A COFs flame-retardant polyethylene composite material for rotational molding and its preparation method

Abstract

The present invention belongs to the technical field of polymer composite materials, and relates to a COFs flame-retardant polyethylene composite material for rotational molding and a preparation method thereof. The composite material comprises the following components: linear low-density polyethylene 15.0% - 35.0%, low-density polyethylene 35.0% - 55.0%, and a flame-retardant masterbatch; the flame-retardant masterbatch comprises the following components: linear low-density polyethylene 10.0% - 35.0%, carbon nanotubes 0% - 10.0%, Cu@COFs-COOH 1.0% - 12.0%, a toughening agent 1.0% - 10.0%, polyethylene wax 1.0% - 10.0%, and an antioxidant 1.0% - 10.0%; the proportions are all in mass percentages. The composite material of the present invention can isolate oxygen under high-temperature conditions, reduce the surface temperature, reduce the release of heat, and form a porous foam carbon layer, so as to significantly improve the flame-retardant effect. Moreover, compared with traditional halogen flame retardants, no toxic gas is generated, and it is more environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer composite materials, and relates to a COFs flame-retardant polyethylene composite material for rotational molding and a preparation method thereof. Background Art

[0002] Rotational molding, also known as rotomolding or rotational moulding, is a molding process for manufacturing hollow plastic products without pressure. It is mainly used to produce large seamless products with uniform wall thickness, especially suitable for manufacturing durable and complex hollow plastic products. Therefore, it has become one of the important branches in the field of plastic processing. Rotationally molded products are widely used in multiple fields, including agriculture (such as large water tanks), military (such as packaging boxes for missiles, rockets, landmines, etc.), automotive industry (such as durable vehicle components), toy industry (such as delicate and safe plastic products), etc. The deficiencies of traditional rotationally molded polyethylene products in terms of flame retardancy, antistatic properties, etc. have greatly restricted their application in special fields (such as electronic and electrical packaging, fuel and chemical storage and transportation, etc.). On the other hand, due to the large dosage of flame retardants added and the significant decline in product performance in traditional polyolefin flame retardant methods, they are not suitable for rotational molding processing and cannot be used in the production of rotationally molded products. Therefore, it is necessary to carry out flame retardant modification on rotationally molded polyethylene to improve its properties.

[0003] Flame-retardant covalent organic framework (COFs) materials are an important development direction. Mainly by introducing flame-retardant elements or functional groups into the COFs structure to improve the flame retardancy. For example, imide COF with rearrangement characteristics releases CO2 during the thermally induced structural rearrangement process, thus showing good flame retardancy (eScience 2(2022)311 - 318). In addition, a COF-based phosphorus, nitrogen, and silicon synergistic flame retardant (PA-COF@MT) is synthesized through phytic acid (PA), montmorillonite (MT), and covalent organic framework (COF), showing excellent flame retardant effects in epoxy resins. In recent years, transition metal compounds (such as copper, cobalt, nickel, etc.) have begun to be studied and applied as flame retardants in a wider range. Among them, copper chelates have a similar aromatic ring structure, and metallic copper will catalyze the formation of carbon during the combustion of polymers to form a denser and tougher carbon layer, which helps to protect the material from further erosion by the flame. At the same time, copper chelates can improve the thermal stability of polymers, making the material remain stable at higher temperatures and not easily burn, showing unique advantages in practical applications. Summary of the Invention

[0004] In order to solve the above technical problems existing in the prior art, the present invention provides a COFs flame-retardant polyethylene composite material for rotational molding and a preparation method thereof, and the specific technical solutions are as follows:

[0005] A preparation method of a COFs flame-retardant polyethylene composite material for rotational molding includes the following steps:

[0006] Step (1) Preparation of COFs, specifically including:

[0007] First step: Dissolve a certain mass of phloroglucinol trialdehyde in DMAc, then add dioxane and a certain mass of 3,5-diamino-1,2,4-triazole. After obtaining a light yellow solution, add an acetic acid aqueous solution to obtain a COF mother liquor. Then introduce the obtained COF mother liquor into a polytetrafluoroethylene-lined autoclave and heat it at 60 - 150 °C for 24 - 96 h. The obtained COF powder is subsequently washed several times with methanol, acetone, and tetrahydrofuran and dried in indoor air to obtain COFs powder, the structural formula of which is shown in formula (I):

[0008]

[0009] Second step: Weigh a certain mass of COFs powder with the structural formula (I), add a certain mass of an acetone solution of succinic acid. The reaction mixture is heated at 40 - 100 °C for 12 - 36 hours, the precipitate is collected by centrifugation and washed with acetone. The obtained powder is dried under vacuum overnight to obtain COFs-COOH powder, the structural formula of which is shown in formula (II):

[0010]

[0011]

[0012] Furthermore, the reaction mixture is heated at 40 - 100 °C for 12 - 36 hours. The optimal reaction temperature is selected as 90 °C and the reaction time is 24 h.

