Method for producing polymer molded products with pretreatment by heating

Abstract

The present invention addresses the problem of providing a method of manufacturing a polymer molded product, the method enabling the temperature range available for partial melting to be broadened. The present invention provides a method for manufacturing a polymer molded product, the method comprising: heat-treating a crystalline polyhydroxyalkanoate at or above the glass transition temperature; and melt-casting the polyhydroxyalkanoate which was obtained by said heat-treating and which contains lamellar crystals having different lamella thicknesses, the melt-casting being conducted at a temperature range in which a portion of the lamellar crystals are melted and fluidized whereas the remainder of the lamellar crystals remain without being melted.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a polymer molded article, characterized in that the thickness of the lamellar crystals of a crystalline polyhydroxyalkanoate is reconstructed, thereby widening the temperature range available for subsequent thermoforming by partial melting. [Background technology]

[0002] Polyhydroxyalkanoates (polyhydroxyalkanoic acids, hereafter abbreviated as PHA) are thermoplastic polyesters that are accumulated by microorganisms. They have attracted attention as biodegradable, biocompatible, and bioabsorbable plastics, and extensive research has been conducted on them (Non-Patent Document 1). More than 100 types of monomer units that make up PHA are known. A typical PHA is poly-3-hydroxybutyrate (hereafter abbreviated as P(3HB)), which is composed of (R)-3-hydroxybutyrate (also called (R)-3-hydroxybutyric acid, hereafter abbreviated as 3HB) (Non-Patent Document 1).

[0003] The melting point of P(3HB) is approximately 175 to 180°C, which is as high as that of polypropylene (hereinafter abbreviated as PP). The breaking strength of P(3HB) is similar to that of PP, but the breaking elongation is 5% or less, and the glass transition point is 4°C (below room temperature).

[0004] Because P(3HB) is a highly crystalline, hard, and brittle material, it is often not used as a single molded body such as a film. When attempting to use PHA industrially, methods known to improve its physical properties (crystallinity, mechanical properties, etc.) include introducing a second component monomer unit to form a copolymer, increasing the molecular weight, and compounding with different polymeric materials.

[0005] On the other hand, PHAs have a significantly slower crystallization rate than traditional industrial polymers, and their glass transition temperatures are below room temperature. When PHAs are molded after being heated and molten, they require long cooling times for solidification, resulting in poor productivity. When melt-spun, PHAs experience slow crystallization, resulting in amorphous fibers being wound up, leading to sticking. To avoid sticking, the fibers must be wound without overlapping. Furthermore, the long cooling times required for solidification (crystallization) after winding are also problematic. Furthermore, slow crystallization rates lead to the growth of large spherulites, which can lead to deterioration of the physical properties of molded products and degradation over time. Copolymerization can further reduce the nucleation density, i.e., the crystallization rate, and even with copolymerization, the above-mentioned molding problems persist. Furthermore, increasing the molecular weight poses another problem: excessively high melt viscosity.

[0006] In the melt processing of thermoplastic polymeric materials such as polyester, various crystal nucleating agents have been investigated to improve the crystallization rate.

[0007] Known crystal nucleating agents include, for example, the following for specific polyesters: Inorganic elements such as Zn powder, Al powder, graphite, and carbon black; Metal oxides such as ZnO, MgO, Al2O3, TiO2, MnO2, SiO2, Fe3O4; nitrides such as aluminum nitride, silicon nitride, titanium nitride, and boron nitride; inorganic salts such as Na2CO3, CaCO3, MgCo3, CaSO4, CaSiO3, BaSO4, Ca3(PO4)3; Clays such as talc, kaolin, clay, and white clay; Organic salts such as calcium oxalate, sodium oxalate, calcium benzoate, calcium phthalate, calcium tartrate, magnesium stearate, polyacrylates; Polymers such as polyester, polyethylene, and polypropylene: It is known to add the following (Patent Document 1).

[0008] Also, particulate materials such as talc, micronized mica, boron nitride, and calcium carbonate have been tried as crystal nucleating agents for PHA.A more effective method is known in which an organic phosphonic acid such as cyclohexylphosphonic acid or an organic phosphinic acid, or an ester thereof, or a derivative of such an acid or ester, and a metal compound such as an oxide, hydroxide, or saturated or unsaturated carboxylate of a metal of Groups IA to VA or IB to VB of the periodic table are intimately mixed together (Patent Document 2).

[0009] Furthermore, as a nucleating agent for PHA, 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, and scyllo-inositol (Patent Document 4); Polyvinyl alcohol, chitin, chitosan (Patent Document 5); Polyalkylene oxides such as polyethylene oxide, polypropylene oxide, and polybutylene oxide (Patent Document 6); aliphatic polyesters such as polylactic acid and PHA, aliphatic carboxylic acid amides, aliphatic carboxylic acid salts, aliphatic alcohols, and aliphatic carboxylic acid esters (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, and 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, and quinacridone magenta (Patent Document 11); Ketopyrroles, which are cyclic compounds having a C═O and an NH group in the molecule (Patent Document 12); Sorbitol derivatives such as bisbenzylidene sorbitol and bis(p-methylbenzylidene) sorbitol (Patent Document 13); Compounds containing a nitrogen-containing heteroaromatic nucleus such as pyridine, pyrimidine, pyrazine, pyridazine, triazine, and imidazole (Patent Document 14); Phosphate ester compounds (Patent Document 15); Bisamides of higher fatty acids and metal salts of higher fatty acids (Patent Document 16); Fatty acids and fatty acid amides (Patent Document 17); Branched polylactic acid (Patent Document 18); Pentaerythritol (Patent Document 19); Pentaerythritol and inorganic or organic fillers (Patent Document 20); Sorbitol acetal, compounds having an amide bond, and pentaerythritol (Patent Document 21) Amino acids such as tryptophan, phenylalanine, p-chloro-phenylalanine, m-tyrosine, phenylglycine, p-hydroxyphenylglycine, methionine, o-tyrosine, and valine, and phosphatidylcholine (Patent Documents 22 to 24); Dipeptides such as aspartame (Patent Document 25); and Nucleic acid bases such as uracil and thymine (Patent Document 26) is known.

[0010] These methods have been adopted to accelerate the slow crystallization rate of aliphatic polyesters such as PHA and polylactic acid and improve their processability during molding. However, they are ineffective, resulting in reduced strength and a poor surface appearance of the molded product, and problems remain, such as the need for additional additives. Furthermore, depending on the type of nucleating agent, as crystallization progresses after molding, differences in compatibility and molecular weight can cause the agent to be pushed out of the crystal, resulting in blooming or bleeding. In such cases, additional additives such as dispersants, anti-agglomerating agents, and compatibilizers may be required. The above-mentioned nucleating agents include those made of fatty acids and amino acids that are easily decomposed, absorbed, or metabolized in the body, i.e., non-toxic, for use in the body. However, a truly effective crystal nucleating agent has yet to be discovered.

[0011] Furthermore, attempts have been made to improve the crystallization properties of PHA by blending it with other PHAs or biodegradable polymers. Patent Documents 27 to 29 disclose the addition of P(3HB), which has a higher melting point, as a crystal nucleating agent (nucleating material) to a P(3HB-co-3HV) copolymer consisting of 3HB and 3-hydroxyvalerate (3-hydroxyvaleric acid, hereinafter abbreviated as 3HV), a P(3HB-co-3HHx) copolymer consisting of 3HB and 3-hydroxyhexanoate (3-hydroxyhexanoic acid, hereinafter abbreviated as 3HHx), or a P(3HB-co-3HO) copolymer consisting of 3HB and 3-hydroxyoctanoate (3-hydroxyoctanoic acid, hereinafter abbreviated as 3HO).

