Preparation process of flame-retardant composite plastic particles

Abstract

The application relates to the technical field of high polymer materials, in particular to a preparation process of a flame-retardant composite plastic particle, the silicon-boron component is modified in a composite manner, and is further compounded with an ammonium polyphosphate flame-retardant component to prepare a silicon-boron-phosphorus composite flame-retardant system, then the system is melt-blended with polypropylene, the composite flame-retardant system is pre-constructed, different flame-retardant components can form a relatively stable composite structure, unevenness caused by the dispersion of each component can be reduced in the melt processing process, the synergistic effect between the flame-retardant components is improved, and therefore the utilization efficiency of the flame retardant is improved; since the flame-retardant components are added into the polypropylene matrix in the form of a composite system, better flame-retardant performance can be obtained under the same flame-retardant addition amount, the flame-retardant effect does not need to be realized by further increasing the flame-retardant addition amount, the material can obtain higher flame-retardant performance while maintaining better comprehensive mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a preparation process for flame-retardant composite plastic particles. Background Technology

[0002] Polypropylene has advantages such as low density, excellent mechanical properties, good chemical corrosion resistance, excellent processing performance, and low cost. It is widely used in household appliances, automotive parts, electronics, building materials, and packaging. With the rapid development of the electronics and information industry, new energy vehicles, and rail transportation, polypropylene products not only need to meet good mechanical and processing performance, but also need to have high flame retardant properties to meet the safety requirements of related fields.

[0003] However, polypropylene is a flammable polymer with a low limiting oxygen index. During combustion, it easily drips and releases a large amount of heat, posing a significant fire hazard. Therefore, flame retardants are typically added for flame retardant modification. Currently, polypropylene flame retardant systems mainly include halogen-based and halogen-free systems. Because halogen-based flame retardants easily produce corrosive and toxic fumes during combustion, they are no longer suitable for environmental protection requirements and market applications. Halogen-free flame retardant systems, due to their advantages of low smoke, low toxicity, and environmental friendliness, have gradually become the main development direction for polypropylene flame retardant modification. Among existing halogen-free flame retardant systems, intumescent flame retardant systems, represented by ammonium polyphosphate, are widely used due to their good flame retardant effect. This type of flame retardant system typically forms an expanded char layer on the material surface through the synergistic effect of acid, carbon, and gas sources, thereby blocking heat and oxygen transfer and improving the material's flame retardant performance. Meanwhile, inorganic components such as silica and boron compounds, due to their good heat resistance and char-promoting effect, are also often used as synergistic flame retardants in polypropylene flame retardant systems to improve the stability of the char layer structure and enhance the material's fire resistance.

[0004] However, while existing technologies can improve the flame retardant properties of polypropylene to some extent by compounding multiple flame retardant components, most systems still involve directly mixing the flame retardant components physically and then adding them to polypropylene for melt blending. Due to the differences in compatibility between different flame retardant components, agglomeration easily occurs during processing, resulting in poor dispersion of each component in the polypropylene matrix. It is difficult for the flame retardant components to form a stable synergistic effect, thus limiting the flame retardant efficiency. In order to achieve a higher flame retardant rating, the amount of flame retardant added is increased, which may lead to a decrease in the mechanical properties of the material. In addition, although some existing technologies use surface modification or multi-component compounding to improve the performance of the flame retardant system, they focus more on the modification of a single component and fail to achieve effective synergistic construction between multiple components. The timing and mode of action of each component during combustion are different, making it difficult to form a structurally stable and continuous dense char layer, which limits the further improvement of flame retardant performance. Therefore, how to improve the synergistic effect between silicon-boron-phosphorus flame retardant components, improve the utilization efficiency of flame retardants, and take into account the mechanical properties of the material has become an urgent technical problem to be solved at this stage. Summary of the Invention

[0005] The purpose of this invention is to provide a preparation process for flame-retardant composite plastic particles, which solves the problem of how to improve the flame-retardant performance of polypropylene materials while taking into account the mechanical properties of the materials, since multi-component flame retardants are usually added to the polypropylene matrix by a simple physical mixing method in existing polypropylene flame-retardant materials.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A process for preparing flame-retardant composite plastic granules includes the following preparation steps:

[0008] Step 1: Place the polypropylene resin, antioxidant, and lubricant in a high-speed mixer and mix thoroughly at 800-1000 rpm for 8-10 minutes to obtain the mixture.

