PHA composite antibacterial material for food and tableware and preparation method of PHA composite antibacterial material

Abstract

The invention belongs to the technical field of polymer environment-friendly materials, and particularly relates to a PHA composite antibacterial material for food and tableware and a preparation method of the PHA composite antibacterial material. The composite material is prepared from the following components in parts by weight: 60 to 70 parts of PHA (Polyhydroxyalkanoate) base material, 20 to 24 parts of PLA (Polylactic Acid) base material, 3 to 4 parts of oligomeric D-lactic acid, 2 to 2.5 parts of ZnO-coated CNC (Computer Numerical Control) antibacterial particles, 4.5 to 5.5 parts of needle-like wollastonite powder, 3.5 to 5 parts of silane modified montmorillonite, 0.05 to 0.1 part of talcum powder, 0.3 to 0.4 part of rosemary extract, 0.6 to 0.9 part of chain extender, 0.4 to 0.5 part of D-sorbitol diglycidyl ether, 0.35 to 0.45 part of glyceryl monostearate and 0.3 to 0.4 part of antioxidant. The PHA base material is used for constructing a bearing framework, and the mechanical strength, the heat-resistant stability, the oil resistance and the long-acting antibacterial property are organically unified by combining the synergistic effect of multiple materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer environmental protection materials, and particularly relates to a PHA composite antibacterial material for food tableware and a preparation method thereof. Background Art

[0002] Polyhydroxyalkanoates (PHA) are a class of natural high molecular polyesters synthesized by microorganisms, which can be degraded by microorganisms into CO2 and water in soil, seawater and compost environments without leaving microplastic residues; their degradation products are non-toxic, meet food contact safety standards, and the raw materials are renewable. They can be prepared by microbial fermentation using carbon sources such as glucose, waste oil and agricultural waste, thus reducing the dependence on fossil resources; with these characteristics, PHA-based materials are regarded as ideal candidates to replace traditional plastics (such as PP, PS), especially suitable for food packaging and tableware. PHA-based materials can directly contact food without adding plasticizers or stabilizers, avoiding the migration of harmful chemical substances; their life cycle carbon footprint is significantly lower than that of traditional plastics; at the same time, PHA-based materials have good processing diversity and can be formed into lunch boxes, forks, spoons, straws, etc. by injection molding, blow molding, hot pressing, etc. However, the large-scale application of PHA in the field of food tableware is still limited by several key defects. For example, the tensile strength and elongation at break of pure PHA are significantly lower than those of conventional plastics, and the products are prone to brittle fracture or compressive deformation, and the toughness further decreases under refrigeration and freezing conditions; its heat resistance is also insufficient, and the heat distortion temperature is only 60–80°C, which cannot meet high-temperature use scenarios, and thermal degradation is likely to occur during melt processing, resulting in non-uniform performance.

[0003] Existing studies have made positive progress by blending with bio-based polymers such as PLA and PBS, or adding reinforcing phases such as cellulose nanocrystals and montmorillonite to improve the mechanical strength, and using crosslinking modification or introducing nano-fillers such as TiO2 and carbon nanotubes to enhance the heat resistance, but still face mechanical attenuation after multiple uses and cost pressure brought by a high proportion of nano-fillers. While solving the mechanical and heat resistance shortboards, endowing PHA with antibacterial properties is also crucial. On the one hand, antibacterial tableware and packaging can effectively inhibit the growth of pathogenic or spoilage microorganisms such as Escherichia coli and Staphylococcus aureus during the use period, extend the food preservation period and reduce the risk of foodborne diseases; on the other hand, as degradable tableware expands from the disposable field to the scenarios of circular recycling and reusable, the antibacterial ability on the material surface can reduce cross-contamination during cleaning and turnover, extend the number of product cycles and improve the use experience. Therefore, based on the above defects, it is extremely necessary to develop an antibacterial PHA composite material with high mechanical strength, heat resistance and stable performance after multiple uses. Summary of the Invention

[0004] Aiming at the defects of the existing technology, the purpose of the present invention is to provide a PHA composite antibacterial material for food tableware and its preparation method. By means of the interpenetrating continuous phase structure of short-chain / medium-chain PHA combined with the in-situ formation of a three-dimensional polycrystalline micro-region, the present invention makes up for the defect that the mechanical properties and heat resistance of traditional bio-based materials are difficult to be compatible, and realizes the effects of high strength, high toughness and high-temperature creep resistance; through the synergistic effect of the silane-modified montmorillonite plate-nail structure and the ZnO@CNC sustained-release antibacterial system, the deficiencies of filler agglomeration, excessive migration of metal ions and attenuation of antibacterial properties are avoided; with the help of the micro-skeleton-nano-barrier double-layer sheet frame and the three-dimensional locking structure, on the premise of maintaining food contact safety, the effective improvement of oil resistance, antibacterial property, rapid heat dissipation and mechanical properties is realized.

[0005] The technical effects of the present invention are achieved through the following technical solutions: a PHA composite antibacterial material for food tableware, the composition of which includes the following components by weight: 60-70 parts of PHA substrate, 20-24 parts of PLA substrate, 3-4 parts of oligo-D-lactic acid, 2-2.5 parts of ZnO@CNC antibacterial particles, 4.5-5.5 parts of acicular wollastonite powder, 3.5-5 parts of silane-modified montmorillonite, 0.05-0.1 part of talc powder, 0.3-0.4 part of rosemary extract, 0.6-0.9 part of chain extender, 0.4-0.5 part of D-sorbitol diglycidyl ether, 0.35-0.45 part of glycerol monostearate and 0.3-0.4 part of antioxidant.

