Low-smoke halogen-free room-temperature self-crosslinking flame-retardant polyolefin material and preparation method thereof

Abstract

The invention relates to the technical field of cross-linked polyolefin materials, and provides a low-smoke halogen-free room-temperature self-cross-linked flame-retardant polyolefin material and a preparation method thereof.The preparation method comprises the steps that an acrylate active branch chain is introduced to an EVA molecular chain through gradient free radical graft copolymerization, and graft modified matrix resin is prepared; the preparation method comprises the following steps: preparing a room-temperature pre-crosslinked flame-retardant composite material comprising modified matrix resin, a flame-retardant phase, a composite peroxide initiator and a metal coordination catalyst through segmented temperature control mixing; through coupling of a shear field and a thermal field, the room-temperature and alternating-current flame-retardant composite material is molded and converted into pre-crosslinked structure granules; and carrying out extrusion molding and room-temperature standing on the pre-crosslinked structure granules to prepare the low-smoke halogen-free room-temperature self-crosslinking flame-retardant polyolefin material. According to the invention, rapid crosslinking of polyolefin at room temperature can be realized, and the flexibility and environmental protection performance are improved while the flame retardant efficiency of the resin material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cross-linked polyolefin materials, and in particular to a low-smoke, halogen-free, room-temperature self-cross-linking, flame-retardant polyolefin material and a preparation method thereof. Background Art

[0002] Low-smoke halogen-free flame-retardant cross-linked polyolefin material is an important electrical insulation coating material for wires and cables. As the application end continues to increase its requirements for the safety and environmental performance of wires and cables, the application of low-smoke halogen-free flame-retardant polyolefin cross-linked material in wires and cables is increasing.

[0003] In manufacturing, the cross-linking methods of low-smoke halogen-free flame-retardant cross-linked polyolefin materials are divided into chemical cross-linking and physical cross-linking. Chemical cross-linking includes silane warm water cross-linking and silane vapor cross-linking, and physical cross-linking includes electron irradiation cross-linking and ultraviolet light cross-linking. The chemical cross-linking method has a long process cycle and high energy consumption, and the temperature and time need to be strictly controlled during the cross-linking process to prevent incomplete or excessive cross-linking. The physical cross-linking method requires special equipment, has high requirements for the operating environment and personnel protection, and is costly. In addition, the existing cross-linking cannot be achieved, and there is still great room for improvement in the synergistic optimization of flame retardancy, room temperature cross-linking and low smoke performance. Usually, it is necessary to sacrifice a certain performance, such as adding halogen flame retardants to reduce the cross-linking temperature, but this leads to increased smoke toxicity.

[0004] In recent years, research has begun to emerge on using peroxides to induce room-temperature crosslinking. However, the problems of slow crosslinking rate, low crosslinking degree, reduced flame retardant efficiency, and localized overcrosslinking remain unresolved. Metal ion catalysis can theoretically lower the crosslinking temperature to a certain extent, but effective coordination between the uniformity of metal ion dispersion, the uniformity of the flame retardant phase, and the uniformity of the crosslinking network is difficult to achieve.

[0005] Chinese patent publication number CN107033432A discloses a room-temperature silane-crosslinked low-smoke halogen-free flame-retardant polyolefin composite material and its preparation method. In practical applications, this patent scheme has the following deficiencies: 1. Grafting must be achieved at a relatively high temperature. High temperature causes the flame retardant to decompose, reducing the flame retardant efficiency. High temperature also causes thermal degradation of the polyolefin molecular chain, reducing the mechanical properties of the material; 2. The flame retardant interferes with the activity of the catalyst, and the flame retardant itself is prone to agglomeration; 3. The grafting rate and cross-linking degree are uncontrollable, and the cross-linking method relies on boiling in water or long-term natural storage.

[0006] Therefore, how to provide a polyolefin material that can quickly self-crosslink at room temperature and has excellent flame retardant properties and low smoke characteristics, get rid of dependence on existing crosslinking conditions, and reduce process costs has become a technical problem that needs to be solved urgently. Summary of the Invention

[0007] In view of this, in order to overcome the deficiencies of the prior art, the present invention aims to provide a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material and a preparation method thereof.

[0008] According to a first aspect of the present invention, there is provided a method for preparing a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material, the method comprising: Step S1: introducing active acrylic acid ester branches into the EVA molecular chain through a gradient free radical graft copolymerization reaction to prepare a graft-modified base resin; Step S2: preparing a room temperature pre-crosslinked flame retardant composite material comprising a modified matrix resin, a flame retardant phase, a composite peroxide initiator and a metal coordination catalyst by segmented temperature-controlled mixing; Step S3: by coupling the shear field and the thermal field, the room temperature and AC flame retardant composite material is molded into a pre-crosslinked structure pellet; Step S4: Extruding the pre-crosslinked structural pellets and allowing them to stand at room temperature to obtain a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material.

[0009] Optionally, the method for preparing the low-smoke halogen-free room temperature self-crosslinking flame-retardant polyolefin sheath material of the present application, step S1, comprises: The EVA resin was preheated to 110°C by shear mixing at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a molten EVA resin, and the torque value of the molten EVA resin was obtained by monitoring. Add 2-6.5 parts by weight of acrylic acid ester monomer and 0.004 parts by weight of benzoyl peroxide to 100 parts by weight of molten EVA resin, raise the temperature to 115°C, and react at a shear speed of 40 rpm for 15 minutes; Add 3-5.8 parts by weight of acrylic acid ester monomer and 0.005 parts by weight of benzoyl peroxide to the reaction melt, raise the temperature to 135° C., and react at a shear speed of 60 rpm for 25 minutes; 2 parts by weight of acrylic acid ester monomer was added to the reaction melt, the temperature was lowered to 110° C., and the reaction was continued at a shear speed of 30 rpm; The torque value of the reaction melt is monitored in real time. When the torque value of the reaction melt reaches twice the torque value of the molten EVA resin, liquid CO2 is injected into the reaction melt to quench the reaction and obtain a graft-modified matrix resin.

[0010] Optionally, in the preparation method of the low-smoke halogen-free room-temperature self-crosslinking flame-retardant polyolefin material of the present application, in step S1, the acrylate monomer is a mixture of butyl acrylate and glycidyl methacrylate, wherein the weight ratio of butyl acrylate to glycidyl methacrylate is 3:1.

