JP4986244B2 - Method for recovering lactide from flame retardant lactic acid polymer composition - Google Patents

Description

The present invention relates to a method for recovering and producing lactide, which is a cyclic dimer of lactic acid, by depolymerizing a lactic acid polymer from a lactic acid polymer composition containing a phosphorus-based flame retardant.

In recent years, it has been pointed out that halogen compounds, which have been widely used as flame retardants for plastic materials used in electrical and electronic equipment products, may generate dioxins when materials are incinerated. Therefore, the conversion to non-halogen flame retardants is progressing. Among them, there is an increasing demand for phosphorus-based flame retardants that exhibit a flame retardant function by promoting dehydration reaction and formation of a flame retardant layer, and metal hydroxide flame retardants that have a large decomposition heat absorption and are safe. Recently, however, there is a growing concern that flame retardant materials inhibit combustion upon disposal.

On the other hand, because of the problem of global warming due to the increase in carbon dioxide gas, lactic acid polymers synthesized from biomass, which is a renewable resource, and biorecyclable and chemically recyclable instead of plastic materials synthesized from fossil fuels Has been actively deployed. The advantage of using lactic acid polymer is that carbon neutral gas has a very small increase throughout the entire process even if it is incinerated because lactic acid polymer is synthesized from biomass with carbon dioxide fixed. Supported by thinking. In addition, depolymerization-type chemical recycling, which efficiently reduces to raw materials, is a measure to return to the original raw material with very little energy, and as an environmental measure, it is a measure that goes one step further from the concept of carbon neutral.

As a method for producing a lactic acid polymer, a technique of synthesizing lactide from a lactic acid oligomer by thermal decomposition and then polymerizing the lactide is well known. In this manufacturing process, it is important to maintain optical purity. This is because a practical lactic acid polymer is produced by ring-opening polymerization of optically active L, L-lactide and is a transparent and high-strength polymer having a melting point of about 175 ° C. This is because it causes a significant decrease and loses its practicality.

Methods for using a phosphorus-based flame retardant as a flame retardant to make a lactic acid polymer synthesized from renewable resources flame retardant are already known, for example, in Patent Documents 1 to 3. Moreover, the method of utilizing a metal hydroxide type flame retardant is already known by patent document 4 and 5, for example. However, since flame retardancy aims to suppress the combustion of lactic acid polymer and thermal decomposition at high temperature, the policy to recover lactide as raw material by depolymerization of lactic acid polymer in the flame retardant composition It has not been studied in the past. In recent years, when aluminum hydroxide, which is a metal hydroxide flame retardant, is used, it has been found that aluminum hydroxide itself acts as a depolymerization catalyst for lactic acid polymers (Non-patent Document 1). A chemical recycling technique for a flame retardant lactic acid polymer composition is disclosed (Patent Document 6). However, it has been pointed out that aluminum hydroxide needs to be added in a large amount in order to exhibit sufficient flame retardancy, and the specific gravity of the composition increases. On the other hand, regarding phosphorus-based flame retardants, the chemical recyclability of lactic acid polymers from a flame-retardant composition of phosphorus-based flame retardants and lactic acid polymers has never been studied or reported so far.
JP 2004-175831 A Japanese Patent Laying-Open No. 2005-089546 JP 2005-162872 A JP 2003-192929 A JP 2004-075752 A International Publication No. 2005/105775 Pamphlet Nishida, Sakai, Mori, Daiyagi, Shirai, Endo "Industrial & Engineering Chemistry Research, Vol. 44, No. 4, 1433-1437 (2005)"

Various catalysts have been found in recovering the starting lactide by thermal decomposition of lactic acid polymers. For example, as a catalyst for recovering lactide from lactic acid oligomers, Non-Patent Document 2 discloses the catalytic properties of Sn compounds, and Non-Patent Document 3 discloses the catalytic properties of Al, Ti, Zn, and Zr compounds. Patent Document 7 also uses an alkali metal salt and a metal from Group 4 to Group 15 of the periodic table and / or a salt thereof in combination with a lactide having a low optical purity from a lactic acid oligomer (meso form content 7 to 40%). A technique for obtaining the above is disclosed. As a method for recovering high-purity lactide from a high molecular weight lactic acid polymer, Patent Document 8 discloses a method using an alkaline earth metal compound as a catalyst. Patent Document 9 discloses that an alkaline earth metal, for example, magnesium oxide, functions as a catalyst for providing a high optical purity lactide for recovering lactide from high molecular weight polylactic acid. However, there have been no studies on the combination of phosphorus-based flame retardants and depolymerization catalysts, and none of the literature describes the effects and effects of the presence of phosphorus-based flame retardants. It has not been.
Noda, Okuyama, Shimazu Review, 56, 83 (1999) Noda, Okuyama, Shimazu Review, 56, 169 (2000) JP-A-6-279434 International Publication No. 2003/91238 Pamphlet JP 2008-231048 A

