A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film and its preparation method and application

Abstract

The present invention provides a bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film and its preparation method and application. The specific preparation process of the composite film includes: (1) extruding the bacterial cellulose hydrogel film to reduce the water content; (2) immersing the above bacterial cellulose hydrogel film in a carbon quantum dot / polyvinyl alcohol aqueous dispersion to absorb and swell until equilibrium; (3) drying the carbon quantum dot / polyvinyl alcohol / bacterial cellulose hydrogel film to obtain its composite film; (4) immersing the carbon quantum dot / polyvinyl alcohol / bacterial cellulose composite film in a resin solution, and preparing the bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film by drying. The preparation process conditions of the present invention are easy to control, and the operation is simple and easy. The composite film of the present invention can improve the optical transparency of the pure bacterial cellulose film while having high strength and ultraviolet shielding performance, and can be widely used in electronic displays, building windows and other fields.

Description

Technical Field

[0001] The invention relates to the technical field of composite materials, and in particular to a bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film and a preparation method and application thereof. Background Art

[0002] With the rapid consumption of fossil energy and the increasingly prominent environmental pollution problem, people are committed to using renewable and degradable green materials to replace or reduce the use of petrochemical products. High-strength, high-transparency, hydrophobic films have important application prospects in the fields of electronic display screens, packaging, optical instruments, architectural lighting, microfluidic equipment, etc., and the demand is huge. Cellulose, as one of the most abundant natural resources with renewable advantages and biodegradability, has attracted more and more attention due to its excellent properties such as non-toxicity, degradability and environmental friendliness.

[0003] Bacterial cellulose (BC) refers to cellulose synthesized by microorganisms such as Acetobacter, Agrobacterium, Rhizobium and Sarcina, with a diameter of 50-100nm. It is a renewable, environmentally friendly, biodegradable nanomaterial with excellent mechanical properties and low thermal expansion coefficient. BC is synthesized by bacteria, without the need to add toxic or harmful chemicals. The process is environmentally friendly, and the purity of cellulose is high, avoiding the chemical treatment and separation process of the components. At the same time, since BC is not chemically or mechanically treated, the crystalline structure of cellulose is completely retained, there are a large number of hydrogen bonds in the molecules, and it has a Young's modulus of up to 1.5GPa, making it an ideal material for preparing high-strength thin film materials. However, due to the large diameter of BC fibers, many pores are easily formed between the fibers, causing strong light scattering, the material has low transparency and poor UV shielding performance, which limits the application of bacterial cellulose membranes in electronic displays, optical instruments, and energy-saving buildings.

[0004] Most studies on bacterial cellulose transparent composite films are devoted to using bacterial cellulose as a reinforcing agent rather than a film matrix. Microfiber or slurry BC is different from complete BC hydrogel films. Not only is the method of processing BC cumbersome, but the processed BC will destroy its original network structure and the mechanical properties will drop significantly. Using BC film to develop new composite materials can avoid the steps of cellulose dissolution, regeneration or uniform dispersion, thereby simplifying the process; at the same time, the unique three-dimensional network structure of bacterial cellulose can be maintained, and BC can easily interact with other components to improve the physical and mechanical properties of the composite film. Cazón et al. prepared a BC / PVA composite film with a tensile strength of only 20.76 MPa by immersing the complete BC hydrogel film in a polyvinyl alcohol (PVA) solution and then drying it naturally. Although the preparation method is simple, the mechanical properties and hydrophobic properties are poor (CAZóNP, VELAZQUEZ G, VáZQUEZ M. Characterization of mechanical and barrier properties of bacterial cellulose, glycerol and polyvinyl alcohol (PVOH) composite films with eco-friendly UV-protective properties [J]. Food Hydrocolloids, 2020, 99: 105323.). In another work by Cazón et al., the tensile strength of the composite film prepared by immersing the complete BC hydrogel film in a mixed solution of polyvinyl alcohol and chitosan and then drying it naturally reached 99.76 MPa, which was significantly improved compared to the tensile strength of the BC / PVA composite film in the previous work. (CAZóN P, VáZQUEZ M, VELAZQUEZ G. Environmentally Friendly Films Combining Bacterial Cellulose, Chitosan, and Polyvinyl Alcohol: Effect of Water Activity on Barrier, Mechanical, and Optical Properties [J]. Biomacromolecules, 2020, 21(2): 753-760.).