[0011] Optionally, the method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of the present application, step S2, comprises: In a dynamic nitrogen protective atmosphere, the -1 100 parts by weight of the modified base resin, 35 parts by weight of the maleic anhydride grafted polyolefin elastomer and 20 parts by weight of the nano-aluminum hydroxide powder with an average particle size of 500 nm and surface modified with a silane coupling agent were premixed at 70° C. for 15 minutes at a shear rate of 100 parts by weight. Add 5.2 parts by weight of composite peroxide initiator to the mixture and incubate at 65°C for 250 seconds. -1 The mixed material was mixed for 20 min at a shear rate of 1.8 parts by weight of metal coordination catalyst was added to the mixture and heated at 60°C for 350s. -1 The mixed material was mixed for 20 min at a shear rate of The mixed material system was heated to 70°C for 250 seconds. -1 The mixture was mixed for 20 min at a shear rate of 100 nm to obtain a room temperature pre-crosslinked flame retardant composite material.

[0012] Optionally, in the preparation method of the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of the present application, in step S2, the composite peroxide initiator is composed of 2.2 parts by weight of dicumyl peroxide, 1.5 parts by weight of tetrahydrofuran peroxide, and 1.5 parts by weight of diisopropyl peroxydicarbonate.

[0013] Optionally, in the preparation method of the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of the present application, in step S2, copper acetylacetonate and zinc acetylacetonate are dissolved in an organic solvent at a molar ratio of Cu:Zn=1:1.5, 2,2'-bipyridine is used as a ligand, and the reaction is refluxed at 60°C for 2 hours, and then the solvent is removed by rotary evaporation to obtain a metal coordination catalyst.

[0014] Optionally, the preparation method of the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of the present application, step S3, includes: using a co-rotating twin-screw extruder to dynamically vulcanize and extrude the room-temperature pre-crosslinked flame-retardant composite material, sequentially setting multiple temperature fields with increasing temperature on the extrusion path, underwater pelletizing the extruded melt, and vacuum drying the obtained material particles to obtain pre-crosslinked structural pellets.

[0015] Optionally, in the preparation method of the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of the present application, in step S3, the speed of the twin screw is 250-350 rpm, the pressure of the vulcanization molding die is 12-15 MPa, and the temperature range of the temperature field zone is 80-85°C, 85-90°C, 90-95°C, 95-100°C, and 100-105°C, respectively.

[0016] Optionally, in the method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of the present application, in step S4, the standing time at room temperature is 8-18 hours.

[0017] According to a second aspect of the present invention, a low-smoke, halogen-free, room-temperature self-crosslinking, flame-retardant polyolefin material is provided. The low-smoke, halogen-free, room-temperature self-crosslinking, flame-retardant polyolefin material is prepared according to the above method.

[0018] The low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of the present invention has the following beneficial technical effects:

[0019] 1. Through gradient free radical graft copolymerization, active acrylate branches are introduced into the EVA molecular chain. Combined with a composite peroxide initiator and a metal ion catalyst system, crosslinking is achieved within 8-18 hours at room temperature (20-25°C), with a crosslinking degree of no less than 77%. This eliminates reliance on high temperatures, steam, or radiation, reducing process energy consumption by over 60% and significantly increasing crosslinking speed. Real-time torque monitoring and segmented temperature control prevent localized over- or under-crosslinking.

[0020] 2. Through the precise introduction of room temperature cross-linking active reaction sites, the interaction energy between the flame retardant phase and the resin matrix is improved. By modifying the surface of nano-aluminum hydroxide, the surface carboxyl groups are chemically bonded with the epoxy groups of the grafted chains, which significantly improves the dispersion uniformity of the flame retardant and reduces the crystallinity of the EVA resin. While improving the flame retardant efficiency of the resin material, the flexibility is also improved, and the oxygen index is not less than 35%.

[0021] 3. Through dynamic vulcanization extrusion, the grafting active sites are used to construct a dynamic vulcanization precursor with a cross-linked network prototype. The flame retardant is chemically bonded to the epoxy groups on the grafted chain to enhance the interfacial bonding strength and avoid the loss of mechanical properties of the matrix resin. 2+ / Zn 2+ Coordination with the carboxyl / epoxy groups of the grafted chains can reduce the cross-linking activation energy, thereby achieving room temperature cross-linking in subsequent processes.

[0022] 4. It does not contain halogen elements or biotoxic organic tin catalysts, which improves the environmental friendliness of the process and products. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1This is an exemplary diagram of the steps of a method for preparing a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to Example 1 of the present application; Figure 2 This is a SEM image of a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material prepared according to Example 3 of the present application; Figure 3 This is a SEM image of a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material prepared according to Example 5 of the present application; Figure 4 TEM image of the pre-crosslinked structured pellets prepared according to Example 2 of the present application; Figure 5 TEM image of the pre-crosslinked structured pellets prepared according to Example 4 of the present application; Figure 6 This is a TEM image of the pre-crosslinked structural pellets prepared according to Example 6 of the present application. DETAILED DESCRIPTION

[0025] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0026] It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments may be combined with each other; and, based on the embodiments in this disclosure, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of this disclosure.

[0027] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on this disclosure, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement an apparatus and / or practice a method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this apparatus and / or practice this method.

[0028] Example 1 Figure 1 1 is an example diagram of the steps of a method for preparing a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to Example 1 of the present application, as shown in FIG. Figure 1 As shown, in this embodiment, the low-smoke halogen-free room temperature self-crosslinking flame-retardant polyolefin material is prepared according to the following steps: Step S1: introducing active acrylic acid ester side chains into the EVA molecular chain through a gradient free radical graft copolymerization reaction to prepare a graft-modified base resin.

[0029] In this example, acrylate branches containing active functional groups were introduced onto the EVA molecular chain via free radical graft copolymerization. This graft copolymerization reaction includes a primary reaction and a side reaction. The primary reaction is that tertiary hydrocarbons (-CH(CH3)-) on the EVA molecular chain, triggered by peroxide, form free radical active sites, which then graft copolymerize with the acrylate monomer. The side reaction is the homopolymerization of the acrylate monomer, which is controlled by controlling the monomer concentration and reaction temperature.

