Cellulose-based composite film as well as preparation method and application thereof

Abstract

The invention discloses a cellulose-based composite film and a preparation method and application thereof, and belongs to the technical field of solar cell packaging materials, cellulose nanofibers are used as raw materials, polyvinyl alcohol is used as a modifier, graphite-like carbon nitride nanosheets are used as an ultraviolet light absorption conversion agent, and a CNNs (at) CNF / PVA ternary composite film is constructed. The cellulose-based composite film can absorb incident light in an ultraviolet wave band of 230-400 nm and convert the incident light into emitted light in a visible light wave band of 400-600 nm, so that the comprehensive light transmittance of the cellulose-based composite film in the visible light wave band can reach 90% or above, and the cellulose-based composite film has haze of 50% or above. Meanwhile, the thin film material has good foldable performance, and the thin film material can be repeatedly folded for more than 1000 times without cracking; the material is simple in preparation process, non-toxic and low in cost, and has a wide application prospect in the field of flexible solar cell packaging materials.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cell encapsulation materials, and particularly relates to a cellulose-based composite film, a preparation method thereof and an application thereof. Background Art

[0002] The development of solar cells has mainly included: single-crystalline / multi-crystalline silicon solar cells, thin-film solar cells, and perovskite solar cells. Although the semiconductor optoelectronic conversion materials used in the above-mentioned solar cells are different, their structures are mainly divided into an encapsulation layer, a semiconductor layer, and a backplane electrode layer.

[0003] The encapsulation layer mainly plays the roles of light transmission and protection of the semiconductor layer. Currently, the commonly used encapsulation layer materials in the market mainly include high-transparency glass, ethylene-vinyl acetate copolymer (EVA), polyethylene terephthalate (PET) and other polymer materials. However, although polymer materials such as EVA and PET can be recycled, they themselves still belong to petrochemical products and are not renewable. The glass-based encapsulation materials have a relatively large density (2.2 - 2.6 g / cm 3 ), so the mass of the solar cell panel per unit area is relatively large, and the existing glass-based encapsulation materials introduce impurities during the preparation process, which affects their light transmittance, thereby reducing the photoelectric conversion efficiency of the solar cells. In addition, most of the current solar cell encapsulation materials are hard materials due to the influence of raw materials and preparation processes during the preparation process. Some have a certain flexibility, but only belong to semi-flexible and cannot be folded at a large angle for use. Summary of the Invention

[0004] The present invention provides a cellulose-based composite film, a preparation method thereof and an application thereof, effectively solving the technical problems that the existing glass-based encapsulation materials introduce impurities during the preparation process, which affects their light transmittance, resulting in poor photoelectric conversion efficiency of the solar cells; most of the current solar cell encapsulation materials are hard materials and cannot be folded at a large angle for use. At the same time, a cellulose-based composite film encapsulation material with ultraviolet conversion and utilization, high visible light transmittance, high haze, repeatable folding and biodegradability is provided.

[0005] The present invention provides a preparation method of a cellulose-based composite film, comprising the following steps:

[0006] Preparing a cellulose nanofiber suspension (CNF suspension);

[0007] Using urea as a precursor, initially calcining at 520 - 580 °C to obtain a crude product of graphitic carbon nitride (g-C 3 N 4 ), grinding to obtain graphitic carbon nitride powder (g-C 3 N 4The powder was calcined again at 520 °C to 580 °C to obtain graphitic carbon nitride nanosheets, which were dispersed in water to obtain a graphitic carbon nitride nanosheet suspension (CNNs suspension).

[0008] Using cellulose nanofibers as raw materials, polyvinyl alcohol (PVA) as a modifier, and graphitic carbon nitride nanosheets as an ultraviolet light absorption and conversion agent, the cellulose nanofiber suspension was mixed with the polyvinyl alcohol solution to obtain a binary mixture, and the graphitic carbon nitride nanosheet suspension was added to obtain a ternary composite membrane agent, which was cast to obtain a cellulose-based composite film (CNNs@CNF / PVA ternary composite film).

