RU2850263C1 - Method for obtaining butadiene-styrene rubbers containing recycled rubber powder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the field of chemistry of high-molecular compounds, namely to the chemistry of rubbers. A method is proposed for producing butadiene-styrene rubber containing micronised powder of recycled rubber, wherein the method comprises several stages. In the first stage, a suspension is prepared containing micronised powder of recycled rubber, water and potassium salt obtained by disproportionation of resin acid containing a mixture of abietic acid, neoabietic acid, palustric acid and levopimaric acid as a surfactant. Then, the suspension obtained in the previous stage is mixed with at least one butadiene-styrene latex to obtain a butadiene-styrene latex containing micronised recycled rubber powder. After that, the latex obtained in the mixing stage is coagulated to obtain coagulated butadiene-styrene rubber containing micronised recycled rubber powder. In this case, the particle size of the micronised recycled rubber powder is in the range from 0.05 to 0.8 mm; at least one surfactant is present in an amount ranging from 0.5 to 3 wt% relative to the total weight of said recycled rubber powder; said micronised recycled rubber powder has a concentration in water ranging from 1 to 50 wt% relative to the total weight of said water. The coagulation stage is carried out in the presence of at least one coagulating agent, selected from alkylamine and epichlorohydrin copolymers, at a temperature in the range from 40 to 90°C and at a pH less than or equal to 5.

EFFECT: proposed approach allows obtaining butadiene-styrene rubber with better physical and mechanical properties compared to analogues, causing less harm to the environment and the health of operators and polluting the production line to a lesser extent.

27 cl, 2 dwg, 7 tbl, 6 ex

Description

The invention relates to a method for producing styrene-butadiene rubbers containing micronized powder of recycled rubber.

More particularly, the present invention relates to a method for producing styrene-butadiene rubber containing micronized recycled rubber powder, said method comprising the following steps: (a) preparing a suspension containing micronized recycled rubber powder, water and at least one surfactant; (b) mixing the suspension obtained in step (a) with at least one styrene-butadiene latex to obtain a styrene-butadiene latex containing micronized recycled rubber powder; (c) coagulating the latex obtained in step (b) to obtain coagulated styrene-butadiene rubber containing micronized recycled rubber powder.

Styrene-butadiene rubber containing micronized powder of recycled rubber obtained by the method described above, as such or in a mixture with other rubbers, such as, for example, natural rubber (NR), polybutadiene (BR), styrene-butadiene copolymers or mixtures thereof, can be advantageously used in vulcanizable elastomer compositions, which, in turn, can be used in various industries, for example, in tires, shoe soles, brake systems, conveyor belts.

Rubber recycling is a constantly evolving industry, attracting increasing interest due to growing attention to issues such as environmental sustainability and the circular economy. As a result, numerous scientific papers and patents exist on this topic.

One of the most widely used methods of processing rubber is to grind it into fine powders and add it to virgin rubbers by dry mechanical mixing.

For example, U.S. Patent No. 9,840,613 relates to a polymer formulation useful as a structural material for the production of a wide variety of articles, said polymer formulation comprising (1) about 45 to 85 wt.% micronized rubber powder, (2) about 15 to 45 wt.% metallocene polyolefin elastomer, and (3) about 1 to 10 wt.% maleic anhydride-grafted polyethylene. The components of said formulation are dried and mixed in a twin-screw extruder.

Also known is the processing of rubber through a technology known as devulcanization, which aims to break down the sulfur bridges to bring the polymer as close as possible to its original form.

For example, U.S. Patent No. 5,602,586 relates to a method for devulcanizing vulcanized rubber by desulfurization, comprising the steps of: contacting crumbs of vulcanized rubber with a solvent and an alkali metal so as to form a reaction mixture; heating the reaction mixture with stirring in the absence of oxygen to a temperature sufficient for the alkali metal to react with sulfur present in the vulcanized rubber; and maintaining the temperature below the temperature at which thermal cracking of the rubber occurs, ensuring devulcanization.

Further details of the desulfurization technology can be found, for example, in US Patents 6,541,526 and 9,527,978.

Methods of processing rubber are also known, including the use of rubbers in emulsion or solution.

For example, Chinese Patent Application CN 101792546 relates to a method for producing a composition consisting of rubber powder and rubber, which comprises the following steps: mixing rubber powder, wherein said rubber powder optionally contains powder additives or a sizing agent containing water or materials containing softening oil, with rubber in emulsion or in solution, or with wet rubber in solid form that has not previously been dried, to obtain intermediate products containing a rubber-(rubber powder) composition, and then carrying out a treatment to remove liquid to obtain products containing a rubber-(rubber powder) composition in a solid state.

Chinese Patent Application CN 102344591 relates to a method for producing a rubber-containing composition, characterized in that it comprises the following steps: (1) mixing, in an internal mixer, recycled rubber powder with a graded or mixed grain size of from 90 mesh (approximately 0.16 mm) to 200 mesh (0.074 mm), said recycled rubber optionally containing powder additives or additives containing water and/or softening oil, with rubber in emulsion or in solution so as to obtain a homogeneous material; or mixing, in a kneader, said recycled rubber powder with wet rubber in solid form that has not previously been dried, so as to obtain a homogeneous material; (2) carrying out dewatering treatment of the homogeneous material obtained in step (1), for example, by demulsification, centrifugation, granulation, hot air fluidization, flue gas annealing, evaporation in a steam cylinder, hot extrusion, traditional liquid removal methods, to obtain a homogeneous composition containing rubber (rubber powder).

However, the methods described above have some disadvantages, such as:

- deterioration of the physical and mechanical properties of the elastomeric compositions in which they are used;

- problems associated with working with them, as well as with the health of operators;

- technical problems associated with contamination of production lines and equipment used.

Micronized recycled rubber powder is known to be highly hygroscopic. Moisture absorption by micronized recycled rubber powder can impair both mechanical mixing ("dry mixing") with virgin rubber and the subsequent vulcanization process, leading to deterioration of the physical and mechanical properties of the final vulcanized product.

Furthermore, the use of micronized recycled rubber powder in mechanical mixing ("dry mixing") requires careful management from both environmental sustainability and operator health perspectives to avoid risks such as explosions or the dispersal of microparticles into the atmosphere, which can lead to increased production costs. Furthermore, the use of micronized recycled rubber powder in mechanical mixing ("dry mixing") can pose a serious problem for improperly equipped facilities.

