WO2024141347A1

WO2024141347A1 - Method for devulcanizing rubber chips from vehicle tires

Info

Publication number: WO2024141347A1
Application number: PCT/EP2023/086737
Authority: WO
Inventors: Julien CHATARD; Magalie HEURTEFEU
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2022-12-27
Filing date: 2023-12-19
Publication date: 2024-07-04

Abstract

The invention relates to a method for devulcanizing rubber chips from vehicle tires, wherein the chips are subjected to a thermomechanical treatment step at a high shear force at a temperature ranging from 100°C to 300°C in the presence of 0.1 to 10% by weight, relative to the chip weight, of a devulcanizing agent selected from among cystine, acetylcysteine and a substituted phenolic antioxidant so as to produce a regenerated mixture.

Description

Process for devulcanizing rubber chips from vehicle tires Technical field of the invention The present invention relates to the field of devulcanization of rubber compositions and to rubber compositions comprising the regenerated mixture. Prior art The desire to reduce pressure on fossil and natural resources and to limit the environmental footprint of elastomer-based products leads manufacturers to think about ways to recycle both scrap, i.e. elements not incorporated into rubber articles, as well as materials from used articles in order to produce new products. The recovery of rubber chips by shredding and sorting is well known to those skilled in the art. These chips are currently mainly crushed and either incorporated in small quantities into new rubber compositions, the recycled quantity being managed so as not to affect the performance of the compositions, or used as is, for example for the manufacture of playing fields. games. Indeed, a difficulty in recycling rubber chips is that they are crosslinked, most often using a sulfur-based system (we then say that they are vulcanized). Also several studies have been carried out on how to devulcanize rubber compositions in order to make their recycling simpler. Document EP 3514200 proposes devulcanizing chips from pneumatic tires at high temperature using a devulcanizing agent of the p-phenylenediamine type. Document WO 200123465 teaches the devulcanization of a highly saturated elastomer, for example an EPDM (ethylene-propylene-diene monomer) rubber, using an amine type devulcanization agent. Document WO2014/084727 teaches the devulcanization of rubber by means of the combination of a devulcanization agent, for example a diphenyldisulfide, and a stabilizing agent, the use of only one of these two agents not allowing good devulcanization of rubber. Document EP 2782958 discloses the devulcanization of rubber using L-cysteine at a temperature below 80°C. This document reminds us that chips from vehicle tires are generally not suitable for recycling. In fact, these chips are complex mixtures of elastomers, reinforcing fillers and chemical additives. In addition, the rubber compositions used for the manufacture of tires for vehicles or articles such as tracks or conveyor belts must have good properties both before crosslinking and once vulcanized. However, none of the solutions proposed in the prior art makes it possible to achieve these objectives. Continuing its research, the applicant discovered that a devulcanization process carried out in the presence of specific devulcanization agents under particular conditions made it possible to obtain a regenerated mixture of excellent quality which could be incorporated in the manufacture of new mixtures without degrading their performance. Definitions Compounds comprising carbon mentioned in the description may be of fossil or biosourced origin. In the latter case, they can be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. This concerns in particular polymers, plasticizers, fillers, etc. Any interval of values designated by the expression "between a and b" represents the range of values going from more than a to less than b (that is to say limits a and b excluded) while any interval of values designated by the expression "from a to b" means the range of values going from a to b (that is to say including the strict limits a and b). By the expression "composition based on", is meant a composition comprising the mixture and/or the in situ reaction product of the different constituents used, some of these constituents being able to react and/or being intended to react with each other, at least less partially, during the different phases of manufacturing the composition. In the more specific case of a rubber composition, the composition can thus be in the totally or partially crosslinked state or in the non-crosslinked state. Detailed description of the invention The invention relates to a process for devulcanizing rubber chips from vehicle tires, in which the chips are subjected to a thermomechanical treatment step under high shear at a temperature ranging from 100°C to 300° C in presence of 0.1 to 10% by weight relative to the weight of chips of a