[0009] Step 2: Transfer the mixture to a twin-screw extruder. Add all the polypropylene resin, antioxidant, lubricant, and a portion of the silicon-boron-phosphorus synergistic flame retardant at the main feed port. After the material enters the third zone for melt mixing, add another portion of the silicon-boron-phosphorus synergistic flame retardant through the side feed device. Set the temperature and screw speed of each zone, and control the feeding rate to match the screw speed so that the residence time of the material in the barrel for melt mixing is ≤2 minutes. The material is then melt-extruded to form plastic strips.

[0010] Step 3: Control the traction speed of the plastic strip and the extrusion line speed so that the plastic strip enters the 70-75℃ hot air insulation zone, stays for 60-65 seconds, and then cools in the 18-22℃ circulating cooling water tank for 1-2 minutes. After pelletizing, composite plastic granules are obtained.

[0011] The silicon-boron-phosphorus synergistic flame retardant has a silicon-boron-phosphorus gradient composite structure, wherein the silicon and boron components are pre-composite with a silane coupling agent and then composited with the phosphorus-based flame retardant components.

[0012] Through the above technical solution, this invention first performs composite modification on the silicon-boron component, and further combines it with flame-retardant components such as ammonium polyphosphate to prepare a silicon-boron-phosphorus composite flame-retardant system. Then, it is melt-blended with polypropylene. Compared with the traditional method of directly adding the flame-retardant components to polypropylene after physical mixing, this invention pre-constructs a composite flame-retardant system so that different flame-retardant components can form a relatively stable composite structure. During the melt processing, it can reduce the unevenness caused by the individual dispersion of each component, improve the synergistic effect between the flame-retardant components, and thus improve the utilization efficiency of the flame retardant. Since the flame-retardant components are added to the polypropylene matrix in the form of a composite system, and the addition of some flame retardant in the early stage is conducive to establishing a uniform dispersion system, while the addition of the remaining flame retardant in the later stage can reduce the long-term thermal degradation of the flame retardant and improve the activity of the flame retardant. Better flame-retardant performance can be obtained with the same amount of flame retardant added, without relying on further increasing the amount of flame retardant added to achieve the flame-retardant effect. It can reduce the adverse effects of high-filled flame retardant on the mechanical properties of polypropylene, so that the material can obtain high flame-retardant performance while maintaining good comprehensive mechanical properties.

[0013] Further, in step one, the antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant; the lubricant is an amide lubricant; based on 80-120 parts by weight of polypropylene resin, the hindered phenolic antioxidant is 0.2-0.8 parts by weight, the phosphite antioxidant is 0.1-0.4 parts by weight, and the amide lubricant is 0.3-1.2 parts by weight.

[0014] Further, in step two, based on 80-120 parts by weight of polypropylene resin, the total weight of the silicon-boron-phosphorus synergistic flame retardant is 18-24 parts; the weight of the partial silicon-boron-phosphorus synergistic flame retardant is 60-65% of the total weight; and the weight of the other partial silicon-boron-phosphorus synergistic flame retardant is 35-40% of the total weight.

[0015] Furthermore, in step two, the temperature of each zone of the twin-screw extruder is 170-175℃ in zone one, 180-185℃ in zone two, 185-190℃ in zone three, 190-195℃ in zone four, and the die head temperature is 185-190℃, while the screw speed is 300-500 rpm.

[0016] Furthermore, in step three, the control of the plastic strip traction speed and the extrusion line speed specifically means that the plastic strip traction speed is 1.02-1.08 times the extrusion line speed.

