阅读说明：本技术 一种包含磺化聚乙烯醇和聚乙二醇的智能控湿阻隔复合薄膜及其制备方法和应用 (Intelligent humidity control barrier composite film containing sulfonated polyvinyl alcohol and polyethylene glycol and preparation method and application thereof ) 是由 张杨 郑萃 宋建会 唐毓婧 姚雪容 潘国元 刘轶群 于 2019-09-20 设计创作，主要内容包括：本发明涉及一种包含磺化聚乙烯醇和聚乙二醇的智能控湿阻隔复合薄膜及其制备方法和应用。所述复合薄膜包括基层和附加层,其中,所述基层为一层或两层结构,所述附加层存在于基层的一侧或者同时存在于基层的两侧；所述基层为多孔薄膜,基层的材料为聚乙烯、聚丙烯、聚苯乙烯、聚对苯二甲酸二醇酯、聚己内酰胺中的至少一种；所述附加层包含磺化聚乙烯醇和聚乙二醇,以及任选的抗菌剂。本发明的智能控湿阻隔复合薄膜具有智能控湿能力,在相对湿度较低时保持果蔬湿度,在相对湿度较高时增大透湿从而防止水果蔬菜结露溃烂,并且具有氧气阻隔性能,可用于具有保鲜功能的果蔬盒及具有保鲜果蔬盒的冰箱。(The invention relates to an intelligent humidity control barrier composite film containing sulfonated polyvinyl alcohol and polyethylene glycol, and a preparation method and application thereof. The composite film comprises a base layer and an additional layer, wherein the base layer is of a one-layer or two-layer structure, and the additional layer is present on one side of the base layer or both sides of the base layer; the base layer is a porous film and is made of at least one of polyethylene, polypropylene, polystyrene, polyethylene terephthalate and polycaprolactam; the additional layer comprises sulfonated polyvinyl alcohol and polyethylene glycol, and optionally an antimicrobial agent. The intelligent humidity control barrier composite film has intelligent humidity control capability, can keep the humidity of fruits and vegetables when the relative humidity is low, can increase the moisture permeability when the relative humidity is high so as to prevent the fruits and vegetables from dewing and festering, has oxygen barrier performance, and can be used for fruit and vegetable boxes with fresh-keeping functions and refrigerators with fresh-keeping fruit and vegetable boxes.)

1. An intelligent humidity control and barrier composite film containing sulfonated polyvinyl alcohol and polyethylene glycol, which is characterized in that the composite film comprises a base layer and additional layers, wherein the base layer is of a one-layer or two-layer structure, and the additional layers are present on one side of the base layer or both sides of the base layer;

the base layer is a porous film and is made of at least one of polyethylene, polypropylene, polystyrene, polyethylene terephthalate and polycaprolactam;

the additional layer comprises sulfonated polyvinyl alcohol and polyethylene glycol, and optionally an antimicrobial agent.

2. The intelligent moisture control barrier composite film of claim 1, wherein:

based on the total weight of the single layer of the additional layer, the content of the sulfonated polyvinyl alcohol is 50-99 wt%, and preferably 66-98 wt%; the content of the polyethylene glycol is 1-50 wt%, preferably 2-34 wt%.

3. The intelligent moisture control barrier composite film of claim 1, wherein:

the content of the antibacterial agent is 0-20 wt%, preferably 0.1-10 wt% based on the total weight of the single layer of the additional layer.

4. The intelligent moisture control barrier composite film of claim 1, wherein:

when the additional layer is a cross-linked structure, the gel content of the additional layer is preferably 75-95 wt%, and more preferably 80-90 wt%.

5. The intelligent moisture control barrier composite film of claim 1, wherein:

the ion exchange capacity of the sulfonated polyvinyl alcohol is 0.5-2.5 mmol/g, preferably 0.75-2.0 mmol/g.

6. The intelligent moisture control barrier composite film of claim 1, wherein:

the molecular weight of the polyethylene glycol is 1000-100000, preferably 5000-50000.

7. The intelligent moisture control barrier composite film of claim 1, wherein:

the sulfonated polyvinyl alcohol is prepared by reacting polyvinyl alcohol with concentrated sulfuric acid, wherein the weight-average molecular weight of the polyvinyl alcohol is 10000-500000, and is preferably 20000-200000; the alcoholysis degree is 70-100%, and preferably 88-99%.