devulcanization agent chosen from cystine, acetylcysteine and a substituted phenolic antioxidant so as to produce a regenerated mixture. Rubber chips Rubber chips from vehicle tires mean elements of vehicle tires not comprising textile or metallic elements. These elements come from the shredding of vehicle tires, used or new (for example non-compliant). Rubber chips from vehicle tires have a number of particularities compared to other rubber compositions such as scrap rubber made from a single type of elastomer, in particular natural rubber. In fact, these chips are, through their process of obtaining (shredding of a vehicle tire) made up of compositions which may include several types of elastomers, as well as reinforcing fillers such as carbon black and silica as well as many additives. Preferably, the rubber chips have a dimension of between 0 and 5 mm, preferably between 0 and 2 mm and preferably between 50 µm and 800 µm. Reduced chip size allows correct feeding into the thermomechanical processing stage and improves contact between the chips and the devulcanization agent. Thermomechanical treatment step The thermomechanical treatment step is carried out under high shear. By “under high shear, we mean that the rubber chips are subjected to strong shear, this shear making it possible to gradually reduce the size of the chips during the thermomechanical treatment step while ensuring intimate contact of the chips and the the devulcanizing agent. Preferably, the thermomechanical treatment step is carried out in a screw extruder, preferably in a single screw extruder. Such a device makes it possible to apply very high shear while ensuring good homogeneity of the mixture between the inlet and outlet of the extruder. In addition, with a large surface to length ratio, a screw extruder makes it possible to effectively control the temperature within the extruder. The temperature of the thermomechanical treatment step ranges from 100°C to 300°C. This temperature must be high enough to allow the processing of rubber chips from vehicle tires, which are vulcanized chips comprising, among others, reinforcing fillers such as silica and carbon black, but must not be too high to preserve the elastomeric chains. Preferably, the thermomechanical treatment step is carried out at a temperature ranging from 100°C to 300°C, and more preferably from 160°C to 270°C. This temperature allows the devulcanization of chips from vehicle tires. A lower temperature does not ensure sufficient reactivity to effectively devulcanize this type of material and a temperature higher than 300°C increases the risk of material degradation. At these temperatures, devulcanizing agents such as cysteine cannot be used because they produce a pressure rise within the thermomechanical processing step as well as toxic fumes. A high temperature associated with a process with a high shear rate, without being linked to any theory, allows an intimate mixing of the devulcanization agent and the material from the rubber chips whose viscosity is reduced. The use of substituted agents, chosen from cystine, acetylcysteine and a substituted phenolic antioxidant, has proven to be particularly effective at these temperatures for the devulcanization of rubber chips from vehicle tires. The residence time in the thermomechanical treatment step of the process according to the invention is preferably between 5 and 90 s. The residence time corresponds to the average time taken by the mixture to pass through the thermomechanical treatment stage. This residence time allows effective action of the devulcanization agents and minimizes the duration of exposure of the rubber chips to high shear, thus limiting the degradation of the elastomeric chains. The thermomechanical treatment step under high shear of the process according to the invention is carried out in the presence of 0.1 to 10% by weight relative to the weight of chips of a devulcanization agent. This devulcanization agent makes it possible to break the sulfur bridges generated during the vulcanization of the rubber compositions constituting the rubber chips. The content of devulcanization agent is adjusted so as to allow, in conjunction with the other operating parameters and in particular the temperature, an effective action on the sulfur bridges while limiting possible parasitic reactions. The devulcanizing agent is chosen from cystine, acetylcysteine and a substituted phenolic antioxidant. These agents have proven to be particularly effective, in conjunction with the operating conditions of the process according to the invention, for treating rubber chips from vehicle tires. By the expression “the devulcanization agent is chosen from cystine, acetylcysteine and a substituted phenolic antioxidant” it is meant that the devulcanization agent introduced into the thermomechanical treatment step is one of these constituents and not a mixture of these constituents. In particular, when the devulcanization agent is a substituted phenolic antioxidant, this