A high strength flame retardant cable jacket material and method of making the same

Abstract

The application discloses a kind of high-strength flame-retardant cable sheath materials and preparation method thereof, belong to cable sheath material technical field.The material includes matrix resin component, carbon-forming carrier component, flame-retardant component, compatibilizer, synergistic carbon-forming agent and auxiliary agent;Wherein, carbon-forming carrier component is composed of lignin graft, ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer, and flame-retardant component is composed of ammonium polyphosphate surface modified by silane coupling agent and zinc borate.Preparation time, first prepare carbon-forming carrier component and flame-retardant component, then melt blend extrusion with matrix resin component.Through the preferential wetting, coating and enrichment of carbon-forming carrier component to flame-retardant component, reduce the damage of flame-retardant component to matrix resin continuous structure;Carbon-forming carrier and flame-retardant component cooperate to form dense carbon layer when burning.The material has higher mechanical strength and flame-retardant performance.

Description

Technical Field

[0001] This invention belongs to the technical field of cable sheath materials, and relates to a high-strength flame-retardant cable sheath material and its preparation method. Background Technology

[0002] Cable sheathing materials, as an important component of wires and cables, are mainly used to protect the conductors from mechanical damage, environmental corrosion, and external impacts, thereby ensuring the safe and stable operation of the cables. With the rapid development of power transmission, rail transportation, new energy vehicles, and communication equipment, the performance requirements for cable sheathing materials are constantly increasing. They are required not only to have good mechanical strength, wear resistance, and impact resistance, but also excellent flame retardant properties to improve the safety of cables during use.

[0003] Currently, to improve the flame retardant properties of cable sheath materials, a large amount of inorganic flame retardant filler is typically added to the polymer matrix. However, as the amount of flame retardant added increases, it easily leads to a decrease in the interfacial bonding force within the material, resulting in a reduction in tensile strength, tear resistance, and abrasion resistance. It also affects the material's processing performance and service life. Therefore, existing flame-retardant cable sheath materials generally suffer from the problem of balancing flame retardant performance and mechanical strength, making it difficult to meet the comprehensive requirements of high strength and high flame retardant performance for cable sheath materials under complex working conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a high-strength flame-retardant cable sheath material and its preparation method, so as to solve the problem that it is difficult to balance the flame-retardant performance and mechanical strength of existing flame-retardant cable sheath materials.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a high-strength flame-retardant cable sheath material, comprising the following components in parts by weight: 70-85 parts of matrix resin component, 15-25 parts of char-forming carrier component, 18-28 parts of flame-retardant component, 3-6 parts of compatibilizer, 2-4 parts of synergistic char-forming agent, and 1.5-3 parts of additives.

[0007] The char-forming carrier component is composed of lignin grafted material, ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer in a mass ratio of (30-50):(30-40):(20-30);

[0008] The flame retardant component is composed of ammonium polyphosphate and zinc borate, which have been surface modified with silane coupling agent, in a mass ratio of (4-6):1.

[0009] Preferably, the matrix resin component is composed of polyethylene and polyolefin elastomer in a mass ratio of (60-85):(15-40).

[0010] Preferably, the polyethylene is linear low-density polyethylene, and the polyolefin elastomer is ethylene-octene copolymer.

[0011] Preferably, the lignin graft is glycidyl methacrylate grafted lignin.

[0012] Preferably, the silane coupling agent is γ-aminopropyltriethoxysilane.

[0013] Preferably, the compatibilizer is maleic anhydride-grafted polyethylene.

[0014] Preferably, the synergistic char-forming agent is pentaerythritol phosphate.

[0015] Preferably, the additives include antioxidants and lubricants, wherein the antioxidant is one or both of hindered phenolic antioxidants and phosphite antioxidants, and the lubricant is polyethylene wax.

[0016] In a second aspect, the present invention provides a method for preparing a high-strength flame-retardant cable sheath material as described in the first aspect, comprising the following steps:

[0017] S1. The lignin graft, ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer are melt-blended and granulated to obtain the char carrier component.

[0018] S2. Surface modification of ammonium polyphosphate is performed using a silane coupling agent, and the modified ammonium polyphosphate is mixed with zinc borate to obtain a flame retardant component;

[0019] S3. Premix the matrix resin component, char carrier component, flame retardant component, compatibilizer, synergistic charring agent and additives to obtain a premix;

[0020] S4. The premixed material is melt-blended and extruded, cooled, and granulated to obtain a high-strength flame-retardant cable sheath material.

