Polyhydroxyalkanoate powder, method for producing same and use thereof

Abstract

This polyhydroxyalkanoate powder contains a polyhydroxyalkanoate (A), a polyvinyl alcohol (B), and an alkylene oxide compound (C). The content of the polyvinyl alcohol (B) is 1.0 parts by weight or more and less than 3.0 parts by weight with respect to 100 parts by weight of the polyhydroxyalkanoate (A). The powder can be produced by spray-drying an aqueous suspension containing the polyhydroxyalkanoate (A), the polyvinyl alcohol (B), and the alkylene oxide compound (C). An aqueous suspension of the polyhydroxyalkanoate powder can be produced by dispersing the powder in an aqueous medium.

Description

Polyhydroxyalkanoate powder, its production method and use

[0001] The present invention relates to polyhydroxyalkanoate powder, its preparation method and use.

[0002] Polyhydroxyalkanoates (hereinafter referred to as PHA) have excellent seawater degradability and have attracted attention as resins that can solve the problem of microplastics in the marine environment. One type of PHA is known to be poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0003] Considering the cost of transporting PHA and maintaining its quality, it is generally more desirable to transport PHA as a PHA powder than as a slurry (hereinafter also referred to as an "aqueous suspension").

[0004] Such PHA powder can be redispersed in an aqueous medium to form a slurry again, which can then be applied to a substrate and dried by heating to form a PHA resin layer.

[0005] Patent Document 1 discloses a PHA powder that exhibits good redispersibility when redispersed in an aqueous medium and good film-forming properties when the slurry is applied. In an example of this document, it is disclosed that the PHA powder is produced by adding 3.0 parts by weight of polyvinyl alcohol to 100 parts by weight of PHA and then spray-drying the mixture.

[0006] International Publication No. 2023 / 149511

[0007] The present inventors redispersed the PHA powder disclosed in Patent Document 1 in an aqueous medium to form the above-mentioned PHA resin layer, and found that, depending on the conditions, some substances may leach out from the resin layer. Such leach-out is undesirable, particularly in applications that come into contact with food.

[0008] In response to this issue, we discovered that reducing the amount of polyvinyl alcohol used in producing PHA powder could suppress the elution of the above-mentioned substances. However, in this case, a new problem arose: the dispersibility of the PHA powder decreased when it was redispersed in an aqueous medium.

[0009] In view of the above-mentioned current situation, an object of the present invention is to provide a polyhydroxyalkanoate powder that has good dispersibility in an aqueous medium and is capable of suppressing the elution of substances.

[0010] The inventors discovered that when producing PHA powder, by reducing the amount of polyvinyl alcohol used and by using a specific dispersant in combination, it is possible to suppress the leaching of substances while maintaining good dispersibility of the PHA powder, and thus completed the present invention.

[0011] Specifically, the present invention relates to a polyhydroxyalkanoate powder containing a polyhydroxyalkanoate (A), a polyvinyl alcohol (B), and an alkylene oxide compound (C), wherein the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A). The present invention also relates to a method for producing a polyhydroxyalkanoate powder, comprising the steps of preparing an aqueous suspension and spray-drying the aqueous suspension, wherein the aqueous suspension contains a polyhydroxyalkanoate (A), a polyvinyl alcohol (B), and an alkylene oxide compound (C), wherein the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A). The present invention also relates to an aqueous suspension of a polyhydroxyalkanoate powder containing the polyhydroxyalkanoate powder and an aqueous medium. The present invention also relates to a method for producing an aqueous suspension of polyhydroxyalkanoate powder, which includes a step of dispersing the polyhydroxyalkanoate powder in an aqueous medium. The present invention also relates to a laminate comprising a substrate layer and a resin layer provided on at least one surface of the substrate layer, the resin layer containing polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), wherein the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A). The present invention also relates to a method for producing a laminate, which includes a step of dispersing the polyhydroxyalkanoate powder in an aqueous medium to prepare an aqueous suspension, and a step of applying the aqueous suspension to at least one surface of a substrate and drying it by heating to form a resin layer on the substrate.

[0012] According to the present invention, it is possible to provide a polyhydroxyalkanoate powder that has good dispersibility in an aqueous medium and is capable of suppressing elution of substances.

[0013] The polyhydroxyalkanoate powder can be dispersed in an aqueous medium to produce an aqueous suspension of the polyhydroxyalkanoate powder, which exhibits good dispersibility in the aqueous medium during the production process.

[0014] The aqueous suspension is applied to a substrate and then dried by heating, thereby producing a laminate in which a resin layer containing polyhydroxyalkanoate is formed on the substrate. The elution of substances from the resin layer of the produced laminate can be suppressed to a low level.

[0015] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0016] [Polyhydroxyalkanoate Powder] One embodiment of the present invention relates to a polyhydroxyalkanoate powder (hereinafter also referred to as PHA powder) containing a polyhydroxyalkanoate (A), a polyvinyl alcohol (B), and an alkylene oxide compound (C).

[0017] [Polyhydroxyalkanoate (A)] The polyhydroxyalkanoate (A) is a homopolymer or copolymer having at least one or more hydroxyalkanoate units as a constituent monomer unit. Hereinafter, the polyhydroxyalkanoate is also referred to as PHA.

[0018] The hydroxyalkanoate unit preferably contains a unit represented by the following general formula (1): [—CHR—CH ２ -CO-O-] (1)

[0019] In the general formula (1), R is C ｐ H ２ｐ＋１ where p is an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as methyl, ethyl, propyl, methylpropyl, butyl, isobutyl, t-butyl, pentyl, and hexyl. p is preferably an integer of 1 to 10, and more preferably an integer of 1 to 8.

[0020] As the PHA, a PHA produced from a microorganism is particularly preferred. In a PHA produced from a microorganism, all of the hydroxyalkanoate units are contained as (R)-hydroxyalkanoate units.

[0021] The PHA preferably contains 3-hydroxyalkanoate units (particularly units represented by general formula (1)) in an amount of 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of the total constituent monomer units. The PHA may contain only one or more types of 3-hydroxyalkanoate units as the constituent monomer units of the polymer, or may contain one or more types of 3-hydroxyalkanoate units as well as other units (e.g., 4-hydroxyalkanoate units).

[0022] From the viewpoints of biodegradability, mechanical properties, productivity, etc., the PHA is preferably a homopolymer of 3-hydroxybutyrate (hereinafter also referred to as 3HB) units or a copolymer containing 3HB units and other hydroxyalkanoate units, and more preferably contains at least such a copolymer. Preferably, the 3-hydroxybutyrate units are all (R)-3-hydroxybutyrate units.

[0023] The other hydroxyalkanoate units may be 3-hydroxyalkanoate units other than 3HB units, or may be hydroxyalkanoate units other than 3-hydroxyalkanoate units (for example, 4-hydroxyalkanoate units). Only one type of other hydroxyalkanoate unit may be included, or two or more types may be included.

