NL2034086B1 - A method for the modification of bitumen - Google Patents
A method for the modification of bitumen Download PDFInfo
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- NL2034086B1 NL2034086B1 NL2034086A NL2034086A NL2034086B1 NL 2034086 B1 NL2034086 B1 NL 2034086B1 NL 2034086 A NL2034086 A NL 2034086A NL 2034086 A NL2034086 A NL 2034086A NL 2034086 B1 NL2034086 B1 NL 2034086B1
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- Prior art keywords
- rubber particles
- bitumen
- tire rubber
- rubber
- devulcanized
- Prior art date
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- 239000010426 asphalt Substances 0.000 title claims abstract description 59
- 238000000034 method Methods 0.000 title claims abstract description 41
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- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims description 4
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- OQCDKBAXFALNLD-UHFFFAOYSA-N octadecanoic acid Natural products CCCCCCCC(C)CCCCCCCCC(O)=O OQCDKBAXFALNLD-UHFFFAOYSA-N 0.000 claims description 2
- 150000001451 organic peroxides Chemical class 0.000 claims description 2
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- 239000008117 stearic acid Substances 0.000 claims description 2
- 239000011787 zinc oxide Substances 0.000 claims description 2
- FACXGONDLDSNOE-UHFFFAOYSA-N buta-1,3-diene;styrene Chemical compound C=CC=C.C=CC1=CC=CC=C1.C=CC1=CC=CC=C1 FACXGONDLDSNOE-UHFFFAOYSA-N 0.000 description 15
- 239000008187 granular material Substances 0.000 description 15
- 229920000468 styrene butadiene styrene block copolymer Polymers 0.000 description 15
- 239000004636 vulcanized rubber Substances 0.000 description 13
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 12
- 229920002209 Crumb rubber Polymers 0.000 description 10
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- 229910052717 sulfur Inorganic materials 0.000 description 6
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- 238000010504 bond cleavage reaction Methods 0.000 description 5
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- 150000002430 hydrocarbons Chemical group 0.000 description 4
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 238000000605 extraction Methods 0.000 description 3
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
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- 206010011906 Death Diseases 0.000 description 2
- 229920002943 EPDM rubber Polymers 0.000 description 2
- 244000043261 Hevea brasiliensis Species 0.000 description 2
- 239000004952 Polyamide Substances 0.000 description 2
- 239000005062 Polybutadiene Substances 0.000 description 2
- 238000000944 Soxhlet extraction Methods 0.000 description 2
- 235000002017 Zea mays subsp mays Nutrition 0.000 description 2
- 241000482268 Zea mays subsp. mays Species 0.000 description 2
- 239000012190 activator Substances 0.000 description 2
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- 230000001070 adhesive effect Effects 0.000 description 2
- 229910052783 alkali metal Inorganic materials 0.000 description 2
- 150000001340 alkali metals Chemical class 0.000 description 2
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- 239000002585 base Substances 0.000 description 2
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- 229920003052 natural elastomer Polymers 0.000 description 2
- 229920001194 natural rubber Polymers 0.000 description 2
- 229920002647 polyamide Polymers 0.000 description 2
- 238000010298 pulverizing process Methods 0.000 description 2
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- 238000011084 recovery Methods 0.000 description 2
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- 229920003048 styrene butadiene rubber Polymers 0.000 description 2
- 230000008961 swelling Effects 0.000 description 2
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- 239000002699 waste material Substances 0.000 description 2
- RSWGJHLUYNHPMX-UHFFFAOYSA-N Abietic-Saeure Natural products C12CCC(C(C)C)=CC2=CCC2C1(C)CCCC2(C)C(O)=O RSWGJHLUYNHPMX-UHFFFAOYSA-N 0.000 description 1
- KHPCPRHQVVSZAH-HUOMCSJISA-N Rosin Natural products O(C/C=C/c1ccccc1)[C@H]1[C@H](O)[C@@H](O)[C@@H](O)[C@@H](CO)O1 KHPCPRHQVVSZAH-HUOMCSJISA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 150000001336 alkenes Chemical class 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 229920005549 butyl rubber Polymers 0.000 description 1
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- 230000001939 inductive effect Effects 0.000 description 1
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- 239000004615 ingredient Substances 0.000 description 1
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- 150000003951 lactams Chemical class 0.000 description 1
- 150000002596 lactones Chemical class 0.000 description 1
- 229920002521 macromolecule Polymers 0.000 description 1
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- 238000002715 modification method Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 150000007524 organic acids Chemical class 0.000 description 1
- 235000005985 organic acids Nutrition 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000004014 plasticizer Substances 0.000 description 1
- 229920002857 polybutadiene Polymers 0.000 description 1
- 229920001195 polyisoprene Polymers 0.000 description 1
