EVA foam and preparation method thereof

Abstract

The application relates to the technical field of foam, and discloses EVA foam and a preparation method thereof.The raw materials of the EVA foam include 100 parts by weight of ethylene-vinyl acetate copolymer, 4-10 parts by weight of EVA modified boron nitride, 2.7-4.2 parts by weight of a foaming agent, 0.9-1.5 parts by weight of a crosslinking agent, 0.8-1.3 parts by weight of an accelerator, 0.9-1.4 parts by weight of an auxiliary agent and the like; the EVA molecular chain is chemically modified on the surface of the boron nitride nanosheet, the boron nitride nanosheet has good compatibility with the EVA foam, is uniformly dispersed in the foam material, has better reinforcing effect, significantly improves the mechanical properties and heat resistance of the foam material, has higher tensile strength, elongation at break, tear strength and thermal decomposition temperature, and is beneficial to improving the heat conduction, insulation and other properties of the foam material.

Description

Technical Field

[0001] This invention relates to the field of foam technology, specifically to an EVA foam and its preparation method. Background Technology

[0002] EVA (ethylene-vinyl acetate copolymer) can be foamed to produce high-performance foam materials, widely used in footwear, insulation materials, home appliances, and medical devices. Ordinary EVA foam materials suffer from low mechanical strength and poor heat resistance, therefore, it is necessary to add fillers such as nanomaterials to improve their overall performance, including graphene, nano-silica, nano-calcium carbonate, and montmorillonite. Nano-boron nitride possesses high mechanical strength, high thermal conductivity, and high resistivity, which can improve the mechanical properties, thermal conductivity, and insulation properties of polymer materials.

[0003] Nano-boron nitride is prone to agglomeration and has poor dispersibility in polymer materials, which limits its practical application. Chinese patent application CN120025760A discloses an insulating and highly thermally conductive EVA encapsulating film for photovoltaic modules and its preparation method. Modified boron nitride with amino or carboxyl active groups on its surface is blended with EVA, which improves the insulation and thermal conductivity of EVA material. However, this modified boron nitride does not improve the tensile strength, tear strength, and other mechanical properties of EVA material. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an EVA foam and its preparation method, which solves the problems of poor mechanical strength and heat resistance of EVA foam materials.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an EVA foam and its preparation method, wherein the raw materials of the EVA foam include 100 parts by weight of ethylene-vinyl acetate copolymer, 4-10 parts by weight of EVA modified boron nitride, 2.7-4.2 parts by weight of foaming agent, 0.9-1.5 parts by weight of crosslinking agent, 0.8-1.3 parts by weight of accelerator, and 0.9-1.4 parts by weight of additives.

[0006] The preparation method of EVA foam includes: adding ethylene-vinyl acetate copolymer, EVA-modified boron nitride, accelerator and additives into a two-roll mill for blending, then adding a foaming agent and mixing; then adding a crosslinking agent and mixing; finally cutting the mixture into sheets, placing them in a foaming machine for molding and foaming to obtain EVA foam.

[0007] Preferably, the blending temperature is 80-90℃; the pressure during foaming is 10-20 MPa, the temperature is 170-180℃, and the time is 5-8 min.

[0008] Preferably, the foaming agent includes azodicarbonamide.

[0009] Preferably, the crosslinking agent includes dicumyl peroxide.

[0010] Preferably, the hair growth promoter includes zinc oxide.

[0011] Preferably, the additives include any one or combination of stearic acid and zinc stearate.

[0012] Preferably, the preparation method of EVA-modified boron nitride includes:

[0013] (1) Add ethylene-vinyl acetate copolymer and dimethacrylate mannitol to toluene, stir, and then add azobisisobutyronitrile under a nitrogen atmosphere. After stirring and reacting, pour the solution into methanol, filter, wash with methanol and acetone in sequence, and dry to obtain grafted EVA.

[0014] (2) Add boron nitride nanosheets and grafted EVA into a ball mill jar, ball mill, discharge the material, and obtain EVA modified boron nitride.

[0015] Preferably, the reaction in (1) is carried out at 80-95℃ for 10-16h.

