A highly transparent oxygen-barrier and water-barrier composite film and its preparation method

Abstract

This invention provides an oxygen- and water-barrier highly transparent composite film and its preparation method, relating to the field of packaging materials. The oxygen- and water-barrier highly transparent composite film provided by this invention improves the oxygen- and water-barrier properties and light transmittance of carboxymethyl cellulose (CMC) film by filling and crosslinking it with hydrotalcite nanosheets and dialdehyde cellulose. The high aspect ratio of the hydrotalcite nanosheets forms a brick-wall structure within the CMC nanosheets, extending the diffusion path of small gas molecules and thus enhancing the barrier properties of the base film. Dialdehyde cellulose acts both as a crosslinking agent and as a void filler in the "brick-wall structure," further improving the barrier properties of the base film and also contributing to the stability of the CMC film in water. The addition of a low proportion of hydrotalcite nanosheets improves the light transmittance of the base film.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials, specifically relating to an oxygen-barrier, water-barrier, highly transparent composite film and its preparation method. Background Technology

[0002] High-barrier packaging films are a crucial category of packaging materials. Traditional general-purpose high-barrier films are widely used for food, cigarette, and beverage preservation and odor control, as well as for moisture-proof packaging in the chemical, pharmaceutical, electronics, and military industries. These include K-film (PVDC coated film), metallized film, and aluminum foil. However, the complexity of their composition presents significant challenges in recycling. Therefore, developing high-barrier films with high recyclability or biodegradability is of great importance.

[0003] Cellulose is the most abundant renewable and biodegradable natural resource on Earth, and its development and utilization have been extensively studied in food, energy, biomedicine, textiles, and other fields. Carboxymethyl cellulose (CMC) is one of the most commonly used cellulose ether derivatives in the food industry, often used as a thickener and stabilizer in food. CMC is safe for consumption and has film-forming properties; its films are typically colorless, odorless, non-toxic, and transparent, exhibiting excellent oxygen, aroma, and oil barrier properties, and possessing certain anti-aging characteristics. Furthermore, CMC-based films can protect and carry functional compounds such as antibacterial agents, antioxidants, anti-browning agents, and nutritional enhancers. However, the abundant hydrophilic groups (such as carboxyl and hydroxyl groups) on the CMC molecular chain result in poor moisture permeability of its films. In addition, pure CMC packaging is insufficient for food and pharmaceutical packaging where high oxygen barrier properties are required; developing high-barrier films (oxygen and water barrier) based on CMC can further expand the application of CMC-based films.

[0004] Layered double hydroxides (LDHs, also known as hydrotalcites) are a class of ionic layered compounds composed of positively charged metal hydroxide plates, with anions and solvent molecules between the plates. Their chemical composition is typically expressed as [M...]. 1-x 2+ M x 3+ [(OH)2](A n- ) x / n ·zH2O, where M 2+ Including Mg 2+ Zn 2+ Ni 2+ Divalent metal ions; M 3+ These are trivalent metal ions on the plate, including Al. 3+ Fe 3+ Ga 3+ 、or Mn 3+A n- These are negatively charged anions between the layers, including CO32-. 2- Cl - NO 3- etc.; x is M 3+ With M 2+ +M 3+ The molar ratio is given by z, where z is the number of molecules between layers. Among them, magnesium-aluminum layered double hydroxide (MgAl-LDH) has been approved by regulators as a pharmaceutical and food contact material. At the same time, due to the high aspect ratio of the synthesized MgAl-LDH nanosheets, it is often blended with polymers to improve the barrier properties of the polymers.

[0005] Dialdehyde cellulose (DAC) can be obtained by selectively oxidizing cellulose with sodium periodate. DAC can be dissolved in boiling water to obtain water-soluble dialdehyde cellulose (sDAC). Because DAC contains a large number of aldehyde groups, it can react with polysaccharides containing -NH2, -OH, and other groups, acting as a cross-linking agent. Reports have confirmed that DAC has low cytotoxicity, exhibits good biocompatibility with mammalian cells, and shows good blood compatibility. Therefore, DAC or sDAC would be a green and safe cross-linking agent with applications in fields such as biomedicine and the food industry.

