High-toughness heat-resistant fully biodegradable PLA shopping bag and preparation method thereof

Abstract

This invention belongs to the field of polylactic acid (PLA) manufacturing technology, specifically relating to a high-toughness, heat-resistant, fully biodegradable PLA shopping bag and its preparation method. This invention introduces a composite nucleating agent into PLA. Silica-modified montmorillonite provides stable nucleation sites, while hydrazide-based nucleating agents enhance nucleation efficiency. Together, these agents improve the crystallinity and crystallization rate of PLA, forming fine crystal nuclei during PLA melting, promoting stable solidification and improving the mechanical uniformity and heat resistance of the resulting shopping bag. The biodegradable elastomer, obtained through bio-based molecular polymerization, is dispersed in PLA in an island-like structure. This effectively disperses stress through deformation, preventing crack propagation and improving the toughness and elasticity of the PLA material. During blow molding, it prevents PLA from easily breaking due to stretching, allowing the resulting shopping bag to maintain practical toughness and heat resistance close to that of traditional plastic bags even when packaging high-temperature food.

Description

Technical Field

[0001] This invention belongs to the field of polylactic acid manufacturing technology, specifically relating to a high-toughness, heat-resistant, fully biodegradable PLA shopping bag and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is a linear thermoplastic aliphatic polyester prepared from renewable plant resources through saccharification, fermentation, and polymerization. It possesses advantages such as biodegradability, good biocompatibility, and ease of processing. However, current PLA materials suffer from slow crystallization speed and insufficient heat resistance. The slow crystallization speed results in excessively large grain sizes during the solidification process, leading to high brittleness. When used in plastic bags, PLA is prone to breakage under load and easily deforms at high temperatures, limiting its application in high-temperature environments. Therefore, it is necessary to blend PLA with other heat-resistant materials to improve its toughness and heat resistance.

[0003] Chinese invention patent CN112500611B discloses a biodegradable plastic bag and its preparation method. The biodegradable plastic bag comprises the following raw materials: modified polylactic acid (PLA), polybutylene adipate / terephthalate (PBDT), corn starch, nano-calcium carbonate, aluminate coupling agent, citric acid, citric acid ester compounds, and a heat stabilizer. This biodegradable plastic bag increases the amount of corn starch and reduces the amount of modified PLA and PBDT, saving raw material costs. Simultaneously, the PLA is modified to obtain modified PLA, which, combined with other raw materials, improves the overall tensile strength, elongation at break, puncture resistance, and water resistance of the biodegradable plastic bag, making it more suitable for market promotion. However, the existing technology has a technical problem: it does not improve the toughness and heat resistance of PLA through the use of nucleating agents. Summary of the Invention

[0004] The purpose of this invention is to provide a high-toughness, heat-resistant, fully biodegradable PLA shopping bag and its preparation method, which solves the technical problem in the prior art of not using nucleating agents to improve the components and further enhance the toughness and heat resistance of polylactic acid.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A high-toughness, heat-resistant, fully biodegradable PLA shopping bag comprises the following raw materials in parts by weight: 100 parts polylactic acid resin, 5-10 parts biodegradable elastomer, 0.5-1.5 parts composite nucleating agent, 0.5-2 parts antioxidant, and 0.5-2 parts lubricant;

[0007] The antioxidant is one or more of antioxidant 1010, antioxidant 168, and antioxidant 1076;

[0008] The lubricant is one or more combinations of calcium stearate, ethylene bis-stearamide, and carnauba wax;

[0009] Preferably, the preparation method of the composite nucleating agent includes the following steps:

[0010] S11. Add montmorillonite and deionized water to a homogenizer and stir. Let it stand to separate into layers. Take the upper clear liquid, add sodium carbonate, then add hexadecyltrimethylammonium bromide and heat to modify. Filter by suction. Wash the obtained filter cake with deionized water, vacuum dry, grind and sieve to obtain modified montmorillonite.

[0011] S12. Modified montmorillonite was added to deionized water, tetraethyl orthosilicate was added, triethanolamine was added dropwise, the mixture was heated and stirred to hydrolyze, the solid was collected by filtration, washed with deionized water, dried, and calcined to obtain a heat-resistant nucleating agent.

[0012] S13. A composite nucleating agent is prepared by mixing a heat-resistant nucleating agent and an acylhydrazine-based nucleating agent.

