Rubber composition for dynamic or static applications, its preparation process and products incorporating it.

Abstract

The invention relates to a crosslinkable rubber composition (I) based on an elastomer and its preparation process. The composition (I) comprises a crosslinking system and a thermoplastic phase dispersed in particles, at melting temperatures Tf or softening Tr, glass transition Tv and, optionally, crystallization Tc, the system comprising sulfur when the elastomer is unsaturated and the phase comprises saturated chains, and a peroxide when the elastomer is saturated, the composition (I) comprising the product:a) of a melt reaction by thermomechanical working of the elastomer and other ingredients except the system, comprising heating the mixture to a maximum temperature Ta greater than Tf or Tr, thenb) mechanical working of the mixture obtained, with addition of the system.The particles comprise filaments or fibrils, the temperature of the mixture during b) being temporarily higher than Tc when the phase is crystalline, or Tv when it is amorphous. Fig. 4.

Description

Description Title of the invention: Rubber composition for dynamic or static applications, its preparation process and products incorporating it. Technical field

[0001] = The invention relates to a crosslinkable rubber composition, its method of preparation, a crosslinked rubber composition, a mechanical organ with a function dynamic and a sealing element at least a part of which comprises this com- crosslinked rubber position. The invention applies in particular to all app- industrial applications using crosslinked rubber compositions, including said mechanical organ with dynamic function in particular chosen from anti- supports vibratory and elastic joints for motor vehicles or in- industrial, and said sealing element in particular chosen from sealing gaskets for vehicle bodywork and sealing profiles for buildings, on a non-commercial basis limiting. Prior art

[0002] … Conventionally, the reinforcement of elastomers within com- rubber positions is achieved by adding fillers such as carbon black or silica, in order to improve the mechanical properties of the compositions thanks to the e[fect hydrodynamics and interactions between the elastomer and the fillers, on the one hand, and between the charges themselves, on the other hand. These charges in powder form are dispersed in the rubber by thermomechanical work during mixing of the in- ingredients of the composition, except for the crosslinking system, by heating the mixing at a maximum temperature usually less than 150°C, typically between 100 and 130°C for an ethylene-terpolymer type rubber propylene-diene (EPDM) loaded with carbon black.

