Preparation method and application of degradable holocellulose composite film

Abstract

The invention provides a preparation method of a degradable holocellulose composite film. The method comprises the following steps: preparing dispersion liquid of poplar cellulose and filiform oxidized nanocellulose, preparing a film, preparing dispersion liquid of paper pulp cellulose and regenerated spherical nanocellulose, and preparing degradable holocellulose composite dispersion liquid. According to the strategy, simple physical mixing is replaced by cooperation and reconstruction of two nanometer units with different dimensions and different chemical properties. Any function of each type of cellulose can act as a'functional unit 'or a'structure modifier'. The invention also provides application for replacing non-degradable plastic materials. According to the degradable holocellulose composite film material prepared by the invention, the mechanical property, the dispersity, the thermal stability and other properties can be adjusted according to the dosage of the oxidized nanocellulose fibrils and the regenerated spherical nanocellulose, the preparation method is simple, and the prepared holocellulose composite film is green, degradable and environment-friendly. The material is a promising material which is expected to replace non-degradable plastics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cellulose composite films, and particularly relates to a preparation method and application of a degradable all-cellulose composite film. BACKGROUND

[0002] The origin of plastic products can be traced back to 1899, and the main preparation material is polyethylene. Rapid development is mainly due to corrosion resistance, non-toxicity, no odor, excellent chemical stability, and strong plasticity. Its emergence has indeed driven the development of different industries. However, while meeting human needs, it has also caused harm to the social environment and human health. Currently, microplastics have been found in oceans, soil, and human bodies. Therefore, it is urgent to seek completely biodegradable, low safety risk, and harmless to the environment, human and animal health alternatives.

[0003] Currently, film materials composed of bio-based or completely biodegradable are gradually becoming the key direction of green material research. Among many materials, cellulose is considered to be the most potential candidate material and environmental material. Moreover, in addition to the advantages of low cost, good biological safety and biological functionality, this resource can also be produced on a large scale and sustainably, and the total amount of cellulose available for processing every year is incalculable. In addition, the raw materials for preparing cellulose are widely sourced, which can be derived from wood and its roots, bast fibers, leaf fibers, seed fibers, core fibers, grass and reed fibers, etc. Cellulose materials as a new green bioeconomic material can provide a new green, environmentally friendly and economically valuable way for agricultural and forestry waste. However, cellulose is affected by the exchange rate of solvents and non-solvents during secondary processing, which affects the high orientation of cellulose and causes aggregation of cellulose, and cellulose films are prone to shrinkage, cracking and other phenomena. The mechanical strength of the film is also quite different in different states. This is the main factor limiting the use of cellulose film materials. The aggregation caused by the interaction between the functional particles and the matrix enhances the body and the matrix. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art, and to provide a preparation method and application of a degradable all-cellulose composite film. The degradable all-cellulose composite film material prepared by the method can adjust the mechanical properties, dispersibility, and thermal stability according to the amount of oxidized nanocellulose filaments and regenerated spherical nanocellulose. The preparation method is simple, the prepared all-cellulose composite film is green and degradable, and it is a promising material that can replace non-degradable plastics.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is: a preparation method of a degradable all-cellulose composite film, which is characterized by comprising the following steps: S1, preparation of poplar cellulose: The poplar chips are dispersed in deionized water, soaked in a water bath at a temperature of 70-90 DEG C for 4-6 hours, impurities are removed, and then the dried poplar chips are added to an H2O2 solution of glacial acetic acid, soaked at room temperature for 12-18 hours, then soaked at a temperature of 70-90 DEG C for 6-12 hours, washed with deionized water until neutral, and dried to obtain poplar cellulose; S2, preparation of a dispersion of oxidized nanocellulose filaments: The poplar cellulose obtained in S1 is dispersed in a Na2CO3-NaHCO3 buffer solution, then NaBr and 2,2,6,6-tetramethylpiperidine oxide are added, an aqueous NaClO solution is added dropwise while stirring at a temperature of 30-60 DEG C, after the dropwise addition is completed, constant temperature stirring is carried out at 30-60 DEG C for 1-4 hours, then anhydrous ethanol is added to terminate the reaction, washed with deionized water until neutral, and then dispersed in deionized water, ultrasonic treatment is carried out to obtain a dispersion of oxidized nanocellulose filaments; S3, preparation of pulp cellulose: The waste pulp is weighed and dispersed in deionized water, soaked in a water bath at a temperature of 75-85 DEG C for 3-5 hours, during which ice acetic acid and sodium chlorite are added 3-5 times at an interval of 1 hour, then left to stand at room temperature for 12-24 hours to obtain pulp cellulose; S4, preparation of a dispersion of regenerated spherical nanocellulose: Sodium hydroxide, thiourea and urea are added to deionized water to obtain a pre-cooled solution at a temperature of -15 to -10 DEG C, then the pulp cellulose obtained in S3 is added to the pre-cooled solution while stirring at a temperature of -15 to -10 DEG C and a rotation speed of 300-450 rpm, stirring is carried out for 30-90 minutes, then centrifugal treatment is carried out at a rotation speed of 5000-8000 rpm for 10-20 minutes to remove the precipitate, deionized water is added to the supernatant, and stirring is carried out at a rotation speed of 300 rpm for 30-60 minutes, then ultrasonic treatment is carried out to obtain a dispersion of regenerated spherical nanocellulose; S5, the dispersion of oxidized nanocellulose filaments obtained in S2 and the dispersion of regenerated spherical nanocellulose obtained in S4 are mixed, ultrasonic treatment is carried out to obtain an all-cellulose composite dispersion, vacuum filtration is carried out to obtain a degradable all-cellulose composite film.

