A foamed polypropylene material for thermal insulation takeaway box and preparation method thereof

Abstract

The present invention belongs to the technical field of foamed polypropylene materials, and specifically relates to a foamed polypropylene material for an insulated takeout box and a preparation method thereof. The present invention uses nano-silica aerogel to encapsulate isooctyl alcohol as a foaming agent, which has lower requirements on equipment and process compared to traditional supercritical carbon dioxide foaming; compared to traditional hollow organic microsphere foaming, its own low thermal conductivity and porosity are better than traditional foaming agent materials. After degassing and uniform impregnation with isooctyl alcohol, the thermal insulation performance of the foamed material is further improved, and it is suitable for use in takeout box applications with higher requirements for thermal insulation performance. The present invention uses polypropylene resin as a matrix material, combined with nano-silica aerogel foaming agent, lubricant and antioxidant, to form a foaming material with a stable structure and excellent thermal insulation performance.

Description

Technical Field

[0001] The invention belongs to the technical field of foamed polypropylene materials, and particularly relates to a foamed polypropylene material for an insulated takeout box and a preparation method thereof. Background Art

[0002] Insulated takeout boxes play an important role in modern catering delivery, especially in the rapidly developing takeout industry. As consumers have higher and higher requirements for food freshness and temperature, how to effectively maintain the temperature of food during delivery has become a key issue. Traditional insulated takeout boxes usually use polystyrene foam materials. Although this material has a certain insulation effect, it has disadvantages such as fragility, difficulty in recycling, and environmental pollution. Therefore, the market urgently needs a new material with better insulation performance, durability and environmental protection performance to replace traditional materials.

[0003] Expanded Polypropylene (EPP) is a new type of high-performance foam material that has gradually attracted attention in the application of insulated takeout boxes in recent years. Expanded Polypropylene has excellent thermal insulation performance, impact resistance and good resilience, and is also lightweight, chemically resistant, and recyclable. These advantages make expanded polypropylene an ideal choice to replace traditional polystyrene foam materials.

[0004] The advantages of foamed polypropylene materials are mainly reflected in the following aspects:

[0005] Excellent thermal insulation performance: The closed-cell structure of foamed polypropylene material can effectively block the conduction and convection of heat, thereby ensuring that food can maintain a suitable temperature for a long time during the takeaway delivery process.

[0006] Good durability: Compared with traditional polystyrene foam materials, expanded polypropylene has higher compressive strength and impact resistance, is not easy to break, has a longer service life, and helps reduce the cost of use.

[0007] Environmental protection: Foamed polypropylene materials can be reused and recycled, reducing pollution to the environment. In addition, its production process does not use substances such as Freon that are harmful to the ozone layer, which meets the requirements of green environmental protection.

[0008] Lightweight: Foamed polypropylene material has low density and light weight, making it easy to carry and transport without increasing the burden on delivery staff.

[0009] Due to the above advantages, foamed polypropylene materials have been widely used in the automotive industry, packaging, construction and other fields, and have gradually been introduced into the manufacture of insulated takeout boxes. The comprehensive performance of foamed polypropylene composite materials is excellent, but compared with other resin foamed composite materials, it is more difficult to foam, mainly because the molecular chain of polypropylene resin is a highly regular linear structure with good flexibility. When the temperature rises above the melting point of polypropylene resin, its melt viscosity drops sharply, and the melt strength is not enough to meet the strength requirements of the resin melt encapsulating the gas. It is difficult to maintain the gas in the resin melt, resulting in gas escape from the system, forming open pores or pore collapse, and reducing the gas foaming efficiency. The entire foaming process is difficult to control. At present, the preparation methods of foamed polypropylene composite materials mainly include three categories: chemical foaming method, physical foaming method and hollow microsphere filling method. Among them, the chemical foaming method is prone to produce low-toxic and harmful residues during the production process, and it is difficult to meet the increasingly stringent environmental protection requirements. The physical foaming method mostly refers to the supercritical carbon dioxide foaming method, which has extremely high requirements for equipment. The hollow microsphere foaming method also has high requirements for the preparation of microspheres, the compatibility of microspheres and polypropylene, and the foaming process.

