High-barrier bio-based pla composite film with ultraviolet shielding property and preparation method thereof

Abstract

The application discloses a high-barrier bio-based PLA composite film with ultraviolet shielding property and a preparation method thereof. The high-barrier bio-based PLA composite film comprises a polylactic acid upper surface layer, a high-barrier intermediate layer and a polylactic acid lower surface layer. The high-barrier intermediate layer is composed of 60-85% polylactic acid resin, 1-15% chain extender and 15-40% bio-based furan polyester in terms of mass percentage. The polylactic acid upper surface layer and the polylactic acid lower surface layer are both composed of 75-80% polylactic acid resin, 1-5% chain extender, 15-25% polylactic acid furan polyester block copolymer and 1-5% functional masterbatch. The high-barrier bio-based PLA composite film not only has good barrier property, mechanical property and processing property, but also has certain ultraviolet shielding property, can effectively delay food oxidation and acidification, and increase the storage period and shelf life of food packaging products.

Description

Technical Field

[0001] This invention relates to the field of PLA composite film technology, specifically to a high-barrier bio-based PLA composite film with ultraviolet shielding properties and its preparation method. Background Technology

[0002] Food packaging products are affected by light during storage and shelf life, especially ultraviolet (UV) radiation, which accelerates the oxidation and acidification of food. Currently available packaging films with UV-shielding capabilities are mostly made of petroleum-based polymers such as PET, PP, PA, and PE, which are non-biodegradable and pose certain environmental hazards. Polylactic acid (PLA), as a bio-based polymer, possesses high elastic modulus (2-4 GPa), high strength (30-50 MPa), good light transmittance, and compostability, making it an ideal packaging material. However, ordinary PLA packaging films have poor barrier and UV-shielding properties, limiting their widespread application in flexible packaging for perishable goods.

[0003] Furan dicarboxylic acid (FDCA) is a bio-based monomer that can be prepared from cellulose and hemicellulose. Due to its structure similar to terephthalic acid, it can replace terephthalic acid in block copolymerization with brittle bioplastics such as PLA, improving material properties. Bio-based furan polyesters and block copolymers of furan dicarboxylic acid and PLA exhibit good barrier properties due to the polarity and nonlinear structure of the furan ring. Furthermore, because the furan groups form conjugations with the carbonyl groups, they also possess certain UV shielding properties.

[0004] Therefore, this application provides a high-barrier bio-based PLA composite film with ultraviolet shielding and its preparation method, in order to solve the problem that ordinary PLA packaging films have poor barrier and ultraviolet shielding properties and cannot be widely used in the flexible packaging of perishable goods. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the existing defects and provide a high-barrier bio-based PLA composite film with ultraviolet shielding and its preparation method. The high-barrier bio-based PLA composite film not only has good barrier properties, mechanical properties and processing properties, but also has a certain ultraviolet shielding property, which can effectively delay the oxidation and acidification of food, increase the storage period and shelf life of food packaging products, and can effectively solve the problems in the background technology.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a high-barrier bio-based PLA composite film with UV shielding properties, comprising a polylactic acid upper layer, a high-barrier intermediate layer, and a polylactic acid lower layer. By mass percentage, the high-barrier intermediate layer is composed of 60-85% polylactic acid resin, 1-15% chain extender, and 15-40% bio-based furan polyester. The polylactic acid upper and lower layers are each composed of 75-80% polylactic acid resin, 1-5% chain extender, 15-25% polylactic acid-furan polyester block copolymer, and 1-5% functional masterbatch.

[0007] As a preferred embodiment of the present invention, the chain extender is one or a mixture of several of the following: styrene-glycidyl methacrylate, isocyanate, dianhydride, styrene-glycidyl methacrylate copolymer, styrene-maleic anhydride copolymer, chain extender ADR, and chain extender XY4370.

[0008] As a preferred embodiment of the present invention, the bio-based furan polyester is one or a mixture of several of PEF, PBF, PAF, PPF, PEN, PHF, PCF, POF, PDeF, PDoF, PPeF, and PECF.

[0009] As a preferred technical solution of the present invention, the specific preparation method of the polylactic acid-furan polyester block copolymer is as follows: under nitrogen protection, lactide and bio-based furan polyester are mixed in a mass ratio of (70-90):(10-30), and after adding the catalyst stannous octoate, the mixture is polycondensed in a vacuum environment at 140°C for 24 hours to obtain the polylactic acid-bio-based furan polyester block copolymer.

[0010] As a preferred embodiment of the present invention, the functional masterbatch comprises 80-95% polylactic acid resin, 2-10% anti-adhesion agent, 2-8% slip agent and 0.3-0.5% antioxidant.

