Low temperature polyolefin packaging film and method of making same

Abstract

This invention relates to the field of packaging film technology and provides a low-temperature polyolefin packaging film and its preparation method. The packaging film comprises a three-layer co-extruded structure consisting of an outer layer, a middle layer, and an inner layer. The components of each layer are as follows: Inner layer: metallocene polyolefin, high-performance polypropylene, modified lignin nanofibers, and erucamide / silica composite microspheres; Middle layer: PCR, modified nano-kaolinite, and trimethylolpropane triacrylate; Outer layer: PCR, modified tourmaline nanotubes, benzoyl peroxide microcapsules, and polydopamine-coated chitosan. This invention uses PCR, which is more energy-efficient and environmentally friendly. The addition of modified lignin nanofibers to the inner layer improves tensile strength; the addition of modified nano-kaolinite to the middle layer improves thermal shrinkage; the addition of modified tourmaline nanotubes to the outer layer lowers the crosslinking reaction initiation temperature and improves shrinkage; and the addition of polydopamine-coated chitosan allows for reversible recombination upon damage, improving puncture strength.

Description

Technical Field

[0001] This invention belongs to the field of packaging film technology, and particularly relates to a low-temperature polyolefin packaging film and its preparation method. Background Technology

[0002] Currently, low-temperature heat shrink packaging films mainly use PVC, PET, or ordinary polyolefin materials. Traditional polyolefin shrink films have significant shortcomings:

[0003] High shrinkage temperature: The initial shrinkage temperature of ordinary LDPE / LLDPE film is >85℃, which cannot meet the low-temperature packaging requirements (<70℃) of heat-sensitive products such as fresh food.

[0004] Poor mechanical properties: The addition of recycled materials (PCR) reduces tensile strength and results in insufficient puncture strength, leading to a high breakage rate during transportation.

[0005] Single function: Although existing nano-reinforcement systems (such as talc and calcium carbonate) can improve strength, they inhibit molecular chain movement, resulting in a decrease in thermal shrinkage rate. Summary of the Invention

[0006] This invention provides a low-temperature polyolefin packaging film, which aims to solve the above-mentioned problems.

[0007] This invention is achieved by providing a low-temperature polyolefin packaging film, comprising a three-layer co-extruded structure consisting of an outer layer, a middle layer, and an inner layer, wherein the components of each layer are as follows by weight:

[0008] Inner layer: 45-55 parts metallocene polyolefin, 15-25 parts high-performance polypropylene, 15-20 parts modified lignin nanofibers, 2-3 parts erucamide / silica composite microspheres

[0009] Intermediate layer: PCR 45-55 parts, modified nano-kaolinite 10-15 parts, trimethylolpropane triacrylate 3-4 parts;

[0010] Outer layer: PCR 50-60 parts, modified tourmaline nanotubes 8-12 parts, benzoyl peroxide microcapsules 3-5 parts, polydopamine-coated chitosan 5-8 parts.

[0011] Preferably, the total film thickness is 20-50 μm, the outer layer:middle layer:inner layer thickness ratio is 1:3-5:1, the heat shrinkage rate at 65℃ is ≥25%, and the heat shrinkage rate at 100℃ is ≥55%.

[0012] Preferably, the metallocene polyolefin is metallocene linear low-density polyethylene, the high-performance polypropylene is copolymer polypropylene, the PCR of the intermediate layer is LLDPE-PCR, and the PCR of the outer layer is LDPE-PCR.

[0013] Preferably, the modified tourmaline nanotubes are borosilicate tourmaline with ZnO quantum dots loaded on the surface, with a ZnO loading of 5-8 wt%, a tube diameter of 50-80 nm, and an aspect ratio >30;

[0014] The benzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), with a core content of 60-70% and a particle size of 200-500 nm.

[0015] Preferably, the modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and the interlayer spacing increased to 1.5-2.0 nm;

[0016] The modified lignin nanofibers, after laccase activation-plasma grafting treatment, have a carboxyl group density ≥ 3.0 groups / nm. 2 .

[0017] Preferably, the dopamine coating thickness in the polydopamine-coated chitosan is 10-20 nm, and the degree of deacetylation of the chitosan is ≥90%.

[0018] The composite microspheres are erucamide-filled mesoporous silica with a pore size of 2-5 nm and a drug loading of 40-50%.

[0019] The present invention also provides a method for preparing the above-mentioned low-temperature polyolefin packaging film, comprising the following steps:

[0020] S1 Prepare all raw materials according to the formula;

[0021] S2 three-layer co-extrusion:

[0022] Outer layer extrusion temperature: 170-190℃, middle layer: 180-200℃, inner layer: 165-185℃;

[0023] Die head clearance 1.2-1.8mm, melt pressure 15-25MPa;

[0024] S3 piezoelectric activation and pre-crosslinking:

[0025] A piezoelectric oscillator (frequency 1-5kHz, voltage 15-25V) is installed at the die outlet to excite tourmaline to release free radicals;

[0026] 75-85℃ hot air tunnel treatment for 10-20 seconds;

[0027] S4 Ultra-Fast Freeze:

[0028] Liquid nitrogen jet cooling at -196℃, contact time 0.3-1.0s, cooling rate ≥500℃ / s;

[0029] S5 synergistic irradiation crosslinking:

[0030] Electron beam (dose 23-27 kGy) and terahertz wave (0.3-0.7 THz) synchrotron irradiation, in three stages:

[0031] Pre-crosslinking 5-8 kGy → activation 10-12 kGy → curing 8-10 kGy; terahertz wave generator (0.5 THz) is embedded in the irradiation area to promote crosslinking uniformity;

[0032] S6 Ultrasonic-Assisted Bidirectional Stretching:

[0033] Longitudinal stretching: 105-110℃, stretching ratio 6.0-7.0, 40kHz ultrasonic assistance;

[0034] Transverse stretching: stretching ratio of 5.5-6.5 at 90-95℃; ultrasonic-assisted stretching is used to induce the formation of a gradient crystal structure.

[0035] S7 Curing and Shaping:

[0036] The product is subjected to hot roller treatment at 50-60℃ for 30-60 seconds, followed by cold roller shaping at 20-30℃.

[0037] Preferably, the modified lignin nanofibers are prepared as follows:

[0038] (a) Enzyme activation treatment: Disperse alkali lignin in phosphate buffer at pH 8-9, add laccase (20-30 U / g lignin) and mediator ABTS (1-2 wt%), and react with shaking at 45-55℃ for 2-4 h;

[0039] (b) Depolymerization of ionic liquid: The reaction products are transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:13-17) and microwaved at 170-180℃ (power 250-350W) for 10-20 min;

[0040] (c) Plasma grafting: The depolymerization product is placed in a plasma reaction chamber (Ar / O2=3-5:1, 45-55Pa), and a pulsed power supply (peak voltage 8-12kV, frequency 4-6kHz) is applied for treatment for 3-5 minutes, while acrylic acid vapor is introduced at the same time.

[0041] (d) Nanofiberization: Nanofibers are obtained by cyclic processing 5-8 times using a high-pressure homogenizer (150-180MPa).