[0010] In addition, although the foamed polypropylene material has shown good thermal insulation performance in take-out insulation boxes, with the development of the industry and the increase in consumer demand, it is necessary to further optimize and improve the thermal insulation performance. This can not only meet higher market demands, but also improve user experience and gain advantages in market competition. At the same time, further improving thermal insulation performance through material innovation and technology upgrades is also in line with the trend of sustainable development and helps reduce resource consumption and environmental impact. Summary of the invention

[0011] In view of the deficiencies in the prior art, the present invention provides a foamed polypropylene material for an insulated takeout box and a preparation method thereof.

[0012] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials: polypropylene resin, nano silicon dioxide aerogel foaming agent, lubricant and antioxidant.

[0013] Preferably, the foamed polypropylene material for the thermal insulation takeaway box is composed of the following raw materials, measured by mass: 80-100 parts of polypropylene resin, 5-20 parts of nano-silicon dioxide aerogel foaming agent, 0.5-5 parts of lubricant, and 0.5-5 parts of antioxidant.

[0014] Preferably, the foamed polypropylene material for the thermal insulation takeaway box is composed of the following raw materials, measured by mass: 80-100 parts of polypropylene resin, 8-15 parts of nano-silicon dioxide aerogel foaming agent, 0.5-2 parts of lubricant, and 0.5-2 parts of antioxidant.

[0015] Preferably, the lubricant is at least one of calcium stearate, oxidized polyethylene wax, zinc stearate, and ethylene bisstearamide; preferably, the lubricant is a mixture of oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:(1-2).

[0016] Preferably, the antioxidant is at least one of antioxidant 1010, antioxidant 168, antioxidant DLTP, and antioxidant 1076.

[0017] Preferably, the method for preparing the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0018] Step S1: placing the nano-silica aerogel in a vacuum drying oven for degassing to remove air in the pores, thereby obtaining a degassed nano-silica aerogel;

[0019] Step S2: immersing the degassed nano-silica aerogel obtained in step S1 in isooctyl alcohol, using the capillary action of the aerogel to gradually infiltrate the liquid into the pores of the aerogel, centrifuging and separating to obtain isooctyl alcohol / nano-silica aerogel;

[0020] Step S3: heating water, then adding polyvinyl alcohol thereto, stirring until the polyvinyl alcohol is dissolved, stopping stirring and heating, and filtering to obtain a polyvinyl alcohol solution;

[0021] Step S4: Immerse the isooctyl alcohol / nano-silica aerogel obtained in step S2 into the polyvinyl alcohol solution obtained in step S3, stir, centrifuge, separate, and dry to obtain the nano-silica aerogel foaming agent.

[0022] Preferably, the method for preparing the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0023] Step S1: degas the nano-silica aerogel in a vacuum drying oven at 80-90° C. for 4-8 hours, with the air pressure of the vacuum drying oven being 10-50 Pa, so as to remove the air in the pores and obtain degassed nano-silica aerogel;

[0024] Step S2: Immerse the degassed nano-silica aerogel obtained in step S1 in isooctyl alcohol for 5-30 minutes, wherein the mass ratio of the nano-silica aerogel to isooctyl alcohol is 1:(1-10), and utilize the capillary action of the aerogel to gradually infiltrate the liquid into the pores of the aerogel, centrifuge and separate to obtain isooctyl alcohol / nano-silica aerogel;

[0025] Step S3: Heat water to 80-90° C., then add polyvinyl alcohol thereto, the mass ratio of polyvinyl alcohol to water being 1:(8-10), stir for 30-40 minutes, stop stirring and heating, and filter with a 0.4-0.5 μm filter membrane to obtain a polyvinyl alcohol solution;

[0026] Step S4: Immerse the isooctyl alcohol / nano-silica aerogel obtained in step S2 into the polyvinyl alcohol solution obtained in step S3, wherein the mass ratio of isooctyl alcohol / nano-silica aerogel to the polyvinyl alcohol solution is 1:(9-11), stir for 30-60 seconds, centrifuge, separate, and dry to obtain the nano-silica aerogel foaming agent.