As a system in which a phosphorus-based flame retardant and an alkaline earth metal compound coexist, Patent Document 10 has an effect of promoting the generation amount of an adiabatic carbonized layer at the time of combustion by causing fatty acid magnesium and polyphenol to coexist with a phosphorus-based flame retardant. It is disclosed. Patent Document 11 discloses a technique used as a neutralizing agent for phosphoric acid produced by decomposition of a phosphorus-based flame retardant by blending an alkaline earth metal compound. However, the alkaline earth metal compound used here is blended in the lactic acid polymer composition and is not added immediately before the decomposition reaction as a catalyst for decomposing the lactic acid polymer after use. That is, none of these documents specifically disclose lactide recovery techniques.
JP 2005-350537 A JP 2006-16446 A

As described above, conventionally, regarding a composition comprising a lactic acid polymer containing a phosphorus-based flame retardant, there is no technical disclosure of recovering high optical purity lactide from the lactic acid polymer in the composition. This is because the decomposition combustion suppression called flame retardancy and the decomposition promotion control called chemical recycling are conceptually incompatible. Under such circumstances, in order to apply lactic acid polymers produced from renewable resources to, for example, electrical and electronic equipment parts and rationally carry out chemical recycling, they are made flame retardant and efficient. There has been a demand for a new technique for achieving both high optical purity lactide recovery.

In order to chemically recycle a flame-retardant lactic acid polymer composition containing a phosphorus-based flame retardant, the present invention selectively depolymerizes a lactic acid polymer containing a phosphorus-based flame retardant to efficiently produce high optical purity lactide. It aims at providing the method of collect | recovering and manufacturing automatically.

As a result of earnest research on the combination of a phosphorus-based flame retardant and a catalyst for depolymerization in a lactic acid polymer composition, the present inventors have found that a combination of a phosphorus-based flame retardant and an alkaline earth metal oxide catalyst. In the case of chemical recycling, the phosphorus flame retardant does not decompose and can be easily separated from lactide which is a depolymerization product of lactic acid polymer, and furthermore, the presence of the phosphorus flame retardant makes it a lactic acid polymer with an alkaline earth metal oxide. The present inventors have found an unexpected effect that the decomposition of is promoted, and have reached the present invention.

An object of the present invention is to recover an alkaline earth metal compound in an amount of 0.1 to 100 parts by weight per 100 parts by weight of a lactic acid polymer component in a lactic acid polymer composition containing a phosphorus-based flame retardant. It is achieved by a method characterized by adding 10 parts by weight, heating to a temperature of 200 to 350 ° C., and recovering lactide having a high optical purity obtained by depolymerization of the lactic acid polymer.

According to the present invention, (1) by adding an alkaline earth metal compound, the decomposition temperature of the lactic acid polymer can be separated from the decomposition temperature of the phosphorus flame retardant, which is another component, and the coexisting general-purpose resin. Can be selectively recycled. (2) Since the lactic acid polymer can be selectively decomposed and removed, other components, phosphorus flame retardant, general-purpose resin, or a mixture of phosphorus flame retardant and general-purpose resin can be recovered and reused. The utility value is very large as a recycling method.

The present invention is a method of recovering lactide by thermally decomposing a mixture of a lactic acid polymer composition containing a phosphorus-based flame retardant and an alkaline earth metal compound at a temperature higher than the melting temperature of the lactic acid polymer. Means a polymer (homopolymer or copolymer) containing a lactic acid ester structure as a main unit as a main unit as described below, and the lactic acid polymer composition refers to such a polymer and other resin components or various types It means a mixture with additives. As the lactic acid polymer composition, if the lactic acid polymer component is 10% by weight or more, selective chemical recycling is possible without any problem. However, considering practical operation efficiency, the lactic acid polymer composition is preferably 20% by weight or more.

In the present invention, the lactic acid polymer is a polymer having a lactic acid ester structure as a basic unit, and in particular, the L- or D-lactic acid ester structure unit is 90% or more, preferably 95% or more, more preferably 98% of all units. The above polymer. As components other than the L- or D-lactic acid ester structural unit, there may be a copolymer component unit derived from lactones, cyclic ethers, cyclic amides, cyclic acid anhydrides and the like copolymerizable with lactide. Is possible. Suitable copolymerization components include lactones such as caprolactone, valerolactone, β-butyrolactone, and baradioxanone; cyclic ethers such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, phenylglycidyl ether, oxetane, and tetrahydrofuran; cyclic amides such as ε-caprolactam; cyclic acid anhydrides such as succinic anhydride and adipic anhydride.

Furthermore, as initiator components, alcohols, glycols, glycerols, other polyhydric alcohols, carboxylic acids, polycarboxylic acids, phenols, etc. are used as units that can coexist in the lactic acid polymer of the present invention. It is done. Specific examples of suitably used initiator components include ethylhexyl alcohol, ethylene glycol, propylene glycol, butanediol, polyethylene glycol, polypropylene glycol, polyvinyl alcohol, glycerin, octylic acid, lactic acid, glycolic acid and the like.

The phosphorus-based flame retardant used in the present invention is not particularly limited, and generally used phosphorus-based flame retardants can be used. Typically, organic phosphorus compounds such as phosphate esters and polyphosphates are used. Or red phosphorus. Among these phosphorus-based flame retardants, phosphate esters and derivatives thereof among organic phosphorus compounds are preferably used from the viewpoint of ease of handling and compatibility with lactic acid polymers.

