A magnesium hydroxide surface modifier and its application

Abstract

The present application relates to the technical field of high polymer composite material, in particular to a magnesium hydroxide surface modifier and its application. The modifier is polyethylene wax. The present application also provides the application of the modifier, a preparation method of modified magnesium hydroxide, modified magnesium hydroxide prepared by the method, and a flame-retardant composite material containing the modified magnesium hydroxide. The present application uses polyethylene wax as the surface modifier of magnesium hydroxide, forms a polymer interface layer on the surface of magnesium hydroxide particles through melting coating, the interface layer is homologous with the polyolefin matrix, can form firm physical bonding points through molecular chain entanglement, and effectively transmits and dissipates stress. The present application can significantly improve the mechanical properties and processing properties of the composite material under the premise of maintaining the original crystal structure and flame-retardant function of magnesium hydroxide, realizes the synergistic improvement of strength and toughness, and has the advantages of simple process, environmental friendliness and low cost.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and in particular to a magnesium hydroxide surface modifier and its application. Background Technology

[0002] Ethylene-vinyl acetate copolymer (EVA) and linear low-density polyethylene (LLDPE) are widely used in wires and cables, packaging films, and pipes due to their good flexibility, resistance to environmental stress cracking, and processing properties. However, both EVA and LLDPE are flammable polymers with low limiting oxygen indexes, high heat generation during combustion, and severe dripping, which greatly limits their application in fields such as electronics, construction, and transportation where high flame retardant properties are required.

[0003] To address the flammability issues of the aforementioned polymers, existing technologies typically employ the addition of flame retardants for modification. Magnesium hydroxide (MH), as an environmentally friendly inorganic flame retardant, is widely used for flame retardant modification of polyolefin materials such as EVA and LLDPE due to its advantages including high decomposition temperature, good thermal stability, smoke suppression, non-toxicity, and lack of corrosive gas production. However, as a polar inorganic filler, MH exhibits poor interfacial compatibility with non-polar polyolefin matrices (such as EVA / LLDPE). When directly blended, MH particles are prone to agglomeration, leading to a significant decrease in the mechanical properties of the composite material. To improve the compatibility between MH and the polymer matrix, existing technologies typically employ small molecule modifiers to pretreat MH, specifically including the following two main methods: (1) Silane coupling agent method: γ-methacryloyloxypropyltrimethoxysilane (KH-570) is used, through which the silanol groups generated by its hydrolysis react with the hydroxyl groups on the surface of MH to form chemical bonds, thereby introducing organic functional groups onto the surface of MH. (2) Stearic acid (salt) method: using stearic acid or zinc stearate, through melting or solution method, the carboxyl group of stearic acid reacts with the alkaline sites on the surface of MH to form a hydrophobic organic layer on the surface of MH particles.

[0004] However, the above-mentioned approach has the following inherent drawbacks: First, the interfacial layer formed by the small molecule modifier on the MH surface is thin, and its molecular chain segments are short, making it unable to form effective chain entanglement with the macromolecular chains of the polymer matrix. When the composite material is subjected to external forces, this weak interfacial layer is unable to effectively transfer and dissipate stress, resulting in limited improvement in the toughness of the composite material. Second, the small molecule modifier mainly binds to MH through chemical bonding or physical adsorption. Among these, physical adsorption is relatively weak and easily desorbed during processing or use; even with chemical bonding, due to the inherent characteristics of small molecules, the interaction between them and the polymer matrix is ​​weak, making it difficult to form a strong and tough interfacial bonding layer. This unstable interface is prone to damage under long-term use or in humid and hot environments, leading to a decline in the mechanical properties of the material. In addition, small molecule modifiers that are not firmly bonded to MH or are added in excess are prone to migrate to the material surface during material processing or service, affecting the appearance, surface properties, and subsequent processing of the product. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a magnesium hydroxide surface modifier and its application. By using polyethylene wax as a surface modifier for magnesium hydroxide, a strong and tough polymer interface layer is successfully constructed while maintaining the original crystal structure and flame retardant function of magnesium hydroxide, effectively improving the mechanical properties and processing performance of the composite material.