[0006] Currently, only a few publications report on the process of preparing thin films using CMC and LDH composites. In 2009, Kang et al. synthesized MgAl-LDH nanosheets using a homogeneous precipitation method and mixed them with a formamide solution of CMC to obtain a CMC / MgAl-LDH composite material, but they did not prepare a thin film. In 2013, Yadolahi et al. used a similar co-precipitation method to mix CMC with Mg and Al nitrates, and synthesized a CMC / MgAl-LDH composite by controlling pH, temperature, and reaction time; they also did not prepare a thin film. Subsequently, in 2014, Yadolahi et al. first prepared MgAl-LDH particles, then mixed their suspension with CMC, and prepared a CMC / MgAl-LDH composite film using a plate casting method. They characterized the film's water vapor barrier properties and light transmittance, but did not investigate the film's oxygen barrier properties. In 2018, Wang et al. synthesized relatively thick MgAl(NO3)-LDH nanosheets using a method similar to that of Kang et al., and then intercalated glass in a formamide solution to obtain monolayer MgAl-LDH nanosheets. Finally, taking advantage of the difference in positive and negative charges between MgAl-LDH nanosheets and CMC, they sequentially immersed and deposited MgAl-LDH nanosheet suspension and CMC solution onto a polypropylene film through layer-by-layer self-assembly to obtain a multilayer composite film of MgAl-LDH nanosheets and CMC (based on a polypropylene film) (the number of MgAl-LDH nanosheet and CMC assembly layers can be increased through multiple depositions). They also tested the barrier properties of the composite film against various gases (including O2, H2O, CO2, CH4, and N2). Meanwhile, in the patent of Han Jingbin, Wang Jiajie, and others (patent number: CN108211816B, the same authors as Wang et al., 2018), they used a similar method to prepare various composite films, including polyethylene / hydrotalcite nanosheets / carboxymethyl cellulose composite films. The preparation process was largely similar to that in their article, with slight modifications in details. For example, instead of alternately soaking and depositing MgAl-LDH nanosheet suspension and CMC solution onto a polypropylene film, they alternately spin-coated it onto a substrate such as polypropylene. Also, the patent did not describe adding formamide for exfoliation during the synthesis of hydrotalcite nanosheets. In the patent, they used GB / T1038-2000 and GB / T 21529-2008 standards to test the oxygen permeability and water vapor permeability of the composite films, respectively.

[0007] Compared with general packaging films, the composite films prepared by the aforementioned existing technologies have improved barrier properties. However, in the food packaging field, the composite films prepared by existing technologies still cannot fully meet the requirements for preservation, odor isolation, moisture protection, and environmental protection. Therefore, there is an urgent need for a transparent film with higher oxygen barrier and water vapor barrier properties. Summary of the Invention

[0008] In view of this, the purpose of this invention is to provide an oxygen- and water-barrier highly transparent composite film and its preparation method. This invention aims to solve the problem that existing films have poor oxygen and water vapor barrier properties, making it difficult to meet market demands.

[0009] To achieve the above objectives, the present invention provides an oxygen-barrier and water-barrier highly transparent composite film, comprising two or three of the following raw materials: carboxymethyl cellulose, hydrotalcite nanosheets, and dialdehyde cellulose.

[0010] The thickness of the composite film is 20–80 μm;

[0011] The hydrotalcite nanosheets have a diameter of 50–400 nm, a thickness of 1–2 nm, and an aspect ratio of 25:400.

[0012] Furthermore, the mass ratio of the hydrotalcite nanosheets to carboxymethyl cellulose is 0.1–50:100.

[0013] Furthermore, the mass ratio of dialdehyde cellulose to carboxymethyl cellulose is 0.1 to 20:100.

[0014] This invention also provides a method for preparing an oxygen-barrier and water-barrier highly transparent composite film, comprising the following steps:

[0015] S1. Preparation of an aqueous dispersion of hydrotalcite nanosheets;

[0016] S2. Preparation of dialdehyde cellulose aqueous solution: Dialdehyde cellulose is prepared and dispersed in distilled water to form a dispersion, which is then treated at high temperature to obtain dialdehyde cellulose aqueous solution;

[0017] S3. Solution mixing;

[0018] Add sodium carboxymethyl cellulose powder to the aqueous dispersion of hydrotalcite nanosheets, and then stir with a magnetic stirrer under water bath heating until the sodium carboxymethyl cellulose powder is completely dissolved. Then add dialdehyde cellulose aqueous solution and stir evenly.

