A modified pha particle and a method of making the same

Abstract

The application relates to a modified PHA particle and a preparation method thereof, relates to the technical field of high polymer materials, and comprises a polyhydroxyalkanoate matrix resin, modified nanocellulose whiskers, decanedioic acid diphenylhydrazide, epoxy soybean oil and antioxidant 1010; the modified nanocellulose whiskers are nanocellulose whiskers covalently grafted with a short PHA chain on the surface. The application has the effects that a stable interface combination between components and the PHA matrix is achieved, and the crystallinity can be improved to obtain heat resistance while the decrease range of toughness is inhibited.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, specifically to a modified PHA particle and its preparation method. Background Technology

[0002] Polyhydroxyalkanoates (PHAs) are intracellular polyesters synthesized by microorganisms under conditions of excess carbon sources and limited nitrogen and phosphorus nutrients. Their molecular structure is a linear polymer composed of (R)-3-hydroxy fatty acid units linked by ester bonds. PHAs can be degraded into low-molecular-weight oligomers by PHA depolymerases secreted by microorganisms in soil, freshwater, and marine environments, ultimately mineralizing into carbon dioxide and water. Therefore, they are considered a candidate material to replace traditional petroleum-based plastics. In disposable straws, PHAs have attracted attention due to their biodegradability and environmentally friendly properties. However, as a semi-crystalline polyester, PHAs have a glass transition temperature close to room temperature and a slow crystallization rate. The heat distortion temperature of pure PHA materials after hot extrusion is typically below 95°C, making them prone to softening and deformation upon contact with boiling water or hot beverages. Furthermore, their elongation at break is less than 10%, making them susceptible to brittle fracture when bent. These performance defects limit the application of PHAs in heat-resistant straws.

[0003] Currently, the industrial production of PHA mainly employs microbial fermentation. This method uses microorganisms such as *Alcaligenes*, *Pseudomonas*, or recombinant *Escherichia coli* as production strains, and glucose, sucrose, or vegetable oil as carbon sources, in batch or fed-batch culture in fermenters. Under nitrogen or phosphorus-limited conditions, the microorganisms convert excess carbon sources into PHA, which accumulates within the cells as inclusion bodies. After fermentation, the cells are collected by centrifugation or membrane filtration, and the cells are then homogenized under high pressure, enzymatically hydrolyzed, or extracted with organic solvents to break down the cell walls and separate the PHA. The PHA powder or granules are then obtained after washing and drying. By controlling the type of carbon source and the feeding strategy during fermentation, PHA copolymers with different monomer compositions can be prepared. For example, using propionic acid as a co-substrate yields PHBV containing 3-hydroxyvalerate units, and using butyrolactone as a co-substrate yields P3HB4HB containing 4-hydroxybutyrate units. The PHA resin obtained by the above-mentioned microbial fermentation method can be directly used for subsequent thermoplastic processing after extrusion granulation. However, the pure PHA resin still has problems with low heat distortion temperature and insufficient impact resistance in straw extrusion molding. It is necessary to add nucleating agents, plasticizers or other modified components to improve its comprehensive performance.

[0004] To address the aforementioned issues, various PHA modification schemes have been disclosed in the prior art, such as adding inorganic nucleating agents to increase crystal nucleus density, blending with rigid polyesters such as polylactic acid to improve heat resistance, and adding plasticizers to improve processing fluidity. In these schemes, the modified components and the PHA matrix are compounded through physical blending. The uniformity of the distribution of the modified components in the matrix and the stability of the interfacial bonding are greatly affected by processing conditions. Furthermore, as the amount of nucleating agent added increases, the density of interfacial defects increases, leading to a further decrease in the material's impact strength. There is a contradiction between improving heat resistance and maintaining toughness.

[0005] Therefore, it is of great significance to provide PHA particles that have a stable interfacial bond between the component and the PHA matrix, and can improve crystallinity to obtain heat resistance while suppressing the decrease in toughness. Summary of the Invention

[0006] This application provides a modified PHA particle and its preparation method, which has the effect of improving crystallinity to obtain heat resistance while suppressing the decrease in toughness.

[0007] Firstly, the modified PHA particles provided in this application adopt the following technical solution: A modified PHA granule is made from the following raw material components in parts by weight: 70-85 parts of polyhydroxyalkanoate matrix resin; 3-8 parts of modified nanocellulose whiskers; Sebacic acid dibenzoylhydrazide 0.3–0.8 parts; 1-3 parts of epoxidized soybean oil; Antioxidant 1010: 0.1–0.3 parts; The polyhydroxy fatty acid ester matrix resin is selected from poly-3-hydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), wherein the molar content of 3-hydroxyvalerate or 4-hydroxybutyrate is 5-12%; The modified nanocellulose whiskers are nanocellulose whiskers with PHA short chains covalently grafted onto their surface, with a grafting rate of 15-30 wt% and a molecular weight of 2000-5000 Da for the grafted PHA short chains.

[0008] By adopting the above technical solution, 5-12% of the comonomers in the matrix resin are excluded from the crystalline region during crystallization, forming flexible segments in the amorphous region, which enables the material to have a certain deformation capability when subjected to force.