[0042] Preferably, the preparation method of the erucamide / silica composite microspheres is as follows: impregnating mesoporous silica with molten erucamide (75-85℃), followed by vacuum adsorption and rapid cooling for solidification.

[0043] Preferably, the modified nano-kaolinite is prepared as follows:

[0044] (a) Supercritical CO2 intercalation: Kaolinite and urea are mixed at a mass ratio of 1:2.5-3.5 and placed in a supercritical reactor (CO2 pressure 20-30MPa, 60-70℃) for 3-4 hours;

[0045] (b) Dispersion treatment: The intercalated product is added to an organic solvent (solid-liquid ratio 1:8-12) and dispersed thoroughly;

[0046] (c) Grafting reaction: Under stirring, slowly add polyethylene glycol-polylactic acid block copolymer (mass ratio of 1-2:1 to intercalation product) and react at 45-50℃ for 4-6 hours.

[0047] (d) Separation and washing: After the reaction is completed, the mixture is centrifuged, washed multiple times with deionized water and ethanol, and then dried at 55-65℃ for 12h.

[0048] Preferably, the modified tourmaline nanotubes are prepared as follows: tourmaline nanotubes are dispersed in a 0.1M Zn(NO3)2 solution, subjected to hydrothermal reaction at 175-185℃ for 3-5 hours, and calcined at 400-500℃ for 1.5-2.5 hours.

[0049] Preferably, the preparation method of the benzoyl peroxide microcapsules is as follows: a double emulsification method (W / O / W) is used, in which a PLGA dichloromethane solution (10 wt%) is coated onto the aqueous phase of the peroxide, followed by ultrasonic emulsification and solvent evaporation. Specifically:

[0050] Internal aqueous phase: 10wt% peroxide aqueous solution;

[0051] Oil phase: 10 wt% PLGA (LA:GA=75:25) in dichloromethane solution;

[0052] Primary emulsification (W / O): Ultrasonic power 200-300W, 2-4min;

[0053] External aqueous phase: 2wt% PVA solution, secondary emulsification (W / O / W): 400-500W, 2-4min;

[0054] Microcapsules were obtained after the solvent was evaporated.

[0055] Preferably, the preparation method of the polydopamine-coated chitosan is as follows:

[0056] (a) Chitosan pretreatment: Chitosan with a degree of deacetylation ≥90% was dissolved in 0.5-1.5wt% acetic acid solution to prepare a 1.5-2.5wt% chitosan solution; 0.1M NaOH was added to adjust the pH to 7.0, and the purified chitosan gel was obtained by centrifugation.

[0057] (b) In-situ polymerization and coating with dopamine: Purified chitosan was dispersed in Tris-HCl buffer (pH=8.5, concentration 10mM); dopamine hydrochloride was added (chitosan:dopamine mass ratio 1:1.5-2.0); the reaction was carried out at 25℃ with shaking for 12-24h, and the precipitate was collected by centrifugation;

[0058] (c) Secondary oxidation crosslinking: The precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+ (H2O2 molar ratio 1:15-25); react at 40℃ for 1 h, dialysis for purification, and then freeze-dry.

[0059] (d) Plasma activation: Under an Ar / O2 (4:1) atmosphere, the final product was obtained by treating with 50W plasma for 3 minutes.

[0060] Compared with the prior art, the embodiments of this application have the following main advantages:

[0061] The low-temperature polyolefin packaging film provided by this invention utilizes PCR, reducing solid waste generation, lowering costs, and being energy-saving and environmentally friendly. The inner layer incorporates modified lignin nanofibers, forming a "reinforced concrete" structure to improve tensile strength. Erucamide / silica composite microspheres are also added to create a slow-release, slippery system. The middle layer incorporates modified nano-kaolinite, guiding the molecular chain orientation during radiation crosslinking and improving thermal shrinkage. The outer layer incorporates modified tourmaline nanotubes with ZnO quantum dots loaded on the surface, generating a piezoelectric field under tensile stress to catalyze the decomposition of peroxides into free radicals, lowering the crosslinking reaction initiation temperature and increasing shrinkage. The addition of polydopamine-coated chitosan forms dynamic quinone-amine bonds in the outer layer, allowing for reversible recombination upon damage and improving puncture strength. Attached Figure Description

[0062] Figure 1 This is a flowchart of a method for preparing a low-temperature polyolefin packaging film provided by the present invention. Detailed Implementation

[0063] 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 herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0064] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0065] Example 1

[0066] This invention provides a low-temperature polyolefin packaging film, comprising a three-layer co-extruded structure consisting of an outer layer, a middle layer, and an inner layer. The components of each layer are as follows by weight:

[0067] Inner layer: 45 parts metallocene polyolefin, 15 parts high-performance polypropylene, 15 parts modified lignin nanofibers, 2 parts erucamide / silica composite microspheres

[0068] Intermediate layer: PCR 45 parts, modified nano-kaolinite 10 parts, trimethylolpropane triacrylate 3 parts;

[0069] Outer layer: 50 PCR samples, 8 modified tourmaline nanotubes, 3 benzoyl peroxide microcapsules, and 5 polydopamine-coated chitosan.

[0070] In this embodiment, the preferred total film thickness is 20-50 μm, the outer layer:middle layer:inner layer thickness ratio is 1:3:1, the heat shrinkage rate at 65℃ is ≥25%, and the heat shrinkage rate at 100℃ is ≥55%.

[0071] The metallocene polyolefin is preferably metallocene linear low-density polyethylene, the high-performance polypropylene is preferably copolymer polypropylene, the PCR of the intermediate layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0072] Specifically, the modified tourmaline nanotubes are borosilicate tourmaline with ZnO quantum dots loaded on the surface, with a ZnO loading of 5-8 wt%, a tube diameter of 50-80 nm, and an aspect ratio of >30;

[0073] The benzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), with a core content of 60-70% and a particle size of 200-500 nm;

[0074] The modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and the interlayer spacing increased to 1.5-2.0 nm;

[0075] The modified lignin nanofibers, after laccase activation-plasma grafting treatment, have a carboxyl group density ≥ 3.0 groups / nm. 2 ;

[0076] The polydopamine-coated chitosan has a dopamine coating layer thickness of 10-20 nm and a chitosan deacetylation degree ≥90%.

[0077] The composite microspheres are erucamide-filled mesoporous silica with a pore size of 2-5 nm and a drug loading of 40-50%.

[0078] This invention also provides a method for preparing the above-mentioned low-temperature polyolefin packaging film, such as... Figure 1 As shown, it includes the following steps:

[0079] S1 Prepare all raw materials according to the formula;

[0080] S2 three-layer co-extrusion:

[0081] Outer layer extrusion temperature: 170℃; middle layer: 180℃; inner layer: 165℃.

[0082] The die head clearance is 1.2mm, and the melt pressure is 15MPa.

