonly known as maple furanone or ethyl fenugreek lactone, of formula (Va)

[0034] - L-ascorbic acid, also known as ascorbic acid (IUPAC name: L-threo-Hex-2- enono-1 ,4-lactone or (R)-3,4-Dihydroxy-5-((S)- 1 ,2-dihydroxyethyl)furan- 2(5H)-one, CAS Registry Number® 50-81-7) of formula (Vb)

[0035] - D-ascorbic acid (IUPAC name: D-f/7/'eo-Hex-2-enono-1 ,4-lactone, CAS Registry Number® 10504-35-5) of formula (Vc) [0036] - L-isoascorbic acid (IUPAC name: L-eryt/?ro-Hex-2-enono-1 ,4-lactone, CAS Registry Number® 26094-91-7) of formula (Vd)

[0037] - D-erythorbic acid, also known as erythorbic acid or D-isoascorbic acid (IUPAC name: (5R)-5-[(1 R)-1 ,2-Dihydroxyethyl]-3,4-dihydroxyfuran-2(5H)- one or D-eryf/7/'o-Hex-2-enono-1 ,4-lactone, CAS Registry Number® 89-65-6), of formula (Ve)

[0038] and mixtures thereof.

[0039] Still other examples of hydroxyfuranone derivatives of formula (I) are 5,6-0- isopropylidene-3-O-methyl-L-ascorbic acid, 5,6-O-isopropylidene-3-O-allyl-L- ascorbic acid, 3-O-methyl-L-ascorbic, 3-O-allyl-L-ascorbic acid, and the like.

[0040] The hydroxyfuranone derivative can be of formula (II).

[0041] In formula (II), R⁷ is preferably hydrogen or methyl; more preferably, R⁷ is hydrogen.

[0042] Besides, in formula (II), R⁸ is preferably Ci-C alkyl or C₂-C₄ alkenyl, more preferably Ci-C alkyl and still more preferably methyl.

[0043] Besides, in formula (II), R¹⁰ is hydrogen or methyl.

[0044] Non limitative examples of hydroxyfuranone derivatives of formula (II) are 4- hydroxy-5-methyl-3-furanone and 4-Hydroxy-2,5-dimethyl-3(2H)-furanone (commonly known as strawberry furanone or furaneol).

[0045] Among all the hydroxyfuranone derivatives in accordance with the present invention, those complying with formula (I) are generally preferred. In particular, good results were obtained when using L-ascorbic acid and/or D-erythorbic acid as the antioxidant, out of which D-erythorbic acid being the more preferred.

[0046] In another first embodiment, the antioxidant is a phenolic derivative of formula (III) as above detailed.

[0047] In formula (III), R¹ is preferably hydrogen or methyl; more preferably, R¹ is hydrogen.

[0048] Besides, in formula (III), R² is preferably selected from the group consisting of hydroxy, Ci-C alkyl, Ci-C alkoxy, -C(=O)H, -COOH and -R^f-COOH wherein R^f is Ci-C alkanediyl or C₂-C₄ alkenediyl; more preferably, R² is selected from the group consisting of hydroxy, Ci-C alkyl, methoxy, -COOH and -CH=CH-COOH; still more preferably, R² is selected from the group consisting of hydroxy, methoxy and te/Y-butyl; the most preferably, R² is hydroxy.

[0049] Besides, in formula (III), R³ is preferably hydrogen or methyl; more preferably, R³ is hydrogen. [0050] Besides, in formula (III), R⁴ is preferably selected from the group consisting of hydrogen, hydroxy, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 hydroxyalkyl, C₂-C₄ alkenyl, -C(=O)H, -COOH, -R^f-COOH wherein R^f is C1-C4 alkanediyl or C2-C4 alkenediyl, and -SO₃Me wherein Me is an alkali metal; more preferably, R⁴ is selected from the group consisting of hydrogen, hydroxy, methyl, methoxy, -CH₂OH, -C(=O)H, - COOH, -CH₂-COOH and -SO₃Na; still more preferably, R⁴ is selected from the group consisting of hydrogen, hydroxy, methoxy and -COOH; the most preferably, R⁴ is -COOH.

[0051] Besides, in formula (III), R⁵ is preferably hydrogen or methyl; more preferably, R⁵ is hydrogen.

[0052] Besides, in formula (III), R⁶ is preferably selected from the group consisting of hydrogen, hydroxy, C1-C4 alkoxy and -SO₃Me wherein Me is an alkali metal; more preferably, R⁶ is selected from the group consisting of hydrogen, hydroxy, methoxy and -SO₃Na; still more preferably, R⁶ is hydroxy.

[0053] Non limitative examples of phenolic derivatives of formula (III) are 2-fe/ -buty I-4- hydroxyanisole, 3-tert-butyl-4-hydroxyanisole, protocatechuyl alcohol, hydroxytyrosol, dihydrocaffeoyl alcohol, caffeoyl alcohol, vanillyl alcohol, homovanillyl alcohol, dihydroconiferyl alcohol, coniferyl alcohol, veratryl alcohol, homoveratryl alcohol, 3-(3,4-dimethoxyphenyl)-1-propanol, galloyl alcohol, 5- methoxy-protocatechuyl alcohol, syringyl alcohol, p-coumaric acid, ferulic acid, sinapic acid, caffeic acid, o-coumaric acid, pyrogallol, veratrole, guaiacol, 4- methylcatechol, salicylic acid, gallic acid, tiron, protocatechuic acid, protocatechuic aldehyde, hydroxychavicol, eugenol, chavibetol, catechol, 4-tert- butylcatechol, 4-allylcatechol, 3-allylcatechol and mixtures thereof.

[0054] A suitable mixture of phenolic derivatives of formula (III) is commonly referred to as butylated hydroxyanisole; this one is a mixture consisting essentially or consisting of 2-tert-butyl-4-hydroxyanisole and 3-tert-butyl-4-hydroxyanisole, and comprises generally more than 50 wt%, very often at least 80 wt% and often at least 90 wt% of 3-tert-butyl-4-hydroxyanisole, based on the total weight of the butylated hydroxyanisole.

[0055] Good results were obtained with phenolic derivatives complying with formula (III) wherein R¹ is hydrogen, R² is C1-C4 alkyl (especially tert-butyl) or hydroxy, R³ is hydrogen, R⁴ is hydrogen or C1-C4 alkoxy (especially methoxy), R⁵ is hydrogen and R⁶ is hydrogen. Excellent results were obtained with 3-tert-butyl-4- hydroxyanisole (possibly contained in butylated hydroxyanisole) and gallic acid, out of which gallic acid is the more preferred.

