Environmentally degradable plastic packaging material and preparation method thereof

Abstract

This invention discloses an environmentally friendly biodegradable plastic packaging material and its preparation method, belonging to the technical field of polymer biodegradable packaging materials. It aims to solve the problems of poor compatibility, low melt strength, and slow degradation of existing polylactic acid (PLA) blends. This invention uses PLA as a matrix, introduces a furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester containing side-chain double bonds as a functionalized flexible component, and adds thiol-modified epoxidized soybean oil as a reactive compatibilizer. Chemical linkages between different polymer chains are achieved through reactive extrusion, constructing a cross-linked network structure of thioether bonds. The resulting packaging material maintains good mechanical properties while exhibiting excellent gas barrier properties and biodegradability.

Description

Technical Field

[0001] This invention belongs to the field of polymer biodegradable packaging materials technology, specifically relating to an environmentally friendly biodegradable plastic packaging material and its preparation method. Background Technology

[0002] With the deepening of the concept of sustainable development, the development of environmentally friendly materials that can replace traditional petroleum-based plastics has become a research focus in the packaging field. Currently, the mainstream biodegradable plastic packaging materials on the market mainly include starch-based materials, polybutylene terephthalate (PBAT), and polylactic acid (PLA). However, existing biodegradable packaging materials still have significant limitations in practical applications: on the one hand, most biodegradable polyester materials have poor gas barrier properties, making it difficult to meet the high standards required for food preservation and modified atmosphere packaging; on the other hand, blended barrier materials often face problems such as poor compatibility between components and weak interfacial adhesion, resulting in insufficient melt strength during film formation. Furthermore, many materials claiming to be biodegradable degrade extremely slowly in the natural environment, often requiring specific industrial composting conditions to complete degradation, which to some extent weakens their environmental significance.

[0003] Existing patent CN115073897A discloses a biodegradable plastic packaging material and its preparation process. Its core technical feature lies in using an aliphatic polymer as the matrix and introducing plant starch, inorganic powder fillers, and chitosan for blending modification, utilizing the synergistic effect of different polyester components to improve barrier properties. However, the introduction of a large amount of plant starch and inorganic fillers into the system leads to a decrease in the transparency of the film product, and uneven filler dispersion during blown film processing easily results in unstable mechanical properties. Furthermore, this system is a physical blend and simple interfacial adsorption, lacking stable chemical bonds between components, making it difficult to fundamentally solve the problems of insufficient melt strength and slow environmental degradation rate under natural conditions.

[0004] In summary, there is an urgent need to develop an environmentally friendly plastic packaging material that possesses excellent gas barrier properties and mechanical strength, can be efficiently biodegraded in natural environments, and whose components exhibit good compatibility and processing stability. Summary of the Invention

[0005] The present invention aims to solve the problems of poor compatibility, low melt strength and slow degradation of existing polylactic acid blends.

[0006] The specific technical solution is as follows: An environmentally friendly and biodegradable plastic packaging material, wherein the plastic packaging material is made from the following raw materials in parts by weight: 50-70 parts of polylactic acid, 20-40 parts of furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester, 3-8 parts of thiol-modified epoxidized soybean oil, 0.01-0.05 parts of triethanolamine, 0.05 to 0.2 parts of antioxidant, and 0.5 to 2 parts of lubricant; wherein the side chains of the furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester retain unsaturated carbon-carbon double bond structures; wherein thiol groups are grafted onto the soybean oil backbone of the thiol-modified epoxidized soybean oil; wherein the unsaturated carbon-carbon double bonds on the side chains of the furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester and the thiol groups grafted onto the backbone of the thiol-modified epoxidized soybean oil undergo an addition reaction during reactive extrusion, catalyzed by the triethanolamine, thereby forming thioether bonds.

[0007] Further, the preparation method of the furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester is as follows: 2,5-furanyl dicarboxylic acid, itaconic acid and 1,5-pentanediol are taken in a molar ratio of 0.85:0.15:1.12; hydroquinone, phenothiazine and dibutyl titanate are added, and the mixture is stirred at 165-175℃ for 3 hours under nitrogen protection; then, the system pressure is reduced to below 50Pa by vacuuming, and the temperature is raised to 190-200℃ for 2-3 hours; after the reaction is completed, nitrogen is introduced into the system to break the vacuum, the melt is discharged, cooled and granulated, and vacuum dried to obtain furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester.

