Heat-resistant polylactic acid straw and preparation method thereof

Abstract

The application relates to a heat-resistant polylactic acid straw and a preparation method thereof, and relates to the field of straw materials and preparation, and comprises the following components in parts by weight: PLA 60-75 parts, P34HB 10-20 parts, PBA 8-15 parts, a nucleating agent 0.3-0.8 parts, an anti-hydrolysis agent 0.4-0.6 parts, a compatilizer 0.4-0.6 parts and a plasticizer 0.2-0.5 parts; the nucleating agent comprises a layered filler and an enzymatic protein. Through a ternary blending system of PLA, P34HB and PBA, and the synergistic addition of the nucleating agent, the anti-hydrolysis agent, the compatilizer and the plasticizer, the thermal stability and the high-temperature dimensional stability of a polylactic acid matrix are remarkably improved, the problems that a PLA straw is easy to bend, deform and collapse in hot water above 70 DEG C are effectively solved, and the use demand of hot drinks is met.

Description

Technical Field

[0001] This application relates to the field of straw materials and their preparation, specifically to a heat-resistant polylactic acid straw and its preparation method. Background Technology

[0002] With the implementation of global plastic bans, traditional non-degradable polypropylene (PP) plastic straws are gradually being phased out. Polylactic acid (PLA), as a biodegradable material, has become the preferred raw material for straw production due to its renewable sources and environmental friendliness. However, PLA itself has an inherent defect of slow crystallization: in conventional extrusion straw drawing processes, PLA melt is rapidly water-cooled and solidified after being extruded from the extruder die, resulting in products that are mostly in an amorphous or partially crystalline state. Its glass transition temperature is only 50-60℃, and it is prone to bending, deformation, and collapse when exposed to hot water above 70℃, which cannot meet the needs of hot beverage use. Summary of the Invention

[0003] To address the problem that PLA is prone to bending, deformation, and collapse when exposed to hot water above 70°C, thus failing to meet the requirements for hot beverage use, this application provides a heat-resistant polylactic acid straw and its preparation method.

[0004] In a first aspect, this application provides a heat-resistant polylactic acid straw, which adopts the following technical solution: A heat-resistant polylactic acid straw comprises the following components in parts by weight: PLA 60-75 parts, P34HB 10-20 parts, PBA 8-15 parts, nucleating agent 0.3-0.8 parts, anti-hydrolysis agent 0.4-0.6 parts, compatibilizer 0.4-0.6 parts, and plasticizer 0.2-0.5 parts; The nucleating agent includes layered fillers and enzymatically hydrolyzed proteins.

[0005] By adopting the above technical solution, the P34HB molecular chain contains flexible hydroxybutyric acid units, which can be inserted into the gaps between PLA molecular chains, reducing the regularity of PLA molecular chains and decreasing intermolecular forces. At the same time, it improves the chain segment movement flexibility of the blend system and reduces the risk of PLA becoming brittle due to excessive rigidity. PBA can be used as a flexible component to further improve the interfacial bonding force of the blend system, alleviate the phase separation problem between PLA and P34HB, and enable the three to form a uniform blend matrix. This synergistically improves the thermal stability and dimensional stability of the system, delays the disordered movement of molecular chains at high temperatures, and effectively alleviates the defects of PLA straws that are prone to deformation and collapse at high temperatures, providing basic heat resistance protection for hot beverage use.

[0006] Layered fillers, with their large specific surface area and layered structure, can serve as heterogeneous nucleation centers, providing numerous attachment sites for the ordered arrangement of PLA molecular chains. This guides the rapid directional crystallization of PLA molecular chains on their surface, refining the crystal grains. Enzymatically hydrolyzed protein molecules contain numerous polar groups such as amino and carboxyl groups, which can form hydrogen bonds with the ester groups in PLA molecular chains, further adsorbing PLA molecular chains, accelerating the orderly arrangement of the molecular chains, and promoting the crystallization process. Furthermore, the polar groups in the enzymatically hydrolyzed protein molecules can also form weak hydrogen bonds with the hydroxyl groups in the P34HB molecular chains, promoting interfacial fusion between the P34HB and PLA molecular chains, further reducing phase separation, and providing a more uniform matrix environment for PLA crystallization.

