Low-temperature polyolefin packaging film and preparation method thereof

Abstract

The invention is suitable for the technical field of packaging films, and provides a low-temperature polyolefin packaging film and a preparation method thereof.The packaging film comprises a three-layer co-extrusion structure of an outer layer, a middle layer and an inner layer, and the inner layer is prepared from metallocene polyolefin, high-performance polypropylene, modified lignin nanofibers and erucyl amide / silicon dioxide composite microspheres; the middle layer is prepared from PCR (Polymerase Chain Reaction), modified nano kaolinite and trimethylolpropane triacrylate; the outer layer is prepared from PCR, modified tourmaline nanotubes, dibenzoyl peroxide microcapsules and polydopamine coated chitosan, the PCR is adopted, more energy is saved, the environment is protected, the modified lignin nanofibers are added into the inner layer, and the tensile strength is improved; the modified nano kaolinite is added into the middle layer, so that the thermal shrinkage rate is increased; the modified tourmaline nanotubes are added to the outer layer, so that the initial temperature of the cross-linking reaction is reduced, and the shrinkage rate is increased; and by adding the polydopamine coated chitosan, reversible recombination is realized during damage, and the puncture strength is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of packaging film, and particularly relates to a low-temperature polyolefin packaging film and a preparation method thereof. BACKGROUND

[0002] Current low-temperature heat-shrinkable packaging films mainly use PVC, PET or ordinary polyolefin materials. The traditional polyolefin shrink film has obvious deficiencies: High shrinkage temperature: the initial shrinkage temperature of ordinary LDPE / LLDPE film is greater than 85 DEG C, which cannot meet the low-temperature packaging requirements (<70 DEG C) of heat-sensitive products such as fresh food; Poor mechanical properties: the tensile strength decreases after adding recycled materials (PCR), and the insufficient puncture strength leads to a high damage rate during transportation; Single function: although the existing nano-enhanced system (such as talc and calcium carbonate) can improve the strength, it will inhibit the movement of molecular chains, resulting in a decrease in heat shrinkage rate. SUMMARY

[0003] The application provides a low-temperature polyolefin packaging film, which aims to solve the above problems.

[0004] The application is implemented as follows: a low-temperature polyolefin packaging film, which comprises an outer layer, an intermediate layer and an inner layer in a three-layer co-extrusion structure, and the components of each layer are as follows in terms of weight parts: The inner layer comprises 45-55 parts of metallocene polyolefin, 15-25 parts of high-performance polypropylene, 15-20 parts of modified lignin nanofiber and 2-3 parts of mustard acid amide / silicon dioxide composite microspheres. The intermediate layer comprises 45-55 parts of PCR, 10-15 parts of modified nano-kaolinite and 3-4 parts of trimethylolpropane triacrylate. The outer layer comprises 50-60 parts of PCR, 8-12 parts of modified tourmaline nanotube, 3-5 parts of dibenzoyl peroxide microcapsule and 5-8 parts of polydopamine-coated chitosan.

[0005] Preferably, the total thickness of the film is 20-50 microns, the thickness ratio of the outer layer: intermediate layer: inner layer is 1:3-5:1, the heat shrinkage rate at 65 DEG C is greater than or equal to 25%, and the heat shrinkage rate at 100 DEG C is greater than or equal to 55%.

[0006] Preferably, the metallocene polyolefin is preferably metallocene linear low-density polyethylene, the high-performance polypropylene is preferably copolymerized polypropylene, the PCR of the intermediate layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0007] Preferably, the modified tourmaline nanotube is a borosilicate tourmaline with ZnO quantum dots loaded on the surface, the loading amount of ZnO is 5-8 wt%, the tube diameter is 50-80 nm, and the aspect ratio is greater than 30. The dibenzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), the capsule core accounts for 60-70%, and the particle size is 200-500nm.

[0008] Preferably, the modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and an interlayer spacing expanded to 1.5-2.0 nm; The modified lignin nanofiber is treated by laccase activation-plasma grafting, and the carboxyl density is ≥3.0 / nm 2 .

[0009] Preferably, the thickness of the dopamine coating layer in the polydopamine-coated chitosan is 10-20 nm, and the deacetylation degree of the chitosan is ≥90%; The composite microspheres are mesoporous silica filled with erucamide, with a pore size of 2-5 nm and a drug loading of 40-50%.

[0010] The present invention also provides a method for preparing the low-temperature polyolefin packaging film, comprising the following steps: S1 prepares the raw materials according to the recipe; S2 three-layer co-extrusion: The extrusion temperature of the outer layer is 170-190℃, the middle layer is 180-200℃, and the inner layer is 165-185℃; Die gap 1.2-1.8mm, melt pressure 15-25MPa; S3 Piezoelectric Activation and Pre-crosslinking: A piezoelectric oscillator (frequency 1-5kHz, voltage 15-25V) is set at the die outlet to stimulate the tourmaline to release free radicals; 75-85℃ hot air tunnel treatment for 10-20s; S4 Super Rapid Freezing: -196℃ liquid nitrogen spray cooling, contact time 0.3-1.0s, cooling rate ≥500℃ / s; S5 synergistic irradiation cross-linking: Electron beam (dose 23-27 kGy) and terahertz wave (0.3-0.7 THz) synchronous irradiation is divided into three stages: Pre-crosslinking 5-8kGy → activation 10-12kGy → curing 8-10kGy; a terahertz wave generator (0.5THz) is embedded in the irradiation area to promote crosslinking uniformity; S6 Ultrasonic Assisted Biaxial Stretching: Longitudinal stretching: 105-110℃, stretching ratio 6.0-7.0, 40kHz ultrasonic assistance; Transverse stretching: 90-95℃ stretching ratio is 5.5-6.5; ultrasonic assisted stretching is used to induce the formation of a gradient crystal structure.

[0011] S7 maturation setting: 50-60℃ hot roller treatment for 30-60s, then 20-30℃ cold roller setting.

[0012] Preferably, the modified nanofibrillated lignin is prepared by the following method (a) enzyme activation treatment: disperse alkali lignin in phosphate buffer solution with pH=8-9, add laccase (20-30U / g lignin) and mediator ABTS (1-2wt%), oscillate and react for 2-4h at 45-55℃; (b) ionic liquid depolymerization: transfer the reaction product to [BMIM]Cl ionic liquid (solid-liquid ratio 1:13-17), microwave treatment (power 250-350W) for 10-20min at 170-180℃; (c) plasma grafting: place the depolymerization product in a plasma reaction chamber (Ar / O2=3-5:1, 45-55Pa), apply pulse power (peak voltage 8-12kV, frequency 4-6kHz) for 3-5min while passing in acrylic acid vapor; (d) nanofibrillation: cycle through a high-pressure homogenizer (150-180MPa) for 5-8 times to obtain nanofibers.

[0013] Preferably, the preparation method of the erucic acid amide / silica composite microspheres is as follows: mesoporous silica is immersed in molten erucic acid amide (75-85℃), vacuum adsorbed and then rapidly solidified.

