Modified EVA resin and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to modified EVA resin and a preparation method thereof. The iron trioxide-loaded porous magnesium hydroxide material is prepared by adopting a hydrothermal method and an impregnation-calcination technology. After the material is subjected to silanization treatment, 12-amino-1-dodecene is further added to modify silanized porous magnesium hydroxide. EVA is grafted into maleimide through a melt grafting technology, and amino and keto-carbonyl are subjected to a Schiff base reaction to form imine bonds, so that modified EVA is obtained. The flame retardant property of EVA is remarkably improved by porous magnesium hydroxide modified by ferric oxide, and meanwhile, the hydrophobicity of the modified EVA resin is enhanced by an introduced long carbon chain. Due to the existence of a long carbon chain and a dynamic bond, the compatibility between magnesium hydroxide and EVA molecules is further enhanced. In the EVA resin cooling forming process, the mechanical property and the flame retardant effect of an EVA resin product are effectively improved through the bonding state formed by imine bonds.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a modified EVA resin and a preparation method thereof. Background Art

[0002] EVA (ethylene-vinyl acetate copolymer) is copolymerized from ethylene and vinyl acetate, and has excellent flexibility, corrosion resistance, processing performance and green environmental protection characteristics, and is widely used in multiple fields such as films, hot melt adhesives, adhesives, wires and cables. However, pure EVA resin has disadvantages of poor flame retardancy and fire resistance in the application of flame-retardant anticorrosive coatings, which limits the application of EVA. Therefore, it is necessary to modify EVA resin.

[0003] Physical filling modification of EVA resin by adding magnesium hydroxide is a relatively common method. This is because magnesium hydroxide decomposes into magnesium oxide and water when heated, and this endothermic reaction helps to cool down and slow down the decomposition of combustibles. The water vapor and magnesium oxide generated by decomposition can dilute combustible gases and form a protective layer, promote carbon formation on the material surface, and inhibit material combustion. In addition, the adsorption effect of magnesium oxide and the dilution effect of water vapor can reduce smoke. Therefore, magnesium hydroxide can improve the flame retardancy of EVA resin. However, there are still problems such as low flame retardancy efficiency, large addition amount, and poor compatibility with EVA resin in the modification of EVA resin by magnesium hydroxide. Summary of the Invention

[0004] The purpose of the present invention is to provide a modified EVA resin and a preparation method thereof to solve the above technical problems.

[0005] To achieve the above technical purpose, the technical solution of the present invention: A preparation method of a modified EVA resin, comprising the following steps: S1. Using magnesium nitrate and urea as raw materials, porous magnesium hydroxide is prepared by a hydrothermal method; S2. Using an impregnation-calcination method, iron oxide is loaded on the porous magnesium hydroxide to obtain porous magnesium hydroxide loaded with iron oxide; S3. The porous magnesium hydroxide loaded with iron oxide is subjected to silanization treatment with triethoxysilane to obtain silanized porous magnesium hydroxide loaded with iron oxide; S4. The silanized porous magnesium hydroxide loaded with iron oxide is dispersed in ethanol, 12-amino-1-dodecene is added thereto, and stirred at 100 °C for 3 h. After the reaction is completed, centrifugation, washing and drying are carried out to obtain amino-silanized Mg(OH)2@Fe2O3; S5. Mix EVA, maleimide, dicumyl peroxide and antioxidant at room temperature for 15 min, then conduct internal mixing at 170 °C - 180 °C under a nitrogen atmosphere for 8 min. After the reaction is completed, cool and crush into particles, extract with a Soxhlet extractor for 24 h after washing with acetone, and finally dry to obtain EVA-g-MI; S6. Blend amino-silanized Mg(OH)₂@Fe₂O₃ with EVA-g-MI at 160 °C for 5 min, then hold at 120 °C and 5 MPa for 30 min, and quickly cool to below 60 °C to obtain the modified EVA resin.

[0006] As a further improvement, in step S3, the preparation of the silanized porous magnesium hydroxide loaded with iron oxide is specifically as follows: dry the porous magnesium hydroxide loaded with iron oxide for 12 h, then disperse it in toluene, perform ultrasonic treatment for 30 min, then add triethoxysilane, and heat to 110 °C under a nitrogen atmosphere for reaction for 12 h. After the reaction is completed, obtain the silanized porous magnesium hydroxide loaded with iron oxide through centrifugation, washing and drying.

[0007] As a further improvement, in step S4, the mass ratio of the silanized porous magnesium hydroxide loaded with iron oxide to 12-amino-1-dodecene is 1.05:1.