[0024] Specific examples of PHA (A) include poly(3-hydroxybutyrate) (abbreviation: P3HB), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HH), poly Examples of suitable poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB), etc. In particular, from the viewpoints of productivity and mechanical properties, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred, with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) being particularly preferred.

[0025] By changing the composition ratio of 3HB units and 3-hydroxyhexanoate (hereinafter also referred to as 3HH) units, the melting point and crystallinity of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) can be changed, and as a result, physical properties such as Young's modulus and heat resistance can be changed, making it possible to impart physical properties between those of polypropylene and polyethylene.

[0026] The PHA (A) may contain at least two types of PHAs having different crystallinity, specifically, at least two types of PHAs having different types of constituent monomers and / or different content ratios of the constituent monomers.

[0027] The average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in all monomer units constituting the entire PHA (A) according to the present embodiment is not particularly limited, but from the viewpoints of mechanical properties, dispersibility, coatability, and suppression of dripping after coating, 3-hydroxybutyrate units / other hydroxyalkanoate units=100 / 0 to 80 / 20 (mol % / mol %) is preferred, 99 / 1 to 84 / 16 (mol % / mol %) is more preferred, 98 / 2 to 86 / 14 (mol % / mol %) is even more preferred, and 97 / 3 to 88 / 12 (mol % / mol %) is even more preferred.

[0028] The average content ratio of each monomer unit in all monomer units constituting the entire PHA (A) can be determined by a method known to those skilled in the art, for example, the method described in paragraph

[0047] of WO 2013 / 147139. The average content ratio means the molar ratio of each monomer unit in all monomer units constituting the entire PHA, and when the PHA is a mixture of two or more resins, it means the molar ratio of each monomer unit in all monomer units contained in the mixture.

[0029] The weight-average molecular weight (hereinafter also referred to as Mw) of PHA (A) is not particularly limited, but from the viewpoints of mechanical properties, processability, dispersibility, coatability, and suppression of dripping after coating, it is preferably 100,000 to 1,000,000, more preferably 150,000 to 900,000, and even more preferably 200,000 to 800,000. When the weight-average molecular weight is 100,000 or more, sufficient mechanical properties and the like can be obtained, and when it is 1,000,000 or less, a sufficient crystallization rate can be obtained and good processability can be achieved. The weight-average molecular weight of PHA (A) can be determined as the molecular weight in terms of polystyrene by gel permeation chromatography (GPC) (Shodex GPC-101 manufactured by Showa Denko K.K.) using a polystyrene gel (Shodex K-804 manufactured by Showa Denko K.K.) as a column and chloroform as the mobile phase.

[0030] PHAs can be produced, for example, from microorganisms capable of producing PHA intracellularly. For example, microorganisms isolated from nature and deposited in a depository institution for strains (e.g., IFO, ATCC, etc.), or mutants and transformants prepared from them, can be used. For example, the first microorganism to produce P3HB, an example of PHA, was Bacillus megaterium, discovered in 1925. Other examples include naturally occurring microorganisms such as Cupriavidus necator (formerly classified as Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. It is known that PHA accumulates intracellularly in these microorganisms.

[0031] Examples of bacteria that produce copolymers of 3-hydroxybutyrate and other hydroxyalkanoates, which are examples of PHAs, include Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligenes eutrophus, which produces P3HB4HB. In particular, with regard to P3HB3HH, more preferred is Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)), into which genes encoding PHA synthases have been introduced, in order to increase the productivity of P3HB3HH. In addition to the above, the bacterial cells may be genetically modified microorganisms into which various PHA synthesis-related genes have been introduced depending on the PHA to be produced.

[0032] PHA can also be produced by, for example, the method described in International Publication No. 2010 / 013483. Commercially available PHA products include Kaneka Biodegradable Polymer Green Planet (registered trademark) manufactured by Kaneka Corporation.

[0033] [Polyvinyl alcohol (B)] The PHA powder according to this embodiment contains a specific amount of polyvinyl alcohol (B). The use of this component makes it easy to recover the PHA powder without agglomeration during spray drying to produce the PHA powder, and also improves the dispersibility of the PHA powder when dispersed in an aqueous medium. Hereinafter, polyvinyl alcohol is also referred to as PVA.

[0034] PVA is typically a saponified vinyl ester polymer (a polymer containing at least a vinyl ester monomer as a constituent monomer), and typically contains vinyl alcohol units and vinyl ester monomer units.

[0035] The PVA (B) may be a fully saponified polyvinyl alcohol or a partially saponified polyvinyl alcohol, but it is preferable to use a partially saponified polyvinyl alcohol.

[0036] The saponification degree of PVA (B) is not particularly limited, but may be, for example, 30 mol% or more and less than 98.5 mol%. Since this improves dispersion stability when the PHA powder is dispersed in an aqueous medium, enables the formation of a uniform resin layer, and prevents dripping after application of an aqueous suspension of the PHA powder, the saponification degree is preferably 50 mol% or more and 90 mol% or less, more preferably 50 mol% or more and 85 mol% or less, even more preferably 50 mol% or more and 79 mol% or less, and particularly preferably 60 mol% or more and 75 mol% or less. Commercially available PVAs exhibiting such a saponification degree can be used. The saponification degree of PVA is measured by the method specified in JIS K6726.

[0037] The viscosity of PVA (B) measured as a 4 wt % aqueous solution at 20°C is not particularly limited, but is preferably 2 mPa·s or more and 20 mPa·s or less. By using PVA (B) having such a specific viscosity, the dispersion stability when the PHA powder is dispersed in an aqueous medium is improved, enabling the formation of a uniform resin layer. Furthermore, the dispersibility of the PHA powder in the aqueous medium is good, and the aqueous suspension obtained by the dispersion can also be easily applied to a substrate. Furthermore, dripping after application of the aqueous suspension can be suppressed.

[0038] From the viewpoint of dispersion stability, the lower limit of the viscosity is preferably 3 mPa s or more, more preferably 4 mPa s or more, and even more preferably 5 mPa s or more. From the viewpoints of dispersibility, coatability, and suppression of dripping after application, the upper limit of the viscosity is preferably 15 mPa s or less, more preferably 10 mPa s or less, and even more preferably 8 mPa s or less. The viscosity is an index showing the degree of polymerization of the PVA, and is measured using a coaxial double cylinder rheometer.

[0039] The PVA (B) may contain units derived from a monomer other than vinyl alcohol and vinyl ester monomers. That is, the PVA may be modified with other monomers. Examples of such modified PVA include carbonyl group-modified, carboxyl group-modified, and silanol group-modified PVA, cation-modified PVA, amino group-modified PVA, and itaconic acid-modified PVA. However, from the viewpoint of suppressing dripping after application, it is preferable to use unmodified PVA.

