A biodegradable high-temperature-resistant food packaging box and a preparation method thereof

Abstract

The application provides a biodegradable high-temperature-resistant food packaging box and a preparation method thereof, and relates to the technical field of packaging boxes.The biodegradable high-temperature-resistant food packaging box comprises the following materials by weight: 60-80 parts of polylactic acid, 15-30 parts of polyhydroxybutyric acid valerate, 3-8 parts of a composite heat-resistant nucleating agent, 1-3 parts of a chain extender, and 0.5-1.5 parts of a lubricant; wherein the composite heat-resistant nucleating agent is a hybrid material of an amino silane modified halloysite nanotube surface in-situ grafted phytic acid-zinc coordination polymer.The application aims to provide a novel biodegradable high-temperature-resistant food packaging box to solve the problems of slow crystallization rate, poor heat resistance and difficulty in meeting the hot food serving requirement of the existing polylactic acid packaging box.

Description

Technical Field

[0001] This invention relates to the field of packaging box technology, specifically to a biodegradable, high-temperature resistant food packaging box and its preparation method. Background Technology

[0002] Polylactic acid (PLA), a biodegradable plastic derived from renewable plant resources, possesses excellent biocompatibility and mechanical strength, along with low carbon emissions, making it an ideal material to replace traditional single-use petroleum-based food packaging. However, pure PLA has several fatal weaknesses in practical applications: First, its molecular chain flexibility is poor, and its crystallization rate is extremely slow. After injection molding, it is usually in an amorphous state with low crystallinity, resulting in a heat distortion temperature of only around 55℃-60℃. This makes it unsuitable for direct microwave heating or for holding hot soup, hot rice, or other foods with temperatures exceeding 70℃, greatly limiting its application in the field of single-use hot food packaging.

[0003] To improve the heat resistance of PLA, industrial manufacturers often use nucleating agents (such as talc, carbon nanotubes, etc.) to promote its crystallization. However, traditional inorganic nucleating agents have poor compatibility with the PLA matrix, easily agglomerating and dispersing unevenly during melt processing, resulting in low nucleation efficiency and difficulty in imparting excellent high-temperature resistance to PLA within a short injection molding cycle. Furthermore, in actual production, the cooling cycle within existing injection molds often lasts several minutes while waiting for PLA to crystallize, leading to extremely low production efficiency. Moreover, blindly pursuing high crystallinity to improve heat resistance further exacerbates the inherent brittleness of PLA, making packaging boxes prone to cracking and damage during rapid, forceful demolding or logistics transportation.

[0004] Therefore, developing a nucleating agent with high nucleation efficiency and uniform dispersion in the matrix, which can shorten the injection molding cycle, significantly increase the heat distortion temperature of PLA, and simultaneously maintain the flexibility and impact resistance of the composite material, is a pressing technical challenge in the field of biodegradable food packaging. Based on this, this invention provides a biodegradable, high-temperature resistant food packaging box and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a biodegradable, high-temperature resistant food packaging box and its preparation method, aiming to solve the problem that existing pure polylactic acid (PLA) has an extremely slow crystallization rate and low crystallinity, resulting in a low heat distortion temperature and making it unsuitable for holding high-temperature foods; at the same time, it solves the technical problems of traditional inorganic nucleating agents being prone to agglomeration and having low nucleation efficiency, as well as the long molding cycle, difficult demolding, and high brittleness and easy breakage of highly crystalline PLA products in actual injection molding production.

[0006] On one hand, the present invention provides a biodegradable high-temperature resistant food packaging box, comprising the following materials in parts by weight: 60-80 parts of polylactic acid; 15-30 parts of polyhydroxybutyrate valerate; 3-8 parts of composite heat-resistant nucleating agent; 1-3 parts of chain extender; and 0.5-1.5 parts of lubricant; wherein the composite heat-resistant nucleating agent is a hybrid material of aminosilane-modified halloysite nanotubes in situ grafted with phytic acid-zinc coordination polymer.

