Degradable composite film, preparation method thereof and food packaging

Abstract

The application provides a degradable composite film, a preparation method thereof and food packaging, and belongs to the field of biodegradable polymer materials. The application is modified by taking polylactic acid as a main body to prepare a composite film with a multilayer structure; the tensile strength of the composite film is 40-50 MPa, the elongation at break is 30-66%, the tensile strength retention rate is 85-95%, the elongation at break retention rate is 80-90%, the mechanical property is excellent, the composite film has high barrier property and anti-aging property to oxygen and water vapor in the air, and the stability and service life of the composite film are improved. The composite film is applied to food packaging, so that the food in the packaging is kept fresh and dry, and the polyethylene glycol in the composite film does not occur precipitation after long-time use, and the composite film has excellent stability.

Description

Technical Field

[0001] This invention relates to the field of biodegradable polymer materials, and more particularly to a biodegradable composite film, its preparation method, and food packaging. Background Technology

[0002] Food packaging films have different performance requirements depending on the type of food. Films for vegetables and fruits need to be permeable to oxygen, while films for meat need to be permeable to water vapor. Films for dried fruits and puffed foods need to be barrier to oxygen, water vapor, and carbon dioxide. Petroleum-based plastic packaging films have good barrier and heat-sealing properties, good mechanical properties, and low cost, making them widely used in food packaging. Petroleum-based plastics mainly include polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS).

[0003] CN214419851U discloses a food sealing packaging film, comprising a polyethylene terephthalate film layer, a polystyrene film layer fixed to the lower surface of the polyethylene terephthalate film layer by heat fusion, a polyphenylene sulfide film layer fixed to the lower surface of the polystyrene film layer by heat fusion, a polyethylene film layer fixed to the lower surface of the polyphenylene sulfide film layer by heat fusion, and a polytetrafluoroethylene protective layer fixed to the lower surface of the polyethylene film layer by heat fusion.

[0004] CN104311980B discloses a high-stiffness polyethylene blown film material, which is made from the following raw materials in parts by weight: 99.93-98.8% ethylene-hexene copolymer polyethylene base resin, 0.015-0.35% main antioxidant, 0.035-0.55% co-antioxidant, and 0.02-0.03% heat stabilizer. After mixing, the mixture is added to an extrusion granulator for granulation. The resulting granules are cooled with cooling water to obtain a granular product, which is the high-stiffness polyethylene blown film material.

[0005] Petroleum-based plastics offer good barrier properties but are difficult to degrade and recycle, requiring incineration and landfill disposal. This leads to severe pollution of water, soil, and air, exacerbating environmental problems. Currently, fully biodegradable materials are gradually replacing petroleum-based plastics. These materials degrade continuously under the influence of biological organisms or bodily fluids and their acids, thus meeting environmental protection requirements. Biodegradable materials include polymers such as peptides, polyamino acids, polyesters, polylactic acid, chitosan, and collagen / gelatin. However, single biodegradable materials used as food-grade packaging films often exhibit poor barrier properties and fail to meet the mechanical properties required for food-grade packaging. Therefore, the modification process of biodegradable materials has been extensively studied.

[0006] CN109720055B discloses a polyvinyl alcohol / polylactic acid composite film and its preparation method. The polyvinyl alcohol / polylactic acid composite film includes a polyvinyl alcohol film layer and a polylactic acid film layer. The polyvinyl alcohol film layer is formed from a polyvinyl alcohol composition containing polyvinyl alcohol, a plasticizer, a lubricant, and optional additives. The plasticizer contains component A, component B, and component C. Component A is one or more of glycerol, ethylene glycol, polyethylene glycol, and pentaerythritol. Component B is one or more of magnesium chloride, magnesium nitrate, calcium chloride, copper sulfate, and sodium acetate. Component C is water. This technical solution incorporates polyvinyl alcohol, which is difficult to degrade, and therefore does not meet the requirements for green and environmentally friendly practices.

[0007] CN103937185B discloses a fully biodegradable composite film and its preparation method. The composite film is composed of the following raw materials: polylactic acid, polyethylene glycol, citrate, ultrafine wool powder, solubilizer, ultrafine zeolite powder, ultrafine aluminum powder, ultrafine volcanic rock powder, silicone oil, and phosphite. This composite film is temperature resistant, tear resistant, and tensile resistant, and is completely biodegradable, causing no environmental pollution. It also has antibacterial properties, good transparency, and high gloss.

[0008] CN109337397A discloses an antibacterial and biodegradable food packaging film and its preparation method, which is made from the following raw materials in parts by weight: 50-80 parts of crop straw, 10-20 parts of succinic acid, 10-20 parts of polybutylene succinate, 12-22 parts of polylactic acid, 8-16 parts of polyvinyl alcohol, 6-12 parts of sepiolite, 5-10 parts of zinc oxide, 8-15 parts of silicon dioxide, 4-8 parts of γ-aminopropyltriethoxysilane, 3-8 parts of dispersant, 8-16 parts of tea polyphenols, 10-16 parts of chitosan, 9-15 parts of sodium benzoate, 15-30 parts of N-methylmorpholine-N-oxide NMMO / water, 4-9 parts of dodecyltrimethylammonium chloride, 2-7 parts of 1-ethyl-3-methylimidazolium tetrafluoroborate, 8-14 parts of isopropanol, and 10-20 parts of water. The formula contains polyvinyl alcohol, which is difficult to degrade. In addition, the oxygen permeability coefficient of the products prepared by it is greater than 100, which cannot meet the requirements of high-barrier food packaging.