[0040] The content of PVA (B) in the PHA powder is in the range of 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of PHA (A). By having a PVA (B) content of 1.0 part by weight or more, the PHA powder can be easily recovered without agglomeration during spray drying to produce the PHA powder, and the dispersibility of the PHA powder in aqueous media can be improved. Furthermore, by limiting the PVA content (B) to less than 3.0 parts by weight, it is possible to suppress the elution of substances from the PHA powder and from articles (especially resin layers) produced using the powder.

[0041] The lower limit of the content of PVA (B) is preferably 1.5 parts by weight or more, more preferably 2.0 parts by weight or more, from the viewpoint of granulation property, and the upper limit of the content of PVA is preferably 2.5 parts by weight or less, from the viewpoint of suppressing dissolution.

[0042] [Alkylene oxide compound (C)] The PHA powder according to this embodiment contains an alkylene oxide compound (C). By using PVA (B) and alkylene oxide compound (C) in combination, the dispersibility of the PHA powder when dispersed in an aqueous medium can be improved, even though the amount of PVA (B) added is limited. In addition, the alkylene oxide compound (C) has the advantage of being less likely to cause elution problems.

[0043] The alkylene oxide compound (C) is not particularly limited, but compounds generally known as alkylene oxide dispersants can be used.

[0044] Among these, the alkylene oxide compound (C) is preferably a compound containing a poly(ethylene oxide) block, since this compound has excellent dispersibility for the PHA (A). The poly(ethylene oxide) block (PEO) refers to a polymer structure formed by polymerization of ethylene oxide (EO).

[0045] Furthermore, the alkylene oxide compound (C) is more preferably a compound containing a poly(propylene oxide) block in addition to the poly(ethylene oxide) block. The poly(propylene oxide) block (PPO) refers to a polymer structure formed by polymerization of propylene oxide (PO).

[0046] In particular, as the alkylene oxide compound (C), a compound represented by PEO-PPO-PEO can be suitably used.

[0047] The content of the alkylene oxide compound (C) in the PHA powder may be set as appropriate, but is preferably 0.2 parts by weight or more per 100 parts by weight of the PHA (A). This allows for better dispersibility of the PHA powder in an aqueous medium. It is more preferably 0.3 parts by weight or more, even more preferably 0.4 parts by weight or more, and particularly preferably 0.5 parts by weight or more.

[0048] On the other hand, if the amount of compound (C) added is large, foaming tends to occur when the PHA powder is dispersed in an aqueous medium. From this viewpoint, the content of compound (C) is preferably 1.0 part by weight or less, more preferably 0.9 part by weight or less, and particularly preferably 0.8 part by weight or less, per 100 parts by weight of PHA (A).

[0049] [Polyhydroxyalkanoate Powder] As described above, the polyhydroxyalkanoate powder according to this embodiment contains the PHA (A), the PVA (B), and the alkylene oxide compound (C).

[0050] The PHA powder may be substantially composed only of PHA (A), PVA (B), and alkylene oxide compound (C), but may also contain, within the scope of the invention, one or more of the following: dispersants or emulsifiers other than those mentioned above, pH adjusters, inorganic fillers, colorants such as pigments and dyes, odor absorbers such as activated carbon and zeolite, fragrances such as vanillin, viscosity modifiers such as dextrin, plasticizers, antioxidants, weather resistance improvers, UV absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, sliding property improvers, etc. Furthermore, the PHA powder may contain, within the scope of the invention, various components resulting from the steps of the manufacturing method described below.

[0051] In the PHA powder according to this embodiment, the main components are PHA (A), PVA (B), and alkylene oxide compound (C). Specifically, the total proportion of PHA (A), PVA (B), and alkylene oxide compound (C) in the entire PHA powder may typically be 60 to 100% by weight, 80 to 100% by weight, 90 to 100% by weight, 95 to 100% by weight, or 99 to 100% by weight. The upper limit may be 99.9% by weight or less, or 99% by weight or less.

[0052] The average particle size (D50) of the PHA powder according to this embodiment is not particularly limited, but from the viewpoint of achieving good fluidity for the PHA powder, it is preferably 10 to 200 μm, more preferably 50 to 180 μm, and even more preferably 60 to 100 μm. The average particle size (D50) of the PHA powder is measured as follows: 0.2 g of the powder to be measured is added to 20 mL of ion-exchanged water and dispersed to obtain a dispersion for measurement. The dispersion for measurement is introduced into a laser diffraction / scattering particle size distribution analyzer LA-950 (Horiba, Ltd.), and measurement is performed.

[0053] The PHA powder according to this embodiment preferably exhibits a pH of 3 or more and 8 or less, measured when the powder is dispersed in water at a concentration of 50% by weight. When the pH is within this range, dripping after application of an aqueous suspension obtained by dispersing the PHA powder in an aqueous medium can be further suppressed, and furthermore, coloration and molecular weight reduction of the PHA due to heating can be suppressed. From the viewpoint of suppressing coloration and molecular weight reduction, the upper limit is more preferably 7 or less, even more preferably 6 or less, particularly preferably 5 or less, and most preferably 4 or less. From the viewpoint of suppressing dripping after application, the lower limit is more preferably 3.1 or more, even more preferably 3.2 or more, and particularly preferably 3.3 or more.

[0054] The PHA powder according to this embodiment can be suitably used to prepare an aqueous suspension by dispersing it in an aqueous medium, as will be described later. However, the PHA powder according to this embodiment is not limited to this application, and may also be used to form various molded articles such as films, sheets, tubes, plates, rods, containers (e.g., bottles), bags, and parts.

[0055] [Method for Producing PHA Powder] The method for producing the PHA powder according to this embodiment is not particularly limited. However, it can be suitably produced by sequentially carrying out the following steps (a) and (b): Step (a): A step of preparing an aqueous suspension containing PHA (A), PVA (B), and an alkylene oxide compound (C); Step (b): A step of spray-drying the aqueous suspension prepared in step (a).

[0056] (Step (a)) In step (a) of the present production method, PVA (B) and alkylene oxide compound (C) may be added to a previously prepared PHA aqueous suspension. In the PHA aqueous suspension, the PHA is present in a dispersed state in an aqueous medium. In this specification, an aqueous suspension containing PHA may be abbreviated as "PHA aqueous suspension."

[0057] The order of addition of PVA (B) and alkylene oxide compound (C) is not particularly limited, but it is preferable to add alkylene oxide compound (C) first and then PVA (B). The amounts of PVA (B) and alkylene oxide compound (C) added are the same as the contents of each component in the PHA powder described above, and therefore will not be described here.

[0058] Step (a) preferably includes the following steps (a1) and (a2): Step (a1): Adding PVA (B) and an alkylene oxide compound (C) to the aqueous PHA suspension; Step (a2): Adjusting the pH of the aqueous PHA suspension to 8 or less. The order in which steps (a1) and (a2) are performed is not particularly limited, but from the viewpoint of suppressing aggregation of PHA in step (a2) and obtaining an aqueous suspension with better PHA dispersion stability, it is preferable to perform step (a2) after step (a1).

