Rubber composition comprising a lignin and a specific hardener

Abstract

The invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system, a lignin-based resin and a methylene donor-type hardener, the hardener being hexamethylenetetramine, denoted HMT, the mass ratio of HMT to lignin being greater than or equal to 0.15.

Description

Title of the invention: Rubber composition comprising a lignin and a specific hardener Technical field of the invention

[0001] The present invention relates to the field of rubber compositions, as well as rubber articles using these compositions and in particular pneumatic or non-pneumatic tires for vehicles, belts and tracks, conveyor belts. Prior art

[0002] The performance of a vehicle tire, whether pneumatic, i.e. capable of supporting the load of the vehicle by means of a pressurized gas, or non-pneumatic, i.e. capable of supporting the load of the vehicle without the means of a pressurized gas, for example by means of stays, a conveyor belt or a belt, is partly linked to the rigidity of some of their constituents. Indeed, rigidity is an important characteristic making it possible to respond to the stresses to which these objects are subjected.

[0003] In addition to rigidity, the mixtures concerned must meet a broader set of specifications, varying according to the positions for which these mixtures are intended.

[0004] The required levels of rigidity can be obtained by two main levers: • Increasing the rate of reinforcing filler (black or silica), • The use of thermosetting resins which constitute a secondary network interpenetrated with the filler-elastomer-vulcanization network.

[0005] However, increasing the reinforcing filler rate can lead to an increase in hysteresis and a deterioration in the processability of the raw mixtures, in particular due to the increase in raw rigidity and the possible appearance of a decohesion phenomenon. Furthermore, the use of thermosetting resins can constitute an additional source of dissipation which can penalize hysteretic performance. In addition, certain resin-hardener systems used in tires are known to release formaldehyde and must therefore be handled with special measures.

[0006] The publication "Application of lignins in rubber compounds", Rohstoffe und An-wendungen, Jan / Feb.2008, pp.26-32, discloses rubber compositions based on natural rubber (NR) or styrene-butadiene rubber (SBR), a crosslinking system and lignin. The addition of lignin in model compositions shows that this compound behaves as a reinforcing filler, in particular when glycerol is used as a plasticizer, but without impact on the mechanical properties dynamic.

[0007] Application WO2014 / 016344 discloses a composition using lignin as a reinforcing resin, the lignin being able to be used with a hardener chosen from polyamines, polyaldimines, polyketimines and their mixtures. The examples, which use a lignin-p-xylylenediamine combination, show that the compositions have increased rigidity while retaining relatively stable or very little degraded hysteretic properties compared to a control using a formo-phenolic resin.

[0008] Application JP2009 / 179299 discloses compositions comprising natural rubber, carbon black, lignin or lignin sulfonates and a Resorcinol-Hexamethylene tetramine (HMT) resin system. These compositions exhibit improved heat and moisture resistance while maintaining adhesion properties to metal reinforcements. The HMT is present in sufficient quantity to act as a hardener for the resorcinol. According to this document, the polyphenolic structure of lignin would improve the oxidation resistance of the rubber composition.

[0009] Continuing its research, the applicant discovered that the combination of lignin and a specific hardener in a rubber composition makes it possible to adjust the stiffness / hysteresis compromise more simply than the reinforcing systems of the prior art. Detailed description of the invention

[0010] The invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system, a lignin-based resin and a hardener of the methylene donor type, the hardener being hexamethylenetetramine, noted HMT, the mass ratio of HMT to lignin being greater than or equal to 0.15.

[0011] Preferably, the HMT to lignin mass ratio is less than or equal to 0.50.

[0012] Preferably, the mass ratio of resin based on compounds chosen from resorcinol, resorcinol derivatives, resorcinol oligomers, cresol, cresol derivatives, cresol oligomers and mixtures thereof on HMT is less than 1.0, preferably less than 0.5 and most preferably less than 0.1.

[0013] Preferably, the composition does not comprise compounds chosen from resorcinol, resorcinol derivatives, resorcinol oligomers, cresol, cresol derivatives, cresol oligomers and mixtures thereof or comprises strictly less than 0.1 pce.