[0007] Preferably, the layered filler is nano-montmorillonite.

[0008] By adopting the above technical solution, nano-montmorillonite has a natural two-dimensional layered structure and a large specific surface area, which can provide more heterogeneous nucleation sites, thereby efficiently guiding PLA molecular chains to be oriented and arranged in an orderly manner on its sheet surface. Moreover, the sheet surface of nano-montmorillonite carries a negative charge, which can form electrostatic interactions with the positively charged amino groups in the enzymatically hydrolyzed protein molecules. At the same time, its interlayer voids can adsorb enzymatically hydrolyzed protein molecules, making the enzymatically hydrolyzed protein more uniformly dispersed in the blend system, effectively reducing the risk of uneven nucleation effect caused by the aggregation of enzymatically hydrolyzed protein.

[0009] Furthermore, the nanoscale sheets of nano-montmorillonite can form a sheet support structure in the blend system. When dispersed between PLA molecular chains and P34HB molecular chains, it can form a physical barrier. The sheets adsorbed on the surface of the enzymatic protein molecules can, to a certain extent, isolate the internal structure of the enzymatic protein molecules from the damage caused by high temperature. At the same time, nano-montmorillonite itself has good thermal stability and can maintain the stability of the layered structure at high temperature, further fixing the conformation of the enzymatic protein molecules and reducing the possibility of thermal denaturation. This ensures that the enzymatic protein can continue to play a role in synergistic nucleation and promote interfacial fusion.

[0010] Preferably, the enzymatically hydrolyzed protein is enzymatically hydrolyzed soybean protein.

[0011] By adopting the above technical solution, the molecular structure of enzymatically hydrolyzed soybean protein retains a large number of polar groups such as amino and carboxyl groups, and the molecular chains are shorter and the dispersibility is better. Compared with other enzymatically hydrolyzed proteins such as enzymatically hydrolyzed whey protein and enzymatically hydrolyzed fish protein, its polar group density is higher and its interaction with PLA and P34HB is stronger, which can maximize the nucleation effect.

[0012] In addition, enzymatically hydrolyzed soybean protein has superior thermal stability compared to other natural enzymatically hydrolyzed proteins. Its short-chain molecular conformation after enzymatic hydrolysis is more stable, and the hydrophobic groups contained in its molecules can form hydrophobic interactions with the layered structure of nano-montmorillonite, further enhancing the adsorption and fixation effect of nano-montmorillonite on it and reducing the destruction of molecular conformation at high temperatures.

[0013] Preferably, the mass ratio of the nano-montmorillonite to the enzymatically hydrolyzed soybean protein is 5:(1.2-1.8).

[0014] By adopting the above technical solution, when the amount of enzymatically hydrolyzed soy protein is too low, it is difficult for the soy protein to adsorb PLA molecular chains through hydrogen bonding and assist in accelerating the α-crystallization process of PLA, resulting in insufficient PLA crystallinity and a decrease in the heat resistance and mechanical properties of the pipette. When the amount of enzymatically hydrolyzed soy protein is too high, the excess soy protein will agglomerate in the blend system, which may occupy the nucleation sites of nano-montmorillonite and hinder the effect of nano-montmorillonite in inducing PLA α-crystallization, which will also lead to insufficient PLA crystallinity and a decrease in the heat resistance and mechanical properties of the pipette. Therefore, after extensive research and experimental verification, the applicant finally determined that the mass ratio of nano-montmorillonite to enzymatically hydrolyzed soy protein in this application is preferably as described above.

[0015] Preferably, the plasticizer comprises glycerol citric acid fatty acid ester.

[0016] By adopting the above technical solution, citric acid fatty acid glycerides can insert into the gaps between PLA molecular chains through molecular plasticization mechanism, weaken the interaction forces between PLA molecular chains, and improve the flexibility and processing flowability of PLA. At the same time, as a nonionic surfactant, the molecular structure of citric acid fatty acid glycerides can form a "bridging effect" at the interface between PLA and P34HB and PBA, enhance the compatibility of flexible components P34HB and PBA with rigid matrix PLA, and alleviate the phase separation problem that may occur when the three are blended.

