Degradable and recyclable plastic food packaging bag and preparation method thereof

Abstract

The invention relates to the field of packaging bag materials, in particular to a degradable and recyclable plastic food packaging bag and a preparation method thereof. The degradable and recyclable plastic food packaging bag is mainly prepared from the following raw materials in parts by mass: a polylactic acid base material, a functional resin material, solid particles, a plasticizer, an antioxidant, a light stabilizer, a lubricant and the like. The finally prepared food packaging bag material can effectively solve the problem that the mechanical property of a packaging bag is reduced in the long-term use process, and can keep excellent waterproof, moisture-proof, heat-resistant stability and the like under the conditions of high humidity and high environment temperature; most importantly, the negative influence of the application environment on the mechanical property and barrier property of the packaging bag material can be handled, obvious decomposition and damage phenomena are avoided, and the packaging bag material has very excellent application prospects.

Description

Technical Field

[0001] This application relates to the field of packaging bag materials, and more specifically, it mentions a degradable and recyclable plastic food packaging bag and its preparation method. Background Art

[0002] With the increasing global awareness of environmental protection, traditional petroleum-based non-degradable plastic packaging bags are gradually restricted due to their difficulty in natural decomposition and easy environmental pollution problems. In order to respond to the environmental protection call and reduce white pollution, the industry has begun to seek more sustainable alternative solutions, that is, to develop new packaging materials that can not only meet the requirements of food packaging but also have good biodegradability or are easy to recycle and reuse. In this context, materials such as polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) have been widely studied and applied in the field of food packaging materials because of their excellent mechanical properties, high transparency, good processability, etc.

[0003] However, although these new packaging materials have alleviated the environmental pressure brought by traditional plastics to a certain extent, there are still many practical application problems that cannot be effectively solved in actual applications. For example, in the actual use process of consumers, the existing degradable and recyclable packaging bags will have obvious problems of mechanical property decline during long-term storage and use, especially in terms of tensile resistance, and their performance decline is more obvious, and they cannot maintain good packaging performance during long-term use; for another example, in a relatively humid and high-temperature environment, some degradable and recyclable packaging materials will have irreversible decomposition, degradation and cracking phenomena, and the barrier property will also drop significantly, which directly affects their packaging protection function for food. Summary of the Invention

[0004] Therefore, in order to effectively solve the above existing problems, this application provides a degradable and recyclable plastic food packaging bag and its preparation method. The finally obtained food packaging bag material can effectively cope with the problem of the decline of the mechanical properties of the packaging bag during long-term use, and can also maintain excellent waterproof, moisture-resistant, heat-resistant stability and other properties in the case of high humidity and high environmental temperature. Most importantly, it can cope with the negative impacts of the above application environment on the mechanical properties and barrier properties of the packaging bag material, and avoid obvious decomposition and damage phenomena, and has very excellent application prospects.

[0005] As a preferred embodiment, for the degradable and recyclable plastic food packaging bag, by mass, its preparation raw materials are: 50 - 70 parts of polylactic acid base material, 20 - 30 parts of functional resin material, 2 - 5 parts of solid particles, 4 - 10 parts of plasticizer, 0.5 - 1 part of antioxidant, 0.3 - 0.5 part of light stabilizer, 0.5 - 1.5 parts of lubricant, 0.5 - 1 part of antistatic agent, and 1 - 3 parts of compatibilizer.

[0006] As a preferred embodiment, the number-average molecular weight of the polylactic acid base material is 40,000 - 70,000 Da.

[0007] As a more preferred embodiment, the number-average molecular weight of the polylactic acid base material is 50,000 - 55,000 Da.

[0008] As a preferred embodiment, the intrinsic viscosity of the polylactic acid base material is 0.6 - 0.8 dL / g, condition: 25 °C.

[0009] As a more preferred embodiment, the intrinsic viscosity of the polylactic acid base material is 0.64 - 0.74 dL / g, condition: 25 °C.

[0010] As a preferred embodiment, the mass ratio of the polylactic acid base material to the functional resin material is (55 - 65):(20 - 27).

