A phA composition and a method for preparing the same

Abstract

This application relates to the field of polymer materials, specifically to a PHA composition and its preparation method, comprising the following components in parts by weight: 55-70 parts PHA, 10-20 parts modified calcium carbonate, 5-15 parts toughening agent, 0.4-1.2 parts chain extender, 0.1-0.3 parts nucleating agent, 0.5-1 part lubricant, and 0.3-1.0 parts antioxidant. The toughening agent is at least one of PBAT or PBS. The modified calcium carbonate is obtained by modifying dopamine. Through the addition of modified calcium carbonate, this application achieves a coating layer rich in catechol and amino groups on the surface of calcium carbonate due to the self-polymerization of dopamine. During melt blending, this coating layer can undergo amidation and esterification reactions with the end groups of PHA and the toughening agent, and coordinate with calcium ions to construct a covalent bond network from the filler to the matrix, forming a "chemical interlocking" structure, thus achieving efficient stress transfer. The synergistic effect of the chain extender, nucleating agent, lubricant, and antioxidant significantly improves toughness, impact resistance, and hot water resistance.

Description

Technical Field

[0001] This application relates to the field of polymer materials, and in particular to a PHA composition and its preparation method. Background Technology

[0002] Polyhydroxyalkanoate (PHA) is a high-molecular-weight polyester synthesized by microorganisms. Due to its good biodegradability, biocompatibility and marine biodegradability, it is regarded as an ideal environmentally friendly material to replace traditional petroleum-based plastics in the preparation of disposable straws.

[0003] Because pure PHA material crystallizes slowly at room temperature and exhibits severe secondary crystallization, its products generally suffer from poor flexibility. This greatly limits the application of PHA material in thin-walled, slender products such as straws that need to withstand bending stress. During use, it is prone to brittle fracture or microcracks, affecting the practicality of the product. Summary of the Invention

[0004] To improve the toughness of PHA compositions, this application provides a PHA composition and a method for preparing the same.

[0005] This application provides a PHA composition and its preparation method, which adopts the following technical solution: Firstly, this application provides a PHA composition, which adopts the following technical solution: A PHA composition comprising the following components in parts by weight: 55-70 parts PHA, 10-20 parts modified calcium carbonate, 5-15 parts toughening agent, 0.4-1.2 parts chain extender, 0.1-0.3 parts nucleating agent, 0.5-1 part lubricant, and 0.3-1.0 parts antioxidant, wherein the toughening agent is at least one of PBAT or PBS; and the modified calcium carbonate is obtained by modification with dopamine.

[0006] By adopting the above technical solution, the modified calcium carbonate is a dopamine-modified product. Its surface is coated with a polydopamine coating layer formed by dopamine self-polymerization. This coating layer is rich in active groups such as catechol groups and amino groups. Unlike the simple physical filling of ordinary calcium carbonate, it can form a stable interfacial binding structure with PHA and PBAT / PBS.

[0007] Specifically, during melt blending, the amino and catechol groups on the surface of modified calcium carbonate undergo amidation and esterification reactions with the carboxyl and hydroxyl groups at the ends of the PHA and PBAT / PBS molecular chains, forming covalent bonds that firmly connect the inorganic filler to the polymer matrix. Simultaneously, the catechol groups in polydopamine form coordination bonds with calcium ions on the calcium carbonate surface, achieving stable anchoring of the filler. This constructs a covalent bond network from the filler through the interface to the polymer matrix, creating an integrated "chemically interlocked" structure. This ensures that stress is efficiently transferred through the interface when the PHA composition is subjected to external impact, preventing stress concentration-induced fracture, and also endows the PHA composition with excellent heat resistance.

[0008] In addition, the molecular chain strengthening effect of the reactive chain extender, as well as the synergistic effect of the nucleating agent, lubricant, and antioxidant, effectively solves the core defect of PHA's inherent brittleness and significantly improves the toughness and impact resistance of the PHA composition.

[0009] Preferably, the method for preparing the modified calcium carbonate includes the following steps: (1) Dissolve dopamine hydrochloride in Tris-HCl buffer, adjust the pH to 8.0-8.5, and stir until completely dissolved to obtain a dopamine mixture; (2) Add calcium carbonate powder to the dopamine mixture, stir and disperse, let stand to react, wash and dry to obtain modified calcium carbonate.