[0030] This embodiment achieves the introduction of active sites and the regulation of topological structure through grafting modification. As an optional example, in this embodiment, the acrylate monomer is a mixture of butyl acrylate and glycidyl methacrylate. Butyl acrylate provides a flexible long chain, which can improve the overall flexibility of the molecular chain and is conducive to promoting the subsequent metal ion migration and coordination cross-linking at room temperature. Glycidyl methacrylate introduces epoxy groups, which can subsequently react with the surface hydroxyl groups of nano-aluminum hydroxide modified with a silane coupling agent to improve the dispersibility of nano-aluminum hydroxide in the resin matrix. The carboxyl groups generated by the side reaction can subsequently react with Zn 2+ / Cu 2+ Form ionic bonds and strengthen the cross-linking network.

[0031] The following is a detailed description of the method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of this embodiment in a specific scenario. In this embodiment, the graft-modified base resin is prepared as follows: The EVA resin was preheated to 110°C by shear mixing at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a molten EVA resin, and the torque value of the molten EVA resin was obtained by monitoring. To 100 parts by weight of molten EVA resin, add 2-6.5 parts by weight of an acrylate monomer and 0.004 parts by weight of benzoyl peroxide, raise the temperature to 115°C, and react at a shear speed of 40 rpm for 15 minutes. The acrylate monomer is a mixture of butyl acrylate and glycidyl methacrylate, wherein the weight ratio of butyl acrylate to glycidyl methacrylate is 3:1; Add 3-5.8 parts by weight of acrylic acid ester monomer and 0.005 parts by weight of benzoyl peroxide to the reaction melt, raise the temperature to 135° C., and react at a shear speed of 60 rpm for 25 minutes; 2 parts by weight of acrylic acid ester monomer was added to the reaction melt, the temperature was lowered to 110° C., and the reaction was continued at a shear speed of 30 rpm; The torque value of the reaction melt is monitored in real time. When the torque value of the reaction melt reaches twice the torque value of the molten EVA resin, liquid CO2 is injected into the reaction melt to quench the reaction and obtain a graft-modified matrix resin.

[0032] In this example, by segmented temperature and time control and torque monitoring, a balance was established between grafting efficiency, degradation, and branch length to achieve a "comb-like" polymer structure. The double bonds and epoxy groups at the ends of the grafted chains became active reaction sites for subsequent room-temperature cross-linking. Quenching the reaction with liquid CO2 preserved the unsaturated double bonds and epoxy groups.

[0033] In practical applications, this embodiment can achieve the precise introduction of room-temperature cross-linking active reaction sites, enhance the interfacial interaction energy between the flame retardant phase and the resin matrix, improve the dispersion uniformity of the flame retardant phase in the resin matrix, and reduce the crystallinity of the EVA resin, thereby improving the flexibility of the material.

[0034] Step S2: preparing a room temperature pre-crosslinked flame retardant composite material comprising a modified matrix resin, a flame retardant phase, a composite peroxide initiator and a metal coordination catalyst by segmented temperature-controlled mixing.

[0035] The following is a detailed description of the method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of this embodiment in a specific scenario. In this embodiment, the room-temperature pre-crosslinking flame-retardant composite material is prepared as follows: In a dynamic nitrogen protective atmosphere, the -1 100 parts by weight of the modified base resin, 35 parts by weight of the maleic anhydride grafted polyolefin elastomer and 20 parts by weight of the nano-aluminum hydroxide powder with an average particle size of 500 nm and surface modified with a silane coupling agent were premixed at 70° C. for 15 minutes at a shear rate of 100 parts by weight. Add 5.2 parts by weight of composite peroxide initiator to the mixture and incubate at 65°C for 250 seconds. -1 The mixed material is mixed for 20 minutes at a shear rate of , wherein the composite peroxide initiator consists of 2.2 parts by weight of dicumyl peroxide, 1.5 parts by weight of tetrahydrofuran peroxide and 1.5 parts by weight of diisopropyl peroxydicarbonate; 1.8 parts by weight of metal coordination catalyst was added to the mixture and heated at 60°C for 350s. -1 The mixture was mixed at a shear rate of 1:1 for 20 minutes. The metal coordination catalyst was prepared as follows: copper acetylacetonate and zinc acetylacetonate were dissolved in an organic solvent at a molar ratio of Cu:Zn=1:1.5, 2,2'-bipyridine was used as a ligand, and the mixture was refluxed at 60°C for 2 hours, followed by removal of the solvent by rotary evaporation to prepare the metal coordination catalyst; The mixed material system was heated to 70°C for 250 seconds. -1 The mixture was mixed for 20 min at a shear rate of 100 nm to obtain a room temperature pre-crosslinked flame retardant composite material.

[0036] In this embodiment, the grafting active sites in step S1 are used to construct a dynamic vulcanization precursor with a cross-linked network prototype; the nano-aluminum hydroxide powder modified with a silane coupling agent is uniformly dispersed in the matrix through the action of the shear field, and the flame retardant is chemically bonded to the epoxy groups retained by the liquid CO2 quenching reaction on the graft chain, thereby improving the interfacial bonding force and avoiding the loss of mechanical properties of the matrix resin; the Cu of the metal coordination catalyst 2+ / Zn 2+ Coordination with the carboxyl / epoxy groups of the grafted chains can reduce the crosslinking activation energy, thereby achieving room temperature crosslinking in subsequent processes. In step S2 of this embodiment, the material is dispersed while suppressing the decomposition of the initiator by temperature control.

[0037] Step S3: The room temperature and AC flame retardant composite material is molded and converted into pre-crosslinked structural pellets through the coupling of shear field and thermal field.

[0038] In this embodiment, the non-equilibrium composite system containing the unactivated initiator, the dispersed flame retardant and the metal coordination catalyst constructed in step S2 is converted into a cross-linkable precursor through the coupling of the shear field and the thermal field.

