EPDM particle surface polarization treatment method for plastic runway

Abstract

The invention discloses an EPDM (Ethylene-Propylene-Diene Monomer) particle surface polarization treatment method for a plastic track. The method comprises the following operation steps: S1, pretreatment: pre-wetting EPDM particles with a proper particle size with an ethanol solution containing 0.8-1.2 wt% of a silane coupling agent; s2, gradient grafting: performing grafting treatment on the pretreated EPDM particles in stages in a nitrogen atmosphere with the oxygen content of less than or equal to 3%; i) preheating stage: treating the pretreated EPDM particles at 100-110 DEG C and 400-600 rpm for 3-5 minutes; ii) grafting sections: treating for 8 to 12 minutes at the temperature of 130 to 140 DEG C and the speed of 1,000 to 1,200 rpm; iii) a stable stage: adding a composite anti-sticking agent when the temperature is reduced to be less than or equal to 110 DEG C; and S3, post-treatment: sequentially carrying out vibration screening and fluidized bed drying on the grafted EPDM particles to obtain modified particles. Non-melting surface modification is achieved through the gradient thermal grafting technology, the interface peel strength of modified particles can be larger than or equal to 3.5 N / mm, VOC emission is smaller than or equal to 30 mg / m, energy consumption is reduced by 60% or above, and the problems that a traditional technology is high in pollution and energy consumption and poor in particle integrity are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of surface modification of polymer materials, and particularly to a method for surface polarization treatment of EPDM particles for plastic runways. Background Art

[0002] In recent years, the annual growth rate of sports injury accidents caused by particle shedding has reached 17%, and 83% of the cases are directly related to the interfacial bonding failure. The interfacial peel strength between unmodified EPDM particles (non-polar) and polyurethane (polar) is ≤1.8 N / mm (ASTM D413 standard), resulting in particle shedding on the runway within 6 - 8 months under frequent impacts. The existing solvent method uses toluene to dissolve and impregnate with MAH, and the VOC emission is as high as 120 mg / m³ (2.4 times the national standard limit of 50 mg / m³), while the extrusion method requires melting EPDM (melting point ≥160°C), the energy consumption is ≥200 kW·h / ton, and the sphericity loss of the particles is ≥30%. Therefore, there is an urgent need to develop a non-molten surface modification process to enhance the polarity while retaining the integrity of EPDM particles and break through the durability bottleneck of runway composite materials. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a method for surface polarization treatment of EPDM particles for plastic runways, which can achieve surface polarization treatment of EPDM particles in a non-molten state by using gradient grafting technology.

[0004] The technical solution provided by the present invention is as follows: A method for surface polarization treatment of EPDM particles for plastic runways, comprising the following operating steps: S1. Pretreatment: Pre-wet EPDM particles with a suitable particle size with an ethanol solution containing 0.8 - 1.2 wt% silane coupling agent to form a surface microporous structure with a specific surface area ≥0.5 m² / g; S2. Gradient grafting: Perform grafting treatment on the pretreated EPDM particles in a nitrogen atmosphere with an oxygen content ≤3% in stages: i) Preheating stage: Treat the pretreated EPDM particles at a temperature of 100 - 110°C and a rotation speed of 400 - 600 rpm for 3 - 5 min to make the penetration depth of the MAH melt ≥5 μm; ii) Grafting stage: Then treat at a temperature of 130 - 140°C and a rotation speed of 1000 - 1200 rpm for 8 - 12 min (when the rotation speed > 1300 rpm, the surface temperature of the particles exceeds 140°C, resulting in partial melting of EPDM (the melt index rises from 0 to 0.8 g / 10 min)), and control the DCP decomposition rate ≥85%; iii) Stabilization stage: Then, when the temperature drops to ≤110°C, a composite anti-sticking agent is added to make the surface friction coefficient of the EPDM particles ≤0.25; S3. Post-treatment: The EPDM particles after grafting treatment are successively subjected to vibrating screening with an amplitude of 2 - 4 mm and fluidized bed drying at 60 - 80°C to obtain modified particles with an interfacial peel strength ≥3.5 N / mm.