Finally, the use of micronized recycled rubber powder can lead to contamination of production lines and equipment, which can lead to blockages and malfunctions, increasing both the time and cost of the process.

Thus, the task was set to find a method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, which is capable of overcoming the problems described above.

A new method has now been discovered for producing styrene-butadiene rubber containing micronized powder of recycled rubber, which, by using a suspension containing micronized powder of recycled rubber of a certain size, water, and at least one surfactant, said surfactant being present in certain amounts, makes it possible to overcome the above-described disadvantages. Said method makes it possible to produce styrene-butadiene rubber containing micronized powder of recycled rubber, which can be successfully used, as such or in a mixture with other rubbers, such as, for example, natural rubber (NR), polybutadiene (BR), styrene-butadiene copolymers, or mixtures thereof, in vulcanizable elastomer compositions, which, in turn, can be used in various industries, for example, in tires, shoe soles, brake systems, and conveyor belts.

Thus, the aim of the present invention is a method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, said method comprising the following steps:

(a) preparing a suspension containing micronized recycled rubber powder, water and at least one surfactant;

(b) mixing the suspension obtained in step (a) with at least one styrene-butadiene latex to obtain a styrene-butadiene latex containing micronized recycled rubber powder;

(c) coagulating the latex obtained in step (b) to obtain coagulated styrene-butadiene rubber containing micronized recycled rubber powder;

Where:

- in step (a) the particle size of said micronized recycled rubber powder is in the range of 0.05 to 0.8 mm, preferably in the range of 0.1 to 0.4 mm;

- in step (a) said at least one surfactant is present in an amount in the range of from 0.5 to 3 wt.%, preferably in the range of from 1 to 2.5 wt.% relative to the total weight of said micronized recycled rubber powder;

- in step (a), said micronized powder of recycled rubber has a concentration in water in the range of 1 to 50 wt.%, preferably in the range of 5 to 30 wt.% relative to the total mass of said water.

In the context of the present description and the following claims, definitions of numerical ranges always include extreme values unless otherwise stated.

In the context of the present description and the following claims, the term "comprising" also includes the terms "which consists essentially of" or "which consists of".

In the context of the present description and the following claims, the particle size of said micronized recycled rubber powder is determined according to ASTM D5644-18.

In the context of the method of the present invention, the micronized recycled rubber powder may come from various types of rubber products, such as, for example, whole end-of-life (ELT) tires or tire parts (e.g., treads). The micronized recycled rubber powder may thus include various types of rubber, such as, for example, natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (BR), as well as fillers such as, for example, carbon black, silicon dioxide, sulfur, and accelerators, additives of various types.

Micronized recycled rubber powder can be produced by methods known in the art. For example, micronized recycled rubber powder can be produced using a cryogenic process, a mechanical grinding process, or a high-pressure, water-based process. In all methods, steel components are removed using a magnetic separator, and fibrous components are separated using air classifiers or other separation equipment. In the cryogenic process, the ground rubber is frozen at an extremely low temperature and then crushed into small particles. The mechanical grinding process, typically carried out at room temperature (25°C), uses various grinding equipment, such as crushing rollers, granulators, and the like, to mechanically break the rubber into small particles. The high-pressure, water-based method involves exposing a rubber product, such as an end-of-life tire, to a high-pressure water jet, which scrapes the outermost portions of the tire, creating small particles.

In the context of the present invention, micronized powder of recycled rubber obtained by any of the methods known in the art, for example, by any of the methods described above, can be used.

Examples of micronized recycled rubber powders that can be successfully used for the purposes of the present invention and that are commercially available today are the products known under the trade name PolyDyne ^™ (d ₉₀ in the range from 0.074 to 0.4 mm) from Lehigh Technologies, rubber powder B.0/0.35 (d ₉₀ <0.35 mm) from Albatros, TyreXol ^™ CWN 0-400 (d ₉₀ <0.33 mm) from Tyre Recycling Solutions.

According to a preferred embodiment of the present invention, in step (a), said at least one surfactant may be selected, for example, from non-ionic surfactants such as, for example, polyoxyethylene fatty acid derivatives, alkyl polyglucosides, ethanolamides, ethoxylated amides, ethoxylated amines, ethoxylated acids, polyoxyethylene alkyl ethers or mixtures thereof.

According to another preferred embodiment of the present invention, in step (a), said at least one surfactant may be selected, for example, from anionic surfactants such as, for example: salts formed by long chains of carbon atoms that terminate in a carboxylate or sulfonate group (e.g., sodium lauryl sulfate (SLS), sodium lauryl ethoxy sulfate (SLES)), alkylbenzenesulfonic acids (ABS), polysulfonated aromatic esters (e.g., Dowfax ^™ 2A1 from Dow Chemical) or mixtures thereof; sodium, potassium, lithium or ammonium salts, preferably sodium or potassium, of fatty acids, saturated or unsaturated, containing from 6 to 22 carbon atoms per molecule, such as, for example, caproic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid or mixtures thereof, or mixtures of the said salts; sodium, potassium, lithium or ammonium salts, preferably sodium or potassium, of modified resin acids which are obtained by dimerization, disproportionation, hydrogenation, modification of mixtures of resin acids including abietic acid, neoabietic acid, palustric acid, levopimaric acid or mixtures thereof, or mixtures of said salts (for example, the potassium salt obtained by disproportionation of the resin acid Potassium Soap 80% Gresinox 578M from Parchem).

According to another preferred embodiment of the present invention, in step (a), said at least one surfactant may be selected, for example, from cationic surfactants, such as, for example, long-chain quaternary ammonium salts (for example, benzalkonium chloride (BAC), cetyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium bromide) or mixtures thereof.

According to another preferred embodiment of the present invention, in step (a), said at least one surfactant may be selected, for example, from amphoteric surfactants such as, for example, cocoamidopropyl betaine, dodecyl betaine, lecithin, aminocarboxylic acids or mixtures thereof.

According to a preferred embodiment of the present invention, said step (a) can be carried out at a temperature in the range of 20 to 90°C, preferably in the range of 50 to 80°C for a variable time depending on the size of the mixer and sufficient to obtain a homogeneous suspension, preferably for a time in the range of 2 to 60 minutes, preferably in the range of 4 to 40 minutes.

