Transparent high-barrier film and preparation method thereof

Abstract

The invention relates to the field of packaging materials, and particularly discloses a transparent high-barrier film and a preparation method thereof. The transparent high-barrier film comprises a matrix film and chitin nanofiber films positioned on two sides of the matrix film, the matrix film is prepared from the following raw materials in parts by weight: 50 to 80 parts of PBAT resin, 20 to 30 parts of PLA resin, 25 to 40 parts of modified poly epsilon-caprolactone, 0.5 to 1 part of compatilizer, 0.1 to 1 part of antioxidant, 15 to 25 parts of filler and 0.5 to 0.8 part of nucleating agent; the modified poly (epsilon-caprolactone) is prepared from the following raw materials in parts by weight: 80 to 100 parts of epsilon-caprolactone, 3 to 5 parts of cellulose nanofiber, 2.5 to 3 parts of halloysite aluminum-magnesium-loaded hydrotalcite, 100 to 120 parts of ionic liquid and 1 to 2 parts of catalyst. The transparent high-barrier film disclosed by the invention not only has excellent oxygen and water vapor barrier properties, mechanical properties and good biodegradability, but also has the light transmittance of 90% or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of packaging materials, and more particularly to a transparent high-barrier film and a preparation method thereof. BACKGROUND

[0002] Food, medicine and electronic components are prone to spoilage or failure in the presence of oxygen and moisture. Using packaging materials with high barrier properties not only looks good, but also effectively protects the product, which is the key to solving this problem.

[0003] The commonly used high-barrier packaging materials on the market include aluminum foil, vacuum aluminum-coated film, EVOH, PVA and PVDC. These materials have good barrier properties, but each has its own obvious defects. For example, aluminum foil has poor ductility and is prone to pinhole formation, resulting in a decrease in barrier properties; vacuum aluminum-coated film has poor adhesion and is not resistant to cooking; and aluminum foil and vacuum aluminum-coated film are not transparent, so the contents of the package cannot be seen, and they cannot be heated in a microwave, limiting their use. The barrier properties of EVOH and PVA are greatly affected by the external humidity environment, and their barrier properties decrease significantly in high-temperature and high-humidity environments. PVDC-coated film has a yellowish appearance, and it produces carcinogenic substances, dioxins, during subsequent incineration. Moreover, these barrier packaging materials cannot be completely degraded when discarded into the environment, resulting in white pollution and microplastic pollution, which can cause deep pollution to the environment.

[0004] Although PBAT and PLA materials are highly concerned in the environmental protection field because of their degradable properties, which can effectively reduce pollution to the environment, they have a relatively obvious defect, i.e., they have no barrier properties. In order to make PBAT and PLA materials meet the actual use requirements, special film plating and coating processing are needed to improve their barrier properties, so that they can be better applied to packaging scenarios with high barrier performance requirements. However, the transparency of the degradable film after film plating and coating processing will be affected to some extent, and the transparency problem may affect the packaging of some products that require visual effects, such as the display of food freshness, color and other effects, which will greatly reduce the application of the degradable film in some high-end packaging fields.

[0005] In view of the related art described above, the inventors have found that it is necessary to provide a degradable film that has both high barrier and high transparency effects. SUMMARY

[0006] In order to make the degradable film have both high barrier and high transparency, the present application provides a transparent high-barrier film and a preparation method thereof.

[0007] In a first aspect, the present application provides a transparent high-barrier film, which adopts the following technical solution: A kind of transparent high-barrier film, including base film and the barrier layer located at both sides of base film, the barrier layer is chitin nanofiber film; The base film includes the following raw materials by weight: 50-80 parts of PBAT resin, 20-30 parts of PLA resin, 25-40 parts of modified poly-epsilon-caprolactone, 0.5-1 parts of a compatibilizer, 0.1-1 parts of an antioxidant, 15-25 parts of a filler, 0.5-0.8 parts of a nucleating agent. The modified poly-epsilon-caprolactone includes the following raw materials by weight: 80-100 parts of epsilon-caprolactone, 3-5 parts of cellulose nanofiber, 2.5-3 parts of aluminum-magnesium-aluminate hydrotalcite, 100-120 parts of an ionic liquid, and 1-2 parts of a catalyst.

[0008] By adopting the above technical solution, PCL and PBAT have certain compatibility in thermodynamics, and when they are blended, a relatively uniform mixture can be formed, and the addition of PCL can improve the crystallinity and processing performance of PBAT, thereby forming a more compact film structure, which helps to resist the penetration of gas and liquid and improves the barrier performance of the film. Under the action of PCL, the compatibility of PBAT resin and PLA resin increases, and a film material with strong mechanical properties is obtained.

