High-barrier and high-transparency nanofiber composite film as well as preparation method and application thereof

Abstract

The invention relates to the field of nanofiber membranes, in particular to a high-barrier and high-transparency nanofiber composite membrane and a preparation method and application thereof. Through a solution blending method, firstly, nano cellulose is uniformly dispersed in a deep eutectic solvent prepared from choline chloride and acrylic acid to achieve high load of cellulose; and paving the blended solution in a silica gel mold, and curing in an ultraviolet lamp environment to obtain the nanofiber film. The nano cellulose is uniformly distributed in the polymer matrix, so that the film has good gas barrier property and high transparency. One of the raw materials is rich in cellulose raw material, green, non-toxic and degradable, and the product has good biocompatibility and conforms to the sustainable development principle; through simple solution blending and ultraviolet lamp curing, the stable thin film with good self-supporting performance can be prepared, industrial preparation is simple, and large-scale industrial production is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of nanofiber membranes, and in particular to a high-barrier and high-transparency nanofiber composite film and a preparation method and application thereof. Background Art

[0002] At present, high barrier materials have been widely used in biochemical protection, food and pharmaceutical packaging, electronic component packaging, aerospace and military fields. Common barrier properties of materials include gas barrier, moisture barrier, light barrier, flame retardancy and other factors. In addition, when used in the field of electronic corrosion protection and photovoltaic packaging, light transmittance is also an important criterion for barrier materials. At present, the more mature barrier film packaging materials are mainly based on petroleum-based polymers, such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), etc. However, these materials are derived from fossil fuel resources, and their large-scale use will not only lead to the depletion of resources, but also bring serious environmental pollution and other problems.

[0003] Cellulose can be produced by plants or bacteria and is one of the most abundant all-green resources on earth. It belongs to the frontier new biomass materials, with natural advantages such as low carbon, environmental protection, biodegradability, light weight, high strength, and high barrier, and is known as one of the most promising new materials. Cellulose is connected to each other by glycosidic bonds to form linear polymer long chains. Its polycyclic structure and long chains can provide sufficient rigidity to build a stable network. The space is straightened, folded, etc., and is rich in polyhydroxy sites. Among them, the hydroxyl groups at positions 2, 3, and 6 can not only form intramolecular and intermolecular hydrogen bonds, but also form hydrogen bonds, covalent bonds, and ionic bonds with other polymers such as chitosan, amino-rich proteins, and polyvinyl alcohol (PVA) containing alcohol hydroxyl groups, etc., to increase the density of the hybrid network, reduce the internal free volume and gas diffusion rate, thereby extending the diffusion path of gas inside the barrier material and reducing the permeation of water vapor and oxygen. Cellulose-based packaging barrier film has become a research hotspot for green and pollution-free barrier films in recent years due to its abundant raw material reserves, low cost, easy processing, and biodegradability. It can provide solutions for sustainable products and achieve a low carbon footprint. Summary of the invention

[0004] Based on the above-mentioned problems such as environmental pollution and resource depletion caused by excessive use of existing petroleum-based polymer packaging materials, the present invention provides a cellulose film having the advantages of low cost, abundant raw materials, and biodegradability, as well as a preparation method and use thereof.

[0005] To achieve the above-mentioned purpose, the present invention provides a method for preparing a high-barrier, high-transparency nanofiber composite film, using a deep eutectic solvent DES to destroy the hydrogen bond network in cellulose, and forming a new hydrogen bond network between cellulose and DES to achieve good dispersion of cellulose; the DES used is composed of choline chloride (ChCl) and acrylic acid (AA), which serve as hydrogen bond acceptors and hydrogen bond donors, respectively. The hydrogen bond donor acrylic acid provides acidic hydrogen ions in the system to destroy the hydrogen bonds in cellulose, and the double bonds in acrylic acid provide polymerization conditions. The hydrogen bond acceptor choline chloride is a quaternary ammonium salt with cationic properties, which can combine with the negative charge on the bacterial cell membrane, destroy the membrane structure, and cause the cell contents to leak, thereby inhibiting or killing bacteria. The specific preparation method is as follows:

[0006] 1) Mix choline chloride (ChCl) and acrylic acid (AA) to prepare a deep eutectic solution (DES);

[0007] 2) dispersing nanocellulose (CNF) in the deep eutectic solution of step 1) at 120-150 °C for 6-24 h, then adding initiator 2-hydroxy-2-methylpropiophenone and cross-linking agent N,N'-methylenebisacrylamide and mixing them evenly to prepare a mixed solution;

[0008] 3) The mixed solution is spread on a film, and then polymerized and cured under ultraviolet light to obtain a high-barrier and high-transparency nanofiber composite film.

[0009] In the present invention, the nanocellulose needs to be broken by the deep eutectic solution under certain temperature conditions to form a new hydrogen bond network, preferably at a temperature of 120-150°C, such as 120°C, 125°C, 130°C, etc.

[0010] As a further preferred technical solution of the present invention, in step 1), the molar ratio of choline chloride to acrylic acid is 1:2.

[0011] As a further preferred technical solution of the present invention, in step 2), nanocellulose is dispersed in the deep eutectic solution at a concentration of 1 to 5 wt%. The present invention prepares films with different nanocellulose contents and various properties. Due to the different nanocellulose contents, the obtained films exhibit different properties, and generally show characteristics such as high transparency and high barrier.

[0012] As a further preferred technical solution of the present invention, steps 1) and 2) are performed under air or nitrogen environment.

[0013] As a further preferred technical solution of the present invention, in step 3), the mixed solution is laid to obtain a high barrier and high transparency nanofiber composite film with a thickness of 100 μm to 500 μm.

[0014] According to another aspect of the present invention, the present invention also provides a nanofiber composite film having high barrier properties to water and oxygen and high transparency.

[0015] According to another aspect of the present invention, the present invention also provides a use of a nanofiber composite film as a transparent film for blocking water vapor and oxygen.

[0016] The present invention adds nanocellulose to the polymer to make the cellulose evenly distributed in the polymer, thus changing the diffusion path of the gas, so that the product exhibits excellent barrier properties while maintaining high transparency.

[0017] The present invention can achieve the following beneficial effects:

[0018] 1) The cellulose raw material, one of the raw materials of the present invention, is abundant, green, non-toxic and degradable. The product has good biocompatibility and complies with the principle of sustainable development.

[0019] 2) The present invention can prepare a film with good self-supporting properties and stability through simple solution blending and UV lamp curing, and the industrial preparation is simple and conducive to large-scale industrial production.

[0020] 3) In the present invention, after adding nanocellulose to the polymer (PAA), the mechanical properties of the polymer are greatly improved.

[0021] 4) Choline chloride exists in the film prepared by the present invention, showing good antibacterial properties.

[0022] 5) In the present invention, the blended liquid is simply spread so that the nanocellulose having a certain aspect ratio presents a certain orientation in the polymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0024] Figure 1 SEM images of the composite films, where: (a) is Example 1 (CNF-1.25 wt% composite film), (b) is Example 2 (CNF-2.50 wt% composite film), (c) is Example 3 (CNF-3.75 wt% composite film), and (d) is Example 4 (CNF-5.0 wt% composite film).

[0025] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0026] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0027] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0028] The nanocellulose used in the following examples was produced and provided by Qingshan Lake National Papermaking Center.

[0029] Comparative Example 1: Preparation of a poly-DES film, wherein the molar ratio of choline chloride to acrylic acid is 1:2.

[0030] Step (1), 10 g of choline chloride solid and 9.8 ml of acrylic acid were added to a reactor, and the solution was blended for 6 h to prepare a deep eutectic solvent DES.

[0031] Step (2), add 0.1 g of initiator and 0.1 g of cross-linking agent into the above reactor respectively, and mix for 1 h.

[0032] Step (3), placing the mixed solution in step (2) into a silicone mold for spreading, and after the solution is spread completely and evenly, curing it under a UV lamp for 30 seconds to obtain a poly DES film with a thickness of about 250 μm, which is recorded as PDES.

