Method for preparing RRP / NRL composite material through waste rubber surface wet coating

Abstract

The invention discloses a method for preparing an RRP / NRL composite material through waste rubber surface wet coating, and belongs to the technical field of waste rubber regeneration, and the method comprises the following steps: S1, adjusting the temperature of an improved twin-screw extruder to 160 DEG C and the screw rotating speed of the twin-screw extruder to 60 rpm, adding waste rubber powder, and extruding to obtain modified rubber powder; s2, preparing a 1% calcium chloride solution; s3, flocculating the natural latex and the rubber powder in a calcium chloride solution to obtain RRP / NRL rubber master batch; s4, adding the rubber master batch, white carbon black, stearic acid, zinc oxide, an anti-aging agent 4020, rubber oil V600 and a silane coupling agent KH-560 into an internal mixer for mixing, then adding sulfur and a vulcanization accelerator CZ, and mixing on an open mill to prepare a rubber compound; and S5, vulcanizing the rubber compound to obtain the RRP / NRL composite material. The method solves the technical problems of high cost and serious environmental pollution of a traditional rubber powder modification method, and is widely applied to waste rubber regeneration production.

Description

Technical Field

[0001] The invention belongs to the technical field of waste rubber regeneration, and in particular relates to a method for preparing an RRP / NRL composite material by wet coating the surface of waste rubber. Background Art

[0002] As the country with the largest rubber consumption in the world, my country produces more than 10 million tons of waste rubber every year, and the amount of waste rubber it brings is also extremely huge. In 2022, my country produced more than 350 million waste tires, about 12.28 million tons, which has become a veritable "black pollution". Therefore, recycling waste tires and regenerating waste rubber is a high-value application worthy of attention, both from the perspective of economic value and environmental protection, in order to solve the current problems of accumulation and pollution of a large number of waste tires. The production and preparation of waste rubber powder is mainly through the coarse and fine crushing of waste tires after washing and stripping steel wire and fabric, and then crushing them into rubber powder through a grinding machine, and finally grading and screening to obtain rubber powder that meets the requirements. Waste rubber powder has certain chemical and physical properties, and can be used again in agricultural tires, roads and other fields through proper treatment and processing.

[0003] Generally speaking, there is no good compatibility between rubber powder and rubber, so there will be many problems when mixing or combining them. Surface modification of rubber powder is an effective way to improve the interfacial bonding between rubber powder and rubber matrix. Traditional rubber powder modification methods are not suitable for large-scale production and application due to high cost and serious environmental pollution.

[0004] Therefore, in the field of waste rubber recycling equipment technology, there is still a need for research and improvement on the method of preparing RRP / NRL composite materials by wet coating of waste rubber surface. This is also a research hotspot and focus in the current field of waste rubber recycling technology, and it is also the starting point for the completion of the present invention. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing RRP / NRL composite materials by wet coating on the surface of waste rubber, so as to solve the technical problems of high cost and serious environmental pollution of traditional rubber powder modification methods.

[0006] In order to solve the above technical problems, the technical scheme of the present invention is: a method for preparing RRP / NRL composite material by wet coating on the surface of waste rubber, comprising the following steps: S1. adjusting the temperature of the improved twin-screw extruder to 160°C and the screw speed of the twin-screw extruder to 60rpm, adding waste rubber powder, and extruding to obtain modified rubber powder; S2. preparing a 1% calcium chloride solution; S3. flocculating natural latex and the rubber powder obtained in step S1 in the calcium chloride solution to obtain RRP / NRL masterbatch, and drying for standby use; S4. adding masterbatch, white carbon black, stearic acid, zinc oxide, antioxidant 4020, rubber oil V600, and silane coupling agent KH-560 to an internal mixer and mixing for 5-10 minutes, after the rubber is discharged and cooled to room temperature, sulfur and vulcanization accelerator CZ are added to the open mixer and mixed, after mixing evenly, the lower sheet is cooled to obtain a mixed rubber; S5. The mixed rubber is placed in a flat vulcanizer and vulcanized to obtain the RRP / NRL composite material.