[0003] — However, these filler-elastomer and filler-filler interactions generate a undesirable phenomenon linked to hysteretic losses which are usually referred to as the name Payne effect and which results in a non-linearity (i.e. stiffening in amplitude) and stiffening, particularly at low temperatures, of the compositions of crosslinked rubber subjected to dynamic stresses. This stiffening results in dynamic properties that may prove unsatisfactory for the com- positions due to the aforementioned interactions with the reinforcing fillers used, dynamic properties which can usually be evaluated by measurement, two amplitudes of dynamic deformations, of a ratio of conservation moduli G' relative to the complex shear moduli G* of the compositions. As a reminder, the complex modulus G* is defined by the equation G* = G' + 1G”', with: G': real part of G* called conservation or elastic modulus, G' characterizing the rigidity or viscoelastic behavior of the composition (i.e. the energy conserved and totally restored); and G”": imaginary part of G* called loss or dissipation modulus, G'” characterizing the viscous behavior of the composition (i.e. the energy dissipated in the form of heat, it being specified that the ratio G'* / G' defines the loss factor tan delta). This ratio typically corresponds to G', measured at a low dynamic strain amplitude, relative to G' measured at a high dynamic strain amplitude, with the two G' moduli being measured at the same frequency and at the same temperature (e.g. G' 0.5% / G' 20%). As is known, G' 0.5% / G' 20% is usually between 1.80 and 2.00 for a rubber composition based on a polyisoprene (IR) and reinforced with 40 phr of a carbon black of grade N330 in order to be usable in dynamic applications (phr: parts by weight per 100 parts of elastomer). Indeed, it is known that in reinforced materials, the viscoelastic behavior varies from low dynamic strain amplitudes, with a significant decrease in G' with a significant increase in strain. US 8,247,494 B2 discloses, to overcome the aforementioned disadvantage of high hysteretic losses of conventionally filled compositions, a rubber composition which may be free of carbon black and silica which is reinforced by a thermoplastic resin dispersed in the form of discrete domains in a continuous phase of a crosslinked olefinic rubber. This document teaches crosslinking the rubber exclusively by hydrosilylation, for the formation of silicon crosslinking bridges. US 3,965,055 A relates to a rubber composition, in which a semi-crystalline thermoplastic resin (a polypropylene in the examples) is dispersed in an elastomer in particles with a transverse dimension D of at most 500 nm and a form factor (length L / D) of at least 2, by mixing above the melting point of the resin and then crosslinking without constraint of the composition below said melting point.More specifically, the mixture obtained by a mixing step A is cooled in a step B below said melting point (for example to room temperature), then the cooled mixture is placed in a step C on another mixer maintained at a temperature sufficiently low to avoid scorching of the mixture, and the crosslinking system is incorporated into the mixture at a temperature of 150 to 170°F in the examples (65 to 93°C), after which, in a step D, the composition obtained is shaped below said melting point, then the article is crosslinked in a step E. The mechanical work of the crosslinkable composition is thus . carried out cold during step C. WO 2020 / 225498 A1 in the name of the Applicant discloses a crosslinkable rubber composition based on an elastomer, which comprises a crosslinking system and a thermoplastic phase which has at least one melting temperature Tf and which is dispersed in nodules (e.g. spherical or ellipsoidal), the crosslinking system comprising sulfur when the elastomer is unsaturated and said phase comprises saturated chains, and a peroxide when the elastomer is saturated. The composition comprises the product: a) a melt reaction by thermomechanical working of the elastomer and the other ingredients except the crosslinking system, with heating of the mixture to a temperature above Tf maintained for a holding time, to obtain a precursor mixture of the composition, then b) mechanical working of the precursor mixture with addition of the crosslinking system to obtain the crosslinkable composition. The examples of WO 2020 / 225498 A1 indicate that step b) of mechanical working (called acceleration on cylinders) is carried out on the day of step a) of thermomechanical working, after prior cooling of the precursor mixture obtained in a) from 160°C to a temperature of 30°C. The method according to WO 2020 / 225498 A1 makes it possible to obtain, thanks to said nodules, improved scorch resistance for the crosslinkable composition and, for the crosslinked composition, reinforcement of the same order and improved mechanical properties even after thermo-oxidative aging or by UV radiation, in comparison with a control composition based on the same ingredients except the carbon black which it contains in place of said thermoplastic phase. During its recent research, the Applicant sought to modify the mixing process according to these examples of WO 2020 / 225498 A1, in particular in order to further improve the mechanical properties of the crosslinked rubber compositions obtained. Statement of the invention An aim of the invention is to provide a rubber composition which not only overcomes the aforementioned drawback of high hysteresis of compositions filled with carbon black or silica, but which also has in particular further improved reinforcing properties compared to those of the compositions tested in WO 2020 / 225498 A1. This aim is achieved in that the Applicant has just surprisingly discovered that if the aforementioned step b) of the precursor mixture according to WO 2020 / 225498 A1 is modified, so that the temperature Tb of the precursor mixture during the mechanical work is temporarily higher than the crystallization temperature Tc or glass transition temperature Tv of the thermoplastic polymer phase when said phase is partly crystalline or amorphous, respectively, then a mixture can be obtained which, after addition of the crosslinking system, gives a crosslinkable composition in which said phase is dispersed homogeneously in the elastomer matrix in the form of filaments or fibrils of specific morphology, which makes it possible, thanks to this mechanical work implemented temporarily above Tc or Tv, as the case may be, to obtain for the crosslinked composition an increased hardness and an improved reinforcement resulting in static and dynamic mechanical properties (including fatigue resistance) which are generally superior, in comparison with those of a control composition of the same formulation (i.e.based on the same ingredients and quantities) but obtained according to the process exemplified in WO 2020 / 225498 A1. More specifically, a crosslinkable composition according to the invention is based on at least one elastomer and comprises other ingredients which comprise a crosslinking system and a thermoplastic polymer phase which has at least one melting temperature Tf or softening temperature Tr, a glass transition temperature Tv and, when said phase is partly crystalline, a crystallization temperature Te, said phase being dispersed in said at least one elastomer in the form of particles, the crosslinking system comprising sulfur when said at least one elastomer is unsaturated and said phase comprises saturated polymer chains, and comprising a peroxide when said at least one elastomer is saturated, the crosslinkable composition comprising the product: a) a melt reaction by thermomechanical working of a reaction mixture comprising said at least one elastomer and said other ingredients with the exception of the crosslinking system to obtain a precursor mixture of the crosslinkable composition, the reaction comprising heating the reaction mixture to a maximum temperature Ta of said reaction mixture which is higher than said at least one temperature Tf or Tr, then b) mechanical working of the precursor mixture with addition of the crosslinking system, to obtain the crosslinkable composition. According to the invention, said particles comprise filaments or fibrils produced by these steps a) and b), the temperature Tb of the precursor mixture during the mechanical working of step b) being temporarily higher than said crystallization temperature Tc when the thermoplastic polymer phase is partly crystalline, or than said glass transition temperature Tv when the thermoplastic polymer phase is amorphous. By the expression "based on" is meant in this description that the com- position or the ingredient considered comprises predominantly by weight the constituent concerned, i.e. according to a mass fraction greater than 50%, preferably greater than 75% and possibly up to 100%. By "unsaturated" and "saturated" is meant, in a manner known in the present description, a thermoplastic elastomer / polymer which comprises at least one unsaturation (i.e. double or triple bond) and which is devoid of unsaturation (i.e. without double or triple bond), respectively. By "partly crystalline thermoplastic polymer phase" is meant in the present description that this phase comprises at least one semi-crystalline thermoplastic polymer and therefore has at least one melting temperature Tf, softening temperature Tr and crystallization temperature Tc, in addition to a glass transition temperature Tv (with by definition Tv < Te < Tr <Tf). By "amorphous thermoplastic polymer phase" is meant in the present description that this phase consists of at least one amorphous thermoplastic polymer having a softening temperature Tr, in addition to a glass transition temperature Tv (Tv < Tr). By "filaments or fibrils" is meant in this description elongated fibers or fibrillated structures (e.g. nanofilaments) which are distinguished from convex solids, such as spheres or ellipsoids, and may for example be of generally constant transverse width along the length (which may be straight, bent or curved) of the filament or fibril. Preferably, the particles dispersed in a composition according to the invention comprise said filaments or fibrils in a volume fraction greater than 70%, advantageously greater than 80%, or even greater than 90%. It will be noted that a crosslinkable composition according to the invention thus unexpectedly makes it possible, following thermomechanical work (with maintenance of heating for a determined period), by said mechanical work at a temperature of the mixture Tb which is temporarily (i.e. for a given period of time) higher than the threshold Tc or Tv (threshold determined by the chosen thermoplastic phase), to obtain a dispersion of this phase in the elastomer matrix in the form of particles, which mainly comprise or are made up of these filaments or fibrils with a further optimized interface between the particles and this matrix, thus giving the composition these improved reinforcement properties under static and dynamic stresses. Thus, as explained below, the crosslinkable composition according to the invention makes it possible, following its thermal crosslinking via the crosslinking system incorporated in step b) which is adapted to the elastomer-thermoplastic phase pair, to give the crosslinked composition a Shore hardness and mechanical properties which are clearly improved compared to those of the control composition of the same formulation obtained according to the examples of WO 2020 / 225498 A1. Generally speaking, any semi-crystalline or amorphous thermoplastic polymers may be used as thermoplastic phase, provided that they have a sufficiently high rigidity at room temperature and a plastic or at least deformable character during mixing. As explained below, the reduction in rigidity may be brought about by