Rubber composition with a bio-based plasticizer from the estolide family

Description

technical field

[0001] The present invention relates to a rubber composition for the tire, particularly usable as a sidewall, comprising a plasticizing system that is entirely or partially bio-based. Previous technique

[0002] In the current context of energy saving and environmental preservation, manufacturers are constantly searching for new renewable sources that can be used as raw materials for product manufacturing.

[0003] With this in mind, tire manufacturers are seeking to reduce the environmental impact of tire production and use. One of the levers at their disposal is the gradual replacement of materials derived from fossil resources with sustainable materials. Bio-based materials constitute a portion of these sustainable materials. However, replacing petroleum-based products in tire compounds with bio-based products must not compromise safety and expected performance. Therefore, bio-based products used in tires must be compatible with the other components of the rubber compound to ensure compositional uniformity and avoid compromising performance, while also being technically as efficient as products made from fossil-based raw materials.

[0004] Among the components of a tire, the outer sidewalls must offer good resistance to external stresses such as impacts and deformation. The outer sidewalls are the radially external areas of the tire, connecting the tread to the two beads. Therefore, it is important that the rubber compounds used in tire sidewalls possess good mechanical properties, particularly good tear resistance.

[0005] Furthermore, estolides and their synthesis are described in WO2012173671A1. This document highlights the advantages of using these fatty acid derivatives in lubricating and plasticized compositions such as plastisol, due to their biodegradable properties. The use of estolides as a base oil is described as reducing pollution and toxicity associated with the release into the environment of these compositions, which typically use fossil-based compounds as base oils.

[0006] The technical challenge now is to provide a tire rubber compound that helps reduce its environmental footprint while maintaining its performance, particularly for use as a sidewall. More specifically, one objective of the present invention is to reduce the environmental footprint of a tire rubber compound while ensuring that the compound's mechanical properties are maintained. Description of the invention

[0007] The Applicant has discovered, surprisingly, that replacing petroleum-based plasticizers in tire rubber compositions with estolides significantly improves breaking strength, while maintaining low-strain stiffness. Such properties are particularly desirable for use in tire sidewalls. Summary of the invention

[0008] The invention therefore relates to a rubber composition based on at least one elastomeric component comprising an isoprene elastomer and a butadien elastomer, a reinforcing filler comprising carbon black as the major filler, a crosslinking system and a plasticizing system comprising a bio-based plasticizer selected from the estolides, according to one of the following embodiments. 1. A rubber composition based on at least: 100 parts per unit area (ppm) of an elastomeric matrix comprising an isoprene elastomer and a butadiene elastomer; 20 to 120 parts per unit area (ppm) of a reinforcing filler comprising carbon black as the major filler; 5 to 120 parts per unit area (ppm) of a plasticizing system comprising at least one estolide with a weight-average molar mass (Mw) of less than 5000 g / mol determined by size-exclusion chromatography (SEC), the method being described in the description; and a crosslinking system. 2. A composition according to the preceding embodiment in which the proportion of isoprene elastomer is in the range of 10 to 60 parts per unit area, preferably 15 to 50 parts per unit area. 3. A composition according to any of the preceding embodiments in which the isoprene elastomer comprises predominantly natural rubber. 4. Composition according to the preceding embodiment in which the isoprene elastomer is essentially made of natural rubber. 5.1. Composition according to any one of the preceding embodiments in which the butadiene elastomer content is in the range of 40 to 90 parts per cent, preferably 50 to 85 parts per cent. 6. Composition according to any one of the preceding embodiments in which the butadiene elastomer is a polybutadiene. 7. Composition according to any one of the preceding embodiments in which the reinforcing filler is essentially carbon black. 8. Composition according to any one of the preceding embodiments in which the carbon black is present in a content in the range of 20 to 100 parts per cent, preferably 20 to 80 parts per cent, more preferably 25 to 60 parts per cent. 9. Composition according to any one of the preceding embodiments in which the estolide(s) content is in the range of 5 to 50 parts per cent, preferably 10 to 30 parts per cent. 10.Composition according to any of the preceding embodiments, wherein the plasticizing system comprises from 10 to 100% by weight of at least one estolide, preferably 40 to 100% by weight, relative to the total weight of the plasticizing system. 11. Composition according to any of the preceding embodiments, wherein the plasticizing system is essentially composed of at least one estolide. 12. Composition according to any of the preceding embodiments, wherein the at least one estolide is an estolide of a saturated or unsaturated, linear or branched fatty acid, in the C8 to C34 range, esterified with a fatty alcohol. 13. Composition according to any one of the preceding embodiments wherein at least one estolide is an estolide of a hydroxylated fatty acid, linear or branched, saturated or unsaturated, in C 12 to C 22, in particular in C 16 to C 20 and more particularly in C 18. 14.Composition according to any one of the preceding embodiments in which at least one estolide is an estolide of ricinoleic acid. 15. Composition according to any one of the preceding embodiments in which the estolide is an estolide esterified with a fatty alcohol, saturated or unsaturated, linear or branched, in the positions of C8 to C34. 16. Composition according to any one of the preceding embodiments in which the estolide is an estolide esterified with a fatty alcohol having an aliphatic carbon chain branched in the positions of C12 to C22, in particular in the positions of C16 to C20 and more particularly in C18. 17. Composition according to any one of the preceding embodiments in which the estolide is an estolide esterified with isoteryl alcohol. 18. Composition according to any one of the preceding embodiments in which at least one estolide is a compound of formula I: . in which, n is an integer ranging from 1 to 5; X is a hydrogen atom H or a hydroxyl group -OH; R1, identical or different, represent divalent aliphatic radicals, saturated or unsaturated, linear or branched, in C1-C20, preferably the R1s are identical; R2, identical or different, are divalent aliphatic radicals, saturated or unsaturated, linear or branched, in C1-C20, preferably the R2s are identical; the number of carbons in each fatty acid unit being in the range of 8 to 34, preferably 12 to 22, preferably again 16 to 20, in particular 18; R3 represents a hydrogen atom H or an aliphatic group, saturated or unsaturated, linear or branched, at C8 to C26, especially at C12 to C22, particularly at C16 to C20 and more particularly at C18. 19. Composition according to embodiment 18 in which, in formula I, X represents a hydroxyl group -OH. 20.Composition according to embodiment 18 or 19 wherein in formula I, the number of carbons in each fatty acid unit is in the range of 16 to 20, in particular 18. 21. Composition according to any one of embodiments 18 to 20 wherein in formula I, R3 represents a saturated aliphatic group branched at C16 to C20 and more particularly at C18. 22. Composition according to any one of the preceding embodiments wherein at least one estolide is a ricinoleic acid estolide esterified with isoteryl alcohol.

