Method for producing polyhydroxyalkanoate sheet and use thereof

Abstract

The object of the present invention is to provide a method for producing a PHA sheet by a simple operation as a technique to replace spray drying. The present invention solves the above-mentioned problems by providing a method for producing a polyhydroxyalkanoate sheet, the method comprising: (a) preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less, and (b) heating and pressurizing the aqueous suspension of polyhydroxyalkanoate prepared in the above step (a) using a hot press apparatus.

Description

Technical Field

[0001] The present invention relates to a method for producing a polyhydroxyalkanoate sheet and its use. Background Art

[0002] Polyhydroxyalkanoates (hereinafter sometimes referred to as "PHA") are known to be biodegradable.

[0003] PHA produced by microorganisms accumulates in the microbial cells of the microorganisms. Therefore, in order to use PHA in the form of plastic, a process of separating / purifying PHA from the microbial cells of the microorganisms is required. In the process of separating / purifying PHA. After the cells of the PHA-containing microorganisms are crushed or the biological components other than PHA are dissolved, PHA can be separated from the obtained aqueous suspension. At this time, for example, separation operations such as centrifugation, filtration, and drying are performed. The drying operation uses a spray dryer, a fluidized bed dryer, etc., and from the perspective of ease of operation, it is preferred to use a spray dryer.

[0004] Heretofore, the present inventors have disclosed a technique for preventing the aggregation of PHA in an aqueous suspension having a pH below 7, in which polyvinyl alcohol (PVA) is added as a dispersant before adjusting the pH of the aqueous suspension to 7 or less, and then the obtained aqueous suspension having a pH below 7 is spray-dried (Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2018 / 070492 Summary of the invention

[0008] Problems to be solved by the invention

[0009] Although the technology of Patent Document 1 is excellent, PHA is obtained in the form of powder during spray drying, and therefore, there is still room for improvement from the perspective of the handleability of PHA. That is, as a material to replace PHA powder, PHA agglomerates (particularly PHA flakes) are desired.

[0010] Therefore, an object of the present invention is to provide a production method capable of obtaining a PHA sheet by a simple operation as a technique replacing spray drying.

[0011] Solution to the problem

[0012] The present inventors have conducted intensive studies to solve the above-mentioned problems and have completed the present invention by finding a new finding that a PHA sheet can be easily obtained by heating and pressurizing a PHA aqueous suspension using a hot press apparatus.

[0013] Therefore, one embodiment of the present invention is a method for producing a polyhydroxyalkanoate sheet, comprising: (a) preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less, and (b) heating and pressurizing the aqueous suspension of polyhydroxyalkanoate prepared in step (a) using a hot press apparatus.

[0014] Another embodiment of the present invention is a polyhydroxyalkanoate sheet containing 97% by weight or more of a polyhydroxyalkanoate and having a thickness of 0.3 to 10.0 mm.

[0015] Effects of the Invention

[0016] According to one embodiment of the present invention, a PHA sheet can be obtained by a simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of a double-belt press machine according to one embodiment of the present invention.

[0018] Figure 2 Schematic diagram showing the temperature behavior of the PHA aqueous suspension in the PHA sheet production process according to one embodiment of the present invention. DETAILED DESCRIPTION

[0019] Hereinafter, one embodiment of the present invention will be described in detail. It should be noted that, in this specification, "A to B" indicating a numerical range means "A or more and B or less" unless otherwise specified. In addition, all documents described in this specification are incorporated herein by reference.

[0020] [1. Summary of the Invention]

[0021] A method for producing a polyhydroxyalkanoate according to one embodiment of the present invention (hereinafter referred to as the "present production method") comprises: (a) preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less, and (b) heating and pressurizing the aqueous suspension of polyhydroxyalkanoate prepared in the step (a) using a hot press.

[0022] The present inventors believe that the following problems exist when spray drying is performed in the manufacture of PHA. For example, in the spray drying operation, a lot of heat energy is required because all the water in the aqueous suspension needs to be evaporated. In addition, the spray dryer used in the spray drying operation tends to become huge, which has problems in terms of increasing the equipment installation area. In addition, in order to transport the high-concentration PHA aqueous suspension below pH 7 to the spray dryer, a low viscosity is preferred. Therefore, a dispersant needs to be added to the aqueous suspension. From the perspective of manufacturing cost and use, the addition of the dispersant still has room for improvement. In addition, in spray drying, PHA is obtained in the form of powder, so from the perspective of the operability of PHA, there is also room for improvement.

[0023] Therefore, intensive research was conducted to develop a technology that can replace spray drying, and as a result, it was found that a method using a hot press device is effective. Specifically, the present inventors first discovered that a PHA sheet can be easily obtained by heating and pressurizing a PHA aqueous suspension using a hot press device. There has been no report on the use of a hot press device in the drying process of a PHA aqueous suspension, and the above findings found by the present inventors are surprising.

[0024] By heating the PHA aqueous suspension using a hot press device, the PHA in the PHA aqueous suspension can be kept at 100°C or above, so that heat fusion can be performed, and it is estimated that a PHA sheet can be obtained as a result. In addition, when using a hot press device, a uniform PHA sheet with little thickness variation can be produced by ensuring sufficient heating and pressure.

[0025] Thus, according to the present manufacturing method, a PHA sheet can be obtained by a simple operation. Therefore, the present manufacturing method is extremely advantageous in the manufacture of a PHA sheet. In addition, according to the present manufacturing method, by forming a sheet, it can be made into a roll for storage, which is also advantageous from the perspective of storage management.

[0026] In addition, according to the above-mentioned structure, the amount of plastic waste generated can be reduced, thereby contributing to the realization of the United Nations Sustainable Development Goals (SDGs), such as Goal 12 "Ensure sustainable consumption and production patterns" and Goal 14 "Conserve and sustainably use the oceans, seas and marine resources for sustainable development".

[0027] [2. Method for producing PHA]

[0028] The present production method is a method including the following steps (a) and (b) as essential steps.

[0029] Step (a): a step of preparing a PHA aqueous suspension having a pH of 7 or less

[0030] Step (b): A step of heating and pressurizing the PHA aqueous suspension prepared in step (a) using a hot press apparatus.

[0031] (Step (a))

[0032] In step (a) of the present production method, an aqueous PHA suspension having a pH of 7 or less is prepared. In the aqueous suspension, PHA is present in a dispersed state in an aqueous medium. In the present specification, an aqueous suspension containing at least PHA may be simply referred to as a "PHA aqueous suspension".

[0033] <PHA>

[0034] In this specification, "PHA" is a general term for polymers having hydroxyalkanoic acid as a monomer unit. The hydroxyalkanoic acid constituting PHA is not particularly limited, and examples thereof include 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxypropionic acid, 3-hydroxyvaleric acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, and 3-hydroxyoctanoic acid. These polymers may be homopolymers or copolymers containing two or more monomer units.