[0009] In summary, to achieve the goal of green and environmentally friendly production, petroleum-based plastic films that cannot be completely degraded have been gradually replaced by biodegradable plastics. However, as food-grade packaging films, biodegradable plastics still cannot guarantee their performance in blocking air and water vapor, and their barrier performance is poor for some moisture-sensitive products. This is a technical problem that urgently needs to be solved. Summary of the Invention

[0010] To address the above problems, this invention provides a biodegradable composite film, its preparation method, and food packaging. The composite film can be completely decomposed by microorganisms without causing environmental pollution. Furthermore, the modified composite film improves the mechanical properties of biodegradable materials while ensuring the barrier properties of the composite film.

[0011] This invention provides a biodegradable composite film, which has a three-layer structure, including an inner layer, a middle layer and an outer layer, wherein the inner layer and the outer layer are film A and the middle layer is film B;

[0012] The components and their contents in membrane A are as follows:

[0013] Polylactic acid 86.2-96.9 parts by weight;

[0014] 3-10 parts by weight of polyethylene glycol;

[0015] Anti-hydrolysis agent 0.1-2 parts by weight;

[0016] Nucleating agent 0.1-1 parts by weight;

[0017] Heat stabilizer 0.2-0.8 parts by weight;

[0018] The components and their contents in the B membrane are as follows:

[0019] Polylactic acid 22.4-82.8 parts by weight;

[0020] 5-15 parts by weight of polyglycolic acid;

[0021] 5-20 parts by weight of polybutylene succinate;

[0022] 5-20 parts by weight of polypropylene carbonate;

[0023] 1-10 parts by weight of polyethylene glycol;

[0024] Inorganic nanomaterials, 1-10 parts by weight;

[0025] Anti-hydrolysis agent 0.1-2 parts by weight;

[0026] Nucleating agent 0.1-1 parts by weight;

[0027] Heat stabilizer 0.1-0.6 parts by weight;

[0028] The composite film has a tensile strength of 40-50 MPa, an elongation at break of 30-66%, a tensile strength retention rate of 85-95%, an elongation at break retention rate of 80-90%, and an oxygen permeability of 4-8 cm³. 3 / m 2 • 24h • 0.1MPa, water vapor transmission rate is 3-7g / m 2• After aging for 3 days at 70℃ and 70%RH for 24 hours, the tensile strength is 35-50MPa and the elongation at break is 25-35%; the compost degradation rate after 180 days is 90-100%.

[0029] Furthermore, the polylactic acid has a weight-average molecular weight of 120,000-200,000 Da.

[0030] Furthermore, the polyglycolic acid has a weight-average molecular weight of 60,000-150,000 Da.

[0031] Furthermore, the polybutylene succinate has a weight-average molecular weight of 80,000-160,000 Da.

[0032] Furthermore, the polypropylene carbonate has a weight-average molecular weight of 50,000-120,000 Da.

[0033] Furthermore, the polyethylene glycol has a molecular weight of 18,000-22,000 and is in powder form.

[0034] Furthermore, the inorganic nanomaterial is one of nano-alumina or nano-montmorillonite.

[0035] Furthermore, the anti-hydrolysis agent is one of 2,2'-(1,3-phenylene)dioxazoline, glycidyl phenyl ether, and triglycidyl isocyanate (TGIC).

[0036] Furthermore, the nucleating agent is one of sebacate dibenzoylhydrazine, N,N'-ethylenebis(1,2-hydroxystearamide), and p-tert-butyl[8]calixarene.

[0037] Furthermore, the heat stabilizer is one of dodecyl thiodipropionate, pentaerythritol tetra(3-lauryl thiopropionate), and 4,6-bis(octylthiomethyl)o-cresol.

[0038] Furthermore, the polylactic acid in the A film is blended with the polyethylene glycol to improve the mechanical properties and transparency of the composite film.

[0039] Furthermore, the polylactic acid in the B film is blended with the polyglycolic acid, the polybutylene succinate, and the polypropylene carbonate, which improves the barrier properties of the composite film.

[0040] This invention also provides a method for preparing a biodegradable composite film, comprising the following steps:

[0041] Step 1: The polylactic acid, polyethylene glycol, anti-hydrolysis agent, nucleating agent and heat stabilizer are stirred and mixed, and then extruded through a twin-screw extruder to obtain modified resin one;

[0042] Step 2: Place the modified resin into a casting machine to cast a film, thereby obtaining film A;

[0043] Step 3: Mix the polylactic acid, polyglycolic acid, polybutylene succinate, polypropylene carbonate, polyethylene glycol, inorganic nanomaterials, anti-hydrolysis agent, nucleating agent and heat stabilizer, and extrude the mixture through a twin-screw extruder to obtain modified resin II.

[0044] Step 4: Place the modified resin II into a casting machine to cast a film, thereby obtaining the B film;

[0045] Step 5: Combine the A film with the B film to obtain the biodegradable composite film.

[0046] Furthermore, the polylactic acid in step 1 has a weight-average molecular weight of 120,000-200,000 Da.

[0047] Furthermore, the polyethylene glycol in step 1 has a molecular weight of 18,000-22,000 and is in powder form.

[0048] Further, the anti-hydrolysis agent in step 1 is one of 2,2'-(1,3-phenylene)dioxazoline, glycidyl phenyl ether, and triglycidyl isocyanurate.