[0009] The invention also relates to a tire, one of whose constituent elements comprises a rubber composition according to any one of the preceding embodiments. More particularly, the invention then relates to a tire having an outer sidewall, said outer sidewall comprising at least one rubber composition according to any one of the preceding embodiments. Definitions

[0010] The expression "part by weight per hundred parts by weight of elastomer" (or pce) is to be understood in the context of the present invention as the part, by mass per hundred parts by mass of elastomer or rubber.

[0011] In this document, unless expressly stated otherwise, all percentages (%) shown are percentages (%) by mass.

[0012] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​from greater than a to less than b (that is, excluding the bounds a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (that is, including the strict bounds a and b). In this context, when an interval of values ​​is designated by the expression "from a to b," it also and preferentially designates the interval represented by the expression "between a and b."

[0013] In this document, the term "composition based on" refers to a composition comprising a mixture and / or the reaction product of the various constituents used, some of which are likely to, or intended to, react with each other, at least partially, during the different stages of manufacturing the composition, particularly during its crosslinking or vulcanization. For example, a composition based on an elastomeric matrix and sulfur includes the elastomeric matrix and sulfur before curing, whereas after curing the sulfur is no longer detectable because it has reacted with the elastomeric matrix, forming sulfur bridges (polysulfides, disulfides, monosulfides).

[0014] When referring to a "major" compound, for the purposes of this invention, it is understood that this compound is the majority among compounds of the same type in the composition; that is, it is the one that represents the largest quantity by mass among compounds of the same type. Preferably, it is the compound that represents, for example, more than 50%, more than 60%, more than 70%, more than 80%, more than 90%, or even 100% by weight relative to the total weight of the compound type. Thus, for example, a major reinforcing filler is the reinforcing filler representing the greatest mass relative to the total mass of reinforcing fillers in the composition. Conversely, a "minor" compound is a compound that does not represent the largest mass fraction among compounds of the same type.

[0015] The compounds mentioned in the description can be of fossil origin or bio-based. In the latter case, they may be partially or entirely derived from biomass or obtained from renewable raw materials derived from biomass. Similarly, the compounds mentioned may also come from the recycling of previously used materials; that is, they may be partially or entirely produced through a recycling process, or obtained from raw materials themselves derived from a recycling process. This includes, in particular, polymers, plasticizers, fillers, etc. Detailed description of the invention 1 Elastomer matrix

[0016] The rubber composition according to the invention comprises an elastomer matrix comprising an isoprene elastomer and a butadiene elastomer.

[0017] More specifically, isoprenoid elastomer and butadiene elastomer are understood to be suitable for use in compositions according to the invention: a) any homopolymer obtained by polymerization of an isoprene monomer or a butadiene monomer; b) any copolymer obtained by copolymerization of an isoprene monomer or a butadiene monomer with one or more other monomers. Examples of other monomers include ethylene, an olefin, and a diene, conjugated or not, other than isoprene or butadiene.

[0018] The terms "isoprene elastomer" or "polyisoprene" are commonly understood to mean a homopolymer or copolymer of isoprene; in other words, a diene elastomer selected from the group consisting of natural rubber (NR), which may be plasticized or peptized, synthetic polyisoprenes (IR), various isoprene copolymers, and mixtures of these elastomers. Among the isoprene copolymers, particular examples include isobutene-isoprene (butyl rubber IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR), and isoprene-butadiene-styrene (SBIR). Preferably, the polyisoprene is selected from the group consisting of natural rubber, a synthetic polyisoprene, and a mixture thereof; even more preferably, the polyisoprene comprises predominantly, or even exclusively, natural rubber.

[0019] Preferably, the polyisoprene has a cis 1,4 bond mass ratio of at least 90%, more preferably of at least 98%, relative to the mass of the polyisoprene.

[0020] Preferably, the polyisoprene content, preferably natural rubber, is 10 to 60 pc, more preferably 15 to 50 pc, more preferably 20 to 50 pc and very preferably 25 to 45 pc.

