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

Abstract

The application 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 components of the flame-retardant plastic are as follows: 12-17 wt% of magnesium hydroxide superfine powder, 4.5-6.2 wt% of modified flame retardant, 5-7 wt% of toughening agent, 0.9-1.2 wt% of lubricant, 0.3-0.4 wt% of antioxidant, and the rest is PBT resin; the modified flame retardant is prepared by reacting pentaerythritol and phosphorus oxychloride to form a cage-shaped phosphate ester containing a hydroxyl group, then acryloyl chloride is esterified with the hydroxyl group of the cage-shaped phosphate ester to form a monoester intermediate, and finally the thiol group of pentaerythritol tetramercaptoacetate is click-added to the double bond of the monoester intermediate; the modified flame retardant interacts with the magnesium hydroxide, a stable hollow carbon net is formed in the flame-retardant process, the smoke particles have a multilayer adsorption and filtration effect, the release of smoke is reduced, and the smoke density is greatly reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flame-retardant high polymer materials, and particularly relates to a low-smoke halogen-free flame-retardant plastic and a preparation method thereof. BACKGROUND

[0002] Polybutylene terephthalate (PBT) is a semi-crystalline thermoplastic engineering plastic with excellent heat resistance (chemical corrosion resistance, mechanical strength and dimensional stability. Its fast crystallization property makes it exhibit high processing efficiency in injection molding, and it is widely used in electronic appliances (such as connectors, relay housings), automotive parts (such as sensor brackets, wire harness sheaths) and household appliances. However, PBT is a flammable material, which is extremely easy to burn and release a large amount of smoke under high temperature or open flame environment, and is difficult to meet the needs of high safety standard application scenarios.

[0003] At present, the technical scheme for the flame-retardant problem of PBT material mainly adds flame retardants, such as common phosphorus-nitrogen flame retardants and intumescent flame retardants, which are difficult to effectively solve the smoke release problem of PBT. Among them, the intumescent flame retardant (such as magnesium hydroxide) can reduce the release of smoke to a certain extent by decomposing and expanding to form a loose flame-retardant expansion layer. However, the existing low-smoke flame-retardant PBT relies on high proportion of magnesium hydroxide for compounding, and has defects such as high density, poor toughness and narrow processing window, so it is urgent to develop innovative technology that takes into account efficient flame retardation, low smoke release and excellent processing performance. SUMMARY

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

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] A low-smoke halogen-free flame-retardant plastic, according to the component percentage by weight:

[0007] Magnesium hydroxide ultrafine powder 12-17wt%, modified flame retardant 4.5-6.2wt%, toughening agent 5-7wt%, lubricant 0.9-1.2wt% and antioxidant 0.3-0.4wt%, and the balance is PBT resin.

[0008] The modified flame retardant is prepared by the following method:

[0009] Step A1: Dissolve and heat pentaerythritol and dioxane to 60-70℃, protect with dry nitrogen, slowly add phosphorus oxychloride and stir for 2.5-3h, then add 4-dimethylaminopyridine solution and mix, continue to heat to 100℃ reflux for 8-10h, then remove dioxane under reduced pressure by rotary evaporation to obtain a cage-shaped phosphate ester;

[0010] The feeding ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylamino pyridine and dioxane in the above step A1 reaction is 0.1 mol: 0.1 mol: 3.5-4.5 g: 150-200 mL, and the specific reaction route is as follows:

[0011]

[0012] Step A2: Mix the cage phosphoric acid ester and acetonitrile, then add potassium carbonate and mix, protect with dry nitrogen, slowly add acryloyl chloride and stir for 1.5-2 h, then heat to 80°C and reflux for 3-4 h, after the reaction is completed, cool, filter to remove potassium carbonate, remove acetonitrile by rotary evaporation, wash the residue with water, and dry under vacuum to obtain a monoester intermediate;

[0013] The feeding ratio of cage phosphoric acid ester, acryloyl chloride, potassium carbonate and acetonitrile in the above step A2 reaction is 0.1 mol: 0.108-0.112 mol: 20-25 g: 250-300 mL, and the specific reaction route is as follows:

[0014]

[0015] Step A3: Mix the monoester intermediate, pentaerythritol tetra-thioglycolate and dimethylacetamide, add a photosensitizer and mix, apply ultraviolet irradiation at 30-40 mW / cm 2 at room temperature for 2.2-2.8 h, after the reaction is completed, add deionized water and mix, centrifuge the water phase, and dry under vacuum to obtain a modified flame retardant;

[0016] The feeding ratio of pentaerythritol tetra-thioglycolate, monoester intermediate, photosensitizer and dimethylacetamide in the above step A2 reaction is 10 mmol: 42-45 mmol: 50-70 mg: 45-55 mL, and the specific reaction route is as follows:

[0017]

[0018] Preferably, the fineness of the magnesium hydroxide ultrafine powder is controlled at 1500-2000 mesh, which has a stable thermal decomposition flame retardant effect at this particle size, while maintaining good dispersibility.

[0019] Preferably, the toughening agent is EMA-g-GMA or SEBS elastomer, which has a good toughening effect on the PBT matrix.

[0020] Preferably, the lubricant is compounded with ethylene bis-stearamide and silicone powder, which has both internal and external lubrication effects, and is beneficial to the molding of plastic materials.

[0021] Preferably, the antioxidant is compounded by antioxidant 1010 and antioxidant 168, which has good thermal stability and is suitable for PBT matrix processing.

[0022] A preparation method of low-smoke halogen-free flame-retardant plastic, specifically: premixing magnesium hydroxide ultrafine powder, modified flame retardant, toughening agent, lubricant and antioxidant, then adding PBT resin and uniformly mixing, and then melt-extruding and pelletizing the mixture by a double-screw extruder to obtain the low-smoke halogen-free flame-retardant plastic.

[0023] The beneficial effects of the present application are:

[0024] The present application is based on the traditional inorganic magnesium hydroxide flame-retardant system, and a modified flame retardant is introduced to achieve efficient flame retardation and low smoke release. The modified flame retardant is prepared by reacting pentaerythritol and phosphorus oxychloride to form a cage-shaped phosphate ester containing hydroxyl groups, then esterifying the hydroxyl groups of the cage-shaped phosphate ester with acryloyl chloride to form a monoester intermediate, and finally click adding the thiol groups of pentaerythritol tetramercaptoacetate to the double bonds of the monoester intermediate. The modified flame retardant interacts with magnesium hydroxide, and the specific mechanism is as follows: magnesium hydroxide has a lamellar structure, and the modified flame retardant has a branched structure. The branched thiodiglyceride in the molecule forms a chelating effect, and is loaded on the surface of the magnesium hydroxide lamella during melt mixing. In a high-temperature environment, magnesium hydroxide decomposes to form larger planar internal pores, and the cage-shaped phosphate ester on the surface of the modified flame retardant decomposes and promotes carbonization, forming a large number of carbonized small pores on the pore wall of the internal pores, ensuring the high-temperature stability of the internal pores. The two form a hollow carbon network, compared with existing flame retardants, the hollow carbon network structure forms a heat barrier, prolonging the conduction path of heat to the interior of the material, and strengthening the flame retardation effect. The stable hollow carbon network structure has a multi-layer adsorption and filtration effect on smoke particles, reducing the release of smoke and greatly reducing the smoke density. The introduction of the modified flame retardant achieves efficient flame retardation, reduces the amount of inorganic magnesium hydroxide, improves the processing performance of PBT materials, and the thiodiglyceride structure has 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, the application of low-smoke plastic is expanded, especially in complex structures or thin-walled products. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0026] Example 1, preparation of low-smoke halogen-free flame-retardant plastic, as follows:

[0027] (1) Synthesis of modified flame retardant

[0028] Step A1: Take pentaerythritol and dioxane as raw materials, mix them, and warm them to 70°C. Then, under dry nitrogen protection, slowly add phosphorus oxychloride and stir the mixture for 2.5 hours. Then, add 4-dimethylaminopyridine solution and continue to warm to 100°C for 8 hours. The raw material ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine, and dioxane is 0.1 mol: 0.1 mol: 4.5 g: 200 mL. The 4-dimethylaminopyridine solution is a saturated solution of tetrahydrofuran at room temperature. After the reaction is completed, remove the dioxane by rotary evaporation under reduced pressure to obtain a cage phosphoric acid ester.