[0083] S3 piezoelectric activation and pre-crosslinking:

[0084] A piezoelectric oscillator (frequency 1kHz, voltage 15V) is installed at the die outlet to excite tourmaline to release free radicals;

[0085] 75℃ hot air tunnel treatment for 10 seconds;

[0086] S4 Ultra-Fast Freeze:

[0087] Liquid nitrogen jet cooling at -196℃, contact time 0.3s, cooling rate ≥500℃ / s;

[0088] S5 synergistic irradiation crosslinking:

[0089] Electron beam (dose 23 kGy) and terahertz wave (0.3 THz) synchrotron irradiation were performed in three stages:

[0090] Pre-crosslinking 5kGy → activation 10kGy → curing 8kGy; terahertz wave generator (0.5THz) embedded in the irradiation area to promote crosslinking uniformity;

[0091] S6 Ultrasonic-Assisted Bidirectional Stretching:

[0092] Longitudinal stretching: 105℃, stretching ratio 6.0, 40kHz ultrasonic assistance;

[0093] Transverse stretching: the stretching ratio at 90℃ is 5.5; ultrasonic-assisted stretching is used to induce the formation of a gradient crystal structure.

[0094] S7 Curing and Shaping:

[0095] The product is treated with a 50℃ hot roller for 30 seconds, and then shaped with a 20℃ cold roller.

[0096] The preparation method of the modified lignin nanofibers is as follows:

[0097] (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH=8, laccase (20U / g lignin) and mediator ABTS (1wt%) were added, and the mixture was shaken at 45℃ for 2h.

[0098] (b) Depolymerization of ionic liquid: The reaction products were transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:13) and microwaved at 170°C (power 250W) for 10 min;

[0099] (c) Plasma grafting: The depolymerization product was placed in a plasma reaction chamber (Ar / O2=3:1, 45Pa), and treated with a pulsed power supply (peak voltage 8kV, frequency 4kHz) for 3min, while acrylic acid vapor was introduced at the same time.

[0100] (d) Nanofiberization: Nanofibers were obtained by 5 cycles of high-pressure homogenization (150MPa).

[0101] 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 rapidly cooled to solidify.

[0102] Furthermore, the preparation method of the modified nano-kaolinite is as follows:

[0103] (a) Supercritical CO2 intercalation: Kaolinite and urea were mixed at a mass ratio of 1:2.5 and placed in a supercritical reactor (CO2 pressure 20MPa, 60℃) for 3h.

[0104] (b) Dispersion treatment: The intercalated product is added to an organic solvent (solid-liquid ratio 1:8) and dispersed thoroughly;

[0105] (c) Grafting reaction: Under stirring, polyethylene glycol-polylactic acid block copolymer (mass ratio of 1:1 to the intercalation product) was slowly added and reacted at 45°C for 4 h.

[0106] (d) Separation and washing: After the reaction is completed, the mixture is centrifuged, washed multiple times with deionized water and ethanol, and then dried at 55°C for 12 hours.

[0107] In a specific implementation, the modified tourmaline nanotubes are prepared as follows: tourmaline nanotubes are dispersed in a 0.1M Zn(NO3)2 solution, hydrothermally reacted at 175℃ for 3 hours, and calcined at 400℃ for 1.5 hours.

[0108] Preferably, the preparation method of the benzoyl peroxide microcapsules is as follows: a double emulsification method (W / O / W) is used, in which a PLGA dichloromethane solution (10 wt%) is coated onto the aqueous phase of the peroxide, followed by ultrasonic emulsification and solvent evaporation. Specifically:

[0109] Internal aqueous phase: 10wt% peroxide aqueous solution;

[0110] Oil phase: 10 wt% PLGA (LA:GA=75:25) in dichloromethane solution;

[0111] Primary emulsification (W / O): Ultrasonic power 200W, 2min;

[0112] External aqueous phase: 2wt% PVA solution, secondary emulsification (W / O / W): 400W, 2min;

[0113] Microcapsules were obtained after the solvent was evaporated.

[0114] Preferably, the preparation method of the polydopamine-coated chitosan is as follows:

[0115] (a) Chitosan pretreatment: Chitosan with a degree of deacetylation ≥90% was dissolved in 0.5wt% acetic acid solution to prepare a 1.5wt% chitosan solution; 0.1M NaOH was added to adjust the pH to 7.0, and the purified chitosan gel was obtained by centrifugation.

[0116] (b) In-situ dopamine polymerization coating: Purified chitosan was dispersed in Tris-HCl buffer (pH=8.5, concentration 10mM); dopamine hydrochloride was added (chitosan:dopamine mass ratio 1:1.5); the reaction was carried out at 25℃ with shaking for 12h, and the precipitate was collected by centrifugation;

[0117] (c) Secondary oxidation crosslinking: The precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+ (H2O2 molar ratio 1:15); react at 40℃ for 1 h, dialysis for purification, and then freeze-dry.

[0118] (d) Plasma activation: Under an Ar / O2 (4:1) atmosphere, the final product was obtained by treating with 50W plasma for 3 minutes.

[0119] Example 2

[0120] This invention provides a low-temperature polyolefin packaging film, comprising a three-layer co-extruded structure consisting of an outer layer, a middle layer, and an inner layer. The components of each layer are as follows by weight:

[0121] Inner layer: 48 parts metallocene polyolefin, 17 parts high-performance polypropylene, 16 parts modified lignin nanofibers, and 2.2 parts erucamide / silica composite microspheres;

[0122] Intermediate layer: PCR 47 parts, modified nano-kaolinite 11 parts, trimethylolpropane triacrylate 3.3 parts;

[0123] Outer layer: PCR 52 parts, modified tourmaline nanotubes 9 parts, benzoyl peroxide microcapsules 3.5 parts, polydopamine-coated chitosan 6 parts.

[0124] In this embodiment, the preferred total film thickness is 20-50 μm, the outer layer:middle layer:inner layer thickness ratio is 1:3:1, the heat shrinkage rate at 65℃ is ≥25%, and the heat shrinkage rate at 100℃ is ≥55%.

[0125] The metallocene polyolefin is preferably metallocene linear low-density polyethylene, the high-performance polypropylene is preferably copolymer polypropylene, the PCR of the intermediate layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0126] Specifically, the modified tourmaline nanotubes are borosilicate tourmaline with ZnO quantum dots loaded on the surface, with a ZnO loading of 5-8 wt%, a tube diameter of 50-80 nm, and an aspect ratio of >30;

[0127] The benzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), with a core content of 60-70% and a particle size of 200-500 nm;

[0128] The modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and the interlayer spacing increased to 1.5-2.0 nm;

[0129] The modified lignin nanofibers, after laccase activation-plasma grafting treatment, have a carboxyl group density ≥ 3.0 groups / nm. 2 ;

[0130] The polydopamine-coated chitosan has a dopamine coating layer thickness of 10-20 nm and a chitosan deacetylation degree ≥90%.

[0131] The composite microspheres are erucamide-filled mesoporous silica with a pore size of 2-5 nm and a drug loading of 40-50%.

[0132] This invention also provides a method for preparing the above-mentioned low-temperature polyolefin packaging film, such as... Figure 1 As shown, it includes the following steps:

[0133] S1 Prepare all raw materials according to the formula;

[0134] S2 three-layer co-extrusion:

[0135] Outer layer extrusion temperature: 170℃; middle layer: 180℃; inner layer: 165℃.

