Efficient environment-friendly flame retardant and preparation method thereof

Abstract

The invention relates to the technical field of flame retardants, in particular to a high-efficiency environment-friendly flame retardant and a preparation method thereof. The high-efficiency environment-friendly flame retardant is prepared from the following raw materials in parts by weight: 30-50 parts of flame retardant, 10-30 parts of complexing agent, 5-10 parts of synergist, 3-8 parts of binder and 2-5 parts of assistant. Efficient activation of agricultural waste rice hull ash is used for replacing commercial white carbon black in commercially available flame retardants with a citric acid matched modification process, the flame retardant achieves breakthrough in the aspects of environmental protection and thermal stability, the comprehensive production cost of the flame retardant can be greatly reduced, meanwhile, the discharge amount of solid waste is reduced, the environmental benefits are remarkably improved, and smoke generation is inhibited; and the nanometer layered double-metal hydroxide promotes decomposition of ammonium polyphosphate under the catalytic action of a laminate to form a continuous and compact pyrophosphoric acid carbon layer to block oxygen diffusion, so that the flame retardant is remarkably superior to a traditional flame-retardant system.

Description

Technical Field

[0001] The present invention relates to the technical field of flame retardants, and specifically relates to a highly efficient and environmentally friendly flame retardant and a preparation method thereof. Background Art

[0002] A flame retardant is a functional additive that imparts flame retardancy to flammable polymers. It is mainly designed for the flame retardancy of polymer materials. There are various types of flame retardants. According to the usage method, they are divided into additive flame retardants and reactive flame retardants. Additive flame retardants are added to polymers by mechanical mixing methods to make the polymers flame retardant, while reactive flame retardants participate in the polymerization reaction as a monomer, so that the polymer itself contains flame retardant components. Its advantage is that it has less impact on the performance of polymer materials and has long-lasting flame retardancy.

[0003] In the prior art, most traditional flame retardants rely on non-renewable minerals such as silica white as reinforcing and smoke-suppressing fillers, resulting in high emissions during the production process, and the halogen and heavy metal components cause environmental toxicity and high pollution problems.

[0004] Based on this, the present invention provides a highly efficient and environmentally friendly flame retardant and a preparation method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly efficient and environmentally friendly flame retardant and a preparation method thereof. The highly efficient and environmentally friendly flame retardant prepared by the present invention can not only effectively reduce production costs, reduce the emission of solid waste, improve environmental benefits, but also has good flame retardant performance.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A highly efficient and environmentally friendly flame retardant and a preparation method thereof, including the following raw materials in parts by weight: 30-50 parts of flame retardant, 10-30 parts of composite agent, 5-10 parts of synergist, 3-8 parts of binder, and 2-5 parts of auxiliary agent.

[0007] Preferably, the flame retardant is made by mixing ammonium polyphosphate and expandable graphite in a weight ratio of (2-4):1. The synergist is selected as nano-layered double metal hydroxide with a particle size ≤ 200 nm. The binder can be selected from at least one or a combination of two of hydroxypropyl methylcellulose or polyvinyl alcohol. The functional auxiliary agent is selected as silane coupling agent of model KH-550.

[0008] Preferably, the expansion ratio of the expandable graphite is 100-300 ml / g, and the degree of polymerization n of the ammonium polyphosphate ≥ 1000.

[0009] Preferably, the metal combination of the nano-layered double metal hydroxide is any one of Mg-Al, Zn-Al or Ca-Al, and the interlayer anion is or Any one of them, after mixing hydroxypropyl methylcellulose and deionized water in a mass ratio of 2:98, at a temperature of 20 °C, the viscosity range is 4000 - 15000 Pa·s.

[0010] Preferably, the preparation method of the composite agent includes the following steps: Weigh activated rice husk ash and modified zinc borate according to a weight ratio of (3 - 5):1, add them to a ball mill, set the ball-to-material ratio to 8:1, and continuously grind for 30 - 60 min under the conditions of a rotation speed of 200 - 300 r / min to obtain the composite agent.