[0005] However, there is no report on bacterial cellulose with high strength, high transparency and UV shielding performance. The currently disclosed composite membranes based on bacterial cellulose cannot meet the requirements of practical application and processing, so it is urgent to seek and develop a new polymer membrane material with high strength, high transparency, hydrophobicity and UV shielding performance. Summary of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a bacterial cellulose high-strength and high-transparency UV-shielding composite film and a preparation method and application thereof.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film comprises the following steps:

[0009] 1) dissolving carbon quantum dots in a polyvinyl alcohol aqueous solution to obtain a carbon quantum dots / polyvinyl alcohol aqueous dispersion;

[0010] 2) squeezing the bacterial cellulose hydrogel film under a certain pressure to reduce its water content;

[0011] 3) immersing the bacterial cellulose hydrogel of step 2) into the carbon quantum dot / polyvinyl alcohol aqueous dispersion of step 1) for immersion treatment, taking out and drying, to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose composite film;

[0012] 4) Immersing the composite film of step 3) in a resin solution for immersion treatment, and drying under pressure and heating conditions to obtain a bacterial cellulose high-strength and high-transparency UV shielding composite film.

[0013] Preferably, the carbon quantum dots in step 1) are water-soluble carbon quantum dots prepared by a hydrothermal method using glucose as a raw material.

[0014] Preferably, in step 1), the concentration of the carbon quantum dots in the carbon quantum dots / polyvinyl alcohol aqueous dispersion is 0.01 mg / mL to 50 mg / mL.

[0015] Preferably, the polyvinyl alcohol in step 1) has a molecular weight of 20,000-500,000.

[0016] Further preferably, the molecular weight of the polyvinyl alcohol in step 1) is 300,000.

[0017] Preferably, the concentration of the polyvinyl alcohol aqueous solution in step 1) is 0.1 wt.% to 20 wt.%.

[0018] Preferably, the extrusion pressure in step 2) is 0.01-100 MPa.

[0019] Preferably, in step 2), the water content (99%) of the bacterial cellulose hydrogel film is reduced to 5% to 70% by extrusion;

[0020] Preferably, in step 3), the bacterial cellulose hydrogel film is immersed in the carbon quantum dots / polyvinyl alcohol aqueous dispersion for 1 to 72 hours.

[0021] Further preferably, in step 3), the bacterial cellulose hydrogel film is immersed in the carbon quantum dots / polyvinyl alcohol aqueous dispersion for 24 to 36 hours.

[0022] Preferably, the drying temperature in step 3) is room temperature to 100°C.

[0023] Preferably, the resin in step 4) is at least one of epoxy resin, acrylic resin and phenolic resin.

[0024] Preferably, in step 4), the carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite membrane is immersed in the resin solution for a time period of 0.1 to 8 hours.

[0025] Further preferably, in step 4), the immersion time of the carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite membrane in the resin solution is 0.1 to 2 hours.

[0026] Preferably, the conditions of the hot pressing treatment in step 3) are: the hot pressing pressure is 0.01 to 100 MPa, the hot pressing temperature is room temperature to 150° C., and the hot pressing time is 12 to 48 hours.

[0027] Further preferably, the conditions of the hot pressing treatment in step 3) are: the hot pressing pressure is 0.01 to 10 MPa, the hot pressing temperature is room temperature to 100° C., and the hot pressing time is 12 to 48 hours.

[0028] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film is prepared by the above preparation method, and its strength can reach about 150MPa.

[0029] The bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film as described above is used in the fields of electronic display, optical instrument, energy-saving building, etc.

[0030] The present invention, without destroying the structure of bacterial cellulose, directly uses bacterial cellulose hydrogel film as a matrix, uses carbon quantum dots and polymers as fillers, composites the complete bacterial cellulose hydrogel film with polyvinyl alcohol and carbon quantum dots by an impregnation method, and then adds resin to prepare a composite film by hot pressing. The impregnation method is simple to operate, and the hot pressing method is the key to further improving the mechanical properties of the composite film. BC, PVA and resin are combined by hydrogen bonds to form a composite film with a dense structure. The addition of resin makes the composite film form a denser structure after hot pressing, and the mechanical properties are further improved. The present invention not only solves the problem of high hydrophilicity of cellulose membranes, but also further improves the mechanical properties and optical properties while retaining the original crystal structure of bacterial cellulose. The experimental method of the present invention is simple to operate, and the prepared composite film has the properties of high strength, high transparency, hydrophobicity and UV shielding.

