High-hardness low-smoke halogen-free flame-retardant polyolefin as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of flame-retardant polyolefin materials, relates to high-hardness, low-smoke, halogen-free and flame-retardant polyolefin as well as a preparation method and application thereof, and discloses the high-hardness, low-smoke, halogen-free and flame-retardant polyolefin. Comprising the following components in parts by weight: 15-80 parts of low density polyethylene (LDPE), 5-60 parts of polypropylene (PP), 35-70 parts of a halogen-free flame retardant, 5-30 parts of a compatilizer, 0.1-3 parts of a lubricant, 0.1-5 parts of an antioxidant and 10-40 parts of a reinforcing filler, the halogen-free flame retardant is composed of nano magnesium hydroxide and a red phosphorus / chitosan / silicon dioxide coating, and the reinforcing filler is a coupling agent modified wollastonite fiber. The invention also discloses a preparation method of the high-hardness low-smoke halogen-free flame-retardant polyolefin and application of the polyolefin in wires and cables. The high-hardness, low-smoke, halogen-free and flame-retardant polyolefin disclosed by the invention not only realizes the performance breakthrough of high hardness, low smoke and flame retardance, but also has good processability and long-term use stability, and has a wide market application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of flame-retardant polyolefin materials and relates to a high-hardness, low-smoke, halogen-free flame-retardant polyolefin and a preparation method and application thereof. Background Art

[0002] As global demands for material safety and environmental protection increase, traditional halogen-containing flame-retardant polyolefins (such as polyvinyl chloride) are gradually being phased out due to the toxic smoke and corrosive gases (such as HBr and HCl) released during combustion. This is particularly true in the construction, electronics, rail transit, automotive, and other fields, where higher demands are placed on flame retardancy, low smoke, non-toxicity, and mechanical strength. This is driving the development and application of low-smoke, halogen-free, flame-retardant polyolefins.

[0003] During the production of horizontal twisted-pair cables for digital communications, the low-smoke, halogen-free, flame-retardant polyolefin (LSH-ZH) framework is often subjected to a certain degree of tension, causing varying degrees of deformation during the cabling process, which in turn affects the cable's electrical performance. Therefore, improving the hardness of LSH-ZHH polyolefin, while achieving a balance between flame retardancy and hardness, achieving LSH-ZH, and improving processing performance, remains a pressing and challenging challenge. Summary of the Invention

[0004] The purpose of the present invention is to address the above problems existing in the prior art and to propose a high-hardness, low-smoke, halogen-free, flame-retardant polyolefin that can not only meet the balance between flame retardancy and hardness, but also achieve low smoke and halogen-free and improve processing performance.

[0005] One object of the present invention is achieved by the following technical solutions:

[0006] A high-hardness, low-smoke, halogen-free flame-retardant polyolefin comprises the following components in parts by weight: 15-80 parts of low-density polyethylene (LDPE), 5-60 parts of polypropylene (PP), 35-70 parts of a halogen-free flame retardant, 5-30 parts of a compatibilizer, 0.1-3 parts of a lubricant, 0.1-5 parts of an antioxidant, and 10-40 parts of a reinforcing filler. The halogen-free flame retardant comprises nano-magnesium hydroxide and a red phosphorus / chitosan / silicon dioxide coating, and the reinforcing filler is wollastonite fiber modified with a coupling agent.

[0007] Preferably, the high-hardness, low-smoke, halogen-free flame-retardant polyolefin comprises the following components in parts by weight: 50-70 parts of LDPE, 10-20 parts of PP, 35-60 parts of halogen-free flame retardant, 10-15 parts of compatibilizer, 0.5-1.0 parts of lubricant, 0.3-2 parts of antioxidant, and 15-25 parts of reinforcing filler, wherein the halogen-free flame retardant is composed of nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating, and the reinforcing filler is wollastonite fiber modified by a coupling agent.

[0008] Preferably, the mass ratio of nano magnesium hydroxide to red phosphorus / chitosan / silicon dioxide coating in the halogen-free flame retardant is (5-30):1.

[0009] More preferably, the mass ratio of nano-magnesium hydroxide to red phosphorus / chitosan / silicon dioxide coating in the halogen-free flame retardant is (7-25):1.

[0010] More preferably, the mass ratio of nano-magnesium hydroxide to red phosphorus / chitosan / silicon dioxide coating in the halogen-free flame retardant is (10-15):1.

