Preparation and application of carboxymethyl cellulose / pearl powder composite film with high barrier property

Abstract

The invention provides a preparation method of a high-barrier-property carboxymethyl cellulose / pearl powder composite membrane, which comprises the following steps: firstly, adding white pearl powder serving as a lamellar filler into a carboxymethyl cellulose solution, and preparing carboxymethyl cellulose / pearl powder composite gel by adopting an acid-assisted gel method; and then, drying the prepared gel by adopting circulating freezing and thawing, directional deposition and vacuum filtration methods to obtain the composite membrane which takes carboxymethyl cellulose as a polymer matrix and white pearl powder as a flaky reinforcing filler. By adding the white pearl powder, the cellulose-based composite film has a compact layered stacked structure and an excellent passive radiation cooling effect, so that the water vapor barrier property of the composite film is remarkably improved, the antibacterial property, oxidation resistance, ultraviolet shielding property and mechanical strength of the composite film are further improved, and the preparation method is simple and easy to implement. The material is easy to degrade and has a wide application prospect in the field of food fresh-keeping barrier packaging.

Description

Technical Field

[0001] The present invention relates to a preparation method of a high-barrier carboxymethyl cellulose / pearlescent powder composite film, belonging to the field of barrier film preservation. Background Art

[0002] Packaging plays an extremely important role in protecting food from environmental pollution and influence, maintaining long-term freshness, and effectively reducing food damage. Packaging materials, especially those used for food preservation, need to have excellent water vapor barrier properties, antibacterial properties, antioxidant properties, ultraviolet shielding properties, and mechanical strength. Currently, petrochemical polymers are widely used in the food packaging industry due to their easy processing, excellent barrier ability, and mechanical strength. However, petroleum resources are non-renewable resources, and most petroleum-based polymers are difficult to decompose, easily causing white pollution and leading to serious environmental pollution problems. Therefore, compared with the limited water vapor barrier property, low-efficiency freshness preservation property, and non-degradability of traditional petroleum-based materials, biomass materials such as cellulose, starch, pectin, chitosan, etc., which have excellent water vapor barrier properties, outstanding food freshness preservation properties, are easily degradable, and have a wide range of sources, are gradually becoming substitutes for traditional petroleum-based polymers. This transformation is crucial for promoting sustainable development goals.

[0003] Cellulose is the most abundant biopolymer in the world, with advantages such as low cost, renewable, safe and non-toxic, and excellent biodegradability. These characteristics make it an ideal material for food preservation barrier films and have considerable development potential. Cellulose has a variety of water-soluble derivatives, such as carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), hydroxyethyl cellulose (HEC). Due to their excellent water solubility and film-forming properties, they are potential sustainable materials for preparing food packaging films. However, the high hydrophilicity of these water-soluble derivatives results in poor water vapor barrier properties. Many methods have been explored to solve this problem, including nanoparticle filling, chemical cross-linking, and hydrophobic modification. For example, Sanos et al. used cellulose nanofibers (CNF) and cellulose nanocrystals (CNC) to enhance the water vapor barrier property of CMC films, and the water vapor transmission rate (WVTR) of the obtained composite film was as low as 3.38 g / m 2· Tian (J.Fernández-Santos, C.Valls, O.Cusola, M.B.Roncero, Composites of cellulose nanocrystals in combination with either cellulose nanofibril or carboxymethylcellulose as functional packaging films, International Journal of Biological Macromolecules 211 (2022) 218-229.). Yu et al. prepared gelatin (GL) / CMC waterproof films by electrostatic interaction and crosslinking modulation. At pH 2.0, CMC and GL were crosslinked by sodium benzoate to form a dense network structure in the film. Compared with pure GL or CMC films, the WVTR of this composite film was reduced by about 90% (K.B. Yu, L. Zhou, H.R. Huang, J. Xu, Y.Y. Li, W.Z. Yu, S.F. Peng, L.Q. Zou, W. Liu, The improvement of water barrier property in gelatin / carboxymethyl cellulose composite film by electrostatic interaction regulation and its application in strawberry preservation, Food Chem 450 (2024)). Although these methods have significantly improved the water vapor barrier performance of degradable cellulose-based composite films, there are still problems such as complex preparation processes, high costs, environmental pollution, and harm to human health. Therefore, it is necessary to find a barrier film material that is green, environmentally friendly, widely sourced, and has excellent food preservation performance to improve the water vapor barrier performance and food preservation performance of cellulose-based composite films through a simple process. Summary of the Invention

