Polyhydroxyalkanoate composition and preparation method thereof

Abstract

The invention discloses a polyhydroxyalkanoate composition and a preparation method thereof. The polyhydroxyalkanoate composition comprises the following components in parts by mass: 100 parts of polyhydroxyalkanoate; 0.5 to 5 parts of unsaturated D-polylactic acid; 0.5 to 5 parts of poly (L-lactic acid); the preparation method comprises the following steps: S1, carrying out melt blending on the polyhydroxyalkanoate and the unsaturated D-polylactic acid, and enabling the polyhydroxyalkanoate and the unsaturated D-polylactic acid to fully react, so as to obtain an intermediate product; and S2, carrying out melt blending on the intermediate product obtained in the step S1, poly-L-lactic acid and an ester exchange inhibitor to finally obtain the polyhydroxyalkanoate composition with excellent thermal stability, high melt strength and high crystallization speed.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a polyhydroxyalkanoate composition and its preparation method. Background Technology

[0002] Polyhydroxyalkanoates (PHA) are among the fastest-growing natural biopolymers in recent years. They are intracellular polyesters synthesized by microorganisms. Research has revealed a wide variety of PHA monomers (more than one hundred have been identified so far), endowing them with excellent properties such as a wide range of structural options and diverse performance characteristics. Furthermore, since PHAs originate from natural microbial fermentation and have existed on Earth for tens of thousands of years, nature has evolved numerous microorganisms capable of digesting and degrading them. Therefore, PHAs exhibit excellent degradability, capable of degradation through various methods including seawater, freshwater, soil, home composting, and industrial composting. The flexible adjustability of material properties and excellent degradability make PHAs highly promising for applications in disposable tableware and packaging. However, PHAs suffer from two key performance defects that severely limit their industrial application: extremely low melt strength and slow crystallization rate.

[0003] First, the extremely low melt strength causes many problems during processing. For example, polyhydroxyalkanoates (PHA) are prone to severe curling and shrinkage at the edges during extrusion coating and calendering; cells are prone to collapse during foaming; thermoformed sheets have poor thickness uniformity and are prone to sag; and PHA melts are prone to bubble breakage, poor stretchability, and low yield during pipe extrusion. There are two main reasons for the low melt strength of PHA. On the one hand, because the molecular chains of PHA are linear, they are not easily entangled. During thermoforming, when the melt is stretched, slippage easily occurs between the molecular chains, making it difficult to resist external forces. On the other hand, the presence of a large number of α-hydrogens in the PHA structure makes it prone to thermal degradation during melt processing, further reducing its melt strength. Current research mainly focuses on chain extension of polyhydroxyalkanoates using isocyanates and epoxy compounds to improve their melt strength. However, due to the small number of end groups involved in the reaction and low reactivity of polyhydroxyalkanoates, these methods are not very effective in improving the melt strength of polyhydroxyalkanoates.

[0004] The slow crystallization rate of polyhydroxyalkanoates (PHA) results in a prolonged crystallization time during processing and molding, leading to low production efficiency. Furthermore, the slow crystallization speed can cause uneven crystallization within the product, resulting in residual internal stress, poor dimensional stability, and other issues that negatively impact product quality. While adding small-molecule nucleating agents is often used to improve the crystallization rate, these agents suffer from problems such as uneven dispersion, easy migration, and reduced biocompatibility, and their nucleation effect is limited.

[0005] Therefore, how to significantly improve the melt strength and crystallization rate of polyhydroxyalkanoates (PHA) to greatly expand their application in processing products such as coating, calendering, foaming, thermoforming, and pipe extrusion, while simultaneously improving production efficiency and product quality, still faces enormous challenges. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the above-mentioned background technology and provide a polyhydroxyalkanoate composition and preparation method, which has the characteristics of high melt strength and high crystallization speed.

[0007] This application provides a polyhydroxyalkanoate composition comprising the following components in parts by weight: Polyhydroxyalkanoate: 100 parts; Unsaturated dextrorotatory polylactic acid: 0.5-5 parts; Polylactic acid (PLA): 0.5-5 parts; Transesterification inhibitor: 0.01-0.2 parts.