[0017] Furthermore, in step two, the preparation method of the silicon-boron-phosphorus synergistic flame retardant includes the following steps:

[0018] S1: Add zinc borate to an ethanol-water solution with a volume ratio of 7-8:2-3, mix well, add hollow silica microspheres, sonicate for 30-35 min, add KH560 silane coupling agent, adjust pH, pre-hydrolyze at room temperature for 20-25 min, then heat to 70-75℃ and react for 2-3 h, filter, wash 2-3 times with anhydrous ethanol, dry, pulverize through a 200-250 mesh sieve, and collect the product to obtain silicon-boron composite particles;

[0019] S2: Add ammonium polyphosphate to a mixed solution of anhydrous ethanol and deionized water with a volume ratio of 8.5-9:1-1.5, stir and disperse thoroughly, then add phytic acid, stir at 50-55℃ for 40-45 min, add lignin, continue stirring for 1-1.5 h, adjust the pH to 4-6 with 0.1-0.2 mol / L acetic acid, heat to 75-80℃ and keep warm for 30-40 min to form a phytic acid-lignin composite layer on the surface of ammonium polyphosphate, and obtain flame retardant base material after post-treatment;

[0020] S3: Add silicon-boron composite particles to flame-retardant base material, add deionized water to prepare a slurry with a mass fraction of 20%, shear at 1500 rpm for 30 min, and spray dry; collect the product after the process to obtain silicon-boron-phosphorus synergistic flame retardant.

[0021] Through the above technical solution, this invention constructs a composite flame retardant system composed of silicon, boron, and phosphorus components, forming a composite structure silicon-boron-phosphorus synergistic flame retardant with gradient distribution characteristics. It uses hollow silica microspheres as the core, a silicon-boron composite layer fixed by a silane coupling agent as the intermediate layer, and a phosphorus-carbon composite flame retardant layer formed by ammonium polyphosphate, phytic acid, and lignin as the outer layer, thus constructing a silicon-boron-phosphorus gradient synergistic flame retardant structure. In this structure, each component plays a different role during material combustion and forms a synergistic flame retardant effect. Ammonium polyphosphate decomposes upon heating to form polyphosphoric acid, which can promote the formation of a char layer on the polypropylene surface and reduce the release of combustible volatiles. The silicon component is beneficial for forming a stable inorganic protective layer under high-temperature conditions, improving the integrity and thermal stability of the char layer. The boron component generates boron oxides upon heating, which can further promote the formation of the protective layer and improve the heat resistance and continuity of the char layer. Through the combined effect of these three components, the protective layer formed during combustion effectively blocks the transfer of heat and oxygen to the interior of the material, while inhibiting the escape of combustible gases, thereby improving the flame retardant efficiency of the polypropylene material.

[0022] Further, in step S1, the pH is adjusted to 4-5 using glacial acetic acid with a concentration of 0.5-1 mol / L.

[0023] Further, in step S1, the amount of KH560 added is 5-15% of the mass of zinc borate; the mass ratio of zinc borate to hollow silica microspheres is 0.3-0.8:1.

[0024] Furthermore, in step S1, the hollow silica microspheres have a particle size of 1-50 μm and a wall thickness of 0.1-5 μm.

[0025] Further, in step S2, the post-processing process specifically includes: filtration, washing with anhydrous ethanol 2-3 times, vacuum drying at 60-80℃ to constant weight, pulverizing through a 200-250 mesh sieve, and collecting the product.

[0026] Further, in step S2, the amount of phytic acid added is 50-70% of the mass of ammonium polyphosphate; the amount of lignin added is 45-60% of the mass of ammonium polyphosphate; and the mass ratio of phytic acid to lignin is 0.8-1.5:1.

[0027] Furthermore, in step S3, the specific settings for the spray drying process are: inlet air temperature 160-170℃, outlet air temperature 80-90℃, atomization pressure 0.6-0.8MPa, and feed rate 5-6ml / min.

[0028] The beneficial effects of this invention are:

[0029] (1) The present invention adopts a silicon, boron and phosphorus composite flame retardant system, which improves the flame retardant efficiency of the flame retardant and can effectively improve the flame retardant performance of polypropylene materials under the same amount of flame retardant added.

