Synthetic method of magnesium hydroxide hybrid flame retardant and flame-retardant polymer composite material for cable

Abstract

The invention discloses a synthesis method of a magnesium hydroxide hybrid flame retardant and a flame-retardant polymer for a cable, and belongs to the technical field of environment-friendly flame retardants. According to the technical scheme, the preparation method comprises the following steps: sequentially adding magnesium hydroxide, an organic phosphorus flame retardant, a hydrogen peroxide solution and an environment-friendly reaction medium into a hydrothermal reaction kettle, ultrasonically mixing uniformly, transferring into a drying oven for heating reaction, cooling, filtering and drying to obtain the magnesium hydroxide hybrid flame retardant. The synthesis method of the magnesium hydroxide hybrid flame retardant provided by the invention has the advantages of simple process, preparation of a target product by one-pot heating, low cost, green and environment-friendly reaction medium, and suitableness for industrial mass production. Compared with a pure magnesium hydroxide flame retardant, the magnesium hydroxide hybrid flame retardant prepared by the preparation method disclosed by the invention shows excellent flame retardant property under a low filling amount, and meanwhile, a flame retardant polymer has good mechanical properties. The magnesium hydroxide hybrid flame retardant prepared by the invention is suitable for being applied to preparation of flame-retardant polymer composite materials for cables.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection flame retardants, and particularly relates to a synthesis method of a magnesium hydroxide hybrid flame retardant and its application in a flame retardant polymer composite for cables. Background Art

[0002] As the current mainstream cable insulation polymers, polyethylene (PE) and polypropylene (PP) have the advantages of light weight, non-toxicity, excellent mechanical properties, electrical insulation properties, and chemical corrosion resistance, and are widely used in various levels of power transmission, control, and instrument cables. However, the limiting oxygen index (LOI) of these polyolefin materials is low, belonging to flammable materials, and there is a significant fire risk under high-voltage electric field thermal effects, external heat sources, or overload conditions, which greatly hinders their practical applications.

[0003] As a typical representative of halogen-free flame retardants, magnesium hydroxide (MH) has the advantages of low price, convenient processing, and environmental friendliness, and occupies a dominant position in the current polymer flame retardant modification. However, due to its low flame retardant efficiency, a high addition amount is required to achieve a good flame retardant effect in the flame retardant modification of polymers for cables. Chinese invention patent CN101712875B discloses a magnesium hydroxide flame retardant and a flame retardant polymer for cables. In 100 parts of the flame retardant polymer for cables, 100-150 parts of a coupling agent-treated magnesium hydroxide flame retardant need to be added, and at the same time, processing aids and functional aids are combined to increase the LOI to more than 30. Gao Shan et al. (《Chinese Science Bulletin》2015, 10(10): 1140-1143) prepared a polypropylene / magnesium hydroxide composite material, and when the mass fraction of magnesium hydroxide was 60-70%, the UL-94 vertical burning test could reach the V-0 grade.

[0004] As an important branch of halogen-free flame retardants, organophosphorus small molecules exhibit high flame retardancy efficiency in flame-retardant polymers. However, they have poor thermal stability and are prone to migration during processing and storage. If organophosphorus small molecules are grafted onto the surface of magnesium hydroxide to synthesize organic-inorganic hybrid flame retardants, they can simultaneously play a role in gas-phase flame retardancy and condensed-phase flame retardancy, not only improving the flame retardancy efficiency of magnesium hydroxide but also solving the migration problem of organophosphorus small molecules. Liu Tingting et al. (Journal of Applied Polymer Science, 2020; 138: e49607) first reacted γ-methacryloyloxypropyltrimethoxysilane (abbreviated as WD70) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (abbreviated as DOPO) to generate DOPO-WD70, and then directly reacted with the hydroxyl groups on the surface of magnesium hydroxide to prepare the hybrid flame retardant (MH-WD70-DOPO). The grafting rate of DOPO-WD70 was calculated to be 1.32 wt%. Further, when 51.32 wt% of this hybrid flame retardant was added to ethylene-vinyl acetate copolymer (EVA), the LOI of the composite material increased to 29.8%. Li Cui et al. (Sustainable Materials and Technologies 2024, 40: e00906) in-situ grew metal-organic framework with amino groups (Fe-MOF) onto the surface of magnesium hydroxide in N,N-dimethylformamide (DMF) medium, and then reacted with diphenylphosphine to synthesize the magnesium hydroxide hybrid flame retardant (MH@Fe-MOF-P). The grafting rate of diphenylphosphine was calculated to be 18.60 wt%. When 20 wt% of MH@Fe-MOF-P was added to polybutylene succinate (PBS), the LOI of the PBS composite material increased to 29.6%, and the UL-94 vertical burning reached V-0 level.