[0008] As a further improvement, in step S5, the mass ratio of EVA, maleimide, dicumyl peroxide and antioxidant is 100:10:1:0.1, and the antioxidant is: pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0009] As a further improvement, in step S5, the content of vinyl acetate in EVA is 28 wt%.

[0010] As a further improvement, in step S6, the mass ratio of the amino-silanized Mg(OH)₂@Fe₂O₃ to EVA-g-MI is 1:4.

[0011] As a further improvement, in step S3, the mass ratio of triethoxysilane to the porous magnesium hydroxide loaded with iron oxide is 1:5.

[0012] The present invention also provides a modified EVA resin.

[0013] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: The present invention provides a modified EVA resin and a preparation method thereof. The porous magnesium hydroxide constructed by the hydrothermal method has a high specific surface area and a hierarchical pore structure, providing rich anchor sites for the uniform loading of iron oxide nanoparticles, which can significantly improve the dispersion of active components and avoid nanoparticle aggregation.

[0014] In the present invention, magnesium hydroxide is first prepared into porous magnesium hydroxide, and then iron(III) oxide is loaded in the pores of the porous magnesium hydroxide, which can improve the flame retardancy efficiency and reduce the filling amount of magnesium hydroxide. After the porous magnesium hydroxide is subjected to silanization treatment, 12-amino-1-dodecene is added. The non-polar long carbon chain reduces the surface free energy by reducing the exposure of polar groups. The long carbon chain tends to migrate to the material surface during processing to form a hydrophobic barrier, and enhances the hydrophobicity through orderly arrangement. These long carbon chains can also form a hydrophobic network to block the penetration of water molecules and fill micro-defects. In some cases, the long carbon chain can induce the formation of a micron / nano-scale rough structure to enhance the hydrophobicity. In addition, the hydrophobic modified filler can improve the compatibility with the hydrophobic polymer matrix and reduce the interfacial defects, thereby alleviating the aging problem of the modified EVA resin material to a certain extent. The porous magnesium hydroxide loaded with iron(III) oxide is subjected to amino-silanization and then blended with EVA. The obtained modified EVA remains stable in the pH range of 3-11, and the performance decay after 1000 h of damp heat aging is better than that of traditional fillers.

[0015] 3. In the present invention, a dynamic bond is inserted between magnesium hydroxide and EVA. The imine bond of the Schiff base, as a reversible covalent bond, constructs a dynamic crosslinking network between the surface of the inorganic material and the polymer chain. The magnesium hydroxide modified with amino groups and the EVA resin molecules containing aldehyde groups form Schiff base bonds through a condensation reaction, thus forming a chemical bridge at the interface. In terms of processing optimization, the dynamic bond breaks during high-temperature processing, which can reduce the system viscosity and promote the uniform dispersion of the inorganic filler; after cooling, the recombination of the imine bond helps to fix the dispersion structure. The polarity of the imine bond is between that of the inorganic material and the polymer material, which helps to reduce the interfacial energy. In terms of topological entanglement, the crosslinking network formed by the dynamic bond increases the entanglement density of the polymer chain on the surface of the inorganic material, thereby enhancing the interfacial shear strength. It improves the compatibility between magnesium hydroxide and EVA resin and solves the problem of poor compatibility between magnesium hydroxide and EVA resin. After the EVA resin cools and forms, the bonding state formed by the imine reversible covalent bond can also improve the mechanical properties of the EVA resin product. Detailed implementation mode

[0016] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0017] Example 1: A preparation method of a modified EVA resin, comprising the following steps: S1. Dissolve 5 g of magnesium nitrate and 3 g of urea in 200 mL of deionized water, magnetically stir at 500 rpm for 20 minutes until completely dissolved, transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, seal it and place it in an oven, and react at 150 °C for 12 h. After the reaction, cool to room temperature, centrifuge at 8000 rpm for 10 minutes, and collect the precipitate. Then wash it three times alternately with deionized water and ethanol to remove impurities. Finally, vacuum dry at 60 °C for 12 h to obtain porous magnesium hydroxide.

[0018] S2. Dissolve 1.2 g of iron nitrate in 20 mL of deionized water and ultrasonically disperse it for 10 min. Slowly add 1 g of dry porous magnesium hydroxide to the solution, magnetically stir at 200 rpm for 2 h, and let it stand for aging for 4 h. Vacuum dry at 60 °C for 6 h, and then heat it to 400 °C at a rate of 2 °C / min in a muffle furnace and calcine for 3 h, so that iron oxide can be uniformly loaded on the surface of the porous magnesium hydroxide, that is, porous magnesium hydroxide loaded with iron oxide, named Mg(OH)2@Fe2O3.

