Composite material of phosphonyl modified silicon dioxide and polyhydroxyalkanoate and preparation method of composite material

Abstract

The invention discloses a polyhydroxyalkanoate (PHA) composite material and a preparation method thereof. The PHA composite material comprises phosphonyl modified silicon dioxide and PHA powder, wherein the phosphonyl modified silicon dioxide is obtained by constructing a double-shell structure to carry out phosphonyl functional modification on silicon dioxide. The silicon dioxide is treated by adopting a specific surface treatment method, and the interfacial compatibility of the silicon dioxide in a PHA matrix is remarkably improved, so that the PHA composite material of which the mechanical property, the thermal stability and the flame retardant property are remarkably improved is prepared.

Description

Technical Field

[0001] This invention belongs to the field of composite materials. More specifically, this invention relates to a composite material of phosphonoyl-modified silica and polyhydroxyalkanoates and its preparation method. Background Technology

[0002] Polyhydroxyalkanoates (PHAs) are a class of fully biodegradable thermoplastic polyesters synthesized by microorganisms. They possess excellent biocompatibility and biodegradability, making them an ideal alternative to traditional petroleum-based plastics. However, PHA materials generally suffer from several drawbacks, including poor thermal stability, a narrow processing window, and susceptibility to thermal degradation during melt processing, thus limiting their applications. Furthermore, PHA materials exhibit insufficient mechanical properties, exhibiting high brittleness and insufficient toughness, making them unsuitable for high-strength applications. Moreover, PHA materials lack flame retardancy, have a low limiting oxygen index, and are easily flammable, posing safety hazards.

[0003] To improve the performance of PHA, inorganic nanoparticles are often used for composite modification. Silica is a commonly used inorganic filler, but its surface has a large number of silanol groups, which are highly hydrophilic and have poor compatibility with the hydrophobic PHA matrix. It is easy for it to agglomerate in the matrix, leading to stress concentration and deteriorating the material's performance.

[0004] In existing technologies, silane coupling agents are commonly used to modify the surface of silica. However, a single silane-modified layer may be unstable under high temperatures or stress, and its function is limited. Phosphonyl compounds have attracted much attention due to their excellent flame retardant properties and strong coordination ability with metal ions. If phosphonyl groups can be stably introduced into the silica surface and used to modify PHA, it is expected that the mechanical properties of PHA can be improved while endowing it with good thermal stability and flame retardancy. However, how to achieve a firm and efficient grafting of phosphonyl groups onto the silica surface and ensure their good dispersion in the PHA matrix is ​​a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention utilizes bilayer phosphonoyl-modified silica to modify polyhydroxy fatty acid esters, thereby improving their thermal stability, mechanical properties, and flame retardant properties. While modifying silica with a single aminosilane layer improves compatibility to some extent, it lacks the thermal stability and flame retardant functions provided by the phosphonoyl groups. This invention, by introducing an outer phosphonoyl layer, unexpectedly achieves a synergistic effect of "mechanical enhancement" and "functionalization (thermal stability, flame retardancy)."

[0006] Therefore, according to one aspect of the invention, a polyhydroxyalkanoate (PHA) composite material is provided, comprising: 5 to 20 (e.g., 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20) parts by weight of phosphonoyl-modified silica, 80 to 95 (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94 or 95) parts by weight of PHA powder, and 0 to 5 (e.g., 0, 1, 2, 3, 4 or 5) parts by weight of optional additives, wherein the phosphonoyl-modified silica is obtained by functionalizing silica with phosphonoyl groups to construct a double-shell structure.

[0007] In one embodiment, the phosphonoacyl functionalization modification includes the following steps: 1) Inner layer modification: Silica is dispersed in an anhydrous solvent, and an amino-containing silane coupling agent is added. The reaction yields aminated silica, forming a strong aminated inner layer on the silica surface; and 2) Outer layer modification: The above-mentioned aminated silica is reacted with a phosphonoacyl compound, and phosphonoacyl groups are grafted onto the aminated inner layer through chemical bonding between the amino group and the phosphonoacyl compound to form a functionalized outer layer.

[0008] In a preferred embodiment, the silica is nano-silica, preferably with a particle size of 1 to 100 nm.

[0009] In a preferred embodiment, the amino-containing silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane (i.e., 3-aminopropyltriethoxysilane), γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane. Preferably, the silica is treated with 1-10 wt% (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wt%) of the silane coupling agent based on the weight of silica, followed by washing and drying to obtain the aminated silica.