[0006] Preferably, the H2O2 solution of glacial acetic acid in S1 is a mixture of glacial acetic acid and H2O2 with a mass ratio of 1: (1-1.5).

[0007] Preferably, the drying conditions in S1 are all 25-40℃ for 48-60h.

[0008] Preferably, the Na2CO3-NaHCO3 buffer solution in S2 is prepared by adding Na2CO3 into deionized water, dissolving, and then adding NaHCO3 to continue dissolving, and the amount ratio of Na2CO3, deionized water, and NaHCO3 in the Na2CO3-NaHCO3 buffer solution is 3.71g:500mL:1.26g; the dropping rate in S2 is 10-15mL / h, and the ultrasonic treatment conditions are 600W for 30-60min.

[0009] Preferably, the NaClO aqueous solution in S2 is a NaClO aqueous solution with a mass fraction of 4-5%; the amount ratio of the poplar cellulose, NaBr, 2,2,6,6-tetramethylpiperidine oxide, and NaClO aqueous solution in S2 is 5g:1.0g:0.1g:(30-60)mL; and the mass fraction of the oxidized nanocellulose fibrils in the dispersion of the oxidized nanocellulose fibrils in S2 is 0.05-0.1%.

[0010] Preferably, the amount ratio of the waste paper pulp, deionized water, added glacial acetic acid, and added sodium chlorite in S3 is (20-25)g:(650-850)mL:(5-10)mL:(7.5-15)g.

[0011] Preferably, the mass ratio of sodium hydroxide, thiourea, urea, and deionized water in the pre-cooled solution in S4 is 8:6.5:8:77.5; the amount ratio of the pre-cooled solution and the paper pulp cellulose in S4 is (77.5-100)mL:1.5g; the mass fraction of the regenerated spherical nanocellulose in the dispersion of the regenerated spherical nanocellulose in S4 is 0.1-0.15%; and the ultrasonic treatment conditions in S4 are 600W for 30-60min.

[0012] Preferably, the mass ratio of the oxidized nanocellulose fibrils in the dispersion of the oxidized nanocellulose fibrils and the regenerated spherical nanocellulose in the dispersion of the regenerated spherical nanocellulose in S5 is 1:(1-5).

[0013] Preferably, the ultrasonic treatment conditions in S5 are 600W for 30-60min, and the thickness of the degradable whole-cellulose composite film in S5 is 40-60μm.

[0014] The present invention also provides the application of the biodegradable all-cellulose composite film prepared by the above preparation method, wherein the biodegradable all-cellulose composite film is used to replace non-degradable plastic materials in the preparation of food packaging materials, novel wound dressings, transparent conductive films or separation filter membranes.

[0015] Compared with the prior art, the present invention has the following advantages: This invention uses agricultural and forestry waste as raw materials, increasing the possibility of high-value utilization of waste; simultaneously, it proposes a green process of "replacing harm with waste," which can replace the use of plastics; the strategy of this invention is to replace simple physical mixing with the synergistic and reconstructive use of two nano-units with different dimensions and chemical properties. Each type of cellulose can act as a "functional unit" or "structural regulator." The biodegradable all-cellulose composite film material prepared by this invention can have its mechanical, dispersible, and thermal stability properties adjusted according to the amount of oxidized cellulose nanofibers and regenerated spherical cellulose nanofibers used. With a dispersion volume of 10 mL of oxidized cellulose nanofibers and 10 mL of regenerated spherical cellulose nanofibers, the mechanical strength is 36 MPa, the absolute value of the potential can reach 45 mV, and the highest degradation temperature can reach 328.3℃. The method for preparing biodegradable all-cellulose composite films is simple, and the resulting all-cellulose composite films are green and biodegradable, making them promising materials that can replace non-degradable plastics. They possess green preparation processes; biodegradability and sustainability; biocompatibility and safety; adjustable mechanical properties, dispersibility, thermal stability, and functional modification capabilities, making them suitable for applications such as food packaging materials, novel wound dressings, transparent conductive films, and separation filtration membranes.

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a SEM image of poplar cellulose prepared in step S1 of Example 1 of the present invention.

[0018] Figure 2 This is a TEM image of the dispersion of fibrous oxidized nanocellulose prepared in step S2 of Example 1 of the present invention.

[0019] Figure 3 This is a SEM image of the pulp cellulose prepared in step S3 of Example 1 of the present invention.

[0020] Figure 4 The images shown are TEM (a) and AFM (b) images of the dispersion of regenerated spherical nanocellulose obtained in step S4 of Example 1 of the present invention.

