Food-grade fully-degradable composite preservative film as well as preparation method and application thereof

Abstract

The invention provides a food-grade fully-degradable composite preservative film as well as a preparation method and application thereof, and belongs to the technical field of food preservative films. The composite preservative film is prepared from the following raw materials in parts by weight: 50-70 parts of poly (butylene adipate-terephthalate), 25-40 parts of polylactic acid and 5-15 parts of thermoplastic starch, wherein the thermoplastic starch is prepared from a composite plasticizer and starch. The longitudinal tensile strength of the prepared food-grade fully-degradable composite preservative film can reach 20 MPa, the elongation at break is 190-320%, the elastic modulus is 500 MPa, the mechanical property requirements of food packaging, disposable articles and other scenes are met, the cost is reduced, the degradability is improved, and meanwhile the use performance of the material is considered.

Description

Technical Field

[0001] This invention relates to the field of food preservation film technology, and in particular to a food-grade fully degradable composite preservation film, its preparation method, and its application. Background Technology

[0002] Plastic materials are widely used in production and daily life, but traditional petroleum-based plastics are difficult to degrade naturally, which can easily cause serious environmental problems. Developing degradable alternative materials has become a research hotspot.

[0003] Polylactic acid (PLA) is a widely used biodegradable material, but its poor thermal stability, high brittleness, and low melt strength greatly limit its applications. Poly(butylene adipate-terephthalate) (PBAT) is also a novel biodegradable material, but its low modulus fails to meet the performance requirements of most plastic products. Based on the complementary properties of PLA and PBAT, physical blending them to prepare PBAT / PLA composites can, to some extent, compensate for the shortcomings of single components and achieve better overall performance. However, the high prices of both PBAT and PLA restrict the large-scale application of this composite material in actual production.

[0004] Starch, as a natural polymer compound, has the advantages of low price and complete biodegradability, making it an ideal filler for PBAT / PLA composite materials. However, strong hydrogen bonds exist between starch molecules, resulting in poor molding and processing performance. Specific treatments are needed to disorder the starch structure and prepare thermoplastic starch (TPS).

[0005] Blending PBAT, PLA, and TPS can further reduce material costs and improve biodegradability. However, the three have poor compatibility, and plasticizers are usually added to improve the mechanical properties of the blend before extrusion blown film processing to obtain a composite film. The plasticizers used in the existing technology have problems such as the difficulty in obtaining raw materials and high cost. Moreover, their safety is not yet clear when applied to food packaging, making it difficult to meet the requirements for food-grade materials.

[0006] Based on this, developing a PBAT / PLA / TPS composite preservation film that uses readily available raw materials, is inexpensive, fully biodegradable, and meets food-grade standards has significant practical application value. Summary of the Invention

[0007] The purpose of this invention is to provide a food-grade fully degradable composite preservation film, its preparation method, and its application, in order to solve the problems of high cost of PBAT / PLA composite preservation film and poor compatibility of PBAT, PLA, and TPS blends.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a food-grade fully biodegradable composite preservation film, mainly made from the following raw materials in parts by weight: Poly(butylene adipate-terephthalate) (PBAT) 50-70 parts; Polylactic acid (PLA) 25-40 parts; Thermoplastic starch (TPS) 5-15 parts; The thermoplastic starch is made from a composite plasticizer and starch.

[0009] Preferably, the composite plasticizer comprises sorbitol and glycerin.

[0010] Preferably, the mass ratio of starch, sorbitol and glycerol is 55~65:25~35:10~20.

[0011] Preferably, the thermoplastic starch is prepared by mixing starch, sorbitol and glycerol to obtain thermoplastic starch.

[0012] Preferably, the raw material also includes a chain extender.

[0013] Preferably, the amount of the chain extender added is 0.5 to 1.0% of the total mass of poly(butylene adipate-terephthalate), polylactic acid and thermoplastic starch.

[0014] The present invention also provides a method for preparing the above-mentioned food-grade fully degradable composite preservation film, comprising the following steps: mixing the above raw materials and then extruding, granulating, and blowing film to obtain the food-grade fully degradable composite preservation film.

[0015] Preferably, the extrusion is carried out in a twin-screw extruder, which is equipped with three temperature zones: zone 1 (140~160℃), zone 2 (150~170℃), and zone 3 (160~185℃), with a screw speed of 40~60 r / min.

[0016] Preferably, the blown film forming is carried out in a blown film machine, the temperature of which is controlled at 155~200℃, the screw speed at 10~20Hz, the fan frequency at 20~50Hz, and the traction speed at 15~20Hz.

[0017] The present invention also provides an application of the above-described food-grade fully degradable composite preservation film in food packaging or disposable products.

