Method for producing pellets containing polyhydroxyalkanoate and pellets produced thereby

Abstract

The present invention relates to a method for producing pellets comprising polyhydroxyalkanoate, and the pellets produced thereby, the method comprising the steps of: (1) introducing raw materials comprising polyhydroxyalkanoate (PHA) and additives into a twin-screw extruder to form a polyhydroxyalkanoate melt; (2) feeding the polyhydroxyalkanoate melt to a die plate via a gear pump; (3) passing the polyhydroxyalkanoate melt through the die plate to form polyhydroxyalkanoate melt strands; and (4) cutting and crystallizing the polyhydroxyalkanoate melt strands in an underwater pellet producer to form pellets.

Description

[Technical Field]

[0001] The present disclosure relates to a method and an apparatus for producing pellets containing polyhydroxyalkanoates having controlled molecular weights. [Background technology]

[0002] In general, synthetic resins are widely used in the manufacture of various products, taking advantage of their excellent physical properties, low cost, light weight, and other characteristics. However, synthetic resins have a major problem in that they are difficult to decompose, and as a result, they are a major cause of environmental pollution. Therefore, in recent years, attention has been focused on biodegradable resins derived from plants that are environmentally friendly and renewable.

[0003] Polyhydroxyalkanoate, one of the above biodegradable resins, has physical properties similar to those of general-purpose synthetic resins such as polyethylene and polypropylene, but has the advantage of being naturally decomposed by microorganisms in the soil or ocean, and attempts have been made to utilize this property to produce various products.

[0004] An example of a process for producing a product from polyhydroxyalkanoate is a procedure in which polyhydroxyalkanoate is produced, pelletized, and then molded. Specifically, polyhydroxyalkanoate is produced by culturing microorganisms, and the microorganisms are crushed and then purified using an organic solvent and / or water to recover the resin component. The recovered polyhydroxyalkanoate may then be extruded using an extruder or the like, and further pelletized by cutting or the like, and then molded to produce a product.

[0005] However, since crystalline or semi-crystalline polyhydroxyalkanoates are sensitive to heat, the molecular weight of the pelletized polyhydroxyalkanoates is rapidly reduced due to the stress caused by the high temperature and high-speed screw friction during the extrusion process. This reduction in molecular weight deteriorates mechanical properties such as elongation and impact strength, limiting the ability to ensure the physical properties of the final product. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent No. 10-1485386 Summary of the Invention [Problem to be solved by the invention]

[0007] In order to solve the above-mentioned conventional problems, an object of the present disclosure is to provide a method for producing pellets that can control the decrease in molecular weight of polyhydroxyalkanoate when producing pellets from a raw material containing polyhydroxyalkanoate.

[0008] Another object of the present disclosure is to provide pellets produced by the above-mentioned production method.

[0009] Another object of the present disclosure is to provide a pellet production apparatus capable of producing pellets while controlling the decrease in the molecular weight of polyhydroxyalkanoate. [Means for solving the problem]

[0010] In order to achieve the above object, the method for producing pellets of the present disclosure includes: (1) feeding raw materials containing polyhydroxyalkanoate (PHA) and additives into a twin-screw extruder to form a polyhydroxyalkanoate melt; (2) feeding the polyhydroxyalkanoate melt to a die plate via a gear pump; (3) passing the polyhydroxyalkanoate melt through the die plate to form polyhydroxyalkanoate melt strands; and (4) cutting and crystallizing the polyhydroxyalkanoate melt strands with an underwater pellet cutter to form pellets.

[0011] According to one embodiment of the present disclosure, in step (1), the barrel temperature of the twin-screw extruder may be 120 to 160°C.

[0012] According to another embodiment of the present disclosure, in step (1), the temperature of the polyhydroxyalkanoate melt may be 130 to 160°C.

[0013] According to another embodiment of the present disclosure, in step (1), the additive may include at least one of a slip agent and a nucleating agent.

[0014] According to another embodiment of the present disclosure, the amount of the additive may be 0.1 to 20 parts by weight based on 100 parts by weight of the polyhydroxyalkanoate.

[0015] According to another embodiment of the present disclosure, in step (1), the polyhydroxyalkanoate may be a crystalline polyhydroxyalkanoate, a semi-crystalline polyhydroxyalkanoate, or an amorphous polyhydroxyalkanoate.

[0016] The polyhydroxyalkanoate according to another embodiment of the present disclosure may be a copolymer containing, in step (1), a repeating unit derived from at least one acid selected from the group consisting of 3-hydroxybutyric acid (3-HB), 3-hydroxypropionic acid (3-HP), 3-hydroxyvaleric acid (3-HV), 3-hydroxyhexanoic acid (3-HH), 4-hydroxybutyric acid (4-HB), 4-hydroxyvaleric acid (4-HV), 4-hydroxyhexanoic acid (4-HH), 5-hydroxyvaleric acid (5-HV), and 6-hydroxyhexanoic acid (6-HH).