[0021] The term "butadiene elastomer" is commonly understood to mean a homopolymer or copolymer of butadiene, in other words, a diene elastomer selected from the group consisting of polybutadienes (BR), butadiene copolymers such as butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-butadiene-styrene copolymers (SBIR), butadiene-acrylonitrile copolymers (NBR), butadiene-styrene-acrylonitrile copolymers (NSBR), or a mixture of two or more of these compounds. Preferably, the butadiene elastomer is selected from the group consisting of polybutadienes (BR) and mixtures thereof.

[0022] Preferably, polybutadiene (BR) has a cis 1,4 bond mass ratio of at least 90% relative to the mass of polybutadiene.

[0023] Preferably, the butadiene elastomer content is 40 to 90 pc, more preferentially 50 to 85 pc, even more preferentially 50 to 80 pc, and very preferentially 55 to 75 pc.

[0024] Isoprene elastomer is different from butadiene elastomer.

[0025] The elastomeric matrix of the rubber composition according to the invention may comprise one or more other diene elastomers besides butadiene elastomer and isoprene elastomer. The diene elastomer(s) may be selected, for example, from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), polybutadienes (BR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.Such copolymers are most preferentially chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-butadiene-styrene copolymers (SBIR), butadiene-acrylonitrile copolymers (NBR), butadiene-styrene-acrylonitrile copolymers (NSBR), ethylene-butadiene copolymers (EBR) and terpolymers of ethylene, butadiene and another conjugated diene monomer, in particular isoprene, myrcene or farnesene, or a mixture of two or more of these compounds.

[0026] Preferably, the elastomeric matrix of the rubber composition according to the invention comprises mainly a mixture of an isoprene elastomer, preferably natural rubber, and a butadiene elastomer, preferably polybutadiene. Even more preferably, the elastomeric matrix of the rubber composition according to the invention is essentially composed of a mixture of an isoprene elastomer, preferably natural rubber, and a butadiene elastomer, preferably polybutadiene. 2 Reinforcing charge

[0027] The rubber composition according to the invention has another essential characteristic of comprising a reinforcing filler including carbon black as the major filler.

[0028] All carbon blacks are suitable, including those conventionally used in tires or their treads. Among these, particularly the reinforcing carbon blacks of the 100, 200, and 300 series, or the 500, 600, and 700 series (ASTM D-1765-2017 grades), such as N115, N134, N234, N326, N330, N339, N347, N375, N550, N683, and N772. These carbon blacks can be used on their own, as commercially available, or in other forms, for example, as a carrier for certain rubber compound additives. Carbon blacks could for example already be incorporated into the diene elastomer, in particular isoprene in the form of a "masterbatch" (see for example applications WO97 / 36724-A2 or WO99 / 16600-A1).

[0029] The reinforcing filler may include another reinforcing filler. Any type of so-called reinforcing filler other than carbon black, known for its ability to strengthen a rubber composition usable particularly for the manufacture of tires, can be used for this purpose; for example, an inorganic filler such as silica.

[0030] Suitable inorganic reinforcing fillers include mineral fillers of the siliceous type, preferably silica (SiO2), or of the aluminous type, particularly alumina (Al2O3). The silica used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenated silica having a specific surface area BET and a specific surface area CTAB both less than 450 m2 / g, preferably within a range of 30 to 400 m2 / g, in particular 60 to 300 m2 / g.

[0031] Any type of precipitated silica can be used, including highly dispersible precipitated silicas (known as "HDS" for "highly dispersible" or "highly dispersible silica"). These precipitated silicas, whether highly dispersible or not, are well known to those skilled in the art. Examples include the silicas described in applications WO03 / 016215-A1 and WO03 / 016387-A1. Among the commercial HDS silicas, one can notably use the silicas “Ulsil ®< 5000GR”, “Ulsil ®< 7000GR” from the company Evonik, the silicas “Zeosil ®< 1085GR”, “Zeosil ®< 1115 MP”, “Zeosil ®< 1165MP”, “Zeosil ®< Premium 200MP”, “Zeosil ®< HRS 1200 MP” from the Solvay Company.As non-HDS silica, the following commercial silicas may be used: “Ultrasil ®< VN2GR”, “Ultrasil ®< VN3GR” silicas from Evonik, “Zeosil ®< 175GR” silica from Solvay, “Hi-Sil EZ120G(-D)”, “Hi-Sil EZ160G(-D)”, “Hi-Sil EZ200G(-D)”, “Hi-Sil 243LD”, “Hi-Sil 210”, “Hi-Sil HDP 320G” silicas from PPG.

[0032] Other examples of inorganic fillers that could be used in the rubber compositions of the invention may also be cited: mineral fillers of the aluminous type, in particular alumina (Al2O3), aluminum oxides, aluminum hydroxides, aluminosilicates, titanium oxides, silicon carbides or nitrides, all of the reinforcing type as described for example in applications WO99 / 28376-A2, WO00 / 73372-A1, WO02 / 053634-A1, WO2004 / 003067-A1, WO2004 / 056915-A2, US6610261-B1 and US6747087-B2. Examples include the aluminas “Baikalox A125” or “CR125” (Baïkowski company), “APA-100RDX” (Condéa), “Aluminoxid C” (Evonik) or “AKP-G015” (Sumitomo Chemicals).

[0033] The physical state of the reinforcing inorganic filler is irrelevant, whether it be in the form of powder, microbeads, granules, spheres, or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing inorganic fillers, particularly silicas as described above.