[0009] And epsilon-caprolactone is used as a reaction monomer, and cellulose nanofiber and aluminum-magnesium-aluminate hydrotalcite are subjected to double grafting of poly-epsilon-caprolactone under the action of a catalyst. First, the hydroxyl groups of the cellulose nanofiber are activated under the action of the ionic liquid, and the active hydroxyl groups on the surface of the cellulose nanofiber initiate the ring-opening reaction of epsilon-caprolactone to form poly-caprolactone on the surface. In addition, after the cellulose nanofiber is dissolved in the ionic liquid, the molecules rearrange and form strong hydrogen bond interactions, so that the poly-caprolactone prepared therefrom has high transparency. Moreover, the ionic liquid can exchange ions with the aluminum-magnesium-aluminate hydrotalcite, thereby improving the interaction between the ionic liquid and the monomer epsilon-caprolactone and increasing the catalytic effect of the ionic liquid on the ring-opening reaction of epsilon-caprolactone. The halloysite can also be used to catalyze the ring-opening polymerization of epsilon-caprolactone to prepare poly-caprolactone. Moreover, the halloysite has good interaction and compatibility with PBAT and PLA. Meanwhile, the halloysite is a natural nanomaterial with good mechanical strength and stability. The aluminum-magnesium-aluminate hydrotalcite has a layered structure and is uniformly dispersed in the poly-caprolactone under the action of the halloysite, which can improve the crystalline structure of the poly-caprolactone and thereby improve the transparency of the poly-caprolactone. Moreover, the layered structure of the aluminum-magnesium-aluminate hydrotalcite can increase the penetration path of gas and increase the tortuosity, thereby reducing the permeability of gas and enhancing the barrier property.

[0010] Therefore, the poly-caprolactone is grafted on the cellulose nanofiber and the aluminum magnesium hydrotalcite loaded on the halloysite, so as to further improve the dispersibility of the cellulose nanofiber and the aluminum magnesium hydrotalcite loaded on the halloysite in the PBAT. The addition of the cellulose nanofiber can improve the transparency of the poly-caprolactone. The cellulose nanofiber has a small diameter and a high specific surface area, can be uniformly dispersed in the poly-caprolactone, reduces the scattering and reflection of light, and thus improves the transparency of the film. The addition of the aluminum magnesium hydrotalcite can improve the barrier property of the poly-caprolactone. The aluminum magnesium hydrotalcite has a layered structure, and can play a certain barrier effect on the gas or small molecules. When the aluminum magnesium hydrotalcite is compounded with the poly-caprolactone, a more compact and regular structure can be formed, the penetration path of the gas or small molecules is reduced, and thus the barrier property is improved.

[0011] The chitin nanofiber film with high transparency is used as the barrier layer on both sides of the base film. The chitin nanofiber film has high light transmittance and low haze. The nanoscale effect of the chitin nanofiber does not obviously reflect light and does not form scattering centers, so as to help maintain the high transparency of the material. The high aspect ratio and nanoscale effect of the chitin nanofiber film can significantly improve the gas barrier property of the composite material. When the chitin nanofiber film is located on both sides of the base film, the high gas barrier property can effectively prevent the penetration of gas molecules, so as to improve the barrier property of the overall film material.

[0012] Optionally, the thickness of the base film is 15 μm, and the thickness of the single-side barrier layer is 1.5 μm.

[0013] By adopting the above technical solution, the appropriate thickness of the base film and the barrier layer can not only provide the packaging material with strong mechanical properties, but also has excellent light transmittance and barrier property.

[0014] Optionally, the preparation method of the modified poly-ε-caprolactone is as follows: The cellulose nanofiber is dissolved in the ionic liquid under the protection of nitrogen, the aluminum magnesium hydrotalcite loaded on the halloysite is added, the ε-caprolactone and the catalyst are added after uniform mixing, and the reaction is carried out at 120-140 ℃ for 8-24 h under the protection of nitrogen. The ionic liquid is removed by washing, dichloromethane is added, and then stirring, filtration and vacuum drying are carried out.

[0015] By adopting the above technical solution, the cellulose nanofiber is dissolved in the ionic liquid, the influence of the morphology of the cellulose nanofiber on the transparency of the film material is reduced, the interlayer ion exchange of the aluminum magnesium hydrotalcite is carried out by using the ionic liquid, and the self-polymerization of the ε-caprolactone is promoted by using the cellulose nanofiber and the aluminum magnesium hydrotalcite loaded on the halloysite, so as to occur graft copolymerization.

[0016] Optionally, the filler is nano-silicon dioxide which is pulverized to 20-50 nm after being mixed with tristearin.