[0013] Preferably, in S11, the mass ratio of montmorillonite to deionized water is 1~3:10, and the mixture is stirred at 3000~4000 rpm for 20~30 min at 70~80℃. The mass ratio of the supernatant, sodium carbonate, and hexadecyltrimethylammonium bromide is 100:2~2.5:0.5~2, and the mixture is reacted at 75~85℃ for 2~4 h. The mixture is washed until no bromide ions can be detected by silver nitrate, and then vacuum dried at 80~90℃ and passed through a 200~300 mesh sieve.

[0014] Preferably, the mass ratio of modified montmorillonite, tetraethyl orthosilicate, deionized water, and triethanolamine in S12 is 8~10:1~3:100~150:0.8~1. The mixture is heated to 70~80℃ and hydrolyzed by stirring at 200~300 rpm for 1~2 hours, dried at 50~60℃, and calcined at 550~570℃ for 2~4 hours at a heating rate of 8~10℃.

[0015] Preferably, the acylhydrazine nucleating agent in S13 is one or both of TMC-300 and TMC-306, and the mass ratio of the heat-resistant nucleating agent to the acylhydrazine nucleating agent is 1~2:3~5.

[0016] Preferably, the method for preparing the biodegradable elastomer includes the following steps:

[0017] S21. Citric acid, succinic acid and ethylene glycol are added to a reaction vessel, heated and stirred to mix, and reacted under a nitrogen atmosphere to obtain prepolymer 1.

[0018] S22. Glycerol is added to prepolymer 1, and the mixture is crosslinked under a nitrogen atmosphere, vacuum polycondensed, and cooled to room temperature to obtain a biodegradable elastomer.

[0019] Preferably, the mass ratio of citric acid, succinic acid and ethylene glycol in S21 is 30~35:20~25:15~20. The mixture is heated to 140~150℃ and stirred at 200~300rpm for 20~30min, and then heated to 170~175℃ for 1~2h.

[0020] Preferably, in S22, the mass ratio of prepolymer 1 to glycerol is 8~10:1~1.5. After adding glycerol, crosslinking is carried out at 175~180℃ for 1~2h, the vacuum degree is less than 0.1MPa, and the temperature is raised to 200~220℃ for condensation for 4~6h.

[0021] A method for preparing a high-toughness, heat-resistant, fully biodegradable PLA shopping bag includes the following steps:

[0022] S1. After heating and vacuum drying the raw material to remove moisture, seal it for later use;

[0023] S2. A mixture of polylactic acid resin, biodegradable elastomer, composite nucleating agent, antioxidant and lubricant is prepared. The mixture is added to an extruder for melt extrusion, pelletized and cooled to obtain high toughness and heat-resistant masterbatch.

[0024] S3. Add the high-toughness and heat-resistant masterbatch to a blow molding machine to inflate it into a film, stretch it, put it into an oven for heating and annealing, cool it, and then cool and wind it up through a traction roller, heat seal it, cut and package it to obtain a high-toughness and heat-resistant fully biodegradable PLA shopping bag.

[0025] Preferably, in step S1, the temperature is raised to 60-80°C and dried for 4-6 hours to control the moisture content to be less than 0.01%.

[0026] Preferably, the temperature zones of the extruder in S2 are set as follows: Zone 1 160~170℃, Zone 2 170~180℃, Zone 3 185~195℃, Zone 4 190~200℃, Die opening 180~190℃, and Die head 195~205℃.

[0027] Preferably, in step S3, the blow molding machine inflates the material at 190~200℃ with an inflation ratio of 1.5~3, stretches it at 40~50℃ with an extension ratio of 35~45, and then anneals it at 80~90℃ for 4~6 hours.

[0028] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0029] 1. This invention improves the compatibility of montmorillonite with polylactic acid (PLA) by intercalating hexadecyltrimethylammonium bromide. Then, tetraethyl orthosilicate is hydrolyzed onto the surface of montmorillonite to form silica. The silicon-oxygen bonds in silica enhance the thermal stability of montmorillonite. The resulting heat-resistant nucleating agent provides nucleation sites for molten PLA polymers, promoting the orderly arrangement and nucleation of PLA. The acylhydrazine-based nucleating agent is uniformly dispersed in the molten PLA, lowering the nucleation barrier and inducing homogeneous nucleation. This invention, by mixing the heat-resistant nucleating agent and the acylhydrazine-based nucleating agent, creates a composite nucleating agent that forms fine crystal nuclei during PLA blow molding, promoting stable curing and shaping of PLA, and improving the mechanical uniformity and heat resistance of the resulting shopping bags.

