High-barrier biodegradable composite film and preparation method thereof

Abstract

The application relates to the technical field of high polymer materials, and particularly discloses a high-barrier biodegradable composite film and a preparation method thereof. The high-barrier biodegradable composite film comprises an outer layer, a sandwich layer and an inner layer, and the outer layer and the inner layer comprise the following raw materials in parts by weight: 60-80 parts of PLA resin, 10-30 parts of PBS resin, 5-20 parts of PGA resin, 1-2 parts of a plasticizer, 2.5-3 parts of a chain extender, 2-4 parts of a barrier enhancer and 1.5-2.5 parts of maleic anhydride grafted PLA; and the sandwich layer is a fiber film prepared by mixing silane-modified nanocellulose and nanosilver-loaded guar gum nanofiber. The composite film has the advantages of high barrier capacity, good antibacterial effect, long-lasting antibacterial property, high mechanical strength and tight interlayer combination.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and more specifically, to a high-barrier biodegradable composite membrane and its preparation method. Background Technology

[0002] In many fields such as packaging, medical, food, and aerospace, the barrier properties of materials are crucial. High-barrier materials possess properties such as oxygen barrier, gas barrier, and oil barrier, which can prevent the intrusion of external substances and maintain the stability of the internal environment of the packaging. Currently, high-barrier materials include metals, glass, and polymer materials. Representative polymer film materials include polyvinylidene fluoride (PVDF) and polyvinylidene chloride (PVDC). Although PVDF and PVDC have good barrier properties, they are difficult to degrade in the natural environment. Long-term accumulation has caused serious "white pollution" problems and damaged the ecological environment.

[0003] Replacing traditional non-degradable plastics with biodegradable plastics is an important way to solve film pollution. Biodegradable plastics that meet biodegradability standards mainly include polylactic acid (PLA), polyhydroxyalkanoates (PHAs), polybutylene succinate (PBS), poly(butylene succinate-co-butylene adipate) (PBSA), polycaprolactone (PCL), and polybutylene adipate / terephthalate (PBAT). However, these materials have poor barrier properties against oxygen and water vapor. When used in food packaging, they easily allow oxygen and other gases to permeate, leading to microbial growth and oxidation of the contents. Water vapor permeation can also cause mold growth, limiting the widespread application of biodegradable materials in food packaging.

[0004] In the prior art, Chinese invention patent application CN 202210863595.8 discloses a method for preparing a biodegradable high-barrier packaging film, comprising the following steps: mixing PGA, PBSA and ADR4468, melt extruding and granulating to obtain a composite material masterbatch; then blow molding the composite material masterbatch into a film to obtain the biodegradable high-barrier packaging film; the raw materials for the biodegradable high-barrier packaging film include, by weight, 60-70 parts of PGA, 30-40 parts of PBSA and 0-0.7 parts of ADR4468, wherein the sum of PGA and PBSA is 100 parts.

[0005] The aforementioned high-barrier packaging film uses PGA as raw material and adds PBSA to solve the problem that PGA has poor toughness and cannot be blown into a film. The resulting packaging film has good barrier and mechanical properties, but it does not have antibacterial properties. It usually needs to add antibacterial agents to give it antibacterial properties. However, antibacterial agents have poor dispersibility in resin, which affects the mechanical and barrier properties of the film. Moreover, the antibacterial components are easy to migrate, resulting in insufficient long-term effectiveness. Summary of the Invention

[0006] In order to improve the barrier properties, antibacterial long-lasting effect and mechanical strength of biodegradable membranes, this application provides a high-barrier biodegradable composite membrane and its preparation method.

[0007] In a first aspect, this application provides a high-barrier biodegradable composite membrane, employing the following technical solution:

[0008] A high-barrier biodegradable composite membrane includes an outer layer, a sandwich layer, and an inner layer. The outer and inner layers comprise the following raw materials in parts by weight: 60-80 parts PLA resin, 10-30 parts PBS resin, 5-20 parts PGA resin, 1-2 parts plasticizer, 2.5-3 parts chain extender, 2-4 parts barrier enhancer, and 1.5-2.5 parts maleic anhydride-grafted PLA.

[0009] The sandwich layer is a fiber membrane made of silane-modified nanocellulose and silver-loaded guar gum nanofibers.

[0010] By adopting the above technical solution, PLA, PBS (polybutylene succinate), and PGA (polyglycolic acid) are used as the substrates for the outer and inner layers. PBS has strong flexibility, which can significantly improve the toughness and processing fluidity of PLA and alleviate the brittleness of PLA. PGA has high barrier properties, especially against oxygen and water vapor, and its rigid segments can improve tensile strength. However, excessive amounts can lead to increased brittleness of the material. The three resins are mixed in appropriate amounts, and a chain extender is added to improve interfacial bonding and improve the tensile strength and other mechanical properties of the outer and inner film.