[0009] During melt processing, the PHA grafted chains on the surface of the modified nanocellulose whiskers become entangled with the molecular chains of the matrix resin. During cooling and crystallization, the grafted chains can participate in the crystallization of the matrix, forming a covalent connection interface between the whisker surface and the PHA crystal region. The whisker itself acts as a heterogeneous surface, reducing the free energy barrier for PHA nucleation and increasing the number of crystal nuclei per unit volume.

[0010] Dibenzoyl sebacate provides additional nucleation surface at a dosage of 0.3–0.8 parts, which superimposes on the nucleation effect of modified whiskers.

[0011] In epoxidized soybean oil, the epoxy groups react with the carboxylic acid end groups generated by the thermal degradation of PHA at the processing temperature to undergo a ring-opening reaction, thereby inhibiting the decrease in molecular weight caused by degradation.

[0012] Antioxidant 1010 captures alkoxy radicals and peroxy radicals generated during thermal processing, thus slowing down the thermal oxidation process.

[0013] With the synergistic effect of the above components, after the particles are extruded through a straw, their heat distortion temperature is higher than that of unmodified PHA, and the reduction in elongation at break is less than that of the system using inorganic nucleating agents alone.

[0014] Optionally, the polyhydroxyalkanoate matrix resin has a melt index of 5 to 15 g / 10 min at 190°C and a load of 2.16 kg.

[0015] By adopting the above technical solution, the melt index reflects the flow resistance of the resin at the processing temperature. When the melt index is below 5 g / 10 min, the screw torque of the extruder increases and the melt conveying efficiency decreases; when the melt index is above 15 g / 10 min, the wall thickness uniformity of the extruded preform deteriorates during traction stretching. Within the range of 5–15 g / 10 min, the melt viscosity allows the modified nanocellulose whiskers to disperse with the melt flow in the screw shear field, and also allows the preform to maintain its cross-sectional shape after leaving the die until cooling and solidification. At the same time, PHA molecular chains in this molecular range have sufficient segment mobility at the crystallization temperature to respond to the nucleating agent-induced ordered arrangement.

[0016] Optionally, the particle size D50 of the sebacic acid dibenzoylhydrazine is ≤5μm.

[0017] By adopting the above technical solution, the reduction in nucleating agent particle size increases the total number of particles of the same mass, and the density of nucleation sites provided in the matrix increases accordingly; at the same time, smaller particles are more closely spaced when dispersed in the melt, and the probability of PHA molecular chains forming complete crystalline regions between adjacent particles increases, which is beneficial to obtaining higher crystallinity within a limited cooling time.

[0018] Optionally, the epoxidized soybean oil has an epoxy value ≥ 6.0% and an acid value ≤ 0.5 mg KOH / g.

[0019] By adopting the above technical solution, an epoxy value ≥6.0% indicates that the number of reactive epoxy groups in a unit mass of epoxidized soybean oil reaches a certain level, which can react with the carboxylic acid end groups generated during PHA degradation to form ester bonds to connect broken molecular chain segments. An acid value ≤0.5mg KOH / g indicates that the epoxidized soybean oil itself contains relatively few free fatty acids, limiting the extent to which additional carboxylic acid catalysts can be introduced into the system during processing, thus avoiding accelerating the hydrolysis of PHA ester bonds.

[0020] Optionally, the method for preparing the modified nanocellulose whiskers includes the following steps: S1. Disperse nanocellulose whiskers in anhydrous toluene, add 3-aminopropyltriethoxysilane, and react at 80-90°C for 10-14 hours under nitrogen protection. After separation, washing and drying, amino-modified nanocellulose whiskers are obtained. S2. Dissolve the polyhydroxy fatty acid ester matrix resin in chloroform, and hydrolyze it at 55-65°C for 3-5 hours in the presence of p-toluenesulfonic acid and deionized water. After precipitation, washing and drying, a carboxyl-terminated PHA oligomer with a number average molecular weight of 2000-5000 Da is obtained. S3. Dissolve the terminal carboxyl PHA oligomer obtained in step S2 in anhydrous N,N-dimethylformamide, add dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and activate the carboxyl group at room temperature for 0.5 to 1.5 hours. S4. The aminated cellulose nanofibers obtained in step S1 are dispersed in anhydrous N,N-dimethylformamide and mixed with the activated terminal carboxyl PHA oligomer solution in step S3 under nitrogen protection. The mixture is reacted at 55-65°C for 20-28 hours. After separation, washing and drying, the modified cellulose nanofibers are obtained.

[0021] By employing the above-mentioned technical solution, nanocellulose whiskers are treated with 3-aminopropyltriethoxysilane to obtain aminated whiskers. The matrix resin is hydrolyzed to obtain carboxyl-terminated PHA oligomers with a molecular weight of 2000–5000 Da. These oligomers are then activated with dicyclohexylcarbodiimide and 4-dimethylaminopyridine and reacted with the aminated whiskers. This method introduces primary amino groups on the whisker surface as grafting anchors using a silane coupling agent. The molecular weight of the carboxyl-terminated PHA oligomers prepared by hydrolysis is controlled within the range of 2000–5000 Da, ensuring that the grafted chain length falls within the order of magnitude of the lamellar thickness during the crystallization of the matrix PHA. The amidation reaction is carried out at room temperature to 60°C to prevent the thermal degradation of the PHA oligomers themselves during the grafting process. Finally, whisker products with surface covalently bonded short PHA chains are obtained.

