Degradable food packaging bag and preparation method thereof

Abstract

The invention provides a degradable food packaging bag and a preparation method thereof. The degradable food packaging bag is prepared from the following raw materials in parts by mass: 50 parts of polylactic acid, 50-100 parts of poly (butylene adipate-co-terephthalate), 5-10 parts of a plasticizer and 4-8 parts of a functional aid, wherein the functional auxiliary agent comprises modified cyclodextrin, and the modified cyclodextrin is beta-cyclodextrin which is formed by grafting terminal epoxy group polyethylene glycol with metal stearate in a clathration manner. According to the degradable food packaging bag, polylactic acid and poly (butylene adipate-co-terephthalate) are used as main materials, so that the mechanical property of the food packaging bag is improved; by using the plasticizer, the brittleness of the food packaging bag is further reduced, and the flexibility is improved; according to the degradable food packaging bag disclosed by the invention, the mechanical property and the water resistance of the degradable food packaging bag are improved by adding modified cyclodextrin as a functional auxiliary agent, and the degradation rate of the food packaging bag can be increased by the included metal stearate, so that the obtained degradable food packaging bag has good water resistance and degradability.

Description

Technical Field

[0001] This application relates to the technical field of food packaging materials, and particularly relates to a degradable food packaging bag and a preparation method thereof. Background Art

[0002] With the increasing prominence of global environmental problems and the exacerbation of plastic pollution problems, traditional petroleum-based plastics are difficult to degrade and remain in landfills and the environment for a long time, bringing a serious burden to the ecosystem. Therefore, the development and promotion of degradable plastics have become an important direction for the global green environmental protection industry. In the field of food packaging, it is required that the material has good mechanical properties, water and oil resistance, and food safety, and at the same time can be efficiently degraded in the natural environment after the end of its service life. Therefore, degradable food packaging bags have attracted wide attention.

[0003] Currently, the main degradable materials used in the market include polylactic acid (PLA), polycaprolactone (PCL), polybutylene terephthalate, and starch- and cellulose-based bioplastics. Although these materials have certain biodegradability, the degradation conditions of these degradable plastics are relatively harsh. For example, PLA can generally only achieve rapid degradation under specific industrial composting conditions (high temperature, high humidity, specific microbial environment), and the degradation rate is slow in the natural environment or household composting conditions, which is likely to cause environmental accumulation.

[0004] Currently, the main research direction for the above problems is generally to use more easily degradable polymer materials, such as natural polysaccharides such as starch, cellulose, and lignin, as the main material or additive doped in the above degradable plastics to accelerate the degradation rate of food packaging bags. However, the problem is that the performance of food packaging bags obtained with the above natural polysaccharides as the main material is poor. In addition, when doped as an additive in degradable plastics, there are problems with the compatibility between components, and the above natural polysaccharides have stronger hydrophilicity, which will further increase the hygroscopicity of degradable food packaging bags and affect their durability.

[0005] Patent CN118652478A discloses a degradable and recyclable plastic food packaging bag. Its raw materials by weight include: 50 - 60 parts of composite starch, 10 - 20 parts of composite plant fiber, 30 - 40 parts of composite polymer composition, 3 - 5 parts of leather powder, 3 - 5 parts of bamboo powder, 3 - 5 parts of chitosan, 5 - 10 parts of gelatin, 1 - 3 parts of calcium stearate, 3 - 5 parts of oleic acid, 1 - 3 parts of oxidative degradation additive, and 1 - 3 parts of citric acid. The present invention relates to the technical field of plastic products. This degradable and recyclable plastic food packaging bag can, while modifying the starch material, add composite plant fiber to greatly improve the tensile strength and toughness of the degradable plastic bag, achieving the purpose of both ensuring the degradation effect of the plastic bag and improving its load-bearing capacity, greatly enhancing the tensile and load-bearing performance of the plastic bag, enabling it to bear heavy items, and well realizing the preparation of a plastic bag with better tensile performance by combining fiber and modified starch.

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

[0007] Currently, there are also relevant literatures recording that by adding microcapsules coated with microbial spores for promoting the degradation of corresponding plastics to degradable plastics, it has no impact on the food packaging bag during use, and during subsequent treatment, the microcapsules release spores to promote the degradation of the food packaging bag. However, the problem is that the process is relatively complex and has high requirements for microorganisms.