[0007] As an improvement, anhydrous calcium chloride and deionized water are mixed in a mass ratio of 1:100 and stirred to fully dissolve, thereby obtaining a 1% calcium chloride solution.

[0008] As a further improvement, in step S3, the ratio of natural rubber latex to rubber powder is 1:1.

[0009] As a further improvement, in step S4, the mass parts of masterbatch, white carbon black, stearic acid, zinc oxide, antioxidant 4020, rubber oil V600, silane coupling agent KH-560, sulfur, and vulcanization accelerator CZ are respectively: 100 parts of masterbatch, 10 parts of white carbon black, 2 parts of stearic acid, 4 parts of zinc oxide, 4 parts of antioxidant 4020, 3 parts of rubber oil V600, 2 parts of silane coupling agent KH-560, 2 parts of sulfur, and 1.3 parts of vulcanization accelerator CZ.

[0010] As a further improvement, in step S5, the vulcanization temperature is 150°C, the pressure is 10 MPa, and the time is 1.3×Tc90. After the vulcanization is completed, the vulcanization is cooled at room temperature for 8-10 hours.

[0011] As a further improvement, the screws of the twin-screw extruder include a feeding section, a softening section, a shear reduction section, a homogenizing section, and an extrusion section in sequence, and gradient elements are respectively provided at the softening section and the shear reduction section of the two screws.

[0012] As a further improvement, the gradual element includes a cylinder, the outer surface annular array of the cylinder has 2N radially protruding ridges (N is a positive integer greater than 2), the ridges extend along the axial direction of the screw, the outer surface annular array of the cylinder has N wedge surfaces, the wedge surfaces extend from the root of the head end of a ridge to the root of the end end of an adjacent ridge, and the wedge surfaces gradually rise radially in the flow direction of the fluid to the same height as the ridges.

[0013] After adopting the above technical solution, the beneficial effects of the present invention are:

[0014] (1) The present invention prepares the RRP / NRL composite material by wet coating the surface of waste rubber powder. Due to the shearing action of the twin screw, the polysulfide bonds and C-S bonds inside the rubber molecules are broken, the waste rubber powder is partially desulfurized, and the surface activity of the waste rubber powder is improved. The modified waste rubber powder has good compatibility with the rubber molecular chain, so the interface interaction between RRP and NRL is improved. Therefore, the prepared RRP / NRL composite material has good mechanical properties and vulcanization characteristics.

[0015] (2) The present invention uses waste rubber powder produced from waste tires as raw material, thereby achieving the recycling of waste materials and meeting the requirements of sustainable development.

[0016] (3) The present invention uses a twin-screw extruder to shear and break bonds of waste rubber powder for desulfurization and regeneration. Since the screws of the twin-screw extruder are sequentially divided into a feeding section, a softening section, a shear reduction section, a homogenization section, and an extrusion section, the regeneration conditions (temperature, rotation speed, etc.) can be controlled more accurately, thereby shortening the regeneration time and improving the regeneration efficiency.

[0017] (4) The screw of the present invention is provided with a gradual change element, and a plurality of flow channels of variable volume or narrow volume are formed between the gradual change element and the barrel and between the gradual change elements. During the flow process, the rubber material is subjected to more complex mechanical shearing, physical extrusion and volume change, and has good distribution mixing and dispersion mixing capabilities. At the same time, the presence of the gradual change element increases the pressure difference in the circumferential direction of the material, indicating that the structure of the gradual change element is conducive to establishing a larger pressure difference for the rubber material in the circumferential direction of the screw, thereby enhancing the mixing effect of the rubber material, which plays a vital role in ensuring the uniformity of the regeneration degree.