[0010] By adopting the above technical solution, the pH of the reaction system is first precisely controlled at 8.0-8.5 using Tris-HCl buffer solution, providing the optimal self-polymerization environment for dopamine. This ensures uniform and moderate oxidative self-polymerization on the calcium carbonate surface, avoiding non-reaction or excessively rapid formation of free particles due to excessively low or high pH. Simultaneously, through static reaction, dopamine has sufficient time to fully polymerize on the calcium carbonate surface, forming a continuous and complete polydopamine coating layer. This constructs a "core-shell" structure with calcium carbonate as the core and polydopamine as the shell, endowing the calcium carbonate surface with abundant catechol groups and amino groups, transforming it from an ordinary inorganic filler into an "organic-inorganic hybrid interface layer." This layer can be firmly anchored to the calcium carbonate surface through the coordination bond between catechol and calcium ions, and can also form covalent bonds with the end groups of subsequent polymer matrices such as PHA and PBAT / PBS using amino and catechol groups. This lays a good foundation for the construction of a complete chemical bond network from the filler through the interface to the matrix in the final PHA composition, providing excellent toughness and impact resistance.

[0011] Preferably, the chain extender is an HMDI, ADR, or MAH graft.

[0012] By employing the above-mentioned technical solutions, chain extenders HMDI, ADR, or MAH grafts can all chemically react with the carboxyl and hydroxyl groups at the ends of the PHA and PBAT / PBS molecular chains through their active functional groups (isocyanate groups, epoxy groups, or maleic anhydride groups). This achieves chain extension, branching, or compatibilization, effectively compensating for the decrease in molecular weight caused by degradation during PHA thermal processing and improving the melt strength and mechanical properties of the matrix. Simultaneously, these three types of chain extenders can react with the amino and catechol groups on the surface of dopamine-modified calcium carbonate. Specifically, HMDI's -NCO and -NH2 form urea bonds, ADR's epoxy groups undergo ring-opening addition with -NH2, and MAH grafts' anhydride groups form amide bonds with -NH2. This covalently anchors the inorganic filler to the polymer network, constructing a complete chemical bonding system from the filler through the interface to the matrix. This allows the PHA composition to maintain high toughness and impact resistance while simultaneously improving heat resistance.

[0013] Preferably, the chain extender is HMDI.

[0014] By employing the above-mentioned technical solution, HMDI molecules contain a highly reactive isocyanate group at each end, exhibiting dual reactivity during melt blending: on the one hand, it reacts with the hydroxyl and carboxyl groups at the ends of PHA and PBAT / PBS molecular chains to generate urethane and amide bonds, respectively, thereby extending the polymer molecular chains, compensating for the molecular weight decrease caused by PHA thermal degradation, and significantly improving the melt strength and mechanical properties of the matrix; on the other hand, it reacts with the amino and catechol groups on the surface of dopamine-modified calcium carbonate to generate urea and urethane bonds, respectively, firmly anchoring the inorganic filler to the polymer network through covalent bonds. Thus, HMDI, acting as a "molecular bridge," simultaneously achieves the dual functions of matrix reinforcement and interfacial bonding, constructing a complete covalent bond network from the filler through the interface to the polymer, enabling the PHA composition to significantly improve its hot water resistance and hydrolysis resistance while maintaining high toughness.

[0015] Preferably, the nucleating agent is talc or an organic nucleating agent.

[0016] By adopting the above technical solution, talc or organic nucleating agent provides heterogeneous nucleation sites for PHA. By reducing the nucleation energy barrier, the PHA molecular chain can rapidly crystallize with these sites as the core during the cooling process, significantly improving the crystallization rate and crystallinity, and refining the spherulite size. This ensures that the PHA composition can be rapidly shaped in the extrusion cooling section and obtain good heat resistance.

[0017] When HMDI is preferred as the chain extender, its isocyanate groups react with the hydroxyl and carboxyl groups at the ends of the PHA molecular chains to form urethane and amide bonds. During this process, due to the interconnection of multiple molecular chains, the movement of the molecular chains is restricted, and the diffusion capacity of the chain segments decreases, resulting in a reduced crystallization rate of PHA. However, the heterogeneous nucleation sites provided by talc or organic nucleating agents can compensate for the retardation effect of HMDI on crystallization. By increasing the nucleation density, crystallization is accelerated, allowing the PHA composition to quickly complete crystallization and shaping in the extrusion cooling section. Thus, while HMDI imparts high melt strength and high interfacial bonding to the matrix, the nucleating agent ensures sufficient crystallization of the product, meets the heat resistance temperature requirements, and has a low post-shrinkage rate, giving the PHA composition both excellent toughness and heat resistance.

[0018] Preferably, the lubricant is stearamide or polyethylene wax.

[0019] By adopting the above technical solution, the lubricant is stearamide or polyethylene wax. Its function is to reduce internal and external friction during the melt blending process of PHAPHA composition, reduce shear heat, prevent PHA from thermal degradation due to overheating, improve melt fluidity, ensure smooth extrusion molding and smooth surface, and improve demolding performance.