[0011] A sandwich layer is set between the outer and inner layers. The sandwich layer is a composite membrane of silane-modified nanocellulose and PGA-modified silver-loaded guar gum nanofibers. The surface of the nanocellulose contains abundant hydroxyl groups, and its own hydrogen bonding ensures its good film-forming properties. However, the abundant hydroxyl groups on its surface make it highly hygroscopic, affecting its ability to block water vapor. By grafting long-chain alkyl groups onto the surface of the nanocellulose, water vapor permeation is reduced, and a continuous network is formed in the sandwich layer, extending the gas permeation path, effectively transferring stress and inhibiting crack propagation, thereby increasing the mechanical strength of the sandwich layer. Guar gum nanofibers and silane-modified nanocellulose are networked together. The guar gum nanofibers are further reinforced to enhance the toughness of the sandwich layer, improve tensile strength and modulus, and provide some barrier effect against water vapor and other gases. After loading silver nanoparticles onto the guar gum nanofibers, the silver nanoparticles are stably present in the gaps between the nanofibers, reducing stress concentration, further hindering the diffusion of small molecules, and improving barrier ability. The silver nanoparticles loaded in the guar gum nanofibers are released slowly, and the sandwich structure can prevent the silver nanoparticles from being directly exposed to the high temperature of processing during the hot melting of polylactic acid resin, reducing agglomeration and deactivation, effectively prolonging the antibacterial effect. Moreover, the outer and inner layers can form a physical barrier to slow down the release rate of silver ions and reduce migration.

[0012] Optionally, in the outer and inner layers, the total amount of PBS resin and PGA resin is 25 wt% of the amount of PLA resin.

[0013] By adopting the above technical solution and compounding the raw materials according to the above dosage, the toughness and strength can be better balanced, resulting in a film with high tensile strength, high breaking strength, and good rigidity and toughness.

[0014] Optionally, the mass ratio of the silane-modified nanocellulose to the silver-loaded guar gum nanofibers is 2-3:1.

[0015] By adopting the above technical solution, cellulose nanofibers are chemically bonded to silver-loaded guar gum nanofibers through silane modification. The high aspect ratio enables the construction of a rigid network, improving tensile strength and modulus. The flexible chain structure of the silver-loaded guar gum nanofibers can buffer stress and intertwine with the silane-modified cellulose nanofibers, further densifying the structure, improving the membrane's impact resistance, and extending the gas permeation path, significantly enhancing barrier properties. If too much silane-modified cellulose nanofiber is used, it is prone to agglomeration, forming stress concentration points and leading to a decrease in toughness. If the amount of silane-modified cellulose nanofiber is too low, the rigid network will be discontinuous, failing to improve tensile strength. Moreover, if too much silver-loaded guar gum nanofiber is used, the guar gum will increase hydrophilicity due to its large number of hydroxyl groups, leading to a decrease in water vapor barrier capacity. Therefore, an appropriate ratio of the two can form a rigid skeleton-flexible filler network structure, balancing rigidity and toughness, and balancing antibacterial activity.

[0016] Optionally, the silver-loaded guar gum nanofibers are prepared by impregnating guar gum nanofibers with a PGA solution containing silver nanoparticles after cross-linking with glutaraldehyde vapor and then drying.

[0017] By employing the above technical solution, uncrosslinked guar gum nanofibers exhibit strong hydrophilicity, a loose structure, and weak water vapor barrier properties. By vapor-crosslinking the guar gum nanofibers with glutaraldehyde, the aldehyde groups on glutaraldehyde react with the hydroxyl groups on guar gum, introducing a chemical crosslinking network between the molecular chains. This improves the toughness, tensile strength, and water vapor barrier properties of the guar gum nanofibers. Then, the nanofibers are impregnated with a PGA solution containing nano-silver particles. PGA, or polyglycolic acid, is a hydrophobic polyester. Impregnating the guar gum nanofibers with PGA enhances their surface... A continuous hydrophobic coating is formed, increasing the mechanical properties of guar nanofibers and encapsulating and anchoring silver nanoparticles onto the fibers. Furthermore, the hydroxyl groups on the surface of the guar nanofibers can form hydrogen bonds with the carbonyl groups in PGA, enhancing the binding force, improving the hydrophobicity of the guar nanofiber surface, and enhancing the water vapor barrier effect. The silver nanoparticles dispersed in the PGA solution can increase the surface roughness of the fibers. When combined with the inner and outer layers, they can embed into the membrane layer, increasing mechanical intercalation. Moreover, the cross-linked guar nanofiber network can limit the diffusion rate of silver ions, achieving a long-lasting antibacterial effect.

[0018] Optionally, the barrier enhancer is silane-modified bacterial cellulose loaded with tea polyphenols.

[0019] By adopting the above technical solution, bacterial cellulose possesses an ultra-fine three-dimensional network structure formed by interwoven nanofibers. It exhibits high tensile strength and rigid molecular chains. The cellulose molecular chains are bonded within and between each other via hydrogen bonds, forming a massive hydrogen bond network. After silane modification, it can be uniformly dispersed in the outer and inner layers, forming a continuous reinforcing phase. This enhances modulus and strength through stress transfer and creates a labyrinth effect within the membrane, extending the gas permeation path. Furthermore, the tea polyphenols loaded into the silane-modified bacterial cellulose possess potent antibacterial activity, effectively inhibiting the growth of various microorganisms and enabling the barrier reinforcing agent to exhibit antibacterial properties. The network structure of bacterial cellulose prolongs the release rate of tea polyphenols, improving antibacterial durability. The reducing properties of tea polyphenols prevent the oxidation of silver nanoparticles, maintaining long-lasting antibacterial activity. Additionally, the phenolic hydroxyl groups of tea polyphenols can form complexes with silver ions, extending the silver ion release cycle. The catalytic effect of silver nanoparticles inhibits the oxidative browning of tea polyphenols, preserving antibacterial activity.