[0007] Furthermore, the preparation method of the composite heat-resistant nucleating agent includes: dispersing aminated halloysite nanotubes obtained by treating halloysite nanotubes with silane coupling agent in deionized water, adding phytic acid solution and zinc sulfate solution in sequence, adjusting the pH to 4.5-5.5, stirring and reacting in situ at room temperature for 4-6 hours, centrifuging, washing with deionized water, and freeze-drying to obtain the composite heat-resistant nucleating agent.

[0008] Furthermore, the preparation method of the aminated halloysite nanotubes includes: dispersing halloysite nanotubes in deionized water, ultrasonically treating them, adding aminopropyltriethoxysilane, refluxing at 70-80℃ for 6-8 hours, centrifuging, washing and drying to obtain aminated halloysite nanotubes.

[0009] Furthermore, the mass ratio of halloysite nanotubes, deionized water, and aminopropyltriethoxysilane is (4-6):(200-300):1.

[0010] Furthermore, the halloysite nanotubes have an inner diameter of 15-25 nm, an outer diameter of 40-50 nm, and a length of 0.5-1.5 μm.

[0011] Furthermore, the mass ratio of the aminated halloysite nanotubes, phytic acid, and zinc sulfate is 10:(2-4):(1-2).

[0012] Furthermore, the polylactic acid melt mass flow rate is 80 g / 10 min, and the test conditions are 210 °C.

[0013] Furthermore, the chain extender is epoxidized soybean oil.

[0014] Furthermore, the lubricant is ethylene bis-stearamide or pentaerythritol stearate.

[0015] On the other hand, the present invention also provides a method for preparing a biodegradable, high-temperature resistant food packaging box, the steps of which include:

[0016] S1. After drying polylactic acid and polyhydroxybutyrate valerate in a vacuum oven to remove moisture, they are mixed evenly with composite heat-resistant nucleating agent, chain extender and lubricant, and fed into a twin-screw extruder. The mixture is then melt-blended, extruded and pelletized at 160℃-190℃ to obtain packaging box substrate particles.

[0017] S2. Add the substrate particles obtained in step S1 into the injection molding machine, inject them into the mold at a barrel temperature of 170℃-195℃, maintain the mold temperature at 90℃-110℃, and maintain constant temperature and pressure for crystallization for 1-2 minutes to promote high crystallization of polylactic acid. Open the mold to obtain the packaging box.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention is the first to utilize aminosilane-modified halloysite nanotubes grafted with phytate-zinc coordination polymers as a composite heat-resistant nucleating agent. The unique hollow tubular structure of halloysite nanotubes provides an extremely large specific surface area, and the phytate-zinc coordination network on the surface forms numerous hydrogen bonds and coordination bonds with active sites, enabling strong interfacial interactions with the PLA matrix. This organic-inorganic hybrid structure significantly reduces the nucleation free energy, resulting in excellent heterogeneous nucleation and promoting the rapid formation of a complete crystal structure in PLA during injection molding cooling. This significantly increases the heat distortion temperature of the packaging box (up to 110°C or higher), meeting the stringent requirements for microwave heating and holding hot soup.

[0020] The composite nucleating agent in this invention completely breaks through the bottleneck of the extremely slow crystallization rate of pure PLA, enabling the substrate particles to achieve rapid and high crystallization demolding with only 1-2 minutes of pressure crystallization at a mold temperature of 90℃-110℃, which greatly solves the problem of low production capacity caused by long cooling cycles in actual production.

[0021] This invention achieves a synergistic effect with PLA and a composite nucleating agent by adding polyhydroxybutyrate valerate (PHBV) and epoxidized soybean oil. PHBV itself has good crystallinity and degradability, while epoxidized soybean oil provides chain extension to repair thermal degradation chain breaks and also plays a certain role in plasticization, improving the inherent brittleness of highly crystalline PLA. This results in a packaging box that is both heat-resistant and has good flexibility and impact resistance. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0023] It should be noted that the polylactic acid (PLA) used in this invention is Ingeo, manufactured by NatureWorks, Inc. TM 3251D injection molding grade polylactic acid, with a melt flow rate of 80 g / 10 min (210℃).