[0056] The MPS may further contain additional component.

[0057] The MPS may further contain water (water moisture). As well known to the skilled person, water (water moisture) is a usual component of any unmodified precipitated silica. Water (water moisture) is generally present in the MPS in an amount that is the same or substantially the same as the one that can be found in an unmodified precipitated silica comprising the same or substantially the same precipitated silica particles.

[0058] Water (water moisture) is generally comprised in the MPS in an amount of from 1 .0 wt% to 20 wt%, very often from 3.0 to 15 wt%, often from 5.0 to 10.0 wt%, especially from 7.0 wt% to 8.0 wt%%, based on the total weight of the MPS.

[0059] The MPS may also further comprise an alkali metal salt. As above mentioned, the precipitated silica particles are usually obtained by a process wherein a silicate is reacted with an acid. Said silicate is usually an alkali metal silicate, often a sodium silicate, while said acid is often sulfuric acid. Therefore, an alkali metal salt, often a sodium salt, especially sodium sulfate, is inevitably co-produced with the precipitated silica particles and a residual amount thereof can be found in the MPS.

[0060] The alkali metal salt is generally comprised in the MPS in an amount of from 0.10 to 5.0 wt%, very often from 0.30 to 3.0 wt%, often from 0.50 to 2.0 wt%, especially from 1 .0 to 1 .5 or from 1 .0 to 2.0 wt%.

[0061] No substantial amount of any other component may be present in the MPS, but possibly as impurity traces. Otherwise said, the MPS may consist essentially of, or may even consist of, the precipitated silica particles, the polyethylene glycol, the antioxidant, water (water moisture) and the alkali metal salt.

[0062] Alternatively, the MPS may further contain additional components, for example a polypropylene glycol, a carboxylic monoacid such as stearic acid or a carboxylic diacid such as 2-methylglutaric acid. These additional components, when present, are generally comprised in the MPS in a combined amount of at most 10 wt%, preferably at most 5.0 wt%, possibly at most 2.0 wt% or at most 1.0 wt% based on the total weight of the MPS. Besides, these additional components, when present, are generally comprised in the MPS in a weight amount that is below that of the polyethylene glycol, typically in a weight amount that is at least twice lower than that of the polyethylene glycol.

[0063] The present invention also concerns a process for the preparation of the modified precipitated silica (MPS) as above described, said process comprising the steps of:

- reacting at least one silicate with at least one acid in an aqueous medium to provide a first precipitated silica suspension;

- submitting said first precipitated silica suspension to a liquid/solid separation step to obtain a cake;

- submitting said cake to a liquefaction step to obtain a second precipitated silica suspension;

- submitting said second precipitated silica suspension to a drying step to recover precipitated silica particles, wherein the polyethylene glycol and the antioxidant, independently of each other, are simultaneously or consecutively added to at least one of (i) the cake before and/or during the liquefaction step, and (ii) the second precipitated silica suspension after the liquefaction step but before the drying step, and/or wherein, after the drying step, the precipitated silica particles are simultaneously or consecutively impregnated with the polyethylene glycol and the antioxidant.

[0064] The silicate is usually an alkali metal silicate, preferably a sodium and/or a potassium silicate, more preferably sodium silicate. The silicate may be in any known form, such as metasilicate and/or disilicate. When sodium silicate is used, the latter generally has a SiO₂/Na₂O weight ratio of from 2.0 to 4.0, in particular from 2.4 to 3.9, for example from 3.1 to 3.8.

[0065] The silicate is generally provided as a solution which typically has a concentration of from 3.9 wt% to 25 wt%, for example from 5.6 wt% to 23 wt%, in particular from 5.6 wt% to 20.7 wt%. Throughout the text, silicate concentration in a solution is expressed in terms of the amount by weight of SiO₂. [0066] Any acid can be used in the process. A mineral acid, such as sulfuric acid, nitric acid or hydrochloric acid, can be used. An organic acid, such as acetic acid, formic acid or carbonic acid, can also be used. Sulfuric acid is preferred.

[0067] The acid can be metered into the reaction medium in diluted or concentrated form. The same acid at different concentrations can be used in different stages of the process.

[0068] In a preferred embodiment of the process, sulfuric acid and sodium silicate are used.

[0069] Several methods can be employed for the precipitation of the silica: notably, the acid can be added to a solution of the silicate, and/or the acid and the silicate can be added simultaneously to water or to a silicate solution already present in the vessel.

[0070] At the end of the precipitation reaction, a suspension comprising precipitated silica particles suspended in the aqueous medium is obtained (here, the “first precipitated silica suspension).

[0071] Then, the precipitated silica particles are separated from the aqueous medium (liquid/solid separation step). Advantageously, the separation step is achieved by filtering the first precipitated silica suspension on a filter, optionally followed by a washing of the precipitated silica particles retained on the filter. The filtration can be performed according to any suitable equipment, for example by means of a belt filter, a rotary filter (e.g. a vacuum filter) or, preferably, by means of a filter press. The solid mass that is recovered after the liquid/solid separation step is commonly named “cake”; in particular, when the liquid/solid separation step is achieved by filtering the first precipitated silica suspension on a filter, the solid mass which is retained on the filter after the aqueous medium that contained it has passed through, is called “filter cake”.

[0072] The cake, esp. the filter cake, is then subjected to a liquefaction step. The term “liquefaction” is intended herein to indicate a unitary operation or method wherein a solid, namely the cake, is converted into a fluid-like mass. After the liquefaction step, the cake is in a flowable, fluid-like form, and constitutes another new suspension comprising precipitated silica particles suspended in the aqueous medium (here, the “second precipitated silica suspension”).

[0073] The liquefaction step comprises advantageously a mechanical treatment which results in a reduction of the granulometry of the precipitated silica particles in suspension. Otherwise said, the precipitated silica particles comprised in the second precipitated silica suspension after the liquefaction step have advantageously an average particle size that is significantly lower than the number average particle size of the precipitated silica particles comprised in the first precipitated silica suspension. The mechanical treatment can be carried out by passing the cake, esp. the filter cake, through a high shear mixer, a colloidal- type mill or a ball mill. Alternatively or complementary, the liquefaction step can be carried out by subjecting the cake, esp. the filter cake, to a chemical action, for instance by adding water and/or an acid such as sulfuric acid.

[0074] The second precipitated silica suspension is then dried to recover the precipitated silica particles that were contained therein. Drying can be performed according to any means known in the art. Preferably, the drying is performed by atomizing (spray drying) the second precipitated silica suspension. To this end, use may be made of any type of suitable atomizer, in particular a turbine, nozzle, liquid pressure or two-fluid spray-dryer.

