Flame-retardant high-barrier degradable film and preparation method thereof

Abstract

This invention belongs to the field of biodegradable film technology, specifically disclosing a flame-retardant high-barrier biodegradable film and its preparation method. The biodegradable film comprises, from top to bottom, a flame-retardant upper surface layer, a barrier core layer, and a flame-retardant lower surface layer. The raw material components of the flame-retardant upper and lower surface layers, by mass percentage, include 1-5 wt% functional masterbatch, 2-5 wt% modified barrier polylactic acid mixture, 1-20 wt% phosphazene flame retardant, 1-5 wt% chain extender, 10-20 wt% biodegradable elastomer, and 45-85 wt% polylactic acid resin. The raw material components of the barrier core layer, by mass percentage, include 1-10 wt% chain extender, 1-20 wt% modified barrier polylactic acid mixture, and 70-98 wt% polylactic acid resin. The preparation method of the modified barrier polylactic acid mixture includes the preparation of MgAl-LDHs, the preparation of lactic acid intercalated LDHs, and the preparation of the modified barrier polylactic acid mixture. The flame-retardant, high-barrier, and biodegradable film of the present invention has good flame retardancy, barrier properties, and biodegradability.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable film technology, specifically relating to a flame-retardant high-barrier biodegradable film and its preparation method. Background Technology

[0002] With the continuous strengthening of ecological and environmental protection management, environmental pollution control has become a key development direction for the industry. Biodegradable polymer materials are gradually replacing traditional non-degradable plastics and are widely used in disposable products, electronic packaging, medical consumables, and automotive auxiliary parts. Polylactic acid (PLA), as a mainstream bio-based biodegradable polymer material, uses natural lactic acid as a polymerization raw material and possesses excellent comprehensive physical and chemical properties. Its elastic modulus is 2-4 GPa, and its tensile strength can reach 30-50 MPa. It also has good light transmittance and degrades to produce only carbon dioxide and water, leaving no toxic or harmful residues. Its green and environmentally friendly attributes are prominent, making it one of the most promising biodegradable substrates for current applications. However, existing PLA materials have significant technical defects that restrict their industrialization and application. PLA itself has poor flame retardancy, with a limiting oxygen index of only 19%-21%, classifying it as a flammable material. The material is extremely easy to ignite when exposed to open flames, and severe dripping occurs during combustion. The high-temperature dripping can easily ignite surrounding combustibles, accelerating the spread of fire and posing a significant fire safety hazard. Meanwhile, conventional polylactic acid films have relatively weak barrier properties, and their ability to block water vapor and oxygen is insufficient to meet the requirements of high-end application scenarios such as food preservation and moisture-proof packaging of electronic components.

[0003] Currently, the technical solutions for flame retardant modification of polylactic acid (PLA) in the industry are relatively limited. Conventional modification methods easily damage the material's biodegradability and reduce the film's light transmittance and mechanical properties. Moreover, most methods only improve the flame retardant property and cannot simultaneously address barrier properties, resulting in poor overall modification effects. In summary, existing PLA films suffer from insufficient flame retardancy, severe combustion dripping, poor barrier properties, and weak overall adaptability, making it difficult to meet the high-standard application requirements of various fields.

[0004] Therefore, developing a modified polylactic acid film that combines flame retardancy, high barrier properties, biodegradability, and excellent mechanical and light transmittance properties, as well as its preparation method, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the existing technology and provide a flame-retardant, high-barrier, biodegradable film and its preparation method.

[0006] To achieve the above objectives, one of the technical solutions of the present invention is: a flame-retardant, high-barrier, biodegradable film, comprising, from top to bottom, a flame-retardant upper surface layer, a barrier core layer, and a flame-retardant lower surface layer; the raw material components of the flame-retardant upper and lower surface layers, by mass percentage, include 1-5 wt% functional masterbatch, 2-5 wt% modified barrier polylactic acid mixture, 1-20 wt% phosphazene flame retardant, 1-5 wt% chain extender, 10-20 wt% biodegradable elastomer, and 45-85 wt% polylactic acid resin; the raw material components of the barrier core layer, by mass percentage, include 1-10 wt% chain extender, 1-20 wt% modified barrier polylactic acid mixture, and 70-98 wt% polylactic acid resin; wherein, the preparation method of the modified barrier polylactic acid mixture is as follows:

[0007] (1) Preparation of MgAl-LDHs: according to n(Mg 2+ ): n(Al 3+ )=(2~4):1、[OH - ] =2[n(Mg 2+ )+ n(Al 3+ )] and [CO3 2- ]=1 / 2 n(Al 3+ Add a 1.0 mol / L MgCl2 and AlCl2 solution and a mixed alkaline solution of NaOH and Na2CO3 to a ball mill, adjust the pH to ≥10, ball mill for 10-15 min, then place in a 60℃ oven to age for 12-48 h, and wash with deionized water until neutral.