[0022] Optionally, in step S1, the mass ratio of the nanocellulose whiskers to 3-aminopropyltriethoxysilane is 1:0.3 to 0.7.

[0023] By adopting the above technical solution, the dosage ratio enables the silane coupling agent to form a monolayer graft mainly based on chemical bonding on the surface of the whisker. When the mass ratio is less than 1:0.3, the surface amino graft density is insufficient, resulting in too few sites for subsequent amidation reaction. When the mass ratio is greater than 1:0.7, the excess silane forms a self-condensation layer on the surface, leaving some free silicon impurities after washing. The graft density and product purity of the amino-modified whiskers are within an acceptable range in the range of 1:0.3 to 0.7.

[0024] Optionally, in step S2, the mass ratio of the polyhydroxyalkanoate matrix resin to p-toluenesulfonic acid is 1:0.03-0.07, and the mass-volume ratio of the polyhydroxyalkanoate matrix resin to deionized water is 1g:0.3-0.7mL.

[0025] By employing the above technical solution, the amount of p-toluenesulfonic acid used is within the range of 1:0.03 to 0.07 to match the ester bond hydrolysis rate with the target reaction time, resulting in oligomers with molecular weights in the range of 2000 to 5000 Da. The amount of water is within the range of 0.3 to 0.7 mL per gram of resin to ensure sufficient water molecules are present for the hydrolysis reaction and that the reaction system does not separate due to excessive water, thus guaranteeing that the hydrolysis reaction proceeds under homogeneous or quasi-homogeneous conditions.

[0026] Optionally, in step S3, the mass ratio of the terminal carboxyl PHA oligomer to dicyclohexylcarbodiimide is 1:0.2-0.4, and the mass ratio of the terminal carboxyl PHA oligomer to 4-dimethylaminopyridine is 1:0.02-0.05.

[0027] By employing the above technical solution, the dicyclohexylcarbodiimide, when used in a ratio of 1:0.2 to 0.4, can convert the terminal carboxyl group of the oligomer chain into an O-acylisourea active intermediate, and the reaction byproduct dicyclohexylurea can be removed in subsequent washing. The use of 4-dimethylaminopyridine, in a ratio of 1:0.02 to 0.05, accelerates the formation of the active ester intermediate, allowing the activation step to be completed within a certain time at room temperature.

[0028] Optionally, in step S4, the mass ratio of the aminated cellulose nanofiber whiskers to the carboxyl-terminated PHA oligomer is 1:2 to 4.

[0029] By adopting the above technical solution, the feed ratio results in an excess of carboxyl groups relative to amino groups in the reaction system, which drives the amidation reaction equilibrium toward the product. Unreacted oligomers are dissolved and removed in subsequent washing, and the grafting rate of the final product is stabilized in the range of 15-30 wt%.

[0030] Secondly, this application provides a method for preparing modified PHA particles, comprising the following steps: S1. Dry the polyhydroxy fatty acid ester matrix resin at 75-85℃ and vacuum degree ≤-0.09MPa until the moisture content is ≤0.05wt%. Mix the epoxidized soybean oil and antioxidant 1010 evenly to obtain a liquid additive mixture. S2. According to the weight ratio, the dried polyhydroxy fatty acid ester matrix resin, modified nanocellulose whiskers, and sebacic acid dibenzoyl hydrazine are put into a high-speed mixer and mixed at 800-1200 rpm for 5-15 minutes. Then, the liquid additive mixture is added under stirring and the mixture is continued for 15-25 minutes to obtain the mixture. S3. Add the mixture obtained in step S2 to a co-rotating twin-screw extruder. The temperatures of each section of the extruder are: feeding section 145-155℃, plasticizing section 155-165℃, homogenizing section 160-170℃, and die head section 155-165℃. The screw speed is 150-200 rpm. After melt extrusion, cooling, and pelletizing, granules are obtained. S4. The granules obtained in step S3 are kept at a constant temperature of 68-72°C for 2.5-3.5 hours to obtain the modified PHA granules.

[0031] By adopting the above technical solutions, a moisture content of ≤0.05wt% allows for controllable reduction in molecular weight caused by ester bond hydrolysis during extrusion. Post-addition of liquid additives avoids premature coating of solid particles by epoxidized soybean oil and antioxidants, which could negatively impact subsequent dispersion. Temperature gradient settings across extruder sections ensure the material remains solid during feeding, completes melting and component dispersion in the plasticizing section, eliminates the melt temperature gradient in the homogenizing section, and establishes stable extrusion pressure at the die head. A screw speed of 150–200 rpm provides the shear strength required for the modified whiskers to disperse in the melt. The granules are kept at a constant temperature of 68–72℃ for 2.5–3.5 hours to allow PHA to fully crystallize on the surface of the modified whiskers, achieving a high level of particle crystallinity before capping extrusion and shortening the crystallization time required after capping formation.

