JP5941729B2 - Biodegradable plastic product with controlled degradation rate and method for producing the product - Google Patents

Description

  The present invention relates to a biodegradable plastic product having a controlled degradation rate and a method for producing the product. Specifically, the present invention relates to a biodegradable plastic product containing polyhydroxyalkanoic acid (PHA) whose decomposition rate is controlled as a component and a method for producing the product. More specifically, the present invention relates to a biodegradable plastic product comprising as a component a strain that produces depolymerase and / or PHA to which spores of the strain are immobilized, and a method for producing the product.

  Petroleum-derived plastics are disposed of in large quantities every year, and the shortage of landfill sites and environmental pollution caused by these large-scale wastes are taken up as serious problems. For this reason, biodegradable plastics that are degraded by the action of microorganisms in the environment, landfills, and compost have attracted attention.

  Biodegradable plastics are being developed for a wide range of applications in agriculture, forestry and fisheries materials used in the environment, food containers that are difficult to collect and reuse after use, packaging materials, sanitary goods, garbage bags, etc. ing.

  Biodegradable plastics include biomass and petroleum biodegradable plastics. The former is natural products (starch, cellulose, etc.), microbial production (polyhydroxyalkanoic acid (PHA)), plant (polylactic acid (PLA), polyglycolic acid (PGA)), the latter is polybutylene succinate (PBS), polybutylene adipate / terephthalate (PBAT), polycaprolactone (PCL) and the like.

  Among these, PHA is a thermoplastic polymer in which microorganisms accumulate in the cells, and a homopolymer or copolymer of 3-hydroxyalkanoic acid is known. A typical homopolymer is polyhydroxybutyric acid (PHB), which is produced by many microorganisms. Examples of the copolymer include 3-hydroxybutyric acid and 3-hydroxyvaleric acid copolymer (PHBV) and 3-hydroxybutyric acid and 3-hydroxyhexanoic acid copolymer (PHBH). Since these copolymer polymers exhibit a wide range of properties from hard to soft, they can be applied to a wide range of applications.

  However, it is expected that materials for agriculture, forestry and fisheries using biodegradable plastics will have different degradation rates depending on the environment in which they are used. This is because the distribution and density of microorganisms capable of degrading and assimilating biodegradable plastics present in the environment are greatly different. For this reason, various methods have been proposed to accelerate the decomposition of the material.

  For example, a method of adding a microbial medium component to a biodegradable material (polylactic acid) (Patent Document 1), a method of adding a hydrolase such as lipase, amylase, cellulase, lactate dehydrogenase to a biodegradable plastic material ( Patent Document 2) and the like have been proposed.

  As for PHA, microorganisms capable of degrading and assimilating this have been searched, and many microorganisms degrading PHB have been reported. As an example, it was found that a microorganism belonging to the genus Pseudomonas separated from soil was isolated, and this strain produced depolymerase, an enzyme that degrades PHB (Patent Document 3). In addition, a depolymerase gene produced by the genus Alkagenes has been cloned, and a method for producing the enzyme and its use have also been proposed (Patent Document 4).

  However, in the method of blending medium components as in Patent Document 1, the degradation rate still depends on the presence of microorganisms in the environment. Moreover, in the method of Patent Document 2, the enzyme generally has poor heat resistance, and the usage mode is limited.

  Although it may be possible to accelerate the degradation of biodegradable plastics and adjust the degradation rate by spraying the degrading enzyme on agricultural materials and compost in use, it takes to manufacture and transport the microorganism and degrading enzyme preparation. Considering the cost and time of spraying, it is practically difficult.

  It has also been proposed that a biodegradable material is coated or blended with a microorganism having an enzymatic activity that degrades the material. For example, in Patent Document 5, a degradation promoting layer made of polyvinyl alcohol or starch mixed with microorganisms is applied to the surface of a biodegradable plastic. In Patent Document 6, microorganisms are previously microencapsulated and contained in a biodegradable material. Furthermore, in a composite resin film containing starch or cellulose as a biodegradable material, it has been proposed that microorganisms capable of producing amylase or cellulase are contained in the resin in the form of spores in the resin production process ( Patent Document 7).