[0008] (2) Preparation of lactic acid intercalated LDHs: Prepare a 20-40 wt% sodium lactate solution, add 2-10 wt% MgAl-LDHs obtained in step (1), stir at 60-80℃ for 2-4 h, then age at the same temperature for 12-48 h, and then obtain lactic acid intercalated LDHs after washing, filtration, drying and grinding.

[0009] (3) Preparation of modified barrier polylactic acid mixture: ethylene glycol, lactic acid, and lactic acid-intercalated LDH were used as monomers, and stannous octoate was used as a catalyst. The amount of stannous octoate added was 0.5-3.0 wt% of lactic acid, and the amount of ethylene glycol added was 0.5-2.0 wt% of lactic acid.

[0010] The amount of lactic acid intercalated LDH added is 0.5-10 wt% of lactic acid; in-situ polymerization is carried out by vacuum reaction at 130-150℃ for 3-5 hours, and the mixture is cooled and allowed to stand at room temperature to obtain modified barrier polylactic acid mixture.

[0011] In a preferred embodiment of the present invention, the thickness of the flame-retardant high-barrier biodegradable film is 15-60 μm; wherein the thickness of the flame-retardant upper and lower surface layers is 3-15 μm, and the thickness of the barrier core layer is 9-30 μm.

[0012] In a preferred embodiment of the present invention, the phosphazene flame retardant is a cyclophosphonitrile derivative containing the following structural units:

[0013] ,

[0014] Where R is one or more of sulfonates, aromatic rings, and phosphonates.

[0015] In a preferred embodiment of the present invention, the functional masterbatch is composed of 75-97 wt% polylactic acid resin, 1-10 wt% opening agent, 1-10 wt% antistatic agent, 0.5-2.5 wt% antioxidant and 0.5-2.5 wt% antihydrolysis agent.

[0016] More preferably, the opening agent is one or more of talc, silica, and cross-linked polystyrene microspheres.

[0017] More preferably, the antistatic agent is one or more of stearic acid esters, alkyl phosphates, and alkyl sulfates.

[0018] More preferably, the antioxidant is one or more of phosphites and hindered phenols.

[0019] In a preferred embodiment of the present invention, the anti-hydrolysis agent is a carbodiimide-based hydrolysis agent.

[0020] In a preferred embodiment of the present invention, the biodegradable elastomer is one or more of polybutylene terephthalate, polybutylene succinate, polybutylene succinate, polycaprolactone, polyhydroxyalkanoate, and carbon dioxide copolymer.

[0021] In a preferred embodiment of the present invention, the chain extender is one or more of styrene-glycidyl methacrylate, isocyanate, dianhydride, styrene-glycidyl methacrylate copolymer, styrene-maleic anhydride copolymer, chain extender ADR, and chain extender XY4370.

[0022] To achieve the above objectives, the second technical solution of the present invention is: a method for preparing a flame-retardant, high-barrier, biodegradable film, specifically comprising the following steps:

[0023] S1 involves drying the raw materials and controlling the moisture content to ≤200ppm;

[0024] S2 weighs the raw materials for the flame-retardant upper surface layer, barrier core layer and flame-retardant lower surface layer according to the group proportions, stirs and mixes them, and then puts them into the main machine and auxiliary machine of the three-layer co-extrusion casting machine respectively. They are melt-extruded at 180-230℃ to obtain composite casting sheets.

[0025] S3 involves biaxially stretching the composite casting obtained in step S2, followed by shaping and heat treatment. After winding, a flame-retardant, high-barrier, biodegradable film with a thickness of 15-60 μm is obtained, wherein the thickness of the flame-retardant upper and lower surface layers is 3-15 μm, and the thickness of the barrier core layer is 9-30 μm.

