Degradable food packaging bag and preparation method thereof

Abstract

The application provides a degradable food packaging bag and a preparation method thereof. The degradable food packaging bag comprises the following raw materials in parts by mass: 50 parts of polylactic acid, 50-100 parts of polybutylene adipate terephthalate, 5-10 parts of a plasticizer, and 4-8 parts of a functional additive; wherein the functional additive comprises modified cyclodextrin, and the modified cyclodextrin is beta-cyclodextrin grafted with an epoxy-terminated polyethylene glycol and containing a metal stearate. The degradable food packaging bag uses polylactic acid and polybutylene adipate terephthalate as main materials to improve the mechanical properties of the food packaging bag; the use of the plasticizer further reduces the brittleness of the food packaging bag and improves the flexibility thereof; the addition of the modified cyclodextrin as the functional additive improves the mechanical properties and water resistance of the food packaging bag, and the metal stearate contained in the modified cyclodextrin improves the degradation rate of the food packaging bag, so that the obtained degradable food packaging bag has good water resistance and degradability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food packaging materials, in particular to a degradable food packaging bag and a preparation method thereof. BACKGROUND

[0002] With the increasing global environmental problems and the aggravation of plastic pollution problems, traditional petroleum-based plastics are difficult to degrade and remain in landfills and the environment for a long time, which brings a serious burden to the ecological system. Therefore, the development and promotion of degradable plastics have become an important direction of global green environmental protection industry. In the field of food packaging, materials are required to have good mechanical properties, water and oil resistance, and food safety, and at the same time, they can be efficiently degraded in the natural environment after the end of service life, so degradable food packaging bags have attracted widespread attention.

[0003] At present, the main degradable materials applied in the market include polylactic acid (PLA), polycaprolactone (PCL), polybutylene terephthalate, and bio-based plastics based on starch and cellulose. Although these materials have certain biodegradability, these degradable plastics have harsh degradation conditions, such as PLA which can only be rapidly degraded under specific industrial composting conditions (high temperature, high humidity, and specific microbial environment), and the degradation rate is slow under natural environment or household composting conditions, which can easily cause environmental accumulation.

[0004] At present, the main research direction for the above problems is to use more easily degradable high molecular materials such as starch, cellulose, and lignin, which are natural polysaccharides, as the main material or additive to be doped in the above degradable plastics, so as to accelerate the degradation rate of food packaging bags. However, the problem is that the performance of the food packaging bag obtained by using the above natural polysaccharides as the main material is poor, and when the natural polysaccharides are used as additives to be doped in the degradable plastics, the compatibility between the components is problematic, and the above natural polysaccharides have stronger hydrophilicity, which can further increase the moisture absorption of the degradable food packaging bag and affect its durability.

[0005] The patent CN118652478A discloses a degradable and recyclable plastic food packaging bag, which is prepared from the following raw materials in parts by weight: composite starch 50-60 parts, composite plant fiber 10-20 parts, composite high polymer composition 30-40 parts, leather powder 3-5 parts, bamboo powder 3-5 parts, chitosan 3-5 parts, gelatin 5-10 parts, calcium stearate 1-3 parts, oleic acid 3-5 parts, oxidative degradation additive 1-3 parts, and citric acid 1-3 parts. The application relates to the technical field of plastic products. The degradable and recyclable plastic food packaging bag can greatly improve the tensile strength and toughness of the degradable plastic bag by modifying the starch material and adding composite plant fiber, thereby achieving the purpose of ensuring the degradation effect of the plastic bag and improving the load-bearing capacity of the plastic bag. The tensile load-bearing performance of the plastic bag is greatly improved, and the plastic bag can be used to carry heavy objects. The combination of fiber and modified starch can prepare a plastic bag with better tensile performance.

[0006] The above patent mainly uses natural polysaccharides as the main material of the food packaging bag, and combines with composite high polymer composition and other additives to obtain a plastic bag with good tensile performance and degradation performance. However, the problem is that the composite high polymer composition used is polyethylene and other non-degradable plastics, and the degradation performance of the food packaging bag is ensured by adding an oxidative degradation agent, which will obviously affect the service life of the food packaging bag.

[0007] Currently, there are also relevant documents that add microcapsule-coated microbial spores to degradable plastics to promote the degradation of the corresponding plastics. The microcapsules release spores during the subsequent treatment process, promoting the degradation of the food packaging bag. However, the process is relatively complex, and the requirements for microorganisms are high.

[0008] Therefore, the present application provides a degradable food packaging bag and a preparation method thereof. SUMMARY

[0009] The present application provides a degradable food packaging bag and a preparation method thereof. The degradable food packaging bag has good water resistance and degradability.

[0010] In a first aspect, the present application provides a degradable food packaging bag, which comprises the following raw materials in parts by weight: 50 parts of polylactic acid, 50-100 parts of polybutylene adipate / terephthalate, 5-10 parts of a plasticizer, and 4-8 parts of a functional additive; wherein the functional additive comprises modified cyclodextrin, and the modified cyclodextrin is beta-cyclodextrin grafted with metal stearate by end epoxy polyethylene glycol.

