A functional packaging film material and a method for manufacturing the same

Abstract

The application relates to the technical field of high-molecular film materials, in particular to a functional packaging film material and a preparation method thereof. The packaging film material is composed of PET, PLA, a modifier and an ultraviolet absorber, the modifier is formed by grafting dimethyl terephthalate, ethylene glycol and double-hydroxyl end-capped polylactic acid onto the surface of carboxylated graphene after ester exchange, the carboxylated graphene nanosheet and the modifier synergistically improve the uniform dispersion and interface bonding strength of the nanofiller, thereby optimizing the compatibility of PET and PLA. The above structural design can significantly improve the comprehensive performance of the composite material, such as tensile strength, toughness, gas barrier property and heat distortion temperature, and meanwhile, the good processability and degradability of the material are ensured. The application provides reliable technical support for developing a novel green packaging film material with high performance and low environmental burden, and has a wide industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular film materials, and particularly relates to a functional packaging film material and a preparation method thereof. BACKGROUND

[0002] With the enhancement of global environmental awareness, the packaging material industry is facing unprecedented pressure for change. Although traditional petroleum-based packaging materials have excellent physical properties, their poor degradability can have a negative impact on the environment. At the same time, consumers' increasing demand for food safety and packaging functionality has prompted the development of packaging materials towards high performance, functionality and environmental friendliness.

[0003] Polyethylene terephthalate (PET) is an important packaging material with excellent mechanical properties, good transparency and chemical stability, and is widely used in food packaging. However, as a petroleum-based polymer, PET has poor biodegradability and cannot meet the increasingly stringent environmental requirements. As a representative of biodegradable polymers, polylactic acid (PLA) has good biocompatibility and complete degradability, and is considered as an ideal choice to replace traditional plastics. However, PLA has defects such as poor heat resistance, insufficient barrier properties and low toughness, which limit its independent application in the packaging field.

[0004] PET and PLA blending modification has become an important technical path to balance performance and environmental requirements. However, due to the significant difference in chemical structure between the two polymers, PET is a linear structure of aromatic polyester, while PLA is an aliphatic polyester, and there are large differences in molecular polarity, crystallization behavior and thermodynamic properties between the two, leading to poor compatibility of the blend and easy phase separation, thereby affecting the macroscopic performance of the material. Traditional compatibilizers can improve the interfacial bonding to some extent, but often at the expense of certain key properties, making it difficult to achieve coordinated improvement in comprehensive performance.

[0005] The introduction of nanofillers provides a new way to solve the above problems. Graphene, as a super-hard ceramic material, has extremely high hardness, excellent chemical stability and good thermal conductivity, and its nanosheet structure shows great potential in improving the mechanical properties and barrier properties of composite materials. However, the surface energy of nanofillers is high, and they are easy to agglomerate, with poor interfacial bonding with the polymer matrix. Direct addition often leads to performance degradation. Existing surface modification methods mostly use small molecule coupling agents or single polymer grafting, which can improve the dispersibility, but have limited adaptability in multiphase polymer systems, and it is difficult to achieve good compatibility with different polymer phases at the same time.

[0006] More importantly, the packaging material needs to achieve a precise balance between mechanical properties, barrier properties and thermal stability. Excessive pursuit of a single performance often leads to the sacrifice of other properties, such as high barrier property usually accompanied by a decrease in toughness, high strength may lead to processing difficulties, etc. The complexity of this multi-objective optimization requires modification techniques not only to solve the compatibility problem, but also to achieve synergistic performance improvement at the molecular design level.

[0007] Current modification strategies are mostly based on empirical component regulation, lacking a deep understanding of the relationship between interface structure and performance. Especially in the aspect of nano-filler modification, how to construct an effective interface layer through precise molecular design to realize the synergistic effect of fillers and multi-phase matrix is still a technical problem to be solved. Therefore, developing a modification technology that can improve the compatibility of PET / PLA and optimize the dispersion of nano-filler has important significance for promoting the industrial application of high-performance environmentally friendly packaging materials. SUMMARY

[0008] Therefore, the purpose of the present application is to provide a functional packaging film material and a preparation method thereof to improve the comprehensive balance performance of mechanical strength, oxygen barrier property and thermal stability of PET / PLA packaging film.