[0032] In summary, this application includes at least one of the following beneficial technical effects: 1. The PHA grafted chains on the surface of the modified nanocellulose whiskers have the same chemical structure as the PHA matrix. During the cooling crystallization process, the grafted chains participate in the matrix crystallization, connecting the whisker surface and the PHA crystalline regions via covalent bonding. The whiskers themselves act as a heterogeneous surface, lowering the nucleation free energy barrier of PHA, while the grafted chains simultaneously induce the matrix molecular chains to align and integrate into the lattice along their direction. This structure ensures that the bonding strength between the whiskers and the matrix is ​​not limited by the van der Waals forces of the physical contact interface. Furthermore, with an increase in the number of nucleation sites, the interface defect density does not increase proportionally with the amount of nucleating agent, helping to alleviate the problem of decreased mechanical properties caused by increased nucleating agent addition in existing technologies. 2. Multiple short PHA chains grafted onto the surface of a single modified nanocellulose whisker embed themselves into multiple independent PHA crystalline regions during crystallization. After crystallization, the rigid whisker acts as a physical bridge, connecting the multiple crystalline regions into a continuous network. When the material is subjected to external force, this network allows stress to be transferred from one crystalline region to an adjacent crystalline region via the rigid whisker, reducing the stress concentration at the interface of a single crystalline region. The whisker deflects and hinders crack propagation paths. This structure allows the material to achieve a higher heat distortion temperature while increasing crystallinity, while the decrease in elongation at break and impact strength is less than that of systems using the same amount of inorganic nucleating agent or inorganic filler alone. 3. The molecular weight of the short PHA chains grafted onto the surface of the modified nanocellulose whiskers is controlled within the range of 2000–5000 Da. When the molecular weight of the grafted chains is below 2000 Da, the chain length is insufficient to embed into the crystalline region and form an anchor. When the molecular weight is above 5000 Da, the grafted chains entangle in the melt, leading to whisker particle aggregation. The grafted chain length of 2000–5000 Da ensures that the whiskers remain dispersed during extrusion processing and crystallize together with the matrix molecular chains during cooling and crystallization, achieving anchoring and bridging functions. The modified nanocellulose whiskers integrate nucleation, anchoring, and bridging functions as a single component, reducing the types and amounts of independent functional additives in the formulation. The reduction in the number of components decreases the number of interface defects caused by differences in compatibility between different components and the PHA matrix, as well as interference between components, thus narrowing the performance fluctuation range between batches. Detailed Implementation

[0033] Preparation Example 1 The modified cellulose nanofiber whiskers are prepared by the following steps: S1, Surface amination and activation of nanocellulose whiskers 5.0 g of spray-dried cellulose nanofibers (CNC, diameter 5-20 nm, length 100-500 nm) were dispersed in 500 mL of anhydrous toluene and sonicated for 30 minutes to form a homogeneous suspension. 2.5 g of 3-aminopropyltriethoxysilane was added dropwise to the suspension, and the mixture was heated to 85 °C under nitrogen protection and magnetically stirred for 12 hours. After the reaction was complete, the mixture was centrifuged, and the resulting precipitate was washed three times each with anhydrous ethanol and deionized water, and dried under vacuum at 60 °C to constant weight to obtain aminated CNC.

[0034] Synthesis of S2, terminal carboxyl group PHA oligomers In a 250 mL three-necked flask, 100 mL of chloroform, 10.0 g of PHA matrix resin (PHBV, 3HV molar content 8%), and 0.5 g of p-toluenesulfonic acid monohydrate were added, and the mixture was heated to 60 °C with stirring to dissolve. 5.0 mL of deionized water was slowly added dropwise to the solution, and the hydrolysis reaction was carried out under reflux for 4 hours. After the reaction was complete, the solution was poured into excess cold methanol to precipitate the product. The precipitate was collected by filtration, washed three times with methanol, and dried under vacuum at 40 °C to obtain carboxyl-terminated PHA oligomers. The number-average molecular weight was determined to be 3500 Da by gel permeation chromatography, and the carboxyl content was determined to be 0.28 mmol / g by titration.

[0035] Synthesis of S3 and PHA oligomers grafted onto CNC 3.0 g of the aminated CNC obtained in step S1 was dispersed in 150 mL of anhydrous N,N-dimethylformamide (DMF) and ultrasonically dispersed for 30 minutes. 9.0 g of the carboxyl-terminated PHA oligomer obtained in step S2 was dissolved in 100 mL of anhydrous DMF, and 2.5 g of dicyclohexylcarbodiimide (DCC) and 0.3 g of 4-dimethylaminopyridine (DMAP) were added. The carboxyl groups were activated by stirring at room temperature for 1 hour. Under nitrogen protection, the activated PHA solution was slowly added dropwise to the aminated CNC suspension, heated to 60 °C, and stirred at a constant temperature for 24 hours. After the reaction, the mixture was centrifuged, and the precipitate was washed thoroughly with DMF, ethanol, and deionized water sequentially. The product was then freeze-dried for 48 hours to obtain the CNC-g-PHA product. The grafting rate was determined to be 22% by thermogravimetric analysis.

