JP4486561B2 - Method for removing foreign materials from polylactic acid stereocomplex polymer - Google Patents

Description

  The present invention relates to a method of removing a foreign material from a polylactic acid stereocomplex polymer recovered material containing the foreign material.

  Conventionally, polylactic acid has been well known as a representative of biodegradable plastics that have a low environmental impact. In recent years, the trend of building a recycling-oriented society has increased, and plastic raw materials have been moved from fossil resources to biomass, and polylactic acid from plants such as starch has attracted much attention. This polylactic acid has excellent transparency, has a wide variety of molding processes, and is highly safe, so it can be used in various fields such as agricultural, forestry and fishery materials, civil engineering / building materials, food packaging / containers, or daily necessities. Use in is expected. Polylactic acid generally distributed is poly L-lactic acid using L-lactic acid as a raw material, and its melting point is about 170 ° C. For this reason, when using it for the heat-resistant use, compared with a general-purpose polyester polymer etc., there existed a problem that a use range was limited.

  On the other hand, lactic acid has an optical isomer, and when a polylactic acid stereocomplex polymer composed of a mixture of poly (L-lactic acid) and poly (D-lactic acid) polymerized from L-lactic acid and D-lactic acid is formed, It is known that the melting point is higher than that of lactic acid or poly D-lactic acid homopolymer (see, for example, Patent Document 1).

  However, used polylactic acid generated in large quantities with the increase in use as described above, and non-qualified products generated in the polylactic acid production stage (hereinafter, these may be abbreviated as polylactic acid recovered materials). ), The polylactic acid part is biodegradable, but takes a long time to decompose, and is expected to become a major social problem in the future. This is also true for used polylactic acid stereocomplex polymers and non-qualified products (hereinafter, these may be abbreviated as polylactic acid stereocomplex polymer recovered materials) generated in the production stage of polylactic acid stereocomplex polymers. The same is true. In response to the above problems, the polylactic acid stereocomplex polymer recovered material is converted and recovered to the original raw material, and polylactic acid polymer and polylactic acid stereocomplex polymer are produced and reused from this raw material by a polymerization reaction again. Is effective. This method is basically a loss-free method that enables resource reuse of compounds, and enables resource reuse.

  For example, as a method of returning to a raw material and recycling, there has been proposed a method of recovering lactate from a polylactic acid product by heating to 200 to 400 ° C. in the presence of water and a catalyst in a screw extruder (for example, Patent Documents). 2). In addition, a method is proposed in which polylactic acid is heated to 170 to 300 ° C. in the presence of a catalyst made of tin or a tin compound, and reduced to a pressure lower than the vapor pressure of lactide, and the produced lactide is distilled off and recovered. (For example, refer to Patent Document 3). Furthermore, a method of recovering lactide generated by adding alcohols and a thermal decomposition catalyst to polylactic acid and heating to alcoholysis under reduced pressure or in an inert gas stream to cause backbite reaction is also proposed. (For example, refer to Patent Document 4). A method of depolymerization using aqueous ammonia has also been proposed (see, for example, Non-Patent Document 1).

Furthermore, not only polylactic acid, but generally when plastic products once distributed to the market are collected, they are often collected in a state in which different types of materials other than the plastics that mainly make up the plastic products are mixed. . These different materials become obstacles when performing chemical recycling as described above. Further, if the different materials cannot be removed, the different materials are mixed in the recycling process. As a result, the different materials partially melt in a solid state or in a high temperature state, thereby causing troubles such as adhesion to equipment in the recycling process, blockage to the piping, or biting into the rotating part. Therefore, when the polylactic acid recovery product is processed by the chemical recycling method as described above, it is important to remove foreign materials contained in the polylactic acid recovery product before chemical recycling. As a method for removing foreign materials from a polylactic acid recovery product during chemical recycling, a method for removing undissolved foreign materials by suspending them in a solution or a method for removing them by solid-liquid separation have been proposed. (For example, see Patent Documents 5 and 6.)
However, there is no technical disclosure about a method for removing a different material targeting a polylactic acid stereocomplex polymer, and no corresponding method is presented when a different material is mixed.