[0009] As a preferred embodiment, the mass fraction of the cellulose nanofiber suspension is 0.2% to 1.0%, the mass fraction of the polyvinyl alcohol solution is 1% to 5%, and the mass ratio of the cellulose nanofiber suspension to the polyvinyl alcohol solution is 5 to 10:1.

[0010] As a preferred embodiment, the mass fraction of the graphitic carbon nitride nanosheet suspension is 0.1% to 0.5%, and the mass ratio of the binary mixture to the graphitic carbon nitride nanosheet suspension is 1:10 to 20.

[0011] As a preferred embodiment, the preparation method of the cellulose nanofiber suspension includes the following steps:

[0012] Water, 2,2,6,6-tetramethylpiperidine oxide and NaBr were added to poplar powder, and then an NaClO solution was added. The pH value was adjusted to 10 to obtain a suspension, which was stirred at room temperature, and the pH value was adjusted to 7 to obtain a crude product, which was vacuum filtered and washed, and dispersed with water to obtain a cellulose nanofiber suspension.

[0013] As a preferred embodiment, based on the mass of the poplar powder, the mass ratio of 2,2,6,6-tetramethylpiperidine oxide is 0.05% to 0.625%, the mass ratio of NaBr is 5% to 6.25%, and the mass ratio of NaClO is 22.35% to 27.94%.

[0014] As a preferred embodiment, the thickness of the cellulose-based composite film is 25 μm to 30 μm.

[0015] As a preferred embodiment, the time for the first calcination is 0.5 to 2 h, and the time for the second calcination is 0.5 to 2 h.

[0016] As a preferred embodiment, after casting, it is dried and dried at 40 °C to 80 °C for 3 h.

[0017] The second object of the present invention is to provide a cellulose-based composite film prepared by the above preparation method.

[0018] The third object of the present invention is to provide an application of the above cellulose-based composite film in the preparation of solar cell encapsulation materials.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The present invention provides a cellulose-based composite film, its preparation method and application. The present invention uses cellulose nanofibers as raw materials, polyvinyl alcohol as a modifier, and graphite-like carbon nitride nanosheets as ultraviolet light absorption and conversion agents to construct a CNNs@CNF / PVA ternary composite film. Since the molecular structure of polyvinyl alcohol is compact and has good light transmittance, the pure polyvinyl alcohol film has high light transmittance and good flexibility, but the haze is almost 0. While the pure cellulose nanofiber film has high light transmittance and high haze, but the film has poor elasticity and mechanical strength. The present invention mixes polyvinyl alcohol and cellulose nanofibers to obtain a film with high light transmittance, high haze and good flexibility, and is supplemented with graphite-like carbon nitride nanosheets as ultraviolet light absorption and conversion agents, so as to achieve the effect of absorbing and converting ultraviolet light into visible light. In addition, since both cellulose nanofibers and polyvinyl alcohol belong to long-chain macromolecular materials and contain a large number of hydroxyl groups, a large number of hydrogen bonds are retained between molecules after drying into a film, making it have good flexibility, thus endowing the cellulose-based composite film with excellent foldability.

[0021] The cellulose-based composite film prepared by the present invention has excellent light transmittance. According to the three-dimensional fluorescence test results: the cellulose-based composite film can absorb the incident light in the ultraviolet band of 230-400 nm and convert it into the emitted light in the visible light band of 400-600 nm. Therefore, the comprehensive light transmittance of the cellulose-based composite film in the visible light band can reach more than 90%, and it also has a haze of more than 50%. At the same time, this film material has good foldability and can be folded repeatedly more than 1000 times without cracking; the preparation process of this material is simple, non-toxic and low-cost, and has broad application prospects in the field of flexible solar cell encapsulation materials. Description of the Drawings

[0022] Figure 1 It is a high light transmittance display diagram of the cellulose-based composite film prepared in Example 1 of the present invention, where A is the cellulose-based composite film.

[0023] Figure 2 It is a high haze display diagram of the cellulose-based composite film prepared in Example 1 of the present invention.

[0024] Figure 3 It is a flexibility display diagram of the cellulose-based composite film prepared in Example 1 of the present invention.