[0006] To achieve the above objectives, the present invention provides a magnesium hydroxide surface modifier, wherein the modifier is polyethylene wax (PE wax).

[0007] In one optional embodiment, the polyethylene wax has a molecular weight distribution index (PDI) of 2-2.6. Preferably, the polyethylene wax has a molecular weight distribution index (PDI) of 2.3.

[0008] In one optional embodiment, the amount of polyethylene wax used is 0.5-2.0% of the mass of magnesium hydroxide. Preferably, the amount of polyethylene wax used is 1.0-1.5% of the mass of magnesium hydroxide.

[0009] The present invention also provides an application of the aforementioned magnesium hydroxide surface modifier, wherein the modifier is used to perform surface modification treatment on magnesium hydroxide.

[0010] This invention also provides a method for preparing modified magnesium hydroxide, comprising the following steps: Magnesium hydroxide is mixed with polyethylene wax and treated at a temperature higher than the melting point of polyethylene wax, so that the polyethylene wax melts and coats the surface of magnesium hydroxide, thus obtaining modified magnesium hydroxide.

[0011] In one optional embodiment, the amount of polyethylene wax used is 0.5-2.0% of the mass of magnesium hydroxide. Preferably, the amount of polyethylene wax used is 1.0-1.5% of the mass of magnesium hydroxide.

[0012] In one optional embodiment, the processing temperature is 100-130°C.

[0013] In a more specific embodiment, the preparation method includes the following steps: adding magnesium hydroxide to a high-speed mixer, preheating it to the treatment temperature at a heating rate of 8-12℃ / min under a stirring speed of 800-1200 r / min; then reducing the stirring speed to 100-300 r / min and adding polyethylene wax; then increasing the stirring speed to 1800-2200 r / min to ensure the materials are fully mixed and reacted, with a reaction time of 8-12 min; after the reaction is complete, stopping the stirring and heating, and cooling the material; finally, sieving through a 150-250 mesh sieve to obtain modified magnesium hydroxide.

[0014] The present invention also provides a modified magnesium hydroxide, prepared according to the preparation method described above.

[0015] The present invention also provides a flame-retardant composite material comprising a matrix resin and the modified magnesium hydroxide.

[0016] In an optional embodiment, the matrix resin comprises at least one of ethylene-vinyl acetate copolymer (EVA) and linear low-density polyethylene (LLDPE).

[0017] In one optional embodiment, the flame-retardant composite material comprises, by weight: 35-45 parts of ethylene-vinyl acetate copolymer, 35-45 parts of linear low-density polyethylene, and 95-105 parts of modified magnesium hydroxide.

[0018] In an optional embodiment, the flame-retardant composite material further comprises an additive; the additive comprises at least one of an antioxidant and a compatibilizer.

[0019] In one optional embodiment, the antioxidant is selected from antioxidant 1010; the compatibilizer is selected from MC226.

[0020] In an optional embodiment, the preparation method of the flame-retardant composite material includes the following steps: after the temperature of the mixer reaches 150-170℃, modified magnesium hydroxide is added and mixed for 5-10 minutes; then the ethylene-vinyl acetate copolymer, linear low-density polyethylene, and optional additives are added, and mixing continues for 10-15 minutes; next, the mixture is melt-extruded and granulated using a twin-screw extruder; finally, the granules are placed on a flat vulcanizing apparatus for compression molding, pre-pressed for 2-5 minutes, then pressurized to 10-15 MPa and held for 3-5 minutes, and the flame-retardant composite material is obtained after compression molding. The melt extrusion temperature is 150-170℃, and the screw speed is 30-40 r / min.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses polyethylene wax as a surface modifier for magnesium hydroxide, which is melt-coated onto the surface of magnesium hydroxide particles to form a flexible polymer interface layer. This interface layer is homologous to the polyolefin matrix and can form a strong physical bond with the matrix resin through molecular chain entanglement, effectively transmitting and dissipating stress under external force. Compared with the thin-layer interface formed on the surface of magnesium hydroxide by small molecule modifiers, the polymer interface layer formed by polyethylene wax can more effectively buffer and absorb impact energy, thereby significantly improving the elongation at break of the composite material while maintaining high tensile strength, and achieving a synergistic improvement in the strength and toughness of the composite material.