[0008] Preferably, the polyhydroxyalkanoate is a homopolymer or copolymer containing at least one of the following hydroxyalkanoic acid monomers: 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvalerate, 5-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, 3-hydroxyoctanoate, 3-hydroxynonanoate, and 3-hydroxydecanoate, and the weight-average molecular weight of the polyhydroxyalkanoate is 50,000-1,000,000.

[0009] Preferably, the unsaturated dextrorotatory polylactic acid is prepared by the following method: dextrorotatory lactic acid, unsaturated dicarboxylic acid, and catalyst are reacted under nitrogen protection at a temperature of 140-180°C for 2-6 hours, wherein the molar ratio of dextrorotatory lactic acid, unsaturated dicarboxylic acid, and catalyst is 100:(5-20):(0.02-0.2), and then dehydrated to obtain unsaturated dextrorotatory polylactic acid.

[0010] Preferably, the unsaturated dicarboxylic acid is one or more of butenic acid, pentenic acid, hexenic acid, adipoderic acid, heptenic acid, and octenic acid.

[0011] Preferably, the catalyst is one or more of ethyl titanate, isopropyl titanate, and n-butyl titanate.

[0012] Preferably, the weight-average molecular weight of the L-polylactic acid is 5,000-200,000.

[0013] Preferably, the transesterification inhibitor is one or more of sodium sulfate, calcium sulfate, dimethyl stannate, and trimethyl stannate.

[0014] A method for preparing a polyhydroxyalkanoate composition includes the following steps: S1 involves melt-blending polyhydroxyalkanoate and unsaturated dextrorotatory polylactic acid to allow them to react fully and obtain an intermediate product. S2 involves melt blending the intermediate product obtained in step S1 with L-polylactic acid and an ester exchange inhibitor to obtain a polyhydroxyalkanoate composition with high melt strength and high crystallization rate.

[0015] Preferably, in step S1, the melt blending is performed using a twin-screw extruder at a temperature of 140-170℃ and a rotation speed of 200-400 rpm; in step S2, the melt blending is performed using a twin-screw extruder at a temperature of 160-180℃ and a rotation speed of 150-300 rpm.

[0016] Compared with related technologies, the present invention has the following advantages: This invention successfully prepared a polyhydroxyalkanoate composition with both high melt strength and high crystallization rate through innovative component synergy and preparation pathway. Its core advantages are based on a clear molecular interaction mechanism and structure-property relationship, specifically manifested in the following logically progressive technical effects: (1) The double bond structure provides excellent thermal stability, laying the foundation for processing and performance: In this invention, dextrorotatory polylactic acid containing carbon-carbon double bonds forms a block copolymer with polyhydroxyalkanoate through transesterification. The double bonds in this copolymer can accurately capture the free radicals generated by the thermal degradation of polyhydroxyalkanoate during melt processing, achieving partial termination of the thermal degradation reaction, thereby effectively improving the thermal stability of polyhydroxyalkanoate. Compared with traditional small molecule heat stabilizers, the double bond component, which is covalently linked to the polyhydroxyalkanoate molecular chain, is more uniformly distributed in the material and has no risk of later migration. This not only more efficiently ensures the thermal stability performance during processing but also significantly reduces food safety hazards.

[0017] (2) The "dendritic" structure strengthens molecular chain entanglement and improves melt strength: The multiple double bonds in the block copolymer can react with free radicals during melt processing to form a "dendritic" structure with multiple branched chains. This structure can significantly enhance the entanglement between molecular chains, improve the core defect of insufficient melt strength of polyhydroxyalkanoates at the molecular level, and lay the structural foundation for subsequent performance upgrades.

[0018] (3) The stereocomposite crystal achieves a breakthrough in dual core performance, taking into account both melt strength and crystallization speed: The L-type polylactic acid added in this invention has opposite chirality to the D-type polylactic acid in the block copolymer. During the melt blending process, the two pair up to form a stereocomposite polylactic acid crystal. This crystal optimizes key performance simultaneously through dual effects: On the one hand, the stereocomposite crystal connects L-type polylactic acid with the "dendritic" polyhydroxyalkanoate copolymer through crystallization, forming a giant "comb-like" structure with L-type polylactic acid as the "comb axis" and the "dendritic" polyhydroxyalkanoate copolymer as the "comb teeth". This unique structure of "comb teeth containing dendrites" further amplifies the entanglement effect of the "dendritic" structure on the molecular chain, achieving a significant improvement in the melt strength of polyhydroxyalkanoate; on the other hand, the stereocomposite crystal is connected to the polyhydroxyalkanoate molecular chain through covalent bonds, simultaneously connecting multiple polyhydroxyalkanoate molecular chains. The large number of multi-level branched structures formed can serve as efficient crystallization nucleation sites, significantly promoting the crystallization nucleation process of polyhydroxyalkanoate. This effect can effectively accelerate the crystallization rate of polyhydroxyalkanoates, shorten the product molding cycle, and improve production efficiency. At the same time, the uniform crystal structure can also improve the dimensional stability and mechanical property consistency of the product.