[0017] The cellulose nanofiber and the halloysite loaded aluminum magnesium hydrotalcite in the modified poly-epsilon-caprolactone in the base film are both water vapor difficult to pass fillers, which forces water vapor to diffuse along a more tortuous path in the material, thereby reducing the diffusion capacity inside the material to improve the water vapor barrier property. However, because water vapor will swell and plasticize the material, the activity of the molecular chain of the matrix increases, making it easier for water vapor to pass through, so the addition of cellulose nanofiber and halloysite loaded aluminum magnesium hydrotalcite has a better barrier effect on oxygen and carbon dioxide and other gases, and the water vapor barrier capacity needs to be improved; by using the above technical solution, the hydrophobicity of glyceryl tristearate is stronger, which is a water vapor barrier phase, and the nano-silica pretreated by glyceryl tristearate can be uniformly dispersed in the resin matrix to prevent agglomeration. At the same time, glyceryl tristearate can reduce the intermolecular force between PBAT and PLA, improve flexibility, and silica can enhance the mechanical properties such as tensile strength. Moreover, the particle size of nano-silica is small, so that the base film has better permeability. Moreover, the hydrophobic treated nano-silica can reduce the water vapor transmission rate of the material and prevent the diffusion of water vapor in the material. Moreover, the nano-silica wrapped with glyceryl tristearate is uniformly distributed in the base film, which can affect the diffusion path of water vapor molecules. Therefore, the addition of glyceryl tristearate can simultaneously reduce the dissolution and diffusion of water vapor in the film material, improve the water vapor barrier property of the material, and additionally, the addition of glyceryl tristearate for nano-silica pretreatment can increase the degradation capacity of the base film because the molecular chain of glyceryl tristearate is short and easy to disintegrate under composting conditions. Therefore, the base film has good water vapor barrier property, high transparency, good mechanical properties and biodegradability.

[0018] Optionally, the chitin nanofiber film is prepared by drying a barrier solution, and the barrier solution is a chitosan acetic acid solution containing maleic anhydride modified chitin nanofiber, and the concentration of the maleic anhydride grafted chitin nanofiber is 1-1.5wt%.

[0019] The maleic anhydride can fully destroy the hydrogen bond and Van der Waals force between the chitin fibers, so that the size of the chitin nanofiber is reduced, and the suspension stability is good. After the chitosan acetic acid solution is dried, a chitosan film can be formed on the base film, the adhesion between the maleic anhydride modified chitin nanofiber and the base film is increased, and the amino group in the molecular structure of the chitosan can interact with the hydroxyl group on the chitin fiber through hydrogen bond, so that a compact barrier layer without phase separation can be formed on the base film. In addition, the barrier film formed by the chitosan acetic acid solution can prevent the chitin fibers from curling, and a flat barrier film can be obtained. The hydrophobicity of chitosan is stronger than that of chitin nanofiber, and the use of chitosan covering can improve the hydrophobicity of the chitin nanofiber film and increase the barrier ability to water vapor. The chitin nanofiber has a high aspect ratio, can form an effective physical network structure in the chitosan film, and can enhance the mechanical properties of the material. The chitin nanofiber itself has good biodegradability, and the interaction with chitosan can make the composite material more easily attacked by microorganisms during the degradation process, thereby accelerating the degradation speed.

[0020] Optionally, the maleic anhydride modified chitin nanofiber is prepared by ultrasonic treatment after mixing maleic anhydride and chitin, and the mass ratio of chitin to maleic anhydride is 1:1-2.

[0021] By using the above technical scheme, when the amount of maleic anhydride is equal to or greater than the amount of chitin, the hydrogen bond and Van der Waals force in the chitin are fully destroyed, and then ultrasonic crushing is used to fully crush the chitin nanofiber and reduce its size, so that the chitin nanofiber is more uniformly distributed in the barrier film, the network structure is more compact, the penetration of gas or liquid molecules is effectively prevented, the barrier property is improved, and the reduced particle size of the chitin nanofiber can reduce the scattering and reflection of light in the film, so that more light can penetrate the barrier film and the transparency of the film is improved.

[0022] Optionally, the surface of the barrier layer is subjected to vapor deposition of perfluorodecyltrichlorosilane.

[0023] By using the above technical scheme, the deposition of perfluorodecyltrichlorosilane on the surface of the barrier layer can significantly reduce the surface of the barrier layer, improve the hydrophobicity of the barrier layer, optimize the barrier property of water vapor, improve the surface flatness of the barrier layer, effectively reduce light scattering, and make the barrier layer have more excellent light transmission performance.

[0024] Optionally, the catalyst is selected from at least one of stannous octoate, anhydrous zinc acetate, 4-dimethylaminopyridine and n-butyl titanate.

[0025] Optionally, the ionic liquid is selected from 1-ethyl-3-methylimidazolium bromide and / or 1-hexyl-3-methylimidazolium bromide.

[0026] Optionally, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 168 and antioxidant 1076; and the compatibilizer is selected from at least one of ADR compatibilizer, polycaprolactone and ethylene-methyl acrylate-glycidyl methacrylate copolymer.

[0027] In a second aspect, the application provides a preparation method of a transparent high-barrier film, which adopts the following technical scheme: A preparation method of a transparent high-barrier film, comprising the following steps: PBAT, PLA and modified poly-epsilon-caprolactone, a compatibilizer, an antioxidant, a filler and a nucleating agent are mixed, melted, extruded and granulated to obtain base film particles; The base film particles are extruded and blow molded to obtain a base film; A chitosan acetic acid solution is mixed with maleic anhydride modified chitin nanofibers to obtain a barrier solution; The barrier solution is uniformly coated on both sides of the base film, and dried at room temperature to form a barrier layer; Perfluorodecyltrichlorosilane is deposited on the barrier layer by a gas deposition method.

