Flame-retardant polypropylene fiber material and method for producing the same

Abstract

The application discloses a kind of polypropylene fiber materials for flame retardation and preparation method thereof, and relates to the technical field of polypropylene.The specific steps include the following steps:S1: polypropylene resin, nano-silicon dioxide is added to high mixer and premixed to obtain premixing material;S2: premixing material, flame retardant, calcium carbonate, talcum powder, antioxidant are added to horizontal stirrer and mixed, using twin-screw extruder to melt extrusion, to obtain polypropylene fiber material for flame retardation;The application develops a kind of flame-retardant polypropylene resin, and the non-woven fabric prepared from polypropylene resin has flame-retardant performance, can be applied to furniture and home industry, can meet CAL TB 117:2013 and British furniture (fireproof) (safety) regulations hidden cloth cigarette test and hidden cloth match fire test flame-retardant requirements.

Description

Technical Field

[0001] This invention relates to the field of polypropylene technology, specifically to a flame-retardant polypropylene fiber material and its preparation method. Background Technology

[0002] Polypropylene (PP) is a flammable polymer material with a limiting oxygen index (LOI) of only 17% to 18%, lower than the 21% oxygen concentration in the air, making it easily ignited under normal usage conditions. When PP burns, it produces violent molten drips; these high-temperature drips can carry flames and ignite combustibles below, accelerating the spread of the fire. Furthermore, PP lacks self-extinguishing properties, releasing a large amount of heat during combustion, further contributing to the fire's spread. Therefore, in applications with high fire safety requirements, such as electronics, automotive interiors, and building decoration, improving the flame-retardant properties of PP is essential to ensure safe use.

[0003] The purpose of flame retardant treatment is to increase the difficulty of ignition, inhibit flame propagation, and reduce molten dripping, thereby delaying the spread of fire and buying time for evacuation and firefighting. It should be noted that flame retardancy does not make the material completely non-combustible, but rather interferes with the combustion process through physical or chemical action, reducing the fire risk in actual use. Furthermore, regulations such as the EU RoHS and REACH directives, the US UL standards, and the Chinese GB standards all have clear requirements for the flame retardant properties of electronic and electrical products, automotive materials, and building materials. Therefore, using flame-retardant PP is a necessary means to meet regulatory requirements and ensure safe use.

[0004] The core of flame retardant mechanism lies in interfering with the combustion process through physical or chemical means. The main pathways include: (1) gas phase flame retardancy, where the flame retardant decomposes and releases active free radical scavengers, interrupting the chain combustion reaction; (2) condensed phase flame retardancy, which promotes char formation or the formation of a heat insulation barrier on the material surface, blocking heat and oxygen transfer; (3) endothermic cooling, where the flame retardant decomposes and absorbs heat, releasing non-combustible gases such as water vapor, reducing the surface temperature of the material and diluting combustible gases; and (4) dilution flame retardancy, where the flame retardant decomposes and releases non-combustible gases such as nitrogen, reducing the concentration of combustible gases and oxygen. In practical applications, the combination of multiple flame retardants often produces a synergistic effect. For example, in the halogen-antimony system, antimony trioxide reacts with hydrogen halides to generate active flame retardant substances, improving the gas phase flame retardant efficiency; in the phosphorus-nitrogen system, phosphorus-based and nitrogen-based flame retardants synergistically promote the formation of a dense char layer, enhancing the condensed phase protection effect.

[0005] Currently, the main approaches to suppressing molten dripping during PP combustion include: (1) promoting charring or cross-linking on the material surface through condensed phase flame retardancy to form a dense char layer and suppress dripping; (2) adding anti-dripping agents (such as polytetrafluoroethylene) to increase melt viscosity and suppress dripping by utilizing its high-temperature fiberization effect. However, anti-dripping agents significantly reduce the mass flow rate of PP melt, limiting their application in processing technologies such as spinning and injection molding. Therefore, improving the density and strength of the char layer through catalytic charring to suppress dripping from the source is an effective approach that balances the flame retardant properties and processing performance of PP.

