Preparation method of degradable preservative film

Abstract

The invention belongs to the technical field of degradable packaging materials, and discloses a preparation method of a degradable preservative film. The anti-fog antibacterial plastic is prepared from the following raw materials in parts by weight: 40 to 45 parts of poly (butylene adipate-co-terephthalate) (PBAT), 8 to 12 parts of polylactic acid (PLA), 28 to 32 parts of modified structural starch, 4 to 6 parts of poly (butylene carbonate) (PBC), 4 to 6 parts of talcum powder, 0.4 to 0.6 part of aluminate, 0.8 to 1.2 parts of a composite antibacterial agent and 2.5 to 3.5 parts of anti-fog master batch. The invention aims to overcome the defects in the prior art, and provides the degradable preservative film and the preparation method thereof, the preservative film not only has good degradability and mechanical properties, but also has excellent antibacterial and antifogging effects, and the preparation process is simple and easy for industrial production.

Description

Technical Field

[0001] This invention relates to the field of biodegradable packaging materials technology, specifically a method for preparing a biodegradable food preservation film. Background Technology

[0002] With increasing environmental awareness, the application of traditional non-degradable plastic cling film is facing more and more restrictions due to its difficulty in natural degradation and its tendency to cause white pollution.

[0003] Most biodegradable food wraps on the market are based on biodegradable polymers such as PBAT and PLA. However, single-base materials have drawbacks such as insufficient mechanical properties and high cost. Therefore, natural polymers such as starch are often added to reduce costs.

[0004] However, starch has poor compatibility with polymer materials, and direct addition can easily lead to a decline in the mechanical properties of the materials; at the same time, existing biodegradable food preservation films lack sufficient antibacterial, anti-fogging and other functionalities, making it difficult to meet the diversified needs of food preservation.

[0005] In addition, some antibacterial agents have poor dispersibility in materials and are prone to agglomeration, resulting in unstable antibacterial effects.

[0006] Therefore, a biodegradable preservation film with good compatibility, excellent mechanical properties, and antibacterial and anti-fogging functions is proposed. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a biodegradable food preservation film and its preparation method. The food preservation film not only has good biodegradability and mechanical properties, but also has excellent antibacterial and anti-fogging effects. Moreover, the preparation process is simple and easy to industrialize.

[0008] To achieve the above objectives, the present invention provides the following technical solution: The technical solution provided by this invention is: A biodegradable food preservation film is prepared from the following raw materials in parts by weight: 40-45 parts of polybutylene terephthalate (PBAT), 8-12 parts of polylactic acid (PLA), 28-32 parts of modified structural starch, 4-6 parts of polybutylene carbonate (PBC), 4-6 parts of talc, 0.4-0.6 parts of aluminate, 0.8-1.2 parts of composite antibacterial agent, and 2.5-3.5 parts of anti-fog masterbatch.

[0009] The modified structured starch is prepared by melt blending structured starch with glyceryl monostearate or sorbitan monostearate at a weight ratio of 95:5. Through the modification effect of glyceryl monostearate or sorbitan monostearate, the compatibility of structured starch with polymer matrices such as PBAT and PLA can be effectively improved, thereby enhancing the mechanical properties of the material.

[0010] The composite antibacterial agent is prepared by mixing nano-silver and nano-titanium dioxide in a 1:1 weight ratio, and then adding 3-5% of silane coupling agent KH550, which accounts for 3% of the total amount of the mixed powder, and then modifying it by ultrasonic dispersion. The addition of silane coupling agent KH550 can enhance the dispersibility of nano-silver and nano-titanium dioxide in the polymer matrix, avoid agglomeration, and thus improve the stability of the antibacterial effect.

[0011] Preferably, the nano-silver has a particle size of 20-30 nm, and the nano-titanium dioxide is anatase with a particle size of 15-25 nm. Nanoparticles in this particle size range have a large specific surface area, which can enhance antibacterial activity.

[0012] Preferably, the anti-fog masterbatch is a compound of polyvinylpyrrolidone and polyethylene glycol in a weight ratio of 7:3. The synergistic effect of the two can effectively reduce the surface tension of the plastic wrap and prevent fog condensation.

[0013] A method for preparing the above-mentioned biodegradable food preservation film includes the following steps: S1: Preparation of modified structured starch: Weigh structured starch and glyceryl monostearate or sorbitan monostearate at a weight ratio of 95:5, add them to a twin-screw extruder, melt-blend and extrude at 110-120℃ and screw speed of 200-220r / min, cool and then pulverize to obtain modified structured starch. S2: Preparation of composite antibacterial agent: Weigh nano silver and anatase nano titanium dioxide at a weight ratio of 1:1, add them to anhydrous ethanol, ultrasonically disperse for 10-15 min, add 3-5% of silane coupling agent KH550 in total powder, stir and react at 60-70℃ for 2-3 h, centrifuge and dry to obtain composite antibacterial agent; S3: Weigh out polybutylene terephthalate (PBAT), PLA, modified structural starch prepared by S1, PBC, talc, aluminate, composite antibacterial agent prepared by S2, and anti-fogging masterbatch according to the weight parts, add them to a high-speed mixer, and mix for 18-20 minutes at 85-90℃ and 900-1000r / min to obtain a mixture. S4: Add the mixture obtained in S3 to a twin-screw extruder and melt-extrude and granulate it at 170-180℃ and screw speed of 180-200r / min to obtain masterbatch; S5: Add the masterbatch obtained in S4 into a blown film machine, blown film at 160-170℃, blow ratio 3-3.5, and traction speed 10-12m / min, and after cooling, traction, and winding, obtain a biodegradable preservation film.

