WO2014096188A1

WO2014096188A1 - Rubber composition comprising cellulose

Info

Publication number: WO2014096188A1
Application number: PCT/EP2013/077369
Authority: WO
Inventors: Benoît DE GAUDEMARIS; Julien Berriot; Anne Veyland; Nicolas Seeboth; Laurent Heux; Sonia BOISSEAU; Matthieu FUMAGALLI
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.; Centre National De La Recherche Scientifique
Priority date: 2012-12-21
Filing date: 2013-12-19
Publication date: 2014-06-26
Also published as: FR3000081A1; EP2934909A1; FR3000081B1

Abstract

The invention relates to a rubber composition containing at least one diene elastomer and at least one reinforcing filler, said reinforcing filler comprising cellulose grafted by molecules of a coupling agent that can bond to the diene elastomer. The aforementioned molecules comprise at least one A function and one B function such that: A represents a functional group (A function) which can bond chemically to the cellulose and which comprises at least one heteroatom selected from among oxygen, phosphorous, halogens, nitrogen and sulphur; and B represents a functional group (B function) which can bond physically and/or chemically to the diene elastomer, said A and B functions being connected by an at least divalent X group.

Description

RUBBER COMPOSITION COMPRISING CELLULOSE

The present invention relates to diene rubber compositions reinforced with an organic filler for the manufacture of tires or semi-finished products for tires, in particular to the treads of these tires.

In order to obtain the optimum reinforcing properties conferred by a load in a tire tread and thus a high wear resistance, it is known that it is generally appropriate for this filler to be present in the elastomeric matrix under final form that is both finely divided possible and distributed in the most homogeneous way possible. However, such conditions can be achieved only to the extent that this charge has a very good ability, on the one hand to incorporate into the matrix during mixing with the elastomer and to deagglomerate, on the other hand to to disperse homogeneously in this matrix.

In a known manner, carbon black has such aptitudes. However, since fuel savings and the need to protect the environment have become a priority, it has been necessary to produce tires with reduced rolling resistance without penalizing their wear resistance, hence the constant interest for new reinforcing loads.

In addition, we also seek to use natural materials, ecologically advantageous. Thus, some documents are interested in the use of natural fibers such as cellulose fibers for rubber compositions for the tire.

It will be noted that in the native state the cellulose is in the form of very elongated microfibrils of nanometric diameter, often organized into fibers. This cellulose can be found in higher plants, but also in certain algae, certain fungi, bacteria, amoebae and even certain marine animals.

The term "micro-fibrils" means these extremely long and fine elements consisting of macromolecular cellulose chains aligned in the fiber direction extracted from the native structure. The micro-fibrils are in the form of highly elongated filaments of indefinite length and consisting of an alternation of crystalline zones and amorphous zones.

The term "cellulose nanocrystals" or "whiskers" is understood to mean anisotropic crystals of finite length and of nanometric diameter obtained by hydrolysis of the amorphous parts of microfibrils and consisting of fiber-oriented macromolecular cellulose chains. However, for reasons of high polarity, these cellulose particles have an unfortunate tendency in the elastomeric matrix to agglomerate with each other. These interactions have the detrimental consequence of limiting the dispersion of the charge and therefore the reinforcing properties to a level substantially lower than that which it would be theoretically possible to achieve if all the connections (charge / elastomer) that can be created during the mixing operation, were actually obtained; these interactions tend on the other hand to increase the consistency in the green state of the rubber compositions and thus to make their implementation ("processability") more difficult than in the presence of carbon black.

To "couple" this reinforcing filler to the diene elastomer, that is to say to ensure the connection between said filler and the elastomer, it is therefore necessary to use a coupling agent (or binding agent) or modify the surface of this charge to ensure a sufficient connection, chemical and / or physical, between the charge (surface of its particles) and the diene elastomer.

Thus, JP2009191198 discloses a rubber composition comprising cellulose nano fibers obtained by liquid mixing in an aqueous medium of the elastomer and cellulose fibers in the presence of a silane coupling agent to improve the adhesion of the fibers. and elastomer.

EP 2072 574 describes the use of chemically modified cellulose microfibrils by an acetylation reaction, alkyl esterification, complex esterification, keto-esterification, alkyl carbamation or aryl carbamation, as as a reinforcing filler in a rubber composition.

The processes for implementing and modifying cellulose are limited by the polar and hydrophilic nature of its surface, which leads to obtaining strong interactions between the surfaces of the substrate, and with polar and protic solvents. Thus, during the evaporative drying of a cellulose suspension, the dry form obtained is aggregated and has a small specific surface area limiting its reinforcing nature. The alternative generally used is to make a premix or masterbatch of the filler and the matrix in suspension, for example using a latex in water. However, the chemical modification of the cellulose in the aqueous medium is limited because of the low reactivity of the substrate and the highly protic nature of the water. It is then possible to use organic solvents to allow this modification. However, cellulose has a strong tendency to aggregate more or less irreversibly depending on the polarity of the solvent used. Moreover, these environments pose problems of toxicity and are not respectful of the environment.

P10-2884 / SC The subject of the invention is the use of cellulose as reinforcing filler of a rubber composition, that is to say capable of reinforcing on its own, without any other means than an intermediate coupling agent, a diene rubber composition. intended for the manufacture of tires, in other words able to replace, in its reinforcing function, a conventional load of carbon black or silica pneumatic grade.

The Applicant has surprisingly discovered that the cellulose formed of microfibrils, chemically modified by grafting on said cellulose coupling agent molecules, could play this role of reinforcing filler, and in particular the cellulose in the form of an airgel or finely divided cellulose powder.

It should be noted that, in a manner known to those skilled in the art, airgel means a gel-like material in which the liquid component is replaced by gas. It is a solid with very low density with several remarkable properties, including a very large accessible surface with a significant value of the ratio between the surface and the mass.

In addition, in the present patent application, the term "cellulose powder" is understood to mean a solid divided into fine particles, these particles being made of cellulose, or even airgel of cellulose, and having a significant value of the ratio between the surface and the mass. .