[0006] In summary, solving the above problems and preparing a flame-retardant polypropylene fiber material and its preparation method is of great significance. Summary of the Invention

[0007] The purpose of this invention is to provide a flame-retardant polypropylene fiber material and its preparation method to solve the problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing flame-retardant polypropylene fiber material includes the following steps: S1: Polypropylene resin and nano-silica are added to a high-speed mixer for premixing to obtain a premix; S2: Add the premix, flame retardant, calcium carbonate, talc, and antioxidant to a horizontal mixer and mix. Then, use a twin-screw extruder to melt-extrude the mixture to obtain flame-retardant polypropylene fiber material. The flame-retardant polypropylene fiber material comprises the following raw materials, by weight: 65-95 parts polypropylene resin, 5-30 parts flame retardant, 1-2 parts nano silica, 0.1-0.5 parts calcium carbonate, 0.1-0.35 parts talc, and 0.05-0.3 parts antioxidant. The flame retardant comprises piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 8 to 12:3.

[0009] More preferably, the flame retardant comprises modified piperazine pyrophosphate, piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 5~8:3~4:3.

[0010] Preferably, the preparation method of the modified piperazine pyrophosphate includes the following steps: (1) Add piperazine pyrophosphate and dodecylphenol polyoxyethylene ether to an ethanol aqueous solution, mix them evenly at 40~50℃, add ammonia aqueous solution to adjust the pH to 10, add tetraethyl orthosilicate, stir the reaction for 4~6h, filter, wash, and dry to obtain silica-coated piperazine pyrophosphate. (2) Add silica-coated piperazine pyrophosphate to xylene and disperse it evenly by ultrasonication to obtain silica-coated piperazine pyrophosphate dispersion; add tetramethylpiperidinol and 3-isocyanate-propyltrimethoxysilane to xylene and mix evenly, stir and react at 40~45℃ for 2~3h, add silica-coated piperazine pyrophosphate dispersion, heat to 120~130℃, stir and react for 10~12h, cool to room temperature, filter, wash and dry to obtain modified piperazine pyrophosphate.

[0011] Preferably, the silica-coated piperazine pyrophosphate comprises the following raw materials, in parts by mass: 8-10 parts piperazine pyrophosphate, 0.12-0.18 parts dodecylphenol polyoxyethylene ether, 50 parts aqueous ethanol solution, and 2.5-3.2 parts tetraethyl orthosilicate; The modified piperazine pyrophosphate comprises the following raw materials, in parts by mass: 8-10 parts silica-coated piperazine pyrophosphate, 0.3-0.55 parts tetramethylpiperidinol, 0.42-0.68 parts 3-isocyanate-propyltrimethoxysilane, and 30-40 parts xylene.

[0012] Preferably, the calcium carbonate needs to be modified before addition to obtain modified calcium carbonate; the preparation method of the modified calcium carbonate includes the following steps: heating the calcium carbonate to 100~105℃, stirring for 20~30min to remove water, adding rare earth coupling agent WOT, and continuing to stir and react for 10~15min to obtain modified calcium carbonate.

[0013] Preferably, the mass ratio of calcium carbonate to rare earth coupling agent WOT is 10:0.1~0.4.

[0014] More preferably, the antioxidant includes one or two of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite.

[0015] Preferably, the premixing process takes 10-15 minutes, and the mixing process takes 5-10 minutes.

[0016] Preferably, during the melt extrusion process of the twin-screw extruder, the melt temperature range is 180~230℃, the screw speed is 300~400rpm / min, and the feed flow rate is 180~200kg / h.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention is based on piperazine pyrophosphate and aluminum hypophosphite as basic flame retardants, and introduces modified piperazine pyrophosphate with a double-layer coating structure, nano-silica and calcium carbonate modified with rare earth coupling agent to form a multi-component synergistic flame retardant system, which significantly improves the flame retardant performance of polypropylene fiber material and maintains excellent mechanical properties.

[0018] Among them, piperazine pyrophosphate, as an intumescent flame retardant with synergistic effects of phosphorus and nitrogen, can promote the formation of a dense and expanded char layer on the material surface when exposed to fire, effectively isolating heat and oxygen, thereby preventing the spread of flames; while aluminum hypophosphite, as an inorganic phosphorus-based flame retardant, can decompose and absorb heat at high temperatures, reducing the surface temperature of the material, and at the same time decomposing to produce substances such as aluminum phosphate, which can also promote the formation of a dense char layer on the material surface, while releasing phosphorus-containing free radicals to capture active free radicals in the combustion process and interrupt the chain reaction of combustion; by adding nano-silica, it can work with calcium carbonate and talc as a nucleating agent to improve the mechanical strength of polypropylene, and can form thermally stable Si-OP bonds with phosphorus elements in the flame retardant during combustion, which also plays a good physical barrier role, prolonging the heat transfer and improving the flame retardant performance.

