Anti-freezing vacuum bag capable of keeping freshness of fresh food and preparation method of anti-freezing vacuum bag

Abstract

The invention relates to the field of vacuum bag materials, in particular to an anti-freezing vacuum bag capable of keeping freshness of fresh food and a preparation method of the anti-freezing vacuum bag. The anti-freezing vacuum bag capable of keeping the freshness of the fresh food comprises the following raw materials: matrix resin, a solid filler, a polymerization compound additive, an antioxidant, a reinforcing agent, a toughening agent and the like. The vacuum bag material not only has good mechanical properties, but also can keep good strength stability in a low-temperature use environment, the probability of embrittlement, damage, softening and mechanical property reduction is greatly reduced, meanwhile, the barrier property of the vacuum bag material to molecules such as moisture and oxygen can be guaranteed, and the service life of the vacuum bag material is prolonged. The vacuum bag has excellent environmental moisture and temperature resistance in the long-term use process, the effective ice crystal resisting effect is achieved, the performance requirements of existing consumers for high-performance vacuum fresh-keeping materials are fully met, and very excellent application prospects are achieved.

Description

Technical Field

[0001] The present application relates to the field of vacuum bag materials, and more specifically to a freeze-resistant vacuum bag for maintaining the freshness of food and a preparation method thereof. Background Art

[0002] As people pay more and more attention to food safety and quality, how to effectively extend the shelf life of fresh food has become an important research topic. Fresh foods such as meat, seafood, and vegetables are extremely susceptible to temperature changes during storage and transportation, resulting in a decline in their quality. Traditional preservation methods often cannot fully meet the needs of modern cold chain logistics, especially when frozen for a long time, which can easily lead to problems such as food drying, discoloration, and texture changes. For example, although frozen storage can extend the shelf life of food, during the freezing and thawing process, food is easily damaged by ice crystals, resulting in damage to the cell structure and affecting the texture and flavor of the food.

[0003] To address these issues, some improved storage technologies have emerged on the market, such as vacuum packaging and antifreeze materials. Vacuum packaging reduces the contact of food with oxygen by extracting air from the bag, thereby delaying oxidation and microbial growth. Antifreeze materials reduce the formation of ice crystals and protect the cell structure of food by adding special ingredients to the packaging material.

[0004] Although the existing technology has improved the performance of vacuum bag materials, some problems still exist. For example, the durability of vacuum bag materials is poor. They are prone to becoming brittle, broken, softened, and their mechanical properties deteriorate at low temperatures, which can easily lead to the vacuum bag rupture and loss of the vacuum effect. On the other hand, due to the raw material problems of existing vacuum bag materials, the barrier properties of vacuum bag materials are poor, especially the poor barrier properties to moisture and oxygen, which can easily lead to a significant decline in the performance of the vacuum bag. Summary of the invention

[0005] Therefore, in order to effectively solve the above existing problems, the present application provides a freeze-resistant vacuum bag for maintaining the freshness of fresh food and a preparation method thereof. The vacuum bag material finally prepared by the present application not only has good mechanical properties, but also can maintain good strength stability in a low-temperature use environment, greatly reducing the probability of brittleness, breakage, softening and mechanical property degradation, and at the same time can ensure its barrier properties to molecules such as moisture and oxygen, maintain the vacuum bag's excellent resistance to environmental moisture and temperature during long-term use and achieve an effective anti-ice crystal effect, fully meet the performance requirements of existing consumers for high-performance vacuum preservation materials, and have very excellent application prospects.

[0006] As a preferred embodiment, the anti-freeze vacuum bag for maintaining freshness of fresh food has the following raw materials, measured by mass: 50 to 70 parts of base resin, 5 to 15 parts of solid filler, 5 to 10 parts of polymerization compounding auxiliary agent, 0.5 to 0.8 parts of antioxidant, 3 to 6 parts of reinforcing agent, 5 to 10 parts of toughening agent, 1 to 2 parts of antistatic agent, 1 to 3 parts of antifogging agent, and 0.3 to 0.6 parts of antibacterial agent.

[0007] As a preferred embodiment, the mass ratio of the base resin, the polymerization compounding auxiliary agent and the toughening agent is (58-65): (6-8): (7-8.5).

