A high melt strength modified polyhydroxyalkanoate material and its preparation and use

Abstract

The application provides a modified polyhydroxyalkanoate material, which comprises polyhydroxyalkanoate segments and polyurethane segments, wherein the polyurethane segments are obtained by the reaction of a melting agent and polyhydroxyalkanoate. The melt strength of PHA is effectively improved, and the mechanical property is enhanced by continuous reaction extrusion. The polyhydroxyalkanoate is modified by using an isocyanate melting agent and a high-performance catalyst, so that the polymer segments are crosslinked, the crystallinity of the modified PHA is effectively reduced, and the mechanical property, elongation and breaking energy of the modified PHA are significantly increased.

Description

Technical Field

[0001] This invention belongs to the field of biomaterials, specifically relating to a high melt strength modified polyhydroxy fatty acid ester material, its preparation method, and its application. Background Technology

[0002] Polyhydroxyalkanoate (PHA) materials, as bio-based biodegradable materials prepared by microbial fermentation, have broad application prospects in the field of biodegradable materials. Due to their preparation via microbial fermentation, they possess advantages such as tunable molecular structure and properties. With optimized industrial scale-up technology, low-cost production is expected. Furthermore, PHA is composed of aliphatic polyesters, making it easily decomposed by microorganisms after use. Therefore, PHA is an excellent bio-based biodegradable material with tunable properties, promising low cost and easy microbial decomposition. (Brandi H et al. Degradation and applications of polyhydroxyalkanoates. Can. J. Microbiol, 1995, 41: 143-153; Ong SY et al. Degradation of polyhydroxyalkanoate (PHA): a review. 2017; Bugnicourt E et al. Polyhydroxyalkanoate (PHA): Review of synthesis, characteristics, processing and potential applications in packaging. 2014).

[0003] However, PHA materials differ from traditional polyester materials in their preparation methods. Due to their different chemical structures and the absence of the high-temperature melt chain extension processes involved in traditional polyesters within a reactor, the resulting polymers often exhibit lower melt strength, poor film processing performance, and typically weak mechanical properties. Furthermore, they suffer from low crystallinity, long crystallization cycles, and a tendency for secondary crystallization. During processing and molding, the high temperatures and screw shearing cause ester bond breakage, leading to thermomechanical degradation and further impacting the mechanical properties of the molded material (Wang S et al. Modification and potential application of short-chain-length polyhydroxyalkanoate (SCL-PHA). Polymers 2016; 8:273). This results in PHA materials generally exhibiting poor mechanical properties, a narrow processing window, low melt strength, and poor processing performance.

[0004] Isocyanates, as highly active hydroxyl-terminated end-capping agents, can effectively reduce the hydroxyl content of PHA, thus improving material stability. For example, Chinese patent CN108377821A uses isocyanate as an end-capping agent in a PHA-based multilayer barrier film material to reduce its own hydroxyl content, weakening the likelihood of the groups capturing water molecules in the environment and undergoing hydrolysis. This improves material stability and water-blocking performance. However, in this patent, only isocyanate is added as an end-capping agent, improving its stability but not its overall mechanical and processing properties.

[0005] Chinese patent CN104245839A describes modifying PHA with thermoplastic polyurethane (TPU) derived from the reaction of adipic acid with diphenylmethane diisocyanate (MDI). This patent employs a physical blending method between PHA and TPU to improve its processing properties, significantly enhancing its impact strength and flexural modulus. However, even after modification using this method, the elongation at break of PHA remains low, at only about 3%, making it difficult to achieve film-grade applications. Summary of the Invention

[0006] To address the aforementioned problems, this invention employs a continuous reactive extrusion method to modify PHA (polyhydroxyalkanoates). Under the action of a highly efficient catalyst, polyisocyanates are added to perform melt reinforcement modification on PHA, urethane-linking the terminal hydroxyl groups of different PHA molecules and introducing a polyurethane-like chemical structure between PHA molecules. This significantly enhances its mechanical elongation and melt strength, ultimately improving the processing and mechanical properties of the PHA material.