[0059] In step (a), the PHA aqueous suspension used as the starting material is not particularly limited, but can be obtained, for example, by a method including a culture step of culturing a microorganism capable of producing PHA intracellularly, and a purification step of decomposing and / or removing substances other than PHA after the culture step.

[0060] The method for producing the PHA powder according to this embodiment may include, prior to step (a), a step of obtaining a PHA aqueous suspension (e.g., a step including the above-described culturing step and purification step). The microorganism used in this step may be, for example, the microorganism described above.

[0061] Since the PHA-containing microorganisms produced by culturing the microorganisms contain a large amount of bacterial cell-derived impurities, a purification step is usually carried out to decompose and / or remove impurities other than PHA. This purification step is not particularly limited, and physical treatment, chemical treatment, biological treatment, etc. that a person skilled in the art can consider can be applied. For example, the purification method described in WO 2010 / 067543 can be preferably applied.

[0062] The amount of impurities remaining in the final product is largely determined by the purification step, so it is preferable to reduce these impurities as much as possible. Depending on the application, impurities may be present as long as they do not impair the physical properties of the final product. However, when a highly pure PHA is required, such as for medical applications, it is preferable to reduce the impurities as much as possible. An example of an index of the degree of purification is the amount of protein in the aqueous PHA suspension. The protein amount is preferably 30,000 ppm or less per weight of PHA, more preferably 15,000 ppm or less, even more preferably 10,000 ppm or less, and most preferably 7,500 ppm or less. The purification method is not particularly limited, and for example, the known methods described above can be applied.

[0063] The aqueous medium constituting the PHA aqueous suspension may be water or a mixed solvent of water and a water-compatible organic solvent. Furthermore, the concentration of the water-compatible organic solvent in the mixed solvent is not particularly limited as long as it is equal to or lower than the solubility of the organic solvent used in water. The water-compatible organic solvent is not particularly limited, and the organic solvents described below can be used as appropriate. The aqueous medium constituting the PHA aqueous suspension may contain other solvents, components derived from bacterial cells, compounds generated during purification, etc., as long as they do not impair the effects of the invention.

[0064] The content of water in the entire aqueous medium constituting the PHA aqueous suspension is not particularly limited, but is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 30% by weight or more, even more preferably 50% by weight or more, particularly preferably 70% by weight or more, and most preferably 90% by weight or more. The upper limit is not particularly limited, and may be 100% by weight or less.

[0065] <Others> The PHA aqueous suspension before being subjected to step (a) usually has a pH of more than 8 due to the above-mentioned purification step. Therefore, the PHA aqueous suspension obtained in step (a1) may have a pH of more than 8. Therefore, it is preferable to adjust the pH of the PHA aqueous suspension to 8 or less in step (a2). The adjustment method is not particularly limited, and examples include a method of adding an acid. The acid is not particularly limited, and may be either an organic acid or an inorganic acid, whether or not it is volatile. More specifically, examples of acids that can be used include sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid.

[0066] The upper limit of the pH of the PHA aqueous suspension adjusted in the adjustment step is preferably 8 or less. By adjusting the pH of the PHA aqueous suspension to 8 or less, discoloration during heat melting is reduced, and a decrease in molecular weight during heating and / or drying can be suppressed. From the viewpoint of reducing discoloration during heat melting of the PHA and ensuring molecular weight stability during heating and / or drying, the pH is more preferably 7 or less, even more preferably 6 or less, even more preferably 5 or less, and particularly preferably 4 or less. Furthermore, from the viewpoint of acid resistance of the container, the lower limit of the pH is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more.

[0067] The concentration of PHA in the PHA aqueous suspension obtained by step (a) is preferably 30% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight or more, because this is economically advantageous in terms of drying utility and improves productivity. Furthermore, the upper limit of the PHA concentration is preferably 65% ​​by weight or less, more preferably 60% by weight or less, to avoid the possibility that the PHA may reach close packing and not be able to ensure sufficient fluidity. The method for adjusting the PHA concentration is not particularly limited, and examples include adding an aqueous medium and removing a portion of the aqueous medium (for example, by centrifuging and then removing the supernatant). The adjustment of the PHA concentration may be performed at any stage of step (a), or may be performed before step (a).

[0068] (Step (b)) In step (b), the aqueous suspension prepared in step (a) (i.e., the aqueous suspension containing PHA (A), PVA (B), and alkylene oxide compound (C)) is spray-dried. Examples of spray-drying methods include a method in which the aqueous suspension is supplied into a dryer in the form of fine droplets and dried while being brought into contact with hot air in the dryer. The method (atomizer) for supplying the aqueous suspension into the dryer in the form of fine droplets is not particularly limited, and known methods such as a method using a rotating disk or a method using a nozzle are included. The method for contacting the droplets with hot air in the dryer is not particularly limited, and examples thereof include a co-current method, a counter-current method, and a method using both of these.

[0069] The drying temperature during spray drying in step (b) may be any temperature capable of removing most of the aqueous medium from the droplets of the aqueous suspension. The drying temperature can be appropriately set under conditions that allow drying to the desired moisture content and minimize the occurrence of quality deterioration (reduction in molecular weight, color tone, etc.), melting, etc. For example, the temperature of the hot air blown into the spray dryer can be appropriately selected within the range of 100 to 300°C. However, if the hot air temperature is high, although the productivity of spray drying improves, the dispersibility of the obtained PHA powder in the aqueous medium tends to decrease. From this perspective, it is desirable to adjust the hot air temperature. The volume of hot air blown into the dryer can also be appropriately set depending on, for example, the size of the dryer.

[0070] [Aqueous Suspension of PHA Powder] Another embodiment of the present invention relates to an aqueous suspension (hereinafter also referred to as an aqueous suspension of PHA powder) containing the above-mentioned PHA powder (powder containing PHA (A), PVA (B), and alkylene oxide compound (C)) and an aqueous medium. In the aqueous suspension of PHA powder, the PHA powder exists in a dispersed state in the aqueous medium.

[0071] The details of the PHA powder contained in the aqueous suspension of PHA powder according to this embodiment are the same as those of the PHA powder described above, and therefore will not be described again.

[0072] The aqueous medium contained in the aqueous suspension of PHA powder may be water or a mixed solvent of water and a water-compatible organic solvent. Furthermore, the concentration of the water-compatible organic solvent in the mixed solvent is not particularly limited, as long as it is equal to or lower than the solubility of the organic solvent used in water. Furthermore, the water-compatible organic solvent is not particularly limited, but examples thereof include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile, and propionitrile, which are preferred because they are easily removed.

