Pha nano-aqueous suspension, its preparation method and application

Abstract

The application discloses a kind of PHA nano aqueous suspensions and its preparation method and application, belong to polymer materials and its processing application field.The suspension with PHA resin as dispersed phase, water as continuous phase, total solid content is 23~65wt%, wherein PHA resin accounts for 80~98.5wt% of total solid, auxiliary accounts for 1.5~20wt%.PHA particle average particle size is 30~140nm, D90≤150nm, polydispersity index PDI<0.3, at pH 6.5~7.5, Zeta potential absolute value>30mV.Its preparation method includes that PHA raw material is pretreated, under the action of dispersion stabilizing auxiliary, in aqueous phase preliminary dispersion is carried out, and high-energy homogenization treatment is carried out.The obtained suspension is storage stable, has excellent barrier property and mechanical property after film formation, is suitable for preparing biodegradable food packaging barrier coating, water-based environmental protection coating, water-based adhesive.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of biodegradable high molecular materials and its processing applications, in particular to a kind of PHA nano-aqueous suspension and its preparation method and application, including the preparation of the suspension, performance and its application in biodegradable food packaging barrier coating, water-based environmental protection coating, water-based adhesive and other fields. BACKGROUND

[0002] Polyhydroxyalkanoate (PHA) is a kind of aliphatic copolyester synthesized by a variety of microorganisms through fermentation. Because of its excellent biodegradability, biocompatibility and the characteristics of being derived from renewable resources, PHA is considered as one of the ideal environmental protection materials to replace traditional petroleum-based plastics. PHA has various types, and the common ones are poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBH) and so on. However, PHA materials usually have high crystallinity, strong hydrophobicity, high melting point and narrow processing window, etc., which makes it difficult to form a uniform, flexible and good barrier film when directly applied, limiting its wide application in many fields.

[0003] Preparation of PHA into aqueous nano-suspension, also known as nano-emulsion or nano-dispersion, is an effective way to improve its processing and application performance. Aqueous system is not only environmentally friendly, but also easy to be applied by conventional coating, spraying and other methods. Nano-sized PHA particles have larger specific surface area and higher surface energy, which is beneficial to form a more compact and uniform film layer, thereby significantly improving the barrier property, gloss and adhesion to the substrate of the material.

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

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

[0006] In view of the above challenges in the prior art in preparing high solid content, nano-sized, high stability PHA aqueous suspension, especially how to meet the technical problems of high solid content, precise particle size control (D90 particle size ≤ 150 nm) and long-term storage stability under the premise of environmental protection, the present application provides a new solution.

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

[0008] A PHA nano-aqueous suspension, comprising polyhydroxyalkanoate PHA resin microparticles, dispersion stabilizing aids and the balance of water, so that the total solid content in the suspension, calculated as the solid components in the PHA resin microparticles and the dispersion stabilizing aids, is between 23 and 65 wt%; wherein, of the total solid content, the PHA resin microparticles account for 80 to 98.5 wt% of the total solid content by dry weight, and the dispersion stabilizing aids account for 1.5 to 20 wt% of the total solid content by dry weight; the dispersion stabilizing aids at least comprise a surfactant, a preservative and a thickening agent. Wherein, the Z-Average average particle size of the PHA resin microparticles is controlled in the range of 30 to 140 nm, D90 ≤ 150 nm, and PDI value < 0.3. The absolute value of Zeta potential of the suspension is > 30 mV at pH 6.5 to 7.5, and the viscosity at 25℃ is 50 to 1000 mPa·s. Through a large number of experimental studies, it is found that the suspension has good stability and subsequent application performance when the average particle size is in this range, especially when D90 ≤ 150 nm. The lower limit of the smaller particle size that can be stably obtained is 30 nm, and the upper limit of the average particle size close to or exceeding 150 nm is that the nano effect is weakened 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 blended combination thereof. It is found that the use of a moderate molecular weight, such as a weight average molecular weight Mw in the range of 2.0 x 10 5 g / mol to 5.0 x 10 5The PHA resin with a molecular weight in the range of 100,000-1,000,000 g / mol and a specific copolymer composition, especially the PHA containing 3-hydroxyvalerate units or 3-hydroxyhexanoate units and other comonomers, is beneficial to form stable and uniform nanoparticles due to its generally lower crystallinity and better processability. The PHA resin is PHBV containing 5-20 mol% 3HV units, or PHBH containing 6-12 mol% 3HHx units, or a blend of the above copolymers and PHB. It is proved by experiments that the crystallization and processability of PHA are improved in this comonomer content range, which is beneficial to the formation and stabilization of the nanosuspension.