[0031] The beneficial effects of the present invention are as follows: the bacterial cellulose high-strength and high-transparency UV shielding composite film of the present invention has the advantages of high strength, high transparency, UV shielding performance, simple preparation process, low production cost, etc., and is suitable for large-scale production and application.

[0032] Specifically:

[0033] (1) The present invention prepares a transparent and hydrophobic bacterial cellulose high-strength and high-transparency UV shielding composite film without destroying the bacterial cellulose film structure. The preparation process is simple and is expected to achieve large-scale production.

[0034] (2) The bacterial cellulose high-strength and high-transparency UV shielding composite film prepared by the present invention uses polyvinyl alcohol to fill the pores between BC fibers to reduce light scattering through the principle of light refractive index matching, so that the composite film has excellent transparency and a visible light transmittance of more than 85%.

[0035] (3) The present invention utilizes the hydrophobic property of resin to overcome the shortcoming of bacterial cellulose membrane having high hydrophilicity. The composite membrane prepared by the present invention forms a dense layered structure through the method of hot pressing, which solves the problem that the propagation direction of part of the light is changed due to the interaction between the interface and light, and at the same time improves the mechanical strength of the composite membrane. The addition of resin can not only solve the problem of hydrophilicity, but also reduce the haze of the composite membrane.

[0036] (4) The present invention uses carbon quanta as the filling phase, which is evenly distributed inside the composite film and synergistically acts with the resin to give the composite film excellent ultraviolet shielding properties.

[0037] (5) The bacterial cellulose high-strength and high-transparency UV shielding composite film prepared by the present invention has good flexibility and is suitable for use in flexible electronic devices and window protective layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Scanning electron microscope images of CQDs / PVA / BC / EP of Example 1: (a) surface and (b) cross section.

[0039] Figure 2 These are the stress-strain curves of the CQDs / PVA / BC / EP composite films and the BC, BC / EP, PVA / BC, and BC / EP / PVA composite films prepared in Example 1 and Comparative Examples 1-4.

[0040] Figure 3 is the molecular structural formula of each component in CQDs / PVA / BC / EP in Example 1.

[0041] Figure 4Atomic force microscopy images and (c) height distribution curves of (a) BC film and (b) CQDs / PVA / BC / EP composite film prepared in Comparative Example 1 and Example 1.

[0042] Figure 5 (a) UV-visible absorption spectra, (b) transmittance curves, and (c) haze curves of the CQDs / PVA / BC / EP composite films and BC, BC / EP, and PVA / BC composite films prepared in Example 1 and Comparative Examples 1-3.

[0043] Figure 6 Schematic diagram of the instantaneous contact angles of the composite films (a) BC film, (b) BC / EP, (c) PVA / BC and (d) CQDs / PVA / BC / EP prepared in Example 1 and Comparative Examples 1-3.

[0044] Figure 7 Schematic diagram of the contact angles of (a) PVA / BC and (b) CQDs / PVA / BC / EP prepared in Example 1 and Comparative Example 3 after standing for 10 minutes. DETAILED DESCRIPTION

[0045] The present invention is further explained and illustrated below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto. Parameter processes not specified here can be performed with reference to conventional techniques.

[0046] Embodiment 1:

[0047] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0048] 1) preparing 300 mL of a 1 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 30 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 0.1 mg / mL;

[0049] 2) extruding the bacterial cellulose hydrogel film at a pressure of 0.1 MPa to reduce its water content, and the water content was reduced to 50%;

[0050] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 48 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at room temperature to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0051] 4) The composite film of step 3) was immersed in an epoxy resin solution for 10 minutes, and then placed in a hot press for hot pressing. The hot pressing temperature was room temperature, the hot pressing pressure was 1 MPa, and the hot pressing time was 48 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / epoxy resin composite film, recorded as CQDs / PVA / BC / EP.

[0052] Performance Test:

[0053] 1) The scanning electron microscope (SEM) image of the carbon quantum dots / polyvinyl alcohol / bacterial cellulose / epoxy resin composite film (CQDs / PVA / BC / EP) of this embodiment is as follows Figure 1 shown.