[0029] Step A2: Take the cage phosphoric acid ester and acetonitrile as raw materials, mix them, and then add potassium carbonate. Then, under dry nitrogen protection, slowly add acryloyl chloride and stir the mixture for 1.5 hours. Then, warm to 80°C and reflux for 3 hours. The raw material ratio of the cage phosphoric acid ester, 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 the potassium carbonate, and then remove the acetonitrile by rotary evaporation. Wash the residue with water and dry it under vacuum to obtain a mono-ester intermediate.

[0030] Step A3: Take the mono-ester intermediate, pentaerythritol tetra-thioglycolate, and dimethylacetamide as raw materials, mix them, and then add a photosensitizer. Then, under room temperature, apply ultraviolet irradiation with a strength of 40 mW / cm 2 for 2.2 hours. The raw material ratio of pentaerythritol tetra-thioglycolate, the mono-ester intermediate, the photosensitizer, and dimethylacetamide is 10 mmol: 45 mmol: 70 mg: 55 mL. The photosensitizer is selected from PI-1173. After the reaction is completed, add deionized water and mix it. Then, centrifuge the water phase and dry it under vacuum to obtain a modified flame retardant.

[0031] (2) Preparation of low-smoke halogen-free flame-retardant plastic

[0032] According to the weight percentage, take the following raw materials: magnesium hydroxide ultra-fine powder 17wt%, selected from commercially available 1500 mesh ultra-fine powder; modified flame retardant 4.5wt%, self-made by this embodiment; toughening agent 5wt%, selected from EPA-810 type EMA-g-GMA elastomer; lubricant 1.2wt%, compounded by ethylene bis-stearamide and silicone powder at a ratio of 1:3; antioxidant 0.4wt%, compounded by antioxidant 1010 and antioxidant 168 at an equal weight ratio; and the rest is PBT resin, selected from 1401X06 type resin raw material.

[0033] First, add the magnesium hydroxide ultra-fine powder, modified flame retardant, toughening agent, lubricant, and antioxidant to a high-speed mixer and mix them at 1000 rpm for 3 minutes. Then, add the PBT resin and continue to mix for 10 minutes. Finally, add the mixed material to a twin-screw extruder, melt extrude and granulate at 255°C to obtain low-smoke halogen-free flame-retardant plastic.

[0034] Example 2, preparation of low smoke halogen-free flame-retardant plastic, as follows:

[0035] (1) Synthesis of modified flame retardant

[0036] Step A1: take pentaerythritol and dioxane as raw materials, mix and heat to 60°C, and then slowly add phosphorus oxychloride under dry nitrogen protection, stir for 3h, then add 4-dimethylaminopyridine solution and continue to heat to 100°C for 10h, wherein the raw material ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane is 0.1mol:0.1mol:3.5g:150mL, 4-dimethylaminopyridine solution is saturated tetrahydrofuran solution at room temperature, and dioxane is removed by rotary evaporation under reduced pressure after the reaction is completed to obtain a cage phosphoric acid ester.

[0037] Step A2: take the cage phosphoric acid ester and acetonitrile as raw materials, mix and add potassium carbonate, then slowly add acryloyl chloride under dry nitrogen protection, stir for 2h, then heat to 80°C and reflux for 4h, wherein the raw material ratio of cage phosphoric acid ester, acryloyl chloride, potassium carbonate and acetonitrile is 0.1mol:0.108mol:20g:250mL, and the potassium carbonate is removed by cooling and filtering after the reaction is completed, and the acetonitrile is removed by rotary evaporation, then the substrate is washed with water and vacuum dried to obtain a monoester intermediate.