[0017] In addition, citric acid fatty acid glycerides can help improve the dispersibility of layered fillers in the blend system. Their surface activity can reduce the agglomeration between the layers of layered fillers, making the layered fillers more uniformly dispersed in the blend matrix of PLA and P34HB, thereby helping to improve the crystallization efficiency of PLA, and thus improving the heat resistance and mechanical properties of the straw.

[0018] Preferably, the plasticizer also includes sorbitol.

[0019] By employing the above-mentioned technical solution, sorbitol molecules contain multiple hydroxyl groups, which can form hydrogen bonds with the ester groups in PLA molecular chains, inserting into the interstices of PLA molecular chains to further weaken intermolecular forces. Synergistically working with citrate fatty acid glycerides, it significantly improves the flexibility and processing flowability of PLA. Simultaneously, the multiple hydroxyl groups of sorbitol can also form multiple hydrogen bonds with the amino and carboxyl groups in enzymatically hydrolyzed protein molecules, forming a hydrogen bond protection network around the enzymatically hydrolyzed protein molecules. This inhibits conformational changes, thermal denaturation, and molecular aggregation of the enzymatically hydrolyzed protein during high-temperature processing or use, maintaining the structural integrity and functional stability of the enzymatically hydrolyzed protein, allowing it to continuously perform nucleation and interfacial compatibility functions. Furthermore, sorbitol can form hydrogen bond bridges between layered fillers and enzymatically hydrolyzed proteins, enhancing the interaction between them and further improving the dispersion stability and thermal stability of the nucleation system in the blend matrix.

[0020] Preferably, the mass ratio of the citrate fatty acid glyceride to sorbitol is 5:(0.8-1.5).

[0021] By adopting the above technical solution, when the amount of sorbitol is too low, a small amount of sorbitol is insufficient to effectively inhibit the aggregation of enzymatically hydrolyzed soybean protein in the blend system. At the same time, its plasticizing effect on PLA molecular chains is also weak, resulting in insignificant improvement in PLA crystallization rate and crystallinity, and insufficient improvement in the heat resistance and mechanical properties of the pipette. When the amount of sorbitol is too high, excessive sorbitol is prone to migration and precipitation in the blend system, interfering with the nucleation synergy between the layered filler and the enzymatically hydrolyzed protein, reducing the degree of PLA crystallization perfection, and causing a decrease in the high-temperature dimensional stability of the pipette. Therefore, after extensive research and experimental verification, the applicant finally determined that the mass ratio of citrate fatty acid glyceride to sorbitol in this application is preferably as described above.

[0022] Secondly, this application provides a method for preparing a heat-resistant polylactic acid straw, which adopts the following technical solution: A method for preparing a heat-resistant polylactic acid (PLA) straw, comprising the following steps: S1. After mechanically mixing the PLA, P34HB, and PBA in the specified amounts, add the nucleating agent, anti-hydrolysis agent, compatibilizer, and plasticizer in the specified amounts, and continue mixing to obtain a uniform mixture; S2. After the mixture is extruded and shaped, it is successively stretched and water-cooled for curing to obtain a straw sample preform containing some uncrystallized PLA; S3. The straw sample is permeated with supercritical carbon dioxide to promote the rapid crystallization of the uncrystallized PLA in the sample, forming a uniform crystalline structure. Then, it is cooled to room temperature, dehydrated, and cut to obtain a heat-resistant polylactic acid straw.

[0023] By employing the above-mentioned technical solution, supercritical carbon dioxide, with its low viscosity, high diffusivity, and strong permeability, can rapidly penetrate the interior of the straw blank and infiltrate the amorphous region of PLA. This significantly reduces the intermolecular forces within the PLA molecular chains, greatly enhancing chain mobility and enabling rapid, orderly arrangement and full crystallization at numerous heterogeneous nucleation sites provided by the nucleating agent. Simultaneously, supercritical carbon dioxide can act uniformly on the overall wall thickness of the straw, promoting the formation of a fine-grained, evenly distributed, and densely structured crystalline system of PLA, ensuring the straw maintains excellent dimensional stability even in hot beverage environments. Furthermore, this process eliminates the need for prolonged high-temperature heat treatment, effectively reducing the risk of thermal degradation, discoloration, or performance decline in PLA and enzymatically hydrolyzed soybean protein.