[0027] A method for preparing a foamed polypropylene material for an insulated takeaway box comprises the following steps:

[0028] The polypropylene resin is placed at 80-90° C. and dried for 8-12 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and subjected to cooling, pulling, and pelletizing to obtain the foamed polypropylene material for the thermal insulation takeout box.

[0029] The temperature of the rear part of the barrel of the extruder is 155-160°C, the temperature of the middle part of the barrel is 160-165°C, the temperature of the front part of the barrel is 165-170°C, the temperature of the head is 170-175°C, and the screw speed is 70-80r / min.

[0030] The present invention adopts polypropylene resin as the base material, and forms a foaming material with stable structure and excellent thermal insulation performance in combination with nano-silicon dioxide aerogel foaming agent, lubricant and antioxidant. The use of nano-silicon dioxide aerogel foaming agent significantly improves the thermal insulation performance of the material, while the selection and proportion of lubricant and antioxidant further optimize the processability and long-term stability of the material.

[0031] Compared with traditional supercritical carbon dioxide foaming, the present invention uses nano-silica aerogel to encapsulate isooctyl alcohol as a foaming agent, which has lower requirements for equipment and process; compared with traditional hollow organic microsphere foaming, the present invention uses nano-silica aerogel as a foaming agent, which has its own low thermal conductivity and porosity better than traditional foaming agent materials. After degassing and uniform impregnation with isooctyl alcohol, the thermal insulation performance of the foaming material is further improved, which is suitable for use in take-out box applications with high requirements for thermal insulation performance.

[0032] Thanks to precise process control and foaming agent encapsulation treatment, the uniformity of the pore structure of the foaming material is greatly improved, avoiding the problems of uneven pore size and distribution common in traditional foaming materials, and ensuring the thermal insulation effect of the material.

[0033] Beneficial effects of the present invention:

[0034] The present invention uses nano-silica aerogel to encapsulate isooctyl alcohol as a foaming agent, which has lower requirements on equipment and process than traditional supercritical carbon dioxide foaming; compared with traditional hollow organic microsphere foaming, its own low thermal conductivity and porosity are better than traditional foaming agent materials. After degassing and uniform impregnation with isooctyl alcohol, the thermal insulation performance of the foaming material is further improved, and it is suitable for use in take-out box applications with high requirements for thermal insulation performance. The present invention uses polypropylene resin as a matrix material, combined with nano-silica aerogel foaming agent, lubricant and antioxidant, to form a foaming material with a stable structure and excellent thermal insulation performance. DETAILED DESCRIPTION

[0035] Nano-silica aerogel, product number: 091458, Shanghai Kelaman Reagent Co., Ltd.

[0036] Polypropylene resin, brand: Moplen EP300K, Shanghai Yizeng Plasticizing Co., Ltd.

[0037] Oxidized polyethylene wax, model: S203, Dongguan Zhenming Chemical Co., Ltd.

[0038] Ethylene bisstearamide, product number: ST2022150, Shandong Suihua Biotechnology Co., Ltd.

[0039] Polyvinyl alcohol, product number: N07802, Shanghai Myrrel Biochemical Technology Co., Ltd.

[0040] Polyvinylidene chloride, product number: BD0521, Hubei Baidu Chemical Co., Ltd.

[0041] Polyurethane, Product No.: CH2916, Hubei Chenghai Chemical Co., Ltd.

[0042] Ethylene-vinyl acetate copolymer, product number: S45075, Shanghai Yuanye Biotechnology Co., Ltd.

[0043] Example 1

[0044] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials, measured by weight: 90 parts of polypropylene resin, 12 parts of nano-silicon dioxide aerogel foaming agent, 1.2 parts of lubricant, and 1.6 parts of antioxidant.

[0045] The lubricant is prepared by mixing oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:1.

[0046] The antioxidant is antioxidant 1010.

