WO2018079662A1

WO2018079662A1 - Resin composition and hydrolysis method therefor

Info

Publication number: WO2018079662A1
Application number: PCT/JP2017/038728
Authority: WO
Inventors: 秀子大山; 大介谷島; 亮平小川; 浦上　達宣
Original assignee: 学校法人立教学院; 三井化学株式会社
Priority date: 2016-10-28
Filing date: 2017-10-26
Publication date: 2018-05-03
Also published as: JP6679072B2; JPWO2018079662A1

Abstract

In order to provide a resin composition that is quickly hydrolyzed, a resin composition that contains a hydrolyzable crystalline polymer (A) and a hydrolysis accelerator (B) is used, wherein the resin composition (C) is characterized in that the degree of crystallinity of the resin composition is 15-60%. In addition, the resin composition (C) is quickly hydrolyzed in an aqueous solution having a pH that is greater than 7.

Description

Resin composition and hydrolysis method thereof

The present invention relates to a resin composition having excellent hydrolyzability and a hydrolysis method thereof.

In recent years, with the deterioration of the global environment, there is an increasing interest in resin recycling and additives that are safe for living organisms and have little 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 moisture and enzymes in a natural environment or in vivo.
For example, PLA is used in applications such as disposable containers and packaging materials because it has good workability and excellent mechanical strength of molded products. However, PLA has a problem that its hydrolysis rate is slower than PGA and PCL.

In order to overcome such problems of PLA, for example, a method of adding a hydrophilic additive such as polyethylene glycol to PLA has been proposed as a method for improving the hydrolysis rate of PLA. However, PLA has low hydrophilicity and is hardly compatible with hydrophilic substances such as polyethylene glycol. Therefore, hydrophilic additives may be raised (bleed out) during molding or after molding, resulting in a decrease in mechanical strength of the molded product. Or the appearance such as transparency is impaired, which is not practical.

Regarding hydrolysis of PLA, acidic and alkaline hydrolysis has been reported (Non-Patent Documents 1 and 2).
The present applicant has proposed to add a copolymer that promotes hydrolysis to PLA (Patent Documents 1 and 2).

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

In Non-Patent Documents 1 and 2, a PLA film is annealed to produce samples having different crystallinity, and the hydrolysis behavior is confirmed. According to Non-Patent Document 1, it is considered that the degradation of the PLA film is due to the erosion of the amorphous part of the film surface, and the higher the crystallinity, the less the weight loss due to the degradation, that is, the less the hydrolysis is. It has been shown. Non-Patent Document 2 further examines the difference in hydrolysis between acidic, neutral and alkaline, and shows that the hydrolyzability at alkaline (pH 12) is higher than neutral and acidic. Similar to Non-Patent Document 1, it has been shown that a sample with a high degree of crystallinity has a slower weight loss rate, whereas a sample with a high degree of crystallinity has a faster decrease in molecular weight. However, it takes a long period of about 200 days to completely decompose. That is, PLA generally has higher heat resistance and mechanical strength due to crystallization, but hydrolysis is slower than when PLA is not crystallized. For this reason, in order to increase the decomposition rate, it is necessary to lower the crystallinity and sacrifice heat resistance and mechanical strength, and it has been difficult to achieve both hydrolysis rate and heat resistance and mechanical strength.

Patent Documents 1 and 2 indicate that the hydrolysis rate is improved by the added copolymer (hydrolysis accelerator). In any case, hydrolyzability at 50 ° C. to 80 ° C. under almost neutral conditions such as distilled water and ion-exchanged water has been studied, and the dependence on the lower temperature conditions and crystallinity has not been studied.

As described above, if both heat resistance and mechanical strength improvement by crystallization can be achieved and hydrolysis rate can be improved, hydrolysis at low temperatures that could not be used until now, for example, heat resistance and machine such as sterilization treatment, etc. It can be used in high temperature and high pressure conditions that require strength.

An object of the present invention is to provide a resin composition that rapidly hydrolyzes and a hydrolysis method.