[0014] Preferably, the preparation method of the modified nanohalloysite is as follows: (a) supercritical CO2 intercalation: mix halloysite and urea at a mass ratio of 1:2.5-3.5, and place in a supercritical reaction kettle (CO2 pressure 20-30MPa, 60-70℃) for 3-4h; (b) dispersion treatment: add the intercalation product to an organic solvent (solid-liquid ratio 1:8-12) and disperse thoroughly; (c) grafting reaction: slowly add polyethylene glycol-poly-lactic acid block copolymer (mass ratio to intercalation product 1-2:1) under stirring, and react for 4-6h at 45-50℃.

[0015] (d) separation and washing: after the reaction is completed, centrifugal separation is performed, deionized water and ethanol are used for multiple washing, and then drying is performed at 55-65℃ for 12h.

[0016] Preferably, the preparation method of the modified tourmaline nanotube is as follows: disperse tourmaline nanotubes in 0.1M Zn(NO3)2 solution, hydrothermal reaction for 3-5h at 175-185℃, and calcination for 1.5-2.5h at 400-500℃.

[0017] Preferably, the preparation method of the dibenzoyl peroxide microcapsule is as follows: using a multiple emulsification method (W / O / W), a PLGA dichloromethane solution (10 wt%) is used to coat the peroxide aqueous phase, and the solvent is volatilized after ultrasonic emulsification. Specifically: Inner aqueous phase: 10 wt% peroxide aqueous solution; Oil phase: 10 wt% PLGA (LA: GA = 75:25) dichloromethane solution; Primary emulsification (W / O): ultrasonic power 200-300 W, 2-4 min; Outer aqueous phase: 2 wt% PVA solution, secondary emulsification (W / O / W): 400-500 W, 2-4 min; After volatilizing the solvent, the microcapsule is obtained.

[0018] Preferably, the preparation method of the polydopamine coated chitosan is as follows: (a) Chitosan pretreatment: Chitosan with a degree of deacetylation of ≥90% is dissolved in a 0.5-1.5 wt% acetic acid solution to prepare a 1.5-2.5 wt% chitosan solution; 0.1M NaOH is added to adjust the pH to 7.0, and the purified chitosan gel is centrifuged; (b) In-situ polymerization coating of dopamine: The purified chitosan is dispersed in a Tris-HCl buffer (pH = 8.5, concentration 10 mM); dopamine hydrochloride is added (chitosan: dopamine mass ratio 1:1.5-2.0); 25℃ constant temperature oscillation reaction for 12-24h, centrifugal collection of precipitate; (c) Secondary oxidative crosslinking: The precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+ :H2O2 molar ratio 1:15-25); 40℃ reaction for 1h, dialysis purification and freeze-drying; (d) Plasma activation: 50W plasma treatment for 3min under Ar / O2 (4:1) atmosphere to obtain the final product.

[0019] Compared with the prior art, the embodiments of the present application have the following beneficial effects: The low-temperature polyolefin packaging film provided by the application reduces the generation of solid waste, reduces cost, saves energy and protects the environment, the modified lignin nanofiber is added in the inner layer to form a "reinforced-concrete" structure in the inner layer, the tensile strength is improved, the mustard amide / silica composite microspheres are added to constitute a slow-release and smooth system, the modified nanometer kaolinite is added in the middle layer to guide the orientation arrangement of molecular chains in radiation crosslinking, and the thermal shrinkage rate is improved, the modified tourmaline nanotube is added in the outer layer, the surface is loaded with ZnO quantum dots, a piezoelectric field is generated under tensile stress, peroxide is catalytically decomposed into free radicals, the crosslinking reaction starting temperature is reduced, and the shrinkage rate is improved, and the polydopamine coated chitosan is added to form a dynamic quinone-amine bond in the outer layer, which can reversibly recombine when damaged, and the puncture strength is improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The application provides a preparation method flow chart of a low-temperature polyolefin packaging film. DETAILED DESCRIPTION

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application; the description and the drawings are to be regarded as illustrative in nature and are not intended to be limiting of the application; the terminology used in the description and the claims of the application and the above description of drawings includes the terms "comprising", "having" and "including" and their variations thereof and is intended to cover the nature of the application but not all embodiments. The terms "first", "second" and the like in the description and the claims of the application and the above description of drawings are used to distinguish different objects and are not intended to describe a particular sequential order.

[0022] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is expressly understood that the embodiments described herein are merely examples from a potentially wide number of embodiments that can be claimed.

[0023] Embodiment 1 The application provides a low-temperature polyolefin packaging film, which comprises an outer layer, a middle layer and an inner layer in a three-layer co-extrusion structure, and the components of each layer are as follows in parts by weight: The inner layer comprises 45 parts of metallocene polyolefin, 15 parts of high-performance polypropylene, 15 parts of modified lignin nanofiber and 2 parts of mustard amide / silica composite microspheres. The middle layer comprises 45 parts of PCR, 10 parts of modified nanometer kaolinite and 3 parts of trimethylolpropane triacrylate. Outer layer: 50 parts of PCR, 8 parts of modified tourmaline nanotubes, 3 parts of dibenzoyl peroxide microcapsules, and 5 parts of polydopamine-coated chitosan.

[0024] In this embodiment, the total thickness of the film is preferably 20-50 μm, the thickness ratio of the outer layer: the middle layer: the inner layer is 1:3:1, the heat shrinkage rate at 65° C. is ≥25%, and the heat shrinkage rate at 100° C. is ≥55%.

[0025] Wherein, the metallocene polyolefin is preferably a metallocene linear low-density polyethylene, the high-performance polypropylene is preferably a copolymerized polypropylene, the PCR of the middle layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0026] Specifically, the modified tourmaline nanotubes are borosilicate tourmaline with surface-loaded ZnO quantum dots, a ZnO loading of 5-8 wt %, a tube diameter of 50-80 nm, and an aspect ratio of >30; The dibenzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), the capsule core accounts for 60-70%, and the particle size is 200-500nm; The modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and an interlayer spacing expanded to 1.5-2.0 nm; The modified lignin nanofiber is treated by laccase activation-plasma grafting, and the carboxyl density is ≥3.0 / nm 2 ; The thickness of the dopamine coating layer in the polydopamine-coated chitosan is 10-20 nm, and the deacetylation degree of the chitosan is ≥90%; The composite microspheres are mesoporous silica filled with erucamide, with a pore size of 2-5 nm and a drug loading of 40-50%.