[0019] S4. Casting to form a film;

[0020] Pour the well-stirred mixture from step S3 onto a square plastic petri dish. After water evaporates, a film is formed, thus obtaining the composite film.

[0021] Furthermore, in step S1, the preparation steps of the hydrotalcite nanosheet aqueous dispersion are as follows:

[0022] S1.1 Aluminum magnesium hydrotalcite was calcined in a muffle furnace at 450°C for 12 hours to obtain aluminum magnesium hydrotalcite;

[0023] S1.2 Alumina magnesium hydrotalcite was mixed evenly with glycine and distilled water, placed in a high-pressure reactor, and reacted at 100°C to obtain a translucent LDH gel.

[0024] S1.3 The LDH gel prepared in step S1.2 is dispersed in distilled water to form a suspension. After dialysis purification in distilled water for 3-5 days, it is then ultrasonically dispersed to obtain an aqueous dispersion of hydrotalcite nanosheets.

[0025] Furthermore, in step S1.3, the conditions for ultrasonic dispersion treatment are: 200–800 W for 20–60 min.

[0026] Furthermore, in step S2, the preparation steps of dialdehyde cellulose are as follows:

[0027] Add 39.6g of sodium periodate to a large beaker containing 2L of water. After the sodium periodate has completely dissolved, add 20g of cellulose. Stir and react at 25°C for 72 hours in the dark. After the reaction is complete, wash repeatedly with deionized water by centrifugation and collect the precipitate to obtain dialdehyde cellulose.

[0028] Furthermore, in step S2, the dissolution conditions for dialdehyde cellulose are: temperature 80–100°C, 1–2 hours.

[0029] Furthermore, in step S3, the water bath heating temperature is 25–90°C.

[0030] Furthermore, in step S4, the temperature at which water evaporates to form a film is 25–80°C.

[0031] Beneficial effects:

[0032] 1. This invention provides an oxygen- and water-blocking, highly transparent composite film with excellent oxygen and water vapor barrier properties as well as light transmittance. The oxygen transmittance of the composite film is 0.005–4.37 cm⁻¹. 3 ·m -2 ·d -1 The water vapor permeability of the composite membrane is 878–1360 g·m⁻¹. -2 ·d -1 The composite film is a transparent material. Compared with general packaging films, the composite film prepared in this application has several orders of magnitude higher oxygen barrier properties and significantly improved water vapor barrier properties. The composite film in this application has added new materials, which actually increases the visible light transmittance and has a certain ultraviolet absorption capacity, fully meeting the market's needs for product preservation, odor isolation, moisture prevention, and environmental protection.

[0033] 2. This invention provides a method for preparing an oxygen- and water-barrier highly transparent composite film. By using hydrotalcite nanosheets and water-soluble dialdehyde cellulose to fill and crosslink carboxymethyl cellulose, the oxygen- and water-barrier properties and light transmittance of the carboxymethyl cellulose film are improved. The hydrotalcite nanosheets with a large aspect ratio form a brick wall structure in the carboxymethyl cellulose nanosheets, which prolongs the diffusion path of small gas molecules (such as oxygen, water vapor, etc.), thereby enhancing the barrier properties of the base film. The water-soluble dialdehyde cellulose not only plays a crosslinking role, but also acts as a void filler in the "brick wall structure", which further improves the barrier properties of the base film and is also beneficial to the stability of the carboxymethyl cellulose film in water. The addition of a low proportion of hydrotalcite nanosheets can improve the light transmittance of the base film.

[0034] 3. The oxygen-barrier and water-barrier high-transparency composite film of the present invention has a simple preparation process and low cost; all materials used in the film are green and non-toxic, and have application potential in the fields of medicine and food.