[0039] The following is a detailed description of the method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material of this embodiment in a specific scenario. In this embodiment, the pre-crosslinked structural pellets are prepared in the following manner: A co-rotating twin-screw extruder is used to dynamically vulcanize and extrude a room-temperature pre-crosslinked flame-retardant composite material. The twin-screw speed is 250-350 rpm, the pressure of the vulcanization molding die is 12-15 MPa, and multiple temperature fields with increasing temperatures are sequentially set on the extrusion path. The temperature ranges of the temperature fields are 80-85°C, 85-90°C, 90-95°C, 95-100°C, and 100-105°C, respectively. The extruded melt is underwater pelletized, and the obtained material particles are vacuum dried to produce pre-crosslinked structural pellets.

[0040] In this embodiment, through dynamic vulcanization extrusion at 80-105°C, the shear force causes the peroxide bonds to break, the activation energy to decrease, and the decomposition of part of the peroxide in the room temperature pre-crosslinked flame retardant composite material is triggered to form 10-15% primary crosslinking points.

[0041] In this step, the non-uniform cross-linked network formed by dynamic vulcanization extrusion has a high degree of surface cross-linking, providing a cross-linking template for subsequent deep cross-linking at room temperature; at the same time, dynamic vulcanization extrusion enables the aluminum hydroxide powder to form a three-dimensional thermal conductive network in the matrix, thereby improving thermal conductivity and promoting the rapid formation of a surface carbon layer during combustion.

[0042] Step S4: Extruding the pre-crosslinked structural pellets and allowing them to stand at room temperature to obtain a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material.

[0043] In this embodiment, the pre-crosslinked structural pellets are extruded and then placed in a room temperature environment. After standing for 8-18 hours, a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material is prepared.

[0044] Example 2 1. Preparation of graft-modified matrix resin: The EVA resin was preheated to 110°C by shear mixing at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a molten EVA resin, and the torque value of the molten EVA resin was obtained by monitoring. To 100 parts by weight of molten EVA resin, 2 parts by weight of an acrylate monomer and 0.004 parts by weight of benzoyl peroxide were added, the temperature was raised to 115° C., and the reaction was carried out at a shear speed of 40 rpm for 15 minutes. The acrylate monomer was a mixture of butyl acrylate and glycidyl methacrylate, wherein the weight ratio of butyl acrylate to glycidyl methacrylate was 3:1; Add 5.8 parts by weight of acrylic acid ester monomer and 0.005 parts by weight of benzoyl peroxide to the reaction melt, raise the temperature to 135° C., and react at a shear speed of 60 rpm for 25 minutes; 2 parts by weight of acrylic acid ester monomer was added to the reaction melt, the temperature was lowered to 110° C., and the reaction was continued at a shear speed of 30 rpm; The torque value of the reaction melt is monitored in real time. When the torque value of the reaction melt reaches twice the torque value of the molten EVA resin, liquid CO2 is injected into the reaction melt to quench the reaction and obtain a graft-modified matrix resin.

[0045] 2. Preparation of room temperature pre-crosslinked flame retardant composite materials: In a dynamic nitrogen protective atmosphere, the -1 100 parts by weight of the modified base resin, 35 parts by weight of the maleic anhydride grafted polyolefin elastomer and 20 parts by weight of the nano-aluminum hydroxide powder with an average particle size of 500 nm and surface modified with a silane coupling agent were premixed at 70° C. for 15 minutes at a shear rate of 100 parts by weight. Add 5.2 parts by weight of composite peroxide initiator to the mixture and incubate at 65°C for 250 seconds. -1 The mixed material is mixed for 20 minutes at a shear rate of , wherein the composite peroxide initiator consists of 2.2 parts by weight of dicumyl peroxide, 1.5 parts by weight of tetrahydrofuran peroxide and 1.5 parts by weight of diisopropyl peroxydicarbonate; 1.8 parts by weight of metal coordination catalyst was added to the mixture and heated at 60°C for 350s. -1The mixture was mixed at a shear rate of 1:1 for 20 minutes. The metal coordination catalyst was prepared as follows: copper acetylacetonate and zinc acetylacetonate were dissolved in an organic solvent at a molar ratio of Cu:Zn=1:1.5, 2,2'-bipyridine was used as a ligand, and the mixture was refluxed at 60°C for 2 hours, followed by removal of the solvent by rotary evaporation to prepare the metal coordination catalyst; The mixed material system was heated to 70°C for 250 seconds. -1 The mixture was mixed for 20 min at a shear rate of 100 nm to obtain a room temperature pre-crosslinked flame retardant composite material.

[0046] 3. Preparation of pre-crosslinked structural granules A co-rotating twin-screw extruder is used to dynamically vulcanize and extrude a room-temperature pre-crosslinked flame-retardant composite material. The twin-screw speed is 250-350 rpm, the pressure of the vulcanization molding die is 12-15 MPa, and multiple temperature fields with increasing temperatures are sequentially set on the extrusion path. The temperature ranges of the temperature fields are 80-85°C, 85-90°C, 90-95°C, 95-100°C, and 100-105°C, respectively. The extruded melt is underwater pelletized, and the obtained material particles are vacuum dried to produce pre-crosslinked structural pellets.

[0047] 4. Preparation of low-smoke halogen-free room temperature self-crosslinking flame-retardant polyolefin materials The pre-crosslinked structural pellets were extruded and allowed to stand at room temperature to obtain a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material, and the standing time at room temperature was 8 hours.

[0048] Example 3 1. Preparation of graft-modified matrix resin: The EVA resin was preheated to 110°C by shear mixing at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a molten EVA resin, and the torque value of the molten EVA resin was obtained by monitoring. To 100 parts by weight of molten EVA resin, 3.3 parts by weight of an acrylate monomer and 0.004 parts by weight of benzoyl peroxide were added, the temperature was raised to 115° C., and the reaction was carried out at a shear speed of 40 rpm for 15 minutes. The acrylate monomer was a mixture of butyl acrylate and glycidyl methacrylate, wherein the weight ratio of butyl acrylate to glycidyl methacrylate was 3:1; Add 5.1 parts by weight of acrylic acid ester monomer and 0.005 parts by weight of benzoyl peroxide to the reaction melt, raise the temperature to 135° C., and react at a shear speed of 60 rpm for 25 minutes; 2 parts by weight of acrylic acid ester monomer was added to the reaction melt, the temperature was lowered to 110° C., and the reaction was continued at a shear speed of 30 rpm; The torque value of the reaction melt is monitored in real time. When the torque value of the reaction melt reaches twice the torque value of the molten EVA resin, liquid CO2 is injected into the reaction melt to quench the reaction and obtain a graft-modified matrix resin.