[0021] Preferably, the twin-screw extruder in step S4 has an aspect ratio of 44-48, a homogenization zone temperature of 170-185℃, and a screw speed of 280-350 rpm.

[0022] The beneficial effects of this invention are:

[0023] (1) This invention constructs a multiphase system consisting of a matrix resin component composed of polyethylene and polyolefin elastomers and a char-forming carrier component composed of lignin grafts, ethylene-vinyl acetate copolymers, and maleic anhydride grafted polyolefin elastomers. Silane coupling agents are used to modify the surface of ammonium polyphosphate, resulting in a stronger interfacial affinity between the flame-retardant component and the char-forming carrier component. During melt blending, the amino active groups on the surface of the modified ammonium polyphosphate can interact strongly with the hydroxyl and epoxy groups in the lignin grafts and the polar groups in the ethylene-vinyl acetate copolymer. Since polyethylene and polyolefin elastomers have relatively low overall polarity, the char-forming carrier component preferentially wets and coats the flame-retardant component particles, causing the flame-retardant component to tend to distribute within the area formed by the char-forming carrier component. As the melt blending process proceeds, the flame-retardant component gradually accumulates within the area formed by the char-forming carrier component and is stably retained during cooling and solidification, thereby reducing the amount of direct contact between the flame-retardant component and the matrix resin component. Compared to the numerous interfacial defects and stress concentrations caused by the random dispersion of flame-retardant fillers throughout the polymer matrix in traditional high-filler flame-retardant systems, this invention reduces the damage to the continuous structure of the matrix resin by controlling the spatial distribution of the flame-retardant components. This allows the matrix resin components to maintain good continuity and integrity, thereby improving the tensile strength and elongation at break of the material and achieving a synergistic improvement in high strength and high flame-retardant performance.

[0024] (2) The present invention uses lignin grafts, ethylene-vinyl acetate copolymers, and maleic anhydride-grafted polyolefin elastomers to construct the carbon carrier component. The lignin grafts have a high char formation rate, the ethylene-vinyl acetate copolymers can provide an auxiliary carbon source, and the maleic anhydride-grafted polyolefin elastomers help improve the system's compatibility and structural stability. When the material is exposed to flame, the polyphosphate released by the decomposition of ammonium polyphosphate can promote the rapid dehydration and char formation of the lignin grafts and ethylene-vinyl acetate copolymers. Zinc borate further improves the density and heat resistance of the carbon layer, thereby forming a continuous and stable organic-inorganic composite carbon layer and improving the material's heat insulation and oxygen barrier capabilities.

[0025] (3) This invention achieves excellent flame retardant performance with a low amount of flame retardant component added through the synergistic effect between ammonium polyphosphate, zinc borate, and pentaerythritol phosphate. Compared with traditional halogen-free flame retardant systems that require large amounts of magnesium hydroxide or aluminum hydroxide, this invention can effectively reduce the amount of flame retardant component, improve the processing fluidity and extrusion stability of the material, while maintaining a high oxygen index and excellent flame retardant rating.

[0026] (4) The preparation method used in this invention is simple and does not require additional construction of microcapsule structures or complex coating processes. The flame retardant components can be preferentially distributed in the char carrier components through conventional melt blending extrusion. The process is highly adaptable and easy to industrialize and continuously produce. It is applicable to fields such as power cables, rail transit cables, new energy vehicle cables and communication cables. Detailed Implementation

[0027] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0028] The following descriptions of some of the raw materials used in the examples and comparative examples are as follows:

[0029] The polyethylene used is linear low-density polyethylene: sourced from Lotte Chemicals, grade UR534.

[0030] The polyolefin elastomer is made of ethylene-octene copolymer: derived from Dow Chemical, grade 8411.

[0031] Ethylene-vinyl acetate copolymer: sourced from Sinopec Yanshan, grade 18J3.

[0032] Lignin graft: This is glycidyl methacrylate grafted modified lignin, and its preparation method is as follows:

[0033] (1) Preparation of acid-precipitated lignin: Alkali lignin (purchased from Sigma-Aldrich, brand name 471003, CAS: 8068-05-1) was added to deionized water, and the pH was adjusted to 10-11 with sodium hydroxide to prepare a 10% mass concentration solution. After stirring until completely dissolved, the pH was adjusted to 2-3 with dilute hydrochloric acid. The solution was stirred at 70℃ for 1 hour, allowed to stand to precipitate, filtered, washed with deionized water until neutral, and dried under vacuum at 60℃ to obtain acid-precipitated lignin.

