Reprocessable flame-retardant polyethylene material as well as preparation method and application thereof

Abstract

The invention discloses a reprocessable flame-retardant polyethylene material, which is prepared from the following raw materials in parts by weight: 60 to 80 parts of ethylene vinyl acetate copolymer; 20 to 40 parts of a composite flame retardant system; the composite flame retardant system is prepared from ammonium polyphosphate, aluminum diethyl hypophosphite and silane modified phosphonitrilic chloride. A reactive flame retardant silane-modified phosphonitrilic chloride used in the reprocessable flame-retardant polyethylene material is matched with ammonium polyphosphate and aluminum diethyl hypophosphite to form a compound flame-retardant system, so that on one hand, the mechanical property of the polyethylene material is not influenced on the premise that the polyethylene material is endowed with good flame-retardant property; meanwhile, a constructed phosphazene cross-linked network with good thermal stability can improve the thermal stability of the ethylene vinyl acetate copolymer material; and on the other hand, a dynamic covalent network is constructed by crosslinking the silane-modified phosphonitrilic chloride and the ethylene-vinyl acetate copolymer to replace a permanent covalent network, so that the recycling performance of the polyethylene material is remarkably improved.

Description

Technical Field

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

[0002] Most polymer materials are flammable, and their combustion is characterized by high heat release rates, rapid flame propagation, and the release of large amounts of smoke, irritating, corrosive, and toxic gases. The resulting fire hazards and fire damage have become a concern for countries worldwide. For example, ethylene-vinyl acetate copolymer, an important member of the polyethylene family, has a low oxygen index (<19%), a high heat release rate during combustion, and is accompanied by molten dripping and large amounts of smoke. Therefore, the preparation of polyolefin materials with high-temperature resistance and flame retardant properties is particularly important.

[0003] In existing technologies, halogenated flame retardants or inorganic fillers such as magnesium hydroxide and aluminum hydroxide are often added when preparing flame-retardant polyethylene materials. However, this technology is gradually being replaced because halogenated flame retardants generate a large amount of smoke and corrosive gases during thermal decomposition or combustion. Inorganic fillers such as aluminum hydroxide and magnesium hydroxide have poor interfacial interactions with polyethylene, and the addition of large amounts of these flame retardants leads to a significant decrease in the mechanical properties of polyethylene.

[0004] To address the aforementioned issues, existing technologies have significantly improved the mechanical properties, solvent resistance, and creep resistance of polyolefin materials through chemical crosslinking, greatly expanding the application range of polyethylene. However, the crosslinked structure of polyethylene formed by irreversible chemical bonds is difficult to destroy, making it difficult to melt when heated and difficult to recycle. As a result, the recycling of crosslinked polyethylene waste is difficult, the recycling rate is low, and this leads to serious white pollution problems.

[0005] Therefore, developing a polyolefin material that simultaneously possesses high temperature resistance, flame retardancy, and excellent mechanical properties has significant application value and academic significance. Summary of the Invention

[0006] In view of this, the present invention provides a reprocessable flame-retardant polyethylene material, its preparation method and application. The reactive flame retardant silane-modified hexachlorocyclophosphamide used in this reprocessable flame-retardant polyethylene material is combined with ammonium polyphosphate and aluminum diethylphosphite to form a compound flame-retardant system. On the one hand, it can impart good flame-retardant properties to the polyethylene material without affecting its mechanical properties. At the same time, the constructed phosphazene crosslinking network with good thermal stability can improve the thermal stability of the ethylene vinyl acetate copolymer material. On the other hand, by constructing a dynamic covalent network by crosslinking the ethylene vinyl acetate copolymer with silane-modified hexachlorocyclophosphamide to replace the permanent covalent network, the recycling performance of the polyethylene material is significantly improved.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A reprocessable flame-retardant polyethylene material comprises the following raw materials in parts by weight: 60-80 parts of ethylene vinyl acetate copolymer (EVA); and 20-40 parts of a composite flame-retardant system; wherein the composite flame-retardant system comprises ammonium polyphosphate, aluminum diethyl phosphite, and silane-modified hexachlorocyclophosphamide; the structure of the silane-modified hexachlorocyclophosphamide is as follows:

[0009]

[0010] Where R represents methyl or ethyl.