[0136] The die head clearance is 1.2mm, and the melt pressure is 15MPa.

[0137] S3 piezoelectric activation and pre-crosslinking:

[0138] A piezoelectric oscillator (frequency 1kHz, voltage 15V) is installed at the die outlet to excite tourmaline to release free radicals;

[0139] 75℃ hot air tunnel treatment for 10 seconds;

[0140] S4 Ultra-Fast Freeze:

[0141] Liquid nitrogen jet cooling at -196℃, contact time 0.3s, cooling rate ≥500℃ / s;

[0142] S5 synergistic irradiation crosslinking:

[0143] Electron beam (dose 23 kGy) and terahertz wave (0.3 THz) synchrotron irradiation were performed in three stages:

[0144] Pre-crosslinking 5kGy → activation 10kGy → curing 8kGy; terahertz wave generator (0.5THz) embedded in the irradiation area to promote crosslinking uniformity;

[0145] S6 Ultrasonic-Assisted Bidirectional Stretching:

[0146] Longitudinal stretching: 105℃, stretching ratio 6.0, 40kHz ultrasonic assistance;

[0147] Transverse stretching: the stretching ratio at 90℃ is 5.5; ultrasonic-assisted stretching is used to induce the formation of a gradient crystal structure.

[0148] S7 Curing and Shaping:

[0149] The product is treated with a 50℃ hot roller for 30 seconds, and then shaped with a 20℃ cold roller.

[0150] The preparation method of the modified lignin nanofibers is as follows:

[0151] (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH=8, laccase (20U / g lignin) and mediator ABTS (1wt%) were added, and the mixture was shaken at 45℃ for 2h.

[0152] (b) Depolymerization of ionic liquid: The reaction products were transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:13) and microwaved at 170°C (power 250W) for 10 min;

[0153] (c) Plasma grafting: The depolymerization product was placed in a plasma reaction chamber (Ar / O2=3:1, 45Pa), and treated with a pulsed power supply (peak voltage 8kV, frequency 4kHz) for 3min, while acrylic acid vapor was introduced at the same time.

[0154] (d) Nanofiberization: Nanofibers were obtained by 5 cycles of high-pressure homogenization (150MPa).

[0155] 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 rapidly cooled to solidify.

[0156] Furthermore, the preparation method of the modified nano-kaolinite is as follows:

[0157] (a) Supercritical CO2 intercalation: Kaolinite and urea were mixed at a mass ratio of 1:2.5 and placed in a supercritical reactor (CO2 pressure 20MPa, 60℃) for 3h.

[0158] (b) Dispersion treatment: The intercalated product is added to an organic solvent (solid-liquid ratio 1:8) and dispersed thoroughly;

[0159] (c) Grafting reaction: Under stirring, polyethylene glycol-polylactic acid block copolymer (mass ratio of 1:1 to the intercalation product) was slowly added and reacted at 45°C for 4 h.

[0160] (d) Separation and washing: After the reaction is completed, the mixture is centrifuged, washed multiple times with deionized water and ethanol, and then dried at 55°C for 12 hours.

[0161] In a specific implementation, the modified tourmaline nanotubes are prepared as follows: tourmaline nanotubes are dispersed in a 0.1M Zn(NO3)2 solution, hydrothermally reacted at 175℃ for 3 hours, and calcined at 400℃ for 1.5 hours.

[0162] Preferably, the preparation method of the benzoyl peroxide microcapsules is as follows: a double emulsification method (W / O / W) is used, in which a PLGA dichloromethane solution (10 wt%) is coated onto the aqueous phase of the peroxide, followed by ultrasonic emulsification and solvent evaporation. Specifically:

[0163] Internal aqueous phase: 10wt% peroxide aqueous solution;

[0164] Oil phase: 10 wt% PLGA (LA:GA=75:25) in dichloromethane solution;

[0165] Primary emulsification (W / O): Ultrasonic power 200W, 2min;

[0166] External aqueous phase: 2wt% PVA solution, secondary emulsification (W / O / W): 400W, 2min;

[0167] Microcapsules were obtained after the solvent was evaporated.

[0168] Preferably, the preparation method of the polydopamine-coated chitosan is as follows:

[0169] (a) Chitosan pretreatment: Chitosan with a degree of deacetylation ≥90% was dissolved in 0.5wt% acetic acid solution to prepare a 1.5wt% chitosan solution; 0.1M NaOH was added to adjust the pH to 7.0, and the purified chitosan gel was obtained by centrifugation.

[0170] (b) In-situ dopamine polymerization coating: Purified chitosan was dispersed in Tris-HCl buffer (pH=8.5, concentration 10mM); dopamine hydrochloride was added (chitosan:dopamine mass ratio 1:1.5); the reaction was carried out at 25℃ with shaking for 12h, and the precipitate was collected by centrifugation;

[0171] (c) Secondary oxidation crosslinking: The precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+ (H2O2 molar ratio 1:15); react at 40℃ for 1 h, dialysis for purification, and then freeze-dry.

[0172] (d) Plasma activation: Under an Ar / O2 (4:1) atmosphere, the final product was obtained by treating with 50W plasma for 3 minutes.

[0173] Example 3

[0174] This invention provides a low-temperature polyolefin packaging film, comprising a three-layer co-extruded structure consisting of an outer layer, a middle layer, and an inner layer. The components of each layer are as follows by weight:

[0175] Inner layer: 50 parts metallocene polyolefin, 20 parts high-performance polypropylene, 17.5 parts modified lignin nanofibers, and 2.5 parts erucamide / silica composite microspheres;

[0176] Intermediate layer: PCR 50 parts, modified nano-kaolinite 12.5 parts, trimethylolpropane triacrylate 3.5 parts;

[0177] Outer layer: PCR 55 parts, modified tourmaline nanotubes 10 parts, benzoyl peroxide microcapsules 4 parts, polydopamine-coated chitosan 6.5 parts.

[0178] In this embodiment, the preferred total film thickness is 20-50 μm, the outer layer:middle layer:inner layer thickness ratio is 1:4:1, the heat shrinkage rate at 65℃ is ≥25%, and the heat shrinkage rate at 100℃ is ≥55%.

[0179] The metallocene polyolefin is preferably metallocene linear low-density polyethylene, the high-performance polypropylene is preferably copolymer polypropylene, the PCR of the intermediate layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0180] Specifically, the modified tourmaline nanotubes are borosilicate tourmaline with ZnO quantum dots loaded on the surface, with a ZnO loading of 5-8 wt%, a tube diameter of 50-80 nm, and an aspect ratio of >30;

[0181] The benzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), with a core content of 60-70% and a particle size of 200-500 nm;

[0182] The modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and the interlayer spacing increased to 1.5-2.0 nm;

[0183] The modified lignin nanofibers, after laccase activation-plasma grafting treatment, have a carboxyl group density ≥ 3.0 groups / nm. 2 ;

[0184] The polydopamine-coated chitosan has a dopamine coating layer thickness of 10-20 nm and a chitosan deacetylation degree ≥90%.

[0185] The composite microspheres are erucamide-filled mesoporous silica with a pore size of 2-5 nm and a drug loading of 40-50%.