[0073] The content of water in the entire aqueous medium constituting the aqueous suspension of PHA powder is not particularly limited, but is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 30% by weight or more, even more preferably 50% by weight or more, particularly preferably 70% by weight or more, and most preferably 90% by weight or more. The upper limit is not particularly limited, and may be 100% by weight or less.

[0074] The content of PHA powder in the aqueous suspension of PHA powder (hereinafter also referred to as PHA powder concentration) is preferably 20% by weight or more, since this can further suppress dripping after application of the aqueous suspension and further improve drying properties after application. The concentration of the PHA powder is more preferably 30% by weight or more, even more preferably 35% by weight or more, even more preferably 40% by weight or more, and particularly preferably 45% by weight or more. The upper limit of the concentration of the PHA powder is preferably 65% ​​by weight or less, more preferably 60% by weight or less, and even more preferably 55% by weight or less, to avoid the possibility that the PHA powder reaches close packing and cannot ensure sufficient fluidity.

[0075] The aqueous suspension of PHA powder preferably has a pH of 3 or more and 8 or less. When the pH is within the above range, dripping of the suspension after application can be further suppressed, and coloration of the PHA and a decrease in molecular weight due to heating can be suppressed. From the viewpoint of suppressing coloration and a decrease in molecular weight, the upper limit is more preferably 7 or less, even more preferably 6 or less, particularly preferably 5 or less, and most preferably 4 or less. From the viewpoint of safety and from the viewpoint of reducing corrosiveness when the container of the aqueous suspension or the substrate to be applied is made of metal, the lower limit is more preferably 4 or more, even more preferably 5 or more, and particularly preferably 6 or more.

[0076] The aqueous suspension of PHA powder may contain, within the scope of the invention, one or more of the following: dispersants or emulsifiers other than those mentioned above, pH adjusters, inorganic fillers, colorants such as pigments and dyes, odor absorbers such as activated carbon and zeolite, fragrances such as vanillin and dextrin, plasticizers, antioxidants, weather resistance improvers, ultraviolet absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, sliding property improvers, etc. Furthermore, the aqueous suspension of PHA powder may contain, within the scope of the invention, various components resulting from the steps of the production method described below.

[0077] In the aqueous suspension of PHA powder according to this embodiment, the aforementioned PHA powder and aqueous medium are the main components. Specifically, the proportion of PHA powder in the total solid content of the aqueous suspension of PHA powder may typically be 60 to 100 wt %, 80 to 100 wt %, 90 to 100 wt %, 95 to 100 wt %, or 99 to 100 wt %. The upper limit may be 99 wt % or less, or 95 wt % or less.

[0078] The volume median diameter of the PHA powder in an aqueous suspension of PHA powder (hereinafter also referred to as "volume median diameter of PHA powder") is preferably 50 times or less the volume median diameter of the primary particles of the PHA powder (hereinafter also referred to as "primary particle diameter"). When the volume median diameter of the PHA powder in an aqueous suspension of PHA powder is 50 times or less the volume median diameter of the primary particle diameter, the aqueous suspension of PHA powder exhibits better fluidity, which tends to further improve the coatability to substrates. The volume median diameter of the PHA powder is more preferably 20 times or less, and even more preferably 10 times or less, the volume median diameter of the primary particle diameter.

[0079] From the viewpoint of achieving excellent fluidity, the volume median diameter of the PHA powder in the aqueous suspension of the PHA powder is preferably 0.5 to 5.0 μm, more preferably 1.0 to 4.5 μm, and even more preferably 1.0 to 4.0 μm. The volume median diameter of the PHA powder in the aqueous suspension is measured using a HORIBA laser diffraction / scattering particle size distribution analyzer LA-950 by the method described in the Examples.

[0080] The volume median diameter of the PHA powder in the aqueous suspension can be used as an indicator of the dispersion state of the PHA in the aqueous suspension of PHA powder. The method for adjusting the volume median diameter of the PHA powder is not particularly limited, and known means (e.g., stirring) can be applied. For example, an aqueous suspension of PHA powder whose dispersion state has been disrupted due to exposure to acidic conditions can be subjected to physical, chemical, or biological treatment that a person skilled in the art would consider, thereby restoring the PHA powder in the aqueous suspension of PHA powder to a dispersed state (e.g., a state having the aforementioned primary particle diameter of the PHA powder).

[0081] The aqueous suspension of PHA powder according to this embodiment can be produced by dispersing the above-mentioned PHA powder in an aqueous medium. Because a PHA powder exhibiting good dispersibility is used, the aqueous suspension according to this embodiment has good productivity and can suppress dripping during heat drying after being applied to a substrate as a coating liquid.

[0082] Although the method for producing an aqueous suspension of PHA powder is not particularly limited, it is preferable to disperse the PHA powder in an aqueous medium, and then apply mechanical shear to separate the partially aggregated PHA powder from each other. Applying mechanical shear is preferable in that it can substantially eliminate aggregates and obtain an aqueous suspension containing PHA powder of uniform particle size. For example, a shear crusher, a stirrer, a homogenizer, ultrasonic waves, etc. can be used to apply mechanical shear.

[0083] After dispersing the PHA powder in an aqueous medium, the pH of the resulting aqueous suspension may be adjusted. Alternatively, the pH of the aqueous medium may be adjusted before dispersing the PHA powder in the aqueous medium. The method for adjusting the pH is not particularly limited, and examples thereof include a method of adding an acid. The acid is not particularly limited, and may be either an organic acid or an inorganic acid, regardless of whether it is volatile. More specifically, examples of acids that can be used include sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid.

[0084] However, such a pH adjustment step does not have to be performed. As described above, when an aqueous suspension of PHA powder is prepared using PHA powder that has a pH of 3 or more and 8 or less when dispersed in water at a concentration of 50 wt %, an aqueous suspension of PHA powder having a pH of 3 or more and 8 or less can be easily obtained without performing the above-mentioned pH adjustment step.

[0085] The aqueous suspension of PHA powder according to this embodiment can be suitably used as an aqueous coating liquid for forming a resin layer by applying it to a substrate and drying it, as will be described later. However, the application is not limited to this, and the aqueous suspension of PHA powder according to this embodiment can also be used as an impregnation processing raw material, a composite material raw material, a building material, a plastic modifier, or an adhesive.

[0086] [Laminate and method for manufacturing the laminate] The aqueous suspension of the PHA powder according to this embodiment is applied to one or both sides of a substrate, and then heated and dried to form a resin layer containing the PHA (A), the PVA (B), and the alkylene oxide compound (C) on the substrate, thereby manufacturing a laminate. Such a method for manufacturing a laminate and the resulting laminate also constitute aspects of the present invention.

[0087] The substrate is not particularly limited, and substrates made of various materials can be used. However, from the viewpoint of enhancing the biodegradability of the entire laminate obtained, it is preferable that the substrate is biodegradable.