[0013] Third step: Under ultrasonic conditions, disperse the COFs-COOH powder in a mixed solution of water and acetone, then add a certain amount of copper sulfate solution, and stir for 2 - 10 h. Filter and wash to obtain Cu@COFs-COOH powder, the structural formula of which is shown in formula (III):

[0014]

[0015] Furthermore, when dispersing the COFs-COOH powder in a mixed solution of water and acetone and then adding a certain amount of copper sulfate solution and stirring for 2 - 10 h, the optimal stirring time is 5 h.

[0016] Step (2) Preparation of masterbatch:

[0017] Weigh Cu@COFs-COOH powder and PE wax according to the weight ratio and add them to a high-speed mixer. The blending temperature is 85 - 110°C and the blending time is 5 - 8 min. Then add LLDPE, carbon nanotube CNT, toughening agent, and antioxidant and blend at 85 - 110°C for 3 - 5 min. Put the above uniformly mixed materials into a twin-screw extruder for extrusion. The extrusion temperature is 195°C, and then cool, pelletize, and dry to obtain the flame-retardant masterbatch.

[0018] Further, the PE wax in the flame-retardant masterbatch is one or a combination of PEW-032, PEW-031, and PEW-030.

[0019] Further, the linear low-density polyethylene LLDPE in the flame-retardant masterbatch is one or a combination of LLDPE-7050, LLDPE-9020, and LLDPE-9085.

[0020] Further, the carbon nanotube CNT in the flame-retardant masterbatch is single-walled carbon nanotube or multi-walled carbon nanotube or a combination of them.

[0021] Further, the toughening agent in the flame-retardant masterbatch is one or a combination of POE-g-MAH, POE-g-GMA, and PE-g-MAH.

[0022] Further, the antioxidant in the flame-retardant masterbatch is one or a combination of BHT, AO-1010, AO-1076, AO-3114, and AO-330.

[0023] Further, when adding the Cu@COFs-COOH powder and PE wax to the high-speed mixer, the blending temperature is 85 - 110°C and the blending time is 5 - 8 min. The optimal blending temperature is 90°C and the blending time is 8 min.

[0024] Further, when adding LLDPE, carbon nanotube CNT, toughening agent, and antioxidant and blending at 85 - 110°C for 3 - 5 min, the optimal blending temperature is 90°C and the blending time is 4 min.

[0025] Step (3) Extrusion and pelletization:

[0026] Weigh LLDPE, LDPE, and Cu@COFs-COOH masterbatch according to the weight ratio and blend them in a high-speed mixer at 85 - 110°C for 10 - 20 min. Then put them into a twin-screw extruder for extrusion (temperature 195°C), and then cool and pelletize. The obtained pellets are dried for standby.

[0027] Further, the low-density polyethylene LDPE is one or a combination of DFDA-7042, DFDB-7042, and DFDC-7042), and the linear low-density polyethylene LLDPE is one or a combination of LLDPE-7050, LLDPE-9020, and LLDPE-9085.

[0028] Further, the LLDPE, LDPE, and Cu@COFs-COOH powder are added to a high-speed mixer, the blending temperature is 85-110°C, the blending time is 10-20 min, the optimal blending temperature is 90°C, and the blending time is 15 min.

[0029] Step (4) Mechanical milling:

[0030] Under the protection of nitrogen, the particles obtained in step (3) are ground into powder of about 40-50 mesh using a milling machine, and a COFs flame-retardant polyethylene composite material for rotational molding is obtained.