[0020] Optionally, the barrier agent is prepared by freeze-drying silane-modified bacterial cellulose, then impregnating it in a polyvinyl alcohol solution containing tea polyphenols, and drying it, wherein the amount of tea polyphenols is 5-10% of the mass of the aerogel.

[0021] By adopting the above technical solution, the aerogel prepared by freeze-drying has ultra-high porosity and specific surface area. After impregnation with tea polyphenols and polyvinyl alcohol, the polyvinyl alcohol encapsulates the tea polyphenols to form a core-shell structure, thereby controlling the release rate of tea polyphenols and extending the antibacterial efficacy. Moreover, after the three-dimensional network of the aerogel is filled with polyvinyl alcohol, the tensile strength is improved. The benzene ring in the tea polyphenols and the hydroxyl groups of polyvinyl alcohol form hydrogen bonds, thereby densifying the membrane structure and further reducing the oxygen permeability.

[0022] Optionally, the silane-modified bacterial cellulose is one of hexadecyltrimethoxysilane, vinyltrimethoxysilane, dodecyltrimethoxysilane, and octyltrimethoxysilane.

[0023] Optionally, the plasticizer is selected from at least one of citric acid, glycerin, and polyethylene glycol.

[0024] Optionally, the total thickness of the composite membrane is 100-150 μm, and the sandwich layer accounts for 15-20%.

[0025] By adopting the above technical solutions, composite films of the above thickness can combine high strength, high barrier properties, and antibacterial properties.

[0026] Secondly, this application provides a method for preparing a high-barrier biodegradable composite membrane, employing the following technical solution:

[0027] A method for preparing a high-barrier biodegradable composite membrane includes the following steps:

[0028] PLA resin, PBS resin and PGA resin are mixed and dried, then mixed evenly with plasticizer, chain extender, barrier reinforcing agent and maleic anhydride-grafted PLA, hot melted, extruded and pelletized to obtain raw material masterbatch.

[0029] The raw material masterbatch is dried, then hot-melted, blown into film, and cooled to obtain a base film.

[0030] Silane-modified nanocellulose and silver-loaded guar gum nanofibers were mixed evenly and then added to deionized water. The mixture was sonicated to form a suspension, which was then vacuum filtered to obtain a fiber membrane.

[0031] Composite membranes are prepared by hot pressing the matrix membrane, fiber membrane, and matrix membrane in that order at 160-170℃ and 5-10MPa for 30-60s.

[0032] By adopting the above technical solution, a composite membrane with a sandwich structure is prepared by using a matrix membrane as the outer and inner layers and a fiber membrane formed by mixing silane-modified nanocellulose and silver-loaded guar gum nanofibers as the sandwich layer. The antibacterial component is sandwiched in the middle by using the outer and inner layers, which reduces the impact of the antibacterial agent on the mechanical strength and barrier properties of the film when it is mixed with the matrix resin. This results in a composite membrane with strong barrier properties, high mechanical strength, and long-lasting antibacterial activity.

[0033] Optionally, before hot pressing, a 5-10% ethyl cellulose ethanol solution is uniformly sprayed onto the surface of the fiber membrane, with a spraying amount of 10-20 g / m³. 2 .

[0034] By adopting the above technical solution, an ethyl cellulose solution is uniformly sprayed onto a fiber membrane formed by mixing silane-modified nanocellulose and silver-loaded guar gum nanofibers. The ethyl cellulose solution has hydrophobic properties and a glass transition temperature of 130-140℃. During hot pressing, it can act as an adhesive and fill the network pores of the fiber membrane to form a denser fiber membrane, increasing the contact area with the outer and inner layers, improving the overall strength of the sandwich layer, reducing interlayer slippage during hot pressing, and delaying the release of silver ions, thus prolonging the antibacterial durability. Moreover, under the action of maleic anhydride grafted PLA in the matrix membrane, the chemical bonding between ethyl cellulose and PLA is promoted, enhancing interfacial interaction and improving the peel force between the sandwich layer and the outer and inner layers.

[0035] In summary, this application has the following beneficial effects:

[0036] 1. Because this application uses PBS resin and PGA resin in combination with PLA resin as the substrate for the outer and inner layers, and adds a barrier reinforcing agent, the outer and inner layers have strong barrier capabilities and excellent mechanical properties. The fiber membrane is made by mixing silane-modified nanocellulose and silver-loaded guar gum nanofibers, which serves as a sandwich layer between the outer and inner layers. The sandwich layer can provide better antibacterial and barrier properties, improve the antibacterial durability of the composite membrane, and provide stronger mechanical strength to the composite membrane.

[0037] 2. In this application, a PGA solution containing silver nanoparticles is preferably used to impregnate guar gum nanofibers that have undergone glutaraldehyde vapor crosslinking treatment to prepare silver-loaded guar gum nanofibers. Glutaraldehyde vapor crosslinking not only increases the mechanical strength of guar gum nanofibers but also reduces their hydrophilicity, enhances their water vapor barrier ability, and improves the interfacial adhesion between guar gum nanofibers and the PGA solution. The adhesion of the PGA solution can load the silver nanoparticles onto the surface of the crosslinked guar gum nanofibers, improving the mechanical strength of the guar gum nanofibers and enhancing the water vapor barrier effect. The silver nanoparticles, in turn, increase the roughness of the nanofibers and, together with the PGA solution, increase the interlayer bonding force.