[0049] Further, the nucleating agent in step 1 is one of sebacate dibenzoylhydrazine, N,N'-ethylenebis(1,2-hydroxystearamide), and p-tert-butyl[8]calixarene.

[0050] Further, the heat stabilizer in step 1 is one of dodecyl thiodipropionate, pentaerythritol tetra(3-lauryl thiopropionate), and 4,6-bis(octylthiomethyl)o-cresol.

[0051] Further, in step 1, the content of polylactic acid is 86.2-96.9 parts by weight, the content of polyethylene glycol is 3-10 parts by weight, the content of anti-hydrolysis agent is 0.1-2 parts by weight, the content of nucleating agent is 0.1-1 parts by weight, and the content of heat stabilizer is 0.2-0.8 parts by weight.

[0052] Furthermore, the stirring speed in step 1 is 200-700 r / min, and the stirring time is 3-10 min.

[0053] Furthermore, the feed rate of the twin-screw extruder in step 1 is 10-30 kg / h.

[0054] Furthermore, in step 1, the main screw speed of the twin-screw extruder is 300-500 rpm.

[0055] Furthermore, the twin-screw extruder in step 1 is divided into eleven temperature zones, with the following temperatures for each zone: Zone 1: 120°C; Zone 2: 145°C; Zone 3: 160°C; Zone 4: 170°C; Zone 5: 180°C; Zone 6: 190°C; Zone 7: 190°C; Zone 8: 195°C; Zone 9: 200°C; Zone 10: 200°C; and Zone 11: 195°C.

[0056] Furthermore, in step 2, the main screw speed of the casting machine is 100-300 rpm.

[0057] Furthermore, the traction speed of the casting machine in step 2 is 10-20 m / min.

[0058] Furthermore, in step 2, the temperature zone of the casting machine is divided into five temperature zones, and the temperature of each zone is: zone 1 is 160°C, zone 2 is 170°C, zone 3 is 180°C, zone 4 is 190°C, and zone 5 is 190°C.

[0059] Furthermore, the drying temperature of the casting machine in step 2 is 160-220℃.

[0060] Furthermore, the thickness of the A membrane in step 2 is 0.01-0.05 mm.

[0061] Furthermore, the polylactic acid in step 3 has a weight-average molecular weight of 120,000-200,000 Da.

[0062] Furthermore, the polyglycolic acid in step 3 has a weight-average molecular weight of 60,000-150,000 Da.

[0063] Furthermore, the polybutylene succinate described in step 3 has a weight-average molecular weight of 80,000-160,000 Da.

[0064] Furthermore, the polypropylene carbonate in step 3 has a weight-average molecular weight of 50,000-120,000 Da.

[0065] Furthermore, the polyethylene glycol in step 3 has a molecular weight of 18,000-22,000 and is in powder form.

[0066] Furthermore, the inorganic nanomaterial in step 3 is one of nano-alumina or nano-montmorillonite.

[0067] Further, the anti-hydrolysis agent in step 3 is one of 2,2'-(1,3-phenylene)dioxazoline, glycidyl phenyl ether, and triglycidyl isocyanurate.

[0068] Further, the nucleating agent in step 3 is one of sebacate dibenzoylhydrazine, N,N'-ethylenebis(1,2-hydroxystearamide), and p-tert-butyl[8]calixarene.

[0069] Further, the heat stabilizer in step 3 is one of dodecyl thiodipropionate, pentaerythritol tetra(3-lauryl thiopropionate), and 4,6-bis(octylthiomethyl)o-cresol.

[0070] Further, in step 3, the content of polylactic acid is 22.4-82.8 parts by weight, the content of polyglycolic acid is 5-15 parts by weight, the content of polybutylene succinate is 5-20 parts by weight, the content of polypropylene carbonate is 5-20 parts by weight, the content of polyethylene glycol is 1-10 parts by weight, the content of inorganic nanomaterials is 1-10 parts by weight, the content of anti-hydrolysis agent is 0.1-2 parts by weight, the content of nucleating agent is 0.1-1 parts by weight, and the content of heat stabilizer is 0.1-0.6 parts by weight.

[0071] Furthermore, in step 3, the stirring speed is 200-700 r / min, and the stirring time is 3-10 min.

[0072] Furthermore, in step 3, the feed rate of the twin-screw extruder is 10-30 kg / h.

[0073] Furthermore, in step 3, the main screw speed of the twin-screw extruder is 300-500 rpm.

[0074] Furthermore, in step 3, the temperature zones of the twin-screw extruder are divided into eleven temperature zones, with the following temperatures: Zone 1: 130℃; Zone 2: 185℃; Zone 3: 190℃; Zone 4: 200℃; Zone 5: 210℃; Zone 6: 220℃; Zone 7: 220℃; Zone 8: 230℃; Zone 9: 230℃; Zone 10: 230℃; and Zone 11: 225℃.

[0075] Furthermore, in step 3, the anti-hydrolysis agent reacts with the end groups of polylactic acid, polyglycolic acid, polybutylene succinate, and polypropylene carbonate to improve the compatibility of the blend material.

[0076] Furthermore, in step 4, the main screw speed of the casting machine is 100-300 rpm.

[0077] Furthermore, the traction speed of the casting machine in step 4 is 10-20 m / min.

[0078] Furthermore, the temperature zone of the casting machine in step 4 is divided into five temperature zones, and the temperature of each zone is: zone 1 temperature is 210℃, zone 2 temperature is 215℃, zone 3 temperature is 220℃, zone 4 temperature is 220℃, and zone 5 temperature is 225℃.