[0018] The beneficial effects of this invention are: This invention uses TPS to replace the expensive PBAT / PLA, which can reduce the cost of food preservation film, effectively solve the problem that the large-scale application of PBAT / PLA composite film is limited due to the high price of raw materials, and greatly enhance the market competitiveness of the product.

[0019] The raw materials PBAT, PLA, and TPS of this invention are all fully biodegradable materials. Under soil burial and composting conditions, they can be completely decomposed by microorganisms into carbon dioxide and water, leaving no environmental residues. This completely solves the "white pollution" problem caused by traditional petroleum-based plastics. The degradation products have no adverse effects on soil and water, which meets the requirements of environmental protection policies.

[0020] This invention effectively improves the interfacial compatibility among PBAT, PLA and TPS by adding chain extenders, inhibits phase separation in the blend system, and ensures the stability of the film forming process. The preparation process uses a conventional twin-screw extruder and blown film machine, without the need for additional equipment modification. All process parameters are clear and controllable, making it suitable for large-scale production.

[0021] The food-grade fully degradable composite preservation film prepared by this invention has a longitudinal tensile strength of up to 20 MPa, an elongation at break of 190-320%, and an elastic modulus of 500 MPa, meeting the mechanical performance requirements of food packaging, disposable products, and other scenarios. While reducing costs and improving degradability, it also takes into account the performance of the material. Detailed Implementation

[0022] This invention provides a food-grade fully biodegradable composite preservation film, mainly made from the following raw materials in parts by weight: Poly(butylene adipate-terephthalate) (PBAT) 50-70 parts; Polylactic acid (PLA) 25-40 parts; Thermoplastic starch (TPS) 5-15 parts; The thermoplastic starch is made from a composite plasticizer and starch.

[0023] In this invention, both PBAT and PLA are made of food contact grade materials.

[0024] In this invention, the specific weight amount of PBAT added can be 50 parts, 55 parts, 60 parts, 65 parts, or 70 parts; the specific weight amount of PLA added can be 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, or 38 parts.

[0025] In this invention, the specific amount of TPS added by weight can be 5 parts, 8 parts, 10 parts, 12 parts, or 15 parts.

[0026] In this invention, the composite plasticizer comprises sorbitol and glycerol.

[0027] In this invention, the mass ratio of starch, sorbitol and glycerol is 55~65:25~35:10~20, preferably 56~62:26~32:12~18, and more preferably 58~60:28~30:14~16.

[0028] In this invention, the thermoplastic starch is prepared by mixing starch, sorbitol and glycerol to obtain thermoplastic starch.

[0029] In this invention, the mixing is carried out in a high-speed mixer at room temperature for 5-8 minutes. This allows the plasticizer to fully penetrate, encapsulate, and disrupt the hydrogen bonds between starch molecules, resulting in thermoplastic starch.

[0030] In this invention, the raw materials also include chain extenders.

[0031] In this invention, the chain extender is preferably an ADR-type chain extender.

[0032] In this invention, the amount of chain extender added is 0.5 to 1.0% of the total mass of poly(butylene adipate-terephthalate), polylactic acid and thermoplastic starch, specifically 0.6%, 0.7%, 0.8% and 0.9%.

[0033] In this invention, the starch is made from food-grade raw materials, and glycerol and sorbitol are food additives permitted by the GB 2760-2024 standard; the chain extender is a food packaging-specific chain extender, with no non-food grade ingredients added.

[0034] The present invention also provides a method for preparing the above-mentioned food-grade fully degradable composite preservation film, comprising the following steps: mixing the above raw materials and then extruding, granulating, and blowing film to obtain the food-grade fully degradable composite preservation film.

[0035] In this invention, the raw materials PBAT, PLA, and TPS are dried separately to control the moisture content to ≤0.05%. Drying is to avoid structural defects such as bubbles and pinholes caused by moisture evaporation during the melt blending process.

[0036] In this invention, the extrusion is carried out in a twin-screw extruder, which is equipped with three temperature zones: zone 1 (140~160℃), zone 2 (150~170℃), and zone 3 (160~185℃), with a screw speed of 40~60 r / min.

[0037] In this invention, the blown film forming is carried out in a blown film machine, the temperature of which is controlled at 155~200℃, the screw speed at 10~20Hz, the fan frequency at 20~50Hz, and the traction speed at 15~20Hz.

[0038] The present invention also provides an application of the above-described food-grade fully degradable composite preservation film in food packaging or disposable products.

[0039] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Raw materials used in the examples and comparative examples: PBAT: Grade TH801T, Xinjiang Lanshan Tunhe Chemical Co., Ltd.; PLA: Grade 2003D, NatureWorks; Chain extender: Brand ADR-4468, BASF.

[0041] PBAT, PLA, and ADR-4468 are all food-grade.