[0010] The surfactant is selected from one or more combinations 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 properties 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; and the block copolymer is selected from one or more combinations of pluronic F68 and pluronic P123. It is found that the combination of non-ionic surfactants such as polysorbate with polymer surfactants such as specific specifications of polyvinyl alcohol which have 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 stable and fine PHA nanosuspensions with high solid content.

[0011] The thickening agent can be selected from xanthan gum, sodium carboxymethyl cellulose or associative thickening agents. The preservative can be selected from the combination of methylisothiazolinone MIT, methylchloroisothiazolinone CMIT and benzisothiazolinone BIT or parahydroxybenzoic acid ester preservatives.

[0012] A solvent-free preparation method of the above PHA nanosuspension, comprising the following steps:

[0013] Step a. Pre-treating the PHA resin to obtain a pre-treated PHA raw material, the pre-treatment including low-temperature pulverization, specifically pulverizing by using a liquid nitrogen-assisted ultrafine pulverizer and passing through a 150-mesh sieve to obtain a micro-powder with an average particle size of <100 μm; or melting it at a temperature 10-30°C higher than its melting point (usually 180-185°C), while trying to shorten the high-temperature residence time and protecting it, such as in a nitrogen atmosphere.

[0014] Step b. The micron-sized powder or molten PHA raw material is added into the aqueous phase to form a preliminary emulsion or dispersion of PHA. The operating conditions of this process are as follows: the temperature of the aqueous phase is maintained at 50-95℃; high-speed shearing stirring is used, with the rotational speed set at 5000-20000 rpm, and the treatment time lasts for 10-120 minutes. The aqueous phase used contains a surfactant, with the amount being 0.5-8wt% of the mass of the PHA resin, and the mass ratio of the PHA raw material to the aqueous phase is controlled within the range of 1:0.5-1:4. It is determined through experiments that within the above process parameter range, the preliminary dispersion of PHA can be effectively achieved, laying a good foundation for the subsequent high-energy homogenization treatment.

[0015] Step c. The above coarse emulsion or coarse dispersion is treated to further refine the PHA particles to the level of D90≤150nm and PDI<0.3, so as to obtain a PHA nanodispersion containing PHA resin microparticles. This treatment can be selected from one of the following devices: a high-pressure homogenizer, with the operating conditions being: homogenization pressure 20-150MPa, and the cycle treatment being 1-5 times; before homogenization, the coarse emulsion can be pre-cooled to 10-25℃, and the equipment needs to be equipped with a cooling system to control the outlet temperature not to exceed 60-70℃. Alternatively, an ultrasonic cell crusher, with the operating conditions being: power 200-1000W, and ultrasonic treatment 1-20 minutes; the treatment can be in an intermittent mode and assisted with ice bath cooling. It is determined through experiments that within the above high-energy homogenization parameter range, the PHA particles can be effectively refined to the target nanometer level, while avoiding the adverse effects that may be caused by excessive treatment.

[0016] Step d. To the PHA nanodispersion containing PHA resin microparticles obtained in step c, 0.05-0.5wt% of thickening agent and 0.05-0.2wt% of preservative, accounting for the total mass of the final suspension, are slowly added, and mixed uniformly under mild stirring to obtain an intermediate PHA nanometer aqueous suspension. These added amounts are intended to ensure the long-term stability and use performance of the suspension, and the solid ingredients will be included in the calculation of the total solid content.

[0017] Step e. The intermediate PHA nanometer aqueous suspension obtained in step d is detected and the pH value of the suspension is adjusted to the range of 6.5-7.5, the solid content is adjusted to the range of 23-65wt%, and the viscosity at 25℃ is adjusted to the range of 50-1000mPa·s, so as to finally obtain the PHA nanometer aqueous suspension.