[0014] Preferably, the rubber composition does not comprise any methylene donor other than HMT or comprises less than 1.0 phr, preferably less than 0.5 pce and preferably less than 0.1 pce.

[0015] Preferably, the lignin content in the composition ranges from 1 to 50 phr, preferably from 3 to 30 phr, and preferably from 10 to 30 phr.

[0016] Preferably, the HMT to lignin mass ratio is between 0.20 and 0.40, preferably between 0.25 and 0.35.

[0017] Preferably, the reinforcing filler is chosen from organic fillers, preferably carbon black, inorganic fillers, preferably silica, and mixtures of these fillers.

[0018] Preferably, the rubber composition comprises at least one diene elastomer chosen from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers.

[0019] Preferably, the reinforcing filler is chosen from the group consisting of carbon black, silica and their mixture.

[0020] Preferably, the crosslinking system is sulfur-based.

[0021] Preferably, the rubber composition is free of formaldehyde and / or free of methylene donor selected from the group consisting of hexamethoxymethylmelamine (H3M), hexaethoxymethylmelamine, lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride, hexamethoxymethylmelamine polymers of formaldehyde trioxane, rhexakis(methoxymethyl)melamine, N,N',N"-trimethyl / -N,N',N"-trimethylolmelamine, hexamethylolmelamine, N-methylolmelamine, N,N'-dimethylolmelamine, N,N',N"-tris(methoxymethyl)melamine, N,N',N"-tributyl-N,N',N"-trimethylolmelamine. Definitions

[0022] The carbon-containing compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. This includes in particular polymers, plasticizers, fillers, etc. Lignin

[0023] The composition according to the invention comprises a resin based on a lignin and a hardener of the methylene donor type, this hardener being hexamethylenetetramine (HMT).

[0024] By the expression "resin based on", it is meant a resin comprising the mixture and / or the product of the reaction between the different basic constituents used for the final condensation of this resin, preferably only the product of the reaction between the different basic constituents used for this resin, some of which may be intended to react or capable of reacting with each other or with their close chemical environment, at least in part, during the different phases of the manufacturing process of the composition, composites or rubber article, in particular during a curing step. Thus the basic constituents are the reactants intended to react together during the final condensation of the resin and are not reactants intended to react together to form these basic constituents.

[0025] Lignin is one of the essential components of plant walls, along with cellulose, hemicelluloses and pectins. Its main functions are to provide rigidity and impermeability to water. All plants produce lignin. Its content is lower in annual plants than in perennials, and it is highest in trees, particularly in their bark. Quantitatively, the lignin content is 3 to 5% in leaves, 5 to 20% in herbaceous stems, 15 to 35% in woody stems. Since lignin is a very abundant biopolymer on Earth, it is interesting to use it in rubber compositions for both economic and environmental reasons.

[0026] Lignin is therefore a natural polymer that provides rigidity to the plant by binding the fibers of the cell walls together. Composed of substituted phenylpropanoic units linked together by various types of CC and CO bonds, lignin is a polymer with a relatively complex structure and is highly dependent on the botanical origin and the extraction method used (D. Fengel G. Wegener, Wood. Chemistry, Ultrastructure, Reactions, Walter de Gruyter and Co., Berlin, 1983, 66-181). Lignin carries on its alkyl-aromatic skeleton a wide variety of functional groups, such as cinnamic double bonds, hydroxyl groups (phenolic and alcoholic), methoxyls, carbonyls and carboxyls.

[0027] The 3 basic units from which lignin is synthesized by the plant are coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. We also speak of p-hydroxyphenyl, guaiacyl and syringyl units. In ortho to the phenol groups, we can find methoxy groups. Depending on the origin of the plant and the species, the different units are more or less present.

[0028] Thus, there are several varieties of lignins depending on their plant origin and their extraction process. Several extraction processes are known to those skilled in the art (see for example Wang et al., “From lignin to valuable products - strategies, challenges, and prospects” Bioresource Technology 271 (2019) 449-461), such as the Kraft process or the Organosolv process.