[0008] As a preferred embodiment, the base resin is a composition of a high-density polyethylene resin and a modified polyethylene resin.

[0009] As a preferred embodiment, the mass ratio of the high-density polyethylene resin to the modified polyethylene resin is (15-25): (35-45).

[0010] As a preferred embodiment, the mass ratio of the high-density polyethylene resin to the modified polyethylene resin is (18-22):(38-43).

[0011] As a preferred embodiment, the density of the high-density polyethylene resin is 0.95-0.97 g / cm 3 .

[0012] As a preferred embodiment, the melt index of the high-density polyethylene resin is 0.3-0.5 g / 10 min, condition: 190° C. / 5 kg.

[0013] As a preferred embodiment, the preparation method of the modified polyethylene resin specifically comprises the following steps: S1: evenly spreading high-density polyethylene resin in an irradiation plate with a thickness of ≤5 cm, and irradiating with an electron accelerator with an irradiation dose of 10 to 15 kGy; S2: premixing the irradiated high-density polyethylene with butyl acrylate, hydroxyethyl acrylate and dicumyl peroxide for 10 to 15 minutes, and putting them into an extruder for melt blending with a residence time of 8 to 10 minutes, and the temperature is divided into the first zone 170 to 175°C, the second zone 180 to 185°C, and the third zone 185 to 1 90℃, 190~195℃ in the fourth zone, screw speed of 180~220rpm, vacuum degassing pressure of -0.07~-0.05MPa, then extrude the material strips and water-cooling and pelletizing, and vacuum dry at 60~65℃ for 4~5h to obtain the pretreated material; S3: premix the pretreated material with glycidyl methacrylate, γ-aminopropyltriethoxysilane and diisopropylbenzene peroxide for 10~15min, melt-blend in an extruder under the same conditions as S2, and finally extrude the material strips and water-cooling and pelletizing, remove the unreacted materials, and vacuum dry at 60~65℃ for 4~5h to obtain.

[0014] As a preferred embodiment, the mass ratio of the high-density polyethylene, butyl acrylate and hydroxyethyl acrylate is (40-45): (3-3.5): (2-2.5).

[0015] As a preferred embodiment, the mass ratio of the pre-treated material, glycidyl methacrylate and γ-aminopropyltriethoxysilane is (35-40): (4-4.5): (1-1.2).

[0016] The use of the modified polyethylene resin as the main material of the vacuum bag material can greatly improve its mechanical properties while maintaining excellent waterproof, moisture-resistant, barrier and low-temperature resistance, thereby greatly reducing the probability of brittleness, breakage, softening and mechanical property degradation, and maintaining the vacuum bag with excellent resistance to environmental moisture and temperature during long-term use and achieving effective anti-ice crystal effect. The glycidyl methacrylate monomer introduced into the modified polyethylene resin can undergo a segmented grafting reaction with polyethylene through its epoxy group, thereby greatly improving the molecular chain polarity of the polyethylene resin system, prompting the polar groups in the system to achieve a guiding effect on gas oxygen molecules and water molecules, thereby greatly extending their diffusion path in the material, and through the silane cross-linking network, the cross-linked molecular chains of high-density polyethylene are arranged to form a densified network, which greatly reduces the size and connectivity of the permeation channels of gas molecules and water molecules in the material, thereby jointly improving the barrier properties of the vacuum bag material and resistance to high humidity environments.

[0017] On the other hand, the added butyl acrylate and hydroxyethyl acrylate are connected to the main chain of high-density polyethylene, and long-chain alkyl flexible side groups are introduced, so that the vacuum bag material can maintain good molecular chain mobility in a low-temperature environment through the flexible side group segments, further absorb impact energy, and inhibit the brittle fracture of long molecular chains in a low-temperature environment. In addition, the silane cross-linking network is used to limit the molecular chain slippage of the vacuum bag material system in a low-temperature environment, and the local stress is evenly dispersed throughout the material to avoid crack propagation caused by stress concentration, thereby obtaining excellent comprehensive performance of the vacuum bag material.

[0018] As a preferred embodiment, the solid filler is at least one of zinc oxide, titanium dioxide, calcium carbonate powder, barium sulfate powder and silicon dioxide.