[0025] Figure 4 is the light transmittance of the cellulose-based composite film prepared in Example 1 of the present invention in the wavelength range of 200 nm to 800 nm. Detailed implementation manners

[0026] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention will be further described below in conjunction with specific embodiments. However, the specific embodiments cited do not limit the present invention. The following test methods and detection methods are all conventional methods unless otherwise specified; the reagents and raw materials are all commercially available unless otherwise specified.

[0027] The existing solar cell encapsulation layer materials mentioned in the background technology of the present invention have the following problems: First, polymer materials such as ethylene-vinyl acetate copolymer (EVA) and polyethylene terephthalate (PET) are non-renewable; Second, the glass-based encapsulation materials result in low photoelectric conversion efficiency of solar cells; Third, most of the existing encapsulation materials are hard materials and cannot be folded at large angles. Based on the above technical problems, the present invention provides a cellulose-based composite film and its preparation method and application. Using cellulose nanofibers as raw materials, polyvinyl alcohol as a modifier, and graphite-like carbon nitride nanosheets as ultraviolet light absorption and conversion agents, a CNNs@CNF / PVA ternary composite film is constructed.

[0028] The technical solution of the present invention will be analyzed and described in detail below.

[0029] The present invention first provides a preparation method of a cellulose-based composite film, including the following steps:

[0030] Prepare a cellulose nanofiber suspension (CNF suspension);

[0031] Using urea as a precursor, calcine it for 0.5 to 2 hours at 520 to 580 °C for the first time to obtain a crude product of graphite-like carbon nitride (g-C 3 N 4 ), grind it to obtain graphite-like carbon nitride powder (g-C 3 N 4 powder), and calcine it again at 520 °C to 580 °C for 0.5 to 2 hours to obtain graphite-like carbon nitride nanosheets, disperse them in water to obtain a graphite-like carbon nitride nanosheet suspension (CNNs suspension); Among the above calcination temperatures, if the temperature is lower than 520 °C, it will lead to insufficient polymerization, and if the temperature is higher than 580 °C, the product will decompose and graphite-like carbon nitride powder cannot be obtained.

[0032] Using cellulose nanofibers as raw materials, polyvinyl alcohol (PVA) as a modifier, and graphitic carbon nitride nanosheets as an ultraviolet light absorption and conversion agent, the cellulose nanofiber suspension is mixed with the polyvinyl alcohol solution to obtain a binary mixture, and the graphitic carbon nitride nanosheet suspension is added to obtain a ternary composite film agent, which is cast to obtain a cellulose-based composite film (CNNs@CNF / PVA ternary composite film) with a thickness of 25 μm to 30 μm.

[0033] In the above technical solution, polyvinyl alcohol and cellulose nanofibers are mixed to obtain a film with high light transmittance, high haze, and good flexibility. Supplementary with graphitic carbon nitride nanosheets as an ultraviolet light absorption and conversion agent, it can absorb and convert ultraviolet light into visible light. In addition, since both cellulose nanofibers and polyvinyl alcohol are long-chain macromolecular materials and contain a large number of hydroxyl groups, a large number of hydrogen bonds are retained between molecules after drying into a film, making it have good flexibility, thus endowing the cellulose-based composite film with excellent foldability.

[0034] To obtain a composite film with excellent properties, the mass fraction of the cellulose nanofiber suspension is 0.2% to 1.0%, the mass fraction of the polyvinyl alcohol solution is 1% to 5%, and the mass ratio of the cellulose nanofiber suspension to the polyvinyl alcohol solution is 5 to 10:1. Under the above ratio of cellulose nanofibers to polyvinyl alcohol, a cellulose-based composite film with better light transmittance, haze, and foldability can be obtained.

[0035] To obtain a cellulose-based composite film that can convert ultraviolet light into visible light with better light conversion efficiency, the mass fraction of the graphitic carbon nitride nanosheet suspension is 0.1% to 0.5%, and the mass ratio of the binary mixture to the graphitic carbon nitride nanosheet suspension is 1:10 to 20.