[0024] The number-average molecular weight of polyhydroxybutyrate valerate (PHBV) is 4.0 × 10⁻⁶. 5 The HV content in polyhydroxybutyrate valerate was 3.0 mol%, purchased from Ningbo Tianan Biomaterials Co., Ltd.

[0025] Halloysite nanotubes (HNTs) were purchased from Sigma-Aldrich.

[0026] Epoxidized soybean oil (ESO) was purchased from Shandong Chuangli New Materials Co., Ltd., product number XYH-9875.

[0027] Ethylene bis-stearamide (EBS) is produced by Lonza AG, Switzerland, using Acrawax. TM Type C lubricant.

[0028] Example 1

[0029] This embodiment provides a biodegradable, high-temperature resistant food packaging box, comprising the following parts by weight of materials:

[0030] 70 parts of polylactic acid, melt flow rate of 20 g / 10 min (test conditions: 190℃); 22 parts of polyhydroxybutyrate valerate; 5 parts of composite heat-resistant nucleating agent; 2 parts of chain extender epoxidized soybean oil; 1 part of lubricant ethylene bis-stearamide.

[0031] The composite heat-resistant nucleating agent is a hybrid material in situ grafted with phytic acid-zinc coordination polymer on the surface of aminosilane-modified halloysite nanotubes. The specific preparation steps are as follows:

[0032] Raw material: Halloysite nanotubes (HNTs), inner diameter 20 nm, outer diameter 45 nm, length 1.0 μm;

[0033] 5 g halloysite nanotubes were dispersed in 250 mL of deionized water and sonicated for 30 min. 1 g of aminopropyltriethoxysilane (APTES) was added and refluxed at 75 °C for 7 h. After the reaction was completed, the mixture was centrifuged, washed three times with deionized water, and freeze-dried to obtain aminated halloysite nanotubes.

[0034] 10 g of the above-mentioned aminated halloysite nanotubes were dispersed in 200 mL of deionized water and ultrasonically dispersed for 30 min; 3 g of phytic acid and 1.5 g of zinc sulfate were added sequentially; the pH was adjusted to 5.0 with dilute acetic acid, and the reaction was stirred at room temperature (25℃) for 5 h; after the reaction was completed, the mixture was centrifuged, washed 3 times with deionized water, and freeze-dried for 24 h to obtain the composite heat-resistant nucleating agent.

[0035] The method for preparing the biodegradable, high-temperature resistant food packaging box in this embodiment includes the following steps:

[0036] S1. Dry polylactic acid and polyhydroxybutyrate valerate in a vacuum oven at 80℃ for 12 h to remove moisture; weigh 70 parts of dried polylactic acid, 22 parts of polyhydroxybutyrate valerate, 5 parts of composite heat-resistant nucleating agent, 2 parts of epoxidized soybean oil, and 1 part of ethylene bis-stearamide according to the formula, and put them into a high-speed mixer and mix for 5 min; add the mixture into a twin-screw extruder, and set the extruder barrel temperature sequentially as follows: 160℃ (feeding section), 170℃, 180℃, 190℃ (distillation head), and the screw speed is 200 rpm; after melt blending, extrude, water cool, and pelletize to obtain packaging box substrate particles with a particle length of 2-3 mm.

[0037] S2. Add the substrate particles obtained in step S1 into the hopper of the injection molding machine, and set the barrel temperature to: 170℃ (rear section), 185℃ (middle section), and 195℃ (front section); control the mold temperature at 100℃; the injection pressure is 80 MPa, the holding pressure is 60 MPa, and the constant temperature holding pressure crystallization time is 1.5 min to promote the full crystallization of polylactic acid; after opening the mold, take out the product to obtain the biodegradable high temperature resistant food packaging box.

[0038] Example 2

[0039] This embodiment provides a biodegradable, high-temperature resistant food packaging box, comprising the following parts by weight of materials:

[0040] 60 parts of polylactic acid, melt flow rate of 15 g / 10 min (test conditions: 190℃); 15 parts of polyhydroxybutyrate valerate; 3 parts of composite heat-resistant nucleating agent; 1 part of chain extender epoxidized soybean oil; 0.5 parts of lubricant ethylene bis-stearamide.