[0026] In a preferred embodiment of the present invention, the thickness of the composite casting obtained in step S2 is 120-300 μm.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The phosphazene flame retardant used in this invention is composed of alternating -N=P bonds, rich in N and P elements, which endows the material with strong flame retardant properties. The cyclophosphonitrile derivative has a conjugated structure similar to the benzene ring, resulting in good thermal stability. During combustion, the N element in the flame retardant can decompose to produce non-flammable gases such as NH3 and N2, diluting the concentration of flammable gases on the surface. The P element can further dehydrate to generate metaphosphoric acid and polymetaphosphoric acid after forming phosphoric acid with a boiling point of up to 300℃, promoting the dehydration and carbonization of the film substrate, forming a dense and continuous carbon layer, isolating air and hindering heat transfer. At the same time, the volatile phosphorus compounds produced by combustion decomposition can efficiently capture free radicals generated during combustion, inhibiting the combustion reaction.

[0029] 2. This invention improves the compatibility of LDHs with the substrate by in-situ polymerization modification of barrier polylactic acid (PLA) mixtures after intercalation with MgAl-LDHs using lactic acid. The modified MgAl-LDHs can act as a material barrier, extending the permeation path of gas and water molecules and improving the barrier properties of the film. It can also act as nucleation sites, enhancing the crystallinity of the PLA film, thereby improving the mechanical properties and barrier properties of the film. Furthermore, the LDHs prepared using this method can produce a synergistic effect with phosphazene flame retardants, enhancing the flame retardant properties of the substrate. The interlayer anions of the LDHs contain CO32-. 2- During combustion, it produces CO2 gas, which, along with water vapor, dilutes and blocks combustion gases. The composite metal oxides formed by its thermal decomposition can react with the degradation products of the substrate, promoting the formation of a char layer. In addition, the combustion products of LDHs have strong alkalinity and a large specific surface area, which can absorb acidic gases and smoke produced by the decomposition of the substrate, thus suppressing smoke and fog while forming compounds.

[0030] 3. This invention introduces chain extenders, antioxidants, and anti-hydrolysis agents. The three work synergistically to significantly improve the thermal processing stability of polylactic acid substrates and prevent performance degradation due to thermal degradation during processing. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of a flame-retardant, high-barrier, biodegradable film according to the present invention.

[0032] In the diagram: 10 - Flame-retardant upper surface layer; 20 - Barrier core layer; 30 - Flame-retardant lower surface layer. Detailed Implementation

[0033] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0034] This invention provides embodiments of the following flame-retardant, high-barrier, biodegradable film, such as... Figure 1 As shown, from top to bottom, it consists of a flame-retardant upper surface layer (10), a barrier core layer (20), and a flame-retardant lower surface layer (30).

[0035] In Examples 1-4 below, the phosphazene flame retardants are cyclophosphonitrile derivatives containing the following structural units;

[0036]

[0037] The structural formulas of R in Examples 1-3 are as follows:

[0038]

[0039] The structural formula of R in Example 4 is as follows:

[0040]

[0041] Example 1

[0042] A flame-retardant, high-barrier, biodegradable film with a total thickness of 40 μm; wherein the flame-retardant upper and lower surface layers are 10 μm thick, and the barrier core layer is 20 μm thick.

[0043] The raw material components of the flame-retardant upper and lower layers of the flame-retardant high-barrier biodegradable film, by weight percentage, include 2 wt% functional masterbatch, 2 wt% modified barrier polylactic acid mixture, 5 wt% phosphazene flame retardant, 1 wt% chain extender, 15 wt% biodegradable elastomer, and 75 wt% polylactic acid resin; the raw material components of the barrier core layer, by weight percentage, include 1 wt% chain extender, 10 wt% modified barrier polylactic acid mixture, and 89 wt% polylactic acid resin.

[0044] The modified barrier polylactic acid mixture is prepared by the following method, including the following steps:

[0045] (1) Preparation of MgAl-LDHs: according to n(Mg 2+ ): n(Al 3+ )=2:1、[OH - ] =2[n(Mg 2+ )+ n(Al 3+ )] and [CO3 2- ]=1 / 2 n(Al 3+ Add a 1.0 mol / L MgCl2 and AlCl2 solution and a mixed alkaline solution of NaOH and Na2CO3 to a ball mill, adjust the pH to ≥10, ball mill for 10 min, and then place it in a 60℃ oven to age for 24 h. Wash with deionized water until neutral.

[0046] (2) Preparation of lactic acid intercalated LDHs: Prepare a 30wt% sodium lactate solution, add 5wt% of the MgAl-LDHs obtained in step (1), stir at 60℃ for 4h, and then put it into an oven to react for 24h. After washing, filtration, drying and grinding, lactic acid intercalated LDHs are obtained.