[0007] One objective of this invention is to provide a modified polyhydroxyalkanoate material comprising polyhydroxyalkanoate segments and polyurethane segments, wherein the polyurethane segments are obtained by reacting a melt improver with the polyhydroxyalkanoate, and the melt improver is a reactive functional additive capable of increasing melt strength. By mass percentage, the polyurethane segment content in the modified polyhydroxyalkanoate material is 0.05–25%, preferably 0.5–10%.

[0008] Specifically, the fluxing agent is selected from binary or polyisocyanate compounds, preferably from at least one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and dicyclohexylmethane-4,4'-diisocyanate (HMDI), and more preferably from one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isoflurone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI).

[0009] A second objective of this invention is to provide a method for preparing the aforementioned modified polyhydroxyalkanoate material, comprising reacting components including polyhydroxyalkanoate and a melt improver to obtain the modified polyhydroxyalkanoate material. Preferably, the preparation method specifically includes the following steps:

[0010] Step 1: Premix the components, including the melt improver and catalyst;

[0011] Step 2: After the premix obtained in Step 1 and the polyhydroxy fatty acid ester are subjected to a melt reaction, the modified polyhydroxy fatty acid ester material is obtained; wherein the premix obtained in Step 1 and the polyhydroxy fatty acid ester can be fed together or separately.

[0012] In the above preparation method, the melt enrichment agent is selected from polyisocyanate compounds, preferably from at least one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and dicyclohexylmethane-4,4'-diisocyanate (HMDI), and more preferably from one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isoflurone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI);

[0013] The catalyst is selected from at least one of tertiary amines and organotin catalysts, preferably from at least one of triethylamine, triethylenediamine, dimethylaniline, stannous octoate, dibutyltin dilaurate, stannous chloride, and dibutyltin dioctanoate, and more preferably from at least one of triethylamine, triethylenediamine, stannous chloride, stannous octoate, and dibutyltin dioctanoate;

[0014] The polyhydroxy fatty acid ester is selected from homopolymers or copolymers of hydroxy fatty acids having 4 to 18 carbon atoms, and has the structure shown in molecular formula (I):

[0015]

[0016] Wherein, R is an alkyl group with a carbon chain length of 1 to 15.

[0017] Preferably, the polyhydroxy fatty acid ester is selected from at least one of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate);

[0018] The weight-average molecular weight M of the polyhydroxy fatty acid ester w ≥50000 g / mol, preferably M w Greater than or equal to 100,000 g / mol.

[0019] In the above preparation method, based on 100 parts by weight of the polyhydroxy fatty acid ester, the amount of the melt enrichment is 0.01 to 5 parts, preferably 0.1 to 2 parts; the amount of the catalyst is 0.001 to 5 parts, preferably 0.01 to 1 part.

[0020] In the above preparation method, in step 1:

[0021] Premixing components including melt improvers and catalysts can be done using common mixing methods and equipment in the prior art, such as kneaders or high-speed mixers.

[0022] In the above preparation method, step 2:

[0023] The melt reaction can be carried out using melt reaction processes commonly used in the field of polymer material processing. The process conditions and equipment can also adopt the conditions and equipment commonly used in the prior art. Specifically, it can be carried out by screw melt extrusion, preferably using a twin-screw extruder for the melt reaction, which can be a co-rotating or counter-rotating twin-screw extruder. Preferably, the melt reaction temperature is 50-300℃, more preferably 100-200℃; the screw speed of the melt reaction is 5-1200 rpm, more preferably 20-400 rpm.

[0024] The twin-screw extruders used in this invention include, but are not limited to: the Micro27 twin-screw extruder manufactured by Leistritz GmbH in Germany, which has the function of switching between co-rotation and counter-rotation; co-rotation twin-screw extruders such as PolyLab and EuroLab manufactured by Thermo Fisher Scientific in the United States; and the ZSK 30 co-rotation parallel twin-screw extruder manufactured by Coperion GmbH in Germany.

[0025] A third objective of this invention is to provide a high melt strength modified polyhydroxyalkanoate (PHA) material, prepared by the above-described method, wherein the melt strength of the modified PHA material is greater than 5 cN. Using the above preparation method, after melt reinforcement modification, the melt strength of PHA is increased to 5–30 cN, the tensile speed is increased to 50–150 mm / s, the elongation at break of PHA is increased by 15 times, reaching up to 300%, and the breaking energy of PHA is increased by more than 15 times, reaching 6.72 J / m. 3 .

