Recyclable flame-retardant polyethylene material and preparation method thereof

Abstract

The invention discloses a recyclable flame-retardant polyethylene material, which is prepared from the following raw materials in parts by weight: 50 to 70 parts of ethylene vinyl acetate copolymer; 18-45 parts of a composite flame-retardant system and 5-12 parts of an amino silane cross-linking agent; the composite flame retardant system comprises ammonium polyphosphate and diethyl aluminum hypophosphite. The flame-retardant grade of the polyethylene material reaches V0, the polyethylene material shows excellent flame-retardant performance, meanwhile, ammonium polyphosphate and aluminum diethyl hypophosphite have an obvious promoting effect on construction of a silyl ether dynamic cross-linked network in the polyethylene material, and the polyethylene material is endowed with excellent reprocessing performance, flame-retardant performance and mechanical performance.

Description

Technical Field

[0001] This invention relates to the field of polyolefin material modification, specifically to a recyclable flame-retardant polyethylene material and its preparation method. Background Technology

[0002] Ethylene-vinyl acetate copolymer (EVA) is an important polyethylene-based polymer in industry. After peroxide crosslinking, it is widely used in footwear, wire and cable, and automotive interiors due to its excellent mechanical properties and dimensional stability. However, because peroxide crosslinking is a permanent covalent crosslinking process, polyethylene materials face recycling challenges despite their widespread use. After reaching the end of their service life, most of these materials are incinerated, landfilled, or improperly disposed of, inevitably causing serious environmental problems.

[0003] Furthermore, polyethylene is a highly flammable polymer material, and its combustion produces molten droplets and releases smoke, posing a significant safety hazard. Therefore, developing polyethylene materials with good flame-retardant and smoke-suppressing properties has become an urgent problem to solve. Existing flame-retardant polyethylene materials often involve adding large amounts of inorganic flame retardants such as magnesium hydroxide or aluminum hydroxide to polyethylene. However, the addition of large amounts of inorganic flame retardants leads to a significant decrease in the mechanical properties of polyethylene, thereby reducing the material's stability.

[0004] Therefore, developing a polyethylene material that combines excellent reprocessing performance, flame retardancy, and mechanical properties is an urgent problem to be solved. Summary of the Invention

[0005] In view of this, the present invention provides a recyclable flame-retardant polyethylene material and its preparation method. The flame retardant rating of the polyethylene material reaches V0, exhibiting excellent flame retardant performance. At the same time, ammonium polyphosphate and aluminum diethylphosphite have a significant promoting effect on the construction of the dynamic cross-linked network of silane ether inside the polyethylene material, endowing the polyethylene material with excellent reprocessing performance, flame retardant performance and mechanical properties.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A recyclable flame-retardant polyethylene material comprises the following raw materials in parts by weight: 50-70 parts of ethylene vinyl acetate copolymer (EVA); 18-45 parts of a composite flame-retardant system and 5-12 parts of an aminosilane crosslinking agent; wherein the composite flame-retardant system comprises ammonium polyphosphate and aluminum diethylphosphite.

[0008] In one optional embodiment, the mass ratio of the ammonium polyphosphate to the aluminum diethylphosphite is 1:(0.2 to 0.7).

[0009] In one optional embodiment, the recyclable flame-retardant polyethylene material comprises the following raw materials in parts by weight: EVA: 60-70 parts; ammonium polyphosphate: 15-35 parts; aluminum diethylphosphite: 3-10 parts; aminosilane crosslinking agent: 5-12 parts. Preferably, the recyclable flame-retardant polyethylene material comprises the following raw materials in parts by weight: EVA: 60-65 parts; ammonium polyphosphate: 20-25 parts; aluminum diethylphosphite: 5-8 parts; aminosilane crosslinking agent: 8-12 parts.

[0010] In one alternative embodiment, the aminosilane crosslinking agent is selected from (3-aminopropyl)triethoxysilane, bis[3-(trimethoxysilyl)propyl]amine, γ-aminopropyltrimethoxysilane, or phenylaminomethyltriethoxysilane.