[0038] Step A3: take the monoester intermediate, pentaerythritol tetra-mercaptoacetate and dimethylacetamide as raw materials, mix and add a photosensitizer, then apply ultraviolet irradiation with an intensity of 30mW / cm 2 at room temperature for 2.8h, wherein the raw material ratio of pentaerythritol tetra-mercaptoacetate, monoester intermediate, photosensitizer and dimethylacetamide is 10mmol:42mmol:50mg:45mL, the photosensitizer is selected from PI-1173, and deionized water is added after the reaction is completed, then the water phase is separated by centrifugation and vacuum dried to obtain a modified flame retardant.

[0039] (2) Preparation of low smoke halogen-free flame-retardant plastic

[0040] Take the following raw materials by weight percentage: magnesium hydroxide ultrafine powder 12wt%, selected from commercially available 1500 mesh ultrafine powder; modified flame retardant 6.2wt%, self-made by this embodiment; toughening agent 7wt%, selected from EPA-810 type EMA-g-GMA elastomer; lubricant 0.9wt%, compounded by using ethylene bis-stearamide and silicone powder in a ratio of 1:3; antioxidant 0.3wt%, compounded by using antioxidant 1010 and antioxidant 168 in an equal weight ratio; and the balance is PBT resin, selected from 1401X06 type resin raw material.

[0041] The magnesium hydroxide ultrafine powder, modified flame retardant, toughening agent, lubricant and antioxidant are first added into a high-speed mixer to pre-mix for 3 minutes at 1000 rpm, then the PBT resin is added to continue mixing for 10 minutes, and then the mixture is added into a twin-screw extruder to melt extrude and granulate at 245°C to obtain the low-smoke halogen-free flame-retardant plastic.

[0042] Example 3, preparation of low-smoke halogen-free flame-retardant plastic, as follows:

[0043] (1) Synthesis of modified flame retardant

[0044] Step A1: Dissolve pentaerythritol and dioxane by heating to 65°C, and then slowly add phosphorus oxychloride under dry nitrogen protection, and stir for 2.8 hours, then add 4-dimethylaminopyridine solution and continue to heat to 100°C for 89 hours. The molar ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane is 0.1:0.1:4:170. The 4-dimethylaminopyridine solution is saturated in tetrahydrofuran at room temperature. After the reaction is completed, the dioxane is removed by rotary evaporation under reduced pressure to obtain a cage phosphoric acid ester.

[0045] Step A2: Dissolve the cage phosphoric acid ester and acetonitrile, then add potassium carbonate and stir for 1.5 hours, then slowly add acryloyl chloride under dry nitrogen protection, and then heat to 80°C for 3.5 hours. The molar ratio of cage phosphoric acid ester, acryloyl chloride, potassium carbonate and acetonitrile is 0.1:0.11:22:280. After the reaction is completed, the potassium carbonate is removed by cooling and filtering, and the acetonitrile is removed by rotary evaporation. The residue is washed with water and dried under vacuum to obtain a monoester intermediate.

[0046] Step A3: Dissolve the monoester intermediate, pentaerythritol tetramercaptoacetate and dimethylacetamide, add a photosensitizer and mix, then apply ultraviolet irradiation at a strength of 40 mW / cm 2 for 2.25 hours at room temperature. The molar ratio of pentaerythritol tetramercaptoacetate, monoester intermediate, photosensitizer and dimethylacetamide is 10:43:60:50. The photosensitizer is selected from PI-1173. After the reaction is completed, deionized water is added to wash, the water phase is separated by centrifugation, and then dried under vacuum to obtain a modified flame retardant.

[0047] (2) Preparation of low-smoke halogen-free flame-retardant plastic

[0048] The following raw materials are taken by weight percentage: magnesium hydroxide superfine powder 15wt%, selected from commercially available 2000 mesh superfine powder; modified flame retardant 5.5wt%, self-made in this embodiment; toughening agent 5.5wt%, selected from EPA-810 type EMA-g-GMA elastomer; lubricant 1.1wt%, compounded by using ethylene bis-stearamide and silicone powder at a ratio of 1:3; antioxidant 0.3wt%, compounded by using antioxidant 1010 and antioxidant 168 at an equal weight ratio; and the balance is PBT resin, selected from 1401X06 type resin raw material.

