Desulfurized rubber, method for manufacturing desulfurized rubber, and use

Abstract

The subject of this invention is a desulfurized rubber having a TAVP of less than 2.7. Desulfurized rubber is produced by crushing vulcanized rubber and reacting it with vinylsilane as a desulfurizing agent at a temperature of 140-180°C for 4-7 minutes, with a vinylsilane concentration of 4-6% by weight based on the vulcanized rubber, and an energy input during the reaction exceeding 140 kNm.

Description

[Technical Field]

[0001] This invention relates to desulfurized rubber, a method for producing the same, and its use.

[0002] One challenge for tire manufacturers is increasing the proportion of recycled rubber in tire production. Granular scrap tires, MRP (material-recycled rubber), and granules from old tire treads can only be reused in very small quantities under certain conditions to avoid significantly degrading tire performance. The reuse of granular scrap tires is limited because the rubber particles involved are already sulfur-crosslinked (vulcanized), but reuse requires unvulcanized particles with significantly lower viscosity.

[0003] Diphenyl disulfide (DPDS) (Asaro, L.; Gratton, M.; Seghar, S.; Hocine, N.; Recycling of rubber wastes by devulcanization. Resour. Conserv. Recycl. 2018, 133, 250-262; Edwards, DW; Danon, B.; van der Gryp, P.; Georgens, JF, 2016. Quantifying and comparing the selectivity for crosslink scission in mechanical and mechanochemical devulcanization) Disulfides such as dibutyl disulfide (DBDS) and dibenzamide diphenyl sulfide (DBD), and polysulfides such as triethoxysilylpropyl tetrasulfide (TESPT) (U.S. Patent No. 9,683,088) are known to be able to desulfurize vulcanized rubber mixtures. For example, in desulfurization which can be carried out at high temperatures in a kneader or extruder, sulfur crosslinks are thermally and / or radically cleaved, and recombination is prevented by grafting with a scavenger such as a disulfide. This produces chemically desulfurized rubber particles (Rubber Recycling: Challenges and Developments, 1st edition, Royal Society of Chemistry, pp. 186-232; Saiwari, S., Dierkes, WK, Noordermeer, JW, 2018. Recycling of individual Waste rubber).

[0004] U.S. Patent No. 5,258,413 discloses the continuous desulfurization of vulcanized elastomers by ultrasound.

[0005] Furthermore, U.S. Patent No. 11,453,758 discloses a process for the continuous production of desulfurized rubber using a multi-stage screw extruder.

[0006] A drawback affecting the use of common desulfurizing agents is that rubber further degrades under thermal load due to the cleavage of CC bonds. As a result of this reduction in molar mass, disulfide-desulfurized rubber particles exhibit significantly lower tensile strain properties than newly manufactured rubber when reused.

[0007] The object of the present invention is to provide a desulfurized rubber in which the breakdown of CC bonds is minimized, and as a result, when reused in a rubber mixture, the tensile strain behavior is improved compared to the prior art.

[0008] At temperatures below the thermal decomposition of polymers, the Total Area of ​​Visible Particles (TAVP) value can be used as a measure of desulfurization selectivity. TAVP is determined by compounding the desulfurized rubber with a so-called white rubber mixture. Here, TAVP represents the size of the total surface area of ​​the visible rubber particles after desulfurization. The more selective the desulfurization, the smaller the total surface area of ​​the visible particles, and the smaller the resulting TAVP value.

[0009] One subject of the present invention is a desulfurized rubber characterized by having a TAVP of less than 2.7, preferably 0.8 to 1.8.

[0010] The desulfurized rubber of the present invention may contain butadiene and / or styrene structural units. The desulfurized rubber may preferably contain SSBR and BR structural units, which may be unfunctionalized or functionalized with, for example, epoxy groups, silyl groups, or amine groups.

[0011] The desulfurized rubber of the present invention may contain 10 to 200 phr, preferably 20 to 120 phr, and more preferably 30 to 100 phr of silica.

[0012] The desulfurized rubber of the present invention may have a network breakdown (NWB) value exceeding 50%.

[0013] The desulfurized rubber of the present invention contains 12.0% or more f sol It may have.

[0014] The desulfurized rubber of the present invention may have a tensile strength value TS exceeding 7.8 MPa.