[0014] Preferably, the ultrasonic dispersion in S2 has a power of 300-400W and a frequency of 20-25kHz, which ensures that the nano-silver and nano-titanium dioxide are fully dispersed.

[0015] Preferably, the temperature distribution of each section of the twin-screw extruder in S4 is as follows: feeding section 140-150℃, compression section 160-170℃, homogenization section 170-180℃. Segmented temperature control can ensure that the material is fully melted and does not degrade.

[0016] Preferably, the cooling in S5 adopts air ring cooling with a cooling air temperature of 20-25℃, which can quickly set the film and ensure the flatness and mechanical properties of the film.

[0017] The beneficial effects of this technical solution are: (1) By using modified starch, the present invention effectively improves the compatibility between starch and polymer matrix, solves the problem of decreased mechanical properties of materials caused by the addition of traditional starch, and makes the plastic wrap have both good biodegradability and mechanical properties. (2) The nano-silver-nano-titanium dioxide composite antibacterial agent modified with silane coupling agent improves the dispersibility of the antibacterial agent in the matrix, achieves a broad-spectrum and long-lasting antibacterial effect, and can effectively inhibit the growth of bacteria on the surface of food. (3) The compounded anti-fog masterbatch can significantly improve the anti-fog performance of the plastic wrap, and avoid the impact of fog condensation on the food preservation effect and appearance observation. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a method for preparing a biodegradable food preservation film proposed in this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The specific implementation process is as follows: Example 1: Please see Figure 1 The present invention provides a technical solution: a method for preparing a biodegradable food preservation film, comprising the following steps: S1: Preparation of modified structured starch: Weigh 95g of corn structured starch and 5g of glyceryl monostearate at a weight ratio of 95:5, add them to a twin-screw extruder, melt-blend and extrude at 110℃ and screw speed of 200r / min, cool and then pulverize to obtain modified structured starch; S2: Preparation of composite antibacterial agent: Weigh 5g of 20nm nano silver and 5g of 15nm anatase nano titanium dioxide at a weight ratio of 1:1, add them to 100mL of anhydrous ethanol, and ultrasonically disperse them for 10min at a power of 300W and a frequency of 20kHz. Then add 0.3g of silane coupling agent KH550, which accounts for 3% of the total amount of mixed powder, and stir the reaction at 60℃ for 2h. After centrifugation, dry at 80℃ for 2h to obtain composite antibacterial agent. S3: Weigh out 40g of PBAT, 8g of PLA, 28g of modified structural starch prepared in S1, 4g of PBC, 4g of talc, 0.4g of aluminate, 0.8g of composite antibacterial agent prepared in S2, and 2.5g of anti-fogging masterbatch made by compounding polyvinylpyrrolidone and polyethylene glycol in a 7:3 ratio according to the following parts by weight. Add them to a high-speed mixer and mix for 18 minutes at 85℃ and 900r / min to obtain a mixture. S4: Add the mixture obtained in S3 to a twin-screw extruder, set the temperature of each section to 140℃ for the feeding section, 160℃ for the compression section, and 170℃ for the homogenization section, and set the screw speed to 180r / min. Melt extrusion granulation is performed to obtain masterbatch. S5: Add the masterbatch obtained in S4 into the blown film machine, blown film at 160℃, blow ratio 3, and traction speed 10m / min, using air ring cooling at 20℃, and obtain biodegradable preservation film after traction and winding. This embodiment uses corn structured starch and glyceryl monostearate to prepare modified structured starch, with low process parameters and low energy consumption; the nanoparticles in the composite antibacterial agent have small particle size and large specific surface area, and the amount of silane coupling agent is moderate, ensuring the dispersibility and antibacterial activity of the antibacterial agent; the proportions of each raw material are within the lower limit of the scope of protection of the claims, and the prepared food preservation film has good biodegradability, meeting the basic requirements for food preservation.

[0021] Performance indicators Test Results Tensile strength 20MPa Elongation at break 500% Antibacterial rate against Escherichia coli 91.2% Antibacterial rate against Staphylococcus aureus 90.5% Anti-fog rating (refrigerated conditions) Level 1 Fog-free period (refrigerated conditions) 120min 6-month natural degradation rate 60.8% The table shows that the properties of the preservation film prepared in Example 1 meet the basic requirements for food preservation. Specifically, the tensile strength of 20 MPa and the elongation at break of 500% demonstrate that the modified starch effectively improves the compatibility between starch and the polymer matrix, preventing a significant decrease in mechanical properties. The antibacterial rate against two common pathogens exceeds 90%, thanks to the large specific surface area of ​​the composite antibacterial agent with small particle size (20 nm nano-silver and 15 nm nano-titanium dioxide), and the silane coupling agent modification ensures a certain degree of dispersibility. The anti-fogging level is Grade 1, and the fog-free retention time reaches 120 minutes, indicating that the compounded anti-fogging masterbatch effectively prevents fogging. The 60.8% natural degradation rate over 6 months meets the environmental protection requirements for biodegradable materials, and the overall performance is suitable for low- to mid-range food preservation scenarios.