[0012] In Patent Documents 27 to 29, Dry mixing involves mixing the blended dry powder PHA either directly or in the presence of dry ice; Solution mixing in which the polymer is partially or completely dissolved in a solvent such as chloroform and then stirred and mixed, and then the solvent is evaporated to precipitate the polymer, or the polymer is precipitated in a poor solvent; and 1. Mix the high-melting P(3HB) to be added at a temperature that does not melt the PHA, but melts the PHA (P(3HB-co-3HV), P(3HB-co-3HHx), or P(3HB-co-3HO) in the examples) to be added, by thoroughly stirring and mixing the PHA, i.e., partial melt mixing, at a temperature that does not melt the PHA; The above mixing methods are described, but it is mentioned that it is necessary for a small amount of P(3HB) on the high melting point side to be mixed to be finely and uniformly dispersed in the PHA copolymer on the low melting point side.

[0013] Each of the above mixing methods has its own disadvantages. Dry mixing, even when mixing polymer powders, limits the ability to achieve uniform mixing below the powder particle size. Solution mixing requires large amounts of good solvents such as chloroform, and when reprecipitation is performed, even larger amounts of poor solvents—5 to 10 times the amount of good solvent—are required. Furthermore, differences in solubility during reprecipitation can lead to uneven precipitation of the polymer species. Even when the blend is partially molten, the added P(3HB) has high crystallinity and a high melting point, making it unsuitable for forming small, uniform crystal nuclei because the P(3HB) particles remain largely unchanged and are mixed without melting. While the method of elevating the temperature above the melting point of P(3HB) to achieve uniform blending is common in melt mixing, PHAs, including P(3HB), inevitably suffer from thermal decomposition, deterioration due to agitation, and molecular weight loss near the melting point of P(3HB).

[0014] Instead of promoting crystallization by blending P(3HB) extracted from the cells with a PHA copolymer, a method has been reported in which P(3HB) or 3HB-rich PHA, which can serve as crystal nuclei, is produced as a blend within the cells during culture together with other PHA copolymers, eliminating the need to blend P(3HB) and PHA after extracting the PHA from the cells. Patent Document 30 describes a method in which the carbon source supply is changed during culture to produce P(3HB) or P(3HB-co-3HHx) with a low 3HHx ratio together with P(3HB-co-3HHx) with an increased 3HHx ratio. Patent Documents 31 and 32 disclose methods for producing PHA blends with different melting points within the same cells by using genetic engineering to contain multiple PHA synthases with different substrate specificities within the same cells. Although it is also stated that molding can be performed at temperatures below 170°C, it is unclear what temperature range is possible for molding. In known molding processes, it is common to melt the polymer at a temperature above its melting point and then mold it. In this document, the purpose is also to improve the solidification rate (crystallization rate) of the PHA blend once it has been melted.

[0015] Non-patent documents 2 to 4 do not aim to demonstrate that P(3HB) can serve as a crystal nucleus, but they do describe PHA-producing wild-type strains that produce a blend of P(3HB) and PHA copolymers within the same bacterium, and describe the production of a blend of P(3HB) homopolymer and C4 to C12 PHA copolymers by naturally maintaining PHA polymerizing enzymes with different substrate specificities within the same bacterium.

[0016] On the other hand, there are also reports using ultra-high molecular weight P(3HB) and reports on controlling crystal formation independently of molecular weight to achieve high strength. For example, ultra-high molecular weight P(3HB) with a number-average molecular weight of 1.5 million or more (weight-average molecular weight of 3 million) was synthesized using genetically modified Escherichia coli, and P(3HB) films with improved physical properties were obtained using this ultra-high molecular weight P(3HB) (Patent Document 33 and Non-Patent Document 5).

[0017] In addition, a molecular weight-independent method for producing P(3HB) fibers has been described in Patent Documents 34 and 35. The method involves melt-extruding P(3HB), rapidly cooling it to a temperature below the glass transition temperature +15°C, and solidifying it to produce amorphous fibers. The amorphous fibers are then cold-stretched to orient the molecular chains of the amorphous fibers, followed by heat treatment (hereinafter also referred to as the "cold stretching method"). Patent Documents 34 and 35 also disclose a fiber production method (hereinafter also referred to as the "microcrystalline nucleus stretching method") in which the melt-extruded fibers are rapidly cooled to a temperature below the glass transition temperature of the PHA +15°C and solidified to produce amorphous fibers. The amorphous fibers are then left at a temperature below the glass transition temperature +15°C to form microcrystalline nuclei (isothermal crystallization) to produce crystallized fibers. The crystallized fibers are then stretched and further heat-treated under tension (hereinafter also referred to as the "microcrystalline nucleus stretching method") (Patent Document 36).

[0018] However, the above methods are industrially disadvantageous for several reasons: the production efficiency of ultra-high molecular weight P(3HB) is low and the costs are high; the cold drawing method requires rapid cooling to a low temperature near the glass transition temperature to obtain amorphous fibers; and the microcrystalline nucleus drawing method requires rapid cooling to a low temperature near the glass transition temperature and then maintaining it at that low temperature for a long period of time to generate microcrystals of the molten P(3HB).

[0019] Ultra-high molecular weight P(3HB) with a weight-average molecular weight of 2.7 million produced by genetically modified E. coli was added to P(3HB) derived from ordinary microorganisms with a weight-average molecular weight of 520,000, and the mixture was dissolved in chloroform and cast into a film. The film was hot-pressed at 200°C, quenched in ice water, and then cold-stretched. Observation of crystal growth in the P(3HB) film containing trace amounts of the ultra-high molecular weight P(3HB) after reheating to 200°C suggests that the ultra-high molecular weight P(3HB) behaves like a nucleating agent and promotes nucleation (Non-Patent Document 6). In one study, 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-spun at 180°C, 190°C, and 200°C (Non-Patent Document 7). While the molecular weight decreased upon heating above the melting point, the addition of ultra-high molecular weight P(3HB) suppressed the initial thermal decomposition of P(3HB) and improved the processability of melt spinning. It was reported that blended P(3HB) fibers containing 5% by weight of ultra-high molecular weight P(3HB) exhibited a strength of 740 MPa after melt spinning and two-stage cold drawing. While this process required only a small amount of ultra-high molecular weight P(3HB), the two-stage cold drawing at 4°C was necessary, making the process unsuitable for industrialization.

[0020] It has also been reported that when a molding material primarily composed of a biodegradable polyester having a melting point within a specific range is melt-molded at a specific heating temperature range to produce a melt-molded product, the cold crystallization heat and the sum of the heat of fusion and the cold crystallization heat are set within specific ranges as indicators of the crystallization ability and degree of crystallization of the resulting melt-molded product (Patent Document 37). It has also been reported that a copolymer of 3HB and 3-hydroxyhexanoate is processed at a temperature (around 160°C) that does not completely melt the crystals (Non-Patent Document 8). Furthermore, a tube made of a poly(3-hydroxybutyrate) resin has been reported in which the difference between the melting point peak temperature and the melting point peak end temperature in differential scanning calorimetry analysis of the poly(3-hydroxybutyrate) resin is 10°C or more (Patent Document 38). Furthermore, a method for producing a biodegradable resin molded article has been reported, in which, when a biodegradable resin composition containing poly(3-hydroxyalkanoate) is heated, melted, and kneaded to form a molded article, the amount of crystals remaining at the outlet of the molding machine after the heating, melting, and kneading is confirmed by near-infrared spectroscopy, and the amount of crystals remaining at the outlet of the molding machine is adjusted so that a crystallization peak by near-infrared spectroscopy of the molded article is observed within 200 seconds after molding (Patent Document 39). However, there is no description of setting the melt molding temperature to a temperature higher than the flow initiation temperature measured by a flow tester heating method and showing that crystalline melting is completely completed as measured by a differential scanning calorimeter (in particular, a temperature lower than the extrapolated melting end temperature). [Prior art documents] [Patent documents]