[0008] Furthermore, the amount of hydroquinone used is 0.1 wt% of the total weight of the 2,5-furandicarboxylic acid, the itaconic acid, and the 1,5-pentanediol; the amount of phenothiazine used is 0.03 wt% of the total weight of the 2,5-furandicarboxylic acid, the itaconic acid, and the 1,5-pentanediol; and the amount of dibutyl titanate used is 0.1 wt% of the total weight of the 2,5-furandicarboxylic acid, the itaconic acid, and the 1,5-pentanediol.

[0009] Furthermore, the method for preparing the thiol-modified epoxidized soybean oil is as follows: epoxidized soybean oil and 3-mercaptopropionic acid are taken in a molar ratio of 1:1.2; then 1,5,7-triazabicyclo[4.4.0]dec-5-ene is added; in a closed nitrogen environment, the system is heated to 95℃-105℃ and the reaction is maintained for 6 hours; after the reaction is completed, the system is subjected to reduced pressure to remove trace volatiles, and after washing with water and vacuum drying, thiol-modified epoxidized soybean oil is obtained.

[0010] Furthermore, the amount of 1,5,7-triazabicyclo[4.4.0]dec-5-ene fed is 0.05-0.1 wt% of the total weight of the epoxidized soybean oil and the 3-mercaptopropionic acid.

[0011] Furthermore, the antioxidant is 2,6-di-tert-butyl-4-methylphenol, Irganox 1010, or Irganox 1076; the lubricant is zinc stearate or polyethylene glycol.

[0012] Furthermore, the method for preparing the aforementioned environmentally friendly and biodegradable plastic packaging material includes the following steps: S1: The dried polylactic acid, furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester, antioxidant and lubricant are mixed evenly, the triethanolamine is added and the mixture is continued to be mixed, the mercapto-modified epoxidized soybean oil is added dropwise and the mixture is continuously mixed under low speed conditions to obtain a uniform premix. S2: The uniform premix is ​​continuously added to a twin-screw extruder for reactive extrusion, and the resulting material flows out of the die to form a melt. S3: The outflowing melt is drawn into the blown film device for blown film production. Under the action of the air cooling ring, a thin film bubble is formed. Then, the traction roller is used to wind it up to obtain the plastic packaging material.

[0013] Furthermore, the rotation speed under the low-speed condition in step S1 is 100-150 rpm, and the continuous mixing time is 15-20 minutes.

[0014] Furthermore, in step S2, the rotational speed of the twin-screw extruder is set to 150-200 rpm; the temperature of the reaction extrusion is set as follows: 130°C in the feeding section; 160-175°C in the mixing reaction section; and 160°C in the metering section and die; the residence time of the melt in the twin-screw extruder is 3-5 minutes.

[0015] Furthermore, during the blown film process described in step S3: the blow-up ratio is controlled at 2.0-3.0, the traction ratio is 3-6, and the cooling air ring speed is 0.5-1.5m / s.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention introduces furan dicarboxylic acid-pentanediol-itaconic acid copolyester (PEFI) as a functional flexible component, which enables the material to maintain good mechanical strength while having excellent gas barrier properties, thereby significantly improving the oxygen barrier and freshness preservation capabilities of the packaging material; at the same time, the flexible segments of PEFI effectively improve the inherent brittleness of PLA material, improve the flexibility and impact resistance of the material, and make the resulting film have better deformation resistance and reliability in actual packaging applications.

[0017] (2) This invention introduces mercapto-modified epoxidized soybean oil (SH-ESO) to construct a reactive compatibility system. During the processing, the epoxy groups in SH-ESO react with the terminal carboxyl or hydroxyl groups of PLA and PEFI to achieve chemical connection between different polymer chains, significantly improving the compatibility and interfacial bonding strength of the PLA and PEFI blend system. At the same time, the mercapto groups of SH-ESO react with the double bonds of the PEFI side chains to form stable thioether bonds, further enhancing the internal network structure of the system, effectively improving the melt strength and blown film processing stability, and significantly improving the toughness, tensile strength and deformation resistance of the film, thereby ensuring the stable forming of the material in industrial blown film processing.