- 229920002635 polyurethane Polymers 0.000 description 1
- 239000004814 polyurethane Substances 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
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- 238000002360 preparation method Methods 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 239000007965 rubber solvent Substances 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 239000000344 soap Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 229920003051 synthetic elastomer Polymers 0.000 description 1
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- 238000012360 testing method Methods 0.000 description 1
- 238000004227 thermal cracking Methods 0.000 description 1
- 229920001169 thermoplastic Polymers 0.000 description 1
- 229920002725 thermoplastic elastomer Polymers 0.000 description 1
- 239000004416 thermosoftening plastic Substances 0.000 description 1
- KHPCPRHQVVSZAH-UHFFFAOYSA-N trans-cinnamyl beta-D-glucopyranoside Natural products OC1C(O)C(O)C(CO)OC1OCC=CC1=CC=CC=C1 KHPCPRHQVVSZAH-UHFFFAOYSA-N 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L95/00—Compositions of bituminous materials, e.g. asphalt, tar, pitch
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2207/00—Properties characterising the ingredient of the composition
- C08L2207/20—Recycled plastic
- C08L2207/24—Recycled plastic recycling of old tyres and caoutchouc and addition of caoutchouc particles
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2555/00—Characteristics of bituminous mixtures
- C08L2555/30—Environmental or health characteristics, e.g. energy consumption, recycling or safety issues
- C08L2555/34—Recycled or waste materials, e.g. reclaimed bitumen, asphalt, roads or pathways, recycled roof coverings or shingles, recycled aggregate, recycled tires, crumb rubber, glass or cullet, fly or fuel ash, or slag
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Civil Engineering (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
Abstract
The present invention relates to a method for the modification of bitumen. More specifically, the present invention relates to a method for the modification of bitumen for the production of asphalts by incorporating a modified binder into the bitumen, as well as to asphalt produced with such a modified bitumen.
Description
Title: A method for the modification of bitumen.
The present invention relates to a method for the modification of bitumen. More specifically, the present invention relates to a method for the modification of bitumen for the production of asphalts by incorporating a modified binder into the bitumen, as well as to asphalt produced with such a modified bitumen.
Bitumens are complex thermoplastic products composed of quite different elements: asphaltenes and malthenes. Bitumens have excellent adhesive properties, but poor mechanical properties, especially according to temperature. In fact, bitumens have an exceptionally low hardness at ambient temperature (25° C.). Moreover, at temperatures below 0° C. (cold), bitumens are rigid and fragile, whereas at temperatures above 38° C. (hot), bitumens are plastic, soft and very adhesive.
It is well known to modify of bitumens by means of chemical and polymer additives in order to essentially modify the nature of bitumens, thus making modified bitumens suitable for the most diverse industrial uses.
It is also well known to modify asphalts and bitumens using granules derived from grinding end-of-life tires. Examples of technical benefits derived from the performance of bitumen modified with the addition of crumb rubber are noise reduction, longer lifetime of finished products, considerably increased elasticity, reduction of fractures and their propagation in manufactured items.
US 2015038621 relates to a production method of a compound for realization of modified bitumen for asphalts, comprising the following steps: grinding of vulcanized rubber to obtain vulcanized crumb rubber with granulometry lower than 0.4 mm; mixing of vulcanized crumb rubber, SBS and lubricant inside an extruder, wherein weight percentage of lubricant is between 1% and 50% with respect to weight of mixture, and vulcanized crumb rubber is in weight percentage equal to weight percentage of
Styrene-Butadiene-Styrene (SBS); extrusion to obtain an extruded compound containing said vulcanized crumb rubber, SBS and lubricant, wherein the extrusion takes place at a temperature between 160 and 200° C. The crumb rubber is obtained from recycled end-of-use tires. The extruded compound is used in a bitumen modification method for production of asphalts.
An article written by W. Vonk and R. Hartemink “Proceedings of the 8th
Conference on Asphalt Pavements for Southern Africa (CAPSA'04), 12 — 16
September 2004, describes the mechanism that leads to the viscosity increase upon
SBS modification and hence the increased resistance to permanent deformation of asphalt mixes. The solubility parameters of SBS are close to those of the vast majority of the components in bitumen, and therefore SBS has a strong interaction with the bitumen. The nature of the SBS is such that it creates a physical, three-dimensional structure having properties comparable to those of vulcanized rubber. The critical conditions for a polymer to be successful and effective in bitumen modification are bitumen/polymer interaction, polymer structure and phase continuity.