[0030] (2) While improving the flame retardant properties of polypropylene materials, the present invention can better maintain the mechanical properties of the materials and improve the comprehensive utilization of the materials;

[0031] (3) The preparation method of the present invention is simple, the process is stable and easy to promote and apply, and it has good industrial application prospects.

[0032] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the structure of the silicon-boron-phosphorus synergistic flame retardant of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The preparation methods of the silicon-boron-phosphorus synergistic flame retardant in the following embodiments and comparative examples of the present invention are as follows:

[0037] Preparation of silicon-boron-phosphorus synergistic flame retardant:

[0038] S1: Add 3g of zinc borate to 100ml of ethanol-water solution with a volume ratio of 7:3, mix well, add 3.5g of hollow silica microspheres, sonicate for 30min, add 0.5g of KH560 silane coupling agent, adjust pH to 4 with glacial acetic acid, pre-hydrolyze at room temperature for 20min, then heat to 70℃ and react for 2h, filter, wash twice with anhydrous ethanol, dry, pulverize through a 200-mesh sieve, and collect the product to obtain silicon-boron composite particles;

[0039] S2: Add 5g of ammonium polyphosphate to 120ml of a mixture of anhydrous ethanol and deionized water in a volume ratio of 9:1. After thorough stirring and dispersion, add 5.5g of phytic acid and stir at 50℃ for 40min. Add 3g of lignin and continue stirring for 1h. Adjust the pH to 4-6 with 0.1mol / L acetic acid and heat to 75℃ for 30-40min to form a phytic acid-lignin composite layer on the surface of ammonium polyphosphate. After filtration and washing twice with anhydrous ethanol, vacuum dry at 60℃ to constant weight and pulverize through a 200-mesh sieve to obtain the flame retardant base material.

[0040] S3: Add silicon-boron composite particles to flame-retardant base material, add deionized water to prepare a slurry with a mass fraction of 20%, shear at 1500 rpm for 30 min, and spray dry. Set the spray drying conditions as follows: inlet air temperature 160℃, outlet air temperature 80℃, atomization pressure 0.6MPa, and feed rate 5ml / min. After the process, collect the product to obtain the silicon-boron-phosphorus synergistic flame retardant.

[0041] Example 1

[0042] Preparation process of composite plastic granules:

[0043] Step 1: Place 80 parts of polypropylene resin, 0.2 parts of antioxidant 1010, 0.1 parts of antioxidant 168, and 0.3 parts of EBS lubricant into a high-speed mixer and mix thoroughly at 800 rpm for 8 minutes to obtain the mixture.

[0044] Step 2: Transfer the mixture to a twin-screw extruder. Add all the polypropylene resin, antioxidant, and lubricant to the main feed port, along with 10.8 parts of silicon-boron-phosphorus synergistic flame retardant. After the material enters the third zone for melt mixing, add the remaining 7.2 parts of silicon-boron-phosphorus synergistic flame retardant through the side feed device. Set the temperatures of each zone as follows: Zone 1: 170℃, Zone 2: 180℃, Zone 3: 185℃, Zone 4: 190℃, and the die head temperature: 185℃. Set the screw speed to 300 rpm. Control the feeding rate to match the screw speed so that the residence time of the material in the barrel for melt mixing is ≤2 minutes. Melt extrusion forms plastic strips.

[0045] Step 3: The plastic strip is pulled at a speed 1.02 times the extrusion line speed and placed in a 70℃ hot air insulation zone. After 60 seconds, it is cooled in an 18℃ circulating cooling water tank for 1 minute. After pelletizing, composite plastic granules are obtained.

[0046] Example 2

[0047] Preparation process of composite plastic granules:

[0048] Step 1: Place 100 parts of polypropylene resin, 0.5 parts of antioxidant 1076, 0.2 parts of antioxidant 626, and 0.6 parts of oleamide lubricant into a high-speed mixer and mix thoroughly at 900 rpm for 9 minutes to obtain the mixture.

