JP3356825B2 - Processing of plastic products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating a degradable polymer composition. More specifically, the present invention relates to a method for decomposing and recovering a thermoplastic polymer composition mainly containing a hydroxycarboxylic acid polymer, and using the obtained hydroxycarboxylic acid as a polymer raw material if necessary.

[0002]

2. Description of the Related Art Conventionally, polyethylene,
Polypropylene, polyethylene terephthalate, polyvinyl chloride, paper, aluminum, or composites thereof have been used. However, among these, packaging materials manufactured from the above-mentioned resins increase the amount of garbage when discarded, and conventional products have a very low decomposition rate in the natural environment. Will remain in the ground. Discarded plastics also cause problems such as spoiling the landscape and destroying the living environment of marine life.

On the other hand, as a biodegradable polymer of a thermoplastic resin, a hydroxycarboxylic acid polymer or copolymer (hereinafter abbreviated as hydroxycarboxylic acid polymer) is known. In particular, polylactic acid or copolymers of lactic acid and other hydroxycarboxylic acids are 100% biodegradable in the body of animals in months to a year, and when exposed to soil or seawater for several weeks in moist environments. The decomposition product disappears in one to several years after being decomposed, and the decomposed product has the property of being harmless to the human body, such as lactic acid, carbon dioxide, and water.

Polylactic acid is synthesized from a cyclic dimer of lactic acid, usually called lactide.
SP1,995,970, USP2,362,511,
No. 2,683,136. In addition, copolymers of lactic acid and other hydroxycarboxylic acids are usually synthesized from lactide, which is a cyclic dimer of lactic acid, and a cyclic ester intermediate of hydroxycarboxylic acid (eg, glycolide, which is a dimer of glycolic acid). Regarding the method, USP 3,636,956 and USP 3,795
7,499.

However, in order to bury the degradable polymer in the soil when discarding it, it is generally necessary to carry it to a remote landfill, and even if it is landfilled, it takes a considerable amount of time to decompose it. There is no immediate solution to the problem of lack of landfills. Even in the case of treatment by incineration, it is necessary to transfer to a treatment facility, or it is necessary to provide a special incinerator near the source of waste. Furthermore, if these polymers are contaminated with spoiled organic matter or pathogenic microorganisms, special care must be taken to prevent odors and infection in order to transport them to a disposal facility. In particular, if the contaminant is a pathogenic microorganism, incineration is essential because normal landfill treatment will lead to an increase in contamination, but in this case, the monomer that is a component of the polymer is recovered. And the raw material is wasted.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a method for safely decomposing a thermoplastic polymer composition containing a polyhydroxycarboxylic acid-based polymer, particularly a polylactic acid-based polymer as a main component, into a hydroxycarboxylic acid monomer with simple equipment. To provide a method for recovering the hydroxycarboxylic acid from the solution and, if necessary, reusing it as a polymer raw material.

[0007]

Means for Solving the Problems The present inventors diligently studied a method for treating a polymer containing a hydroxycarboxylic acid-based polymer as a main component. As a result, the hydroxycarboxylic acid-based polymer was easily prepared in an alkaline solution having a pH of 10 or more. When the hydroxycarboxylic acid in the polymer has an asymmetric carbon, it is decomposed while maintaining its configuration, and the hydroxycarboxylic acid is recovered from the solution, and if necessary, it is decomposed into monomer units. The present inventors have found that they can be used again as a polymer raw material, and have completed the present invention. According to the present invention, the hydroxycarboxylic acid-based thermoplastic polymer composition is treated and decomposed in an alkaline solution,
An efficient and industrially useful method of recovering hydroxycarboxylic acid from this solution and using it again as a polymer raw material if necessary can be provided. When the hydroxycarboxylic acid in the polymer has an asymmetric carbon, it can be recovered while maintaining its steric configuration, and the ratio of the optically active substance in the polymer can be easily controlled even when used again as a polymer raw material. be able to.

That is, the present invention decomposes a thermoplastic polymer composition containing a polymer or copolymer of hydroxycarboxylic acid as a main component into monomer units in an alkaline solution having a pH of 10 or more. When the compound has an asymmetric carbon, it is decomposed while maintaining its steric configuration, the hydroxycarboxylic acid is recovered from the solution, and the obtained hydroxycarboxylic acid is used again as a polymer raw material if necessary.

