JPH09241417A - Recovery of raw material for lactic acid-based polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover a lactide which is a reutilizable raw material for a lactic acid-based polymer from lactic acid-based polymer wastes, etc., by adding specific alcohols and a pyrolytic catalyst to the lactic acid-based polymer and carrying out the alcoholysis. SOLUTION: (B) Alcohols having >=170 deg.C boiling point under 7.5Torr pressure (e.g. a >=6C monohydric alcohol, a diol, a >=5C triol or a tetrol) and (C) a pyrolytic catalyst such as a compound containing tin as an element are added to (A) a lactic acid-based polymer such as a copolymer of a polyester comprising a diol and a dicarboxylic acid and a lactide or a polylactic acid and the resultant mixture is then heated under a reduced pressure in an inert gas stream to carry out the alcoholysis. Thereby, the buckbite reaction is conducted.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lactic acid-based polymer containing lactic acid as a structural unit, particularly a waste lactic acid-based polymer produced during molding and used lactic acid-based polymer products containing alcohols and a thermal decomposition catalyst. In addition, the present invention relates to a method of subjecting lactide, which is a raw material of a reusable lactic acid polymer, to alcoholysis and recovery.

[0002]

2. Description of the Related Art Biodegradable polymers are expected to be applied to general-purpose resins for the purpose of improving environmental problems. However, even if it is a biodegradable polymer, it is desirable to collect and reuse used products as much as possible, because excessive disposal promotes environmental pollution.

Japanese Unexamined Patent Publication No. 6-49266 discloses a method of recovering a hydroxy acid by hydrolyzing a plastic with an alkali. However, in this process, the hydrolysis reaction is a stoichiometric reaction of alkali,
Due to the presence of the alkali metal, racemization of lactide and lactic acid occurs, and a device for resynthesizing lactide from the obtained lactic acid is required.

Further, JP-A-5-287056 discloses a method of obtaining a lactide by thermally decomposing a lactic acid oligomer in the presence of alcohol. However, in this method, lactic acid is oligomerized and then lactic acid is thermally decomposed to obtain lactide, and lactic acid is not decomposed to decompose high molecular weight polylactic acid or lactic acid-based copolymer.

[0005]

The problem to be solved by the present invention is to efficiently decompose a product consisting of a recovered or used lactic acid-based polymer and recover a reusable raw material lactide in a high yield. It is to provide a method for recovering a raw material of a polymer.

[0006]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that a lactic acid-based polymer (A) contains a high-boiling alcohol (B) and a thermal decomposition catalyst ( It was found that the lactide can be recovered in a high yield by adding C) and thermally decomposing it, and has completed the present invention.

That is, the present invention relates to a lactic acid-based polymer (A)
To the alcohol (B) having a boiling point of 170 ° C. or higher at 7.5 Torr and a thermal decomposition catalyst (C),
A method for recovering a raw material for a lactic acid-based polymer, comprising recovering lactide produced by heating and decomposing alcohol by heating under a reduced pressure or under an inert gas stream to carry out a back-bite reaction.

In the method for recovering a lactic acid-based polymer raw material according to the present invention, the lactic acid-based polymer (A) is polylactic acid, or the lactic acid-based polymer (A) is a polyester composed of a diol and a dicarboxylic acid and lactide. A method for recovering a raw material for a lactic acid-based polymer, which is characterized in that it is a polymer, and more specifically, the thermal decomposition catalyst (C) contains tin as an element.

The method for recovering a lactic acid-based polymer material according to the present invention is characterized in that the reaction pressure of the back-bite reaction is 20 Torr or less, and the back-bite reaction is carried out under an inert gas flow. Is carried out in a twin-screw extruder or using a thin-film distillation apparatus.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a high-boiling alcohol (B) and a thermal decomposition catalyst (C) are added to a lactic acid-based polymer (A) containing lactic acid as a structural unit to undergo alcoholysis, and under reduced pressure, A method for recovering lactide, which comprises recovering lactide from a polymer.

The lactic acid-based polymer (A) containing lactic acid as a structural unit as referred to in the present invention includes polylactic acid, which is a homopolymer of lactic acid, and lactic acid-based copolymers containing a lactic acid residue as a structural unit. . That is, the polymer (A) containing lactic acid as a structural unit here is a homopolymer of lactic acid of any optical purity, which contains D-form and L-form in a block or random manner, alcohols and lactic acid. And copolymers of various polymers and lactic acid, and the like.