The subject of the invention is therefore a rubber composition based on at least one diene elastomer and at least one reinforcing filler, this reinforcing filler comprising cellulose grafted with coupling agent molecules capable of binding it to Diene elastomer, these molecules comprising at least one function A and one function B such that:

A represents a functional group ("A" function) capable of binding chemically to cellulose, and which comprises at least one heteroatom chosen from oxygen, phosphorus, halogens, nitrogen and sulfur,

- B represents a functional group (function "B") capable of binding physically and / or chemically to the diene elastomer;

the functions A and B being connected by a group X at least divalent. According to one embodiment of the invention, A is chosen from acyl chlorides, anhydrides, carboxylic acids, isocyanates, organic or inorganic esters, alkyl chlorides and epoxides.

According to another embodiment of the invention, B carries mono or polysulfide functions.

P10-2884 / SC Advantageously, the coupling agent corresponds to formula (I): AXB, in which the group X represents a divalent linking group comprising from 1 to 18 carbon atoms, preferably a C 1 -C 18 alkylene group or a group arylene in

According to another variant embodiment of the invention, the coupling agent corresponds to formula (II):

AT

A-X-B,

in which the X group represents a trivalent group

According to another variant embodiment of the invention, the coupling agent corresponds to formula (III): AXBXA, in which the group X represents a divalent linking group comprising from 1 to 18 carbon atoms, preferably a group C1-C18 alkylene or a C6-C12 arylene group, preferably B is Sp where p is a number greater than or equal to 2, preferably 2 to 8 (preferably 2 to 5).

The invention also relates to a tire comprising a composition as described above.

The subject of the invention is also a cellulose formed of micro fibrils, chemically modified by grafting onto said cellulose coupling agent molecules capable of binding it to a diene elastomer, these molecules comprising at least one function A and one function B such as than :

the functions A and B being connected by an at least divalent group X; said cellulose being in the form of an airgel or a cellulose powder.

The invention finally relates to a process for obtaining an airgel or a cellulose powder as described above.

I. MEASUREMENTS AND TESTS USED

P10-2884 / SC Bonding rate of the coupling agent on cellulose a) Gravimetric measurement of DSg (degree of gravimetric substitution)

The measurement of a degree of functionalization of the load, here called DS, can be performed from gravimetric measurements. This quantity then makes it possible to quantify within the modified filler, the graft fraction and the rigid phase fraction.

Protocol

For a CellOH + RX → CellOR + HX reaction

With Cell the cellulosic substrate, RX the graft and X the leaving group

A quantity of cellulose airgel between 1 and 10 g is stored in a beaker of 50 to 500 ml previously tared on a Mettler AE 163 scale providing a measurement with an accuracy of 4 * 10 ^-4 g.

The substrate is dried for at least 6 h at 60 ° C. in a Jouan oven.

The dry substrate is weighed on a Mettler AE 163 providing a measure with an accuracy of 4 * 10 ^"4 g (m _this ii i).

After reaction and purification, the product is stored in a beaker of 50 to 500 ml previously calibrated on a Mettler AE 163 scale providing a measurement with an accuracy of 4 * 10 ^"4 g.

The product is dried for at least 6 hours at 60 ° C. in a Jouan oven.

The dry product was weighed on a Mettler AE 163 providing a measure with an accuracy of 4 * 10 ^"4 g (m _this ii F).

The DSg is then obtained using the formula:

DS _g = (m _C eii F - mceu i) mceu i * 162 / (M _R / fM _HX )

With molar mass of M _R reagent, 162 molecular weight of the anhydroglucose unit and Μχ molar mass of the leaving group X, and f number of reactive functions of the graft.

Moreover, it is also possible to evaluate the graft mass gain of the substrate for the formulation of the charge in the material:

% graft = (m _ce ii _F - m _ce in) / m _ce in * 100 b) Spectroscopic measurements to confirm the presence of a graft

The control of the chemical modification can be reinforced by the use of spectroscopic techniques sensitive to the chemical environment, in our case IR and solid NMR. For example, in the case where the graft is an acyl chloride, it is observed by Infra-Red the appearance of a vibration band of the carbonyl function at about 1750 cm ^-1 distinct from that of the acyl chloride ( reagent, 1800 cm ^-1 ), and carboxylic acid (hydrolyzed reactant, 1700 cm ^-1 ), For the same case, in solid NMR, the carbon of carbonyl function appears to be about 175 This signal is present in the ester (product), but also in the reagent which also has a specific band at 45 ppm, which makes it possible to differentiate them.It is also present in the acid (hydrolysed reagent) but has was then identified at around 180

P10-2884 / SC ppm. Thus, these techniques make it possible to characterize the presence of the chemical bond of the graft with the cellulose.

IR protocol

About 1 mg of product and 100 mg of KBr are mixed in a mortar with a pestle. The resulting powder is pressed as a pellet at 3000 psi for one minute. The pellet is analyzed on Perkin Elmer 1720X Fourier Transform IR (FTIR) equipment by 8 acquisitions between 400 and 4000 cm ^-1 .

NMR protocol for solid

About 100 mg of product are introduced into a zirconium rotor.

The analyzes are carried out on a Brucker Avance 400 MHz spectrometer, by magic angle rotation (MAS) at 12000Hz, accumulating about 2000 acquisitions. c) Estimation of the hydroxyl density on a crystalline cellulose surface

We consider the crystalline structure of the allomorph Ιβ, which is widespread among the native cellulose structures of higher plants. Consideration of the other allomorph as found in the primitive walls, algae or in cellulose derived from bacteria brings only minor modifications. Considering a monocrystal of square section of dimension a, and of length L in the direction corresponding to the chain axis. The interchain distances are 0.54 and 0.6 nm (see figure). For the rest of the treatment, an average distance of 0.57 nm is considered. In addition, two anhydroglucose units represent a length of 1.038 nm for six hydroxyl functions, only half of which are considered to be accessible on the surface of the crystalline structure.

We can then estimate the surface density of hydroxyl functions as being:

Density OH / nm ² area = 3 / (0.57 * 1.038) ~ 5 d) Calculation of an equivalent square section from a specific surface area

A specific surface area, Ssp in m ² / cc, can be converted to a lateral dimension of an equivalent square-section square fiber a in nm, using the following relationship:

P10-2884 / SC a = 4 * 1000 / Ssp

For the conversion of a BET in m ² / g a crystalline density value of the cellulose of 1.5 is used.

e) Surface area DS calculation and conversion to link rate

We consider the crystalline structure of the allomorph Ιβ, always with an average interchain distance of 0.57 nm.

