A kind of atmosphere-controlled fresh-keeping film and its application

Abstract

The present invention discloses a modified atmosphere fresh-keeping film and its application. The raw material composition of the modified atmosphere fresh-keeping film includes hyperbranched polyethylene, branched polyethylene, and ethylene-vinyl acetate resin. By mass, the hyperbranched polyethylene is 15-45 parts, the branched polyethylene is 25-55 parts, and the ethylene-vinyl acetate resin is 15-40 parts. The fresh-keeping film processed with the raw material formula of the present invention not only ensures the air permeability of O2 and CO2, but also changes the water-permeable structure of the fresh-keeping film. In the packaging space, it can not only ensure a certain humidity environment to maintain the survival of fruits and vegetables, but also ensure that the water vapor generated during the respiration of fruits and vegetables is discharged outside the packaging. Thus, on the basis of achieving continuous and uniform water permeability, it effectively avoids the secondary pollution of fruits and vegetables caused by the water-permeable structure of the existing technology fresh-keeping film. The fresh-keeping film processed with the raw material formula of the present invention simultaneously realizes the air permeability and water permeability of the fresh-keeping film, thereby effectively prolonging the fresh-keeping time of fruits and vegetables.

Description

Technical Field

[0001] The invention belongs to the technical field of cling film, and in particular relates to a modified atmosphere cling film and application thereof. Background Art

[0002] Post-harvest decay of fruits and vegetables is a global problem. About 25% of fruit and vegetable products worldwide cannot be used due to decay and deterioration, and the loss rate of some perishable fruits and vegetables is even as high as 30% or more. According to statistics, the post-harvest loss rate of fruits in my country is about 25%, and that of vegetables is as high as 40% to 50%, with an economic value of about 75 billion yuan. The deterioration of fruits and vegetables is mainly due to the respiration, evaporation, growth of microorganisms, oxidation or browning of food ingredients, etc., and these effects are closely related to the environmental gases in which food is stored, such as O2, CO2, moisture and temperature. After being picked, fresh fruits will still undergo vigorous metabolic reactions, and at the same time, water will evaporate, consuming their own sugars and nutrients, decomposing to produce CO2, water and heat, resulting in the loss of nutrients and the deterioration of taste and flavor, which not only reduces its edible value, but also reduces its storage resistance and disease resistance. Therefore, in addition to adopting low-temperature storage to reduce its physiological activity, reduce respiration, and reduce the loss of nutrients, if the gas content and relative humidity of the food storage environment can be controlled, a low oxygen (generally 02 content of 1% to 5%) and appropriate CO2 concentration environment can be created to control the factors of food deterioration, so that it can maintain normal life activities, ensure disease resistance, and maximally inhibit respiration, the purpose of extending the shelf life or storage period of food can be achieved. Controlled atmosphere technology (i.e. reducing oxygen concentration and increasing carbon dioxide concentration) helps to inhibit the respiration of fruits and vegetables and extend the shelf life of fruits and vegetables. Its effect in fruit storage has been widely recognized by the industry.

[0003] On the other hand, with regard to the control of relative humidity in the fruit and vegetable storage environment, that is, the water permeability of the cling film, since water vapor is a polar substance, while oxygen and carbon dioxide are non-polar substances, the cling film that uses the modified atmosphere technology in the prior art cannot achieve the purpose of allowing both to pass through at the same time.

[0004] To this end, the existing technology uses a silicon window or micro-hole on the film to achieve this; however, the silicon window can only achieve limited local water permeability, and fruits and vegetables far away from the silicon window will still rot due to local water accumulation. Although the micro-hole method can achieve uniform water permeability, bacteria or viruses can also easily enter through the micro-holes, causing secondary infection and rotting of fruits and vegetables. In addition, the existing technology also uses a method of placing water-absorbing materials in the fresh-keeping bag to achieve dehumidification, such as a layer of water-absorbing material for each layer of fruits and vegetables, but this is not only cumbersome to package and too costly, but also wastes storage space.

[0005] In view of the above situation, the purpose of the present invention is to adjust the structure of the cling film by changing the formula of the cling film, and simultaneously achieve the air permeability and water permeability of the cling film, thereby extending the preservation time of fruits and vegetables. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides a controlled atmosphere fresh-keeping film and application of the controlled atmosphere fresh-keeping film in preserving fruits and vegetables.

[0007] The technical solution adopted by the present invention to solve the technical problem is:

[0008] A modified atmosphere fresh-keeping film, the raw materials of which include hyperbranched polyethylene, branched polyethylene and polyethylene vinyl acetate resin; wherein, by weight, the hyperbranched polyethylene accounts for 15-45 parts, the branched polyethylene accounts for 25-55 parts, and the polyethylene vinyl acetate resin accounts for 15-40 parts.