[0042] Example 1 Food-grade corn starch powder was placed in an 80℃ electric hot air drying oven and dried for 12 hours to completely remove free moisture. It was then cooled to room temperature for later use.

[0043] Add 29g of food-grade corn starch, 14g of food-grade sorbitol, and 7g of food-grade glycerin (mass ratio 58:28:14) to a high-speed mixer and stir evenly at room temperature for 2 minutes to obtain TPS. Seal and store for later use.

[0044] PBAT, PLA and TPS were dried in an electric heating drying oven at 75℃ for 24 hours, with the moisture content controlled to be ≤0.05%.

[0045] Then, 60 parts (600g) of PBAT, 35 parts (350g) of PLA, 5 parts (50g) of TPS, and 0.8 phr (8g) of ADR-4468 were added to a high-speed mixer and stirred at room temperature for 5 minutes to disperse evenly. The resulting mixture was fed into a twin-screw extruder, with the temperature set at 155℃ in zone 1, 165℃ in zone 2, and 175℃ in zone 3, and the screw speed at 50 r / min. After melt extrusion, the mixture was air-cooled and pelletized. The pellets were dried at 75℃ for 6 hours to obtain dried pellets. The dried pellets were then added to a blown film machine, with the temperature of each section controlled at 155~185℃, the main screw speed at 18Hz, the blower frequency at 30Hz, and the traction speed at 16.3Hz. After blowing, the film was wound up to obtain a food-grade fully biodegradable composite preservation film, denoted as A-5.

[0046] Example 2 The difference from Example 1 is that the amount of PLA added is 32 parts (320g), the amount of TPS added is 8 parts (80g), and all other conditions are the same, resulting in a food-grade fully degradable composite preservation film, denoted as A-8.

[0047] Example 3 The difference from Example 1 is that the amount of PLA added is 30 parts (300g), the amount of TPS added is 10 parts (100g), and all other conditions are the same, to obtain a food-grade fully degradable composite preservation film, denoted as A-10.

[0048] Example 4 The difference from Example 1 is that the amount of PLA added is 25 parts (250g), the amount of TPS added is 15 parts (150g), and all other conditions are the same, to obtain a food-grade fully degradable composite preservation film, denoted as A-15.

[0049] Comparative Example PBAT and PLA were dried in an electric heating oven at 75℃ for 24 hours, with the moisture content controlled to be ≤0.05%.

[0050] Then, 60 parts (600g) of PBAT, 40 parts (400g) of PLA, and 0.8phr (8g) of ADR-4468 were added to a high-speed mixer and stirred at room temperature for 5 minutes to disperse evenly. The resulting mixture was fed into a twin-screw extruder, with the temperature set at 150℃ in zone 1, 160℃ in zone 2, and 170℃ in zone 3, and the screw speed at 50r / min. After melt extrusion, the mixture was air-cooled and pelletized. The pellets were dried at 75℃ for 6 hours to obtain dried pellets. The dried pellets were then added to a blown film machine, with the temperature of each section controlled at 150~175℃, the main screw speed at 18Hz, the blower frequency at 28Hz, and the traction speed at 16.3Hz. After blowing, the film was wound up to obtain a food-grade fully biodegradable composite preservation film, denoted as A-0.

[0051] The performance of the composite preservation films prepared in Examples 1-4 and the comparative examples was verified. The test methods are as follows. All test data are the mean ± standard error after multiple repeated tests. The test results are shown in Table 1: (1) Tensile properties were tested according to GB / T 1040.3-2022 standard. At room temperature, the composite plastic wrap was cut into strips with a length of 150mm × width of 15mm × gauge length of 50mm. The transverse and longitudinal tensile properties were tested respectively. The tensile rate was 50mm / min. Each sample was repeated 5 times and the average value was taken. (2) The oxygen permeability was tested by the differential pressure method. The test temperature was 23℃, the pre-permeability time was 30 min, and the vacuum time was 8 h. Each sample was repeated 3 times and the average value was taken. (3) The water vapor transmission rate was tested by the weight reduction method. The test temperature was 38℃, the relative humidity was 90%, the preheating time was 1.5h, and each sample was repeated 3 times. The average value was taken. (4) The hydrophilicity and hydrophobicity of the film surface were tested using a contact angle meter. Five test points were randomly selected for each sample, and the average value was taken.

[0052] Table 1 Test results of Examples 1-4 and comparative examples Tensile properties: As can be seen from Table 1, the longitudinal and transverse tensile strengths of Examples 1-4 (A-5-A-15) decreased slightly with the increase of TPS addition, but still met the requirements for use in food packaging, disposable products and other scenarios; among them, the longitudinal elongation at break of A-5 reached 317.36%, which was significantly higher than that of the comparative example A-0, reflecting the synergistic toughening effect of TPS and PBAT / PLA, indicating that the optimization of the raw material formulation for preparing the composite preservation film of the present invention effectively balanced cost and mechanical properties.