Considering a monocrystal of square section of dimensions a (parameter obtainable from the specific surface).

The number of chains n by section a is worth:

n = a / 0.57

The number of surface chains is then worth:

% chain area = 4 * n / (n + 1) ²

Whereas only half of the 3 hydroxyl functions per unit

anhydroglucose occurs outside the crystalline structure, we obtain:

DS max area =% chain area * 3/2

Considering a surface grafting, and that DS max area equals 5 bonds per nm ² , DSg can then be converted into bond density by the formula:

Bond density = 5 * DSg / DS max area

The protocol can be followed identically in the case of a cellulose powder.

BET specific surface area

In the present disclosure, the BET surface area is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938, more precisely according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - with a modification compared to the standard by applying a degassing for 5 hours at 50 ° C - relative pressure range p / po: 0.05 to 0.17)

Traction tests

These tests make it possible to determine the elasticity stresses and the properties at break; those carried out on the cooked mixtures are made according to the AFNOR-NF-T46-002 standard of September 1988. The true secant modules (in MPa) are measured at 50% elongation (M50) and 150% elongation ( M 150). Unless otherwise indicated in the text, all these tensile measurements are carried out under the normal conditions of temperature and hygrometry according to the AFNOR-NF-T40-101 standard of December 1979. The M150 / M50 ratio is a good indicator of the reinforcement obtained. for a given composition.

P10-2884 / SC II. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a rubber composition based on at least one diene elastomer and at least one reinforcing filler, said reinforcing filler comprising cellulose grafted with coupling agent molecules capable of binding to the diene elastomer, these molecules comprising at least one function A and one function B such that:

the functions A and B being connected by a group X at least divalent.

Advantageously, this grafted cellulose is in the form of an airgel or a cellulose powder.

The present invention also relates to cellulose formed of micro fibrils, chemically modified by grafting on said cellulose coupling agent molecules capable of binding to a diene elastomer, these molecules comprising at least one function A and one function B such that :

the functions A and B being connected by an at least divalent group X; said cellulose being in the form of an airgel or a powder of celllulose.

By the term "composition-based" is meant a composition comprising the mixture and / or the reaction product of the various constituents used, some of these basic constituents being capable of or intended to react with one another, less in part, during the various phases of manufacture of the composition, in particular during its crosslinking or vulcanization.

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass. On the other hand, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e. terminals a and b excluded) while any range of values designated by the term "from a to b" means the range from a to b (i.e., including the strict limits a and b).

P10-2884 / SC Airgel and cellulose powder

Cellulose is an organic polymer of formula

It is a linear homopolymer composed of numerous D-Anhydroglucopyranose (AGU) units linked together by β- (1 → 4) glyco diket linkages. These linear chains are maintained in extended conformation by intramolecular bonds and associate with each other by intermolecular side bonds of the hydrogen bonding type, which gives the cellulose its fibrous and rigid structure.

The following schematic representation illustrates the inter and intramolecular hydrogen bonds of the 2 allomorphs of cellulose.

The cellulose microfibrils are derived from biosynthetic processes and are in the form of objects of nanometric diameter (typically 4 to 1000 nm in diameter) and of indefinite length well above one micron. They consist of a succession of zones with long macromolecular chains aligned in the fiber direction (nanocrystals) and short disordered amorphous zones (defects).

The individualization of the micro-fibrils (or micro-fibrillation) can be obtained by known methods of high-pressure mechanical homogenization, as described by way of example in the document USP 4,483,743, AF Turbak, "Microfibrillated cellulose", 1984, USA, or enzymatic or chemical or a combination of several of these techniques on cellulosic substrates such as paper pulps, agricultural waste, by-products of the food industry or any other cellulosic source terrestrial or marine, d animal, plant or microbial origin. All these processes have in common the obtaining of a suspension of microfibrils of diameter

P10-2884 / SC nanometer whose precise characteristics will depend on both the process and the origin.

It can for example be obtained from the hardwood pulp that is treated on a refiner (as marketed for example by Valley). Then the fiber dispersion is treated in a high pressure homogenizer (such as, for example, high pressure homogenizers marketed by the company APV Manton). The product obtained is a dispersion in water having mass concentrations of the order of 1 to 2%.

The drying step is then carried out by any method preserving the accessibility of the cellulose surfaces and therefore the formation of airgel or powders having a much larger surface area than a simple evaporative drying and a much less dense structure. The use of cryoprotectant additive, rapid freezing, atomization (or spray-drying), supercritical CO 2, fluidized bed drying or lyophilization from a solvent can thus be mentioned in a non-limiting manner. non-crystallizable. The suspension may be previously pre-concentrated by centrifugation, by gravity filtration or under vacuum or by osmotic pressure or by means of an evaporator / concentrator (Rotavapor).

Thus, the colloidal dispersion formed by the cellulose microfibrils can be, for example, centrifuged and then redispersed in tertbutanol alcohol, then frozen in liquid nitrogen and then freeze-dried in order to obtain a cellulose airgel formed of micro-fibrils. The use of this alcoholic solvent before the drying step by lyophilization avoids aggregation of the particles and therefore the formation of open aerogels to have a larger surface area.

A cellulose airgel is thus obtained, the BET specific surface area is greater than or equal to 10 mVg, and preferably greater than or equal to 50 m ² / g.

The airgel obtained or the cellulose powder is then subjected to modification by a graft (the reaction pattern of which follows) carried out in a heterogeneous phase on the surface of the particles and in particular in the gas phase in order to graft a coupling agent onto the microparticles. fibrils of cellulose.

Cell-OH + RX Cell-O-Pv + HX

P10-2884 / SC

In order to graft the coupling agent onto the cellulose microfibrils, the previously obtained airgel or the powder undergoes a substitution reaction which is preferably carried out in the heterogeneous phase, in particular in the gas phase.