Specific examples of the phosphate ester in the above organic phosphorus compound include trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri (
2-ethylhexyl) phosphate, tributoxyethyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, tris (
Isopropylphenyl) phosphate, tris (phenylphenyl) phosphate, trinaphthyl phosphate, cresyl diphenyl phosphate, xylenyl diphenyl phosphate, diphenyl (
2-ethylhexyl) phosphate, di (isopropylphenyl) phenyl phosphate, monoisodecyl phosphate, 2-acryloyloxyethyl acid phosphate, 2
-Methacryloyloxyethyl acid phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, melamine phosphate, dimelamine phosphate, melamine pyrophosphate, triphenylphosphine oxide, tricresylphosphine oxide, methanephosphonic acid Non-condensable phosphoric acid such as diphenyl, diethyl phenylphosphonate, resorcinol polyphenyl phosphate, resorcinol poly (di-2,6-xylyl) phosphate, bisphenol A-polycresyl phosphate, hydroquinone poly (2,6-xylyl) phosphate Mention may be made of condensed phosphate esters such as esters and their condensates. Examples of commercially available condensed phosphate esters include P manufactured by Daihachi Chemical Co.
X-200, PX-201, PX-202, CR-733S, CR-741, CR-747 and the like can be mentioned.

The mixing amount of the phosphorus flame retardant with respect to the lactic acid polymer composition is suitably 5 to 30 parts by weight, and more preferably 10 to 25 parts by weight with respect to 100 parts by weight of the lactic acid polymer composition. If the amount is less than 5 parts by weight, the effect as a flame retardant is small.

In the present invention, when a lactic acid polymer composition containing a phosphorus-based flame retardant having a lower boiling point than lactide is used, the phosphorus-based flame retardant can also be recovered simultaneously with the recovery of lactide. Non-condensation types such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri (2-ethylhexyl) phosphate, tributoxyethyl phosphate, triphenyl phosphate among the above flame retardants as phosphorus-based flame retardant having a lower boiling point than lactide Phosphate esters are applicable.

These non-condensed phosphates are vaporized and recovered prior to or simultaneously with lactide in the chemical recycling process. In the case of vaporizing prior to lactide, non-condensable phosphate ester and lactide can be separated and recovered by using another vent port, when implemented using an extruder provided with a vent port described later. In the case of simultaneous vaporization, first, lactide and non-condensable phosphate ester are collected as a mixture, and then separated by a crystallization operation using the high crystallinity of lactide as shown in Example 5 described later. Can do. In the crystallization operation, a mixture of lactide and a non-condensable phosphate ester is dissolved as it is or in an appropriate solvent, and lactide is precipitated as crystals by a temperature raising method and / or a concentration method, and thereafter, a generally known solid solution is obtained. Separation can be performed using a liquid separation means, for example, a method such as filtration or centrifugation. Solvents used for the crystallization operation include aromatic solvents such as toluene, xylene and ethylbenzene; ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as methyl isobutyl ether and tetrahydrofuran; alcohol solvents such as methanol and ethanol. Preferably used. Depending on the type of non-condensable phosphate ester, it may show higher crystallinity than lactide. In that case, the non-condensable phosphate ester can be crystallized first and separated from lactide by the same method. It is.

The alkaline earth metal compound used in the present invention need not be special. Commonly known alkaline earth metal compounds include calcium compounds, magnesium compounds, barium compounds and the like, and oxides, hydroxides, carbonates, salts with organic acids, and the like are preferably used. A mixture of these may also be used. Preferably, a calcium compound and a magnesium compound are preferably used because of their availability. More preferably, magnesium oxide is suitably used from the viewpoint of the thermal decomposition reaction selectivity.

As the oxide of magnesium which is the catalyst most suitably used in the present invention, any magnesium oxide generally produced from seawater or ore can be used without any particular limitation. Examples of magnesium oxide that can be suitably used include light-burned magnesia, heavy-burned magnesia, and electrofused magnesia.

In the present invention, the alkaline earth metal compound is added in an amount of 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight, per 100 parts by weight of the lactic acid polymer component in the lactic acid polymer composition containing the phosphorus flame retardant. It is done.

In the present invention, a mixture of a lactic acid polymer composition containing a phosphorus-based flame retardant and an alkaline earth metal compound is thermally decomposed in a temperature range from the melting temperature of the lactic acid polymer to 350 ° C., preferably from 200 to 350 ° C. , High optical purity lactide is selectively recovered. Below the melting temperature of the lactic acid polymer, the thermal decomposition of the lactic acid polymer hardly proceeds, and at a temperature exceeding 350 ° C., the lactic acid ester structural unit in the lactic acid polymer tends to racemize, resulting in the formation of meso-lactide. Increases and the optical purity of the resulting lactide decreases. The preferred temperature range is 200 to 350 ° C., and more preferably, the optimum temperature range according to the thermal and reaction characteristics of the phosphorus flame retardant and the alkaline earth metal compound is used.

