Novel fire-resistant flame-retardant polypropylene material, preparation method and application thereof in cables

Abstract

This invention discloses a novel fire-resistant and flame-retardant polypropylene material, its preparation method, and its application in cables, belonging to the technical field of flame-retardant polymer materials. The material comprises 85-100 parts of propylene resin, 15-45 parts of a halogen-free intumescent flame retardant, 5-15 parts of a flame-retardant synergist, 3.5-7 parts of a compatibilizer, 0.5-2 parts of an antioxidant, 2-6 parts of a filler, and 2-3 parts of a lubricant. The flame-retardant synergist is prepared by reacting DOPO-PhOH, SPDPC, and trimethylamine, and has intramolecular chemical bonds of DOPO, a bispiral cyclic phosphorus structure, and aromatic groups. This invention utilizes the synergistic effect of the condensed-phase charring and gas-phase free radical capture of this flame-retardant synergist to achieve a UL94 V-0 rating for polypropylene at low addition levels, significantly suppressing dripping and reducing smoke density while maintaining good tensile strength and elongation at break. This solves the contradiction between flame-retardant efficiency and mechanical properties in traditional halogen-free flame-retardant systems, making it suitable for cable insulation layers.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant polymer materials technology, specifically to novel fire-resistant and flame-retardant polypropylene materials, their preparation methods, and their application in cables. Background Technology

[0002] Polypropylene (PP) is a high-performance thermoplastic general-purpose plastic with characteristics such as low density, high heat resistance, low dielectric constant, high mechanical strength, good insulation properties, and excellent processing performance. It is widely used in home appliances, automobiles, construction, and wire and cable industries. Especially in the field of cable insulation materials, polypropylene has attracted significant attention due to its excellent heat resistance, high current carrying capacity, and low dielectric constant. However, polypropylene itself is highly flammable, with a limiting oxygen index (LOI) of only about 17%. During combustion, it has a high calorific value, extremely low char yield, and is accompanied by severe molten dripping, making it highly susceptible to flame propagation and ignition. This inherent defect severely restricts its application in flame-retardant and fire-resistant cables.

[0003] To impart flame-retardant properties to polypropylene materials, traditional techniques primarily rely on adding halogenated flame retardants (such as synergistic systems of brominated flame retardants and antimony compounds). While these flame retardants offer high flame-retardant efficiency, they release large amounts of toxic hydrogen halide gases, corrosive fumes, and dense smoke during material combustion or thermal decomposition, posing a serious threat to human safety and the environment. With increasingly stringent environmental regulations, the EU's RoHS Directive and other regulations have explicitly restricted the use of halogens, making the halogen-free development of flame retardants an inevitable trend. Against this backdrop, halogen-free intumescent flame retardants (IFRs), with phosphorus and nitrogen as their core elements, have gradually become a research hotspot. IFRs promote the formation of an expanded char layer on the material surface during combustion, providing insulation, oxygen barrier, smoke suppression, and anti-dripping effects, while also offering the advantages of being halogen-free, low-toxicity, and low-smoke.

[0004] However, existing halogen-free intumescent flame retardant technologies still face numerous bottlenecks, limiting their application in polypropylene cable materials. Patent CN101735514A discloses a flame-retardant polypropylene material and its preparation method, employing a traditional IFR system physically compounded from ammonium polyphosphate (APP), pentaerythritol (PER), and melamine. While this technology improves the flame retardancy of PP, the addition amount is often high, which severely degrades the material's mechanical and electrical insulation properties, making it difficult to meet the comprehensive requirements of cable insulation materials for mechanical strength and dielectric properties. Patent EA201800493A1 discloses a polypropylene composition using phosphorus-containing inorganic derivatives (such as aluminum hypophosphite) as a flame retardant. These inorganic phosphorus-based flame retardants have good thermal stability, but their flame-retardant mechanism is relatively simple, mainly inhibiting combustion by capturing key free radicals in the combustion chain reaction in the gas phase. However, they suffer from interfacial compatibility issues between inorganic particles and the organic matrix. To balance flame retardancy and mechanical properties, its formulation design is relatively complex, often requiring the introduction of a large number of auxiliary components such as plastics for compatibilization and toughening.