The reactions for forming the covalent bond are those conventionally described in the field of cellulose chemistry and may be, without being exhaustive, carried out by esterification from acid derivatives chosen in particular from acyl chloride, anhydrides, the carboxylic acids, by carbamylation with isocyanates, by acetalization with aldehydes or by etherification from alkyl chlorides or epoxide. They can be easily carried out on a native cellulose substrate or on an oxidized substrate, or selectively in C6 (TEMPO, NO2 oxidation) or by oxidative cleavage of the C2-C3 glycol linkage (oxidation periodate). On the oxidized substrates, the modification can be carried out by ester formation with the aid of organic or inorganic alcohol or esters, or else alkylating agents, by formation of acyl chloride by SOCL2, anhydrides with a carboxylic acid, and or by amidation with amines (carboxylic acid) or imines (aldehydes). Advantageously, the reaction is carried out by placing in a reactor, the airgel or the powder, formed of cellulose microfibrils and the reagent at a temperature and pressure that are stable so as to vaporize the reagent, and introducing a controlled flow of nitrogen through the reactor inlet; the reaction products (leaving groups and / or reagent residues) being discharged through the outlet connected to a vacuum pump. The reagent can also be vaporized separately and introduced into the reactor chamber.

Other equivalent methods of heterogeneous phase grafting are possible, in particular in the case of a cellulose powder, grafting in a fluidized bed by a stream of vaporized reagent. The degree of grafting of the cellulose is preferably greater than 0.1 bonds per nm ² measured by gravimetry and relative to the BET surface, it varies more preferably from 1 to 20 bonds per nm ² and even more preferably from 3 to 12 bonds. by nm ² , and even more preferably from 3 to 6 bonds per nm ² .

P10-2884 / SC Coupling agent

The coupling agent is in the form of molecules comprising at least one function A and one function B such that:

the functions A and B being connected by a group X at least divalent.

As specified in the preceding paragraph, A is preferably chosen from acyl chlorides, anhydrides, carboxylic acids, isocyanates, alkyl chlorides, organic or inorganic esters, aldehydes, epoxides or amines, primary or secondary.

Preferentially B carries mono or polysulfide functions.

The coupling agent may correspond to formula (I): AXB, in which X represents a divalent linking group comprising from 1 to 18 carbon atoms, and preferably a C 1 -C 18 alkylene group or a C 5 arylene group. ₆ -C 12, more particularly a C 1 -C 10 alkylene group, especially a C 1 -C 4 alkylene group.

According to another embodiment of the invention, the coupling agent corresponds to formula (II):

AT

A-X-B, wherein X is a trivalent group such as tri-substituted cycloalkyl, especially tri-substituted cyclohexane. Advantageously, when the coupling agent corresponds to formula (I) or to formula (II), B is in the form of a blocked mercapto function of formula:

- S _m - C (= 0) - R in which:

R represents hydrogen or a monovalent hydrocarbon group chosen from alkyls, linear or branched, cycloalkyls or aryls, having from 1 to 18 carbon atoms,

m is a number greater than or equal to 1; m preferably ranges from 1 to 8, even more preferably m is equal to 1 (preferably from 2 to 5).

P10-2884 / SC According to another preferred variant, B is in the form of a polysulfurized function of formula:

- S _r - R in which:

R represents a monovalent hydrocarbon group chosen from alkyls, linear or branched, cycloalkyls or aryls, having from 1 to 30 carbon atoms,

r is a number greater than or equal to 2, preferably from 2 to 8 (preferably from 2 to 5).

According to another embodiment, the coupling agent corresponds to formula (III): ## STR2 ## in which:

the group X represents a divalent linking group comprising from 1 to 18 carbon atoms, preferably a C 1 -C 18 alkylene group or an arylene group in

According to an advantageous variant embodiment, B represents S _p where p is a number greater than or equal to 2, preferably from 2 to 8 (preferably from 2 to 5). Particularly suitable 3,3'-dithio-dipropionic acid chloride.

Reinforcing charge

The composition in accordance with the invention comprises at least one reinforcing filler comprising a cellulose grafted with coupling agent molecules as described in the preceding paragraphs.

Advantageously, this grafted cellulose represents the majority reinforcing filler. Preferably it is in the form of an airgel or a chemically modified cellulose powder as described above.

The reinforcing filler may also comprise other fillers, in particular with an organic filler and / or an inorganic filler.

P10-2884 / SC As organic filler, especially carbon blacks, especially reinforcing carbon blacks of the series 100, 200 or 300 (ASTM grades), such as blacks NI 15, N134, N234, N326, N330, N339, N347 , N375, or, depending on the intended applications, blacks of higher series (for example N400, N660, N683, N772).

By "reinforcing inorganic filler" must be understood here, in known manner, any inorganic or mineral filler, regardless of its color and origin (natural or synthetic), also called "white" charge, "clear" charge or "black non-black" filler as opposed to carbon black, this inorganic filler being capable of reinforcing on its own, without any other means than an intermediate coupling agent, a rubber composition intended for manufacturing a tire tread, in other words able to replace, in its reinforcing function, a conventional tire grade carbon black for tread. Such a filler is generally characterized by the presence of functional groups, in particular hydroxyl (-OH), at its surface, thereby requiring the use of an agent or coupling system intended to ensure a stable chemical bond between the isoprene elastomer and said charge. Preferably, the reinforcing inorganic filler is a filler of the siliceous or aluminous type, or a mixture of these two types of filler.

The silica (SiO ₂ ) used may be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica having a BET surface and a CTAB specific surface area both less than 450 m ² / g, preferably 30 to 400 m ² / g.

Preferably, the total reinforcing filler content will be chosen between 10 and 200 phr, more preferably between 10 and 150 phr, more preferably between 20 and 110 phr.

Diene elastomer

The composition according to the invention comprises at least one diene elastomer.

By "diene" elastomer (or indistinctly rubber), whether natural or synthetic, must be understood in known manner an elastomer consisting at least in part (ie, a homopolymer or a copolymer) of monomeric diene units (monomers carrying two carbon-carbon double bonds, conjugated or not).

P10-2884 / SC These diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". The term "essentially unsaturated" is generally understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a level of units or units of diene origin (conjugated dienes) which is greater than 15% (mol%); Thus, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the above definition and may in particular be described as "substantially saturated" diene elastomers ( low or very low diene origin, always less than 15%). In the category of "essentially unsaturated" diene elastomers, the term "highly unsaturated" diene elastomer is particularly understood to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.