[0018] (3) The material of the present invention has good environmental degradation characteristics while maintaining excellent performance. In the natural environment, the material can gradually undergo structural relaxation and chain segment breakage through the synergistic effect of oxidation and hydrolysis, thereby accelerating the overall degradation process of the material. This degradation effect comes from the easily oxidized thioether bonds and hydrolyzable polyester main chain in the cross-linked network of the material, which allows water and microorganisms to penetrate efficiently and promote the breakage of the main chain, overcoming the problem of slow degradation rate of traditional polyester biodegradable materials, and achieving a balance between maintaining stable performance during the use period and being able to degrade quickly after disposal. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation process of an environmentally friendly and biodegradable plastic packaging material according to the present invention. Figure 2 This is a schematic diagram of the reaction for preparing PEFI copolyester and SH-ESO reactive compatibilizer according to the present invention; Figure 3 The Fourier transform infrared spectrum of the product obtained in Example 1 of this invention; Figure 4 Fourier transform infrared spectra of pure epoxidized soybean oil, SH-ESO, PEFI, and the biodegradable plastic film of this invention. Figure 5 This is a comparison chart showing the test results of gas barrier performance, tensile strength, and elongation at break of the embodiments and comparative examples of the present invention. Figure 6 This is a comparison chart of the degradation weight loss rates of the embodiments and comparative examples of the present invention under soil burial conditions. Detailed Implementation

[0020] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0021] This invention provides an environmentally friendly and biodegradable plastic packaging material and its preparation method. The plastic packaging material is made from the following raw materials in parts by weight: PLA 50-70 parts, PEFI 20-40 parts, SH-ESO 3-8 parts, triethanolamine 0.01-0.05 parts, antioxidant 0.05-0.2 parts, and lubricant 0.5-2 parts.

[0022] The PLA serves as a rigid continuous phase matrix, providing the material with mechanical strength and processing properties.

[0023] The PEFI is obtained by polycondensation of 2,5-furandicarboxylic acid (FDCA), itaconic acid, and 1,5-pentanediol (PDO). The furan ring structure provides excellent gas barrier properties, while the five-carbon linear chain of 1,5-pentanediol imparts good flexibility to the polyester segments. Itaconic acid partially replaces furandicarboxylic acid in the polycondensation process, allowing the polyester main chain side chains to retain unsaturated carbon-carbon double bonds, thus providing reactive chemical anchors for subsequent reactions.

[0024] The SH-ESO is a reactive compatibilizer. Its molecule has thiol groups grafted onto the soybean oil skeleton while retaining epoxy groups. This allows it to undergo ring-opening polymerization with the terminal carboxyl groups of PLA and the terminal hydroxyl groups of PEFI, and to form a stable thioether crosslinking network with the itaconic acid double bonds of the PEFI side chain through thiol-Michael addition. This enables the in-situ construction of a stable covalent macromolecular network structure during processing.

[0025] The triethanolamine is used to selectively catalyze the thiol-Michael addition reaction of SH-ESO thiol groups with α,β-unsaturated double bonds in the PEFI side chain without causing degradation of the PLA or PEFI polyester backbone.

[0026] The antioxidant is 2,6-di-tert-butyl-4-methylphenol (BHT), Irganox 1010, or Irganox 1076, used to inhibit the thermal oxidative degradation of PLA and PEFI under high-temperature processing conditions. The lubricant is zinc stearate or polyethylene glycol, used to improve melt flowability, reduce processing resistance, and optimize film surface properties.

[0027] Preparation of PEFI copolyester and SH-ESO reactive compatibilizer, as shown in the appendix. Figure 2 The reaction diagram is shown below. (1) Preparation of PEFI copolyester: FDCA, itaconic acid, and PDO were added to a reactor equipped with a water separator and mechanical stirrer, with the molar ratio of FDCA:itaconic acid:PDO = 0.85:0.15:1.12. Subsequently, 0.1 wt% hydroquinone, 0.03 wt% phenothiazine, and 0.1 wt% dibutyl titanate (Ti(OBu)2) were added. Hydroquinone prevents high-temperature self-crosslinking of itaconic acid double bonds; phenothiazine inhibits thermally induced free radical crosslinking of itaconic acid double bonds. Specific reaction process: First, esterification was carried out, and the mixture was slowly stirred at 165-175℃ for 3 hours under nitrogen protection to remove the by-product water; then, melt polycondensation was carried out, and the system pressure was slowly reduced to below 50 Pa by vacuuming, and the temperature was raised to 190-200℃ for 2-3 hours. As the degree of polymerization increased, the viscosity of the system gradually increased. The polymerization reaction was judged to be near completion by monitoring the change in stirring torque, and then the reaction was stopped. Nitrogen gas is introduced into the system to break the vacuum, the melt is discharged, cooled and granulated, and then vacuum dried to obtain PEFI copolyester particles with carbon-carbon double bond structures in the side chains.