[0011] As a preferred embodiment of the present invention, the anti-adhesion agent is one or a mixture of several of talc, silica, and cross-linked polystyrene microspheres.

[0012] As a preferred embodiment of the present invention, the slip agent is one or a mixture of several of ethylene bis-stearamide, silicone, and erucamide.

[0013] As a preferred embodiment of the present invention, the antioxidant is one or a mixture of several of the following: 1010, 1076, 264, 425, 330, 626, 627, DSTP, and DLTP.

[0014] As a preferred embodiment of the present invention, the thickness of the high-barrier intermediate layer is 3-5 μm; the thickness of the polylactic acid upper surface layer and the polylactic acid lower surface layer are both 6-10 μm.

[0015] A method for preparing a high-barrier bio-based PLA composite film with ultraviolet shielding properties specifically includes the following steps:

[0016] S1. Ply lactide and bio-based furan polyester are polycondensed at a mass ratio of (70-90):(10-30) to obtain polylactic acid furan polyester block copolymer;

[0017] S2. Weigh the raw materials of polylactic acid upper surface layer, high barrier intermediate layer and polylactic acid lower surface layer according to the mass percentage in the formula, and stir to obtain resin mixture.

[0018] S3. The resin mixture of each layer is fed into the main machine and auxiliary machine of the three-layer co-extrusion casting machine for melt extrusion to obtain composite casting sheet, wherein the processing temperature of the high barrier layer is 190-260℃, and the processing temperature of the polylactic acid upper and lower surface layers is 190-260℃.

[0019] S4. After biaxial stretching of the composite casting, a high-barrier bio-based PLA composite film with UV shielding is obtained, wherein the stretching ratio is 2.0*2.0-5.0*5.0, the stretching temperature is 80-150℃, and the heat setting temperature is 100-175℃.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The monomers of polylactic acid, polylactic acid-furan block copolymer and bio-based furan polyester used in this invention are partially or entirely derived from biomass and are easily degradable, which helps to reduce the use of petroleum resources and has low environmental harm.

[0022] 2. The bio-based furan polyester and polylactic acid furan polyester block copolymer added in this invention can provide the film with good barrier and UV shielding properties. At the same time, the polylactic acid furan polyester block copolymer can also play a role in toughening and modifying PLA to a certain extent.

[0023] 3. The chain extender used in this invention contains highly reactive groups that can promote the formation of copolymers between polylactic acid and bio-based furan polyester, thereby effectively reducing the size of the dispersed phase and making it uniformly distributed, enhancing interfacial bonding, and improving the mechanical properties of the film. At the same time, the chain extender can also promote the formation of covalent bonds between PLAs, which helps to improve melt strength and extend the processing window of PLA substrate while retaining the molecular weight of PLA and offsetting the degradation caused by the increase in processing temperature. Attached Figure Description

[0024] Figure 1This is a schematic diagram of the structure of the present invention.

[0025] In the diagram: 1. Polylactic acid top layer, 2. High-barrier intermediate layer, 3. Polylactic acid bottom layer. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] A high-barrier bio-based PLA composite film with UV shielding properties includes a polylactic acid (PLA) upper layer, a high-barrier intermediate layer, and a PLA lower layer. By mass percentage, the high-barrier intermediate layer is composed of 80% PLA resin, 5% chain extender, and 15% bio-based furan polyester. The PLA upper and lower layers are each composed of 75% PLA resin, 1% chain extender, 20% PLA furan polyester block copolymer, and 4% functional masterbatch.

[0029] A method for preparing a high-barrier bio-based PLA composite film with ultraviolet shielding properties includes the following steps:

[0030] S1. PLE and PEF are polycondensed at a mass ratio of 90:10 to obtain PLA-b-PEF.

[0031] S2. Weigh the raw materials of polylactic acid upper surface layer, high barrier intermediate layer and polylactic acid lower surface layer according to the mass percentage in the formula, and stir to obtain resin mixture.

[0032] S3. The resin mixture of each layer is fed into the main machine and auxiliary machine of the three-layer co-extrusion casting machine for melt extrusion to obtain a composite casting sheet. The processing temperature of the high barrier layer is 225℃, and the processing temperature of the polylactic acid upper and lower surface layers is 195℃.

[0033] S4. After biaxial stretching of the composite casting, a high-barrier bio-based PLA composite film with UV shielding is obtained, wherein the stretching ratio is 3.3*3.3, the stretching temperature is 85℃, and the heat setting temperature is 150℃.