Given these definitions, the term "diene elastomer" can be understood more particularly to be used in the compositions according to the invention:

(a) - any homopolymer of a conjugated diene monomer, especially any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b) - any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

(c) - a ternary copolymer obtained by copolymerization of ethylene, an α-olefin having 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, for example elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene;

(d) - a copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated versions, in particular chlorinated or brominated, of this type of copolymer. Although it applies to any type of diene elastomer, the person skilled in the tire art will understand that the present invention is preferably implemented with essentially unsaturated diene elastomers, in particular of the type (a) or (b). ) above. By way of conjugated dienes 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C 1 -C 5) alkyl-1,3-butadienes, such as for example 2 3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1, 3-butadiene, aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinylaromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial vinyl-toluene mixture, para-methylstyrene and the like.

P10-2884 / SC tert-butylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene, vinylnaphthalene.

The copolymers may contain between 99% and 20% by weight of diene units and between 80% and 80% by weight of vinylaromatic units. The elastomers may have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the amounts of modifying and / or randomizing agent used. The elastomers can be for example block, statistical, sequenced, microsequenced, and be prepared in dispersion or in solution; they may be coupled and / or starred or functionalized with a coupling agent and / or starring or functionalization. For coupling with carbon black, there may be mentioned, for example, functional groups comprising a C-Sn bond or amino functional groups such as aminobenzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may be made, for example, of silanol or polysiloxane functional groups having a silanol end (as described for example in FR 2 740 778 or US Pat. No. 6,013,718 and WO 2008/141702) , alkoxysilane groups (as described for example in FR 2,765,882 or US 5,977,238), carboxylic groups (as described for example in WO 01/92402 or US 6,815,473, WO 2004/096865 or US 2006 / 0089445) or polyether groups (as described for example in EP 1 127 909 or US 6,503,973, WO 2009/000750 and WO 2009/000752).

Functional elastomers that may be mentioned are those prepared by the use of a functional initiator, especially those carrying an amine or tin function (see, for example, WO 2010072761).

As other examples of functionalized elastomers, mention may also be made of elastomers (such as SBR, BR, NR or IR) of the epoxidized type.

Suitable polybutadienes and in particular those having a content (mol%) in units -1.2 between 4%> and 80%> or those having a content (%> molar) in cis-1,4 greater than 80%> polyisoprenes, butadiene-styrene copolymers and in particular those having a Tg (glass transition temperature (Tg, measured according to ASTM D3418) between 0 ° C. and -70 ° C. and more particularly between -10 ° C. and 60 ° C, a styrene content of between 5% and 60% by weight and more particularly between 20% and 50%, a content (%> molar) in -1,2 bonds of the butadiene part between 4% and 75%, a content (mol%) of trans-1,4 bonds of between 10% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content of between 5% and 90%. % by weight and a Tg of -40 ° C to -80 ° C, the isoprene-styrene copolymers and especially those having a styrene content of between 5% and 50% by weight and a e Tg between -5 ° C and -50 ° C. In the case of butadiene-styrene-isoprene copolymers, it is particularly suitable for those having a

P10-2884 / SC styrene content between 5% and 50% by weight and more particularly between 10%> and 40%>, an isoprene content of between 15% and 60% by weight and more particularly between 20% and 50%, a content of in butadiene of between 5% and 50% by weight and more particularly between 20% and 40%, a content (mol%) in -1,2 units of the butadiene part of between 4% and 85%; content (mol%) in trans-1,4 units of the butadiene part of between 6% and 80%, a content (mol%) in units -1,2 plus -3,4 of the isoprene part of between 5% and 70% and a content (mol%) in trans units -1.4 of the isoprene part of between 10% and 50%), and more generally any butadiene-styrene-isoprene copolymer having a Tg of between -5 ° C. and 70 ° C.

In summary, the diene elastomer (s) of the composition according to the invention are preferably chosen from the group of highly unsaturated diene elastomers consisting of polybutadienes (abbreviated as "BR"), synthetic polyisoprenes (IR) and natural rubber ( NR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR) and isoprene-copolymers. butadiene-styrene (SBIR).

According to one particular embodiment, the diene elastomer is predominantly (ie, for more than 50 phr) an SBR, whether it is an emulsion-prepared SBR ("ESBR") or an SBR prepared in solution ("SSBR"), or a blend (blend) SBR / BR, SBR / NR (or SBR / IR), BR NR (or BR / IR), or SBR BR NR (or SBR / BR / IR). In the case of an SBR elastomer (ESBR or SSBR), an SBR having an average styrene content, for example between 20% and 35% by weight, or a high styrene content, for example 35% by weight, is used in particular. at 45%, a vinyl content of the butadiene part of between 15% and 70%, a content (mol%) of trans-1,4 bonds of between 15% and 75% and a Tg of between -10 ° C. and - 55 ° C; such an SBR can be advantageously used in admixture with a BR preferably having more than 90% (mol%) of cis-1,4 bonds.

According to another particular embodiment, the diene elastomer is predominantly (for more than 50 phr) an isoprene elastomer. This is particularly the case when the compositions of the invention are intended to constitute, in tires, the rubber matrices of certain treads (for example for industrial vehicles), crown reinforcing plies (for example work webs, protective webs or hoop webs), carcass reinforcement plies, flanks, beads, protectors, underlayments, rubber blocks and other internal gums providing the interface between aforementioned areas of the tires.

P10-2884 / SC By "isoprene elastomer" is meant in known manner a homopolymer or copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), different isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will in particular be made of copolymers of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene (SBIR). This isoprene elastomer is preferably natural rubber or synthetic cis-1,4 polyisoprene; of these synthetic polyisoprenes, polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used.

