Composite packaging film and preparation method thereof

Abstract

The invention provides a composite packaging film and a preparation method thereof, and belongs to the technical field of packaging films. The composite packaging film comprises the following raw materials: poly (butylene adipate-terephthalate), polylactic acid, a maleic anhydride grafted PS copolymer and a chain extender, wherein the addition amount of the maleic anhydride grafted PS copolymer accounts for 1-5% of the total mass of the poly (butylene adipate-terephthalate) and polylactic acid. According to the invention, inorganic filler does not need to be added, and the chain extender ADR4370S and the compatilizer PS-MA are added to form a synergistic regulation mechanism in a melt blending process: the chain extender acts on a molecular chain layer to improve the length of the molecular chain and the rheological behavior of a melt; the compatilizer PS-MA acts on a phase interface layer surface to enhance interface bonding between PLA and PBAT phases, so that the molecular structure and the interface structure of a blending system are optimized at the same time, and the mechanical property, the processing stability and the structural uniformity of the film are improved.

Description

Technical Field

[0001] This invention relates to the field of packaging film technology, and in particular to a composite packaging film and its preparation method. Background Technology

[0002] Polylactic acid (PLA) has broad application prospects in the field of green packaging due to its renewable and biodegradable sources. However, PLA has high molecular chain rigidity, low elongation at break, and significant brittleness, making it prone to cracking and breakage during film processing and use, which makes it difficult to meet the requirements of flexible packaging. PBAT, as a flexible aliphatic-aromatic copolyester, has certain complementarity with PLA and is widely used in PLA blend modification systems. However, in existing PLA / PBAT blend systems, due to differences in molecular structure and polarity, direct blending easily leads to significant phase separation and insufficient interfacial bonding, resulting in unstable mechanical properties. Current technologies typically modify the PLA / PBAT system by introducing inorganic fillers or natural functional additives, but these methods generally suffer from poor filler dispersibility, insufficient processing stability, limited functional stability, and are not conducive to industrial production. Therefore, how to achieve stable improvement in the comprehensive performance of PLA / PBAT blend films through synergistic regulation of molecular and interfacial structures without relying on inorganic fillers is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] The purpose of this invention is to provide a composite packaging film and its preparation method, so as to solve the problem that the PLA / PBAT blend system in the prior art has a phase separation structure and insufficient interfacial bonding force, resulting in unstable mechanical properties of the material.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a composite packaging film, wherein the raw materials of the composite packaging film include poly(butylene adipate-terephthalate) (PBAT), polylactic acid (PLA), maleic anhydride-grafted PS copolymer (PS-MA) and a chain extender; the amount of maleic anhydride-grafted PS copolymer added accounts for 1 to 5% of the total mass of poly(butylene adipate-terephthalate) and polylactic acid.

[0005] Preferably, the mass ratio of poly(butylene adipate-terephthalate) to polylactic acid is 5~7:3~4.

[0006] Preferably, the amount of chain extender added is 0.5 to 2% of the total mass of poly(butylene adipate-terephthalate) and polylactic acid.

[0007] Preferably, the chain extender is ADR4370S.

[0008] The present invention also provides a method for preparing the above-mentioned composite packaging film, comprising the following steps: mixing raw materials and then performing melt extrusion, pelletizing, and blown film to obtain the composite packaging film.

[0009] Preferably, the process parameters for melt extrusion are: screw speed of 10~13 r / min, and temperature control from the feed end to the die head of 120~155℃.

[0010] Preferably, the main machine speed during blown film blowing is 18~35Hz.

[0011] The beneficial effects of this invention are: This invention eliminates the need for inorganic fillers when preparing composite packaging films using PLA and PBAT. By adding the compatibilizer PS-MA, it is evident that the two biodegradable materials fuse more fully, improving interfacial bonding, enhancing material structural stability, and achieving a comprehensive balance between tensile strength, elongation at break, and processing stability.

[0012] This invention improves the strength and mechanical properties of the melt by adding chain extenders to regulate the molecular chain structure.

[0013] The process for preparing composite packaging films according to this invention is simple and suitable for application in existing industrial blown film production lines. Attached Figure Description

