A biodegradable composite material for packaging and a method for preparing the same

Abstract

The application belongs to the technical field of films, and particularly relates to a biodegradable composite material for packaging and a preparation method thereof. The biodegradable composite material for packaging comprises the following raw materials in parts by weight: polybutylene adipate terephthalate 50-60 parts, polylactic acid 40-50 parts, filler 1-3 parts, modified cellulose nanowhisker 0.5-1.5 parts, chain extender 0.1-0.5 parts, and compatilizer 1-3 parts. The biodegradable composite material for packaging has excellent barrier property, mechanical property, antibacterial property and anti-aging property.

Description

Technical Field

[0001] This invention belongs to the field of thin film technology, specifically relating to a biodegradable packaging composite material and its preparation method. Background Technology

[0002] As a crucial outer packaging material for cigarettes, cigarette packaging film not only needs excellent mechanical properties to ensure the integrity and damage resistance of the packaging, but also superior barrier and sealing properties to prevent the product inside from being affected by external environmental factors such as moisture, oxygen, and microorganisms. Simultaneously, it must effectively prevent the loss of cigarette aroma, maintaining the taste and quality of the cigarettes. Currently, the most widely used cigarette packaging film on the market is biaxially oriented polypropylene film. While this type of film possesses good mechanical strength and barrier properties, it is derived from petroleum-based materials and is difficult to degrade in the natural environment.

[0003] Polylactic acid (PLA), a biodegradable material derived from renewable plant resources, possesses excellent biocompatibility and processability, demonstrating broad application prospects in the packaging materials field. However, PLA itself has poor barrier properties, with high water vapor and oxygen permeability, making it difficult to effectively prevent the evaporation of cigarette aroma and the intrusion of external moisture. When used alone, it cannot meet the high barrier requirements of cigarette packaging.

[0004] Polybutylene terephthalate (PET) is another high-performance biodegradable material with good flexibility and toughness, but its mechanical strength is relatively low, and its barrier properties against water vapor and oxygen are limited. Blending polylactic acid (PLA) with PET can, to some extent, compensate for the shortcomings of both materials. However, due to their significant polarity difference, direct blending leads to poor compatibility and weak interfacial bonding, making it difficult to achieve the ideal overall performance of the blended material.

[0005] Furthermore, cigarettes are susceptible to microbial contamination during storage and transportation. Ordinary packaging films lack antibacterial properties and cannot effectively inhibit microbial growth, affecting the product's hygiene, safety, and shelf life. Therefore, developing a cigarette packaging film material with superior overall performance—while maintaining its biodegradability—has become a pressing technical challenge in this field. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the first objective of the present invention is to provide a biodegradable packaging composite material with excellent barrier properties, mechanical properties, antibacterial properties and anti-aging properties.

[0007] The second objective of this invention is to provide a simple method for preparing a biodegradable packaging composite material.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A biodegradable packaging composite material, by weight, comprises the following raw materials: 50-60 parts of polybutylene terephthalate-adipate, 40-50 parts of polylactic acid, 1-3 parts of filler, 0.5-1.5 parts of modified cellulose nanofibers, 0.1-0.5 parts of chain extender, and 1-3 parts of compatibilizer;

[0010] The preparation process of the modified cellulose nanocrystals is as follows:

[0011] (1) Add cellulose nanocrystals to deionized water to obtain a cellulose nanocrystal dispersion; under light-protected conditions, add sodium periodate to the cellulose nanocrystal dispersion to adjust the pH, and purify after reaction to obtain aldehyde-modified cellulose nanocrystals.

[0012] (2) The aldehyde-modified cellulose nanocrystals were added to deionized water, and then β-alanyl-L-histidine was added. After the reaction, the mixture was purified to obtain the modified cellulose nanocrystals.

[0013] Furthermore, in step (1), the mass ratio of sodium periodate to cellulose nanofiber dispersion is 1:(8-10); the concentration of cellulose nanofiber dispersion is 0.1-0.2wt%; the reaction temperature is 40-60℃ and the reaction time is 3-5h; and the pH is adjusted to 3-4.

[0014] Furthermore, in step (2), the mass ratio of β-alanyl-L-histidine to aldehyde-modified cellulose nanocrystals is 1:(1-5); the reaction temperature is 40-45℃ and the time is 5-8h.