  However, in the method of Patent Document 5, in order to promote the decomposition inside the plastic, prior to the application of the decomposition accelerating layer, a process such as roughening the surface of the plastic or providing a through hole is performed. The method of Patent Document 6 also requires microencapsulation processing. Moreover, in patent document 7, the process of coat | covering the biodegradable plastic to which the degrading enzyme adhered and the spore of the microorganisms which produce the said enzyme with vegetable oil is required. Therefore, these methods are complicated and not advantageous in terms of cost. Moreover, all the methods using the above-mentioned microorganisms are reports on biodegradable materials that are different from PHA. Regarding PHA, there is a report on a promising method that promotes the decomposition by a simple method and decomposes it in an appropriate period. It has not been.

JP-A-4-168150 Japanese Patent Laid-Open No. 4-168149 JP 7-155180 A Japanese Patent Laid-Open No. 9-191887 JP 2006-137717 A JP 2002-356623 A Japanese Patent Laid-Open No. 03-179036

  In view of the above situation, an object of the present invention is to provide a method for adjusting the degradation rate of biodegradable plastics, particularly PHA, used in environments such as materials for agriculture, forestry and fisheries.

  As a result of intensive studies to solve the above problems, the present inventors have determined that at least one of the spore of a microorganism that produces PHA-degrading enzyme or the thermophilic bacterium that produces the enzyme is biodegradable plastic containing PHA. The present inventors have found a method of adding to the present invention and have completed the present invention.

That is, the present invention provides the following (1) to (15).
(1) A biodegradable plastic containing polyhydroxyalkanoic acid, comprising at least one spore of a microorganism producing a polyhydroxyalkanoate-degrading enzyme or a thermophilic bacterium producing the enzyme, Biodegradable plastic.
(2) The biodegradable plastic according to (1), comprising a spore of a microorganism that produces a polyhydroxyalkanoate-degrading enzyme.
(3) The polyhydroxyalkanoic acid is poly-3-hydroxybutyric acid, poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid), poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid-co-3) -Hydroxyhexanoic acid), poly (3-hydroxybutyric acid-co-3-hydroxyhexanoic acid), poly (3-hydroxybutyric acid-co-4-hydroxybutyric acid) (1) or (2) biodegradable plastic .
(4) The biodegradable plastic of (3), wherein the polyhydroxyalkanoic acid is poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid) or poly (3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) .
(5) Acidovorax genus, Alcaligenes spp, Aureobacterium sp, Comamonas sp, Marinobacter genus, Paucimonas spp, Pseudomonas spp, Steptomyces sp, Ilyobacter genus, Clostridum genus, Paecilomayces genus, Penicillium genus, Aspergillus genus, Xanthomonas spp, Bacillus spp, Thermobifida spp Or the biodegradable plastic according to any one of (1) to (4), which comprises a microorganism belonging to any of the genus Cellulomonas, or a spore thereof.
(6) The biodegradable plastic according to any one of (1) to (4), comprising spores of microorganisms belonging to any of the genus Steptomyces, Clostridium, Penicillium, Aspergillus, Bacillus, and Thermobifida.
(7) The biodegradable plastic according to (5) or (6), wherein the microorganism or a spore thereof is Bacillus megaterium or Thermobifida fusca, or a spore thereof.
(8) A method for producing a biodegradable plastic containing a polyhydroxyalkanoic acid, wherein at least one of a spore of a microorganism producing a polyhydroxyalkanoic acid-degrading enzyme or a thermophilic bacterium producing the enzyme is obtained from the plastic A manufacturing method characterized by adding at the time of melt kneading.
(9) The production method of (8), wherein a spore of a microorganism is added.
(10) A method for producing a biodegradable plastic containing a polyhydroxyalkanoic acid, wherein at least one of a spore of a microorganism that produces a polyhydroxyalkanoate-degrading enzyme or a thermophilic bacterium that produces the enzyme, A manufacturing method characterized by being added at the time of molding.
(11) The production method of (10), wherein at least one of the microorganism spores or thermophilic bacteria is sprayed or applied to the surface of the plastic before the molded plastic surface is solidified, and then the plastic surface is pressurized. .
(12) The method according to (10) or (11), wherein microbial spores are added.

  The present invention makes it possible to adjust the degradation rate of the biodegradable plastic used in the environment.

  Hereinafter, the present invention will be described in detail.

(Polyhydroxyalkanoic acid)
In the present invention, the biodegradable plastic that is subject to degradation rate adjustment is a biodegradable plastic containing polyhydroxyalkanoic acid (PHA).

  PHA is a thermoplastic polymer in which microorganisms accumulate in the cells, and a homopolymer or copolymer of 3-hydroxyalkanoic acid is known. Among them, the copolymer polymer exhibits a wide range of properties from hard to soft depending on the composition ratio of the constituent monomer components, and can be applied to a wide range of uses.