[0011] According to the present application, the degradable food packaging bag takes polylactic acid and polybutylene adipate-co-terephthalate (PBAT) as the main materials, both of which are degradable polymer materials and have good compatibility, and the melt blending can improve the inherent brittleness of polylactic acid material and the mechanical properties of the food packaging bag; the use of plasticizers can further reduce the brittleness and improve the flexibility of the food packaging bag; in addition, by adding a functional additive including modified cyclodextrin, which has a terminal epoxy group polyethylene glycol segment grafted thereon, the compatibility of cyclodextrin between the main materials can be effectively improved, so that it is uniformly dispersed in the system; in addition, the terminal epoxy group has reactivity with the end groups of polylactic acid and polybutylene adipate-co-terephthalate, and during the melt blending process, the modified cyclodextrin acts as a crosslinking center to increase the crosslinking density of the material, thereby improving its mechanical properties; at the same time, the metal stearate is included in the hydrophobic cavity of the β-cyclodextrin in the modified cyclodextrin, on the one hand, the modified cyclodextrin is uniformly dispersed in the material, and due to the reduction of the hydrophilicity of the cyclodextrin surface by crosslinking reaction, the hydrophobic cavity therein coordinates with the metal stearate to form a hydrophobic barrier in the material, reducing the penetration of water in the food packaging bag, improving the water resistance of the food packaging bag, reducing the influence of water on the PLA and PBAT segments, and improving the service life of the food packaging bag; on the other hand, during the recycling and degradation process of the degradable food packaging bag, β-cyclodextrin is a polysaccharide and is more easily decomposed and utilized by microorganisms, thereby reducing the crosslinking density and making the food packaging bag more easily degradable, and the released metal stearate, wherein the metal ions can promote the hydrolysis of the ester bonds in the PLA and PBAT segments, thereby further improving the degradation rate of the degradable food packaging bag; therefore, the obtained degradable food packaging bag has good water resistance and degradability.

[0012] In some embodiments, the raw materials include the following mass parts: 50 parts of polylactic acid, 50-75 parts of polybutylene adipate-co-terephthalate, 5-8 parts of plasticizer, and 5-7 parts of functional additive.

[0013] In some embodiments, the preparation method of the modified cyclodextrin includes the following steps:

[0014] S1: reacting polyethylene glycol with a weight average molecular weight of 300-1500 with epichlorohydrin in an alkaline methanol solution to react the hydroxyl groups at both ends of the polyethylene glycol with the epichlorohydrin, grafting epoxy groups at both ends of the polyethylene glycol, and obtaining epoxy group polyethylene glycol;

[0015] S2: reacting the epoxy group polyethylene glycol with β-cyclodextrin in an alkaline aqueous solution to react the epoxy group at one end of the epoxy group polyethylene glycol with the hydroxyl group on the β-cyclodextrin, grafting the terminal epoxy group polyethylene glycol segment on the β-cyclodextrin, and obtaining a terminal epoxy group polyethylene glycol grafted β-cyclodextrin aqueous solution;

[0016] S3: adding the ethanol dispersion of metal stearate into the terminal epoxy group polyethylene glycol grafted β-cyclodextrin aqueous solution, and allowing the metal stearate to be included in the cavity of the β-cyclodextrin through hydrophobic interaction to obtain modified cyclodextrin.

[0017] In some embodiments, the metal stearate comprises at least one of zinc stearate, calcium stearate, and iron stearate.

[0018] In some embodiments, the metal stearate comprises zinc stearate and calcium stearate, and the mass ratio of the zinc stearate and the calcium stearate is 1:0.2-0.6.

[0019] In some embodiments, S1 specifically comprises:

[0020] 10 parts by mass of polyethylene glycol with a weight average molecular weight of 300-1500 is dissolved in 150-300 parts by mass of a methanol solution of sodium hydroxide with a pH of 11-13, 5-10 parts by mass of epichlorohydrin is added, and the reaction is carried out at 40-60℃ for 12-24h to obtain epoxy group polyethylene glycol.

[0021] In some embodiments, S2 specifically comprises:

[0022] 10 parts by mass of epoxy group polyethylene glycol and 3-6 parts by mass of β-cyclodextrin are dissolved in 400-600 parts by mass of an aqueous solution of sodium hydroxide with a pH of 10-12, and the reaction is carried out at 90-110℃ for 18-32h to obtain terminal epoxy group polyethylene glycol grafted β-cyclodextrin aqueous solution.

[0023] In some embodiments, S3 specifically comprises:

[0024] 1-3 parts by mass of metal stearate is ultrasonically dispersed in 20-50 parts by mass of ethanol to obtain an ethanol dispersion of metal stearate; the pH of the terminal epoxy group polyethylene glycol grafted β-cyclodextrin aqueous solution is adjusted to 8-10 by adding acid, and the ethanol dispersion of metal stearate is added, and the reaction is carried out at 25-30℃ for 2-4h to obtain modified cyclodextrin.

[0025] In some embodiments, the weight average molecular weight of the polylactic acid is 100000-200000.

[0026] In some embodiments, the weight average molecular weight of the polybutylene adipate / terephthalate is 150000-300000.

[0027] In some embodiments, the plasticizer comprises at least one of triacetyl glycerol citrate, tributyl citrate, triethyl citrate, polybutylene adipate, and epoxidized soybean oil.

[0028] In some embodiments, further comprising 0.5-2 parts of an antioxidant; the antioxidant comprises at least one of 2,6-di-tert-butyl-p-cresol, dilaurylthiopropionate, vitamin E.

[0029] In a second aspect, the present application provides a method for preparing a degradable food packaging bag, comprising:

[0030] Providing raw materials for the degradable food packaging bag according to any one of the embodiments of the first aspect;

[0031] After drying the raw materials, melt blending, extruding, granulating and blow molding to obtain the degradable food packaging bag.

