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

Abstract

The invention discloses a method for preparing a modified polyhydroxyalkanoate (PHA) aqueous dispersion. Through a chemical modification method, PHA particles in a PHA aqueous dispersion are taken as a core, and the PHA particles are coated with a monomer polymer through an emulsion polymerization method. The PHA aqueous dispersion treated by the method is uniform in polarity among particles, does not have a layering phenomenon during storage, improves the stability of a PHA composite system, and has good water resistance and oil resistance.

Description

Technical Field

[0001] This invention relates to the field of waterborne coatings. More specifically, this invention relates to a PHA waterborne dispersion, its preparation method, and its application. Background Technology

[0002] Polyhydroxyalkanoates (PHA) are a class of natural high-molecular-weight polyesters synthesized by microorganisms through fermentation. They have gained wide application due to their biodegradability, biocompatibility, thermoplastic processability, and diversity of structure and varieties. One important application is to make PHA into an aqueous dispersion and use it as a barrier coating for paper to achieve water-blocking, oil-blocking, and oxygen-blocking effects.

[0003] To overcome the shortcomings of PHA materials, such as the lack of polar groups and poor adhesion to the substrate after film formation, one possible method is to physically mix and compound PHA aqueous dispersions with acrylic emulsions (including pure acrylic emulsions, styrene-acrylic emulsions, silicone-acrylic emulsions, vinyl acetate-acrylic emulsions, ethylene-acrylic emulsions, etc.) to improve the adhesion between the coating and the substrate.

[0004] PHA aqueous dispersions are physically mixed and compounded with acrylic emulsions (including pure acrylic emulsions, styrene-acrylic emulsions, silicone-acrylic emulsions, vinyl-acrylic emulsions, ethylene-acrylic emulsions, etc.) to improve the adhesion between the coating and the substrate.

[0005] However, acrylic emulsions generally have a particle size of nanometers (100-500 nanometers) and contain polar groups such as hydroxyl and carboxyl groups, while PHA aqueous dispersions generally have a particle size of micrometers (1-100 micrometers) and do not contain polar groups. The large difference in particle size and polarity between the two leads to instability of the system after compounding, which is prone to stratification. Specifically, the upper layer is a clear liquid, and the lower layer is a mixture of PHA aqueous dispersion and acrylic emulsion, which seriously affects the storage and use of PHA aqueous dispersion. Summary of the Invention

[0006] To address the aforementioned problems of PHA, the inventors have provided a method for preparing modified polyhydroxyalkanoates (PHA) aqueous dispersions. Specifically, this invention utilizes a chemical modification method, using PHA particles in the PHA aqueous dispersion as the core, and coats the PHA particles with monomeric polymers (e.g., acrylic polymers) via emulsion polymerization. The PHA aqueous dispersion treated in this way exhibits uniform polarity between particles, prevents stratification during storage, improves the stability of the PHA composite system, and possesses excellent water and oil blocking properties.

[0007] This invention provides a method for preparing an aqueous dispersion of modified polyhydroxy fatty acid ester (PHA), the method comprising the following steps:

[0008] 1) Disperse PHA powder in water to form an aqueous dispersion of PHA;

[0009] 2) Mix the monomer, emulsifier, and water to prepare a monomer emulsion;

[0010] 3) Mix the initiator and water to prepare an initiator aqueous solution; and

[0011] 4) The monomer emulsion and the initiator aqueous solution are added together to the PHA aqueous dispersion, mixed and subjected to emulsion polymerization to form the modified PHA aqueous dispersion.

[0012] In one specific embodiment, the emulsion polymerization reaction can be carried out at a certain temperature and time, such as 75-85°C for 45-120 minutes, to form a coating structure.