[0006] Further, the PHA substrate is composed of 90% short-chain PHA substrate and 10% medium-chain PHA substrate; preferably, the short-chain PHA substrate is preferably 3-hydroxybutyric acid; the medium-chain PHA substrate is preferably 3-hydroxyoctanoic acid; Further, the PLA substrate is L-PLA, and the L-PLA is L-lactic acid polymer; Further, the specific preparation steps of the ZnO@CNC antibacterial particles are as follows: S1: Add cellulose nanocrystals to deionized water, and ultrasonically disperse them evenly to obtain a cellulose nanocrystal dispersion; add Zn(NO3)2·6H2O to deionized water, stir and dissolve it evenly, and then slowly drop it into the cellulose nanocrystal dispersion, and stir at 400-600 rpm for 1-2 h to obtain a mixed solution; S2: Add sodium hydroxide to deionized water, stir to dissolve evenly, and then slowly drop it into the mixed solution prepared in step S1 at a rate of 1 - 2 mL / min. Add 0.1% cetyltrimethylammonium bromide, continuously stir at a speed of 600 rpm during the dropping process. After the dropping is completed, continue to stir for 1 - 2 h, let it stand for 4 - 6 h, centrifuge at 5000 rpm for 10 - 15 min, wash until neutral, and vacuum dry at 50 °C for 12 - 24 h to obtain ZnO@CNC antibacterial particles; Further, in step S1, the dosage ratio of the cellulose nanocrystals to deionized water is 1 g:50 - 100 mL; the dosage ratio of Zn(NO3)2·6H2O, deionized water, and the cellulose nanocrystal dispersion is 0.7 - 0.8 g:4 mL:50 - 100 mL; Further, in step S2, the dosage ratio of the sodium hydroxide, deionized water, and the mixed solution is 0.2 - 0.25 g:2 mL:50 - 100 mL; Further, the specific preparation steps of the silane - modified montmorillonite are as follows: S101: Add the nano - montmorillonite to an 80 wt% ethanol solution, with a power of 100 - 150 W and a frequency of 30 kHz, and ultrasonically treat for 20 - 30 min to obtain a nano - montmorillonite suspension; slowly drop octadecyltrichlorosilane into the nano - montmorillonite suspension within 10 min, raise the temperature to 50 - 60 °C, adjust the pH to 4 - 5, and stir - react at 300 rpm for 3 - 5 h; S102: After the reaction in step S101 ends, let it stand and cool to room temperature, centrifuge at 8000 - 10000 rpm for 15 min, add deionized water and ethanol to wash alternately 5 times, and vacuum dry at 60 - 80 °C until constant weight to obtain the silane - modified montmorillonite; Further, in step S101, the dosage ratio of the nano - montmorillonite to the ethanol solution is 1 g:20 - 30 mL; the dosage ratio of the octadecyltrichlorosilane to the nano - montmorillonite is 1.5 - 2 mL:1 g; Further, the chain extender is Joncryl ADR - 4368 epoxy chain extender; Further, the antioxidant is tris(2,4 - di - tert - butylphenyl) phosphite; Further, another aspect of the present invention is to provide a preparation method of a PHA composite antibacterial material for food tableware, and the specific preparation steps are as follows: S201: Vacuum dry the PHA substrate and the PLA substrate at 80 °C for 6 - 8 h to obtain a pretreated PHA substrate and a pretreated PLA substrate; heat-treat ZnO@CNC antibacterial particles, acicular wollastonite powder, and silane-modified montmorillonite at 100 °C for 4 - 6 h with hot air, sieve through a 150-mesh sieve to obtain pretreated ZnO@CNC antibacterial particles, pretreated acicular wollastonite powder, and pretreated silane-modified montmorillonite; S202: Feed the pretreated PHA substrate, the pretreated PLA substrate, an antioxidant, and glycerol monostearate at 160 °C, raise the temperature to 175 °C for plasticization treatment for 2 - 3 min, and then raise the temperature to 185 °C for preliminary mixing treatment for 3 - 5 min; S203: After completing the operation of step S202, add the pretreated acicular wollastonite powder prepared in step S201, with a shear rate of 240 - 280 rpm, and treat for 1 - 2 min; sequentially add the pretreated ZnO@CNC antibacterial particles and the pretreated silane-modified montmorillonite, with a shear rate of 150 - 200 rpm, and treat for 50 - 90 s; S204: After completing the operation of step S203, raise the temperature to 200 - 205 °C, sequentially add talc powder, oligomeric D-lactic acid, rosemary extract, a chain extender, and D-sorbitol diglycidyl ether, maintain the reaction for 60 - 90 s, then perform a cooling treatment, evacuate under vacuum, maintain the extrusion temperature at 170 - 180 °C, and cool the material by water-ring granulation to obtain a PHA composite antibacterial material; Further, in step S204, the parameters of the cooling treatment are: cool to 180 - 185 °C and then perform a reaction treatment for 40 - 80 s.

[0007] The beneficial effects of the present invention are as follows: The present invention first constructs a load-bearing framework with a short-chain PHA substrate having high crystallinity and excellent rigidity, and then introduces an appropriate amount of medium-chain PHA as a flexible chain segment and an energy dissipation region. The two form an interpenetrating continuous phase in the molten state: not only ensuring that the material has sufficient tensile strength, but also endowing it with a considerable elongation at break, providing a toughness buffer space for the high proportion of inorganic fillers added subsequently. Then, in the high-temperature blending section, oligomeric D-lactic acid (ODL) is melt-contacted with polylactic acid (L-PLA) to in-situ generate stereocomplex crystal microdomains with a relatively high melting point; in addition, the multi-epoxy groups of Joncryl ADR-4368 undergo a chain extension reaction with the terminal hydroxyl and carboxyl groups of each polyester, locking the oligomeric D-lactic acid in the main chain and overall increasing the molecular weight, while D-sorbitol diglycidyl ether introduces reversible β-ester bonds locally to construct a certain self-healing ability, enabling the material to still maintain viscoelasticity and structural integrity after repeated heating-cooling cycles.