[0024] Preferably, the pressure holding temperature of supercritical carbon dioxide permeation in S3 is 60-80℃.

[0025] By adopting the above technical solution, when the holding temperature is too low, the permeability and diffusion rate of supercritical carbon dioxide decrease, making it difficult to fully enter the amorphous region inside the straw blank. The mobility of PLA molecular chain segments decreases, the crystallization driving force is weak, resulting in a slow PLA crystallization rate and low crystallinity, and the improvement of straw heat resistance is limited. When the holding temperature is too high, it may cause thermal degradation of PLA molecular chains, leading to a decrease in the mechanical strength of the straw. Therefore, after extensive research and experimental verification, the applicant finally determined that the holding temperature for supercritical carbon dioxide permeation in S3 of this application is preferably as described above.

[0026] Preferably, the holding pressure of supercritical carbon dioxide permeation in S3 is 8-10 MPa, and the holding time is 5-15 min.

[0027] By adopting the above technical solution, when the holding pressure is too low and the holding time is too long, supercritical carbon dioxide is difficult to form a stable supercritical state, resulting in weak penetration into the interior of the straw blank, insufficient and uneven crystallization of the amorphous region of PLA, and excessive processing time will reduce production efficiency and increase energy consumption and production costs. When the holding pressure is too high and the holding time is too short, excessive pressure can easily cause defects such as bubbling, uneven wall thickness, or even local cracking inside the straw blank, while excessively short holding time is also difficult to allow the uncrystallized PLA to fully crystallize, leading to a decrease in the heat resistance of the straw. Therefore, after extensive research and experimental verification, the applicant finally determined that the holding pressure and holding time for supercritical carbon dioxide penetration in S3 of this application are preferably as described above.

[0028] In summary, this application has the following beneficial effects: 1. This application utilizes a ternary blend system of PLA, P34HB, and PBA, along with the synergistic addition of nucleating agents, anti-hydrolysis agents, compatibilizers, and plasticizers, to significantly improve the thermal stability and high-temperature dimensional stability of the polylactic acid matrix. This effectively solves the problem of PLA straws being prone to bending, deformation, and collapse in hot water above 70°C, thus meeting the needs of hot beverage use. 2. This application uses nano-montmorillonite and enzymatically hydrolyzed soybean protein as a nucleation system. The two work synergistically through electrostatic interaction, hydrophobic interaction and hydrogen bonding. On the one hand, they provide PLA with a large number of efficient heterogeneous nucleation sites, refine grains, and improve crystallinity and crystal perfection. On the other hand, they promote the interfacial compatibility between PLA and P34HB, reduce phase separation, and improve the thermal stability of the nucleation system itself, further enhancing the heat resistance and mechanical properties of the pipette. 3. This application uses a combination of citric acid fatty acid glycerides and sorbitol as a plasticizing system. While improving the processing fluidity and flexibility of PLA, it enhances the interfacial compatibility between the components and helps to improve the uniformity of nucleating agent dispersion. Sorbitol can also protect the structure of enzymatically hydrolyzed soybean protein through multiple hydrogen bonds, inhibit its high-temperature denaturation and aggregation, and ensure long-term stability of nucleation and interfacial compatibility effects. 4. This application uses supercritical carbon dioxide permeation process to perform post-crystallization treatment on the straw blank, which can rapidly and uniformly improve the crystallinity of PLA at a lower temperature, forming a crystal system with fine grains and dense structure, further improving the high-temperature dimensional stability of the straw; at the same time, it avoids the risk of degradation and discoloration caused by long-term high-temperature heat treatment, taking into account both product performance and production feasibility. Detailed Implementation