[0005] Compared with pure magnesium hydroxide, the synthesized magnesium hydroxide hybrid flame retardants have the advantage of improving the flame retardancy efficiency, but still face problems such as cumbersome synthesis steps and unfriendly reaction medium environment. Therefore, simplifying the synthesis steps and using green and environmentally friendly reaction media are the key technical problems that need to be solved in the current field of synthesis of magnesium hydroxide hybrid flame retardants. Summary of the Invention

[0006] In view of the problem of low flame retardancy efficiency of magnesium hydroxide, the present invention develops a simple and environmentally friendly synthesis method of a magnesium hydroxide hybrid flame retardant, and provides the application of the magnesium hydroxide hybrid flame retardant in a flame retardant polymer for cables. To achieve this purpose, magnesium hydroxide, an organophosphorus flame retardant, a hydrogen peroxide solution, and an environmentally friendly reaction medium are sequentially added to a hydrothermal reaction kettle. After ultrasonic mixing evenly, a one-pot heating reaction is carried out. After cooling, filtration and drying are carried out to obtain the magnesium hydroxide hybrid flame retardant. During the reaction process, H2O2 in the hydrogen peroxide solution can not only activate magnesium hydroxide and increase the number of its surface hydroxyl groups (MH-OH), but also convert O=P-H in the organophosphorus compound into O=P-OH. Then, MH-OH and O=P-OH undergo an esterification reaction to form the magnesium hydroxide hybrid flame retardant. Subsequently, the above-mentioned magnesium hydroxide hybrid flame retardant and processing aids are added to the polymer for cables to prepare a flame retardant polymer composite for cables with good flame retardancy and excellent mechanical properties.

[0007] The technical solution of the present invention is as follows:

[0008] In the first aspect, the present invention provides a simple and environmentally friendly synthesis method of a magnesium hydroxide hybrid flame retardant. Magnesium hydroxide, an organophosphorus flame retardant, a hydrogen peroxide solution, and an environmentally friendly reaction medium are sequentially added to a hydrothermal reaction kettle, ultrasonically mixed evenly, and then transferred to an oven for heating reaction. After cooling, filtration and drying are carried out to obtain the magnesium hydroxide hybrid flame retardant.

[0009] Preferably, magnesium hydroxide, an organophosphorus flame retardant, a hydrogen peroxide solution, and an environmentally friendly reaction medium are sequentially added to a hydrothermal reaction kettle, ultrasonically treated at 20-40 °C for 1-2 h, then transferred to an oven and heated to 105-150 °C for reaction for 3-6 h. After cooling and filtration, drying is carried out at 110-130 °C for 5-10 h to obtain the magnesium hydroxide hybrid flame retardant.

[0010] Preferably, the mass fraction of magnesium hydroxide is 100 parts, the mass fraction of the organophosphorus flame retardant is 30-60 parts, the mass fraction of the hydrogen peroxide solution is 2-8 parts, and the mass fraction of the environmentally friendly reaction medium is 200-400 parts.

[0011] Preferably, the magnesium hydroxide is hexagonal flaky particles, the organophosphorus flame retardant is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (abbreviated as DOPO), the mass concentration of the hydrogen peroxide solution is 10-30%, and the environmentally friendly reaction medium is a mixture of ethanol and distilled water.

[0012] Preferably, the mass ratio of ethanol to distilled water in the environmentally friendly reaction medium is 1-3:1.