[0026] The fourth objective of this invention is to apply the above-mentioned high melt strength modified polyhydroxy fatty acid ester material to biodegradable film materials.

[0027] In this invention, a continuous reactive extrusion method is used to induce reactions between the isocyanate melt modifier and PHA molecular chains under the action of a catalyst, including in-situ chain extension and cross-linking of PHA. This process modifies PHA in situ, forming a polyurethane structure that significantly enhances its mechanical properties (such as elongation at break) and melt strength. The elongation at break of PHA is increased by 15 times, reaching 300%; the breaking energy of PHA is increased by more than 15 times, reaching 6.72 J / m. 3 This significantly improves the melt strength and mechanical properties of PHA, resulting in a significant increase in parameters such as melt strength, elongation at break, and fracture energy, effectively improving the processability of PHA.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention employs isocyanate-based melt expanders and high-performance catalysts to modify polyhydroxyalkanoates (PHAs) through melt expansion. The introduction of the catalyst significantly enhances the melt expansion effect of PHAs, causing chain extension and cross-linking of the PHA chains. This results in a significant reduction in the melt index, an increase in melt strength, and superior processing performance.

[0030] 2. The present invention uses isocyanate-based melt modifiers to modify polyhydroxy fatty acid esters, which significantly improves the mechanical properties of the modified polyhydroxy fatty acid ester materials, and its elongation at break and fracture energy are significantly improved.

[0031] 3. The preparation method provided by this invention is simple and easy to implement, can be continuously produced, is green and environmentally friendly, and is easy to industrialize. Attached Figure Description

[0032] Figure 1 DSC cooling curves of the blank example and the modified PHA particles in Examples 1-5;

[0033] Figure 2 Total reflectance infrared curves of unmodified PHA and HDI-modified PHA particles with different addition amounts;

[0034] Figure 3 Melt strength of the modified PHA particles in Examples 1-5;

[0035] Figure 4 XRD patterns of PHA particles modified with different amounts of HDI;

[0036] Figure 5 Elongation at break of blank examples, Examples 1-5 and Comparative Examples 1-2 injection molded specimens. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0038] The testing instruments and conditions used in this embodiment are as follows:

[0039] Melt flow index (MFR) determination method: According to ISO 1133 standard, the Lloyd Davenport MFI–10 / 230 melt flow indexer was used for determination. The barrel temperature was 150℃, the mass load was 2.16kg, the die diameter was 2.095mm and the length was 8mm, the preheating time was 4min, the sample was automatically cut at set time intervals, 5 samples were taken and the average value was calculated. The result was expressed as grams per 10 minutes (g / 10min).

[0040] Thermal performance analysis (DSC): Tests were performed on a Discovery series differential scanning calorimeter (DSC) manufactured by TA Instruments, using TA Instruments Trios version 3.1.5 software. This DSC instrument is equipped with a Refrigerated Cooling System 90 mechanical refrigeration accessory. The test atmosphere was nitrogen at a flow rate of 50 mL / min, and the required sample volume was 5–10 mg. The test procedure was as follows: the temperature was first stabilized at 40 °C, then increased to 220 °C at a rate of 10 °C / min and held for 1 min to remove thermal history. The temperature was then decreased to -50 °C at a rate of 10 °C / min and held for 1 min, followed by an increase to 220 °C at a rate of 10 °C / min. The cooling process and the second heating process were recorded to study the thermal properties of the sample. The crystallization temperature ("T") of the sample can be directly obtained from the DSC test using software. c Melting temperature (T) m ”), glass transition (“T”) g Information such as enthalpy change ("H"), etc.

[0041] Total reflectance infrared testing (ATR-FTIR): Total reflectance infrared spectroscopy testing is performed using a Frontier FTIR (Waltham, MA, USA) manufactured by PerkinElmer in the United States, equipped with universal ATR accessories.

[0042] Melt strength test: Measured using a Rosand RH7 / 10 capillary rheometer. The tube orifice diameter was 15 mm, and the diaphragm diameter was 1 mm. The test temperature was 155℃, the initial stretching rate was 2 m / min, the final stretching rate was 100 m / min, and the test time was 5 min.