[0009] Preferably, the hyperbranched polyethylene is 25-35 parts, the branched polyethylene is 35-45 parts, and the polyethylene vinyl acetate resin is 20-30 parts.

[0010] Preferably, the hyperbranched polyethylene is 35 parts, the branched polyethylene is 40 parts, and the polyethylene vinyl acetate resin is 25 parts.

[0011] An application of a modified atmosphere fresh-keeping film, using the fresh-keeping film to package and store fruits and vegetables.

[0012] The beneficial effects of the present invention are:

[0013] The technical solution of the present invention uses hyperbranched polyethylene as a basic material to build a three-dimensional mesh gas channel for the cling film. The hyperbranched polyethylene has a uniformly distributed short branched structure and no long branched structure, so that after processing, no crystalline region will be formed to affect the gas permeability. The crystallinity of polyethylene is reduced by adjusting the composition of hyperbranched polyethylene and branched polyethylene, and the gas channel is formed by the polyethylene branch to ensure the permeability of carbon dioxide and oxygen; and the polyethylene vinyl acetate resin in the raw material formula can form an island structure on the cling film after processing. By adjusting its dosage, the density distribution of the island structure can be adjusted, thereby realizing the adjustment of the water permeability of the cling film. The cling film processed by the raw material formula of the present invention not only ensures the air permeability of O2 and CO2, but also changes the water permeable structure of the cling film, and can ensure a certain humidity environment in the packaging space to maintain the survival of fruits and vegetables, and can ensure that the water vapor generated by fruits and vegetables during the breathing process is discharged outside the packaging, thereby effectively avoiding the secondary pollution caused to fruits and vegetables by the water permeable structure of the prior art cling film on the basis of achieving continuous and uniform water permeability.

[0014] The invention adjusts the structure of the fresh-keeping film by changing the formula of the fresh-keeping film, and simultaneously realizes the air permeability and water permeability of the fresh-keeping film, thereby effectively prolonging the fresh-keeping time of fruits and vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1A This is a photo of the pakchoi before storage;

[0016] Figure 1B This is a photo of pakchoi after being sealed and stored at 5° C. for one month using the plastic wrap of Example 1;

[0017] Figure 2A This is a photo of the cucumbers before they were stored;

[0018] Figure 2B This is a photograph of the appearance of a cucumber after being sealed and stored at 5° C. for one month using the cling film of Example 1;

[0019] Figure 2C yes Figure 2B Photos of cucumbers after being cut open;

[0020] Figure 3A This is a photo of the lychees before they were stored;

[0021] Figure 3B This is a photograph of the appearance of litchi after being sealed and stored at 5° C. for one month using the preservative film of Example 1;

[0022] Figure 3C yes Figure 3B Photos of the preservation effect of lychee pulp;

[0023] Figure 4A This is a photo of the red plum before it was stored;

[0024] Figure 4B This is a photograph of the appearance of red plums after being sealed and stored at 5° C. for one month using the cling film of Example 1;

[0025] Figure 4C yes Figure 4B Photos of the preservation effect of red plum pulp;

[0026] Figure 5 It is an electron microscope picture of the cling film of Example 1. DETAILED DESCRIPTION

[0027] The invention provides a modified atmosphere fresh-keeping film, the raw materials of which include hyperbranched polyethylene, branched polyethylene and polyethylene vinyl acetate resin; wherein, by weight, the hyperbranched polyethylene accounts for 15-45 parts, the branched polyethylene accounts for 25-55 parts, and the polyethylene vinyl acetate resin accounts for 15-40 parts.

[0028] Preferably, the hyperbranched polyethylene is 25-35 parts, the branched polyethylene is 35-45 parts, and the polyethylene vinyl acetate resin is 20-30 parts.

[0029] The main factors affecting the air permeability of polyethylene are: the type, number and distribution of branches, molecular weight and molecular weight distribution; among them, the type and number of branches have a greater impact on the performance. Polyethylene is a crystalline polymer, and the crystallinity of polyethylene of different densities is also different. Crystallinity is linearly related to density, and they have a significant impact on many properties of polyethylene. Given that the presence of short branches in polyethylene will interfere with the crystallization of the main chain, increasing short branches will destroy crystallization and reduce density. Homopolymer high-density polyethylene contains very few short branches, so it has high crystallinity and density. Although LLDPE and HDPE are both linear polyethylene, LLDPE is completely copolymerized with ethylene and α-olefins. Since LLDPE contains more comonomers than high-density copolymers, there are many short branches on the linear main chain of LLDPE, resulting in low crystallinity and density; and because the type and number of its short branches vary with different comonomers, if the comonomer has a large number of carbon atoms and a large content in the copolymer, the density of the copolymer will also decrease greatly. The relationship between the air permeability and density of polyethylene is: the increase in density will cause the increase in the crystal barrier layer, and the air permeability will decrease accordingly. Compared with other plastic films, polyethylene films have greater air permeability to nitrogen, oxygen, and carbon dioxide, especially low-density polyethylene films have greater air permeability than polystyrene, polyvinyl chloride, polyethylene terephthalate and other films. The air permeability of various media to ethylene has a great relationship with its solubility in ethylene. Generally speaking, the air permeability of non-polar substances is greater than that of polar substances. Therefore, the present invention reduces the crystallinity of polyethylene by adjusting the composition of hyperbranched polyethylene and branched polyethylene, ensures the air permeability of the film, and forms gas channels through the side chains of polyethylene to achieve the guarantee of the permeability of carbon dioxide and oxygen.