[0018] The present application also provides the use of the PHA nanometer 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, paperboard, biodegradable plastic film or other food contact substrates by means of blade coating, spray coating, dip coating, casting or printing, and after drying at 50-120℃ for 1-30 minutes to form a film, a biodegradable coating layer with water vapor barrier property, oxygen barrier property and oil resistance is formed.

[0020] The PHA nano-aqueous suspension is mixed and dispersed uniformly in an aqueous system with pigments, fillers, film forming aids, rheology modifiers, wetting dispersants and other common coating aids as the main film forming material or auxiliary film forming material through conventional coating preparation process to prepare an aqueous environmental friendly coating with low volatile organic compound (VOC) emission, biodegradable coating film.

[0021] The PHA nano-aqueous suspension is directly used as an adhesive, or is used as an aqueous adhesive for bonding paper products, wood, fiber products, non-woven fabrics or other porous substrates after being 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 glue such as casein glue or gelatin, polyvinyl acetate emulsion, and acrylate emulsion, and the adhesive layer is biodegradable after completing the service life.

[0022] The nano-scale dispersion of PHA in water is effectively promoted by selecting the type and molecular characteristics of PHA raw material, optimizing the compounding of surfactants, precisely controlling high-energy homogenization process parameters such as pressure, temperature, processing time and shear rate, and the synergistic effect of additives, and the obtained suspension has excellent physical and chemical stability and application performance.

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

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

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

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

[0027] The preparation process is environmentally friendly, mainly uses water as the dispersion medium, significantly reduces or avoids the use of organic solvents, and conforms to the development trend of green chemistry.

[0028] The prepared PHA nano-aqueous suspension is widely applicable, and can be used in the fields of food packaging, environment-friendly coatings, adhesives, etc., and the obtained products have good biodegradability and application performance. DETAILED DESCRIPTION

[0029] The present application is further described in detail below in combination with specific examples and comparative examples. Unless otherwise specified, the conventional experimental methods used in the examples of the present application are all referred to the general standards in the art or the operation guidelines provided by the manufacturers. The raw materials and reagents used are commercially available products unless otherwise specified.

[0030] The determination method of particle size, D90, PDI and Zeta potential:

[0031] A laser particle size analyzer based on the principle of dynamic light scattering (DLS) is used for determination. The instrument that can be used is Zetasizer Nano ZS90 of Malvern Panalytical Company in the United Kingdom. Before testing, an appropriate amount of polyhydroxyalkanoate (PHA) nano-aqueous suspension sample is diluted with deionized water to an appropriate concentration required by the instrument for detection. After equilibration at 25℃ for 120 seconds, the measurement is carried out, and each sample is measured repeatedly for 3 times, and the average value is taken. The particle size is reported as Z-Average average particle size, and the D90 value and PDI value are recorded at the same time. Zeta potential is measured by electrophoresis light scattering mode of the same instrument, using DTS1070 capillary electrophoresis cell, and the sample is diluted with 1mM KCl aqueous solution with pH value of 7 before determination.

[0032] Main experimental raw materials and specifications

[0033] Table 1: Main experimental raw material chemical name / category, product model and supplier

[0034]

[0035] Specifications / main parameter explanations:

[0036] PHBV powder, Enmat Y1000 series, Ningbo Tianan Biomaterials Co., Ltd:

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

[0038] When the 3HV content is 15mol%, 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 typically in the range of 3.0 x 10 5 - 3.5 x 10 5 g / mol.

[0040] PHB powder, Enmat Y3000 series, Ningbo Tianan Biomaterials Co., Ltd: weight average molecular weight Mw of 4.0 x 10 5 - 4.5 x 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 typically in the range of 3.0 x 10 5 - 4.5 x 10 5 g / mol.

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

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

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

[0046] Polysorbate 20 (Tween 20), P1379, Sigma-Aldrich: CAS Number 9005-64-5, pharmaceutical excipient grade or food grade.

[0047] Polysorbate 80 (Tween 80), P1754, Sigma-Aldrich: CAS Number 9005-65-6, pharmaceutical excipient grade or food grade.

