JP7049627B2 - Hydrolysis method of resin composition - Google Patents

Description

The present invention relates to a method for rapidly hydrolyzing a hydrolyzable resin composition in a decomposition solution having a specific pH.

In recent years, with the deterioration of the global environment, there has been increasing interest in resin recycling and additives that are safe for living organisms and have a low impact on the global environment. Resins typified by polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL) and the like are used as biodegradable resins that are decomposed by water or enzymes in a natural environment or in a living body. For example, PLA is used for disposable containers, packaging materials, etc. because it has good workability and excellent mechanical strength of molded products. However, PLA has a slower hydrolysis rate than PGA and PCL.

As a method for improving the hydrolysis rate of PLA, for example, a method of blending a hydrophilic additive such as polyethylene glycol with PLA has been proposed. However, PLA has low hydrophilicity and is difficult to be compatible with hydrophilic substances such as polyethylene glycol. Therefore, it is not practical because the hydrophilic additive may be embossed during or after molding (bleed out), the mechanical strength of the molded product may be lowered, or the appearance such as transparency may be impaired.

Regarding the hydrolysis of PLA, hydrolysis in acidity or alkalinity has been reported (for example, Non-Patent Documents 1 and 2). In particular, Non-Patent Document 2 examines the difference in hydrolyzability between acidic, neutral and alkaline, and describes that the hydrolyzability at alkaline (pH 12) is higher than that at neutral and acidic.

The applicant also proposes to promote the hydrolysis of PLA by adding a copolymer having a specific structural unit (for example, Patent Documents 1 and 2). In particular, Patent Documents 1 and 2 study hydrolyzability at 50 ° C. to 80 ° C. in a substantially neutral liquid such as distilled water or ion-exchanged water.

International Publication No. 2012/137681 International Publication No. 2014/038608

Properties and Morphology of Poly (L-lactide). II. Hydrolysis in Alkaline Solution, Journal of Polymer Science, Part A, Polymer Chemistry, Vol. 36, 59-66 (1998) Poly (L-lactide). IX. Hydrolysis in Acid Media, Journal of Applied Polymer Science, Vol. 86, 186-194 (2002)

As described above, it is known that the hydrolyzable resin composition has a faster hydrolysis rate under alkaline conditions than under neutral or acidic conditions. Further, even if the resin composition is hydrolyzed in an alkaline decomposition solution, the pH of the decomposition solution may decrease as the hydrolysis reaction progresses, and the hydrolysis rate may decrease.

That is, an object of the present invention is to provide a method for rapidly hydrolyzing a hydrolyzable resin composition in a decomposition solution having a specific pH.

The present inventors have found that it is possible to increase the hydrolysis rate of the resin composition even under specific pH conditions by increasing the salt concentration of the decomposition solution to a specific value or higher, and the present invention has been made. Has been completed. That is, the present invention is specified by the following matters.

[1] A resin composition (C) containing a hydrolyzable polymer (A) and a hydrolysis accelerator (B) is hydrolyzed in a decomposition solution having a pH of 1.0 or more and 9.6 or less. A method for hydrolyzing a resin composition, wherein the decomposition solution has a salt concentration of 0.1 mol / L or more.

[2] The hydrolysis method according to [1], wherein the hydrolyzable polymer (A) is polyester.

[3] The hydrolysis method according to [2], wherein the hydrolyzable polymer (A) is polylactic acid.

[4] The hydrolyzable polymer (A) has a structural unit (a-1) derived from a hydroxycarboxylic acid, and the hydrolysis accelerator (B) has the structural unit (a-1) and a polyvalent carboxylic acid. The hydrolysis method according to any one of [1] to [3], which has a structural unit (b-1) derived from an acid.

[5] The water addition according to [4], wherein the polyvalent carboxylic acid of the constituent unit (b-1) is one or more polyvalent carboxylic acids selected from the group consisting of aspartic acid, glutamic acid, citric acid and malic acid. Disassembly method.

[6] The hydrolysis method according to [5], wherein the polyvalent carboxylic acid of the constituent unit (b-1) is one or more polyvalent carboxylic acids selected from the group consisting of aspartic acid and glutamic acid.

[7] The hydrolysis method according to [5], wherein the polyvalent carboxylic acid of the structural unit (b-1) is one or more polyvalent carboxylic acids selected from the group consisting of citric acid and malic acid.