[0047] (3) Preparation of modified barrier polylactic acid mixture: ethylene glycol, lactic acid and lactic acid intercalated LDH obtained in step (3) are used as monomers, and stannous octoate is used as catalyst. The amount of stannous octoate added is 1 wt% of lactic acid, the amount of ethylene glycol added is 1 wt% of lactic acid, and the amount of lactic acid intercalated LDH added is 10 wt% of the mass of lactic acid. The reaction is carried out in situ polymerization at 150℃ for 3.5 h under reduced pressure and vacuum. The mixture is then cooled and allowed to stand at room temperature to obtain modified barrier polylactic acid mixture.

[0048] The functional masterbatch used consists of 95 wt% polylactic acid resin, 1 wt% opening agent, 1 wt% antistatic agent, 2 wt% antioxidant and 1 wt% anti-hydrolysis agent.

[0049] The chain extender used in this embodiment is chain extender ADR; the biodegradable elastomer is PBAT; the opening agent is silica; the antistatic agent is stearic acid ester; the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1; and the antihydrolysis agent is carbodiimide.

[0050] The preparation method of the flame-retardant, high-barrier, biodegradable film in this embodiment specifically includes the following steps:

[0051] S1 involves drying the raw materials and controlling the moisture content to ≤200ppm;

[0052] S2 weighs the raw materials for the flame-retardant upper surface layer, barrier core layer and flame-retardant lower surface layer according to the group proportions, stirs and mixes them, and then puts them into the main machine and auxiliary machine of the three-layer co-extrusion casting machine respectively. They are melt-extruded at 185-195℃ to obtain a composite casting sheet of 240-260μm.

[0053] S3 performs biaxial stretching on the composite casting sheet, followed by shaping and heat treatment, and then winds it up to obtain a flame-retardant, high-barrier, biodegradable film.

[0054] Example 2

[0055] A flame-retardant, high-barrier, biodegradable film with a total thickness of 40 μm; wherein the flame-retardant upper and lower surface layers are 10 μm thick, and the barrier core layer is 20 μm thick.

[0056] The raw material components of the flame-retardant upper and lower layers of the flame-retardant high-barrier biodegradable film, by weight percentage, include 2 wt% functional masterbatch, 2 wt% modified barrier polylactic acid mixture, 5 wt% phosphazene flame retardant, 1 wt% chain extender, 15 wt% biodegradable elastomer, and 75 wt% polylactic acid resin; the raw material components of the barrier core layer, by weight percentage, include 1 wt% chain extender, 20 wt% modified barrier polylactic acid mixture, and 79 wt% polylactic acid resin.

[0057] The modified barrier polylactic acid mixture is prepared by the following method, including the following steps:

[0058] (1) Preparation of MgAl-LDHs: according to n(Mg 2+ ): n(Al 3+ )=3:1、[OH - ] =2[n(Mg 2+ )+ n(Al 3+ )] and [CO3 2- ]=1 / 2 n(Al 3+ Add a 1.0 mol / L MgCl2 and AlCl2 solution and a mixed alkaline solution of NaOH and Na2CO3 to a ball mill, adjust the pH to ≥10, ball mill for 15 min, then place in a 60℃ oven to age for 24 h, and wash with deionized water until neutral.

[0059] (2) Preparation of lactic acid intercalated LDHs: Prepare a 20wt% sodium lactate solution, add 10wt% MgAl-LDHs, stir at 60℃ for 4h, then place in an oven to react for 24h, wash, filter, dry, and grind to obtain lactic acid intercalated LDHs;

[0060] (3) Preparation of modified barrier polylactic acid mixture: ethylene glycol, lactic acid and lactic acid intercalated LDH were used as monomers, and stannous octoate was used as catalyst. The amount of stannous octoate added was 1 wt% of lactic acid, the amount of ethylene glycol added was 1 wt% of lactic acid, and the amount of lactic acid intercalated LDH added was 10 wt% of the mass of lactic acid. In-situ polymerization was carried out at 150℃ for 3.5 h under reduced pressure and vacuum. After cooling and standing to room temperature, the modified barrier polylactic acid mixture was obtained.

[0061] The functional masterbatch used consists of 95 wt% polylactic acid resin, 1 wt% opening agent, 1 wt% antistatic agent, 2 wt% antioxidant and 1 wt% anti-hydrolysis agent;

[0062] The chain extender used in this embodiment is chain extender ADR; the biodegradable elastomer is PCL; the opening agent is silica; the antistatic agent is stearic acid ester; the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1; and the antihydrolysis agent is carbodiimide.