[0041] The composite heat-resistant nucleating agent is a hybrid material in situ grafted with phytic acid-zinc coordination polymer on the surface of aminosilane-modified halloysite nanotubes. The specific preparation steps are as follows:

[0042] Raw material: Halloysite nanotubes (HNTs), with an inner diameter of 15 nm, an outer diameter of 40 nm, and a length of 0.5 μm;

[0043] 4 g halloysite nanotubes were dispersed in 200 mL of deionized water and sonicated for 30 min. 1 g of aminopropyltriethoxysilane (APTES) was added and refluxed at 70 °C for 6 h. After the reaction was completed, the mixture was centrifuged, washed three times with deionized water, and freeze-dried to obtain aminated halloysite nanotubes.

[0044] 10 g of the above-mentioned aminated halloysite nanotubes were dispersed in 200 mL of deionized water and ultrasonically dispersed for 30 min; 2 g of phytic acid and 1 g of zinc sulfate were added sequentially; the pH was adjusted to 4.5 with dilute acetic acid, and the reaction was stirred at room temperature (25℃) for 4 h; after the reaction was completed, the mixture was centrifuged, washed 3 times with deionized water, and freeze-dried for 24 h to obtain the composite heat-resistant nucleating agent.

[0045] The method for preparing the biodegradable, high-temperature resistant food packaging box in this embodiment includes the following steps:

[0046] S1. Dry polylactic acid and polyhydroxybutyrate valerate in a vacuum oven at 80℃ for 12 h to remove moisture; weigh 60 parts of dried polylactic acid, 15 parts of polyhydroxybutyrate valerate, 3 parts of composite heat-resistant nucleating agent, 1 part of epoxidized soybean oil, and 0.5 parts of ethylene bis-stearamide according to the formula, and put them into a high-speed mixer and mix for 5 min; add the mixture into a twin-screw extruder, and set the extruder barrel temperature sequentially as follows: 160℃ (feeding section), 170℃, 180℃, 190℃ (die head), and the screw speed is 200 rpm; after melt blending, extrude, water cool, and pelletize to obtain packaging box substrate particles with a particle length of 2-3 mm.

[0047] S2. Add the substrate particles obtained in step S1 into the hopper of the injection molding machine, and set the barrel temperature to: 170℃ (rear section), 185℃ (middle section), and 195℃ (front section); control the mold temperature at 90℃; the injection pressure is 80 MPa, the holding pressure is 60 MPa, and the constant temperature holding pressure crystallization time is 1 min to promote the full crystallization of polylactic acid; after opening the mold, take out the product to obtain the biodegradable high temperature resistant food packaging box.

[0048] Example 3

[0049] This embodiment provides a biodegradable, high-temperature resistant food packaging box, comprising the following parts by weight of materials:

[0050] 80 parts of polylactic acid, melt flow rate of 25 g / 10 min (test conditions: 190℃); 30 parts of polyhydroxybutyrate valerate; 8 parts of composite heat-resistant nucleating agent; 3 parts of chain extender epoxidized soybean oil; 1.5 parts of lubricant ethylene bis-stearamide.

[0051] The composite heat-resistant nucleating agent is a hybrid material in situ grafted with phytic acid-zinc coordination polymer on the surface of aminosilane-modified halloysite nanotubes. The specific preparation steps are as follows:

[0052] Raw material: Halloysite nanotubes (HNTs), with an inner diameter of 25 nm, an outer diameter of 50 nm, and a length of 1.5 μm;

[0053] 6 g halloysite nanotubes were dispersed in 300 mL of deionized water and sonicated for 30 min. 1 g of aminopropyltriethoxysilane (APTES) was added and refluxed at 80 °C for 8 h. After the reaction was completed, the mixture was centrifuged, washed three times with deionized water, and freeze-dried to obtain aminated halloysite nanotubes.