[0036] In the present invention, the preparation method of the cellulose nanofiber suspension includes the following steps:

[0037] Water, 2,2,6,6-tetramethylpiperidine oxide, and NaBr are added to poplar powder, and then an NaClO solution is added. The pH value is adjusted to 10 to obtain a suspension, stirred at room temperature, the pH value is adjusted to 7 to obtain a crude product, vacuum filtered and washed, and dispersed in water to obtain a cellulose nanofiber suspension.

[0038] It should be noted that the above cellulose nanofiber suspension is prepared by the TEMPO oxidation method, specifically as follows: Poplar wood is crushed into 200-mesh wood powder using a high-speed crusher. 4 - 5 g of poplar wood powder is mixed into 500 mL of deionized water, 0.025 g of 2,2,6,6-tetramethylpiperidine oxide (Tempo) and 0.25 g of NaBr are added, and then 1.25 g of an NaClO solution with a concentration of 12 mmol / g is added dropwise. The pH value of the solution is adjusted to 10 using a 0.1 mmol / L NaOH solution. The resulting suspension is stirred at a speed of 300 r / min at room temperature for 6 hours. Finally, HCl is added dropwise to adjust the pH of the solution to 7 to terminate the reaction. The obtained Tempo-oxidized product is repeatedly washed by vacuum filtration with distilled water, and then the obtained sample is added to distilled water and ultrasonically dispersed in an ice bath for 1 hour to obtain the CNF suspension.

[0039] In order to obtain a cellulose-based composite film with better flatness, after casting, it is dried at 40°C to 80°C for 3 h. If the temperature is higher than 80°C, the drying is too fast, resulting in bubbles and wrinkles in the composite film; if the temperature is lower than 40°C, the drying speed is slow and the efficiency is low.

[0040] The technical effects of the present invention will be described in detail below through specific examples and comparative examples.

[0041] Example 1

[0042] A preparation method of a cellulose-based composite film includes the following steps:

[0043] S1. Prepare a 0.5% CNF suspension by the TEMPO oxidation method and name it Reagent A.

[0044] S2. Prepare a 5% PVA solution and name it Reagent B.

[0045] S3. Weigh 2 g of urea and place it in a muffle furnace, calcine it at 550°C for 2 hours to obtain a g-C 3 N 4 coarse product. After grinding it evenly, place it in a muffle furnace at 550°C again for 2 hours. The powder obtained after cooling is ultrasonically treated and dispersed in water to prepare a 0.1% CCNs suspension;

[0046] S4. Mix Reagent A and Reagent B in a mass ratio of 5:1, and after mixing evenly, obtain a compound reagent C;

[0047] S5. Add the CCNs suspension to the compound reagent C in a mass ratio of 1:10, and after mixing evenly, obtain a ternary composite film agent;

[0048] S6. Pour the ternary composite film agent into a mold and place it in a drying oven at 50 °C for 3 hours to obtain a cellulose-based composite film with a thickness of 25 μm. Its light transmittance, haze, and flexibility are as Figures 1 to 3 shown, and its light transmittance in the wavelength range of 200 nm to 800 nm is as Figure 4 shown.

[0049] Example 2

[0050] A preparation method of a cellulose-based composite film includes the following steps:

[0051] S1. Prepare a CNF suspension with a mass fraction of 0.5% by TEMPO oxidation method and name it Reagent A.

[0052] S2. Prepare a PVA solution with a mass fraction of 5% and name it Reagent B.

[0053] S3. Weigh 2 g of urea and place it in a muffle furnace. Calcinate it at 550 °C for 2 hours to obtain g-C 3 N 4 crude product. After grinding it evenly, place it in a muffle furnace at 550 °C again for 2 hours. The powder obtained after cooling is dispersed in water by ultrasonic treatment to prepare a CCNs suspension with a mass fraction of 0.5%.

[0054] S4. Mix Reagent A and Reagent B in a mass ratio of 10:1 and mix them evenly to obtain a compound reagent C.

[0055] S5. Add the CCNs suspension to the compound reagent C according to a mass ratio of 1:20 and mix them evenly to obtain a ternary composite film agent.