[0048] Polyvinyl alcohol PVA, high polymerization degree, Poval PVA-217, Kuraray: CAS Number 9002-89-5, alcoholysis degree 87-89 mol%, polymerization degree 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 Number 9002-89-5, alcoholysis degree 87-89 mol%, degree of polymerization 500-600, viscosity of 4% aqueous solution at 20 °C 5-7 mPa-s.

[0050] Sodium dodecyl sulfate SDS, L3771 BioReagent, Sigma-Aldrich: CAS Number 151-21-3, analytical or BioReagent grade, purity ≥ 98.5%.

[0051] Pluronic F68 (Pluronic F-68), P1300, Sigma-Aldrich: CAS Number 9003-11-6, PEO-PPO-PEO block copolymer.

[0052] Pluronic P123 (Pluronic P-123), 435465, Sigma-Aldrich: CAS Number 9003-11-6, PEO-PPO-PEO block copolymer.

[0053] Xanthan gum, Keltrol CG-F, CP Kelco: CAS Number 11138-66-2, food grade or industrial grade, in accordance with the corresponding standards.

[0054] CMIT / MIT and BIT complex preservative, Preventol D 7, LANXESS: complex of methylisothiazolinone CMIT / methylchloroisothiazolinone MIT and benzisothiazolinone BIT, 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 46%, viscosity 3200 mPa-s.

[0058] Example 1: PHBV nano-aqueous suspension

[0059] Raw materials: PHBV powder with 15 mol% 3HV unit content, Enmat Y1000 series from Ningbo Tianan Biomaterials Co., Ltd., 50 g; Polysorbate 20 (Tween 20), 1.5 g; Polyvinyl alcohol PVA (high polymerization degree), 0.5 g; deionized water 100 g. The mass ratio of PHA to water phase is 1:2 at this time. The amount of surfactant is 4.0 wt% of the mass of PHA.

[0060] Coarse dispersion: The PHBV powder is cryogenically micronized (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 using a high-speed shearing disperser (12000 rpm) for 90 minutes.

[0061] Refinement and homogenization: After the coarse emulsion is cooled, it is intermittently treated with a probe-type ultrasonic processor (power 500 W) for 10 minutes. Subsequently, it is homogenized by a high-pressure homogenizer (50 MPa) for 2 cycles. The outlet temperature is controlled to be no more than 65°C during the homogenization process.

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

[0063] Finished product: The obtained PHBV nano-aqueous suspension has the performance as shown in Table 2 and Table 3 of Example 1 (average particle size 80 nm, D90 140 nm, solid content 45 wt%). In addition, when a PHBV powder with 20 mol% 3HV unit content (Enmat Y1000 series from Ningbo Tianan Biomaterials Co., Ltd. or the like) is used, and the remaining conditions and steps are the same as in this example, a suspension with similar performance can also be prepared, such as an average particle size of 85 nm, D90 142 nm, PDI value 0.16, and Zeta potential -37 mV. This shows that the method of the present application is suitable for PHBV with 3HV content of 5-20 mol%.

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

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

[0066] Melt emulsification and primary dispersion: The PHB and PHBH mixture was melted at 180-185°C under nitrogen protection. The preheated (85°C) surfactant-containing aqueous solution was slowly added dropwise into the molten PHA under mechanical stirring (3000 rpm) for 20 minutes, and then rapidly cooled to obtain a crude dispersion.

[0067] High-energy refinement: The crude dispersion was treated by a high-pressure microfluidizer (100 MPa) for 3 cycles. The outlet temperature was controlled to be no more than 65°C.

[0068] Post-treatment: Xanthan gum and a compounded preservative were added, and the pH was adjusted to 7.5.

[0069] Finished product: The performance of the obtained PHB / PHBH blended nano-aqueous suspension is shown in Table 2 and Table 3 of Example 2 (average particle size 115 nm, D90 148 nm). Similarly, when the PHBH raw material is replaced by PHBH powder (Kaneka Corporation AONilex series) with a 3HHx unit content of 6 mol% and 12 mol% respectively, and the remaining conditions and steps are the same as in this example, nano-aqueous suspensions with similar performance can also be prepared, with average particle sizes of 112 nm and 117 nm respectively, D90 values of 146 nm and 150 nm respectively, and PDI values of 0.17 and 0.19 respectively. This shows that the method of the present application is suitable for PHBH with a 3HHx content of 6-12 mol%.