[0021] [Patent Document 1] Japanese Patent Application Publication No. 07-126496 [Patent Document 2] Japanese Patent Application Publication No. 03-024151 [Patent Document 3] WO2006 / 012917 publication [Patent Document 4] WO2008 / 099586 publication [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-077232 [Patent Document 6] Japanese Patent Application Laid-Open No. 2010-229407 [Patent Document 7] Japanese Patent Application Publication No. 09-278991 [Patent Document 8] Japanese Patent Application Publication No. 11-005849 [Patent Document 9] Japanese Patent Application Publication No. 07-188537 [Patent Document 10] Japanese Patent Application Publication No. 11-116783 [Patent Document 11] Japanese Patent Application Laid-Open No. 2003-238779 [Patent Document 12] Japanese Patent Application Laid-Open No. 2003-327803 [Patent Document 13] Japanese Patent Application Publication No. 10-158369 [Patent Document 14] Special Publication No. 2007-517126 [Patent Document 15] Japanese Patent Application Laid-Open No. 2003-192884 [Patent Document 16] Japanese Patent Application Publication No. 6-299054 [Patent Document 17] Japanese Patent Application Publication No. 8-27363 [Patent Document 18] Japanese Patent Application Laid-Open No. 2009-024058 [Patent Document 19] Japanese Patent Application Laid-Open No. 2017-101256 [Patent Document 20] WO2015 / 052876 publication [Patent Document 21] WO2014 / 068943 publication [Patent Document 22] Japanese Patent Application Laid-Open No. 2006-282940 [Patent Document 23] Japanese Patent Application Publication No. 06-345950 [Patent Document 24] Special Publication No. 10-504583 [Patent Document 25] Japanese Patent Application Publication No. 2019-119839 [Patent Document 26] Japanese Patent Application Publication No. 2019-119840 [Patent Document 27] Special Publication No. 08-510498 [Patent Document 28] WO2002 / 055581 publication [Patent Document 29] WO2002 / 050461 publication [Patent Document 30] Japanese Patent Application Laid-Open No. 2004-250629 [Patent Document 31] WO2015 / 146195 publication [Patent Document 32] WO2017 / 056442 publication [Patent Document 33] Japanese Patent Application Publication No. 10-176070 [Patent Document 34] Japanese Patent Application Laid-Open No. 2003-328230 [Patent Document 35] Japanese Patent Application Laid-Open No. 2003-328231 [Patent Document 36] WO2006 / 038373 publication [Patent Document 37] Patent No. 4245306 [Patent Document 38] WO2020 / 040093 publication [Patent Document 39] Japanese Patent Application Laid-Open No. 2010-241075 [Non-patent literature]

[0022] [Non-Patent Document 1] Alistair J. Anderson et al.,Microbiological Reviews,Vol.54,No.4,450-472,1990 [Non-patent document 2] H. Abe, et al., International Journal of Biological Macromolecules, 1994, vol. 16, 115-119. [Non-patent document 3] M.Kato et Aal.,Bull.Chem.Soc.Jpn,1996,vol.69,515-520. [Non-patent document 4] H.Matsusaki et al., Journal of bacteriology, 1998, vol.180, 6459-6467. [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. [Non-patent document 6] T. Kabe et al., Macromolecules, 2012, 45, 1858-1865. [Non-Patent Document 7] T. Kabe en al., ACS symposium series on Biobased Monomers, Polymers, and Materials,Chapter 5,63-75. [Non-patent document 8] Journal of the Japan Society of Packaging Science, Vol. 28, No. 2 (2019) 109-115 Summary of the Invention [Problem to be solved by the invention]

[0023] As mentioned above, conventional methods have been developed with the aim of rapidly forming primary nuclei after melting a slow-crystallizing crystalline polymer (polyester), preventing the formation of large, defective spherulites, crystallizing to increase strength, and solidifying and crystallizing to facilitate processing. In the melt-molding of biodegradable crystalline polymers, various attempts have been made to promote crystallization in order to improve the poor processability caused by the slow crystallization rate and to increase strength, but there is still room for improvement.

[0024] As a means for solving the above problems, a method has been investigated in which the polymer is melted (i.e., partially melted) at a temperature lower than the temperature at which the entire polymer can be melted, but at a temperature at which the fine lamellar crystals and amorphous regions, which are relatively thin and have a lower melting point, become fluid, thereby melt-molding the polymer while the fine but thick lamellar crystals do not melt. When producing polymer molded articles by such partial melting, a problem has been found in that the temperature range available for partial melting is sometimes narrow. An object of the present invention is to provide a method for producing polymer molded articles that can expand the temperature range available for partial melting. [Means for solving the problem]

[0025] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that by heat-treating a crystalline polyhydroxyalkanoate at a temperature equal to or higher than its glass transition point and then subjecting it to partial melt molding, it is possible to expand the temperature range in which partial melt thermoforming can be performed. The present invention was completed based on these findings.

[0026] According to the present invention, the following inventions are provided. <1> A method for producing a polymer molded product, comprising: heat-treating a crystalline polyhydroxyalkanoate at a temperature equal to or higher than the glass transition point; and melt-molding the polyhydroxyalkanoate containing lamellar crystals having different lamellar thicknesses obtained by the heat treatment in a temperature range in which some of the lamellar crystals melt and become fluid, while the remaining lamellar crystals remain unmelted. <2> The heat treatment is a gas-, liquid- or solid-mediated heat treatment; <1> The method described below. <3> The heat treatment is a heat treatment mediated by a liquid, and the polyhydroxyalkanoate does not completely dissolve in the liquid under heating. <1> or <2> The method described below. <4> The temperature range is higher than the flow-out initiation temperature measured by a flow tester temperature rising method and lower than the temperature at which crystal melting is completely completed as measured by a differential scanning calorimeter. <1> from <3> 1. The method according to claim 1 , <5> The temperature range is higher than the outflow start temperature measured by a flow tester temperature rising method and lower than the extrapolated melting end temperature. <1> from <4> 1. The method according to claim 1 , <6> cooling the molten polymer in air within a temperature range in which some lamellar crystals melt and become fluid, while the remaining lamellar crystals remain unmelted; <1> from <5> 1. The method according to claim 1 , <7> The thermoforming is formed by melt extrusion; <1> from <6> 1. The method according to claim 1 , <8> The thermoforming is formed by melt extrusion spinning; <1> from <7> 1. The method according to claim 1 , <9> The crystalline polyhydroxyalkanoate is a copolymer containing 3-hydroxybutyric acid and 4-hydroxybutyric acid as monomer units. <1> from <8> 1. The method according to claim 1 , <10> 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. <1> from <9> 1. The method according to claim 1 , [Effects of the Invention]