[0032] According to the present application, since it is prepared by using the raw materials for the degradable food packaging bag according to any one of the embodiments of the first aspect, it has the beneficial effects of the first aspect. DETAILED DESCRIPTION

[0033] Each embodiment or implementation in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments.

[0034] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0035] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0036] The present application provides a degradable food packaging bag and a preparation method thereof. The degradable food packaging bag has good water resistance and degradability by optimizing the components of the raw materials. The specific embodiments provided by the present application are described in detail below.

[0037] In a first aspect, the application provides a degradable food packaging bag, comprising the following raw materials by mass: 50 parts of polylactic acid, 50-100 parts of polybutylene adipate-co-terephthalate (PBAT), 5-10 parts of a plasticizer, and 4-8 parts of a functional additive; wherein the functional additive comprises modified cyclodextrin, and the modified cyclodextrin is β-cyclodextrin grafted with an end-epoxy polyethylene glycol segment and complexed with a metal stearate.

[0038] According to the application, the degradable food packaging bag uses polylactic acid and polybutylene adipate-co-terephthalate (PBAT) as main materials, both of which are degradable polymer materials and have good compatibility; melt blending can improve the inherent brittleness of polylactic acid material and improve the mechanical properties of the food packaging bag; the use of a plasticizer can further reduce the brittleness and improve the flexibility of the food packaging bag; in addition, the addition of a functional additive comprising modified cyclodextrin, which is grafted with an end-epoxy polyethylene glycol segment, can effectively improve the compatibility of cyclodextrin between the main materials, thereby uniformly dispersing in the system; in addition, the end-epoxy group has reactivity with the end groups of polylactic acid and polybutylene adipate-co-terephthalate, and during melt blending, the modified cyclodextrin acts as a crosslinking center to increase the crosslinking density of the material, thereby improving its mechanical properties; at the same time, the β-cyclodextrin in the modified cyclodextrin is complexed with a metal stearate in its hydrophobic cavity, on the one hand, the modified cyclodextrin is uniformly dispersed in the material, and due to the crosslinking reaction, the hydrophilicity of the cyclodextrin surface is reduced, while the hydrophobic cavity therein complexed with the metal stearate can form a hydrophobic barrier in the material, reducing the penetration of water in the food packaging bag, improving the water resistance of the food packaging bag, reducing the influence of water on the PLA and PBAT segments, and improving the service life of the food packaging bag; on the other hand, during the recycling and degradation process of the degradable food packaging bag, β-cyclodextrin is a polysaccharide and is more easily decomposed and utilized by microorganisms, thereby reducing the crosslinking density and making the food packaging bag more easily degradable, and the complexed metal stearate is released, and the metal ions can promote the hydrolysis of ester bonds in the PLA and PBAT segments, thereby further improving the degradation rate of the degradable food packaging bag; therefore, the obtained degradable food packaging bag has good water resistance and degradability.

[0039] Specifically, the inventors discovered that the main problem with current biodegradable food packaging bags lies in the contradiction between the performance and lifespan of the food packaging bags and their biodegradability. While adding polysaccharides such as starch and cellulose as additives can improve biodegradability to some extent by using biodegradable plastic as the main material, their compatibility with the main material and strong hygroscopicity also affect the performance and lifespan of the food packaging bags. In addition, if substances that promote the degradation of the main material are added directly to the main material, it will obviously also affect the performance of the plastic packaging bags during production and use. Based on this, the inventors added modified cyclodextrin as a functional additive to a system primarily composed of polylactic acid and poly(butylene adipate / terephthalate). This modified cyclodextrin is a β-cyclodextrin grafted with epoxy-terminated polyethylene glycol and containing metal stearate. Because β-cyclodextrin has an internally hydrophobic and externally hydrophilic structure, unmodified β-cyclodextrin exhibits poor dispersibility in the system. By grafting polyethylene glycol segments onto its inner surface, the inventors effectively improved its dispersibility within the system. Simultaneously, the epoxy-terminated groups of the polyethylene glycol segments exhibit good reactivity with the end groups of PLA and PBAT. Therefore, the modified cyclodextrin can act as a crosslinking agent in the system, increasing the crosslinking density of the material, thereby improving mechanical strength and reducing water penetration. Furthermore, the metal stearate encapsulated within the hydrophobic cavity of the modified cyclodextrin allows it to disperse within the material... To form a hydrophobic barrier, the hydrophobicity of the material is improved, further reducing the penetration of water into the biodegradable plastic bag and minimizing the damage to its strength caused by water. Simultaneously, the metal stearate, contained within the hydrophobic cavity of the cyclodextrin, does not directly contact the main material, thus not affecting the service life of the biodegradable food packaging bag before the β-cyclodextrin is destroyed. On the other hand, β-cyclodextrin is a polysaccharide that is more readily utilized by microorganisms during the recycling and degradation process of the biodegradable food packaging bag compared to the main material. This reduces the cross-linking density of the food packaging bag, destroys the hydrophobic barrier, and allows water to penetrate more easily. Simultaneously, the metal stearate encapsulated in the β-cyclodextrin is released, and the metal ions within can catalyze the hydrolysis of PLA and PBAT segments, further promoting the degradation of the food packaging bag. Therefore, the resulting biodegradable food packaging bag exhibits excellent water resistance and biodegradability.

