PHA (polyhydroxyalkanoate) nano aqueous suspension as well as preparation method and application thereof

Abstract

The invention discloses a PHA nano aqueous suspension as well as a preparation method and application thereof, and belongs to the field of high polymer materials and processing and application thereof. The suspension takes PHA resin as a dispersion phase and water as a continuous phase, the total solid content is 23-65wt%, the PHA resin accounts for 80-98.5 wt% of the total solid, and the assistant accounts for 1.5-20wt% of the total solid. The average particle size of PHA particles is 30-140 nm, D90 is smaller than or equal to 150 nm, the polydispersity index PDI is smaller than 0.3, and when the pH is 6.5-7.5, the absolute value of Zeta potential is larger than 30 mV. The preparation method comprises the following steps: pretreating the PHA raw material, preliminarily dispersing in a water phase under the action of the dispersion stabilizing aid, and carrying out high-energy homogenization treatment. The obtained suspension is stable in storage, has excellent barrier property and mechanical property after film formation, and is suitable for preparing biodegradable food packaging barrier coatings, water-based environment-friendly coatings and water-based adhesives.

Description

Technical Field

[0001] The present invention relates to the field of biodegradable polymer materials and their processing applications, and specifically relates to a PHA nano-aqueous suspension, a preparation method thereof, and applications thereof, including the preparation, properties of the suspension, and its applications in fields such as biodegradable food packaging barrier coatings, water-based environmental protection coatings, and water-based adhesives. Background Art

[0002] Polyhydroxyalkanoates (PHA) are a class of aliphatic copolyesters synthesized by various microorganisms through fermentation. Due to their excellent biodegradability, biocompatibility, and the characteristic of being derived from renewable resources, they are considered to be one of the ideal environmentally friendly materials to replace traditional petroleum-based plastics. There are many types of PHA, and common ones include poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), poly-3-hydroxyalkanoate-co-3-hydroxyhexanoate (PHBH), etc. However, PHA materials usually have disadvantages such as high crystallinity, strong hydrophobicity, relatively high melting point, and narrow processing window. When directly applied, it is difficult to form a uniform, flexible, and well-barrier film, which limits its wide application in many fields.

[0003] Preparing PHA into an aqueous nano-scale suspension, also known as nanoemulsion or nano-dispersion, is an effective way to improve its processing performance and application performance. The aqueous system is not only environmentally friendly but also easy to construct by conventional coating, spraying, etc. The nano-sized PHA particles have a larger specific surface area and higher surface energy, which is conducive to forming a denser and more uniform film layer, thus significantly improving the barrier property, glossiness, and adhesion to the substrate of the material.

[0004] At present, there have been various studies and reports on PHA aqueous dispersions at home and abroad. For example, some existing technologies prepare poly-PHA aqueous dispersions by the solvent emulsification-evaporation method, but such methods often involve the use of organic solvents, which may have problems such as solvent residues, environmental unfriendliness, and relatively long process flows. Some other studies use solvent-free methods such as melt shearing or high-pressure homogenization, but usually when achieving a high solid content, such as when the solid content exceeds 40 wt%, it is difficult to precisely control the average particle size, D90 value, and polydispersity index (PDI) value of PHA nanoparticles. Among them, the D90 value is usually required to be below 200 nm to obtain excellent performance, and the PDI value is required to be <0.3 to ensure particle size uniformity. Moreover, the long-term storage stability of the obtained dispersion, especially the stability at high solid content, still needs to be improved. In addition, the energy consumption of some preparation processes is relatively high or the equipment requirements are harsh, which is not conducive to cost-effective large-scale production.

[0005] Therefore, there is an urgent need for an environmentally friendly and highly efficient preparation method to achieve the stable preparation of a high-solid-content PHA nano-aqueous suspension, while precisely controlling the particle size, improving the storage stability, and reducing energy consumption to meet the requirements of large-scale production and environmental protection applications. Summary of the Invention

[0006] In view of the above challenges in the prior art for preparing a high-solid-content, nano-scale, and highly stable PHA aqueous suspension, especially the technical problems of how to simultaneously meet the requirements of high solid content, precise particle size control (i.e., D90 particle size ≤ 150 nm and polydispersity index PDI < 0.3), and long-term storage stability under the premise of environmental protection, the present invention provides a new solution.

[0007] The technical solution of the present invention is as follows:

[0008] A PHA nano-aqueous suspension, comprising polyhydroxyalkanoate PHA resin particles, a dispersion stabilizing aid, and the balance water, such that the total solid content based on the solid components in the PHA resin particles and the dispersion stabilizing aid in the suspension is between 23 and 65 wt%; wherein, in the total solid content, the PHA resin particles account for 80 to 98.5 wt% of the total solid content by dry weight, and the dispersion stabilizing aid accounts for 1.5 to 20 wt% of the total solid content by dry weight; the dispersion stabilizing aid at least comprises a surfactant, a preservative, and a thickener. Among them, the average particle size of the PHA resin particles is controlled to be between 30 and 140 nm, D90 ≤ 150 nm, and the PDI value < 0.3. The absolute value of the Zeta potential of the suspension is > 30 mV at pH 6.5 to 7.5, and the viscosity at 25 °C is 50 to 1000 mPa·s. Through a large number of experimental studies, it is found that within this range of average particle size, especially when D90 ≤ 150 nm, the suspension has good stability and subsequent application performance. 30 nm is the lower limit of the smaller particle size that can be stably obtained, while when the average particle size approaches or exceeds the upper limit of 150 nm, the nano effect weakens and the stability may decrease.

