A cellulose-based barrier membrane, its preparation method and application

Abstract

This invention relates to the field of packaging film technology, providing a cellulose-based barrier film, its preparation method, and its applications. Using cellulose as the base material, nanosheets as additives, and polyvinyl alcohol as an auxiliary material, a cellulose-based composite aerogel with a honeycomb-like porous structure is obtained through a nacre-like structure design and a combination of hydroxyl crosslinking and freeze-drying. The composite aerogel is then hot-pressed to obtain a multilayered cellulose-based barrier film. Based on the synergistic effects of the multilayer structure, nanosheets, and polyvinyl alcohol, the cellulose-based barrier film prepared by this invention exhibits high water and oxygen barrier properties. Simultaneously, the nacre-like structure plays a crucial role in the anti-fracture process of the cellulose-based barrier film, effectively enhancing its mechanical properties. In summary, the cellulose-based barrier film prepared by this invention possesses excellent water and oxygen barrier properties and mechanical properties, showing broad application prospects in the high-end packaging field.

Description

Technical Field

[0001] This invention relates to the field of packaging film technology, and in particular to a cellulose-based barrier film, its preparation method, and its application. Background Technology

[0002] Packaging materials play an indispensable and crucial role in the entire chain of commodity production, distribution, and consumption. They protect goods by isolating them from external moisture, oxygen, dust, and other contaminants, maintaining the stability of the goods' quality and safety, and preventing spoilage or damage during transportation, storage, and sales.

[0003] Traditional petroleum-based packaging materials (such as polyethylene, polypropylene, and polyvinyl chloride) have long dominated the packaging materials market due to their low cost, excellent processing performance, and stable mechanical strength, and are widely used in the packaging industry. However, discarded petroleum-based packaging materials are difficult to effectively degrade in the natural environment, and with the increasing use of these materials, serious environmental pollution problems have gradually emerged. Furthermore, during use and disposal, petroleum-based packaging materials continuously release microplastic particles, which can enter the human body through various pathways, posing a significant threat to human health. Cellulose, as the most abundant natural polymer material in nature, has significant advantages such as wide availability, renewability, complete biodegradability, and non-toxicity. Cellulose membranes, as a new type of green and environmentally friendly packaging material, have become a research hotspot in the packaging materials field. High-end packaging encompasses key industries such as food, pharmaceuticals, and electronics, requiring the preservation of fresh food, the stability of pharmaceuticals, and the protection of electronic components from damage. This necessitates extremely high barrier properties for packaging materials. However, the porosity and hydrophilicity of cellulose membranes result in poor barrier properties, which greatly limits their application in high-end packaging. Summary of the Invention

[0004] In view of this, the present invention provides a cellulose-based barrier film, its preparation method, and its application. The cellulose-based barrier film prepared by the present invention has excellent barrier properties, effectively blocking the penetration of water vapor and oxygen, and has broad application prospects in the field of high-end packaging.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for preparing a cellulose-based barrier membrane includes the following steps: Cellulose, polyvinyl alcohol, nanosheets, a crosslinking agent, and an alkaline urine solution were mixed and subjected to a crosslinking reaction to obtain a cellulose-based composite hydrogel; the mass fraction of polyvinyl alcohol was greater than or equal to 20% and less than or equal to 30%, calculated based on the total mass of cellulose and polyvinyl alcohol as 100%. The cellulose-based composite hydrogel was freeze-dried to obtain a cellulose-based composite aerogel. The cellulose-based composite aerogel was subjected to hot pressing to obtain a cellulose-based barrier membrane.

[0006] Preferably, the nanosheets include one or more of carbon nitride, graphene, and montmorillonite; the mass ratio of cellulose to nanosheets is (3~4):(0.2~0.4).

[0007] Preferably, the crosslinking agent is epichlorohydrin; the mass ratio of cellulose to crosslinking agent is 1:(1.5~3).

[0008] Preferably, the alkaline urine solution comprises sodium hydroxide, urea, and water; the mass fraction of sodium hydroxide in the alkaline urine solution is 6-8%, and the mass fraction of urea is 10-15%.