[0027] According to the method for producing a polymer molded article of the present invention, the temperature range available for partial melting can be widened. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 shows the flow curve (solid line) and DSC curve (dashed line) of sample S1 (P(3HB) homopolymer) measured by a flow tester temperature ramp method. [Figure 2] FIG. 2 shows the flow curve (solid line) and DSC curve (dashed line) of sample S2 (P(3HB) homopolymer) measured by a flow tester temperature ramp method. [Figure 3] FIG. 3 shows the flow curve (solid line) and DSC curve (dashed line) of sample S3 (P(3HB) homopolymer) measured by a flow tester temperature ramp method. [Figure 4] FIG. 4 shows the superposition of the DSC curves of sample S1 (solid line), sample S2 (dashed line), and sample S3 (rough dashed line). [Figure 5] Figure 5 shows the flow curve (solid line) and DSC curve (dashed line) of sample S4 (P(3HB-co-13.1 mol% 4HB)) measured by a flow tester heating method. The extrapolated melting end temperature and the temperature at which the DSC curve returns to the baseline are also shown. [Figure 6] Figure 6 shows the flow curve (solid line) and DSC curve (dashed line) of sample S5 (P(3HB-co-13.1 mol% 4HB)) measured by a flow tester heating method. The extrapolated melting end temperature and the temperature at which the DSC curve returns to the baseline are also shown. [Figure 7] Figure 7 shows the flow curve (solid line) and DSC curve (dashed line) of sample S6 (P(3HB-co-13.1 mol% 4HB)) measured by a flow tester heating method. The extrapolated melting end temperature and the temperature at which the DSC curve returns to the baseline are also shown. [Figure 8] FIG. 8 shows the superposition of DSC curves for sample S4 (solid line), sample S5 (dashed line), sample S6 (dotted line), and sample S7 (roughly dashed line). [Figure 9] FIG. 9 shows the flow curve (solid line) and DSC curve (dashed line) of sample S8 (P(3HB-co-61.5 mol % 3HV)) measured by a flow tester temperature ramp method. [Figure 10]FIG. 10 shows the flow curve (solid line) and DSC curve (dashed line) of sample S9 (P(3HB-co-61.5 mol % 3HV)) measured by a flow tester temperature ramp method. [Figure 11] FIG. 11 shows the flow curve (solid line) and DSC curve (dashed line) of sample S10 (P(3HB-co-61.5 mol % 3HV)) measured by a flow tester temperature ramp method. [Figure 12] FIG. 12 shows the superposition of the DSC curves of sample S8 (solid line), sample S9 (dashed line), and sample S10 (roughly dashed line). [Figure 13] FIG. 13 shows the changes in the DSC curves of sample S11 with respect to various heat pretreatments. [Figure 14] FIG. 14 shows the change in the DSC curve of sample S11 with respect to the heat treatment in liquid. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be described in detail below. The method for producing a polymer molded product according to the present invention comprises: heat-treating a crystalline polyhydroxyalkanoate (PHA) at a temperature equal to or higher than the glass transition point; and melt-molding the polyhydroxyalkanoate containing lamellar crystals having different lamellar thicknesses obtained by the heat treatment in a temperature range in which some of the lamellar crystals melt and become fluid, while the remaining lamellar crystals remain unmelted.

[0030] [About heat treatment] In the present invention, crystalline polyhydroxyalkanoate is heat-treated at a temperature equal to or higher than the glass transition point, which reconstructs the thickness of the lamellar crystals and thereby broadens the temperature range in which it can be melt-molded.

[0031] When an amorphous solid is heated, it becomes as hard and immobile as a crystal at low temperatures, but within a narrow temperature range, its rigidity and viscosity decrease rapidly and its fluidity increases. This temperature is the glass transition point.

[0032] The heating temperature is preferably in a range that is equal to or higher than the glass transition point of the crystalline polyhydroxyalkanoate but does not melt all of the crystals. In general, the crystalline polyhydroxyalkanoate can be heat-treated at a temperature 20 to 170°C higher (preferably 40 to 120°C higher) than the glass transition point.

[0033] The heating time is not particularly limited, but generally, the heating time is 1 hour to 72 hours, preferably 6 hours to 48 hours, and more preferably 12 hours to 36 hours.

[0034] The means of the heat treatment is not particularly limited, and the heat treatment may be any of heat treatments mediated by gas, liquid, or solid.

[0035] Gas-mediated heat treatment refers to heat treatment of crystalline polyhydroxyalkanoate in a gas, such as air or an inert gas (such as nitrogen).

[0036] Liquid-mediated heat treatment refers to heat treatment of crystalline polyhydroxyalkanoate in a liquid. Examples of the liquid include water, lower alcohols (e.g., methanol, ethanol), polyhydric alcohols (e.g., glycerin, propylene glycol), organic solvents such as hexane and acetone, and mixtures thereof. In liquid-mediated heat treatment, it is preferable that the polyhydroxyalkanoate does not completely dissolve in the liquid under heating.

[0037] Heat treatment mediated by a solid refers to, for example, heat treatment in which the crystalline polyhydroxyalkanoate is brought into contact with a solid medium (e.g., a plate, etc.) Examples of the solid include metals (aluminum, copper, silver, iron, stainless steel, etc.), ceramics, and glass.

[0038] [About crystalline polyhydroxyalkanoates] Polyhydroxyalkanoates include: Homopolymers of hydroxyalkanoic acids (e.g., poly 3-hydroxypropionic acid, poly 3-hydroxybutyric acid, poly 3-hydroxyvaleric acid, poly 4-hydroxybutyric acid, poly 3-hydroxyhexanoic acid, poly 3-hydroxyoctanoic acid, poly 4-hydroxyvaleric acid, poly 4-hydroxyhexanoic acid, poly 5-hydroxyvaleric acid, poly 2-hydroxybutyric acid, poly 2-hydroxyvaleric acid, poly 2-hydroxyhexanoic acid, etc.); Copolymers of hydroxyalkanoic acids (e.g., copolymers of 3-hydroxypropionic acid and 3-hydroxybutyric acid, copolymers of 3-hydroxypropionic acid and 3-hydroxyvaleric acid, copolymers of 3-hydroxypropionic acid and 4-hydroxybutyric acid, copolymers of 3-hydroxypropionic acid and 3-hydroxyhexanoic acid, copolymers of 3-hydroxypropionic acid and 3-hydroxyoctanoic acid, copolymers of 3-hydroxybutyric acid and 3-hydroxyvaleric acid, copolymers of 3-hydroxybutyric acid and 4-hydroxybutyric acid, copolymers of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid, copolymers of 3-hydroxybutyric acid and 3-hydroxyoctanoic acid, copolymers of 3-hydroxyvaleric acid and 4-hydroxybutyric acid, 3-hydroxyvaleric acid and 3-hydroxyhexanoic acid copolymer, 3-hydroxyvaleric acid and 3-hydroxyoctanoic acid copolymer, lactic acid and 3-hydroxypropionic acid copolymer, lactic acid and 3-hydroxybutyric acid copolymer, lactic acid and 3-hydroxyvaleric acid copolymer, lactic acid and 3-hydroxybutyric acid copolymer, lactic acid and 3-hydroxyhexanoic acid copolymer, lactic acid and 3-hydroxyoctanoic acid copolymer, glycolic acid and 3-hydroxypropionic acid copolymer, glycolic acid and 3-hydroxybutyric acid copolymer, glycolic acid and 3-hydroxyvaleric acid copolymer, glycolic acid and 4-hydroxybutyric acid copolymer, glycolic acid and 3-hydroxyhexanoic acid copolymer, glycolic acid and 3-hydroxyoctanoic acid copolymer); and Copolymers consisting of three or more types of monomers, such as terpolymers, The following can be mentioned:

[0039] The polyhydroxyalkanoates may be used singly or in combination of two or more.

[0040] In the polyhydroxyalkanoates used in the present invention, in order to form a polymer structure of crystalline segments such as lamellar crystals, fringed micellar structures, spherulites, dendrites, shish kebab structures, and extended chain crystals, it is desirable that highly crystalline continuous monomer unit chains, such as 3-hydroxypropionic acid chains, 3-hydroxybutyric acid chains, 3-hydroxyvaleric acid chains, 4-hydroxybutyric acid chains, 3-hydroxyhexanoic acid chains, 3-hydroxyhexanoic acid chains, 3-hydroxyoctanoic acid chains, 4-hydroxyvaleric acid chains, 4-hydroxyhexanoic acid chains, 5-hydroxyvaleric acid chains, 2-hydroxybutyric acid chains, 2-hydroxyvaleric acid chains, and 2-hydroxyhexanoic acid chains, be repeatedly present in the polymer chain in a sufficient number to form a crystalline microstructure. When stereoisomers or optical isomers exist as monomer units, crystalline segments consisting of chains of the same stereoisomers are necessary. For example, a chain structure of the same stereoisomers, such as a chain of R-3-hydroxybutyrate, a chain of S-3-hydroxybutyrate, a chain of R-3-hydroxyvalerate, a chain of S-3-hydroxyvalerate, a chain of R-3-hydroxyhexanoate, and a chain of S-3-hydroxyhexanoate, is an important element for forming a crystalline structure. In the case of polyhydroxyalkanoates containing monomer units with stereoisomers or optical isomers, crystallinity decreases, making it difficult to obtain crystalline segments. In particular, when synthesizing polymers consisting of these monomer units biologically, binary copolymers or ternary or higher copolymers containing R-3-hydroxybutyrate chains and other monomer units as the second component are more preferred.