[0008] In the present invention, octadecyltrichlorosilane (ODTCS) is used to perform surface organic modification on nano-montmorillonite. The long-chain alkyl groups are firmly attached to the lamellae through the Si-O-Si anchoring reaction, converting the originally hydrophilic and negatively charged lamellae into weakly polar hydrophobic surfaces. Meanwhile, the interlayer spacing is enlarged synchronously, and the flexibility of the lamellae is significantly improved. Under the action of high temperature and high shear, the silane-modified montmorillonite lamellae can be fully wetted, exfoliated and preferentially oriented by the polyester melt, and interlock with the surrounding SC-PLA grains to form a plate-nail structure that inhibits high-temperature creep. Its hydrophobic shell can also delay the leaching of metal ions, complementing the slow-release strategy of the ZnO@CNC antibacterial particles described later and avoiding the overshoot of antibacterial metals resulting in migration exceeding the standard. In the present invention, nano-ZnO is uniformly embedded on the surface of cellulose nanocrystals (CNC) through in-situ aqueous deposition to form a porous coating layer; Zn 2+ Before release, it needs to penetrate through the hydroxyl-hydrogen bond network, and its release rate is significantly decreased. Therefore, even after multiple dishwasher or microwave cycles, the antibacterial efficiency can still be maintained at a high level, and the durability is much better than that of bare ZnO or traditional silver-based fillers. At the same time, the hydroxyl groups on the surface of cellulose nanocrystals can form hydrogen bonds with the ester carbonyl groups of PHA / PLA, and can also undergo weak chemical coupling with the remaining hydroxyl terminals after chain extension, thereby increasing the interfacial shear strength; the deposition of ZnO also makes the surface potential of cellulose nanocrystals close to neutral, and its dispersibility in the hydrophobic polyester melt is greatly improved, and agglomeration can be avoided without additional coupling agents, saving unnecessary additives and costs. The filler system is jointly constructed by acicular wollastonite and silane-modified montmorillonite: Wollastonite is rapidly oriented in the high-temperature and high-shear zone to form a longitudinal micro-skeleton, significantly improving the flexural modulus and thermal conductivity; the modified montmorillonite is exfoliated and arranged in parallel to form a nano-barrier shell under the induction of SC-PLA. The micro-skeleton-nano-barrier double-layer sheet structure formed by their superposition not only further inhibits high-temperature creep, but also significantly reduces the oil permeability, and provides a fast heat dissipation channel for the system with high aspect ratio sheets to prevent warping caused by local overheating. ZnO@CNC antibacterial particles enter the melt in the same shear zone, and their high aspect ratio fibers are intertwined with the double-layer sheet structure to form a three-dimensional locking structure, dispersing the impact load through multiple paths, continuously enhancing the comprehensive mechanical strength, and simultaneously slowly releasing Zn 2+ endows the product with long-lasting, stable and broad-spectrum antibacterial properties.

[0009] In summary, through the synergistic effect of multiple materials, the present invention realizes the organic unity of mechanical strength, heat-resistant shape stability, oil barrier performance and long-term antibacterial properties, and is a high-performance PHA composite material that can be reused and meets the food contact safety requirements. Description of the Drawings

[0010] To more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0011] Figure 1 It is a thermal decomposition test result diagram of PHA composite material samples prepared in Example 3 and Comparative Examples 1 - 4 of the present invention; Figure 2 It is an antibacterial property test result diagram of PHA composite material samples prepared in Example 3 and Comparative Examples 1 - 4 of the present invention; Figure 3 It is an antibacterial test result diagram after 50 cycles of PHA composite material samples prepared in Example 3 and Comparative Examples 1 - 4 of the present invention; Figure 4 It is a zinc ion migration amount test result diagram of PHA composite material samples prepared in Example 3 and Comparative Examples 1 - 4 of the present invention; Figure 5 It is a weather resistance test result diagram of PHA composite material samples prepared in Example 3 and Comparative Examples 1 - 4 of the present invention; Figure 6 It is an SEM scanning electron microscope diagram of the PHA composite material sample prepared in Example 3 of the present invention. Specific Embodiments

[0012] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. It should be noted that unless otherwise specified, the raw materials involved in the present invention are purchased through conventional commercial channels.

[0013] Example 1: A PHA composite antibacterial material for food tableware, and its composition includes the following components by weight: 60 parts of PHA substrate, 20 parts of PLA substrate, 3 parts of oligo-D-lactic acid, 2 parts of ZnO@CNC antibacterial particles, 4.5 parts of acicular wollastonite powder, 3.5 parts of silane-modified montmorillonite, 0.05 part of talc powder, 0.3 part of rosemary extract, 0.6 part of chain extender, 0.4 part of D-sorbitol diglycidyl ether, 0.35 part of glycerol monostearate and 0.3 part of antioxidant; 1 part of the above raw material components corresponds to a specific weight of 2 g.