[0022] Example 2: Please see Figure 1 The present invention provides a technical solution: a method for preparing a biodegradable food preservation film, comprising the following steps: S1: Preparation of modified structured starch: Weigh 95g of potato structured starch and 5g of dehydrated sorbitan monostearate at a weight ratio of 95:5, add them to a twin-screw extruder, melt-blend and extrude at 115℃ and screw speed of 210r / min, cool and then pulverize to obtain modified structured starch; S2: Preparation of composite antibacterial agent: Weigh 5g of 25nm nano silver and 5g of 20nm anatase nano titanium dioxide at a weight ratio of 1:1, add them to 100mL of anhydrous ethanol, and ultrasonically disperse them for 12min at a power of 350W and a frequency of 22kHz. Then add 0.4g of silane coupling agent KH550, which accounts for 4% of the total amount of mixed powder, and stir the reaction at 65℃ for 2.5h. After centrifugation, dry at 80℃ for 2h to obtain composite antibacterial agent. S3: Weigh out 43g of PBAT, 10g of PLA, 30g of modified structural starch prepared in S1, 5g of PBC, 5g of talc, 0.5g of aluminate, 1g of composite antibacterial agent prepared in S2, and 3g of anti-fogging masterbatch made of polyvinylpyrrolidone and polyethylene glycol in a 7:3 ratio according to the following weight proportions. Add them to a high-speed mixer and mix for 19 minutes at 88℃ and 950r / min to obtain the mixture. S4: Add the mixture obtained in S3 to a twin-screw extruder, set the temperature of each section to 145℃ for the feeding section, 165℃ for the compression section, and 175℃ for the homogenization section, and set the screw speed to 190r / min. Melt extrusion granulation is performed to obtain masterbatch. S5: Add the masterbatch obtained in S4 into the blown film machine, blown film at 165℃, blow ratio 3.2, and traction speed 11m / min, using air ring cooling at 22℃, and obtain biodegradable preservation film after traction and winding. In this embodiment, potato structured starch and dehydrated sorbitan monostearate were selected for modification, and the raw materials are widely available. During the preparation of the composite antibacterial agent, the ultrasonic power and frequency were moderate and the reaction time was sufficient to ensure that the coupling agent was fully grafted. The ratio of each raw material was the median value of the scope of protection of the claims, and the synergistic effect between the raw materials was optimal. The prepared food preservation film has excellent comprehensive performance, taking into account mechanical properties, functionality and biodegradability.

[0023] Performance indicators Test Results Tensile strength 25MPa Elongation at break 550% Antibacterial rate against Escherichia coli 95.8% Antibacterial rate against Staphylococcus aureus 96.2% Anti-fog rating (refrigerated conditions) Level 1 Fog-free period (refrigerated conditions) 150min 6-month natural degradation rate 70.5% The data in the table reflects that the overall performance of the food preservation film of Example 2 is optimal; the tensile strength is increased to 25MPa and the elongation at break reaches 550%, mainly due to the better synergistic effect of the modified potato structural starch and dehydrated sorbitan monostearate, and the raw material ratio is the median value of the claims, achieving optimal compatibility between the matrix and the modified starch; the antibacterial rate exceeds 95%, thanks to the more uniform dispersion of the composite antibacterial agent by ultrasonic dispersion with a power of 350W, and the 4% silane coupling agent further enhances the binding force between the antibacterial agent and the matrix; the anti-fogging performance is better, with the fog-free retention time extended to 150min, due to the appropriate system of 3g compound anti-fogging masterbatch; the 70.5% degradation rate reflects the balance between starch content and biodegradable polymers, and all performance characteristics are suitable for the preservation needs of mid-to-high-end foods.

[0024] Example 3: Please see Figure 1 The present invention provides a technical solution: a method for preparing a biodegradable food preservation film, comprising the following steps: S1: Preparation of modified structured starch: Weigh 95g of corn structured starch and 5g of glyceryl monostearate at a weight ratio of 95:5, add them to a twin-screw extruder, melt-blend and extrude at 120℃ and screw speed of 220r / min, cool and then pulverize to obtain modified structured starch; S2: Preparation of composite antibacterial agent: Weigh 5g of 30nm nano silver and 5g of 25nm anatase nano titanium dioxide at a weight ratio of 1:1, add them to 100mL of anhydrous ethanol, and ultrasonically disperse them for 15min at a power of 400W and a frequency of 25kHz. Then add 0.5g of silane coupling agent KH550, which accounts for 5% of the total amount of mixed powder, and stir the reaction at 70℃ for 3h. After centrifugation, dry at 80℃ for 2h to obtain composite antibacterial agent. S3: Weigh out 45g of PBAT, 12g of PLA, 32g of modified structural starch prepared in S1, 6g of PBC, 6g of talc, 0.6g of aluminate, 1.2g of composite antibacterial agent prepared in S2, and 3.5g of anti-fogging masterbatch made by compounding polyvinylpyrrolidone and polyethylene glycol in a 7:3 ratio. Add them to a high-speed mixer and mix for 20 minutes at 90℃ and 1000r / min to obtain a mixture. S4: Add the mixture obtained in S3 to a twin-screw extruder, set the temperature of each section to 150℃ for the feeding section, 170℃ for the compression section, and 180℃ for the homogenization section, and set the screw speed to 200r / min. Melt extrusion granulation is performed to obtain masterbatch. S5: Add the masterbatch obtained in S4 into the blown film machine, blown film at 170℃, blow ratio 3.5, and traction speed 12m / min, using air ring cooling at 25℃, and obtain biodegradable preservation film after traction and winding. The process parameters in this embodiment are at the upper limit of the scope of protection of the claims. The high speed and temperature of the twin-screw extruder ensure that the materials are fully melted and mixed. The high amount of silane coupling agent in the composite antibacterial agent further improves the compatibility between the antibacterial agent and the matrix. The high amount of PBAT and PLA makes the plastic wrap have better mechanical properties, making it suitable for preservation scenarios with high mechanical performance requirements.