[0011] As a preferred embodiment, the functional resin material is a composition of modified PBAT and modified starch-based resin.

[0012] As a preferred embodiment, the mass ratio of the modified PBAT to the modified starch-based resin is (1.5 - 3):(0.5 - 1.5).

[0013] As a more preferred embodiment, the mass ratio of the modified PBAT to the modified starch-based resin is (2 - 2.5):(1 - 1.2).

[0014] As a preferred embodiment, the preparation method of the modified PBAT specifically includes the following steps: S1: Mix PBAT with maleic anhydride, add dicumyl peroxide and carry out reactive extrusion in a twin-screw extruder at a temperature of 160 - 180 °C and a residence time of 20 - 25 min to obtain functionalized PBAT; S2: Mix the functionalized PBAT, terephthalic acid, itaconic acid and 1,4-butanediol and add them to a reaction kettle, heat up to 150 - 160 °C under nitrogen protection and stir and react for 2 - 3 h to generate a pretreatment product; S3: Continue to gradually heat up to 180 - 190 °C and continue to react for 1 - 2 h until the acid value of the reaction system drops below 10 mg KOH / g, then cool the pretreatment product to 120 - 130 °C, add epoxidized soybean oil, glycidyl methacrylate and trimethylolpropane triacrylate, and react at a rotation speed of 100 - 120 rpm for 2 - 3 h; S4: Finally, add dicumyl peroxide, stir evenly and heat up to 160 - 170 °C, react for 1 - 1.5 h, and after the reaction is completed, quickly cool to room temperature to obtain the product.

[0015] As a preferred embodiment, the mass ratio of the PBAT to maleic anhydride is (8 - 10):(0.6 - 1).

[0016] As a preferred embodiment, the mass ratio of the functionalized PBAT, terephthalic acid, itaconic acid and 1,4 - butanediol is (8.5 - 9.5):(1 - 1.5):(0.6 - 0.8):(0.3 - 0.6).

[0017] As a preferred embodiment, the mass ratio of the pretreatment product, epoxidized soybean oil, glycidyl methacrylate and trimethylolpropane triacrylate is (12 - 13):(0.2 - 0.4):(2 - 2.2):(1.1 - 1.4).

[0018] By adding the modified PBAT, not only the mechanical properties of the packaging bag material are further effectively improved, but also its aging resistance, thermal stability and waterproof and moisture resistance under high temperature, high humidity and long - term storage environments can be effectively guaranteed, thereby greatly reducing the negative impact on the mechanical properties of the packaging bag material due to the above - mentioned usage conditions.

[0019] The modified PBAT added in this application can form a microscopic phase - separation structure with the rigid segments of the polylactic acid base material through its formed multi - flexible segments, thereby effectively absorbing impact energy and improving mechanical toughness. On the other hand, the hydrophobic segments of the modified PBAT can more easily embed into the surface structure of the material, thereby greatly reducing the surface hydrophilic groups and the pore size of the surface film micropores by using the hydrophobic segments and cross - linked structures, so as to provide a greater surface resistance to the penetration of water and active molecules. And through the introduction of functional monomers, its more dense internal cross - linked structure network and heat - resistant groups greatly increase the glass transition temperature of the material system, and thus excellent waterproof, moisture - resistant, heat - resistant and aging - resistant comprehensive properties are obtained in a high - humidity environment.

[0020] Finally, the added modified PBAT can act together with the added modified starch - based resin through the added active reaction structure and the polylactic acid base material to improve the interfacial bonding effect and form a co - continuous structure, forming a uniform and dense dispersed phase in the polylactic acid continuous phase. While effectively transmitting stress and absorbing energy, it can better cope with the relative slip phenomenon through the action of cross - linked molecular chains, so as to obtain excellent mechanical stability and thermal stability in long - term use or complex use environments; and the construction of a more complex internal three - dimensional network structure can improve the mutual adhesion between molecular chains, improve the mechanical effect while hindering the further penetration of water molecules.