[0027] The present invention also provides a method for preparing the low-temperature polyolefin packaging film, such as Figure 1 As shown, the following steps are included: S1 prepares the raw materials according to the recipe; S2 three-layer co-extrusion: The extrusion temperature of the outer layer is 170°C, the middle layer is 180°C, and the inner layer is 165°C; Die gap 1.2mm, melt pressure 15MPa; S3 Piezoelectric Activation and Pre-crosslinking: A piezoelectric oscillator (frequency 1 kHz, voltage 15 V) is set at the die outlet to stimulate the tourmaline to release free radicals; 75℃ hot air tunnel treatment for 10s; S4 Super Rapid Freezing: -196℃ liquid nitrogen spray cooling, contact time 0.3s, cooling rate ≥500℃ / s; S5 Synergistic irradiation crosslinking: Electron beam (dose 23 kGy) and terahertz wave (0.3 THz) irradiation in synchronization, in three stages: Pre-crosslinking 5 kGy→ activation 10 kGy→ curing 8 kGy; irradiation zone embedded with terahertz wave generator (0.5 THz), to promote crosslinking uniformity; S6 Ultrasonic-assisted biaxial stretching: Longitudinal stretching: 105℃, stretching ratio 6.0, 40 kHz ultrasonic wave assisted; Transverse stretching: 90℃ stretching ratio 5.5; ultrasonic wave assisted stretching is adopted to induce formation of gradient crystalline structure.

[0028] S7 Maturation setting: 50℃ hot roller treatment for 30 s, and then 20℃ cold roller setting.

[0029] The preparation method of the modified lignin nanofiber is as follows (a) Enzymatic activation treatment: disperse the alkali lignin in a phosphate buffer solution with pH = 8, add laccase (20 U / g of lignin) and mediator ABTS (1 wt%), and oscillate at 45℃ for 2 h; (b) Ionic liquid depolymerization: transfer the reaction product to [BMIM]Cl ionic liquid (solid-liquid ratio 1:13), and microwave treat (power 250 W) at 170℃ for 10 min; (c) Plasma grafting: place the depolymerization product in a plasma reaction chamber (Ar / O2=3:1, 45 Pa), apply a pulse power (peak voltage 8 kV, frequency 4 kHz) for 3 min, and simultaneously introduce acrylic acid vapor; (d) Nanofibrillation: cycle treatment 5 times by a high-pressure homogenizer (150 MPa) to obtain nanofibers.

[0030] Further, the preparation method of the erucic acid amide / silicon dioxide composite microsphere is as follows: mesoporous silicon dioxide is immersed in molten erucic acid amide (75℃), vacuum adsorbed, and then rapidly solidified.

[0031] Still further, the preparation method of the modified nanometer kaolinite is as follows: (a) Supercritical CO2 intercalation: mix kaolinite and urea at a mass ratio of 1:2.5, and place in a supercritical reaction kettle (CO2 pressure 20 MPa, 60℃) for 3 h; (b) Dispersion treatment: add the intercalation product to an organic solvent (solid-liquid ratio 1:8) and disperse thoroughly; (c) Grafting reaction: slowly add polyethylene glycol-poly lactic acid block copolymer (mass ratio of 1:1 with the intercalation product) under stirring, and react at 45℃ for 4 h.

[0032] (d) Separation and washing: After the reaction, the product was centrifuged, washed with deionized water and ethanol several times, and then dried at 55°C for 12 h.

[0033] In a specific implementation, the preparation method of the modified tourmaline nanotubes is as follows: the tourmaline nanotubes are dispersed in a 0.1M Zn(NO3)2 solution, subjected to a hydrothermal reaction at 175°C for 3 hours, and calcined at 400°C for 1.5 hours.

[0034] Preferably, the preparation method of the dibenzoyl peroxide microcapsules is as follows: using a double emulsification method (W / O / W), PLGA dichloromethane solution (10wt%) is coated with a peroxide aqueous phase, and the solvent is volatilized after ultrasonic emulsification. Specifically: Internal aqueous phase: 10wt% peroxide aqueous solution; Oil phase: 10 wt% PLGA (LA:GA=75:25) in dichloromethane solution; Primary emulsification (W / O): ultrasonic power 200 W, 2 min; External aqueous phase: 2 wt% PVA solution, secondary emulsification (W / O / W): 400 W, 2 min; After evaporating the solvent, microcapsules are obtained.

[0035] Preferably, the preparation method of the polydopamine-coated chitosan is as follows: (a) Chitosan pretreatment: Chitosan with a degree of deacetylation ≥90% was dissolved in 0.5 wt % acetic acid solution to prepare a 1.5 wt % chitosan solution. 0.1 M NaOH was added to adjust the pH to 7.0, and the chitosan gel was purified by centrifugation. (b) Dopamine in situ polymerization coating: Purified chitosan was dispersed in Tris-HCl buffer (pH = 8.5, concentration 10 mM); dopamine hydrochloride was added (chitosan:dopamine mass ratio 1:1.5); the reaction was kept constant at 25°C with shaking for 12 h, and the precipitate was collected by centrifugation. (c) Secondary oxidation crosslinking: The precipitate was immersed in 0.01M CuSO4 / H2O2 solution (Cu 2+ :H2O2 molar ratio 1:15); react at 40°C for 1 h, dialyze and lyophilize; (d) Plasma activation: The final product was obtained by plasma treatment at 50 W for 3 min in an Ar / O2 (4:1) atmosphere.

[0036] Example 2 The embodiment of the present invention provides a low-temperature polyolefin packaging film, comprising a three-layer co-extruded structure of an outer layer, a middle layer, and an inner layer, wherein the components of each layer are as follows in parts by weight: Inner layer: 48 parts of metallocene polyolefin, 17 parts of high-performance polypropylene, 16 parts of modified lignin nanofiber, 2.2 parts of erucamide / silica composite microspheres; Middle layer: PCR 47 parts, modified nano-kaolinite 11 parts, trimethylolpropane triacrylate 3.3 parts; Outer layer: 52 parts of PCR, 9 parts of modified tourmaline nanotubes, 3.5 parts of dibenzoyl peroxide microcapsules, and 6 parts of polydopamine-coated chitosan.

[0037] In this embodiment, the total thickness of the film is preferably 20-50 μm, the thickness ratio of the outer layer: the middle layer: the inner layer is 1:3:1, the heat shrinkage rate at 65° C. is ≥25%, and the heat shrinkage rate at 100° C. is ≥55%.

[0038] Wherein, the metallocene polyolefin is preferably a metallocene linear low-density polyethylene, the high-performance polypropylene is preferably a copolymerized polypropylene, the PCR of the middle layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0039] Specifically, the modified tourmaline nanotubes are borosilicate tourmaline with surface-loaded ZnO quantum dots, a ZnO loading of 5-8 wt %, a tube diameter of 50-80 nm, and an aspect ratio of >30; The dibenzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), the capsule core accounts for 60-70%, and the particle size is 200-500nm; The modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and an interlayer spacing expanded to 1.5-2.0 nm; The modified lignin nanofiber is treated by laccase activation-plasma grafting, and the carboxyl density is ≥3.0 / nm 2 ; The thickness of the dopamine coating layer in the polydopamine-coated chitosan is 10-20 nm, and the deacetylation degree of the chitosan is ≥90%; The composite microspheres are mesoporous silica filled with erucamide, with a pore size of 2-5 nm and a drug loading of 40-50%.