[0019] As a preferred embodiment, the solid filler is a composition of titanium dioxide and silicon dioxide.

[0020] As a preferred embodiment, the mass ratio of titanium dioxide to silicon dioxide is (2-3):(6-8).

[0021] As a preferred embodiment, the mass ratio of titanium dioxide to silicon dioxide is (2-2.5):(6.5-7.5).

[0022] As a preferred embodiment, the polymer compounding auxiliary agent is a compound composition of polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol.

[0023] As a preferred embodiment, the mass ratio of the polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol is (3-4): (2-2.5): (0.6-1).

[0024] As a preferred embodiment, the mass ratio of the polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol is (3-3.5): (2-2.2): (0.8-1).

[0025] As a preferred embodiment, the degree of polymerization of the polyvinyl alcohol is 1600-1800.

[0026] As a preferred embodiment, the average molecular weight of the polyethylene glycol is 2000-6000.

[0027] As a preferred embodiment, the average molecular weight of the polyethylene glycol is 3000-4000.

[0028] By adding the above-mentioned polymer compounding additives, the barrier properties, waterproof and moisture resistance, and mechanical properties of the vacuum bag material can be jointly improved, while the low temperature resistance and anti-ice crystal properties of the material can be further improved. First, the hydrophilic glycerol groups and hydrophobic fatty acid chains in the compounding additives can effectively adsorb on ice crystal nucleation sites, such as impurities or polymer surface defects, and the ice-liquid interfacial energy is reduced through the joint action of the compounding additives, thereby inhibiting the rate of ice nucleation; secondly, the hydrogen bonds formed by the compounding additives work together with the modified polyethylene to bind the internal free water into bound water, restrict the migration of free water and slow down the formation of ice crystals, and finally delay the process of water molecules being orderly arranged into ice crystals through the dynamic action of hydrogen bonds. At the same time, its flexible chain segments interfere with the directional growth of ice crystals, thereby ensuring the comprehensive performance of the vacuum bag material, especially the anti-ice crystal performance.

[0029] As a preferred embodiment, the antioxidant is at least one of antioxidant 1010, antioxidant 1076, antioxidant DLTDP, antioxidant BHT and ascorbyl palmitate.

[0030] As a preferred embodiment, the antioxidant is antioxidant 1010.

[0031] As a preferred embodiment, the reinforcing agent is a composition of ethylene-vinyl alcohol copolymer and polyamide 6.

[0032] As a preferred embodiment, the mass ratio of the ethylene-vinyl alcohol copolymer to polyamide 6 is (3-4): (0.5-0.9).

[0033] As a preferred embodiment, the mass ratio of the ethylene-vinyl alcohol copolymer to polyamide 6 is (3.2-3.5): (0.6-0.8).

[0034] As a preferred embodiment, the toughening agent is a composition of ethylene-octene copolymer and styrene-butadiene-styrene block copolymer.

[0035] As a preferred embodiment, the mass ratio of the ethylene-octene copolymer to the styrene-butadiene-styrene block copolymer is (6-8):(2-3).

[0036] As a preferred embodiment, the mass ratio of the ethylene-octene copolymer to the styrene-butadiene-styrene block copolymer is (7-7.5):(2-2.5).

[0037] As a preferred embodiment, the antistatic agent is at least one of glycerol monostearate, polyetheresteramide and sodium dodecylbenzenesulfonate.

[0038] As a preferred embodiment, the antistatic agent is sodium dodecylbenzene sulfonate.

[0039] As a preferred embodiment, the antifogging agent is a composition of polyoxyethylene sorbitan monooleate and sorbitan monostearate.

[0040] As a preferred embodiment, the mass ratio of polyoxyethylene sorbitan monooleate to sorbitan monostearate is (2-2.4):(0.3-0.5).

[0041] As a preferred embodiment, the antibacterial agent is at least one of chitosan, polyhexamethylene biguanide hydrochloride and silver ion carrier.

[0042] As a preferred embodiment, the antibacterial agent is chitosan.