[0088] The biodegradable substrate is not particularly limited, but examples thereof include paper (mainly composed of cellulose), cellophane, cellulose ester; polyvinyl alcohol, polyamino acid, polyglycolic acid, pullulan; wood, etc. Paper or cellophane is preferred, and paper is particularly preferred, because it has excellent heat resistance and is inexpensive. The type of paper is also not particularly limited, and examples thereof include cup base paper, kraft paper, fine paper, coated paper, tissue paper, glassine paper, and cardboard. The paper may contain additives such as water-resistant agents, water-repellents, and inorganic substances, as needed.

[0089] The substrate may be previously subjected to a surface treatment such as corona treatment, flame treatment, anchor coating treatment, etc. These surface treatments may be performed alone or in combination.

[0090] The method for applying the aqueous suspension of the PHA powder to the substrate is not particularly limited, and any known method capable of forming a resin layer on the substrate can be used as appropriate. Specifically, a spraying method, a scattering method, a slit coater method, an air knife coater method, a roll coater method, a bar coater method, a comma coater method, a blade coater method, a screen printing method, a gravure printing method, etc. can be used. Before applying the aqueous suspension, a step of subjecting the substrate to a surface treatment such as a corona treatment may be carried out.

[0091] The drying treatment after coating can be carried out using a known heating method. Examples include hot air heating, infrared heating, ultrasonic irradiation, microwave heating, roll heating, and hot plate heating. These can be used alone or in combination of two or more. Conventionally, dripping of the coating film is likely to occur during such drying treatment, which can hinder the formation of a uniform resin layer. However, by using the aqueous suspension of PHA powder according to this embodiment, such dripping can be suppressed, and a highly uniform resin layer can be formed.

[0092] In the drying treatment after application, the resin layer may be heated to a temperature at which the PHA, which is the main resin component contained in the resin layer, can be melted to form a film. As a result, the PHA in the resin layer is melted once and then cooled and solidified, which can smooth the surface of the resin layer and improve the bonding strength between the base layer and the resin layer.

[0093] From the above viewpoints, the heating temperature in the drying treatment after application is preferably 130° C. to 180° C. The heating time may be, for example, 10 seconds to 10 minutes.

[0094] The above-mentioned coating and drying steps may be carried out batchwise or continuously while transporting the film-like substrate between a plurality of rolls.

[0095] The weight per unit of PHA in the resin layer (hereinafter also referred to as basis weight) is not particularly limited, but is, for example, 5 to 100 g / m ２ When the basis weight is within this range, defects such as pinholes can be prevented, the resin layer can have a strength sufficient for use, and functions such as water resistance can be efficiently exhibited.

[0096] The contents of the PVA (B) and the alkylene oxide compound (C) in the resin layer are the same as the contents of each component in the PHA powder described above, and therefore will not be described here.

[0097] The thickness of the resin layer is not particularly limited, but may be about 5 to 100 μm from the viewpoint of preventing water absorption and ensuring flexibility.

[0098] The laminate according to this embodiment includes at least a substrate layer and a PHA-containing resin layer provided on one or both sides of the substrate layer. The laminate may be composed of only these layers, or may include other layers in addition to these layers. Examples of such other layers include a gas barrier layer, a printed layer, and other resin layers. The gas barrier layer may be a known layer, such as a metal foil, a metal vapor deposition film, a metal oxide vapor deposition film, a silicon oxide vapor deposition film, a polyvinyl alcohol film, or an ethylene-vinyl alcohol copolymer film. The gas barrier layer may be bonded to the substrate via an adhesive layer.

[0099] The laminate according to this embodiment can be subjected to secondary processing to form various molded articles. Examples of such molded articles include tubes, plates, rods, packaging materials (e.g., bags), containers (e.g., bottle containers), and parts. In particular, the molded articles can be suitably used as various packaging container materials, such as shopping bags, various bags, food and confectionery packaging materials, cups, trays, and cartons, in various fields such as food, cosmetics, electronics, medicine, and pharmaceuticals. Furthermore, the molded articles can be suitably used as containers for holding liquids, particularly as containers for hot contents, such as cups for food and beverages such as instant noodles, instant soup, and coffee, trays for prepared meals, boxed lunches, and microwaveable foods.

[0100] The secondary processing can be carried out by any method known in the technical field, for example, using various bag-making machines, filling and packaging machines, etc. Processing can also be carried out using devices such as paper cup forming machines, punching machines, and box making machines. In these processing machines, known techniques can be used to bond the laminate, for example, heat sealing, impulse sealing, ultrasonic sealing, high-frequency sealing, hot air sealing, and frame sealing. In particular, it is preferable that the molded body is one that has been secondary processed using a heat sealing method. The heat sealing may be carried out between the base layer and the resin layer, or may be carried out between the resin layers.

[0101] In order to improve the physical properties of the molded article, the molded article can be composited with another molded article made of a material different from the molded article (for example, fiber, thread, rope, woven fabric, knitted fabric, nonwoven fabric, paper, film, sheet, tube, plate, rod, container, bag, part, foam, etc.). These materials are also preferably biodegradable.

[0102] The following items list preferred embodiments of the present disclosure, but the present invention is not limited to them. [Item 1] A polyhydroxyalkanoate powder containing a polyhydroxyalkanoate (A), a polyvinyl alcohol (B), and an alkylene oxide compound (C), wherein the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A). [Item 2] The polyhydroxyalkanoate powder according to Item 1, wherein the alkylene oxide compound (C) contains a block of poly(ethylene oxide). [Item 3] The polyhydroxyalkanoate powder according to Item 1 or 2, wherein the content of the alkylene oxide compound (C) is 0.2 part by weight or more and 1.0 part by weight or less per 100 parts by weight of the polyhydroxyalkanoate (A). [Item 4] The polyhydroxyalkanoate powder according to any one of Items 1 to 3, wherein the polyhydroxyalkanoate (A) comprises a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units. [Item 5] The polyhydroxyalkanoate powder according to Item 4, wherein the other hydroxyalkanoate units are 3-hydroxyhexanoate units. [Item 6] A method for producing a polyhydroxyalkanoate powder, comprising the steps of preparing an aqueous suspension and spray-drying the aqueous suspension, wherein the aqueous suspension contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A). [Item 7] An aqueous suspension of polyhydroxyalkanoate powder, comprising a polyhydroxyalkanoate powder and an aqueous medium, wherein the polyhydroxyalkanoate powder contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A).[Item 8] A method for producing an aqueous suspension of polyhydroxyalkanoate powder, comprising a step of dispersing polyhydroxyalkanoate powder in an aqueous medium, wherein the polyhydroxyalkanoate powder contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A). [Item 9] A laminate comprising a base layer and a resin layer provided on at least one surface of the base layer, wherein the resin layer contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A). [Item 10] The laminate according to item 9, wherein the base layer is paper. [Item 11] A method for producing a laminate, comprising: a step of dispersing a polyhydroxyalkanoate powder in an aqueous medium to prepare an aqueous suspension; and a step of applying the aqueous suspension to at least one surface of a substrate and drying by heating to form a resin layer on the substrate, wherein the polyhydroxyalkanoate powder contains a polyhydroxyalkanoate (A), a polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A).