[0022] (2) Polyethylene wax itself has excellent internal lubrication properties, which can reduce the viscosity of the composite melt during melt processing, reduce the frictional resistance between the melt and the surface of the processing equipment, and thus improve the processing fluidity of the material. This characteristic is beneficial to increasing the extrusion speed, reducing energy consumption, and at the same time helping to improve the surface quality of the product and reduce surface defects.

[0023] (3) Polyethylene wax, as a high molecular weight polymer, has excellent compatibility with polyolefin matrices (such as EVA and LLDPE). It can form a strong interfacial bonding layer through the mutual diffusion and entanglement of molecular chains. Its interfacial bonding strength is much higher than that of the interface formed by small molecule modifiers through physical adsorption or limited chemical bonding. This strong interfacial bonding layer effectively avoids the defects of small molecule modifiers that are easy to migrate and desorb, making the mechanical properties of composite materials more durable and stable under long-term use or complex stress environment.

[0024] (4) The modification of magnesium hydroxide by polyethylene wax is mainly physical coating and does not involve chemical reaction with magnesium hydroxide crystals, so it does not change the crystal structure of magnesium hydroxide. This allows the inherent thermal stability and flame retardant efficiency of magnesium hydroxide to be fully preserved, and it can maintain its good flame retardant function while improving the mechanical properties and processing properties of composite materials.

[0025] (5) The present invention adopts a dry modification process, which directly mixes polyethylene wax and magnesium hydroxide at a temperature higher than the melting point of polyethylene wax to achieve surface coating. No organic solvents are required, the process is simple and easy to industrialize, and avoids the problems of using and recycling organic solvents, which is environmentally friendly. At the same time, polyethylene wax is widely available and has a low cost, which has obvious economic advantages compared with small molecule modifiers such as silane coupling agents.

[0026] In summary, this invention, by using polyethylene wax as a surface modifier for magnesium hydroxide, successfully constructs a strong and tough polymer interface layer while maintaining the original crystal structure and flame-retardant function of magnesium hydroxide. This effectively improves the mechanical and processing properties of the composite material, and its overall performance is superior to existing unmodified and small molecule modification technologies, showing promising prospects for industrial applications. Attached Figure Description

[0027] Figure 1 This is a comparison chart of the elongation at break of different flame-retardant composite materials in this invention; Figure 2 This is a comparison diagram of the tensile strength of different flame-retardant composite materials in this invention; Figure 3 This is a comparison chart of the melt flow index of different flame-retardant composite materials in this invention; Figure 4 These are the infrared spectra of different modified magnesium hydroxides in this invention; Figure 5 These are X-ray diffraction patterns of different modified magnesium hydroxides in this invention. Detailed Implementation

[0028] The following embodiments are provided to better understand the present invention and are not limited to the described embodiments. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0029] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0030] In the following embodiments and comparative examples of the present invention, the molecular weight distribution index (PDI) of the polyethylene wax was 2.3; MC226 was provided by Ningbo Nengzhiguang New Material Technology Co., Ltd.

[0031] Example 1 This embodiment provides a method for preparing modified magnesium hydroxide, including the following steps: 100 parts by weight of magnesium hydroxide were added to a high-speed mixer and preheated to 100°C at a stirring speed of 1000 r / min and a heating rate of 10°C / min. Then the stirring speed was reduced to 200 r / min, and 0.5 parts by weight of polyethylene wax were added. The stirring speed was then increased to 2000 r / min to ensure that the materials were fully mixed and reacted for 10 min. After the reaction was completed, stirring and heating were stopped, and the materials were cooled. Finally, the mixture was sieved through a 200-mesh sieve to obtain modified magnesium hydroxide.