[0009] The PHA resin is selected from poly-3-hydroxybutyrate PHB, poly-3-hydroxybutyrate-co-3-hydroxyvalerate PHBV, poly-3-hydroxybutyrate-co-3-hydroxyhexanoate PHBH, or a blend combination thereof. It is found that by selecting a PHA resin with a moderate molecular weight, such as a weight average molecular weight Mw in 2.0×10 5 g / mol to 5.0×10 5PHA resins within the range of g / mol and with specific copolymer compositions, especially PHA containing comonomers such as 3-hydroxyvaleric acid units or 3-hydroxyhexanoic acid units, usually have lower crystallinity and better processing properties, which are beneficial to the formation of stable and uniformly sized nanoparticles. The PHA resin is PHBV containing 3HV units at 5 - 20 mol%, or PHBH containing 3HHx units at 6 - 12 mol%, or a blend system of the above copolymers and PHB. It has been experimentally confirmed that within this range of comonomer content, the crystallization and processing properties of PHA are improved, which is beneficial to the formation and stability of the nano-suspension.

[0010] The surfactant is selected from one or a combination of non-ionic surfactants, anionic surfactants, or block copolymers; the non-ionic surfactant is selected from polysorbate 20, polysorbate 80, and a polyvinyl alcohol with an alcoholysis degree of 87 - 89 mol%, and its characteristics are as follows: when the viscosity of its 4% aqueous solution at 20 °C is 20 - 35 mPa·s, its degree of polymerization is 1700 - 1800; or when the viscosity of its 4% aqueous solution at 20 °C is 5 - 7 mPa·s, its degree of polymerization is 500 - 600; the anionic surfactant is sodium dodecyl sulfate; the block copolymer is selected from one or a combination of pluronic F68 and pluronic P123. It has been found that the compounding of non-ionic surfactants such as polysorbates with polymeric surfactants such as polyvinyl alcohol with a certain steric hindrance ability, or the combination of non-ionic surfactants with a small amount of anionic surfactants such as sodium dodecyl sulfate, or the combination of non-ionic surfactants with block copolymers has a good effect on obtaining a stable and fine-particle-size PHA nano-suspension at high solid contents.

[0011] The thickener can be selected from xanthan gum, sodium carboxymethyl cellulose, or associative thickeners. The preservative can be selected from methylisothiazolinone MIT, a compound of methylchloroisothiazolinone CMIT and benzisothiazolinone BIT, or parabens.

[0012] A method for preparing the above PHA nano-aqueous suspension, comprising the following steps:

[0013] Step a. Pretreat the PHA resin to obtain a pretreated PHA raw material. The pretreatment includes cryogenic pulverization, specifically by using a superfine pulverizer assisted by liquid nitrogen and passing through a 150-mesh sieve to obtain a fine powder with an average particle size < 100 μm; or melting it at a temperature 10 - 30 °C higher than its melting point (usually 180 - 185 °C), while minimizing the high-temperature residence time and protecting it, such as carrying out in a nitrogen atmosphere.

[0014] Step b. Add the pretreated PHA raw material into the aqueous phase to form a preliminary emulsion or dispersion of PHA. The operating conditions for this process are as follows: the temperature of the aqueous phase is maintained at 50 - 95 °C; high-speed shear stirring is used, with the rotation speed set at 5000 - 20000 rpm, and the treatment time lasts for 10 - 120 minutes. The aqueous phase used contains a surfactant, and its dosage is 0.5 - 8 wt% of the mass of the PHA resin. Moreover, the mass ratio of the PHA raw material to the aqueous phase is controlled within the range of 1:0.5 - 1:4. Through experiments, it is determined that within this range of process parameters, the preliminary dispersion of PHA can be effectively achieved, laying a good foundation for subsequent high-energy homogenization treatment.

[0015] Step c. Treat the above-mentioned crude emulsion or crude dispersion to further refine the PHA particles to reach the level of D90 ≤ 150 nm and PDI < 0.3, and obtain a PHA nano-dispersion containing PHA resin microparticles. One of the following devices can be selected for this treatment: a high-pressure homogenizer, whose operating conditions are: the homogenization pressure is 20 - 150 MPa, and the cyclic treatment is carried out 1 - 5 times; before homogenization, the crude emulsion can be pre-cooled to 10 - 25 °C, and the equipment is required to be equipped with a cooling system to control the outlet temperature not exceeding 60 - 70 °C. Or, an ultrasonic cell disruptor, whose operating conditions are: the power is 200 - 1000 W, and the ultrasonic treatment is carried out for 1 - 20 minutes; the intermittent mode can be adopted during the treatment and supplemented with ice bath cooling. Through experiments, it is determined that within the above range of high-energy homogenization parameters, the PHA particles can be effectively refined to the target nano-level, while avoiding the adverse effects that may be brought by over-treatment.

[0016] Step d. Slowly add a thickener accounting for 0.05 - 0.5 wt% of the total mass of the final suspension and a preservative accounting for 0.05 - 0.2 wt% of the total mass of the final suspension to the PHA nano-dispersion containing PHA resin microparticles obtained in step c, and mix evenly under gentle stirring conditions to obtain an intermediate PHA nano-aqueous suspension. These addition amounts are designed to ensure the long-term stability and service performance of the suspension, and at the same time, their solid components will be included in the calculation of the dispersion stabilizer in the total solid content.