[0049] Step 2: Transfer the mixture to a twin-screw extruder. Add all the polypropylene resin, antioxidant, and lubricant to the main feed port, along with 12.4 parts of silicon-boron-phosphorus synergistic flame retardant. After the material enters the third zone for melt mixing, add the remaining 7.6 parts of silicon-boron-phosphorus synergistic flame retardant through the side feed device. Set the temperatures of each zone as follows: Zone 1 172℃, Zone 2 183℃, Zone 3 187℃, Zone 4 192℃, and the die head temperature 187℃. Set the screw speed to 400 rpm. Control the feeding rate to match the screw speed so that the residence time of the material in the barrel for melt mixing is ≤2 minutes. Melt extrusion forms plastic strips.

[0050] Step 3: The plastic strip is pulled at a speed 1.05 times the extrusion line speed and placed in a 72℃ hot air insulation zone. After staying for 63 seconds, it is cooled in a 20℃ circulating cooling water tank for 1.5 minutes. After pelletizing, composite plastic granules are obtained.

[0051] Example 3

[0052] Preparation process of composite plastic granules:

[0053] Step 1: Place 120 parts of polypropylene resin, 0.8 parts of antioxidant 1098, 0.4 parts of antioxidant 168, and 1.2 parts of stearamide lubricant into a high-speed mixer and mix thoroughly at 1000 rpm for 10 minutes to obtain the mixture.

[0054] Step 2: Transfer the mixture to a twin-screw extruder. Add all the polypropylene resin, antioxidant, and lubricant to the main feed port, along with 15.6 parts of silicon-boron-phosphorus synergistic flame retardant. After the material enters the third zone for melt mixing, add the remaining 8.4 parts of silicon-boron-phosphorus synergistic flame retardant through the side feed device. Set the temperatures of each zone as follows: Zone 1: 175℃, Zone 2: 185℃, Zone 3: 190℃, Zone 4: 195℃, and the die head temperature: 190℃. Set the screw speed to 500 rpm. Control the feeding rate to match the screw speed so that the residence time of the material in the barrel for melt mixing is ≤2 minutes. Melt extrusion forms plastic strips.

[0055] Step 3: The plastic strip is pulled at a speed 1.08 times the extrusion line speed and placed in a 75℃ hot air insulation zone. After staying for 65 seconds, it is cooled in a 22℃ circulating cooling water tank for 2 minutes. After pelletizing, composite plastic granules are obtained.

[0056] Comparative Example 1

[0057] Preparation process of composite plastic granules:

[0058] Step 1: Place 100 parts of polypropylene resin, 0.5 parts of antioxidant 1076, 0.2 parts of antioxidant 626, and 0.6 parts of oleamide lubricant into a high-speed mixer and mix thoroughly at 900 rpm for 9 minutes to obtain the mixture.

[0059] Step 2: Transfer the mixture to a twin-screw extruder and set the temperatures of each zone as follows: Zone 1: 172℃, Zone 2: 183℃, Zone 3: 187℃, Zone 4: 192℃, and the die head temperature: 187℃. Set the screw speed to 400 rpm and control the feeding rate to match the screw speed so that the residence time of the material in the barrel for melting and mixing is ≤2 minutes. The material is then melt-extruded to form plastic strips.

[0060] Step 3: The plastic strip is pulled at a speed 1.05 times the extrusion line speed and placed in a 72℃ hot air insulation zone. After staying for 63 seconds, it is cooled in a 20℃ circulating cooling water tank for 1.5 minutes. After pelletizing, composite plastic granules are obtained.

[0061] Comparative Example 2

[0062] Preparation process of composite plastic granules:

[0063] Step 1: According to the composition ratio of the silicon-boron-phosphorus synergistic flame retardant in Example 2, weigh out 3g of zinc borate, 3.5g of hollow silica microspheres, 0.5g of KH560 silane coupling agent, 5g of ammonium polyphosphate, 5.5g of phytic acid and 3g of lignin respectively, and add the above components into a high-speed mixer and mix thoroughly to obtain a physically mixed silicon-boron-phosphorus flame retardant for later use.