For example, in the case of a condensed phosphate ester flame retardant, the temperature range is 200 to 300 ° C. Moreover, in the case of a non-condensation type | mold phosphate ester type flame retardant, it is the temperature range of 300-350 degreeC. This temperature range also depends somewhat on the molecular weight of the lactic acid polymer. Generally, a polymer having a lower molecular weight tends to progress in a lower temperature region. However, racemization of lactic acid ester structural units becomes significant at temperatures exceeding 350 ° C. regardless of molecular weight. Such knowledge about the decomposition action and temperature-dependent decomposition characteristics of the phosphorus-based flame retardant, the alkaline earth metal compound, and the lactic acid polymer has been found for the first time in the present invention.

As already described as the background art of the present invention, the lactic acid polymer and phosphorus flame retardant composition itself is known as a flame retardant composition. However, as will be described in detail in Examples below, the temperature range where the lactic acid polymer composition is actually exposed during combustion (about 650 ° C. or more even in the case of cigarette fire, and flame is said to be 1200 ° C. or more) The temperature ranges to be controlled are very different, and the types of reactions that proceed in each temperature range are also different. Therefore, it has not been known at all how the phosphorus flame retardant affects the reaction during chemical recycling of the lactic acid polymer. By adding an alkaline earth metal compound that is a decomposition catalyst, a lactic acid polymer is selectively converted into lactide that is a raw material monomer without substantial influence of a phosphorus-based flame retardant, and it is possible to recover lactide with extremely high optical purity. This fact has been found for the first time in the present invention.

Further, as described in the background art of the present invention, a technique for reducing a lactic acid polymer to lactide by the catalytic action of an alkaline earth metal compound is already known. However, when a phosphorus-based flame retardant coexists, a technology for separating and selectively depolymerizing a phosphorus-based flame retardant and a lactic acid polymer has not yet been disclosed, and further, as described in the examples described later, a phosphate ester A new function that the type flame retardant promotes the depolymerization activity of calcium oxide was first found in the present invention.

In the method of the present invention, even if the mixture of the lactic acid polymer composition and the phosphorus-based flame retardant to be subjected to chemical recycling is a mixture of only the lactic acid polymer and the phosphorus-based flame retardant, other practical properties are imparted. Therefore, a so-called resin composition in which other general-purpose resins, reinforcing fibers, fillers, additives, and the like coexist may be used. As components that can coexist, it is necessary to prevent the flame retardant function of the phosphorus-based flame retardant during combustion and not to prevent chemical recycling of the lactic acid polymer.

Other general-purpose resins for imparting practical physical properties include, for example, polyolefins such as polyethylene and polypropylene; styrene resins such as polystyrene, ABS and AS; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate ( PC), PC / ABS, PC / AS, and other polycarbonate resins; polyvinyl alcohol, polyethylene vinyl alcohol, and other vinyl alcohol resins; modified polyphenylene ether, polyamide, polyoxymethylene, and other engineering plastics; butadiene rubber, styrene-butadiene Rubbers for improving impact resistance such as rubber, isoprene rubber, acrylonitrile-butadiene rubber; polyhydroxybutyrate, polyhydroxyalkanoate, polytetramethylene Shineto, polytetramethylene succinate adipate, polycaprolactone, polyglycolic acid, polyparadioxanone, acetyl cellulose, poly -γ- glutamic acid, etc. biodegradable modifiers such as polylysine is preferably used. The amount of these resins added can be appropriately selected according to the physical properties required for the product physical properties, but is generally 900 parts by weight or less, preferably 400 parts by weight or less, based on 100 parts by weight of the lactic acid polymer. More preferably, it is 100 parts by weight or less. These resins are usually melted during chemical recycling of the lactic acid polymer composition, and material recycling is performed by re-pelletizing.

The reinforcing fibers and fillers are not particularly limited, and known reinforcing fibers and fillers are used without any limitation. Examples of the fibers that are preferably used include, for example, glass fibers, carbon fibers, Cellulose fibers derived from plants such as kenaf and the like, and fillers that are preferably used include glass microbeads, chalk, quartz, feldspar, mica, talc, silicate, kaolin, zeolite, alumina, silica, Inorganic fillers such as magnesia, ferrite, barium sulfate, calcium carbonate; organic fillers such as epoxy resin, melamine resin, urea resin, acrylic resin, phenol resin, polyimide resin, polyamide resin, unsaturated polyester resin, perfluoro resin, etc. These fillers can be used alone or in combination of two or more. It may also be used. The addition amount of these fillers can be appropriately selected according to the physical properties required for the product, but is generally 200 parts by weight or less, preferably 100 parts by weight or less with respect to 100 parts by weight of the lactic acid polymer composition. More preferably, it is 50 parts by weight or less.

Other additives that can coexist in the lactic acid polymer composition include flame retardants other than phosphorus flame retardants, hydrolysis inhibitors, crystallization accelerators, lubricants, UV absorbers, antioxidants, mold release agents, and compatibilizers. Agents, antistatic agents and the like. These additives can be added within a range that does not significantly affect the flame retarding action of the phosphorus-based flame retardant and the chemical recycling of the lactic acid polymer by the alkaline earth metal compound. 5 parts by weight or less, preferably 3 parts by weight or less based on parts. Flame retardants other than phosphorus flame retardants include metal hydroxide flame retardant compounds such as aluminum hydroxide; boric acid flame retardant compounds; metal sulfate compounds, antimony compounds, iron oxide compounds, metal nitrate compounds, Inorganic flame retardant compounds such as titanium compounds, zirconium compounds, molybdenum compounds, aluminum compounds; nitrogen flame retardant compounds such as cyanurate compounds having a triazine ring; silicone oil, low melting glass, organosiloxane, etc. Silica flame retardant compounds; colloidal flame retardant compounds such as magnesium hydroxide, calcium hydroxide and calcium aluminate are used.