[0004] In view of the problems in the prior art, such as low water vapor barrier performance of the barrier film, poor food preservation performance, and complex processes, the present invention provides a method for preparing a carboxymethyl cellulose / pearlescent powder composite film with high barrier properties. The preparation process of this method is simple, the raw materials of the barrier film used are green, environmentally friendly, and widely sourced. The prepared carboxymethyl cellulose / pearlescent powder composite film has a high water vapor barrier performance because the acid-assisted gelation, cyclic freeze-thaw, and vacuum filtration processes induce the white pearlescent powder flake fillers to perform dense parallel stacking, thereby extending the water vapor penetration path. At the same time, due to the photocatalytic activity, free radical scavenging ability, strong ultraviolet absorption and scattering ability of the white pearlescent powder, the composite film is endowed with excellent antibacterial, antioxidant, and ultraviolet shielding properties, thereby further improving the food preservation performance of the carboxymethyl cellulose / pearlescent powder composite film.

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

[0006] 1. A method for preparing a carboxymethyl cellulose / pearlescent powder composite film with high barrier properties, characterized by comprising the following steps:

[0007] Step 1: Add white pearlescent powder as a lamellar filler to a carboxymethyl cellulose solution, and prepare a carboxymethyl cellulose / pearlescent powder composite gel by an acid-assisted gelation method.

[0008] Step 2: Subject the composite gel prepared in Step 1 to cyclic freeze-thaw, directional deposition, and vacuum filtration methods, and dry it to obtain a composite film with carboxymethyl cellulose as the polymer matrix and white pearlescent powder as the lamellar reinforcing filler.

[0009] 2. Further, in Step 1, the white pearlescent powder is mica loaded with titanium dioxide nanoparticles on its surface, presenting a lamellar structure, with a particle size of 3 - 10 μm and excellent passive radiative cooling effect.

[0010] 3. Further, in Step 1, the mass ratio of the white pearlescent powder is 0.5 - 5 wt%.

[0011] 4. Further, in Step 1, the added acid is sulfuric acid, with a concentration of 1.0 - 2.5 mol / L, and stir for 1 - 2 h.

[0012] 5. Further, in Step 2, the composite gel is subjected to triple treatments of cyclic freeze-thaw, directional deposition, and vacuum filtration, inducing the pearlescent powder flake fillers to perform dense parallel stacking, thereby extending the water vapor penetration path.

[0013] 6. Further, in step two, the cyclic freeze-thaw temperature is -10 to -40 °C, freeze for 4 to 12 hours, thaw for 3 to 8 hours, repeat 2 to 6 times to obtain a stable hydrogel; then wash the hydrogel with deionized water 2 to 6 times, and after treatment, vacuum filter it for 3 to 6 h and dry it into a film at 45 to 65 °C.

[0014] 7. Further, the solar reflectance of the composite film is higher than 93%, and the infrared emissivity is higher than 96%, which can reduce the surface temperature of the film by more than 10 °C.

[0015] 8. Further, the water vapor permeability coefficient (WVP) of the composite film is lower than 3.5×10 -11 g·m / m 2 ·Pa·s, the oxygen free radical scavenging rate exceeds 45%, and the ultraviolet shielding rate is higher than 90%.

[0016] 9. Further, when the composite film is used for strawberry preservation, it can significantly reduce the probability of mildew and deterioration and extend the shelf life by more than 2 times.

[0017] 10. Further, the degradation rate of the composite film exceeds 95% after being buried in the soil for 60 days.

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) By means of acid-assisted gelation, cyclic freeze-thaw and vacuum filtration processes, white pearlescent powder flake fillers are induced to stack densely and parallelly, so that the cellulose-based composite film has a dense layered stacking structure, thereby extending the water vapor permeation path, and further significantly improving the water vapor barrier performance of the composite film. At the same time, due to the photocatalytic activity, free radical scavenging ability, strong ultraviolet absorption and scattering ability of the white pearlescent powder, the composite film is endowed with excellent antibacterial, antioxidant and ultraviolet shielding properties, thus further improving the food preservation performance of the carboxymethyl cellulose / pearlescent powder composite film. The close arrangement of CMC molecular chains and the stability of the hydrogen bond network endow the composite film with good water resistance and durability.

[0020] (2) The cellulose-based composite film added with white pearlescent powder has good radiative cooling performance. Since the white pearlescent powder has both radiative cooling and high reflectivity, it can significantly reduce the surface temperature of the composite film and the temperature of the internal food under sunlight irradiation. The decrease in temperature not only slows down the migration speed of CMC molecular chains, helps to maintain the dense lamellar stacking structure of the composite film, but also slows down the diffusion rate of water vapor molecules, and at the same time slows down the self-metabolism of food and the growth of microorganisms, reducing the probability of its deterioration and mildew, thus significantly improving the water vapor barrier performance and food preservation performance of the composite film.