[0005] The present invention adopts a non-melting grafting mechanism: By the synergistic temperature control of heat generation by friction in a high-speed mixer (≤140°C) and a heating jacket, MAH is grafted within a 10 - 50 μm layer on the surface of the EPDM particles (observed by SEM), and the internal structure remains intact (the change in melting enthalpy detected by DSC ≤5%); A three-stage temperature field design is adopted: Function of the preheating stage: MAH melts and penetrates into the surface micropores; Function of the grafting stage: Trigger the decomposition of DCP and the grafting reaction; Function of the stabilization stage: Terminate the reaction and prevent particle adhesion.

[0006] Preferably, in the step S1, the particle size of the EPDM particles is 1.5 - 4 mm.

[0007] Preferably, in the pre-wetting process of the step S1, the spraying speed is 20 - 30 mL / min, the atomizing pressure is 0.15 - 0.25 MPa, and the input of mixing energy ≥0.8 kW·h / t.

[0008] Preferably, in the step S2, the composite anti-sticking agent is a mixture of zinc stearate and silicone powder.

[0009] Preferably, the mass ratio between the zinc stearate and the silicone powder is (3 - 5):1. This composite anti-sticking agent can make the dynamic friction coefficient of the particle surface ≤0.25, prevent high-temperature adhesion and terminate the reaction. When the proportion of the anti-sticking agent exceeds 3 - 5:1, striped grafting appears on the particle surface and the peel strength decreases by ≥25%.

[0010] Preferably, the present invention establishes a surface grafting concentration gradient model. The surface grafting concentration gradient in step S2 satisfies: C(h) = C0·e^(-0.015h) (h = 0 - 50 μm), and the internal melting enthalpy change rate ≤ 5%. The grafting rate decays exponentially with the particle surface layer depth (h). The surface grafting concentration gradient satisfies: when h ≤ 10 μm, the MAH grafting rate ≥ 12 mol%, significantly improving the interfacial polarity with polyurethane; when h = 30 μm, the grafting rate decays to (6.5 ± 0.3) mol%, balancing the mechanical properties and particle integrity; when h ≥ 50 μm, the grafting rate ≤ 1.2 mol% (measured by TOF - SIMS to ensure that the internal structure of EPDM is not melted (melting enthalpy change rate ≤ 5%). The verification methods include: 1. TOF - SIMS test: the primary ion beam current is 1 pA, the scanning area is 200×200 μm², and the grafting concentration is analyzed layer by layer; 2. DSC detection: the melting enthalpy change rate ≤ 5%, proving the protection effect of the non - melting process on the particle body.

[0011] Preferably, during the mixing treatment in the grafting section of step S2, a vacuum with a vacuum degree of P = -0.02n + 5 (kPa) is applied synchronously to facilitate the removal of by - products, where n is the rotational speed in the above formula. A linear relationship between the vacuum degree and the rotational speed is established through fluid mechanics simulation (Reynolds number Re = 1200 - 1500). This formula ensures that the vacuum degree increases with the increase of the rotational speed, ensuring that the by - product discharge rate matches the reaction rate (correlation coefficient R² = 0.96). Through the protection of inert gas (nitrogen) (oxygen content ≤ 3%), the side reaction of MAH oxidation can be inhibited (the retention rate of acid anhydride groups detected by FTIR ≥ 95%). When the vacuum degree < 0.05 MPa, the by - product removal rate < 70% (residual maleic acid detected by GC - MS ≥ 120 ppm).

[0012] Preferably, the heating and / or cooling rate during the grafting treatment in step S2 is 8 - 11 °C / min.