[0030] Furthermore, generally speaking, water vapor is a polar substance, while oxygen and carbon dioxide are non-polar substances. To achieve the permeation of both, special design is required in the membrane formula and structure. Using hyperbranched polyethylene as the basic material, a three-dimensional network of gas channels is built for the membrane. Hyperbranched polyethylene has a uniformly distributed short branch structure and no long branch structure, so that after processing, no crystalline area is formed. The crystalline area has a great influence on gas permeation, which will greatly reduce the permeability of oxygen and carbon dioxide.

[0031] In addition, polyvinyl acetate resin has very good water vapor permeability due to the presence of ester groups. However, if polyvinyl acetate resin is used alone, it cannot be completely formed into a film and cannot be processed if the addition amount exceeds 5% because of its poor compatibility with polyethylene resin. However, polyethylene vinyl acetate resin improves its compatibility with polyethylene due to the presence of polyethylene structure, making production and processing possible. Therefore, polyethylene vinyl acetate resin is selected to form an island structure on the membrane, and the water permeability is adjusted by the density distribution of the island structure.

[0032] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments. It is to be understood that the present invention is not limited by the specific embodiments disclosed below, and those skilled in the art should know that improvements or changes made without departing from the spirit of the present invention should still be included in the protection scope of the present invention.

[0033] Example 1, the raw materials of the atmosphere-controlled fresh-keeping film are prepared according to the following mass parts:

[0034] Hyperbranched polyethylene 35 parts

[0035] 40 parts of branched polyethylene

[0036] 25 parts of polyethylene vinyl acetate resin

[0037] The resin particles are mixed, and a conventional fresh-keeping film blowing process (ie, a screw extrusion film blowing machine is used for preparation) is used to prepare a modified atmosphere fresh-keeping film with a film thickness of 28 μm.

[0038] The relevant performance indicators of the obtained film were measured, among which the CO2 permeability and O2 permeability were measured with reference to GB / T1038-2000 Plastic film and sheet gas permeability test method pressure difference method, and the water vapor permeability was measured with reference to GB / T1037-2021 Plastic film and sheet water vapor permeability performance measurement cup weight gain and weight loss method. The measured performance index results are as follows; at the same time, for the convenience of comparison, the performance indicators of the cling film with equivalent air permeability in the prior art are also given.

[0039]

[0040]

[0041] It can be seen from the data in the table that, compared with the cling film in the prior art, the water vapor permeability of the cling film in Example 1 is significantly improved when the air permeability is equivalent, so that the cling film has excellent air permeability and water permeability.

[0042] The storage experiment of vegetables and fruits was carried out using the cling film of Example 1, and the experimental results are shown in Figures 1 to 4. As can be seen from the figures, after the vegetables were refrigerated for one month, there was no yellowing, wilting or partial rot, and after the fruits were refrigerated for one month, there was no obvious shrinkage on the surface, and the flesh still retained a certain amount of moisture and no pathology occurred.

[0043] Reference Figure 5 , electron microscope image of Example 1; the image is generated by a SEM5000 scanning electron microscope of Guoyi Quantum. The electron microscope image clearly shows the island structure, and the size and distribution of the island structure are relatively uniform.

[0044] The following Examples 2-7 differ from Example 1 only in the mass fraction of the raw materials, and their processing technology and the method for determining the performance indexes of the membranes are the same as those of Example 1.