[0029] The Kraft process was developed in 1870 in Germany, it is based on the use of soda and sodium sulfide. It was very developed in the 1930s and it is the The most widely used process in the paper industry today. This process is described, for example, by Ciullo PA in “Papermaking, in Industrial Minerais and their uses - A Handbook of formulary, 1996; pp. 166-169”.

[0030] The Organosolv process is a process for extracting lignin using a solvent, such as a mixture of water and ethanol.

[0031] A chemical structure of lignin can be represented as follows- below (structure from the “Lignin” file of the online encyclopedia Wikipedia):

[0032] The lignin used in the composition according to the invention may be a lignin as obtained after extraction. Preferably, the lignin used in the composition according to the invention is not functionalized, that is to say has not been modified by a process such as oxyakylation, epoxidation, phenolation, carboxylation, methylolation, sulfonation, acrylation, phosphorylation.

[0033] The lignin content in the composition is preferably in a range from 1 to 50 phr; below the minimum indicated, the intended technical effect is insufficient, whereas above the maximum indicated, there is a risk of very high stiffening and increased hysteresis. Preferably, the lignin content in the composition according to the invention ranges from 3 to 30 phr and, even more preferably, from 10 to 30 phr.

[0034] In the composition according to the invention, lignin acts as a methylene acceptor. In order to form the reinforcing resin of the composition according to the invention, the lignin is combined with a specific methylene donor, hexamethylenetetramine. (HMT).

[0035] The HMT to lignin mass ratio is greater than or equal to 0.15 and preferably less than 0.50. This mass ratio allows the crosslinking of lignin by HMT, it is preferably between 0.20 and 0.40, even more preferably between 0.25 and 0.35.

[0036] The specific association of lignin as a methylene acceptor with HMT makes it possible to obtain compositions of high rigidity without penalizing the hysteretic properties and provides great flexibility for adjusting the rigidity / hysteresis compromise of these compositions, which facilitates their implementation in rubber articles.

[0037] Consequently, it is not useful for the composition according to the invention to comprise a methylene acceptor other than lignin. Thus, and preferably, the mass ratio of resin based on compounds chosen from resorcinol, resorcinol derivatives, resorcinol oligomers, cresol, cresol derivatives, cresol oligomers and their mixtures to HMT is less than 1, preferably less than 0.5 and more preferably less than 0.1. Such a mass ratio does not allow the HMT to correctly crosslink the compounds chosen from resorcinol, resorcinol derivatives, resorcinol oligomers, cresol, cresol derivatives, cresol oligomers and their mixtures possibly present.Preferably, the composition according to the invention does not comprise compounds chosen from resorcinol, resorcinol derivatives, resorcinol oligomers, cresol, cresol derivatives, cresol oligomers and their mixtures or comprises strictly less than 0.1 pce.

[0038] Preferably, the composition according to the invention does not comprise any methylene donor other than HMT or comprises less than 1 phr, preferably less than 0.5 phr and preferably less than 0.1 phr. By methylene donor is meant, according to the common understanding in the field of resins, a crosslinking agent for phenolic compounds.

[0039] Preferably, when the composition according to the invention comprises other additional constituents, these other additional constituents are free of formaldehyde and / or free of methylene donor chosen from the group consisting of hexamethoxymethylmelamine (H3M), hexaethoxymethylmelamine, lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride, polymers of hexamethoxymethylmelamine of trioxane of formaldehyde, rhexakis(methoxymethyl)melamine, N,N',N"-trimethyl / -N,N',N"-trimethylolmelamine, hexamethylolmelamine, N-methylolmelamine, N,N'-dimethylolmelamine, N,N',N"-tris(methoxymethyl)melamine, N,N',N"-tributyl-N,N',N"-trimethylolmelamine. More preferentially, these others additional constituents are formaldehyde-free and free of the methylene donors described in this paragraph. Diene elastomer

[0040] The rubber composition according to the invention, this composition being in the crosslinkable or crosslinked state, is based on at least one diene elastomer.

[0041] By "diene" elastomer (or indistinctly rubber), whether natural or synthetic, must be understood in a known manner an elastomer consisting at least in part (i.e., a homopolymer or a copolymer) of diene monomer units (monomers carrying two carbon-carbon double bonds, conjugated or not).