Said step (a) can be carried out by mixing micronized recycled rubber powder, water and at least one surfactant in a mixer equipped with a mixing system suitable for obtaining a homogeneous suspension, i.e., a suspension in which the micronized recycled rubber powder is homogeneously distributed throughout the volume of water and surfactant. Preferably, said mixing system can consist of an impeller with a mixed secondary flow, such as, for example, an impeller with a 45° "Pitch Blade" blade angle, or an impeller on hydrofoils with a purely axial flow, such as, for example, the 3-blade mixer A310 from Lightning.

It should be noted that, when proceeding as described above, a stable, homogeneous ("opaque") suspension is obtained at the end of step (a). In the context of this description, the term "stable, homogeneous suspension" means that such a suspension does not exhibit visible stratification, phase separation, or sedimentation for at least 5 minutes without stirring at room temperature (25°C).

In the context of the process of the present invention, the styrene-butadiene latex used can be obtained by methods known in the art, for example, by emulsion radical copolymerization, as reported, for example, in U.S. Patents 4,070,324 and 5,504,168 or in the publication El-Aasser MS, Sudol D., " Emulsion Polymerization and Emulsion Polymers " (1997), Klein A., Daniel ES Ed., John Wiley and Sons, New York, Chapter VI, pages 37-55.

According to a preferred embodiment of the present invention, in said step (b), said at least one styrene-butadiene latex may have an amount of styrene-butadiene polymer in the range of 10 to 50 wt.%, preferably in the range of 15 to 30 wt.% relative to the total weight of said latex and an amount of bound styrene in the range of 10 to 60 wt.%, preferably in the range of 20 to 50 wt.% relative to the total weight of said latex.

According to a preferred embodiment of the present invention, in said step (b), the suspension obtained in step (a) can be added in such an amount as to obtain an amount of micronized recycled rubber powder in the range of 5 to 95% by weight, preferably in the range of 8 to 35% by weight, relative to the total weight of styrene-butadiene rubber present in the latex.

Said step (b) can be carried out in a mixer (called a "pre-mixer") equipped with a mixing system suitable for producing styrene-butadiene latex containing micronized recycled rubber powder, wherein said micronized recycled rubber powder is homogeneously distributed in the latex. Preferably, said mixing system can consist of an impeller with a mixed secondary flow, such as, for example, a 45° "Pitch Blade" impeller, or an impeller with an axial flow hydrofoil, such as, for example, a 3-blade mixer A310 from Lightning.

According to an embodiment of the present invention, said step (b) can be carried out in a mixer (called a pre-mixer) at a temperature in the range of 20 to 90°C, preferably in the range of 50 to 80°C, for a variable time depending on the size of the mixer and sufficient to obtain a styrene-butadiene latex containing micronized recycled rubber powder, wherein said powder is homogeneously distributed in the latex, preferably for a period of time in the range of 1 to 45 minutes, preferably in the range of 5 to 15 minutes.

Into said mixer (called a pre-mixer) may be added further components commonly used in emulsion radical copolymerization processes for the production of styrene-butadiene rubbers (emulsion polymerized, e-SBR), such as, for example, surfactants selected from the surfactants presented above, extender oils, antioxidants; More detailed information relating to the said emulsion radical polymerization processes for the production of styrene-butadiene rubbers (e-SBR) can be found, for example, in U.S. Patent Nos. 4,070,324 and 5,504,168 or in the publication El-Aasser M.S., Sudol D. " Emulsion Polymerization and Emulsion Polymers " (1997), Lovell P.A., El-Aasser Ed., John Wiley and Sons, New York, Chapter VI, pages 208-234, reported above.

On the other hand, said step (b) can be carried out in the same coagulation mixer (called "coagulation tank") where said step (c) (coagulation) is carried out: in this case, the mixing between the suspension obtained in step (a) and the styrene-butadiene latex takes place directly in said coagulation mixer (called "coagulation tank") (step (c1)).

Thus, another object of the present invention is a method comprising the following steps:

(a1) preparing a suspension containing micronized recycled rubber powder, water and at least one surfactant;

(c1) mixing the suspension obtained in step (a) with at least one styrene-butadiene rubber and coagulating all of this to obtain a coagulated styrene-butadiene rubber containing micronized powder of recycled rubber;

Where:

- in step (a1), the particle size of said micronized recycled rubber powder is in the range of 0.05 to 0.8 mm, preferably in the range of 0.1 to 0.4 mm;

- in step (a1), said at least one surfactant is present in an amount in the range of from 0.5 to 3 wt.%, preferably in the range of from 1 to 2.5 wt.%, relative to the total weight of said micronized recycled rubber powder;

- in step (a1), said micronized powder of recycled rubber has a concentration in water in the range of 1 to 50 wt.%, preferably in the range of 5 to 30 wt.% relative to the total mass of said water.

It should be noted that in the case where said step (b) is carried out in the same coagulation mixer (called a "coagulation vessel") in which said step (c) (coagulation) is carried out, that is, step (c1), mixing can still be carried out in the mixer (called a "pre-mixer") between the additional components presented above and the styrene-butadiene latex to obtain a styrene-butadiene latex, where said additional components are homogeneously distributed in the latex, operating under the same conditions described above for step (b).

The said step (a1) is carried out working under the same conditions as described above for step (a).

According to a preferred embodiment of the present invention, in said step (c1), said at least one styrene-butadiene latex may have an amount of styrene-butadiene polymer in the range of 10 to 50 wt.%, preferably in the range of 15 to 30 wt.% relative to the total weight of said latex and an amount of bound styrene in the range of 10 to 60 wt.%, preferably in the range of 20 to 50 wt.% relative to the total weight of said latex.

According to a preferred embodiment of the present invention, in said step (c1), the suspension obtained in step (a1) can be added in such an amount as to obtain an amount of micronized recycled rubber powder in the range of 5 to 95% by weight, preferably in the range of 8 to 35% by weight, relative to the total weight of styrene-butadiene rubber present in the latex.

According to a preferred embodiment of the present invention, said step (c) and step (c1) may be carried out in the presence of at least one coagulating agent, which may be selected, for example, from among copolymers of alkylamine and epichlorohydrin (for example, a copolymer of dimethylamine and epichlorohydrin, known under the trade name ^Floquat® FL 2250 from NSF).

The amount of coagulating agent and other components that may be present, such as surfactants, extender oils, antioxidants, varies depending on the latex used and the amount of micronized recycled rubber powder.