[0019] In a further embodiment, this application obtains silica-coated piperazine pyrophosphate by in-situ coating a layer of silica on the surface of piperazine pyrophosphate particles through the hydrolysis and condensation reaction of tetraethyl orthosilicate. Then, a trimethoxysilane intermediate with hindered amine groups is formed by reacting the isocyanate bond of 3-isocyanate-propyltrimethoxysilane with the hydroxyl group of tetramethylpiperidinol. The trimethoxysilane in this intermediate further undergoes a de-alcoholization condensation reaction with the hydroxyl group on the surface of the silica coating layer to form modified piperazine pyrophosphate with a double-layer coating structure.

[0020] In this invention, some piperazine pyrophosphate particles are encapsulated with silica. This is because piperazine pyrophosphate is a polar nitrogen- and phosphorus-containing compound with poor compatibility with the polypropylene matrix. It is prone to agglomeration or migration during processing and may decompose prematurely at high temperatures, leading to a decrease in flame retardant properties. Encapsulation with silica improves the thermal stability and dispersibility of piperazine pyrophosphate. Furthermore, the introduction of a tetramethylpiperidine-containing intermediate, with its hindered amine groups, can capture active free radicals generated during high-temperature processing and combustion, further reducing the decomposition of piperazine pyrophosphate and improving flame retardant efficiency. The steric hindrance effect also enhances dispersibility and reduces agglomeration, thus improving mechanical properties. However, to maintain the material's rapid expansion and charring ability in the early stages of combustion, some unmodified piperazine pyrophosphate must be retained, employing a synergistic compounding approach to improve the flame retardant properties of polypropylene.

[0021] In this invention, rare earth coupling agents are used to modify calcium carbonate, forming a rare earth-containing organic modification layer on the surface of calcium carbonate. This improves the dispersibility and compatibility of calcium carbonate in polypropylene resin, reduces viscosity, and enhances processing performance. Simultaneously, during combustion, rare earth ions can participate in catalytic polymer dehydrogenation cyclization, thereby promoting the synergistic formation of a dense carbon layer by piperazine pyrophosphate, aluminum hypophosphite, and nano-silica, thus improving flame retardant performance. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that all raw materials involved in this invention are commercially available, and the parts refer to parts by weight.

[0024] Piperazine pyrophosphate was purchased from Qingyuan Pusefur Phosphate Chemical Co., Ltd.; aluminum hypophosphite was purchased from Dongguan Xinzhiyuan New Materials Co., Ltd.; nano silica was purchased from Dongguan Dongchao New Materials Technology Co., Ltd.; calcium carbonate had a particle size of 10~15μm; talc had a particle size of 10~15μm.