[0032] This embodiment also provides a method for preparing a flame-retardant composite material, including the following steps: After the temperature of the mixer reaches 160℃, add 100 parts by weight of modified magnesium hydroxide and mix for 8 minutes; then add 40 parts by weight of EVA, 40 parts by weight of LLDPE, 0.5 parts by weight of antioxidant 1010, and 10 parts by weight of MC226, and continue mixing for 12 minutes; next, melt extrude the mixture through a twin-screw extruder (temperature 160℃, screw speed 35r / min) and granulate; finally, place the granules on a flat vulcanizing machine for pressing and molding, first pre-press for 3 minutes, then pressurize to 12 MPa and hold for 4 minutes, and the flame-retardant composite material is obtained after molding.

[0033] Example 2 This embodiment provides a method for preparing modified magnesium hydroxide, which differs from Example 1 only in that the amount of polyethylene wax added is adjusted to 1 part by mass.

[0034] This embodiment also provides a method for preparing flame-retardant composite materials, which is exactly the same as in Example 1.

[0035] Example 3 This embodiment provides a method for preparing modified magnesium hydroxide, which differs from Example 1 only in that the amount of polyethylene wax added is adjusted to 1.5 parts by mass.

[0036] This embodiment also provides a method for preparing flame-retardant composite materials, which is exactly the same as in Example 1.

[0037] Example 4 This embodiment provides a method for preparing modified magnesium hydroxide, which differs from Example 1 only in that the amount of polyethylene wax added is adjusted to 2 parts by mass.

[0038] This embodiment also provides a method for preparing flame-retardant composite materials, which is exactly the same as in Example 1.

[0039] Comparative Example 1 This comparative example provides a method for preparing a flame-retardant composite material, which differs from Example 1 in that the modified magnesium hydroxide is replaced with unmodified magnesium hydroxide.

[0040] Comparative Example 2 This comparative example provides a method for preparing KH570 modified magnesium hydroxide, which differs from Example 2 in that polyethylene wax is replaced with KH570.

[0041] This comparative example provides a method for preparing a flame-retardant composite material, which differs from Example 1 in that the modified magnesium hydroxide is replaced with the above-mentioned KH570 modified magnesium hydroxide.

[0042] Experimental Example 1 The flame-retardant composite materials in Examples 1-4 were labeled P1, P2, P3, and P4, respectively; the flame-retardant composite material in Comparative Example 1 was labeled KB, and the flame-retardant composite material in Comparative Example 2 was labeled KH. Subsequently, the tensile strength and elongation at break of the above materials were tested according to GB / T 1040.1-2018 standard, and their melt flow index was tested according to GB / T 3682.1-2018 standard. The test results are recorded in Table 1.

[0043] Table 1 Test Results

[0044] In addition, a comparison chart of the elongation at break of different flame-retardant composite materials was drawn, such as... Figure 1 As shown in the figure; a comparison chart of the tensile strength of different flame-retardant composite materials, as follows. Figure 2 As shown in the figure; a comparison chart of melt flow indexes for different flame-retardant composite materials, as follows. Figure 3 As shown.

[0045] Based on the test results in Table 1 and combined with Figure 1-3It can be seen that: (1) The flame-retardant composite materials prepared by modifying magnesium hydroxide with polyethylene wax according to the present invention (Examples 1-4) have significantly higher elongation at break than Comparative Example 1 (unmodified) and Comparative Example 2 (KH570 modified). Among them, the elongation at break of Example 2 (polyethylene wax dosage 1.0 part) reached 168.4%, which was 34.9% higher than Comparative Example 1 and 28.8% higher than Comparative Example 2, indicating that polyethylene wax modification can significantly improve the toughness of the composite material. (2) The flame-retardant composite materials prepared by modifying magnesium hydroxide with polyethylene wax according to the present invention (Examples 1-4) have slightly lower tensile strength than Comparative Example 1 (unmodified), but all are higher than Comparative Example 2 (KH570 modified). This shows that polyethylene wax modification can significantly improve the elongation at break of the material while maintaining high tensile strength, achieving a good balance between strength and toughness. (3) The melt index of the flame-retardant composite materials prepared by modifying magnesium hydroxide with polyethylene wax according to the present invention (Examples 1-4) gradually increases with the increase of polyethylene wax dosage, and is significantly higher than Comparative Example 1 and Comparative Example 2. This indicates that polyethylene wax, as a modifier, has good internal lubrication properties and can effectively improve the processing fluidity of composite materials.