[0005] In summary, existing halogen-free intumescent flame retardants suffer from low flame retardant efficiency and poor thermal stability. When used in combination with PP, they also exhibit poor compatibility with the matrix. Furthermore, when the addition amount reaches a certain level, the mechanical properties of the polypropylene material will significantly decrease. Summary of the Invention

[0006] The purpose of this invention is to provide a novel fire-resistant and flame-retardant polypropylene material, its preparation method, and its application in cables. This material is synthesized by introducing an organophosphorus flame retardant with excellent thermal stability and strong flame retardancy into a polypropylene matrix, resulting in a novel flame-retardant polypropylene insulation material rich in phosphorus and aromatic structures. When this insulation material is used as the insulation layer of cables, it can effectively suppress dripping during combustion and the release of toxic fumes, significantly improving the flame-retardant performance and fire safety of cables.

[0007] The technical solution of the present invention is as follows: A novel fire-resistant and flame-retardant polypropylene material, comprising, by weight parts, 85 to 100 parts of polypropylene resin, 15 to 45 parts of halogen-free intumescent flame retardant, 5 to 15 parts of flame retardant synergist, 3.5 to 7 parts of compatibilizer, 0.5 to 2 parts of antioxidant, 2 to 6 parts of filler, and 2 to 3 parts of lubricant. The flame retardant synergist is prepared by reacting DOPO-PhOH, SPDPC and trimethylamine in a mass ratio of 3:1.5:1; wherein, DOPO-PhOH is obtained by reacting 9,10-dihydro-9-oxo-10-phosphobenzophenanthrene-10-one with 4,4'-dihydroxybenzophenone in a mass ratio of 2:1, and SPDPC is obtained by reacting phosphorus oxychloride with pentaerythritol in a mass ratio of 3:1.

[0008] Furthermore, the halogen-free intumescent flame retardant is at least one of melamine-coated ammonium polyphosphate and aluminum diethylphosphite.

[0009] Furthermore, the compatibilizer is a maleic anhydride graft, selected from at least one of PE-g-ST, PP-g-ST, ABS-g-MAH, PE-g-MAH, and PP-g-MAH.

[0010] Furthermore, the antioxidant is a compound of hindered phenolic antioxidants and phosphite antioxidants in a mass ratio of 1:1 to 3:1; the hindered phenolic antioxidants include antioxidant 1010, and the phosphite antioxidants include antioxidant 168.

[0011] Furthermore, the filler is selected from one of graphene, nano-montmorillonite, and calcium carbonate.

[0012] Furthermore, the lubricant is selected from one of ethylene bis-stearamide, pentaerythritol stearate, calcium stearate, and polypropylene wax.

[0013] A method for preparing a novel fire-resistant and flame-retardant polypropylene material includes the following steps: Step 1: Place the flame retardant synergist and the halogen-free intumescent flame retardant in a ball mill at a mass ratio of 1:3 to 4 to mix them, and obtain the first mixture; Step 2: Mix the polypropylene resin, the first mixture, the compatibilizer, the antioxidant, the filler, and the lubricant in a high-speed mixer for 15-30 minutes to obtain a premix, wherein the amount of the first mixture added is 18%-25% of the total mass of the premix; Step 3: Add the premixed material to a twin-screw extruder for melt blending and extrusion at an extrusion temperature of 165-250℃. After cooling and pelletizing, dry at 60-85℃ for 6-12 hours to obtain flame-retardant polypropylene material.

[0014] Furthermore, the preparation method of the flame retardant synergist is as follows: Step 1: Preparation of DOPO-PhOH: 9,10-dihydro-9-oxo-10-phosphobenzophenanthrene-10-one and 4,4'-dihydroxybenzophenone were mixed at a mass ratio of 2:1, heated to 160℃ and stirred for 20 minutes, then heated to 190℃ and reacted for 2 hours. After cooling, the mixture was soaked in tetrahydrofuran for 10-12 hours, filtered, washed with acetone, and finally dried at 60℃ to obtain a white solid reactant, DOPO-PhOH. Step 2: Preparation of SPDPC: Phosphorus oxychloride and pentaerythritol were mixed at a mass ratio of 3:1 and reacted at 75°C for 6-8 hours under nitrogen protection. The temperature was then raised to 105°C and reacted for 12-24 hours. After cooling, the mixture was filtered, washed with chloroform and ether, and finally dried under vacuum at 60°C to obtain a white powder product, SPDPC. Step 3: Dissolve the DOPO-PhOH and SPDPC prepared in Step 1 and Step 2 in N,N-dimethylformamide, and add trimethylamine dropwise while stirring. React at 70°C for 24-48 hours. After the reaction is complete, pour the reaction mixture into 10 times the volume of deionized water, and then centrifuge, filter, wash and dry to obtain the flame retardant synergist DOPO-PhOH.