[0186] This invention also provides a method for preparing the above-mentioned low-temperature polyolefin packaging film, such as... Figure 1 As shown, it includes the following steps:

[0187] S1 Prepare all raw materials according to the formula;

[0188] S2 three-layer co-extrusion:

[0189] Outer layer extrusion temperature: 180℃; middle layer: 190℃; inner layer: 175℃.

[0190] Die head clearance 1.5mm, melt pressure 20MPa;

[0191] S3 piezoelectric activation and pre-crosslinking:

[0192] A piezoelectric oscillator (3kHz frequency, 20V voltage) is installed at the die outlet to excite tourmaline to release free radicals;

[0193] 80℃ hot air tunnel treatment for 15 seconds;

[0194] S4 Ultra-Fast Freeze:

[0195] Liquid nitrogen jet cooling at -196℃, contact time 0.6s, cooling rate ≥500℃ / s;

[0196] S5 synergistic irradiation crosslinking:

[0197] Electron beam (dose 25 kGy) and terahertz wave (0.5 THz) synchrotron irradiation, in three stages:

[0198] Pre-crosslinking 6.5 kGy → activation 11 kGy → curing 9 kGy; a terahertz wave generator (0.5 THz) is embedded in the irradiation area to promote crosslinking uniformity;

[0199] S6 Ultrasonic-Assisted Bidirectional Stretching:

[0200] Longitudinal stretching: 108℃, stretching ratio 6.5, 40kHz ultrasonic assistance;

[0201] Transverse stretching: stretching ratio of 6 at 92℃; ultrasonic-assisted stretching is used to induce the formation of a gradient crystal structure.

[0202] S7 Curing and Shaping:

[0203] The product is subjected to hot roller treatment at 50-60℃ for 45 seconds, followed by cold roller shaping at 25℃.

[0204] The preparation method of the modified lignin nanofibers is as follows:

[0205] (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH 8.5, and laccase (25 U / g lignin) and mediator ABTS (1.5 wt%) were added. The mixture was shaken at 50 °C for 3 h.

[0206] (b) Depolymerization of ionic liquid: The reaction products were transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:15) and microwaved at 175°C (power 300W) for 15 min;

[0207] (c) Plasma grafting: The depolymerization product was placed in a plasma reaction chamber (Ar / O2=4:1, 50Pa), and a pulsed power supply (peak voltage 10kV, frequency 5kHz) was applied for 4min, while acrylic acid vapor was introduced at the same time.

[0208] (d) Nanofiberization: Nanofibers were obtained by cyclic processing 6 times using a high-pressure homogenizer (165MPa).

[0209] Furthermore, the preparation method of the erucamide / silica composite microspheres is as follows: mesoporous silica is impregnated with molten erucamide (80°C), and then rapidly cooled and solidified after vacuum adsorption.

[0210] Furthermore, the preparation method of the modified nano-kaolinite is as follows:

[0211] (a) Supercritical CO2 intercalation: Kaolinite and urea were mixed at a mass ratio of 1:3 and placed in a supercritical reactor (CO2 pressure 25MPa, 65℃) for 3.5h.

[0212] (b) Dispersion treatment: The intercalated product is added to an organic solvent (solid-liquid ratio 1:10) and dispersed thoroughly;

[0213] (c) Grafting reaction: Under stirring, polyethylene glycol-polylactic acid block copolymer (mass ratio of 1.5:1 to intercalation product) was slowly added and reacted at 48°C for 5 h.

[0214] (d) Separation and washing: After the reaction is completed, the mixture is centrifuged, washed multiple times with deionized water and ethanol, and then dried at 60°C for 12 hours.

[0215] In a specific implementation, the modified tourmaline nanotubes are prepared as follows: tourmaline nanotubes are dispersed in a 0.1M Zn(NO3)2 solution, hydrothermally reacted at 180℃ for 4 hours, and calcined at 450℃ for 2 hours.

[0216] Preferably, the preparation method of the benzoyl peroxide microcapsules is as follows: a double emulsification method (W / O / W) is used, in which a PLGA dichloromethane solution (10 wt%) is coated onto the aqueous phase of the peroxide, followed by ultrasonic emulsification and solvent evaporation. Specifically:

[0217] Internal aqueous phase: 10wt% peroxide aqueous solution;

[0218] Oil phase: 10 wt% PLGA (LA:GA=75:25) in dichloromethane solution;

[0219] Primary emulsification (W / O): Ultrasonic power 250W, 3min;

[0220] External aqueous phase: 2wt% PVA solution, secondary emulsification (W / O / W): 450W, 3min;

[0221] Microcapsules were obtained after the solvent was evaporated.

[0222] Preferably, the preparation method of the polydopamine-coated chitosan is as follows:

[0223] (a) Chitosan pretreatment: Chitosan with a degree of deacetylation ≥90% was dissolved in 1wt% acetic acid solution to prepare a 2wt% chitosan solution; 0.1M NaOH was added to adjust the pH to 7.0, and the purified chitosan gel was obtained by centrifugation.

[0224] (b) In-situ dopamine polymerization coating: Purified chitosan was dispersed in Tris-HCl buffer (pH=8.5, concentration 10mM); dopamine hydrochloride was added (chitosan:dopamine mass ratio 1:1.75); the reaction was carried out at 25℃ with shaking for 18h, and the precipitate was collected by centrifugation;

[0225] (c) Secondary oxidation crosslinking: The precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+(H2O2 molar ratio 1:20); react at 40℃ for 1 h, dialysis for purification, and then freeze-dry.

[0226] (d) Plasma activation: Under an Ar / O2 (4:1) atmosphere, the final product was obtained by treating with 50W plasma for 3 minutes.

[0227] Example 4

[0228] This invention provides a low-temperature polyolefin packaging film, comprising a three-layer co-extruded structure consisting of an outer layer, a middle layer, and an inner layer. The components of each layer are as follows by weight:

[0229] Inner layer: 53 parts metallocene polyolefin, 22 parts high-performance polypropylene, 19 parts modified lignin nanofibers, and 2.8 parts erucamide / silica composite microspheres;

[0230] Intermediate layer: PCR 52 parts, modified nano-kaolinite 14 parts, trimethylolpropane triacrylate 3.8 parts;

[0231] Outer layer: PCR 58 parts, modified tourmaline nanotubes 11 parts, benzoyl peroxide microcapsules 4.5 parts, polydopamine-coated chitosan 7 parts.

[0232] In this embodiment, the preferred total film thickness is 20-50 μm, the outer layer:middle layer:inner layer thickness ratio is 1:5:1, the heat shrinkage rate at 65℃ is ≥25%, and the heat shrinkage rate at 100℃ is ≥55%.