[0011] In the reprocessable flame-retardant polyethylene material provided by the present invention, the ammonium polyphosphate and aluminum diethylphosphite in the composite flame-retardant system simultaneously act as flame retardants and catalyze the crosslinking of polyethylene with silane-modified hexachlorocyclophosphonitrile; the silane-modified hexachlorocyclophosphonitrile simultaneously acts as a flame retardant and a crosslinking agent for polyethylene.

[0012] This invention provides a reprocessable flame-retardant polyethylene material, using ethylene vinyl acetate copolymer as the main body and phosphorus-nitrogen-based ammonium polyphosphate, diethylaluminum hypophosphite, and silane-modified hexachlorocyclophosphamide as the composite flame-retardant system. This composite flame-retardant system exhibits synergistic flame-retardant properties, quenching free radicals generated during the combustion of ethylene vinyl acetate copolymer, releasing non-flammable gases such as ammonia and nitrogen, and catalyzing the dehydration and char formation of the ethylene vinyl acetate copolymer matrix to form a dense, expanded char layer, thus imparting V0-level flame-retardant performance to the ethylene vinyl acetate copolymer. Simultaneously, the cross-linking reaction between ammonium polyphosphate and diethylaluminum hypophosphite and the silane-modified hexachlorocyclophosphamide cross-linking ethylene vinyl acetate copolymer accelerates the speed and strength of the internal construction of a dynamic covalent cross-linking network, endowing the ethylene vinyl acetate copolymer with excellent reprocessing and mechanical properties. This invention, based on reactive flame retardants and the construction of a dynamic covalent cross-linking network, has significant application value in preparing reprocessable flame-retardant polyethylene materials.

[0013] In one optional embodiment, the mass ratio of the ammonium polyphosphate, the aluminum diethylphosphite, and the silane-modified hexachlorocyclophosphonitrile in the composite flame retardant system is 1:(0.2-0.7):(0.4-0.8).

[0014] The present invention also provides a method for preparing the above-mentioned reprocessable flame-retardant polyethylene material, comprising the following steps:

[0015] After mixing the ethylene vinyl acetate copolymer with the composite flame retardant system, dispersion crosslinking is performed to obtain the reprocessable flame retardant polyethylene material; preferably, the mixing is performed in a high-speed mixer and dispersion crosslinking is performed in an internal mixer.

[0016] In one alternative embodiment, the high-speed mixer operates at a speed of 500–700 rpm.

[0017] In one optional embodiment, the temperature of the internal mixer is 200-230°C in zone one, 200-230°C in zone two, and 200-230°C in zone three; the rotor speed is 40-60 rpm.

[0018] In one optional embodiment, the preparation method of silane-modified hexachlorocyclophosphamide in the composite flame retardant system includes the following steps:

[0019] Hexachlorocyclophosphonitrile, (3-aminopropyl)triethoxysilane / (3-aminopropyl)trimethoxysilane, an acid-binding agent, and an organic solvent are mixed and reacted. After the reaction is completed, the mixture is purified to obtain the silane-modified hexachlorocyclophosphonitrile. Preferably, the reaction temperature is 50-120°C and the reaction time is 2-10 h.

[0020] In one optional embodiment, the molar ratio of the hexachlorocyclophosphonitrile to the (3-aminopropyl)triethoxysilane / (3-aminopropyl)trimethoxysilane is 1:(6-6.1).

[0021] In one alternative embodiment, the acid-binding agent is selected from pyridine and / or triethylamine, etc.

[0022] In one optional embodiment, the molar ratio of the acid-binding agent to the hexachlorocyclophosphamide is 6 to 8:1.

[0023] In one alternative embodiment, the organic solvent is selected from toluene or tetrahydrofuran, etc.

[0024] In one alternative embodiment, the process further includes the step of extruding and granulating the dispersed crosslinked product (to obtain reprocessable flame-retardant polyethylene granules).

[0025] In one optional embodiment, the extrusion is carried out in a twin-screw extruder with the following parameters: die head temperature control 170-185°C, zone 5 temperature control 170-180°C, zone 4 temperature control 165-175°C, zone 3 temperature control 155-165°C, zone 2 temperature control 150-155°C, zone 1 temperature control 145-150°C, and main extruder frequency 10-30Hz.