[0075] When the drying operation is performed using a nozzle spray-dryer, the precipitated silica particles that are recovered from are the second precipitated silica suspension are usually in the form of substantially spherical beads (commonly referred to as “micropearls”).

[0076] After drying, an additional step of milling or micronizing can be performed on the recovered the precipitated silica particles; the precipitated silica particles that result from this optional additional step are then generally in the form of a powder.

[0077] Finally, the dried and optionally further milled or micronized precipitated silica particles can be further subjected to an agglomeration step, which can consist of a direct compression, a wet granulation (i.e. with use of a binder, such as water, silica suspension, etc.), an extrusion or, preferably, a dry compacting operation. The precipitated silica particles that result from this optional additional agglomeration step are generally in the form of granules.

[0078] Notable, non-limiting examples of suitable processes for the preparation of precipitated silica particles are disclosed for instance in EP396450A, EP520862A, EP647591A, EP670813A, EP670814A, EP901986A, EP762992A, EP762993A, EP917519A, EP983966A, EP1355856A, W003/016215, W02009/112458, WO2011/117400.

[0079] Compared to these processes of the prior art, the invented process is characterized in that:

- a polyethylene glycol and an antioxidant, independently of each other, are simultaneously or consecutively added to at least one of (i) the cake, before and/or during the liquefaction step, and (ii) the second precipitated silica suspension, after the liquefaction step but before the drying step and/or after the drying step, the precipitated silica particles are simultaneously or consecutively impregnated with the polyethylene glycol and the antioxidant.

[0080] When the antioxidant is a solid, a suitable vehicle can be used to facilitate its incorporation to, as the case may be, the cake, the second precipitated silica suspension and/or the dried precipitated silica particles. For example, an organic solvent such as an alcohol or a ketone can serve as the vehicle.

[0081] Preferably, the polyethylene glycol and the antioxidant are simultaneously added to or are simultaneously caused to impregnate, as the case may be, the cake, the second precipitated silica suspension and/or the dried precipitated silica particles.

[0082] More preferably, the polyethylene glycol and the antioxidant are simultaneously added to or are simultaneously caused to impregnate, as the case may be, the cake, the second precipitated silica suspension and/or the dried precipitated silica particles in the form of a single solution (preferably, a single homogeneous solution) comprising the polyethylene glycol and the antioxidant. The solution of concern may optionally comprise water and/or an organic solvent such as an alcohol.

[0083] Still more preferably, the polyethylene glycol and the antioxidant are simultaneously added to or are simultaneously caused to impregnate, as the case may be, the cake, the second precipitated silica suspension and/or the dried precipitated silica particles in the form of a single solution (preferably, a single homogeneous solution) consisting essentially of (or even consisting of) the polyethylene glycol, the antioxidant and, optionally in addition, water. The homogeneous solution can consist essentially of or can even consist of the polyethylene glycol and the antioxidant. However, preferably, some water is comprised in the solution (preferably, the homogeneous solution), preferably in an amount of at least 5 wt%, more preferably of at least 8 wt%, still more preferably of at least 11 wt%, based on the combined weight of the water and the polyethylene glycol; besides, for economic reasons, water is advantageously comprised in the solution in an amount of at most 25 wt%, preferably at most 20 wt%, still more preferably at most 15 wt%, based on the combined weight of the water and the polyethylene glycol. When water is comprised in the solution, this one is advantageously prepared by, firstly, forming a liquid mixture consisting essentially of the polyethylene glycol and water, then adding the antioxidant to the liquid mixture.

[0084] To operate the preferred above embodiments wherein the antioxidant and the polyethylene glycol are contained in a single homogeneous solution, said single homogeneous solution is prepared at a pressure which is generally the atmospheric pressure and at a temperature which is advantageously of at least 10°C, preferably at least 20°C and more preferably at least 25°C higher than the melting point of the polyethylene glycol on the one hand and which is advantageously of at least 20°C, preferably at least 30°C and more preferably at least 40°C on the other hand; besides, the temperature of preparation does not usually exceed 90°C; preferably, it is of at most 70°C.

[0085] In some preferred embodiments, the polyethylene glycol and the antioxidant (possibly in the form of a single homogeneous solution consisting essentially of the polyethylene glycol, the antioxidant and, optionally in addition, water) are added to the cake just before or during the liquefaction step. More preferably, the polyethylene glycol and the antioxidant are fully added to the cake before the liquefaction step or during the first half of its whole duration. Still more preferably, the polyethylene glycol and the antioxidant are fully added to the cake before the liquefaction step has started.

[0086] The addition of the polyethylene glycol and the antioxidant, possibly in the form of a single homogeneous solution consisting essentially of the polyethylene glycol, the antioxidant and, optionally in addition, water, is operated at a pressure which is generally the atmospheric pressure. Besides, said addition is operated at a temperature which is advantageously of at least 10°C, preferably at least 20°C and more preferably at least 25°C higher than the melting point of the polyethylene glycol on the one hand and which is advantageously of at least 20°C, preferably of at least 30°C and more preferably of at least 40°C on the other hand; besides, the temperature of addition does not usually exceed 90°C; preferably, it is of at most 70°C.

[0087] As it transpires from the above, to optimize the introduction of the polyethylene glycol and of the antioxidant, some parameters are preferably adapted such as flow rate, temperature, form (i.e. physical state) of the polyethylene glycol and of the antioxidant, and mechanical agitation conditions. For example, the polyethylene glycol can be introduced as a pure solid or liquid, or as a dispersion or solution in a solvent; the same applies to the antioxidant. The flow rate of the polyethylene glycol and antioxidant addition is preferably adapted to their form (solid or liquid). One shot for solid polyethylene glycol and antioxidant is convenient in practice, while for polyethylene glycol and antioxidant in the form of a liquid solution or dispersion, progressive or one-time introductions can be made.

[0088] Finally, to favour homogeneous repartition of the polyethylene glycol and antioxidant in the cake or in the second precipitated silica suspension, it is preferable to add the polyethylene glycol and the antioxidant under agitation; in particular, when the polyethylene glycol and the antioxidant are added to the cake, the agitation is preferably vigorous, at a rate of at least 300 rpm, and preferably through a shearing blade to break enough the cake.

[0089] Using a low molecular weight polyethylene glycol makes it possible to obtain a second precipitated silica suspension with a low viscosity even if the polyethylene glycol used absent water or in an aqueous solution or dispersion with a polyethylene glycol concentration of more than 85 wt% or so. Having a slurry with a low viscosity makes it “pumpable” which is very useful for the drying step which is often spray-drying.