The polymer used in the present invention is mainly composed of a hydroxycarboxylic acid-based polymer, and the hydroxycarboxylic acids include lactic acid, glycolic acid, and 3-hydroxycarboxylic acid.
Hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid and the like are used. Hydroxycarboxylic acid-based polymers can be obtained by (1) a method of directly dehydrating polycondensation from hydroxycarboxylic acid, (2) lactide which is a cyclic dimer of lactic acid, or glycolide (GL) which is a cyclic dimer of glycolic acid.
Ring-opening polymerization of a cyclic dimer such as D), (3) ring-opening polymerization of ε-caprolactone (CL) which is a cyclic ester of 6-hydroxycaproic acid such as polycaprolactone, or (4) ) They are obtained by a method of mixing and ring-opening polymerization. When a cyclic material is used as a reaction raw material, it is necessary to convert the recovered hydroxycarboxylic acid into a cyclic material again.

The average molecular weight of the hydroxycarboxylic acid polymer of the present invention is not particularly limited. For applications requiring strength, those having about 10,000 to 1,000,000 are usually used. 1
With a molecular weight of 10,000 or less, the strength is low for forming a film or molded product. On the other hand, when the molecular weight is higher than 1,000,000, the viscosity in the molten state is high and the moldability is poor. The hydroxycarboxylic acid-based polymer is generally added with a known thermoplastic polymer or plasticizer, and further various modifiers, to obtain a thermoplastic polymer composition. The proportion of the hydroxycarboxylic acid-based polymer in the thermoplastic polymer composition is determined by the intended degradability, but is generally preferably 50% or more.

In the present invention, the alkaline solution used for decomposing the thermoplastic polymer composition can be prepared by adding an inorganic base to an aqueous solvent. Examples of the inorganic base include hydroxides, oxides and carbonates of alkali metals such as sodium and potassium, and aqueous solutions or suspensions of hydroxides and oxides of alkaline earth metals such as calcium, magnesium and barium. Suspensions can be used. However, usually, sodium hydroxide or calcium hydroxide is preferred from the economical viewpoint and the recovery of hydroxycarboxylic acid. The pH of the alkaline aqueous solution of the present invention is 10 or more. At a pH of 9 or less, it takes a very long time until the polymer is completely hydrolyzed to a monomer, which is not practical. The concentration of the alkaline solution is not particularly limited, but the higher the concentration, the faster the decomposition is preferable. Usually, it is used at a concentration of 1% or more. The solution can be used repeatedly to decompose the polymer, but if the alkali component in the alkaline solution is consumed by the treatment, the alkali component is added to increase the pH of the solution to pH.
Must be kept at 10 or more. The higher the temperature at which the treatment is performed, the faster the polymer is decomposed, and the temperature is usually 40 ° C. or higher, but is not particularly limited.

The alkaline aqueous solution of the present invention may contain an organic solvent such as alcohol. The hydroxycarboxylic acid in the solution obtained by subjecting the hydroxycarboxylic acid-based polymer to alkali treatment retains the configuration in the polymer even when it has an asymmetric carbon. Medical equipment consisting of a thermoplastic polymer composition mainly composed of hydroxycarboxylic acid polymer used in hospitals, and hydroxycarboxylic acid polymer mainly used for contact with human and animal excrement The substance comprising the thermoplastic polymer composition may be contaminated with a pathogenic substance, and special consideration is required when disposing the substance. However, in the treatment method of the present invention, a contaminant such as a pathogenic microorganism is used. Is used as a suitable treatment method because there is no possibility that the pathogenic microorganisms will be killed and the contamination spread at the same time as the polymer is decomposed.

The treatment of the present invention can be carried out by placing an alkaline solution in an ordinary tank or a stirring tank or the like while heating, or by charging a polymer molding as it is and keeping it for a predetermined time. The polymer molded product to be charged may be as it is or may be finely crushed or pulverized.