[0056] S6. Pour the ternary composite film agent into a mold and place it in a drying oven at 50 °C for 3 hours to obtain a cellulose-based composite film with a thickness of 28 μm.

[0057] Example 3

[0058] A preparation method of a cellulose-based composite film includes the following steps:

[0059] S1. Prepare a CNF suspension with a mass fraction of 0.5% by TEMPO oxidation method and name it Reagent A.

[0060] S2. Prepare a PVA solution with a mass fraction of 5% and name it Reagent B.

[0061] S3. Weigh 2 g of urea and place it in a muffle furnace. Calcinate it at 550 °C for 2 hours to obtain g-C 3 N 4The crude product was ground evenly and then calcined in a muffle furnace at 550 °C for 2 hours. After cooling, the obtained powder was dispersed in water by ultrasonic treatment to prepare a CNNs suspension with a mass fraction of 0.3%;

[0062] S4, Reagent A and Reagent B were mixed in a mass ratio of 8:1, and after mixing evenly, the compound reagent C was obtained;

[0063] S5, According to a mass ratio of 1:16, the CNNs suspension was added to the compound reagent C, and after mixing evenly, a ternary composite film agent was obtained;

[0064] S6, The ternary composite film agent was poured into a mold and placed in a drying oven at 50 °C for 3 hours to obtain a cellulose-based composite film with a thickness of 30 μm.

[0065] Example 4

[0066] A preparation method of a cellulose-based composite film, comprising the following steps:

[0067] S1, A CNF suspension with a mass fraction of 0.5% was prepared by the TEMPO oxidation method and named Reagent A.

[0068] S2, A PVA solution with a mass fraction of 5% was prepared and named Reagent B.

[0069] S3, Weigh 2 g of urea and place it in a muffle furnace, calcine it at 550 °C for 2 hours to obtain g-C 3 N 4 The crude product was ground evenly and then calcined in a muffle furnace at 550 °C for 2 hours. After cooling, the obtained powder was dispersed in water by ultrasonic treatment to prepare a CNNs suspension with a mass fraction of 0.2%;

[0070] S4, Reagent A and Reagent B were mixed in a mass ratio of 6:1, and after mixing evenly, the compound reagent C was obtained;

[0071] S5, According to a mass ratio of 1:12, the CNNs suspension was added to the compound reagent C, and after mixing evenly, a ternary composite film agent was obtained;

[0072] S6, The ternary composite film agent was poured into a mold and placed in a drying oven at 50 °C for 3 hours to obtain a cellulose-based composite film with a thickness of 26 μm.

[0073] Example 5

[0074] A preparation method of a cellulose-based composite film, comprising the following steps:

[0075] S1, A CNF suspension with a mass fraction of 0.5% was prepared by the TEMPO oxidation method and named Reagent A.

[0076] S2. Prepare a PVA solution with a mass fraction of 5% and name it Reagent B.

[0077] S3. Weigh 2 g of urea and place it in a muffle furnace. Calcinate it at 550 °C for 2 hours to obtain g-C 3 N 4 crude product. After grinding it evenly, place it in a muffle furnace at 550 °C again for 2 hours. The powder obtained after cooling is dispersed in water by ultrasonic treatment to prepare a CNNs suspension with a mass fraction of 0.4%.

[0078] S4. Mix Reagent A and Reagent B in a mass ratio of 9:1. After mixing evenly, obtain the compound reagent C.

[0079] S5. Add the CNNs suspension to the compound reagent C according to a mass ratio of 1:18. After mixing evenly, obtain the ternary composite film agent.

[0080] S6. Pour the ternary composite film agent into a mold and place it in a drying oven at 50 °C for 3 hours to obtain a cellulose-based composite film with a thickness of 25 μm.

[0081] Example 6

[0082] A preparation method of a cellulose-based composite film, comprising the following steps:

[0083] S1. Prepare a CNF suspension with a mass fraction of 0.5% by TEMPO oxidation method and name it Reagent A.

[0084] S2. Prepare a PVA solution with a mass fraction of 5% and name it Reagent B.