[0011] Preferably, the preparation method of the activated rice husk ash includes the following steps: Step 1: Select rice husk as the raw material, crush it to a particle size of ≤ (5 - 10) mm through a crusher, put it into a rotary kiln, after introducing nitrogen to displace the air in the kiln, raise the temperature, set the heating rate to 10 °C / min, heat up to 450 - 550 °C, and keep it calcined for 2 - 3 h to obtain the calcined product; Step 2: Place the calcined product into a container, add a hydrochloric acid solution with a mass fraction of (5 - 8)%, soak it for 1 - 2 h, the solid-liquid ratio of the hydrochloric acid solution and the calcined product is 10:1, then wash it with deionized water until neutral, and then place it in an oven, raise the temperature to 110 - 130 °C and continuously dry for 1 - 2 h to obtain a solid; Step 3: Add the solid to a jet mill for treatment until D90 ≤ 10 μm to obtain activated rice husk ash.

[0012] Preferably, the preparation method of the modified zinc borate includes the following steps: Step 1: Weigh zinc borate as needed and add it to a mixer, then add citric acid, start the mixer, set the rotation speed to 200 - 300 r / min, and continuously mix for 30 - 60 min to obtain a mixed material; Step 2: Add deionized water to the mixer, the mass ratio of the mixed material and deionized water is (3 - 4):10, raise the temperature to 60 - 80 °C, increase the rotation speed to 400 - 600 r / min, and continuously stir for 2 - 4 h to obtain a slurry; Step 3: Add the slurry to a centrifuge, set the rotation speed to 2000 - 4000 r / min to obtain a precipitate, then place it in a vacuum dryer, set the temperature to 80 - 100 °C, and vacuum dry until the moisture content ≤ 1% to obtain a modified product; Step 4: Add the modified product to an ultrafine mill for treatment until D50 ≤ 2 μm to obtain surface-modified zinc borate.

[0013] Preferably, in the step 4, when the modified product is ultrafinely pulverized, magnesium stearate with a mass fraction of (0.5 - 1)% is added.

[0014] Preferably, the preparation method of an efficient and environmentally friendly flame retardant includes the following steps: S1: Weigh the composite agent and the flame retardant as needed and put them into a high-speed mixer. Set the temperature at 70 - 90 °C and continuously process for 20 - 30 min under the condition of a rotation speed of 1200 - 1500 r / min; S2: Weigh the synergist, binder and additives as needed and add them into the high-speed mixer. Raise the temperature to 80 - 100 °C, reduce the rotation speed to 1000 - 1200 r / min, and continuously process for 1 - 2 h. Then, co-mix and granulate through a twin-screw extruder to obtain particulate matter; S3: Dry the particulate matter through a fluidized bed until the moisture content ≤ 0.5% to obtain a highly efficient and environmentally friendly flame retardant.

[0015] Preferably, in S2, the aspect ratio of the twin-screw extruder is 40:1, the temperature gradient is 120 - 160 °C, the rotation speed is set at 300 - 400 r / min, and the head pressure is set at 2 - 4 MPa. In S3, the inlet temperature of the fluidized bed is 80 - 100 °C, and the wind speed is (2 - 3) m / s.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. In this preparation method, through the efficient activation of agricultural waste rice husk ash to replace commercial silica in commercially available flame retardants and combined with the citric acid modification process, this flame retardant achieves a breakthrough in environmental protection and thermal stability. After the rice husk ash is calcined under nitrogen protection, its amorphous content is increased to 92%, and the thermal weight loss rate at 300 °C is only 3.8%, avoiding the risk of thermal decomposition during the processing. The citric acid modification forms a carboxylic acid group coating layer on the surface of zinc borate, and the dissolution rate is reduced to 42 ppm, and the heavy metal migration amount is far lower than the requirements of environmental protection regulations. In addition, the raw material cost of rice husk ash is only 1 / 5 of that of traditional silicon-based flame retardants, which can greatly reduce the comprehensive production cost of the flame retardant and at the same time reduce the solid waste discharge, significantly improving the environmental benefits.

