Multi-additive synergistic enhanced degradable packaging composite film and preparation method thereof

Abstract

The invention relates to the technical field of composite film preparation, in particular to a multi-additive synergistic enhanced degradable packaging composite film and a preparation method thereof, and the multi-additive synergistic enhanced degradable packaging composite film comprises a matrix material group, a barrier system, an anti-hydrolysis system and a stable system; the base material comprises the following components in parts by mass: 25-35 parts of polylactic acid; 15 to 25 parts of poly (butylene adipate / terephthalate); and 8-15 parts of thermoplastic starch. Through multi-dimensional collaborative design of the matrix material, the barrier system, the hydrolysis-resistant system and the stable system, the performance bottleneck of a traditional material is broken through, and the contradiction between brittleness and flexibility is solved through rigid-flexible blending of matrix components; according to the present invention, the uniform dispersion and the interface strengthening of the nano-filler are ensured by using the melt co-extrusion and the directional arrangement technology, and the composite film prepared by using the process has characteristics of excellent degradation rate, high strength, high barrier property and environmental adaptability, can be widely used in the high-end fields of cold chain food and medicine packaging, and solves the problems existing in the traditional technology.

Description

Technical Field

[0001] The present invention relates to the technical field of composite film preparation, in particular to a multi-adjuvant synergistically enhanced degradable packaging composite film and a preparation method thereof. Background Art

[0002] Degradable packaging composite film is an environmentally friendly packaging material made through multi-layer material composite technology. It can be decomposed into water, carbon dioxide and biomass by microorganisms under specific environmental conditions and eventually return to the natural cycle. Its materials are based on bio-based or degradable polymers, combined with functional additives and reinforcing components. It not only meets the mechanical strength and barrier properties of traditional packaging, but also avoids the long-term pollution of traditional plastics to the environment. Therefore, with the improvement of global environmental awareness, degradable packaging composite film has evolved from a single material to a composite system. Early bio-based materials were difficult to promote due to poor mechanical properties, high cost and uncontrollable degradation cycle. In recent years, through the introduction of nanofillers, blending modification and multi-layer composite technology, a balance between performance and environmental protection has been gradually achieved. However, traditional technologies still face challenges such as poor component compatibility, insufficient barrier properties and easy failure in humid environments.

[0003] Generally, traditional degradable composite films are mostly made of a single bio-based material and a small amount of inorganic filler. Their components are simple but their functions are limited. For example, pure PLA is highly brittle, starch-based materials are easily degraded by moisture absorption, and the uneven dispersion of inorganic fillers leads to insufficient barrier properties. In addition, the additive system is single and lacks anti-hydrolysis and stability synergistic mechanisms, resulting in rapid deterioration of the material in high temperature and high humidity environments, making it difficult to meet the long-term stability and functionality requirements of the food and pharmaceutical fields.

[0004] Based on this, the present invention provides a multi-adjuvant synergistically enhanced degradable packaging composite film and a preparation method thereof to solve the above-mentioned technical problems. Summary of the Invention

[0005] The object of the present invention is to provide a multi-adjuvant synergistically enhanced degradable packaging composite film and a preparation method thereof, so as to solve the problems mentioned in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a multi-adjuvant synergistically enhanced degradable packaging composite film, comprising a base material group, a barrier system, an anti-hydrolysis system and a stabilizing system;

[0008] The matrix material group comprises, by mass, 25-35 parts of polylactic acid; 15-25 parts of polybutylene adipate / terephthalate; and 8-15 parts of thermoplastic starch.

[0009] The barrier system comprises, by weight: 5-8 parts of nanocellulose whiskers; 4-6 parts of nano-montmorillonite; and 3-5 parts of chitosan-polylactic acid graft copolymer.

[0010] In the barrier system, nanocellulose whiskers and nano-montmorillonite form a three-dimensional network through hydrogen bonding and electrostatic interaction, synergistically reducing oxygen transmission rate by 40-60%;

[0011] The anti-hydrolysis system comprises, by mass, 1-3 parts of a carbodiimide anti-hydrolysis agent, 1-2 parts of nano zinc oxide, and 2-4 parts of epoxy soybean oil.

[0012] In the anti-hydrolysis system, carbodiimide and nano-zinc oxide capture carboxyl radicals and ultraviolet light respectively, inhibiting the hydrolysis chain reaction;

[0013] The stabilizing system comprises, by mass, 2-4 parts of titanium dioxide, 0.5-1.5 parts of calcium stearate, and 0.3-0.8 parts of dicumyl peroxide.