[0021] Figure 5The image shows a cross-sectional SEM image of the biodegradable all-cellulose composite film prepared in Example 1 of the present invention, where a is a 10 μm dimension and b is a 500 nm dimension.

[0022] Figure 6 shows an SEM image of the surface of the biodegradable all-cellulose composite film prepared in Example 1 of the present invention.

[0023] Figure 7 The potential test spectra are those of the regenerated spherical nanocellulose dispersion prepared in step S4 of Example 1 of the present invention and the biodegradable whole cellulose composite dispersion prepared in step S5.

[0024] Figure 8 The mechanical property test spectrum of the biodegradable all-cellulose composite film prepared in Example 1 of the present invention.

[0025] Figure 9 The thermal stability test spectrum is shown for the biodegradable all-cellulose composite film prepared in Example 1 of the present invention.

[0026] Figure 10 This is a photograph of the biodegradable all-cellulose composite film prepared in Example 1 of the present invention.

[0027] Figure 11 This is a photograph of the biodegradable all-cellulose composite film prepared in Example 2 of the present invention after adsorbing wastewater.

[0028] Figure 12 This is a photograph of the biodegradable all-cellulose composite film prepared in Example 3 of the present invention after degradation in soil. Detailed Implementation

[0029] Example 1 The method for preparing the biodegradable all-cellulose composite film in this embodiment is as follows: S1. Preparation of poplar cellulose: Poplar wood chips were dispersed in deionized water and soaked in a water bath at 80°C for 4 hours to remove impurities. After drying at 25°C for 48 hours, the dried poplar wood chips were added to a solution of glacial acetic acid (H2O2) and soaked at room temperature for 12 hours, then soaked at 80°C for 6 hours. After washing with deionized water until neutral, the chips were dried at 25°C for 48 hours to obtain poplar cellulose. The glacial acetic acid H2O2 solution is a mixture of glacial acetic acid and H2O2 in a mass ratio of 1:1; like Figure 1 As shown, the poplar cellulose prepared in this step all maintain a relatively long length and presents as fibrous bands.

[0030] S2. Preparation of a dispersion of fibrous oxidized cellulose nanoparticles: 5g of poplar cellulose obtained from S1 was dispersed in 500mL of Na2CO3-NaHCO3 buffer solution, and then 1.0g of NaBr and 0.1g of TEMPO (2,2,6,6-tetramethylpiperidine oxide) were added. At 30℃, 30mL of 5% (w / w) NaClO aqueous solution was added dropwise at a rate of 10 mL / h while stirring. After the addition was complete, the mixture was stirred at 30℃ for 1h, and then the reaction was stopped with anhydrous ethanol. After rinsing with deionized water until neutral, the mixture was dispersed in deionized water and ultrasonically treated for 30min at 600W to obtain a dispersion of oxidized nanocellulose fibers. The mass fraction of oxidized nanocellulose fibers in the dispersion was 0.05%. The dispersion of oxidized cellulose nanofibers prepared in this step was vacuum filtered to prepare a cellulose nanofiber film with a thickness of 40 μm, which will be used subsequently. Figures 8-9 A control group in the performance testing of biodegradable all-cellulose composite films; The preparation method of Na2CO3-NaHCO3 buffer solution is as follows: Na2CO3 is added to deionized water and dissolved. Then, NaHCO3 is added and dissolved further. The ratio of Na2CO3, deionized water and NaHCO3 in the Na2CO3-NaHCO3 buffer solution is 3.71g:500mL:1.26g. This step involves oxidizing the hydroxyl groups on poplar cellulose, allowing the cellulose to be better "disassembled" into fine filaments. Simultaneously, the introduction of carboxyl groups improves the dispersibility of the oxidized cellulose nanofiber dispersion. This is then combined with ultrasonic treatment to obtain poplar-based oxidized cellulose nanofibers. This method allows fine fibers to peel off from the fiber bundle, forming well-dispersed fine filaments. These finitely reduced fine filaments create numerous contact points, forming an interconnected three-dimensional network. The average diameter is 7.7 nm, and the network structure formed by the interconnected contact points expands the size to 44 nm. Figure 2 ).

[0031] S3. Preparation of pulp cellulose: Weigh 20g of waste paper pulp and disperse it in 650mL of deionized water. Soak it in a water bath at 75℃ for 4 hours. During this period, add 5mL of glacial acetic acid and 7.5g of sodium chlorite every 1 hour for a total of 4 times. Then let it stand at room temperature for 12 hours to obtain paper pulp cellulose. like Figure 3 As shown, the pulp cellulose prepared in this step is smooth overall, presents a ribbon shape, and has a size of 20-60 μm, which is in the micrometer range.