[0063] The preparation method of the flame-retardant, high-barrier, biodegradable film in this embodiment specifically includes the following steps:

[0064] S1 involves drying the raw materials and controlling the moisture content to ≤200ppm;

[0065] S2 weighs the raw materials for the flame-retardant upper surface layer, barrier core layer and flame-retardant lower surface layer according to the group proportions, stirs and mixes them, and then puts them into the main machine and auxiliary machine of the three-layer co-extrusion casting machine respectively. The mixture is melt-extruded at 185-195℃ to obtain a composite casting sheet with a thickness of 240-260μm.

[0066] S3 performs biaxial stretching on the composite casting sheet, followed by shaping and heat treatment. After winding, a flame-retardant, high-barrier, biodegradable film with a thickness of 40 μm is obtained, wherein the thickness of the flame-retardant upper and lower surface layers is 10 μm, and the thickness of the barrier core layer is 20 μm.

[0067] Example 3

[0068] A flame-retardant, high-barrier, biodegradable film with a total thickness of 40 μm; wherein the flame-retardant upper and lower surface layers are 10 μm thick, and the barrier core layer is 20 μm thick.

[0069] The raw material components of the flame-retardant upper and lower layers of the flame-retardant high-barrier biodegradable film, by weight percentage, include 2 wt% functional masterbatch, 2 wt% modified barrier polylactic acid mixture, 5 wt% phosphazene flame retardant, 1 wt% chain extender, 15 wt% biodegradable elastomer, and 75 wt% polylactic acid resin; the raw material components of the barrier core layer, by weight percentage, include 5 wt% chain extender, 20 wt% modified barrier polylactic acid mixture, and 75 wt% polylactic acid resin.

[0070] The modified barrier polylactic acid mixture is prepared by the following method, including the following steps:

[0071] (1) Preparation of MgAl-LDHs: according to n(Mg 2+ ): n(Al 3+ )=2:1、[OH - ] =2[n(Mg 2+ )+ n(Al 3+ )] and [CO3 2- ]=1 / 2 n(Al 3+ Add a 1.0 mol / L MgCl2 and AlCl2 solution and a mixed alkaline solution of NaOH and Na2CO3 to a ball mill, adjust the pH to ≥10, ball mill for 15 min, then place in a 60℃ oven to age for 24 h, and wash with deionized water until neutral.

[0072] (2) Preparation of lactic acid intercalated LDHs: Prepare a 30wt% sodium lactate solution, add 10wt% MgAl-LDHs, stir at 60℃ for 4h, then place in an oven to react for 24h, wash, filter, dry, and grind to obtain lactic acid intercalated LDHs;

[0073] (3) Preparation of modified barrier polylactic acid mixture: ethylene glycol, lactic acid and lactic acid intercalated LDH were used as monomers, and stannous octoate was used as catalyst. The amount of stannous octoate added was 1 wt% of lactic acid, the amount of ethylene glycol added was 1 wt% of lactic acid, and the amount of lactic acid intercalated LDH added was 10 wt% of the mass of lactic acid. In-situ polymerization was carried out at 150℃ for 3.5 h under reduced pressure and vacuum. After cooling and standing to room temperature, the modified barrier polylactic acid mixture was obtained.

[0074] The functional masterbatch used consists of 95 wt% polylactic acid resin, 1 wt% opening agent, 1 wt% antistatic agent, 2 wt% antioxidant and 1 wt% anti-hydrolysis agent;

[0075] In this embodiment, the chain extender is chain extender ADR; the biodegradable elastomer is PBAT; the opening agent is silica; the antistatic agent is stearic acid ester; the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1; and the antihydrolysis agent is carbodiimide.

[0076] The preparation method of the flame-retardant, high-barrier, biodegradable film in this embodiment specifically includes the following steps:

[0077] S1 involves drying the raw materials and controlling the moisture content to ≤200ppm;

[0078] S2 weighs the raw materials for the flame-retardant upper surface layer, barrier core layer and flame-retardant lower surface layer according to the mass percentage in the formula, stirs and mixes them, and then puts them into the main machine and auxiliary machine of the three-layer co-extrusion casting machine respectively, and melts and extrudes them at 185-195℃ to obtain a composite casting sheet with a thickness of 240-260μm.