[0016] Preferably, in (1), the amount of ethylene-vinyl acetate copolymer is 100 parts by weight, the amount of dimethacrylate mannitol is 8-15 parts by weight, and the amount of azobisisobutyronitrile is 0.6-0.9 parts by weight.

[0017] Preferably, in (2), the amount of boron nitride nanosheets is 100 parts by weight, and the amount of grafted EVA is 2-7 parts by weight.

[0018] Preferably, in (2), the ball milling speed is 300-800 r / min and the ball milling time is 12-24 h.

[0019] Preferably, the preparation method of dimethacrylate mannitol includes: adding 900-980 parts by weight of pyridine and 100 parts by weight of mannitol to N,N-dimethylformamide, adding dropwise an N,N-dimethylformamide solution containing 130-150 parts by weight of methacryloyl chloride at 0-5°C, reacting for 12-15 hours, filtering, adding the filtrate to diethyl ether, precipitating a gel-like substance, filtering, and drying to obtain dimethacrylate mannitol.

[0020] The reaction formula is:

[0021]

[0022] The technical effects of this invention are as follows: EVA is grafted onto mannitol dimethacrylate to obtain grafted EVA, and then boron nitride nanosheets are modified by ball milling. The grafted EVA contains a polyhydroxy structure, which forms a strong interaction force with the surface of boron nitride nanosheets during the ball milling process. EVA molecular chains are modified on the surface of boron nitride nanosheets, thereby achieving surface modification of boron nitride and reducing the aggregation of boron nitride nanosheets.

[0023] This invention involves blending and foaming EVA ethylene-vinyl acetate copolymer, EVA-modified boron nitride, a foaming agent, and a crosslinking agent to obtain EVA foam. Because the surface of the boron nitride nanosheets chemically modifies the EVA molecular chains, the boron nitride nanosheets exhibit excellent compatibility with the EVA foam, are uniformly dispersed in the foam material, and provide better reinforcement. This significantly improves the mechanical and heat resistance properties of the foam material, exhibiting higher tensile strength, elongation at break, tear strength, and thermal decomposition temperature. Furthermore, the uniform dispersion of the boron nitride nanosheets in the EVA foam material helps improve the material's thermal conductivity and insulation properties. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The ethylene-vinyl acetate copolymer described below, model number UL15028, is from Guangzhou Binlong Chemical Co., Ltd. The boron nitride nanosheets, 200nm in size, were purchased from Zhejiang Yamei Nanotechnology Co., Ltd.

[0026] Example 1:

[0027] (1) Add 9.8 g pyridine and 1 g mannitol to 20 mL of N,N-dimethylformamide, and add 5 mL of N,N-dimethylformamide solution containing 1.3 g methacryloyl chloride dropwise at 5 °C. React for 12 h, filter, add the filtrate to diethyl ether, and precipitate a gel-like substance. Filter and dry to obtain dimethacrylate mannitol.

[0028] (2) Add 10g of ethylene-vinyl acetate copolymer and 1.2g of dimethacrylate mannitol to 120mL of toluene. After stirring, add 0.08g of azobisisobutyronitrile in a nitrogen atmosphere, heat to 80℃, stir and react for 16h. Pour the solution into methanol, filter, wash with methanol and acetone in sequence, and dry to obtain grafted EVA.

[0029] (3) Add 50g of boron nitride nanosheets and 1g of grafted EVA into a ball mill jar, and mill for 12 hours at an ion rotation speed of 500r / min. The material is then discharged to obtain EVA-modified boron nitride.

[0030] (4) 1 kg of ethylene-vinyl acetate copolymer, 40 g of EVA-modified boron nitride, 10 g of accelerator zinc oxide, 8 g of auxiliary agent stearic acid, and 6 g of zinc stearate were added to a two-roll mill for blending. Then, 36 g of foaming agent azodicarbonamide was added and the mixture was kneaded at 90 °C. Then, 12 g of crosslinking agent dicumyl peroxide was added and kneaded. Finally, the mixture was cut into pieces and placed in a foaming machine for compression molding. The pressure was 10 MPa, the temperature was 180 °C, and the time was 6 min to obtain EVA foam.