[0047] The preparation method of the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0048] Step S1: placing the nano-silica aerogel in a vacuum drying oven at 80° C. for degassing for 6 h, with the vacuum drying oven pressure being 50 Pa, to obtain degassed nano-silica aerogel;

[0049] Step S2: Immerse the degassed nano-silica aerogel obtained in step S1 in isooctyl alcohol for 10 minutes, wherein the mass ratio of the nano-silica aerogel to the isooctyl alcohol is 1:9, and centrifuge and separate to obtain isooctyl alcohol / nano-silica aerogel;

[0050] Step S3: Heat water to 85° C., then add polyvinyl alcohol thereto, the mass ratio of polyvinyl alcohol to water being 1:9, stir for 35 minutes, stop stirring and heating, and filter with a 0.4 μm filter membrane to obtain a polyvinyl alcohol solution;

[0051] Step S4: Immerse the isooctyl alcohol / nano-silica aerogel obtained in step S2 into the polyvinyl alcohol solution obtained in step S3, the mass ratio of isooctyl alcohol / nano-silica aerogel to polyvinyl alcohol solution being 1:10, stir for 40 seconds, centrifuge, separate, and dry to obtain the nano-silica aerogel foaming agent.

[0052] The method for preparing the foamed polypropylene material for the thermal insulation takeaway box comprises the following steps:

[0053] The polypropylene resin is placed at 80° C. and dried for 10 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and after cooling, pulling, and pelletizing, the foamed polypropylene material for the thermal insulation takeout box is obtained.

[0054] The temperature of the rear part of the barrel of the extruder was 160°C, the temperature of the middle part of the barrel was 165°C, the temperature of the front part of the barrel was 170°C, the temperature of the head was 175°C, and the screw speed was 75r / min.

[0055] Example 2

[0056] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials, measured by weight: 90 parts of polypropylene resin, 12 parts of nano-silicon dioxide aerogel foaming agent, 1.2 parts of lubricant, and 1.6 parts of antioxidant.

[0057] The lubricant is prepared by mixing oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:1.

[0058] The antioxidant is antioxidant 1010.

[0059] The preparation method of the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0060] Step S1: immersing the nano-silica aerogel in isooctyl alcohol for 10 minutes, wherein the mass ratio of the nano-silica aerogel to the isooctyl alcohol is 1:9, and centrifuging and separating to obtain isooctyl alcohol / nano-silica aerogel;

[0061] Step S2: Heat water to 85° C., then add polyvinyl alcohol thereto, the mass ratio of polyvinyl alcohol to water being 1:9, stir for 35 minutes, stop stirring and heating, and filter with a 0.4 μm filter membrane to obtain a polyvinyl alcohol solution;

[0062] Step S3: Immerse the isooctyl alcohol / nano-silica aerogel obtained in step S1 into the polyvinyl alcohol solution obtained in step S2, wherein the mass ratio of isooctyl alcohol / nano-silica aerogel to the polyvinyl alcohol solution is 1:10, stir for 40 seconds, centrifuge, separate, and dry to obtain the nano-silica aerogel foaming agent.

[0063] The method for preparing the foamed polypropylene material for the thermal insulation takeaway box comprises the following steps:

[0064] The polypropylene resin is placed at 80° C. and dried for 10 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and after cooling, pulling, and pelletizing, the foamed polypropylene material for the thermal insulation takeout box is obtained.

[0065] The temperature of the rear part of the barrel of the extruder was 160°C, the temperature of the middle part of the barrel was 165°C, the temperature of the front part of the barrel was 170°C, the temperature of the head was 175°C, and the screw speed was 75r / min.

[0066] Example 3

[0067] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials, measured by weight: 90 parts of polypropylene resin, 12 parts of nano-silicon dioxide aerogel foaming agent, 1.2 parts of lubricant, and 1.6 parts of antioxidant.

[0068] The lubricant is prepared by mixing oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:1.

[0069] The antioxidant is antioxidant 1010.

[0070] The preparation method of the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0071] Step S1: placing the nano-silica aerogel in a vacuum drying oven at 80° C. for degassing for 6 h, with the vacuum drying oven pressure being 50 Pa, to obtain degassed nano-silica aerogel;

[0072] Step S2: The degassed nano-silica aerogel obtained in step S1 is immersed in isooctyl alcohol for 10 minutes, the mass ratio of the degassed nano-silica aerogel to isooctyl alcohol being 1:9, and centrifuged and separated to obtain the nano-silica aerogel foaming agent.