[0013] Preferably, the fluidized bed drying in step S3 adopts a three - temperature zone control: the first zone is 60 - 65 °C, the humidity ≤ 30%RH, initially evaporating the surface free moisture; the second zone is 75 - 80 °C, the humidity ≤ 15%RH, deeply removing the bound water to avoid particle agglomeration; the third zone is 50 - 55 °C, the humidity ≤ 40%RH, cooling and shaping to stabilize the particle surface contact angle (≤ 85°); the total residence time in the fluidized bed is 25 - 35 min, the moisture content ≤ 0.5%, the VOC emission ≤ 30 mg / m³ (national standard limit 50 mg / m³), and there is no solvent residue such as toluene.

[0014] Preferably, the surface contact angle of the EPDM particles after drying in step S3 ≤ 85°.

[0015] The present invention has the following advantages over the prior art: The surface polarization treatment method of EPDM particles for plastic runways in the present invention realizes the surface polarization treatment of EPDM particles in a non-molten state by using gradient grafting technology, especially an innovative process that improves the grafting uniformity through the synergistic effect of infrared thermal imaging feedback control and anti-sticking agent; the method of the present invention controls the by-product removal efficiency through the vacuum degree-rotation speed dynamic equation (P=-0.02n+5 kPa), combines the three-temperature zone fluidized bed drying technology, realizes VOC emissions ≤ 30 mg / m³, energy consumption reduction of 60%, and precise control of grafting reaction, solves the technical problems of high energy consumption and uneven modification in traditional processes, and is especially suitable for composite material fields such as sports plastic runways and courts that require high durability. Specific Embodiments

[0016] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0017] Example 1: A method for surface polarization treatment of EPDM particles for plastic runways includes the following operation steps: S1. Pretreatment: 100 kg of EPDM particles with a particle size of 2-3 mm are dried in hot air at 80°C for 4 h (water content ≤ 0.5%), sprayed with 1% ethanol solution of silane coupling agent (KH-570), and mixed at 60°C for 10 min; S2. Gradient grafting: The pretreated EPDM particles are mixed with 4 kg of MAH (purity ≥ 99.5%, water content ≤ 0.3%, vacuum dried at 80°C), 0.36 kg (9% of the mass of MAH) of DCP (dicumyl peroxide) (fed into a high-speed mixer (PTFE-coated, volume 500 L)) and subjected to grafting treatment in stages in a nitrogen atmosphere with an oxygen content ≤ 3%: i) Preheating stage: The pretreated EPDM particles are treated at a temperature of 105°C and a rotation speed of 500 rpm for 5 min to melt MAH; ii) Grafting stage: Then, it is treated at a temperature of 135°C and a rotation speed of 1200 rpm for 10 min for grafting reaction, and the vacuum degree is -0.05 MPa for exhaust; iii) Stabilization stage: Then, when the temperature drops to 110°C, a composite anti-sticking agent composed of 1.2 kg of zinc stearate and 0.4 kg of silicone powder (particle size 5 μm) is added, and it is mixed and treated at a rotation speed of 600 rpm for 3 min to cool and shape after the grafting reaction; S3. Post-treatment: The EPDM particles after grafting treatment are cooled to 50 °C and discharged, then subjected to vibrating screening (qualified products with a size of 2 - 4 mm), and enter a fluidized bed at 60 - 80 °C for drying until the moisture content ≤ 0.5% to obtain modified particles.

[0018] Performance tests were carried out on the above-obtained modified particles, and the test results are as follows: Interface performance: The peel strength is 3.9 N / mm (an increase of 116% compared to the unmodified ones); Wet heat aging (70 °C / 95% RH, 1000 h): The strength retention rate is 89%; Sphericity retention rate: 92%; Energy consumption: 82 kW·h / ton; Impact shedding rate: 0.5%; UV aging (QUV 2000 h): The peel strength retention rate is 86%; Characterization of surface microporous structure: The BET specific surface area is 0.68 m² / g (measured by Micromeritics ASAP 2460); DCP decomposition rate detection: 89.3% (by HPLC method, Agilent 1260 Infinity II); Contact angle: 79°; Freeze-thaw cycle (-30 °C to 50 °C, 50 times): The particle mass loss rate ≤ 0.3%; Environmental protection: The VOC emission is 26 mg / m³ (meeting the GB 36246 - 2018 limit ≤ 50 mg / m³).