[0042] These diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". "Essentially unsaturated" is generally understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or patterns 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 such as EPDM do not fall within the preceding definition and can in particular be described as "essentially saturated" diene elastomers (low or very low content of patterns of diene origin, always less than 15%). The diene elastomers included in the composition according to the invention are preferably essentially unsaturated.

[0043] The term diene elastomer capable of being used in the compositions in accordance with the invention is particularly understood to mean: a. any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms; b. any copolymer of a diene, conjugated or not, having from 4 to 18 carbon atoms and at least one other monomer.

[0044] The other monomer may be ethylene, an olefin or a diene, conjugated or not.

[0045] Suitable conjugated dienes are conjugated dienes having from 4 to 12 atoms. of carbon, in particular 1,3-dienes, such as 1,3-butadiene and isoprene.

[0046] Suitable olefins are vinylaromatic compounds having from 8 to 20 carbon atoms and aliphatic α-monoolefins having from 3 to 12 carbon atoms.

[0047] Suitable vinylaromatic compounds include, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial mixture "vinyl-toluene", para-tert-butylstyrene.

[0048] Suitable aliphatic α-monoolefins include, in particular, α-monoolefins acyclic aliphatic having from 3 to 18 carbon atoms.

[0049] The diene elastomer of the rubber composition according to the invention comprises preferably at least one essentially unsaturated diene elastomer.

[0050] Preferably, the rubber composition according to the invention comprises, for diene elastomers, at least one elastomer chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. The butadiene copolymers are particularly chosen from the group consisting of butadiene-styrene copolymers (SBR). Preferably, the rubber composition according to the invention comprises, for diene elastomers, at least one elastomer chosen from the group consisting of natural rubber and synthetic polyisoprenes.

[0051] Preferably, the rubber composition according to the invention comprises at least 80 phr, preferably at least 90 phr, and very preferably 100 phr of an elastomer chosen from natural rubber, synthetic polyisoprenes and their mixtures. Reinforcing charge

[0052] The rubber composition according to the invention comprises a reinforcing filler, this filler being able to be organic or inorganic.

[0053] Preferably, the reinforcing filler, organic or inorganic, is chosen from the group consisting of carbon black, silica and their mixture.

[0054] Suitable carbon blacks are all carbon blacks, in particular HAF, ISAF, SAF type blacks conventionally used in tires (so-called tire grade blacks). Among the latter, mention will be made more particularly of reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as for example blacks NI 15, N134, N234, N326, N330, N339, N347, N375, or even, depending on the intended applications, blacks of higher series (for example N660, N683, N772). These carbon blacks can be used in the isolated state, as commercially available, or in any other form, for example as a support for certain of the rubber additives used. Carbon blacks could, for example, already be incorporated into an isoprene elastomer in the form of a masterbatch (see, for example, applications WO 97 / 36724 or WO 99 / 16600).

[0055] Carbon blacks are characterized by various properties, including specific surface area and the oil absorption index of compressed samples (CO AN for "Compressed Oil Absorption Number"). The CO AN of carbon blacks is measured according to ASTM D3493-16.

[0056] The BET specific surface area of ​​carbon blacks is measured according to standard D6556-10 (multi-point method (at least 5 points) - gas: nitrogen - relative pressure range P / P0: 0.1 to 0.3).

[0057] The physical state in which the inorganic charge is present is indifferent, whether it either in the form of powder, granules, beads or any other suitable densified form.

[0058] The inorganic filler is preferably chosen from mineral fillers of the siliceous type, in particular silica (SiO2), or of the aluminous type, in particular alumina (A12O3), chalk, clay, bentonite, talc, kaolin and mixtures thereof, preferably from silica, chalk, talc, kaolin and mixtures thereof, preferentially from silica, talc, kaolin and mixtures thereof. Very preferably, the inorganic filler is chosen from silica, kaolin and mixtures thereof.