[0013] In one specific embodiment, the PHA includes one or a combination of two or more of the following: poly-3-hydroxybutyrate (PHB), poly-3-hydroxyvalerate (PHV), poly-3-hydroxypropionate (P3HP), a copolymer of 3-hydroxybutyric acid and 3-hydroxyvalerate (PHBV), poly-3-hydroxyoctanoate (PHO), poly-3-hydroxynonanoate (PHN), a copolymer of 3-hydroxybutyric acid and 4-hydroxybutyric acid (P34HB), a copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoate (PHBHHx), a copolymer of 3-hydroxybutyric acid, 4-hydroxybutyric acid and 3-hydroxyvalerate (P3HB4HB3HV), or a copolymer of 3-hydroxybutyric acid, 4-hydroxybutyric acid and 5-hydroxyvalerate (P3HB4HB5HV).

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

[0015] In one specific embodiment, the PHA is PHB, P34HB, PHBV, PHBHHx, P3HB4HB3HV, or a combination thereof, which satisfies one or more of the following conditions: 1) a molecular weight of 30 to 1,000,000 (Da) (e.g., 20, 30, 40, 50, 60, 70, 80, 90, and 1,000,000 Da); 2) a molecular weight distribution (PDI, Mw / Mn) of 1 to 2.3 (e.g., 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, and 2.3); and 3) a particle size of 3 to 20 micrometers (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 micrometers).

[0016] In one specific embodiment, the monomer is selected from styrene monomers, acrylic monomers, or combinations thereof. Preferably, the styrene monomer is selected from styrene, methylstyrene, or combinations thereof, and the acrylic monomer is selected from acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, hydroxyethyl acrylate, methyl methacrylate, hexafluorobutyl acrylate, or combinations thereof. Preferably, the weight ratio of the PHA aqueous dispersion to the monomer is 30-50 (e.g., 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50):30-50 (e.g., 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50).

[0017] In one specific embodiment, the emulsifier is selected from one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, polyoxyethylene (24EO) cholesterol ether, glyceryl monostearate, sodium polyacrylate, styrene-maleic anhydride ammonium salt, sorbitan monoglyceride, polysorbate, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, and sodium oleate. Preferably, the weight ratio of the PHA aqueous dispersion to the emulsifier is 30-50 (e.g., 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50): 0.5-10 (0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10).

[0018] In one specific embodiment, the initiator is selected from one or more of sodium persulfate, potassium persulfate, ammonium persulfate, benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, tert-butyl hydroperoxide, and sodium formaldehyde sulfoxylate. Preferably, the weight ratio of the PHA aqueous dispersion to the initiator is 30-50 (e.g., 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50): 0.1-1 (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0).

[0019] In one specific implementation, the solid content of the PHA aqueous dispersion in step 1) is 30% to 60% (e.g., 30%, 35%, 40%, 45%, 50%, 55% or 60%).

[0020] In one specific implementation, the weight ratio of monomer, emulsifier and water in step 2) is 30-50 (e.g. 30 / 35 / 40 / 45 / 50): 0.5-10 (e.g. 0.5 / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10): 10-20 (e.g. 10 / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18 / 19 / 20).

[0021] In one specific implementation, the weight ratio of the initiator to water in step 3) is 0.1-1 (e.g., 0.1 / 0.2 / 0.3 / 0.4 / 0.5 / 0.6 / 0.7 / 0.8 / 0.9 / 1.0):1-2 (e.g., 1.0 / 1.5 / 2.0).

[0022] In one specific implementation, in step 4), a rheology modifier, a bactericide, or a combination thereof is also added to the PHA aqueous dispersion.

[0023] In one specific embodiment, the rheology modifier is selected from one or more of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, alkali-swellable acrylic thickener, xanthan gum, guar gum, sodium alginate, bentonite, and polyurethane rheology modifier. Preferably, the weight ratio of the PHA aqueous dispersion to the rheology modifier is 30-50 (e.g., 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50): 1-5 (1, 2, 3, 4, 5).

[0024] In one specific embodiment, the bactericide is selected from one or more of ethylenediaminetetraacetic acid, benzisothiazolinone, zinc oxide, benzalkonium chloride, methylisothiazolinone, methylchloroisothiazolinone, and 2,2-dibromopropionamide. Preferably, the weight ratio of the PHA aqueous dispersion to the bactericide is 30-50 (e.g., 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50): 0.1-1 (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0).

