Method for manufacturing a polymer molded article including a heat-utilizing pretreatment

Abstract

An object of the present invention is to provide a method for manufacturing a polymer molded article capable of expanding the temperature range available for partial melting. According to the present invention, there is provided a method for manufacturing a polymer molded article, comprising: a step of heating a crystalline polyhydroxyalkanoate at a temperature above the glass transition temperature; and a step of melt-molding the polyhydroxyalkanoate obtained by the above heating treatment in a temperature range where a part of the lamellae melts and flows while the other remaining lamellae do not melt and remain.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a polymer molded article, characterized in that by reconfiguring the thickness of the lamellae of a crystalline polyhydroxyalkanoate, the temperature range available for subsequent thermoforming using partial melting is expanded. Background Art

[0002] Polyhydroxyalkanoate (PHA, hereinafter also simply referred to as PHA) is a thermoplastic polyester accumulated by microorganisms and has attracted much attention as a biodegradable, biocompatible, and bioabsorbable plastic, and a large amount of research has been carried out (Non-Patent Document 1). More than 100 kinds of monomer units constituting PHA are known. A representative PHA is poly-3-hydroxybutyrate (hereinafter referred to as P(3HB)) composed of (R)-3-hydroxybutyrate (also referred to as (R)-3-hydroxybutyric acid. Hereinafter simply referred to as 3HB) (Non-Patent Document 1).

[0003] The melting point of P(3HB) is about 175 to 180°C and has a high melting point comparable to that of polypropylene (hereinafter referred to as PP). Although the breaking strength of P(3HB) is comparable to that of PP, the elongation at break is 5% or less, and the glass transition temperature is 4°C (below room temperature).

[0004] Since P(3HB) is a material with high crystallinity, hard and brittle, it cannot be used as a molded article such as a film alone in most cases. When using PHA industrially, as methods for improving its physical properties (crystallinity, mechanical properties, etc.), there are known methods such as introducing a second component monomer unit to form a copolymer, increasing the molecular weight, and compounding with different kinds of polymer materials.

[0005] On the other hand, the crystallization rate of PHA is significantly slower than that of conventional industrial polymers, and the glass transition temperature is below room temperature. When molding PHA in a heated and molten state, there are the following several problems in molding processing: the cooling time for curing is long and the productivity is poor; in melt spinning, due to slower crystallization, entanglement occurs in the amorphous state, resulting in sticking of the filaments; in order to avoid sticking, it is necessary to wind up in a non-overlapping state; after winding up, a long cooling time is required for curing (crystallization), etc. In addition, the slower crystallization rate causes larger growth of spherulites, which also affects the physical properties of the molded article and aging over time. Copolymerization sometimes leads to a lower nucleation density, in other words, a lower crystallization rate, and even after copolymerization, the above problems in molding processing still exist. Moreover, when having a high molecular weight, there are other problems such as an excessively high melt viscosity.

[0006] In the melt molding of thermoplastic polymers such as polyesters, various crystallization nucleating agents have been studied for the purpose of improving the crystallization rate.

[0007] As well-known crystallization nucleating agents, for example, adding elemental inorganic substances such as Zn powder, Al powder, graphite, and carbon black to specific polyesters; ZnO, MgO, Al 2 O 3 、TiO 2 、MnO 2 、SiO 2 、Fe 3 O 4 and other metal oxides; nitrides such as aluminum nitride, silicon nitride, titanium nitride, and boron nitride; Na 2 CO 3 、CaCO 3 、MgCO 3 、CaSO 4 、CaSiO 3 、BaSO 4 、Ca 3 (PO 4 ) 3 and other inorganic salts; clay minerals such as talc, kaolin, clay, and clay; organic salts such as calcium oxalate, sodium oxalate, calcium benzoate, calcium phthalate, calcium tartrate, magnesium stearate, and polyacrylate; high molecular compounds such as polyesters, polyethylene, and polypropylene, etc. (Patent Document 1).

[0008] In addition, as crystallization nucleating agents for PHA, granular substances such as talc, micronized mica, boron nitride, and calcium carbonate have been tried. As more effective crystallization nucleating agents, a method of densely mixing together an organic phosphonic acid such as cyclohexylphosphonic acid or an organic hypophosphorous acid or their esters, or derivatives of these acids or esters, and metal compounds such as oxides, hydroxides, and saturated or unsaturated carboxylates of metals in Groups IA to VA or IB to VB of the periodic table is known (Patent Document 2).

[0009] In addition, as nucleating agents for PHA, the following are known: sorbitol and sodium benzoate (Patent Document 3); sugar alcohols such as erythritol, D-arabitol, ribitol, xylitol, galactitol, D-mannitol, L-mannitol, D-sorbitol, myo-inositol, scyllo-inositol (Patent Document 4); polyvinyl alcohol, chitin, chitosan (Patent Document 5); polyalkylene oxides such as polyethylene oxide, polypropylene oxide, polybutylene oxide (Patent Document 6); aliphatic carboxylic acid amides, aliphatic carboxylates, aliphatic alcohols, and aliphatic carboxylic acid esters for aliphatic polyesters such as polylactic acid or PHA (Patent Documents 7 to 9); fatty acid esters such as dimethyl adipate, di-2-ethylhexyl adipate, diisobutyl adipate, dibutyl adipate, diisodecyl adipate, dibutyl diglycol adipate, dibutyl sebacate, di-2-ethylhexyl sebacate (Patent Document 10); cyclic compounds having C=O and a functional group selected from NH, S, and O in the molecule such as indigo, quinacridone, quinacridone magenta (Patent Document 11); ketopyrroles as cyclic compounds having C=O and an NH group in the molecule (Patent Document 12); sorbitol-based derivatives such as dibenzylidene sorbitol, bis(p-methylbenzylidene) sorbitol (Patent Document 13); compounds containing a nitrogen-containing heteroaromatic nucleus such as pyridine, pyrimidine, pyrazine, pyridazine, triazine, imidazole (Patent Document 14); phosphate compounds (Patent Document 15); bisamides of higher fatty acids and metal salts of higher fatty acids (Patent Document 16); fatty acids, fatty acid amides (Patent Document 17); branched poly(lactic acid) (Patent Document 18); pentaerythritol (Patent Document 19); pentaerythritol and an inorganic filler or an organic filler (Patent Document 20); sorbitol acetals, compounds having an amide bond, and pentaerythritol (Patent Document 21); amino acids such as tryptophan, phenylalanine, p-chlorophenylalanine, m-tyrosine, phenylglycine, p-hydroxyphenylglycine, methionine, o-tyrosine, and valine, or phosphatidylcholine (Patent Documents 22 to 24); dipeptides such as aspartame (Patent Document 25); and nucleobases such as uracil, thymine (Patent Document 26).

[0010] These nucleating agents are means adopted to promote the relatively slow crystallization rate of aliphatic polyesters such as PHA and polylactic acid, aiming to improve the processability during molding. However, there are still problems such as a decrease in strength and a deterioration in the surface appearance of the molded article, resulting in insufficient effects and the need to add other additives. In addition, depending on the type of nucleating agent, there may be cases where, as crystallization progresses after molding, due to differences in compatibility or molecular weight, it is extruded outside the crystal, causing blooming or bleeding. In such cases, additives such as dispersants, anti-aggregation agents, and compatibilizers also need to be added. Although the above-mentioned solutions also envision the use in living organisms and include nucleating agents composed of non-toxic fatty acids or amino acids that are easily decomposed, absorbed, or metabolized in living organisms, the current situation is that no nucleating agent with high practical effects has been found.

[0011] In addition, in order to improve the crystallization characteristics of PHA, attempts have also been made to blend other PHA or biodegradable polymers. Patent Documents 27 to 29 disclose adding higher melting point P(3HB) as a crystallization nucleating agent (nucleating agent) to a copolymer of P(3HB-co-3HV) composed of 3HB and 3-hydroxyvalerate (3-hydroxyvaleric acid, hereinafter referred to as 3HV), a copolymer of P(3HB-co-3HHx) composed of 3HB and 3-hydroxyhexanoate (3-hydroxyhexanoic acid, hereinafter referred to as 3HHx), or a copolymer of P(3HB-co-3HO) composed of 3HB and 3-hydroxyoctanoate (3-hydroxyoctanoic acid, hereinafter referred to as 3HO).

[0012] Patent Documents 27 to 29 describe dry mixing in which the blended dry powder PHA is directly mixed or mixed in the presence of dry ice; solution mixing in which part or all of it is dissolved in a solvent such as chloroform and stirred, and then the solvent is evaporated to precipitate the polymer or it is precipitated in a poor solvent; and so-called partial melting mixing in which thorough stirring and mixing are carried out at a temperature at which the added higher melting point side P(3HB) does not melt but the added lower melting point side PHA (P(3HB-co-3HV), P(3HB-co-3HHx), or P(3HB-co-3HO) in the examples) is in a molten state. However, it is mentioned that a small amount of the added higher melting point side P(3HB) must be finely and uniformly dispersed in the lower melting point side PHA copolymer.