[0021] As a preferred embodiment, the preparation method of the modified starch-based resin specifically comprises the following steps: S1: Mix natural corn starch with deionized water, stir evenly to form a starch suspension, and then add sodium hydroxide to the starch suspension to adjust the pH to 8-10; S2: Under stirring conditions, slowly add maleic anhydride, stir for 10-15 min to ensure uniform dispersion, then continue to add octenyl succinic anhydride and epichlorohydrin and ensure uniform mixing, heat up to 55-60 °C and continuously stir and react for 3-5 h to ensure complete reaction; S3: After the reaction is completed, neutralize the pH of the reaction system to 6-7 with acetic acid, stop the reaction, and after obtaining the product, wash it repeatedly with deionized water to remove unreacted substances, thus obtaining the product.

[0022] As a preferred embodiment, the mass ratio of the natural corn starch to maleic anhydride is (6-8):(1.2-1.4).

[0023] As a preferred embodiment, the mass ratio of the natural corn starch, octenyl succinic anhydride and epichlorohydrin is (6-8):(1.5-1.8):(0.3-0.5).

[0024] As a preferred embodiment, the solid particles are at least one of silica, carbon nanotubes, calcium carbonate, talcum powder and glass fiber.

[0025] As a more preferred embodiment, the solid particles are silica or calcium carbonate.

[0026] As a more preferred embodiment, the solid particles are silica.

[0027] As a preferred embodiment, the average particle size of the silica is 15-30 nm.

[0028] As a more preferred embodiment, the plasticizer is a composition of tributyl acetylcitrate and poly(propylene adipate).

[0029] As a preferred embodiment, the mass ratio of the tributyl acetylcitrate to poly(propylene adipate) is (5-6):(1.2-2).

[0030] As a preferred embodiment, the antioxidant is Irganox 1010 or Irganox 1076.

[0031] As a more preferred embodiment, the antioxidant is Irganox 1076.

[0032] As a preferred embodiment, the light stabilizer is Tinuvin 622 or Chimassorb 944.

[0033] As a more preferred embodiment, the light stabilizer is Tinuvin 622.

[0034] As a preferred embodiment, the lubricant is at least one of calcium stearate, zinc stearate, ethylene bis-stearamide and polyethylene wax.

[0035] As a more preferred embodiment, the lubricant is calcium stearate.

[0036] As a preferred embodiment, the antistatic agent is glycerol monostearate or ethoxylated fatty amine.

[0037] As a more preferred embodiment, the antistatic agent is ethoxylated fatty amine.

[0038] As a preferred embodiment, the compatibilizer is a composition of maleic anhydride grafted polypropylene and ethylene-methyl acrylate copolymer.

[0039] As a preferred embodiment, the mass ratio of maleic anhydride grafted polypropylene to ethylene-methyl acrylate copolymer is (3 - 5):(1.2 - 2.4).

[0040] As a more preferred embodiment, the mass ratio of maleic anhydride grafted polypropylene to ethylene-methyl acrylate copolymer is (3.5 - 4.2):(1.6 - 1.8).

[0041] As a preferred embodiment, the preparation method of the degradable and recyclable plastic food packaging bag specifically includes the following steps: S1: Add the polylactic acid base material and the functional resin material into a high-speed mixer, mix evenly at a temperature of 100 - 120°C, and fully disperse to form a homogeneous mixture; S2: First add solid particles, plasticizer and antioxidant into the mixture, continue to stir at the same temperature for 10 - 15 min until completely fused, and finally add the remaining raw materials, raise the temperature to 130 - 140°C and stir for 10 - 15 min to obtain the final mixture; S3: Feed the final mixture into a twin-screw extruder, melt and blend in the temperature range of 180 - 200°C, and then extrude through a die to form a film-like or bag-like product. After cooling and forming, it is cut and trimmed to obtain the product.

[0042] The beneficial effects of this application are: 1. The degradable and recyclable plastic food packaging bag provided in this application can effectively address the problem of the decline in the mechanical properties of the packaging bag during long-term use, and can also maintain excellent waterproof, moisture-resistant, heat-resistant stability and other properties in high humidity and high environmental temperature conditions. Most importantly, it can address the negative impacts of the above application environment on the mechanical properties and barrier properties of the packaging bag material, and avoid obvious decomposition and damage phenomena, having a very excellent application prospect.