[0025] In one specific embodiment, the total weight ratio of the PHA aqueous dispersion to the water used to prepare the monomer emulsion and the initiator aqueous solution is 30-50 (e.g., 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50): 10-20 (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20).

[0026] In one specific embodiment, the modified PHA aqueous dispersion comprises 30-50 parts (by weight, the same below) of PHA aqueous dispersion, 30-50 parts of styrene and acrylic monomers combined, 10-20 parts of water for monomer emulsification and initiator dissolution, 0.1-1 part of initiator, 0.5-10 parts of emulsifier, 1-5 parts of rheology modifier, and 0.1-1 part of bactericide.

[0027] In one specific implementation, the method includes: weighing each component according to the mass ratio, adding the PHA aqueous dispersion to a reaction vessel, turning on the stirrer and heating to 75-85 degrees Celsius, mixing the monomer, emulsifying water, and emulsifier at high speed to form a monomer emulsion, dissolving the initiator in water to form an initiator aqueous solution, and slowly adding the monomer emulsion and the initiator aqueous solution dropwise together to the reaction vessel, with a total dropwise addition time of 2-4 hours, maintaining the temperature for 1-2 hours, cooling to below 40 degrees Celsius, adding a rheology modifier and a bactericide, and mixing at low speed for 10-30 minutes to obtain a PHA aqueous dispersion with good stability.

[0028] In one specific embodiment, the PHA is PHB, the monomer is a mixture of butyl acrylate and methyl acrylate, the initiator is sodium persulfate, the emulsifier is sorbitan monoglyceride, the bactericide is benzisothiazolinone, and the rheology modifier is an alkali-swellable acrylic thickener. In a preferred embodiment, the modified PHA aqueous dispersion is formulated as follows: 50 parts of PHB aqueous dispersion, 30 parts of a mixture of butyl acrylate and methyl acrylate, 8 parts of emulsifying water, 0.1 parts of sodium persulfate, 2 parts of water for dissolving sodium persulfate, 0.5 parts of sorbitan monoglyceride, 1 part of benzisothiazolinone, and 5 parts of an alkali-swellable acrylic thickener.

[0029] In one specific embodiment, the PHA is P34HB, the monomer is a mixture of styrene, ethyl acrylate, and isooctyl acrylate, the initiator is potassium persulfate, the emulsifier is octylphenol polyoxyethylene ether, the bactericide is methylchloroisothiazolinone, and the rheology modifier is carboxymethyl cellulose. In a preferred embodiment, the formulation of the modified PHA aqueous dispersion includes: 30 parts of P34HB aqueous dispersion, 40 parts of a mixture of styrene, ethyl acrylate, and isooctyl acrylate, 15 parts of emulsifying water, 0.5 parts of potassium persulfate, 5 parts of water for dissolving potassium persulfate, 10 parts of octylphenol polyoxyethylene ether, 0.1 parts of methylchloroisothiazolinone, and 1 part of carboxymethyl cellulose.

[0030] In one specific embodiment, the PHA is PHBV, the monomer is a mixture of styrene, acrylic acid, and butyl acrylate, the initiator is ammonium persulfate, the emulsifier is sodium dodecyl sulfate, the bactericide is methylchloroisothiazolinone, and the rheology modifier is xanthan gum. In a preferred embodiment, the formulation of the modified PHA aqueous dispersion includes: 40 parts of PHBV aqueous dispersion, 30 parts of a mixture of styrene, acrylic acid, and butyl acrylate, 10 parts of emulsifying water, 1 part of ammonium persulfate, 5 parts of water for dissolving ammonium persulfate, 5 parts of sodium dodecyl sulfate, 0.3 parts of methylchloroisothiazolinone, and 5 parts of xanthan gum.