[0017] 2. In this preparation method, in the flame retardant raw materials, rice husk ash with a micron-scale porous silica skeleton, modified zinc borate with sub-micron-scale particles, and nano-layered double metal hydroxide with a layered structure are gradient compounded to form a triple synergistic effect of "physical isolation - chemical smoke suppression - catalytic carbonization". Rice husk ash rapidly forms a dense and porous heat insulation layer at the initial stage of combustion, effectively blocking the transfer of heat to the matrix. Modified zinc borate decomposes at high temperature to generate glass-like substances, reducing the combustion temperature and capturing free radicals through endothermic reactions to inhibit smoke generation. Nano-layered double metal hydroxide promotes the decomposition of ammonium polyphosphate through the catalytic action of the layer board to form a continuous and dense pyrophosphate carbon layer, blocking the diffusion of oxygen, and thus making this flame retardant significantly superior to traditional flame retardant systems.

[0018] 3. In this preparation method, rice husk ash and zinc borate are designed through particle size gradient and modified at the interface with silane coupling agent, so that the flame retardant is highly uniformly dispersed in the polymer matrix. The nitrogen calcination of rice husk ash inhibits carbonization, and zinc borate is modified by citric acid coating to improve thermal stability. The addition of silane coupling agent achieves the effect of chemical bonding to inhibit volatilization, so that no irritating gas is released during the processing. At the same time, micron-sized rice husk ash acts as a rigid particle to bear stress, and sub-micron-sized zinc borate fills the voids, reducing stress concentration points and improving the tensile strength of the products using this flame retardant, which is significantly better than the industry average level and meets the requirements of high-strength application scenarios such as automotive parts and electronic enclosures. Detailed implementation manners

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Embodiment 1

[0020] This embodiment provides an efficient and environmentally friendly flame retardant and its preparation method, including the following raw materials in parts by weight: 30 parts of flame retardant, 10 parts of compound agent, 5 parts of synergist, 3 parts of binder, and 2 parts of auxiliary agent.

[0021] In some embodiments, the flame retardant is made by mixing ammonium polyphosphate and expandable graphite in a weight ratio of 2:1. The synergist is selected as nano-layered double metal hydroxide with a particle size ≤ 200 nm. The binder can be selected as hydroxypropyl methylcellulose, and the functional auxiliary agent is selected as silane coupling agent of model KH-550.

[0022] In some embodiments, the expansion ratio of expandable graphite is 100 ml / g, and the degree of polymerization n of ammonium polyphosphate ≥ 1000.

[0023] In some embodiments, the metal combination of the nano-layered double metal hydroxide is Mg-Al, and the interlayer anion is , hydroxypropyl methylcellulose and deionized water are mixed in a mass ratio of 2:98 and at a temperature of 20 °C, and the viscosity range is 4000 Pa·s.

[0024] In some embodiments, the preparation method of the compound agent includes the following steps: Weigh activated rice husk ash and modified zinc borate in a weight ratio of 3:1, add them to a ball mill, set the ball-to-material ratio to 8:1, and continuously grind for 30 min at a rotation speed of 200 r / min to obtain the compound agent.

[0025] In some embodiments, the preparation method of activated rice husk ash includes the following steps: Step 1: Select rice husk as raw material, crush it to a particle size of ≤5 mm by a crusher, put it into a rotary furnace, introduce nitrogen to displace the air in the furnace, then heat up, set the heating rate at 10 °C / min, heat up to 450 °C, and keep calcining for 2 h to obtain a calcined product; Step 2: Place the calcined product into a container, add a hydrochloric acid solution with a mass fraction of 5%, soak for 1 h, the solid-liquid ratio of the hydrochloric acid solution to the calcined product is 10:1, then wash with deionized water until neutral, and then place it in an oven, heat up to 110 °C and keep drying for 1 h to obtain a solid product; Step 3: Add the solid product to a jet mill for treatment until D90 ≤ 10 μm to obtain activated rice husk ash.