[0043] 2. A degradable and recyclable plastic food packaging bag provided in the present application. The added modified PBAT can comprehensively enhance the various properties of the food packaging bag, especially effectively ensure the aging resistance, thermal stability, water resistance and moisture resistance of the packaging bag under high temperature, high humidity and long-term storage environments, thereby greatly reducing the negative impact on the mechanical properties of the packaging bag material due to the above-mentioned usage conditions.

[0044] 3. A degradable and recyclable plastic food packaging bag provided in the present application. By further adding modified starch-based resin to the packaging bag material, not only the excellent degradable and recyclable performance of the packaging bag system is continued, but also the molecular chain network structure of the modified starch-based resin can absorb and disperse the external force, thereby effectively preventing the formed cracks from further expanding. On the other hand, it is easier to form a hydrophobic film barrier, reduce the overall water absorption, form a more stable covalent bond network structure, inhibit the thermal movement of the molecular chains of starch and polylactic acid materials, and prevent excessive agglomeration of internal particles during use or preparation through lubrication, ensuring the stability of the overall performance. Detailed implementation manners

[0045] In the detailed implementation manners, specific implementation cases will be used to more intuitively display and explain the content in the inventive content of the present application. And the following embodiments are only actual examples for illustrating and explaining the content of the technical solutions in the specification, and should not limit the scope of the claims to be protected by the present application.

[0046] Example 1 For the degradable and recyclable plastic food packaging bag, calculated by mass fraction, the raw materials are: 61.5 parts of polylactic acid base material, 24.2 parts of functional resin material, 3.2 parts of solid particles, 5.8 parts of plasticizer, 0.6 part of antioxidant, 0.3 part of light stabilizer, 0.8 part of lubricant, 0.6 part of antistatic agent, and 2.2 parts of compatibilizer.

[0047] The number average molecular weight of the polylactic acid base material is 52000 Da, the intrinsic viscosity is 0.68 dL / g at 25 °C, and it is a product of model 3052D sold by NatureWorks LLC, USA.

[0048] The functional resin material is a composition of modified PBAT and modified starch-based resin, and the mass ratio of the two is 2.3:1.2.

[0049] The preparation method of modified PBAT specifically includes the following steps, in parts by mass: S1: Mix 9.5 parts of PBAT with 0.8 parts of maleic anhydride, add 0.08 parts of diisopropylbenzene peroxide, and carry out reactive extrusion in a twin-screw extruder at a temperature of 170 °C and a residence time of 22 min to obtain functionalized PBAT; S2: Mix 8.8 parts of functionalized PBAT, 1.3 parts of terephthalic acid, 0.75 parts of itaconic acid, and 0.4 parts of 1,4-butanediol and add them to a reaction kettle. Under nitrogen protection, heat up to 155 °C and stir and react for 2.5 h to generate a pre-treatment product; S3: Continue to gradually heat up to 182 °C and continue to react for 1.5 h until the acid value of the reaction system drops below 10 mgKOH / g. Then cool 12.5 parts of the pre-treatment product to 120 °C, add 0.3 parts of epoxidized soybean oil, 2.1 parts of glycidyl methacrylate, and 1.2 parts of trimethylolpropane triacrylate, and react at a rotation speed of 120 rpm for 3 h; S4: Finally, add 0.11 parts of diisopropylbenzene peroxide, stir evenly, heat up to 165 °C, and react for 1.5 h. After the reaction is completed, quickly cool to room temperature to obtain the product.

[0050] PBAT was purchased from the Ecoflex® F Blend C1200 model product sold by BASF Corporation in Germany.

[0051] Epoxidized soybean oil was purchased from the industrial plasticizer grade product sold by Hubei Xingyan New Materials Technology Co., Ltd. in China.