The present inventors have improved the crystallinity of a resin composition in which a hydrolysis accelerator is combined with a hydrolyzable crystalline polymer, thereby making it hydrolyzable, particularly in an alkaline aqueous solution, contrary to the conventional teaching. It has been found that the hydrolysis rate is significantly faster.

That is, one form of the present invention is a resin composition containing a crystalline polymer (A) having hydrolyzability and a hydrolysis accelerator (B), and the crystallinity of the resin composition is 15 % To 60% or less of the resin composition (C).
Another embodiment of the present invention relates to a hydrolysis method for the resin composition (C), wherein the hydrolysis is performed in an aqueous solution having a pH higher than 7.

According to the present invention, a resin composition having excellent heat resistance and mechanical strength and improved hydrolyzability can be provided. Moreover, the hydrolysis method according to the present invention can hydrolyze the resin composition in a very short period of time.

<Crystalline polymer (A) having hydrolyzability>
The hydrolyzable crystalline polymer (A) used in the present invention (hereinafter simply referred to as “crystalline polymer (A)”) is not particularly limited as long as it is a hydrolyzable crystalline polymer. For example, polyester is exemplified, and an aliphatic polyester resin composed of polyhydroxycarboxylic acid, diol and dicarboxylic acid can be used.

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

Specific examples of the hydroxycarboxylic acid include lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methyl. Butyric acid, 2-methyl lactic 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 Ring-opening products of lactones such as 2-hydroxy-3-methylbutyric acid, 2-cyclohexyl-2-hydroxyacetic acid, mandelic acid, salicylic acid and caprolactone. Two or more of these may be mixed and used.

The polyhydroxycarboxylic acid may have other structural units (copolymerization components) other than the hydroxycarboxylic acid as long as the hydrolyzability is not greatly impaired, but in 100 mol% of all the structural units of the polyhydroxycarboxylic acid. The structural unit (a-1) derived from hydroxycarboxylic acid is preferably 20 mol% or more, more preferably 50 mol% or more, and particularly preferably 100%.

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

In the present invention, the aliphatic polyester resin composed of diol and dicarboxylic acid means a polymer or copolymer having a repeating unit (constituent unit) derived from diol and dicarboxylic acid. The aliphatic polyester resin may have other structural units (copolymerization components) other than the structural units derived from the diol and the dicarboxylic acid, unless the hydrolyzability as the crystalline polymer (A) is greatly impaired. Good.

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, polybutylene succinate. , Polybutylene adipate, polybutylene succinate adipate, and polybutylene sebacate.

The molecular weight of the crystalline polymer (A) is not particularly limited, but is preferably larger than that of the hydrolysis accelerator (B). Considering the ease of mixing with the hydrolysis accelerator (B), the weight average molecular weight of the crystalline polymer (A) is preferably 2,000 to 2,000,000, more preferably 3,000 to 1. 1,000,000, particularly preferably more than 50,000 and 500,000 or less. This weight average molecular weight is a value determined by gel permeation chromatography (GPC) under the conditions described in the Examples described later.

<Hydrolysis accelerator (B)>
As the hydrolysis accelerator (B) used in the present invention, any one can be used as long as it promotes the hydrolyzability of the crystalline polymer (A). In particular, the structural unit derived from hydroxycarboxylic acid (a -2) and a copolymer having a structural unit (b-1) derived from a polyvalent carboxylic acid. The “structural 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. Examples of the structural unit (a-2) derived from hydroxycarboxylic acid include those exemplified as the structural unit (a-1) derived from hydroxycarboxylic acid constituting the crystalline polymer (A). It is preferable to use the same structural unit (a-1) as (A). In particular, the structural unit (a-2) derived from hydroxycarboxylic acid is preferably a unit derived from lactic acid.

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 at least one selected from divalent or trivalent polyvalent carboxylic acids, among which aminodicarboxylic acid, hydroxydicarboxylic acid, and hydroxytricarboxylic acid are more preferable, aspartic acid, glutamic acid, Particularly preferred is at least one selected from malic acid, citric acid and tartaric acid. These polyvalent carboxylic acids may have one kind or two or more different kinds. The structural unit derived from the polyvalent carboxylic acid may form a ring structure such as an imide ring, the ring structure may be ring-opened, or the ring structure and the ring-opened structure are mixed. Alternatively, two or more different ring structures and / or ring-opened structures may be included.