[0019] S3. Vacuum dry the porous magnesium hydroxide loaded with iron oxide at 120 °C for 12 h to remove adsorbed water and activate the surface hydroxyl groups. Disperse 1 g of magnesium hydroxide loaded with iron oxide in 50 mL of toluene, ultrasonically treat it for 30 min, then add 0.2 g of triethoxysilane, heat it to 110 °C and reflux for 12 h under a nitrogen atmosphere, centrifuge at 8000 rpm for 10 min, and wash it three times with toluene and ethanol in turn. Finally, vacuum dry at 60 °C for 6 h to obtain the silanized porous magnesium hydroxide loaded with iron oxide, that is, silanized Mg(OH)2@Fe2O3.

[0020] S4. Disperse 1.05 g of silylated Mg(OH)₂@Fe₂O₃ in 30 mL of ethanol, then add 1 g of 12-amino-1-dodecene thereto, stir at 100 °C and 500 rpm for 3 h. After the reaction is complete, centrifuge at 8000 rpm for 10 min, wash with ethanol three times, and finally dry in vacuum at 60 °C for 6 h to obtain amino-silylated Mg(OH)₂@Fe₂O₃.

[0021] S5. First, place maleimide powder and EVA (vinyl acetate content is 28%) particles in vacuum drying at 60 °C for 6 h to remove moisture. Weigh each component according to the mass ratio of EVA:maleimide (MI):dicumyl peroxide (DCP) = 100:10:1. Then add EVA, maleimide, dicumyl peroxide, and 0.1 g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010) to a high-speed mixer and mix at room temperature for 15 min until homogeneous. Preheat the internal mixer to 175 °C, with a rotor speed of 50 rpm. Under a nitrogen atmosphere, add the mixture to the internal mixer and knead for 8 min to ensure that DCP is fully decomposed to initiate a free radical reaction. After waiting for the reaction to complete, discharge the material. Cool the reaction product and crush it into particles. After washing with acetone, extract with a Soxhlet extractor for 24 h to remove unreacted maleimide and homopolymers. Finally, dry in vacuum at 60 °C for 12 h until constant weight to obtain EVA-g-MI.

[0022] S6. Blend 20 g of amino-silylated Mg(OH)₂@Fe₂O₃ with 80 g of EVA-g-MI in an internal mixer at 160 °C for 5 min, then keep the blend in a hot press at 120 °C and 5 MPa for 30 min to promote the complete formation of reversible covalent bonds, and make the amino group react with the ketone carbonyl group of the dienophile to form reversible covalent bonds through a Schiff base reaction. Quickly cool to below 60 °C, and the reversible covalent bonds are reorganized to form a dynamic crosslinked network to obtain a modified EVA resin.

[0023] Example 2: A method for preparing a modified EVA resin, comprising the following steps: S1. Dissolve 5 g of magnesium nitrate and 3 g of urea in 200 mL of deionized water, stir magnetically at 500 rpm for 20 minutes until completely dissolved, transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, seal it and place it in an oven, and react at 150 °C for 12 h. After the reaction is completed, cool to room temperature, centrifuge at 8000 rpm for 10 minutes, and collect the precipitate. Then wash it alternately with deionized water and ethanol three times to remove impurities. Finally, dry in vacuum at 60 °C for 12 h to obtain porous magnesium hydroxide.

[0024] S2. Dissolve 1.2 g of iron nitrate in 20 mL of deionized water and ultrasonically disperse for 10 min. Slowly add 1 g of dry porous magnesium hydroxide to the solution, magnetically stir at 200 rpm for 2 h, and let it stand for aging for 4 h. Vacuum dry at 60 °C for 6 h, and then heat to 400 °C at a rate of 2 °C / min in a muffle furnace and calcine for 3 h, so that iron oxide can be uniformly loaded on the surface of porous magnesium hydroxide, namely porous magnesium hydroxide loaded with iron oxide, named Mg(OH)2@Fe2O3.

[0025] S3. Vacuum dry the porous magnesium hydroxide loaded with iron oxide at 120 °C for 12 h to remove adsorbed water and activate surface hydroxyl groups. Disperse 1 g of magnesium hydroxide loaded with iron oxide in 50 mL of toluene, ultrasonically treat for 30 min, then add 0.2 g of triethoxysilane, heat to 140 °C and reflux for 12 h under a nitrogen atmosphere, centrifuge at 8000 rpm for 10 min, and then wash with toluene and ethanol three times in sequence. Finally, vacuum dry at 60 °C for 6 h to obtain the silanized porous magnesium hydroxide loaded with iron oxide, namely silanized Mg(OH)2@Fe2O3.