[0030] 2. This invention produces a biodegradable elastomer by pre-crosslinking citric acid, succinic acid, and ethylene glycol, followed by crosslinking and polymerization with glycerol. The reaction of succinic acid and ethylene glycol forms long aliphatic flexible segments. Citric acid and glycerol introduce a three-dimensional crosslinking network, giving the elastomer rubber elasticity and allowing it to flow to a certain extent at processing temperatures. The resulting elastomer is dispersed in polylactic acid in an island structure, absorbing impact energy through deformation and preventing crack propagation. During blow molding, it helps stabilize the film bubble, improving the toughness and elasticity of the polylactic acid material.

[0031] 3. This invention introduces a composite nucleating agent into polylactic acid (PLA). Silica-modified montmorillonite provides stable nucleation sites, while hydrazide-based nucleating agents enhance nucleation efficiency. Together, they improve the crystallinity and crystallization rate of PLA. During PLA melting, fine crystal nuclei are formed, promoting stable solidification and shaping of PLA, thus improving the mechanical uniformity and heat resistance of the resulting shopping bags. The biodegradable elastomer, obtained by bio-based molecular polymerization, is dispersed in PLA in an island-like structure. It effectively disperses stress through deformation, preventing crack propagation and improving the toughness and elasticity of PLA materials. During blow molding, it prevents PLA from easily breaking due to stretching, ensuring that the resulting shopping bags retain practical toughness and heat resistance close to traditional plastic bags even when packaging high-temperature food. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The polylactic acid resin involved in this invention is of type 4032D.

[0034] Example 1: A high-toughness, heat-resistant, fully biodegradable PLA shopping bag, comprising the following raw materials: 100 kg of polylactic acid resin, 5 kg of biodegradable elastomer, 0.5 kg of composite nucleating agent, 1 kg of antioxidant and 1 kg of lubricant.

[0035] The antioxidant is prepared by mixing antioxidant 1010 and antioxidant 168 in a mass ratio of 1:2;

[0036] The lubricant is prepared by mixing calcium stearate and ethylene bis-stearamide in a mass ratio of 3:1.

[0037] The preparation method of the composite nucleating agent in this embodiment includes the following steps:

[0038] S11. Add 1 kg of montmorillonite and 10 kg of deionized water to a homogenizer and stir at 3000 rpm for 30 min at 70 °C. Let it stand and separate into layers. Take 1 kg of the upper clear liquid, add 25 g of sodium carbonate, and then add 10 g of hexadecyltrimethylammonium bromide. Heat to 75 °C and react for 2 h to modify the mixture. Filter the mixture and wash the resulting filter cake with deionized water. Dry it under vacuum at 90 °C and grind it through a 200 mesh sieve to obtain modified montmorillonite.

[0039] S12. Add 80g of modified montmorillonite to 1000g of deionized water, add 10g of tetraethyl orthosilicate, add 8g of triethanolamine dropwise, heat to 70℃ and stir at 200rpm for 1h to hydrolyze, filter to collect solid, wash with deionized water, dry at 60℃, and calcine at 550℃ for 2h at a heating rate of 8℃ to obtain heat-resistant nucleating agent.

[0040] S13. A composite nucleating agent is prepared by mixing 100g of heat-resistant nucleating agent and 500g of TMC-300 hydrazide-based nucleating agent.

[0041] The method for preparing the biodegradable elastomer in this embodiment includes the following steps:

[0042] S21. Add 6 kg of citric acid, 4 kg of succinic acid and 3 kg of ethylene glycol to a reaction vessel, heat to 140°C and stir at 200 rpm for 20 min, then heat to 170°C under a nitrogen atmosphere and react for 1 h to obtain prepolymer 1.

[0043] S22. Add 1 kg of glycerol to 8 kg of prepolymer 1, heat to 175 °C in a nitrogen atmosphere for 1 h for crosslinking, vacuum degree less than 0.1 MPa, heat to 200 °C for condensation for 4 h, and cool to room temperature to obtain a biodegradable elastomer.

[0044] The preparation method of a high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to this embodiment includes the following steps:

[0045] S1. Heat the raw material to 60℃ under vacuum and dry for 4 hours. After controlling the moisture content to be less than 0.01%, seal and store for later use.

[0046] S2. Polylactic acid resin, biodegradable elastomer, composite nucleating agent, antioxidant and lubricant are mixed to prepare a mixture. The mixture is added to an extruder for melt extrusion. The temperature zones of the extruder are set as follows: Zone 1 160℃, Zone 2 170℃, Zone 3 185℃, Zone 4 190℃, Die 180℃, Die head 195℃. The mixture is then pelletized and cooled to obtain high-toughness heat-resistant masterbatch.