The hydrolysis accelerator (B) is not particularly limited as long as it is a copolymer having the structural unit (a-2) and the structural unit (b-1) described above. Of these, aspartic acid-lactic acid copolymer, malic acid-lactic acid copolymer, and citric acid-lactic acid copolymer are particularly preferable.

The molar composition ratio [(a-2) / (b-1)] of the structural unit (a-2) and the structural unit (b-1) in the hydrolysis accelerator (B) is preferably a charged amount 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 excellent in the decomposition rate promoting effect and excellent in compatibility with the crystalline polymer (A) can be obtained.

In the hydrolysis accelerator (B), structural units other than the structural units (a-2) and (b-1) (units derived from other copolymerization components) may be present. However, the amount must be such that the properties of the hydrolysis accelerator (B) are not significantly impaired. From this point, the amount of the other structural unit is desirably about 20 mol% or less in 100 mol% of the entire structural unit of the hydrolysis accelerator (B).

The weight average molecular weight of the hydrolysis accelerator (B) is 1,000 or more and 50,000 or less, preferably 2,500 or more and 30,000 or less, and particularly preferably in the range of 2,500 to 10,000. Is within. This weight average molecular weight is a value determined by gel permeation chromatography (GPC) under the conditions described in the Examples described later.

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

<Resin composition (C)>
The resin composition (C) according to the present invention is obtained by mixing the crystalline polymer (A) and the hydrolysis accelerator (B). The mass composition ratio [(A) / (B)] is 95/5 to 50/50, preferably 95/50, where the total amount of the crystalline polymer (A) and the hydrolysis accelerator (B) is 100. 5 to 55/45, more preferably 95/5 to 60/40, and particularly preferably 95/5 to 80/20. It is preferable that the mass composition ratio is within these ranges because the decomposition rate promoting effect by the hydrolysis accelerator (B) is exhibited while maintaining the properties of the crystalline polymer (A). Moreover, a resin composition (C) with a large decomposition rate is obtained, so that there is much quantity of a hydrolysis accelerator (B). On the other hand, when the mass composition ratio is larger than 95/5, the decomposition promoting effect by addition of the hydrolysis accelerator (B) is not sufficient, and when it is smaller than 50/50, the crystallinity of the resin composition (C) is large. Moreover, since the property which a crystalline polymer (A) has is impaired, it is not preferable.

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

The resin composition (C) is an additive that can be added to a polymer other than the hydrolysis accelerator (B) and the crystalline polymer (A) or a normal resin as long as the properties of the crystalline polymer (A) are not significantly impaired. An agent may be included.

The crystallinity of the resin composition (C) is 15% or more and 60% or less. The crystallinity referred to in the present invention is determined as a function of melting enthalpy, crystallization enthalpy, and recrystallization enthalpy obtained by differential thermal analysis (DSC), as shown in the examples described later. The lower limit of the crystallinity is preferably 20% and more preferably 25% from the viewpoint of heat resistance. The upper limit of the degree of crystallinity is preferably 55% and more preferably 50% from the viewpoint of heat resistance and simplification of the crystallization process. When the crystallinity is less than 15%, not only the effect of improving the heat resistance of the resin composition (C) by crystallization is small, but also the effect of adding the hydrolysis accelerator (B) is manifested, and crystallization and hydrolysis A synergistic effect with the addition of the accelerator (B) does not appear. In order to obtain a crystallinity exceeding 60%, not only a long crystallization step is required, but when the crystallinity exceeds 60%, hydrolysis is difficult due to a decrease in the amorphous region.
A known method can be applied to adjust the degree of crystallinity. A method of adjusting the heating temperature, temperature rising rate, cooling rate, etc. during molding of a molded product using the resin composition (C), or crystallization of the molded product. Examples thereof include a method of reheating (annealing) at a temperature not lower than the temperature and lower than the melting temperature. In addition, the use of a crystal nucleating agent, a method for increasing the degree of crystallinity by stretching treatment, and the like can also be mentioned. Usually, polylactic acid, which is an example of the crystalline polymer (A), has a low crystallization rate, and a product that has been rapidly cooled by molding is low in crystallinity.