[0028] By adopting the above technical scheme, the raw materials of the base film are first blended and granulated to obtain uniformly mixed raw materials, the base film is obtained by blow molding, the barrier solution is coated on both sides of the base film, and the barrier layer is formed by drying at room temperature, and the barrier layer is treated by gas deposition, so that a film material with high transparency and good barrier property can be obtained.

[0029] In summary, the application has the following beneficial effects: 1. In the application, PBAT resin, PLA resin and modified poly-epsilon-caprolactone are used as raw materials of the base film, and chitin nanofiber film is arranged as a barrier layer on both sides of the base film. The chitin nanofiber has high light transmittance and does not scatter or reflect light, which can increase the transparency of the film and improve the barrier property and biodegradation rate of the film material. The modified poly-epsilon-caprolactone is prepared by grafting epsilon-caprolactone on the surface of cellulose nanofiber and halloysite loaded with aluminum magnesium hydrotalcite, which can improve the dispersibility of cellulose nanofiber and halloysite loaded with aluminum magnesium hydrotalcite in PBAT and PLA, and reduce the influence on transparency while increasing the barrier property. Thus, a film material with high transparency, high barrier property and biodegradable performance is prepared, which is more environmentally friendly, widely used in the packaging field, and can produce good social and economic benefits.

[0030] 2, The application preferably uses a chitosan acetic acid solution containing maleic anhydride modified chitin nanofibers to prepare the barrier layer. Maleic anhydride can destroy the hydrogen bonds and van der Waals forces in chitin, reduce the size of chitin nanofibers, and make them more easily dispersed uniformly in the chitosan acetic acid solution to obtain a high-transparency barrier layer. At the same time, chitosan also improves the water vapor barrier performance of maleic anhydride modified chitin nanofibers. DETAILED DESCRIPTION

[0031] The following examples further illustrate the application.

[0032] Preparation example I of halloysite loaded aluminum magnesium hydrotalcite: 0.5 g of calcined halloysite at 600°C was mixed with 0.75 g of aluminum nitrate nonahydrate, 1.02 g of magnesium nitrate hexahydrate and 30 ml of water, and placed in a water bath at 50°C while adding a 20 ml aqueous solution containing 0.07 g of sodium carbonate and 0.42 g of sodium hydroxide dropwise to maintain a pH of 10, and then crystallized at 80°C for 24 h, washed with deionized water 3 times, and vacuum dried at 60°C overnight. The halloysite was selected from the Lingshou County Tuoyun Mine product with the product code TY-002.

[0033] Preparation example II of aluminum magnesium hydrotalcite: 0.75 g of aluminum nitrate nonahydrate, 1.02 g of magnesium nitrate hexahydrate and 30 ml of water were mixed, placed in a water bath at 50°C, while adding a 20 ml aqueous solution containing 0.07 g of sodium carbonate and 0.42 g of sodium hydroxide dropwise to maintain a pH of 10, and then crystallized at 80°C for 24 h, washed with deionized water 3 times, and vacuum dried at 60°C overnight.

[0034] Preparation examples 1-5 of modified poly-ε-caprolactone Preparation example 1: 5 g of cellulose nanofiber was added to 120 g of ionic liquid and dissolved under nitrogen protection, 3 g of halloysite loaded aluminum magnesium hydrotalcite was added, and after uniform mixing, 80 g of ε-caprolactone and 2 g of catalyst were added, and reacted at 140°C for 8 h under nitrogen protection. After cooling to room temperature, it was poured into deionized water for precipitation, and repeatedly filtered and washed to remove the ionic liquid. Anhydrous ethanol was used to wash off the excess ε-caprolactone, dichloromethane was added, and stirred at room temperature for 48 h. The generated homopolymer was removed by filtration and washed with dichloromethane several times. After removing the dichloromethane by volatilization, vacuum drying was carried out for 12 h. The ionic liquid was 1- and 3-methyl imidazole bromide salt, the catalyst was stannous octoate, the cellulose nanofiber was selected from Funnano New Material Technology (Shanghai) with the product code 9112 and the model number 201, and the halloysite loaded aluminum magnesium hydrotalcite was prepared by preparation example I.