[0026] S4. Disperse 1.05 g of silanized Mg(OH)2@Fe2O3 in 30 mL of ethanol, then add 1 g of 12-amino-1-dodecene and stir at 100 °C and 500 rpm for 6 h. After the reaction is complete, centrifuge at 8000 rpm for 10 min, wash with ethanol three times, and finally vacuum dry at 60 °C for 6 h to obtain amino-silanized Mg(OH)2@Fe2O3.

[0027] S5. First, place maleimide powder and EVA (vinyl acetate content is 28%) particles in a vacuum dryer at 60 °C for 6 h to remove moisture. Weigh each component according to the mass ratio of EVA:maleimide (MI):dicumyl peroxide (DCP)=100:10:1. Then add EVA, maleimide, dicumyl peroxide, and 0.1 g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to a high-speed mixer and mix at room temperature for 15 min until homogeneous. Preheat the internal mixer to 175 °C, with a rotor speed of 50 rpm. Under a nitrogen atmosphere, add the mixture to the internal mixer and knead for 15 min to ensure that DCP is fully decomposed to initiate a free radical reaction. After waiting for the reaction to complete, discharge the material. Cool the reaction product and crush it into particles. After washing with acetone, extract with a Soxhlet extractor for 24 h to remove unreacted maleimide and homopolymers. Finally, vacuum dry at 60 °C for 12 h until constant weight to obtain EVA-g-MI.

[0028] S6. Blend 20 g of amino-silanized Mg(OH)₂@Fe₂O₃ with 80 g of EVA-g-MI in a mixer at 170 °C for 5 min. Then, keep the blend in a hot press at 125 °C and 6 MPa for 30 min to promote the complete formation of reversible covalent bonds, enabling the amino group to react with the ketone carbonyl of the dienophile to form reversible covalent bonds through a Schiff base reaction. Rapidly cool it to below 60 °C, and the reversible covalent bonds will recombine to form a dynamic crosslinked network, obtaining the modified EVA resin.

[0029] Example 3: A method for preparing a modified EVA resin, comprising the following steps: S1. Dissolve 5 g of magnesium nitrate and 3 g of urea in 200 mL of deionized water, magnetically stir at 500 rpm for 20 min until completely dissolved, transfer the solution to a 100 mL polytetrafluoroethylene reactor, seal it, and place it in an oven for reaction at 150 °C for 12 h. After the reaction, cool it to room temperature, centrifuge at 8000 rpm for 10 min, and collect the precipitate. Then, wash it three times alternately with deionized water and ethanol to remove impurities. Finally, vacuum dry it at 60 °C for 12 h to obtain porous magnesium hydroxide.

[0030] S2. Dissolve 3 g of iron nitrate in 20 mL of deionized water and ultrasonically disperse it for 10 min. Slowly add 1 g of dry porous magnesium hydroxide to the solution, magnetically stir at 200 rpm for 2 h, and let it stand for aging for 4 h. Vacuum dry it at 60 °C for 6 h, and then heat it in a muffle furnace to 400 °C at a rate of 2 °C / min and calcine it for 3 h to uniformly load iron oxide on the surface of the porous magnesium hydroxide, namely, porous magnesium hydroxide loaded with iron oxide, named Mg(OH)₂@Fe₂O₃.

[0031] S3. Vacuum dry the porous magnesium hydroxide loaded with iron oxide at 120 °C for 12 h to remove adsorbed water and activate the surface hydroxyl groups. Disperse 1 g of the magnesium hydroxide loaded with iron oxide in 50 mL of toluene, ultrasonically treat it for 30 min, then add 0.2 g of triethoxysilane, heat it to reflux at 150 °C in a nitrogen atmosphere for 12 h, centrifuge at 8000 rpm for 10 min, and wash it three times with toluene and ethanol in sequence. Finally, vacuum dry it at 60 °C for 6 h to obtain the silanized porous magnesium hydroxide loaded with iron oxide, namely, silanized Mg(OH)₂@Fe₂O₃.

[0032] S4. Disperse 1.05 g of silanized Mg(OH)₂@Fe₂O₃ in 30 mL of ethanol, add 1 g of 12-amino-1-dodecene to it, stir at 100 °C and 500 rpm for 2 h. After the reaction is complete, centrifuge at 8000 rpm for 10 min, wash it three times with ethanol, and finally vacuum dry it at 60 °C for 6 h to obtain amino-silanized Mg(OH)₂@Fe₂O₃.