[0017] According to another embodiment of the present disclosure, the polyhydroxyalkanoate may be a copolymer containing 1 to 60 wt % of repeating units derived from 4-hydroxybutyric acid (4-HB) based on the total weight of the copolymer.

[0018] According to another embodiment of the present disclosure, the polyhydroxyalkanoate may be poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0019] According to another embodiment of the present disclosure, in step (2), the pressure difference between before and after the polyhydroxyalkanoate melt passes through the gear pump may be 60 to 180 bar.

[0020] According to another embodiment of the present disclosure, in step (3), the temperature of the die plate may be 120 to 190°C.

[0021] According to another embodiment of the present disclosure, in step (4), the temperature of the circulating water tank provided in the underwater pellet cutter may be 40 to 80°C.

[0022] The method for producing pellets according to another embodiment of the present disclosure may further include (5) dehydrating and drying the pellets formed in step (4).

[0023] According to another embodiment of the present disclosure, the molecular weight reduction rate of polyhydroxyalkanoate (M d ) may be 15% or less according to the following formula 1.

[0024] [Formula 1] M d ={(M1-M2) / M1}×100 In formula 1, M1 is the weight average molecular weight of the polyhydroxyalkanoate contained in the raw material, and M2 is the weight average molecular weight of the polyhydroxyalkanoate contained in the pellets.

[0025] On the other hand, in order to achieve the above object, the present disclosure provides pellets produced by the above production method.

[0026] Furthermore, in order to achieve the above-mentioned object, the pellet manufacturing apparatus of the present disclosure comprises a twin-screw extruder that forms a polyhydroxyalkanoate melt from raw materials containing polyhydroxyalkanoate (PHA) and additives, a gear pump that is provided at the rear end of the twin-screw extruder and that transports the polyhydroxyalkanoate melt, a die plate that forms polyhydroxyalkanoate melt strands from the polyhydroxyalkanoate melt transported via the gear pump, and an underwater pellet cutter that cuts and crystallizes the polyhydroxyalkanoate melt strands formed through the die plate to form pellets. [Effects of the Invention]

[0027] In the present disclosure, raw materials containing polyhydroxyalkanoate are processed in a twin-screw extruder under a low-temperature, low-pressure environment to obtain a polyhydroxyalkanoate melt, which is then conveyed by a gear pump. This solves the conventional problem of rapid reduction in the molecular weight of polyhydroxyalkanoate during the pelletization process due to stress caused by the high-temperature, high-pressure environment of the twin-screw extruder. Furthermore, in the present disclosure, the reduction in the molecular weight of polyhydroxyalkanoate can be controlled by adding an additive to the twin-screw extruder during the pelletization process.

[0028] This makes it possible to provide pellets containing polyhydroxyalkanoate with minimal molecular weight reduction. When the pellets are used to produce various products, products (e.g., films, straws, containers, trays, cups, etc.) with excellent physical properties (mechanical properties) can be obtained. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a flowchart illustrating a method for manufacturing pellets according to an embodiment of the present disclosure. [Figure 2] 1 is a schematic diagram illustrating a pellet manufacturing apparatus according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present disclosure will be described in detail below. The present disclosure is not limited to the following and can be modified into various forms without departing from the spirit of the disclosure.

[0031] In this specification, the term "comprises" is used to explicitly identify certain features, regions, steps, treatments, elements, and / or components, and does not exclude the presence or addition of other features, regions, steps, treatments, components, elements, and / or components, unless specifically stated to the contrary.

[0032] Numerical values ​​and expressions relating to amounts of components, reaction conditions, etc. used herein can be understood even if modified by the word "approximately," unless otherwise specified.

[0033] For the sake of clarity, the dimensions of each element in the accompanying drawings may be exaggerated and may differ from the actual dimensions.

[0034] The present disclosure is characterized by controlling the decrease in molecular weight (weight average molecular weight or number average molecular weight) of polyhydroxyalkanoate (PHA) by minimizing exposure of raw materials containing polyhydroxyalkanoate (PHA) to a high-temperature and high-pressure environment during the pelletization process. The present disclosure will be described in detail below.