[0013] Each of the above mixing methods has disadvantages. In dry mixing, even if polymer powders are mixed, the uniform mixing below the powder particle size is still limited. In solution mixing, a large amount of good solvents such as chloroform is required, and when reprecipitation recovery is carried out, an even larger amount of poor solvents, which is 5 to 10 times the amount of the good solvent, is required. Moreover, when reprecipitation is carried out, due to the difference in solubility, the types of precipitated polymers may deviate. In the partially molten state of the blend, the added P(3HB) with high crystallinity and high melting point is hardly melted in its original size and is thus not suitable for forming fine and uniform microcrystalline nuclei. The method of raising the temperature above the melting point of P(3HB) to mix the blend uniformly is the usual melt mixing method, but near the melting point of P(3HB), PHA such as P(3HB) cannot avoid deterioration and molecular weight reduction caused by thermal cracking or stirring.

[0014] In addition to the method of attempting to promote crystallization by blending P(3HB) taken out from the bacterial cells with PHA copolymers, the following method has also been reported. In this method, P(3HB) capable of forming crystal nuclei or PHA rich in 3HB is generated as a blend in the bacterial cells during the cultivation period together with other PHA copolymers, so that it is not necessary to blend P(3HB) with PHA after taking out PHA from the bacterial cells. In Patent Document 30, a method is described in which by changing the carbon source supply during cultivation, P(3HB) or P(3HB-co-3HHx) with a low 3HHx ratio is generated together with P(3HB-co-3HHx) with an increased 3HHx ratio. In Patent Documents 31 and 32, a method is disclosed in which by using genetic recombination technology, multiple PHA polymerases with different substrate specificities are retained in the same bacterial cell, and thus, a blend of PHAs with different melting points is produced in the same cell. Although it is also described that molding can be carried out at a temperature of 170°C or lower, it is not clear within what temperature range molding can be carried out. In known molding processes, melting is usually carried out above the melting point of the polymer and then molding is carried out. Moreover, in this document, it is also aimed at increasing the solidification rate (crystallization rate) of the once-melted PHA blend by one degree.

[0015] Although the purposes of Non-Patent Documents 2 to 4 are not to make P(3HB) capable of becoming crystal nuclei, they also describe PHA-producing wild strains in which P(3HB) and PHA copolymers are blended and generated in the same bacterial cell, and describe that by naturally retaining PHA polymerases with different substrate specificities in the same bacterial cell, a blend of P(3HB) homopolymer and PHA copolymers of C4 to C12 is produced.

[0016] On the other hand, it has also been reported that high strength is achieved by using ultra-high molecular weight P(3HB) and controlling crystal formation regardless of molecular weight. For example, ultra-high molecular weight P(3HB) with a number average molecular weight of 1.5 million (weight average molecular weight of 3 million) or more is biosynthesized using recombinant Escherichia coli, and a P(3HB) film with improved physical properties is obtained using this ultra-high molecular weight P(3HB) (Patent Document 33 and Non-Patent Document 5).

[0017] In addition, as a method for fibrillating P(3HB) that does not depend on molecular weight, a method has been disclosed in which P(3HB) is melt-extruded, quenched to a temperature below the glass transition temperature + 15°C to solidify it, an amorphous fiber is produced, the amorphous fiber is cold-drawn to orient the molecular chains of the amorphous fiber, and heat treatment is performed to obtain a P(3HB) fiber (hereinafter also referred to as the "cold drawing method") (Patent Document 34 and Patent Document 35). A method for manufacturing a fiber has also been disclosed, which is characterized in that the melt-extruded fiber is quenched to a temperature below the glass transition temperature + 15°C of PHA to solidify it, an amorphous fiber is produced, the amorphous fiber is left at a temperature below the glass transition temperature + 15°C to produce a crystalline fiber with microcrystal nuclei formed (isothermal crystallization), the crystalline fiber is drawn, and then tension heat treatment is performed (hereinafter also referred to as the "microcrystal nucleus drawing method") (Patent Document 36).

[0018] However, since the manufacturing efficiency of ultra-high molecular weight P(3HB) is poor and the cost is high; in the cold drawing method, it is necessary to quench to a low temperature near the glass transition temperature to obtain an amorphous fiber; in the microcrystal nucleus drawing method, since microcrystals of molten P(3HB) are first formed, it is necessary to quench to a low temperature near the glass transition temperature and keep it at a low temperature for a long time. Therefore, the above methods are not conducive to industrial production.

[0019] Ultra-high molecular weight P(3HB) with a weight-average molecular weight of 2.7 million produced by genetically recombinant Escherichia coli was added to P(3HB) with a weight-average molecular weight of 520,000 derived from common microorganisms. After being dissolved in chloroform, it was formed into a cast film, hot-pressed at 200 °C, then quenched with ice water, and then cold-drawn. A P(3HB) film with a small amount of ultra-high molecular weight polymer added was obtained. When the film was reheated to 200 °C and the crystal growth was observed, the ultra-high molecular weight P(3HB) played a role similar to a nucleating agent, suggesting that it could promote nucleation (Non-Patent Document 6). There is also a report that a small amount of ultra-high molecular weight P(3HB) with a weight-average molecular weight of 3.47 million was added to P(3HB) with a weight-average molecular weight of 520,000, and melt spinning was carried out at 180 °C, 190 °C, and 200 °C (Non-Patent Document 7). Among them, although the molecular weight decreased due to heating and melting above the melting point, the addition of ultra-high molecular weight P(3HB) inhibited the thermal cracking at the initial stage of the cracking of P(3HB), and the processability of melt spinning was improved. There is also a report that by cooling to 4 °C after melt spinning and using two-step cold drawing, the blended P(3HB) fiber containing 5 wt% of ultra-high molecular weight P(3HB) showed a strength of 740 MPa. The amount of ultra-high molecular weight P(3HB) used can be small. However, since two-step cold drawing needs to be carried out in a cooling state of 4 °C, the operation is cumbersome and it cannot be said to be suitable for industrialization.

[0020] In addition, it has been reported that when manufacturing a melt-molded article by melt-molding a molding material mainly composed of a biodegradable polyester having a melting point within a specific range at a heating temperature within a specific range, the cold crystallization heat and the sum of its heat of fusion and cold crystallization heat are used as indices of the crystallization ability and crystallinity of the obtained melt-molded article respectively, and the melt-molded article is manufactured by setting within a specific range (Patent Document 37). It has also been reported that a copolymer of 3HB and 3-hydroxyhexanoate is processed at a temperature at which crystallization is not completely melted (around 160°C) (Non-Patent Document 8). In addition, it has been reported that a pipe is composed of a poly(3-hydroxybutyrate)-based resin, and the difference between the peak temperature of the melting point and the end temperature of the melting point peak in the differential scanning calorimetry of the poly(3-hydroxybutyrate)-based resin is 10°C or more (Patent Document 38). It has also been reported that a method for manufacturing a biodegradable resin molded body is characterized in that when a biodegradable resin composition containing poly(3-hydroxyalkanoate) is heated and melt-kneaded and molded into a molded body, the residual crystallization amount at the outlet of the molding machine after heating and melt-kneading is confirmed by the spectrum of near-infrared spectroscopy, and the residual crystallization amount at the outlet of the molding machine is adjusted so that the crystallization peak obtained by near-infrared spectroscopy of the above-mentioned molded body can be observed within 200 seconds after molding (Patent Document 39). However, it is not described that the melt-molding temperature is set higher than the starting temperature of outflow obtained by the method of raising the temperature with a flow tester and lower than the temperature indicating the complete end of crystallization melting measured by a differential scanning calorimeter (especially a temperature lower than the extrapolated end temperature of melting).

[0021] Prior Art Documents

[0022] Patent Documents

[0023] Patent Document 1: Japanese Patent Laid-Open No. 07-126496

[0024] Patent Document 2: Japanese Patent Laid-Open No. 03-024151

[0025] Patent Document 3: WO2006 / 012917

[0026] Patent Document 4: WO2008 / 099586

[0027] Patent Document 5: Japanese Patent Laid-Open No. 2007-077232

[0028] Patent Document 6: Japanese Patent Laid-Open No. 2010-229407

[0029] Patent Document 7: Japanese Patent Laid-Open No. 09-278991

[0030] Patent Document 8: Japanese Patent Laid-Open No. 11-005849

[0031] Patent Document 9: Japanese Unexamined Patent Application Publication No. 07-188537

[0032] Patent Document 10: Japanese Unexamined Patent Application Publication No. 11-116783

[0033] Patent Document 11: Japanese Unexamined Patent Application Publication No. 2003-238779

[0034] Patent Document 12: Japanese Unexamined Patent Application Publication No. 2003-327803

[0035] Patent Document 13: Japanese Unexamined Patent Application Publication No. 10-158369

[0036] Patent Document 14: Japanese Patent Application Laid-Open Under the PCT Treaty No. 2007-517126

[0037] Patent Document 15: Japanese Unexamined Patent Application Publication No. 2003-192884

[0038] Patent Document 16: Japanese Unexamined Patent Application Publication No. 6-299054