[0040] It is also worth noting that the inventors discovered that by grafting polyethylene glycol segments onto the surface of β-cyclodextrin, the stability of β-cyclodextrin can be effectively improved, making it more stable during the preparation and processing of biodegradable food packaging bags and less prone to premature decomposition and release of the contents in the hydrophobic cavity, thereby improving the stability of the performance of biodegradable food packaging bags.

[0041] In some embodiments, the raw materials include the following parts by weight: 50 parts polylactic acid, 50-75 parts polybutylene adipate / terephthalate, 5-8 parts plasticizer, and 5-7 parts functional additives.

[0042] In some embodiments described above, by further optimizing the content of each component of the raw material, the degradable food packaging bag has better water resistance and degradability.

[0043] In some embodiments, the method for preparing the modified cyclodextrin comprises the following steps:

[0044] S1: reacting polyethylene glycol with a weight average molecular weight of 300-1500 with epichlorohydrin in an alkaline methanol solution to react the hydroxyl groups at both ends of the polyethylene glycol with the epichlorohydrin, grafting epoxy groups at both ends of the polyethylene glycol, to obtain epoxy- functionalized polyethylene glycol;

[0045] S2: reacting the epoxy-functionalized polyethylene glycol with β-cyclodextrin in an alkaline aqueous solution to react the epoxy group at one end of the epoxy-functionalized polyethylene glycol with the hydroxyl group on the β-cyclodextrin, grafting the end epoxy polyethylene glycol segment on the β-cyclodextrin, to obtain an end epoxy polyethylene glycol grafted β-cyclodextrin aqueous solution;

[0046] S3: adding a metal stearate ethanol dispersion to the end epoxy polyethylene glycol grafted β-cyclodextrin aqueous solution, to encapsulate the metal stearate into the cavity of the β-cyclodextrin through hydrophobic interaction, to obtain the modified cyclodextrin.

[0047] In some embodiments described above, the modified cyclodextrin is prepared by the above preparation method. Specifically, in step S1, in the alkaline methanol solution, the polyethylene glycol with a weight average molecular weight of 300-1500 can react with epichlorohydrin, and the chlorine atom in epichlorohydrin can react with the hydroxyl groups at both ends of the polyethylene glycol, so as to graft epoxy groups at both ends of the polyethylene glycol. In addition, the inventors found that the length of the polyethylene glycol segment affects the dispersibility of the modified cyclodextrin in the host material and the thermal stability of the modified cyclodextrin itself, thereby affecting the performance of the degradable food packaging bag. It can be understood that longer polyethylene glycol segments can improve the thermal stability of the modified cyclodextrin, but too long polyethylene glycol segments have certain flexibility and hydrophilicity, which will also affect the hydrophobic performance of the hydrophobic barrier formed thereby. Therefore, the modified cyclodextrin obtained using the above polyethylene glycol with a weight average molecular weight can more effectively improve the water resistance of the degradable food packaging bag. Preferably, the weight average molecular weight of the polyethylene glycol in step S1 is 600-1000.

[0048] In step S2, the epoxy groups on the epoxy-modified polyethylene glycol can react with the hydroxyl groups on the surface of the β-cyclodextrin in the alkaline aqueous solution, so that the β-cyclodextrin is grafted with the polyethylene glycol segment having an epoxy group at one end. It can be understood that after the epoxy group at one end of the epoxy-modified polyethylene glycol reacts with the β-cyclodextrin, the epoxy group at the other end is less likely to further react with the β-cyclodextrin grafted with the polyethylene glycol segment due to steric hindrance, so that the active epoxy group on the β-cyclodextrin is grafted, thereby making it have reactivity with the end groups of PLA and PBAT.

[0049] In step S3, an ethanol dispersion of metal stearate is obtained by using ethanol as a dispersion medium, and the ethanol dispersion of metal stearate is added to the aqueous solution of the β-cyclodextrin grafted with the epoxy-modified polyethylene glycol in step S2. Since only the hydrophobic cavity inside the β-cyclodextrin exists in the system, part of the metal stearate is included in the hydrophobic cavity of the β-cyclodextrin under hydrophobic interaction, thereby obtaining a modified cyclodextrin. It can be understood that the metal stearate will not be completely included in the hydrophobic cavity of the β-cyclodextrin. An excess amount of metal stearate is used to fully load the hydrophobic cavity inside the β-cyclodextrin in the system, and the complexation of the cyclodextrin can ensure that the included metal stearate does not damage the stability of the packaging bag while providing certain long-chain hydrophobic effects. Since the metal stearate mainly plays a catalytic role in the degradation process to promote the breaking of ester bonds, it is easier to obtain small molecule monomers or segments that can be directly utilized by microorganisms, and therefore a small amount of metal stearate can effectively promote the degradation of the main material.

[0050] In some embodiments, the metal stearate includes at least one of zinc stearate, calcium stearate, and iron stearate. Based on the above embodiments, the metal ions in the above metal stearate can effectively promote the hydrolysis of ester bonds in the PLA and PBAT segments, decompose into small molecule segments or monomers that are more conducive to microbial utilization, and thereby improve the degradability of the degradable food packaging bag.

[0051] In some embodiments, the metal stearate includes zinc stearate and calcium stearate, and the mass ratio of the zinc stearate to the calcium stearate is 1:0.2-0.6.