[0010] In a preferred embodiment, the anhydrous solvent is selected from alcohols, including methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, tert-butanol, n-octanol, or isooctanol, preferably anhydrous ethanol, or the anhydrous solvent is selected from aromatic hydrocarbon solvents, including toluene or xylene.

[0011] In a preferred embodiment, the phosphonoyl group-containing compound is selected from vinylphosphonic acid, vinylphosphonate, and phenylphosphonic acid, and reacts with the aminated silica in the presence of an azo initiator, preferably selected from azobisisobutyronitrile (AIBN) and azobisisoheptanenitrile (ABVN).

[0012] In a preferred embodiment, the outer layer modification is carried out in a nitrogen-containing polar aprotic solvent, preferably selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO). Preferably, the aminated silica is treated with 1-10 wt% (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wt%) of the phosphonoacyl-containing compound based on the weight of the aminated silica, followed by washing and drying to obtain the phosphonoacyl-modified silica.

[0013] In a preferred embodiment, the phosphonoacyl-modified silica is obtained as follows: 1) Disperse (gas-phase) nano-silica in anhydrous toluene, sonicate, add 3-aminopropyltriethoxysilane dropwise under nitrogen protection and stirring, reflux the reaction (e.g., at 110°C), then centrifuge, wash (e.g., with toluene and ethanol), and dry (vacuum) to obtain aminated silica; and 2) The aminated silica is dispersed in N,N-dimethylformamide (DMF), vinylphosphonic acid and free radical initiator azobisisobutyronitrile (AIBN) are added and reacted (e.g., at 60-100°C), then centrifuged, washed (e.g. using DMF and ethanol) and dried (vacuum) to obtain the phosphonoacyl modified silica.

[0014] In one embodiment, the PHA is PHA powder. Preferably, the PHA powder is prepared by microbial fermentation. Preferably, the PHA powder can be obtained by the following steps: a) fermenting recombinant bacteria, such as Escherichia coli or halophilic bacteria, in a culture medium to obtain PHA fermentation broth; b) centrifuging the PHA fermentation broth to remove the supernatant and washing it with water; c) breaking down the PHA emulsion after washing to precipitate intracellular PHA products in the broken-down liquid; d) separating and concentrating the PHA products in the solution using a centrifuge to obtain a suspension concentrate with a dry matter content of 25% to 30%; e) drying the concentrate to obtain powdered PHA product.

[0015] In one embodiment, the PHA is a homopolymer or copolymer of monomers selected from: 2-hydroxypropionic acid (2HP or LA), 3-hydroxybutyric acid (3HB), 4-hydroxybutyric acid (4HB), 3-hydroxyvalerate (3HV), 3-hydroxypropionic acid (3HP), 5-hydroxyvalerate (5HV), 3-hydroxyhexanoic acid (3HHx), 3-hydroxyheptanoic acid (3HHp), 6-hydroxyhexanoic acid (6HHx), 3-hydroxyoctanoic acid (3HO), 3-hydroxynonanoic acid (3HN), 3-hydroxydecanoic acid (3HD), 3-hydroxyundecanoic acid (3HUD), or 3-hydroxydodecanoic acid (3HDD), preferably the PHA. Selected from poly(3-hydroxybutyrate-lactic acid ester) copolymer (P(HB-LA)), polyhydroxypropionate (P3HP), polyhydroxybutyrate (PHB), polyhydroxyoctanoate (PHO), poly(3-hydroxynonanoate) (PHN), poly(3-hydroxydecanoate) (PHD), polyhydroxyvalerate (PHV), poly(3-hydroxybutyrate) (P3HB), poly(4-hydroxybutyrate) (P4HB), poly(3-hydroxypropionate) (P3HP), poly(3-hydroxyvalerate) (P3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). (PHBHHx), poly(3-hydroxybutyrate-co-3-hydroxyheptanoate) (PHBHHp), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (P3HO3HHx), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PHBVHHx), poly(3-hydroxybutyrate-co-4-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB4HB3HV), or poly(3-hydroxybutyrate-co-4-hydroxybutyrate-co-5-hydroxyvalerate) (P3HB4HB5HV).

[0016] In one embodiment, the additive is selected from one or more of antioxidants, lubricants, nucleating agents, fillers, chain extenders and compatibilizers, and preferably the PHA composite material contains 0.1 to 0.5 parts by weight of antioxidant and 0.5 to 1 part by weight of lubricant.

