Polypropylene halogen-free flame-retardant composite material and preparation method thereof

Abstract

The application discloses a kind of polypropylene halogen-free flame-retardant composite material and preparation method thereof, the flame retardant of the present application is compounded by polypropylene resin, phosphorus-nitrogen flame retardant, modified barium sulfate, antioxidant and EBS wax, wherein the phosphorus-nitrogen flame retardant is obtained by reacting with phosphoric acid using piperazine and melamine, then using pentaerythritol in molten state at high temperature, which can be fully mixed with the solid powder, and then obtained by thermal polymerization reaction;The modified barium sulfate is aluminum hypophosphite coated modified barium sulfate powder.The application realizes the anti-migration of phosphorus-nitrogen flame retardant, modified barium sulfate and other designs and adjustments, high flame-retardant efficiency and little influence on material mechanical properties, and then obtains high-performance polypropylene halogen-free flame-retardant composite material.

Description

Technical Field

[0001] This invention relates to a halogen-free flame-retardant polypropylene composite material and its preparation method, belonging to the field of polymer composite materials. Background Technology

[0002] Polypropylene (PP) possesses advantages such as being non-toxic, lightweight, having excellent mechanical properties, good electrical insulation, and resistance to chemical corrosion, making it widely used in packaging, textiles, building materials, automobiles, electronics, and office supplies. However, PP itself is a flammable material with a limiting oxygen index of only 17.4–18.5% and a low char formation rate. During combustion, it produces molten droplets that easily spread the flame, posing a significant safety hazard and causing immense harm to life and property in the event of a fire. Therefore, flame-retardant modification of PP materials is essential.

[0003] Currently, flame retardants used in polypropylene materials mainly include antimony halogen flame retardants, metal hydroxides, and intumescent flame retardants. Among these, antimony halogen flame retardants readily react with hindered amine stabilizers and release large amounts of hydrogen halide gas during combustion, which then absorbs water to form highly corrosive hydrohalic acids, corroding equipment, polluting the environment, and harming human health. Metal hydroxides have poor compatibility with polypropylene, and due to their large addition amounts, they significantly impact processing and mechanical properties. While intumescent flame retardants meet the current demand for halogen-free materials, they suffer from poor migration resistance, hygroscopicity, and low temperature resistance. Therefore, finding a flame retardant with excellent flame-retardant properties and minimal impact on the material's mechanical properties is of great significance for preparing high-performance flame-retardant polypropylene composite materials. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a halogen-free flame-retardant polypropylene composite material and its preparation method. The flame retardant of this invention is a compound of polypropylene resin, a phosphorus-nitrogen flame retardant, modified barium sulfate, an antioxidant, and EBS wax. The phosphorus-nitrogen flame retardant is obtained by reacting piperazine and melamine with phosphoric acid to obtain a mixed solid powder, which is then fully mixed with pentaerythritol in a molten state at high temperature, followed by a thermal polymerization reaction. The modified barium sulfate is barium sulfate powder coated with aluminum hypophosphite. Through the design and adjustment of the phosphorus-nitrogen flame retardant and modified barium sulfate, this invention achieves anti-migration properties, high flame-retardant efficiency, and minimal impact on the mechanical properties of the material, thereby obtaining a high-performance halogen-free flame-retardant polypropylene composite material.

[0005] The technical solution of the present invention is: a halogen-free flame-retardant polypropylene composite material, characterized in that it is composed of the following components in parts by weight: 40-60 parts of polypropylene resin, 20-28 parts of phosphorus-nitrogen flame retardant, 10-25 parts of modified barium sulfate, 2-3 parts of antioxidant, and 1-3 parts of EBS wax (vinyl bis-stearamide wax).

[0006] The above-mentioned antioxidants are compounded by main antioxidant 1010 (high molecular weight hindered phenolic antioxidant) and auxiliary antioxidant 168 (phosphite antioxidant) in a weight ratio of 2.5-3.5:1.