[0035] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0036] Figure 1 This is a flowchart of a method for preparing an oxygen-barrier, water-barrier, highly transparent composite film according to the present invention;

[0037] Figure 2 TEM image of hydrotalcite nanosheets;

[0038] Figure 3 Comparison of oxygen permeability of CMC, CMC / LDH-NS, CMC / sDAC, and CMC / LDH-NS / sDAC composite films;

[0039] Figure 4 Water vapor transmission rate diagrams for CMC, CMC / LDH-NS, CMC / sDAC, and CMC / LDH-NS / sDAC composite films;

[0040] Figure 5 UV-Vis spectra of CMC, CMC / LDH-NS, CMC / sDAC, and CMC / LDH-NS / sDAC composite films;

[0041] Figure 6 Tensile strength diagrams for CMC, CMC / LDH-NS, CMC / sDAC, and CMC / LDH-NS / sDAC composite films;

[0042] Figure 7 Figures showing the elongation at break of CMC, CMC / LDH-NS, CMC / sDAC, and CMC / LDH-NS / sDAC composite films;

[0043] Figure 8 The effect of different LDH-NS contents on the oxygen permeability of CMC / LDH-NS composite films;

[0044] Figure 9 The effect of different LDH-NS contents on the water vapor transmission rate of CMC / LDH-NS composite films;

[0045] Figure 10 The effect of different s-DAC contents on the oxygen permeability of CMC / s-DAC composite films;

[0046] Figure 11 The effect of different s-DAC contents on the water vapor transmission rate of CMC / s-DAC composite films. Detailed Implementation

[0047] To make the technical solutions, advantages, and objectives of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the protection scope of this application.

[0048] This invention provides an oxygen-barrier and water-barrier highly transparent composite film, comprising two or three of the following raw materials: carboxymethyl cellulose, hydrotalcite nanosheets, and dialdehyde cellulose.

[0049] The thickness of the composite film is 20–80 μm;

[0050] Hydrotalcite nanosheets (magnesium aluminum hydrotalcite nanosheets, abbreviated as LDH-NS) are prepared by calcination reduction method. They are generated by recrystallizing commercially available hydrotalcite under high temperature and high pressure conditions in glycine aqueous solution. Hydrotalcite nanosheets have a diameter of 50-400 nm, a thickness of 1-2 nm, and an aspect ratio of 25:400.

[0051] The mass ratio of hydrotalcite nanosheets to carboxymethyl cellulose is 0.1–50:100, preferably 0.1–10:100, and more preferably 0.5–5:100;

[0052] The mass ratio of dialdehyde cellulose to carboxymethyl cellulose is 0.1 to 20:100, preferably 0.5 to 10:100, and more preferably 0.5 to 5:100.

[0053] like Figure 1 As shown, the present invention also provides a method for preparing an oxygen-barrier and water-barrier highly transparent composite film, comprising the following steps:

[0054] S1. Preparation of an aqueous dispersion of hydrotalcite nanosheets;

[0055] S1.1 Aluminum magnesium hydrotalcite was calcined in a muffle furnace at 450°C for 12 hours to obtain aluminum magnesium hydrotalcite;

[0056] S1.2 Alumina magnesium hydrotalcite was mixed evenly with glycine and distilled water, placed in a high-pressure reactor, and reacted at 100°C to obtain a translucent LDH gel.

[0057] S1.3 The LDH gel prepared in step S1.2 is dispersed in distilled water to form a suspension. The suspension is purified by dialyzing in distilled water for 3-5 days, and then ultrasonically dispersed to obtain an aqueous dispersion of hydrotalcite nanosheets.

[0058] The ultrasonic dispersion conditions are: 200–800 W for 20–60 min. The hydrotalcite nanosheets prepared by this invention do not need to be dried after dialysis purification and can be directly stored as a dispersion for later use.

[0059] S2. Preparation of dialdehyde cellulose aqueous solution: Dialdehyde cellulose is prepared and dispersed in distilled water to form a dispersion, which is then treated at high temperature to obtain dialdehyde cellulose aqueous solution;

[0060] The preparation steps of dialdehyde cellulose are as follows:

[0061] Take 39.6g of sodium periodate and add it to a large beaker containing 2L of water. After the sodium periodate is completely dissolved, add 20g of cellulose. Stir and react at 25℃ for 72h in the dark. After the reaction is completed, wash repeatedly with deionized water by centrifugation and collect the precipitate to obtain dialdehyde cellulose.

[0062] The dissolution conditions for water-soluble dialdehyde cellulose are: temperature 80–100℃, 1–2 h.

[0063] S3. Solution mixing;

[0064] Add sodium carboxymethyl cellulose powder to the aqueous dispersion of hydrotalcite nanosheets, and then stir with a magnetic stirrer under water bath heating until the sodium carboxymethyl cellulose powder is completely dissolved. Then add dialdehyde cellulose aqueous solution and stir evenly.