[0059] The silica used may be any silica known to those skilled in the art, in particular any precipitated or pyrogenic reinforcing silica having a BET surface area and a CTAB specific surface area both less than 450 m2 / g, preferably from 30 to 400 m2 / g. Examples of highly dispersible precipitated silicas (known as "HDS") include "Ultrasil 7000" and "Ultrasil 7005" silicas from Degussa, "Zeosil 1165MP", "1135MP" and "1115MP" silicas from Rhodia, "Hi-Sil EZ150G" silica from PPG, "Zeopol 8715", "8745" and "8755" silicas from Huber, and high specific surface area silicas as described in application WO 03 / 16837.

[0060] The BET specific surface area of ​​silica 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 - degassing: 1 hour at 160°C - relative pressure range p / po: 0.05 to 0.17).

[0061] The CTAB specific surface area of ​​silica is determined according to French standard NF T 45-007 of November 1987 (method B).

[0062] In the preferred case where the rubber composition according to the invention comprises silica, the latter preferably has a BET surface area of ​​between 45 and 400 m2 / g, more preferably of between 60 and 300 m2 / g.

[0063] When the rubber composition according to the invention comprises silica as reinforcing filler, it also preferably comprises an inorganic filler-elastomer coupling agent.

[0064] By “coupling agent” (or “bonding agent”) is meant, in a known manner, an agent capable of coupling the inorganic filler to the elastomer.

[0065] The rubber composition according to the invention preferably comprises from 5 to 100 phr of reinforcing filler, preferably from 10 to 75 phr of reinforcing filler. Crosslinking system

[0066] The rubber composition according to the invention comprises a retraction system culation, preferably a sulfur-based crosslinking system.

[0067] The sulfur can be provided in any form, in particular in the form of molecular sulfur, or a sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and, optionally, also preferably, various known vulcanization activators can be used such as zinc oxide, stearic acid or equivalent compound such as stearic acid salts and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or even known vulcanization retarders.

[0068] Sulphur is used at a preferential rate of between 0.5 and 12 pce, in particular between 1 and 10 pce. The vulcanisation accelerator is used at a preferential rate of between 0.5 and 10 pce, more preferentially between 0.5 and 5 pce and very preferentially between 0.5 and 3 pce.

[0069] Any compound capable of acting as an accelerator for the vulcanization of diene elastomers in the presence of sulfur may be used as an accelerator, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. Examples of such accelerators include, but are not limited to, the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated as "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazyl sulfenamide ("DCBS"), N-tert-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-tert-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds. Other additives

[0070] The rubber composition according to the invention may also comprise all or part of the usual additives and processing agents, known to those skilled in the art and usually used in rubber compositions, in particular for vehicle tires, such as for example plasticizers (such as plasticizing oils and / or plasticizing resins), pigments, protective agents such as antiozone waxes, chemical antiozonants, antioxidants, anti-fatigue agents. Preparation of rubber composition

[0071] The rubber composition in accordance with the invention is manufactured in suitable mixers, using preparation phases well known to those skilled in the art: a thermomechanical working or mixing phase, which can be carried out in a single thermomechanical step during which the mixture is introduced into a suitable mixer such as a conventional internal mixer (for example of the type 'Banbury'), all the necessary constituents, in particular the elastomeric matrix, the fillers, any other various additives. The incorporation of the filler into the elastomer can be carried out in one or more stages by thermomechanically mixing. In the case where the filler, in particular carbon black, is already incorporated in whole or in part into the elastomer in the form of a masterbatch as described for example in applications WO 97 / 36724 or WO 99 / 16600, it is the masterbatch which is directly mixed and where appropriate the other elastomers or fillers present in the composition which are not in the form of a masterbatch are incorporated, as well as any other various additives.

[0072] The thermomechanical mixing is carried out at high temperature, up to a maximum temperature of between 110°C and 200°C, preferably between 130°C and 185°C, for a duration generally of between 2 and 10 minutes. • a second phase of mechanical work can then be carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first phase to a lower temperature, typically below 120°C, for example between 40°C and 100°C.

[0073] The crosslinking system is added during the second phase. Examples Preparation of rubber compositions

[0074] The rubber compositions are prepared, in a conventional manner, in two phases: a so-called “non-productive” phase and a so-called “productive” phase.