  As copolymerized PHA, poly (3-hydroxybutyric acid), poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid), poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid-co-3-hydroxyhexanoic acid) ), Poly (3-hydroxybutyric acid-co-3-hydroxyhexanoic acid), poly (3-hydroxybutyric acid-co-4-hydroxybutyric acid) and the like, and poly (3-hydroxybutyric acid-co-3-hydroxybutyric acid). Herbic acid) or poly (3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) is more preferred.

  In the case of starch and cellulose described in Patent Document 7, enzyme treatment is indispensable for particle size adjustment. As a result, when appropriate particle size is obtained, spores of enzymes and microorganisms are coated with vegetable oil and decomposed. There was a need to deter the excessive progress. On the other hand, in the case of PHA, the molecular weight can be adjusted by subjecting the production bacteria to culture conditions or chemical hydrolysis after separation from the cells. For this reason, like the said patent document 7, the microorganisms and spore which produce a PHA degrading enzyme can be contained, without passing through the complicated process of coating | covering with vegetable oil.

(Polyhydroxyalkanoic acid degrading microorganism, its spore)
The microorganism of the present invention can be separated from the environment such as soil, compost, activated sludge, river, seawater and the like. Various methods are known for the separation of microorganisms (Agricultural Chemistry Experiments, Vol. 2), but any separation method can be used as long as it can separate microorganisms that degrade biodegradable plastics. As an example, various samples obtained from the environment are suspended in sterilized water or physiological saline to prepare a cell suspension. The suspension is diluted to an appropriate bacterial concentration, and then applied to a solid medium containing polyhydroxyalkanoic acid as the sole or main carbon source, and cultured at a temperature at which the strain can grow. The culture temperature is not particularly limited as long as it is a temperature at which microorganisms can grow, but when isolating thermophilic bacteria, the culture temperature is set to a high temperature. The biodegradable plastic added to the medium can be used in any shape, but a fine powder is preferred. The concentration is not particularly limited, but a concentration at which white turbidity is caused by the biodegradable plastic added to the solid medium is preferable. Microorganisms that degrade biodegradable plastics can be detected and separated by forming a halo indicating that the polymer has been degraded around the growing bacterial colonies.

  In this way, microorganisms that degrade polyhydroxyalkanoic acids such as poly (3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) include the genera Acidovorax, Alcaligenes, Aurebacterium, Comonas, Marinobacter, Paucimonas , Pseudomonas genus, Steptomyces genus, Ilyobacter genus, Clostridium genus, Paecilomyces genus, Penicillium genus, Aspergillus genus, Xanthomonas genus, Bacillus genus, or Thermobifida genus microorganisms can be obtained.

  In the production of plastic products, high temperature conditions are often used during melt-kneading and molding, and thermophilic bacteria are preferred among the above microorganisms. In the present invention, the thermophile represents a microorganism that can grow at 42 ° C. or higher, more preferably a microorganism having an optimal growth temperature of 45 ° C. or higher, and still more preferably a microorganism having an optimal growth temperature of 55 ° C. or higher.

  Moreover, it is preferable to select a spore-forming bacterium from these microorganisms and to make the biodegradable plastic contain it in the form of a spore. Spores are highly durable, have a higher survival rate than microorganisms (viable cells) under high temperature conditions during the production of biodegradable plastic products, and should be used suitably for the production of biodegradable plastic products with a controlled degradation rate Can do.

  The spores may be endospores (including spores) or exogenous spores. The spore-forming bacteria can be selected by culturing the aforementioned microorganisms under spore-forming conditions well known to those skilled in the art and observing them under a microscope.

  Suitable spore-forming microorganisms for the present invention include microorganisms belonging to the genus Steptomyces, Clostridium, Penicillium, Aspergillus, Bacillus, Thermobifida, and the spores of these microorganisms are preferably used.

  Among these, microorganisms belonging to the genus Bacillus or Thermobifida are more preferable, Bacillus megaterium or Thermobifida fusca is further preferable, and spores of these microorganisms are particularly preferable.

  A cell cake can be produced by culturing the microorganism, washing and centrifuging the culture broth. Moreover, a dry microbial cell can also be produced by freeze-drying or spray-drying a microbial cell cake. Since degradation of biodegradable plastics is affected by the number of viable bacteria, a mild method such as freeze-drying is suitable for the cells, but it can be used as long as the microorganisms are alive.