According to a preferred embodiment of the present invention, said step (c) and step (c1) can be carried out at a temperature in the range of 40 to 90°C, preferably in the range of 60 to 80°C, for a variable time depending on the size of the coagulation mixer (called "coagulation vessel"), the amounts of suspension obtained in step (a) or in step (a1) and the styrene-butadiene latex used, the temperature and pH of the mixing system used, preferably for a time in the range of 5 to 120 min, preferably in the range of 10 to 60 min.

According to a preferred embodiment of the present invention, said step (c) and step (c1) may be carried out at a pH lower than or equal to 5, preferably in the range from 2.5 to 4.

According to a preferred embodiment of the present invention, at least one inorganic acid, such as, for example, sulfuric acid, phosphoric acid, preferably sulfuric acid, can be added in said step (c) and step (c1).

According to a preferred embodiment of the present invention, said at least one organic acid may be added in such an amount as to maintain the pH value below or equal to 5, preferably in the range from 2.5 to 4, during the entire duration of said step (c) and step (c1).

Said step (c) and step (c1) can be carried out in a coagulation mixer (called a "coagulation vessel") equipped with a mixing system. It should be noted that said mixing system is also suitable for achieving a homogeneous distribution of the micronized recycled rubber powder in the styrene-butadiene latex if said step (b) is carried out in the same coagulation mixer (called a "coagulation vessel") as said step (c) (step (c1)). Preferably, said mixing system can consist of an impeller with a mixed secondary flow, such as, for example, a 45° "Pitch Blade" impeller, or a hydrofoil impeller with a purely axial flow, such as, for example, a 3-blade mixer A310 from Lightning.

After coagulation, styrene butadiene rubber containing micronized recycled rubber powder is usually in the form of crumbs.

Preferably, said crumbs are neutralized by adding an aqueous solution containing at least one organic base, such as, for example, a sodium carbonate solution, followed by rinsing with water. The water used for said rinsing may be deionized water or non-deionized water.

Preferably, said rinsing with water can be carried out at a temperature in the range of 35 to 90°C, preferably in the range of 40 to 90°C.

The styrene-butadiene rubber containing micronized recycled rubber powder may be subjected to one or more water washes, for example, one to seven washes, which can be performed periodically or continuously, preferably continuously. Partial drying of the styrene-butadiene rubber containing micronized recycled rubber powder may also be performed between washes.

After washing with water, the styrene-butadiene rubber containing micronized recycled rubber powder is usually subjected to water removal ("dewatering"). Water removal can be carried out in two stages, by first subjecting the styrene-butadiene rubber containing micronized recycled rubber powder to mechanical treatment, for example, by means of screw devices, and then to evaporation, for example, by means of a drying chamber, a hot plate; or in one stage, by directly subjecting the styrene-butadiene rubber containing micronized recycled rubber powder to evaporation, for example, by means of a drying chamber, a hot plate. The said water removal ("dewatering") can be carried out at a temperature in the range of from 40 to 150 °C, preferably in the range of from 60 to 120 °C, for a time greater than 5 minutes, preferably in the range of from 8 to 45 minutes; however, the time must be sufficient to obtain styrene-butadiene rubber containing micronized recycled rubber powder with a residual moisture content of less than 1% by weight of the total weight of styrene-butadiene rubber.

According to a preferred embodiment of the present invention, said method can be carried out in either a batch or continuous mode, preferably in a continuous mode.

As mentioned above, styrene-butadiene rubber containing micronized powder of recycled rubber obtained by the above method, as such or in a mixture with other rubbers, such as, for example, natural rubber (NR), polybutadiene (BR), styrene-butadiene copolymers or mixtures thereof, can be advantageously used in vulcanizable elastomer compositions, which, in turn, can be used in various industries, for example, in tires, shoe soles, brake systems, conveyor belts.

For example, the said styrene-butadiene rubber containing micronized recycled rubber powder can be used in a mixture with carbon black and/or silica in vulcanizable elastomer compositions suitable for producing tires.

Thus, another object of the present invention is a vulcanizable elastomer composition comprising at least one styrene-butadiene rubber comprising micronized recycled rubber powder obtained as described above, at least one filler selected from carbon black, silicon dioxide or mixtures thereof, and at least one vulcanizing agent. Preferably, said filler may be present in said vulcanizable elastomer composition in an amount in the range of 5 to 500 ppm.

The said vulcanizable elastomer composition may contain, in addition to the said styrene-butadiene rubber containing micronized powder of recycled rubber, other elastomers, such as, for example, natural rubber (NR), polybutadiene (BR) or mixtures thereof.

In the context of the present invention and the following claims, the term "ppm" means parts by weight of a given component per 100 parts by weight of the styrene-butadiene rubber present, comprising micronized recycled rubber powder, and other optionally present elastomers in the vulcanizable elastomer composition.

The said vulcanizing agent may be selected, for example, from soluble or insoluble elemental sulfur, or from sulfur donors, or mixtures thereof.

Sulfur donors include, for example, dimorpholyl disulfide (DTDM), 2-morpholinodithiobenzothiazole (MBSS), caprolactam disulfide, dipentamethylenethiuram tetrasulfide (DPTT), tetramethylthiuram disulfide (TMTD) or mixtures thereof.

If the vulcanizing agent is selected from sulfur or sulfur donors, it may also be advantageous to use other additives (e.g. accelerators), such as, for example, dithiocarbamates, thiurams, thiazoles, sulfenamides, xanthates, guanidine derivatives, caprolactams, thiourea derivatives or mixtures thereof, to increase the vulcanization yield.

In said vulcanizable elastomer composition, said sulfur and/or said sulfur donors and said other above-mentioned additives, optionally present, are usually in an amount in the range of 0.05 to 10 ppm, preferably in the range of 0.1 to 8 ppm.

Other components may be added to the vulcanizable elastomer compositions of the present invention.

Inorganic or organic compounds may be added, for example. Examples of such compounds include zinc oxide, zinc carbonate, lead oxide, saturated or unsaturated organic fatty acids or their zinc salts, polyalcohols, aminoalcohols (e.g., triethanolamine), amines (e.g., dibutylamine, dicyclohexylamine, cyclohexylethylamine), polyetheramines, or mixtures thereof.

Vulcanization inhibitors may also be added, such as, for example, N-cyclohexylthiophthalimide (PVI), N,N'-dinitroso-pentamethylenetetramine (DNPT), phthalic anhydride (PTA), diphenyl nitrosamine or mixtures thereof.