[0034] Those skilled in the art will understand that, in place of the inorganic reinforcing filler described above, a reinforcing filler of another nature could be used, provided that this reinforcing filler of another nature is coated with an inorganic layer such as silica, or has functional sites on its surface, particularly hydroxyl sites, requiring the use of a coupling agent to establish the bond between this reinforcing filler and the diene elastomer. Examples include carbon blacks partially or fully coated with silica, or carbon blacks modified with silica, such as, but not limited to, the "Ecoblack®" fillers of the "CRX2000" or "CRX4000" series from Cabot Corporation.

[0035] The reinforcing filler consists mainly of carbon black. Preferably, for the invention, the reinforcing filler is essentially made of carbon black.

[0036] Preferably the carbon black content is in the range of 20% to 100%, preferably from 20% to 80%, more preferably from 25% to 60%.

[0037] A person skilled in the art will be able to adjust the total reinforcing filler content according to the intended use, ranging from 20 to 120 parts per annum, depending on the intended application of the rubber compound. Thus, according to certain embodiments of the invention, the total reinforcing filler content is 30 to 80 parts per annum, preferably 35 to 70 parts per annum.

[0038] In this presentation, the specific surface area BET is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Vol. 60, page 309, February 1938), and more specifically according to a method adapted from the standard NF ISO 5794-1, Annex E of June 2010 [multipoint volumetric method (5 points) - gas: nitrogen - degassing under vacuum: one hour at 160°C - relative pressure range w / in: 0.05 to 0.17].

[0039] For inorganic fillers such as silica, for example, the CTAB specific surface area values ​​were determined according to the NF ISO 5794-1 standard, Annex G of June 2010. The process is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the "external" surface of the reinforcing filler.

[0040] To couple the reinforcing inorganic filler to the diene elastomer, a well-known coupling agent (or bonding agent) can be used. This agent must be at least bifunctional and ensure sufficient chemical and / or physical interaction between the inorganic filler (the surface of its particles) and the diene elastomer. Organosilanes or polyorganosiloxanes, at least bifunctional, are particularly suitable. "Bifunctional" refers to a compound possessing a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer.For example, such a bifunctional compound may comprise a first functional group comprising a silicon atom, said first functional group being able to interact with the hydroxyl groups of an inorganic charge and a second functional group comprising a sulfur atom, said second functional group being able to interact with the diene elastomer.

[0041] Preferably, organosilanes are chosen from the group consisting of polysulfide organosilanes (symmetric or asymmetric) such as bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated TESPT and marketed under the name "Si69" by Evonik, or bis-(triethoxysilylpropyl) disulfide, abbreviated TESPD and marketed under the name "Si75" by Evonik; polyorganosiloxanes; mercaptosilanes; and blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl) octanethioate, marketed by Momentive under the name "NXT Silane". More preferably, the organosilane is a polysulfide organosilane.

[0042] Of course, mixtures of the coupling agents described above could also be used.

[0043] The coupling agent content in the composition of the invention is advantageously less than or equal to 30 parts per liter, it being understood that it is generally desirable to use as little as possible. Typically, the coupling agent content represents 0.5% to 15% by weight relative to the amount of reinforcing inorganic filler. This percentage is easily adjusted by those skilled in the art according to the percentage of reinforcing inorganic filler used in the composition of the invention. 3 Plasticizer system

[0044] The rubber composition according to the invention comprises 5 to 120 parts of a plasticizing system and preferably 10 to 80 parts.

[0045] The plasticizing system of a rubber composition for the tire may include one or more plasticizers.

[0046] According to the invention, the plasticizing system of the rubber composition comprises at least one estolide with a weight-average molar mass (Mw) of less than 5000 g / mol, preferably within a range of 700 to 5000 g / mol, and more preferably within a range of 700 to 3500 g / mol. The weight-average molar mass (Mw) of the estolides is measured by SEC (Size Exclusion Chromatography) according to the method described below.

[0047] By "at least one estolide", we mean, according to the invention, one or more estolides.

[0048] According to alternative embodiments of the invention, the plasticizing system comprises from 10% to 100% by weight of at least one estolide, preferably from 40% to 100% by weight, relative to the total weight of the plasticizing system. According to particular embodiments of the invention, the plasticizing system comprises 100% by weight of at least one estolide, that is to say, the plasticizing system is essentially composed of at least one estolide.

[0049] According to the invention, the rubber composition preferably comprises 5 to 50 parts, more preferably 10 to 30 parts, of at least one estolide.

[0050] Estolides are obtained from unsaturated and / or saturated fatty acids. Estolides are a class of esters that are 100% bio-based when the fatty acids are of natural origin. According to the invention, "bio-based" means partially or totally derived from biomass or partially or totally obtained from renewable raw materials derived from biomass. The oligomeric structure of estolides contains repeating fatty acid units, each fatty acid unit being esterified by another fatty acid unit. For example, document WO2012173671A1 describes such compounds.

[0051] Some estolides can be obtained from naturally hydroxylated fatty acids or from fatty acids that have undergone hydroxylation, where the hydroxyl group of each unit of one fatty acid is esterified by the acid group of another fatty acid. According to other synthetic methods, the estolide is formed by the production of a carbocation at the unsaturation site of an unsaturated fatty acid, followed by a nucleophilic attack on the carbocation by the carboxyl group of another fatty acid. These synthetic methods are known and within the capabilities of those skilled in the art. For example, document WO2012173671A1 describes methods for the synthesis of estolides.