[0011] The present invention also provides a method for preparing the above-mentioned recyclable flame-retardant polyethylene material, comprising the following steps: mixing ethylene vinyl acetate copolymer, ammonium polyphosphate and aluminum diethyl phosphite, and then adding an aminosilane crosslinking agent to crosslink the mixture to obtain the recyclable flame-retardant polyethylene material.

[0012] In one alternative implementation, both the mixing and crosslinking steps are performed in an internal mixer.

[0013] In one optional embodiment, the temperature of the internal mixer is 200-230℃ in zone one, 200-230℃ in zone two, 200-230℃ in zone three, and the rotor speed is 20-60 rpm.

[0014] In one alternative embodiment, the method further includes the steps of extruding and granulating the crosslinked product (to obtain polyethylene granules); or the step of directly molding the crosslinked product.

[0015] In one optional embodiment, the extrusion is carried out in a twin-screw extruder, the twin-screw extruder being configured with the following parameters: die head temperature control 170-185℃, zone five temperature control 170-180℃, zone four temperature control 165-175℃, zone three temperature control 155-165℃, zone two temperature control 150-155℃, zone one temperature control 145-150℃, and main extruder frequency 10-30Hz.

[0016] The present invention also provides a method for preparing polyethylene products, comprising the following steps: injecting the above-mentioned recyclable flame-retardant polyethylene material or the recyclable flame-retardant polyethylene material prepared by any of the above-mentioned methods into a polyethylene product by injection molding.

[0017] In one optional embodiment, the temperature parameters of the injection molding machine are 165-170℃ for the first stage, 170-175℃ for the second stage, and 175-180℃ for the third stage.

[0018] Compared with the prior art, the present invention has at least the following advantages:

[0019] 1. The recyclable flame-retardant polyethylene material provided by this invention uses EVA as the main body, and forms a dynamic cross-linking network of silane ethers by cross-linking with the acetoxy groups in the EVA structure using an aminosilane cross-linking agent. Ammonium polyphosphate and diethylaluminum hypophosphite are used as the flame-retardant system. This polyethylene material possesses excellent reprocessing performance, flame-retardant properties, and mechanical properties. Specifically,

[0020] The phosphorus-based, environmentally friendly, halogen-free flame retardant system composed of ammonium polyphosphate and aluminum diethylphosphite exhibits excellent synergistic flame retardant effects in both the condensed and gas phases. It not only simultaneously improves the char residue and char layer quality, effectively suppresses dripping, but also reduces smoke generation during combustion, making it a more environmentally friendly flame retardant system. Compared to inorganic flame retardants such as magnesium hydroxide and aluminum hydroxide, ammonium polyphosphate and aluminum diethylphosphite show stronger dispersibility in the polyethylene matrix and greater interfacial compatibility with polyethylene. They not only form a flame-retardant network within polyethylene with relatively small addition amounts, resulting in excellent flame retardant performance, but also have minimal impact on the mechanical properties of polyethylene materials. Furthermore, ammonium polyphosphate and aluminum diethylphosphite have a significant positive catalytic effect on the crosslinking reaction of polyethylene with aminosilane crosslinking agents, accelerating the formation of a dynamic crosslinking network of silane ethers within polyethylene. This endows polyethylene materials with excellent reprocessing properties and solves the problem of recycling and reusing traditional polyethylene materials.

[0021] 2. The recyclable flame-retardant polyethylene material provided by this invention is low in cost and environmentally friendly, and has strong feasibility; at the same time, the flame-retardant system is a halogen-free flame retardant, and polyethylene will not cause secondary pollution when burning. Attached Figure Description

[0022] Figure 1 The processing torque-time curves of polyethylene materials obtained in Example 1, Comparative Example 1, and Comparative Example 4 of this invention are shown below.

[0023] Figure 2 The swelling behavior of the polyethylene material prepared in toluene in Example 1 of this invention;

[0024] Figure 3 The reprocessing performance of the polyethylene material obtained in Example 1 of this invention;

[0025] Figure 4 This is the reprocessing stress-strain curve of the polyethylene material obtained in Example 1 of the present invention. Detailed Implementation

[0026] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0027] For any experimental steps or conditions not specified in the following examples and comparative examples, the procedures and conditions described in the literature in this field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0028] Commercially available raw materials such as ethylene vinyl acetate copolymer (EVA), ammonium polyphosphate (APP), aluminum diethyl phosphite (ADP), and aminosilane crosslinking agents can all meet the requirements for implementing the technical solution of this invention. However, for ease of comparison, the following raw materials are used:

[0029] Ethylene vinyl acetate copolymer (EVA), a product of Jiangsu Sirbang Petrochemical Co., Ltd.