[0031] In one specific embodiment, the PHA is PHBHHx, the monomer is a mixture of methacrylic acid, methyl methacrylate, and butyl acrylate, the initiator is benzoyl peroxide, the emulsifier is sodium dodecylbenzenesulfonate, the bactericide is zinc oxide, and the rheology modifier is bentonite. In a preferred embodiment, the formulation of the modified PHA aqueous dispersion includes: 35 parts of PHBHHx aqueous dispersion, 45 parts of a mixture of methacrylic acid, methyl methacrylate, and butyl acrylate, 10 parts of emulsifying water, 1 part of benzoyl peroxide, 3 parts of benzoyl peroxide dissolving water, 3 parts of sodium dodecylbenzenesulfonate, 0.3 parts of zinc oxide, and 3 parts of bentonite.

[0032] In one specific embodiment, the PHA is P3HB4HB3HV, the monomer is a mixture of acrylic acid, methyl methacrylate, and ethyl acrylate, the initiator is dicumyl peroxide, the emulsifier is sodium oleate, the bactericide is 2,2-dibromopropionamide, and the rheology modifier is a polyurethane rheology modifier. In a preferred embodiment, the formulation of the modified PHA aqueous dispersion includes: 40 parts of P3HB4HB3HV aqueous dispersion, 35 parts of a mixture of acrylic acid, methyl methacrylate, and ethyl acrylate, 12 parts of emulsifying water, 1 part of dicumyl peroxide, 3 parts of dicumyl peroxide dissolving water, 5 parts of sodium oleate, 0.3 parts of 2,2-dibromopropionamide, and 5 parts of polyurethane rheology modifier.

[0033] Another aspect of the present invention provides an aqueous dispersion of modified polyhydroxy fatty acid ester (PHA) prepared by the method according to the present invention.

[0034] In another aspect, the present invention provides the application of the modified PHA aqueous dispersion according to the present invention in the preparation of aqueous coatings or as an aqueous coating.

[0035] In one specific implementation, the application includes coating the substrate surface (using a scraper, wire bar, air knife, spraying, etc.) and then drying it at a temperature of 110-180°C for 30-120 seconds.

[0036] The beneficial effects of this invention are:

[0037] A) The PHA aqueous dispersion treated by this method has uniform polarity between particles, and no stratification occurs during storage, which improves the stability of the PHA composite system as well as its water and oil blocking properties.

[0038] B) The production process is simple and has broad application prospects. Attached Figure Description

[0039] The above features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0040] Figure 1 The images show the layers before modification, with comparative examples 1-5 from left to right.

[0041] Figure 2 The images show the modified layers, with Examples 1-5 from left to right. Detailed Implementation

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0043] Unless otherwise indicated, the terms used herein have their general technical meanings as understood by those skilled in the art.

[0044] In this invention, the singular articles “a” and “the” cover a plurality of indicators unless the context clearly indicates otherwise. All references cited herein are incorporated herein by reference in their entirety.

[0045] The use of "comprising" or "including" in this invention is an open-ended description that includes all specified components or steps described, as well as other specified components or steps that do not materially affect the description.

[0046] The term "and / or" as used in this invention encompasses all combinations of items connected by the term, and should be considered as if each combination had been individually listed herein. For example, "A and / or B" includes "A", "A and B", and "B". As another example, "A, B and / or C" includes "A", "B", "C", "A and B", "A and C", "B and C", and "A and B and C".

[0047] The present invention is further illustrated in the following embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, the reagents, materials, etc., used in the embodiments are commercially available. All quantitative experiments were performed in triplicate, and the results were averaged. In the embodiments, "parts" refers to parts by weight / parts by mass unless the context otherwise indicates.

[0048] Example 1

[0049] Formulation composition: 50 parts of PHB (Beijing Microstructure Workshop Biotechnology Co., Ltd.) aqueous dispersion (50% solids content, Mw = 750,000, PDI = 2.3), 30 parts of a mixture of butyl acrylate and methyl acrylate (weight ratio = 1:1), 8 parts of emulsifying water, 0.1 parts of sodium persulfate, 2 parts of water for dissolving sodium persulfate, 0.5 parts of dehydrated sorbitan monoglyceride (Maclean's reagent), 1 part of benzisothiazolinone (Sinopharm Group), and 5 parts of alkali-swellable acrylic thickener (Dow).