[0054] 10 g of the above-mentioned aminated halloysite nanotubes were dispersed in 200 mL of deionized water and ultrasonically dispersed for 30 min; 4 g of phytic acid and 2 g of zinc sulfate were added sequentially; the pH was adjusted to 5.5 with dilute acetic acid and the reaction was stirred at room temperature (25℃) for 6 h; after the reaction was completed, the mixture was centrifuged, washed 3 times with deionized water, and freeze-dried for 24 h to obtain the composite heat-resistant nucleating agent.

[0055] The method for preparing the biodegradable, high-temperature resistant food packaging box in this embodiment includes the following steps:

[0056] S1. Dry polylactic acid and polyhydroxybutyrate valerate in a vacuum oven at 80℃ for 12 h to remove moisture; weigh 80 parts of dried polylactic acid, 30 parts of polyhydroxybutyrate valerate, 8 parts of composite heat-resistant nucleating agent, 3 parts of epoxidized soybean oil, and 1.5 parts of ethylene bis-stearamide according to the formula, and put them into a high-speed mixer and mix for 5 min; add the mixture into a twin-screw extruder, and set the extruder barrel temperature to 160℃ (feeding section), 170℃, 180℃, and 190℃ (distillation head) in sequence, and the screw speed to 200 rpm; after melt blending, extrude, water cool, and pelletize to obtain packaging box substrate particles with a particle length of 2-3 mm.

[0057] S2. Add the substrate particles obtained in step S1 into the hopper of the injection molding machine, and set the barrel temperature to: 170℃ (rear section), 185℃ (middle section), and 195℃ (front section); control the mold temperature at 110℃; the injection pressure is 80 MPa, the holding pressure is 60 MPa, and the constant temperature holding pressure crystallization time is 2 min to promote high crystallization of polylactic acid; after opening the mold, take out the product to obtain the biodegradable high temperature resistant food packaging box.

[0058] Comparative Example 1

[0059] The only difference from Example 1 is that no composite heat-resistant nucleating agent is added; the other components and preparation methods are exactly the same.

[0060] Specifically, the composition is: 70 parts polylactic acid, 22 parts polyhydroxybutyrate valerate, 2 parts epoxidized soybean oil, 1 part ethylene bis-stearamide, and 0 parts composite heat-resistant nucleating agent. The preparation method is the same as in Example 1.

[0061] In Comparative Example 1, due to the lack of nucleating agent, polylactic acid crystallization was insufficient, and the heat distortion temperature dropped significantly, failing to meet the high temperature resistance requirements.

[0062] Comparative Example 2

[0063] The only difference from Example 1 is that the composite heat-resistant nucleating agent is replaced with an equal amount (5 parts) of unmodified original halloysite nanotubes, while the other components and preparation methods are exactly the same.

[0064] In Comparative Example 2, the unmodified halloysite nanotubes lacked amino and phytic acid-zinc coordination polymers on their surface, resulting in poor compatibility with the polylactic acid matrix, uneven dispersion, low nucleation efficiency, limited improvement in heat resistance, and decreased mechanical properties.

[0065] Comparative Example 3

[0066] The only difference from Example 1 is that the composite heat-resistant nucleating agent uses only aminated halloysite nanotubes, that is, it does not carry out the in-situ coordination reaction of phytic acid and zinc sulfate, and the amount added is still 5 parts. The other components and preparation methods are exactly the same.

[0067] Comparative Example 3 lacks phytic acid-zinc coordination polymers, and the nucleating agent surface lacks a metal coordination network structure, resulting in a significant reduction in heterogeneous nucleation ability. At the same time, the hybrid material has insufficient thermal stability.

[0068] Comparative Example 4

[0069] The only difference from Example 1 is that the aminosilane modification step is omitted in the preparation of the composite heat-resistant nucleating agent, and the original halloysite nanotubes (without APTES treatment) are directly used for the in-situ coordination reaction of phytic acid and zinc sulfate. The other components and preparation methods are exactly the same.