the passage, during step b) of mechanical working, of the temperature of the precursor mixture above Tc for an at least partly crystalline phase, or above Tv for an amorphous phase (e.g. consisting of at least one polystyrene as an amorphous polymer, with in this example Tv being typically between 80 and 105°C). It will further be noted that a composition according to the invention, characterized by a dispersion of the thermoplastic phase in said at least one elastomer, is not to be confused with a thermoplastic vulcanizate in which the thermoplastic base contains a dispersion of rubber nodules. Also generally, the duration of maintaining the heating in step a) may be at least 10 seconds, preferably being between 10 seconds and 10 minutes, more preferably between 20 seconds and 5 minutes and for example between 30 seconds and 3 minutes. According to another characteristic of the invention, the mechanical work of step b) can be initiated at an initial temperature TbO of the precursor mixture, with Tb0 > Tc or Tb0 > Tv when the thermoplastic polymer phase is partly crystalline or amorphous, respectively, and preferably the mechanical work of step b) is initiated while said phase is in the molten or softened state in the precursor mixture. It will be noted that the mechanical work according to the invention can thus be initiated at a temperature TbO0 sufficiently high for the thermoplastic phase to pass from a non-crystallized or non-vitreous state to a crystallized or vitreous state, respectively, during step b), and preferably for this phase to be melted or at least softened in the precursor mixture, which can then be softened, or even almost liquid during the initiation of step b). According to a preferred embodiment of the invention, the temperature Tb of the precursor mixture during step b) is maximum during the initiation of mechanical work where Tb=Tb0, then decreases until Tb < Tc or Tb < Tv, when the thermoplastic phase is partly crystalline or amorphous, respectively. It will be noted that during this decrease of Tb with time from the initial instant tO corresponding to Tb=Tb0, the thermoplastic phase passes from a non-crystallized or non-glassy state to a crystallized or glassy state, respectively, during the first minutes of mechanical work (i.e. at the beginning of step b)). Preferably according to said preferred embodiment of the invention, the mechanical work is initiated at said initial temperature TbO which is between - Tc or Ty, depending on whether the thermoplastic polymer phase is partly crystalline or amorphous, respectively, and - said maximum temperature Ta of the reaction mixture, which may coincide with the drop temperature Tt (e.g. “pit drop”) of the precursor mixture. In other words, TbO is preferably between Tc and Ta or between Tv and Ta, and preferably Tb0 is between 110 and 220°C, Even more preferably, TbO is between 150 and 190°C when the thermoplastic phase is partly crystalline (comprising e.g. a propylene homopolymer or copolymer) or amorphous (comprising e.g. a polystyrene), and the temperature Tb of the precursor mixture is maximum at the initiation of mechanical work where Tb=Tb0, then decreases until Tb is between 10 and 90°C, for example. In this case, the final value of Tb is then lower than Tc or Tv as explained above, this final value being able to vary to a large extent depending on the architecture chosen for the mixing and thermal regulation system. Generally speaking, said crosslinking system is preferably incorporated into the precursor mixture after a homogenization time of the latter, which time (counted from the initiation of mechanical work) is for example between 1 min. and 5 minutes, eg between 2 min. and 4 min. It will be noted that the initial temperature TbO of the precursor mixture at which step b) is initiated may be such that the mechanical work begins when the precursor mixture is in the molten state (for example liquid or pasty) or at least softened, before the temperature Tb of the precursor mixture decreases as explained above. According to another general characteristic of the invention, step a) can be followed by step b) so that a time interval At separates the extraction of the precursor mixture at the end of step a) and the initiation of mechanical work in step b) after transfer of the precursor mixture, providing a temperature difference AT = Tt-Tb0 between the drop temperature Tt (e.g. "pitted drop") of the precursor mixture at the end of step a) and the initial temperature TbO at the start of step b), such that AT / Tt < 30% and preferably AT / T1 < 20%. Preferably, At < 10 minutes (more preferably At < 2 minutes), so that AT / Tt < 10% and for example AT / Tt < 1%, the precursor mixture then being cooled at the end of step a) essentially during said mechanical work, so that the precursor mixture is subjected to generally continuous shear from the initiation of step a) and until the end of step b). It will be noted that the present invention can in fact be translated by the fact that the cooling of the precursor mixture since its extraction at the end of step a) is essentially implemented by this shearing, i.e. almost without cooling to ambient temperature while waiting for mechanical work. According to a general aspect of the invention, said particles dispersed in the composition (which particles are made up of said filaments or fibrils according to a volume fraction of at least 70%, preferably at least 80%, more preferably at least 90%) may have at least one of the following morphology characteristics: (a) for their equivalent diameter, defined as the diameter of a hypothetical spherical particle of the same volume: (i) an equivalent diameter which varies from 5 nm to 1000 nm and preferably from 10 nm to 330 nm for all the particles, (ii) a median equivalent diameter of between 20 nm and 200 nm and preferably of 30 nm to 60 nm, and (iii) an average equivalent diameter of between 30 nm and 300 nm and preferably of between 40 nm and 70 nm; and / or (b) for their form factor, defined by the ratio of the greatest length to the smallest width of each particle: (i) an average form factor equal to or greater than 2 and preferably between 2.0 and 2.5, and (ii) a maximum form factor for all particles which is greater than 5, preferably between 10 and 15. These particles may thus have the characteristics [(a) (i) and / or (a) (ii) and / or (a) (iii)] and / or [(b) (i) and / or (b) (ii)], advantageously at least (a) (iii) and (b) (i). These characteristics are measured by focused ion beam (FIB) scanning electron microscopy (SEM), a technique called FIF-SEM (“FIB-SEM” in English for “focused ion beam-scanning electron microscopy”). By "equivalent diameter" is meant in the present description a diameter of the equivalent sphere which corresponds to the diameter of a sphere which would have the same volume as the particle itself, but not the same projected surface. This equivalent diameter thus corresponds to the diameter of a virtual spherical particle of radius R and of the same volume, i.e. this equivalent diameter is calculated from the volume V of the segmented object defined by V = 4 / 3.x.R3. By "mean equivalent diameter" is meant here the arithmetic mean equivalent diameter in number of the equivalent diameters of the particles, i.e. for a sample split into classes. By "median equivalent diameter" is meant here the median ds of the volume distribution, i.e. by definition the cor- equivalent diameter corresponding to the cumulative frequency of 50% which divides the histogram of relative frequencies into two parts of the same area. By "average form factor" is meant here the arithmetic mean form factor in number of the particles. Generally speaking, the crosslinkable composition of the invention may comprise said thermoplastic phase in an amount of between 1 and 150 phr (phr: parts by weight per 100 parts of elastomer(s)) and preferably between 5 and 70 phr (even more preferably between 10 and 30 phr). According to another characteristic of the invention, the crosslinkable composition may comprise, as powder filler dispersed in said at least one elastomer: - from 0 to 100 pce (preferably from 0 to 50 pce and even more preferably from 0 to 10 pce, or even from 0 to 5 pce) of an organic filler such as carbon black, and - from 0 to 150 pce (for example from 10 to 100 pce) of a non-reinforcing inorganic filler other than a silica (pce: parts by weight per 100 parts of elastomer(s)). Advantageously, the crosslinkable composition can be completely free of organic or inorganic powder filler. By "filler" is meant in the present description one or more individual fillers of reinforcing or non-reinforcing grade(s) for the elastomer concerned which is / are dispersed homogeneously in powder form in the composition (unlike the nodules of the present invention), and by "inorganic filler" is meant a clear filler (sometimes called "white filler"), as opposed to organic fillers such as carbon blacks and graphite, for example. It will be noted that a composition according to the invention is thus free of carbon black or contains at most 100 phr (preferably at most 50 phr, or even at most 10 phr or even at most 5 phr), and that this composition of the invention may be free of silica and may optionally comprise at most 70 phr of a non-reinforcing inorganic filler, such as chalk or an aluminosilicate such as Kaolin, without limitation. According to a first embodiment of the invention, the crosslinking system comprises sulfur and optionally also a peroxide, said at least one elastomer being a rubber chosen from: - functionalized or non-functionalized olefinic rubbers, such as ethylene-alpha olefin(s) copolymers such as ethylene-propylene copolymers (EPM) and ethylene-propylene-diene terpolymers (EPDM), and - functionalized or non-functionalized diene rubbers derived at least in part from conjugated diene monomers, such as natural rubber (NR), homopolymers and copolymers of isoprene and homopolymers and copolymers of butadiene, and said thermoplastic polymeric phase comprises at least one saturated polymer of preferably chosen from functionalized or non-functionalized aliphatic or aromatic polyolefins, such as for example homopolymers or copolymers of ethylene or propylene. It should be noted that this sulfur crosslinking system includes, in a known manner, in addition to sulfur, all or part of the usual vulcanization accelerators and activators. As ethylene-alpha olefin(s) copolymers for olefinic rubbers, mention may generally be made of those derived from ethylene and an alpha-olefin having from 3 to 20 carbon atoms and preferably from 3 to 12 carbon atoms, such as propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, heptene-1, octene-1, nonene-1, decene-1, undecene-1 and dodecene-1. Alpha-olefins chosen from propylene, butene-1, hexene-1, 4-methylpentene-1 and octene-1 are preferred. Examples of isoprene and butadiene copolymers for diene rubbers include isoprene-butadiene copolymers (BIR), copolymers of isoprene and / or butadiene with a vinylaromatic comonomer such as styrene (SIR, SBR, SBIR). According to an example of this first embodiment of the invention, said at least one elastomer is an EPDM whose mass content of units derived from ethylene is between 15% and 80% and said thermoplastic polymeric phase comprises at least one said aliphatic polyolefin chosen from ethylene homopolymers, propylene homopolymers and polypropylene-ethylene-diene terpolymers having a mass content of units derived from ethylene between 1% and 15%. It will be noted that the EPDM usable as an elastomer in the composition of the invention can thus have a relatively high mass content of units derived from ethylene of between 60 and 80%, or conversely of between 15 and 20%. As for the aliphatic polyolefin forming the thermoplastic phase of the invention, it can be a “PEDM” derived mainly from polypropylene, according