[0052] In some embodiments described above, the inventors found that the degradable food packaging bag has better degradability when the metal stearate comprises zinc stearate and calcium stearate in the mass ratio described above; the possible reason is that calcium ions and zinc ions can promote the decomposition of PLA and PBAT segments through different pathways, wherein calcium ions can form Lewis acid sites to promote the attack of water molecules on PLA and PBAT, and zinc ions have more empty electron orbitals to combine with the lone pair electrons on the oxygen atoms in PLA and PBAT through coordination to catalyze the decomposition of PLA and PBAT segments; through appropriate proportioning, the two can synergize to further improve the degradability of the degradable food packaging bag.

[0053] In some embodiments, S1 specifically comprises:

[0054] 10 parts by mass of polyethylene glycol with a weight average molecular weight of 300-1500 is dissolved in 150-300 parts by mass of a methanol solution of sodium hydroxide with a pH of 11-13, 5-10 parts by mass of epichlorohydrin is added, and the reaction is carried out at 40-60°C for 12-24 hours to obtain epoxy- functionalized polyethylene glycol.

[0055] In some embodiments described above, the hydroxyl groups at both ends of the polyethylene glycol can react with epichlorohydrin under the above conditions to obtain epoxy-functionalized polyethylene glycol.

[0056] In some embodiments, S2 specifically comprises:

[0057] 10 parts by mass of epoxy-functionalized polyethylene glycol, 3-6 parts by mass of β-cyclodextrin is dissolved in 400-600 parts by mass of an aqueous solution of sodium hydroxide with a pH of 10-12, and the reaction is carried out at 90-110°C for 18-32 hours to obtain an aqueous solution of epoxy-terminated polyethylene glycol grafted β-cyclodextrin.

[0058] In some embodiments described above, the epoxy-functionalized polyethylene glycol can be grafted onto β-cyclodextrin under the above conditions to obtain epoxy-terminated polyethylene glycol grafted β-cyclodextrin.

[0059] In some embodiments, S3 specifically comprises:

[0060] 1-3 parts by mass of metal stearate is ultrasonically dispersed in 20-50 parts by mass of ethanol to obtain an ethanol dispersion of metal stearate; the pH of the aqueous solution of epoxy-terminated polyethylene glycol grafted β-cyclodextrin is adjusted to 8-10 by adding acid, and then the ethanol dispersion of metal stearate is added, and the mixture is stirred at 25-30°C for 2-4 hours to obtain modified cyclodextrin.

[0061] In some of the above embodiments, under the above conditions, since the metal stearate is insoluble in ethanol and water, the metal stearate is first dispersed in the ethanol dispersion by ultrasonic to obtain a metal stearate with small particles suspended, so as to increase the specific surface area of the metal stearate, so that the metal stearate is more easily to enter the hydrophobic cavity of the β-cyclodextrin through hydrophobic interaction to obtain the modified cyclodextrin; at the same time, the solution is first adjusted to weak alkaline, then mixed with the dispersion, and stirred at a low temperature, which can improve the stability of the epoxy group in the system and improve the reactivity of the modified cyclodextrin.

[0062] In some embodiments, the weight average molecular weight of the polylactic acid is 100000-200000. Based on the above embodiments, the polylactic acid with the above weight average molecular weight can better balance the mechanical properties and degradability, and as an example, the polylactic acid with a weight average molecular weight of 150000 is used in an embodiment of the present application.

[0063] In some embodiments, the weight average molecular weight of the polybutylene adipate terephthalate is 150000-300000. Based on the above embodiments, the polybutylene adipate terephthalate with the above weight average molecular weight can make the degradable food packaging bag have better mechanical properties. As an example, the polybutylene adipate terephthalate with a weight average molecular weight of 200000 is used in an embodiment of the present application.

[0064] In some embodiments, the plasticizer includes at least one of triacetyl glycerol citrate, tributyl citrate, triethyl citrate, polybutylene adipate, and epoxidized soybean oil. As an example, triacetyl glycerol citrate is used as a plasticizer in an embodiment of the present application.

[0065] In some embodiments, 0.5-2 parts of an antioxidant are further included; the antioxidant includes at least one of 2,6-di-tert-butyl-p-cresol, dilaurylthiopropionate, and vitamin E. Based on the above embodiments, the further addition of the antioxidant can reduce the oxidative decomposition of the main material and improve the service life of the food packaging bag, and as an example, 2,6-di-tert-butyl-p-cresol is used as an antioxidant in an embodiment of the present application.

[0066] In a second aspect, the present application provides a method for preparing a degradable food packaging bag, comprising:

[0067] Providing raw materials in the degradable food packaging bag according to any one of the embodiments of the first aspect;

[0068] After drying the raw materials, melt blending, extruding, granulating, and blow molding to obtain the degradable food packaging bag.

[0069] According to the present application, the raw material in the degradable food packaging bag is prepared by using any of the embodiments of the first aspect, thus having the beneficial effects of the first aspect.

[0070] In some embodiments, specifically comprising: drying 50 parts of polylactic acid, 50-100 parts of polybutylene adipate / terephthalate, 4-8 parts of functional auxiliary, then adding 5-10 parts of plasticizer and 0.5-2 parts of antioxidant for uniform dispersion, using a twin-screw extruder for extrusion granulation, blow molding to obtain a degradable food packaging bag.

[0071] In some embodiments, the feeding zone temperature of the twin-screw extruder is 140-150°C, the melting zone temperature is 160-180°C, the homogenization zone temperature is 180-190°C, the extrusion zone temperature is 170-180°C, and the screw shear rate is 20-60 rpm.