[0019] (4) Synergistic adaptation of processing and performance improvement to achieve simultaneous optimization of multiple benefits: In actual processing such as extrusion, casting, coating, and foaming, the polyhydroxyalkanoate composition of the present invention can produce a dual synergistic effect through stretching: First, it further promotes the formation of polylactic acid stereocomposite crystals, resulting in a larger melt stretching ratio, a faster stretching rate, a stronger molecular chain entanglement effect, and a unique advantage of "the more it is stretched, the stronger it becomes" in melt strength; Second, the formation of more stereocomposite crystals further optimizes its crystallization promoting effect on polyhydroxyalkanoate, and simultaneously improves the crystallization speed. Ultimately, through the synergistic adaptation of processing and performance improvement, the present invention achieves simultaneous improvement in the processing speed, product quality, and production efficiency of the polyhydroxyalkanoate composition. Detailed Implementation

[0020] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of this application and are not intended to limit the scope of protection of the embodiments of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0021] A polyhydroxyalkanoate composition comprising, by weight, the following components: Polyhydroxyalkanoate: 100 parts; Unsaturated dextrorotatory polylactic acid: 0.5-5 parts; Polylactic acid (PLA): 0.5-5 parts; Transesterification inhibitor: 0.01-0.2 parts.

[0022] A method for preparing a polyhydroxyalkanoate composition includes the following steps: (1) Add dextrorotatory lactic acid, unsaturated dicarboxylic acid and catalyst into a reaction vessel and react under nitrogen protection. Then dehydrate to obtain unsaturated dextrorotatory polylactic acid. The reaction temperature is 140-180℃ and the reaction time is 2-6 hours.

[0023] (2) Polyhydroxyalkanoate and unsaturated dextrorotatory polylactic acid obtained in step (1) are added to a twin-screw extruder for melt blending to allow them to react fully and obtain an intermediate product; (3) The intermediate product obtained in step (2) is added to a twin-screw extruder and melt-blended with L-polylactic acid and transesterification inhibitor to obtain a polyhydroxyalkanoate composition with high melt strength and high crystallization rate.

[0024] In step (2), the twin-screw extruder is melt-granulated at a temperature of 140-170℃ and a speed of 200-400rpm; in step (3), the twin-screw extruder is melt-granulated at a temperature of 160-180℃ and a speed of 150-300rpm.

[0025] Example 1 (1) D-lactic acid, butenedioic acid, and ethyl titanate in a molar ratio of 100:5:0.02 were added to a reaction vessel and reacted under nitrogen protection. Then, the mixture was dehydrated to obtain unsaturated polylactic acid. The reaction temperature was 140℃ and the reaction time was 6 hours.

[0026] (2) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxyvalerate) with a weight average molecular weight of 50,000 and 0.5 parts of unsaturated dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and melt-blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) is added to a twin-screw extruder along with 0.5 parts of polylactic acid with a weight average molecular weight of 5000 and 0.01 parts of sodium sulfate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0027] Example 2 (1) D-lactic acid, pentenedic acid, and isopropyl titanate in a molar ratio of 100:10:0.05 were added to a reaction vessel and reacted under nitrogen protection. Then, the mixture was dehydrated to obtain unsaturated polylactic acid. The reaction temperature was 150℃ and the reaction time was 5 hours.

[0028] (2) 100 parts of poly(3-hydroxybutyric acid, 5-hydroxyvalerate) with a weight average molecular weight of 100,000 and 1 part of unsaturated dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and melt-blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) is added to a twin-screw extruder along with 1 part of L-polylactic acid with a weight average molecular weight of 10,000 and 0.03 parts of calcium sulfate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0029] Example 3 (1) D-lactic acid, hexanediol, and tetrabutyl titanate in a molar ratio of 100:12:0.07 were added to a reaction vessel and reacted under nitrogen protection. Then, the mixture was dehydrated to obtain unsaturated polylactic acid. The reaction temperature was 160℃ and the reaction time was 4 hours.