[0029] The raw materials in this application include the following: PLA: Polylactic acid, optical purity ≥99%, melt index ≤10g / 10min; P34HB: Poly(3-hydroxybutyrate) 4-hydroxybutyrate, acid value ≤30mol / t, melt index ≤10g / 10min; PBA: Poly(butylene adipate) with acid value ≤30mol / t and melt index ≤10g / 10min. Anti-hydrolysis agent: Taking polycarbodiimide as an example, degree of polymerization ≥2000; Compatibilizer: Taking methyl styrene-methacrylate-glycidyl acrylate polymer as an example, the weight average molecular weight is 5000-6000; Citric acid fatty acid glycerides: ester content ≥99%; Sorbitol: Effective content ≥99%; Nano-montmorillonite: cation exchange capacity ≥100 meq / 100g, interlayer spacing ≥1.5nm, specific surface area ≥750m² 2 / g Graphene: Thickness 1-5nm, specific surface area ≥90m² 2 / g; Alkaline protease: enzyme activity ≥ 4 × 10 4 U / g, purchased from Wuxi Genentech Biotechnology Co., Ltd.; Acidic protease: enzyme activity ≥ 3 × 10 4 U / g, purchased from Wuxi Genentech Biotechnology Co., Ltd.; Flavor protease: Enzyme activity ≥ 1 × 10 5 U / g, purchased from Wuxi Genentech Biotechnology Co., Ltd.; Preparation Example 1 The method for preparing enzymatically hydrolyzed soybean protein includes the following steps: A1. Dissolve 1 kg of soy protein isolate in 11.5 L of water, stir well, and heat in a 90 °C water bath for 10 minutes to obtain protein solution A; A2. Cool the above protein solution A to 55°C, adjust the pH to 8.5, add 0.02 kg of alkaline protease, stir continuously for 2 h, then cool to 37°C, adjust the pH to 2.0, add 0.03 kg of acidic protease, stir continuously for 2 h, and obtain the crude enzymatically hydrolyzed soybean protein product. A3. The above-mentioned crude enzymatically hydrolyzed soybean protein product is heated in a 90°C water bath for 15 minutes to inactivate the protease. After concentration and drying, the enzymatically hydrolyzed soybean protein is obtained.

[0030] Preparation Example 2 A method for preparing enzymatically hydrolyzed whey protein includes the following steps: B1. Dissolve 1 kg of whey protein isolate in 19 L of water, stir well, and heat in an 80 °C water bath for 10 minutes to obtain protein solution B; B2. Cool the above protein solution to 45°C, adjust the pH to 8.5, add 0.01 kg of alkaline protease, stir continuously for 4 h, then cool to 37°C, adjust the pH to 7.0, add 0.005 kg of flavor protease, stir continuously for 2 h to obtain the crude product of enzymatically hydrolyzed whey protein. B3. The above-mentioned crude enzymatically hydrolyzed soybean protein product is heated in a 90°C water bath for 10 minutes to inactivate the protease. After concentration and drying, enzymatically hydrolyzed whey protein is obtained.

[0031] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0032] Example 1 A method for preparing a heat-resistant polylactic acid straw includes the following steps: S1. Add 68 kg of PLA, 15 kg of P34HB, and 12 kg of PBA into a high-speed mixer and mix for 10 min at 80°C and 300 r / min. Then add 0.5 kg of nucleating agent, 0.5 kg of polycarbodiimide, 0.5 kg of methylstyrene-methacrylate-glycidyl acrylate polymer, and 0.35 kg of citric acid fatty acid glyceride. Continue mixing for 12 min at 60°C and 200 r / min to obtain a uniform mixture. The nucleating agent is a mixture of nano-montmorillonite and enzymatically hydrolyzed soybean protein, with a mass ratio of nano-montmorillonite to enzymatically hydrolyzed soybean protein of 5:1.5. S2. The above mixture is fed into a twin-screw extruder, and the extrusion process parameters are set as follows: temperature of zone 1 of the barrel is 160℃, temperature of zone 2 is 175℃, temperature of zone 3 is 180℃, and temperature of the die head is 175℃. After being extruded through the extruder die, it is stretched by the traction equipment at a speed of 6m / min and cooled and solidified by the water cooling device at a water temperature of 20℃ to obtain a straw sample preform containing some uncrystallized PLA. S3. Place the above-mentioned straw sample into a high-temperature and high-pressure sealed container, inject supercritical carbon dioxide fluid, and set the process parameters as follows: holding temperature 70℃, holding pressure 9MPa, holding time 10min, and pressure release rate 30MPa / s. Through the permeation effect of supercritical carbon dioxide, the uncrystallized PLA in the sample is rapidly crystallized to form a uniform crystalline structure. After soaking and crystallizing, the straw is taken out, cooled to room temperature by an air-cooling device, and cut to a length of 200mm after dehydration to obtain a heat-resistant polylactic acid straw.