[0041] Polyhydroxyalkanoates may be produced by either chemical synthesis or biological synthesis, but in order to ensure crystalline segments due to the chain structure, if they contain a monomer unit with a stereoisomer, it is desirable that the copolymer be a copolymer consisting of one of the stereoisomers, such as a copolymer of R-3-hydroxybutyric acid and 4-hydroxybutyric acid, or a copolymer of S-3-hydroxybutyric acid and 4-hydroxybutyric acid.

[0042] When the polyhydroxyalkanoate contains 3-hydroxybutyric acid units and 4-hydroxybutyric acid units, the ratio of the 4-hydroxybutyric acid units to all monomer units is preferably 5 mol% or more and 40 mol% or less, or may 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, or may be 17 mol% or more, 18 mol% or more, 19 mol% or more, or 20 mol% or more. The ratio of 4-hydroxybutyric acid units to all monomer units may be 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. When the polyester contains 3-hydroxybutyric acid units and 3-hydroxyvaleric acid units, the proportion of the 3-hydroxyvaleric acid units relative to all monomer units is preferably 5 mol% or more and 90 mol% or less. The proportion of the 3-hydroxyvaleric acid units relative to all monomer units may 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, or even 45 mol% or more, 50 mol% or more, 55 mol% or more, or 60 mol% or more. The proportion of the 3-hydroxyvalerate units relative to all monomer units may be 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, 70 mol% or less, or 65 mol% or less.

[0043] <Polyhydroxyalkanoate molecular weight> The weight-average molecular weight of polyhydroxyalkanoates measured by gel permeation chromatography relative to polystyrene standards is preferably 100,000 or more, more preferably 200,000 or more, and may even be 300,000 or more, 400,000 or more, or 500,000 or more. The weight-average molecular weight measured by gel permeation chromatography relative to polystyrene standards may 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. The upper limit of the weight-average molecular weight measured by gel permeation chromatography relative to polystyrene standards is not particularly limited, but is generally 20,000,000 or less, and may 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, when melt molding is performed, taking into consideration the reduction in molecular weight due to thermal decomposition and the viscosity during melting to be not too high, the weight average molecular weight as measured by gel permeation chromatography in terms of polystyrene is desirably 400,000 or more and 2,500,000 or less, more preferably 500,000 or more and 2,200,000 or less, and even more preferably 600,000 or more and 2,000,000 or less.

[0044] When partial melt molding is performed, it is often possible to use a melting temperature lower than the temperature range around 170°C at which a decrease in molecular weight due to thermal decomposition is observed. Therefore, from the viewpoint that a decrease in molecular weight due to thermal decomposition is more likely to be suppressed when partial melt molding is performed, the molecular weight of the polymer used may be lower than that used in melt molding. The weight average molecular weight measured by gel permeation chromatography in terms of polystyrene is desirably 200,000 or more and 2,500,000 or less, more preferably 400,000 or more and 2,000,000 or less, and even more preferably 600,000 or more and 1,500,000 or less.

[0045] <Preferred embodiments of polyhydroxyalkanoates> The polymer of the present invention may be a random polymer, a block polymer, an alternating polymer, or a graft polymer, but is preferably a random polymer.

[0046] The polyhydroxyalkanoate may be a thermoplastic resin. The polyhydroxyalkanoate is preferably a biodegradable polymer, more preferably a bioabsorbable polymer. Biodegradable means that it can be decomposed by microorganisms or enzymes in the natural environment (e.g., soil, compost, lakes, marshes, seawater, etc.) or can be decomposed into non-toxic components in the living body. Bioabsorbable means that it can be metabolized by the living body, such as a human or animal.

[0047] The melting point of the polyhydroxyalkanoate is not particularly limited, but is preferably 180°C or lower, more preferably 175°C or lower (or lower than 175°C), and even 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, but is generally 40°C or higher, and may be 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 multiple melting points, it is sufficient that the melting point of the main component is within the above range.

[0048] [About melt molding] In the present invention, the processability of a thermoplastic resin that crystallizes slowly and has poor processability can be improved by melting the crystalline polyhydroxyalkanoate in a temperature range that is equal to or higher than the flow-out initiation temperature measured when the fluidity of the crystalline polyhydroxyalkanoate is evaluated by a flow tester temperature rising method and lower than the temperature at which crystalline melting is completely completed as measured by a differential scanning calorimeter (DSC), and then molding the melted crystalline polyhydroxyalkanoate. By heat treating the polyhydroxyalkanoate at a temperature above its glass transition point prior to melt molding, the thickness of the lamellar crystals of the crystalline polyhydroxyalkanoate can be reconstructed, thereby expanding the temperature range that can be used for subsequent thermoforming by partial melting. The "temperature indicating the complete completion of crystalline melting as measured by differential scanning calorimetry (DSC)" is preferably the extrapolated melting end temperature of the melting peak. The extrapolated melting end temperature of the melting peak can be determined as described in the Examples below. That is, when the melting peak is sharp, the extrapolated melting end temperature of the melting peak is the temperature at the intersection of a tangent drawn at the point of maximum slope before the end of the peak and the baseline after the peak, in accordance with JIS-K7121 (recognized using Rigaku's Thermo plus EVO software). When multiple melting peak shapes overlap, the tangent line is manually redrawn to the higher-temperature peak, and the intersection with the baseline is determined as the extrapolated melting end temperature.

[0049] Furthermore, in conventional melt molding, materials are typically melted at temperatures above the melting point, such as melting point +20°C, melting point +10°C, or melting point +5°C, and then molded. In contrast, molding in a partially molten state as in the present invention involves partial melting at a temperature lower than the melting point. This prevents thermal decomposition, i.e., molecular weight reduction, in polymers whose melting point and thermal decomposition point are close, and allows the molecular weight of the polymer to be maintained at a high level after molding, which is more beneficial in terms of physical properties. Furthermore, because the temperature for melting in a partially molten state is lower than that for complete melting, it is presumed that not only thermal decomposition of the polymer but also hydrolysis of the molecular chain of the polyhydroxyalkanoate, which is involved in heating due to trace amounts of water mixed in, can be reduced. Therefore, although a low moisture content in the raw material is generally desirable, there is no need to reduce or maintain a specially low moisture content. This is also expected to have the advantage of eliminating the need for special equipment to strictly maintain the dry state of the dry raw material polyhydroxyalkanoate, which could otherwise transfer moisture from the atmosphere to the raw polymer in spinning or molding equipment.

[0050] The present invention improves the molding processability of polyesters that have slow melt crystallization even without the addition of a crystal nucleating agent, thereby improving productivity, but does not preclude the use of a crystal nucleating agent.

[0051] In one 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-extruding P(3HB-co-4HB) at a temperature between the temperature at which crystalline and amorphous regions, including relatively thin lamellar crystals composed of 3HB segments within the polymer, begin to melt and flow, and the temperature at which relatively thicker lamellar crystals composed of 3HB segments begin to melt.

[0052] The present invention relates to a method for producing a biodegradable polyester molded product, characterized in that the product is melt-molded while leaving behind some of the crystals, including lamellar crystals, contained in polyhydroxyalkanoate, and the remaining crystals become crystal nuclei, making it possible to mold the product without waiting for primary nucleation, which is required in general melt-molding.

[0053] Therefore, the poor molding processability of crystalline thermoplastic polyhydroxyalkanoates, which crystallize slowly, is improved, and molding is possible immediately after partial melting without waiting for primary crystalline nucleation, as is the case when the material is completely melted, thereby improving productivity. Some of the crystals, including lamellar crystals already dispersed in the bulk of the crystalline thermoplastic polyhydroxyalkanoate, remain undissolved and act as crystal nuclei, eliminating the need for a waiting period for primary nucleation, reducing stickiness due to low crystallinity immediately after melt extrusion, making molded products such as fibers and films less likely to stick together, and enabling winding and stretching immediately after melt spinning or film formation, thereby improving productivity.