[0073] The method for preparing the foamed polypropylene material for the thermal insulation takeaway box comprises the following steps:

[0074] The polypropylene resin is placed at 80° C. and dried for 10 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and after cooling, pulling, and pelletizing, the foamed polypropylene material for the thermal insulation takeout box is obtained.

[0075] The temperature of the rear part of the barrel of the extruder was 160°C, the temperature of the middle part of the barrel was 165°C, the temperature of the front part of the barrel was 170°C, the temperature of the head was 175°C, and the screw speed was 75r / min.

[0076] Example 4

[0077] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials, measured by weight: 90 parts of polypropylene resin, 12 parts of nano-silicon dioxide aerogel foaming agent, 1.2 parts of lubricant, and 1.6 parts of antioxidant.

[0078] The lubricant is prepared by mixing oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:1.

[0079] The antioxidant is antioxidant 1010.

[0080] The preparation method of the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0081] Step S1: placing the nano-silica aerogel in a vacuum drying oven at 80° C. for degassing for 6 h, with the vacuum drying oven pressure being 50 Pa, to obtain degassed nano-silica aerogel;

[0082] Step S2: heating water to 85° C., then adding polyvinyl alcohol thereto, wherein the mass ratio of polyvinyl alcohol to water is 1:9, stirring for 35 minutes, stopping stirring and heating, and filtering with a 0.4 μm filter membrane to obtain a polyvinyl alcohol solution;

[0083] Step S3: Immerse the degassed nano-silica aerogel obtained in step S1 into the polyvinyl alcohol solution obtained in step S2, with the mass ratio of nano-silica aerogel to polyvinyl alcohol solution being 1:10, stir for 40 seconds, centrifuge, separate, and dry to obtain the nano-silica aerogel foaming agent.

[0084] The method for preparing the foamed polypropylene material for the thermal insulation takeaway box comprises the following steps:

[0085] The polypropylene resin is placed at 80° C. and dried for 10 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and after cooling, pulling, and pelletizing, the foamed polypropylene material for the thermal insulation takeout box is obtained.

[0086] The temperature of the rear part of the barrel of the extruder was 160°C, the temperature of the middle part of the barrel was 165°C, the temperature of the front part of the barrel was 170°C, the temperature of the head was 175°C, and the screw speed was 75r / min.

[0087] Comparative Example 1

[0088] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials, measured by weight: 90 parts of polypropylene resin, 12 parts of nano-silicon dioxide aerogel, 1.2 parts of lubricant, and 1.6 parts of antioxidant.

[0089] The lubricant is prepared by mixing oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:1.

[0090] The antioxidant is antioxidant 1010.

[0091] The method for preparing the foamed polypropylene material for the thermal insulation takeaway box comprises the following steps:

[0092] The polypropylene resin is placed at 80° C. and dried for 10 hours; then the polypropylene resin, nano-silica aerogel, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and after cooling, pulling, and pelletizing, the foamed polypropylene material for the thermal insulation takeout box is obtained.

[0093] The temperature of the rear part of the barrel of the extruder was 160°C, the temperature of the middle part of the barrel was 165°C, the temperature of the front part of the barrel was 170°C, the temperature of the head was 175°C, and the screw speed was 75r / min.

[0094] Comparative Example 2

[0095] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials, measured by weight: 90 parts of polypropylene resin, 12 parts of nano-silicon dioxide aerogel foaming agent, 1.2 parts of lubricant, and 1.6 parts of antioxidant.

[0096] The lubricant is prepared by mixing oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:1.

[0097] The antioxidant is antioxidant 1010.