[0008] Based on this, the present application provides a degradable food packaging bag and its preparation method. Summary of the Invention

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

[0010] In the first aspect, the present application provides a degradable food packaging bag, including the following raw materials in parts by mass: 50 parts of polylactic acid, 50 - 100 parts of polybutylene adipate / terephthalate, 5 - 10 parts of plasticizer, 4 - 8 parts of functional auxiliary agent; wherein, the functional auxiliary agent includes modified cyclodextrin, and the modified cyclodextrin is β-cyclodextrin grafted with terminal epoxy group polyethylene glycol and inclusion complexed with metal stearate.

[0011] According to the present application, the degradable food packaging bag uses polylactic acid and poly(butylene adipate-co-terephthalate) (PBAT) as the main materials. Both are degradable polymer materials and have good compatibility. Melt blending can improve the inherent brittleness of the polylactic acid material and improve the mechanical properties of the food packaging bag. By using a plasticizer, the brittleness of the food packaging bag is further reduced and its flexibility is improved. In addition, by adding a modified cyclodextrin as a functional additive, the modified cyclodextrin is grafted with a terminal epoxy group polyethylene glycol segment, which can effectively improve the compatibility of cyclodextrin between the main materials, so as to be evenly dispersed in the system. In addition, the terminal epoxy group has reactivity with the end groups of polylactic acid and poly(butylene adipate-co-terephthalate). 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 hydrophobic cavity of β-cyclodextrin in the modified cyclodextrin encapsulates metal stearate. On the one hand, the modified cyclodextrin is evenly dispersed in the material. Due to the crosslinking reaction, the hydrophilicity of the cyclodextrin surface is reduced, and the hydrophobic cavity cooperates with the metal stearate to form a hydrophobic barrier in the material, reducing the penetration of moisture in the food packaging bag, improving the water resistance of the food packaging bag, reducing the influence of moisture on the PLA and PBAT segments, and increasing 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. At the same time, the encapsulated metal stearate is released, and the metal ions can promote the hydrolysis of the ester bonds in the PLA and PBAT segments, thereby further increasing 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 parts by mass: 50 parts of polylactic acid, 50 - 75 parts of poly(butylene 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: React polyethylene glycol with an average weight molecular weight of 300 - 1500 and epichlorohydrin in an alkaline methanol solution, so that the hydroxyl groups at both ends of the polyethylene glycol react with epichlorohydrin, and epoxy groups are grafted at both ends of the polyethylene glycol to obtain epoxidized polyethylene glycol.

[0015] S2: React epoxidized polyethylene glycol with β-cyclodextrin in an alkaline aqueous solution, so that the epoxy group at one end of the epoxidized polyethylene glycol reacts with the hydroxyl group on β-cyclodextrin, and a terminal epoxy group polyethylene glycol segment is grafted on β-cyclodextrin to obtain an aqueous solution of terminal epoxy group polyethylene glycol grafted β-cyclodextrin.

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

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

[0018] In some embodiments, 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.

[0019] In some embodiments, S1 specifically includes:

[0020] 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 a pH of 11 - 13, add 5 - 10 parts by mass of epichlorohydrin, and react at 40 - 60 °C for 12 - 24 h to obtain epoxidized polyethylene glycol.

[0021] In some embodiments, S2 specifically includes:

[0022] Dissolve 10 parts by mass of epoxidized polyethylene glycol and 3 - 6 parts by mass of β-cyclodextrin in 400 - 600 parts by mass of sodium hydroxide aqueous solution with a pH of 10 - 12, and react at 90 - 110 °C for 18 - 32 h to obtain an aqueous solution of terminal epoxy group polyethylene glycol grafted β-cyclodextrin.

[0023] In some embodiments, S3 specifically includes:

[0024] Ultrasonically disperse 1 - 3 parts by mass of metal stearate in 20 - 50 parts by mass of ethanol to obtain an ethanol dispersion of metal stearate; add acid to the aqueous solution of terminal epoxy group polyethylene glycol grafted β-cyclodextrin to adjust the solution pH to 8 - 10, then add the ethanol dispersion of metal stearate, and stir at 25 - 30 °C for 2 - 4 h 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 includes at least one of glyceryl triacetylcitrate, tributyl citrate, triethyl citrate, polybutylene adipate, and epoxidized soybean oil.

[0028] In some embodiments, it further includes 0.5 to 2 parts of antioxidant; the antioxidant includes at least one of 2,6-di-tert-butyl-p-cresol, dilauryl thiodipropionate, and vitamin E.

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

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

[0031] Drying the raw materials, then melt-blending, extruding, granulating, and blow molding to obtain a degradable food packaging bag.

[0032] According to the present application, since it is prepared by using the raw materials in 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. Specific Embodiments

[0033] In the present specification, the embodiments or implementation schemes are described in a progressive manner, and each embodiment focuses on the differences from other embodiments.

