DEVULCANIZING ADDITIVE, RELATIVE METHOD OF DEVULCANIZATION AND DEVULCANIZED PRODUCT

Abstract

A devulcanizing additive for vulcanized elastomers is described, said additive having improved efficiency and selectivity, together with the relative method of devulcaniztion, in continuous and batchwise, and the devulcanized product obtained by means of said devulcaniztion method of vulcanized elastomers.

Claims

1-17. (canceled)

18. A devulcanizing additive for vulcanized elastomers, in particular sulfur-vulcanized rubbers, consisting of: an acid-base adduct obtained starting from a dicarboxylic organic acid having a number of carbon atoms ranging from 2 to 18 and from urea or mono-, di- or tri-substituted derivatives of urea having the following formula: ##STR00005## wherein R1, R2 and R3, the same as or different from each other, are taken from the group consisting of hydrogen, and linear alkyl chains having from 2 to 18 carbon atoms; a peroxide, said peroxide optionally mixed and absorbed on an inert inorganic filler, taken from the group consisting of silicas, calcium carbonates, kaolins, aluminum silicates, clays and mixtures thereof; and optionally, a compatibilizer selected from the group consisting of ethylene-vinyl acetate copolymer, zinc dimethylacrylate, NR-g-PDMMMP (grafted copolymer of natural rubber (NR) and poly(dimethyl(methacryloyloxymethyl)phosphonate (PDMMMP)), liquid butadiene-isoprene copolymer rubber, GMA & MAH (grafted polyolefin polymers), epoxidized natural rubber, trans-polyoctenamer (TOR) and mixtures thereof, wherein the acid-base adduct is obtained from organic dicarboxylic acid and urea or mono, di or trisubstituted derivatives of urea, in a molar ratio ranging from 1:1 to 1:2.

19. The additive according to claim 18, wherein the acid-base adduct is obtained from a dicarboxylic organic acid having a number of carbon atoms ranging from 2 to 10, and from urea or mono, di- or tri-substituted derivatives of urea, in a molar ratio ranging from 1:1 to 1:2.

20. The additive according to claim 18, wherein the devulcanizing additive is a solid.

21. The additive according to claim 18, wherein the organic dicarboxylic acid is selected from the group consisting of oxalic acid, tartaric acid, and malic acid, and wherein the base is urea.

22. The additive according to claim 18, wherein the acid-base adduct is an oxalic acid-urea adduct in a molar ratio of 1:2.

23. The additive according to claim 18, wherein the peroxide is selected from the group consisting of an organic or inorganic peroxide, an organic peroxide selected from the group consisting of dicumyl peroxide, 1,3-1,4-bis (tert-butylperoxyisopropyl) benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, Tert-butylcumyl peroxide, 2,5-dimethyl-2,5-di(tertbutylperoxy)hex-3-ine, n-butyl-4,4-di(tert-butylperoxy) valeriate, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, di(2,4-dichloro-benzoyl) peroxide, and mixtures thereof, optionally with scorch protection.

24. The additive according to claim 18, wherein the peroxide is absorbed on silica, calcium carbonate, aluminum silicates, kaolin or mixtures thereof.

25. The additive according to claim 18, wherein the peroxide is dicumyl peroxide absorbed on calcium carbonate and silica.

26. The additive according to claim 18, wherein the compatibilizer, when optionally included, is trans-polyoctenamer (TOR).

27. The additive according to claim 26, wherein the trans-polyoctenamer (TOR) is a powder or pure granulate.

28. A method of using an additive according to claim 18, for the devulcanization of sulfur-vulcanized rubbers, wherein, when the devulcanizing additive consists of adduct and peroxide, comprising adding said additive in a quantity ranging from 0.5 to 5% by weight with respect to the weight of the elastomer to be devulcanized, the adduct being added in a quantity ranging from 0.4 to 4.5% by weight and the peroxide being added in a quantity ranging from 0.1 to 3% by weight with respect to the weight of the elastomer to be devulcanized.