[0020] When HMDI is preferred as the chain extender, the isocyanate group of HMDI has extremely high reactivity and is prone to side reactions with substances containing active hydrogen. Stearamide or polyethylene wax are both inert lubricants. Although stearamide contains amide groups, its reaction rate with -NCO at the melt processing temperature is much lower than that with the reaction of -NCO with the terminal hydroxyl group of PHA. Moreover, its molecular weight is small and it migrates quickly, mainly accumulating on the surface to play an external lubricating role. Its consumption of HMDI is negligible. Polyethylene wax is a non-polar inert substance and does not interfere with the chemical reaction of HMDI at all.

[0021] Therefore, this lubricant system effectively reduces processing shear heat, protects the heat-sensitive PHA and dopamine coating, while avoiding interference with the chain extension reaction and interfacial anchoring reaction of HMDI. This ensures that the -NCO of HMDI can preferentially react with the terminal hydroxyl groups of PHA and the amino groups on the surface of dopamine-modified calcium carbonate to build a complete covalent network. This achieves stable processing, low shear heat, and excellent surface quality, enabling the PHA composition to maintain a smooth appearance and dimensional accuracy while possessing high toughness, impact resistance, and heat resistance.

[0022] Preferably, the antioxidants include hindered phenols and phosphites.

[0023] By employing the above technical solution, hindered phenolic antioxidants act as free radical scavengers, capturing alkoxy and peroxy free radicals generated during the thermal oxidative degradation of PHA at high temperatures, thus terminating the oxidation chain reaction. Phosphite antioxidants act as hydroperoxide decomposers, reducing the source of free radicals by reducing hydroperoxides to stable alcohol compounds. The combined use of these two antioxidants forms a synergistic antioxidant system of "free radical scavenging-hydroperoxide decomposition," significantly inhibiting the thermal degradation of PHA, protecting the integrity of the molecular chain, and reducing the formation of acidic end groups.

[0024] When HMDI is the preferred chain extender, the thermal degradation of PHA at high temperatures generates a large number of terminal carboxyl groups. The isocyanate groups of HMDI react with these terminal carboxyl groups to form amide bonds and release CO2. This side reaction consumes the -NCO groups intended for chain extension and interfacial anchoring, reducing the utilization efficiency of HMDI. Hindered phenolic and phosphite antioxidants inhibit the thermal degradation of PHA, reducing the generation of terminal carboxyl groups at the source. This protects the -NCO groups of HMDI from excessive consumption by the terminal carboxyl groups, allowing them to preferentially react with the terminal hydroxyl groups of PHA and the amino groups on the surface of dopamine-modified calcium carbonate. Simultaneously, the antioxidants also protect the catechol groups in the dopamine coating from high-temperature oxidation and degradation, maintaining their reactivity in interfacial anchoring. Thus, the antioxidants and HMDI form a synergistic mechanism of "source inhibition of degradation - active site protection," ensuring that HMDI efficiently performs its chain extension and interfacial bonding functions, giving the PHA composition excellent toughness, impact resistance, and hot water resistance.

[0025] Preferably, the PHA composition further includes an anti-hydrolysis agent, wherein the amount of the anti-hydrolysis agent added is 0.2-0.6 parts.

[0026] By employing the above technical solution, the dopamine coating achieves anchorage through the formation of coordination bonds between catechols and calcium ions on the calcium carbonate surface. These coordination bonds are easily broken in acidic environments, and the terminal carboxyl groups generated by PHA hydrolysis locally lower the system's pH, thereby weakening the stability of the coordination bonds. The anti-hydrolysis agent molecule contains active groups that can react with the terminal carboxyl groups, preferentially capturing them and maintaining a near-neutral environment in the system, thus protecting the catechol-Ca... 2+ The coordination bonds remain intact, ensuring the filler remains firmly anchored during long-term use. Simultaneously, the antioxidant inhibits thermal degradation during processing, reducing the initial formation of terminal carboxyl groups; the anti-hydrolysis agent continuously captures newly formed terminal carboxyl groups during use. Together, they form a complementary mechanism of "processing-induced degradation inhibition and use-induced hydrolysis inhibition," providing comprehensive protection of material properties over time and significantly improving the toughness and heat resistance of the PHA composition.

[0027] Preferably, the anti-hydrolysis agent is polycarbodiimide or monomeric carbodiimide.

[0028] By employing the above technical solution, the highly reactive carbodiimide groups in polycarbodiimide or monomeric carbodiimide molecules can preferentially and rapidly react with the terminal carboxyl groups generated by thermal degradation or hydrolysis of PHA molecular chains, converting them into stable urea derivatives. Compared to other anti-hydrolysis agents such as oxazoline or epoxy compounds, carbodiimides exhibit higher reactivity and faster reaction rates with terminal carboxyl groups, achieving highly efficient end-capping even with small amounts added.