[0072] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not specified in the embodiments, it is carried out according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0073] Example 1

[0074] Preparation of the degradable food packaging bag:

[0075] Drying 50 parts by mass of polylactic acid with a weight average molecular weight of 150,000, 70 parts by mass of polybutylene adipate / terephthalate with a weight average molecular weight of 200,000, 6 parts by mass of modified cyclodextrin, then adding 8 parts by mass of triacetyl glyceryl tricitrate and 1 part by mass of 2,6-di-tert-butyl-p-cresol for uniform dispersion, using a twin-screw extruder for extrusion granulation (the feeding zone temperature is 145°C, the melting zone temperature is 175°C, the homogenization zone temperature is 185°C, the extrusion zone temperature is 175°C, and the screw shear rate is 30 rpm), blow molding to obtain a degradable food packaging bag.

[0076] The modified cyclodextrin is prepared by the following method:

[0077] Dissolving and dispersing 10 parts by mass of polyethylene glycol with a weight average molecular weight of 600 in 200 parts by mass of a sodium hydroxide methanol solution with a pH of 12, adding 8 parts by mass of epichlorohydrin dropwise, reacting at 50°C for 18 h, performing rotary evaporation concentration after the reaction is completed, dissolving in diethyl ether after adding, and drying to obtain epoxy-alkylated polyethylene glycol;

[0078] A water solution of epoxy group-terminated polyethylene glycol grafted β-cyclodextrin was obtained by dissolving 10 parts by mass of epoxy group-terminated polyethylene glycol and 5 parts by mass of β-cyclodextrin in 500 parts by mass of an aqueous sodium hydroxide solution having a pH of 10 and refluxing the mixture at 100°C for 20 hours;

[0079] A dispersion was obtained by ultrasonically dispersing 1.25 parts by mass of zinc stearate and 0.75 parts by mass of calcium stearate in 40 parts by mass of ethanol for 1 hour. The pH of the above-mentioned water solution of epoxy group-terminated polyethylene glycol grafted β-cyclodextrin was adjusted to 8 by adding hydrochloric acid, and the solution was mixed with the above-mentioned dispersion. The mixture was stirred at 25°C for 3 hours, and the suspended metal stearate was separated by centrifugation. The supernatant was dialyzed against water using a semi-permeable membrane having a permeation capacity of 1800 Da for 48 hours, with the water being changed every 12 hours. The dialyzed solution was concentrated by rotary evaporation and dried under vacuum to obtain modified β-cyclodextrin.

[0080] Example 2

[0081] Preparation of a degradable food packaging bag:

[0082] The example was substantially the same as Example 1, except that 2 parts by mass of zinc stearate was used instead of 1.25 parts by mass of zinc stearate and 0.75 parts by mass of calcium stearate in the preparation of the modified β-cyclodextrin.

[0083] Example 3

[0084] Preparation of a degradable food packaging bag:

[0085] The example was substantially the same as Example 1, except that 2 parts by mass of calcium stearate was used instead of 1.25 parts by mass of zinc stearate and 0.75 parts by mass of calcium stearate in the preparation of the modified β-cyclodextrin.

[0086] Example 4

[0087] Preparation of a degradable food packaging bag:

[0088] The example was substantially the same as Example 1, except that polyethylene glycol having a weight average molecular weight of 1000 was used in the preparation of the modified β-cyclodextrin.

[0089] Example 5

[0090] Preparation of a degradable food packaging bag:

[0091] The example was substantially the same as Example 1, except that polyethylene glycol having a weight average molecular weight of 300 was used in the preparation of the modified β-cyclodextrin.

[0092] Example 6

[0093] Preparation of a degradable food packaging bag:

[0094] The same as Example 1, except that the only difference is that, in the preparation of the modified cyclodextrin, polyethylene glycol with a weight average molecular weight of 1500 is used.

[0095] Comparative Example 1

[0096] Preparation of a degradable food packaging bag:

[0097] 50 parts by mass of polylactic acid with a weight average molecular weight of 150000, 70 parts by mass of polybutylene adipate / terephthalate with a weight average molecular weight of 200000, 2 parts by mass of β-cyclodextrin dried, 4 parts by mass of polyethylene glycol with a weight average molecular weight of 600, 8 parts by mass of glyceryl triacetate, and 1 part by mass of 2,6-di-tert-butyl-p-cresol were uniformly dispersed, and extrusion granulation was performed using a twin-screw extruder (temperature of the feeding zone was 145°C, temperature of the melting zone was 175°C, temperature of the homogenizing zone was 185°C, temperature of the extrusion zone was 175°C, and screw shear rate was 30 rpm), and blow molding was performed, thereby obtaining a degradable food packaging bag.

[0098] Comparative Example 2

[0099] Preparation of a degradable food packaging bag:

[0100] 50 parts by mass of polylactic acid with a weight average molecular weight of 150000, 70 parts by mass of polybutylene adipate / terephthalate with a weight average molecular weight of 200000, 2 parts by mass of β-cyclodextrin dried, 4 parts by mass of polyethylene glycol with a weight average molecular weight of 600, 8 parts by mass of glyceryl triacetate, and 1 part by mass of 2,6-di-tert-butyl-p-cresol were uniformly dispersed, and extrusion granulation was performed using a twin-screw extruder (temperature of the feeding zone was 145°C, temperature of the melting zone was 175°C, temperature of the homogenizing zone was 185°C, temperature of the extrusion zone was 175°C, and screw shear rate was 30 rpm), and blow molding was performed, thereby obtaining a degradable food packaging bag.

