ELASTOMERIC COMPOSITIONS FOR HEAVY-LOAD TIRES COMPRISING PRECIPITATED SILICA

Abstract

ELASTOMERIC COMPOSITIONS FOR HEAVY-LOAD TIRES COMPRISING A PRECIPITATED SILICA The present invention relates to elastomer compositions for heavy-load tires comprising at least one specific precipitated silica improving the mechanical properties of said composition. The invention also relates to semi-finished articles for heavy-load tires and a heavy tire comprising such elastomer compositions for tires.

Description

Title of the invention: ELASTOMERIC COMPOSITIONS FOR TIRES CARRYING HEAVY LOADS COMPRISING A PRECIPITATED SILICA Technical field

[0001] The present invention relates to reinforced elastomer compositions specially intended for the manufacture of tires capable of supporting heavy loads or semi-finished products for tires carrying heavy loads, in particular for the treads of these tires.

[0002] Background

[0003] Tires for vehicles carrying heavy loads must have very different technical characteristics from those of tires intended for vehicles which travel exclusively on roads (i.e. on a tarmac surface), such as passenger cars, because tires for vehicles carrying heavy loads must be able to withstand a load which may be extremely heavy, regardless of the nature of the terrain on which they travel (i.e. on the road or off-road). The tires of such heavy vehicles have treads which, in comparison with the thickness of the treads of tires for light vehicles, in particular for passenger cars or vans, have large thicknesses of rubber material.

[0004] Typically, the tread wear portion of a heavy-duty tire has a thickness of at least 15 mm and that of a civil engineering vehicle is at least 30 mm, or even up to 120 mm. Furthermore, due to the heavy loads they carry, their treads are stiffer than those of passenger cars. Indeed, it is desirable that the materials constituting the treads of such tires have good stiffness for low and moderate deformations, while being able to accept certain deformations without being damaged under the effect of higher stresses or deformations amplified by the heavy loads carried. In other words, it is desirable to have a material which, while being stiff in order to give the tire low rolling resistance, has a high elongation at break or tensile strength in order to provide satisfactory wear resistance.

[0005] Therefore, the solutions known for tires running on a bituminous surface, such as passenger car tires, are not directly applicable to tires carrying heavy loads, such as tires for civil engineering vehicles, tires for agricultural vehicles or for heavy goods vehicles.

[0006] Furthermore, when these tires for heavy vehicles are rolling, their treads are subjected to mechanical stresses and attacks resulting from direct contact with the ground. In the case of a tire mounted on a vehicle supporting heavy loads, the mechanical stresses and attacks to which the tire is subjected are amplified by the effect of the weight supported by the tire.

[0007] As a result, the incipient cracks that are created in the tread under the effect of these stresses and attacks tend to propagate to the surface or inside the tread, which can lead to a localized or generalized tear of the tread. These stresses can therefore damage the tread and reduce its service life and therefore that of the tire. A tire that rolls on stony ground is very exposed to attacks and therefore to incipient cracks and cuts. The actual aggressiveness of the surface of the stony ground exacerbates not only this type of attack on the tread but also its consequences on the tread.

[0008] This is particularly true for tires fitted to civil engineering vehicles that generally travel in mines and quarries. This is also the case for tires fitted to agricultural vehicles, due to the stony surface of arable land. Tires fitted to construction vehicles carrying heavy loads, which travel on both stony and bituminous soils, also suffer these same attacks. Due to the two aggravating factors of the weight supported by the tire and the aggressive nature of the rolling surface, resistance to the initiation and / or propagation of cracks in a tread of a tire for a civil engineering vehicle, an agricultural vehicle or a heavy construction vehicle proves crucial to minimize the impact of the attacks suffered by the tread.

[0009] It is therefore important to have tires for vehicles, particularly those intended to run on stony ground and to carry heavy loads, whose tread has a sufficiently high fatigue resistance to minimize the number of incipient cracks or the effect of an incipient crack on the life of the tread.

[0010] One of the objectives of the present invention is to provide an elastomer composition for tires carrying heavy loads having good fatigue resistance.

[0011] There also remains a need to further improve elastomer compositions for tires carrying heavy loads, and in particular to have compositions exhibiting a good compromise of mechanical properties in terms of rigidity, elongation at break, fatigue resistance and rolling resistance.

[0012] In light of the above, a further objective is to provide elastomeric compositions for tires carrying heavy loads which exhibit a good compromise of performance between stiffness, elongation at break, fatigue strength and rolling resistance. Summary of the invention

[0013] It has been found that elastomeric compositions for heavy-load tires with improved mechanical properties can be obtained with a specific precipitated silica.

[0014] An object of the present invention is an elastomer composition for tires carrying heavy loads based on an elastomer matrix comprising at least one diene elastomer, at least one reinforcing filler comprising at least one precipitated silica, at least one coupling agent coupling the diene elastomer to the precipitated silica and at least one crosslinking system, in which: • said elastomer matrix comprising at least 30 pce of an isoprene elastomer, • said precipitated silica being characterized by: • a CT AB surface area in the range of 40 to 525 m2 / g, • primary particles with an average size measured by SAXS less than 15 nm, • a quantity of aluminum WAi of at least 0.50% by weight, • a proportion (by weight) of particles with a size less than 1 pm after ultrasonic deagglomeration, which is at least 91%; and • a particle size distribution measured by centrifugal sedimentation using a CPS, such that for a given value of the surface area CT AB, the FWHM parameter is defined by the relation (I): I FWHM I > -0.16 x I CTAB 1 + 130 (I).

[0015] Surprisingly, it has been found that the use of said specific precipitated silica as described above makes it possible to obtain elastomer compositions for tires carrying heavy loads having a good compromise of mechanical properties, in particular a good compromise between the properties of rigidity / elongation at break / rolling resistance / fatigue resistance.

[0016] Description of the invention

[0017] In this specification, the terms "silica" and "precipitated silica" are used synonymously.

[0018] In this specification, numerical ranges defined by the expression "between a and b" indicate a numerical range that excludes the final values ​​a and b. Numerical ranges defined by the expression "from a to b" or "from a to b" indicate a numerical range that includes the final values ​​a and b.

[0019] The numerical ranges defined by the expression “a is at least b” indicate the ranges in which a is equal to or greater than b.

[0020] The term "below" is used herein in its usual and commonly accepted sense, i.e., "less than a particular quantity or level," as found in, inter alia, Cambridge's Dictionary (online version available at https: / / dictionary.cambridge.org / dictionary / english / below"); similarly, the term "lower" is also used herein in its usual and commonly accepted sense, i.e., "positioned below," as found in, inter alia, Cambridge's Dictionary, so that the terms "below" and "less than," as used herein, have the same meaning, which is their usual and commonly accepted meaning.

[0021] To avoid ambiguity, the symbol "x" in relation (I) represents the multiplication sign, so that the expression "axb" means a multiplied by b.

[0022] In the relationship, as for example in relationship (I), ICTABI represents the numerical value of the surface area CT AB expressed in m2 / g. ICTABI is a dimensionless number. For example, if the measured value of CT AB is 200 m2 / g, ICTABI is equal to 200.

[0023] The same applies to the other values ​​between 11 below, which are all the dimensionless numerical value of the parameter between said vertical bars.

[0024] The term "particles" is used to refer to the smallest aggregates of primary silica particles that can be broken by mechanical action. In other words, the term "particles" refers to assemblages / aggregates of indivisible primary particles, said aggregates being characterized by the claimed median particle size d50, while indivisible primary particles are characterized by their claimed average size.

[0025] The term "at least one," when referring to the ingredient of the composition, is used herein to indicate that one or more of each type of ingredient may be present in the composition.

[0026] The expression “copolymer” is used here to designate polymers comprising recurring units derived from at least two monomer units of different nature.

[0027] The expression “based on” composition must be understood as meaning a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents being capable of reacting or intended to react with each other, at least in part, during the various phases of manufacture of the composition, in particular during the crosslinking or vulcanization thereof.

[0028] In this description, unless expressly indicated otherwise, all percentages (%) indicated are percentages by weight.

[0029] The abbreviation "pce" (percent elastomers) means parts by weight per hundred parts by weight of elastomers (of the total elastomers, if several elastomers are present) or rubber present in the elastomer composition.

[0030] When reference is made to a “predominant” compound, it is understood, for the purposes of the present invention, that this compound is predominant among the compounds of the same type in the composition, that is to say that it is the one which represents the greatest quantity by mass among the compounds of the same type. Thus, for example, a predominant elastomer is the elastomer representing the greatest mass relative to the total mass of the elastomers in the composition. Similarly, a so-called majority filler is the one which represents the greatest mass among the fillers in the composition. For example, in a system comprising a single elastomer, this is predominant for the purposes of the present invention; and in a system comprising two elastomers, the predominant elastomer represents more than half of the mass of the elastomers.Preferably, the term "predominant" is understood to mean present at more than 50%, preferably at more than 60%, 70%, 80% and 90%, and more preferably the "predominant" compound represents 100%.

[0031] The compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of materials already used, that is to say they may be, partially or totally, derived from a recycling process, or obtained from raw materials themselves derived from a recycling process. This concerns in particular polymers, plasticizers, fillers, etc.

[0032] The glass transition temperature Tg of the elastomer is measured in accordance with ASTM D3418 (2008).

[0033] Heavy-duty vehicle tires or semi-finished articles for heavy-duty vehicles are particularly suitable for use on "heavy-duty vehicles" such as, for example, truck tires, bus tires, subway tires, tractor tires, trailer tires, aircraft tires, agricultural tires, earth-moving tires, and other off-road tires. "Heavy-duty vehicle tire treads and / or underlays" as used herein may include those of new tires, those of tires that have been retreaded, and treads (cured or uncured) that may be applied to polished tires during the retreading process. Therefore, particular embodiments of the present invention do not relate to passenger car tires and other light tires.The underlay, as used herein, is defined as the elastomeric composition located between the belt assembly and the tread.

[0034] Silica

[0035] As indicated above, the elastomer composition for tires carrying heavy fillers of the present invention comprise at least one reinforcing filler comprising at least one precipitated silica having: • a CTAB surface area in the range of 40 to 525 m2 / g; • primary particles with an average size measured by SAXS in less than 15 nm; • a quantity of aluminum WAi of at least 0.50% by weight, • a proportion (by weight) of particles with a size less than 1 pm after ultrasonic deagglomeration, which is at least 91%; and • a particle size distribution measured by centrifugal sedimentation using a CPS, such that for a given value of the CTAB surface area, the FWHM parameter is defined by the relation (I): I FWHM I > -0.16 xl CTAB I + 130 (I).

[0036] CTAB surface area is a measure of the external specific surface area determined by measuring the amount of N-hexadecyl-N,N,N-trimethylammonium bromide adsorbed on the silica surface at a given pH.

[0037] The CTAB surface area is at least 40 m2 / g, generally at least 60 m2 / g. The CTAB surface area may be greater than 70 m2 / g. The CTAB surface area may even be greater than 110 m2 / g, greater than 120 m2 / g, greater than 130 m2 / g, or even greater than 150 m2 / g.

[0038] The CTAB surface area does not exceed 525 m2 / g, typically not 300 m2 / g. The CTAB surface area may be less than 280 m2 / g, less than 250 m2 / g, less than 230 m2 / g, or even less than 210 m2 / g, less than 190 m2 / g, less than 180 m2 / g or less than 170 m2 / g.

[0039] Particularly for elastomeric reinforcement applications, advantageous ranges for the CTAB surface area are: from 50 to 300 m2 / g, preferably from 70 to 300 m2 / g, more preferably from 80 to 270 m2 / g or alternatively, from 120 to 275 m2 / g. Good results have been obtained in particular when the CTAB surface area was greater than 70 m2 / g and less than 250 m2 / g, in particular when the CTAB surface area was greater than 120 m2 / g and less than 230 m2 / g, more particularly when the CTAB surface area was greater than 120 m2 / g and less than 180 m2 / g.

[0040] The BET surface area of ​​the inventive silica used in the tire elastomer compositions of the invention is not particularly limited, but is preferably at least 10 m2 / g greater than the CTAB surface area. The BET surface area is generally at least 80 m2 / g, at least 100 m2 / g, at least 120 m2 / g, at least 140 m2 / g, at least 160 m2 / g, at least 170 m2 / g, at least 180 m2 / g, or even at least 200 m2 / g. The BET surface area may reach 300 m2 / g, or even 350 m2 / g; the BET surface area may also be at most 260 m2 / g, at most 240 m2 / g, at most 220 m2 / g, or even at most 200 m2 / g, at most 180 m2 / g or at most 170 m2 / g. In many embodiments, the BET surface area is from 100 m2 / g to 300 m2 / g.

[0041] The difference between the BET surface area and the CTAB surface area is generally considered representative of the microporosity of the precipitated silica, as it provides a measure of the pores in the silica that are accessible to nitrogen molecules but not to larger molecules, such as N-hexadecyl-N,N,N-trimethylammonium bromide.

[0042] The precipitated silica used in the elastomeric compositions of the invention can be defined by a difference between the BET surface area and the CTAB surface area of ​​at least 5 m2 / g, preferably at least 10 m2 / g. This difference is preferably less than or equal to 40 m2 / g, preferably less than or equal to 35 m2 / g.

[0043] The inventive silica used in the tire elastomer compositions of the invention contains aluminum in an amount WAi of at least 0.50 wt.% and typically at most 3.00 wt.%. Other suitable aluminum ranges WAi are from 0.50 wt.% to 1.50 wt.% (in particular, from 0.50 wt.% to 1.00 wt.%), and from more than 1.50 wt.% up to 3.00 wt. In the present text, the amount of aluminum, WAi, is defined as the weight percentage of aluminum, i.e., aluminum metal, relative to the weight of SiO2. The amount of aluminum is preferably measured by wavelength dispersive X-ray fluorescence spectrometry XRF. This aluminum generally comes at least in part from the raw materials. In some embodiments, an aluminum compound (such as sodium aluminate) is added during the synthesis of the precipitated silica and / or during the liquefaction step described below.

[0044] It should be understood that the inventive silica used in the elastomeric compositions for tires of the invention may contain elements of which non-limiting examples are for example Ga, B, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Fe, Co, Mg, Ca or Zn. Thus, in one embodiment, the silica used in the elastomeric compositions for tires of the invention contains at least one element selected from Ga, B, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Fe, Co, Mg, Ca or Zn.

[0045] The precipitated silica used in the tire elastomer compositions of the invention is further characterized by a broad particle size distribution and by small primary particles. The term "particle" refers to the smallest aggregate of primary silica particles that can be broken up by mechanical action. In other words, the term "particles" refers to assemblages / aggregates of indivisible primary particles, said aggregates being defined by the claimed FWHM while the indivisible primary particles are defined by their claimed average size. The aggregates preferably have a core / shell structure. Advantageously, the core is composed of primary particles larger than the envelope, the said core therefore being more friable.

[0046] The precipitated silica used in the tire elastomer compositions of the invention has primary particles having a dzs size measured by S AXS (Small Angle X-ray Scattering as described below) of less than 15 nm, preferably less than 14 nm, more preferably less than 13 nm. In general, the size of the primary particles is greater than 4 nm, preferably greater than 5 nm and more preferably greater than 6 nm. Some suitable ranges for dzs are between 5 and 15 nm, preferably between 6 and 14 nm, optionally 6 to 13 nm, 7 to 13 nm, 6 to 12 nm, 7 to 12 nm, 6 to 11 nm, 7 to 11 nm, 6 to 10 nm or 7 to 10 nm.Typically, the primary particles of the silica according to the invention all have a particle size in the same range (generally between 5 and 15 nm, preferably between 6 and 14 nm, more preferably between 5 and 11 nm and even more preferably between 6 and 10 nm), which in fact means that there is a population of primary particles.