In addition to the above-mentioned vulcanizing agents and/or other compounds, the vulcanizable elastomer composition of the present invention may contain additional additives traditionally used in elastomer compositions and known to those skilled in the art, such as other fillers, filler activators, ozone protection agents, aging inhibitors, antioxidants, processing aids, extender oils, plasticizers, reinforcing materials, mold release agents.

Other fillers that can be used in the context of the present invention are, for example, barium sulfate, titanium dioxide, zinc oxide, calcium oxide, calcium carbonate, magnesium oxide, aluminum oxide, iron oxide, aluminum hydroxide, magnesium hydroxide, aluminosilicates, diatomaceous earth, talc, kaolins, bentonites, carbon nanotubes, ^Teflon® (preferably in powder form), silicates, or mixtures thereof. However, the total amount of fillers is in the range of 5 to 500 ppm.

Filler activators that can be used in the context of the invention include, for example, organic silanes such as bis(triethoxysilylpropyl)polysulfide, vinyltrimethylsilane, vinyldimethoxymethylsilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, N-cyclohexyl-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, isooctyltrimethoxysilane, isooctyltriethoxysilane, hexadecyltrimethoxysilane, octadecylmethyldimethoxysilane or mixtures thereof. Additional filler activators are, for example, surfactants such as triethanolamine, ethylene glycols or mixtures thereof. The amount of filler activators is usually in the range from 0 to 10 ppm.

Another object of the present invention is a vulcanized product obtained by vulcanizing said vulcanizable elastomer compositions.

The present invention is further illustrated in more detail by means of an embodiment with reference to FIGS. 1 and 2 below.

FIG. 1 schematically shows a first embodiment of the method according to the invention. In this case, micronized powder of recycled rubber (micronized powder), water and at least one surfactant (e.g. Potassium Soap 80% Gresinox 578M) are fed into a first mixer (1) equipped with a mixing system (e.g. an impeller with a blade angle of 45° "Pitch Blade" or a 3-blade mixer A310 from Lightnin), obtaining a suspension ("opaque") (step (a)). The slurry ('opaque') obtained in step (a) is fed into a second mixer (2) ('called pre-mixer') equipped with a mixing system (e.g. 45° 'Pitch Blade' impeller or 3-blade mixer A310 from Lightnin') where styrene-butadiene latex (SBR latex) and any other components (e.g. surfactants, extender oils, antioxidants (other components)) are also fed, to obtain styrene-butadiene latex containing micronized recycled rubber powder (step (b)) (SBR latex+micronized powder). The resulting latex is fed into a third mixer (i.e., a coagulation mixer, called a "coagulation tank") (3) equipped with a mixing system (e.g., a 45° "Pitch Blade" impeller or a 3-blade A310 stirrer from Lightnin), into which an acid (e.g., sulfuric acid) and a coagulating agent (e.g., Floquat FL 2250) are also fed, and subjected to coagulation [step (c)], pH neutralization (e.g., with an aqueous sodium carbonate solution), water washing, and water removal ("dewatering"), to obtain styrene butadiene rubber containing micronized recycled rubber powder (eSBR rubber+micronized powder).

FIG. 2 schematically shows a second embodiment of the method according to the invention. In this case, micronized powder of recycled rubber (micronized powder), water and at least one surfactant (e.g. Potassium Soap 80% Gresinox 578 M) are fed into a first mixer (1) equipped with a mixing system (e.g. a 45° "Pitch Blade" impeller or a 3-blade A310 mixer from Lightnin), obtaining a suspension ("opaque") (step (a1)). The second mixer (2) (called "pre-mixer"), equipped with a mixing system (e.g. 45° impeller "Pitch Blade" or 3-blade mixer A310 from Lightnin), is fed with styrene butadiene latex (SBR latex) and any other components ((e.g. surfactants, extender oils, antioxidants (additional components)), obtaining styrene butadiene rubber containing said other components (SBR + additional components). The obtained latex is fed to the third mixer (i.e. coagulation mixer, known as "coagulation tank") (3), equipped with a mixing system (e.g. 45° impeller "Pitch Blade" or 3-blade mixer A310 from Lightnin), which is also fed with the slurry ("opaque") obtained in step (a1), acid (e.g. sulfuric acid) and a coagulating agent (e.g. Floquat FL 2250), and the whole is subjected to coagulation (step (c1)), pH neutralization (e.g. with an aqueous sodium carbonate solution), washing with water and removing water (“dewatering”), obtaining styrene butadiene rubber containing micronized recycled rubber powder (eSBR rubber+micronized powder).

For a better understanding of the present invention and its practical application, some illustrative, non-limiting examples are given below.

Example 1

In a first 20-litre mixer equipped with a mixing system consisting of a 45° pitch blade impeller, 67.5 g of micronised end-of-life tyre (ELT) rubber powder (rubber powder B.0/0.35 (d ₉₀ <0.35 mm), Albatros), 675 ml of water and 13.5 g of a 10% by weight aqueous solution of anionic surfactant (Potassium Soap 80% Gresinox 578 M, Parchem) are added; the whole is kept under stirring at 310 rpm for 5 min at 60°C to obtain 765 g of a suspension (opaque).

The suspension ("opaque") is fed into a second 20-liter mixer (called "premixer"), equipped with a mixing system consisting of a 45° "Pitch Blade" impeller, into which 3.2 liters of styrene-butadiene latex (the amount of styrene-butadiene polymer is 21% by weight and the amount of styrene is 40% by weight relative to the total weight of said latex), 2.7 g of antioxidant (Irganox ^® 1520L, BASF), 252 g of aromatic oil (RAE ("residual aromatic extract"), Clematis RL, Eni) and 25 g of a 10% (by weight) aqueous solution of anionic surfactant (Potassium Soap 80% Gresinox 578M, Parchem) are loaded; All this is kept with stirring at 310 rpm for 10 minutes at 60°C, to obtain 4.25 liters of butadiene-styrene latex containing micronized powder of recycled rubber.