[0030] Ammonium polyphosphate (APP), aluminum diethylphosphite (ADP), (3-aminopropyl)triethoxysilane (APTS), bis[3-(trimethoxysilyl)propyl]amine (BTSPA), γ-aminopropyltrimethoxysilane, phenylaminomethyltriethoxysilane, Shanghai McLean Co., Ltd.

[0031] Evaluation and analysis methods:

[0032] Mechanical performance testing standard: GB / T 528-2009, test speed 10mm / min.

[0033] Flame retardant performance testing standard: GB / T 13488-1992 (UL-94).

[0034] Example 1

[0035] 60 parts by weight of EVA, 20 parts by weight of APP and 10 parts by weight of ADP were mixed in an internal mixer, and then 10 parts by weight of aminosilane crosslinking agent APTS were added for crosslinking. The mixture was then extruded and granulated by a twin-screw extruder and a granulator to obtain polyethylene material.

[0036] The above-mentioned polyethylene material is injection molded using an injection molding machine to obtain polyethylene products.

[0037] The internal mixer is set to a temperature of 230℃ for zones one, two, and three, and a rotation speed of 20 rpm. The twin-screw extruder is set to a die head temperature control of 185℃, zone five temperature control of 180℃, zone four temperature control of 175℃, zone three temperature control of 165℃, zone two temperature control of 155℃, zone one temperature control of 150℃, and a main unit frequency of 10Hz. The injection molding machine is set to a temperature control of 170℃ for zone one, 175℃ for zone two, and 180℃ for zone three.

[0038] Example 2

[0039] 60 parts by weight of EVA, 25 parts by weight of APP and 3 parts by weight of ADP are mixed in an internal mixer, and then 12 parts by weight of aminosilane crosslinking agent APTS are added for crosslinking. The resulting polyethylene material is directly molded to obtain polyethylene products.

[0040] The internal mixer is set to a temperature of 230℃ for zones one, two, and three, and a rotation speed of 20 rpm. The compression molding pressure is 10 MPa, and the temperature is 230℃.

[0041] Example 3

[0042] 65 parts by weight of EVA, 15 parts by weight of APP and 10 parts by weight of ADP were mixed in an internal mixer, and then 10 parts by weight of aminosilane crosslinking agent APTS were added for crosslinking. The mixture was then extruded and granulated by a twin-screw extruder and a granulator to obtain polyethylene material.

[0043] The above-mentioned polyethylene material is injection molded using an injection molding machine to obtain polyethylene products.

[0044] The internal mixer is set to a temperature of 220℃ for zones one, two, and three, and a rotation speed of 40 rpm. The twin-screw extruder is set to a die head temperature control of 175℃, zone five temperature control of 175℃, zone four temperature control of 170℃, zone three temperature control of 160℃, zone two temperature control of 150℃, zone one temperature control of 145℃, and a main motor frequency of 20Hz. The injection molding machine is set to a temperature control of 165℃ for zone one, 170℃ for zone two, and 175℃ for zone three.

[0045] Example 4

[0046] 65 parts by weight of EVA, 15 parts by weight of APP and 10 parts by weight of ADP were mixed in an internal mixer, and then 10 parts by weight of aminosilane crosslinking agent APTS were added for crosslinking. The mixture was then extruded and granulated by a twin-screw extruder and a granulator to obtain polyethylene material.

[0047] The internal mixer is set with the following parameters: Zone 1 temperature 210℃, Zone 2 temperature 220℃, Zone 3 temperature 230℃, and rotation speed 50 rpm. The twin-screw extruder is set with the following parameters: Die head temperature control 175℃, Zone 5 temperature control 175℃, Zone 4 temperature control 170℃, Zone 3 temperature control 160℃, Zone 2 temperature control 155℃, Zone 1 temperature control 150℃, and main extruder frequency 20Hz.