[0017] In a preferred embodiment, the antioxidant is a hindered phenolic primary antioxidant, preferably selected from antioxidant 1010, antioxidant 1076, antioxidant BHT (butylated hydroxyanisole), antioxidant CA, antioxidant 164, antioxidant DNP, and combinations thereof.

[0018] In a preferred embodiment, the lubricant is selected from calcium stearate, ethylene bis-stearamide (EBS), talc, mica powder, potassium carbonate, hexagonal boron nitride, and combinations thereof.

[0019] In a preferred embodiment, the nucleating agent is selected from: inorganic nucleating agents, organic nucleating agents, and polymeric nucleating agents, preferably from fatty acid amides including ethylene bis-stearamide (EBS), erucamide, oleamide, linoleamide, and palmitamide; fatty alcohol derivatives including xylitol, neopentyl glycol, trimethylolethane, pentaerythritol, isosorbide, sorbitol, mannitol, maltitol, and erythritol; hexagonal crystal compounds including boron nitride, silicon nitride, titanium nitride, boron carbide, silicon carbide, titanium carbide, magnesium oxide, and aluminum oxide; AD-506; LD-6; and combinations thereof.

[0020] In a preferred embodiment, the filler is selected from inorganic fillers including talc, calcium carbonate, silica, montmorillonite, and Le zeolite.

[0021] In a preferred embodiment, the chain extender is selected from CE-100, CE-208, CE301, ADR4468, ADR4370S, ADR4400, ADR4300, 7200N, and combinations thereof.

[0022] In a preferred embodiment, the compatibilizer is selected from CA-200, CA-100, EsunBio5004K, compatibilizer 8110, compatibilizer 8210, compatibilizer AX8900, and combinations thereof.

[0023] In one implementation, the PHA satisfies one or more of the following conditions: 1) Molecular weight from 30 to 1,000,000 Da (e.g., 30, 40, 50, 60, 70, 80, 90 and 1,000,000 Da); 2) Molecular weight distribution (Mw / Mn) is 1 to 3.0 (e.g., 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0); 3) Particle size is 3 to 20 micrometers (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 micrometers).

[0024] According to another aspect of the present invention, a method for preparing a modified PHA material is provided, the method comprising: mixing the PHA composite material according to the present invention and then melting, extruding, cooling, drying and granulating it in a twin-screw extruder, optionally further comprising hot pressing.

[0025] In a preferred embodiment, the twin-screw extruder is configured as follows: feed rate: 5 to 160 kg / h (e.g., 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 or 160 kg / h); zone temperature: 110 to 180°C (e.g., 110, 120, 130, 140, 150, 160, 170 or 180°C); screw speed: 80 to 200 rpm (e.g., 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200 rpm); cooling (air-cooled or water-cooled) temperature controlled at 40 to 60°C (e.g., 40, 45, 50, 55 or 60°C).

[0026] According to another aspect of the present invention, the application of the PHA composite material or modified PHA material according to the present invention in the preparation of packaging materials, biomedical materials, drug carriers, biodegradable agricultural films, slow-release fertilizers, eco-friendly building materials, conductive materials, food or cosmetics is provided.

[0027] In a preferred embodiment, a phosphonoyl-modified silica / PHA composite material is provided, characterized in that it is made from the following components in parts by weight: Polyhydroxyalkanoates: 80-95 parts Double-shell phosphonoyl modified silica: 5 ~ 20 parts Antioxidant: 0.1 ~ 0.5 parts Lubricant: 0.5 ~ 1 part.

[0028] The preparation method of the double-shell phosphonoyl modified silica includes the following steps: Inner layer modification: Nano-silica is dispersed in an anhydrous solvent, and an amino-containing silane coupling agent is added. After the reaction, a strong aminated inner layer is formed on the surface of silica.

[0029] Outer layer modification: The above-mentioned aminated silica is reacted with a phosphonoacyl compound. Through the chemical bonding between the amino group and the phosphonoacyl compound, phosphonoacyl groups are grafted onto the amino inner layer to form a functionalized outer layer.

[0030] The phosphonoyl group-containing compound is preferably a phosphonoyl group-containing compound containing a functional group that can react with an amino group, such as vinylphosphonic acid or phosphonate.

[0031] This invention also provides a method for preparing a phosphonoyl-modified silica / PHA composite material, characterized by comprising the following steps: PHA, double-shell phosphonoyl modified silica, antioxidant and lubricant are mixed evenly in a high-speed mixer according to the specified ratio.

[0032] The mixed materials are melt-blended, extruded, and granulated using a twin-screw extruder to obtain composite material particles.

