An organic-inorganic hybrid magnesium hydroxide flame retardant and halogen-free flame-retardant ethylene-vinyl acetate copolymer composite

Abstract

The application provides a preparation method and application of an organic-inorganic hybrid magnesium hydroxide flame retardant. The application belongs to the field of flame retardant modification and preparation of flame-retardant composite materials, and particularly relates to a method for preparing a flame-retardant ethylene-vinyl acetate copolymer (EVA) composite material by using the flame retardant and coated red phosphorus, wherein the organic-inorganic hybrid magnesium hydroxide is prepared by surface modification of magnesium hydroxide with boric acid and its derivatives and p-phenylenediamine and its derivatives. The boric acid and its derivatives, the p-phenylenediamine and its derivatives and the magnesium hydroxide are blended and reacted to obtain the organic-inorganic hybrid magnesium hydroxide, and then the organic-inorganic hybrid magnesium hydroxide, the coated red phosphorus, EVA, an antioxidant and a lubricant are mixed into a rubber compound by a banbury mixer, and the rubber compound is extruded and granulated by a double-screw extruder to obtain the flame-retardant EVA composite material. The application improves the compatibility of the magnesium hydroxide and the matrix, and introduces boron and nitrogen elements to form synergy with the magnesium hydroxide, thereby improving the flame-retardant efficiency of the magnesium hydroxide flame retardant.

Description

Technical Field

[0001] This invention relates to the field of flame retardants and flame retardant composite materials, specifically to an organic-inorganic hybrid magnesium hydroxide flame retardant and a halogen-free flame retardant ethylene vinyl acetate copolymer composite material. Background Technology

[0002] Ethylene-vinyl acetate copolymers (EVCs), as important polyolefin materials, possess excellent flexibility, processability, and low density. However, because EVCs are primarily composed of aliphatic segments, they are highly flammable and prone to dripping, leading to frequent fires. Typically, combustion produces corrosive or toxic gases, causing severe environmental and property damage. Therefore, research into flame-retardant EVC composites is crucial. The production and use of flame retardants and materials, and their harmful effects on human health and the environment during fires, are receiving increasing attention. Researching flame retardants and materials that meet both fire safety standards and human health and environmental requirements has become a key development direction in the flame retardant field.

[0003] Magnesium hydroxide, as a green flame retardant, decomposes upon heating to produce magnesium oxide and water vapor, both of which are non-toxic and harmless. The entire production and processing process, as well as the waste, is environmentally friendly. Furthermore, magnesium hydroxide absorbs a significant amount of heat during thermal decomposition, lowering the ambient temperature and thus reducing the thermal decomposition rate of the matrix material. Despite these advantages, some challenges remain in its flame-retardant applications. First, the abundant highly polar hydroxyl groups on the surface of magnesium hydroxide result in poor compatibility with the polymer matrix. Second, magnesium hydroxide exhibits relatively low flame-retardant efficiency, requiring large addition amounts to achieve the desired flame-retardant effect, which significantly reduces the mechanical properties of the composite material. This limits the development of magnesium hydroxide applications, making its modification crucial. Developing efficient flame-retardant technology for magnesium hydroxide remains a pressing issue. Current research indicates that combining various methods for modifying magnesium hydroxide and seeking more efficient surface modifiers are becoming the future directions for magnesium hydroxide flame retardant modification. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the existing technology, the present invention aims to provide a method for surface modification of magnesium hydroxide to improve its compatibility with the polymer matrix; the second objective is to provide a method for preparing flame-retardant EVA composite materials using magnesium hydroxide.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an organic-inorganic hybrid magnesium hydroxide flame retardant, characterized in that it is prepared by the following method: Step 1.1 At room temperature, boric acid and its derivatives, magnesium hydroxide and anhydrous ethanol are stirred evenly to form a suspension. The temperature is raised to 50-70°C and stirred for 3-7 h. The intermediate product is named MB. Step 1.2: Add p-phenylenediamine and its derivatives to the suspension obtained in Step 1.1 and stir at 50-70°C for 5-9 hours. Step 1.3 The product obtained in Step 1.2 was washed several times with ethanol and water and dried at 80°C to obtain surface-modified magnesium hydroxide, and the final product was named MBP; Further, the boric acid and its derivatives mentioned in step 1.1 are at least one of boric acid, borate ester coupling agent, and borate solution; the mass ratio of boric acid and its derivatives to magnesium hydroxide is (1.5~4):1.

