JPH08245779A - Method for purifying lactic acid-based polymer - Google Patents

Abstract

PURPOSE: To provide a method for purifying a lactic acid-based polymer capable of removing a remaining lactide without using a large amount of a solvent' and without exerting an undesirable influence on the lactic acid-based polymer to be produced. CONSTITUTION: A remaining lactide is extracted and removed from a lactic acid-based polymer by using a solvent having >=1.0% polymer solubility at 23 deg.C, >=4% lactide solubility and >=1.01 and <=2.00 swelling degree of the polymer defined by W/M when the mass of the polymer in the absolute dry state is M and the mass in equilibrium swelling is W.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying a lactic acid-based polymer, which comprises extracting and removing residual lactide using a specific solvent.

[0002]

2. Description of the Related Art It is known that lactic acid-based polymers generally have a high molecular weight by polymerizing lactides. However, it is known that it is necessary to remove residual raw material lactide from the polymer in order to improve the thermal or mechanical properties of the produced polymer.

As a means thereof, for example, a polymer is dissolved in an unsaturated hydrocarbon type solvent or a halogen type solvent,
A method of removing lactide by reprecipitation in an alcoholic solvent that is well miscible with the solvent. A method of removing lactide by devolatilizing a lactic acid-based polymer and purifying it (Japanese Patent Laid-Open No. 5-93050) is known.

However, in the method, the amount of the poor solvent is required to be about 100 times that of the polymer, and in the case of using the halogen-based solvent, there is a drawback that environmental pollution and health of the experimenter are not taken into consideration. In the other method, since the lactide is regenerated from the polymer produced by lactide by a backbite reaction, the temperature cannot be raised to a sufficiently high temperature, and the lactide cannot be completely removed. Has the drawback that it deteriorates the physical properties of the molded product, and that the polymer is subjected to extra heat history.

[0005]

Therefore, the problem to be solved by the present invention is to eliminate residual lactide in the lactic acid-based polymer without using a large amount of solvent and without affecting the lactic acid-based polymer to be produced. It is intended to provide a method for purifying a lactic acid-based polymer that can be easily removed.

[0006]

Means for Solving the Problems As a result of intensive investigations by the present inventors, solvent extraction using a specific solvent does not substantially affect the polymer component and only the raw material lactide is reduced to 0. The inventors have found that it can be removed in an amount of 0.3% by weight or less, and completed the present invention.

That is, in the present invention, the lactic acid-based polymer is
The solubility of the polymer is 1.0% or less at ℃, and the swelling degree defined as W / M is 1.01 to 2.00, where M is the mass when completely dried and W is the mass at equilibrium swelling. A method for purifying a lactic acid-based polymer, characterized in that the residual lactide is extracted and removed using a solvent having the following solubility of lactide of 4% or more.

More specifically, in the present invention, the extraction solvent has 4 carbon atoms.
A method for purifying a lactic acid-based polymer which is the following alcohol, a ketone having a carbon number of 6 or less, an ester having a carbon number of 6 or less, or an unsaturated hydrocarbon having a carbon number of 13 or less, and particularly, the lactic acid-based polymer is polylactic acid or a lactic acid-based polymer. Is a method for purifying a lactic acid-based polymer, which is a lactic acid-based copolymer containing 25% or more by weight of a lactic acid unit.

The present invention also uses a mixer to grind and stir the lactic acid-based polymer in the presence of the above-mentioned solvent,
A method for purifying a lactic acid-based polymer, which comprises extracting and removing residual lactide, characterized in that the residual lactide is extracted and removed by immersing a film, sheet, pellet or powder of lactic acid-based polymer in the solvent. A method for purifying a lactic acid-based polymer, and a method for purifying a lactic acid-based polymer characterized by extracting and removing residual lactide while kneading the lactic acid-based polymer in the presence of a solvent using a kneader or a kneading extruder. .