According to another particular embodiment, especially when it is intended for a tire sidewall, a tubeless tire sealing inner liner (or other airtight element), the composition according to the invention may contain less than an essentially saturated diene elastomer, in particular at least one EPDM copolymer or a butyl rubber (optionally chlorinated or brominated), that these copolymers are used alone or in admixture with highly unsaturated diene elastomers as mentioned above, in particular NR or IR, BR or SBR. According to another preferred embodiment of the invention, the rubber composition comprises a blend of one (or more) diene elastomers called "high Tg" having a Tg between -70 ° C and 0 ° C and d one (or more) diene elastomers known as "low Tg" between -110 ° C and -80 ° C, more preferably between -105 ° C and -90 ° C. The high Tg elastomer is preferably selected from the group consisting of S-SBR, E-SBR, natural rubber, synthetic polyisoprenes (having a (mol%) content of cis-1,4 linkages of preferably greater than 95%>), BIR, SIR, SBIR, and mixtures of these elastomers. The low Tg elastomer preferably comprises butadiene units at a level (mol%) of at least 70%); it consists preferably of a polybutadiene (BR) having a content (mol%) of cis-1,4 chains greater than 90%.

According to another particular embodiment of the invention, the rubber composition comprises, for example, from 30 to 100 phr, in particular from 50 to 100 phr, of a high Tg elastomer in a blend with 0 to 70 phr, in particular from 0 to 50 phr, of a low Tg elastomer; according to another example, it comprises for all 100 pce one or more SBR prepared (s) in solution.

According to another particular embodiment of the invention, the diene elastomer of the composition according to the invention comprises a blend of a BR (as low elastomer Tg) having a rate (mol%) of cis chains -1.4 greater than 90%, with one or more S-SBR or E-SBR (as elastomer (s) high Tg).

P10-2884 / SC The composition according to the invention may contain a single diene elastomer or a mixture of several diene elastomers, the diene elastomer or elastomers which may be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.

Crosslinking system The crosslinking system is preferably a vulcanization system, that is to say a system based on sulfur (or a sulfur-donor agent) and a primary vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the production phase as described later, various known secondary accelerators or vulcanization activators such as zinc oxide. stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine).

Sulfur is used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The primary vulcanization accelerator is used at a preferred level of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr.

As accelerator (primary or secondary) can be used any compound capable of acting as an accelerator of vulcanization of diene elastomers in the presence of sulfur, in particular thiazole-type accelerators and their derivatives, accelerators of thiuram type, zinc dithiocarbamates. These accelerators are for example selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), tetrabenzylthiuram disulfide ("TBZTD"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N, N dicyclohexyl-2-benzothiazyl sulphenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulphenamide ("TBBS"), N-tert-butyl-2-benzothiazyl sulphenimide ("TBSI"), zinc dibenzyldithiocarbamate (" ZBEC ") and mixtures of these compounds.

Various additives The rubber compositions in accordance with the invention may also comprise all or part of the usual additives normally used in elastomer compositions intended for the manufacture of tires, in particular treads, for example plasticizers or oils. of extension, whether these are of aromatic or non-aromatic nature, pigments, protective agents such as anti-ozone waxes, chemical antiozonants, anti-oxidants, agents

P10-2884 / SC anti-fatigue, reinforcing resins, acceptors (for example phenolic novolak resin) or methylene donors (for example HMT or H3M) as described for example in application WO 02/10269, a crosslinking system based on either sulfur, either of sulfur and / or peroxide and / or bismaleimide donors, vulcanization accelerators, vulcanization activators.

Preferably, these compositions comprise, as preferential non-aromatic or very weakly aromatic plasticizing agent, at least one compound chosen from the group consisting of naphthenic, paraffinic, MES, TDAE, ester (especially trioleate) oils. glycerol, the hydrocarbon plasticizing resins having a high Tg preferably greater than 30 ° C, and mixtures of such compounds.

These compositions may also contain, in addition to the coupling agents, coupling activators, reinforcing filler recovery agents or, more generally, processing aid agents that are capable in a known manner, by means of an improvement in the dispersion of the filler in the rubber matrix and a lowering of the viscosity of the compositions, to improve their ability to implement in the green state. To the reinforcing filler described above, may also be added, depending on the intended application, inert fillers (ie, non-reinforcing) such as clay particles, bentonite, talc, chalk, kaolin, used for example in flanks or treads of colored tires. Manufacture of rubber compositions

The rubber compositions of the invention are manufactured in appropriate mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art: a first phase of work or thermomechanical mixing (sometimes called phase "non-productive") at a high temperature, up to a maximum temperature of between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C, followed by a second mechanical working phase (sometimes referred to as "Productive" phase) at lower temperature, typically below 120 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system or vulcanization.

III-EXAMPLES OF CARRYING OUT THE INVENTION

P10-2884 / SC The following examples illustrate the invention, the latter can not however be limited to these examples only.

III- 1 Preparation of chemically modified cellulose aerogels. a) Preparation of Aerogels A ', A "of Microfibrils of Cellulose

The airgel of cellulose microfibrils A is obtained from the hardwood pulp obtained by sulphite treatment.

The pulp is treated on a refiner (model marketed by Valley Laboratory Equipment of the Voith brand Serial No. 109-F-1627 X81734, 22L capacity) at the concentration of 2% by weight for 6 hours.

Then 1.5 L of the fiber dispersion is treated in a high-pressure homogenizer (homogenizer model 15MR-8TB A, marketed by the company APV Manton) at 500 kg / cm ² for 45 minutes.

The whole of this suspension is adjusted to the concentration of 1.25% by weight and divided into 300mL batches, these batches being frozen in liquid nitrogen and freeze-dried in order to obtain a low specific surface area. The airgel A 'is thus obtained.

Part of the aqueous dispersion obtained undergoes a different treatment, being centrifuged for 30 minutes at a speed of 11200 rpm at 25 ° C. The cake thus obtained is redispersed in pure terbutanol to a concentration of 1.25% by weight in a homogenizer such as UltraTurrax. The suspension obtained is freeze-dried in order to obtain a high surface area airgel: "open" aerogel A. After drying, the aerogels are stored at 60 ° C. until the start of the esterification reaction to avoid a return to water. aerogels.

The specific surfaces of the different aerogels obtained are measured and presented in Table 1. b) Preparation of Ag '"Ag" calibrated aerogels

In order to graft the coupling agent onto the cellulose microfibrils, the previously obtained aerogels undergo esterification in the gas phase. The aerogels are thus contacted with acyl chloride in a 2L reactor at a controlled temperature under a controlled flow of nitrogen through the reactor inlet; the reaction products (hydrochloric acid and reagent residues) being discharged through the outlet connected to a vacuum pump.