[0011] Preferably, the average particle size of the nano-magnesium hydroxide is ≤100 nm.

[0012] Preferably, the red phosphorus / chitosan / silicon dioxide coating is prepared by sequentially wrapping chitosan and silicon dioxide with pretreated red phosphorus.

[0013] More preferably, the pretreatment of the red phosphorus comprises: adding red phosphorus to a sodium hydroxide solution and boiling, followed by filtering, drying, and ball milling to obtain pretreated red phosphorus with an average particle size of ≤5 μm.

[0014] More preferably, the mass ratio of red phosphorus, chitosan and silicon dioxide in the red phosphorus / chitosan / silicon dioxide coating is 1:(0.2-0.6):(0.3-0.8).

[0015] More preferably, the mass ratio of red phosphorus, chitosan and silicon dioxide in the red phosphorus / chitosan / silicon dioxide coating is 1:(0.2-0.4):(0.4-0.8).

[0016] More preferably, the mass ratio of red phosphorus, chitosan and silicon dioxide in the red phosphorus / chitosan / silicon dioxide coating is 1:0.3:0.6.

[0017] Preferably, the preparation method of the red phosphorus / chitosan / silicon dioxide coating comprises:

[0018] (1) The pretreatment of red phosphorus comprises: adding red phosphorus to a 0.1-10 wt% sodium hydroxide solution and boiling for 10-240 minutes, filtering, drying, and wet ball milling to obtain pretreated red phosphorus with an average particle size of 0.1-5 μm;

[0019] (2) adding chitosan to an acetic acid solution and adjusting the solution pH to 3-6; adding pretreated red phosphorus, stirring, and using ultrasonic assisted dispersion; then adding sodium hydroxide solution dropwise to adjust the solution pH to 8-10, filtering, and drying to obtain a red phosphorus / chitosan coating;

[0020] (3) adding ethyl orthosilicate to ethanol, adding ammonia water to adjust the solution pH to 10-11, stirring for 4 hours and then letting it stand to obtain silica sol; adding red phosphorus / chitosan coating and ammonia water catalyst to the silica sol, heating and stirring in a water bath to react, filtering and drying to obtain red phosphorus / chitosan / silica coating.

[0021] More preferably, 0.01 to 2 g of red phosphorus is added to every 100 ml of sodium hydroxide solution in (1).

[0022] More preferably, the mass ratio of chitosan to pretreated red phosphorus in (2) is (0.1-0.6):1.

[0023] More preferably, the mass ratio of ethyl orthosilicate to red phosphorus / chitosan coating in (3) is (0.5-5):1.

[0024] More preferably, the mass ratio of ethyl orthosilicate to red phosphorus / chitosan coating in (3) is (1.5-3):1.

[0025] More preferably, the water bath heating temperature in (3) is 30-90° C. and the heating time is 1-12 h.

[0026] More preferably, the average particle size of the red phosphorus / chitosan / silicon dioxide coating in (3) is 5 to 20 μm.

[0027] Preferably, the mass ratio of the halogen-free flame retardant to the reinforcing filler is (2-3):1.

[0028] Preferably, the preparation method of the coupling agent-modified wollastonite fiber comprises:

[0029] (1) adding wollastonite fiber to a phosphoric acid solution, stirring continuously, filtering, and drying to obtain pretreated wollastonite fiber;

[0030] (2) adding a titanate coupling agent to an ethanol solution and mixing the mixture; adding hydrochloric acid to adjust the pH of the solution to 5-6 to obtain a coupling agent solution; adding the pretreated wollastonite fiber to the coupling agent solution and stirring, and using ultrasonic wave-assisted dispersion; filtering and drying to obtain coupling agent-modified wollastonite fiber.

[0031] More preferably, the mass ratio of the titanate coupling agent to the pretreated wollastonite fiber is 1:(5-70).

[0032] Preferably, the high-hardness, low-smoke, halogen-free flame-retardant polyolefin has a Shore D hardness greater than 54, an oxygen index greater than 30%, a tensile strength greater than 15 MPa, and a flammability rating of UL 94 of V-0.

[0033] More preferably, the high-hardness, low-smoke, halogen-free flame-retardant polyolefin has a Shore D hardness greater than 56, an oxygen index greater than 31.5%, and a tensile strength greater than 15.5 MPa.