[0035] More specifically, examples of PHA include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (P3HB3HO), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (P3HB3HOD), poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (P3HB3HD), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH). Among them, P3HB, P3HB3HH, P3HB3HV, and P3HB4HB are preferred from the viewpoint of easy industrial production.

[0036] In addition, by changing the composition ratio of the repeating units, the melting point and the crystallinity, as a result, the physical properties such as Young's modulus and heat resistance can be changed, and the physical properties between polypropylene and polyethylene can be imparted. As mentioned above, it is easy to produce industrially. From the perspective of a plastic that is useful in terms of physical properties, a copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid, i.e., P3HB3HH, is more preferred.

[0037] In one embodiment of the present invention, for the composition ratio of the repeating units of P3HB3HH, from the viewpoint of the balance between flexibility and strength, the composition ratio of 3-hydroxybutyrate unit / 3-hydroxyhexanoate unit is preferably 80 / 20 to 99 / 1 (mol / mol), and more preferably 83 / 17 to 97 / 3 (mo1 / mo1). When the composition ratio of 3-hydroxybutyrate unit / 3-hydroxyhexanoate unit is 99 / 1 (mol / mol) or less, sufficient flexibility can be obtained, and when it is 80 / 20 (mol / mol) or more, sufficient hardness can be obtained. When the content of 3HB units in the above-mentioned P3HB3HH increases, the melting temperature of the obtained PHA (PHA sheet) increases, resulting in improved heat resistance. In addition, when the content of 3HB units in the above-mentioned P3HB3HH increases, the crystallization rate of the obtained PHA (PHA sheet) is accelerated, resulting in improved processability. From the viewpoint of improving the heat resistance and processability of the PHA (PHA sheet), the composition ratio of 3HB unit / 3HH unit in the P3HB3HH is particularly preferably 100 / 0, that is, P3HB.

[0038] In step (a), the aqueous PHA suspension used as a starting material is not particularly limited, and can be obtained, for example, by a method comprising a culturing step of culturing a microorganism having an ability to produce PHA intracellularly, and a purification step of decomposing and / or removing substances other than PHA after the culturing step.

[0039] The present production method may include a step of obtaining an aqueous suspension of PHA before step (a) (for example, a step including the above-mentioned culturing step and purification step). The microorganism used in this step is not particularly limited as long as it is a microorganism that can produce PHA in the cell. For example, microorganisms isolated from nature, microorganisms preserved in a strain preservation agency (for example, IFO, ATCC, etc.), or mutants and transformants prepared therefrom can be used. More specifically, for example, Cupriavidus, Alcaligenes, Ralstonia, Pseudomonas, Bacillus, Azotobacter, Nocardia, Aeromonas, etc. can be cited. Among them, microorganisms belonging to the genus Aeromonas, Alcaligenes, Ralstonia, or Cupriavidus are preferred. In particular, strains of A. lipolytica, A. latus, A. caviae, A. hydrophila, C. necator and the like are more preferred, and C. necator is most preferred.

[0040] In addition, when the microorganism does not originally have the ability to produce PHA, or the production of PHA is low, a transformant obtained by introducing a synthase gene and / or a mutant of the target PHA into the microorganism can also be used. The synthase gene of PHA used for the preparation of such a transformant is not particularly limited, and preferably a gene of a PHA synthase derived from Aeromonas caviae. By culturing these microorganisms under appropriate conditions, a microbial cell that accumulates PHA in the cell can be obtained. The method for culturing the microbial cell is not particularly limited, and for example, the method described in Japanese Patent Laid-Open No. 05-93049 can be used.

[0041] Since the PHA-containing microorganisms prepared by culturing the above-mentioned microorganisms contain a large amount of bacterial cell-derived components as impurities, a purification step for decomposing and / or removing impurities other than PHA may be generally performed. In the purification step, physical treatment, chemical treatment, biological treatment, etc. that can be conceived by a person skilled in the art can be applied without particular limitation, and for example, the purification method described in International Publication No. 2010 / 067543 is preferably applied.

[0042] Through the above-mentioned purification process, the amount of impurities remaining in the final product can be roughly determined, so it is preferred to minimize these impurities. Of course, depending on the purpose, impurities can be mixed without damaging the physical properties of the final product, but in the case of medical uses that require high-purity PHA, it is preferred to minimize impurities. As an indicator of the degree of purification at this time, for example, the amount of protein in the PHA aqueous suspension can be cited. The protein amount is preferably less than 30,000 ppm per unit PHA weight, more preferably less than 15,000 ppm, further preferably less than 10,000 ppm, and most preferably less than 7,500 ppm. The purification method is not particularly limited, and for example, the above-mentioned known method can be applied.

[0043] It should be noted that the solvent ("solvent" is also referred to as "aqueous medium") constituting the aqueous suspension of PHA in the present production method may be water, or a mixed solvent of water and an organic solvent. In addition, in the mixed solvent, the concentration of the organic solvent miscible with water is not particularly limited as long as it is less than the solubility of the organic solvent to be used in water. In addition, the organic solvent miscible with water is not particularly limited, and examples thereof include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, pentanol, hexanol, and heptanol; ketones such as acetone and methyl ethyl ketone; tetrahydrofuran, dihydrofuran, and isobutyl alcohol; and Ethers such as oxane; nitriles such as acetonitrile and propionitrile; amides such as dimethylformamide and acetamide; dimethyl sulfoxide, pyridine, piperidine, etc. Among them, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, dimethyl sulfoxide, pyridine, piperidine, etc. are preferred from the viewpoint of easy removal. In addition, methanol, ethanol, 1-propanol, 2-propanol, butanol, acetone, etc. are more preferred from the viewpoint of easy availability. In addition, methanol, ethanol, and acetone are particularly preferred. It should be noted that the aqueous medium constituting the PHA aqueous suspension may contain other solvents, components derived from the bacterial cells, compounds produced during purification, etc., without impairing the essence of the present invention.

[0044] The aqueous medium constituting the aqueous PHA suspension of the present production method preferably contains water. The water content in the aqueous medium is preferably 5 wt % or more, more preferably 10 wt % or more, further preferably 30 wt % or more, and particularly preferably 50 wt % or more.

[0045] <Other>

[0046] In step (a) of the present production method, the PHA aqueous suspension used as the starting material is usually subjected to the above-mentioned purification step, so that it has a pH value exceeding 7. Therefore, the pH of the above-mentioned PHA aqueous suspension is adjusted to 7 or less by step (a) of the present production method. The adjustment method is not particularly limited, and for example, a method of adding an acid can be cited. The acid is not particularly limited, and can be any acid of an organic acid or an inorganic acid, regardless of volatility. More specifically, as the acid, for example, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, etc. can be used.

