Chemical treatment method for refining waste rubber powder particles

Abstract

The invention discloses a chemical treatment method for refining waste rubber powder particles, and belongs to the technical field of solid waste resource utilization. According to the chemical treatment method disclosed by the invention, coarse rubber powder obtained by recycling waste rubber products is taken as a raw material, and refined rubber powder with uniform particle size is finally obtained through a multi-step chemical treatment process of raw material pretreatment, chemical crosslinking bond breakage, surface modification and ultrasonic-assisted cleaning and drying. According to the method, the problems of high energy consumption, non-uniform particle size and rubber powder performance degradation caused by excessive etching of a chemical method in a traditional physical grinding method are solved, the particle size of the prepared superfine rubber powder can be stably controlled to be 0.1-50 microns, and the method can be widely applied to the fields of rubber regeneration, asphalt modification and the like.

Description

Technical Field

[0001] This invention relates to a chemical treatment method for refining waste adhesive powder particles, belonging to the field of solid waste resource utilization technology. Background Technology

[0002] Waste tire recycling is a core issue in environmental protection and resource recycling. my country produces approximately 330 million waste tires annually. With a shortage of rubber resources and a high dependence on imports, recycling waste rubber into rubber powder for reuse in rubber, plastics, asphalt, and other fields is a common and economical recycling method. The particle size of the rubber powder directly determines its reuse value; the smaller the particle size, the higher the reuse value. The efficient preparation of ultrafine rubber powder has become a key technological challenge in the industry. Currently, the mainstream refining technologies are divided into physical and chemical methods, both of which have significant limitations and cannot meet the synergistic requirements of mild conditions, environmental friendliness, and ultrafine particle size.

[0003] In terms of physical methods, traditional rolling extrusion can only produce coarse rubber powder of 28-40 mesh due to the plastic resilience of rubber, limiting its application scenarios. Although a patent report proposes a high-speed grinding process using grinding wheels (CN1043199C), which uses dual motors to drive the grinding wheel and tire to rotate at high speed relative to each other, increasing the rubber powder particle size to 100-200 mesh, it still relies on mechanical shearing force and suffers from high energy consumption and insufficient particle size uniformity. The room-temperature additive method (CN100494254C) improves the pulverization characteristics by adding solid additives such as silicates and carbonates, and can obtain rubber powder of 120-400 mesh, reducing energy consumption. However, it requires specialized umbrella-shaped pulverizing machinery, and the cyclone separation process between the additives and the rubber powder increases the complexity of operation. The low-temperature freezing method abroad requires freezing the rubber to below -200°C for crushing. Although it can produce fine powder, the equipment is expensive and the freezing environment is difficult to maintain, resulting in high production costs and a lack of feasibility for large-scale application.

[0004] In the field of chemical methods, related technologies have been gradually optimized, but defects still exist: the swelling agent method (CN1162462C) uses polar solvents in combination with volatilization inhibitors, which has broken through the bottleneck of preparing ultrafine rubber powder of 200 mesh or above at room temperature. However, traditional chemical methods generally have problems such as difficulty in solvent recovery, easy agglomeration of rubber powder, or reliance on high-pressure equipment and high cost of large-scale application.

[0005] In summary, existing technologies cannot efficiently refine 75-380μm coarse rubber powder to 0.1-50μm (>300 mesh) under mild conditions. Therefore, developing a chemical refining method with controllable particle size, environmental protection, and low consumption has significant technical value and application prospects. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of uncontrollable particle size and deterioration of rubber powder performance in the chemical refining process of waste rubber powder in the prior art, and to provide a chemical treatment method for refining waste rubber powder particles. This method uses selective destruction of polymer chain cross-linking bonds to achieve precise control of rubber powder particle refining, combined with surface modification, to finally obtain ultrafine rubber powder with uniform particle size and excellent performance.

[0007] To achieve the above objectives, the technical solution of this invention is characterized by: employing a synergistic mechanism of "selective chemical bond breaking as the main method and physical swelling as the auxiliary method," and by precisely controlling the reaction conditions, destroying the three-dimensional cross-linked structure of the rubber polymer network in the waste rubber powder, causing it to depolymerize and soften at the microscopic level, thereby achieving particle refinement; and subsequently, through a surface modification process, improving the surface activity and compatibility of the refined rubber powder, ultimately obtaining an ultrafine rubber powder product with uniform particle size and excellent performance.