The alcohols include methanol, ethanol, propanol, butanol, amyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol,
Undecyl alcohol, dodecyl alcohol, tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, hexadecyl alcohol, heptadecyl alcohol, octadecyl alcohol, nonadecyl alcohol, t-amyl alcohol,

Isobutyl alcohol, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, polyethylene glycol monomethyl ether, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, 1,4 -Butanediol, polytetramethylene glycol, 1,3-butanediol, 1,2-butanediol, 1,6-hexanediol, xylylenediol,

Examples include neopentyl glycol, glycerin, trimethylolmethane, trimethylolethane, trimethylolpropane, trihydric alcohols such as α, α ′, α ″ -trihydroxytrimethylbenzene, and tetrahydric alcohols such as pentaerythritol. You can Further, as the other copolymerization component, polyether, polyether ester, polyester, polycaprolactone, polycarbonate, polyoxepandione and the like can be mentioned.

However, in order to reuse the recovered lactide, it is preferable that the lactic acid-based polymer used for recovering the raw material does not contain a hydrolyzable bond in the polymer to be copolymerized, and particularly preferably polyether or poly-ether. Examples thereof include ether monools, polyether polyols, copolymers of various monohydric or polyhydric alcohols with lactic acid or lactide, and similarly preferably lactic acid block or random copolymers. I can.

The molecular weight of the lactic acid-based copolymer used in the present invention is not particularly limited, but it is desirable that the weight average molecular weight is 2000 or more. Although lactide having a molecular weight lower than that can be recovered by this method, the quality and yield of the obtained lactide will be low. On the other hand, if the molecular weight is too large, the viscosity of the polymer in the reaction system becomes too high, so it is preferable to use one having a molecular weight of 350,000 or less.

The alcohol (B) is preferably 7.5.
Those having a boiling point of 170 ° C. or higher at Torr, more preferably those having a boiling point of 200 ° C. or higher at 7.5 Torr are preferably used. For that purpose, those having other functional groups such as ketones, ethers and thioethers, which are relatively difficult to hydrolyze, and polyfunctional alcohols are preferable. The use of such alcohols has an advantage that the lactide produced can be more easily purified.

Examples of these compounds include monoalcohols having 6 or more carbon atoms, diols, triols and tetraols having 5 or more carbon atoms, and more specifically, pentadecyl alcohol, hexadecyl alcohol, heptadecyl. Alcohol, octadecyl alcohol, nonadecyl alcohol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, triethylene glycol and its monomethyl ether, monoethyl ether, tetraethylene glycol and its monomethyl ether, monoethyl ether, polyethylene glycol , Polypropylene glycol, polytetramethylene glycol and the like.

The amount of these alcohols (B) is 25 μmo in total with the hydroxyl value in the whole polymer in the reaction system.
1 / polymer 1 g or more and 1 mmol / polymer 1 g or less is preferable, and more preferably 1
It is particularly preferable that the amount is 00 μmol / polymer 1 g or more and 0.5 mmol / polymer 1 g or less.

By preparing in this way, the back-bite reaction can be caused at a good rate, and a good quality lactide can be obtained. Therefore, it is preferable to track the hydroxyl value of the polymer in the reaction system and adjust the hydroxyl value in the reaction system by adding alcohols (B) and lactic acid polymer (A) in the corresponding amounts.

As the thermal decomposition catalyst (C), any compound can be used as long as it is a compound containing tin as an element, but it is desirable to use a carboxylate such as tin octoate, tin stearate or dibutyltin dilaurylate. , Dibutyltin dichloride, tin dichloride, tin dibromide and other halides, dibutyltin oxide, tin oxide and other oxides,
Known and conventional compounds such as alcoholate compounds such as tin diacetylate, dibutyltin diacetylate and dibutyltin dimethoxide, cyclic or acyclic stannoxane compounds, and metal tin can be used. But particularly preferably,
It is preferable to use tin octoate, which is used as a thermal decomposition catalyst and has low toxicity.

The amount of the thermal decomposition catalyst (C) is 0.01% to 5% by weight, more preferably 0.1% to 1.5% by weight, based on the amount of the lactic acid-based polymer in the reaction system. . With such an amount, the amount of harmful residues can be reduced and the reaction rate can be sufficiently increased.