[0043] Plastic tensile testing: Following ISO 527–2 standard, the test was conducted using an Instron 3344 material testing machine with Bluehill version 2.31 software. The films were cut into Type 5A shapes according to ISO 527–2, parallel to the tensile direction (MD) and perpendicular to the tensile direction (CD), and placed in a Bluepard BPS-100CB constant temperature and humidity chamber (23℃, 50% relative humidity) at Shanghai Yiheng Scientific Instruments Co., Ltd. for 24 hours. During testing, the initial clamp spacing was 50 mm, the tensile rate was 10 mm / min, and each sample was tested at least 5 times, with the average value taken.

[0044] Wide-angle X-ray diffraction (XRD) testing: XRD tests were performed on a Scintag XDS-2000 instrument. The appropriate scattering amount was q = 1.5–40 nm. -1 Wide-angle X-ray diffraction (WAXRD) analysis was performed at room temperature.

[0045] The raw materials used and their sources in the examples are as follows:

[0046] The hexamethylene diisocyanate (HDI) used in this invention is selected from Bailingwei Technology, and the polyhydroxyalkanoate (PHA) has a weight-average molecular weight (M). w The 300,000 g / mol concentration was selected from Tianjin Green Su Company. Stannous chloride (SnCl2) was selected from Maclean's reagents. Diphenylmethane diisocyanate (MDI) was selected from Shanghai Maclean Biochemical Technology Co., Ltd.

[0047]

Blank example 1

[0048] In blank example 1, PolyLab HAAKE from Thermo Fisher Scientific, Inc., was selected. TMA Rheomex OSPTW16 co-rotating twin-screw extruder (screw diameter 16mm, L / D = 40) was used for melt extrusion of PHA. 100 parts by weight of PHA powder were added to the twin-screw extruder, which consisted of 11 sections from the feed port to the die, numbered 1–11. Section 1 only served as the feeding section and was not heated. The temperatures of sections 2–11 were 120℃, 140℃, 140℃, 150℃, 150℃, 160℃, 160℃, 160℃, 160℃, and 140℃, respectively, with the screw speed set at 50 rpm. PHA was fed into section 1 of the twin-screw extruder using a loss-in-weight feeder at a feed rate of 0.6 kg / h. After stable operation, the twin-screw extrusion pressure was 10–20 bar, and the torque was approximately 82%. The extruder is equipped with two circular outlets, each with a diameter of 4 mm. After the sample is extruded from the die, it passes through a water bath cooling tank and is cut into cylindrical particles with a length of about 5 mm by a pelletizer. After being vacuumed in a vacuum drying oven at 70℃ for 4 hours, the particles are collected, packaged, and ready for use.

[0049] [Examples 1-5] Preparation of high melt strength polyhydroxy fatty acid value

[0050] Example 1 included different amounts of the melt expander HDI. PolyLab HAAKE from Thermo Fisher Scientific, USA, was selected. TM PHA was modified using a Rheomex OS PTW16 co-rotating twin-screw extruder (screw diameter 16mm, L / D=40).

[0051] By weight, 0.03 parts of stannous chloride catalyst, different amounts of HDI, and 100 parts of PHA powder were premixed in a mixer and then injected into a twin-screw extruder for melt reaction. The amounts of HDI added were 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts, and 1 part, respectively.

[0052] The twin-screw extruder consists of 11 sections from the feed inlet to the die, numbered 1–11. Section 1 only serves as the feeding section and is not heated. The temperatures of sections 2–11 are 120℃, 140℃, 140℃, 150℃, 150℃, 160℃, 160℃, 160℃, 160℃, and 140℃, respectively, with the screw speed set at 50 rpm. PHA mixture is fed into section 1 of the twin-screw extruder using a loss-in-weight feeder at a feeding rate of 0.6 kg / h. After stable operation, the extrusion pressure of the twin-screw extruder is 10–30 bar, and the torque is approximately 77%–82%. The die has two circular outlets, each with a diameter of 4 mm. After extrusion, the sample passes through a water bath cooling tank and is then cut into cylindrical particles approximately 5 mm in length using a pelletizer. After being vacuum-dried in a 70℃ vacuum drying oven for 4 hours, the particles are collected, packaged, and ready for use.