[0017] Step e. Detect the intermediate PHA nano-aqueous suspension obtained in step d and adjust the pH value of the suspension to the range of 6.5 - 7.5, the solid content to the range of 23 - 65 wt%, and the viscosity at 25 °C to the range of 50 - 1000 mPa·s, and finally obtain the PHA nano-aqueous suspension.

[0018] The present invention also provides the application of the PHA nano-aqueous suspension in the preparation of biodegradable food packaging barrier coatings, water-based environmentally friendly coatings, and water-based adhesives.

[0019] The PHA nano-aqueous suspension is coated on the surface of paper, cardboard, biodegradable plastic film or other food-contact substrates by means of knife coating, spraying, dip coating, casting or printing. After drying at 50-120 °C for 1-30 minutes to form a film, a biodegradable coating with water vapor barrier property, oxygen barrier property and oil resistance is formed.

[0020] The PHA nano-aqueous suspension is used as the main film-forming substance or auxiliary film-forming substance, and is mixed and dispersed uniformly with pigments, fillers, film-forming aids, rheological modifiers, wetting and dispersing agents and other common coating auxiliaries in an aqueous system through conventional coating preparation processes, so as to prepare an environmentally friendly aqueous coating with low volatile organic compound (VOC) emissions, environmental friendliness and biodegradable coating film.

[0021] The PHA nano-aqueous suspension is directly used as an adhesive, or is compositely modified with one or more natural polymers or synthetic aqueous resins selected from the group consisting of starch, modified starch, cellulose derivatives such as carboxymethyl cellulose or hydroxyethyl cellulose, protein adhesives such as casein glue or gelatin, polyvinyl acetate emulsion, and acrylate emulsion, and is used as an aqueous adhesive for bonding paper products, wood, fiber products, non-woven fabrics or other porous substrates. Its bonding layer can be biodegradable after completing its service life.

[0022] Through the selection of PHA raw material types and molecular characteristics, the optimized compounding of surfactants, the precise control of high-energy homogenization process parameters such as pressure, temperature, treatment time, and shear rate, and the synergistic effect of auxiliaries, the nano-scale dispersion of PHA in the aqueous phase is effectively promoted, and the obtained suspension is given excellent physical and chemical stability and application performance.

[0023] Compared with the prior art, using a PHA nano-aqueous suspension and its preparation method and application of the present invention can obtain the following remarkable beneficial effects:

[0024] The stable preparation of a PHA nano-aqueous suspension with a high solid content is realized, and the solid content can be regulated within the range of 23wt% - 65wt%, which is beneficial to improving the coating efficiency and reducing the drying energy consumption.

[0025] The particle size of PHA nanoparticles can be precisely controlled, with an average particle size of 30 - 140nm, D90 ≤ 150nm, and PDI < 0.3, and the particle size distribution is narrow, which is beneficial to forming a uniform and dense film layer and improving the barrier properties and other properties of the product.

[0026] The prepared PHA nano-aqueous suspension has excellent storage stability, can be stably stored at room temperature for more than 6 months, has a high absolute value of Zeta potential, and is not prone to agglomeration and sedimentation.

[0027] The preparation process is environmentally friendly, mainly using water as the dispersion medium, significantly reducing or avoiding the use of organic solvents, and conforming to the development trend of green chemistry.

[0028] The prepared PHA nano-aqueous suspension has a wide range of applications and can be used in fields such as food packaging, environmental protection coatings, adhesives, etc. The resulting products have good biodegradability and application performance. Specific Embodiments

[0029] The present invention will be further described in detail below with reference to specific examples and comparative examples. Unless otherwise specified, the conventional experimental methods used in the embodiments of the present invention all refer to the general standards in the art or the operation guides provided by the manufacturers. The raw materials and reagents used are all commercially available products unless otherwise specified.

[0030] Measurement methods for particle size, D90, PDI and Zeta potential:

[0031] Measurement is carried out using a laser particle size analyzer based on the principle of dynamic light scattering (DLS). Instruments that can be used include the Zetasizer Nano ZS90 from Malvern Panalytical, UK. Before testing, an appropriate amount of the PHA nano-aqueous suspension sample is diluted with deionized water to a suitable concentration required for instrument detection. At 25 °C, after equilibration for 120 seconds, measurements are taken. Each sample is measured 3 times and the average value is taken. The particle size is reported as the Z-Average average particle size, and the D90 value and PDI value are also recorded. The Zeta potential is measured by the electrophoretic light scattering mode of the same instrument. Using a DTS1070 capillary electrophoresis cell, the sample is diluted with a 1 mM KCl aqueous solution with a pH of 7 and then measured.

[0032] Main experimental raw materials and specifications

[0033] Table 1 Chemical names / categories, product models and suppliers of main experimental raw materials

[0034]

[0035] Specifications / main parameter descriptions:

[0036] PHBV powder, Enmat Y1000 series, Ningbo Tian'an Biomaterials Co., Ltd.:

[0037] When the 3HV content is 20 mol%, the weight-average molecular weight Mw is 2.8×10 5 ~3.5×10 5 g / mol.

[0038] When the 3HV content is 15 mol%, the weight-average molecular weight Mw is 3.0×10 5 ~3.8×105 g / mol.

[0039] When the 3HV content is 5 mol%, the weight-average molecular weight Mw is 3.0×10 5 ~3.5×10 5 g / mol.

[0040] PHB powder, Enmat Y3000 series, Ningbo Tian'an Biomaterials Co., Ltd.: The weight-average molecular weight Mw is 4.0×10 5 ~4.5×10 5 g / mol.