The present invention will be described in more detail below. Solvent extraction is generally known as an effective means of organic synthesis, but it depends on the properties of the substance to be extracted and removed and the mutual solubility and swelling degree of the target polymer. For example, JP-A-63-254128 describes that a crystalline lactic acid-based polymer swells into a jelly when contacted with a precipitating agent (poor solvent), making it difficult to do anything. On the other hand, in the opposite case, the polymer and the solvent have no affinity at all and the polymer itself is solidified, which may not be useful for anything.

The lactic acid-based polymer used in the present invention includes polylactic acid which is a polymer of lactic acid, and as the lactic acid-based copolymer, it contains 25% by weight or more of a lactic acid unit, and other polyester components such as diol, dicarboxylic acid, It specifically includes a so-called lactic acid-based polyester containing a hydroxycarboxylic acid or the like as its constituent unit. The lactic acid-based copolymer can be synthesized according to a known method. For example, as a concrete method

Copolymerization of lactide and lactones. Copolymerize lactic acid with diol, dicarboxylic acid, hydroxycarboxylic acid and the like. Copolymerize lactide with polyester prepared from diol, dicarboxylic acid, hydroxycarboxylic acid. A transesterification reaction is performed with a polyester prepared from poly (lactic acid) and a diol, a dicarboxylic acid, a hydroxycarboxylic acid, or the like.

Polyester prepared from lactide, lactones, diol, dicarboxylic acid and hydroxycarboxylic acid is copolymerized. Copolymerize lactide with polyethers. Etc. can be mentioned.

The lactones useful for copolymerization with lactide are caprolactone, valerolactone, propiolactone, undecalactone, 1,5-oxepan-2-one, 4-methyl-1,5-. Oxepan-2-one, 4-ethyl-1,5-oxepan-2-one, 4-propyl-1,5-oxepan-2-one,
4-Butyl-1,5-oxepan-2-one, 2,5-
Diketomorpholine, 2,5-diketo-3,6-dimethylmorpholine, 2,5-diketo-3-methylmorpholine,
Examples thereof include dimethyltriethylene carbonate.

The diol units used in the polyester useful for copolymerizing with lactide include ethylene glycol, propylene glycol and 1,3-
Propanediol, 1,4-butanediol, 1,3-
Butanediol, 1,2-butanediol, 1,5-pentanediol, 1,4-pentanediol, 1,3-
Pentanediol, 1,2-pentanediol, 1,6
-Hexanediol, 1,5-hexanediol, 1,
4-hexanediol,

1,3-hexanediol, 1,2-hexanediol, 1,7-heptanediol, 1,6-heptanediol, 1,5-heptanediol, 1,4-
Heptanediol, 1,3-heptanediol, 1,2
-Heptanediol, 1,8-octanediol, 1,
7-octanediol, 1,6-octanediol,
1,5-octanediol, 1,4-octanediol, 1,3-octanediol, 1,2-octanediol, 1,9-nonanediol,

1,8-nonanediol, 1,7-nonanediol, 1,6-nonanediol, 1,5-nonanediol, 1,4-nonanediol, 1,3-nonanediol, 1,2-nonane Diol, 1,10-decanediol, 1,9-decanediol, 1,8-decanediol, 1,7-decanediol, 1,6-decanediol, 1,5-decanediol, 1,4-decanediol ,

1,3-decanediol, 1,2-decanediol, 1,2-dimethyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol,
1,3-dimethyl-1,3-propanediol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, 1,2-undecanediol, 1,3-undecanediol, 1,4-undecanediol, 1,5-undecane Diol, 1,6-undecanediol, 1,7-undecanediol, 1,8
-Undecanediol, 1,9-undecanediol,

1,10-undecanediol, 1,11
-Undecanediol, 1,12-dodecanediol,
1,13-tridecanediol, 1,14-tetradecanediol, 1,15-pentadecanediol, 1,1
Examples thereof include 6-hexadecanediol, hydroquinone, resorcin, naphthalenediol, 4,4′-dihydroxybiphenyl, α, α′-xylylenediol.