[0009] Based on the above purpose, the present application provides a functional packaging film material, which is prepared from the following raw materials in parts by weight: 150-250 parts of PET, 60-120 parts of PLA, 25-45 parts of modifier and 0.2-1 part of ultraviolet absorber.

[0010] Preferably, the intrinsic viscosity of the PET is 0.8-0.9 dL / g.

[0011] Preferably, the weight average molecular weight of the PLA is 130000-180000, and the L-isomer content is higher than 90%.

[0012] Preferably, the ultraviolet absorber is ultraviolet absorber UV-531.

[0013] Further, the modifier is obtained by grafting dimethyl terephthalate, ethylene glycol and dihydroxy-terminated polylactic acid onto the surface of carboxylated graphene after ester exchange.

[0014] Preferably, the weight ratio of dimethyl terephthalate, ethylene glycol, dihydroxy-terminated polylactic acid and carboxylated graphene is 20-35:6-15:10-20:10-20.

[0015] Preferably, the preparation method of the double-hydroxyl terminated polylactic acid is as follows: L-lactic acid is heated to 115-125 DEG C, pre-polymerized for 2-4 h, then stannous chloride, p-toluenesulfonic acid and ethylene glycol are added, heated to 175-185 DEG C, stirred for 5-7 h, precipitated by cold methanol, vacuum dried to obtain the double-hydroxyl terminated polylactic acid.

[0016] Preferably, the weight ratio of the L-lactic acid, stannous chloride, p-toluenesulfonic acid and ethylene glycol is 15-25:0.03-0.05:0.04-0.08:0.5-1.5.

[0017] Preferably, the carboxylated graphene is obtained by modifying graphene nanosheets by a mixed acid solution composed of concentrated nitric acid and concentrated sulfuric acid.

[0018] Preferably, the average thickness of the graphene nanosheet is 3-10 nm, and the average diameter is 5-10 mu m.

[0019] Further, the application also provides a preparation method of a functional packaging film material, comprising the following steps: melting PET in a double-screw extruder, adding PLA, a modifier and an ultraviolet absorber after the PET is completely melted, melt blending, extruding and pelletizing, injection molding into a film, and stretching to obtain the functional packaging film material.

[0020] Preferably, the length-diameter ratio of the double-screw extruder is 40:1.

[0021] Preferably, the temperature of the feeding section of the double-screw extruder is 215-225 DEG C, the temperature of the melting section is 225-235 DEG C, and the temperature of the mixing section is 235-245 DEG C.

[0022] Preferably, the screw rotation speed of the melt blending is 100-150 rpm, the shear stress is 0.3-0.5 MPa, and the time is 8-12 min.

[0023] Preferably, the stretching is 3-3.5 times in the longitudinal direction and 2.5-3.5 times in the transverse direction.

[0024] The application realizes significant improvement of the comprehensive performance of the PET / PLA packaging film through unique design of the modifier, and has the following beneficial effects:

[0025] Optimization effect of interfacial compatibility: the modifier contains double-hydroxyl terminated polylactic acid segments and polyester segments, forming a molecular-level compatible bridge. The double-hydroxyl terminated polylactic acid segments have good compatibility with PLA, while the polyester segments form strong interaction with PET, which effectively reduces the interfacial tension of PET / PLA, inhibits the phase separation phenomenon, and improves the microstructure uniformity of the blend.

[0026] Uniform dispersion of nanofillers: The active groups on the surface of carboxylated graphene nanosheets form chemical bonds with modifier molecules, constructing a stable interfacial layer. This interfacial layer not only prevents the aggregation of nanosheets but also maintains the uniform dispersion of the filler through steric hindrance. Simultaneously, the gradient structure of the interfacial layer achieves a smooth transition from the rigid nanofiller to the flexible polymer matrix, eliminating interfacial stress concentration.