[0031] Example 2:

[0032] (1) Add 9g pyridine and 1g mannitol to 20mL N,N-dimethylformamide, and add 5mL of N,N-dimethylformamide solution containing 1.5g methacryloyl chloride dropwise at 0℃. React for 15h, filter, add the filtrate to diethyl ether, and precipitate a gel-like substance. Filter and dry to obtain dimethacrylate mannitol.

[0033] (2) Add 10g of ethylene-vinyl acetate copolymer and 1.5g of dimethacrylate mannitol to 150mL of toluene. After stirring, add 0.09g of azobisisobutyronitrile in a nitrogen atmosphere, heat to 85℃, stir and react for 16h. Pour the solution into methanol, filter, wash with methanol and acetone in sequence, and dry to obtain grafted EVA.

[0034] (3) Add 50g of boron nitride nanosheets and 2.5g of grafted EVA into a ball mill jar, and mill for 24 hours at an ion rotation speed of 300r / min. The material is then discharged to obtain EVA-modified boron nitride.

[0035] (4) 1 kg of ethylene-vinyl acetate copolymer, 70 g of EVA-modified boron nitride, 13 g of accelerator zinc oxide, 5 g of auxiliary agent stearic acid, and 4 g of zinc stearate were added to a two-roll mill for blending. Then, 27 g of foaming agent azodicarbonamide was added and the mixture was kneaded at 80 °C. Then, 15 g of crosslinking agent dicumyl peroxide was added and kneaded. Finally, the mixture was cut into pieces and placed in a foaming machine for compression molding. The pressure was 20 MPa, the temperature was 170 °C, and the time was 7 min to obtain EVA foam.

[0036] Example 3:

[0037] (1) Mannitol dimethacrylate was prepared according to the method of Example 1.

[0038] (2) Add 10g of ethylene-vinyl acetate copolymer and 0.8g of dimethacrylate mannitol to 120mL of toluene. After stirring, add 0.06g of azobisisobutyronitrile in a nitrogen atmosphere, heat to 95℃, stir and react for 10h. Pour the solution into methanol, filter, wash with methanol and acetone in sequence, and dry to obtain grafted EVA.

[0039] (3) Add 50g of boron nitride nanosheets and 3.5g of grafted EVA into a ball mill jar, and mill for 24 hours at an ion rotation speed of 800r / min. The material is then discharged to obtain EVA-modified boron nitride.

[0040] (4) Add 1 kg of ethylene-vinyl acetate copolymer, 100 g of EVA-modified boron nitride, 8 g of accelerator zinc oxide, 6 g of auxiliary agent stearic acid, and 5 g of zinc stearate to a two-roll mill for blending. Then add 42 g of foaming agent azodicarbonamide and mix at 80°C. Then add 9 g of crosslinking agent dicumyl peroxide for mixing. Finally, cut the mixture into pieces and place them in a foaming machine for compression molding. The pressure is 15 MPa, the temperature is 180°C, and the time is 5 min to obtain EVA foam.

[0041] Comparative Example 1:

[0042] (1) Add 1 kg of ethylene-vinyl acetate copolymer, 10 g of accelerator zinc oxide, 8 g of auxiliary agent stearic acid and 6 g of zinc stearate to a two-roll mill for blending, then add 36 g of foaming agent azodicarbonamide and mix at 90°C; then add 12 g of crosslinking agent dicumyl peroxide for mixing, and finally cut the mixture into pieces, place them in a foaming machine for molding and foaming, with a pressure of 10 MPa, a temperature of 180°C and a time of 6 min, to obtain EVA foam.

[0043] Comparative Example 2:

[0044] (1) 1 kg of ethylene-vinyl acetate copolymer, 40 g of boron nitride nanosheets, 10 g of accelerator zinc oxide, 8 g of auxiliary agent stearic acid, and 6 g of zinc stearate were added to a two-roll mill for blending. Then, 36 g of foaming agent azodicarbonamide was added and the mixture was kneaded at 90 °C. Then, 12 g of crosslinking agent dicumyl peroxide was added and kneaded. Finally, the mixture was cut into sheets and placed in a foaming machine for compression molding. The pressure was 10 MPa, the temperature was 180 °C, and the time was 6 min to obtain EVA foam.