[0026] In some embodiments, the preparation method of modified zinc borate includes the following steps: Step 1: Weigh zinc borate as needed and add it to a mixer, then add citric acid, start the mixer, set the rotation speed at 200 r / min, and keep mixing for 30 min to obtain a mixed material; Step 2: Add deionized water to the mixer, the mass ratio of the mixed material to the deionized water is 3:10, heat up to 60 °C, increase the rotation speed to 400 r / min, and keep stirring for 2 h to obtain a slurry; Step 3: Add the slurry to a centrifuge, set the rotation speed at 2000 r / min to obtain a precipitate, then place it in a vacuum dryer, set the temperature at 80 °C, and vacuum dry until the moisture content ≤ 1% to obtain a modified product; Step 4: Add the modified product to an ultrafine mill for treatment until D50 ≤ 2 μm to prepare surface-modified zinc borate.

[0027] In some embodiments, in Step 4, 0.5% by mass of magnesium stearate is added during the ultrafine grinding of the modified product.

[0028] In some embodiments, the preparation method of an efficient and environmentally friendly flame retardant includes the following steps: S1: Weigh the composite agent and the flame retardant as needed and put them into a high-speed mixer, set the temperature at 70 °C, and keep processing for 20 min under the condition of a rotation speed of 1200 r / min; S2: Weigh the synergist, the binder and the auxiliary agent as needed and add them to the high-speed mixer, increase the temperature to 80 °C, reduce the rotation speed to 1000 r / min, keep processing for 1 h, and then carry out co-mixing granulation by a twin-screw extruder to obtain particulate matter; S3: Dry the particulate matter by a fluidized bed until the moisture content ≤ 0.5% to prepare an efficient and environmentally friendly flame retardant.

[0029] In some embodiments, in S2, the aspect ratio of the twin-screw extruder is 40:1, the temperature gradient is 120 °C, the rotation speed is set at 300 r / min, the head pressure is set at 2 MPa, in S3, the inlet temperature of the fluidized bed is 80 °C, and the wind speed is 2 m / s. Example 2

[0030] An efficient and environmentally friendly flame retardant and its preparation method, comprising the following raw materials in parts by weight: 50 parts of flame retardant, 30 parts of composite agent, 10 parts of synergist, 8 parts of binder, and 5 parts of auxiliary agent.

[0031] In some embodiments, the flame retardant is made by mixing ammonium polyphosphate and expandable graphite in a weight ratio of 4:1. The synergist is selected as nano-layered double metal hydroxide with a particle size ≤ 200 nm. The binder is selected as polyvinyl alcohol, and the functional auxiliary agent is selected as silane coupling agent of model KH-550.

[0032] In some embodiments, the expansion ratio of expandable graphite is 300 ml / g, and the degree of polymerization n of ammonium polyphosphate ≥ 1000.

[0033] In some embodiments, the metal combination of nano-layered double metal hydroxide is Zn-Al, the interlayer anion is NO3⁻. Hydroxypropyl methylcellulose and deionized water are mixed in a mass ratio of 2:98 and at a temperature of 20 °C, and the viscosity range is 15000 Pa·s.

[0034] In some embodiments, the preparation method of the composite agent includes the following steps: Weigh activated rice husk ash and modified zinc borate according to a weight ratio of 3:1, add them to a ball mill, set the ball-to-material ratio to 8:1, and continuously grind for 60 min at a rotation speed of 300 r / min to obtain the composite agent.

[0035] In some embodiments, the preparation method of activated rice husk ash includes the following steps: Step 1: Select rice husk as the raw material, crush it to a particle size ≤ 10 mm through a crusher, put it into a rotary furnace, introduce nitrogen to displace the air in the furnace and then heat up. The heating rate is set at 10 °C / min, heat up to 550 °C, and keep calcining for 3 h to obtain a calcined product. Step 2: Place the calcined product into a container, add an 8% hydrochloric acid solution by mass fraction, soak for 2 h, the solid-liquid ratio of the hydrochloric acid solution to the calcined product is 10:1, then wash it with deionized water until neutral, and then put it into an oven and heat up to 130 °C and keep drying for 2 h to obtain a solid product. Step 3: Add the solid product to a jet mill for treatment until D90 ≤ 10 μm to obtain activated rice husk ash.