[0038] 3. In this application, silane-modified bacterial cellulose loaded with tea polyphenols is preferred as a barrier reinforcing agent. After silane modification, the hydrophilicity of the bacterial cellulose surface is reduced, increasing the barrier force against water vapor and improving the compatibility between bacterial cellulose and the matrix resin. It also improves the dispersibility of bacterial cellulose in the outer and inner layers. The loading of tea polyphenols gives the barrier reinforcing agent a certain antibacterial activity. When combined with nano-silver particles, it improves the antibacterial rate and enhances the antibacterial durability. Detailed Implementation

[0039] The following embodiments provide a further detailed description of this application.

[0040] Example I of guar gum nanofiber preparation: Hexadecyltrimethylammonium bromide was added to deionized water and stirred to dissolve at 60°C. Guar gum was then added and stirred to dissolve at room temperature. The mixture was centrifuged at 5000 rpm for 30 min to remove foam, resulting in a 2.4 wt% mixture. The mass ratio of guar gum to hexadecyltrimethylammonium bromide was 2:0.4.

[0041] The mixture was electrospun using aluminum foil as the receiving material at a spinning temperature of 35℃, a humidity of 10%, a voltage of 28kV, a spinning speed of 5.9ml / h, and a receiving distance of 15cm to obtain guar gum nanofibers.

[0042] Preparation Examples of Silver-Loaded Guar Gum Nanofibers 1-4

[0043] Preparation Example 1: 1g of guar gum nanofibers prepared in Preparation Example I were dispersed in deionized water, stirred, and then silver nitrate solution (1g of silver nitrate dissolved in 50ml of deionized water) was added. The mixture was stirred for 30min, and then 10mL of 1% (w / v) sodium citrate solution was added dropwise. The mixture was stirred for 15min, cooled, and then 3 times the volume of ethanol was added. The mixture was centrifuged at 10000rpm for 30min. The precipitate was washed with 75% (v / v) ethanol and centrifuged at 10000rpm for 30min. The precipitate was placed in deionized water to obtain a suspension. The suspension was then vacuum filtered to obtain silver-loaded guar gum nanofibers.

[0044] Preparation Example 2: 50g of PGA resin was added to hexafluoroisopropanol to prepare a solution with a concentration of 5wt%. Nano-silver particles and polyvinylpyrrolidone were added, and the solution was sonicated for 30min to obtain a treatment solution. The PGA was selected from Dongguan Weixin Materials, product number J2029. The nano-silver particles were selected from Xuzhou Jiechuangxin Materials, model A110, with a particle size of 20nm. The amount of nano-silver particles was 2wt% of the PGA resin, and the amount of polyvinylpyrrolidone was 1wt% of the nano-silver particles.

[0045] 1g of guar gum nanofibers prepared by Preparation Example I were placed in glutaraldehyde vapor (prepared by heating a 20% glutaraldehyde aqueous solution) for crosslinking for 24h. Then, the crosslinked guar gum nanofibers were immersed in a treatment solution and vacuum dried at 60°C for 4h.

[0046] Preparation Example 3: 50g of PGA resin was added to hexafluoroisopropanol to prepare a 5wt% solution. Nano silver particles and polyvinylpyrrolidone were added and the solution was sonicated for 30min to obtain a treatment solution. The PGA was selected from Dongguan Weixin Materials, product number J2029. The nano silver particles were selected from Xuzhou Jiechuangxin Materials, model A110, with a particle size of 20nm. The amount of nano silver particles was 2wt% of the PGA resin and the amount of polyvinylpyrrolidone was 1wt% of the nano silver particles.

[0047] 1g of guar gum nanofibers prepared in Preparation Example I were immersed in a treatment solution and vacuum dried at 60°C for 4 hours.

[0048] Preparation Example 4: 1g of silver nanoparticles and polyvinylpyrrolidone were added to 950g of deionized water and sonicated for 30min to obtain a treatment solution. The silver nanoparticles were selected from Xuzhou Jiechuang Innovation Materials, model A110, with a particle size of 20nm. The amount of polyvinylpyrrolidone used was 1wt% of the silver nanoparticles.

[0049] 1g of guar gum nanofibers prepared by Preparation Example I were placed in glutaraldehyde vapor (prepared by heating a 20% glutaraldehyde aqueous solution) for crosslinking for 24h. Then, the crosslinked guar gum nanofibers were immersed in a treatment solution and vacuum dried at 60°C for 4h.

[0050] Example

[0051] Example 1: A high-barrier biodegradable composite membrane with a thickness of 100 μm, comprising an outer layer, a core layer, and an inner layer in contact with each other. The thickness of the core layer is 20% of the total thickness. The core layer is a fiber membrane formed by mixing silane-modified nanocellulose and silver-loaded guar gum nanofibers in a mass ratio of 3:1. The silver-loaded guar gum nanofibers were prepared as in Example 1. The silane-modified nanocellulose was prepared by the following method: 1 g of nanocellulose was dispersed in 200 g of anhydrous ethanol and 10 mL of ammonia water was added, followed by 3 g of hexadecyltrimethoxysilane. The mixture was ultrasonicated for 30 min at 40 °C and 300 W, washed three times by centrifugation with anhydrous ethanol, and dried. The raw material amounts for the outer and inner layers were the same, as shown in Table 1. The PLA resin was selected from Nxtuer, USA. Works, model number 4032D, PBS resin is selected from Dongguan Renju Plastics, brand number Xinjiang Tunhe TH803S, PGA resin is selected from Dongguan Weixin Materials, item number J2029, plasticizer is glycerin, chain extender is BASF ADR-4370S, barrier reinforcing agent is montmorillonite, maleic anhydride grafted PLA is selected from Shanghai Wanluji Plastic Technology, model number J230, item number 0-99.

