JP4234043B2 - Method for crystallizing aliphatic polyester - Google Patents

Description

  The present invention relates to an improved method for crystallizing aliphatic polyesters, which are biodegradable polymers useful as resins for general and medical applications.

Patent Document 1 discloses a technique relating to a method for producing a high molecular weight aliphatic polyester. That is, an aliphatic polyester having a specific relative viscosity ηrel (1.5) or higher is crystallized, and then subjected to solid phase polymerization under specific conditions, thereby having a high molecular weight that can be molded as a fishing line and the like and having a high melting point. It is said that aliphatic polyester can be obtained.
However, with regard to the crystallization technique, it is only described that various conventionally known methods that promote crystallization, such as crystallization at room temperature and water cooling, can be used. There is no suggestion or disclosure about crystallization by contact.

Patent Document 2 discloses a technique related to a method for producing a lactic acid-based copolymer polyester granular material. In other words, the fusion problem can be solved by crystallizing a lactic acid-based copolymer polyester composed of a lactic acid component, a dicarboxylic acid component, and a diol component at a glass transition temperature or higher and lower than a melting temperature. Has been.
As described in Paragraph Nos. [0014] to [0016] of the published patent publication, a lactic acid copolymer polyester is extruded from a die in a molten state to form a strand, and the molten strand is cooled at a constant cooling rate. A technique for crystallizing and cutting the crystallized strands into granules is disclosed. However, there is no suggestion or disclosure regarding crystallization by contact with an alkaline aqueous solution.

  Patent Document 3 discloses that an aliphatic polyester polymer containing 50% or more of an aliphatic hydroxycarboxylic acid unit having a weight average molecular weight of 2,000 to 100,000 is solid-phase polymerized in the presence of a catalyst to obtain an aliphatic hydroxy having a weight average molecular weight of 50,000 to 1,000,000. A technique relating to a method for producing an aliphatic polyester containing 50% or more of a carboxylic acid unit is disclosed. In this invention, a technique for crystallizing an aliphatic polyester polymer by bringing it into contact with a liquid that does not dissolve the aliphatic polyester polymer, and a description that an organic acid may be added to the liquid used for crystallization There is. However, there is no mention of contacting with an alkaline aqueous solution.

  Patent Document 4 discloses a technique in which a solid aliphatic polyester is brought into contact with a liquid and crystallized. The liquid of the present invention is an organic solvent in which aliphatic polyester such as water and alcohol does not dissolve, but there is no mention of crystallization by contacting with an alkaline aqueous solution.

  Patent Document 5 discloses a method of crystallization using a solution in which an organic compound, particularly an organic sulfonic acid as a catalyst component, is added to water. In this method, crystallization is performed under low temperature and stirring to avoid fusion, but there is no mention of crystallization by contact with an alkaline aqueous solution.

  When crystallization is performed by the method described in Patent Documents 1 to 5 and solid phase polymerization is performed thereafter to obtain a high molecular weight polymer, the pellet after solid phase polymerization is colored and is used for solid phase polymerization. In addition, there are problems such as fusion between particles, breakage of particles, and blockage in a solid phase polymerization apparatus.

JP-A-8-34843 JP-A-8-165339 European Patent No. 953589 specification JP 2000-302855 A JP 2001-192442 A

  The problem to be solved by the present invention is that when aliphatic polyester is crystallized, it is easily and continuously crystallized without causing problems such as fusion of the particles of the resin by contacting with an alkaline aqueous solution. Furthermore, by performing solid-phase polymerization thereafter, a method of crystallizing an aliphatic polyester capable of efficiently producing a high-molecular-weight aliphatic polyester with less coloration that could not be achieved by the prior art Is to provide.

  As a result of intensive studies in view of the above situation, the present inventors have completed the present invention. That is, the present invention is a method for crystallizing an aliphatic polyester, wherein the aliphatic polyester is crystallized by contacting with an alkaline aqueous solution having a pH ≧ 8.

The present invention provides a method for crystallizing an aliphatic polyester , wherein the aliphatic polyester is crystallized by contacting with an alkaline aqueous solution of 8 ≦ pH ≦ 13 at a temperature equal to or higher than the glass transition point of the aliphatic polyester.