[0013] In a second aspect, the present invention also provides an application of the magnesium hydroxide hybrid flame retardant prepared by the above synthesis method, specifically: melting and blending the magnesium hydroxide hybrid flame retardant, a processing aid and a polymer for cables, and then processing and shaping them to obtain a flame retardant polymer composite material for cables.

[0014] Preferably, the polymer for cables is polyethylene (PE) or polypropylene (PP); the processing aids are compatibilizers, antioxidants, etc. commonly used in the industry. The function of the compatibilizer is to enhance the interfacial interaction between the polymer matrix and the flame retardant particles, thereby improving the flame retardancy and mechanical properties of the obtained polymer composite material. The function of the antioxidant is to prevent the oxidative degradation of the polymer molecular chain during the melt processing, which is also beneficial to improving the flame retardancy and mechanical properties of the obtained polymer composite material.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The synthesis method of the magnesium hydroxide hybrid flame retardant provided by the present invention has a simple process. The target product is prepared by one-pot heating, with low cost, and the reaction medium is green and environmentally friendly, suitable for large-scale industrial production.

[0017] 2. In the synthesis method of the magnesium hydroxide hybrid flame retardant designed and developed by the present invention, the hydrogen peroxide solution plays a "double-edged sword" dual role. It not only increases the number of surface hydroxyl groups (MH-OH) on magnesium hydroxide, but also converts O=P-H in the organophosphorus compound into O=P-OH, thus promoting the esterification reaction of the organophosphorus small molecule on the surface of magnesium hydroxide. The highest grafting rate of the organophosphorus flame retardant reaches 36.8 wt%.

[0018] 3. The magnesium hydroxide hybrid flame retardant designed and developed by the present invention shows excellent flame retardancy at a low filling amount compared with pure magnesium hydroxide. At the same time, the flame retardant polymer for cables prepared has more excellent mechanical properties. For example: ① In the polyethylene matrix, to achieve a V-0 rating in the vertical burning test, the mass fraction of pure magnesium hydroxide to be added is 70 wt%, while the mass fraction of the magnesium hydroxide hybrid flame retardant to be added is only 40 wt%; ② In the polyethylene matrix, under the same conditions of the amount of flame retardant, processing aids and processing technology, the tensile strength and notched impact strength of the polyethylene composite material prepared by adding the magnesium hydroxide hybrid flame retardant are higher than those of the polyethylene composite material added with pure magnesium hydroxide, which indicates that the magnesium hydroxide hybrid flame retardant improves the flame retardancy of the polyethylene composite material while synchronously enhancing its mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a reaction route diagram for the one-pot synthesis of the magnesium hydroxide hybrid flame retardant (MH-g-DOPO) of the present invention

[0020] Figure 2 Scanning electron microscope images of (a) magnesium hydroxide hybrid flame retardant (MH-g-DOPO1) and (b) pure magnesium hydroxide (MH) prepared in Example 1 of the present invention

[0021] Figure 3 Infrared spectra of magnesium hydroxide hybrid flame retardant (MH-g-DOPO1) and pure magnesium hydroxide (MH) prepared in Example 1 of the present invention

[0022] Figure 4 X-ray photoelectron spectroscopy of magnesium hydroxide hybrid flame retardant (MH-g-DOPO1) and pure magnesium hydroxide (MH) prepared in Example 1 of the present invention Detailed implementation manners

[0023] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0024] Performance test description:

[0025] Limiting oxygen index test (LOI) test: Tested according to the method described in GB / T 2046-2009, and the test sample size is 100 mm × 6.5 mm × 3.2 mm.

[0026] Vertical burning test: Tested according to the method described in GB / T 2408-2008, and the test sample size is 100 mm × 13 mm × 3.2 mm.

[0027] Mechanical property tests (including tensile test and notched impact test): The tensile test is carried out according to the method described in GB / T 1040.1-2018, and the effective part size of the test sample is 20 mm × 4 mm × 1 mm. The notched impact test is carried out according to the method described in GB / T 1843-2008, and the test sample size is 80 mm × 10 mm × 4.0 mm.