[0053] [Comparative Example 1] Modified polyhydroxy fatty acid esters with only HDI added

[0054] Comparative Example 1 investigated the reactive extrusion modification of PHA by adding only HDI. PolyLab HAAKE from Thermo Fisher Scientific, USA, was used. TM A Rheomex OS PTW16 co-rotating twin-screw extruder (screw diameter 16 mm, L / D = 40) was used to modify PHA. 100 parts by weight of PHA powder were premixed with 0.8 parts by weight of HDI, and then extruded via a melt reaction in the twin-screw extruder to obtain modified PHA particles. The main reaction temperature of the extruder was 160°C, and the screw speed was 50 rpm. Other conditions were controlled the same as in Example 1. After stable operation, the twin-screw extrusion pressure was 10–30 bar, and the torque was approximately 65%. The extruder was equipped with two circular outlets, each with a diameter of 4 mm. After extrusion, the sample was cooled in a water bath and then cut into cylindrical particles approximately 5 mm in length using a pelletizer. After vacuum drying in a 70°C vacuum drying oven for 4 hours, the particles were collected, packaged, and stored for later use.

[0055] [Comparative Example 2] ADR chain-extended modified polyhydroxy fatty acid ester

[0056] Comparative Example 2 investigated the chain extension of PHA using the epoxy chain extender ADR4468 (BASF, molecular weight 7250, number of epoxy groups: 9), and employed PolyLab HAAKE from Thermo Fisher Scientific, USA. TM PHA was extruded using a Rheomex OSPTW16 co-rotating twin-screw extruder (screw diameter 16 mm, L / D = 40). 100 parts by weight of PHA powder were premixed with 0.8 parts by weight of ADR, and then melt-extruded through the twin-screw extruder to obtain modified PHA. The main reaction temperature of the extruder was 160°C, and the screw speed was 50 rpm. Other conditions were controlled the same as in Example 1. After stable operation, the twin-screw extrusion pressure was 10–30 bar, and the torque was approximately 70%. The extruder was equipped with two circular outlets, each with a diameter of 4 mm. After extrusion through the die, the sample was cooled in a water bath, then cut into cylindrical particles approximately 5 mm in length using a pelletizer. After vacuum drying in a 70°C vacuum drying oven for 4 hours, the particles were collected, packaged, and stored for later use.

[0057] [Comparative Example 3] MDI chain-extended modified polyhydroxy fatty acid ester

[0058] Comparative Example 3 illustrates the use of MDI to modify PHA for melt enhancement, employing PolyLab HAAKE from Thermo Fisher Scientific, Inc. TMA Rheomex OS PTW16 co-rotating twin-screw extruder (screw diameter 16 mm, L / D = 40) was used to modify PHA. 100 parts by weight of PHA powder were premixed with 0.8 parts by weight of MDI, and then extruded via a twin-screw melt reaction to obtain modified PHA particles. The main reaction temperature of the extruder was 160°C, and the screw speed was 50 rpm. Other conditions were controlled the same as in Example 1. After stable operation, the twin-screw extrusion pressure was 10–30 bar, and the torque was approximately 58%. The extruder was equipped with two circular outlets, each with a diameter of 4 mm. After extrusion, the samples passed through a water bath cooling tank and were cut into cylindrical particles with a length of approximately 5 mm using a pelletizer. After being vacuum-dried in a 70°C vacuum drying oven for 4 hours, the particles were collected, packaged, and stored for later use.

[0059] [Example 6] Melt Flow Index Test

[0060] The modified PHA particles prepared in Examples 1-5, Blank Example 1, and Comparative Examples 1-3 were subjected to melt flow index testing. The measurement method was as described above. The melt flow index of the PHA particles prepared in Examples 1-5 and Comparative Examples 1-3 was tested at a temperature of 155°C and a mass of 2.16 kg. The measured melt flow indexes are shown in Table 1.