[0040] The present invention also provides a method for preparing the low-temperature polyolefin packaging film, such as Figure 1 As shown, the following steps are included: S1 prepares the raw materials according to the recipe; S2 three-layer co-extrusion: The extrusion temperature of the outer layer is 170°C, the middle layer is 180°C, and the inner layer is 165°C; Die gap 1.2mm, melt pressure 15MPa; S3 Piezoelectric Activation and Pre-crosslinking: A piezoelectric oscillator (frequency 1 kHz, voltage 15 V) is set at the die outlet to stimulate the tourmaline to release free radicals; 75℃ hot air tunnel treatment for 10s; S4 Super Rapid Freezing: -196℃ liquid nitrogen spray cooling, contact time 0.3s, cooling rate ≥500℃ / s; S5 synergistic irradiation cross-linking: Electron beam (dose 23kGy) and terahertz wave (0.3THz) synchronous irradiation is divided into three stages: Pre-crosslinking 5kGy → activation 10kGy → curing 8kGy; a terahertz wave generator (0.5THz) is embedded in the irradiation area to promote crosslinking uniformity; S6 Ultrasonic Assisted Biaxial Stretching: Longitudinal stretching: 105°C, stretch ratio 6.0, 40kHz ultrasonic assistance; Transverse stretching: 90°C stretching ratio is 5.5; ultrasonic assisted stretching is used to induce the formation of a gradient crystal structure.

[0041] S7 maturation and setting: The product was treated with a hot roller at 50℃ for 30s and then shaped with a cold roller at 20℃.

[0042] The preparation method of the modified lignin nanofiber is as follows: (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH 8, laccase (20 U / g lignin) and mediator ABTS (1 wt%) were added, and the reaction was shaken at 45 °C for 2 h. (b) Ionic liquid depolymerization: The reaction product was transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:13) and microwave-treated at 170 °C (power 250 W) for 10 min; (c) Plasma grafting: The depolymerized product was placed in a plasma reaction chamber (Ar / O2 = 3:1, 45 Pa) and treated with a pulsed power supply (peak voltage 8 kV, frequency 4 kHz) for 3 min while introducing acrylic acid vapor; (d) Nanofibrillation: The nanofibers were obtained by 5 cycles of high-pressure homogenization (150 MPa).

[0043] Furthermore, the preparation method of the erucamide / silica composite microspheres is as follows: mesoporous silica is impregnated with molten erucamide (75° C.), and then vacuum-adsorbed and then rapidly cooled and solidified.

[0044] Furthermore, the preparation method of the modified nano-kaolinite is as follows: (a) Supercritical CO2 intercalation: Kaolinite and urea were mixed in a mass ratio of 1:2.5 and placed in a supercritical reactor (CO2 pressure 20 MPa, 60°C) for 3 h; (b) dispersion treatment: the intercalation product was added to an organic solvent (solid-liquid ratio 1:8) and dispersed thoroughly; (c) grafting reaction: under stirring, polyethylene glycol-poly lactic acid block copolymer (mass ratio 1:1 with the intercalation product) was slowly added, and reacted at 45℃ for 4h.

[0045] (d) separation and washing: after the reaction, centrifugal separation was performed, and deionized water and ethanol were used for washing multiple times, followed by drying at 55℃ for 12h.

[0046] In a specific implementation, the preparation method of the modified tourmaline nanotube is as follows: the tourmaline nanotube is dispersed in a 0.1M Zn(NO3)2 solution, hydrothermal reaction is performed at 175℃ for 3h, and calcination is performed at 400℃ for 1.5h.

[0047] Preferably, the preparation method of the dibenzoyl peroxide microcapsule is as follows: a multiple emulsification method (W / O / W) is used, a PLGA dichloromethane solution (10wt%) is used to coat the peroxide aqueous phase, the solvent is volatilized after ultrasonic emulsification, and specifically: inner aqueous phase: 10wt% peroxide aqueous solution; oil phase: 10wt% PLGA (LA:GA=75:25) dichloromethane solution; primary emulsification (W / O): ultrasonic power 200W, 2min; outer aqueous phase: 2wt% PVA solution, secondary emulsification (W / O / W): 400W, 2min; After the solvent is volatilized, the microcapsule is obtained.

[0048] Preferably, the preparation method of the polydopamine-coated chitosan is as follows: (a) chitosan pretreatment: chitosan with a degree of deacetylation of ≥90% is dissolved in a 0.5wt% acetic acid solution to prepare a 1.5wt% chitosan solution; 0.1M NaOH is added to adjust the pH to 7.0, and the purified chitosan gel is separated by centrifugation; (b) in-situ polymerization coating of dopamine: the purified chitosan is dispersed in a Tris-HCl buffer solution (pH=8.5, concentration 10mM); dopamine hydrochloride is added (chitosan:dopamine mass ratio 1:1.5); 25℃ constant temperature oscillation reaction is performed for 12h, and the precipitate is collected by centrifugation; (c) secondary oxidation crosslinking: the precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+ :H2O2 molar ratio 1:15); 40℃ reaction is performed for 1h, and the product is purified by dialysis and freeze-dried; (d) plasma activation: 50W plasma treatment is performed for 3min under an Ar / O2 (4:1) atmosphere to obtain the final product.

[0049] Example 3 The low-temperature polyolefin packaging film provided by the embodiment of the present application comprises a three-layer co-extrusion structure of an outer layer, an intermediate layer and an inner layer, and the components of each layer are as follows in parts by weight: The inner layer comprises 50 parts of metallocene polyolefin, 20 parts of high-performance polypropylene, 17.5 parts of modified lignin nanofiber and 2.5 parts of erucic acid amide / silica composite microspheres. The intermediate layer comprises 50 parts of PCR, 12.5 parts of modified nano-kaolin and 3.5 parts of trimethylolpropane triacrylate. The outer layer comprises 55 parts of PCR, 10 parts of modified tourmaline nanotube, 4 parts of dibenzoyl peroxide microcapsule and 6.5 parts of polydopamine-coated chitosan.

[0050] In the embodiment, the total thickness of the film is preferably 20-50 μm, the thickness ratio of the outer layer: intermediate layer: inner layer is 1:4:1, the thermal shrinkage rate at 65°C is ≥25%, and the thermal shrinkage rate at 100°C is ≥55%.

[0051] Preferably, the metallocene polyolefin is metallocene linear low-density polyethylene, the high-performance polypropylene is copolymerized polypropylene, the PCR of the intermediate layer is LLDPE-PCR, and the PCR of the outer layer is LDPE-PCR.