[0006] Further, the p-phenylenediamine and its derivatives mentioned in step 1.2 are at least one of p-phenylenediamine, 4-aminodiphenylamine, 2-nitro-p-phenylenediamine, etc.; the mass ratio of p-phenylenediamine and its derivatives to magnesium hydroxide is (3~7):1.

[0007] A halogen-free flame-retardant ethylene vinyl acetate copolymer composite material, characterized in that, by weight, it comprises: 30-70 parts of ethylene vinyl acetate copolymer resin, 30-70 parts of organic-inorganic magnesium hydroxide flame retardant, 1-7 parts of coated red phosphorus, 0.5-3 parts of antioxidant, and 0.5-3 parts of lubricant; Further, the organic-inorganic hybrid magnesium hydroxide flame retardant is any of the organic-inorganic hybrid magnesium hydroxide flame retardants described in steps 1.1-1.3 above.

[0008] The halogen-free flame-retardant ethylene vinyl acetate copolymer composite material described above is characterized in that the antioxidant is at least one of antioxidant 168 and antioxidant 1010.

[0009] Furthermore, the lubricant is at least one of zinc stearate, calcium stearate, and magnesium stearate.

[0010] Furthermore, the preparation method of the halogen-free flame-retardant ethylene vinyl acetate copolymer composite material; Step 2.1 Mix organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, antioxidant, lubricant and ethylene vinyl acetate copolymer resin evenly to obtain a premix; Step 2.2: Add the premixed material to a mixer for melt blending to obtain a rubber compound. Extrude the obtained rubber compound in an extruder to granulate and press it into sheets to obtain the halogen-free flame-retardant ethylene vinyl acetate copolymer composite material. Furthermore, the internal mixer processing temperature in step 2.2 is 100~140°C, the extruder is a twin-screw extruder, and the heating temperature of the twin-screw extruder during extrusion granulation is controlled as follows: Zone 1 is 90~110 ℃, Zone 2 is 110~130 ℃, and Zone 3 is 130~150 ℃; the screw speed of the twin-screw extruder is 30~150 rpm; Further, the tableting conditions described in step 2.2 are 130~150°C, 3~25 MPa, and holding pressure for 3~15 min.

[0011] The beneficial effects of this invention are as follows: This invention provides an organic-inorganic hybrid magnesium hydroxide flame retardant copolymer with ethylene vinyl acetate. By modifying the surface of magnesium hydroxide with boric acid and its derivatives and p-phenylenediamine and its derivatives, boron and nitrogen elements are introduced, forming a synergistic effect of boron, nitrogen and magnesium hydroxide, which improves the flame retardant efficiency of the magnesium hydroxide flame retardant.

[0012] Magnesium hydroxide flame retardants modified with boric acid and its derivatives and p-phenylenediamine and its derivatives have better compatibility with ethylene vinyl acetate copolymer matrix. Compared with traditional magnesium hydroxide flame retardants, they can achieve the same flame retardant effect with less addition and have less adverse effect on the processing performance and mechanical properties of polymer substrates. Attached Figure Description

[0013] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0014] Figure 1 The infrared spectrum of the organic-inorganic hybrid modified magnesium hydroxide flame retardant of this invention is shown.

[0015] Figure 2 Images of the vertical combustion test of the sample in Example 2 and the sample in Comparative Example 2 of this invention.

[0016] Figure 3 The heat release rate and total heat release amount of the sample in Example 2 and the sample in Comparative Example 1 of this invention are shown.