[0014] The PHA substrate is composed of 90% 3-hydroxybutyric acid and 10% 3-hydroxyoctanoic acid; 1. The specific preparation steps of ZnO@CNC antibacterial particles are as follows: S1: Add 5 g of cellulose nanocrystals to 250 mL of deionized water, and disperse them evenly by ultrasonic treatment to obtain a cellulose nanocrystal dispersion; add 3.5 g of Zn(NO3)2·6H2O to 20 mL of deionized water, stir and dissolve it evenly, and then slowly drop it into 250 mL of the cellulose nanocrystal dispersion, and stir at 400 rpm for 1 h to obtain a mixed solution; S2: Add 1 g of sodium hydroxide to 10 mL of deionized water, stir and dissolve it evenly, and then slowly drop it into the 250 mL of the mixed solution prepared in step S1 at a speed of 1 mL / min, and add 0.25 g of cetyltrimethylammonium bromide. During the dropping process, continuously stir at a speed of 600 rpm. After the dropping is completed, continue to stir for 1 h, let it stand for 4 h, centrifuge at 5000 rpm for 10 min, wash until neutral, and vacuum dry at 50 °C for 12 h to obtain ZnO@CNC antibacterial particles; 2. The specific preparation steps of silane-modified montmorillonite are as follows: S101: Add 10 g of nano-montmorillonite to 200 mL of 80 wt% ethanol solution, with a power of 100 W and a frequency of 30 kHz, and perform ultrasonic treatment for 20 min to obtain a nano-montmorillonite suspension; slowly drop 15 mL of octadecyltrichlorosilane into the nano-montmorillonite suspension within 10 min, raise the temperature to 50 °C, adjust the pH to 4, and stir and react at 300 rpm for 3 h; S102: After the reaction in step S101 is completed, let it stand and cool to room temperature, centrifuge at 8000 rpm for 15 min, add deionized water and ethanol to wash alternately 5 times, and vacuum dry at 60 °C to constant weight to obtain silane-modified montmorillonite; 3. The specific preparation steps of the PHA composite antibacterial material for food tableware are as follows: S201: Vacuum dry the PHA substrate and the PLA substrate at 80 °C for 6 h to obtain a pretreated PHA substrate and a pretreated L-PLA substrate; heat-treat ZnO@CNC antibacterial particles, acicular wollastonite powder, and silane-modified montmorillonite at 100 °C for 4 h, and screen them through a 150-mesh sieve to obtain pretreated ZnO@CNC antibacterial particles, pretreated acicular wollastonite powder, and pretreated silane-modified montmorillonite; S202: Feed the pretreated PHA substrate, the pretreated L-PLA substrate, tris(2,4-di-tert-butylphenyl) phosphite, and glycerol monostearate at 160 °C, raise the temperature to 175 °C for plasticization treatment for 2 min, and then raise the temperature to 185 °C for preliminary mixing treatment for 3 min; S203: After completing the operation in S202, add the pretreated acicular wollastonite powder prepared in S201, with a shear rate of 240 rpm and process for 1 min; sequentially add the pretreated ZnO@CNC antibacterial particles and the pretreated silane-modified montmorillonite, with a shear rate of 150 rpm and process for 50 s; S204: After completing the operation in S203, raise the temperature to 203 °C, sequentially add talc powder, oligomeric D-lactic acid, rosemary extract, Joncryl ADR-4368 epoxy chain extender and D-sorbitol diglycidyl ether, maintain the reaction for 60 s, then cool down to 180 °C and react for another 40 s, evacuate under vacuum, maintain the extrusion temperature at 170 °C, and cool the material by water ring pelletizing to obtain the PHA composite antibacterial material.

[0015] Example 2: A PHA composite antibacterial material for food tableware, whose composition includes the following components by weight: 70 parts of PHA substrate, 24 parts of PLA substrate, 4 parts of oligomeric D-lactic acid, 2.5 parts of ZnO@CNC antibacterial particles, 5.5 parts of acicular wollastonite powder, 5 parts of silane-modified montmorillonite, 0.1 part of talc powder, 0.4 part of rosemary extract, 0.9 part of chain extender, 0.5 part of D-sorbitol diglycidyl ether, 0.45 part of glycerol monostearate and 0.4 part of antioxidant; 1 part in the above raw material components corresponds to a specific weight of 2 g.

[0016] The PHA substrate is composed of 90% 3-hydroxybutyric acid and 10% 3-hydroxyoctanoic acid; 1. The specific preparation steps of the ZnO@CNC antibacterial particles are as follows: S1: Add 5 g of cellulose nanocrystals to 400 mL of deionized water, ultrasonically disperse evenly to obtain a cellulose nanocrystal dispersion; add 3.8 g of Zn(NO3)2·6H2O to 20 mL of deionized water, stir and dissolve evenly, then slowly drip it into 400 mL of the cellulose nanocrystal dispersion, stir and process at 600 rpm for 2 h to obtain a mixed solution; S2: Add 1.25 g of sodium hydroxide to 10 mL of deionized water, stir and dissolve evenly, then slowly drip it into the 400 mL of the mixed solution prepared in S1 at a speed of 2 mL / min, and add 0.4 g of cetyltrimethylammonium bromide. Continuously stir at a speed of 600 rpm during the dripping process. After the dripping is completed, continue to stir and process for 2 h, stand for 5 h, centrifuge at 5000 rpm for 15 min, wash until neutral, and vacuum dry at 50 °C for 24 h to obtain the ZnO@CNC antibacterial particles; 2. The specific preparation steps of the silane-modified montmorillonite are as follows: S101: Add 10 g of nano-montmorillonite into 250 mL of 80 wt% ethanol solution, with a power of 150 W, a frequency of 30 kHz, and ultrasonic treatment for 30 min to obtain a nano-montmorillonite suspension; slowly drop 18 mL of octadecyltrichlorosilane into the nano-montmorillonite suspension within 10 min, raise the temperature to 60 °C, adjust the pH to 4, and stir and react at 300 rpm for 5 h; S102: After the reaction in step S101 is completed, let it stand and cool to room temperature, centrifuge at 10000 rpm for 15 min, add deionized water and ethanol to wash alternately for 5 times, and vacuum dry at 80 °C to constant weight to obtain silane-modified montmorillonite; 3. The specific preparation steps of the PHA composite antibacterial material for food tableware are as follows: S201: Vacuum dry the PHA substrate and the PLA substrate at 80 °C for 8 h to obtain a pretreated PHA substrate and a pretreated L-PLA substrate; heat-treat ZnO@CNC antibacterial particles, acicular wollastonite powder, and silane-modified montmorillonite at 100 °C for 6 h, and sieve through a 150-mesh sieve to obtain pretreated ZnO@CNC antibacterial particles, pretreated acicular wollastonite powder, and pretreated silane-modified montmorillonite; S202: Feed the pretreated PHA substrate, the pretreated L-PLA substrate, tris(2,4-di-tert-butylphenyl) phosphite, and glycerol monostearate at 160 °C, raise the temperature to 175 °C for plasticization treatment for 3 min, and then raise the temperature to 185 °C for preliminary mixing treatment for 5 min; S203: After completing the operation in step S202, add the pretreated acicular wollastonite powder prepared in step S201, with a shear rate of 280 rpm and treat for 2 min; sequentially add the pretreated ZnO@CNC antibacterial particles and the pretreated silane-modified montmorillonite, with a shear rate of 200 rpm and treat for 90 s; S204: After completing the operation in step S203, raise the temperature to 205 °C, sequentially add talc powder, oligomeric D-lactic acid, rosemary extract, Joncryl ADR-4368 epoxy chain extender, and D-sorbitol diglycidyl ether, maintain the reaction for 90 s, then cool down to 185 °C, and react for another 80 s, evacuate under vacuum, maintain the extrusion temperature at 180 °C, and cool the material by water ring granulation to obtain the PHA composite antibacterial material.