[0045] Comparative Example 3:

[0046] (1) Add 50g of boron nitride nanosheets and 1g of EVA ethylene-vinyl acetate copolymer to a ball mill jar, and ball mill for 12h at an ion rotation speed of 500r / min. Discharge the material to obtain EVA-boron nitride blend.

[0047] (2) 1 kg of ethylene-vinyl acetate copolymer, 40 g of EVA-boron nitride blend, 10 g of accelerator zinc oxide, 8 g of auxiliary agent stearic acid, and 6 g of zinc stearate were added to a two-roll mill for blending. Then, 36 g of foaming agent azodicarbonamide was added and the mixture was kneaded at 90 °C. Then, 12 g of crosslinking agent dicumyl peroxide was added and kneaded. Finally, the mixture was cut into pieces and placed in a foaming machine for compression molding. The pressure was 10 MPa, the temperature was 180 °C, and the time was 6 min to obtain EVA foam.

[0048] Comparative Example 4:

[0049] (1) Add 10g of ethylene-vinyl acetate copolymer and 1.2g of hydroxyethyl methacrylate to 120mL of toluene, stir, add 0.08g of azobisisobutyronitrile in a nitrogen atmosphere, heat to 80℃, stir and react for 16h, pour the solution into methanol, filter, wash with methanol and acetone in turn, dry, and obtain grafted EVA.

[0050] (2) Add 50g of boron nitride nanosheets and 1g of grafted EVA into a ball mill jar, and mill for 12 hours at an ion rotation speed of 500r / min. The material is then discharged to obtain EVA-modified boron nitride.

[0051] (3) 1 kg of ethylene-vinyl acetate copolymer, 40 g of EVA-modified boron nitride, 10 g of accelerator zinc oxide, 8 g of auxiliary agent stearic acid, and 6 g of zinc stearate were added to a two-roll mill for blending. Then, 36 g of foaming agent azodicarbonamide was added and the mixture was kneaded at 90 °C. Then, 12 g of crosslinking agent dicumyl peroxide was added and kneaded. Finally, the mixture was cut into pieces and placed in a foaming machine for compression molding. The pressure was 10 MPa, the temperature was 180 °C, and the time was 6 min to obtain EVA foam.

[0052] The tensile properties of EVA foam were tested according to GB / T 6344-2008 standard. The tear strength was tested according to GB / T529-2008 standard.

[0053] Weigh 5mg of EVA foam and perform thermal performance testing in a thermogravimetric analyzer under a nitrogen atmosphere, heating from 25℃ to 700℃ at a rate of 10℃ / min.

[0054] Table 1 Performance of EVA foam

[0055]

[0056] After testing, compared with Comparative Example 1, the addition of boron nitride nanosheets to the EVA foam material in Comparative Example 2 increased the tensile properties, tear strength, and thermal decomposition temperature of the foam material, and improved the mechanical properties and heat resistance. However, the boron nitride nanosheet solution agglomerated, and its compatibility with EVA was poor. It was easy to agglomerate in the foam material, resulting in poor reinforcement effect of boron nitride nanosheets and a low increase in tensile properties, tear strength, and thermal decomposition temperature.

[0057] Examples 1-3 utilize dimethacrylate-mannitol-grafted EVA to modify boron nitride nanosheets through ball milling. The grafted EVA contains a polyhydroxy structure. During ball milling, strong interaction forces are formed between the boron nitride nanosheets and the EVA molecular chains on the surface of the boron nitride nanosheets, thus achieving surface modification of boron nitride and reducing the aggregation of boron nitride nanosheets. Further, it is blended and foamed with ethylene-vinyl acetate copolymer (EVA). Due to the chemical modification of the EVA molecular chains on the surface of the boron nitride nanosheets, the compatibility between the boron nitride nanosheets and EVA foam is very good, and they are uniformly dispersed in the foam material, resulting in better reinforcement effect. This significantly improves the mechanical properties and heat resistance of the foam material, exhibiting higher tensile strength, elongation at break, tear strength, and thermal decomposition temperature.