[0033] Comparative Example 2: Preparation of nanocellulose composite film

[0034] Step (1), 10 g of choline chloride solid and 9.8 ml of acrylic acid were added to a reactor, and the solution was blended for 6 h to prepare a deep eutectic solvent DES.

[0035] Step (2), add 0.25 g of nanocellulose (CNF), 0.1 g of initiator and 0.1 g of cross-linking agent into the above reactor respectively and blend for 1 h.

[0036] Step (3), placing the mixed solution in step (2) into a silicone mold for spreading, and after the solution is spread completely and evenly, curing it under a UV lamp for 30 seconds to obtain a nanocellulose composite film with a thickness of about 250 μm.

[0037] Comparative Example 3: Preparation of nanocellulose composite film

[0038] Step (1), 10 g of choline chloride solid and 9.8 ml of acrylic acid were added to a reactor, and the solution was blended for 6 h to prepare a deep eutectic solvent DES.

[0039] Step (2), add 0.25 g of nanocellulose (CNF) to the reactor of step (1) above, and blend the solution at room temperature for 12 h.

[0040] Step (3), add 0.1 g of initiator and 0.1 g of cross-linking agent to the reactor of step (2) above, and mix for 1 hour.

[0041] Step (4), placing the mixed solution in step (3) into a silicone mold for spreading, and after the solution is spread completely and evenly, curing it under a UV lamp for 30 seconds to obtain a nanocellulose composite film with a thickness of about 250 μm.

[0042] Example 1: Preparation of a nanocellulose composite film, wherein the nanocellulose content is 1.25 wt%.

[0043] Step (1), 10 g of choline chloride solid and 9.8 ml of acrylic acid were added to a reactor, and the solution was blended for 6 h to prepare a deep eutectic solvent DES.

[0044] Step (2), add 0.25 g of nanocellulose (CNF) to the reactor of step (1), blend the solution at 120 °C for 12 h, and then cool the solution to room temperature.

[0045] Step (3), add 0.1 g of initiator and 0.1 g of cross-linking agent to the reactor of step (2) above, and mix for 1 hour.

[0046] Step (4), placing the mixed solution in step (3) into a silicone mold for spreading, and after the solution is spread completely and evenly, curing it under a UV lamp for 30 seconds to obtain a nanocellulose composite film with a thickness of about 250 μm, which is recorded as CNF-1.25 wt% composite film.

[0047] Example 2: Preparation of a nanocellulose composite film, wherein the nanocellulose content is 2.50 wt%.

[0048] Step (1), 10 g of choline chloride solid and 9.8 ml of acrylic acid were added to a reactor, and the solution was blended for 6 h to prepare a deep eutectic solvent DES.

[0049] Step (2), adding 0.50 g of nanocellulose to the reactor of step (1), blending the solution at 120 °C for 12 h, and then cooling the solution to room temperature.

[0050] Step (3), add 0.1 g of initiator and 0.1 g of cross-linking agent to the reactor of step (2) above, and mix for 1 hour.

[0051] Step (4), placing the mixed solution in step (3) into a silicone mold for spreading, and after the solution is spread completely and evenly, curing it under a UV lamp for 30 seconds to obtain a nanocellulose composite film with a thickness of about 250 μm, which is recorded as CNF-2.50 wt% composite film.

[0052] Example 3: Preparation of a nanocellulose composite film, wherein the nanocellulose content is 3.75 wt%.

[0053] Step (1), 10 g of choline chloride solid and 9.8 ml of acrylic acid were added to a reactor, and the solution was blended for 6 h to prepare a deep eutectic solvent DES.

[0054] Step (2), adding 0.75 g of nanocellulose to the reactor of step (1), blending the solution at 120 °C for 12 h, and then cooling the solution to room temperature.

[0055] Step (3), add 0.1 g of initiator and 0.1 g of cross-linking agent to the reactor of step (2) above, and mix for 1 hour.