[0009] Preferably, the method of mixing cellulose, polyvinyl alcohol, nanosheets, crosslinking agent, and alkaline urine solution includes: Cellulose and polyvinyl alcohol were dissolved separately in alkaline urine solution to obtain cellulose alkaline urine solution and polyvinyl alcohol alkaline urine solution; The polyvinyl alcohol alkaline urine solution and the cellulose alkaline urine solution are mixed to obtain a mixed solution; The mixed solution, nanosheets, and crosslinking agent are mixed.

[0010] Preferably, the crosslinking reaction is carried out at a temperature of 50-70°C for 6-8 hours.

[0011] Preferably, the freeze-drying temperature is -80~-90℃ and the time is 15~18h.

[0012] Preferably, the hot pressing treatment is performed at a temperature of 160~170℃, for a time of 18~22min, and at a pressure of 28~32MPa.

[0013] The present invention also provides a cellulose-based barrier membrane prepared by the preparation method described above.

[0014] The present invention also provides the application of the cellulose-based barrier film described above in packaging films.

[0015] This invention provides a method for preparing a cellulose-based barrier membrane, comprising the following steps: mixing cellulose, polyvinyl alcohol, nanosheets, a crosslinking agent, and an alkaline urine solution to undergo a crosslinking reaction to obtain a cellulose-based composite hydrogel; wherein, based on the total mass of cellulose and polyvinyl alcohol as 100%, the mass fraction of polyvinyl alcohol is greater than or equal to 20% and less than or equal to 30%; freeze-drying the cellulose-based composite hydrogel to obtain a cellulose-based composite aerogel; and hot-pressing the cellulose-based composite aerogel to obtain a cellulose-based barrier membrane. This invention uses cellulose, a natural polymer derived from non-grain biomass, as the base material, nanosheets as the additive material, and polyvinyl alcohol as the auxiliary material. Through a nacre-like structure design, a cellulose-based composite aerogel with a honeycomb-like porous structure is obtained using a combination of hydroxyl crosslinking and freeze-drying. The composite aerogel is then hot-pressed, which causes the internal pore surfaces of the composite aerogel to come into close contact and form a layered structure. Simultaneously, thermal induction causes hydroxyl dehydration and etherification of polyvinyl alcohol, achieving interfacial point crosslinking between the layers, thus providing interlayer adhesion, thereby obtaining a multilayered cellulose-based barrier membrane. The multilayered structure of the cellulose-based barrier film effectively isolates airflow and prevents moisture penetration. Simultaneously, the nanosheets form a physical barrier, effectively blocking water vapor and oxygen penetration. The presence of polyvinyl alcohol (PVA) endows the cellulose-based barrier film with excellent oxygen barrier properties. In summary, based on the synergistic effects of the multilayered structure, nanosheets, and PVA, the cellulose-based barrier film prepared by this invention exhibits high water and oxygen barrier properties. Furthermore, during the film stretching process, the nacreous layer structure plays a crucial role in the fracture resistance of the cellulose-based barrier film, achieving a good balance between material strength and toughness, effectively enhancing the mechanical properties of the cellulose-based barrier film. In conclusion, the cellulose-based barrier film prepared by this invention possesses excellent water and oxygen barrier properties and mechanical properties, showing broad application prospects in the high-end packaging field.

[0016] The results of the examples show that the cellulose-based barrier membrane prepared by the present invention has the following effects: (1) According to ASTM D3985 standard, under the synergistic effect of multilayer structure, nanosheets and PVA, the water vapor transmission coefficient (WVP) of the cellulose-based barrier membrane under constant temperature and humidity (25℃, 50% RH) conditions is less than 2.0×10. -10 g·Pa -1 ·s -1 ·m -1 The oxygen permeability (OP) is less than 1.5 × 10⁻⁶. -5 cm 3 ·mm -1 ·d -1 ·atm -1 (2) According to the ASTM D882-02 standard test, the tensile strength of the cellulose-based barrier membrane is greater than 50 MPa and the elongation at break is greater than 20%. Attached Figure Description