[0047] The Ld of the precipitated silica used in the elastomeric compositions for tires of the invention is generally at least 1.00, preferably at least 1.25, more preferably at least 1.50. This Ld is generally less than 2.10, typically less than 2.00. The Ld of the inventive silica used in the elastomeric compositions for tires of the invention is preferably between 1.00 and 2.00, more preferably between 1.50 and 1.90. The Ld is defined as follows: Ld = (d84-di6) / d5o, where dn is the particle diameter below which n% of the total measured mass is found. Ld is a dimensionless number calculated on the cumulative particle size curve.

[0048] The FWHM parameter, determined by centrifugal sedimentation in a disk centrifuge using a CPS as detailed below, is used to define the width of the particle size distribution of the precipitated silica used in the tire elastomer compositions of the invention. The FWHM (Full Width at Half Maximum) is obtained from the differential curve of the CPS. The FWHM measures the width of the distribution of silica objects around an average size defined by the mode (in nm). If the FWHM is large around the average value, the silica product is heterogeneous. If the FWHM is narrow around the average value, the silica product is more homogeneous. In the case of a Gaussian particle size distribution (which is rarely the case in practice), the FWHM parameter is correlated with the Ld parameter.

[0049] The FWHM of the precipitated silica according to the invention is generally at least 80, very often at least 90 nm, often at least 100 nm and sometimes at least 110 nm. In addition, the FWHM parameter is generally at most 300 nm, very often at most 250 nm, often at most 200 nm, and possibly at most 190 nm, at most 180 nm, at most 170 nm or at most 160 nm. Good results were obtained with a FWHM ranging from 100 nm to 250 nm.

[0050] As indicated above, the FWHM parameter of the precipitated silica according to the invention is in accordance with the relation (I): I FWHM I > -0.16 xl CT AB I + 130 (I)

[0051] It is possible that the FWHM parameter of the precipitated silica according to the invention is in accordance with the relation (IJ: I FWHM I > ki x -0.16 xl CT AB I + 130 (I)i where ki is a dimensionless number equal to 1.20.

[0052] Furthermore, the FWHM parameter of the precipitated silica according to the invention is generally in accordance with the relation (I2): I FWHM I < k2 x -0.16 xl CT AB 1+130 (I)2 where k2 is a dimensionless number equal to 3.00.

[0053] Often, the FWHM parameter of the precipitated silica according to the invention is in accordance with the relation (I3): I FWHM I < k3 x -0.16 xl CTAB 1 + 130 (I)3 where k3 is a dimensionless number equal to 2.20.

[0054] Sometimes, the FWHM parameter of the precipitated silica according to the invention is in accordance with the relation (I4): I FWHM I < k4 x -0.16 xl CTAB 1 + 130 (I)4 where k4 is a dimensionless number equal to 1.80.

[0055] The FWHM of the precipitated silica according to the invention may be in accordance with relations (I) and (I2). It may also be in accordance with relations (I) and (I3). It may also be in accordance with relations (I) and (L). It may also be in accordance with relations (L) and (I2). It may also be in accordance with relations (L) and (I3). It may also be in accordance with relations (L) and (I4).

[0056] The d50 of the precipitated silica according to the invention is determined by means of centrifugal sedimentation in a disc centrifuge using a CPS as detailed below. d50 actually represents the particle diameter below (and above) which 50% of the total particle mass is found. Thus, d50 represents the median particle size of a given distribution, the term "size" being understood as "diameter" in this context.

[0057] The d50 of the inventive silica used in the elastomeric compositions for tires of the invention is preferably characterized by the following relationship: ld501 > -0.8Ix ICTABI + 263 (IV).

[0058] Generally, this d50 is between 110 nm and 240 nm, preferably between 130 and 220 nm.

[0059] The d84 of the inventive silica used in the elastomeric compositions for tires of the invention is preferably characterized by the following relationship: ld84 I < 2.81 x I FWHM I + 35 (V).

[0060] Generally, this d84 is between 200 and 550 nm, preferably between 250 and 500 nm.

[0061] The fines rate (rf), i.e. the proportion (by weight) of particles with a size less than 1 pm after deagglomeration by ultrasound (determined by the method of "sedigraph" test described below), is also a means of illustrating the dispersibility of the precipitated silicas that are used in the tire elastomer compositions of the invention. According to the invention, rf is at least 91%. In a preferred embodiment, this rf fines content is at least 92%. The rf fines content is more preferably at least 94% and even more preferably at least 95%; in certain particularly preferred embodiments, rf may be at least 96%, at least 97%, at least 98% or at least 99%. Often, rf is at most 99%; sometimes, it is at most 98%. Some suitable ranges for the rf fines content are from 95% to 99% and from 96% to 99%. It is understood that these values ​​can be applied to any precipitated silica, regardless of its form. In particular, they can be applied to a product that has not been granulated, i.e. a powder or microbeads.They can also be applied to pellets.

[0062] Specifically, the form of the precipitated silica used in the elastomer composition for tires of the invention is not particularly limited. Thus, said silica may in particular be in a form chosen from the group consisting of a powder, essentially spherical beads (commonly called "microbeads"), granules and mixtures thereof. In certain embodiments, it is a powder. In other embodiments, it is in the form of microbeads. In still other embodiments, it is in the form of granules.

[0063] Surprisingly, the morphology of said precipitated silica and the specific distribution of its particles make it possible to obtain elastomer compositions for tires having a good compromise between different sometimes contradictory mechanical properties. Indeed, for example, the person skilled in the art knows that one of the requirements for a tire is to provide optimal grip on the road, in particular on wet ground. One way to give the tire better grip on wet ground is to use an elastomer composition in its tread, which composition has a large hysteresis potential. But at the same time, the tire tread must also minimize its contribution to the tire's rolling resistance, i.e. have the lowest possible hysteresis.Surprisingly, the specific precipitated silica used in the elastomeric compositions for tires of the present invention can notably exhibit both good wet grip and good rolling resistance. The elastomeric compositions for tires of the invention can advantageously exhibit good wear properties (evaluated by measuring tensile strength and strain at break) while maintaining good wet grip.

[0064] The precipitated silica used in the elastomer compositions for tires of the invention is advantageously obtained by a process comprising: i. the provision of a starting solution having a pH of 2.00 to 5.50, ii. the simultaneous addition of a silicate and an acid to said starting solution for obtain a reaction medium whose pH is maintained in the range from 2.00 to 5.50, iii. stopping the addition of the acid and the silicate and adding a base to the reaction medium to bring the pH of said reaction medium to a value ranging from 7.00 to 10.00, iv. the simultaneous addition to the reaction medium of a silicate and an acid, so that the pH of the reaction medium is maintained in the range from 7.00 to 10.00, v. stopping the addition of the silicate while continuing the addition of the acid to the reaction medium to reach a pH of the reaction medium below 6.00 and obtain a suspension of precipitated silica, wherein step (i) comprises the following steps:

[0065] (ia) providing an aqueous medium optionally comprising an electrolyte as initial stock,

[0066] (ib) the simultaneous addition to this aqueous medium of a silicate and an acid, so that the pH of the aqueous medium is maintained in the range from 7.00 to 10.00, the quantity of silicate added to the aqueous medium being between 1% and 10% of the total quantity of silicate necessary for the reaction, preferably between 5% and 9% of the total quantity of silicate necessary for the reaction,

[0067] (ic) stopping the addition of silicate while continuing the addition of the acid to the aqueous medium obtained in step (ib) in order to provide the starting solution having a pH of 2.00 to 5.50.

[0068] The total amount of silicate to obtain a given final amount of silica can be determined by a person skilled in the art at the start of the process according to common general knowledge. The amount of silicate added during step (ib) will be referred to below as the silicate ratio AS0.

[0069] The term "base" is used herein to refer to one or more bases that may be added during said process and includes the group consisting of silicates as defined below. Any base may be used in the process. In addition to silicates, notable and non-limiting examples of suitable bases are, for example, alkali metal hydroxides and ammonia. Preferably, the base is a silicate and, more preferably, the same silicate as used in the process.

[0070] The term "silicate" is used herein to refer to one or more silicates that may be added during this process. The silicate is generally selected from the group consisting of alkali metal silicates. The silicate is advantageously selected from the group consisting of sodium and potassium silicates. The silicate may be in any known form, such as metasilicate or disilicate. It may be derived from various materials such as sand, natural sources containing silica, whether burned (such as RHA or rice husk ash) or as is, and even waste (construction, mining, etc.).

[0071] In the case where sodium silicate is used, the latter generally has a Si2O / Na2O weight ratio of 2.0 to 4.0, in particular of 2.4 to 3.9, for example of 3.1 to 3.8.

[0072] The silicate may have a concentration (expressed in terms of SiO2) of 3.9 wt% to 25.0 wt%, for example 5.6 wt% to 23.0 wt%, in particular 5.6 wt% to 21.0 wt%.

[0073] The term "acid" is used herein to mean one or more acids that may be added during said process. Any acid may be used in the process. Generally, a mineral acid, such as sulfuric acid, nitric acid, phosphoric acid or hydrochloric acid, or an organic acid, such as a carboxylic acid, for example, acetic acid, formic acid or carbonic acid, is used. Good results have been obtained with sulfuric acid.

[0074] The acid may be dosed into the reaction medium in dilute or concentrated form. The same acid at different concentrations may be used at different stages of the process. Preferably, a dilute acid is used until the gel point is reached (which occurs during step (ii)) and a concentrated acid is used after the gel point is reached. Preferably, the dilute acid is dilute sulfuric acid (i.e. with a concentration much lower than 80% by mass, preferably a concentration lower than 20% by mass, generally lower than 14% by mass, in particular not more than 10% by mass, for example between 5% and 10% by mass).Advantageously, the concentrated acid is concentrated sulfuric acid, i.e. sulfuric acid with a concentration of at least 80% by mass (and generally at most 98% by mass), preferably at least 90% by mass; in particular, its concentration is between 90% and 98% by mass, for example between 91% and 97% by mass.

[0075] In a preferred embodiment of the process, sulfuric acid and sodium silicate are used in all steps of the process. Preferably, the same sodium silicate, i.e. a sodium silicate having the same concentration expressed as SiO2, is used in all steps of the process.

[0076] During step (i) of the process, a starting solution having a pH of 2.00 to 5.00 is introduced into the reaction vessel. Preferably, the starting solution has a pH of 2.50 to 5.00, in particular 3.00 to 4.50; for example, the starting solution has a pH of 3.50 to 4.50.

[0077] According to said method, this starting solution is prepared using in particular the following steps (ia) to (ic) as described above.

[0078] Without wishing to be bound by any theory, the applicant believes that during these sub-steps of step (i), larger primary particles are generated than in steps following stages of the process (namely during steps (ii) and (iv)), which makes it possible to obtain inhomogeneous aggregates with a wide particle size distribution.

[0079] The starting solution of step (i) may or may not comprise an electrolyte. Preferably, the starting solution of step (i) contains an electrolyte in order to facilitate the recycling of water streams in the process.

[0080] The term "electrolyte" is used herein in its generally accepted sense, i.e., to identify any ionic or molecular substance which, in solution, decomposes or dissociates to form ions or charged particles. The term "electrolyte" is used herein to indicate that one or more electrolytes may be present. These may be electrolytes such as alkali metal and alkaline earth metal salts. Advantageously, the electrolyte to be used in the starting solution is the salt of the metal of the starting silicate and the acid used in the process. Notable examples are, for example, sodium chloride, in the case of the reaction of a sodium silicate with hydrochloric acid, or, preferably, sodium sulfate, in the case of the reaction of a sodium silicate with sulfuric acid. Preferably, the electrolyte does not contain aluminum.

[0081] Preferably, when sodium sulfate is used as electrolyte in step (i), its concentration in the starting solution is from 5 to 40 g / l, in particular from 8 to 30 g / l, for example from 10 to 25 g / l.

[0082] Step (ii) of the process comprises the simultaneous addition of an acid and a silicate to the starting solution. The addition rates of the acid and the silicate during step (ii) are controlled so that the pH of the reaction medium is maintained in the range from 2.00 to 5.50. The pH of the reaction medium is preferably maintained in the range from 2.50 to 5.00, in particular from 3.00 to 5.00, for example from 3.20 to 4.80.

[0083] The simultaneous addition in step (ii) is advantageously carried out so that the pH of the reaction medium is always equal (to within ± 0.20 pH units) to the pH reached at the end of step (i).

[0084] Preferably, step (ii) consists of a simultaneous addition of acid and silicate, as indicated above. Generally, a gel point is reached during step (ii). In one embodiment, the amount of silicate added during step (ii) after the gel point has been reached is between 5% and 55% of the total amount of silicate added during step (ii), preferably between 10% and 50% and more preferably between 15% and 45% of the total amount of silicate added during step (ii). The gel point is defined as the point where the reaction medium undergoes a sudden change in viscosity, which can be determined by measuring the stirrer torque. In general, the stirring torque increases by a value between 20% and 60% compared to the torque value before the freezing point, preferably by a value between 25% and 55%, more preferably by a value between 30% and 50% relative to the torque value before the freezing point.

[0085] Then, in step (iii), the addition of the acid and the silicate is stopped and a base is added to the reaction medium. The addition of the base is stopped when the pH of the reaction medium has reached a value of 7.00 to 10.00, preferably 7.50 to 9.50.

[0086] In a first embodiment of the process, the base is a silicate. Thus, in step (iii), the addition of the acid is stopped while the addition of the silicate to the reaction medium is continued until a pH of 7.00 to 10.00, preferably 7.50 to 9.50, is reached.

[0087] In a second embodiment of the process, the base is not a silicate and is selected from the group of alkali metal hydroxides, preferably sodium or potassium hydroxide. When sodium silicate is used in the process, a preferred base may be sodium hydroxide.

[0088] Thus, in this second embodiment of the process, in step (iii), the addition of the acid and the silicate is stopped and a base, other than a silicate, is added to the reaction medium until a pH of 7.00 to 10.00, preferably 7.50 to 9.50, is reached.

[0089] At the end of step (iii), that is to say after stopping the addition of the base, it may be advantageous to carry out a step of maturation of the reaction medium. This step is preferably carried out at the pH obtained at the end of step (iii). The maturation step may be carried out with stirring of the reaction medium. The maturation step is preferably carried out with stirring of the reaction medium for a period of 2 to 45 minutes, in particular 5 to 25 minutes. Preferably, the maturation step does not include the addition of acid or silicate.

[0090] After step (iii) and the optional maturation step, a simultaneous addition of an acid and a silicate is carried out, so that the pH of the reaction medium is maintained in the range from 7.00 to 10.00, preferably from 7.50 to 9.50.

[0091] The simultaneous addition of an acid and a silicate (step (iv)) is typically carried out in such a way that the pH value of the reaction medium is maintained equal to the pH reached at the end of the previous step (to within ± 0.20 pH units), namely step (iii).

[0092] Preferably, the amount of silicate added to the reaction medium during step (iv) represents at least 45% of the total amount of silicate required for the reaction.

[0093] It should be noted that said method may comprise additional steps. For example, between step (iii) and step (iv), and in particular between the optional maturation step following step (iii) and step (iv), an acid may be added to the reaction medium. The pH of the reaction medium after this addition of acid must remain in the range from 7.00 to 9.50, preferably from 7.50 to 9.50.

[0094] In step (v), the addition of the silicate is stopped while continuing the addition of the acid to the reaction medium so as to obtain a pH value in the medium re action less than 6.00, preferably from 3.00 to 5.50, in particular from 3.00 to 5.00. A suspension of precipitated silica is obtained in the reaction vessel.

[0095] At the end of step (v), and therefore after stopping the addition of the acid to the reaction medium, a maturation step can advantageously be carried out. This maturation step can be carried out at the same pH as that obtained at the end of step (v) and under the same time conditions as those described above for the maturation step which can optionally be carried out between steps (iii) and (iv) of the process.

[0096] The reaction vessel in which the entire reaction of the silicate with the acid takes place is generally equipped with a suitable stirring and heating device.

[0097] The entire reaction of the silicate with the acid (steps (i) to (v)) is generally carried out at a temperature of 40 to 97°C, in particular 60 to 95°C, preferably 80 to 95°C, more preferably 85 to 95°C.