[0054] Depend on Figure 1 It can be seen that the CQDs / PVA / BC / EP composite film has a relatively dense structure and a smooth surface. A dense layered structure is formed in the composite film, and the gaps between layers are very small. Polyvinyl alcohol and epoxy resin fill the pores between BC fibers and on the surface of the composite film, respectively, to reduce light scattering.

[0055] 2) The stress-strain curve of the carbon quantum dots / polyvinyl alcohol / bacterial cellulose / epoxy resin composite film (CQDs / PVA / BC / EP) of this embodiment and the schematic diagram of the hydrogen bonding between the molecular formulas of PVA, BC and EP are shown in FIG. Figure 2 and Figure 3 shown.

[0056] Depend on Figure 2 It can be seen that the tensile strength of the CQDs / PVA / BC / EP composite film is 149.46MPa, which is 1.19 times that of the BC film, 1.17 times that of the PVA / BC composite film, 1.51 times that of the BC / EP composite film, and 2.08 times that of the BC / EP / PVA composite film. The CQDs / PVA / BC / EP composite film is better than the single film (BC) and the composite film of the two (PVA / BC, BC / EP); the strength of the BC / EP / PVA composite film prepared by different addition sequences is significantly lower than that of the CQDs / PVA / BC / EP composite film.

[0057] Depend on Figure 3 It can be seen that PVA, BC and EP all have abundant hydroxyl groups, and PVA, BC and EP are connected by hydrogen bonds to form a dense CQDs / PVA / BC / EP composite film. The structure of the material is related to the order of adding materials. Under the process of the present invention, PVA is first bonded to BC through hydrogen bonds, and EP is then bonded to PVA / BC through hydrogen bonds. Hot pressing further enhances the density of the composite film, so that the composite film has more excellent mechanical properties.

[0058] 3) Atomic force microscopy images and height distribution curves of the carbon quantum dots / polyvinyl alcohol / bacterial cellulose / epoxy resin composite film (CQDs / PVA / BC / EP) and BC film of this embodiment are shown in Figure 4 (a is the atomic force microscope image of BC, b is the atomic force microscope image of CQDs / PVA / BC / EP, and c is the height distribution curve).

[0059] Depend on Figure 4 It can be seen that the surface roughness value (Ra) of the CQDs / PVA / BC / EP composite film is 16.6nm, and the height variation is about 50nm. The CQDs / PVA / BC / EP composite film has extremely low roughness and high surface flatness.

[0060] 4) The UV-visible absorption spectrum, transmittance curve and haze curve of the carbon quantum dots / polyvinyl alcohol / bacterial cellulose / epoxy resin composite film (CQDs / PVA / BC / EP) of this embodiment are as follows: Figure 5 (a is the UV-visible absorption spectrum, b is the transmittance curve, and c is the haze curve).

[0061] Depend on Figure 5 It can be seen that the CQDs / PVA / BC / EP composite film has a wide absorption peak in the ultraviolet region of the UV-visible absorption spectrum and a high absorption intensity; in the transmittance curve, the CQDs / PVA / BC / EP composite film has an extremely low transmittance in the range of 200-300nm, and the transmittance is as high as 89.3% at 800nm; in the haze curve, the CQDs / PVA / BC / EP composite film has a haze of 20% at 550nm, indicating that the CQDs / PVA / BC / EP composite film has excellent transparency, low haze and UV shielding properties.

[0062] 5) The contact angle photo of the carbon quantum dots / polyvinyl alcohol / bacterial cellulose / epoxy resin composite film (CQDs / PVA / BC / EP) of this embodiment is shown in Figure 6 D and Figure 7 As shown in b.

[0063] Depend on Figure 6 It can be seen that the instantaneous contact angle of the CQDs / PVA / BC / EP composite film of this embodiment is as high as 98°, which has excellent hydrophobic properties.

[0064] Depend on Figure 7 It can be seen that the contact angle of the water drop on the surface of the CQDs / PVA / BC / EP composite film after standing for 10 minutes is 79°, and the contact angle decreases slightly. This shows that the surface of the CQDs / PVA / BC / EP composite film has good hydrophobicity, and the surface hydrophobicity remains stable for a long time.