[0033] S5. First, place maleimide powder and EVA (vinyl acetate content is 28%) particles in a vacuum dryer at 60 °C for 6 h to remove moisture. Weigh each component according to the mass ratio of EVA: maleimide (MI): dicumyl peroxide (DCP) = 100:10:1. Then, add EVA, maleimide, dicumyl peroxide, and 0.1 g of pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] to a high-speed mixer and mix at room temperature for 15 min until homogeneous. Preheat the internal mixer to 180 °C with a rotor speed of 50 rpm. Under a nitrogen atmosphere, add the mixture to the internal mixer and knead for 15 min to ensure that DCP fully decomposes to initiate a free radical reaction. After waiting for the reaction to complete, discharge the material. Cool the reaction product and crush it into particles. After washing with acetone, extract it with a Soxhlet extractor for 24 h to remove unreacted maleimide and homopolymers. Finally, dry it in a vacuum dryer at 60 °C for 12 h until constant weight to obtain EVA-g-MI.

[0034] S6. Blend 20 g of amino-silanized Mg(OH)2@Fe2O3 with 80 g of EVA-g-MI in an internal mixer at 180 °C for 10 min. Then, keep the blend in a hot press at 130 °C and 7 MPa for 30 min to promote the complete formation of reversible covalent bonds, and make the amino group react with the ketone carbonyl group of the dienophile to form a Schiff base reaction to form reversible covalent bonds. Quickly cool it to below 60 °C, and the reversible covalent bonds recombine to form a dynamic crosslinked network to obtain the modified EVA resin.

[0035] Comparative Example 1: Compared with Example 1, in Comparative Example 1, iron(III) oxide was not filled in the pores or on the surface of porous magnesium hydroxide. The specific method is as follows: S1. Dissolve 5 g of magnesium nitrate and 3 g of urea in 200 mL of deionized water, stir magnetically at 500 rpm for 20 min until completely dissolved, transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, seal it, and place it in an oven at 150 °C for 12 h. After the reaction is completed, cool it to room temperature, centrifuge at 8000 rpm for 10 min, and collect the precipitate. Then, wash it three times alternately with deionized water and ethanol to remove impurities. Finally, dry it in a vacuum dryer at 60 °C for 12 h to obtain porous magnesium hydroxide.

[0036] S2. Vacuum dry the porous magnesium hydroxide loaded with iron oxide at 120 °C for 12 h to remove adsorbed water and activate the surface hydroxyl groups. Disperse 1 g of the magnesium hydroxide loaded with iron oxide in 50 mL of toluene, ultrasonically treat for 30 min, then add 0.2 g of triethoxysilane, heat to 110 °C under a nitrogen atmosphere and reflux for 12 h. After centrifuging at 8000 rpm for 10 min, wash with toluene and ethanol three times in sequence, and finally vacuum dry at 60 °C for 6 h to obtain the silanized porous magnesium hydroxide loaded with iron oxide, which is silanized Mg(OH)₂@Fe₂O₃.

[0037] S3. Disperse 1.05 g of silanized Mg(OH)₂@Fe₂O₃ in 30 mL of ethanol, then add 1 g of 12-amino-1-dodecene and stir at 100 °C and 500 rpm for 3 h. After the reaction is complete, centrifuge at 8000 rpm for 10 min, then wash with ethanol three times, and finally vacuum dry at 60 °C for 6 h to obtain amino-silanized Mg(OH)₂@Fe₂O₃.

[0038] S4. First, place maleimide powder and EVA (vinyl acetate content is 28%) particles in a vacuum dryer at 60 °C for 6 h to remove moisture. Weigh each component according to the mass ratio of EVA: maleimide (MI): dicumyl peroxide (DCP) = 100:10:1. Then add EVA, maleimide, dicumyl peroxide and 0.1 g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to a high-speed mixer and mix at room temperature for 15 min until homogeneous. Preheat the internal mixer to 175 °C, with a rotor speed of 50 rpm. Under a nitrogen atmosphere, add the mixture to the internal mixer and knead for 8 min to ensure that DCP is fully decomposed to initiate a free radical reaction. After waiting for the reaction to complete, discharge the material. Cool the reaction product and crush it into particles. After washing with acetone, extract with a Soxhlet extractor for 24 h to remove unreacted maleimide and homopolymers. Finally, vacuum dry at 60 °C for 12 h until constant weight to obtain EVA-g-MI.