[0061] Table 1. Melt index of Examples 1-5, Blank Example 1, and Comparative Examples 1-3 at 155℃ and 2.16 kg

[0062]

[0063] Comparing blank example 1 with Examples 1-5 (with different amounts of HDI and catalyst), it can be observed that after HDI modification, the melt flow rate (MFR) of the modified PHA significantly decreases as the amount of HDI added in the twin-screw extruder modification process gradually increases. When 0.2% HDI is added, the MFR decreases significantly from 2.8 g / 10 min to 0.78 g / 10 min; when 0.8% HDI is added, the MFR further decreases to 0.24 g / 10 min; when HDI is further added to 1%, the MFR increases slightly, indicating that HDI modification has the best melting enhancement effect on PHA and yields the lowest MFR when the HDI addition reaches 0.8%. Further addition of HDI may lead to excess HDI undergoing transesterification, resulting in an increase in MFR and a decrease in melt strength. Similarly, the melt flow rate also decreases after MDI modification.

[0064] In contrast, in Comparative Example 1, the MFR (Melt Flow Rate) was 3.2 g / 10 min after adding only 0.8% HDI, showing no significant decrease. This indicates that simply adding HDI for end-capping cannot improve the melt strength of PHA. The introduction of a catalyst can greatly enhance the melting effect of PHA, forming a polyurethane-like structure between PHA chains, causing chain extension and cross-linking, thereby increasing its melt strength.

[0065] In Comparative Example 2, ADR couples with the hydroxyl / carboxyl groups of the polyester through epoxy functional groups to generate a polyester structure, achieving a chain extension effect. After adding 0.8% ADR in Comparative Example 2, the melt flow rate (MFR) decreased slightly to 2.2 g / 10 min. Compared to Examples 1-5 with added HDI and catalyst, the MFR is still relatively high. This indicates that adding ADR to PHA for chain extension does not achieve a significant melt enhancement effect. Therefore, this indirectly verifies that the melt strengthening effect of PHA in this invention mainly comes from the reaction of HDI with the PHA chain under the action of a catalyst. Isocyanates condense with isocyanate groups to form urethane structures, and the molecular chain segments have a polyurethane structure. Significant chain extension and cross-linking occur between the chains, increasing the elongation of the PHA material and improving its melt strength.

[0066]

Example 7

[0067] Examples 1-5 and blank example 1 were subjected to differential scanning calorimetry (DSC) tests according to the steps described above, and their second melting temperature (T) was determined. m Enthalpy of fusion (ΔH) m ), glass transition temperature (T) g ) and recrystallization enthalpy (ΔH) c The values ​​of ) are shown in Table 2.

[0068] Table 2. DSC results of Examples 1-5 and Blank Example 1

[0069]

[0070] Cooling curves of high melt strength polyhydroxy fatty acid values ​​at different temperatures and rotation speeds are shown below. Figure 1 As shown in the figure, with the increase of HDI content, the crystallization peak of PHA gradually decreases and reaches its lowest point when 0.8% HDI is added. Its enthalpy of cooling crystallization (ΔH) c The enthalpy of crystallization decreased from 22.35 J / g to 10.97 J / g after the addition of 0.8% HDI. Further addition of HDI increased the enthalpy of crystallization to 19.26 J / g. This indicates that HDI, under the catalytic action, caused chain extension and cross-linking of the PHA segments, resulting in a significant decrease in its crystalline structure.

[0071] [Example 8] Total Internal Reflection Infrared Test

[0072] The particles from Examples 1-5 and Blank Example 1 were subjected to total reflectance infrared spectroscopy testing using a Frontier FTIR spectrometer (Waltham, MA, USA) manufactured by PerkinElmer, USA, as described above. The test results are shown in Figure 2. Figure 2 shows that as the amount of HDI added increases, the concentration at 1059 cm⁻¹... -1 1279cm -1 , and located at 1376cm -1 The characteristic peaks all decreased, representing the stretching vibration peaks of CO and -OH, respectively. This indicates that the introduction of HDI effectively reduced the number of terminal hydroxyl groups.

[0073] [Example 9] Melt strength test

[0074] The melt strength tests of Examples 1-5 were performed in a capillary rheometer as described above, and the results are as follows: Figure 3 As shown. It should be noted that unmodified PHA particles, due to their low melt strength, cannot be wound into shape in a capillary rheometer, and their melt strength is close to zero and undetectable. It can be seen that as the HDI addition increases from 0.2% to 0.8%, the melt strength of PHA is significantly enhanced. The melt strength of modified PHA increases from 8 cN and tensile speed of 139 mm / s to a melt strength of 23 cN and a tensile speed of 137 mm / s. When further increased to 1%, the melt strength decreases slightly. The conclusion regarding melt strength corroborates the melt index in Example 6, indicating that HDI modification can significantly improve the melt strength of PHA under the action of a catalyst.