[0036] Preparation Example 2 The modified nanocellulose whiskers differ from those in Preparation Example 1 in that, in step S2, the amount of p-toluenesulfonic acid was adjusted to 0.6 g, the hydrolysis time was extended to 5 hours, and the number-average molecular weight of the resulting carboxyl-terminated PHA oligomers was 4500 Da; in step S3, the amount of aminated CNC was 3.0 g, the amount of carboxyl-terminated PHA oligomers was adjusted to 10.5 g, the amount of DCC was adjusted to 2.8 g, the reaction time was extended to 28 hours, and the grafting rate of the resulting product was 28%.

[0037] Preparation Example 3 The modified nanocellulose whiskers differ from those in Preparation Example 1 in that, in step S2, the amount of p-toluenesulfonic acid was adjusted to 0.7 g, the hydrolysis time was 3 hours, and the number-average molecular weight of the resulting carboxyl-terminated PHA oligomers was 2500 Da; in step S3, the amount of aminated CNC was 3.0 g, the amount of carboxyl-terminated PHA oligomers was adjusted to 6.0 g, the amount of DCC was adjusted to 1.8 g, the reaction time was 20 hours, and the grafting rate of the resulting product was 16%.

[0038] Preparation Example 4 The modified nanocellulose whiskers differ from those in Preparation Example 1 in that, in step S2, the hydrolysis time is 3.5 hours, and the number-average molecular weight of the resulting terminal carboxyl PHA oligomers is 3000 Da; in step S3, the amount of terminal carboxyl PHA oligomers is adjusted to 7.5 g, the amount of DCC is adjusted to 2.1 g, and the grafting rate of the resulting product is 20%.

[0039] Preparation Example 5 The modified nanocellulose whiskers differ from those in Preparation Example 1 in that, in step S2, the amount of p-toluenesulfonic acid was adjusted to 0.4 g, the hydrolysis time was 4.5 hours, and the number-average molecular weight of the resulting terminal carboxyl PHA oligomers was 5000 Da; in step S3, the amount of terminal carboxyl PHA oligomers was adjusted to 6.0 g, the amount of DCC was adjusted to 1.8 g, and the grafting rate of the resulting product was 15%.

[0040] Preparation Example 6 The modified nanocellulose whiskers differ from those in Preparation Example 1 in that the spray-dried nanocellulose whiskers were used directly without amination or subsequent grafting reactions, and were simply vacuum-dried at 80°C for 4 hours before being blended with the matrix resin.

[0041] Preparation Example 7 The modified nanocellulose whiskers differ from those in Preparation Example 1 in that the terminal carboxyl group PHA oligomers were synthesized under the same conditions as step S2 in Preparation Example 1, with a number average molecular weight of 3500 Da. Steps S1 and S3 were not performed, and the resulting oligomers were used directly as the modifying component.

[0042] Preparation Example 8 The modified nanocellulose whiskers differ from those in Preparation Example 1 in that, in step S2, the amount of p-toluenesulfonic acid was adjusted to 0.3 g, the hydrolysis time was 3 hours, and the number-average molecular weight of the resulting terminal carboxyl PHA oligomers was 8000 Da; in step S3, the amount of terminal carboxyl PHA oligomers was adjusted to 6.0 g, the reaction time was 18 hours, and the grafting rate of the resulting product was 10%.

[0043] Preparation Example 9 The modified nanocellulose whiskers differ from those in Preparation Example 1 in that the amount of terminal carboxyl PHA oligomer in step S3 was adjusted to 3.0 g, the amount of DCC was adjusted to 1.0 g, the reaction time was 12 hours, and the grafting rate of the resulting product was 8%.

[0044] Example 1 A modified PHA granule is made from the following raw material components in parts by weight: 80 parts of PHA matrix resin, 5 parts of modified nanocellulose whiskers, 0.5 parts of sebacic acid dibenzoyl hydrazine, 2 parts of epoxidized soybean oil, and 0.2 parts of antioxidant 1010. The PHA matrix resin is PHBV, with a 3HV molar content of 8% and a melt index of 8 g / 10min; the modified nanocellulose whiskers were specifically obtained using Preparation Example 1; the sebacic acid dibenzoyl hydrazine particle size D50 < 5 μm; the epoxidized soybean oil has an epoxy value of 6.2% and an acid value of 0.3 mg KOH / g.

[0045] A method for preparing modified PHA particles includes the following steps: S1. The polyhydroxyalkanoate matrix resin is dried at 80°C and vacuum degree ≤ -0.09MPa until the moisture content is ≤ 0.05wt%. Epoxidized soybean oil and antioxidant 1010 are mixed evenly to obtain a liquid additive mixture. S2. According to the weight ratio, the dried polyhydroxy fatty acid ester matrix resin, modified nanocellulose whiskers, and sebacic acid dibenzoyl hydrazine are put into a high-speed mixer and mixed at 1000 rpm for 10 minutes. Then, the liquid additive mixture is added under stirring and the mixture is continued to be mixed for 20 minutes to obtain the mixture. S3. Add the mixture obtained in step S2 to a co-rotating twin-screw extruder. The temperatures of each section of the extruder are: 150°C for the feeding section, 160°C for the plasticizing section, 165°C for the homogenizing section, and 160°C for the die head section. The screw speed is 180 rpm. After melt extrusion, cooling, and pelletizing, granules are obtained. S4. The granules obtained in step S3 are placed at a constant temperature of 70°C for 3 hours to obtain the modified PHA granules.

