A high-yield granulation molding method of polyhydroxyalkanoate

Abstract

This invention provides a high-yield granulation method for polyhydroxyalkanoates (PHA), wherein the method pre-processes PHA powder with a medium particle size (D50) of 1-50 μm to agglomerate the PHA powder and increase its bulk density to 0.4-0.6 g / cm³. 3 Within the specified range, the agglomerated material is extruded and granulated. This invention pre-processes the polyhydroxyalkanoate powder before granulation, causing it to agglomerate and compact, increasing its bulk density to 0.4-0.6 g / cm³. 3 This method increases production while effectively preventing powder flying and bridging during subsequent extrusion granulation. It also ensures uniform material feeding and produces uniform granules. The high-yield granulation method of this invention is simple, low-cost, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of biochemical technology, and in particular to a high-yield granulation method for polyhydroxyalkanoates. Background Technology

[0002] Polyhydroxyalkanoates (PHAs) are intracellular polyesters synthesized by numerous bacteria. As a biosynthetic thermoplastic polymer, they possess physicochemical properties similar to synthetic plastics, as well as many superior properties not found in synthetic plastics, such as biodegradability, biocompatibility, optical activity, piezoelectricity, and gas barrier properties. PHAs have broad application prospects in biodegradable packaging materials, tissue engineering materials, sustained-release materials, electrical materials, and medical materials; however, large-scale application is only possible after reducing the production cost of PHAs.

[0003] Currently, the conventional production method for PHA includes: breaking the cell walls of the PHA fermentation broth to precipitate the intracellular PHA products, separating and concentrating them, and then spray-drying the concentrate to obtain powdered PHA products. At this stage, the powdered product is generally not used directly as a raw material for downstream applications; instead, it is extruded and granulated into pellets for further processing.

[0004] However, during the twin-screw extrusion granulation process, problems such as unstable feeding and bridging of powder in the hopper are prone to occur, which ultimately result in uneven particle size of the produced granules, and the presence of irregular and unqualified particles, as well as low granule output.

[0005] Current solutions generally involve increasing forced feeding to improve output, or adding vibration or anti-bridging devices to the feed hopper to address bridging issues. However, these methods only treat the symptoms, not the root cause, and do not fundamentally solve the problem. Furthermore, forced feeding is prone to unstable feeding and uneven feed thickness. Summary of the Invention

[0006] This invention provides a high-yield granulation method for polyhydroxyalkanoates, which solves the defects of easy powder flying, easy bridging and low yield in the granulation process of the prior art, and realizes high-yield granulation of polyhydroxyalkanoates.

[0007] This invention provides a high-yield granulation method for polyhydroxyalkanoates, comprising:

[0008] Polyhydroxyalkanoate powder with a particle size D50 of 1-50 μm is pre-processed to agglomerate the powder and increase its bulk density to 0.4-0.6 g / cm³. 3 Within the scope; the aggregated material is extruded and granulated.

[0009] This invention has revealed that, compared to conventional synthetic plastics such as polyolefins and polyaromatics, polyhydroxyalkanoates possess unique characteristics. Due to their relationship with upstream production processes, the final product is a powder with a particle size D50 (medium particle size) of approximately 1-50 μm. This results in a very small particle size, large specific surface area, and low bulk density (approximately 0.2 g / cm³). 3 Powders with poor flowability are prone to problems such as powder flying, bridging, and low yield during extrusion granulation. Polymers such as PP and PE do not have such problems during extrusion granulation because they do not have excessively small particle sizes.

[0010] To address the unique granulation problem of polyhydroxyalkanoates (PHA), this invention pre-processes the PHA powder before granulation, increasing its bulk density to 0.4-0.6 g / cm³. 3 The main purpose is to agglomerate the powder and prevent it from dispersing again due to pressure or other processing conditions during subsequent processing. This effectively avoids phenomena such as powder flying and bridging during subsequent extrusion granulation, while also significantly increasing output.