[0014] Preferably, the polylactic acid is prepared by ring-opening polymerization of L-lactide at a temperature of 170-190° C. and a pressure of less than 10 Pa in a vacuum environment using stannous octoate as a catalyst.

[0015] Preferably, the polybutylene adipate / terephthalate is prepared by ester exchange polycondensation reaction of terephthalic acid, adipic acid and butanediol under nitrogen protection.

[0016] Preferably, the thermoplastic starch is prepared by esterification modification of corn starch and glycerol under acidic conditions of pH 3-5 and temperature 90-110°C.

[0017] Preferably, the nanocellulose whiskers are prepared by acid hydrolysis-ultrasonic stripping of wood pulp cellulose in a sulfuric acid solution, and have a particle size of 50-100 nm.

[0018] Preferably, the nano-montmorillonite is prepared by ion exchange intercalation of sodium montmorillonite and hexadecyltrimethylammonium bromide in an aqueous phase at a temperature of 70-80° C., and the interlayer spacing is ≥2.5 nm.

[0019] Preferably, the chitosan-polylactic acid graft copolymer is prepared by ring-opening graft copolymerization of chitosan and lactide under vacuum conditions, with a grafting rate of ≥25%.

[0020] Preferably, the carbodiimide anti-hydrolysis agent is prepared by condensing diphenylmethane diisocyanate and aniline in a toluene solvent at a temperature of 80-100°C.

[0021] Based on the above composite film formula components, the present invention also proposes a method for preparing a multi-adjuvant synergistically enhanced degradable packaging composite film, comprising the following steps:

[0022] S1. Drying the polylactic acid, polybutylene adipate / terephthalate, and thermoplastic starch matrix materials separately:

[0023] Polylactic acid is dried in a vacuum drying oven at 80-90°C for 4-6 hours to ensure a moisture content of ≤0.05%. Polybutylene adipate / terephthalate is dried at 60-70°C for 3-4 hours to control the moisture content to ≤0.1%. Thermoplastic starch is dried at 50-60°C for 2-3 hours to ensure a moisture content of ≤5%. Nanocellulose whiskers, nano-montmorillonite, and chitosan-polylactic acid graft copolymer barrier materials are dried at 40-50°C for 1-2 hours to prevent agglomeration. All additives are stored in a desiccator with a humidity of ≤30% in advance. After drying, the components are initially packaged using a high-speed mixer to ensure the stability of the raw materials in subsequent processes.

[0024] S2. The dried matrix material group: 25-35 parts of polylactic acid, 15-25 parts of polybutylene adipate / terephthalate, 8-15 parts of thermoplastic starch were put into a high-speed mixer equipped with a heating jacket, set the temperature to 50-60 ° C, and mixed at 800-1200 rpm for 10-15 minutes to form a uniform matrix premix;

[0025] Add 5-8 parts of nanocellulose whiskers, 4-6 parts of nano-montmorillonite and 3-5 parts of chitosan-polylactic acid graft copolymer of the barrier system, turn on the ultrasonic disperser, frequency 20-40kHz, power 300-500W, and continuously mix at 1500-2000rpm at 60-70℃ for 20-30 minutes to fully disperse the nanomaterials and embed them into the matrix interface;

[0026] Add 1-3 parts of carbodiimide anti-hydrolysis agent, 1-2 parts of nano zinc oxide, 2-4 parts of epoxidized soybean oil, and 2-4 parts of titanium dioxide, 0.5-1.5 parts of calcium stearate, and 0.3-0.8 parts of dicumyl peroxide as the anti-hydrolysis system in sequence, turn off the ultrasonic wave, and mix at a low speed of 500-800 rpm for 5-8 minutes to avoid the loss of additives flying, so as to form a homogeneous mixture;

[0027] S3. The mixture is fed into a twin-screw extruder for melt blending, and the extruder temperature is set in a zone and extruded. The screw speed is set to 180-220 rpm, the back pressure is 2.0-3.5 MPa, and the directional arrangement is characterized by taking a slice of the granulated particles and testing the diffraction angle of the nano-montmorillonite (001) crystal plane by X-ray diffraction (XRD). The calculated interlayer spacing is expanded to 3.8-4.2 nm (the original sodium-montmorillonite is 1.2 nm), indicating that high shear force achieves lamellar exfoliation and directional arrangement. The extruded molten strip is cooled in a water-cooling tank at a water temperature of 15-25 ° C and cut into particles with a diameter of 2-3 mm and a length of 3-5 mm by a pelletizer. The moisture content of the particles is ≤0.1%, and the granulation is completed;

[0028] S4. Put the pellets into the three-layer co-extrusion film blowing unit and extrude them in three layers simultaneously:

[0029] The temperature of the upper main matrix layer is 160-170℃;

[0030] Middle barrier layer 165-175℃;

[0031] The lower functional layer temperature is 155-165℃, and the die temperature is 170-175℃;

[0032] The melt pressure is maintained at 12-18MPa. The bubble diameter is controlled to 500-600mm by adjusting the blowing ratio: 2.8-3.2:1 and the pulling speed. The film thickness is accurate to 20-50μm. The cooling air ring is 200-300m 3 / h air volume is used to quickly cool and shape the film bubble to form a uniform composite film structure;

[0033] S5. The formed film is further cooled on double-sided chill rolls, with the upper roll at 20-25°C and the lower roll at 15-20°C to prevent shrinkage and deformation caused by thermal stress. It is then corona treated with a power of 3-5kW and a treatment speed of 10-15m / min to achieve a surface tension of ≥42mN / m to improve adhesion for subsequent printing or aluminum plating. During winding, taper tension control is used, with an initial tension of 50-60N and a final tension of 30-40N to prevent adhesion between film layers due to excessive pressure.

[0034] S6. The rolled composite film is fed into the slitting machine. The slitting width is adjusted according to demand. The blade linear speed is synchronized with the pulling speed to ensure that the cut edges are smooth and burr-free. The slit film rolls are vacuum-packed in aluminum foil composite bags and stored in a cool, dry environment with a temperature of 15-25°C and a humidity of ≤40% to avoid moisture absorption or oxidative degradation.

[0035] Preferably, the extruder temperature in step S3 is set to:

[0036] The feeding section of zone 1 is at 140-150℃ to prevent degradation of thermoplastic starch; the melting section of zone 2 is at 160-170℃ to promote compatibility of matrix materials; the mixing section of zone 3 is at 175-185℃ to strengthen the exfoliation and interface bonding of nano-montmorillonite sheets; the homogenizing section of zone 4 is at 170-175℃ to reduce melt viscosity; and the die head temperature is 165-170℃.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The multi-additive synergistically enhanced degradable packaging composite film of the present invention breaks through the performance bottleneck of traditional materials through the multi-dimensional collaborative design of the matrix material, barrier system, anti-hydrolysis system and stabilization system. The rigid-flexible blending of the matrix components solves the contradiction between brittleness and flexibility; the composite barrier system of nanocellulose and montmorillonite significantly reduces the oxygen permeability; the combination of carbodiimide anti-hydrolysis agent and nano zinc oxide inhibits uncontrolled degradation in a humid environment. At the same time, through melt co-extrusion and directional arrangement technology, the uniform dispersion and interface strengthening of the nanofiller are ensured. Compared with the traditional scheme, the composite film prepared by the process of the present invention has high strength, high barrier properties and environmental adaptability while maintaining an excellent degradation rate. It can be widely used in the high-end fields of cold chain food and pharmaceutical packaging, and solves the problems existing in traditional technologies. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0040] 1. Materials:

[0041] The components of the multi-adjuvant synergistically enhanced degradable packaging composite film material of the present invention are all commercially available unless otherwise specified.

[0042] The present invention provides a multi-adjuvant synergistically enhanced degradable packaging composite film, comprising a base material group, a barrier system, an anti-hydrolysis system and a stabilizing system;

[0043] The matrix material group includes, by weight: polylactic acid: 25-35 parts; polybutylene adipate / terephthalate: 15-25 parts; thermoplastic starch: 8-15 parts;

[0044] The barrier system comprises, by weight: 5-8 parts of nanocellulose whiskers; 4-6 parts of nano-montmorillonite; and 3-5 parts of chitosan-polylactic acid graft copolymer.

[0045] The anti-hydrolysis system includes, by mass: carbodiimide anti-hydrolysis agent: 1-3 parts; nano zinc oxide: 1-2 parts; epoxidized soybean oil: 2-4 parts;

[0046] The stabilizing system comprises, by weight, 2-4 parts of titanium dioxide, 0.5-1.5 parts of calcium stearate, and 0.3-0.8 parts of dicumyl peroxide.

[0047] It should be noted that polylactic acid is prepared by ring-opening polymerization of L-lactide at a temperature of 170-190°C and a pressure of less than 10 Pa in a vacuum environment by catalyzing stannous octoate.

[0048] It should be noted that polybutylene adipate / terephthalate is prepared by ester exchange polycondensation reaction of terephthalic acid, adipic acid and butanediol under nitrogen protection.

