Low-smoke halogen-free flame-retardant plastic and preparation method thereof

Abstract

The invention relates to a low-smoke halogen-free flame-retardant plastic and a preparation method thereof, and belongs to the technical field of flame-retardant high polymer materials. The flame-retardant plastic is prepared from the following components: 12 to 17 weight percent of magnesium hydroxide superfine powder, 4.5 to 6.2 weight percent of modified flame retardant, 5 to 7 weight percent of flexibilizer, 0.9 to 1.2 weight percent of lubricant, 0.3 to 0.4 weight percent of antioxidant and the balance of PBT (Polybutylene Terephthalate) resin, the modified flame retardant is prepared by the following steps: reacting pentaerythritol with phosphorus oxychloride to prepare hydroxyl-containing polyhedral oligomeric phosphate, esterifying acryloyl chloride and the hydroxyl of the polyhedral oligomeric phosphate to prepare a monoester intermediate, and finally performing click addition on sulfydryl of pentaerythritol tetramercaptoacetate and double bonds of the monoester intermediate. The modified flame retardant interacts with magnesium hydroxide, a stable hollow carbon net is formed in the flame retardant process, and the hollow carbon net has a multi-layer adsorption and filtration effect on smoke particles, so that the release of smoke is reduced, and the smoke density is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame-retardant polymer materials, and in particular relates to a low-smoke halogen-free flame-retardant plastic and a preparation method thereof. Background Art

[0002] Polybutylene terephthalate (PBT) is a semi-crystalline thermoplastic engineering plastic with excellent heat resistance (chemical resistance), mechanical strength, and dimensional stability. Its rapid crystallization properties enable high processing efficiency in injection molding, and it is widely used in electronic devices (such as connectors and relay housings), automotive parts (such as sensor brackets and wiring harness sheaths), and household appliances. However, PBT is a flammable material that easily burns and releases large amounts of smoke in high-temperature or open-flame environments, making it difficult to meet the requirements of high-safety applications.

[0003] At present, the technical solution to the flame retardancy problem of PBT materials is mainly to add flame retardants, such as the common phosphorus-nitrogen flame retardants and intumescent flame retardants, which are difficult to effectively solve the smoke release problem of PBT. Among them, intumescent flame retardants (such as magnesium hydroxide) form a loose flame-retardant intumescent layer by decomposition and expansion, which can reduce smoke release to a certain extent. However, existing low-smoke flame-retardant PBT mostly relies on a high proportion of magnesium hydroxide compounding, and has defects such as high density, poor toughness, and a narrow processing window. There is an urgent need to develop innovative technologies that take into account high-efficiency flame retardancy, low smoke release and excellent processing performance. Summary of the Invention

[0004] In order to solve the technical problems mentioned in the background technology, the purpose of the present invention is to provide a low-smoke halogen-free flame retardant plastic and a preparation method thereof.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A low-smoke, halogen-free, flame-retardant plastic, comprising the following components in percentage by weight: The invention comprises 12-17wt% of superfine magnesium hydroxide powder, 4.5-6.2wt% of modified flame retardant, 5-7wt% of toughening agent, 0.9-1.2wt% of lubricant and 0.3-0.4wt% of antioxidant, and the balance is PBT resin.

[0006] Wherein, the modified flame retardant is prepared by the following method: Step A1: Pentaerythritol and dioxane were mixed and heated to 60-70°C. Dry nitrogen was introduced, and phosphorus oxychloride was slowly added and stirred for 2.5-3 hours. 4-dimethylaminopyridine solution was then added and mixed. The mixture was heated to 100°C and refluxed for 8-10 hours. After the reaction was completed, the dioxane was removed by vacuum rotary evaporation to obtain a cage-type phosphate. In the reaction of step A1 above, the feed ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane is 0.1 mol: 0.1 mol: 3.5-4.5 g: 150-200 mL. The specific reaction route is:

[0007] Step A2: Mix the caged phosphate and acetonitrile, add potassium carbonate, and mix. Pour dry nitrogen into the mixture, slowly add acryloyl chloride, and stir to react for 1.5-2 hours. Then, heat to 80°C and reflux for 3-4 hours. After the reaction is complete, cool and filter to remove potassium carbonate. Rotary evaporate to remove acetonitrile. Wash the rotary evaporated substrate with water and vacuum dry to obtain a monoester intermediate. In the reaction of step A2 above, the feed ratio of caged phosphate, acryloyl chloride, potassium carbonate and acetonitrile is 0.1 mol: 0.108-0.112 mol: 20-25 g: 250-300 mL. The specific reaction route is:

[0008] Step A3: Dissolve the monoester intermediate, pentaerythritol tetrathioglycolate and dimethylacetamide, add photosensitizer and mix well, apply 30-40 mW / cm at room temperature. 2 Irradiate with ultraviolet radiation of high intensity and stir to react for 2.2-2.8 hours. After the reaction is completed, add deionized water for washing, centrifuge to separate the aqueous phase, and vacuum dry to obtain a modified flame retardant. In the reaction of step A2 above, the feed ratio of pentaerythritol tetrathioglycolate, monoester intermediate, photosensitizer and dimethylacetamide is 10 mmol: 42-45 mmol: 50-70 mg: 45-55 mL. The specific reaction route is:

[0009] Preferably, the fineness of the ultrafine magnesium hydroxide powder is controlled at 1500-2000 meshes, which has a stable thermal decomposition flame retardant effect while maintaining good dispersibility.

[0010] Preferably, the toughening agent is EMA-g-GMA or SEBS elastomer, which has a good toughening effect on the PBT matrix.

[0011] Preferably, the lubricant is a compound of ethylene bisstearamide and silicone powder, which has both internal and external lubrication effects and is beneficial to the molding of plastic materials.

[0012] Preferably, the antioxidant is a compound of antioxidant 1010 and antioxidant 168, which has good thermal stability and is suitable for PBT matrix processing and molding.

[0013] A method for preparing a low-smoke, halogen-free flame-retardant plastic comprises the following steps: premixing ultrafine magnesium hydroxide powder, a modified flame retardant, a toughening agent, a lubricant, and an antioxidant, adding PBT resin and mixing evenly, and then melt-extruding and pelletizing the mixture using a twin-screw extruder to obtain the low-smoke, halogen-free flame-retardant plastic.

[0014] Beneficial effects of the present invention: The present invention is based on a traditional inorganic magnesium hydroxide flame retardant system and introduces a modified flame retardant for synergistic effect to achieve high-efficiency flame retardancy and low smoke release. The modified flame retardant is prepared by reacting pentaerythritol and phosphorus oxychloride to form a hydroxyl-containing cage-type phosphate ester, which is then esterified by acryloyl chloride and the hydroxyl group of the cage-type phosphate ester to form a monoester intermediate. Finally, the thiol group of pentaerythritol tetramercaptoacetate is subjected to double-bond click addition with the monoester intermediate, which interacts with magnesium hydroxide. The specific mechanism is as follows: magnesium hydroxide has a lamellar structure, and the modified flame retardant has a branched structure. The branched thiodiester in its molecules forms a chelating effect and is loaded onto the surface of the magnesium hydroxide lamellar layer during the melt mixing process. Under high temperature environment, the magnesium hydroxide decomposes to form larger planar internal pores, and the cage-type phosphate of the modified flame retardant on the surface decomposes and promotes carbonization. A large number of carbonized small pores are formed on the pore walls of the inner pores, ensuring the high-temperature stability of the inner pores. The two form a hollow carbon network. Compared with existing flame retardants, the hollow carbon network structure forms a heat transfer barrier, extends the heat conduction path to the inside of the material, and enhances the flame retardant effect. The stable hollow carbon network structure has a multi-layer adsorption and filtration effect on smoke particles, reduces the release of smoke, and greatly reduces the smoke density. The introduction of modified flame retardants achieves a high-efficiency flame retardant effect, reduces the amount of inorganic magnesium hydroxide, and improves the processing performance of PBT materials. The thiodiester structure has a high compatibility with PBT. The surface of magnesium hydroxide is modified to improve its compatibility and improve the mechanical properties of the composite material. At the same time, it expands the application of low-smoke plastics, especially in complex structures or thin-walled products. DETAILED DESCRIPTION

[0015] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0016] Example 1: Preparation of low-smoke halogen-free flame-retardant plastic, specifically as follows: (1) Synthetic modified flame retardants Step A1: Pentaerythritol and dioxane were mixed and heated to 70°C. Dry nitrogen was introduced for protection. Phosphorus oxychloride was slowly added and stirred for reaction for 2.5 hours. Then, a 4-dimethylaminopyridine solution was added and mixed. The temperature was continued to rise to 100°C and refluxed for 8 hours. The feed ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane was 0.1 mol: 0.1 mol: 4.5 g: 200 mL. The 4-dimethylaminopyridine solution was a saturated tetrahydrofuran solution at room temperature. After the reaction was completed, the dioxane was removed by vacuum rotary evaporation to obtain a cage-type phosphate.