[0079] S3 performs biaxial stretching on the composite casting sheet, followed by shaping and heat treatment. After winding, a flame-retardant, high-barrier, biodegradable film with a thickness of 40 μm is obtained. The flame-retardant upper and lower surface layers are 10 μm thick, and the barrier core layer is 20 μm thick.

[0080] Example 4

[0081] A flame-retardant, high-barrier, biodegradable film with a total thickness of 40 μm; wherein the flame-retardant upper and lower surface layers are 10 μm thick, and the barrier core layer is 20 μm thick.

[0082] The raw material components of the flame-retardant upper and lower layers of the flame-retardant high-barrier biodegradable film, by weight percentage, include 2 wt% functional masterbatch, 2 wt% modified barrier polylactic acid mixture, 5 wt% phosphazene flame retardant, 1 wt% chain extender, 15 wt% biodegradable elastomer, and 75 wt% polylactic acid resin; the raw material components of the barrier core layer, by weight percentage, include 1 wt% chain extender, 20 wt% modified barrier polylactic acid mixture, and 79 wt% polylactic acid resin.

[0083] The modified barrier polylactic acid mixture is prepared by the following method, including the following steps:

[0084] (1) Preparation of MgAl-LDHs: according to n(Mg 2+ ): n(Al 3+ )=2:1、[OH - ] =2[n(Mg 2+ )+ n(Al 3+ )] and [CO3 2- ]=1 / 2 n(Al 3+ Add a 1.0 mol / L MgCl2 and AlCl2 solution and a mixed alkaline solution of NaOH and Na2CO3 to a ball mill, adjust the pH to ≥10, ball mill for 10 min, and then place it in a 60℃ oven to age for 24 h. Wash with deionized water until neutral.

[0085] (2) Preparation of lactic acid intercalated LDHs: Prepare a 30wt% sodium lactate solution, add 10wt% MgAl-LDHs, stir at 60℃ for 4h, then place in an oven to react for 24h, wash, filter, dry, and grind to obtain lactic acid intercalated LDHs;

[0086] (3) Preparation of modified barrier polylactic acid mixture: ethylene glycol, lactic acid and lactic acid intercalated LDH were used as monomers, and stannous octoate was used as catalyst. The amount of stannous octoate added was 1 wt% of lactic acid, the amount of ethylene glycol added was 1 wt% of lactic acid, and the amount of lactic acid intercalated LDH added was 10 wt% of the mass of lactic acid. The mixture was subjected to in-situ polymerization at 150℃ for 3.5 h under reduced pressure and vacuum. After cooling and standing at room temperature, the mixture was further polymerized in-situ to obtain the modified barrier polylactic acid mixture.

[0087] The functional masterbatch used consists of 95 wt% polylactic acid resin, 1 wt% opening agent, 1 wt% antistatic agent, 2 wt% antioxidant and 1 wt% anti-hydrolysis agent.

[0088] The chain extender used in this embodiment is chain extender ADR; the biodegradable elastomer is PBAT; the opening agent is silica; the antistatic agent is stearic acid ester; the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 2:1; and the antihydrolysis agent is carbodiimide.

[0089] The preparation method of the flame-retardant, high-barrier, biodegradable film in this embodiment specifically includes the following steps:

[0090] S1 involves drying the raw materials and controlling the moisture content to ≤200ppm;

[0091] S2 weighs the raw materials for the flame-retardant upper surface layer, barrier core layer and flame-retardant lower surface layer according to the mass percentage in the formula, stirs and mixes them, and then puts them into the main machine and auxiliary machine of the three-layer co-extrusion casting machine respectively, and melts and extrudes them at 185-195℃ to obtain a composite casting sheet with a thickness of 240-260μm.

[0092] S3 performs biaxial stretching on the composite casting sheet, followed by shaping and heat treatment. After winding, a flame-retardant, high-barrier, biodegradable film with a thickness of 40 μm is obtained. The flame-retardant upper and lower surface layers are 10 μm thick, and the barrier core layer is 20 μm thick.

[0093] Comparative Example 1

[0094] 100% pure polylactic acid membrane with a thickness of 40μm.

[0095] Comparative Example 2

[0096] A flame-retardant, high-barrier, biodegradable film with a total thickness of 40 μm differs from Example 1 in that:

[0097] The raw material components of the flame-retardant upper and lower layers, by mass percentage, include 2 wt% functional masterbatch, 2 wt% modified barrier polylactic acid mixture, 5 wt% phosphazene flame retardant, 1 wt% chain extender, 15 wt% biodegradable elastomer and 80 wt% polylactic acid resin.