[0035] Preparation Example 2: 3g cellulose nanofiber was added into 100g ionic liquid and dissolved under nitrogen protection, 2.5g aluminosilicate supported magnesium hydrotalcite was added, after mixing evenly, 50g ε-caprolactone and 1g catalyst were added, and the mixture was reacted at 120℃ for 24h under nitrogen protection. After cooling to room temperature, it was poured into deionized water for precipitation, and repeated filtration and washing to remove ionic liquid. Excess ε-caprolactone was washed away with anhydrous ethanol, dichloromethane was added, and the mixture was stirred at room temperature for 48h. The generated homopolymer was removed by filtration and washing with dichloromethane several times. After removing dichloromethane by volatilization, vacuum drying was carried out for 12h. The ionic liquid was 1-hexyl-3-methylimidazolium bromide salt, the catalyst was anhydrous zinc acetate, and the cellulose nanofiber was selected from Funnan New Material Technology (Shanghai) with a product number of 9112 and a model number of 201. The aluminosilicate supported magnesium hydrotalcite was prepared by Preparation Example I.

[0036] Preparation Example 3: The difference from Preparation Example 1 is that aluminosilicate supported magnesium hydrotalcite is used instead of aluminosilicate supported magnesium hydrotalcite in equal mass. The aluminosilicate supported magnesium hydrotalcite is prepared by Preparation Example II.

[0037] Preparation Example 4: The difference from Preparation Example 1 is that no aluminosilicate supported magnesium hydrotalcite is added.

[0038] Preparation Example 5: The difference from Preparation Example 1 is that no cellulose nanofiber is added. Example

[0039] Example 1: A transparent high-barrier film, comprising a base film and a barrier layer located on both sides of the base film, the barrier layer being a chitin nanofiber film, the thickness of the base film being 15μm, and the thickness of the single-sided barrier layer being 1.5μm. The amount of raw material for the base film is shown in Table 1. The PBAT resin is selected from Dongguan Renju Plastic, with a model number of PBAT-801T. The PLA resin is selected from Dongguan Yili Plastic, with a model number of Nature Works4060D. The modified poly-ε-caprolactone is prepared by Preparation Example 1. The compatibilizer is ADR compatibilizer, selected from Shangxi (Shanghai) Chemical Auxiliary Agent Co., Ltd., with a model number of ADR-4468. The antioxidant is antioxidant 1010. The filler is nano-silicon dioxide with a particle size of 50nm. The nucleating agent is selected from Henan Ruichete Chemical, with a model number of RQT-CH-6.

[0040] The preparation method of the above-mentioned transparent high-barrier film, comprising the following steps: S1, PBAT, PLA and modified poly-ε-caprolactone, compatibilizer, antioxidant, filler and nucleating agent were mixed at a speed of 300 rpm for 3 min, and then the mixed material was added into a double screw extruder with a length-diameter ratio of 50:1 for hot melt extrusion, drawing, cooling, and granulation to prepare the base film particles, and the temperature of each zone in the extruder was: zone 1 temperature 140℃, zone 2 temperature 150℃, zone 3 temperature 160℃, zone 4 temperature 160℃, zone 5 temperature 170℃, zone 6 temperature 170℃, die temperature 165℃, and screw speed 180 rpm; S2, the base film particles were put into a single screw extruder with a length-diameter ratio of 35:1 for extrusion blow molding to prepare a base film with a thickness of 15μm, and the temperature of each zone in the extruder was: zone 1 temperature 135℃, zone 2 temperature 145℃, zone 3 temperature 155℃, zone 4 temperature 160℃, zone 5 temperature 170℃, zone 6 temperature 170℃, die temperature 165℃, screw speed 250 rpm, drawing speed 10 m / min, and blow ratio 4:1; S3, chitin was treated by ultrasonic at a frequency of 22KHz and a power of 500W for 30min to prepare chitin nanofibers, which were then dispersed in pure water to prepare a barrier solution with a concentration of 1wt%; S4, the barrier solution was uniformly coated on both sides of the base film, and dried at room temperature for 24h to form a barrier layer with a single side thickness of 1.5μm.

[0041] Table 1 Raw material usage of base film in transparent high barrier film in examples 1-4 Example 2: A transparent high barrier film comprising a base film and a barrier layer on both sides of the base film, the barrier layer being a chitin nanofiber film, the thickness of the base film being 15μm, the thickness of the single side barrier layer being 1.5μm, and the raw material usage of the base film being shown in Table 1, wherein the PBAT resin is selected from Dongguan Renju Plastic, model number PBAT-801T, the PLA resin is selected from Dongguan Yili Plastic, model number Nature Works 4060D, the modified poly-ε-caprolactone is prepared by Preparation Example 2, the compatibilizer is ethylene-methyl acrylate-glycidyl methacrylate copolymer, selected from France Arkema, model number LOTADER AX8900, the antioxidant is antioxidant 68, the filler is nano-silicon dioxide with a particle size of 20nm, and the nucleating agent is selected from Henan Ruichete Chemical, model number RQT-CH-6.