[0025] Example 1: A method for preparing a flame-retardant polypropylene fiber material includes the following steps: S1: Add 89.1 parts of polypropylene resin (MFR=25g / 10min) and 1 part of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 12:3 as flame retardants; add the premix, 9 parts flame retardant, 0.3 parts calcium carbonate, 0.3 parts talc, 0.1 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Use a twin-screw extruder for melt extrusion at a temperature range of 180~230℃, control the screw speed at 350 rpm / min, and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0026] Example 2: A method for preparing a flame-retardant polypropylene fiber material includes the following steps: S1: Add 84.1 parts of polypropylene resin (MFR=25g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 12:3 as flame retardants; add the premix, 13 parts flame retardant, 0.3 parts calcium carbonate, 0.3 parts talc, 0.1 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Use a twin-screw extruder for melt extrusion at a temperature range of 180~230℃, control the screw speed at 350 rpm / min, and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0027] Example 3: A method for preparing a flame-retardant polypropylene fiber material includes the following steps: S1: Add 79.1 parts of polypropylene resin (MFR=40g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 12:3 as flame retardants; add the premix, 18 parts of flame retardant, 0.3 parts of calcium carbonate, 0.3 parts of talc, 0.1 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts of tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Use a twin-screw extruder for melt extrusion at a temperature range of 180~230℃, control the screw speed at 350 rpm / min, and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0028] Example 4: A method for preparing a flame-retardant polypropylene fiber material includes the following steps: S1: Add 74.1 parts of polypropylene resin (MFR=40g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 12:3 as flame retardants; add the premix, 23 parts flame retardant, 0.3 parts calcium carbonate, 0.3 parts talc, 0.1 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Use a twin-screw extruder for melt extrusion at a temperature range of 180~230℃, control the screw speed at 350 rpm / min, and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0029] Comparative Example 1: Based on Example 1, without the addition of flame retardants and nano-silica, as follows: S1: Add 99.1 parts of polypropylene resin (MFR=25g / 10min) to a high-speed mixer and premix for 10min to obtain a premix; S2: Add the premix, 0.3 parts calcium carbonate, 0.3 parts talc, 0.1 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Then, use a twin-screw extruder to melt-extrude at a temperature range of 180~230℃, controlling the screw speed at 350 rpm / min and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0030] Comparative Example 2: Based on Example 1, the amounts of flame retardant and nano-silica were reduced by half, as follows: S1: Add 94.1 parts of polypropylene resin (MFR=25g / 10min) and 0.5 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 12:3 as flame retardants; add the premix, 4.5 parts flame retardant, 0.3 parts calcium carbonate, 0.3 parts talc, 0.1 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Use a twin-screw extruder for melt extrusion at a temperature range of 180~230℃, control the screw speed at 350 rpm / min, and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0031] Comparative Example 3: Based on Example 4: Increase the amount of flame retardant and nano-silica used, as follows: S1: Add 69.1 parts of polypropylene resin (MFR=40g / 10min) and 4 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 12:3 as flame retardants; add the premix, 26 parts of flame retardant, 0.3 parts of calcium carbonate, 0.3 parts of talc, 0.1 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts of tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Then, use a twin-screw extruder to melt-extrude at a temperature range of 180~230℃, controlling the screw speed at 350 rpm / min and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0032] Performance Test 1: Samples were obtained by injection molding of the flame-retardant polypropylene fiber materials prepared in Examples 1-4 and Comparative Examples 1-3, and the following tests were conducted: (1) The melt flow rate of flame-retardant polypropylene fiber material was measured by a melt flow rate meter in accordance with GB / T 3682.1-2018 and the test was carried out under condition M. (2) The yellow index of the sample was measured using a yellow index meter in accordance with GB / T 39822-2021; (3) After calcining 10g of sample at 850℃ according to GB / T 9345.1-2008, weigh the sample and test the ash content. (4) Prepare type 1A tensile specimens according to GB / T 1040.2-2022, measure tensile strength, and tensile rate is 50 mm / min; (5) Prepare Type I test samples according to GB / T 2406.2-2009 and measure the limiting oxygen index (LOI) of the samples. (6) Samples were prepared in accordance with GB / T 2408-2008 and vertical combustion tests were conducted; the experimental data are shown in Table 1.

[0033] Table 1

[0034] Performance Test 2: The flame-retardant polypropylene fiber materials prepared in Examples 1-4 and Comparative Examples 1-3 were injection molded into non-woven fabric samples for the following tests: (1) The flammability test of the prepared polypropylene nonwoven fabric sample was carried out in accordance with Section 1 of CAL TB 117:2013: Testing of Covering Fabrics. The test requirements are as follows: 1. A single test sample model will not meet the requirements if the following conditions occur during the testing process: The test sample model continued to smolder after 45 minutes of testing. b has a vertical carbonization length of over 1.8 inches (45 mm) on the cover fabric; c. The test sample model produced an open flame; 2. If all three initial sample models pass the test, meaning the cigarette smolders along the entire length and the model does not smolder for a particularly long period, then the covering fabric passes the test; 3. If more than one initial sample fails the test, then the covering fabric fails the test; 4. If one of the three initial samples fails the test, three additional samples are added for repeated testing; 5. If all three additional samples pass the test, the cover fabric passes the test; if any one of the three additional samples fails, the cover fabric fails the test. The experimental data are shown in Table 2.

[0035] (2) In accordance with the UK Furniture (Fire Protection) (Safety) Regulations 1988 (1989, 1993, 2010 and 2025 revisions), Chapter 4, Part 2: Cigarette Test for Hidden Fabrics, the prepared polypropylene nonwoven fabric samples were subjected to a flammability test. The test requirements are as follows: 1. Smoldering failure criteria: If smoldering (spontaneous combustion without open flame) is found in the sample at any time within one hour after the cigarette is placed on it, the sample is deemed to have failed. 2. Criteria for judging failure of open flame: If an open flame is found on the sample at any time within one hour after the cigarette is placed on the sample, the sample is judged as unsuccessful. The experimental data is shown in Table 3.

[0036] (3) In accordance with Chapter 5, Part 3 – Hidden Fabric Match Test – of the British Furniture (Fireproof) (Safety) Regulations 1988 (revised in 1989, 1993, 2010 and 2025), the flammability of the prepared polypropylene nonwoven fabric sample was tested. The test requirements are as follows: 1. Smoldering failure criteria: If smoldering (spontaneous combustion without open flame) is found in the sample at any time within one hour after the ignition source is removed, the sample is deemed unqualified.