[0008] Specifically, the chemical treatment method for refining waste adhesive powder particles provided by the present invention includes the following steps: S1. Raw material pretreatment: The crude rubber powder recycled from waste rubber is subjected to impurity removal (e.g., using magnetic separation to remove metal impurities such as iron filings) and drying treatment to obtain dried raw rubber powder. This step can prevent moisture from interfering with the reaction system in subsequent chemical treatments; S2, Chemical cross-linking bond breaking: The dried raw rubber powder is mixed with the treatment liquid and reacted under sealed conditions. The cross-linking bonds of the rubber powder are broken and the rubber powder is swollen and refined through the synergistic effect of the desulfurizing agent and solvent in the treatment liquid. The rubber powder is then filtered and collected. S3. Surface modification: The adhesive powder obtained in step S2 is reacted with the modification liquid, and the modified adhesive powder is obtained by filtration and drying. S4. Ultrasonic-assisted cleaning and drying: The modified adhesive powder is ultrasonically cleaned with deionized water and then dried to obtain ultrafine adhesive powder.

[0009] In step S1, the particle size of the coarse adhesive powder is 75-380 μm; In step S1, the drying conditions are: hot air drying at 60-80℃ for 4-10 hours to completely remove surface adsorbed moisture.

[0010] In step S2, the desulfurizing agent selectively breaks the sulfur-sulfur (SS) or carbon-sulfur (CS) crosslinking bonds between rubber molecular chains, weakening the overall strength of the rubber network and making it easier to break down. Optional desulfurizing agents include, but are not limited to, reducing compounds such as dithiothreitol (DTT) and diphenyl disulfide, and their mass fraction in the treatment liquid is preferably 1%-10%. The solvent's role is to swell the rubber molecular chains, penetrate into the cross-linked network, increase the molecular chain spacing, and help the desulfurizer to more effectively contact and destroy the cross-linking points. At the same time, the solvation effect also helps large particles dissociate into smaller particles under mechanical stress (such as stirring, subsequent ultrasound). Optional solvents include phenethyl ether, dioctyl phthalate (DOP), xylene, and other organic media with good swelling ability for rubber.

[0011] In step S2, the dried raw gum powder and the treatment liquid are mixed at a solid-liquid ratio of 1 g: 5-10 mL. The reaction is carried out at a temperature of 120-200℃ for 12-72 hours. Under these mild pressure (system-generated pressure) and temperature conditions, the desulfurizing agent and solvent work synergistically to achieve deep and controllable destruction of the cross-linked network of the rubber powder. After the reaction is completed, the solid rubber powder is separated by filtration.

[0012] After chemical bond breaking and refining in step S2, the surface of the rubber powder exposes more active groups, but its surface energy is high, making it prone to agglomeration. Step S3 aims to impart new surface properties to the rubber powder through chemical grafting or coating. The rubber powder obtained in the previous step is immersed in a modification solution and stirred at 40℃-50℃ for 15-30 minutes. The modification solution mainly contains silane coupling agents, such as 3-methacryloyloxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, bis-[γ-(triethoxysilyl)propyl]tetrasulfide, or tetraethyl orthosilicate, etc. One end of the coupling agent can react with the active groups on the surface of the rubber powder, while the other end has functional groups that can be well compatible with or react with the target application matrix (such as rubber, asphalt, resin), thereby significantly improving the dispersibility and interfacial bonding of the rubber powder in the composite material. After the reaction is completed, the modified rubber powder is obtained by filtration and drying.

[0013] To thoroughly remove residual chemical reagents from the surface of the adhesive powder and ensure product purity, the modified adhesive powder from step S3 was ultrasonically cleaned with deionized water at 30 ℃. After each cleaning, it was centrifuged at 8000 rpm for 5 minutes to achieve solid-liquid separation. This cleaning process was repeated 3 times. Finally, the cleaned adhesive powder was placed in a vacuum drying oven at 50℃-60℃ and dried for 6-8 hours to obtain the final product—high-performance ultrafine adhesive powder.

[0014] The ultrafine adhesive powder prepared by the method of the present invention has a particle size range of 0.1-50 μm and a D50 of 1-20 μm.