[0017] Step A2: Take a caged phosphate and acetonitrile and mix them, then add potassium carbonate and mix, pass dry nitrogen protection, slowly add acryloyl chloride and stir to react for 1.5 hours, then raise the temperature to 80°C and reflux for 3 hours, wherein the feed ratio of caged phosphate, acryloyl chloride, potassium carbonate and acetonitrile is 0.1 mol: 0.112 mol: 25 g: 300 mL. After the reaction is completed, cool and filter to remove potassium carbonate, and remove acetonitrile by rotary evaporation. The rotary evaporation substrate is washed with water and vacuum dried to obtain a monoester intermediate.

[0018] Step A3: Take the monoester intermediate, pentaerythritol tetrathioglycolate and dimethylacetamide, mix them, add the photosensitizer and mix well, apply 40mW / cm 2 The mixture was stirred and reacted under ultraviolet irradiation with high intensity for 2.2 hours, wherein the feed ratio of pentaerythritol tetrathioglycolate, monoester intermediate, photosensitizer and dimethylacetamide was 10 mmol:45 mmol:70 mg:55 mL, and the photosensitizer was selected from PI-1173. After the reaction was completed, deionized water was added for washing, the aqueous phase was centrifuged and vacuum dried to obtain a modified flame retardant.

[0019] (2) Preparation of low-smoke halogen-free flame-retardant plastics The following raw materials are taken in percentage by weight: 17wt% of magnesium hydroxide ultrafine powder, selected from commercially available 1500 mesh powder; 4.5wt% of modified flame retardant, homemade in this embodiment; 5wt% of toughening agent, selected from EPA-810 type EMA-g-GMA elastomer; 1.2wt% of lubricant, prepared by mixing ethylene bisstearamide and silicone powder in a ratio of 1:3; 0.4wt% of antioxidant, prepared by mixing antioxidant 1010 and antioxidant 168 in an equal weight ratio; the remainder is PBT resin, selected from 1401X06 type resin raw material.

[0020] Ultrafine magnesium hydroxide powder, modified flame retardant, toughening agent, lubricant and antioxidant were first added to a high-speed mixer and premixed at 1000 rpm for 3 minutes, then PBT resin was added and mixed for 10 minutes, and then the mixture was added to a twin-screw extruder and melt-extruded and granulated at 255°C to obtain low-smoke halogen-free flame retardant plastic.

[0021] Example 2: Preparation of low-smoke halogen-free flame-retardant plastics, specifically as follows: (1) Synthetic modified flame retardants Step A1: Pentaerythritol and dioxane are mixed and heated to 60°C. Dry nitrogen is introduced for protection. Phosphorus oxychloride is slowly added and stirred for reaction for 3 hours. Then, a 4-dimethylaminopyridine solution is added and mixed. The temperature is further raised to 100°C and refluxed for 10 hours. The feed ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane is 0.1 mol: 0.1 mol: 3.5 g: 150 mL. The 4-dimethylaminopyridine solution is a saturated tetrahydrofuran solution at room temperature. After the reaction is completed, the dioxane is removed by vacuum rotary evaporation to obtain a cage-type phosphate.

[0022] Step A2: Take a caged phosphate and acetonitrile and mix them, then add potassium carbonate and mix, pass dry nitrogen protection, slowly add acryloyl chloride and stir to react for 2 hours, then raise the temperature to 80°C and reflux for 4 hours, wherein the feed ratio of caged phosphate, acryloyl chloride, potassium carbonate and acetonitrile is 0.1 mol: 0.108 mol: 20 g: 250 mL. After the reaction is completed, cool and filter to remove potassium carbonate, and remove acetonitrile by rotary evaporation. The rotary evaporation substrate is washed with water and vacuum dried to obtain a monoester intermediate.

[0023] Step A3: Mix the monoester intermediate, pentaerythritol tetrathioglycolate and dimethylacetamide, add the photosensitizer and mix well, and apply 30mW / cm 2 The mixture was stirred and reacted under ultraviolet irradiation with high intensity for 2.8 hours, wherein the feed ratio of pentaerythritol tetrathioglycolate, monoester intermediate, photosensitizer and dimethylacetamide was 10 mmol:42 mmol:50 mg:45 mL, and the photosensitizer was selected from PI-1173. After the reaction was completed, deionized water was added for washing, the aqueous phase was centrifuged and vacuum dried to obtain a modified flame retardant.