In the method of the present invention, the following method can be used to recover the hydroxycarboxylic acid from the decomposed solution. (1) Sodium hydroxide decomposition-electrodialysis method When an aqueous solution of sodium hydroxide is used as the alkaline solution, an aqueous solution of hydroxycarboxylic acid can be efficiently obtained by using electrodialysis. Electrodialysis is performed by a device equipped with an ion exchange membrane and electrodes. The device is All
Aquatech etc. of ied company, Nafion membrane (Du Pont company name), Cell as ion exchange membrane
Mion film (trade name of Asahi Glass Co., Ltd.) is exemplified. In this case, the higher the concentration of the hydroxycarboxylate solution supplied to the electrodialysis device is, the higher the efficiency is. If the concentration of the solution treated with the alkaline solution is low, the concentration should be increased beforehand. Is good. Preferably, the treatment with the alkaline solution is performed in advance so that the concentration of the hydroxycarboxylate is increased. (2) Calcium hydroxide decomposition-crystallization method When the hydroxycarboxylic acid of the present invention is lactic acid,
An aqueous calcium hydroxide solution or suspension is used as the alkaline solution. When calcium hydroxide is used, calcium lactate can be efficiently isolated from the solution after decomposition. For example, the polymer is added to an aqueous suspension of calcium hydroxide and the polymer is completely decomposed at 50-100 ° C. under stirring. Unreacted calcium hydroxide is removed from the solution after decomposition by filtration or the like. The precipitated calcium lactate is once separated by cooling the filtrate. Next, after dissolving the calcium lactate in water again, sulfuric acid equivalent to calcium is added to the aqueous solution to release lactic acid, and the precipitated calcium sulfate is removed by filtration. Thus, an aqueous lactic acid solution containing almost no calcium can be obtained. The obtained hydroxycarboxylic acid solution or lactic acid aqueous solution contains trace amounts of cations such as sodium and calcium, and anions such as sulfate ions. If a high-purity product is required, the product is further purified with an ion exchange resin or the like. You can also.

However, since the method of the present invention is usually carried out at a relatively low temperature, there are few by-products in the decomposition and recovery steps, and the hydroxycarboxylic acid can be recovered with high purity.
Therefore, the obtained hydroxycarboxylic acid can be used again as a polymer raw material without particular purification.
Furthermore, when the hydroxycarboxylic acid has an asymmetric carbon, it can be recovered as a hydroxycarboxylic acid monomer while maintaining the steric configuration in the polymer. It is easy to control the ratio of the active form. For example, from a polymer of L-lactic acid, almost pure L
-Lactic acid is obtained, and the polylactic acid synthesized using this L-lactic acid contains almost no D-lactic acid.

[0016]

The method of measuring the molecular weight and analyzing the DL composition according to the present invention will be described below. (1) Method for measuring molecular weight. The weight average molecular weight of the polymer was measured by gel permeation chromatography using polystyrene as a standard under the following conditions. Apparatus: Shimadzu LC-10AD Detector: Shimadzu RID-6A Column: Hitachi Chemical GL-S350DT-5, GL-S3
70DT-5 Solvent: chloroform Concentration: 1% Injection volume: 20 μl Flow rate: 1.0 ml / min (2) Method for analyzing DL composition of lactic acid. The polymer was hydrolyzed by holding the polymer in a 5N sodium hydroxide solution at 60 ° C. for 10 hours, and L-lactic acid in the obtained solution was converted to L-lactic acid.
Lactate dehydrogenase and nicotinamide adenine dinucleotide (hereinafter abbreviated as NAD) are acted on, and the amount of NADH, which is a reduced form of NAD, produced when lactic acid is oxidized to pyruvate is quantified by absorption spectrometry. -Lactic acid was quantified, and D-lactic acid was similarly treated with D-lactate dehydrogenase and NAD to determine the amount of D-lactic acid, and the ratio of L-lactic acid to D-lactic acid was calculated. In addition, it was confirmed that L-lactic acid itself was kept in a 5N sodium hydroxide solution for 10 hours and racemicization of lactic acid did not occur under hydrolysis conditions. First, the polymer used in the examples and the method for producing the film thereof will be described.