Examples of the dicarboxylic acid unit contained in the polyester include carbonic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, 1,4-dicarboxybutane, 1,5-dicarboxypentane, 1,6-dicarboxyhexane. ,
1,7-dicarboxyheptane, 1,8-dicarboxyoctane, 1,9-dicarboxynonane, 1,10-dicarboxydecane, 1,11-dicarboxyundecane, 1,12-dicarboxydodecane, 1, 13-dicarboxytridecane, 1,14-dicarboxytetradecane, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and the like can be mentioned.

The hydroxycarboxylic acid units contained in the polyester include hydroxyacetic acid, 3-hydroxypropionic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid 4-hydroxybutyric acid, 2-hydroxyvaleric acid,
3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 2-hydroxycaproic acid, 3-hydroxycaproic acid, 4-hydroxycaproic acid, 5-hydroxycaproic acid, 6-hydroxycaproic acid, 4-
Examples thereof include hydroxybenzoic acid, 3-hydroxybenzoic acid and 2-hydroxybenzoic acid.

As the polyether used for copolymerization, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can be mentioned. Further, if necessary, acid anhydride, polyisocyanate such as hexamethylene diisocyanate having a functionality of two or more and acid anhydride such as pyromellitic acid, glycerin,
A lactic acid-based polymer whose molecular weight is increased by using a polyol such as pentaerythritol or trimethylolethane can also be used in the present invention.

As the solvent used in the present invention, a solvent which has a low solubility of the polymer, can be appropriately swollen, and can sufficiently dissolve lactide can be used. More specifically, it is 23 ° C. The solubility of the lactic acid-based polymer is 1% by weight or less, and the swelling degree of the polymer is 10
It is desirable to simultaneously satisfy the three conditions of 1% or more and 200% or less and the solubility of lactide of 4% or more.

Examples of such a solvent include alcohols, aromatic hydrocarbons, halogenated hydrocarbons, ketones, ethers and esters. Among them, preferable solvents are alcohols having 4 or less carbon atoms and 6 or less carbon atoms. Examples thereof include ketones or esters, and aromatic hydrocarbons having 13 or less carbon atoms, and more preferable examples include methanol, ethanol, methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, toluene, xylene, mesitylene, pseudocumene, and methylnaphthalene. I can.

In particular, an alcohol having a carbon number of 4 or less, a ketone or an ester having a carbon number of 6 or less can be preferably used for extraction of a sheet, a film, a pellet, a molded article or a crushing stirring extraction using a mixer or a mill. Aromatic hydrocarbons having a number of 13 or less can be preferably used for kneading and devolatilization with a kneader.

On the other hand, the temperature at the time of extraction and pulverization is −20 ° C. to 200 ° C., preferably 0 ° C. to 50 ° C., more preferably when the solvent is potentially reactive, such as primary alcohols. 0 ° C to 30 ° C is preferable. If the temperature is lower than this, it is meaningless because of wasteful cooling, and the solubility of lactide decreases, which is not preferable.

If the temperature is higher than this, the polymer reacts with the alcohols of the solvent to lower the molecular weight, or the pulverization efficiency of the polymer deteriorates.
It is not preferable because the polymers block each other. However, when the solvent is not reactive with the polymer under normal conditions or heating conditions such as ketone, the temperature can be further raised.

The lactic acid-based polymer at the time of extraction may be in the form of a film, sheet, crushed powder, pellets, molded product, etc. In order to perform extraction uniformly and increase efficiency. Is preferably performed in the form of a sheet or film, pellets or powder, and more preferably pellets or powder considering that clouding or welding may occur depending on the solvent used for extraction. Further, in the case of performing extraction with powder or pellets, operations such as crushing and cutting can be performed prior to the extraction, or can be performed while performing the extraction operation such as mixing with a mixer.

As a means for extraction, in addition to crushing the polymer with a mixer and extracting with a solvent, a method of crushing with a mill and then extracting, a film, a sheet, a molded product, pellets, etc. are suitable. The method of immersing in a different solvent is also
It can be used, and a suitable solvent that does not react with the polymer at all, such as an aromatic hydrocarbon, is added to the molten polymer, and the solvent is volatilized while increasing the surface area using a biaxial extruder or the like. At the same time, the residual lactide can be removed.