As a hydrolysis inhibitor that can coexist in the lactic acid polymer composition, a known hydrolysis inhibitor having a function of suppressing hydrolysis of the lactic acid polymer can be used without any limitation. The hydrolysis inhibitors preferably used are carbodiimide compounds, isocyanate compounds, and oxazoline compounds, and the addition amount of these hydrolysis inhibitors is 5 parts by weight with respect to 100 parts by weight of the lactic acid polymer composition. The amount is preferably 3 parts by weight or less, more preferably 1 part by weight or less.

The lactic acid polymer composition containing a phosphorus flame retardant can be applied to various uses. For example, by using this resin composition, molded articles such as casings of electric / electronic devices such as radios, microphones, televisions, keyboards, portable music players, mobile phones, personal computers, and various recorders can be obtained. It can also be used for applications such as automobile interior parts, various packing materials, and various decorative sheets. Examples of molding methods for these molded products include film molding, sheet molding, extrusion molding, and injection molding. Among them, injection molding is preferably used for molding electrical / electronic device product parts. More specifically, the extrusion molding can be performed according to a conventional method, for example, using a known extrusion molding machine such as a single-screw extruder, a multi-screw extruder, or a tandem extruder. The injection molding can be performed according to a conventional method using a known injection molding machine such as an in-line screw injection molding machine, a multilayer injection molding machine, or a two-head injection molding machine.

In the present invention, when recovering lactide, a method for adding and mixing a lactic acid polymer composition containing a phosphorus-based flame retardant and an alkaline earth metal compound is not particularly limited and can be used. . The important point in the present invention is that the alkaline earth metal compound is considered to be an essential factor that the alkaline earth metal compound is uniformly dispersed in the lactic acid polymer composition containing the phosphorus-based flame retardant. However, a means that facilitates fine dispersion is preferably implemented. Preferred addition / mixing methods include a melt mixing method, a solution mixing method, a powder mixing and melt dispersion method, a masterbatch method, and the like. When the lactic acid polymer containing a phosphorus-based flame retardant is used alone or as a molded product as a resin composition, it is preferable to pulverize it beforehand and then mix it with an alkaline earth metal compound.

In the present invention, as a method for recovering lactide having high optical purity, a lactic acid polymer composition containing a phosphorus-based flame retardant is introduced into, for example, a thermal decomposition reactor set to a temperature range of 200 to 350 ° C. However, a method of raising the temperature from a lower temperature can also be selected. In particular, in the case of a composition containing a non-condensable phosphate ester having a lower boiling point than lactide, a method of vaporizing and separating and recovering the non-condensate phosphate ester at a lower temperature before recovering the lactide is preferable. . As the pyrolysis reactor suitably used, either batch type or continuous type can be implemented. Suitable reactors include extruders, autoclaves, fluidized bed reactors, and the like. When using an extruder, control of the pyrolysis temperature and pyrolysis rate and the heating rate are controlled according to the temperature setting of each block of the cylinder, the number of rotations of the screw, the shape of the screw, and the type of uniaxial / biaxial screw. It is possible to set the temperature range at.

When these pyrolysis reactors are used to thermally decompose a lactic acid polymer composition containing a phosphorus-based flame retardant, the produced lactide and the low-boiling non-condensable phosphate ester are volatilized in the gas phase. Therefore, a process for extracting the gas phase component is indispensable. Each of the reactors described above has a discharge port for taking out the gas phase component and / or an inlet of an inert gas such as nitrogen gas for extruding and replacing the gas phase component. For example, in the case of an extruder reactor, a vent port is preferably used as the discharge port. When taking out the gas phase component from the vent port, generally, a method of taking it out under reduced pressure is preferably carried out. The degree of decompression and / or the exhaust speed can be set according to the amount and temperature of the vaporized component, but is usually suitably carried out at a degree of decompression of 100 mmHg or less, preferably 50 mmHg or less, more preferably 10 mmHg or less.

In this manner, high optical purity lactide can be obtained by carrying out the method of the present invention and by chemical recycling. A conventionally known method can be used to evaluate the optical purity of the obtained lactide. For example, when racemization occurs in one lactic acid ester structural unit and subsequent elimination occurs in lactide units, meso-lactide is generated. When racemization occurs in two consecutive lactic acid ester structural units and the two lactic acid ester structural units are eliminated as lactide, an optically isomeric lactide opposite to the original lactic acid polymer is produced. In general, when the racemization reaction proceeds randomly, meso-lactide is produced as the main degradation product. The ratio of these meso-lactides, L, L-lactides, and D, D-lactides can be confirmed by gas chromatographic analysis. However, when a column that cannot be optically resolved is used, D, D-lactide and L, L-lactide are detected as the same fraction, so the evaluation of racemization is based on the meso-lactide production rate. Can be used as Therefore, the production ratio of meso-lactide should be 10 mol% or less, preferably 5 mol% or less, more preferably 2 mol% or less in the obtained lactide.