[0007] The preparation method of the phosphorus-nitrogen flame retardant is as follows:

[0008] (1) Melamine and water are mixed evenly to form a melamine suspension; the weight ratio of melamine to water is 1:4-6;

[0009] (2) Mix piperazine and water evenly to form a piperazine solution; the weight ratio of piperazine to water is 1:3-5;

[0010] (3) Add an 85% phosphoric acid solution to the reaction vessel, and simultaneously and slowly add melamine suspension and piperazine solution to the phosphoric acid solution. React at 98-100℃ for 3-4 hours, cool, filter, wash and dry to obtain solid powder;

[0011] (4) Mix the solid powder prepared in step (3) with pentaerythritol evenly, place it in a muffle furnace, and calcine at 265-280℃ for 4-5 hours to obtain a phosphorus-nitrogen composite flame retardant.

[0012] The weight ratio of piperazine, melamine, phosphoric acid solution and pentaerythritol in the phosphorus-nitrogen flame retardant is 1:0.7-1.1:3.4-3.8:0.5-0.8.

[0013] The performance indicators of the phosphorus-nitrogen flame retardants prepared by the above method are shown in Table 1:

[0014] Table 1: Performance Indicators of Phosphate Flame Retardants

[0015] project index Appearance White powder Environmental protection requirements Compliant with RoHS Directive and REACH Regulations N content, % 16-20.5 P content, % 16.5-18.5 Whiteness, % ≥90

[0016] The method for preparing the modified barium sulfate is as follows:

[0017] (1) Sodium hypophosphite and water are mixed evenly to form a sodium hypophosphite solution; the weight ratio of sodium hypophosphite to water is 2:0.8-1.5;

[0018] (2) Mix aluminum sulfate and water evenly to form an aluminum sulfate solution; the weight ratio of aluminum sulfate to water is 4:2-4;

[0019] (3) Add barium sulfate to aluminum sulfate solution and stir evenly; then add 20% ammonia water dropwise to coat the surface of barium sulfate with a layer of aluminum sol, then heat to 90-100℃, then add sodium hypophosphite solution from step (1), react at constant temperature for 2-4 hours, filter, wash and dry to obtain aluminum hypophosphite coated modified barium sulfate powder.

[0020] In the above-mentioned method for preparing modified barium sulfate, the weight ratio of barium sulfate, aluminum sulfate, ammonia, and sodium hypophosphite is 4-4.5:1.05-1.1:1.3-1.5:1.

[0021] The preparation method of the above-mentioned halogen-free flame-retardant polypropylene composite material is as follows:

[0022] S1: Add phosphorus and nitrogen flame retardant, modified barium sulfate, antioxidant, and EBS wax to a high-speed mixer in proportion and stir until evenly mixed. Then add polypropylene resin and stir until evenly mixed.

[0023] S2: The uniformly mixed materials are mixed into rubber blocks using an internal mixer at 180-190℃, and then extruded, granulated and dried using a twin-screw extruder at 170-180℃ to obtain halogen-free flame-retardant polypropylene composite material.

[0024] The polypropylene halogen-free flame-retardant composite material prepared by the above method was tested for flame retardancy using a horizontal and vertical combustion tester, and it achieved a UL-94V0 rating of 1.6mm. Furthermore, after being treated under double 85 test conditions for 7 days, the flame retardant performance of the polypropylene halogen-free flame-retardant composite material still reached a UL-94V0 rating of 1.6mm.

[0025] The technical effects of this invention are:

[0026] 1. This invention first utilizes the fact that both piperazine and melamine can react with phosphoric acid to obtain a mixed solid powder. Then, it utilizes the fact that pentaerythritol is in a molten state at high temperature, which can be fully mixed with the solid powder. Finally, a phosphorus-nitrogen flame retardant is obtained through a thermal polymerization reaction. Because this flame retardant contains melamine, phosphoric acid, piperazine and other groups, it can itself act as an acid source, gas source and char formation. Compared with traditional single flame retardants, it has better flame retardant performance. Compared with physically compounded flame retardants, the components of this flame retardant are more evenly distributed, and it has better anti-migration and flame retardant performance.