[0032] S4. Preparation of a dispersion of regenerated spherical nanocellulose: Sodium hydroxide, thiourea, and urea were added to deionized water at a temperature of -10℃ to obtain a pre-cooled solution; the mass ratio of sodium hydroxide, thiourea, urea, and deionized water in the pre-cooled solution was 8:6.5:8:77.5. Then, under conditions of -10℃ and 300 rpm, 1.5 g of pulp cellulose obtained in S3 was added to 77.5 mL of the pre-cooled solution while stirring. After stirring for 30 min, the solution was centrifuged at 8000 rpm for 10 min to remove precipitates. Deionized water was added to the supernatant, and the solution was regenerated by stirring at 300 rpm for 30 min. After ultrasonic treatment at 600 W for 30 min, a dispersion of regenerated spherical nanocellulose was obtained. The mass fraction of regenerated spherical nanocellulose in the dispersion was 0.1%. The dispersion of regenerated spherical nanocellulose prepared in this step was vacuum filtered to prepare a 40 μm thick film of regenerated spherical nanocellulose, which will be used subsequently... Figure 7 and Figure 9 A control group in the performance testing of biodegradable all-cellulose composite films; In this step, using deionized water as a protic solvent as the coagulation bath provides higher proton affinity, molecular steric effects, and competitive hydrogen bonding, resulting in rapid regeneration. These dissolved cellulose clusters act as growth points, gradually forming spherical particles during the rapid regeneration process. Because the original highly oriented arrangement of cellulose molecules is disrupted, the strong hydrogen bonding of the newly formed cellulose molecular chains causes the cellulose molecules to aggregate, exhibiting severe aggregation phenomena, such as... Figure 4 As shown in Figure a. The spherical shape is clearly visible, but the size is relatively large, as... Figure 4 As shown in Figure b, how to achieve the dispersion of regenerated spherical nanocellulose is a pressing problem that needs to be solved.

[0033] S5. The dispersion of oxidized nanocellulose filaments obtained in S2 and the dispersion of regenerated spherical nanocellulose obtained in S4 are mixed and ultrasonically treated for 30 minutes under a power of 600W to obtain a whole cellulose composite dispersion. After vacuum filtration, a biodegradable whole cellulose composite film with a thickness of 40μm is obtained. The mass ratio of the oxidized nanocellulose fibers in the dispersion of the oxidized nanocellulose fibers to the regenerated spherical nanocellulose in the dispersion of the regenerated spherical nanocellulose is 1:1.

[0034] In this step, oxidized cellulose nanofibers with a filamentous morphology and regenerated spherical cellulose nanofibers with a spherical morphology underwent assisted self-assembly under vacuum filtration. During this process, the network structure of the oxidized cellulose nanofibers effectively disperses and fills the regenerated spherical cellulose nanofibers, filling cracks. Due to its nanoscale effect and strong interaction with the regenerated spherical cellulose nanofibers, intermolecular and intramolecular hydrogen bonds are established, gradually making the structure of the biodegradable all-cellulose composite film denser, resulting in a smooth and uniform longitudinal section. Figure 5 As shown in Figure a, when the longitudinal section of the all-cellulose composite film is magnified to 500 nm, a distinct longitudinal structure composed of spherical particles can be observed. These spherical particles are regenerated spherical nanocellulose, as shown in Figure a. Figure 5 As shown in Figure b, due to the synergistic effect of oxidized nanocellulose filaments and regenerated spherical nanocellulose, the spherical particles are uniformly dispersed, small in size, and capable of forming a dense structure.

[0035] The surface of the prepared biodegradable all-cellulose composite film is as follows: Figure 6 As shown, since both oxidized cellulose nanofibers and regenerated spherical cellulose nanofibers are composed of cellulose materials, there is no clear boundary between them. This allows for the formation of a relatively dense, biodegradable all-cellulose composite film with spherical protrusions on its surface.

[0036] (a) Dispersion characterization: The dispersion performance of different types of cellulose solutions was tested using a potentiometer (Zeta potential, Zetasizer Nano ZS 90 Zeta).

[0037] In this embodiment, the Zeta potentials of the regenerated spherical nanocellulose dispersion prepared in step S4 and the biodegradable whole cellulose composite dispersion prepared in step S5 are as follows: Figure 7 As shown, the dispersion of regenerated spherical nanocellulose exhibits poor dispersibility. Even after ultrasonic treatment, it re-aggregates after a brief dispersion, with a potential of -20 mV. This weak electrostatic repulsion cannot resist the hydrogen bonds formed between the regenerated spherical nanocellulose fibers, leading to severe flocculation. A synergistic effect between electrostatic and steric repulsion stabilization mechanisms can achieve uniform distribution of regenerated spherical nanocellulose and prevent aggregation. A stable dispersion is achieved when the absolute value of the zeta potential of the dispersion exceeds 30 mV. After 40 days of storage, the zeta potential of the all-cellulose composite dispersion is -45 mV, demonstrating its excellent stability.

[0038] (ii) Mechanical characterization: The mechanical properties of the thin film samples were tested using a micromechanical testing machine (5948).