[0034] The second object of the present invention is achieved through the following technical solutions:

[0035] A method for preparing high-hardness, low-smoke, halogen-free flame-retardant polyolefin, comprising:

[0036] (1) weighing raw materials in proportion, and premixing LDPE, PP and halogen-free flame retardant to obtain a premix;

[0037] (2) After adding the remaining components to the premix, secondary mixing is performed, and the premix is melt-blended and extruded through a twin-screw extruder, water-cooled, pelletized, and dried to obtain a high-hardness, low-smoke, halogen-free, flame-retardant polyolefin.

[0038] Preferably, the rotation speed of the premixing process is 300-600 rpm, the temperature is 40-70° C., and the time is 1-30 min.

[0039] Preferably, the rotation speed of the secondary mixing process is 600-1200 rpm, the temperature is 70-100° C., and the time is 1-30 min.

[0040] Preferably, the temperature of the melt blending process is 160-180°C.

[0041] The third object of the present invention is achieved through the following technical solutions:

[0042] The invention discloses an application of high-hardness, low-smoke, halogen-free flame-retardant polyolefin in wires and cables.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. The raw materials of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin of the present invention use nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating as compound halogen-free flame retardants to achieve effective flame retardancy; and the red phosphorus / chitosan / silicon dioxide coating has a three-layer structure, with chitosan and silicon dioxide sequentially coated on the surface of the red phosphorus to further enhance the flame retardant effect.

[0045] 2. The raw materials of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin of the present invention use wollastonite fiber modified with a coupling agent as a reinforcing filler, which further improves the mechanical properties compared with ordinary wollastonite fiber or commercially available modified calcium carbonate.

[0046] 3. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin of the present invention uses LDPE and PP as the matrix, and adds halogen-free flame retardants, compatibilizers, lubricants, antioxidants, and reinforcing fillers to achieve high hardness, low smoke, and flame retardancy at the same time; during the combustion process, it effectively suppresses the spread of flame without releasing toxic and harmful gases, which meets environmental protection and safety requirements; the compatibilizer greatly improves the compatibility of the matrix resin with other components, making them evenly dispersed, and enhancing the uniformity and stability of the overall performance; the lubricant improves the fluidity of each component, making it easier to form and process, and can also reduce the wear of processing equipment and extend the service life of the equipment; the antioxidant can effectively capture the free radicals generated by the material during processing and use, prevent or delay the oxidative degradation of the material, significantly improve the aging resistance of the material, and extend its service life; the reinforcing filler can fill the gaps inside the material, enhance the intermolecular force, thereby greatly improving the hardness and mechanical strength of the material, so that it can meet the needs of more high-hardness application scenarios.

[0047] 4. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin of the present invention not only achieves breakthroughs in high hardness, low smoke, and flame retardancy, but also has good processing performance and long-term stability.

[0048] 5. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin of the present invention can be widely used in many fields such as wires and cables, electronic appliances, and architectural decoration, and has broad market application prospects and significant social and economic benefits. DETAILED DESCRIPTION

[0049] The technical solutions of the present invention are further described below through specific embodiments. It should be understood that the specific embodiments described herein are only used to help understand the present invention and are not used to specifically limit the present invention.

[0050] Unless otherwise specified, the raw materials used in the examples of the present invention are all commonly used raw materials in the art, and the methods used in the examples are all conventional methods in the art.

[0051] In this article, high hardness, low smoke, halogen-free flame retardant polyolefins were tested:

[0052] 1. Hardness test

[0053] According to GB / T 2411-2008, "Determination of Indentation Hardness (Shore Hardness) of Plastics and Ebonite Using a Durometer," high-hardness, low-smoke, halogen-free, flame-retardant polyolefin is injection molded into a 10mm*10mm*5mm square plate. After 24 hours, it is used as a test sample. Place the sample to be tested on a horizontal surface and hold the D-type durometer, ensuring that the indenter is perpendicular to the sample surface. Gently rotate the handle of the D-type durometer to press the indenter onto the sample surface. Maintain a uniform rotation speed as the indenter presses into the sample surface. When the indenter is fully pressed into the sample surface, read the hardness value on the D-type durometer.

