High-barrier polysaccharide polymer film based on freeze dehydration rate control

Abstract

The invention provides a preparation method and application of a high-barrier polysaccharide polymer film based on freeze dehydration rate control. The method comprises the following steps: firstly, preparing a water-soluble polysaccharide polymer-based aqueous solution; thirdly, taking the aqueous solution system obtained in the first step as a precursor solution, adding sulfuric acid to promote gelation and casting to form a film, and then carrying out circulating freeze thawing treatment; and the polysaccharide polymer film with high water vapor barrier property is prepared by controlling the dehydration rate in the freezing process in the circulating freezing and thawing process. The dehydration rate in the freezing process is controlled, so that the polymer solution strengthens the compactness of the film and formation of a lamellar structure in the circulating freezing and thawing process, more structure defects are avoided, and the water vapor barrier property of the film is remarkably improved. Besides, the preparation process and the required materials are simple, convenient and feasible, the environmental protection requirement is met, and the preparation process is subjected to accurate quantitative design, fine regulation and optimization, so that the obtained polysaccharide polymer-based film has excellent water vapor barrier property and high practicability, and has wide development potential in the field of barrier packaging.

Description

Technical Field

[0001] The invention relates to the field of barrier films, in particular to a preparation method and application of a high-barrier polysaccharide polymer film based on freeze-dehydration rate control. Background Art

[0002] Packaging plays a key role in the protection of food, medicine and electronic products. It can prevent environmental pollution, extend shelf life and reduce waste. Ideal packaging materials should have low water vapor transmission rate (WVTR), oxygen transmission rate (OTR), and excellent water and grease barrier properties. Polymer-based packaging materials usually have good grease barrier properties, but it is more important to improve their water, steam and oxygen barrier properties. Petrochemical polymers are widely used in the packaging field because of their lightness, easy processing, strong mechanical properties and excellent barrier properties. However, petroleum resources are limited, petroleum-based polymers are difficult to degrade, and are prone to cause white pollution and environmental damage (Kim D, Seo J. Trends in Food Science & Technology, 2018, 76: 15-27.). Therefore, green and environmentally friendly biomass materials have gradually become an ideal substitute for traditional petroleum-based polymers due to their renewability, wide sources and excellent oxygen barrier properties. Compared with the non-degradability and limited barrier properties of petroleum-based materials, biomass materials can not only effectively reduce environmental pollution, but also meet the demand for barrier properties of packaging materials while reducing dependence on non-renewable resources. In addition, the development and application of these materials are in line with the global pursuit of sustainable development and circular economy, driving the packaging industry towards a more environmentally friendly direction.

[0003] In the context of increasingly important environmental protection, the use of petroleum resources as non-renewable resources and the problems of difficult-to-degrade polymers, such as white pollution, have attracted widespread attention. To solve this problem, degradable polymer barrier films are gradually becoming the preferred materials in the packaging field due to their environmental friendliness and efficient oxygen barrier properties. These degradable materials can be divided into two categories: one is bio-based degradable polymers derived from nature, including cellulose and its modified products, chitosan, starch, alginate, etc.; the other is non-bio-based but equally degradable polymers treated by special processes, such as polyvinyl alcohol (PVA). Although these materials have many advantages, their natural hydrophilic properties limit their performance in water vapor barrier. Therefore, the current research trend focuses on optimizing and improving the water vapor barrier capacity of these degradable polymers through innovative technologies and methods to meet a wider range of application needs, while further promoting the development of environmentally friendly packaging materials. For example, Wang et al. used CNF to enhance the water vapor barrier properties of the film, and the WVTR of the film was as low as 1.0g / m 2·day (Lu Wang, Cong Chen, Jinwu Wang, et al. Food Packaging and Shelf Life, 2020, 23: 100464.). Ma et al. used modified cellulose spheres to improve the performance of chitosan film, significantly improving the water vapor barrier properties of the film, with a water vapor permeability coefficient (WVP) as low as 0.98×10- -6 g·m -1· h -1 .Pa -1 (Xiaofei Ma, Miaomiao Lv, Debbie P. Anderson, et al. Food Hydrocolloids, 2017, 66: 276-285.) Ramakrishnan et al. prepared alginate / carboxymethyl cellulose / starch ternary blend films for packaging applications. The study showed that when the starch content was 50%, the minimum WVP was 2.36×10 -5 g·mm -2· d -1 ·Pa -1 (Ejish Ramakrishnan, Senthil Vadivu Kulandhaivelu, Swarup Roy, et al. Industrial Crops and Products, 2023, 193: 116114.). Although these methods significantly improve the water resistance of degradable polymer films, there are still problems such as complex preparation process, high cost, environmental hazards and possible harm to the human body. Therefore, it is necessary to find a green and environmentally friendly natural material to improve the water resistance and barrier properties of polysaccharide polymer films through a simple preparation process. Summary of the invention