[0018] (5) The present invention uses calcium chloride solution as a flocculant, which can effectively neutralize the negative charge on the surface of latex particles, weaken electrostatic repulsion, and promote the rubber particles to approach each other and aggregate, greatly promoting the coagulation and precipitation of rubber particles, thereby realizing the transformation from latex to solid rubber. The preparation method is simple, low-cost, and green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0020] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0021] Figure 1 Schematic diagram of the structure of the twin screws of the twin screw extruder in an embodiment of the present invention;

[0022] Figure 2 is a schematic structural diagram of a gradual change element in an embodiment of the present invention;

[0023] Figure 3 Schematic diagram of strain amplitude dependence of tanδ of #1-#4 RRP / NRL composite materials in embodiments of the present invention;

[0024] Figure 4 Schematic diagram of the change of loss factor (tanδ) of #1-#4 RRP / NRL composite materials with temperature in the embodiments of the present invention;

[0025] Among them, 1. feeding section, 2. softening section, 3. shear reduction section, 4. homogenization section, 5. extrusion section, 6. gradient element, 601. cylinder, 602. convex ridge, 603. wedge surface. DETAILED DESCRIPTION

[0026] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The terms such as "front", "back", "left", "right", "inside", "outside", "middle", etc. cited in this specification are only for the convenience of description and are not intended to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as within the scope of implementation of the present invention without substantially changing the technical content.

[0028] In the following embodiments:

[0029] Natural rubber (NR) is a natural polymer compound mainly composed of cis-1,4-polyisoprene. About 91% to 94% of its components are rubber hydrocarbons (cis-1,4-polyisoprene), and the remaining components include non-rubber substances such as proteins, fatty acids, ash, and sugars. Natural rubber is one of the most widely used general-purpose rubbers.

[0030] The main components of waste rubber powder include:

[0031] 1. Rubber substrate: The main component of waste rubber powder is rubber substrate, which can be natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (BR) or other synthetic rubbers. The type of substrate depends on the raw material of the waste rubber products.

[0032] 2. Carbon black: As a filler, carbon black is widely used to enhance the strength, wear resistance and UV stability of rubber;

[0033] 3. Vulcanizing agent residues: such as sulfur. Vulcanizing agents are chemicals used in the rubber vulcanization process. Waste rubber powder usually contains vulcanizing agent residues;

[0034] 4. Plasticizer: used to increase the flexibility and processability of rubber. Some plasticizer may remain in the waste rubber powder;

[0035] 5. Additives: including antioxidants, anti-aging agents, etc. These chemicals are added during the production process of rubber to extend the life of rubber products. There will also be a certain amount of residue in the waste rubber powder;

[0036] 6. Other fillers: such as calcium carbonate, white carbon black, etc. These fillers are used to adjust the physical properties of rubber.

[0037] These ingredients give waste rubber powder certain mechanical properties and chemical stability, making it useful in a variety of recycling applications.

[0038] The invention provides a method for preparing an RRP / NRL composite material by wet coating on the surface of waste rubber, comprising the following steps: S1. adjusting the temperature of an improved twin-screw extruder to 160°C and the screw speed of the twin-screw extruder to 60rpm, adding waste rubber powder (RRP), and extruding to obtain modified powder; S2. mixing anhydrous calcium chloride and deionized water at a mass ratio of 1:100, stirring to fully dissolve them, and preparing a 1% calcium chloride solution; S3. flocculating natural rubber latex (NRL) and the powder obtained in step S1 in the calcium chloride solution to obtain an RRP / NRL masterbatch, and drying for standby use; , wherein the ratio of natural rubber latex to rubber powder is 1:1; S4. Add masterbatch, white carbon black, stearic acid, zinc oxide, antioxidant 4020, rubber oil V600, and silane coupling agent KH-560 to an internal mixer and mix for 5-10 minutes. After the rubber is discharged and cooled to room temperature, sulfur and vulcanization accelerator CZ are added and mixed on an open mixer. The mass parts of masterbatch, white carbon black, stearic acid, zinc oxide, antioxidant 4020, rubber oil V600, silane coupling agent KH-560, sulfur, and vulcanization accelerator CZ are: 100 parts of masterbatch, 10 parts of white carbon black, 2 parts of stearic acid, 4 parts of zinc oxide, and 4 parts of antioxidant 4020. 4 parts, rubber oil V600 3 parts, silane coupling agent KH-560 2 parts, sulfur 2 parts, vulcanization accelerator CZ 1.3 parts, mix well, cool down and obtain a rubber compound; S5. Put the rubber compound into a flat vulcanizer for vulcanization at a temperature of 150°C, a pressure of 10MPa and a time of 1.3×Tc90. After the vulcanization is completed, cool at room temperature for 8-10h to obtain an RRP / NRL composite material.