[0052] The reader will understand that, in order to reduce the environmental impact of the rubber composition according to the invention, fatty acid is very preferably understood to mean a fatty acid of natural origin, obtained by hydrolysis of vegetable oils, such as, to cite only a few examples, the fatty acids of orange oil, avocado oil, macadamia oil, olive oil, hydrogenated soybean oil, rapeseed oil, jojoba oil, palm oil, castor oil, wheat germ oil, saffron oil, linseed oil, safflower oil, corn oil, pine oil, sunflower oil, coconut oil, peanut oil, grapeseed oil, cottonseed oil, macadamia oil and mixtures thereof.

[0053] Examples of naturally occurring fatty acids include: Saturated linear fatty acids such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid; branched-chain fatty acids, saturated or unsaturated, such as isostearic acid, isopalmic acid; unsaturated linear fatty acids, such as linderic acid, myristoleic acid, palmitoleic acid, oleic acid, linoleic acid, elaidic acid, gadolenoid acid, eicosapentaenoic acid, docosahexaenoic acid, erucic acid, brassidic acid, arachidonic acid; hydroxylated fatty acids such as ricinoleic acid, hydroxystearic acids.

[0054] According to the invention, "fatty acid" means a fatty acid, saturated or unsaturated, linear or branched, in the range of C8 to C34, in particular in C8 to C26, in particular in C12 to C22, and especially in C16 to C22. According to preferred embodiments of the invention, the fatty acid is a hydroxylated fatty acid, linear or branched, saturated or unsaturated, in the range of C12 to C22, in particular in C16 to C20 and more particularly in C18. Preferably, the fatty acid is ricinoleic acid.

[0055] According to preferred embodiments of the invention, the estolide is an estolide that has undergone ultimate esterification with a saturated or unsaturated, linear or branched, aliphatic fatty alcohol in the C1 to C34 range, preferably a fatty alcohol. Within the scope of the invention, such an esterified estolide is also referred to as an "estolide".

[0056] For the purposes of the present invention, the term "fatty alcohol" is more particularly understood to mean an alcohol obtained by hydrogenation of a fatty acid, saturated or unsaturated, linear or branched, in C8 to C34, in particular in C8 to C26, in particular in C12 to C22, in particular in C16 to C20 and more particularly in C18.

[0057] Fatty alcohol can be a linear fatty alcohol, saturated or unsaturated, in C 8 to C 34, preferably a linear fatty alcohol in C 8 to C 26, especially in C 12 to C 22 and more particularly in C 18 like for example stearyl alcohol, oleyl alcohol and linoleyl alcohol.

[0058] Fatty alcohols can be branched. According to the invention, the term "branched fatty alcohol" refers to an alcohol derived from a fatty acid possessing a methyl group attached to the penultimate or antepenultimate carbon atom, or several methyl groups distributed along the chain. These branched fatty alcohols are preferably C8 to C26, particularly C12 to C22, and more especially C18, like isostearyl alcohol.

[0059] According to variants of the invention, at least one estolide is preferably a compound obtained from a hydroxylated fatty acid, preferably ricinoleic acid, having undergone esterification with a C12 to C22 branched fatty alcohol and more particularly with a C18 branch, preferably isostearyl alcohol.

[0060] According to the invention, at least one estolide is preferably a compound of Formula I: in which, n is an integer ranging from 1 to 5; X is a hydrogen atom or an -OH group, preferably an -OH group; R1, identical or different, represent divalent aliphatic radicals, saturated or unsaturated, linear or branched, in C1-C20, preferably the R1s are identical; R2, identical or different, are divalent aliphatic radicals, saturated or unsaturated, linear or branched, in C1-C20, preferably the R2s are identical; the number of carbons in each fatty acid unit being in the range of 8 to 34, preferably 12 to 22, preferably again 16 to 20, in particular 18; R3 represents H (hydrogen atom) or an aliphatic group, saturated or unsaturated, linear or branched, in C8-C34, preferably an aliphatic group in C8 to C26, especially in C12 to C22, particularly in C16 to C20 and more particularly in C18.

[0061] According to embodiments of the invention, at least one estolide is a compound obtained from a hydroxylated fatty acid. Examples of hydroxylated fatty acids include ricinoleic acid and hydroxylated stearic acids. In these embodiments, the estolide is preferably a compound obtained from ricinoleic acid.

[0062] According to these variants, in Formula I, X represents an -OH group.

[0063] According to these variants, in Formula I, preferably the number of carbons in each fatty acid unit is in the range of 16 to 20, in particular 18. The term "fatty acid unit" refers to the unit in Formula II:

[0064] According to variants of the invention, estolide is a compound obtained from a fatty acid, hydroxylated or non-hydroxylated, having undergone esterification with a fatty alcohol.

[0065] According to these variants of the invention, R3 is preferably the carbon chain from a fatty alcohol and represents an aliphatic radical preferably at C12 to C22, in particular at C16 to C20 and more particularly at C18.

[0066] Most preferably, at least one estolide is a ricinoleic acid estolide esterified by isostearyl alcohol.

[0067] Advantageously, ricinoleic acid is obtained from castor oil. Other plasticizers

[0068] According to preferred variants of the invention, the plasticizing system essentially consists of at least one estolide.

[0069] Thus, according to other variants of the invention, the plasticizing system may include one or more other plasticizing compounds among the plasticizing resins and liquid plasticizers at room temperature (around 23°C) usually used in rubber compositions for tires.