Production Example 1 216 g (1.5 mol) of L-lactide, 0.01% by weight of tin octoate and 0.03% of lauryl alcohol
% By weight was charged into a thick cylindrical stainless steel polymerization vessel equipped with a stirrer, degassed under vacuum for 2 hours, and then replaced with nitrogen gas. The mixture was stirred at 200 ° C. under a nitrogen atmosphere.
For 3 hours. While maintaining the temperature as it is, slowly deaerate with a vacuum pump through an exhaust pipe and a glass receiver, reduce the pressure in the reaction vessel to 3 mmHg, react for 1 hour from the start of deaeration, and distill monomer and low molecular weight volatile components. I went out. The inside of the container was replaced with nitrogen, and the poly-L-lactic acid obtained from the lower portion of the container was extracted in a string form, and cut into pellets. The average molecular weight of the pelletized polymer was Mw = 100,000, and the composition ratio of L-lactic acid and D-lactic acid was 99.5: 0.5.

Production Example 2 216 g of L-lactide was added to 172 g of L-lactide and D
Pelletization was performed in the same manner as in Production Example 1 except that L-lactide was changed to 44 g to obtain polylactic acid. The average molecular weight of this polymer was Mw = 100,000.

Production Example 3 The procedure of Production Example 1 was repeated except that 216 g of L-lactide was changed to 108 g of L-lactide and 108 g of glycolide.
A pellet of the L-lactide-glycolide copolymer was obtained. The average molecular weight of the obtained pellet was Mw = 100,0.
00.

Production Example 4 216 g of L-lactide was combined with 108 g of L-lactide and ε.
-A pellet of L-lactide-ε-caprolactone copolymer was obtained in the same manner as in Production Example 1 except that the amount was changed to 108 g of caprolactone. The average molecular weight of the obtained pellet was Mw =
70,000.

Production Example 5 10.0 kg of 90% L-lactic acid was added at 150 ° C./50 mmHg.
After distilling water while stirring for 3 hours, 6.2 g of tin powder was obtained.
Was added, and the mixture was further stirred at 150 ° C./30 mmHg for 2 hours to oligomerize. 28.8 g of tin powder was added to this oligomer.
And 21.1 kg of diphenyl ether,
An azeotropic dehydration reaction was performed at 35 mmHg, and distilled water and the solvent were separated by a water separator, and only the solvent was returned to the reactor. After 2 hours, the organic solvent to be returned to the reactor was passed through a column filled with 4.6 kg of molecular sieve 3A, and then returned to the reactor. The reaction was carried out at 150 ° C./35 mmHg for 40 hours, and the average molecular weight Mw = 110,000 Was obtained. The solution was diluted by adding 44 kg of dehydrated diphenyl ether, cooled to 40 ° C., and the precipitated crystals were filtered, washed three times with 10 kg of n-hexane, and washed at 60 ° C. /
Dry at 50 mmHg. This powder is mixed with 0.5N-HCl
12. After adding 1 kg of ethanol and 12.0 kg of ethanol, the mixture was stirred at 35 ° C. for 1 hour, filtered, and dried at 60 ° C./50 mmHg to obtain 6.1 kg of polylactic acid powder (yield: 85%).
This powder was processed by a pelletizer to form a pellet and used in the following tests. The average molecular weight of the obtained polymer is Mw
= 110,000, and the composition ratio of L-lactic acid to D-lactic acid was 98.5: 1.5.

Production Example 6 10.0 kg of 90% L-lactic acid was replaced with 9.0 kg of 90% L-lactic acid.
g and 70% glycolic acid were changed to 1.3 kg, and polymerization and pelletization were carried out in the same manner as in Production Example 5 to obtain a copolymer of L-lactic acid and glycolic acid. The average molecular weight of this polymer was Mw = 100,000. The film used in the following examples was prepared by dissolving the polymers obtained in Production Examples 1 to 6 in chloroform so as to have a concentration of about 10 to 20%, coating the solution on a glass plate, and drying at 60 ° C. under reduced pressure. This is a film having a thickness of 25 to 30 μ obtained as described above.

