Functional packaging film material and preparation method thereof

Abstract

The invention relates to the technical field of polymeric membrane materials, in particular to a functional packaging membrane material and a preparation method thereof. The packaging film material is prepared from PET, PLA, a modifier and an ultraviolet absorbent, wherein the modifier is formed by grafting dimethyl terephthalate, ethylene glycol and dihydroxyl-terminated polylactic acid to the surface of carboxylated graphene after ester exchange. Under the synergistic effect of the carboxylated graphene nanosheets and the modifier, the uniform dispersion and interface bonding strength of the nanofiller are effectively improved, so that the compatibility of PET (Polyethylene Terephthalate) and PLA (Polylactic Acid) is optimized. According to the structural design, the comprehensive performance such as tensile strength, toughness, gas barrier property and thermal deformation temperature of the composite material can be remarkably improved, and meanwhile, good processability and degradability of the material are guaranteed. The invention provides reliable technical support for developing a novel green packaging film material with high performance and low environmental burden, and has 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 a unique design of the modifier, and has the following beneficial effects: 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.

[0025] Uniform dispersion of nanofillers: the active groups on the surface of carboxylated graphene nanoplatelets form chemical bonds with the modifier molecules, building a stable interfacial layer. This interfacial layer not only prevents the agglomeration of nanoplatelets, but also maintains the uniform dispersion state of fillers through steric hindrance effect. At the same time, the gradient structure of the interfacial layer realizes the smooth transition from rigid nanofillers to flexible polymer matrix, eliminating the interfacial stress concentration phenomenon.

[0026] Synergistic enhancement of mechanical properties: uniformly dispersed graphene nanoplatelets form an effective load transfer network, significantly improving the tensile strength of the material. The presence of the interfacial layer ensures the continuity of stress transfer, avoiding premature failure caused by interfacial debonding. At the same time, the introduction of flexible polylactic acid segments maintains the toughness of the material, achieving a balance between strength and ductility.

[0027] Barrier property improvement mechanism: the sheet-shaped graphene nanofiller builds a detour diffusion path for gas molecules, significantly extending the diffusion distance of oxygen through the film. The dense structure of the interfacial layer further reduces the interfacial defects, blocking the preferential permeation channels of gas molecules. The improvement of compatibility also reduces the micropore defects at the phase interface, overall improving the barrier effect of the material.

[0028] Comprehensive improvement of thermal stability: the excellent thermal stability of graphene 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. The improvement of PET / PLA compatibility also promotes more regular crystallization behavior, enhancing the heat resistance of the material.

[0029] Environmental performance is maintained: the biodegradable nature of the polylactic acid component in the modifier is maintained, which does not affect the environmental friendliness of the overall material. At the same time, the amount of modifier used is relatively small, which does not significantly increase the cost of the material, and has good industrial application prospects.

[0030] The synergistic effect of these beneficial effects enables the functional packaging film material prepared by the present application to maintain environmental properties while achieving comprehensive improvement of overall performance. DETAILED DESCRIPTION

[0031] To make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below with specific examples.

[0032] In the specific embodiment of the present application, the average thickness of the graphene nanoplatelets is 5.2 nm, and the average diameter is 6.8 μm; the intrinsic viscosity of PET is 0.85 dL / g, the weight average molecular weight of PLA is 150000, and the L-isomer content is ≥95%.

[0033] Example 1

[0034] (1) 15 g graphene nanosheets were dispersed in 100 g mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), and ultrasonically treated at 75 °C for 3 h. After centrifugation, the product was washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene; (2) 15 g L-lactic acid was heated to 115 °C, and pre-polymerized for 2 h. Then 0.03 g stannous chloride, 0.04 g p-toluenesulfonic acid and 0.5 g ethylene glycol were added, and the mixture was heated to 175 °C and stirred for 5 h. After precipitation with cold methanol and vacuum drying, a dihydroxyl-terminated polylactic acid was obtained; (3) 20 g dimethyl terephthalate, 6 g ethylene glycol, 10 g dihydroxyl-terminated polylactic acid and 0.2 g zinc acetate were mixed, and heated to 185 °C and stirred for 1.5 h. Then 0.2 g antimony trioxide and 0.1 g triphenyl phosphate were added, and the mixture was stirred for another 0.5 h. The temperature was lowered to 178 °C, 10 g carboxylated graphene was added, and the mixture was ultrasonically treated for 20 min. Then 0.01 g p-toluenesulfonic acid was added, and the mixture was stirred for 2 h. After cooling to room temperature, the product was centrifuged, washed with anhydrous toluene for 3 times, and vacuum dried to obtain a modifier; (4) 150 g PET was fed into a twin-screw extruder (length-diameter ratio 40:1) with the temperature set at 215 °C for feeding section, 225 °C for melting section and 235 °C for mixing section. After the PET was completely melted, 60 g PLA, 25 g modifier and 0.2 g ultraviolet absorber UV-531 were added, and the mixture was blended for 8 min at a screw speed of 100 rpm and a shear stress of 0.3 MPa. The melt was cut into particles with a diameter of 1.5 mm by a water ring cutter, and then injection molded into a film (thickness 50 μm). Finally, the film was stretched by 3.2 times in the longitudinal direction and 3 times in the transverse direction in a biaxial stretching machine to obtain a functional packaging film material.