[0011] In some specific embodiments of the present invention, the polyhydroxyalkanoate (PHA) powder is prepared by microbial fermentation. Currently, PHA can be synthesized through microbial fermentation (also called bacterial fermentation), genetically modified plants, activated sludge, and chemical synthesis. Among these, microbial fermentation is the most widely used and lowest-cost method. The present invention also targets PHA powder obtained by microbial fermentation, which can be prepared according to conventional microbial fermentation methods known in the art.

[0012] In some specific embodiments of the present invention, the polyhydroxyalkanoate powder is obtained by the following steps:

[0013] a. Ferment recombinant bacteria, such as Escherichia coli and halophilic bacteria, in a culture medium to obtain PHA fermentation broth;

[0014] b. The PHA fermentation broth is centrifuged to remove the supernatant and then washed with clean water.

[0015] c. After washing, the PHA emulsion is subjected to cell wall disruption, causing intracellular PHA products to precipitate in the disruption solution.

[0016] d. Use centrifuge equipment to separate and concentrate the PHA product in the solution to obtain a suspension concentrate with a dry matter content of 25% to 30%;

[0017] e. The concentrated liquid is dried to obtain powdered PHA product.

[0018] In a specific embodiment of the present invention, in order to agglomerate the polyhydroxyalkanoate powder, the bulk density is increased to 0.4-0.6 g / cm³.3 Within the scope, the pre-processing includes pressurizing and heating the polyhydroxyalkanoate powder, wherein the pressurizing pressure is 1-3 MPa and the heating temperature is 5-10°C higher than the melting point of the polyhydroxyalkanoate powder.

[0019] This invention uses specific heat and pressure to initially melt, sinter, and extrude polyhydroxyalkanoate powder into dense granules, thereby increasing the material's density. After the aforementioned pressurized heating treatment, the agglomerated powder is less likely to disperse again, which is beneficial for extrusion granulation.

[0020] In some specific embodiments of the present invention, the heating duration is 10-30 seconds.

[0021] The heating duration can be any value between 10 and 30 seconds, such as 10, 12, 15, 18, 20, 23, 25, 28, or 30 seconds. The specific heating duration needs to be adjusted according to the type or melting point of the polyhydroxyalkanoate, the pressure applied, and the compaction conditions.

[0022] In some specific embodiments of the present invention, the pressurizing device employs two metal tracks rotating in the same or opposite directions, with the pressure between the metal tracks being adjustable from 1 to 3 MPa. The duration of the heating is controlled by adjusting the length and speed of the metal tracks.

[0023] The metal track may have grooves, and the number and size of the grooves can be set according to the actual situation.

[0024] In some specific embodiments of the present invention, the pressurizing device employs two metal plates rotating in the same or opposite directions, with the pressure between the metal plates being adjustable from 1 to 3 MPa. The duration of the heating is controlled by adjusting the length and speed of the metal plates.

[0025] In some specific embodiments of the present invention, a metal track and a metal deck can be combined to form a pressurizing device. Specifically, they can rotate in the same direction or in opposite directions, and the pressure between them is adjustable from 1 to 3 MPa. The duration of heating is controlled by adjusting their length and speed.

[0026] In some specific embodiments of the present invention, the pressurizing device employs two metal rollers rotating in the same or opposite directions, with the pressure between the metal rollers being adjustable from 1 to 3 MPa. The duration of the heating is controlled by adjusting the rotational speed of the metal rollers.

[0027] Preferably, the diameter of the metal roller is 0.3-1 meter, for example, it can be 0.3 meters, 0.4 meters, 0.5 meters, 0.6 meters, 0.7 meters, 0.8 meters, 0.9 meters, or 1 meter. In one specific embodiment of the present invention, the diameter of the metal roller is 0.5 meters.