[0070] Any extending oil, whether aromatic or non-aromatic, any liquid plasticizing agent known for its plasticizing properties towards diene elastomers can be used in addition to estolide as a liquid plasticizer. Examples of liquid plasticizers that can be used in the context of the invention include those chosen from liquid diene polymers, polyolefinic oils, naphthenic oils, paraffinic oils, DAE oils, MES (Medium Extracted Solvates) oils, TDAE (Treated Distillate Aromatic Extracts) oils, RAE (Residual Aromatic Extract oils), TRAE (Treated Residual Aromatic Extract) oils and SRAE (Safety Residual Aromatic Extract oils), mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and mixtures of these compounds.

[0071] The reader will understand that in order to reduce the environmental footprint, in particular products of fossil origin, in the composition of rubber according to the invention, if at least one other plasticizer is used in the composition of rubber, it will preferably be of a renewable nature, in particular of bio-based origin. 4 Crosslinking System

[0072] The crosslinking system can be any type of system known to those skilled in the art in the field of tire rubber compounds. It may, in particular, be sulfur-based, and / or peroxide-based, and / or bismaleimide-based.

[0073] Preferably, the crosslinking system is sulfur-based; this is then referred to as a vulcanization system. The sulfur can be supplied in any form, including molecular sulfur or a sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and optionally, various known vulcanization activators such as zinc oxide, stearic acid, or equivalent compounds such as stearic acid salts and transition metal salts, guanidine derivatives (particularly diphenylguanidine), or known vulcanization retarders may be used.

[0074] Sulfur is used at a preferential rate of between 0.2% and 10%. The primary vulcanization accelerator is used at a preferential rate of between 0.5% and 10%, more preferably between 0.5% and 5%.

[0075] Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used as an accelerator, including thiazole-type accelerators and their derivatives, sulfenamide-type accelerators, thiurams, dithiocarbamates, dithiophosphates, thioureas and xanthates. Examples of such accelerators include the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-ter-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-ter-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds. 5 Possible Additives

[0076] The rubber compositions according to the invention may optionally also include all or part of the usual additives commonly used in tire elastomer compositions, such as pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, antioxidants other than the phenolic antioxidant of general formula (I), anti-fatigue agents, adhesion promoters on metallic reinforcements, in particular based on cobalt salts (such as cobalt acetylacetonate, cobalt resinate, cobalt 2-ethylhexanoate or cobalt hydroxide), or reinforcing resins (such as those described for example in application WO 02 / 10269). 6. Preparation of rubber compositions

[0077] The compositions according to the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: A first thermomechanical working or mixing phase (the so-called "non-productive" phase) can be carried out in one or more thermomechanical steps. During this phase, all the necessary constituents, including the elastomer matrix, the reinforcing filler, the estolide, and any other miscellaneous additives, with the exception of the crosslinking system, are introduced into a suitable mixer, such as a standard internal mixer (e.g., a Banbury mixer). The incorporation of any filler into the elastomer can be achieved in one or more stages by thermomechanical mixing.Where the filler is already fully or partially incorporated into the elastomer as a masterbatch, as described, for example, in applications WO 97 / 36724 or WO 99 / 16600, the masterbatch is mixed directly. If necessary, other elastomers or fillers present in the composition that are not in masterbatch form are also incorporated, along with the estolide and any other miscellaneous additives other than the crosslinking system. The non-productive phase can be carried out at high temperature, up to a maximum temperature between 110°C and 200°C, preferably between 130°C and 185°C, for a duration generally between 2 and 10 minutes.a second mechanical working phase (the so-called "productive" phase), which is carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example between 5 and 15 min.

[0078] The resulting final composition is then calendered, for example, into a sheet or plate, particularly for laboratory characterization, or extruded (or co-extruded with another rubber compound) into a semi-finished product (or profile) usable, for example, as a tire sidewall. These products can then be used to manufacture tires, according to techniques known to those skilled in the art.

[0079] The composition can be either in its raw state (before crosslinking or vulcanization), or in its cooked state (after crosslinking or vulcanization), and can be a semi-finished product that can be used in a tire.

[0080] Crosslinking (or curing), where applicable vulcanization, is carried out in a known manner at a temperature generally between 130°C and 200°C, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the curing temperature, the crosslinking system adopted and the crosslinking kinetics of the composition considered. 7 Tire

[0081] The invention also relates to a tire comprising in one of its components a rubber composition as described above.

[0082] It is possible to define three types of zones within the tire: The outer radial zone, in contact with the ambient air, is essentially made up of the tread and the outer sidewall of the tire. The inner radial zone, in contact with the inflation gas, is generally made up of the gas-tight layer, sometimes called the inner liner. The inner zone of the tire is the area between the outer and inner zones. This zone includes layers or plies that are called the tire's inner layers.

[0083] In particular, in view of the significant improvement in the breaking properties of the rubber composition according to the invention compared to a composition comprising a conventional plasticizing system of fossil origin, the rubber composition as described above is particularly suitable for use in the outer sidewall of a tire.

[0084] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several examples of embodiments of the invention, given by way of illustration and not limitation. Examples Measurements and tests used Size exclusion chromatography

[0085] The SEC (Size Exclusion Chromatography) technique separates macromolecules in solution according to their size using columns filled with a porous gel. The macromolecules are separated according to their hydrodynamic volume, with the largest being eluted first.

[0086] While not an absolute method, SEC allows for the determination of the molar mass distribution of a polymer. Using commercial standard products, the various number-average (Mn) and weight-average (Mw) molar masses can be determined via a Moore calibration. Operating procedure

[0087] The number-average molar mass (Mn) and the weight-average molar mass (Mw) of the constituents usable in compositions according to the invention are determined in a known manner by conventional size-exclusion chromatography (SEC) with RI detection and PS (polystyrene) calibration. The PS standards are from the "PSS-kitr1l" kit from PSS-Polymers.