[0052] The preparation method of the modified starch-based resin specifically includes the following steps, in parts by mass: S1: Mix 7.5 parts of natural corn starch with 120 parts of deionized water, stir evenly to form a starch suspension, and then add sodium hydroxide to the starch suspension to adjust the pH to 9; S2: Under stirring conditions, slowly add 1.3 parts of maleic anhydride, stir for 12 min to ensure uniform dispersion, then continue to add 1.6 parts of octenyl succinic anhydride and 0.4 parts of epichlorohydrin and ensure uniform mixing, heat up to 60 °C and continuously stir and react for 4.5 h to ensure complete reaction; S3: After the reaction is completed, neutralize the pH of the reaction system to 6.5 with acetic acid, stop the reaction, and after obtaining the product, wash it repeatedly with deionized water to remove unreacted substances to obtain the product.

[0053] The solid particles are silica with an average particle size of 20 nm.

[0054] The plasticizer is a composition of tributyl acetylcitrate and poly(propylene adipate), and the mass ratio of the two is 5.6:1.4.

[0055] The antioxidant is Irganox 1076; the light stabilizer is Tinuvin 622; the lubricant is calcium stearate; the antistatic agent is ethoxylated fatty amine.

[0056] The compatibilizer is a composition of maleic anhydride grafted polypropylene and ethylene-methyl acrylate copolymer, and the mass ratio of the two is 3.8:1.8.

[0057] The preparation method of the degradable and recyclable plastic food packaging bag specifically includes the following steps: S1: Add the polylactic acid base material and the functional resin material into a high-speed mixer, mix evenly at a temperature of 110°C, and fully disperse to form a homogeneous mixture; S2: First add solid particles, plasticizer and antioxidant to the mixture, continue to stir at the same temperature for 15 minutes until completely fused, and finally add the remaining raw materials, raise the temperature to 130°C and stir for 15 minutes to obtain the final mixture; S3: Feed the final mixture into a twin-screw extruder, melt and blend within a temperature range of 190°C, and then extrude through a die to form a film-like or bag-like product. After cooling and forming, it is cut and trimmed to obtain the product.

[0058] Example 2 This example is only different from Example 1 in the following aspects: For the degradable and recyclable plastic food packaging bag, by mass, the raw materials are: 55.8 parts of polylactic acid base material, 20.6 parts of functional resin material, 3.4 parts of solid particles, 5.2 parts of plasticizer, 0.5 part of antioxidant, 0.3 part of light stabilizer, 0.6 part of lubricant, 0.5 part of antistatic agent, and 1.5 parts of compatibilizer.

[0059] The functional resin material is a composition of modified PBAT and modified starch-based resin, and the mass ratio of the two is 2.5:1.

[0060] The plasticizer is a composition of tributyl acetylcitrate and poly(propylene adipate), and the mass ratio of the two is 5:2.

[0061] The compatibilizer is a composition of maleic anhydride grafted polypropylene and ethylene-methyl acrylate copolymer, and the mass ratio of the two is 4.2:1.6.

[0062] Example 3 This example is only different from Example 1 in the following aspects: For the degradable and recyclable plastic food packaging bag, by mass, the raw materials are: 64.5 parts of polylactic acid base material, 26.8 parts of functional resin material, 4.1 parts of solid particles, 6.4 parts of plasticizer, 0.8 part of antioxidant, 0.4 part of light stabilizer, 1.1 part of lubricant, 0.6 part of antistatic agent, and 1.9 parts of compatibilizer.

[0063] The functional resin material is a composition of modified PBAT and modified starch-based resin, and the mass ratio of the two is 2:1.2.

[0064] The plasticizer is a composition of tributyl acetylcitrate and poly(propylene adipate), and the mass ratio of the two is 6:1.3.

[0065] The compatibilizer is a composition of maleic anhydride grafted polypropylene and ethylene-methyl acrylate copolymer, and the mass ratio of the two is 3.5:1.7.

[0066] Comparative Example 1 The only difference between this comparative example and Example 1 is as follows: For the degradable and recyclable plastic food packaging bag, by mass, the raw materials are: 70 parts of polylactic acid base material, 10.5 parts of functional resin material, 4.1 parts of solid particles, 4.2 parts of plasticizer, 0.6 part of antioxidant, 0.3 part of light stabilizer, 0.5 part of lubricant, 0.5 part of antistatic agent, and 1.2 parts of compatibilizer.