[0065] Embodiment 2:

[0066] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0067] 1) preparing 300 mL of a 3 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 60 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 0.01 mg / mL;

[0068] 2) extruding the bacterial cellulose hydrogel film at a pressure of 0.01 MPa to reduce its water content, and the water content was reduced to 70%;

[0069] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 48 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at 50° C. to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0070] 4) The composite membrane of step 3) was immersed in an epoxy resin solution for 30 minutes, and then placed in a hot press for hot pressing treatment. The hot pressing temperature was 40°C, the hot pressing pressure was 10 MPa, and the hot pressing time was 36 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / epoxy resin composite membrane.

[0071] Embodiment 3:

[0072] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0073] 1) preparing 300 mL of a 5 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 90 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 10 mg / mL;

[0074] 2) extruding the bacterial cellulose hydrogel membrane under a pressure of 10 MPa to reduce its water content, and the water content was reduced to 60%;

[0075] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 24 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at 80° C. to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0076] 4) The composite membrane of step 3) was immersed in the epoxy resin solution for 1 hour, and then placed in a hot press for hot pressing treatment. The hot pressing temperature was 60°C, the hot pressing pressure was 35 MPa, and the hot pressing time was 24 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / epoxy resin composite membrane.

[0077] Embodiment 4:

[0078] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0079] 1) preparing 300 mL of 8 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 120 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 30 mg / mL;

[0080] 2) extruding the bacterial cellulose hydrogel film at a pressure of 30 MPa to reduce its water content, and the water content was reduced to 40%;

[0081] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 24 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at room temperature to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0082] 4) The composite membrane of step 3) is immersed in the epoxy resin solution for 2 hours, and then placed in a hot press for hot pressing treatment. The hot pressing temperature is 80°C, the hot pressing pressure is 10MPa, and the hot pressing time is 24 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / epoxy resin composite membrane.

[0083] Embodiment 5:

[0084] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0085] 1) preparing 300 mL of a 1 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 30 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 10 mg / mL;

[0086] 2) extruding the bacterial cellulose hydrogel film at a pressure of 50 MPa to reduce its water content, and the water content was reduced to 25%;

[0087] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 24 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at room temperature to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0088] 4) The composite membrane of step 3) was immersed in an acrylic resin solution for 30 minutes, and then placed in a hot press for hot pressing treatment. The hot pressing temperature was 60° C., the hot pressing pressure was 3 MPa, and the hot pressing time was 48 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / acrylic resin composite membrane.

[0089] Embodiment 6:

[0090] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0091] 1) preparing 300 mL of a 3 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 90 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 30 mg / mL;

[0092] 2) extruding the bacterial cellulose hydrogel film at a pressure of 70 MPa to reduce its water content, and the water content was reduced to 15%;

[0093] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 24 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at 50° C. to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0094] 4) The composite membrane of step 3) was immersed in an acrylic resin solution for 1 hour, and then placed in a hot press for hot pressing treatment. The hot pressing temperature was 80°C, the hot pressing pressure was 5 MPa, and the hot pressing time was 24 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / acrylic resin composite membrane.

[0095] Embodiment 7:

[0096] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0097] 1) preparing 300 mL of a 5 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 150 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 50 mg / mL;

[0098] 2) extruding the bacterial cellulose hydrogel film under a pressure of 100 MPa to reduce its water content to 5%;

[0099] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 24 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at 80° C. to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0100] 4) The composite membrane of step 3) is immersed in an acrylic resin solution for 2 hours, and then placed in a hot press for hot pressing treatment. The hot pressing temperature is 100° C., the hot pressing pressure is 8 MPa, and the hot pressing time is 24 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / acrylic resin composite membrane.

[0101] Embodiment 8:

[0102] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0103] 1) preparing 300 mL of a 1 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 30 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 0.1 mg / mL;

[0104] 2) extruding the bacterial cellulose hydrogel membrane under a pressure of 10 MPa to reduce its water content, and the water content was reduced to 60%;

[0105] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 24 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at room temperature to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0106] 4) The composite membrane of step 3) is immersed in a phenolic resin solution for 30 minutes, and then placed in a hot press for hot pressing treatment. The hot pressing temperature is 60° C., the hot pressing pressure is 3 MPa, and the hot pressing time is 48 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / phenolic resin composite membrane.