[0030] (2) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxyhexanoic acid) with a weight average molecular weight of 200,000 and 2 parts of unsaturated dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and melt-blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) is added to a twin-screw extruder along with 2 parts of L-polylactic acid with a weight average molecular weight of 20,000 and 0.05 parts of dimethyl stannate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0031] Example 4 (1) D-lactic acid, adipate, and ethyl titanate in a molar ratio of 100:15:0.1 were added to a reaction vessel and reacted under nitrogen protection. The mixture was then dehydrated to obtain unsaturated polylactic acid. The reaction temperature was 170℃ and the reaction time was 3 hours.

[0032] (2) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxyheptanoic acid) with a weight average molecular weight of 400,000 and 3 parts of unsaturated dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and melt-blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) is added to a twin-screw extruder along with 3 parts of L-polylactic acid with a weight average molecular weight of 30,000 and 0.1 parts of trimethylstannate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0033] Example 5 (1) D-lactic acid, heptenedic acid, and isopropyl titanate in a molar ratio of 100:17:0.12 were added to a reaction vessel and reacted under nitrogen protection. Then, the mixture was dehydrated to obtain unsaturated polylactic acid. The reaction temperature was 180℃ and the reaction time was 2 hours.

[0034] (2) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxyoctanoic acid) with a weight average molecular weight of 600,000 and 4 parts of unsaturated dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and melt-blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) is added to a twin-screw extruder along with 4 parts of L-polylactic acid with a weight average molecular weight of 40,000 and 0.15 parts of calcium sulfate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0035] Example 6 (1) D-lactic acid, octenedioic acid, and tetrabutyl titanate in a molar ratio of 100:20:0.15 were added to a reaction vessel and reacted under nitrogen protection. Then, the mixture was dehydrated to obtain unsaturated polylactic acid. The reaction temperature was 170℃ and the reaction time was 3 hours.

[0036] (2) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxynonanoic acid) with a weight average molecular weight of 800,000 and 5 parts of unsaturated dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and melt-blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) is added to a twin-screw extruder along with 5 parts of L-polylactic acid with a weight average molecular weight of 50,000 and 0.2 parts of dimethyl stannate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0037] Example 7 (1) D-lactic acid, butenedioic acid, and tetrabutyl titanate in a molar ratio of 100:15:0.2 were added to a reaction vessel and reacted under nitrogen protection. Then, the mixture was dehydrated to obtain unsaturated polylactic acid. The reaction temperature was 180℃ and the reaction time was 3 hours.

[0038] (2) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxydecanoic acid) with a weight average molecular weight of 1,000,000 and 4 parts of unsaturated dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and melt-blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) is added to a twin-screw extruder along with 4 parts of L-polylactic acid with a weight average molecular weight of 20,000 and 0.15 parts of trimethylstannate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0039] Comparative Example 1 (without double bonds) (1) D-lactic acid and tetraethyl titanate in a molar ratio of 100:0.02 were added to a reaction vessel and reacted under nitrogen protection. Then, the mixture was dehydrated to obtain polylactic acid. The reaction temperature was 140℃ and the reaction time was 2 hours.

[0040] (2) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxyvalerate) with a weight average molecular weight of 50,000 and 0.5 parts of dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and reactively blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) is added to a twin-screw extruder along with 0.5 parts of polylactic acid with a weight average molecular weight of 5000 and 0.01 parts of sodium sulfate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0041] Comparative Example 2 (without polylactic acid) (1) D-lactic acid, butenedioic acid, and ethyl titanate in a molar ratio of 100:5:0.02 were added to a reaction vessel and reacted under nitrogen protection. Then, the mixture was dehydrated to obtain unsaturated polylactic acid. The reaction temperature was 140℃ and the reaction time was 6 hours.