[0101] Comparative Example 3

[0102] Preparation of a degradable food packaging bag:

[0103] 50 parts by mass of polylactic acid with a weight average molecular weight of 150000, 70 parts by mass of polybutylene adipate / terephthalate with a weight average molecular weight of 200000, 3 parts by mass of β-cyclodextrin occluded metal stearate, 3 parts by mass of epoxy group-containing polyethylene glycol, 8 parts by mass of triacetyl glycerol citrate, and 1 part by mass of 2,6-di-tert-butyl-p-cresol were uniformly dispersed, and extrusion granulation was performed using a twin-screw extruder (feed zone temperature: 145°C, melting zone temperature: 175°C, homogenization zone temperature: 185°C, extrusion zone temperature: 175°C, screw shear rate: 30 rpm), and blow molding was performed, thereby obtaining a degradable food packaging bag.

[0104] The β-cyclodextrin occluded metal stearate is prepared by the following method: 1.25 parts by mass of zinc stearate and 0.75 parts by mass of calcium stearate are ultrasonically dispersed in 40 parts by mass of ethanol for 1 h to obtain a dispersion liquid, 5 parts by mass of β-cyclodextrin is dissolved in 500 parts by mass of water, and then the above dispersion liquid is mixed therewith, stirred at 25°C for 3 h, and then centrifuged to separate the suspended metal stearate, and the supernatant is concentrated by rotary evaporation and vacuum dried to obtain the β-cyclodextrin occluded metal stearate;

[0105] The epoxy group-containing polyethylene glycol is prepared by the following method: 10 parts by mass of polyethylene glycol with a weight average molecular weight of 600 is dissolved and dispersed in 200 parts by mass of a sodium hydroxide methanol solution with a pH of 12, 8 parts by mass of epichlorohydrin is added dropwise, and the reaction is performed at 50°C for 18 h, and then concentrated by rotary evaporation, dissolved in diethyl ether, and dried to obtain the epoxy group-containing polyethylene glycol.

[0106] Test Part

[0107] The degradable food packaging bags obtained in the above examples and comparative examples were determined for water vapor transmission rate (WVT value) according to GB / T 1037-2021 “Determination of water vapor transmission properties of plastic films and sheets”, and for maximum tensile stress according to GB / T 1040-2006 “Determination of tensile properties of plastics”; the results are shown in Table 1.

[0108] The soil burial degradation experiment was simulated according to the GB / T 19811-2005 standard, and the weight loss rate (%) was determined; the results are shown in Table 2.

[0109] Table 1

[0110]

[0111] Table 2

[0112]

[0113] According to Table 1 and Table 2, the WVT value of the degradable food packaging bag obtained by each embodiment is lower than that of each comparative example, the maximum tensile stress is higher than that of each comparative example, and the degradable performance is better than that of Comparative Example 1; it shows that the degradable food packaging bag obtained by the present application has better water resistance, mechanical properties and degradable performance. The reason may be that in Comparative Example 1, the compatibility between the unmodified β-cyclodextrin and the main material is poor, and the heat resistance of the unmodified β-cyclodextrin is poor, which is easily degraded during the processing process, and is not easy to disperse uniformly in the material, so it cannot effectively form a hydrophobic barrier in the material, and the additional polyethylene glycol cannot effectively improve the heat resistance and dispersibility of β-cyclodextrin, and it also does not have reactivity, in addition, it also does not contain materials to promote the degradation of the main material, so its water resistance, mechanical properties and degradable performance are poorer than each embodiment; in Comparative Example 2, although it has good degradation performance, the water resistance and mechanical properties of the degradable food packaging bag are poor, it can be understood that the metal stearate directly contacts with the material, which also reduces the service life of the degradable food packaging bag; in addition, according to Comparative Example 2, a small amount of metal stearate is added to the degradable food packaging bag, which can effectively improve the degradation efficiency in the soil burial degradation environment; in Comparative Example 3, epoxy polyethylene glycol and metal stearate β-cyclodextrin are added respectively, the reactivity provided by the epoxy polyethylene glycol, combined with the improvement of the water resistance and mechanical properties of the degradable food packaging bag by the metal stearate β-cyclodextrin, cannot effectively form a complete hydrophobic barrier in the material, and the metal stearate in the metal stearate β-cyclodextrin is released during the processing process, which affects the service life of the food packaging bag.

[0114] According to Examples 1-3, the type of metal stearate included in the modified cyclodextrin has little effect on the water resistance and mechanical properties of the degradable food packaging bag, but has some effect on the degradable performance thereof, wherein the modified cyclodextrin including a certain proportion of zinc stearate and calcium stearate in Example 1 has better degradable performance than the modified cyclodextrin including only zinc stearate or calcium stearate in Examples 2 and 3; the reason may be that zinc ions and calcium ions can promote the degradation of the main material through different ways, and the two together make the food packaging bag have better degradable performance.