[0067] Comparative Example 2 The only difference between this comparative example and Example 1 is as follows: For the degradable and recyclable plastic food packaging bag, by mass, the raw materials are: 52.2 parts of polylactic acid base material, 36.8 parts of functional resin material, 2.2 parts of solid particles, 5.8 parts of plasticizer, 1 part of antioxidant, 0.3 part of light stabilizer, 0.8 part of lubricant, 0.6 part of antistatic agent, and 2.8 parts of compatibilizer.

[0068] Comparative Example 3 The only difference between this comparative example and Example 1 is as follows: The functional resin material is a composition of modified PBAT and modified starch-based resin, and the mass ratio of the two is 5:0.6.

[0069] Comparative Example 4 The only difference between this comparative example and Example 1 is as follows: The functional resin material is a composition of modified PBAT and modified starch-based resin, and the mass ratio of the two is 1:2.5.

[0070] Comparative Example 5 This comparative example is only different from Example 1 in the following aspects: The preparation method of the modified PBAT specifically includes the following steps, in parts by mass: S1: Mix 15.5 parts of PBAT with 0.2 parts of maleic anhydride, add 0.08 parts of diisopropylbenzene peroxide, and carry out reactive extrusion in a twin-screw extruder at a temperature of 170 °C and a residence time of 22 min to obtain functionalized PBAT; S2: Mix 8.8 parts of functionalized PBAT, 1.5 parts of terephthalic acid, 0.9 parts of itaconic acid, and 0.8 parts of 1,4-butanediol and add them to a reaction kettle, heat up to 155 °C under nitrogen protection, and stir and react for 2.5 h to generate a pretreatment product; S3: Continue to gradually heat up to 182 °C and continue to react for 1.5 h until the acid value of the reaction system drops below 10 mg KOH / g. Then cool 12.5 parts of the pretreatment product to 120 °C, add 0.3 parts of epoxidized soybean oil, 2.1 parts of glycidyl methacrylate, and 1.2 parts of trimethylolpropane triacrylate, and react at a rotation speed of 120 rpm for 3 h; S4: Finally, add 0.11 parts of diisopropylbenzene peroxide, stir evenly, heat up to 165 °C, and react for 1.5 h. After the reaction is completed, quickly cool to room temperature to obtain the product.

[0071] Comparative Example 6 This comparative example is only different from Example 1 in the following aspects: The preparation method of the modified PBAT specifically includes the following steps, in parts by mass: S1: Mix 9.5 parts of PBAT with 0.8 parts of maleic anhydride, add 0.08 parts of diisopropylbenzene peroxide, and carry out reactive extrusion in a twin-screw extruder at a temperature of 170 °C and a residence time of 22 min to obtain functionalized PBAT; S2: Mix 12 parts of functionalized PBAT, 0.6 parts of terephthalic acid, 0.15 parts of itaconic acid, and 0.2 parts of 1,4-butanediol and add them to a reaction kettle, heat up to 155 °C under nitrogen protection, and stir and react for 2.5 h to generate a pretreatment product; S3: Continue to gradually heat up to 182 °C and continue to react for 1.5 h until the acid value of the reaction system drops below 10 mg KOH / g. Then cool 12.5 parts of the pretreatment product to 120 °C, add 0.1 parts of epoxidized soybean oil, 0.8 parts of glycidyl methacrylate, and 0.3 parts of trimethylolpropane triacrylate, and react at a rotation speed of 120 rpm for 3 h; S4: Finally, add 0.11 parts of diisopropylbenzene peroxide, stir evenly, heat up to 165 °C, and react for 1.5 h. After the reaction is completed, quickly cool to room temperature to obtain the product.