[0039] Patent Document 17: Japanese Unexamined Patent Application Publication No. 8-27363

[0040] Patent Document 18: Japanese Unexamined Patent Application Publication No. 2009-024058

[0041] Patent Document 19: Japanese Unexamined Patent Application Publication No. 2017-101256

[0042] Patent Document 20: WO2015 / 052876

[0043] Patent Document 21: WO2014 / 068943

[0044] Patent Document 22: Japanese Unexamined Patent Application Publication No. 2006-282940

[0045] Patent Document 23: Japanese Unexamined Patent Application Publication No. 06-345950

[0046] Patent Document 24: Japanese Patent Application Laid-Open Under the PCT Treaty No. Hei 10-504583

[0047] Patent Document 25: Japanese Unexamined Patent Application Publication No. 2019-119839

[0048] Patent Document 26: Japanese Unexamined Patent Application Publication No. 2019-119840

[0049] Patent Document 27: Japanese Patent Application Laid-Open Under the PCT Treaty No. Hei 08-510498

[0050] Patent Document 28: WO2002 / 055581

[0051] Patent Document 29: WO2002 / 050461 Gazette

[0052] Patent Document 30: Japanese Unexamined Patent Application Publication No. 2004-250629

[0053] Patent Document 31: WO2015 / 146195 Gazette

[0054] Patent Document 32: WO2017 / 056442 Gazette

[0055] Patent Document 33: Japanese Unexamined Patent Application Publication No. 10-176070

[0056] Patent Document 34: Japanese Unexamined Patent Application Publication No. 2003-328230

[0057] Patent Document 35: Japanese Unexamined Patent Application Publication No. 2003-328231

[0058] Patent Document 36: WO2006 / 038373 Gazette

[0059] Patent Document 37: Japanese Patent No. 4245306 Gazette

[0060] Patent Document 38: WO2020 / 040093 Gazette

[0061] Patent Document 39: Japanese Unexamined Patent Application Publication No. 2010-241075 Gazette Non-Patent Document

[0062] Non-Patent Document 1: Alistair J. Anderson et al., Microbiological Reviews, Vol. 54, No. 4, 450 - 472, 1990.

[0063] Non-Patent Document 2: H. Abe, et al., International Journal of Biological Macromolecules, 1994, vol. 16, 115 - 119.

[0064] Non-Patent Document 3: M. Kato et Aal., Bull. Chem. Soc. Jpn, 1996, vol. 69, 515 - 520.

[0065] Non-Patent Document 4: H. Matsusaki et al., Journal of bacteriorogy, 1998, vol. 180, 6459 - 6467.

[0066] Non-Patent Document 5: Kusaka et al., Appl. Microbiol. Biotechnol., 47 140-143(1997). Molecular mass of poly[(R)-3-hydroxybutyric acid] produced in a recombinant Escherichia coli.

[0067] Non-Patent Document 6: T. Kabe et al., Macromolecules, 2012, 45, 1858-1865.

[0068] Non-Patent Document 7: T. Kabe en al., ACS symposium series on Biobased Monomers, Polymers, and Materials, Chaper 5, 63-75.

[0069] Non-Patent Document 8: Journal of the Packaging Institute of Japan Vo.28, No.2(2019)109-115. Summary of the Invention

[0070] Technical Problem to be Solved by the Invention

[0071] As described above, in the existing methods, a crystalline polymer (polyester) with a slow crystallization rate is melted and then rapidly subjected to primary nucleation, crystallized in a manner that does not form defective large spherulites and improves strength, and solidified / crystallized in an easy-to-process manner. From this perspective, it has been developed. Although in the melt molding of biodegradable crystalline polymers, various attempts have been made to promote crystallization in order to improve poor processability due to slow crystallization rate or to increase strength, there is still room for improvement.

[0072] As a means for solving the above problems, a method of melting the polymer (in other words, partially melting) at a temperature lower than the temperature at which the entire polymer can be melted and at a temperature at which relatively thin and lower-melting fine lamellae or amorphous regions can flow has been studied. In the case of manufacturing a polymer molded article by such partial melting, it has been found that the temperature range available for partial melting is sometimes narrow. The subject of the present invention is to provide a method for manufacturing a polymer molded article that can widen the temperature range available for partial melting.

[0073] Technical Solution for Solving the Technical Problem

[0074] The inventors of the present invention conducted in-depth research to solve the above problems, and as a result, noticed that after heat-treating a crystalline polyhydroxyalkanoate at a temperature above the glass transition temperature and then performing partial melt molding, it is possible to broaden the temperature range applicable to thermoforming by partial melting. The present invention was completed based on the above knowledge.

[0075] According to the present invention, the following inventions are provided.

[0076] <1>A method for manufacturing a polymer molded article, comprising: a step of heat-treating a crystalline polyhydroxyalkanoate at a temperature above the glass transition temperature; and a step of melt-molding the polyhydroxyalkanoate obtained by the above heat treatment within a temperature range where a part of the lamellae melts and flows and the remaining part of the lamellae does not melt and remains.

[0077] <2>The method according to <1>, wherein the above heat treatment is a heat treatment carried out using a gas, a liquid, or a solid as a medium.

[0078] <3>The method according to <1> or <2>, wherein the above heat treatment is a heat treatment carried out using a liquid as a medium, and in the heated state, the polyhydroxyalkanoate is not completely dissolved in the liquid.

[0079] <4>The method according to any one of <1> to <3>, wherein the above temperature range is a range higher than the starting temperature of outflow obtained by the method of raising the temperature with a flow tester and lower than the temperature indicating the complete end of crystal melting measured by a differential scanning calorimeter.

[0080] <5>The method according to any one of <1> to <4>, wherein the above temperature range is a range higher than the starting temperature of outflow obtained by the method of raising the temperature with a flow tester and lower than the extrapolated melting end temperature.

[0081] <6>The method according to any one of <1> to <5>, comprising: a step of cooling the polymer melted within a temperature range where a part of the lamellae melts and flows and the remaining part of the lamellae does not melt and remains in air.

[0082] <7>The method according to any one of <1> to <6>, wherein the above thermoforming is molding using melt extrusion.

[0083] <8>The method according to any one of <1> to <7>, wherein the above thermoforming is molding using melt extrusion spinning.

[0084] <9>The method according to any one of <1> to <8>, wherein the above crystalline polyhydroxyalkanoate is a copolymer containing 3-hydroxybutyric acid and 4-hydroxybutyric acid as monomer units.

[0085] <10>The method according to any one of <1> to <9>, wherein the crystalline polyhydroxyalkanoate is a copolymer containing 3-hydroxybutyric acid and 4-hydroxybutyric acid as monomer units, and the proportion of 4-hydroxybutyric acid is 5 mol% or more and 40 mol% or less.

[0086] Effects of the Invention

[0087] According to the method for manufacturing a polymer molded article of the present invention, the temperature range applicable to partial melting can be broadened. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-rising method of a flow tester for sample S1 (P(3HB) homopolymer).

[0089] Figure 2 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-rising method of a flow tester for sample S2 (P(3HB) homopolymer).

[0090] Figure 3 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-rising method of a flow tester for sample S3 (P(3HB) homopolymer).

[0091] Figure 4 Superimposed are the DSC curves of sample S1 (solid line), sample S2 (dashed line), and sample S3 (thick dashed line).

[0092] Figure 5 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-rising method of a flow tester for sample S4 (P(3HB-co-13.1 mol% 4HB)). Shows the extrapolated end melting temperature of sample S4 and the temperature when the DSC curve returns to the baseline.

[0093] Figure 6 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-rising method of a flow tester for sample S5 (P(3HB-co-13.1 mol% 4HB)). Shows the extrapolated end melting temperature of sample S5 and the temperature when the DSC curve returns to the baseline.

[0094] Figure 7 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-rising method of a flow tester for sample S6 (P(3HB-co-13.1 mol% 4HB)). Shows the extrapolated end melting temperature of sample S6 and the temperature when the DSC curve returns to the baseline.

[0095] Figure 8Superimposed are the DSC curves of specimen S4 (solid line), specimen S5 (dashed line), specimen S6 (dotted-dashed line), and specimen S7 (thick dashed line).

[0096] Figure 9 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-raising method using a flow tester for specimen S8 (P(3HB-co-61.5 mol% 3HV)).

[0097] Figure 10 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-raising method using a flow tester for specimen S9 (P(3HB-co-61.5 mol% 3HV)).

[0098] Figure 11 Shows the flow curve (solid line) and DSC curve (dashed line) obtained by the temperature-raising method using a flow tester for specimen S10 (P(3HB-co-61.5 mol% 3HV)).

[0099] Figure 12 Superimposed are the DSC curves of specimen S8 (solid line), specimen S9 (dashed line), and specimen S10 (thick dashed line).

[0100] Figure 13 Shows the change in the DSC curve for various heat pre-treatments of specimen S11.

[0101] Figure 14 Shows the change in the DSC curve for heat treatment of specimen S11 in a liquid. Detailed implementation mode

[0102] The present invention will be described in detail below.