[0035] Pellets manufacturing method The method for producing pellets of the present disclosure includes: (1) feeding raw materials including polyhydroxyalkanoate (PHA) and additives into a twin-screw extruder to form a polyhydroxyalkanoate melt; (2) feeding the polyhydroxyalkanoate melt to a die plate via a gear pump; (3) passing the polyhydroxyalkanoate melt through the die plate to form polyhydroxyalkanoate melt strands; and (4) cutting and crystallizing the polyhydroxyalkanoate melt strands with an underwater pellet cutter to form pellets.

[0036] Each step will be described below with reference to FIG.

[0037] Step (1): Formation of a polyhydroxyalkanoate melt According to the present disclosure, step (1) is a step of feeding raw materials including polyhydroxyalkanoate (PHA) and additives into a twin-screw extruder to form a polyhydroxyalkanoate melt.

[0038] The polyhydroxyalkanoates contained in the raw materials have similar physical properties to petroleum-derived synthetic biodegradable polymers such as polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polybutylene succinate terephthalate (PBST), and polybutylene succinate adipate (PBSA), and have excellent biodegradability and biocompatibility.

[0039] Polyhydroxyalkanoates may be obtained by disrupting cells by mechanical or physical methods, or by non-mechanical or chemical methods.

[0040] Specifically, the polyhydroxyalkanoate may be a copolymer containing repeating units derived from at least one species (at least one monomer) selected from the group consisting of 3-hydroxybutyric acid (3-HB), 3-hydroxypropionic acid (3-HP), 3-hydroxyvaleric acid (3-HV), 3-hydroxyhexanoic acid (3-HH), 4-hydroxybutyric acid (4-HB), 4-hydroxyvaleric acid (4-HV), 4-hydroxyhexanoic acid (4-HH), 5-hydroxyvaleric acid (5-HV), and 6-hydroxyhexanoic acid (6-HH), but is not limited thereto.

[0041] Depending on the type of monomer and the content of repeating units derived therefrom, polyhydroxyalkanoates may be crystalline polyhydroxyalkanoates (cPHAs), semicrystalline polyhydroxyalkanoates (scPHAs), or amorphous polyhydroxyalkanoates (aPHAs). Specifically, polyhydroxyalkanoates may be classified into cPHAs, scPHAs, and aPHAs, with their crystallinity controlled according to the content of repeating units derived from 4-hydroxybutyric acid (4-HB).

[0042] The polyhydroxyalkanoate may be a copolymer containing repeating units derived from 4-HB (4-hydroxybutyric acid) in an amount of 1 to 60 wt%, 1 to 55 wt%, 1 to 50 wt%, 1 to 45 wt%, 1 to 40 wt%, 1 to 35 wt%, 1 to 30 wt%, 1 to 25 wt%, 2 to 23 wt%, 3 to 20 wt%, 4 to 15 wt%, 5 to 15 wt%, 6 to 14 wt%, or 7 to 13 wt%, based on the total weight of the copolymer (polyhydroxyalkanoate), but is not limited to this.

[0043] For example, the polyhydroxyalkanoate may be poly(3-hydroxybutyrate-co-4-hydroxybutyrate), in which the content of 4-HB repeat units may be, but is not limited to, 1 to 60 wt%, 1 to 55 wt%, 1 to 50 wt%, 1 to 45 wt%, 1 to 40 wt%, 1 to 35 wt%, 1 to 30 wt%, 1 to 25 wt%, 2 to 23 wt%, 3 to 20 wt%, 4 to 15 wt%, 5 to 15 wt%, 6 to 14 wt%, or 7 to 13 wt%, based on the total weight of the poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0044] When the polyhydroxyalkanoate is scPHA, the crystallization temperature (Tc) may be, but is not limited to, 50 to 120°C, 55 to 115°C, 65 to 105°C, or 75 to 95°C. When the polyhydroxyalkanoate is scPHA, the melting point (Tm) may be, but is not limited to, 110 to 170°C, 115 to 160°C, or 120 to 150°C.

[0045] The weight average molecular weight (Mw) of the polyhydroxyalkanoate may be, but is not limited to, 100,000 to 800,000 g / mol, 150,000 to 750,000 g / mol, 200,000 to 700,000 g / mol, or 250,000 to 650,000 g / mol.

[0046] The polyhydroxyalkanoate may have a polydispersity index (PDI) of 1.0 or more, 1.2 or more, 1.5 or more, 1.8 or more, 1.9 or more, or 2.0 or more, and 5.0 or less, 4.0 or less, 3.0 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, or 2.5 or less, but is not limited thereto.

[0047] The raw material containing polyhydroxyalkanoate may contain, in addition to polyhydroxyalkanoate, a known synthetic resin (e.g., polyethylene (PE), polypropylene (PP), or a mixture thereof, etc.) and / or a biodegradable resin (e.g., polylactic acid (PLA), polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), polybutylene adipate-co-terephthalate (PBAT), polybutylene succinate (PBS), polycaprolactone (PCL), or a mixture thereof, etc.) as needed.