[0017] Example 3: A PHA composite antibacterial material for food tableware, whose composition includes the following components by weight: 65 parts of PHA substrate, 22 parts of PLA substrate, 3.5 parts of oligo-D-lactic acid, 2.3 parts of ZnO@CNC antibacterial particles, 5 parts of acicular wollastonite powder, 4.3 parts of silane-modified montmorillonite, 0.08 part of talc powder, 0.35 part of rosemary extract, 0.75 part of chain extender, 0.45 part of D-sorbitol diglycidyl ether, 0.4 part of glycerol monostearate and 0.35 part of antioxidant; 1 part of the above raw material components corresponds to a specific weight of 2 g.

[0018] The PHA substrate is composed of 90% 3-hydroxybutyric acid and 10% 3-hydroxyoctanoic acid; 1. The specific preparation steps of ZnO@CNC antibacterial particles are as follows: S1: Add 5 g of cellulose nanocrystals to 500 mL of deionized water, ultrasonically disperse evenly to obtain a cellulose nanocrystal dispersion; add 4 g of Zn(NO3)2·6H2O to 20 mL of deionized water, stir and dissolve evenly, and then slowly drop it into the cellulose nanocrystal dispersion, and stir at 500 rpm for 1.5 h to obtain a mixed solution; S2: Add 1.2 g of sodium hydroxide to 10 mL of deionized water, stir and dissolve evenly, then slowly drop it into the 500 mL mixed solution prepared in step S1 at a speed of 1.5 mL / min, and add 0.5 g of cetyltrimethylammonium bromide. During the dropping process, continuously stir at a speed of 600 rpm. After the dropping is completed, continue to stir for 2.5 h, stand for 6 h, centrifuge at 5000 rpm for 12 min, wash until neutral, and vacuum dry at 50 °C for 18 h to obtain ZnO@CNC antibacterial particles; 2. The specific preparation steps of silane-modified montmorillonite are as follows: S101: Add 10 g of nano-montmorillonite to 300 mL of 80 wt% ethanol solution, with a power of 120 W and a frequency of 30 kHz, ultrasonically treat for 25 min to obtain a nano-montmorillonite suspension; slowly drop 20 mL of octadecyltrichlorosilane into the nano-montmorillonite suspension within 10 min, raise the temperature to 55 °C, adjust the pH to 4.5, and stir and react at 300 rpm for 4 h; S102: After the reaction in step S101 is completed, stand and cool to room temperature, centrifuge at 9000 rpm for 15 min, add deionized water and ethanol to wash alternately 5 times, and vacuum dry at 70 °C to constant weight to obtain silane-modified montmorillonite; 3. The specific preparation steps of the PHA composite antibacterial material for food tableware are as follows: S201: Vacuum dry the PHA substrate and the PLA substrate at 80 °C for 7 h to obtain a pretreated PHA substrate and a pretreated L-PLA substrate; subject ZnO@CNC antibacterial particles, acicular wollastonite powder, and silane-modified montmorillonite to hot air treatment at 100 °C for 5 h, and screen through a 150-mesh sieve to obtain pretreated ZnO@CNC antibacterial particles, pretreated acicular wollastonite powder, and pretreated silane-modified montmorillonite; S202: Feed the pretreated PHA substrate, the pretreated L-PLA substrate, tris(2,4-di-tert-butylphenyl) phosphite, and glycerol monostearate at 160 °C, raise the temperature to 175 °C for plasticization treatment for 2.5 min, and then raise the temperature to 185 °C for preliminary mixing treatment for 4 min; S203: After completing the operation of step S202, add the pretreated acicular wollastonite powder prepared in step S201, with a shear rate of 260 rpm and treat for 1.5 min; sequentially add the pretreated ZnO@CNC antibacterial particles and the pretreated silane-modified montmorillonite, with a shear rate of 180 rpm and treat for 80 s; S204: After completing the operation of step S203, raise the temperature to 200 °C, sequentially add talc powder, oligomeric D-lactic acid, rosemary extract, Joncryl ADR-4368 epoxy chain extender, and D-sorbitol diglycidyl ether, maintain the reaction for 80 s, then cool down to 183 °C and react for another 60 s, evacuate under vacuum, maintain the extrusion temperature at 175 °C, and cool the material by water ring pelletization to obtain the PHA composite antibacterial material.

[0019] Comparative Example 1: The operation procedures of Comparative Example 1 and Example 3 are basically the same, except that in Comparative Example 1, only nano-montmorillonite is used to replace the silane-modified montmorillonite.

[0020] Comparative Example 2: The operation procedures of Comparative Example 2 and Example 3 are basically the same, except that in Comparative Example 2, only ZnO is used to replace the ZnO@CNC antibacterial particles and directly added to the substrate for blending.