  The aliphatic polyester crystallization method, in which the aliphatic polyester is a polymer of an aliphatic hydroxycarboxylic acid, is a preferred embodiment of the present invention.

  A method for crystallizing the aliphatic polyester, in which the aliphatic polyester is a copolymer of an aliphatic hydroxycarboxylic acid, an aliphatic polyhydric alcohol, and an aliphatic polycarboxylic acid, is also a preferred embodiment of the present invention.

  A method for crystallizing the aliphatic polyester in which the aliphatic hydroxycarboxylic acid is lactic acid and / or glycolic acid is also a preferred embodiment of the present invention.

  A preferred embodiment of the present invention is a method for crystallizing an aliphatic polyester comprising at least one alkali component in the alkaline aqueous solution selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, and ammonia. It is.

The present invention further includes Yellowness having a weight average molecular weight of 100,000 or more and a thickness per 2 mm obtained by solid-phase polymerization of the aliphatic polyester crystallized by the method of the present invention.
An aliphatic polyester having an Index of 5 or less is provided.

  According to the method of the present invention, when an aliphatic polyester is crystallized, it can be crystallized without causing problems of fusion and breakage under the condition that suppresses a decrease in molecular weight, and is subsequently increased by solid-phase polymerization. An aliphatic polyester having a low molecular weight and a low degree of coloration is obtained. Therefore, by crystallization of the aliphatic polyester according to the method of the present invention, stable operation can be performed without causing problems such as fusion of particles, breakage of particles, and blockage in the apparatus, and high quality aliphatic polyester. Can be provided.

The aliphatic polyester of the present invention has a weight average molecular weight of 2000 or more, preferably 5000 or more, and includes an aliphatic polyhydroxycarboxylic acid unit, and is of the following types.
(1) Aliphatic polyhydroxycarboxylic acid homopolymers or copolymers obtained from one or more aliphatic hydroxycarboxylic acids or mixtures thereof (2) One or more aliphatic hydroxycarboxylic acids and aliphatic polyhydric alcohols Copolymer of aliphatic polyester composed of aliphatic polycarboxylic acid or a mixture thereof

  Specific examples of the aliphatic hydroxycarboxylic acid include lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid and the like. Among these, lactic acid and glycolic acid are preferable. These hydroxycarboxylic acids may be used alone or in combination of two or more. In the case of having an asymmetric carbon atom in the molecule like lactic acid, D-form, L-form, and an equivalent mixture (racemic form) thereof exist, any of which can be used.

  The aliphatic polyhydric alcohol is not particularly limited. Examples of the divalent alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1 , 6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol, 1,4-cyclohexanedimethanol and the like. These can be used alone or in combination of two or more. Examples of the trihydric or higher aliphatic polyhydric alcohol include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, xylitol, and inositol. These can be used alone or in combination of two or more.

  The aliphatic polycarboxylic acid is not particularly limited. Examples of the aliphatic dicarboxylic acid include succinic acid, oxalic acid, malonic acid, glutamic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, and 3,3-dimethylpentane. Aliphatic dicarboxylic acids such as diacids and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be mentioned. These can be used alone or in combination of two or more. Examples of trivalent or higher aliphatic polyvalent carboxylic acids include 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, tetrahydrofuran 2R, 3T, 4T, 5C-tetracarboxylic acid, 1,2,3,4-cyclobutanetetracarboxylic acid, 4-carboxy-1,1-cyclohexanediacetic acid, 1,3,5-cyclohexanetricarboxylic acid, (1α, 3α, 5β) -1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic acid, cyclic compounds such as 2,3,4,5-furantetracarboxylic acid and anhydrides thereof, butane-1,2,3,4- Tetracarboxylic acid, meso-butane-1,2,3,4-tetracarboxylic acid, 1,3,5-pentanetricarboxylic acid, 2-methylolpropane tricarboxylic acid, , 2,3-propane tricarboxylic acid, 1,1,2-ethane tricarboxylic acid, compounds and anhydrides thereof, such as 1,2,4-butane tricarboxylic acid. Moreover, you may contain aromatic compounds, such as terephthalic acid, in the range which does not impair the physical property of a polymer remarkably. These can be used alone or in combination of two or more.