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

[0035] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0036] The present application provides a degradable food packaging bag and a method for preparing the same. The degradable food packaging bag has good water resistance and degradability by optimizing its raw material components. The following provides a detailed description of the specific embodiments provided by the present application.

[0037] In a first aspect, the present application provides a degradable food packaging bag, which comprises raw materials in the following parts by mass: 50 parts of polylactic acid, 50-100 parts of polybutylene adipate / terephthalate (PBAT), 5-10 parts of plasticizer, and 4-8 parts of functional auxiliary agent; wherein, the functional auxiliary agent includes modified cyclodextrin, and the modified cyclodextrin is β-cyclodextrin grafted with terminal epoxy group polyethylene glycol and inclusion-complexed with metal stearate.

[0038] According to the present application, the degradable food packaging bag uses polylactic acid and polybutylene adipate / terephthalate (PBAT) as the main materials. Both of them are degradable polymer materials and have good compatibility at the same time. Melting and blending can improve the inherent brittleness of the polylactic acid material and improve the mechanical properties of the food packaging bag; by using a plasticizer, the brittleness of the food packaging bag is further reduced and its flexibility is improved; in addition, by adding modified cyclodextrin as a functional auxiliary agent, a terminal epoxy group polyethylene glycol chain segment is grafted on the modified cyclodextrin, which can effectively improve the compatibility of cyclodextrin between the main materials, so as to be evenly dispersed in the system. In addition, the terminal epoxy group has reactivity with the end groups of polylactic acid and polybutylene adipate / terephthalate. During the melting and blending process, the modified cyclodextrin serves as a crosslinking center to increase the crosslinking density of the material, thereby improving its mechanical properties; at the same time, metal stearate is included in the hydrophobic cavity of β-cyclodextrin in the modified cyclodextrin. On the one hand, the modified cyclodextrin is evenly dispersed in the material. Due to the crosslinking reaction, the hydrophilicity of the cyclodextrin surface is reduced, and the hydrophobic cavity therein cooperates with the metal stearate to form a hydrophobic barrier in the material, reducing the penetration of moisture in the food packaging bag, improving the water resistance of the food packaging bag, reducing the influence of moisture on the PLA and PBAT chain segments, and increasing 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. At the same time, the included metal stearate is released, and the metal ions therein can promote the hydrolysis of the ester bonds in the PLA and PBAT chain segments, thereby further increasing 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 found that the problems existing in current degradable food packaging bags mainly lie in the contradiction between the use performance and lifespan of food packaging bags and their degradable performance. Using degradable plastics as the main body of food packaging bags and adding polysaccharide substances such as starch and cellulose as auxiliaries can, to a certain extent, improve their degradability. However, their compatibility with the main material and strong hygroscopicity will also affect the use performance and lifespan of food packaging bags. Additionally, if substances that promote the degradation of the main material are directly added to the main material, it will obviously also affect the performance of plastic packaging bags during production and use. Based on this, the inventors added modified cyclodextrin as a functional auxiliary in a system with polylactic acid and polybutylene adipate / terephthalate as the main materials. This modified cyclodextrin is β-cyclodextrin grafted with a polyethylene glycol chain segment capped with an epoxy group and inclusion-complexed with metal stearate. Due to the structure of β-cyclodextrin with a hydrophobic interior and a hydrophilic exterior, the dispersibility of unmodified β-cyclodextrin in the system is poor. By grafting a polyethylene glycol chain segment on its inner surface, the inventors can effectively improve its dispersibility in the system. At the same time, the end group of the polyethylene glycol chain segment is an epoxy group, which has good reactivity with the end groups of PLA and PBAT. Therefore, the modified cyclodextrin can act as a crosslinking agent in the system to increase the crosslinking density of the material, thereby improving the mechanical strength and reducing the water penetration. At the same time, the hydrophobic inner cavity of the modified cyclodextrin inclusion-complexes with metal stearate, and the modified cyclodextrin can form a hydrophobic barrier inside the material, thereby improving the hydrophobicity of the material, further reducing the water penetration in the degradable plastic bag, reducing the damage of water to the strength. At the same time, the metal stearate is in the hydrophobic cavity of cyclodextrin and does not directly contact the main material. Therefore, before β-cyclodextrin is damaged, it will not affect the service life of the degradable food packaging bag. On the other hand, β-cyclodextrin is a polysaccharide substance. During the recycling and degradation process of the degradable food packaging bag, it is more easily utilized by microorganisms compared to the main material, thereby reducing the crosslinking density of the food packaging bag, destroying the hydrophobic barrier, making water more easily penetrate, and at the same time, the metal stearate included in β-cyclodextrin is released, and the metal ions therein can catalyze the hydrolysis of PLA and PBAT chain segments, thereby further promoting the degradation of the food packaging bag. Thus, the obtained degradable food packaging bag has good water resistance and degradable performance.