[0037] 2. Criteria for judging failure of open flame: If, in one or more instances, the open flame burns for more than 120 seconds after the fire source is removed, it is considered a failure. The experimental data is shown in Table 3.

[0038] Table 2

[0039] Table 3

[0040] Example 5: Based on Example 4, a method for preparing flame-retardant polypropylene fiber material includes the following steps: Step 1: Preparation of modified piperazine pyrophosphate: (1) Add 10 parts of piperazine pyrophosphate and 0.15 parts of dodecylphenol polyoxyethylene ether to 50 parts of 70wt% ethanol aqueous solution, mix evenly at 45℃, add ammonia aqueous solution to adjust pH to 10, add 2.8 parts of tetraethyl orthosilicate, stir for 5h, filter, wash, and dry to obtain silica-coated piperazine pyrophosphate; (2) Add 10 parts of silica-coated piperazine pyrophosphate to 20 parts of xylene and disperse evenly by ultrasonication to obtain silica-coated piperazine pyrophosphate dispersion; Add 0.38 parts of tetramethylpiperidinol and 0.55 parts of 3-isocyanate propyltrimethoxysilane to 10 parts of xylene and mix evenly, stir for 3h at 40℃, add silica-coated piperazine pyrophosphate dispersion, heat to 120℃, stir for 12h, cool to room temperature, filter, wash, and dry to obtain modified piperazine pyrophosphate; Step 2: Preparation of modified calcium carbonate: Heat 10 parts of calcium carbonate to 100℃, stir for 30 min to remove water, add 0.2 parts of rare earth coupling agent WOT, and continue stirring for 15 min to obtain modified calcium carbonate.

[0041] Step 3: Preparation of flame-retardant polypropylene fiber material: S1: Add 73.9 parts of polypropylene resin (MFR=40g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh modified piperazine pyrophosphate, piperazine pyrophosphate, and aluminum hypophosphite in a mass ratio of 7:4:3 as flame retardants; add the premix, 23 parts of flame retardant, 0.5 parts of modified calcium carbonate, 0.3 parts of talc, 0.1 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts of tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Then, use a twin-screw extruder to melt-extrude at a temperature range of 180~230℃, controlling the screw speed at 350 rpm / min and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0042] Example 6: Based on Example 4, a method for preparing flame-retardant polypropylene fiber material includes the following steps: Step 1: Preparation of modified piperazine pyrophosphate: (1) Add 10 parts of piperazine pyrophosphate and 0.15 parts of dodecylphenol polyoxyethylene ether to 50 parts of 70wt% ethanol aqueous solution, mix evenly at 45℃, add ammonia aqueous solution to adjust pH to 10, add 2.8 parts of tetraethyl orthosilicate, stir for 5h, filter, wash, and dry to obtain silica-coated piperazine pyrophosphate; (2) Add 10 parts of silica-coated piperazine pyrophosphate to 20 parts of xylene and disperse evenly by ultrasonication to obtain silica-coated piperazine pyrophosphate dispersion; Add 0.38 parts of tetramethylpiperidinol and 0.55 parts of 3-isocyanate propyltrimethoxysilane to 10 parts of xylene and mix evenly, stir for 3h at 40℃, add silica-coated piperazine pyrophosphate dispersion, heat to 120℃, stir for 12h, cool to room temperature, filter, wash, and dry to obtain modified piperazine pyrophosphate; Step 2: Preparation of modified calcium carbonate: Heat 10 parts of calcium carbonate to 100℃, stir for 30 min to remove water, add 0.2 parts of rare earth coupling agent WOT, and continue stirring for 15 min to obtain modified calcium carbonate.