[0015] Application of a novel fire-resistant and flame-retardant polypropylene material in cable insulation.

[0016] Furthermore, the cable is a medium- or low-voltage power cable, a high-voltage cable, a communication cable, a photovoltaic power generation system cable, a rail transit cable, or a mining cable, and its extrusion temperature is 165–220°C.

[0017] The beneficial effects of this invention are as follows: By introducing DPS, a flame retardant synergist chemically bonded with DOPO, bispiral rings, and aromatic groups, the invention achieves a highly efficient synergistic effect between condensed-phase char formation and gas-phase free radical capture. Even with low addition amounts, polypropylene can achieve a UL94 V-0 rating, significantly suppressing dripping and reducing smoke density. Simultaneously, the rich aromatic structure improves the compatibility between the flame retardant and the matrix, enabling the material to maintain good tensile strength and elongation at break while achieving excellent flame retardant and smoke suppression properties. This resolves the technical contradiction of traditional halogen-free flame retardant systems where flame retardant efficiency and mechanical properties are difficult to balance. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments, but it should not be construed as limiting the scope of the subject matter of the present invention to the following embodiments. All modifications, substitutions and alterations made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0019] This invention successfully prepared a novel fire-resistant and flame-retardant polypropylene material by introducing the flame-retardant synergist DPS into polypropylene. This material effectively improves the flame-retardant rating in cable applications with low addition amounts of flame retardant, suppresses dripping, and reduces the heat release rate and total heat release, demonstrating excellent flame-retardant efficiency and promising application prospects. The flame-retardant synergist (DPS) introduces DOPO structural units, bispiral SPDPC structural units, and abundant aromatic groups into the same molecule through chemical bonding, promoting molecular-level interactions between the functional components and significantly enhancing the overall flame-retardant capability. Specifically, the DOPO structural unit decomposes at high temperatures, releasing PO• free radicals in the gas phase. These free radicals effectively capture the highly reactive H• and OH• free radicals generated during polymer combustion, inhibiting the chain reaction and reducing the heat released in the gas phase, thus achieving gas-phase flame retardancy. Furthermore, the phosphoric acid substances generated from the decomposition of DOPO can catalyze the char formation process in the condensed phase. Meanwhile, the bispiral SPDPC structural units contained in DPS, composed of acid and carbon sources, can dehydrate and form char during combustion, further constructing a dense char layer barrier. Furthermore, the abundant aromatic groups not only enhance the compatibility of DPS with the polymer matrix but also promote the crosslinking and graphitization of the char layer at high temperatures, enhancing its thermal stability and heat and oxygen insulation properties. Thanks to the chemical bonding and synergistic effects of these structural units, DPS can effectively improve the flame retardancy of the polymer, suppress dripping, and reduce the heat release rate and total heat release even at low addition levels.

[0020] A novel fire-resistant and flame-retardant polypropylene material, the raw materials used by way of mass parts include: 85-100 parts of polypropylene resin, 15-45 parts of halogen-free intumescent flame retardant, 5-15 parts of flame retardant synergist, 3.5-7 parts of compatibilizer, 0.5-2 parts of antioxidant, 2-6 parts of filler, and 2-3 parts of lubricant. The preparation steps of flame retardant synergists include: Step 1: 9,10-dihydro-9-oxo-10-phosphobenzophenanthrene-10-one (DOPO) and 4,4'-dihydroxybenzophenone (DHBP) were added to a round-bottom flask at a mass ratio of 2:1, and heated to 160°C. The mixture was stirred and stirred until homogeneous, and then reacted for 20 min. The temperature was then increased to 190°C, and the reaction was continued at this temperature for 2 h to obtain a white suspension.

[0021] Step 2: After the white suspension has cooled to room temperature, tetrahydrofuran (THF) is added to the flask and soaked for 10-12 hours. Subsequently, the mixture is filtered, the solid is collected and washed three times with acetone, and finally dried at 60°C to obtain a white solid reactant (DOPO-PhOH).