[0017] Figure 4 The TG / DTG curves are for the sample in Example 2 and Comparative Example 2 of this invention. Detailed Implementation

[0018] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0019] Example 1 This embodiment provides a method for preparing a halogen-free flame-retardant ethylene vinyl acetate copolymer composite material: Ethylene vinyl acetate copolymer resin, organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, and antioxidant were mixed evenly in a certain proportion and then blended in an internal mixer at 140°C to obtain a uniformly mixed matrix and modified flame retardant. The mixture was then extruded and granulated using a twin-screw extruder, and finally pressed into sheets to obtain a halogen-free flame-retardant ethylene vinyl acetate copolymer composite material. Specifically, the ethylene vinyl acetate copolymer resin and organic-inorganic hybrid magnesium hydroxide were dried separately in an oven at 80°C for 20-24 hours to fully remove moisture before use. By weight fraction, the raw material composition was: 55 parts ethylene vinyl acetate resin, 40 parts organic-inorganic hybrid magnesium hydroxide, 3 parts coated red phosphorus, 1 part antioxidant 168, and 1 part zinc stearate. Organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, antioxidant, lubricant, and ethylene vinyl acetate copolymer resin were mixed evenly to obtain a premix. The premix was added to a mixer for melt blending to obtain a rubber compound. The obtained rubber compound was added to a twin-screw extruder for extrusion granulation. The temperatures of each zone of the twin-screw extruder were: zone 1 100 ℃, zone 2 120 ℃, and zone 3 140 ℃, and the screw speed was 50~100 rpm. The obtained granules were pressed into tablets for 10~15 min in a tablet press at a temperature of 120 ℃ and a pressure of 9~13 MPa to obtain a halogen-free flame-retardant ethylene vinyl acetate composite material. Example 2 This embodiment provides a method for preparing a halogen-free flame-retardant ethylene vinyl acetate copolymer composite material: Ethylene vinyl acetate copolymer resin, organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, and antioxidant were mixed evenly in a certain proportion and then blended in a Banbury mixer at 140°C to obtain a uniformly mixed matrix and modified flame retardant. The mixture was then extruded and granulated using a twin-screw extruder, and finally compressed into sheets to obtain a halogen-free flame-retardant ethylene vinyl acetate copolymer composite material. Specifically, the ethylene vinyl acetate copolymer resin and organic-inorganic hybrid magnesium hydroxide were dried separately in an oven at 80°C for 20-24 hours to fully remove moisture before use. By weight fraction, the raw material composition was: 50 parts ethylene vinyl acetate resin, 45 parts organic-inorganic hybrid magnesium hydroxide, 3 parts coated red phosphorus, 1 part antioxidant 168, and 1 part zinc stearate. Organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, antioxidant, lubricant, and ethylene vinyl acetate copolymer resin were mixed evenly to obtain a premix. The premix was added to a mixer for melt blending to obtain a rubber compound. The obtained rubber compound was added to a twin-screw extruder for extrusion granulation. The temperatures of each zone of the twin-screw extruder were: zone 1 100 ℃, zone 2 120 ℃, and zone 3 140 ℃, and the screw speed was 50~100 rpm. The obtained granules were pressed into tablets for 10~15 min in a tablet press at a temperature of 120 ℃ and a pressure of 9~13 MPa to obtain a halogen-free flame-retardant ethylene vinyl acetate composite material. Example 3 This embodiment provides a method for preparing a halogen-free flame-retardant polyamide 6 composite material: Ethylene vinyl acetate copolymer resin, organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, and antioxidant were mixed evenly in a certain proportion and then blended in an internal mixer at 140°C to obtain a rubber compound in which the matrix and modified flame retardant were evenly mixed. The compound was then extruded and granulated using a twin-screw extruder, and then pressed into sheets to obtain a halogen-free flame-retardant ethylene vinyl acetate copolymer composite material. Specifically, the ethylene vinyl acetate copolymer resin and organic-inorganic hybrid magnesium hydroxide were dried separately in an oven at 80°C for 20-24 hours to completely remove moisture before use. By weight fraction, the raw material composition was: 45 parts ethylene vinyl acetate resin, 55 parts organic-inorganic hybrid magnesium hydroxide, 3 parts coated red phosphorus, 1 part antioxidant 168, and 1 part zinc stearate. The organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, antioxidant, lubricant, and ethylene vinyl acetate copolymer resin were mixed evenly to obtain a premix; the premix was then added to an internal mixer for melt blending to obtain the rubber compound. The obtained rubber compound was added to a twin-screw extruder for granulation. The temperatures of each zone of the twin-screw extruder were: 100 ℃ in zone 1, 120 ℃ in zone 2, and 140 ℃ in zone 3, with a screw speed of 50~100 rpm. The obtained granules were then pressed into tablets for 10~15 min in a tablet press at a temperature of 120 ℃ and a pressure of 9~13 MPa to obtain halogen-free flame-retardant ethylene vinyl acetate composite material. Comparative Example 1 This comparative example provides a method for preparing pure ethylene vinyl acetate copolymer: Comparative Example 1 The ethylene vinyl acetate copolymer resin was dried at 80 °C for 20–24 h to completely remove moisture before use. Specifically, the ethylene vinyl acetate copolymer resin was dried in an oven at 80 °C for 20–24 h to completely remove moisture, obtaining the dried components. Subsequently, the ethylene vinyl acetate copolymer resin was added to a mixer for melt blending to obtain a rubber compound. The obtained rubber compound was added to a twin-screw extruder for granulation. The temperatures of each zone of the twin-screw extruder were: zone 1 100 °C, zone 2 120 °C, and zone 3 140 °C, with a screw speed of 50–100 rpm. The obtained granules were then pressed into tablets for 10–15 min at a temperature of 120 °C and a pressure of 9–13 MPa to obtain halogen-free flame-retardant ethylene vinyl acetate composite material.