[0040] In addition, it is worth noting that the inventors found that by grafting a polyethylene glycol chain segment on the surface of β-cyclodextrin, the stability of β-cyclodextrin can be effectively improved, making it more stable during the preparation and processing of degradable food packaging bags, not easily decomposing and releasing the contents in the hydrophobic cavity in advance, thereby improving the stability of the performance of degradable food packaging bags.

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

[0042] In some of the above embodiments, by further optimizing the contents of the components of the raw materials, the degradable food packaging bag obtained has better water resistance and degradability.

[0043] In some embodiments, the preparation method of the modified cyclodextrin comprises the following steps:

[0044] S1: React polyethylene glycol with a weight-average molecular weight of 300 to 1500 and epichlorohydrin in an alkaline methanol solution, so that the hydroxyl groups at both ends of the polyethylene glycol react with epichlorohydrin, and epoxy groups are grafted at both ends of the polyethylene glycol to obtain epoxidized polyethylene glycol;

[0045] S2: React the epoxidized polyethylene glycol with β-cyclodextrin in an alkaline aqueous solution, so that the epoxy group at one end of the epoxidized polyethylene glycol reacts with the hydroxyl group on β-cyclodextrin, and a terminal epoxy group polyethylene glycol chain segment is grafted onto β-cyclodextrin to obtain an aqueous solution of terminal epoxy group polyethylene glycol grafted β-cyclodextrin;

[0046] S3: Add the aqueous solution of terminal epoxy group polyethylene glycol grafted β-cyclodextrin to an ethanol dispersion of metal stearate, and through hydrophobic interaction, incorporate the metal stearate into the cavity of β-cyclodextrin to obtain the modified cyclodextrin.

[0047] In some of the above embodiments, the modified cyclodextrin is prepared by the above preparation method. Specifically, in step S1, in the alkaline methanol solution, polyethylene glycol with a weight-average molecular weight of 300 to 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 that epoxy groups are grafted at both ends of the polyethylene glycol; in addition, the inventors found that the length of the polyethylene glycol chain segment will affect the dispersion of the finally obtained modified cyclodextrin in the matrix material and its own thermal stability, thereby affecting the performance of the degradable food packaging bag; it can be understood that a longer polyethylene glycol chain segment can improve the thermal stability of the modified cyclodextrin, but if it is too long, due to the certain flexibility and hydrophilicity of the polyethylene glycol chain segment, it will also affect its hydrophobic property of forming a hydrophobic barrier. Therefore, the modified cyclodextrin obtained by using polyethylene glycol with the above 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 to 1000.

[0048] In step S2, in an alkaline aqueous solution, the epoxy groups on the epoxidized polyethylene glycol can react with the hydroxyl groups on the surface of β-cyclodextrin, so that β-cyclodextrin is grafted with a polyethylene glycol chain segment with an epoxy group at the end; it can be understood that after the epoxy group at one end of the epoxidized polyethylene glycol reacts with β-cyclodextrin, the epoxy group at the other end is less likely to further react with the β-cyclodextrin grafted with the polyethylene glycol chain segment due to steric hindrance. Therefore, active epoxy groups can be grafted onto β-cyclodextrin, so that it has reactive activity with the end groups of PLA and PBAT.

[0049] In step S3, an ethanol dispersion of metal stearate is obtained using ethanol as the dispersion medium, and it is added to the aqueous solution of β-cyclodextrin grafted with end-epoxy polyethylene glycol. Since there is only the hydrophobic cavity inside β-cyclodextrin in the system, under the action of hydrophobic interaction, part of the metal stearate is included in the hydrophobic cavity of β-cyclodextrin, thus obtaining modified cyclodextrin; it can be understood that not all of the metal stearate will be included in the hydrophobic cavity of β-cyclodextrin. Using an excessive amount of metal stearate can fully load the hydrophobic cavity inside β-cyclodextrin in the system, and the complexation of cyclodextrin can ensure that the included metal stearate will not damage the use stability of the packaging bag while providing a certain long-chain hydrophobic effect. Since metal stearate mainly plays a catalytic role in promoting the cleavage of ester bonds during the degradation process and is more likely to obtain small molecule monomers or segments that can be directly utilized by microorganisms, 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 stearates can effectively promote the hydrolysis of ester bonds in the PLA and PBAT segments, decomposing into smaller molecule segments or monomers that are more beneficial for microbial utilization, thereby improving 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 zinc stearate to calcium stearate is 1:0.2 - 0.6.