[0052] The preparation method of the above-mentioned high-barrier biodegradable composite membrane includes the following steps:

[0053] According to the raw material dosage in Table 1, PLA resin, PBS resin and PGA resin were mixed and dried at 60℃ for 8 hours. Then, they were mixed evenly with plasticizer, chain extender, barrier reinforcing agent and maleic anhydride grafted PLA, hot melted, extruded, cooled and pelletized to obtain raw material masterbatch. The extruder screw diameter was 20mm, the length-to-diameter ratio was 40, the set temperature bar from the barrel to the die head was 140℃, 230℃, 230℃, 230℃, 230℃ and 230℃, and the screw speed was 120rpm.

[0054] After drying the raw material masterbatch at 60℃ for 2 hours, it was placed in a vacuum oven at 60℃ for 6 hours. The film was then blown and cooled to obtain the base film. The temperatures of the material conveying sections 1-3 were 225℃, 230℃, and 230℃, respectively. The temperature of the mold area was 230℃. The screw speed was 60 rpm, the blow-up ratio was 3.3, and the traction speed was 15 m / min.

[0055] Silane-modified nanocellulose and silver-loaded guar gum nanofibers were mixed evenly at a mass ratio of 3:1 and then added to deionized water. The mixture was ultrasonically homogenized, vacuum filtered, and dried at 60℃ for 24 hours to obtain a fiber membrane. The amount of deionized water used was three times the total amount of silane-modified nanocellulose and silver-loaded guar gum nanofibers. A 5% ethyl cellulose ethanol solution was uniformly sprayed onto the surface of the fiber membrane at a spraying rate of 20 g / m². 2 ,dry;

[0056] Using the base membrane as the outer and inner layers respectively, and following the placement order of the base membrane, fiber membrane, and base membrane, a high-barrier biodegradable composite membrane was prepared by hot pressing at 170℃ and 5MPa for 30s.

[0057] Table 1. Raw material usage of high-barrier biodegradable composite membranes in Examples 1-5

[0058]

[0059] Example 2: A high-barrier biodegradable composite membrane with a thickness of 100 μm, comprising an outer layer, a core layer, and an inner layer in contact with each other. The thickness of the core layer is 15% of the total thickness. The core layer is a fiber membrane formed by silane-modified nanocellulose and silver-loaded guar gum nanofibers in a mass ratio of 2:1. The silver-loaded guar gum nanofibers were prepared in Preparation Example 1. The silane-modified nanocellulose was prepared by the following method: 1 g of nanocellulose was dispersed in 200 g of anhydrous ethanol and 10 mL of ammonia water was added, followed by the addition of 3 g of hexadecyltrimethoxysilane. The mixture was subjected to superheating at 40 °C and 300 W. The mixture was heated for 30 minutes, washed three times with anhydrous ethanol by centrifugation, and dried. The raw material amounts for the outer and inner layers were the same, as shown in Table 1. The PLA resin was selected from NxtuerWorks (USA), model 4032D; the PBS resin was selected from Renju Plastics (Dongguan City), brand number Xinjiang Tunhe TH803S; the PGA resin was selected from Weixin Materials (Dongguan City), item number J2029; the plasticizer was glycerol; the chain extender was BASF ADR-4370S (Germany); the barrier reinforcing agent was montmorillonite; and the maleic anhydride-grafted PLA was selected from Shanghai Wanluji Plastic Technology, model J230, item number 0-99.

[0060] The preparation method of the above-mentioned high-barrier biodegradable composite membrane includes the following steps:

[0061] According to the raw material dosage in Table 1, PLA resin, PBS resin and PGA resin were mixed and dried at 60℃ for 8 hours. Then, they were mixed evenly with plasticizer, chain extender, barrier reinforcing agent and maleic anhydride grafted PLA, hot melted, extruded, cooled and pelletized to obtain raw material masterbatch. The extruder screw diameter was 20mm, the length-to-diameter ratio was 40, the set temperature bar from the barrel to the die head was 145℃, 225℃, 225℃, 225℃ and 225℃, and the screw speed was 120rpm.

[0062] After drying the raw material masterbatch at 60℃ for 2 hours, it was placed in a vacuum oven at 60℃ for 6 hours. The film was then blown and cooled to obtain the base film. The temperatures of the material conveying sections 1-3 were 225℃, 230℃, and 230℃, respectively. The temperature of the mold area was 230℃. The screw speed was 60 rpm, the blow-up ratio was 3.3, and the traction speed was 15 m / min.

[0063] Silane-modified nanocellulose and silver-loaded guar gum nanofibers were mixed evenly at a mass ratio of 2:1 and then added to deionized water. The mixture was ultrasonically homogenized, vacuum filtered, and dried at 60℃ for 24 hours to obtain a fiber membrane. The amount of deionized water used was three times the total amount of silane-modified nanocellulose and silver-loaded guar gum nanofibers. A 10% ethyl cellulose ethanol solution was uniformly sprayed onto the surface of the membrane at a spraying rate of 10 g / m². 2 ,dry;

[0064] Using the base membrane as the outer and inner layers respectively, and following the placement order of the base membrane, fiber membrane, and base membrane, a high-barrier biodegradable composite membrane was prepared by hot pressing at 160℃ and 10MPa for 60s.