[0050] Preparation: Weigh each component according to the mass ratio. Add the PHB aqueous dispersion to the reaction vessel, turn on the stirrer and heat to 75°C. Mix the monomer mixture, emulsifying water, and dehydrated sorbitan monoglyceride at high speed to form a monomer emulsion. Dissolve sodium persulfate in water to form an initiator aqueous solution. Slowly add the monomer emulsion and the initiator aqueous solution together to the reaction vessel. The total adding time is 2 hours, and the temperature is maintained for 1 hour. Cool down to below 40°C, add the alkali-swellable acrylic thickener and benzisothiazolinone, and mix at low speed for 10 minutes to obtain a PHA aqueous dispersion with good stability.

[0051] Stability test: Weigh 50 ml of the prepared PHB aqueous dispersion and place it in a 50 ml centrifuge tube. Let it stand for 7 days, observe whether it separates into layers, and measure the height of the supernatant.

[0052] Application: Apply the coating to the substrate surface using methods such as scraper, wire bar, air knife, or spraying, and then dry it at 180℃ for 30 seconds.

[0053] Example 2

[0054] Formulation composition: 30 parts of P34HB (Beijing Microstructure Workshop Biotechnology Co., Ltd.) aqueous dispersion (30% solid content, Mw = 300,000, PDI = 2.0), 40 parts of a mixture of styrene, ethyl acrylate, and isooctyl acrylate (weight ratio of the three = 2:1:1), 15 parts of emulsifying water, 0.5 parts of potassium persulfate, 5 parts of water for dissolving potassium persulfate, 10 parts of octylphenol polyoxyethylene ether (Dow), 0.1 parts of methylchloroisothiazolinone (Sinopharm Group), and 1 part of carboxymethyl cellulose (Maclean's reagent).

[0055] Preparation: Weigh each component according to the mass ratio. Add the P34HB aqueous dispersion to the reactor, turn on the stirrer and heat to 85°C. Mix the monomer mixture, emulsifying water, and octylphenol polyoxyethylene ether at high speed to form a monomer emulsion. Dissolve potassium persulfate in water to form an initiator aqueous solution. Slowly add the monomer emulsion and the initiator aqueous solution to the reactor together. The total adding time is 4 hours, and the temperature is maintained for 2 hours. Cool down to below 40°C, add carboxymethyl cellulose and methylchloroisothiazolinone, and mix at low speed for 30 minutes to obtain a PHA aqueous dispersion with good stability.

[0056] Stability test: Weigh 50 ml of P34HB aqueous dispersion, place it in a 50 ml centrifuge tube and let it stand for 7 days. Observe whether it separates into layers and measure the height of the supernatant.

[0057] Application: Apply the coating to the substrate surface using methods such as scraper, wire bar, air knife, or spraying, and then dry it at 150℃ for 60 seconds.

[0058] Example 3

[0059] Formula composition: 40 parts of PHBV (Beijing Microstructure Workshop Biotechnology Co., Ltd.) aqueous dispersion (solid content 40%, Mw = 650,000, PDI = 1.8), 30 parts of a mixture of styrene, acrylic acid, and butyl acrylate (weight ratio 5:1:4), 10 parts of emulsifying water, 1 part of ammonium persulfate, 5 parts of ammonium persulfate dissolving water, 5 parts of sodium dodecyl sulfate (Maclean's reagent), 0.3 parts of methylchloroisothiazolinone (Sinopharm Group), and 5 parts of xanthan gum (Tongchao Biotechnology).

[0060] Preparation: Weigh each component according to the mass ratio. Add the PHBV aqueous dispersion to the reactor, turn on the stirrer and heat to 80°C. Mix the monomer mixture, emulsifying water, and sodium dodecyl sulfate at high speed to form a monomer emulsion. Dissolve ammonium persulfate in water to form an initiator aqueous solution. Slowly add the monomer emulsion and the initiator aqueous solution together to the reactor. The total adding time is 3 hours, and the temperature is maintained for 1.5 hours. Cool down to below 40°C, add xanthan gum and methylchloroisothiazolinone, and mix at low speed for 20 minutes to obtain a PHA aqueous dispersion with good stability.