[0017] Figure 1 A flowchart illustrating the preparation of cellulose-based barrier membranes according to this invention; Figure 2 This is a schematic diagram of the cross-linking reaction process and the chemical structural formula of the cellulose-based composite hydrogel; Figure 3 This is a schematic diagram of the freeze-drying process; Figure 4 This is a schematic diagram of the hot pressing process and the structure of the cellulose-based barrier membrane. Detailed Implementation

[0018] This invention provides a method for preparing a cellulose-based barrier membrane, comprising the following steps: Cellulose, polyvinyl alcohol, nanosheets, a crosslinking agent, and an alkaline urine solution were mixed and subjected to a crosslinking reaction to obtain a cellulose-based composite hydrogel; the mass fraction of polyvinyl alcohol was greater than or equal to 20% and less than or equal to 30%, calculated based on the total mass of cellulose and polyvinyl alcohol as 100%. The cellulose-based composite hydrogel was freeze-dried to obtain a cellulose-based composite aerogel. The cellulose-based composite aerogel was subjected to hot pressing to obtain a cellulose-based barrier membrane.

[0019] The route diagram for preparing the cellulose-based barrier membrane of this invention is as follows: Figure 1 As shown below, in conjunction with Figure 1 Please provide a detailed explanation.

[0020] This invention involves mixing cellulose, polyvinyl alcohol (PVA), nanosheets, a crosslinking agent, and an alkaline urine solution to undergo a crosslinking reaction, resulting in a cellulose-based composite hydrogel. In this invention, the number-average molecular weight of the PVA is preferably 74,800-82,000, and the weight-average molecular weight is preferably 166,000-204,000; specifically, the PVA can be of type 1799. The nanosheets preferably include one or more of carbon nitride, graphene, and montmorillonite; the average lateral dimension of the nanosheets is preferably 100-120 nm; the mass ratio of cellulose to nanosheets is preferably (3-4):(0.2-0.4), specifically 4:0.35 or 3.5:0.35; the crosslinking agent is preferably epichlorohydrin; the mass ratio of cellulose to crosslinking agent is preferably 1:1.5-1:3; the alkaline urine solution preferably comprises sodium hydroxide, urea, and water; the mass fraction of sodium hydroxide in the alkaline urine solution is preferably 6-8%, specifically 7%, and the mass fraction of urea is preferably 10-15%, specifically 12%. This invention uses an alkaline urine solution, which can effectively dissolve cellulose and provide alkaline conditions for the cross-linking reaction.

[0021] In this invention, the total mass of cellulose and polyvinyl alcohol is calculated as 100%, and the mass fraction of polyvinyl alcohol is greater than or equal to 20% and less than or equal to 30%, specifically 20%, 25% or 30%.

[0022] In this invention, the method of mixing cellulose, polyvinyl alcohol, nanosheets, crosslinking agent, and alkaline urine solution preferably includes: Cellulose and polyvinyl alcohol were dissolved separately in alkaline urine solution to obtain cellulose alkaline urine solution and polyvinyl alcohol alkaline urine solution; The polyvinyl alcohol alkaline urine solution and the cellulose alkaline urine solution are mixed to obtain a mixed solution; The mixed solution, nanosheets, and crosslinking agent are mixed.

[0023] In this invention, the preferred dissolution temperature of the cellulose is -10 to -15°C, specifically -12°C; the preferred dissolution temperature of the polyvinyl alcohol is 80 to 90°C, specifically 85°C; the preferred mass fraction of cellulose in the cellulose alkaline solution is 4 to 6%, specifically 5%; the preferred mass fraction of polyvinyl alcohol in the polyvinyl alcohol alkaline solution is 4 to 6%, specifically 5%; preferably, the polyvinyl alcohol alkaline solution is added dropwise to the cellulose alkaline solution under room temperature and stirring conditions; the mixing of the mixed solution, nanosheets, and crosslinking agent is preferably carried out using a disperser; after the mixed solution, nanosheets, and crosslinking agent are mixed, the resulting mixture is preferably ultrasonically degassed for 5 to 10 minutes before the crosslinking reaction is carried out.