[0029] When HMDI is preferred as the chain extender, the carbodiimide group in the anti-hydrolysis agent preferentially captures the terminal carboxyl groups generated by the thermal degradation or hydrolysis of PHA, converting them into inert urea derivatives. This avoids excessive consumption of the isocyanate groups of HMDI by the terminal carboxyl groups, allowing HMDI to fully react with the terminal hydroxyl groups of PHA and the amino groups on the surface of dopamine-modified calcium carbonate, thus efficiently exerting its chain extension and interface anchoring effects. At the same time, the anti-hydrolysis agent continuously removes newly generated terminal carboxyl groups during use, completely blocking the autocatalytic hydrolysis chain reaction of ester bonds, protecting the urea and urethane bond network constructed by HMDI from being destroyed. The two work together to ensure the efficient construction of the chemical bond network from the filler through the interface to the matrix during the processing stage and the long-term stability during the use stage, thereby ensuring that the PHA composition can still maintain high toughness under high temperature and high humidity usage scenarios.

[0030] Secondly, this application provides a method for preparing a PHA composition, which adopts the following technical solution: A method for preparing a PHA composition includes the following steps: melt-blending PHA, toughening agent, modified calcium carbonate, chain extender, nucleating agent, lubricant, antioxidant and anti-hydrolysis agent in a specified amount, and then extruding, stretching and granulating the mixture to obtain the PHA composition.

[0031] In summary, this application includes at least one of the following beneficial technical effects: 1. This application utilizes modified calcium carbonate to form a polydopamine coating layer via dopamine self-polymerization, with the surface rich in active groups such as catechol and amino groups. During melt blending, amino groups, catechols, and the terminal carboxyl and hydroxyl groups of PHA and PBAT / PBS undergo amidation and esterification reactions to form covalent bonds, firmly connecting the filler to the matrix. Simultaneously, catechols coordinate with calcium ions on the calcium carbonate surface, achieving stable anchoring of the filler and constructing a covalent bond network from the filler through the interface to the matrix, forming a "chemical interlocking" structure. This allows for efficient stress transfer, prevents breakage, and imparts excellent hot water resistance to the PHA composition. Combined with the molecular chain reinforcement of reactive chain extenders and the synergistic effects of nucleating agents, lubricants, and antioxidants, the brittleness of PHA is effectively overcome, significantly improving toughness and impact resistance, meeting daily use and environmental protection requirements. 2. The isocyanate groups at both ends of the HMDI molecule in this application exhibit dual reactivity during melt blending: on the one hand, they react with the terminal hydroxyl and carboxyl groups of PHA and PBAT / PBS to generate urethane and amide bonds, thereby extending the molecular chain, compensating for the decrease in molecular weight caused by the thermal degradation of PHA, and improving the melt strength and mechanical properties of the matrix; on the other hand, they react with the amino and catechol groups on the surface of dopamine-modified calcium carbonate to generate urea and urethane bonds, covalently anchoring the filler to the polymer network. Thus, HMDI acts as a "molecular bridge," constructing a complete covalent bond network from the filler through the interface to the polymer, enabling the PHA composition to significantly improve its heat resistance and hydrolysis resistance while maintaining high toughness. 3. In this application, when the chain extender is preferably HMDI, the carbodiimide group in the anti-hydrolysis agent preferentially captures the terminal carboxyl groups generated by the thermal degradation or hydrolysis of PHA, converting them into inert urea derivatives. This avoids the excessive consumption of the isocyanate groups of HMDI by the terminal carboxyl groups, allowing HMDI to fully react with the terminal hydroxyl groups of PHA and the amino groups on the surface of dopamine-modified calcium carbonate, thus efficiently exerting the chain extension and interface anchoring effects. At the same time, the anti-hydrolysis agent continuously removes newly generated terminal carboxyl groups during use, completely blocking the autocatalytic hydrolysis chain reaction of ester bonds, protecting the urea bond and urethane bond network constructed by HMDI from being destroyed. The two work together to ensure the efficient construction of the chemical bond network from the filler through the interface to the matrix during the processing stage and the long-term stability during the use stage, thereby ensuring that the PHA composition can still maintain high toughness under high temperature and high humidity usage scenarios. Detailed Implementation

[0032] The raw materials in this application include the following: Tris-HCl buffer solution: The commercially available product CAS#1185-53-1 from Wuhan Desheng Biochemical Technology Co., Ltd. was used.

[0033] Dopamine hydrochloride: Use the commercially available product with CAS number 62-31-7.

[0034] Calcium carbonate: Commercially available product with CAS number 471-34-1 and particle size of 2-5μm.

[0035] PHA: Uses product brand Blue Crystal from Blue Crystal Biotechnology Co., Ltd. TM The commercially available product PHABH2-ES004.