[0075] [Example 10] Crystallization properties

[0076] The particles from Examples 1-5 and Blank Example 1 were injection molded in a HAAKE MiniLab micro injection molding machine. The injection temperature was 155°C, the grinding head temperature was 40°C, and the injection pressure was 400 bar. The cooling time was 30 seconds. The obtained injection-molded specimens were subjected to XRD testing using the above method, and the results are as follows: Figure 3 As shown, after HDI modification, the crystallization peak intensity of modified PHA decreased significantly, and the minimum value was obtained when the HDI addition amount was 0.8%. This is also verified by the DSC results in Example 7, indicating that under the action of catalyst, the introduction of HDI can cause significant chain extension or cross-linking of PHA chains, thereby improving mechanical properties.

[0077] [Example 11] Mechanical property testing

[0078] All particles from Examples 1-5, Blank Example 1, and Comparative Examples 1-3 were injection molded in a HAAKE MiniLab micro injection molding machine. The resulting plastic specimens were subjected to mechanical property testing as described above, and the elongation at break was obtained as follows: Figure 4 As shown.

[0079] like Figure 4 As shown, it is evident that with increasing HDI addition, the elongation at break of the PHA-modified sample initially remains stable. When the HDI addition reaches 0.6%, the elongation at break begins to increase from 20% to 55%. When the addition reaches 0.8%, the elongation at break significantly increases to 300%, which is 15 times that of the unmodified PHA. However, when the HDI content further increases to 1%, the elongation at break slightly decreases. Furthermore, the elongation at break of the modified PHA samples in Comparative Examples 1 and 2 is not significantly higher than that of the unmodified PHA, only 3% and 10% respectively. This further indicates that the significant increase in elongation at break is caused by the introduction of HDI, which induces reactions between PHA chains, increasing the entanglement between PHA molecular chains. This is consistent with the conclusions in Examples 7-10. Moreover, after HDI modification, the fracture energy of the modified PHA sample is 0.37 J / m², which is significantly lower than that of the unmodified sample. 3 The efficiency was significantly increased to 6.72 J / m³ after modification with 0.8% HDI. 3 Adding MDI also significantly improves the mechanical properties of PHA, increasing its elongation to 169%.

[0080] Mechanical tests confirmed that, under the action of a catalyst, the mechanical elongation and fracture energy of modified PHA were significantly improved after HDI modification via reactive extrusion.

[0081] Comparative Example 4

[0082] According to Chinese Patent CN104245839A, PHA is modified using thermoplastic polyurethane (TPU) that reacts with MDI (see item 14 in the examples). The resulting modified PHA material exhibits improved processing properties, impact strength, and flexural modulus. However, the elongation at break of the modified PHA obtained using this method remains low, at only about 10%, making it difficult to achieve film-grade applications. Therefore, the elongation at break of PHA modified by the physical blending method is still low, far below the nearly 300% elongation at break achieved by the modified PHA material provided by this invention.