[0015] This invention's ultrafine rubber powder can overcome the limitations of traditional low-value applications of rubber powder and can be widely used in higher-value fields such as aerospace (e.g., high-end resins, rubber-based composite materials) and medical (e.g., medical rubber, resin-based consumables). Combined with surface modification and compounded with various matrix materials, it can effectively improve the mechanical properties and environmental resistance of materials. This not only expands the high-value utilization path of waste rubber resources, but also provides a low-cost modification solution for high-end fields, with very broad application prospects.

[0016] The present invention has the following beneficial technical effects: 1. The fineness of the adhesive powder is highly controllable. Through selective bond breaking and swelling-assisted treatment, the reaction temperature can be controlled at 120-200℃ and the reaction time at 12-72h. Combined with surface modification, ultrafine adhesive powder in the range of 0.1-50μm can be precisely prepared.

[0017] 2. The process has low energy consumption and excellent environmental performance, meeting the requirements of green production: it does not require high-energy-consuming physical grinding equipment, but refines the adhesive powder through chemical action; the liquid only wets the adhesive powder, there is no strong corrosive acid, and no large amount of waste liquid is generated.

[0018] 3. High process flexibility and adaptability to multiple scenarios: Different particle size adhesive powders can be precisely prepared by controlling the "temperature-time" ratio. It can be combined with a variety of modification systems to adapt to different application scenarios. Moreover, the process parameters are uniform, which makes it easy to switch and adjust the production line.

[0019] 4. Strong industrial adaptability and significant benefits: The process is simple, the parameters are compatible with existing production lines, and mass production can be achieved with only simple modification of the reaction vessel, without the need for large-scale new equipment; the ultrafine rubber powder has a wide range of applications, promotes the resource utilization of waste rubber, and has both environmental and economic value. Attached Figure Description

[0020] Figure 1 The image shows the particle size distribution of the rubber powder (SR-RP-1 / 2 / 3) and the original rubber powder (R-RP) prepared in Examples 1-3 of this invention. The horizontal axis represents the particle size (μm), and the vertical axis represents the mass percentage (%).

[0021] Figure 2 Tensile curves of the rubber powder-natural rubber (SR-RP-1-NR) and the virgin rubber powder-natural rubber (R-RP-NR) prepared in Example 1 of this invention; the horizontal axis represents strain (%) and the vertical axis represents strength (MPa).

[0022] Figure 3 The image shows the particle size distribution of the adhesive powder (SR-RP-4 / 5) and coarse adhesive powder (R-RP-30-80) prepared in Examples 4-5 of this invention. The horizontal axis represents the particle size (μm), and the vertical axis represents the mass percentage (%). Detailed Implementation

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0024] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0025] To address the technical bottlenecks of existing physical grinding methods, such as high energy consumption and uneven particle size, as well as the tendency of traditional chemical methods to over-etch and damage the performance of adhesive powder, this invention provides a finer method that achieves precise particle size control under mild conditions, is environmentally friendly, and maintains the excellent performance of adhesive powder.

[0026] The core of this invention lies in the synergistic process of "selective chemical bond breaking" combined with "swelling assistance" and "surface modification". This method uses coarse rubber powder recovered from waste rubber as raw material, and proceeds sequentially through: (1) pretreatment to remove impurities and moisture; (2) selectively breaking cross-links in the rubber network using a treatment liquid containing a desulfurizing agent at a specific temperature and time, and achieving particle refinement with solvent swelling assistance; (3) surface modification of the refined rubber powder using a coupling agent to improve its interfacial compatibility; and (4) obtaining the final product through ultrasonic cleaning and vacuum drying. By controlling the reaction parameters, ultrafine rubber powder with a uniform particle size distribution in the range of 0.1-50 micrometers can be stably prepared.

[0027] This invention achieves controllable refining of rubber powder while preserving high performance; the process conditions are mild, requiring no high-energy-consuming equipment, making it environmentally friendly; the process flow is simple and flexible, facilitating industrial production. The resulting ultrafine rubber powder can be widely used in rubber recycling, asphalt modification, and high-end composite materials, providing an effective way to utilize waste rubber for high-value purposes.