[0036] PBAT: Uses commercially available product with brand name BX7011 from Suzhou Guoyao New Materials Co., Ltd.

[0037] HMDI: Hexamethylene diisocyanate, using the commercially available product from Shanghai Jinjinle Industrial Co., Ltd. with CAS number 822-06-0.

[0038] Talc powder: The product used is a commercially available product with a particle size of 1250 mesh from Foshan Huiyisheng Technology Co., Ltd.

[0039] Stearamide: The product used is a commercially available product from Zhongshan Dixin Chemical Co., Ltd. with CAS number 124-26-5.

[0040] Antioxidant 1010: The product used is a commercially available product from Zhihua Hecheng Chemical (Jinan) Co., Ltd. with CAS number 6683-19-8.

[0041] Antioxidant 168: The product used is a commercially available product from Jiangsu Leien Environmental Protection Technology Co., Ltd. with CAS number 31570-04-4.

[0042] PBS: The commercially available product from Wuhan Kemic Biomedical Technology Co., Ltd., with CAS number 25777-14-4, was used.

[0043] ADR: Uses commercially available products from BASF, specifically the Joncryl® model ADR-4468.

[0044] MAH graft: namely maleic anhydride grafted PBAT, using commercially available product CYD-190A from Weihai Chenyuan Molecular New Materials Co., Ltd.

[0045] Sodium benzoate: The product used is a commercially available product from Henan Wanshan New Material Technology Co., Ltd. with CAS number 532-32-1.

[0046] Mica: Commercially available products with a particle size of 400-5000 mesh from Guangdong Yongfeng Chemical Co., Ltd.

[0047] Polyethylene wax: The product used is commercially available from Quzhou Baimao Technology Co., Ltd., model number BM-020.

[0048] Polycarbodiimide: The product used is the commercially available product UN-557 from Shanghai Bolino New Materials Technology Co., Ltd.

[0049] Monomer carbodiimide: The commercially available product with CAS number 2162-74-5 from Wuhan Kemic Biomedical Technology Co., Ltd.

[0050] Preparation Example 1 The preparation method of modified calcium carbonate includes the following steps: A1. Preparation of Tris-HCl buffer solution with pH=8.3: Weigh 1 kg of dopamine hydrochloride and dissolve it in 100 kg of Tris-HCl buffer solution, adjust the pH to 8.3, stir until completely dissolved, and obtain dopamine mixture; A2. Weigh 10 kg of calcium carbonate powder and add it to the above dopamine mixture. Stir and disperse at 300 rpm for 30 minutes at room temperature, then let it stand for 24 hours. After the reaction is complete, wash it three times with deionized water and dry it under vacuum at 60°C for 24 hours to obtain modified calcium carbonate.

[0051] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0052] Example 1

[0053] A PHA composition comprising the following steps: S1. Weigh 60 kg of PHA, 15 kg of modified calcium carbonate obtained from Preparation Example 1 above, 10 kg of PBAT, 0.8 kg of HMDI, 0.2 kg of talc, 0.8 kg of stearamide, and 0.6 kg of antioxidant 1010 and antioxidant 168 compounded in a mass ratio of 1:1. Then, put all the above raw materials into a high-speed mixer and mix at 500 rpm for 5 minutes at room temperature to obtain a premix. S2. The above premixed material is added to a twin-screw extruder for melt blending at a blending temperature of 160-175℃ (zone 1: 140℃, zone 2: 155℃, zone 3: 165℃, zone 4: 165℃, zone 5: 160℃, die head: 155℃, screw speed: 200r / min). The mixture is then extruded into strands, water-cooled, and pelletized to obtain the PHA composition.

[0054] Example 2

[0055] Example 2 is based on the preparation method of Example 1, except that PBAT is replaced with an equal amount of PBS, and all other conditions remain the same.

[0056] Examples 3-4 Examples 3-4 are based on the preparation method of Example 1, but the weight parts of each component in the formula are adjusted, while the other conditions remain unchanged.

[0057] Comparative Example 1 Comparative Example 1 was prepared using the same method as in Example 1, but the modified calcium carbonate was replaced with ordinary calcium carbonate, while all other conditions remained unchanged.

[0058] Comparative Example 2 Comparative Example 2 was prepared using the same method as in Example 1, but without the addition of modified calcium carbonate, and all other conditions remained unchanged.

[0059] The PHA compositions from Examples 1-4 and Comparative Examples 1-2 were fed into a single-screw extruder for melt extrusion molding. After vacuum sizing, cooling, traction, and cutting, PHA straws with an outer diameter of 6 mm and a wall thickness of 0.2 mm were obtained. The process parameters of the single-screw extruder were: (zone 1 temperature 150℃, zone 2 temperature 165℃, zone 3 temperature 170℃, die head temperature 165℃, screw speed 50 rpm). The obtained PHA straws were subjected to the following performance tests, and the specific test methods are as follows: Performance testing (1) Toughness The test was conducted in accordance with GB / T1040.2-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", using type 5 specimens and a tensile speed of 50 mm / min, to test the longitudinal tensile elongation at break (%) of the PHA composition.