[0028] (2) Preparation of SH-ESO reactive compatibilizer: Epoxidized soybean oil (ESO) and 3-mercaptopropionic acid were added to a reactor equipped with a reflux device and mechanical stirrer, with a molar ratio of ESO to 3-mercaptopropionic acid of 1:1.2. Subsequently, an organic base catalyst, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), was added at a rate of 0.05-0.1 wt% of the total weight of the reaction substrate. The system was heated to 95-105℃ in a sealed nitrogen atmosphere and maintained for 6 hours, with the reaction temperature controlled not exceeding 120℃ to avoid excessive ring-opening of the epoxy groups. During the reaction, the carboxyl groups in the 3-mercaptopropionic acid molecule nucleophilically grafted some of the epoxy groups in the ESO molecule. After the reaction, the system was subjected to reduced pressure to remove trace amounts of volatiles, washed with water to remove the catalyst, and then vacuum dried to obtain the SH-ESO reactive compatibilizer.

[0029] The preparation of environmentally friendly and biodegradable plastic packaging materials, as shown in the attached document. Figure 1 The preparation process is shown in the flowchart below: (1) Premixing: The fully dried PLA particles, PEFI copolyester particles, antioxidants and lubricants are added into a high-speed mixer in proportion and mixed evenly. Then, triethanolamine is added and mixing continues. Subsequently, SH-ESO reactive compatibilizer is slowly added dropwise and mixed at 100-150 rpm for 15-20 minutes under low speed conditions to obtain a uniform premix.

[0030] (2) Reactive extrusion: The premixed material is continuously fed into a co-rotating twin-screw extruder for reactive extrusion. The extruder temperature is set as follows: feeding section 130℃; mixing reaction section 160-175℃; metering section and die 160℃. The main machine speed is set to 150-200 rpm, and the average residence time of the material in the extruder is 3-5 minutes. Under high temperature and high shear conditions, the following reaction process occurs in the system: First, the epoxy group in the SH-ESO molecule undergoes ring-opening polymerization with the terminal carboxyl group of the PLA molecule and the terminal carboxyl group or hydroxyl group of the PEFI molecule, realizing the chemical connection between different polymer chains, thereby significantly improving the compatibility between PLA and PEFI and promoting chain extension. Subsequently, under the catalysis of triethanolamine, the thiol group in the SH-ESO molecule undergoes a thiol-Michael addition click reaction with the α,β-unsaturated double bond of the PEFI side chain to form a stable thioether bond, thereby constructing a cross-linked network structure inside the material.

[0031] (3) Film blowing and winding: The melt flowing out of the extruder die is drawn into the blown film device. The blow ratio is controlled at 2.0-3.0, the traction ratio is 3-6, and the cooling air ring speed is 0.5-1.5m / s. Stable film bubbles are formed under the cooling effect of air. Then, it is wound up by the traction roller to obtain the environmentally friendly and biodegradable plastic packaging film material of the present invention.

[0032] Example 1 Preparation of PEFI copolyester: 884 parts FDCA, 130 parts itaconic acid, and 777 parts PDO were added to a reactor equipped with a water separator and mechanical stirrer. Then, 1.8 parts hydroquinone, 0.5 parts phenothiazine, and 1.8 parts Ti(OBu)₂ were added. The mixture was first slowly stirred at 170°C for 3 hours under nitrogen protection to remove byproducts such as water or methanol. Subsequently, a vacuum was slowly applied to reduce the system pressure to below 50 Pa, and the temperature was raised to 195°C for 2.5 hours before the reaction was stopped. Nitrogen was then introduced to break the vacuum, the melt was discharged, cooled, granulated, and vacuum dried to obtain PEFI copolyester particles.

[0033] Preparation of SH-ESO reactive compatibilizer: 98 parts ESO and 13 parts 3-mercaptopropionic acid were added to a reactor equipped with a reflux device and mechanical stirrer. Then, 0.1 parts TBD were added. Under nitrogen protection, the system was heated to 100°C and reacted for 6 hours. After the reaction, the system was subjected to reduced pressure to remove trace volatiles, and after washing away the catalyst with water, it was vacuum dried to obtain the SH-ESO reactive compatibilizer.

[0034] The formula for preparing environmentally friendly and biodegradable plastic packaging materials is as follows: PLA 60 parts, PEFI 30 parts, SH-ESO 5 parts, triethanolamine 0.02 parts, BHT 0.1 parts, and zinc stearate 1 part. The specific steps are as follows: (1) The fully dried PLA particles, PEFI copolyester particles, BHT and zinc stearate were put into a high-speed mixer and mixed evenly. Then, triethanolamine was added and the mixture was continued. Then, SH-ESO reactive compatibilizer was slowly added dropwise and mixed at 120 rpm for 18 minutes to obtain a uniform premix.