[0048] On the other hand, in the present disclosure, even if the polyhydroxyalkanoate is a heat-sensitive cPHA or scPHA, by controlling the twin-screw extruder that processes the raw material containing cPHA or scPHA to operate at a relatively low temperature and pressure, it is possible to prevent a rapid decrease in the molecular weight of the cPHA or scPHA due to exposure of the cPHA or scPHA to a high-temperature and high-pressure environment.

[0049] Specifically, the barrel temperature when operating the twin-screw extruder may be, but is not limited to, 120 to 160°C, more specifically, 120 to 158°C, 120 to 155°C, 123 to 155°C, 125 to 153°C, or 125 to 150°C. Furthermore, the screw rotation speed when operating the twin-screw extruder may be, but is not limited to, 60 to 150 rpm, specifically, 65 to 145 rpm, 70 to 140 rpm, 75 to 130 rpm, or 80 to 120 rpm. By keeping the barrel temperature and screw rotation speed of the twin-screw extruder within the above ranges, a polyhydroxyalkanoate melt can be smoothly formed while suppressing a decrease in the molecular weight of the polyhydroxyalkanoate.

[0050] The additives contained in the raw materials have the property of increasing the fluidity of the polyhydroxyalkanoate melt. The additives include at least one of a slip agent and a nucleating agent. By introducing at least one of a slip agent and a nucleating agent into the twin-screw extruder, the crystallinity of the polyhydroxyalkanoate is controlled and the fluidity (flow ability) of the polyhydroxyalkanoate melt is increased, allowing the polyhydroxyalkanoate melt to be smoothly discharged from the twin-screw extruder.

[0051] Specifically, the slip agent may serve to smoothly discharge the polyhydroxyalkanoate melt from the twin-screw extruder, and may also serve to prevent the polyhydroxyalkanoate melt from adhering to the die plate and the cut polyhydroxyalkanoate pellets from adhering to each other during the cutting step for pellet formation.

[0052] The slip agent is not particularly limited as long as it is a known slip agent that can be used for polymer resins, and specifically, it may be at least one selected from the group consisting of amide-based substances, metal fatty acid salts, and wax-based substances.

[0053] The amide-based substance is not particularly limited, and specifically may contain at least one selected from the group consisting of ethylene bis(stearamide), oleamide, erucamide, and stearamide.

[0054] The metal fatty acid salt is not particularly limited, and specifically may contain at least one selected from the group consisting of calcium stearate, zinc stearate, magnesium stearate, aluminum stearate, potassium oleate, zinc oleate, magnesium oleate, aluminum oleate, calcium palmitate, zinc palmitate, magnesium palmitate, and aluminum palmitate.

[0055] The wax-based substance is not particularly limited, and specifically may contain at least one selected from the group consisting of beeswax, carnauba wax, and candelilla wax.

[0056] In addition, the nucleating agent can affect the crystallinity of the polyhydroxyalkanoate during the process of converting raw materials containing the polyhydroxyalkanoate into a melt, and can improve the cooling and cutting process of the polyhydroxyalkanoate melt for pellet formation.

[0057] The nucleating agent is not particularly limited as long as it is a known nucleating agent that can be used in polymer resins, and specifically may include at least one selected from the group consisting of calcium carbonate, silica, talc, boron nitride, and sorbitol derivatives.

[0058] On the other hand, the additives may further contain other known additives applicable to polymer resins (biodegradable resins) in addition to the slip agent and the nucleating agent.

[0059] The additives may be mixed with the polyhydroxyalkanoate in advance and then fed to the twin-screw extruder, or may be fed to the twin-screw extruder separately from the polyhydroxyalkanoate via a separate feeder.

[0060] The amount of additive added may be 0.1 to 20 parts by weight per 100 parts by weight of polyhydroxyalkanoate contained in the raw material, specifically, but not limited to, 0.1 to 15 parts by weight, 0.2 to 13 parts by weight, 0.2 to 10 parts by weight, 0.3 to 8 parts by weight, or 0.5 to 5 parts by weight. By adding the additive in the above range, the fluidity of the polyhydroxyalkanoate melt and the efficiency of the cooling and cutting process can be significantly improved while minimizing the decrease in molecular weight of the polyhydroxyalkanoate. For example, the amount of additive added may be 0.1 to 10 parts by weight per 100 parts by weight of polyhydroxyalkanoate contained in the raw material, specifically, but not limited to, 0.2 to 8 parts by weight, 0.3 to 7 parts by weight, 0.4 to 6 parts by weight, 0.5 to 5 parts by weight, or 0.8 to 3 parts by weight of slip agent. The amount of nucleating agent added may be 0.1 to 10 parts by weight per 100 parts by weight of polyhydroxyalkanoate contained in the raw material, but specifically may be 0.2 to 8 parts by weight, 0.3 to 7 parts by weight, 0.4 to 6 parts by weight, 0.5 to 5 parts by weight, or 0.8 to 3 parts by weight, but is not limited to these.