[0088] To determine the average molar masses, a 1.5 g / L sample solution, previously prepared and filtered through a 0.45 µm PTFE filter, is injected into the chromatographic system. The equipment used is a WATERS alliance e2695 chromatographic system with a Waters RI 410 detector. The elution solvent is tetrahydrofuran, the flow rate is 1 mL / min, the system temperature is 35°C, and the analysis time is 50 min. Four AGILENT columns are used (2 PLGEL 5 µm MIXED-D and 2 PLGEL 3 µm MIXED-E). The injected volume of the sample solution is 100 µL.

[0089] The software used to process the chromatographic data is the "Empower" system from WATERS. Differential calorimetry

[0090] The glass transition temperatures (Tg) of elastomers are determined using a differential scanning calorimeter, according to ASTM D3418 (1999). Low stiffness criterion deformation:

[0091] Stiffness is represented by the value of the G* modulus back to 10% during strain sweep measurements at 60°C from 0.1 to 100% peak-to-peak.

[0092] The dynamic properties G* are measured on a viscoelastic analyzer (Metravib VA4000) according to ASTM D 5992-96. The response of a vulcanized composite sample (cylindrical specimen 2 mm thick and 79 mm² cross-section) is recorded under sinusoidal alternating simple shear loading at a frequency of 10 Hz, under standard temperature conditions (60°C) according to ASTM D 1349-99. A strain amplitude sweep is performed from 0.1% to 100% peak-to-peak (forward cycle), then from 100% to 0.1% peak-to-peak (return cycle). The result used is the stiffness modulus G* at 10% strain. The higher this number, the greater the stiffness at low strain. High rigidity criterion deformation:

[0093] High-strain stiffness is represented by the elongation and stress-at-break values ​​measured during tensile tests. Traction tests

[0094] These tensile tests determine yield strength and tensile properties. Unless otherwise specified, they are performed in accordance with the French standard NF ISO 37 of December 2005. Tensile strength (in MPa) and elongation at break (in %) are measured under normal temperature (23°C ± 2°C) and humidity (50 ± 10% relative humidity) conditions. Analysis of the tensile test data also allows for the plotting of the modulus-elongation curve. Tests Obtaining estolide.

[0095] The bio-based plasticizer based on ricinoleic acid estolide was obtained according to the following protocol:

[0096] The esterified estolide was obtained in four steps. The first step consisted of synthesizing an estolide with a well-defined structure, between two and four chains of ricinoleic acid units. The second step involved distilling the excess acid present in the medium using molecular distillation. The esterification of the available acidic groups on the estolide was then carried out with an excess of isostearyl alcohol. Finally, the last step consisted of distilling the excess unreacted alcohol. Step 1: Synthesis of the oligomer Operating procedure

[0097] Stirred batch reactor conditions: 180°C / 600mbar / 14h Analytical monitoring: SEC (Equivalent PS) Step 2: Molecular distillation, also known as "short path" Terms :

[0098] Trap temperature: -22°C Addition pump speed: 230 mL / h Double jacket temperature: 200°C Vacuum: 5 x 10⁻² mbar Analytical monitoring: SEC (Specific Pressure Equivalent) Step 3: Esterification of acidic functions

[0099] Addition of 3 molar eq. of isostearyl alcohol Operating procedure

[0100] Stirred batch reactor. Conditions: 160°C / under vacuum to distill the water formed during the reaction. Analytical monitoring: Acid value according to standard NF EN ISO 660 and SEC (Equivalent PS). Step 4: Distillation of excess alcohol, known as "short-path" distillation Terms :

[0101] Trap temperature: -22°C Addition pump speed: 230mL / h Double jacket temperature: 200°C Vacuum: 8.7 x 10⁻² mbar Analytical monitoring: SEC (Specific Pressure Equivalent)

[0102] The table below gives the characteristics of average molar mass by weight (Mw) and glass transition temperature (Tg) of the bio-based plasticizer according to the invention in comparison with the non-bio-based oil (MES Oil). Table 1 Components Nature Tg (°C) Mw (g.mol) MES Oil (8) Parafin -60 711 Oil n°1 (9) Ricinoleic acid estolide -68 2062 Compositions

[0103] The so-called reference composition T is shown in Table 2 below and it includes a MES oil which is of fossil origin.

[0104] Note that composition C1, according to the present invention, is formulated so as to be at the same volume dilution in oil (%v) as the control composition T.

[0105] The compositions are as follows (in pieces). Table 2 Components T C 1 NR(1) 35 35 BR (2) 65 65 Black (3) 48 48 6PPD (4) 1.5 1.5 IPPD (5) 1.5 1.5 TMQ (6) 1 1 Wax (7) 1 1 MES Oil (8) 18 Oil No. 1 (9) 18 ZnO (10) 2.4 2.4 Ac. Stearic (11) 1 1 Acc (12) 1.4 1.4 Sulfur 1.4 1.4 (1) Natural rubber with a Tg equal to -70°C (2) Poly butadiene with a Tg equal to -108°C (3) Black ASTM “N550” from the company CABOT (4) “Santoflex 6PPD” from the company SOLUTIA (5) “Santoflex IPPD” from the company SOLUTIA (6) Antioxidant “DQ” from the company Akrochem (7) Anti-ozone wax “ Varazon 6500” from the company Sasol (8) MES oil “Flexion 683” from the company Exxon-Mobil (9) Oil no. 1: Ricinoleic acid estolide of Mw=2062 g / mol and Tg=-68°C (10) Industrial grade zinc oxide – Umicore company (11) Stearin “Pristerene 4931” from the company Uniqema (12) Cylohexyl-benzothiazyl sulfenamide CBS from AKROCHEM Preparation of compositions