[0024] (2) Preparation of low-smoke halogen-free flame-retardant plastics The following raw materials are taken in percentage by weight: 12wt% of magnesium hydroxide ultrafine powder, selected from commercially available 1500 mesh powder; 6.2wt% of modified flame retardant, homemade in this embodiment; 7wt% of toughening agent, selected from EPA-810 type EMA-g-GMA elastomer; 0.9wt% of lubricant, prepared by mixing ethylene bisstearamide and silicone powder in a ratio of 1:3; 0.3wt% of antioxidant, prepared by mixing antioxidant 1010 and antioxidant 168 in an equal weight ratio; the remainder is PBT resin, selected from 1401X06 type resin raw material.

[0025] Ultrafine magnesium hydroxide powder, modified flame retardant, toughening agent, lubricant and antioxidant were first added to a high-speed mixer and premixed at 1000 rpm for 3 minutes, then PBT resin was added and mixed for 10 minutes, and then the mixture was added to a twin-screw extruder and melt-extruded and granulated at 245°C to obtain low-smoke halogen-free flame retardant plastic.

[0026] Example 3, preparation of low-smoke halogen-free flame retardant plastic, specifically as follows: (1) Synthetic modified flame retardants Step A1: Pentaerythritol and dioxane were mixed and heated to 65°C. Dry nitrogen was introduced for protection. Phosphorus oxychloride was slowly added and stirred for reaction for 2.8 hours. Then, a 4-dimethylaminopyridine solution was added and mixed. The temperature was continued to rise to 100°C and refluxed for 89 hours. The feed ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane was 0.1 mol:0.1 mol:4 g:170 mL. The 4-dimethylaminopyridine solution was a saturated tetrahydrofuran solution at room temperature. After the reaction was completed, the dioxane was removed by vacuum rotary evaporation to obtain a cage-type phosphate.

[0027] Step A2: Take a caged phosphate and acetonitrile and mix them, then add potassium carbonate and mix, pass dry nitrogen protection, slowly add acryloyl chloride and stir to react for 1.5 hours, then raise the temperature to 80°C and reflux for 3.5 hours, wherein the feed ratio of caged phosphate, acryloyl chloride, potassium carbonate and acetonitrile is 0.1 mol: 0.11 mol: 22 g: 280 mL. After the reaction is completed, cool and filter to remove potassium carbonate, and remove acetonitrile by rotary evaporation. The rotary evaporation substrate is washed with water and vacuum dried to obtain a monoester intermediate.

[0028] Step A3: Mix the monoester intermediate, pentaerythritol tetrathioglycolate and dimethylacetamide, add the photosensitizer and mix well, apply 40mW / cm 2 The mixture was stirred and reacted under ultraviolet irradiation with high intensity for 2.25 hours, wherein the feed ratio of pentaerythritol tetrathioglycolate, monoester intermediate, photosensitizer and dimethylacetamide was 10 mmol:43 mmol:60 mg:50 mL, and the photosensitizer was selected from PI-1173. After the reaction was completed, deionized water was added for washing, the aqueous phase was centrifuged and vacuum dried to obtain a modified flame retardant.

[0029] (2) Preparation of low-smoke halogen-free flame-retardant plastics The following raw materials are taken in percentage by weight: 15wt% of magnesium hydroxide ultrafine powder, selected from commercially available 2000 mesh powder; 5.5wt% of modified flame retardant, homemade in this embodiment; 5.5wt% of toughening agent, selected from EPA-810 type EMA-g-GMA elastomer; 1.1wt% of lubricant, prepared by mixing ethylene bisstearamide and silicone powder in a ratio of 1:3; 0.3wt% of antioxidant, prepared by mixing antioxidant 1010 and antioxidant 168 in an equal weight ratio; the remainder is PBT resin, selected from 1401X06 type resin raw material.

[0030] Ultrafine magnesium hydroxide powder, modified flame retardant, toughening agent, lubricant and antioxidant were first added to a high-speed mixer and premixed at 1000 rpm for 3 minutes, then PBT resin was added and mixed for 10 minutes, and then the mixture was added to a twin-screw extruder and melt-extruded and granulated at 250°C to obtain low-smoke halogen-free flame retardant plastic.