According to the present invention, lactide in which racemization is suppressed can be recovered, but the optical purity of the obtained lactide depends on the optical purity of the lactic acid polymer used. That is, the higher the optical purity of the lactic acid polymer used, the higher the optical purity of the obtained lactide. Therefore, the optical purity of the lactic acid polymer is 80% e.e. e. Or more, preferably 90% e.e. e. Or more, more preferably 95% e.e. e. If it is above, the optical purity of the lactide obtained by chemical recycling will also become proportionally high. Here,% e. e. Is the percentage of the excess of one enantiomer present in a mixture of enantiomers called enantiometric excess.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

[Example 1] and [Comparative Examples 1 to 4]
160 mg of poly-L-lactic acid (PLLA) (Mn = 142000, Mw = 286000) containing almost no metal treated with hydrochloric acid, 40 mg of aromatic condensed phosphate ester flame retardant (PX-200: manufactured by Daihachi Chemical Industry), and oxidation 10 mg of magnesium (MgO) (particle size: 50 × 5 × 5 μm ³ , manufactured by Wako Pure Chemical Industries, Ltd.) is placed in a sample tube, 6 mL of chloroform is added thereto, and the mixture is dissolved and dispersed by vigorous magnetic stirring at room temperature for 15 hours. I let you. Next, a cast film was prepared from the solution in a flat petri dish.

The obtained cast film was subjected to vacuum drying at room temperature for 1 day after washing the surface with methanol. A sample of about 5 mg was cut out from the obtained film at a time, and the temperature was increased by 9 ° C./min in a temperature range from room temperature to 400 ° C. in a nitrogen atmosphere (100 mL / min) using TG / DTA6200 manufactured by SEIKO. Thermal decomposition was performed at a temperature rate. The results are shown in FIG. The pyrolysis product was analyzed using a pyrolysis chromatograph / mass spectrometer (Py-GC / MS, QP-5050A manufactured by Shimadzu Corporation). The analysis result of the decomposition product is shown in FIG.

For the composition of Example 1 above, in the case of PLLA alone (Comparative Example 1), in the case of PX-200 alone (Comparative Example 2), in the case of adding only MgO to PLLA (Comparative Example 3), and PLLA When only PX-200 was added (Comparative Example 4), a cast film was prepared in the same manner as PLLA / PX-200 / MgO, and pyrolysis was performed in the same manner. The results are also shown in FIG.

In the case of only PLLA (Comparative Example 1) and the composition containing 20 parts by weight of PX-200 in 80 parts by weight of PLLA (Comparative Example 4), the weight loss due to decomposition began to exceed 300 ° C., and was about 390 to 400 ° C. Decomposed almost completely. On the other hand, in the case of PX-200 alone (Comparative Example 2), the weight loss started exceeding 250 ° C., and almost completely decomposed at 400 ° C. These results indicate that PX-200 decomposes simultaneously with the decomposition of PLLA, and the decomposition temperature of PLLA itself does not change. When MgO was added to PLLA (Comparative Example 3), thermal decomposition started at around 230 ° C., and decomposition was completed at about 310 ° C. completely.

In the case of PLLA / PX-200 / MgO (80/20/5 wt / wt / wt) (Example 1), thermal decomposition started at around 230 ° C., leaving about 20% residue at around 310 ° C. The first stage was completed, and then the second stage of thermal decomposition continued to 380 ° C., and the decomposition was completed. This result shows that the decomposition catalyst MgO has caused the decomposition temperature of PLLA and the phosphorus-based flame retardant to be separated, and only PLLA is preferentially decomposed.

From the result of the decomposition product of FIG. 2, PLLA / PX-200 / MgO (80/20/5
wt / wt / wt) (Example 1), the ratio of L, L-lactide, which is the direct raw material of PLLA, was the highest at 99.6%, indicating that selective depolymerization of PLLA occurred. Show.

From the above Example 1 and Comparative Examples 1 to 4, by adding the decomposition catalyst MgO to the lactic acid polymer composition containing the condensed phosphate ester type flame retardant, the thermal decomposition of PLLA is performed preferentially, It was found that some L, L-lactide was recovered with high purity.

[Example 2] and [Comparative Examples 5 to 6]
160 mg of poly-L-lactic acid (PLLA) (Mn = 142000, Mw = 286000) containing almost no metal treated with hydrochloric acid and triphenyl phosphate (TPP: Wako Pure Chemical Industries, Ltd.), an aromatic non-condensable phosphate ester flame retardant 40 mg, and 10 mg of magnesium oxide (MgO) (particle size: 50 × 5 × 5 μm ³ , manufactured by Wako Pure Chemical Industries, Ltd.) are placed in a sample tube, 6 mL of chloroform is added thereto, and the mixture is vigorously stirred at room temperature for 15 hours. It was dissolved and dispersed by performing. Next, a cast film was prepared from the solution in a flat petri dish.