[0049] It should also be noted that thermoplastic starch is prepared by esterification modification of corn starch and glycerol under acidic conditions of pH 3-5 and temperature 90-110°C.

[0050] It should also be noted that the nanocellulose whiskers are prepared by acid hydrolysis-ultrasonic exfoliation of wood pulp cellulose in a sulfuric acid solution, with a particle size of 50-100 nm.

[0051] It should also be noted that nano-montmorillonite is prepared by ion exchange intercalation of sodium montmorillonite and hexadecyltrimethylammonium bromide in an aqueous phase at a temperature of 70-80°C, with an interlayer spacing of ≥2.5nm.

[0052] It should be noted that the chitosan-polylactic acid graft copolymer is prepared by ring-opening graft copolymerization of chitosan and lactide under vacuum conditions, with a grafting rate of ≥25%.

[0053] It should also be noted that the carbodiimide anti-hydrolysis agent is prepared by condensing diphenylmethane diisocyanate and aniline in a toluene solvent at a temperature of 80-100°C.

[0054] 2. Process:

[0055] Based on the above composite film formula components, the present invention also proposes a method for preparing a multi-adjuvant synergistically enhanced degradable packaging composite film, comprising the following steps:

[0056] S1. Drying the polylactic acid, polybutylene adipate / terephthalate, and thermoplastic starch matrix materials separately:

[0057] Polylactic acid is dried in a vacuum drying oven at 80-90°C for 4-6 hours to ensure a moisture content of ≤0.05%. Polybutylene adipate / terephthalate is dried at 60-70°C for 3-4 hours to control the moisture content to ≤0.1%. Thermoplastic starch is dried at 50-60°C for 2-3 hours to ensure a moisture content of ≤5%. Nanocellulose whiskers, nano-montmorillonite, and chitosan-polylactic acid graft copolymer barrier materials are dried at 40-50°C for 1-2 hours to prevent agglomeration. All additives are stored in a desiccator with a humidity of ≤30% in advance. After drying, the components are initially packaged using a high-speed mixer to ensure the stability of the raw materials in subsequent processes.

[0058] S2. The dried matrix material group: 25-35 parts of polylactic acid, 15-25 parts of polybutylene adipate / terephthalate, 8-15 parts of thermoplastic starch were put into a high-speed mixer equipped with a heating jacket, set the temperature to 50-60 ° C, and mixed at 800-1200 rpm for 10-15 minutes to form a uniform matrix premix;

[0059] Add 5-8 parts of nanocellulose whiskers, 4-6 parts of nano-montmorillonite and 3-5 parts of chitosan-polylactic acid graft copolymer of the barrier system, turn on the ultrasonic disperser, frequency 20-40kHz, power 300-500W, and continuously mix at 1500-2000rpm at 60-70℃ for 20-30 minutes to fully disperse the nanomaterials and embed them into the matrix interface;

[0060] Add 1-3 parts of carbodiimide anti-hydrolysis agent, 1-2 parts of nano zinc oxide, 2-4 parts of epoxidized soybean oil, and 2-4 parts of titanium dioxide, 0.5-1.5 parts of calcium stearate, and 0.3-0.8 parts of dicumyl peroxide as the anti-hydrolysis system in sequence, turn off the ultrasonic wave, and mix at a low speed of 500-800 rpm for 5-8 minutes to avoid the loss of additives flying, so as to form a homogeneous mixture;

[0061] S3. The mixture is fed into a twin-screw extruder for melt blending, and the extruder temperature is set in a zone and extruded. The screw speed is set to 180-220 rpm, the back pressure is 2.0-3.5 MPa, and the directional arrangement is characterized by taking a slice of the granulated particles and testing the diffraction angle of the nano-montmorillonite (001) crystal plane by X-ray diffraction (XRD). The calculated interlayer spacing is expanded to 3.8-4.2 nm (the original sodium-montmorillonite is 1.2 nm), indicating that high shear force achieves lamellar exfoliation and directional arrangement. The extruded molten strip is cooled in a water-cooling tank at a water temperature of 15-25 ° C and cut into particles with a diameter of 2-3 mm and a length of 3-5 mm by a pelletizer. The moisture content of the particles is ≤0.1%, and the granulation is completed;

[0062] S4. Put the pellets into the three-layer co-extrusion film blowing unit and extrude them in three layers simultaneously:

[0063] The temperature of the upper main matrix layer is 160-170℃;

[0064] Middle barrier layer 165-175℃;

[0065] The lower functional layer temperature is 155-165℃, and the die temperature is 170-175℃;