[0025] Performance indicators Test Results Tensile strength 28MPa Elongation at break 600% Antibacterial rate against Escherichia coli 98.3% Antibacterial rate against Staphylococcus aureus 98.7% Anti-fog rating (refrigerated conditions) Level 1 Fog-free period (refrigerated conditions) 180min 6-month natural degradation rate 65.2% The table data shows that the food preservation film of Example 3 has the best mechanical and antibacterial properties; the tensile strength is 28 MPa and the elongation at break is 600%, mainly due to the highest dosage of PBAT (45g) and PLA (12g), the increased proportion of polymer matrix, and the high temperature of 120℃ and high rotation speed of 220r / min, which makes the modified starch melt more fully with the matrix; the antibacterial rate is close to 99%, thanks to the increased dosage of 1.2g of composite antibacterial agent, and the 400W ultrasonic dispersion and 5% silane coupling agent modification completely solve the problem of nanoparticle agglomeration; the anti-fog performance is the best, with a fog-free retention time of 180min, due to the highest dosage of 3.5g of anti-fog masterbatch, which has a stronger surface tension adjustment effect; the degradation rate of 65.2% is slightly lower than that of Example 2, due to the increased proportion of polymer matrix, but it still meets the requirements for biodegradability and is suitable for food preservation scenarios with strict requirements for mechanical and antibacterial properties.

[0026] Example 4: Please see Figure 1 The present invention provides a technical solution: a method for preparing a biodegradable food preservation film, comprising the following steps: S1: Preparation of modified structured starch: Weigh 95g of potato structured starch and 5g of glyceryl monostearate at a weight ratio of 95:5, add them to a twin-screw extruder, melt-blend and extrude at 115℃ and screw speed of 210r / min, cool and then pulverize to obtain modified structured starch; S2: Preparation of composite antibacterial agent: Weigh 5g of 25nm nano silver and 5g of 20nm anatase nano titanium dioxide at a weight ratio of 1:1, add them to 100mL of anhydrous ethanol, and ultrasonically disperse them for 13min at a power of 350W and a frequency of 22kHz. Then add 0.4g of silane coupling agent KH550, which accounts for 4% of the total amount of mixed powder, and stir the reaction at 65℃ for 2.5h. After centrifugation, dry at 80℃ for 2h to obtain composite antibacterial agent. S3: Weigh out 42g of PBAT, 11g of PLA, 31g of modified structural starch prepared in S1, 5g of PBC, 5g of talc, 0.5g of aluminate, 1g of composite antibacterial agent prepared in S2, and 3.2g of anti-fogging masterbatch made by compounding polyvinylpyrrolidone and polyethylene glycol in a 7:3 ratio according to the following parts by weight. Add them to a high-speed mixer and mix for 19 minutes at 89℃ and 980r / min to obtain the mixture. S4: Add the mixture obtained in S3 to a twin-screw extruder, set the temperature of each section to 148℃ for the feeding section, 168℃ for the compression section, and 178℃ for the homogenization section, and set the screw speed to 195r / min. Melt extrusion granulation is performed to obtain masterbatch. S5: Add the masterbatch obtained in S4 into the blown film machine and blow the film at 168℃, blow ratio 3.3 and traction speed 11.5m / min. Use air ring cooling with cooling air temperature of 23℃. After traction and winding, a biodegradable food preservation film is obtained. In this embodiment, the raw material ratios and process parameters are selected from the upper-middle range of the scope of protection of the claims, taking into account both raw material costs and product performance; the preparation process of modified structural starch and composite antibacterial agent is stable, ensuring their performance consistency; the prepared food preservation film has balanced comprehensive performance and is suitable for large-scale industrial production and wide application.

[0027] Performance indicators Test Results Tensile strength 26MPa Elongation at break 580% Antibacterial rate against Escherichia coli 96.5% Antibacterial rate against Staphylococcus aureus 96.8% Anti-fog rating (refrigerated conditions) Level 1 Fog-free period (refrigerated conditions) 160min 6-month natural degradation rate 68.3% The data in this table demonstrates the balanced performance of the food preservation film in Example 4; its tensile strength of 26 MPa and elongation at break of 580% fall between those of Examples 2 and 3, due to the moderate amounts of PBAT and PLA, and the combination of potato structural starch and glyceryl monostearate balancing compatibility and cost; its antibacterial rate exceeds 96%, thanks to the stabilizing effect of 350W ultrasonic dispersion and 4% silane coupling agent, achieving optimal cost-effectiveness with a 1g amount of composite antibacterial agent; its anti-fog and fog-free retention time is 160 min, with 3.2g of anti-fog masterbatch balancing the anti-fog effect and cost; its degradation rate of 68.3% is close to the optimal level of Example 2, with no obvious shortcomings in overall performance, making it suitable for the cost and performance requirements of large-scale industrial production.

[0028] Comparative Example 1: Please see Figure 1 The present invention provides a comparative solution comprising the following steps: Weigh out 43g of PBAT, 10g of PLA, 30g of unmodified corn structural starch, 5g of PBC, 5g of talc, 0.5g of aluminate, 1g of composite antibacterial agent prepared by S2, and 3g of anti-fogging masterbatch made by compounding polyvinylpyrrolidone and polyethylene glycol in a 7:3 ratio. Add them to a high-speed mixer and mix for 19 minutes at 88℃ and 950r / min to obtain a mixture. The remaining steps are the same as in Example 2; This comparative example did not use modified structural starch, but directly added unmodified corn structural starch. Due to the poor compatibility between unmodified starch and the polymer matrix, the mechanical properties of the prepared food preservation film decreased significantly, with a tensile strength of only 12 MPa and an elongation at break of 200%. The film was also prone to brittleness and could not meet the actual use requirements. This highlights the key role of modified structural starch in improving the compatibility and mechanical properties of the material in this invention.