[0027] Synergistic enhancement of mechanical properties: Uniformly dispersed graphene nanosheets form an effective load transfer network, significantly improving the tensile strength of the material. The presence of the interface layer ensures the continuity of stress transfer, avoiding premature failure caused by interface debonding. At the same time, the introduction of flexible polylactic acid segments maintains the toughness of the material, achieving a balanced optimization of strength and ductility.

[0028] Mechanism for enhanced barrier performance: Sheet-like graphene nanofillers construct a circuitous diffusion path for gas molecules, significantly extending the diffusion distance of oxygen through the membrane. The dense structure of the interface layer further reduces interface defects, blocking preferential permeation channels for gas molecules. Improved compatibility also reduces microporous defects at the phase interface, enhancing the overall barrier effect of the material.

[0029] Overall Improvement in Thermal Stability: Graphene's excellent thermal stability provides thermal protection for the composite material, while the constraint effect of the interfacial layer on the movement of polymer molecular chains increases the glass transition temperature and heat distortion temperature of the material. Improved PET / PLA compatibility also promotes more ordered crystallization behavior, enhancing the material's heat resistance.

[0030] Environmental performance is maintained: the biodegradable properties of the polylactic acid component in the modifier are preserved, without affecting the overall environmental friendliness of the material. At the same time, the amount of modifier used is relatively small, which will not significantly increase the material cost, and it has good prospects for industrial application.

[0031] The synergistic effect of these beneficial effects enables the functional packaging film material prepared by this invention to achieve a comprehensive improvement in overall performance while maintaining its environmental protection characteristics. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0033] In a specific embodiment of the present invention, the graphene nanosheets have an average thickness of 5.2 nm and an average diameter of 6.8 μm; the intrinsic viscosity of PET is 0.85 dL / g; the weight-average molecular weight of PLA is 150,000; and the L-isomer content is ≥95%.

[0034] Example 1

[0035] (1) 15g of graphene nanosheets were dispersed in 100g of mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), ultrasonically treated at 75℃ for 3h, centrifuged, washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene.

[0036] (2) 15g of L-lactic acid was heated to 115℃ and prepolymerized for 2h. Then 0.03g of stannous chloride, 0.04g of p-toluenesulfonic acid and 0.5g of ethylene glycol were added. The temperature was raised to 175℃ and stirred for 5h. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid was obtained.

[0037] (3) Mix 20g dimethyl terephthalate, 6g ethylene glycol, 10g dihydroxy-terminated polylactic acid and 0.2g zinc acetate, heat to 185℃, stir for 1.5h, then add 0.2g antimony trioxide and 0.1g triphenyl phosphate, continue stirring for 0.5h, cool to 178℃, add 10g carboxylated graphene, sonicate for 20min, add 0.01g p-toluenesulfonic acid, stir for 2h, cool to room temperature, centrifuge, wash 3 times with anhydrous toluene, vacuum dry to obtain the modifier;

[0038] (4) Add 150g of PET to a twin-screw extruder (length-to-diameter ratio 40:1), set the feeding section temperature to 215℃, the melting section temperature to 225℃, and the mixing section temperature to 235℃. After the PET is completely melted, add 60g of PLA, 25g of modifier and 0.2g of UV absorber UV-531. The screw speed is 100rpm and the mixture is mixed for 8min under a shear stress of 0.3MPa. The melt is pelletized into particles with a diameter of 1.5mm by a water ring pelletizer and injection molded into a film (thickness 50μm). Finally, it is stretched 3.2 times in the longitudinal direction and 3 times in the transverse direction in a biaxial stretching machine to obtain the functional packaging film material.

[0039] Example 2

[0040] (1) 20g of graphene nanosheets were dispersed in 200g of mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), ultrasonically treated at 80℃ for 4h, centrifuged, washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene.

[0041] (2) 20g of L-lactic acid was heated to 120℃ and prepolymerized for 3h. Then 0.04g of stannous chloride, 0.06g of p-toluenesulfonic acid and 1g of ethylene glycol were added. The temperature was raised to 180℃ and stirred for 6h. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid was obtained.