8. The intelligent moisture control barrier composite film of claim 1, wherein:

the antibacterial agent is at least one of nano zinc oxide, nano titanium oxide, nano silver, nano copper, sericin, quaternary ammonium salt, methyl hydroxybenzoate, potassium sorbate and chitosan.

9. The intelligent moisture control barrier composite film of claim 1, wherein:

the aperture of the base porous film is 0.02-10 microns, preferably 0.05-5 microns; the porosity is 30-80%, preferably 40-70%.

10. The intelligent moisture control barrier composite film of claim 1, wherein:

the thickness of the base layer is 5-1000 microns, preferably 10-100 microns; the thickness of the additional layer is 0.5-100 microns, and preferably 2-20 microns.

11. A method for preparing the intelligent moisture control barrier composite film according to any one of claims 1 to 10, which is characterized by comprising the following steps:

(1) dissolving or dispersing all components of the additional layer into a solvent to prepare a solution or dispersion liquid, and adjusting the pH value to 1-4;

(2) attaching the solution or dispersion liquid obtained in the step (1) to one surface or two surfaces of the base layer, and drying to obtain the composite film;

alternatively, in the case where the solution or dispersion of the additional layer is attached to both sides of the base layer in the above-described method, the solution or dispersion of the additional layer in step (1) is prepared as two additional layer solutions or dispersions having different component contents, which are attached to both sides of the base layer, respectively.

12. The method for producing a composite film according to claim 11, characterized in that:

the additional layer component in the step (1) comprises a cross-linking agent, and the dosage of the cross-linking agent is 0-10 wt%, preferably 0.1-7 wt% of the total weight of the sulfonated polyvinyl alcohol and the polyethylene glycol.

13. The method for producing a composite film according to claim 12, characterized in that:

the cross-linking agent is at least one of formaldehyde, glyoxal, malonaldehyde, succinaldehyde and glutaraldehyde.

14. The method for producing a composite film according to claim 11, characterized in that:

in the solution or dispersion liquid in the step (1), the mass concentration of the sulfonated polyvinyl alcohol is 1-10%, preferably 2-5%; the mass concentration of the polyethylene glycol is 0.1-5%, preferably 0.2-2.5%; and/or

The additional layer component in the step (1) comprises a cross-linking agent, and the mass concentration of the cross-linking agent is 0.1-2%, preferably 0.2-1%; and/or

In the step (1), the additional layer component comprises an antibacterial agent, and the mass concentration of the antibacterial agent is 0.1-1%, preferably 0.2-0.8%.

15. The method for producing a composite film according to claim 11, characterized in that:

the drying temperature in the step (2) is 50-100 ℃, and preferably 60-90 ℃.

16. The method for producing a composite film according to claim 11, characterized in that:

and (2) when the additional layer comprises a cross-linking agent, adding the cross-linking agent in the step (1) and/or drying the additional layer in the step (2) and then coating, wherein the coating step comprises independently preparing the cross-linking agent into a solution or a dispersion liquid, coating the solution or the dispersion liquid containing the cross-linking agent on one side or two sides of the dried film in the step (2) and drying the film again, and the mass concentration of the cross-linking agent in the coated solution or dispersion liquid is 0.5-10%, preferably 1-5%.

17. Use of the intelligent moisture control barrier composite film of any one of claims 1 to 10 in fresh-keeping packaging of vegetables and fruits.

Technical Field

The invention relates to the field of functional films, in particular to an intelligent humidity control barrier composite film containing sulfonated polyvinyl alcohol and polyethylene glycol, and a preparation method and application thereof.