[0027] 2. In traditional polypropylene flame-retardant composite materials, barium sulfate is used as a filler. On the one hand, it can reduce costs, and on the other hand, it can improve the rigidity, heat resistance and dimensional stability of the composite. In this invention, the modified barium sulfate is coated with a layer of aluminum phosphate flame retardant. In addition to having the functions of ordinary barium sulfate, it can also cooperate with the phosphorus and nitrogen flame retardants in the formulation to play a synergistic role in flame retardancy and improve the flame retardant performance of polypropylene halogen-free flame-retardant composite materials.

[0028] 3. Because the flame retardants and additives used in this polypropylene halogen-free flame retardant composite material are all halogen-free and environmentally friendly materials, and have good anti-migration properties, this polypropylene halogen-free flame retardant composite material can still exhibit excellent flame retardant performance in high temperature and high humidity environments. Attached Figure Description

[0029] Figure 1The images show SEM images of the modified barium sulfate in Example 1; the left image shows unmodified barium sulfate, and the right image shows modified barium sulfate. Detailed Implementation

[0030] The effects are illustrated below with reference to the embodiments and accompanying drawings. The antioxidant is mainly antioxidant 1010 (high molecular weight hindered phenolic antioxidant) and auxiliary antioxidant 168 (phosphite antioxidant) are compounded in a weight ratio of 3:1.

[0031] Example 1

[0032] (1) Mix 80g of melamine and 400g of water evenly to form a melamine suspension; mix 100g of piperazine and 400g of water evenly to form a piperazine solution; add 358g of 85% phosphoric acid solution to a four-necked flask, and slowly add the melamine suspension and piperazine solution dropwise to the phosphoric acid solution simultaneously using a constant pressure funnel. React at 98℃ for 3.5h, cool, filter, wash, and dry to obtain a solid powder; mix the solid powder with 60g of pentaerythritol evenly, place in a muffle furnace, and calcine at 270℃ for 4h to prepare a phosphorus-nitrogen composite flame retardant;

[0033] (2) Mix 100g of sodium hypophosphite and 50g of water evenly to form a sodium hypophosphite solution for later use; mix 108g of aluminum sulfate and 81g of water evenly to form an aluminum sulfate solution; add 420g of barium sulfate to the aluminum sulfate solution and stir evenly; slowly add 135g of 20% ammonia water dropwise using a constant pressure funnel to coat the surface of the barium sulfate with an aluminum sol; then heat to 92℃, add sodium hypophosphite solution, and react at a constant temperature for 3h; filter, wash, and dry to obtain aluminum hypophosphite-coated modified barium sulfate powder. Figure 1 The images show SEM images of the modified barium sulfate in Example 1; the left image shows unmodified barium sulfate, and the right image shows modified barium sulfate.

[0034] (3) First, add 250g of phosphorus-nitrogen flame retardant, 200g of modified barium sulfate, 27g of antioxidant, and 23g of EBS wax to a high-speed mixer. Stir at 150r / min for 5min, then at 600r / min for 15min until the mixture is uniform and then stop the machine. Then add 500g of polypropylene resin and stir at low speed for 15min until the mixture is uniform. Then use an internal mixer to knead the uniformly mixed material into a rubber block at 185℃. Finally, use a twin-screw extruder to extrude, granulate, and dry the material at 170-180℃ to obtain polypropylene halogen-free flame retardant composite material A.

[0035] Example 2

[0036] (1) Mix 90g of melamine and 450g of water evenly to form a melamine suspension; mix 100g of piperazine and 400g of water evenly to form a piperazine solution; add 375g of 85% phosphoric acid solution to a four-necked flask, and simultaneously and slowly add the melamine suspension and piperazine solution to the phosphoric acid solution using a constant pressure funnel. React at 98℃ for 3.5h, cool, filter, wash, and dry to obtain a solid powder; mix the solid powder with 80g of pentaerythritol evenly, place in a muffle furnace, and calcine at 275℃ for 4.5h to prepare a phosphorus-nitrogen composite flame retardant.