[8] The mass ratio (A / B) of the hydrolyzable polymer (A) and the hydrolysis accelerator (B) in the resin composition (C) is 95/5 to 50/50 [1]. ] To [7]. The hydrolysis method according to any one of.

[9] The hydrolysis method according to any one of [1] to [8], wherein the salt concentration in the decomposition liquid is 0.2 mol / L or more and 30 mol / L or less.

[10] The hydrolysis method according to [9], wherein the salt concentration in the decomposition liquid is 0.4 mol / L or more and 10 mol / L or less.

[11] The hydrolysis method according to any one of [1] to [10], wherein the pH of the decomposition solution is 1.0 or more and 8.0 or less.

In the present invention, since a decomposition solution having a specific pH having a salt concentration of a specific value or higher is used, the hydrolyzable resin composition can be rapidly hydrolyzed.

<Polymer having hydrolyzability (A)>
The hydrolyzable polymer (A) (hereinafter, simply referred to as “polymer (A)”) used in the present invention may be any hydrolyzable polymer, and the type thereof is not particularly limited. As the polymer (A), for example, polyester is preferable, and an aliphatic polyester resin composed of polyhydroxycarboxylic acid, diol and dicarboxylic acid is more preferable.

In the present invention, the polyhydroxycarboxylic acid means a polymer or a copolymer having a repeating unit (constituent unit) (a-1) derived from a hydroxycarboxylic acid having both a hydroxyl group and a carboxyl group.

Specific examples of hydroxycarboxylic acid include lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, and 2-hydroxy-3-methyl. Butyric acid, 2-methyllactic acid, 2-hydroxyvaleric acid, 2-hydroxycaproic acid, 2-hydroxylauric acid, 2-hydroxymyristic acid, 2-hydroxypalmitic acid, 2-hydroxystearic acid, malic acid, citric acid, tartaric acid , 2-Hydroxy-3-methylbutyric acid, 2-cyclohexyl-2-hydroxyacetic acid, mandelic acid, salicyric acid, caprolactone and other lactones, ring-opening products. Two or more of these may be mixed and used.

The polyhydroxycarboxylic acid may contain a structural unit (copolymer component) other than the hydroxycarboxylic acid as long as the hydrolytic property is not significantly impaired. However, the ratio of the hydroxycarboxylic acid-derived structural units to 100 mol% of the total structural units of the polyhydroxycarboxylic acid is preferably 20 mol% or more, more preferably 50 mol% or more, and particularly preferably 100%.

Among the polyhydroxycarboxylic acids, a polymer or a copolymer in which the hydroxycarboxylic acid is lactic acid is preferable, and polylactic acid (a homopolymer) is more preferable, from the viewpoint of compatibility with the hydrolysis accelerator (B). Polylactic acid may be synthesized using lactic acid as a starting material or lactide as a starting material.

In the present invention, the aliphatic polyester resin composed of a diol and a dicarboxylic acid means a polymer or a copolymer containing a repeating unit (constituent unit) derived from the diol and the dicarboxylic acid. The aliphatic polyester resin may contain a structural unit (copolymer component) other than the structural unit derived from the diol and the dicarboxylic acid, as long as the hydrolyzability is not significantly impaired.

Specific examples of the aliphatic polyester resin composed of diol and dicarboxylic acid include polyethylene succinate, polyethylene adipate, polyethylene sebacate, polydiethylene succinate, polydiethylene adipate, polyethylene succinate adipate, polydiethylene sebacate, and polybutylene succinate. , Polybutylene adipate, polybutylene succinate adipate, polybutylene sebacate and the like.

The molecular weight of the polymer (A) is not particularly limited, but it is preferably larger than the molecular weight of the hydrolysis accelerator (B). Considering the ease of mixing with the hydrolysis accelerator (B), the weight average molecular weight of the polymer (A) is preferably 2,000 to 2,000,000, more preferably 3,000 to 1,000. It is 000, particularly preferably more than 50,000 and less than 500,000. This weight average molecular weight is a value measured under the conditions described in Examples described later.