[0031] A COFs flame-retardant polyethylene composite material for rotational molding specifically comprises the following components:

[0032] LLDPE 15.0% - 35.0%,

[0033] LDPE 35.0% - 55.0%,

[0034] Flame retardant masterbatch;

[0035] Among them, the flame retardant masterbatch comprises the following components:

[0036] LLDPE 10.0% - 35.0%,

[0037] CNT 0% - 10.0%,

[0038] Cu@COFs-COOH 1.0% - 12.0%,

[0039] Toughening agent 1.0% - 10.0%,

[0040] PE wax 1.0% - 10.0%,

[0041] Antioxidant 1.0% - 10.0%,

[0042] The proportions are all in mass percentages.

[0043] Compared with the prior art, the advantages of the present invention are as follows:

[0044] In the Cu@COFs-COOH powder provided by the present invention, the COF is rich in imine bonds (-CH=N-) or other nitrogen-containing functional groups, and can release non-combustible gases such as nitrogen, water vapor, and ammonia under high-temperature conditions. The generated non-combustible gases will adhere to the surface of the polymer, isolating oxygen and preventing combustion, thereby achieving a flame-retardant effect. At the same time, the heat decomposition will also take away a large amount of heat, reducing the surface temperature and making it difficult to burn or even stop burning. At the same time, the carboxylic acid groups in the COF can act as dehydrating agents. During the esterification reaction and melting process, the generated non-combustible gases cause the molten system to expand and foam, forming inorganic substances and carbon residues, further foaming, and finally forming a porous foam carbon layer.

[0045] In the Cu@COFs-COOH powder provided by the present invention, the carboxylic acid groups (-COOH) have relatively rich copper chelating active sites, which promote the formation of coordination bonds. This enables the copper chelate to promote the formation of a carbon layer during the combustion process, isolating oxygen and heat, slowing down the combustion rate and heat release rate of the polyethylene material, reducing the release of heat, and improving the flame-retardant effect of the material. The copper chelate has good chemical stability and is not easily decomposed in the environment, which can improve the thermal stability of the polymer, making it more difficult to decompose at high temperatures, thereby improving the flame-retardant performance. On the other hand, compared with some traditional halogen flame retardants, it generates no toxic gases and is more environmentally friendly.

[0046] Traditional intumescent flame retardants require 3 components to be compounded, and have the disadvantages of large addition amount, poor compatibility, easy migration, and reduced flame-retardant effect. Moreover, the ratio is difficult to control, which also has a great impact on the mechanical properties of the polymer. In contrast, in the structure of the Cu@COFs-COOH powder provided by the present invention, the imine bond (-CH=N-) or other nitrogen-containing functional groups, carboxylic acid, and chelated copper elements on the COF ring will produce a synergistic effect during the combustion of polyethylene, and the synergistic effect of the three significantly improves the flame-retardant effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the COFs-COOH powder obtained during the preparation of COFs in this example. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the objectives, technical solutions, and technical effects of the present invention clearer, the following further elaborates on the present invention in detail with reference to the specification drawings and embodiments.

[0049] The embodiment of the present invention discloses a COFs flame-retardant polyethylene composite material for rotational molding, which comprises the following components:

[0050] LLDPE 15.0% - 35.0%,

[0051] LDPE 35.0% - 55.0%,

[0052] Flame retardant masterbatch;

[0053] Among them, the flame retardant masterbatch comprises the following components:

[0054] LLDPE 10.0% - 35.0%,

[0055] CNT 0% - 10.0%,

[0056] Cu@COFs - COOH 1.0% - 12.0%,

[0057] Toughening agent 1.0% - 10.0%,

[0058] PE wax 1.0% - 10.0%,

[0059] Antioxidant 1.0% - 10.0%,

[0060] The proportions therein are all mass percentages.

[0061] Example 1:

[0062] A preparation method of a COFs flame - retardant polyethylene composite for rotational molding, comprising the following steps:

[0063] Step (1) COFs preparation:

[0064] First step: Dissolve a certain mass of phloroglucinol tri - aldehyde in DMAc, then add dioxane and a certain mass of 3,5 - diamino - 1,2,4 - triazole. After obtaining a light yellow solution, add an acetic acid aqueous solution, and then introduce the obtained solution, i.e., the COF mother liquor, into a polytetrafluoroethylene - lined autoclave and heat at 90 °C for 48 h. The obtained COF powder is subsequently washed several times with methanol, acetone, and tetrahydrofuran and dried in indoor air to obtain COFs powder, the structural formula of which is as shown in formula (I):

[0065]