29. A method of using an additive according to claim 26, for the devulcanization of sulfur-vulcanized rubbers, wherein, when the devulcanizing additive consists of adduct, peroxide and compatibilizer, comprising adding said additive in a quantity ranging from 1 to 20% by weight with respect to the weight of the elastomer to be devulcanized, the adduct being added in a quantity ranging from 0.5 to 4.5% by weight, the peroxide being added in a quantity ranging from 0.1 to 3% by weight and the compatibilizer being added in a quantity ranging from 0.4 to 19.4% by weight with respect to the weight of the elastomer to be devulcanized.

30. A method for the devulcanization of sulfur-vulcanized rubbers, batchwise, comprising the following steps: i) mixing the devulcanizing additive consisting of: an acid-base adduct obtained from a dicarboxylic organic acid having a number of carbon atoms ranging from 2 to 18 and from urea or mono-, di- or tri-substituted derivative of urea having the following formula: ##STR00006## wherein R1, R2 and R3, the same as or different from each other, are taken from the group consisting of hydrogen and linear alkyl chains having from 2 to 18 carbon atoms, and a peroxide; with the vulcanized elastomer to be devulcanized; the acid base adduct being obtained from the dicarboxylic organic acid and from urea or the derivatives of mono-, di- or tri-substituted urea, in a molar ratio ranging from 1:1 to 1:2; with the possible addition of a compatibilizer; ii) optionally heating the mixture thus obtained; iii) compressing and mechanically stretching, in an open or closed mixer; iv) repeating the compressing and mechanically stretching step iv) for a number of times ranging from 0 to 40.

31. The method according to claim 30, wherein steps iv) and v) are effected by controlling the temperature in a range from 20 to 110? C.

32. A method for the devulcanization of sulfur-vulcanized rubbers, in continuous, comprising the steps: i) mixing the devulcanizing additive consisting of: an acid-base adduct obtained from a dicarboxylic organic acid having a number of carbon atoms ranging from 2 to 18 and from urea or mono-, di- or tri-substituted derivatives of urea having the following formula: ##STR00007## wherein R1, R2 and R3, the same as or different from each other, are taken from the group consisting of hydrogen and linear alkyl chains having from 2 to 18 carbon atoms, and a peroxide; with the vulcanized elastomer to be devulcanized; the acid base adduct being obtained from the dicarboxylic organic acid and from urea or the derivatives of mono-, di- or tri-substituted urea, in a molar ratio ranging from 1:1 to 1:2; with the optional addition of a compatibilizer; ii) optionally heating the mixture thus obtained; and iii) extruding the devulcanized product.

33. A devulcanized product obtained from the method according to claim 30, suitable for use as a raw material in blends with virgin elastomers to obtain sulfur-vulcanized rubbers, in a percentage ranging from 5% to 100% with respect to the weight of the blend.

34. The additive according to claim 1, wherein the acid-base adduct is obtained from a monocarboxylic or dicarboxylic organic acid having a number of carbon atoms ranging from 2 to 10 and from urea or mono-, di- or tri-substituted derivatives of urea, in a molar ratio ranging from 1:1 to 1:2.

Description

[0107] The invention will also appear more evident from the attached figures, in which:

[0108] FIG. 1 shows the devulcanization degree for the devulcanized products obtained in the following examples 1, 2, 4, 5 and 6, measured according to the standard ASTM D6814;

[0109] FIG. 2 shows the analysis of the Horikx diagram for the devulcanized products obtained in the following examples 1, 2, 4, 5 and 6;

[0110] FIG. 3 shows a multi-screw extruder, planetary extruder or Ring-Extruder, with 12 co-rotating screws;

[0111] FIG. 4 shows a schematic sectional view of the multi-screw extruder to demonstrate that the cooling is effective both inside and outside the planetary arrangement of the screws;

[0112] FIG. 5 shows that the elongational flow values of a multi-screw extruder are higher than those of a normal twin-screw extruder;

[0113] FIG. 6 is a table showing the physical-mechanical properties measured for a technical article (example Bushing), subjected to testing;