[0031] Example 4: Preparation of low-smoke halogen-free flame-retardant plastics, as follows: (1) Synthetic modified flame retardants Step A1: Pentaerythritol and dioxane were mixed and heated to 60°C. Dry nitrogen was introduced for protection. Phosphorus oxychloride was slowly added and stirred for reaction for 3 hours. Then, a 4-dimethylaminopyridine solution was added and mixed. The temperature was continued to rise to 100°C and refluxed for 8.5 hours. The feed ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane was 0.1 mol: 0.1 mol: 3.8 g: 180 mL. The 4-dimethylaminopyridine solution was a saturated tetrahydrofuran solution at room temperature. After the reaction was completed, the dioxane was removed by vacuum rotary evaporation to obtain a cage-type phosphate.

[0032] Step A2: Take a caged phosphate and acetonitrile and mix them, then add potassium carbonate and mix, pass dry nitrogen protection, slowly add acryloyl chloride and stir to react for 2 hours, then raise the temperature to 80°C and reflux for 3.5 hours, wherein the feed ratio of caged phosphate, acryloyl chloride, potassium carbonate and acetonitrile is 0.1 mol: 0.11 mol: 25 g: 300 mL. After the reaction is completed, cool and filter to remove potassium carbonate, and remove acetonitrile by rotary evaporation. The rotary evaporation substrate is washed with water and vacuum dried to obtain a monoester intermediate.

[0033] Step A3: Mix the monoester intermediate, pentaerythritol tetrathioglycolate and dimethylacetamide, add the photosensitizer and mix well, and apply 30mW / cm 2 The mixture was stirred and reacted under ultraviolet irradiation with high intensity for 2.6 hours, wherein the feed ratio of pentaerythritol tetrathioglycolate, monoester intermediate, photosensitizer and dimethylacetamide was 10 mmol:42 mmol:65 mg:55 mL, and the photosensitizer was selected from PI-1173. After the reaction was completed, deionized water was added for washing, the aqueous phase was centrifuged and vacuum dried to obtain a modified flame retardant.

[0034] (2) Preparation of low-smoke halogen-free flame-retardant plastics The following raw materials are taken in percentage by weight: 14wt% of magnesium hydroxide ultrafine powder, selected from commercially available 1500 mesh powder; 5.8wt% of modified flame retardant, homemade in this embodiment; 6wt% of toughening agent, selected from EPA-810 type EMA-g-GMA elastomer; 1wt% of lubricant, prepared by mixing ethylene bisstearamide and silicone powder in a ratio of 1:3; 0.3wt% of antioxidant, prepared by mixing antioxidant 1010 and antioxidant 168 in an equal weight ratio; the remainder is PBT resin, selected from 1401X06 type resin raw material.

[0035] Ultrafine magnesium hydroxide powder, modified flame retardant, toughening agent, lubricant and antioxidant were first added to a high-speed mixer and premixed at 1000 rpm for 3 minutes, then PBT resin was added and mixed for 10 minutes, and then the mixture was added to a twin-screw extruder and melt-extruded and granulated at 250°C to obtain low-smoke halogen-free flame retardant plastic.

[0036] Comparative Example 1: Referring to the implementation process of Example 4, the modified flame retardant is replaced by pentaerythritol caged phosphate TRIMER, and the rest of the implementation process is exactly the same.

[0037] Comparative Example 2, referring to the implementation process of Comparative Example 1, the amount of ultrafine magnesium hydroxide powder is increased to 22wt%, and the balance is adjusted to 100wt% by PBT resin. The rest of the implementation process is exactly the same.

[0038] Samples were taken from the flame-retardant plastic prepared as described above, hot-pressed at 240°C and 5 MPa, and subjected to tensile testing according to GB / T 1040.2-2006; and impact testing according to ISO 179-1-2023. The specific test results are shown in Table 1: Table 1 Tensile strength / MPa Elongation at break / % <![CDATA[Impact strength / kJ·m -2 > Example 1 65.2 31.9 8.35 Example 2 60.7 35.3 10.06 Example 3 63.4 33.7 9.14 Example 4 61.9 34.2 9.62 Comparative Example 1 60.5 32.6 8.57 Comparative Example 2 57.1 27.5 6.24 It can be seen from the test results in Table 1 that the flame retardant plastics prepared in the examples and comparative examples have similar mechanical properties. Combining comparative examples 1-2 and example 4, it can be seen that the toughness of example 4 is slightly higher than that of the comparative example. After analysis, it should be that the modified flame retardant is modified with the surface of the magnesium hydroxide particles, which improves the interface bonding performance and thus improves the overall toughness.