[0035] Example 2

[0036] (1) 20 g graphene nanosheets were dispersed in 200 g mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), and ultrasonically treated at 80 °C for 4 h. After centrifugation, the product was washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene; (2) 20 g L-lactic acid was heated to 120 °C, and pre-polymerized for 3 h. Then 0.04 g stannous chloride, 0.06 g p-toluenesulfonic acid and 1 g ethylene glycol were added, and the mixture was heated to 180 °C and stirred for 6 h. After precipitation with cold methanol and vacuum drying, a dihydroxyl-terminated polylactic acid was obtained; (3) 28.5 g of dimethyl terephthalate, 9.5 g of ethylene glycol, 15 g of dihydroxyl-terminated polylactic acid and 0.5 g of zinc acetate were mixed, heated to 190 °C, stirred for 2 h, then 0.3 g of antimony trioxide and 0.2 g of triphenyl phosphate were added, and stirring was continued for 1 h, 15 g of carboxylated graphene was added at 180 °C, ultrasonic treatment was performed for 30 min, 0.05 g of p-toluenesulfonic acid was added, and stirring was performed for 3 h, and then the temperature was lowered to room temperature, centrifugation was performed, and the product was washed with anhydrous toluene three times and vacuum dried to obtain a modifier; (4) 200 g of PET was added to a twin-screw extruder (length-diameter ratio 40:1), the temperature of the feeding section was set to 220 °C, the temperature of the melting section was set to 230 °C, and the temperature of the mixing section was set to 240 °C, after the PET was completely melted, 90 g of PLA, 35 g of the modifier and 0.5 g of ultraviolet absorber UV-531 were added, the screw rotation speed was 120 rpm, the shear stress was 0.45 MPa, and the mixture was blended for 10 min, the melt was cut into particles with a diameter of 2 mm by a water ring cutter, and a film (thickness 50 μm) was prepared by injection molding, and finally the film was stretched by 3.2 times in the longitudinal direction and 3 times in the transverse direction in a two-way stretching machine to obtain a functional packaging film material.

[0037] Example 3

[0038] (1) 25 g of graphene nanosheets were dispersed in 300 g of mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), ultrasonic treatment was performed at 85 °C for 5 h, centrifugation was performed, and the product was washed with deionized water until it was neutral, and then vacuum dried to obtain carboxylated graphene; (2) 25 g of L-lactic acid was heated to 125 °C, pre-polymerized for 4 h, and then 0.05 g of stannous chloride, 0.08 g of p-toluenesulfonic acid and 1.5 g of ethylene glycol were added, the temperature was raised to 185 °C, and stirring was performed for 7 h, and then the product was precipitated in cold methanol and vacuum dried to obtain dihydroxyl-terminated polylactic acid; (3) 35 g of dimethyl terephthalate, 15 g of ethylene glycol, 20 g of dihydroxyl-terminated polylactic acid and 0.8 g of zinc acetate were mixed, heated to 195 °C, stirred for 2.5 h, then 0.4 g of antimony trioxide and 0.3 g of triphenyl phosphate were added, and stirring was continued for 1.5 h, 20 g of carboxylated graphene was added at 155 °C, ultrasonic treatment was performed for 40 min, 0.1 g of p-toluenesulfonic acid was added, and stirring was performed for 4 h, and then the temperature was lowered to room temperature, centrifugation was performed, and the product was washed with anhydrous toluene three times and vacuum dried to obtain a modifier; (4) 250 g of PET was added into a twin-screw extruder (length-diameter ratio 40:1), the temperature of feeding section was set at 225 °C, the temperature of melting section was set at 235 °C, the temperature of mixing section was set at 245 °C, after the PET was completely melted, 120 g of PLA, 45 g of the modifier and 1 g of the ultraviolet absorber UV-531 were added, the screw rotation speed was 150 rpm, the shear stress was 0.5 MPa, the melt was blended for 12 min, the melt was cut into particles with a diameter of 2.5 mm by a water ring cutter, the particles were injection molded into a film (thickness 50 μm), finally the film was stretched in a biaxial stretching machine, the film was stretched by 3.2 times in the longitudinal direction and 3 times in the transverse direction, and the functional packaging film material was prepared.