It is also preferable to appropriately stir the solvent or perform Soxhlet type extraction because the amount of the solvent can be reduced and the extraction efficiency can be increased. Hereinafter, the present invention will be described more specifically with reference to examples.

[0031]

EXAMPLE Here, 30 parts by weight of polyester obtained from sebacic acid and propylene glycol and a D / L ratio of 5 /
Table 1 shows an example of the swelling degree in a solvent and the solubility of lactide of a lactic acid-based polymer obtained from 70 parts by weight of lactide of 95. Here, the degree of swelling is represented by W / M, where M is the mass of the polymer film in an absolutely dry state, and W is the mass of the film soaked at 23 ° C. for 3 days.

The solubility of lactide was determined by dissolving an excess amount of lactide in a solvent and using benzophenone as an internal standard by GLC, and expressed by the weight of lactide dissolved in 100 ml of the solvent. T-AmOH in Table 1 represents tertiary amyl alcohol.

[0033]

[Table 1] Swelling degree of lactic acid polymer and solubility of lactide

Example 1 5 parts by weight of a polyester obtained from sebacic acid and propylene glycol, 94 parts by weight of L-lactide, 1 part by weight of D-lactide, and 0.05 part of pyromellitic dianhydride as a crosslinking agent. 40 ml of 10 g of lactic acid-based polymer having Mn of 102,000 and Mw of 175,000 (residual lactide content = 2.4%)
With methanol at 18 ° C., using a mixer for about 7 minutes. The obtained white powdery polymer was filtered off, and GPC was measured after drying. No change was observed in the molecular weight, and only the residual lactide content was reduced to 0.1%.

Example 2 30 parts by weight of polyester obtained from sebacic acid and propylene glycol, 66.5 parts by weight of L-lactide, 3.5 parts by weight of D-lactide,
And 10 g of a lactic acid-based polymer having Mn = 510,000 and Mw = 1119,000 (residual lactide content = 2.8%) obtained from 0.03 part by weight of pyromellitic dianhydride as a crosslinking agent, and 40 ml of methanol. The mixture was stirred at 18 ° C for about 7 minutes using a mixer. The obtained white powdery polymer was filtered off, and GPC was measured after drying. No change was observed in the molecular weight, and only the residual lactide content was reduced to 0.1%.

(Example 3) 97.5 parts by weight of L-lactide and 2.5 parts by weight of D-lactide were used to obtain Mn = 12.
10,000, Mw = 1999,000 (residual lactide content = 2.8
%) Lactic acid-based polymer (10 g) was stirred with 40 ml of ethanol at 18 ° C. for about 7 minutes using a mixer. The obtained white powdery polymer was filtered off, and GPC was measured after drying. No change was observed in the molecular weight, and only the residual lactide content was reduced to 0.1%.

Example 4 10 g of lactic acid-based polymer having Mn = 201,000 and Mw = 34,900 (residual lactide content = 2.9%) obtained from 100 parts by weight of L-lactide was used.
Stir with 0 ml of methyl acetate at 18 ° C. for about 7 minutes using a mixer. The obtained white powdery polymer was filtered off, and GPC was measured after drying. No change was observed in the molecular weight, and only the residual lactide content was reduced to 0.1%.

Example 5 100 parts by weight of a lactic acid-based polymer obtained from succinic acid, ethylene glycol, propylene glycol, and lactide was added to 30 parts by weight of toluene at 170 ° C. in a vented 30 mmφ twin-screw extruder to remove volatilization at 1 mmHg. I went. When the obtained polymer was dried and GPC was measured, the molecular weight did not change at all, but the residual lactide was reduced to 0.1%.

Example 6 10 g of pellets of a lactic acid-based polymer having Mn = 201,000 and Mw = 34,900 (residual lactide content = 2.9%) obtained from 100 parts by weight of L-lactide was added to 600 ml of 600 ml. The mixture was stirred at 18 ° C. for about 40 minutes with a mixed solution of methanol and 200 ml of acetone. When the pellets were filtered off and GPC was measured after drying, no change was observed in the molecular weight, and only the residual lactide content was 0.
It was reduced to 1%.