[0036] In some embodiments, the preparation method of modified zinc borate includes the following steps: Step 1: Weigh zinc borate as needed and add it to a mixer, then add citric acid, start the mixer, set the rotation speed at 300 r / min, and continuously mix for 60 min to obtain a mixed material. Step 2: Add deionized water to the mixer. The mass ratio of the de-mixed material to the ion water is 4:10. Heat up to 80 °C, increase the rotation speed to 600 r / min, and continuously stir for 4 h to obtain a slurry. Step 3: Add the slurry to a centrifuge, set the rotation speed at 4000 r / min to obtain a precipitate, and then place it in a vacuum dryer. Set the temperature at 100 °C and vacuum dry until the moisture content ≤ 1% to obtain a modified product. Step 4: Add the modified product to an ultrafine grinder and process it until D50 ≤ 2 μm to produce surface-modified zinc borate.

[0037] In some embodiments, in Step 4, 1% by mass of magnesium stearate is added during the ultrafine grinding of the modified product.

[0038] In some embodiments, a preparation method of an efficient and environmentally friendly flame retardant includes the following steps: S1: Weigh the composite agent and the flame retardant as required and put them into a high-speed mixer. Set the temperature at 90 °C and continuously process for 30 min under the condition of a rotation speed of 1500 r / min. S2: Weigh the synergist, the binder, and the auxiliary agent as required and add them to the high-speed mixer. Increase the temperature to 100 °C, reduce the rotation speed to 1200 r / min, and continuously process for 2 h. Then, carry out co-blending granulation through a twin-screw extruder to obtain particulate matter. S3: Dry the particulate matter through a fluidized bed until the moisture content ≤ 0.5% to produce an efficient and environmentally friendly flame retardant.

[0039] In some embodiments, in S2, the length-diameter ratio of the twin-screw extruder is 40:1, the temperature gradient is 160 °C, the rotation speed is set at 400 r / min, the head pressure is set at 4 MPa, in S3, the inlet temperature of the fluidized bed is 100 °C, and the wind speed is 3 m / s. Example 3

[0040] An efficient and environmentally friendly flame retardant and its preparation method include the following raw materials in parts by weight: 40 parts of flame retardant, 20 parts of composite agent, 8 parts of synergist, 5 parts of binder, and 3 parts of auxiliary agent.

[0041] In some embodiments, the flame retardant is made by mixing ammonium polyphosphate and expandable graphite in a weight ratio of 3:1. The synergist is selected as nano-layered double metal hydroxide with a particle size ≤ 200 nm. The binder is selected as an equal combination of hydroxypropyl methylcellulose and polyvinyl alcohol. The functional auxiliary agent is selected as silane coupling agent of model KH-550.

[0042] In some embodiments, the expansion ratio of the expandable graphite is 200 ml / g, and the degree of polymerization n of the ammonium polyphosphate ≥ 1000.

[0043] In some embodiments, the metal combination of the nano-layered double metal hydroxide is Ca-Al, and the interlayer anion is , hydroxypropyl methylcellulose and deionized water are mixed at a mass ratio of 2:98 and at a temperature of 20 °C, with a viscosity range of 10,000 Pa·s.

[0044] In some embodiments, the preparation method of the composite agent includes the following steps: Weigh activated rice husk ash and modified zinc borate at a weight ratio of 4:1, add them to a ball mill, set the ball-to-material ratio to 8:1, and continuously grind for 45 min under the condition of a rotation speed of 250 r / min to obtain the composite agent.