[0034] (2) Lignin melt grafting modification: 100 parts of the above-mentioned acid-precipitated lignin, 15 parts of glycidyl methacrylate (GMA), 0.3 parts of dicumyl peroxide and 0.2 parts of liquid paraffin were added to a high-speed mixer and mixed at 300 rpm for 5 minutes at room temperature. Then, the premix was added to a co-rotating twin-screw extruder (L / D ratio L / D=46) for melt grafting reaction. The barrel temperature was set as follows: conveying section 120℃, melting section 150℃, reaction section 165℃, die head 160℃, and screw speed 200 rpm. The extrudate was cooled in a water bath, air-dried and pelletized to obtain the lignin graft. The softening point of the obtained product was 145-165℃, and the char yield (at 600℃ under nitrogen) was ≥43%.

[0035] Maleic anhydride-grafted polyolefin elastomer: This is a maleic anhydride-grafted ethylene-octene copolymer. Its preparation method is as follows: 100 parts of ethylene-octene copolymer (from Dow Chemical, grade 8411), 1.5 parts of maleic anhydride, 0.15 parts of dicumyl peroxide, and 0.2 parts of liquid paraffin are added to a high-speed mixer and mixed at 300 rpm for 5 minutes at room temperature. Then, the premix is ​​added to a co-rotating twin-screw extruder (L / D ratio = 46) for melt grafting. The barrel temperatures are set as follows: conveyor section 140℃, melt section 160℃, reaction section 175℃, die head 175℃, and screw speed 220 rpm. The extrudate is cooled in a water bath, air-dried, and pelletized to obtain the maleic anhydride-grafted polyolefin elastomer.

[0036] Maleic anhydride-grafted polyethylene: 100 parts of linear low-density polyethylene (from Lotte Chemicals, grade UR534), 1.5 parts of maleic anhydride, 0.15 parts of dicumyl peroxide, and 0.2 parts of liquid paraffin were added to a high-speed mixer and mixed at 300 rpm for 5 minutes at room temperature. The premix was then fed into a co-rotating twin-screw extruder (L / D ratio L / D = 46) for melt grafting. The barrel temperatures were set as follows: conveyor section 140℃, melt section 160℃, reaction section 170℃, die head 170℃, and screw speed 220 rpm. The extrudate was cooled in a water bath, air-dried, and pelletized to obtain maleic anhydride-grafted polyethylene.

[0037] Silane coupling agent: γ-aminopropyltriethoxysilane, purchased from Hangzhou Jessica Chemical Co., Ltd., brand name KH-550.

[0038] Ammonium polyphosphate: purchased from Jinan Nihuo New Materials Co., Ltd., model AP101.

[0039] Pentaerythritol phosphate: purchased from Jiangsu Liside New Materials Co., Ltd., CAS: 5301-78-0.

[0040] Zinc borate: Industrial grade, purchased from Shandong Yueyang New Materials Co., Ltd.

[0041] Polyethylene wax: Industrial grade, purchased from Jinan Huijinchuan Chemical Co., Ltd.

[0042] Magnesium hydroxide: Industrial grade, purchased from Jinan Chaoyixing Chemical Co., Ltd.

[0043] Except for the raw materials explicitly mentioned above, all other raw materials not specifically mentioned are conventional industrial-grade products that can be easily obtained through commercial channels.

[0044] Example 1

[0045] A high-strength flame-retardant cable sheath material, by weight, is composed of the following components:

[0046]

[0047] A method for preparing a high-strength flame-retardant cable sheath material includes the following steps:

[0048] S1. The lignin graft, ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer are added to a twin-screw extruder at a mass ratio of 40:35:25, melt-blended and granulated at 160°C to obtain the char carrier component.

[0049] S2. Ammonium polyphosphate was vacuum dried at 110℃ for 2 hours and then transferred to a high-speed mixer. 2.5% (by weight) of silane coupling agent KH-550 was added, and the mixture was stirred at 2000 rpm for 10 minutes at room temperature under nitrogen protection. Subsequently, it was heat-treated in an oven at 120℃ for 30 minutes to obtain modified ammonium polyphosphate. The modified ammonium polyphosphate and zinc borate were then mixed evenly in a high-speed mixer at a mass ratio of 4.4:1 to obtain the flame-retardant component.