[0033] Composite material particles are injection molded into standard test strips using an injection molding machine.

[0034] Beneficial effects of the present invention 1) Advantages of the double-shell structure: The inner aminosilane forms a strong Si-O-Si covalent bond with the hydroxyl groups on the silica surface, providing a stable anchoring point. The outer phosphonoyl group is chemically bonded to the inner amino group, forming a stable and dense functionalized shell. This structure avoids the disadvantage of easy detachment of a single modified layer, ensuring the durability of the modification effect.

[0035] 2) Excellent interfacial compatibility: The phosphonoyl group has a certain polarity and interacts with the ester groups that may exist in the PHA molecular chain, which improves the interfacial compatibility between silica and the PHA matrix, promotes the uniform dispersion of nanoparticles in the matrix, and reduces stress concentration.

[0036] 3) Significantly improves thermal stability: Phosphonyl groups can promote the cross-linking of PHA molecular chains to form a carbon layer at high temperatures, effectively inhibiting the thermal decomposition of PHA chains and greatly increasing the thermal decomposition temperature of the composite material.

[0037] 4) Imparting flame retardant properties: Phosphonyl groups are highly efficient flame retardant groups that can promote char formation during combustion, isolate oxygen and heat, exert flame retardant effects in both the gas phase and condensed phase, and significantly improve the limiting oxygen index of composite materials.

[0038] 5) Enhanced mechanical properties: The uniformly dispersed modified silica, as a nanofiller, can effectively transfer and disperse stress. At the same time, the good interaction between the phosphono groups and the matrix contributes to the improvement of the tensile strength and impact toughness of the composite material. The two have a synergistic effect. Detailed Implementation

[0039] Unless otherwise indicated, the terms used herein have their general technical meanings as understood by those skilled in the art.

[0040] In this invention, the singular articles “a” and “the” cover a plurality of indicators unless the context clearly indicates otherwise. All references cited herein are incorporated herein by reference in their entirety.

[0041] In this invention, the terms "comprising" or "including" are open-ended expressions that refer to a specific ingredient or step described, without excluding other ingredients or steps that do not have a substantial effect.

[0042] The term "and / or" as used in this invention encompasses all combinations of items connected by the term, and should be considered as if each combination had been individually listed herein. For example, "A and / or B" includes "A", "A and B", and "B". As another example, "A, B and / or C" includes "A", "B", "C", "A and B", "A and C", "B and C", and "A and B and C".

[0043] The present invention is further illustrated in the following embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All experimental materials were conventional biochemical reagents. All quantitative experiments were performed in triplicate, and the results were averaged. Example Example 1: Preparation of double-shell phosphonoyl modified silica:

[0044] 10 g of fumed silica nanoparticles were weighed and dispersed in 200 mL of anhydrous toluene, and sonicated for 30 minutes. Under nitrogen protection and stirring, 5 mL of 3-aminopropyltriethoxysilane (Aladdin Scientific) was slowly added dropwise to the system. The mixture was heated to 110 °C and refluxed for 12 hours. After the reaction was completed, the mixture was separated by centrifugation and washed three times alternately with toluene and ethanol. It was then dried under vacuum at 80 °C for 12 hours to obtain aminated silica.

[0045] The aminated silica was redispersed in 150 mL of N,N-dimethylformamide. 3 g of vinylphosphonic acid (Shanghai Maclean Biochemical Technology Co., Ltd.) and a small amount of the free radical initiator azobisisobutyronitrile (AIBN) were added. The reaction was carried out at 80 °C for 8 hours. After the reaction was completed, the mixture was centrifuged, thoroughly washed with DMF and ethanol, and vacuum dried at 80 °C for 12 hours to obtain the final product—double-shell phosphonyl-modified silica.

[0046] Preparation of composite materials: Weigh 90 parts by weight of P(3HB-co-4HB) (Beijing Microstructure Factory Biotechnology Co., Ltd.), 5 parts by weight of the prepared double-shell phosphonoyl modified silica, 0.3 parts by weight of antioxidant 1010, and 0.7 parts by weight of calcium stearate. Mix the above materials in a high-speed mixer for 5 minutes. Add the mixture to a twin-screw extruder (TDY45, Nanjing Yuesheng Extrusion Machinery Co., Ltd.) for melt blending. The extruder temperatures are set as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 165℃, Zone 4 165℃, Die Head 160℃, and Screw Speed ​​200 rpm. The extruded strip is water-cooled and pelletized to obtain composite material particles. After drying the particles at 80℃ for 4 hours, they are injection molded into standard tensile, impact, and limiting oxygen index test strips using an injection molding machine. Example 2 Preparation of double-shell phosphonoyl modified silica:

[0047] 10 g of fumed silica nanoparticles were weighed and dispersed in 200 mL of anhydrous toluene, and sonicated for 30 minutes. Under nitrogen protection and stirring, 5 mL of 3-aminopropyltriethoxysilane was slowly added dropwise to the system. The mixture was heated to 110 °C and refluxed for 12 hours. After the reaction was completed, the mixture was separated by centrifugation and washed three times alternately with toluene and ethanol. It was then dried under vacuum at 80 °C for 12 hours to obtain aminated silica.

[0048] The aminated silica was redispersed in 150 mL of N,N-dimethylformamide. 3 g of phenylphosphonic acid (Shanghai Maclean Biochemical Technology Co., Ltd.) and a small amount of free radical initiator AIBN were added. The reaction was carried out at 80 °C for 8 hours. After the reaction was completed, the mixture was centrifuged, thoroughly washed with DMF and ethanol, and vacuum dried at 80 °C for 12 hours to obtain the final product—double-shell phosphonoyl modified silica.

[0049] Preparation of composite materials: Weigh 85 parts by weight of P(3HB-co-4HB) (Beijing Microstructure Factory Biotechnology Co., Ltd.), 15 parts by weight of the above-mentioned double-shell phosphonoyl modified silica, 0.3 parts by weight of antioxidant 1010, and 0.7 parts by weight of calcium stearate. Mix the above materials in a high-speed mixer for 5 minutes. Add the mixture to a twin-screw extruder (TDY45, Nanjing Yuesheng Extrusion Machinery Co., Ltd.) for melt blending. The temperatures of each section of the extruder are set as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 165℃, Zone 4 165℃, Die Head 160℃, and Screw Speed ​​200 rpm. The extruded strip is water-cooled and pelletized to obtain composite material particles. After drying the particles at 80℃ for 4 hours, they are injection molded into standard tensile, impact, and limiting oxygen index test strips using an injection molding machine. Example 3 Preparation of double-shell phosphonoyl modified silica:

[0050] 10 g of fumed silica nanoparticles were weighed and dispersed in 200 mL of anhydrous toluene, and sonicated for 30 minutes. Under nitrogen protection and stirring, 8 mL of 3-aminopropyltriethoxysilane was slowly added dropwise to the system. The mixture was heated to 110 °C and refluxed for 12 hours. After the reaction was completed, the mixture was separated by centrifugation, washed three times alternately with toluene and ethanol, and dried under vacuum at 80 °C for 12 hours to obtain aminated silica.

[0051] The aminated silica was redispersed in 150 mL of N,N-dimethylformamide. 5 g of vinylphosphonic acid and a small amount of free radical initiator AIBN were added. The reaction was carried out at 80 °C for 8 hours. After the reaction was complete, the mixture was centrifuged, thoroughly washed with DMF and ethanol, and vacuum dried at 80 °C for 12 hours to obtain the final product—bi-shell phosphonoyl modified silica.

[0052] Preparation of composite materials: Weigh 80 parts by weight of PHB (Beijing Microstructure Workshop Biotechnology Co., Ltd.), 20 parts by weight of the above-mentioned double-shell phosphonoyl modified silica, 0.3 parts by weight of antioxidant 1010, and 0.7 parts by weight of calcium stearate. Mix the above materials in a high-speed mixer for 5 minutes. Add the mixture to a twin-screw extruder (TDY45, Nanjing Yuesheng Extrusion Machinery Co., Ltd.) for melt blending. The temperatures of each section of the extruder are set as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 165℃, Zone 4 165℃, Die Head 160℃, and Screw Speed ​​200 rpm. The extruded strip is water-cooled and pelletized to obtain composite material particles. After drying the particles at 80℃ for 4 hours, they are injection molded into standard tensile, impact, and limiting oxygen index test strips using an injection molding machine.

[0053] Comparative Example 1 This comparative example uses unmodified virgin silica.