[0066]

[0067] Second step: Weigh a certain mass of (I) COFs powder, add a certain mass of an acetone solution of succinic acid, heat the reaction mixture at 90 °C for 24 h, centrifuge to collect the precipitate, wash it with acetone, and dry the obtained powder under vacuum overnight to obtain the Figure 1 shown COFs - COOH powder, the structural formula of which is as shown in formula (II):

[0068]

[0069] Step 3: Under ultrasonic conditions, disperse the COFs-COOH powder in a mixed solution of water and acetone, then add a certain amount of copper sulfate solution, stir for 5 h, filter, and wash to obtain the Cu@COFs-COOH powder, the structural formula of which is as shown in Formula (III):

[0070]

[0071] Preparation of masterbatch in step (2):

[0072] Weigh 9 parts of Cu@COFs-COOH powder and 2 parts of PE wax PEW-031 and add them to a high-speed mixer. The blending temperature is 90 °C and the blending time is 8 min; then add 15 parts of LLDPE DFDA-7042, 2 parts of toughening agent POE-g-MAH, and 2 parts of antioxidant AO-1010 and blend under the condition of about 90 °C for 4 min; put the above uniformly mixed materials into a twin-screw extruder for extrusion, the extrusion temperature is 195 °C, then cool, pelletize, and dry to obtain the flame-retardant masterbatch.

[0073] Extrusion granulation in step (3):

[0074] Weigh LLDPE DFDB-7042, HDPE HDPE-7000F, and Cu@COFs-COOH masterbatch according to the weight ratio, blend them in a high-speed mixer at 90 °C for 15 min, and then put them into a twin-screw extruder for extrusion again. The extrusion temperature is 195 °C, then cool and pelletize, and the obtained pellets are dried for standby.

[0075] Mechanical grinding in step (4):

[0076] Under the protection of nitrogen, use a grinding machine to grind the particles obtained in step (3) into powder with a size of about 40 - 50 mesh to obtain a COFs flame-retardant polyethylene composite material for rotational molding.

[0077] The testing devices used are: Instron 5567 of Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z of Chengde Dahua Company (impact properties, testing standard for notched Izod impact strength: ASTM D256).

[0078] Example 2:

[0079] A preparation method of a COFs flame-retardant polyethylene composite material for rotational molding, comprising the following steps:

[0080] The preparation method of COFs in step (1) is the same as that in Example 1;

[0081] Preparation of masterbatch in step (2):

[0082] Weigh 8 portions of Cu@COFs-COOH powder and 2 portions of PE wax PEW-031, add them to a high-speed mixer, with a blending temperature of 90 °C and a blending time of 8 min; then add 15 portions of LLDPE DFDA-7042 and 1 portion of carbon nanotubes 2 portions of toughening agent POE-g-MAH and 2 portions of antioxidant AO-1010 are blended for 4 min under the condition of about 90 °C; the above-mentioned uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing, and drying to obtain the flame-retardant masterbatch;

[0083] The extrusion granulation method in step (3) is the same as that in Example 1;

[0084] The mechanical milling method in step (4) is the same as that in Example 1.

[0085] The testing devices used are: Instron 5567 from Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z from Chengde Dahua Company (impact properties, testing standard for Izod notched impact strength: ASTM D256).

[0086] Example 3:

[0087] A preparation method of a COFs flame-retardant polyethylene composite for rotational molding, comprising the following steps:

[0088] The COFs preparation method in step (1) is the same as that in Example 1;

[0089] Step (2) Masterbatch preparation:

[0090] Weigh 7 portions of Cu@COFs-COOH powder and 2 portions of PE wax PEW-031, add them to a high-speed mixer, with a blending temperature of 90 °C and a blending time of 8 min; then add 15 portions of LLDPE DFDA-7042 and 2 portions of carbon nanotubes 2 portions of toughening agent POE-g-MAH and 2 portions of antioxidant AO-1010 are blended for 4 min under the condition of about 90 °C; the above-mentioned uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing, and drying to obtain the flame-retardant masterbatch;

[0091] The extrusion granulation method in step (3) is the same as that in Example 1;

[0092] The mechanical milling method in step (4) is the same as that in Example 1.

[0093] The testing devices used are: Instron 5567 from Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z from Chengde Dahua Company (impact properties, testing standard for Izod notched impact strength: ASTM D256).