[0035] (2) The premixed material is continuously fed into a co-rotating twin-screw extruder for reactive extrusion. The extruder temperature is set as follows: 130°C for the feeding section; 170°C for the mixing and reaction section; and 160°C for the metering section and die. The main engine speed is set to 180 rpm, and the average residence time of the material in the extruder is 4 minutes.

[0036] (3) The melt flowing out of the extruder die is drawn into the blown film device with a blow ratio of 2.5, a traction ratio of 4.5, and a cooling air ring speed of 1.0 m / s to obtain a stable film bubble. Then it is wound up by the traction roller to obtain the environmentally friendly and biodegradable plastic packaging film material of the present invention.

[0037] Example 2 Both PEFI copolyester and SH-ESO reactive compatibilizer were taken from the same batch as in Example 1. The formulation for the plastic packaging material in this example is as follows: PLA 70 parts, PEFI 40 parts, SH-ESO 8 parts, triethanolamine 0.05 parts, Irganox 1010 0.2 parts, and polyethylene glycol 2 parts. The specific steps are as follows: after adding SH-ESO, mix at 150 rpm for 20 minutes; extruder speed 200 rpm, mixing reaction section temperature 175℃, average residence time of material in extruder 5 minutes; blow-up ratio 3.0, traction ratio 6, and cooling air ring speed 1.5 m / s during blown film production; the remaining steps are the same as in Example 1.

[0038] Example 3 Both the PEFI copolyester and the SH-ESO reactive compatibilizer were taken from the same batch as in Example 1. The formulation for the plastic packaging material in this example is as follows: PLA 50 parts, PEFI 20 parts, SH-ESO 3 parts, triethanolamine 0.01 parts, Irganox 1076 0.05 parts, and zinc stearate 0.5 parts. The specific steps are as follows: after adding SH-ESO, mix at 100 rpm for 15 minutes; the extruder speed is 150 rpm, the mixing reaction section temperature is 160℃, and the average residence time of the material in the extruder is 3 minutes; during the blown film process, the blow-up ratio is 2.0, the traction ratio is 3, and the cooling air ring speed is 0.5 m / s; the remaining steps are the same as in Example 1.

[0039] Comparative Example 1 This embodiment uses a traditional biodegradable blend system to prepare packaging materials. The formula is as follows: 60 parts PLA, 35 parts polybutylene terephthalate (PET), 5 parts ESO, 0.1 parts BHT, and 1 part zinc stearate. The preparation steps are the same as in Example 1.

[0040] Comparative Example 2 The formulation in this embodiment is: 60 parts PLA, 30 parts PEFI, 5 parts ESO, 0.1 parts BHT, and 1 part zinc stearate. The preparation steps are the same as in Example 1.

[0041] Product testing: 1. Fourier Transform Infrared Spectroscopy (FT-IR) Structural Characterization (1) Parameter setting and detection process: The chemical structure of the environmentally friendly biodegradable plastic packaging film prepared by blown film in Example 1 of this invention was analyzed using a high-sensitivity Fourier transform infrared spectrometer. An ATR total internal reflection assembly was used to directly sample the film, ensuring that the film surface was tightly adhered to the crystal at the focal point of the infrared light path. The scanning range was set to 4000 cm⁻¹. -1 Up to 500cm -1 The mid-infrared region.

[0042] (2) Characterization results: as shown in the appendix Figure 3 As shown in the spectrum, 1805 cm⁻¹ -1 The extremely strong and sharp absorption peak corresponds to the carbonyl stretching vibration of the ester group in the system, at 1180 cm⁻¹. -1 and 1080cm -1 The bimodal peaks at 2950 cm⁻¹ correspond to the asymmetric and symmetric stretching vibrations of ester bonds in the polyester backbone, and also to the bimodal peaks at 2950 cm⁻¹. -1 aliphatic carbon-hydrogen bond stretching vibrations at 1450 cm⁻¹ -1 The bending and deformation vibrations of the carbon-hydrogen bonds at the 3120 cm⁻¹ region jointly confirmed that the abundant polyester macromolecular backbone structure in the PLA matrix, PEFI copolyester, and SH-ESO soybean oil skeleton remained intact. Meanwhile, the spectrum at 3120 cm⁻¹... -1 The weak peak appearing at 1610 cm⁻¹ is attributed to the stretching vibration of the carbon-hydrogen bonds on the furan ring, and... -1 With 1580cm -1 The spectrum retains distinct characteristic peaks, corresponding to the carbon-carbon double bond skeletal vibrations on the furan ring, proving the successful introduction of the PEFI copolyester component. The spectrum is located at 1630-1650 cm⁻¹. -1 The characteristic absorption of unsaturated double bonds in PEFI copolyesters is significantly weakened or even disappears in the corresponding range, and at 625 cm⁻¹... -1 An absorption peak for the stretching vibration of a thioether bond appeared at [location missing]. In summary, the infrared spectroscopy results indicate that a thioether bond structure was successfully introduced into the material, achieving chemical bonding between components.