On the other hand, the lactic acid-based polymer (A), the alcohols (B) and the thermal decomposition catalyst (C) may be mixed in any order, but for the purpose of recycling, less waste is preferable. It is preferable that the polymer is added to the reaction system containing the alcohol (B) and the thermal decomposition catalyst (C) while heating to carry out the alcoholysis and the thermal decomposition reaction to recover the produced lactide.

It is also possible to carry out these processes continuously. That is, it is a method of continuously obtaining a lactide produced by alcoholysis using the alcohols (B) and the thermal decomposition catalyst (C) in the system while adding the polymer to the system.

Thus, the lactic acid-based polymer (A) is added to the reaction system.
The amount of alcohols (B) and thermal decomposition catalyst (C) is significantly smaller than that of the lactic acid-based polymer to be reacted because alcohol is added to the reaction vessel and the polymer is subjected to alcoholysis and thermal decomposition to recover lactide. Is the preferred method.

As another process, a lactide produced by melting a molded product in the presence of an alcohol (B) and a thermal decomposition catalyst (C) and causing a back-bite reaction using a thin film distillation apparatus or the like. It is also possible to recover the lactide produced by reacting with a twin screw extruder or the like. At this time, by adding the remaining oligomer to the original polymer, it is possible to further improve the lactide recovery efficiency and reduce the amount of waste.

At the initial stage of the reaction, the linear lactide and water are mixed and recovered in the recovery lactide, so that it depends on the composition and the molecular weight of the polymer to be used, but the weight of the polymer initially charged in the kettle is about. It is preferable to take about 1% to 10% of the above as the pre-distillation.

The reaction rate can be increased by heating the reaction under reduced pressure. The reaction temperature is 170
C. to 250.degree. C., preferably 180.degree. C. to 210.degree.
By setting the temperature in this way, it is possible to obtain a recyclable product of good quality in which lactide is produced at a sufficient reaction rate and the obtained lactide or lactic acid does not cause racemization.

The reaction pressure is preferably 20 Torr or less, and more preferably 10 Torr or less in order to obtain a good reaction rate. There is no suitable minimum pressure,
Even if the pressure is further reduced, there is no point in simply making useless and expensive equipment investment, and substantially sufficient reaction can be achieved in a reduced pressure state of about 1 Torr.

Even if the system is not depressurized, the reaction rate can be improved by carrying out under an inert gas stream. It is preferable to bring the system into an inert gas atmosphere in this way in order to prolong the life of the tin compound which is the thermal decomposition catalyst (C). Further, the thermal decomposition reaction can be caused by using the reduced pressure and the inert gas together. Again,
It is possible to obtain a recovered lactide having the same composition as in the case of simple decompression.

On the other hand, the lactide thus obtained can be used as a raw material for a polymer or various biodegradable chemicals after further purification according to the use. As specific means therefor, known means such as distillation, melt crystallization, solution crystallization and the like can be mentioned.

[0032]

EXAMPLES The present invention will be described in more detail with reference to the following examples. In the following examples and comparative examples, the composition of lactide was analyzed by gas chromatography (column: OV).
-1), the water content was measured using a Karl Fischer moisture meter MKA-210 manufactured by Kyoto Electronics Co., Ltd., and the acid value was measured using an automatic potentiometric titrator APB-310. The molecular weight of the polymer was measured by GPC using THF as a solvent. In the text, Mn represents the number average molecular weight, and Mw represents the weight average molecular weight.

The raw materials used will be described below. P-202: Polypropylene sebacate (manufactured by Dainippon Ink and Chemicals). The molecular weight was PE-75: polypropylene glycol-polyethylene glycol block copolymer, which was prepared by appropriately performing a reduced pressure treatment under heating. Mn: about 4500 (manufactured by Sanyo Kasei)

Example 1 Polylactic acid (Mn = 13000)
0, Mw = 200000) 150.2 g (however, D / L =
5/95), tin octoate (0.51 g) and cetyl alcohol (6.98 g) were added, and the mixture was heated at 195 ° C. under nitrogen to 30
After stirring for a minute, the pre-distillation was taken at 27.5 torr. It was subsequently depressurized to 5 torr and lactide was distilled off over a period of about 1 hour. 137.5 g of recovered lactide was obtained. Its composition is shown below.