[0028] In some specific embodiments of the present invention, the temperature of the pressurizing device is raised to 5-10°C above the melting point of the polyhydroxyalkanoate powder and maintained at that temperature.

[0029] By raising the temperature of the pressurizing device and then transferring the heat to the polyhydroxyalkanoate powder inside the pressurizing device, the polyhydroxyalkanoate powder is simultaneously heated to 5-10°C above its melting point during the pressurization process, allowing it to melt smoothly and be extruded into dense particles.

[0030] In a specific embodiment of the present invention, the agglomerated material is extruded and granulated using commonly used extrusion granulation equipment in the art, such as parallel co-rotating twin-screw extruders, parallel counter-rotating twin-screw extruders, conical twin-screw extruders, and single-screw extruders with different aspect ratios. Among these, twin-screw extruders are more commonly used for granulation.

[0031] Specifically, the agglomerated material is placed in the hopper of a twin-screw extruder. The temperature of the extruder is set at around the melting point of the material, and the feed rate is adjusted according to the production capacity. Subsequently, pelleting can be carried out by various pelleting methods such as air-cooled string pelletizing, water bath string pelletizing, grinding surface hot cutting, water ring pelletizing, and underwater pelletizing. The prepared particles are then dried.

[0032] The high-yield granulation method of this invention is basically applicable to various polyhydroxy fatty acid esters. The polyhydroxy fatty acid ester can be a homopolymer or a copolymer. Common monomers include 3-hydroxy fatty acids, 4-hydroxy fatty acids, and 5-hydroxy fatty acids, such as 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvalerate, 3-hydroxyhexanoic acid, and 5-hydroxyvalerate.

[0033] In some specific embodiments of the present invention, the polyhydroxy fatty acid esters include, but are not limited to, one or more of poly(3-hydroxybutyrate) (PHB), poly(4-hydroxybutyrate) (P4HB), poly(3-hydroxyvalerate) (PHV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx).

[0034] In a specific embodiment of the present invention, according to the granulation method, the granulation yield of the polyhydroxyalkanoate is more than 5.5 times that of the polyhydroxyalkanoate powder directly extruded and granulated.

[0035] For example, in some specific embodiments of the present invention, when a twin-screw extruder of model Nanjing Juli SHJ-75D is used to directly extrude and granulate polyhydroxy fatty acid ester powder, the granulation output is only 70-80 kg / h, while the granulation and molding method of the present invention can achieve a granulation output of more than 400 kg / h.

[0036] It is understandable that after obtaining the granules, they can be further processed into various forms of molded bodies, such as films, fibers, straws, and sheets, for application in various fields. These molded bodies can be prepared using various thermoforming methods such as extrusion molding, injection molding, calendering, casting, blow molding, and biaxial stretching, or they can be prepared using non-thermal forming methods such as solution casting. This invention achieves high-yield production of uniformly sized granules, laying the foundation for the further large-scale application of PHA.

[0037] This invention provides a high-yield granulation method for polyhydroxyalkanoates (PHA). The method involves pre-processing the PHA powder before granulation to agglomerate and compact it, increasing its bulk density to 0.4-0.6 g / cm³. 3 This method increases production while effectively preventing powder flying and bridging during subsequent extrusion granulation. It also ensures uniform material feeding and produces uniform granules. The high-yield granulation method of this invention is simple, low-cost, and has broad application prospects. Attached Figure Description

[0038] Figure 1 This is a comparison image of the granules obtained according to the method of the present invention in Example 1 of the present invention and the product obtained by direct twin-screw extrusion granulation using polyhydroxyalkanoate powder as raw material. Detailed Implementation

[0039] The terms “comprising” or “including” in this invention are open-ended descriptions that include the specified ingredients or steps described, as well as other specified ingredients or steps that do not materially affect them.

[0040] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0041] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "specific implementation," or "some specific implementations," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0044] In the following examples, the twin-screw extruder used is manufactured by Nanjing Juli Chemical Machinery Co., Ltd., and its model is SHJ-75D.