[0021] Comparative Example 3: The operation procedures of Comparative Example 3 and Example 3 are basically the same, except that the specific preparation steps of the PHA composite antibacterial material in Comparative Example 3 are as follows: S201: Vacuum dry the PHA substrate and the PLA substrate at 80 °C for 7 h to obtain a pretreated PHA substrate and a pretreated L-PLA substrate; subject ZnO@CNC antibacterial particles, acicular wollastonite powder, and silane-modified montmorillonite to hot air treatment at 100 °C for 5 h, and screen through a 150-mesh sieve to obtain pretreated ZnO@CNC antibacterial particles, pretreated acicular wollastonite powder, and pretreated silane-modified montmorillonite; S202: Feed the pretreated PHA substrate, pretreated PLA substrate, antioxidant, and glycerol monostearate at 160 °C, heat up to 175 °C for plasticization treatment for 2.5 min, and then heat up to 185 °C for preliminary mixing treatment for 4 min; S203: After completing the operation of step S202, sequentially add the pretreated acicular wollastonite powder, pretreated ZnO@CNC antibacterial particles, pretreated silane-modified montmorillonite prepared in step S201, as well as talc powder, oligomeric D-lactic acid, rosemary extract, chain extender, and D-sorbitol diglycidyl ether, with a shear rate of 180 rpm, treat for 180 s, evacuate under vacuum, maintain the extrusion temperature at 175 °C, and cool the material through water-ring pelletization to obtain the PHA composite antibacterial material.

[0022] Comparative Example 4: The operation processes of Comparative Example 4 and Example 3 are basically the same. The difference is that in Comparative Example 4, only 10% of the medium-chain PHA substrate in the PHA substrate is removed and replaced with a short-chain PHA substrate.

[0023] Inject and mold the PHA composite material samples prepared in Examples 1 to 3 and Comparative Examples 1 to 4 at a barrel temperature of 170 °C, a mold temperature of 60 °C, and an injection pressure of 90 MPa for the following test.

[0024] Mechanical property test: Conduct the following tests on the PHA composite material samples prepared in Examples 1 to 3 and Comparative Examples 1 to 4. Adjust the test sample specifications to a total length of 150 mm, a gauge section length of 50 mm, a width of 10 mm, and a thickness of 4 mm for tensile strength and elongation at break tests. The tensile strength is carried out in accordance with GB / T 1040.1-2018, and the elongation at break is carried out in accordance with GB / T 1447-2005; Adjust the test sample specifications to 80 mm × 10 mm × 4 mm (length × width × height) for flexural strength test, and the flexural strength is carried out in accordance with GB / T 9341-2008; Adjust the test sample specifications to 80 mm × 10 mm × 4 mm with a notch radius of 0.25 mm for impact strength test. Determine the impact strength according to GB / T 1843-2008 through a plastic pendulum impact testing machine. The test results are shown in Table 1 below.

[0025] Table 1. Mechanical strength test of PHA composite materials

[0026] As can be seen from the results in Table 1, the PHA composite material prepared by the present invention exhibits excellent mechanical strength performance through the synergistic action of multiple substances and can be effectively applied to the field of food tableware. From the results of Comparative Example 1 and Example 3, it can be seen that the surface of unmodified nano-montmorillonite is hydrophilic, has poor compatibility with the hydrophobic polyester matrix, and is prone to agglomeration to form stress concentration points, resulting in a decrease in tensile and flexural strength. In addition, lacking the lubricating effect of the silane long chain, it is difficult for montmorillonite to exfoliate into nano-sheets under high shear, the impact resistance decreases, and the arrangement of the sheets is disordered, leading to an increase in the oil penetration rate, which in turn affects the flexural strength. From the results of Comparative Example 2 and Example 3, it can be seen that bare ZnO nanoparticles are prone to agglomeration in the polyester melt, forming defects, resulting in a significant decrease in impact strength and elongation at break. Lacking the hydroxyl-hydrogen bond network of CNC, the interfacial bonding between ZnO and the matrix is weak, and the tensile strength decreases. And the release rate of Zn 2+ may be too fast, which may trigger local oxidative degradation, thereby affecting the mechanical strength. From the results of Comparative Example 3 and Example 3, it can be seen that the one-step mixing process replaces the staged mixing process. The needle-shaped wollastonite and montmorillonite are not added in stages and cannot be preferentially oriented in the shear flow field, and the micro-skeleton-nano-barrier structure is not formed, resulting in a significant decrease in flexural strength. In addition, the chain extender and the filler are added synchronously, and the reaction time is insufficient, and the molecular weight increase is limited, resulting in a significant decrease in the interfacial bonding strength, which significantly affects the mechanical strength. From the results of Comparative Example 4 and Example 2, it can be seen that after removing the medium-chain PHA, the material loses the energy dissipation ability of the flexible chain segment, and the elongation at break and impact resistance drop sharply. In addition, the short-chain PHA accounts for 100%, the increase in the crystalline region leads to an increase in brittleness, lacking the plasticizing effect of the medium-chain PHA, the melt viscosity increases, and the difficulty of exfoliating the silane-modified montmorillonite increases. Although the flexural strength increases slightly, it may be prone to fracture due to brittleness in practical applications.

[0027] Thermal decomposition test: The PHA composite material samples (10 mg of granulated particles) prepared in Example 3 and Comparative Examples 1-4 were dried in a vacuum drying oven at 80 °C for 12 h to remove residual moisture for testing. Under a nitrogen atmosphere, the temperature was raised from room temperature (25 °C) to 150 °C at a rate of 10 °C / min, held at a constant temperature for 5 min, and then raised to 600 °C at a rate of 10 °C / min, and the percentage of mass loss was recorded. The results are as Figure 1 shown.

[0028] From Figure 1It can be seen from the results that the PHA composite material prepared by the present invention has excellent thermal stability and can remain stable at a relatively high temperature; from the results of Comparative Example 1 and Example 3, it can be seen that unmodified montmorillonite is more likely to agglomerate, with poor barrier effect, earlier decomposition of PLA segments, and the lack of a plate-nail structure, which accelerates the escape of decomposition gases and speeds up the decomposition rate; from the results of Comparative Example 2 and Example 3, it can be seen that bare ZnO catalyzes the cleavage of ester groups, causing premature decomposition of PLA / PHA segments. Without the hydroxyl network of CNC, a carbon layer protection cannot be formed, and the decomposition rate is significantly accelerated; from the results of Comparative Example 3 and Example 3, it can be seen that the SC-PLA polycrystals are incomplete, the montmorillonite is not oriented, the barrier efficiency is reduced, and the chain extension is insufficient, resulting in a lower molecular weight and poor thermal stability; from the results of Comparative Example 3 and Example 2, it can be seen that the short-chain PHA crystal regions are dense, lacking the plasticization of medium-chain PHA. The high melt viscosity leads to poor filler dispersion, weak barrier effect, and increased brittleness of the material, which may have caused premature thermal decomposition.