[0114] FIG. 7 is a table showing the physical-mechanical properties measured for the Tyre, truck treadPremium Truck Tyre, subjected to testing;

[0115] FIG. 8 shows a visual comparison of the raw product, i.e. between the appearance of the product of the state of the art and the appearance of the product according to the present invention, wherein the devulcanized product has been added at 10% by weight on top on a base blend for a technical article (Bushing), also comprising vulcanizing and accelerating products, the blend was then processed and photographed before vulcanization;

[0116] FIG. 9 shows a visual comparison of the cured product, i.e. between the appearance of a state-of-the-art product and the appearance of a product according to the present invention, obtained according to the method indicated for FIG. 8, starting from a base blend for truck treadPremium Truck Tyre and wherein the product was photographed after vulcanization;

[0117] FIG. 10 is a table showing the physical-mechanical properties measured for the tyre, car treadPassenger Tyre, tested.

[0118] By way of non-limiting example of the present invention, some representative examples of the present invention are provided hereunder.

[0119] In the following examples 1-3, an ELT powder was used with the following characteristics, deriving from thermogravimetric analysis (TGA):

TABLE-US-00001 % Value NR 37% SBR 22% Carbon Black 26% White fillers 9% Volatile products 5%

Example 1

[0120] An example of devulcanization, with a batch plant with a roll-mill, was carried out with the devulcanizing additive according to the present invention as follows.

[0121] 100 kg of ELT powder, deriving from truck tread, with a particle size ranging from 0.05 mm to 3 mm, mainly equal to 0.8 mm, were weighed.

[0122] 3% by weight of oxalic acid-urea adduct was added to the powder in a molar ratio of 1:2 and 0.25% by weight of dicumyl peroxide at 40%, adsorbed on a mixture of silica and calcium carbonate.

[0123] The mixture thus obtained was homogenized for 5 minutes and brought to the surface temperature (measured by means of an infrared thermometer) of 70? C. by means of a high-speed turbomixer, with a mixing tool profile and a number of blades suitable for transferring quantities of motion to the mixture in order to form a correct mixing cone and at the same time transfer sufficient energy for a constant temperature increase in the times established.

[0124] A mixing tool suitable for the purpose has from one to 4 mixing steps, in the case of the present example three mixing steps, with a blunt or rounded blade profile to allow adequate fluidization of the material.

[0125] The temperature is a parameter that can be subject to interpretation errors: the rubber in fact undergoes heating due to mechanical action and its temperature, measured with an infrared thermometer, drops extremely rapidly over time. For this reason, positioning the infrared probe too far downstream from the rolls can result in a significantly lower temperature measurement. The product becomes lukewarm in a very short time, so much so that it mistakenly induces the impression of a low-temperature process.

[0126] The mixture thus homogenized and heated, was passed for 6 minutes in a roll-mill, with a relative speed of 1:1.2, the span between the rolls set to the minimum (virtually zero, compatibly with the grinding of the rolls), and appropriate thermostat-regulation of the rolls, said rolls being kept at a temperature below 35? C. More specifically, the span between the rolls is 0.1 mm.

[0127] 2% by weight of TOR in powder form was added to the mixture thus processed, distributing it homogeneously over the mass of the mixture.

[0128] The mixture was again processed in the roll-mill for a further 4 minutes, until complete melting and incorporation of the compatibilizer within the mixture.

[0129] The mixture was then discharged and sent for packaging, then proceeding with a new processing batch.

[0130] The preheating temperature, the number of steps in the mixer, the times, the rotation rate and the relative speed of the rolls, as well as the percentages of modifiers and compatibilizers, the operating temperatures, can vary according to the type of powder, which must be previously analyzed to define the best process conditions.

Example 2

[0131] A second example of devulcanization with the devulcanizing additive according to the present invention was carried out following exactly the same method as Example 1 with the difference that the peroxide used is a dicumyl peroxide with a scorch protection system (Luperox with Scorch Protection SP2, marketed by Arkema).