The obtained cast film was subjected to vacuum drying at room temperature for 1 day after washing the surface with methanol. A sample of about 5 mg was cut out from the obtained film at a time, and the temperature was increased by 9 ° C./min in a temperature range from room temperature to 400 ° C. in a nitrogen atmosphere (100 mL / min) using TG / DTA6200 manufactured by SEIKO. Thermal decomposition was performed at a temperature rate. The results are shown in FIG. The pyrolysis product was analyzed using a pyrolysis chromatograph / mass spectrometer (Py-GC / MS, QP-5050A manufactured by Shimadzu Corporation). The analysis result of the decomposition product is shown in FIG.

For the composition of Example 2 above, only PLLA (Comparative Example 1), only TPP (Comparative Example 5), only MgO added to PLLA (Comparative Example 3), and TPP to PLLA In the case of adding only (Comparative Example 6), a cast film was prepared in the same manner as PLLA / TPP / MgO, and pyrolysis was performed in the same manner. The results are also shown in FIG.

In the case of only TPP (Comparative Example 5), the weight loss due to the volatilization of TPP started from around 200 ° C. and was completely volatilized by 300 ° C. A composition containing 20 parts by weight of TPP in 80 parts by weight of PLLA (Comparative Example 6) begins to gradually lose weight from around 200 ° C., the same as the TPP volatilization temperature, and is the same temperature range as the decomposition of PLLA alone (Comparative Example 1). When the value reached, degradation of PLLA was started. From this, it was found that TPP volatilizes at a low temperature irrespective of the thermal decomposition of PLLA.

In the case of PLLA / TPP / MgO (80/20/5 wt / wt / wt) (Example 2), weight loss due to TPP volatilization started from around 200 ° C., and about 70% of the residue was obtained at around 330 ° C. The first stage was completed, and then the weight reduction in the second stage proceeded rapidly, and the decomposition was completely completed by 340 ° C. This result is different from the weight loss behavior of the PLLA and MgO compositions (Comparative Example 3).

From the result of the decomposition product of FIG. 4, PLLA / TPP / MgO (80/20/5
The product from (wt / wt / wt) (Example 2) is occupied by L, L-lactide, which is the direct raw material of volatile TPP and PLLA, TPP 59.5%, L, L-lactide 39 6%, and meso-lactide 0.9%, and the composition of lactide alone excluding TPP is 97.8% L, L-lactide and 2.2% meso-lactide, and is selective PLLA This indicates that depolymerization of The TPP recovered at the same time can be separated from L, L-lactide by the method described in Example 5.

From the results of Example 2 and Comparative Examples 1, 3, 5, and 6, the thermal decomposition of PLLA was performed by adding the decomposition catalyst MgO to the lactic acid polymer composition containing the non-condensable phosphate ester flame retardant TPP. It was found that L, L-lactide as a raw material was recovered with high purity together with recovery of volatile TPP.

[Examples 3 and 4] and [Comparative Example 7]
Poly-L-lactic acid (PLLA) (Mn = 142000, Mw = 286000) containing almost no metal treated with hydrochloric acid, aromatic condensed phosphate ester (PX-200: manufactured by Daihachi Chemical Industry), triphenyl phosphate (TPP: Wako Pure Chemical Industries, Ltd.) and calcium oxide (CaO) (Wako Pure Chemical Industries, Ltd.) are put in a sample tube at the ratio shown in Table 1, and 6 mL of chloroform is added thereto, followed by vigorous magnetic stirring at room temperature for 15 hours. To dissolve and disperse. Next, a cast film was prepared from the solution in a flat petri dish.

The obtained cast film was subjected to vacuum drying at room temperature for 1 day after washing the surface with methanol. A sample of about 5 mg was cut out from the obtained film at a time, and the temperature was increased by 9 ° C./min in a temperature range from room temperature to 400 ° C. in a nitrogen atmosphere (100 mL / min) using TG / DTA6200 manufactured by SEIKO. Thermal decomposition was performed at a temperature rate. The results are shown in FIG. The pyrolysis product was analyzed using a pyrolysis chromatograph / mass spectrometer (Py-GC / MS, QP-5050A manufactured by Shimadzu Corporation). FIG. 6 shows the analysis results of the decomposition products in the case of PLLA / PX-200 / CaO and PLLA / CaO, and FIG. 7 shows the analysis results of the decomposition products in the case of PLLA / TPP / CaO and PLLA / TPP. Indicated.

For the compositions of Examples 3 and 4 above, when PLLA alone (Comparative Example 1), when PX-200 alone is added to PLLA (Comparative Example 4), when only TPP is added to PLLA (Comparison) In Example 6), and when only CaO was added to PLLA (Comparative Example 7), cast films were prepared in the same manner as in Examples 3 and 4, and pyrolysis was performed in the same manner. The results are also shown in FIG.

When CaO was added to PLLA (Comparative Example 7), thermal decomposition started at around 220 ° C., and the decomposition was completed at around 330 ° C. In the case of PLLA / PX-200 / CaO (80/20/1 wt / wt / wt) (Example 3), thermal decomposition started at around 210 ° C., leaving about 20% residue at around 300 ° C. The first stage was completed, and then the second stage of thermal decomposition continued to 380 ° C., and the decomposition was completed. This result shows that the decomposition catalyst CaO caused the decomposition temperature of PLLA and the phosphorus-based flame retardant to dissociate preferentially only PLLA. Furthermore, it was found that the coexistence of PX-200 improves the depolymerization activity of CaO, and the decomposition proceeds in a lower temperature range than PLLA / CaO (Comparative Example 7).