  Moreover, the said spore can be adjusted in large quantities by culture | cultivating the microorganisms which form a spore on sporulation conditions. The formed spores can be separated from the microorganisms and recovered by various methods. In this case, the microorganism and spore can be used without separation.

(Addition of microorganisms and spores to PHA)
A biodegradable plastic product containing the microorganism or spore can be obtained by adding a spore of a microorganism that produces a degrading enzyme of the biodegradable plastic or a thermophilic bacterium that produces the enzyme in a kneaded state before molding processing. Can be manufactured. The biodegradable plastic product according to the present invention can be easily prepared by a known method generally used as a method for preparing a known resin composition.

  In the present invention, the spore or thermophile can be added to the biodegradable plastic without additional treatment such as coating with vegetable oil or microencapsulation. However, although spores and thermophilic bacteria have heat resistance compared to general microorganisms, it is preferable to apply a processing method that minimizes the thermal history of spores and thermophilic bacteria. For example, after mixing biodegradable plastics and microbial spores that produce biodegradable plastic degrading enzymes or thermophilic bacteria that produce the enzymes, and if necessary, other ingredients, an extruder, a roll mill, Examples thereof include a method of kneading with a known melt kneader such as a Banbury mixer or a kneader to form pellets and then subjecting to molding.

  In addition, a method of preparing a high-concentration master batch containing the spore or thermophile in advance and mixing it with a biodegradable plastic at a desired ratio and immediately using it for molding can be used.

  The spore and thermophilic bacterium are introduced into a melt kneader at the same time as the biodegradable plastic and kneaded. In addition, the biodegradable plastic is melted in advance, and then a spore of a microorganism that produces a degrading enzyme later. Alternatively, a method of adding and kneading thermophilic bacteria that produce the enzyme can also be used.

  In addition, when the biodegradable plastic is continuously produced in a strand form like an extruder, the strand is put in a spore of a microorganism that produces a degrading enzyme or a bath containing a thermophilic bacterium that produces the enzyme. A method of adhering to the surface of the strand by dipping and passing can also be suitably used.

  The resin composition of the present invention can be molded by a known method. Examples thereof include inflation molding, sheet molding, injection molding, blow molding, fiber spinning, extrusion foaming, and bead foaming. As described above, the spore of a microorganism that produces a biodegradable plastic and a degrading enzyme or a thermophilic bacterium that produces the enzyme is added at the time of melt-kneading or is attached to the surface after melt-kneading and then subjected to molding processing. However, it is also possible to use a method of directly molding by mixing the biodegradable plastic and the spore of the microorganism producing the degrading enzyme or the thermophilic bacterium producing the enzyme during the molding process.

  In addition, the spore of the microorganism producing the degrading enzyme or the thermophilic bacterium producing the enzyme is directly sprayed or applied to the biodegradable plastic product at the time of the molding process so that the spore or thermophilic bacterium is fixed. Plastic products can be manufactured. More preferably, the spore or thermophile is sprayed or applied before the molded biodegradable plastic surface is solidified and then the biodegradable plastic surface is pressurized. According to this method, spores and thermophilic bacteria can be more firmly fixed to the surface of the biodegradable plastic.

  For example, when spinning continuously as in fiber spinning, the surface of the fiber is immersed in a spore containing a microbial spore producing a degrading enzyme or a thermophilic bacterium producing the enzyme. It can be applied and adhered to. In the case of sheet molding, before the sheet is solidified, spore of microorganisms that produce degrading enzymes and thermophilic bacteria that produce the enzymes are applied or sprayed to adhere to the surface, and then from both sides of the sheet by a pressure roll. By applying pressure, microorganisms attached to the surface and spores of the microorganisms can be fixed to the sheet.

  In this production method, the above-mentioned thermophilic bacteria and spores can be used without particular limitation, but since they are exposed to high temperatures during the molding process of the plastic product, they are more excellent in heat resistance among the above-mentioned thermophilic bacteria and spores. It is more preferable to use thermophilic bacteria and spores, and it is more preferable to use spores excellent in heat resistance.

  Since the biodegradability of a biodegradable plastic product depends on the number of proliferating microorganisms or spores immobilized on the product surface and / or inside the product, the number of viable microorganisms or viable spores of the microorganisms By adjusting, the degradation rate of the biodegradable plastic product can be adjusted. When fixed inside the product, the surface of the product undergoes biodegradation, and then the microorganisms and / or spores existing inside grow to accelerate the degradation.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention does not limit the technical scope by these Examples.