[0004] The present invention aims at the deficiencies in the prior art and provides a method for preparing a high barrier polysaccharide polymer film based on freeze dehydration rate control and its application. The method has a simple preparation process, uses environmentally friendly and economical raw materials, and the prepared high water vapor barrier film has high water resistance, water vapor barrier performance and mechanical properties.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] On the one hand, a method for preparing a high barrier polysaccharide polymer film based on freeze dehydration rate control is adopted, characterized in that it comprises the following steps:

[0007] Step 1: prepare a water-soluble polysaccharide polymer solution.

[0008] Step 2: Using the aqueous solution system obtained in step 1 as a precursor solution, sulfuric acid is added to promote gelation and cast into a film, followed by a freeze-thaw cycle. During the freeze-thaw cycle, the dehydration rate in the freezing process is controlled to prepare a polysaccharide polymer film with high water vapor barrier properties.

[0009] Furthermore, in step 1, the method for preparing a high barrier polysaccharide polymer film based on freeze dehydration rate control is characterized in that in step 1, the water-soluble polysaccharide polymer is one of water-soluble cellulose derivatives (such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, etc.), water-soluble chitosan derivatives, water-soluble starch derivatives, sodium alginate, etc. Further, in step 1, the high molecular weight of the polysaccharide is in the range of 90,000 to 1,500,000.

[0010] Furthermore, in step 1, the concentration range of the polysaccharide solution is 1 to 5 wt%.

[0011] Furthermore, in step 2, the solution casting method is used to form a gel film (at room temperature), and the absolute dry mass per unit area ranges from 30 to 80 g / m 2 . Furthermore, in step 2, the dehydration rate during the freezing process is controlled by placing the cast gel film in a semi-closed container with an adjustable opening area and transferring it to a low-temperature refrigerator. By changing the surface opening rate of the container (0% to 100%, the opening diameter of each small hole is 0.5 to 1.0 mm) at a freezing temperature of -20°C, the dehydration rate during the freezing process can be controlled to be between 2.32 and 21.43 g / (h·m 2 ) range, the freezing time is 6 to 12 hours. Further, in step 2, the cyclic freeze-thaw process is to melt the frozen and dehydrated gel film at room temperature in a closed container and then freeze it again. The freeze-thaw process can be repeated 2 to 5 times, and the total dehydration amount of the cyclic freeze-thaw process is 5 to 15% of the total mass of the gel film. Further, in step 2, the cyclic freeze-thawed gel film is immersed and cleaned in deionized water for 3 to 5 times, and then naturally dried at 40 to 70°C to form the final membrane product.

[0012] Furthermore, the dehydration control of the polysaccharide polymer film during the freezing process can, on the one hand, enhance the density and lamellar structure formation of the film by dehydration to a certain extent, and on the other hand, avoid the formation of structural defects by controlling the dehydration rate, thereby improving the water vapor barrier performance of the film.

[0013] Furthermore, the water vapor permeability coefficient of the polysaccharide polymer film is in the range of 2.0 to 26.10×10 -11 g m / m 2· Pa·s.