[0052] In some of the above embodiments, the inventors found that when the metal stearate includes zinc stearate and calcium stearate in the above mass ratio, the degradable food packaging bag has better degradation performance; the possible reason is that calcium ions and zinc ions can promote the decomposition of PLA and PBAT segments through different pathways. Among them, 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, which can bind to the lone pair electrons on the oxygen atoms in PLA and PBAT through coordination, catalyzing the decomposition of PLA and PBAT segments; through a suitable ratio, the two can cooperate to further improve the degradability of the degradable food packaging bag.

[0053] In some embodiments, S1 specifically includes:

[0054] Dissolve 10 parts by mass of polyethylene glycol with a weight average molecular weight of 300 to 1500 in 150 to 300 parts by mass of sodium hydroxide methanol solution with a pH of 11 to 13, add 5 to 10 parts by mass of epichlorohydrin, and react at 40 to 60 °C for 12 to 24 h to obtain epoxidized polyethylene glycol.

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

[0056] In some embodiments, S2 specifically includes:

[0057] Dissolve 10 parts by mass of epoxidized polyethylene glycol and 3 to 6 parts by mass of β-cyclodextrin in 400 to 600 parts by mass of sodium hydroxide aqueous solution with a pH of 10 to 12, and react at 90 to 110 °C for 18 to 32 h to obtain an aqueous solution of polyethylene glycol grafted β-cyclodextrin with terminal epoxy groups.

[0058] In some of the above embodiments, under the above conditions, epoxidized polyethylene glycol can be grafted onto β-cyclodextrin to obtain polyethylene glycol grafted β-cyclodextrin with terminal epoxy groups.

[0059] In some embodiments, S3 specifically includes:

[0060] Ultrasonically disperse 1 to 3 parts by mass of metal stearate in 20 to 50 parts by mass of ethanol to obtain an ethanol dispersion of metal stearate; add acid to the aqueous solution of polyethylene glycol grafted β-cyclodextrin with terminal epoxy groups to adjust the solution pH to 8 to 10, and then add the ethanol dispersion of metal stearate and stir at 25 to 30 °C for 2 to 4 h to obtain modified cyclodextrin.

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

[0062] In some embodiments, the weight-average molecular weight of polylactic acid is 100,000 to 200,000. Based on the above embodiments, the polylactic acid with the above weight-average molecular weight can better balance mechanical properties and degradability. As an example, in an embodiment of the present application, polylactic acid with a weight-average molecular weight of 150,000 is used.

[0063] In some embodiments, the weight-average molecular weight of polybutylene adipate / terephthalate is 150,000 to 300,000. Based on the above embodiments, the polybutylene adipate / terephthalate with the above weight-average molecular weight can endow the degradable food packaging bag with better mechanical properties. As an example, in an embodiment of the present application, polybutylene adipate / terephthalate with a weight-average molecular weight of 200,000 is used.

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

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

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

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

[0068] Drying the raw materials, then melt-blending, extruding, pelletizing, and blow molding to obtain a degradable food packaging bag.

[0069] According to the present application, since it is prepared by using the raw materials in the degradable food packaging bag of any embodiment of the first aspect, it has the beneficial effects of the first aspect.

[0070] In some embodiments, specifically, it includes: drying 50 parts of polylactic acid, 50 - 100 parts of polybutylene adipate / terephthalate, and 4 - 8 parts of functional additives, then adding 5 - 10 parts of plasticizer and 0.5 - 2 parts of antioxidant and uniformly dispersing them, and using a twin-screw extruder to extrude and pelletize, and then blow molding to obtain a degradable food packaging bag.

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

[0072] Hereinafter, examples of the present application will be described. The examples described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those techniques or conditions not specified in the examples, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial 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, and 6 parts by mass of modified cyclodextrin, then adding 8 parts by mass of triacetyl citrate glycerol ester and 1 part by mass of 2,6-di-tert-butyl-p-cresol and uniformly dispersing them, and using a twin-screw extruder to extrude and pelletize (the temperature of the feeding zone is 145 °C, the temperature of the melting zone is 175 °C, the temperature of the homogenizing zone is 185 °C, the temperature of the extrusion zone is 175 °C, and the screw shear rate is 30 rpm), and then blow molding to obtain a degradable food packaging bag.