[0070] Specific modification steps: 5 g of original halloysite nanotubes were dispersed in 250 mL of deionized water, sonicated for 30 min, and then 3 g of phytic acid and 1.5 g of zinc sulfate were added sequentially. The pH was adjusted to 5.0, and the reaction was stirred at room temperature for 5 h. After centrifugation, washing, and freeze-drying, the comparative nucleating agent was obtained.

[0071] Comparative Example 4 lacked aminosilane modification, resulting in a lack of amino active sites on the halloysite nanotube surface. Consequently, the phytic acid-zinc coordination polymer could not be effectively grafted onto the nanotube surface, only undergoing physical adsorption, leading to low and unstable grafting amounts. The nucleating agent exhibited poor dispersibility in the polylactic acid matrix, significantly reducing the heterogeneous nucleation effect.

[0072] Comparative Example 5

[0073] The only difference from Example 1 is that in the preparation of aminopropyltriethoxysilane nanotubes, aminopropyltriethoxysilane (APTES) is replaced with an equal amount of γ-methacryloyloxypropyltrimethoxysilane (KH570), while the other steps and components are exactly the same.

[0074] Specific modification steps: 5 g halloysite nanotubes were dispersed in 250 mL of deionized water, 1 g KH570 was added, and the mixture was refluxed at 75 °C for 7 h to obtain KH570 modified halloysite nanotubes; phytic acid-zinc grafting was then performed as in Example 1.

[0075] The silane coupling agent KH570 used in Comparative Example 5 does not contain amino groups and cannot provide electrostatic adsorption or chemical bonding sites for subsequent phytic acid, resulting in low and uneven grafting efficiency of the phytic acid-zinc coordination polymer. Furthermore, the methacryloyloxy group introduced by KH570 is not reactive with phytic acid, leading to an incomplete hybrid material structure, reduced nucleation efficiency, and limited improvement in heat resistance.

[0076] Comparative Example 6

[0077] The only difference from Example 1 is that zinc sulfate is replaced with calcium sulfate in the preparation of the composite heat-resistant nucleating agent, while the other steps and components are exactly the same.

[0078] Specific modification steps: Disperse 10 g of aminated halloysite nanotubes in 200 mL of deionized water, add 3 g of phytic acid and 1.2 g of calcium sulfate (CaSO4·2H2O) in 22 batches, adjust the pH to 5.0, stir the reaction at room temperature for 5 h, centrifuge, wash and freeze dry.

[0079] Different metal ions exhibit varying coordination abilities, coordination structures, and thermal stability with phytic acid. Zinc ions possess a moderate coordination constant and good Lewis acidity, enabling them to form stable coordination networks. In Comparative Example 6, the coordination polymer structure of calcium ions is loose, exhibiting poor thermal stability and prone to decomposition during melt processing, resulting in a weakened heterogeneous nucleation ability of the nucleating agent.

[0080] Comparative Example 7

[0081] The only difference from Example 1 is that the composite heat-resistant nucleating agent is prepared by physical blending rather than in-situ grafting. That is, aminated halloysite nanotubes and phytic acid-zinc coordination polymer precipitates are prepared separately, and then the two are simply mechanically mixed. The remaining components and preparation methods are exactly the same.

[0082] Specific modification steps:

[0083] Aminated halloysite nanotubes were prepared according to the method in Example 1; phytic acid aqueous solution and zinc sulfate aqueous solution were prepared separately, mixed and the pH was adjusted to 5.0, stirred for 5 h, and centrifuged to obtain phytic acid-zinc coordination polymer precipitate; 10 g of aminated halloysite nanotubes and 3 g (calculated based on phytic acid) of phytic acid-zinc coordination polymer precipitate were physically ground and mixed in a mortar for 30 min to obtain a comparative nucleating agent.

[0084] In Comparative Example 7, the physical mixing method failed to achieve uniform grafting and firm anchoring of the phytic acid-zinc coordination polymer on the halloysite nanotube surface. Phase separation easily occurred during subsequent melt blending, resulting in a reduced effective concentration and uneven dispersion of the nucleating agent. The synergistic nucleation effect of the hybrid materials could not be fully realized, and the heat distortion temperature of the packaging box was significantly lower than that of Example 1.