[0050] S3. Add the matrix resin component, char carrier component, flame retardant component, maleic anhydride grafted polyethylene, pentaerythritol phosphate, antioxidant 1010, antioxidant 168 and polyethylene wax to a high-speed mixer according to the formula amount, and mix at room temperature and 300 rpm for 5 minutes to obtain a premix.

[0051] S4. Feed the premixed material into a co-rotating twin-screw extruder (length-to-diameter ratio L / D=46). Set the temperature as follows: conveying section 135℃, plasticizing section 160℃, homogenizing section 180℃, die head 165℃, screw speed 300 rpm. After extrusion, cool in a water tank, air dry, and pelletize to obtain high-strength flame-retardant cable sheath material pellets.

[0052] Example 2

[0053] A high-strength flame-retardant cable sheath material, by weight, is composed of the following components:

[0054]

[0055] A method for preparing a high-strength flame-retardant cable sheath material includes the following steps:

[0056] S1. The lignin graft, ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer are added to a twin-screw extruder at a mass ratio of 45:30:25, melt-blended and granulated at 160°C to obtain the char carrier component.

[0057] S2. Ammonium polyphosphate was vacuum dried at 110℃ for 2 hours and then transferred to a high-speed mixer. 2.5% (by weight) of silane coupling agent KH-550 was added, and the mixture was stirred at 2000 rpm for 10 minutes at room temperature under nitrogen protection. Subsequently, it was heat-treated in an oven at 120℃ for 30 minutes to obtain modified ammonium polyphosphate. The modified ammonium polyphosphate was then mixed with zinc borate at a mass ratio of 4:1 in a high-speed mixer until homogeneous to obtain the flame-retardant component.

[0058] S3. Add the matrix resin component, char carrier component, flame retardant component, maleic anhydride grafted polyethylene, pentaerythritol phosphate, antioxidant 1010, antioxidant 168 and polyethylene wax to a high-speed mixer according to the formula amount, and mix at room temperature and 300 rpm for 5 minutes to obtain a premix.

[0059] S4. Feed the premixed material into a co-rotating twin-screw extruder (length-to-diameter ratio L / D=46). Set the temperature as follows: conveying section 135℃, plasticizing section 160℃, homogenizing section 180℃, die head 165℃, screw speed 300 rpm. After extrusion, cool in a water tank, air dry, and pelletize to obtain high-strength flame-retardant cable sheath material pellets.

[0060] Example 3

[0061] A high-strength flame-retardant cable sheath material, by weight, is composed of the following components:

[0062]

[0063] A method for preparing a high-strength flame-retardant cable sheath material includes the following steps:

[0064] S1. The lignin graft, ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer are added to a twin-screw extruder at a mass ratio of 45:35:20, melt-blended and granulated at 160°C to obtain the char carrier component.

[0065] S2. Ammonium polyphosphate was vacuum dried at 110℃ for 2 hours and then transferred to a high-speed mixer. 2.5% (by weight) of silane coupling agent KH-550 was added, and the mixture was stirred at 2000 rpm for 10 minutes at room temperature under nitrogen protection. Subsequently, it was heat-treated in an oven at 120℃ for 30 minutes to obtain modified ammonium polyphosphate. The modified ammonium polyphosphate was then mixed with zinc borate at a mass ratio of 6:1 in a high-speed mixer until homogeneous to obtain the flame-retardant component.

[0066] S3. Add the matrix resin component, char carrier component, flame retardant component, maleic anhydride grafted polyethylene, pentaerythritol phosphate, antioxidant 1010, antioxidant 168 and polyethylene wax to a high-speed mixer according to the formula amount, and mix at room temperature and 300 rpm for 5 minutes to obtain a premix.