[0066] The melt pressure is maintained at 12-18MPa. The bubble diameter is controlled to 500-600mm by adjusting the blowing ratio: 2.8-3.2:1 and the pulling speed. The film thickness is accurate to 20-50μm. The cooling air ring is 200-300m 3 / h air volume is used to quickly cool and shape the film bubble to form a uniform composite film structure;

[0067] S5. The formed film is further cooled on double-sided chill rolls, with the upper roll at 20-25°C and the lower roll at 15-20°C to prevent shrinkage and deformation caused by thermal stress. It is then corona treated with a power of 3-5kW and a treatment speed of 10-15m / min to achieve a surface tension of ≥42mN / m to improve adhesion for subsequent printing or aluminum plating. During winding, taper tension control is used, with an initial tension of 50-60N and a final tension of 30-40N to prevent adhesion between film layers due to excessive pressure.

[0068] S6. The rolled composite film is fed into the slitting machine. The slitting width is adjusted according to demand. The blade linear speed is synchronized with the pulling speed to ensure that the cut edges are smooth and burr-free. The slit film rolls are vacuum-packed in aluminum foil composite bags and stored in a cool, dry environment with a temperature of 15-25°C and a humidity of ≤40% to avoid moisture absorption or oxidative degradation.

[0069] It should be noted that the extruder temperature in step S3 is set to:

[0070] The first zone feeding section is 140-150℃ to prevent degradation of thermoplastic starch; the second zone melting section is 160-170℃ to promote compatibility of the matrix material; the third zone mixing section is 175-185℃ to strengthen the exfoliation of nano-montmorillonite sheets and interface bonding; the fourth zone homogenization section is 170-175℃ to reduce melt viscosity; the die head temperature is 165-170℃;

[0071] Example 1. In this example, a method for preparing a multi-adjuvant synergistically enhanced degradable packaging composite film is provided. According to step S1, each component is dried to a specified moisture content. According to step S2, a matrix, barrier, anti-hydrolysis and stabilization system are mixed. According to step S3, zone-controlled extrusion is performed: zone 1 is 145°C, zone 2 is 165°C, zone 3 is 180°C, zone 4 is 172°C, and the die is 168°C. According to step S4, three layers are co-extruded: upper layer is 160°C, middle layer is 165°C, and lower layer is 155°C.

[0072] Among them, 30 parts of polylactic acid, 20 parts of polybutylene adipate / terephthalate, 10 parts of thermoplastic starch, 6 parts of nanocellulose whiskers, 5 parts of nano-montmorillonite, 4 parts of chitosan-polylactic acid graft copolymer, 2 parts of carbodiimide anti-hydrolysis agent, 1.5 parts of nano zinc oxide, 3 parts of epoxidized soybean oil, 3 parts of titanium dioxide, 1.0 part of calcium stearate, and 0.5 parts of dicumyl peroxide;

[0073] After co-extrusion is completed, cut according to steps S5-S6;

[0074] Example 2: In this example, the polylactic acid is reduced to 25 parts, the thermoplastic starch is increased to 12 parts, and the other process and material component parameters are the same as those in Example 1;

[0075] Example 3: In this example, the polylactic acid is increased to 35 parts, the thermoplastic starch is reduced to 15 parts, and the other process and material component parameters are the same as those in Example 1;

[0076] Example 4: In this example, the amount of thermoplastic starch was increased to 12 parts, and other process and material component parameters were the same as those in Example 1;

[0077] Example 5: In this example, the amount of epoxidized soybean oil was increased to 5 parts, and other process and material component parameters were the same as those in Example 1;

[0078] The material component parameters of Examples 1 to 5 are shown in Table 1:

[0079] Table 1 Material composition parameters of the embodiment

[0080]

[0081]

[0082] Comparative Example 1: In this comparative example, 40 parts of polylactic acid were used, and other process and material component parameters were the same as those in Example 1;

[0083] Comparative Example 2: In this comparative example, 30 parts of thermoplastic starch were used, and other process and material component parameters were the same as those in Example 1;

[0084] Comparative Example 3: In this comparative example, 20 parts of thermoplastic starch were used, and other process and material component parameters were the same as those in Example 1;

[0085] Comparative Example 4: In this comparative example, 10 parts of nanocellulose whiskers were used, and other process and material component parameters were the same as those in Example 1;

[0086] Comparative Example 5: In this comparative example, 8 parts of nano-montmorillonite were used, and other process and material component parameters were the same as those in Example 1;

[0087] The material component parameters of Comparative Examples 1 and 2 are shown in Table 2:

[0088] Table 2 Comparative Example Material Component Parameters

[0089]

[0090] 3. Performance test:

[0091] The controlled variable method was used to adjust the ratio of the base material group, barrier system, and additives to test the mechanical properties (tensile strength, elongation at break), barrier properties (oxygen permeability), and degradation rate (180-day natural degradation rate) of five examples and five comparative examples. The steps are as follows:

[0092] a. Tensile strength and elongation at break test:

[0093] Test standards: ISO527-3, GB / T1040.3-2006;

[0094] Sample size parameters shape: dumbbell-shaped specimen (Type1B);

[0095] size:

[0096] Total length: ≥150mm;

[0097] Gauge length: 25mm;

[0098] Gauge width: 4mm;

[0099] Thickness: consistent with the actual thickness of the film (20-50μm);

[0100] a1. Sample preparation: Use a standard cutter to cut the specimens, with at least 5 specimens per group;

[0101] a2. Pretreatment: Condition at 23±2°C, 50±5% humidity for 48 hours;

[0102] Testing equipment: Universal material testing machine (accuracy ±1%)

[0103] Parameter settings:

[0104] Clamping distance: 50mm;

[0105] Tensile speed: 50 mm / min;

[0106] a3. Calculation of results: Tensile strength (MPa) = maximum load (N) / (sample width × thickness);

[0107] Elongation at break (%) = (elongation of the gauge section at break / original gauge section length) × 100;

[0108] b. Oxygen Transmission Rate (OTR) Test:

[0109] Test standards: ASTM D3985 or ISO 15105-1, GB / T 1038-2000;

[0110] Sample size parameters shape: circular film sheet;

[0111] Diameter: ≥70mm (effective test area ≥50cm 2 );

[0112] Thickness: consistent with the actual thickness of the film (20-50μm);

[0113] b1. Sample preparation: Cut smooth, defect-free circular specimens, 3 specimens per group;

[0114] b2. Pretreatment: Conditioned at 23±2°C, 50±5% humidity for 24 hours;

[0115] Test equipment: oxygen transmission rate tester (MOCONOX-TRAN2 / 21);

[0116] Parameter settings:

[0117] Test temperature: 23±0.5℃;

[0118] Test humidity: 0% RH (dry conditions) or 50% RH (as required)

[0119] Oxygen pressure difference: normal pressure (pure oxygen on one side and nitrogen as carrier gas on the other side);

[0120] b3. Calculation of results: oxygen transmission rate (cm 3 / (m 2 ·day·atm)) = oxygen permeation rate per unit time / (film area × oxygen partial pressure difference);

[0121] c.180-day natural degradation rate test

[0122] Test standards: ISO14855-1, GB / T19277.1-2011;

[0123] Sample size parameters shape: square film

[0124] Size: 20mm×20mm

[0125] Thickness: consistent with the actual thickness of the film (20-50μm);

[0126] c1. Sample preparation: Cut the specimens, with at least 3 specimens per group, dry them and weigh them (initial mass m0);

[0127] c2. Degradation environment:

[0128] Composting conditions: mature compost (containing cellulose, sawdust, etc.) at 58±2°C, 50-60% humidity, and pH 6-8;

[0129] Natural burial conditions: simulate natural soil environment (temperature 25±5℃, humidity 30-50%);

[0130] Test period: 180 days, regular sampling (every 30 days);

[0131] c3. Cleaning and weighing:

[0132] Take out the sample, remove the surface attachments, and dry to constant weight (final mass m1);

[0133] c4. Calculation of results: degradation rate (%) = (m0-m1) / m0×100;

[0134] It should be noted that if the CO2 release method is used, the CO2 accumulation amount must be measured by an infrared detector to calculate the carbon conversion rate;

[0135] The performance data of the packaging films prepared in Examples 1 to 5 are shown in Table 3:

[0136] Table 3 Performance data of the embodiment

[0137]

[0138] The performance data of the packaging films prepared in Comparative Examples 1 to 5 are shown in Table 3:

[0139] Table 4 Comparative Example Performance Data

[0140]

[0141] As can be seen from Tables 2, 3, and 4, the parameters of the samples prepared in the comparative examples were significantly lower than those of the packaging films prepared in the examples after performance testing. Therefore, the component intervals in the examples of the present invention are scientifically reasonable.

[0142] It can be seen from Table 1 and Table 3 that in Example 1, 30 parts of polylactic acid, 20 parts of thermoplastic starch, and 10 parts of thermoplastic starch form a balance of rigidity and flexibility, 6 parts of nanocellulose whiskers, 5 parts of nano-montmorillonite, and 4 parts of chitosan-polylactic acid graft copolymer synergistically improve the barrier properties, 2 parts of carbodiimide anti-hydrolysis agent and 1.5 parts of nano zinc oxide effectively inhibit hydrolysis, and the melt co-extrusion temperature gradient is: 145°C in zone 1, 165°C in zone 2, 180°C in zone 3, 172°C in zone 4, and 168°C in die head, the screw speed is 200rpm, and the back pressure is 3.0MPa to ensure the directional arrangement of the nanomaterials.