[0115] According to embodiments 1, 4-6, the length of the polyethylene glycol segment grafted on the modified cyclodextrin has certain influence on the water resistance, mechanical property and degradability of the food packaging bag; among them, the water resistance and mechanical property of example 5 are relatively poor compared with examples 1 and 4, but the degradability is better, the reason may be that the polyethylene glycol segment in example 5 is shorter, which leads to the relatively poor heat resistance of the modified cyclodextrin, which may cause part of the modified cyclodextrin to decompose during processing, so the crosslinking density is smaller than examples 1 and 4, the hydrophobicity of the hydrophobic barrier is weaker than examples 1 and 4, which leads to the water resistance and mechanical property are not as good as examples 1 and 4, and the release of the metal stearate included in the modified cyclodextrin during processing, although it improves the degradability, but also affects its service life; the water resistance of example 6 is significantly lower than that of examples 1 and 4, the reason may be that the polyethylene glycol segment in example 6 is longer, and its crosslinking density is lower than examples 1 and 4, and the hydrophobicity of the hydrophobic barrier formed is weaker than examples 1 and 4, so its water resistance is not as good as examples 1 and 4. It is shown that the modified cyclodextrin obtained by using polyethylene glycol with a weight average molecular weight of 600-1000 can better balance the water resistance, mechanical property and degradability of the degradable food packaging bag.

[0116] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A biodegradable food packaging bag, characterized in that, The raw materials include the following parts by weight: 50 parts polylactic acid, 50-100 parts polybutylene adipate / terephthalate, 5-10 parts plasticizer, 4-8 parts functional additives; The functional additive includes modified cyclodextrin, and the preparation method of the modified cyclodextrin includes the following steps: S1: Polyethylene glycol with a weight-average molecular weight of 300-1500 is reacted with epichlorohydrin in an alkaline methanol solution, so that the hydroxyl groups at both ends of polyethylene glycol react with epichlorohydrin, and epoxy groups are grafted onto both ends of polyethylene glycol to obtain epoxy-modified polyethylene glycol. S2: Reaction of epoxy-oxidized polyethylene glycol with β-cyclodextrin in an alkaline aqueous solution, so that the epoxy group at one end of the epoxy-oxidized polyethylene glycol reacts with the hydroxyl group on the β-cyclodextrin, and end-epoxy-oxidized polyethylene glycol segments are grafted onto the β-cyclodextrin to obtain an aqueous solution of end-epoxy-oxidized polyethylene glycol grafted with β-cyclodextrin. S3: The epoxy-terminated polyethylene glycol-grafted β-cyclodextrin aqueous solution is added to the ethanol dispersion of metal stearate. Through hydrophobic interaction, the metal stearate is incorporated into the cavity of β-cyclodextrin to obtain modified cyclodextrin.

2. The biodegradable food packaging bag according to claim 1, characterized in that, The raw materials include the following parts by weight: 50 parts polylactic acid, 50-75 parts polybutylene adipate / terephthalate, 5-8 parts plasticizer, and 5-7 parts functional additives.

3. The biodegradable food packaging bag according to claim 1, characterized in that, The metal stearate includes at least one of zinc stearate, calcium stearate, and iron stearate.

4. The biodegradable food packaging bag according to claim 3, characterized in that, The metal stearate includes zinc stearate and calcium stearate, wherein the mass ratio of zinc stearate to calcium stearate is 1:0.2~0.

6.

5. The biodegradable food packaging bag according to claim 1, characterized in that, S1 specifically includes: Dissolve 10 parts by mass of polyethylene glycol with a weight average molecular weight of 300-1500 in 150-300 parts by mass of sodium hydroxide methanol solution with pH 11-13, add 5-10 parts by mass of epichlorohydrin, and react at 40-60℃ for 12-24 h to obtain epoxy-oxidized polyethylene glycol.

6. The biodegradable food packaging bag according to claim 1, characterized in that, S2 specifically includes: 10 parts by weight of epoxy-modified polyethylene glycol and 3-6 parts by weight of β-cyclodextrin are dissolved in 400-600 parts by weight of sodium hydroxide aqueous solution with pH 10-12, and reacted at 90-110℃ for 18-32 h to obtain an aqueous solution of epoxy-terminated polyethylene glycol grafted with β-cyclodextrin.

7. The biodegradable food packaging bag according to claim 5, characterized in that, S3 specifically includes: 1-3 parts by weight of metal stearate were ultrasonically dispersed in 20-50 parts by weight of ethanol to obtain an ethanol dispersion of metal stearate; acid was added to the aqueous solution of the terminal epoxy polyethylene glycol grafted β-cyclodextrin to adjust the pH of the solution to 8-10, and then the ethanol dispersion of metal stearate was added. The mixture was stirred at 25-30°C for 2-4 hours to obtain modified cyclodextrin.

8. The biodegradable food packaging bag according to claim 1 or 2, characterized in that, The biodegradable food packaging bag meets at least one of the following conditions: 1) The weight-average molecular weight of the polylactic acid is 100,000 to 200,000; 2) The weight-average molecular weight of the poly(butylene adipate / terephthalate) is 150,000 to 300,000; 3) The plasticizer includes at least one of triacetyl citrate, tributyl citrate, triethyl citrate, polybutylene adipate, and epoxidized soybean oil; 4) It also includes 0.5 to 2 parts of antioxidants; the antioxidants include at least one of 2,6-di-tert-butyl-p-cresol, dilauryl thiopropionate, and vitamin E.

9. A method for preparing biodegradable food packaging bags, characterized in that, include: Provide raw materials for biodegradable food packaging bags according to any one of claims 1 to 8; The raw materials are dried, melt-blended, extruded, granulated, and blow-molded to obtain biodegradable food packaging bags.

Images