JP6233566B2 - Degradation method of biodegradable resin - Google Patents

Description

  The present invention relates to a method for efficiently degrading a biodegradable resin.

  Biodegradable resins such as polylactic acid-based resins have been expanded in use such as packaging materials, multi-films in the agricultural field, and well drilling methods for excavating underground resources. Along with this, there is a demand for development of technologies for various applications such as improvement of the degradation rate of biodegradable resins, development of degradation triggers or degradation rate control technologies. In the case of the rotary drilling method, drilling with a drill while circulating mud water, a dehydration regulator is used as the finishing fluid, forming a kind of filtration membrane called mud wall, and keeping the pit wall stable and collapsing Prevents friction and reduces friction. In addition, the hydraulic fracturing method pressurizes the fluid filling the well at high pressure, thereby generating a crack (fracture) in the vicinity of the well, improving the permeability (fluidity of fluid flow) in the vicinity of the well, It expands the effective cross section of resources such as oil and gas into the well, and increases the productivity of the well.

  In the case of finishing fluids, calcium carbonate and granular salts are mainly used as dehydration regulators, but they require acid treatment when removing them and cause production problems due to root clogging in well formations. Yes. The fluid used in the hydraulic fracturing method is also called a fracturing fluid. In the past, viscous fluid such as gel-like gasoline was used, but recently it has been produced from a shale layer that exists in a relatively shallow place. With the development of shale gas and the like, an aqueous dispersion in which a polymer is dissolved or dispersed in water has been used in consideration of the influence on the environment. Polylactic acid is known as such a polymer.

That is, polylactic acid is a substance exhibiting hydrolyzability and enzymatic decomposability, and even if it remains in the ground, it is not adversely affected by the environment because it is degraded by moisture and enzymes in the ground. In addition, it can be said that water used as a dispersion medium has little influence on the environment as compared with gasoline.
Moreover, when such an aqueous dispersion of polylactic acid is filled in a well and pressurized, the polylactic acid penetrates into the vicinity of the well, but this polylactic acid is hydrolyzed and loses its resin form. As a result, a space (that is, a crack) is generated in a portion where the polylactic acid has permeated, and therefore, it is possible to increase a space for inflow of resources to the well.
Furthermore, polylactic acid also functions as a dehydration regulator, and has the function of suppressing excessive penetration of water used as a dispersion medium into the ground and minimizing environmental changes to the formation. ing. Since it decomposes in the ground, no acid treatment is required.
Lactic acid, which is a degradation product of polylactic acid, is a kind of organic acid. After polylactic acid is decomposed, lactic acid is released, and the shale of the shale layer is eroded by acid, thereby promoting the porosity of the shale.

  However, although polylactic acid hydrolyzes relatively quickly at temperatures of 100 ° C. or higher, the hydrolysis rate is slow at less than 100 ° C., and therefore, it is applied to collection of shale gas and the like produced from places with low underground temperatures. In some cases, the efficiency is poor and improvement is required.

On the other hand, it has been proposed to use polyglycolic acid instead of polylactic acid. Polyglycolic acid is also known as a biodegradable resin, and is more hydrolyzable than polylactic acid. For example, the hydrolysis rate at a temperature of about 80 ° C. is considerably faster than polylactic acid. Effective as an alternative to lactic acid.
However, polyglycolic acid has a problem that it is considerably more expensive than polylactic acid, which is a fatal defect in the hydraulic fracturing method in which a large amount of fracturing fluid is used. Also, sufficiently satisfactory decomposability cannot be obtained under specific temperature conditions.

  In order to efficiently decompose the biodegradable resin, for example, an easily degradable resin composition having improved biodegradability has been developed by blending an aliphatic polyester that releases acid by hydrolysis (International Publication 2008). In addition, a method for decomposing the above easily decomposable resin composition has been reported (Japanese Patent Laid-Open No. 2010-138389). However, in addition to the above technique, development of a technique for further improving the degradation rate of the biodegradable resin is desired.

International Publication No. 2008-038648 JP 2010-138389 A

  An object of this invention is to provide the method of decomposing | disassembling biodegradable resin efficiently.

  The present inventors have found that when decomposing a biodegradable resin in a buffer solution, the biodegradable resin can be efficiently decomposed by using a predetermined biodegradable resin degrading enzyme and a buffer solution. It came to complete.