Example 7 30 parts by weight of polyester obtained from sebacic acid and propylene glycol, 66.5 parts by weight of L-lactide, 3.5 parts by weight of D-lactide,
And 5.0 g of pellets of a lactic acid-based polymer having Mn = 48,000 and Mw = 92,000 (residual lactide content = 0.4%) obtained from 0.03 part by weight of pyromellitic dianhydride as a crosslinking agent. Was stirred with a mixture of 100 ml of methanol and 100 ml of acetone at 18 ° C. for about 5 hours. When the pellet was filtered off and dried, GPC was measured, and no change was observed in the molecular weight, and residual lactide was not observed at all.

(Example 8) 30 parts by weight of polyester obtained from sebacic acid and propylene glycol, 66.5 parts by weight of L-lactide, 3.5 parts by weight of D-lactide,
And 3.01 g of pellets of lactic acid-based polymer having Mn = 81,000 and Mw = 135,000 (residual lactide weight 3, 1%) obtained from 0.03 part by weight of pyromellitic dianhydride as a crosslinking agent. Stir with 120 ml of acetone at 18 ° C. for about 2 hours. When the pellet was filtered off and dried, GPC was measured, and no change was observed in the molecular weight, and only residual lactide was not observed at all.

Example 9 30 parts by weight of polyester obtained from sebacic acid and propylene glycol, 66.5 parts by weight of L-lactide, 3.5 parts by weight of D-lactide,
And a mass of lactic acid-based polymer of Mn = 910,000 and Mw = 15.7000 (residual lactide content = 3.1%) obtained from 0.03 part by weight of pyromellitic dianhydride as a crosslinking agent.
01g was crushed with ice water using a mixer, 120m
Stir with 1 l of acetone at 18 ° C. for about 2 hours. When the pellet was filtered off and dried, GPC was measured, and no change was observed in the molecular weight, and only residual lactide was not observed at all.

Comparative Example The polymer used in Example 1 (M
n = 102,000, Mw = 175,000, 3.0 g of pellets with residual lactide content = 2.5%) was added to 200 m of hexane.
It was stirred with 23 at 23 ° C. for 10 hours. The molecular weight of the obtained polymer did not decrease at all, but the amount of residual lactide did not decrease at all.

[0044]

INDUSTRIAL APPLICABILITY The present invention provides a method for purifying a lactic acid-based polymer capable of easily removing the residual lactide without affecting the lactic acid-based polymer to be produced without using a large amount of solvent. it can.

Claims (7)

[Claims] 1. A lactic acid-based polymer is defined as W / M when the solubility of the polymer at 23 ° C. is 1.0% or less, the mass at absolute dryness is M, and the mass at equilibrium swelling is W. A method for purifying a lactic acid-based polymer, which comprises extracting and removing residual lactide using a solvent having a swelling degree of 1.01 or more and 2.00 or less and a solubility of lactide of 4% or more. 2. The purification of the lactic acid polymer according to claim 1, wherein the extraction solvent is an alcohol having 4 or less carbon atoms, a ketone having 6 or less carbon atoms, an ester having 6 or less carbon atoms, or an unsaturated hydrocarbon having 13 or less carbon atoms. Method. 3. The method for purifying a lactic acid-based polymer according to claim 1, wherein the lactic acid-based polymer is polylactic acid. 4. The lactic acid-based polymer is a lactic acid-based copolymer containing 25% or more by weight of a lactic acid unit.
A method for purifying a lactic acid-based polymer as described. 5. The lactic acid according to claim 1, wherein the lactic acid-based polymer is pulverized in a solvent in the presence of a solvent and stirred to extract and remove residual lactide. -Based polymer purification method. 6. The residual lactide is extracted and removed by immersing a lactic acid-based polymer film, sheet, pellet or powder in a solvent.
The method for purifying a lactic acid-based polymer according to any one of 1. 7. The residual lactide is extracted and removed while kneading the lactic acid-based polymer in the presence of a solvent by using a kneading machine or a kneading extruder. The method for purifying a lactic acid-based polymer.