[0098] According to a variant of said process, the entire reaction of the silicate with the acid is carried out at a constant temperature, generally from 40 to 97°C, in particular from 80 to 95°C, or even from 85 to 95°C.

[0099] According to another variant of said process, the temperature at the end of the reaction is higher than the temperature at the start of the reaction: thus, the temperature at the start of the reaction (for example during steps (i) to (iii)) is preferably maintained in the range of 40 to 85°C and the temperature is then increased, preferably up to a value in the range of 80 to 95°C, or even 85 to 95°C, at which value it is maintained (for example during steps (iv) and (v)), until the end of the reaction.

[0100] At the end of the steps just described, a suspension of precipitated silica is obtained, which is then separated (liquid / solid separation). The process generally comprises an additional step (vi) of filtration of the suspension and drying of the precipitated silica.

[0101] The separation carried out during this preparation process generally comprises filtration, followed by washing, if necessary. The filtration is carried out by any suitable method, for example by means of a belt filter, a rotary filter, for example a vacuum filter, or, preferably, a filter press.

[0102] The filter cake is then subjected to a liquefaction operation. The term "liquefaction" herein refers to a process by which a solid, namely the filter cake, is converted into a fluid mass, generally by the addition of a liquid. After the liquefaction step, the filter cake is in a fluid and flowable form and the precipitated silica is in suspension.

[0103] The liquefaction step may comprise a mechanical treatment which results in a reduction of the particle size of the suspended silica. Said mechanical treatment may be carried out by passing the filter cake through a high-pressure mixer. projection, a colloidal mill or a ball mill. Alternatively, the liquefaction step may be carried out by subjecting the filter cake to chemical action by the addition of, for example, an acid or an aluminum compound, for example sodium aluminate. Alternatively, the liquefaction step may comprise both mechanical treatment and chemical action.

[0104] The precipitated silica suspension obtained after the optional liquefaction step is then preferably dried, optionally after being treated with additional chemicals, such as organic products for example (e.g. polycarboxylic acids).

[0105] This drying may be carried out by means known in the art. Preferably, the drying is carried out by atomization. For this purpose, any suitable type of atomizer may be used, in particular a turbine, a nozzle, a liquid pressure or two-fluid atomizer dryer. In general, when the filtration is carried out using a filter press, a nozzle atomizer dryer is used, and when the filtration is carried out using a vacuum filter, a turbine atomizer dryer is used.

[0106] When the drying operation is carried out using a nozzle atomizer dryer, the precipitated silica that can then be obtained is generally in the form of essentially spherical beads, commonly called "microbeads". After this drying operation, it is optionally possible to carry out a grinding or micronization step on the recovered product; the precipitated silica that can then be obtained is generally in the form of a powder. After this drying operation, it is also possible to carry out a step in which the recovered microbeads are subjected to an agglomeration step, which consists for example of direct compression, wet granulation, extrusion or, preferably, dry compaction; the precipitated silica that is then obtained is generally in the form of granules.

[0107] When the drying operation is carried out using a turbine atomizer dryer, the precipitated silica obtained may be in the form of a powder.

[0108] In one embodiment of said method, the filter cake is not subjected to a liquefaction step but is directly dried by a rotating flash dryer (for example by the Hosokawa type method).

[0109] Finally, the dried, ground or micronized product as indicated above may optionally be subjected to an agglomeration step, which consists, for example, of direct compression, wet granulation (i.e. with the use of a binder, such as water, a silica suspension, etc.), extrusion or, preferably, dry compaction.

[0110] The precipitated silica which can then be obtained by this agglomeration step is generally in the form of granules.

[0111] The proportion by weight of the inventive precipitated silica used in the elastomeric compositions for heavy-duty tires of the invention can vary within a fairly wide range. It normally represents from 30 to 85 phr, in particular from 35 to 65 phr.

[0112] The inventive precipitated silica used in the elastomer compositions for heavy-load tires of the invention then preferably constitutes at least 60%, or even at least 80% by weight, of the total amount of the weight of the reinforcing filler of the elastomer composition for heavy-load tires.

[0113] Preferably, the proportion by weight of the inventive precipitated silica used in the elastomer compositions for tires carrying heavy loads of the invention ranges from 30 to 85 phr, in particular from 35 to 65 phr, and the inventive precipitated silica constitutes at least 60%, or even at least 80% by weight, of the total amount of the weight of the reinforcing filler of the elastomer composition for tires carrying heavy loads.

[0114] The inventive precipitated silica used in the heavy-load tire elastomer compositions of the invention may advantageously constitute the entire reinforcing inorganic filler of the heavy-load tire elastomer composition.

[0115] The inventive precipitated silica used in the elastomeric compositions for heavy-load tires of the invention may optionally be combined with at least one other reinforcing filler, for example with a conventional silica or a highly dispersible silica, such as Zeosil® Premium SW, Zeosil® Premium 200MP, Zeosil® 1165MP, Zeosil® 1115MP or Zeosil® 1085 GR (commercially available from Solvay), or another reinforcing inorganic filler, such as nano-clays, alumina. Alternatively, the silica used in the elastomeric compositions for heavy-load tires of the invention may be combined with a reinforcing organic filler, such as carbon black nanotubes, graphene, starch, cellulose, carbon black and the like.

[0116] All carbon blacks may be used in the elastomer compositions for heavy-duty tires of the invention, in particular HAF, ISAF or SAF type blacks, conventionally used in tires ("tire-grade" blacks) are suitable as carbon blacks. Among the latter, mention will be made more particularly of reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as, for example, blacks NI 15, N134, N234, N326, N330, N339, N347 or N375, or, depending on the intended applications, blacks of higher series (for example N660, N683 or N772). Carbon blacks may, for example, already be incorporated into an elastomer, in particular an isoprene elastomer, in the form of a masterbatch (see, for example, applications WO 97 / 36724 or WO 99 / 16600).

[0117] When present, carbon black is preferably used at a content ranging from 0.1 to 15 pce, more preferably from 0.5 to 15 pce, in particular from 1 to 13 pce.

[0118] The amount of total reinforcing filler (i.e. the amount of inventive silica used in the elastomeric compositions for heavy load bearing tires and the amount of carbon black when present or other reinforcing fillers when present) is in the range of 30 to 100 phr, in particular 30 to 85 phr.

[0119] The amount of total reinforcing filler (i.e. the amount of inventive silica used in the elastomeric compositions for heavy load tires and the amount of carbon black when present or other reinforcing fillers when present) are in the range of 30 to 100 phr, in particular 30 to 85 phr and the inventive precipitated silica preferably constitutes at least 60%, or even at least 80% by weight, of the total amount of the weight of the reinforcing filler of the elastomeric composition for heavy load tires.

[0120] The heavy-load tire elastomer compositions of the present invention comprise at least one coupling agent that binds the diene elastomer to the precipitated silica. In certain embodiments, the heavy-load tire elastomer compositions of the present invention may preferably further comprise at least one capping agent.

[0121] Non-limiting examples of suitable coupling agents between the diene elastomer and the precipitated silica are, for example, "symmetrical" or "non-symmetrical" silane polysulfides; mention may be made more particularly of bis((Cl-C4)alkoxyl(Cl-C4)alkylsilyl(Cl-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 bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, of formula [(C2H5O)3Si(CH2)3S2]2, or bis(triethoxysilylpropyl) disulfide, abbreviated to TESPD, of formula [(C2H5O)3Si(CH2)3S]2.Also mentioned are monoethoxydimethylsilylpropyl tetrasulfide and silanes with blocked or free thiol functional groups (such as NXT™ or NXT™ Z45 silanes), mercaptopropyltriethoxysilane and a mixture of mercaptopropyltriethoxysilane + octyltriethoxysilane (such as Evonik's SI 363®).

[0122] The coupling agent may be grafted beforehand to the diene elastomer of the elastomer matrix. It may also be used in the free state (i.e. not grafted beforehand) or grafted to the surface of the silica. The same applies to the optional covering agent. In the case where a coupling agent is added to the silica after drying (i.e. grafted onto it), it is generally an ethoxy- or a chloro-silane.

[0123] The coupling agent may optionally be associated with a suitable “coupling activator”, i.e. a compound which, mixed with this coupling agent, increases the effectiveness of the latter.

[0124] Elastomeric matrix

[0125] The elastomer composition for tires carrying heavy loads is based on an elastomer matrix. The expression "elastomer matrix", well known to those skilled in the art, designates all the elastomers present in the composition. It may be a set of different elastomers or a single elastomer.

[0126] The elastomer matrix of the composition for heavy-duty tires comprises at least 30 pce of an isoprene elastomer.

[0127] The term "isoprene elastomer" is understood to mean, in a known manner, a homopolymer or copolymer of isoprene, i.e. a diene elastomer selected from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), different isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene copolymers (butyl rubber-IIR), isoprene-styrene copolymers (SIR), isoprene-butadiene copolymers (BIR) or isoprene-butadiene-styrene copolymers (SBIR). This isoprene elastomer is preferably natural rubber or a synthetic cis-1,4 polyisoprene, preferably natural rubber. For example, the synthetic polyisoprene may be a polyisoprene having a cis-1,4 bond content (mol %) greater than 90%, more preferably greater than 98%.Preferably, the elastomer matrix of the elastomer composition for heavy-duty tires of the invention comprises at least 30 phr of an isoprene elastomer selected from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR) and mixtures thereof.

[0128] In a preferred embodiment of the invention, the elastomer matrix comprises another diene elastomer different from the isoprene elastomer, this other diene elastomer being chosen from the group consisting of polybutadienes, styrene-butadiene copolymers and mixtures of these elastomers. Thus, the elastomer matrix comprises at least 30 phr of an isoprene elastomer as described above and another diene elastomer chosen from the group consisting of polybutadienes, butadiene copolymers, and mixtures of said elastomers. Among these other diene elastomers, mention may be made, for example, of polybutadienes (BR), butadiene copolymers and in particular styrene / butadiene copolymers (SBR, in particular ESBR (emulsion) or SSBR (solution)) and also associated functionalized polymers (having, for example, pendant polar or reactive groups). or polar groups at the end of the chain, which can interact or react with the silica).

[0129] The other diene elastomer different from the isoprene elastomer may have any microstructure, which depends on the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used. These elastomers may, for example, be coupled and / or star-shaped or even functionalized with a coupling and / or star-shaped or functionalizing agent. Preferably, the diene elastomers are random polymers.

[0130] Preferably, if a functionalized diene elastomer is present in the elastomer matrix of the heavy-duty tire composition, the functionalized diene elastomer may be a functionalized butadiene / styrene copolymer.

[0131] By "functionalized diene elastomer" is meant a synthetic diene elastomer which comprises at least one chemical group comprising one or more heteroatoms, such as, for example, a sulfur atom S, a nitrogen atom N, an oxygen atom O, a silicon atom Si or a tin atom Sn. In the context of the present description, this chemical group is also called "function". The two terms are used without distinction.

[0132] This chemical group can be located at the end of the chain, that is to say at one of the ends of the linear main chain of the elastomer. We will then say that the diene elastomer is functionalized "at the end of the chain". It is generally an elastomer obtained by reaction of a living elastomer with a functionalizing agent, that is to say any molecule that is at least monofunctional, the function being any type of chemical group known to those skilled in the art for reacting with a living chain end.

[0133] This chemical group can be located in the linear main chain of the elastomer. We will then say that the diene elastomer is coupled or functionalized "in the middle of the chain", as opposed to the "end of the chain" position, although the group is not located precisely in the middle of the elastomer chain. It is generally an elastomer obtained by reaction of two chains of the living elastomer with a coupling agent, that is to say any molecule that is at least difunctional, the function being any type of chemical group known to those skilled in the art to react with a living end of the chain.

[0134] This group can be central, to which n elastomer chains (n>2) are linked, forming a star structure of the elastomer. We will then say that the diene elastomer is star-shaped. It is generally an elastomer obtained by reaction of n chains of the living elastomer with a star-forming agent, that is to say any polyfunctional molecule, the function being any type of chemical group known to man. job to react with a living piece of chain.

[0135] Those skilled in the art will understand that a functionalization reaction with an agent comprising more than one reactive function with respect to the living elastomer leads to a mixture of functionalized entities at the end of the chain and in the middle of the chain, constituting the linear chains of the functionalized diene elastomer, as well as, where appropriate, star-shaped entities. Depending on the operating conditions, mainly the molar ratio of the functionalizing agent to the living chains, certain entities are predominant in the mixture.

[0136] Preferably, the functionalized diene elastomer comprises at least one polar function comprising at least one oxygen atom.

[0137] Preferably, the polar function may be chosen from the group consisting of silanols, alkoxysilanes, alkoxysilanes carrying an amine group, epoxides, ethers, esters, carboxylic acids and hydroxyls. The polar function particularly improves the interaction between the reinforcing inorganic filler and the elastomer. Such functionalized elastomers are known per se and are described in particular in the following documents: FR2740778, US6013718, WO2008 / 141702, FR2765882, WO01 / 92402, WO2004 / 09686, EPI 127909, US6503973, WO2009 / 000750 and WO 2009 / 000752.

[0138] The functionalized diene elastomer is preferably a diene elastomer comprising a polar function which is a silanol.

[0139] Preferably, the silanol is located at the end of the chain or in the middle of the main chain of the functionalized diene elastomer. More preferably, the silanol is located in the middle of the main chain of the functionalized diene elastomer.

[0140] Preferably, the functionalized diene elastomer (in particular SBRs) comprises a polar function which is an alkoxysilane carrying or not another function (or carrying another chemical group, these expressions being synonymous).

[0141] According to other variants, the alkoxysilane group (carrying or not another function) is located in the main chain of the elastomer (middle of the chain). The silicon atom of this function links the two branches of the main chain of the diene elastomer.

[0142] The alkoxysilane group (whether or not carrying another function) comprises a C1-C10 alkoxyl radical, optionally partially or totally hydrolyzed to give a hydroxyl, or even a C1-C8 alkoxyl radical, preferably C1-C4, and is more preferably methoxy and ethoxy.

[0143] The other function is preferably carried by the silicon of the alkoxysilane group, directly or via a spacer group, defined as being a saturated or unsaturated, cyclic or non-cyclic, divalent, linear or branched atom or radical, based on C1-C18 aliphatic hydrocarbons, or a divalent aromatic radical C6-C18 hydrocarbon base.

[0144] The other function is preferably a function comprising at least one heteroatom chosen from N, S, O or P. Among these functions, mention may be made, by way of example, of cyclic or non-cyclic primary, secondary or tertiary amines, isocyanates, imines, cyanos, thiols, carboxylates, epoxides or primary, secondary or tertiary phosphines.

[0145] Mention may thus be made, as secondary or tertiary amine function, of amines substituted by C1-C10 alkyl radicals, preferably C1-C4, more preferably a methyl or ethyl radical, or cyclic amines forming a heterocycle containing a nitrogen atom and at least one carbon atom, preferably from 2 to 6 carbon atoms. For example, the methylamino-, dimethylamino-, ethylamino-, diethylamino-, propylamino-, dipropylamino-, butylamino-, dibutylamino-, pentylamino-, dipentylamino-, hexylamino-, dihexylamino- or hexamethyleneamino- groups, preferably the diethylamino- and dimethylamino- groups, are suitable.

[0146] As imine function, ketimines may be mentioned. For example, (1,3-dimethylbutylidene)amino-, (ethylidene)amino-, (1-methylpropylidene)amino-, (4-N,N-dimethylaminobenzylidene)amino-, (cyclohexylidene)amino-, dihydroimidazole and imidazole groups are suitable.

[0147] We can thus cite, as carboxylate function, acrylates or methacrylates. Such a function is preferably a methacrylate.

[0148] As epoxide function, mention may be made of epoxy or glycidyloxy groups.