[0048] Example 5

[0049] 70 parts by weight of EVA, 20 parts by weight of APP and 5 parts by weight of ADP were mixed in an internal mixer, and then 5 parts by weight of aminosilane crosslinking agent APTS were added for crosslinking. The mixture was then extruded and granulated by a twin-screw extruder and a granulator to obtain polyethylene material.

[0050] The above-mentioned polyethylene material is injection molded using an injection molding machine to obtain polyethylene products.

[0051] The internal mixer is set to a temperature of 230℃ for zones one, two, and three, and a rotation speed of 60 rpm. The twin-screw extruder is set to a die head temperature control of 170℃, zone five temperature control of 170℃, zone four temperature control of 165℃, zone three temperature control of 155℃, zone two temperature control of 150℃, zone one temperature control of 145℃, and a main motor frequency of 30Hz. The injection molding machine is set to a temperature control of 165℃ for zone one, 170℃ for zone two, and 175℃ for zone three.

[0052] Example 6

[0053] 65 parts by weight of EVA, 18 parts by weight of APP and 7 parts by weight of ADP were mixed in an internal mixer, and then 10 parts by weight of aminosilane crosslinking agent BTSPA were added for crosslinking. The mixture was then extruded and granulated by a twin-screw extruder and a granulator to obtain polyethylene material.

[0054] The above-mentioned polyethylene material is injection molded using an injection molding machine to obtain polyethylene products.

[0055] The internal mixer is set to a temperature of 220℃ for zones one, two, and three, and a rotation speed of 40 rpm. The twin-screw extruder is set to a die head temperature control of 175℃, zone five temperature control of 175℃, zone four temperature control of 170℃, zone three temperature control of 160℃, zone two temperature control of 150℃, zone one temperature control of 145℃, and a main motor frequency of 20Hz. The injection molding machine is set to a temperature control of 165℃ for zone one, 170℃ for zone two, and 175℃ for zone three.

[0056] Example 7

[0057] 60 parts by weight of EVA, 25 parts by weight of APP and 3 parts by weight of ADP were mixed in an internal mixer, and then 12 parts by weight of aminosilane crosslinking agent BTSPA were added for crosslinking. The mixture was then extruded and granulated by a twin-screw extruder and a granulator to obtain polyethylene material.

[0058] The above-mentioned polyethylene material is injection molded using an injection molding machine to obtain polyethylene products.

[0059] The internal mixer is set to a temperature of 230℃ for zones one, two, and three, and a rotation speed of 20 rpm. The twin-screw extruder is set to a die head temperature control of 185℃, zone five temperature control of 180℃, zone four temperature control of 175℃, zone three temperature control of 165℃, zone two temperature control of 155℃, zone one temperature control of 150℃, and a main unit frequency of 10Hz. The injection molding machine is set to a temperature control of 170℃ for zone one, 175℃ for zone two, and 180℃ for zone three.

[0060] Example 8

[0061] 50 parts by weight of EVA, 25 parts by weight of APP and 10 parts by weight of ADP were added to a mixer and mixed. Then, 15 parts by weight of γ-aminopropyltrimethoxysilane were added to crosslink the mixture to obtain polyethylene material.

[0062] The internal mixer is set to a temperature of 200℃ for Zone 1, Zone 2, and Zone 3, and a rotation speed of 30 rpm.

[0063] Example 9

[0064] 50 parts by weight of EVA, 25 parts by weight of APP and 10 parts by weight of ADP are mixed in an internal mixer, and then 15 parts by weight of phenylaminomethyltriethoxysilane are added for crosslinking to obtain polyolefin powder. The powder is then injection molded to obtain polyethylene products.

[0065] The internal mixer is set to a temperature of 210℃ for all three zones and a rotation speed of 30 rpm. The injection molding machine is set to a temperature of 170℃ for the first zone, 175℃ for the second zone, and 180℃ for the third zone.

[0066] Comparative Example 1

[0067] Add 90 parts by weight of EVA to a mixer and preheat for 5 minutes; then add 10 parts by weight of aminosilane crosslinking agent APTS to crosslink the material to obtain polyethylene material.