[0026] This invention also provides a method for preparing a polyethylene product, comprising the following steps:

[0027] The reprocessable flame-retardant polyethylene material described above, or the reprocessable flame-retardant polyethylene material prepared by the above method, or the reprocessable flame-retardant polyethylene granules prepared by the above method, are injection molded to obtain the polyethylene product. Specific injection molding conditions can be adjusted according to actual needs.

[0028] In one optional embodiment, the injection molding is performed in an injection molding machine with temperature parameters of 165-170°C for the first stage, 170-175°C for the second stage, and 175-180°C for the third stage.

[0029] Compared with the prior art, the present invention has at least the following advantages:

[0030] 1. The reprocessable flame-retardant polyethylene material provided by this invention utilizes a novel silane-modified hexachlorocyclophosphamide flame retardant combined with commercially available phosphorus-nitrogen flame retardants ammonium polyphosphate and diethylaluminum hypophosphite as a composite flame-retardant system. This flame-retardant system, through synergistic effects in both the condensed and gaseous phases, can impart the highest V0 vertical flammability rating and a thermal decomposition temperature of 335°C to the ethylene vinyl acetate copolymer with a small amount of filler, exhibiting excellent flame-retardant and high-temperature resistance properties. Furthermore, by crosslinking the ethylene vinyl acetate copolymer with silane-modified hexachlorocyclophosphamide, a dynamic covalent network of silane ethers is constructed within it, replacing the traditional permanent covalent network, thus endowing the ethylene vinyl acetate copolymer with excellent reprocessing properties. Silane-modified hexachlorocyclophosphamide possesses dual functions of flame retardancy and crosslinking, exhibiting good dispersibility and interfacial strength in the ethylene vinyl acetate copolymer matrix, thus endowing it with excellent mechanical properties and high-temperature resistance.

[0031] 2. The reprocessable flame-retardant polyethylene material provided by this invention employs a reactive flame-retardant system. Ammonium polyphosphate and diethylaluminum hypophosphite, which simultaneously possess flame-retardant properties and catalytic silane-modified hexachlorocyclophosphonitrile, react and crosslink with the polymer EVA, giving the polymer EVA durable flame retardancy. Furthermore, the reactive flame retardant exhibits high compatibility and dispersibility with the polymer EVA, with minimal impact on the mechanical properties of the polymer EVA. Only a small amount is needed to achieve good flame-retardant effects, making it more promising for the preparation of flame-retardant polyolefin materials.

[0032] 3. The preparation method of reprocessable flame-retardant polyethylene material provided by the present invention uses simple equipment, has low cost, and is easy to realize large-scale industrial application. Attached Figure Description

[0033] Figure 1 The infrared comparison images are of the silane-modified hexachlorocyclophosphamide prepared in this invention and the raw materials.

[0034] Figure 2The processing torque-time curves of the polyethylene materials / products obtained in Examples 2, 4, 6 and Comparative Example 1 of this invention are shown.

[0035] Figure 3 The TGA curves of the polyethylene materials / products prepared in Examples 1, 6, Comparative Example 1 and Comparative Example 2 of this invention are shown.

[0036] Figure 4 This is a graph showing the reprocessing performance of the polyethylene product obtained in Example 2 of the present invention. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] Commercially available raw materials such as ethylene vinyl acetate copolymer (EVA), ammonium polyphosphate (APP), and aluminum diethyl phosphite (ADP), as well as silane-modified hexachlorocyclophosphonitrile (Si-HCCP) prepared by existing methods, can all meet the requirements for implementing the technical solution of this invention. However, for ease of comparison, the following raw materials are used:

[0040] Ethylene vinyl acetate copolymer (EVA), Jiangsu Sirbang Petrochemical Co., Ltd.

[0041] Ammonium polyphosphate (APP), Shanghai McLean Co., Ltd.

[0042] Aluminum diethylphosphite (ADP), Shanghai McLean Company

[0043] Silane-modified hexachlorocyclophosphamide (Si-HCCP) was prepared using the following method:

[0044] Hexachlorocyclophosphamide (HCCP, 24 g) and tetrahydrofuran (200 mL) were added to a flask and stirred until completely dissolved. (3-aminopropyl)triethoxysilane (APTS, 96 g) and triethylamine (21 g) were diluted with tetrahydrofuran (100 mL) and slowly added to the hexachlorocyclophosphamide tetrahydrofuran solution. After the addition was complete, the temperature was raised to 70 °C and the reaction was carried out for 10 h. The generated triethylamine hydrochloride was removed by filtration, and tetrahydrofuran and excess triethylamine were removed by rotary evaporation. The product was then dried under vacuum at 50 °C to obtain silane-modified hexachlorocyclophosphamide (Si-HCCP-Me) with a yield of 95%.