[0042] The above-mentioned method for preparing a transparent high barrier film comprises the following steps: S1, PBAT, PLA and modified poly-ε-caprolactone, compatibilizer, antioxidant, filler and nucleating agent were mixed at a speed of 400 rpm for 5 min, and then the mixed material was added into a twin-screw extruder with a length-diameter ratio of 50:1 for hot melt extrusion, drawing, cooling, granulation to prepare the base film particles, and the temperature of each zone in the extruder was as follows: the temperature of the first zone was 145℃, the temperature of the second zone was 155℃, the temperature of the third zone was 165℃, the temperature of the fourth zone was 165℃, the temperature of the fifth zone was 175℃, the temperature of the sixth zone was 175℃, the die temperature was 170℃, and the screw speed was 150 rpm; S2, the base film particles were put into a single-screw extruder with a length-diameter ratio of 35:1 for extrusion blow molding to prepare a base film with a thickness of 15 μm, and the temperature of each zone in the extruder was as follows: the temperature of the first zone was 140℃, the temperature of the second zone was 145℃, the temperature of the third zone was 150℃, the temperature of the fourth zone was 165℃, the temperature of the fifth zone was 175℃, the temperature of the sixth zone was 165℃, the die temperature was 16-℃, the screw speed was 250 rpm, the pulling speed was 10 m / min, and the blow-up ratio was 4:1; S3, chitin was treated by ultrasonic at a frequency of 22 KHz and a power of 500 W for 30 min to prepare chitin nanofiber, and then the chitin nanofiber was dispersed in pure water to prepare a barrier solution with a concentration of 1.5 wt%; S4, the barrier solution was uniformly coated on both sides of the base film, and dried at room temperature for 24 h to form a barrier layer chitin nanofiber film with a single-side thickness of 1.5 μm.

[0043] Example 3-4: a transparent high-barrier film, which is different from example 1 in that the amount of raw materials for the base film is shown in Table 1.

[0044] Example 5: a transparent high-barrier film, which is different from example 1 in that the nano-silica is pretreated as follows: glyceryl tristearate is vacuum dried at 40℃ for 12 h, then the glyceryl tristearate and nano-silica are mixed at a mass ratio of 0.2:1, and then subjected to closed mixing at a temperature of 80℃ and a speed of 50 r / min for 6 min, and then subjected to closed mixing at a temperature of 100℃ for 4 min, and then cooled and crushed to 50 nm.

[0045] Example 6: a transparent high-barrier film, which is different from example 5 in that the barrier solution is a chitosan acetic acid solution containing maleic anhydride modified chitin nanofiber, the concentration of the maleic anhydride modified chitin nanofiber is 1 wt%, the concentration of the chitosan acetic acid solution is 1 wt%, the maleic anhydride modified chitin nanofiber is prepared by mixing chitin and maleic anhydride at a mass ratio of 1:2, sealing, and then reacting at a constant temperature of 120℃ for 3 h, washing with ethanol, washing with pure water until the pH is 7, then dropping a 1 mol / l sodium hydroxide solution until the pH is 11, centrifuging and washing until the pH is 7.8, treating by ultrasonic at a frequency of 22 KHz and a power of 500 W for 30 min, and the rest of the parameters are the same as those in example 1.

[0046] Example 7: A kind of transparent high barrier film, the difference with example 5 is that the barrier liquid is the chitosan acetic acid solution containing maleic anhydride modified chitin nanofiber, the concentration of maleic anhydride modified chitin nanofiber is 1.5wt%, the concentration of chitosan acetic acid solution is 2wt%, maleic anhydride modified chitin nanofiber is mixed by chitin and maleic anhydride according to the mass ratio of 1:1, after sealing, constant temperature reaction is 3h under 120℃, ethanol washing, washing with pure water until pH is 7, then drop into the concentration of 1mol / l sodium hydroxide solution to pH is 11, centrifugal, washing until pH is 7.8, by frequency 22KHz, power 500W ultrasonic treatment 30min is prepared, and the rest parameters are same with example 1.

[0047] Example 8: A kind of transparent high barrier film, the difference with example 5 is that the barrier liquid is the chitosan acetic acid solution containing chitin nanofiber, the concentration of chitin nanofiber is 1wt%, the concentration of chitosan acetic acid solution is 2wt%, chitin nanofiber is prepared by chitin through frequency 22KHz, power 500W ultrasonic treatment 30min, and the rest parameters are same with example 1.

[0048] Example 9: A kind of transparent high barrier film, the difference with example 5 is that the barrier liquid is the aqueous solution containing maleic anhydride modified chitin nanofiber, the concentration of maleic anhydride modified chitin nanofiber is 1wt%, maleic anhydride modified chitin nanofiber is prepared by mixing chitin and maleic anhydride according to the mass ratio of 1:2, after sealing, constant temperature reaction is 3h under 120℃, ethanol washing, washing with pure water until pH is 7, then drop into the concentration of 1mol / l sodium hydroxide solution to pH is 11, centrifugal, washing until pH is 7.8, by frequency 22KHz, power 500W ultrasonic treatment 30min, and the rest parameters are same with example 1.