Example 3

[0132] A third example of devulcanization with the devulcanizing additive according to the present invention was carried out following exactly the same method as Example 1 with the difference that the material to be devulcanized is a SBR (styrene-butadiene Rubber) resulting from the grinding of waste processing of the footwear industry, particularly shoe soles, and destined for re-use in the same application: 100 kg of SBR rubber powder were then weighed, with a particles size ranging from 0.5 mm to 3 mm, mainly equal to 1, 2 mm.

Example 4

[0133] A fourth example of devulcanization with the devulcanizing additive according to the present invention was carried out as follows.

[0134] 100 kg of ELT powder, deriving from truck tread, of a production batch different from the previous examples and not previously analyzed, with a particle size ranging from 0.5 mm to 3 mm, mainly equal to 1.2 mm, were weighed.

[0135] 3.5% by weight of oxalic acid-urea adduct in a molar ratio of 1:2 and 0.30% by weight of dicumyl peroxide at 40%, adsorbed on a mixture of silica and calcium carbonate was added to the powder.

[0136] The mixture thus obtained was homogenized in a low-speed horizontal mixer for 8 minutes, under cold conditions.

[0137] The mixture thus homogenized was passed 25 times in a roll-mill, the span between the rolls being equal to 0.2 mm to adapt to the greater particle size of the product, whereas the speed ratio was brought to 1:1.3, to increase the stretching of the product. An appropriate thermostat-regulation of the rolls was always maintained, keeping said rolls at a temperature below 35? C.

[0138] This process took 12 minutes to reach a temperature of 95? C., measured on the rubber with an infrared thermometer.

[0139] The mixture was then discharged and sent for packaging, then proceeding with a new processing batch.

[0140] In this example, the mixture, due to its characteristics, was processed with a greater number of steps and did not require the use of a compatibilizer or preheating; in this case it was therefore possible to homogenize the components under cold conditions in a horizontal mixer, with a slow-rotating internal mixing reel and directly process the mixture thus obtained in a roll-mill. In particular the horizontal mixer is a ribbon blender.

Example 5

[0141] A further example of devulcanization with the devulcanizing additive according to the present invention was carried out using the same method as in Example 4, with the difference that the peroxide used is an inorganic peroxide.

[0142] 3.5% by weight of oxalic acid-urea adduct in a molar ratio of 1:2 and 0.15% by weight of potassium peroxymonosulfate, in the form of a granular powder as a triple salt, called Oxone, were added to the ELT powder, not previously analyzed, with a particle size ranging from 0.5 mm to 3 mm, mainly equal to 1.2 mm.

[0143] Also in this case it was not necessary to use the compatibilizer, or preheating.

Example 6

[0144] A sixth example of devulcanization with the devulcanizing additive according to the present invention was carried out as follows.

[0145] 100 kg of Rubber Buffing, deriving from an end-of-life tyre, with a particle size ranging from 0.5 mm to 10 mm, very irregular, were weighed: this is a product deriving from the coarse grinding of the tyre tread. This product, called Rubber Buffing, derives directly from buffing, and has a very irregular, elongated, frayed shape with dimensions of even a few centimeters.

[0146] 3 phr (parts per 100 parts of rubber) of oxalic acid-urea adduct in a molar ratio of 1:2 and 2.5 phr of 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane at 40%, adsorbed on a mixture of calcium carbonate and sodium aluminum silicate, were added to the Rubber Buffing.

[0147] The mixture thus obtained was homogenized in a low-speed horizontal mixer for 8 minutes, under cold conditions.

[0148] The homogenized mixture was passed 20 times in a roll-mill, the span between the rolls having been set at 0.1 mm, whereas the speed ratio was set at 1:1.5. An adequate thermostat-regulation of the rolls was always maintained, by means of a heating/cooling unit or by means of a refrigerator alone, keeping the temperature of said rolls below 40? C.

[0149] The speed of the rollers was set at 80 RPM and the processing was continued until the buffing form had dissolved and the classic flaky form had been produced, which is obtained by devulcanization.