to a mass content of at least 80% (with for example between 5 and 15% of ethylene and between 2.5 and 5% of diene). According to a second embodiment of the invention, the crosslinking system comprises a peroxide and optionally also sulfur, said at least one elastomer being saturated and said phase comprising saturated or unsaturated polymer chains, and preferably said at least one elastomer is a silicone rubber, for example chosen from polydimethylsiloxanes (PDMS), and said phase comprises at least one saturated polymer, for example chosen from phenyl silicone or alkyl silicone resins. It will be noted that this peroxide crosslinking system may advantageously comprise an organic peroxide as crosslinking agent and a crosslinking coagent comprising, for example, triallyl cyanurate (TAC) or triallyl iso- cyanurate (TAIC). As silicone rubber, any polyorganosiloxane can generally be used, and as saturated polymer any thermoplastic silicone resin, for example of the alkyl (e.g. methyl) silicone or phenyl silicone type. The present invention also relates to a crosslinked rubber composition, which is the product of thermal crosslinking of the crosslinkable composition as defined above by chemical reaction with said crosslinking system. This crosslinking can be obtained via a temperature setting of between 140 and 220°C, preferably between 150 and 200°C. It will be noted that a crosslinked composition according to the invention may have, like the crosslinkable composition, at least one of the aforementioned morphology characteristics [(a) (i) and / or (a) (ii) and / or (a) (ii)] and / or [(b) (i) and / or (b) (ii)] for said particles dispersed in the composition. According to another aspect of the invention, said crosslinked rubber composition may have at least one of the following properties (a), (b), (c) and (d): (a) a Shore A hardness measured according to ASTM D 2240 which is equal to or greater than 60, preferably between 65 and 70; (b) secant moduli M100, M200 and M300 at 100%, 200% and 300% strain, measured in uniaxial tension according to ASTM D 412, which are respectively greater than 3 MPa, 6 MPa and 9 MPa and which are preferably respectively greater than 6 MPa, 9 MPa and 12 MPa; (c) a moduli ratio M 155Hz / M 15Hz and a loss factor tan D at 15 Hz which are measured at 23°C via a frequency sweep according to ISO 4664 by a Metravib® visco-analyzer on Metravib® stud-type specimens and which satisfy at least one of the following conditions (i) and (ii): (i) M 155Hz / M 15Hz < 1.50, (ii) a dynamic modulus at 15 Hz > 7 MPa, and (iii) tan D at 15 Hz < 0.10; and (d) a fatigue resistance greater than 5.10° cycles, measured at a frequency of 5 Hz and a temperature of 23° C by a hydraulic endurance machine “MTS 831.02 Elastomer Test System” with a maximum capacity of 25 kN, equipped with a 15 kN force cell and a cylinder with a stroke of + / - 60 mm, controlled by the software “MTS Flex(est 40” on “mini-diabolos” test pieces with a minimum force of 0 N and a maximum force of 250 N, 200 N, 125 N and 100 N. Preferably, these properties (a), (b), (c) and / or (d) are obtained in accordance with said first embodiment of the invention, i.e. with the crosslinking system which is sulfur, said at least one elastomer which is an olefinic rubber (eg EPM or EPDM) or a diene rubber derived from conjugated dienes (eg NR), and said thermo-phase plastic that comprises a saturated polymer (e.g. aliphatic or aromatic polyolefin, such as for example a homopolymer or copolymer of ethylene or propylene, or a polystyrene). It will be noted that the hardness and mechanical properties of the crosslinked composition according to the invention are advantageously superior to those of a control composition based on the same ingredients, but obtained according to the process exemplified in WO 2020 / 225498 A1 (and therefore incorporating nodules, instead of the filaments or fibrils dispersed according to the invention). Indeed, the Applicant has verified that a crosslinked composition according to the invention has static moduli very significantly increased compared to those of the control composition obtained according to the examples of WO 2020 / 225498 A1, as well as dynamic properties also improved compared to those of said control composition, including a fatigue resistance much higher than that of the latter. As indicated above for the crosslinkable composition, the crosslinked composition of the invention may be free of any powder filler (organic or inorganic). According to said second embodiment of the invention where said at least one elastomer comprises said silicone rubber preferably chosen from PDMS and said thermoplastic phase comprises said at least one saturated polymer preferably chosen from phenyl or alkyl silicone resins, the crosslinked composition can thus be completely free of silica. Surprisingly, it will be noted that this absence of silica in such a rubber composition based on a silicone rubber (which usually contains silica as a reinforcing filler), the high level of reinforcement obtained thanks to the dispersion of the filaments or fibrils of phenyl or alkyl silicone resin does not result in mechanical non-linearities observed under dynamic stresses, which advantageously results in a Payne effect also reduced for this second mode in comparison with a control composition based on the same ingredients (e.g. same elastomer matrix and crosslinking system) but loaded with carbon black as a replacement for this resin. It will also be noted that the mechanical properties set out above for the crosslinked compositions of the invention are almost not penalized following thermo-oxidative aging (i.e. under hot air), nor following aging by exposure to UV radiation. A mechanical member with a dynamic function according to the invention is in particular chosen from anti-vibration supports and elastic joints for motor vehicles or industrial devices, said member comprising at least one elastic part which is made of a crosslinked rubber composition and which is suitable for To be subjected to dynamic stresses, and according to the invention said crosslinked composition is as defined above, A sealing element according to the invention is in particular chosen from sealing joints for vehicle bodywork and sealing profiles for buildings, said sealing element comprising an elastic part which is made of a crosslinked rubber composition, and according to the invention the crosslinked rubber composition is as defined above. It will be noted that in this case, for example in a joint ensuring the sealing of a motor vehicle body, it is possible to incorporate into the composition of the invention at most 100 pce of carbon black and between 10 and 60 pce of an inorganic filler other than silica, for example chalk or an aluminosilicate such as Kaolin, combined with a metal oxide such as calcium oxide. A process for preparing according to the invention a crosslinkable composition as defined above comprises the following steps: a) In an internal mixer, for example tangential or meshing (i.e. with meshing rotors), or in a screw extruder, for example twin-screw: a0) introduction of said at least one elastomer then of said other ingredients with the exception of said crosslinking system; al) thermomechanical work comprising melt mixing of said reaction mixture with the exception of the crosslinking system, to obtain a precursor mixture of the crosslinkable composition; a2) heating the reaction mixture up to said maximum temperature Ta of the reaction mixture which is higher than said at least one melting temperature Tf or softening temperature Tr of the thermoplastic polymer phase, preferably by a difference Ta-Tf or Ta-Tr between 1 and 100°C; a3) stabilization of said heating for a holding time of at least 10 seconds which is preferably between 20 seconds and 5 min.; a4) extraction of the precursor mixture from the internal mixer or screw extruder; then b) Mechanical working of the precursor mixture in an external cylinder mixer or in a conical twin-screw device, with the addition of said crosslinking system comprising sulfur and / or a peroxide to obtain the crosslinkable rubber composition, in such a way that the temperature Tb of the precursor mixture is temporarily higher: - at said crystallization temperature Tc when the thermoplastic polymer phase is partly crystalline, and - at said glass transition temperature Tv when the thermoplastic polymer phase is amorphous. Preferably, step b) is initiated at a maximum initial temperature Tb0 of the precursor mixture, with Tb0 > Tc or Tb0 > Tv when the thermoplastic phase is partly crystalline or amorphous, respectively. More preferably, step b) is initiated while the thermoplastic phase is in the softened state and for example melted in the precursor mixture, the temperature Tb decreasing until Tb < Tc or Tb < Tv. Even more preferably, step a4) is followed by step b) so that a time interval At separates the extraction of the precursor mixture from the internal mixer or the screw extruder and the initiation of mechanical work in step b) (after transfer of the precursor mixture into said external mixer with cylinders or into said conical twin-screw device), providing a temperature difference AT = Tt-TbO between the falling temperature Tt (e.g. "pitted falling") of the precursor mixture at the end of step a4) and the initial temperature TbO at the start of step b), such that AT / Tt < 30% and preferably AT / Tt < 20%. Advantageously, Ât < 10 minutes and for example At < 2 minutes, so that AT / Tt < 10% and for example AT / Tt < 1%. As explained above, it will be noted that in this way the precursor mixture is cooled at the end of step a4) essentially by the mechanical work of step b), being subjected to a globally continuous shear from step a1) and until the end of step b). Concerning step a2) of the process of the invention, the difference Ta-Tf or Ta-Tr as the case may be, may advantageously be between 5 and 100°C, preferably between 10 and 70°C. It will be noted that the value chosen for Ta thus depends on that of Tf or Tr which characterizes the thermoplastic polymer phase used, and that in the case where the latter is based on an aliphatic polyolefin such as a homopolymer or copolymer of propylene, Ta can for example be between 160 and 220°C, preferably between 170 and 200°C, whereas in the case where this thermoplastic phase is an alkyl or phenyl silicone resin, Ta can for example be between 70 and 150°C, preferably between 80 and 120°C. Advantageously, the warm-up of step a2) can be carried out by using: - in said internal mixer: a shear rate of said reaction mixture in the internal mixer of at least 80 s-!, preferably at least 150 s!, for example carried out at a rotation speed of rotor blades in the internal mixer of between 10 and 200 rpm and preferably between 50 and 120 rpm, and / or of a double wall in the internal mixer receiving a heat transfer fluid, and / or using an internal mixer fill rate greater than 100%; or - in said screw extruder, heating elements which equip the extruder. It should be noted that such a shear rate (for example between 100 and 300 s-!) can be used in a tangential internal mixer (e.g. Banbury type) or meshing (Haake type). It should also be noted that a rotation speed of 200 rpm is particularly suitable for a Haake mixer, while a rotation speed of around 100 rpm is more suitable for a Shaw 3.6L mixer. Concerning step b) of mechanical working according to the invention, it should be noted that it could be implemented other than in an external mixer with cylinders or in a conical twin-screw device, provided that the precursor mixture resulting from step a4) is cooled immediately by the sole mechanical work of step b), thus being subjected to a globally continuous shear between step a4) and the end of step b) by passing from an initial molten, softened or at least non-crystallized state