[0024] In this invention, the temperature of the crosslinking reaction is preferably 50~70℃, specifically 60℃, and the time of the crosslinking reaction is preferably 6~8h, specifically 7h. In a specific embodiment of this invention, a mixture of cellulose, polyvinyl alcohol, nanosheets, crosslinking agent and alkaline urine solution is preferably injected into a mold, and then the mold is placed horizontally in an oven for the crosslinking reaction. The depth of the mold is preferably 2~5mm, specifically 3mm. During the crosslinking reaction, the crosslinking reaction between cellulose and polyvinyl alcohol under the action of epichlorohydrin includes: (1) crosslinking between adjacent cellulose -OH groups; (2) crosslinking between cellulose and polyvinyl alcohol -OH groups; (3) crosslinking between adjacent polyvinyl alcohol -OH groups. A cellulose-based composite hydrogel is formed through the above crosslinking reaction. A schematic diagram of the crosslinking reaction process and the chemical structural formula of the cellulose-based composite hydrogel are shown below. Figure 2 As shown.

[0025] After obtaining the cellulose-based composite hydrogel, the present invention freeze-dries the cellulose-based composite hydrogel to obtain a cellulose-based composite aerogel. Preferably, the cellulose-based composite hydrogel is first soaked in a hydrochloric acid solution to remove residual sodium hydroxide, then washed with deionized water, and then freeze-dried. The concentration of the hydrochloric acid solution is preferably 1 mol / L; the freeze-drying temperature is preferably -80 to -90°C, specifically -85°C, and the time is preferably 15 to 18 hours, specifically 16 hours. During the freeze-drying process, water is removed from the cellulose-based composite hydrogel, forming a honeycomb structure. A schematic diagram of the freeze-drying process is shown below. Figure 3 As shown.

[0026] After obtaining the cellulose-based composite aerogel, the present invention subjectes the cellulose-based composite aerogel to hot-pressing treatment to obtain a cellulose-based barrier membrane. In the present invention, the preferred temperature for the hot-pressing treatment is 160-170℃, specifically 165℃; the preferred time is 18-22 min, specifically 20 min; and the preferred pressure is 28-32 MPa, specifically 30 MPa. The hot-pressing treatment is preferably performed using a flat vulcanizing machine. During the hot-pressing process, the pressure causes the surfaces of the internal pores of the aerogel to come into close contact and form an integrated pearl-like layer structure. Thermal induction causes the PVA to undergo hydroxyl dehydration and etherification, forming interfacial crosslinking points between the pearl-like layers, ultimately forming a multi-layered cellulose-based barrier membrane. A schematic diagram of the hot-pressing process and the structure of the cellulose-based barrier membrane are shown below. Figure 4 As shown.

[0027] This invention also provides a cellulose-based barrier membrane prepared by the method described above. The cellulose-based barrier membrane provided by this invention has a pearl-like structure, good barrier performance, and can effectively block the penetration of water vapor and oxygen, while also possessing good mechanical properties.

[0028] The present invention also provides the application of the cellulose-based barrier film described above in packaging films.

[0029] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] The alkaline urine solution used in the following examples was prepared from sodium hydroxide, urea, and water, wherein the mass ratio of sodium hydroxide, urea, and water was 7:12:81.

[0031] Example 1 (1) Dissolve 20 g of cellulose in 380 g of alkaline urine solution at -12℃ to obtain 400 g of 5 wt% cellulose alkaline urine solution.

[0032] (2) Dissolve 5 g of polyvinyl alcohol in 95 g of alkaline urine solution at 85°C to prepare 100 g of 5 wt% polyvinyl alcohol alkaline urine solution.