JP-A-61-36321 JP-A-7-309863 (Claims) JP-A-9-77904 (Claims) JP-A-9-241417 (Claims) Japanese Patent Laying-Open No. 2005-131856 (Claims) Japanese Patent Laying-Open No. 2005-132901 (Claims) Yoshito Shirai et al., Industrial Materials, 2003, 51 (3), 27-29

  The object of the present invention is to solve the problems of the prior art, and to prevent the different materials contained in the polylactic acid stereocomplex polymer recovered material from decreasing the active ingredient recovery yield of the polylactic acid stereocomplex polymer recovered material. An object of the present invention is to provide a method for removing from a polylactic acid stereocomplex polymer.

  As a result of intensive studies in view of the above-described prior art, the present inventors have completed the present invention. That is, the present invention depolymerizes a polylactic acid stereocomplex polymer recovered material containing a different material to obtain a depolymerization reaction solution having a viscosity of 0.0001 to 0.1 Pa · s (0.1 centipoise to 100 centipoise). Or a polylactic acid stereocomplex polymer solution in the same viscosity range by dissolving in a dissolving solvent, and performing a solid-liquid separation operation on undissolved different materials present in these solutions, or a polylactic acid stereocomplex polymer This is a method for removing foreign materials from a polylactic acid stereocomplex polymer separated from a solution.

  According to the method of the present invention, when an active ingredient of a polylactic acid stereocomplex polymer is recovered from a polylactic acid stereocomplex polymer recovered product by a chemical recycling method, foreign materials contained in the polylactic acid stereocomplex polymer recovered product are efficiently removed. It is possible. As a result, troubles caused by different materials in the chemical recycling process can be prevented.

  In the present invention, the polylactic acid stereocomplex polymer recovered product is a polylactic acid stereocomplex polymer as a main component, and the polylactic acid stereocomplex polymer is a blend of a poly L-lactic acid polymer and a poly D-lactic acid polymer. The complex polymer has characteristic properties. A part of the polylactic acid polymer also has a stereocomplex polymer property. Moreover, it is preferable that this polylactic acid stereocomplex polymer contains 60 weight% or more of the whole polylactic acid stereocomplex polymer collection thing, More preferably, it is 80 weight% or more. Furthermore, the polylactic acid stereocomplex polymer recovered product may contain various different materials in addition to the polylactic acid stereocomplex polymer. Examples of the different materials include polyolefins such as polyethylene, polypropylene, and polyvinyl chloride, aromatic polyesters, polyamides, paper, earth and sand, dust, metals, residual catalyst, and wood. Furthermore, in the method of the present invention, it is preferable that the polylactic acid stereocomplex polymer recovered material is generally subjected to a pretreatment such as water washing and coarse pulverization, and then put into a shape suitable for depolymerization reaction or dissolution in a solvent. . In this case, it is preferable because a foreign material that is extremely soluble in water can be removed. Further, before and / or after this pretreatment, it is preferable to remove foreign materials from the polylactic acid stereocomplex polymer recovered material as much as possible by simple mechanical or physical means. For example, there are a method of removing a material that can be visually discriminated from a different material, or a method of removing a metal attracted to the magnet using a magnet.

  The first step in the implementation of the method of the present invention is to depolymerize the polylactic acid stereocomplex polymer recovered material so that the viscosity is 0.0001 to 0.1 Pa · s (0.1 centipoise to 100 centipoise). It is to make a reaction solution. In another embodiment of the present invention, the polylactic acid stereocomplex polymer recovered material is dissolved in a solvent in which the polylactic acid stereocomplex polymer can be dissolved, and 0.0001 to 0.1 Pa · s (0.1 centipoise to 100 centipoise). ). In any case, the viscosity range is more preferably 0.0005 to 0.03 Pa · s (0.5 centipoise to 30 centipoise). Regarding the temperature at which the viscosity is measured, the type and average molecular weight of the polylactic acid stereocomplex polymer, the degree of depolymerization of the recovered polylactic acid stereocomplex polymer, whether or not to add a solvent, the type of solvent to be added, and after depolymerization Or it can select arbitrarily in the range which can be handled with the density | concentration after melt | dissolution.

  There is no particular limitation on the depolymerization method of the polylactic acid stereocomplex polymer, and any polylactic acid depolymerization method can be used without any problem. It is necessary to implement the present invention that the viscosity is 0.0001 to 0.1 Pa · s (0.1 centipoise to 100 centipoise) by these depolymerization methods. In order to make the viscosity within this range, those skilled in the art can perform trial and error by appropriately adjusting the type and amount of the solvent and catalyst added to the polylactic acid stereocomplex polymer, and the temperature, pressure, and reaction time of the depolymerization reaction. Can be achieved. The depolymerization reaction can be either batchwise or continuous.