[0070] Example 3: PHB homopolymer nano-aqueous suspension

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

[0072] Preparation process: After low-temperature crushing of the PHB powder, the PVA aqueous solution was dispersed at 85°C under high-speed shearing (12000 rpm, 90 minutes). The high-pressure homogenization conditions were 80 MPa for 5 cycles.

[0073] Post-treatment: Additives were added, and the pH was adjusted to 6.8.

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

[0075] Example 4: PHBV nano-aqueous suspension covering the lower limit of multiple parameters

[0076] This example aims to verify the feasibility of the method of the present application when the lower limit values of multiple parameters are taken.

[0077] Raw materials: PHBV powder (15 mol% HV), 25 g; polysorbate 20, 0.125 g (0.5 wt% of PHA); xanthan gum and preservative in proper amount. Deionized water 100 g, so that the mass ratio of PHA to water phase is 1:4.

[0078] Preparation process parameters: water phase temperature 50°C; high-speed shearing stirring, speed 5000 rpm, processing time 10 minutes. High-energy homogenization treatment uses a high-pressure homogenizer, homogenization pressure 20 MPa, 1 cycle; and at the same time, an ultrasonic cell crusher can be selected, power 200 W, ultrasonic treatment 1 minute (Note: high-pressure homogenization and ultrasonic here are optional refinement methods, and this embodiment aims to demonstrate the feasibility of the lower limit of each single process parameter).

[0079] Post-processing: 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 microparticles account for 98.5 wt% of the total solid content by dry weight, and the dispersion stabilizing agent (mainly surfactant, a small amount of thickening agent and preservative) accounts 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. The specific performance parameters are shown in Table 2 and Table 3, Example 4.

[0081] Example 5: PHBV / PHBH blended nanometer aqueous suspension covering multiple upper parameter limits

[0082] This embodiment aims to verify the feasibility of the method of the present application when multiple parameters take their upper limit values.

[0083] Raw materials: PHBV powder (containing 10 mol% HV), 32 g; PHBH powder (Kaneka Corporation AONilex series, using a specification with 3HHx unit content of 10 mol%), 32 g (total PHA 64 g); polysorbate 80, 5.12 g (8.0 wt% of PHA); xanthan gum and preservative in proper amount. Deionized water 32 g, so that the mass ratio of PHA to water phase is 1:0.5.

[0084] Preparation process parameters: water phase temperature 95°C; high-speed shearing stirring, speed 20000 rpm, processing time 120 minutes. High-energy homogenization treatment uses a high-pressure homogenizer, homogenization pressure 150 MPa, 4 cycles; and at the same time, an ultrasonic cell crusher can be selected, power 1000 W, ultrasonic treatment 20 minutes (Note: high-pressure homogenization and ultrasonic here are optional refinement methods, and this embodiment aims to demonstrate the feasibility of the upper limit of each single process parameter).

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

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

[0087] Example 6: PHBV / PHBH blended nanometer aqueous suspension covering the lower limit of 3HV content

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

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

[0090] Post-treatment: Add calculated amount of xanthan gum to make the viscosity of the final suspension 1000 mPa-s at 25°C, and add preservatives. Adjust pH to 7.0.

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

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

[0093] Raw materials: PHBV powder, 3HV unit content 15mol%, Enmat Y1000 series product of Ningbo Tianan Biomaterials Co., Ltd., 50 grams; polysorbate 20 (Tween 20), CAS number 9005-64-5, Sigma-Aldrich product P1379, 2.5 grams; deionized water 75 grams.

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

[0095] Coarse dispersion: PHBV powder was directly added into deionized water with Tween 20 dissolved in it. The system was heated and maintained at 80°C. A high-speed shearing disperser, IKA T25 digital ULTRA-TURRAX, was used to stir at 12000 rpm for 60 minutes to form a coarse dispersion.

[0096] Refining homogenization: The coarse dispersion was cooled to 60°C and passed through a high-pressure homogenizer, ATS Engineering Inc. AH-BASIC, for 1 cycle at 30 MPa. The coarse dispersion was pre-cooled to 15°C before homogenization. The homogenization equipment was equipped with a cooling jacket to ensure that the material outlet temperature did not exceed 65°C.