[0043] Appendix Figure 4 The image shows the FT-IR stacking images of pure ESO, SH-ESO, PEFI, and the biodegradable plastic film of this invention. As can be seen from the image, pure ESO at 1735 cm⁻¹... -1 A strong, sharp peak appears at 842 cm⁻¹, attributed to the stretching vibration of the carbonyl group (C=O) of the triglyceride ester group. -1 The peak at 1735 cm⁻¹ represents the stretching vibration of the COC ring of the epoxy group, both of which are typical structural characteristic peaks of ESO. SH-ESO shows a peak at 1735 cm⁻¹. -1 and 842cm -1 The corresponding peaks at 2565 cm⁻¹ are still clearly distinguishable, namely the C=O on the ESO framework and the residual epoxy group COC; SH-ESO at 2565 cm⁻¹ -1 A novel characteristic peak, not present in pure ESO, appears at 625 cm⁻¹, attributed to the thiol group (-SH), and is also observed at 625 cm⁻¹. -1 The absence of CSC thioether bond characteristic peaks at this location demonstrates that, under the reaction conditions described in this application, the thiol terminus was successfully retained in free form on the SH-ESO product backbone and was not consumed or converted into a thioether structure. SH-ESO exhibits peaks at approximately 3500-3200 cm⁻¹. -1 The presence of hydroxyl stretching vibrations in this region indicates the formation of hydroxyl groups after epoxy ring-opening. Pure ESO exhibits a flat baseline in this region without this absorption, further confirming the occurrence of the grafting reaction and the correctness of the ring-opening pathway. The biodegradable plastic film of this invention exhibits absorption at 625 cm⁻¹. -1 The presence of CSC sulfide bond characteristic peaks confirms the formation of a cross-linked network; the biodegradable plastic film shows a peak at 842 cm⁻¹. -1 The near disappearance of the COC characteristic peak of the epoxy group at the point of extrusion is consistent with the fact that the residual epoxy group of SH-ESO further undergoes a ring-opening coupling reaction and is largely consumed under the high temperature and high shear conditions of reactive extrusion. This proves that SH-ESO, as a reactive compatibilizer, fully participates in the chemical bonding within the system during the processing.

[0044] 2. Gas barrier property testing Refer to GB / T 1038.1-2022 "Test methods for gas permeability of plastic films and sheets - Part 1: Differential pressure method".

[0045] Sample preparation: Take the blown film material prepared in the examples and comparative examples, cut it into circular samples with a diameter of about 10 cm, and place it at 23°C and 50% relative humidity for 24 hours for constant temperature and humidity treatment before testing.

[0046] Testing Procedure: A differential pressure gas permeation analyzer was used for testing. The sample was sealed and installed in the test chamber. Pure oxygen gas was introduced into one side and maintained at a certain pressure, while the other side was kept under vacuum. The oxygen permeation rate was calculated by measuring the volume of oxygen permeating through the membrane per unit time. The test temperature was controlled at 23℃. Each sample was measured in triplicate, and the average value was taken. The results are expressed as oxygen permeation rate, with units of cc / (m³). 2 ·24h·0.1MPa).

[0047] 3. Tensile strength / elongation at break testing Refer to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics".

[0048] Sample preparation: Take the blown film materials prepared in the examples and comparative examples, and cut them into dumbbell-shaped samples according to standard requirements. Before testing, place the samples at 23°C and 50% relative humidity for 24 hours to condition them.

[0049] Testing Procedure: Tensile testing was conducted using an electronic universal testing machine. The test temperature was 23℃, and the loading rate was 5 mm / min. The maximum load and elongation at break were recorded, and the tensile strength (MPa) and elongation at break (%) were calculated. Each group of samples was tested in triplicate, and the average value was taken.