[0054] Preparation of composite materials: Weigh 90 parts by weight of P(3HB-co-4HB) (Beijing Microstructure Factory Biotechnology Co., Ltd.), 5 parts by weight of the prepared double-shell phosphonoyl modified silica, 0.3 parts by weight of antioxidant 1010, and 0.7 parts by weight of calcium stearate. Mix the above materials in a high-speed mixer for 5 minutes. Add the mixture to a twin-screw extruder (TDY45, Nanjing Yuesheng Extrusion Machinery Co., Ltd.) for melt blending. The extruder temperatures are set as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 165℃, Zone 4 165℃, Die Head 160℃, and Screw Speed ​​200 rpm. The extruded strip is water-cooled and pelletized to obtain composite material particles. After drying the particles at 80℃ for 4 hours, they are injection molded into standard tensile, impact, and limiting oxygen index test strips using an injection molding machine.

[0055] Comparative Example 2 This comparative example uses silica modified with a single silane layer (i.e., only the inner layer is modified, without the outer phosphonoyl group modification).

[0056] Preparation of aminated silica: The steps are exactly the same as those in the "inner layer modification" section of Example 1.

[0057] Preparation of inner shell phosphonoyl modified silica: 10 g of fumed silica nanoparticles were weighed and dispersed in 200 mL of anhydrous toluene, and sonicated for 30 minutes. Under nitrogen protection and stirring, 5 mL of 3-aminopropyltriethoxysilane was slowly added dropwise to the system. The mixture was heated to 110 °C and refluxed for 12 hours. After the reaction was completed, the mixture was separated by centrifugation and washed three times alternately with toluene and ethanol. It was then dried under vacuum at 80 °C for 12 hours to obtain aminated silica.

[0058] Preparation of composite materials: Weigh 90 parts by weight of P(3HB-co-4HB) (Beijing Microstructure Factory Biotechnology Co., Ltd.), 5 parts by weight of the above-prepared aminated silica, 0.3 parts by weight of antioxidant 1010, and 0.7 parts by weight of calcium stearate. Mix the above materials in a high-speed mixer for 5 minutes. Add the mixture to a twin-screw extruder (TDY45, Nanjing Yuesheng Extrusion Machinery Co., Ltd.) for melt blending. The extruder temperatures are set as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 165℃, Zone 4 165℃, Die Head 160℃, and Screw Speed ​​200 rpm. The extruded strip is water-cooled and pelletized to obtain composite material particles. After drying the particles at 80℃ for 4 hours, they are injection molded into standard tensile, impact, and limiting oxygen index test strips using an injection molding machine.

[0059] Comparative Example 3 This comparative example uses pure PHA material.

[0060] Weigh out 100 parts of P(3HB-co-4HB) (Beijing Microstructure Factory Biotechnology Co., Ltd.), 0.3 parts of antioxidant 1010, and 0.7 parts of calcium stearate.

[0061] The preparation process of the composite material is exactly the same as that in Example 1.

[0062] Weigh 90 parts by weight of P(3HB-co-4HB) (Beijing Microstructure Factory Biotechnology Co., Ltd.), 0.3 parts by weight of antioxidant 1010, and 0.7 parts by weight of calcium stearate. Mix the above materials in a high-speed mixer for 5 minutes. Add the mixture to a twin-screw extruder (TDY45, Nanjing Yuesheng Extrusion Machinery Co., Ltd.) for melt blending. The extruder temperatures are set as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 165℃, Zone 4 165℃, Die Head 160℃, and Screw Speed ​​200 rpm. The extruded strip is water-cooled and pelletized to obtain composite material particles. After drying the particles at 80℃ for 4 hours, they are injection molded into standard tensile, impact, and limiting oxygen index test strips using an injection molding machine.

[0063] Test case Testing and characterization methods: Mechanical properties: Tensile strength and elongation at break were tested according to ASTM D638; notched impact strength of cantilever beam was tested according to ASTM D256 (Universal testing machine, Chengde Jinjian Inspection Instrument Co., Ltd., model UTM-1432).

[0064] Heat distortion temperature: The test method is in accordance with the "Test Method for Heat Deflection Temperature of Plastics" (GB / T 10561-2007), using a YF-8475 heat distortion Vicat tester (Yangzhou Yuanfeng Testing Equipment Co., Ltd.).

[0065] Thermal stability: Thermogravimetric analysis (GB / T 31850—2015; thermogravimetric analyzer, Mettler Toledo, model TGA2) was used to record the temperature (Td5%) at which 5% weight loss was achieved by heating from 50℃ to 600℃ at a rate of 10℃ / min under a nitrogen atmosphere.

[0066] Limiting Oxygen Index (LOI): The determination method is in accordance with GB / T 2406-2009, "Determination of Limiting Oxygen Index (LOI)", using a JF-3 digital display oxygen index meter (Guangdong Shurui Technology Co., Ltd.).

[0067] The performance test results are shown in Table 1 below.