[0039] The mechanical properties of the fibrous oxidized cellulose nanofilm prepared in step S2 and the biodegradable all-cellulose composite film prepared in step S5 are as follows: Figure 8 As shown, preparing thin film materials with a spherical morphology is challenging. Once the interfiber bonding reaches a sufficiently high level, further improvements in mechanical strength increasingly depend on the integrity and density of the fiber network, while shortening the fiber length compromises this integrity and density. Furthermore, the preparation of regenerated spherical nanocellulose films requires the breaking and recombination of hydrogen bonds, which has a significant impact on mechanical properties. Regenerated spherical nanocellulose materials often suffer from poor film-forming properties, frequently exhibiting defects such as poor dispersibility, shrinkage, wrinkling, and cracking; some materials even cannot undergo mechanical strength testing. When filamentous oxidized nanocellulose is used as a reinforcing agent, and a water-evaporation-induced film self-assembly method is employed to strengthen the regenerated spherical nanocellulose matrix, the characteristics of different cellulose materials are fully utilized. This multi-scale, multi-morphological cellulose structure retains both the film-forming properties and flexibility of filamentous oxidized nanocellulose and the strength of regenerated spherical nanocellulose, achieving a perfect balance between tensile strength and flexibility. With the increase of the proportion of filamentous oxidized cellulose nanofibers, the cellulose nanofibers embed into the molecular chains of regenerated spherical cellulose nanofibers, thereby improving the dispersibility of the biodegradable all-cellulose composite film and inhibiting crack propagation. The tensile strength of the filamentous oxidized cellulose nanofiber film is 22 MPa, while the mechanical strength of the biodegradable all-cellulose composite film increases to 36 MPa. This is a synergistic enhancement strategy where 1+1 is greater than 2, enabling the simultaneous improvement of the mechanical properties of both the filamentous oxidized cellulose nanofiber film and the regenerated spherical cellulose nanofiber film. In particular, it improves the mechanical properties of the regenerated spherical cellulose nanofiber film that could not be tested.

[0040] (III) Thermal stability characterization: The thermal stability of different types of cellulose samples was tested using a thermogravimetric analyzer (TA-Q600).

[0041] The thermal stability properties of the fibrous oxidized cellulose nanofilm prepared in step S2, the regenerated spherical cellulose nanofilm prepared in step S4, and the biodegradable all-cellulose composite film prepared in step S5 are as follows: Figure 9As shown, the regenerated spherical nanocellulose film exhibits better thermal stability than the filamentous oxidized nanocellulose film. The maximum degradation temperature of the regenerated spherical nanocellulose film is 346.7℃, while the filamentous oxidized nanocellulose film has two peaks, at 276.5℃ and 324.7℃. This is due to the decarbonization / decarboxylation behavior of the thermally unstable sodium gluconate units after oxidation. The maximum degradation temperature of the biodegradable all-cellulose composite film is reduced to 328.3℃, which is still better than that of the filamentous oxidized nanocellulose film. This is a simple and green method for preparing biodegradable all-cellulose composite films, and it is a promising material to replace non-biodegradable plastics. Through a mutual reinforcement strategy, the regenerated spherical nanocellulose serves as the matrix material, with the reinforcing material filamentous oxidized nanocellulose filling the gaps and preventing crack propagation. At the same time, the regenerated spherical nanocellulose can improve the thermal stability of the filamentous oxidized nanocellulose.

[0042] The transparency of the biodegradable all-cellulose composite film prepared in step S5 is shown in the physical image. Figure 10 As shown, placing the biodegradable all-cellulose composite film on a green leaf allows for clear observation of the leaf's texture. This demonstrates that the biodegradable all-cellulose composite film also possesses good light transmittance. It can be used for food packaging films and packaging materials requiring transparency and mechanical properties. It is a low-risk alternative to plastic products that is harmless to the environment, human health, and animal health.

[0043] The biodegradable all-cellulose composite film prepared in this embodiment can be used to replace non-degradable plastic products. It has a green preparation process; biodegradability and sustainability, biocompatibility and safety; adjustable mechanical properties, dispersibility, thermal stability and functional modification, making it suitable for food packaging materials, novel wound dressings, transparent conductive films, separation and filtration membranes, etc.