[0067] S4. Feed the premixed material into a co-rotating twin-screw extruder (length-to-diameter ratio L / D=46). Set the temperature as follows: conveying section 135℃, plasticizing section 160℃, homogenizing section 180℃, die head 165℃, screw speed 300 rpm. After extrusion, cool in a water tank, air dry, and pelletize to obtain high-strength flame-retardant cable sheath material pellets.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that instead of preparing premixed granules of carbon carrier components in advance, lignin grafts, ethylene-vinyl acetate copolymer, maleic anhydride grafted polyolefin elastomer, modified ammonium polyphosphate, zinc borate, linear low-density polyethylene, ethylene-octene copolymer, maleic anhydride grafted polyethylene, pentaerythritol phosphate, antioxidant 1010, antioxidant 168 and polyethylene wax are added to a high-speed mixer at once and mixed. Then, the mixture is melt-blended and extruded through a twin-screw extruder, cooled and granulated to obtain cable sheath material. The amount of other raw materials and processing parameters are the same as in Example 1.

[0070] Comparative Example 2

[0071] The difference from Example 1 is that: instead of using a silane coupling agent for surface modification, the unmodified ammonium polyphosphate is directly mixed with zinc borate at a mass ratio of 4.4:1 to obtain the flame retardant component; the other raw material types, amounts and processing parameters are the same as in Example 1.

[0072] Comparative Example 3

[0073] The difference from Example 1 is that no char carrier component premixed granules are added, and 20 parts of the char carrier component in Example 1 are replaced with 20 parts of the matrix resin component. After the replacement, the total amount of the matrix resin component is 98 parts, wherein the mass ratio of linear low-density polyethylene and ethylene-octene copolymer is the same as that of the matrix resin component in Example 1; the other raw material types, amounts and processing parameters are the same as those in Example 1.

[0074] Comparative Example 4

[0075] The difference from Example 1 is that no lignin grafting material is added, and the lignin grafting material in the char carrier component is replaced with an equal amount of ethylene-vinyl acetate copolymer. After the replacement, the char carrier component is composed of ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer in a mass ratio of 75:25. The other raw material types, amounts and processing parameters are the same as in Example 1.

[0076] Comparative Example 5

[0077] The difference from Example 1 is that maleic anhydride-grafted polyolefin elastomer is not added, and the char carrier component is composed of lignin graft and ethylene-vinyl acetate copolymer in a mass ratio of 40:35; the other raw material types, amounts and processing parameters are the same as in Example 1.

[0078] Comparative Example 6

[0079] The difference from Example 1 is that the modified ammonium polyphosphate and zinc borate in Example 1 are replaced with an equal amount of magnesium hydroxide, and no char-forming carrier component premixed granules are added. The char-forming carrier component is replaced with an equal amount of matrix resin component, and the total amount of matrix resin component after replacement is 98 parts. The mass ratio of linear low-density polyethylene and ethylene-octene copolymer is the same as that of matrix resin component in Example 1. The other raw material types, amounts and processing parameters are the same as those in Example 1.

[0080] Test case

[0081] The granules obtained in Examples 1-3 and Comparative Examples 1-6 were respectively molded into 2.0 mm thick test pieces at 170°C on a flat vulcanizing machine, cut into standard test samples, and subjected to the following performance tests.

[0082] 1. Tensile strength and elongation at break tests

[0083] Dumbbell-shaped specimens were used, with a total length of approximately 120 mm, a gauge length of 25 mm, a width of 6 mm for the parallel section in the middle, and a thickness of 2.0 mm. Before testing, the specimens were conditioned for 24 hours in an environment with a temperature of 23℃±2℃ and a relative humidity of 50%±10%. Tensile testing was performed on a universal testing machine with an initial clamping distance of 80 mm and a testing speed of 250 mm / min. Tensile strength (maximum stress) and elongation at break (the ratio of the increase in gauge length at break to the initial gauge length) were recorded. Five specimens were tested in each group, and the arithmetic mean was taken as the final result.

[0084] 2. Limiting Oxygen Index Test

[0085] The test was conducted according to GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test". Sample strips with dimensions of 150 mm × 10 mm × 2.0 mm were cut. Before testing, the samples were conditioned in an environment with a temperature of 23℃ ± 2℃ and a relative humidity of 50% ± 10% for at least 24 hours. The oxygen index test was performed on an oxygen index meter using the top-side ignition method, with the gas flow rate controlled at 40 mm / s ± 2 mm / s. After setting the initial oxygen concentration, the flow rate ratio of oxygen and nitrogen was adjusted until the lowest oxygen concentration at which the sample could sustain combustion for just 3 minutes or achieve a combustion length of 50 mm was reached; this lowest oxygen concentration is the limiting oxygen index value. Each test group consisted of at least 15 samples, and the final critical oxygen concentration was taken as the limiting oxygen index for the material.