[0021] (3) The raw materials for the preparation of the present invention are green, environmentally friendly, widely sourced, have excellent biodegradability, and the preparation method is simple and pollution-free to the environment. The preparation process has also undergone quantitative design, regulation, and optimization, enabling the prepared carboxymethyl cellulose / pearlescent powder composite film with high water vapor barrier properties, antibacterial and antioxidant properties, high UV shielding performance, and high mechanical strength to have good practicability and economy. Description of the Drawings

[0022] Figure 1 is the microstructure of the carboxymethyl cellulose / pearlescent powder composite film (V-CMC / Mica@TiO2) prepared by vacuum filtration and then drying. (a) Surface SEM image of V-CMC / Mica(@TiO2); (b) Cross-sectional SEM image of V-CMC / Mica@TiO2; (c) Partially enlarged surface SEM image of V-CMC / Mica@TiO2

[0023] Figure 2 (a) Histogram of water vapor permeability coefficients of carboxymethyl cellulose films (P-CMC) directly dried without acid-assisted gelation, cyclic freeze-thawing, and vacuum filtration, carboxymethyl cellulose films (CMC) directly dried without vacuum filtration, carboxymethyl cellulose / mica composite films (CMC / Mica) directly dried without vacuum filtration, and carboxymethyl cellulose / pearlescent powder composite films (CMC / Mica@Mica) directly dried without vacuum filtration; (b) Histogram of water vapor permeability coefficients of carboxymethyl cellulose films (V-CMC) prepared by vacuum filtration and then drying, carboxymethyl cellulose / mica composite films (V-CMC / Mica) prepared by vacuum filtration and then drying, and V-CMC / Mica@TiO2; (c) Water vapor permeability coefficients of V-CMC / Mica@TiO2 at different temperatures (values are mean ± standard deviation, represented by error bars). Different letters at the same time point indicate significant differences (p < 0.05)).

[0024] Figure 3 (a) Reflectance of different samples; (b) Solar reflectance and emissivity of V-CMC / Mica@TiO2. (c) Temperatures of strawberries on the surface and inside of different films over time under continuous simulated sunlight irradiation.

[0025] Figure 4 is a schematic diagram of the water vapor barrier mechanism of V-CMC / Mica@TiO2.

[0026] Figure 5 is the wet tensile strength of different films before and after vacuum filtration.

[0027] Figure 6(a) Changes in the number of colonies in the blank control group (CK), V-CMC, and V-CMC / Mica@TiO2; (b) Oxygen free radical scavenging rates of different samples; (c) Transmittance of different samples varying with wavenumber.

[0028] Figure 7 It is the appearance change of strawberries after 7 days in different packaging films.

[0029] Figure 8 It is the physical appearance change of different films buried in the soil over time. Detailed implementation manners

[0030] The present invention will be described in detail below with reference to the accompanying drawings

[0031] The present invention provides a preparation method of a carboxymethyl cellulose (CMC) / pearlescent powder (Mica@TiO2) composite film with high water vapor barrier, antibacterial antioxidant, and ultraviolet shielding properties, comprising the following steps:

[0032] Preparation of the carboxymethyl cellulose / pearlescent powder composite film: Dissolve an appropriate amount of CMC powder in water to obtain a CMC solution with a total solution mass of 12 g and a concentration of 2.5 wt%. Add an aqueous solution of Mica@TiO2 (3 ml, 0.5 wt%) to the CMC solution, and then stir for 1 hour. Subsequently, add sulfuric acid (1.15 mL, 2.0 mol / L) to the obtained mixture and stir for another 1 hour. Pour the well-mixed CMC solution into a petri dish with a diameter of 8.5 cm, cover it with a clean lid, and prepare a CMC / Mica@TiO2 composite gel. Place the gel in a -17°C refrigerator and freeze for 8 hours, then thaw at room temperature for 3 hours, and repeat the freeze-thaw process 3 times to obtain a stable CMC hydrogel. After that, soak the hydrogel in deionized water for 5 minutes and repeat this process 3 times to remove excess acid. Place the obtained hydrogel on a 0.22 μm filter membrane and evacuate for 4 hours to make Mica@TiO2 stack in parallel. Dry the filtered composite gel in a drum oven at 55°C for 5 hours to make a composite film, recorded as V-CMC / Mica@TiO2. The film dried without vacuum filtration is denoted as CMC / Mica@TiO2.