[0043] As a preferred embodiment, the preparation method of the anti-freezing vacuum bag for maintaining freshness of fresh food specifically includes the following steps: S1: preferentially mixing the matrix resin with the solid filler, the polymerization compounding auxiliary agent and the toughening agent in a high-speed mixer for 15 to 20 minutes, the mixing speed is 800 to 1000 rpm, and the mixing temperature is 80 to 90°C; S2: adding the remaining raw materials, increasing the speed to 1200 to 1400 rpm and mixing for 15 to 20 minutes to obtain a mixture; S3: granulating the mixture through a twin-screw extruder, the temperature segmentation is 175 to 180°C in zone one, 185 to 190°C in zone two, 192 to 195°C in zone three, and 200 to 205°C in zone four, the screw speed is 150 to 180 rpm, and mixed particles are obtained; S4: the mixed particles are made into a film through an extrusion casting mechanism, the die temperature is 210 to 215°C, the cooling roller temperature is 25 to 30°C, and the pulling speed is 15 to 20 m / min, and the mixture is obtained after completion.

[0044] The beneficial effects of this application are:

[0045] 1. The present application provides an anti-freezing vacuum bag for maintaining the freshness of fresh food, which not only has good mechanical properties, but also can maintain good strength stability in a low-temperature use environment, greatly reducing the probability of brittleness, breakage, softening and mechanical property degradation, and at the same time can ensure its barrier properties to molecules such as moisture and oxygen, maintain the vacuum bag's excellent resistance to environmental moisture and temperature during long-term use and achieve an effective anti-ice crystal effect, fully meeting the performance requirements of existing consumers for high-performance vacuum preservation materials.

[0046] 2. The present application provides an anti-freeze vacuum bag for maintaining the freshness of fresh food. The addition of modified polyethylene resin can improve the polarity of the molecular chain segments, prompting the polar groups in the system to achieve a guiding effect on the gas oxygen molecules and water molecules, thereby greatly extending their diffusion paths in the material. The silane cross-linked network arranges the cross-linked molecular chains of high-density polyethylene to form a densified network, which greatly reduces the size and connectivity of the penetration channels of gas molecules and water molecules in the material, thereby jointly improving the barrier properties of the vacuum bag material and its resistance to high humidity environments.

[0047] 3. The present application provides a freeze-resistant vacuum bag for maintaining the freshness of fresh food. Modified polyethylene resin is added, connected to the main chain of high-density polyethylene through butyl acrylate and hydroxyethyl acrylate, and long-chain alkyl flexible side groups are introduced, so that the vacuum bag material can maintain good molecular chain mobility in a low-temperature environment through the flexible side group segments, further absorb impact energy, and inhibit the brittle fracture of long molecular chains in a low-temperature environment. The silane cross-linking network is also used to limit the molecular chain slippage of the vacuum bag material system in a low-temperature environment, and the local stress is evenly dispersed throughout the material to avoid crack expansion caused by stress concentration, thereby obtaining excellent comprehensive performance of the vacuum bag material.

[0048] 4. The present application provides an anti-freeze vacuum bag for maintaining the freshness of fresh food. The addition of polymer compounding additives reduces the ice-liquid interfacial energy under the joint action, thereby inhibiting the rate of ice nucleation, and can also limit the migration of free water to slow down the formation of ice crystals. Finally, the dynamic action of hydrogen bonds delays the process of water molecules arranging into ice crystals in an orderly manner. At the same time, its flexible chain segments interfere with the directional growth of ice crystals, thereby ensuring the comprehensive performance of the vacuum bag material. DETAILED DESCRIPTION

[0049] The specific implementation examples will be used to more intuitively demonstrate and illustrate the contents of the invention content of this application. The following embodiments are only practical examples used to illustrate and explain the contents of the technical solutions in the specification and should not limit the scope of the claims to be protected by this application.

[0050] Example 1

[0051] The anti-freeze vacuum bag for keeping fresh food is composed of the following raw materials, by mass: 60.5 parts of base resin, 9.2 parts of solid filler, 6.5 parts of polymerization compounding auxiliary agent, 0.6 parts of antioxidant, 4.2 parts of reinforcing agent, 8.1 parts of toughening agent, 1.2 parts of antistatic agent, 1.6 parts of antifogging agent and 0.4 parts of antibacterial agent.