[0045] When (3-aminopropyl)trimethoxysilane is used as a raw material, the yield of silane-modified hexachlorocyclophosphamide (Si-HCCP-Et) is 96%.

[0046] Figure 1 The infrared spectra of Si-HCCP (Si-HCCP-Me) and the raw materials APTS and HCCP are shown below. Figure 1 It can be seen that, compared with the raw material HCCP, the characteristic peaks of P-Cl and -NH2 in the product Si-HCCP-Me disappeared and a new characteristic peak of -NH appeared, while the characteristic peaks of P=N and Si-OC were retained, confirming the successful synthesis of alkoxysilyl hexachlorocyclophosphonitrile (Si-HCCP-Me). Similarly, the successful synthesis of Si-HCCP-Et was verified by infrared spectroscopy.

[0047] Evaluation and analysis methods:

[0048] Mechanical performance testing standard: GB / T 528-2009, test speed 10mm / min.

[0049] Flame retardant performance testing standard: GB / T 13488-1992 (UL-94).

[0050] Thermal stability test standard: GB / T 33047.1-2016.

[0051] The kinetic curve of the internal crosslinking network of polyolefins was determined by observing the torque change curve in an internal mixer.

[0052] Example 1

[0053] Weigh 60 parts by weight of EVA, 20 parts by weight of APP, 8 parts by weight of ADP, and 12 parts by weight of Si-HCCP-Me and put them into a high-speed mixer. Mix them evenly at a speed of 600 rpm. Then add them to a Banbury mixer for dispersion and crosslinking to obtain a reprocessable flame-retardant polyethylene powder. The Banbury mixer is set with the following parameters: Zone 1 temperature set to 220℃, Zone 2 and Zone 3 temperatures both set to 230℃, and speed set to 40 rpm.

[0054] The above-mentioned reprocessable flame-retardant polyethylene powder is extruded and granulated through a twin-screw extruder and a granulator. The resulting reprocessable flame-retardant polyethylene granules are then injection molded through an injection molding machine, which involves mold closing, filling, pressure holding, cooling, mold opening, and demolding to obtain polyethylene products.

[0055] The twin-screw extruder's temperature settings are: die head temperature control 185℃, zone 5 temperature control 175℃, zone 4 temperature control 175℃, zone 3 temperature control 160℃, zone 2 temperature control 155℃, zone 1 temperature control 150℃, and main unit frequency 10Hz. The injection molding machine's temperature settings are: zone 1 170℃, zone 2 175℃, and zone 3 180℃.

[0056] Example 2

[0057] Weigh 60 parts by weight of EVA, 25 parts by weight of APP, 5 parts by weight of ADP, and 10 parts by weight of Si-HCCP-Me and put them into a high-speed mixer. Mix them evenly at a speed of 500 rpm. Then add them to a Banbury mixer for dispersion and crosslinking to obtain a reprocessable flame-retardant polyethylene powder. The settings of the Banbury mixer are set as follows: temperature of zone 1, zone 2, and zone 3 are all set to 200℃, and the speed is 60 rpm.

[0058] The above-mentioned reprocessable flame-retardant polyethylene powder is extruded and granulated through a twin-screw extruder and a granulator. The resulting reprocessable flame-retardant polyethylene granules are then injection molded through an injection molding machine, which involves mold closing, filling, pressure holding, cooling, mold opening, and demolding to obtain polyethylene products.

[0059] The twin-screw extruder's temperature settings are: die head temperature control 175℃, zone 5 temperature control 175℃, zone 4 temperature control 170℃, zone 3 temperature control 165℃, zone 2 temperature control 155℃, zone 1 temperature control 145℃, and main unit frequency 20Hz. The injection molding machine's temperature settings are: zone 1 170℃, zone 2 170℃, and zone 3 175℃.