[0061] Stability test: Weigh 50 ml of PHBV aqueous dispersion, place it in a 50 ml centrifuge tube and let it stand for 7 days. Observe whether it separates into layers and measure the height of the supernatant.

[0062] Application: Apply the coating to the substrate surface using methods such as scraper, wire bar, air knife, or spraying, and then dry it at 160℃ for 90 seconds.

[0063] Example 4

[0064] Formula composition: 35 parts of PHBHHx (Beijing Microstructure Workshop Biotechnology Co., Ltd.) aqueous dispersion (solid content 45%, Mw = 420,000, PDI = 2.2), 45 parts of a mixture of methacrylic acid, methyl methacrylate, and butyl acrylate (weight ratio = 1:6:3), 10 parts of emulsifying water, 1 part of benzoyl peroxide, 3 parts of benzoyl peroxide dissolving water, 3 parts of sodium dodecylbenzenesulfonate (Maclean's reagent), 0.3 parts of zinc oxide, and 3 parts of bentonite (United Micro Powder).

[0065] Preparation: Weigh each component according to the mass ratio. Add the PHBHHx aqueous dispersion to the reactor, turn on the stirrer and heat to 83°C. Mix the monomer mixture, emulsifying water, and sodium dodecylbenzenesulfonate at high speed to form a monomer emulsion. Dissolve benzoyl peroxide in water to form an initiator aqueous solution. Slowly add the monomer emulsion and the initiator aqueous solution to the reactor together. The total adding time is 1.5 hours, and the temperature is maintained for 2 hours. Cool down to below 40°C, add bentonite and zinc oxide, and mix at low speed for 15 minutes to obtain a PHA aqueous dispersion with good stability.

[0066] Stability test: Weigh 50 ml of PHBHHx aqueous dispersion and place it in a 50 ml centrifuge tube. Let it stand for 7 days, observe whether it separates into layers, and measure the height of the supernatant.

[0067] Application: Apply the coating to the substrate surface using methods such as scraper, wire bar, air knife, or spraying, and then dry it at 140℃ for 50 seconds.

[0068] Example 5

[0069] Formulation composition: 40 parts of P3HB4HB3HV (Beijing Microstructure Workshop Biotechnology Co., Ltd.) aqueous dispersion (35% solids content, Mw = 530,000, PDI = 2.1), 35 parts of a mixture of acrylic acid, methyl methacrylate, and ethyl acrylate (weight ratio = 1:7:2), 12 parts of emulsifying water, 1 part of dicumyl peroxide (Merck Chemicals), 3 parts of dicumyl peroxide dissolving water, 5 parts of sodium oleate, 0.3 parts of 2,2-dibromopropionamide (Maclean's reagent), and 5 parts of polyurethane rheology modifier (Dow).

[0070] Preparation: Weigh each component according to the mass ratio. Add the P3HB4HB3HV aqueous dispersion to the reactor, start stirring and heat to 78°C. Mix the monomer mixture, emulsifying water, and sodium oleate at high speed to form a monomer emulsion. Dissolve dicumyl peroxide in water to form an initiator aqueous solution. Slowly add the monomer emulsion and the initiator aqueous solution to the reactor together. The total adding time is 1.5 hours, and the temperature is maintained for 1.5 hours. Cool down to below 40°C, add polyurethane rheology modifier and 2,2-dibromopropionamide, and mix at low speed for 10 minutes to obtain a PHA aqueous dispersion with good stability.

[0071] Stability test: Weigh 50 ml of PHA aqueous complex dispersion, place it in a 50 ml centrifuge tube and let it stand for 7 days. Observe whether it separates into layers and measure the height of the supernatant.

[0072] Application: Apply the coating to the substrate surface using a scraper, wire bar, air knife, spraying, or other methods, followed by drying at 110℃ for 120 seconds.

[0073] Unless otherwise stated, the components / reagents and operating procedures used in the following comparative examples are the same as those in Examples 1 to 5 above.