In a third 70-liter mixer (i.e., the coagulation mixer, called "coagulation tank"), equipped with a mixing system consisting of a 45° "Pitch Blade" impeller, 10 liters of deionized water are added and, after bringing the temperature to 70°C, sulfuric acid (Aldrich) is gradually added until a pH of 3 is reached; then 4.25 liters of styrene-butadiene latex containing micronized recycled rubber powder obtained as above are added at a flow rate of approximately 0.7 liters/min and 13.4 g of coagulating agent (Floquat FL 2250, SNF). Finally, the whole is kept under stirring at 100 rpm for another 30 minutes at a temperature of 70°C and a pH of 3; During coagulation, sulfuric acid (Aldrich) must be added again to maintain a pH of 3. Then, while still stirring at 100 rpm, after bringing the temperature to 80°C, sodium carbonate (Aldrich) is added to bring the pH to 6.5-7. Once the desired pH is reached, the coagulated latex is filtered, separating the styrene-butadiene rubber crumbs containing micronized recycled rubber powder, which are then washed in a stream of deionized water at approximately 70°C for 10 minutes.

After 10 minutes, the styrene-butadiene rubber crumbs containing micronized recycled rubber powder are dried in an air oven at 100°C for 24 hours (residual moisture: less than 1%).

Example 2

Example 2 is conducted under the same operating conditions as Example 1, using different amounts of components. Table 1 shows the amounts of different components for the production of styrene-butadiene rubber containing micronized recycled rubber powder.

Table 1

PREPARATION OF SUSPENSION ("OPAQUEOUS")
(FIRST MIXER) COMPONENTS QUANTITY Water 1.35 l Potassium Soap 80% Gresinox 578 M (aqueous solution at 10 wt.%) 27 g ELT rubber powder B.0/0.35 (d ₉₀ <0.35 mm) 135 g SECOND MIXER
(PRE-MIXER) COMPONENTS QUANTITY Styrene butadiene latex 3.2 l RAE (Residual Aromatic Extract), Clematis RL 252 g Irganox ^® 1520 L 2.7 g Potassium Soap 80% Gresinox 578 M (aqueous solution at 10 wt.%) 25 g Suspension (“opaque”) 1512 THIRD MIXER
("COAGULATION CAPACITY") COMPONENTS QUANTITY Water 10 l Latex from a premixer 4.99 l Floquat FL 2250 13.4 g Sulfuric acid q.s.* Sodium carbonate q.s.*

*: as much as needed

Example 3

Example 3 was carried out under the same operating conditions as in Example 1, using different amounts of the components and a different aromatic oil (TDAE ("Purified Distilled Aromatic Extract"), Norman 346, ORGKHIM). Table 2 presents the amounts of the different components for the production of styrene-butadiene rubber containing micronized recycled rubber powder.

Table 2

PREPARATION OF SUSPENSION ("OPAQUEOUS")
(FIRST MIXER) COMPONENTS QUANTITY Water 1.35 l Potassium Soap 80% Gresinox 578 M (aqueous solution at 10 wt.%) 27 g ELT rubber powder B.0/0.35 (d ₉₀ <0.35 mm) 135 g SECOND MIXER
(PRE-MIXER) COMPONENTS QUANTITY SBR latex 3.2 l TDAE (Turn-Stilled Aromatic Extract), Norman 346 252 g Irganox ^® 1520 L 2.7 g Potassium Soap 80% Gresinox 578 M (aqueous solution at 10 wt.%) 25 g Suspension (“opaque”) 1512 THIRD MIXER
("COAGULATION CAPACITY") COMPONENTS QUANTITY Water 10 l Latex from a premixer 4.99 l Floquat FL 2250 13.4 g Sulfuric acid q.s.* Sodium carbonate q.s.*

*: as much as needed

EXAMPLE 4

Example 4 was carried out under the same operating conditions as in Example 1, using different amounts of components, a different styrene-butadiene latex (the amount of styrene-butadiene polymer was 21% by weight and the amount of styrene was 23.5% by weight relative to the total weight of the said latex), and without aromatic oil. Table 3 presents the amounts of different components for the production of styrene-butadiene rubber containing micronized recycled rubber powder.

Table 3

PREPARATION OF SUSPENSION ("OPAQUEOUS")
(FIRST MIXER) COMPONENTS QUANTITY Water 1.35 l Potassium Soap 80% Gresinox 578 M (aqueous solution at 10 wt.%) 27 g ELT rubber powder B.0/0.35 (d ₉₀ <0.35 mm) 135 g SECOND MIXER
(PRE-MIXER) COMPONENTS QUANTITY SBR latex 3.2 l Irganox ^® 1520 L 2.7 g Potassium Soap 80% Gresinox 578 M (aqueous solution at 10 wt.%) 25 g Suspension (“opaque”) 1512 THIRD MIXER
("COAGULATION CAPACITY") COMPONENTS QUANTITY Water 10 l Latex from a premixer 4.99 l Floquat FL 2250 13.4 g Sulfuric acid q.s.* Sodium carbonate q.s.*

*: as much as needed

Example 5

The styrene-butadiene rubbers containing micronized recycled rubber powder obtained in Examples 1 and 2 above are used to produce tire compounds.

The styrene-butadiene rubber-containing compound containing the micronized recycled rubber powder obtained in Example 1 is hereinafter referred to as (A).

The styrene-butadiene rubber-containing compound containing the micronized recycled rubber powder obtained in Example 2 is hereinafter referred to as (B).

The physical and mechanical properties of the above compounds are compared with those of two other compounds defined as follows:

(C) a compound containing styrene-butadiene rubber ( ^Europrene® 1739, Versalis) and micronized recycled rubber powder obtained from end-of-life tires (ELT) (rubber powder B.0/0.35 (d ₉₀ <0.35 mm), Albatros) (10 ppm), added by dry mixing;

(D) A compound containing styrene-butadiene rubber (Europrene ^® 1739, Versalis) and micronized recycled rubber powder obtained from end-of-life tires (ELT) (rubber powder B.0/0.35 (d ₉₀ <0.35 mm), Albatros) (20 ppm), added by dry mixing.

Preparation of compounds

The compounds are prepared in a 1.6-liter Banbury closed mixer. Operating conditions are presented in Table 4, and components and quantities are listed in Table 5.