[0049] Example 10: A kind of transparent high barrier film, the difference with example 6 is that the preparation method of transparent high barrier film further includes step S5: using gas deposition method to deposit perfluorodecyltrichlorosilane on the barrier layer, the specific method is: the distance between barrier layer and perfluorodecyltrichlorosilane is 10cm, in the vacuum drying box with vacuum degree of 85kPa, keep 20min at room temperature 25℃.

[0050] Comparative example Comparative example 1: A kind of transparent high barrier film, the difference with example 1 is that the modified poly-epsilon-caprolactone is made by preparation example 3.

[0051] Comparative example 2: A kind of transparent high barrier film, the difference with example 1 is that the modified poly-epsilon-caprolactone is made by preparation example 4.

[0052] Comparative Example 3: A transparent high-barrier film, which is different from Example 1 in that the modified poly-ε-caprolactone is prepared according to Preparation Example 5.

[0053] Comparative Example 4: A transparent high-barrier film, which differs from Example 1 in that no barrier layer is provided on both sides of the base film, and the thickness of the prepared base film is 18 μm.

[0054] Performance testing Transparent high-barrier films were prepared according to the methods in the examples and comparative examples, and performance tests were performed according to the following methods. The test results are recorded in Table 2.

[0055] 1. Oxygen permeability: Refer to GB / T19789-2005 “Plastic Film and Sheeting for Packaging Materials - Oxygen Permeability Test - Coulometer Method”, test conditions: 23°C, 90% RH.

[0056] 2. Water vapor transmission rate: Refer to GB / T1037-1988 "Plastic film and sheeting water vapor transmission rate performance test cup method", test conditions 38 ℃, 90% RH.

[0057] 3. Light transmittance: Tested with reference to GB / T2410-2008 “Determination of light transmittance and haze of transparent plastics”, using Jinan Sanquan Zhongshi WD-120 light transmittance and haze meter.

[0058] 4. Tensile strength: Refer to GB / T1040.2-2006 standard 5A specimen, use SANS CMT4104 universal material testing machine, the tensile rate is 300mm / min, test 5 specimens for each group of samples, and take the average value of the results.

[0059] 5. Mass loss rate: Using the compost degradation method, prepare compost dishes according to the standard for determination of the disintegration rate of plastics in laboratory simulated composting conditions (ISO20200-2004). Place a transparent high-barrier film in the compost dish and maintain the compost temperature at 40°C. Add water to the dish and stir according to the time specified in the standard. Remove the 70-day compost sample, clean it, dry it in a vacuum oven to a constant weight, and then weigh it. Calculate the mass loss rate of the sample according to the following formula: D = (Mi - Mr) / Mi, where D is the mass loss rate, %; Mi is the initial mass of the test material, g; and Mr is the mass of the composted sample, g.

[0060] Table 2 Performance test results of transparent high barrier film It can be seen from the test data in Examples 1-4 and Table 2 that the modified poly-ε-caprolactone prepared by the specific preparation method in Examples 1-4 is blended with PBAT resin, PLA resin and the like to prepare a base film, and a dispersion liquid of chitin nanofiber is used to form a barrier layer on both sides of the base film, so that the film material prepared has good barrier ability to oxygen and water vapor, and the light transmittance is higher than 90%, the transparency is good, the mechanical strength is high, and the biodegradation speed is relatively fast, and the use is more environmentally friendly.

[0061] Compared with Example 1, Example 5 also uses glyceryl tristearate to pretreat nano-silicon dioxide, which is then used as a filler. It can be seen that the barrier ability of the film material prepared to water vapor is enhanced, the tensile strength is increased, the mass loss rate is increased, and the biodegradation speed is accelerated.

[0062] Compared with Example 5, Examples 6 and 7 also use maleic anhydride modified chitin nanofiber and chitosan acetic acid solution as a barrier liquid. It can be seen from Table 2 that the high barrier film has stronger barrier ability to water vapor, and the barrier effect to oxygen is not particularly obvious, but the light transmittance and mass loss rate are increased. It can be seen that the barrier layer formed by using maleic anhydride modified chitin nanofiber and chitosan acetic acid solution as a barrier liquid can increase the barrier property, light transmittance and degradation speed of the high barrier film.

[0063] Compared with Example 5, the barrier liquid in Example 8 is made of chitin nanofiber and chitosan acetic acid solution. As shown in Table 2, the light transmittance of the high barrier film prepared is not greatly affected, although the barrier ability to water vapor and oxygen is improved, but the improvement effect is obviously not as good as that of Examples 6 and 7.

[0064] In Example 9, the barrier liquid is formed by maleic anhydride modified chitin nanofiber and water, and the barrier layer is formed thereby. Compared with Example 5, the barrier ability to water vapor is not as good as that of Example 5, but the transparency is improved, the biodegradation speed is accelerated, but the improvement effect is not as good as that of Examples 6 and 7.

[0065] Compared with Example 6, Example 10 also performs gas phase deposition of perfluorodecyltrichlorosilane on the barrier layer, which improves the barrier ability of the high barrier film to water vapor, and increases the transparency, but affects the degradation speed to some extent.