[0015] A further subject of the present invention is a process for producing desulfurized rubber of the present invention, characterized in that vulcanized rubber is pulverized and reacted with vinylsilane as a desulfurizing agent for 4 to 7 minutes at a temperature of 140 to 180°C, preferably 150 to 160°C, wherein the concentration of the desulfurizing agent is 4 to 6% by weight based on the vulcanized rubber, and the energy input during the reaction is greater than 130 kNm, preferably 150 to 180 kNm.

[0016] Vulcanized rubber can be pulverized by water jet, cryogenic or ambient mechanical grinding. The particle size of the pulverized rubber may be 50 μm to 5000 μm, preferably 50 μm to 2000 μm, and more preferably 75 μm to 1500 μm.

[0017] Vulcanized rubber can be derived from the tread of a scrap tire or the entire shredded scrap tire.

[0018] Before adding vinylsilane, the pulverized vulcanized rubber may be swollen with oil, preferably distilled aromatic oil.

[0019] Vinylsilane is, Formula I [ka] (In the formula, R 1 , R 2 and R 3 R is independently H, C1-C8 alkyl, C1-C8 alkoxy, or phenoxy, and 4 It can be a silane (which is a divalent aliphatic and / or aromatic unbranched or branched hydrocarbon group or bond).

[0020] Vinylsilane is preferably of formula I (wherein R 1 , R 2 and R 3 It can be a silane (which is a C1-C8 alkoxy).

[0021] The vinyl silane can be more preferably vinyltrialkoxysilane, and very preferably vinyltriethoxysilane.

[0022] The vinyl silane can be an oligomer of vinyl silane and / or a co - oligomer of vinyl and alkyl silane.

[0023] The vinyl silane can be used in an amount of 1 to 20% by weight, preferably 3 to 10% by weight, based on the vulcanized rubber used.

[0024] <着 The vinyl silane can be used in combination with a peroxide. The peroxide used can include dicumyl peroxide and / or benzoyl peroxide. Preferably, dicumyl peroxide, for example, DYNASYLAN® SILFIN 301 (a mixture of vinyltriethoxysilane and dicumyl peroxide) manufactured by Evonik Industries AG can be used.

[0025] The peroxide can be used in an amount of 1 to 20% by weight, preferably 1 to 10% by weight, based on the vinyl silane.

[0026] The reaction (desulfurization) can be carried out in a kneader, such as a Brabender mixer, an E - kneader or an N - kneader, or an extruder, such as a single - screw extruder, a twin - screw extruder or a planetary roller extruder.

[0027] In the process of the present invention, it is preferable that the vulcanized rubber is pulverized and reacted with vinyltriethoxysilane and a peroxide at a temperature of 140 to 180°C.

[0028] In the process of the present invention, it is more preferable that the vulcanized rubber from scrap tires is pulverized and reacted with vinyltriethoxysilane and dicumyl peroxide at a temperature of 140 to 180°C.

[0029] A further subject of the present invention is the use of vinylsilane, optionally with added peroxide, for the desulfurization of vulcanized products.

[0030] A further subject of the present invention is the use of the desulfurized rubber of the present invention as a raw material in a vulcanized rubber mixture.

[0031] A further subject of the present invention is a vulcanized rubber mixture containing the desulfurized rubber of the present invention.

[0032] The present invention is advantageous in that the proportion of decomposed polymer chains is significantly reduced compared to desulfurization reagents from the prior art, and as a result, when the desulfurized rubber is reused in a new rubber mixture, the tensile strain properties are significantly improved, and therefore the proportion of desulfurized rubber in the new rubber mixture can be increased.

[0033] Measurement method The following methods are used for characterization.

[0034] Tensile strain test Tensile strain characteristics are determined after the revulcanization step using a Z010 tensile strength testing machine manufactured by Zwich Roell GmbH & Co.KG, in accordance with ASTM D412-16e1.

[0035] Determining Mooney viscosity Viscosity measurements are performed using an MV 2000 VS viscometer manufactured by Alpha Technologies GmbH, in accordance with ASTM D1646-19a.