[0233] The metallocene polyolefin is preferably metallocene linear low-density polyethylene, the high-performance polypropylene is preferably copolymer polypropylene, the PCR of the intermediate layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0234] Specifically, the modified tourmaline nanotubes are borosilicate tourmaline with ZnO quantum dots loaded on the surface, with a ZnO loading of 5-8 wt%, a tube diameter of 50-80 nm, and an aspect ratio of >30;

[0235] The benzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), with a core content of 60-70% and a particle size of 200-500 nm;

[0236] The modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and the interlayer spacing increased to 1.5-2.0 nm;

[0237] The modified lignin nanofibers, after laccase activation-plasma grafting treatment, have a carboxyl group density ≥ 3.0 groups / nm. 2 ;

[0238] The polydopamine-coated chitosan has a dopamine coating layer thickness of 10-20 nm and a chitosan deacetylation degree ≥90%.

[0239] The composite microspheres are erucamide-filled mesoporous silica with a pore size of 2-5 nm and a drug loading of 40-50%.

[0240] This invention also provides a method for preparing the above-mentioned low-temperature polyolefin packaging film, such as... Figure 1 As shown, it includes the following steps:

[0241] S1 Prepare all raw materials according to the formula;

[0242] S2 three-layer co-extrusion:

[0243] Outer layer extrusion temperature: 190℃; middle layer: 200℃; inner layer: 185℃.

[0244] Die head clearance 1.8mm, melt pressure 25MPa;

[0245] S3 piezoelectric activation and pre-crosslinking:

[0246] A piezoelectric oscillator (frequency 5kHz, voltage 25V) is installed at the die outlet to excite tourmaline to release free radicals;

[0247] 85℃ hot air tunnel treatment for 20 seconds;

[0248] S4 Ultra-Fast Freeze:

[0249] Liquid nitrogen jet cooling at -196℃, contact time 1.0s, cooling rate ≥500℃ / s;

[0250] S5 synergistic irradiation crosslinking:

[0251] Electron beam (dose 27 kGy) and terahertz wave (0.7 THz) synchrotron irradiation were performed in three stages:

[0252] Pre-crosslinking 8kGy → Activation 12kGy → Curing 10kGy; A terahertz wave generator (0.5THz) is embedded in the irradiation area to promote crosslinking uniformity;

[0253] S6 Ultrasonic-Assisted Bidirectional Stretching:

[0254] Longitudinal stretching: 110℃, stretching ratio 7.0, 40kHz ultrasonic assistance;

[0255] Transverse stretching: the stretching ratio at 95℃ is 6.5; ultrasonic-assisted stretching is used to induce the formation of a gradient crystal structure.

[0256] S7 Curing and Shaping:

[0257] The product is subjected to a 60℃ hot roller treatment for 60 seconds, followed by a 30℃ cold roller setting.

[0258] The preparation method of the modified lignin nanofibers is as follows:

[0259] (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH=9, laccase (30U / g lignin) and mediator ABTS (2wt%) were added, and the mixture was shaken at 55℃ for 4h.

[0260] (b) Depolymerization of ionic liquid: The reaction products were transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:17) and microwaved at 180°C (power 350W) for 20 min;

[0261] (c) Plasma grafting: The depolymerization product was placed in a plasma reaction chamber (Ar / O2=5:1, 55Pa), and a pulsed power supply (peak voltage 12kV, frequency 6kHz) was applied for 5min, while acrylic acid vapor was introduced at the same time.

[0262] (d) Nanofiberization: Nanofibers were obtained by cyclic processing 8 times using a high-pressure homogenizer (180MPa).

[0263] Furthermore, the preparation method of the erucamide / silica composite microspheres is as follows: mesoporous silica is impregnated with molten erucamide (85°C), and then vacuum adsorbed and rapidly cooled to solidify.

[0264] Furthermore, the preparation method of the modified nano-kaolinite is as follows:

[0265] (a) Supercritical CO2 intercalation: Kaolinite and urea were mixed at a mass ratio of 1:3.5 and placed in a supercritical reactor (CO2 pressure 30MPa, 70℃) for 4h.

[0266] (b) Dispersion treatment: The intercalated product is added to an organic solvent (solid-liquid ratio 1:12) and dispersed thoroughly;

[0267] (c) Grafting reaction: Under stirring, polyethylene glycol-polylactic acid block copolymer (mass ratio of 2:1 to intercalation product) was slowly added and reacted at 50°C for 6 h.

[0268] (d) Separation and washing: After the reaction is completed, the mixture is centrifuged, washed multiple times with deionized water and ethanol, and then dried at 65°C for 12 hours.

[0269] In a specific implementation, the modified tourmaline nanotubes are prepared as follows: tourmaline nanotubes are dispersed in a 0.1M Zn(NO3)2 solution, hydrothermally reacted at 185℃ for 3-5 hours, and calcined at 500℃ for 2.5 hours.

[0270] Preferably, the preparation method of the benzoyl peroxide microcapsules is as follows: a double emulsification method (W / O / W) is used, in which a PLGA dichloromethane solution (10 wt%) is coated onto the aqueous phase of the peroxide, followed by ultrasonic emulsification and solvent evaporation. Specifically:

[0271] Internal aqueous phase: 10wt% peroxide aqueous solution;

[0272] Oil phase: 10 wt% PLGA (LA:GA=75:25) in dichloromethane solution;

[0273] Primary emulsification (W / O): Ultrasonic power 300W, 4min;

[0274] External aqueous phase: 2wt% PVA solution, secondary emulsification (W / O / W): 500W, 4min;

[0275] Microcapsules were obtained after the solvent was evaporated.

[0276] Preferably, the preparation method of the polydopamine-coated chitosan is as follows:

[0277] (a) Chitosan pretreatment: Chitosan with a degree of deacetylation ≥90% was dissolved in 1.5wt% acetic acid solution to prepare a 2.5wt% chitosan solution; 0.1M NaOH was added to adjust the pH to 7.0, and the purified chitosan gel was obtained by centrifugation.

[0278] (b) In-situ dopamine polymerization coating: Purified chitosan was dispersed in Tris-HCl buffer (pH=8.5, concentration 10mM); dopamine hydrochloride was added (chitosan:dopamine mass ratio 1:2.0); the reaction was carried out at 25℃ with shaking for 24h, and the precipitate was collected by centrifugation;

[0279] (c) Secondary oxidation crosslinking: The precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+ (H2O2 molar ratio 1:25); react at 40℃ for 1 h, dialysis for purification, and then freeze-dry.

[0280] (d) Plasma activation: Under an Ar / O2 (4:1) atmosphere, the final product was obtained by treating with 50W plasma for 3 minutes.

[0281] Example 5

[0282] This invention provides a low-temperature polyolefin packaging film, comprising a three-layer co-extruded structure consisting of an outer layer, a middle layer, and an inner layer. The components of each layer are as follows by weight:

[0283] Inner layer: 55 parts metallocene polyolefin, 25 parts high-performance polypropylene, 20 parts modified lignin nanofibers, and 3 parts erucamide / silica composite microspheres.

[0284] Intermediate layer: PCR 55 parts, modified nano-kaolinite 15 parts, trimethylolpropane triacrylate 4 parts;

[0285] Outer layer: 60 PCR components, 12 modified tourmaline nanotubes, 3-5 benzoyl peroxide microcapsules, and 8 polydopamine-coated chitosan.

[0286] In this embodiment, the preferred total film thickness is 20-50 μm, the outer layer:middle layer:inner layer thickness ratio is 1:5:1, the heat shrinkage rate at 65℃ is ≥25%, and the heat shrinkage rate at 100℃ is ≥55%.