[0014] Figure 1 Infrared spectra of the composite packaging films prepared in Examples 1-3 and Comparative Examples 1-3; Figure 2 SEM image of the composite packaging film prepared for Comparative Example 1; Figure 3 SEM image of the composite packaging film prepared for Comparative Example 2; Figure 4 SEM image of the composite packaging film prepared for Comparative Example 3; Figure 5 SEM image of the composite packaging film prepared in Example 1; Figure 6 SEM image of the composite packaging film prepared in Example 2; Figure 7 SEM image of the composite packaging film prepared in Example 3; Figure 8 Comparison chart showing the mechanical property test results of the composite packaging films prepared in Examples 1-3 and Comparative Examples 1-3; Figure 9 Thermogravimetric curves of the composite packaging films prepared in Examples 1-3 and Comparative Examples 1-3 are shown. Figure 10The ultraviolet spectra of the composite packaging films prepared in Examples 1-3 and Comparative Examples 1-3 are shown below. Figure 11 The following is a bar chart showing the oxygen permeability of the composite packaging films prepared in Examples 1-3 and Comparative Examples 1-3; Figure 12 Bar charts showing the water vapor transmission rate of the composite packaging films prepared in Examples 1-3 and Comparative Examples 1-3; Figure 13 The contact angle test results are for the composite packaging films prepared in Examples 1-3 and Comparative Examples 1-3, where a is Comparative Example 1, b is Comparative Example 2, c is Comparative Example 3, d is Example 1, e is Example 2, and f is Example 3. Detailed Implementation

[0015] The present invention provides a composite packaging film, wherein the raw materials of the composite packaging film include poly(butylene adipate-terephthalate), polylactic acid, maleic anhydride-grafted PS copolymer and chain extender; the amount of maleic anhydride-grafted PS copolymer added accounts for 1 to 5% of the total mass of poly(butylene adipate-terephthalate) and polylactic acid.

[0016] In this invention, the amount of maleic anhydride-grafted PS copolymer added can be 1%, 3%, or 5%.

[0017] In this invention, the mass ratio of poly(butylene adipate-terephthalate) to polylactic acid is 5~7:3~4, preferably 6:4.

[0018] The compatibilizer maleic anhydride-grafted PS copolymer added in this invention can be well dispersed in the film. Scanning electron microscopy and infrared spectroscopy can clearly prove its presence in the film. In the prior art, the ratio of PBAT to PLA in the preparation of composite packaging film is generally maintained at 5:5. However, the cost of PBAT is much lower than that of polylactic acid. This invention adjusts the ratio of PBAT to PLA, reducing the amount of PLA used and reducing the cost of preparing composite packaging film. In the embodiments of this invention, the preferred mass ratio of poly(butylene adipate-terephthalate) to polylactic acid in the preparation of composite packaging film is 6:4.

[0019] In this invention, the amount of chain extender added is 0.5-2% of the total mass of poly(butylene adipate-terephthalate) and polylactic acid, specifically 0.5%, 1.0%, or 2.0%.

[0020] In this invention, the chain extender is ADR4370S.

[0021] PLA is an aliphatic polyester obtained by polycondensation or ring-opening polymerization of lactic acid monomers. Its main chain structure contains a large number of ester bonds (—COO—). PLA has good biodegradability, biocompatibility, and high rigidity, making it one of the main film-forming matrices for composite packaging films. In blend systems, PLA mainly provides mechanical strength, structural support, and biodegradability for composite packaging films. However, due to its high molecular chain rigidity and low elongation at break, it is difficult to meet the requirements of flexible composite packaging films for ductility and processing stability when used alone.

[0022] PBAT is an aliphatic-aromatic copolyester whose molecular chain contains both aromatic terephthalic acid and aliphatic adipic acid structural units, giving the material good flexibility and high elongation at break. PBAT is introduced as a flexible phase to form a blend system with PLA, which is used to improve the film's ductility, impact resistance, and processing properties.

[0023] The compatibilizer PS-MA is a styrene graft copolymer containing maleic anhydride functional groups. Its molecular structure includes both nonpolar styrene segments and reactive maleic anhydride groups. The styrene segments can interact with the PBAT phase, while the maleic anhydride groups can undergo esterification or ring-opening reactions with the hydroxyl groups at the ends of the PLA or PBAT molecular chains during melt processing. Through these interactions, PS-MA can form a "molecular bridge" structure at the PLA-PBAT interface, reducing interfacial tension, enhancing interfacial bonding, thereby reducing phase separation and improving the interfacial compatibility and structural stability of the blend system.

[0024] Chain extender ADR4370S is a multifunctional epoxy chain extender containing multiple epoxy groups in its molecular structure, exhibiting high reactivity. During melt blending, the epoxy groups of ADR4370S can react with the carboxyl or hydroxyl groups at the ends of PLA and PBAT molecular chains, thereby achieving the following effects: promoting molecular chain growth or branching, increasing the average molecular weight of the system; enhancing melt strength, improving stability during blown film processing; and reducing performance degradation caused by molecular chain breakage during processing.

[0025] In this invention, the chain extender ADR4370S and the compatibilizer PS-MA do not act independently, but rather form a synergistic regulatory mechanism during melt blending: the chain extender ADR4370S mainly acts at the molecular chain level, improving molecular chain length and melt rheological behavior; the compatibilizer PS-MA mainly acts at the phase interface level, enhancing the interfacial bonding between the PLA and PBAT phases. Their synergistic effect optimizes the blend system at both the molecular and interfacial structure levels, thereby achieving a comprehensive improvement in the mechanical properties, processing stability, and structural uniformity of the composite packaging film.