[0086] 3. Vertical flammability test

[0087] The test was conducted according to GB / T 2408-2021 "Determination of Burning Performance of Plastics - Horizontal and Vertical Methods". Strip specimens measuring 125 mm × 13 mm × 2.0 mm were cut. Before testing, the specimens were conditioned in an environment with a temperature of 23℃±2℃ and a relative humidity of 50%±10% for at least 48 hours. The test was conducted in a vertical burning chamber using a 20 mm high blue flame. The flame was applied for the first time for 10 seconds, and the flaming time was recorded after removal. After the flaming time extinguished, a second flame was applied at the same location for 10 seconds, and the flaming and extinguished times were recorded. Five specimens were tested in each group. The flame retardancy rating was determined based on the total burning time, the longest single burning time, and whether it ignited absorbent cotton.

[0088] The test data for the above tests are shown in Table 1.

[0089] Table 1

[0090]

[0091] As shown in Table 1, the tensile strength of Examples 1-3 was 15.8-17.2 MPa, the elongation at break was 400-460%, the limiting oxygen index was 36-38%, and all achieved V-0 rating in vertical burning. Compared with the traditional high-filler halogen-free flame retardant system (Comparative Example 6, tensile strength 12.0 MPa, elongation at break 280%, oxygen index 26%, vertical burning V-1 rating), the tensile strength of the examples was increased by 32-43%, and the oxygen index was increased by 10-12 percentage points. This is because in traditional systems, magnesium hydroxide is directly dispersed in the matrix resin, and the large amount of filler-matrix interface leads to stress concentration, deterioration of mechanical properties, and lack of synergistic char formation mechanism, resulting in low flame retardant efficiency. In contrast, this invention pre-constructs enriched micro-regions by char-forming carrier components, in which flame retardant components are selectively enriched and spatially isolated from the matrix resin, effectively reducing interface defects. At the same time, the flame retardant components are highly concentrated in the char-forming carrier micro-regions, forming a close-proximity synergistic acid source-carbon source with lignin grafts and ethylene-vinyl acetate copolymers, significantly improving char formation efficiency. Higher flame retardant ratings are obtained with lower addition amounts, demonstrating the beneficial effect of the invention in synergistically improving high strength and high flame retardancy.

[0092] Compared to Example 1, Comparative Example 1 (where all components were directly blended in a single step) showed a decrease in tensile strength from 16.5 MPa to 11.8 MPa (a 28% decrease), elongation at break from 430% to 310%, oxygen index from 37% to 32%, and vertical burning efficiency from V-0 to V-1. This is because the char-forming carrier component in Comparative Example 1 was not pre-melted and blended to form a stable micro-region structure, and the flame-retardant component was randomly dispersed in the matrix resin. This increased interfacial defects and prevented the formation of a close-proximity synergistic effect with the char-forming precursor, resulting in reduced char-forming efficiency. This verifies the necessity of using a pre-mixing process to construct a char-forming carrier enrichment structure.

[0093] Compared to Example 1, Comparative Example 2 (ammonium polyphosphate without silane coupling agent modification) showed a 14% decrease in tensile strength and a 3 percentage point decrease in oxygen index. This is because the surface of unmodified KH-550 ammonium polyphosphate lacks amino active groups, making it unable to form effective hydrogen bonds with the hydroxyl and ester groups in the char-forming carrier component. During melt blending, it is difficult to be preferentially wetted and coated by the char-forming carrier micro-regions, resulting in a reduced enrichment degree of the flame-retardant component. This verifies the crucial role of flame retardant surface modification in achieving selective enrichment.

[0094] Comparative Example 3 (without char-forming carrier component) exhibited the worst performance across all aspects, with a tensile strength of only 10.5 MPa, an oxygen index of only 28%, and a vertical combustion rating dropping to V-1. This is because, in the absence of a char-forming carrier component, the flame-retardant components are directly dispersed in the matrix resin, causing numerous interfacial defects. Simultaneously, during combustion, the acid source and carbon source cannot form a spatially close and synergistic relationship, resulting in low char formation efficiency and a loose and discontinuous char layer. This verifies the core role of the char-forming carrier component as an enrichment carrier and char formation reaction center.