[0036] Determination of crosslinking density The crosslink density of the desulfurized rubber is determined based on the Flory-Rehner equation in accordance with ASTM D6814-02. For this purpose, first, the desulfurized rubber is dried overnight at 80 °C in an oven of the Heraeus brand, and after cooling, it is weighed to obtain the parameter m1. Next, the rubber sample is wrapped with filter paper of the Whatman brand and placed in a flask filled with 500 ml of acetone. Subsequently, the flask is attached to a Soxhlet apparatus and heated at 56 °C for 48 hours. After cooling, the rubber sample is dried again overnight in an oven at 80 °C, the filter paper is removed, and the dried rubber sample is weighed to obtain the parameter m2. Subsequently, the rubber sample is wrapped again with filter paper and placed in a flask filled with 500 ml of tetrahydrofuran (THF). The flask is attached to a Soxhlet apparatus and heated at 66 °C for 72 hours. After cooling, the rubber sample is dried again overnight in an oven at 80 °C, the filter paper is removed, and the dried rubber sample is weighed to obtain the parameter m3. Then, the rubber sample is placed in a 50 ml vial, 40 ml of toluene is added, and the sample is swollen for at least 4 days until equilibrium is reached. After swelling, the rubber sample is taken out of the toluene solution and weighed again to obtain the parameter m4.

[0037] The ratio of the sol fraction is calculated as follows:

Number

[0038] Subsequently, the network density v is calculated using the Flory-Rehner equation:

Number

[0039] In this equation, v ms is the molar volume of the swelling agent, χ is the interaction parameter, which is 0.39 here. The volume fraction f p is calculated as follows:

Number

[0040] In this equation, ρ p ρ is the density of the rubber sample. s m is the density of the swelling agent. s This is determined as follows:

number

[0041] The network breakdown rate (NWB) is calculated as the difference between the network density of the vulcanized rubber (v1) and the network density of the desulfurized rubber sample (v2).

number

[0042] TAVP - White Rubber Analysis The total visible particle area (TAVP) can be determined using so-called white rubber analysis. This requires the preparation of test specimens. The TiO2 and MBTS (mercaptobenzothiazole sulfenamide) materials used for this purpose are available from Sigma Aldrich.

[0043] To prepare the test specimens, in the initial compounding step, 100 phr of polybutadiene rubber CB24 was mixed with 85 phr of TiO2, 5 phr of ZnO, and 1 phr of stearic acid, and the mixture was then treated in a Brabender internal mixer at 60°C for 4 minutes with a stirring speed of 100 rpm. The resulting white rubber mixture was left to stand at room temperature for 1 day. The following day, 171 phr of the white rubber mixture was mixed with 5 phr of sulfur and 2.5 phr of MBTS, and the mixture was vulcanized in a Brabender internal mixer at 60°C and 100 rpm for 2 minutes.

[0044] Next, the white rubber mixture is mixed with desulfurized rubber in a 90:10 ratio and kneaded in a double-roll mill at room temperature for 3 minutes. Then, this rubber mixture is vulcanized in a Wickert press at 170°C for 10 minutes and processed to obtain a disc with a thickness of 5 mm and a radius of 50 mm. Subsequently, the vulcanized rubber is cooled in liquid nitrogen for 15 minutes and the surface is polished with abrasive paper (120 grade).

[0045] To determine TAVP, specimens are examined using a Keyence brand VHX 5000 3D digital microscope and evaluated using the onboard ImageJ software. The settings used for this purpose are as follows: -Parameters:Conditions - Imaging mode: 2D stitching -Stitch: 5x6 - Zoom: 20x to 30x -Light: Full Ring - Coverage area: Circular - Base angle relative to the lens: 90° [Examples]

[0046] Model compound The desulfurization experiments and characterization of the following materials are presented and elucidated using model compounds as examples. The desulfurization experiments and characterization of the materials were conducted by the research groups of Prof. Dr. Blume and Dr. Dierkes at the University of Twente. The preparation of the model compounds is guided by the standard formulations for automotive tire treads shown in Table 1.

[0047] [Table 1]

[0048] Sprintan SLR 4601 was supplied by Trinseo, polybutadiene rubber CB 24 by Arlanxeo, ULTRASIL® 7000 GR by Evonik, zinc oxide, stearic acid, and sulfur by Merck, TDAE oil Vivatec 500 by Hansen & Rosenthal, accelerator Santocer CBS and Perkacit DPG by Flexsys, and Si 266® by Evonik.

[0049] The model compound was prepared using a Brabender brand 350S internal mixer with a capacity of 390 ml and a Schwabenthan two-roll mill.