to a crystallized state (in the case of a partly crystalline thermoplastic phase), or by passing from an initial softened or at least non-glassy state to a glassy state (in the case of an amorphous thermoplastic phase). Brief description of the drawings Other characteristics, advantages and details of the present invention will emerge from reading the following description of several exemplary embodiments of the invention, given for illustrative and non-limiting purposes in relation to the attached drawings, among which: Fig. 1 [Fig.1] is a relative enthalpy - temperature graph showing the thermal behavior of polypropylene “PPH 3060” forming the thermoplastic polymer phase in the crosslinkable composition I according to the invention and the control crosslinkable composition C3. Fig.2 [Fig.2] is a photograph obtained by an infrared camera of the precursor mixture of the crosslinkable composition I according to the invention, at the outlet of the internal mixer used in step a). Fig. 3 [Fig.3] is a photograph obtained by the infrared camera of the crosslinkable composition I according to the invention, at the outlet of the external mixer used in step b). Fig. 4 [Fig.4] is a graph showing the evolution as a function of time, during step b) of mechanical working, of the temperatures of the respective precursor mixtures of the crosslinkable composition I and the crosslinkable composition C3, these temperatures being measured from the initial instant t0 = O min. O s corresponding to the temperature initial TbO of each precursor mixture at the initiation of step b). Fig.5 [Fig.5] is a first image illustrating the three-dimensional morphology (axes in nm) of the dispersion in the form of nodules of the polypropylene forming the thermoplastic polymer phase of the crosslinked composition C3 control, obtained by segmentation via the FIF-MEB technique of focused ion beam (FIF) scanning electron microscopy (SEM). Fig.6 [Fig.6] is a second image illustrating the two-dimensional morphology (in nm) of the dispersion in the form of nodules of polypropylene in the control C3 crosslinked composition, obtained by segmentation using the same FIF-MEB technique. Fig. 7 [Fig.7] is a first image illustrating the three-dimensional morphology (in nm) of the dispersion in the form of filaments or fibrils of the polypropylene forming the thermoplastic phase of the crosslinked composition I according to the invention, obtained by segmentation via the same FIF-MEB technique as for [Fig.5]. Fig. 8 [Fig.8] is a second image illustrating the two-dimensional morphology (in nm) of the dispersion in the form of filaments or fibrils of polypropylene in the crosslinked composition I according to the invention, obtained by segmentation via the same FIF-MEB technique as for [Fig.6]. Fig. 9 [Fig.9] is a diagram illustrating, after analysis by FIF-SEM, the volume distribution of the equivalent diameters of the filaments or fibrils of the crosslinked composition I according to the invention, and that of the nodules of the control crosslinked composition C3, the equivalent diameters being weighted by their volume fractions in the total dispersed polypropylene. Fig. 10 [Fig.10] is a diagram illustrating, after analysis by FIF-MEB, the number distribution of the form factors of the filaments or fibrils of the crosslinked composition I according to the invention, and that of the form factors of the nodules of the control crosslinked composition C3. Fig. 11 [Fig.11] is a diagram illustrating, after analysis by FIF-SEM, the correlations measured for the crosslinked composition I according to the invention and the control crosslinked composition C3, between the form factors of the particles (i.e. filaments or fibrils for I and nodules for C3) and their equivalent diameters. Fig. 12 [Fig.12] is a graph combining the characteristic stress-strain curves for the crosslinked composition I according to the invention and for the control crosslinked compositions C1, C2 and C3. Fig. 13 [Fig.13] is a graph of fatigue resistance-applied force combining the curves of number of cycles without rupture as a function of the intensity of the forces applied, for the crosslinked composition I according to the invention and the control crosslinked composition C2. Examples of embodiments of the invention In the examples presented below, we have prepared: - crosslinkable compositions C1, C2 and C3 control based on the same natural rubber (NR), CI not being reinforced, C2 being reinforced only by carbon black and C3 being reinforced only by polypropylene nodules (PP abbreviated below), and - a crosslinkable composition I according to the invention based on the same natural rubber and the same other ingredients as composition C3, but composition I being reinforced by nanofilaments or nanofibrils of the same PP in place of said nodules, and having been obtained by a mixing process different from that used for composition C3, as explained below. Table 1 details the formulations in pce (parts by weight per 100 parts of NR elastomer) of the masterbatches (constituting the precursor mixtures obtained by step a) of thermomechanical working, before step b) of mechanical working and the addition of the crosslinking systems), and of the crosslinkable compositions C1-C3 and I which were derived from these masterbatches. [Tables 1] Ingredients / compositions ci C2 C3 qe (zmo 5 5 5 5 Stearic Acid 2 2 8 we Black N330 0 41 PPH 3060 0 0 | 8 Protectors 35 2.0 2.0 2.0 Plasticizers and conditioning agents = a = = Protectors 35 2.0 2.0 20 Plasticizers and processing agents + = + > TOTAL in pce of the mixture 1155 — |1553 [1270 |1270 master Sulphur crosslinking system 3.5 3.5 3.5 3.5 TOTAL (pce) 119.0 158.8 130.5 130.5 The enthalpy diagram of PP “PPH 3060” used in compositions C3 and I for obtaining the particles dispersed in the NR matrix, as visible in [Fig.1], shows, on the one hand, the melting temperature Tf of PP (upper peak of endothermic transition) which is approximately 165°C and, on the other hand, the crystallization temperature Tc of PP (lower peak of exothermic transition) which is 100-110°C. In the present description, the thermal behavior of the thermoplastic polymer phase, e.g. consisting of “PPH 3060” (density 0.905, measured according to ISO 1183) which includes the measured temperatures Tf, Tr, Tc and Tv, was obtained by differential enthalpy analysis (differential scanning calorimetry “DSC” according to ISO 11357), as explained below. Programming: double scan from -80°C to 250°C at 20°C / min. under N, at 50 mL / min. with a 5 min. isotherm at each level. Reproducibility: two tests / sample. Equipment: Heat flow DSC - DSCI — “METTLER-TOLEDO”. Calibration: METTLER TOLEDO-specific procedure, with standards: N-octane / indium / zinc. The above-mentioned crosslinkable compositions C1-C3 and I were prepared by implementing: - step a) of thermomechanical work on an internal “Shaw” mixer with a volume of 3160 cm? with meshing rotors, using a filling coefficient of 1.00 for composition C2 and 1.10 for compositions C3 and I. and - step b) of mechanical work (step commonly called “acceleration”) on an open “Comerio” cylinder mixer. More specifically, the following successive steps were implemented to prepare each of compositions C1-C2, composition C3 and composition I, as detailed in the three processes detailed below. Preparation of each of the two compositions C1-C2 without polypropylene: Filling the internal mixer: t=0 min. material: NR speed: 50 rpm. T regulation = 80°C. Lamination: all = 1 min. matter : - speed: 50 rpm. Regulation = 80° C. Filling: crazy = 1 min. material: filler (for composition C2) + additives (for compositions C1-C2) speed: 50 rpm. T regulation = 30°C. Mixing: t+1min. matter : - speed: 50 rpm. Mixing with self-heating: all = [3 min. ; 3 min. 30 s] matter : - speed: 96 rpm. Tauco-heating = 150° C. Fall of the mixture. Cooling on the open cylinder mixer: 1=0 Duration = | min. "T regulation = 20° €. Acceleration on the open mixer cylinders: Addition of the crosslinking system after t = 3 min. Preparation of L ition C3 pollen dules: Filling the internal mixer: t=0 min. material: NR speed: 50 rpm and regulation T = 80° C. Lamination: all = 1 min. matter : - speed: 50 rpm and regulation = 80° C. Filling: all = 1 min. material: PP + additives speed: 50 rpm and regulation = 80° C. Mixing with self-heating: crazy = [3 min. ; 3 min. 30 s] matter : - speed: 96 rpm and self-heating = 140° C. Maintaining self-heating: temperature maintained for 30 s. speed: 96 rpm. Fall of the mixture. Cooling: for about 24 hours and Tregulation = 20°C. 'Transfer of the cooled mixture into the open mixer and acceleration: Addition of the crosslinking system after t = 3 min on the cylinders. Filling of the internal mixer: t=0 min. material: NR speed: 50 rpm and regulation = 80° C. Lamination: all = 1 min. matter : - speed: 50 rpm and regulation = 80° C. Filling: all = 1 min. material: PP + additives speed: 50 rpm and regulation = 80° C. Mixing with self-heating: crazy = [3 min. ; 3 min. 30 s] matter : - speed: 96 rpm and Tauo-échautfemen = 140° C, Maintaining self-heating: temperature maintained for 30 s. speed: 96 rpm. Fall of the mixture. Immediate cooling in the open cylinder mixer: t=0: extraction of the mixture from the internal mixer Introduction to the cylinders: 1 min. after extraction, with T,regulation = 20° C. Acceleration on the open mixer cylinders: Addition of the crosslinking system after t = 3 min. Steps a) and b) implemented for crosslinkable compositions C3 and I: Table 2 below compares the implementation of steps a) of thermomechanical mixing and b) of mechanical working according to the control temperatures used and the temperatures precisely measured at the heart of the precursor mixture, for the crosslinkable compositions C3 and I. [Tables 2] [149 C [7 |148° C |< 24h 20h [Almost |1 min. |<24h Almost zero 110° C 23°C [>110° C [170>C [Bmin205 | / |Bmin105 | <s0°c 67°c |< 90° c 70° 70° C qe 70° C Steps Temperatures and times Composition C3 Composition I Mixer | Theory | Measured [Theory | Measured internally Ambient temperature / 21.5°C | / 20.4° C MI ME Melting start temperature |140° C [14e C |140°C [145 le measured by probe in MI Holding time at 140° jO 0.5 min. [0.5 min. [0.5 min. C Drop temperature / [tag C y [48° C measured by probe in MI [dropped temperature | / 168.9° C | / [171 C Mixer [Regulation temperature 20° C 20° C 20°C 20°C open to |on the cylinders cylinders Time between extraction of the |< 24h 20h Almost [1 min. MI and deposition on the cylinders Mixture temperature: |<110°C (23°C [1 10°C |170° C when deposition on cylinders Homogenization time | / |smin205 / |3min 105 | before crosslinking system Mixture temperature |< 90°C |67°C |< 90°C |70°C during work Mixture temperature at | / 70°C / 70° C outlet of the cylinders More specifically, it should be noted that all temperatures measured during steps a) and b) (i.e. indicated by “measured” in the second column for composition C3 and composition I) were precisely measured in each precursor mixture of composition C3 and I. The image in [Fig.2] shows the appearance of the precursor mixture of the crosslinkable composition I according to the invention at the outlet of the internal mixer, and the image in [Fig.3] shows the appearance of this composition I after acceleration on the cylinders of the open mixer (i.e. at the end of mechanical work), these images having been obtained by a high definition infrared camera “FLIR SC660”. Thus, composition I according to the invention was extracted from the internal mixer at a temperature of 171°C, which was the so-called "pit drop" temperature, taken at the heart of the precursor mixture using a "Testo 925" pyrometer. Then the precursor mixture of composition I was immediately deposited on the open cylinder mixer. As illustrated in the graph of [Fig.4], during mechanical work on these cylinders, the