[0026] The present invention also provides a method for preparing the above-mentioned composite packaging film, comprising the following steps: mixing raw materials and then performing melt extrusion, pelletizing, and blown film to obtain the composite packaging film.

[0027] In this invention, the process parameters for melt extrusion are: screw speed of 10~13 r / min, and temperature control from feed end to die head of 120~155℃.

[0028] In this invention, the main machine rotation speed during blown film blowing is 18~35Hz.

[0029] 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.

[0030] Raw materials used in the embodiments and comparative examples of this invention: PBAT: Grade TH801T, Xinjiang Lanshan Tunhe Chemical Co., Ltd.; PLA: Grade 2003D, NatureWorks, USA; Chain extender ADR4370S, BASF; PS-MA: Model KJ-9909, Dongguan Kangjin New Material Technology Co., Ltd.

[0031] Example 1 Raw material dosage: 60 parts PBAT, 40 parts PLA, the addition amount of chain extender ADR4370S is 1% of the total mass of PBAT and PLA, the addition amount of PS-MA is 3% of the total mass of PBAT and PLA, and the resulting composite packaging film is designated as BM4.

[0032] PBAT and PLA were dried separately in a 60℃ forced-air drying oven for 12 hours. Then, all raw materials were mixed evenly and placed in a co-rotating twin-screw extruder for melt blending and extrusion. The screw speed was 11 r / min, and the temperature distribution from the feed end to the die head was 120℃, 130℃, 140℃, and 145℃. After extrusion, the material was water-cooled and granulated. Finally, the dried granules were blown into film using a small blown film machine with the main machine speed set at 35Hz to obtain a composite packaging film.

[0033] Example 2 Raw material dosage: 60 parts PBAT, 40 parts PLA, the amount of chain extender ADR4370S added is 1% of the total mass of PBAT and PLA, the amount of PS-MA added is 1% of the total mass of PBAT and PLA, and the resulting composite packaging film is designated as BM5.

[0034] The preparation method is the same as in Example 1.

[0035] Example 3 Raw material dosage: 60 parts PBAT, 40 parts PLA, the amount of chain extender ADR4370S added is 1% of the total mass of PBAT and PLA, the amount of PS-MA added is 5% of the total mass of PBAT and PLA, and the resulting composite packaging film is designated as BM6.

[0036] The preparation method is the same as in Example 1.

[0037] Comparative Example 1 Raw material dosage: 60 parts PBAT, 40 parts PLA, and the amount of chain extender ADR4370S added is 0.5% of the total mass of PBAT and PLA. The resulting composite packaging film is denoted as BM1.

[0038] The preparation method is the same as in Example 1.

[0039] Comparative Example 2 Raw material dosage: 60 parts PBAT, 40 parts PLA, and the addition amount of chain extender ADR4370S is 1% of the total mass of PBAT and PLA. The resulting composite packaging film is denoted as BM2.

[0040] The preparation method is the same as in Example 1.

[0041] Comparative Example 3 Raw material dosage: 60 parts PBAT, 40 parts PLA, and the amount of chain extender ADR4370S added is 2% of the total mass of PBAT and PLA. The resulting composite packaging film is denoted as BM3.

[0042] The preparation method is the same as in Example 1.

[0043] The performance of the composite packaging films prepared in Examples 1-3 and Comparative Examples 1-3 was tested: (1) Tensile properties were tested according to GB / T 1040.3-2022 standard. At room temperature, the composite packaging film was cut into strips with a length of 150mm × width of 15mm × gauge length of 50mm. The tensile rate was 50mm / min. The test results are as follows: Figure 8 As shown; (2) The oxygen permeability was tested using the differential pressure method at a test temperature of 23℃, a pre-permeability time of 30 min, and a vacuuming time of 8 h. The test results are shown in [reference to the results]. Figure 11 ; (3) The water vapor transmission rate was tested using the weight reduction method. The test temperature was 38℃, the relative humidity was 90%, and the preheating time was 1.5h. The test results are shown in […]. Figure 12 ; (4) The water contact angle of the composite packaging film was tested using a contact angle measuring instrument, and the results are as follows: Figure 13 As shown.

[0044] (5) Thermal stability was tested using a thermogravimetric analyzer. A 5 mg sample of composite packaging film was cut into pieces and placed in a crucible. Pure thermal pyrolysis was carried out in a nitrogen atmosphere (nitrogen flow rate of 50 mL / min). The heating rate was set to 10 °C / min, increasing from 30 °C to 800 °C. The test results are shown in […]. Figure 9 .