<Hydrolysis promoter (B)>
The type of the hydrolysis accelerator (B) used in the present invention is not particularly limited as long as it promotes the hydrolysis property of the polymer (A). In particular, it is preferable that the copolymer contains a structural unit (a-1) derived from a hydroxycarboxylic acid and a structural unit (b-1) derived from a polyvalent carboxylic acid. The "constituent unit" is a unit derived from a polymerizable monomer and does not include a terminal group. The hydrolysis accelerator (B) may be a random copolymer, a block copolymer, or a graft copolymer.

The structural unit (b-1) is not particularly limited as long as it is a structural unit derived from a polyvalent carboxylic acid. The polyvalent carboxylic acid is preferably one or more polyvalent carboxylic acids selected from divalent or trivalent polyvalent carboxylic acids. Among them, aminodicarboxylic acid, hydroxydicarboxylic acid and hydroxytricarboxylic acid are more preferable, and one or more selected from aspartic acid, glutamic acid, malic acid, citric acid and tartrate acid are particularly preferable. Two or more of these polyvalent carboxylic acids may be used in combination. The structural unit (b-1) may form a ring structure such as an imide ring, the ring structure may be ring-opened, or these may be mixed.

When the hydrolysis accelerator (B) is a copolymer having the structural unit (a-1) and the structural unit (b-1) described above, the specific type thereof is not particularly limited, but aspartic acid-lactic acid. Copolymers, malic acid-lactic acid copolymers and citric acid-lactic acid copolymers are particularly preferred.

The molar composition ratio [(a-1) / (b-1)] of the structural unit (a-1) and the structural unit (b-1) in the hydrolysis accelerator (B) is preferably the amount charged at the time of polymerization. Is 1/1 to 50/1, more preferably 10/1 to 20/1. When the molar composition ratio is within these ranges, a copolymer having an excellent effect of promoting the decomposition rate and an excellent compatibility with the polymer (A) can be obtained.

The hydrolysis accelerator (B) may contain a structural unit (a unit derived from another copolymerization component) other than the polyvalent carboxylic acid and the hydroxycarboxylic acid. However, the amount needs to be such that the properties of the hydrolysis accelerator (B) are not significantly impaired. From this point of view, the amount thereof is preferably 20 mol% or less in 100 mol% of the total constituent units of the hydrolysis accelerator (B).

The weight average molecular weight of the hydrolysis accelerator (B) is preferably 1,000 or more and 50,000 or less, more preferably 2,500 or more and 30,000 or less, and particularly preferably 2,500 or more and 10,000 or less. be. This weight average molecular weight is a value measured under the conditions described in Examples described later.

The method for producing the hydrolysis accelerator (B) is not particularly limited. Generally, it is obtained by mixing a polyvalent carboxylic acid and a hydroxycarboxylic acid in a desired ratio and dehydrating and polycondensing them in the presence or absence of a catalyst under heating and reduced pressure. It can also be obtained by reacting an anhydrous cyclic compound of a hydroxycarboxylic acid such as lactide, glycolide, or caprolactone with a polyvalent carboxylic acid.

<Resin composition (C)>
The resin composition (C) used in the present invention can be obtained by mixing the polymer (A) and the hydrolysis accelerator (B). The mass composition ratio (A / B) is preferably 95/5 to 50/50, more preferably 95/5 to 55/45, with the total amount of the polymer (A) and the hydrolysis accelerator (B) being 100. Particularly preferably, it is 95/5 to 60/40, and most preferably 95/5 to 80/20. When the mass composition ratio is within these ranges, the decomposition rate promoting effect of the hydrolysis accelerator (B) tends to be more exhibited while maintaining the properties of the polymer (A). Further, the larger the amount of the hydrolysis accelerator (B), the higher the decomposition rate of the resin composition (C) tends to be obtained.

The method of mixing the hydrolysis accelerator (B) with the polymer (A) is not particularly limited. Preferably, both are melt-kneaded or dissolved in a solvent and stirred and mixed. By such a method, a uniform resin composition having both components can be obtained.

The resin composition (C) contains a hydrolysis accelerator (B) and an additive that can be added to a polymer other than the polymer (A) or an ordinary resin within a range that does not significantly impair the properties of the polymer (A). You may have.

The molecular weight of the resin composition (C) is not particularly limited. Considering moldability, the weight average molecular weight of the resin composition (C) is preferably 1,000 to 1,000,000, more preferably 5,000 to 500,000, and particularly preferably 50,000 to 300, It is 000. This weight average molecular weight is a value measured under the conditions described in Examples described later.