[0103] The present invention will be specifically explained below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0104] (Method for measuring primary particle diameter of PHA powder) The spray-dried stock solution before spray drying was diluted with ion-exchanged water to a solids concentration of 5 wt %, to obtain a dispersion for measurement. The dispersion for measurement was introduced into a laser diffraction / scattering particle size distribution measuring device LA-950 (Horiba, Ltd.), and measurement was performed. The obtained volume median diameter (particle diameter D50) was used as the measured value of the primary particle diameter of the PHA powder.

[0105] (Method for measuring the average particle size of PHA powder) 0.2 g of the PHA powder to be measured was added to 20 mL of ion-exchanged water and dispersed to obtain a dispersion for measurement. The dispersion for measurement was introduced into a laser diffraction / scattering particle size distribution measuring device LA-950 (Horiba, Ltd.), and measurement was performed. The obtained volume median diameter (particle size D50) was used as the measured value of the average particle size of the PHA powder.

[0106] (Method for measuring the volume median diameter of PHA powder in aqueous suspension) An aqueous suspension of PHA powder was diluted with ion-exchanged water to a solids concentration of 5 wt %, to obtain a dispersion for measurement. The dispersion for measurement was introduced into a laser diffraction / scattering particle size distribution measuring device LA-950 (Horiba, Ltd.), and measurement was performed. The obtained volume median diameter (particle size D50) was used as the measured value of the volume median diameter of the PHA powder in the aqueous suspension.

[0107] [Example 1] (Culturing) Ralstonia eutropha described in International Publication No. WO 2019 / 142717 was cultured by the method described in paragraphs

[0041] to

[0048] of the same document to obtain a fungal cell culture solution containing fungal cells containing PHA. Note that Ralstonia eutropha is currently classified as Capriavidus necator. The composition ratio of the repeating units of PHA (composition ratio of 3HB unit / 3HH unit) was 89.9 / 10.1 (mol / mol).

[0108] (Inactivation) The bacterial cell culture solution obtained above was sterilized by heating and stirring at an internal temperature of 70°C for 8 hours to obtain an inactivated culture solution. The weight-average molecular weight of PHA in the inactivated culture solution was 1,210,000. The solid content of the inactivated culture solution was 30% by weight.

[0109] (Molecular Weight Adjustment) 30% sodium hydroxide was added to the sterilized culture solution (inactivated culture solution) obtained above to adjust the pH to 10.0±1.0, and the internal temperature was set to 70±2° C., and the molecular weight of PHA in the bacterial cells was adjusted for 19 hours. The weight average molecular weight was 250,000.

[0110] (Enzyme Treatment) 95% sulfuric acid was added to the liquid after molecular weight adjustment (liquid after molecular weight adjustment) obtained above to adjust the pH to 7.0±0.2. After adding IW (industrial water) to adjust the solids concentration to 18%, lysozyme (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), an enzyme (lytic enzyme) that degrades sugar chains (peptidoglycans) in cell walls, was added and maintained at 50°C for 2 hours. Subsequently, Alcalase 2.5L (manufactured by Novozyme), an alkaline protease, was added, and then 30% sodium hydroxide was added at 50°C to adjust the pH to 9.0 and maintained for 2 hours.

[0111] (Hydrogen peroxide treatment) Hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the enzyme-treated solution obtained above. Next, 30% aqueous sodium hydroxide solution was added to adjust the pH to 10.5. While maintaining the solution at 50°C, 30% aqueous sodium hydroxide solution was continued to be added, thereby maintaining the pH at 10.5 for 4 hours, and a hydrogen peroxide-treated solution was obtained.

[0112] (Bacteriolysis) Sodium dodecyl sulfate (SDS, manufactured by Kao Corporation) was added to the hydrogen peroxide treatment solution to a concentration of 0.4 wt %, and then the pH was adjusted to 11.0±0.2 using an aqueous sodium hydroxide solution.

[0113] (Centrifugation) After removing the supernatant, water was added again to form a suspension, and protease (Novozymes, Esperase) was added. The mixture was stirred for 2 hours at 45°C at pH 11. The mixture was then centrifuged (4500 rpm, 10 minutes) and the supernatant was removed, resulting in a 2x concentration. An equal amount of aqueous sodium hydroxide solution (pH 11.0) was added and centrifuged (4500 rpm, 10 minutes). Finally, the supernatant was removed, and the PHA concentration was adjusted to 54±2 wt% to obtain an aqueous PHA suspension. The volume median diameter (particle size D50) of the PHA powder in the aqueous suspension, i.e., the primary particle diameter, was 3.3 μm. An aqueous PHA suspension with a solids concentration of 30 wt% (PHA particle content: 300 g / L) was obtained.

[0114] (Membrane filtration) In a filtration apparatus using a tubular membrane (MEMBRALOX (registered trademark) 1T1-70, manufactured by PALL, material: alumina ceramic) as a filtration membrane, the PHA aqueous suspension was circulated and supplied to the tubular membrane, and filtration was carried out until the solid content concentration reached 50 wt %. The linear velocity during filtration (linear velocity at which the liquid passed through the tubular membrane) was 3 to 4 m / s, and the transmembrane pressure difference was 80 kPa.

[0115] (Preparation of aqueous suspension) To the PHA aqueous suspension (solid content concentration 50 wt%) obtained above, 0.5 parts by weight of polyethylene glycol-polypropylene glycol block ether type polymer (trade name: Pronon #208, hereinafter also referred to as EOPO block polymer) as alkylene oxide compound (C) (0.5 parts by weight relative to 100 parts by weight of PHA present in the aqueous suspension), polyvinyl alcohol (B) PVA (trade name: Kuraray Poval L-508W, saponification degree: 72.5 mol%, viscosity of 4 wt% aqueous solution at 20 ° C: 6.5 mPa s) was dissolved in water to a solid content of 2.5 parts by weight and added, and then the solid content concentration was adjusted to 46.8 wt%. After stirring this liquid for 30 minutes, sulfuric acid was added and the pH was adjusted to 4 until stable, to obtain a PHA aqueous suspension. The primary particle diameter (particle size D50) of the PHA powder was 3.1 μm. The weight average molecular weight was 240,000.

[0116] (Spray Drying Treatment) The PHA aqueous suspension obtained as described above was sent to an atomizer using an OC-16 general-purpose spray dryer manufactured by Okawara Kakoki Co., Ltd., and spray-dried (hot air temperature: 130°C, exhaust air temperature: 60°C). This resulted in a PHA powder containing 100 parts by weight of PHA, 2.5 parts by weight of PVA, and 0.5 parts by weight of EOPO block polymer. The primary particle diameter of the PHA powder was 3.1 μm, and the average particle diameter (D50) of the PHA powder was 76.0 μm.