[0049] 2. Preparation of room temperature pre-crosslinked flame retardant composite materials: In a dynamic nitrogen protective atmosphere, the -1 100 parts by weight of the modified base resin, 35 parts by weight of the maleic anhydride grafted polyolefin elastomer and 20 parts by weight of the nano-aluminum hydroxide powder with an average particle size of 500 nm and surface modified with a silane coupling agent were premixed at 70° C. for 15 minutes at a shear rate of 100 parts by weight. Add 5.2 parts by weight of composite peroxide initiator to the mixture and incubate at 65°C for 250 seconds. -1 The mixed material is mixed for 20 minutes at a shear rate of , wherein the composite peroxide initiator consists of 2.2 parts by weight of dicumyl peroxide, 1.5 parts by weight of tetrahydrofuran peroxide and 1.5 parts by weight of diisopropyl peroxydicarbonate; 1.8 parts by weight of metal coordination catalyst was added to the mixture and heated at 60°C for 350s. -1 The mixture was mixed at a shear rate of 1:1 for 20 minutes. The metal coordination catalyst was prepared as follows: copper acetylacetonate and zinc acetylacetonate were dissolved in an organic solvent at a molar ratio of Cu:Zn=1:1.5, 2,2'-bipyridine was used as a ligand, and the mixture was refluxed at 60°C for 2 hours, followed by removal of the solvent by rotary evaporation to prepare the metal coordination catalyst; The mixed material system was heated to 70°C for 250 seconds. -1 The mixture was mixed for 20 min at a shear rate of 100 nm to obtain a room temperature pre-crosslinked flame retardant composite material.

[0050] 3. Preparation of pre-crosslinked structural granules A co-rotating twin-screw extruder is used to dynamically vulcanize and extrude a room-temperature pre-crosslinked flame-retardant composite material. The twin-screw speed is 250-350 rpm, the pressure of the vulcanization molding die is 12-15 MPa, and multiple temperature fields with increasing temperatures are sequentially set on the extrusion path. The temperature ranges of the temperature fields are 80-85°C, 85-90°C, 90-95°C, 95-100°C, and 100-105°C, respectively. The extruded melt is underwater pelletized, and the obtained material particles are vacuum dried to produce pre-crosslinked structural pellets.

[0051] 4. Preparation of low-smoke halogen-free room temperature self-crosslinking flame-retardant polyolefin materials The pre-crosslinked structural pellets were extruded and allowed to stand at room temperature to obtain a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material. The standing time at room temperature was 11 hours.

[0052] Example 4 1. Preparation of graft-modified matrix resin: The EVA resin was preheated to 110°C by shear mixing at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a molten EVA resin, and the torque value of the molten EVA resin was obtained by monitoring. To 100 parts by weight of molten EVA resin, 4.5 parts by weight of an acrylate monomer and 0.004 parts by weight of benzoyl peroxide were added, the temperature was raised to 115° C., and the reaction was carried out at a shear speed of 40 rpm for 15 minutes. The acrylate monomer was a mixture of butyl acrylate and glycidyl methacrylate, wherein the weight ratio of butyl acrylate to glycidyl methacrylate was 3:1; Add 4.4 parts by weight of acrylic acid ester monomer and 0.005 parts by weight of benzoyl peroxide to the reaction melt, raise the temperature to 135° C., and react at a shear speed of 60 rpm for 25 minutes; 2 parts by weight of acrylic acid ester monomer was added to the reaction melt, the temperature was lowered to 110° C., and the reaction was continued at a shear speed of 30 rpm; The torque value of the reaction melt is monitored in real time. When the torque value of the reaction melt reaches twice the torque value of the molten EVA resin, liquid CO2 is injected into the reaction melt to quench the reaction and obtain a graft-modified matrix resin.

[0053] 2. Preparation of room temperature pre-crosslinked flame retardant composite materials: In a dynamic nitrogen protective atmosphere, the -1 100 parts by weight of the modified base resin, 35 parts by weight of the maleic anhydride grafted polyolefin elastomer and 20 parts by weight of the nano-aluminum hydroxide powder with an average particle size of 500 nm and surface modified with a silane coupling agent were premixed at 70° C. for 15 minutes at a shear rate of 100 parts by weight. Add 5.2 parts by weight of composite peroxide initiator to the mixture and incubate at 65°C for 250 seconds. -1 The mixed material is mixed for 20 minutes at a shear rate of , wherein the composite peroxide initiator consists of 2.2 parts by weight of dicumyl peroxide, 1.5 parts by weight of tetrahydrofuran peroxide and 1.5 parts by weight of diisopropyl peroxydicarbonate; 1.8 parts by weight of metal coordination catalyst was added to the mixture and heated at 60°C for 350s. -1 The mixture was mixed at a shear rate of 1:1 for 20 minutes. The metal coordination catalyst was prepared as follows: copper acetylacetonate and zinc acetylacetonate were dissolved in an organic solvent at a molar ratio of Cu:Zn=1:1.5, 2,2'-bipyridine was used as a ligand, and the mixture was refluxed at 60°C for 2 hours, followed by removal of the solvent by rotary evaporation to prepare the metal coordination catalyst; The mixed material system was heated to 70°C for 250 seconds.-1 The mixture was mixed for 20 min at a shear rate of 100 nm to obtain a room temperature pre-crosslinked flame retardant composite material.

[0054] 3. Preparation of pre-crosslinked structural granules A co-rotating twin-screw extruder is used to dynamically vulcanize and extrude a room-temperature pre-crosslinked flame-retardant composite material. The twin-screw speed is 250-350 rpm, the pressure of the vulcanization molding die is 12-15 MPa, and multiple temperature fields with increasing temperatures are sequentially set on the extrusion path. The temperature ranges of the temperature fields are 80-85°C, 85-90°C, 90-95°C, 95-100°C, and 100-105°C, respectively. The extruded melt is underwater pelletized, and the obtained material particles are vacuum dried to produce pre-crosslinked structural pellets.