[0074] Comparative Example 1

[0075] Formula composition: 50 parts of PHB aqueous dispersion, 30 parts of pure acrylic emulsion (Wanhua Chemical, Wantipro0208), 1 part of benzisothiazolinone, and 5 parts of alkali-swellable acrylic thickener.

[0076] Preparation: Weigh each component according to the mass ratio, and add PHB aqueous dispersion, pure acrylic emulsion, benzisothiazolinone, and alkali-swellable acrylic thickener in sequence, and mix at low speed for 10 min.

[0077] Stability test: Weigh 50 ml of PHA aqueous complex dispersion, place it in a 50 ml centrifuge tube and let it stand for 7 days. Observe whether it separates into layers and measure the height of the supernatant.

[0078] Comparative Example 2

[0079] Formulation composition: 30 parts of P34HB aqueous dispersion, 40 parts of styrene-acrylic emulsion (Wanhua Chemical, Wantipro0205), 0.1 parts of methylchloroisothiazolinone, and 1 part of carboxymethyl cellulose.

[0080] Preparation: Weigh each component according to the mass ratio, add P34HB aqueous dispersion, styrene-acrylic emulsion, methylchloroisothiazolinone, carboxymethyl cellulose in sequence, and mix at low speed for 30 min.

[0081] Stability test: Weigh 50 ml of PHA aqueous complex dispersion, place it in a 50 ml centrifuge tube and let it stand for 7 days. Observe whether it separates into layers and measure the height of the supernatant.

[0082] Comparative Example 3

[0083] The PHA aqueous dispersion consists of: 40 parts of PHBV aqueous dispersion, 30 parts of styrene-acrylic emulsion (Wanhua Chemical, Wantipro 0205), 0.3 parts of methylchloroisothiazolinone, and 5 parts of xanthan gum.

[0084] Preparation of PHA aqueous dispersion: Weigh each component according to the mass ratio, add PHBV aqueous dispersion, styrene-acrylic emulsion, methylchloroisothiazolinone, and xanthan gum in sequence, and mix at low speed for 20 min.

[0085] Stability test: Weigh 50 ml of PHA aqueous complex dispersion, place it in a 50 ml centrifuge tube and let it stand for 7 days. Observe whether it separates into layers and measure the height of the supernatant.

[0086] Comparative Example 4

[0087] The PHA aqueous dispersion consists of 35 parts of PHBHHx aqueous dispersion, 45 parts of pure acrylic emulsion (Wanhua Chemical, Wantipro0208), 0.3 parts of zinc oxide, and 3 parts of bentonite.

[0088] Preparation of PHA aqueous dispersion: Weigh each component according to the mass ratio, add PHBHHx aqueous dispersion, pure acrylic emulsion, zinc oxide and bentonite in sequence, and mix at low speed for 15 min.

[0089] Stability test: Weigh 50 ml of PHA aqueous complex dispersion, place it in a 50 ml centrifuge tube and let it stand for 7 days. Observe whether it separates into layers and measure the height of the supernatant.

[0090] Comparative Example 5

[0091] The PHA aqueous dispersion consists of: 40 parts of P3HB4HB3HV aqueous dispersion, 35 parts of pure acrylic emulsion (Wanhua Chemical, Wantipro0208), 0.3 parts of 2,2-dibromopropionamide, and 5 parts of polyurethane rheology modifier.

[0092] Preparation of PHA aqueous dispersion: Weigh each component according to the mass ratio, and add P3HB4HB3HV aqueous dispersion, pure acrylic emulsion, 2,2-dibromopropionamide and polyurethane rheology modifier in sequence, and mix at low speed for 10 min.

[0093] Stability test: Weigh 50 ml of PHA aqueous complex dispersion, place it in a 50 ml centrifuge tube and let it stand for 7 days. Observe whether it separates into layers and measure the height of the supernatant.

[0094] Table 1 below shows the stability test results for Examples 1 to 5 and Comparative Examples 1 to 5. See also... Figure 1 and Figure 2 .