RU 2011 139 767 relates to the production of synthetic rubber, in particular diene (copolymers, such as polybutadiene, polyisoprene and styrene-butadiene rubber (SBR), used in production of tyres and industrial rubber articles, in modifying bitumen, in electrical engineering and in other fields.
US 2013/023595 relates a method of regenerating vulcanized crumb rubber which comprises the steps of introducing vulcanized crumb rubber and a lubricant into a first mixer, mixing the crumb rubber and lubricant at room temperature, transferring the mixture into a thermokinetic mixer, raising the speed of the rotor shaft of the thermokinetic mixer in order to increase a temperature of the mixture during a first period of time until a devulcanizing temperature is reached, reducing the temperature of the mixture to a lower temperature during a second period of time, and recovering regenerated crumb rubber from the chamber.
US 3 658 259 relates to process for grinding granular material at low temperatures in a jet mill comprising the steps of contacting the granular material with a first stream of cold gas before the granular material is fed to the jet mill to precool the granular material, feeding the precooled granular material to the jet mill, pulverizing the granular material in the jet mill, by means of introducing an expanding second cold gas stream into the jet mill effecting the granular material being pulverized and to reduce the temperature of the granular material as it is being pulverized.
BR 9 611 260 relates to process for devulcanizing a rubber vulcanizate by desulfunzation, comprising the steps of contacting rubber vulcanizate crumb with a solvent and an alkali metal to form a reaction mixture, heating the reaction mixture in the absence of oxygen and with mixing to a temperature sufficient to cause the alkali metal to react with sulfur in the rubber vulcanizate, and maintaining the temperature below that at which thermal cracking of the rubber occurs, thereby devulcanizing the rubber vulcanizate.
CZ 236 098 relates to a method of preparing vulcanizing mixtures from devulcanized rubber and recycled polymers, wherein rubber crumb from used tires or other waste rubber material is heated to a temperature of 140 to 230 °C in the presence of lactams and/or lactones of organic acids and/or raw rosin, and subsequently mixed with vulcanizing agents and/or with rubber material already containing vulcanizing agents and/or with poly-olefins and/or with polyesters and/or with polyamides and/or with polyurethanes.
CN 105 906 236 relates to a method for preparing the waste tire devulcanized rubber and its chlorinated derivative modified asphalt composite material comprising the steps of heat and melt the asphalt, selectively add modifiers and/or fillers as needed, heat and pressurize, and stir to mix evenly, mix waste tire devulcanized rubber and waste tire devulcanized rubber chlorinated derivatives with melted asphalt in proportion by weight, heat and pressurize, stir to mix evenly, and leave to solidify.
RU 2 130 952 relates to a method of tyre regenerate in which rubber crumb is mixed with specific ingredients and devulcanization is accomplished through mechanical destruction, wherein a regenerate is refined on special rolls.
RU 2 701 026 relates to a method for the preparation of elastomeric modifier for petroleum bitumens in which pre-ground rubber articles, for example shock- absorbing tires, are crushed to the state of crumbs with a particle size of 3-6 mm and fed into a screw disperser-devulcanizer. The crumb, passing through the first process zone, is subjected to surface devulcanization under pressure and dissipative heating.
In a second process zone, the final devulcanization of the material takes place in a range of 170-230°C.
US 2020/095424 relates to a method of producing a bitumen additive comprising a step of mixing tire rubber crumbs, devulcanizing agent, heavy metal soap, antiozonant and plasticizer together at a temperature of about 40 to about 50 °C until an even mixture is produced.
A SBS type thermoplastic elastomer is thus intended for use as a bitumen modifier for the production of polymer-bitumen binder or modified bitumen and its further use in the production of asphalt concrete of various types. It ensures a high level of strength properties of asphalt concrete, a wide range of performance and extends the service life of the roadway.
In a general rubber devulcanization, the process for devulcanizing involves cleaving of the monosulfidic, disulfidic and polysulfidic crosslinks (C-S or S-S bonds) existing in a vulcanized rubber. Vulcanized rubber comprises networks of hydrocarbon chains (C-C) linked together through C-S and S-S bonds and can be said to be made of a network of polymer macromolecules. A vulcanized rubber network can be thought of as many long and entangled hydrocarbon chains wherein the chains themselves are linked together by C-S and S-S bonds. Consequently, the vulcanized rubber networks contain chemical bonds of carbon to carbon (C-C), chemical bonds of carbon to sulfur (C-S) and chemical bonds of sulfur to sulfur (S-S), each having different bond energies where C-C > C-S > S-S thus providing opportunities for selective bond cleavage.