  In order to obtain desired resin properties, aliphatic polyester production methods include a method of dehydrating polycondensation of hydroxycarboxylic acid and a method of ring-opening polymerization of a cyclic dimer or cyclic ester which is a dehydration product of hydroxycarboxylic acid. A known reaction method can be used as appropriate.

  Further, during the polyhydric condensation of an aliphatic hydroxycarboxylic acid or in the ring-opening polymerization of a cyclic dimer, which is a dehydration product of a hydroxycarboxylic acid, an aliphatic polyhydric alcohol and an aliphatic polycarboxylic acid are added. In order to obtain a copolymer, a well-known reaction method can be used suitably.

  In addition, as aliphatic hydroxycarboxylic acid, lactic acid alone or glycolic acid alone or a method of dehydration polycondensation of lactic acid and glycolic acid, and lactide dehydration product lactide and glycolic acid dehydration product glycolide are each subjected to ring-opening polymerization. In order to obtain a copolymer, a well-known reaction method can be used suitably.

  The weight average molecular weight of the aliphatic polyester suitable for the crystallization method of the present invention is not particularly limited as long as it is 2000 or more. However, the weight average molecular weight is preferably 5000 or more in consideration of the crystallization speed and the like.

  The form of the aliphatic polyester suitable for the crystallization method of the present invention may be solid, molten, or solution. In the solid state, the shape is not particularly limited, and a plate shape, a lump shape, a string shape, a pellet shape, a granular shape, and the like can be used. From the viewpoint of uniform crystallization and ease of handling, pellets or granules are preferred. The method for molding the polymer into pellets or granules is not particularly limited, and a known method is used.

  In the molten state and the solution state, the method of contacting with the liquid is not limited at all. For example, an aliphatic polyester melt or an aliphatic polyester solution in which an aliphatic polyester is dissolved in a solvent can be dropped into an alkaline aqueous solution to solidify and crystallize. In this case, spherical pellets can be obtained. it can.

  The pellet shape and grain shape are not particularly limited. The pellet shape and particle shape need not be a specific shape such as a pulverized shape, a chip shape, a spherical shape, a cylindrical shape, a marble shape, or a tablet shape, but in general, a spherical shape, a cylindrical shape, or a marble shape is preferable.

  The pellet manufacturing apparatus is not particularly limited. For example, Sandvik strip former, funnel former, double roll feeder, Kaiser rotary drop former, piston drop former, Mitsubishi Examples include a drum cooler manufactured by Kasei Engineering, a steel belt cooler manufactured by Nippon Belling, and a hybrid former.

A polylactic acid molten droplet generator and a polylactic acid solution droplet generator are not particularly limited, but specific examples thereof include a Kastor pastilator.
The size of the pellets and grains is not particularly limited, but is preferably 0.1 mm to 10 mm and more preferably 1 mm to 5 mm in consideration of handling in the manufacturing process and handling in the secondary molding.

  In the present invention, it is preferable that pH ≧ 8 during crystallization, but more preferably 8 ≦ pH ≦ 13. At pH <8, the effect of adding an alkali component is hardly exhibited, fusion between polymers occurs, and polymer coloring after solid-phase polymerization is extremely yellowish, which is not preferable. A pH> 13 is not preferable because hydrolysis of the polymer becomes remarkable and the polymer yield is remarkably lowered.

  In the present invention, crystallization is a differential scanning calorimeter (DSC) measurement of a polymer having a weight average molecular weight> 2000 (measurement conditions; sample weight = about 10 mg, temperature conditions = 20 ° C. to 200 ° C., heating rate = 10 ° C. / Min), and the measured heat of crystallization is less than 30 J / g.

  In the present invention, the method for contacting the polymer with the aqueous alkaline solution is not particularly limited. When the polymer is in a solid state, it can be charged and brought into contact with an aqueous alkaline solution, or the aqueous alkaline solution can be poured into the solid polymer to make contact.