[0079] Furthermore, the film thickness of the cast film in step 4 is 0.01-0.05 mm.

[0080] Furthermore, in step 5, the A membrane and the B membrane are bonded together using an adhesive.

[0081] Furthermore, the adhesive in step 5 is one or more of polyurethane, polyvinyl acetate, paraffin wax, and rosin.

[0082] Furthermore, the biodegradable composite film in step 5 has a three-layer structure, including an inner layer, a middle layer, and an outer layer, wherein the inner and outer layers are film A, and the middle layer is film B.

[0083] Furthermore, the thickness of the biodegradable composite film in step 5 is 0.1-0.15 mm.

[0084] The present invention also provides a food packaging, which is made of the biodegradable composite film and is used for sealing.

[0085] Furthermore, the food packaging is sealed by blocking oxygen and water vapor in the air.

[0086] The beneficial effects of this invention are:

[0087] 1. The biodegradable composite film of the present invention uses polylactic acid as the main body of the composite film. The polylactic acid will be gradually decomposed into lactic acid monomers under the action of microorganisms, and then metabolized into carbon dioxide and water, and finally enter the biological cycle.

[0088] 2. The polylactic acid and polyethylene glycol of the present invention are blended and modified to improve the mechanical properties of the composite film and maintain the transparency of the composite film.

[0089] 3. The polylactic acid of the present invention is blended and modified with polyglycolic acid, polybutylene succinate and polypropylene carbonate, which improves the barrier properties of the composite film.

[0090] 4. The biodegradable composite film described in this invention has a multi-layer structure, which improves the barrier properties of the composite film, as well as its tensile strength and anti-aging properties, thereby increasing the service life of the composite film.

[0091] 5. The biodegradable composite film described in this invention is made by blending high molecular weight, powdered polyethylene glycol with polylactic acid, which improves the toughness and transparency of the composite film. At the same time, the high molecular weight of polyethylene glycol ensures that the composite film retains high stability after long-term use and will not precipitate from the composite film. Detailed Implementation

[0092] The invention will be described in detail below with reference to the embodiments:

[0093] This invention provides a biodegradable composite film, its preparation method, and food packaging. The composite film uses biodegradable polylactic acid as the modified main body, which improves the barrier properties and mechanical properties of the composite film, as well as its anti-aging properties.

[0094] Example 1

[0095] This embodiment provides a biodegradable composite film, which has a three-layer structure, including an inner layer, a middle layer and an outer layer. The inner layer and the outer layer are film A, and the middle layer is film B.

[0096] The components and contents of the A membrane are as follows: 96.1 parts by weight of polylactic acid, 3 parts by weight of polyethylene glycol, 0.5 parts by weight of 2,2'-(1,3-phenylene)dioxazoline, 0.2 parts by weight of dibenzoyl hydrazine sebacate, and 0.2 parts by weight of dodecyl thiodipropionate.

[0097] The components and contents of the B membrane are as follows: 65.5 parts by weight of polylactic acid, 15 parts by weight of polyglycolic acid, 10 parts by weight of polybutylene succinate, 5 parts by weight of polypropylene carbonate, 1 part by weight of polyethylene glycol, 3 parts by weight of nano-alumina, 0.3 parts by weight of 2,2'-(1,3-phenylene)dioxazoline, 0.1 parts by weight of dibenzoyl hydrazine sebacate, and 0.1 parts by weight of disodium thiodipropionate.

[0098] The composite film has a tensile strength of 44.9 MPa, an elongation at break of 36.2%, a tensile strength retention rate of 88.5%, an elongation at break retention rate of 85.4%, and an oxygen permeability of 4.3 cm. 3 / m 2 • 24h • 0.1MPa, water vapor transmission rate is 5.1g / m 2 • After aging for 3 days at 70℃ and 70%RH for 24 hours, the tensile strength of the composite film is 39.7MPa and the elongation at break is 30.9%; the composting degradation rate after 180 days is 99.99%.

[0099] This embodiment also provides a method for preparing a biodegradable composite film, including the following steps:

[0100] Step 1: 96.1 parts by weight of polylactic acid, 3 parts by weight of polyethylene glycol, 0.5 parts by weight of 2,2'-(1,3-phenylene)dioxazoline, 0.2 parts by weight of dibenzoyl hydrazine sebacate, and 0.2 parts by weight of disodium thiopropionate were stirred and mixed at 500 rpm for 3 minutes. The mixture was then melt-extruded and granulated in eleven temperature zones of a twin-screw extruder with a main screw speed of 300 rpm at a feed rate of 20 kg / h. The temperatures of each zone of the twin-screw extruder were: Zone 1: 120℃, Zone 2: 145℃, Zone 3: 160℃, Zone 4: 170℃, Zone 5: 180℃, Zone 6: 190℃, Zone 7: 190℃, Zone 8: 195℃, Zone 9: 200℃, Zone 10: 200℃, and Zone 11: 195℃; This yielded modified resin one.

[0101] Step 2: Place the modified resin one into a casting machine with a main screw speed of 200 rpm, and cast it into a film at a traction speed of 15 m / min. The casting machine is divided into five temperature zones, with the following temperatures: Zone 1: 160℃, Zone 2: 170℃, Zone 3: 180℃, Zone 4: 190℃, and Zone 5: 190℃. Dry the cast modified resin one film at 200℃ to obtain the 0.04 mm A film.