[0022] Step 3: Phosphorus oxychloride and pentaerythritol (PER) were added to a three-necked flask equipped with a reflux condenser connected to a hydrogen chloride gas absorber at a mass ratio of 3:1. Under nitrogen protection, the reaction mixture was heated to 75°C and stirred for 6–8 h. The temperature was then further increased to 105°C and the reaction was continued at this temperature for 12–24 h. After cooling to room temperature, the mixture was filtered, washed 3–5 times each with chloroform and diethyl ether, and finally dried under vacuum at 60°C to obtain a white powder product (SPDPC).

[0023] Step 4: Dissolve DOPO-PhOH and SPDPC in N,N-dimethylformamide (DMF), and add trimethylamine dropwise with stirring. React at 70°C for 24–48 h. After the reaction is complete, pour the reaction mixture into 10 times its volume of deionized water, then centrifuge, filter, wash several times with water, and dry at 70°C to obtain the flame retardant synergist (DPS).

[0024] The mass ratio of DOPO-PhOH, SPDPC, and trimethylamine is 3:1.5:1.

[0025] The preparation steps of the new fire-resistant and flame-retardant polypropylene material are as follows: Step 1: Place the flame retardant synergist (DPS) and the halogen-free intumescent flame retardant in a ball mill at a ratio of 1:3-4 and mix them (200 rpm, 2 h) to obtain a novel mixture.

[0026] Step 2: Place the polypropylene resin, mixture, compatibilizer, antioxidant, filler and lubricant in a high-speed mixer and mix for 15-30 minutes to obtain a uniform premixed material; Step 3: The premixed material is added to a twin-screw extruder for melt blending and extrusion. The extrusion temperature is set to 165–250℃. After cooling in a water cooling tank, the extrudate is pelletized using a pelletizer and then dried in an oven at 60–85℃ for 6–12 hours to obtain novel fire-resistant and flame-retardant polypropylene material pellets. The amount of the mixture added is 18%–25%.

[0027] The halogen-free intumescent flame retardant is one of melamine-coated ammonium polyphosphate (APP-M) or aluminum diethyl phosphite (ADP). The compatibilizer is a maleic anhydride graft, specifically one or more of PE-g-ST, PP-g-ST, ABS-g-MAH, PE-g-MAH, and PP-g-MAH. The antioxidant is a mixture of hindered phenolic antioxidants (such as antioxidant 1010) and phosphite antioxidants (such as antioxidant 168) in a mass ratio of 1:1 to 3:1. The filler is one of graphene, nano-montmorillonite, or calcium carbonate. The lubricant is one of ethylene bis-stearamide (EBS), pentaerythritol stearate (PETS), calcium stearate (CAST), and polypropylene wax (PP wax).

[0028] The application of novel fire-resistant and flame-retardant polypropylene materials in cables, including medium and low voltage power cables, high voltage cables, communication cables, photovoltaic power generation system cables, rail transit cables, and mining cables. It is used in the insulation layer of cables, with an extrusion temperature of 165-220℃.

[0029] All embodiments of this invention share the following common preparation steps. Step 1: Place the flame retardant synergist (DPS) and halogen-free intumescent flame retardant in a ball mill at a mass ratio of 1:3 to 4, and mix them at 200 rpm for 2 hours to obtain a mixture.

[0030] Step 2: Place the polypropylene resin, mixture 1, compatibilizer, antioxidant, filler, and lubricant in a high-speed mixer and mix for 15-30 minutes to obtain a premixed material. The amount of mixture 1 added is 18%-25% of the total mass of the premixed material. Step 3: Add the premixed material to a twin-screw extruder for melt blending and extrusion at an extrusion temperature of 165-250℃. After water cooling and pelletizing, dry in an oven at 60-85℃ for 6-12 hours to obtain the final product.

[0031] Example 1: The following components were prepared by weight: 100 parts polypropylene resin, 15 parts halogen-free intumescent flame retardant (APP-M), 5 parts flame retardant synergist (DPS), 3.5 parts compatibilizer (PP-g-MAH), 1 part antioxidant (1010:168=2:1), 2 parts filler (nano-montmorillonite), and 2 parts lubricant (EBS). Following a common preparation procedure, the mass ratio of flame retardant synergist to halogen-free intumescent flame retardant was 1:3.