[0043] Step 3: Preparation of flame-retardant polypropylene fiber material: S1: Add 74.1 parts of polypropylene resin (MFR=40g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh modified piperazine pyrophosphate, piperazine pyrophosphate, and aluminum hypophosphite in a mass ratio of 7:4:3 as flame retardants; add the premix, 23 parts of flame retardant, 0.3 parts of modified calcium carbonate, 0.3 parts of talc, 0.1 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts of tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Then, use a twin-screw extruder to melt-extrude at a temperature range of 180~230℃, controlling the screw speed at 350 rpm / min and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0044] Example 7: Based on Example 4, a method for preparing flame-retardant polypropylene fiber material includes the following steps: Step 1: Preparation of modified piperazine pyrophosphate: (1) Add 10 parts of piperazine pyrophosphate and 0.15 parts of dodecylphenol polyoxyethylene ether to 50 parts of 70wt% ethanol aqueous solution, mix evenly at 45℃, add ammonia aqueous solution to adjust pH to 10, add 2.8 parts of tetraethyl orthosilicate, stir for 5h, filter, wash, and dry to obtain silica-coated piperazine pyrophosphate; (2) Add 10 parts of silica-coated piperazine pyrophosphate to 20 parts of xylene and disperse evenly by ultrasonication to obtain silica-coated piperazine pyrophosphate dispersion; Add 0.38 parts of tetramethylpiperidinol and 0.55 parts of 3-isocyanate propyltrimethoxysilane to 10 parts of xylene and mix evenly, stir for 3h at 40℃, add silica-coated piperazine pyrophosphate dispersion, heat to 120℃, stir for 12h, cool to room temperature, filter, wash, and dry to obtain modified piperazine pyrophosphate; Step 2: Preparation of modified calcium carbonate: Heat 10 parts of calcium carbonate to 100℃, stir for 30 min to remove water, add 0.2 parts of rare earth coupling agent WOT, and continue stirring for 15 min to obtain modified calcium carbonate.

[0045] Step 3: Preparation of flame-retardant polypropylene fiber material: S1: Add 73.9 parts of polypropylene resin (MFR=40g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh modified piperazine pyrophosphate, piperazine pyrophosphate, and aluminum hypophosphite in a mass ratio of 5:3:3 as flame retardants; add the premix, 23 parts of flame retardant, 0.5 parts of modified calcium carbonate, 0.3 parts of talc, 0.1 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts of tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Then, use a twin-screw extruder to melt-extrude at a temperature range of 180~230℃, controlling the screw speed at 350 rpm / min and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0046] Comparative Example 4: Based on Example 5, piperazine pyrophosphate was completely replaced with modified piperazine pyrophosphate as follows: Step 1: Preparation of modified piperazine pyrophosphate: (1) Add 10 parts of piperazine pyrophosphate and 0.15 parts of dodecylphenol polyoxyethylene ether to 50 parts of 70wt% ethanol aqueous solution, mix evenly at 45℃, add ammonia aqueous solution to adjust pH to 10, add 2.8 parts of tetraethyl orthosilicate, stir for 5h, filter, wash, and dry to obtain silica-coated piperazine pyrophosphate; (2) Add 10 parts of silica-coated piperazine pyrophosphate to 20 parts of xylene and disperse evenly by ultrasonication to obtain silica-coated piperazine pyrophosphate dispersion; Add 0.38 parts of tetramethylpiperidinol and 0.55 parts of 3-isocyanate propyltrimethoxysilane to 10 parts of xylene and mix evenly, stir for 3h at 40℃, add silica-coated piperazine pyrophosphate dispersion, heat to 120℃, stir for 12h, cool to room temperature, filter, wash, and dry to obtain modified piperazine pyrophosphate; Step 2: Preparation of modified calcium carbonate: Heat 10 parts of calcium carbonate to 100℃, stir for 30 min to remove water, add 0.2 parts of rare earth coupling agent WOT, and continue stirring for 15 min to obtain modified calcium carbonate.

[0047] Step 3: Preparation of flame-retardant polypropylene fiber material: S1: Add 73.9 parts of polypropylene resin (MFR=40g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh out a modified piperazine pyrophosphate / aluminum hypophosphite in a mass ratio of 11:3 as a flame retardant; add the premix, 23 parts of flame retardant, 0.5 parts of modified calcium carbonate, 0.3 parts of talc, 0.1 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts of tris(2,4-di-tert-butylphenyl) phosphite into a horizontal mixer and mix for 10 min. Then, use a twin-screw extruder to melt-extrude at a temperature range of 180~230℃, control the screw speed at 350 rpm / min, and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0048] Comparative Example 5: Based on Example 5, only silica was used for encapsulation during the piperazine pyrophosphate modification process, as detailed below: Step 1: Preparation of modified piperazine pyrophosphate: (1) Add 10 parts of piperazine pyrophosphate and 0.15 parts of dodecylphenol polyoxyethylene ether to 50 parts of 70wt% ethanol aqueous solution, mix evenly at 45℃, add ammonia aqueous solution to adjust pH to 10, add 2.8 parts of tetraethyl orthosilicate, stir and react for 5h, filter, wash, dry to obtain modified piperazine pyrophosphate; Step 2: Preparation of modified calcium carbonate: Heat 10 parts of calcium carbonate to 100℃, stir for 30 min to remove water, add 0.2 parts of rare earth coupling agent WOT, and continue stirring for 15 min to obtain modified calcium carbonate.