[0056] Step (4), placing the mixed solution in step (3) into a silicone mold for spreading, and after the solution is spread completely and evenly, curing it under a UV lamp for 30 seconds to obtain a nanocellulose composite film with a thickness of about 250 μm, which is recorded as CNF-3.75 wt% composite film.

[0057] Example 4: Preparation of a nanocellulose composite film, wherein the nanocellulose content is 5.0 wt%.

[0058] Step (1), 10 g of choline chloride solid and 9.8 ml of acrylic acid were added to a reactor, and the solution was blended for 6 h to prepare a deep eutectic solvent DES.

[0059] Step (2), adding 1.0 g of nanocellulose to the reactor of step (1), blending the solution at 120 °C for 12 h, and then cooling the solution to room temperature.

[0060] Step (3), add 0.1 g of initiator and 0.1 g of cross-linking agent to the reactor of step (2) above, and mix for 1 hour.

[0061] Step (4), placing the mixed solution in step (3) into a silicone mold for spreading, and after the solution is spread completely and evenly, curing it under a UV lamp for 30 seconds to obtain a nanocellulose composite film with a thickness of about 250 μm, which is recorded as CNF-5.0 wt% composite film.

[0062] Performance test: The performance of the samples obtained in the comparative examples and embodiments was measured.

[0063] Water and oxygen barrier test: Labthink BTY-B2P air permeability tester is used to test the water and oxygen barrier performance, the models are MOCON 3 / 33MA and MOCON 221MD.

[0064] Transmittance / haze measurement: The transmittance and haze were measured using a WGT-S transmittance / haze meter, provided by Shanghai Shenguang Instrument Co., Ltd.

[0065] The tensile strength was determined by uniaxial tensile test.

[0066] Table 1 is a summary of the specific data of the above examples and comparative examples:

[0067] Table 1

[0068] The present invention is further analyzed below in conjunction with Table 1 and specific embodiments.

[0069] The thickness of the nanocellulose film prepared by the silicone mold in the above Examples 1-4 is about 250 μm, the film is uniform and stable, and has good transparency, self-support and adhesion overall. In Examples 1-4, by increasing the amount of cellulose added, it can be seen that the surface color of the film gradually changes from colorless and transparent to light yellow, and the transparency decreases. It can be seen from the data in Table 1 that the light transmittance of the film is at a relatively high level (above 85%), and the haze increases with the increase in the amount of cellulose added.

[0070] The film shows good transparency mainly because the nanocellulose is well dispersed in DES, and there is no agglomeration and precipitation phenomenon, which shows that in the process of nanocellulose dispersion, the internal hydrogen bond network is successfully destroyed by the hydrogen ions and chloride ions in DES, and forms a new hydrogen bond network with DES, so the nanocellulose can be evenly dispersed in DES, achieving the purpose of high loading of nanocellulose in DES. When the nanocellulose loading is constant, the pre-dispersion degree of nanocellulose in DES is also an important factor affecting the performance of the film. It can be seen from the data in Table 1 that in Comparative Example 2, nanocellulose, crosslinking agent and initiator are added at the same time and directly polymerized. Since nanocellulose fails to be evenly dispersed, agglomeration and precipitation occur, which affect the transparency of the film and affect the permeability of water vapor and oxygen; in Comparative Example 3, although the pre-dispersion treatment is taken for a sufficient time, it is carried out at room temperature, and the reaction activity is poor, and the degree to which the hydrogen bond network inside the nanocellulose is destroyed by the hydrogen ions and chloride ions in DES is limited. Therefore, based on Comparative Example 3, by extending the pre-dispersion treatment time of nanocellulose to 24, 36, and 48 hours, it was found that the respective dispersion effects were still not obvious, which illustrates the importance of reaction temperature.

[0071] By comparing the tensile strength of Example 1 and Comparative Examples 2 and 3, it was found that, under the condition of the same nanocellulose content, as the dispersion degree of nanocellulose in DES increased, the mechanical properties increased accordingly. This was due to the formation of a new hydrogen bond network after the internal hydrogen bond network of nanocellulose was successfully destroyed by the hydrogen ions and chloride ions in DES during the dispersion process of nanocellulose.