Background

Fruits and vegetables are important food products for humans and are the main source from which people obtain basic nutrients (vitamins, minerals, complex carbohydrates, etc.). With the increasing living standard of people, the requirement on the freshness of fresh fruits and vegetables is higher and higher. The fruits and vegetables can continue to breathe and transpire after being harvested, and water dispersion and nutrient substance consumption can occur in the storage process. The respiration intensity of the fruits and vegetables is doubled when the temperature is increased by 10 ℃. The household fruit and vegetable fresh-keeping method is to put the fruits and vegetables in a refrigerator for refrigeration to slow down the respiration of the fruits and vegetables. In fruits and vegetables, moisture is an important ingredient, affecting the tenderness, freshness and taste of fruits and vegetables. Too low ambient humidity can result in water loss and weight loss in fruits and vegetables, but too high humidity can cause condensation of water on the surfaces of fruits and vegetables, growth of fungi, and acceleration of rotting and deterioration of fruits and vegetables. Therefore, the control of the storage humidity of the fresh fruits and vegetables is very important, and the preservation time of the fruits and vegetables can be prolonged. The barrier film can prevent the permeation of oxygen and other gases, inhibit the respiration of fresh fruits and vegetables and prolong the fresh-keeping time of fruits and vegetables.

The effects of several functional films, namely a temperature-sensitive moisture-permeable film, a silicon filter film and a moisture-sensitive moisture-permeable film, on the fruit and vegetable box for reducing the water loss in the market are not satisfactory. The temperature-sensitive moisture-permeable film is easy to dewet on the surface of the film under high humidity and low temperature; the silicon filter membrane has the function of moisture retention, but the moisture permeability cannot be changed along with the humidity; the moisture-sensitive and moisture-permeable membrane is formed by coating an adhesive solution on a paper-based substrate, the performance meets the requirement, but the preparation process is not environment-friendly, the process is complex, and the problem that the chlorine content exceeds the standard possibly exists in the processing process.

CN105986511A discloses a technique of applying natural high molecular polymer with good hydrophilic water retention and film forming property on base paper with high dry and wet strength, but the cost is high. CN104029449B discloses a coating film with large moisture permeability, wherein the base layer is an expanded polytetrafluoroethylene film layer, the coating is a polyurethane emulsion copolymerization coating containing hemp stem core superfine micropowder, and the film is used for an automobile lamp shell but does not have intelligent moisture control performance. CN103507339A discloses a moisture-sensitive and moisture-permeable film which retains regenerated cellulose in a substrate of nonwoven fabric, but does not have gas barrier properties. CN103107301A discloses an inorganic coating lithium ion battery diaphragm, contains multilayer structure, is porous flexible basement membrane and the coating of coating in basement membrane both sides respectively, and the coating contains polyvinyl alcohol and zeolite particle, and the auxiliary component of this coating does not have the metal salt composition, and the complex film does not have the function of intelligent accuse humidity. CN1864829A discloses a hydrophilic-hydrophobic bipolar composite membrane and a preparation method thereof, the membrane has a double-layer structure, the bottom layer is a porous support layer, the upper layer is a hydrophilic membrane containing lithium chloride, the membrane has high moisture permeability and strong barrier effect on other gas molecules, but does not have intelligent moisture control property. WO2013066012a1 discloses a porous membrane containing inorganic particles and a polymer binder layer containing hydrophilic and hydrophobic substances, which membrane is used to improve the thermal stability of a lithium battery separator and does not have intelligent humidity control properties. WO2012133805a1 discloses a moisture-permeable film whose porous substrate is preferably polytetrafluoroethylene, which is expensive, and whose high moisture-permeability is not good. US20030054155a1 discloses a waterproof moisture-permeable composite film, the hydrophobic layer being polytetrafluoroethylene and the hydrophilic layer being polyurethane, which has high moisture permeability but does not have intelligent moisture control properties.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide an intelligent humidity control barrier composite film which can keep moisture under the condition of low humidity, has strong humidity elimination capability under the condition of high humidity and has oxygen barrier property. The invention further provides a preparation method of the film, and the method is simple in process and low in cost. Therefore, the film provided by the invention is particularly suitable for being applied to fresh-keeping packaging of vegetables and fruits.

One of the objects of the present invention is to provide an intelligent moisture control barrier composite film comprising sulfonated polyvinyl alcohol and polyethylene glycol, the composite film comprises a base layer and an additional layer, wherein the base layer has a structure of one layer or two layers, and the additional layer is present on one side of the base layer or both sides of the base layer; the base layer is a porous film and is made of at least one of polyethylene, polypropylene, polystyrene, polyethylene terephthalate and polycaprolactam; the additional layer comprises sulfonated polyvinyl alcohol and polyethylene glycol, and optionally an antimicrobial agent.