Example 1 The polymer obtained in Production Example 1 was 150 mm long and 15 mm wide.
A film having a thickness of 0 mm and a thickness of 30 μm was placed in 50 ml of a 4% aqueous sodium hydroxide solution and kept at 60 ° C. for 1 hour.
The film completely dissolved and disappeared. The pH of this solution is 12
As described above, as a result of analysis of the reaction solution by HLC, it was found that lactic acid was produced in an amount equivalent to the lactic acid unit in the polymer.

Example 2 The same operation as in Example 1 was performed except that the polymer of Production Example 2 was used instead of the polymer of Production Example 1. The film completely dissolved and disappeared. The pH of this solution was 12 or more, and as a result of analysis of the reaction solution by HLC, it was found that lactic acid units were produced in an amount substantially equivalent to the lactic acid units in the polymer.

Example 3 The same operation as in Example 1 was performed except that 5% calcium hydroxide was used instead of 4% sodium hydroxide. When the mixture was filtered through a 10-mesh sieve, no film retaining its shape was found. The pH of this solution was 12 or more, and as a result of analysis of the reaction solution by HLC, it was found that lactic acid units were produced in an amount substantially equivalent to the lactic acid units in the polymer.

Example 4 150 mm in length and 15 in width obtained from the polymer of Production Example 3
A film having a thickness of 0 mm and a thickness of 25 μm was placed in 50 ml of 5% aqueous ammonia and kept at 40 ° C. for 5 hours. The film completely dissolved and disappeared. The pH of this solution was 12 or more, and as a result of analysis of the reaction solution by HLC, lactic acid and glycolic acid were formed in approximately equivalent amounts to lactic acid units and glycolic acid in the polymer.

Example 5 A film having a thickness of 25 μm obtained from the polymer of Production Example 4 and measuring 150 mm × 150 mm was placed in 50 ml of 10% potassium hydroxide and kept at 60 ° C. for 5 hours. The film completely dissolved and disappeared. The pH of this solution was 12 or more. As a result of analysis of the reaction solution by HLC, lactic acid units and ε-caproic acid almost equivalent to lactic acid units and
-Caproic acid had formed.

Example 6 Escherichia coli adhered to a 30 μm thick film obtained from the polymer of Production Example 1 having a size of 150 mm × 150 mm was placed in 50 ml of a 4% aqueous sodium hydroxide solution.
C. for 5 hours. The film completely dissolved and disappeared.
The pH of this solution was 12 or more. As a result of analysis of the reaction solution by HLC, it was found that lactic acid units were produced in an amount equivalent to the lactic acid units in the polymer. Escherichia coli was not detected in the solution after the treatment.

Example 7 200 g of the polymer pellets of Production Example 5 were kept in 1 liter of a 5N aqueous sodium hydroxide solution at 80 ° C. for 2 hours. The pH of the solution was always 12 or more, and the pellet completely dissolved and disappeared. When a part of this solution was analyzed by HLC, it was found that lactic acid units were formed in an amount equivalent to lactic acid units in the polymer. The ratio of L-lactic acid to D-lactic acid in the solution was 98.
5: 1.5, and the configuration of the asymmetric carbon of lactic acid in the polymer was retained.

Next, 600 ml of the obtained hydrolysis solution was used.
Dialysis membrane, effective area 9cm ^Two Sellemio
Using an n-type CMR cation exchange membrane (made by Asahi Glass),
Using a cell with poles and cathodes, add polymer to the anode compartment.
Add the water splitting solution and add sodium hydroxide to the cathode compartment
And electrodialysis while circulating the solution to obtain a concentration of 4
552 g of a 3% L-lactic acid solution was obtained. The yield is 95% (for
Polymer equivalent). Concentrate this solution for polymerization
Lactic acid. Lactic acid monomer recovered in this way
And the polymerization was performed in the same manner as in Production Example 6.
As a result, a polymer having an average molecular weight Mw = 100,000 was obtained.
Was.

Comparative Example 1 20 g of the polymer pellets of Production Example 5 were adjusted to a pH of 9 with a 1N sodium hydroxide solution and 1N hydrochloric acid to obtain a 100 m solution.
and kept at 80 ° C. for 2 hours. Most of the 15 g pellets retained their shape. A portion of the solution was quantified by HLC and found to contain 1 g of lactic acid. The ratio of L-lactic acid to D-lactic acid in the solution was 98.6: 1.
It was 4.