agent is not used in combination with another devulcanization agent. The devulcanization agent chosen from substituted phenolic antioxidants is preferably chosen from pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] distributed by BASF under the trade name “IRGANOX 1010”, 2,2-thio-diethylene bis-[(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate)] distributed by BASF under the trade name “IRGANOX 1035”, octadecyl-3-( 3,5-di-t-butyl-4-hydroxyphenyl)propionate distributed by BASF under the trade name “IRGANOX 1076”, isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate distributed by BASF under the trade name “IRGANOX 1135”, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene distributed by BASF under the trade name “ IRGANOX 1330”, 4,6-bis(dodecylthiomethyl)-o-cresol distributed by BASF under the trade name “IRGANOX 1726”, 4,6-bis(octytiomethyl)-o-cresol distributed by BASF under the trade name “ IRGANOX 1520 L”, triethyleneglycol-bis[(3-(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate)] distributed by BASF under the trade name “IRGANOX 245” and 1,6-hexanediol- bis[(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] distributed by BASF under the trade name “IRGANOX 259”. Preferably, the devulcanization agent chosen from substituted phenolic antioxidants is chosen from 2,2-thio-diethylene bis-[(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate)] , isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl- 4-hydroxybenzyl)benzene, 4,6-bis(dodecylthiomethyl)-o-cresol, 4,6-bis(octytiomethyl)-o-cresol, triethyleneglycol-bis[(3-(3-t-butyl-5 -methyl-4- hydroxyphenyl) propionate)] and 1,6-hexanediol-bis [(3- (3,5-di-t-butyl-4- hydroxyphenyl) propionate]. Very preferably, the devulcanization is chosen from cystine, acetylcysteine, isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 4,6-bis(octytiomethyl)-o-cresol. the devulcanization agent is chosen from cystine and acetylcysteine, which makes it possible to obtain particularly interesting performances, particularly in terms of hysteretic losses, fatigue resistance and elongation at break. At the end of the thermomechanical treatment step under high shear, a regenerated mixture is obtained which can be incorporated into non-crosslinked rubber compositions, for any type of application, and in particular into rubber compositions intended for tracks. , conveyor belts, vehicle tires, and particularly for vehicle tires. The process according to the invention makes it possible to obtain a regenerated mixture which can be integrated into rubber compositions intended for vehicle tires without requiring the critical properties of these compositions, such as for example their raw processability and their characteristics once vulcanized. such as stiffness, hysteretic losses, fatigue or breaking properties, are not impacted. It is thus possible to increase the proportion of recycled rubber in vehicle tires without significantly impacting their performance. Rubber composition Thus, the invention also relates to a rubber composition, this composition being in the crosslinkable or crosslinked state, comprising from 0.1 to 100 phr of regenerated mixture prepared by the process according to the invention, and preferably a rubber composition intended for vehicle tires comprising from 0.1 to 100 phr of regenerated mixture prepared by the process according to the invention. Preferably, the rubber composition in the crosslinkable or crosslinked state comprises from 0.1 to 80 phr of regenerated mixture prepared by the process according to the invention. Preferably, the invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system, and 0.1 to 100 phr of regenerated mixture prepared by a process according to the invention . Preferably, this rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system comprises from 0.1 to 80 phr of regenerated mixture prepared by the process according to the invention. By "diene" elastomer (or indiscriminately rubber), whether natural or synthetic, must be understood in a known manner an elastomer constituted at least in part (ie, a homopolymer or a copolymer) of diene monomer units (monomers carrying two carbon-carbon double bonds, conjugated or not). These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. We generally mean by “essentially unsaturated”, 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% (mole %); this is why diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the previous definition and can be described in particular as "essentially saturated" diene elastomers (rate of motifs of weak or very weak diene origin, always less than 15%). The diene elastomers included in the composition according to the invention are preferably essentially unsaturated. By diene elastomer capable of being used in the compositions according to the invention is particularly understood: 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 4 to 18 carbon atoms and at least one other monomer. The other monomer may be ethylene, an olefin or a