In the invention, in order to realize intelligent humidity control, the base layer needs to be a porous film, and the additional layer needs to be a compact (thin) film. The concepts and terminology categories of porous and dense (thin) membranes are well known to those skilled in the art. The dense film as the additional layer is opposite to the concept of a porous film, i.e. a non-porous (thin) film, and can be prepared by applying a solution containing the additional layer components to the surface of the base layer and drying.

According to the invention, in the base material, the polyethylene is preferably at least one of High Density Polyethylene (HDPE), Linear Low Density Polyethylene (LLDPE) and Low Density Polyethylene (LDPE); the polypropylene is preferably at least one of homo-polypropylene, random co-polypropylene, block co-polypropylene and impact co-polypropylene.

According to the invention, the relative content of the sulfonated polyvinyl alcohol and the polyethylene glycol is limited to that a compact film can be formed, and preferably, in a single layer of the additional layer, the content of the sulfonated polyvinyl alcohol is 50-99 wt%, preferably 66-98 wt%, and more preferably 70-95 wt% based on the total weight of the single layer of the additional layer; the content of the polyethylene glycol is 1-50 wt%, preferably 2-34 wt%, and more preferably 5-30 wt%.

According to the present invention, the sulfonated polyvinyl alcohol may be commercially available or may be prepared by a conventional method of sulfonating polyvinyl alcohol. Preferably, the sulfonated polyvinyl alcohol is prepared by the reaction of polyvinyl alcohol with concentrated sulfuric acid. The reaction process is a common process in the prior art. Wherein the weight average molecular weight of the polyvinyl alcohol is 10000-500000, preferably 20000-200000; the alcoholysis degree is 70-100%, and preferably 88-99%; the ion exchange capacity of the prepared sulfonated polyvinyl alcohol is 0.5-2.5 mmol/g, preferably 0.75-2.0 mmol/g.

According to the invention, the molecular weight of the polyethylene glycol is preferably 1000-100000, and more preferably 5000-50000.

According to the invention, the antibacterial agent is an optional component, and the addition of the antibacterial agent can enable the intelligent humidity control film to have antibacterial performance.

In the single layer of the additional layer, the content of the antimicrobial agent is preferably 0 to 20 wt%, and more preferably 0.1 to 10 wt%, based on the total weight of the single layer of the additional layer. The antibacterial agent can be selected from antibacterial agents commonly used in the field, preferably at least one of nano zinc oxide, nano titanium oxide, nano silver, nano copper, sericin, quaternary ammonium salt, methyl hydroxybenzoate, potassium sorbate or chitosan, and more preferably at least one of nano zinc oxide, nano silver and quaternary ammonium salt. The quaternary ammonium salt can be selected from common quaternary ammonium salt bactericides, such as cetylpyridinium chloride.

According to the invention, the additional layer may also be a crosslinked structure. When the additional layer is a cross-linked structure, the gel content of the additional layer is preferably 75-95 wt%, and more preferably 80-90 wt%.

The crosslinking structure can be obtained by adding a crosslinking agent into the additional layer, and the addition of the crosslinking agent can enable the intelligent humidity control film to have better oxygen barrier property.

Preferably, the amount of the cross-linking agent is 0 to 10 wt%, more preferably 0.1 to 7 wt%, and still more preferably 2 to 6 wt% of the total weight of the sulfonated polyvinyl alcohol and the polyethylene glycol. The cross-linking agent can be selected from aldehyde cross-linking agents commonly used in the art, preferably one or a mixture of formaldehyde, glyoxal, malonaldehyde, succinaldehyde and glutaraldehyde, more preferably at least one of formaldehyde and glutaraldehyde, and more preferably glutaraldehyde.

The above-mentioned preferred components can give a film superior in moisture permeability and gas barrier properties.

In the invention, the pore diameter of the porous film is preferably 0.02-10 microns, more preferably 0.05-5 microns, and more preferably 0.1-2 microns; the porosity is 30-80%, preferably 40-70%; pores with a pore diameter within plus or minus one order of magnitude of the average pore diameter account for more than 50% of the total pores, preferably more than 80% of the total pores.