[0052] The matrix resin is a composition of high-density polyethylene resin and modified polyethylene resin, with a mass ratio of 20:40.5.

[0053] The preparation method of the modified polyethylene resin specifically comprises the following steps, calculated by mass: S1: spreading high-density polyethylene resin evenly on an irradiation plate with a thickness of ≤5 cm, and irradiating with an electron accelerator with an irradiation dose of 10 kGy; S2: premixing 42.5 parts of irradiated high-density polyethylene with 3.4 parts of butyl acrylate, 2.2 parts of hydroxyethyl acrylate and 0.09 parts of diisopropylbenzene peroxide for 15 minutes, and putting them into an extruder for melt blending with a residence time of 9 minutes, and the temperature is divided into the first zone at 175°C, the second zone at 180°C and the third zone at 190°C. 85℃, 195℃ in zone 4, screw speed of 200rpm, vacuum degassing pressure of -0.07MPa, then the extruded material strips are water-cooled and pelletized, and vacuum dried at 60℃ for 4h to obtain the pretreated material; S3: 38.8 parts of the pretreated material and 4.4 parts of glycidyl methacrylate, 1.1 parts of γ-aminopropyltriethoxysilane and 0.08 parts of diisopropyl peroxide are premixed for 12min, melt-blended in an extruder under the same conditions as S2, and finally extruded material strips are water-cooled and pelletized, the unreacted materials are removed, and vacuum dried at 60℃ for 4h to obtain.

[0054] The density of high-density polyethylene resin is 0.96g / cm 3 , melt index is 0.32 g / 10 min, condition: 190°C / 5 kg, purchased from DGDA-2463NT model product sold by The Dow Chemical Company of the United States.

[0055] The solid filler is a composition of titanium dioxide and silicon dioxide with a mass ratio of 2.2:7.

[0056] The polymer compounding auxiliary agent is a compound composition of polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol, with a mass ratio of 3.3:2.2:1.

[0057] Polyglycerol fatty acid esters were purchased from Hebei Hongtao Bioengineering Co., Ltd., China as industrial grade products.

[0058] The degree of polymerization of polyvinyl alcohol is 1700, and the product is PVA-1788.

[0059] The polyethylene glycol is a PEG-4000 product.

[0060] The antioxidant is antioxidant 1010.

[0061] The reinforcing agent is a composition of ethylene-vinyl alcohol copolymer and polyamide 6, with a mass ratio of 3.4:0.6; the ethylene-vinyl alcohol copolymer was purchased from the EVOH-F171B model product sold by Kuraray Co., Ltd. of Japan; and the polyamide 6 was purchased from the B3WG7 model product sold by BASF Co., Ltd. of Germany.

[0062] The toughening agent is a composition of ethylene-octene copolymer and styrene-butadiene-styrene block copolymer, with a mass ratio of 7.2:2.3; the ethylene-octene copolymer was purchased from the Engage 8150 model product sold by Dow Chemical Company of the United States; the styrene-butadiene-styrene block copolymer was purchased from the YH-791 model product sold by China Baling Petrochemical Company.

[0063] The antistatic agent is sodium dodecylbenzene sulfonate; the antifogging agent is a composition of polyoxyethylene sorbitan monooleate and sorbitan monostearate, with a mass ratio of 2.2:0.2.

[0064] The antimicrobial agent was chitosan with a deacetylation degree ≥ 90%, purchased from Jiangsu Dongju Biotechnology Co., Ltd., China.

[0065] The preparation method of a freeze-resistant vacuum bag for maintaining the freshness of fresh food specifically comprises the following steps: S1: preferentially mixing a matrix resin with a solid filler, a polymerization compounding auxiliary agent and a toughening agent in a high-speed mixer for 18 minutes, with a mixing speed of 800 rpm and a mixing temperature of 85°C; S2: adding the remaining raw materials and increasing the speed to 1200 rpm and mixing for 15 minutes to obtain a mixture; S3: granulating the mixture through a twin-screw extruder, with the temperature segmented into 180°C in zone one, 185°C in zone two, 195°C in zone three and 205°C in zone four, with a screw speed of 180 rpm, to obtain mixed particles; S4: making a film of the mixed particles through an extrusion casting mechanism, with a die temperature of 210°C, a cooling roller temperature of 25°C and a traction speed of 20 m / min, to obtain the bag after completion.