[0047] S3. Add the high-toughness and heat-resistant masterbatch to a blow molding machine and blow it into a film at 190°C with a blow-up ratio of 1.5. Stretch it at 40°C with a stretch ratio of 35. Place it in an oven and heat it to 80°C for annealing for 4 hours. After cooling, cool and wind it up using traction rollers, heat seal it, and cut and package it to obtain a high-toughness, heat-resistant, fully biodegradable PLA shopping bag.

[0048] Example 2: A high-toughness, heat-resistant, fully biodegradable PLA shopping bag, comprising the following raw materials: 100 kg of polylactic acid resin, 6 kg of biodegradable elastomer, 0.8 kg of composite nucleating agent, 0.5 kg of antioxidant and 0.5 kg of lubricant;

[0049] The antioxidant is prepared by mixing antioxidant 1010 and antioxidant 1076 in a mass ratio of 1:1;

[0050] The lubricant is prepared by mixing calcium stearate and palm wax in a mass ratio of 1:1;

[0051] The preparation method of the composite nucleating agent in this embodiment includes the following steps:

[0052] S11. Add 1.5 kg of montmorillonite and 10 kg of deionized water to a homogenizer and stir at 3500 rpm for 25 min at 75 °C. Let it stand and separate into layers. Take 1 kg of the upper clear liquid, add 22 g of sodium carbonate, and then add 15 g of hexadecyltrimethylammonium bromide. Heat to 80 °C and react for 3 h to modify the mixture. Filter the mixture and wash the resulting filter cake with deionized water. Dry it under vacuum at 80 °C and grind it through a 200 mesh sieve to obtain modified montmorillonite.

[0053] S12. Add 85g of modified montmorillonite to 1100g of deionized water, add 15g of tetraethyl orthosilicate, add 9g of triethanolamine dropwise, heat to 75℃ and stir at 250rpm for 1.5h to hydrolyze, filter to collect solid, wash with deionized water, dry at 60℃, and calcine at 560℃ for 2.5h at a heating rate of 9℃ to obtain heat-resistant nucleating agent;

[0054] S13. A composite nucleating agent is prepared by mixing 150g of heat-resistant nucleating agent and 350g of TMC-300 hydrazide-based nucleating agent.

[0055] The method for preparing the biodegradable elastomer in this embodiment includes the following steps:

[0056] S21. Add 6 kg of citric acid, 4 kg of succinic acid and 3.5 kg of ethylene glycol to a reaction vessel, heat to 145°C and stir at 250 rpm for 30 min. Then, heat to 175°C under a nitrogen atmosphere and react for 1 h to obtain prepolymer 1.

[0057] S22. Add 1.1 kg of glycerol to 8.5 kg of prepolymer 1, heat to 180 °C for 1 h in a nitrogen atmosphere, crosslink for 1 h, vacuum degree less than 0.1 MPa, heat to 210 °C for 5 h for condensation, and cool to room temperature to obtain a biodegradable elastomer.

[0058] The preparation method of a high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to this embodiment includes the following steps:

[0059] S1. Heat the raw material to 70℃ under vacuum and dry for 4 hours. After controlling the moisture content to be less than 0.01%, seal and store for later use.

[0060] S2. Polylactic acid resin, biodegradable elastomer, composite nucleating agent, antioxidant and lubricant are mixed to prepare a mixture. The mixture is added to an extruder for melt extrusion. The temperature zones of the extruder are set as follows: Zone 1 165℃, Zone 2 175℃, Zone 3 185℃, Zone 4 195℃, Die 185℃, Die head 200℃. The mixture is then pelletized and cooled to obtain high-toughness heat-resistant masterbatch.

[0061] S3. Add the high-toughness and heat-resistant masterbatch to a blow molding machine and blow it into a film at 190°C with a blow-up ratio of 1.8. Stretch it at 50°C with a stretch ratio of 40. Place it in an oven and heat it to 80°C for annealing for 6 hours. After cooling, cool and wind it up using traction rollers, heat seal it, and cut and package it to obtain a high-toughness, heat-resistant, fully biodegradable PLA shopping bag.

[0062] Example 3: A high-toughness, heat-resistant, fully biodegradable PLA shopping bag, comprising the following raw materials: 100 kg of polylactic acid resin, 7 kg of biodegradable elastomer, 1 kg of composite nucleating agent, 1 kg of antioxidant and 2 kg of lubricant.