diene, conjugated or not. Suitable conjugated dienes are conjugated dienes having 4 to 12 carbon atoms, in particular 1,3-dienes, such as in particular 1,3-butadiene and isoprene. Suitable olefins are vinylaromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms. Suitable vinyl aromatic compounds include, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, and para-tertiobutylstyrene. Suitable aliphatic α-monoolefins are in particular acyclic aliphatic α-monoolefins having from 3 to 18 carbon atoms. The diene elastomer of the rubber composition according to the invention preferably comprises at least one essentially unsaturated diene elastomer. Preferably, the rubber composition according to the invention comprises for 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 copolymers of butadiene are particularly chosen from the group consisting of butadiene-styrene copolymers (SBR). By "isoprene elastomer" is meant in a known manner a homopolymer or a 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 be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers. (SBIR). This isoprene elastomer is preferably chosen from the group consisting of natural rubber, synthetic cis-1,4 polyisoprenes and their mixtures; among these synthetic polyisoprenes, polyisoprenes having a rate (molar %) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%, are preferably used. Preferably and according to any of the arrangements herein, the diene elastomer is natural rubber. Very preferably, the rubber composition according to the invention comprises as elastomers at least one elastomer chosen from the group consisting of natural rubber, synthetic polyisoprenes, butadiene-styrene copolymers and mixtures of these elastomers. The rubber composition according to the invention according to the invention comprises a reinforcing filler, organic or inorganic. Preferably, the organic or inorganic filler is chosen from the group consisting of carbon black, silica and their mixture. All carbon blacks are suitable as carbon blacks, in particular blacks of the HAF, ISAF, SAF type conventionally used in tires (so-called pneumatic grade blacks). Among the latter, we will particularly mention the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as for example blacks N115, 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 some of the rubber additives used. The 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). Carbon blacks are characterized by different properties, in particular by the specific surface area, and by the oil absorption index of compressed samples (COAN for “Compressed Oil Absorption Number” in English). The COAN of carbon blacks is measured according to the ASTM D3493-16 standard. 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). The physical state in which the inorganic filler appears is irrelevant, whether in the form of powder, granules, beads or any other suitable densified form. The inorganic filler is preferably chosen from mineral fillers of the siliceous type, in particular silica (SiO ₂ ), or of the aluminous type, in particular alumina (Al ₂ O ₃ ), chalk, clay , bentonite, talc, kaolin and their mixtures, preferably from silica, chalk, talc, kaolin and their mixtures, preferably from silica, talc, kaolin and their mixture. Very preferably, the inorganic filler is chosen from silica, kaolin and mixtures thereof. The silica used can be any silica known to those skilled in the art, in particular any precipitated or pyrogenic reinforcing silica having a BET surface area as well as a CTAB specific surface area both less than 450 m ² /g, preferably 30 to 400 m ² /g. As highly dispersible precipitated silicas (called "HDS"), we will cite for example the silicas "Ultrasil 7000" and "Ultrasil 7005" from the company Degussa, the silicas "Zeosil 1165MP", "1135MP" and "1115MP" from the company Degussa. Rhodia company, “Hi-Sil EZ150G” silica from PPG company, “Zeopol 8715”, “8745” and “8755” silicas from Huber company, silicas with high specific surface area as described in application WO 03/ 16837. 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 (multi-point volumetric method (5 points) - gas: nitrogen - degassing: 1 hour at 160°C - relative pressure range p/in: 0.05 to 0.17). The CTAB specific surface area of the silica is determined according to the French standard NF T 45-007 of November 1987 (method B). 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 m ² /g, more preferably between 60 and 300 m ² /g. When the rubber composition according to the invention comprises silica as reinforcing filler, it also preferably comprises an inorganic filler-elastomer coupling agent. By “coupling agent” (or “binding agent”) is meant in a known manner an agent capable of coupling the inorganic filler to the elastomer. 