[0042] (2) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxyvalerate) with a weight average molecular weight of 50,000 and 0.5 parts of unsaturated dextrorotatory polylactic acid obtained in step (1) were added to a twin-screw extruder and reactively blended at 160°C and 300 rpm to obtain an intermediate product. (3) The intermediate product obtained in step (2) and 0.01 parts of sodium sulfate were added to a twin-screw extruder and melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0043] Comparative Example 3 (non-reactive blend of polylactic acid and polyhydroxyalkanoate) (1) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxyvalerate) with a weight average molecular weight of 50,000 and 0.5 parts of commercially available dextrorotatory polylactic acid with a weight average molecular weight of 5,000 were added to a twin-screw extruder and blended at 160°C and 300 rpm to obtain an intermediate product. (2) The intermediate product obtained in step (1) is added to a twin-screw extruder along with 0.5 parts of polylactic acid with a weight average molecular weight of 5000 and 0.01 parts of sodium sulfate. The mixture is then melt-blended at 170°C and 200 rpm to obtain a polyhydroxyalkanoate composition.

[0044] Comparative Example 4 (pure polyhydroxyalkanoate) (1) 100 parts of poly(3-hydroxybutyric acid, 3-hydroxyvalerate) with a weight average molecular weight of 50,000 were added to a twin-screw extruder and extruded at 160°C and 300 rpm to obtain an intermediate product; (2) The intermediate product obtained in step (1) is further added to a twin-screw extruder and extruded at 170°C and 200 rpm to obtain polyhydroxyalkanoate.

[0045] Effect Example The thermal decomposition temperature, melt strength, and crystallization rate of the polyhydroxyalkanoates obtained in Examples 1-7 and Comparative Examples 1-4 were tested.

[0046] Thermal decomposition temperature test: The test was conducted according to GB / T27761-2011 standard. The test conditions were: nitrogen atmosphere, heating rate of 10℃ / min, and temperature scan range of 20-700℃. The temperature corresponding to 5% weight loss of the material on the thermogravimetric curve was taken as the thermal decomposition temperature of the material.

[0047] Melt strength test: The experimental setup consisted of a single-screw extruder with a 2mm die diameter and a Gottfert Rheotens 71.97 melt strength tester. First, the resin melt to be tested was extruded from the extruder die. Then, the resulting extruded melt bundle was pulled by two rollers moving in opposite directions on a balance beam. The force exerted on the stretched melt bundle is a function of roller speed and time. The rollers rotated at a uniform acceleration until the melt bundle broke; the force exerted at the breakage point was defined as the melt strength. The test temperature was 170℃.

[0048] Crystallization rate test: Differential scanning calorimetry (DSC) was used to test the crystallization rate according to GB / T19466.3-2004 standard. The test conditions were as follows: the sample was heated from 20℃ to 180℃ and held at that temperature for 5 min to eliminate thermal history. Then, the sample was cooled to 10℃ at a cooling rate of 10℃ / min. The onset temperature, peak temperature and crystallization enthalpy of the exothermic crystallization peak were recorded. The half-crystallization time (t1 / 2) was used as the evaluation index of crystallization rate. The shorter the half-crystallization time, the faster the crystallization rate.

[0049] The test results are shown in Table 1.

[0050] Table 1. Performance test data for each embodiment and comparative example Results Analysis Compared to Example 1, Comparative Example 1 did not introduce unsaturated double bonds into dextrorotatory polylactic acid. A comparison of the data from both examples revealed that the introduction of unsaturated bonds into the polyhydroxyalkanoate composition not only significantly improved the thermal stability and melt strength of the polyhydroxyalkanoate, but also promoted the crystallization of the polyhydroxyalkanoate by forming more branched structures, thus shortening its crystallization time.

[0051] Compared to Example 1, Comparative Example 2 did not add L-polylactic acid to the polyhydroxyalkanoate composition. A comparison of the data from both examples revealed that the introduction of L-polylactic acid is one of the key prerequisites for the formation of stereocomposite crystals. It not only significantly improves the melt strength and thermal stability of polyhydroxyalkanoate, but also forms stereocomposite crystals with covalent bonds to polyhydroxyalkanoate by pairing with unsaturated dextrorotatory polylactic acid, which significantly accelerates the crystallization of polyhydroxyalkanoate. This effect cannot be achieved by simply adding unsaturated dextrorotatory polylactic acid.