[0095] Table 1

[0096]

[0097] To demonstrate that the modified PHA aqueous dispersion of the present invention, while addressing stability issues, does not significantly alter or even improve its performance as a coating (e.g., water and oil resistance), water and oil resistance properties were tested on the dispersions prepared in Examples 1 to 5 and Comparative Examples 1 to 5. Water resistance was tested according to GB / T 1540-2002, and oil resistance was tested according to GB / T 22805.2-2008. The data are shown in the table below. Cobb1800 represents the Cobb value at 1800 seconds (in g / m²), with a smaller value indicating better water resistance. The kit value represents oil resistance, ranging from 1 to 12, with a larger value indicating better oil resistance. Table 2 shows that the dispersions prepared in Examples 1 to 5 exhibited better water and oil resistance properties compared to Comparative Examples 1 to 5.

[0098] Table 2

[0099]

[0100] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0101] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, and should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing an aqueous dispersion of modified polyhydroxy fatty acid ester (PHA), the method comprising the following steps: 1) Disperse PHA powder in water to form an aqueous dispersion of PHA; 2) Mix the monomer, emulsifier, and water to prepare a monomer emulsion; 3) Mix the initiator and water to prepare an initiator aqueous solution; and 4) The monomer emulsion and the initiator aqueous solution are added together to the PHA aqueous dispersion, mixed and subjected to emulsion polymerization to form the modified PHA aqueous dispersion.

2. The method according to claim 1, wherein the monomer is selected from styrene monomers, acrylic monomers, or combinations thereof, preferably, the styrene monomer is selected from styrene, methylstyrene, or combinations thereof, and the acrylic monomer is selected from acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, hydroxyethyl acrylate, methyl methacrylate, hexafluorobutyl acrylate, or combinations thereof, preferably the weight ratio of the PHA aqueous dispersion to the monomer is 30-50:30-50.

3. The method according to claim 1 or 2, wherein the emulsifier is selected from one or more of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, polyoxyethylene (24EO) cholesterol ether, glyceryl monostearate, sodium polyacrylate, styrene-maleic anhydride ammonium salt, sorbitan monoglyceride, polysorbate, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, and sodium oleate, preferably the weight ratio of the PHA aqueous dispersion to the emulsifier is 30-50:0.5-10.

4. The method according to any one of claims 1 to 3, wherein the initiator is selected from one or more of sodium persulfate, potassium persulfate, ammonium persulfate, benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, tert-butyl hydroperoxide, and sodium formaldehyde sulfoxylate, preferably the weight ratio of the PHA aqueous dispersion to the initiator is 30-50:0.1-1.

5. The method according to any one of claims 1 to 4, wherein: A) The solid content of the PHA aqueous dispersion in step 1) is 30% to 60%; B) The weight ratio of monomer, emulsifier and water in step 2) is 30-50:0.5-10:10-20; C) The weight ratio of the initiator to water in step 3) is 0.1-1:1-2; and / or D) In ​​step 4), a rheology modifier, a bactericide, or a combination thereof are also added to the PHA aqueous dispersion.

6. The method according to claim 5, wherein the rheology modifier is selected from one or more of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, alkali-swellable acrylic thickener, xanthan gum, guar gum, sodium alginate, bentonite, and polyurethane rheology modifier, preferably the weight ratio of the PHA aqueous dispersion to the rheology modifier is 30-50:1-5.

7. The method according to claim 5 or 6, wherein the bactericide is selected from one or more of ethylenediaminetetraacetic acid, benzisothiazolinone, zinc oxide, benzalkonium chloride, methylisothiazolinone, methylchloroisothiazolinone, and 2,2-dibromopropionamide, preferably the weight ratio of the PHA aqueous dispersion to the bactericide is 30-50:0.1-1.

8. The method according to any one of claims 1 to 7, wherein the total weight ratio of the PHA aqueous dispersion to the water used to prepare the monomer emulsion and the initiator aqueous solution is 30-50:10-20.

9. A modified polyhydroxy fatty acid ester (PHA) aqueous dispersion prepared by the method according to any one of claims 1 to 8.

10. The application of the modified PHA aqueous dispersion according to claim 9 in the preparation of aqueous coatings.

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