[0032] Example 2: The following components were prepared by weight: 100 parts polypropylene resin, 20 parts halogen-free intumescent flame retardant (APP-M), 5 parts flame retardant synergist (DPS), 3.5 parts compatibilizer (PP-g-MAH), 1 part antioxidant (1010:168=2:1), 2 parts filler (nano-montmorillonite), and 2 parts lubricant (EBS). Following a common preparation procedure, the mass ratio of flame retardant synergist to halogen-free intumescent flame retardant was 1:4.

[0033] Example 3: The following components were prepared by weight: 100 parts polypropylene resin, 15 parts halogen-free intumescent flame retardant (APP-M), 7 parts flame retardant synergist (DPS), 3.5 parts compatibilizer (PP-g-MAH), 1 part antioxidant (1010:168=2:1), 2 parts filler (nano-montmorillonite), and 2 parts lubricant (EBS). Following a common preparation procedure, the mass ratio of the flame retardant synergist to the halogen-free intumescent flame retardant was approximately 1:2.1.

[0034] Comparative Example 1 (without flame retardant synergist, with flame retardant): The following components by weight were used: 100 parts polypropylene resin, 15 parts halogen-free intumescent flame retardant (APP-M), 3.5 parts compatibilizer (PP-g-MAH), 1 part antioxidant (1010:168=2:1), 2 parts filler (nano-montmorillonite), and 2 parts lubricant (EBS). Without adding flame retardant synergist, the polypropylene resin, halogen-free intumescent flame retardant, compatibilizer, antioxidant, filler, and lubricant were directly mixed and extruded according to steps 2 and 3 of the common preparation process.

[0035] Comparative Example 2 (pure PP, without flame retardants or flame retardant synergists): 100 parts by weight of polypropylene resin, 3.5 parts of compatibilizer (PP-g-MAH), 1 part of antioxidant (1010:168=2:1), 2 parts of filler (nano-montmorillonite), and 2 parts of lubricant (EBS). No flame retardants or flame retardant synergists were added; the mixture was directly mixed and extruded according to steps 2 and 3 of the common preparation process.

[0036] The materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested for tensile strength, elongation at break, and oxygen index. The details are shown in the table below: Tensile strength and elongation at break were tested according to GB / T 8804.2-2016; oxygen index was tested according to GB / T 2406.2-2009; vertical burning was tested according to UL-94 standard; smoke density was tested according to GB / T 17651.1-2021.

[0037] The oxygen index of Examples 1-3 was ≥29.4%, achieving UL94 V-0 rating, and the smoke density was significantly lower than that of Comparative Example 1 (without DPS) and Comparative Example 2 (pure PP). This demonstrates that the addition of the flame retardant synergist DPS, through multiple synergistic effects of gas-phase free radical capture, condensed-phase catalytic char formation, and dehydration char formation of the bispiral ring structure, constructs a denser and more stable expanded char layer, thereby achieving efficient flame retardancy and smoke suppression with a low amount of flame retardant added.

[0038] Compared to Comparative Example 2 (pure PP), the decrease in tensile strength and elongation at break in Examples 1-3 was controllable, and the performance retention rate was high. This is attributed to the fact that the abundant aromatic groups in the DPS molecule improve the interfacial compatibility between the flame retardant and the PP matrix, reduce stress concentration defects caused by flame retardant agglomeration, and achieve a good balance between flame retardant enhancement and mechanical properties.

[0039] The present invention has provided a detailed description of the novel fire-resistant and flame-retardant polypropylene material, its preparation method, and its application in cables. Specific examples have been used to illustrate the structure and working principle of the invention. The descriptions of the embodiments are merely for the purpose of helping to understand the method and core ideas of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A novel fire-resistant and flame-retardant polypropylene material, characterized in that: The product comprises, by weight parts, 85 to 100 parts of polypropylene resin, 15 to 45 parts of halogen-free intumescent flame retardant, 5 to 15 parts of flame retardant synergist, 3.5 to 7 parts of compatibilizer, 0.5 to 2 parts of antioxidant, 2 to 6 parts of filler, and 2 to 3 parts of lubricant. The flame retardant synergist is prepared by reacting DOPO-PhOH, SPDPC and trimethylamine in a mass ratio of 3:1.5:1; wherein, DOPO-PhOH is obtained by reacting 9,10-dihydro-9-oxo-10-phosphobenzophenanthrene-10-one with 4,4'-dihydroxybenzophenone in a mass ratio of 2:1, and SPDPC is obtained by reacting phosphorus oxychloride with pentaerythritol in a mass ratio of 3:

1.