[0046] Example 2 A modified PHA granule differs from Example 1 in that the PHA matrix resin is replaced with P3HB4HB (4HB molar content 10%, melt index 12 g / 10min), with an amount of 75 parts; the modified nanocellulose whiskers are the product obtained in Preparation Example 2 (grafting rate 28%, graft chain molecular weight 4500 Da), with an amount of 8 parts; the amount of sebacic acid dibenzoyl hydrazine is 0.8 parts; the amount of epoxidized soybean oil is 3 parts, with an epoxy value of 6.5% and an acid value of 0.2 mg KOH / g; the amount of antioxidant 1010 is 0.3 parts; and the granules in step S4 are kept at a constant temperature of 72°C for 3.5 hours.

[0047] Example 3 A modified PHA granule differs from Example 1 in that the PHA matrix resin is replaced with PHB (melt index 6 g / 10 min), with an amount of 85 parts; the modified nanocellulose whiskers are the product obtained in Preparation Example 3 (grafting rate 16%, graft chain molecular weight 2500 Da), with an amount of 3 parts; the amount of sebacic acid dibenzoyl hydrazine is 0.3 parts; the amount of epoxidized soybean oil is 1 part, with an epoxy value of 6.0% and an acid value of 0.4 mg KOH / g; the amount of antioxidant 1010 is 0.1 parts; and the granules in step S4 are kept at a constant temperature of 68°C for 2.5 hours.

[0048] Example 4 A modified PHA particle, differing from Example 1 in that the PHA matrix resin is replaced with PHBV (3HV molar content 5%, melt index 5 g / 10min), with an amount of 80 parts; the modified nanocellulose whiskers are the product obtained in Preparation Example 1 (same as Example 1), with an amount of 6 parts; the amount of sebacic acid dibenzoyl hydrazine is 0.6 parts; the amount of epoxidized soybean oil is 2.5 parts, with an epoxy value of 6.3% and an acid value of 0.25 mg KOH / g; and the amount of antioxidant 1010 is 0.25 parts.

[0049] Example 5 A modified PHA particle, which differs from Example 1 in that the modified nanocellulose whiskers are specifically obtained using Preparation Example 5.

[0050] Comparative Example 1 A modified PHA particle, which differs from Example 1 in that the modified nanocellulose whiskers are specifically obtained using Preparation Example 1.

[0051] Comparative Example 2 A modified PHA particle differs from Example 1 in that 5 parts of modified nanocellulose whiskers are removed from the raw materials, and only 0.5 parts of sebacic acid dibenzoyl hydrazine are retained as nucleating agents, and the amount of PHA matrix resin is adjusted to 85 parts.

[0052] Comparative Example 3 A modified PHA particle, which differs from Example 1 in that the modified nanocellulose whiskers are specifically obtained using Preparation Example 7.

[0053] Comparative Example 4 A modified PHA particle, which differs from Example 1 in that the modified nanocellulose whiskers are specifically obtained using Preparation Example 8.

[0054] Comparative Example 5 A modified PHA particle, which differs from Example 1 in that the modified nanocellulose whiskers are specifically obtained using Preparation Example 9.

[0055] Comparative Example 6 A modified PHA particle, which differs from Example 1 in that the amount of modified nanocellulose whiskers is adjusted to 1 part and the amount of PHA matrix resin is adjusted to 84 parts.

[0056] Comparative Example 7 A modified PHA particle, which differs from Example 1 in that 0.5 parts of sebacic acid dibenzoyl hydrazine are removed from the raw materials, and the amount of PHA matrix resin is adjusted to 80.5 parts.

[0057] Comparative Example 8 A modified PHA particle, which differs from Example 1 in that 2 parts of epoxidized soybean oil are removed from the raw materials, and the amount of PHA matrix resin is adjusted to 82 parts.

[0058] Detection example Heat distortion temperature: According to GB / T 1634.2-2019 "Determination of Deflection Temperature of Plastics under Load - Part 2: Plastics and Hard Rubber", modified PHA granules were extruded into straws, and tubular specimens with a length of 80 mm, an outer diameter of 6 mm, and a wall thickness of 0.5 mm were cut. Test conditions: The specimen was placed flat, a bending stress of 1.80 MPa was applied, and the heating rate was 120℃ / h. The temperature at which the deflection of the specimen reached 0.34 mm was recorded as the heat distortion temperature. Tensile strength and elongation at break: According to GB / T 1040.2-2022 "Determination of tensile properties of plastics – Part 2: Test conditions for molded and extruded plastics", modified PHA granules were injection molded into standard dumbbell-shaped specimens (Type 1A, total length 150 mm, narrow section width 10 mm, thickness 4 mm). Test conditions: test speed 5 mm / min, gauge length 50 mm, ambient temperature 23℃±2℃, relative humidity 50%±10%. The maximum tensile stress was recorded as the tensile strength, and the elongation at break was recorded. The specific test results are shown in Table 1.