[0041] PHBH powder, Kaneka Corporation AONilex series:

[0042] When the 3HHx content is 12 mol%, the weight-average molecular weight Mw is usually in the range of 3.0×10 5 ~4.5×10 5 g / mol.

[0043] When the 3HHx content is 10 - 11 mol%, the weight-average molecular weight Mw is usually 3.5×10 5 ~4.5×10 5 g / mol.

[0044] When the 3HHx content is 8 mol%, the weight-average molecular weight Mw is usually 3.2×10 5 ~4.0×10 5 g / mol.

[0045] When the 3HHx content is 6 mol%, the weight-average molecular weight Mw is usually in the range of 3.0×10 5 ~4.5×10 5 g / mol.

[0046] Polysorbate 20 (Tween 20), P1379, Sigma-Aldrich: CAS No. 9005-64-5, pharmaceutical excipient grade or food grade.

[0047] Polysorbate 80 (Tween 80), P1754, Sigma-Aldrich: CAS No. 9005-65-6, pharmaceutical excipient grade or food grade.

[0048] Polyvinyl alcohol PVA, high degree of polymerization, Poval PVA-217, Kuraray: CAS No. 9002-89-5, degree of alcoholysis 87 - 89 mol%, degree of polymerization 1700 - 1800, viscosity of 4% aqueous solution at 20 °C is 27 - 33 mPa·s.

[0049] Polyvinyl alcohol PVA, low degree of polymerization, Poval PVA-205, Kuraray: CAS No. 9002-89-5, degree of alcoholysis 87 - 89 mol%, degree of polymerization 500 - 600, viscosity of 4% aqueous solution at 20 °C is 5 - 7 mPa·s.

[0050] Sodium dodecyl sulfate SDS, L3771 BioReagent, Sigma-Aldrich: CAS No. 151-21-3, analytical pure or BioReagent grade, purity ≥98.5%.

[0051] Pluronic F68 (Pluronic F-68), P1300, Sigma-Aldrich: CAS No. 9003-11-6, PEO-PPO-PEO block copolymer.

[0052] Pluronic P123 (Pluronic P-123), 435465, Sigma-Aldrich: CAS No. 9003-11-6, PEO-PPO-PEO block copolymer.

[0053] Xanthan gum, Keltrol CG-F, CP Kelco: CAS No. 11138-66-2, food grade or industrial grade, meeting corresponding standards.

[0054] CMIT / MIT and BIT compound preservative, Preventol D 7, LANXESS: A complex of methylisothiazolinone CMIT / methylchloroisothiazolinone MIT and benzisothiazolinone BIT, a broad-spectrum preservative for aqueous systems.

[0055] Deionized water: Conductivity < 5 μS / cm.

[0056] Sodium hydroxide NaOH, Tianjin Yongda Chemical Reagent Co., Ltd.: Analytical pure.

[0057] Commercially available PVA white latex, such as Titebond Original Wood Glue, solid content is 46%, viscosity is 3200 mPa·s.

[0058] Example 1: PHBV nano-aqueous suspension

[0059] Raw materials: PHBV powder with a 3HV unit content of 15 mol%, which is the Enmat Y1000 series product of Ningbo Tianan Biomaterials Co., Ltd., 50 grams in total; polysorbate 20 (Tween 20), 1.5 grams in total; polyvinyl alcohol PVA (high degree of polymerization), 0.5 grams in total; deionized water 100 grams. At this time, the mass ratio of PHA to the aqueous phase is 1:2. The dosage of the surfactant is 4.0 wt% of the mass of PHA.

[0060] Coarse dispersion: The PHBV powder is cryo-ultrafinely pulverized (passing through a 150-mesh sieve). The pretreated powder is added to the deionized water containing the surfactant, and the system is stirred at 80 °C for 90 minutes using a high-speed shear disperser (12,000 rpm).

[0061] Refinement and homogenization: After the coarse emulsion is cooled, it is intermittently ultrasonically treated for 10 minutes using a probe-type ultrasonic processor (power 500 W). Subsequently, it is circulated and homogenized 2 times through a high-pressure homogenizer (50 MPa). The outlet temperature during the homogenization process is controlled not to exceed 65 °C.

[0062] Post-treatment: Xanthan gum and a compound preservative of CMIT / MIT and BIT are added. The pH value is adjusted to 7.2 using a 0.1 M NaOH solution.

[0063] Finished product: The properties of the obtained PHBV nano-aqueous suspension are as shown in Examples 1 in Table 2 and Table 3 (average particle size 80 nm, D90 140 nm, solid content 45 wt%). In addition, when using PHBV powder with a 3HV unit content of 20 mol% (Enmat Y1000 series of Ningbo Tianan Biomaterials Co., Ltd. or equivalent products), and the other conditions and steps are the same as those in this example, a suspension with similar properties can also be prepared, such as an average particle size of 85 nm, D90 142 nm, PDI value of 0.16, and Zeta potential of -37 mV. This indicates that the method of the present invention is applicable to PHBV with a 3HV content of 5 - 20 mol%.

[0064] Example 2: PHB / PHBH blended nano-aqueous suspension

[0065] Raw materials: PHB powder, 25 grams in total; PHBH powder (AONilex series of Kaneka Corporation, with a 3HHx unit content of 10 - 11 mol%), 25 grams in total; Pluronic F68, 1.2 grams in total; sodium dodecyl sulfate SDS, 0.3 grams in total; appropriate amount of deionized water to adjust the final solid content to 42 wt%. The mass ratio of PHA to the aqueous phase is 1:1.3. The dosage of the surfactant is 3.0 wt% of the mass of PHA.