[0076] Among them, 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 sodium hydroxide methanol solution with a pH of 12, dropwise adding 8 parts by mass of epichlorohydrin, reacting at 50 °C for 18 h, after the reaction is completed, performing rotary evaporation and concentration, and then adding ether to dissolve and drying to obtain epoxidized polyethylene glycol;

[0078] Dissolve 10 parts by mass of epoxidized polyethylene glycol and 5 parts by mass of β-cyclodextrin in 500 parts by mass of an aqueous sodium hydroxide solution with a pH of 10, and reflux and react at 100 °C for 20 h to obtain an aqueous solution of β-cyclodextrin grafted with polyethylene glycol having an epoxy group at the end;

[0079] Ultrasonically disperse 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 h to obtain a dispersion. Add hydrochloric acid to the above-mentioned aqueous solution of β-cyclodextrin grafted with polyethylene glycol to adjust the pH to 8, then mix it with the above-mentioned dispersion, stir at 25 °C for 3 h, and after the stirring is completed, centrifuge to separate the suspended metal stearate. Dialyze the obtained supernatant solution through a semipermeable membrane with a permeation amount of 1800 Da in water for 48 h, change the water every 12 h, and concentrate by rotary evaporation and then dry in vacuo to obtain the modified cyclodextrin.

[0080] Example 2

[0081] Preparation of a degradable food packaging bag:

[0082] It is substantially the same as Example 1, except that in the preparation process of the modified cyclodextrin, 2 parts by mass of zinc stearate are used instead of 1.25 parts by mass of zinc stearate and 0.75 parts by mass of calcium stearate.

[0083] Example 3

[0084] Preparation of a degradable food packaging bag:

[0085] It is substantially the same as Example 1, except that in the preparation process of the modified cyclodextrin, 2 parts by mass of calcium stearate are used instead of 1.25 parts by mass of zinc stearate and 0.75 parts by mass of calcium stearate.

[0086] Example 4

[0087] Preparation of a degradable food packaging bag:

[0088] It is substantially the same as Example 1, except that in the preparation process of the modified cyclodextrin, polyethylene glycol with a weight-average molecular weight of 1000 is used.

[0089] Example 5

[0090] Preparation of a degradable food packaging bag:

[0091] It is substantially the same as Example 1, except that in the preparation process of the modified cyclodextrin, polyethylene glycol with a weight-average molecular weight of 300 is used.

[0092] Example 6

[0093] Preparation of a degradable food packaging bag:

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

[0095] Comparative Example 1

[0096] Preparation of the degradable food packaging bag:

[0097] Dry 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, and 2 parts by mass of β-cyclodextrin, then add 4 parts by mass of polyethylene glycol with a weight average molecular weight of 600, 8 parts by mass of triacetyl citrate glycerol ester, and 1 part by mass of 2,6-di-tert-butyl-p-cresol and disperse them evenly. Use a twin-screw extruder to extrude and granulate (the temperature of the feeding zone is 145 °C, the temperature of the melting zone is 175 °C, the temperature of the homogenization zone is 185 °C, the temperature of the extrusion zone is 175 °C, and the screw shear rate is 30 rpm), and then blow-mold to obtain the degradable food packaging bag.

[0098] Comparative Example 2

[0099] Preparation of the degradable food packaging bag:

[0100] Dry 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, and 2 parts by mass of β-cyclodextrin, then add 4 parts by mass of polyethylene glycol with a weight average molecular weight of 600, 0.15 parts by mass of zinc stearate, 0.05 parts by mass of calcium stearate, 3 parts by mass of polyethylene glycol with a weight average molecular weight of 600, 8 parts by mass of triacetyl citrate glycerol ester, and 1 part by mass of 2,6-di-tert-butyl-p-cresol and disperse them evenly. Use a twin-screw extruder to extrude and granulate (the temperature of the feeding zone is 145 °C, the temperature of the melting zone is 175 °C, the temperature of the homogenization zone is 185 °C, the temperature of the extrusion zone is 175 °C, and the screw shear rate is 30 rpm), and then blow-mold to obtain the degradable food packaging bag.

[0101] Comparative Example 3

[0102] Preparation of the degradable food packaging bag:

[0103] 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, and 3 parts by mass of β-cyclodextrin inclusion metal stearate are dried, and then 3 parts by mass of epoxidized polyethylene glycol, 8 parts by mass of triacetyl citric acid glycerol ester, and 1 part by mass of 2,6-di-tert-butyl-p-cresol are added and uniformly dispersed. Extrusion granulation is carried out using a twin-screw extruder (the temperature of the feeding zone is 145 °C, the temperature of the melting zone is 175 °C, the temperature of the homogenization zone is 185 °C, the temperature of the extrusion zone is 175 °C, and the screw shear rate is 30 rpm), and blow molding is carried out to obtain a degradable food packaging bag.