The resin composition (C) according to the present invention can be molded into various shapes such as films, sheets, fibers, tablets and the like by a known molding method.

<Hydrolyzing method>
The hydrolysis method of the present invention is a method of hydrolyzing the resin composition (C) in a decomposition solution having a salt concentration of a specific value or more and a specific pH. It is considered that when the salt concentration of this decomposition liquid is high, the hydrophilicity of the components in the resin composition (C) is further increased, and as a result, the hydrolysis of the entire resin composition (C) is promoted.

The salt concentration of the decomposition liquid is 0.06 mol / L or more, preferably 0.2 mol / L or more, 30 mol / L or less, and more preferably 0.4 mol / L or more and 10 mol / L or less.

The pH of the decomposition liquid is 1.0 or more and 9.6 or less, preferably 1.0 or more and 8.0 or less, and more preferably 2.0 or more and 7.5 or less. If the pH of the decomposition solution drops too much during hydrolysis, it may be replaced with a new decomposition solution to continue hydrolysis. Further, as another preferred mode of the decomposition liquid, a decomposition liquid having a pH of more than 9.6 may be adjusted to a pH of 9.6 or less by adding the following inorganic salt or organic salt.

The type of decomposition liquid is not particularly limited. For example, known acidic or neutral buffers can be used. The type of the inorganic salt or the organic salt contained in the buffer solution is not particularly limited. Specific examples of the inorganic salt include sodium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and potassium chloride. Specific examples of the organic salt include formic acid, acetic acid, oxalic acid, citric acid, lactic acid, benzoic acid, phthalic acid and glucuronic acid, methanesulfonic acid having a sulfonic acid group, benzenesulfonic acid and p-toluenesulfonic acid, and other phenols. Examples thereof include salts composed of a combination of an organic acid such as pyridine, diethylamine, triethylamine and an organic base such as histidine. Specific examples of the buffer solution include C ₈ H ₅ KO ₄ -HCl buffer solution, phosphate buffer solution, acetate buffer solution, citrate buffer solution, citrate phosphate buffer solution, borate buffer solution, Tris buffer solution, and tartrate acid. A buffer solution can be mentioned. If the salt concentration of the buffer solution is too low, the salt concentration may be adjusted by adding a component such as NaCl.

Hydrolysis is usually carried out by immersing a molded product made of the resin composition (C) in a decomposition solution having a specific pH. Further, the decomposition liquid may be sprayed on the molded product made of the resin composition (C) by spraying or the like.

The temperature of the decomposition liquid at the time of hydrolysis is not particularly limited, but it is preferably 20 ° C. or higher and lower than the melting point of the resin composition (C). The higher the temperature, the higher the hydrolysis rate can be, but the energy cost rises accordingly. Therefore, the temperature is appropriately adjusted to a preferable temperature according to the purpose.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The method for measuring the weight average molecular weight is as follows.

<Weight average molecular weight (Mw)>
The sample was dissolved in chloroform (concentration: about 0.5% by mass), and the weight average molecular weight (Mw) was determined as a polystyrene-equivalent value by size exclusion chromatography (SEC). The measurement conditions are shown below.
RI detector: JASCO RI-2031
Column: LF-G and LF-804 made by SHODEX
Column temperature: 40 ° C
Solvent: Chloroform Flow rate: 1.0 ml / min

<Production Example 1> Production of PLA-PAL blend film 39.9 g (0.3 mol) of L-aspartic acid manufactured by Wako Pure Chemical Industries, Ltd. in a 500 ml size glass reactor equipped with a stirrer and a deaerator. 90% L-lactic acid manufactured by 300.3 g (3.0 mol) was charged. The reactor was immersed in an oil bath and dehydrated and polymerized for 7 hours while circulating nitrogen at 180 ° C. The obtained brown solid was pulverized to obtain a powdery copolymer of lactic acid and aspartic acid (PAL). The weight average molecular weight of this PAL was 3700.