[0090] The Applicant has also found that if the polyethylene glycol is present during liquefaction, it results in an increase of the size of the precipitated silica particles, (viz. silica particles aggregates), which in turn increases the cohesion of the micropearls or the granules obtained from these aggregates and this with less production of fines and without altering the dispersibility (i.e. the ability to disperse) of the MPS in polymeric compositions, especially in elastomeric ones.

[0091] The MPS according to the present invention can be used in numerous applications, in particular as a filler of a polymer composition, especially a polymer composition comprising at least one elastomer and the invented MPS.

[0092] The elastomer exhibits preferably at least one glass transition temperature of from -150°C to +30°C, for example from -150°C to +20°C.

[0093] Mention may be made, as possible elastomers, of diene elastomers. Among diene elastomers mention may be made, for example, of polybutadienes (BRs or butadiene rubbers), polyisoprenes (IRs or isoprene rubbers), butadiene copolymers, isoprene copolymers, or their mixtures, and in particular styrene/butadiene copolymers (SBRs, in particular ESBRs (emulsion) or SSBRs (solution)), isoprene/butadiene copolymers (BIRs), isoprene/styrene copolymers (SIRs), isoprene/butadiene/styrene copolymers (SBIRs) and ethylene/propylene/diene terpolymers (EPDMs). Mention may also be made of natural rubber (NR) and epoxidized natural rubber (ENR). Good results were obtained with SBR, possibly in combination with BR and/or NR.

[0094] The polymer composition can be vulcanized with sulfur or crosslinked, in particular with a peroxides or other crosslinking system (for example, a diamine or a phenolic resin).

[0095] In general, the polymer composition additionally comprises at least one (silica/elastomer) coupling agent and/or at least one covering agent.

[0096] Non-limiting examples of suitable coupling agents are for instance “symmetrical” or “unsymmetrical” silane polysulfides; mention may more particularly be made of bis((Ci-C4)alkoxyl(Ci-C4)alkylsilyl(Ci-C4)alkyl) polysulfides (in particular disulfides, trisulfides or tetrasulfides), such as, for example, bis(3- (trimethoxysilyl)propyl) polysulfides or bis(3-(triethoxysilyl)propyl) polysulfides, such as triethoxysilylpropyl tetrasulfide. Mention may also be made of monoethoxydimethylsilylpropyl tetrasulfide. Mention may also be made of silanes comprising masked or free thiol functional groups.

[0097] The coupling agent can be grafted beforehand to the elastomer. It can also be employed in the free state or grafted at the surface of the silica. It is the same for the optional covering agent.

[0098] The precipitated silica can advantageously be the sole reinforcing filler of the polymer composition. Alternatively, the invented MPS can be combined with at least one other reinforcing filler, such as another modified precipitated silica (for example, a precipitated silica “doped” with a cation, such as aluminium) and/or a reinforcing filler other than a MPS, such as an unmodified precipitated silica, alumina or a carbon black.

[0099] The proportion by weight of the MPS in the composition can vary within a fairly wide range. It normally represents from 10 wt% to 200 wt%, based on the weight of the elastomer (i.e. 10-200 phr or per hundred “rubber”, wherein rubber, as herein used, has the same meaning as “elastomer”). In particular, it amounts to from 20 to 150 phr in case the MPS is used as predominant filler, and from 10 to 50 phr in case the MPS is used in combination with another filler, generally carbon black, wherein the other filler is contained in the polymer composition in a weight amount that is greater than the weight amount of the MPS.

[00100] These polymer compositions may be used for the manufacture of numbers of articles. Non-limiting examples of semi-finished or finished articles comprising the polymer composition as described above are for instance footwear soles, floor coverings, gas barriers, flame-retardant materials and also engineering components, such as rollers for cableways, seals for domestic electrical appliances, seals for liquid or gas pipes, braking system seals, pipes (flexible), sheathings (in particular cable sheathings), cables, engine supports, battery separators, conveyor belts, transmission belts and, preferably, tires and tire parts, in particular tire treads, tire sub-treads and tire belt components (especially for light vehicles or for heavy-goods vehicles, e.g. trucks).

[00101] The invented MPS has the advantage of better processing and improved performances compared to unmodified precipitated silicas. The invented MPS meets the need for a modified precipitated silica that has a substantially higher thermal stability than a “merely” polyethylene glycol-modified silica, such as the one of CA2255456, and offers advantageously a thermal stability level that is approaches that of an unmodified precipitated silica, while retaining a good ability to disperse in elastomeric matrices and still allowing for the preparation of elastomeric compositions with a good balance of mechanical properties, similar or possibly even better to the one achieved with a prior art polyethylene glycol- modified silica. In particular, the invented MPS, when contained in a tire rubber composition, provides said tire rubber composition with a better compromise between wear resistance and rolling resistance than the one that can be obtained with an unmodified precipitated silica, while preserving a high thermal stability, substantially higher than the one that can be obtained with a precipitated silica of the prior art that was modified with a polyethylene glycol in the absence of an antioxidant of the specific nature required by the present invention.

[00102] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[00103] EXAMPLES

[00104] Example 1. Preparation of a modified silica S1 (according to the invention) [00105] ZEOSIL® 1165MP silica powder (commercially available from Solvay, sometimes also referred to as ZEOSIL® 160 silica, identified as CS1 here below) was used as a starting material for the preparation of a modified silica. PEG 600 polyethylene glycol (CAS number 25322-68-3, commercially available from Sigma-Aldrich, product No. 8.07486, batch S8111586 121) was heated during 12 h in an oven at 50°C. Then, 870.03 g of the PEG 600 thus heated were mixed with 130.3 g of distilled water to obtain a PEG solution at 87 wt%. 3.47 g of 2(3)-f- butyl-4-hydroxyanisole (BHA, CAS number 25013-16-5, commercially available from Sigma-Aldrich, product No. B1253, batch 59995) were added under agitation to 400 g of the PEG solution. The weight concentration of BHA in the PEG-BHA solution was equal to 0.86%; the solution comprised 1 .00 pbw of BHA per 100 parts of PEG.