[0028] Example 1: Preparation of SR-RP-1 adhesive powder 1. Raw material pretreatment: Take the raw rubber powder (denoted as R-RP, particle size distribution 75-380μm) from the waste tires, remove the iron filings and dry the rubber powder in an 80℃ hot air drying oven for 5 hours.

[0029] 2. Breaking of chemical cross-links: Add the dried raw rubber powder to the treatment solution (the desulfurizing agent is dithiothreitol, mass fraction 5%, and the solvent is phenylethyl ether) at a solid-liquid ratio of 1g:5mL. After stirring evenly, transfer it to a hydrothermal reactor and react at 120℃ for 12h. After the reaction is completed, filter under normal pressure and let stand at room temperature for 10min to drain the residual treatment solution on the surface to obtain desulfurized refined rubber powder.

[0030] 3. Surface modification: Place the above desulfurized refined rubber powder in an ethanol solution (95%), sonicate for 10 min, add a certain amount of 3-methacryloyloxypropyltrimethoxysilane at 12% of the rubber powder mass, stir at room temperature for 3-5 min, filter, and dry to obtain surface-modified rubber powder.

[0031] 4. Ultrasonic-assisted cleaning and drying: Transfer the surface-modified adhesive powder to a beaker, add deionized water, and ultrasonically clean for 5 minutes. Then, centrifuge at 8000 rpm for 5 minutes at room temperature to achieve solid-liquid separation, and discard the supernatant. Repeat the above ultrasonic cleaning-centrifugation separation operation 3 times to ensure complete removal of residual reagents on the surface. Place the cleaned adhesive powder in a vacuum drying oven and dry at 60℃ and -0.08MPa for 6 hours. After drying, maintain the vacuum state and cool to room temperature before removing to obtain ultrafine adhesive powder SR-RP-1.

[0032] Particle size characterization: A laser particle size analyzer was used for testing, with ethanol as the dispersion medium. Results are as follows: Figure 1 As shown: the original rubber powder R-RP has a broad distribution with a single peak and D50 > 100 μm; the particle size distribution of SR-RP-1 prepared in this example is concentrated in 10-40 μm, D50 = 20 μm, with no large particles > 100 μm, and the refining effect is significant.

[0033] Mechanical properties of the composite material: SR-RP-1 and natural rubber (NR) were blended at a mass ratio of 3:7, and a vulcanization system (2.5 parts zinc oxide, 0.4 parts stearic acid, 1.2 parts sulfur, and 0.8 parts N-cyclohexyl-2-benzothiazole sulfenamide accelerator, based on the total mass of the blend) was added. The mixture was hot-pressed at 160℃ and 10MPa in a flat vulcanizing press for 15 min, followed by holding and cooling for 10 min to prepare dumbbell-shaped Type I specimens (GB / T 528-2019). Mechanical properties were tested at room temperature using an electronic universal testing machine at a tensile speed of 500 mm / min, with 5 parallel tests performed. The results are as follows: Figure 2 As shown: the tensile strength of SR-RP-1-NR is 6.62 MPa and the elongation at break is 797%; the tensile strength of the control group R-RP-NR (a blend of unrefined rubber powder and NR) is 6.97 MPa and the elongation at break is 666%. Compared with the control group, the tensile strength of SR-RP-1-NR is reduced by 5%, the elongation at break is increased by 20%, and the flexibility is significantly improved.

[0034] Example 2: Preparation of SR-RP-2 adhesive powder 1. Raw material pretreatment: The raw material pretreatment process is completely consistent with that in Example 1.

[0035] 2. Breaking of chemical cross-links: Compared with Example 1, the solvent of the treatment solution is dioctyl phthalate, the reaction temperature is 200°C, and the reaction time, filtration and draining operations are the same as in Example 1.

[0036] 3. Surface modification: The surface modification process is completely consistent with that in Example 1.

[0037] 4. Ultrasonic-assisted cleaning and drying: The ultrasonic-assisted cleaning and drying process is completely consistent with that in Example 1.

[0038] Test results: Particle size distribution as shown Figure 1 As shown, the particle size distribution of SR-RP-2 is concentrated in 5-30 μm, exhibiting a single-peak narrow distribution characteristic, with D50=10 μm. The particle size uniformity is significantly improved compared to Example 1, indicating that the particle size refinement effect is better under high temperature conditions.