[0039] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that the dihydroxyl-terminated polylactic acid in step (3) is replaced by ethylene glycol. The specific steps are as follows: (1) 20 g of graphene nanosheets were dispersed in 200 g of mixed acid solution (concentrated nitric acid: concentrated sulfuric acid = 3:1 v / v), ultrasonic treatment was performed at 80 °C for 4 h, centrifugation was performed, deionized water was used for washing until neutral, and vacuum drying was performed, to obtain carboxylated graphene; (2) 20 g of L-lactic acid was heated to 120 °C, pre-polymerization was performed for 3 h, then 0.04 g of stannous chloride, 0.06 g of p-toluenesulfonic acid and 1 g of ethylene glycol were added, heating was performed to 180 °C, and stirring was performed for 6 h, after precipitation by cold methanol and vacuum drying, dihydroxyl-terminated polylactic acid was obtained; (3) 28.5 g of dimethyl terephthalate, 14.5 g of ethylene glycol and 0.5 g of zinc acetate were mixed, heating was performed to 190 °C, and stirring was performed for 2 h, then 0.3 g of antimony trioxide and 0.2 g of triphenyl phosphate were added, stirring was continued for 1 h, 15 g of carboxylated graphene was added after the temperature was lowered to 180 °C, ultrasonic treatment was performed for 30 min, 0.05 g of p-toluenesulfonic acid was added, stirring was performed for 3 h, the temperature was lowered to room temperature, centrifugation was performed, anhydrous toluene was used for washing for 3 times, and vacuum drying was performed, to obtain the modifier; (4) 200 g of PET was added into a twin-screw extruder (length-diameter ratio 40:1), the temperature of feeding section was set at 220 °C, the temperature of melting section was set at 230 °C, the temperature of mixing section was set at 240 °C, after the PET was completely melted, 90 g of PLA, 35 g of the modifier and 0.5 g of the ultraviolet absorber UV-531 were added, the screw rotation speed was 120 rpm, the shear stress was 0.45 MPa, the melt was blended for 10 min, the melt was cut into particles with a diameter of 2 mm by a water ring cutter, the particles were injection molded into a film (thickness 50 μm), finally the film was stretched in a biaxial stretching machine, the film was stretched by 3.2 times in the longitudinal direction and 3 times in the transverse direction, and the packaging film material was prepared.

[0040] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that the ethylene glycol in step (3) is replaced by dihydroxyl-terminated polylactic acid. The specific steps are as follows: (1) 20 g of graphene nanosheets were dispersed in 200 g of mixed acid solution (concentrated nitric acid:concentrated sulfuric acid = 3:1 v / v), ultrasonically treated at 80 °C for 4 h, centrifuged, washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene; (2) 20 g of L-lactic acid was heated to 120 ° C and prepolymerized for 3 h. Then 0.04 g of stannous chloride, 0.06 g of p-toluenesulfonic acid and 1 g of ethylene glycol were added, and the temperature was raised to 180 ° C. The mixture was stirred and reacted for 6 h. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid was obtained. (3) 28.5 g of dimethyl terephthalate, 14.5 g of dihydroxy-terminated polylactic acid and 0.5 g of zinc acetate were mixed, heated to 190 °C, stirred and reacted for 2 h, then 0.3 g of antimony trioxide and 0.2 g of triphenyl phosphate were added, and stirring was continued for 1 h. The temperature was cooled to 180 °C, 15 g of carboxylated graphene was added, and ultrasonication was performed for 30 min. 0.05 g of p-toluenesulfonic acid was added, and stirring was performed for 3 h. The temperature was cooled to room temperature, centrifuged, washed with anhydrous toluene 3 times, and vacuum dried to obtain a modifier. (4) 200 g of PET was added to a twin-screw extruder (length-to-diameter ratio 40:1), and the feeding section temperature was set at 220 °C, the melting section temperature at 230 °C, and the mixing section temperature at 240 °C. After the PET was completely melted, 90 g of PLA, 35 g of modifier, and 0.5 g of UV absorber UV-531 were added. The screw speed was 120 rpm, and the mixture was blended under a shear stress of 0.45 MPa for 10 min. The melt was pelletized into particles with a diameter of 2 mm by a water ring pelletizer, and then injection molded into a film (thickness 50 μm). Finally, the film was stretched 3.2 times in the longitudinal direction and 3 times in the transverse direction in a biaxial stretching machine to obtain a packaging film material.