[0061] The temperature of the polyhydroxyalkanoate melt formed through step (1) may be, but is not limited to, specifically 130 to 160° C., more specifically 130 to 158° C., 133 to 155° C., 133 to 153° C., or 135 to 150° C. If the temperature of the polyhydroxyalkanoate melt is within the above range, the polyhydroxyalkanoate melt can maintain a stable molten state while preventing thermal decomposition of the polyhydroxyalkanoate.

[0062] Step (2): Supply by gear pump According to the present disclosure, step (2) is a step of supplying a polyhydroxyalkanoate melt to a die plate via a gear pump. Step (2) ensures the fluidity (flow ability) of the polyhydroxyalkanoate melt and improves pellet production efficiency. That is, when a twin-screw extruder is operated at a relatively low temperature and pressure to control the reduction in molecular weight of the polyhydroxyalkanoate in step (1), the resulting polyhydroxyalkanoate melt may have high viscosity and poor fluidity. In the present disclosure, conveying the polyhydroxyalkanoate melt using a gear pump ensures the fluidity of the polyhydroxyalkanoate melt and improves the overall efficiency of pellet production.

[0063] The operating conditions of the gear pump that supplies the polyhydroxyalkanoate melt to the die plate are not particularly limited. However, the pressure difference between the polyhydroxyalkanoate melt before and after passing through the gear pump may be 60 to 180 bar. In such a case, the pressure of the gear pump may be higher after the polyhydroxyalkanoate melt has passed through the gear pump than before. Specifically, the difference (P2 - P1) between the pressure (P1) of the gear pump before the polyhydroxyalkanoate melt passes through the gear pump and the pressure (P2) of the gear pump after the polyhydroxyalkanoate melt has passed through the gear pump may be, but is not limited to, 60 to 180 bar, 60 to 175 bar, 60 to 170 bar, 65 to 165 bar, 70 to 160 bar, 75 to 150 bar, or 80 to 140 bar. By keeping the difference (P2-P1) in the gear pump within the above range, it becomes possible to smoothly supply the polyhydroxyalkanoate melt to the die plate while suppressing a decrease in the molecular weight of the polyhydroxyalkanoate.

[0064] On the other hand, the flow rate of the polyhydroxyalkanoate melt supplied through the gear pump (the flow rate of the polyhydroxyalkanoate melt supplied to the die plate) is not particularly limited and may be adjusted appropriately depending on the scale of the twin-screw extruder.

[0065] Step (3): Formation of polyhydroxyalkanoate molten strands According to the present disclosure, step (3) is a step of passing the polyhydroxyalkanoate melt fed to the die pump by the gear pump through a die plate to form polyhydroxyalkanoate melt strands.

[0066] The temperature of the die plate for forming the polyhydroxyalkanoate molten strand is not particularly limited, but specifically includes 120 to 190° C. More specifically, the die plate temperature may be 123 to 188° C., 125 to 185° C., 128 to 185° C., 130 to 185° C., 133 to 182° C., 135 to 180° C., 138 to 178° C., or 140 to 175° C. When the die plate temperature is within the above range, the polyhydroxyalkanoate molten strand can be smoothly formed while controlling the decrease in the molecular weight of the polyhydroxyalkanoate.

[0067] Step (4): Pellets formation According to the present disclosure, step (4) is a step of cutting and crystallizing the polyhydroxyalkanoate molten strands in an underwater pellet cutter to form pellets. Specifically, when the polyhydroxyalkanoate molten strands are fed to the underwater pellet cutter, they are cut into pieces of a predetermined size to form polyhydroxyalkanoate pieces, which are then passed through a circulating water bath provided in the underwater pellet cutter and crystallized to form pellets.

[0068] The temperature of the circulating water bath provided in the underwater pellet cutter is not particularly limited, but may be 40 to 80° C. More specifically, the temperature of the circulating water bath may be, but is not limited to, 43 to 80° C., 45 to 80° C., 48 to 78° C., 50 to 75° C., 53 to 73° C., or 55 to 70° C. If the temperature of the circulating water bath is within the above range, cooling crystallization of the cut polyhydroxyalkanoate is carried out well, and pellets having the desired physical properties can be produced.