[0015] Furthermore, the preparation process of the filler is as follows:

[0016] Talc powder was added to a zinc chloride solution, followed by sodium hydroxide. After stirring, the mixture was filtered, washed, and dried to obtain the filler.

[0017] Furthermore, the ratio of talc powder, sodium hydroxide, and zinc chloride solution is 1g:(0.2-0.4)g:(10-15)mL; the concentration of zinc chloride solution is 0.1-0.2mol / L; and the stirring time is 2-3h.

[0018] Furthermore, the chain extender is SG-20 chain extender; the compatibilizer is maleic anhydride-grafted polylactic acid.

[0019] The preparation method of the above-mentioned biodegradable packaging composite material includes the following steps:

[0020] S1. According to the stated weight parts, polybutylene terephthalate, polylactic acid, and compatibilizer are mixed evenly to obtain premix A;

[0021] S2. Mix the filler and modified cellulose nanofibers evenly to obtain premix B;

[0022] S3. After premixing the premix A with the chain extender, it is then blended with the premix B, and then extruded, granulated, cooled, dried, granulated, and blown into film.

[0023] Furthermore, in step S3, the extrusion temperature is 150-175℃; the blown film temperature is 155-165℃, the rotation speed is 30-50 rpm, the blow-up ratio is 2-5 times, and the stretch ratio is 2-5 times.

[0024] The beneficial technical effects of this invention are as follows:

[0025] 1. This invention provides a biodegradable packaging composite material, comprising the following components: polybutylene terephthalate (PET), polylactic acid (PLA), filler, modified cellulose nanofibers, chain extender, and compatibilizer. Through the synergistic effect of each component, this composite material exhibits excellent barrier properties, mechanical properties, antibacterial properties, and anti-aging properties.

[0026] 2. This invention improves the mechanical properties, barrier properties, and anti-aging properties of composite materials by introducing modified cellulose nanofibers. The preparation method of the modified cellulose nanofibers is as follows: First, cellulose nanofibers are selectively oxidized using sodium periodate to oxidize the ortho-diol structure into an active aldehyde group, obtaining aldehyde-modified cellulose nanofibers, providing stable reaction sites for subsequent grafting modification. Then, the primary amino group of β-alanyl-L-histidine reacts with the aldehyde group on the surface of the cellulose nanofibers via a Schiff base reaction, covalently fixing β-alanyl-L-histidine onto the surface of the nanofibers. The imidazole ring, amide bond, and carboxyl group in the β-alanyl-L-histidine molecule can improve the dispersibility of cellulose nanofibers in the PLA / PBAT biodegradable matrix and enhance the interfacial bonding force with the matrix through hydrogen bonding and polar interactions, effectively improving the oxygen and moisture barrier properties of the packaging material. Furthermore, the modified cellulose nanofibers can act as heterogeneous nucleation and physical crosslinking points, significantly improving the tensile strength and elastic modulus of the composite material. Meanwhile, the imidazole ring endows the material with free radical scavenging ability, effectively inhibiting the aging and yellowing of the composite material.

[0027] 3. This invention enhances the mechanical and antibacterial properties of composite materials by introducing fillers. The filler uses talc as a carrier to support zinc-containing compounds. On one hand, the rigid structure of talc improves the mechanical properties of the composite material; on the other hand, it imparts antibacterial and antifungal effects. Simultaneously, the imidazole rings on the surface of the modified cellulose nanocrystals possess excellent metal ion chelating ability, further improving the stability of zinc in packaging materials and prolonging its antibacterial durability. Furthermore, this filler exhibits good safety. Attached Figure Description

[0028] Figure 1 This is a SEM image of the modified cellulose nanocrystals prepared in Example 1. Detailed Implementation

[0029] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all reagents or instruments used are conventional products obtained through commercial channels.

[0030] The average diameter of the cellulose nanocrystals of this invention is 40-60 nm.