[0039] The rubber particles in synthetic rubber latex usually carry negative charges, which allows them to maintain a stable suspension state in water. Calcium chloride, as a cationic coagulant, can effectively neutralize the negative charges on the surface of latex particles, weaken electrostatic repulsion, and promote the rubber particles to approach each other and aggregate, greatly promoting the coagulation and precipitation of rubber particles, thereby realizing the transformation from emulsion to solid rubber. In addition, the use of white carbon black instead of carbon black as a rubber filler has the following advantages: white carbon black has high chemical stability and can enhance the rubber's antioxidant, ozone and UV resistance; the production process of white carbon black produces fewer pollutants, which is more in line with green environmental protection requirements; in addition, its light color also facilitates the regeneration and recycling of waste materials; rubber oil V600, as a rubber softener, can significantly enhance the compatibility between rubber and filler and improve the dispersion effect of filler.

[0040] like Figure 1 As shown, the screws of the twin-screw extruder sequentially include a feeding section 1, a softening section 2, a shear reduction section 3, a homogenizing section 4, and an extrusion section 5. Gradient elements 6 are respectively provided at the softening section 2 and the shear reduction section 3 on the two screws. Figure 2As shown, the gradual change element 6 includes a cylinder 601, and the outer surface annular array of the cylinder 601 has 2N radially protruding ridges 602 (N is a positive integer greater than 2), and the ridges 602 extend along the axial direction of the screw. The outer surface annular array of the cylinder 601 has N wedge surfaces 603, and the wedge surface 603 extends from the root of the head end of a ridge 602 to the root of the terminal end of the adjacent ridge 602. The wedge surface 603 gradually rises along the radial direction in the flow direction of the fluid to the same height as the ridge 602. The height of the ridge 602 of the gradual change element 6 is lower than the height of the twin screw thread, so that there is a small flow channel between the ridges 602 of the two screws. The ridges 602 of the two corresponding gradual change elements 6 on the two screws are staggered with a phase difference of 45 degrees. The corresponding relationship of the wedge surfaces 603 on the two screws is: The gradual element 6 is arranged with a phase difference of 45 degrees. Since a wedge surface 603 is provided on the gradual element 6, a plurality of flow channels of variable volume or narrow volume are formed between the gradual element 6 and the barrel and between the gradual element 6 and the gradual element 6. During the flow process, the rubber material is subjected to more complex mechanical shearing, physical extrusion and volume change, and has good distribution mixing and dispersion mixing capabilities. Experiments have shown that the gradual element 6 has a larger minimum shear rate, which is increased by 7.8%, and can provide a better shear regeneration effect. At the same time, the presence of the gradual element 6 increases the pressure difference in the circumferential direction of the material, indicating that the structure of the gradual element 6 is conducive to the rubber material Establish a larger pressure difference in the circumferential direction of the screw, and enhances the mixing effect of the rubber material, which plays a vital role in ensuring the uniformity of the regeneration degree.

[0041] Experimental example:

[0042] RRP / NRL composite materials #1-#4 were prepared under the experimental conditions in the following table, as shown in the following table.

[0043] #1 Pass through twin screw 0 times / NR #2 Pass through twin screw 0 times / (RRP / NR) #3 Pass through twin screw once / (RRP / NR) #4 Pass through twin screw 2 times / (RRP / NR)

[0044] (1) The RRP / NRL composite material prepared by the present invention has good filler dispersibility. Figure 3 As shown in the figure, the filler of the rubber compound that has not been regenerated on the screw surface has poor dispersion in RRP / NR, a strong filler network, and tanδ increases sharply with the increase of strain. As the number of times passing through the screw increases, the dispersion of the filler increases and the strain dependence of tanδ decreases.