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

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

[0099] Table 2 Composition and key performance parameters of PHA nanometer aqueous suspension of Examples

[0100]

[0101] Table 3 Key process parameters for the preparation of PHA nanometer aqueous suspension of Examples

[0102]

[0103] Note: US indicates ultrasonic treatment.

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

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

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

[0107] Application Example 1: Application as environmentally friendly adhesive for paper products

[0108] The PHA nano-aqueous suspension prepared by the present application can be used as environmentally friendly adhesive for paper products. To verify its bonding performance, each of the PHA nano-aqueous suspension prepared in Examples 1-6 was used to bond two pieces of corrugated paper board with basis weight of 80 g / m 2 . The specific operation was as follows: take the suspension of each example, uniformly coat it on the surface of one piece of corrugated paper board, control the coating amount at 100 g / m 2 wet weight, then adhere to another piece of corrugated paper board, apply 0.5 kg / cm 2 pressure at room temperature for 24 hours. Then test its T-type peel strength and peel strength after immersion. At the same time, the PHBV water dispersion prepared by Comparative Example 1 and the commercially available PVA white latex, such as Titebond Original Wood Glue of Franklin International, with typical solid content of 46% and viscosity of 3200 mPa·s, were used as control groups to perform the same test. The specific results are shown in Table 4.

[0109] Application Example 2: Application as barrier coating for paper food containers

[0110] The PHA nano-aqueous suspension prepared by the present application can be used as biodegradable barrier coating for paper food containers. To evaluate its barrier performance, each of the PHA nano-aqueous suspension prepared in Examples 1-6 was uniformly coated on the inner surface of food-grade white cardboard (basis weight of 250 g / m 2 ) without lamination treatment by a small-scale knife coater (coating gap of 200 μm), and the dry film thickness was controlled at 20 μm. The coated paper sample was dried in an oven at 100°C for 10 minutes. Then, the coated paper sample was tested for water vapor transmission rate (WVTR), water immersion durability and other performances. At the same time, the PHBV water dispersion prepared by Comparative Example 1 was used as a control group to perform the same coating preparation and test, and the performance was compared with that of traditional petroleum-based materials or uncoated paper. The specific results are shown in Table 4 and the description.

[0111] Table 4 Test results of application examples (coating and adhesive)

[0112]

[0113] Experimental results and analysis

[0114] Through Examples 1 to 6 and Comparative Example 1, the feasibility of preparing nano-aqueous suspension 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 Tables 2 and 3, it can be seen that:

[0116] Coverage of parameter ranges:

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

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

[0119] Dispersing stabilizer ratio: Example 4 (1.5 wt%) and Example 5 (20 wt%) cover the range of 1.5-20 wt%.

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

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

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

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

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

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

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

[0127] When applied as an adhesive, the paper-to-paper peel strength of Examples 1-6 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 superior to the dry peel strength of 3.5 N / 25 mm and the wet peel strength of 1.5 N / 25 mm (partially failed) of Comparative Example 1. Compared with the dry peel strength of 4.0 N / 25 mm and the complete failure after immersion of the conventional PVA white latex, the inventive examples also show comparable or superior levels. It is particularly important that the PHA materials prepared by all of the inventive examples and the PHA material used in Comparative Example 1 can be substantially degraded under 8-week composting conditions, which is in sharp contrast to the conventional PVA white latex, which is not biodegradable; and the inventive examples, with their excellent application performance, are more practically valuable in environmentally friendly applications than Comparative Example 1, which is also biodegradable but has poor performance.

[0128] These results above fully and directly demonstrate that the technical solution of the present application, through the selection of specific components and the optimization of process parameters, can effectively solve the challenges in the background art, achieve the preparation of the target PHA nanometer aqueous suspension in a wide range of parameters, and support the scope claimed by the present application and its beneficial effects.

[0129] The above examples are merely illustrative of the technical solutions of the present application, and are not intended to limit the scope thereof. Various modifications, equivalent replacements or variations of the above embodiments can be made by those skilled in the art without departing from the principles and spirit of the present application, and these modifications, equivalent replacements or variations shall all fall within the scope of protection defined by the claims of the present application.