[0104] Among them, β-cyclodextrin inclusion 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 it is mixed with the above dispersion liquid and stirred at 25 °C for 3 h. After the stirring is completed, the suspended metal stearate is centrifuged and separated, and the supernatant is concentrated by rotary evaporation and then dried under vacuum to obtain β-cyclodextrin inclusion metal stearate;

[0105] Epoxidized 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 sodium hydroxide methanol solution with a pH of 12, and 8 parts by mass of epichlorohydrin is added dropwise and reacted at 50 °C for 18 h. After the reaction is completed, rotary evaporation concentration is carried out, and then it is dissolved in ether and dried to obtain epoxidized polyethylene glycol.

[0106] Test part

[0107] The water vapor transmission rate (WVT value) of the degradable food packaging bags obtained in the above examples and comparative examples is measured with reference to GB / T 1037-2021 "Determination of Water Vapor Transmission Performance of Plastic Films and Sheets"; the maximum tensile stress is measured with reference to GB / T 1040-2006 "Determination of Tensile Properties of Plastics"; the results are shown in Table 1;

[0108] The weight loss rate (%) is measured by testing with reference to the standard of GB / T 19811-2005 for simulating soil burial degradation experiment; the results are shown in Table 2.

[0109] Table 1

[0110] <![CDATA[WVT value [g / (m 2 ·d)]]]> Maximum tensile stress / N Example 1 321 54.6 Example 2 326 53.9 Example 3 317 54.3 Example 4 326 55.1 Example 5 426 47.3 Example 6 381 51.8 Comparative Example 1 516 38.5 Comparative Example 2 513 36.7 Comparative Example 3 482 41.3

[0111] Table 2

[0112]

[0113]

[0114] As can be seen from Table 1 and Table 2, the WVT values of the degradable food packaging bags obtained in each example are lower than those in each comparative example, the maximum tensile stress is higher than that in each comparative example, and the degradable performance is better than that of Comparative Example 1; this shows that the degradable food packaging bags obtained in this application have better water resistance, mechanical properties and degradable performance. The reason may be that in Comparative Example 1, the compatibility between unmodified β-cyclodextrin and the matrix material is poor, and its heat resistance is poor. It is easy to degrade during the processing process and is not easily uniformly dispersed in the material. Therefore, it cannot effectively form a hydrophobic barrier inside the material. The additional addition of polyethylene glycol cannot effectively improve the heat resistance and dispersibility of β-cyclodextrin, and it does not have reactive activity. In addition, it does not contain materials that promote the degradation of the matrix material. Therefore, its water resistance, mechanical properties and degradable performance are worse than those in each example; in Comparative Example 2, although it has good degradable performance, the water resistance and mechanical properties of the degradable food packaging bag are poor. It can be understood that the direct contact of metal stearate with the material will also reduce the service life of the degradable food packaging bag; in addition, according to Comparative Example 2, adding a small amount of metal stearate to the degradable food packaging bag and cooperating with the soil burial degradation environment can effectively improve its degradation efficiency; in Comparative Example 3, epoxidized polyethylene glycol and β-cyclodextrin inclusion complex of metal stearate are added respectively. The reactive activity provided by epoxidized polyethylene glycol, in cooperation with the β-cyclodextrin inclusion complex of metal stearate, has limited improvement on the water resistance and mechanical properties of the degradable food packaging bag. It cannot effectively form a complete hydrophobic barrier inside the material, and during the processing process, part of the metal stearate in the β-cyclodextrin inclusion complex of metal stearate is released, which will affect the service life of the food packaging bag.

[0115] As can be seen from Examples 1 to 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 it has a certain effect on its degradable performance. Among them, in Example 1, a modified cyclodextrin containing a certain proportion of zinc stearate and calcium stearate is used. Compared with Examples 2 and 3 using modified cyclodextrins containing single zinc stearate or calcium stearate, the obtained degradable food packaging bag has better degradable performance; the reason may be that zinc ions and calcium ions can promote the degradation of the matrix material through different channels, and the two work together to make the food packaging bag have better degradable performance.