[0053] Barrier performance: As can be seen from Table 1, the oxygen permeability coefficients of A-5 to A-10 show a decreasing trend, with A-10 dropping to 1.258 cm³·cm / cm²·s·Pa. The barrier performance is better than that of the comparative example, making it suitable for packaging scenarios with certain requirements for oxygen barrier. Although the water vapor permeability fluctuates, it is generally within a reasonable range and can be further optimized through subsequent process fine-tuning.

[0054] Surface properties: As can be seen from Table 1, the contact angles of A-10 to A-15 are greater than those of the comparative examples, and the surface hydrophobicity is improved, which helps to reduce the risk of moisture absorption of the composite preservation film, extend the shelf life, and meet the surface properties requirements of food packaging.

[0055] Food contact safety testing was conducted on the composite preservation films of Examples 1-4, and plasticizer migration tests were performed. No plasticizers were detected, which meets the GB-4806 series food contact material standards and can be safely used in direct contact scenarios such as food packaging and fresh food preservation.

[0056] Based on the market bulk purchase price (wholesale price), calculate the total raw material cost of each sample and compare the cost advantages, as detailed in Table 2.

[0057] Table 2 Raw Material Cost Accounting Results Note: Wholesale prices are calculated based on market bulk purchasing conditions and are 70-80% of retail prices, which is in line with the industry's conventional pricing logic; cost accounting is based on the actual raw material ratio of each sample. Comparative example A-0 does not contain corn starch, sorbitol, or glycerin (because there is no TPS preparation step). In Examples 1-4, as the amount of TPS added increases, the amount of corn starch, sorbitol, and glycerin increases proportionally, the amount of PBAT is fixed, and the amount of PLA decreases according to the formula.

[0058] As can be seen from Table 2, the total cost of raw materials in Examples 1 to 4 is 3.9% to 4.0% lower than that in Comparative Example A-0. Moreover, the cost continues to decrease as the amount of TPS added increases. The total cost of A-15 is 4.0% lower than that of A-0. Based on a large-scale production of 1000kg, it can save about 10.6 yuan in costs. Long-term promotion and application can significantly reduce production costs and enhance market competitiveness.

[0059] The composite film prepared by this invention achieves synergistic optimization of food contact safety, biodegradability and cost while maintaining basic performance. All performance indicators meet expectations and have strong practical application value and market promotion potential.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A food-grade fully biodegradable composite preservation film, characterized in that, It is mainly made from the following raw materials in parts by weight: Poly(butylene adipate-terephthalate) 50-70 parts; Polylactic acid 25-40 parts; 5-15 parts of thermoplastic starch; The thermoplastic starch is made from a composite plasticizer and starch.

2. The food-grade fully degradable composite preservation film according to claim 1, characterized in that, The composite plasticizer contains sorbitol and glycerin.

3. The food-grade fully degradable composite preservation film according to claim 2, characterized in that, The mass ratio of starch, sorbitol and glycerol is 55~65:25~35:10~20.

4. The food-grade fully degradable composite preservation film according to any one of claims 1 to 3, characterized in that, The thermoplastic starch is prepared by mixing starch, sorbitol and glycerol to obtain thermoplastic starch.

5. The food-grade fully degradable composite preservation film according to claim 4, characterized in that, The raw materials also include chain extenders.

6. The food-grade fully degradable composite preservation film according to claim 5, characterized in that, The amount of the chain extender added is 0.5 to 1.0% of the total mass of poly(butylene adipate-terephthalate), polylactic acid and thermoplastic starch.

7. The method for preparing the food-grade fully degradable composite preservation film according to any one of claims 1 to 6, characterized in that, The process includes the following steps: mixing the above raw materials and then extruding, granulating, and blowing the film to obtain a food-grade fully biodegradable composite preservation film.

8. The method for preparing the food-grade fully degradable composite preservation film according to claim 7, characterized in that, The extrusion is carried out in a twin-screw extruder, which is equipped with three temperature zones: zone 1 (140~160℃), zone 2 (150~170℃), and zone 3 (160~185℃), with a screw speed of 40~60 r / min.

9. The method for preparing the food-grade fully degradable composite preservation film according to claim 7 or 8, characterized in that, The blown film forming is carried out in a blown film machine, with the temperature of the blown film machine controlled at 155~200℃, the screw speed at 10~20Hz, the fan frequency at 20~50Hz, and the traction speed at 15~20Hz.

10. The application of the food-grade fully degradable composite preservation film according to any one of claims 1 to 6 in food packaging or disposable products.

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