[0143] The packaging film sample prepared in Example 1 has a tensile strength of 37.2 MPa, an elongation at break of 280%, and an oxygen permeability of 38 cm3 / m 2 The natural degradation rate after 180 days was 92%. The comprehensive performance was the best among the embodiments and comparative examples. Therefore, embodiment 1 of the present invention was the best embodiment.

[0144] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0145] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A multi-adjuvant synergistically enhanced degradable packaging composite film, characterized in that: Including base material group, barrier system, anti-hydrolysis system and stabilization system; The matrix material group comprises, by mass, 25-35 parts of polylactic acid; 15-25 parts of polybutylene adipate / terephthalate; and 8-15 parts of thermoplastic starch. The barrier system comprises, by weight, 5-8 parts of nanocellulose whiskers, 4-6 parts of nano-montmorillonite, and 3-5 parts of chitosan-polylactic acid graft copolymer. The nanocellulose whiskers and nano-montmorillonite in the barrier system form a three-dimensional network through hydrogen bonding and electrostatic interaction, synergistically reducing oxygen transmission rate by 40-60%. The anti-hydrolysis system comprises, by mass, 1-3 parts of a carbodiimide anti-hydrolysis agent, 1-2 parts of nano zinc oxide, and 2-4 parts of epoxidized soybean oil. The carbodiimide and nano zinc oxide in the anti-hydrolysis system capture carboxyl radicals and ultraviolet light, respectively, to inhibit the hydrolysis chain reaction. The stabilizing system comprises, by mass, 2-4 parts of titanium dioxide, 0.5-1.5 parts of calcium stearate, and 0.3-0.8 parts of dicumyl peroxide.

2. The multi-adjuvant synergistically enhanced degradable packaging composite film according to claim 1, characterized in that: The polylactic acid is prepared by subjecting L-lactide to a ring-opening polymerization reaction catalyzed by stannous octoate at a temperature of 170-190° C. and a pressure of less than 10 Pa in a vacuum environment.

3. The multi-adjuvant synergistically enhanced degradable packaging composite film according to claim 2, characterized in that: The polybutylene adipate / terephthalate is prepared by ester exchange polycondensation reaction of terephthalic acid, adipic acid and butanediol under nitrogen protection.

4. The multi-adjuvant synergistically enhanced degradable packaging composite film according to claim 1, characterized in that: The thermoplastic starch is prepared by esterification modification of corn starch and glycerol under acidic conditions of pH 3-5 and temperature 90-110°C.

5. The multi-adjuvant synergistically enhanced degradable packaging composite film according to claim 4, characterized in that: The nano cellulose whiskers are prepared by acid hydrolysis-ultrasonic stripping of wood pulp cellulose in a sulfuric acid solution, and have a particle size of 50-100 nm.

6. The multi-adjuvant synergistically enhanced degradable packaging composite film according to claim 4, characterized in that: The nano-montmorillonite is prepared by intercalating sodium-montmorillonite and hexadecyltrimethylammonium bromide in an aqueous phase at a temperature of 70-80° C. through ion exchange, and the interlayer spacing is ≥2.5 nm.

7. The multi-adjuvant synergistically enhanced degradable packaging composite film according to claim 1, characterized in that: The chitosan-polylactic acid graft copolymer is prepared by ring-opening graft copolymerization of chitosan and lactide under vacuum conditions, with a grafting rate of ≥25%.

8. The multi-adjuvant synergistically enhanced degradable packaging composite film according to claim 1, characterized in that: The carbodiimide anti-hydrolysis agent is prepared by condensing diphenylmethane diisocyanate and aniline in a toluene solvent at a temperature of 80-100°C.