[0107] Embodiment 9:

[0108] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0109] 1) preparing 300 mL of a 3 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 90 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 25 mg / mL;

[0110] 2) extruding the bacterial cellulose hydrogel film at a pressure of 50 MPa to reduce its water content, and the water content was reduced to 25%;

[0111] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 24 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at 50° C. to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0112] 4) The composite membrane of step 3) is immersed in a phenolic resin solution for 1 hour, and then placed in a hot press for hot pressing treatment. The hot pressing temperature is 80°C, the hot pressing pressure is 5 MPa, and the hot pressing time is 24 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / phenolic resin composite membrane.

[0113] Embodiment 10:

[0114] A bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, the preparation method of which comprises the following steps:

[0115] 1) preparing 300 mL of a 5 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000), and then dissolving 150 mg of water-soluble carbon quantum dot powder in the polyvinyl alcohol solution to prepare a carbon quantum dot / polyvinyl alcohol aqueous dispersion with a carbon quantum dot concentration of 45 mg / mL;

[0116] 2) extruding the bacterial cellulose hydrogel film under a pressure of 100 MPa to reduce its water content to 5%;

[0117] 3) Soaking the bacterial cellulose hydrogel of step 2) in the aqueous dispersion of step 1) for 24 hours, taking out the carbon quantum dots / polyvinyl alcohol / bacterial cellulose hydrogel film and drying it at 80° C. to obtain a carbon quantum dots / polyvinyl alcohol / bacterial cellulose composite film.

[0118] 4) The composite membrane of step 3) is immersed in a phenolic resin solution for 2 hours, and then placed in a hot press for hot pressing treatment. The hot pressing temperature is 100° C., the hot pressing pressure is 8 MPa, and the hot pressing time is 24 hours to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose / phenolic resin composite membrane.

[0119] Comparative Example 1:

[0120] A bacterial cellulose membrane, the preparation method of which comprises the following steps:

[0121] 1) extruding the bacterial cellulose hydrogel film at a pressure of 0.1 MPa to reduce the water content to 50%;

[0122] 2) The bacterial cellulose hydrogel membrane of step 1) is placed at room temperature to dry to obtain a bacterial cellulose membrane, which is denoted as BC.

[0123] Performance Test:

[0124] 1) The atomic force microscope image and height distribution curve of the bacterial cellulose membrane (BC) of this comparative example are as follows Figure 4 (a is the atomic force microscope image, c is the height distribution curve).

[0125] Depend on Figure 4It can be seen that the surface roughness value (Ra) of the BC film is 47.8 nm, and the height variation is about 220 nm, which indicates that the surface of the BC film is rough and has low flatness.

[0126] 2) The stress-strain curve of the bacterial cellulose membrane (BC) of this comparative example is as follows Figure 2 shown.

[0127] Depend on Figure 2 It can be seen that the tensile strength of the BC film is 125.22MPa, and BC itself has good mechanical properties.

[0128] 3) The transmittance curve and haze curve of the bacterial cellulose film (BC) of this comparative example are as follows: Figure 5 (b is the transmittance curve, c is the haze curve).

[0129] Depend on Figure 5 It can be seen that the transmittance of the BC film at 800 nm in the transmittance curve is 62%, which is relatively low; the haze at 550 nm in the haze curve is 92%, which has a high haze.

[0130] 4) The contact angle photo of the bacterial cellulose membrane (BC) of this comparative example is as follows Figure 6 As shown in a.

[0131] Depend on Figure 6 It can be seen that the contact angle of BC is 38°, indicating that the surface hydrophobicity is poor.

[0132] Comparative Example 2:

[0133] A bacterial cellulose / resin composite film, the preparation method of which comprises the following steps:

[0134] 1) extruding the bacterial cellulose hydrogel film at a pressure of 0.1 MPa to reduce its water content to 50%;

[0135] 2) drying the bacterial cellulose hydrogel film obtained in step 1) at room temperature to obtain a bacterial cellulose film;

[0136] 3) The bacterial cellulose membrane of step 2) was immersed in an epoxy resin solution for 10 minutes, and then placed in a hot press for hot pressing. The hot pressing temperature was room temperature, the hot pressing pressure was 1 MPa, and the hot pressing time was 48 hours to obtain a bacterial cellulose / epoxy resin composite membrane, recorded as BC / EP.