[0103] The method for manufacturing a polymer molded article of the present invention includes a step of heat-treating a crystalline polyhydroxyalkanoate (PHA) at a temperature above the glass transition temperature; and a step of melt-molding the polyhydroxyalkanoate obtained by the above heat treatment in a temperature range where a part of the lamellae melts and flows and the other remaining part of the lamellae does not melt and remains.

[0104] [Regarding heat treatment]

[0105] In the present invention, the crystalline polyhydroxyalkanoate is heat-treated at a temperature above the glass transition temperature. By this heat treatment, the thickness of the lamellae is reconfigured, thereby enabling the expansion of the temperature region available for melt molding.

[0106] In the case of heating an amorphous solid, a solid that is as hard as a crystal and has no fluidity at low temperatures rapidly decreases in rigidity and viscosity and increases in fluidity within a relatively narrow temperature range. This temperature is the glass transition temperature.

[0107] Regarding the heating temperature, it is preferably in a temperature range above the glass transition temperature for the crystalline polyhydroxyalkanoate and not causing all the crystals to melt. Generally, the crystalline polyhydroxyalkanoate can be heat-treated at a temperature 20 to 170 °C higher than the glass transition temperature (preferably a temperature 40 to 120 °C higher).

[0108] The heating time is not particularly limited, and it is usually possible to heat for 1 hour to 72 hours, preferably 6 hours to 48 hours, more preferably 12 hours to 36 hours.

[0109] The means of heat treatment is not particularly limited, and the heat treatment can be any heat treatment using a gas, a liquid, or a solid as a medium.

[0110] Heat treatment using a gas as a medium means heating the crystalline polyhydroxyalkanoate in a gas. Examples of the gas include air, inert gases (such as nitrogen), etc.

[0111] Heat treatment using a liquid as a medium means heating the crystalline polyhydroxyalkanoate in a liquid. Examples of the liquid include water, lower alcohols (such as methanol, ethanol), polyols (such as glycerol, propylene glycol), hexane, acetone, and other organic solvents or mixtures thereof. In the heat treatment using a liquid as a medium, it is preferred that the polyhydroxyalkanoate does not completely dissolve in the liquid in the heated state.

[0112] Heat treatment using a solid as a medium means, for example, heating the crystalline polyhydroxyalkanoate in contact with a solid medium (such as a plate). Examples of the solid include metals (such as aluminum, copper, silver, iron, stainless steel), ceramics, glass, etc.

[0113] [Regarding crystalline polyhydroxyalkanoate]

[0114] Examples of polyhydroxyalkanoates include: homopolymers of hydroxyalkanoic acids (e.g., poly-3-hydroxypropionic acid, poly-3-hydroxybutyric acid, poly-3-hydroxypentanoic acid, poly-4-hydroxybutyric acid, poly-3-hydroxyhexanoic acid, poly-3-hydroxyoctanoic acid, poly-4-hydroxypentanoic acid, poly-4-hydroxyhexanoic acid, poly-5-hydroxypentanoic acid, poly-2-hydroxybutyric acid, poly-2-hydroxypentanoic acid, poly-2-hydroxyhexanoic acid, etc.); copolymers of hydroxyalkanoic acids (e.g., copolymer of 3-hydroxypropionic acid and 3-hydroxybutyric acid, copolymer of 3-hydroxypropionic acid and 3-hydroxypentanoic acid, copolymer of 3-hydroxypropionic acid and 4-hydroxybutyric acid, copolymer of 3-hydroxypropionic acid and 3-hydroxyhexanoic acid, copolymer of 3-hydroxypropionic acid and 3-hydroxyoctanoic acid, copolymer of 3-hydroxybutyric acid and 3-hydroxypentanoic acid, copolymer of 3-hydroxybutyric acid and 4-hydroxybutyric acid, copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid, copolymer of 3-hydroxybutyric acid and 3-hydroxyoctanoic acid, copolymer of 3-hydroxypentanoic acid and 4-hydroxybutyric acid, copolymer of 3-hydroxypentanoic acid and 3-hydroxyhexanoic acid, copolymer of 3-hydroxypentanoic acid and 3-hydroxyoctanoic acid, copolymer of lactic acid and 3-hydroxypropionic acid, copolymer of lactic acid and 3-hydroxybutyric acid, copolymer of lactic acid and 3-hydroxypentanoic acid, copolymer of lactic acid and 3-hydroxybutyric acid, copolymer of lactic acid and 3-hydroxyhexanoic acid, copolymer of lactic acid and 3-hydroxyoctanoic acid, copolymer of glycolic acid and 3-hydroxypropionic acid, copolymer of glycolic acid and 3-hydroxybutyric acid, copolymer of glycolic acid and 3-hydroxypentanoic acid, copolymer of glycolic acid and 4-hydroxybutyric acid, copolymer of glycolic acid and 3-hydroxyhexanoic acid, copolymer of glycolic acid and 3-hydroxyoctanoic acid; and copolymers composed of three or more monomers such as terpolymers, etc.).

[0115] In addition, polyhydroxyalkanoates can be used alone or in combination of two or more kinds.

[0116] In the polyhydroxyalkanoate used in the present invention, in order to form a crystalline chain segment polymer structure such as a lamellar crystal or a fringed micelle structure, spherulite, dendrite, shish-kebab structure, extended chain crystal, etc., it is preferable that a highly crystalline continuous monomer unit chain repeatedly exists in the polymer chain. For example, a 3-hydroxypropionic acid chain, 3-hydroxybutyric acid chain, 3-hydroxypentanoic acid chain, 4-hydroxybutyric acid chain, 3-hydroxyhexanoic acid chain, 3-hydroxyhexanoic acid chain, 3-hydroxyoctanoic acid chain, 4-hydroxypentanoic acid chain, 4-hydroxyhexanoic acid chain, 5-hydroxypentanoic acid chain, 2-hydroxybutyric acid chain, 2-hydroxypentanoic acid chain, 2-hydroxyhexanoic acid chain, etc., a chain structure sufficient to achieve a crystalline microstructure. When there are stereoisomers or optical isomers as monomer units, it is necessary to use a crystalline chain segment composed of chains formed by the same stereoisomers. For example, R-3-hydroxybutyric acid chain, S-3-hydroxybutyric acid chain, R-3-hydroxypentanoic acid chain, S-3-hydroxypentanoic acid chain, R-3-hydroxyhexanoic acid chain, S-3-hydroxyhexanoic acid chain, etc. The chain structure of the same stereoisomer is an important factor for forming a crystal structure. In the case of a polyhydroxyalkanoate containing monomer units with stereoisomers or optical isomers, the crystallinity decreases, and it is difficult to obtain a crystalline chain segment. Especially in the case of synthesizing a polymer composed of these monomer units by a biological method, a binary copolymer or a copolymer of three or more components having an R-3-hydroxybutyric acid chain and having other monomer units introduced as a second component is more preferable.

[0117] The polyhydroxyalkanoate can be produced by either a chemical synthesis method or a biological synthesis method. In order to ensure a crystalline chain segment obtained from the chain structure, in the case of containing monomer units with stereoisomers, a copolymer composed of any stereoisomer such as a copolymer of R-3-hydroxybutyric acid and 4-hydroxybutyric acid, a copolymer of S-3-hydroxybutyric acid and 4-hydroxybutyric acid, etc. is preferable.

[0118] When the polyhydroxyalkanoate contains 3-hydroxybutyric acid units and 4-hydroxybutyric acid units, the proportion of 4-hydroxybutyric acid units is preferably 5 mol% or more and 40 mol% or less, relative to all monomer units. The proportion of 4-hydroxybutyric acid can be 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, 10 mol% or more, 11 mol% or more, 12 mol% or more, 13 mol% or more, 14 mol% or more, 15 mol% or more or 16 mol% or more, and can also be 17 mol% or more, 18 mol% or more, 19 mol% or more, 20 mol% or more. The proportion of 4-hydroxybutyric acid units is 35 mol% or less, 34 mol% or less, 33 mol% or less, 32 mol% or less, 31 mol% or less, 30 mol% or less, 29 mol% or less, 28 mol% or less, 27 mol% or less, 26 mol% or less, 25 mol% or less, 24 mol% or less, 23 mol% or less, 22 mol% or less or 21 mol% or less, relative to all monomer units.

[0119] When the polyester contains 3-hydroxybutyric acid units and 3-hydroxypentanoic acid units, the proportion of 3-hydroxypentanoic acid units is preferably 5 mol% or more and 90 mol% or less, relative to all monomer units. The proportion of 3-hydroxypentanoic acid units can be 5 mol% or more, 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, 10 mol% or more, 15 mol% or more, 20 mol% or more, 25 mol% or more, 30 mol% or more, 35 mol% or more or 40 mol% or more, and can also be 45 mol% or more, 50 mol% or more, 55 mol% or more, 60 mol% or more. The proportion of 3-hydroxypentanoate units is 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, 70 mol% or less, 65 mol% or less, relative to all monomer units.