[0063] The antioxidant is prepared by mixing antioxidant 168 and antioxidant 1076 in a mass ratio of 1:1;

[0064] The lubricant is ethylene bis-stearamide;

[0065] The preparation method of the composite nucleating agent in this embodiment includes the following steps:

[0066] S11. Add 2 kg of montmorillonite and 10 kg of deionized water to a homogenizer and stir at 4000 rpm for 30 min at 80 °C. Let it stand and separate into layers. Take 1 kg of the upper clear liquid, add 23 g of sodium carbonate, and then add 20 g of hexadecyltrimethylammonium bromide. Heat to 85 °C and react for 3 h to modify the mixture. Filter the mixture and wash the resulting filter cake with deionized water. Dry it under vacuum at 90 °C and grind it through a 250 mesh sieve to obtain modified montmorillonite.

[0067] S12. Add 100g of modified montmorillonite to 1500g of deionized water, add 30g of tetraethyl orthosilicate, add 10g of triethanolamine dropwise, heat to 80℃ and stir at 300rpm for 2h to hydrolyze, filter to collect solid, wash with deionized water, dry at 60℃, and calcine at 560℃ for 4h at a heating rate of 8℃ to obtain heat-resistant nucleating agent.

[0068] S13. A composite nucleating agent is prepared by mixing 200g of heat-resistant nucleating agent and 500g of TMC-306 hydrazide-based nucleating agent.

[0069] The method for preparing the biodegradable elastomer in this embodiment includes the following steps:

[0070] S21. Add 6.5 kg of citric acid, 3 kg of succinic acid and 3.8 kg of ethylene glycol to a reaction vessel, heat to 150°C and stir at 300 rpm for 30 min. Then, heat to 175°C under a nitrogen atmosphere and react for 1-2 h to obtain prepolymer 1.

[0071] S22. Add 1.3 kg of glycerol to 9.5 kg of prepolymer 1, heat to 180 °C in a nitrogen atmosphere for 1 h for crosslinking, vacuum degree less than 0.1 MPa, heat to 220 °C for condensation for 6 h, and cool to room temperature to obtain a biodegradable elastomer.

[0072] The preparation method of a high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to this embodiment includes the following steps:

[0073] S1. Heat the raw material to 80℃ under vacuum and dry for 4 hours. After controlling the moisture content to be less than 0.01%, seal and store for later use.

[0074] S2. Polylactic acid resin, biodegradable elastomer, composite nucleating agent, antioxidant and lubricant are mixed to prepare a mixture. The mixture is added to an extruder for melt extrusion. The temperature zones of the extruder are set as follows: Zone 1 170℃, Zone 2 180℃, Zone 3 185℃, Zone 4 200℃, Die 190℃, Die head 205℃. The mixture is then pelletized and cooled to obtain high-toughness heat-resistant masterbatch.

[0075] S3. Add the high-toughness and heat-resistant masterbatch to a blow molding machine and blow it into a film at 195°C with a blow-in ratio of 2. Stretch it at 50°C with a stretch ratio of 45. Place it in an oven and heat it to 90°C for annealing for 6 hours. After cooling, cool and wind it up using traction rollers, heat seal it, and cut and package it to obtain a high-toughness, heat-resistant, fully biodegradable PLA shopping bag.

[0076] Example 4: A high-toughness, heat-resistant, fully biodegradable PLA shopping bag, comprising the following raw materials: 100 kg of polylactic acid resin, 5 kg of biodegradable elastomer, 1.5 kg of composite nucleating agent, 2 kg of antioxidant and 2 kg of lubricant.

[0077] The antioxidant is antioxidant 1010;

[0078] The lubricant is prepared by mixing calcium stearate, ethylene bis-stearamide and carnauba wax in a mass ratio of 1:1:2.

[0079] The preparation method of the composite nucleating agent in this embodiment includes the following steps:

[0080] S11. Add 3 kg of montmorillonite and 10 kg of deionized water to a homogenizer and stir at 3500 rpm for 30 min at 80 °C. Let it stand and separate into layers. Take 1 kg of the upper clear liquid, add 20 g of sodium carbonate, and then add 20 g of hexadecyltrimethylammonium bromide. Heat to 85 °C and react for 3 h to modify the mixture. Filter the mixture and wash the resulting filter cake with deionized water. Dry it under vacuum at 90 °C and grind it through a 300 mesh sieve to obtain modified montmorillonite.

[0081] S12. Add 100g of modified montmorillonite to 1000g of deionized water, add 20g of tetraethyl orthosilicate, add 9.5g of triethanolamine dropwise, heat to 80℃ and stir at 300rpm for 1.5h to hydrolyze, filter to collect solid, wash with deionized water, dry at 60℃, and calcine at 560℃ for 4h at a heating rate of 9.5℃ to obtain heat-resistant nucleating agent.

[0082] S13. A composite nucleating agent is prepared by mixing 150g of heat-resistant nucleating agent and 450g of TMC-306 hydrazide-based nucleating agent.