[0094] Example 4:

[0095] A preparation method of a COFs flame-retardant polyethylene composite material for rotational molding, comprising the following steps:

[0096] Step (1) The preparation method of COFs is the same as that in Example 1;

[0097] Step (2) Masterbatch preparation:

[0098] Weigh 6 parts of Cu@COFs-COOH powder and 2 parts of PE wax PEW-031 and add them to a high-speed mixer. The blending temperature is 90°C and the blending time is 8 min; then add 15 parts of LLDPE DFDA-7042, 3 parts of carbon nanotubes 2 parts of toughening agent POE-g-MAH and 2 parts of antioxidant AO-1010 are blended for 4 min under the condition of about 90°C; the above-mentioned uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing and drying to obtain the flame-retardant masterbatch;

[0099] Step (3) The extrusion granulation method is the same as that in Example 1;

[0100] Step (4) The mechanical grinding method is the same as that in Example 1.

[0101] The testing devices used: Instron 5567 of Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z of Chengde Dahua Company (impact properties, testing standard for Izod notched impact strength: ASTM D256).

[0102] Example 5:

[0103] A preparation method of a COFs flame-retardant polyethylene composite material for rotational molding, comprising the following steps:

[0104] Step (1) The preparation method of COFs is the same as that in Example 1;

[0105] Step (2) Masterbatch preparation:

[0106] Weigh 4 parts of Cu@COFs-COOH powder and 2 parts of PE wax PEW-031 and add them to a high-speed mixer. The blending temperature is 90°C and the blending time is 8 min; then add 15 parts of LLDPE DFDA-7042, 4 parts of carbon nanotubes 2 parts of toughening agent POE-g-MAH and 2 parts of antioxidant AO-1010 are blended for 4 min under the condition of about 90°C; the above-mentioned uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing and drying to obtain the flame-retardant masterbatch;

[0107] Step (3) The extrusion granulation method is the same as that in Example 1;

[0108] The mechanical milling method in step (4) is the same as that in Example 1.

[0109] The testing devices used are: Instron 5567 from Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z from Chengde Dahua Company (impact properties, testing standard for Izod notched impact strength: ASTM D256).

[0110] Example 6:

[0111] A COFs flame-retardant polyethylene composite material for rotational molding and its preparation method, comprising the following steps:

[0112] The COFs preparation method in step (1) is the same as that in Example 1;

[0113] Step (2) Masterbatch preparation:

[0114] Weigh 4 parts of Cu@COFs-COOH powder and 2 parts of PE wax PEW-031 and add them to a high-speed mixer. The blending temperature is 90 °C and the blending time is 8 min; then add 15 parts of LLDPE DFDA-7042, 5 parts of carbon nanotubes 2 parts of toughening agent POE-g-MAH and 2 parts of antioxidant AO-1010 are blended for 4 min under the condition of about 90 °C; the above uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing, and drying to obtain the flame-retardant masterbatch;

[0115] The extrusion granulation method in step (3) is the same as that in Example 1;

[0116] The mechanical milling method in step (4) is the same as that in Example 1.

[0117] The testing devices used are: Instron 5567 from Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z from Chengde Dahua Company (impact properties, testing standard for Izod notched impact strength: ASTM D256).

[0118] Example 7:

[0119] A preparation method of a COFs flame-retardant polyethylene composite material for rotational molding, comprising the following steps:

[0120] The COFs preparation method in step (1) is the same as that in Example 1;

[0121] Step (2) Masterbatch preparation:

[0122] Weigh 3 parts of Cu@COFs-COOH powder and 2 parts of PE wax PEW-031 and add them to a high-speed mixer. The blending temperature is 90 °C and the blending time is 8 min; then add 15 parts of LLDPE DFDA-7042, 6 parts of carbon nanotubes 2 parts of toughening agent POE-g-MAH and 2 parts of antioxidant AO-1010 are blended for 4 min under the condition of about 90 °C; the above-mentioned uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing and drying to obtain the flame-retardant masterbatch;

[0123] The extrusion granulation method in step (3) is the same as that in Example 1;

[0124] The mechanical milling method in step (4) is the same as that in Example 1.

[0125] The testing devices used are: Instron 5567 of Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z of Chengde Dahua Company (impact properties, testing standard for cantilever beam notched impact strength: ASTM D256).