[0047] The upper limit of the pH of the aqueous PHA suspension adjusted in the adjustment step is 7 or less, preferably 5 or less, and more preferably 4 or less, from the viewpoint of reducing coloration when the PHA is heated and melted and ensuring the stability of the molecular weight during heating and / or drying. In addition, the lower limit of the pH is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, from the viewpoint of the acid resistance of the container. By setting the pH of the aqueous PHA suspension to 7 or less, it is possible to obtain PHA in which coloration during heating and melting is reduced and a decrease in molecular weight during heating and / or drying is suppressed.

[0048] The concentration of PHA in the aqueous suspension of PHA obtained by step (a) of the present production method is economically advantageous from the perspective of dry application. In order to improve productivity, it is, for example, 20% by weight or more, preferably 22.5% by weight or more, more preferably 25% by weight or more, further preferably 27.5% by weight or more, particularly preferably 30% by weight or more, particularly preferably 32.5% by weight or more, particularly further preferably 35% by weight or more, and particularly more preferably 37.5% by weight or more. In addition, the upper limit of the concentration of PHA is, for example, 70% by weight or less, preferably 65% ​​by weight or less, and more preferably 60% by weight or less, because it may not be possible to ensure sufficient fluidity when the closest packing is achieved. The method for adjusting the concentration of PHA is not particularly limited, and examples thereof include methods such as adding an aqueous medium and removing a portion of the aqueous medium (for example, by removing the supernatant after centrifugation). The concentration of PHA can be adjusted at any stage of step (a) or at a stage before step (a).

[0049] In one embodiment of the present invention, the concentration of the polyhydroxyalkanoate in the aqueous suspension prepared in step (a) of the present production method is 20 to 70% by weight.

[0050] In one embodiment of the present invention, the volume median particle size of PHA in the PHA aqueous suspension obtained by step (a) of the present production method (hereinafter referred to as "the volume median particle size of PHA") is preferably 0.5 to 5 μm, more preferably 1 to 4.5 μm, and even more preferably 1 to 4 μm, for example, from the viewpoint of achieving excellent fluidity. The volume median particle size of PHA can be measured using a laser diffraction / scattering particle size distribution measuring apparatus LA-950 manufactured by HORIBA.

[0051] In one embodiment of the present invention, the viscosity of the PHA aqueous suspension obtained by step (a) of the present manufacturing method is preferably 1 to 120 Pa·s, more preferably 2 to 100 Pa·s, and further preferably 3 to 80 Pa·s when subjected to a shear rate of 10 1 / s. When the viscosity of the PHA aqueous suspension is within the above range, in the step (b) described later, it can be pressurized by a hot pressing device. In addition, when the viscosity of the PHA aqueous suspension is within the above range, excellent stacking properties can be achieved. The viscosity of the PHA aqueous suspension can be measured using MCR302 manufactured by Anton Paar.

[0052] (Step (b))

[0053] In step (b) of the present production method, the PHA aqueous suspension prepared in step (a) is heated and pressurized using a hot press. In other words, step (b) of the present production method is a step of heating and pressurizing the PHA aqueous suspension prepared in step (a) using a hot press to form a sheet of PHA. In step (b) of the present production method, the PHA in the PHA aqueous suspension is thermally melted by heating and pressurizing the surface of the hot press, and as a result, a PHA sheet can be obtained.

[0054] In this specification, "hot pressing device" refers to a device used to heat and pressurize an object (e.g., a PHA aqueous suspension), and is not particularly limited as long as it is a device that can heat and pressurize PHA in the PHA aqueous suspension to produce a PHA sheet.

[0055] The method of the hot pressing device is not particularly limited, and for example, it may be any of intermittent, semi-batch, and continuous. That is, in one embodiment of the present invention, step (b) may be a step of heating and pressurizing the PHA aqueous suspension prepared in step (a) by using a hot pressing device in an intermittent manner to form a rectangular sheet of PHA. In addition, in one embodiment of the present invention, step (b) may be a step of heating and pressurizing the PHA aqueous suspension prepared in step (a) by using a hot pressing device in a continuous manner to form a long sheet of PHA.

[0056] As the hot pressing device, for example, a rotary drum dryer, a belt dryer, a disc dryer, a heating roller, a double-belt press (for example, a double-belt hot press), a hot press, a double rotary drum dryer, etc. can be cited. In the case of using a belt dryer, for example, a method of casting a PHA aqueous suspension on a belt dryer through a die head, heating and pressurizing can be exemplified. In addition, in the case of using a rotary drum dryer, for example, a method of supplying a PHA aqueous suspension to a rotary drum and heating it can be exemplified. Among them, from the viewpoint of excellent thermal efficiency, rapidity, and continuous operability, a rotary drum dryer and a double-belt press are preferred. As a rotary drum dryer, for example, a single rotary drum dryer, a double rotary drum dryer, a twin rotary drum dryer, etc. can be cited, and a twin rotary drum dryer can be preferably used. When a double drum dryer is used, the step of supplying the PHA aqueous suspension between the two drums and heating the PHA aqueous suspension between the two drums can be mentioned. In addition, when a double belt press is used, the step of supplying the PHA aqueous suspension between the two belts and heating the PHA aqueous suspension between the two belts can be mentioned.

[0057] The hot pressing device may be (1) a device that performs heating as the main purpose and additionally applies pressure, or may be (2) a device that can heat the object while applying pressure for a desired time. As the device of (1) above, for example, a double-drum dryer may be cited. In addition, as the device of (2) above, for example, a double-belt press may be cited. Below, as an example of a hot pressing device, a double-drum dryer and a double-belt press are cited for explanation.

[0058] <Double drum dryer>

[0059] In a double drum dryer, two drums are used to heat the PHA aqueous suspension. The PHA aqueous suspension is additionally pressurized by the two drums as it passes between the two drums.

[0060] In one embodiment of the present invention, the surface temperature of the hot pressing device is, for example, 80 to 180° C., preferably 80 to 170° C., more preferably 85 to 160° C., and particularly preferably 90 to 155° C. When the surface temperature of the hot pressing device is within the above range, thermal fusion of the PHA in the PHA aqueous suspension proceeds, and a PHA sheet having a certain thickness can be obtained.

[0061] In one embodiment of the present invention, when the hot pressing device is a double drum dryer, the surface temperatures of the two drum dryers in the double drum dryer can be set to the same temperature or different temperatures. When the surface temperatures of the two drum dryers are set to different temperatures, the PHA sheet made from the PHA aqueous suspension fed into the double drum dryer is attached to the drum dryer on the side with a higher temperature, which has the advantage of being easy to recover.