[0066] Melting Emulsification and Preliminary Dispersion: Under nitrogen protection, the mixture of PHB and PHBH was melted at 180 - 185 °C. An aqueous solution containing surfactant preheated to 85 °C was slowly added dropwise to the molten PHA under mechanical stirring (3000 rpm), emulsified for 20 minutes, and then rapidly cooled to obtain a coarse dispersion.

[0067] High - energy Refinement: The coarse dispersion was circulated through a high - pressure microfluidic homogenizer (100 MPa) 3 times. The outlet temperature was controlled not to exceed 65 °C.

[0068] Post - treatment: Xanthan gum and compound preservative were added. The pH was adjusted to 7.5.

[0069] Finished Product: The properties of the obtained PHB / PHBH blend nano - aqueous suspension are shown in Examples 2 of Table 2 and Table 3 (average particle size 115 nm, D90 is 148 nm). Similarly, when the PHBH raw material was replaced with PHBH powders (Kaneka Corporation AONilex series) with 3HHx unit contents of 6 mol% and 12 mol% respectively, and the remaining conditions and steps were the same as in this example, suspensions with similar properties could also be prepared, such as average particle sizes of 112 nm and 117 nm, D90 values of 146 nm and 150 nm, and PDI values of 0.17 and 0.19 respectively. This indicates that the method of the present invention is applicable to PHBH with 3HHx contents of 6 - 12 mol%.

[0070] Example 3: PHB Homopolymer Nano - aqueous Suspension

[0071] Raw Materials: 50 grams of PHB powder; 2.0 grams of polyvinyl alcohol PVA (low degree of polymerization); appropriate amount of deionized water to adjust the final solid content to 38 wt%. The mass ratio of PHA to the aqueous phase is 1:1.55. The dosage of surfactant is 4.0 wt% of the mass of PHA.

[0072] Preparation Process: After the PHB powder was cryogenically pulverized, it was dispersed by high - speed shearing (12000 rpm, 90 minutes) with the PVA aqueous solution at 85 °C. The high - pressure homogenization conditions were 80 MPa and circulated 5 times.

[0073] Post - treatment: Auxiliary agent was added and the pH was adjusted to 6.8.

[0074] Finished Product: The properties of the obtained PHB nano - aqueous suspension are shown in Example 3 of Table 2 and Table 3 (average particle size 120 nm, D90 is 148 nm).

[0075] Example 4: PHBV Nano - aqueous Suspension Covering the Lower Limits of Multiple Parameters

[0076] This example aims to verify the feasibility of the method of the present invention when multiple parameters take their lower limit values.

[0077] Raw materials: PHBV powder (15 mol% HV), 25 g in total; polysorbate 20, 0.125 g in total (0.5 wt% of the PHA mass); appropriate amounts of xanthan gum and preservatives. 100 g of deionized water, making the mass ratio of PHA to the aqueous phase 1:4.

[0078] Preparation process parameters: Aqueous phase temperature 50 °C; high-speed shear stirring, rotation speed 5000 rpm, treatment time 10 minutes. For high-energy homogenization treatment, a high-pressure homogenizer is selected, homogenization pressure 20 MPa, 1 cycle; and at the same time, an ultrasonic cell disruptor can be selected, power 200 W, ultrasonic treatment 1 minute (Note: Here, high-pressure homogenization and ultrasonic treatment are optional refinement methods, and this example aims to illustrate the feasibility of the lower limits of each single process parameter).

[0079] Post-treatment: Add a calculated amount of xanthan gum to make the viscosity of the final suspension 50 mPa·s at 25 °C, and add a preservative. Adjust the pH to 7.0.

[0080] Finished product: The total solid content is adjusted to 23 wt%. Under this condition, the PHA resin particles can be adjusted to 98.5 wt% of the total solid content by dry weight, and the dispersion stabilizing aids (mainly surfactants, a small amount of thickeners and preservatives) account for 1.5 wt% of the total solid content by dry weight. The average particle size of the obtained suspension is 30 nm, and D90 is 50 nm. Specific performance parameters are shown in Examples 4 in Tables 2 and 3.

[0081] Example 5: PHBV / PHBH blended nano-aqueous suspension covering the upper limits of multiple parameters

[0082] This example aims to verify the feasibility of the method of the present invention when the upper limit values are taken for multiple parameters.

[0083] Raw materials: PHBV powder (containing 10 mol% HV), 32 g in total; PHBH powder (Kaneka Corporation AONilex series, select the specification with 3HHx unit content of 10 mol%), 32 g in total (total PHA 64 g); polysorbate 80, 5.12 g in total (8.0 wt% of the PHA mass); appropriate amounts of xanthan gum and preservatives. 32 g of deionized water, making the mass ratio of PHA to the aqueous phase 1:0.5.

[0084] Preparation process parameters: Aqueous phase temperature 95 °C; high-speed shear stirring, rotation speed 20000 rpm, treatment time 120 minutes. For high-energy homogenization treatment, a high-pressure homogenizer is selected, homogenization pressure 150 MPa, 4 cycles; and at the same time, an ultrasonic cell disruptor can be selected, power 1000 W, ultrasonic treatment 20 minutes (Note: Here, high-pressure homogenization and ultrasonic treatment are optional refinement methods, and this example aims to illustrate the feasibility of the upper limits of each single process parameter).