[0098] The raw material components of the barrier core layer, by mass percentage, include 1% chain extender and 99% polylactic acid resin.

[0099] Comparative Example 3

[0100] A flame-retardant, high-barrier, biodegradable film with a total thickness of 40 μm differs from Example 1 in that:

[0101] The raw material components of the flame-retardant upper and lower layers, by mass percentage, include 2 wt% functional masterbatch, 2 wt% modified barrier polylactic acid mixture, 5 wt% phosphazene flame retardant, 1 wt% chain extender, 15 wt% biodegradable elastomer and 80 wt% polylactic acid resin.

[0102] The raw material components of the barrier core layer, by mass percentage, include 1 wt% chain extender, 20 wt% modified barrier polylactic acid mixture and 79 wt% polylactic acid resin.

[0103] Comparative Example 4

[0104] A flame-retardant, high-barrier, biodegradable film with a total thickness of 40 μm differs from Example 1 in that:

[0105] The raw material components of the flame-retardant upper and lower layers, by mass percentage, include 2 wt% functional masterbatch, 5 wt% phosphazene flame retardant, 1 wt% chain extender, 15 wt% biodegradable elastomer and 77 wt% polylactic acid resin.

[0106] The raw material components of the barrier core layer, by mass percentage, include 1 wt% chain extender and 99 wt% polylactic acid resin.

[0107] Comparative Example 5

[0108] A flame-retardant, high-barrier, biodegradable film with a total thickness of 40 μm differs from Example 1 in that:

[0109] The raw material components of the flame-retardant upper and lower layers, by mass percentage, include 2 wt% functional masterbatch, 5 wt% phosphazene flame retardant, 1 wt% chain extender, 15 wt% biodegradable elastomer, and 77 wt% polylactic acid resin.

[0110] The raw material components of the barrier core layer, by mass percentage, include 1 wt% chain extender, 20 wt% modified barrier polylactic acid mixture and 79 wt% polylactic acid resin.

[0111] The thin films prepared in Examples 1-4 and Comparative Examples 1-5 were subjected to performance tests, and the results are shown in Table 1:

[0112] Table 1. Test results of thin film performance in Examples 1-4 and Comparative Examples 1-5

[0113]

[0114] The tensile strength and elongation at break of the aforementioned flame-retardant, high-barrier, biodegradable film were tested according to GB / T 1040; the barrier properties were tested according to ASTM D3985; and the flame retardancy rating was tested according to ANSL-UL94-2009.

[0115] Note: Table 1 evaluates barrier properties, with the best performance marked as "★★★★★" and the worst as "☆☆☆☆☆". The more "★" marks, the better the performance.

[0116] The data above show that Comparative Example 1 indicates that the pure polylactic acid film has poor barrier properties and no flame retardancy. Comparative Examples 2 and 3 indicate that LDHs can improve the barrier properties of the film and impart a certain degree of flame retardancy. Comparative Examples 4 and 5 indicate that phosphazene flame retardants and LDHs can synergistically enhance the flame retardancy of the film.

[0117] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flame-retardant, high-barrier, biodegradable film, characterized in that, The structure comprises, from top to bottom, a flame-retardant upper layer, a barrier core layer, and a flame-retardant lower layer. The raw material components of the flame-retardant upper and lower layers, by mass percentage, include 1-5 wt% functional masterbatch, 2-5 wt% modified barrier polylactic acid mixture, 1-20 wt% phosphazene flame retardant, 1-5 wt% chain extender, 10-20 wt% biodegradable elastomer, and 45-85 wt% polylactic acid resin. The raw material components of the barrier core layer, by mass percentage, include 1-10 wt% chain extender, 1-20 wt% modified barrier polylactic acid mixture, and 70-98 wt% polylactic acid resin. The preparation method of the modified barrier polylactic acid mixture is as follows: (1) MgAl-LDHs preparation: MgCl2 and AlCl2 solution with a metal ion concentration of 1.0 mol / L and mixed alkali liquor of NaOH and Na2CO3 were added into a ball mill in a proportion of n(Mg 2+ ) : n(Al 3+ )=(2~4):1, [OH - ]=2[n(Mg 2+ )+ n(Al 3+ )] and [CO3 2- ]=1 / 2 n(Al 3+ ), and the PH was adjusted to be greater than or equal to 10, and then the ball milling reaction was performed for 10-15 min, and then the product was placed into a 60°C oven for aging for 12-48 h, and then washed with deionized water until neutralization; (2) Preparation of lactic acid intercalated LDHs: Prepare a 20-40 wt% sodium lactate solution, add 2-10 wt% MgAl-LDHs obtained in step (1), stir at 60-80℃ for 2-4 h, then age at the same temperature for 12-48 h, and then obtain lactic acid intercalated LDHs after washing, filtration, drying and grinding; (3) Preparation of modified barrier polylactic acid mixture: ethylene glycol, lactic acid and lactic acid intercalated LDH are used as monomers, and stannous octoate is used as catalyst. The amount of stannous octoate added is 0.5-3.0 wt% of lactic acid, the amount of ethylene glycol added is 0.5-2.0 wt% of lactic acid, and the amount of lactic acid intercalated LDH added is 0.5-10 wt% of lactic acid. In-situ polymerization is carried out by vacuum reaction at 130-150℃ for 3-5 hours. After cooling and standing to room temperature, the modified barrier polylactic acid mixture is obtained.