[0065] The water bath heating temperature is 25–90℃;

[0066] S4. Casting to form a film;

[0067] Pour the well-stirred mixture from step S3 onto a square plastic petri dish. After water evaporation, a film is formed at a temperature of 25–80°C. The composite film is then peeled off the plastic petri dish.

[0068] Example 1

[0069] 1. 5g of aluminum magnesium hydrotalcite was calcined in a muffle furnace at 450℃ for 12h to obtain approximately 2.7g of aluminum magnesium hydrotalcite (LDO). The obtained approximately 2.7g of LDO was mixed evenly with 4.1g of glycine and 28mL of distilled water, placed in a high-pressure reactor, and reacted at 100℃ for 48h to obtain a translucent LDH gel. The gel was then dispersed in distilled water to form a suspension. After dialysis in distilled water for 5 days, a two-dimensional layered hydroxide nanosheet (LDH-NS) suspension (colloidal) was obtained. The concentration of the prepared nanosheet suspension was determined and stored at 4℃ for later use.

[0070] 2. Add 39.6g of sodium periodate to a large beaker containing 2L of water. After the sodium periodate has completely dissolved, add 20g of cellulose (the molar ratio of sodium periodate to cellulose is 1.5:1). Stir the mixture at 25℃ for 72 hours in the dark. After the reaction is complete, repeatedly centrifuge and wash the precipitate with deionized water to collect the precipitate dialdehyde cellulose (DAC). Disperse the DAC in distilled water to form a dispersion, and then stir at 100℃ for about 1 hour to obtain an aqueous solution of DAC.

[0071] 3. Dilute the 0.05g LDH-NS suspension to 100mL solution, add 1g CMC powder and dissolve it in 100mL of diluted LDH-NS suspension. At this time, the mass ratio of LDH-NS to CMC is 5:100.

[0072] 4. Mix the powder thoroughly with a magnetic stirrer under water bath heating conditions at 50°C. After the CMC powder is completely dissolved, add an aqueous solution containing 0.02g of dialdehyde cellulose (sDAC). At this point, the mass ratio of sDAC to CMC is 5:100.

[0073] 5. The mixture was thoroughly stirred in a 50℃ water bath, and then poured onto a square plastic petri dish. The amount of membrane solution poured was such that the solid content in the membrane solution was approximately 5 mg / cm³. 2 The film was dried in a drying oven at 40°C for 24 hours to fully evaporate the solvent. After that, the dried film was peeled off, and the film thickness was about 40 μm. It was then stored under constant temperature and humidity conditions. The film prepared in this example was named CMC / LDH-NS / sDAC.

[0074] like Figure 2As shown, the LDH-NS prepared in step 1 of this embodiment was characterized using transmission electron microscopy (TEM). Measurements showed that the LDH-NS prepared in this embodiment had an average diameter of 260 nm, an average thickness of 1.5 nm, and an aspect ratio of 173. Figure 1 It can be seen that the hydrotalcite nanosheets prepared in this embodiment have a two-dimensional layered structure, uniform particle size distribution, and a large aspect ratio.

[0075] The oxygen permeability of the thin film prepared in this embodiment was tested according to GB / T 19789-2021 standard, and the water vapor permeability was tested according to GB / T1037-2021 standard. The light transmittance was measured using a dual-beam UV-Vis spectrophotometer from Beijing Purkinje General Chemicals Co., Ltd., within the range of 200–800 nm. The test results are as follows: Figure 3 , Figure 4 , Figure 5 As shown, the CMC-based composite film with 5 wt% LDH-NS and 5 wt% sDAC added in this embodiment has an oxygen permeability of 0.0053 cm⁻¹. 3 ·m -2 ·d -1 Water vapor transmission rate: 10¹⁰ g·m -2 ·d -1 Within the wavelength range of 420–800 nm, the light transmittance of the composite film in this embodiment is significantly higher than that of the pure CMC film, and it is a transparent material.

[0076] The tensile strength (TS) and elongation at break (EB) of the film were determined using an electronic universal testing machine according to the GB1040.3-2006 standard. The results are as follows: Figure 6 , Figure 7 As shown, compared to pure CMC film, the CMC / LDH-NS composite film prepared in this embodiment has a 22% higher TS and a 42% lower EB.