[0075] The “non-productive” phase is carried out in a 0.4 liter mixer for 4 minutes, with an average rotation speed of the mixing spindle of 60 rpm, into which the entire elastomer, the reinforcing filler, and the lignin are introduced until a maximum drop temperature of 160°C is reached.

[0076] The “productive” phase is carried out in a cylinder tool, where the vulcanization system as well as the hardener (depending on the hardeners some may be introduced during the “non-productive” phase) are introduced at 40°C, the composition being mixed for 5 minutes. The crosslinking of the composition was carried out at a temperature of 150°C, under pressure. Measurement methods

[0077] The dynamic properties are measured on a Metravib viscoanalyzer, according to the ASTM D 5992-96 standard. The response of a sample of crosslinked composition (cylindrical specimen 4 mm thick and 400 mm2 in cross-section) is recorded, subjected to sinusoidal stress in alternating simple shear, at a frequency of 10 Hz at 40°C. A strain amplitude sweep from 0.1 to 50% is carried out. (forward cycle), then from 50% to 0.1% (return cycle). The results used are the complex dynamic shear modulus G* and the loss factor tan(d). For the return cycle, the maximum value of tan(d) observed, noted tan(d)max, is indicated, as well as the complex dynamic shear modulus G*(10%) at 10% deformation, at 40°C.

[0078] The different compositions presented in Table 1 are prepared. The results in terms of dynamic properties G*(10%) and tan(d) max at 40°C are reported. The results are expressed on a base of 100, taking the TL composition as a reference. A value greater than 100 for the G* value corresponds to an increased low-deformation rigidity. A value less than 100 for the tan(d) value corresponds to an increased hysteretic loss, which is an indicator of less favorable composition properties in terms of rolling resistance.

[0079] [Tables 1] Composition T0 Tl T2 Cl T3 T4 T5 T6 C2 C3 NR (1) 100 100 100 100 100 100 100 100 100 100 N326 (2) 75 75 91 91 91 91 91 75 91 91 Formophenolic resin (3) 0 10 0 0 10 0 0 0 0 0 Organosolv lignin (4) 0 0 0 10 0 30 30 30 30 0 Kraft lignin (5) 0 0 0 0 0 0 0 0 0 30 ZnO (6) 9 9 9 9 9 9 9 9 9 9 Stearic acid (7) 1 1 1 1 1 1 1 1 1 1 6 PPD (8) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 HMT (9) 0 3.1 0 3.1 3.1 0 3.8 0 9.3 9.3 H3M (10) 0 0 0 0 0 0 5.5 0 0 0 p-xylylenediamine (H) 0 0 0 0 0 9.3 0 0 0 0 Sulfur (12) 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 TBBS (13) 1 1 1 1 1 1 1 1 1 1 Hardener / Lignin - - - 0.31 - 0.31 0.31 0.00 0.31 0.31 HMT / Lignin - - - 0.31 - 0.00 0.13 0.00 0.31 0.31 Results (base 100 = Tl) G*(10%) at 40°C 50 100 77 100 163 83 118 50 108 121 Tan(d)max at 40°C 108 100 90 100 84 96 90 100 100 100 1. Natural Rubber 2. Carbon black N326 (designation according to ASTM D-1765) 3. Novolac formophenolic resin (“Peracit 4536K” from Perstorp) 4. Organosolv lignin from wheat straw_FORTUM 5. Kraft lignin marketed by Aldrich under the name “lignin, alkaki, pH = 6.5” 6. Zinc oxide (industrial grade - Umicore company) 7. Stearin (“Pristerene 4931” from Uniqema) 8. Nl,3-dimethylbutyl-N-phenylparaphenylenediamine Santoflex 6-PPD from Flexsys 9. Hexamethylenetetramine (from Degussa) 10. Hexa(methoxymethyl)melamine 11. p-xylylenediamine (from Sigma-Aldrich) 12. Sulfur 13. N-tert-buty lbenzothiazol-2-sulfenamide

[0080] Compositions T1 and T3 are based on lignin-free formophenolic resin, composition T3 comprising more carbon black than composition T1. Comparison of these two compositions shows that increasing the amount of carbon black increases rigidity at the expense of hysteresis.