[0037] (2) Mix 100g of sodium hypophosphite and 50g of water evenly to form a sodium hypophosphite solution for later use; mix 107g of aluminum sulfate and 80.25g of water evenly to form an aluminum sulfate solution; add 430g of barium sulfate to the aluminum sulfate solution and stir evenly; slowly add 140g of 20% ammonia water dropwise using a constant pressure funnel to coat the surface of the barium sulfate with an aluminum sol; then heat to 95℃, add sodium hypophosphite solution, and react at a constant temperature for 2.5h; filter, wash, and dry to obtain aluminum hypophosphite-coated modified barium sulfate powder.

[0038] (3) First, add 250g of phosphorus-nitrogen flame retardant, 180g of modified barium sulfate, 20g of antioxidant, and 20g of EBS wax to a high-speed mixer. Stir at 150r / min for 5min, then at 600r / min for 15min until the mixture is uniform and stop the machine. Then add 530g of polypropylene resin and stir at low speed for 15min until the mixture is uniform. Then use an internal mixer to knead the uniformly mixed material into a rubber block at 185℃. Finally, use a twin-screw extruder to extrude, granulate, and dry the material at 170-180℃ to obtain polypropylene halogen-free flame retardant composite material B.

[0039] Example 3

[0040] (1) Mix 100g of melamine and 500g of water evenly to form a melamine suspension; mix 100g of piperazine and 400g of water evenly to form a piperazine solution; add 375g of 85% phosphoric acid solution to a four-necked flask, and simultaneously and slowly add the melamine suspension and piperazine solution to the phosphoric acid solution using a constant pressure funnel. React at 99°C for 4h, cool, filter, wash, and dry to obtain a solid powder; mix the solid powder with 70g of pentaerythritol evenly, place in a muffle furnace, and calcine at 278°C for 4h to prepare a phosphorus-nitrogen composite flame retardant.

[0041] (2) Mix 100g of sodium hypophosphite and 50g of water evenly to form a sodium hypophosphite solution for later use; mix 106g of aluminum sulfate and 79.5g of water evenly to form an aluminum sulfate solution; add 430g of barium sulfate to the aluminum sulfate solution and stir evenly; slowly add 140g of 20% ammonia water dropwise using a constant pressure funnel to coat the surface of the barium sulfate with an aluminum sol; then heat to 98℃, add sodium hypophosphite solution, and react at a constant temperature for 3h; filter, wash, and dry to obtain aluminum hypophosphite-coated modified barium sulfate powder.

[0042] (3) First, add 260g of phosphorus-nitrogen flame retardant, 250g of modified barium sulfate, 20g of antioxidant, and 20g of EBS wax to a high-speed mixer. Stir at 150r / min for 5min, then at 600r / min for 15min until the mixture is uniform and stop the machine. Then add 450g of polypropylene resin and stir at low speed for 15min until the mixture is uniform. Then use an internal mixer to knead the uniformly mixed material into a rubber block at 185℃. Finally, use a twin-screw extruder to extrude, granulate, and dry the material at 170-180℃ to obtain polypropylene halogen-free flame retardant composite material C.

[0043] Example 4

[0044] (1) Mix 85g of melamine and 425g of water evenly to form a melamine suspension; mix 100g of piperazine and 400g of water evenly to form a piperazine solution; add 360g of 85% phosphoric acid solution to a four-necked flask, and simultaneously and slowly add the melamine suspension and piperazine solution to the phosphoric acid solution using a constant pressure funnel. React at 100℃ for 3h, cool, filter, wash, and dry to obtain a solid powder; mix the solid powder with 65g of pentaerythritol evenly, place in a muffle furnace, and calcine at 270℃ for 5h to prepare a phosphorus-nitrogen composite flame retardant.

[0045] (2) Mix 100g of sodium hypophosphite and 50g of water evenly to form a sodium hypophosphite solution for later use; mix 109g of aluminum sulfate and 81.75g ​​of water evenly to form an aluminum sulfate solution; add 440g of barium sulfate to the aluminum sulfate solution and stir evenly; slowly add 145g of 20% ammonia water using a constant pressure funnel to coat the surface of the barium sulfate with an aluminum sol; then heat to 100℃, add sodium hypophosphite solution, and react at a constant temperature for 3.5h; filter, wash, and dry to obtain aluminum hypophosphite-coated modified barium sulfate powder.