[0014] The beneficial effects of the present invention are:

[0015] (1) By controlling the dehydration rate during the freezing process, the polymer solution can strengthen the film density and lamellar structure formation during the freeze-thaw cycle and avoid the formation of many structural defects, thereby significantly improving the water vapor barrier performance of the film.

[0016] (2) Based on the polysaccharide polymer film controlled by freeze dehydration rate, the dehydration rate during the freezing process is 2.32 g / (h·m 2 )~21.43g / (h·m 2 ) when the water vapor permeability coefficient ranges from 2.0 to 26.10×10 -11 g m / m 2 ·Pa·s.

[0017] (3) The raw materials and preparation method used in the present invention are simple and green and environmentally friendly. The preparation process has been quantitatively designed, regulated and optimized, so that the prepared polysaccharide polymer film with high water vapor barrier performance has good practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of dehydration rate control during the freezing process.

[0019] Figure 2 Water vapor permeability coefficient and dehydration rate during freezing of CMC films prepared with different opening areas during the cyclic freeze-thaw process of CMC aqueous solution.

[0020] Figure 3 Water vapor barrier properties between different raw material samples under the same film preparation conditions. DETAILED DESCRIPTION

[0021] The present invention will be described in detail below with reference to the accompanying drawings.

[0022] In Example 1, the present invention provides a method for preparing a high barrier polysaccharide polymer film based on freeze-dehydration rate control, comprising the following steps:

[0023] Preparation of carboxymethyl cellulose (CMC) film: First, prepare a 2wt% CMC aqueous solution at 50°C. After cooling to room temperature, take 15g of the 2wt% CMC solution in a 50ml beaker, add 1.15mL of 2.0mol / LH2SO4 to the beaker and stir for 1h, then pour into a culture dish with a diameter of 8.5cm. Use plastic wrap to control the porosity of the culture dish between 0% and 100%, and the diameter of each small hole is 1mm. Then put it in a refrigerator at -20°C and freeze it for 8h, thaw it at room temperature for 3h, and repeat three times. Wash the obtained hydrogel three times with deionized water, dry it at 55°C for 5h, and obtain a CMC film, which is recorded as FT-A-CMC.

[0024] The water vapor permeability coefficient of the above film was measured using a water vapor transmission rate measuring instrument (UAS, MOCON) according to the test standard ASTM-F1249 to evaluate the water vapor barrier performance of the film. Figure 2 As shown in the figure, the water vapor barrier properties of various carboxymethyl cellulose films were compared and it was found that the water vapor barrier properties of FT-A-CMC films could be adjusted by controlling the dehydration rate during the freezing process, and the water vapor permeability coefficient (WVP) could be as low as 2.0×10 -11 g m / m 2 ·Pa·s.

[0025] In another embodiment 2, the present invention provides a method for preparing a high-barrier polysaccharide polymer film based on freeze-dehydration rate control of another polysaccharide raw material, comprising the following steps:

[0026] Preparation of hydroxyethyl cellulose (HEC) film: First, prepare a 2wt% HEC aqueous solution at 50°C, cool to room temperature, take 15g of 2wt% HEC solution in a 50ml beaker, add 1.15mL of 2.0mol / LH2SO4 to the beaker, stir for 1h, and pour into a culture dish with a diameter of 8.5cm. Use plastic wrap to control the porosity of the culture dish between 0% and 100%, and the diameter of each small hole is 1mm. Then put it in a refrigerator at -20°C and freeze it for 8h, thaw it at room temperature for 3h, and repeat three times. Wash the obtained hydrogel three times with deionized water, dry it at 55°C for 5h, and obtain a HEC film, which is recorded as FT-A-HEC.

[0027] The water vapor permeability coefficient of the above film was measured using a water vapor transmission rate measuring instrument (UAS, MOCON) according to the test standard ASTM-F1249 to evaluate the water vapor barrier performance of the film. Figure 3 As shown in the figure, by controlling the dehydration rate during the freezing process, the water vapor barrier properties of the FT-A-HEC film can be adjusted, and the water vapor permeability coefficient (WVP) can be as low as 5.35×10 -11 g m / m 2 ·Pa·s.