D, L-lactide: 91.5% Mesolactide: 8.2% Others: 0.3% Moisture: 3200 ppm Acid value: 30.1 meq / kg

Example 2 Polylactic acid (Mn = 8100)
0, Mw = 120,000) 151.3 g (however, D / L =
5/95), tin octoate (0.51 g) and pentaerythritol (0.472 g) were added, and the mixture was stirred at 195 ° C. under nitrogen for 30 minutes, and then pre-distilled at 27.5 torr. The pressure was further reduced to 5 torr, and lactide was distilled out over about 1 hour. 138.2 g of recovered lactide was obtained. Its composition is shown below.

D, L-lactide: 90.1% Mesolactide: 8.7% Others: 1.2% Moisture: 3400 ppm Acid value: 17.8 meq / kg

(Example 3) P-202 (Mn = 4500)
0, Mw = 140,000) 30% by weight and lactide (D
/ L = 5/95) 70% by weight lactic acid-based copolymer (Mn = 70000, Mw = 220,000) 152.0
3.51 g of cetyl alcohol was added to g of 195
After stirring at ℃ for 30 minutes under nitrogen, pre-distillation was carried out at 27.5 torr. The pressure was further reduced to 5 torr, and lactide was distilled out over about 1 hour. Recovery Lactide
80.86 g was obtained. Its composition is shown below.

D, L-lactide: 88.0% Mesolactide: 8.5% Others: 3.5% Moisture: 4900ppm Acid value: 42.2 meq / kg

Example 4 Polylactic acid (Mn = 150,000, Mw = 2) obtained by polymerizing lactide (L / D = 97.5 / 2.5) using trimethylolethane as an initiator.
60000) 152.0 g of tin octoate (0.51 g) and stearyl alcohol (4.12 g) were added, and the mixture was stirred at 195 ° C. under nitrogen for 30 minutes, then 27.5 torr.
The ryo was taken in r. The pressure was further reduced to 5 torr, and lactide was distilled out over about 1 hour. 137.2 g of recovered lactide was obtained. Its composition is shown below.

D, L-lactide: 94.3% Mesolactide: 4.7% Others: 1.0% Moisture: 3000 ppm Acid value: 18.8 meq / kg

Example 5 Polylactic acid (D / L = 2.5 /
97.5, Mn = 190000, Mw = 282000)
Stearyl alcohol 4.05 for 151.5 g
g and 0.50 g of tin octanoate were added, and the mixture was stirred at 195 ° C. under nitrogen for 30 minutes, and then pre-distilled at 27.5 torr. The pressure was further reduced to 5 torr, and the same polylactic acid was added to the system in the molten state while distilling out lactide, and alcoholysis and backbite reaction were repeated.
The total amount of polylactic acid added was 1060.5 g, and 1047.2 g of recovered lactide was obtained. Reaction time is about 7
It was time.

The composition is shown below. D, L-lactide: 92.9% Mesolactide: 5.4% Others: 1.7% Moisture: 2600ppm Acid value: 20.8meq / kg

Comparative Example 1 Polylactic acid (Mn = 8100)
0, Mw = 120,000) 151.3 g (however, D / L =
5/95), only 0.51 g of tin octoate was added without adding any alcohol, and the mixture was stirred at 195 ° C. for 30 minutes under nitrogen, and then pre-distilled at 27.5 torr. The pressure was further reduced to 5 torr, and lactide was distilled out over about 1 hour. Only 27.2 g of recovered lactide was obtained.

Example 6 Polyethylene glycol-polylactic acid copolymer (Mn = 24000, Mw = 32000) 155.3 obtained from the polymerization of PE-75 and lactide.
2.24 g of cetyl alcohol and 0.51 g of tin octanoate were added to g (however, D / L = 5/95), and 1
After stirring at 95 ° C. under nitrogen for 30 minutes, pre-distillation was carried out at 27.5 torr. The pressure was further reduced to 5 torr, and lactide was distilled out over about 1 hour. 139.2 g of recovered lactide was obtained.

The composition is shown below. D, L-lactide: 88.6% Mesolactide: 10.1% Others: 1.3% Moisture: 4400ppm Acid value: 16.9meq / kg

Example 7 Polylactic acid (d / l = 2.5 /
97.5) 5820 g (Mn = 134000, Mw = 3)
11000) to 15 stearyl alcohol
180g by adding 3.7g and tin octoate 19.3g
After thoroughly stirring at 1, the mixture was sent to a twin-screw extruder, the pressure was reduced to 1 Torr, and the lactide was distilled. 5770 g of recovered lactide was obtained.