[0085] S3. Weigh 2 g of urea and place it in a muffle furnace. Calcinate it at 550 °C for 2 hours to obtain g-C 3 N 4 crude product. After grinding it evenly, place it in a muffle furnace at 550 °C again for 2 hours. The powder obtained after cooling is dispersed in water by ultrasonic treatment to prepare a CNNs suspension with a mass fraction of 0.25%.

[0086] S4. Mix Reagent A and Reagent B in a mass ratio of 7:1. After mixing evenly, obtain the compound reagent C.

[0087] S5. Add the CNNs suspension to the compound reagent C according to a mass ratio of 1:14. After mixing evenly, obtain the ternary composite film agent.

[0088] S6. Pour the ternary composite film agent into a mold and place it in a drying oven at 50 °C for 3 hours to obtain a cellulose-based composite film with a thickness of 27 μm.

[0089] To further illustrate the technical effects of the present invention, the present invention also sets up comparative examples, which are specifically as follows:

[0090] Comparative Example 1

[0091] Compared with Example 1, the difference lies in that the mass ratio of Reagent A and Reagent B is adjusted to 3:1.

[0092] A preparation method of a cellulose-based composite film includes the following steps:

[0093] S1. Prepare a CNF suspension with a mass fraction of 0.5% by TEMPO oxidation method, named Reagent A.

[0094] S2. Prepare a PVA solution with a mass fraction of 5%, named Reagent B.

[0095] S3. Weigh 2 g of urea and place it in a muffle furnace, calcine it at 550 °C for 2 hours to obtain g-C 3 N 4 crude product. After grinding evenly, place it in a muffle furnace at 550 °C again for 2 hours. The powder obtained after cooling is dispersed in water by ultrasonic treatment to prepare a CNNs suspension with a mass fraction of 0.1%.

[0096] S4. Mix Reagent A and Reagent B in a mass ratio of 3:1, and obtain a compound reagent C after mixing evenly.

[0097] S5. Add the CNNs suspension to the compound reagent C according to a mass ratio of 1:10, and obtain a ternary composite film agent after mixing evenly.

[0098] S6. Pour the ternary composite film agent into a mold and place it in a drying oven at 50 °C for 3 hours to obtain a cellulose-based composite film with a thickness of 25 μm.

[0099] Comparative Example 2

[0100] Compared with Example 1, the difference lies in that the mass ratio of Reagent A and Reagent B is adjusted to 12:1.

[0101] A preparation method of a cellulose-based composite film includes the following steps:

[0102] S1. Prepare a CNF suspension with a mass fraction of 0.5% by TEMPO oxidation method, named Reagent A.

[0103] S2. Prepare a PVA solution with a mass fraction of 5%, named Reagent B.

[0104] S3. Weigh 2 g of urea and place it in a muffle furnace, calcine it at 550 °C for 2 hours to obtain g-C 3 N 4The crude product was ground evenly and then calcined in a muffle furnace at 550 °C for 2 hours. After cooling, the obtained powder was dispersed in water by ultrasonic treatment to prepare a CNNs suspension with a mass fraction of 0.1%;

[0105] S4. Reagent A and Reagent B were mixed in a mass ratio of 12:1 and uniformly mixed to obtain a compound reagent C;

[0106] S5. According to a mass ratio of 1:10, the CNNs suspension was added to the compound reagent C and uniformly mixed to obtain a ternary composite film agent;

[0107] S6. The ternary composite film agent was poured into a mold and placed in a drying oven at 50 °C for 3 hours to obtain a cellulose-based composite film with a thickness of 25 μm.

[0108] The properties of the cellulose-based composite films prepared in Examples 1 to 6 and Comparative Examples 1 to 2 of the present invention were detected, and the results are shown in Table 1 below.