[0137] Performance Test:

[0138] 1) The stress-strain curve of the bacterial cellulose / resin composite film (BC / EP) of this comparative example is as follows: Figure 2 shown.

[0139] Depend on Figure 2It can be seen that the tensile strength of the BC / EP composite film is 98.96 MPa, and the tensile strength of the BC / EP composite film is significantly lower than that of BC, indicating that the addition of EP will lead to a decrease in the tensile strength of the composite film.

[0140] 2) The UV-visible absorption spectrum and transmittance curve of the bacterial cellulose / resin composite film (BC / EP) of this comparative example are as follows: Figure 5 (a is the UV-visible absorption spectrum, b is the transmittance curve).

[0141] Depend on Figure 5 It can be seen that the absorption peak of the BC / EP composite film in the UV-visible absorption spectrum is broad but the intensity is low; the transmittance of BC / EP at 800nm ​​is 79.2%, which is low.

[0142] 3) The contact angle photo of the bacterial cellulose / resin composite film (BC / EP) of this comparative example is as follows Figure 6 As shown in b.

[0143] Depend on Figure 6 It can be seen that the contact angle of the BC / EP composite film of this comparative example is 73°, which has a relatively small contact angle, but the surface has certain hydrophobic properties.

[0144] Comparative Example 3:

[0145] A polyvinyl alcohol / bacterial cellulose composite film, the preparation method of which comprises the following steps:

[0146] 1) Prepare 300 mL of 1 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000);

[0147] 2) extruding the bacterial cellulose hydrogel film at a pressure of 0.1 MPa to reduce its water content, and the water content was reduced to 50%;

[0148] 3) The bacterial cellulose hydrogel of step 2) is placed in the aqueous dispersion of step 1) and soaked for 48 hours, and the polyvinyl alcohol / bacterial cellulose hydrogel film is taken out and dried at room temperature to obtain a polyvinyl alcohol / bacterial cellulose composite film, which is recorded as PVA / BC.

[0149] Performance Test:

[0150] 1) The stress-strain curve of the polyvinyl alcohol / bacterial cellulose composite film (PVA / BC) of this comparative example is as follows: Figure 2 shown.

[0151] Depend on Figure 2 It can be seen that the tensile strength of the PVA / BC composite film is 127.37 MPa, and the composite of PVA and BC does not significantly improve the tensile strength of BC.

[0152] 2) The UV-visible absorption spectrum, transmittance curve and haze curve of the polyvinyl alcohol / bacterial cellulose composite film (PVA / BC) of this comparative example are as follows: Figure 5 (a is the UV-visible absorption spectrum, b is the transmittance curve, and c is the haze curve).

[0153] Depend on Figure 5 It can be seen that although the absorption intensity of the PVA / BC composite film in the UV-visible absorption spectrum is high, the absorption peak is narrow; the transmittance at 800nm ​​in the transmittance curve is 88%, which is relatively low; the haze at 550nm in the haze curve is 67%, which has a relatively high haze.

[0154] 3) The contact angle photo of the polyvinyl alcohol / bacterial cellulose composite film (PVA / BC) of this comparative example is as follows Figure 6 C and Figure 7 As shown in a.

[0155] Depend on Figure 6 It can be seen that the instantaneous contact angle of the PVA / BC composite film is 98°, which has a large contact angle.

[0156] Depend on Figure 7 It can be seen that the contact angle of the PVA / BC composite film dropped to 48° after standing for 10 minutes, and the contact angle dropped significantly. Since both PVA and BC are hydrophilic, the surface hydrophobicity cannot remain stable for a long time.

[0157] Comparative Example 4:

[0158] A bacterial cellulose / epoxy resin / polyvinyl alcohol composite film, the preparation method of which comprises the following steps:

[0159] 1) extruding the bacterial cellulose hydrogel film at a pressure of 0.1 MPa to reduce its water content to 50%;

[0160] 2) drying the bacterial cellulose hydrogel film obtained in step 1) at room temperature to obtain a bacterial cellulose film;

[0161] 3) immersing the bacterial cellulose membrane of step 2) in an epoxy resin solution for 10 minutes, and then placing it in a hot press for hot pressing, the hot pressing temperature is room temperature, the hot pressing pressure is 1 MPa, and the hot pressing time is 48 hours to obtain a bacterial cellulose / epoxy resin composite membrane;

[0162] 4) preparing 300 mL of 1 wt.% polyvinyl alcohol solution (the molecular weight of polyvinyl alcohol is 300,000);

[0163] 5) Soak the bacterial cellulose / epoxy resin composite film of step 3) in the polyvinyl alcohol solution of step 4) for 48 hours, take out the bacterial cellulose / epoxy resin / polyvinyl alcohol composite film and dry it at room temperature to obtain a bacterial cellulose / epoxy resin / polyvinyl alcohol composite film, recorded as BC / EP / PVA.