[0098] The preparation method of the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0099] Step S1: placing the nano-silica aerogel in a vacuum drying oven at 80° C. for degassing for 6 h, with the vacuum drying oven pressure being 50 Pa, to obtain degassed nano-silica aerogel;

[0100] Step S2: Immerse the degassed nano-silica aerogel obtained in step S1 in isooctyl alcohol for 10 minutes, wherein the mass ratio of the nano-silica aerogel to the isooctyl alcohol is 1:9, and centrifuge and separate to obtain isooctyl alcohol / nano-silica aerogel;

[0101] Step S3: dimethylformamide and polyvinylidene chloride are mixed, the mass ratio of polyvinyl alcohol to dimethylformamide is 1:9, stirring for 35 minutes and then stopping the stirring, filtering with a 0.4 micron filter membrane to obtain a polyvinylidene chloride solution;

[0102] Step S4: Immerse the isooctyl alcohol / nano-silica aerogel obtained in step S2 into the polyvinylidene chloride solution obtained in step S3, the mass ratio of isooctyl alcohol / nano-silica aerogel to polyvinylidene chloride solution being 1:10, stir for 40 seconds, centrifuge, separate, and dry to obtain the nano-silica aerogel foaming agent.

[0103] The method for preparing the foamed polypropylene material for the thermal insulation takeaway box comprises the following steps:

[0104] The polypropylene resin is placed at 80° C. and dried for 10 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and after cooling, pulling, and pelletizing, the foamed polypropylene material for the thermal insulation takeout box is obtained.

[0105] The temperature of the rear part of the barrel of the extruder was 160°C, the temperature of the middle part of the barrel was 165°C, the temperature of the front part of the barrel was 170°C, the temperature of the head was 175°C, and the screw speed was 75r / min.

[0106] Comparative Example 3

[0107] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials, measured by weight: 90 parts of polypropylene resin, 12 parts of nano-silicon dioxide aerogel foaming agent, 1.2 parts of lubricant, and 1.6 parts of antioxidant.

[0108] The lubricant is prepared by mixing oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:1.

[0109] The antioxidant is antioxidant 1010.

[0110] The preparation method of the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0111] Step S1: placing the nano-silica aerogel in a vacuum drying oven at 80° C. for degassing for 6 h, with the vacuum drying oven pressure being 50 Pa, to obtain degassed nano-silica aerogel;

[0112] Step S2: Immerse the degassed nano-silica aerogel obtained in step S1 in isooctyl alcohol for 10 minutes, wherein the mass ratio of the nano-silica aerogel to the isooctyl alcohol is 1:9, and centrifuge and separate to obtain isooctyl alcohol / nano-silica aerogel;

[0113] Step S3: dimethylformamide and polyurethane are mixed, the mass ratio of polyurethane to dimethylformamide is 1:9, stirring for 35 minutes and then stopping the stirring, filtering with a 0.4 micron filter membrane to obtain a polyurethane solution;

[0114] Step S4: Immerse the isooctyl alcohol / nano-silica aerogel obtained in step S2 into the polyurethane solution obtained in step S3, the mass ratio of isooctyl alcohol / nano-silica aerogel to polyurethane solution being 1:10, stir for 40 seconds, centrifuge, separate, and dry to obtain the nano-silica aerogel foaming agent.

[0115] The method for preparing the foamed polypropylene material for the thermal insulation takeaway box comprises the following steps:

[0116] The polypropylene resin is placed at 80° C. and dried for 10 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and after cooling, pulling, and pelletizing, the foamed polypropylene material for the thermal insulation takeout box is obtained.

[0117] The temperature of the rear part of the barrel of the extruder was 160°C, the temperature of the middle part of the barrel was 165°C, the temperature of the front part of the barrel was 170°C, the temperature of the head was 175°C, and the screw speed was 75r / min.

[0118] Comparative Example 4

[0119] A foamed polypropylene material for an insulated take-out box is composed of the following raw materials, measured by weight: 90 parts of polypropylene resin, 12 parts of nano-silicon dioxide aerogel foaming agent, 1.2 parts of lubricant, and 1.6 parts of antioxidant.

[0120] The lubricant is prepared by mixing oxidized polyethylene wax and ethylene bisstearamide in a mass ratio of 1:1.

[0121] The antioxidant is antioxidant 1010.