[0059] Table 1

[0060] The performance test data from Example 1 and Comparative Example 1 show that the heat distortion temperature, tensile strength, and elongation at break of Example 1 are all higher than those of Comparative Example 1. Comparative Example 1 uses unmodified CNC, and the CNC surface has no PHA grafted chains, with only a physical contact interface between it and the PHA matrix. In Example 1, the PHA grafted chains on the surface of the modified nanocellulose whiskers participate in matrix crystallization to form a covalent anchoring interface, which improves the bonding strength between the whiskers and the matrix. This makes the interface less prone to failure under heat and stress, resulting in superior heat distortion temperature and mechanical properties compared to Comparative Example 1.

[0061] The performance test data from Example 1 and Comparative Example 2 show that the heat distortion temperature, tensile strength, and elongation at break of Example 1 are all higher than those of Comparative Example 2. Comparative Example 2 only added a small-molecule nucleating agent; the system lacked rigid whiskers to provide intergranular bridging. Although the nucleating agent promoted crystallization and increased the heat distortion temperature compared to pure PHA, the high crystallinity restricted the movement of chain segments in the amorphous regions, resulting in a significant decrease in elongation at break. In Example 1, the modified nanocellulose whiskers promoted crystallization while bridging multiple crystalline regions through rigid whiskers. Under stress, they transferred stress and hindered crack propagation, resulting in a smaller decrease in elongation at break compared to Comparative Example 2.

[0062] The performance test data from Example 1 and Comparative Example 3 show that the heat distortion temperature and tensile strength of Example 1 are higher than those of Comparative Example 3. Although the free PHA oligomer added in Comparative Example 3 can co-crystallize with the matrix, it lacks a rigid CNC framework as a physical crosslinking node, thus failing to form an intercrystalline bridging network and contributing only a limited amount to the heat distortion temperature. In Example 1, the rigid rod-like structure of the CNC acts as a bridging node between crystalline regions, restricting the thermal movement of amorphous chain segments and further increasing the heat distortion temperature.

[0063] The performance test data from Example 1 and Comparative Examples 4 and 5 show that when the molecular weight of the grafted chains of the modified nanocellulose whiskers exceeds the range of 2000-5000 Da (Comparative Example 4, molecular weight 8000 Da) or the grafting rate is less than 15% (Comparative Example 5, grafting rate 8%), the heat distortion temperature and elongation at break are both lower than those of Example 1. In Comparative Example 4, the excessively long grafted chains cause the CNC particles to entangle and aggregate in the melt, resulting in decreased dispersion uniformity. Local whisker agglomeration leads to uneven distribution of nucleation sites, increased performance fluctuations, and a decrease in the average value. In Comparative Example 5, the excessively low grafting rate results in insufficient number of covalent anchoring points between the CNC surface and the matrix, reduced interfacial bonding strength, and impacts both the heat distortion temperature and toughness.

[0064] The performance test data from Example 1 and Comparative Example 6 show that the heat distortion temperature of Example 1 is higher than that of Comparative Example 6. In Comparative Example 6, the amount of modified nanocellulose whiskers is only 1 part, which is lower than the range of 3-8 parts in the previous example. The number of whiskers is insufficient to form a continuous crystal bridge network that penetrates the matrix, and the effect of limiting the thermal movement of chain segments in the amorphous region is limited. Therefore, the increase in heat distortion temperature is less than that of Example 1.

[0065] The performance test data from Example 1 and Comparative Example 7 show that the heat distortion temperature of Example 1 is slightly higher than that of Comparative Example 7. Comparative Example 7 did not add sebacic acid dibenzoylhydrazine as an auxiliary nucleating agent; only modified nanocellulose whiskers provided nucleation in the system, resulting in a relatively low nucleation site density. Under the same cooling conditions, its crystallinity was slightly lower than that of Example 1, manifested as a slight decrease in heat distortion temperature.

[0066] The performance test data from Example 1 and Comparative Example 8 show that the tensile strength and elongation at break of Example 1 are higher than those of Comparative Example 8. Comparative Example 8 did not contain epoxidized soybean oil, and the lack of epoxy groups during the extrusion process resulted in a significant decrease in molecular weight and consequently, reduced mechanical properties.

[0067] Performance test data from Examples 1 to 5 show that, within the range of PHA matrix resin type, modified nanocellulose whisker dosage, grafted chain molecular weight, and grafting rate defined in the claims, the heat distortion temperature of each example reaches above 120°C, the tensile strength is in the range of 39–45 MPa, and the elongation at break is in the range of 18–25%. This indicates that the technical solution can obtain modified PHA particles with both high heat resistance and certain toughness under different parameter combinations, demonstrating good versatility. Example 2 has the highest heat distortion temperature due to its higher modified nanocellulose whisker dosage and larger grafting rate; Example 3 has the highest tensile strength but a slightly lower heat distortion temperature due to its lower modified nanocellulose whisker dosage and the relatively high crystallinity of the PHB homopolymer matrix. The differences in performance indicators among the examples are consistent with the direction of component dosage and parameter adjustments.