US 2017/009044 relates to an apparatus for producing devulcanized rubber comprising: a devulcanization tank in which the reaction between vulcanized rubber particles and a chemical composition is carried out, at least one mass stirrer positioned in the devulcanization tank in which the mass stirrer rotates in circular motion to generate impact forces; at least one rotating shaft positioned in the devulcanization tank in which the rotating shaft has at least one axial blade and at least one radial blade to facilitate impact forces generation; and a blanket of cooling fluid enveloping the devulcanization tank to control the temperature, wherein the impact forces generated from the mass stirrer, the axial blade and the radial blade of the rotating shaft cause the vulcanized rubber particles to react with the chemical composition for producing devulcanized rubber. The chemical composition comprises of at least an accelerator, at least an inorganic activator and at least an organic activator.
US6133413 relates to a method of manufacturing devulcanized rubber comprising rubber with sulfur crosslinks thereof severed and carbon black particles of 100 nm or less in diameter comprising the steps of pulverizing vulcanized rubber selected from the group consisting of EPDM (ethylene-propylene-diene terpolymer) rubber, natural rubber, styrene-butadiene rubber and butyl rubber containing carbon black, heating the pulverized vulcanized rubber containing carbon black, applying a shearing pressure in the pressure range of 10 to 50 kg/cm? while heating the pulverized vulcanized rubber containing carbon black, whereby sulfur crosslinking bonds in the vulcanized rubber are cut while main chains of the rubber are not cut, thereby preparing said devulcanized rubber.
It is an object of the present invention to provide a method for (partially) replacing SBS in a bitumen binder. 5 It is another object of the present invention to provide a method for producing devulcanized rubber that can be used in a method for the production of asphalts by incorporating such devulcanized rubber into the bitumen.
It is further an object of the present invention to improve the visco-elastic properties of a composition comprising bitumen by the incorporation of a specific binder into the composition.
The present invention thus relates to a method for the modification of bitumen for the production of asphalts by incorporating a modified binder into the bitumen, the method provides for addition of devulcanized tyre rubber particles obtained by a method comprising the steps of: introducing tyre rubber particles to a mill; introducing a gaseous flow in the mill for generating a field of high turbulence, strong eddies and high energy impact between the tyre rubber particles which causes micronization and rupture of the tyre rubber particles due to extreme hysteresis and mechanical forces sufficient to at least partially devulcanize the tyre rubber particles; and fast dissipation of the heat generated into the gaseous flow; recovering devulcanized tyre rubber particles from the mill; and adding the devulcanized tyre rubber particles to a composition comprising bitumen.
The present inventors found that by such a method one or more of the objects have been achieved. The present inventors found that the devulcanized tyre rubber particles thus prepared dissolves in the asphalt, thereby creating a homogeneous and compatible binder. In addition, the present inventors also found that by incorporating the devulcanized tyre rubber particles thus prepared into a bitumen the fatigue resistance and low temperature cracking resistance are improved.
In the present method the mill relies on extremely high gaseous flow throughput and velocities. The present inventors found that the heating and cooling of tyre rubber particles occur virtually instantaneously during the grinding. Surprisingly for tyre rubber granulates this mechanism provides sufficient thermo-mechanical energy to cause devulcanization to occur within an extremely short timeframe (~1 second), thereby restricting undesirable oxidation and main chain (C-C) scission.
In the present method the mill relies on extremely high gaseous flow throughput and velocities. The present inventors found that the heating and cooling of tyre rubber particles occur virtually instantaneously during the grinding. Surprisingly for tyre rubber granulates this mechanism provides sufficient thermo-mechanical energy to cause devulcanization to occur within an extremely short timeframe (~1 second), thereby restricting undesirable oxidation and main chain (C-C) scission.
Without being bound to any specific theory, the present inventors assume that the thermo-mechanical energy comes from the externally generated air flow that accelerates the tyre rubber particles to subsonic speeds. In the mill the particle to particle impacts are therefore extremely rapid and violent and much of the kinetic particle to particle impact energy is converted to particle heat by hysteresis. The effect of hysteresis in rubber particles is to transfer kinetic energy to its molecules, resulting in heating. Hysteresis occurs for every particle to particle impact.