  That is, the present invention is a method for degrading a biodegradable resin in a buffer solution containing a biodegradable resin degrading enzyme having an optimum pH of 7.5 or more, wherein the buffer solution is an equilibrium type of the buffer. Provided is a method in which an anion derived from a buffer component does not exist on one side, and the pH is adjusted within a pH range that gives a condition that the equilibrium is inclined to the side on which no anion exists.

  According to the present invention, the biodegradable resin can be decomposed at high speed.

The results of degradation of polylactic acid films using different types and pH buffers are shown.

  In the present invention, the biodegradable resin is not particularly limited, and generally, an aliphatic polyester having biodegradability is used. Examples of the aliphatic polyester having biodegradability include polylactic acid resin, polybutylene succinate, polycaprolactone, polyhydroxybutyrate, polybutylene succinate / adipate copolymer, and a copolymer of the above aliphatic polyester, Examples thereof include a copolymer of an aromatic polyester such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate and the above aliphatic polyester. These may be used alone or in combination of two or more.

Examples of the component that forms the aliphatic polyester copolymer include ethylene glycol, propylene glycol, butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, polyethylene glycol, and the like. Dihydric alcohols such as succinic acid, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, anthracene dicarboxylic acid; glycolic acid, L-lactic acid, D-lactic acid, hydroxy Hydroxycarboxylic acids such as propionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, mandelic acid, hydroxybenzoic acid; glycolide, caprolactone, butyrolactone Lactones such as valerolactone, poropiolactone and undecalactone.
Examples of the polymer to be blended include celluloses, chitin, glycogen, chitosan, polyamino acid, starch and the like. In addition, the lactic acid used for the polymerization when using polylactic acid may be either L-form or D-form, or a mixture of L-form and D-form.

Examples of preferable aliphatic polyester having biodegradability include polylactic acid resins and polybutylene succinates, and polylactic acid resins are particularly preferable.
The molecular weight of the aliphatic polyester having biodegradability is not particularly limited, but considering the mechanical properties and processability when manufacturing containers using biodegradable resins containing aliphatic polyester. The weight average molecular weight is preferably in the range of 5,000 to 1,000,000, and more preferably in the range of 10,000 to 500,000.

  For the biodegradable resin decomposed by the method of the present invention, known plasticizers, heat stabilizers, light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, colorants, pigments, fillers may be used as necessary. Additives such as fillers, mold release agents, antistatic agents, fragrances, lubricants, foaming agents, antibacterial / antifungal agents, and nucleating agents may be blended. Moreover, you may mix | blend resin other than the aliphatic polyester which has biodegradability in the range which does not impair the effect of this invention. For example, in addition to water-soluble resins such as polyethylene glycol and polyvinyl alcohol, polyethylene, polypropylene, ethylene-propylene copolymer, acid-modified polyolefin, ethylene-methacrylic acid copolymer, ethylene-vinyl acetate copolymer, ionomer resin, polyethylene Terephthalate, polybutylene terephthalate, polyvinyl acetate, polyvinyl chloride, polystyrene, polyester rubber, polyamide rubber, styrene-butadiene-styrene copolymer, and the like can be blended.

The above-mentioned enzyme-decomposable resin may be blended with an esterolysis-promoting hydrolyzed resin (hereinafter sometimes simply referred to as “ester-decomposable resin”) in order to improve degradability.
This ester-decomposable resin does not exhibit ester resolution by itself, but releases acid or alkali that functions as a catalyst for ester decomposition when mixed with moisture.

  Such an ester-decomposable resin is usually uniformly dispersed inside the above-mentioned hardly hydrolyzable hydrolyzable resin, and the hydrolyzable resin is hydrolyzed by an acid or alkali released from the ester-decomposable resin. In order to accelerate the decomposition rapidly, for example, those having a weight average molecular weight of about 1,000 to 200,000 are used.

  In addition, as such an ester-decomposing resin, alkali-releasing ones such as alkali metal salts of acrylic acid such as sodium acrylate and sodium alginate can be used. Acid releasing agents are preferably used.