[0085] Post-treatment: Add xanthan gum with a certain amount of computational load to make the viscosity of the final suspension 1000 mPa·s at 25°C, and add preservatives. Adjust the pH to 7.0.

[0086] Finished product: Adjust the total solid content to 65 wt%. Under this condition, the PHA resin particles can be adjusted to 80 wt% of the total solid content by dry weight, and the dispersion stabilizing aids (mainly surfactants, more thickeners and preservatives) account for 20 wt% of the total solid content by dry weight. The average particle size of the obtained suspension is 140 nm, and D90 is 150 nm. The specific performance parameters are shown in Examples 5 in Table 2 and Table 3.

[0087] Example 6: PHBV / PHBH blend nano-aqueous suspension covering the lower limit of 3HV content

[0088] Raw materials: 30 g of PHBV powder (containing 5 mol% of 3HV units); 20 g of PHBH powder (Kaneka Corporation AONilex series, select the specification with 8 mol% of 3HHx units); 1.0 g of polysorbate 80; 1.0 g of Pluronic P123; appropriate amount of deionized water to adjust the final solid content to 45 wt%. The mass ratio of PHA to the aqueous phase is 1:1.1. The dosage of the surfactant is 4.0 wt% of the mass of PHA.

[0089] Preparation process: Refer to the method of Example 1 (low-temperature pulverization pretreatment, aqueous phase temperature 80°C, high-speed shearing at 12000 rpm for 90 minutes), high-pressure homogenization pressure 60 MPa, circulating 3 times.

[0090] Post-treatment: Add additives and adjust the pH to 7.0.

[0091] Finished product: The performance of the obtained PHBV / PHBH blend nano-aqueous suspension is shown in Example 6 in Table 2 and Table 3 (average particle size 100 nm, D90 is 145 nm).

[0092] Comparative Example 1: Preparation of PHBV aqueous dispersion using a simplified process

[0093] Raw materials: 50 g of PHBV powder with 15 mol% of 3HV units, which is the Enmat Y1000 series product of Ningbo Tianan Biomaterials Co., Ltd.; 2.5 g of polysorbate 20 (Tween 20), CAS No. 9005-64-5, Sigma-Aldrich product P1379; 75 g of deionized water.

[0094] PHA pretreatment: None. Directly use PHBV powder.

[0095] Coarse dispersion: The PHBV powder was directly added to deionized water containing dissolved Tween 20. The system was heated and maintained at 80 °C. Using a high-speed shear disperser, such as the IKA T25 digital ULTRA-TURRAX, it was stirred at a high speed of 12,000 rpm for 60 minutes to form a coarse dispersion.

[0096] Refinement and homogenization: The coarse dispersion was cooled to 60 °C and circulated and homogenized once at a pressure of 30 MPa using a high-pressure homogenizer, such as the ATS Engineering Inc. AH-BASIC. Before homogenization, the coarse dispersion was precooled to 15 °C. The homogenization equipment was equipped with a cooling jacket to ensure that the outlet temperature of the material did not exceed 65 °C.

[0097] Post-treatment: Under low-speed stirring, xanthan gum (specifically, CP Kelco Keltrol CG-F) accounting for 0.05 wt% of the total mass of the final suspension and a compound preservative of CMIT / MIT and BIT (specifically, LANXESS Preventol D 7) accounting for 0.1 wt% of the total mass of the final suspension were slowly added to the homogenized PHBV dispersion. The pH value of the emulsion was adjusted to 7.1 with 0.1 M NaOH solution.

[0098] Finished product: A PHBV aqueous dispersion with the performance shown in Comparative Example 1 in Tables 2 and 3 was obtained. Its average particle size was 280 nm, D90 was 450 nm, PDI was 0.45, and the Zeta potential was -25 mV. The solid content was 41.2 wt%.

[0099] Table 2 Composition and key performance parameters of the PHA nano-aqueous suspension in the examples

[0100]

[0101] Table 3 Key preparation process parameters of the PHA nano-aqueous suspension in the examples

[0102]

[0103] Note: US indicates ultrasonic treatment.

[0104] The storage stability (25 °C, 6 months) of each example and comparative example is as follows:

[0105] Examples 1-6: The appearance was uniform, without stratification or (obvious) precipitation, and the particle size change rate was generally <10% (slightly higher under high solid content or boundary parameter conditions, but still within the acceptable range, such as <15%).

[0106] Comparative Example 1: Obvious stratification and precipitation occurred within 3 months, and the particle size change rate >20%.

[0107] Application Example 1: Application as an Environmentally Friendly Paper Adhesive

[0108] The PHA nano-aqueous suspension prepared by the present invention can be used as an environmentally friendly paper adhesive. To verify its bonding performance, each PHA nano-aqueous suspension prepared in Examples 1-6 was used to bond two corrugated papers with a basis weight of 80 g / m². The specific operation was as follows: Take the suspension of each example, uniformly coat it on the surface of one corrugated paper, control the coating amount at 100 g / m² wet weight, then fit it with another corrugated paper, and apply a pressure of 0.5 kg / cm² at room temperature and keep it for 24 hours. Subsequently, its T-peel strength and peel strength after immersion in water were tested. At the same time, the PHBV aqueous dispersion prepared in Comparative Example 1 and commercially available PVA white latex, such as Franklin International's Titebond Original Wood Glue, with a typical solid content of 46% and a viscosity of 3200 mPa·s, were used as the control group for the same test. The specific results are shown in Table 4.