  In the method of the present invention, a solvent may be added before depolymerization and / or after depolymerization. For example, a solvent can be added before depolymerization to promote the depolymerization reaction, or the polylactic acid stereocomplex polymer recovered before depolymerization can be easily handled. For this purpose, it is preferable to use various glycols such as ethylene glycol and diethylene glycol, or water. As another example, a solvent is added before and / or after depolymerization to lower the viscosity of the depolymerization reaction solution to facilitate the separation operation of different materials, or to increase the specific gravity of the depolymerization reaction solution. Different materials can be easily suspended. Here, the ease of the separation operation specifically means that the liquid feeding operation and the selection of the pump used for the liquid feeding become easy. The solvent used for this can be added before or after depolymerization. Preferably, it is added after completion. Further, the solvent can be added in any amount depending on the state of the depolymerization reaction solution. As a kind of this solvent, in order to reduce a viscosity, methanol, ethanol, or hexane etc. can be mentioned preferably, for example. On the other hand, in order to increase the specific gravity, for example, methylene chloride, chloroform, or an aqueous sodium chloride solution can be preferably exemplified.

  On the other hand, with respect to the method for dissolving the polylactic acid stereocomplex polymer recovered material in the dissolving solvent, the polylactic acid stereocomplex polymer recovered material is dissolved in the polylactic acid stereocomplex polymer by using a sufficient amount of dissolving solvent. It is necessary to make a polylactic acid stereocomplex polymer solution of 0.0001 to 0.1 Pa · s (0.1 centipoise to 100 centipoise). In order to make the viscosity within this range, those skilled in the art can achieve it by trial and error by appropriately adjusting the kind and amount of the dissolving solvent for the polylactic acid stereocomplex polymer. Representative examples of suitable dissolving solvents include solvents selected from orthochlorophenol, 1,1,1,3,3,3-hexafluoro-2-propanol, trifluoroacetic acid, chloroform, or dichloromethane, or these solvents. It is preferable to select at least one of the above mixtures. The sufficient amount is preferably 2 to 150 times by weight based on the recovered polylactic acid stereocomplex polymer. Moreover, the batch stage or the continuous type can be employed for the dissolution step in these dissolution solvents. Furthermore, when dissolving, if necessary, the polylactic acid stereocomplex polymer or the dissolving solvent may be heated to such an extent that it does not cause alteration such as thermal decomposition. Moreover, dissolving with stirring is a preferred method for rapid dissolution.

  In the method of the present invention, a solvent may be further added before and / or after dissolution in the dissolution solvent. For example, a solvent can be added before dissolution to swell for easy dissolution, or handling of the polylactic acid stereocomplex polymer recovered before dissolution can be facilitated. For this purpose, it is preferable to use, for example, the same solvent as the dissolving solvent described above. Another example is to reduce the viscosity of the polylactic acid stereocomplex polymer solution to facilitate separation of different materials, or to increase the specific gravity of the polylactic acid stereocomplex polymer solution to make it easier to float different materials. Can do. Hereinafter, the detailed description regarding this point is the same as the above description.

  Of the different materials contained in the recovered polylactic acid stereocomplex polymer in the first stage, the specific gravity is small relative to the depolymerization reaction solution or polylactic acid stereocomplex polymer solution (hereinafter referred to as “depolymerization reaction solution etc.”). Different materials, for example, polyolefins represented by polyethylene, polypropylene, and polystyrene, natural fibers, metal compounds, and the like are generally present in a solid state in a depolymerization reaction solution. For that purpose, it is preferable to leave it still, for example, so that different materials can be separated by solid-liquid separation operation in the depolymerization reaction solution of the polylactic acid stereocomplex polymer. Specifically, the time is preferably 5 minutes to 2 hours. Also, in this case, if the different materials are present in a solid state, the polylactic acid stereocomplex polymer is not completely depolymerized or dissolved. The present invention can be carried out even if it remains in such a size that it can pass through.

  As a second stage, it is necessary to remove the solid foreign material present in the depolymerization reaction solution and the like out of the system. A general solid-liquid separation operation can be applied to the removal method. As a typical example, a filtration operation using a filter, a centrifugal separation method, a sedimentation separation operation, or the like can be employed. For example, for the filtration operation with a filter, a conventionally known method may be employed. For example, a method of attaching a filter to a line (pipe) for extracting a depolymerization reaction solution from a tank and collecting solid matter with a filter There is.

Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, what is called "part" in an Example and a comparative example represents a weight part.
(1) Method for Measuring Viscosity The depolymerization reaction solution or polylactic acid stereocomplex polymer solution of the recovered polylactic acid stereocomplex polymer was measured with a viscometer (apparatus: Brookfield DV-III) to determine the viscosity. It was.

[Example 1]
52 parts of a polylactic acid stereocomplex polymer recovered product containing 2 parts of polyvinyl chloride was charged with 500 parts of 10% ammonia water in a depolymerization reaction tank and kept at 80 ° C. for 2.5 hours while stirring at 100 rpm. At this time, the depolymerization of the charged polylactic acid stereocomplex polymer was completed. At this time, the viscosity of the depolymerization reaction solution was 0.0008 Pa · s (0.8 centipoise) under the temperature condition of 80 ° C. On the other hand, polyvinyl chloride did not react and was present in the solid state in the depolymerization reaction solution. Stirring was temporarily stopped in this state, the depolymerization reaction solution was extracted, and a filter was attached to the extraction line (pipe). After extracting the whole amount of the depolymerization reaction solution, the solid matter in the filter was collected and dried, and the weight was measured to find 2 parts. In addition, the filtered filtrate was free of solid foreign materials, and the entire amount of the polylactic acid stereocomplex polymer was depolymerized, and a depolymerization solution free from polyvinyl chloride was obtained.

[Example 2]
52 parts of a polylactic acid stereocomplex polymer recovered containing 2 parts of polyvinyl chloride, 250 parts of 1,1,1,3,3,3-hexafluoro-2-propanol and 250 parts of chloroform are put into a dissolution tank, and 100 rpm And kept at 40 ° C. for 1 hour with stirring. At this time, the viscosity of the polylactic acid stereocomplex polymer solution was 0.0015 Pa · s (1.5 centipoise) under the temperature condition of 40 ° C., and the charged polylactic acid stereocomplex polymer was almost dissolved. On the other hand, polyvinyl chloride did not dissolve and was present in the liquid in a solid state. Stirring was temporarily stopped in this state, the polylactic acid stereocomplex polymer solution was extracted, and a filter was attached to the extraction line (pipe). After extracting the whole amount of the polylactic acid stereocomplex polymer solution, the solid matter in the filter was recovered and dried to measure the weight, which was 2 parts. Further, the filtered filtrate had no solid foreign material, and the whole amount of the polylactic acid stereocomplex polymer was dissolved, and a polylactic acid stereocomplex polymer solution free of polyvinyl chloride was obtained.

  According to the present invention, a foreign material can be removed from a recovered polylactic acid stereocomplex polymer containing a different material such as polyolefin without reducing the yield of the active ingredient recovered from the recovered polylactic acid stereocomplex polymer. In addition, troubles in the recycling process due to mixing of different materials can be avoided, and its industrial significance is great.

Claims (5)

  A polylactic acid stereocomplex polymer recovered material containing a different material is depolymerized to obtain a depolymerization reaction solution having a viscosity of 0.0001 to 0.1 Pa · s (0.1 centipoise to 100 centipoise), and the depolymerization reaction solution A method of removing foreign materials from a polylactic acid stereocomplex polymer, which is separated from a depolymerization reaction solution by subjecting undissolved foreign materials present therein to solid-liquid separation.   A polylactic acid stereocomplex polymer recovered material containing a different material is dissolved in a dissolving solvent to form a polylactic acid stereocomplex polymer solution having a viscosity of 0.0001 to 0.1 Pa · s (0.1 centipoise to 100 centipoise), A method of removing a foreign material from a polylactic acid stereocomplex polymer that is separated from the polylactic acid stereocomplex polymer solution by subjecting an undissolved foreign material present in the polylactic acid stereocomplex polymer solution to a solid-liquid separation operation.   The method for removing foreign materials according to claim 1, wherein a solvent is added before and / or after depolymerization.   The method for removing a foreign material according to claim 2, wherein a solvent is further added before and / or after dissolution in the dissolution solvent.   The method for removing foreign materials according to any one of claims 1 to 4, wherein the solid-liquid separation operation is a filtration operation.