[0066] Example 2

[0067] The only difference between this embodiment and Embodiment 1 is that the anti-freeze vacuum bag for maintaining the freshness of fresh food has the following raw materials, in parts by mass: 58 parts of base resin, 9 parts of solid filler, 7.6 parts of polymerization compounding auxiliary agent, 0.5 parts of antioxidant, 4.1 parts of reinforcing agent, 7.2 parts of toughening agent, 1.3 parts of antistatic agent, 1.8 parts of antifogging agent and 0.3 parts of antibacterial agent.

[0068] The matrix resin is a composition of high-density polyethylene resin and modified polyethylene resin, with a mass ratio of 25:40.

[0069] The solid filler is a composition of titanium dioxide and silicon dioxide with a mass ratio of 2.5:6.5.

[0070] The polymer compounding auxiliary agent is a compound composition of polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol, with a mass ratio of 4:2:0.6.

[0071] Example 3

[0072] The only difference between this embodiment and Embodiment 1 is that the raw materials of the anti-freeze vacuum bag for maintaining the freshness of fresh food are, by mass, 58 parts of base resin, 9.5 parts of solid filler, 6 parts of polymerization compounding auxiliary agent, 0.6 parts of antioxidant, 3.8 parts of reinforcing agent, 8.3 parts of toughening agent, 1.5 parts of antistatic agent, 1.4 parts of antifogging agent and 0.3 parts of antibacterial agent.

[0073] The matrix resin is a composition of high-density polyethylene resin and modified polyethylene resin, with a mass ratio of 18:40.

[0074] The solid filler is a composition of titanium dioxide and silicon dioxide, with a mass ratio of 2:7.5.

[0075] The polymer compounding auxiliary agent is a compound composition of polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol, with a mass ratio of 3:2.5:1.

[0076] Comparative Example 1

[0077] The only difference between this comparative example and Example 1 is that the anti-freeze vacuum bag for maintaining the freshness of fresh food has the following raw materials, calculated by mass: 75 parts of base resin, 9 parts of solid filler, 2.2 parts of polymerization compounding auxiliary agent, 0.5 parts of antioxidant, 4.1 parts of reinforcing agent, 7.2 parts of toughening agent, 1.3 parts of antistatic agent, 1.8 parts of antifogging agent and 0.3 parts of antibacterial agent.

[0078] Comparative Example 2

[0079] The only difference between this comparative example and Example 1 is that the anti-freeze vacuum bag for maintaining the freshness of fresh food has the following raw materials, calculated by mass: 45 parts of base resin, 7.2 parts of solid filler, 14.5 parts of polymerization compounding auxiliary agent, 0.5 parts of antioxidant, 4.1 parts of reinforcing agent, 6.5 parts of toughening agent, 1.3 parts of antistatic agent, 1.8 parts of antifogging agent and 0.3 parts of antibacterial agent.

[0080] Comparative Example 3

[0081] The only difference between this comparative example and Example 1 is that the base resin is a composition of a high-density polyethylene resin and a modified polyethylene resin, with a mass ratio of 45:15.5.

[0082] Comparative Example 4

[0083] The only difference between this comparative example and Example 1 is that the base resin is a composition of a high-density polyethylene resin and a modified polyethylene resin, with a mass ratio of 30:30.5.

[0084] Comparative Example 5

[0085] The only difference between this comparative example and Example 1 is that the polymer compounding auxiliary agent is a compound composition of polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol, with a mass ratio of 5.5:1:0.2.

[0086] Comparative Example 6

[0087] The only difference between this comparative example and Example 1 is that the polymer compounding auxiliary agent is a compound composition of polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol, with a mass ratio of 1:3:2.