[0109] Application Example 2: Application as a Barrier Coating for Paper Food Containers

[0110] The PHA nano-aqueous suspension prepared by the present invention can be used as a biodegradable barrier coating for paper food containers. To evaluate its barrier performance, each PHA nano-aqueous suspension prepared in Examples 1-6 was uniformly coated on the inner surface of food-grade white cardboard (basis weight 250 g / m²) without lamination treatment through a small blade coater (coating gap 200 μm), and the dry film thickness was controlled at 20 μm. The coated paper samples were dried in an oven at 100 °C for 10 minutes. Subsequently, performance tests such as water vapor transmission rate (WVTR) and immersion durability of the coated paper samples were carried out. At the same time, the PHBV aqueous dispersion prepared in Comparative Example 1 was used as the control group for the same coating preparation and testing, and compared with the performance of traditional petroleum-based materials or uncoated papers. The specific results are shown in Table 4 and the description.

[0111] Table 4 Test Results of Application Examples (Coatings and Adhesives)

[0112]

[0113] Experimental Results and Analysis

[0114] Through the above Examples 1 to 6 and Comparative Example 1, the feasibility of preparing nano-aqueous suspensions of different types of PHA and their blends under different component contents and process parameters and the performance of the obtained products were systematically studied.

[0115] Referring to the data in Table 2 and Table 3, it can be seen that:

[0116] Coverage of Parameter Range:

[0117] Total solids content: Examples 4 (23 wt%) and 5 (65 wt%) cover the range of 23 - 65 wt%.

[0118] Proportion of PHA resin: Examples 5 (80 wt%) and 4 (98.5 wt%) cover the range of 80 - 98.5 wt%.

[0119] Proportion of dispersion stabilizer: Examples 4 (1.5 wt%) and 5 (20 wt%) cover the range of 1.5 - 20 wt%.

[0120] Average particle size: Examples 4 (30 nm) and 5 (140 nm) cover the range of 30 - 140 nm. The D90 of all examples is ≤ 150 nm, and PDI < 0.3.

[0121] 3HV content: Examples 6 (5 mol%) and 1 (15 mol%, and the applicability of 20 mol% is mentioned in the description) cover the range of 5 - 20 mol% of 3HV unit content in PHBV.

[0122] 3HHx content: Example 2 (10 - 11 mol%, and the applicability of 6 mol% and 12 mol% is mentioned in the description) cover the range of 6 - 12 mol% of 3HHx unit content in PHBH.

[0123] Viscosity: Examples 4 (50 mPa·s) and 5 (1000 mPa·s) cover the range of 50 - 1000 mPa·s.

[0124] Preparation process parameters: Examples 4 and 5 respectively combine the lower and upper limit values of each process parameter defined in the present invention, including aqueous phase temperature (50 - 95 °C), shear rate (5000 - 20000 rpm), shear time (10 - 120 minutes), ratio of PHA to water (1:0.5 - 1:4), surfactant dosage (0.5 - 8 wt%), high-pressure homogenization pressure (20 - 150 MPa), high-pressure homogenization times (1 - 5 times, and Example 3 also verifies 5 times), ultrasonic power (200 - 1000 W), ultrasonic treatment time (1 - 20 minutes). These results show that the method of the present invention has good applicability within the said parameter range.

[0125] Particle size control and stability: All examples (Examples 1 - 6) can obtain nano-scale PHA particles meeting the requirements through the preparation method described in the present invention, and show good physical stability (absolute value of Zeta potential > 30 mV, good storage stability).

[0126] Comparison with Comparative Examples: Compared with Comparative Example 1 using a simplified or non-optimized process, Examples 1 to 6 of the present invention show significant advantages in terms of particle size control, stability, and final application performance of the PHA suspension. Specifically, referring to the data in Table 4, when applied as a paper barrier coating, the dry film thickness of the coatings formed in Examples 1 to 6 of the present invention is 20 μm. The water vapor transmission rate (WVTR) values of these example coatings are in the range of 100 g / (m²·24 h) to 130 g / (m²·24 h), which are significantly lower than 180 g / (m²·24 h) of Comparative Example 1 and 220 g / (m²·24 h) of the traditional PVA white latex control group, demonstrating excellent barrier performance. Among them, Example 4 has the best WVTR value of 100 g / (m²·24 h) among all examples with an extremely small average particle size of 30 nm and a D90 value of 50 nm. At the same time, the immersion durability of the coatings in Examples 1 to 6 is 24 h, far superior to 10 h of Comparative Example 1 and 2 h of the traditional PVA white latex.

[0127] When applied as an adhesive, the peel strength between paper and paper in Examples 1 to 6 is in the range of 4.2 N / 25 mm to 5.0 N / 25 mm, and the peel strength after immersion is in the range of 3.2 N / 25 mm to 4.3 N / 25 mm. These adhesion performance values are all comprehensively superior to the dry peel strength of 3.5 N / 25 mm and the wet peel strength of 1.5 N / 25 mm (partial failure) of Comparative Example 1. Compared with the dry peel strength of 4.0 N / 25 mm of the traditional PVA white latex and the performance of complete failure after immersion, the examples of the present invention also show comparable or better levels. Particularly importantly, the PHA materials prepared in all examples of the present invention and the PHA material used in Comparative Example 1 can be basically degraded under 8-week composting conditions, which is in sharp contrast to the non-biodegradable traditional PVA white latex; moreover, due to their excellent application performance, the examples of the present invention have more practical value in environmental protection applications compared with Comparative Example 1 which is also biodegradable but has poor performance.