[0068] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A modified PHA particle, characterized in that, Made from the following raw material components in parts by weight: 70-85 parts of polyhydroxyalkanoate matrix resin; 3-8 parts of modified nanocellulose whiskers; Sebacic acid dibenzoylhydrazide 0.3–0.8 parts; 1-3 parts of epoxidized soybean oil; Antioxidant 1010: 0.1–0.3 parts; The polyhydroxy fatty acid ester matrix resin is selected from poly-3-hydroxybutyrate, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), wherein the molar content of 3-hydroxyvalerate or 4-hydroxybutyrate is 5-12%; The modified nanocellulose whiskers are nanocellulose whiskers with PHA short chains covalently grafted onto their surface, with a grafting rate of 15-30 wt% and a molecular weight of 2000-5000 Da for the grafted PHA short chains.

2. The modified PHA particles according to claim 1, characterized in that, The polyhydroxyalkanoate matrix resin has a melt index of 5–15 g / 10 min at 190°C and a load of 2.16 kg.

3. The modified PHA particles according to claim 1, characterized in that, The particle size D50 of the sebacic acid dibenzoylhydrazine is ≤5μm.

4. The modified PHA particles according to claim 1, characterized in that, The epoxidized soybean oil has an epoxy value ≥ 6.0% and an acid value ≤ 0.5 mg KOH / g.

5. The modified PHA particles according to claim 1, characterized in that, The method for preparing the modified nanocellulose whiskers includes the following steps: S1. Disperse nanocellulose whiskers in anhydrous toluene, add 3-aminopropyltriethoxysilane, and react at 80-90°C for 10-14 hours under nitrogen protection. After separation, washing and drying, amino-modified nanocellulose whiskers are obtained. S2. Dissolve the polyhydroxy fatty acid ester matrix resin in chloroform, and hydrolyze it at 55-65°C for 3-5 hours in the presence of p-toluenesulfonic acid and deionized water. After precipitation, washing and drying, a carboxyl-terminated PHA oligomer with a number average molecular weight of 2000-5000 Da is obtained. S3. Dissolve the terminal carboxyl PHA oligomer obtained in step S2 in anhydrous N,N-dimethylformamide, add dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and activate the carboxyl group at room temperature for 0.5 to 1.5 hours. S4. The aminated cellulose nanofibers obtained in step S1 are dispersed in anhydrous N,N-dimethylformamide and mixed with the activated terminal carboxyl PHA oligomer solution in step S3 under nitrogen protection. The mixture is reacted at 55-65°C for 20-28 hours. After separation, washing and drying, the modified cellulose nanofibers are obtained.

6. The modified PHA particles according to claim 5, characterized in that, In step S1, the mass ratio of the nanocellulose whiskers to 3-aminopropyltriethoxysilane is 1:0.3-0.

7.

7. The modified PHA particles according to claim 5, characterized in that, In step S2, the mass ratio of the polyhydroxyalkanoate matrix resin to p-toluenesulfonic acid is 1:0.03-0.07, and the mass-volume ratio of the polyhydroxyalkanoate matrix resin to deionized water is 1g:0.3-0.7mL.

8. The modified PHA particles according to claim 5, characterized in that, In step S3, the mass ratio of the terminal carboxyl PHA oligomer to dicyclohexylcarbodiimide is 1:0.2-0.4, and the mass ratio of the terminal carboxyl PHA oligomer to 4-dimethylaminopyridine is 1:0.02-0.

05.

9. A modified PHA particle according to claim 5, characterized in that, In step S4, the mass ratio of the aminated cellulose nanofiber whiskers to the carboxyl-terminated PHA oligomer is 1:2 to 4.

10. The method for preparing modified PHA particles according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Dry the polyhydroxy fatty acid ester matrix resin at 75-85℃ and vacuum degree ≤-0.09MPa until the moisture content is ≤0.05wt%. Mix the epoxidized soybean oil and antioxidant 1010 evenly to obtain a liquid additive mixture. S2. According to the weight ratio, the dried polyhydroxy fatty acid ester matrix resin, modified nanocellulose whiskers, and sebacic acid dibenzoyl hydrazine are put into a high-speed mixer and mixed at 800-1200 rpm for 5-15 minutes. Then, the liquid additive mixture is added under stirring and the mixture is continued for 15-25 minutes to obtain the mixture. S3. Add the mixture obtained in step S2 to a co-rotating twin-screw extruder. The temperatures of each section of the extruder are: feeding section 145-155℃, plasticizing section 155-165℃, homogenizing section 160-170℃, and die head section 155-165℃. The screw speed is 150-200 rpm. After melt extrusion, cooling, and pelletizing, granules are obtained. S4. The granules obtained in step S3 are kept at a constant temperature of 68-72°C for 2.5-3.5 hours to obtain the modified PHA granules.

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