[0046] (3) First, add 280g of phosphorus-nitrogen flame retardant, 100g of modified barium sulfate, 25g of antioxidant, and 15g of EBS wax to a high-speed mixer. Stir at 150r / min for 5min, then at 600r / min for 15min until the mixture is uniform and stop the machine. Then add 580g of polypropylene resin and stir at low speed for 15min until the mixture is uniform. Then use an internal mixer to knead the uniformly mixed material into a rubber block at 185℃. Finally, use a twin-screw extruder to extrude, granulate, and dry the material at 170-180℃ to obtain polypropylene halogen-free flame retardant composite material D.

[0047] Example 5

[0048] (1) Mix 95g of melamine and 475g of water evenly to form a melamine suspension; mix 100g of piperazine and 400g of water evenly to form a piperazine solution; add 370g of 85% phosphoric acid solution to a four-necked flask, and simultaneously and slowly add the melamine suspension and piperazine solution to the phosphoric acid solution using a constant pressure funnel. React at 98℃ for 4h, cool, filter, wash, and dry to obtain a solid powder; mix the solid powder with 60g of pentaerythritol evenly, place in a muffle furnace, and calcine at 278℃ for 4h to prepare a phosphorus-nitrogen composite flame retardant.

[0049] (2) Mix 100g of sodium hypophosphite and 50g of water evenly to form a sodium hypophosphite solution for later use; mix 108g of aluminum sulfate and 81g of water evenly to form an aluminum sulfate solution; add 410g of barium sulfate to the aluminum sulfate solution and stir evenly; slowly add 130g of 20% ammonia water dropwise using a constant pressure funnel to coat the surface of the barium sulfate with an aluminum sol; then heat to 96℃, add sodium hypophosphite solution, and react at a constant temperature for 4h; filter, wash, and dry to obtain aluminum hypophosphite-coated modified barium sulfate powder.

[0050] (3) First, add 230g of phosphorus-nitrogen flame retardant, 250g of modified barium sulfate, 25g of antioxidant, and 15g of EBS wax to a high-speed mixer. Stir at 150r / min for 5min, then at 600r / min for 15min until the mixture is uniform and then stop the machine. Then add 480g of polypropylene resin and stir at low speed for 15min until the mixture is uniform. Then use a mortar mixer at 185℃ to knead the uniformly mixed material into a rubber block. Finally, use a twin-screw extruder at 170-180℃ to extrude, granulate, and dry to obtain polypropylene halogen-free flame retardant composite material E.

[0051] Application Examples

[0052] The physicochemical properties of the phosphorus-nitrogen flame retardants synthesized in Examples 1-5 are shown in Table 2.

[0053] Table 2: Test Results of Physicochemical Properties of Phosphorus-Nitrogen Flame Retardants

[0054] project Example 1 Example 2 Example 3 Example 4 Example 5 Appearance White powder White powder White powder White powder White powder N content, % 17.7 17.9 19.3 18.1 18.9 P content, % 17.8 17.1 17.3 17.6 17.5 Whiteness, % 92.29 93.12 91.62 92.34 91.27

[0055] As can be seen from Table 2, the phosphorus-nitrogen flame retardants synthesized in Examples 1-5 meet the technical specifications in Table 1.

[0056] Five composite material particles AE in the example were injection molded into standard test strips using an injection molding machine. Half of the standard test strips were placed in a constant temperature and humidity chamber at 85°C and 85% for 7 days. The flame retardant properties of the test strips before and after treatment were then tested, and the results are shown in Table 3.

[0057] Table 3: Test results of flame retardant properties of composite materials before and after treatment

[0058]

[0059] As can be seen from Table 3, this polypropylene halogen-free flame-retardant composite material can still achieve UL-94V0 level after being treated in a high temperature and high humidity environment, indicating that the material of the present invention has good resistance to deliquescence and migration.