[0060] (2) Impact resistance The test was conducted in accordance with GB / T1843-2008 "Determination of Impact Strength of Plastic Cantilever Beams". A type A notch was used, the sample size was 80mm×10mm×4mm, the pendulum energy was 2.75J, and the notched impact strength (kJ / m²) of the PHA composite material was tested.

[0061] (3) Heat resistance The Vicat softening temperature (VST) of the PHA composition material was tested in accordance with GB / T1633-2000 "Determination of Vicat softening temperature (VST) of thermoplastic plastics". The A50 method was used, the heating rate was 50℃ / h, the load was 10N, and the cross-sectional area of ​​the indenter was 1mm².

[0062] Based on the above detection method, the test results of Examples 1-4 and Comparative Examples 1-2 were obtained, as shown in Table 1 below.

[0063] Table 1. Components and performance test results of the PHA compositions in Examples 1-4 and Comparative Examples 1-2.

[0064] Referring to Table 1, a comparison of Examples 1-4 and Comparative Examples 1-2 shows that the toughness, impact resistance, and heat resistance of Examples 1-4 are significantly better than those of Comparative Examples 1-2. This is because Examples 1-4 use dopamine-modified calcium carbonate, which forms a polydopamine shell rich in amino and catechol groups on its surface. On the one hand, it is firmly anchored to the calcium carbonate surface through coordination bonds; on the other hand, under the synergistic effect of HMDI chain extender, it undergoes esterification and amidation reactions with the PHA and PBAT / PBS matrix, constructing a continuous covalent bond network from the filler to the polymer matrix, forming a strong interfacial "chemical interlocking" structure, effectively transferring stress, inhibiting crack propagation, and significantly improving the material's toughness and impact resistance. At the same time, the dense cross-linked network and the synergistic effect of nucleation crystallization significantly improve the heat resistance. Comparative Example 1 uses ordinary calcium carbonate, which is only a physical filler, resulting in poor interfacial compatibility, easy debonding, obvious stress concentration, and a significant decrease in mechanical properties and heat resistance. Comparative Example 2, without the addition of calcium carbonate, lacks both the reinforcement of the inorganic rigid framework and the interfacial bonding and crystallization regulation effects. The matrix molecular chains are easily deformed by heat and are brittle, resulting in the worst toughness, impact resistance, and heat resistance.

[0065] Examples 5-8 Examples 5-8 are based on the preparation method of Example 1, but the pH in A1 of Preparation Example 1 is adjusted while the other conditions remain unchanged. The specific adjustments are shown in Table 2.

[0066] The PHA straws prepared from the PHA compositions of Examples 5-8 were subjected to the above performance tests, and the test results are shown in Table 2.

[0067] Table 2. pH and performance test results in Examples 1 and 5-8

[0068] Referring to Table 2, a comparison of Examples 1 and 5-8 shows that the toughness and impact resistance of Example 1 are significantly better than those of Examples 5-8. This is because the optimal oxidative self-polymerization range of dopamine is the weakly alkaline pH range of 8.0–8.5. When the pH is within this range, dopamine can polymerize uniformly and moderately on the surface of calcium carbonate, forming a dense, complete polydopamine coating layer rich in amino and catechol active groups. This layer exhibits the highest interfacial bonding activity, providing a foundation for sufficient bonding reactions with the subsequent polymer matrix and HMDI, thus constructing a continuous and dense covalent bond network. Therefore, this endows the material with optimal toughness and impact resistance.

[0069] Example 9 Example 9 is based on the preparation method of Example 1, except that HMDI is replaced with an equal amount of ADR, and all other conditions remain unchanged.

[0070] Example 10

[0071] Example 10 is based on the preparation method of Example 1, except that HMDI is replaced with an equal amount of MAH graft material, and all other conditions remain unchanged.

[0072] The PHA straws prepared from the PHA compositions of Examples 9-10 were subjected to the above performance tests, and the test results are shown in Table 3.

[0073] The PHA pipettes prepared from the PHA compositions of Examples 9-10 above were analyzed using the following specific detection methods: (4) Hydrolysis resistance The test was conducted according to GB / T7141-2008 "Test Method for Thermal Aging of Plastics". The PHA straw was placed in a constant temperature and humidity chamber and aged for 7 days at 70℃ and 95% relative humidity. After removal, the tensile elongation at break was tested according to GB / T1040.3-2006, and the retention rate was calculated using the following formula: Retention rate (%) = (Elongation at break after aging / Elongation at break before aging) × 100% Based on the above detection method, the test results of Examples 9-10 were obtained, as shown in Table 3 below.