[0150] The mixture was then discharged and sent for packaging, then proceeding with a new processing batch.

Example 7

[0151] A further example was carried out with the same recipe as in Example 4, with the difference that the mixture was processed using a multi-screw extruder, planetary extruder or Ring-Extruder, with 12 co-rotating screws (shown in FIG. 3), with a profile suitable for the purpose. The particular feature of this extruder is to allow optimal temperature control to avoid depolymerization phenomena, thanks to the high contact area with the cooled parts of the roll. The cooling is also effective both outside and inside the planetary arrangement of the screws (FIG. 4).

[0152] This extruder has proved to be particularly suitable for the devulcanization reaction, due to the property of optimal thermal control. The screw profile used basically provides for a large preponderance of conveyance elements and a reduced quantity of mixing elements concentrated in the final part, responsible for the greater mechanical stress and increase in temperature. Although speeds and pressures are similar to normal extrusion processes, the particular geometry of the ring extruder itself has a greater intermeshing area, thus achieving better mixing while keeping the temperature low. Furthermore, this extruder allows much higher elongational flow values (FIG. 5) to be obtained compared to a normal twin-screw extruder, values even 50% higher. This allows a greater number of compression and decompression movements of the rubber, similar to what takes place in roll-mills; this kind of mechanical stress has proved to be extraordinarily effective for the highly selective devulcanization process.

[0153] The use of these extruders for the preparation of rubber blends, wherein this particular temperature management is exploited, is known from the state of the art (DE102015120586); the use for devulcanization is, on the contrary, innovative.

[0154] 200 kg of ELT powder, deriving from truck tread, with a particle size ranging from 0.5 mm to 3 mm, mainly equal to 1.2 mm, were weighed.

[0155] 2.5% by weight of oxalic acid-urea adduct in a molar ratio of 1:2 and 0.25% by weight of 40% dicumyl peroxide, adsorbed on a mixture of silica and calcium carbonate, were added to the powder.

[0156] The mixture thus obtained was homogenized in a turbomixer for a time of 2 minutes, without a significant increase in temperature, reaching 40? C.

[0157] The homogenized mixture was extruded with a multi-screw extruder, also called Ring-Extruder or planetary extruder, always keeping the temperature below the polymer depolymerization temperature. The operating temperature was kept at a value ranging from 100 to 150? C. according to the areas, the screw revolutions equal to 600 RPM, whereas the diameter of the screws was 30 mm, with an LD ratio of 55. The productivity was 350 kg per hour.

[0158] The particular conformation of this equipment allowed an optimal management of the process. The extruded mixture was then sent for packaging.

[0159] As clearly explained, this particular extruder, unlike other types, allows efficient processing, resulting in optimal temperature control with the same stress applied, an excellent productivity and, if necessary, effective degassing.

Example 8

[0160] This example was carried out with the same recipe as Example 7, with the difference that the mixture was processed by means of a co-rotating twin-screw extruder, having a special profile of the screws, suitable for the purpose: this is in particular an increased number of conveyance screw elements and a balanced number of grinding and mixing elements, such as to effectively control the excessive temperature increase.

[0161] The process temperature was kept at values ranging from 80 to 270? C. depending on the areas, with a vacuum degassing at ?850 mbars, and a pressure of 7 bars. The extruder had a screw diameter of 35 mm, with an LD ratio of 48 and screw revolutions equal to about 300 RPM; the productivity was equal to about 50 kg per hour.

[0162] The presence of an adequate number of elements with an inverse profile allowed a correct management of the melt pressures and allowed a vacuum degasser to be inserted for an effective removal of the gases. It was possible to arrange the final degassing, before the supply chain, in a particularly efficient way.

Result Analysis.

[0163] The devulcanized products obtained at the end of Examples 1-8 were analyzed and are characterized by devulcanization degrees ranging from 74% to 45%, with percentage increases ranging from +80% to +32% with respect to the product treated with the oxalic acid-urea adduct alone in a molar ratio of 1:2.