[0045] In some embodiments, the preparation method of activated rice husk ash includes the following steps: Step 1: Select rice husks as raw materials, crush them to a particle size of ≤8 mm through a crusher, put them into a rotary furnace, introduce nitrogen to displace the air in the furnace, then heat up, set the heating rate to 10 °C / min, heat up to 500 °C, and keep calcining for 2.5 h to obtain a calcined product; Step 2: Place the calcined product into a container, add a hydrochloric acid solution with a mass fraction of 7%, soak for 1.5 h, the solid-liquid ratio of the hydrochloric acid solution to the calcined product is 10:1, then wash with deionized water until neutral, and then place it in an oven, heat up to 120 °C and continuously dry for 1.5 h to obtain a solid; Step 3: Add the solid to a jet mill for treatment until D90 ≤ 10 μm to obtain activated rice husk ash.

[0046] In some embodiments, the preparation method of modified zinc borate includes the following steps: Step 1: Weigh zinc borate as needed and add it to a mixer, then add citric acid, start the mixer, set the rotation speed to 250 r / min, and continuously mix for 45 min to obtain a mixed material; Step 2: Add deionized water to the mixer, the mass ratio of the mixed material to the deionized water is 3.5:10, heat up to 70 °C, increase the rotation speed to 500 r / min, and continuously stir for 3 h to obtain a slurry; Step 3: Add the slurry to a centrifuge, set the rotation speed to 3000 r / min to obtain a precipitate, then place it in a vacuum dryer, set the temperature to 90 °C, and vacuum dry until the moisture content ≤ 1% to obtain a modified product; Step 4: Add the modified product to a ultrafine mill for treatment until D50 ≤ 2 μm to obtain surface-modified zinc borate.

[0047] In some embodiments, in Step 4, 0.8% by mass of magnesium stearate is added during the ultrafine grinding of the modified product.

[0048] In some embodiments, the preparation method of a highly efficient and environmentally friendly flame retardant includes the following steps: S1: Weigh the composite agent and the flame retardant as needed and put them into a high-speed mixer, set the temperature to 80 °C, and continuously process for 25 min under the condition of a rotation speed of 1350 r / min; S2: Weigh the synergist, binder and additives as needed and add them to a high-speed mixer. Raise the temperature to 90 °C, reduce the rotation speed to 1100 r / min, and continuously process for 1.5 h. Then, perform co-blending and pelletizing through a twin-screw extruder to obtain particulate matter; S3: Dry the particulate matter through a fluidized bed until the moisture content ≤ 0.5% to obtain a highly efficient and environmentally friendly flame retardant.

[0049] In some embodiments, the aspect ratio of the twin-screw extruder in S2 is 40:1, the temperature gradient is 145 °C, the rotation speed is set to 350 r / min, the head pressure is set to 3 MPa, the inlet temperature of the fluidized bed in S3 is 90 °C, and the wind speed is 2.5 m / s.

[0050] Comparative Example 1. The difference between this comparative example and Experiment 1 is that activated rice husk ash was not added during the preparation of the composite agent in this comparative example.

[0051] Comparative Example 2. The difference between this comparative example and Experiment 1 is that modified zinc borate was not added during the preparation of the composite agent in this comparative example.

[0052] Comparative Example 3. The difference between this comparative example and Experiment 1 is that the composite agent was not added during the preparation of the highly efficient and environmentally friendly flame retardant in this comparative example.

[0053] Perform performance tests on the highly efficient and environmentally friendly flame retardants prepared in Examples 1-3, Comparative Examples 1, 2 and 3. The test items and test methods are as follows: Limiting oxygen index (LOI) test: Conduct the test according to the test method in GB / T 2406.2-2009 and record the obtained data in Table 1; Peak heat release rate test: Conduct the test according to the test method in ISO 5660-1 and record the obtained data in Table 1; Vertical burning rating test: Conduct the test according to the standard of GB / T 2408-2021 and record the obtained data in Table 1; Dissolution rate test: Conduct the test according to the test method in GB / T 30805-2014 and record the obtained data in Table 2; Thermogravimetric rate (300 °C) test: Conduct the test according to the test method in GB / T 27761-2011 and record the obtained data in Table 2; Dispersion uniformity test: Conduct the test according to the standard of ASTM E2809-2022 and record the obtained data in Table 3; Tensile strength retention rate test: Conduct the test according to the standard of GB / T 1040.2-2006 and record the obtained data in Table 3.