[0045] In the following examples, the standard particle shape after granulation is a cylinder with a diameter of 3 mm and a length of 3 mm; if the size error is controlled within ±5%, it is judged as uniform in size, otherwise it is considered as non-uniform.

[0046] Example 1

[0047] This embodiment provides a high-yield granulation method for polyhydroxy fatty acid esters, wherein the polyhydroxy fatty acid ester is poly(3-hydroxybutyrate), which is a powder material prepared by microbial fermentation, with a particle size D50 of 5 μm and a melting point of 170°C.

[0048] In this embodiment, powdered material is fed through a hopper between two 3-meter-long metal conveyor belts moving in the same direction. The temperature of the metal conveyor belts is raised to 175°C, and the belt speed is adjusted to control the heating duration of the material to 30 seconds. The pressure between the belts is 2 MPa. This process produces pre-compacted granules for downstream twin-screw extrusion granulation.

[0049] In this embodiment, twin-screw extrusion granulation includes:

[0050] S1. Feeding: Place the compacted granules into the feed hopper of the twin-screw extruder;

[0051] S2, Extrusion: Set the extruder conditions to perform extrusion at a melt temperature of approximately 170°C;

[0052] S3. Granulation and Cooling: Granulation is carried out by water bath stretching and cutting, with the water bath temperature set at 50℃, and the resulting granules are dried.

[0053] Using polyhydroxyalkanoate powder as raw material for direct twin-screw extrusion granulation as a control example, the extrusion granulation conditions were the same, and the comparison results are shown in Table 1 below.

[0054] Table 1

[0055]

[0056]

[0057] Figure 1 The image shows a comparison between the granules obtained according to the method of this embodiment (right) and the product granulated directly from polyhydroxyalkanoate powder using twin-screw extrusion (left). It can be seen that the granules prepared by the method of this invention have a uniform particle shape.

[0058] Example 2

[0059] This embodiment provides a high-yield granulation method for polyhydroxy fatty acid esters, wherein the polyhydroxy fatty acid ester is poly(3-hydroxybutyrate-co-4-hydroxybutyrate), with 4-hydroxybutyrate accounting for 15%, and is a powder material prepared by microbial fermentation, with a particle size D50 of 50 μm and a melting point of 135 °C.

[0060] In this embodiment, powdered material is fed through a hopper between two 2-meter-long metal plates moving in the same direction. The temperature of the metal plates is raised to 145°C, and the plate speed is adjusted to control the heating duration of the material to 10 seconds. The pressure between the plates is 1 MPa. This process produces pre-compacted granules for downstream twin-screw extrusion granulation.

[0061] In this embodiment, twin-screw extrusion granulation includes:

[0062] S1. Feeding: Place the compacted granules into the feed hopper of the twin-screw extruder;

[0063] S2, Extrusion: Set the extruder conditions to perform extrusion at a melt temperature of approximately 135°C;

[0064] S3. Granulation and Cooling: Granulation is carried out by air-cooled strip cutting and the resulting granules are dried.

[0065] Using polyhydroxyalkanoate powder as raw material for direct twin-screw extrusion granulation as a control example, the extrusion granulation conditions were the same, and the comparison results are shown in Table 2 below.

[0066] Table 2

[0067]

[0068] Example 3

[0069] This embodiment provides a high-yield granulation method for polyhydroxy fatty acid esters, wherein the polyhydroxy fatty acid ester is poly(3-hydroxybutyric acid-co-4-hydroxybutyrate) with a 4-hydroxybutyric acid ratio of 8%, and is a powder material prepared by microbial fermentation with a particle size D50 of 1 μm and a melting point of 145°C.