initial temperature TbO of 170°C at the heart of the precursor mixture at t0=0 (initial instant of mechanical work) decreased during approximately the first 3 minutes of mixing, until stabilizing at approximately 70°C (see the decrease in the temperature Tb of the precursor mixture of composition I, almost linear in this example, then the clear slowing down of this decrease shortly before 3 min. of work). The crosslinking system was added after approximately 3 min. after t0. Thus, the PP contained in the precursor mixture of composition I was worked first in the liquid state, then during its crystallization (at approximately 100-110°C) occurring under shear, i.e. in accordance with the invention as generally defined in the present description. As a result, the aforementioned nanofilaments or nanofibrils were obtained, dispersed homogeneously in the crosslinkable composition I, as illustrated in Figures 7 and 8. It will be noted that the cooling kinetics according to the method of the invention, kinetics which in the example of [Fig.4] for composition I is defined by a temperature which continuously decreases with time and then becomes substantially constant, resulting in a globally convex curve (i.e. with concavity facing upwards), nevertheless depends on the quantity of precursor mixture and the equipment used for the mechanical work (dimensions of the cylinders, power of the thermoregulators, etc.). Unlike this method of the invention, after step a) of thermomechanical working in the internal mixer, the precursor mixture of the crosslinkable composition C3 was allowed to cool for 20 h without any shear (i.e., cooling at rest for almost a day in ambient air). During this period of time, the temperature of the precursor mixture of composition C3 decreased from 168.9°C (the “pitted fall” temperature, i.e., the extraction of the precursor mixture from the internal mixer) to 23°C (the TbO temperature for initiation of mechanical work at t0=0), the PP having crystallized around 100-110°C at rest (i.e., in the absence of any shear), contrary to the general principle of the invention defined above. Mechanical work was thus started on the open cylinder mixer at room temperature (TbO = 23°C), then self-heating of the C3 precursor mixture was generated up to approximately 70°C by adding the crosslinking system approximately 3 min after t0, but without going above the melting point of PP (Tm of 165°C). As illustrated in Figures 5-6, the morphology of globally spherical or ellipsoidal nodules for the C3 composition, acquired during the work, was thus preserved. thermomechanical of step a). It can be seen in [Fig.4] that the cooling kinetics according to the process not in accordance with the invention implemented for the control composition C3, kinetics which is defined by a temperature continuously increasing with time then substantially constant, results in a globally concave curve (i.e. with concavity turned downwards), very different and even almost opposite to that characterizing composition I of the invention (on either side of the horizontal line defined by the final temperature of 70°C). Vulcanization of compositions C1-C3 control and I according to the invention: Table 3 below details the vulcanization conditions followed (temperature of 155°C for 20 min.) for compositions C1-C3 and I. [Tables 3] Rheological properties |e |ez |e3 | at 155°C for 20 min. Con (AN.m) 06 |La7 0.26 0, Crmax (AN.m) 6.8 1637 9.01 9 Delta C (dN.m) 63 |1490 8.75 8, t 05 (min.) t 90 (min.) t95 (min.) Morphological characterization of crosslinked compositions C3 and I: The morphology of compositions C3 and I was analyzed by segmentation using the FIF-SEM technique of focused ion beam (FIB-SEM), as explained below. Sample preparation: Each sample was previously surfaced by cryo-ultramicrotomy to obtain a flat surface. The resulting surface was placed in contact with an osmium tetroxide solution (4% in water) for 3 days. After contrast, a second surfacing of the treated area was carried out by cryo-ultramicrotomy to remove the surface layer altered by direct contact with osmium. Implementation of the FIF-MEB technique (“FIB-SEM” in English): ACQUISITION FIF-MEB (XB540 Zeiss, “Atlas V software”). SEM: 1.5 kV, 149 pA — exposure time per voxel: 0.3 us. average per line: 18. voxel size: 10 nm. Detector: EsB. FIF: 30 kV, 300 pA — Grinding speed: 6.6 nm / min. 3D tracking: exposure time per voxel: 0.6 us. Average per line: 20. Volume: 20 x 5 x 4 um. - PRE-TREATMENT: Non-local average denoising - patch 7, search 21, similarity 0.5. Normalization, corrections C and B. Z resampling to 10 nm (cubic). Equalization, median filter. - SEGMENTATION: Machine learning (“Ilastik”). Resampling to 20 nm. Opening 1 for the PP phase. Global and individual analysis with “AVIZO”. The pictures in Figures 5-6 illustrate, in relation to the diagrams in Figures 9-11, the morphology of the globally spherical or ellipsoidal nodules dispersed in the crosslinked composition C3 (morphology also characterizing the composition C3 in the crosslinkable state obtained following step b) of mechanical working, before crosslinking). As explained above: - each measured equivalent diameter refers to the diameter of a hypothetical spherical particle of the same volume as the observed particle (the "mean equivalent diameter" refers to the arithmetic number-mean equivalent diameter of the equivalent diameters of the particles for the sample split into classes, and the "median equivalent diameter" refers to the median ds, of the volume distribution); - the form factor designates the ratio of the greatest length to the smallest width of each observed particle, the width being able to be assimilated to a minimum diameter in the case of an ellipsoidal nodule or a globally cylindrical filament (by "average form factor" we mean the arithmetic mean form factor in number of the particles); and - "volume fraction of total PP" (on the ordinate in [Fig.9]) means the ratio between the total volume of class X particles and the total volume of PP (ratio multiplied by 100 to obtain this fraction in %). Table 4 below details the individual analyses carried out to quantify the morphological parameters of the PP nodules in the crosslinked composition C3, and of the filaments or fibrils dispersed in the crosslinked composition I. [Tables 4] Analysis of the dispersion of PP Composition C3 Composition I |Average equivalent diameter 211 nm 50 nm Median equivalent diameter 140 nm 37 nm Average form factor 1.6 2.1 Maximum form factor 4 13 These parameters demonstrate the significant difference between the nanofilaments or fibrils of reduced equivalent diameters characterizing the dispersion of PP in composition I of the invention, and the spherical or ellipsoidal nodules characterizing the dispersion of PP in the control composition C3. Standardized measurements: Oscillating die rheometer (“MDR” for Moving Die Rheometer): according to ISO 6502:2016. Shore Hardness A: According to ASTM D 2240. Tensile tests: according to ASTM D 412 standard. Dynamic Mechanical Analysis tests: For these “DMA” tests, the ISO 4664 standard was followed, using the Metravib® visco-analyzer: - Conditions: -10% + / -0.1% at 155 Hz and -10% + 2% at 15 Hz; - Test tubes: Metravib® type plots; - Number of test pieces: three per condition; - Measuring temperature: 23°C; - Lubricant: silicone oil spray. Fatigue resistance: The elastomer testing system used was a hydraulic endurance machine "MTS 831.02", with a maximum capacity of 25 kN, equipped with a 15 kN load cell and a cylinder with a stroke of + / - 60 mm. The test was controlled by the software "MTS Flextest 40". The following were used: - “mini-diabolos” test tubes, 2-3 test tubes per condition; - a minimum effort of 0 N, and a maximum effort defined by the four conditions: 250 N, 200 N, 125 N or 100 N: and - a frequency of 5 Hz and a temperature of 23° C. Test 1 itions C1-C3 control and I of the invention crosslinked: The aforementioned morphology of the thermoplastic phase dispersed in the crosslinked composition I according to the invention (as illustrated in figures 7-8 and 9-11) allows, thanks to the aforementioned mixing process, to obtain an overall improved reinforcement for composition I in comparison with compositions C1-C3, as shown by the mechanical properties of composition I compared to the three control compositions C1-C3. In particular, the hardness and tensile tests (whose stress-elongation curves for compositions C1-C3 and I are combined in [Fig. 12] and whose results are detailed in Table 5 below), establish this improved reinforcement for composition I in particular compared to composition C3, which was nevertheless characterized by the same mass (and volume) fraction of PP. The tensile curves in [Fig. 12] show the reinforcement obtained from composition I, which was significantly higher than that of unreinforced composition C1 and composition C3 reinforced with PP nodules, and was also comparable to that of composition C2 reinforced only with carbon black. [Tables 5] Static properties of the compositions |e1 |ez |es jt ​​crosslinked in the initial state (155° C for t 95 min.) Shore hardness À at 3 s (#2 points) |(Points) |38 _\e2 [49 Je 8 |L7 ) (38 62 0.8 3.1 67 6.8 ) [(ointed) (MPa) | |CMPa) [La 2 2 Jos Secant modulus M100 (MPa) 0.8 3.1 | 1.7 6.8 at 100% strain Secant modulus M200 |oPa) |L3 8.2 3.2 9.5 at 200% strain Secant modulus M300 (MPa) 20 14.7 5.6 12.5 at 300% strain Stress at break (MPa) 222 25.3 22.1 22.4 Elongation at break (%) 670 461 555 480 This table 5 shows in particular that: - the Shore A hardness of composition I of the invention was not only 37% higher than that of composition C3 reinforced with PP nodules, but was also 8% higher than that of composition C2 reinforced with carbon black, - the moduli M100, M200 and M300 of composition I of the invention were very clearly higher than those of composition C3 (by 300%, 197% and 123%, respectively) and were higher (cf. M100 and M200) or comparable (cf. M300) to those of composition C2, and that - the breaking properties of composition I of the invention were satisfactory, being generally of the same order as those of compositions C2 and C3. Table 6 below details the dynamic properties obtained for compositions C1-C3 and I, by the aforementioned dynamic mechanical analysis “DMA”. [Tables 6] Compositions jez | [es |1 Static modulus (MPa) 6.034 3.790 5.327 Dynamic properties (Goodrich plot, measured at 195 + 8 min. at 155°C) Modulus at 15 Hz (MPa) 8.04 4.04 7.14 Tan D at 15 Hz | 0.107 0.056 0.098 Modulus at 155 Hz (MPa) 11.20 4.66 9.27 [M155 Hz / MI5 Hz |(MPa) [1303 [ha53 [1208 These dynamic properties show a significant increase in the dynamic moduli at 15 Hz, at 155 Hz and in the M155 / M15 Hz ratio of composition I according to the invention compared to composition C3 reinforced by PP nodules (increase of 77% for MIS Hz and 99% for M155 Hz), which advantageously results in a reduction in mechanical non-linearities in frequency sweep, for composition I of the invention compared to composition C3. The fatigue resistance tests carried out as explained above and the results of which are illustrated in [Fig. 13] (with the number of cycles without rupture on the abscissa and the forces in N on the ordinate) for the crosslinked compositions C2 and I, show excellent fatigue resistance of the test pieces made of composition I of the invention compared to those made of composition C2 reinforced with carbon black. Indeed, composition I had a fatigue resistance increased by a factor of approximately 2.5 for high forces (cf. forces of 250 N or 200 N, for example), compared to composition C2. For lower forces, composition I of the invention had a fatigue resistance greater than 5 million cycles without rupture (test stopped at 5 million cycles), whereas composition C2 was the site of a rupture at approximately 500,000 cycles only.