[0029] Performance indicators Test Results Tensile strength 12MPa Elongation at break 200% Antibacterial rate against Escherichia coli 95.5% Antibacterial rate against Staphylococcus aureus 95.9% Anti-fog rating (refrigerated conditions) Level 1 Fog-free period (refrigerated conditions) 148min 6-month natural degradation rate 71.2% The data in the table shows that Comparative Example 1 and Example 2 have similar antibacterial, antifogging, and degradation properties (similar antibacterial and antifogging rates, slightly higher degradation rate), but significantly lower mechanical properties. The tensile strength is only 12 MPa and the elongation at break is 200%, which is much lower than the 25 MPa and 550% of Example 2. The core reason is that modified structural starch was not used. The hydroxyl groups on the molecular chains of unmodified corn structural starch are prone to forming hydrogen bonds, leading to aggregation. It has poor compatibility with PBAT and PLA matrices, weak interfacial bonding, and is prone to stress concentration under external force, resulting in deterioration of the film's mechanical properties and inability to meet the tensile and encapsulation requirements in actual use.

[0030] Comparative Example 2: Please see Figure 1 The present invention provides a comparative solution comprising the following steps: Preparation of modified structured starch: Same as in Example 2S1; Weigh out 43g of PBAT, 10g of PLA, 30g of modified structural starch prepared from S1, 5g of PBC, 5g of talc, 0.5g of aluminate, 2g of unmodified nano-silver-nano-titanium dioxide mixed powder (mixed at a weight ratio of 1:1), and 3g of anti-fogging masterbatch made of polyvinylpyrrolidone and polyethylene glycol in a 7:3 ratio. Add them to a high-speed mixer and mix for 19 minutes at 88℃ and 950r / min to obtain the mixture. The remaining steps are the same as in Example 2; This comparative example uses unmodified nano-silver-nano-titanium dioxide mixed powder as an antibacterial agent. Due to the tendency of unmodified nanoparticles to agglomerate and disperse unevenly in the matrix, the antibacterial effect of the plastic wrap is poor, with antibacterial rates of only 60% and 65% against Escherichia coli and Staphylococcus aureus, respectively. Moreover, the antibacterial effect is unstable, and the antibacterial rate drops below 40% after one month. This indicates that the modification with silane coupling agent in this invention can effectively improve the dispersibility and antibacterial durability of the antibacterial agent.

[0031] Performance indicators Test results (initial) Test results (after 1 month) Tensile strength 19.2MPa 18.8MPa Elongation at break 380% 370% Antibacterial rate against Escherichia coli 62% 40% Antibacterial rate against Staphylococcus aureus 65% 42% Anti-fog rating (refrigerated conditions) Level 1 Level 1 Fog-free period (refrigerated conditions) 149min 147min 6-month natural degradation rate 70.2% 70.2% The data in the table shows that the mechanical properties of Comparative Example 2 were significantly deteriorated due to the agglomeration of the antibacterial agent, with a significant difference in antibacterial performance and poor stability. Initially, the tensile strength was only 19.2 MPa and the elongation at break was 380%, far lower than the 25 MPa and 550% of Example 2. After one month, it further decreased to 18.8 MPa and 370%. The core reason is that the surface energy of the unmodified nano-silver-nano-titanium dioxide mixed powder is high, and the agglomeration phenomenon intensifies after the dosage is increased to 2g, forming a large number of agglomerates with a size of 50-100 nm, which become stress concentration points, leading to the film... The unmodified nanoparticles are more prone to damage under external forces, resulting in a significant deterioration in mechanical properties. At the same time, the unmodified nanoparticles have weak bonding with the polymer matrix and are easily lost over time. The initial antibacterial rates against Escherichia coli and Staphylococcus aureus are only 62% and 65%, respectively, which are far lower than the 95.8% and 96.2% of Example 2. After one month of storage, the antibacterial rates further decreased to 40% and 42%. The anti-fogging performance is determined by the compounded anti-fogging masterbatch and is not related to whether the antibacterial agent is modified. Therefore, the anti-fogging level (Level 1) and the fog-free retention time (initially 149 min, after storage 147 min) are basically the same as those in Example 2 and are not affected.

[0032] Comparative Example 3: Please see Figure 1 The present invention provides a comparative solution comprising the following steps: Preparation of modified structured starch: Same as in Example 2S1; Preparation of the composite antibacterial agent: Same as in Example 2S2; Weigh out 43g of PBAT, 10g of PLA, 30g of modified structural starch prepared by S1, 5g of PBC, 5g of talc, 0.5g of aluminate, 1g of composite antibacterial agent prepared by S2, and 3g of single polyvinylpyrrolidone anti-fogging masterbatch according to the following weight proportions. Add them to a high-speed mixer and mix for 19 minutes at 88℃ and 950r / min to obtain the mixture. The remaining steps are the same as in Example 2; This comparative example uses a single polyvinylpyrrolidone as the anti-fogging masterbatch, rather than the compound anti-fogging masterbatch of this invention. The anti-fogging effect of the single anti-fogging masterbatch is poor, and obvious fog droplets appear on the surface of the plastic wrap within 10 minutes under refrigeration conditions, with an anti-fogging performance level of 4, making it impossible to clearly observe the internal food condition. In contrast, the compound anti-fogging masterbatch of this invention can prevent obvious fog droplets from appearing on the plastic wrap within 2 hours under refrigeration conditions, fully demonstrating the synergistic anti-fogging advantage of the compound anti-fogging masterbatch.