Claims

1. A halogen-free flame-retardant polypropylene composite material, characterized in that, It is composed of the following components in parts by weight: 40-60 parts polypropylene resin, 20-28 parts phosphorus and nitrogen flame retardant, 10-25 parts modified barium sulfate, 2-3 parts antioxidant, and 1-3 parts EBS wax. The preparation method of the phosphorus-nitrogen flame retardant includes the following steps: (1) Mix melamine and water evenly to form a melamine suspension; (2) Mix piperazine and water thoroughly to form a piperazine solution; (3) Add phosphoric acid solution to the reaction vessel, and slowly add melamine suspension and piperazine solution dropwise to phosphoric acid solution at the same time. React at 98-100℃ for 3-4 hours, cool, filter, wash and dry to obtain solid powder; (4) Mix the solid powder prepared in step (3) with pentaerythritol evenly, place it in a muffle furnace, and calcine at 265-280℃ for 4-5 hours to obtain a phosphorus-nitrogen composite flame retardant. The modified barium sulfate is prepared as follows: (1) Mix sodium hypophosphite and water evenly to form a sodium hypophosphite solution; (2) Mix aluminum sulfate and water thoroughly to form an aluminum sulfate solution; (3) Add barium sulfate to aluminum sulfate solution and stir evenly; then add ammonia water dropwise to coat the surface of barium sulfate with a layer of aluminum sol, then heat to 90-100℃, then add sodium hypophosphite solution from step (1), react at constant temperature for 2-4 hours, filter, wash and dry to obtain aluminum hypophosphite coated modified barium sulfate powder.

2. The polypropylene halogen-free flame-retardant composite material as described in claim 1, characterized in that, The antioxidant is a compound of primary antioxidant 1010 and secondary antioxidant 168 in a weight ratio of 2.5-3.5:

1.

3. The polypropylene halogen-free flame-retardant composite material as described in claim 1, characterized in that, In the preparation method of the phosphorus-nitrogen flame retardant, the weight ratio of melamine to water in step (1) is 1:4-6.

4. The polypropylene halogen-free flame-retardant composite material as described in claim 1, characterized in that, In the preparation method of the phosphorus-nitrogen flame retardant, the weight ratio of piperazine to water in step (2) is 1:3-5.

5. The polypropylene halogen-free flame-retardant composite material as described in claim 1, characterized in that, In the preparation method of the phosphorus-nitrogen flame retardant, the phosphoric acid solution is an 85% phosphoric acid solution by mass concentration; the weight ratio of piperazine, melamine, phosphoric acid solution and pentaerythritol in the phosphorus-nitrogen flame retardant is 1:0.7-1.1:3.4-3.8:0.5-0.

8.

6. The polypropylene halogen-free flame-retardant composite material as described in claim 1, characterized in that, In the preparation method of the modified barium sulfate, the weight ratio of sodium hypophosphite to water in step (1) is 2:0.8-1.5; and the weight ratio of aluminum sulfate to water in step (2) is 4:2-4.

7. The polypropylene halogen-free flame-retardant composite material as described in claim 1, characterized in that, In the preparation method of the modified barium sulfate, the concentration of ammonia water is 20%, and the weight ratio of barium sulfate, aluminum sulfate, ammonia water, and sodium hypophosphite is 4-4.5:1.05-1.1:1.3-1.5:

1.

8. The method for preparing the halogen-free flame-retardant polypropylene composite material as described in claim 1 or 2, characterized in that, Specifically, the following steps are included: S1: Add phosphorus and nitrogen flame retardant, modified barium sulfate, antioxidant and EBS wax into a high-speed mixer and stir until evenly mixed, then add polypropylene resin and stir until evenly mixed. S2: The uniformly mixed materials are mixed into rubber blocks using an internal mixer at 180-190℃, and then extruded, granulated and dried using a twin-screw extruder at 170-180℃ to obtain halogen-free flame-retardant polypropylene composite material.

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