[0044] Example 2 The method for preparing the biodegradable all-cellulose composite film in this embodiment is as follows: S1. Preparation of poplar cellulose: Poplar wood chips were dispersed in deionized water and soaked in a water bath at 70°C for 6 hours to remove impurities. After drying at 40°C for 60 hours, the dried poplar wood chips were added to a solution of glacial acetic acid and H2O2 and soaked at room temperature for 18 hours, followed by soaking at 70°C for 12 hours. The chips were then washed with deionized water until neutral and dried to obtain poplar cellulose. The glacial acetic acid and H2O2 solution was a mixture of glacial acetic acid and H2O2 in a mass ratio of 1:1.5. S2. Preparation of a dispersion of fibrous oxidized cellulose nanoparticles: The poplar cellulose obtained in S1 was dispersed in a Na2CO3-NaHCO3 buffer solution, and then NaBr and 2,2,6,6-tetramethylpiperidine oxide were added. At 60℃, a 4% (w / w) NaClO aqueous solution was added dropwise at a rate of 15 mL / h while stirring. After the addition was complete, the mixture was stirred at 60℃ for 4 h. The reaction was then stopped with anhydrous ethanol. After rinsing with deionized water until neutral, the mixture was dispersed in deionized water and subjected to a reaction at a power of 600... After ultrasonic treatment for 30 min under W conditions, a dispersion of oxidized nanocellulose fibers was obtained. The Na2CO3-NaHCO3 buffer solution was prepared by adding Na2CO3 to deionized water, dissolving it, and then adding NaHCO3 to continue dissolving. The ratio of Na2CO3, deionized water, and NaHCO3 in the Na2CO3-NaHCO3 buffer solution was 3.71 g: 500 mL: 1.26 g. The ratio of poplar cellulose, NaBr, 2,2,6,6-tetramethylpiperidine oxide, and NaClO aqueous solution was 5 g: 1.0 g: 0.1 g: 60 mL. The mass fraction of oxidized nanocellulose fibers in the dispersion of oxidized nanocellulose fibers in S2 was 0.1%. S3. Preparation of pulp cellulose: Weigh waste paper pulp, disperse it in deionized water, and soak it in a water bath at 85°C for 5 hours. During this period, add glacial acetic acid and sodium chlorite every 1 hour for a total of 5 times. Then let it stand at room temperature for 24 hours to obtain paper pulp cellulose. The ratio of waste pulp, deionized water, glacial acetic acid (previously added), and sodium chlorite (previously added) is 25g:850mL:10mL:15g. S4. Preparation of a dispersion of regenerated spherical nanocellulose: Sodium hydroxide, thiourea, and urea were added to deionized water at a temperature of -15℃ to obtain a pre-cooled solution. Then, at -15℃ and 450 rpm, the pulp cellulose obtained in step S3 was added to the pre-cooled solution while stirring. After stirring for 90 min, the solution was centrifuged at 8000 rpm for 20 min to remove precipitates. Deionized water was added to the supernatant, and the solution was regenerated by stirring at 450 rpm for 90 min. Finally, the solution was ultrasonically treated at 600 W for 60 min to obtain a dispersion of regenerated spherical nanocellulose. The mass ratio of sodium hydroxide, thiourea, urea, and deionized water in the pre-cooled solution was 8:6.5:8:77.5. The ratio of the pre-cooled solution to the pulp cellulose in step S4 was 100 mL:1.5 g. The mass fraction of regenerated spherical nanocellulose in the dispersion of regenerated spherical nanocellulose in step S4 was 0.15%. S5. The dispersion of oxidized nanocellulose fibers obtained in S2 and the dispersion of regenerated spherical nanocellulose obtained in S4 are mixed and ultrasonically treated for 60 minutes at a power of 600W to obtain a whole cellulose composite dispersion. The dispersion is then vacuum filtered to obtain a biodegradable whole cellulose composite film with a thickness of 60μm. The mass ratio of oxidized nanocellulose fibers in the dispersion of oxidized nanocellulose fibers to regenerated spherical nanocellulose in the dispersion of regenerated spherical nanocellulose is 1:5.

[0045] This embodiment also provides an application of the biodegradable all-cellulose composite film prepared by the above preparation method, wherein the biodegradable all-cellulose composite film is used to replace non-degradable plastic materials for the preparation of separation and filtration membranes.

[0046] When the biodegradable all-cellulose composite membrane prepared in this embodiment is used as a separation filtration membrane, the biodegradable all-cellulose composite membrane that adsorbs wastewater is as follows: Figure 11 As shown.

[0047] The biodegradable all-cellulose composite film prepared in this embodiment was placed under wastewater containing Congo red and a fluorescent whitening agent. As the wastewater flowed through, it was adsorbed onto the film, thus clarifying the wastewater. Compared to synthetic adsorbent materials, the biodegradable all-cellulose composite film prepared in this embodiment has low production energy consumption and is environmentally friendly after disposal. Its dense structure allows for repeated reuse, making a significant contribution to environmental protection.