80 parts by mass of polylactic acid (Laceia H400) as the polymer (A) and 20 parts by mass of PAL as the hydrolysis accelerator (B) using a laboplast mill (4M150 manufactured by TOYOSEIKI) at 50 rpm and 180 ° C. for 5 minutes. Kneaded. The obtained composition was heat-pressed at 180 ° C. and 10 MPa for 5 minutes and rapidly cooled at 0 ° C. to obtain a polylactic acid (PLA) -lactic acid-aspartic acid copolymer (PAL) blend film.

<Production Example 2> Production of PLA-OLA blend film A 500 ml size glass reactor equipped with a stirrer and a degassing port is charged with 30.3 g (3.0 mol) of 90% L-lactic acid manufactured by Purac. bottom. The reactor was immersed in an oil bath and dehydrated and polymerized for 7 hours while circulating nitrogen at 160 ° C. The obtained colorless and transparent solid was pulverized to obtain a powdery lactic acid oligomer (OLA). The weight average molecular weight of this OLA was 3700.

As the polymer (A), 80 parts by mass of polylactic acid (Lasia H400) and 20 parts by mass of OLA were kneaded using a laboplast mill (4M150 manufactured by TOYOSEIKI) at 50 rpm and 180 ° C. for 5 minutes. The obtained composition was heat-pressed at 180 ° C. and 10 MPa for 5 minutes and rapidly cooled at 0 ° C. to obtain a polylactic acid (PLA) -lactic acid oligomer (OLA) blend film.

<Production Example 3> Production of PLA film Using only 100 parts by mass of polylactic acid (Laceia H400) as the polymer (A), heat press at 180 ° C. and 10 MPa for 5 minutes, quench at 0 ° C., and polylactic acid (polylactic acid (Production Example 3). PLA) film was obtained.

<Example 1>
NaCl was added to C ₈ H ₅ KO ₄ -HCl buffer having a pH of 3.4 to obtain a decomposition solution 1 having a salt concentration of 1.0 mol / L.

The decomposition liquid 1 and the 0.2 mm thick, 20 mm square PLA-PAL blend film obtained in Production Example 1 were placed in a glass container and allowed to stand at 40 ° C. for hydrolysis. During the hydrolysis, the pH of the decomposition liquid 1 was measured, and when the pH of the decomposition liquid 1 dropped by 1 or more, it was replaced with a new decomposition liquid 1 to continue the hydrolysis.

After a lapse of a predetermined number of days, the film was collected, washed with distilled water, vacuum dried at room temperature for 24 hours, and its mass was measured. This measurement was performed at each time point after 30 days, 40 days, 60 days, and 100 days, and the mass retention rate was calculated by the following formula. The results are shown in Table 2.
Mass retention rate (%) = W _d / W ₀ x 100 (%)
W ₀ : Mass of film before hydrolysis W _d : Mass of film after hydrolysis

<Example 2>
Hydrolysis was carried out in the same manner as in Example 1 except that the decomposition solution 2 composed of the phosphate buffer solution having a pH of 7.4 and a salt concentration of 1.0 mol / L shown in Table 1 was used. The results are shown in Table 2.

<Comparative Example 1>
Hydrolysis was carried out in the same manner as in Example 1 except that the decomposition solution 3 consisting of C ₈ H ₅ KO ₄ -HCl buffer having a pH of 3.4 and a salt concentration of 0.04 mol / L shown in Table 1 was used. .. The results are shown in Table 2.

<Comparative Example 2>
Hydrolysis was carried out in the same manner as in Example 1 except that the decomposition solution 4 composed of the phosphate buffer solution having a pH of 7.4 and a salt concentration of 0.04 mol / L shown in Table 1 was used. The results are shown in Table 2.

<Comparative Examples 3 to 6>
Hydrolysis was carried out in the same manner as in Example 1 except that the PLA-OLA blend film obtained in Production Example 2 and the decomposition liquids 1 to 4 were used. The results are shown in Table 2.

<Comparative Examples 7 to 10>
Hydrolysis was carried out in the same manner as in Example 1 except that the PLA film obtained in Production Example 3 and the decomposition solutions 1 to 4 were used. The results are shown in Table 2.