[0020] Comparative Example 2 This comparative example provides a method for preparing an ethylene vinyl acetate copolymer composite material: Ethylene vinyl acetate copolymer resin, magnesium hydroxide, coated red phosphorus, antioxidant 168, and magnesium stearate were mixed evenly in a certain proportion and then added to a mixer at 140°C for blending to obtain a rubber compound in which the matrix and modified flame retardant were evenly mixed. The compound was then extruded and granulated using a twin-screw extruder, and then pressed into sheets to obtain a halogen-free flame-retardant ethylene vinyl acetate copolymer composite material. Specifically, the ethylene vinyl acetate copolymer resin, magnesium hydroxide, and coated red phosphorus were dried in an oven at 80°C for 20-24 hours to remove moisture completely before use. By weight fraction, the raw material composition was: 50 parts ethylene vinyl acetate copolymer resin, 45 parts magnesium hydroxide, 3 parts coated red phosphorus, 1 part antioxidant 168, and 1 part magnesium stearate. An organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, antioxidant, lubricant, and ethylene vinyl acetate copolymer resin were mixed evenly to obtain a premix; the premix was then added to a mixer for melt blending to obtain the rubber compound. The obtained rubber compound was added to a twin-screw extruder for granulation. The temperatures of each zone of the twin-screw extruder were: 100 ℃ in zone 1, 120 ℃ in zone 2, and 140 ℃ in zone 3, with a screw speed of 50~100 rpm. The obtained granules were then pressed into tablets for 10~15 min in a tablet press at a temperature of 120 ℃ and a pressure of 9~13 MPa to obtain halogen-free flame-retardant ethylene vinyl acetate composite material. The combustion performance and mechanical properties of the ethylene vinyl acetate copolymer composite were tested according to the following standards, and the results are shown in Tables 1 and 2.

[0021] Combustion performance: LOI standard test according to GB / T 2406-2015, UL-94 standard test according to GB / T 2408-2008; cone calorimetry test according to ISO 5660.