[0106] The rubber compositions, the detailed formulations of which are shown in Table 2, were prepared as follows: The elastomer matrix is ​​introduced into an internal mixer (final fill level: approximately 70% by volume and paddle speed: 50 rpm), with an initial tank temperature of approximately 90°C. When the temperature reaches 100°C, carbon black and the plasticizer are added. A single-stage thermomechanical process (non-productive phase) is then carried out, lasting approximately 3 to 4 minutes in total, until a maximum "drop" temperature of 160°C is reached. The resulting mixture is collected, cooled, and then sulfur and vulcanization accelerators are incorporated in a mixer (homo-finisher) at 30°C, with the mixture being blended for an appropriate time (e.g., approximately ten minutes).

[0107] The compositions thus obtained are then calendered either in the form of plates (2 to 3mm thick) or thin sheets of rubber and vulcanized at their optimum at a temperature of 160°C for the measurements of their physical and mechanical properties which are shown in Table 3. Results

[0108] Table 3 Properties Descriptors T C1 Dynamics: In Deformation G*10% return to 60°C (MPa) 1.2 1.2 Mechanics: Uniaxial traction Elongation Break (%) 100 111 Break stress (MPa) 100 103

[0109] The G*10% stiffness criterion under deformation remains unchanged. The mechanical properties of the rubber composition comprising a bio-based plasticizer according to the invention are maintained at low deformation compared to the mechanical properties of a standard rubber composition comprising a conventional plasticizer of fossil origin.

[0110] Moreover, and surprisingly, the composition according to the invention comprising a bio-based plasticizer improves resistance to breakage by improving stiffness at high deformation, as elongation and breaking stress are significantly improved compared to the standard rubber composition comprising a conventional plasticizer of fossil origin.

Claims

1. Rubber composition based on at least: - 100 phr of an elastomer matrix comprising an isoprene elastomer and a butadiene elastomer, - 20 to 120 phr of a reinforcing filler comprising carbon black as predominant filler, - 5 to 120 phr of a plasticizing system comprising at least one estolide with a weight-average molar mass (Mw) of less than 5000 g / mol determined by size exclusion chromatography (SEC), the method being described in the description, - a crosslinking system.

2. Composition according to the preceding claim, in which the content of isoprene elastomer is within a range extending from 10 to 60 phr, preferably from 15 to 50 phr.

3. Composition according to either one of the preceding claims, in which the isoprene elastomer predominantly comprises natural rubber.

4. Composition according to any one of the preceding claims, in which the content of butadiene elastomer is within a range extending from 40 to 90 phr, preferably from 50 to 85 phr.

5. Composition according to any one of the preceding claims, in which the butadiene elastomer is a polybutadiene.

6. Composition according to any one of the preceding claims, in which the reinforcing filler consists essentially of carbon black.

7. Composition according to any one of the preceding claims, in which the carbon black is present at a content within a range extending from 20 phr to 100 phr, preferably ranging from 20 to 80 phr, more preferentially ranging from 25 to 60 phr.

8. Composition according to any one of the preceding claims, in which the content of estolide(s) is within a range extending from 5 to 50 phr, preferably from 10 to 30 phr.

9. Composition according to any one of the preceding claims, in which the plasticizing system comprises from 10% to 100% by weight of at least one estolide, preferably from 40% to 100% by weight, relative to the total weight of the plasticizing system.

10. Composition according to any one of the preceding claims, in which the at least one estolide is an estolide esterified with a linear or branched, saturated or unsaturated C8 to C34 fatty alcohol.

11. Composition according to any one of the preceding claims, in which the at least one estolide is an estolide of a linear or branched, saturated or unsaturated C12 to C22, in particular C16 to C20 and more particularly C18 fatty acid.

12. Composition according to any one of the preceding claims, in which the at least one estolide is an estolide of a hydroxy fatty acid, preferably ricinoleic acid.

13. Composition according to any one of the preceding claims, in which the at least one estolide is an estolide esterified with a branched C12 to C22, preferably C16 to C20 and more particularly C18 fatty alcohol, more preferably with isostearyl alcohol.

14. Composition according to any one of the preceding claims, in which the at least one estolide is a compound of formula I: in which: n is an integer ranging from 1 to 5; X is a hydrogen atom or an -OH group, preferably an -OH group; R1, which may be identical or different, represent linear or branched, saturated or unsaturated, divalent aliphatic C1 - C20 radicals, preferentially the R1 are identical; R2, which may be identical or different, are linear or branched, saturated or unsaturated, divalent aliphatic C1 - C20 radicals, preferentially the R2 are identical; the number of carbons in each fatty acid unit being within a range extending from 8 to 34, preferably from 12 to 22, more preferentially from 16 to 20, in particular 18; R3 represents H (hydrogen atom) or a linear or branched, saturated or unsaturated aliphatic C8-C34 group, preferably an aliphatic C8 to C26, more preferably C12 to C22, in particular C16 to C20 and more particularly C18 group.

15. Tyre having an outer sidewall, said outer sidewall comprising at least one rubber composition according to any one of the preceding claims.