[0085] Comparative Example 8

[0086] The only difference from Example 1 is the order of preparation of the composite heat-resistant nucleating agent. In Example 1, aminosilane modification was performed first, followed by in-situ grafting of phytic acid-zinc; in this comparative example, phytic acid-zinc was grafted first, followed by aminosilane modification, while the remaining raw material ratios and reaction conditions were the same.

[0087] Specific modification steps:

[0088] 5 g of raw halloysite nanotubes were dispersed in 250 mL of deionized water, and 3 g of phytic acid and 1.5 g of zinc sulfate were added sequentially. The pH was adjusted to 5.0, and the mixture was stirred at room temperature for 5 h to obtain phytic acid-zinc modified halloysite. The above product was dispersed in 250 mL of deionized water, and 1 g of APTES was added. The mixture was refluxed at 75 °C for 7 h, centrifuged, washed, and freeze-dried to obtain the comparative nucleating agent.

[0089] During post-amylation treatment, the phytate-zinc coordination layer on the halloysite surface hinders the reaction between APTES and the hydroxyl groups on the halloysite surface, resulting in low and uneven amino grafting rates. Simultaneously, electrostatic interactions may occur between the amino groups and phytate, disrupting the original coordination structure and leading to unstable nucleating agent performance. Comparative Example 8 showed poor heat resistance and batch repeatability in its packaging.

[0090] Experimental Example 1: The biodegradable, high-temperature resistant food packaging boxes prepared in Examples 1-3 and Comparative Examples 1-8 were subjected to the following tests:

[0091] Heat distortion temperature (HDT): Tested according to ISO 75-2:2013 standard, with a test load of 0.45 MPa;

[0092] Crystallinity (Xc): Tested using differential scanning calorimetry (DSC) at a heating rate of 10℃ / min;

[0093] Tensile strength: Tested according to ISO 527-2:2012 standard, tensile speed 50 mm / min;

[0094] Notched impact strength: Tested using an Izod cantilever beam impact testing machine according to ISO 180:2023 standard. Five specimens were tested in each group, and the average value was taken. The results are shown in Table 1 below.

[0095] Table 1

[0096] Grouping Heat distortion temperature (°C) Crystallinity (%) Tensile strength (MPa) <![CDATA[Notched impact strength (kJ / m 2 ).]]> Example 1 115.6 48.2 62.5 8.5 Example 2 112.3 46.5 60.1 8.1 Example 3 114.2 47.1 58.6 7.8 Comparative Example 1 58.5 12.3 45.2 4.2 Comparative Example 2 82.4 28.5 50.6 5.3 Comparative Example 3 92.1 35.6 54.2 6.1 Comparative Example 4 88.5 32.4 52.8 5.8 Comparative Example 5 93.6 36.1 55.3 6.3 Comparative Example 6 95.2 38.2 56.1 6.5 Comparative Example 7 96.8 39.5 55.8 6.2 Comparative Example 8 91.3 34.8 53.5 6

[0097] Based on the above data, Examples 1-3 significantly outperformed all comparative examples in terms of heat distortion temperature, crystallinity, tensile strength, and notched impact strength, fully verifying the excellent synergistic nucleation effect of the composite heat-resistant nucleating agent, aminosilane-modified halloysite nanotubes grafted with phytic acid-zinc coordination polymer, in the PLA / PHBV system. In particular, Example 1 achieved the best overall performance, indicating that the composite nucleating agent, at an addition amount of approximately 5 parts, exhibited the best dispersibility in the matrix and the strongest synergistic nucleation effect. In Example 3, due to the increased addition amount of the composite nucleating agent to 8 parts, the nanomaterials showed a slight tendency to aggregate in the matrix, resulting in a slight decrease in mechanical properties and heat distortion temperature compared to Example 1. However, its heat distortion temperature still far exceeded 110°C, fully meeting the requirements for high-temperature food packaging.