Claims

Demands

1. Composition of crosslinkable rubber (I) with a base of at least one elastomer, composition (I) comprising other ingredients which com- take a crosslinking system and a thermo- polymeric phase plastic that exhibits at least a melting point Tf or ra- softening Tr, a glass transition temperature Tv and, when said phase is partly crystalline, a crystallization temperature You, said phase being dispersed in said at least one elastomer under particle form, the crosslinking system includes sulfur when said at least one elastomer is unsaturated and said phase includes saturated polymer chains, and comprising a peroxide when said at least one elastomer is saturated, the crosslinkable rubber composition (I) comprising the product: a) of a reaction in the molten state by thermomechanical work of a reaction mixture comprising said at least one elastomer and said other ingredients with the exception of the crosslinking system for obtaining a precursor mixture of the crosslinkable composition (I), the reaction involving heating the reaction mixture until a maximum temperature Ta of said reaction mixture which is su- higher than said at least a melting temperature Tf or softening temperature Tr smoothing, then b) mechanical work on the precursor mixture, with the addition of the system crosslinking to obtain the crosslinkable composition (I), in which said particles comprise filaments or fibrils, the temperature Tb of the precursor mixture during operation mechanics of step b) being temporarily superior: - at said crystallization temperature Tc when said phase is in crystalline part, or - at said glass transition temperature Tv when said phase is amorphous.

2. Crosslinkable rubber composition (I) according to claim 1, in at which the mechanical work of step b) is initiated at a temperature initial TbO of the precursor mixture, with Tb0 > Tc or Tb0 > Tv when said phase is partly crystalline or amorphous, respectively, and preferably in which the mechanical work of step b) is initiated while the thermoplastic polymer phase is in a molten state or softened in the precursor mixture.