[0068]

[0069] Results analysis: Compared to Comparative Example 3 (pure PHA): the mechanical properties, thermal stability, and flame retardancy of all embodiments were significantly improved. This demonstrates the effective modification effect of double-shell phosphonoyl groups on silica.

[0070] Compared to Comparative Example 1 (unmodified silica): Comparative Example 1 showed limited improvement in various properties, and even a decrease in elongation at break, indicating that unmodified SiO2 has poor compatibility with PHA, causing it to agglomerate in the matrix and have a negative effect. In contrast, the performance of the embodiments was comprehensively superior to Comparative Example 1, demonstrating the crucial role of double-shell modification in improving dispersibility and interfacial bonding.

[0071] Compared to Comparative Example 2 (single amino-modified silica): Comparative Example 2 outperformed Comparative Example 1, but was far inferior to the embodiments of the present invention. This indicates that while a single aminosilane layer improves compatibility to some extent, it lacks the thermal stability and flame retardant properties provided by phosphonoyl groups. The present invention, by introducing a phosphonoyl outer layer, unexpectedly achieves a synergistic effect of "mechanical enhancement" and "functionalization (thermal stability, flame retardancy)".

[0072] Comparison between examples: With the increase of modified silica content (Examples 1→3), the rigidity, heat resistance, and flame retardancy of the material are further improved, but the toughness decreases slightly, which is a normal phenomenon with the increase of filler content. By adjusting the ratio, the needs of different application scenarios can be met.

[0073] Conclusion: This invention successfully prepared a high-performance PHA composite material by constructing a double-shell phosphonoyl modified silica. While maintaining its biodegradability, it significantly overcomes the shortcomings of poor thermal stability, insufficient mechanical properties and lack of flame retardancy, and has broad application prospects.

[0074] Those skilled in the art should understand that although the present invention has been specifically described with reference to the above embodiments, the present invention is not limited to these specific embodiments. Based on the methods and technical solutions taught in this invention, those skilled in the art can make appropriate modifications or improvements without departing from the spirit of the present invention, and the equivalent embodiments obtained therefrom are all within the scope of the present invention.

Claims

1. A polyhydroxyalkanoate (PHA) composite material comprising: 5 to 20 parts by weight of phosphonoacyl-modified silica; 80 to 95 parts by weight of PHA powder; and 0 to 5 parts by weight of optional additives, wherein the phosphonoacyl-modified silica is obtained by functionalizing silica with phosphonoacyl groups to construct a double-shell structure.

2. The PHA composite material according to claim 1, wherein the phosphonoyl functionalization modification includes the following steps: 1) Inner layer modification: Silica is dispersed in an anhydrous solvent, and an amino-containing silane coupling agent is added. The reaction yields aminated silica, forming a strong aminated inner layer on the silica surface; and 2) Outer layer modification: The above-mentioned aminated silica is reacted with a phosphonoacyl compound, and phosphonoacyl groups are grafted onto the aminated inner layer through chemical bonding between the amino group and the phosphonoacyl compound to form a functionalized outer layer.

3. The PHA composite material according to claim 2, wherein: 1) The silica is nano-silica, preferably with a particle size of 1 to 100 nm; 2) The amino-containing silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane; 3) The anhydrous solvent is selected from alcohols, including methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, tert-butanol, n-octanol or isooctanol, preferably anhydrous ethanol, or the anhydrous solvent is selected from aromatic hydrocarbon solvents, including toluene or xylene; 4) The phosphonoyl group-containing compound is selected from vinylphosphonic acid, vinylphosphonate, and phenylphosphonic acid, and reacts with the aminated silica in the presence of an azo initiator, preferably selected from azobisisobutyronitrile (AIBN) and azobisisoheptanenitrile (ABVN); and / or 5) The outer layer modification is carried out in a nitrogen-containing polar aprotic solvent, preferably selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).

4. The PHA composite material according to any one of claims 1 to 3, wherein the phosphonoyl-modified silica is obtained as follows: 1) Nano-silica was dispersed in anhydrous toluene, sonicated, and then 3-aminopropyltriethoxysilane was added dropwise under nitrogen protection and stirring. The mixture was heated to reflux, then centrifuged, washed, and dried to obtain aminated silica; and 2) The aminated silica was dispersed in N,N-dimethylformamide (DMF), vinylphosphonic acid and free radical initiator azobisisobutyronitrile (AIBN) were added and reacted, followed by centrifugation, washing and drying to obtain the phosphonoacyl modified silica.