[0066] Compared with Example 1, Comparative Example 1 uses the modified poly-ε-caprolactone prepared in Preparation Example 3, in which aluminum magnesium hydrotalcite is used, but not loaded on halloysite. It can be seen that the barrier ability of the high barrier film prepared to water vapor and oxygen is reduced, the gloss is reduced, and the tensile strength is reduced.

[0067] Comparative Example 2 uses the modified poly-ε-caprolactone prepared in Preparation Example 4, and no attapulgite loaded aluminum magnesium hydrotalcite is added compared with Preparation Example 1, so the barrier film has weakened barrier ability to water vapor and oxygen.

[0068] Comparative Example 3 uses the modified poly-ε-caprolactone prepared in Preparation Example 5, and no cellulose nanofiber is added compared with Preparation Example 1 in Example 1, and Table 2 shows that the high barrier film prepared in Comparative Example 3 has weakened barrier ability to water vapor and oxygen, and the transparency slightly decreases.

[0069] In Comparative Example 4, no barrier layer is provided, so the high barrier film prepared therefrom has weakened barrier ability to water vapor and oxygen, and the tensile strength significantly decreases, and the biodegradation rate also decreases.

[0070] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A transparent high barrier film, characterized in that: It includes a base film and barrier layers located on both sides of the base film, wherein the barrier layers are chitosan nanofiber films; The base film comprises the following raw materials in parts by weight: 50-80 parts of PBAT resin, 20-30 parts of PLA resin, 25-40 parts of modified poly-ε-caprolactone, 0.5-1 parts of compatibilizer, 0.1-1 parts of antioxidant, 15-25 parts of filler, and 0.5-0.8 parts of nucleating agent; The modified polyε-caprolactone comprises the following raw materials in parts by weight: 80-100 parts of ε-caprolactone, 3-5 parts of cellulose nanofibers, 2.5-3 parts of halloysite-supported aluminum-magnesium hydrotalcite, 100-120 parts of ionic liquid and 1-2 parts of catalyst.

2. The transparent high-barrier film according to claim 1, characterized in that: The preparation method of the modified poly-ε-caprolactone is as follows: Cellulose nanofibers are added to the ionic liquid and dissolved under nitrogen protection. Halloysite-loaded aluminum magnesium hydrotalcite is added and mixed evenly. ε-caprolactone and a catalyst are added. Under nitrogen protection, the reaction is carried out at 120-140°C for 8-24 hours. The ionic liquid is removed by washing, dichloromethane is added, stirred, filtered, and vacuum dried.

3. The transparent high-barrier film according to claim 1, characterized in that: The filler is nano silicon dioxide which is crushed to 20-50 nm after being subjected to banburying treatment with tristearate.

4. The transparent high-barrier film according to claim 1, characterized in that: The chitosan nanofiber membrane is prepared by drying a barrier liquid, wherein the barrier liquid is a chitosan acetic acid solution containing maleic anhydride-modified chitosan nanofibers, and the concentration of the maleic anhydride-grafted chitosan nanofibers is 1-1.5 wt %.

5. The transparent high-barrier film according to claim 4, characterized in that: The maleic anhydride modified chitin nanofibers are prepared by mixing maleic anhydride and chitin and then ultrasonically treating the mixture. The mass ratio of chitin to maleic anhydride is 1:1-2.

6. The transparent high-barrier film according to claim 1, characterized in that: Perfluorodecyltrichlorosilane is vapor-deposited on the surface of the barrier layer.

7. The transparent high-barrier film according to claim 1, characterized in that: The catalyst is selected from at least one of stannous octoate, anhydrous zinc acetate, 4-dimethylaminopyridine and n-butyl titanate.

8. The transparent high-barrier film according to claim 1, characterized in that: The ionic liquid is selected from 1-ethyl-3-methylimidazolyl bromide and / or 1-hexyl-3-methylimidazolyl bromide.

9. The transparent high-barrier film according to claim 1, characterized in that: The antioxidant is selected from at least one of antioxidant 1010, antioxidant 168 and antioxidant 1076; The compatibilizer is selected from at least one of ADR compatibilizer, polycaprolactone and ethylene-methyl acrylate-glycidyl methacrylate copolymer.

10. The method for preparing the transparent high-barrier film according to any one of claims 1 to 9, characterized in that: The following steps are involved: PBAT, PLA, modified poly-ε-caprolactone, a compatibilizer, an antioxidant, a filler, and a nucleating agent are mixed, melted, extruded, and granulated to obtain base film particles; Extrusion blow molding is performed on the base film particles to obtain a base film; The barrier liquid is prepared by mixing chitosan acetic acid solution with maleic anhydride modified chitin nanofibers; The barrier liquid is evenly coated on both sides of the base film and dried at room temperature to form a barrier layer; Perfluorodecyltrichlorosilane is deposited on the barrier layer by vapor deposition.

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