[0031] Preparation Example 1

[0032] This preparation example provides a modified cellulose nanofiber, and the preparation process is as follows:

[0033] (1) Add cellulose nanocrystals to deionized water to obtain a cellulose nanocrystal dispersion with a concentration of 0.15wt%; with a mass ratio of sodium periodate to cellulose nanocrystal dispersion of 1:9, add sodium periodate to the cellulose nanocrystal dispersion under light-protected conditions, adjust the pH to 3.5 with 0.1mol / L dilute hydrochloric acid solution, react at 50℃ for 4h, add ethylene glycol to terminate the reaction, filter, wash the filter cake to neutral, add deionized water for dialysis for 3d, freeze dry to obtain aldehyde-modified cellulose nanocrystals;

[0034] (2) The aldehyde-modified cellulose nanofibers were dispersed in deionized water at a mass ratio of 1:3 with β-alanyl-L-histidine and aldehyde-modified cellulose nanofibers. Then, β-alanyl-L-histidine (CAS: 305-84-0) was added, and the mixture was reacted at 42℃ for 7 h. After the reaction was complete, the mixture was centrifuged, and the precipitate was washed successively with deionized water and anhydrous ethanol, and then freeze-dried to obtain modified cellulose nanofibers. See the SEM image of the modified cellulose nanofibers. Figure 1 .

[0035] Preparation Example 2

[0036] This preparation example provides a modified cellulose nanofiber, and the preparation process is as follows:

[0037] (1) Add cellulose nanocrystals to deionized water to obtain a cellulose nanocrystal dispersion with a concentration of 0.1wt%; with a mass ratio of sodium periodate to cellulose nanocrystal dispersion of 1:8, add sodium periodate to the cellulose nanocrystal solution under light-protected conditions, adjust the pH to 3 with 0.1mol / L dilute hydrochloric acid solution, react at 40℃ for 5h, add ethylene glycol to terminate the reaction, filter, wash the filter cake to neutral, add deionized water for dialysis for 3d, freeze dry to obtain aldehyde-modified cellulose nanocrystals;

[0038] (2) With a mass ratio of β-alanyl-L-histidine to aldehyde-modified cellulose nanocrystals of 1:1, the aldehyde-modified cellulose nanocrystals were dispersed in deionized water, and then β-alanyl-L-histidine was added. The reaction was carried out at 40°C for 8 hours. After the reaction was completed, the precipitate was centrifuged and washed with deionized water and anhydrous ethanol in sequence. The precipitate was then freeze-dried to obtain modified cellulose nanocrystals.

[0039] Preparation Example 3

[0040] This preparation example provides a modified cellulose nanofiber, and the preparation process is as follows:

[0041] (1) Add cellulose nanocrystals to deionized water to obtain a cellulose nanocrystal dispersion with a concentration of 0.2wt%; with a mass ratio of sodium periodate to cellulose nanocrystal dispersion of 1:10, add sodium periodate to the cellulose nanocrystal dispersion under light-protected conditions, adjust the pH to 4 with 0.1mol / L dilute hydrochloric acid solution, react at 60℃ for 3h, add ethylene glycol to terminate the reaction, filter, wash the filter cake to neutral, add deionized water for dialysis for 3d, freeze dry to obtain aldehyde-modified cellulose nanocrystals;

[0042] (2) With a mass ratio of β-alanyl-L-histidine to aldehyde-modified cellulose nanocrystals of 1:5, the aldehyde-modified cellulose nanocrystals were dispersed in deionized water, and then β-alanyl-L-histidine was added. The reaction was carried out at 45°C for 5 hours. After the reaction was completed, the precipitate was centrifuged and washed with deionized water and anhydrous ethanol in sequence. The precipitate was then freeze-dried to obtain modified cellulose nanocrystals.

[0043] Preparation Example 4

[0044] This preparation example provides a packing material, and the preparation process is as follows:

[0045] The filler was prepared by adding talc powder, sodium hydroxide, and zinc chloride solution in a ratio of 1g:0.3g:12mL, then adding sodium hydroxide, stirring for 2.5h, filtering, washing, and drying at 130℃ for 6h.

[0046] Preparation Example 5

[0047] This preparation example provides a packing material, and the preparation process is as follows:

[0048] The filler was prepared by adding talc powder, sodium hydroxide, and zinc chloride solution in a ratio of 1g:0.2g:10mL, then adding sodium hydroxide, stirring for 2 hours, filtering, washing, and drying at 130℃ for 6 hours.

[0049] Preparation Example 6

[0050] This preparation example provides a packing material, and the preparation process is as follows:

[0051] The filler was prepared by adding talc powder, sodium hydroxide, and zinc chloride solution in a ratio of 1g:0.4g:15mL, then adding sodium hydroxide, stirring for 3 hours, filtering, washing, and drying at 130℃ for 6 hours.