As the acid-releasing ester-decomposing resin, the pH (25 ° C.) in an aqueous solution or dispersion having a concentration of 0.005 g / ml is 4 or less, particularly 3 or less, and when mixed with water, Polymers that readily hydrolyze to release acid are preferably used.
Examples of the polymer include polyoxalate and polyglycolic acid. These may be copolymers, used alone or in combination of two or more.
Examples of the components forming the copolymer include polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethylene glycol; succinic acid, adipine Acids, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, anthracene dicarboxylic acid and other dicarboxylic acids; glycolic acid, L-lactic acid, D-lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxy Hydroxycarboxylic acids such as valeric acid, hydroxycaproic acid, mandelic acid, hydroxybenzoic acid; glycolide, caprolactone, butyrolactone, valerolactone, polo Examples include lactones such as piolactone and undecalactone.

  In the present specification, a polymer obtained by polymerizing oxalic acid as at least one monomer in a homopolymer, copolymer, or blend is referred to as polyoxalate.

  In particular, the above-mentioned polyoxalate and polyglycolic acid are easily hydrolyzable hydrolyzable resins and rapidly hydrolyze, so that they are excellent in the ability to promote hydrolysis of hardly hydrolyzable resins. Among these, polyoxalates, particularly polyethylene oxalate, show remarkably high hydrolysis promoting ability compared to polyglycolic acid, and hydrolyze hardly hydrolyzable resins such as polylactic acid even at a temperature of 80 ° C. or lower. It can be remarkably accelerated, and is considerably cheaper than polyglycolic acid, and the merit of cost is extremely large.

  The biodegradable resin that is decomposed by the method of the present invention can adopt forms such as pellets, films, powders, single-layer fibers, core-sheath fibers, and capsules, but is not limited thereto and is known per se. It can manufacture by the method of.

  The biodegradable resin-degrading enzyme used in the present invention is not particularly limited as long as the optimum pH is 7.5 or more and generally decomposes the biodegradable resin. Can be used. The optimum pH of the enzyme is more preferably 8.0 or more, and even more preferably 8.5 or more. As such an enzyme, alkaline protease, alkaline cellulase, esterase, cutinase, lipase and the like are preferable, and for example, Savinase manufactured by novozymes can be used. The amount of the enzyme can be appropriately determined by those skilled in the art. For example, the amount of the enzyme can be determined according to the type of biodegradable resin to be decomposed based on the activity unit for each enzyme used.

  As the buffer used in the present invention, there is no anion derived from the buffer component on one side of the buffer equilibrium type, and the pH is a pH range that gives a condition that the equilibrium is inclined to the side where the anion does not exist An adjusted buffer is used. As such a buffer solution, good buffer components such as Tris-HCl buffer solution (Trisaminomethane) or 2-cyclohexylaminoethanesulfonic acid (CHES) buffer solution, Bistris buffer solution, MOPS buffer solution, HEPES buffer solution, etc. Examples include those having a buffer solution, and the above-mentioned buffer solution is used by adjusting it so as to be within a pH range that gives a condition that the equilibrium is inclined to the side where the anion derived from the buffer component does not exist. Further, on the premise that the above pH condition is satisfied, the pH of the buffer solution is preferably 7.5 or more, more preferably 8.0 or more, 8.5 or more, 9.0 or more, It is particularly preferably 9.5 or more and 10.0 or more.

  In the present invention, “the pH range that gives the condition that the equilibrium is inclined toward the side where no anion (derived from the buffer component) does not exist” completely excludes the presence of the anion derived from the buffer component in the buffer solution. It is not a thing. Typically, the pH range that gives the condition that the equilibrium is tilted to the side without an anion is determined as a range that is larger or smaller than the pKa value (depending on the equilibrium equation), based on the pKa value of the equilibrium. Is possible. As long as the above conditions are satisfied, the pH of the buffer solution may be outside the buffer pH range.

For example, when Tris-HCl buffer (trisaminomethane) (pKa = 8.06) (see Example 1 described later) is used as the buffer, the pH is higher than 8.06, for example, 8.5 or more, 9.0 or more, 10.0 or more, 10.5 It can be set as above. Similarly, when CHES buffer (pKa = 9.3) (see Example 2 described later) is used, the pH can be lower than 9.3, for example, 9.0 or less, 8.5 or less, 8.0 or less, etc. In view of the active pH range of the enzyme to be used, the lower limit of the pH of the buffer solution is preferably 7.5 or more, 8.0 or more, 8.5 or more.
The concentration of the buffer solution can be appropriately determined by those skilled in the art. For example, a buffer solution having a salt concentration of 10 mM to 200 mM, preferably 50 mM to 150 mM can be used.