9. The method for preparing a multi-adjuvant synergistically enhanced degradable packaging composite film according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Drying the polylactic acid, polybutylene adipate / terephthalate, and thermoplastic starch matrix materials separately: Polylactic acid is dried in a vacuum drying oven at 80-90°C for 4-6 hours to ensure a moisture content of ≤0.05%. Polybutylene adipate / terephthalate is dried at 60-70°C for 3-4 hours to control the moisture content to ≤0.1%. Thermoplastic starch is dried at 50-60°C for 2-3 hours to ensure a moisture content of ≤5%. Nanocellulose whiskers, nano-montmorillonite, and chitosan-polylactic acid graft copolymer barrier materials are dried at 40-50°C for 1-2 hours to prevent agglomeration. All additives are stored in a desiccator with a humidity of ≤30% in advance. After drying, the components are initially packaged using a high-speed mixer to ensure the stability of the raw materials in subsequent processes. S2. The dried matrix material group: 25-35 parts of polylactic acid, 15-25 parts of polybutylene adipate / terephthalate, 8-15 parts of thermoplastic starch were put into a high-speed mixer equipped with a heating jacket, set the temperature to 50-60 ° C, and mixed at 800-1200 rpm for 10-15 minutes to form a uniform matrix premix; Add 5-8 parts of nanocellulose whiskers, 4-6 parts of nano-montmorillonite and 3-5 parts of chitosan-polylactic acid graft copolymer of the barrier system, turn on the ultrasonic disperser, frequency 20-40kHz, power 300-500W, and continuously mix at 1500-2000rpm at 60-70℃ for 20-30 minutes to fully disperse the nanomaterials and embed them into the matrix interface; Add 1-3 parts of carbodiimide anti-hydrolysis agent, 1-2 parts of nano zinc oxide, 2-4 parts of epoxidized soybean oil, and 2-4 parts of titanium dioxide, 0.5-1.5 parts of calcium stearate, and 0.3-0.8 parts of dicumyl peroxide as the anti-hydrolysis system in sequence, turn off the ultrasonic wave, and mix at a low speed of 500-800 rpm for 5-8 minutes to avoid the loss of additives flying, so as to form a homogeneous mixture; S3. The mixture is fed into a twin-screw extruder for melt blending, and the extruder temperature is set in a zone and extruded. The screw speed is set to 180-220 rpm, the back pressure is 2.0-3.5 MPa, and the directional arrangement is characterized by taking a slice of the granulated particles and testing the diffraction angle of the nano-montmorillonite (001) crystal plane by X-ray diffraction (XRD). The calculated interlayer spacing is expanded to 3.8-4.2 nm (the original sodium-montmorillonite is 1.2 nm), indicating that high shear force achieves lamellar exfoliation and directional arrangement. The extruded molten strip is cooled in a water-cooling tank at a water temperature of 15-25 ° C and cut into particles with a diameter of 2-3 mm and a length of 3-5 mm by a pelletizer. The moisture content of the particles is ≤0.1%, and the granulation is completed; S4. Put the pellets into the three-layer co-extrusion film blowing unit and extrude them in three layers simultaneously: The temperature of the upper main matrix layer is 160-170℃; Middle barrier layer 165-175℃; The lower functional layer temperature is 155-165℃, and the die temperature is 170-175℃; The melt pressure is maintained at 12-18MPa. The bubble diameter is controlled to 500-600mm by adjusting the blowing ratio: 2.8-3.2:1 and the pulling speed. The film thickness is accurate to 20-50μm. The cooling air ring is 200-300m 3 / h air volume is used to quickly cool and shape the film bubble to form a uniform composite film structure; S5. The formed film is further cooled on double-sided chill rolls, with the upper roll at 20-25°C and the lower roll at 15-20°C to prevent shrinkage and deformation caused by thermal stress. It is then corona treated with a power of 3-5kW and a treatment speed of 10-15m / min to achieve a surface tension of ≥42mN / m to improve adhesion for subsequent printing or aluminum plating. During winding, taper tension control is used, with an initial tension of 50-60N and a final tension of 30-40N to prevent adhesion between film layers due to excessive pressure. S6. The rolled composite film is fed into the slitting machine. The slitting width is adjusted according to demand. The blade linear speed is synchronized with the pulling speed to ensure that the cut edges are smooth and burr-free. The slit film rolls are vacuum-packed in aluminum foil composite bags and stored in a cool, dry environment with a temperature of 15-25°C and a humidity of ≤40% to avoid moisture absorption or oxidative degradation.

10. The method for preparing a multi-adjuvant synergistically enhanced degradable packaging composite film according to claim 9, characterized in that: In step S3, the extruder temperature is set to: The feeding section of zone 1 is at 140-150℃ to prevent degradation of thermoplastic starch; the melting section of zone 2 is at 160-170℃ to promote compatibility of matrix materials; the mixing section of zone 3 is at 175-185℃ to strengthen the exfoliation and interface bonding of nano-montmorillonite sheets; the homogenizing section of zone 4 is at 170-175℃ to reduce melt viscosity; and the die head temperature is 165-170℃.

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