[0039] S5. Blend 20 g of amino-silanized Mg(OH)₂@Fe₂O₃ with 80 g of EVA-g-MI in an internal mixer at 160 °C for 5 min, then keep the blend in a hot press at 120 °C and 5 MPa for 30 min to promote the complete formation of reversible covalent bonds, and make the amino group react with the ketone carbonyl group of the dienophile to form reversible covalent bonds. Quickly cool to below 60 °C, and the reversible covalent bonds are reorganized to form a dynamic crosslinked network to obtain the modified EVA resin.

[0040] Comparative Example 2: Compared with Example 2, in Comparative Example 2, no dynamic bonds were inserted between the porous magnesium hydroxide loaded with iron oxide and the EVA resin. The specific method is as follows: S1. Dissolve 5 g of magnesium nitrate and 3 g of urea in 200 mL of deionized water, and magnetically stir at 500 rpm for 20 minutes until completely dissolved. Transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, seal it, and place it in an oven for reaction at 150 °C for 12 h. After the reaction, cool it to room temperature, centrifuge at 8000 rpm for 10 minutes, and collect the precipitate. Then wash it three times alternately with deionized water and ethanol to remove impurities. Finally, vacuum dry at 60 °C for 12 h to obtain porous magnesium hydroxide.

[0041] S2. Dissolve 1.2 g of iron nitrate in 20 mL of deionized water and ultrasonically disperse for 10 min. Slowly add 1 g of dry porous magnesium hydroxide to the solution, magnetically stir at 200 rpm for 2 h, and let it stand for aging for 4 h. Vacuum dry at 60 °C for 6 h, and then heat it to 400 °C at a rate of 2 °C / min in a muffle furnace and calcine for 3 h to uniformly load iron(III) oxide on the surface of the porous magnesium hydroxide, that is, porous magnesium hydroxide loaded with iron(III) oxide, named Mg(OH)2@Fe2O3.

[0042] S3. Vacuum dry the porous magnesium hydroxide loaded with iron(III) oxide at 120 °C for 12 h to remove adsorbed water and activate surface hydroxyl groups. Disperse 1 g of magnesium hydroxide loaded with iron(III) oxide in 50 mL of toluene, ultrasonically treat for 30 min, then add 0.2 g of triethoxysilane, heat to 140 °C and reflux for 12 h under a nitrogen atmosphere, centrifuge at 8000 rpm for 10 min, and wash it three times with toluene and ethanol in turn. Finally, vacuum dry at 60 °C for 6 h to obtain the silanized porous magnesium hydroxide loaded with iron(III) oxide, that is, silanized Mg(OH)2@Fe2O3.

[0043] S4. First, place maleimide powder and EVA (vinyl acetate content is 28%) particles in a vacuum dryer at 60 °C for 6 h to remove moisture. Weigh each component according to the mass ratio of EVA:maleimide (MI):dicumyl peroxide (DCP) = 100:10:1. Then add EVA, maleimide, dicumyl peroxide, and 0.1 g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to a high-speed mixer and mix at room temperature for 15 min until uniform. Preheat the internal mixer to 180 °C, with a rotor speed of 50 rpm. Under a nitrogen atmosphere, add the mixture to the internal mixer and knead for 15 min to ensure that DCP is fully decomposed to initiate a free radical reaction. Wait for the reaction to complete and then discharge. Cool the reaction product, crush it into particles, wash it with acetone, and extract it with a Soxhlet extractor for 24 h to remove unreacted maleimide and homopolymers. Finally, vacuum dry at 60 °C for 12 h until constant weight to obtain EVA-g-MI.

[0044] S5. Blend 20 g of silanized Mg(OH)2@Fe2O3 with 80 g of EVA-g-MI in a kneader at 150 °C for 15 min. Use a twin-screw extruder with the temperature zones set as follows: the feeding section at 120 °C, the melting section at 160 - 170 °C, and the die head at 160 °C. Extrude and pelletize, and dry at 60 °C for 6 h for standby. The blend is hot-pressed in a hot press at 150 °C and 15 MPa for 10 min, cooled, and demolded to obtain EVA resin modified by porous magnesium hydroxide loaded with iron oxide.

[0045] For the modified EVA resin material samples prepared in Examples 1 - 3 and Comparative Examples 1 - 2, the following performance tests were carried out.