Claims

1. A PHA nano-aqueous suspension, characterized in that: The PHA nano-aqueous suspension comprises polyhydroxyalkanoate PHA resin microparticles, dispersion stabilizing aids and water; 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 blended combination thereof; the total solid content of the suspension is 23-65 wt%, wherein the PHA resin microparticles account for 80-98.5 wt% of the total solid content by dry weight, the dispersion stabilizing aids account for 1.5-20 wt% of the total solid content by dry weight, and the sum of the two accounts for 100 wt% of the total solid content; the Z-Average average particle size of the PHA resin microparticles is 30-140 nm, D90≤150 nm, and the polydispersity index PDI<0.3, and the absolute value of Zeta potential at pH 6.5-7.5 is >30 mV.

2. The PHA nano-aqueous suspension according to claim 1, characterized by: When the PHA resin is PHBV, the 3-hydroxyvalerate 3HV unit content is 5-20 mol%; when the PHA resin is PHBH, the 3-hydroxyhexanoate 3HHx unit content is 6-12 mol%.

3. The PHA nano-aqueous suspension according to claim 1, characterized by: The dispersion stabilizing aids comprise a surfactant, a preservative and a thickening agent; the surfactant is selected from one or more combinations of non-ionic surfactants, anionic surfactants or block copolymers; the non-ionic surfactant is selected from polysorbate 20, polysorbate 80, polyvinyl alcohol with an alcoholysis degree of 87-89 mol% and a viscosity of 20-35 mPa·s in a 4% aqueous solution at 20℃, or polyvinyl alcohol with an alcoholysis degree of 87-89 mol% and a viscosity of 5-7 mPa·s in a 4% aqueous solution at 20℃; the anionic surfactant is sodium dodecyl sulfate; and the block copolymer is selected from one or more of pluronic F68 and pluronic P123.

4. The PHA nano-aqueous suspension of claim 1, characterized by: The viscosity of the suspension at 25℃ is 50-1000 mPa·s.

5. A process for the solvent-free preparation of a PHA nano-aqueous suspension as claimed in claim 1, characterized in that, The method comprises the following steps: Step a. pretreating the PHA resin to obtain pretreated PHA raw material, the pretreatment comprising freezing and grinding into micron-sized powder or heating to a molten state; Step b. adding the micron-sized powder or molten PHA raw material into an aqueous phase containing a surfactant, and stirring at a high speed shear rate of 5000-20000 rpm at 50-95℃ for 10-120 minutes to form a coarse emulsion or coarse dispersion; Step c. subjecting the coarse emulsion or coarse dispersion to high-energy homogenization treatment, the high-energy homogenization treatment being selected from high-pressure homogenization with a homogenization pressure of 20-150 MPa and 1-5 cycles of treatment, or ultrasonic dispersion with an ultrasonic power of 200-1000 W and a treatment time of 1-20 minutes, to refine the PHA particles to D90≤150 nm to obtain a PHA nano-dispersion comprising PHA resin microparticles; Step d. adding a thickening agent and a preservative to the PHA nano-dispersion comprising PHA resin microparticles obtained in step c, and mixing uniformly to obtain an intermediate PHA nano-aqueous suspension; and Step e. adding a preservative to the intermediate PHA nano-aqueous suspension obtained in step d, and mixing uniformly to obtain the PHA nano-aqueous suspension. Step e. adjusting the pH value of the intermediate PHA nano-aqueous suspension obtained in step d to 6.5-7.5, the solid content to 23-65wt%, and the viscosity measured at 25℃ to 50-1000mPa·s, to obtain the PHA nano-aqueous suspension.

6. The method of claim 5, wherein: In step d, the thickening agent is selected from one or more of xanthan gum, sodium carboxymethyl cellulose or associative thickening agent; the preservative is selected from one or a combination of methylisothiazolinone MIT, methylchloroisothiazolinone CMIT and benzisothiazolinone BIT complex or p-hydroxybenzoic acid ester preservative.

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

8. Use of the PHA nano-aqueous suspension according to claim 1 in the preparation of biodegradable water-based environmentally friendly coating.

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

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