[0116] According to Examples 1, 4 to 6, the length of the polyethylene glycol segment grafted on the modified cyclodextrin has a certain influence on the water resistance, mechanical properties and degradability of the food packaging bag; among them, the water resistance and mechanical properties in 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, resulting in relatively poor heat resistance of the modified cyclodextrin, and partial decomposition of the modified cyclodextrin may occur during the processing, resulting in a lower crosslinking density compared with Examples 1 and 4, and the hydrophobicity of the hydrophobic barrier is weaker than that in Examples 1 and 4, resulting in worse water resistance and mechanical properties than Examples 1 and 4. At the same time, the metal stearate included in the modified cyclodextrin is released during the processing, which improves the degradability but also affects its service life; the water resistance in Example 6 is significantly lower than that in Examples 1 and 4. The reason may be that the polyethylene glycol chain in Example 6 is longer, and its crosslinking density is lower than that in Examples 1 and 4, and the hydrophobicity of the formed hydrophobic barrier is weaker than that in Examples 1 and 4. Therefore, its water resistance is not as good as that in Examples 1 and 4. It shows that the degradable food packaging bag obtained by using the modified cyclodextrin obtained from polyethylene glycol with a weight average molecular weight of 600 to 1000 can better balance the water resistance, mechanical properties and degradability.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some 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 degradable food packaging bag, characterized in that: The invention 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 plasticizer, 4-8 parts of functional additives; The functional additive comprises modified cyclodextrin, which is β-cyclodextrin grafted with terminal epoxy polyethylene glycol and encapsulated with metal stearate.

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

3. The degradable food packaging bag according to claim 1 or 2, characterized in that: The preparation method of the modified cyclodextrin comprises the following steps: S1: reacting polyethylene glycol having a weight average molecular weight of 300 to 1500 with epichlorohydrin in an alkaline methanol solution, so that the hydroxyl groups at both ends of the polyethylene glycol react with the epichlorohydrin, and grafting epoxy groups on both ends of the polyethylene glycol to obtain epoxylated polyethylene glycol; S2: reacting epoxylated polyethylene glycol with β-cyclodextrin in an alkaline aqueous solution, so that the epoxy group at one end of the epoxylated polyethylene glycol reacts with the hydroxyl group on the β-cyclodextrin, grafting an epoxy-terminated polyethylene glycol segment onto the β-cyclodextrin, and obtaining an epoxy-terminated polyethylene glycol grafted β-cyclodextrin aqueous solution; S3: adding the terminal epoxy polyethylene glycol grafted β-cyclodextrin aqueous solution to the ethanol dispersion of metal stearate, and including the metal stearate into the cavity of β-cyclodextrin through hydrophobic interaction to obtain modified cyclodextrin.

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

5. The degradable food packaging bag according to claim 4, characterized in that: The metal stearate comprises zinc stearate and calcium stearate, wherein the mass ratio of the zinc stearate to the calcium stearate is 1:0.2-0.

6.

6. The degradable food packaging bag according to claim 3, characterized in that: The S1 specifically includes: 10 parts by weight of polyethylene glycol with a weight average molecular weight of 300 to 1500 is dissolved in 150 to 300 parts by weight of a sodium hydroxide methanol solution with a pH of 11 to 13, 5 to 10 parts by weight of epichlorohydrin is added, and the mixture is reacted at 40 to 60° C. for 12 to 24 hours to obtain epoxylated polyethylene glycol.

7. The degradable food packaging bag according to claim 3, characterized in that: The S2 specifically includes: 10 parts by weight of epoxylated polyethylene glycol and 3 to 6 parts by weight of β-cyclodextrin are dissolved in 400 to 600 parts by weight of an aqueous sodium hydroxide solution having a pH of 10 to 12, and reacted at 90 to 110° C. for 18 to 32 hours to obtain an aqueous solution of epoxy-terminated polyethylene glycol grafted β-cyclodextrin.

8. The degradable food packaging bag according to claim 6, characterized in that: The S3 specifically includes: Ultrasonic dispersion of 1 to 3 parts by weight of metal stearate in 20 to 50 parts by weight of ethanol is performed to obtain an ethanol dispersion of the metal stearate; acid is added to the epoxy-terminated polyethylene glycol-grafted β-cyclodextrin aqueous solution to adjust the pH value of the solution to 8 to 10, and then the ethanol dispersion of the metal stearate is added, and the mixture is stirred at 25 to 30° C. for 2 to 4 hours to obtain a modified cyclodextrin.

9. The degradable food packaging bag according to claim 1 or 2, characterized in that: The degradable 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 polybutylene 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 an antioxidant; the antioxidant includes at least one of 2,6-di-tert-butyl-p-cresol, dilaurylthiopropionate, and vitamin E.

10. A method for preparing a degradable food packaging bag, characterized in that: include: Providing a raw material for a degradable food packaging bag according to any one of claims 1 to 9; The raw materials are dried, melt-blended, extruded, granulated, and blow-molded to obtain a degradable food packaging bag.

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