[0120] <Molecular weight of polyhydroxyalkanoate>

[0121] Regarding polyhydroxyalkanoate, the weight-average molecular weight measured by gel permeation chromatography in terms of polystyrene is preferably 100,000 or more, more preferably 200,000 or more, and further can be 300,000 or more, 400,000 or more, or 500,000 or more. The weight-average molecular weight measured by gel permeation chromatography in terms of polystyrene can be 600,000 or more, 700,000 or more, 800,000 or more, 900,000 or more, 1,000,000 or more, 1,100,000 or more, 1,200,000 or more, 1,300,000 or more, 1,400,000 or more, 1,500,000 or more, 2,000,000 or more, 3,000,000 or more, or 4,000,000 or more. There is no particular limitation on the upper limit of the weight-average molecular weight measured by gel permeation chromatography in terms of polystyrene, and it is usually 20,000,000 or less, and can be 10,000,000 or less, 8,000,000 or less, 7,000,000 or less, 6,000,000 or less, 5,000,000 or less, 4,000,000 or less, or 3,000,000 or less. However, in the case of melt molding, considering the reduction in molecular weight due to thermal cracking and the viscosity during melting not becoming too high, the weight-average molecular weight measured by gel permeation chromatography in terms of polystyrene is preferably 400,000 or more and 2,500,000 or less, more preferably 500,000 or more and 2,200,000 or less, and further preferably 600,000 or more and 2,000,000 or less.

[0122] In the case of partial melt molding, in most cases, a melting temperature lower than the temperature range of about 170 °C where a reduction in molecular weight due to thermal cracking can be observed can be used. Therefore, in the case of partial melt molding, from the viewpoint of easily suppressing the reduction in molecular weight due to thermal cracking, the molecular weight of the polymer used can be a molecular weight lower than that during melt molding. The weight-average molecular weight measured by polystyrene gel permeation chromatography is preferably 200,000 or more and 2,500,000 or less, more preferably 400,000 or more and 2,000,000 or less, and further preferably 600,000 or more and 1,500,000 or less.

[0123] <Preferred form of polyhydroxyalkanoate>

[0124] The polymer of the present invention can be any one of a random polymer, a block polymer, an alternating polymer, or a graft polymer, and is preferably a random polymer.

[0125] The polyhydroxyalkanoate can also be a thermoplastic resin.

[0126] The polyhydroxyalkanoate is preferably a biodegradable polymer, and more preferably a bioabsorbable polymer. Biodegradability means that it can be decomposed by microorganisms or enzymes in the natural environment (such as soil, compost, lakes, seawater, etc.), or can be decomposed into non-toxic components in the living body. Bioabsorbability means that it can be metabolized by living organisms such as humans or animals.

[0127] The melting point of the polyhydroxyalkanoate is not particularly limited, preferably 180 °C or lower, more preferably 175 °C or lower (or lower than 175 °C), and still more preferably 170 °C or lower. The melting point of the polyhydroxyalkanoate may be 160 °C or lower, 150 °C or lower, 140 °C or lower, or 130 °C or lower. The lower limit of the melting point of the polyhydroxyalkanoate is not particularly limited, and generally may be 40 °C or higher, 50 °C or higher, 60 °C or higher, 70 °C or higher, 80 °C or higher, 90 °C or higher, or 100 °C or higher. When the polyhydroxyalkanoate has a plurality of melting points, it is sufficient that the melting point of the main component is within the above range.

[0128] [Regarding melt molding]

[0129] In the present invention, by melting within the temperature range above the starting temperature of flow measured when evaluating the fluidity of the crystalline polyhydroxyalkanoate by the temperature-rising method using a flow tester and lower than the temperature indicating the complete end of crystal melting measured by a differential scanning calorimeter (DSC), and then performing molding, the processability of a thermoplastic resin with slow crystallization and poor processing characteristics can be improved.

[0130] By performing heat treatment at a temperature above the glass transition temperature before melt molding to reconfigure the thickness of the lamellae of the crystalline polyhydroxyalkanoate, the temperature range applicable to subsequent thermoforming using partial melting can be broadened.

[0131] The "temperature indicating the complete end of crystal melting measured by a differential scanning calorimeter (DSC)" is preferably the extrapolated end temperature of the melting peak. The extrapolated end temperature of the melting peak can be obtained according to the description in the following examples. That is, when the melting peak is a sharp peak, according to JIS-K7121, the extrapolated end temperature of the melting peak is the temperature at the intersection of the tangent line drawn from the maximum slope point before the end of the peak and the baseline after the peak (identified by Rigaku, Thermo plus EVO software). When the melting peak shape is a superposition of multiple peaks, manually redraw the tangent line for the peak on the higher temperature side, and use the intersection of it and the baseline as the extrapolated end temperature of melting.

[0132] Moreover, in the past, melt molding was usually carried out by melting at temperatures above the melting point, such as the melting point + 20°C, the melting point + 10°C, the melting point + 5°C, etc., and then performing molding. In contrast, in the case of molding in a partially molten state as in the present invention, partial melting is carried out at a temperature below the melting point. Therefore, in the case of a polymer in which the melting point is close to the thermal decomposition temperature, decomposition caused by heat can be suppressed, that is, a decrease in molecular weight can be suppressed. Moreover, since the molecular weight of the polymer after molding can be maintained at a high level, it is also beneficial in terms of physical properties. Furthermore, compared with complete melting, melting in a partially molten state is carried out at a lower temperature. Therefore, it is speculated that not only can the thermal decomposition of the polymer be reduced, but also the hydrolysis of the polyhydroxyalkanoate molecular chain interfered by trace amounts of mixed water under a heated state can be reduced. Therefore, although it is generally desirable to have a low moisture content in the raw material, the necessity to reduce or maintain the concentration to an extremely low level can be reduced. Thus, the following advantage can also be anticipated, that is, in a spinning or molding apparatus, there is no need to provide a special apparatus for strictly maintaining the dry state of the dry raw material polyhydroxyalkanoate in order to prevent moisture in the atmosphere from transferring to the raw material polymer.

[0133] In addition, the present invention can improve the moldability of a polyester with slow melt crystallization without adding a crystallization nucleating agent, thereby improving productivity, but the use of a crystallization nucleating agent is not excluded.

[0134] As an example of the present invention, P(3HB-co-4HB) can be used as the polyhydroxyalkanoate. In this case, the method of the present invention is characterized by including a step of melt extrusion between the temperature at which crystallization and amorphous regions represented by relatively thin lamellae composed of 3HB segments inside the polymer start to melt and flow and the temperature at which relatively thick lamellae composed of 3HB segments etc. melt during the melting of P(3HB-co-4HB).

[0135] The present invention relates to a method for manufacturing a biodegradable polyester molded article, which is characterized in that melt molding is carried out in a state where a part of the crystals represented by lamellae contained in the polyhydroxyalkanoate remains, and the crystals that remain unmolten become crystal nuclei. Thus, molding can be carried out without waiting for primary nucleation in normal melt molding.

[0136] Therefore, the poor moldability of a crystalline thermoplastic polyhydroxyalkanoate with slow crystallization can be improved. Different from the case of complete melting, there is no need to wait for primary crystallization nucleation, and molding can be carried out immediately after partial melting, thereby improving productivity.

[0137] Crystalline partially crystalline portions such as lamellae dispersed in the bulk of the crystalline thermoplastic polyhydroxyalkanoate remain unmolten and function as crystal nuclei. Therefore, there is no need to wait for the time for primary nucleation, and the adhesiveness due to the low crystallinity immediately after melt extrusion can be reduced, making it difficult for molded articles such as fibers or films to stick together. Moreover, immediately after melt spinning or film formation, winding and stretching can be carried out, thereby improving productivity.

[0138] Melt spinning is carried out in a state where the partially crystalline portion remains unmolten, and then stretching is immediately carried out. As a result, the unmolten remaining lamellae are oriented, the polymer chains in the amorphous state are highly oriented, and continuous chain segments of monomer units that are easy to form crystals aggregate, thereby promoting crystallization. Since melting at a high temperature that causes thermal cracking is not carried out, a decrease in molecular weight due to thermal cracking can be suppressed, and the molecular weight of the molded article can be maintained. In other words, thermal degradation can be prevented. Moreover, even when there is moisture remaining in the polymer, or even for a polymer that easily absorbs moisture in the air, since the temperature can be reduced by partial melting molding, compared with complete melting molding, the degree of hydrolysis affected by heat and moisture can be reduced, and a decrease in the molecular weight of the polyhydroxyalkanoate can be suppressed, and the molecular weight of the molded article can be maintained.

[0139] In the present invention, polyhydroxyalkanoate is melt-molded. When melt-molding polyhydroxyalkanoate, additives can also be added as long as the effects of the present invention are not lost.