[0054] By melt-spinning the polymer with some remaining crystals and then stretching it immediately afterward, the remaining lamellar crystals become oriented, the amorphous polymer chains become highly oriented, and the continuous monomer unit segments that are easy to form crystals gather together, promoting crystallization. By avoiding melting at high temperatures that would cause thermal decomposition, molecular weight loss due to thermal decomposition is suppressed, which helps maintain the molecular weight of the molded product, i.e., prevents thermal degradation. Furthermore, even if the polymer contains residual moisture or is prone to absorbing moisture from the air, partial melt molding can lower the temperature, thereby reducing the degree of hydrolysis caused by heat and moisture compared to complete melt molding. This suppresses the molecular weight loss of the polyhydroxyalkanoate and helps maintain the molecular weight of the molded product.

[0055] In the present invention, the polyhydroxyalkanoate is melt-molded. When melt-molding the polyhydroxyalkanoate, additives may be added as long as the effects of the present invention are not impaired. Examples of additives include one or more selected from antioxidants, heat stabilizers (e.g., hindered phenols, hydroquinone, phosphites, and substituted derivatives thereof), ultraviolet absorbers (e.g., resorcinol, salicylate), color inhibitors (phosphites, hypophosphites, etc.), lubricants, mold release agents (montanic acid and its metal salts, its esters, its half esters, stearyl alcohol, stearamide, polyethylene wax, etc.), colorants (dyes or pigments, etc.), conductive agents or carbon black as a colorant, plasticizers, flame retardants (bromine-based flame retardants, phosphorus-based flame retardants, red phosphorus, silicone-based flame retardants, etc.), flame retardant assistants, and antistatic agents.

[0056] The method for blending the additive with the polyhydroxyalkanoate is not particularly limited, and examples thereof include dry blending, solution blending, and addition during chemical polymerization of the polyhydroxyalkanoate.

[0057] Polyhydroxyalkanoates can be subjected to known melt molding methods such as injection molding, injection compression molding, compression molding, extrusion molding (melt extrusion molding), blow molding, press molding, and spinning (melt extrusion spinning). The number of times of melt molding is not particularly limited, but it is preferably carried out only once.

[0058] In the present invention, the solidification step after molding can be carried out in a molding die, in a gas (e.g., air, nitrogen, etc.), or in a liquid (e.g., water, alcohol, glycerin, or a mixture thereof, etc.). That is, the polyhydroxyalkanoate partially melted by the method of the present invention can be solidified by cooling it in a molding die, in a gas, or in a liquid. 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.

[0059] Examples of polyhydroxyalkanoate molded articles produced by the method of the present invention include injection-molded articles, extrusion-molded articles, press-molded articles, sheets, pipes, various films such as unstretched films, uniaxially stretched films, and biaxially stretched films, various fibers such as unstretched yarns and ultrastretched yarns, etc. The polymer molded articles produced by the method of the present invention may be tubular or may have shapes other than tubular.

[0060] The present invention will be described in detail below with reference to examples and comparative examples. Note that the descriptions of the examples and comparative examples in the specification of this application are provided to aid in understanding the contents of the present invention, and are not intended to provide a basis for narrowly interpreting the technical scope of the present invention. [Example]

[0061] <Polymer used> The poly(3-hydroxybutyrate) (P(3HB)) used was "Biogreen" (MW 940,000, melting point approximately 175°C, glass transition point approximately 2°C) manufactured by Mitsubishi Gas Chemical. The P(3HB-co-4HB) copolymer can be 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 can be produced. P(3HB-co-61.5 mol% 3HV) was produced by a cultivation method according to the method described in JP-A-01-069622. As the method for extracting PHA from bacterial cells is already known, a solvent extraction method may be used, in which extraction is performed using a halogenated hydrocarbon solvent such as chloroform and precipitation is carried out with a poor solvent such as hexane or methanol, or an aqueous extraction method may be used as described in JP-B-04-061638, JP-A-07-177894, WO2004029266.

[0062] <Measurement of the molecular weight of PHA (gel permeation chromatography (GPC) method)> The measurement of the PHA molecular weight was carried out by the gel permeation chromatography method as follows. Chloroform was added so that PHA became about 0.5 mg / ml, and after dissolving at 60 °C for 4 hours, it was returned to room temperature, filtered through a PTFE filter with a pore size of 0.2 μm to remove insolubles, and used as a measurement sample. The GPC conditions are as follows.

[0063] Apparatus: HPLC Prominence system manufactured by Shimadzu Corporation Column: Shodex K-806L (two columns in series) manufactured by Showa Denko KK Column temperature: 40 °C Mobile phase: chloroform (1 ml / min) Detector: RI (40 °C) Standard: Shodex polystyrene molecular weight standard (6.87 million - 12.7 million) Injection volume: 60 μl Analysis time: 30 minutes

[0064] <Measurement of the PHA outflow start temperature by a flow tester> The PHA is measured using a capillary rheometer flow tester, model CFT-500D (manufactured by Shimadzu Corporation) or CFT-500EX (manufactured by Shimadzu Corporation). The amount of sample used for measurement is approximately 1.2 g of PHA in the form of pellets, powder, film, etc., which is filled into a cylinder for measurement. When using powdered polymers, they may be molded using an appropriate granulator and press machine and then filled into the cylinder. A die (nozzle) with a diameter of 1.0 mm and a thickness of 1.0 mm is used, an extrusion load of 5 kg is applied, and after a preheating time of 240 seconds at an initial setting temperature of 30°C to 140°C (appropriately selected according to the type and melting point of the polymer), the curve of the stroke length (mm) versus temperature is determined when the temperature is increased at a rate of 3°C / min to 130 - 260°C (appropriately selected according to the type and melting point of the polymer). As the temperature rises, the PHA is heated and the polymer begins to flow out of the die. The temperature at this time is defined as the outflow start temperature.

[0065] <Measurement of the melting behavior of PHA: Measurement of thermal properties by differential scanning calorimeter (DSC)> The melting behavior of PHA was measured using a differential scanning calorimeter (Rigaku, Thermo plus EVO DSC8230). The measurement atmosphere was nitrogen (30 ml / min), and the temperature was raised from 30°C to 130 - 260°C (appropriately selected according to the type and melting point of PHA) at a rate of 20°C / min. The sample was approximately 1 mg, and an aluminum sample pan was used. Indium was used for temperature calibration.

[0066] When the melting peak is sharp, in accordance with JIS-K7121, the extrapolated melting end temperature of the melting peak is taken as the temperature of the intersection of the tangent line drawn at the point of the maximum slope before the peak end and the baseline after the peak (recognized by the Rigaku, Thermo plus EVO software). However, when the melting peak shapes overlap, the tangent line is manually redrawn for the peak on the higher temperature side, and the intersection with the baseline is taken as the extrapolated melting end temperature.

[0067] The glass transition temperature (Tg) of each sample was measured in a nitrogen atmosphere (20 mL / min) using a differential scanning calorimeter (DSC) model: DSC 8500 (PerkinElme, USA) equipped with an intracooler. 1 st In one run, the temperature was raised from 50 °C to 200 °C at a heating rate of 10 °C / min, and the sample was melted by isothermal treatment at 200 °C for 1 minute. Then, it was rapidly cooled to -50 °C at 200 °C / min, isothermally treated at -50 °C for 1 minute, and then the temperature was raised from -50 °C to 200 °C at 10 °C / min. 2 nd T was measured in run. Aluminum sample pans were used. Indium was used for temperature calibration. g

[0068] <Partial melting extrusion and melting extrusion of PHA: Melt spinning at a constant temperature using a flow tester> Melt extrusion spinning was carried out using a flow tester CFT-500D type (manufactured by Shimadzu Corporation) or CFT-500EX (manufactured by Shimadzu Corporation).