[0149] Mention may be made, as secondary or tertiary phosphine function, of phosphines substituted by C1-C10 alkyl radicals, preferably C1-C4, more preferably by a methyl or ethyl radical, or by diphenylphosphine. For example, the methylphosphino, dimethylphosphino, ethylphosphino, diethylphosphino, ethylmethylphosphino and diphenylphosphino groups are suitable.

[0150] Preferably, the other function is a tertiary amine, more preferably a diethylamino- or dimethylamino- group.

[0151] Preferably, the functionalized diene elastomer (in particular an SBR) may comprise a polar function which is an alkoxysilane carrying or not an amine group.

[0152] Preferably, the alkoxysilane carrying or not an amine group is located at the end of chain or in the middle of the main chain of the functionalized diene elastomer. More preferably, the alkoxysilane group carrying or not carrying the amine group is located in the middle of the chain of the main chain of the functionalized diene elastomer.

[0153] Preferably, the amine group is a tertiary amine.

[0154] Preferably, the alkoxysilane group may be represented by the formula (III):

[0155] (*—)aSi (OR')bRcX (III)

[0156] in which: • *— represents the bond with an elastomer chain; • the radical R represents a C1-C10, or even C1-C8, alkyl radical, substituted or unsubstituted, preferably a C1-C4 alkyl radical, more preferably methyl and ethyl; • in the alkoxyl radical(s) of formula -OR', which is or are optionally partially or totally hydrolyzed to give a hydroxyl, R' represents a C1-C10, or even C1-C8, substituted or unsubstituted alkyl radical, preferably a C1-C4 alkyl radical, more preferably methyl and ethyl; • X represents a group including the other function; • a is equal to 1 or 2, b is equal to 1 or 2, and c is equal to 0 or 1, provided that a + b + c =3.

[0157] More preferably, the functionalized diene elastomer is a diene elastomer (in particular an SBR) which comprises, in its main chain, at least one alkoxysilane group of formula (III), in which: • *— represents the bond with an elastomer chain; • the radical R represents a substituted or unsubstituted C1-C4 alkyl radical, more preferably methyl and ethyl; • in the alkoxyl radical(s) of formula -OR', which is or are optionally partially or totally hydrolyzed to give a hydroxyl, R' represents a substituted or unsubstituted C1-C4 alkyl radical, more preferably methyl and ethyl; • X represents a group comprising the other function; preferably a tertiary amine; • a is equal to 1 or 2, b is equal to 1 or 2, and c is equal to 0 or 1, provided that a + b + c = 3.

[0158] This type of elastomer is mainly obtained by functionalization of a living elastomer resulting from an anionic polymerization. It should be noted that it is known to those skilled in the art that, when an elastomer is modified by reaction of a functionalizing agent with the living elastomer resulting from an anionic polymerization step, a mixture of modified entities of this elastomer is obtained, the composition of which depends on the conditions of the modification reaction and in particular on the proportion of reactive sites of the functionalizing agent relative to the number of chains of the living elastomer. This mixture comprises entities functionalized at the end of the chain, coupled, star-shaped and / or non-functionalized.

[0159] According to a particularly preferred variant, the modified diene elastomer comprises, as the predominant entity, the diene elastomer functionalized in the middle of the chain by an alkoxysilane group linked to the two branches of the diene elastomer via the silicon atom. More particularly still, the diene elastomer functionalized in the middle of the chain by an alkoxysilane group represents at least 55% by weight of the modified diene elastomer.

[0160] These functionalized elastomers can be used in admixture with each other or with non-functionalized elastomers.

[0161] Thus, in one embodiment, the elastomer matrix of the elastomer composition for heavy-duty tires comprising the inventive precipitated silica described above (including the preferred embodiment of said silica) comprises at least 30 phr of an isoprene elastomer and at least one other diene elastomer selected from the group consisting of polybutadienes, styrene-butadiene copolymers, and mixtures of said elastomers, said other diene elastomers being functionalized or not.For example, the elastomer matrix may contain at least 30 pce of an isoprene elastomer and at least one styrene-butadiene elastomer, or the elastomer matrix may contain at least 30 pce of an isoprene elastomer and at least two styrene-butadiene elastomers different from each other (e.g. one styrene-butadiene elastomer is functionalized and the other is not) or the elastomer matrix may contain at least 30 pce of an isoprene elastomer and a mixture of at least one polybutadiene and at least one styrene-butadiene copolymer, etc.

[0162] In a preferred embodiment, the elastomer matrix may contain from 30 to 95 phr of an isoprene elastomer and from 5 to 70 phr of said other diene elastomer; preferably, the elastomer matrix may contain from 35 to 90 phr of an isoprene elastomer and from 10 to 65 phr of said other diene elastomer; more preferably, the elastomer matrix may contain from 35 to 85 phr of an isoprene elastomer and from 15 to 65 phr of said other diene elastomer. The combination of said elastomer matrix with the inventive precipitated silica makes it possible to surprisingly obtain elastomer compositions for tires carrying heavy loads having a good compromise of mechanical properties, in particular a good compromise between the properties of rigidity / elongation at break / rolling resistance / fatigue resistance, in particular good fatigue resistance properties.

[0163] Advantageously, in this preferred embodiment, the elastomer matrix may contain from 30 to 95 pce of an isoprene elastomer chosen from the group consisting of natural rubber, polyisoprene rubber and their mixtures and from 5 to 70 pce of said other diene elastomer which is chosen from the group consisting of polybutadienes, styrene-butadiene copolymers and their mixtures; preferably, the elastomer matrix may contain from 35 to 90 pce of an isoprene elastomer selected from the group consisting of natural rubber, polyisoprene rubber and their mixtures, and from 10 to 65 pce of said other diene elastomer selected from the group consisting of polybutadienes, styrene-butadiene copolymers and their mixtures; more preferably, the elastomer matrix may contain from 35 to 85 pce of an isoprene elastomer selected from the group consisting of natural rubber, polyisoprene rubber and their mixtures, and from 15 to 65 pce of said other diene elastomer selected from the group consisting of polybutadienes, styrene-butadiene copolymers and their mixtures.The combination of said elastomer matrix with the inventive precipitated silica makes it possible to surprisingly obtain elastomer compositions for tires carrying heavy loads having a good compromise of mechanical properties, in particular a good compromise between the properties of rigidity / elongation at break / rolling resistance / fatigue resistance, in particular good fatigue resistance properties.

[0164] In a preferred embodiment, the elastomer matrix may contain from 30 to 95 phr of natural rubber and from 5 to 70 phr of at least one styrene-butadiene copolymer; preferably, the elastomer matrix may contain from 35 to 90 phr of natural rubber and from 10 to 65 phr of at least one styrene-butadiene copolymer; more preferably, the elastomer matrix may contain from 35 to 85 phr of natural rubber and from 15 to 65 phr of at least one styrene-butadiene copolymer. The combination of said elastomer matrix with the inventive precipitated silica makes it possible to surprisingly obtain elastomer compositions for tires carrying heavy loads having a good compromise of mechanical properties, in particular a good compromise between the properties of rigidity / elongation at break / rolling resistance / fatigue resistance, in particular good fatigue resistance properties.

[0165] In another embodiment of the present invention, the elastomer matrix may contain from 30 to 95 phr of an isoprene elastomer, the other diene elastomer is a blend of a polybutadiene and a styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 2.5 to 35 phr and the amount of styrene-butadiene copolymer ranging from 2.5 to 35 phr;preferably, the amount of isoprene elastomer in the elastomer matrix ranges from 35 to 90 phr, the other diene elastomer is a mixture of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranges from 5 to 35 phr and the amount of styrene-butadiene copolymer ranges from 5 to 30 phr, more preferably, the amount of isoprene elastomer in the elastomer matrix ranges from 35 to 85 phr, the other diene elastomer is a mixture of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranges from 7.5 to 35 phr; and the amount of styrene-butadiene copolymer ranging from 7.5 to 30 phr. In said embodiment, the styrene-butadiene copolymer may preferably be functionalized as defined above, preferably is functionalized by a silanol group in the middle of its chain (as defined above). The combination of said elastomer matrix with the inventive precipitated silica makes it possible to surprisingly obtain elastomer compositions for tires carrying heavy loads having a good compromise of mechanical properties, in particular a good compromise between the properties of rigidity / elongation at break / rolling resistance / fatigue resistance, in particular good fatigue resistance properties. As is known to those skilled in the art, the sum of the amounts of the three different diene elastomers is 100 phr.

[0166] In another embodiment of the present invention, the elastomer matrix may contain from 30 to 95 phr of an isoprene elastomer selected from the group consisting of natural rubber, polyisoprene rubber and mixtures thereof, the other diene elastomer being a mixture of a polybutadiene and a styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 2.5 to 35 phr and the amount of styrene-butadiene copolymer ranging from 2.5 to 35 phr; preferably, in the elastomer matrix, the amount of isoprene elastomer chosen from the group consisting of natural rubber, polyisoprene rubber and their mixtures ranges from 35 to 90 phr, the other diene elastomer is a mixture of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 5 to 35 phr and the amount of styrene-butadiene copolymer ranging from 5 to 30 phr, more preferably in the elastomer matrix,the amount of isoprene elastomer selected from the group consisting of natural rubber, polyisoprene rubber and their mixtures ranges from 35 to 85 phr, the other diene elastomer is a mixture of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 7.5 to 35 phr and the amount of styrene-butadiene copolymer ranging from 7.5 to 30 phr. In said embodiment, the styrene-butadiene copolymer may be functionalized as defined above, preferably is functionalized by a silanol group in the middle of its chain (as defined above). The combination of said elastomer matrix with the inventive precipitated silica makes it possible to surprisingly obtain elastomer compositions for tires carrying heavy loads having a good compromise of mechanical properties, in particular a good compromise between the properties of rigidity / elongation at break / rolling resistance / fatigue resistance,in particular good fatigue resistance properties. As is known to the person skilled in the art, the sum of the quantities of the three different diene elastomers is 100 pce.

[0167] Crosslinking system

[0168] The elastomeric compositions for heavy-load tires of the invention comprise at least one chemical crosslinking system. Any type of crosslinking system known to those skilled in the art for elastomeric compositions may be used.

[0169] Elastomeric compositions for heavy load tires may be vulcanized with sulfur or crosslinked, particularly with peroxides or other crosslinking systems (e.g., diamines or phenolic resins).

[0170] The crosslinking system is preferably a vulcanization system, i.e. a system based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. Various known secondary vulcanization accelerators or vulcanization activators, such as zinc oxide, stearic acid or equivalent compounds, or guanidine derivatives (in particular diphenyl-guanidine), may be added to this basic vulcanization system, being incorporated during the first non-productive phase and / or during the productive phase, as described below.

[0171] When sulfur is used, it is used at a preferred content ranging from 0.5 to 12 phr, in particular ranging from 1 to 10 phr. The primary vulcanization accelerator is used at a preferred content ranging from 0.5 to 10 phr, more preferably ranging from 0.5 to 5.0 phr.

[0172] The vulcanization system of the elastomeric compositions for heavy-load tires of the invention may also comprise one or more additional accelerators, for example compounds of the thiuram family, zinc dithiocarbamate derivatives, sulfenamide derivatives, guanidine derivatives or thiophosphate derivatives.

[0173] Additional additives

[0174] The elastomer compositions for heavy-load tires of the invention may optionally also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of heavy-load tires or semi-finished articles for heavy-load tires, such as, for example, pigments, protective agents, such as anti-ozone waxes, chemical anti-ozonants or antioxidants, anti-fatigue agents, crosslinking agents other than those mentioned above, reinforcing resins, methylene acceptors (for example, phenolic novolak resin) or methylene donors (for example, HMT or H3M), as described, for example, in application WO 02 / 10269.

[0175] For example, said additional additives may be activators (stearic acid, zinc oxide), manufacturing aids (fatty acids, zinc soaps, PEG, etc.), wax (PE wax) acting as a protector, antioxidants, pro- UV detectors and antiozonants such as 6PPD, TMQ...

[0176] Plasticizing agent

[0177] The heavy-duty tire elastomer composition of the present invention may or may not include a plasticizing agent.

[0178] Preferably, when the elastomer compositions for tires carrying heavy loads of the invention comprise at least one plasticizing agent, this is chosen from the group consisting of solid hydrocarbon-based resins (or plasticizing resins such as terpenes, C5 resins, etc., trade name Wingtack, Dercolyte, etc.), extender oils (plasticizing oils) or a mixture of plasticizing oils and resins.

[0179] Preferably, when the elastomer compositions for heavy-duty tires according to the invention comprise at least one plasticizing agent, the amount of said plasticizing agent is in the range from 0.5 to 10 phr, preferably from 0.75 to 8 phr.

[0180] Preferably, when the elastomer compositions for heavy-duty tires according to the invention comprise at least one plasticizing agent, said plasticizing agent is a resin and the amount of said resin is in the range from 0.5 to 10 phr, preferably from 0.75 to 8 phr.

[0181] Preferably, in the embodiment of the present invention, where the elastomer matrix may consist of an isoprene elastomer, the heavy load tire composition does not comprise a plasticizing agent.

[0182] Preferably, in the embodiment (including the preferred variant of said preferred embodiment) of the present invention, wherein the elastomer matrix may contain from 30 to 95 phr of an isoprene elastomer and from 5 to 70 phr of said other diene elastomer; preferably from 35 to 90 phr of an isoprene elastomer and from 10 to 65 phr of said other diene elastomer; more preferably from 35 to 85 phr of an isoprene elastomer and from 15 to 65 phr of said other diene elastomer, the composition for heavy-load tires does not comprise a plasticizing agent.

[0183] Preferably, in the embodiment (including the preferred variant of said preferred embodiment) of the present invention, wherein the elastomer matrix may contain from 30 to 95 phr of an isoprene rubber and from 5 to 70 phr of another diene rubber which is a blend of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 2.5 phr to 35 phr and the amount of styrene-butadiene copolymer ranging from 2.5 phr to 35 phr; more preferably, the elastomer matrix may contain from 35 to 90 pce of an isoprene rubber and from 10 to 65 pce of another diene rubber which is a mixture of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 5 to 35 pce and the amount of styrene-butadiene copolymer ranging from 5 to 30 pce, even more preferably, the elastomer matrix may contain from 35 to 85 pce of an isoprene rubber and from 15 to 65 pce of another diene rubber which is a mixture of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 7.5 pce to 35 pce and the amount of styrene-butadiene copolymer ranging from 7.5 pce to 30 pce, the elastomer composition for tires carrying heavy loads may contain a plasticizing agent, preferably a resin, in an amount ranging from 0.5 to 10 pce, preferably from 0.75 to 8 pce.

[0184] Process for preparing the rubber composition

[0185] The inventive heavy-duty tire elastomer compositions comprising the inventive precipitated silica may be used for the manufacture of a number of semi-finished or finished articles for heavy-duty tires.

[0186] The elastomer compositions for heavy-load tires of the invention, intended in particular for the manufacture of heavy-load tires or semi-finished products for heavy-load tires, can be produced by any process well known to those skilled in the art.

[0187] For example, these elastomeric compositions for heavy-load tires of the invention can be produced in suitable mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first thermomechanical working or kneading phase (sometimes called the "non-productive" phase) at high temperature, up to a maximum temperature (denoted Tmax) of between 130°C and 200°C, preferably between 145°C and 185°C, followed by a second mechanical working phase (sometimes called the "productive" phase) at a lower temperature, typically below 120°C, for example between 60°C and 100°C, a finishing phase during which the crosslinking or vulcanization system is incorporated; such phases have been described, for example, in applications EP-A-0501227, EP-A-0735088 and EP-A-0810258.