[0050] Preparation of model compounds: First, polymers SBR (70 phr) and BR (30 phr) were placed in an internal mixer and kneaded at 80°C at 70 rpm for 1 minute. Subsequently, ULTRASIL® 7000 GR (40 phr) and Si 266® (2.9 phr) were added, and the mixture was kneaded for a further 1 minute under the above reaction conditions. Then, the following components were added: 40 phr of ULTRASIL® 7000 GR, 2.9 phr of Si 266®, 3 phr of ZnO, 2 phr of stearic acid, and 25 phr of TDAE oil. This mixture was first kneaded at 140°C for 1 minute. Then, the temperature was raised to 145°C, and the mixture was mixed for a further 4 minutes at 70 rpm. Next, this mixture was left to stand overnight at room temperature (RT). The following day, the mixture was transferred to a two-roll mill and processed at room temperature. The roll speed of the front roll was set to 20 rpm, and the roll speed of the rear roll was set to 25 rpm, with a roll nip of 1.5-2.0 mm. After a 2-minute kneading time, a crosslinking system consisting of 1.5 phr of sulfur, 1.7 phr of CBS, and 2.5 phr of DPG was added, and the mixture was processed for a further 7 minutes. Subsequently, the resulting mixture was pressed to obtain a 2 mm thick plate at a temperature of 160°C with a vulcanization time of t-95 (i.e., 1305 seconds).

[0051] Desulfurization of model compounds: In the next step, the vulcanized material was first placed in liquid nitrogen for 3 minutes, and then ground to a mesh size of 0.7 mm using a Fritsch laboratory mill.

[0052] Subsequent desulfurization was performed using a Brabender 50cm rotor with tangential and counter-rotating rotor drive mechanisms. 3 The process was carried out in an internal mixer. The vulcanization system included a Wickert press.

[0053] As a preliminary step to desulfurization of the model compound, the ground material was first swollen with TDAE oil as follows: 400 g of ground model compound was mixed with 20 g (5 wt%) of TDAE oil and stirred with a spoon at room temperature for 10 minutes. This mixture was left to stand overnight at room temperature, and the next day it was swollen with a desulfurizing agent. For this purpose, 105 g of swollen compound (containing 100 g of ground model compound + 5 g of TDAE oil) was mixed with a desulfurizing agent of the corresponding concentration (wt%) based on the ground model compound. The mixture was stirred with a spoon at room temperature for 10 minutes, and then left to stand overnight at room temperature. Subsequently, the model compound was placed in an internal mixer and desulfurized for a reaction time t (min) at an internal mixer temperature T (°C) and rotor speed R (rpm). After the desulfurization step, the desulfurized rubber was transferred to a double-roll mill and processed at room temperature. Here, the roll speed of the front roll was set to 20 rpm, the roll speed of the rear roll was set to 25 rpm, and a roll nip of 0.2 mm to 1.0 mm was selected.

[0054] Re-sulfurization of model compounds: For the re-vulcanization of the model compound, desulfurized rubber was processed in a double-roll mill. The roll speed of the front roll was set to 20 rpm, the roll speed of the rear roll was set to 25 rpm, and the roll nip was adjusted to 0.5 mm to 1.0 mm. The desulfurized rubber was first kneaded at room temperature for 1 minute, after which 4 g of ZnO and 2 g of stearic acid were added. The mixture was kneaded again at room temperature for 2 minutes. Then, 1.5 g of sulfur and 1.7 g of CBS were added, and the mixture was kneaded for a further 4 minutes. The mixture was left to stand overnight at room temperature, and the following day it was vulcanized at 160°C and pressed to obtain a 2 mm thick plate.

[0055] Following the protocol described above, the following desulfurized products (or desulfurized rubber samples) were prepared and tested using various desulfurizing agents (DAs) under the following conditions (Table 2).

[0056] [Table 2-1] [Table 2-2]

[0057] The desulfurized rubber of the present invention is characterized by having a TAVP of less than 2.7%. TAVP can be controlled by operating conditions, in particular, temperature (T), residence time in the internal mixer (DT), desulfurizer concentration (C), and total energy input (TEI) in the internal mixer. In principle, it is true that the lower the TAVP, the more selective and efficient the desulfurization. Similarly, the degree of network breakdown (NWB) can be used as a measure of desulfurization quality. Here, higher network breakdown is considered desirable. As the desulfurization temperature increases, TAVP decreases and NWB increases. However, TAVP is only meaningful at temperatures below the thermal decomposition of the polymer. Below the polymer decomposition temperature, low TAVP results in improved mechanical properties of the revulcanized product, as can be observed from increases in tensile strength (TS) and tensile elongation (EAB). Above the thermal decomposition temperature of the polymer, low TAVP is due to polymer decomposition and not to the selective removal of sulfur crosslinks. In this temperature range, despite low TAVP values, the tensile strength (TS) and tensile elongation (EAB) of revulcanized materials are indeed more degraded, i.e., lower.