[0122] The preparation method of the nano-silicon dioxide aerogel foaming agent comprises the following steps:

[0123] Step S1: placing the nano-silica aerogel in a vacuum drying oven at 80° C. for degassing for 6 h, with the vacuum drying oven pressure being 50 Pa, to obtain degassed nano-silica aerogel;

[0124] Step S2: Immerse the degassed nano-silica aerogel obtained in step S1 in isooctyl alcohol for 10 minutes, wherein the mass ratio of the nano-silica aerogel to the isooctyl alcohol is 1:9, and centrifuge and separate to obtain isooctyl alcohol / nano-silica aerogel;

[0125] Step S3: mixing toluene and ethylene-vinyl acetate copolymer, wherein the mass ratio of ethylene-vinyl acetate copolymer to toluene is 1:9, stirring for 35 minutes and then stopping the stirring, filtering with a 0.4 micron filter membrane to obtain an ethylene-vinyl acetate copolymer solution;

[0126] Step S4: Immerse the isooctyl alcohol / nano-silica aerogel obtained in step S2 into the ethylene-vinyl acetate copolymer solution obtained in step S3, the mass ratio of isooctyl alcohol / nano-silica aerogel to the ethylene-vinyl acetate copolymer solution being 1:10, stir for 40 seconds, centrifuge, separate, and dry to obtain a nano-silica aerogel foaming agent.

[0127] The method for preparing the foamed polypropylene material for the thermal insulation takeaway box comprises the following steps:

[0128] The polypropylene resin is placed at 80° C. and dried for 10 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant, and antioxidant are uniformly mixed according to mass parts, extruded through a twin-screw extruder, and after cooling, pulling, and pelletizing, the foamed polypropylene material for the thermal insulation takeout box is obtained.

[0129] The temperature of the rear part of the barrel of the extruder was 160°C, the temperature of the middle part of the barrel was 165°C, the temperature of the front part of the barrel was 170°C, the temperature of the head was 175°C, and the screw speed was 75r / min.

[0130] Test Example 1:

[0131] Thermal conductivity test: refer to GB / T 3139-2005 standard for testing, cut the sample into a standard size of 300mm×300mm×10mm for testing, test three times, take the average value of the results, the results are shown in Table 1.

[0132] Table 1: Thermal conductivity

[0133]

[0134] Test Example 2

[0135] Cell density test:

[0136] Sample preparation: Cut the insulated takeaway boxes prepared in the examples and comparative examples into 1 mm thin slices using foamed polypropylene material, ensuring that the cut surface is flat.

[0137] Microscope observation: A scanning electron microscope (SEM) was used to observe the cross section of the sample and obtain microscopic images of the cells.

[0138] Image analysis: The microscopic images were analyzed by image processing software (ImageJ), the number of cells per unit area was counted, and the cell density was calculated.

[0139] Data calculation: The cell density was calculated based on the cross-sectional area of ​​the sample and the number of cells counted. There were 6 samples in each group and the average value was taken. The results are shown in Table 2.

[0140] Table 2: Cell density

[0141]

[0142] As can be seen from Tables 1 and 2, the thermal conductivity of Example 1 is the best, the pore density is the largest, and Example 2 is slightly worse than Example 1. This difference is mainly attributed to the use of degassed nano-silica aerogel in Example 1. In Example 1, the aerogel is degassed under vacuum conditions, and the air in the pores is removed, making it easier for isooctyl alcohol to evenly penetrate into the pores of the aerogel. This uniform filling reduces the air voids inside the aerogel, enhances the uniformity of isooctyl alcohol during the foaming process, forms a more dense and uniform pore structure, and results in a lower thermal conductivity. In contrast, Example 2 is not degassed, and the residual air in the aerogel may hinder the uniform penetration of isooctyl alcohol, resulting in a relatively uneven pore structure, and thus a slightly higher thermal conductivity.

[0143] Example 3 is slightly worse than Example 1. The main reason is that Example 3 does not use polyvinyl alcohol to encapsulate isooctyl alcohol / nano-silica aerogel. This makes isooctyl alcohol easy to volatilize or escape during the foaming process, and it is impossible to form pores uniformly in the aerogel. The lack of encapsulated nano-silica aerogel cannot effectively maintain the uniform distribution of isooctyl alcohol, resulting in uneven foaming, a significant decrease in pore density, and poor thermal insulation performance.