[0033] Example 2-3 Examples 2-3 are based on the preparation method of Example 1, but the amount of each component is adjusted, as shown in Table 1.

[0034] Comparative Examples 1-2 Comparative Example 1 was prepared using the same method as in Example 1, but the nucleating agent was replaced by an equal amount of a mixture of nano-montmorillonite and enzymatically hydrolyzed soybean protein with nano-montmorillonite, while all other conditions remained unchanged.

[0035] Comparative Example 2 was prepared using the same method as in Example 1, but the nucleating agent was replaced by an equal amount of a mixture of nano-montmorillonite and enzymatically hydrolyzed soybean protein with enzymatically hydrolyzed soybean protein, while all other conditions remained unchanged.

[0036] The heat-resistant polylactic acid straws prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to the following performance tests, and the test results are shown in Table 1.

[0037] Performance testing (1) Impact strength The impact strength of the sample was tested according to the ATSM D6110 test standard; (2) Crystallinity The crystallinity of the sample was tested using a DSC instrument (Netzsch DSC 204, Germany) under a nitrogen atmosphere. The temperature was increased from 20°C to 180°C at a rate of 10°C / min, and the enthalpy curve of the temperature increase was recorded. The crystallinity (Xc) of polylactic acid was calculated using the DSC method. Xc=(△Hm-△Hc) / △Hm0×100%; Where △Hm represents the enthalpy of melting of the pipette sample; △Hc represents the enthalpy of cold crystallization of the pipette sample; △Hm0 represents the melting enthalpy (theoretical enthalpy, equal to 96.30 J / g) of fully crystalline polylactic acid.

[0038] (3) Load heat distortion temperature Test the load heat distortion temperature of the sample according to GB / T 1634-1979.

[0039] Table 1. Raw material list and performance test table for Examples 1-3 and Comparative Examples 1-2

[0040] Referring to Table 1, comparing Examples 1-3 and Comparative Examples 1-2, it can be seen that the overall performance of the heat-resistant polylactic acid straws prepared in Examples 1-3 is better than that in Comparative Examples 1-2. Comparative Example 1 only uses nano-montmorillonite as a nucleating agent, and Comparative Example 2 only uses enzymatically hydrolyzed soybean protein as a nucleating agent. This indicates that the combination of nano-montmorillonite and enzymatically hydrolyzed soybean protein has a better synergistic nucleation effect, which can significantly improve the crystallinity and high-temperature dimensional stability of PLA straws, thereby improving the problem of PLA straws being easily deformed at high temperatures.

[0041] In comparison, the heat-resistant polylactic acid straw prepared in Example 1 has better overall performance, therefore Example 1 is preferred.

[0042] Examples 4-5 Example 4 is based on the preparation method of Example 1, except that the nano-montmorillonite is replaced with an equal amount of graphene, and the other conditions remain unchanged.

[0043] Example 5 is based on the preparation method of Example 1, except that an equal amount of enzymatically hydrolyzed soybean protein is replaced with enzymatically hydrolyzed collagen, while the other conditions remain unchanged.

[0044] The heat-resistant polylactic acid straws prepared in Examples 4-5 were subjected to the above performance tests, and the test results are shown in Table 2.