[0109] Table 1 Performance detection table of the cellulose-based composite film of the present invention

[0110] Transmittance / % Haze / % Number of repeated foldings Tensile stress / MPa Elongation at break / % Example 1 94.8 51.2 1059 64.2 60.5 Example 2 95.2 52.5 1086 63.2 61.4 Example 3 96.4 56.1 1108 64.8 60.8 Example 4 93.7 52.6 1068 62.8 59.4 Example 5 94.6 55.3 1114 61.7 58.7 Example 6 95.1 51.8 1049 63.0 60.2 Comparative Example 1 97.2 30.1 1038 52.0 82.7 Comparative Example 2 90.2 57.4 1102 68.5 30.5

[0111] As can be seen from Table 1, the cellulose-based composite film prepared by the present invention has excellent light transmittance. According to the three-dimensional fluorescence test results, the cellulose-based composite film can absorb the incident light in the ultraviolet band of 230-400 nm and convert it into the emitted light in the visible light band of 400-600 nm. Therefore, the comprehensive light transmittance of the cellulose-based composite film in the visible light band can reach more than 90%, and it also has a haze of more than 50%. At the same time, this film material has good foldability and can be folded repeatedly more than 1000 times without cracking. Comparative Examples 1 and 2 were based on the technical solution of Example 1, and the amounts of cellulose nanofibers and polyvinyl alcohol were reduced respectively. The obtained cellulose composite films had poor mechanical properties. The composite film of Comparative Example 1 had good light transmittance, but poor haze and high elongation at break; the composite film of Comparative Example 2 had good haze, but the light transmittance decreased.

[0112] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a cellulose-based composite film, characterized in that: The following steps are involved: preparing a cellulose nanofiber suspension; Using urea as a precursor, calcining at 520-580° C. to obtain a graphite-like carbon nitride crude product, grinding to obtain a graphite-like carbon nitride g-C3N4 powder, calcining again at 520-580° C. to obtain a graphite-like carbon nitride nanosheet, dispersing in water to obtain a graphite-like carbon nitride nanosheet suspension; Cellulose nanofibers are used as raw materials, polyvinyl alcohol is used as a modifier, and graphite-like carbon nitride nanosheets are used as ultraviolet light absorption conversion agents. The cellulose nanofiber suspension is mixed with a polyvinyl alcohol solution to obtain a binary mixture, and the graphite-like carbon nitride nanosheet suspension is added to obtain a ternary composite film agent, which is then injection molded to obtain a cellulose-based composite film.

2. The preparation method according to claim 1, characterized in that: The mass fraction of the cellulose nanofiber suspension is 0.2% to 1.0%, the mass fraction of the polyvinyl alcohol solution is 1% to 5%, and the mass ratio of the cellulose nanofiber suspension to the polyvinyl alcohol solution is 5 to 10:

1.

3. The preparation method according to claim 1, characterized in that: The mass fraction of the graphite-like carbon nitride nanosheet suspension is 0.1% to 0.5%, and the mass ratio of the binary mixture to the graphite-like carbon nitride nanosheet suspension is 1:10 to 20.

4. The preparation method according to claim 1, characterized in that: The method for preparing the cellulose nanofiber suspension comprises the following steps: Water, 2,2,6,6-tetramethylpiperidinyl oxide and NaBr were added to poplar wood powder, and then NaClO solution was added, and the pH value was adjusted to 10 to obtain a suspension. The suspension was stirred at room temperature and the pH value was adjusted to 7 to obtain a crude product. The crude product was washed by vacuum filtration and dispersed in water to obtain a cellulose nanofiber suspension.

5. The preparation method according to claim 4, characterized in that: Based on the mass of the poplar wood powder, the mass ratio of the 2,2,6,6-tetramethylpiperidinyl oxide is 0.05% to 0.625%, the mass ratio of NaBr is 5% to 6.25%, and the mass ratio of NaClO is 22.35% to 27.94%.

6. The preparation method according to claim 1, characterized in that: The thickness of the cellulose-based composite film is 25 μm to 30 μm.

7. The preparation method according to claim 1, characterized in that: The time of the first calcination is 0.5 to 2 hours, and the time of the second calcination is 0.5 to 2 hours.

8. The preparation method according to claim 1, characterized in that: The injection molding is followed by drying at 40° C. to 80° C. for 3 hours.

9. A cellulose-based composite film prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the cellulose-based composite film according to claim 9 in preparing solar cell packaging materials.

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