[0060] Example 3

[0061] Weigh 60 parts by weight of EVA, 20 parts by weight of APP, 5 parts by weight of ADP, and 15 parts by weight of Si-HCCP-Me and put them into a high-speed mixer. Mix them evenly at a speed of 700 rpm. Then add them to a Banbury mixer for dispersion and crosslinking to obtain a reprocessable flame-retardant polyethylene powder. The Banbury mixer is set with the following parameters: Zone 1 temperature is 220℃, Zone 2 and Zone 3 temperatures are both set to 210℃, and the speed is 40 rpm.

[0062] The above-mentioned reprocessable flame-retardant polyethylene powder is injected into a molding machine through mold closing, filling, pressure holding, cooling, mold opening, and demolding to obtain polyethylene products.

[0063] Example 4

[0064] Weigh 65 parts by weight of EVA, 15 parts by weight of APP, 10 parts by weight of ADP, and 10 parts by weight of Si-HCCP-Me and put them into a high-speed mixer. Mix them evenly at a speed of 700 rpm. Then add them to a Banbury mixer for dispersion and crosslinking to obtain a reprocessable flame-retardant polyethylene powder. The Banbury mixer is set with the temperature of Zone 1, Zone 2, and Zone 3 all set to 200℃ and the speed at 50 rpm.

[0065] The above-mentioned reprocessable flame-retardant polyethylene powder is extruded and granulated through a twin-screw extruder and a granulator to obtain reprocessable flame-retardant polyethylene granules.

[0066] The settings for the twin-screw extruder are as follows: head temperature control 170℃, zone 5 temperature control 170℃, zone 4 temperature control 165℃, zone 3 temperature control 155℃, zone 2 temperature control 150℃, zone 1 temperature control 145℃, and main unit frequency 30Hz.

[0067] Example 5

[0068] Weigh 75 parts by weight of EVA, 14 parts by weight of APP, 4 parts by weight of ADP, and 7 parts by weight of Si-HCCP-Me and put them into a high-speed mixer. Mix them evenly at a speed of 700 rpm. Then add them to a Banbury mixer for dispersion and crosslinking to obtain a reprocessable flame-retardant polyethylene powder. The Banbury mixer is set with the temperature of Zone 1, Zone 2, and Zone 3 all set to 200℃ and the speed to 60 rpm.

[0069] The above-mentioned reprocessable flame-retardant polyethylene powder is extruded and granulated through a twin-screw extruder and a granulator to obtain reprocessable flame-retardant polyethylene granules.

[0070] The settings for the twin-screw extruder are as follows: head temperature control 180℃, zone 5 temperature control 170℃, zone 4 temperature control 165℃, zone 3 temperature control 155℃, zone 2 temperature control 150℃, zone 1 temperature control 145℃, and main unit frequency 30Hz.

[0071] Example 6

[0072] Weigh 80 parts by weight of EVA, 10 parts by weight of APP, 5 parts by weight of ADP, and 5 parts by weight of Si-HCCP-Et and put them into a high-speed mixer and mix them evenly at a speed of 700 rpm. Then add them to a Banbury mixer for dispersion and crosslinking to obtain a reprocessable flame-retardant polyethylene powder. The settings of the Banbury mixer are as follows: temperature of zone 1, temperature of zone 2, and temperature of zone 3 are all set to 200℃, and speed is 60 rpm.

[0073] Comparative Example 1

[0074] This comparative example is similar to Example 1, except that APP and ADP are not added in this comparative example. The specific preparation method of this comparative example includes the following steps:

[0075] 88 parts by weight of EVA were weighed and placed in an internal mixer for preheating for 5 minutes. 12 parts by weight of Si-HCCP-Me were weighed and added to the internal mixer for crosslinking to obtain low-density dynamically crosslinked polyethylene powder. The polyethylene powder was then extruded and granulated using a twin-screw extruder and a granulator to obtain polyethylene granules. These granules were then injection molded using an injection molding machine through mold closing, filling, pressure holding, cooling, mold opening, and demolding to obtain polyethylene products.

[0076] The internal mixer's settings are as follows: Zone 1 temperature set to 220℃, Zones 2 and 3 both set to 230℃, and speed 40 rpm. The twin-screw extruder's settings are: die head temperature control 185℃, Zone 5 temperature control 175℃, Zone 4 temperature control 175℃, Zone 3 temperature control 160℃, Zone 2 temperature control 155℃, Zone 1 temperature control 150℃, and main extruder frequency 10Hz. The injection molding machine's temperature settings are: Zone 1 170℃, Zone 2 175℃, and Zone 3 180℃.