[0039] The above samples were subjected to flame retardant performance tests, including: vertical burning test according to UL-94; oxygen index test according to ASTM D2863-23; and smoke density test according to ASTM E662-2017. The specific test results are shown in Table 2: Table 2 Flame retardant grade (2mm) Oxygen index / % Smoke density Example 1 V-0 33.2 206 Example 2 V-0 30.5 193 Example 3 V-0 32.1 185 Example 4 V-0 31.7 171 Comparative Example 1 V-0 32.5 372 Comparative Example 2 V-0 33.9 304 It can be seen from the test results in Table 2 that the above samples can all reach the V-0 flame retardant grade, and the limiting oxygen index reaches more than 30%, showing good flame retardant properties. Combined with the data analysis of Comparative Examples 1-2 and Example 4, increasing the proportion of magnesium hydroxide can reduce the smoke density to a certain extent. Combined with the data in Table 1, the toughness will be greatly affected, and the smoke density of Example 4 is lower than 200, showing good low smoke characteristics.

[0040] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0041] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A low-smoke, halogen-free flame-retardant plastic, characterized in that: The specific components are: 12-17wt% of magnesium hydroxide ultrafine powder, 4.5-6.2wt% of modified flame retardant, 5-7wt% of toughening agent, 0.9-1.2wt% of lubricant and 0.3-0.4wt% of antioxidant, and the balance is PBT resin; The modified flame retardant is prepared by the following method: Step A1: Pentaerythritol and dioxane were mixed and heated to 60-70°C. Dry nitrogen was introduced, phosphorus oxychloride was slowly added, stirred and reacted for 2.5-3 hours, and then 4-dimethylaminopyridine solution was added and mixed. The mixture was further heated to 100°C and refluxed for 8-10 hours to prepare a caged phosphate ester. Step A2: Cage-type phosphate and acetonitrile were mixed and dissolved, followed by the addition of potassium carbonate, and the mixture was purged with dry nitrogen. Acryloyl chloride was slowly added and stirred for 1.5-2 hours, and then the mixture was heated to 80°C and refluxed for 3-4 hours to prepare a monoester intermediate. Step A3: Dissolve the monoester intermediate, pentaerythritol tetrathioglycolate and dimethylacetamide, add photosensitizer and mix well, apply 30-40 mW / cm at room temperature. 2 The mixture was stirred and reacted under ultraviolet irradiation of high intensity for 2.2-2.8 hours to prepare a modified flame retardant.

2. The low-smoke, halogen-free, flame-retardant plastic according to claim 1, characterized in that: The feed ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane is 0.1 mol: 0.1 mol: 3.5-4.5 g: 150-200 mL.

3. The low-smoke, halogen-free, flame-retardant plastic according to claim 2, characterized in that: The feeding ratio of caged phosphate, acryloyl chloride, potassium carbonate and acetonitrile is 0.1 mol: 0.108-0.112 mol: 20-25 g: 250-300 mL.

4. The low-smoke, halogen-free flame-retardant plastic according to claim 3, characterized in that: The feeding ratio of pentaerythritol tetrathioglycolate, monoester intermediate, photosensitizer and dimethylacetamide is 10 mmol: 42-45 mmol: 50-70 mg: 45-55 mL.

5. The low-smoke, halogen-free, flame-retardant plastic according to claim 1, characterized in that: The fineness of the magnesium hydroxide ultrafine powder is controlled at 1500-2000 mesh.

6. The low-smoke, halogen-free, flame-retardant plastic according to claim 1, characterized in that: The toughening agent is EMA-g-GMA or SEBS elastomer.

7. The low-smoke, halogen-free, flame-retardant plastic according to claim 1, characterized in that: The lubricant is compounded from ethylene bisstearamide and silicone powder.

8. The low-smoke, halogen-free, flame-retardant plastic according to claim 1, characterized in that: The antioxidant is a compound of antioxidant 1010 and antioxidant 168.

9. A method for preparing the low-smoke halogen-free flame retardant plastic according to any one of claims 1 to 8, characterized in that: Specifically, ultrafine magnesium hydroxide powder, modified flame retardant, toughening agent, lubricant and antioxidant are premixed, and then PBT resin is added and mixed evenly. The mixture is then melt-extruded and pelletized using a twin-screw extruder to obtain low-smoke halogen-free flame retardant plastic.

Images