2. The novel fire-resistant and flame-retardant polypropylene material according to claim 1, characterized in that: The halogen-free intumescent flame retardant is at least one of melamine-coated ammonium polyphosphate and diethyl aluminum hypophosphite.

3. The novel fire-resistant and flame-retardant polypropylene material according to claim 1, characterized in that: The compatibilizer is a maleic anhydride graft, selected from at least one of PE-g-ST, PP-g-ST, ABS-g-MAH, PE-g-MAH, and PP-g-MAH.

4. The novel fire-resistant and flame-retardant polypropylene material according to claim 1, characterized in that: The antioxidant is a compound of hindered phenolic antioxidants and phosphite antioxidants in a mass ratio of 1:1 to 3:1; the hindered phenolic antioxidants include antioxidant 1010, and the phosphite antioxidants include antioxidant 168.

5. The novel fire-resistant and flame-retardant polypropylene material according to claim 1, characterized in that: The filler is selected from one of graphene, nano-montmorillonite, and calcium carbonate.

6. The novel fire-resistant and flame-retardant polypropylene material according to claim 1, characterized in that: The lubricant is selected from one of ethylene bis-stearamide, pentaerythritol stearate, calcium stearate, and polypropylene wax.

7. A method for preparing a novel fire-resistant and flame-retardant polypropylene material as described in any one of claims 1-6, characterized in that: Includes the following steps: Step 1: Place the flame retardant synergist and the halogen-free intumescent flame retardant in a ball mill at a mass ratio of 1:3 to 4 to mix them, and obtain the first mixture; Step 2: Mix the polypropylene resin, the first mixture, the compatibilizer, the antioxidant, the filler, and the lubricant in a high-speed mixer for 15-30 minutes to obtain a premix, wherein the amount of the first mixture added is 18%-25% of the total mass of the premix; Step 3: Add the premixed material to a twin-screw extruder for melt blending and extrusion at an extrusion temperature of 165-250℃. After cooling and pelletizing, dry at 60-85℃ for 6-12 hours to obtain flame-retardant polypropylene material.

8. The preparation method according to claim 7, characterized in that: The preparation method of the flame retardant synergist is as follows: Step 1: Preparation of DOPO-PhOH: 9,10-dihydro-9-oxo-10-phosphobenzophenanthrene-10-one and 4,4'-dihydroxybenzophenone were mixed at a mass ratio of 2:1, heated to 160℃ and stirred for 20 minutes, then heated to 190℃ and reacted for 2 hours. After cooling, the mixture was soaked in tetrahydrofuran for 10-12 hours, filtered, washed with acetone, and finally dried at 60℃ to obtain a white solid reactant, DOPO-PhOH. Step 2: Preparation of SPDPC: Phosphorus oxychloride and pentaerythritol were mixed at a mass ratio of 3:1 and reacted at 75°C for 6-8 hours under nitrogen protection. The temperature was then raised to 105°C and reacted for 12-24 hours. After cooling, the mixture was filtered, washed with chloroform and ether, and finally dried under vacuum at 60°C to obtain a white powder product, SPDPC. Step 3: Dissolve the DOPO-PhOH and SPDPC prepared in Step 1 and Step 2 in N,N-dimethylformamide, and add trimethylamine dropwise while stirring. React at 70°C for 24-48 hours. After the reaction is complete, pour the reaction mixture into 10 times the volume of deionized water, and then centrifuge, filter, wash and dry to obtain the flame retardant synergist DOPO-PhOH.

9. The application of the novel fire-resistant and flame-retardant polypropylene material as described in any one of claims 1-7 in cable insulation layers.

10. The application according to claim 9, characterized in that: The cable is a medium- or low-voltage power cable, a high-voltage cable, a communication cable, a photovoltaic power generation system cable, a rail transit cable, or a mining cable, and its extrusion temperature is 165–220°C.

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