[0022] Mechanical properties: Tested according to GB / T 1040.1-2018 standard, at a test speed of 50 mm / min; Figure 1 The image shows the FTRI spectrum of magnesium hydroxide after modification with boric acid and p-phenylenediamine. Figure 1 As shown, after surface modification, there are obvious vibrational peaks of benzene ring and Mg-OB, indicating that magnesium hydroxide has been successfully modified.

[0023] Figure 2 This is a comparison diagram of the effects of vertical combustion in Example 2 and Comparative Example 2. Figure 2 As can be seen, the Comparative Example 2 sample exhibits a V-2 flammability rating: it continues to burn (<30 s) after the flame is removed, accompanied by significant dripping. The dripping can ignite the absorbent cotton below, indicating that the material has a high fire risk. In contrast, the Example 2 sample exhibits a V-0 rating: it self-extinguishes rapidly (<10 s) after the flame is removed, no dripping is observed during combustion, and the absorbent cotton is not ignited. This phenomenon confirms that organic-inorganic hybrid magnesium hydroxide can effectively promote the formation of a stable char layer in the ethylene vinyl acetate copolymer matrix, achieving a gas-phase-condensed phase synergistic flame retardant mechanism by isolating heat and oxygen transfer, thereby significantly inhibiting dripping and blocking the combustion chain reaction.

[0024] Figure 3 The data provided are cone calorimetry test data for Example 2 and Comparative Example 1, including heat release rate (HRR) and total heat release (THR). Example 2 comprises a composite material consisting of 50 parts ethylene vinyl acetate copolymer, 45 parts organic-inorganic hybrid magnesium hydroxide, three parts coated red phosphorus, 1 part antioxidant 168, and 2 parts magnesium stearate. Figure 3 As can be seen, compared with Comparative Example 1, Example 2 exhibits better flame retardant behavior, with its HRR and THR values ​​reduced by 57% and 40%, respectively. The heat release rate and total heat release of the material are significantly reduced, improving the flame retardant performance of the material.

[0025] Figure 4 The TG / DTG curves for the sample of Example 2 and Comparative Example 2 are shown. Referring to the data in Table 2, the TTG of the sample of Example 2 is... 5% With T max Both were significantly higher than the comparative example, indicating that it has better thermal stability; at the same time, its experimental char residue was 35.6%, which was higher than that of comparative example 2, indicating that organic-inorganic hybrid magnesium hydroxide can effectively promote the char formation of ethylene vinyl acetate copolymer and increase the char residue.

[0026] The flame retardant and mechanical properties of the ethylene vinyl acetate copolymer composites in Examples 1 to 3 and Comparative Examples 1 and 2 were tested using the appropriate standards. The results are shown in Table 1. Table 1. Test results of flame retardant and mechanical properties of ethylene vinyl acetate copolymer composites in Examples 1 to 3 and Comparative Examples 1 to 2. Table 2. Thermal stability test results of ethylene vinyl acetate composite materials in Comparative Example 2 and Example 2. in conclusion: 1. The test results of Examples 1-3 show that as the amount of organic-inorganic hybrid magnesium hydroxide added gradually increases from 45 parts to 55 parts, the LOI increases from 35.9% to 40.2%, the material maintains the UL-94 V-0 flame retardant rating, and the mechanical properties gradually decrease with the amount of flame retardant added. The tensile strength gradually decreases from 8.4 MPa to 6.5 MPa, and the elongation at break decreases from 632.6% to 500.1%. Overall, Example 2 shows the most balanced and outstanding performance when the amount added is 45 parts.

[0027] 2. The test results of Example 2 and Comparative Example 1 show that the flame retardant rating of Example 2 was improved from NR to V-0, and the LOI increased to 38.7%; at the same time, the peak heat release rate decreased by 57%, and the total heat release decreased by 40%. This indicates that the solution can effectively improve the flame retardant performance of the material.

[0028] 3. As can be seen from Example 2, Comparative Example 2 and comparative analysis, under the same amount of flame retardant added, the surface-modified magnesium hydroxide has higher elongation at break and tensile strength than the unmodified magnesium hydroxide sample; indicating that the organic-inorganic hybrid magnesium hydroxide has better compatibility with the matrix than the unmodified magnesium hydroxide.