[0083] The method for preparing the biodegradable elastomer in this embodiment includes the following steps:

[0084] S21. Add 7 kg of citric acid, 4 kg of succinic acid and 4 kg of ethylene glycol to a reaction vessel, heat to 150°C and stir at 200 rpm for 25 min, then heat to 175°C under a nitrogen atmosphere and react for 1.5 h to obtain prepolymer 1.

[0085] S22. Add 1.5 kg of glycerol to 10 kg of prepolymer 1, heat to 180 °C for 2 h in a nitrogen atmosphere for crosslinking, vacuum degree less than 0.1 MPa, heat to 220 °C for condensation for 4 h, and cool to room temperature to obtain a biodegradable elastomer.

[0086] The preparation method of a high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to this embodiment includes the following steps:

[0087] S1. Heat the raw material to 70℃ under vacuum and dry for 6 hours. After controlling the moisture content to be less than 0.01%, seal and store for later use.

[0088] S2. Polylactic acid resin, biodegradable elastomer, composite nucleating agent, antioxidant and lubricant are mixed to prepare a mixture. The mixture is added to an extruder for melt extrusion. The temperature zones of the extruder are set as follows: Zone 1 170℃, Zone 2 180℃, Zone 3 185℃, Zone 4 190℃, Die 190℃, Die head 195℃. The mixture is then pelletized and cooled to obtain high-toughness heat-resistant masterbatch.

[0089] S3. Add the high-toughness and heat-resistant masterbatch to a blow molding machine and blow it into a film at 200°C with a blow-up ratio of 2.5. Stretch it at 40°C with a stretch ratio of 35. Place it in an oven and heat it to 90°C for annealing for 4 hours. After cooling, cool and wind it up using traction rollers, heat seal it, and cut and package it to obtain a high-toughness, heat-resistant, fully biodegradable PLA shopping bag.

[0090] Example 5: A high-toughness, heat-resistant, fully biodegradable PLA shopping bag, comprising the following raw materials: 100 kg of polylactic acid resin, 10 kg of biodegradable elastomer, 0.5 kg of composite nucleating agent, 0.5 kg of antioxidant and 1.5 kg of lubricant;

[0091] The antioxidant is antioxidant 1076;

[0092] The lubricant is prepared by mixing calcium stearate and ethylene bis-stearamide in a mass ratio of 1:1.

[0093] The preparation method of the composite nucleating agent in this embodiment includes the following steps:

[0094] S11. Add 2.5 kg of montmorillonite and 10 kg of deionized water to a homogenizer and stir at 4000 rpm for 30 min at 75 °C. Let it stand and separate into layers. Take 1 kg of the upper clear liquid, add 25 g of sodium carbonate, and then add 30 g of hexadecyltrimethylammonium bromide. Heat to 85 °C and react for 3 h to modify the mixture. Filter the mixture and wash the resulting filter cake with deionized water. Dry it under vacuum at 80 °C and grind it through a 300 mesh sieve to obtain modified montmorillonite.

[0095] S12. Add 90g of modified montmorillonite to 1300g of deionized water, add 25g of tetraethyl orthosilicate, add 10g of triethanolamine dropwise, heat to 80℃ and stir at 200rpm for 2h to hydrolyze, filter to collect solid, wash with deionized water, dry at 60℃, and calcine at 550℃ for 2h at a heating rate of 10℃ to obtain heat-resistant nucleating agent.

[0096] S13. A composite nucleating agent is prepared by mixing 200g of heat-resistant nucleating agent and 300g of TMC-300 hydrazide-based nucleating agent.

[0097] The method for preparing the biodegradable elastomer in this embodiment includes the following steps:

[0098] S21. Add 6.5 kg of citric acid, 4.5 kg of succinic acid and 3.8 kg of ethylene glycol to a reaction vessel, heat to 150°C and stir at 200 rpm for 30 min. Then, heat to 170°C under a nitrogen atmosphere and react for 2 h to obtain prepolymer 1.

[0099] S22. Add 1.3 kg of glycerol to 10 kg of prepolymer 1, heat to 180 °C in a nitrogen atmosphere for 1.5 h for crosslinking, vacuum degree less than 0.1 MPa, heat to 210 °C for condensation for 4 h, and cool to room temperature to obtain a biodegradable elastomer.

[0100] The preparation method of a high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to this embodiment includes the following steps:

[0101] S1. Heat the raw material to 60℃ under vacuum and dry for 6 hours. After controlling the moisture content to be less than 0.01%, seal and store for later use.