[0028] Reaction mechanism description:

[0029] As Figure 1 shown, the reaction route for synthesizing magnesium hydroxide hybrid flame retardant (MH-g-DOPO) by one-pot method: In a hydrothermal reaction kettle, magnesium hydroxide (MH) reacts with hydrogen peroxide (H2O2) in the hydrogen peroxide solution to form hydroxyl groups (MH-OH) on its surface; at the same time, the O=P-H in 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (abbreviated as DOPO) also reacts with H2O2 to be converted into O=P-OH; subsequently, MH-OH and O=P-OH undergo an esterification reaction (O=P-OH is acidic, self-catalytic esterification reaction) to form magnesium hydroxide hybrid flame retardant (MH-g-DOPO).

[0030] Example 1

[0031] The synthesis method of the magnesium hydroxide hybrid flame retardant in this example includes the following steps:

[0032] 100 parts of magnesium hydroxide, 60 parts of DOPO, 3 parts of 20% hydrogen peroxide solution and 300 parts of environmentally friendly reaction medium (200 parts of ethanol and 100 parts of distilled water) were successively added into a hydrothermal reaction kettle, ultrasonically treated at 20 °C for 1 h, then transferred to an oven and heated to 120 °C for reaction for 6 h. After cooling, filtration was carried out, and drying was carried out at 110 °C for 8 h to obtain the magnesium hydroxide hybrid flame retardant, named MH-g-DOPO1.

[0033] By weighing before and after the reaction and calculating, the grafting rate of DOPO in MH-g-DOPO1 prepared in this example is 36.8 wt%.

[0034] The scanning electron microscope image of MH-g-DOPO1 prepared in this example is as Figure 2 shown in a. The surface of the sheet becomes rough, and protruding particles can be observed, while in contrast, Figure 2 the surface of pure magnesium hydroxide (MH) in b is smooth. At the same time, Figure 3 the infrared spectra of MH and MH-g-DOPO1 are shown. By comparison, it is found that MH-g-DOPO1 has strong absorption peaks at (1596 cm -1 , 1479 cm -1 and 1430 cm -1 ), corresponding to the benzene ring structure (Ph); the absorption peak at (1236 cm -1 ) corresponds to the P=O structure; the absorption peak at (1117 cm -1 ) corresponds to the P-O-Ph structure, which indicates that MH-g-DOPO1 contains the typical groups in the DOPO molecule. Subsequently, Figure 3 the X-ray photoelectron spectra of MH and MH-g-DOPO1 are shown. By comparison, new peaks of C 1s , P 2s and P 2P appear in MH-g-DOPO1, which also corresponds to the elemental composition in DOPO. It is thus determined that DOPO is grafted onto the surface of MH, further proving the successful synthesis of MH-g-DOPO1.

[0035] In this embodiment, the synthesized MH-g-DOPO1 is used to prepare a polyethylene composite material, and the specific method is as follows: 50 parts of polyethylene, 45 parts of MH-g-DOPO1, and 5 parts of processing aids (4 parts of compatibilizer polyethylene grafted maleic anhydride and 1 part of antioxidant 1010) are stirred and mixed, and then a polyethylene composite material is prepared by melt blending, and finally a test specimen is prepared by hot pressing.

[0036] Example 2

[0037] The synthesis method of the magnesium hydroxide hybrid flame retardant in this embodiment includes the following steps:

[0038] 100 parts of magnesium hydroxide, 40 parts of DOPO, 2 parts of 30% hydrogen peroxide solution, and 400 parts of environmentally friendly reaction medium (200 parts of ethanol and 200 parts of distilled water) are sequentially added to a hydrothermal reaction kettle, ultrasonically treated at 30 °C for 2 h, then transferred to an oven and heated to 130 °C for reaction for 3 h, filtered after cooling, and dried at 120 °C for 5 h to obtain the magnesium hydroxide hybrid flame retardant, named MH-g-DOPO2.

[0039] By weighing before and after the reaction and calculating, the grafting rate of DOPO in the MH-g-DOPO2 prepared in this embodiment is 31.2 wt%.