[0042] (3) Mix 28.5g dimethyl terephthalate, 9.5g ethylene glycol, 15g dihydroxy-terminated polylactic acid and 0.5g zinc acetate, heat to 190℃, stir for 2h, then add 0.3g antimony trioxide and 0.2g triphenyl phosphate, continue stirring for 1h, cool to 180℃, add 15g carboxylated graphene, sonicate for 30min, add 0.05g p-toluenesulfonic acid, stir for 3h, cool to room temperature, centrifuge, wash 3 times with anhydrous toluene, vacuum dry to obtain the modifier;

[0043] (4) Add 200g of PET to a twin-screw extruder (length-to-diameter ratio 40:1), set the feeding section temperature to 220℃, the melting section temperature to 230℃, and the mixing section temperature to 240℃. After the PET is completely melted, add 90g of PLA, 35g of modifier and 0.5g of UV absorber UV-531. The screw speed is 120rpm and the mixture is blended for 10min under a shear stress of 0.45MPa. The melt is then processed into particles with a diameter of 2mm by a water ring pelletizer and injection molded into a film (thickness 50μm). Finally, the film is stretched 3.2 times in the longitudinal direction and 3 times in the transverse direction in a biaxial stretching machine to obtain the functional packaging film material.

[0044] Example 3

[0045] (1) 25g of graphene nanosheets were dispersed in 300g of mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), ultrasonically treated at 85℃ for 5h, centrifuged, washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene.

[0046] (2) 25g of L-lactic acid was heated to 125℃ and prepolymerized for 4h. Then 0.05g of stannous chloride, 0.08g of p-toluenesulfonic acid and 1.5g of ethylene glycol were added. The temperature was raised to 185℃ and stirred for 7h. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid was obtained.

[0047] (3) Mix 35g of dimethyl terephthalate, 15g of ethylene glycol, 20g of dihydroxy-terminated polylactic acid and 0.8g of zinc acetate, heat to 195℃, stir and react for 2.5h, then add 0.4g of antimony trioxide and 0.3g of triphenyl phosphate, continue stirring for 1.5h, cool to 155℃, add 20g of carboxylated graphene, sonicate for 40min, add 0.1g of p-toluenesulfonic acid, stir and react for 4h, cool to room temperature, centrifuge, wash 3 times with anhydrous toluene, and vacuum dry to obtain the modifier;

[0048] (4) Add 250g of PET to a twin-screw extruder (length-to-diameter ratio 40:1), set the feeding section temperature to 225℃, the melting section temperature to 235℃, and the mixing section temperature to 245℃. After the PET is completely melted, add 120g of PLA, 45g of modifier and 1g of UV absorber UV-531. The screw speed is 150rpm and the mixture is blended for 12min under a shear stress of 0.5MPa. The melt is then processed into particles with a diameter of 2.5mm by a water ring pelletizer and injection molded into a film (thickness 50μm). Finally, the film is stretched 3.2 times in the longitudinal direction and 3 times in the transverse direction in a biaxial stretching machine to obtain the functional packaging film material.

[0049] Comparative Example 1

[0050] The difference between Comparative Example 1 and Example 2 is that the dihydroxy-terminated polylactic acid in step (3) is replaced with ethylene glycol;

[0051] The specific steps are as follows:

[0052] (1) 20g of graphene nanosheets were dispersed in 200g of mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), ultrasonically treated at 80℃ for 4h, centrifuged, washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene.

[0053] (2) 20g of L-lactic acid was heated to 120℃ and prepolymerized for 3h. Then 0.04g of stannous chloride, 0.06g of p-toluenesulfonic acid and 1g of ethylene glycol were added. The temperature was raised to 180℃ and stirred for 6h. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid was obtained.