[0052] Compared to Example 1, Comparative Example 3 did not include unsaturated dextrorotatory polylactic acid (DPL) in the polyhydroxyalkanoate composition; instead, it included conventional DPL. Therefore, the polymers L-PL, DPL, and polyhydroxyalkanoate were merely physically blended without establishing effective covalent bonds. A comparison of the data revealed that in Example 1, unsaturated DPL and polyhydroxyalkanoate underwent a transesterification reaction catalyzed by ethyl titanate, forming covalent bonds. Simultaneously, the stereocomplex formed by unsaturated DPL and L-PL synergistically constructed an effective hierarchical branched structure, significantly improving melt strength and promoting polyhydroxyalkanoate crystallization. In contrast, in Comparative Example 3, the stereocomplex formed by DPL and L-PL was simply physically blended with polyhydroxyalkanoate without forming effective covalent bonds. Therefore, it could not assist in the formation of a hierarchical branched structure in polyhydroxyalkanoate, and thus could not significantly improve melt strength and crystallization speed.

[0053] Comparative Example 4 is pure polyhydroxyalkanoate, which has the lowest thermal decomposition temperature and melt strength, and the slowest crystallization rate (half-crystallization time as long as 2.01 min). This fully demonstrates that the present invention achieves a synergistic improvement in melt strength, thermal stability and crystallization rate by combining unsaturated dextrorotatory polylactic acid, levorotatory polylactic acid and transesterification inhibitor, thus solving the multiple performance defects of pure polyhydroxyalkanoate.

[0054] Those skilled in the art will readily understand that the above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0055] The above description is merely a specific embodiment of this application. However, the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A polyhydroxyalkanoate composition, characterized in that, The following components are included by mass: Polyhydroxyalkanoate: 100 parts; Unsaturated dextrorotatory polylactic acid: 0.5-5 parts; Polylactic acid (PLA): 0.5-5 parts; Transesterification inhibitor: 0.01-0.2 parts.

2. The polyhydroxyalkanoate composition according to claim 1, characterized in that, The polyhydroxyalkanoate is a homopolymer or copolymer containing at least one of the following hydroxyalkanoic acid monomers: 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvalerate, 5-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, 3-hydroxyoctanoate, 3-hydroxynonanoate, and 3-hydroxydecanoate, and the weight-average molecular weight of the polyhydroxyalkanoate is 50,000-1,000,000.

3. The polyhydroxyalkanoate composition according to claim 1, characterized in that, The unsaturated dextrorotatory polylactic acid is prepared by the following method: dextrorotatory lactic acid, unsaturated dicarboxylic acid, and catalyst are reacted under nitrogen protection at a temperature of 140-180℃ for 2-6 hours, wherein the molar ratio of dextrorotatory lactic acid, unsaturated dicarboxylic acid, and catalyst is 100:(5-20):(0.02-0.2), and then dehydrated to obtain unsaturated dextrorotatory polylactic acid.

4. The polyhydroxyalkanoate composition according to claim 3, characterized in that, The unsaturated dicarboxylic acid is one or more of butenic acid, pentenic acid, hexenic acid, adipoderic acid, heptenic acid, and octenic acid.

5. The polyhydroxyalkanoate composition according to claim 3, characterized in that, The catalyst is one or more of ethyl titanate, isopropyl titanate, and n-butyl titanate.

6. The polyhydroxyalkanoate composition according to claim 1, characterized in that, The weight-average molecular weight of the L-polylactic acid is 5,000-200,000.

7. The polyhydroxyalkanoate composition according to claim 1, characterized in that, The transesterification inhibitor is one or more of sodium sulfate, calcium sulfate, dimethyl stannate, and trimethyl stannate.

8. A method for preparing a polyhydroxyalkanoate composition according to any one of claims 1-7, characterized in that, Includes the following steps: S1 involves melt-blending polyhydroxyalkanoate and unsaturated dextrorotatory polylactic acid to allow them to react fully and obtain an intermediate product. S2 involves melt blending the intermediate product obtained in step S1 with L-polylactic acid and an ester exchange inhibitor to obtain a polyhydroxyalkanoate composition with high melt strength and high crystallization rate.

9. The method for preparing the polyhydroxyalkanoate composition according to claim 8, characterized in that, In step S1, melt blending is performed using a twin-screw extruder at a temperature of 140-170℃ and a speed of 200-400 rpm; in step S2, melt blending is performed using a twin-screw extruder at a temperature of 160-180℃ and a speed of 150-300 rpm.

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