[0074] Table 3 Performance test results for Examples 1 and 9-10

[0075] Referring to Table 3, a comparison of Examples 1 and 9-10 shows that the toughness, impact resistance, heat resistance, and hydrolysis resistance of Example 1 are significantly better than those of Examples 9-10. This is because the HMDI molecule in Example 1 has highly active isocyanate groups at both ends, which can efficiently extend the chain and repair the PHA-degraded molecular chain, and at the same time form strong covalent bonds with the amino and catechol groups on the surface of dopamine-modified calcium carbonate, acting as a "molecular bridge" to construct a continuous and dense filler-interface-matrix covalent network. This allows the PHA composition to significantly improve hot water resistance and hydrolysis resistance while maintaining high toughness and high impact resistance. In contrast, the ADR in Example 9 only achieves chain extension and compatibilization through epoxy groups, and its reaction efficiency with the modified filler is relatively low. The MAH graft in Example 10 has fewer reaction sites with active groups and relatively weaker bonding ability. The two are not as effective as HMDI in improving interface anchoring and overall crosslinking.

[0076] Example 11

[0077] Example 11 is based on the preparation method of Example 1, except that talc powder is replaced with sodium benzoate, and all other conditions remain the same.

[0078] Example 12

[0079] Example 12 is based on the preparation method of Example 1, except that talc powder is replaced with mica, and all other conditions remain the same.

[0080] The PHA straws prepared from the PHA compositions of Examples 11-12 were subjected to the above performance tests, and the test results are shown in Table 4.

[0081] Table 4 Performance test results for Examples 1 and 11-12

[0082] Referring to Table 4, a comparison of Examples 1 and 11-12 shows that the toughness and heat resistance of Examples 1 and 11 are significantly better than those of Example 12. This is because both talc and sodium benzoate can play a good heterogeneous nucleation role for PHA, which can improve the crystallization rate and crystallinity, counteract the restriction of molecular chain movement by HMDI crosslinking, and enable the material to maintain high heat resistance and excellent toughness. However, the surface inertness of mica sheet structure and poor bonding with the resin interface make it difficult to disperse and easy to introduce defects. Not only is the nucleation efficiency low and it is difficult to promote PHA crystallization, but it will also destroy the covalent bond network composed of filler, interface and matrix, resulting in obvious stress concentration, which leads to a significant decrease in the heat resistance and a significant deterioration in toughness of the product.

[0083] Example 13

[0084] Example 13 is based on the preparation method of Example 1, except that stearamide is replaced with polyethylene wax, and all other conditions remain the same.

[0085] The PHA straws prepared from the PHA composition of Example 13 were subjected to the above performance test, and the test results are shown in Table 5.

[0086] Table 5 Performance test results for Examples 1 and 13

[0087] Referring to Table 5, it can be seen from the comparison between Example 1 and Example 13 that stearamide and polyethylene wax are both inert lubricants. During the processing, they only reduce internal and external friction and reduce shear heat. They do not undergo side reactions with the isocyanate groups of HMDI, which can ensure that HMDI can fully exert its chain extension and interfacial bonding effects and maintain a complete covalent network. Therefore, it has excellent toughness, impact resistance and heat resistance.

[0088] Example 14

[0089] Example 14 is based on the preparation method of Example 1, except that the mixture of antioxidant 1010 and antioxidant 168 is replaced with antioxidant 1010, while the other conditions remain unchanged.

[0090] Example 15

[0091] Example 15 is based on the preparation method of Example 1, except that the mixture of antioxidant 1010 and antioxidant 168 is replaced with antioxidant 168, while the other conditions remain unchanged.

[0092] The PHA straws prepared from the PHA compositions of Examples 14-15 were subjected to the performance tests described above, and the test results are shown in Table 6.

[0093] Table 6 Performance Test Tables for Examples 1 and 14-15

[0094] Referring to Table 6, a comparison of Example 1 and Examples 14-15 shows that the toughness, impact resistance, and heat resistance of Example 1 are significantly better than those of Examples 14-15. This is because Example 1 uses a combined antioxidant system of hindered phenol 1010 and phosphite 168. The two form a synergistic antioxidant effect by capturing hydrogen peroxide decomposition with free radicals, which can effectively inhibit the thermal oxidative degradation of PHA during high-temperature processing, reduce the generation of terminal carboxyl groups from the source, avoid excessive consumption of HMDI isocyanate groups, ensure the integrity of chain extension and interfacial covalent network construction, and protect the polydopamine coating layer from oxidation failure, thus achieving optimal toughness, impact resistance, and heat resistance of the material. Examples 14-15, on the other hand, all use a single antioxidant mechanism, which is insufficient in antioxidant effect, exacerbates PHA degradation, severely damages the molecular chain, and reduces the interfacial bonding strength, resulting in a significant decrease in performance.