[0054] (3) Mix 28.5g dimethyl terephthalate, 14.5g ethylene glycol and 0.5g zinc acetate, heat to 190℃, stir for 2h, then add 0.3g antimony trioxide and 0.2g triphenyl phosphate, continue stirring for 1h, cool to 180℃ and add 15g carboxylated graphene, sonicate for 30min, add 0.05g p-toluenesulfonic acid, stir for 3h, cool to room temperature, centrifuge, wash 3 times with anhydrous toluene, vacuum dry to obtain the modifier;

[0055] (4) Add 200g of PET to a twin-screw extruder (length-to-diameter ratio 40:1), set the feeding section temperature to 220℃, the melting section temperature to 230℃, and the mixing section temperature to 240℃. After the PET is completely melted, add 90g of PLA, 35g of modifier and 0.5g of UV absorber UV-531. The screw speed is 120rpm and the mixture is blended for 10min under a shear stress of 0.45MPa. The melt is then processed into 2mm diameter particles by a water ring pelletizer and injection molded into a film (thickness 50μm). Finally, the film is stretched 3.2 times in the longitudinal direction and 3 times in the transverse direction in a biaxial stretching machine to obtain the packaging film material.

[0056] Comparative Example 2

[0057] The difference between Comparative Example 2 and Example 2 is that the ethylene glycol in step (3) is replaced with dihydroxy-terminated polylactic acid;

[0058] The specific steps are as follows:

[0059] (1) 20g of graphene nanosheets were dispersed in 200g of mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), ultrasonically treated at 80℃ for 4h, centrifuged, washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene.

[0060] (2) 20g of L-lactic acid was heated to 120℃ and prepolymerized for 3h. Then 0.04g of stannous chloride, 0.06g of p-toluenesulfonic acid and 1g of ethylene glycol were added. The temperature was raised to 180℃ and stirred for 6h. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid was obtained.

[0061] (3) Mix 28.5g of dimethyl terephthalate, 14.5g of dihydroxy-terminated polylactic acid and 0.5g of zinc acetate, heat to 190℃, stir for 2h, then add 0.3g of antimony trioxide and 0.2g of triphenyl phosphate, continue stirring for 1h, cool to 180℃, add 15g of carboxylated graphene, sonicate for 30min, add 0.05g of p-toluenesulfonic acid, stir for 3h, cool to room temperature, centrifuge, wash 3 times with anhydrous toluene, vacuum dry to obtain the modifier;

[0062] (4) Add 200g of PET to a twin-screw extruder (length-to-diameter ratio 40:1), set the feeding section temperature to 220℃, the melting section temperature to 230℃, and the mixing section temperature to 240℃. After the PET is completely melted, add 90g of PLA, 35g of modifier and 0.5g of UV absorber UV-531. The screw speed is 120rpm and the mixture is blended for 10min under a shear stress of 0.45MPa. The melt is then processed into 2mm diameter particles by a water ring pelletizer and injection molded into a film (thickness 50μm). Finally, the film is stretched 3.2 times in the longitudinal direction and 3 times in the transverse direction in a biaxial stretching machine to obtain the packaging film material.

[0063] Comparative Example 3

[0064] The difference between Comparative Example 3 and Example 2 is that the modifier is dihydroxy-terminated polylactic acid-grafted graphene;

[0065] The specific steps are as follows:

[0066] (1) 20g of graphene nanosheets were dispersed in 200g of mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), ultrasonically treated at 80℃ for 4h, centrifuged, washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene.

[0067] (2) 20g of L-lactic acid was heated to 120℃ and prepolymerized for 3h. Then 0.04g of stannous chloride, 0.06g of p-toluenesulfonic acid and 1g of ethylene glycol were added. The temperature was raised to 180℃ and stirred for 6h. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid was obtained.

[0068] (3) Heat 15g of dihydroxy-terminated polylactic acid to 180℃, add 15g of carboxylated graphene, sonicate for 30min, add 0.05g of p-toluenesulfonic acid, stir for 3h, cool to room temperature, centrifuge, wash 3 times with anhydrous toluene, and vacuum dry to obtain the modifier.

[0069] (4) Add 200g of PET to a twin-screw extruder (length-to-diameter ratio 40:1), set the feeding section temperature to 220℃, the melting section temperature to 230℃, and the mixing section temperature to 240℃. After the PET is completely melted, add 90g of PLA, 35g of modifier and 0.5g of UV absorber UV-531. The screw speed is 120rpm and the mixture is blended for 10min under a shear stress of 0.45MPa. The melt is then processed into 2mm diameter particles by a water ring pelletizer and injection molded into a film (thickness 50μm). Finally, the film is stretched 3.2 times in the longitudinal direction and 3 times in the transverse direction in a biaxial stretching machine to obtain the packaging film material.