[0033] Performance indicators Test Results Tensile strength 24.7MPa Elongation at break 548% Antibacterial rate against Escherichia coli 95.6% Antibacterial rate against Staphylococcus aureus 96.0% Anti-fog rating (refrigerated conditions) Level 4 Fog-free period (refrigerated conditions) 8min 6-month natural degradation rate 70.3% The table shows that the mechanical, antibacterial, and degradation properties of Comparative Example 3 are only slightly different from those of Example 2 (tensile strength 24.7 MPa vs 25 MPa, antibacterial rate 95.6% vs 95.8%), but its anti-fogging performance is seriously inadequate: the anti-fogging level is only level 4 (the film surface is covered with fog droplets and is completely opaque), and the fog-free retention time is only 8 minutes, far lower than level 1 and 150 minutes of Example 2. The core reason is that the hydrophilicity of the single polyvinylpyrrolidone anti-fogging masterbatch is limited, and it cannot quickly form a uniform and continuous water film on the film surface, and the fog easily condenses into large fog droplets. However, the polyethylene glycol compounded in this invention can synergistically regulate the surface tension gradient with polyvinylpyrrolidone, promote the spread of the water film, and thus achieve long-lasting anti-fogging.

[0034] Comparative Example 4: Please see Figure 1 The present invention provides a comparative solution comprising the following steps: Prepare modified structured starch, as in Example 2 S1; Preparation of the composite antibacterial agent, same as in Example 2 S2; Weigh out 43g of PBAT, 10g of PLA, 30g of modified structural starch, 5g of PBC, 5g of talc, 0.5g of aluminate, 1g of compound antibacterial agent, and 3g of single PEG anti-fogging masterbatch according to the weight proportions, add them to a high-speed mixer, and mix for 19 minutes at 88℃ and 950r / min to obtain the mixture. S4-S5: Same as Example 2 S4-S5.

[0035] Performance indicators Test Results Tensile strength 24.9MPa Elongation at break 546% Antibacterial rate against Escherichia coli 95.7% Antibacterial rate against Staphylococcus aureus 96.1% Anti-fog rating (refrigerated conditions) Level 3 Fog-free period (refrigerated conditions) 35min 6-month natural degradation rate 70.4% Compared with the compound antifog masterbatch of Example 2 (antifog level 1, antifog-free retention time 150 min), the antifog performance of the single PEG antifog agent is significantly deteriorated: the antifog-free retention time is only 35 min, the antifog level drops to level 3, and the surface is covered with fine fog droplets, which significantly affects the transparency; at the same time, its performance is also inferior to that of single PVP, with a fog-free retention time of 8 min and an antifog level of 4 in Comparative Example 3.

[0036] Therefore, although PEG alone has a certain degree of hydrophilicity, its molecular chain structure is simple, and the fog is easily condensed into fine droplets. However, when PVP and PEG are combined, the film-forming properties of PVP and the hydrophilicity of PEG work synergistically. PVP anchors itself on the film surface to provide a film-forming framework, while the hydrophilic segments of PEG quickly adsorb water molecules and spread into a continuous water film, thereby achieving long-lasting transparent anti-fog effect. This proves that the combined system is significantly better than the single component.

[0037] Comparative Example 5: Please see Figure 1 The present invention provides a comparative solution comprising the following steps: Three parallel control groups (5-1, 5-2, and 5-3) were set up. Except for the type of starch modifier, the types, weights, and process parameters of the other raw materials were completely consistent with those in Example 2.

[0038] Modifier replacement scheme: Comparative Example 5-1: 5g of sodium dodecylbenzenesulfonate, anionic surfactant; Comparative Example 5-2: Tween 805g of nonionic surfactant; Comparative Example 5-3: 5g of commonly used starch modifier maleic anhydride grafted polyethylene.

[0039] The rest is the same as in Example 2; Only S1 (preparation of modified structured starch) was adjusted as follows: 95g of potato structured starch and 5g of the corresponding modifier were weighed at a ratio of 95:5, added to a twin-screw extruder, and melt-blended and extruded at 115℃ and a screw speed of 210r / min. After cooling, the mixture was pulverized to obtain modified starch. The remaining steps were the same as in Example 2.

[0040] Performance indicators Comparative Example 5-1 (Sodium dodecylbenzenesulfonate) Comparative Example 5-2 (Twain 80) Comparative Example 5-3 (Maleic anhydride grafted polyethylene) Example 2 (Sorbitol monostearate) Tensile strength: 16.2 MPa, 18.5 MPa, 20.3 MPa, 25 MPa; Elongation at break: 280%, 350%, 420%, 550%; Interfacial compatibility (SEM observation): Severe aggregation, obvious interfacial voids; Local aggregation, blurred interface; Minor aggregation, relatively clear interface; No aggregation, good interfacial fusion; Natural degradation rate after 6 months: 71.0%, 70.8%, 69.5%, 70.5% Compared with Example 2, the effects of other modifiers all have obvious shortcomings: Sodium dodecylbenzenesulfonate (5-1): The anionic group has weak binding force with starch hydroxyl groups and poor compatibility with nonpolar PBAT / PLA matrix, resulting in severe starch agglomeration. The tensile strength is only 16.2 MPa (a decrease of 35.2%) and the elongation at break is 280% (a decrease of 50.9%). Tween 80 (5-2): Although it is a nonionic surfactant, the hydrophilicity and hydrophobicity of the molecular chain are not good. After modification, starch still has local agglomeration, and the improvement of mechanical properties is limited. Maleic anhydride-grafted polyethylene (5-3): Although it can improve compatibility, the grafting rate is unstable and its hydrophobicity is too strong, which leads to a slight decrease in the degradability of starch, while the mechanical properties are still lower than those in Example 2.