[0046] Experiment Example 2 The modified magnesium hydroxide (or unmodified magnesium hydroxide) prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to infrared spectroscopy and X-ray diffraction analysis, respectively, to obtain infrared spectra of different modified magnesium hydroxides, such as... Figure 4 As shown; X-ray diffraction patterns of magnesium hydroxide with different modifications, as follows. Figure 5 As shown. From Figure 4 As can be seen, compared with Comparative Example 1 (unmodified magnesium hydroxide), new characteristic absorption peaks appeared in the infrared spectra of Examples 1-4 (polyethylene wax-modified magnesium hydroxide) and Comparative Example 2 (KH570-modified magnesium hydroxide), indicating that the modifier had been successfully coated onto the surface of the magnesium hydroxide particles. Specifically, the infrared spectra of Examples 1-4 showed characteristic peaks of polyethylene wax, confirming that polyethylene wax was loaded onto the surface of magnesium hydroxide through physical coating. Figure 5 As can be seen, compared with Comparative Example 1 (unmodified magnesium hydroxide), the characteristic diffraction peak positions and intensities of magnesium hydroxide in Examples 1-4 (polyethylene wax modified magnesium hydroxide) and Comparative Example 2 (KH570 modified magnesium hydroxide) did not change significantly. This indicates that neither chemical modification with KH570 nor physical coating modification with polyethylene wax alters the crystal structure of magnesium hydroxide, and therefore does not affect its thermal stability and flame-retardant function as a flame retardant.

[0047] In summary, this invention uses polyethylene wax as a surface modifier for magnesium hydroxide, which successfully forms a polymer coating layer on the particle surface while maintaining the original crystal structure of magnesium hydroxide. Applying this modified magnesium hydroxide to EVA / LLDPE composites significantly improves the elongation at break and melt flow index while maintaining high tensile strength, resulting in superior overall performance compared to unmodified and KH570-modified comparative samples.

[0048] Finally, it should be noted that the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A magnesium hydroxide surface modifier, characterized in that, The modifier is polyethylene wax.

2. The magnesium hydroxide surface modifier according to claim 1, characterized in that, The amount of polyethylene wax used is 0.5-2.0% of the mass of magnesium hydroxide.

3. The application of a magnesium hydroxide surface modifier as described in claim 1 or 2, characterized in that, The modifier is used to perform surface modification treatment on magnesium hydroxide.

4. A method for preparing modified magnesium hydroxide, characterized in that, Includes the following steps: Magnesium hydroxide is mixed with polyethylene wax and treated at a temperature higher than the melting point of polyethylene wax, so that the polyethylene wax melts and coats the surface of magnesium hydroxide, thus obtaining modified magnesium hydroxide.

5. The preparation method according to claim 4, characterized in that, The amount of polyethylene wax used is 0.5-2.0% of the mass of magnesium hydroxide.

6. The preparation method according to claim 4 or 5, characterized in that, The processing temperature is 100-130℃.

7. A modified magnesium hydroxide, characterized in that, Prepared by the preparation method according to any one of claims 4-6.

8. A flame-retardant composite material, characterized in that, It comprises a matrix resin and the modified magnesium hydroxide as described in claim 7.

9. The flame-retardant composite material according to claim 8, characterized in that, The matrix resin comprises at least one of ethylene-vinyl acetate copolymer and linear low-density polyethylene.

10. The flame-retardant composite material according to claim 9, characterized in that, The flame-retardant composite material comprises, by weight: 35-45 parts of ethylene-vinyl acetate copolymer, 35-45 parts of linear low-density polyethylene, and 95-105 parts of modified magnesium hydroxide.

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