[0164] In particular, the devulcanization degree measured for the product treated with the oxalic acid-urea adduct alone in a molar ratio of 1:2 was equal to 56%?1, whereas the devulcanization degree of the product obtained according to Example 1 was equal to 74%?3, with an increase of +32%. (see FIG. 1) demonstrating the considerable improvement, in terms of devulcanization efficacy, obtained with the devulcanizing additive according to the present invention compared to the state of the art.

[0165] In Example 2, the devulcanization degree measured for the product treated with the oxalic acid-urea adduct alone in a molar ratio of 1:2 was equal to 56%?1, whereas the devulcanization degree of the product obtained according to Example 2 was equal to 64%?1, with an improvement of +14%.

[0166] In Example 3, the devulcanization degree was not measured, but the processability in the blend and the performances obtained in the production of new shoe soles from which the scraps derived, was measured. The processability of the mixture treated with the devulcanizing additive according to the present invention was found to be optimal, resulting in a percentage of re-use in new blends up to 66% higher than in the state of the art.

[0167] In Example 4, the devulcanization degree measured for the product treated with the oxalic acid-urea adduct alone, at low temperature, in a molar ratio of 1:2, was equal to 13%?3, whereas the devulcanization degree of the product obtained according to Example 4 was equal to 63%, with a substantial improvement.

[0168] In Example 5, the devulcanization degree with the oxalic acid-urea adduct alone, at low temperature, in a molar ratio of 1:2 was equal to 13%?3, as in Example 4; whereas the devulcanization degree of the product according to Example 5 was equal to 60%, with a substantial improvement, and also demonstrating the effectiveness and possibility of also using inorganic peroxides for the purposes of the present invention.

[0169] In Example 6, the devulcanization degree measured for the product treated with the oxalic acid-urea adduct alone in a molar ratio of 1:2 was equal to 31%?18, wherein the wide variability of the result is a consequence of the non-uniform particle size of the Buffing, whereas the devulcanization degree of the product obtained according to Example 6-5 was equal to 45%?7, with an improvement of +45% in the example in question, both for the devulcanization degree, but also for a lesser variability of the result with the same Buffing particle size.

[0170] The results of Examples 7 and 8 in multi-screw and twin-screw extrusion confirm the improvements of the previous examples effected in roll-mills. In order to take into account the different processing methods, which have greater temperature variations and a greater fraction of volatile gases extracted through degassing, the devulcanization degree was not evaluated, but rather the behaviour in the blend, which results in a percentage of re-use, in new blends, up to 50% higher than in the state of the art.

[0171] The analysis of the Horikx diagram (see FIG. 2) also indicates an extremely selective devulcanization with respect to the sulfur bonds, both polysulfide, mono- and di-sulfide, preserving the Carbon-Carbon bonds of the molecular chain from breakage and thus preserving the molecular weight of the elastomer.

[0172] It can therefore be concluded that the devulcanizing additive according to the present invention allows a devulcanized product to be obtained, characterized by a high degree of devulcanization compared to the prior art and at the same time a homogeneous and high-quality devulcanization.

[0173] In the present patent application, base blend refers to the blend produced with only elastomers and virgin polymers, fillers, additives and the package of specific vulcanizing products.

[0174] In the present patent application, final blend refers to the base blend to which a certain quantity of devulcanized product, according to the present invention, has been added.

[0175] As previously indicated, the devulcanized product thus obtained can be mixed with a base blend. i.e. a blend with elastomers and virgin polymers, including additives, fillers, vulcanizers and accelerators, said devulcanized product being added in quantities ranging from 10% to 90% % by weight, intended as a percentage by weight with respect to the weight of the final blend.

[0176] Said final blend, once vulcanized, has mechanical and chemical properties very similar to those of the respective starting base blend, devoid of devulcanized product. i.e. produced only with elastomers and virgin polymers, additives, fillers, vulcanizers and accelerators, demonstrating that the devulcanized product according to the present invention is effectively devulcanized and allows a final blend to be obtained which behaves very similarly to a blend produced with only first-rate virgin components.