According to the invention, the thicknesses of the base layer and the additional layer can be determined according to needs, generally, the thickness of the base layer can be 5-1000 micrometers, preferably 10-100 micrometers, and further preferably 60-90 micrometers; the thickness of the additional layer can be 0.5-100 micrometers, and preferably 2-20 micrometers.

The invention also aims to provide a preparation method of the intelligent humidity control and barrier composite film containing the sulfonated polyvinyl alcohol and the polyethylene glycol, which comprises the following steps:

(1) fully dissolving or dispersing all components of the additional layer of the intelligent humidity control barrier composite film in water to prepare a solution or dispersion liquid, and adjusting the pH value to 1-4;

(2) coating the solution or dispersion liquid obtained in the step (1) on one surface or two surfaces of the base layer, and drying to obtain the composite film;

alternatively, in the case where the solution or dispersion of the additional layer is attached to both sides of the base layer in the above-described method, the solution or dispersion of the additional layer in step (1) is prepared as two additional layer solutions or dispersions having different component contents, which are attached to both sides of the base layer, respectively.

The base porous film may be commercially available as a single layer, or may be prepared by a conventional film-forming method in the prior art. For example, the film of the support layer is obtained by stretching polyethylene, polypropylene, polystyrene, polyethylene terephthalate and polycaprolactam or a combination thereof using a film stretching machine of the prior art by a general film stretching process. The film stretcher may be a unidirectional or bidirectional stretcher.

When the base layer is two layers, the two layers may be made of different materials. The base layer can be obtained commercially or can be prepared by a conventional film-making method of a composite film in the prior art.

The additional layer component in the step (1) may include a cross-linking agent, and the amount of the cross-linking agent is 0 to 10 wt%, preferably 0.1 to 7 wt% of the total weight of the sulfonated polyvinyl alcohol and the polyethylene glycol.

The cross-linking agent can be selected from aldehyde cross-linking agents commonly used in the art, preferably one or a mixture of formaldehyde, glyoxal, malonaldehyde, succinaldehyde and glutaraldehyde, more preferably at least one of formaldehyde and glutaraldehyde, and more preferably glutaraldehyde.

According to the invention, in the solution or dispersion liquid in the step (1), the mass concentration of the sulfonated polyvinyl alcohol is 1-10%, preferably 2-5%; the mass concentration of the polyethylene glycol is 0.1-5%, preferably 0.2-2.5%; and/or the additional layer component in the step (1) comprises a cross-linking agent, wherein the mass concentration of the cross-linking agent is 0.1-2%, and preferably 0.2-1%; and/or the additional layer component in the step (1) comprises an antibacterial agent, and the mass concentration of the antibacterial agent is 0.1-1%, preferably 0.2-0.8%.

The solvent used in step (1) may be a common solvent, and is preferably distilled water.

The solution or dispersion obtained in step (1) may be applied to a substrate using any conventional coating method, including but not limited to: brushing, curtain coating and spraying.

According to the invention, the drying temperature in the step (2) is preferably 50-100 ℃, and more preferably 60-90 ℃. The drying step may be accomplished in a variety of conventional heating devices, such as an oven. The drying time can be determined according to the requirement, for example, 5-30 min.

When the additional layer comprises a crosslinking agent, the crosslinking agent may be applied after the addition in step (1) and/or the drying in step (2), and the applying step comprises separately preparing the crosslinking agent into a solution or dispersion, applying the solution or dispersion containing the crosslinking agent to one or both sides of the dried film in step (2), and drying again.

According to the invention, the crosslinker can be added during the preparation of the solution or dispersion of the additional layer, or can be applied separately after drying, or can be added in two steps at both times. The step of separately coating after drying includes: and (3) independently preparing a cross-linking agent into a solution or a dispersion, coating the solution or the dispersion containing the cross-linking agent on one surface or two surfaces of the dried film in the step (2), and drying again to obtain the intelligent humidity control barrier composite film. In the solution or dispersion to be coated, the mass concentration of the crosslinking agent is preferably 0.5 to 10%, and more preferably 1 to 5%. The condition of the re-drying may be the same as the first drying condition.