  The method for charging the solid polymer into the liquid is not particularly limited, and specific examples thereof include a method using a tank and a method using a tower. In the case of using a tank, a polymer is gradually poured into an aqueous alkaline solution kept at a predetermined temperature while stirring, and batch processing is performed. Can be taken in a continuous tank type. In addition, when using a tower, a method of circulating an alkaline aqueous solution using a polymer as a fixed layer or a method of circulating an alkaline aqueous solution simultaneously using a polymer as a moving layer can be taken, and the contact method with the alkaline aqueous solution is subject to these restrictions. A known method is used instead.

  When the polymer is in a molten state or a solution state, it can be charged and brought into contact with an alkaline aqueous solution. As a typical method, there is a method of dropping in an alkaline aqueous solution kept at a predetermined temperature.

  Alternatively, after dripping into an alkaline aqueous solution and solidifying, it can be crystallized by contacting with a liquid by the method described above as a solid state polymer.

  The weight of the polymer used for crystallization is preferably 0.001 to 100, more preferably 0.005 to 50, based on the weight of the aqueous alkali solution. Within the above range, crystallization can be suitably performed.

  The alkali component in the alkaline aqueous solution used for the crystallization of the present invention is preferably sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, or ammonia. These alkaline components consist of any one component or a mixture of two or more components.

  The crystallization temperature of the present invention is preferably not less than the glass transition point (Tg) of the polymer and not more than the boiling point of the aqueous alkali solution.

  Although the crystallization time of the present invention depends on the crystallization temperature, it is preferably 10 to 120 minutes, more preferably 30 to 100 minutes. Within the above range, crystallization can be suitably performed.

  An object of the present invention is to provide a method for crystallizing an aliphatic polyester, which can produce a high-molecular-weight aliphatic polyester with little coloration by solid-phase polymerization after crystallization in an aqueous alkali solution. The present inventors move the coloring component from the polymer phase to the aqueous phase by crystallizing the polymer in an alkaline aqueous solution, or decompose the coloring component with the alkaline aqueous solution, so that coloring during solid phase polymerization can be achieved. The knowledge that it can be reduced is obtained.

  In this way, it can be dried to remove the water in the polymer crystallized with an alkaline aqueous solution to obtain a final product, or the polymer crystallized with an alkaline aqueous solution can be subjected to solid phase polymerization to increase the molecular weight. it can.

[Solid-state polymerization]
The term “solid phase polymerization” of the present invention means a polymerization method in which the molecular weight is increased by carrying out a polymerization reaction at a temperature lower than the melting point of the polymer present in the reaction system. That is, it means a polymerization method in which the molecular weight is increased by carrying out a polymerization reaction while maintaining the solid state of the polymer present in the reaction system. The reaction temperature of the solid phase polymerization is generally preferably a temperature lower than the melting point of the polymer existing in the reaction system and a temperature equal to or higher than the glass transition temperature Tg, and a temperature lower than the melting point of the polymer existing in the reaction system. More preferably, the temperature is 100 ° C. or higher.

  In addition, solid-phase polymerization methods include, for example, a method in which a polymerization reaction is performed in a circulating gas atmosphere in which an inert gas such as nitrogen gas, helium gas, argon gas, xenon gas, krypton gas, or dry air is circulated, or under reduced pressure or There is a method of performing a polymerization reaction under pressure, but there is no particular limitation as long as the molecular weight of the aliphatic polyester after the completion of the solid-phase polymerization is not less than the value of the molecular weight before the start of the solid-phase polymerization. When the polymerization reaction is carried out under reduced pressure or under pressure, the pressure in the reaction system depends on the polymerization rate, the type and amount of catalyst used, and in the case of dehydration polycondensation reaction, the rate at which water produced by the reaction is removed. It is set in consideration of efficiency and molecular weight reached.

  In the present invention, the weight average molecular weight is 100,000 or more, preferably 130,000 or more, more preferably 190,000 or more, and the Yellowness Index per 2 mm thickness is 5 or less, preferably 4.8 or less, more preferably 4 It is possible to obtain an aliphatic polyester having a molecular weight of 5 or less, preferably a polymer of an aliphatic hydroxycarboxylic acid, more preferably a polymer containing lactic acid as a main component, more preferably polylactic acid.