[0098] Comparative Example 1 lacked a nucleating agent, resulting in extremely low polylactic acid crystallinity and a heat distortion temperature of only 58.5°C. Comparative Example 2 used unmodified nanotubes, which had a limited effect on improving performance. Comparative Examples 3-5 and 8 had incomplete surface structures of the nucleating agents, leading to significantly lower crystallinity and heat distortion temperature. Comparative Example 6 used calcium salt instead of zinc salt, which limited the improvement in heat resistance. Comparative Example 7 used physical blending instead of in-situ grafting, which caused phytic acid-zinc to easily agglomerate, failing to achieve the high nucleation efficiency of the examples.

[0099] Finally, it should be noted that the above embodiments and comparative examples are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A biodegradable, high-temperature resistant food packaging box, characterized in that, The material comprises the following parts by weight: 60-80 parts of polylactic acid; 15-30 parts of polyhydroxybutyrate valerate; 3-8 parts of composite heat-resistant nucleating agent; 1-3 parts of chain extender; and 0.5-1.5 parts of lubricant. The composite heat-resistant nucleating agent is a hybrid material of aminosilane-modified halloysite nanotubes grafted with phytic acid-zinc coordination polymer in situ.

2. The biodegradable, high-temperature resistant food packaging box according to claim 1, characterized in that, The preparation method of the composite heat-resistant nucleating agent includes: dispersing aminated halloysite nanotubes obtained by treating halloysite nanotubes with silane coupling agent in deionized water, adding phytic acid solution and zinc sulfate solution in sequence, adjusting the pH to 4.5-5.5, stirring and coordinating in situ at room temperature for 4-6 hours, centrifuging, washing with deionized water, and freeze-drying to obtain the composite heat-resistant nucleating agent.

3. The biodegradable, high-temperature resistant food packaging box according to claim 2, characterized in that, The preparation method of the aminated halloysite nanotubes includes: dispersing halloysite nanotubes in deionized water, ultrasonically treating them, adding aminopropyltriethoxysilane, refluxing at 70-80℃ for 6-8 hours, centrifuging, washing and drying to obtain aminated halloysite nanotubes.

4. A biodegradable, high-temperature resistant food packaging box according to claim 3, characterized in that, The mass ratio of halloysite nanotubes, deionized water and aminopropyltriethoxysilane is (4-6):(200-300):

1.

5. A biodegradable, high-temperature resistant food packaging box according to claim 1, characterized in that, The halloysite nanotubes have an inner diameter of 15-25 nm, an outer diameter of 40-50 nm, and a length of 0.5-1.5 μm.

6. A biodegradable, high-temperature resistant food packaging box according to claim 2, characterized in that, The mass ratio of the aminated halloysite nanotubes, phytic acid and zinc sulfate is 10:(2-4):(1-2).

7. A biodegradable, high-temperature resistant food packaging box according to claim 1, characterized in that, The mass flow rate of the polylactic acid melt was 80 g / 10 min, and the test conditions were 210 °C.

8. A biodegradable, high-temperature resistant food packaging box according to claim 1, characterized in that, The chain extender is epoxidized soybean oil.

9. A biodegradable, high-temperature resistant food packaging box according to claim 1, characterized in that, The lubricant is ethylene bis-stearamide or pentaerythritol stearate.

10. The method for preparing a biodegradable, high-temperature resistant food packaging box as described in any one of claims 1-9, characterized in that step include: S1. After drying polylactic acid and polyhydroxybutyrate valerate in a vacuum oven to remove moisture, they are mixed evenly with composite heat-resistant nucleating agent, chain extender and lubricant, and fed into a twin-screw extruder. The mixture is then melt-blended, extruded and pelletized at 160℃-190℃ to obtain packaging box substrate particles. S2. Add the substrate particles obtained in step S1 into the injection molding machine, inject them into the mold at a barrel temperature of 170℃-195℃, maintain the mold temperature at 90℃-110℃, and maintain constant temperature and pressure for crystallization for 1-2 minutes to promote high crystallization of polylactic acid. Open the mold to obtain the packaging box.