[0049] The magnesium hydroxide superfine powder, modified flame retardant, toughening agent, lubricant and antioxidant are first added to a high-speed mixer for pre-mixing at 1000 rpm for 3 minutes, then the PBT resin is added for further mixing for 10 minutes, and then the mixture is added to a twin-screw extruder for melt extrusion and granulation at 250°C to obtain a low-smoke halogen-free flame-retardant plastic.

[0050] Example 4, preparation of low-smoke halogen-free flame-retardant plastic, as follows:

[0051] (1) Synthesis of modified flame retardant

[0052] Step A1: Dissolve pentaerythritol and dioxane by heating to 60°C, and then slowly add phosphorus oxychloride under dry nitrogen protection, stirring for 3 hours, then add 4-dimethylaminopyridine solution and continue to heat to 100°C for 8.5 hours. The ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane is 0.1 mol:0.1 mol:3.8 g:180 mL. The 4-dimethylaminopyridine solution is a saturated solution of tetrahydrofuran at room temperature. After the reaction is completed, the dioxane is removed by rotary evaporation under reduced pressure to obtain a cage-shaped phosphate ester.

[0053] Step A2: Dissolve the cage-shaped phosphate ester and acetonitrile, then add potassium carbonate and mix, then slowly add acryloyl chloride under dry nitrogen protection, stirring for 2 hours, then heat to 80°C for 3.5 hours. The ratio of cage-shaped phosphate ester, acryloyl chloride, potassium carbonate and acetonitrile is 0.1 mol:0.11 mol:25 g:300 mL. After the reaction is completed, the potassium carbonate is removed by cooling and filtering, and the acetonitrile is removed by rotary evaporation. The rotary evaporation residue is washed with water and vacuum dried to obtain a monoester intermediate.

[0054] Step A3: Dissolve the monoester intermediate, pentaerythritol tetramercaptoacetate and dimethylacetamide, add a photosensitizer and mix, apply 30 mW / cm 2The reaction was stirred under strong ultraviolet irradiation for 2.6 h, wherein the feeding ratio of pentaerythritol tetramercaptoacetate, monoester intermediate, photosensitizer and dimethylacetamide was 10 mmol: 42 mmol: 65 mg: 55 mL, the photosensitizer was selected from PI-1173, and deionized water was added to wash after the reaction was completed. The aqueous phase was separated by centrifugation and vacuum dried to obtain the modified flame retardant.

[0055] (2) Preparation of low-smoke halogen-free flame-retardant plastic

[0056] The following raw materials were taken according to weight percentage: magnesium hydroxide ultrafine powder 14 wt%, selected from commercially available 1500 mesh ultrafine powder; modified flame retardant 5.8 wt%, self-made by the present embodiment; toughening agent 6 wt%, selected from EPA-810 type EMA-g-GMA elastomer; lubricant 1 wt%, compounded by ethylene bis-stearamide and silicone powder at a ratio of 1:3; antioxidant 0.3 wt%, compounded by antioxidant 1010 and antioxidant 168 at an equal weight ratio; and the balance was PBT resin, selected from 1401X06 type resin raw material.

[0057] The magnesium hydroxide ultrafine powder, modified flame retardant, toughening agent, lubricant and antioxidant were first added to the high-speed mixer and premixed at 1000 rpm for 3 min, then the PBT resin was added and mixed for another 10 min. The mixture was then added to a twin-screw extruder and melted and extruded at 250°C to obtain low-smoke halogen-free flame-retardant plastic.

[0058] Comparative Example 1, referring to the implementation process of Example 4, the modified flame retardant was replaced by pentaerythritol cage phosphoric acid ester TRIMER, and the rest of the implementation process was exactly the same.

[0059] Comparative Example 2, referring to the implementation process of Comparative Example 1, the amount of magnesium hydroxide ultrafine powder was increased to 22 wt%, and the balance was adjusted to 100 wt% by PBT resin, and the rest of the implementation process was exactly the same.