[0062] In one embodiment of the present invention, when the hot pressing device is a double drum dryer, the gap between the two drums can be appropriately set. For example, it is preferably 0.10 to 1.0 mm, more preferably 0.12 to 0.8 mm, and even more preferably 0.14 to 0.6 mm. The film thickness of the obtained PHA sheet can be controlled by the size of the gap.

[0063] In one embodiment of the present invention, when the hot pressing device is a rotary dryer, the rotation speed of the rotary dryer is, for example, 1.0 to 15 rpm, preferably 1.2 to 12 rpm, and more preferably 1.5 to 10 rpm. When the rotation speed of the rotary dryer is within the above range, the PHA in the PHA aqueous suspension is thermally melted, and a PHA sheet having a certain thickness can be obtained.

[0064] In one embodiment of the present invention, the heating of the PHA aqueous suspension can also be performed by pressurized steam. The steam pressure of the pressurized steam is not particularly limited as long as the surface temperature of the hot pressing device reaches the above range (i.e., 80 to 180° C.), and is, for example, 0.05 to 0.8 MPa, preferably 0.06 to 0.7 MPa, and more preferably 0.07 to 0.6 MPa.

[0065] In the present manufacturing method, the moisture content of the obtained PHA sheet is not particularly limited, and is, for example, 5 to 45% by weight, preferably 6 to 42.5% by weight, and more preferably 7 to 40% by weight. The moisture content of the present PHA sheet can be measured by the method described in the Examples. As a method for adjusting the moisture content, for example, when a double drum dryer is used as a hot pressing device, a wider gap between the drums can increase the moisture content.

[0066] In one embodiment of the present invention, when the moisture content of the PHA sheet obtained in the present production method is high, a step of further drying the obtained PHA sheet (for example, a step of drying under reduced pressure, etc.) may be included after step (b).

[0067] <Double belt press>

[0068] As a hot press device in one embodiment of the present invention, a double belt press is used as an example. Figure 1 It should be noted that the hot pressing device used in this manufacturing method is certainly not limited to Figure 1 Double belt press as shown. Alternatively, use Figure 2 The temperature behavior of the PHA aqueous suspension in the PHA sheet production step of the present production method will be described.

[0069] exist Figure 1 In the process, the PHA aqueous suspension introduced from the left side of the double-belt press undergoes a preheating process, a heating / pressurizing process, and a cooling process to be formed into a sheet, and is discharged from the right side of the double-belt press. That is, when a hot pressing device is used, process (b) may include a preheating process, a heating / pressurizing process, and a cooling process. The water content of the PHA aqueous suspension evaporates in the above-mentioned heating / pressurizing process, and the PHA is thermally melted to form a PHA sheet. The transportation of the PHA aqueous suspension in the double-belt press is carried out by the steel belt equipped in the double-belt press.

[0070] Here, for the temperature behavior of PHA aqueous suspension, Figure 2 As shown in FIG. 1 , the temperature of the aqueous PHA suspension is temporarily lowered after the preheating step and becomes a substantially constant stable state ( Figure 2 The temperature rises again after the temperature rises. It is presumed that this is because the temperature temporarily drops due to the heat of vaporization as the water in the PHA aqueous suspension evaporates, and the temperature becomes a substantially constant stable state until the evaporation of the water is completed, and then the temperature rises due to the thermal melting of the PHA. As a result, two temperature peaks are formed before and after the above-mentioned region k in the heating / pressurizing process, showing the characteristic temperature behavior of the PHA aqueous suspension brought about by the present production method.

[0071] In one embodiment of the present invention, the temperature of the PHA aqueous suspension in the heating / pressurizing process is, for example, 100 to 180°C, preferably 105 to 175°C, and more preferably 110 to 170°C. The temperature of the PHA aqueous suspension in the heating / pressurizing process can be measured, for example, by inserting a thermocouple or the like into the PHA aqueous suspension. When the temperature of the PHA aqueous suspension is within the above range, PHA is easily recrystallized and sheet-like PHA can be formed. In particular, when the temperature is too high, it is difficult to recrystallize PHA, resulting in difficulty in forming PHA sheets. It should be noted that in this specification, "the temperature of the PHA aqueous suspension" refers to "the highest reached temperature of the heating / pressurizing process." That is, at Figure 2 In the figure, "temperature of the PHA aqueous suspension" refers to the peak temperature on the right side.

[0072] The surface temperature of the heating part of the hot press device in the heating / pressing process is not particularly limited as long as it can reach the temperature of the PHA aqueous suspension in the above-mentioned heating / pressing process. In one embodiment of the present invention, the surface temperature of the heating part of the hot press device is, for example, 135 to 210°C, preferably 140 to 208°C, and more preferably 145 to 205°C. When the surface temperature of the heating part of the hot press device is within the above range, the thermal fusion of the PHA in the PHA aqueous suspension proceeds, and a PHA sheet having a certain thickness can be obtained.

[0073] In one embodiment of the present invention, the pressure in the heating / pressing step is, for example, 1.5 to 15 N / cm 2 , preferably 2 to 10 N / cm 2 , more preferably 3 to 8 N / cm 2 When the pressure is within the above range, the PHA in the PHA aqueous suspension is melted and a PHA sheet with a certain thickness can be obtained. 2 When the temperature is below 500 °C, the water in the PHA aqueous suspension can be discharged, and bubbles are less likely to be generated in the manufactured PHA sheet.

[0074] In one embodiment of the present invention, the heating residence time of the PHA aqueous suspension in the heating / pressurizing step is, for example, 10 to 100 seconds, preferably 15 to 90 seconds, and more preferably 20 to 80 seconds. It should be noted that in this specification, "heating residence time" refers to the time for both heating and pressurizing in the above-mentioned heating / pressurizing step.

[0075] In one embodiment of the present invention, Figure 1As shown, the PHA aqueous suspension may be preheated before the heating / pressing step. The surface temperature of the preheating portion of the hot pressing device is, for example, 135 to 210° C., preferably 140 to 208° C., and more preferably 145 to 205° C. When the surface temperature of the preheating portion of the hot pressing device is within the above range, the thermal fusion of the PHA in the PHA aqueous suspension proceeds, and a PHA sheet having a certain thickness can be obtained.

[0076] In one embodiment of the present invention, the preheating residence time is, for example, 5 to 100 seconds, preferably 10 to 90 seconds, and more preferably 15 to 80 seconds. It should be noted that in this specification, "preheating residence time" refers to the time for heating in the preheating step.