[0040] In this embodiment, the synthesized MH-g-DOPO2 is used to prepare a polyethylene composite material, and the specific method is as follows: 51 parts of polyethylene, 45 parts of MH-g-DOPO2, and 4 parts of processing aids (5 parts of compatibilizer polyethylene grafted acrylic acid and 1 part of antioxidant 1010) are stirred and mixed, and then a polyethylene composite material is prepared by melt blending, and finally a test specimen is prepared by hot pressing.

[0041] Example 3

[0042] The synthesis method of the magnesium hydroxide hybrid flame retardant in this embodiment includes the following steps:

[0043] 100 parts of magnesium hydroxide, 50 parts of DOPO, 8 parts of 10% hydrogen peroxide solution, and 200 parts of environmentally friendly reaction medium (100 parts of ethanol and 100 parts of distilled water) are sequentially added to a hydrothermal reaction kettle, ultrasonically treated at 25 °C for 1.5 h, then transferred to an oven and heated to 105 °C for reaction for 6 h, filtered after cooling, and dried at 110 °C for 6 h to obtain the magnesium hydroxide hybrid flame retardant, named MH-g-DOPO3.

[0044] By weighing before and after the reaction and calculating, the grafting rate of DOPO in the MH-g-DOPO3 prepared in this embodiment is 33.6 wt%.

[0045] In this example, the synthesized MH-g-DOPO3 was used to prepare a polyethylene composite material, and the specific method is as follows: 55 parts of polyethylene, 45 parts of MH-g-DOPO3, and 5 parts of processing aids (5 parts of compatibilizer polyethylene grafted maleic anhydride, 1 part of antioxidant 1010) were stirred and mixed, and then an EVA composite material was prepared by melt blending, and finally a test specimen was prepared by hot pressing.

[0046] Example 4

[0047] The synthesis method of the magnesium hydroxide hybrid flame retardant in this example includes the following steps:

[0048] 100 parts of magnesium hydroxide, 50 parts of DOPO, 6 parts of 10% hydrogen peroxide solution, and 300 parts of environmentally friendly reaction medium (200 parts of ethanol and 100 parts of distilled water) were successively added to a hydrothermal reaction kettle, ultrasonically treated at 40 °C for 1 h, then transferred to an oven and heated to 150 °C for reaction for 3 h, cooled and filtered, and dried at 120 °C for 6 h to obtain the magnesium hydroxide hybrid flame retardant, named MH-g-DOPO4.

[0049] By weighing before and after the reaction and calculating, the grafting rate of DOPO in the MH-g-DOPO4 prepared in this example was 32.8 wt%.

[0050] In this example, the synthesized MH-g-DOPO4 was used to prepare a polypropylene composite material, and the specific method is as follows: 56 parts of polypropylene, 40 parts of MH-g-DOPO4, and 4 parts of processing aids (3 parts of compatibilizer polypropylene grafted maleic anhydride, 1 part of antioxidant 1010) were stirred and mixed, and then a polypropylene composite material was prepared by melt blending, and finally a test specimen was prepared by hot pressing.

[0051] Example 5

[0052] The synthesis method of the magnesium hydroxide hybrid flame retardant in this example includes the following steps:

[0053] 100 parts of magnesium hydroxide, 30 parts of DOPO, 2 parts of 30% hydrogen peroxide solution, and 300 parts of environmentally friendly reaction medium (200 parts of ethanol and 100 parts of distilled water) were successively added to a hydrothermal reaction kettle, ultrasonically treated at 30 °C for 2 h, then transferred to an oven and heated to 140 °C for reaction for 4 h, cooled and filtered, and dried at 130 °C for 5 h to obtain the magnesium hydroxide hybrid flame retardant, named MH-g-DOPO5.

[0054] By weighing before and after the reaction and calculating, the grafting rate of DOPO in the MH-g-DOPO5 prepared in this example was 29.8 wt%.

[0055] In this example, the synthesized MH-g-DOPO5 was used to prepare a polypropylene composite material, and the specific method was as follows: 55 parts of polypropylene, 40 parts of MH-g-DOPO5, and 5 parts of processing aids (3 parts of compatibilizer polypropylene grafted maleic anhydride and 1 part of antioxidant 1010) were stirred and mixed, and then the polypropylene composite material was prepared by melt blending, and finally test specimens were prepared by hot pressing.