[0019] Example 2: A method for surface polarization treatment of EPDM particles for plastic runway, including the following operation steps: S1. Pretreatment: 120 kg of EPDM particles with a particle size of 1.5 - 2 mm are dried in hot air at 85 °C for 5 h (moisture content ≤ 0.4%), sprayed with 0.8 wt% ethanol solution of silane coupling agent (KH-570) (spray speed 25 mL / min, atomization pressure 0.2 MPa), and mixed at 70 °C for 12 min, with the mixing energy input of 1.0 kW·h / t; S2. Gradient grafting: The pretreated EPDM particles are mixed with 5 kg of MAH (purity ≥ 99.5%) and 0.45 kg of DCP (9% of the mass of MAH), and processed in stages in a nitrogen atmosphere with an oxygen content ≤ 2%: i) Preheating section: Treat at a temperature of 110 °C and a rotation speed of 550 rpm for 4 min, with the penetration depth of MAH ≥ 6 μm; ii) Grafting segment: Treat at a temperature of 138°C and a rotation speed of 1100 rpm for 11 min, while applying a vacuum degree of P = -0.02×1100 + 5 = -17 kPa synchronously, and the DCP decomposition rate ≥ 88%; iii) Stabilization segment: When the temperature is lowered to 105°C, add 1.5 kg of zinc stearate and 0.5 kg of silicone powder (mass ratio 3:1), and mix for 4 min; S3. Post-treatment: After vibrating screening (amplitude 3 mm), enter fluidized bed drying (zone 1 at 63°C / 25%RH, zone 2 at 78°C / 12%RH, zone 3 at 52°C / 35%RH, total residence time 30 min), and the final contact angle of the particle surface is 82°.

[0020] Perform performance tests on the modified particles obtained above, and the test results are as follows: Interface peeling strength: 4.0 N / mm; VOC emission: 25 mg / m³; Sphericity retention rate: 93%; Energy consumption: 80 kW·h / ton; Impact shedding rate: 0.4%.

[0021] Example 3: A method for surface polarization treatment of EPDM particles for plastic runway, including the following operation steps: S1. Pretreatment: Dry 80 kg of EPDM particles with a particle size of 3 - 4 mm in hot air at 75°C for 6 h (water content ≤ 0.3%), spray 1.2 wt% of silane coupling agent (KH-550) ethanol solution (spray speed 28 mL / min, atomization pressure 0.18 MPa), mix at 55°C for 15 min, and the mixing energy input is 1.2 kW·h / t; S2. Gradient grafting: Mix the pretreated EPDM particles with 3 kg of MAH and 0.27 kg of DCP (9% of the mass of MAH), and treat in a nitrogen atmosphere with an oxygen content ≤ 1%: i) Preheating segment: Treat at a temperature of 100°C and a rotation speed of 600 rpm for 3 min, and the MAH penetration depth ≥ 5 μm; ii) Grafting segment: Treat at a temperature of 130°C and a rotation speed of 1000 rpm for 12 min, the vacuum degree P = -0.02×1000 + 5 = -15 kPa, and the DCP decomposition rate ≥ 90%; iii) Stabilization segment: When the temperature is lowered to 100°C, add 0.9 kg of zinc stearate and 0.3 kg of silicone powder (mass ratio 3:1), and mix for 5 min; S3. Post-treatment: After vibrating screening (amplitude 4 mm), perform fluidized bed drying (zone 1 at 65°C / 28%RH, zone 2 at 80°C / 10%RH, zone 3 at 55°C / 38%RH, total residence time 35 min), and the final contact angle of the particle surface is 78°.

[0022] Perform performance tests on the modified particles obtained above. Test results: Interface peeling strength: 3.6 N / mm; VOC emission: 30 mg / m³; Sphericity retention rate: 90%; Energy consumption: 88 kW·h / ton; Impact shedding rate: 0.6%.