[0041] Therefore, glyceryl monostearate / sorbitan monostearate has an amphiphilic molecular structure. The stearic acid chain has a high affinity for the ester bond structure of PBAT / PLA, and the glycerol / sorbitan groups can form hydrogen bonds with the starch hydroxyl groups to achieve interfacial bonding. This matching property cannot be replicated by other modifiers, proving the superiority of the selected modifier.

[0042] Comparative analysis of Examples 1-4 and Comparative Examples 1-5 shows that the biodegradable food preservation film technology of the present invention overcomes the technical problems of weak mechanical properties, poor functional stability, and difficulty in achieving multiple performances in existing biodegradable food preservation films. This invention uses glyceryl monostearate or sorbitan monostearate to modify the structure of starch. Compared with the direct addition of unmodified corn starch in Comparative Example 1, it fundamentally improves the compatibility between starch and PBAT / PLA matrix. The tensile strength of Examples 1-4 reaches 20-28 MPa and the elongation at break is 500-600%, which is 66.7%-133.3% and 150%-200% higher than Comparative Example 1 (12 MPa, 200%), respectively. Moreover, the film does not exhibit brittleness. This solves the problem that cost reduction of traditional starch-based materials inevitably leads to performance degradation. By utilizing the hydrophobic groups of ester modifiers to bond with the polymer matrix and the hydrophilic groups to bond with the starch hydroxyl groups, a bridge-like interface is constructed, which takes into account both biodegradability (degradation rate of 70.5% in Example 2, close to 71.2% in Comparative Example 1) and mechanical properties, far exceeding the existing unmodified starch composite system. In terms of functional enhancement, the silane coupling agent KH550 modified nano-silver-nano-titanium dioxide composite antibacterial agent of this invention exhibits outstanding ingenuity: Examples 1-4 show an initial antibacterial rate of 90.5%-98.7%, which remains above 90% after one month, while Comparative Example 2 (unmodified antibacterial agent) shows an initial antibacterial rate of only 60%-65%, which drops sharply to 38%-42% after one month. This is because the silane coupling agent reduces the surface energy of nanoparticles through chemical grafting, avoiding aggregation (the uniformity of antibacterial agent dispersion is improved by more than 40% in the examples), while enhancing the bonding force with the matrix, thus solving the problems of easy loss and diminishing effect of nano-antibacterial agents. The technical challenges of reducing the amount of anti-fog agent are overcome, achieving broad-spectrum and long-lasting antibacterial properties, which are superior to existing single antibacterial agents or unmodified nanocomposite systems. In addition, the anti-fog masterbatch of polyvinylpyrrolidone and polyethylene glycol in a 7:3 ratio (Examples 1-4) achieves a qualitative leap in anti-fog performance compared with Comparative Example 3 (single PVP): the anti-fog retention time of Examples is 120-180 min and the anti-fog level is 1, while that of Comparative Example 3 is only 8 min and level 4. Its innovation lies in using the synergistic effect of the two components to regulate the surface tension gradient and promote the uniform spread of the water film, breaking through the limitations of short-term effectiveness and poor compatibility of single anti-fog agents. More importantly, this invention achieves synergistic multi-performance through optimized raw material ratios (such as the intermediate ratio in Example 2 and the high-performance ratio in Example 3): while exhibiting superior mechanical, antibacterial, and anti-fogging properties compared to the comparative examples, it achieves a natural degradation rate of 60.8%-70.5% within 6 months, meeting environmental protection requirements; and the preparation process parameters are controllable (such as segmented temperature control using a twin-screw extruder and air ring cooling), with production stability exceeding 98% in Examples 1-4, demonstrating potential for industrial scale-up. Compared to existing technologies that optimize only a single performance but suffer from multiple performance imbalances, this invention constructs a new system integrating mechanics, function, degradation, and process through the synergistic design of modified starch, composite antibacterial agents, and compounded anti-fogging masterbatches. Its performance improvement, stability, and practicality all demonstrate significant technological progress, providing a novel solution for biodegradable food packaging materials that combines environmental protection and functionality.

[0043] The testing method is as follows: I. Tensile Strength and Elongation at Break Test: Dumbbell-shaped strips, 150 mm long and 10 mm wide, were cut from the prepared cling film. Five samples were tested in each group. Before testing, the strips were placed in an environment of 23℃ and 50% relative humidity for 24 hours to adjust their condition. The test was conducted using an electronic universal testing machine with a tensile speed of 50 mm / min. The maximum tensile force and gauge length at break were recorded. The tensile strength was calculated as "maximum tensile force / initial cross-sectional area of ​​the strip", and the elongation at break was calculated as "(gauge length at break - initial gauge length) / initial gauge length × 100%". The final result was the average of the five samples.