[0102] S2. Polylactic acid resin, biodegradable elastomer, composite nucleating agent, antioxidant and lubricant are mixed to prepare a mixture. The mixture is added to an extruder for melt extrusion. The temperature zones of the extruder are set as follows: Zone 1 160℃, Zone 2 175℃, Zone 3 185℃, Zone 4 195℃, Die 190℃, Die head 200℃. The mixture is then pelletized and cooled to obtain high-toughness heat-resistant masterbatch.

[0103] S3. Add the high-toughness and heat-resistant masterbatch to a blow molding machine and blow it into a film at 200°C with a blow-up ratio of 2.8. Stretch it at 50°C with a stretch ratio of 40. Place it in an oven and heat it to 90°C for annealing for 6 hours. After cooling, cool and wind it up using traction rollers, heat seal it, and cut and package it to obtain a high-toughness, heat-resistant, fully biodegradable PLA shopping bag.

[0104] Comparative Example 1 differs from Example 1 in that the heat-resistant nucleating agent is replaced with talc powder with an average particle size of 10 μm.

[0105] Comparative Example 2 differs from Example 1 in that the annealing process is omitted in step S3 of the shopping bag preparation, and the blown film is directly cooled and wound after stretching.

[0106] Comparative Example 3 differs from Example 1 in that it does not contain biodegradable elastomer.

[0107] Performance testing

[0108] The tensile strength and elongation at break of the shopping bags prepared in each example and comparative example were measured according to GB / T 1040.1-2025 "Determination of tensile properties of plastics - Part 1: General". The shopping bags were aged at 50°C for 168 hours, and the tensile strength and elongation at break of the shopping bags after heat aging were measured.

[0109] The biodegradability of the shopping bags prepared in each embodiment and comparative example was measured using the composting degradation method:

[0110] The shopping bags prepared in each embodiment and comparative example were cut into sizes of 3cm × 4cm to obtain test samples.

[0111] The compost substrate is prepared from the following components: 1 kg of mature compost, 1 kg of starch, 0.5 kg of sucrose, 0.4 kg of corn oil, 0.1 kg of urea, 3 kg of alfalfa-based rabbit feed, and 4 kg of sawdust.

[0112] After mixing all components thoroughly, deionized water was added to control the moisture content at 55 wt% to obtain the compost substrate. 1 kg of the compost substrate and 20 g of the test sample were added to a composting container and degraded for 14 days in a ventilated environment at 58°C and 60% relative humidity. Large, undisintegrated residues larger than 2 mm were sieved out, and the mass of the undisintegrated residues was weighed. The degree of disintegration of the test samples from each example and comparative example was determined. The formula for calculating the degree of disintegration is shown below:

[0113]

[0114] D represents the degree of disintegration;

[0115] m0 is the initial mass of the test sample, in grams;

[0116] m1 is the undisintegrated mass of the test sample, in grams;

[0117] The test results are shown below:

[0118] Table 1 Test Results

[0119]

[0120] As shown in Table 1, the shopping bags prepared in Examples 1-5 have a tensile strength of 44.3-46.8 MPa and an elongation at break of 70.6-71.5%. After 168 hours of heat aging, the tensile strength is 38.3-39 MPa and the elongation at break is 56.9-57.8%. In Comparative Example 1, the heat-resistant nucleating agent was replaced with talc powder with an average particle size of 10 μm. Its tensile strength was 41.6 MPa and the elongation at break was 68.4%. After 168 hours of heat aging, the tensile strength was 28.1 MPa and the elongation at break was 53.6%. This indicates that the nucleation efficiency of talc powder and... The heat aging resistance is lower than that of heat-resistant nucleating agents, further demonstrating that the shopping bags prepared by the present invention have excellent toughness and heat aging resistance. The disintegration degree of the shopping bags prepared in Examples 1 to 5 is 95.2% to 96.4%. Although the biodisintegration degree of Comparative Example 3, which does not contain biodegradable elastomer, is 98.3%, its elongation at break is only 29%. This shows that the biodegradable elastomer has the function of enhancing the toughness of the shopping bag while having biodegradability. This shows that the shopping bags prepared by the present invention have excellent biodegradability while ensuring that their toughness matches that of traditional shopping bags.

[0121] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0122] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-toughness, heat-resistant, fully biodegradable PLA shopping bag, characterized in that, The raw materials include the following parts by weight: 100 parts polylactic acid resin, 5-10 parts biodegradable elastomer, 0.5-1.5 parts composite nucleating agent, 0.5-2 parts antioxidant and 0.5-2 parts lubricant.