Table 4

Loading the Banbury Mixer Time (min) Operating conditions in the Banbury mixer
60 rpm; FF*: 0.70; T: 60°C Compounds (A) and (B) Compounds (C) and (D) 0 Styrene butadiene rubber+ELT (obtained in Example 1 and Example 2) Europrene ^® 1739 1 1/2 carbon black + oil + other components listed in Table 5 (except sulfur, TBBS and TBDT 80) 1/2 carbon black+ELT+oil+other components listed in Table 5 (except sulfur, TBBS and TBDT 80) 3 1/2 carbon black 1/2 carbon black 6 Unloading (T _max 140°C) Unloading (T _max 140°C) Acceleration Time (min) Operating conditions in the Banbury mixer
60 rpm; FF*: 0.70; T: 60°C 0 Unloaded compound + sulfur + TBBS and TBDT 80 Unloaded compound + sulfur + TBBS and TBDT 80 2 Unloading (T _max 105°C) Unloading (T _max 105°C)

*FF: Load Factor.

The samples are then vulcanized at 160°C in accordance with ISO 6502-1:2018.

Table 5

COMPONENTS Compound A (ppm) Compound B (ppm) Compound C (ppm) Compound D (ppm) e-SBR+micronized powder 147.5 157.5 - - Europrene ^® 1739 - - 137.5 137.5 ELT - - 10 20 N 220 80 80 80 80 Essential oil 10 10 10 10 WB 220 2 2 2 2 6-PPD 0.8 0.8 0.8 0.8 Stearic acid 2.0 2.0 2.0 2.0 TMQ 0.6 0.6 0.6 0.6 ZnO 80 3.8 3.8 3.8 3.8 TBBS 2.0 2.0 2.0 2.0 TBTD 80 0.4 0.4 0.4 0.4 Sulfur 2.3 2.3 2.3 2.3

e-SBR+micronized powder: styrene butadiene rubber containing micronized recycled rubber powder obtained as shown in Examples 1 and 2 above;

Europrene ^® 1739 (e-SBR): oil-extended styrene butadiene rubber produced in emulsion (TDAE oil) (Versalis);

ELT: rubber powder B.0/0.35 (d ₉₀ <0.35 mm), Albatros;

N220: carbon black;

Aromatic oil: TDAE (Turn-Dried Distilled Aromatic Extract), NORMAN 346, ORGKHIM;

WB 220 (technological auxiliary): Struktol;

Stearic acid: Sigma Aldrich;

TMQ (antioxidant): 2,2,4-trimethyl-1,2-dihydroquinoline, polymerized (Nord Chemie);

Rhenogran ^® ZnO 80 (activator): zinc oxide (Lanxess);

TBBS (accelerator): N -tert-butyl-2-benzothiazyl sulfenamide, Vulkacit ^® NZ/EGC (Lanxess);

TBTD 80 (accelerator): tetrabutylthiuram disulfide (Sigma Aldrich).

Table 6 presents the physical and mechanical properties of the obtained vulcanized compounds and the corresponding measurement methods.

Table 6

Properties Compounds Definition Unit of measurement Standard method (A) (B) (C) (D) Mooney viscosity (sing. Muni) ASTM D1646 (2018) 62.2 74.5 62.8 65.9 Destructive stress (MPa) ASTM D412C (2016) 16.8 16.5 16.4 15.9 Elongation at break (%) ASTM D412C (2016) 501 479 475 467 Hardness (according to Shore A) ASTM D2240 (2015) 60 60 59 60 Tear resistance (N/mm) DELFT ISO34 (2015) 33.4 35.2 32.5 33.3 Abraded volume (mm ³ /40 m) ASTM D5963 (2019) 125 123 136 139

From the data presented in Table 6, it is evident that the compounds containing styrene-butadiene rubber containing micronized recycled rubber powder obtained by the method of the present invention (compound (A) and compound (B)) maintain or even improve the physical and mechanical properties compared to compounds containing styrene-butadiene rubber and recycled rubber powder obtained by dry mixing (compound (C) and compound (D)). In particular, it should be noted that compound (A) and compound (B) show an improvement in tear resistance and abrasion volume compared to compound (C) and compound (D), respectively.

Example 6

The physical and mechanical properties of compound (B) are compared with the properties of compound (E) containing styrene-butadiene rubber containing micronized powder of recycled rubber SBR+20 ppm ELT with a particle size in the range from 0.8 to 2.5 mm (Tritogran 1 - P - 0.8-2.5 mm, Tritogom), said rubber being obtained by working as described in Example 1.

Compound (E) is prepared by working under the operating conditions specified in Example 5 (i.e., the same mixing, acceleration and vulcanization cycle) and with the same components and amounts as given in Table 5 for compound (B) (i.e., 157.5 ppm e-SBR+micronized recycled rubber powder+the same amount in ppm of the additional components specified).

Table 7 shows the properties of the obtained vulcanized compounds and the corresponding measurement methods.

Table 7

Properties Compounds Definition Unit of measurement Method (B) (E) Mooney viscosity (sing. Muni) ASTM D1646 (2018) 74.5 65.4 Destructive stress (MPa) ASTM D412C (2016) 16.5 12.3 Elongation at break (%) ASTM D412C (2016) 479 434 Hardness (According to Shore A) ASTM D2240 (2015) 60 58 Tear resistance (N/mm) DELFT ISO34 (2015) 35.2 34.9 Abraded volume (mm ³ /40 m) ASTM D5963 (2019) 123 128

From the data given in Table 7, it is evident that the compound containing styrene-butadiene rubber containing micronized powder of recycled rubber obtained by the method of the present invention (compound (B)), has improved physical and mechanical properties compared to the compound containing styrene-butadiene rubber and recycled rubber powder having a larger particle size (compound (E)).

Claims (48)

1. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, said method comprising the following steps: (a) preparing a suspension containing micronized powder of recycled rubber, water and a potassium salt obtained by disproportionation of a resin acid containing a mixture of abietic acid, neoabietic acid, palustric acid, levopimaric acid, as a surfactant; (b) mixing the suspension obtained in step (a) with at least one styrene-butadiene latex to obtain a styrene-butadiene latex containing micronized recycled rubber powder; (c) coagulating the latex obtained in step (b) to obtain coagulated styrene-butadiene rubber containing micronized recycled rubber powder; Where: - in step (a) the particle size of said micronized recycled rubber powder is in the range from 0.05 to 0.8 mm; - in step (a) said at least one surfactant is present in an amount in the range of 0.5 to 3% by weight relative to the total weight of said recycled rubber powder; - in step (a) said micronized powder of processed rubber has a concentration in water in the range of 1 to 50% by weight relative to the total weight of said water; - said step (c) is carried out in the presence of at least one coagulating agent selected from copolymers of alkylamine and epichlorohydrin, at a temperature in the range from 40 to 90°C and at a pH less than or equal to 5. 2. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, according to claim 1, in which: - in step (a) the particle size of said micronized recycled rubber powder is in the range from 0.1 to 0.4 mm; - in step (a) said at least one surfactant is present in an amount in the range of 1 to 2.5 wt.% relative to the total weight of said recycled rubber powder; - in step (a), said micronized powder of processed rubber has a concentration in water in the range of 5 to 30% by weight relative to the total weight of said water. 3. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 1, wherein said step (a) is carried out at a temperature in the range from 20 to 90°C for a variable time depending on the size of the mixer and sufficient to obtain a homogeneous suspension. 4. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 3, wherein said step (a) is carried out at a temperature in the range from 50 to 80°C. 5. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, according to claim 3, wherein said step (a) is carried out for a time in the range from 5 to 60 minutes. 6. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 5, wherein said step (a) is carried out for a time in the range from 10 to 40 minutes. 7. A method for producing styrene-butadiene rubber containing micronized recycled rubber powder according to claim 1, wherein in said step (b) said at least one styrene-butadiene latex has an amount of styrene-butadiene polymer in the range of 10 to 50 wt.% relative to the total weight of said latex and an amount of bound styrene in the range of 10 to 60 wt.% relative to the total weight of said latex. 8. A method for producing styrene-butadiene rubber containing micronized recycled rubber powder according to claim 7, wherein in said step (b) said at least one styrene-butadiene latex has an amount of styrene-butadiene polymer in the range of 15 to 30 wt.% relative to the total weight of said latex and an amount of bound styrene in the range of 20 to 60 wt.% relative to the total weight of said latex. 9. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 1, wherein in said step (b) the suspension obtained in step (a) is added in such an amount as to obtain an amount of micronized powder of recycled rubber in the range from 5 to 95% by weight relative to the total weight of styrene-butadiene rubber present in the latex. 10. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 9, wherein in said step (b) the suspension obtained in step (a) is added in such an amount as to obtain an amount of micronized powder of recycled rubber in the range from 8 to 35% by weight relative to the total weight of styrene-butadiene rubber present in the latex. 11. The method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 1, wherein said step (b) is carried out at a temperature in the range from 20 to 90°C for a variable time depending on the size of the mixer and sufficient to produce styrene-butadiene latex containing micronized powder of recycled rubber, where said powder is homogeneously distributed in the latex. 12. The method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 11, in which said step (b) is carried out at a temperature in the range from 50 to 80°C. 13. A method for producing styrene-butadiene rubber containing micronized recycled rubber powder according to claim 11, wherein said step (b) is carried out for a period of time in the range of 1 to 45 minutes. 14. The method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 13, wherein said step (b) is carried out for a period of time in the range of 5 to 15 minutes. 15. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, comprising the following stages: (a1) preparing a suspension containing micronized powder of recycled rubber, water and a potassium salt obtained by disproportionation of a resin acid containing a mixture of abietic acid, neoabietic acid, palustric acid, levopimaric acid, as a surfactant; (c1) mixing the suspension obtained in step (a1) with at least one styrene-butadiene rubber and coagulating all of this to obtain a coagulated styrene-butadiene rubber containing micronized powder of recycled rubber; Where: - at step (a1), the particle size of said micronized recycled rubber powder is in the range from 0.05 to 0.8 mm; - in step (a1), said at least one surfactant is present in an amount in the range of 0.5 to 3% by weight relative to the total weight of said micronized recycled rubber powder; - in step (a1), said micronized powder of recycled rubber has a concentration in water in the range from 1 to 50 wt.%; - said step (c1) is carried out in the presence of at least one coagulating agent selected from copolymers of alkylamine and epichlorohydrin, at a temperature in the range from 40 to 90°C and at a pH less than or equal to 5. 16. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, according to claim 15, where: - at step (a1), the particle size of said micronized recycled rubber powder is in the range from 0.1 to 0.4 mm; - in step (a1), said at least one surfactant is present in an amount in the range of 1 to 2.5 wt.% relative to the total weight of said micronized recycled rubber powder; - in step (a1), said micronized powder of processed rubber has a concentration in water in the range of 5 to 30% by weight relative to the total weight of said water. 17. A method for producing styrene-butadiene rubber containing micronized recycled rubber powder according to claim 15, wherein said step (a1) is carried out in accordance with the conditions of claim 3. 18. The method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 1 or 15, wherein said step (c) or step (c1) is carried out at a temperature in the range from 60 to 80°C for a variable time depending on the size of the coagulation mixer, the amount of suspension obtained in step (a) or step (a1), and the styrene-butadiene latex used, the temperature and pH of the mixing system used. 19. The method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 18, wherein said step (c) and step (c1) are carried out for a time in the range from 5 to 120 minutes. 20. The method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 19, wherein said step (c) and step (c1) are carried out for a time in the range from 10 to 60 minutes. 21. A method for producing styrene-butadiene rubber containing micronized recycled rubber powder according to claim 1 or 15, wherein said step (c) or step (c1) is carried out at a pH in the range from 2.5 to 4. 22. A method for producing styrene-butadiene rubber containing micronized recycled rubber powder according to claim 1 or 15, wherein at least one inorganic acid selected from sulfuric acid, phosphoric acid is added in said step (c) or step (c1), and at least one organic acid is added in such an amount as to maintain a pH lower than or equal to 5 throughout the duration of said step (c) or step (c1). 23. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber according to claim 21, wherein at least one inorganic acid selected from sulfuric acid, phosphoric acid is added in said step (c) or step (c1), and at least one organic acid is added in such an amount as to maintain the pH in the range from 2.5 to 4 during the entire duration of said step (c) or step (c1). 24. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, according to claim 1, wherein said method is carried out periodically or continuously. 25. A method for producing styrene-butadiene rubber containing micronized powder of recycled rubber, according to claim 23, wherein said method is carried out continuously. 26. A vulcanizable elastomer composition suitable for use in tires, shoe soles, brake systems, conveyor belts and containing at least one styrene-butadiene rubber containing micronized powder of recycled rubber obtained according to claim 1, at least one filler selected from carbon black, silicon dioxide or mixtures thereof, and at least one vulcanizing agent. 27. A vulcanized product obtained by vulcanizing the elastomer composition according to claim 26.