[0049] Step 3: Preparation of flame-retardant polypropylene fiber material: S1: Add 73.9 parts of polypropylene resin (MFR=40g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh modified piperazine pyrophosphate, piperazine pyrophosphate, and aluminum hypophosphite in a mass ratio of 7:4:3 as flame retardants; add the premix, 23 parts of flame retardant, 0.5 parts of modified calcium carbonate, 0.3 parts of talc, 0.1 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts of tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Then, use a twin-screw extruder to melt-extrude at a temperature range of 180~230℃, controlling the screw speed at 350 rpm / min and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0050] Comparative Example 6: Based on Example 5, the calcium carbonate was not modified, as follows: Step 1: Preparation of modified piperazine pyrophosphate: (1) Add 10 parts of piperazine pyrophosphate and 0.15 parts of dodecylphenol polyoxyethylene ether to 50 parts of 70wt% ethanol aqueous solution, mix evenly at 45℃, add ammonia aqueous solution to adjust pH to 10, add 2.8 parts of tetraethyl orthosilicate, stir for 5h, filter, wash, and dry to obtain silica-coated piperazine pyrophosphate; (2) Add 10 parts of silica-coated piperazine pyrophosphate to 20 parts of xylene and disperse evenly by ultrasonication to obtain silica-coated piperazine pyrophosphate dispersion; Add 0.38 parts of tetramethylpiperidinol and 0.55 parts of 3-isocyanate propyltrimethoxysilane to 10 parts of xylene and mix evenly, stir for 3h at 40℃, add silica-coated piperazine pyrophosphate dispersion, heat to 120℃, stir for 12h, cool to room temperature, filter, wash, and dry to obtain modified piperazine pyrophosphate; Step 2: Preparation of flame-retardant polypropylene fiber material: S1: Add 73.9 parts of polypropylene resin (MFR=40g / 10min) and 2 parts of nano silica to a high-speed mixer and premix for 10min to obtain a premix; S2: Weigh modified piperazine pyrophosphate, piperazine pyrophosphate, and aluminum hypophosphite in a mass ratio of 7:4:3 as flame retardants; add the premix, 23 parts of flame retardant, 0.5 parts of calcium carbonate, 0.3 parts of talc, 0.1 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.2 parts of tris(2,4-di-tert-butylphenyl) phosphite to a horizontal mixer and mix for 10 min. Then, use a twin-screw extruder to melt-extrude at a temperature range of 180~230℃, controlling the screw speed at 350 rpm / min and the feed flow rate at 200 kg / h to obtain flame-retardant polypropylene fiber material.

[0051] Performance Test 3: The samples obtained by injection molding of flame-retardant polypropylene fiber materials from Examples 5-7 and Comparative Examples 4-6 were subjected to the following tests: (1) Prepare type 1A tensile specimens according to GB / T 1040.2-2006, measure tensile strength, and tensile rate is 50 mm / min; (2) Prepare type I test samples according to GB / T 2406.2-2009 and measure the limiting oxygen index (LOI) of the samples; the experimental data are shown in Table 4.

[0052] Table 4

[0053] As shown in Table 4, Example 5, by introducing double-layer coated modified piperazine pyrophosphate and rare earth coupling agent modified calcium carbonate, improved its dispersibility in the polypropylene matrix, enhanced its flame retardancy, and restored the tensile strength to the performance when the flame retardant addition was 13%. In Comparative Example 4, replacing all piperazine pyrophosphate with modified piperazine pyrophosphate, although further improving dispersibility and slightly enhancing mechanical properties, lacked the rapid expansion and gas generation capacity of unmodified piperazine pyrophosphate, resulting in a reduced rate of expanded char formation and decreased flame retardancy. In Comparative Example 5, only silica was used for coating during the piperazine pyrophosphate modification process. Due to the hydrophilic surface, the compatibility with the polypropylene matrix was reduced, and the lack of hindered amine for free radical capture led to a decrease in tensile strength and flame retardancy. In Comparative Example 6, calcium carbonate was not modified, resulting in decreased dispersibility and the lack of rare earth catalytic char formation, thus both tensile strength and flame retardancy decreased.

[0054] In summary, the polypropylene fiber material prepared by this invention has excellent flame retardant properties while ensuring excellent mechanical properties.