[0102] Step 3: Mix 65.5 parts by weight of polylactic acid, 15 parts by weight of polyglycolic acid, 10 parts by weight of polybutylene succinate, 5 parts by weight of polypropylene carbonate, 1 part by weight of polyethylene glycol, 3 parts by weight of nano-alumina, 0.3 parts by weight of 2,2'-(1,3-phenylene)dioxazoline, 0.1 parts by weight of dibenzoyl hydrazine sebacate, and 0.1 parts by weight of disodium thiopropionate at 500 rpm for 3 minutes. Then, feed the mixture through the main machine screw conveyor at a rate of 20 kg / h. Eleven temperature zones of a twin-screw extruder with a screw speed of 300 rpm were used for melt extrusion granulation. The temperatures of each zone of the twin-screw extruder were as follows: Zone 1: 130℃, Zone 2: 185℃, Zone 3: 190℃, Zone 4: 200℃, Zone 5: 210℃, Zone 6: 220℃, Zone 7: 220℃, Zone 8: 230℃, Zone 9: 230℃, Zone 10: 230℃, and Zone 11: 225℃, to obtain modified resin II.

[0103] Step 4: Place the modified resin II into a casting machine with a main screw speed of 200 rpm, and cast it into a film at a traction speed of 15 m / min. The casting machine is divided into five temperature zones, with the following temperatures: Zone 1: 210℃, Zone 2: 215℃, Zone 3: 220℃, Zone 4: 220℃, and Zone 5: 225℃. Dry the cast modified resin I at 200℃ to obtain the 0.04 mm B film.

[0104] Step 5: Bond the A film and the B film together with a polyurethane adhesive to form a three-layer structure, including an inner layer, a middle layer and an outer layer. The inner layer and the outer layer are the A film, and the middle layer is the B film, to obtain the biodegradable composite film.

[0105] In this embodiment, the polylactic acid has a weight-average molecular weight of 122,000 Da, the polyglycolic acid has a weight-average molecular weight of 67,000 Da, the polybutylene succinate has a weight-average molecular weight of 81,000 Da, the polypropylene carbonate has a weight-average molecular weight of 59,000 Da, and the polyethylene glycol has a molecular weight of 20,000.

[0106] Example 2

[0107] This embodiment provides a biodegradable composite film, which has a three-layer structure, including an inner layer, a middle layer and an outer layer. The inner layer and the outer layer are film A, and the middle layer is film B.

[0108] The components and contents of the A membrane are as follows: 96.1 parts by weight of polylactic acid, 3 parts by weight of polyethylene glycol, 0.5 parts by weight of glycidyl phenyl ether, 0.2 parts by weight of p-tert-butylcalix[8] aromatic hydrocarbon, and 0.2 parts by weight of pentaerythritol tetra(3-lauryl thiopropionate);

[0109] The components and contents of the B membrane are as follows: 65.5 parts by weight of polylactic acid, 15 parts by weight of polyglycolic acid, 10 parts by weight of polybutylene succinate, 5 parts by weight of polypropylene carbonate, 1 part by weight of polyethylene glycol, 3 parts by weight of nano-montmorillonite, 0.2 parts by weight of glycidyl phenyl ether, 0.2 parts by weight of p-tert-butylcalix[8] aromatic hydrocarbon, and 0.1 parts by weight of pentaerythritol tetra(3-lauryl thiopropionate);

[0110] The composite film has a tensile strength of 43.8 MPa, an elongation at break of 38.5%, a tensile strength retention rate of 86.1%, an elongation at break retention rate of 83%, and an oxygen permeability of 4.9 cm⁻¹. 3 / m 2 • 24h • 0.1MPa, water vapor transmission rate is 5.3g / m 2• After aging for 3 days at 70℃ and 70%RH for 24 hours, the tensile strength of the composite film is 37.7MPa and the elongation at break is 32%; the composting degradation rate after 180 days is 99.99%.

[0111] This embodiment also provides a method for preparing a biodegradable composite film, including the following steps:

[0112] Step 1: 96.1 parts by weight of polylactic acid, 3 parts by weight of polyethylene glycol, 0.5 parts by weight of glycidyl phenyl ether, 0.2 parts by weight of p-tert-butylcalix[8] aromatic hydrocarbon and 0.2 parts by weight of pentaerythritol tetra(3-lauryl thiopropionate) were stirred and mixed for 3 minutes at a speed of 500 r / min. The mixture was then melt-extruded and granulated in eleven temperature zones of a twin-screw extruder with a main screw speed of 300 rpm at a feed rate of 20 kg / h. The temperature of each temperature zone of the twin-screw extruder was as follows: Zone 1: 120℃, Zone 2: 145℃, Zone 3: 160℃, Zone 4: 170℃, Zone 5: 180℃, Zone 6: 190℃, Zone 7: 190℃, Zone 8: 195℃, Zone 9: 200℃, Zone 10: 200℃, Zone 11: 195℃; thus, modified resin 1 was obtained.

[0113] Step 2: Place the modified resin one into a casting machine with a main screw speed of 200 rpm, and cast it into a film at a traction speed of 15 m / min. The casting machine is divided into five temperature zones, with the following temperatures: Zone 1: 160℃, Zone 2: 170℃, Zone 3: 180℃, Zone 4: 190℃, and Zone 5: 190℃. Dry the cast modified resin one film at 200℃ to obtain the 0.04 mm A film.