[0052] Example 1

[0053] This embodiment provides a biodegradable packaging composite material, which, by weight, includes the following raw materials: 54 parts of polybutylene terephthalate-adipate, 43 parts of polylactic acid, 2 parts of filler from Preparation Example 4, 1 part of modified cellulose nanofibers from Preparation Example 1, 0.2 parts of SG-20 chain extender, and 2 parts of maleic anhydride-grafted polylactic acid.

[0054] This embodiment also provides a method for preparing the above-mentioned biodegradable packaging composite material, including the following steps:

[0055] S1. Weigh each raw material according to the stated weight parts, place polybutylene terephthalate-adipate, polylactic acid, and maleic anhydride-grafted polylactic acid in a high-speed mixer, mix at room temperature for 8 minutes to obtain premix A;

[0056] S2. Place the filler and modified cellulose nanocrystals in a high-speed mixer and mix at room temperature for 8 minutes to obtain premix B;

[0057] S3. After premixing the premix A with SG-20 chain extender, it is then blended with premix B and transferred to a twin-screw extruder. The extruder processing temperature is set as follows: Zone 1 150-160℃, Zone 2 160-170℃, Zone 3 170-175℃, Zone 4 170-175℃, and the die head 170-175℃. After extrusion granulation, cooling and stretching, air drying, and pelletizing, the material is blown into film using a blown film machine. The blown film machine body and die head temperature is set to 155-165℃, the main machine speed is 40 rpm, the blow-up ratio is 3 times, and the stretching ratio is 3 times. After cooling, traction, and winding, the film is ready.

[0058] Example 2

[0059] This embodiment provides a biodegradable packaging composite material, which, by weight, includes the following raw materials: 50 parts of polybutylene terephthalate-adipate, 40 parts of polylactic acid, 1 part of the filler of Preparation Example 5, 0.5 parts of the modified cellulose nanofibers of Preparation Example 2, 0.1 parts of SG-20 chain extender, and 1 part of maleic anhydride-grafted polylactic acid.

[0060] This embodiment also provides a method for preparing the above-mentioned biodegradable packaging composite material, including the following steps:

[0061] S1. Weigh each raw material according to the stated weight parts, place polybutylene terephthalate-adipate, polylactic acid, and maleic anhydride-grafted polylactic acid in a high-speed mixer, mix at room temperature for 5 minutes to obtain premix A;

[0062] S2. Place the filler and modified cellulose nanocrystals in a high-speed mixer and mix at room temperature for 5 minutes to obtain premix B;

[0063] S3. After premixing the premix A with SG-20 chain extender, it is then blended with premix B and transferred to a twin-screw extruder. The extruder processing temperature is set as follows: Zone 1 150-160℃, Zone 2 160-170℃, Zone 3 170-175℃, Zone 4 170-175℃, and the die head 170-175℃. After extrusion granulation, cooling and stretching, air drying, and pelletizing, the material is blown into film using a blown film machine. The blown film machine body and die head temperature is set to 155-165℃, the main machine speed is 30 rpm, the blow-up ratio is 2 times, and the stretching ratio is 2 times. After cooling, traction, and winding, the film is ready.

[0064] Example 3

[0065] This embodiment provides a biodegradable packaging composite material, which, by weight, includes the following raw materials: 60 parts of polybutylene terephthalate-adipate, 50 parts of polylactic acid, 3 parts of the filler of Preparation Example 6, 1.5 parts of the modified cellulose nanofibers of Preparation Example 3, 0.5 parts of SG-20 chain extender, and 3 parts of maleic anhydride-grafted polylactic acid.