[0188] For example, in a process for preparing the elastomeric compositions for heavy-load tires of the invention, said precipitated silica as described above, combined or not with another reinforcing inorganic filler, such as an additional silica for example, or with carbon black and the agent for coupling the elastomer to the silica, are incorporated by kneading into the (diene) elastomer or elastomers (diene) during the first "non-productive" phase, that is to say that at least these ingredients are introduced into the mixer and kneaded thermomechanically, in one or more times. Then, after for example one to two minutes of kneading, any additional covering agents or manufacturing auxiliaries and other various additives, with the exception of the crosslinking or vulcanization system, are added to the internal mixer.This mixture is kneaded thermomechanically until the aforementioned maximum temperature Tmax is reached. It is possible to consider one or more additional steps in order to . preparing elastomer / reinforcing filler masterbatches for introduction during the first “non-productive” phase. The elastomer / reinforcing filler masterbatches comprising at least one inventive precipitated silica may preferably be obtained by bulk mixing or by liquid mixing from an elastomer latex and an aqueous dispersion of said reinforcing filler.

[0189] The mixture is then cooled, and the crosslinking system (preferably the vulcanizing system) is then incorporated at low temperature (typically less than 100°C), generally in an external mixer, such as an open mill; the combined mixture is then mixed for a few minutes, for example between 5 and 15 min. This second phase is the “productive” phase.

[0190] The process for preparing an elastomer composition for tires carrying heavy loads of the invention preferably comprises the following steps: • at least 30 pce of an isoprene elastomer and optionally the other diene elastomers as described above, at least one reinforcing filler and at least one agent for coupling the elastomer to the precipitated silica are brought into contact; said reinforcing filler comprising a precipitated silica having: • a CTAB surface area in the range of 40 to 525 m2 / g; • primary particles with an average size measured by SAXS in less than 15 nm; • a quantity of aluminum WAi of at least 0.50% by weight; • a proportion (by weight) of particles with a size less than 1 pm after ultrasonic deagglomeration, which is at least 91%; and • a particle size distribution measured by centrifugal sedimentation using a CPS, such that for a given value of the CTAB surface area, the FWHM parameter is defined by the relation (I): I FWHM I > -0.16 xl CTAB I + 130 (I), • these ingredients are kneaded thermomechanically, once or several times, until reaching a maximum temperature of between 110°C and 190°C, • the mixture from the previous step is cooled to a temperature below 100°C, • a crosslinking system is incorporated into the mixture cooled in the previous step, • the mixture comprising the crosslinking system is kneaded up to a maximum temperature below 110°C.

[0191] The final composition thus obtained is then calendered, for example in the form of a sheet or plate, in particular for laboratory characterization, or even extruded, in order to form, for example, a profiled rubber element used in the manufacture of semi-finished products for tires carrying heavy loads. These products can then be used for the manufacture of tires carrying heavy loads, according to techniques known to those skilled in the art, with the advantage of the invention, namely a good compromise of mechanical properties, in particular good fatigue resistance properties.

[0192] Preferably, the process for preparing an elastomer composition for heavy-load tires of the invention also comprises a step during which the kneaded mixture comprising the crosslinking system is cured.

[0193] This crosslinking (or vulcanization) step is carried out according to methods well known to those skilled in the art. It is in particular carried out in a known manner at a temperature generally between 130°C and 200°C, under a pressure of several hundred bars, for a sufficient time which may be within a range going, for example, from 5 to 90 min, depending in particular on the curing temperature, the crosslinking system adopted, the vulcanization kinetics of the composition in question or even the size of the tire.

[0194] Another subject of the present invention relates to a semi-finished article, in particular for tires carrying heavy loads, comprising at least one elastomer composition for tires carrying heavy loads of the invention as defined above. The semi-finished products of the present invention advantageously have in particular a good compromise of mechanical properties, in particular good fatigue resistance properties.

[0195] The heavy-load tire elastomer composition of the semi-finished product may be either in the uncured state (before crosslinking) or in the cured state (after crosslinking).

[0196] The semi-finished article may be any article used for the manufacture of finished rubber articles such as a tire.

[0197] Preferably, the semi-finished article for a heavy-load tire may be selected from underlays, treads, and tread underlays.

[0198] It is recognized that in particular embodiments of the present invention, the entire tread and / or the entire underlayment and / or all underlayments may be formed from the heavy-load tire elastomer composition disclosed herein, while in other embodiments, only portions of the tread and / or portions of the tread underlayment and / or portions of the underlayments may be formed from the heavy-load tire elastomer composition or combinations thereof.

[0199] For example, in some embodiments, only certain blocks / ribs of a tread may be made of the disclosed heavy-load tire elastomer composition, while in other embodiments, only portions of individual blocks / ribs may be made of the disclosed heavy-load tire elastomer composition.

[0200] In particular embodiments of the treads disclosed herein, the treads comprise at least 80% by volume of the heavy-load tire elastomer composition disclosed herein or, alternatively, at least 90% or 100% of such heavy-load tire elastomer composition.

[0201] The semi-finished articles are obtained by methods well known to those skilled in the art.

[0202] Another subject of the present invention relates to a heavy-load tire comprising at least one elastomer composition for heavy-load tires according to the invention as described above or comprising at least one semi-finished article as described above. The tires of the present invention advantageously have in particular a good compromise of mechanical properties.

[0203] The tires of the invention may in particular be intended to equip vehicles carrying heavy loads such as airplanes, metros, buses, heavy road transport vehicles (trucks, tractors, trailers, heavy goods vehicles) or all-terrain vehicles, such as heavy agricultural or construction site vehicles, and other transport or handling vehicles.

[0204] The tires of the invention are obtained by methods well known to those skilled in the art.

[0205] ANALYTICAL METHODS

[0206] The physicochemical properties of the precipitated silica used in the elastomeric compositions for heavy-load tires of the invention were determined using the methods described below.

[0207] Possible pretreatment of precipitated silica

[0208] When the precipitated silica is in the form of highly agglomerated particles, typically when the precipitated silica is in a form other than a powder, it is desirable to pretreat it before applying certain analytical methods, such as a CTAB surface area determination method and / or a SAXS primary particle size determination method (both methods concerned being detailed below).

[0209] In particular, on the one hand, when the precipitated silica is in the form of microbeads, that is to say a first form of highly agglomerated particles, it is desirable, before applying the method for determining the size of the particles primary by S AXS, to deagglomerate the microbeads in order to obtain a sample of precipitated silica in powder form.

[0210] On the other hand, when the precipitated silica is in the form of granules, that is to say in another form of highly agglomerated particles, it is desirable, before applying the method for determining the size of the primary particles by SAXS and also before applying the method for determining the surface area CTAB, to deagglomerate the granules in order to obtain a sample of precipitated silica in the form of powder.

[0211] In both cases, the same deagglomeration pretreatment, detailed below, was applied.

[0212] Deagglomeration pretreatment for precipitated silica in the form of highly agglomerated particles, in particular in the form of microbeads or granules.

[0213] Samples of precipitated silicas in the form of highly agglomerated particles, particularly in the form of granules or microbeads, were gently ground using a hand-operated agate mortar and pestle, manually applying gentle pressure and friction to the silica samples so as to cause the destruction of the agglomerates and other lumps contained therein. The grinding was carried out for a sufficient time for the samples to acquire a visually homogeneous consistency which is that of a powder; this time was generally a few tens of seconds and generally did not exceed 1 min.

[0214] For the sake of clarity, the aforementioned pretreatment need not be applied when the precipitated silica is in the form of a powder. The aforementioned pretreatment can, but need not, and therefore generally should not be applied when applying a BET surface area determination method, a "sedigraphy" fines determination method, a WAi aluminum determination method, or a water moisture determination method (all of which are detailed below) to precipitated silica in any form. The aforementioned pretreatment could also be applied, but need not, and therefore generally will not be applied when applying a CTAB surface area determination method to precipitated silica in the form of microbeads.

[0215] Determination of CTAB surface area

[0216] CTAB surface area (SCTab) values ​​were determined according to an internal method derived from standard NF ISO 5794-1, annex G. The method is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the “external” surface of the silica.

[0217] In this method, CTAB was allowed to adsorb onto the silica under magnetic stirring. The silica and residual CTAB solution were then separated. The excess of unadsorbed CT AB was determined by back titration with sodium bis(2-ethylhexyl)sulfosuccinate salt (hereinafter “AOT”) using a titroprocessor, the end point being given by the maximum turbidity of the solution and determined using an optrode.

[0218] Equipment

[0219] Metrohm Optrode (wavelength: 520 nm) connected to the Metrohm 662 photometer; Metrohm titrator: Titrino DMS 716; Metrohm titration software: Tiamo.

[0220] Glass beaker (2000 ml); volumetric flasks (2000 ml); sealed glass bottles (1000 and 2000 ml); disposable beakers (100 ml); micropipette (500 - 5000 µl); magnetic stirring bars with 25 mm discs (Ref VWR 442-9431) for adsorption; magnetic stirring bars (straight) for titration; polycarbonate centrifuge tubes (at least 20 ml), centrifuge (allowing a speed of 10,000 rpm); glass flasks (30 ml); thermobalance.

[0221] Preparation of solutions

[0222] Preparation of CTAB solution: at 5.5 g / l (buffered to about pH 9.6): in a 2000 ml beaker containing about 1000 ml of distilled water at 25 °C were added: 54.25 g of boric acid solution ([c]= 4%); 2.60 g of KCl, 25.8 ml (±0.1 ml) of sodium hydroxide. The solution thus obtained was stirred for 15 minutes before adding 11.00 g ± 0.01 g of CTAB powder (purity 99.9%, purchased from Merck). After stirring, the solution was transferred to a 2000 ml volumetric flask maintained at 25 °C and the volume was brought to 2000 ml with distilled water. The solution was transferred into a 2000 ml glass bottle. The solution was kept at a temperature not lower than 22 °C to avoid crystallization of CTAB (which occurs at 20 °C).

[0223] Preparation of AOT solution: Approximately 1200 ml of distilled water in a 2000 ml beaker was heated to 35 °C under magnetic stirring. 3.7038 g of AOT (purity 98%, purchased from Aldrich) was added. The solution was transferred to a 2000 ml volumetric flask and allowed to cool to 25 °C. The volume was brought to 2000 ml with distilled water and the solution was transferred to two 1000 ml glass bottles which were stored at 25 °C away from light.

[0224] All materials and solutions were kept at 25°C during analysis.

[0225] Procedure at the beginning and end of each experiment

[0226] Start of the experiment: the solutions were stirred before use. The device of The assay was purged before use. At least 40 ml of AOT was passed through the device to ensure that the device was clean and all air bubbles were removed. End of experiment: Purge the assay device to remove the AOT solution. Clean the optrode. Soak the optrode in distilled water.

[0227] Determination of the white factor

[0228] The variation in the concentrations of AOT and CTAB solutions over time is corrected by determining a daily “blank factor” called the ratio RI = Vl / ml.

[0229] In a 100 ml disposable beaker: 4.9000 g ± 0.0100 g of the 5.5 g / l (ml) CTAB solution was accurately weighed. The tare was set and 23.0000 g ± 1.0000 g of distilled water (MEAU) was accurately added. The solution was placed under stirring using a magnetic stirrer at 500 rpm on the dosing device and the titration was started. The stirring speed must be strictly constant throughout the titration without generating too many air bubbles.

[0230] Vi is the final volume of AOT solution required to titrate CTAB solution ml.

[0231] The determination of Ri is carried out at least in duplicate. If the standard deviation of Ri = Vi / mi exceeds 0.010, the titration is repeated until the standard deviation is less than or equal to 0.010. The daily ratio Ri is calculated as the average of the 2 or 3 measurements. Note: the optrode must be washed with distilled water after each measurement and dried with absorbent paper.

[0232] Adsorption of CTAB on silica

[0233] The moisture content (%H2O) of each silica sample was determined using a thermobalance (temperature: 160 °C) before the adsorption step as follows: tare the balance with an aluminum cup; weigh approximately 2 g of silica and evenly distribute the powder on the cup, close the balance; record the moisture percentage. In a 100 ml disposable beaker: 0.0100 g of silica (m0) was accurately weighed. 50.0000 ml + 1.0000 ml of the CTAB stock solution (Vo) was added. The total mass was recorded. The suspension was stirred for 40 minutes ±1 minute on the stir plate at 450 rpm using magnetic stirring bars with disc-shaped ends. After 40 minutes, the sample was removed from the stir plate.

[0234] 25 to 50 ml of the suspension was transferred into a centrifuge tube (the volume depends on the size of the centrifuge tube) and centrifuged for 35 minutes at a speed of 10,000 rpm at 25 °C. After centrifugation, the tube was carefully removed from the centrifuge so as not to destabilize the silica. 10 to 20 ml of CTAB solution was transferred to a glass vial which was then capped and stored at 25 °C.

[0235] Titration of CTAB solution

[0236] In a 100 ml disposable beaker = 4.0000 g ± 0.0100 g of the CTAB solution of unknown concentration (m2) were accurately weighed.

[0237] The tare was set and 19.4000 g ± 1.0000 g of distilled water (Meau) was added. solution was placed under stirring at 500 rpm on the dosing device and titration with the AOT solution began.

[0238] V2 is the volume of AOT at the end point required to titrate a quantity m2 of CT AB solution.

[0239] The CTAB surface area SCTab is calculated as follows:

[0240] [Math.l] R. -< V„ S = x ICTABÎî x 578.435 x

[0241] where:

[0242] Sctab = surface area of ​​silica (including moisture content correction) [m2 / g]

[0243] Ri = Vi / mi;

[0244] mi = mass of CTAB stock solution titrated as blank (kg);

[0245] Vi = final volume of AOT required to titrate ml of CTAB stock solution as blank (L)

[0246] R2 = V2 / m2;

[0247] m2 = mass of the CTAB solution titrated after adsorption and centrifugation (kg);

[0248] V2 = final volume of AOT required to titrate m2 of CTAB stock solution after adsorption and centrifugation (L)

[0249] [CTAB]; = ​​Concentration of CTAB stock solution (gd)

[0250] Vo = Volume of CTAB mother solution used for adsorption on silica (L)

[0251] Mes = Solid content of silica used for adsorption (g) corrected for the content of humidity as follows:

[0252] Mes = m0 x (100 - %H2O) / 100 where m0 = initial mass of silica (g).

[0253] Determination of the BET surface area

[0254] The BET surface area SBet was determined according to the Brunauer - Emmett -Teller method as detailed in standard NF ISO 5794-1, Annex E (June 2010) with the following adjustments: the sample was pre-dried at 160 °C±10 °C; the partial pressure used for the P / P° measurement was between 0.05 and 0.2.

[0255] Determination of particle distribution and size by centrifugal sedimentation in a disc centrifuge using a centrifugal photosedimentometer (CPS)

[0256] The values ​​of d50, di6, d84, FWHM and Ld were determined by centrifugal sedimentation in a disc centrifuge using a centrifugal photosedimentometer of the type “CPS DC 24000UHR”, marketed by the company CPS Ins instruments. This instrument is equipped with the operating software supplied with the device (operating software version 11g).

[0257] Instruments used: for the purposes of the measurement, the following materials and products were used: Ultrasonic system: 1,500 watt generator of the Sonies Vibracell VCF1500 type, equipped with a converter of the Sonies Vibracell CV154 type, a booster of the Sonies Vibracell BHN15GD (xl.5) type and a Sonies Vibracell 207-10 probe of 19 mm, with an interchangeable tip of 19 mm of the Sonies Vibracell 630-0407 type.

[0258] Analytical balance with an accuracy of 0.1 mg (e.g., Mettler AE260); syringes: 1.0 ml and 2.0 ml with 20 g needles; 50 ml tall glass beaker (SCHOTT DURAN: 38 mm diameter, 70 mm high); magnetic stirrer with a 2 cm stir bar; container for the ice bath during sonication.

[0259] Chemicals: Deionized water; Ethanol 96%; Sucrose 99%; Dodecane, all from Merck; PVC reference standard from CPS Instrument Inc; The peak maximum of the reference standard used should be between 200 and 600 nm (e.g., 239 nm).