[0069] Meanwhile, the method for producing pellets according to the present disclosure may further include dehydrating and drying the pellets formed in step (4) (step (5)). Specifically, the pellets may be dehydrated using a centrifugal dehydrator to primarily remove water contained in the pellets, and then dried at 40 to 100°C for 1 to 24 hours to secondary remove water contained in the pellets.

[0070] In the present disclosure, as described above, the polyhydroxyalkanoate contained in the raw material is processed in a twin-screw extruder under a low-temperature, low-pressure environment, conveyed by a gear pump, and then exposed to a high-pressure environment only immediately before pelletization, thereby minimizing the decrease in molecular weight of the polyhydroxyalkanoate during the pelletization process.

[0071] Specifically, in the present disclosure, when pellets are produced using the above-mentioned production method, the molecular weight of the polyhydroxyalkanoate contained in the raw material in step (1) and the molecular weight of the polyhydroxyalkanoate contained in the pellets formed in step (4) may be approximately the same. Specifically, when pellets are produced according to the present disclosure, the molecular weight of the polyhydroxyalkanoate (M d ) may be reduced by 15% or less. More specifically, the molecular weight (M d The rate of decrease in the molecular weight (M) of the polyhydroxyalkanoate may be 14% or less, 13% or less, 12% or less, 11% or less, or 10% or less (for example, 0.05 to 15%, 0.1 to 10%, 0.1 to 5%, or 0.2 to 1%). dWhen the reduction rate of the elongation coefficient t) is 15% or less, an article (molded product) having high mechanical properties such as elongation and impact strength can be provided.

[0072] [Formula 1] M d ={(M1-M2) / M1}×100 In formula 1, M1 is the weight average molecular weight of the polyhydroxyalkanoate contained in the raw material, and M2 is the weight average molecular weight of the polyhydroxyalkanoate contained in the pellets.

[0073] pellet The present disclosure provides pellets produced by the above-described production method. When the pellets according to the present disclosure are produced by the above-described production method, the molecular weight of the polyhydroxyalkanoate contained in the pellets may be the same as (or close to) the molecular weight of the polyhydroxyalkanoate initially used as a raw material.

[0074] The pellets according to the present disclosure contain polyhydroxyalkanoate in which the decrease in molecular weight is suppressed as described above, and therefore may have excellent mechanical properties such as elongation and impact strength. Therefore, when various articles are produced using the pellets according to the present disclosure, articles having excellent mechanical properties and biodegradability can be produced.

[0075] Examples of the article include, but are not limited to, a film, a straw, a container, a tray, or a cup.

[0076] Pellet manufacturing equipment The present disclosure provides an apparatus for producing the above-mentioned pellets. Specifically, the pellet production apparatus of the present disclosure includes a twin-screw extruder that forms a polyhydroxyalkanoate melt from raw materials containing polyhydroxyalkanoate (PHA) and additives, a gear pump that is provided at the rear end of the twin-screw extruder and that transports the polyhydroxyalkanoate melt, a die plate that forms a polyhydroxyalkanoate melt strand from the polyhydroxyalkanoate melt transported via the gear pump, and an underwater pellet cutter that cuts and crystallizes the polyhydroxyalkanoate melt strand formed through the die plate to form pellets. The following description will be made with reference to FIG. 2.

[0077] Twin Screw Extruder(10) The twin-screw extruder (10) provided in the pellet manufacturing apparatus according to the present disclosure forms a polyhydroxyalkanoate melt from raw materials containing polyhydroxyalkanoate (PHA) and additives. The twin-screw extruder (10) is not particularly limited as long as it is a known twin-screw extruder capable of kneading polymer resins. Specifically, the twin-screw extruder (10) may be an intermesh co-rotating twin-screw extruder, an intermesh counter-rotating twin-screw extruder, or a tangential counter-rotating twin-screw extruder.

[0078] As described above, this twin-screw extruder (10) may be operated under relatively low temperature and pressure conditions (by controlling the barrel temperature and screw rotation speed), thereby minimizing the stress applied to the polyhydroxyalkanoate contained in the raw material and controlling the decrease in the molecular weight of the polyhydroxyalkanoate.

[0079] Gear Pump(20) The gear pump (20) provided in the pellet production apparatus according to the present disclosure is disposed at the rear end of the twin-screw extruder (10) and conveys the polyhydroxyalkanoate melt. Specifically, the gear pump (20) supplies the polyhydroxyalkanoate melt formed and discharged from the twin-screw extruder (10) to the die plate (30). By disposing the gear pump (20) at the rear end of the twin-screw extruder (10), the present disclosure can smoothly convey even a highly viscous polyhydroxyalkanoate melt.