[0066] This embodiment also provides a method for preparing the above-mentioned biodegradable packaging composite material, including the following steps:

[0067] S1. Weigh each raw material according to the stated weight parts, place polybutylene terephthalate-adipate, polylactic acid, and maleic anhydride-grafted polylactic acid in a high-speed mixer, mix at room temperature for 10 minutes to obtain premix A;

[0068] S2. Place the filler and modified cellulose nanocrystals in a high-speed mixer and mix at room temperature for 10 minutes to obtain premix B;

[0069] S3. After premixing the premix A with SG-20 chain extender, it is then blended with premix B and transferred to a twin-screw extruder. The extruder processing temperature is set as follows: Zone 1 150-160℃, Zone 2 160-170℃, Zone 3 170-175℃, Zone 4 170-175℃, and the die head 170-175℃. After extrusion granulation, cooling and stretching, air drying, and pelletizing, the material is blown into film using a blown film machine. The blown film machine body and die head temperature is set to 155-165℃, the main machine speed is 50 rpm, the blow-up ratio is 5 times, and the stretching ratio is 5 times. After cooling, traction, and winding, the film is ready.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 1 is that cellulose nanocrystals are used instead of the modified cellulose nanocrystals used in Example 1.

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 1 is that talc powder is used instead of the filler in Preparation Example 4.

[0074] Experimental Example 1

[0075] The water vapor barrier properties of the composite materials prepared in the examples or comparative examples were tested according to standard GB / T 1037-2021, and the results are shown in Table 1.

[0076] The oxygen barrier properties of the composite materials prepared in the examples or comparative examples were tested according to standard GB / T 1038.1-2022, and the results are shown in Table 1.

[0077] Table 1

[0078]

[0079] As shown in Table 1, the composite materials prepared in Examples 1-3 of the present invention have low water vapor and oxygen permeability, exhibiting excellent barrier properties.

[0080] Compared to Example 1, the water vapor and oxygen permeability of the composite material prepared using unmodified cellulose nanofibers in Comparative Example 1 were significantly increased. This is because unmodified cellulose nanofibers have poor compatibility with the PLA / PBAT matrix, are prone to aggregation, and cannot form an effective physical barrier. In contrast, this invention, through β-alanyl-L-histidine graft modification, introduces imidazole rings, amide bonds, and carboxyl groups on the surface of the nanofibers, significantly improving their dispersibility in the matrix and their interfacial bonding with the matrix, thereby significantly enhancing the barrier properties of the composite material.

[0081] Experimental Example 2

[0082] Antibacterial properties: The antibacterial properties of the composite materials prepared in the examples or comparative examples were tested according to standard QB / T 31402-2015. The test strains were Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 25922. The test results are shown in Table 2.

[0083] Table 2

[0084]

[0085] As shown in Table 2, the composite materials prepared in Examples 1-3 of this invention exhibit excellent antibacterial properties against Staphylococcus aureus and Escherichia coli.

[0086] Compared to Example 1, the antibacterial effect of the composite material prepared using unmodified cellulose nanofibers in Comparative Example 1 was reduced. This may be because the unmodified cellulose nanofibers lack imidazole rings and cannot effectively chelate and stabilize zinc ions, resulting in partial loss of zinc ions during the test and a weakened antibacterial effect. Compared to Example 1, the antibacterial effect of the composite material prepared using unmodified talc in Comparative Example 2 was significantly reduced. This result fully demonstrates that the zinc-modified talc filler prepared in this invention is the key component that imparts antibacterial properties to the composite material. This filler achieves highly efficient antibacterial effects by loading zinc-containing compounds onto the surface of talc and slowly releasing zinc ions into the material.

[0087] Experimental Example 3

[0088] Mechanical tests: The tensile strength and elastic modulus of the composite materials prepared in the examples or comparative examples were tested using a universal electronic testing machine in accordance with the standard GB / T 1040.3-2006. The tensile rate was 50 mm / min. The results are shown in Table 3.

[0089] Yellowing test: Refer to GB / T 16422.2-2022 "Exposure test method for laboratory light sources for plastics - Part 2: Xenon arc lamp", the specific test conditions and parameters are as follows: Xenon lamp exposure yellowing test chamber for 1000h, color difference (∆E) is measured by spectrophotometer, and the results are shown in Table 3.

[0090] Table 3

[0091]

[0092] As shown in Table 3, the composite materials prepared in Examples 1-3 of this invention have excellent mechanical properties and aging resistance.