[0070] In this embodiment, powdered material is fed through a hopper between two counter-moving metal rollers, each with a diameter of 0.5 meters. The temperature of the metal rollers is raised to 150°C, and the roller speed is adjusted to control the heating duration of the material to 10 seconds. The pressure between the metal rollers is 3 MPa. This process produces pre-compacted granules for downstream twin-screw extrusion granulation.

[0071] In this embodiment, twin-screw extrusion granulation includes:

[0072] S1. Feeding: Place the compacted granules into the feed hopper of the twin-screw extruder;

[0073] S2, Extrusion: Set the extruder conditions to perform extrusion at a melt temperature of approximately 145°C;

[0074] S3. Granulation and Cooling: Granulation is carried out by water bath stretching and cutting, with the water bath temperature set at 50℃, and the resulting granules are dried.

[0075] Using polyhydroxyalkanoate powder as raw material for direct twin-screw extrusion granulation as a control example, the extrusion granulation conditions were the same, and the comparison results are shown in Table 3 below.

[0076] Table 3

[0077]

[0078]

[0079] Example 4

[0080] This embodiment provides a high-yield granulation method for polyhydroxy fatty acid esters, wherein the polyhydroxy fatty acid ester is poly(3-hydroxybutyric acid-co-3-hydroxyvalerate), with a 3-hydroxyvalerate ratio of 2%, and is a powder material prepared by microbial fermentation, with a particle size D50 of 5 μm and a melting point of 170°C.

[0081] In this embodiment, powdered material is fed through a hopper between two 3-meter-long metal conveyor belts moving in the same direction. The temperature of the metal conveyor belts is raised to 175°C, and the belt speed is adjusted to control the heating duration of the material to 30 seconds. The pressure between the belts is 2 MPa. This process produces pre-compacted granules for downstream twin-screw extrusion granulation.

[0082] In this embodiment, twin-screw extrusion granulation includes:

[0083] S1. Feeding: Place the compacted granules into the feed hopper of the twin-screw extruder;

[0084] S2, Extrusion: Set the extruder conditions to perform extrusion at a melt temperature of approximately 170°C;

[0085] S3. Granulation and Cooling: Granulation is carried out by water bath stretching and cutting, with the water bath temperature set at 50℃, and the resulting granules are dried.

[0086] Using polyhydroxyalkanoate powder as raw material for direct twin-screw extrusion granulation as a control example, the extrusion granulation uses forced feeding, specifically by adding a single screw that is vertically perpendicular to the horizontal twin-screw extruder. The powder conveyed from the feeder is forced to the top of the twin screw through the conveying of the single screw to enhance the feeding effect. The comparison results are shown in Table 4 below.

[0087] Table 4

[0088]

[0089]

[0090] Example 5

[0091] This embodiment provides a high-yield granulation method for polyhydroxy fatty acid esters, wherein the polyhydroxy fatty acid ester is poly(3-hydroxybutyric acid-co-3-hydroxyhexanoate), with 3-hydroxyhexanoate accounting for 5%, and is prepared as a powder by microbial fermentation, with a particle size D50 of 4 μm and a melting point of 145℃.

[0092] In this embodiment, powdered material is fed through a hopper between two counter-moving metal rollers, each with a diameter of 0.5 meters. The temperature of the metal rollers is raised to 150°C, and the roller speed is adjusted to control the heating duration of the material to 10 seconds. The pressure between the metal rollers is 3 MPa. This process produces pre-compacted granules for downstream twin-screw extrusion granulation.

[0093] In this embodiment, twin-screw extrusion granulation includes:

[0094] S1. Feeding: Place the compacted granules into the feed hopper of the twin-screw extruder;

[0095] S2, Extrusion: Set the extruder conditions to perform extrusion at a melt temperature of approximately 145°C;

[0096] S3. Granulation and Cooling: Granulation is carried out by water bath stretching and cutting, with the water bath temperature set at 50℃, and the resulting granules are dried.