5. The PHA composite material according to any one of claims 1 to 4, wherein the PHA is a homopolymer or copolymer of monomers, and the monomers are selected from: 2-hydroxypropionic acid (2HP or LA), 3-hydroxybutyric acid (3HB), 4-hydroxybutyric acid (4HB), 3-hydroxyvalerate (3HV), 3-hydroxypropionic acid (3HP), 5-hydroxyvalerate (5HV), 3-hydroxyhexanoic acid (3HHx), 3-hydroxyheptanoic acid (3HHp), 6-hydroxyhexanoic acid (6HHx), 3-hydroxyoctanoic acid (3HO), 3-hydroxynonanoic acid (3HN), 3-hydroxydecanoic acid (3HD), 3-hydroxyundecanoic acid (3HUD), or 3-hydroxydodecanoic acid (3HDD). Preferably, the PHA is selected from poly(3-hydroxybutyrate-lactic acid ester) copolymer (P(HB-LA)), polyhydroxypropionate (P3HP), polyhydroxybutyrate (PHB), polyhydroxyoctanoate (PHO), poly(3-hydroxynonanoate) (PHN), poly(3-hydroxydecanoate) (PHD), polyhydroxyvalerate (PHV), poly(3-hydroxybutyrate) (P3HB), poly(4-hydroxybutyrate) (P4HB), poly(3-hydroxypropionate) (P3HP), poly(3-hydroxyvalerate) (P3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). (PHBHHx), poly(3-hydroxybutyrate-co-3-hydroxyheptanoate) (PHBHHp), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (P3HO3HHx), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PHBVHHx), poly(3-hydroxybutyrate-co-4-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB4HB3HV), or poly(3-hydroxybutyrate-co-4-hydroxybutyrate-co-5-hydroxyvalerate) (P3HB4HB5HV).

6. The PHA composite material according to any one of claims 1 to 5, wherein the additive is selected from one or more of antioxidants, lubricants, nucleating agents, fillers, chain extenders and compatibilizers, preferably the PHA composite material contains 0.1 to 0.5 parts by weight of antioxidant and 0.5 to 1 part by weight of lubricant.

7. The PHA composite material according to claim 6, wherein: 1) The antioxidant is a hindered phenolic primary antioxidant, preferably selected from antioxidant 1010, antioxidant 1076, antioxidant BHT (butylated hydroxyanisole), antioxidant CA, antioxidant 164, antioxidant DNP and combinations thereof; 2) The lubricant is selected from calcium stearate, ethylene bis-stearamide (EBS), talc, mica powder, potassium carbonate, hexagonal boron nitride, and combinations thereof; 3) The nucleating agent is selected from: inorganic nucleating agents, organic nucleating agents, and polymeric nucleating agents, preferably from fatty acid amides including erucamide, oleamide, linoleamide, and palmitamide; fatty alcohol derivatives including xylitol, neopentyl glycol, trimethylolethane, pentaerythritol, isosorbide, sorbitol, mannitol, maltitol, and erythritol; hexagonal crystal compounds including boron nitride, silicon nitride, titanium nitride, boron carbide, silicon carbide, titanium carbide, magnesium oxide, and aluminum oxide; AD-506; LD-6; and combinations thereof; 4) The filler is selected from inorganic fillers including talc, calcium carbonate, silica, montmorillonite and Le zeolite; 5) The chain extender is selected from CE-100, CE-208, CE301, ADR4468, ADR4370S, ADR4400, ADR4300, 7200N and combinations thereof; and / or 6) The compatibilizer is selected from CA-200, CA-100, EsunBio5004K, compatibilizer 8110, compatibilizer 8210, compatibilizer AX8900 and combinations thereof.

8. A method for preparing modified PHA materials, the method comprising: The PHA composite material according to any one of claims 1 to 7 is mixed and then melted, extruded, cooled, dried and granulated in a twin-screw extruder, optionally further comprising hot pressing.

9. The method according to claim 8, wherein the twin-screw extruder is configured as follows: feeding speed: 5 to 160 kg / h; temperature of each zone: 110 to 180°C; screw speed: 80 to 200 r / min; cooling (air cooling or water cooling) temperature controlled at 40 to 60°C.

10. The application of the PHA composite material according to any one of claims 1 to 7 or the modified PHA material according to claim 8 or 9 in the preparation of packaging materials, biomedical materials, drug carriers, biodegradable agricultural films, slow-release fertilizers, ecological building materials, conductive materials, food or cosmetics.

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