[0287] The metallocene polyolefin is preferably metallocene linear low-density polyethylene, the high-performance polypropylene is preferably copolymer polypropylene, the PCR of the intermediate layer is preferably LLDPE-PCR, and the PCR of the outer layer is preferably LDPE-PCR.

[0288] Specifically, the modified tourmaline nanotubes are borosilicate tourmaline with ZnO quantum dots loaded on the surface, with a ZnO loading of 5-8 wt%, a tube diameter of 50-80 nm, and an aspect ratio of >30;

[0289] The benzoyl peroxide microcapsule wall material is polylactic acid-glycolic acid copolymer (PLGA), with a core content of 60-70% and a particle size of 200-500 nm;

[0290] The modified nano-kaolinite is grafted with polyethylene glycol-polylactic acid (PEG-PLA) block copolymer, with a grafting rate of 15-25% and the interlayer spacing increased to 1.5-2.0 nm;

[0291] The modified lignin nanofibers, after laccase activation-plasma grafting treatment, have a carboxyl group density ≥ 3.0 groups / nm. 2 ;

[0292] The polydopamine-coated chitosan has a dopamine coating layer thickness of 10-20 nm and a chitosan deacetylation degree ≥90%.

[0293] The composite microspheres are erucamide-filled mesoporous silica with a pore size of 2-5 nm and a drug loading of 40-50%.

[0294] This invention also provides a method for preparing the above-mentioned low-temperature polyolefin packaging film, such as... Figure 1 As shown, it includes the following steps:

[0295] S1 Prepare all raw materials according to the formula;

[0296] S2 three-layer co-extrusion:

[0297] Outer layer extrusion temperature: 190℃; middle layer: 200℃; inner layer: 185℃.

[0298] Die head clearance 1.8mm, melt pressure 25MPa;

[0299] S3 piezoelectric activation and pre-crosslinking:

[0300] A piezoelectric oscillator (frequency 5kHz, voltage 25V) is installed at the die outlet to excite tourmaline to release free radicals;

[0301] 85℃ hot air tunnel treatment for 20 seconds;

[0302] S4 Ultra-Fast Freeze:

[0303] Liquid nitrogen jet cooling at -196℃, contact time 1.0s, cooling rate ≥500℃ / s;

[0304] S5 synergistic irradiation crosslinking:

[0305] Electron beam (dose 27 kGy) and terahertz wave (0.7 THz) synchrotron irradiation were performed in three stages:

[0306] Pre-crosslinking 8kGy → Activation 12kGy → Curing 10kGy; A terahertz wave generator (0.5THz) is embedded in the irradiation area to promote crosslinking uniformity;

[0307] S6 Ultrasonic-Assisted Bidirectional Stretching:

[0308] Longitudinal stretching: 110℃, stretching ratio 7.0, 40kHz ultrasonic assistance;

[0309] Transverse stretching: the stretching ratio at 95℃ is 6.5; ultrasonic-assisted stretching is used to induce the formation of a gradient crystal structure.

[0310] S7 Curing and Shaping:

[0311] The product is subjected to a 60℃ hot roller treatment for 60 seconds, followed by a 30℃ cold roller setting.

[0312] The preparation method of the modified lignin nanofibers is as follows:

[0313] (a) Enzyme activation treatment: Alkali lignin was dispersed in phosphate buffer at pH=9, laccase (30U / g lignin) and mediator ABTS (2wt%) were added, and the mixture was shaken at 55℃ for 4h.

[0314] (b) Depolymerization of ionic liquid: The reaction products were transferred to [BMIM]Cl ionic liquid (solid-liquid ratio 1:17) and microwaved at 180°C (power 350W) for 20 min;

[0315] (c) Plasma grafting: The depolymerization product was placed in a plasma reaction chamber (Ar / O2=5:1, 55Pa), and a pulsed power supply (peak voltage 12kV, frequency 6kHz) was applied for 5min, while acrylic acid vapor was introduced at the same time.

[0316] (d) Nanofiberization: Nanofibers were obtained by cyclic processing 8 times using a high-pressure homogenizer (180MPa).

[0317] Furthermore, the preparation method of the erucamide / silica composite microspheres is as follows: mesoporous silica is impregnated with molten erucamide (85°C), and then vacuum adsorbed and rapidly cooled to solidify.

[0318] Furthermore, the preparation method of the modified nano-kaolinite is as follows:

[0319] (a) Supercritical CO2 intercalation: Kaolinite and urea were mixed at a mass ratio of 1:3.5 and placed in a supercritical reactor (CO2 pressure 30MPa, 70℃) for 4h.

[0320] (b) Dispersion treatment: The intercalated product is added to an organic solvent (solid-liquid ratio 1:12) and dispersed thoroughly;

[0321] (c) Grafting reaction: Under stirring, polyethylene glycol-polylactic acid block copolymer (mass ratio of 2:1 to intercalation product) was slowly added and reacted at 50°C for 6 h.

[0322] (d) Separation and washing: After the reaction is completed, the mixture is centrifuged, washed multiple times with deionized water and ethanol, and then dried at 65°C for 12 hours.

[0323] In a specific implementation, the modified tourmaline nanotubes are prepared as follows: tourmaline nanotubes are dispersed in a 0.1M Zn(NO3)2 solution, hydrothermally reacted at 185℃ for 3-5 hours, and calcined at 500℃ for 2.5 hours.

[0324] Preferably, the preparation method of the benzoyl peroxide microcapsules is as follows: a double emulsification method (W / O / W) is used, in which a PLGA dichloromethane solution (10 wt%) is coated onto the aqueous phase of the peroxide, followed by ultrasonic emulsification and solvent evaporation. Specifically:

[0325] Internal aqueous phase: 10wt% peroxide aqueous solution;

[0326] Oil phase: 10 wt% PLGA (LA:GA=75:25) in dichloromethane solution;

[0327] Primary emulsification (W / O): Ultrasonic power 300W, 4min;

[0328] External aqueous phase: 2wt% PVA solution, secondary emulsification (W / O / W): 500W, 4min;

[0329] Microcapsules were obtained after the solvent was evaporated.

[0330] Preferably, the preparation method of the polydopamine-coated chitosan is as follows:

[0331] (a) Chitosan pretreatment: Chitosan with a degree of deacetylation ≥90% was dissolved in 1.5wt% acetic acid solution to prepare a 2.5wt% chitosan solution; 0.1M NaOH was added to adjust the pH to 7.0, and the purified chitosan gel was obtained by centrifugation.

[0332] (b) In-situ dopamine polymerization coating: Purified chitosan was dispersed in Tris-HCl buffer (pH=8.5, concentration 10mM); dopamine hydrochloride was added (chitosan:dopamine mass ratio 1:2.0); the reaction was carried out at 25℃ with shaking for 24h, and the precipitate was collected by centrifugation;

[0333] (c) Secondary oxidation crosslinking: The precipitate is immersed in a 0.01M CuSO4 / H2O2 solution (Cu 2+ (H2O2 molar ratio 1:25); react at 40℃ for 1 h, dialysis for purification, and then freeze-dry.