[0054] Table 1:

[0055] By comparing and analyzing the data in Table 1, it can be seen that the flame retardants prepared by the preparation methods of Examples 1-3 have significantly better performance than the flame retardants prepared by the preparation methods of Comparative Example 1, Comparative Example 2, and Comparative Example 3. This shows that through the gradient compounding of rice husk ash (micron-scale porous silica skeleton), modified zinc borate (sub-micron-scale particles), and nano-layered double metal hydroxide (layered structure), a triple synergistic effect of "physical isolation - chemical smoke suppression - catalytic carbonization" is formed. Under the synergistic action of the three, the peak value of the heat release rate during the combustion process of the material can reach below 120 kW / m², the limiting oxygen index (LOI) breaks through 32%, and it meets the UL94 V-0 level flame retardant standard, significantly superior to the performance of traditional flame retardants.

[0056] Table 2:

[0057] By comparing and analyzing the data in Table 2, it can be seen that the flame retardants prepared by the preparation methods of Examples 1-3 have significantly better performance than the flame retardants prepared by the preparation methods of Comparative Example 1, Comparative Example 2, and Comparative Example 3. This shows that through the efficient activation of agricultural waste rice husk ash (replacing 30% of commercial silica) and the citric acid modification process, this flame retardant has achieved breakthroughs in terms of environmental protection and thermal stability, and the dissolution rate is reduced to 42 ppm (the national standard limit is 200 ppm), and the heavy metal migration amount is far lower than the requirements of environmental protection regulations. In addition, the raw material cost of rice husk ash is only 1 / 5 of that of traditional silicon-based flame retardants, which also enables the comprehensive production cost to be greatly reduced, while reducing the solid waste discharge amount and significantly improving the environmental benefits.

[0058] Table 3:

[0059] By comparing and analyzing the data in Table 3, it can be seen that the flame retardants prepared by the preparation methods of Examples 1-3 have significantly better performance than the flame retardants prepared by the preparation methods of Comparative Example 1, Comparative Example 2, and Comparative Example 3. The test results in Table 3 show that the maximum agglomeration size of the flame retardant particles ≤ 9.8 μm (traditional process > 20 μm). This shows that through the particle size gradient design (rice husk ash D90 ≤ 10 μm, zinc borate D50 ≤ 2 μm) and the interfacial modification of silane coupling agent, this flame retardant is highly uniformly dispersed in the polymer matrix, and the tensile strength retention rate can reach more than 85% (conventional products ≤ 70), significantly superior to the industry average level, meeting the requirements of high-strength application scenarios such as automotive parts and electronic enclosures, and having good market competitiveness.

[0060] In the description of this specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples.

[0061] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. An efficient and environmentally friendly flame retardant and its preparation method, characterized in that, It includes the following raw materials in parts by weight: 30 - 50 parts of flame retardant, 10 - 30 parts of composite agent, 5 - 10 parts of synergist, 3 - 8 parts of binder, and 2 - 5 parts of auxiliary agent.

2. The preparation method of the high-efficiency and environmentally friendly flame retardant according to claim 1, wherein The flame retardant is made by mixing ammonium polyphosphate and expandable graphite in a weight ratio of (2 - 4):

1. The synergist is selected as nano - layered double - metal hydroxide with a particle size ≤ 200 nm. The binder can be at least one or a combination of two of hydroxypropyl methylcellulose or polyvinyl alcohol. The functional auxiliary agent is selected as silane coupling agent of model KH - 550.

3. The preparation method of the high-efficiency and environment-friendly flame retardant according to claim 1, wherein, The expansion ratio of the expandable graphite is 100 - 300 ml / g, and the degree of polymerization n of the ammonium polyphosphate ≥ 1000.

4. The preparation method of the high-efficiency and environment-friendly flame retardant according to claim 1, characterized in that, The metal combination of the nano-layered double metal hydroxide is any one of Mg-Al, Zn-Al or Ca-Al, and the interlayer anion is or Any one of them. After the hydroxypropyl methylcellulose and deionized water are mixed in a mass ratio of 2:98, the viscosity ranges from 4000 to 15000 Pa·s at a temperature of 20°C.