[0064] Step 2: Place 100 parts of polypropylene resin, 0.5 parts of antioxidant 1076, 0.2 parts of antioxidant 626, and 0.6 parts of oleamide lubricant into a high-speed mixer and mix thoroughly at 900 rpm for 9 minutes to obtain the mixture.

[0065] Step 3: Transfer the mixture to a twin-screw extruder. Add all the polypropylene resin, antioxidant, and lubricant to the main feed port, along with 12.4 parts of physically mixed silicon-boron-phosphorus flame retardant. After the material enters the third zone for melt mixing, add the remaining 7.6 parts of physically mixed silicon-boron-phosphorus flame retardant through the side feed device. Set the temperatures of each zone as follows: Zone 1: 172℃, Zone 2: 183℃, Zone 3: 187℃, Zone 4: 192℃, and the die head temperature: 187℃. Set the screw speed to 400 rpm. Control the feeding rate to match the screw speed so that the residence time of the material in the barrel for melt mixing is ≤2 minutes. The material is then melt-extruded to form plastic strips.

[0066] Step 4: The plastic strip is pulled at a speed 1.05 times the extrusion line speed and placed in a 72℃ hot air insulation zone. After staying for 63 seconds, it is cooled in a 20℃ circulating cooling water tank for 1.5 minutes. After pelletizing, composite plastic granules are obtained.

[0067] Performance testing

[0068] The composite plastic granules prepared in Examples 1-3 and Comparative Examples 1-2 were made into samples that met the specifications. The limiting oxygen index of the samples was tested according to standard GB / T2406.2, the flame retardancy rating of the samples was tested according to UL-94 standard, the tensile properties of the samples were tested according to standard GB / T1040.2, and the impact strength of the samples was tested according to standard GB / T1843. The specific test results are shown in the table below:

[0069]

[0070] As shown in the table above, the samples prepared in Examples 1-3 have excellent flame retardant ability and good mechanical properties. The sample prepared in Comparative Example 1 did not contain any flame retardant components and had poor flame retardant ability. The sample prepared in Comparative Example 2 directly added silicon, boron, and phosphorus flame retardant components with the same composition as in Example 2 and simply mixed them. The limiting oxygen index was improved, but the flame retardant level could only reach V-2, and the mechanical properties decreased significantly. It can be seen that the silicon-boron-phosphorus synergistic flame retardant system of the present invention can effectively improve the flame retardant efficiency and take into account the mechanical properties of the material while maintaining high flame retardant performance, thus verifying that the technical solution described in the present invention has a good synergistic flame retardant effect.

[0071] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above 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 one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0072] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. A preparation process for flame-retardant composite plastic granules, characterized in that, The preparation steps include the following: Step 1: Place the polypropylene resin, antioxidant, and lubricant in a high-speed mixer and mix thoroughly at 800-1000 rpm for 8-10 minutes to obtain the mixture. Step 2: Transfer the mixture to a twin-screw extruder. Add all the polypropylene resin, antioxidant, lubricant, and a portion of the silicon-boron-phosphorus synergistic flame retardant at the main feed port. After the material enters the third zone for melt mixing, add another portion of the silicon-boron-phosphorus synergistic flame retardant through the side feed device. Set the temperature and screw speed of each zone, and control the feeding rate to match the screw speed so that the residence time of the material in the barrel for melt mixing is ≤2 minutes. The material is then melt-extruded to form plastic strips. Step 3: Control the traction speed of the plastic strip and the extrusion line speed so that the plastic strip enters the 70-75℃ hot air insulation zone, stays for 60-65 seconds, and then cools in the 18-22℃ circulating cooling water tank for 1-2 minutes. After pelletizing, composite plastic granules are obtained. The silicon-boron-phosphorus synergistic flame retardant has a silicon-boron-phosphorus gradient composite structure, wherein the silicon and boron components are pre-composite with a silane coupling agent and then composited with the phosphorus-based flame retardant components.