[0334] (d) Plasma activation: Under an Ar / O2 (4:1) atmosphere, the final product was obtained by treating with 50W plasma for 3 minutes.

[0335] Comparative Example 1: The difference from Example 3 is that the inner layer of modified lignin nanofibers was removed.

[0336] Comparative Example 2: The difference from Example 3 is that the modified nano-kaolinite was removed from the intermediate layer.

[0337] Comparative Example 3: The difference from Example 3 is that the modified tourmaline nanotubes were removed from the outer layer.

[0338] Comparative Example 4: The difference from Example 3 is that the outer layer of polydopamine-coated chitosan was removed.

[0339] Comparative Example 5: The difference from Example 3 is that the S3 piezoelectric activation step is omitted in the preparation process.

[0340] Comparative Example 6: The difference from Example 3 is that the preparation process omits the S4 ultra-rapid freezing and replaces it with conventional water cooling (cooling rate 50°C / s).

[0341] Comparative Example 7: The difference from Example 3 is that the outer layer is replaced with dicumyl peroxide (DCP) instead of dibenzoyl peroxide microcapsules.

[0342] Performance testing

[0343] Test methods and standards

[0344] Heat shrinkage rate (GB / T 13519-2016):

[0345] Shrinkage (MD / TD average) was tested at 65℃ (10 min), 100℃ (30 s) and 130℃ (30 s) respectively.

[0346] Mechanical properties (ASTM D882):

[0347] Tensile strength (MPa), elongation at break (%), tensile rate 500 mm / min;

[0348] Puncture strength (ASTM F1306): 2mm diameter puncture head, speed 50mm / min (unit: N / mm).

[0349] Elongation at break (GB / T 1040.3-2006).

[0350] The mechanical property test results are shown in Table 1 below:

[0351] Table 1

[0352]

[0353] The results above show that the packaging film prepared by this invention has good mechanical properties.

[0354] The results of the heat shrinkage performance test are shown in Table 2 below:

[0355] Table 2

[0356]

[0357] The results above show that the packaging film prepared by this invention has good heat shrinkage properties, especially with the advantage of low-temperature shrinkage.

[0358] It should be noted that, for the sake of simplicity, the foregoing embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0359] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A low temperature polyolefin packaging film characterized by, The structure comprises a three-layer co-extruded structure consisting of an outer layer, a middle layer, and an inner layer. The components of each layer are as follows by weight: Inner layer: 45-55 parts metallocene polyolefin, 15-25 parts copolymer polypropylene, 15-20 parts modified lignin nanofibers, and 2-3 parts erucamide / silica composite microspheres. Intermediate layer: PCR 45-55 parts, modified nano-kaolinite 10-15 parts, trimethylolpropane triacrylate 3-4 parts; Outer layer: PCR 50-60 parts, modified tourmaline nanotubes 8-12 parts, benzoyl peroxide microcapsules 3-5 parts, polydopamine-coated chitosan 5-8 parts; The modified lignin nanofiber is a lignin nanofiber activated by laccase-plasma grafting treatment, and the carboxyl density is ≥3.0 / nm 2 ; The composite microspheres are erucic acid amide-filled mesoporous silica with a pore size of 2-5 nm and a drug loading of 40-50%. The modified nano-kaolinite is nano-kaolinite grafted with polyethylene glycol-polylactic acid block copolymer, with a grafting rate of 15-25% and an interlayer spacing increased to 1.5-2.0 nm. The modified tourmaline nanotubes are borosilicate tourmaline with ZnO quantum dots loaded on the surface, with a ZnO loading of 5-8 wt%, a tube diameter of 50-80 nm, and an aspect ratio of >30.

2. The cryogenic polyolefin packaging film according to claim 1, wherein, The metallocene polyolefin is metallocene linear low-density polyethylene, the PCR of the middle layer is LLDPE-PCR, and the PCR of the outer layer is LDPE-PCR.

3. The cryogenic polyolefin packaging film according to claim 1, wherein, The benzoyl peroxide microcapsule wall material is a polylactic acid-glycolic acid copolymer, with a core content of 60-70% and a particle size of 200-500 nm.

4. The cryogenic polyolefin packaging film according to claim 1, wherein, The polydopamine-coated chitosan has a dopamine coating layer thickness of 10-20 nm and a chitosan deacetylation degree ≥90%.

5. The process for the preparation of a low temperature polyolefin packaging film according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1 Prepare all raw materials according to the formula; S2 three-layer co-extrusion; S3 piezoelectric activation and pre-crosslinking: A piezoelectric oscillator is installed at the die head outlet, and a 75-85℃ hot air tunnel treatment is performed for 10-20 seconds. S4 Ultra-Fast Freezing; S5 synergistic irradiation crosslinking: Electron-terahertz wave synchronous irradiation; S6 Ultrasonic-Assisted Bidirectional Stretching; S7 curing and shaping.

6. The process for the production of a cryogenic polyolefin packaging film according to claim 5, characterized in that, The preparation method of the modified lignin nanofibers is as follows: (a) Enzyme activation treatment: Disperse alkali lignin in phosphate buffer at pH 8-9, add laccase and mediator ABTS, and react with shaking at 45-55℃ for 2-4 hours. (b) Depolymerization of ionic liquid: The reaction products are transferred to [BMIM]Cl ionic liquid and microwaved at 170-180℃ for 10-20 min. (c) Plasma grafting: The depolymerization product is placed in a plasma reaction chamber and treated with a pulsed power supply for 3-5 minutes, while acrylic acid vapor is introduced. (d) Nanofiberization: Nanofibers are obtained by 5-8 cycles of high-pressure homogenization.

7. The method for preparing the low-temperature polyolefin packaging film as described in claim 5, characterized in that, The modified nano-kaolinite is prepared as follows: (a) Supercritical CO2 intercalation: Kaolinite and urea are mixed at a mass ratio of 1:2.5-3.5 and placed in a supercritical reactor for 3-4 hours; (b) Dispersion treatment: The intercalation product is added to an organic solvent and dispersed thoroughly; (c) Grafting reaction: Under stirring, polyethylene glycol-polylactic acid block copolymer is slowly added and reacted at 45-50℃ for 4-6 hours; (d) Separation and washing: After the reaction is completed, the mixture is centrifuged, washed multiple times with deionized water and ethanol, and then dried at 55-65℃ for 12h.

8. The method for preparing the low-temperature polyolefin packaging film as described in claim 5, characterized in that, The modified tourmaline nanotubes are prepared as follows: tourmaline nanotubes are dispersed in 0.1M zinc nitrate solution, hydrothermally reacted at 175-185℃ for 3-5 hours, and calcined at 400-500℃ for 1.5-2.5 hours.

9. The method for preparing the low-temperature polyolefin packaging film as described in claim 5, characterized in that, The preparation method of the benzoyl peroxide microcapsules is as follows: a polyemulsification method is used, in which a dichloromethane solution of polylactic acid-glycolic acid copolymer is coated with an aqueous phase of peroxide, and the solvent is evaporated after ultrasonic emulsification.

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