In an example of the present invention the amount of devulcanized tyre rubber particles in the composition comprising bitumen is at least 5 wt.%, preferably at least 10 wt.%, more preferably at least 20 wt.% and at most 95 wt.%, preferably at most 80 wt.%, more preferably at most 60 wt.%, based on the total weight of the composition.
In an example of the present invention the composition may further comprise curatives chosen from the group of sulphur, sulphur doners, accelerators, organic peroxides, zinc oxide, stearic acid, crosslinking resins and organosilanes. These curatives would be pre-mixed to the devulcanized product, not directly to the bitumen or the bitumen/ devulcanized mixture.
The present inventors found that the amount of energy put in the mill is of influence on the percentage of devulcanization (%) of the devulcanized tyre rubber particles. In an example is the amount of energy in a range of 0.6 MWhr — 2.0 MWhr.
The present inventors found that, inter alia, by controlling the energy input of the mill the percentage of devulcanization (%) of the devulcanized tyre rubber particles isin a range of at least 40%, preferably at least 60%, more preferably at least 80%. In other words, the higher the amount of energy, the higher the percentage of devulcanization (%) of the devulcanized tyre rubber particles. In an example the percentage of devulcanization (%) of the devulcanized tyre rubber particles is as high as 90%, thereby significantly decreasing the amount of bitumen in an asphalt compasition.
The term tyre as used here includes all kind of tyres that are used on many types of vehicles, including cars, bicycles, motorcycles, buses, trucks, heavy equipment, and aircraft.
In the multi-chamber-like grinding zone of the mill, the gaseous flow generates a field of high turbulence and strong eddies which causes micronization and rupture of the tyre rubber particles. Within the grinding chamber, the tyre rubber particles are always kept in a free-flowing situation. The micronization and particle rupture produces enormous amounts of new particle surfaces and thermal energy, which is largely converted to heat by hysteresis. Excess heat is quickly carried away by the intense gaseous flow and turbulence resulting in only a very short exposure to heat for rubber granulate materials.
In an example tyre rubber particles having a particle size of 0.001 mm — 10 mm, preferably 2 — 8 mm, more preferably 2 — 5 mm are introduced in the mill. Such tyre rubber particles are obtained by shredding and crushing the waste rubber to make the relevant tyre rubber particles.
In an example the temperature of the tyre rubber particles in the mill increases to at least 250 DegC, preferably at least 300 DegC, and to a temperature of at most 350 DegC. If the temperature of the tyre rubber particles in the mill is below the under limit of 250 DegC, the process of devulcanizing the tyre rubber particles will not take place sufficiently. If the temperature of the tyre rubber particles is above the higher limit of 350 DegC the thermo-mechanical energy will cause undesirable scission of the hydrocarbon main chain (C-C bonds) to occur.
In an example the residence time of the tyre rubber particles in the mill is less than 2 seconds, preferably less than 1 second. A residence time of the tyre rubber particles in the mill longer than 2 seconds will result in an excessive exposure to thermo-mechanical forces capable of inducing high degrees of C-C scission and oxidation of the product, which is undesirable.
During the process for devulcanizing tyre rubber particles volatiles originally present in the tyre rubber particles may be released and accumulate in the mill.
Therefore, the volatiles are preferably removed from a vent.
In an example the gaseous flow is chosen from the group of air and inert gas, such as nitrogen.
The present invention also relates to devulcanized tyre rubber particles having a sticky and popcorn like surface structure resulting in a material that has flow characteristics somewhere between a powder and a friable solid.
The devulcanized tyre rubber particles can be used as a viable substitute to virgin rubber in different types of applications, such as in tyres and general rubber goods such as conveyor belts, sheeting, extrusion profiles and moulded products. The devulcanized tyre rubber particles can also be used as a highly dispersible modifier and as a replacement or partial replacement of bitumen binders in asphalt to enhance the visco-elastic, durability and sound-deadening performance of pavements and road surfaces.
For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawings the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction, and operation and many of its advantages would be readily understood and appreciated.
The devulcanized tyre rubber was characterized by Soxhlet extraction in toluene, according to Ed. (1). The insoluble fraction, or gel fraction of the rubber can be separated from the soluble fraction with this extraction technique. Extraction was for 18 h followed by drying the samples for 12 h at 80 °C to remove the solvent.
Sel Fraction {%) = (1 — wy 100 (1) \ where Mi and MF stand for the mass of rubber before and after the extraction, respectively.