P10-2884 / SC Thus approximately 5 g of cellulose airgel are placed on a 5 cm grid above the reagent (coupling agent) in order to avoid direct contact between the airgel and the reagent. Two reagents are used for each airgel: respectively a non-reactive hydrophobation agent on the polymer, C16 palmitic acid chloride of formula CH ₃ (CH ₂ ) ₄ COCl and the coupling agent 3,3 'chloride of dithiodipropanoyl (DTDPC).

The latter reagent, DTPC, is synthesized as follows:

weighed in a weighed IL glass flask, 100 g of 3,3'-dithiodipropionic acid

(CAS 1119-62-6, MM = 210.27g / mol, 99% pure, supplied by Aldrich); Addition under protective hood (glove, telescope) 4 molar equivalents of pure thionyl chloride or 226.37g ( CAS 7719-09-7, MM = 119 g / mol, supplied by Aldrich), installation of the flask on a mounting in a hood with coolant, magnetic stirring and oil bath at a temperature of 50 ° C, for a duration of 72 hours;

disassembly of the flask and purification by vacuum extraction of the residues at about 1 mbar and 50 ° C for 6 hours using Buchi Rotavapor equipment, storage of the product in a sealed container in the refrigerator at 5 ° C,

product quality control by liquid NMR.

For each of the aerogels obtained above, the operating conditions followed as well as the reagents are detailed in Table 2, in particular the molar ratio of the acyl functions introduced into the reactor relative to the number of moles of anhydroglucose unit of the cellulose.

The grafting rates of the graft aerogels obtained are shown in Table 3.

III-2 Preparation of rubber compositions

The following tests are carried out in the following manner: an internal mixer with a volume of 28 cm.sup.3 ("Brabender" brand model FD0234H), filled to 70% and having an initial tank temperature of about 90, is introduced. ° C. at 85 rpm, the diene elastomer (SBR), the reinforcing filler (silica or grafted airgel) supplemented with a small amount of carbon black, the coupling agent if appropriate and then, after one to two minutes mixing, the various other ingredients with the exception of the vulcanization system. Theromechanical work (non-productive phase) is then carried out in one step (total mixing time equal to about 5 minutes), until a maximum "falling" temperature of about 165 ° C. is reached. The mixture thus obtained is recovered, cooled and the vulcanization system (sulfur and sulfenamide accelerator) is added to the mixer at 70 ° C. at 20 rpm, mixing the whole (productive phase) for about 5 to 6 minutes. .

P10-2884 / SC The compositions thus obtained are then hot pressed ("Carver" press with heating plates) in the form of plates (thickness 0.8 mm) of rubber for the measurement of their physical or mechanical properties. III-3 Test

This test aims to demonstrate the interest of graft aerogels according to the invention as reinforcing filler of rubber compositions.

For this purpose, 6 diene elastomer (SBR) compositions reinforced respectively by silica (control composition) and various cellulose aerogels were prepared according to the process described in section III-2.

These compositions all correspond to the basic formulation, expressed in parts by weight per hundred parts of elastomers, phr, which follows:

SBR (l) 100

Carbon black (2) 3

Antioxidant (3) 2

DPG (4) 0.9

Stearic acid 2

ZnO 2.5

Sulfur 1, 5

Accelerator (5) 2,5

(1) SBR marketed by Lanxess under the name "VSL 2525-OM" (having 25% of styrene unit, 25% of unit 1, 2, Tg = -54 ° C.)

(2) N234

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

(4) diphenylguanidine (Perkacit DPG from Flexsys)

(5) N-cyclohexyl-2-benzothiazyl sulfenamide ("Santocure CBS" from Flexsys).

These different compositions differ from each other essentially by the following technical characteristics:

Cl is a composition not in accordance with the invention comprising an ungrafted aerogel A 'as a reinforcing filler,

C2 is a composition not in accordance with the invention comprising an ungrafted airgel A '' as a reinforcing filler,

C3 is a composition not in accordance with the invention comprising an aerogel A 'grafted with palmitic acid chloride, as a reinforcing filler

P10-2884 / SC C4 is a composition according to the invention comprising an airgel A 'grafted with DTDPC, as a reinforcing filler,

C5 is a composition not in accordance with the invention comprising a palmitic acid chloride-grafted aerogel A, as a reinforcing filler,

C6 is a composition according to the invention comprising an airgel A "grafted with DTDPC, as a reinforcing filler.

It should be noted that all the compositions comprise 100 phr of SBR. The content (in phr) of cellulose microfibrils and the level of the grafted compounds were calculated using the elements of Table 3 for each composition. It will be noted that the differences in the content of cellulose microfibrils (Table 4) correspond for all the compositions to an identical percentage by volume of cellulose microfibrils (this percentage being defined by the ratio of the volume of microfibrils of cellulose to the volume total constituents of the composition)

The reinforcing properties of these compositions are measured after firing at 150 ° C for 60 minutes, the results obtained are shown in Table 5.

The observation in Table 5 shows that non-grafted cellulose aerogels (such as those contained in compositions C1 and C2) do not make it possible to obtain satisfactory reinforcement (very low or non-measurable M150 / M50 values).

Compositions C3 and C5 including palmitic acid chloride-grafted cellulose aerogels exhibit insignificant reinforcement (value less than 1), however these values remain very low for use in a tire rubber composition. In contrast, the compositions according to the invention C4 and C6 have reinforcing properties corresponding to acceptable values for tire rubber compositions.

Thus, cellulose aerogels formed of microfibrils, chemically modified by grafting on said cellulose coupling agent molecules according to the invention, can surprisingly act as a reinforcing filler for rubber compositions for tires.

P10-2884 / SC Table 1

Table 2

P10-2884 / SC Table 3

Table 4

Table 5

P10-2884 / SC

Claims

A rubber composition based on at least one diene elastomer and at least one reinforcing filler, said reinforcing filler comprising cellulose grafted with coupling agent molecules capable of binding to the diene elastomer, these molecules comprising at least one function A and one function B such that:

the functions A and B being connected by a group X at least divalent.