[0039] Example 3: Preparation of SR-RP-3 adhesive powder 1. Raw material pretreatment: The raw material pretreatment process is completely consistent with that in Example 1.

[0040] 2. Breaking of chemical cross-links: The treatment solution is diphenyl disulfide and dioctyl phthalate. The reaction temperature is the same as in Example 2, the reaction time is extended to 36 hours, and the filtration and draining operations are the same as in Example 1.

[0041] 3. Surface modification: The surface modification process is completely consistent with that in Example 1.

[0042] 4. Ultrasonic-assisted cleaning and drying: The ultrasonic-assisted cleaning and drying process is completely consistent with that in Example 1.

[0043] Test results: Particle size distribution as shown Figure 1 As shown, the particle size distribution of SR-RP-3 ranges from 1 to 5 μm, exhibiting a typical single-peak narrow distribution with D50 = 2 to 3 μm. This achieves efficient refinement and size uniformity control of the rubber powder particle size, laying the microstructural foundation for its excellent dispersibility and interfacial bonding strength in the rubber matrix. Example 4: Preparation of SR-RP-4 adhesive powder 1. Raw material pretreatment: Take waste tire rubber powder (particle size 30-80μm, denoted as R-RP-30-80) that has been screened by a standard sieve, remove iron filings and impurities, and dry the rubber powder in an 80℃ hot air circulating drying oven for 5 hours to obtain dried rubber powder.

[0044] 2. Breaking of chemical cross-links: Add the dried rubber powder to the treatment solution (the desulfurizing agent is dithiothreitol, mass fraction 5%; the solvent is xylene) at a solid-liquid ratio of 1g:5mL. After stirring evenly, transfer it to a hydrothermal reactor and react at 120℃ for 12h. After the reaction is completed, filter under normal pressure and let stand at room temperature for 10min to drain the residual liquid to obtain desulfurized refined rubber powder.

[0045] 3. Surface modification: The modification liquid is silane coupling agent Si-69, and the rest is the same as the surface modification process in Example 1. This process can enhance the surface activity of waste rubber powder and improve its interfacial compatibility with the rubber matrix.

[0046] 4. Ultrasonic-assisted cleaning and drying: The ultrasonic-assisted cleaning and drying process is completely consistent with that in Example 1.

[0047] Test results: Particle size distribution as shown Figure 3 As shown, the particle size distribution of SR-RP-4 ranges from 0.5 to 2 μm, exhibiting a unimodal symmetrical distribution with D50 = 1.0 μm. This indicates that the dithiothreitol-xylene system can efficiently refine 30-80 μm rubber powder into ultrafine particles of 1 μm.

[0048] Example 5: Preparation of SR-RP-5 adhesive powder 1. Raw material pretreatment: The raw material pretreatment process is completely consistent with that in Example 4.

[0049] 2. Breaking of chemical cross-links: The content of dithiothreitol in the treatment solution was reduced to 33% of that in Example 4, and the remaining operations were completely consistent with those in Example 4.

[0050] 3. Surface modification: The surface modification process is completely consistent with that in Example 4; 4. The ultrasonic-assisted cleaning and drying process is completely consistent with the ultrasonic-assisted cleaning and drying process in Example 1.

[0051] Test results: such as Figure 3 As shown, the particle size distribution of SR-RP-5 ranges from 1 to 4 μm, exhibiting a unimodal distribution with D50 = 2 to 3 μm. The results indicate that when the concentration of dithiothreitol in the treatment solution is reduced to 33% as in Example 4, the refining effect of the rubber powder decreases systematically, verifying the positive correlation between the concentration of the desulfurizing agent and the degree of rubber powder refining, and providing experimental basis for the precise control of process parameters.

[0052] Comparative Example 1: Surface modification steps omitted The steps of Example 1 were completely repeated, but ultrasonic cleaning and drying were performed directly after the chemical crosslinking bonds were broken, omitting surface modification.

[0053] result: The particle size of the adhesive powder was similar to that of Example 1 (D50=20μm), but it showed obvious agglomeration and clumps after standing.

[0054] When compounded with natural rubber, dispersion is difficult, the tensile strength of the composite material is 8% lower than that of Example 1, and obvious defects are visible at the interface.