[0055] 4. Preparation of low-smoke halogen-free room temperature self-crosslinking flame-retardant polyolefin materials The pre-crosslinked structural pellets were extruded and allowed to stand at room temperature to obtain a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material. The standing time at room temperature was 13 hours.

[0056] Example 5 1. Preparation of graft-modified matrix resin: The EVA resin was preheated to 110°C by shear mixing at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a molten EVA resin, and the torque value of the molten EVA resin was obtained by monitoring. To 100 parts by weight of molten EVA resin, 5.1 parts by weight of an acrylate monomer and 0.004 parts by weight of benzoyl peroxide were added, the temperature was raised to 115° C., and the reaction was carried out at a shear speed of 40 rpm for 15 minutes. The acrylate monomer was a mixture of butyl acrylate and glycidyl methacrylate, wherein the weight ratio of butyl acrylate to glycidyl methacrylate was 3:1; Add 3.7 parts by weight of acrylic acid ester monomer and 0.005 parts by weight of benzoyl peroxide to the reaction melt, raise the temperature to 135° C., and react at a shear speed of 60 rpm for 25 minutes; 2 parts by weight of acrylic acid ester monomer was added to the reaction melt, the temperature was lowered to 110° C., and the reaction was continued at a shear speed of 30 rpm; The torque value of the reaction melt is monitored in real time. When the torque value of the reaction melt reaches twice the torque value of the molten EVA resin, liquid CO2 is injected into the reaction melt to quench the reaction and obtain a graft-modified matrix resin.

[0057] 2. Preparation of room temperature pre-crosslinked flame retardant composite materials: In a dynamic nitrogen protective atmosphere, the -1100 parts by weight of the modified base resin, 35 parts by weight of the maleic anhydride grafted polyolefin elastomer and 20 parts by weight of the nano-aluminum hydroxide powder with an average particle size of 500 nm and surface modified with a silane coupling agent were premixed at 70° C. for 15 minutes at a shear rate of 100 parts by weight. Add 5.2 parts by weight of composite peroxide initiator to the mixture and incubate at 65°C for 250 seconds. -1 The mixed material is mixed for 20 minutes at a shear rate of , wherein the composite peroxide initiator consists of 2.2 parts by weight of dicumyl peroxide, 1.5 parts by weight of tetrahydrofuran peroxide and 1.5 parts by weight of diisopropyl peroxydicarbonate; 1.8 parts by weight of metal coordination catalyst was added to the mixture and heated at 60°C for 350s. -1 The mixture was mixed at a shear rate of 1:1 for 20 minutes. The metal coordination catalyst was prepared as follows: copper acetylacetonate and zinc acetylacetonate were dissolved in an organic solvent at a molar ratio of Cu:Zn=1:1.5, 2,2'-bipyridine was used as a ligand, and the mixture was refluxed at 60°C for 2 hours, followed by removal of the solvent by rotary evaporation to prepare the metal coordination catalyst; The mixed material system was heated to 70°C for 250 seconds. -1 The mixture was mixed for 20 min at a shear rate of 100 nm to obtain a room temperature pre-crosslinked flame retardant composite material.

[0058] 3. Preparation of pre-crosslinked structural granules A co-rotating twin-screw extruder is used to dynamically vulcanize and extrude a room-temperature pre-crosslinked flame-retardant composite material. The twin-screw speed is 250-350 rpm, the pressure of the vulcanization molding die is 12-15 MPa, and multiple temperature fields with increasing temperatures are sequentially set on the extrusion path. The temperature ranges of the temperature fields are 80-85°C, 85-90°C, 90-95°C, 95-100°C, and 100-105°C, respectively. The extruded melt is underwater pelletized, and the obtained material particles are vacuum dried to produce pre-crosslinked structural pellets.

[0059] 4. Preparation of low-smoke halogen-free room temperature self-crosslinking flame-retardant polyolefin materials The pre-crosslinked structural pellets were extruded and allowed to stand at room temperature to obtain a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material. The standing time at room temperature was 16 hours.

[0060] Example 6 1. Preparation of graft-modified matrix resin: The EVA resin was preheated to 110°C by shear mixing at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a molten EVA resin, and the torque value of the molten EVA resin was obtained by monitoring. To 100 parts by weight of molten EVA resin, 6.5 parts by weight of an acrylate monomer and 0.004 parts by weight of benzoyl peroxide were added, the temperature was raised to 115° C., and the mixture was reacted at a shear speed of 40 rpm for 15 minutes. The acrylate monomer was a mixture of butyl acrylate and glycidyl methacrylate, wherein the weight ratio of butyl acrylate to glycidyl methacrylate was 3:1. Add 3 parts by weight of acrylic acid ester monomer and 0.005 parts by weight of benzoyl peroxide to the reaction melt, raise the temperature to 135° C., and react at a shear speed of 60 rpm for 25 minutes; 2 parts by weight of acrylic acid ester monomer was added to the reaction melt, the temperature was lowered to 110° C., and the reaction was continued at a shear speed of 30 rpm; The torque value of the reaction melt is monitored in real time. When the torque value of the reaction melt reaches twice the torque value of the molten EVA resin, liquid CO2 is injected into the reaction melt to quench the reaction and obtain a graft-modified matrix resin.

[0061] 2. Preparation of room temperature pre-crosslinked flame retardant composite materials: In a dynamic nitrogen protective atmosphere, the -1 100 parts by weight of the modified base resin, 35 parts by weight of the maleic anhydride grafted polyolefin elastomer and 20 parts by weight of the nano-aluminum hydroxide powder with an average particle size of 500 nm and surface modified with a silane coupling agent were premixed at 70° C. for 15 minutes at a shear rate of 100 parts by weight. Add 5.2 parts by weight of composite peroxide initiator to the mixture and incubate at 65°C for 250 seconds. -1 The mixed material is mixed for 20 minutes at a shear rate of , wherein the composite peroxide initiator consists of 2.2 parts by weight of dicumyl peroxide, 1.5 parts by weight of tetrahydrofuran peroxide and 1.5 parts by weight of diisopropyl peroxydicarbonate; 1.8 parts by weight of metal coordination catalyst was added to the mixture and heated at 60°C for 350s. -1 The mixture was mixed at a shear rate of 1:1 for 20 minutes. The metal coordination catalyst was prepared as follows: copper acetylacetonate and zinc acetylacetonate were dissolved in an organic solvent at a molar ratio of Cu:Zn=1:1.5, 2,2'-bipyridine was used as a ligand, and the mixture was refluxed at 60°C for 2 hours, followed by removal of the solvent by rotary evaporation to prepare the metal coordination catalyst; The mixed material system was heated to 70°C for 250 seconds. -1 The mixture was mixed for 20 min at a shear rate of 100 nm to obtain a room temperature pre-crosslinked flame retardant composite material.