[0028] Preferably, in Examples 1 and 2, the concentrations of CMC and HEC may be 1 wt %, 2 wt %, 2.5 wt % or 3 wt %.

[0029] Preferably, in Examples 1 and 2, the concentration of sulfuric acid is 1 mol / L, 1.5 mol / L or 2 mol / L.

[0030] Preferably, in Examples 1 and 2, the freezing time of the freeze-thaw cycle is 6 h, 9 h, or 12 h.

[0031] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a high barrier polysaccharide polymer film based on freeze-dehydration rate control, characterized in that: The steps include: Step 1: prepare a water-soluble polysaccharide polymer solution. Step 2: Using the aqueous solution system obtained in step 1 as a precursor solution, sulfuric acid is added to promote gelation and cast into a film, followed by a freeze-thaw cycle. During the freeze-thaw cycle, the dehydration rate in the freezing process is controlled to prepare a polysaccharide polymer film with high water vapor barrier properties.

2. The method for preparing a high barrier polysaccharide polymer film based on freeze-dehydration rate control according to claim 1, characterized in that: In step 1, the water-soluble polysaccharide polymer is one of water-soluble cellulose derivatives (such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, etc.), water-soluble chitosan derivatives, water-soluble starch derivatives, sodium alginate, etc.

3. The method for preparing a high barrier polysaccharide polymer film based on freeze-dehydration rate control according to claim 1, characterized in that: The molecular weight of the polysaccharide ranges from 90,000 to 1,500,000.

4. The method for preparing a high barrier polysaccharide polymer film based on freeze-dehydration rate control according to claim 1, characterized in that: In step 1, the concentration of the polysaccharide solution is in the range of 1 to 5 wt%.

5. The method for preparing a high barrier polysaccharide polymer film based on freeze dehydration rate control according to claim 1, characterized in that: In the step 2, the solution casting method is used to form a gel film (at room temperature), and the absolute dry mass per unit area ranges from 30 to 80 g / m 2 .

6. The method for preparing a high barrier polysaccharide polymer film based on freeze dehydration rate control according to claim 1, characterized in that: The control of the dehydration rate during the freezing process described in step 2 is specifically to place the cast gel film in a semi-closed container with an adjustable opening area and transfer it to a low-temperature refrigerator. By changing the opening rate of the container surface (0% to 100%, the opening diameter of each small hole is 0.5 to 1.0 mm) under the condition of a freezing temperature of -20°C, the dehydration rate during the freezing process can be controlled to be between 2.32 and 21.43 g / (h·m 2 ) range, the freezing time is 6 to 12 hours.

7. The method for preparing a high barrier polysaccharide polymer film based on freeze dehydration rate control according to claim 1, characterized in that: In step 2, the freeze-thaw cycle is to melt the frozen and dehydrated gel film at room temperature in a closed container and then freeze it again. The freeze-thaw process can be repeated 2 to 5 times, and the total dehydration amount during the freeze-thaw cycle is 5 to 15% of the total mass of the gel film.

8. The method for preparing a high barrier polysaccharide polymer film based on freeze dehydration rate control according to claim 1, characterized in that: In step 2, the gel membrane after freeze-thaw cycles is immersed in deionized water for cleaning for 3 to 5 times, and then naturally dried at 40 to 70° C. to form a final membrane product.

9. The method for preparing a high barrier polysaccharide polymer film based on freeze-dehydration rate control according to claim 1, characterized in that The dehydration control during the freezing process, on the one hand, synergistically strengthens the density and internal crystalline structure of the film through a certain degree of dehydration, and on the other hand, avoids the formation of structural defects by controlling the dehydration rate, thereby improving the water vapor barrier performance of the film.

10. The method for preparing a high barrier polysaccharide polymer film based on freeze-dehydration rate control according to claim 1, characterized in that: The water vapor permeability coefficient of the polysaccharide polymer film is in the range of 2.0 to 26.10×10 -11 g m / m 2 ·Pa·s.

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