Example 8 200 g of the polymer pellets of Production Example 6 were kept at 80 ° C. for 2 hours in 1 L of a 5N aqueous sodium hydroxide solution. The pellet was completely dissolved. This solution was concentrated to 600 ml, and subjected to decomposition electrodialysis with the same device as in Example 7, to obtain a solution of 540 g containing 217 g of L-lactic acid and 24 g of glycolic acid. The solution was concentrated and polymerized in the same manner as in Production Example 6 to obtain a polymer having an average molecular weight of 90,000.

Example 9 100 g of the polymer pellets of Production Example 1 were added to 1 liter of a 10% calcium hydroxide suspension and kept at 80 ° C. for 2 hours.
The pH of the solution was always 12 or more, and the pellet completely dissolved and disappeared. As a result of HLC analysis of the filtrate from which the insolubles of calcium hydroxide were removed by filtration, almost equivalent lactic acid was generated in the lactic acid unit in the polymer, and the ratio of L-lactic acid to D-lactic acid was 99. At 5: 0.5, the configuration of lactic acid in the polymer was retained. The solution was concentrated and allowed to stand at 10 ° C. overnight, and the precipitated calcium lactate crystals were isolated by filtration. The same amount of water was added to the obtained crystals and dissolved at 65 ° C., and 98% sulfuric acid was added in the same amount as calcium to the solution to release lactic acid, and the precipitated calcium sulfate was filtered. The filtrate was concentrated under reduced pressure to obtain an 88% L-lactic acid aqueous solution. The yield was 84%. The solution was concentrated and polymerized in the same manner as in Production Example 6, resulting in an average molecular weight of 10
000 polymer was obtained.

[0034]

According to the treatment method of the present invention, by-products in the decomposition and recovery steps are small, and hydroxycarboxylic acid can be recovered with high purity. Therefore, the obtained hydroxycarboxylic acid can be used again as a polymer raw material without particular purification. Furthermore, when the hydroxycarboxylic acid has an asymmetric carbon, it can be recovered as a hydroxycarboxylic acid monomer while maintaining the steric configuration in the polymer. The proportion of actives can be controlled.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-313377 (JP, A) JP-A-63-115845 (JP, A) US Patent 4,853,387 (US, A) (58) Fields studied (Int .Cl. ⁷ , DB name) C08J 11/10-11/16 C07C 51/09 C07C 59/01

Claims (7)

(57) [Claims] 1. A thermoplastic polymer composition based on a polymer or copolymer of a hydroxycarboxylic acid,
A method comprising decomposing in an alkaline solution having a pH of 10 or more and recovering hydroxycarboxylic acid from the solution. 2. When the hydroxycarboxylic acid has an asymmetric carbon, it decomposes while maintaining the configuration in the polymer,
2. The method according to claim 1, wherein the method comprises recovering. 3. The method according to claim 2, wherein the hydroxycarboxylic acid is lactic acid. 4. The method of claim 1, wherein the thermoplastic polymer composition is contaminated with contaminants. 5. A thermoplastic polymer composition based on a hydroxycarboxylic acid polymer or copolymer,
pH10 was decomposed with more sodium hydroxide solution, a method for recovering a hydroxycarboxylic acid of claim 1, wherein the recovered by electrodialysis hydroxycarboxylic acid from the solution. 6. Decomposing a thermoplastic polymer composition containing a lactic acid polymer as a main component in a calcium hydroxide solution having a pH of 10 or more, separating calcium lactate from the solution, and adding sulfuric acid to the calcium lactate. method of recovering lactic acid of claim 1, wherein the recovering is converted to lactic acid by. 7. A thermoplastic polymer composition based on a hydroxycarboxylic acid polymer or copolymer,
decomposes at pH10 or more alkaline solution, the solution hydroxycarboxylic acid is recovered from the in process of claim 1 wherein the resulting hydroxycarboxylic acid is characterized by using as the polymeric material.