  The method for producing an aliphatic polyester having a weight average molecular weight of 100,000 or more and a Yellowness Index per 2 mm of thickness of 5 or less is not particularly limited. For example, a molecular weight of 2000 or more obtained by a known method, preferably 5000 or more, More preferably, after the 6000 to 20000 aliphatic polyester is crystallized by contacting with an alkaline aqueous solution of pH ≧ 8 according to the present invention, the solid phase polymerization method described above is performed. The crystallization method and the solid phase polymerization method can be appropriately selected according to the purpose.

  The Yellowness Index (YI) shown in the present invention is a melting of an aliphatic polyester sample at Tm or more to prepare a 2 mm thick plate, and an SM color computer (model: SM-6-IS-2) according to JIS K-7103. -B, measured by Suga Test Instruments Co., Ltd.)

  The aliphatic polyester having a weight average molecular weight of 100,000 or more and a Yellowness Index per 2 mm of thickness of 5 or less has practically sufficient mechanical properties and low coloration, and is used for a wide range of applications. It can be suitably used for applications that require particularly low coloration, such as packaging containers, bottles, films, packaging materials, and the like.

Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples. The evaluation methods used in the examples are as follows.
(1) Weight average molecular weight Aliphatic polyester was dissolved in chloroform and measured at 40 ° C. using gel permeation chromatography (GPC) with chloroform as a solvent. At this time, polystyrene was used as a standard sample.
(2) Yellowness Index (YI)
An aliphatic polyester sample was melted at a melting point (Tm) or more to prepare a 2 mm thick plate, and in accordance with JIS K-7103, an SM color computer (model: SM-6-IS-2-B, Suga Test Instruments Co., Ltd.) ).
Evaluation criteria were good: YI ≦ 5 and defective YI> 5.

[Production Example 1]
A 2000 ml glass round bottom flask was charged with 1070 g of 90% L-lactic acid and 3.85 g of methanesulfonic acid. After nitrogen substitution, the temperature was gradually raised and the pressure was reduced. The reaction was finally carried out at a reaction temperature of 160 ° C. and a reaction pressure of 1300 Pa for 15 hours. The reaction mass was spread on an ice-cooled vat, quenched, ground and sieved to obtain 500 g of an amorphous granulated product having a size of 2 to 2.8 mm. The resulting polylactic acid had a weight average molecular weight of 10,000 and Tg = 45 ° C.

[Example 1]
20 g of the amorphous granulated product obtained in Production Example 1 was slowly added to 80 g of an aqueous sodium hydroxide solution at pH 11 and 70 ° C. over 1 minute. Stirring was carried out for 5 minutes from the start of adding the granulated product, and then allowed to stand, and after a total of 80 minutes, the granulated product was collected by filtration. There was no fusion or breakage between the polymers during crystallization. No heat of crystallization was observed by DSC. The weight average molecular weight was 0.98 million. The obtained crystallized polymer was subjected to solid phase polymerization at 140 ° C. for 100 hours under a nitrogen gas stream. As a result, it was a polymer having a weight average molecular weight of 195,000 and YI = 2.5. There was no fusion during solid phase polymerization, and the color of the polymer after solid phase polymerization was good.

[Example 2]
The same operation as in Example 1 was performed except that the pH 11 sodium hydroxide aqueous solution was changed to a pH 11 calcium hydroxide aqueous solution. The weight average molecular weight after crystallization was 10,000 and the heat of crystallization was 0 J / g. There was no fusion during crystallization. As a result of solid phase polymerization of the obtained polymer at 140 ° C. for 100 hours under a nitrogen gas stream, the weight average molecular weight was 200,000 and YI = 3.6. Further, there was no fusion during solid phase polymerization, and the hue of the polymer after solid phase polymerization was good.