The invention also aims to provide the intelligent humidity control barrier composite film containing sulfonated polyvinyl alcohol and polyethylene glycol and/or the application of the intelligent humidity control barrier composite film prepared by the preparation method in fresh-keeping packaging of vegetables and fruits.

According to the intensive research of the inventor, on one hand, the hydrophilicity of the polyethylene glycol is helpful for improving the moisture permeability of the membrane, and on the other hand, the adjacent oxygen atoms in the polyethylene glycol and sodium sulfonate groups in the sulfonated polyvinyl alcohol have ion chelation (shown in the following formula) to play a role of a macromolecular cross-linking agent, so that the free volume between the molecular chains of the sulfonated polyvinyl alcohol in the functional layer of the composite membrane is reduced, and the gas barrier property of the membrane is improved.

When the environment humidity is low, molecular chains of the functional layer of the composite film are arranged tightly, so that moisture is prevented from permeating; when the environmental humidity is high, the free volume among molecular chains is increased, and the moisture permeability is increased; therefore, the intelligent humidity control barrier composite film has intelligent humidity control capability. The humidity of the fruits and vegetables is kept when the relative humidity is low, the moisture permeability is increased when the relative humidity is high, so that the fruits and vegetables are prevented from dewing and festering, and the oxygen barrier property is realized, so that the fruit and vegetable box can be used for a fruit and vegetable box with a fresh-keeping function and a refrigerator with the fresh-keeping fruit and vegetable box.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Detailed Description

Preferred embodiments of the present invention will be described in more detail below.

The thicknesses of the base layer and the additional layer of the intelligent humidity control film are measured by a Shanghai Heishizi thickness meter; the pore structure including pore size and porosity was measured by mercury intrusion using an instrument, model autopore iii-9420 mercury intrusion gauge.

Polypropylene, F1002B, medium petrochemical Yangtze river petrochemical.

Polyethylene, L501(5000S), medium petrochemical actinolite.

Polystyrene, GH-660, China petrochemical Guangzhou petrochemical.

Dense biaxially oriented polypropylene film, medium petrochemical and marine refinery, F280Z.

Polyvinyl alcohol A, chemical industry of Xilonggan, with a trademark of PVA124, a weight average molecular weight of 105000 and an alcoholysis degree of 99%.

Polyvinyl alcohol B, chemical industry of Xilong, with a trademark of PVA1788, a weight-average molecular weight of 74800, and an alcoholysis degree of 88%.

Polyethylene glycol, carbofuran, number average molecular weight 5000.

Polyethylene glycol, carbofuran, number average molecular weight 10000.

Polyethylene glycol, carbofuran, number average molecular weight 20000.

Polyethylene glycol, carbofuran, number average molecular weight 50000.

99.5 percent of nano zinc oxide and carbofuran, and the grain diameter is 10-30 nm.

99.5 percent of nano-silver and carbofuran, and the grain diameter is 10-30 nm.

Formaldehyde, carbofuran, 50% aqueous solution.

Glutaraldehyde, carbofuran, 50% aqueous solution.

Sulfuric acid, national drug group chemical reagents ltd, analytical grade.

Film uniaxial stretcher, common in Guangzhou, MESI-LL.

Preparation example 1

This preparation is illustrative of the preparation of sulfonated polyvinyl alcohol and is represented by the following reaction scheme:

first, 2g of PVA (A) was dissolved in a beaker containing 30mL of distilled water, and the mixture was heated to completely dissolve the PVA (A), and then the beaker was placed in an ice-water bath at 0 to 5 ℃ and 1.0g of concentrated sulfuric acid (98 wt% in concentration, the same applies hereinafter) was slowly added thereto with continuous stirring. And then putting the beaker into a water bath kettle at 40 ℃, heating and stirring for reaction for 3h, then pouring 100mL of absolute ethyl alcohol into the reacted mixture, separating out white precipitate, carrying out centrifugal separation, continuously washing the white precipitate with absolute ethyl alcohol until the pH value of the white precipitate reaches 6.0, putting the obtained product into a drying oven, drying for 24h at 50 ℃ to obtain sulfonated polyvinyl alcohol, and measuring the ion exchange capacity of the sulfonated polyvinyl alcohol to be 1.12mmol/g by an acid-base titration method. Soaking the sulfonated polyvinyl alcohol in an ethanol-water solution containing 2% NaOH (the mass ratio of ethanol to water is 1:1) for 24h, filtering, and washing with a 50% ethanol water solution to be neutral to obtain sodium sulfonate type sulfonated polyvinyl alcohol (SPVA-A).