[0034] The high-barrier intermediate layer has a thickness of 3 μm, and the upper and lower polylactic acid layers have a thickness of 6 μm.

[0035] Example 2

[0036] A high-barrier bio-based PLA composite film with UV shielding properties includes a polylactic acid (PLA) upper layer, a high-barrier intermediate layer, and a PLA lower layer. By mass percentage, the high-barrier intermediate layer is composed of 80% PLA resin, 5% chain extender, and 15% bio-based furan polyester. The PLA upper and lower layers are each composed of 75% PLA resin, 1% chain extender, 20% PLA furan polyester block copolymer, and 4% functional masterbatch.

[0037] A method for preparing a high-barrier bio-based PLA composite film with ultraviolet shielding properties includes the following steps:

[0038] S1. Ply lactide and PBF are polycondensed at a mass ratio of 90:10 to obtain PLA-b-PBF.

[0039] S2. Weigh the raw materials of polylactic acid upper surface layer, high barrier intermediate layer and polylactic acid lower surface layer according to the mass percentage in the formula, and stir to obtain resin mixture.

[0040] S3. The resin mixture of each layer is fed into the main machine and auxiliary machine of the three-layer co-extrusion casting machine for melt extrusion to obtain a composite casting sheet, wherein the processing temperature of the high barrier layer is 205℃, and the processing temperature of the polylactic acid upper and lower surface layers is 190℃.

[0041] S4. After biaxial stretching of the composite casting, a high-barrier bio-based PLA composite film with UV shielding is obtained, wherein the stretching ratio is 3.3*3.3, the stretching temperature is 85℃, and the heat setting temperature is 150℃.

[0042] The high-barrier intermediate layer has a thickness of 3 μm, and the upper and lower polylactic acid layers have a thickness of 6 μm.

[0043] Example 3

[0044] A high-barrier bio-based PLA composite film with UV shielding properties includes a polylactic acid (PLA) upper layer, a high-barrier intermediate layer, and a PLA lower layer. By mass percentage, the high-barrier intermediate layer is composed of 80% PLA resin, 5% chain extender, and 15% bio-based furan polyester. The PLA upper and lower layers are each composed of 85% PLA resin, 1% chain extender, 10% PLA furan polyester block copolymer, and 4% functional masterbatch.

[0045] A method for preparing a high-barrier bio-based PLA composite film with ultraviolet shielding properties includes the following steps:

[0046] S1. PLE and PEF are polycondensed at a mass ratio of 70:30 to obtain PLA-b-PEF.

[0047] S2. Weigh the raw materials of polylactic acid upper surface layer, high barrier intermediate layer and polylactic acid lower surface layer according to the mass percentage in the formula, and stir to obtain resin mixture.

[0048] S3. The resin mixture of each layer is fed into the main machine and auxiliary machine of the three-layer co-extrusion casting machine for melt extrusion to obtain a composite casting sheet. The processing temperature of the high barrier layer is 225℃, and the processing temperature of the polylactic acid upper and lower surface layers is 195℃.

[0049] S4. After biaxial stretching of the composite casting, a high-barrier bio-based PLA composite film with UV shielding is obtained, wherein the stretching ratio is 3.3*3.3, the stretching temperature is 85℃, and the heat setting temperature is 150℃.

[0050] The high-barrier intermediate layer has a thickness of 3 μm, and the upper and lower polylactic acid layers have a thickness of 6 μm.

[0051] Comparative Example 1

[0052] The difference between Comparative Example 1 and Example 1 is that the upper and lower polylactic acid layers do not contain polylactic acid-furan polyester block copolymers, and step S1 is not included in the preparation process.

[0053] Comparative Example 2

[0054] The difference between Comparative Example 2 and Example 1 is that the high-barrier intermediate layer does not contain a chain extender.

[0055] Comparative Example 3

[0056] The difference between Comparative Example 2 and Example 1 is that the high-barrier interlayer does not contain bio-based furan polyester.

[0057] Comparative Example 4

[0058] Ordinary PLA pure membrane.

[0059] The performance of the PLA composite films prepared in Examples 1-3 and Comparative Examples 1-4 was tested, and the results are shown in Table 1.

[0060]

[0061] Table 1 Performance test results for Examples 1-3 and Comparative Examples 1-4

[0062] The tensile strength and elongation at break of the PLA composite film were tested according to GB / T 1040; the oxygen permeability was determined according to GB / T 1038; and the ultraviolet shielding was tested using an ultraviolet-visible spectrophotometer.