[0088] Comparative Example 7

[0089] The only difference between this comparative example and Example 1 is as follows: The preparation method of the modified polyethylene resin, calculated by mass, specifically comprises the following steps: S1: evenly spreading the high-density polyethylene resin in an irradiation plate with a thickness of ≤5 cm, and irradiating it with an electron accelerator with an irradiation dose of 10 kGy; S2: premixing 55.5 parts of the irradiated high-density polyethylene with 1.5 parts of butyl acrylate and 0.04 parts of diisopropylbenzene peroxide for 15 minutes, and putting them into an extruder for melt blending, with a residence time of 9 minutes, and the temperature is divided into 175°C in the first zone and 180°C in the second zone. The temperature of zone three is 185℃, that of zone four is 195℃, the screw speed is 200rpm, the vacuum degassing pressure is -0.07MPa, and then the extruded material strips are water-cooled and pelletized, and vacuum dried at 60℃ for 4h to obtain the pretreated material; S3: 58.5 parts of the pretreated material and 2.2 parts of glycidyl methacrylate, 0.5 parts of γ-aminopropyltriethoxysilane and 0.04 parts of diisopropyl peroxide are premixed for 12min, melt-blended in an extruder under the same conditions as S2, and finally extruded material strips are water-cooled and pelletized, the unreacted materials are removed, and vacuum dried at 60℃ for 4h to obtain the material.

[0090] Performance Evaluation

[0091] 1. The vacuum bag materials prepared in the examples and comparative examples were subjected to barrier property tests, and oxygen and water vapor transmission rates were tested according to ASTM D3985 and ASTM E96, respectively. The average values ​​of 10 tests were recorded in Table 1.

[0092] 2. The vacuum bag materials prepared in the examples and comparative examples were subjected to mechanical tests of tensile strength, referring to ASTM D638, and the average values ​​of 10 tests were recorded in Table 1.

[0093] 3. The vacuum bag materials prepared in the examples and comparative examples were subjected to low-temperature impact resistance tests, referring to ASTM F1306, and the average values ​​of 10 tests were recorded in Table 1.

[0094] 4. The vacuum bag materials prepared in the embodiments and comparative examples were subjected to a hydrolysis resistance test in an environment of 95% relative humidity and 53±2°C. After storage for 30 days, the tensile strength was tested again (according to the method of performance evaluation 2), and the tensile strength retention rate before and after the test was calculated. Tensile strength retention rate (%) = tensile strength after test / tensile strength before test × 100%. The average value of 10 tests was taken and recorded in Table 1.

[0095] Table 1 Performance evaluation results

[0096]

[0097] From the final performance test results of the embodiments and comparative examples, comparative examples 1 to 7 achieved worse performance results than the embodiments, while the embodiments adopted the best combination of modified resin and compounding auxiliary agent, which enabled the polar groups in the system to guide the gas oxygen molecules and water molecules, thereby greatly extending their diffusion paths in the material, and forming a densified network through the cross-linked molecular chains of high-density polyethylene arranged by the silane cross-linking network, which greatly reduced the size and connectivity of the permeation channels of gas molecules and water molecules in the material, thereby jointly improving the barrier properties of the vacuum bag material and the resistance to high humidity environments; and jointly reducing the ice-liquid interfacial energy, thereby inhibiting the ice nucleation rate, and limiting the migration of free water to slow down the formation of ice crystals, and finally delaying the process of water molecules being orderly arranged into ice crystals through the dynamic action of hydrogen bonds, while its flexible chain segments interfere with the directional growth of ice crystals, thereby ensuring the comprehensive performance of the vacuum bag material.