[0046] Tensile strength and elongation at break test: According to GB / T6344 - 2008 "Determination of Tensile Strength and Elongation at Break of Flexible Cellular Plastics", use an electronic universal testing machine with the model: Shimadzu AGS-X5KN from Japan. The specimen size is 140 mm × 12 mm × 10 mm, with a rectangular cross-section; the tensile speed is 500 mm / min ± 50 mm / min; Flammability test: The oxygen index is defined as the lowest oxygen concentration required for the material to continue burning. A higher value indicates better flame retardancy of the material. Use an oxygen index tester (model YG813), and the oxygen index is tested according to the GB / T 2406.2 - 2009 standard; Viscosity test: According to the GB / T 3682 - 2000 standard, a melt flow rate instrument can test the viscosity of the material, but it indirectly reflects the fluid viscosity by measuring the melt flow rate. Test using a melt flow rate instrument at 190 °C and 2.16 kg conditions; the results obtained are shown in Table 1.

[0047] Table 1 Mechanical properties, flame retardancy, and viscosity test results of each group of modified EVA resins

[0048] As can be seen from Table 1, compared with Comparative Examples 1 and 2, the modified EVA resins of Examples 1, 2, and 3 have significant improvements in terms of oxygen index, tensile strength, elongation at break, and viscosity. This indicates that the modified EVA resin obtained by the preparation method of the present invention not only has higher flame retardancy performance but also exhibits excellent mechanical properties and appropriate viscosity, thus showing better comprehensive performance in practical applications. Specifically, the modified EVA resin of Example 1 has an oxygen index as high as 37%, a tensile strength of 19 MPa, an elongation at break reaching 623%, and the viscosity also remains at a relatively low level of 2265 Pa·s. These performance indicators are superior to those of other examples and comparative examples, demonstrating the superiority and practicality of this preparation method.

[0049] Combining Examples 1-3 with Comparative Example 1 and referring to Table 1, it can be seen that in the present invention, by filling iron(III) oxide in the pores of porous magnesium hydroxide, the flame retardancy of magnesium hydroxide towards EVA can be effectively improved. The porous magnesium hydroxide loaded with iron(III) oxide system significantly outperforms the unloaded porous magnesium hydroxide in terms of flame retardancy effect. Its specific advantages are as follows: reducing the thermal decomposition temperature, which helps the pyrolysis products of EVA to form a dense carbon layer; Fe 3+ can capture free radicals during the combustion process, thereby interrupting the chain combustion reaction; the large specific surface area enhances the efficiency of heat absorption; the porous structure can adsorb harmful gases and reduce the generation of smoke; only a small amount of addition can achieve an efficient flame retardancy effect, and it can also enhance the tensile strength of the material. Through the synergistic effect of these three mechanisms, this material realizes an all-round improvement in flame retardancy, smoke reduction, and environmental protection performance.

[0050] Combining Examples 1-3 with Comparative Example 2 and referring to Table 1, it can be seen that the dynamic bonds in the present invention can improve the mechanical properties and flame retardancy of EVA. This is because by inserting dynamic bonds between magnesium hydroxide and EVA, the imine bond of Schiff base, as a reversible covalent bond, constructs a dynamic crosslinking network between the surface of the inorganic material and the polymer chain. The magnesium hydroxide modified with amino groups and the EVA resin molecules containing aldehyde groups form Schiff base bonds through a condensation reaction, thereby forming a chemical bridge at the interface. In terms of processing optimization, the dynamic bonds break during the high-temperature processing process, which can reduce the viscosity of the system and promote the uniform dispersion of inorganic fillers; after cooling, the recombination of imine bonds helps to fix the dispersed structure. The polarity of the imine bond is between that of inorganic materials and polymer materials, which helps to reduce the interfacial energy. In terms of topological entanglement, the crosslinking network formed by dynamic bonds increases the entanglement density of polymer chains on the surface of inorganic materials, thereby enhancing the interfacial shear strength. It improves the compatibility between magnesium hydroxide and EVA resin and solves the problem of poor compatibility between magnesium hydroxide and EVA resin. After the EVA resin cools and forms, the bonding state formed by the imine reversible covalent bond can also improve the mechanical properties of the EVA resin product.

[0051] Wet and heat aging test: According to the GB / T 2423.3 standard, the modified EVA resins obtained in each group were continuously wet and heat aged in a wet and heat aging test chamber at 85 °C and 85% RH for 1000 h; the results obtained are shown in Table 2.