(Example 1) Isolation of biodegradable plastic (PHA) degrading bacteria Using an extract obtained from compost subjected to primary and secondary fermentation in Niitsu City, Niigata Prefecture, 30 ° C, 37 ° C or 55 ° C on NB medium Microorganisms that formed colonies at ℃ were cultured at 37 ℃ or 55 ℃ on agar medium in which 0.3% PHBH powder (manufactured by Kaneka Co., Ltd., trade name Aonilex) was mixed with NB medium to form a lysis zone We searched for microorganisms to do.
As a result, various microorganisms were isolated from the agar medium cultured at 37 ° C., and identified as Bacullus megaterium, Cellulomonas cellurans, Cellulomicrobacterium cellurans based on the 16SrDNA sequence. In addition, a high-temperature microorganism was isolated from the agar medium cultured at 55 ° C., and identified as Thermobifida fusca based on the 16S rDNA sequence. Of these, Bacullus megaterium and Thermobifida fusca form spores.

  The Bacullus megaterium and Cellulonas cellurans are deposited at the Patent Organism Depositary (National Institute of Advanced Industrial Science and Technology, 1-11, Tsukuba City, Castle Prefecture) under the accession numbers of FERM P-20422 and FERM P-20423, respectively. ing.

(Example 2) Spore adjustment of biodegradable plastic (PHA) -degrading bacteria Thermobifida fusca (Japanese Patent Application No. 2008-054082) was cultured in an LB medium containing 10 mg / L of PHBH powder at 50 ° C for 2 days. After confirming that the added PHBH powder was decomposed and spore formation with a microscope, cells and spores were obtained by centrifugation. After washing twice with sterilized water, the cells and spore pellets were prepared by centrifugation. The resulting pellet was freeze-dried to obtain bacterial cells and spore powder. A part of the powder was resuspended in sterilized water, and the diluted solution was applied to an LB agar medium and cultured at 50 ° C. to confirm the viable cell count.

  In this example, Thermobifida fusca obtained by the present inventors was used, but the effect of the present invention is not limited to this specific strain, and microorganisms such as American Type Culture Collection (ATCC) can be preserved. It goes without saying that other strains of Thermobifida fusca available from the institution may be used.

(Examples 3 to 5) Manufacture of biodegradable plastic product with controlled biodegradation rate PHBH powder (stock) The product was manufactured by Kaneka Co., Ltd. (trade name: Aonilex) and kneaded into pellets. The obtained pellets were molded using a single screw extruder (labor plast mill 20C200, manufactured by Toyo Seiki Seisakusho Co., Ltd.) equipped with a T-shaped die having a width of 150 mm and a lip thickness of 0.25 mm, and a screw rotation speed of 80 rpm. Extrusion molding was performed under the following conditions. By rapidly cooling with a cooling roll and applying the aqueous suspension of microorganisms producing the degrading enzyme prepared in Example 2 and the spores before solidifying the sheet surface, and then applying pressure from both sides of the sheet with a pressure roll The microorganisms and spores of the above microorganisms were fixed on the sheet surface. The concentration of microorganisms and spores in the aqueous suspension (colony forming unit: CFU) was 10 ³ / ml, 10 ⁵ / ml, 10 ⁷ / ml. The thickness of the obtained sheet was about 100 μm.
The obtained sheet was cut into a square of about 10 cm, and a biodegradation test was performed in a planting sowing soil “flower and vegetable soil” (components: peat moss, bark compost) manufactured by Garden Fantasy. The surface state of the sheet was visually observed and evaluated by the number of days required for starting decomposition and the number of days required for disappearance. The evaluation results are shown in Table 1.
(Comparative Example 1)
A sheet was molded in the same manner as in Example 3 except that the microorganisms producing the degrading enzyme and spores were not applied, and a biodegradation test was performed. The results are shown in Table 1.

Claims (2)

A method for producing a biodegradable plastic containing polyhydroxyalkanoic acid, wherein at least one of a spore of a microorganism producing a polyhydroxyalkanoic acid degrading enzyme or a thermophilic bacterium producing the enzyme is formed on the surface of the molded plastic A method of manufacturing, characterized in that the material is sprayed or applied to the surface of the plastic before it is solidified, and then added during molding of the plastic by pressurizing the plastic surface . The process according to claim 1, wherein the addition of microbial spores.