[0029] Antibacterial property test: The PHA composite material samples (50 mm × 50 mm × 2 mm) prepared in Example 3 and Comparative Examples 1-4 were dried at 80 °C for 12 h. 50 μL of bacterial solution (Escherichia coli and Staphylococcus aureus at 1 × 10 5 CFU / mL) was dropped on the surface of the samples, covered with a polyethylene film to prevent evaporation, and cultured at 37 °C / 90% humidity for 24 h. The bacteria were eluted with a neutralizing solution (PBS buffer containing 0.5% sodium thiosulfate), serially diluted and then spread on agar plates, and counted after culturing at 37 °C for 24 h. In the long-term effectiveness test, the PHA composite material samples prepared in Example 3 and Comparative Examples 1-4 after 50 cycles of dishwasher treatment were used for the antibacterial property test. The antibacterial rate (%) = (number of colonies in the control group - number of colonies in the experimental group) / number of colonies in the control group × 100%. The results of the antibacterial property test are as Figure 2 and the results of the long-term effectiveness test are as Figure 3 shown.

[0030] From Figure 2 and Figure 3 the results, it can be seen that the PHA composite material prepared by the present invention has excellent antibacterial properties; from the results of Comparative Example 1 and Example 3, it can be seen that unmodified montmorillonite is hydrophilic and has a small interlayer spacing, unable to form a hydrophobic sheet barrier. Water is more likely to penetrate into the matrix interior during dishwasher cycles, and the ZnO@CNC has a significant shedding rate during flushing; from the results of Comparative Example 2 and Example 3, it can be seen that bare ZnO directly releases Zn 2+ , with a relatively high initial antibacterial rate, but lacking a CNC slow-release barrier, and ZnO aggregates form defects in the matrix, resulting in a large amount of ZnO loss and shedding after 50 cycles; from the results of Comparative Example 3 and Example 3, it can be seen that ZnO@CNC does not preferentially bind to the matrix interface, and some particles are embedded. The initial Zn 2+Release is restricted, and the montmorillonite is not oriented, resulting in low barrier efficiency and accelerated loss of ZnO@CNC after cycling; without medium-chain PHA plasticization, the high melt viscosity leads to uneven dispersion of ZnO@CNC, slightly affecting the initial release. The high-crystallinity matrix effectively inhibits water penetration, but the brittleness of the material may lead to an increase in internal microcracks and a certain degree of loss of ZnO@CNC after cycling.

[0031] Zinc ion migration test: The zinc ion migration of the PHA composite material samples (10 mm × 10 mm × 2 mm) prepared in Example 3 and Comparative Examples 1-4 was tested according to GB 31604.8-2016. The test results are as Figure 4 shown.

[0032] As Figure 4 can be seen from the results, the zinc ion migration of the PHA composite material prepared in the present invention is extremely low. The multi-level structure of the composite material can effectively coat ZnO to prevent its migration and leakage, meeting the food tableware safety standards; from the results of Comparative Example 1 and Example 3, it can be seen that the unmodified montmorillonite is hydrophilic and has a small interlayer spacing, so water is more likely to penetrate into the matrix, accelerating the hydrolysis of ZnO@CNC, and the Zn 2+ release is significantly increased; from the results of Comparative Example 2 and Example 3, it can be seen that the bare ZnO is directly exposed on the surface of the matrix, without a CNC sustained-release barrier, and the Zn 2+ rapidly dissolves, and the edge defects of the aggregates significantly increase the migration amount; from the results of Comparative Example 3 and Example 3, it can be seen that the one-step mixing leads to uneven dispersion of ZnO@CNC, and some particles are embedded, but a dense barrier layer is not formed, and the migration amount is still relatively high; from the results of Comparative Example 4 and Example 3, it can be seen that the pure short-chain PHA substrate has a high crystallinity and a high melt viscosity, and the dispersion degree of ZnO@CNC decreases, but the high-crystalline region inhibits water penetration, which limits the migration and leakage of zinc ions to a certain extent.

[0033] Weather resistance test: The PHA composite material samples (50 mm × 50 mm × 2 mm) prepared in Example 3 and Comparative Examples 1-4 were dried at 80 °C for 12 h, and then placed at 85 °C / 85% humidity for 500 and 1000 h. The change in elongation at break / (%) after 500 h and 1000 h was tested = (elongation at break before testing - elongation at break after testing) / elongation at break before testing × 100%. The test results are as Figure 5 shown.

[0034] As Figure 5It can be seen from the results that the PHA composite material prepared by the present invention has excellent weather resistance and can maintain good performance in extreme environments; from the results of Comparative Example 1 and Example 3, it can be seen that the unmodified montmorillonite is hydrophilic and has poor barrier properties, moisture quickly penetrates into the matrix, PLA is preferentially hydrolyzed, and interfacial debonding leads to crack propagation; from the results of Comparative Example 2 and Example 3, it can be seen that the zinc ions lacking the loaded zinc oxide can catalyze the cleavage of ester bonds, and stress concentration is induced at the edges of the aggregates, which may accelerate fracture. In addition, microcracks are easily induced at the edges of the bare ZnO aggregates, and the cracks propagate along the aggregates in a humid and hot environment, resulting in a significant decrease in weather resistance; from the results of Comparative Example 3 and Example 3, it can be seen that without adding fillers in stages, the acicular wollastonite and montmorillonite are not oriented in the shear flow field, and the synergistic structure of the longitudinal micro-skeleton and the nano-barrier shell cannot be formed. The one-step process may cause the fillers (silanized montmorillonite, ZnO@CNC) that could have been used for reinforcement to become weaknesses instead, and the disordered dispersion induces stress concentration, resulting in poorer weather resistance; from the results of Comparative Example 4 and Example 3, it can be seen that the high crystallinity of the short-chain PHA delays water penetration, and the change rate within 500 h is relatively low. Without the plasticization of the medium-chain PHA, the brittleness index of the material increases significantly, and the crack propagation rate accelerates, resulting in a sharp drop in the elongation at break after 1000 h.