[0070] Comparative Example 4

[0071] The difference between Comparative Example 4 and Example 2 is that the modifier is graphene nanosheets;

[0072] The specific steps are as follows:

[0073] 200g of PET was added to a twin-screw extruder (length-to-diameter ratio 40:1). The feeding section temperature was set to 220℃, the melting section temperature to 230℃, and the mixing section temperature to 240℃. After the PET was completely melted, 90g of PLA, 35g of graphene nanosheets, and 0.5g of UV absorber UV-531 were added. The screw speed was 120rpm, and the mixture was blended for 10min under a shear stress of 0.45MPa. The melt was then pelletized into particles with a diameter of 2mm by a water ring pelletizer and injection molded into a film (thickness 50μm). Finally, the film was stretched 3.2 times longitudinally and 3 times transversely in a biaxial stretching machine to obtain the packaging film material.

[0074] Performance testing:

[0075] Mechanical property testing: Referring to GB / T1040.3-2006, the film sample was cut into a long strip of 150×15mm and placed in the fixture of a microcomputer-controlled electronic universal testing machine. The initial spacing between the fixtures was 100mm. The sample was stretched at a rate of 50mm / min until it broke. Each test was repeated 10 times and the average value was taken. The tensile strength and elongation at break were recorded. The results are shown in Table 1.

[0076] Oxygen barrier performance test: Refer to GB / T31354-2014, seal the film sample in the air permeability test chamber (effective area 50cm²). 2 The chamber was kept at a constant temperature of 23°C. 99% high-purity oxygen was introduced into one side of the chamber and a pressure difference of 0.1 MPa was maintained. The oxygen permeation per unit time was measured by gas chromatography. The results are shown in Table 1.

[0077] Heat distortion temperature test: Referring to GB / T1634.2-2019, the film samples were stacked and pressed into a size of 4.0×10×80mm. 3 Composite laminates (meeting standard specimen size requirements) were installed on the heat distortion tester bracket (support span 64mm), and a bending stress of 1.8MPa was applied. The temperature was increased at a uniform rate of 120℃ / h, and the temperature at which the specimen deformation reached 0.34mm (standard deflection) was recorded. Five specimens were tested in parallel for each group, and the average value was taken. The results are shown in Table 1.

[0078]

[0079] Data Analysis:

[0080] Overall performance analysis of Examples 1-3: Through specific material formulations and process control, the resulting functional packaging films exhibited a balanced improvement in mechanical properties, gas barrier properties, and thermal stability. This may be due to the copolymerization reaction between the rationally proportioned dihydroxy-terminated polylactic acid in the modifier and the polyester precursor, which constructs a molecular interface layer with both rigidity and flexibility on the surface of the graphene nanosheets. This structure promotes the uniform dispersion of nanosheets in the polymer matrix, forming an effective stress transfer network; at the same time, the interface layer may reduce the continuity of oxygen molecule diffusion channels, enhancing the barrier effect; the synergistic effect of the nanofiller and the polymer also improves the material's resistance to thermal deformation, presumably due to the restrictive effect of the interface layer on the movement of the matrix molecular chains.

[0081] Comparative analysis of Example 2 and Comparative Example 1: After removing the polylactic acid (PLA) segments from Comparative Example 1, the mechanical properties and thermal stability of the material decreased, while the oxygen barrier properties remained relatively good. This difference may be due to the reduced compatibility between graphene and the PET / PLA matrix after the modifier lacks flexible PLA segments, leading to decreased stress transfer efficiency and weakened heat deformation resistance.