[0033] The microstructure of the V-CMC / Mica@TiO2 composite barrier film was observed using a field emission scanning electron microscope (JSM-7600F, Hitachi High-Technologies, Japan). As Figure 1 shown in the surface morphology diagram of a, the lamellar fillers in the composite film are evenly distributed and the surface is smooth and flat. As Figure 1 shown in the cross-sectional morphology diagram of b, it can be seen that V-CMC / Mica@TiO2 has a dense layered stacking structure. Figure 1c is a partial enlarged surface SEM image of V-CMC / Mica@TiO2.

[0034] Using a water vapor transmission rate measuring instrument (UAS, MOCON), the test follows the ASTM-F1249 standard, and the actual test area is 4.4 cm 2 , the test conditions are set at 37 °C and 65% RH, and the water vapor permeability coefficients (WVP) of different films are tested to evaluate the water vapor barrier properties of different films. As Figure 2 shown, compared with the untreated CMC film, the V-CMC / Mica@TiO2 composite film added with white pearlescent powder and treated by acid-assisted gelation, cyclic freeze-thaw and vacuum filtration has the largest reduction in WVP, and the WVP can be as low as 2.8×10 -11 g ·m / m 2 ·Pa·s, and its water vapor barrier property is significantly improved. In addition, the water vapor barrier property of the V-CMC / Mica@TiO2 composite film at different temperatures was studied, and it was found that the water vapor barrier property of the composite film increases with the decrease of temperature.

[0035] Measure the reflectivity of different films to evaluate the cooling performance of different films. As Figure 3 shown in a, compared with other cellulose-based films, the solar reflectivity of the V-CMC / Mica@TiO2 composite film is significantly improved, up to 93.81%. Further, the solar reflectivity and emissivity of CMC / Mica@TiO2 (within the atmospheric transparent window of 8-13 μm) were measured as Figure 3 shown in b, and it can be obtained that the emissivity of the carboxymethyl cellulose-based film added with white pearlescent powder can be as high as 96.57%, further indicating that the V-CMC / Mica@TiO2 composite film has excellent passive radiative cooling effect. In addition, different films were processed into packaging boxes, fresh strawberries were loaded, and then the surface of the packaging box was irradiated with simulated sunlight, and the surface and internal strawberry temperatures of the samples were measured with an infrared thermal imager every 30 minutes to test the changes in the surface and internal strawberry temperatures of the film over time. As Figure 3 shown in c, the temperature of the strawberries in the V-CMC / Mica@TiO2 composite film is 12.1 °C lower than that of the strawberries in the V-CMC film, indicating that the passive radiative cooling effect of the V-CMC / Mica@TiO2 composite film significantly improves the cooling performance of the film, thereby effectively improving the water vapor barrier property and food preservation property of the composite film.

[0036] As Figure 4It is a schematic diagram of the water vapor barrier mechanism of the V--CMC / Mica@TiO2 composite film. Since the V-CMC / Mica@TiO2 composite film has a dense layered stacking structure, the penetration path of water vapor is extended; in addition, due to the excellent passive radiative cooling effect of the V-CMC / Mica@TiO2 composite film added with white pearlescent powder, its high reflectivity reduces the heating rate of the film under sunlight, and its high emissivity accelerates the heat dissipation rate of the film, thereby reducing the surface temperature of the film and the temperature of the internal food. The decrease in temperature not only slows down the migration speed of CMC molecular chains, helps to maintain the dense lamellar stacking structure of the composite film, but also slows down the diffusion rate of water vapor molecules, and at the same time slows down the self-metabolism of food and the growth of microorganisms, reducing the probability of its deterioration and mildew, thereby significantly improving the water vapor barrier performance and food preservation performance of the film.

[0037] The wet tensile properties of different films were measured to verify the water resistance. The films were cut into strips 0.5 cm wide and loaded at a speed of 5 mm / min. Before the wet tensile test, the films were soaked in water for 2 hours, taken out, and the surface moisture was removed with filter paper. Then the tensile test was carried out in time with a universal testing machine (AGS-X 500N, Shimadzu, Kyoto, Japan). As Figure 5 shown, for the V-CMC / Mica@TiO2 composite film, its wet tensile strength was significantly improved, with excellent wet tensile properties, thus improving the water resistance and durability of the composite film.