[0072] Comparative Example 7 This comparative example is only different from Example 1 in the following aspects: The preparation method of the modified starch-based resin specifically includes the following steps, in parts by mass: S1: Mix 7.5 parts of natural corn starch with 120 parts of deionized water, stir evenly to form a starch suspension, and then add sodium hydroxide to the starch suspension to adjust the pH to 9; S2: Under stirring conditions, slowly add 0.8 part of maleic anhydride, stir for 12 min to ensure uniform dispersion, then continue to add 0.2 part of octenyl succinic anhydride and 0.2 part of epichlorohydrin and ensure uniform mixing, heat up to 60 °C and continuously stir and react for 4.5 h to ensure full completion of the reaction; S3: After the reaction is completed, neutralize the pH of the reaction system to 6.5 with acetic acid, stop the reaction, and after obtaining the product, wash it repeatedly with deionized water to remove the unreacted substances, and then obtain it.

[0073] Performance testing 1. Refer to the standard GB / T 20197-2006 to conduct biodegradability tests on the food packaging bags prepared in the examples and comparative examples, and the results are the average values of 10 groups of tests and are recorded in Table 1.

[0074] 2. Refer to the standard ASTM D638 to conduct tensile strength and elongation at break tests on the food packaging bags prepared in the examples and comparative examples, and the results are the average values of 10 groups of tests and are recorded in Table 1.

[0075] 3. Conduct heat and aging resistance tests on the food packaging bags prepared in the examples and comparative examples. The test conditions are 400 h aging resistance tests at 55 °C ± 2 °C and 75% relative humidity. After the test is completed, take it out and test its tensile strength according to the method of Performance Test 2. And according to the tensile strength values before and after the test, obtain the tensile strength retention rate % after the heat and aging resistance test. Tensile strength retention rate % = (tensile strength after test / tensile strength before test) × 100%. The results are the average values of 10 groups of tests and are recorded in Table 1.

[0076] 4. Refer to the standard ASTM E96 to conduct water resistance and moisture permeability tests on the food packaging bags prepared in the examples and comparative examples, and the results are the average values of 10 groups of tests and are recorded in Table 1.

[0077] From the final performance test results of the examples and comparative examples, Comparative Examples 1-7 achieved worse performance results compared to the examples. The examples, due to the adoption of the modified resin composition solution, significantly improved the intermolecular chain segment adhesion and the construction of a three-dimensional network within the packaging material system, enhanced the absorption and dissipation of external stress by the material system, increased its resistance to intermolecular chain slip, significantly enhanced the density of surface hydrophobic groups, reduced surface micropore voids, and enhanced the moisture penetration resistance. As a result, excellent resistance to moisture and active molecules was maintained under high humidity and high temperature environments, and excellent mechanical property retention and waterproof and moisture permeation resistance effects were obtained.

Claims

1. A degradable and recyclable plastic food packaging bag, characterized in that: The raw materials for its preparation are: 50 - 70 parts of polylactic acid base material, 20 - 30 parts of functional resin material, 2 - 5 parts of solid particles, 4 - 10 parts of plasticizer, 0.5 - 1 part of antioxidant, 0.3 - 0.5 part of light stabilizer, 0.5 - 1.5 parts of lubricant, 0.5 - 1 part of antistatic agent, and 1 - 3 parts of compatibilizer; The number - average molecular weight of the polylactic acid base material is 40000 - 70000 Da; The intrinsic viscosity of the polylactic acid base material is 0.6 - 0.8 dL / g, condition: 25°C; The functional resin material is a composition of modified PBAT and modified starch - based resin; the mass ratio of the modified PBAT to the modified starch - based resin is (1.5 - 3):(0.5 - 1.5); The solid particles are at least one of silicon dioxide, carbon nanotubes, calcium carbonate, talcum powder, and glass fiber; The plasticizer is a composition of tributyl acetylcitrate and poly(propylene adipate); the mass ratio of tributyl acetylcitrate to poly(propylene adipate) is (5 - 6):(1.2 - 2); The compatibilizer is a composition of maleic anhydride - grafted polypropylene and ethylene - methyl acrylate copolymer.