[0054] 2. Flame retardant performance test

[0055] The oxygen index (LOI) refers to the minimum oxygen concentration required for a material to burn with a flame in an oxygen-nitrogen mixture under specified conditions. A higher oxygen index indicates better flame retardancy. This test is based on the test method specified in the standard GB / T2406.2-2009, "Determination of Combustion Behavior of Plastics by Oxygen Index Method - Part 2: Room Temperature Test."

[0056] 3. Tensile properties test

[0057] Tensile testing involves stretching a specimen at a constant rate along its longitudinal principal axis until it breaks or reaches a predetermined stress or strain value. The load and elongation of the specimen are measured during this process. This test is conducted according to the test method specified in GB / T 1040.1-2018, "Determination of Tensile Properties of Plastics - Part 1: General Principles."

[0058] 4. Combustion performance test

[0059] Combustion performance tests examine a specimen's reaction to fire or resistance to fire by subjecting it to specified combustion conditions. This test is conducted according to the test method specified in GB / T 2408-2021, "Plastics - Determination of Combustion Performance - Horizontal and Vertical Methods."

[0060] In this article, the brand of commercially available microencapsulated red phosphorus flame retardant is HTJ (particle size is 6 to 20 μm), and the model of commercially available modified calcium carbonate is KH-3500.

[0061] Example 1

[0062] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0063] The mass ratio of nano-magnesium hydroxide to red phosphorus / chitosan / silicon dioxide coating is 12:1.

[0064] The preparation method of the red phosphorus / chitosan / silicon dioxide coating (1:0.3:0.6) comprises:

[0065] (1) The pretreatment of red phosphorus includes: adding 3 g of red phosphorus to 300 ml of 5 wt% sodium hydroxide solution, boiling for 120 min, filtering, and drying; and then wet-milling in a ball mill at 300 rpm for 360 min to obtain pretreated red phosphorus with an average particle size of 3 μm.

[0066] (2) Add 0.6 g of chitosan to 50 ml of 2 wt% acetic acid solution and adjust the solution pH to 5; add 2 g of pretreated red phosphorus, stir, and use ultrasonic assisted dispersion; then dropwise add sodium hydroxide solution to adjust the solution pH to 9, filter, and dry to obtain a red phosphorus / chitosan coating (1:0.3);

[0067] (3) 5.2 g of tetraethyl orthosilicate was added to 200 ml of ethanol, and 30 wt% ammonia water was added to adjust the pH of the solution to 10. The solution was stirred for 4 hours and then allowed to stand to obtain a silica sol. 2.6 g of red phosphorus / chitosan coating and 0.1 mol of ammonia water catalyst were added to the silica sol. The mixture was heated in a water bath at 40°C and stirred for 6 hours. After filtration and drying, a red phosphorus / chitosan / silica coating (red phosphorus / chitosan coating: tetraethyl orthosilicate = 1:2) with an average particle size of 8 μm was obtained.

[0068] The preparation method of the coupling agent-modified wollastonite fiber comprises:

[0069] (1) Add 30 g of wollastonite fiber to 300 ml of 2 wt% phosphoric acid solution and stir continuously, filter and dry to obtain pretreated wollastonite fiber;

[0070] (2) Add 0.2 g of titanate coupling agent to the ethanol solution and mix well, add hydrochloric acid to adjust the pH of the solution to 5 to obtain a coupling agent solution; add 20 g of pretreated wollastonite fiber to the coupling agent solution and stir, and use ultrasonic assisted dispersion; after filtering and drying, obtain coupling agent-modified wollastonite fiber.

[0071] The preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin comprises the following steps:

[0072] (1) LDPE, PP and halogen-free flame retardant were premixed in a high-speed mixer at a speed of 500 rpm and 60°C for 5 min;

[0073] (2) adding reinforcing filler, compatibilizer, lubricant and antioxidant into the high-speed mixer at a rate of 800 rpm and mixing for a second time at 80° C. for 8 min; then, melting and blending are extruded through a twin-screw extruder, and the mixture is water-cooled, pelletized and dried to obtain a high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product.

[0074] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0075] Example 2

[0076] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0077] Compared with Example 1, the mass ratio of nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating is 12:1; the mass ratio of red phosphorus, chitosan and silicon dioxide as raw materials of the red phosphorus / chitosan / silicon dioxide coating is 1:0.2:0.4.