[0063] Note: Table 1 evaluates UV shielding performance, with the best performance marked as "★★★★★" and the worst as "☆☆☆☆☆". The more "★" marks, the better the performance.

[0064] The data above show that Comparative Example 1 indicates that the block copolymer of polylactic acid bio-based furan polyester is beneficial to improving the mechanical properties of the film; Comparative Example 2 indicates that the chain extender can help the distribution of bio-based furan polyester in the PLA substrate, thereby improving the film performance; Comparative Examples 3 and 4 indicate that bio-based furan polyester can give the composite film better UV shielding and barrier properties.

[0065] The structure of this high-barrier bio-based PLA composite membrane is as follows: Figure 1 As shown, it not only possesses excellent barrier properties, mechanical properties, and processing performance, but also exhibits a certain degree of UV shielding, effectively delaying food oxidation and acidification, and increasing the shelf life and storage period of food packaging products.

[0066] All parts not disclosed in this invention are prior art, and their specific structures, materials, and working principles will not be described in detail. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-barrier bio-based PLA composite film with UV shielding, comprising a polylactic acid upper layer, a high-barrier middle layer, and a polylactic acid lower layer, characterized in that: The high-barrier intermediate layer consists of 60-85% polylactic acid resin, 1-15% chain extender, and 15-40% bio-based furan polyester by mass percentage, and the polylactic acid upper surface layer and the polylactic acid lower surface layer each consists of 75-80% polylactic acid resin, 1-5% chain extender, 15-25% polylactic acid furan polyester block copolymer, and 1-5% functional masterbatch; the polylactic acid furan polyester block copolymer is prepared by condensation polymerization of lactide and bio-based furan polyester under nitrogen protection and vacuum condition at 140℃ for 24h, and the mass ratio of the two is (70-90):(10-30); the functional masterbatch consists of 80-95% polylactic acid resin, 2-10% anti-adhesion agent, 2-8% slip agent, and 0.3-0.5% antioxidant.

2. The high-barrier biobased PLA composite film with UV-shielding property according to claim 1, characterized in that: The chain extender is one or a mixture of several of styrene-glycidyl methacrylate, isocyanate, diacid anhydride, styrene-glycidyl methacrylate copolymer, styrene-maleic anhydride copolymer, chain extender ADR, and chain extender XY4370.

3. The high-barrier biobased PLA composite film with UV-shielding property according to claim 1, characterized in that: The bio-based furan polyester is one or a mixture of several of PEF, PBF, PAF, PPF, PEN, PHF, PCF, POF, PDeF, PDoF, PPeF, and PECF.

4. The high-barrier biobased PLA composite film with UV-shielding property according to claim 1, characterized in that: The anti-adhesion agent is one or a mixture of several of talc, silicon dioxide, and crosslinked polystyrene microspheres.

5. The high-barrier biobased PLA composite film with UV-shielding property according to claim 1, characterized in that: The slip agent is one or a mixture of several of ethylene bis-stearamide, silicone, and erucic amide.

6. The high-barrier biobased PLA composite film with UV-shielding property according to claim 1, characterized in that: The antioxidant is one or a mixture of several of 1010, 1076, 264, 425, 330, 626, 627, DSTP, and DLTP.

7. The high-barrier biobased PLA composite film with UV-shielding property according to claim 1, characterized in that: The thickness of the high-barrier intermediate layer is 3-5μm, and the thickness of the polylactic acid upper surface layer and the polylactic acid lower surface layer is 6-10μm.

8. A method of producing a high-barrier bio-based PLA composite film with UV shielding properties according to any one of claims 1-7, characterized in that: Specifically comprising the following steps: S1, condensing polylactic acid furan polyester block copolymer by condensation polymerization of lactide and bio-based furan polyester at a mass ratio of (70-90):(10-30); S2, respectively weighing the raw materials of the polylactic acid upper surface layer, the high-barrier intermediate layer, and the polylactic acid lower surface layer according to the mass percentage in the formula, and stirring to obtain a resin mixture; S3, melting and extruding the resin mixtures of the three layers into the main machine and auxiliary machine of a three-layer co-extrusion flow casting machine to obtain a composite casting piece, wherein the processing temperature of the high-barrier layer is 190-260℃, and the processing temperature of the polylactic acid upper surface layer and the polylactic acid lower surface layer is 190-260℃; S4, obtaining a high-barrier bio-based PLA composite film with ultraviolet shielding property by bidirectional stretching of the composite casting piece, wherein the stretching ratio is 2.0*2.0-5.0*5.0, the stretching temperature is 80-150℃, and the heat setting temperature is 100-175℃.

Images