[0080] The gear pump (20) is not particularly limited as long as it is a known pump that can transport a molten polymer resin.

[0081] Die plate (30) The die plate (30) provided in the pellet manufacturing apparatus of the present disclosure forms polyhydroxyalkanoate molten strands from the polyhydroxyalkanoate melt conveyed through the gear pump (20).

[0082] The die plate (30) is not particularly limited as long as it is a commonly known die plate having a structure capable of extruding a polymer resin melt into a molten strand having a predetermined diameter.

[0083] Underwater pellet cutter(40) The underwater pellet cutter (40) provided in the pellet manufacturing apparatus according to the present disclosure cuts and crystallizes the molten strands of polyhydroxyalkanoate formed through the die plate (30) to form pellets.

[0084] The underwater pellet cutter (40) may include a cutter for cutting the polyhydroxyalkanoate molten strands and a circulating water bath for cooling and crystallizing the polyhydroxyalkanoate pieces cut by the cutter.

[0085] The underwater pellet cutter (40) is not particularly limited as long as it is a commonly known underwater pellet cutter equipped with a cutter and a circulating water tank.

[0086] Mode of Invention The present disclosure will be explained in more detail below by way of examples, but the scope of the present disclosure should not be construed as being limited by the examples shown below.

[0087] [Example 1] Production of pellets 100 parts by weight of polyhydroxyalkanoate (manufactured by CJ Cheiljaedan Co., Ltd.; 4-HB repeat unit ratio; 8-12 wt%) and 0.5 phr (per hundred resin, additive unit per 100 parts by weight of polymer) of magnesium stearate were mixed and fed into the hopper of a twin-screw extruder (L / D 24, 30 mm). The twin-screw extruder was then operated at a barrel temperature of 120-160°C and a screw rotation speed of 70-100 rpm to form a polyhydroxyalkanoate melt. The formed polyhydroxyalkanoate melt was then fed via a gear pump to a die plate, where it was passed through holes in the die plate at a temperature of 120-190°C to form polyhydroxyalkanoate melt strands. The formed polyhydroxyalkanoate molten strands were then fed to an underwater pellet cutter and cut, and then passed through a circulating water bath at 40 to 80°C for crystallization. The resulting pellets (polyhydroxyalkanoate pieces) were then dried at a temperature of 40°C or higher to produce pellets containing polyhydroxyalkanoate.

[0088] [Comparative Example 1] Production of pellets Pellets containing polyhydroxyalkanoate were produced in the same manner as in Example 1, except that the polyhydroxyalkanoate melt was formed without adding any additive (magnesium stearate) and was fed directly to the die plate without using a gear pump.

[0089] [Comparative Example 2] Production of pellets Pellets containing polyhydroxyalkanoate were produced in the same manner as in Example 1, except that the polyhydroxyalkanoate melt was fed directly to the die plate without passing through a gear pump.

[0090] [Comparative Example 3] Production of pellets Pellets containing polyhydroxyalkanoate were produced following the same procedure as in Example 1, except that the polyhydroxyalkanoate melt was formed without the addition of an additive (magnesium stearate).

[0091] [Test Example 1] Analysis of weight average molecular weight and determination of molecular weight reduction rate In Example 1 and Comparative Examples 1 to 3, the weight-average molecular weight of the polyhydroxyalkanoate (PHA before extrusion) supplied to the twin-screw extruder and the weight-average molecular weight of the polyhydroxyalkanoate (PHA after extrusion) contained in the pellets were analyzed using gel permeation chromatography (GPC). The results are shown in Table 1 below. In the GPC analysis, a refractive index detector (RID) using chloroform as the mobile phase was used, and polystyrene (PS) was used as the standard substance.

[0092] In addition, the molecular weight reduction rate (M d ) was calculated using the following formula 1. [Formula 1] M d ={(M1-M2) / M1}×100 In formula 1, M1 is the weight average molecular weight of the polyhydroxyalkanoate contained in the raw material (PHA before extrusion), and M2 is the weight average molecular weight of the polyhydroxyalkanoate contained in the pellet (PHA after extrusion).

[0093] [Table 1]

[0094] Referring to Table 1 above, it was confirmed that in Example 1 of the present disclosure, the molecular weight reduction rate was 0.29% due to the use of additives and a gear pump, resulting in almost no change in the molecular weight of the PHA. From the above, by employing a gear pump, the PHA is treated in a low-temperature, low-pressure environment when passing through the screw section of the twin-screw extruder, and the treated PHA is transported by passing through the gear pump and exposed to a high-pressure environment only immediately before pelletization, thereby making it possible to control the reduction in molecular weight of the PHA during the pelletization process. Furthermore, the use of additives can also control the reduction in molecular weight of the PHA.