[0093] Compared with Example 1, the tensile strength of the composite material obtained in Comparative Example 1 decreased to 27.9 MPa, the elastic modulus decreased to 388 MPa, and the yellowing value increased to 2.7. This indicates that the modified cellulose nanofibers used in this invention, through surface grafting of β-alanyl-L-histidine, introduce imidazole rings, amide bonds, and carboxyl groups on the surface of the nanofibers, significantly improving their dispersibility in the PLA / PBAT matrix. Furthermore, the interfacial bonding with the matrix is ​​enhanced through hydrogen bonding and polar interactions, thereby effectively improving the tensile strength and elastic modulus of the material. Simultaneously, the imidazole rings in the grafted molecules act as free radical scavengers, effectively scavenging free radicals generated during photothermal aging, inhibiting polymer oxidative degradation, and endowing the material with excellent anti-yellowing properties.

[0094] The composite material obtained in Comparative Example 2 had a tensile strength of 32.4 MPa, an elastic modulus of 432 MPa, and a yellowing value of 1.8, which was better than Comparative Example 1 but still lower than Example 1. This indicates that the zinc-modified talc filler prepared in this invention further synergistically improves the overall performance of the composite material by enhancing the compatibility and physical barrier effect between the filler and the matrix.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A biodegradable packaging composite material, characterized in that, By weight, it includes the following raw materials: 50-60 parts of polybutylene terephthalate-adipate, 40-50 parts of polylactic acid, 1-3 parts of filler, 0.5-1.5 parts of modified cellulose nanofibers, 0.1-0.5 parts of chain extender, and 1-3 parts of compatibilizer; The preparation process of the modified cellulose nanocrystals is as follows: (1) Add cellulose nanocrystals to deionized water to obtain a cellulose nanocrystal dispersion; under light-protected conditions, add sodium periodate to the cellulose nanocrystal dispersion to adjust the pH, and purify after reaction to obtain aldehyde-modified cellulose nanocrystals. (2) The aldehyde-modified cellulose nanocrystals were added to deionized water, and then β-alanyl-L-histidine was added. After the reaction, the mixture was purified to obtain the modified cellulose nanocrystals. The preparation process of the filler is as follows: Talc powder was added to a zinc chloride solution, followed by sodium hydroxide. After stirring, the mixture was filtered, washed, and dried to obtain the filler. The preparation method of the biodegradable packaging composite material is as follows: S1. According to the stated weight parts, polybutylene terephthalate, polylactic acid, and compatibilizer are mixed evenly to obtain premix A; S2. Mix the filler and modified cellulose nanofibers evenly to obtain premix B; S3. After premixing the premix A with the chain extender, it is then blended with the premix B, and the mixture is then extruded, granulated, cooled, dried, granulated, and blown into film.

2. The biodegradable packaging composite material according to claim 1, characterized in that, In step (1), the mass ratio of sodium periodate to cellulose nanofiber dispersion is 1:(8-10); the concentration of cellulose nanofiber dispersion is 0.1-0.2wt%; the reaction temperature is 40-60℃ and the reaction time is 3-5h; and the pH is adjusted to 3-4.

3. The biodegradable packaging composite material according to claim 1, characterized in that, In step (2), the mass ratio of β-alanyl-L-histidine to aldehyde-modified cellulose nanocrystals is 1:(1-5); the reaction temperature is 40-45℃ and the reaction time is 5-8h.

4. The biodegradable packaging composite material according to claim 1, characterized in that, The ratio of talc powder, sodium hydroxide, and zinc chloride solution is 1g:(0.2-0.4)g:(10-15)mL; the concentration of zinc chloride solution is 0.1-0.2mol / L; and the stirring time is 2-3h.

5. The biodegradable packaging composite material according to claim 1, characterized in that, The chain extender is SG-20 chain extender; the compatibilizer is maleic anhydride-grafted polylactic acid.

6. A method for preparing a biodegradable packaging composite material according to any one of claims 1-5, characterized in that, Includes the following steps: S1. According to the stated weight parts, polybutylene terephthalate, polylactic acid, and compatibilizer are mixed evenly to obtain premix A; S2. Mix the filler and modified cellulose nanofibers evenly to obtain premix B; S3. After premixing the premix A with the chain extender, it is then blended with the premix B, and the mixture is then extruded, granulated, cooled, dried, granulated, and blown into film.

7. The method for preparing the biodegradable packaging composite material according to claim 6, characterized in that, The extrusion temperature in step S3 is 150-175℃; the blown film temperature is 155-165℃, the rotation speed is 30-50 rpm, the blow-up ratio is 2-5 times, and the stretch ratio is 2-5 times.

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