[0023] Example 4: A method for surface polarization treatment of EPDM particles for plastic runway, including the following operation steps: S1. Pretreatment: Dry 150 kg of EPDM particles with a particle size of 2.5 - 3.5 mm in hot air at 90°C for 3 h (moisture content ≤ 0.2%), spray 1.0 wt% silane coupling agent (KH-792) ethanol solution (spray speed 22 mL / min, atomization pressure 0.22 MPa), mix at 65°C for 8 min, and the input of mixing energy is 0.9 kW·h / t; S2. Gradient grafting: Mix the pretreated EPDM particles with 6 kg of MAH and 0.54 kg of DCP (9% of the mass of MAH), and treat them in a nitrogen atmosphere with an oxygen content ≤ 2.5%: i) Preheating section: Treat at a temperature of 105°C and a rotation speed of 450 rpm for 5 min, and the penetration depth of MAH ≥ 7 μm; ii) Grafting section: Treat at a temperature of 140°C and a rotation speed of 1200 rpm for 9 min, the vacuum degree P = -0.02×1200 + 5 = -19 kPa, and the decomposition rate of DCP ≥ 87%; iii) Stabilization section: Add 2.0 kg of zinc stearate and 0.5 kg of silicone powder (mass ratio 4:1) when the temperature is lowered to 108°C, and mix for 3 min; S3. Post-treatment: After vibrating screening (amplitude 2 mm), fluidized bed drying (zone 1: 60°C / 30%RH, zone 2: 75°C / 14%RH, zone 3: 50°C / 40%RH, total residence time 25 min), and the final contact angle of the particle surface is 75°.

[0024] Perform performance tests on the modified particles obtained above. Test results: Interface peeling strength: 4.2 N / mm; VOC emission: 22 mg / m³; Sphericity retention rate: 95%; Energy consumption: 78 kW·h / ton; Impact shedding rate: 0.3%.

[0025] Comparative Example 1: This Comparative Example 1 adopts the known solvent method in the prior art. The specific operation steps are as follows: S1. Immerse the EPDM particles in a toluene solution containing 10 wt% MAH (liquid-solid ratio 5:1), and stir at 60 °C for 4 h; S2. After filtration, dry at 80 °C for 6 h to remove the residual solvent; S3. Without using an anti-sticking agent, directly screen to obtain the product.

[0026] Perform performance tests on the product obtained above. The test results are as follows: Interface peeling strength: 2.1 N / mm; VOC emission: 105 mg / m³ (toluene volatilization); Sphericity retention rate: 78%; Energy consumption: 220 kW·h / ton; Impact shedding rate: 2.8%.

[0027] Table 1 below shows the comparison of the experimental results of Examples 1-4 of this application and Comparative Example 1.

[0028] Table 1 shows the comparison of the experimental results of Examples 1-4 and Comparative Example 1

[0029] It can be seen from Table 1 that the modified particles obtained in Examples 1-4 of the present invention are significantly superior to Comparative Example 1 (solvent method) in terms of various performance indicators. Specifically, it is shown as follows: 1. Interface peeling strength: The interface strength (3.6 - 4.2 N / mm) of the modified particles obtained in Examples 1-4 of the present invention is increased by 71% - 100% compared with Comparative Example 1 (2.1 N / mm); 2. Environmental protection: The VOC emission (22 - 30 mg / m³) of the modified particles obtained in Examples 1-4 of the present invention is much lower than that of the solvent method (105 mg / m³), only 44% - 60% of the national standard limit (50 mg / m³); 3. Energy consumption: The energy consumption (78 - 88 kW·h / ton) of the modified particles obtained in Examples 1-4 of the present invention is reduced by 60% - 65% compared with the solvent method (220 kW·h / ton); 4. Particle integrity: The sphericity retention rate (90% - 95%) of the modified particles obtained in Examples 1-4 of the present invention is significantly higher than that of the solvent method (78%), and the impact shedding rate (0.3% - 0.6%) is only 1 / 5 - 1 / 9 of that of Comparative Example 1; 5. Process stability: The surface grafting concentration gradient (C(h)=C0·e^(-0.015h)) and the change rate of melting enthalpy (≤5%) of the modified particles obtained in Examples 1-4 both meet the design requirements, verifying the reliability of the non-melting grafting process.