3. Crosslinkable rubber composition (I) according to claim 2, in which said temperature Tb of the precursor mixture during step b) is maximal at the initiation of mechanical work where Tb=Tb0, then decreases until Tb < Tc or Tb < Tv, when said phase is partly crystalline or amorphous, respectively.

4. Crosslinkable rubber composition (I) according to claim 2 or 3, in which step a) is followed by step b) in such a way that an in- The time interval at time Δt separates the extraction of the precursor mixture at the end from step a) and the initiation of mechanical work in step b) after transfer of the precursor mixture, providing a temperature difference The temperature AT = Tt-Tb0 between a settling temperature Tt of the mixture precursor at the end of step a) and the initial temperature TbO at the beginning of step b) such that AT / Tt < 30% and preferably < 20%.

5. Crosslinkable rubber composition (I) according to claim 4, in which At < 10 minutes and preferably At < 2 minutes, so that AT / Tt < 10% and for example AT / Tt < 1%, the precursor mixture being cooled at the end of step a) essentially by mechanical work of step b), so that the precursor mixture is subjected to a ci- overall continuous protrusion from the initiation of step a) and until the end of step b).

6. Crosslinkable rubber composition (I) according to any one of the claims 2 to 5, in which mechanical work is initiated at said temperature initial TbO which is between - Tc or Tv, depending on whether the said phase is partly crystalline or amorphous, respectively, and - said maximum temperature Ta of the reaction mixture, which coincides with a settling temperature Tt of the precursor mixture, and preferably in which TbO is between 110 and 220°C.

7. Crosslinkable rubber composition (I) according to claim 6, in which TbO is between 150 and 190°C, said phase being: - partly crystalline and comprising, for example, a homopolymer or a propylene copolymer, or - amorphous and comprising, for example, polystyrene, and in which said temperature Tb of the precursor mixture is maximum at the initiation of mechanical work where Tb=Tb0, then decreases until Tb is between 10 and 90°C. and preferably in which said crosslinking system is incorporated to the precursor mixture after a homogenization period of the mixture precursor counted from the initiation of mechanical work, the said homogenization time being, for example, between | min. and 5 minutes.

8. Crosslinkable rubber composition (I) according to any one of the claims previous, in which said particles have at least one the following morphological characteristics: (a) for their equivalent diameter, defined as the diameter of a hypothetical spherical particle of the same volume: (i) an equivalent diameter that varies from 5 nm to 1000 nm and preferably from 10 nm to 330 nm for all of these particles, (ii) a median equivalent diameter between 20 nm and 200 nm and of preferably from 30 nm to 60 nm, and (iii) an average equivalent diameter between 30 nm and 300 nm and of preferably between 40 nm and 70 nm; and / or {b) for their form factor, defined by the ratio of the largest length over the smallest width of each of said particles: (1) an average form factor equal to or greater than 2 and preferably between 2.0 and 2.5, and (ii) a maximum form factor for all of said particles which is greater than 5 and preferably between 10 and 15; and preferably in which the particles include filaments or fibrils with a volume fraction greater than 70%, by example greater than 80%.

9. Crosslinked rubber composition, wherein the composition of Crosslinked rubber is the product of a thermal crosslinking of a crosslinkable rubber composition (I) according to one of the claims previous by chemical reaction with said crosslinking system, and in which the cross-linked rubber composition exhibits one at least the following properties: (a) a Shore A hardness measured according to ASTM D 2240 which is equal to or greater than 60, preferably between 65 and 70; (b) M100, M200 and M300 secant modules at 100%, 200% and 300% of deformation, measured in uniaxial tension according to ASTM D 412, which are respectively greater than 3 MPa, 6 MPa and 9 MPa and which are preferably respectively greater than 6 MPa, 9 MPa and 12 MPa; (c) a ratio of moduli M 155Hz / M 15Hz and a loss factor tan D at 15 Hz which are measured at 23°C via a frequency sweep according to the ISO 4664 standard by a Metravib® visco-analyzer on Metravib® test tubes of the stud type and which verify at least one of the the following conditions (i) and (ii): {i) M 155Hz / M 15Hz < 1.50, (ii) a dynamic modulus at 15 Hz > 7 MPa, and (ii) tan D at 15 Hz < 0.10; and (d) a fatigue resistance greater than 5.106 cycles, measured at a frequency of 5 Hz and a temperature of 23°C by a machine hydraulic endurance test “MTS 831.02 Elastomer Test System” of a maximum capacity of 25 kN, equipped with a 15 kN force cell and of a stroke cylinder + / - 60mm, controlled by the "MTS Flextest" software 40" on "mini-diabolo" test tubes with a minimum effort of 0 N and a maximum force of 250 N, 200 N, 125 N and 100 N.

10. | Mechanical component with a dynamic function, in particular selected from anti-vibration mounts and elastic joints for vehicles engine or industrial devices, said component comprising at least one elastic part made of a cross-linked rubber composition adapted to withstand dynamic stresses, in which said cross-linked rubber composition is according to claim 9.

11. | Sealing element in particular selected from the sealing gaskets for vehicle bodywork and building sealing profiles, said sealing element comprising an elastic part which is consisting of a cross-linked rubber composition, in which the crosslinked rubber composition is according to claim 9.

12. | Process for preparing a crosslinkable rubber composition (I) according to any one of claims 1 to 8, wherein the method comprises the Next steps: a) In an internal mixer, for example tangential or meshing, or in a screw extruder, for example a twin-screw extruder: a0) introduction of said at least one elastomer and then of said other in- ingredients with the exception of said crosslinking system; al) thermomechanical work in the internal mixer or in the screw extruder, comprising a melt-mixing of said reaction mixture excluding the crosslinking system, for obtaining a precursor mixture of the rubber composition crosslinkable (D); a2) heating the reaction mixture to said temperature maximum Ta of the reaction mixture which is greater than said at minus a melting temperature Tf or softening temperature Tr of the phase thermoplastic polymer, preferably with a Ta-Tf or Ta-Tr gap between 1 and 100° C; a3) stabilization of said heating for a duration of maintenance of at minus 10 seconds, preferably between 20 and 5 seconds min.; a4) extraction of the precursor mixture from the internal mixer or of the screw extruder; then b) Mechanical work of the precursor mixture in an external mixer with cylinders or in a conical twin-screw device, with the addition of said crosslinking system comprising sulfur and / or a peroxide for obtaining the crosslinkable rubber composition (I), such in such a way that the temperature Tb of the precursor mixture is tempo- rarely superior: - at said crystallization temperature Tc when the polymeric phase Thermoplastic is partly crystalline, and - at said glass transition temperature Tv when the phase po- Thermoplastic lymeric is amorphous.

13. Process for preparing a crosslinkable rubber composition (I) according to claim 12, wherein step b) is initiated at a time maximum initial temperature TbO of the precursor mixture, with TbO > Tc or Tb0 > Tv when the thermoplastic polymer phase is partly crystalline or amorphous, respectively, and preferably in which step b) is initiated while the phase po- lymeric thermoplastic is in a softened state and, for example, melted in the precursor mixture, the temperature Tb decreasing until Tb < Tc or that Tb < Tv.

14. Process for preparing a crosslinkable rubber composition (I) according to claim 13, wherein step a4) is followed by step b) so that a time interval Åt separates the extraction of the mixture precursor outside the internal mixer or screw extruder and the initiation of mechanical work in step b) after transfer of the mixture precursor in said external roller mixer or in said conical twin-screw device, providing a temperature difference AT = Tt-Tb0 between a settling temperature Tt of the mixture precursor at the end of step a4) and the initial temperature TbO at beginning of step b), such that AT / Tt < 30% and preferably AT / Tt < 20 %œ.

15. Process for preparing a crosslinkable rubber composition (I) according to claim 14, wherein At < 10 minutes and by For example, if ATt < 2 minutes, then AT / Tt < 10%, and for example, AT / Tt < 1%, so that the precursor mixture is cooled at the end of step a4) essentially by the mechanical work of step b) in being subjected to a generally continuous shear from the stage al) and until the end of step b).