[0045] Example 2, the raw materials of the atmosphere-controlled fresh-keeping film are prepared according to the following mass parts:

[0046] Hyperbranched polyethylene 35 parts

[0047] 25 parts of branched polyethylene

[0048] 40 parts of polyethylene vinyl acetate resin The obtained modified atmosphere fresh-keeping film with a film thickness of 28 μm was tested and the performance index results were as follows:

[0049]

[0050] Example 3, the raw materials of the atmosphere-controlled fresh-keeping film are prepared according to the following mass parts:

[0051] Hyperbranched polyethylene 35 parts

[0052] 45 parts of branched polyethylene

[0053] 20 parts of polyethylene vinyl acetate resin The obtained modified atmosphere fresh-keeping film with a film thickness of 28 μm was tested and the performance index results were as follows:

[0054]

[0055] Example 4, the raw materials of the atmosphere-controlled fresh-keeping film are prepared according to the following mass parts:

[0056] Hyperbranched polyethylene 45 parts

[0057] 40 parts of branched polyethylene

[0058] Polyethylene vinyl acetate resin 15 parts The obtained modified atmosphere fresh-keeping film with a film thickness of 28 μm was tested and the performance index results were as follows:

[0059]

[0060] Example 5, the raw materials of the atmosphere-controlled fresh-keeping film are prepared according to the following mass parts:

[0061] Hyperbranched polyethylene 40 parts

[0062] 30 parts of branched polyethylene

[0063] 30 parts of polyethylene vinyl acetate resin The obtained modified atmosphere fresh-keeping film with a film thickness of 28 μm was tested and the performance index results were as follows:

[0064]

[0065] Example 6, the raw materials of the atmosphere-controlled fresh-keeping film are prepared according to the following mass parts:

[0066] Hyperbranched polyethylene 15 parts

[0067] 55 parts of branched polyethylene

[0068] 30 parts of polyethylene vinyl acetate resin The obtained modified atmosphere fresh-keeping film with a film thickness of 28 μm was tested and the performance index results were as follows:

[0069]

[0070] Example 7, the raw materials of the atmosphere-controlled fresh-keeping film are prepared according to the following mass parts:

[0071] Hyperbranched polyethylene 25 parts

[0072] 35 parts of branched polyethylene

[0073] 40 parts of polyethylene vinyl acetate resin The obtained modified atmosphere fresh-keeping film with a film thickness of 28 μm was tested and the performance index results were as follows:

[0074]

[0075] It can be seen from the above embodiments that the modified atmosphere cling film prepared by the raw material formula of the technical solution of the present invention can simultaneously achieve the air permeability and water permeability of the cling film, meet the needs of different fruits and vegetables, thereby extending the preservation time of fruits and vegetables and achieving the purpose of extending the storage period.

[0076] The technical solution of the present invention uses hyperbranched polyethylene as a basic material to build a three-dimensional mesh gas channel for the cling film. The hyperbranched polyethylene has a uniformly distributed short branched structure and no long branched structure, so that after processing, no crystalline region will be formed to affect the gas permeability. The crystallinity of polyethylene is reduced by adjusting the composition of hyperbranched polyethylene and branched polyethylene, and the gas channel is formed by the polyethylene branch to ensure the permeability of carbon dioxide and oxygen; and the polyethylene vinyl acetate resin in the raw material formula can form an island structure on the cling film after processing. By adjusting its dosage, the density distribution of the island structure can be adjusted, thereby realizing the adjustment of the water permeability of the cling film. The cling film processed by the raw material formula of the present invention not only ensures the air permeability of O2 and CO2, but also changes the water permeable structure of the cling film, and can ensure a certain humidity environment in the packaging space to maintain the survival of fruits and vegetables, and can ensure that the water vapor generated by fruits and vegetables during the breathing process is discharged outside the packaging, thereby effectively avoiding the secondary infection of fruits and vegetables caused by the water permeable structure of the prior art cling film on the basis of achieving continuous and uniform water permeability. The fresh-keeping film processed by the raw material formula of the present invention realizes the air permeability and water permeability of the fresh-keeping film simultaneously, thereby effectively prolonging the fresh-keeping time of fruits and vegetables.

Claims

1. A modified atmosphere fresh-keeping film, characterized in that: The raw materials of modified atmosphere cling film include hyperbranched polyethylene, branched polyethylene, polyethylene vinyl acetate resin; Wherein, by weight, the hyperbranched polyethylene is 15-45 parts, the branched polyethylene is 25-55 parts, and the polyethylene vinyl acetate resin is 15-40 parts.

2. The modified atmosphere cling film according to claim 1, characterized in that: The hyperbranched polyethylene accounts for 25-35 parts, the branched polyethylene accounts for 35-45 parts, and the polyethylene vinyl acetate resin accounts for 20-30 parts.

3. The modified atmosphere fresh-keeping film according to claim 1, characterized in that: The hyperbranched polyethylene accounts for 35 parts, the branched polyethylene accounts for 40 parts, and the polyethylene vinyl acetate resin accounts for 25 parts.

4. An application of the modified atmosphere cling film according to any one of claims 1 to 3, characterized in that: The modified atmosphere fresh-keeping film is used to package and store fruits and vegetables.

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