[0030] In summary, through the gradient thermal grafting technology, the present invention realizes the efficient polarization modification of EPDM particles in a non-molten state, with the advantages of high interfacial strength, low energy consumption, environmental protection and retention of particle integrity, effectively solving the technical defects of the traditional solvent method and extrusion method, and also meeting the requirements of the green environmental protection runway (GFPT).

[0031] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for surface polarization treatment of EPDM particles for plastic runway, characterized in that, The operation steps are as follows: S1. Pretreatment: Pre-wet EPDM particles with appropriate particle sizes with an ethanol solution containing 0.8 - 1.2 wt% silane coupling agent; S2. Gradient grafting: Perform grafting treatment on the pretreated EPDM particles in stages in a nitrogen atmosphere with an oxygen content ≤ 3%: i) Preheating stage: Treat the pretreated EPDM particles at a temperature of 100 - 110 °C and a rotation speed of 400 - 600 rpm for 3 - 5 min; ii) Grafting stage: Then treat at a temperature of 130 - 140 °C and a rotation speed of 1000 - 1200 rpm for 8 - 12 min; iii) Stabilization stage: Add a composite anti-sticking agent when the temperature drops to ≤ 110 °C; S3. Post-treatment: The grafted EPDM particles are successively subjected to vibration screening with an amplitude of 2 - 4 mm and fluidized bed drying at 60 - 80 °C to obtain modified particles.

2. The surface polarization treatment method of EPDM particles for plastic runway according to claim 1, characterized in that, In step S1, the particle size of the EPDM particles is 1.5 - 4 mm.

3. The method for surface polarization treatment of EPDM particles for plastic runway according to claim 1, characterized in that, In the pre-wetting process of step S1, the spraying speed is 20 - 30 mL / min, the atomization pressure is 0.15 - 0.25 MPa, and the input of mixing energy is ≥ 0.8 kW·h / t.

4. The surface polarization treatment method of EPDM particles for plastic runway according to any one of claims 1-3, characterized in that, In step S2, the composite anti-sticking agent is a mixture of zinc stearate and silicone powder.

5. The method for surface polarization treatment of EPDM particles for plastic runway according to claim 4, characterized in that, The mass ratio between the zinc stearate and the silicone powder is (3 - 5):

1.

6. The surface polarization treatment method of EPDM particles for plastic runway according to any one of claims 1-3, characterized in that, In step S2, the surface grafting concentration gradient satisfies: C(h)=C0·e^(-0.015h) (h = 0 - 50 μm), and the internal melting enthalpy change rate ≤ 5%.

7. The surface polarization treatment method of EPDM particles for plastic runway according to any one of claims 1-3, characterized in that In the mixing treatment of the grafting stage in step S2, apply a vacuum with a vacuum degree of P = -0.02n + 5 (kPa) synchronously to facilitate the removal of by-products, where n is the rotation speed in the above formula.

8. The surface polarization treatment method of EPDM particles for plastic runway according to any one of claims 1-3, characterized in that, In the grafting treatment process of step S2, the heating rate and / or cooling rate is 8 - 11 °C / min.

9. The surface polarization treatment method of EPDM particles for plastic runway according to any one of claims 1-3, characterized in that, In step S3, the fluidized bed drying is controlled by three temperature zones: the first zone is 60 - 65 °C, the humidity ≤ 30%RH; the second zone is 75 - 80 °C, the humidity ≤ 15%RH; the third zone is 50 - 55 °C, the humidity ≤ 40%RH; the total residence time in the fluidized bed is 25 - 35 min.

10. The surface polarization treatment method of EPDM particles for plastic runway according to claim 9, characterized in that, In step S3, the surface contact angle of the dried EPDM particles ≤ 85°.

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