The composition is shown below. D, L-lactide: 95.0% Mesolactide: 4.8% Others: 0.2% Moisture: 2200ppm Acid value: 13.8meq / kg

(Comparative Example 2) Polylactic acid produced by directly dehydrating lactic acid (Mn = 950, Mw = 1600)
To 151.3 g (however, D / L = 5/95), alcohol was not added at all, only 0.51 g of tin octanoate was added, and after stirring at 195 ° C. for 30 minutes under nitrogen, 27.5 t
I took the advance reservation at orr. The pressure was further reduced to 5 torr, and lactide was distilled out over about 1 hour. 70.0 g of recovered lactide was obtained.

The composition is shown below. D, L-lactide: 84.1% Mesolactide: 7.3% Others: 8.6% Moisture: 8500ppm Acid value: 58meq / kg

Example 8 Lactic acid homopolymer (d / l =
2.5 / 97.5) 5990 g (Mn = 126000,
Mw = 298000), 194.9 g of stearyl alcohol and 17.3 g of tin octanoate were added to obtain 1
After stirring well at 80 ° C, it was put on a thin-film distillation apparatus to obtain 190
The pressure was reduced to 1 Torr at ℃ and lactide was distilled off.
5620 g of recovered lactide was obtained.

The composition is shown below. D, L-lactide: 94.3% Mesolactide: 5.2% Others: 0.5% Moisture: 2050 ppm Acid value: 21.3 meq / kg

Example 9 Polylactic acid 1.2 kg (Mn = 14500) obtained by reacting 0.92 g of glycerin with 1.49 kg of lactide (d / l = 2.5 / 97.5)
0, Mw = 250000), 39.9 g of cetyl alcohol and 4.0 g of tin octanoate were added, and the temperature was 180 ° C.
After stirring well at 1, the mixture was brought into contact with dry nitrogen at 190 ° C., and lactide was distilled using a nitrogen stream. 1110 g of recovered lactide was obtained.

The composition is shown below. D, L-lactide: 94.3% Mesolactide: 4.7% Others: 1.0% Moisture: 3200ppm Acid value: 32meq / kg

Example 10 The recovered lactides obtained in Examples 1 to 9 and Comparative Examples 1 to 2 were recrystallized twice with toluene in an inert gas atmosphere (thus obtained). Lactide was referred to as refined lactide), 3 g of each was placed in an ampoule, and tin octoate was added at 400 ppm to carry out a polymerization reaction at 170 ° C. for 6 hours.
Table 1 shows the recovery rate and Mw of the polymer obtained by polymerizing the purified lactide.

[0056]

[Table 1]

[0057]

INDUSTRIAL APPLICABILITY The present invention efficiently decomposes recovered or used lactic acid polymer products and wastes, recovers reusable raw material lactide in good yield, and re-submits the polymerization reaction to obtain a high yield. It is possible to provide a method for recovering a raw material of a lactic acid-based polymer, which can obtain a lactic acid-based polymer having a molecular weight.

Claims (8)

[Claims] 1. The lactic acid-based polymer (A) is added with 7.5 Tor
The alcohol (B) having a boiling point of 170 ° C. or higher and the thermal decomposition catalyst (C) are added, and the mixture is heated under reduced pressure or under an inert gas stream to be subjected to alcoholysis and a backbite reaction. A method for recovering a raw material for a lactic acid-based polymer, which comprises recovering lactide produced as a result. 2. The method for recovering a lactic acid polymer raw material according to claim 1, wherein the lactic acid polymer (A) is polylactic acid. 3. The method for recovering a raw material for a lactic acid-based polymer according to claim 1, wherein the lactic acid-based polymer (A) is a copolymer of a lactide and a polyester composed of a diol and a dicarboxylic acid. 4. The method for recovering a raw material for a lactic acid-based polymer according to claim 1, wherein the thermal decomposition catalyst (C) contains tin as an element. 5. The reaction pressure of the back-bite reaction is 20 To.
It is below rr, The raw material recovery method of the lactic acid type polymer as described in any one of Claims 1-4 characterized by the above-mentioned. 6. The method for recovering a raw material for a lactic acid-based polymer according to claim 1, wherein the backvite reaction is performed in an inert gas stream. 7. The method for recovering a raw material for a lactic acid-based polymer according to claim 1, wherein the backbite reaction is performed in a twin-screw extruder. 8. The method for recovering a raw material for a lactic acid-based polymer according to claim 1, wherein the backbite reaction is performed using a thin film distillation apparatus.