[0077] In one embodiment of the present invention, Figure 1 As shown, the PHA sheet after being pressed between the belts can be cooled. This can promote the recrystallization of PHA in the PHA sheet. The temperature and time for cooling the PHA sheet can be appropriately set.

[0078] In one embodiment of the present invention, when the hot pressing device is a double belt press, the gap between the two belts can be appropriately set. For example, it is preferably 1 to 15 mm, more preferably 1.5 to 10 mm, and even more preferably 2 to 5 mm. The film thickness of the obtained PHA sheet can be controlled by the size of the gap.

[0079] In one embodiment of the present invention, when the hot pressing device is a double belt press, the belt speed is, for example, 0.1 to 10 m, preferably 0.2 to 5 m, and more preferably 0.25 to 4 m. When the belt speed is within the above range, the PHA in the PHA aqueous suspension is thermally melted to obtain a PHA sheet having a certain thickness. It should be noted that the heating residence time and the preheating residence time can be controlled by appropriately setting the belt speed.

[0080] In one embodiment of the present invention, the manufacturing method may include any process after process (b) according to the purpose. Such a process is not particularly limited, and examples thereof include: a printing process, a vapor deposition process, a lamination process, a bag making process, a crushing process, etc. In addition, a PHA sheet conveying process may be included after process (b). In this case, a long PHA sheet having a desired length can be obtained.

[0081] 〔3. Polyhydroxyalkanoate sheet〕

[0082] The polyhydroxyalkanoate sheet (hereinafter referred to as "the present PHA sheet") according to one embodiment of the present invention contains 97% by weight or more of PHA when the entire sheet is 100% by weight, and has a thickness of 0.3 to 10.0 mm. The content of PHA in the present PHA sheet refers to the content based on the solid content excluding water (i.e., solid content concentration). In other words, a solid content concentration of 100% by weight is a state after all water has evaporated.

[0083] In one embodiment of the present invention, the PHA sheet contains 97% by weight or more of PHA, preferably 98% by weight or more, more preferably 99% by weight or more, and further preferably 100% by weight. In one embodiment of the present invention, the PHA sheet is preferably formed only by PHA. The present manufacturing method is a method to replace spray drying, so the addition of various components required for spray drying can be avoided, and a higher purity PHA can be obtained. For example, in the case of food use, medical use, etc. requiring high cleanliness, the PHA sheet preferably does not contain a dispersant, etc.

[0084] In one embodiment of the present invention, the thickness of the PHA sheet is 0.3 to 10.0 mm, preferably 0.32 to 9.0 mm, and more preferably 0.34 to 8.0 mm. In one embodiment of the present invention, when a rotary dryer, a belt dryer, a disc dryer, or a heated roller is used, the thickness of the PHA sheet is, for example, 0.3 to 3.0 mm, preferably 0.32 to 2.5 mm, and more preferably 0.34 to 2.0 mm. In one embodiment of the present invention, when a double-belt press (e.g., a double-belt hot press), a hot press, or a double-drum dryer is used, the thickness of the PHA sheet is, for example, 1.0 to 10.0 mm, preferably 1.2 to 9.0 mm, and more preferably 1.4 to 8.0 mm. For example, when a double-drum dryer is used, the thickness of the PHA sheet can be controlled by, for example, adjusting the gap (gap) between the two rotary dryers in the double-drum dryer. In addition, for example, when a double steel belt hot press is used, the thickness of the PHA sheet can be controlled by adjusting the gap (gap) between the two belts in the double steel belt hot press. It should be noted that the thickness of the PHA sheet can be measured by the method described in the Examples.

[0085] In one embodiment of the present invention, the thickness of the PHA sheet is preferably uniform. The uniformity of the thickness of the PHA sheet can be evaluated by measuring the thickness of multiple locations in the PHA sheet and calculating the standard deviation and / or coefficient of variation of the sheet thickness. The lower the values ​​of the standard deviation and coefficient of variation of the sheet thickness, the more uniform the thickness of the PHA sheet can be evaluated. It should be noted that the coefficient of variation is a value calculated by dividing the standard deviation of the sheet thickness by the average value of the sheet thickness.

[0086] In one embodiment of the present invention, the standard deviation of the sheet thickness is, for example, less than 0.2, preferably less than 0.18, and more preferably less than 0.15. The lower limit is not particularly limited, for example, it is greater than 0.005. In addition, in one embodiment of the present invention, the coefficient of variation is, for example, less than 0.100, preferably less than 0.090, and more preferably less than 0.080. The lower limit is not particularly limited, for example, it is greater than 0.001. It should be noted that the present PHA sheet includes not only sheets with uniform thickness, but also lumps with uneven thickness formed by agglomeration of PHA powder. In addition, the present PHA sheet can be a sheet with holes (for example, mesh-like).

[0087] In one embodiment of the present invention, the moisture content of the PHA sheet is as described above.

[0088] As described above, the PHA sheet is obtained by hot-melting the primary particles of PHA. In one embodiment of the present invention, the PHA sheet is, for example, formed by hot-melting PHA having a volume median particle size of primary particles of PHA (hereinafter referred to as "primary particle size") of 0.5 to 6 μm, preferably formed by hot-melting PHA having a primary particle size of 0.5 to 5 μm, and more preferably formed by hot-melting PHA having a primary particle size of 0.5 to 4 μm.

[0089] It should be noted that the PHA sheet is also allowed to contain various components generated or not removed during the manufacturing process.

[0090] The PHA sheet can be used for various purposes in agriculture, fishery, forestry, horticulture, medicine, sanitary products, clothing, non-clothing materials, packaging, automobiles, building materials, and other fields.

[0091] The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0092] That is, one embodiment of the present invention is the following aspect.

[0093] <1> A method for producing a polyhydroxyalkanoate sheet, the method comprising:

[0094] (a) a step of preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less, and

[0095] (b) A step of heating and pressurizing the polyhydroxyalkanoate aqueous suspension prepared in the step (a) using a hot press apparatus.

[0096] <2> The method for producing a polyhydroxyalkanoate sheet according to <1>, wherein in the step (b), the surface temperature of the hot press device is 80 to 180°C.

[0097] <3> The method for producing a polyhydroxyalkanoate sheet according to <1> or <2>, further comprising the step (a) of adjusting the viscosity of the polyhydroxyalkanoate aqueous suspension to 1 to 120 Pa·s when subjected to a shear rate of 10 1 / s.

[0098] <4> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <3>, wherein in the step (b), the temperature of the polyhydroxyalkanoate aqueous suspension is 80 to 180°C.

[0099] <5> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <4>, wherein the heat pressing device is a device selected from a drum dryer, a belt dryer, a tray dryer, a heating roll, and a double-belt press device.