[0065] Examples 3-4: A high-barrier biodegradable composite membrane, which differs from Example 1 in that the amount of raw materials used is shown in Table 1.

[0066] Example 5: A high-barrier biodegradable composite membrane, which differs from Example 1 in that ethyl cellulose ethanol solution was not sprayed onto the surface of the fiber membrane.

[0067] Example 6: A high-barrier biodegradable composite membrane, which differs from Example 1 in that the mass ratio of silane-modified nanocellulose and silver-loaded guar gum nanofibers is 1:3.

[0068] Example 7: A high-barrier biodegradable composite membrane, which differs from Example 1 in that the silver-loaded guar gum nanofibers are made from Preparation Example 2.

[0069] Example 8: A high-barrier biodegradable composite membrane, which differs from Example 1 in that the silver-loaded guar gum nanofibers are made from Preparation Example 3.

[0070] Example 9: A high-barrier biodegradable composite membrane, which differs from Example 1 in that the silver-loaded guar gum nanofibers are made from Preparation Example 4.

[0071] Example 10: A high-barrier biodegradable composite membrane, differing from Example 7 in that the barrier enhancer is silane-modified bacterial cellulose loaded with tea polyphenols. The specific preparation method is as follows: 1g of bacterial cellulose dispersion is circulated 10 times at 100MPa using a high-pressure homogenizer, and hexadecyltrimethoxysilane is added. The molar ratio of hexadecyltrimethoxysilane to the repeating unit on the cellulose molecular chain is 1:1. The pH is adjusted to 3 with dilute hydrochloric acid, and the reaction is carried out at 80℃ for 4h. After washing with water until neutral, silane-modified bacterial cellulose is obtained. Then, it is freeze-dried at -56℃ for 24h to obtain an aerogel. The bacterial cellulose dispersion is selected from Guilin Qihong Technology and has a content of 0.8wt%.

[0072] Add 5g of polyvinyl alcohol to deionized water to prepare a 5wt% polyvinyl alcohol solution. Add tea polyphenols and mix well. Immerse the aerogel in the polyvinyl alcohol solution containing tea polyphenols. After immersion at -0.05MPa for 30 minutes, dry. The amount of tea polyphenols used is 10% of the mass of silane-modified bacterial cellulose.

[0073] Example 11: A high-barrier biodegradable composite membrane, differing from Example 7 in that the barrier enhancer is silane-modified bacterial cellulose loaded with tea polyphenols. The specific preparation method is as follows: 1g of bacterial cellulose dispersion is circulated 10 times at 100MPa using a high-pressure homogenizer, and hexadecyltrimethoxysilane is added. The molar ratio of hexadecyltrimethoxysilane to the repeating unit on the cellulose molecular chain is 1:2. The pH is adjusted to 4 with dilute hydrochloric acid, and the reaction is carried out at 80℃ for 3h. After washing with water until neutral, silane-modified bacterial cellulose is obtained. Then, it is freeze-dried at -56℃ for 24h to obtain an aerogel. The bacterial cellulose dispersion is selected from Guilin Qihong Technology and has a content of 0.8wt%.

[0074] Add 5g of polyvinyl alcohol to deionized water to prepare a 5wt% polyvinyl alcohol solution. Add tea polyphenols and mix well. Immerse the aerogel in the polyvinyl alcohol solution containing tea polyphenols. After immersion at -0.05MPa for 30 minutes, dry. The amount of tea polyphenols used is 5% of the mass of silane-modified bacterial cellulose.

[0075] Example 12: A high-barrier biodegradable composite membrane, differing from Example 7 in that the barrier enhancer uses silane-modified bacterial cellulose loaded with tea polyphenols. The specific preparation method is as follows: 1g of bacterial cellulose dispersion is circulated 10 times at 100MPa using a high-pressure homogenizer. Hexadecyltrimethoxysilane is added, with a molar ratio of hexadecyltrimethoxysilane to repeating units on the cellulose molecular chain of 1:2. The pH is adjusted to 4 with dilute hydrochloric acid, and the reaction is carried out at 80℃ for 3 hours. After washing with water until neutral, tea polyphenols are added and mixed evenly to obtain the barrier enhancer. The bacterial cellulose dispersion is selected from Guilin Qihong Technology, with a content of 0.8wt%, and the amount of tea polyphenols added is 10wt% of the amount of silane-modified bacterial cellulose.

[0076] Comparative Example

[0077] Comparative Example 1: A high-barrier biodegradable composite membrane, which differs from Example 1 in that the sandwich layer is a fiber membrane formed by silver-loaded guar gum nanofibers. The silver-loaded guar gum nanofibers are cut and dispersed in deionized water to form a suspension. After vacuum filtration and drying, a fiber membrane is formed. The matrix membrane, fiber membrane and matrix membrane are hot-pressed to obtain a high-barrier biodegradable composite membrane. The remaining process parameters are the same as those in Example 1.

[0078] Performance testing

[0079] High-barrier biodegradable composite membranes were prepared according to the methods in the examples and comparative examples, and their performance was tested according to the following methods. The test results are recorded in Table 2.