[0048] Example 3 The method for preparing the biodegradable all-cellulose composite film in this embodiment is as follows: S1. Preparation of poplar cellulose: Poplar wood chips were dispersed in deionized water and soaked in a water bath at 90°C for 5 hours to remove impurities. After drying at 30°C for 55 hours, the dried poplar wood chips were added to a solution of glacial acetic acid and H2O2 and soaked at room temperature for 16 hours, followed by soaking at 90°C for 10 hours. The chips were then washed with deionized water until neutral and dried to obtain poplar cellulose. The glacial acetic acid and H2O2 solution was a mixture of glacial acetic acid and H2O2 in a mass ratio of 1:1.2. S2. Preparation of a dispersion of fibrous oxidized cellulose nanoparticles: The poplar cellulose obtained in S1 was dispersed in a Na2CO3-NaHCO3 buffer solution, and then NaBr and 2,2,6,6-tetramethylpiperidine oxide were added. At 40°C, a 5% (w / w) NaClO aqueous solution was added dropwise at a rate of 12 mL / h while stirring. After the addition was complete, the mixture was stirred at 40°C for 2 h. The reaction was then stopped with anhydrous ethanol. After rinsing with deionized water until neutral, the mixture was dispersed in deionized water and subjected to a reaction at a power of 600... After ultrasonic treatment for 40 min under W conditions, a dispersion of oxidized nanocellulose fibers was obtained. The Na2CO3-NaHCO3 buffer solution was prepared by adding Na2CO3 to deionized water, dissolving it, and then adding NaHCO3 to continue dissolving. The ratio of Na2CO3, deionized water, and NaHCO3 in the Na2CO3-NaHCO3 buffer solution was 3.71 g: 500 mL: 1.26 g. The ratio of poplar cellulose, NaBr, 2,2,6,6-tetramethylpiperidine oxide, and NaClO aqueous solution was 5 g: 1.0 g: 0.1 g: 40 mL. The mass fraction of oxidized nanocellulose fibers in the dispersion of oxidized nanocellulose fibers in S2 was 0.08%. S3. Preparation of pulp cellulose: Weigh waste paper pulp, disperse it in deionized water, and soak it in a water bath at 80°C for 3 hours. During this period, add glacial acetic acid and sodium chlorite every 1 hour for a total of 3 times. Then let it stand at room temperature for 20 hours to obtain paper pulp cellulose. The ratio of waste pulp, deionized water, glacial acetic acid (previously added), and sodium chlorite (previously added) is 22g:750mL:8mL:10g. S4. Preparation of a dispersion of regenerated spherical nanocellulose: Sodium hydroxide, thiourea, and urea were added to deionized water at a temperature of -12℃ to obtain a pre-cooled solution. Then, at -12℃ and 350 rpm, the pulp cellulose obtained in step S3 was added to the pre-cooled solution while stirring. After stirring for 50 min, the solution was centrifuged at 6000 rpm for 15 min to remove precipitates. Deionized water was added to the supernatant, and the solution was regenerated by stirring at 350 rpm for 50 min. Finally, the solution was ultrasonically treated at 600 W for 40 min to obtain a dispersion of regenerated spherical nanocellulose. The mass ratio of sodium hydroxide, thiourea, urea, and deionized water in the pre-cooled solution was 8:6.5:8:77.5. The ratio of the pre-cooled solution to the pulp cellulose in step S4 was 90 mL:1.5 g. The mass fraction of regenerated spherical nanocellulose in the dispersion of regenerated spherical nanocellulose in step S4 was 0.12%. S5. The dispersion of oxidized nanocellulose fibers obtained in S2 and the dispersion of regenerated spherical nanocellulose obtained in S4 are mixed and ultrasonically treated for 40 minutes at a power of 600 W to obtain a whole cellulose composite dispersion. The dispersion is then vacuum filtered to obtain a biodegradable whole cellulose composite film with a thickness of 50 μm. The mass ratio of oxidized nanocellulose fibers in the dispersion of oxidized nanocellulose fibers to regenerated spherical nanocellulose in the dispersion of regenerated spherical nanocellulose is 1:3.

[0049] This embodiment also provides the application of the biodegradable all-cellulose composite film prepared by the above preparation method. The biodegradable all-cellulose composite film is used to replace non-degradable plastic materials. The biodegradable all-cellulose composite film prepared in this embodiment has good soil degradability.

[0050] The biodegradable all-cellulose composite film prepared in this embodiment, after being degraded in soil, is shown in the following image. Figure 12 The biggest difference between bioplastics and traditional plastics is their biodegradability. Because both are composed of cellulose and no other functional components are added, the biodegradable all-cellulose composite film is fully biodegradable. This example compares the soil degradability of commercially available plastic films, biodegradable films, and the biodegradable all-cellulose composite film prepared in this example.

[0051] Plastic film, purchased from Xinghong Home & Daily Necessities Store, material is polyethylene; Biodegradable film, commercially available, purchased from the Leshute flagship store, made of polylactic acid film.