[0081] Composition T6 shows that in the absence of hardener, the presence of lignin does not allow the rigidity objectives to be achieved compared to composition TL.

[0082] In composition C1, the novolac formophenolic resin of composition T1 is replaced by an equivalent content of lignin. The carbon black content is adjusted so as to obtain a rigidity similar to the control composition TL. The two compositions have identical hysteretic properties evaluated through the value of tan(d), whereas the increase in the carbon black content should have led to an increase in hysteresis. The composition according to the invention makes it possible to achieve properties similar to the compositions of the prior art without the use of formophenolic resin.

[0083] By increasing the lignin content (compositions C2, C3), the rigidity of the composition is increased. Surprisingly, the hysteretic performances are similar. The compositions according to the invention therefore make it possible to adjust the rigidity / hysteresis compromise in a very simple manner.

[0084] Compositions C2 and C3 show that this effect is obtained regardless of the origin of the lignin.

[0085] Composition T5 shows that when the HMT / Lignin ratio is less than 0.15 the technical effects of the invention are not achieved, even though another hardener is added, here H3M, so as to maintain the overall hardener / lignin ratio.

[0086] When methylene donors other than HMT are used, the hysteretic performances and / or the rigidity of the compositions are impacted. In particular, composition T4, in accordance with the teachings of document WO2014 / 016344, does not exhibit performances as good as the composition according to the invention.

Claims

Claims

1. Rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system, a lignin-based resin and a methylene donor type hardener, the hardener being hexamethylenetetramine, denoted HMT, the HMT to lignin mass ratio being greater than or equal to 0.

15.

2. Rubber composition according to the preceding claim in which the HMT to lignin mass ratio is less than or equal to 0.

50.

3. Rubber composition according to the preceding claim in which the composition does not comprise compounds chosen from resorcinol, resorcinol derivatives, resorcinol oligomers, cresol, cresol derivatives, cresol oligomers and mixtures thereof or comprises strictly less than 0.1 phr.

4. Rubber composition according to the preceding claim in which the mass ratio of resin based on compounds chosen from resorcinol, resorcinol derivatives, resorcinol oligomers, cresol, cresol derivatives, cresol oligomers and their mixtures on HMT is less than 1.0, preferably less than 0.5 and more preferably less than 0.

1.

5. A rubber composition according to any preceding claim does not comprise any methylene donor other than HMT or comprises less than 1.0 phr, preferably less than 0.5 phr and most preferably less than 0.1 phr.

6. Rubber composition according to any one of the preceding claims in which the lignin content in the composition ranges from 1 to 50 phr, preferably ranges from 3 to 30 phr, and most preferably ranges from 10 to 30 phr.

7. Rubber composition according to any one of the preceding claims in which the HMT to lignin mass ratio is between 0.20 and 0.40, preferably between 0.25 and 0.

35.

8. Rubber composition according to any one of the preceding claims in which the reinforcing filler is chosen from organic fillers, preferably carbon black, inorganic fillers, preferably silica, and mixtures of these fillers.

9. A rubber composition according to any preceding claim comprising at least one diene elastomer selected from the

10.

11.

12. group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. A rubber composition according to any preceding claim wherein the reinforcing filler is selected from the group consisting of carbon black, silica and a mixture thereof. A rubber composition according to any preceding claim wherein the crosslinking system is sulfur-based.A rubber composition according to any preceding claim wherein the rubber composition is free of formaldehyde and / or free of a methylene donor selected from the group consisting of hexamethoxymethylmelamine (H3M), hexaethoxymethylmelamine, lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride, hexamethoxymethylmelamine polymers of formaldehyde trioxane, hexakis(methoxymethyl)melamine, N,N',N"-trimethyl / -N,N',N"-trimethylolmelamine, hexamethylolmelamine, N-methylolmelamine, N,N'-dimethylolmelamine, N,N',N"-tris(methoxymethyl)melamine, N,N',N"-tributyl-N,N',N"-trimethylolmelamine.