[0072] like Figure 1 As shown, the SEM images of Example 1 (CNF-1.25 wt% composite film), Example 2 (CNF-2.50 wt% composite film), Example 3 (CNF-3.75 wt% composite film) and Example 4 (CNF-5.0 wt% composite film) show that in the film, the compatibility of nanocellulose and DES is good, the cross-sectional morphology is regular and uniform, and the distribution of nanocellulose can be clearly observed at a magnification of 10 K. Through SEM characterization, it was observed that the diameter of cellulose was between 60-70 nm and the length was between 2-3 μm. The cellulose was arranged in parallel along the cross-sectional direction, the distribution was relatively uniform, and the spacing was between 1-2 μm. Since the nanocellulose itself has a certain aspect ratio, there is a phenomenon of preferential arrangement during the film laying process. Therefore, the nanocellulose in the prepared nanocellulose film presents a certain orientation, so the cellulose constructs an excellent gas barrier network in the material, enhancing its gas barrier performance.

[0073] From the data in Table 1, it can be seen that after adding cellulose to PDES, the water vapor permeability of the film is greatly reduced from 240.06 g / (m 2 •24 h) to a minimum of 65.43 g / (m 2 •24 h)(CNF-5.0 wt%), this is because the presence of cellulose in the film lengthens the diffusion path of water vapor after entering the film, thereby greatly reducing the water vapor permeability of the film. Similarly, after adding cellulose, it lengthens the diffusion path of oxygen inside the film, thereby greatly reducing the oxygen permeability, from the highest 160.87 ml•mm / m 2 •24h•atm decreased to 65.59 ml•mm / m 2 •24h•atm(CNF-3.75 wt%). The addition of cellulose can modify PDES and greatly improve and optimize its high barrier properties.

[0074] In summary, the nanocellulose composite film prepared by simple solution blending and UV curing achieved a high loading of nanocellulose and a high compatibility of nanocellulose and DES. The cellulose body was evenly dispersed and arranged inside the composite film, showing a certain orientation. When the mass fraction of cellulose in the nanocellulose composite film was 3.75%, its comprehensive performance reached the best. At this time, the composite film had good transparency and excellent water and oxygen barrier performance. By changing the amount of cellulose added, the macroscopic morphology and performance of PDES can be controlled, and the effective modification of PDES can be achieved.

[0075] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a high-barrier, high-transparency nanofiber composite film, characterized in that: The following steps are involved: 1) mixing choline chloride and acrylic acid to prepare a deep eutectic solution; 2) dispersing the nanocellulose in the deep eutectic solution of step 1) at 120-150° C. for 6-24 h, then adding an initiator 2-hydroxy-2-methylpropiophenone and a crosslinking agent N,N'-methylenebisacrylamide and mixing them evenly to prepare a mixed solution; 3) The mixed solution of step 2) is spread on a film, and then polymerized and cured under ultraviolet light to obtain a high-barrier and high-transparency nanofiber composite film.

2. The method for preparing a high-barrier, high-transparency nanofiber composite film according to claim 1, characterized in that: In step 1), the molar ratio of choline chloride to acrylic acid is 1:

2.

3. The method for preparing the high-barrier and high-transparency nanofiber composite film according to claim 1, characterized in that: In step 2), nanocellulose is dispersed in the deep eutectic solution at a concentration of 1-5 wt%.

4. The method for preparing the high-barrier and high-transparency nanofiber composite film according to claim 1, characterized in that: Steps 1) and 2) are performed under air or nitrogen atmosphere.

5. The method for preparing the high-barrier and high-transparency nanofiber composite film according to claim 1, characterized in that: Step 3) The thickness of the obtained high barrier and high transparency nanofiber composite film is 100 μm to 500 μm.

6. A nanofiber composite film, characterized in that: The method is prepared by any one of claims 1 to 5.

7. Use of the nanofiber composite film as claimed in claim 6 as a transparent film for blocking water vapor and oxygen.

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