[0052] The biodegradable all-cellulose composite film showed slight degradation on day 10 and significant degradation on day 20, with most of it breaking down and disappearing into the soil, posing no harm to the environment and reducing its long-term burden. However, on day 20, the morphological changes between the plastic film and the biodegradable film were not significant, and no degradation was observed. These results indicate that the biodegradable all-cellulose composite film prepared in this embodiment is a type of green biomass composite film with good biodegradability. Biodegradable all-cellulose composite films are key materials for promoting sustainable agricultural development and building a circular economy.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a biodegradable all-cellulose composite film, characterized in that, The method comprises the following steps: S1, preparation of poplar cellulose: Disperse the poplar chips in deionized water, soak for 4-6 hours in a water bath at a temperature of 70-90℃, remove impurities, dry, then add the dried poplar chips to an H2O2 solution of glacial acetic acid, soak for 12-18 hours at room temperature, then soak for 6-12 hours at a temperature of 70-90℃, then wash with deionized water until neutral, dry, and obtain poplar cellulose; S2, preparation of a dispersion of fibrillar oxidized nanocellulose: Disperse the poplar cellulose obtained in S1 in a Na2CO3-NaHCO3 buffer solution, then add NaBr and 2,2,6,6-tetramethylpiperidine oxide, add an aqueous NaClO solution dropwise while stirring at a temperature of 30-60℃, after the dropwise addition is completed, stir at a constant temperature of 30-60℃ for 1-4 hours, then stop the reaction with anhydrous ethanol, rinse with deionized water until neutral, disperse in deionized water, and obtain a dispersion of oxidized nanocellulose fibrils after ultrasonic treatment; S3, preparation of pulp cellulose: Weigh the waste paper pulp, disperse it in deionized water, soak for 3-5 hours in a water bath at a temperature of 75-85℃, add ice acetic acid and sodium chlorite every 1 hour, a total of 3-5 times, then stand at room temperature for 12-24 hours, and obtain pulp cellulose; S4, preparation of a dispersion of regenerated spherical nanocellulose: Under the condition of a temperature of -15 to -10℃, add sodium hydroxide, thiourea and urea to deionized water to obtain a pre-cooled solution; then under the condition of a temperature of -15 to -10℃ and a rotation speed of 300-450 rpm, add the pulp cellulose obtained in S3 to the pre-cooled solution while stirring, stir for 30-90 minutes, then centrifuge at a rotation speed of 5000-8000 rpm for 10-20 minutes to remove the precipitate, add deionized water to the supernatant, stir for 30-90 minutes at a rotation speed of 300-450 rpm, and obtain a dispersion of regenerated spherical nanocellulose after ultrasonic treatment; S5, mix the dispersion of oxidized nanocellulose fibrils obtained in S2 and the dispersion of regenerated spherical nanocellulose obtained in S4, ultrasonic treatment, obtain a whole cellulose composite dispersion, and vacuum filtration to obtain a degradable whole cellulose composite film.

2. The method for preparing a biodegradable all-cellulose composite film according to claim 1, characterized in that, The H2O2 solution of glacial acetic acid in S1 is a mixture of glacial acetic acid and H2O2 with a mass ratio of 1: (1-1.5).

3. The method for preparing a biodegradable all-cellulose composite film according to claim 1, characterized in that, The drying conditions in S1 are all 25-40℃ for 48-60 hours.

4. The method for preparing a biodegradable all-cellulose composite film according to claim 1, characterized in that, The preparation method of the Na2CO3-NaHCO3 buffer solution in S2 is as follows: Na2CO3 is added into deionized water, and after dissolution, NaHCO3 is added to continue dissolving to form the Na2CO3-NaHCO3 buffer solution, wherein the dosage ratio of Na2CO3, deionized water and NaHCO3 in the Na2CO3-NaHCO3 buffer solution is 3.71 g: 500 mL: 1.26 g; the dropping rate in S2 is 10 mL / h-15 mL / h, and the ultrasonic treatment condition is 600 W, 30 min-60 min.

5. The method for preparing a biodegradable all-cellulose composite film according to claim 1, characterized in that, The NaClO aqueous solution in S2 is a NaClO aqueous solution with a mass fraction of 4%-5%; the dosage ratio of the poplar cellulose, NaBr, 2,2,6,6-tetramethylpiperidine oxide and the NaClO aqueous solution in S2 is 5 g: 1.0 g: 0.1 g: (30-60) mL; the mass fraction of the oxidized nanocellulose fibrils in the dispersion of the oxidized nanocellulose fibrils in S2 is 0.05%-0.1%.

6. The method for preparing a biodegradable all-cellulose composite film according to claim 1, characterized in that, The dosage ratio of the waste paper pulp, deionized water, added ice acetic acid once, added sodium chlorite once in S3 is (20-25) g: (650-850) mL: (5-10) mL: (7.5-15) g.

7. The method for preparing a biodegradable all-cellulose composite film according to claim 1, characterized in that, The mass ratio of sodium hydroxide, thiourea, urea and deionized water in the pre-cooled solution in S4 is 8:6.5:8:77.5; the dosage ratio of the pre-cooled solution and the paper pulp cellulose in S4 is (77.5-100) mL: 1.5 g; the mass fraction of the regenerated spherical nanocellulose in the dispersion of the regenerated spherical nanocellulose in S4 is 0.1%-0.15%; the ultrasonic treatment condition in S4 is 600 W, 30 min-60 min.

8. The method for preparing a biodegradable all-cellulose composite film according to claim 1, characterized in that, The mass ratio of the oxidized nanocellulose fibrils in the dispersion of the oxidized nanocellulose fibrils and the regenerated spherical nanocellulose in the dispersion of the regenerated spherical nanocellulose in S5 is 1: (1-5).

9. The method for preparing a biodegradable all-cellulose composite film according to claim 1, characterized in that, The ultrasonic treatment condition in S5 is 600 W, 30 min-60 min; the thickness of the degradable whole-cellulose composite film in S5 is 40 μm-60 μm.

10. Use of a degradable all-cellulose composite film prepared by the method according to any one of claims 1 to 9, characterized in that The degradable whole-cellulose composite film is used to replace non-degradable plastic materials to prepare food packaging materials, new wound dressings, transparent conductive films or separation filtration membranes. The degradable whole-cellulose composite film is used to replace non-degradable plastic materials to prepare food packaging materials, new wound dressings, transparent conductive films or separation filtration membranes.

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