[0052] Specifically, the modified tourmaline nanotube is a borosilicate tourmaline loaded with ZnO quantum dots on the surface, the loading amount of ZnO is 5-8 wt%, the tube diameter is 50-80 nm, and the aspect ratio is >30. The wall material of the dibenzoyl peroxide microcapsule is polylactic acid-hydroxyacetic acid copolymer (PLGA), the proportion of the capsule core is 60-70%, and the particle size is 200-500 nm. The modified nano-kaolin is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, the grafting rate is 15-25%, and the interlayer spacing is expanded to 1.5-2.0 nm. The modified lignin nanofiber is treated by laccase activation-plasma grafting, and the carboxyl density is ≥3.0 / nm 2 ; The thickness of the dopamine coating layer in the polydopamine-coated chitosan is 10-20 nm, and the deacetylation degree of chitosan is ≥90%. The composite microspheres are erucic acid amide filled mesoporous silica with a pore size of 2-5 nm and a drug loading amount of 40-50%.

[0053] The present application also provides a preparation method of the low-temperature polyolefin packaging film, as shown in Figure 1 The preparation method comprises the following steps: S1 preparing each raw material according to the formula; S2 three-layer co-extrusion: Outer layer extrusion temperature 180℃, middle layer 190℃, inner layer 175℃; Die gap 1.5mm, melt pressure 20MPa; S3 Piezoelectric activation and pre-crosslinking: A piezoelectric oscillator (frequency 3kHz, voltage 20V) was set at the die exit to excite the tourmaline to release free radicals; 80℃ hot air tunnel treatment for 15s; S4 Ultra-rapid freezing: Liquid nitrogen spray cooling at -196℃, contact time 0.6s, cooling rate ≥500℃ / s; S5 Synergistic irradiation crosslinking: Synchronous irradiation of electron beam (dose 25kGy) and terahertz wave (0.5THz) in three stages: Pre-crosslinking 6.5kGy→activation 11kGy→curing 9kGy; the irradiation zone is embedded with a terahertz wave generator (0.5THz) to promote crosslinking uniformity; S6 Ultrasonic-assisted biaxial stretching: Longitudinal stretching: 108℃, stretching ratio 6.5, 40kHz ultrasonic wave assistance; Transverse stretching: 92℃ stretching ratio 6; ultrasonic-assisted stretching is adopted to induce the formation of gradient crystalline structure.

[0054] S7 Maturation setting: 50-60℃ hot roller treatment for 45s, followed by 25℃ cold roller setting.

[0055] The preparation method of the modified lignin nanofiber is as follows (a) Enzymatic activation treatment: disperse the alkali lignin in a phosphate buffer solution with pH=8.5, add laccase (25U / g of lignin) and mediator ABTS (1.5wt%), and perform oscillation reaction at 50℃ for 3h; (b) Ionic liquid depolymerization: transfer the reaction product to [BMIM]Cl ionic liquid (solid-liquid ratio 1:15), and perform microwave treatment (power 300W) at 175℃ for 15min; (c) Plasma grafting: place the depolymerization product in a plasma reaction chamber (Ar / O2=4:1, 50Pa), apply a pulse power supply (peak voltage 10kV, frequency 5kHz) for treatment for 4min, and simultaneously introduce acrylic acid vapor; (d) Nanofibrillation: perform cyclic treatment for 6 times by a high-pressure homogenizer (165MPa) to obtain nanofibers.

[0056] Further, the preparation method of the erucic acid amide / silica composite microsphere is as follows: immerse mesoporous silica in molten erucic acid amide (80℃), perform vacuum adsorption, and then quench and solidify.

[0057] Further, the preparation method of the modified nanometer kaolinite is as follows: (a) Supercritical CO2 intercalation: kaolinite is mixed with urea at a mass ratio of 1:3, and is placed in a supercritical reaction kettle (CO2 pressure 25 MPa, 65°C) for 3.5 h; (b) Dispersion treatment: the intercalation product is added to an organic solvent (solid-liquid ratio 1:10) and is fully dispersed; (c) Grafting reaction: under stirring, polyethylene glycol-poly lactic acid block copolymer is slowly added (mass ratio of 1.5:1 with the intercalation product), and is reacted at 48°C for 5 h.

[0058] (d) Separation and washing: after the reaction is completed, centrifugal separation is performed, deionized water and ethanol are used for multiple times of washing, and then drying is performed at 60°C for 12 h.

[0059] In a specific implementation, the preparation method of the modified tourmaline nanotube is as follows: the tourmaline nanotube is dispersed in a 0.1M Zn(NO3)2 solution, hydrothermal reaction is performed at 180°C for 4 h, and calcination is performed at 450°C for 2 h.

[0060] Preferably, the preparation method of the microcapsule of dibenzoyl peroxide is as follows: a multiple emulsification method (W / O / W) is used, a PLGA dichloromethane solution (10wt%) is used to coat a peroxide aqueous phase, the solvent is volatilized after ultrasonic emulsification, and specifically: Inner aqueous phase: 10wt% peroxide aqueous solution; Oil phase: 10wt% PLGA (LA:GA=75:25) dichloromethane solution; Primary emulsification (W / O): ultrasonic power 250W, 3min; Outer aqueous phase: 2wt% PVA solution, secondary emulsification (W / O / W): 450W, 3min; The microcapsule is obtained after the solvent is volatilized.

[0061] Preferably, the preparation method of the polydopamine-coated chitosan is as follows: (a) Chitosan pretreatment: chitosan with a degree of deacetylation of ≥90% is dissolved in a 1wt% acetic acid solution to prepare a 2wt% chitosan solution; 0.1M NaOH is added to adjust the pH to 7.0, and a purified chitosan gel is separated by centrifugation; (b) Dopamine in-situ polymerization coating: the purified chitosan is dispersed in a Tris-HCl buffer solution (pH=8.5, concentration 10mM); dopamine hydrochloride is added (mass ratio of chitosan:dopamine 1:1.75); 25°C constant temperature oscillation reaction is performed for 18h, and the precipitate is collected by centrifugation; (c) Secondary oxidative crosslinking: the precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+: H2O2 molar ratio 1:20); 40℃ for 1h, freeze-drying after dialysis purification; (d) Plasma activation: 50W plasma treatment for 3min under Ar / O2 (4:1) atmosphere to obtain the final product.

[0062] Example 4 The low-temperature polyolefin packaging film provided by the embodiment of the application comprises an outer layer, an intermediate layer and an inner layer in a three-layer co-extrusion structure, and the components of each layer are as follows in parts by weight: The inner layer comprises 53 parts of metallocene polyolefin, 22 parts of high-performance polypropylene, 19 parts of modified lignin nanofiber and 2.8 parts of erucamide / silica composite microspheres. The intermediate layer comprises 52 parts of PCR, 14 parts of modified nanometer kaolinite and 3.8 parts of trimethylolpropane triacrylate. The outer layer comprises 58 parts of PCR, 11 parts of modified tourmaline nanotube, 4.5 parts of dibenzoyl peroxide microcapsule and 7 parts of polydopamine-coated chitosan.

[0063] In the embodiment, the total thickness of the film is preferably 20-50μm, the thickness ratio of the outer layer: intermediate layer: inner layer is 1:5:1, the heat shrinkage rate at 65℃ is ≥25%, and the heat shrinkage rate at 100℃ is ≥55%.