[0114] Step 3: Mix 65.5 parts by weight of polylactic acid, 15 parts by weight of polyglycolic acid, 10 parts by weight of polybutylene succinate, 5 parts by weight of polypropylene carbonate, 1 part by weight of polyethylene glycol, 3 parts by weight of nano-montmorillonite, 0.2 parts by weight of glycidyl phenyl ether, 0.2 parts by weight of p-tert-butylcalix[8] aromatics, and 0.1 parts by weight of pentaerythritol tetra(3-lauryl thiopropionate) at a speed of 500 r / min for 3 min, and feed the mixture through the main screw at a rate of 20 kg / h. Eleven temperature zones of a twin-screw extruder with a rotation speed of 300 rpm were used for melt extrusion granulation. The temperatures of each zone of the twin-screw extruder were as follows: Zone 1: 130°C, Zone 2: 185°C, Zone 3: 190°C, Zone 4: 200°C, Zone 5: 210°C, Zone 6: 220°C, Zone 7: 220°C, Zone 8: 230°C, Zone 9: 230°C, Zone 10: 230°C, and Zone 11: 225°C, to obtain modified resin II.

[0115] Step 4: Place the modified resin II into a casting machine with a main screw speed of 200 rpm, and cast it into a film at a traction speed of 15 m / min. The casting machine is divided into five temperature zones, with the following temperatures: Zone 1: 210℃, Zone 2: 215℃, Zone 3: 220℃, Zone 4: 220℃, and Zone 5: 225℃. Dry the cast modified resin I at 200℃ to obtain the 0.04 mm B film.

[0116] Step 5: Bond the A film and the B film together with a polyurethane adhesive to form a three-layer structure, including an inner layer, a middle layer and an outer layer. The inner layer and the outer layer are the A film, and the middle layer is the B film, to obtain the biodegradable composite film.

[0117] In this embodiment, the polylactic acid has a weight-average molecular weight of 146,000 Da, the polyglycolic acid has a weight-average molecular weight of 75,000 Da, the polybutylene succinate has a weight-average molecular weight of 85,000 Da, the polypropylene carbonate has a weight-average molecular weight of 67,000 Da, and the polyethylene glycol has a molecular weight of 20,000.

[0118] Example 3

[0119] This embodiment provides a biodegradable composite film, which has a three-layer structure, including an inner layer, a middle layer and an outer layer. The inner layer and the outer layer are film A, and the middle layer is film B.

[0120] The components and contents of the A membrane are as follows: 96.1 parts by weight of polylactic acid, 3 parts by weight of polyethylene glycol, 0.5 parts by weight of triglycidyl isocyanate, 0.2 parts by weight of N,N'-ethylenebis(1,2-hydroxystearamide), and 0.2 parts by weight of 4,6-bis(octylthiomethyl)o-cresol.

[0121] The components and contents of the B membrane are as follows: 65.5 parts by weight of polylactic acid, 15 parts by weight of polyglycolic acid, 10 parts by weight of polybutylene succinate, 5 parts by weight of polypropylene carbonate, 1 part by weight of polyethylene glycol, 3 parts by weight of nano-alumina, 0.2 parts by weight of triglycidyl isocyanate, 0.2 parts by weight of N,N'-ethylenebis(1,2-hydroxystearamide), and 0.1 parts by weight of 4,6-bis(octylthiomethyl)o-cresol.

[0122] The composite film has a tensile strength of 41.8 MPa, an elongation at break of 32.5%, a tensile strength retention rate of 89.4%, an elongation at break retention rate of 82.7%, and an oxygen permeability of 5.9 cm³. 3 / m 2 • 24h • 0.1MPa, water vapor transmission rate is 7.3g / m 2• After aging for 3 days at 70℃ and 70%RH for 24 hours, the tensile strength of the composite film is 37.4MPa and the elongation at break is 26.9%; the composting degradation rate after 180 days is 99.99%.

[0123] This embodiment also provides a method for preparing a biodegradable composite film, including the following steps:

[0124] Step 1: Mix 96.1 parts by weight of polylactic acid, 3 parts by weight of polyethylene glycol, 0.5 parts by weight of triglycidyl isocyanate, 0.2 parts by weight of N,N'-ethylenebis(1,2-hydroxystearamide), and 0.2 parts by weight of 4,6-di(octylthiomethyl)o-cresol at 500 rpm for 3 minutes. Then, feed the mixture through a twin-screw extruder with a main screw speed of 300 rpm at a feed rate of 20 kg / h. Eleven-zone melt extrusion granulation was performed, with the following temperatures for each zone of the twin-screw extruder: Zone 1: 120℃, Zone 2: 145℃, Zone 3: 160℃, Zone 4: 170℃, Zone 5: 180℃, Zone 6: 190℃, Zone 7: 190℃, Zone 8: 195℃, Zone 9: 200℃, Zone 10: 200℃, and Zone 11: 195℃; resulting in modified resin one.

[0125] Step 2: Place the modified resin one into a casting machine with a main screw speed of 200 rpm, and cast it into a film at a traction speed of 15 m / min. The casting machine is divided into five temperature zones, with the following temperatures: Zone 1: 160℃, Zone 2: 170℃, Zone 3: 180℃, Zone 4: 190℃, and Zone 5: 190℃. Dry the cast modified resin one film at 200℃ to obtain the 0.04 mm A film.