[0177] After carrying out the analysis of the results according to the standard ASTM D6814-02 and with the Horikx diagram through which the devulcanization degree and the selectivity degree of the devulcanization were measured, a test campaign was then effected for verifying the physical-mechanical properties in the final blend of the devulcanized products object of the present invention, wherein the devulcanized product according to the present invention is used for replacing elastomers and virgin polymers, in percentages that depend on the application sector for which the final blend is intended.

[0178] It is not significant, nor at times possible, in fact, to test the physical-mechanical properties of the devulcanized rubber/product as such, according to the present invention: these properties must in fact be tested on specimens obtained starting from a non-vulcanized blend in which the devulcanized rubber is added in percentages ranging from 5% to 90% by weight (more commonly from 10% to 30% by weight) with respect to the total weight of the final compound, adding the fillers and package of specific vulcanizing products, and then vulcanizing the whole mixture: specimens are then obtained from the final vulcanized and moulded blend, on which the physical-mechanical properties are measured, which are then compared with the corresponding properties of specimens similarly obtained from the corresponding base blend, without devulcanized rubber.

[0179] The physical-mechanical properties of devulcanized rubber are therefore more significant when tested in specific final blends for the various application sectors, wherein the devulcanized rubber is added in variable percentages depending on the criticality of the application. In a tyre, for example, it is preferable to limit the quantity of devulcanized product present in the blend within the range of 10% to 30% by weight with respect to the weight of the final blend, whereas in footwear that has less stringent technical requirements, it is possible to use a quantity of devulcanized product in the blend ranging from 50% to 80% by weight with respect to the weight of the final blend.

[0180] More specifically, the use of a devulcanized rubber from ELTs according to the present invention was tested in blends for the following application sectors: [0181] Technical article (example of Bushing, bushes for the automobile sector), [0182] Tyre, truck tread (example of Premium Truck Tyre), [0183] Tyre, car tread (example of Passenger Tyre).

[0184] The use of recycled rubber from processing scraps, devulcanized according to the present invention, was also tested in the sector of: [0185] Footwear (example of a shoe sole).

[0186] The devulcanized rubber was added in quantities ranging from 10% to 50% by weight with respect to the total weight of the final blend depending on the application.

[0187] The final blends used in the various application sectors are very different in chemical composition, mixing and vulcanization methods, and the addition of the devulcanized rubber according to the present invention allows an optimal re-use of the same, with different effects depending on the type of blend.

[0188] The base blends, produced with only elastomers and virgin polymers, fillers, additives and the package of vulcanizing products specific for the various application sectors, can be exemplified as indicated in the following tables:

Base Blend for a Technical Article being Tested (Bushing)

TABLE-US-00002 Material Phr (parts per 100 parts of rubber) Natural rubber (NR) 100 Carbon black FEF N550 55 Oils, plasticizers, antioxidants 9 Zinc oxide 5 Sulfur and accelerators 3

Base Blend for Truck TyresPremium Truck TyreSubjected to Testing:

[0189]

TABLE-US-00003 Material Phr (parts per 100 parts of rubber) Natural rubber (NR) 70 High-CIS polybutadiene rubber (BR) 30 Carbon black SAF N220 50 Oils, plasticizers, antioxidants 5 Zinc oxide 3 Sulfur and accelerators 3

Basic Blend for Car TyresPassenger TyreSubjected to Testing:

[0190]

TABLE-US-00004 Material Phr (parts per 100 parts of rubber) Styrene Butadiene Rubber Solution 96.25 (S-SBR, oil extended 37.5 phr) High-CIS polybutadiene rubber (BR) 30 Silica/TESPT 70/7 Carbon black SAF N220 15 Oils, plasticizers, antioxidants 15 Zinc oxide 3 Sulfur and accelerators 4

Base Blend for Footwear (Shoe Sole) Subjected to Testing

[0191]