[0077] Comparative Example 2

[0078] This comparative example is similar to Example 6, except that (3-aminopropyl)triethoxysilane is used instead of Si-HCCP-Et in this comparative example. The specific preparation method of this comparative example includes the following steps:

[0079] Weigh 80 parts by weight of EVA, 10 parts by weight of APP, 5 parts by weight of ADP, and 5 parts by weight of (3-aminopropyl)triethoxysilane and put them into a high-speed mixer and mix them evenly at a speed of 700 rpm. Then add them to a Banbury mixer for dispersion and crosslinking to obtain a reprocessable flame-retardant polyethylene powder. The settings of the Banbury mixer are as follows: temperature of zone 1, temperature of zone 2, and temperature of zone 3 are all set to 200℃, and speed is 60 rpm.

[0080] Comparative Example 3

[0081] This comparative example is similar to Example 1, except that ADP was not added and APP was used instead of ADP. The specific preparation method of this comparative example includes the following steps:

[0082] Weigh 60 parts by weight of EVA, 28 parts by weight of APP, and 12 parts by weight of Si-HCCP-Me and put them into a high-speed mixer. Mix them evenly at a speed of 600 rpm. Then add them to a Banbury mixer for dispersion and crosslinking to obtain reprocessable flame-retardant polyethylene powder. The Banbury mixer is set with the following parameters: Zone 1 temperature is set to 220℃, Zone 2 and Zone 3 temperatures are both set to 230℃, and the speed is 40 rpm.

[0083] The above-mentioned reprocessable flame-retardant polyethylene powder is extruded and granulated through a twin-screw extruder and a granulator. The resulting reprocessable flame-retardant polyethylene granules are then injection molded through an injection molding machine, which involves mold closing, filling, pressure holding, cooling, mold opening, and demolding to obtain polyethylene products.

[0084] The twin-screw extruder's temperature settings are: die head temperature control 185℃, zone 5 temperature control 175℃, zone 4 temperature control 175℃, zone 3 temperature control 160℃, zone 2 temperature control 155℃, zone 1 temperature control 150℃, and main unit frequency 10Hz. The injection molding machine's temperature settings are: zone 1 170℃, zone 2 175℃, and zone 3 180℃.

[0085] 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.

[0086] Table 1

[0087]

[0088]

[0089] As shown in Table 1, the polyolefin materials prepared based on the flame-retardant system of this invention not only possess excellent mechanical properties but also achieve the highest flame-retardant rating of V0. The polyolefin material in Comparative Example 1 (without added flame retardant) lacks flame-retardant properties and exhibits poor tensile strength (only 5.4 MPa) due to its low degree of crosslinking. Comparing the data from Example 6 and Comparative Example 2, it is evident that the EVA material crosslinked using a traditional silane crosslinking agent only achieves a flame-retardant rating of V2. In contrast, the silane-modified cyclophosphonitrile used in this invention not only possesses crosslinking capabilities but also acts as a reactive flame retardant, integrating into the EVA crosslinking network, thus improving the material's mechanical properties while achieving a flame-retardant rating of V0. In Comparative Example 3, only ammonium polyphosphate and silane-modified cyclophosphonitrile were added, resulting in relatively poor flame-retardant properties (V2) and mechanical properties of the prepared EVA material.

[0090] Through the torque-time processing curve of polyethylene material ( Figure 2 As can be seen, the material prepared in Comparative Example 1 without APP and ADP showed a particularly slow torque increase within 60 minutes of processing, with a maximum torque of only 2 N·m. Examples 2, 4, and 6, which added APP and ADP, exhibited higher maximum torque values ​​(10–12 N·m) and reached the maximum torque value more quickly (12–30 minutes), indicating that APP and ADP not only have flame-retardant properties but also significantly catalyze the construction of the dynamic cross-linked network of silyl ethers within polyethylene.