The cross-link density of untreated tyre rubber and the devulcanized sample was determined via swelling tests according to ASTM D 297-15. The cross-link density value was calculated using the Flory-Rehner Eq. (2) after equilibrium swelling (72h followed by drying to constant mass at 80 °C) in toluene. a Dl VAV a V‚7] (2) [Vi Vi VoA2]
where ve is cross-link density {(mol/cm3); V, is the molar volume of the solvent (for toluene: 106.13 cm? mol); Xx; is the rubber-solvent interaction parameter (0.39), and V, is the volume fraction of rubber in the swollen sample, which can be determined with the Ellis and Welding Eq. (3).
Te 8) feof where ms is the mass of the swollen rubber sample (g), mr is the mass of the dry rubber sample (g), ps is the density of the solvent, toluene (0.8669 g/cm3) and p; is the density of the rubber sample (1.20 g/cm*). The degree of devulcanization was calculated with
Eq. (4) pesto = (1-20) 100 (4) where pf is the cross-link density of the devulcanized sample and vi is the cross-link density of untreated tyre rubber.
A rubber granulate having a particle size of as 2-5 mm produced from EOL (end-of-life) whole truck and bus tyres was used as raw material. The natural rubber content of the rubber granulate was between 40 and 45 wt.% and the total hydrocarbon content of the rubber granulate was between 60 and 65 wt.%. The raw material was 99% free from steel and textile and its moisture content was < 1 wt. %.
The mill used was a Jaeckering Ultra-Rotor Model “UR la S” (manufactured by
Altenburger Maschinen Jackering GmbH (DE)) fitted with a 18kW main motor, an 11kW fan motor, an air inlet temperature of 20 DegC. An airflow of at least 30,000 and at most 90,000 parts by volume of atmospheric air for one part by volume of tyre rubber particles and a residence time of the ground material of a maximum of 1.2 s was introduced in the mill for generating a field of high turbulence, strong eddies, and high energy impact between the tyre rubber particles. Particle to particle impact speeds are dramatically increased to around the speed of sound. This air flow causes micronization and rupture of the tyre rubber particles resulting in thermo-mechanically devulcanized tyre rubber particles. During the devulcanization process the temperature of the tyre rubber particles exceeded the melting temperature of the few remaining textile fibres (predominantly polyamide and polyester types), where polyester fibres melt at around 295 DegC. The outlet temperature of the air was 125
DegC.
Table 1: Soxhlet extraction results of devulcanization experiment
Sample Sol fraction (%) Cross-link density | Devulcanization 1074 mol/cm? (%) rubber
Devulcanized 18.0 64.9 sample
From Table 1 one will conclude that the treatment of the tyre rubber particles in the mill has resulted in a devulcanization grade of 64.9 %.
In Table 2 a comparison is made for different recipes, i.e. base bitumen, bitumen including 6 wt.% SBS, and bitumen including 22 wt.% devulcanized rubber and 1 wt.% SBS. From Table 2 one can deduce the positive effects on the visco-elastic properties when using devulcanized rubber particles obtained according to the method as described here in bitumen. The devulcanized rubber particles shown in Table 2 are the devulcanized rubber particles shown in Table 1.
Table 2: a comparison of bitumen, SBS, and devulcanized rubber in modification of bitumen.
Parameter Base 6 % SBS 22%
Bitumen Devulcanized
Rubber, 1%
SBS
Rutting Parameter (Pa — 70 °C) 10000
Multiple Stress Creep Recovery (MSCR) (% 75 85
Rec. @ 3.2 kPa} -58 °C
Multiple Stress Creep Recovery (MSCR) (% 45 45
Rec. @ 3.2 kPa) -82 °C
Max. Elongation (mm)
Linear amplitude sweep (LAS) fatigue (Nf2.5 - | 1785 3086 4272 fatigue life @ 2.5 % strain)
Linear amplitude sweep (LAS) fatigue (Nf5 - 372 503 753 fatigue life @ 5 % strain)
Tensile strength in pull off test @ 15 °C (kPa)
The structure of the devulcanized sample can be described in terms of a sticky and popcorn like surface structure. Such a structure is characteristic for the cleavage of the monosulfidic, disulfidic and polysulfidic crosslinks existing in a vulcanized rubber.
Claims (10)
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| NL2034086A NL2034086B1 (en) | 2023-02-03 | 2023-02-03 | A method for the modification of bitumen |
| PCT/NL2024/050044 WO2024162847A1 (en) | 2023-02-03 | 2024-01-31 | A method for the modification of bitumen |
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| WO2024162847A1 (en) | 2024-08-08 |
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