Preparation example 2

This preparation is intended to illustrate the preparation of sulfonated polyvinyl alcohols.

The same as in preparation 1, except that the amount of concentrated sulfuric acid was 0.5g to obtain SPVA-B, whose ion exchange capacity was 0.53mmol/g as measured by acid-base titration.

Preparation example 3

This preparation is intended to illustrate the preparation of sulfonated polyvinyl alcohols.

The same as in preparation 1, except that the amount of concentrated sulfuric acid was 1.7g to obtain SPVA-C, whose ion exchange capacity was 1.90mmol/g as measured by acid-base titration.

Preparation example 4

This preparation is intended to illustrate the preparation of sulfonated polyvinyl alcohols.

Same as in preparation 1, except that PVA-B was used in place of PVA-A to give SPVA-D, whose ion exchange capacity was 1.05mmol/g as measured by acid-base titration.

Example 1

2kg of polypropylene was stretched on a film uniaxial stretcher to form a polypropylene porous film.

7g of SPVA-A was added to 100mL of distilled water and sufficiently dissolved. 2.1g of polyethylene glycol (number average molecular weight: 10000), 0.2g of nano zinc oxide and 0.35g of glutaraldehyde were added to the obtained solution, and sufficiently stirred until uniform mixing was achieved, and the pH of the solution was adjusted to 2, to obtain a coating solution. Uniformly brushing the coating solution on one surface of a polypropylene porous film, then placing the polypropylene porous film in a drying oven, and drying for 10min at 70 ℃ to obtain an intelligent humidity control barrier composite film A1, wherein the thickness of a base layer is 70 microns, the pore diameter is 0.25 micron, the porosity is 50%, and the pores with the pore diameter within the range of plus or minus one order of magnitude of average pore diameter account for more than 85% of all pores; the thickness of the additional layer was 10 microns; the gel content of the additional layer was 90%.

Comparative example 1

A film was produced in the same manner as in example 1, except that the sulfonated polyvinyl alcohol was replaced with polyvinyl alcohol A in the coating liquid to give a film D1 with an additional layer having a thickness of 8.5. mu.m.

Comparative example 2

A film was produced in the same manner as in example 1, except that, instead of the polypropylene porous film, a dense polypropylene biaxially oriented film was used to obtain a film D2, the additional layer having a thickness of 12 μm.

Comparative example 3

A film was prepared according to the same method as in example 1, except that the coating solution contained no polyethylene glycol, to give an intelligent moisture control barrier composite film D3 with an additional layer thickness of 7 μm.

Example 2

2kg of polypropylene was stretched on a film uniaxial stretcher to form a polypropylene porous film.

7g of SPVA-B was added to 100mL of distilled water and sufficiently dissolved. 1.4g of polyethylene glycol (with a number average molecular weight of 5000), 0.2g of nano zinc oxide and 0.4g of formaldehyde were added to the obtained solution, and sufficiently stirred until uniform mixing was achieved, and the pH of the solution was adjusted to 2, to obtain a coating solution. Uniformly brushing the coating solution on one surface of a polypropylene porous film, then placing the polypropylene porous film in a drying oven, and drying for 12min at 60 ℃ to obtain an intelligent humidity control barrier composite film A2, wherein the thickness of a base layer is 70 microns, the pore diameter is 0.25 micron, the porosity is 50%, and the pores with the pore diameter within the range of plus or minus one order of magnitude of average pore diameter account for more than 85% of all pores; the thickness of the additional layer was 8 microns; the gel content of the additional layer was 85%.

Example 3

2kg of polyethylene was stretched on a film uniaxial stretcher to form a polyethylene porous film.