[0260] Preparation of the disc centrifuge

[0261] For the measurements, the following parameters were established (Table 1). For the standard parameters, the PVC reference information provided by the supplier was used: [Tables 1] Sample parameters max diameter, pm 0.79 min diameter, pm 0.02 particle density g / ml 2.11 particle refractive index 1.46 particle absorption K 0.001 non-sphericity factor 1 Standard parameters peak diameter nm 239 peak width at half height pm 0.027 particle density 1.385 Fluid parameters fluid density g / ml 1.051 fluid refractive index 1.3612 fluid viscosity cps* 1.28 *cps=centipoise

[0262] System Configuration

[0263] The measurement wavelength was set to 405 nm. The following runtime option parameters were established (Table 2): [Tables2] Force Baseline: Yes Correct for Non-Stokes: No Extra Software Noise Filtering: No Baseline Drift Display: Show Calibration Method: External Samples per Calibration: 1

[0264] All other software options are left as defined by the instrument manufacturer.

[0265] Preparation of the disc centrifuge

[0266] The centrifugal disk is rotated at 24,000 rpm for 30 min. The gradient of sucrose density (CAS No. 57-50-l) is prepared as follows:

[0267] In a 50 ml beaker, a 24% by weight aqueous sucrose solution is prepared. In a 50 ml beaker, an 8% by weight aqueous sucrose solution is prepared. Once these two solutions have been homogenized separately, samples are taken from each solution using a 2 ml syringe which is injected into the rotating disk in the following order:

[0268] Sample 1: 1.8 ml of the 24% by weight solution

[0269] Sample 2: 1.6 ml of the 24% by weight solution + 0.2 ml of the 8% by weight solution weight

[0270] Sample 3: 1.4 ml of the 24% by weight solution + 0.4 ml of the 8% by weight solution

[0271] Sample 4: 1.2 ml of the 24% by weight solution + 0.6 ml of the 8% by weight solution

[0272] Sample 5: 1.0 ml of the 24% by weight solution + 0.8 ml of the 8% by weight solution

[0273] Sample 6: 0.8 ml of the 24% by weight solution + 1.0 ml of the 8% by weight solution

[0274] Sample 7: 0.6 ml of the 24% by weight solution + 1.2 ml of the 8% by weight solution

[0275] Sample 8: 0.4 ml of the 24% by weight solution + 1.4 ml of the 8% by weight solution

[0276] Sample 9: 0.2 ml of the 24% by weight solution + 1.6 ml of the 8% by weight solution

[0277] Sample 10: 1.8 ml of the 8% by weight solution

[0278] Before each injection into the disc, the two solutions are homogenized in the syringe by drawing in approximately 0.2 ml of air followed by brief manual agitation for a few seconds, taking care not to lose any liquid.

[0279] These injections, whose total volume is 18 ml, are intended to create a useful density gradient to eliminate certain instabilities that may appear during the injection of the sample to be measured. To protect the density gradient from evaporation, we add 1 ml of dodecane to the rotating disk using a 2 ml syringe. The disk is then left to rotate at 24,000 rpm for 60 min before any first measurement.

[0280] Sample preparation

[0281] 3.2 g of silica were weighed into a 50 ml glass beaker (SCHOTT DURAN: diameter 38 mm, height 70 mm) and 40 ml of demineralized water were added. The suspension was stirred using a magnetic stirrer at 300 rpm (minimum 20 s) before placing the beaker in a crystallization dish filled with ice and water cold. The magnetic stirrer was removed and the crystallization dish was placed under the ultrasonic probe placed 1 cm below the air-liquid interface. The ultrasonic probe was set to 60% of its maximum amplitude and was activated for 8 minutes. At the end of sonication, the beaker was placed back on the magnetic stirrer with a 2 cm magnetic stir bar stirring at a minimum of 500 rpm until sampling was completed.

[0282] The ultrasonic probe must be in good working order. The following checks must be carried out and, in case of negative results, a new probe must be used. As is known to those skilled in the art, an acceptable wear condition is generally considered to be a surface condition with no visually perceptible roughness. As a reference for an unacceptable wear condition, one can use, for example, the right image of Figure 3, page 14, published in “Preparation of Nano-particle Dispersions from Powdered Material Using Ultrasonic Disruption, version 1.1, [JS Taurozzi, VA Hackley, MR Wiesner], National Institute of Standards and Technology Special Publication 1200-2, June 2012” (CODEN NSPUE, publication available via the digital identifier dx.doi.org / 10.6028 / NIST.SP. 1200-2); The measured d50 of commercial silica Zeosil® 1165MP should be 93 nm ± 3 nm.

[0283] Analysis

[0284] Before the analysis of each sample, a standard was recorded. In each case, 0.1 ml of the PVC standard supplied by CPS Instruments and whose characteristics had been previously entered into the software was injected. It is important to start the measurement in the software simultaneously with this first injection of the PVC standard. Confirmation from the device must be received before injecting 100 μl of the previously sonicated sample, ensuring that the measurement is started simultaneously with the injection.

[0285] These injections were carried out using two clean 1 ml syringes.

[0286] At the end of the measurement, which is reached at the end of the time required to sediment all particles with the smallest diameter (configured in the software at 0.02 pm), the ratio for each diameter class was obtained. The curve obtained is called the particle size distribution of the aggregates. Integrating the particle size distribution of the aggregates as a function of diameter makes it possible to obtain a so-called "cumulative" distribution, i.e. the total weight of the aggregates between the minimum diameter measured and a diameter of interest.

[0287] Results

[0288] The values ​​d50, di6, d84 and Ld are based on distributions plotted in a linear scale. Integrating the diameter particle size distribution function yields a "cumulative" distribution, i.e. the total mass of particles between the minimum diameter and the diameter of interest.

[0289] d5o: this is the diameter below and above which 50% of the population is found by mass. The d50 is called the median size, i.e. diameter, of the silica particle. It is expressed in nm.

[0290] d84: this is the diameter below which 84% of the total mass of the particles is measured. It is expressed in nm.

[0291] di6: this is the diameter below which 16% of the total mass of the particles is measured. It is expressed in nm.

[0292] Ld: is calculated according to the equation: Ld=(d84-di6) / d50. Ld is a dimensionless number.

[0293] FWHM: is calculated on the curve derived from the aforementioned cumulative distribution, as explained above in the specification.

[0294] Determination of the fines rate by the “sedigraphy” method.

[0295] In this test, the dispersion capacity of silica is measured by a measurement of the particle size (by sedimentation) carried out on a suspension of silica previously deagglomerated by ultrasonication. The deagglomeration (or dispersion) under ultrasound is carried out using a VIBRACELL BIOBLOCK sonicator (1500 W), equipped with a 19 mm diameter probe. The measurement of the particle size is carried out using a SEDIGRAPH granulometer (sedimentation in the gravity field + scanning by X-ray beam).

[0296] 6.4 grams of silica are weighed in a tall beaker (volume equal to 100 ml) and completed to 80 grams by adding deionized water: an 8% aqueous suspension of silica is thus obtained, which is homogenized for 2 minutes by magnetic stirring. Deagglomeration (dispersion) under ultrasound is then carried out as follows: the probe being immersed over a length of 3 cm, the output power is adjusted to deliver 58 kJ to the suspension) in 480 seconds. The particle size is then measured using a SEDIGRAPH granulometer. The measurement is made between 85 pm and 0.3 pm with a density of 2.1 g / ml. The deagglomerated silica suspension, possibly previously cooled, is then circulated in the SEDIGRAPH granulometric cell. The analysis stops automatically as soon as the size of 0.3 pm is reached (approximately 45 minutes). The fines rate (rf) is then calculated, i.e. the proportion (by weight) of particles smaller than 1 pm.The higher this rate of fines (rf) or particles smaller than 1 pm, the better the dispersibility of the silica.

[0297] It is understood that the ultrasonic probe must be in good working order. For this purpose, the following checks may be carried out: (i) visual inspection of the physical integrity of the probe tip (roughness depth less than 2 mm measured using a fine caliper); and / or (ii) the rf measurement of the commercial silica Zeosil® 1165MP, aged for at least 2 years, must be 97%. In case of negative results, the output power must be readjusted. If the negative results persist, a new probe must be used.

[0298] Determination of primary particle size by SAXS 1. Principle of the method

[0299] Small angle X-ray scattering (SAXS) consists of exploiting the deflection of an incident X-ray beam, of wavelength X, passing through the sample, in a cone of a few degrees of angle. A scattering angle 0 corresponds to a wave vector defined by the following relation

[0300] [Math.2] JA 2

[0301] whose unit is  1 .

[0302] Each scattering angle corresponds to a wave vector q defined in reciprocal space. This wave vector corresponds to a spatial scale defined in real space, and which is equivalent to 2ir / q. Scattering at small angles therefore characterizes large distances in the sample, and conversely scattering at large angles characterizes small distances in the sample. The technique is sensitive to how the matter is distributed in space.

[0303] Basic references on this technique are given below:

[0304] [1] Small Angle Scattering of X rays, Guinier A., ​​Fournet G., (1955), Wiley, New 5 York.

[0305] [2] Small Angle X Ray Scattering, Glatter O., Krattky O., (1982), Academie Press, New York.

[0306] [3] Analysis of the Small-Angle Intensity Scattered by a Porous and Granular Medium, Spalla O., Lyonnard S., Testard F., J. Appl. Crystal. (2003), 36, 338-347. 10.

[0307] The conditions required for SAXS to characterize silica according to the following criterion are as follows: - the SAXS assembly operates in a transmission geometry (i.e. the incident beam passes through the sample), with an incident wavelength between 0.5 and 2 Angstroms (Â), - the wave vector q range is between 0.015 Â 1 and 0.30 Â ', which allows to characterize distances in real space ranging from 420 to 20 Â, - the whole is verified on the q scale using an appropriate standard (e.g. silver behenate, octadecanol or any other compound giving a thin SAXS line included in the q range above), - one-dimensional or, preferably, two-dimensional linear detector, - the assembly must allow the transmission of the preparation to be measured, i.e. the ratio between the intensity transmitted by the sample and the incident intensity.

[0308] Such a set may be, for example, a laboratory set, operating on an X-ray tube or rotating anode source, preferably using the Ka emission of copper at 1.54 Å. The detector can be a CCD detector, an image plate or a gas detector. It can also be a SAXS mount on a synchrotron. In the present application, a CCD detector was used.

[0309] 2) Procedure:

[0310] The silica sample is analyzed as a solid powder. The powder is placed between two X-ray transparent windows. Independently of this preparation, an empty cell is made with only two transparent windows, without silica inside. The scattering by the empty cell must be recorded separately from the scattering from the silica. During this operation, called "background measurement", the scattered intensity comes from all external contributions to the silica, such as electronic background noise, scattering through the transparent windows, residual divergence of the incident beam.

[0311] These transparent windows must provide a low background noise compared to the intensity scattered by the silica over the range of the wave vector being explored. They can be made of mica, Kapton or mylar film, or preferably an adhesive Kapton or mylar film covered with a thin layer of grease.

[0312] Before SAXS acquisition of silica, the quality of the preparation must be checked by measuring the transmission of the silica-loaded cell.

[0313] The measures to be taken are therefore as follows:

[0314] 2.1) Development of a cell composed of two windows without silica (empty cell).

[0315] 2.2) Development of a cell composed of two windows, with a sample of silica powder inside.

[0316] The amount of silica introduced must be less than 50 mg. The silica must form a layer with a thickness of less than 100 qm. It is preferable to obtain a monolayer of silica grains arranged on a window, which is easier to achieve with adhesive windows. The quality of the preparation is controlled by measuring the transmission (step 2.3)).

[0317] 2.3) Measurement of the transmission of the empty cell and the silica cell.

[0318] The ratio R is defined as follows:

[0319] R = silica cell transmission / empty cell transmission

[0320] R should be between 0.85 and 1, in order to minimize the risk of multiple diffusion, while maintaining a satisfactory signal-to-noise ratio for large q. If the R value is too low, the amount of silica visible to the beam must be reduced; if it is too high, silica must be added.

[0321] 2.4) SAXS acquisition on the empty cell and on the silica cell.

[0322] The acquisition times are determined so that the signal / noise ratio at large q is acceptable. They are such that in the immediate vicinity of q = 0.12 Â 1 , the fluctuations of the function F(q) defined below do not exceed + / - 5% compared to the value taken by the function F at this point.

[0323] 2.5) If a two-dimensional detector was used: radial grouping of each of the two two-dimensional profiles to obtain the scattered intensity as a function of the wave vector q. The determination of the scattered intensity must take into account the exposure time, the intensity of the incident beam, the transmission of the sample, the solid angle intercepted by the detector pixel. The determination of the wave vector must take into account the wavelength of the incident beam and the sample-detector distance.

[0324] 2.6) If a one-dimensional detector was used: the previous determinations regarding the scattered intensity and wave vector must be performed, but there is no radial clustering to be expected.

[0325] 2.7) This leads to two profiles reducing the information to the variation of the intensity scattered as a function of the wave vector q: one profile for the empty cell and one profile for the silica cell.

[0326] 2.8) Subtraction of the intensity scattered by the empty cell from the intensity scattered by the silica cell (subtraction of the “background”).

[0327] 2.9) The SAXS profile of silica, after subtraction of the “background”, shows a de monotonic growth which occurs according to a regime close to the Porod regime, that is to say that the intensity decreases very quickly with the wave vector according to a law close to a power law in q 4 . The small deviations from this Porod law are better visible by representing the data according to the so-called Krattky-Porod method. This involves representing F(q) as a function of q, with:

[0328] F(q) = I x q4

[0329] where F represents a SAXS profile according to the Kratty-Porod method, I represents the scattered intensity after subtraction of the “background” and q represents the wave vector (in A1).

[0330] 2.10) In the Krattky-Porod representation, when describing the profile, we can possibly observe a maximum, which is linked to the existence of primary particles of a roughly defined size. The maximum is all the more marked as the polydispersity is low. In the case of monodisperse primary particles, a second, or even a third oscillation to the right of the maximum is observed. The position of the maximum is linked to the average size of the primary particle by a 2ir / q law.

[0331] Two different determinations can be made, both providing information on the dimensions of the primary particles.

[0332] A first determination is based on the position of the maximum in I x q4 = F(q). It corresponds to a spatial scale, given by 2ir / qmax. In the case of a po spheres to a band, this distance does not correspond exactly to the diameter but to 115% of the diameter (in Â). This exploitation does not give access to a size distribution, but only to an average diameter in which the largest particles have a strong influence.

[0333] Another determination provides the average size dzs (Zimm-Schultz mean diameter) in accordance with the present invention. Thus, a SAXS profile in I x q4 = F(q) is modeled by a distribution of independent spheres (having different diameters), of the Zimm-Schultz distribution type.

[0334] The person skilled in the art is well aware of the use of such a distribution to adapt to numerous distributions observed in various fields of chemistry. As reference articles, the following may be cited in particular: - J. Welch, VA Bloomfield, J. Pol. Sci., Polymer Physics Edition, vol. 11 (1973), entitled "Fitting Polymer Distribution Data to a Schulz-Zimm Function" - HJ Angerman, G. ten Brinke, JJM Slot, The European Physical Journal B, 12, 397-404 (1999), entitled "Influence of polydispersity on the phase behavior of statistical multiblock copolymers with Schultz-Zimm block molecular weight distributions", and - LH Hanus, HJ Ploehn, Langmuir, 15, 3091-3100 (1999), entitled “Conversion of Intensity-averaged Photon Correlation Spectroscopy Measurements to Number-Averaged Particle Size Distributions. 1. Theoretical Development".

[0335] The latter article concerns the determination of the mean diameter of a particle distribution, as is the case for the inventive silica. The Zimm-Schultz distribution function, as presented in Table 1 of the latter article, was evaluated, and general expressions for converting the mean particle diameter to intensity and the polydispersity index to mean and standard deviation of the Zimm-Schultz distribution function are presented in Table 2 of the latter article.