[0097] Using polyhydroxyalkanoate powder as raw material for direct twin-screw extrusion granulation as a control example, an arch breaker was added to the feed hopper during the extrusion granulation process. The comparison results are shown in Table 5 below.

[0098] Table 5

[0099]

[0100]

[0101] Comparative Example 1

[0102] This comparative example provides a granulation method for polyhydroxy fatty acid esters, wherein the polyhydroxy fatty acid ester is poly(3-hydroxybutyrate), which is a powder material prepared by microbial fermentation, with a particle size D50 of 5 μm and a melting point of 170℃.

[0103] In this embodiment, powdered material is fed through a hopper between two 3-meter-long metal conveyor belts moving in the same direction. The temperature of the metal conveyor belts is raised to 175°C, and the belt speed is adjusted to control the heating duration of the material to 10 seconds. The pressure between the belts is 1 MPa. This process produces pre-compacted granules for downstream twin-screw extrusion granulation.

[0104] In this embodiment, twin-screw extrusion granulation includes:

[0105] S1. Feeding: Place the compacted granules into the feed hopper of the twin-screw extruder;

[0106] S2, Extrusion: Set the extruder conditions to perform extrusion at a melt temperature of approximately 170°C;

[0107] S3. Granulation and Cooling: Granulation is carried out by water bath stretching and cutting, with the water bath temperature set at 50℃, and the resulting granules are dried.

[0108] Using polyhydroxyalkanoate powder as raw material for direct twin-screw extrusion granulation as a control example, the extrusion granulation conditions were the same, and the comparison results are shown in Table 6 below.

[0109] Table 6

[0110]

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-yield granulation method for polyhydroxyalkanoates, characterized in that, include: Polyhydroxyalkanoate powder with a particle size D50 of 1-50 μm is pre-processed to agglomerate the powder and increase its bulk density to 0.4-0.6 g / cm³. 3 Within the range; The aggregated material is then extruded and granulated. The pre-processing includes pressurizing and heating the polyhydroxyalkanoate powder, wherein the pressurizing pressure is 1-3 MPa and the heating temperature is 5-10°C higher than the melting point of the polyhydroxyalkanoate powder. The heating duration is 10-30 seconds.

2. The high-yield granulation method for polyhydroxyalkanoates according to claim 1, characterized in that, The polyhydroxy fatty acid ester powder is prepared by microbial fermentation.

3. The high-yield granulation method for polyhydroxyalkanoates according to claim 1, characterized in that, The pressurization device uses two metal tracks and / or metal plates that rotate in the same or opposite directions. The pressure between the metal tracks and / or metal plates is adjustable from 1 to 3 MPa. The duration of heating is controlled by adjusting the length and speed of the metal tracks and / or metal plates.

4. The high-yield granulation method for polyhydroxyalkanoates according to claim 1, characterized in that, The pressurizing device uses two metal rollers that rotate in the same or opposite directions. The pressure between the metal rollers is adjustable from 1 to 3 MPa. The duration of heating is controlled by adjusting the rotation speed of the metal rollers.

5. The high-yield granulation method for polyhydroxyalkanoates according to claim 4, characterized in that, The diameter of the metal roller is 0.3-1 meter.

6. The high-yield granulation method for polyhydroxyalkanoates according to any one of claims 3-5, characterized in that, The temperature of the pressurizing device is increased to 5-10°C above the melting point of the polyhydroxyalkanoate powder and maintained at that temperature.

7. The high-yield granulation method for polyhydroxyalkanoates according to any one of claims 1-5, characterized in that, The polyhydroxy fatty acid ester is a homopolymer or copolymer.

8. The high-yield granulation method for polyhydroxyalkanoates according to claim 6, characterized in that, The polyhydroxy fatty acid ester is a homopolymer or copolymer.

9. The high-yield granulation method for polyhydroxyalkanoates according to claim 7, characterized in that, The polyhydroxy fatty acid esters include one or more of poly(3-hydroxybutyrate), poly(4-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

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