2. The degradable and recyclable plastic food packaging bag according to claim 1, wherein: The preparation method of the modified PBAT specifically includes the following steps: S1: Mix PBAT and maleic anhydride, add diisopropylbenzene peroxide and carry out reactive extrusion in a twin - screw extruder at a temperature of 160 - 180°C and a residence time of 20 - 25 min to obtain functionalized PBAT; S2: Mix the functionalized PBAT, terephthalic acid, itaconic acid, and 1,4 - butanediol and add them to a reaction kettle, heat up to 150 - 160°C under nitrogen protection, and stir and react for 2 - 3 h to generate a pretreatment product; S3: Continue to gradually heat up to 180 - 190°C and continue to react for 1 - 2 h until the acid value of the reaction system drops below 10 mg KOH / g, then cool the pretreatment product to 120 - 130°C, add epoxidized soybean oil, glycidyl methacrylate, and trimethylolpropane triacrylate, and react at a rotation speed of 100 - 120 rpm for 2 - 3 h; S4: Finally, add diisopropylbenzene peroxide, stir evenly, heat up to 160 - 170°C, react for 1 - 1.5 h, and after the reaction is completed, quickly cool to room temperature to obtain the product.

3. The degradable and recyclable plastic food packaging bag according to claim 2, wherein: The mass ratio of the PBAT to maleic anhydride is (8 - 10):(0.6 - 1); the mass ratio of the functionalized PBAT, terephthalic acid, itaconic acid, and 1,4 - butanediol is (8.5 - 9.5):(1 - 1.5):(0.6 - 0.8):(0.3 - 0.6).

4. The degradable and recyclable plastic food packaging bag according to claim 3, characterized in that: The mass ratio of the pretreatment product, epoxidized soybean oil, glycidyl methacrylate, and trimethylolpropane triacrylate is (12 - 13):(0.2 - 0.4):(2 - 2.2):(1.1 - 1.4).

5. The degradable and recyclable plastic food packaging bag according to claim 4, characterized in that: The preparation method of the modified starch-based resin specifically includes the following steps: S1: Mix natural corn starch with deionized water, stir evenly to form a starch suspension, and then add sodium hydroxide to the starch suspension to adjust the pH to 8-10; S2: Under stirring conditions, slowly add maleic anhydride, stir for 10-15 min to ensure uniform dispersion, then continue to add octenyl succinic anhydride and epichlorohydrin and ensure uniform mixing, heat up to 55-60 °C and continuously stir and react for 3-5 h to ensure complete reaction; S3: After the reaction is completed, neutralize the pH of the reaction system to 6-7 with acetic acid, stop the reaction, and after obtaining the product, wash it repeatedly with deionized water to remove the unreacted substances, and then obtain it.

6. The degradable and recyclable plastic food packaging bag according to claim 5, wherein: The mass ratio of the natural corn starch to maleic anhydride is (6-8):(1.2-1.4); the mass ratio of the natural corn starch, octenyl succinic anhydride and epichlorohydrin is (6-8):(1.5-1.8):(0.3-0.5).

7. The degradable and recyclable plastic food packaging bag according to claim 6, wherein: The antioxidant is Irganox 1010 or Irganox 1076; the light stabilizer is Tinuvin 622 or Chimassorb 944.

8. The degradable and recyclable plastic food packaging bag according to claim 7, characterized in that: The antistatic agent is glycerol monostearate or ethoxylated fatty amine.

9. The degradable and recyclable plastic food packaging bag according to claim 8, characterized in that: The mass ratio of the maleic anhydride grafted polypropylene to ethylene-methyl acrylate copolymer is (3-5):(1.2-2.4).

10. A method for preparing a degradable and recyclable plastic food packaging bag according to any one of claims 1 to 9, characterized in that: Specifically includes the following steps: S1: Add the polylactic acid base material and the functional resin material into a high-speed mixer, mix evenly at a temperature of 100-120 °C, and fully disperse to form a homogeneous mixture; S2: First add solid particles, plasticizer and antioxidant to the mixture, continue to stir at the same temperature for 10-15 min until completely fused, and finally add the remaining raw materials, heat up to 130-140 °C and stir for 10-15 min to obtain a final mixture; S3: Feed the final mixture into a twin-screw extruder, melt and blend in the temperature range of 180-200 °C, and then extrude through a die to form a film-like or bag-like product. After cooling and forming, cut and trim it to obtain.

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