[0336] The modeled SAXS profile is based on the well-known SAXS shape factor. Consequently, for a sphere with diameter d (d = 2 x r, where r is the radius of the sphere, in Â), we have

[0337] [Math.3] kx V 2 x [ sin (q xr) - q xrx cos (qxr) l 2 l(q J) ----------------------------— q 6 xr 6 [equation (SF)]

[0338] where I(q,r) is the scattered intensity of the sphere of diameter d at the wave vector q (in  1 ), k is a multiplicative constant, V is the volume of the sphere [i.e. V = 4 / 3 x ir x r3] and sin and cos denote the sine and cosine functions respectively.

[0339] For a distribution of independent spheres having different diameters, the (total) scattered intensity I(q) after subtracting the “background” from the wave vector q is

[0340] [Math.4] l(q) = ( f(r) xl(q,r) dr

[0341] where f(r) is the distribution function of the independent spheres, and I(q,r), r and q are as defined previously; the corresponding SAXS profile F(q) is

[0342] [Math.5] F(q) = q 4 xl(q) = q 4 x ! f(r) x I(q,r) dr

[0343] The independent-sphere Zimm-Schultz distribution function f(r) = fzs(r) is generally represented by

[0344] [Math.6] has t+1 x K x exp (- axr) r

[0345] where exp denotes the exponential function, F denotes the gamma function, r is the radius of the sphere, and t and a are two parameters related to the mean diameter dzs (in Â) and the dimensionless polydispersity index ip by the following equations

[0346] [Math.7]

[0347] [Math. 8] __2 x (t + 1 ) a — dzs

[0348] The modeled SAXS profile based on independent spheres having a Zimm-Schultz distribution in accordance with the invention Fzs (q) is therefore

[0349] [Math.9]

[0350] where q (in Â1), r (in Â), V (in Â3), k, a and t are as defined previously, and where exp, T, sin and cos denote the same functions as those specified above.

[0351] Thus, the modeled profile requires two inputs to be adjusted: 1) the diameter average dzs and 2) the polydispersity index ip (via the parameters t and a).

[0352] Additionally, the multiplicative constant k is used to fit the profile Fzs on the y-axis.

[0353] These inputs can be determined using conventional numerical tools or by trial and error, in order to best fit F(q) = I.q4 (SAXS profile in the Krattky-Porod representation) within a wavevector interval [qmin, qmax] which must include the point on the wavevector where F(q) reaches its maximum (for the avoidance of doubt, qmin and qmax, expressed in  1 , represent the lower and upper limits of the wavevector interval, respectively). The fit is optimal when the modeled and experimental data match as closely as possible in the interval surrounding the maximum (i.e., when the sum of the differences between the squares of the experimental values ​​of F(q) and the modeled values ​​of Fzs (q) is minimal).

[0354] In practice, the Zimm-Schultz distribution is discretized into classes within a selected radius interval [rmin, rmax]. For a given wavevector, each class of the discretized Zimm-Schultz distribution contributes to the modeled SAXS profile Fzs (q) through its shape factor [I(q,r), equation (SF)] and its weight fzs (r):

[0355] [Math. 10] Fzs(q) = Q4 x lzs(q)

[0356] [Math. 11] bs(q) s i fes(r) xl(qdr Dm

[0357] where Fzs(q) is the modeled SAXS profile, Izs(q) is the modeled scattered intensity, fzs(r) is the Zimm Schultz distribution function, I(q,r) is the scattered intensity of a sphere, q is the wave vector, r is the radius of the sphere, and rmin and rmax are the lower and upper limits of the selected range for the radius of the sphere. The selected range should include the mean Zimm Schultz radius rzs (rzs = dzs / 2). Typically, a skilled person might choose for rmin a value close to the expected value rzs / 20 (r°zs / 20, with r°zs as defined below) and define 50 values ​​that follow a geometric progression with a ratio of 1.1. Other choices are possible provided that the diameter distribution is properly accounted for in the modeled profile.The choice of the initial values ​​for the determination of rzs and ip (respectively, r°zs and i°p) as the starting point of an iterative determination method is not particularly critical. A person skilled in the art may, for example, advantageously use r°zs = 40 Å and ip = 0.50 as starting values; these values ​​are particularly suitable for the silicas according to the present invention. Alter . natively, or in addition, the person skilled in the art can rely on TEM measurements.

[0358] For convenience, the calculations can be performed after entering the above formulas into a spreadsheet.

[0359] This model does not take into account aggregation, and therefore the existence of correlations between the spheres; it also does not take into account consolidation, that is to say the presence of an additional material which welds the primary particles.

[0360] 2.11) From the Zimm-Schultz distribution model, we determine the size SAXS particles which is a mean diameter dzs (Zimm-Schultz mean diameter).

[0361] Measurement of the quantity of aluminum (W) Ai

[0362] The weight amount of aluminum, based on the weight amount of SiO2, was measured by wavelength dispersive X-ray fluorescence spectrometry using a Panalytical WDXRF instrument. Sample analyses were performed under helium in a 4 cm diameter cell using silica, particularly silica powder, contained in the cell and covered with a thin film of Prolene (4 pm Chemplex®) over an Al / SiO2 range of 0.1 to 3.0% (by weight).

[0363] Fluorescence of Ai and Si was measured using the following parameters: Al 20 angle Ka = 144.9468° (20 s), background signal 20 angle = -1.2030° (4s), Si 20 angle Ka = 109.1152° (10 s), tube power 4 kW (32 kV, 125 mA), PE002 crystal and 550 pm collimator, gas flow detector.

[0364] Glass transition temperature Tg

[0365] The glass transition temperature Tg is measured in a known manner by DSC (differential scanning calorimetry) according to ASTM D3418 (2008).

[0366] Microstructure of the elastomer

[0367] Near infrared (NIR) spectroscopy is used to quantitatively determine the weight content of styrene in the elastomer and its microstructure (relative distribution of 1,2-vinyl, trans-1,4 and cis-1,4-butadiene units). The principle of the method is based on the generalized Beer-Lambert law for a multi-component system. Since the method is indirect, it involves a multivariate calibration [Vilmin, F., Dussap, C. and Coste, N., Applied Spectroscopy, 2006, 60, 619-29] carried out using standard elastomers whose composition is determined by 13C NMR. The styrene content and microstructure are then calculated from the NIR spectrum of an elastomer film with a thickness of approximately 730 pm. The spectrum was acquired in transmission between 4000 and 6200 cm 1 with a resolution of 2 cm 1 using a Bruker Tensor 37 Fourier transform near infrared spectrometer equipped with a Peltier-cooled InGaAs detector.

[0368] Tensile tests

[0369] Tensile tests are used to determine the breaking properties; those carried out on hardened mixtures according to the NF ISO 37 standard of December 2005. The tensile strength, in MPa, and the elongation at break, in %, are measured at 60°C ± 2°C, and in normal humidity conditions (50 ± 5% relative humidity), according to the French standard NF T 40-101 (December 1979).

[0370] For better readability in the presentation of the results below and for easier comparison, the results are given in base 100, the value 100 being fixed for the control. The value in base 100 for the sample is calculated according to the operation: (value of the elongation at break of the sample / value of the elongation at break of the control) x 100. A result greater than 100 in terms of elongation at break indicates an increased value and therefore an improved performance in terms of elongation at break, for the composition compared to the control.

[0371] Dynamic properties of elastomeric compositions for tires carrying heavy loads (after vulcanization)

[0372] The dynamic properties G* and tan(ô) are measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D5992-96 standard. The response of a sample of vulcanized composition (cylindrical specimen 4 mm thick and 10 mm in diameter) subjected to a sinusoidal stress in simple alternating shear, at a frequency of 10 Hz.

[0373] For the measurement of the G* modulus at 50% deformation, noted G*50% return, and of tan(ô)max, a scan is carried out with a deformation amplitude of 0.1% to 100% peak to peak (forward cycle), then from 100% to 0.1% peak to peak (return cycle) at a temperature of 60 °C. The results used are the complex dynamic shear modulus (G*) and the loss factor tan(ô). The maximum value of tan(ô) observed (tan(ô)max) between the values ​​of 0.1% to 100% deformation is indicated for the forward cycle.

[0374] The results of tan(ô)max at 60 °C are expressed in terms of performance in base 100, i.e., the value 100 is arbitrarily assigned to the control, in order to consecutively compare the tan(ô)max at 60 °C (i.e., the hysteresis properties) of the different sample compositions tested. The value in base 100 for the sample is calculated according to the operation: (tan(ô)max value at 60 °C of the control / tan(ô)max value at 60 °C of the sample) x 100. A result greater than 100 indicates improved performance, i.e., the composition of the sample under consideration has improved hysteresis properties corroborating better rolling resistance compared to the control elastomer composition.

[0375] The results of G*50% return to 60°C are expressed in terms of performance in base 100, i.e. the value 100 is arbitrarily assigned to the control, in order to consecutively compare the G*50% return to 60°C (i.e. the stiffness) of the different compositions of samples tested. The value in base 100 of the sample of com tested position is calculated according to the operation: (G value * 50% return to 60 °C of the sample / G value * 50% return to 60 °C of the control) x 100. Therefore, a score above 100 indicates an improvement in performance, i.e. an improvement in stiffness.

[0376] Fatigue test

[0377] An elastomeric compound may also be characterized, with respect to its resistance to cracking, by a fatigue test. The fatigue resistance, expressed in number of cycles or in relative units (percentage of a number of cycles compared to a reference number of cycles), is measured on 12 test pieces subjected to repeated low-frequency tractions up to an elongation of 75%, at a temperature of 23°C, using a Monsanto apparatus (type "MFTR") until rupture of the test piece, by applying the protocol described in STANDARD ASTM D4482-85 and ISO 6943 to rectangular test pieces (65 mm useful length, 1.5 mm thickness, 15 mm width) having a central notch of 3 mm. With results expressed in relative units, a value higher than that of a control taken as a reference, arbitrarily set at 100, indicates an improved result, i.e. better fatigue resistance of the elastomer compound samples.The value in base 100 of the tested composition sample is calculated according to the operation: (fatigue resistance value of the sample / fatigue resistance value of the control) x 100. Correlatively, a value lower than 100 indicates a degraded result, that is to say a less good fatigue resistance of the elastomer compound samples.

[0378] EXAMPLES

[0379] Examples 1 to 3: synthesis of silica

[0380] Example 1 - Comparative silica 1 (SCI)

[0381] The comparative silica, Zeozil 1165MP, is marketed by Solvay.

[0382] The properties of SCI precipitated silica are shown in Table 3.

[0383] Example 2- Comparative Silica 2 (SC2)

[0384] In a 2500 1 stainless steel reactor, 1126 1 of water and 29.7 kg of Na2SO4 (solid) were introduced. The resulting solution was stirred and heated to 92 °C. The entire reaction was carried out at this temperature. A 96% by weight sulfuric acid solution was introduced into the reactor to reach a pH of 3.90. A sodium silicate solution (SiO2 / Na2O ratio = 3.45; SiO2 concentration = 19.3% by weight) at a flow rate of 420 1 / h was introduced into the reactor over a period of 51 s. The same sodium silicate solution was used throughout the process. Then, a sodium silicate solution at a flow rate of 445 l / h, a water flow rate of 575 l / h and a 96% by weight sulfuric acid solution were introduced simultaneously over a period of 14.9 minutes. The sulfuric acid flow rate was regulated by so that the pH of the reaction medium was maintained at a value of 4.30. At the end of this step, sodium silicate at a flow rate of 445 1 / h and a 96% by weight sulfuric acid solution were introduced simultaneously over a period of 9.45 min. The flow rate of the 96% by weight sulfuric acid solution was regulated so as to maintain the pH of the reaction medium at a value of 4.30.

[0385] The introduction of the acid was then stopped while the addition of sodium silicate was made at the rate of 579 1 / h until the reaction medium reached the pH value of 8.00.

[0386] Sodium silicate at a flow rate of 708 1 / h and a 96% by weight sulfuric acid solution were then introduced simultaneously over a period of 3 minutes. The flow rate of the 96% by weight sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0387] Simultaneously, over a period of 14.8 min, the following were introduced: sodium silicate, at a flow rate of 706 1 / h, a sodium aluminate solution (% by weight of Al: 12.2% - weight of Na2O: 19.4%), at a flow rate of 47.6 kg / h and a 96% sulfuric acid solution. The flow rate of the 96% sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0388] At the end of this simultaneous addition, the pH of the reaction medium was brought to a value of 4.40 with 96% by weight of sulfuric acid. Water was then introduced to lower the temperature to 85 °C and the reaction mixture was matured for 5 minutes. A suspension was obtained.

[0389] The reaction suspension was filtered and washed on a filter press to give a precipitated silica cake with a solids content of 23% by weight.

[0390] The obtained silica cake was then subjected to a liquefaction step in a vigorously stirred continuous reactor. 200 g of a 7.7% sulfuric acid solution was then added to the mixture to adjust the pH. The pH value of the liquefied cake was 6.0 and its solids content was 23% by weight.

[0391] The obtained suspension was dried using a nozzle atomizer dryer and then granulated to obtain precipitated silica SC2.

[0392] The properties of precipitated silica SC2 are shown in Table 3.

[0393] Example 3 - Silica SI

[0394] In a 2500 L stainless steel reactor, 1124 L of water and 29.7 kg of Na2SO4 (solid). The resulting solution was stirred and heated to 92 °C. The entire reaction was carried out at this temperature.

[0395] A sodium silicate solution (SiO2 / Na2O ratio = 3.45; SiO2 concentration = 19.3% by weight) at a flow rate of 445 1 / h, a water flow rate of 575 1 / h and a 96% by weight sulfuric acid solution were introduced simultaneously over a period of 6.2 min. The sulfuric acid flow rate was regulated so that the pH of the medium reaction is maintained at a value of 8.2.

[0396] The introduction of sodium silicate was then stopped until the reaction medium reached the pH value of 4.0.

[0397] Next, a sodium silicate solution at a flow rate of 445 1 / h, a water flow rate of 575 1 / h and a 96% by weight sulfuric acid solution were introduced simultaneously over a period of 7.1 minutes. The sulfuric acid flow rate was regulated so that the pH of the reaction medium was maintained at a value of 3.85. At the end of this step, sodium silicate at a flow rate of 445 1 / h and a 96% by weight sulfuric acid solution were introduced simultaneously over a period of 6 min. The flow rate of the 96% by weight sulfuric acid solution was regulated so as to maintain the pH of the reaction medium at a value of 3.85.

[0398] The introduction of the acid was then stopped while the addition of sodium silicate was made at the rate of 610 1 / h until the reaction medium reached the pH value of 8.00.

[0399] Sodium silicate at a flow rate of 705 1 / h and a 96% by weight sulfuric acid solution were then introduced simultaneously over a period of 22.4 min. The flow rate of the 96% by weight sulfuric acid solution was regulated so that the pH of the reaction medium was maintained at a value of 8.00.

[0400] At the end of this simultaneous addition, the pH of the reaction medium was brought to a value of 4.80 with 96% by weight of sulfuric acid. Water was then introduced to lower the temperature to 85 °C and the reaction mixture was matured for 5 minutes. A suspension was obtained.

[0401] Each reaction suspension was filtered and washed on a filter press to give a precipitated silica cake with a solids content of 23% by weight.

[0402] The obtained silica cake was then subjected to a liquefaction step in a vigorously stirred continuous reactor with the addition of a sodium aluminate solution ([Al]: 12.5% ​​by weight - [Na2O]: 19.5% by weight) and a 7.7% by weight sulfuric acid solution to adjust the pH. The amount of sodium aluminate solution is added to achieve an Al / SiO2% ratio of 0.55%. The pH value of the liquefied cake was 6.4 and its solids content was 23% by weight.