[0126] Step 3: Mix 65.5 parts by weight of polylactic acid, 15 parts by weight of polyglycolic acid, 10 parts by weight of polybutylene succinate, 5 parts by weight of polypropylene carbonate, 1 part by weight of polyethylene glycol, 3 parts by weight of nano-alumina, 0.2 parts by weight of triglycidyl isocyanate, 0.1 parts by weight of N,N'-ethylenebis(1,2-hydroxystearamide), and 0.2 parts by weight of 4,6-di(octylthiomethyl)o-cresol at 500 rpm for 3 minutes. Then, feed the mixture at a rate of 20 kg / h. Modified resin II was obtained by melt extrusion granulation in eleven temperature zones of a twin-screw extruder with a main screw speed of 300 rpm. The temperatures of each temperature zone of the twin-screw extruder were as follows: Zone 1: 130℃, Zone 2: 185℃, Zone 3: 190℃, Zone 4: 200℃, Zone 5: 210℃, Zone 6: 220℃, Zone 7: 220℃, Zone 8: 230℃, Zone 9: 230℃, Zone 10: 230℃, and Zone 11: 225℃.

[0127] Step 4: Place the modified resin II into a casting machine with a main screw speed of 200 rpm, and cast it into a film at a traction speed of 15 m / min. The casting machine is divided into five temperature zones, with the following temperatures: Zone 1: 210℃, Zone 2: 215℃, Zone 3: 220℃, Zone 4: 220℃, and Zone 5: 225℃. Dry the cast modified resin I at 200℃ to obtain the 0.04 mm B film.

[0128] Step 5: Bond the A film and the B film together with a polyurethane adhesive to form a three-layer structure, including an inner layer, a middle layer and an outer layer. The inner layer and the outer layer are the A film, and the middle layer is the B film, to obtain the biodegradable composite film.

[0129] In this embodiment, the polylactic acid has a weight-average molecular weight of 164,000 Da, the polyglycolic acid has a weight-average molecular weight of 92,000 Da, the polybutylene succinate has a weight-average molecular weight of 105,000 Da, the polypropylene carbonate has a weight-average molecular weight of 87,000 Da, and the polyethylene glycol has a molecular weight of 20,000.

[0130] Comparative Example 1

[0131] This comparative example provides a single-layer film, the components and their contents of which are as follows: 92.5 parts by weight of polylactic acid, 5 parts by weight of polybutylene adipate terephthalate, 0.2 parts by weight of diphenylmethane diisocyanate as a chain extender, 0.1 parts by weight of stearic acid as a lubricant, 0.2 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant, and 2 parts by weight of epoxidized soybean oil as a plasticizer.

[0132] The monolayer film has a tensile strength of 47.8 MPa, an elongation at break of 12.3%, a tensile strength retention rate of 71 MPa, an elongation at break retention rate of 69.5%, and an oxygen permeability of 55.9 cm³. 3 / m 2 • 24h • 0.1MPa, water vapor transmission rate is 67.3g / m 2 • After aging for 3 days at 70°C and 70% RH for 24 hours, the tensile strength of the monolayer film is 33.9 MPa and the elongation at break is 8.5%.

[0133] This comparative example also provides a method for preparing a single-layer thin film, comprising the following steps:

[0134] Step 1: Mix 92.5 parts by weight of polylactic acid, 5 parts by weight of polybutylene adipate terephthalate, 0.2 parts by weight of diphenylmethane diisocyanate, 0.1 parts by weight of stearic acid, 0.2 parts by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 2 parts by weight of epoxidized soybean oil at 500 rpm for 3 minutes. Feed the mixture at a rate of 20 kg / h through the main machine screw at a speed of 300 rpm. Eleven temperature zones of a twin-screw extruder were used for melt extrusion granulation, with the following temperatures for each zone: Zone 1: 120°C, Zone 2: 145°C, Zone 3: 160°C, Zone 4: 170°C, Zone 5: 180°C, Zone 6: 190°C, Zone 7: 190°C, Zone 8: 195°C, Zone 9: 200°C, Zone 10: 200°C, and Zone 11: 195°C; resulting in modified resin.

[0135] Step 2: Place the modified resin into a casting machine with a main screw speed of 200 rpm, and cast it into a film at a traction speed of 15 m / min. The casting machine is divided into five temperature zones, with the following temperatures: Zone 1: 160℃, Zone 2: 170℃, Zone 3: 180℃, Zone 4: 190℃, and Zone 5: 190℃. Dry the cast modified resin at 200℃ to obtain the single-layer film.

[0136] Table 1. Components and content of the biodegradable composite films described in Examples 1-3 of this paper.

[0137]

[0138] Table 2 Performance tests of the biodegradable composite films and single-layer films described in Examples 1-3 and Comparative Example 1

[0139] project Example 1 Example 2 Example 3 Comparative Example 1 Tensile strength (MPa) 44.9 43.8 41.8 47.8 Elongation at break (%) 36.2 38.5 32.5 12.3 Tensile strength retention rate (%) 88.5 86.1 89.4 71.0 Elongation at break retention rate (%) 85.4 83.0 82.7 69.5 <![CDATA[Oxygen transmission rate (cm 3 / m 2 *24h*0.1MPa)]]> 4.3 4.9 5.9 55.9 <![CDATA[Water vapor transmission rate (g / m 2 *24h)]]> 5.1 5.3 7.3 67.3 Tensile strength (MPa) after 3 days of aging 39.7 37.7 37.4 33.9 Elongation at break (%) after 3 days of aging 30.9 32.0 26.9 8.5

[0140] As shown in Table 2, the biodegradable composite films described in Examples 1-3 have low oxygen and water vapor permeability, and their barrier properties are superior to those of the single-layer film in Comparative Example 1; their mechanical properties after aging are also higher than those of the single-layer film in Comparative Example 1.