[0117] (Redispersibility Evaluation Test) The PHA powder obtained above was mixed with distilled water at a weight ratio of 1:1. Thereafter, the mixture was crushed at 22,000 s using a high-shear crusher (Homomixer Model MARK II manufactured by Primix Corporation). －１The PHA powder was re-dispersed at a shear rate of 100 rpm for 75 minutes. 2 ml of aliquots were sampled at 5, 10, 20, 30, 40, 50, and 60 minutes. 0.3 g of the aqueous suspension to be measured was added to 20 mL of ion-exchanged water and dispersed to obtain a dispersion for measurement. The dispersion for measurement was introduced into a laser diffraction / scattering particle size distribution analyzer LA-950 (Horiba, Ltd.) and measurements were performed. In the obtained particle size distribution, the total volume frequency of particles of 17 μm or larger was calculated as the residual coarse particle frequency. The calculated residual coarse particle frequency for the aqueous suspension obtained 10 minutes after the start of crushing is shown in Table 1. The smaller this value, the more thoroughly the powder was dispersed in a short period of time, indicating better dispersibility.

[0118] (Aqueous suspension of PHA powder) According to the method described in the above (Evaluation test of redispersibility), an aqueous suspension of PHA powder with a solid content of 50 wt % was prepared by dispersing until the frequency of residual coarse particles became 0%. The pH of this aqueous suspension was measured at 25° C. The results are shown in Table 1.

[0119] (Preparation of Laminate) The prepared aqueous suspension of PHA powder was applied to a bleached kraft paper [Kujira, basis weight: 50 g / m ２ The resulting laminate was heated for 2 minutes in an oven set at 180°C to form a resin layer, thereby obtaining a laminate. The potassium permanganate consumption was measured using the resulting laminate as described below.

[0120] (Evaluation test for elution amount) A metal ring having an inner diameter of 4.9 cm, an outer diameter of 5.4 cm, and a height of 3.0 cm was pressed against the surface of the resin layer of the laminate and fixed in place. 150 mL of hot water at 60°C was poured inside the ring, and the surface of the laminate was left in contact with the hot water, and the water temperature was maintained while the laminate was left standing for 30 minutes. The hot water after leaving the ring was collected and used as the eluate.

[0121] 100 mL of the eluate was placed in an Erlenmeyer flask and 5 mL of sulfuric acid was added. 10 mL of 0.002 mol / L potassium permanganate solution was then added, and the mixture was heated and boiled for 5 minutes. Heating was stopped, and 10 mL of 0.005 mol / L sodium oxalate solution was immediately added to decolorize the mixture. The mixture was then titrated with 0.002 mol / L potassium permanganate solution until a slight pink color remained. A blank test was conducted using a similar method, and the amount of potassium permanganate consumed was calculated from the difference between the titration amount in the eluate and the titration amount in the empty container. The measurement results are shown in Table 1.

[0122] [Examples 2 to 5 and Comparative Examples 1 to 4] PHA powders were prepared and similar evaluation tests were carried out in the same manner as in Example 1, except that the amounts of polyvinyl alcohol (B) and alkylene oxide compound (C) added were changed according to the descriptions in Table 1, and the hot air temperature and exhaust air temperature during spray drying were changed as described in Table 1. The results are shown in Table 1.

[0123]

[0124] The following can be seen from Table 1. In Comparative Example 1, a PHA powder was prepared using 3.0 parts by weight of polyvinyl alcohol (B) per 100 parts by weight of PHA, as in the examples of Patent Document 1. In this comparative example, the value of the frequency of remaining coarse particles after 10 minutes was relatively small, and redispersibility was good, but the potassium permanganate consumption was a large value of 12 μg / ml, indicating a large amount of elution.

[0125] In Comparative Examples 2 to 4, the amount of polyvinyl alcohol (B) used was reduced to less than 3.0 parts by weight. As a result, the amount of potassium permanganate consumed was smaller than in Comparative Example 1, and the amount of elution was suppressed. However, the frequency of remaining coarse particles after 10 minutes was significantly larger than in Comparative Example 1, indicating that redispersibility was reduced.

[0126] In contrast to these comparative examples, in Examples 1 to 5, the amount of polyvinyl alcohol (B) used was reduced to less than 3.0 parts by weight, and an alkylene oxide compound (C) was used to produce PHA powder. As a result, the amount of potassium permanganate consumed was smaller than in Comparative Example 1, the amount of elution was suppressed, and the frequency of residual coarse particles after 10 minutes was small, indicating good redispersibility.

Claims

1. A polyhydroxyalkanoate powder comprising a polyhydroxyalkanoate (A), a polyvinyl alcohol (B), and an alkylene oxide compound (C), wherein the content of the polyvinyl alcohol (B) is 1.0 parts by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A).

2. The polyhydroxyalkanoate powder of claim 1, wherein the alkylene oxide compound (C) contains blocks of poly(ethylene oxide).

3. A polyhydroxyalkanoate powder according to claim 1 or 2, wherein the content of the alkylene oxide compound (C) is 0.2 parts by weight or more and 1.0 parts by weight or less per 100 parts by weight of the polyhydroxyalkanoate (A).

4. The polyhydroxyalkanoate powder according to claim 1 or 2, wherein the polyhydroxyalkanoate (A) comprises a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units.

5. The polyhydroxyalkanoate powder according to claim 4, wherein said other hydroxyalkanoate units are 3-hydroxyhexanoate units.

6. A method for producing a polyhydroxyalkanoate powder, comprising the steps of preparing an aqueous suspension and spray-drying the aqueous suspension, wherein the aqueous suspension contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A).

7. An aqueous suspension of polyhydroxyalkanoate powder, comprising a polyhydroxyalkanoate powder and an aqueous medium, wherein the polyhydroxyalkanoate powder contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A).

8. A method for producing an aqueous suspension of polyhydroxyalkanoate powder, comprising a step of dispersing polyhydroxyalkanoate powder in an aqueous medium, wherein the polyhydroxyalkanoate powder contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A).

9. A laminate comprising a base layer and a resin layer provided on at least one surface of the base layer, wherein the resin layer contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A).

10. The laminate of claim 9, wherein the substrate layer is paper.

11. A method for producing a laminate, comprising: a step of dispersing polyhydroxyalkanoate powder in an aqueous medium to prepare an aqueous suspension; and a step of applying the aqueous suspension to at least one surface of a substrate and drying by heating to form a resin layer on the substrate, wherein the polyhydroxyalkanoate powder contains polyhydroxyalkanoate (A), polyvinyl alcohol (B), and an alkylene oxide compound (C), and the content of the polyvinyl alcohol (B) is 1.0 part by weight or more and less than 3.0 parts by weight per 100 parts by weight of the polyhydroxyalkanoate (A).

Images