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. The rubber composition according to the invention comprises a sulfur-based crosslinking system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or of a sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and, optionally, also preferentially, various known vulcanization activators can be used such as zinc oxide, stearic acid or equivalent compound such as stearic acid salts and salts. transition metals, guanidic derivatives (in particular diphenylguanidine), or even known vulcanization retarders. Sulfur is used at a preferential rate of between 0.5 and 12 pce, in particular between 1 and 10 pce. The vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably between 0.5 and 5 phr and very preferably between 0.5 and 3 phr. Any compound capable of acting as an accelerator for the vulcanization of diene elastomers in the presence of sulfur can be used as an accelerator, in particular accelerators of the thiazole type as well as their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types. As examples of such accelerators, the following compounds may be cited in particular: 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N,N-dicyclohexyl- 2-benzothiazyl sulfenamide ("DCBS"), N-ter-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-ter-butyl-2-benzothiazyl sulfenimide ("TBSI"), disulfide tetrabenzylthiuram ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds. 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 tires for vehicles, such as for example plasticizers (such as plasticizing oils and/or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, anti-oxidants, anti-fatigue agents. The rubber composition according to the invention is manufactured in suitable mixers, using preparation phases well known to those skilled in the art: ^ a working phase or thermomechanical mixing, which can be carried out in a single thermomechanical step at during which we introduce, into a suitable mixer such as a usual internal mixer (for example of the 'Banbury' type), 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 several times by thermomechanical 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 (“masterbatch” in English) as described for example in the applications WO 97/36724 or WO 99/16600, it is the masterbatch which is directly kneaded and where appropriate the other elastomers or fillers present in the composition which are not in the form of masterbatch are incorporated, as well as as any other various additives. 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 period 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 less than 120°C, by example between 40°C and 100°C. The crosslinking system is added during the second phase. The regenerated mixture prepared by the process according to the invention can be incorporated into the rubber composition during the first phase or during the second phase. Examples Manufacturing of regenerated mixtures Different regenerated mixtures are produced under the conditions presented below. Rubber chips in the form of aggregates of size between 0 and 400 µm are introduced into a screw extruder. The residence time in the screw extruder is approximately 60 s and the operating temperature is between 160°C and 270°C. We introduce with the chips 2.5% by weight relative to the weight of chips of a devulcanization agent whose nature varies for each regenerated mixture produced in the manner presented in table 1. [Table 1] Regenerated mixture MR1 MR2 MR3 MR4 MR5 MR6 Irganox Irganox devulcanization agent none 6-PPD 1520 L 1135 Cystine Acetylcysteine The regenerated products are then integrated into rubber compositions whose properties are measured raw (before crosslinking) and cooked (after crosslinking). We make several compositions. A first composition C-1, which serves as a reference, does not contain any regenerated mixture. Compositions are manufactured starting from composition C-1 and adding 20% by weight of micronized rubber powder (composition C-2) or 20% by weight of regenerated mixture (compositions C-3 to C-9). Composition C-10 is manufactured by integrating 20% by weight of micronized rubber powder as well as 3% by weight relative to the weight of micronized cystine rubber powder during the first phase of manufacturing the rubber composition as described. below. Composition C-11 is manufactured by integrating 20% by weight of regenerated mixture without MR1 devulcanization agent as well as 3% by weight relative to the weight of micronized cystine rubber powder during the first phase of manufacturing the rubber composition as described below. The vulcanization system of compositions C-2 to C-11 is adjusted in relation to that of composition C-1 by increasing the mass content of each of its constituents by 20% by weight to take into account the addition of 20% by weight of regenerated mixture or micronized rubber powder. The resulting compositions are indicated in Table 2. [Table 2] compositions in pce C-1 C-2 to C-11 NR (1) 80 80 BR (2) 20 20 N234 (3) 50 50 Rubber powder or regenerated 0 40.8 Wax (4) 1 1 6-PPD (5) 3 3.6 STEARIC ACID (6) 2 2.4 ZNO (7) 2.5 3 CBS (8) 1 1.2 SULFUR 1.5 1.8 Table 3 summarizes the different compositions tested. [Table 