[0068] The above-mentioned polyethylene material is injection molded using an injection molding machine to obtain polyethylene products.

[0069] The internal mixer is set to a temperature of 230℃ for zones one, two, and three, and a rotation speed of 20 rpm. The twin-screw extruder is set to a die head temperature control of 185℃, zone five temperature control of 180℃, zone four temperature control of 175℃, zone three temperature control of 165℃, zone two temperature control of 155℃, zone one temperature control of 150℃, and a main unit frequency of 10Hz. The injection molding machine is set to a temperature control of 170℃ for zone one, 175℃ for zone two, and 180℃ for zone three.

[0070] Comparative Example 2

[0071] 60 parts by weight of EVA and 28 parts by weight of APP were added to a mixer and mixed. Then, 12 parts by weight of aminosilane crosslinking agent APTS were added to crosslink the mixture. The resulting polyethylene powder was directly molded to obtain polyethylene products.

[0072] The internal mixer is set to a temperature of 230℃ for zones one, two, and three, and a rotation speed of 20 rpm. The compression molding pressure is 10 MPa, and the temperature is 230℃.

[0073] Comparative Example 3

[0074] 60 parts by weight of EVA and 28 parts by weight of ADP are mixed in an internal mixer, and then 12 parts by weight of aminosilane crosslinking agent APTS are added for crosslinking. The resulting polyethylene powder is directly molded to obtain polyethylene products.

[0075] The internal mixer is set to a temperature of 230℃ for zones one, two, and three, and a rotation speed of 20 rpm. The compression molding pressure is 10 MPa, and the temperature is 230℃.

[0076] Comparative Example 4

[0077] 60 parts by weight of EVA and 28 parts by weight of expanded graphite were mixed in an internal mixer, and then 12 parts by weight of aminosilane crosslinking agent APTS were added for crosslinking. The resulting polyethylene powder was directly molded to obtain polyethylene products.

[0078] The internal mixer is set to a temperature of 230℃ for zones one, two, and three, and a rotation speed of 20 rpm. The compression molding pressure is 10 MPa and the temperature is 230℃.

[0079] The polyethylene products / polyethylene powder / polyethylene granules obtained in each embodiment and comparative example were tested for their mechanical and flame retardant properties according to the aforementioned evaluation and analysis methods. The specific test structures are shown in the table below.

[0080] Table 1

[0081] Tensile strength (MPa) Elongation at break % UL-94 flame retardant rating Example 1 8.2 450 V0 Example 2 7.5 406 V0 Example 3 10.2 562 V0 Example 4 10.8 506 V0 Example 5 11.2 928 V0 Example 6 9.7 470 V0 Example 7 10.1 580 V0 Example 8 9.8 760 V0 Example 9 10.2 640 V0 Comparative Example 1 4.5 1300 No flame retardant properties Comparative Example 2 5.3 950 V2 Comparative Example 3 5.0 200 No flame retardant properties Comparative Example 4 5.8 340 V2

[0082] As shown in Table 1, the polyolefin materials provided by this invention not only possess excellent mechanical properties but also achieve the highest flame retardant rating, V0. The polyolefin material in Comparative Example 1 (without flame retardant) not only lacks flame retardant properties but also exhibits poor tensile strength due to its low degree of crosslinking. Comparative Examples 2 and 3, which only added one flame retardant, not only failed to reach the V0 flame retardant rating but also suffered from poor overall mechanical properties due to poor catalytic effect on the silicone ether crosslinking network and compatibility issues. Comparative Example 4, which added expanded graphite as a flame retardant, also resulted in poor flame retardant and mechanical properties of the polyolefin material.

[0083] Depend on Figure 1 It can be seen from the torque-time processing curve of polyethylene material ( Figure 1 As can be seen, compared with Comparative Examples 1 and 4 (with expanded graphite as a flame retardant), Example 1 exhibits a higher maximum torque value (14 N·m) and reaches the maximum torque value more quickly (approximately 60 minutes). The polyolefin material without the added flame retardant system shows a particularly slow torque increase within 240 minutes, while the polyolefin material with the added expanded graphite flame retardant reaches its maximum torque value (11 N·m) at 120 minutes. These results indicate that the flame retardant system (ammonium polyphosphate and aluminum diethylphosphite) provided by this invention not only provides flame retardancy but also significantly promotes the construction of the dynamic crosslinking network of silyl ether within polyethylene.