6g of SPVA-C was added to 100mL of distilled water, and sufficiently stirred until completely dissolved. Then, 0.8g of polyethylene glycol (with a number average molecular weight of 20000) and 0.2g of nano-silver were added, and the mixture was sufficiently stirred until uniform mixing was achieved, thereby obtaining a coating solution. Uniformly brushing the coating solution on two sides of a polyethylene porous film, then placing the polyethylene porous film in a drying oven, drying for 8min at 80 ℃ to obtain a dried film, uniformly brushing 10mL of aqueous solution containing 0.2g of formaldehyde and having a pH value of 2 on two sides of the dried film, and drying for 8min at 80 ℃ to obtain an intelligent humidity-controlling barrier composite film A3, wherein the thickness of a base layer is 75 micrometers, the pore diameter is 0.18 micrometers, the porosity is 42%, and pores with the pore diameter within the range of plus or minus one order of magnitude of average pore diameter account for more than 75% of all pores; the additional layer thickness was 7 microns; the gel content of the additional layer was 75%.

Example 4

Preparing a film according to the same method as the example 1, except that SPVA-D is used for replacing SPVA-A in the coating liquid to obtain an intelligent humidity control barrier composite film A4, and the thickness of the additional layer is 9 microns; the gel content of the additional layer was 83%.

Example 5

A film was prepared according to the same method as in example 1, except that the molecular weight of polyethylene glycol was 50000 to obtain an intelligent humidity-controlling barrier composite film a5 with an additional layer thickness of 10 μm; the gel content of the additional layer was 80%.

Example 6

2kg of polystyrene was stretched on a film uniaxial stretcher to obtain a polystyrene porous film.

7g of SPVA-A was added to 100mL of distilled water and sufficiently dissolved. 2.1g of polyethylene glycol (number average molecular weight: 10000), 0.2g of nano zinc oxide and 0.35g of glutaraldehyde were added to the obtained solution, and sufficiently stirred until uniform mixing was achieved, and the pH of the solution was adjusted to 2, to obtain a coating solution. Uniformly brushing the coating solution on one surface of a polystyrene porous film, then placing the polystyrene porous film in a drying oven, and drying the polystyrene porous film for 10min at 70 ℃ to obtain an intelligent humidity control film A6, wherein the thickness of a base layer is 82 microns, the pore diameter is 0.15 micron, the porosity is 35%, and the pores with the pore diameter within the range of plus or minus one order of magnitude of average pore diameter account for more than 80% of all pores; the thickness of the additional layer was 10 microns; the gel content of the additional layer was 87%.

Example 7

A film was prepared according to the same method as in example 1, except that no crosslinking agent was added to the coating solution to obtain an intelligent moisture-controlling barrier composite film a7 with an additional layer thickness of 8.7 μm; the gel content of the additional layer was 0.

Test example

The films were tested for water vapour transmission according to GB/T1037-1988 at a test temperature ofThe water vapor transmission per square meter of film per day (g/m) was obtained under test conditions of 50% and 90% of the transmitted surface humidity, respectively, at 25 DEG C²Day), data results are shown in table 1.

The gas barrier performance of the film is detected according to GB/T19789-³·cm/(cm²·s·Pa)]The data results are shown in table 1.

Table 1: test results of moisture permeability and gas barrier property of film

Serial number	Moisture permeability (50% RH)	Moisture permeability (90% RH)	Gas barrier property (O)2)
				A1	360	1697	6.4×10-6
D1	125	815	3.2×10-5
				D2	8	13	4.1×10-6
D3	328	1416	3.2×10-4
				A2	273	1355	8.5×10-6
A3	402	1584	4.6×10-6
				A4	393	1456	5.5×10-6
A5	346	1562	7.8×10-6
				A6	102	635	5.0×10-6
A7	358	1688	9.5×10-4

As can be seen from table 1, the addition of the polyethylene glycol of the present invention improves the oxygen barrier property of the intelligent moisture-control barrier composite film, and the film has the intelligent moisture-control capability, i.e., when the humidity is low, the moisture permeability of the intelligent moisture-control barrier composite film is reduced, and the intelligent moisture-control barrier composite film has the moisture-preserving capability, and can maintain the humidity of fruits and vegetables; on the contrary, when the humidity is higher, the moisture permeability of the intelligent moisture-control barrier composite film is improved, and the intelligent moisture-control barrier composite film has strong moisture-removing capacity, so that the fruit and vegetable can be prevented from dewing and festering.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.