[0078] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0079] Example 3

[0080] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0081] Compared with Example 1, the mass ratio of nano-magnesium hydroxide to red phosphorus / chitosan / silicon dioxide coating is 12:1; the mass ratio of red phosphorus, chitosan and silicon dioxide as raw materials of the red phosphorus / chitosan / silicon dioxide coating is 1:0.4:0.8.

[0082] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0083] Example 4

[0084] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0085] The mass ratio of nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating is 25:1; the mass ratio of red phosphorus, chitosan and silicon dioxide, the raw materials of the red phosphorus / chitosan / silicon dioxide coating, is 1:0.3:0.6.

[0086] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0087] Example 5

[0088] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0089] The mass ratio of nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating is 13:1; the mass ratio of red phosphorus, chitosan and silicon dioxide, the raw materials of the red phosphorus / chitosan / silicon dioxide coating, is 1:0.3:0.6.

[0090] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0091] Example 6

[0092] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0093] The mass ratio of nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating is 7.67:1; the mass ratio of red phosphorus, chitosan and silicon dioxide, the raw materials of the red phosphorus / chitosan / silicon dioxide coating, is 1:0.3:0.6.

[0094] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0095] Example 7

[0096] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0097] The mass ratio of nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating is 12:1; the mass ratio of red phosphorus, chitosan and silicon dioxide, the raw materials of the red phosphorus / chitosan / silicon dioxide coating, is 1:0.6:0.3.

[0098] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0099] Example 8

[0100] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0101] Among them, the proportion of halogen-free flame retardants added is 32.65%.

[0102] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0103] Example 9

[0104] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this embodiment are shown in Table 1.

[0105] Among them, the proportion of halogen-free flame retardants added is 30.31%.

[0106] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0107] Comparative Example 1

[0108] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0109] The preparation method of the coupling agent-modified wollastonite fiber and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1.

[0110] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0111] Comparative Example 2

[0112] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0113] The preparation method of the coupling agent-modified wollastonite fiber and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1.

[0114] Preparation method of red phosphorus / silicon dioxide coating (1:0.6):

[0115] (1) The same as step (1) of the method for preparing the red phosphorus / chitosan / silicon dioxide coating in Example 1;

[0116] (2) Compared with step (3) of the method for preparing the red phosphorus / chitosan / silica coating in Example 1, the difference is that the red phosphorus pretreated in (1) is added to the silica sol instead of the red phosphorus / chitosan coating to prepare the red phosphorus / silica coating.

[0117] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0118] Comparative Example 3

[0119] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0120] The preparation method of the coupling agent-modified wollastonite fiber and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1.

[0121] The preparation method of the red phosphorus / chitosan coating (1:0.3) is the same as steps (1-2) of the preparation method of the red phosphorus / chitosan / silicon dioxide coating in Example 1.

[0122] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0123] Comparative Example 4

[0124] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0125] The preparation method of the coupling agent-modified wollastonite fiber and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1.

[0126] The red phosphorus / silicon dioxide / chitosan coating has red phosphorus as the core, and is coated with silicon dioxide and chitosan in sequence, with the mass ratio of red phosphorus, silicon dioxide and chitosan being 1:0.3:0.6. The preparation method includes:

[0127] (1) The same as step (1) of the method for preparing the red phosphorus / chitosan / silicon dioxide coating in Example 1, to obtain red phosphorus;

[0128] (2) Compared with step (3) of the method for preparing the red phosphorus / chitosan / silica coating in Example 1, the difference is that the red phosphorus pretreated in step (1) of this comparative example is added to obtain the red phosphorus / silica coating;

[0129] (3) Compared with step (2) of the method for preparing the red phosphorus / chitosan / silica coating in Example 1, the difference is that the red phosphorus / silica coating of step (2) of this comparative example is added to obtain the red phosphorus / silica / chitosan coating.

[0130] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0131] Comparative Example 5

[0132] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0133] The preparation method of the coupling agent-modified wollastonite fiber and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1.

[0134] The chitosan / silicon dioxide / red phosphorus coating has chitosan as the core, and is coated with silicon dioxide and red phosphorus in sequence, with the mass ratio of chitosan, silicon dioxide and red phosphorus being 0.6:0.3:1. The preparation method includes:

[0135] (1) Compared with step (2) of the method for preparing the red phosphorus / chitosan / silicon dioxide coating in Example 1, the difference is that no pretreated red phosphorus is added, and chitosan is obtained;

[0136] (2) Compared with step (3) of the method for preparing the red phosphorus / chitosan / silica coating in Example 1, the difference is that chitosan in step (1) of this comparative example is added to obtain a chitosan / silica coating.