[0041] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that the modifier is dihydroxy-terminated polylactic acid grafted graphene; The specific steps are as follows: (1) 20 g of graphene nanosheets were dispersed in 200 g of mixed acid solution (concentrated nitric acid:concentrated sulfuric acid = 3:1 v / v), ultrasonically treated at 80 °C for 4 h, centrifuged, washed with deionized water until neutral, and vacuum dried to obtain carboxylated graphene; (2) 20 g of L-lactic acid was heated to 120 ° C and prepolymerized for 3 h. Then 0.04 g of stannous chloride, 0.06 g of p-toluenesulfonic acid and 1 g of ethylene glycol were added, and the temperature was raised to 180 ° C. The mixture was stirred and reacted for 6 h. After precipitation with cold methanol and vacuum drying, dihydroxy-terminated polylactic acid was obtained. (3) 15 g of dihydroxy-terminated polylactic acid was heated to 180 °C, 15 g of carboxylated graphene was added, ultrasonicated for 30 min, 0.05 g of p-toluenesulfonic acid was added, stirred for 3 h, cooled to room temperature, centrifuged, washed with anhydrous toluene 3 times, and vacuum dried to obtain a modifier; (4) 200 g of PET was added into a twin-screw extruder (length-diameter ratio 40:1), the temperature of feeding section was set to 220 °C, the temperature of melting section was set to 230 °C, and the temperature of mixing section was set to 240 °C. After the PET was completely melted, 90 g of PLA, 35 g of the modifier, and 0.5 g of the ultraviolet absorber UV-531 were added. The screw rotation speed was 120 rpm, and the shear stress was 0.45 MPa. The blending was performed for 10 min. The melt was cut into particles with a diameter of 2 mm by a water ring cutter. The particles were injection-molded into a film (thickness 50 μm). Finally, the film was stretched by 3.2 times in the longitudinal direction and by 3 times in the transverse direction in a biaxial stretching machine to obtain a packaging film material.

[0042] Comparative Example 4 The difference between Comparative Example 4 and Example 2 is that the modifier is graphene nanoplatelets. The specific steps are as follows: 200 g of PET was added into a twin-screw extruder (length-diameter ratio 40:1), the temperature of feeding section was set to 220 °C, the temperature of melting section was set to 230 °C, and the temperature of mixing section was set to 240 °C. After the PET was completely melted, 90 g of PLA, 35 g of graphene nanoplatelets, and 0.5 g of the ultraviolet absorber UV-531 were added. The screw rotation speed was 120 rpm, and the shear stress was 0.45 MPa. The blending was performed for 10 min. The melt was cut into particles with a diameter of 2 mm by a water ring cutter. The particles were injection-molded into a film (thickness 50 μm). Finally, the film was stretched by 3.2 times in the longitudinal direction and by 3 times in the transverse direction in a biaxial stretching machine to obtain a packaging film material.

[0043] Performance test: Mechanical property test: according to GB / T1040.3-2006, the film sample was cut into a 150×15 mm long strip-shaped sample, which was placed between the clamps of a microcomputer-controlled electronic universal testing machine. The initial distance between the clamps was 100 mm. The sample was stretched at a rate of 50 mm / min until it was broken. Each test was repeated 10 times to obtain the average value. The tensile strength and elongation at break were recorded. The results are shown in Table 1.

[0044] Oxygen barrier property test: according to GB / T31354-2014, the film sample was sealed in a gas permeation test chamber (effective area 50 cm 2 ). The temperature was kept at 23 °C. One side of the chamber was connected to a 99% high-purity oxygen source and maintained at a pressure difference of 0.1 MPa. The oxygen permeation amount per unit time was measured by a gas chromatograph. The results are shown in Table 1.

[0045] Heat distortion temperature test: according to GB / T1634.2-2019, the film sample was stacked and pressed to obtain a 4.0×10×80 mm 3The composite laminates (satisfying the standard sample size requirements) were installed on the hot deformation instrument support (supporting span 64 mm), 1.8 MPa bending stress was applied, the temperature was uniformly increased at 120 ℃ / h, the temperature when the sample deformation reached 0.34 mm (standard deflection) was recorded, 5 samples were tested in parallel for each group to take the average value, and the results are shown in Table 1.