[0044] II. Antibacterial Rate Test: *Escherichia coli* and *Staphylococcus aureus* were inoculated separately into nutrient broth medium and cultured at 37°C with shaking for 18 hours to prepare a concentration of 1×10⁻⁶. 6 For a bacterial suspension of CFU / mL, take a 20mm × 20mm plastic wrap sample, sterilize it with ultraviolet light for 30 minutes, add 0.2mL of bacterial suspension, cover it with a sterile polyethylene film to ensure the bacterial suspension is evenly in contact with the sample surface, and incubate it in an incubator at 37℃ and 90% relative humidity for 24 hours. After incubation, add 10mL of sterile physiological saline to elute the bacteria on the sample surface. Take the eluent and perform serial dilutions, spread it on nutrient agar medium, and incubate it at 37℃ for 24 hours. Count the number of colonies. At the same time, set up a bacterial suspension that has not been in contact with the sample as a control sample. The antibacterial rate is calculated as "(number of colonies in control sample - number of colonies in sample) / number of colonies in control sample × 100%".

[0045] III. Anti-fog level test: Cut a 100mm×100mm sample from the plastic wrap and stretch it tightly to the opening of an open glass container (500mL volume, containing 50mL of 4℃ distilled water). Ensure the sample and container are well sealed. Place the container in a refrigerated environment at 4℃ and 85% relative humidity. After 30 minutes, observe the fog droplets on the sample surface. The anti-fog level is divided into 1-4 levels: Level 1: No obvious fog droplets on the sample surface, completely transparent; Level 2: A small number of fine fog droplets on the sample surface, slightly affecting transparency; Level 3: The sample surface is covered with fine fog droplets, significantly affecting transparency; Level 4: Large fog droplets or water film form on the sample surface, completely opaque.

[0046] IV. Fog-free retention time test: The test conditions are the same as the anti-fog level test. After placing the glass container with the sample fixed in a refrigerated environment of 4℃ and 85% relative humidity, start timing and continuously observe the surface state of the sample. Record the time from the start of the test to the first obvious fog droplets appearing on the sample surface (i.e., reaching the anti-fog level 2 standard), which is the fog-free retention time.

[0047] V. 6-month natural degradation rate test: Cut the plastic wrap into 50mm×50mm samples, with 3 samples per group. Weigh and label each sample. Select natural soil with pH value of 6.5-7.5 and humidity of 60%-70%. Dig a pit 20cm deep, bury the sample in the soil, cover it with soil and compact it. Take samples every month to observe the degradation status. After 6 months, take out the samples, rinse them with distilled water, place them in a 60℃ oven to dry to constant weight, and weigh them again. The degradation rate is calculated as "(initial weight - weight after degradation) / initial weight × 100%". The final result is the average of the 3 samples.

[0048] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific technical solutions or characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A biodegradable food preservation film, characterized in that, It is prepared from the following raw materials in parts by weight: 40-45 parts of polybutylene terephthalate (PBAT), 8-12 parts of polylactic acid (PLA), 28-32 parts of modified structural starch, 4-6 parts of polybutylene carbonate (PBC), 4-6 parts of talc, 0.4-0.6 parts of aluminate, 0.8-1.2 parts of composite antibacterial agent, and 2.5-3.5 parts of anti-fogging masterbatch; The modified structured starch is prepared by melt blending and modifying structured starch with glyceryl monostearate or sorbitan monostearate at a weight ratio of 95:

5. The composite antibacterial agent is prepared by mixing nano-silver and nano-titanium dioxide in a 1:1 weight ratio, adding 3-5% of the total mixed powder with silane coupling agent KH550, and then modifying it by ultrasonic dispersion.

2. The biodegradable food preservation film according to claim 1, characterized in that, The nano-silver has a particle size of 20-30 nm, and the nano-titanium dioxide is anatase with a particle size of 15-25 nm.

3. The biodegradable food preservation film according to claim 1, characterized in that, The anti-fog masterbatch is a mixture of polyvinylpyrrolidone and polyethylene glycol in a weight ratio of 7:

3.

4. A method for preparing a biodegradable food preservation film as described in any one of claims 1-3, characterized in that, Includes the following steps: S1: Preparation of modified structured starch: Weigh structured starch and glyceryl monostearate or sorbitan monostearate at a weight ratio of 95:5, add them to a twin-screw extruder, melt-blend and extrude at 110-120℃ and screw speed of 200-220r / min, cool and then pulverize to obtain modified structured starch. S2: Preparation of composite antibacterial agent: Weigh nano silver and anatase nano titanium dioxide at a weight ratio of 1:1, add them to anhydrous ethanol, ultrasonically disperse for 10-15 min, add 3-5% of silane coupling agent KH550 in total powder, stir and react at 60-70℃ for 2-3 h, centrifuge and dry to obtain composite antibacterial agent; S3: Weigh out polybutylene terephthalate (PBAT), PLA, modified structural starch prepared by S1, PBC, talc, aluminate, composite antibacterial agent prepared by S2, and anti-fogging masterbatch according to the weight parts, add them to a high-speed mixer, and mix for 18-20 minutes at 85-90℃ and 900-1000r / min to obtain a mixture. S4: Add the mixture obtained in S3 to a twin-screw extruder and melt-extrude and granulate it at 170-180℃ and screw speed of 180-200r / min to obtain masterbatch; S5: Add the masterbatch obtained in S4 into a blown film machine, blown film at 160-170℃, blow ratio 3-3.5, and traction speed 10-12m / min, and after cooling, traction, and winding, obtain a biodegradable preservation film.

5. The preparation method according to claim 4, characterized in that, The ultrasonic dispersion power in S2 is 300-400W, and the frequency is 20-25kHz.

6. The preparation method according to claim 4, characterized in that, The temperature distribution of each section of the twin-screw extruder in S4 is as follows: feeding section 140-150℃, compression section 160-170℃, homogenization section 170-180℃.

7. The preparation method according to claim 4, characterized in that, The S5 uses a fan ring cooling system with a cooling air temperature of 20-25℃.

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