[0137] (3) The same as step (1) of the method for preparing the red phosphorus / chitosan / silicon dioxide coating in Example 1, to obtain red phosphorus;

[0138] (4) The chitosan / silica coating was dispersed in ethanol, and then the red phosphorus in step (3) of this comparative example was added to obtain a chitosan / silica / red phosphorus coating.

[0139] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0140] Comparative Example 6

[0141] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0142] The preparation method of the coupling agent-modified wollastonite fiber and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1.

[0143] The red phosphorus / chitosan / silicon dioxide coating is replaced by separate red phosphorus, chitosan, and silicon dioxide, and red phosphorus, chitosan, and silicon dioxide are directly mixed in a mass ratio of 1:0.3:0.6 and then added. The preparation method includes:

[0144] (1) The same as step (1) of the method for preparing the red phosphorus / chitosan / silicon dioxide coating in Example 1, to obtain red phosphorus;

[0145] (2) Compared with step (2) of the method for preparing the red phosphorus / chitosan / silica coating in Example 1, the difference is that the pretreated red phosphorus is not added, and chitosan is obtained;

[0146] (3) Compared with step (3) of the method for preparing the red phosphorus / chitosan / silicon dioxide coating in Example 1, the difference is that the red phosphorus / chitosan coating is not added, and silicon dioxide is obtained.

[0147] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0148] Comparative Example 7

[0149] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0150] The preparation method of the red phosphorus / chitosan / silicon dioxide coating and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1.

[0151] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0152] Comparative Example 8

[0153] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0154] The preparation method of the coupling agent-modified wollastonite fiber and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1; the wollastonite fiber pretreated in Example 1 is used instead of the coupling agent-modified wollastonite fiber.

[0155] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0156] Comparative Examples 9 to 15

[0157] The raw material components and weight proportions of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin in this comparative example are shown in Table 2.

[0158] The preparation methods of the red phosphorus / chitosan / silicon dioxide coating, the preparation method of the coupling agent-modified wollastonite fiber, and the preparation method of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin are the same as those in Example 1.

[0159] The high-hardness, low-smoke, halogen-free flame-retardant polyolefin finished product was subjected to performance testing, and the results are shown in Table 3.

[0160] Table 1. Ratio of raw materials for high hardness, low smoke, halogen-free flame retardant polyolefins in the examples

[0161]

[0162] Table 2. Ratio of raw materials for high hardness, low smoke, halogen-free flame retardant polyolefins in comparative examples

[0163]

[0164] Table 3. Performance test table of high hardness, low smoke, halogen-free flame retardant polyolefin

[0165]

[0166] In summary, the high-hardness, low-smoke, halogen-free flame-retardant polyolefin of the present invention uses LDPE and PP as base resins, adds halogen-free flame retardants, compatibilizers, lubricants, antioxidants, and reinforcing fillers, and simultaneously achieves high hardness, low smoke, and flame retardancy; and the present invention uses nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating as compound halogen-free flame retardants to achieve effective flame retardancy; wherein the red phosphorus / chitosan / silicon dioxide coating is a three-layer structure, and a certain proportion of chitosan and silicon dioxide are sequentially wrapped on the surface of red phosphorus to further enhance the flame retardant effect.

[0167] The various aspects, embodiments, and features of the present invention should be considered in all respects as illustrative and not limiting, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0168] In the preparation method of the present invention, the order of the steps is not limited to the order listed. Persons skilled in the art will appreciate that variations in the order of the steps are within the scope of the present invention without inventive effort. Furthermore, two or more steps or actions may be performed simultaneously.

[0169] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit its implementation. Persons skilled in the art may make various modifications, additions, or substitute similar methods for the described specific embodiments. It is not necessary and impossible to provide comprehensive examples of all implementations here. However, obvious variations or modifications arising from the essential spirit of the present invention remain within the scope of protection of the present invention, and interpreting them as any additional limitations would be contrary to the spirit of the present invention.