[0140] Examples of the additives include one or more selected from antioxidants, heat stabilizers (such as hindered phenols, hydroquinones, phosphite esters and their substituents, etc.), ultraviolet absorbers (such as resorcinol, salicylate esters), anti-coloring agents (phosphites, hypophosphites, etc.), lubricants, mold release agents (montanic acid and its metal salts, its esters, its semi-esters, stearyl alcohol, stearamide, and polyethylene wax, etc.), coloring agents (dyes or pigments, etc.), carbon black as a conductive agent or coloring agent, plasticizers, flame retardants (brominated flame retardants, phosphorus-based flame retardants, red phosphorus, silicone-based flame retardants, etc.), flame retardant aids, and antistatic agents.

[0141] There is no particular limitation on the method of incorporating the additives into the polyhydroxyalkanoate, and examples include dry blending, solution blending, and addition during the chemical polymerization of polyhydroxyalkanoate.

[0142] Polyhydroxyalkanoate can be molded by known melt molding methods such as injection molding, injection compression molding, compression molding, extrusion molding (melt extrusion molding), blow molding, molding press, and spinning (melt extrusion spinning).

[0143] There is no particular limitation on the number of times of melt molding, and it is preferably carried out only once.

[0144] In the present invention, the step of curing after molding can be carried out in a molding die, in a gas (such as air, nitrogen, etc.) or in a liquid (such as water, alcohol, glycerin or a mixture thereof, etc.). That is, the polyhydroxyalkanoate partially melted by the method of the present invention can be cooled in a molding die, in a gas or in a liquid, thereby being cured. Preferably, the partially melted polyhydroxyalkanoate can be cooled in a molding die, in air or in water. More preferably, the partially melted polyhydroxyalkanoate can be cooled in a molding die or in air.

[0145] Examples of the polyhydroxyalkanoate molded article produced by the method of the present invention include injection molded articles, extrusion molded articles, compression molded articles, sheets, pipes, various films such as unstretched films, uniaxially stretched films, and biaxially stretched films, and various fibers such as unstretched filaments and super stretched filaments. In addition, the polymer molded article produced by the method of the present invention can be tubular or can have a shape other than tubular.

[0146] Hereinafter, examples and comparative examples will be shown to explain the present invention in detail. In addition, the descriptions of the examples and comparative examples in the specification of the present invention are for helping to understand the content of the present invention, and such descriptions cannot be used as a basis for narrowly interpreting the technical scope of the present invention.

[0147] Examples

[0148] <Polymer used>

[0149] Poly-3-hydroxybutyric acid (P(3HB)) produced by Mitsubishi Gas Chemical Company, Inc. is "Biogreen (registered trademark) (Mw: 9.4 million, melting point of about 175 °C, glass transition temperature of about 2 °C)".

[0150] The P(3HB-co-4HB) copolymer was produced by a cultivation method according to the method described in WO2019 / 044837. By appropriately changing the type and supply ratio of the carbon source used, P(3HB-co-4HB) copolymers with various 4HB ratios were produced.

[0151] P(3HB-co-61.5 mol% 3HV) was produced by a cultivation method according to the method described in Japanese Patent Laid-Open No. 01-069622.

[0152] As is well known, the method for extracting PHA from bacterial cells can adopt a solvent extraction method of using a halogenated hydrocarbon solvent represented by chloroform for extraction and precipitating it with a poor solvent such as hexane or methanol, or can adopt an aqueous extraction method as described in Japanese Patent Publication No. 04-061638, Japanese Patent Laid-Open No. 07-177894, and WO2004 / 029266.

[0153] <Measurement of molecular weight of PHA (gel permeation chromatography (GPC) method)>

[0154] The molecular weight of PHA was determined by gel permeation chromatography as follows.

[0155] Chloroform was added to make the concentration of PHA about 0.5 mg / ml, and it was dissolved at 60 °C for 4 hours. Then it was cooled to room temperature, and the insoluble matter was removed by filtration using a PTFE filter with a pore size of 0.2 μm to prepare a test sample for measurement. The GPC conditions are as follows.

[0156] Apparatus: HPLC Prominence system manufactured by Shimadzu Corporation;

[0157] Column: Shodex K-806L manufactured by Showa Denko K.K. (two columns connected in series);

[0158] Column temperature: 40 °C;

[0159] Mobile phase: chloroform (1 ml / min);

[0160] Detector: RI (40 °C);

[0161] Standard: Shodex polystyrene molecular weight standard (6.87 million - 12.7 million);

[0162] Injection volume: 60 μl;

[0163] Analysis time: 30 minutes.

[0164] <Measurement of the initial outflow temperature of PHA using a flow tester>

[0165] PHA was measured using a flow tester CFT-500D type (Capillary Rheometer Flowtester, manufactured by Shimadzu Corporation) or CFT-500EX (manufactured by Shimadzu Corporation). Regarding the amount of sample used for measurement, for PHA in the form of granules, powder, film, etc., about 1.2 g was filled into a cylinder for measurement. In the case of using powdered polymers, they can also be molded using an appropriate granulator or molding press and then filled into the cylinder. The die (nozzle) used was a product with a diameter of 1.0 mm and a thickness of 1.0 mm. An extrusion load of 5 kg was applied, and after a preheating time of 240 seconds at an initial set temperature of 30 °C - 140 °C (appropriately selected according to the type and melting point of the polymer), the curve of the travel length (mm) versus temperature was obtained when the temperature was increased at a constant rate of 3 °C / min to 130 °C - 260 °C (appropriately selected according to the type and melting point of the polymer). As the temperature rises, PHA is heated and the polymer begins to flow out of the die. The temperature at this time was taken as the initial outflow temperature.

[0166] <PHA Melting Behavior Measurement: Measurement of Thermal Properties Using a Differential Scanning Calorimeter (DSC)>

[0167] The melting behavior of PHA was measured using a differential scanning calorimeter (Rigaku, Thermo plus EVO DSC8230). The measurement atmosphere was set to nitrogen (30 ml / min), and the temperature was raised from 30°C to 130°C - 260°C (appropriately selected according to the type and melting point of PHA) at a rate of 20°C / min. The sample was set to about 1 mg, and an aluminum sample pan was used. Indium was used for temperature calibration.

[0168] When the melting peak is a sharp peak, according to JIS-K7121, the extrapolated end temperature of the melting peak is set to the temperature at the intersection of the tangent line drawn from the maximum slope point before the peak end and the baseline after the peak (identified by the Rigaku, Thermo plus EVO software). When the melting peak shape is a multi-peak overlap, the tangent line of the melting peak on the high-temperature side is redrawn manually, and the intersection of it and the baseline is taken as the extrapolated end temperature of melting.

[0169] The glass transition temperature (Tg) of each sample was measured using a differential scanning calorimeter (DSC) model: DSC 8500 (PerkinElme, USA) equipped with an internal cooler under a nitrogen atmosphere (20 mL / min). In the first cycle, the temperature was raised from 50°C to 200°C at a heating rate of 10°C / min, and an isothermal treatment was carried out at 200°C for 1 minute to melt the sample. Then, it was quenched to -50°C at a rate of 200°C / min, and after an isothermal treatment at -50°C for 1 minute, the temperature was raised from -50°C to 200°C at a rate of 10°C / min, and T was measured in the second cycle g . The sample pan was made of aluminum. Indium was used for temperature calibration.

[0170] <Partial Melting Extrusion and Melting Extrusion of PHA: Melting Spinning at a Certain Temperature Using a Flow Tester>

[0171] Melting extrusion spinning was carried out using a flow tester CFT-500D type (manufactured by Shimadzu Corporation) or CFT-500EX (manufactured by Shimadzu Corporation).

[0172] <Comparative Example 1>P(3HB) powder, without heat treatment, sample S1

[0173] The water-system refined P(3HB) powder was used as Specimen S1. The Mw of Specimen S1 was 940,000. Specimen S1 was analyzed by CFT (Capillary Flow Tester) and DSC. The CFT outflow starting temperature was 181.0 °C, and the width of the crystallization melting peak measured by DSC was about 140 - 189 °C. The crystallization melting peak apex was 175.0 °C, the DSC extrapolated melting end temperature was 179.5 °C, and the temperature at which the melting peak reached the baseline was 188.7 °C. It was confirmed that the DSC extrapolated melting end temperature was lower than the CFT outflow starting temperature, and if it was not in a completely molten state, it would not flow out. Figure 1 Shows the measurement results of CFT and DSC.

[0174] In addition, the temperature at which the melting peak reached the baseline was higher than the CFT outflow starting temperature. If this point was concerned, it could be considered from the measured values that Specimen S1 could also be partially melted. However, since the molten state of the polymer was affected not only by temperature but also by other factors such as heating time, and if the pressure during melt extrusion was high, partial melt extrusion was likely to occur, there were factors that should be considered. Therefore, in the table, the temperature range from the CFT outflow starting temperature to the DSC extrapolated melting end temperature was recorded as the temperature at which partial melt extrusion could occur.