[0077] Example 2

[0078] 1. 5g of aluminum magnesium hydrotalcite was calcined in a muffle furnace at 450℃ for 12h to obtain approximately 2.7g of aluminum magnesium hydrotalcite (LDO). The obtained 2.7g LDO was mixed evenly with 4.1g glycine and 28mL distilled water, and placed in a high-pressure reactor. The mixture was reacted at 100℃ for 48h to obtain a translucent LDH gel. The gel was then dispersed in distilled water to form a suspension. After dialysis purification in distilled water for 5 days, a two-dimensional layered hydroxide nanosheet (LDH-NS) suspension (colloidal) was obtained. The concentration of the prepared nanosheet suspension was determined and stored at 4℃ for later use.

[0079] 2. Dilute the LDH-NS suspensions with contents of 0.01g, 0.05g, 0.15g, and 0.5g to 100mL each. Then, add 1g of CMC powder to each of the five 100mL LDH-NS diluted suspensions. After the CMC powder is completely dissolved, the mass ratio of LDH-NS to CMC in the five solutions is 1:100, 5:100, 15:100, and 50:100.

[0080] 3. The solution was thoroughly mixed in a 50℃ water bath, and then the membrane solution was poured onto a square plastic petri dish. The amount of membrane solution poured was such that the solid content in the membrane solution was 5 mg / cm³. 2 The film was dried in a drying oven at 40°C for 24 hours to fully evaporate the solvent. After that, the dried film was peeled off. The film thickness was about 40 μm. The film was stored under constant temperature and humidity conditions. The films prepared in this example were named CMC / LDH-NS-1, CMC / LDH-NS-5, CMC / LDH-NS-15, and CMC / LDH-NS-50, respectively.

[0081] The oxygen permeability of the film prepared in this embodiment was tested according to GB / T 19789-2021 standard, and the water vapor permeability of the film prepared in this embodiment was tested according to GB / T1037-2021 standard. The results are as follows: Figure 8 , Figure 9 As shown, the addition of LDH-NS to CMC can significantly reduce its oxygen barrier properties. The oxygen permeability of the CMC / LDH-NS composite film is 0.0309–2.144 cm⁻¹. 3 ·m -2 ·d -1 The water vapor transmission rate of the CMC / LDH-NS-50 composite membrane is 889~1663 g·m⁻¹. -2 ·d -1 .

[0082] Example 3

[0083] 1. Add 39.6g of sodium periodate to a large beaker containing 2L of water. After the sodium periodate has completely dissolved, add 20g of cellulose (the molar ratio of sodium periodate to cellulose is 1.5:1). Stir the mixture at 25℃ for 72h in the dark. After the reaction is complete, repeatedly centrifuge and wash the precipitate with deionized water to collect the precipitate dialdehyde cellulose (DAC). Disperse the DAC in distilled water to form a dispersion, and then stir at 100℃ for about 1h to obtain an aqueous solution of DAC.

[0084] 2. Weigh five portions of CMC, each 1g. Dissolve each portion of CMC in five 100mL cups of water. Then add sDAC solution to the five solutions. The solid sDAC content added to the five solutions is 0.005g, 0.02g, 0.05g, 0.1g, and 0.2g, respectively. At this time, the mass ratio of sDAC to CMC in the five solutions is 0.5:100, 2:100, 5:100, 10:100, and 20:100.

[0085] 3. The solution was thoroughly mixed in a 50℃ water bath, and then the membrane solution was poured onto a square plastic petri dish. The amount of membrane solution poured was such that the solid content in the membrane solution was 5 mg / cm³. 2 The film was dried in a drying oven at 40°C for 24 hours to fully evaporate the solvent. After that, the dried film was peeled off, and the film thickness was about 40 μm. It was then stored under constant temperature and humidity conditions. The films prepared in this example were named CMC / sDAC-0.5, CMC / sDAC-2, CMC / sDAC-5, CMC / sDAC-10, and CMC / sDAC-20, respectively.

[0086] The oxygen permeability of the film prepared in this embodiment was tested according to GB / T 19789-2021 standard, and the water vapor permeability of the film prepared in this embodiment was tested according to GB / T1037-2021 standard. The results are as follows: Figure 10 , Figure 11 As shown, the oxygen permeability of the CMC / sDAC composite membrane is 0.2651–1.118 cm⁻¹. 3 ·m -2 ·d -1 The water vapor transmission rate of the CMC / sDAC composite membrane is 878–1205 g·m⁻¹. -2 ·d -1 .