[0141] The tensile strength test standard described in this embodiment conforms to GB / T1040.3-2006, the oxygen transmission rate test standard conforms to GB / T1037-2021, the water vapor transmission rate test standard conforms to GB / T1038-2000, and the compost degradation rate test standard conforms to GB / T19277.1-2011.

[0142] As can be seen from the above, the biodegradable composite film described in this patent has high barrier properties, good mechanical properties, a wide range of applications, low cost, and a very high market prospect.

[0143] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A degradable composite film, characterized by, The composite film is a three-layer structure, comprising an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are A films, and the intermediate layer is a B film; The components and contents in the A film are: Polylactic acid 86.2-96.9 parts by weight; Polyethylene glycol 3-10 parts by weight; Anti-hydrolysis agent 0.1-2 parts by weight; Nucleating agent 0.1-1 parts by weight; Thermal stabilizer 0.2-0.8 parts by weight; The components and contents in the B film are: Polylactic acid 65.5-82.8 parts by weight; Polyglycolic acid 5-15 parts by weight; Polybutylene succinate 5-20 parts by weight; Polypropylene carbonate 5-20 parts by weight; Polyethylene glycol 1-10 parts by weight; Inorganic nanomaterial 1-10 parts by weight; Anti-hydrolysis agent 0.1-2 parts by weight; Nucleating agent 0.1-1 parts by weight; Thermal stabilizer 0.1-0.6 parts by weight; The composite film has a tensile strength of 40-50 MPa, an elongation at break of 30-66%, a tensile strength retention rate of 85-95%, an elongation at break retention rate of 80-90%, an oxygen transmission amount of 4-8 cm 3 / m 2 • 24h; a water vapor transmission amount of 3-7 g / m 2 • 24h; a tensile strength of 35-50 MPa, an elongation at break of 25-35% after aging at 70°C, 70% RH for 3 days; a compost degradation rate of 90-100% after 180 days.

2. The composite film according to claim 1, wherein The molecular weight of the polyethylene glycol is 20000-40000, and the state is powdery.

3. A method of producing the degradable composite film according to claim 1 or 2, characterized by, The steps are as follows: Step 1, stir and mix polylactic acid, polyethylene glycol, anti-hydrolysis agent, nucleating agent and thermal stabilizer, and extrude through a double-screw extruder to obtain modified resin one; Step 2, place the modified resin one into a casting machine to cast a film to obtain the A film; Step 3, stir and mix polylactic acid, polyglycolic acid, polybutylene succinate, polypropylene carbonate, polyethylene glycol, inorganic nanomaterial, anti-hydrolysis agent, nucleating agent and thermal stabilizer, and extrude through a double-screw extruder to obtain modified resin two; Step 4, place the modified resin two into a casting machine to cast a film to obtain the B film; Step 5, composite the A film and the B film by using an adhesive to bond the A film and the B film to obtain the degradable composite film.

4. The production method according to claim 3, characterized by, The region temperature of the double-screw extruder in step 1 is divided into eleven temperature zones, and the temperature of each temperature zone is: the temperature of the first zone is 120℃, the temperature of the second zone is 145℃, the temperature of the third zone is 160℃, the temperature of the fourth zone is 170℃, the temperature of the fifth zone is 180℃, the temperature of the sixth zone is 190℃, the temperature of the seventh zone is 190℃, the temperature of the eighth zone is 195℃, the temperature of the ninth zone is 200℃, the temperature of the tenth zone is 200℃, and the temperature of the eleventh zone is 195℃.

5. The preparation method according to claim 3, characterized in that, The region temperature of the casting machine in step 2 is divided into five temperature zones, and the temperature of each temperature zone is: the temperature of the first zone is 160℃, the temperature of the second zone is 170℃, the temperature of the third zone is 180℃, the temperature of the fourth zone is 190℃, and the temperature of the fifth zone is 190℃.

6. The preparation method according to claim 3, characterized in that, The region temperature of the double-screw extruder in step 3 is divided into eleven temperature zones, and the temperature of each temperature zone is: the temperature of the first zone is 130℃, the temperature of the second zone is 185℃, the temperature of the third zone is 190℃, the temperature of the fourth zone is 200℃, the temperature of the fifth zone is 210℃, the temperature of the sixth zone is 220℃, the temperature of the seventh zone is 220℃, the temperature of the eighth zone is 230℃, the temperature of the ninth zone is 230℃, the temperature of the tenth zone is 230℃, and the temperature of the eleventh zone is 225℃.

7. The preparation method according to claim 3, characterized in that, The temperature of the casting machine in step 4 is divided into five temperature zones, and the temperature of each temperature zone is as follows: the temperature of the first zone is 210℃, the temperature of the second zone is 215℃, the temperature of the third zone is 220℃, the temperature of the fourth zone is 220℃, and the temperature of the fifth zone is 225℃.

8. The preparation method according to claim 3, characterized in that, The adhesive in step 5 is one or more of polyurethane, polyvinyl acetate, paraffin, and pine tar.

9. The preparation method according to claim 3, characterized in that, The thickness of the degradable composite film in step 5 is 0.1-0.15mm.

10. A food package, characterized in that The food packaging is prepared from the degradable composite film of claim 1 or 2, and the food packaging is used for sealing.

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