[0175] <Example 1> P(3HB) powder, heat treatment in a 70 °C water bath, Specimen S2

[0176] The water-system refined P(3HB) powder of Specimen S1 was immersed in water, subjected to a 24-hour hot water bath treatment at 70 °C, and then vacuum dried to obtain Specimen S2. The Mw of Specimen S2 was 940,000. Specimen S2 was analyzed by CFT and DSC. The CFT outflow starting temperature was 178.6 °C, and the width of the crystallization melting peak measured by DSC was about 140 - 188 °C. The crystallization melting peak apex was 175.1 °C, the DSC extrapolated melting end temperature was 182.0 °C, and the temperature at which the melting peak reached the baseline was 188.0 °C. It was confirmed that the DSC extrapolated melting end temperature was higher than the CFT outflow starting temperature. Although it could flow out in a partially molten state, the CFT outflow starting temperature and the DSC extrapolated melting end temperature were in almost the same temperature range (temperature difference 3.4 °C). Substantially, strict temperature control was required for forming in a partially molten state. Figure 2 Shows the measurement results of CFT and DSC.

[0177] <Example 2> P(3HB) powder, heat treatment in a 70 °C dry environment, Specimen S3

[0178] The P(3HB) powder of the sample S1 refined by the aqueous system was heat-treated in a dry-heat furnace at 70 °C for 24 hours and then returned to room temperature to obtain the sample S3. The Mw of the sample S3 was 940,000. The starting temperature of the CFT effluent was 178.6 °C, and the width of the crystallization melting peak measured by DSC was about 140-187 °C. The vertex of the crystallization melting peak was 174.9 °C, the extrapolated melting end temperature of DSC was 180.5 °C, and the temperature at which the melting peak reached the baseline was 186.9 °C. It was confirmed that the extrapolated melting end temperature of DSC was higher than the starting temperature of the CFT effluent, and it could flow out in a partially molten state. However, the starting temperature of the CFT effluent and the extrapolated melting end temperature of DSC were in almost the same temperature range (temperature difference 1.9 °C). Substantially, strict temperature control was required to achieve molding in a partially molten state. Figure 3 Shows the measurement results of CFT and DSC.

[0179] In Figure 4 The DSC curves of the samples S1, S2, and S3 of Comparative Example 1, Example 1, and Example 2 are superimposed and shown. P(3HB) is composed of a continuous monomer unit chain of (R)-3HB with high crystallinity, and the peak position of the main melting point peak does not change significantly due to heat treatment like that of PHA copolymers, and it is basically the same DSC curve. Through the 70 °C water bath / dry-heat heat treatment of bulk P(3HB), the starting temperature of the CFT effluent only shifts slightly to the lower temperature side of 181.0 °C (178.6 °C).

[0180] <Example 3>P(3HB-co-13.1 mol% 4HB) powder, sample S4

[0181] The P(3HB-co-13.1 mol% 4HB) refined by the aqueous system through a 35-hour aqueous reaction at 70 °C was used as the sample S4. The Mw of the sample S4 was 1,000,000, and the glass transition temperature (Tg) was about -4 °C. The sample S4 was analyzed by CFT and DSC. The starting temperature of the CFT effluent was 125.1 °C, and the width of the crystallization melting peak measured by DSC was about 49-157 °C. The vertices of the crystallization melting peak were 63.7 °C and 114.8 °C, the extrapolated melting end temperature of DSC was 135.1 °C, and the temperature at which the melting peak reached the baseline was 155.0 °C. As a result, the extrapolated melting end temperature of DSC was higher than the starting temperature of the CFT effluent, and partial melt extrusion could be carried out in the range above 125.1 °C and below 135.1 °C. Figure 5 Shows the measurement results of CFT and DSC.

[0182] Melt spinning was carried out at 126 °C, 130 °C, and 135 °C as the temperature for partial melting and at 150 °C, 160 °C, and 170 °C as the temperature for almost complete melting.

[0183] The Mw before melt spinning was 1 million. After partial melt spinning at 126°C, the Mw was 950,000; after partial melt spinning at 130°C, the Mw was 970,000; after partial melt spinning at 135°C, the Mw was 970,000; after melt spinning at 150°C, the Mw was 820,000; after melt spinning at 160°C, the Mw was 650,000; and after melt spinning at 170°C, the Mw was 540,000. Regarding the residual rate of the molecular weight Mw after melt spinning at each temperature, when the molecular weight Mw before melt spinning of 1 million was taken as 100%, it was 95% at 126°C, 97% at 130°C, 97% at 135°C, 91% at 140°C, 82% at 150°C, 65% at 160°C, and 53% at 170°C. It was clarified that being able to perform spinning at a lower temperature was effective in suppressing the decrease in molecular weight. Especially when performing partial melt spinning below 135°C where it was clearly not in a completely molten state, the suppression of the decrease in molecular weight was significant.

[0184] The results are shown in Table 2.

[0185] In the melt spinning at 170°C, the extruded polymer had strong adhesiveness, and sticking was observed, and the polymer cured after winding could not be unwound. On the other hand, the filaments obtained by partial melt extrusion spinning below 135°C showed almost no adhesiveness, and could be wound and stretched in a state without sticking immediately after spinning. That is, it was shown that by partial melt extrusion spinning, the crystallization time could be shortened, the melt processability of the polymer could be improved, and the productivity could be increased.

[0186] <Example 4>P(3HB-co-13.1 mol% 4HB) powder, sample S5

[0187] The sample S4 of P(3HB-co-13.1 mol% 4HB) after aqueous purification was immersed in water again and subjected to a hot water bath treatment at 70°C for 24 hours, and then vacuum dried to obtain sample S5. The Mw of sample S5 was 1 million. Sample S5 was analyzed by CFT and DSC. The initial outflow temperature of CFT was 109.8°C, and the width of the crystallization melting peak measured by DSC was about 88 - 159°C. The crystallization melting peak vertices were 95.0°C and 118.6°C, the extrapolated melting end temperature of DSC was 139.1°C, and the temperature at which the melting point peak reached the baseline was 158.5°C. It was confirmed that the extrapolated melting end temperature of DSC was higher than the initial outflow temperature of CFT, and partial melt extrusion could be performed in the range above 109.8°C and below 139.8°C. Figure 6 The measurement results of CFT and DSC are shown.

[0188] Specimen S4 can be partially melt-extruded within the range above 125.1 °C and below 140.2 °C, while specimen S5 after being heat-treated with water at 70 °C can be partially melt-extruded within the range above 109.8 °C and below 139.8 °C. Through the heat treatment, the temperature range in which partial melt-extrusion can be carried out is widened by about 15 °C towards the low-temperature side.

[0189] <Example 5>P(3HB-co-13.1 mol% 4HB) powder, specimen S6

[0190] The dried specimen S4 of P(3HB-co-13.1 mol% 4HB) after aqueous purification was heat-treated at 70 °C in an oven for 24 hours and then restored to room temperature to obtain specimen S6. The Mw of specimen S6 is 1 million. Specimen S6 was analyzed by CFT and DSC. The starting temperature of the effluent of CFT is 110.0 °C, and the width of the crystallization melting peak measured by DSC is about 75 - 160 °C. The vertices of the crystallization melting peak are 81.9 °C and 119.1 °C, the extrapolated melting end temperature of DSC is 137.8 °C, and the temperature at which the melting point peak reaches the baseline is 158.8 °C. It was confirmed that the extrapolated melting end temperature of DSC is higher than the starting temperature of the effluent of CFT, and partial melt-extrusion can be carried out within the range above 110.0 °C and below 137.8 °C. Figure 7 The measurement results of CFT and DSC are shown.

[0191] In Figure 8 the DSC curves of specimens S4, S5, and S6 of Example 3, Example 4, and Example 5 are superimposed and shown. Furthermore, after specimen S4 was dissolved in chloroform, a cast film was made and aged at room temperature for more than 1 week to obtain a film (specimen S7), and the DSC curve of this film (specimen S7) is also shown together. Different from the DSC curve of P(3HB) shown in Figure 4 the DSC curve of the P(3HB-co-4HB) copolymer has changed greatly in the shape of the melting peak due to the application method of its thermal process and dissolution and solvent evaporation in the solvent.

[0192] Specimen S4 can be partially melt-extruded within the range above 125.1 °C and below 140.2 °C, while specimen S5 after being heat-treated with water at 70 °C can be partially melt-extruded within the range above 109.8 °C and below 139.8 °C, and specimen S6 after being heat-treated with dry heat at 70 °C can be partially melt-extruded within the range above 110.0 °C and below 139.1 °C. Through the heat treatment, the temperature range in which partial melt-extrusion can be carried out is widened by about 15 °C towards the low-temperature side. <Comparative Example 2> Specimen S8 Solvent extraction without heat treatment

[0193] P(3HB-co-61.5 mol% 3HV) refined by solvent extraction precipitation (chloroform extraction - hexane precipitation system) was used as Specimen S8. The Mw of Specimen S8 was 730,000, and the glass transition temperature (Tg) was about -11°C. Specimen S8 was analyzed by CFT and DSC. The CFT effluent start temperature was 84.5°C, and the width of the crystallization melting peak measured by DSC was about 56 - 179°C. The crystallization melting peak apex was 90.5°C, and at 166.3°C, there was also the apex of a small melting peak considered to originate from 3HB-rich crystals. The DSC extrapolated melting end temperature of the main melting peak was 97.5°C, the DSC extrapolated melting end temperature of the high-temperature side melting peak was 173.2°C, and the temperature at which the melting point peak reached the baseline was 178.5°C. It was confirmed that the DSC extrapolated melting end temperature was higher than the CFT effluent start temperature, and partial melting extrusion could be performed in the range above 84.5°C and below 173.2°C. Even assuming that there was no component showing the small melting peak on the high-temperature side considered to originate from 3HB-rich crystals, the extrapolated melting end temperature of the low-temperature side melting peak also reached 97.5°C, and thus it was known that in this case, partial melting extrusion could be performed in the range above 84.5°C and below 97.5°C. Figure 9 Shows the measurement results of CFT and DSC.