Claims

1. A modified polyhydroxyalkanoate material comprising polyhydroxyalkanoate segments, polyurethane segments, wherein, The polyurethane segment is obtained by reacting a fluxing agent and a polyhydroxyaliphatic acid ester in the presence of a catalyst, the fluxing agent is at least one selected from toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, the polyhydroxyaliphatic acid ester is at least one selected from poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-4-hydroxybutyrate), poly(3-hydroxybutyrate-3-hydroxyvalerate), poly(3-hydroxybutyrate-3-hydroxyhexanoate), the weight average molecular weight M of the polyhydroxyaliphatic acid ester is greater than or equal to 300000 g / mol, the catalyst is at least one selected from organic tin catalysts, the amount of the fluxing agent is 0.01-5 parts by mass based on 100 parts by mass of the polyhydroxyaliphatic acid ester, the amount of the catalyst is 0.001-5 parts by mass, and the melt strength of the modified polyhydroxyaliphatic acid ester material is greater than 5 cN. co co co w The polyurethane segment is obtained by reacting a fluxing agent and a polyhydroxyaliphatic acid ester in the presence of a catalyst, the fluxing agent is at least one selected from toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, the polyhydroxyaliphatic acid ester is at least one selected from poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-4-hydroxybutyrate), poly(3-hydroxybutyrate-3-hydroxyvalerate), poly(3-hydroxybutyrate-3-hydroxyhexanoate), the weight average molecular weight M of the polyhydroxyaliphatic acid ester is greater than or equal to 300000 g / mol, the catalyst is at least one selected from organic tin catalysts, the amount of the fluxing agent is 0.01-5 parts by mass based on 100 parts by mass of the polyhydroxyaliphatic acid ester, the amount of the catalyst is 0.001-5 parts by mass, and the melt strength of the modified polyhydroxyaliphatic acid ester material is greater than 5 cN.​​​ 2. The modified polyhydroxyalkanoate material according to claim 1, wherein the polyurethane segment content in the modified polyhydroxyalkanoate material is 0.05-25% by mass.

3. The modified polyhydroxyalkanoate material according to claim 2, wherein the polyurethane segment content in the modified polyhydroxyalkanoate material is 0.5-10% by mass.

4. A method for preparing the modified polyhydroxyalkanoate material according to any one of claims 1-3, comprising reacting components comprising a polyhydroxyalkanoate and a fluxing agent to obtain the modified polyhydroxyalkanoate material. The method for preparing the modified polyhydroxyalkanoate material specifically comprises the following steps: Step 1, mixing components comprising a fluxing agent and a catalyst in advance; 5. The preparation method according to claim 4, characterized in that, Step 2, obtaining the modified polyhydroxyalkanoate material by melt reaction of the premix obtained in Step 1 and a polyhydroxyalkanoate; wherein the premix obtained in Step 1 and the polyhydroxyalkanoate can be fed together or separately.

6. The method for preparing the modified polyhydroxyalkanoate material according to claim 5, wherein the catalyst is selected from at least one of organic tin catalysts; and / or, 7. The method for preparing the modified polyhydroxyalkanoate material according to claim 6, wherein the fluxing agent is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate; and / or, 8. The method for preparing the modified polyhydroxyalkanoate material according to claim 5, wherein the fluxing agent is used in an amount of 0.01-5 parts and the catalyst is used in an amount of 0.001-5 parts, based on 100 parts by mass of the polyhydroxyalkanoate.

9. The method for preparing the modified polyhydroxyalkanoate material according to claim 8, wherein the fluxing agent is used in an amount of 0.1-2 parts and the catalyst is used in an amount of 0.01-1 parts, based on 100 parts by mass of the polyhydroxyalkanoate. The polyhydroxyalkanoate has a weight average molecular weight Mw w greater than or equal to 300,000 g / mol.

10. The method for preparing the modified polyhydroxyalkanoate material according to claim 5, wherein the melt reaction in Step 2 is carried out in a twin-screw extruder; and / or, The melt reaction temperature in Step 2 is 50-300°C; and / or, The screw rotation speed of the melt reaction in Step 2 is 5-1200 rpm. The polyhydroxy fatty acid ester is selected from poly(3-hydroxybutyrate), poly(3-hydroxybutyrate- 11. The method for preparing the modified polyhydroxyalkanoate material according to claim 10, wherein the melt reaction temperature in Step 2 is 100-200°C; and / or, 4-hydroxybutyrate), poly(3-hydroxybutyrate- The screw rotation speed of the melt reaction in Step 2 is 20-400 rpm. 3-hydroxyvalerate), poly(3-hydroxybutyrate- 12. A high-melt-strength modified polyhydroxyalkanoate material prepared by the method for preparing the modified polyhydroxyalkanoate material according to any one of claims 4-11. At least one of (-3-hydroxyhexanoate). The melt strength of the modified polyhydroxyalkanoate material is greater than 5 cN.

14. The high-melt-strength modified polyhydroxyalkanoate material according to claim 12 or 13, which is used in a biodegradable film material. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 13. The high melt strength modified polyhydroxyalkanoate material of claim 12, wherein, ​ ​

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