[0050] 4. Degradation performance testing Refer to GB / T 19277.1-2025 "Determination of final aerobic biodegradability of plastics under controlled composting conditions - Part 1: General method".

[0051] Sample preparation: Take the blown film material prepared in the examples and comparative examples, cut it into 5cm×5cm samples, place it under constant temperature and humidity conditions for 24h before testing, and accurately weigh the initial mass W0.

[0052] Test Procedure: Samples were buried in a culture system containing natural compost soil. The soil contained common microbial communities such as fungi and actinomycetes, and a trace amount of reduced glutathione was added to promote microbial activity. Culture conditions were controlled at a temperature of 45±2℃ and a relative humidity of approximately 50%. Within the set degradation cycle, samples were removed at 30, 60, and 100 days. The surface soil particles were gently washed away with deionized water, and then dried at 60℃ to constant weight, and the mass W1 was measured. The degradation weight loss rate (%) was calculated as (W0-W1)×100% / W0. Each sample was measured in triplicate, and the average value was taken as the final result.

[0053] Table 1. Test results of gas barrier properties, tensile strength, and elongation at break for the examples and comparative examples. Table 2. Degradation performance test results of the examples and comparative examples. Results analysis: (1) As can be seen from the data in Tables 1 and 2, the packaging materials prepared in Examples 1 to 3 exhibit excellent comprehensive performance. Regarding gas barrier properties, the oxygen permeability of each example remained at an extremely low level, indicating that the copolyester containing the furan ring structure significantly enhanced the oxygen barrier capacity of the system. At the mechanical level, each example exhibited excellent tensile strength and elongation at break, possessing both excellent rigidity and flexibility, as shown in the attached table. Figure 5 Meanwhile, as the cultivation time progressed, the degradation weight loss rate of each embodiment steadily and significantly increased, as shown in the attached figure. Figure 6 This fully demonstrates that the core components of this invention successfully construct a dense and stable chemical cross-linked network during the reactive extrusion process, perfectly achieving a balance between the mechanical strength, freshness-preserving barrier properties, and efficient biodegradability of the packaging material.

[0054] (2) Comparative Example 1, which uses traditional biodegradable components for simple physical blending, is significantly inferior to the embodiments of the present invention in terms of preservation barrier ability, mechanical strength, and degradation performance. Specifically, it exhibits higher oxygen permeability, insufficient tensile strength and elongation at break, and a slower degradation rate. This indicates that the traditional system without functionalized copolyester and reactive compatibility system suffers from phase separation drawbacks, making it difficult to optimize the material's structural density and overall performance. This further demonstrates that the technical feature of the present invention, which constructs a chemical connection network through PEFI copolyester and SH-ESO reactive compatibility, can effectively improve the gas barrier performance, mechanical properties, and environmental degradation capability of the material.

[0055] (3) In Comparative Example 2, because thiol-modified epoxidized soybean oil was not used, a thioether crosslinking network could not be effectively formed within the system, resulting in an overall decrease in the material's preservation barrier properties, mechanical strength, and degradation performance. This indicates that the construction of the thioether crosslinking network not only enhances the interfacial bonding and structural density of the blend system, improving the mechanical stability and processing performance of the film, but also provides channels for moisture and microbial penetration through the easily oxidized thioether bonds in the crosslinking network, fundamentally ensuring that the material achieves a synergistic effect of rapid degradation while maintaining excellent performance.

[0056] In summary, this invention introduces an SH-ESO reactive compatibilizer into the PLA and PEFI copolyester system, and forms a stable chemical linkage structure under the action of a catalyst, enabling effective bonding between different polymer chains, thereby significantly improving the interfacial compatibility and structural density of the material. The resulting material not only possesses excellent mechanical and gas barrier properties, but also maintains good degradation ability in a composting environment, thus achieving a harmonious balance between the performance and environmental friendliness of packaging materials.

Claims

1. An environmentally friendly and biodegradable plastic packaging material, characterized in that, The plastic packaging material is made from the following raw materials by weight: 50-70 parts polylactic acid, 20-40 parts furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester, 3-8 parts thiol-modified epoxidized soybean oil, 0.01-0.05 parts triethanolamine, 0.05 to 0.2 parts antioxidant, and 0.5 to 2 parts lubricant. The side chains of the furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester retain unsaturated carbon-carbon double bond structures. The soybean oil backbone of the thiol-modified epoxidized soybean oil has thiol groups grafted onto it. During reactive extrusion, the unsaturated carbon-carbon double bonds on the side chains of the furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester and the thiol groups grafted onto the backbone of the thiol-modified epoxidized soybean oil undergo an addition reaction catalyzed by the triethanolamine, thereby forming thioether bonds.