[0100] <6> The method for producing a polyhydroxyalkanoate sheet according to <5>, wherein the heat pressing device is a rotary drum dryer,

[0101] The rotation speed of the rotary drum dryer is 1 to 15 rpm.

[0102] <7> The method for producing a polyhydroxyalkanoate sheet according to <5> or <6>, wherein the heat pressing device is a double drum dryer,

[0103] The surface temperatures of the two drum dryers in the twin drum dryer were set to different temperatures.

[0104] <8> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <7>, wherein in the step (b), the heating residence time of the polyhydroxyalkanoate aqueous suspension in the hot press device is 10 to 100 seconds.

[0105] <9> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <8>, wherein in the step (a), the polyhydroxyalkanoate concentration in the polyhydroxyalkanoate aqueous suspension is 20 to 70% by weight.

[0106] <10> A polyhydroxyalkanoate sheet comprising 97% by weight or more of a polyhydroxyalkanoate and having a thickness of 0.3 to 10.0 mm.

[0107] Furthermore, another embodiment of the present invention is the following.

[0108] <1> A method for producing a polyhydroxyalkanoate sheet, the method comprising:

[0109] (a) a step of preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less, and

[0110] (b) A step of heating the polyhydroxyalkanoate aqueous suspension prepared in the step (a) using a heating device.

[0111] <2> The method for producing a polyhydroxyalkanoate sheet according to <1>, wherein in the step (b), the surface temperature of the heating device is 80 to 170°C.

[0112] <3> The method for producing a polyhydroxyalkanoate sheet according to <1> or <2>, wherein the heating device is a device selected from a drum dryer, a belt dryer, a disk dryer, and a heating roll.

[0113] <4> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <3>, wherein the heating device is a drum dryer.

[0114] The rotation speed of the rotary drum dryer is 1 to 15 rpm.

[0115] <5> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <4>, wherein the heating device is a double-drum dryer.

[0116] The surface temperatures of the two drum dryers in the twin drum dryer were set to different temperatures.

[0117] <6> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <5>, wherein in the step (a), the polyhydroxyalkanoate concentration in the polyhydroxyalkanoate aqueous suspension is 20 to 70% by weight.

[0118] <7> A polyhydroxyalkanoate sheet comprising 97% by weight or more of a polyhydroxyalkanoate and having a thickness of 0.3 to 3.0 mm.

[0119] Furthermore, another embodiment of the present invention is the following.

[0120] <1> A method for producing a polyhydroxyalkanoate sheet, the method comprising:

[0121] (a) a step of preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less, and

[0122] (b) A step of heating the polyhydroxyalkanoate aqueous suspension prepared in the step (a) using a hot press apparatus.

[0123] <2> The method for producing a polyhydroxyalkanoate sheet according to <1>, further comprising the step (a) of adjusting the viscosity of the polyhydroxyalkanoate aqueous suspension to 1 to 120 Pa·s when a shear rate of 10 1 / s is applied.

[0124] <3> The method for producing a polyhydroxyalkanoate sheet according to <1> or <2>, wherein in the step (b), the temperature of the polyhydroxyalkanoate aqueous suspension is 100 to 180°C.

[0125] <4> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <3>, wherein in the step (b), the heating residence time of the polyhydroxyalkanoate aqueous suspension in the hot press device is 10 to 100 seconds.

[0126] <5> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <4>, wherein the heat press device is a double-belt press device.

[0127] <6> The method for producing a polyhydroxyalkanoate sheet according to any one of <1> to <5>, wherein in the step (a), the polyhydroxyalkanoate concentration in the polyhydroxyalkanoate aqueous suspension is 30 to 70% by weight.

[0128] <7> A polyhydroxyalkanoate sheet comprising 97% by weight or more of a polyhydroxyalkanoate and having a thickness of 1.0 to 10.0 mm.

[0129] Example

[0130] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. It should be noted that in the examples, "P3HB3HH" is used as "PHA", and "PHA" can be replaced by "P3HB3HH".

[0131] 〔Measurement and evaluation methods〕

[0132] The measurements and evaluations in the examples were performed according to the following methods.

[0133] (Water content)

[0134] The moisture content of the sheet was measured using a heat-drying moisture meter ML-50 manufactured by A&D Co., Ltd. The measurement was carried out at a heating temperature of 130° C., and the moisture content was measured based on the change in sheet weight.

[0135] (Thickness of sheet)

[0136] The thickness of the obtained sheet was measured at 10 locations using a digital caliper, and the average value was defined as the sheet thickness.

[0137] [Example 1]

[0138] (Preparation of bacterial culture fluid)

[0139] The Ralstonia eutropha KNK-005 strain described in paragraph

[0049] of International Publication No. 2008 / 010296 was cultured using the method described in paragraphs

[0050] to

[0053] of the document to obtain a bacterial culture solution containing PHA. It should be noted that Ralstonia eutropha is currently classified as an insecticidal copper-greedy bacterium. The composition ratio of the repeating units of PHA (composition ratio of 3HB units / 3HH units) is 92 / 8 to 99 / 1 (mol / mol).

[0140] (Sterilization treatment)

[0141] The bacterial cell culture solution obtained above was sterilized by heating and stirring at an internal temperature of 60 to 80°C for 20 minutes.

[0142] (High-pressure crushing treatment)

[0143] 0.2 wt% sodium dodecyl sulfate was added to the sterilized bacterial culture solution obtained above. A sodium hydroxide aqueous solution was further added to make the pH reach 11.0, and then kept at 50°C for 1 hour. Then, a high-pressure crusher (high-pressure homogenizer model PA2K, manufactured by Niro Soavi) was used to pulsate at 450-550 kgf / cm 2 High pressure crushing was carried out under the pressure of

[0144] (Purification treatment)

[0145] An equal amount of distilled water was added to the crushed liquid after high-pressure crushing obtained above. After centrifugation, the supernatant was removed and concentrated twice. To the concentrated PHA aqueous suspension, an equal amount of sodium hydroxide aqueous solution (pH 11.0) as the removed supernatant was added and centrifuged. Then, after removing the supernatant, water was added again to suspend it, and 0.2% by weight of sodium dodecyl sulfate and 1 / 100 weight of protease (Esperase, Novozymes) of PHA were added, and stirred for 2 hours at 50°C at pH 10.0. Then, the supernatant was removed by centrifugation and concentrated four times. Water was further added to adjust the PHA concentration to 53.5% by weight.