[0080] 1. Tensile strength: The test was conducted in accordance with ASTM D882-12 "Test for tensile properties of plastic sheets and films". The samples were pretreated in an environment of 23±1℃ and 50±5% relative humidity for 24 hours. Then, the tensile strength and elastic modulus were tested under the same environment. The samples were cut into strips of 70mm×10mm. The tensile rate was 10mm / min. A 500N sensor was used. The initial clamping distance was 40mm. The data was the average of three measurements.

[0081] 2. Barrier properties: (1) Oxygen permeability: Tested according to ASTM D3985-10 "Test method for oxygen permeability of plastic films and sheets (sensor method)". The sample was cut into a 40mm×40mm square and mounted on the accessory of the permeability instrument. The test temperature was 23±0.2℃, the relative humidity was 50±2%, the oxygen flow rate was 20cc / min, the carrier gas (nitrogen-hydrogen mixture, hydrogen concentration 2%) flow rate was 10cc / min, and the test area was 5cm². 2 The data is the average of three measurements.

[0082] (2) Water vapor transmission rate: The test was conducted according to ASTM E96-16 "Standard Test Method for Determination of Water Vapor Transmission Rate of Materials by Weight". The water vapor transmission rate of the sample was measured by the weight reduction method using a permeameter. A circular sample with a diameter of 100 mm was placed in a permeameter cup filled with distilled water. Then the permeameter cup was placed in a permeameter chamber at 38±0.2℃ and 90±2% relative humidity for testing. The data was the average of three measurements.

[0083] 3. Peel strength between outer layer and core layer: The test was conducted in accordance with ASTM D1876-2008, "Standard Test Method for Peel Resistance of Adhesives (T-Peel Test)". The test angle was 90°, the sample width was 25 mm, the length was 200 mm, the peeling speed was 300 mm / min, and a 50 mm pre-peel was made between the layers with a sharp blade to facilitate clamping. The test was conducted at 23±2℃ and 50±5%RH. The data was the average of three measurements.

[0084] 4. Antibacterial rate test: After cooling 15-20 ml of sterilized nutrient agar solution to a suitable temperature at room temperature, pour it into a sterile petri dish. Once the culture medium has solidified, set it aside. Then, cut 0.1 g of the sample into small pieces, sterilize it under UV light for 1 hour, and set it aside. Dilute the *E. coli* ATCC10536 bacterial suspension to 10⁻⁶. 5 After adding CFU / ml, the solution was mixed with the sample and shaken in a constant temperature water bath at 37℃ and 250 rpm for 2 hours to ensure full contact between the bacterial solution and the composite membrane. Finally, the bacterial solution containing the sample was diluted 10-fold three times using a serial dilution method to a final concentration of 10-fold. 4 CFU / mL, 10 3 CFU / mL, 10 2 For each CFU / mL culture medium, 0.1 mL of bacterial suspension was inoculated onto the culture medium and evenly dispersed using a sterilized glass spreader. The culture dishes were then inverted and placed in an incubator at 37°C and 72% humidity for 1 day. Two parallel samples were used in the experiment. The bacterial suspension without the sample was used as a control to calculate the inhibition rate. The inhibition rate was then measured after 28 days in the incubator, and the rate of decrease in inhibition ability was calculated as (28-day inhibition rate - 1-day inhibition rate) / 1-day inhibition rate × 100%.

[0085] Table 2 Performance test results of high-barrier biodegradable composite membranes

[0086]

[0087]

[0088] Combining the data from Examples 1-4 and Table 2, it can be seen that in Examples 1-4, silver-loaded guar gum nanofibers were prepared by reducing guar gum nanofibers with silver nitrate solution and sodium citrate. These nanofibers were then mixed with silane-modified cellulose nanofibers to prepare a fiber membrane as a sandwich layer. Matrix membranes prepared using PLA, PBS, and PGA were used as the outer and inner layers. The resulting high-barrier biodegradable composite membrane exhibited high tensile strength, excellent mechanical strength, and a water vapor permeability of less than 25 g / (m²). 2 • 24h), oxygen permeability less than 15cm 3 / (m 2 It has a high interlayer peel force (24h·atm), high adhesion, is not easy to peel off, and has a good antibacterial effect and strong antibacterial durability.

[0089] In Example 5, no ethyl cellulose solution was sprayed onto the fiber membrane. The data in Table 2 shows that, compared with Example 1, the composite membrane prepared in Example 5 has a decreased peel force between the outer layer and the sandwich layer, an increased water vapor and oxygen permeability, a decreased barrier capacity, and a decreased antibacterial rate and reduced antibacterial durability after 28 days. This indicates that the spraying of ethyl cellulose can improve interlayer adhesion, enhance the density of the sandwich layer, improve barrier capacity, and delay the release of silver ions.

[0090] Compared with Example 1, Example 6 increased the amount of silver-loaded guar gum nanofibers. It can be seen that although the antibacterial rate of the composite membrane prepared in Example 6 increased, the water vapor barrier capacity decreased significantly and the tensile strength weakened. This indicates that the fiber membrane formed by appropriately modified silane nanocellulose and silver-loaded guar gum nanofibers has better antibacterial rate, mechanical strength and barrier properties.

[0091] Compared with Example 1, Example 7 uses the guar gum nanofibers loaded with silver nanoparticles prepared in Example 2. It can be seen that the composite film prepared in Example 7 has increased tensile strength and enhanced antibacterial durability. Compared with Example 1, the coating with glutaraldehyde and PGA solution can not only increase mechanical strength and antibacterial durability, but also improve interlayer peeling force and enhance barrier ability.