5. The preparation method of the high-efficiency environmental protection flame retardant according to claim 1, wherein, The preparation method of the composite agent includes the following steps: Weigh activated rice husk ash and modified zinc borate in a weight ratio of (3 - 5):1, add them to a ball mill, set the ball - to - material ratio to 8:1, and continuously grind for 30 - 60 min under the condition of a rotation speed of 200 - 300 r / min to obtain the composite agent.

6. The preparation method of the high-efficiency and environment-friendly flame retardant according to claim 5, characterized in that, The preparation method of the activated rice husk ash includes the following steps: Step 1: Select rice husk as the raw material, crush it to a particle size ≤ (5 - 10) mm by a crusher, put it into a rotary furnace, after introducing nitrogen to displace the air in the furnace, heat it up, set the heating rate to 10℃ / min, heat it up to 450 - 550℃, and keep it calcined for 2 - 3 h to obtain the calcined product. Step 2: Put the calcined product into a container, add hydrochloric acid solution with a mass fraction of (5 - 8)%, soak it for 1 - 2 h, the solid - liquid ratio of the hydrochloric acid solution to the calcined product is 10:1, then wash it with deionized water until neutral, and then put it into an oven, heat it up to 110 - 130℃ and keep it dried for 1 - 2 h to obtain a solid product. Step 3: Add the solid product to a jet mill for treatment until D90 ≤ 10 μm to obtain activated rice husk ash.

7. The preparation method of the high-efficiency environmental protection flame retardant according to claim 5, characterized in that, The preparation method of the modified zinc borate includes the following steps: Step 1: Weigh zinc borate as required and add it to a mixer, then add citric acid, start the mixer, set the rotation speed to 200 - 300 r / min, and continuously mix for 30 - 60 min to obtain a mixed material. Step 2: Add deionized water to the mixer, the mass ratio of the mixed material to the deionized water is (3 - 4):10, heat it up to 60 - 80℃, increase the rotation speed to 400 - 600 r / min, and continuously stir for 2 - 4 h to obtain a slurry. Step 3: Add the slurry to a centrifuge, set the rotation speed to 2000 - 4000 r / min to obtain a precipitate, then put it into a vacuum dryer, set the temperature to 80 - 100℃, and vacuum - dry it until the moisture content ≤ 1% to obtain a modified product. Step 4: Add the modified product to an ultrafine grinder for treatment until D50 ≤ 2 μm to obtain surface - modified zinc borate.

8. The preparation method of the high-efficiency and environment-friendly flame retardant according to claim 7, characterized in that, In the above - mentioned step 4, when the modified product is ultrafinely ground, magnesium stearate with a mass ratio of (0.5 - 1)% is added.

9. A preparation method of the high-efficiency environmental protection flame retardant according to any one of claims 1 to 8, characterized in that, It includes the following steps: S1: Weigh the composite agent and the flame retardant as required and put them into a high - speed mixer, set the temperature to 70 - 90℃, and continuously process for 20 - 30 min under the condition of a rotation speed of 1200 - 1500 r / min. S2: Weigh the synergist, binder and additives as needed and add them to a high-speed mixer. Raise the temperature to 80 - 100 °C, reduce the rotation speed to 1000 - 1200 r / min, and continuously process for 1 - 2 h. Then, carry out co-blending granulation through a twin-screw extruder to obtain particulate matter; S3: Dry the particulate matter through a fluidized bed until the moisture content ≤ 0.5% to prepare a highly efficient and environmentally friendly flame retardant.

10. The preparation method of the high-efficiency environmental protection flame retardant according to claim 9, characterized in that, In S2, the length-diameter ratio of the twin-screw extruder is 40:1, the temperature gradient is 120 - 160 °C, the rotation speed is set at 300 - 400 r / min, and the head pressure is set at 2 - 4 MPa. In S3, the inlet temperature of the fluidized bed is 80 - 100 °C, and the wind speed is (2 - 3) m / s.

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