[0052] Table 2.a Test results of the initial values of wet and heat aging of each group of modified EVA resins

[0053] Table 2.b Test results of wet and heat aging for 1000 h of each group of modified EVA resins

[0054] As can be seen from Table 2a and Table 2b, by comparing the data in Table 2a and Table 2b, it can be seen that after 1000 hours of damp heat aging test, the modified EVA resins in Example 1, Example 2 and Example 3 showed excellent performance in terms of mass, tensile strength, elongation at break and surface crack density. Relatively speaking, the modified EVA resins in Comparative Example 1 and Comparative Example 2 were significantly inferior in these properties, especially the surface crack density was significantly higher than that of the examples. The modified EVA resin obtained by the preparation method of the present invention has better heat aging resistance. After the porous magnesium hydroxide is silanized, 12-amino-1-dodecene is added. The non-polar long carbon chain reduces the surface free energy by reducing the exposure of polar groups. The long carbon chain tends to migrate to the material surface during processing to form a hydrophobic barrier, and enhances the hydrophobicity through orderly arrangement. These long carbon chains can also form a hydrophobic network to block the penetration of water molecules and fill the micro-defects. In some cases, the long carbon chain can induce the formation of a micron / nano-scale rough structure to enhance the hydrophobicity. In addition, the hydrophobic modified amino-silanized porous magnesium hydroxide can improve the compatibility with the hydrophobic EVA resin material and reduce the interface defects. The modified EVA resin remains stable in the pH range of 3-11, and can maintain good physical properties in a long-term high-temperature and high-humidity environment. Its performance attenuation is better than that of traditional fillers, thus alleviating the aging problem of the modified EVA resin material to a certain extent. The obtained modified EVA resin has stronger heat and damp heat aging resistance, can maintain more stable physical properties and longer service life in practical applications, and has a wider application prospect.

[0055] The specific embodiments of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A preparation method of a modified EVA resin, characterized in that, It includes the following steps: S1. Using magnesium nitrate and urea as raw materials, prepare porous magnesium hydroxide by hydrothermal method; S2. Using the impregnation-calcination method, load iron(III) oxide on the porous magnesium hydroxide to obtain porous magnesium hydroxide loaded with iron(III) oxide; S3. Perform silanization treatment on the porous magnesium hydroxide loaded with iron(III) oxide with triethoxysilane to obtain silanized porous magnesium hydroxide loaded with iron(III) oxide; S4. Disperse the silanized porous magnesium hydroxide loaded with iron(III) oxide in ethanol, add 12-amino-1-dodecene thereto, stir at 100 °C for 3 h, after the reaction is completed, centrifuge, wash and dry to obtain amino-silanized Mg(OH)₂@Fe₂O₃; S5. Mix EVA, maleimide, dicumyl peroxide and antioxidant at room temperature for 15 min, then carry out internal mixing at 170 °C - 180 °C under a nitrogen atmosphere for 8 min, after the reaction is completed, cool and crush into particles, wash with acetone and extract with a Soxhlet extractor for 24 h, and finally dry to obtain EVA-g-MI; S6. Blend the amino-silanized Mg(OH)₂@Fe₂O₃ and EVA-g-MI at 160 °C for 5 min, then hold at 120 °C and 5 MPa for 30 min, and quickly cool to below 60 °C to obtain a modified EVA resin.

2. The preparation method of the modified EVA resin according to claim 1, wherein, In step S3, the preparation of the silanized porous magnesium hydroxide loaded with iron(III) oxide is specifically as follows: dry the porous magnesium hydroxide loaded with iron(III) oxide for 12 h, then disperse it in toluene, perform ultrasonic treatment for 30 min, then add triethoxysilane, heat to 110 °C under a nitrogen atmosphere and react for 12 h, after the reaction is completed, centrifuge, wash and dry to obtain the silanized porous magnesium hydroxide loaded with iron(III) oxide.

3. The preparation method of the modified EVA resin according to claim 1, wherein, In step S4, the mass ratio of the silanized porous magnesium hydroxide loaded with iron(III) oxide to 12-amino-1-dodecene is 1.05:

1.

4. The preparation method of the modified EVA resin according to claim 1, characterized in that, In step S5, the mass ratio of EVA, maleimide, dicumyl peroxide and antioxidant is 100:10:1:0.1, and the antioxidant is: pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

5. The preparation method of the modified EVA resin according to claim 1, characterized in that, In step S5, the content of vinyl acetate in EVA is 28 wt%.

6. The preparation method of the modified EVA resin according to claim 1, wherein, In step S6, the mass ratio of the amino-silanized Mg(OH)₂@Fe₂O₃ to EVA-g-MI is 1:

4.

7. The preparation method of the modified EVA resin according to claim 2, characterized in that, The mass ratio of triethoxysilane to the porous magnesium hydroxide loaded with iron(III) oxide is 1:

5.

8. A modified EVA resin prepared by the preparation method of the modified EVA resin described in claim 1.

Images