[0095] Example 16

[0096] Example 16 is based on the preparation method of Example 1, but 0.4 kg of anti-hydrolysis agent polycarbodiimide is added to the formula, while the other conditions remain unchanged.

[0097] Example 17

[0098] Example 17 is based on the preparation method of Example 16, except that the anti-hydrolysis agent polycarbodiimide is replaced by an equal amount of monomeric carbodiimide, while the other conditions remain unchanged.

[0099] Examples 18-21 Examples 18-21 are based on the preparation method of Example 16, with adjustments made to the weight of the anti-hydrolysing agent, while keeping the other conditions unchanged. The specific adjustments are shown in Table 7.

[0100] The PHA straws prepared from the PHA compositions of Examples 16-21 were subjected to the above performance tests, and the test results are shown in Table 7.

[0101] Table 7. Anti-hydrolysis agent dosage and performance test results for Examples 1 and 16-21

[0102] Referring to Table 7, a comparison of Examples 1 and 16-17 shows that the toughness and heat resistance of the PHA composition after adding the anti-hydrolysis agent are significantly better than those of Example 1 without the anti-hydrolysis agent. This is because, without the anti-hydrolysis agent, PHA is easily degraded during processing and use, generating terminal carboxyl groups, making the system locally acidic, disrupting the coordination bond between dopamine and calcium carbonate, and consuming some HMDI, weakening the interfacial bonding and covalent network stability. However, the addition of polycarbodiimide or monomeric carbodiimide can quickly capture the terminal carboxyl groups generated by degradation, maintain a near-neutral environment in the system, and protect catechol-Ca. 2+ The covalent bond network formed by the coordination bonds and HMDI enhances the toughness and heat resistance of the material.

[0103] Comparing Examples 16 and 18-21, it is evident that both excessively high and low amounts of anti-hydrolysis agent will decrease the toughness and heat resistance of the material. This is because when the amount of anti-hydrolysis agent is too low, it cannot effectively capture the terminal carboxyl groups generated by PHA degradation, increasing the acidity of the system, breaking the coordination bond between dopamine and calcium carbonate, and consuming some HMDI, resulting in decreased interfacial bonding and reduced toughness and heat resistance. When the amount is too high, excessive anti-hydrolysis agent will form a small molecule enriched phase in the system, disrupting the matrix continuity and interfering with the covalent bonding between HMDI and the polymer and modified filler, weakening the interfacial anchoring effect, which also leads to a decrease in toughness and heat resistance.

[0104] 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 PHA composition, characterized in that, The product comprises the following components in parts by weight: 55-70 parts PHA, 10-20 parts modified calcium carbonate, 5-15 parts toughening agent, 0.4-1.2 parts chain extender, 0.1-0.3 parts nucleating agent, 0.5-1 part lubricant, and 0.3-1.0 parts antioxidant, wherein the toughening agent is at least one of PBAT or PBS; and the modified calcium carbonate is obtained by modification with dopamine.

2. The PHA composition according to claim 1, characterized in that, The method for preparing the modified calcium carbonate includes the following steps: (1) Dissolve dopamine hydrochloride in Tris-HCl buffer, adjust the pH to 8.0-8.5, and stir until completely dissolved to obtain a dopamine mixture; (2) Add calcium carbonate powder to the dopamine mixture, stir and disperse, let stand to react, wash and dry to obtain modified calcium carbonate.

3. The PHA composition according to claim 1, characterized in that, The chain extender is an HMDI, ADR, or MAH graft.

4. The PHA composition according to claim 3, characterized in that, The chain extender is HMDI.

5. The PHA composition according to claim 1, characterized in that, The nucleating agent is talc or an organic nucleating agent.

6. The PHA composition according to claim 1, characterized in that, The lubricant is stearamide or polyethylene wax.

7. The PHA composition according to claim 1, characterized in that, The antioxidants include hindered phenols and phosphites.

8. The PHA composition according to claim 1, characterized in that, The PHA composition further includes an anti-hydrolysis agent, wherein the amount of the anti-hydrolysis agent added is 0.2-0.6 parts.

9. The PHA composition according to claim 8, characterized in that, The anti-hydrolysis agent is polycarbodiimide or monomeric carbodiimide.

10. A method for preparing a PHA composition according to any one of claims 1-9, characterized in that, The process includes the following steps: melt-blending the formulated amounts of PHA, toughening agent, modified calcium carbonate, chain extender, nucleating agent, lubricant, antioxidant, and anti-hydrolysis agent, and then extruding, stretching, and granulating the mixture to obtain the PHA composition.

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