[0064] Preferably, the metallocene polyolefin is metallocene linear low-density polyethylene, the high-performance polypropylene is copolymerized polypropylene, the PCR of the intermediate layer is LLDPE-PCR, and the PCR of the outer layer is LDPE-PCR.

[0065] Specifically, the modified tourmaline nanotube is a borosilicate tourmaline loaded with ZnO quantum dots on the surface, the loading amount of ZnO is 5-8wt%, the tube diameter is 50-80nm, and the aspect ratio is >30. The wall material of the dibenzoyl peroxide microcapsule is polylactic acid-hydroxyacetic acid copolymer (PLGA), the proportion of the capsule core is 60-70%, and the particle size is 200-500nm. The modified nanometer kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, the grafting rate is 15-25%, and the interlayer spacing is expanded to 1.5-2.0nm. The modified lignin nanofiber is treated by laccase activation-plasma grafting, and the carboxyl density is ≥3.0 / nm 2 ; The thickness of the dopamine coating layer in the polydopamine-coated chitosan is 10-20nm, and the deacetylation degree of chitosan is ≥90%. The composite microspheres are erucamide-filled mesoporous silica with a pore size of 2-5nm and a drug loading amount of 40-50%.

[0066] The present invention also provides a method for preparing the low-temperature polyolefin packaging film, such as Figure 1 As shown, the following steps are included: S1 prepares the raw materials according to the recipe; S2 three-layer co-extrusion: The extrusion temperature of the outer layer is 190°C, the middle layer is 200°C, and the inner layer is 185°C; Die gap 1.8mm, melt pressure 25MPa; S3 Piezoelectric Activation and Pre-crosslinking: A piezoelectric oscillator (frequency 5 kHz, voltage 25 V) is set at the die outlet to stimulate the tourmaline to release free radicals; 85℃ hot air tunnel treatment for 20s; S4 Super Rapid Freezing: -196℃ liquid nitrogen spray cooling, contact time 1.0s, cooling rate ≥500℃ / s; S5 synergistic irradiation cross-linking: Electron beam (dose 27 kGy) and terahertz wave (0.7 THz) synchronous irradiation is divided into three stages: Pre-crosslinking 8kGy → activation 12kGy → curing 10kGy; a terahertz wave generator (0.5THz) is embedded in the irradiation area to promote crosslinking uniformity; S6 Ultrasonic Assisted Biaxial Stretching: Longitudinal stretching: 110°C, stretch ratio 7.0, 40kHz ultrasonic assistance; Transverse stretching: 95℃ stretching ratio is 6.5; ultrasonic assisted stretching is used to induce the formation of a gradient crystal structure.

[0067] S7 maturation and setting: The product was treated with a hot roller at 60℃ for 60s and then shaped with a cold roller at 30℃.

[0068] The preparation method of the modified lignin nanofiber is as follows: (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH 9, laccase (30 U / g lignin) and mediator ABTS (2 wt%) were added, and the reaction was shaken at 55 °C for 4 h. (b) Ionic liquid depolymerization: The reaction product was transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:17) and microwave-treated at 180 °C (power 350 W) for 20 min. (c) Plasma grafting: The depolymerized product was placed in a plasma reaction chamber (Ar / O2 = 5:1, 55 Pa) and treated with a pulsed power supply (peak voltage 12 kV, frequency 6 kHz) for 5 min while introducing acrylic acid vapor. (d) Nanofibrillation: The nanofibers were obtained by 8 cycles of treatment in a high-pressure homogenizer (180 MPa).

[0069] Further, the preparation method of the erucic acid amide / silica composite microspheres is as follows: mesoporous silica is immersed in molten erucic acid amide (85℃), vacuum adsorption, and then rapid cooling and solidification.

[0070] Still further, the preparation method of the modified nanometer kaolinite is as follows: (a) Supercritical CO2 intercalation: kaolinite is mixed with urea at a mass ratio of 1:3.5, and placed in a supercritical reaction kettle (CO2 pressure 30 MPa, 70℃) for 4h; (b) Dispersion treatment: the intercalation product is added to an organic solvent (solid-liquid ratio 1:12) and dispersed thoroughly; (c) Grafting reaction: under stirring, polyethylene glycol-poly lactic acid block copolymer (mass ratio of 2:1 to the intercalation product) is slowly added, and reacted at 50℃ for 6h.

[0071] (d) Separation and washing: after the reaction is completed, centrifugal separation is performed, deionized water and ethanol are used for multiple washing, and then drying is performed at 65℃ for 12h.

[0072] In specific implementation, the preparation method of the modified tourmaline nanotube is as follows: the tourmaline nanotube is dispersed in 0.1M Zn(NO3)2 solution, hydrothermal reaction is performed at 185℃ for 3-5h, and calcination is performed at 500℃ for 2.5h.

[0073] Preferably, the preparation method of the dibenzoyl peroxide microcapsule is as follows: using multiple emulsification method (W / O / W), PLGA dichloromethane solution (10wt%) is used to coat the peroxide water phase, the solvent is volatilized after ultrasonic emulsification, and specifically: Inner water phase: 10wt% peroxide aqueous solution; Oil phase: 10wt% PLGA (LA:GA=75:25) dichloromethane solution; Primary emulsification (W / O): ultrasonic power 300W, 4min; Outer water phase: 2wt% PVA solution, secondary emulsification (W / O / W): 500W, 4min; After volatilizing the solvent, the microcapsule is obtained.

[0074] Preferably, the preparation method of the polydopamine coated chitosan is as follows: (a) Chitosan pretreatment: chitosan with a degree of deacetylation of ≥90% is dissolved in 1.5wt% acetic acid solution to prepare a 2.5wt% chitosan solution; 0.1M NaOH is added to adjust the pH to 7.0, and the purified chitosan gel is separated by centrifugation; (b) Dopamine in situ polymerization coating: disperse purified chitosan in Tris-HCl buffer (pH = 8.5, concentration 10 mM); add dopamine hydrochloride (mass ratio of chitosan:dopamine 1:2.0); constant temperature oscillation reaction at 25℃ for 24h, centrifugal collection of precipitate; (c) Secondary oxidative crosslinking: immerse the precipitate in 0.01M CuSO4 / H2O2 solution (Cu 2+ : H2O2 molar ratio 1:25); 40℃ reaction for 1h, freeze-drying after dialysis purification; (d) Plasma activation: 50W plasma treatment for 3min under Ar / O2 (4:1) atmosphere to obtain the final product.

[0075] Example 5 The low-temperature polyolefin packaging film provided by the embodiment of the present application comprises a three-layer co-extrusion structure of an outer layer, an intermediate layer and an inner layer, and the components of each layer are as follows in parts by weight: The inner layer comprises 55 parts of metallocene polyolefin, 25 parts of high-performance polypropylene, 20 parts of modified lignin nanofiber and 3 parts of erucic acid amide / silica composite microspheres. The intermediate layer comprises 55 parts of PCR, 15 parts of modified nano-kaolin and 4 parts of trimethylolpropane triacrylate. The outer layer comprises 60 parts of PCR, 12 parts of modified tourmaline nanotube, 3-5 parts of dibenzoyl peroxide microcapsule and 8 parts of polydopamine-coated chitosan.