[0095] On the other hand, in Comparative Example 1, which did not use either an additive or a gear pump, the molecular weight decreased significantly, with the molecular weight reduction rate reaching 55.63%.In Comparative Examples 2 and 3, which used an additive or employed a gear pump, a large change was confirmed, with the molecular weight of PHA decreasing by more than 15%. [Explanation of symbols]

[0096] 10 Twin-screw extruder 20 Gear pump 30 Die Plate 40 Underwater pellet cutter

Claims

1. (1) feeding a raw material including a polyhydroxyalkanoate (PHA) and additives into a twin-screw extruder to form a polyhydroxyalkanoate melt; (2) feeding the polyhydroxyalkanoate melt to a die plate via a gear pump; (3) passing the polyhydroxyalkanoate melt through the die plate to form polyhydroxyalkanoate melt strands; (4) cutting the polyhydroxyalkanoate molten strands with an underwater pellet cutter to crystallize them and form pellets; A method for producing pellets comprising:

2. 2. The method for producing pellets according to claim 1, wherein in step (1), the barrel temperature of the twin-screw extruder is 120 to 160°C.

3. 2. The method for producing pellets according to claim 1, wherein in step (1), the temperature of the polyhydroxyalkanoate melt is 130 to 160°C.

4. The method for producing pellets according to claim 1, wherein in step (1), the additive comprises at least one of a slip agent and a nucleating agent.

5. 5. The method for producing pellets according to claim 4, wherein the amount of the additive is 0.1 to 20 parts by weight based on 100 parts by weight of the polyhydroxyalkanoate.

6. 2. The method for producing pellets according to claim 1, wherein in step (1), the polyhydroxyalkanoate is a crystalline polyhydroxyalkanoate, a semi-crystalline polyhydroxyalkanoate, or an amorphous polyhydroxyalkanoate.

7. 2. The method for producing pellets according to claim 1, wherein in step (1), the polyhydroxyalkanoate is a copolymer containing a repeating unit derived from at least one selected from the group consisting of 3-hydroxybutyric acid (3-HB), 3-hydroxypropionic acid (3-HP), 3-hydroxyvaleric acid (3-HV), 3-hydroxyhexanoic acid (3-HH), 4-hydroxybutyric acid (4-HB), 4-hydroxyvaleric acid (4-HV), 4-hydroxyhexanoic acid (4-HH), 5-hydroxyvaleric acid (5-HV), and 6-hydroxyhexanoic acid (6-HH).

8. The method for producing pellets according to claim 7, wherein the polyhydroxyalkanoate is a copolymer containing 1 to 60% by weight of repeating units derived from 4-hydroxybutyric acid (4-HB) based on the total weight of the copolymer.

9. The method for producing pellets according to claim 7, wherein the polyhydroxyalkanoate is poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

10. 2. The method for producing pellets according to claim 1, wherein in step (2), the pressure difference between before and after the polyhydroxyalkanoate melt passes through the gear pump is 60 to 180 bar.

11. 2. The method for producing pellets according to claim 1, wherein in step (3), the temperature of the die plate is 120 to 190°C.

12. 2. The method for producing pellets according to claim 1, wherein in step (4), the temperature of the circulating water bath provided in the underwater pellet cutter is 40 to 80°C.

13. 10. The method of claim 1, further comprising: (5) dehydrating and drying the pellets formed in step (4).

14. The molecular weight of the polyhydroxyalkanoate in the following formula 1 (M ｄ 2. The method for producing pellets according to claim 1, wherein the reduction rate of the total weight of the pellets is 15% or less. [Formula 1] M ｄ ={(M １ -M ２ ) / M １ }×100 In formula 1, M １ is the weight average molecular weight of the polyhydroxyalkanoate contained in the raw material, and M ２ is the weight average molecular weight of the polyhydroxyalkanoate contained in the pellet.

15. Pellets produced by the method according to any one of claims 1 to 14.

16. a twin-screw extruder for forming a polyhydroxyalkanoate melt from a raw material including a polyhydroxyalkanoate (PHA) and additives; a gear pump provided at the rear end of the twin-screw extruder for conveying the polyhydroxyalkanoate melt; a die plate for forming polyhydroxyalkanoate melt strands from the polyhydroxyalkanoate melt conveyed through the gear pump; an underwater pellet cutter for cutting and crystallizing the polyhydroxyalkanoate molten strands formed through the die plate to form pellets; A pellet manufacturing apparatus comprising:

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