[0062] 3. Preparation of pre-crosslinked structural granules A co-rotating twin-screw extruder is used to dynamically vulcanize and extrude a room-temperature pre-crosslinked flame-retardant composite material. The twin-screw speed is 250-350 rpm, the pressure of the vulcanization molding die is 12-15 MPa, and multiple temperature fields with increasing temperatures are sequentially set on the extrusion path. The temperature ranges of the temperature fields are 80-85°C, 85-90°C, 90-95°C, 95-100°C, and 100-105°C, respectively. The extruded melt is underwater pelletized, and the obtained material particles are vacuum dried to produce pre-crosslinked structural pellets.

[0063] 4. Preparation of low-smoke halogen-free room temperature self-crosslinking flame-retardant polyolefin materials The pre-crosslinked structural pellets were extruded and allowed to stand at room temperature to obtain a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material. The standing time at room temperature was 18 hours.

[0064] Example 7 The microstructure of the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin materials prepared in Examples 3 and 5 was observed using a Zeiss Ultra Plus scanning electron microscope produced by Zeiss AG of Germany. The experimental process and test parameters included: spraying gold on the sample and evenly dispersing it on the conductive adhesive, and sticking it on the sample stage for observation using the instrument. The acceleration voltage was 5 kV. Figure 2 This is a SEM image of the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material prepared according to Example 3 of the present application. Figure 3 This is a SEM image of the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material prepared according to Example 5 of the present application. Figure 2 and Figure 3 As shown, the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material prepared in the embodiment of the present application has nano-aluminum hydroxide surface-modified with a silane coupling agent evenly distributed in the resin matrix.

[0065] Transmission electron microscopy (TEM, JEM-2100F, JEOL, Japan) was used to characterize the morphology and structure of the pre-crosslinked structured pellets prepared in Examples 2, 4, and 6. The experimental process was as follows: the material was dispersed in an ethanol solution, dropped onto a copper grid, and observed using the instrument. Figure 4 TEM image of the pre-crosslinked structured pellets prepared according to Example 2 of the present application, Figure 5 TEM image of the pre-crosslinked structured pellets prepared according to Example 4 of the present application, Figure 6 TEM image of the pre-crosslinked structured pellets prepared according to Example 6 of the present application, as shown in FIG. Figure 4 、 Figure 5 and Figure 6 As shown, by dynamic sulfurization extrusion, the metal ions in the metal coordination catalyst are oriented along the shear field, that is, Cu 2+ / Zn 2+Enrichment along the shear streamline direction.

[0066] The crosslinking degree of the low-smoke, halogen-free, room-temperature, self-crosslinking, flame-retardant polyolefin materials prepared in Examples 2 to 6 of this application was tested according to ASTM D2765-16 Standard Test Methods for Determination of Gel Content and Swell Ratio of Crosslinked Ethylene Plastics. The uncrosslinked portion was extracted with toluene solvent, and the remaining insoluble mass percentage was determined as the crosslinking degree. The crosslinking degrees of the low-smoke, halogen-free, room-temperature, self-crosslinking, flame-retardant polyolefin materials prepared in Examples 2 to 6 of this application are shown in Table 1 below.

[0067] Table 1

[0068] As shown in Table 1, the low-smoke, halogen-free, room-temperature self-crosslinking, flame-retardant polyolefin material prepared in the examples of the present application has a crosslinking degree of up to 77% after standing for 8 hours. Among them, the low-smoke, halogen-free, room-temperature self-crosslinking, flame-retardant polyolefin material prepared in Example 4 has a crosslinking degree of up to 85% after standing for 13 hours.

[0069] According to the performance requirements of halogen-free, low-smoke, flame-retardant cross-linked polyolefin insulation materials in "GB / T 32129 Halogen-free, low-smoke, flame-retardant cable materials for wires and cables", the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin materials prepared in Examples 2 to 6 of the present application were tested. The test results are shown in Table 2 below.

[0070] Table 2

[0071] As can be seen from Table 2, the volume resistivity of the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material prepared in the embodiment of the present application at 20°C is not less than 1.2×10 12 Ω·m, dielectric strength is not less than 26MV / m, oxygen index is not less than 32%, and smoke density is not more than 30 under flame conditions, indicating that the material has excellent insulating electrical properties and flame retardant properties.

[0072] According to the non-electrical requirements for halogen-free and low-smoke cross-linked polyolefin insulation in "JB / T 10491-2022 Cross-linked Polyolefin Insulated Wires and Cables with Rated Voltages of 450 / 750V and Below", the low-smoke and halogen-free room-temperature self-cross-linking flame-retardant polyolefin materials prepared in Examples 2 to 6 of the present application were tested. The test results are shown in Table 3 below.

[0073] Table 3

[0074] As can be seen from Table 3, the room temperature self-crosslinking flame-retardant insulating material prepared in the embodiment of the present application has a tensile strength of not less than 17.5 MPa and an elongation at break of not less than 201%; the hot extension elongation at 200°C and a load of 0.2 MPa is not more than 25%, and the elongation after hot extension cooling is not more than 9%; the thermal shrinkage rate at 180°C is less than 1%, the low-temperature bending test at -20°C does not crack, and the elongation at -20°C is not less than 135%, indicating that the material has excellent mechanical and physical properties and environmental performance.