[00106] 1008 g of the ZEOSIL® 1165MP silica powder were placed in a six-litre WAM blade mixer. The PEG-BHA solution (403.47 g) was injected into the mixer, operating at 160 rpm, through a nozzle at a relative pressure of 1 bar (1 bar g) and at 33.7°C. The injection operation was carried out for a duration of 6.31 min, deemed to correspond to an injection of 92.60 g of the PEG-BHA solution into the mixer, out of which 80.64 g of PEG and BHA (that is to say 8.00 parts by weight (pbw) in total of PEG and BHA per 100 parts of the ZEOSIL® 1165MP silica already contained therein) and 11 .96 g of water. The injection operation was then stopped. The mixer content, viz. a ZEOSIL® 1165MP silica co-impregnated with 7.921 pbw PEG and 0.079 pbw BHA per 100 parts of the silica, was let at rest for a few minutes, and then recovered from the mixer; this one is reported as modified silica S1. Modified silica S1 had a moisture content, determined by means of a thermobalance, of 7.22 wt%, based on the total weight of S1 . The thermobalance was a HC103 moisture analyser from Mettler Toledo; 3000 mg of a sample were dried at 105°C; as soon as the measured weight loss became lower than 1 mg for 50 s, the measurement was stopped. The same equipment and method were used for all further moisture content determinations.

[00107] Example 2. Preparation of a modified silica S2 (according to the invention) [00108] ZEOSIL® 1165MP silica powder (commercially available from Solvay, identified as CS1 here below) was used as a starting material for the preparation of a modified silica. PEG 600 polyethylene glycol (CAS number 25322-68-3, commercially available from Sigma-Aldrich, product No. 8.07486, batch S8111586 121) was heated during 12 h in an oven at 50°C. Then, 174 g of the PEG 600 thus heated were mixed with 26 g of distilled water to obtain 200 g of a PEG solution at 87 wt%. 1.74 g of gallic acid (CAS number 149-91-7, commercially available from Sigma-Aldrich, product No. G7384) was added under agitation to the thus obtained PEG solution. The weight concentration of gallic acid in the PEG-gallic acid solution was equal to 0.86%; the solution comprised 1.00 pbw of gallic acid per 100 parts of PEG.

[00109] 1008 g of the ZEOSIL® 1165MP silica powder were placed in a six-litre WAM blade mixer. The PEG-gallic acid solution (201.74 g) was injected into the mixer, operating at 160 rpm, through a nozzle at a relative pressure of 1 bar (1 bar g) and at 50°C. The injection operation was carried out for a duration of 7.48 min, deemed to correspond to an injection of 97.05 g of the PEG-acid gallic solution into the mixer, out of which 84.54 g of PEG and acid gallic (that is to say 8.39 parts by weight (pbw) in total of PEG and gallic acid per 100 parts of the ZEOSIL® 1165MP silica already contained therein). The injection operation was then stopped. The mixer content, viz. a ZEOSIL® 1165MP silica co-impregnated with 8.304 pbw PEG and 0.083 pbw gallic acid per 100 parts of the silica, was let at rest for a few minutes, and then recovered from the mixer; this one is reported as modified silica S2. Modified silica S2 had a moisture content of 7.60 wt%, based on the total weight of S2.

[00110] Example 3. Preparation of a modified silica S3 (according to the invention)

[00111] ZEOSIL® 1165MP silica powder (commercially available from Solvay, identified as CS1 here below) was used as a starting material for the preparation of a modified silica. PEG 600 polyethylene glycol (CAS number 25322-68-3, commercially available from Sigma-Aldrich, product No. 8.07486, batch S8111586 121) was heated during 12 h in an oven at 50°C. Then, 174 g of the PEG 600 thus heated were mixed with 26 g of distilled water to obtain 200 g of a PEG solution at 87 wt%. 1.74 g of D-erythorbic acid (commercially available from Sigma-Aldrich, product No. 856061) was added under agitation to the PEG solution. The weight concentration of D-erythorbic acid in the PEG/D-erythorbic acid solution was equal to 0.86%; the solution comprised 1.00 pbw of D- erythorbic acid per 100 parts of PEG.

[00112] 1008 g of the ZEOSIL® 1165MP silica powder were placed in a six-litre WAM blade mixer. The PEG/D-erythorbic acid solution (201.74 g) was injected into the mixer, operating at 160 rpm, through a nozzle at a relative pressure of 1 bar (1 bar g) and at 50°C. The injection operation was carried for a duration of 7.08 min, deemed to correspond to an injection of 97.05 g of the PEG/D-erythorbic acid solution into the mixer, out of which 84.54 g of PEG and D-erythorbic acid (that is to say 8.39 parts by weight (pbw) in total of PEG and D-erythorbic acid per 100 parts of the ZEOSIL® 1165MP silica already contained therein). The injection operation was then stopped. The mixer content, viz. a ZEOSIL® 1165MP silica co-impregnated with 8.304 pbw PEG and 0.083 pbw D-erythorbic acid per 100 parts of the silica, was let at rest for a few minutes, and then recovered from the mixer; this one is reported as modified silica S3. Modified silica S3 had a moisture content of 7.76 wt%, based on the total weight of S3.

[00113] Example 4. Preparation of a modified silica S4 (according to the invention) [00114] - Preparation of a silica cake

[00115] An aqueous suspension of a precipitated silica (hereinafter ’’the silica suspension”) was prepared at pilot scale according to a recipe substantially as described in example 3 of US Patent No. 9,938,154.

[00116] The silica suspension was filtered and washed on a filter press to obtain a silica cake having a silica content equal to 19.73 wt%, based on the total weight of the silica cake.

[00117] The so-prepared silica cake was similar to the cake obtained during the manufacture of ZEOSIL® 1165MP silica at industrial scale before its disintegration (“liquefaction”) and drying.

[00118] - Preparation of a modified silica from a silica cake [00119] PEG 600 polyethylene glycol (CAS number 25322-68-3, commercially available from Sigma-Aldrich, product No. 8.07486, batch S8111586 121) was heated during 12 h in an oven at 50 °C. Then, 870.03 g of the PEG 600 thus heated were mixed with 130.3 g of distilled water to obtain a PEG solution at 87% wt%. 3.47 g of 2(3)-f-butyl-4-hydroxyanisole (BHA, CAS number 25013-16-5, commercially available from Sigma-Aldrich, product No. B1253, batch 59995) were added under agitation to 400 g of the PEG solution. The weight concentration of BHA in the PEG-BHA solution was equal to 0.86%; the solution comprised 1.00 pbw of BHA per 100 parts of PEG.

[00120] 2000 g of the silica cake with a silica concentration equal to 19.73 wt% were disintegrated mechanically and chemically by addition of a sulfuric acid solution at 7.7 wt%. A flowrate of 0.76 g/min of the sulfuric acid solution was used to reach pH 3.0. Then, 34.31 g of the PEG-BHA solution were added to the disintegrated silica cake during 10 min at constant flowrate (3.43 g/min) under agitation. At the end of this step, the so-modified disintegrated filter cake comprised 7.57 parts by weight (pbw) in total of PEG and BHA per 100 parts of silica, viz. 7.497 pbw PEG and 0.074 pbw BHA. The so-modified disintegrated silica cake was subsequently spray-dried using a nozzle atomizer; the atomizer was put under inert atmosphere. A silica powder modified with PEG and BHA was recovered; this one is reported as modified silica S4.