[0069] <Comparative Example 1> P(3HB) powder, without heat treatment, Sample S1 The water-purified P(3HB) powder was used as Sample S1. The Mw of Sample S1 was 9.4 million. Sample S1 was analyzed using a CFT (Capillary Flowtester) and DSC. The CFT outflow start temperature was 181.0 °C, and the width of the crystal melting peak by DSC was approximately 140 - 189 °C. The top of the crystal melting peak 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 found that the DSC extrapolated melting end temperature was lower than the CFT outflow start temperature, and it would not flow out unless it was in a completely molten state. The measurement results of CFT and DSC are shown in Figure 1.

[0070] ​The temperature at which the baseline of the melting point peak is reached is higher than the CFT outflow start temperature, and if we pay attention to this, it is possible to think that sample S1 is also partially meltable based on the measured values. However, there are points to consider, such as the fact that the molten state of a polymer can be affected not only by temperature but also by other factors such as the heating time, and that partial melt extrusion becomes easier if the pressure during melt extrusion is high, so the range from the CFT outflow start temperature to the DSC extrapolated melting end temperature is listed in the table as the temperature at which partial melt extrusion is possible.

[0071] Example 1: P(3HB) powder, heat-treated in a 70°C water bath Sample S2 The aqueous-purified P(3HB) powder of sample S1 was immersed in water, heated at 70°C for 24 hours, and then vacuum-dried to obtain sample S2. The Mw of sample S2 was 940,000. Sample S2 was analyzed by CFT and DSC. The CFT flow-initiating temperature was 178.6°C, and the DSC crystalline melting peak range was approximately 140–188°C. The crystalline melting peak peak peak peak was 175.1°C, the DSC extrapolated melting end temperature was 182.0°C, and the melting point peak baseline temperature was 188.0°C. The DSC extrapolated melting end temperature was higher than the CFT flow-initiating temperature, making it possible to flow in a partially molten state. However, the CFT flow-initiating temperature and the DSC extrapolated melting end temperature are in nearly the same temperature range (temperature difference of 3.4°C), suggesting that strict temperature control is required to effectively mold the material in a partially molten state. Figure 2 shows the CFT and DSC measurement results.

[0072] Example 2: P(3HB) powder, dry heat treatment at 70°C Sample S3 The aqueous-purified P(3HB) powder from Sample S1 was dry-heat treated in a dry-heat oven at 70°C for 24 hours and then returned to room temperature to obtain Sample S3. The Mw of Sample S3 was 940,000. The CFT flow-initiating temperature was 178.6°C, and the DSC crystalline melting peak range was approximately 140–187°C. The crystalline melting peak ...

[0073] Figure 4 shows an overlay of the DSC curves for Samples S1, S2, and S3 from Comparative Example 1, Example 1, and Example 2. P(3HB) is composed of highly crystalline (R)-3HB continuous monomer unit chains, and unlike PHA copolymers, the peak top position of the main melting point peak does not change significantly with or without heat treatment, resulting in nearly identical DSC curves. Water bath and dry heat treatment of bulk P(3HB) at 70°C slightly shifted the CFT flow initiation temperature to a slightly lower temperature (178.6°C) than 181.0°C.

[0074] Example 3: P(3HB-co-13.1 mol% 4HB) powder, sample S4 Sample S4 was prepared by aqueous reaction at 70°C for 35 hours and then purified in water (P(3HB-co-13.1 mol% 4HB)). The Mw of Sample S4 was 1,000,000, and the glass transition temperature (Tg) was approximately -4°C. Sample S4 was analyzed by CFT and DSC. The CFT flow-out onset temperature was 125.1°C, and the DSC crystalline melting peak range was approximately 49-157°C. The crystalline melting peak peak peaks were 63.7°C and 114.8°C. The DSC extrapolated melting end temperature was 135.1°C, and the melting point peak baseline temperature was 155.0°C. The DSC extrapolated melting end temperature was higher than the CFT flow-out onset temperature, demonstrating that partial melt extrusion was possible in the range of 125.1°C to 135.1°C. Figure 5 shows the CFT and DSC measurement results.

[0075] Melt spinning was carried out at temperatures of 126°C, 130°C, and 135°C, which allow partial melting, and at temperatures of 150°C, 160°C, and 170°C, which allow almost complete melting. The Mw before melt spinning was 1 million, whereas the Mw after partial melt spinning at 126 ° C was 950,000, the Mw after partial melt spinning at 130 ° C was 970,000, the Mw after partial melt spinning at 135 ° C was 970,000, the Mw after melt spinning at 150 ° C was 820,000, the Mw after melt spinning at 160 ° C was 650,000, and the Mw after melt spinning at 170 ° C was 540,000. If the molecular weight Mw of 1 million before melt spinning is taken as 100%, the residual rate of molecular weight Mw after melt spinning at each temperature 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 became clear that being able to spin at lower temperatures is effective in suppressing molecular weight reduction. In particular, the suppression of molecular weight reduction was remarkable in partial melt spinning at temperatures below 135°C, where it was clear that the polymer was not in a completely molten state.

[0076] The results are shown in Table 2.

[0077] When melt-spun at 170°C, the extruded polymer was highly tacky and stuck together, and the polymer solidified after winding, making it impossible to unwind. On the other hand, yarns partially extruded at 135°C or below showed almost no stickiness, and could be wound and drawn immediately after spinning without sticking. This shows that partial-melt extrusion spinning can shorten crystallization time, improve the melt processability of polymers, and increase productivity.

[0078] Example 4: P(3HB-co-13.1 mol% 4HB) powder, sample S5 Sample S4, a dried, aqueous-purified P(3HB-co-13.1 mol% 4HB), was again immersed in water and treated in a hot bath at 70°C for 24 hours, followed by vacuum drying to obtain Sample S5. The Mw of Sample S5 was 1,000,000. Sample S5 was analyzed by CFT and DSC. The CFT flow-initiation temperature was 109.8°C, and the DSC crystalline melting peak range was approximately 88–159°C. The crystalline melting peak peak apexes were 95.0°C and 118.6°C. The DSC extrapolated melting end temperature was 139.1°C, and the melting point peak reached the baseline at 158.5°C. The DSC extrapolated melting end temperature was higher than the CFT flow-initiation temperature, demonstrating that partial melt extrusion was possible in the range of 109.8°C to 139.8°C. Figure 6 shows the CFT and DSC measurement results. Sample S4 could be partially melt extruded in the range of 125.1°C or higher but lower than 140.2°C, whereas sample S5, which was heat-treated in water at 70°C, could be partially melt extruded in the range of 109.8°C or higher but lower than 139.8°C. Heat treatment broadened the temperature range for partial melt extrusion by approximately 15°C toward the lower end.

[0079] Example 5: P(3HB-co-13.1 mol% 4HB) powder, sample S6 Sample S4, a dry, aqueous-purified P(3HB-co-13.1 mol% 4HB), was dry-heat treated in an oven at 70°C for 24 hours and then returned to room temperature to obtain Sample S6. The Mw of Sample S6 was 1,000,000. Sample S6 was analyzed by CFT and DSC. The CFT flow-initiating temperature was 110.0°C, and the DSC crystalline melting peak range was approximately 75–160°C. The crystalline melting peak peak peaks were 81.9°C and 119.1°C, the DSC extrapolated melting end temperature was 137.8°C, and the melting peak baseline temperature was 158.8°C. The DSC extrapolated melting end temperature was higher than the CFT flow-initiating temperature, demonstrating that partial melt extrusion was possible in the range of 110.0°C to 137.8°C. Figure 7 shows the CFT and DSC measurement results.

[0080] Figure 8 shows an overlay of the DSC curves for Samples S4, S5, and S6 from Examples 3, 4, and 5. Additionally, the DSC curve for Sample S7, which was obtained by dissolving Sample S4 in chloroform, creating a cast film, and aging it at room temperature for at least one week, is also shown. Unlike the DSC curve for P(3HB) shown in Figure 4, the shape of the melting peak in the DSC curve for the P(3HB-co-4HB) copolymer changed significantly depending on its thermal history, dissolution in a solvent, and solvent evaporation.