[0045] Table 2 Performance test results for Examples 1 and 4-5

[0046] Referring to Table 2, comparing Examples 1 and 4-5, it can be seen that the heat-resistant polylactic acid straw prepared in Example 1 has better overall performance than that in Examples 4-5. In Example 4, the nano-montmorillonite was replaced with graphene. Although it still had a certain nucleation effect, the density of heterogeneous nucleation sites and the synergistic effect with enzymatically hydrolyzed soybean protein were weaker than those of nano-montmorillonite. Therefore, the crystallinity and heat resistance were reduced. In Example 5, the enzymatically hydrolyzed soybean protein was replaced with enzymatically hydrolyzed collagen. The density of polar groups and the hydrogen bonding effect with PLA and layered fillers were weaker. The nucleation and interfacial compatibility effects were reduced, and the overall performance was further reduced.

[0047] Examples 6-9 Examples 6-9 are based on the preparation method of Example 1, keeping the mass of nano-montmorillonite and enzymatically hydrolyzed soybean protein unchanged, but adjusting the mass ratio of nano-montmorillonite and enzymatically hydrolyzed soybean protein. The specific adjustments are shown in Table 3.

[0048] The heat-resistant polylactic acid straws prepared in Examples 6-9 were subjected to the above performance tests, and the test results are shown in Table 3.

[0049] Table 3. Mass ratio of nano-montmorillonite and enzymatically hydrolyzed soybean protein and performance test results in Examples 1 and 6-9.

[0050] Referring to Table 3, comparing Examples 1 and 6-9, it can be seen that the optimal overall performance of the pipette was achieved when the ratio of nano-montmorillonite to enzymatically hydrolyzed soybean protein was 5:(1.2-1.8) in Examples 1 and 6-7. In Example 8, the proportion of enzymatically hydrolyzed soybean protein was too low, resulting in insufficient assisted nucleation and interfacial compatibility, and a significant decrease in performance. In Example 9, the proportion of enzymatically hydrolyzed soybean protein was too high, leading to agglomeration and occupation of nucleation sites, further reducing crystallinity and heat resistance. This indicates that controlling the ratio of nano-montmorillonite to enzymatically hydrolyzed soybean protein within the range of 5:(1.2-1.8) can achieve a better synergistic nucleation effect, ensuring that the pipette has excellent heat resistance and mechanical properties.

[0051] Examples 10-14 In Example 10, based on the preparation method of Example 1, 0.084 kg of sorbitol was added to S1 along with citric acid fatty acid glyceride, while the other conditions remained unchanged.

[0052] Examples 11-14 are based on the preparation method of Example 10, with the mass of citrate fatty acid glycerides and sorbitol remaining unchanged, and the mass ratio of citrate fatty acid glycerides and sorbitol being adjusted as shown in Table 4.

[0053] The heat-resistant polylactic acid straws prepared in Examples 10-14 were subjected to the above performance tests, and the test results are shown in Table 4.

[0054] Table 4. Mass ratio of citrate fatty acid glycerides and sorbitol in Examples 1 and 10-14, and their performance test results.

[0055] Referring to Table 4, a comparison of Examples 1 and 10-14 shows that the overall performance of the heat-resistant polylactic acid straws prepared in Examples 10-14 is better than that in Example 1, indicating that the addition of sorbitol can further optimize the heat-resistant polylactic acid straws. In Examples 10-12, when the mass ratio of citric acid fatty acid glyceride to sorbitol is 5:(0.8-1.5), the plasticizing and synergistic nucleation effects are better, and the impact strength, crystallinity, and load heat distortion temperature are all improved. In Example 13, the proportion of sorbitol is too low, resulting in insufficient protection and plasticizing synergistic effects on enzymatically hydrolyzed soybean protein, and the performance is somewhat reduced. In Example 14, the proportion of sorbitol is too high, which easily leads to migration and precipitation, interfering with nucleation and crystallization, resulting in further performance reduction.

[0056] Examples 15-18 Examples 15-18 are based on the preparation method of Example 10, but the pressure holding temperature of supercritical carbon dioxide permeation is adjusted, as shown in Table 5.

[0057] The heat-resistant polylactic acid straws prepared in Examples 15-18 were subjected to the above performance tests, and the test results are shown in Table 5.

[0058] Table 5. Pressure holding temperature and performance test results of supercritical carbon dioxide permeation in Examples 10 and 15-18.