TABLE-US-00005 Material Phr (parts per 100 parts of rubber) Natural rubber (NR) 40 Styrene Butadiene Emulsion Rubber 40 Rubber (E-SBR) High-CIS polybutadiene rubber (BR) 20 White fillers 70 Oils, plasticizers, antioxidants 28 Zinc oxide 3 Sulfur and accelerators 5

[0192] The base blends (without devulcanized product/rubber) indicated in the previous tables represent standard blend recipes for the verification of the physical-mechanical tests in the blend; many producers of rubber blends use other products or additives or components, often reserved, and in varying concentrations compared to the examples. It should be noted however that these differences produce results in line with those specified in the present description.

[0193] Base blends (without devulcanized product/rubber as reference) were therefore created for each application sector: furthermore, as a comparison, blends containing different quantities of a devulcanized product obtained with the oxalic acid-urea adduct (Urea-oxalic acid Blends) were produced, and finally blends containing different quantities of the devulcanized product according to the present invention, i.e. obtained with the devulcanizing agent according to the present invention (This Patent Blends).

[0194] The improvements in the mechanical characteristics have been indicated as a percentage, normalizing the result obtained for the base blend to 100.

[0195] The physical-mechanical properties indicated were selected by identifying those most significant for the specific reference sector.

[0196] The Standard methods used for the measurements of these properties indicated in the attached figures are the following:

TABLE-US-00006 ASTM D6814-02(2018) % Devulcanization degree ASTM D2240-15(2021) Shore A Hardness ASTM D412-16(2021) Mpa Tensile ASTM D624-00(2020) N/mm Tear UNI7716:2000 % Rebound UNI 9185:1988 mm3 Abrasion ASTM D395-18(2018) % Compression Set ASTM D5992-96(2018) Mpa Dynamic ASTM D1646-19a(2019) MU Mooney Viscosity ASTM D5289-19a(2019) min Curing

[0197] For the technical article (for example Bushing), as evident from the attached FIG. 6, a significant increase in the tear strength, tensile strength, rebound, scorch (t5) and curing efficiency was found (t90). Furthermore, extremely important aspects for this application, a normalization of the Mooney viscosity and an improvement in the dynamic properties, essential for the absorption of vibrations, were observed.

[0198] For the Tyre, truck treadPremium Truck Tyre, as evident from the attached FIG. 7, a significant increase in the tensile strength, tear resistance, modulus at 300% elongation, and a normalization of abrasion was observed. Furthermore, an extremely important aspect for both these applications, an improvement in the appearance of the blend was observed (as shown in FIGS. 8 and 9), both in the raw blend (before vulcanization) and in the blend after vulcanization, a clear sign of obtaining of a better and more intense devulcanization. On comparing the photographs of FIGS. 8 and 9, in fact, it is evident that the ELT particles are no longer visible in the blend object of the present invention, whereas they are still evident in the blend according to the state of the art, obtained with the oxalic acid-urea adduct.

[0199] For the Tyre, car treadPassenger Tyre, as is evident from FIG. 10, a significant increase in the tensile strength, in the modulus at 100% elongation, in the Toughness was detected. Particularly interesting for the sector is the increase beyond the reference in tear resistance.

[0200] For the footwearSole, the devulcanized product obtained from its own processing waste was added to the base blend in the amount of 50% by weight.

[0201] The sector does not provide for particularly critical technical-mechanical requirements, but rather requires that the processability and recolourability (understood as the possibility of mass recolouring the blends containing the devulcanized product) is optimal.

[0202] It has been verified that the re-use of the devulcanized product according to the state of the art, leads to obtaining a vulcanized blend with an orange-peel appearance and which is difficult to recolour. The non-recolourability is due to the fact that the dye does not penetrate sufficiently into the devulcanized product according to the state of the art and consequently the vulcanized blend shows very evident streaks and aesthetic defects, even with low percentages of devulcanized product.

[0203] With the devulcanized product according to the present invention, on the other hand, the processability is improved and the colourability, for example recolouring to black or grey, is homogeneous and free of defects.