[0045] (6) Absorbance test: The absorbance was measured using a UV-Vis spectrophotometer in absorbance mode. The scanning wavelength range was 200–800 nm, and the scanning step / speed was 1 nm. The composite packaging film was clamped in the sample holder, with air as the reference background. The sample thickness was in the range of 20–50 μm. The vertical axis represents absorbance, and the horizontal axis represents wavelength (nm). 200–300 nm is the UV region, and 300–800 nm is the visible light region. Test results: From the 200–300 nm UV region, all tested samples showed high absorbance (≥4), indicating that the amount of different modifiers added had no significant effect on the UV shielding performance. Entering the visible light region (300–800 nm), the absorbance of each sample varied significantly. The ADR series films (comparative examples 1–3) exhibited the lowest absorbance and the highest transparency. Higher PS-MA content resulted in greater absorbance and lower transparency, particularly in the 3% PS-MA group (BM4), which showed the highest visible light absorption and a significant decrease in optical transparency. This suggests that PS-MA may induce enhanced light scattering or increased interfacial incompatibility within the system, thereby reducing film transparency.

[0046] from Figures 2-7 It can be seen that with the increase of PS-MA addition, the cross-sectional structure of the composite film gradually transforms from a "phase-separated state" to a "continuous phase," with enhanced interfacial bonding, reduced particle size, increased boundary ambiguity, and a more compact overall structure. This trend is highly consistent with the test data for tensile properties, contact angle, and barrier properties, verifying that the present invention achieves a synergistic improvement in mechanical properties, flexibility, and barrier properties by regulating the interfacial structure through compatibilizers. A reasonable amount of PS-MA addition provides a stable interfacial bridging structure for the composite packaging film, improving the composite performance of the film material.

[0047] from Figure 13 It can be seen that as the amount of PS-MA added increases, the surface contact angle of the composite packaging film gradually increases and the hydrophobicity is enhanced. This is because the anhydride groups effectively reduce the polarity and wettability of the film surface.

[0048] from Figure 11 , Figure 12It can be seen that the addition of PS-MA enhances the interfacial bonding strength, forming a denser chain arrangement and lengthening the gas permeation path. Comparative Example 1 has a permeability of 29.741 cm³ / m²·24h·0.1MPa and a permeability coefficient of 8.950E-16 cm³·cm / cm²·s·Pa; Comparative Example 2 has a permeability of 20.367 cm³ / m²·24h·0.1MPa and a permeability coefficient of 6.130E-16 cm³·cm / cm²·s·Pa; Comparative Example 3 has a permeability of 8.857 cm³ / m²·24h·0.1MPa and a permeability coefficient of 2.668E-16 cm³·cm / cm²·s·Pa; and Example 1 has a permeability of 14.122 cm³ / m²·24h·0.1MPa and a permeability coefficient of 4.254E-16. The transmittance of Example 2 was 18.029 cm³ / m²·24h·0.1 MPa, and the transmittance coefficient was 5.436E-16 cm³ / m²·s·Pa. The transmittance of Example 3 was 8.443 cm³ / m²·24h·0.1 MPa, and the transmittance coefficient was 2.542E-16 cm³ / m²·24h·0.1 MPa. The barrier properties and reproducibility of the film were further improved. The average WVTR decreased to 305.4 g / m²·24h, demonstrating superior stability and barrier effect.

[0049] The composite packaging film prepared by this invention is significantly superior to the composite packaging film without added PS-MA in terms of mechanical properties, processing stability, and structural uniformity.

[0050] 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 composite packaging film, characterized in that, The raw materials of the composite packaging film include poly(butylene adipate-terephthalate), polylactic acid, maleic anhydride-grafted PS copolymer and chain extender; the amount of maleic anhydride-grafted PS copolymer added accounts for 1 to 5% of the total mass of poly(butylene adipate-terephthalate) and polylactic acid.

2. The composite packaging film according to claim 1, characterized in that, The mass ratio of poly(butylene adipate-terephthalate) to polylactic acid is 5~7:3~4.

3. The composite packaging film according to claim 1 or 2, characterized in that, The amount of chain extender added is 0.5-2% of the total mass of poly(butylene adipate-terephthalate) and polylactic acid.

4. The composite packaging film according to claim 3, characterized in that, The chain extender is ADR4370S.

5. The method for preparing the composite packaging film according to any one of claims 1 to 4, characterized in that, The process includes the following steps: mixing raw materials and then performing melt extrusion, pelletizing, and blown film to obtain a composite packaging film.

6. The method for preparing the composite packaging film according to claim 5, characterized in that, The process parameters for melt extrusion are: screw speed of 10~13 r / min, and temperature control from feed end to die head of 120~155℃.

7. The method for preparing the composite packaging film according to claim 5 or 6, characterized in that, The main machine speed during blown film blowing is 18~35Hz.

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