[0046]

[0047] Data analysis: Overall performance analysis of examples 1-3: through specific material formula and process control, the obtained functional packaging film presents balanced improvement in mechanical properties, gas barrier property and thermal stability. This may be due to the reasonable ratio of double hydroxyl terminated polylactic acid in the modifier and the copolymerization reaction of polyester precursor, which builds a molecular interface layer with rigidity and flexibility on the surface of graphene nanosheet. This structure promotes the uniform dispersion of nanosheet in the polymer matrix, forming an effective stress transfer network; at the same time, the interface layer may reduce the continuity of the diffusion channel of oxygen molecules, enhance the barrier effect; the synergistic effect of nanofiller and polymer also improves the thermal deformation resistance of the material, which is speculated to be due to the limiting effect of the interface layer on the movement of the matrix molecular chain.

[0048] Comparative analysis of example 2 and comparative example 1: after removing the polylactic acid segment in comparative example 1, the mechanical properties and thermal stability of the material decrease, while the oxygen barrier property remains good. This difference may be due to the lack of flexible polylactic acid segment in the modifier, which reduces the compatibility of graphene and PET / PLA matrix, resulting in reduced stress transfer efficiency and thermal deformation resistance.

[0049] Comparative analysis of example 2 and comparative example 2: when excessive polylactic acid segment is used in comparative example 2, the barrier performance of the material is significantly deteriorated and the mechanical strength decreases. This may be due to the excessive flexible polylactic acid segment disrupting the balance of the molecular structure: the difference in compatibility between polylactic acid and PET leads to increased phase separation, forming gas permeation channels; at the same time, the excessive plasticizing effect weakens the orientation ability of the molecular chain, reducing the rigidity of the material; and the decrease in thermal stability is related to the decrease in molecular chain packing density. It shows that reasonable control of the ratio of polylactic acid and PET segment is a key factor to realize performance optimization.

[0050] Comparative analysis of example 2 and comparative example 3: when a simple graft structure is used in comparative example 3, the material presents high ductility but insufficient strength and barrier property. This phenomenon may be due to the structural defects of the graft modifier. Although single-phase grafting of polylactic acid improves the compatibility with PLA, the lack of PET segment leads to poor dispersion in the PET phase, causing stress concentration and nanosheet aggregation, which weakens the strength and barrier effect; the high elongation rate indicates that the flexible segment can promote local deformation absorption; its excellent thermal stability may be due to the induction effect of the graft on PLA crystallization.

[0051] Comparative analysis of Example 2 and Comparative Example 4: when the unmodified filler is directly added in Comparative Example 4, all the properties of the material are greatly deteriorated. The results clearly show that the graphene nanosheets without interface modification are easy to agglomerate in the matrix, forming stress concentration defect points, leading to the collapse of mechanical properties; the agglomerates destroy the continuity of the barrier network of the nanosheets, causing the oxygen permeation resistance to sharply decrease; at the same time, the agglomerates interfere with the polymer crystallization process, significantly reducing the heat resistance of the material. It is confirmed that the modifier design of the present application plays a decisive role in achieving uniform dispersion of the filler.

[0052] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to suggest that the scope of the present application is limited to these examples; the above embodiments or technical features among different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of the different aspects of the present application as described above, which are not provided in details for the sake of brevity.

Claims

1. A functional packaging film material, characterized in that: Prepared from the following raw materials: 150-250 parts of PET, 60-120 parts of PLA, 25-45 parts of modifier and 0.2-1 part of UV absorber; The modifier is obtained by grafting dimethyl terephthalate, ethylene glycol and dihydroxyl-terminated polylactic acid onto the surface of carboxylated graphene after ester exchange.

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 weight average molecular weight of the PLA is 130,000-180,000, and the L-isomer content is higher than 90%.

4. The functional packaging film material according to claim 1, characterized in that: The weight ratio of dimethyl terephthalate, ethylene glycol, dihydroxy-terminated polylactic acid and carboxylated graphene is 20-35:6-15:10-20:10-20.

5. 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° C., prepolymerized for 2-4 hours, stannous chloride, p-toluenesulfonic acid and ethylene glycol are added, the temperature is raised to 175-185° C., stirred for reaction for 5-7 hours, precipitated with cold methanol, and vacuum dried to obtain the dihydroxy-terminated polylactic acid.

6. The functional packaging film material according to claim 5, characterized in that: 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.

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

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

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

10. The method for preparing a functional packaging film material according to claim 9, wherein: The temperature of the feeding section of the twin-screw extruder is 215-225°C, the temperature of the melting section is 225-235°C, and the temperature of the mixing section is 235-245°C.

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