From the result of the decomposition product of FIG. 6, in the case of PLLA / PX-200 / CaO (80/20/1 wt / wt / wt) (Example 3), L, L-lactide which is a direct raw material of PLLA Is higher than that of PLLA / CaO, indicating that more selective PLLA depolymerization occurred.

As can be seen from FIG. 5, in the case of PLLA / TPP / CaO (80/20/1 wt / wt / wt) (Example 4), the weight decrease due to TPP volatilization started from around 210 ° C., and around 330 ° C. The first stage was completed with approximately 70% of the residue remaining, followed by a rapid decrease in weight in the second stage, and the decomposition was completely completed by 360 ° C. This result is different from the weight loss behavior of the PLLA and CaO compositions (Comparative Example 7). From the results of the degradation product (FIG. 7), the product from PLLA / TPP / CaO (80/20/1 wt / wt / wt) (Example 4) is the composition of PLLA / TPP (80/20 wt / wt). Compared with the above, the purity of L-lactide is high, indicating that more selective depolymerization of PLLA has occurred.

From the results of Examples 3 and 4 and Comparative Examples 1, 4, 6, and 7, the thermal decomposition of PLLA can be achieved by adding the decomposition catalyst CaO to the lactic acid polymer composition containing the condensed phosphate ester type flame retardant. It was found that L, L-lactide, which is a direct raw material, was recovered with high purity. In addition, by adding a decomposition catalyst CaO to a lactic acid polymer composition containing a phosphoric ester-type flame retardant TPP, the thermal decomposition of PLLA is selectively carried out, and L, L-lactide which is a direct raw material along with the recovery of volatile TPP Was recovered with high purity.

[Example 5]
By adding an equal amount (40.6 g) of toluene to 40.6 g of a mixture of L, L-lactide and TPP (lactide 32.48 g, TPP 8.12 g), heating to 80 ° C. using a mantle heater, and stirring. The mixture was dissolved to make a uniform solution. After uniformly dissolving, the mixture was allowed to cool to 30 ° C. with stirring. Lactide crystals were precipitated in the cooled solution. In order to take out L, L-lactide crystals from this solution, treatment was performed at room temperature of 25 ° C. and a rotation speed of 3000 rpm for 10 minutes using a centrifugal separator using a filter cloth to separate the lactide crystals from the toluene solution. Lactide crystals were dried under reduced pressure. 24.4 g of L, L-lactide was recovered, and from ¹ H-NMR analysis, the optical purity of L, L-lactide was 100%, and no racemization occurred during the separation process. On the other hand, most of toluene was removed from the toluene solution separated by the centrifuge using an evaporator. The remaining toluene solution was cooled in a refrigerator (4 ° C.) to crystallize the remaining lactide and separated from the TPP toluene solution. The toluene solution of TPP completely removed toluene using an evaporator, and the precipitated white solid (5.03 g) was analyzed using ¹ H-NMR and gas chromatographic analysis. As a result, it was 100% pure TPP.

The present invention makes it possible to efficiently and easily produce and recover lactide having a high optical purity from a lactic acid polymer composition containing a phosphorus-based flame retardant. This is extremely effective for chemical recycling of a molded product comprising the lactic acid polymer composition contained therein.

The TG curve of the various compositions which consist of PLLA, condensation type phosphate ester type flame retardant PX-200, and MgO. The composition of the thermal decomposition product by Py-GC / MS of the various composition which consists of PLLA, condensation type | mold phosphate ester type flame retardant PX-200, and MgO. TG curves of various compositions comprising PLLA, phosphate ester type flame retardant TPP, and MgO. Composition of thermal decomposition products by Py-GC / MS of various compositions comprising PLLA, phosphate ester type flame retardant TPP, and MgO. TG curves of various compositions comprising PLLA, condensed phosphate ester type flame retardant PX-200, phosphate ester type flame retardant TPP, and CaO. The composition of the thermal decomposition product by Py-GC / MS of the various composition which consists of PLLA, the condensation type | mold phosphate ester type | mold flame retardant PX-200, and CaO. Composition of thermal decomposition products by Py-GC / MS of various compositions comprising PLLA, phosphate ester type flame retardant TPP, and CaO.

Claims (3)

In the method for recovering lactide from a lactic acid polymer composition containing a phosphorus-based flame retardant, 0.1 to 10 parts by weight of an alkaline earth metal compound is added per 100 parts by weight of the lactic acid polymer component in the lactic acid polymer composition , A method for recovering lactide , comprising heating to a temperature of 200 to 350 ° C. and recovering lactide having high optical purity obtained by depolymerization of the lactic acid polymer. The method for recovering lactide according to claim 1, wherein the alkaline earth metal compound is a magnesium compound or a calcium compound. The method for recovering lactide according to claim 1 or 2, wherein a lactate polymer composition containing a phosphorus-based flame retardant having a boiling point lower than that of lactide is used, and at the same time, the phosphorus-based flame retardant is also recovered.

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