[0403] The obtained suspension was dried using a nozzle atomizer dryer to obtain precipitated silica SL. The properties of precipitated silica SI are shown in Table 3. [Tables 3] Products CTA B (m2 / g) BET (m2 / g) WAi (% by weight s) dso (nm ) ds4 (nm ) FW HM (nm ) Ld rf (%) FWHM: -0.16 xICTABI + 130 Silicate ratio AS0 (%) Primary particle size dzs (nm) SCI 155 160 0.33 93 175 65 1.3 98 105 n,c 15.1 SC2 158 208 1.39 146 336 131 1.8 88 105 0.0 7.2 SI 161 177 0.56 138 301 136 1.7 99 104 9.9 8.1 nc: not communicated

[0404] EXAMPLE 4: Use of silica in elastomeric compositions

[0405] The objective of the following tests is to demonstrate that the property compromise is improved for the elastomer composition for heavy-duty tires according to the invention, based on inventive precipitated silicas, compared to an elastomer composition for heavy-duty tires comprising a silica of the prior art.

[0406] Tables 4, 6, 8 below give the formulation of the different compositions, the contents being expressed in pce (parts by weight per hundred parts by weight of elastomers).

[0407] The optimal content of diphenylguanidine (DPG) is adapted according to the BET specific surface area of ​​the silica to be tested. Indeed, the larger the BET specific surface area of ​​a silica, the more it is necessary to use a high content of DPG to cover the surface of the silica and promote its dispersion. Those skilled in the art know how to adapt these contents according to the nature of the silica used. The formulations can be compared.

[0408] The optimal content of coupling agent between the silica and the diene elastomer is adapted according to the CTAB surface area of ​​the silica to be tested. Indeed, the greater the CTAB specific surface area of ​​the silica, the more it is necessary to use a high content of said coupling agent in order to maintain an equivalent quantity of diene elastomer / silica bonds per unit of surface area of ​​the silica. Those skilled in the art know how to adapt these contents according to the nature of the silica used. The formulations can be compared.

[0409] The compromise of the four properties which are elongation at break at 60°C, stiffness at 60°C, fatigue resistance at 23°C and rolling resistance at 60°C can be obtained by calculating the arithmetic mean of the results presented in base 100.

[0410] The elastomer compositions to be tested are prepared in the following manner: the diene elastomers, then the silica to be tested, the coupling agent coupling the diene elastomer to the silica, then, after mixing for one to two minutes, the various other ingredients, with the exception of the sulfur and the sulfenamide primary accelerator, are introduced into an internal mixer filled to 72% (% by volume) and whose initial tank temperature is approximately 70°C. The thermomechanical work is then carried out (non-productive phase) in one or two stages (total mixing time equal to approximately 3 to 5 min, until a maximum “fall” temperature of approximately 165-170 °C is reached. The mixture thus obtained is recovered and cooled, then the sulfur and the sulfenamide accelerator are added on an external mixer (homofinisher) at 70 °C, the whole being mixed (productive phase) for 11 to 12 minutes.

[0411] The compositions are then shaped for the measurement of their properties. physical or mechanical (e.g. in the form of 4 mm test pieces, etc.) and, where appropriate, are hardened (or vulcanized) for the measurement of properties after vulcanization (see tables 5, 7 and 9).

[0412] Test A

[0413] The objective of this test is to demonstrate that the compromise of properties is improved for the elastomer composition for tires carrying heavy loads according to the invention (composition C1), based on inventive precipitated silica, compared to an elastomer composition for tires carrying heavy loads comprising a silica of the state of the art (compositions T1 and T2). [Tables 4] Tl T2 Cl Elastomer (1) 100.0 100.0 100.0 Silica SCI 41.0 (-) (-) Silica SC2 (-) 41.0 (-) Silica SI (-) (-) 41.0 Carbon black (2) 10.0 10.0 10.0 Anti-ozone wax (3) 1.0 1.0 1.0 Antioxidant (4) 1.5 1.5 1.5 Coupling agent (5) 3.2 3.3 3.4 DPG (6) 0.4 0.5 0.4 Stearic acid and ZnO 5.0 5.0 5.0 Accelerator (7) 1.5 1.5 1.5 Sol Sulphur 2H 2.5 2.5 2.5

[0414] Table 4 1. Diene elastomer: natural rubber; 2. Carbon Black: Sold by Cabot Corporation Carbon Black Grade N347 per ASTM D1765-14; 3. Anti-ozone wax “Varazon 4959” from Sasol; 4. Antioxidant: N-(l,3-dimethylbutyl)-N-phenyl-para-phenylenediamine sold by Flexsys under the reference Santoflex 6-PPD; 5. Coupling agent: Bis[3-(triethoxysilyl)propyl] tetrasulfide silane (TESPT) sold by Evonik under the reference Si69; 6. DPG: diphenylguanidine, sold by Flexsys under the reference Perkacit; 7. Accelerator: N-cyclohexyl-2-benzothiazolesulfenamide sold by Flexsys under the reference Santocure CBS.

[0415] The properties of these compositions, measured after vulcanization at 140°C for 40 minutes, are indicated in Table 5. [Tables 5] Tl T2 Cl Elongation at break at 60°C (base 100) 100 87 92 G*50% return at 60°C (base 100) 100 99 97 Tan(ô)max at 60°C (base 100) 100 151 124 Fatigue resistance (base 100) 100 53 102 Compromise on properties 100 98 104

[0416] Table 5

[0417] Compared to the control elastomer composition T1 for tires carrying heavy loads, the elastomer composition Cl of the present invention for tires carrying heavy loads surprisingly exhibits better fatigue resistance and rolling resistance (tan (δ) max at 60°C) while the stiffness (G*50% return at 60°C) and elongation at break properties are comparable.

[0418] Test B

[0419] The objective of this test is to demonstrate that the compromise of properties is improved for the elastomer composition for tires carrying heavy loads according to the invention (composition C2), based on inventive precipitated silica, compared to an elastomer composition for tires carrying heavy loads comprising a silica of the state of the art (compositions T3 and T4). [Tableauxô] T3 T4 C2 Elastomer (1) 80.0 80.0 80.0 Elastomer (8) 20.0 20.0 20.0 Silica SCI 54.0 (-) (-) Silica SC2 (-) 54.0 (-) Silica SI (-) (-) 54.0 Carbon black (12) 3.0 3.0 3.0 Anti-ozone wax (3) 1.0 1.0 1.0 Antioxidant (4) 1.5 1.5 1.5 Coupling agent (5) 5.2 5.3 5.4 DPG (6) 0.5 0.6 0.5 Stearic acid and ZnO 3.5 3.5 3.5 Accelerator (7) 2.0 2.0 2.0 Sol Sulphur 2H 1.8 1.8 1.8

[0420] Table 6

[0421] Ingredients (2) to (7) of composition T3, T4 and C2 are the same as those listed in Table 4.

[0422] (8) Diene elastomer: Non-functional, non-functional SBR styrene-butadiene copolymer extended, obtained by solution polymerization. It contains 24 mol% of 1,2-polybutadiene units relative to the butadiene unit; 26.5 wt% of styrene units relative to the total weight of the copolymer and has a Tg = -48 °C measured according to the D3418 standard of 2008.

[0423] (12) Carbon Black: Sold by Cabot Corporation Carbon Black Grade N234 according to ASTM D1765-14.

[0424] The properties of these compositions (T3, T4 and C2) measured after vulcanization at 140°C for 30 minutes are indicated in Table 7. [Paintings?] T3 T4 C2 Elongation at break at 60°C (base 100) 100 80 114 G*50% return at 60°C (base 100) 100 98 99 Tan(ô)max at 60°C (base 100) 100 166 125 Fatigue resistance (base 100) 100 36 129 Compromise on properties 100 95 117

[0425] Table 7

[0426] Compared to the control elastomer composition T3 for tires carrying heavy loads, the elastomer composition C2 of the present invention for tires carrying heavy loads surprisingly exhibits better fatigue resistance and rolling resistance (tan (δ) max at 60°C) while the stiffness (G*50% return at 60°C) and elongation at break properties are comparable.

[0427] Compared to the control elastomer composition for heavy load tires T4, the elastomer composition for heavy load tires C2 of the present invention surprisingly exhibits improved elongation at break and fatigue resistance properties for comparable stiffness properties.

[0428] Test C

[0429] The objective of this test is to demonstrate that the compromise of properties is improved for the elastomer composition for tires carrying heavy loads according to the invention (composition C3), based on inventive precipitated silica, compared to an elastomer composition for tires carrying heavy loads comprising a silica of the state of the art (compositions T5 and T6). [Tables 8] T5 T6 C3 Elastomer (1) 45.0 45.0 45.0 Elastomer (9) 30.0 30.0 30.0 Elastomer (10) 25.0 25.0 25.0 Silica SCI 58.0 (-) (-) Silica SC2 (-) 58.0 (-) Silica SI (-) (-) 58.0 Carbon black (12) 4.0 4.0 4.0 Anti-ozone wax (3) 1.0 1.0 1.0 Antioxidant (4) 2.0 2.0 2.0 Coupling agent (5) 5.8 5.9 6.0 DPG (6) 0.6 0.7 0.6 Stearic acid and ZnO 3.0 3.0 3.0 Accelerator (7) 1.0 1.0 1.0 Plasticizing agent (11) 4.4 4.4 4.4 Sol Sulfur 2H 1.5 1.5 1.5

[0430] Table 8

[0431] Ingredients (2) to (7) of composition T5, T6 and C3 are the same as those listed in Table 4.

[0432] (9) Diene elastomer: polybutadiene obtained using an Nd catalyst, having at least less than 94% by mass of cis 1-4 polybutadiene units and having a Tg of -108 °C measured according to standard D3418 of 2008.

[0433] (10) Diene elastomer: Styrene / butadiene copolymer SBR, having a tertiary amine-alkoxysilane function in the middle of the chain and whose glass transition temperature, measured according to the D3418 standard of 2008, is equal to -48 °C. Its microstructure, determined by the NIR method, is as follows: the content by weight of 1,4-trans units is 48%, that of 1,4-cis units is 28% and that of 1,2 units is 24% (each of these three contents concerns the butadiene units). The content by weight of the styrene units is 24.5% by weight relative to the total weight of the elastomer.

[0434] (11) Plasticizing agent: Escorez ECR-373 resin sold by Exxon Mobil, cut C5 / C9 having a Tg of 44°C measured according to the D3418 standard of 2008.

[0435] (12) Carbon Black: Sold by Cabot Corporation Carbon Black Grade N234 according to ASTM D1765-14.

[0436] The properties of this composition, measured after vulcanization at 140°C for 60 minutes, are indicated in Table 9. [Tables 9] T5 T6 C3 Elongation at break at 60°C (base 100) 100 82 100 G*50% return at 60°C (base 100) 100 95 98 Tan(ô)max at 60°C (base 100) 100 131 107 Fatigue resistance (base 100) 100 72 193 Compromise on properties 100 95 125 Table 9

[0437] Compared to the control elastomer composition for heavy-load tires T5, the elastomer composition for heavy-load tires C3 of the present invention surprisingly exhibits improved fatigue resistance and rolling resistance properties (tan (δ) max at 60°C) while the stiffness properties (G*5o%ret0ur at 60°C) and elongation at break properties are comparable.

[0438] Compared to the control heavy-load tire elastomer composition T6, the heavy-load tire elastomer composition C3 of the present invention surprisingly exhibits improved elongation at break and fatigue resistance properties for comparable stiffness properties.

Claims

Claims

1. Elastomeric composition for tires carrying heavy loads based on an elastomeric matrix comprising at least one diene elastomer, at least one reinforcing filler comprising at least one precipitated silica, at least one coupling agent coupling the diene elastomer to the precipitated silica and at least one crosslinking system, wherein: - said elastomeric matrix comprising at least 30 phr of an isoprene elastomer, - said precipitated silica being characterized by: o a CTAB surface area in the range from 40 to 525 m2 / g, o primary particles having an average size dzs measured by S AXS of less than 15 nm, o an amount of aluminum WAi of at least 0.5% by weight, o a fines content rf, i.e. a proportion (by weight) of particles with a size less than 1 pm after ultrasonic deagglomeration, which is at least 91%;and o a particle size distribution measured by centrifugal sedimentation using a CPS, such that, for a given value of CTAB surface area, the FWHM parameter is defined by the relation (I):l FWHM 1 > -0.16 xl CTAB 1+130 (I).;

2. An elastomeric composition for heavy-duty tires according to claim 1, wherein the precipitated silica has a CTAB surface area of 50 to 300 m2 / g, preferably 70 to 300 m2 / g, more preferably 80 to 270 m2 / g or alternatively, 120 to 275 m2 / g, more preferably 120 to 230 m2 / g.

3. A heavy-duty tire elastomer composition according to any preceding claim, wherein the precipitated silica has a FWHM ranging from 100 to 250 nm.

4. A heavy-duty tire elastomer composition according to any preceding claim, wherein the precipitated silica has a d50 characterized by the following relationship: ld501 > -0.81 x ICTABI + 263 (IV).

5. Elastomeric composition for heavy load bearing tires according to claim 4, wherein the precipitated silica has a d50 between 110 nm and 240 nm, preferably between 130 and 220 nm.

6. Elastomeric composition for tires carrying heavy loads according to any one of the preceding claims, wherein the precipitated silica has a d84 characterized by the following relationship: ld84 1 < 2.81 x 1 FWHM 1 + 35 (V).

7. Elastomeric composition for heavy load bearing tires according to claim 6, wherein the precipitated silica has a d84 of between 200 and 550 nm, preferably between 250 and 500 nm.

8. Elastomeric composition for heavy load tires according to any one of the preceding claims, wherein the precipitated silica has a fines content rf of at least 92%, preferably at least 94%, at least 95%, at least 97%.

9. An elastomer composition for heavy-duty tires according to any preceding claim, wherein the elastomer matrix comprises another diene elastomer other than the isoprene elastomer, said other diene elastomer being selected from the group consisting of polybutadienes, styrene-butadiene copolymers and mixtures of said elastomers.

10. Elastomer composition for heavy-duty tires according to claim 9, wherein the amount of isoprene elastomer in the elastomer matrix is from 30 to 95 phr and the amount of said other diene elastomer is from 5 to 70 phr, preferably the amount of isoprene elastomer in the elastomer matrix is from 35 to 90 phr and the amount of said other diene elastomer is from 10 to 65 phr, even more preferably the amount of isoprene elastomer in the elastomer matrix is from 35 to 85 phr and the amount of said other diene elastomer is from 15 to 65 phr.

11. The elastomer composition for heavy-duty tires according to claim 9, wherein the amount of isoprene elastomer in the elastomer matrix is from 30 to 95 phr, the other diene elastomer is a blend of a polybutadiene and a styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix is from 2.5 to 35 phr, and the amount of styrene-butadiene copolymer is from 2.5 to 35 phr; preferably, the amount of isoprene elastomer in the elastomer matrix ranges from 35 to 90 phr, the other diene elastomer is a mixture of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 5 to 35 phr and the amount of styrene-butadiene copolymer ranging from 5 to 30 phr, more preferably, the amount of isoprene elastomer in the elastomer matrix ranges from 35 to 85 phr, the other diene elastomer is a mixture of polybutadiene and styrene-butadiene copolymer, the amount of polybutadiene in the elastomer matrix ranging from 7.5 to 35 pce and the amount of styrene-butadiene copolymer ranging from 7.5 to 30 pce.

12. A heavy-duty tire elastomer composition according to any one of claims 1 to 11 above, wherein the isoprene elastomer is selected from the group consisting of natural rubber, polyisoprene rubber and mixtures thereof.

13. An elastomeric composition for heavy-duty tires according to any preceding claim, wherein the composition further comprises a plasticizing agent, the amount of said plasticizing agent being in the range of 0.5 to 10 phr, preferably 0.75 to 8 phr.

14. A heavy-duty tire elastomer composition according to any one of preceding claims 1 to 12, wherein the composition does not comprise a plasticizing agent.

15. An elastomeric composition for heavy-duty tires according to any preceding claim, wherein the amount of said precipitated silica is in the range of 30 to 85 phr, preferably in the range of 35 to 65 phr.

16. Semi-finished article comprising at least one composition according to any one of claims 1 to 15.

17. A heavy goods vehicle tire comprising at least one elastomer composition for heavy load tires according to any one of claims 1 to 15 or comprising at least one semi-finished article as defined in claim 16.