[0033] (3) At room temperature, 5 wt% polyvinyl alcohol alkaline urine solution was added dropwise to 5 wt% cellulose alkaline urine solution under stirring to form a mixed solution, wherein the mass ratio of cellulose alkaline urine solution to polyvinyl alcohol alkaline urine solution was 8:2 (the amount of cellulose alkaline urine solution used was 80g and the amount of polyvinyl alcohol alkaline urine solution used was 20g). 0.35 g carbon nitride and 9 g epichlorohydrin were added to the mixed solution and homogenized using a homogenizer. The mixture was then sonicated for 5 min to remove air bubbles. The mixture was then poured into a 3 mm deep mold and placed horizontally in a drying oven at 60 °C for hydroxyl crosslinking. The reaction time was 7 h to obtain a cellulose-based composite hydrogel.

[0034] (4) The cellulose-based composite hydrogel was first soaked in 0.1 mol / L hydrochloric acid solution to remove sodium hydroxide from the hydrogel, and then washed with deionized water. The cleaned cellulose-based composite hydrogel was freeze-dried at -85℃ for 16h to obtain cellulose-based composite aerogel.

[0035] (5) The cellulose-based composite aerogel in step (4) is subjected to hot pressing treatment using a flat vulcanizing machine. The hot pressing temperature is 165℃, the pressure is 30MPa, and the time is 20min to obtain a cellulose-based barrier membrane.

[0036] The tensile strength and elongation at break of the cellulose-based barrier membrane were tested according to the method in ASTM D882-02. The water and oxygen barrier properties of the cellulose-based barrier membrane under constant temperature and humidity (25℃, 50% RH) conditions were tested according to the method in ASTM D3985. The test results showed that the tensile strength was 63.38 MPa, the elongation at break was 23.84%, and the water vapor transmission coefficient (WVP) was 1.86 × 10⁻⁶. -10 g·Pa -1 ·s -1 ·m -1 The oxygen permeability (OP) is 1.41 × 10⁻⁶. -5 cm 3 ·mm -1 ·d -1 ·atm -1 .

[0037] Example 2 Other conditions were the same as in Example 1, except that in step (3), the mass ratio of cellulose alkaline urine solution to polyvinyl alcohol alkaline urine solution was controlled to be 7:3 (the amount of cellulose alkaline urine solution used was 70g, and the amount of polyvinyl alcohol alkaline urine solution used was 30g). The tensile strength, elongation at break, and water and oxygen barrier properties of the obtained cellulose-based barrier membrane were tested according to the method in Example 1. The results showed that the tensile strength was 58.13 MPa, the elongation at break was 26.58%, and the water vapor transmission coefficient (WVP) was 1.95 × 10⁻⁶. -10 g·Pa -1 ·s -1 ·m -1 The oxygen permeability (OP) is 1.48 × 10⁻⁶. -5 cm 3 ·mm -1 ·d -1 ·atm -1 .

[0038] Comparative Example 1 Other conditions were the same as in Example 1, except that in step (3), the mass ratio of cellulose alkaline urine solution to polyvinyl alcohol alkaline urine solution was controlled to be 9:1 (the amount of cellulose alkaline urine solution used was 90g, and the amount of polyvinyl alcohol alkaline urine solution used was 10g). The tensile strength, elongation at break, and water and oxygen barrier properties of the obtained cellulose-based barrier membrane were tested according to the method in Example 1. The results showed that the tensile strength was 54.65 MPa, the elongation at break was 16.45%, and the water vapor transmission coefficient (WVP) was 3.08 × 10⁻⁶. -10 g·Pa -1 ·s -1 ·m -1 The oxygen permeability (OP) is 2.38 × 10⁻⁶. -5 cm 3 ·mm -1 ·d -1 ·atm -1 .

[0039] Comparative Example 2 Other conditions were the same as in Example 1, except that in step (3), the mass ratio of cellulose alkaline urine solution to polyvinyl alcohol alkaline urine solution was controlled to be 6:4 (60g of cellulose alkaline urine solution and 40g of polyvinyl alcohol alkaline urine solution). The tensile strength, elongation at break, and water and oxygen barrier properties of the obtained cellulose-based barrier membrane were tested according to the method in Example 1. The results showed that the tensile strength was 48.69 MPa, the elongation at break was 28.77%, and the water vapor transmission coefficient (WVP) was 2.79 × 10⁻⁶. -10 g·Pa -1 ·s -1 ·m -1 The oxygen permeability (OP) is 1.64 × 10⁻⁶.-5 cm 3 ·mm -1 ·d -1 ·atm -1 .