[0075] In practical applications, the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material and the preparation method thereof according to the embodiments of the present application have the following beneficial technical effects: 1. Through gradient free radical graft copolymerization, active acrylate branches are introduced into the EVA molecular chain. Combined with a composite peroxide initiator and a metal ion catalyst system, crosslinking is achieved within 8-18 hours at room temperature (20-25°C), with a crosslinking degree of no less than 77%. This eliminates reliance on high temperatures, steam, or radiation, reducing process energy consumption by over 60% and significantly increasing crosslinking speed. Real-time torque monitoring and segmented temperature control prevent localized over- or under-crosslinking.

[0076] 2. Through the precise introduction of room temperature cross-linking active reaction sites, the interaction energy between the flame retardant phase and the resin matrix is improved. By modifying the surface of nano-aluminum hydroxide, the surface carboxyl groups are chemically bonded with the epoxy groups of the grafted chains, which significantly improves the dispersion uniformity of the flame retardant and reduces the crystallinity of the EVA resin. While improving the flame retardant efficiency of the resin material, the flexibility is also improved, and the oxygen index is not less than 35%.

[0077] 3. Through dynamic vulcanization extrusion, the grafting active sites are used to construct a dynamic vulcanization precursor with a cross-linked network prototype. The flame retardant is chemically bonded to the epoxy groups on the grafted chain to enhance the interfacial bonding strength and avoid the loss of mechanical properties of the matrix resin. 2+ / Zn 2+ Coordination with the carboxyl / epoxy groups of the grafted chains can reduce the cross-linking activation energy, thereby achieving room temperature cross-linking in subsequent processes.

[0078] 4. It does not contain halogen elements or biotoxic organic tin catalysts, which improves the environmental friendliness of the process and products.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material, characterized in that: The method comprises: Step S1: introducing active acrylic acid ester branches into the EVA molecular chain through a gradient free radical graft copolymerization reaction to prepare a graft-modified base resin; Step S2: preparing a room temperature pre-crosslinked flame retardant composite material comprising a modified matrix resin, a flame retardant phase, a composite peroxide initiator and a metal coordination catalyst by segmented temperature-controlled mixing; Step S3: by coupling the shear field and the thermal field, the room temperature and AC flame retardant composite material is molded into a pre-crosslinked structure pellet; Step S4: Extruding the pre-crosslinked structural pellets and allowing them to stand at room temperature to obtain a low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material.

2. The method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to claim 1, characterized in that: Step S1 includes: The EVA resin was preheated to 110°C by shear mixing at a heating rate of 10°C / min in a nitrogen atmosphere to obtain a molten EVA resin, and the torque value of the molten EVA resin was obtained by monitoring. Add 2-6.5 parts by weight of acrylic acid ester monomer and 0.004 parts by weight of benzoyl peroxide to 100 parts by weight of molten EVA resin, raise the temperature to 115°C, and react at a shear speed of 40 rpm for 15 minutes; Add 3-5.8 parts by weight of acrylic acid ester monomer and 0.005 parts by weight of benzoyl peroxide to the reaction melt, raise the temperature to 135° C., and react at a shear speed of 60 rpm for 25 minutes; 2 parts by weight of acrylic acid ester monomer was added to the reaction melt, the temperature was lowered to 110° C., and the reaction was continued at a shear speed of 30 rpm; The torque value of the reaction melt is monitored in real time. When the torque value of the reaction melt reaches twice the torque value of the molten EVA resin, liquid CO2 is injected into the reaction melt to quench the reaction and obtain a graft-modified matrix resin.

3. The method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to claim 2, characterized in that: In step S1 , the acrylic ester monomer is a mixture of butyl acrylate and glycidyl methacrylate, wherein the weight ratio of butyl acrylate to glycidyl methacrylate is 3:

1.

4. The method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to claim 1, characterized in that: Step S2 includes: In a dynamic nitrogen protective atmosphere, the -1 100 parts by weight of the modified base resin, 35 parts by weight of the maleic anhydride grafted polyolefin elastomer and 20 parts by weight of the nano-aluminum hydroxide powder with an average particle size of 500 nm and surface modified with a silane coupling agent were premixed at 70° C. for 15 minutes at a shear rate of 100 parts by weight. Add 5.2 parts by weight of composite peroxide initiator to the mixture and incubate at 65°C for 250 seconds. -1 The mixed material was mixed for 20 min at a shear rate of 1.8 parts by weight of metal coordination catalyst was added to the mixture and heated at 60°C for 350s. -1 The mixed material was mixed for 20 min at a shear rate of The mixed material system was heated to 70°C for 250 seconds. -1 The mixture was mixed for 20 min at a shear rate of 100 nm to obtain a room temperature pre-crosslinked flame retardant composite material.

5. The method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to claim 4, characterized in that: In step S2, the composite peroxide initiator consists of 2.2 parts by weight of dicumyl peroxide, 1.5 parts by weight of tetrahydrofuran peroxide, and 1.5 parts by weight of diisopropyl peroxydicarbonate.

6. The method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to claim 4, characterized in that: In step S2, copper acetylacetonate and zinc acetylacetonate are dissolved in an organic solvent at a molar ratio of Cu:Zn=1:1.5, 2,2'-bipyridine is used as a ligand, and the reaction is refluxed at 60°C for 2 hours, followed by rotary evaporation to remove the solvent to prepare a metal coordination catalyst.

7. The method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to claim 1, characterized in that: Step S3 includes: using a co-rotating twin-screw extruder to dynamically vulcanize and extrude the room temperature pre-crosslinked flame retardant composite material, sequentially setting multiple temperature fields with increasing temperatures on the extrusion path, underwater pelletizing the extruded melt, and vacuum drying the obtained material particles to obtain pre-crosslinked structural pellets.

8. The method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to claim 7, characterized in that: In step S3, the rotation speed of the twin screw is 250-350 rpm, the pressure of the vulcanization molding die is 12-15 MPa, and the temperature ranges of the temperature field zones are 80-85°C, 85-90°C, 90-95°C, 95-100°C, and 100-105°C, respectively.

9. The method for preparing the low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material according to claim 1, characterized in that: In step S4, the time of standing at room temperature is 8-18 hours.

10. A low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material, characterized in that: The low-smoke, halogen-free, room-temperature self-crosslinking flame-retardant polyolefin material is prepared according to the method according to any one of claims 1-9.

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