[0095] The oxygen index of Comparative Example 4 (without lignin grafted compound) decreased more significantly (from 37% to 33%), while the elongation at break of Comparative Example 5 (without maleic anhydride-grafted polyolefin elastomer) decreased more significantly (from 430% to 350%). This is because the lignin grafted compound has a high char-forming rate and abundant polar groups, mainly contributing to char-forming ability and anchoring effect on flame-retardant components; its absence leads to a more significant decrease in flame-retardant performance. The maleic anhydride-grafted polyolefin elastomer mainly improves the interfacial compatibility between the char-forming carrier microregions and the matrix resin and plays a toughening role; its absence leads to a more significant decrease in flexibility, verifying the different functional positioning and synergistic effect of the two in the char-forming carrier component.

[0096] In summary, this invention constructs a multiphase system of matrix resin components and char-forming carrier components, and uses a silane coupling agent to modify the surface of ammonium polyphosphate. During melt blending, this achieves selective enrichment of the flame-retardant component into the char-forming carrier component, forming an in-situ encapsulated structure. This structure effectively isolates the flame-retardant component from the matrix resin component in space, reducing filler-matrix interface defects and giving the material high tensile strength and elongation at break. When exposed to fire, the flame-retardant component enriched in the char-forming carrier component forms a close-proximity synergistic acid-carbon source with the char-forming precursor, rapidly forming a continuous and dense expanded char layer, endowing the material with excellent flame-retardant properties. This invention achieves a balance between high strength and high flame retardancy with a relatively low amount of flame-retardant component added. Furthermore, the preparation process is simple, requiring only conventional melt blending and extrusion, making it easy for industrial production and suitable for various flame-retardant cable sheath applications.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high-strength flame-retardant cable sheath material, characterized in that, It includes the following components in parts by weight: 70-85 parts of matrix resin, 15-25 parts of char carrier, 18-28 parts of flame retardant, 3-6 parts of compatibilizer, 2-4 parts of synergistic charring agent, and 1.5-3 parts of additives. The char-forming carrier component is composed of lignin grafted material, ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer in a mass ratio of (30-50):(30-40):(20-30); The flame retardant component is composed of ammonium polyphosphate and zinc borate, which have been surface modified with silane coupling agent, in a mass ratio of (4-6):

1.

2. The high-strength flame-retardant cable sheath material according to claim 1, characterized in that, The matrix resin component is composed of polyethylene and polyolefin elastomer in a mass ratio of (60-85):(15-40).

3. The high-strength flame-retardant cable sheath material according to claim 1, characterized in that, The polyethylene is linear low-density polyethylene, and the polyolefin elastomer is ethylene-octene copolymer.

4. The high-strength flame-retardant cable sheath material according to claim 1, characterized in that, The lignin graft is glycidyl methacrylate grafted lignin.

5. The high-strength flame-retardant cable sheath material according to claim 1, characterized in that, The silane coupling agent is γ-aminopropyltriethoxysilane.

6. The high-strength flame-retardant cable sheath material according to claim 1, characterized in that, The compatibilizer is maleic anhydride-grafted polyethylene.

7. The high-strength flame-retardant cable sheath material according to claim 1, characterized in that, The synergistic char-forming agent is pentaerythritol phosphate.

8. The high-strength flame-retardant cable sheath material according to claim 1, characterized in that, The additives include antioxidants and lubricants. The antioxidants are one or both of hindered phenolic antioxidants and phosphite antioxidants, and the lubricant is polyethylene wax.

9. A method for preparing a high-strength flame-retardant cable sheath material as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. The lignin graft, ethylene-vinyl acetate copolymer and maleic anhydride grafted polyolefin elastomer are melt-blended and granulated to obtain the char carrier component. S2. Surface modification of ammonium polyphosphate is performed using a silane coupling agent, and the modified ammonium polyphosphate is mixed with zinc borate to obtain a flame retardant component; S3. Premix the matrix resin component, char carrier component, flame retardant component, compatibilizer, synergistic charring agent and additives to obtain a premix; S4. The premixed material is melt-blended and extruded, cooled, and granulated to obtain a high-strength flame-retardant cable sheath material.

10. The method for preparing a high-strength flame-retardant cable sheath material according to claim 9, characterized in that, The twin-screw extruder described in step S4 has an aspect ratio of 44-48, a homogenization zone temperature of 170-185℃, and a screw speed of 280-350rpm.

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