[0038] The antibacterial, antioxidant and ultraviolet shielding properties of the V-CMC / Mica@TiO2 composite film were tested to evaluate the food preservation performance of the V-CMC / Mica@TiO2 composite film. As Figure 6 shown in a, the number of bacterial colonies of V-CMC / Mica@TiO2 was the least, and its antibacterial property was significantly improved. At the same time, the oxygen radical scavenging rates of different films were measured. As Figure 6 shown in b, the oxygen radical scavenging rate of V-CMC / Mica@TiO2 was much higher than that of other films, and its antioxidant property was significantly excellent. The ultraviolet-visible transmittance of different films is as Figure 6 shown in c. It can be seen that the addition of Mica@TiO2 greatly improved the ultraviolet shielding performance of CMC / Mica@TiO2. The above results show that the food preservation performance of CMC / Mica@TiO2 is very excellent.

[0039] The appearance changes of strawberries under different packaging films were observed to verify whether the V-CMC / Mica@TiO2 composite film effectively improved the food preservation performance in practical applications. As Figure 5As shown in a, compared with other films, the color of strawberries packaged with V-CMC / Mica@TiO2 only slightly darkened after 7 days, and there was no obvious decay or deterioration, proving that the composite film indeed has outstanding food preservation performance.

[0040] Different films were buried in the soil, and the degradation situation was systematically observed regularly to evaluate the biodegradability of different films. As Figure 6 shown, the biodegradability performance of V-CMC / Mica@TiO2 was significantly improved. By the 60th day, V-CMC / Mica@TiO2 was almost completely degraded, while PE maintained its original structure without any degradation.

[0041] Preferably, the concentration of carboxymethyl cellulose can be 1.0 wt%, 2.0 wt%, 2.5 wt% or 3.0 wt%.

[0042] Preferably, the concentration of sulfuric acid is 1.5 mol / L, 2.0 mol / L or 2.5 mol / L.

[0043] Preferably, the freezing temperature of cyclic freeze-thaw can be -10°C, -20°C, -40°C.

[0044] Preferably, the freezing time of cyclic freeze-thaw is 4 h, 6 h, 8 h.

[0045] Preferably, the time of vacuum filtration is 2 h, 4 h, 6 h.

[0046] Preferably, the concentration of Mica@TiO2 solution can be 0.5 wt.%, 1.0 wt%, 2.0 wt% or 2.5 wt%.

[0047] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should be regarded as within the protection scope of the present invention.

Claims

1. A method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film, characterized in that: The steps include: Step 1: Add white pearl powder as a lamellar filler into a carboxymethyl cellulose solution, and use an acid-assisted gelation method to prepare a carboxymethyl cellulose / white pearl powder composite gel. Step 2: Dry the composite gel obtained in step 1 by freeze-thaw cycle, directional deposition and vacuum filtration to obtain a composite membrane with carboxymethyl cellulose as a polymer matrix and white pearl powder as a flaky reinforcing filler.

2. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: In step 1, the white pearlescent powder is mica surface loaded with titanium dioxide nanoparticles, presenting a lamellar structure, with a particle size of 3 to 10 μm, and has an excellent passive radiation cooling effect.

3. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: In step 1, the mass percentage of the white pearlescent powder is 0.5-5wt%.

4. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: In step 1, the acid added is sulfuric acid with a concentration of 1.0 to 2.5 mol / L, and stirring is performed for 1 to 2 hours.

5. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: In step 2, the composite gel is combined with a triple treatment of cyclic freeze-thaw, directional deposition and vacuum filtration to induce the pearlescent powder flake fillers to be densely stacked in parallel, thereby extending the water vapor permeation path.

6. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: In step 2, the freeze-thaw cycle temperature is -10 to -40°C, freezing for 4 to 12 hours, thawing for 3 to 16 hours, and repeated 2 to 6 times to obtain a stable hydrogel; the hydrogel is then placed in deionized water and washed 2 to 6 times, and after treatment, it is vacuum filtered for 3 to 6 hours and dried at 40 to 70°C to form a film.

7. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: The composite film has a solar reflectivity higher than 93%, an infrared emissivity higher than 96%, and can reduce the surface temperature of the film by more than 10°C.

8. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: The water vapor permeability (WVP) of the composite membrane is less than 3.5×10 -11 g·m / m 2 ·Pa·s, the oxygen free radical scavenging rate exceeds 45%, and the UV shielding rate is higher than 90%.

9. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: When composite films are used to preserve strawberries, they can significantly reduce the probability of mold and deterioration and extend the shelf life by more than 2 times.

10. The method for preparing a high barrier carboxymethyl cellulose / pearl powder composite film according to claim 1, characterized in that: The degradation rate of the composite film after being buried in soil for 60 days exceeds 95%.

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