[0128] The above results fully and directly prove that through the selection of specific components and the optimization of process parameters, the technical solution of the present invention can effectively solve the challenges in the background art, realize the preparation of the target PHA nano-aqueous suspension within a wide range of parameters, and support the scope and beneficial effects claimed in the present invention.

[0129] The above examples are only for illustrating the technical solution of the present invention, rather than limiting its scope. Those skilled in the art can make various modifications, equivalent substitutions, or variations to the above embodiments without departing from the principle and spirit of the present invention, and these modifications, equivalent substitutions, or variations should all be included within the protection scope defined by the claims of the present invention.

Claims

1. A PHA nano-aqueous suspension, characterized in that: The PHA nano-aqueous suspension contains polyhydroxyalkanoate (PHA) resin particles, a dispersion stabilizing aid, and water; the total solid content of the suspension is 23 - 65 wt%, wherein the PHA resin particles account for 80 - 98.5 wt% of the total solid content by dry weight, and the dispersion stabilizing aid accounts for 1.5 - 20 wt% of the total solid content by dry weight; the average particle size of the PHA resin particles is 30 - 140 nm, D90 ≤ 150 nm, the polydispersity index (PDI) < 0.3, and the absolute value of the Zeta potential is > 30 mV at pH 6.5 - 7.

5.

2. The PHA nano-aqueous suspension according to claim 1, wherein: The PHA resin is selected from poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBH), or a blend combination thereof; when the PHA resin is PHBV, the content of 3-hydroxyvalerate (3HV) units is 5 - 20 mol%; when the PHA resin is PHBH, the content of 3-hydroxyhexanoate (3HHx) units is 6 - 12 mol%.

3. The PHA nano-aqueous suspension according to claim 1, characterized in that: The dispersion stabilizing aid includes a surfactant, a preservative, and a thickener; the surfactant is selected from one or a combination of nonionic surfactants, anionic surfactants, or block copolymers; the nonionic surfactant is selected from polysorbate 20, polysorbate 80, polyvinyl alcohol with a degree of alcoholysis of 87 - 89 mol% and a viscosity of 20 - 35 mPa·s in a 4% aqueous solution at 20°C, or polyvinyl alcohol with a degree of alcoholysis of 87 - 89 mol% and a viscosity of 5 - 7 mPa·s in a 4% aqueous solution at 20°C; the anionic surfactant is sodium dodecyl sulfate; the block copolymer is selected from Pluronic F68 and Pluronic P123.

4. The PHA nano-aqueous suspension according to claim 1, characterized in that: The viscosity of the suspension at 25°C is 50 - 1000 mPa·s.

5. A method for preparing the PHA nano-aqueous suspension according to claim 1, characterized in that, It includes the following steps: Step a. Pretreat the PHA resin to obtain a pretreated PHA raw material, and the pretreatment includes cryogenic grinding to a micron-sized powder or heating to a molten state. Step b. Add the pretreated PHA raw material to an aqueous phase containing a surfactant, and perform high-speed shear stirring at 50 - 95°C to form a coarse emulsion or a coarse dispersion. Step c. Perform high-energy homogenization treatment on the coarse emulsion or coarse dispersion to refine the PHA particles to D90 ≤ 150 nm, and obtain a PHA nano-dispersion containing PHA resin particles. Step d. Add a thickener and a preservative to the PHA nano-dispersion containing PHA resin particles obtained in step c, and mix evenly to obtain an intermediate PHA nano-aqueous suspension. Step e. Adjust the pH value of the intermediate PHA nano-aqueous suspension obtained in step d to 6.5 - 7.5, the solid content to 23 - 65 wt%, and the viscosity measured at 25°C to 50 - 1000 mPa·s to obtain the PHA nano-aqueous suspension.

6. The preparation method according to claim 5, characterized in that: In step b, the mass ratio of the PHA raw material to the aqueous phase is 1:0.5 to 1:4; the dosage of the surfactant is 0.5 to 8 wt% of the mass of the PHA resin; the rate of high-speed shear stirring is 5000 to 20000 rpm, and the treatment time is 10 to 120 minutes.

7. The preparation method according to claim 5, characterized in that: In step c, the high-energy homogenization treatment is selected from one or a combination of high-pressure homogenization, ultrasonic dispersion, microfluidic homogenization, or colloid mill grinding; when high-pressure homogenization is used, the homogenization pressure is 20 to 150 MPa, and the cyclic treatment is carried out 1 to 5 times; when ultrasonic dispersion is used, the ultrasonic power is 200 to 1000 W, and the treatment time is 1 to 20 minutes.

8. The preparation method according to claim 5, characterized in that: In step d, the thickener is selected from one or more of xanthan gum, sodium carboxymethyl cellulose, or associative thickeners; the preservative is selected from one or a combination of a compound of methylisothiazolinone MIT, methylchloroisothiazolinone CMIT and benzisothiazolinone BIT, or a paraben preservative.

9. Use of the PHA nano-aqueous suspension according to claim 1 in the preparation of a biodegradable food packaging barrier coating.

10. Use of the PHA nano-aqueous suspension according to claim 1 in the preparation of a biodegradable water-based environmental protection coating.

11. Use of the PHA nano-aqueous suspension according to claim 1 in the preparation of a biodegradable water-based adhesive.

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