3] Composition Rubber powder or regenerated C-1 none C-2 PCM C-3 Commercial regenerated C-4 MR2 C-5 MR3 C-6 MR4 C-7 MR5 C-8 MR6 C-9 PCM + cystine C- 10 MR1 + cystine PCM: Micronized Rubber Powder “PolyDyne 84” or “MicroDyn 184” from the company Lehigh Commercial regenerated: “Ecorr RNR30B01” from the company Rubber Ressources Manufacture of rubber compositions The compositions are manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first working phase or thermomechanical mixing (sometimes referred to as a "non-productive" phase) at high temperature, up to a maximum temperature between 130°C and 180°C, followed by a second phase of mechanical work (sometimes referred to as the "productive" phase) at a lower temperature, typically below 110°C, for example between 60°C and 100°C, finishing phase during which the crosslinking or vulcanization system is incorporated. The first (non-productive) phase is carried out in several thermomechanical stages. During a first step, the elastomers and the regenerated material are introduced into a suitable mixer such as a usual internal mixer, at a temperature of 40°C. After the temperature rises to 90°C, the other ingredients which were not initially added are added at once, with the exception of the crosslinking system. We continue mixing for several minutes. The total mixing time, in this non-productive phase, is approximately 5 minutes at a temperature less than or equal to 165°C. The final filling rate in the internal mixer is approximately 70% by volume. After cooling the mixture thus obtained, the crosslinking system is then incorporated at low temperature, between 70 and 80°C, generally in an external mixer such as a roller mixer; everything is then mixed (productive phase) for 11 to 13 min. The final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for characterization in the laboratory, or even extruded, to form for example a rubber profile used for the manufacture of semi- finishes for tires. These products can then be used for the manufacture of tires, according to techniques known to those skilled in the art. The crosslinking (or cooking) is carried out in a known manner at a temperature generally between 130°C and 170°C, under pressure, for a sufficient time which can vary for example between 10 and 40 min depending in particular on the cooking temperature. , the crosslinking system adopted, the crosslinking kinetics of the composition considered or even the size of the tire. Properties of rubber compositions: Measurement of Mooney viscosity (or Mooney plasticity) An oscillating consistometer is used as described in the French standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the composition in the raw state (before cooking) is molded in a cylindrical enclosure heated to 100°C. After one minute of preheating, the rotor rotates within the test piece at 2 revolutions/minute and the torque useful to maintain this movement is measured after 4 minutes of rotation. Mooney plasticity (ML 1+4) is expressed in “Mooney unit” (MU, with 1 MU=0.83 Newton.meter). The lower the Mooney value, the lower the viscosity before cooking and the better the processability of the composition. The results are expressed in performance in base 100, that is to say that we arbitrarily assign the value 100 to composition 1, to calculate and then compare the Mooney of the different other compositions tested. A value less than 100 represents a lower Mooney value, that is, a composition that is easier to format, while a value greater than 100 represents a higher Mooney value. Dynamic properties The dynamic properties G*(50%) and tan(d) are measured on a viscoanalyzer (Metravib VA4000), according to the ASTM D 5992-96 standard. The response of a sample of vulcanized composition (cylindrical specimen 2 mm thick and 79 mm ² in section) is recorded, subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, under the controlled conditions of temperature at 60°C. A deformation amplitude sweep is carried out from 0.1% to 100% (forward cycle), then from 100% 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, we indicate the maximum value of tan(d) observed, denoted tan(d)max, as well as the complex modulus at 50% deformation (G*(50%)). The results are expressed in performance in base 100, that is to say that we arbitrarily assign the value 100 to composition 1, to calculate and then compare the tan(d)max and the G*(50%) of the various other compositions tested. For tan(d)max, a value less than 100 represents a decrease in hysteretic losses (i.e. a lower tan(d)max value) while a value greater than 100 represents hysteretic losses superior. For G*(50%), a value less than 100 represents a stiffness lower than the control mixture while a value greater than 100 represents a stiffness greater than the control mixture. Tensile tests The stresses at break (in MPa) and the elongations at break (AR in %) are measured, at 23°C ± 2°C, according to standard NF T 46-002, on raw samples or on samples cooked for 25 minutes at 150°C or 