[0091] The high-temperature resistance of EVA material was obtained using thermogravimetric analysis (TGA) curves. Figure 3 It can be seen that the materials prepared by this invention have excellent high-temperature resistance. Specifically, the EVA materials prepared in Examples 1 and 6 can withstand temperatures up to 335°C, while the EVA material prepared in Comparative Example 1 without APP and ADP only withstands temperatures up to 310°C, and the EVA material prepared in Comparative Example 2, which uses (3-aminopropyl)triethoxysilane instead of Si-HCCP, only withstands temperatures up to 315°C. Furthermore, the char residue of the EVA materials prepared in Examples 1 and 6 (measured according to TGA results) is 20%, higher than the 0.8% of Comparative Example 1 and 13% of Comparative Example 2; this indicates that the polyolefin materials prepared based on the flame-retardant system of this invention have greater advantages in the preparation of high-temperature resistant wires and cables.

[0092] The polyethylene product obtained in Example 2 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 4 ).from Figure 4 It can be seen that the polyethylene products prepared by the invention have smooth surfaces before and after reprocessing, exhibiting excellent reprocessing performance.

[0093] 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 reprocessable flame-retardant polyethylene material, characterized in that, The raw materials include the following parts by weight: 60-80 parts of ethylene vinyl acetate copolymer; 20-40 parts of composite flame retardant system; the composite flame retardant system includes ammonium polyphosphate, aluminum diethyl phosphite, and silane-modified hexachlorocyclophosphamide; the structure of the silane-modified hexachlorocyclophosphamide is as follows: Where R is methyl or ethyl.

2. The reprocessable flame-retardant polyethylene material as described in claim 1, characterized in that, In the composite flame retardant system, the mass ratio of ammonium polyphosphate, aluminum diethylphosphite, and silane-modified hexachlorocyclophosphonitrile is 1:(0.2-0.7):(0.4-0.8).

3. A method for preparing the reprocessable flame-retardant polyethylene material according to claim 1 or 2, characterized in that, Includes the following steps: After mixing the ethylene vinyl acetate copolymer with the composite flame retardant system, dispersion crosslinking is performed to obtain the reprocessable flame retardant polyethylene material; preferably, the mixing is performed in a high-speed mixer and dispersion crosslinking is performed in an internal mixer.

4. The preparation method according to claim 3, characterized in that, The high-speed mixer operates at a speed of 500–700 rpm; The internal mixer has a zone temperature of 200-230℃, a zone temperature of 200-230℃, and a zone temperature of 200-230℃; the rotor speed is 40-60 rpm.

5. The preparation method according to claim 3, characterized in that, The preparation method of silane-modified hexachlorocyclophosphamide in the composite flame retardant system includes the following steps: Hexachlorocyclophosphonitrile, (3-aminopropyl)triethoxysilane / ((3-aminopropyl)trimethoxysilane), an acid-binding agent, and an organic solvent are mixed and reacted. After the reaction is completed, the mixture is purified to obtain the silane-modified hexachlorocyclophosphonitrile. Preferably, the reaction temperature is 50-120°C and the reaction time is 2-10 h.

6. The preparation method according to claim 5, characterized in that, The molar ratio of the hexachlorocyclophosphonitrile to the (3-aminopropyl)triethoxysilane / (3-aminopropyl)trimethoxysilane is 1:(6-6.1); The molar ratio of the acid-binding agent to the hexachlorocyclophosphamide is 6-8:

1.

7. The preparation method according to claim 5, characterized in that, The acid-binding agent is selected from pyridine and / or triethylamine; The organic solvent is selected from toluene or tetrahydrofuran.

8. The preparation method according to any one of claims 3-7, characterized in that, The method also includes the steps of extruding and granulating the dispersed crosslinked product; preferably, the extrusion is carried out in a twin-screw extruder, and the parameters of the twin-screw extruder are: die head temperature control 170-185°C, zone 5 temperature control 170-180°C, zone 4 temperature control 165-175°C, zone 3 temperature control 155-165°C, zone 2 temperature control 150-155°C, zone 1 temperature control 145-150°C, and main engine frequency 10-30Hz.

9. A method for preparing a polyethylene product, characterized in that, Includes the following steps: The reprocessable flame-retardant polyethylene material prepared by the preparation method of the reprocessable flame-retardant polyethylene material according to claim 1 or 2, or according to any one of claims 3-8, is injection molded to obtain the polyethylene product.

10. The preparation method according to claim 9, characterized in that, The injection molding is performed in an injection molding machine, and 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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