2. The high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to claim 1, characterized in that, The antioxidant is one or more of antioxidant 1010, antioxidant 168, and antioxidant 1076; the lubricant is one or more of calcium stearate, ethylene bis-stearamide, and palm wax.

3. The high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to claim 1, characterized in that, The preparation method of the composite nucleating agent includes the following steps: S11. Add montmorillonite and deionized water to a homogenizer and stir. Let it stand to separate into layers. Take the upper clear liquid, add sodium carbonate, then add hexadecyltrimethylammonium bromide and heat to modify. Filter by suction. Wash the obtained filter cake with deionized water, vacuum dry, grind and sieve to obtain modified montmorillonite. S12. Modified montmorillonite was added to deionized water, tetraethyl orthosilicate was added, triethanolamine was added dropwise, the mixture was heated and stirred to hydrolyze, the solid was collected by filtration, washed with deionized water, dried, and calcined to obtain a heat-resistant nucleating agent. S13. A composite nucleating agent is prepared by mixing a heat-resistant nucleating agent and an acylhydrazine-based nucleating agent.

4. The high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to claim 3, characterized in that, The mass ratio of montmorillonite to deionized water in S11 is 1~3:

10. The mixture is stirred at 3000~4000 rpm for 20~30 min at 70~80℃. The mass ratio of the supernatant, sodium carbonate, and hexadecyltrimethylammonium bromide is 100:2~2.5:0.5~2. The mixture is reacted at 75~85℃ for 2~4 h, dried under vacuum at 80~90℃, and passed through a 200~300 mesh sieve.

5. A high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to claim 3, characterized in that, In S12, the mass ratio of modified montmorillonite, tetraethyl orthosilicate, deionized water, and triethanolamine is 8~10:1~3:100~150:0.8~1. The mixture is heated to 70~80℃ and stirred at 200~300 rpm for 1~2 hours, dried at 50~60℃, and calcined at 550~570℃ for 2~4 hours at a heating rate of 8~10℃. In S13, the acylhydrazine nucleating agent is one or both of TMC-300 and TMC-306, and the mass ratio of the heat-resistant nucleating agent to the acylhydrazine nucleating agent is 1~2:3~5.

6. The high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to claim 1, characterized in that, The method for preparing the biodegradable elastomer includes the following steps: S21. Citric acid, succinic acid and ethylene glycol are added to a reaction vessel, heated and stirred to mix, and reacted under a nitrogen atmosphere to obtain prepolymer 1. S22. Glycerol is added to prepolymer 1, and the mixture is crosslinked under a nitrogen atmosphere, vacuum polycondensed, and cooled to room temperature to obtain a biodegradable elastomer.

7. A high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to claim 6, characterized in that, In S21, the mass ratio of citric acid, succinic acid, and ethylene glycol is 30-35:20-25:15-20. The mixture is heated to 140-150℃ and stirred at 200-300 rpm for 20-30 minutes, then heated to 170-175℃ and reacted for 1-2 hours. In S22, the mass ratio of prepolymer 1 and glycerol is 8-10:1-1.

5. After adding glycerol, the mixture is crosslinked at 175-180℃ for 1-2 hours, with a vacuum degree of less than 0.1 MPa, and then heated to 200-220℃ for condensation polymerization for 4-6 hours.

8. A method for preparing a high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to any one of claims 1-7, characterized in that, Includes the following steps: S1. After heating and vacuum drying the raw material to remove moisture, seal it for later use; S2. A mixture of polylactic acid resin, biodegradable elastomer, composite nucleating agent, antioxidant and lubricant is prepared. The mixture is added to an extruder for melt extrusion, pelletized and cooled to obtain high toughness and heat-resistant masterbatch. S3. Add the high-toughness and heat-resistant masterbatch to a blow molding machine to inflate it into a film, stretch it, put it into an oven for heating and annealing, cool it, and then cool and wind it up through a traction roller, heat seal it, cut and package it to obtain a high-toughness and heat-resistant fully biodegradable PLA shopping bag.

9. The method for preparing a high-toughness, heat-resistant, fully biodegradable PLA shopping bag according to claim 8, characterized in that, In step S1, the temperature is raised to 60-80℃ and dried for 4-6 hours, controlling the moisture content to be less than 0.01%. In step S2, the temperature zones of the extruder are set as follows: Zone 1 160-170℃, Zone 2 170-180℃, Zone 3 185-195℃, Zone 4 190-200℃, Die opening 180-190℃, and Die head 195-205℃. In step S3, the blow molding machine inflates at 190-200℃ with an inflation ratio of 1.5-3, stretches at 40-50℃ with a stretching ratio of 35-45, and anneals at 80-90℃ for 4-6 hours.

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