[0055] It improves the compatibility and dispersibility of flame retardants with polypropylene, hindered amine groups capture free radicals to reduce thermal degradation during processing, and rare earth ions catalyze the formation of a dense char layer, thus synergistically enhancing flame retardant efficiency and mechanical properties.

[0056] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing flame-retardant polypropylene fiber material, characterized in that: Includes the following steps: S1: Polypropylene resin and nano-silica are added to a high-speed mixer for premixing to obtain a premix; S2: Add the premix, flame retardant, calcium carbonate, talc, and antioxidant to a horizontal mixer and mix. Then, use a twin-screw extruder to melt-extrude the mixture to obtain flame-retardant polypropylene fiber material. The flame-retardant polypropylene fiber material comprises the following raw materials, by weight: 65-95 parts polypropylene resin, 5-30 parts flame retardant, 1-2 parts nano silica, 0.1-0.5 parts calcium carbonate, 0.1-0.35 parts talc, and 0.05-0.3 parts antioxidant. The flame retardant comprises piperazine pyrophosphate and aluminum hypophosphite in a mass ratio of 8 to 12:

3.

2. The method for preparing a flame-retardant polypropylene fiber material according to claim 1, characterized in that: The flame retardant comprises modified piperazine pyrophosphate, piperazine pyrophosphate, and aluminum hypophosphite in a mass ratio of 5~8:3~4:

3.

3. The method for preparing a flame-retardant polypropylene fiber material according to claim 2, characterized in that: The preparation method of the modified piperazine pyrophosphate includes the following steps: (1) Add piperazine pyrophosphate and dodecylphenol polyoxyethylene ether to an ethanol aqueous solution, mix them evenly at 40~50℃, add ammonia aqueous solution to adjust the pH to 10, add tetraethyl orthosilicate, stir the reaction for 4~6h, filter, wash, and dry to obtain silica-coated piperazine pyrophosphate. (2) Add silica-coated piperazine pyrophosphate to xylene and disperse it evenly by ultrasonication to obtain silica-coated piperazine pyrophosphate dispersion; add tetramethylpiperidinol and 3-isocyanate-propyltrimethoxysilane to xylene and mix evenly, stir and react at 40~45℃ for 2~3h, add silica-coated piperazine pyrophosphate dispersion, heat to 120~130℃, stir and react for 10~12h, cool to room temperature, filter, wash and dry to obtain modified piperazine pyrophosphate.

4. The method for preparing a flame-retardant polypropylene fiber material according to claim 3, characterized in that: The silica-coated piperazine pyrophosphate comprises the following raw materials, in parts by weight: 8-10 parts piperazine pyrophosphate, 0.12-0.18 parts dodecylphenol polyoxyethylene ether, 50 parts aqueous ethanol solution, and 2.5-3.2 parts tetraethyl orthosilicate; The modified piperazine pyrophosphate comprises the following raw materials, in parts by mass: 8-10 parts silica-coated piperazine pyrophosphate, 0.3-0.55 parts tetramethylpiperidinol, 0.42-0.68 parts 3-isocyanate-propyltrimethoxysilane, and 30-40 parts xylene.

5. The method for preparing a flame-retardant polypropylene fiber material according to claim 1, characterized in that: The calcium carbonate needs to be modified before addition to obtain modified calcium carbonate; the preparation method of the modified calcium carbonate includes the following steps: heating the calcium carbonate to 100~105℃, stirring for 20~30min to remove water, adding rare earth coupling agent WOT, and continuing to stir and react for 10~15min to obtain modified calcium carbonate.

6. The method for preparing a flame-retardant polypropylene fiber material according to claim 5, characterized in that: The mass ratio of calcium carbonate to rare earth coupling agent WOT is 10:0.1~0.

4.

7. The method for preparing a flame-retardant polypropylene fiber material according to claim 1, characterized in that: The antioxidant includes one or both of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite.

8. The method for preparing a flame-retardant polypropylene fiber material according to claim 1, characterized in that: The premixing process takes 10-15 minutes; the mixing process takes 5-10 minutes.

9. The method for preparing a flame-retardant polypropylene fiber material according to claim 1, characterized in that: During the melt extrusion process of the twin-screw extruder, the melt temperature range is 180~230℃, the screw speed is 300~400rpm / min, and the feed flow rate is 180~200kg / h.

10. The flame-retardant polypropylene fiber material prepared by the method for preparing flame-retardant polypropylene fiber material according to any one of claims 1 to 9.

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