[0146] (PHA sheet molding using a drum dryer)

[0147] Sulfuric acid was added to the PHA aqueous suspension obtained above to adjust the pH to 3.0. The obtained slurry was put into a double drum type drum dryer (D0405 type, surface area 1.25 m2, manufactured by Katsuragi Industry Co., Ltd.) 2), and formed into a PHA sheet with a drum gap of 0.2-0.3 mm, a drum speed of 2 rpm, and a surface temperature of 134°C (vapor pressure 0.3 MPa) on both drums. The moisture content of the obtained PHA sheet was 17.6% by weight. After drying at 50°C overnight, the thickness of the sheet was measured and the result was 0.93 mm. The solid content concentration of the polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0148] [Example 2]

[0149] A PHA sheet was obtained by the same method as in Example 1 except that the drum gap was set to 0.15 to 0.2 mm. The moisture content of the sheet after molding was 7.4 wt %, and the thickness of the sheet after drying was 0.62 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0150] [Example 3]

[0151] A PHA sheet was obtained by the same method as in Example 2 except that the drum rotation speed was set to 3 rpm. The moisture content of the sheet after molding was 10.7 wt %, and the thickness of the obtained sheet after drying was 0.38 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0152] [Example 4]

[0153] A PHA sheet was obtained by the same method as in Example 2 except that the drum rotation speed was set to 4 rpm. The moisture content of the sheet after molding was 13.6 wt %, and the thickness of the sheet obtained after drying was 0.55 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0154] [Example 5]

[0155] A PHA sheet was obtained by the same method as in Example 1 except that the drum speed was set to 5 rpm, the drum surface temperature on one side was set to 134°C (vapor pressure 0.3 MPa), and the surface temperature on the other side was set to 107°C (vapor pressure 0.13 MPa). The moisture content of the sheet after molding was 24.2% by weight, and the thickness of the obtained sheet after drying was 0.40 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0156] [Example 6]

[0157] A PHA sheet was obtained by the same method as in Example 1 except that the drum speed was set to 4 rpm, the drum gap was set to 0.3 to 0.4 mm, the drum surface temperature on one side was set to 144°C (vapor pressure 0.4 MPa), and the surface temperature on the other side was set to 107°C (vapor pressure 0.13 MPa). The moisture content of the sheet after molding was 32.3% by weight, and the thickness of the sheet obtained after drying was 0.61 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0158] [Example 7]

[0159] A PHA sheet was obtained by the same method as in Example 6 except that the drum speed was set to 5 rpm, the drum surface temperature on one side was set to 152°C (vapor pressure 0.5 MPa), and the surface temperature on the other side was set to 107°C (vapor pressure 0.13 MPa). The moisture content of the sheet after molding was 27.9% by weight, and the thickness of the sheet obtained after drying was 0.68 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0160] [Example 8]

[0161] A PHA sheet was obtained by the same method as in Example 7 except that the drum rotation speed was set to 6 rpm. The moisture content of the sheet after molding was 32.0 wt %, and the thickness of the obtained sheet after drying was 0.66 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0162] [Example 9]

[0163] A PHA sheet was obtained by the same method as in Example 2 except that the composition ratio of the repeating units of PHA (composition ratio of 3-hydroxybutyrate unit / 3-hydroxyhexanoate unit) was set to 80 / 20 to 91 / 9 (mol / mol) and the pH of the PHA aqueous suspension was adjusted to 4.0. The moisture content after the sheet was formed was 7.4% by weight, and the thickness of the obtained sheet after drying was 0.47 mm. The solid content concentration of the polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0164] [Example 10]

[0165] A PHA sheet was obtained by the same method as in Example 9 except that the drum rotation speed was set to 3 rpm. The moisture content of the sheet after molding was 7.5 wt %, and the thickness of the obtained sheet after drying was 0.52 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0166] [Example 11]

[0167] A PHA sheet was obtained by the same method as in Example 9 except that the drum rotation speed was set to 4 rpm. The moisture content of the sheet after molding was 8.7 wt %, and the thickness of the obtained sheet after drying was 0.52 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0168] [Example 12]

[0169] A PHA sheet was obtained by the same method as in Example 9 except that the drum rotation speed was set to 2 rpm and the drum gap was set to 0.2 to 0.3 mm. The moisture content of the sheet after molding was 8.6% by weight, and the thickness of the sheet obtained after drying was 0.58 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0170] [Example 13]

[0171] A PHA sheet was obtained by the same method as in Example 12 except that the drum rotation speed was set to 6 rpm. The moisture content of the sheet after molding was 23.1% by weight, and the thickness of the obtained sheet after drying was 0.62 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0172] [Example 14]

[0173] A PHA sheet was obtained by the same method as in Example 13 except that the drum gap was set to 0.3 to 0.4 mm. The moisture content of the sheet after molding was 26.6 wt %, and the thickness of the sheet obtained after drying was 0.66 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0174] [Example 15]

[0175] A PHA sheet was obtained by the same method as in Example 13 except that the PHA concentration was adjusted to 30.0% by weight and the vapor pressure of the two drums was set to 0.08 MPa during the purification treatment. The moisture content of the sheet after molding was 37.4% by weight, and the thickness of the sheet obtained after drying was 0.55 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0176] [Example 16]

[0177] A PHA sheet was obtained by the same method as in Example 15 except that the drum gap was set to 0.3 to 0.4 mm. The moisture content of the sheet after molding was 33.9 wt %, and the thickness of the sheet obtained after drying was 0.62 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0178]

[0179] [result]

[0180] According to Examples 1 to 4, it is known that a PHA sheet having a certain thickness can be obtained by heating and pressurizing the polyhydroxyalkanoate aqueous suspension using a hot press device.

[0181] Furthermore, it was found from Examples 5 to 8 that a PHA sheet having a constant thickness can be obtained even when the surface temperatures of the two drum dryers in the twin drum dryer are set to different temperatures.

[0182] Furthermore, it can be seen from Examples 9 to 16 that even if the composition of PHA is changed, a PHA sheet having a certain thickness can be obtained.

[0183] [Example 17]

[0184] (Preparation of bacterial culture fluid)

[0185] The culture was carried out according to the method described in International Publication No. 2010 / 067543 to obtain a bacterial culture solution containing PHA. It should be noted that Ralstonia eutropha is currently classified as an insecticidal copper-greedy bacterium. The composition ratio of the repeating units of PHA contained in the above-mentioned bacterial cells (composition ratio of 3HB unit / 3HH unit) is 92 / 8 to 99 / 1 (mol / mol).