[0076] In the embodiment, the total thickness of the film is preferably 20-50μm, the thickness ratio of the outer layer: intermediate layer: inner layer is 1:5:1, the heat shrinkage rate at 65℃ is ≥25%, and the heat shrinkage rate at 100℃ is ≥55%.

[0077] Preferably, the metallocene polyolefin is metallocene linear low-density polyethylene, the high-performance polypropylene is preferably copolymerized polypropylene, the PCR of the intermediate layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0078] Specifically, the modified tourmaline nanotube is a borosilicate tourmaline with surface-loaded ZnO quantum dots, the loading amount of ZnO is 5-8wt%, the tube diameter is 50-80nm, and the aspect ratio is >30. The wall material of the dibenzoyl peroxide microcapsule is polylactic acid-hydroxyacetic acid copolymer (PLGA), the core proportion is 60-70%, and the particle size is 200-500nm. The modified nano-kaolin is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, the grafting rate is 15-25%, and the interlayer spacing is expanded to 1.5-2.0nm. The modified lignin nanofiber is treated by laccase activation-plasma grafting, and the carboxyl density is ≥3.0 / nm2 ; The thickness of the dopamine coating layer in the polydopamine-coated chitosan is 10-20 nm, and the deacetylation degree of the chitosan is ≥90%; The composite microspheres are mesoporous silica filled with erucamide, with a pore size of 2-5 nm and a drug loading of 40-50%.

[0079] The present invention also provides a method for preparing the low-temperature polyolefin packaging film, such as Figure 1 As shown, the following steps are included: S1 prepares the raw materials according to the recipe; S2 three-layer co-extrusion: The extrusion temperature of the outer layer is 190°C, the middle layer is 200°C, and the inner layer is 185°C; Die gap 1.8mm, melt pressure 25MPa; S3 Piezoelectric Activation and Pre-crosslinking: A piezoelectric oscillator (frequency 5 kHz, voltage 25 V) is set at the die outlet to stimulate the tourmaline to release free radicals; 85℃ hot air tunnel treatment for 20s; S4 Super Rapid Freezing: -196℃ liquid nitrogen spray cooling, contact time 1.0s, cooling rate ≥500℃ / s; S5 synergistic irradiation cross-linking: Electron beam (dose 27 kGy) and terahertz wave (0.7 THz) synchronous irradiation is divided into three stages: Pre-crosslinking 8kGy → activation 12kGy → curing 10kGy; a terahertz wave generator (0.5THz) is embedded in the irradiation area to promote crosslinking uniformity; S6 Ultrasonic Assisted Biaxial Stretching: Longitudinal stretching: 110°C, stretch ratio 7.0, 40kHz ultrasonic assistance; Transverse stretching: 95℃ stretching ratio is 6.5; ultrasonic assisted stretching is used to induce the formation of a gradient crystal structure.

[0080] S7 maturation and setting: The product was treated with a hot roller at 60℃ for 60s and then shaped with a cold roller at 30℃.

[0081] The preparation method of the modified lignin nanofiber is as follows: (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH 9, laccase (30 U / g lignin) and mediator ABTS (2 wt%) were added, and the reaction was shaken at 55 °C for 4 h. (b) Ionic liquid depolymerization: The reaction product was transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:17) and microwave-treated at 180 °C (power 350 W) for 20 min. (c) Plasma grafting: The depolymerization product was placed in a plasma reaction chamber (Ar / O2=5:1, 55 Pa), and a pulsed power source (peak voltage 12 kV, frequency 6 kHz) was applied for 5 min while propylene acid vapor was introduced; (d) Nanofibrillation: The product was treated by a high-pressure homogenizer (180 MPa) for 8 cycles to obtain nanofibers.

[0082] Further, the preparation method of the erucic acid amide / silica composite microspheres is as follows: mesoporous silica is immersed in molten erucic acid amide (85°C), vacuum adsorbed, and then rapidly cooled and solidified.

[0083] Still further, the preparation method of the modified nanometer kaolinite is as follows: (a) Supercritical CO2 intercalation: kaolinite and urea are mixed at a mass ratio of 1:3.5, and placed in a supercritical reaction kettle (CO2 pressure 30 MPa, 70°C) for 4 h; (b) Dispersion treatment: the intercalation product is added to an organic solvent (solid-liquid ratio 1:12) and dispersed thoroughly; (c) Grafting reaction: under stirring, polyethylene glycol-poly lactic acid block copolymer (mass ratio of 2:1 to the intercalation product) is slowly added, and reacted at 50°C for 6 h.

[0084] (d) Separation and washing: after the reaction is completed, centrifugal separation is performed, deionized water and ethanol are used for multiple washing, and then drying is performed at 65°C for 12 h.

[0085] In specific implementation, the preparation method of the modified tourmaline nanotube is as follows: the tourmaline nanotube is dispersed in a 0.1M Zn(NO3)2 solution, hydrothermal reaction is performed at 185°C for 3-5 h, and calcination is performed at 500°C for 2.5 h.

[0086] Preferably, the preparation method of the dibenzoyl peroxide microcapsule is as follows: a multiple emulsification method (W / O / W) is used, a PLGA dichloromethane solution (10wt%) is used to coat the peroxide water phase, the solvent is volatilized after ultrasonic emulsification, and specifically: Inner water phase: 10wt% peroxide aqueous solution; Oil phase: 10wt% PLGA (LA:GA=75:25) dichloromethane solution; Primary emulsification (W / O): ultrasonic power 300W, 4min; Outer water phase: 2wt% PVA solution, secondary emulsification (W / O / W): 500W, 4min; The microcapsule is obtained after volatilization of the solvent.

[0087] Preferably, the preparation method of the polydopamine-coated chitosan is as follows: (a) Chitosan pretreatment: Chitosan with a degree of deacetylation of ≥90% was dissolved in 1.5 wt% acetic acid solution to form a 2.5 wt% chitosan solution; 0.1 M NaOH was added to adjust the pH to 7.0, and the purified chitosan gel was centrifuged; (b) In-situ polymerization of dopamine coating: The purified chitosan was dispersed in Tris-HCl buffer (pH = 8.5, concentration 10 mM); dopamine hydrochloride was added (chitosan: dopamine mass ratio 1:2.0); 25°C constant temperature oscillation reaction for 24 h, and the precipitate was collected by centrifugation; (c) Secondary oxidative crosslinking: The precipitate was immersed in a 0.01 M CuSO4 / H2O2 solution (Cu 2+ :H2O2 molar ratio 1:25); 40°C reaction for 1 h, dialysis purification, and freeze-drying; (d) Plasma activation: 50W plasma treatment for 3 min under Ar / O2 (4:1) atmosphere to obtain the final product.

[0088] Comparative Example 1: The difference from Example 3 is that the inner layer removes modified lignin nanofiber.