[0040] Comparative Example 3 Other conditions were the same as in Example 1, except that in step (3), the mass ratio of cellulose alkaline urine solution to polyvinyl alcohol alkaline urine solution was controlled to be 10:0 (the amount of cellulose alkaline urine solution used was 100g, and the addition of polyvinyl alcohol alkaline urine solution was omitted). The tensile strength, elongation at break, and water and oxygen barrier properties of the obtained cellulose-based barrier membrane were tested according to the method in Example 1. The results showed that the tensile strength was 42.52 MPa, the elongation at break was 8.85%, and the water vapor transmission coefficient (WVP) was 4.31×10⁻⁶. -10 g·Pa -1 ·s -1 ·m -1 The oxygen permeability (OP) is 3.56 × 10⁻⁶. -5 cm 3 ·mm -1 ·d -1 ·atm -1 .

[0041] In summary, this invention aims to improve the barrier properties of cellulose-based membrane materials to broaden their application fields. Addressing the problem of poor barrier properties in cellulose-based membrane materials, this invention uses cellulose as the base material, nanosheets as additives, and polyvinyl alcohol as an auxiliary material. Through biomimetic structural design, a multilayer cellulose-based barrier membrane is prepared via hydroxyl crosslinking, nanosheet reinforcement, freeze-drying, and hot-pressing. This significantly improves the water and oxygen barrier properties of cellulose-based membrane materials, and is of great significance for solving the problem of poor barrier properties in cellulose-based membrane materials and realizing high-end applications.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a cellulose-based barrier film, characterized by, Includes the following steps: Cellulose, polyvinyl alcohol, nanosheets, a crosslinking agent, and an alkaline urine solution are mixed and subjected to a crosslinking reaction to obtain a cellulose-based composite hydrogel; the mass fraction of polyvinyl alcohol is greater than or equal to 20% and less than or equal to 30%, calculated based on the total mass of cellulose and polyvinyl alcohol as 100%; the nanosheets include one or more of carbon nitride, graphene, and montmorillonite; the mass ratio of cellulose to nanosheets is (3~4):(0.2~0.4); The cellulose-based composite hydrogel was freeze-dried to obtain a cellulose-based composite aerogel; the freeze-drying temperature was -80~-90℃ and the time was 15~18h. The cellulose-based composite aerogel is subjected to hot pressing to obtain a cellulose-based barrier membrane; the hot pressing temperature is 160~170℃, the time is 18~22min, and the pressure is 28~32MPa.

2. The production method according to claim 1, characterized by, The crosslinking agent is epichlorohydrin; the mass ratio of cellulose to crosslinking agent is 1:(1.5~3).

3. The production method according to claim 1, characterized by, The alkaline urine solution comprises sodium hydroxide, urea, and water; the mass fraction of sodium hydroxide in the alkaline urine solution is 6-8%, and the mass fraction of urea is 10-15%.

4. The preparation method according to claim 1, characterized in that, The method of mixing cellulose, polyvinyl alcohol, nanosheets, crosslinking agent and alkaline urine solution includes: Cellulose and polyvinyl alcohol were dissolved separately in alkaline urine solution to obtain cellulose alkaline urine solution and polyvinyl alcohol alkaline urine solution; The polyvinyl alcohol alkaline urine solution and the cellulose alkaline urine solution are mixed to obtain a mixed solution; The mixed solution, nanosheets, and crosslinking agent are mixed.

5. The preparation method according to claim 1, characterized in that, The cross-linking reaction is carried out at a temperature of 50-70°C for 6-8 hours.

6. The cellulose-based barrier membrane prepared by the preparation method according to any one of claims 1 to 5.

7. The use of the cellulose-based barrier film according to claim 6 in packaging films.

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