[00121] Example 5. Preparation of a modified silica CS2 (for comparison purposes)

[00122] ZEOSIL® 1165MP silica powder (commercially available from Solvay, identified as CS1 here below) was used as a starting material for the preparation of a modified silica. PEG 600 polyethylene glycol (CAS number 25322-68-3, commercially available from Sigma-Aldrich, product No. 8.07486, batch S8111586 121) was heated during 12 h in an oven at 50°C. Then, 870.03 g of the PEG 600 thus heated were mixed with 130.3 g of distilled water to obtain a PEG solution at 87 wt%.

[00123] 1008 g of the ZEOSIL® 1165MP silica powder were placed in a six-litre WAM blade mixer. 400 g of the PEG solution were injected into the mixer, operating at 160 rpm, through a nozzle at a relative pressure of 1 bar (1 bar g) and at 33.7°C. The injection operation was carried out for a duration of 6.32 min, deemed to correspond to an injection of 92.70 g of the PEG solution into the mixer, out of which 80.62 g of PEG (that is to say 8.00 parts by weight (pbw) in total of PEG per 100 parts of the ZEOSIL® 1165MP silica already contained therein) and 12.08 g of water. The injection operation was then stopped. The mixer content, viz. a ZEOSIL® 1165MP silica co-impregnated with 8.00 pbw PEG per 100 parts of the silica, was let at rest for a few minutes, and then recovered from the mixer; this one is reported as modified silica CS2. Modified silica CS2 had a moisture content of 7.30 wt%, based on the total weight of CS2.

[00124] Example 6. Preparation of a modified silica S5 (according to the invention)

[00125] ZEOSIL® 1165 MP silica powder (commercially available from Solvay, identified as CS1 here below) was used as a starting material for the preparation of a modified silica. PEG 600 polyethylene glycol (CAS number 25322-68-3, commercially available from Sigma-Aldrich, product No. 8.07486, batch S8111586 121) was heated during 12 h in an oven at 50°C. Then, 522 g of the PEG 600 thus heated were mixed with 78 g of distilled water to obtain 600 g of a PEG solution at 87 wt%. 3.91 g of gallic acid (CAS number 149-91-7, commercially available from Sigma-Aldrich, product No. G7384) were added under agitation to the thus obtained PEG solution. The weight concentration of gallic acid in the PEG-gallic acid solution was equal to 0.65%; the solution comprised 0.75 pbw of gallic acid per 100 parts of PEG.

[00126] 1008 g of the ZEOSIL® 1165 MP silica powder were placed in a six-litre WAM blade mixer. The PEG-gallic acid solution (605.22 g) was injected into the mixer, operating at 160 rpm, through a nozzle at a relative pressure of 1 bar (1 bar g) and at 50°C, to impregnate the silica powder. The injection operation was carried out for a duration of 7.48 min, deemed to correspond to an injection of 97.05 g of the PEG-acid gallic solution into the mixer, out of which 83.46 g of PEG and acid gallic (that is to say 8.28 parts by weight (pbw) in total of PEG and gallic acid per 100 parts of the ZEOSIL® 1165 MP silica already contained therein). The injection operation was then stopped. The mixer content, viz. a ZEOSIL® 1165 MP silica co-impregnated with 8.304 pbw PEG and 0.083 pbw gallic acid per 100 parts of the silica, was let at rest for a few other minutes, and then recovered from the mixer; this one is reported as modified silica S5. Modified silica S5 had a moisture content of 6.80 wt%, based on the total weight of S5.

[00127] Example 7. Preparation of a modified silica CS3 (for comparison purposes)

[00128] - Preparation of a silica cake

[00129] An aqueous suspension of a precipitated silica (hereinafter ’’the silica suspension”) was prepared at pilot scale according to a recipe substantially as described in example 3 of US Patent No. 9,938,154.

[00130] The silica suspension was filtered and washed on a filter press to obtain a silica cake having a silica content equal to 19.73 wt%, based on the total weight of the silica cake.

[00131] The so-prepared silica cake was similar to the cake obtained during the manufacture of ZEOSIL® 1165MP silica at industrial scale before its disintegration (“liquefaction”) and drying.

[00132] - Preparation of a modified silica from a silica cake

[00133] PEG 600 polyethylene glycol (CAS number 25322-68-3, commercially available from Sigma-Aldrich, product No. 8.07486, batch S8111586 121) was heated during 12 h in an oven at 50 °C. Then, 870.03 g of the PEG 600 thus heated were mixed with 130.3 g of distilled water to obtain a PEG solution at 87% wt%.

[00134] 2000 g of the silica cake with a silica concentration equal to 19.73 wt% were disintegrated mechanically and chemically by addition of a sulfuric acid solution at 7.7 wt%. A flowrate of 0.76 g/min of the sulfuric acid solution was used to reach pH 3.0. Then, 34.31 g of the PEG solution were added to the disintegrated silica cake during 10 min at constant flowrate (3.43 g/min) under agitation. At the end of this step, the so-modified disintegrated filter cake comprised 7.57 parts by weight (pbw) in total of PEG per 100 parts of silica. The so-modified disintegrated silica cake was subsequently spray-dried using a nozzle atomizer; the atomizer was put under inert atmosphere. A silica powder modified with PEG was recovered; this one is reported as modified silica CS3.

[00135] Example 8. Thermal stability tests

[00136] The thermal stability of precipitated silicas samples was evaluated by thermal gravimetric analysis (TGA). Samples were analysed using a LF1100 thermobalance from Mettler, according to the following protocol: - temperature ramp from 25°C to 800°C at 10°C/min under air; - the thermal stability of the samples was considered above 130 °C, that is after the water removal from the samples;

- the temperature at which the mass of the samples started (again) to decrease (after the water removal) was determined ; this one is called Tdegradation start.

[00137] The thermal stability results are shown in table 1.

[00138] Table 1. Thermal stability of modified precipitated silicas

[00139] Modified precipitated silicas S1 , S2, S3 and S5, which contain PEG and an antioxidant of a specific nature in accordance with the present invention, exhibited a much higher thermal stability than the antioxidant-free PEG-modified precipitated silica CS3 : Tdegradation start was increased by at least 27°C, up to 70°C with silica S1.