[0082] Comparative analysis of Example 2 and Comparative Example 2: In Comparative Example 2, the material's barrier properties significantly deteriorated and its mechanical strength decreased when excessive polylactic acid (PLA) segments were used. This may be because the excessive flexible PLA segments disrupted the balance of the molecular structure: the compatibility difference between PLA and PET led to intensified phase separation, forming gas permeation channels; simultaneously, the excessive plasticizing effect weakened the orientation ability of the molecular chains, reducing the material's rigidity; and the decrease in thermal stability was related to the reduction in molecular chain packing density. This indicates that rationally controlling the ratio of PLA to PET segments is a key factor in achieving performance optimization.

[0083] Comparative analysis of Example 2 and Comparative Example 3: When Comparative Example 3 uses a simple grafting structure, the material exhibits high ductility but insufficient strength and barrier properties. This phenomenon may stem from structural defects in the grafting modifier. Although single-phase grafting of polylactic acid improves compatibility with PLA, the lack of PET segments leads to poor dispersion in the PET phase, causing stress concentration and nanosheet aggregation, thus weakening the strength and barrier effect. The high elongation indicates that the flexible segments can promote local deformation absorption. Its excellent thermal stability may be due to the inducing effect of the graft on PLA crystallization.

[0084] Comparative analysis of Example 2 and Comparative Example 4: When unmodified filler was directly added to Comparative Example 4, all properties of the material deteriorated significantly. This result clearly shows that unmodified graphene nanosheets are prone to agglomeration in the matrix, forming stress concentration defects that lead to a collapse in mechanical properties; the agglomerates disrupt the continuity of the nanosheet barrier network, causing a sharp decrease in oxygen permeation resistance; simultaneously, agglomeration interferes with the polymer crystallization process, significantly reducing the material's heat resistance. This confirms that the modifier design of this invention plays a decisive role in achieving uniform dispersion of the filler.

[0085] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A functional packaging film material, characterized in that, It is prepared from the following raw materials: 150-250 parts PET, 60-120 parts PLA, 25-45 parts modifier and 0.2-1 parts UV absorber; The modifier is obtained by grafting dimethyl terephthalate, ethylene glycol and dihydroxy-terminated polylactic acid onto the surface of carboxylated graphene via transesterification. The weight ratio of dimethyl terephthalate, ethylene glycol, dihydroxy-terminated polylactic acid, and carboxylated graphene is 20-35:6-15:10-20:10-20.

2. The functional packaging film material according to claim 1, characterized in that, The intrinsic viscosity of the PET is 0.8-0.9 dL / g.

3. The functional packaging film material according to claim 1, characterized in that, The PLA has a weight-average molecular weight of 130,000-180,000 and an L-isomer content of over 90%.

4. The functional packaging film material according to claim 1, characterized in that, The preparation method of the dihydroxy-terminated polylactic acid is as follows: L-lactic acid is heated to 115-125℃ and prepolymerized for 2-4 hours. Then, stannous chloride, p-toluenesulfonic acid and ethylene glycol are added, and the temperature is raised to 175-185℃. The mixture is stirred and reacted for 5-7 hours. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid is obtained.

5. The functional packaging film material according to claim 4, characterized in that, The weight ratio of L-lactic acid, stannous chloride, p-toluenesulfonic acid, and ethylene glycol is 15-25:0.03-0.05:0.04-0.08:0.5-1.

5.

6. The functional packaging film material according to claim 1, characterized in that, The carboxylated graphene was obtained by modifying graphene nanosheets with a mixed acid solution composed of concentrated nitric acid and concentrated sulfuric acid.

7. The functional packaging film material according to claim 6, characterized in that, The graphene nanosheets have an average thickness of 3-10 nm and an average diameter of 5-10 μm.

8. A method for preparing a functional packaging film material according to any one of claims 1-7, characterized in that, Includes the following steps: PET is added to a twin-screw extruder to melt. After the PET is completely melted, PLA, modifier and UV absorber are added, melt-blended, extruded and pelletized, injection molded into film, and stretched to obtain the functional packaging film material.

9. The method for preparing the functional packaging film material according to claim 8, characterized in that, The temperature of the feeding section of the twin-screw extruder is 215-225℃, the temperature of the melting section is 225-235℃, and the temperature of the mixing section is 235-245℃.

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