[0029] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing an organic-inorganic hybrid magnesium hydroxide flame retardant, characterized in that, It is prepared by the following method: Step 1.1 At room temperature, boric acid and its derivatives, magnesium hydroxide and anhydrous ethanol are stirred evenly to form a suspension. The temperature is raised to 50-70°C and stirred for 3-7 h. The intermediate product is named MB. Step 1.2: Add p-phenylenediamine and its derivatives to the suspension obtained in Step 1.1 and stir at 50-70°C for 5-9 h. Step 1.3 The product obtained in Step 1.2 was washed several times with ethanol and water and dried at 80°C to obtain surface-modified magnesium hydroxide, and the final product was named MBP.

2. The organic-inorganic hybrid magnesium hydroxide according to claim 1, characterized in that, The boric acid and its derivatives mentioned in step 1.1 are at least one of boric acid, borate ester coupling agent, and borate solution; the mass ratio of boric acid and its derivatives to magnesium hydroxide is (1.5~4):

1.

3. The organic-inorganic hybrid magnesium hydroxide according to claim 1, characterized in that, The p-phenylenediamine and its derivatives mentioned in step 1.2 are at least one of p-phenylenediamine, 4-aminodiphenylamine, 2-nitro-p-phenylenediamine, etc.; the mass ratio of p-phenylenediamine and its derivatives to magnesium hydroxide is (3~7):

1.

4. A halogen-free flame-retardant ethylene vinyl acetate copolymer composite material, characterized in that, The product, by weight, comprises: 30-70 parts of ethylene vinyl acetate copolymer resin, 30-70 parts of organic-inorganic magnesium hydroxide flame retardant, 1-7 parts of coated red phosphorus, 0.5-3 parts of antioxidant, and 0.5-3 parts of lubricant.

5. The halogen-free flame-retardant ethylene vinyl acetate copolymer composite material according to claim 4, characterized in that, The organic-inorganic hybrid magnesium hydroxide flame retardant is any one of the organic-inorganic hybrid magnesium hydroxide flame retardants described in claims 1-4.

6. The halogen-free flame-retardant ethylene vinyl acetate copolymer composite material according to claim 4, characterized in that, The antioxidant is at least one of antioxidant 168 and antioxidant 1010.

7. The halogen-free flame-retardant ethylene vinyl acetate copolymer composite material according to claim 4, characterized in that, The lubricant is at least one of zinc stearate, calcium stearate, magnesium stearate, etc.

8. The halogen-free flame-retardant ethylene vinyl acetate copolymer composite material according to claim 4, characterized in that, Preparation method of the halogen-free flame-retardant ethylene vinyl acetate copolymer composite material: Step 2.1 Mix organic-inorganic hybrid magnesium hydroxide, coated red phosphorus, antioxidant, lubricant and ethylene vinyl acetate copolymer resin evenly to obtain a premix; Step 2.2 Add the premixed material to the internal mixer for melt blending to obtain a rubber compound. Extrude the obtained rubber compound into granules and then into sheets in an extruder to obtain the halogen-free flame-retardant ethylene vinyl acetate copolymer composite material.

9. The halogen-free flame-retardant ethylene vinyl acetate copolymer composite material according to claim 8, characterized in that, The internal mixer processing temperature in step 2.2 is 100~140°C, and the extruder is a twin-screw extruder. The heating temperature of the twin-screw extruder during extrusion granulation is controlled as follows: Zone 1 is 90~110 ℃, Zone 2 is 110~130 ℃, and Zone 3 is 130~150 ℃; the screw speed of the twin-screw extruder is 30~150 rpm.

10. The halogen-free flame-retardant ethylene vinyl acetate copolymer composite material according to claim 8, characterized in that, The tableting conditions described in step 2.2 are 130~150°C, 3~25 MPa, and holding pressure for 3~15 min.

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