Crumb rubber as a secondary raw material from 2 waste rubber. A short review of processing methods.

: Despite the development of technologies, modern methods of disposal of end-of-life tires most often represent either the incineration in cement kilns or the destruction of tires in 16 special landfills, showing a lack of sustainable recycling of this valuable material. The fundamental role of recycling is evident, and the development of high-efficiency processes represents a priority for the European market. Therefore, investigation of end-of-life rubber processing methods is of high importance for manufacturers and recyclers of rubber materials. In this paper, methods of processing of end-of-life tires are reviewed in order to obtain rubber 21 crumb, which can later be used in the production of new industrial rubber goods and composite The processes of separation end-of-life tire into fractions by type of materials using mechanical 23 processing methods along with mechanochemical and mechanical processes of processing the materials of used tires in order to obtain crumb rubber of various fractions and chemical 25 reactivity are considered.


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Processing of end-of-life tires and rubber is one of the critical aspects for up-to-date waste 31 management. End-of-life tyres (ELT) and elastomer products are recognised by the European Union 32 as a critical, valuable resource for the circular economy 1 . In this regard the use of the principles of 33 sustainable development requires a smart approach to waste using environmentally-friendly

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One of the known approaches to recycle ELTs is to process them through mechanical in 23 , thiol acid is suggested by Jana et al. 24  which leads to cracking of the rubber and the separation of reinforcing elements from it without mechanical cutting or crushing.
The main technological line is an ozone disintegration unit. Ozone acts as a "chemical knife", 154 and the rubber is separated from the metal frame and textile frame. Cracking of rubber in the presence 155 of ozone occurs primarily in the places of stress concentration, i.e. along growing cracks. Therefore 156 the ozonation process goes along the cavities of the "cut" while the rubber practically retains its Benefits of ozone technology: 159 -low energy consumption (5 -10 times less than mechanical crushing);

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-the process takes place at room temperature.

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The ozone method of rubber destruction can be considered as one of the promising techniques,

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Ozone is used as an active agent for surface oxidation and modification of rubber (tire) crumb.

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The crumb rubber reacts with ozone to produce CO2 in the initial stages, resulting in a surface 168 oxidised product. The reaction rate constant between ozone and crumb rubber is determined by 169 Fourier transform infrared spectroscopy, which monitors the absorption of ozone in the gas phase in 170 the presence of crumb. The oxidation state is determined using the intensity of the ketone band at rubber (in grams) is used as a parameter for the surface oxidation state. Thermogravimetric analysis, differential thermal analysis, and pyrolysis gas chromatography showed that ozonation of crumb 174 rubber exclusively occurs on the surface and does not affect the properties in the mass. The surface 175 of the oxidised crumb is characterised by surface acidity and hydrophilicity 28 .

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When recycling waste, it is essential to preserve the original structure and properties of the 179 polymers they contain. From this position, the best way to process rubber waste is mechanical

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The disadvantage of the cryogenic method is the high consumption of refrigerant, especially for conditions determining the possibility of polymer grinding at positive temperatures is the creation 202 of a temperature regime, the lower limit of which would be equal to 80-100 ° C.

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The process is carried out by supplying the material to the abrasive tool 33 , which is usually made 208 in the form of a tape or a circle, at negative and positive temperatures. To prevent sticking of the 209 crushed material on the tool and to ensure intensive cooling of the treatment zone, water is supplied 210 to the product to reduce the temperature in the contact zone of the instrument.

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The fineness of the resulting product and the performance of the equipment is mainly influenced 212 by the tool rotation frequency and the rubber feed rate. The quality of the material obtained affects 213 the subsequent possibility of its use in the production of industrial rubber goods 34 .

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This method makes it possible to grind tires without preliminary crushing of the tire, which is a 215 distinct advantage. However, the need to dry the resulting product and the significant heterogeneity  designed for modelling the grinding process of intact tyres and for producing rubber crumbs in size 251 of 1-3 mm. This result was achieved using in special compound tool. The preliminary results enable 252 to design a compound grinder that can process tyres to 1-3 mm rubber powder directly. Tyres can be 253 worked up saving tyre-beads and extracting spikes.
Processing of rubber composites is particularly effective, in which textiles and metal cords 255 become stress concentrators and facilitate fracture 37 .

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The results of changing the size of the rubber composite and separating the constituent 257 components from it using the example of processing the tread of a car tire using the SD-25 setup are 258 shown in Figure 6.

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Cutting is the process of dividing the body into parts by stress concentrators (knives).

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The production and use of highly dispersed active rubber powders have significant advantages 267 in comparison with reclaimed, therefore, in many countries, reclaim plants are being closed, and a 268 transition to processing rubber waste into crushed vulcanizates is taking place 38 .

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In paper 39 the possibility of producing composites is shown by joint crushing of rubber crumb 270 and textile cord in a disk grinder. The resulting material contains from 5 to 20% cord. In this case, the

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The paper describes a method for crushing rubber waste using an ultra-high-pressure water 275 flow (180-300 MPa). This method can be used to obtain IV with a particle size of 100-800 µ m. This

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With a constrained impact, the destruction of the material occurs between two colliding surfaces.

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The destructive effect depends on the impulse of the working fluid.

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With a free impact, destruction occurs due to the collision of material particles between 285 themselves and the working parts of the equipment. Therefore, the destructive effect depends on the temperatures. They are used to obtain lumps from the bulky waste and their further processing into 289 fine powders.

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The known method, which allows you to reduce energy consumption during crushing by the 291 impact. In this case, crushing and crushing of rubber-based material, for example, car tires are 292 performed with simultaneous or preliminary deformation of the rubber base in a plane perpendicular 293 to the direction of impact. This allows when the impact speed is exceeded by 20% or more over sound 294 in rods and plates, to reduce energy consumption by about 2.5 times.

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The disintegrator is an impact grinder that refines material by collisions 37 (Figure 7), where the

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Unlike the traditional grinding methods, disintegration breaks up the material by a series of 302 high-speed impacts, which generate stress within the material particle tens of times greater than its 303 ultimate strength. Combined with a built-in inertial separation system makes it possible to produce 304 powders of materials that are generally considered impossible to obtain using such types of mills 42 .

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A variant of such built-in inertial separation system (selective grinding mode in Figure 8) also makes 306 it possible to separate the components of complex composites released by impact from each other.

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The processes accompanying disintegration also significantly alter the mechanical and chemical

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The mass ratio of absorbed oil or oil products by this sorbent is 6.5-7.0 : 1. They do not sink in water,

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Research has been carried out to determine the effect of crumb rubber with an average particle

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Unfortunately, it is not possible to distinguish from the described rubber processing methods 407 the one universal or optimal method that would be considered the best for all situations. It would be 408 useful for everyone if the best methods were known in the search for an optimal solution to a 409 particular technological problem and some methods were excluded to avoid confusion. It is also 410 useful to know the alternatives from which the appropriate method could be chosen based on cost-411 benefit analysis, environmental impact and feasibility.

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The rapid development of production, the ever-increasing requirements for the technological