  Furthermore, conditions such as time and temperature for degrading the biodegradable resin in the buffer can be appropriately determined by those skilled in the art according to the type and amount of the enzyme used and the biodegradable resin.

  Hereinafter, the present invention will be specifically described by way of examples.

Preparation of polylactic acid film A polylactic acid film (manufactured by Natureworks) was formed into a 100 μm polylactic acid film at 210 ° C. using a lab plast mill (manufactured by Toyo Seiki Seisakusho).

The biodegradable resin-degrading enzymes used are as follows.
Savinase enzyme solution
Savinase 16.0L (novozymes) was used.

The following buffers were used.
(i) Tris buffer (7.0-9.0 pKa = 8.06)

(ii) CHES buffer (8.6-10.0 pKa = 9.3)

(iv) Bicine緩衝液(7.0〜9.0 pKa=8.06)

(v) TAPS緩衝液(7.5〜9.4 pKa=8.44)

(vi) Tricine緩衝液(7.2〜9.1 pKa1=2.3 pKa2=8.15)

(iii) Phosphate buffer (5.8-8.0 pKa1 = 2.12 pKa2 = 7.21 pKa3 = 12.67)

(iv) Bicine buffer (7.0-9.0 pKa = 8.06)

(v) TAPS buffer (7.5-9.4 pKa = 8.44)

(vi) Tricine buffer (7.2-9.1 pKa1 = 2.3 pKa2 = 8.15)

  Two types of pH 9.0 and pH 10.5 were prepared for the above (ii) CHES buffer, and those adjusted to pH 10.5 were used for the other buffers.

Enzymatic degradation test for biodegradable film
Polylactic acid film cut into 2cm x 2cm (120mg) by adding 100μL of Savinase enzyme solution to 30ml of each buffer solution adjusted to 100mM, pH10.5 (pH9.0 and pH10.5 only for CHES buffer) Was soaked and shaken at 45 ° C. and 100 rpm for 16 hours. After 16 hours, the film was taken out and dried at 70 ° C. for 3 hours. The initial weight of the film−the weight after decomposition = the amount of decomposition (mg).

Example 1
100 μL of Savinase enzyme solution was added to 30 ml of Tris buffer solution adjusted to 100 mM and pH 10.5 to make a decomposition solution, and the polylactic acid film cut out to 2 cm × 2 cm (120 mg) was immersed and shaken at 45 ° C. and 100 rpm for 16 hours. After 16 hours, the film was taken out and dried at 70 ° C. for 3 hours. The initial weight of the film−the weight after decomposition = the amount of decomposition (mg).
(Example 2)
The same procedure as in Example 1 was carried out except that the buffer solution was CHES buffer adjusted to 100 mM and pH 9.0.
(Comparative Example 1)
The same procedure as in Example 1 was performed except that the buffer solution was a phosphate buffer solution.
(Comparative Example 2)
The same procedure as in Example 1 was performed except that the buffer was changed to Bicine buffer.
(Comparative Example 3)
The same procedure as in Example 1 was performed except that the buffer solution was TAPS buffer solution.
(Comparative Example 4)
The same procedure as in Example 1 was performed except that the buffer solution was Tricine buffer.
(Comparative Example 5)
The same procedure as in Example 2 was performed except that the pH of the CHES buffer was 10.5.

The results of the degradation of the polylactic acid films in Examples 1-2 and Comparative Examples 1-5 are shown in Table 2 below and FIG.
From these results, it is understood that Examples 1 and 2 using the predetermined buffer solution of the present application can highly decompose the polylactic acid film.

Claims (6)

A method of degrading a biodegradable resin in a buffer containing a biodegradable resin-degrading enzyme having an optimum pH of 7.5 or higher, wherein the buffer is trisaminomethane adjusted to a pH of 9.5 or higher. There is a way.   The method according to claim 1, wherein the buffer is trisaminomethane adjusted to pH 10.0 or higher.   The method according to claim 1 or 2, wherein the buffer is trisaminomethane adjusted to pH 10.5 or higher. The method according to any one of claims 1 to 3 , wherein the biodegradable resin-degrading enzyme is an alkaline protease. Biodegradable resin comprises a polylactic acid resin, Process according to any one of claims 1-4. Biodegradable resin, pellets, film, powder, monolayer fibers, in the form of core-sheath fibers or capsule, the method according to any one of claims 1-5.

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