[0081] Sample S4 could be partially melt extruded in the range of 125.1°C or higher but lower than 140.2°C, while sample S5, which had been heat-treated in water at 70°C, could be partially melt extruded in the range of 109.8°C or higher but lower than 139.8°C, and sample S6, which had been heat-treated in dry heat at 70°C, could be partially melt extruded in the range of 110.0°C or higher but lower than 139.1°C. The heat treatments expanded the temperature range for partial melt extrusion by approximately 15°C toward the lower end.

[0082] <Comparative Example 2> Sample S8 Solvent extraction No heat treatment Sample S8 was purified by solvent extraction and precipitation (chloroform extraction-hexane precipitation system) using P(3HB-co-61.5 mol% 3HV). The Mw of sample S8 was 730,000, and the glass transition temperature (Tg) was approximately -11°C. Sample S8 was analyzed by CFT and DSC. The CFT flow-out onset temperature was 84.5°C, and the DSC crystalline melting peak range was approximately 56-179°C. The crystalline melting peak ... Even if we assume that no components exhibiting a small melting peak on the high-temperature side, which is thought to be derived from 3HB-rich crystals, are mixed in, the extrapolated melting end temperature of the melting peak on the low-temperature side is 97.5°C, and in this case, partial melt extrusion is possible in the range of 84.5°C to 97.5°C. Figure 9 shows the results of CFT and DSC measurements.

[0083] Example 6: Sample S9 Solvent extraction Heat treatment in water at 70°C Sample S8 (3HB-co-61.5 mol% 3HV), purified by solvent extraction and precipitation, was immersed in water, heated at 70°C for 24 hours, and then vacuum-dried to obtain sample S9. The Mw of sample S9 was 720,000. Sample S9 was analyzed by CFT and DSC. The CFT flow-out onset temperature was 80.8°C, and the DSC crystalline melting peak range was approximately 49–178°C. The crystalline melting peak ... Even if we assume that no components exhibiting a small melting peak on the high-temperature side, which is thought to be derived from 3HB-rich crystals, are mixed in, the extrapolated melting end temperature of the melting peak on the low-temperature side is 96.9°C, and in this case, partial melt extrusion is possible in the range of 80.8°C to 96.9°C. Figure 10 shows the results of CFT and DSC measurements.

[0084] <Example 7> Sample S10 Solvent extraction Dry heat treatment at 70°C Sample S8 (3HB-co-61.5 mol% 3HV), purified by solvent extraction and precipitation, was again dry-heat treated in an oven at 70°C for 24 hours 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 flow onset temperature was 79.8°C, and the DSC crystalline melting peak ranged from approximately 75 to 178°C. The crystalline melting peak ... The DSC extrapolated melting end temperature was higher than the CFT outflow initiation temperature, and it was found that partial melt extrusion was possible in the range of 79.8°C to less than 173.3°C. Even if we assume that no components showing a small melting peak on the high-temperature side, which is thought to be derived from 3HB-rich crystals, are mixed in, the extrapolated melting end temperature of the melting peak on the low-temperature side is 97.5°C, and in that case it is clear that partial melt extrusion is possible in the range of 79.8°C to less than 97.5°C. Figure 11 shows the CFT and DSC measurement results.

[0085] Figure 12 shows an overlay of the DSC curves for Samples S8, S9, and S10 of Comparative Example 2, Example 6, and Example 7. Unlike the DSC curve for P(3HB) shown in Figure 4, the shape of the melting peak in the DSC curve for the P(3HB-co-3HV) copolymer changed significantly depending on the thermal history applied.

[0086] Sample S8 could be partially melt extruded in the range of 84.5°C or higher and lower than 173.2°C, while sample S9, which had been heat-treated in water at 70°C, could be partially melt extruded in the range of 80.8°C or higher and lower than 172.6°C, and sample S10, which had been heat-treated in dry heat at 70°C, could be partially melt extruded in the range of 79.8°C or higher and lower than 173.3°C. The heat treatments expanded the temperature range for partial melt extrusion by about 5°C toward the lower end.

[0087] <Example> Sample S11 was an aqueous-purified P(3HB-co-16.0 mol% 4HB) powder with a Mw of 620,000 and a glass transition temperature (Tg) of approximately -5°C. Sample S11 was treated in air at 70°C for 24 hours, in water at 50°C for 24 hours, in water at 60°C for 24 hours, in water at 70°C for 24 hours, and in water at 80°C for 24 hours. The PHA heat-treated in water was freeze-dried to obtain a dried product. Each heat-treated sample was evaluated by DSC, and the DSC curves (thermograms) of the first heating cycle are overlaid and shown in Figure 13. The same sample S11 was further treated in water at 50°C for 24 hours, in methanol for 12 hours, in ethanol for 12 hours, and in hexane for 12 hours at 50°C, and then vacuum dried to obtain a dried sample. Each heat-treated sample was evaluated by DSC, and the DSC curves (thermograms) of the first heating cycle are shown in Figure 14. The melting peak shapes varied with the heat treatment. It is known that the DSC melting peak temperature of crystalline polymers depends on the thickness of the lamellar crystals. Among PHAs, P(3HB) showed no significant change in the main DSC melting peak position after heat treatment in water at 70°C or after dry heat treatment, as shown in Figure 4. However, P(3HB-co-4HB) showed a major melting peak shape that depended on the treatment temperature in water, solvent, and air, as shown in Figures 13 and 14. The phenomenon of the peak shape changing with heat treatment was also observed in the P(3HB-co-3HV) copolymer (Figure 12). Heat treatment above the glass transition temperature of the PHA, but below the melting point of the PHA itself, induces lamellar crystal reorganization, leading to control of the lamellar crystal thickness. This technology is linked to control of melt processability and is useful as a pretreatment for partial melt molding.

[0088] [Table 1]

[0089] [Table 2]

Claims

1. A method for producing a polymer molded product, comprising: heat-treating a crystalline polyhydroxyalkanoate at a temperature equal to or higher than the glass transition point; and melt-molding the polyhydroxyalkanoate obtained by the heat treatment, which contains lamellar crystals having different lamellar thicknesses, within a temperature range in which some of the lamellar crystals melt and become fluid, while the remaining lamellar crystals remain unmelted, wherein the temperature range is higher than the flow-out initiation temperature measured by a flow tester heating method and lower than the extrapolated melting end temperature, and the polymer is a copolymer containing 3-hydroxybutyric acid and 4-hydroxybutyric acid as monomer units, with the proportion of 4-hydroxybutyric acid being 5 mol % or more and 40 mol % or less, or a copolymer containing 3-hydroxybutyric acid and 3-hydroxyvaleric acid as monomer units, with the proportion of 3-hydroxyvaleric acid being 5 mol % or more and 90 mol % or less.

2. 2. The method of claim 1, wherein the heat treatment is a gas-, liquid-, or solid-mediated heat treatment.

3. 3. The method according to claim 1 or 2, wherein the heat treatment is a liquid-mediated heat treatment, and the polyhydroxyalkanoate does not completely dissolve in the liquid under heating.

4. 4. The method according to claim 1, further comprising cooling the molten polymer in air at a temperature range in which some of the lamellar crystals melt and become fluid, while the remaining lamellar crystals remain unmelted.

5. 5. The method according to claim 1, wherein the thermoforming is by melt extrusion.

6. 6. The method according to claim 1, wherein the thermoforming is by melt extrusion spinning.

7. A method according to any one of claims 1 to 6, wherein the polymer is a copolymer containing 3-hydroxybutyric acid and 4-hydroxybutyric acid as monomer units, in which the proportion of 4-hydroxybutyric acid is 5 mol% or more and 40 mol% or less, and the temperature range is 109.8 to 139.1°C.

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