The composition of claim 1, wherein the diene elastomer is selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers and mixtures of these elastomers.

A composition according to any of claims 1 or 2, wherein A is selected from acyl chlorides, anhydrides, carboxylic acids, isocyanates, alkyl chlorides, organic or inorganic esters, aldehydes, epoxides or amines, primary or secondary.

A composition according to any of claims 1 or 2, wherein B bears mono or polysulfide functions.

Composition according to any one of Claims 1 to 4, in which the coupling agent corresponds to formula (I): A-X-B,

wherein the group X represents a divalent linking group having 1 to 18 carbon atoms, preferably a C 1 -C 18 alkylene group or a C ₆ -C ₁₂ arylene group.

Composition according to Claim 5, in which the group X represents a C1-C10 alkylene group, in particular a C1-C4 alkylene group.

Composition according to any one of Claims 1 to 4, in which the coupling agent corresponds to formula (II):

AT

A-X-B,

wherein the group X represents a trivalent group.

P10-2884 / SC 8) Composition according to any one of claims 5 to 7, wherein B represents a blocked mercapto group of formula:

- S _m - C (= 0) - R in which:

m is a number greater than or equal to 1; and preferably equal to 1.

9) Composition according to any one of claims 5 to 7, wherein B represents a polysulfide group of formula:

- S, - R in which:

10) Composition according to any one of claims 1 to 4, wherein the coupling agent corresponds to formula (III):

A-X-B-X-A, wherein:

the group X represents a divalent linking group comprising from 1 to 18 carbon atoms, preferably a C ₁ -C 18 alkylene group or a C ₆ -C ₁₂ arylene group.

1 1) The composition of claim 10 wherein B is S _p where p is a number greater than or equal to 2, preferably 2 to 8 (preferably 2 to 5).

12) Composition according to any one of claims 10 or 1 1, wherein the coupling agent is 3,3'-chloride dithiodipropanoyl.

P10-2884 / SC 13) Composition according to any one of claims 11 to 12, wherein the cellulose is constituted by microfibers.

14) Composition according to any one of claims 1 to 13, wherein the cellulose is in the form of a cellulose airgel formed of microfibrils, chemically modified by grafting on said cellulose coupling agent molecules.

A composition according to any one of claims 1 to 13 wherein the cellulose is in the form of a microfibrous cellulose powder chemically modified by grafting coupling agent molecules onto said cellulose.

16) Composition according to any one of claims 1 to 15, wherein the grafted cellulose is the majority reinforcing filler.

17) Composition according to any one of claims 1 to 16, wherein the reinforcing filler also comprises a reinforcing inorganic filler. 18) Composition according to claim 17, wherein the reinforcing inorganic filler is a siliceous or aluminous filler.

19) Composition according to any one of claims 1 to 18, wherein the amount of reinforcing filler is between 10 and 150 phr, preferably between 20 and 110 phr.

20) A tire comprising a composition according to any one of claims 1 to 19. 21) Cellulose formed of microfibers, chemically modified by grafting on said cellulose coupling agent molecules capable of binding to a diene elastomer, these molecules comprising at least one function A and one function B such that:

the functions A and B being connected by an at least divalent group X; cellulose in the form of airgel or powder.

P10-2884 / SC 22) Cellulose according to claim 21, wherein A is chosen from acyl chlorides, anhydrides, carboxylic acids, isocyanates, alkyl chlorides, organic or inorganic esters, aldehydes, epoxides or amines. , primary or secondary.

23) Cellulose according to any one of claims 21 or 22, wherein B carries mono or polysulfide functions.

24) Cellulose according to any one of claims 21 to 23, wherein the coupling agent has the formula (I): A-X-B,

25) Cellulose according to claim 24, wherein the group X represents a C1-C10 alkylene group, especially C1-C4. 26) Cellulose according to any one of claims 21 to 23, wherein the coupling agent corresponds to formula (II):

AT

A-X-B,

wherein the group X represents a trivalent group.

27) Cellulose according to any one of claims 24 to 26, wherein B represents a blocked mercapto group of formula:

- S _m - C (= 0) - R in which:

m is a number greater than or equal to 1; and preferably equal to 1.

28) Cellulose according to any one of claims 24 to 26, wherein B represents a polysulfide group of formula:

- S, - R

P10-2884 / SC in which :

29) Cellulose according to any one of claims 21 to 23, wherein the coupling agent corresponds to formula (III):

A-X-B-X-A, wherein:

30) Cellulose according to claim 29, wherein B is S _p where p is a number greater than or equal to 2, preferably 2 to 8 (preferably 2 to 5).

31) Cellulose according to any one of claims 29 or 30, wherein the coupling agent is 3,3'-dithiodipropanoyl chloride. 32) Cellulose according to any one of claims 21 to 31, wherein the BET specific surface measured before grafting is greater than or equal to the OmVg.

33) Cellulose according to claim 32, wherein the BET specific surface measured before grafting is greater than or equal to 50m ² / g.

34) Cellulose according to any one of claims 21 to 33, wherein the degree of grafting of the cellulose is greater than 0.1 links per nm ² measured by gravimetry and reported to the BET surface. 35) Cellulose according to claim 34, wherein the degree of grafting of the cellulose varies from 1 to 20 bonds per nm ² measured by gravimetry and reported on the BET surface.

36. Cellulose according to claim 35, wherein the degree of grafting of the cellulose varies from 3 to 6 bonds per nm ² measured by gravimetry and reported on the BET surface.

P10-2884 / SC 37) A process for obtaining a chemically modified cellulose airgel according to any one of claims 31 to 36, which comprises the following successive steps:

- formation of a cellulose airgel, the cellulose being formed of micro fibrils,

heterogeneous phase grafting of the coupling agent molecules.

38. The method of claim 37, wherein the formation of the cellulose airgel is obtained by freeze-drying a colloidal dispersion of cellulose microfibrils in terbutanol.

39. The method of claim 38, wherein the colloidal dispersion is made in water before being transferred to terbutanol.

40) Method according to any one of claims 37 to 39, wherein the grafting is carried out in the gas phase.

P10-2884 / SC