[0194] <Example 6> Specimen S9 Solvent extraction Water 70°C heat treatment

[0195] P(3HB-co-61.5 mol% 3HV) of Specimen S8 refined by solvent extraction precipitation was immersed in water and subjected to a 24-hour hot water bath treatment at 70°C, followed by vacuum drying to obtain Specimen S9. The Mw of Specimen S9 was 720,000. Specimen S9 was analyzed by CFT and DSC. The CFT effluent start temperature was 80.8°C, and the width of the crystallization melting peak measured by DSC was about 49 - 178°C. The crystallization melting peak apex was 90.7°C, and at 165.6°C, there was also the apex of a small melting peak considered to originate from 3HB-rich crystals. The DSC extrapolated melting end temperature of the main melting peak was 96.9°C, the DSC extrapolated melting end temperature of the high-temperature side melting peak was 172.6°C, and the temperature at which the melting point peak reached the baseline was 176.2°C. It was confirmed that the DSC extrapolated melting end temperature was higher than the CFT effluent start temperature, and partial melting extrusion could be performed in the range above 80.8°C and below 172.6°C. Even assuming that there was no component showing the small melting peak on the high-temperature side considered to originate from 3HB-rich crystals, the extrapolated melting end temperature of the low-temperature side melting peak also reached 96.9°C, and thus it was known that in this case, partial melting extrusion could be performed in the range above 80.8°C and below 96.9°C. Figure 10 Shows the measurement results of CFT and DSC.

[0196] <Example 7> Specimen S10 Solvent extraction Dry heat 70°C heat treatment

[0197] The sample S8 of P(3HB-co-61.5 mol% 3HV) refined by solvent extraction precipitation was heat-treated at 70 °C for 24 hours in an oven again, and then returned to room temperature to obtain sample S10. The Mw of sample S10 was 730,000. Sample S10 was analyzed by CFT and DSC. The CFT effluent starting temperature was 79.8 °C, and the width of the crystallization melting peak measured by DSC was about 75 - 178 °C. The crystallization melting peak apex was 88.9 °C, and there was also a vertex of a small melting peak considered to originate from the crystallization rich in 3HB at 167.0 °C. The DSC extrapolated melting end temperature of the main melting peak was 97.5 °C, the DSC extrapolated melting end temperature of the high-temperature side melting peak was 173.3 °C, and the temperature at which the melting point peak reached the baseline was 177.3 °C. It was confirmed that the DSC extrapolated melting end temperature was higher than the CFT effluent starting temperature, and partial melting extrusion could be carried out in the range above 79.8 °C and below 173.3 °C. Even assuming that there was no component showing the small high-temperature side melting peak considered to originate from the crystallization rich in 3HB, the extrapolated melting end temperature of the low-temperature side melting peak also reached 97.5 °C, so it can be known that in this case, partial melting extrusion can be carried out in the range above 79.8 °C and below 97.5 °C. Figure 11 The measurement results of CFT and DSC are shown.

[0198] In Figure 12 , the DSC curves of samples S8, S9, and S10 of Comparative Example 2, Example 6, and Example 7 are superimposed and shown. Different from the DSC curve of P(3HB) shown in Figure 4 , the DSC curve of the P(3HB-co-3HV) copolymer showed a large change in the shape of the melting peak due to the application method of the heat treatment process.

[0199] Sample S8 could be partially melt-extruded in the range above 84.5 °C and below 173.2 °C, while sample S9 after being heat-treated by heating in water at 70 °C could be partially melt-extruded in the range above 80.8 °C and below 172.6 °C, and sample S10 after being heat-treated by dry heat at 70 °C could be partially melt-extruded in the range above 79.8 °C and below 173.3 °C. Through the heat treatment, the temperature range in which partial melt extrusion could be carried out was widened by about 5 °C to the low-temperature side.

[0200] <Example>

[0201] The P(3HB-co-16.0 mol% 4HB) powder with a weight-average molecular weight (Mw) of 620,000 and a glass transition temperature (Tg) of about -5°C after aqueous purification was used as Specimen S11. Specimen S11 was subjected to dry heat treatment at 70°C for 24 hours in air, treatment at 50°C for 24 hours in water, treatment at 60°C for 24 hours in water, treatment at 70°C for 24 hours in water, and treatment at 80°C for [hour] in water. The PHA heat-treated in water was freeze-dried to obtain a dried body. Each heat-treated specimen was evaluated by DSC, and the DSC curves (thermograms) of the first heating cycle were recorded overlapped and shown in Figure 13 .

[0202] Furthermore, the same Specimen S11 was subjected to treatment at 50°C for 24 hours in water, treatment at 50°C for 12 hours in methanol, treatment at 50°C for 12 hours in ethanol, and treatment at 50°C for 12 hours in hexane, and then vacuum-dried to obtain a dried body. Each heat-treated specimen was evaluated by DSC, and the DSC curves (thermograms) of the first heating cycle were recorded overlapped and shown in Figure 14 .

[0203] Through various heat treatments, the melting peak shapes corresponding to various heat treatments were shown. It is known that in crystalline polymers, the DSC melting peak temperature depends on the lamellar thickness. In PHA, in the case of P(3HB), as Figure 4 shown, in the heat treatment in water or dry heat treatment at 70°C, no large change was seen in the position of the main DSC melting peak, but in the case of P(3HB-co-4HB), as Figure 13 and Figure 14 shown, the shapes of the main melting peaks depending on the treatment temperature in water, solvents, and air were shown. The phenomenon that the peak shape changes due to heat treatment was also observed in the P(3HB-co-3HV) copolymer ( Figure 12 ), and by performing heat treatment in the temperature range above the glass transition temperature of PHA and not melting PHA itself, the reconstruction of lamellae was caused, related to the control of lamellar thickness, and became a technique related to the control of melt processability, which was very effective as a pretreatment for strongly promoting partial melting molding.

[0204] [Table 1]

[0205]

[0206] W70 means heat treatment at 70°C for 24 hours in water after purification;

[0207] D70 means dry heat treatment at 70°C for 24 hours after purification.

[0208] [Table 2]

[0209] Table 2 Changes in the melting state before and after melt extrusion and the molecular weight Mw after melt extrusion of sample S4 (P(3HB-co-13.1 mol% 4HB)) at each temperature

[0210]

[0211] *1: Mw before melt extrusion;

[0212] *2: Mw after melt extrusion;

[0213] *3: Mw residual rate: [weight-average molecular weight (Mw) after melt extrusion ÷ weight-average molecular weight (Mw) before melt extrusion] × 100.

Claims

1. A method for manufacturing a polymer molded article, characterized in that, comprising: before melt molding, a step of heat-treating a crystalline polyhydroxyalkanoate at a temperature above the glass transition temperature and not causing all crystals to melt; and a step of melt molding the polyhydroxyalkanoate containing lamellae with different lamellar thicknesses obtained by the above heat treatment within a temperature range where a part of the lamellae melts and flows while the other remaining lamellae do not melt and remain, and the temperature range is higher than the outflow start temperature obtained by the temperature increase method of a flow tester and lower than the extrapolated melting end temperature, the crystalline polyhydroxyalkanoate is a copolymer containing 3-hydroxybutyric acid and 4-hydroxybutyric acid as monomer units, and the proportion of 4-hydroxybutyric acid is 5 mol% or more and 40 mol% or less, or, the crystalline polyhydroxyalkanoate is a copolymer containing 3-hydroxybutyric acid and 3-hydroxyvaleric acid as monomer units, and the proportion of 3-hydroxyvaleric acid is 5 mol% or more and 90 mol% or less.

2. The method according to claim 1, characterized in that: the heat treatment is a heat treatment carried out using a gas, a liquid or a solid as a medium.

3. The method according to claim 1 or 2, characterized in that: the heat treatment is a heat treatment carried out using a liquid as a medium, and in the heating state, the polyhydroxyalkanoate is not completely dissolved in the liquid.

4. The method according to claim 1 or 2, characterized in that: it includes a step of cooling the polymer melted within a temperature range where a part of the lamellae melts and flows while the other remaining lamellae do not melt and remain in the air.

5. The method according to claim 1 or 2, characterized in that: the melt molding is molding carried out by melt extrusion.

6. The method according to claim 1 or 2, characterized in that: the melt molding is molding carried out by melt extrusion spinning.

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