[0060] Samples were taken from the flame-retardant plastic prepared as above, hot-pressed at 240°C and 5 MPa, and tested according to GB / T 1040.2-2006 standard for tensile test; and according to ISO 179-1-2023 standard for impact test; the specific test results are shown in Table 1:

[0061] Table 1

[0062] Tensile strength / MPa Elongation at break / % 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

[0063] As can be seen from the test results in Table 1, the flame-retardant plastics prepared in the examples and comparative examples have similar mechanical properties. Combined with 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 examples. After analysis, it is believed that the modification of the modified flame retardant on the surface of the magnesium hydroxide particles improves the interfacial bonding performance, thereby improving the overall toughness.

[0064] The samples were taken for flame retardant performance test, specifically including: vertical combustion test according to UL-94; oxygen index test according to ASTM D2863-23 standard; smoke density test according to ASTM E662-2017 standard; the specific test results are shown in Table 2:

[0065] Table 2

[0066] Flame retardant rating (2 mm) 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

[0067] From the test results in Table 2, the above samples can all achieve V-0 flame retardant grade, and the limiting oxygen index is above 30%, showing good flame retardant performance. 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.

[0068] In the description of the specification, the description of the reference terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0069] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific embodiments, as long as they do not deviate from the invention or exceed the scope defined by the present claims, which shall belong to the protection scope of the present application.

Claims

1. A low smoke, halogen-free, flame retardant plastic, characterized in that, The specific components are: magnesium hydroxide superfine powder 12-17wt%, modified flame retardant 4.5-6.2wt%, toughening agent 5-7wt%, lubricant 0.9-1.2wt% and antioxidant 0.3-0.4wt%, and the balance is PBT resin; The modified flame retardant is prepared by the following method: Step A1: dissolve and mix pentaerythritol and dioxane, and warm to 60-70℃, then slowly add phosphorus oxychloride under dry nitrogen protection, stir for 2.5-3h, then add 4-dimethylaminopyridine solution and mix, continue to warm to 100℃ reflux for 8-10h to prepare cage phosphoric acid ester, wherein the feeding ratio of pentaerythritol, phosphorus oxychloride, 4-dimethylaminopyridine and dioxane is 0.1mol:0.1mol:3.5-4.5g:150-200mL; Step A2: dissolve and mix cage phosphoric acid ester and acetonitrile, then add potassium carbonate and mix, then slowly add acryloyl chloride under dry nitrogen protection, stir for 1.5-2h, then warm to 80℃ reflux for 3-4h to prepare monoester intermediate, wherein the feeding ratio of cage phosphoric acid ester, acryloyl chloride, potassium carbonate and acetonitrile is 0.1mol:0.108-0.112mol:20-25g:250-300mL; Step A3: The monoester intermediate, pentaerythritol tetramercaptoacetate and dimethylacetamide are mixed to be miscible, the photosensitizer is added and mixed, and the reaction is stirred under the application of 30-40 mW / cm 2 intense ultraviolet irradiation for 2.2-2.8 h to produce a modified flame retardant, wherein the feed ratio of pentaerythritol tetramercaptoacetate, monoester intermediate, photosensitizer and dimethylacetamide is 10 mmol: 42-45 mmol: 50-70 mg: 45-55 mL.

2. A low smoke, halogen-free flame retardant plastic as claimed in claim 1, wherein, The fineness of magnesium hydroxide superfine powder is controlled at 1500-2000 mesh.

3. A low smoke, halogen-free flame retardant plastic as claimed in claim 1, wherein, The toughening agent is EMA-g-GMA or SEBS elastomer.

4. A low smoke, halogen-free flame retardant plastic as claimed in claim 1, wherein, The lubricant is compounded with ethylene bis-stearamide and silicone powder.

5. A low smoke, halogen-free flame retardant plastic as claimed in claim 1, wherein, The antioxidant is compounded with antioxidant 1010 and antioxidant 168.

6. A process for the preparation of a low smoke halogen-free flame retardant plastic according to any one of claims 1 to 5, characterized in that, Specifically: premix magnesium hydroxide superfine powder, modified flame retardant, toughening agent, lubricant and antioxidant, then add PBT resin and mix evenly, then melt extrude and cut the mixture with a twin-screw extruder to obtain low-smoke halogen-free flame-retardant plastic.

Images