[0126] Example 8:

[0127] A preparation method of a COFs flame-retardant polyethylene composite material for rotational molding, comprising the following steps:

[0128] The preparation method of COFs in step (1) is the same as that in Example 1;

[0129] Step (2) Masterbatch preparation:

[0130] Weigh 2 parts of Cu@COFs-COOH powder and 2 parts of PE wax PEW-031 and add them to a high-speed mixer. The blending temperature is 90 °C and the blending time is 8 min; then add 15 parts of LLDPE DFDA-7042 and 7 parts of carbon nanotubes 2 parts of toughening agent POE-g-MAH and 2 parts of antioxidant AO-1010 are blended for 4 min under the condition of about 90 °C; the above-mentioned uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing and drying to obtain the flame-retardant masterbatch;

[0131] The extrusion granulation method in step (3) is the same as that in Example 1;

[0132] The mechanical milling method in step (4) is the same as that in Example 1.

[0133] The testing devices used are: Instron 5567 of Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z of Chengde Dahua Company (impact properties, testing standard for cantilever beam notched impact strength: ASTM D256).

[0134] Example 9:

[0135] A preparation method of a COFs flame-retardant polyethylene composite material for rotational molding, comprising the following steps:

[0136] Step (1): The preparation method of COFs is the same as that in Example 1;

[0137] Step (2): Preparation of masterbatch:

[0138] Weigh 1 part of Cu@COFs-COOH powder and 2 parts of PE wax PEW-031, add them into a high-speed mixer, with a blending temperature of 90 °C and a blending time of 8 min; then add 15 parts of LLDPE DFDA-7042 and 8 parts of carbon nanotubes 2 parts of toughening agent POE-g-MAH and 2 parts of antioxidant AO-1010 are blended for 4 min under the condition of about 90 °C; the above-mentioned uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing and drying to obtain the flame-retardant masterbatch;

[0139] Step (3): The extrusion granulation method is the same as that in Example 1;

[0140] Step (4): The mechanical grinding method is the same as that in Example 1.

[0141] The testing devices used: Instron 5567 of Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z of Chengde Dahua Company (impact properties, testing standard for notched Izod impact strength: ASTM D256).

[0142] Comparative Example 1:

[0143] A preparation method of a COFs flame-retardant polyethylene composite for rotational molding, comprising the following steps:

[0144] Step (1): The preparation method of COFs is the same as that in Example 1;

[0145] Step (2): Preparation of masterbatch:

[0146] Weigh 2 parts of PE wax PEW-031, 15 parts of LLDPE DFDA-7042 and 3 parts of carbon nanotubes 2 parts of toughening agent POE-g-MAH and 2 parts of antioxidant AO-1010 are blended for 4 min under the condition of about 90 °C; the above-mentioned uniformly mixed materials are put into a twin-screw extruder for extrusion, cooling, pelletizing and drying to obtain the flame-retardant masterbatch;

[0147] Step (3): The extrusion granulation method is the same as that in Example 1;

[0148] Step (4): The mechanical grinding method is the same as that in Example 1.

[0149] Testing devices used: Instron 5567 of Instron Corporation in the United States (tensile properties, testing standard: ASTM D638); XJ-50Z of Chengde Dahua Company (impact properties, testing standard for Izod notched impact strength: ASTM D256).

[0150] The material ratios of the above-mentioned examples and comparative examples are shown in Table 1 below:

[0151]

[0152] Table 2 below shows the performance comparison of the above-mentioned examples and comparative examples:

[0153]

[0154]