[0092] In Example 8, the guar gum nanofibers loaded with silver prepared in Example 3 were used. In this case, the guar gum nanofibers were not cross-linked with glutaraldehyde vapor. Compared with Example 2 in Example 7, the composite film prepared in Example 8 showed a decrease in tensile strength and a weakening of water vapor barrier ability. However, the interlayer peeling force and antibacterial effect did not change significantly. This indicates that cross-linking with glutaraldehyde vapor can improve the mechanical strength of the guar gum nanofibers, reduce their hydrophilicity, and enhance their water vapor barrier ability.

[0093] Compared with Example 7, Example 9 used the guar gum nanofibers loaded with silver nanoparticles prepared in Example 4. Compared with Example 2, PGA coating was not used. The guar gum nanofibers were only impregnated with a treatment solution containing silver nanoparticles and treated with glutaraldehyde vapor. It can be seen that the tensile strength of the composite film decreased, the barrier ability weakened, and the 28-day antibacterial rate decreased significantly, which was greater than that in Example 1. This indicates that when impregnating with silver nanoparticles, the loading of silver nanoparticles is not firm, and PGA coating is required to achieve a more durable antibacterial effect.

[0094] Compared with Example 7, Examples 10 and 11 also used silane-modified bacterial cellulose loaded with tea polyphenols as a barrier reinforcing agent. It can be seen that the tensile strength of the composite membranes prepared in Examples 10 and 11 is significantly increased, and the barrier ability against oxygen and water vapor is enhanced. The 1-day and 28-day antibacterial rates are significantly increased.

[0095] Compared with Example 7, Example 12 was prepared without the use of polyvinyl alcohol solution and without freeze-drying, which resulted in a decrease in tensile strength and a weakening of barrier properties in the composite film.

[0096] In Comparative Example 1, no silane-modified nanocellulose was added. Compared with Example 1, guar nanofibers loaded with silver nanoparticles were used as the sandwich layer. Although it had good antibacterial ability, its tensile strength, antibacterial durability and barrier ability were all reduced.

[0097] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-barrier biodegradable composite membrane, characterized in that, It includes an outer layer, a sandwich layer, and an inner layer, wherein the outer and inner layers comprise the following raw materials in parts by weight: 60-80 parts PLA resin, 10-30 parts PBS resin, 5-20 parts PGA resin, 1-2 parts plasticizer, 2.5-3 parts chain extender, 2-4 parts barrier reinforcing agent, and 1.5-2.5 parts maleic anhydride-grafted PLA; The sandwich layer is a fiber membrane made of silane-modified nanocellulose and silver-loaded guar gum nanofibers.

2. The high-barrier biodegradable composite membrane according to claim 1, characterized in that: The mass ratio of the silane-modified nanocellulose to the silver-loaded guar gum nanofibers is 2-3:

1.

3. The high-barrier biodegradable composite membrane according to claim 1, characterized in that: The silver-loaded guar gum nanofibers were prepared by impregnating guar gum nanofibers with a PGA solution containing silver nanoparticles after cross-linking with glutaraldehyde vapor and drying. The mass ratio of guar gum nanofibers to silver nanoparticles was 1:

1.

4. The high-barrier biodegradable composite membrane according to claim 1, characterized in that: The barrier enhancer is silane-modified bacterial cellulose loaded with tea polyphenols.

5. The high-barrier biodegradable composite membrane according to claim 4, characterized in that: The barrier agent is prepared by freeze-drying silane-modified bacterial cellulose, then impregnating it in a polyvinyl alcohol solution containing tea polyphenols, and drying it. The amount of tea polyphenols used is 5-10% of the mass of the silane-modified bacterial cellulose.

6. The high-barrier biodegradable composite membrane according to claim 4, characterized in that: The silane in the silane-modified bacterial cellulose is one of hexadecyltrimethoxysilane, vinyltrimethoxysilane, dodecyltrimethoxysilane, and octyltrimethoxysilane.

7. The high-barrier biodegradable composite membrane according to claim 1, characterized in that: The plasticizer is selected from at least one of citric acid, glycerin and polyethylene glycol.

8. The high-barrier biodegradable composite membrane according to claim 1, characterized in that: The total thickness of the composite membrane is 100-150 μm, and the sandwich layer accounts for 15%.

9. A method for preparing the high-barrier biodegradable composite membrane according to any one of claims 1-8, characterized in that: Includes the following steps: PLA resin, PBS resin and PGA resin are mixed and dried, then mixed evenly with plasticizer, chain extender, barrier reinforcing agent and maleic anhydride-grafted PLA, hot melted, extruded and pelletized to obtain raw material masterbatch. The raw material masterbatch is dried, blown into a film, and cooled to obtain a matrix film; Silane-modified nanocellulose and silver-loaded guar gum nanofibers were mixed evenly and then added to deionized water. The mixture was sonicated to form a suspension, which was then vacuum filtered and dried to obtain a fiber membrane. A high-barrier biodegradable composite membrane was prepared by hot-pressing the matrix membrane, fiber membrane, and matrix membrane in that order at 160-170℃ and 5-10MPa for 30-60s.

10. The method for preparing the high-barrier biodegradable composite membrane according to claim 9, characterized in that: Before hot pressing, a 5-10% ethyl cellulose ethanol solution is uniformly sprayed onto the surface of the fiber membrane, with a spraying amount of 10-20 g / m³. 2 .

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