[0084] A swelling experiment was conducted by immersing 500 mg of the EVA material prepared in Example 1 in 18 mL of toluene at 50°C for 2 days to observe whether the sample dissolved. The results are as follows. Figure 2 As shown, the EVA material exhibits the swelling phenomenon characteristic of cross-linked materials, confirming that the EVA material prepared in Example 1 is a cross-linked material.

[0085] The polyethylene product obtained in Example 1 was crushed into small pieces using a crusher, and then hot-pressed at 200°C for 30 minutes to achieve the recycling and reprocessing of polyolefin materials. Figure 3 ), and perform mechanical property tests, the test results are as follows Figure 4 And the data in the table below, by Figure 4 As can be seen from the data in the table below, the polyethylene material prepared by this invention exhibits almost no loss of mechanical properties before and after reprocessing, demonstrating excellent reprocessing performance.

[0086] Table 2

[0087] sample Tensile strength (MPa) Elongation at break (%) original 8.6 487 Reprocessing first time 8.4 572 Reprocessing a second time 8.2 602 Third processing 8.4 658

[0088] Of course, the present invention may have other embodiments and variations. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and variations according to the present invention, but these corresponding changes and variations should all fall within the protection scope of the claims of the present invention.

Claims

1. A recyclable flame-retardant polyethylene material, characterized in that, The raw materials include the following parts by weight: 50-70 parts of ethylene vinyl acetate copolymer; 18-45 parts of composite flame retardant system and 5-12 parts of aminosilane crosslinking agent; wherein the composite flame retardant system includes ammonium polyphosphate and aluminum diethylphosphite.

2. The recyclable flame-retardant polyethylene material as described in claim 1, characterized in that, The mass ratio of the ammonium polyphosphate to the aluminum diethylphosphite is 1:(0.1-0.7).

3. The recyclable flame-retardant polyethylene material as described in claim 1 or 2, characterized in that, The aminosilane crosslinking agent is selected from (3-aminopropyl)triethoxysilane, bis[3-(trimethoxysilyl)propyl]amine, γ-aminopropyltrimethoxysilane, or phenylaminomethyltriethoxysilane.

4. A method for preparing a recyclable flame-retardant polyethylene material according to any one of claims 1-3, characterized in that, The process includes the following steps: mixing ethylene vinyl acetate copolymer, ammonium polyphosphate and aluminum diethyl phosphite, and then adding an aminosilane crosslinking agent to crosslink the mixture to obtain the recyclable flame-retardant polyethylene material.

5. The preparation method according to claim 4, characterized in that, Both the mixing and crosslinking steps are performed in an internal mixer.

6. The preparation method according to claim 5, characterized in that, The internal mixer has a zone temperature of 200-230℃, a zone temperature of 200-230℃, a zone temperature of 200-230℃, and a rotor speed of 20-60 rpm.

7. The preparation method according to claim 4, characterized in that, It also includes the steps of extruding and granulating the cross-linked product; or the steps of directly molding the cross-linked product.

8. The preparation method according to claim 7, characterized in that, The extrusion is carried out in a twin-screw extruder, the set parameters of which are: die head temperature control 170-185℃, zone 5 temperature control 170-180℃, zone 4 temperature control 165-175℃, zone 3 temperature control 155-165℃, zone 2 temperature control 150-155℃, zone 1 temperature control 145-150℃, and main extruder frequency 10-30Hz.

9. A method for preparing a polyethylene product, characterized in that, The process includes the following steps: injecting the recyclable flame-retardant polyethylene material prepared by the preparation method of any one of claims 1-3 or any one of claims 4-8 into a polyethylene product using an injection molding machine.

10. The preparation method according to claim 9, characterized in that, The temperature parameters of the injection molding machine are: 165-170℃ for the first stage, 170-175℃ for the second stage, and 175-180℃ for the third stage.

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