[Production Example 2]
400 kg of L-lactic acid and 2 kg of methanesulfonic acid as a catalyst were charged, and crude dehydration was performed at 140 ° C. and 6700 Pa for 2 hours, and then polycondensation was performed at 160 ° C. and 1300 Pa for 8 hours. Thereafter, pelletized to obtain 250 kg of amorphous polylactic acid having a particle size of 2.8 to 3.4 mm and a weight average molecular weight of 10,000.

[Example 3]
The polylactic acid pellets obtained in Production Example 2 were supplied at 10 kg / hr from the top of the tower having an inner diameter of 250 mm and a height of 1000 mm, and at the same time, a pH 8 sodium hydroxide aqueous solution maintained at 70 ° C. was contacted in parallel at 50 kg / hr. . The pellets moved smoothly toward the bottom of the tower without fusing. The average residence time of the pellets was 60 minutes. The pellets obtained from the bottom of the tower were immediately dehydrated with a screw decanter. The heat of crystallization of the obtained pellet was not observed. After the pellet was sufficiently dried, the measured weight average molecular weight was 10,000. Subsequently, solid phase polymerization was carried out at 140 ° C. for 60 hours under a nitrogen gas stream. The weight-average molecular weight was 130,000 and YI = 3.5. Further, there was no fusion during solid phase polymerization, and the hue of the polymer after solid phase polymerization was good.

[Example 4]
50 kg of the polylactic acid pellets obtained in Production Example 2 were added to 200 L of sodium hydroxide aqueous solution at 70 ° C. and pH 11 with stirring over 5 minutes, and crystallization was performed for 70 minutes. During the crystallization, no fusion of pellets was observed. Thereafter, the pellet was filtered and collected.

  The heat of crystallization of the obtained pellet was not observed. The pellets were sufficiently dried and the weight average molecular weight measured was 11,000. Subsequently, solid phase polymerization was performed at 140 ° C. for 100 hours under a nitrogen gas stream. The weight-average molecular weight was 190,000 and YI = 4.2. Further, there was no fusion during solid phase polymerization, and the hue of the polymer after solid phase polymerization was good.

[Comparative Example 1]
20 g of the amorphous granulated product obtained in Production Example 1 was slowly added to 80 g of hydrochloric acid aqueous solution at pH 6 and 70 ° C. over 1 minute. Immediately after the start of the addition of the granulated product, the pellets were fused together, and when the whole amount was added, the mixture became incapable of stirring. After standing for 80 minutes, the pellet lump was filtered and collected. The heat of crystallization of the obtained pellet was not observed. The pellets were sufficiently dried and the weight average molecular weight measured was 0.950,000. Subsequently, solid phase polymerization was performed at 140 ° C. for 100 hours under a nitrogen gas stream. As a result, the weight average molecular weight was 180,000, YI = 7, and the color of the polymer was poor.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the crystallization method of the aliphatic polyester for obtaining the high molecular weight aliphatic polyester with a low coloring degree by a solid phase polymerization method.

Claims (6)

A method for crystallizing an aliphatic polyester, characterized in that the aliphatic polyester is crystallized by contacting with an alkaline aqueous solution of 8 ≦ pH ≦ 13 at a temperature equal to or higher than the glass transition point of the aliphatic polyester.   2. The method for crystallizing an aliphatic polyester according to claim 1, wherein the aliphatic polyester is a polymer of an aliphatic hydroxycarboxylic acid.   2. The method for crystallizing an aliphatic polyester according to claim 1, wherein the aliphatic polyester is a copolymer of an aliphatic hydroxycarboxylic acid, an aliphatic polyhydric alcohol, and an aliphatic polycarboxylic acid. The method for crystallizing an aliphatic polyester according to claim 2 or 3, wherein the aliphatic hydroxycarboxylic acid is lactic acid and / or glycolic acid. The method for crystallizing an aliphatic polyester according to claim 1, wherein the alkaline component in the aqueous alkaline solution comprises at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, and ammonia. An aliphatic polyester obtained by solid-phase polymerization of the aliphatic polyester crystallized by the method according to claim 1 and having a weight average molecular weight of 100,000 or more and a yellowness index per 2 mm of thickness of 5 or less. polyester.