[0059] Referring to Table 5, a comparison of Examples 10 and 15-18 shows that the heat-resistant polylactic acid straws prepared in Examples 10 and 15-16 have the best overall performance when the holding temperature is 60-80°C. In Example 17, the holding temperature is too low, resulting in weak supercritical carbon dioxide permeation and insufficient PLA crystallization, leading to a decrease in performance. In Example 18, the holding temperature is too high, which may cause partial degradation of PLA, reduce the degree of crystallization, and further deteriorate the performance.

[0060] Examples 19-22 Examples 19-22 are based on the preparation method of Example 10, but the pressure holding parameters of supercritical carbon dioxide permeation are adjusted, as shown in Table 6.

[0061] The heat-resistant polylactic acid straws prepared in Examples 19-22 were subjected to the above performance tests, and the test results are shown in Table 6.

[0062] Table 6. Pressure holding parameters and performance test results for supercritical carbon dioxide permeation in Examples 10 and 19-22.

[0063] Referring to Table 6, a comparison of Examples 10 and 10-22 shows that the heat-resistant polylactic acid straws prepared in Examples 10 and 19-20 have the best overall performance when the holding pressure is 8-10 MPa and the holding time is 5-15 min. In Example 21, the holding pressure is too low and the holding time is too long, resulting in insufficient supercritical carbon dioxide permeation, incomplete PLA crystallization, and decreased performance. In Example 22, the holding pressure is too high and the holding time is too short, which easily causes defects in the straw blank and incomplete crystallization, further deteriorating the performance.

[0064] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A heat-resistant polylactic acid straw, characterized in that, It includes the following components in parts by weight: PLA 60-75 parts, P34HB 10-20 parts, PBA 8-15 parts, nucleating agent 0.3-0.8 parts, anti-hydrolysis agent 0.4-0.6 parts, compatibilizer 0.4-0.6 parts, and plasticizer 0.2-0.5 parts; The nucleating agent includes layered fillers and enzymatically hydrolyzed proteins.

2. The heat-resistant polylactic acid straw according to claim 1, characterized in that: The layered filler is nano-montmorillonite.

3. The heat-resistant polylactic acid straw according to claim 2, characterized in that: The enzymatically hydrolyzed protein is enzymatically hydrolyzed soybean protein.

4. The heat-resistant polylactic acid straw according to claim 3, characterized in that: The mass ratio of nano-montmorillonite to enzymatically hydrolyzed soybean protein is 5:(1.2-1.8).

5. The heat-resistant polylactic acid straw according to claim 1, characterized in that: The plasticizer includes glycerol citric acid fatty acid esters.

6. The heat-resistant polylactic acid straw according to claim 5, characterized in that: The plasticizer also includes sorbitol.

7. The heat-resistant polylactic acid straw according to claim 6, characterized in that: The mass ratio of the citric acid fatty acid glyceride to sorbitol is 5:(0.8-1.5).

8. The method for preparing the heat-resistant polylactic acid straw according to any one of claims 1-7, characterized in that, Includes the following steps: S1. After mechanically mixing the PLA, P34HB, and PBA in the specified amounts, add the nucleating agent, anti-hydrolysis agent, compatibilizer, and plasticizer in the specified amounts, and continue mixing to obtain a uniform mixture; S2. After the mixture is extruded and shaped, it is successively stretched and water-cooled for curing to obtain a straw sample preform containing some uncrystallized PLA; S3. The straw sample is permeated with supercritical carbon dioxide to promote the rapid crystallization of the uncrystallized PLA in the sample, forming a uniform crystalline structure. Then, it is cooled to room temperature, dehydrated, and cut to obtain a heat-resistant polylactic acid straw.

9. The method for preparing the heat-resistant polylactic acid straw according to claim 8, characterized in that, The pressure holding temperature for supercritical carbon dioxide permeation in S3 is 60-80℃.

10. The method for preparing the heat-resistant polylactic acid straw according to claim 8, characterized in that: The holding pressure for supercritical carbon dioxide permeation in S3 is 8-10 MPa, and the holding time is 5-15 min.

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