[0164] Performance Test:

[0165] 1) The stress-strain curve of the bacterial cellulose / epoxy resin / polyvinyl alcohol composite film (BC / EP / PVA) of this comparative example is as follows: Figure 2 shown.

[0166] Depend on Figure 2 It can be seen that the tensile strength of the BC / EP / PVA composite film is 71.78MPa, which is much lower than that of the CQDs / PVA / BC / EP composite film. EP is a hydrophobic polymer. After the BC / EP composite film is cured, it is difficult for PVA to further form hydrogen bonds with BC / EP; and when the BC / EP composite film is compounded with PVA, BC and EP first form a dense structure through hydrogen bonding and hot pressing, which will be destroyed in the PVA solution, resulting in a significant decrease in tensile strength. The solution of EP before curing is a non-water-soluble solution, and CQDs cannot dissolve in it, so CQDs cannot be evenly dispersed in the composite film with BC as the matrix.

[0167] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film, characterized in that: The following steps are involved: 1) dissolving carbon quantum dots in a polyvinyl alcohol aqueous solution to obtain a carbon quantum dots / polyvinyl alcohol aqueous dispersion; 2) extruding the bacterial cellulose hydrogel film to reduce its water content; 3) immersing the bacterial cellulose hydrogel of step 2) into the carbon quantum dot / polyvinyl alcohol aqueous dispersion of step 1) for immersion treatment, taking out and drying to obtain a carbon quantum dot / polyvinyl alcohol / bacterial cellulose composite film; 4) immersing the composite film of step 3) in a resin solution for immersion treatment, and drying under pressure and heating conditions to obtain a bacterial cellulose high-strength and high-transparency ultraviolet shielding composite film; Step 1) The carbon quantum dots are water-soluble carbon quantum dots prepared by a hydrothermal method using glucose as a raw material; Step 4) The resin is at least one of epoxy resin, acrylic resin and phenolic resin.

2. The method for preparing the bacterial cellulose high-strength and high-transparency UV-shielding composite film according to claim 1, characterized in that: Step 1) The concentration of the carbon quantum dots in the carbon quantum dots / polyvinyl alcohol aqueous dispersion is 0.01 mg / mL to 50 mg / mL.

3. The method for preparing the bacterial cellulose high-strength and high-transparency UV shielding composite film according to claim 1, characterized in that: The molecular weight of the polyvinyl alcohol in step 1) is 20,000 to 500,000; the concentration of the polyvinyl alcohol aqueous solution in step 1) is 0.1wt.% to 20wt.%.

4. The method for preparing the bacterial cellulose high-strength and high-transparency UV shielding composite film according to claim 1, characterized in that: Step 2) The extrusion pressure is 0.01-100 MPa, so that the water content of the bacterial cellulose hydrogel film is reduced to 5%-70%.

5. The method for preparing the bacterial cellulose high-strength and high-transparency UV-shielding composite film according to claim 1, characterized in that: The bacterial cellulose hydrogel film in step 3) is immersed in the carbon quantum dots / polyvinyl alcohol aqueous dispersion for 1 to 72 hours; the drying temperature in step 3) is room temperature to 100°C.

6. The method for preparing the bacterial cellulose high-strength and high-transparency UV shielding composite film according to claim 1, characterized in that: In step 4), the carbon quantum dot / polyvinyl alcohol / bacterial cellulose composite membrane is immersed in the resin solution for 0.1 to 8 hours; in step 4), the pressure is 0.01 to 100 MPa, the temperature is room temperature to 150° C., and the hot pressing time is 12 to 48 hours.

7. A bacterial cellulose high-strength and high-transparency UV shielding composite film, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.

8. An application of the bacterial cellulose high-strength and high-transparency UV shielding composite film as claimed in claim 7 in electronic displays, optical instruments and energy-saving buildings.

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