[0055] Comparative Example 2, Solvent-free swelling aid Repeat Example 1, but without adding phenethyl ether to the treatment solution, only dithiothreitol (solid) is used to mix with the adhesive powder.

[0056] result: The reaction efficiency is low, the refining effect is poor, and D50 = 100 μm.

[0057] The swelling effect of the solvent is demonstrated to be crucial for the penetration of the desulfurizing agent and the dissociation of particles.

[0058] Comparative Example 3: Insufficient reaction temperature Method: Repeat Example 1, but lower the chemical crosslinking bond breaking reaction temperature to 90 °C.

[0059] result: The reaction was incomplete, and the particle size of the adhesive powder remained basically unchanged, with D50 = 200 μm.

[0060] This demonstrates that the temperature window (120-200°C) of the present invention is a necessary condition for achieving effective selective bond breaking.

[0061] Comparative Example 4: Traditional Physical Grinding Method The same batch of coarse rubber powder (75-380μm) was mechanically ground for 30 minutes using a two-roll mill.

[0062] result: The resulting adhesive powder has a D50 of 100μm and an extremely wide distribution (30-275μm), containing a large number of unbroken coarse particles.

[0063] When compounded with natural rubber, the tensile strength decreased by 6%, and the elongation at break did not improve.

Claims

1. A chemical treatment method for refining waste adhesive powder particles, comprising the following steps: S1. Raw material pretreatment: The crude rubber powder recovered from waste rubber is cleaned and dried to obtain dried raw rubber powder; S2, Chemical cross-linking bond breaking: The dried raw rubber powder is mixed with the treatment liquid and reacted under sealed conditions. The cross-linking bonds of the rubber powder are broken and the rubber powder is swollen and refined through the synergistic effect of the desulfurizing agent and solvent in the treatment liquid. The rubber powder is then filtered and collected. S3. Surface modification: The adhesive powder obtained in step S2 is reacted with the modification liquid, and the modified adhesive powder is obtained by filtration and drying. S4. Ultrasonic-assisted cleaning and drying: The modified adhesive powder is ultrasonically cleaned with deionized water and then dried to obtain ultrafine adhesive powder.

2. The chemical treatment method according to claim 1, characterized in that: In step S1, the particle size of the coarse adhesive powder is 75-380 μm; In step S4, the particle size range of the ultrafine adhesive powder is 0.1-50 μm, and the D50 is 1-20 μm.

3. The chemical treatment method according to claim 1 or 2, characterized in that: In step S1, the drying conditions are: hot air drying at 60-80℃ for 4-10 hours.

4. The chemical treatment method according to any one of claims 1-3, characterized in that: In step S2, the dried raw gum powder and the treatment liquid are mixed at a solid-liquid ratio of 1 g: 5-10 mL. The reaction is carried out at a temperature of 120-200℃ for a time of 12-72 h.

5. The chemical treatment method according to any one of claims 1-4, characterized in that: In step S2, the desulfurizing agent is selected from at least one of dithiothreitol and diphenyl disulfide; the solvent is selected from at least one of phenethyl ether, dioctyl phthalate, and xylene. The desulfurizing agent has a mass fraction of 1-10% in the treatment liquid.

6. The chemical treatment method according to any one of claims 1-5, characterized in that: In step S3, the modified liquid is an ethanol solution of a silane coupling agent; The silane coupling agent is 3-methacryloxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, bis-[γ-(triethoxysilane)propyl]tetrasulfide, or tetraethyl orthosilicate.

7. The chemical treatment method according to any one of claims 1-6, characterized in that: In step S3, the reaction temperature is 40-50℃ and the time is 15-30 min.

8. The chemical treatment method according to any one of claims 1-7, characterized in that: In step S4, the conditions for ultrasonic cleaning are: 30°C deionized water, ultrasonic cleaning 3 times, centrifugation at 8000 rpm for 5 min after each cleaning. The drying process is vacuum drying, with the following conditions: temperature 50-60℃ and time 6-8 h.

9. An ultrafine adhesive powder, prepared by the chemical treatment method according to any one of claims 1-8.

10. The ultrafine adhesive powder according to claim 9, characterized in that: The ultrafine adhesive powder has a particle size range of 0.1-50 μm and a D50 of 1-20 μm.

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