[00140] Example 9. Use of precipitated silicas for preparing elastomeric compositions

[00141] - Materials

[00142] Precipitated silicas were evaluated in a SBR/BR matrix suitable for the manufacture of a tire tread. The nature and amount of the ingredients of the elastomeric compositions is specified in table 2 here below. Each amount is expressed as phr, that is to say as parts by weight per 100 parts of the elastomers comprised in the elastomeric compositions.

[00143] Table 2. Elastomeric compositions

⁽¹⁾ SBR: SBR solution with 59% of vinyl units and 27% of styrene units, having a T_g of -28°C, available from JSR

⁽²⁾ BR: Buna CB 25 butyl rubber from Lanxess

⁽³⁾ TESPD: bis[3-(triethoxysilyl)propyl]disulfide, Xiameter Z-6920 from Dow Corning

⁽⁴⁾ TDAE oil: Vivatec 500 from Hansen & Rosenthal KG ⁽⁵⁾ Hydrocarbon resin: Sylvatraxx 4101 from Arizona Chemical

⁽⁶⁾ 6PPD: N-(1 ,3-dimethylbutyl)-N-phenyl-para-phenylenediamine, Santoflex 6- PPD from Flexsys

⁽⁷⁾ CBS: N-Cyclohexyl-2-benzothiazolesulfenamide, Rhenogran CBS-80 from RheinChemie

⁽⁸⁾ DPG: Diphenylguanidine, Rhenogran DPG-80 from RheinChemie

[00144] - Process for the preparation of the elastomeric compositions

[00145] The preparation of the elastomeric compositions was carried out in three successive preparation phases: two phases of high-temperature thermomechanical working, followed by a third phase of mechanical working at temperatures of less than 110°C to introduce the vulcanization system. The two first phases were carried out using a mixing device of internal mixer type, of Brabender brand (capacity of 380 ml_).

[00146] In a first pass of the first phase, the elastomers and the precipitated silica (introduction in instalments) were mixed with the coupling agent, the plasticizers, the stearic acid and the carbon black. The duration was 4 min and the dropping temperature was about 150°C.

[00147] During a second phase, 6-PPD and ZnO were added to the compositions and milled during 3 min30. The dropping temperature was about 150°C.

[00148] After cooling the mixture (temperature of less than 100°C), the vulcanization system was added during the third phase. It was carried out on an open mill, preheated at 50°C. The duration of this phase was between 2 and 6 minutes. Each final mixture was subsequently calendered in the form of plaques with a thickness of 2-3 mm.

[00149] - Properties of the vulcanisates

[00150] The measurements were carried out after vulcanization at 160°C.

[00151] The hardness of the samples was measured with a Shore A Hildebrand HD3000 durometer according to the ISO7619-1 standard procedure. On all samples, each measurement was made 6 times.

[00152] Values for the loss factor (tan 5) and amplitude of elastic modulus in dynamic shear (AG’) were recorded on vulcanised samples (parallelepiped specimens: cross section 8 mm² and height 7 mm). The samples were subjected to a double alternating sinusoidal shear strain at a temperature of 40° C and at a frequency of 10 Hz. The strain amplitude sweeping processes were performed according to an outward-return cycle, proceeding outward from 0.1% to 50% and then returning from 50% to 0.1%. The values reported in Table 3 here below were obtained from the return strain amplitude scanning and represent the maximum value of the loss factor (tan 5 max) and the amplitude of the elastic modulus (AG’) between the values at 0.1%and 50% of strain (Payne effect). Measurements were performed on a Metravib DMA+1000 according to standard ASTM D5992.

[00153] Uniaxial tensile tests were carried out in accordance with the instructions of standard NF ISO 37 with test specimens of H2 type at a rate of 500 mm/min on an Instron 5564 device. The x% moduli, corresponding to the stress measured at x% of tensile strain, are expressed in MPa. The tensile strength is expressed in MPa; elongation at break is expressed in MPa. On all samples, each measurement was made 10 times.

[00154] The results are shown in Table 3 below. [00155] Table 3. Properties of elastomeric compositions

⁰ Wherever a ± b format is used, a is the average value of the measurements (6 for hardness and 10 for the properties at break) and b is 2 times the standard deviation of these measurements (“2 sigma”).

[00156] The lower the Mooney viscosity, the better the processability. Thus, the processability of the compositions comprising PEG-modified precipitated silicas, namely compositions CS2, S3 and S5, was greatly improved by decreasing their Mooney viscosity. The lowest Mooney viscosities were measured with invented silicas S3 and S5, which comprised a PEG/antioxidant (of a specific nature) combination according to the invention.

[00157] The use of a PEG or of a PEG/antioxidant (of a specific nature) combination as precipitated silica modifier led also to a better hardness/hysteresis compromise, compared to unmodified precipitated silica CS1 : both PEG and PEG/antioxidant (of a specific nature) combination increased the hardness while decreasing the dissipation (tan 5 max) at 40°C. Besides, the ultimate properties (tensile strength at break, elongation at break), which are known by the skilled person to influence the wear resistance of the compositions, were not or hardly affected.

[00158] Thus, it could be seen that precipitated silicas S3 and S5 in accordance with the invention, which had been modified with a combination of PEG and an antioxidant of the specific nature required by the present invention, exhibited a better wear/rolling resistance compromise than unmodified precipitated silica CS1 , and said compromise was at least as good as the one achieved with a precipitated silica CS2 that had been modified with PEG but without antioxidant.

[00159] All in all, when integrating the thermal stability test results of table 2 and the mechanical properties test results of table 3, the invented MPS, when contained in a tire rubber composition, were able to provide said tire rubber composition with a better compromise between wear resistance and rolling resistance than the one that could be obtained with an unmodified precipitated silica, while preserving a high thermal stability, substantially higher than the one that could be obtained with a precipitated silica of the prior art that was modified with a polyethylene glycol in the absence of antioxidant of the specific nature required by the present invention.