90 minutes at 160°C. The rupture energy is equal to the product of the rupture elongation and the rupture stress. The tests were carried out in accordance with the French standard NF T 46-002 of September 1988. All traction measurements were carried out under normal conditions of temperature (23±2°C) and humidity (50±5% d relative humidity), according to French standard NF T 40-101 (December 1979). Fatigue measurement Fatigue resistance, expressed in number of cycles or in relative unit (ur), is measured in a known manner on 12 specimens subjected to repeated low frequency traction up to an elongation of 75%, at 23 °C, using a Monsanto device (“MFTR” type) until the test piece breaks, according to standards ASTM D4482-85 and ISO 6943. The result is expressed in relative units (ur). A value higher than that of the control, arbitrarily set at 100, indicates an improved result, that is to say better fatigue resistance of the rubber samples. Results Table 4 shows the results obtained for the different rubber compositions. [Table 4] Base results C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9 C-10 100 Mooney (UM) 100 120 92 79 78 80 89 101 117 80 Elongation 100 89 78 93 94 88 97 93 84 92 rupture (%) Stress 100 88 58 79 78 75 90 89 78 79 rupture (Mpa) MFTR at 23°C 100 49 41 95 99 92 97 88 38 81 G*50 % at 60°C 100 118 86 100 95 100 101 103 120 84 Tan D max 100 95 120 118 114 113 103 100 90 119 60°C Attempts to manufacture a regenerated mixture using cysteine as a devulcanization agent were made but could not be completed (smoke was released). It is observed that the rubber compositions manufactured from a mixture regenerated according to the process of the invention have performances comparable to the control mixture once vulcanized. These compositions also have excellent processability with a slightly lower Mooney value, which allows easier shaping of these compositions. The incorporation of devulcanization agent in the first phase of manufacturing rubber compositions does not make it possible to obtain compositions having satisfactory performance, even if the rubber chips have undergone a thermomechanical treatment step under high shear (composition C -11).

Claims

CLAIMS [Claim 1] Process for devulcanizing rubber chips from vehicle tires, in which the chips are subjected to a thermomechanical treatment step under high shear at a temperature ranging from 100°C to 300°C in the presence of 0. 1 to 10% by weight relative to the weight of chips of a devulcanizing agent chosen from cystine, acetylcysteine and a substituted phenolic antioxidant so as to produce a regenerated mixture. [Claim 2] Devulcanization process according to the preceding claim in which the devulcanization agent chosen from substituted phenolic antioxidants is chosen from 2,2-thio-diethylene bis-[(3-(3,5-di-t- butyl-4-hydroxyphenyl)propionate)], isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3 ,5-di-t-butyl-4-hydroxybenzyl)benzene, 4,6-bis(dodecylthiomethyl)-o-cresol, 4,6-bis(octythiomethyl)-o-cresol, triethylene glycol-bis[(3 -(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate)] and 1,6-hexanediol-bis[(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]. [Claim 3] Devulcanization process according to one of claims 1 or 2 in which the devulcanization agent is chosen from cystine, acetylcysteine and a substituted antioxidant chosen from isooctyl-3-(3,5-di -t-butyl-4-hydroxyphenyl)propionate and 4,6-bis(octythiomethyl)-o-cresol [Claim 4] Devulcanization process according to claim 1 in which the devulcanization agent is chosen from cystine and l. acetylcysteine. [Claim 5] Devulcanization process according to any one of the preceding claims in which the rubber chips have a dimension between 0 and 5 mm, preferably between 0 and 2 mm and preferably between 50 µm and 800 µm. [Claim 6] Devulcanization process according to any one of the preceding claims in which the thermomechanical treatment step is carried out in a screw extruder, preferably in a single screw extruder. [Claim 7] Devulcanization process according to any one of the preceding claims in which the thermomechanical treatment step is carried out at a temperature ranging from 160°C to 270°C. [Claim 8] Devulcanization process according to any one of the preceding claims in which the residence time in the thermomechanical treatment step is between 5 and 90 s. [Claim 9] Rubber composition comprising from 0.1 to 100 phr of regenerated mixture prepared by a process according to any one of the preceding claims, preferably comprising from 0.1 to 80 phr of regenerated mixture prepared by a process according to any of the preceding claims. [Claim 10] Rubber composition according to the preceding claim based on at least one diene elastomer, a reinforcing filler, a crosslinking system, and 0.1 to 100 phr of regenerated mixture prepared by a process according to any one of claims 1 to 8, preferably comprising from 0.1 to 80 phr of regenerated mixture prepared by a process according to any one of claims 1 to 8.