[0087] Comparative analysis

[0088] The composite films prepared in Examples 1-3 were compared and analyzed with general packaging films, as shown in Table 1.

[0089] Table 1

[0090]

[0091]

[0092] As shown in Table 1, the composite films prepared in Examples 1-3 have oxygen barrier properties that are several orders of magnitude higher than those of general packaging films.

[0093] The visible light transmittance of pure CMC films was compared with that of CMC / LDH-NS composite films, CMC / sDAC composite films, and CMC / LDH-NS / sDAC composite films prepared using the method of this invention. The transmittance performance of the films prepared in this embodiment was tested by spectral scanning in the range of 200–800 nm using a dual-beam UV-Vis spectrophotometer from Beijing Purkinje General Chemical Company.

[0094] pass Figure 5 It is known that, within the wavelength range of 420–800 nm, the CMC / sDAC composite film and the CMC / LDH-NS / sDAC composite film prepared by the method of this invention have higher visible light transmittance, which is significantly higher than that of pure CMC film. They are transparent materials and have a certain ultraviolet absorption capacity.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A method for preparing an oxygen-barrier, water-barrier, highly transparent composite film, characterized in that, Includes the following steps: S1. Preparation of an aqueous dispersion of hydrotalcite nanosheets; In step S1, the preparation steps of the hydrotalcite nanosheet aqueous dispersion are as follows: S1.1 Aluminum magnesium hydrotalcite was calcined in a muffle furnace at 450°C for 12 hours to obtain aluminum magnesium hydrotalcite; S1.2 Alumina magnesium hydrotalcite was mixed evenly with glycine and distilled water, placed in a high-pressure reactor, and reacted at 100°C to obtain a translucent LDH gel. S1.3 Disperse the LDH gel prepared in step S1.2 in distilled water to form a suspension. Purify by dialyzing in distilled water for 3-5 days, and then disperse by ultrasonication to obtain an aqueous dispersion of hydrotalcite nanosheets. S2. Preparation of dialdehyde cellulose aqueous solution: Dialdehyde cellulose is prepared and dispersed in distilled water to form a dispersion, which is then treated at high temperature to obtain dialdehyde cellulose aqueous solution; S3. Solution mixing; Add sodium carboxymethyl cellulose powder to the aqueous dispersion of hydrotalcite nanosheets, and then stir with a magnetic stirrer under water bath heating until the sodium carboxymethyl cellulose powder is completely dissolved. Then add dialdehyde cellulose aqueous solution and stir evenly. The mass ratio of the hydrotalcite nanosheets to carboxymethyl cellulose is 0.1~50:100, and the mass ratio of the dialdehyde cellulose to carboxymethyl cellulose is 0.1~20:

100. S4. Casting to form a film; Pour the well-stirred mixture from step S3 onto a square plastic petri dish. After water evaporates, a film is formed, thus obtaining the composite film.

2. The method for preparing an oxygen-barrier, water-barrier, highly transparent composite film according to claim 1, characterized in that: In step S1.3, the conditions for ultrasonic dispersion treatment are: 200~800W, 20~60min.

3. The method for preparing an oxygen-barrier, water-barrier, highly transparent composite film according to claim 1, characterized in that: In step S2, the preparation steps of dialdehyde cellulose are as follows: Add 39.6g of sodium periodate to a large beaker containing 2L of water. After the sodium periodate has completely dissolved, add 20g of cellulose. Stir and react at 25°C for 72 hours in the dark. After the reaction is complete, wash repeatedly with deionized water by centrifugation and collect the precipitate to obtain dialdehyde cellulose.

4. The method for preparing an oxygen-barrier, water-barrier, highly transparent composite film according to claim 1, characterized in that: In step S2, the dissolution conditions for dialdehyde cellulose are: temperature 80~100℃, 1~2h.

5. The method for preparing an oxygen-barrier, water-barrier, highly transparent composite film according to claim 1, characterized in that: In step S3, the water bath heating temperature is 25~90℃.

6. The method for preparing an oxygen-barrier, water-barrier, highly transparent composite film according to claim 1, characterized in that: In step S4, the temperature for water evaporation to form a film is 25~80℃.

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