Claims

C L A I M S

1. A modified precipitated silica (MPS) comprising

- at least 70 wt%, based on the total weight of the MPS, of precipitated silica particles,

- at least 1 .0 wt%, based on the total weight of the MPS, of at least one polyethylene glycol, and

- at least 0.0010 wt%, based on the total weight of the MPS, of at least one antioxidant, wherein the antioxidant is:

(i) at least one hydroxyfuranone derivative selected from the group consisting of dehydroascorbic acid and its hydrates, hydroxyfuranone derivatives of formula (I) and hydroxyfuranone derivatives of formula (II) wherein

- R⁷ is hydrogen or C1-C4 alkyl

- R⁸ is selected from the group consisting of hydroxy, C1-C4 alkyl, C1-C4 alkoxy, C₂-C₄ alkenyl and C₂-C₄ alkenyloxy

- R⁹ is selected from the group consisting of hydrogen, C1-C4 alkyl, C1-C4 hydroxyalkyl, Ci-

R^c

C₄ dihydroxyalkyl, ^Rd wherein R^c and R^d, independently from each other, are selected from the group consisting of hydrogen and C1-C4 alkyl

- R¹⁰ is hydrogen or C1-C4 alkyl and/or

(ii) a phenolic derivative of formula (III) wherein

- R¹, R³ and R⁵, independently of each other, are hydrogen or C1-C4 alkyl

- R² is selected from the group consisting of hydroxy, C1-C4 alkyl, C1-C4 alkoxy, Ci- 04 hydroxyalkyl, C2-C4 alkenyl, C2-C4 alkenyloxy, C₂-C₄ hydroxyalkenyl, -C(=O)H, -COOH, -COOMe wherein Me is an alkali metal, -COOR^f wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl, -R^f-COOH wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl and -R^f-COOMe wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl and Me is an alkali metal

- R⁴ is selected from the group consisting of hydrogen, hydroxy, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 hydroxyalkyl, C₂-C₄ alkenyl, C₂-C₄ alkenyloxy, C₂-C₄ hydroxyalkenyl, -C(=O)H, -COOH, -COOMe wherein Me is an alkali metal, -COOR^fwherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl, -R^f-COOH wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl, -R^f-COOMe wherein R^f is C1-C4 alkanediyl or C₂-C₄ alkenediyl and Me is an alkali metal, and -SO₃Me wherein Me is an alkali metal,

- R⁶ is hydrogen, hydroxy, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 hydroxyalkyl, C₂-C₄ alkenyl and -SO₃Me wherein Me is an alkali metal.

2. The MPS according to claim 1 , wherein the antioxidant is a hydroxyfuranone derivative of formula (I).

3. The MPS according to claim 2, wherein R⁷ is hydrogen.

4. The MPS according to claim 2 or 3, wherein R⁸ is hydroxy.

5. The MPS according to any one of claims 2 to 4, wherein R⁹ is -CHOH-CH₂OH.

6. The MPS according to claim 2, wherein the hydroxyfuranone derivative is selected from the group consisting of maple furanone, L-ascorbic acid, D-ascorbic acid, L-isoascorbic acid, D-erythorbic acid and mixtures thereof, and is preferably D-erythorbic acid.

7. The MPS according to claim 1 , wherein the antioxidant is a phenolic derivative of formula (III).

8. The MPS according to claim 7, wherein R¹ is hydrogen.

9. The MPS according to claim 7 or 8, wherein R² is hydroxy.

10. The MPS according to any one of claims 7 to 9, wherein R⁴ is -COOH.

11 . The MPS according to any one of claims 7 to 10, wherein R⁶ is hydroxy.

12. The MPS according to any one of claims 7 to 11 , wherein R³ and R⁵ are hydrogen.

13. The MPS according to claim 7, wherein the phenolic derivative is selected from the group consisting of 2-tert-butyl-4- hydroxyanisole, 3-te/Y-butyl-4-hydroxyanisole, protocatechuyl alcohol, hydroxytyrosol, dihydrocaffeoyl alcohol, caffeoyl alcohol, vanillyl alcohol, homovanillyl alcohol, dihydroconiferyl alcohol, coniferyl alcohol, veratryl alcohol, homoveratryl alcohol, 3-(3,4- dimethoxyphenyl)-1-propanol, galloyl alcohol, 5-methoxy-protocatechuyl alcohol, syringyl alcohol, p-coumaric acid, ferulic acid, sinapic acid, caffeic acid, o-coumaric acid, pyrogallol, veratrole, guaiacol, 4-methylcatechol, salicylic acid, gallic acid, tiron, protocatechuic acid, protocatechuic aldehyde, hydroxychavicol, eugenol, chavibetol, catechol, 4-tert-butylcatechol, 4-allylcatechol, 3-allylcatechol and mixtures thereof, and is preferably gallic acid.

14. The MPS according to any one of the preceding claims wherein either the antioxidant is a solid at temperature T_s and atmospheric pressure, wherein T_s is equal to the temperature of the melting point of the polyethylene glycol plus 30 °C, and the weight amount of the antioxidant, based on the weight amount of the polyethylene glycol, is below the solubility limit of the antioxidant in the polyethylene glycol as determined at temperature T_s and atmospheric pressure, wherein the weight amount of the antioxidant based on the weight amount of the polyethylene glycol and the solubility limit of the antioxidant in the polyethylene glycol are expressed in the same unit, e.g. in grams of antioxidant per 100 grams of polyethylene glycol, or the antioxidant is a liquid at temperature T_s and atmospheric pressure, and the weight amounts of the antioxidant and of the polyethylene glycol contained in the MPS are such that, when the antioxidant and the polyethylene glycol are combined at temperature T_s and atmospheric pressure in such weight amounts to form a binary liquid mixture consisting of the antioxidant and the polyethylene glycol, the binary liquid mixture resulting from such a combination is a homogeneous solution.

15. A process for the preparation of the modified precipitated silica (MPS) according to any one of claims 1 to 14, said process comprising the steps of:

- reacting at least one silicate with at least one acid in an aqueous medium to provide a first precipitated silica suspension;

- submitting said first precipitated silica suspension to a liquid/solid separation step to obtain a filter cake;

- submitting said filter cake to a liquefaction step to obtain a second precipitated silica suspension; - submitting said second precipitated silica suspension to a drying step to recover precipitated silica particles, wherein the polyethylene glycol and the antioxidant, independently of each other, are simultaneously or consecutively added to at least one of (i) the filter cake, before and/or during the liquefaction step, and (ii) the second precipitated silica suspension, after the liquefaction step but before the drying step, and/or wherein, after the drying step, the precipitated silica particles are simultaneously or consecutively impregnated with the polyethylene glycol and the antioxidant.

16. The process of claim 15, wherein the polyethylene glycol and the antioxidant are simultaneously added to or are simultaneously caused to impregnate, as the case may be, the cake, the second precipitated silica suspension and/or the dried precipitated silica particles in the form of a single solution homogeneous solution consisting essentially of the polyethylene glycol, the antioxidant and, optionally in addition, water.

17. A composition of matter or a semi-finished or finished article, in particular a tire part, comprising at least one elastomer and the modified precipitated silica (MPS) according to any one of claims 1 to 14.