[0035] Spectrum test: The PHA composite material sample (granulated particles 0.5 mm) prepared in Example 3 was scanned using a scanning electron microscope to obtain an SEM scanning electron micrograph. The results are as Figure 6 shown.

[0036] From Figure 6 the results, it can be seen that a large number of dense parallel stripes extending in the same direction can be seen in the image, indicating that the material has formed an oriented needle-like crystal structure under the synergistic action of shear and tension. The microscopic morphology presents three significant characteristics: a highly oriented banded fiber-sheet composite structure, a dense matrix phase, and a uniformly distributed particle phase, clarifying the formation mechanism of the multi-scale structure of the PHA composite material.

[0037] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A PHA composite antibacterial material for food tableware, characterized in that: The composition includes the following components in parts by weight: 60 to 70 parts of PHA substrate, 20 to 24 parts of PLA substrate, 3 to 4 parts of oligomeric D-lactic acid, 2 to 2.5 parts of ZnO@CNC antibacterial particles, 4.5 to 5.5 parts of needle-shaped wollastonite powder, 3.5 to 5 parts of silane-modified montmorillonite, 0.05 to 0.1 parts of talc powder, 0.3 to 0.4 parts of rosemary extract, 0.6 to 0.9 parts of chain extender, 0.4 to 0.5 parts of D-sorbitol diglycidyl ether, 0.35 to 0.45 parts of glyceryl monostearate and 0.3 to 0.4 parts of antioxidant.

2. The PHA composite antibacterial material for food tableware according to claim 1, characterized in that: The PHA matrix consists of 90% of a short-chain PHA matrix and 10% of a medium-chain PHA matrix.

3. The PHA composite antibacterial material for food tableware according to claim 2, characterized in that: The specific preparation steps of the ZnO@CNC antibacterial particles are as follows: S1: adding cellulose nanocrystals to deionized water, dispersing them uniformly by ultrasonic treatment, and obtaining a cellulose nanocrystal dispersion; adding Zn(NO3)2·6H2O to deionized water, stirring to dissolve them uniformly, and then slowly dropping them into the cellulose nanocrystal dispersion, stirring to obtain a mixed solution; S2: adding sodium hydroxide into deionized water, stirring to dissolve evenly, and then slowly dropping it into the mixed solution prepared in step S1, stirring continuously during the dropping process, and continuing stirring after the dropping is completed, standing, centrifuging, washing to neutrality, and vacuum drying to obtain ZnO@CNC antibacterial particles.

4. The PHA composite antibacterial material for food tableware according to claim 3, characterized in that: In step S1, the ratio of the amount of the cellulose nanocrystal to the deionized water is 1 g: 50-100 mL; the ratio of the amount of the Zn(NO3)2·6H2O, deionized water and cellulose nanocrystal dispersion is 0.7-0.8 g: 4 mL: 50-100 mL.

5. The PHA composite antibacterial material for food tableware according to claim 4, characterized in that: In step S2, the ratio of the amount of sodium hydroxide, deionized water and the mixed solution is 0.2-0.25 g: 2 mL: 50-100 mL.

6. The PHA composite antibacterial material for food tableware according to claim 5, characterized in that: The specific preparation steps of the silane-modified montmorillonite are as follows: S101: adding nano-montmorillonite to an ethanol solution, performing ultrasonic treatment, and obtaining a nano-montmorillonite suspension; slowly dropping octadecyltrichlorosilane into the nano-montmorillonite suspension, increasing the temperature, adjusting the pH, and stirring the reaction; S102: After the reaction in step S101 is completed, the mixture is allowed to stand and cool to room temperature, centrifuged, and alternately washed with deionized water and ethanol, and vacuum dried to a constant weight to obtain silane-modified montmorillonite.

7. The PHA composite antibacterial material for food tableware according to claim 6, characterized in that: In step S101, the ratio of the amount of the nano-montmorillonite to the ethanol solution is 1 g: 20-30 mL; the ratio of the amount of octadecyltrichlorosilane to the nano-montmorillonite is 1.5-2 mL: 1 g.

8. A method for preparing the PHA composite antibacterial material for food tableware according to any one of claims 1 to 7, characterized in that: The specific preparation steps are as follows: S201: vacuum drying the PHA substrate and the PLA substrate to obtain a pretreated PHA substrate and a pretreated PLA substrate; hot air treating the ZnO@CNC antibacterial particles, the needle-shaped wollastonite powder and the silane-modified montmorillonite, and screening them to obtain pretreated ZnO@CNC antibacterial particles, pretreated needle-shaped wollastonite powder and pretreated silane-modified montmorillonite; S202: adding the pretreated PHA substrate, the pretreated PLA substrate, the antioxidant and glyceryl monostearate into the reaction system, heating and plasticizing the system, and then heating the system again for preliminary mixing; S203: After completing step S202, add the pretreated needle-shaped wollastonite powder prepared in step S201, and perform shearing treatment; add the pretreated ZnO@CNC antibacterial particles and the pretreated silane-modified montmorillonite in sequence, and perform shearing treatment; S204: After completing step S203, the temperature is raised, and talcum powder, oligomeric D-lactic acid, rosemary extract, chain extender and D-sorbitol diglycidyl ether are added in sequence for reaction treatment, and then the temperature is lowered, vacuum exhaust is performed, and the extrusion temperature is maintained at 170-180° C. The material is cooled by water ring granulation to obtain a PHA composite antibacterial material.

9. A method for preparing the PHA composite antibacterial material for food tableware according to claim 8, characterized in that: In step S204, the temperature reduction treatment parameters are: cooling to 180-185°C, and then reacting for 40-80 seconds.

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