[0056] Example 6

[0057] The synthesis method of the magnesium hydroxide hybrid flame retardant in this example includes the following steps:

[0058] 100 parts of magnesium hydroxide, 50 parts of DOPO, 3 parts of 20% hydrogen peroxide solution, and 400 parts of environmentally friendly reaction medium (300 parts of ethanol and 100 parts of distilled water) were successively added to a hydrothermal reaction kettle, ultrasonicated at 20 °C for 2 h, then transferred to an oven and heated to 120 °C for reaction for 5 h, filtered after cooling, and dried at 110 °C for 10 h to obtain the magnesium hydroxide hybrid flame retardant, named MH-g-DOPO6.

[0059] By weighing before and after the reaction and calculating, the grafting rate of DOPO in the MH-g-DOPO6 prepared in this example was 32.4 wt%.

[0060] In this example, the synthesized MH-g-DOPO6 was used to prepare a polypropylene composite material, and the specific method was as follows: 56 parts of polypropylene, 40 parts of MH-g-DOPO6, and 4 parts of processing aids (3 parts of compatibilizer polypropylene grafted maleic anhydride and 1 part of antioxidant 1010) were stirred and mixed, and then the polypropylene composite material was prepared by melt blending, and finally test specimens were prepared by hot pressing.

[0061] Comparative Example 1

[0062] 45 parts of pure magnesium hydroxide flame retardant was used to prepare a polyethylene composite material, and the specific method was the same as that in Example 1.

[0063] Comparative Example 2

[0064] The difference from Comparative Example 1 was that the addition amount of the pure magnesium hydroxide flame retardant was 70 parts.

[0065] Comparative Example 3

[0066] 40 parts of pure magnesium hydroxide flame retardant was used to prepare a polypropylene composite material, and the specific method was the same as that in Example 4.

[0067] Comparative Example 4

[0068] The difference from Comparative Example 3 was that the addition amount of the pure magnesium hydroxide flame retardant was 65 parts.

[0069] Comparative Example 5

[0070] Without adding flame retardants, 95 parts of polyethylene and 5 parts of processing aids (4 parts of compatibilizer polyethylene grafted maleic anhydride and 1 part of antioxidant 1010) were prepared into a polyethylene composite material by melt blending. The specific method was the same as that in Example 1.

[0071] Comparative Example 6

[0072] Without adding flame retardants, 96 parts of polypropylene and 4 parts of processing aids (3 parts of compatibilizer polypropylene grafted maleic anhydride and 1 part of antioxidant 1010) were prepared into a polypropylene composite material by melt blending. The specific method was the same as that in Example 4.

[0073] The flame retardant properties and mechanical properties of the polymer composites of Examples 1-6 and Comparative Examples 1-6 were tested, and the test results are shown in Table 1.

[0074] Table 1 Flame retardant properties and mechanical properties of the polymer composites in Examples 1-6 and Comparative Examples 1-6

[0075]

[0076] As can be seen from Examples 1-3 in Table 1, in the polyethylene system, by adding 45 parts of magnesium hydroxide hybrid flame retardant, the limiting oxygen index of the prepared polyethylene composite material exceeded 30% and the vertical burning level reached V-0. In Comparative Example 1, by adding the same amount of pure magnesium hydroxide flame retardant, the limiting oxygen index of the prepared polyethylene composite material was only 26.3% and the vertical burning level only reached V-2. This shows that the magnesium hydroxide hybrid flame retardant is more effective in increasing the limiting oxygen index value and improving the vertical burning level of the polyethylene composite material. Therefore, the magnesium hydroxide hybrid flame retardant of the present invention is a highly efficient flame retardant. Moreover, by comparing Examples 1-3 with Comparative Example 1, it can be seen that on the premise of the same amount of flame retardant, the tensile strength and notched impact strength of the polyethylene composite material prepared by adding the magnesium hydroxide hybrid flame retardant are higher than those of the polyethylene composite material prepared by adding pure magnesium hydroxide. This shows that the magnesium hydroxide hybrid flame retardant improves the mechanical properties of the polyethylene composite material while improving the flame retardant properties.