As shown in Table 2, since the decomposition solutions 1 and 2 having a high salt concentration were used in Examples 1 and 2, the rate at which the mass retention rate decreased (hydrolysis rate) was high. On the other hand, in Comparative Examples 1 and 2, since the decomposition solutions 3 and 4 having a low salt concentration were used, the hydrolysis rate was slower than in Examples 1 and 2. From this result, it can be seen that the higher the salt concentration of the acidic or neutral decomposition solution, the faster the hydrolysis rate. This is because the hydrolyzable polymer (A) such as polylactic acid is hydrolyzed due to the influence of the acid derived from the hydrolysis accelerator (B) and the hydrophilicity of the hydrolysis accelerator (B) in a state where the salt concentration is high. It is considered that the acid thus produced formed salts with the cationic species in the decomposition liquid, thereby further increasing their hydrophilicity and promoting the hydrolysis of the entire resin composition (C).

Comparative Examples 3 to 6 are examples in which the PLA-OLA blend film obtained in Production Example 2 is used instead of the PLA-PAL blend film obtained in Production Example 1. The former PAL is a copolymer of lactic acid and aspartic acid, and is a component that acts as a hydrolysis accelerator (B). The latter OLA is simply a lactic acid oligomer having the same molecular weight as PAL. In Comparative Examples 3 to 6 in which the hydrolysis accelerator (B) was not used, the hydrolysis rate was slow regardless of which of the decomposition solutions 1 to 4 was used. From this result, it can be seen that the reason why the hydrolysis was promoted in Examples 1 and 2 was that the function of the hydrolysis accelerator (B) was enhanced under the high salt concentration.

Comparative Examples 7 to 10 are examples in which the PLA film obtained in Production Example 3 is used instead of the PLA-PAL blend film obtained in Production Example 1. In Comparative Examples 7 to 10 in which the hydrolysis accelerator (B) was not used, the hydrolysis rate was not promoted by using any of the decomposition solutions 1 to 4. From this result, even with the PLA film alone, hydrolysis was not promoted at a high salt concentration in the pH range of the present invention, and the reason why the hydrolysis was promoted was that the function of the hydrolysis accelerator (B) was enhanced under a high salt concentration. It turns out that it was done.

The resin composition (C) can be applied to molded products that require an excellent decomposition rate, such as films, food packaging materials, packaging materials for sanitary goods, agricultural and horticultural materials, fibers, non-woven fabrics, and sustained-release chemicals. According to the hydrolysis method of the present invention, the resin composition (C) can be easily and quickly hydrolyzed by using a basic aqueous solution having a specific salt concentration.

Claims (8)

A method of hydrolyzing a resin composition (C) containing a hydrolyzable polymer (A) and a hydrolysis accelerator (B) in a decomposition solution having a pH of 1.0 or more and 9.6 or less. There,
The hydrolyzable polymer (A) is a polyhydroxycarboxylic acid having a repeating unit (constituent unit) (a-1) derived from the hydroxycarboxylic acid.
The hydrolysis accelerator (B) is a copolymer containing the structural unit (a-1) and the structural unit (b-1) derived from the polyvalent carboxylic acid, and the polyvalent carboxylic acid is aspartic acid. One or more selected from the group consisting of glutamate, citric acid and aspartic acid.
A method for hydrolyzing a resin composition, which comprises a salt concentration of 0.06 mol / L or more in the decomposition liquid. The hydrolysis method according to claim 1 , wherein the hydrolyzable polymer (A) is polylactic acid. The hydrolysis method according to claim 1 or 2 , wherein the polyvalent carboxylic acid of the structural unit (b-1) is one or more polyvalent carboxylic acids selected from the group consisting of aspartic acid and glutamic acid. The hydrolysis method according to claim 1 or 2 , wherein the polyvalent carboxylic acid of the structural unit (b-1) is one or more polyvalent carboxylic acids selected from the group consisting of citric acid and malic acid. Claims 1 to 4 in which the mass ratio (A / B) of the hydrolyzable polymer (A) and the hydrolysis accelerator (B) in the resin composition (C) is 95/5 to 50/50. The hydrolysis method according to any one of. The hydrolysis method according to any one of claims 1 to 5 , wherein the salt concentration in the decomposition liquid is 0.2 mol / L or more and 30 mol / L or less. The hydrolysis method according to claim 6 , wherein the salt concentration in the decomposition liquid is 0.4 mol / L or more and 10 mol / L or less. The hydrolysis method according to any one of claims 1 to 7 , wherein the pH of the decomposition liquid is 1.0 or more and 8.0 or less.