[0058] From the overview table, it is clear that SILFIN (DYNASYLAN® SILFIN 301) and VTEO (vinyltriethoxysilane) yield the desulfurized rubber of the present invention at a temperature of 140-180°C, a residence time of 4-7 minutes, a desulfurizing agent concentration of 4-6% by weight, and an energy input exceeding 130 kNm.

[0059] Temperatures below 140°C (see Table 2, #1, 17-19) result in high TAVP values, which are attributed to insufficient desulfurization. The opening and radical reactions of sulfur crosslinking proceed more effectively above 140°C. Above approximately 180°C, tensile strength decreases, which can be explained by the initiation of thermal decomposition of the polymer (see Table 2, #7, 27). Above the thermal degradation temperature, the mechanical properties of TS and EAB decrease as the TAVP value decreases (see Table 2, #7). The effect of total energy input (TEI) on desulfurization selectivity is evident from entries including Table 2, #9, 11-14. This indicates that desulfurization selectivity increases as the energy input of the internal mixer increases.

[0060] Desulfurization experiments conducted using the desulfurizing agents TESPT and DPDS, respectively (see Table 2, #28-47), demonstrate that the desulfurized rubber of the present invention cannot be achieved with conventional techniques.

Claims

1. A desulfurized rubber obtained by reacting vulcanized rubber with vinylsilane, A desulfurized rubber characterized in that the total surface area (TAVP) of visible particles in the desulfurized rubber is less than 2.7%.

2. The desulfurized rubber according to claim 1, characterized by containing butadiene and / or styrene structural units.

3. The desulfurized rubber according to claim 1, characterized by containing 10 to 200 phr, preferably 20 to 120 phr, and more preferably 30 to 100 phr of silica.

4. The desulfurized rubber according to claim 1, characterized by having NWB exceeding 50%.

5. f 12.0% or higher ｓｏｌ The desulfurized rubber according to claim 1, characterized by having the following features.

6. A method for producing desulfurized rubber according to claim 1, characterized in that vulcanized rubber is crushed and reacted with vinylsilane as a desulfurizing agent at a temperature of 140 to 180°C for 4 to 7 minutes, the concentration of the desulfurizing agent is 4 to 6% by weight based on the vulcanized rubber, and the energy input during the reaction exceeds 140 kNm.

7. The method for producing desulfurized rubber according to claim 6, characterized in that the vulcanized rubber is pulverized by water jet, cryogenic or ambient mechanical grinding.

8. The method for producing desulfurized rubber according to claim 6, characterized in that the pulverized vulcanized rubber is swollen with oil before the vinylsilane is added.

9. The method for producing desulfurized rubber according to claim 6, characterized in that the vinylsilane used includes vinyltrialkoxysilane, preferably vinyltriethoxysilane.

10. The method for producing desulfurized rubber according to claim 6, characterized in that the vinylsilane is used in an amount of 1 to 20% by weight, preferably 3 to 10% by weight, based on the vulcanized rubber used.

11. The method for producing desulfurized rubber according to claim 6, characterized in that the vinylsilane is used together with a peroxide.

12. A method for producing desulfurized rubber according to claim 6, characterized in that the peroxide used includes dicumyl peroxide and / or benzoyl peroxide.

13. The method for producing desulfurized rubber according to claim 6, characterized in that the peroxide is used in an amount of 1 to 20% by weight, preferably 1 to 10% by weight, based on the vinylsilane.

14. A method for producing desulfurized rubber according to claim 6, characterized by crushing vulcanized rubber from scrap tires, swelling the crushed rubber with oil, and desulfurizing it with vinyltriethoxysilane and dicumyl peroxide.

15. Use of vinylsilane, with optional peroxide addition, for desulfurization of vulcanized products.

16. Use of the desulfurized rubber described in claim 1 as a raw material in a vulcanized rubber mixture.

17. A vulcanized rubber mixture comprising the desulfurized rubber described in claim 1.

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