Claims

1. A high-hardness, low-smoke, halogen-free flame-retardant polyolefin, characterized in that: The invention comprises the following components in parts by weight: 15 to 80 parts of low-density polyethylene (LDPE), 5 to 60 parts of polypropylene (PP), 35 to 70 parts of halogen-free flame retardant, 5 to 30 parts of compatibilizer, 0.1 to 3 parts of lubricant, 0.1 to 5 parts of antioxidant, and 10 to 40 parts of reinforcing filler, wherein the halogen-free flame retardant is composed of nano-magnesium hydroxide and red phosphorus / chitosan / silicon dioxide coating, and the reinforcing filler is wollastonite fiber modified by a coupling agent.

2. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to claim 1, characterized in that: The mass ratio of nano magnesium hydroxide to red phosphorus / chitosan / silicon dioxide coating in the halogen-free flame retardant is (5-30):

1.

3. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to claim 1, characterized in that: The mass ratio of red phosphorus, chitosan and silicon dioxide in the red phosphorus / chitosan / silicon dioxide coating is 1: (0.2-0.6): (0.3-0.8).

4. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to claim 1, characterized in that: The high-hardness, low-smoke, halogen-free flame-retardant polyolefin comprises the following components in parts by weight: 50-70 parts of LDPE, 10-20 parts of PP, 35-60 parts of a halogen-free flame retardant, 10-15 parts of a compatibilizer, 0.5-1.0 parts of a lubricant, 0.3-2 parts of an antioxidant, and 15-25 parts of a reinforcing filler. The halogen-free flame retardant comprises nano-magnesium hydroxide and a red phosphorus / chitosan / silicon dioxide coating in a mass ratio of (10-15):1, and the reinforcing filler is wollastonite fiber modified with a coupling agent. The red phosphorus / chitosan / silicon dioxide coating is prepared by sequentially wrapping chitosan and silicon dioxide with pretreated red phosphorus. The mass ratio of red phosphorus, chitosan, and silicon dioxide in the red phosphorus / chitosan / silicon dioxide coating is 1:(0.2-0.4):(0.4-0.8).

5. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to claim 1, characterized in that: The preparation method of the red phosphorus / chitosan / silicon dioxide coating comprises: (1) The pretreatment of red phosphorus comprises: adding red phosphorus to a 0.1-10 wt% sodium hydroxide solution and boiling for 10-240 minutes, filtering, drying, and wet ball milling to obtain pretreated red phosphorus with an average particle size of 0.1-5 μm; (2) adding chitosan to an acetic acid solution and adjusting the solution pH to 3-6; adding pretreated red phosphorus, stirring, and using ultrasonic assisted dispersion; then adding sodium hydroxide solution dropwise to adjust the solution pH to 8-10, filtering, and drying to obtain a red phosphorus / chitosan coating; (3) adding ethyl orthosilicate to ethanol, adding ammonia water to adjust the solution pH to 10-11, stirring for 4 hours and then letting it stand to obtain silica sol; adding red phosphorus / chitosan coating and ammonia water catalyst to the silica sol, heating and stirring in a water bath to react, filtering and drying to obtain red phosphorus / chitosan / silica coating.

6. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to claim 5, characterized in that: The average particle size of the red phosphorus / chitosan / silicon dioxide coating in (3) is 5 to 20 μm.

7. The high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to claim 1, characterized in that: The mass ratio of the halogen-free flame retardant to the reinforcing filler is (2-3):

1.

8. A method for preparing high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to claim 1, characterized in that: The preparation method comprises: (1) weighing raw materials in proportion, and premixing LDPE, PP and halogen-free flame retardant to obtain a premix; (2) After adding the remaining components to the premix, secondary mixing is performed, and the premix is melt-blended and extruded through a twin-screw extruder, water-cooled, pelletized, and dried to obtain a high-hardness, low-smoke, halogen-free, flame-retardant polyolefin.

9. The method for preparing high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to claim 8, characterized in that: The speed of the premixing process is 300-600 rpm, the temperature is 40-70° C., and the time is 1-30 min; the speed of the secondary mixing process is 600-1200 rpm, the temperature is 70-100° C., and the time is 1-30 min; the temperature of the melt blending process is 160-180° C.

10. Use of the high-hardness, low-smoke, halogen-free flame-retardant polyolefin according to any one of claims 1 to 7 in wires and cables.

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