[0077] As can be seen from Examples 1-3 and Comparative Example 2 in Table 1, in the polyethylene system, to reach the vertical burning V-0 level, only 45 parts of magnesium hydroxide hybrid flame retardant need to be added, while 70 parts of pure magnesium hydroxide flame retardant need to be added. This fully shows that after the magnesium hydroxide of the present invention is hybrid modified, its flame retardant efficiency is greatly improved.

[0078] In the polypropylene system, by comparing Examples 4 - 6 with Comparative Example 3, it can be seen that based on the same addition amount, in terms of increasing the limiting oxygen index value and improving the vertical burning level, the flame retardant effect of the magnesium hydroxide hybrid flame retardant is more significant than that of the pure magnesium hydroxide flame retardant. Moreover, by comparing Examples 4 - 6 with Comparative Example 3, it can be seen that on the premise of the same amount of flame retardant, the tensile strength and notched impact strength of the polypropylene composite material prepared by adding the magnesium hydroxide hybrid flame retardant are higher than those of the polyethylene composite material prepared by adding pure magnesium hydroxide. This indicates that while improving the flame retardant performance of the polypropylene composite material, the magnesium hydroxide hybrid flame retardant simultaneously enhances the mechanical properties.

[0079] By comparing Examples 4 - 6 with Comparative Example 4, it can be seen that on the premise of achieving the same vertical burning level V - 0, only 40 parts of the magnesium hydroxide hybrid flame retardant need to be added, while 65 parts of the pure magnesium hydroxide flame retardant are required. This fully proves that the magnesium hydroxide hybrid flame retardant of the present invention has greatly improved the flame retardant efficiency.

[0080] Finally, Comparative Example 5 and Comparative Example 6 respectively give the flame retardant properties of pure polymers (PE and PP) obtained without using any flame retardants, which are used to compare with the polymer composite materials obtained by adding the magnesium hydroxide hybrid flame retardant of the present invention in the Examples, further illustrating that the flame retardant efficiency of the synthesized magnesium hydroxide hybrid flame retardant of the present invention has been greatly improved.

[0081] Although the present invention has been described in detail by referring to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope covered by the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for synthesizing a magnesium hydroxide hybrid flame retardant, characterized in that, Magnesium hydroxide, an organic phosphorus flame retardant, a hydrogen peroxide solution, and an environmentally friendly reaction medium are successively added to a hydrothermal reaction kettle, ultrasonically mixed evenly, then transferred to an oven for heating reaction, and after cooling, filtered and dried to obtain a magnesium hydroxide hybrid flame retardant.

2. The synthesis method of the magnesium hydroxide hybrid flame retardant according to claim 1, characterized in that, The mass fraction of magnesium hydroxide is 100 parts, the mass fraction of the organic phosphorus flame retardant is 30 - 60 parts, the mass fraction of the hydrogen peroxide solution is 2 - 8 parts, and the mass fraction of the environmentally friendly reaction medium is 200 - 400 parts.

3. The synthesis method of the magnesium hydroxide hybrid flame retardant according to claim 1, characterized in that, The magnesium hydroxide is hexagonal flaky particles, the organic phosphorus flame retardant is 9,10 - dihydro - 9 - oxa - 10 - phosphaphenanthrene - 10 - oxide, the mass concentration of the hydrogen peroxide solution is 10 - 30%, the environmentally friendly reaction medium is a mixture of ethanol and distilled water, and the mass ratio of ethanol to distilled water is 1 - 3:

1.

4. The synthesis method of the magnesium hydroxide hybrid flame retardant according to claim 1, characterized in that, Ultrasonic for 1 - 2 h at 20 - 40 °C, then transfer to an oven and heat up to 105 - 150 °C for reaction for 3 - 6 h. After cooling and filtering, dry at 110 - 130 °C for 5 - 10 h to obtain the magnesium hydroxide hybrid flame retardant.

5. Use of the magnesium hydroxide hybrid flame retardant prepared by the synthesis method according to any one of claims 1-4, characterized in that, The magnesium hydroxide hybrid flame retardant, a processing aid, and a cable - used polymer are melt - blended and processed into shape to obtain a flame - retardant polymer composite for cables.

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