2. The environmentally friendly and biodegradable plastic packaging material as described in claim 1, characterized in that, The preparation method of the furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester is as follows: 2,5-furanyl dicarboxylic acid, itaconic acid and 1,5-pentanediol are taken in a molar ratio of 0.85:0.15:1.12; hydroquinone, phenothiazine and dibutyl titanate are added, and the mixture is stirred at 165-175℃ for 3 hours under nitrogen protection; then, the system pressure is reduced to below 50Pa by vacuuming, and the temperature is raised to 190-200℃ for 2-3 hours; after the reaction is completed, nitrogen is introduced into the system to break the vacuum, the melt is discharged, cooled and granulated, and vacuum dried to obtain furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester.

3. The environmentally friendly and biodegradable plastic packaging material as described in claim 2, characterized in that, The amount of hydroquinone used is 0.1 wt% of the total weight of 2,5-furandicarboxylic acid, itaconic acid, and 1,5-pentanediol; the amount of phenothiazine used is 0.03 wt% of the total weight of 2,5-furandicarboxylic acid, itaconic acid, and 1,5-pentanediol; and the amount of dibutyl titanate used is 0.1 wt% of the total weight of 2,5-furandicarboxylic acid, itaconic acid, and 1,5-pentanediol.

4. The environmentally friendly and biodegradable plastic packaging material as described in claim 1, characterized in that, The method for preparing the thiol-modified epoxidized soybean oil is as follows: epoxidized soybean oil and 3-mercaptopropionic acid are taken in a molar ratio of 1:1.2; then 1,5,7-triazabicyclo[4.4.0]dec-5-ene is added; in a closed nitrogen environment, the system is heated to 95℃-105℃ and the reaction is maintained for 6 hours; after the reaction is completed, the system is subjected to reduced pressure to remove trace volatiles, and after washing with water and vacuum drying, thiol-modified epoxidized soybean oil is obtained.

5. The environmentally friendly and biodegradable plastic packaging material as described in claim 4, characterized in that, The amount of 1,5,7-triazabicyclo[4.4.0]dec-5-ene fed into the feed is 0.05-0.1 wt% of the total weight of the epoxidized soybean oil and the 3-mercaptopropionic acid.

6. The environmentally friendly and biodegradable plastic packaging material as described in claim 1, characterized in that, The antioxidant is 2,6-di-tert-butyl-4-methylphenol, Irganox 1010, or Irganox 1076; the lubricant is zinc stearate or polyethylene glycol.

7. A method for preparing an environmentally friendly and biodegradable plastic packaging material according to any one of claims 1-6, characterized in that, Includes the following steps: S1: The dried polylactic acid, furanyl dicarboxylic acid-pentanediol-itaconic acid copolyester, antioxidant and lubricant are mixed evenly, the triethanolamine is added and the mixture is continued to be mixed, the mercapto-modified epoxidized soybean oil is added dropwise and the mixture is continuously mixed under low speed conditions to obtain a uniform premix. S2: The uniform premix is ​​continuously added to a twin-screw extruder for reactive extrusion, and the resulting material flows out of the die to form a melt. S3: The outflowing melt is drawn into the blown film device for blown film production. Under the action of the air cooling ring, a thin film bubble is formed. Then, the traction roller is used to wind it up to obtain the plastic packaging material.

8. The method for preparing an environmentally friendly and biodegradable plastic packaging material as described in claim 7, characterized in that, The rotation speed under the low-speed condition in step S1 is 100-150 rpm, and the continuous mixing time is 15-20 minutes.

9. The method for preparing an environmentally friendly and biodegradable plastic packaging material as described in claim 7, characterized in that, In step S2, the twin-screw extruder speed is set to 150-200 rpm; the reaction extrusion temperature is set as follows: 130℃ in the feeding section; 160-175℃ in the mixing reaction section; and 160℃ in the metering section and die. The residence time of the melt in the twin-screw extruder is 3-5 minutes.

10. The method for preparing an environmentally friendly and biodegradable plastic packaging material as described in claim 7, characterized in that, During the blown film process described in step S3: the blow-up ratio is controlled at 2.0-3.0, the traction ratio is 3-6, and the cooling air ring speed is 0.5-1.5m / s.

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