Claims

1. A freeze-resistant vacuum bag for maintaining freshness of fresh food, characterized in that: The anti-freezing vacuum bag for maintaining freshness of fresh food, calculated by weight, comprises the following raw materials: 50-70 parts of base resin, 5-15 parts of solid filler, 5-10 parts of polymerization compounding auxiliary agent, 0.5-0.8 parts of antioxidant, 3-6 parts of reinforcing agent, 5-10 parts of toughening agent, 1-2 parts of antistatic agent, 1-3 parts of antifogging agent, and 0.3-0.6 parts of antibacterial agent; The base resin is a composition of high-density polyethylene resin and modified polyethylene resin, with a mass ratio of (15-25): (35-45); The preparation method of the modified polyethylene resin specifically comprises the following steps: S1: evenly spreading high-density polyethylene resin in an irradiation plate with a thickness of ≤5 cm, and irradiating the plate with an electron accelerator, with an irradiation dose of 10-15 kGy; S2: premixing the irradiated high-density polyethylene with butyl acrylate, hydroxyethyl acrylate and dicumyl peroxide for 10-15 minutes, and putting the mixture into an extruder for melt blending with a residence time of 8-10 minutes, and dividing the temperature into the first zone 170-175°C, the second zone 180-185°C, the third zone 185-190°C, and the fourth zone 190-200°C. The temperature in the zone is 190-195°C, the screw speed is 180-220rpm, the vacuum degassing pressure is -0.07--0.05MPa, and then the extruded material is water-cooled and pelletized, and vacuum dried at 60-65°C for 4-5h to obtain a pretreated material; S3: premix the pretreated material with glycidyl methacrylate, γ-aminopropyltriethoxysilane and diisopropylbenzene peroxide for 10-15min, melt-blended using an extruder under the same conditions as S2, and finally extruded and water-cooled, pelletized, the unreacted materials are removed, and vacuum dried at 60-65°C for 4-5h to obtain the pretreated material.

2. The freeze-resistant vacuum bag for maintaining freshness of food according to claim 1, characterized in that: The mass ratio of the base resin, the polymerization compounding auxiliary agent and the toughening agent is (58-65): (6-8): (7-8.5).

3. The freeze-resistant vacuum bag for maintaining freshness of food according to claim 2, characterized in that: The mass ratio of the high-density polyethylene, butyl acrylate and hydroxyethyl acrylate is (40-45): (3-3.5): (2-2.5).

4. The freeze-resistant vacuum bag for maintaining freshness of food according to claim 3, characterized in that: The mass ratio of the pretreated material, glycidyl methacrylate and γ-aminopropyltriethoxysilane is (35-40): (4-4.5): (1-1.2).

5. The freeze-resistant vacuum bag for maintaining freshness of food according to claim 4, characterized in that: The solid filler is at least one of zinc oxide, titanium dioxide, calcium carbonate powder, barium sulfate powder and silicon dioxide.

6. The freeze-resistant vacuum bag for maintaining freshness of food according to claim 5, characterized in that: The polymer compounding auxiliary agent is a compound composition of polyglycerol fatty acid ester, polyvinyl alcohol and polyethylene glycol, and the mass ratio is (3-4): (2-2.5): (0.6-1).

7. The freeze-resistant vacuum bag for maintaining freshness of food according to claim 6, characterized in that: The polymerization degree of the polyvinyl alcohol is 1600-1800; the average molecular weight of the polyethylene glycol is 2000-6000.

8. The freeze-resistant vacuum bag for maintaining freshness of food according to claim 7, characterized in that: The reinforcing agent is a composition of ethylene-vinyl alcohol copolymer and polyamide 6, with a mass ratio of (3-4): (0.5-0.9).

9. The freeze-resistant vacuum bag for maintaining freshness of food according to claim 8, characterized in that: The toughening agent is a composition of ethylene-octene copolymer and styrene-butadiene-styrene block copolymer, with a mass ratio of (6-8): (2-3).

10. A method for preparing a freeze-resistant vacuum bag for maintaining freshness according to any one of claims 1 to 9, characterized in that: The specific steps include: S1: The matrix resin is preferentially mixed with the solid filler, the polymerization compounding auxiliary agent and the toughening agent in a high-speed mixer for 15-20 minutes, the mixing speed is 800-1000 rpm, and the mixing temperature is 80-90°C; S2: The remaining raw materials are added and the speed is increased to 1200-1400 rpm and mixed for 15-20 minutes to obtain a mixture; S3: The mixture is granulated by a twin-screw extruder, the temperature is divided into zone 1 175-180°C, zone 2 185-190°C, zone 3 192-195°C, zone 4 200-205°C, the screw speed is 150-180 rpm, and mixed particles are obtained; S4: The mixed particles are made into a film by an extrusion casting mechanism, the die temperature is 210-215°C, the cooling roller temperature is 25-30°C, and the pulling speed is 15-20 m / min. After completion, it is obtained.

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