[0186] (PHA sheet molding using a double steel belt hot press)

[0187] By the same method as in Example 1, (sterilization treatment) to (purification treatment) were performed to obtain a PHA aqueous suspension having a PHA concentration of 50.0 wt%. Sulfuric acid was added to the obtained PHA aqueous suspension to adjust the pH to 3.5. The viscosity of the PHA aqueous suspension was 9.1 Pa·s when subjected to a shear rate of 10 1 / s. The obtained PHA aqueous suspension was put into Figure 1 The double steel belt hot press (manufactured by DYMCO) shown in the figure was set with a belt gap of 3 mm, a belt speed of 0.3 m / min, a preheating belt temperature of 170°C, and a pressure of 4.9 N / cm 2 , the heating zone temperature during pressurization was 170°C, and the cooling zone temperature was 35°C. It should be noted that the heating residence time was 60 seconds, and the preheating residence time was 32 seconds. The thickness of the PHA formed into a sheet was 1.7 mm. The solid content concentration of the polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0188] In addition, the temperature of the PHA aqueous suspension in the double-belt hot press was measured by inserting a thermocouple into the PHA aqueous suspension.

[0189] [Example 18]

[0190] A PHA sheet was obtained by the same method as in Example 17 except that the heating zone temperature during pressurization was set to 150° C. The thickness of the PHA sheet was 1.8 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0191] [Example 19]

[0192] A PHA sheet was obtained by the same method as in Example 18 except that the preheating zone temperature was set to 150° C. The thickness of the PHA sheet was 1.8 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0193] [Example 20]

[0194] A PHA sheet was obtained in the same manner as in Example 17 except that the preheating zone temperature was set to 200° C. and the zone speed was set to 0.6 m / min. The PHA sheet thickness was 1.7 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100 wt %.

[0195] [Example 21]

[0196] A PHA sheet was obtained in the same manner as in Example 20 except that the heating zone temperature during pressurization was set to 180° C. The thickness of the PHA sheet was 1.6 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0197] [Example 22]

[0198] A PHA sheet was obtained by the same method as in Example 20 except that a PHA aqueous suspension having a composition ratio of PHA repeating units (composition ratio of 3HB units / 3HH units) of 80 / 20 to 91 / 9 (mol / mol) and a viscosity of 13.4 Pa·s when subjected to a shear rate of 10 1 / s was used. The thickness of the PHA sheet was 2.2 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0199] [Example 23]

[0200] A PHA sheet was obtained by the same method as in Example 22 except that the band gap was changed to 5 mm. The thickness of the PHA sheet was 3.4 mm. The solid content concentration of polyhydroxyalkanoate in the obtained PHA sheet was 100% by weight.

[0201] [Comparative Example 1]

[0202] The aqueous suspension of PHA was obtained by the same method as in Example 22 until the purification treatment. The aqueous suspension of PHA obtained was dried in a box dryer at 60° C. for 2 days to powderize PHA. The powder was heated and pressurized by the same method as in Example 22 except that the PHA powder was put into a double steel belt hot press. The PHA was not sufficiently hot-melted and did not form a sheet, but became a powder.

[0203] [Comparative Example 2]

[0204] The aqueous PHA suspension was obtained by the same method as in Example 22 until the purification treatment. 5 g of the obtained aqueous PHA suspension was placed in a SUS container with a diameter of 5 cm and heated at 110° C. in an oil bath (TBX183SB manufactured by ADVANTEC). Although the water content of the aqueous PHA suspension evaporated, it did not form flakes but became powder.

[0205] [result]

[0206] Table 2 shows the specific production conditions of Examples 17 to 23 and Comparative Examples 1 and 2.

[0207]

[0208] Table 3 shows the results of evaluation of the sheet thickness average value, sheet thickness standard deviation, and coefficient of variation of the obtained PHA.

[0209] [Table 3]

[0210]

[0211] According to Examples 17 to 23 in Tables 2 and 3, a PHA sheet having a certain thickness can be obtained by heating and pressurizing the polyhydroxyalkanoate aqueous suspension using a hot press device. In addition, according to Examples 17 to 23 and Comparative Example 1, it can be seen that if the PHA aqueous suspension is not heated and pressurized, it cannot be formed into a sheet. It can be inferred that this is because when the PHA powder is put in, the contact with the heating part of the belt press is poor and it is not fully heated. In addition, according to Comparative Example 2, a sheet cannot be formed even when the PHA aqueous suspension is not pressurized but only heated. Therefore, it can be seen that in order to obtain a PHA sheet, it is necessary to both heat and pressurize the PHA aqueous suspension. Moreover, according to Examples 22 and 23, it can be seen that the thickness of the obtained PHA sheet can be controlled by the belt gap.

[0212] The above results show that, through the present production method, a PHA sheet having a certain thickness can be produced through a simple operation.

[0213] Industrial Applicability

[0214] The present production method can produce PHA sheets with simple operation, and thus can be advantageously used in the production of PHA sheets. In addition, the PHA sheets obtained by the present production method can be suitably used in agriculture, fisheries, forestry, gardening, medicine, sanitary products, clothing, non-clothing materials, packaging, automobiles, building materials, and other fields.

Claims

1. A method for producing a polyhydroxyalkanoate sheet, the method comprising: (a) a step of preparing an aqueous suspension of polyhydroxyalkanoate having a pH of 7 or less, and (b) A step of heating and pressurizing the polyhydroxyalkanoate aqueous suspension prepared in the step (a) using a hot press apparatus.

2. The method for producing a polyhydroxyalkanoate sheet according to claim 1, wherein In the step (b), the surface temperature of the hot pressing device is 80 to 180°C.

3. The method for producing a polyhydroxyalkanoate sheet according to claim 1 or 2, wherein: The step (a) further comprises the step of adjusting the viscosity of the polyhydroxyalkanoate aqueous suspension to 1 to 120 Pa·s when subjected to a shear rate of 10 1 / s.

4. The method for producing a polyhydroxyalkanoate sheet according to claim 1 or 2, wherein: In the step (b), the temperature of the polyhydroxyalkanoate aqueous suspension is 80 to 180°C.

5. The method for producing a polyhydroxyalkanoate sheet according to claim 1 or 2, wherein: The heat pressing device is a device selected from a rotary drum dryer, a belt dryer, a disc dryer, a heating roller and a double-belt pressurizing device.

6. The method for producing a polyhydroxyalkanoate sheet according to claim 5, wherein The hot pressing device is a rotary drum dryer, The rotating speed of the rotary drum dryer is 1 to 15 rpm.

7. The method for producing a polyhydroxyalkanoate sheet according to claim 5, wherein The hot pressing device is a double drum dryer. The surface temperatures of the two drum dryers in the twin drum dryer were set to different temperatures.

8. The method for producing a polyhydroxyalkanoate sheet according to claim 1 or 2, wherein In the step (b), the heating residence time of the polyhydroxyalkanoate aqueous suspension in the hot press device is 10 to 100 seconds.

9. The method for producing a polyhydroxyalkanoate sheet according to claim 1 or 2, wherein: In the step (a), the concentration of the polyhydroxyalkanoate in the polyhydroxyalkanoate aqueous suspension is 20 to 70% by weight.

Images