[0155] Table 2

[0156] The above is only the preferred embodiment of the present invention and does not impose any formal restrictions on the present invention. Although the implementation process of the present invention has been described in detail above, those skilled in the art can still modify the technical solutions recorded in the foregoing examples or make equivalent replacements for some of the technical features. Any modifications, equivalent replacements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a COF flame-retardant polyethylene composite material for rotational molding, characterized in that, It includes the following steps: Step (1) Preparation of COFs, specifically including: The first step: Dissolve phloroglucinol trialdehyde in DMAc, then add dioxane and 3,5-diamino-1,2,4-triazole. After obtaining a pale yellow solution, add an aqueous acetic acid solution. Then introduce the obtained solution, i.e., the COF mother liquor, into a polytetrafluoroethylene-lined autoclave and heat it at 60~150 °C for 24~96 h. The obtained COF powder is then washed several times with methanol, acetone, and tetrahydrofuran and dried in indoor air to obtain COFs powder, the structural formula of which is shown in formula (I): ， （I）； The second step: Weigh the COFs powder, add an acetone solution of succinic acid, heat the reaction mixture at 90 °C for 24 hours, centrifuge to collect the precipitate, wash it with acetone, and dry the obtained powder under vacuum overnight to obtain COFs-COOH powder, the structural formula of which is shown in formula (II): ， (II); The third step: Under ultrasonic conditions, disperse the COFs-COOH powder in a mixed solution of water and acetone, then add a copper sulfate solution, stir for 2~10 h, filter, and wash to obtain Cu@COFs-COOH powder, the structural formula of which is shown in formula (III): ， (III); Step (2) Preparation of masterbatch: Weigh the Cu@COFs-COOH powder and PE wax according to the weight ratio and add them to a high-speed mixer. The blending temperature is 85~110 °C and the blending time is 5~8 min; then add linear low-density polyethylene LLDPE, carbon nanotubes CNT, toughening agent, and antioxidant and blend them at 85~110 °C for 3~5 min; put the above uniformly mixed materials into a twin-screw extruder for extrusion, then cool, pelletize, and dry to obtain the flame-retardant masterbatch; Step (3) Extrusion granulation: Weigh linear low-density polyethylene LLDPE, low-density polyethylene LDPE, and flame-retardant masterbatch according to the weight ratio, blend them in a high-speed mixer at 85~110 °C for 10~20 min, and then put them into a twin-screw extruder for extrusion again, then cool and pelletize. The obtained pellets are dried for standby; Step (4) Mechanical grinding: Under the protection of nitrogen, use a grinding machine to grind the pellets obtained in step (3) into a powder of 40~50 mesh, and then a COFs flame-retardant polyethylene composite material for rotational molding is obtained.

2. The preparation method of the COFs flame-retardant polyethylene composite material for rotational molding according to claim 1, wherein, In the third step, the stirring time is 5 h.

3. The preparation method of the rotational molding COFs flame-retardant polyethylene composite material according to claim 1, characterized in that, In step (2), the PE wax is one or a combination of PEW-032, PEW-031, and PEW-030; the linear low-density polyethylene LLDPE is one or a combination of LLDPE-7050, LLDPE-9020, and LLDPE-9085; the carbon nanotubes CNT are one or a combination of single-walled carbon nanotubes ZEONANO® or multi-walled carbon nanotubes ZEONANO®; the toughening agent is one or a combination of POE-g-MAH, POE-g-GMA, and PE-g-MAH; the antioxidant is one or a combination of BHT, AO-1010, AO-1076, AO-3114, and AO-330.

4. The preparation method of the rotational molding COFs flame-retardant polyethylene composite material according to claim 1, characterized in that, In step (2), the blending temperature of the Cu@COFs-COOH powder and PE wax in the high-speed mixer is 90 °C, and the blending time is 8 min; the blending temperature of adding linear low-density polyethylene LLDPE, carbon nanotube CNT, toughening agent, and antioxidant is 90 °C, and the blending time is 4 min.

5. The preparation method of the rotational molding COFs flame-retardant polyethylene composite material according to claim 1, characterized in that, In step (3), the low-density polyethylene LDPE is one or a combination of DFDA-7042, DFDB-7042, and DFDC-7042.

6. The preparation method of the rotational molding COFs flame-retardant polyethylene composite material according to claim 1, characterized in that, In step (3), the blending temperature in the high-speed mixer is 90 °C, and the blending time is 15 min.

7. A rotomolding COFs flame-retardant polyethylene composite prepared by the preparation method described in any one of claims 1 to 6, characterized in that, Specifically, it includes the following components: Linear low-density polyethylene LLDPE 15.0% - 35.0%, Low-density polyethylene LDPE 35.0% - 55.0%, Flame retardant masterbatch; Among them, the flame retardant masterbatch includes the following components: Linear low-density polyethylene LLDPE 10.0% - 35.0%, Carbon nanotube CNT 0% - 10.0%, Cu@COFs-COOH 1.0% - 12.0%, Toughening agent 1.0% - 10.0%, Polyethylene wax 1.0% - 10.0%, Antioxidant 1.0% - 10.0%; The proportions therein are all mass percentages.

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