2. The preparation process of flame-retardant composite plastic particles according to claim 1, characterized in that, In step one, the antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant; the lubricant is an amide lubricant; based on 80-120 parts by weight of polypropylene resin, the hindered phenolic antioxidant is 0.2-0.8 parts by weight, the phosphite antioxidant is 0.1-0.4 parts by weight, and the amide lubricant is 0.3-1.2 parts by weight.

3. The preparation process of flame-retardant composite plastic particles according to claim 1, characterized in that, In step two, based on 80-120 parts by weight of polypropylene resin, the total weight of the silicon-boron-phosphorus synergistic flame retardant is 18-24 parts; the weight of the partial silicon-boron-phosphorus synergistic flame retardant is 60-65% of the total weight; and the weight of the other partial silicon-boron-phosphorus synergistic flame retardant is 35-40% of the total weight.

4. The preparation process of flame-retardant composite plastic particles according to claim 1, characterized in that, In step two, the temperature of each zone of the twin-screw extruder is 170-175℃ in zone one, 180-185℃ in zone two, 185-190℃ in zone three, 190-195℃ in zone four, and the die head temperature is 185-190℃. The screw speed is 300-500 rpm.

5. The preparation process of flame-retardant composite plastic particles according to claim 1, characterized in that, In step three, the control of the plastic strip traction speed and the extrusion line speed specifically means that the plastic strip traction speed is 1.02-1.08 times the extrusion line speed.

6. The preparation process of flame-retardant composite plastic particles according to claim 1, characterized in that, In step two, the preparation method of the silicon-boron-phosphorus synergistic flame retardant includes the following steps: S1: Add zinc borate to an ethanol-water solution with a volume ratio of 7-8:2-3, mix well, add hollow silica microspheres, sonicate for 30-35 min, add KH560 silane coupling agent, adjust pH, pre-hydrolyze at room temperature for 20-25 min, then heat to 70-75℃ and react for 2-3 h, filter, wash 2-3 times with anhydrous ethanol, dry, pulverize through a 200-250 mesh sieve, and collect the product to obtain silicon-boron composite particles; S2: Add ammonium polyphosphate to a mixed solution of anhydrous ethanol and deionized water with a volume ratio of 8.5-9:1-1.5, stir and disperse thoroughly, then add phytic acid, stir at 50-55℃ for 40-45 min, add lignin, continue stirring for 1-1.5 h, adjust the pH to 4-6 with 0.1-0.2 mol / L acetic acid, heat to 75-80℃ and keep warm for 30-40 min to form a phytic acid-lignin composite layer on the surface of ammonium polyphosphate, and obtain flame retardant base material after post-treatment; S3: Add silicon-boron composite particles to flame-retardant base material, add deionized water to prepare a slurry with a mass fraction of 20%, shear at 1500 rpm for 30 min, and spray dry; collect the product after the process to obtain silicon-boron-phosphorus synergistic flame retardant.

7. The preparation process of flame-retardant composite plastic particles according to claim 6, characterized in that, In step S1, the pH is adjusted to 4-5 using glacial acetic acid with a concentration of 0.5-1 mol / L.

8. The preparation process of flame-retardant composite plastic particles according to claim 6, characterized in that, In step S1, the hollow silica microspheres have a particle size of 1-50 μm and a wall thickness of 0.1-5 μm.

9. The preparation process of flame-retardant composite plastic particles according to claim 6, characterized in that, In step S2, the post-processing process specifically includes: filtration, washing with anhydrous ethanol 2-3 times, vacuum drying at 60-80℃ to constant weight, pulverizing through a 200-250 mesh sieve, and collecting the product.

10. The preparation process of flame-retardant composite plastic particles according to claim 6, characterized in that, In step S3, the specific settings for the spray drying process are: inlet air temperature 160-170℃, outlet air temperature 80-90℃, atomization pressure 0.6-0.8MPa, and feed rate 5-6ml / min.

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