[0144] Example 4 did not perform isooctyl alcohol adsorption, which means that there was not enough blowing agent (isooctanol) to generate bubbles during the foaming process, resulting in almost no effective cell structure. This directly led to extremely low cell density and a significant decrease in the thermal insulation performance of the material.

[0145] The nano-silica aerogel used in Comparative Example 1 was used directly without any treatment. This resulted in the pores of the aerogel being filled with air and failing to uniformly adsorb isooctyl alcohol. During foaming, the air in the aerogel could not effectively participate in the foaming process, resulting in extremely low cell density and very poor thermal insulation performance.

[0146] Comparative Examples 2-4 used different packaging materials. Their oil solubility caused part of the isooctyl alcohol adsorbed by the silica aerogel to dissolve and detach during the packaging process. In addition, the packaging capabilities of polyvinylidene chloride, polyurethane, and ethylene-vinyl acetate copolymer were also poor. Therefore, polyvinyl alcohol had the best packaging effect.

Claims

1. A foamed polypropylene material for an insulated takeaway box, characterized in that: The composition is composed of the following raw materials by weight: 80-100 parts of polypropylene resin, 5-20 parts of nano-silicon dioxide aerogel foaming agent, 0.5-5 parts of lubricant, and 0.5-5 parts of antioxidant; The preparation method of the nano-silicon dioxide aerogel foaming agent comprises the following steps: Step S1: placing the nano-silica aerogel in a vacuum drying oven for degassing to obtain a degassed nano-silica aerogel; Step S2: immersing the degassed nano-silica aerogel obtained in step S1 in isooctyl alcohol, centrifuging and separating to obtain isooctyl alcohol / nano-silica aerogel; Step S3: heating water to 80-90° C., then adding polyvinyl alcohol thereto, stirring until the polyvinyl alcohol is dissolved, stopping stirring and heating, and filtering to obtain a polyvinyl alcohol solution; Step S4: immersing the isooctyl alcohol / nano-silica aerogel obtained in step S2 into the polyvinyl alcohol solution obtained in step S3, stirring, centrifuging, separating, and drying to obtain the nano-silica aerogel foaming agent; The degassing temperature in step S1 is 80-90°C, the time is 4-8h, and the air pressure in the vacuum drying oven is 10-50Pa; In step S2, the mass ratio of nano-silica aerogel to isooctyl alcohol is 1:(1-10); The mass ratio of isooctyl alcohol / nano-silica aerogel to polyvinyl alcohol solution in step S4 is 1:(9-11).

2. The foamed polypropylene material for the thermal insulation takeaway box according to claim 1, characterized in that: The lubricant is at least one of calcium stearate, oxidized polyethylene wax, zinc stearate, and ethylene bisstearamide.

3. The foamed polypropylene material for the thermal insulation take-out box according to claim 1, characterized in that: The antioxidant is at least one of antioxidant 1010, antioxidant 168, antioxidant DLTP, and antioxidant 1076.

4. The foamed polypropylene material for the thermal insulation take-out box according to claim 1, characterized in that: The mass ratio of polyvinyl alcohol to water in step S3 is 1:(8-10).

5. The method for preparing the foamed polypropylene material for the thermal insulation takeaway box according to any one of claims 1 to 4, characterized in that: The following steps are involved: The polypropylene resin is placed at 80-90° C. and dried for 8-12 hours; then the polypropylene resin, nano-silica aerogel foaming agent, lubricant and antioxidant are mixed uniformly according to mass parts, extruded through a twin-screw extruder, and subjected to cooling, pulling and pelletizing to obtain the foamed polypropylene material for the thermal insulation takeaway box; the temperature of the rear part of the barrel of the extruder is 155-160° C., the temperature of the middle part of the barrel is 160-165° C., the temperature of the front part of the barrel is 165-170° C., the head temperature is 170-175° C., and the screw speed is 70-80 r / min.

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