2. The flame-retardant, high-barrier, biodegradable film as described in claim 1, characterized in that, The thickness of the flame-retardant high-barrier biodegradable film is 15-60 μm; wherein the thickness of the flame-retardant upper and lower surface layers is 3-15 μm, and the thickness of the barrier core layer is 9-30 μm.

3. The flame-retardant, high-barrier, biodegradable film as described in claim 1, characterized in that, The phosphazene flame retardant is a cyclophosphazene derivative containing the following structural units: ， Where R is one or more of sulfonates, aromatic rings, and phosphonates.

4. The flame-retardant, high-barrier, biodegradable film as described in claim 1, characterized in that, The functional masterbatch consists of 75-97 wt% polylactic acid resin, 1-10 wt% opening agent, 1-10 wt% antistatic agent, 0.5-2.5 wt% antioxidant and 0.5-2.5 wt% anti-hydrolysis agent.

5. The flame-retardant, high-barrier, biodegradable film as described in claim 4, characterized in that, The functional masterbatch consists of 75-97 wt% polylactic acid resin, 1-10 wt% opening agent, 1-10 wt% antistatic agent, 0.5-2.5 wt% antioxidant and 0.5-2.5 wt% anti-hydrolysis agent.

6. The flame-retardant, high-barrier, biodegradable film as described in claim 5, characterized in that, The opening agent is one or more of talc, silica, and cross-linked polystyrene microspheres.

7. The flame-retardant, high-barrier, biodegradable film as described in claim 5, characterized in that, The antistatic agent is one or more of stearic acid esters, alkyl phosphates, and alkyl sulfates; the antioxidant is one or more of phosphites and hindered phenols; and the antihydrolysis agent is a carbodiimide hydrolysant.

8. The flame-retardant, high-barrier, biodegradable film as described in claim 1, characterized in that, The biodegradable elastomer is one or more of the following: polybutylene terephthalate, polybutylene succinate, polybutylene succinate, polycaprolactone, polyhydroxyalkanoate, and carbon dioxide copolymer.

9. The flame-retardant, high-barrier, biodegradable film as described in claim 1, characterized in that, The chain extender is one or more of the following: styrene-glycidyl methacrylate, isocyanate, dianhydride, styrene-glycidyl methacrylate copolymer, styrene-maleic anhydride copolymer, chain extender ADR, and chain extender XY4370.

10. A method for preparing a flame-retardant, high-barrier, biodegradable film as described in any one of claims 1-8, characterized in that, Includes the following steps: S1 involves drying the raw materials and controlling the moisture content to ≤200ppm; S2 weighs the raw materials of flame-retardant upper surface layer, barrier core layer and flame-retardant lower surface layer according to the group proportion, stirs and mixes them, and then puts them into the main machine and auxiliary machine of the three-layer co-extrusion casting machine respectively. They are melt-extruded at 180-230℃ to obtain a composite casting sheet with a thickness of 120-300 μm. S3 involves biaxially stretching the composite casting obtained in step S2, followed by shaping and heat treatment. After winding, a flame-retardant, high-barrier, biodegradable film with a thickness of 15-60 μm is obtained, wherein the thickness of the flame-retardant upper and lower surface layers is 3-15 μm, and the thickness of the barrier core layer is 9-30 μm.

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