[0089] Comparative Example 2: The difference from Example 3 is that the middle layer removes modified nanokingite.

[0090] Comparative Example 3: The difference from Example 3 is that the outer layer removes modified tourmaline nanotube.

[0091] Comparative Example 4: The difference from Example 3 is that the outer layer removes polydopamine-coated chitosan.

[0092] Comparative Example 5: The difference from Example 3 is that the preparation process cancels the S3 piezoelectric activation step.

[0093] Comparative Example 6: The difference from Example 3 is that the preparation process cancels S4 ultra-rapid freezing and replaces it with conventional water cooling (cooling rate 50°C / s).

[0094] Comparative Example 7: The difference from Example 3 is that the outer layer uses dicumyl peroxide (DCP) instead of dibenzoyl peroxide microcapsules.

[0095] Performance test Test method and standard Thermal shrinkage (GB / T 13519-2016): Test the shrinkage (MD / TD average value) at 65°C (10 min), 100°C (30 s), and 130°C (30 s), respectively; Mechanical properties (ASTM D882): Tensile strength (MPa), elongation at break (%), tensile rate 500 mm / min; Puncture strength (ASTM F1306): 2 mm diameter puncture head, speed 50 mm / min (unit: N / mm); Elongation at break (GB / T 1040.3-2006).

[0096] The mechanical property test results are as follows Table 1: Table 1

[0097] From the above results, it can be seen that the packaging film prepared by the application has good mechanical properties.

[0098] The heat shrinkage performance test results are as follows Table 2: Table 2

[0099] From the above results, it can be seen that the packaging film prepared by the application has good heat shrinkage performance, especially with low temperature shrinkage advantage.

[0100] It should be noted that for the foregoing embodiments, in order to simply describe, they are all expressed as a series of action combinations, but those skilled in the art should know that the application is not limited by the order of the described actions, because according to the application, certain steps can be performed in other order or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification all belong to preferred embodiments, and the actions and modules involved are not necessarily necessary for the application.

[0101] The above examples are only used to illustrate the technical solutions of the application, and do not limit the protection scope of the application. Obviously, the described embodiments are only some of the embodiments of the application, not all the embodiments. Based on these embodiments, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope to be protected by the application.

Claims

1. A low-temperature polyolefin packaging film, characterized in that: It includes a three-layer co-extrusion structure of outer layer, middle layer and inner layer. The components of each layer are calculated by weight: Inner layer: 45-55 parts of metallocene polyolefin, 15-25 parts of high-performance polypropylene, 15-20 parts of modified lignin nanofiber, 2-3 parts of erucamide / silica composite microspheres Middle layer: PCR 45-55 parts, modified nano-kaolinite 10-15 parts, trimethylolpropane triacrylate 3-4 parts; Outer layer: 50-60 parts of PCR, 8-12 parts of modified tourmaline nanotubes, 3-5 parts of dibenzoyl peroxide microcapsules, and 5-8 parts of polydopamine-coated chitosan.

2. The low-temperature polyolefin packaging film according to claim 1, characterized in that: The metallocene polyolefin is a metallocene linear low-density polyethylene, the high-performance polypropylene is a copolymerized polypropylene, the PCR of the middle layer is LLDPE-PCR, and the PCR of the outer layer is LDPE-PCR.

3. The low-temperature polyolefin packaging film according to claim 1, characterized in that: The modified tourmaline nanotubes are borosilicate tourmaline with surface-loaded ZnO quantum dots, a ZnO loading of 5-8 wt %, a tube diameter of 50-80 nm, and an aspect ratio of >30; The dibenzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer, the capsule core accounts for 60-70%, and the particle size is 200-500nm.

4. The low-temperature polyolefin packaging film according to claim 1, characterized in that: The modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid block copolymer, with a grafting rate of 15-25% and an interlayer spacing expanded to 1.5-2.0 nm; The modified lignin nanofiber is acetylated alkali lignin with an acetylation degree of 0.5-0.8 and a fiber diameter of 80-120 nm.

5. The low-temperature polyolefin packaging film according to claim 1, characterized in that: The thickness of the dopamine coating layer in the polydopamine-coated chitosan is 10-20 nm, and the deacetylation degree of the chitosan is ≥90%; The composite microspheres are mesoporous silica filled with erucamide, with a pore size of 2-5 nm and a drug loading of 40-50%.

6. The method for preparing a low-temperature polyolefin packaging film according to any one of claims 1 to 5, characterized in that: The steps include: S1 prepares the raw materials according to the recipe; S2 three-layer co-extrusion; S3 Piezoelectric Activation and Pre-crosslinking: A piezoelectric oscillator is set at the die outlet and treated in a hot air tunnel at 75-85°C for 10-20s; S4 super rapid freezing; S5 synergistic irradiation cross-linking: Synchronous irradiation of electrons and terahertz waves; S6 ultrasound-assisted biaxial stretching; S7 maturation and setting.

7. The method for preparing the low-temperature polyolefin packaging film according to claim 6, wherein: The preparation method of the modified lignin nanofiber is as follows (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH 8-9, laccase and mediator ABTS were added, and the reaction was shaken at 45-55°C for 2-4 h; (b) Ionic liquid depolymerization: The reaction product was transferred to [BMIM]Cl ionic liquid and microwave-treated at 170-180 °C for 10-20 min; (c) Plasma grafting: The depolymerized product is placed in a plasma reaction chamber and pulsed with power for 3–5 min while simultaneously introducing acrylic acid vapor. (d) Nanofibrillation: The nanofibers were obtained by cyclically treating the nanofibers with a high-pressure homogenizer for 5-8 times.

8. The method for preparing the low-temperature polyolefin packaging film according to claim 6, wherein: The preparation method of the modified nano-kaolinite is as follows: (a) Supercritical CO2 intercalation: Kaolinite and urea were mixed in a mass ratio of 1:2.5-3.5 and placed in a supercritical reactor for 3-4 hours; (b) Dispersion treatment: adding the intercalated product into an organic solvent and fully dispersing it; (c) Grafting reaction: Slowly add polyethylene glycol-polylactic acid block copolymer under stirring and react at 45-50°C for 4-6 hours; (d) Separation and washing: After the reaction, the product was centrifuged, washed with deionized water and ethanol several times, and then dried at 55-65°C for 12 h.

9. The method for preparing a low-temperature polyolefin packaging film according to claim 6, wherein: The preparation method of the modified tourmaline nanotubes is as follows: dispersing the tourmaline nanotubes in a 0.1M zinc nitrate solution, hydrothermally reacting at 175-185°C for 3-5 hours, and calcining at 400-500°C for 1.5-2.5 hours.

10. The method for preparing a low-temperature polyolefin packaging film according to claim 6, wherein: The preparation method of the dibenzoyl peroxide microcapsule is as follows: adopting a double emulsification method, coating a peroxide aqueous phase with a dichloromethane solution of a polylactic acid-glycolic acid copolymer, and volatilizing the solvent after ultrasonic emulsification.

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