[0045] (2) The RRP / NRL composite material prepared by the present invention has good anti-skid performance and low rolling resistance. Figure 4 As shown, at 0℃, the tanδ value of #3 rubber is the largest and its anti-skid performance is the best; at 60℃, the tanδ of #3 rubber is lower and its rolling resistance is small.

[0046] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for preparing RRP / NRL composite materials by wet coating of waste rubber surface, characterized in that: The following steps are involved: S1. Adjust the temperature of the improved twin-screw extruder to 160°C and the screw speed of the twin-screw extruder to 60 rpm, add waste rubber powder, and extrude the modified rubber powder; S2. Prepare a 1% calcium chloride solution; S3. Flocculate the natural rubber latex and the rubber powder obtained in step S1 in the calcium chloride solution to obtain RRP / NRL masterbatch, and dry it for use; S4. Add masterbatch, white carbon black, stearic acid, zinc oxide, antioxidant 4020, rubber oil V600 and silane coupling agent KH-560 into an internal mixer and mix for 5-10 minutes. After the rubber is discharged and cooled to room temperature, sulfur and vulcanization accelerator CZ are added and mixed on an open mixer. After mixing evenly, the mixture is cooled to obtain a rubber mixture. S5. Put the rubber mixture into a flat vulcanizer and vulcanize it to obtain an RRP / NRL composite material.

2. The method for preparing RRP / NRL composite material by wet coating of waste rubber surface according to claim 1, characterized in that: Anhydrous calcium chloride and deionized water are mixed in a mass ratio of 1:100, and stirred to fully dissolve, thereby obtaining a 1% calcium chloride solution.

3. The method for preparing RRP / NRL composite material by wet coating of waste rubber surface according to claim 1, characterized in that: In step S3, the ratio of natural rubber latex to rubber powder is 1:

1.

4. The method for preparing RRP / NRL composite material by wet coating of waste rubber surface according to claim 3, characterized in that: In step S4, the mass parts of masterbatch, white carbon black, stearic acid, zinc oxide, antioxidant 4020, rubber oil V600, silane coupling agent KH-560, sulfur, and vulcanization accelerator CZ are respectively: 100 parts of masterbatch, 10 parts of white carbon black, 2 parts of stearic acid, 4 parts of zinc oxide, 4 parts of antioxidant 4020, 3 parts of rubber oil V600, 2 parts of silane coupling agent KH-560, 2 parts of sulfur, and 1.3 parts of vulcanization accelerator CZ.

5. The method for preparing RRP / NRL composite material by wet coating of waste rubber surface according to claim 1, characterized in that: In step S5, the vulcanization temperature is 150° C., the pressure is 10 MPa, and the time is 1.3×Tc90. After the vulcanization is completed, the mixture is cooled at room temperature for 8-10 hours.

6. The method for preparing RRP / NRL composite material by wet coating of waste rubber surface according to any one of claims 1 to 5, characterized in that: The screws of the twin-screw extruder sequentially include a feeding section, a softening section, a shear reduction section, a homogenizing section, and an extrusion section. Gradient elements are respectively provided at the softening section and the shear reduction section of the two screws.

7. The method for preparing RRP / NRL composite material by wet coating of waste rubber surface according to claim 6, characterized in that: The gradual element includes a cylinder, and the outer surface annular array of the cylinder has 2N radially protruding ridges (N is a positive integer greater than 2), and the ridges extend along the axial direction of the screw. The outer surface annular array of the cylinder has N wedge surfaces, and the wedge surfaces extend from the root of the head end of a ridge to the root of the end end of an adjacent ridge. The wedge surfaces gradually rise radially in the flow direction of the fluid to the same height as the ridges.

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