[0058] Comparative Example 3 uses EVA-ethylene-vinyl acetate copolymer to ball-mill-modify boron nitride nanosheets. EVA does not contain polyhydroxyl structures and cannot form interactions with the surface of boron nitride nanosheets. Therefore, EVA molecular chains cannot be chemically modified on the surface of boron nitride. When it is subsequently blended and foamed with EVA, the compatibility between boron nitride nanosheets and EVA foam is poor, the dispersion is poor, the reinforcing effect of boron nitride nanosheets is low, and the tensile properties, tear strength and thermal decomposition temperature of the foam material are lower than those of Example 1.

[0059] Comparative Example 4 involved grafting EVA with hydroxyethyl methacrylate, followed by ball milling modification of boron nitride nanosheets. The grafted EVA had few hydroxyl groups, resulting in low interaction with the surface of the boron nitride nanosheets. This made it difficult to effectively chemically modify the EVA molecular chains on the boron nitride surface. Consequently, when the EVA was blended and foamed with EVA, the compatibility and dispersibility between the boron nitride nanosheets and the EVA foam were poor, and the reinforcing effect of the boron nitride nanosheets was inadequate. The tensile properties, tear strength, and thermal decomposition temperature of the foam material were lower than those in Example 1.

[0060] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An EVA foam, characterized in that, The raw materials of the EVA foam include 100 parts by weight of ethylene-vinyl acetate copolymer, 4-10 parts by weight of EVA-modified boron nitride, 2.7-4.2 parts by weight of foaming agent, 0.9-1.5 parts by weight of crosslinking agent, 0.8-1.3 parts by weight of accelerator, and 0.9-1.4 parts by weight of additives. The preparation method of the EVA-modified boron nitride includes: (1) Add ethylene-vinyl acetate copolymer and dimethacrylate mannitol to toluene, stir, add azobisisobutyronitrile under nitrogen atmosphere, stir to react, pour the solution into methanol, filter, wash, and dry to obtain grafted EVA. (2) Add boron nitride nanosheets and grafted EVA into a ball mill jar, ball mill, discharge the material, and obtain EVA modified boron nitride. The amount of ethylene-vinyl acetate copolymer used in (1) is 100 parts by weight, mannitol dimethacrylate is 8-15 parts by weight, and azobisisobutyronitrile is 0.6-0.9 parts by weight. In step (2), the amount of boron nitride nanosheets is 100 parts by weight, and the amount of grafted EVA is 2-7 parts by weight.

2. The EVA foam according to claim 1, characterized in that, The foaming agent includes azodicarbonamide; the crosslinking agent includes dicumyl peroxide.

3. The EVA foam according to claim 1, characterized in that, The accelerator includes zinc oxide; the additives include any one or a combination of stearic acid and zinc stearate.

4. The EVA foam according to claim 1, characterized in that, The reaction in (1) is carried out at 80-95℃ for 10-16 hours.

5. The EVA foam according to claim 1, characterized in that, The preparation method of the dimethacrylate mannitol includes: adding 900-980 parts by weight of pyridine and 100 parts by weight of mannitol to N,N-dimethylformamide, adding dropwise an N,N-dimethylformamide solution containing 130-150 parts by weight of methacryloyl chloride at 0-5℃, reacting for 12-15 hours, filtering, adding the filtrate to diethyl ether, precipitating a viscous substance, filtering, washing with diethyl ether, and drying to obtain dimethacrylate mannitol.

6. The EVA foam according to claim 1, characterized in that, In (2), the ball milling speed is 300-800 r / min and the ball milling time is 12-24 h.

7. A method for preparing EVA foam as described in any one of claims 1-6, characterized in that, The preparation method includes: adding ethylene-vinyl acetate copolymer, EVA-modified boron nitride, accelerator, and additives into a two-roll mill for blending, then adding a foaming agent for mixing; then adding a crosslinking agent for mixing, and finally cutting the mixture into sheets, placing them in a foaming machine for molding and foaming to obtain EVA foam.

8. The method for preparing EVA foam according to claim 7, characterized in that, The blending temperature is 80-90℃; the pressure during foaming is 10-20 MPa, the temperature is 170-180℃, and the time is 5-8 min.

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