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 300,000. This weight average molecular weight is a value determined by gel permeation chromatography (GPC) under the conditions described in the Examples described later.

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

<Hydrolysis method>
The hydrolysis method according to the present invention is a method in which the resin composition (C) is hydrolyzed in an aqueous solution (referred to as an alkaline aqueous solution) having a pH higher than 7. The pH is preferably 7.1 or higher, more preferably 8 or higher. As a preferable embodiment of the aqueous solution, an aqueous solution having an initial pH greater than 7 before immersion of the resin composition (C) can be mentioned. Another embodiment includes an aqueous solution in which an initial pH is 7 or less and a basic substance is added and dissolved so that the pH becomes higher than 7 after immersion in the resin composition (C). In any method, the pH is preferably higher than 7 in most of the decomposition process of the resin composition (C).
Usually, a molded article made of the resin composition (C) is immersed in an alkaline aqueous solution. Moreover, it can also hydrolyze by spraying alkaline aqueous solution with a spray etc. on the molded article which consists of a resin composition (C). The temperature of the alkaline aqueous solution is not particularly limited, but is preferably 30 ° C. or higher and lower than the melting point of the resin composition (C). The higher the temperature is, the higher the hydrolysis rate can be. However, the energy cost increases accordingly, so that the temperature is appropriately adjusted according to the purpose. In the present invention, faster hydrolysis is possible at a temperature lower than the temperature studied in Patent Documents 1 and 2. Further, the resin composition (C) has improved heat resistance by being crystallized, and can be used for applications that require hydrolysis under high temperature and high pressure. In this case, since the resin composition (C) melts at the hydrolysis temperature equal to or higher than the melting point of the resin composition (C), the effect of adding the decomposition accelerator (B) is lost. It is necessary to perform hydrolysis below the melting point of the product (C).

The basic substance contained in the alkaline aqueous solution is not particularly limited, but in view of versatility and safety, an alkali metal hydroxide is preferable, and sodium hydroxide is more preferable. Moreover, it is good also as a buffer solution by adding inorganic salt and organic salt.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In the examples, “part” means part by mass. Each measuring method in an Example is as follows.

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

<Crystallinity>
Using a DSC apparatus (DSC Q-200TA manufactured by TA Instrument), a sample of about 4 to 5 mg is measured in a temperature range of 0 ° C. to 200 ° C. at a temperature rising rate of 10 ° C./min, and the enthalpy of fusion (ΔHm) Crystallization enthalpy (ΔHc), recrystallization enthalpy (ΔHr), melting point (Tm) and glass transition temperature (Tg) were determined. The crystallinity (Xc) was calculated by the following formula.
Xc (%) = {(| ΔHm | − | ΔHc | − | ΔHr |) / | ΔHf |} × 100
Here, the melting enthalpy (ΔHf) when polylactic acid was crystallized 100% was set to 93.1 J / g. Crystallinity was expressed as the crystallinity of the entire blend.

<Hydrolysis test>
A sample having a thickness of 0.2 mm and a 20 mm square was placed in a glass container, immersed in the following solutions having different pH values, and allowed to stand in a water bath controlled at 40 ° C. The solution was exchanged to keep the pH constant so that the pH did not change during decomposition. After a predetermined time had elapsed, the sample was collected, washed with distilled water, and then vacuum dried at room temperature for 24 hours to measure the mass. Mass retention by hydrolysis was calculated by the following formula. When the sample could not be collected, the mass retention was set to 0% assuming that the sample was completely decomposed.
When the mass of the sample before the test is W ₀ and the mass of the vacuum-dried sample after the test is W _d ,
Mass retention rate (%) = (W _d / W ₀ ) × 100
Solutions with different pH used (1) pH 7.4: phosphate buffer (2) pH 12.0: KCl-NaOH buffer

<Production Example 1> Production of lactic acid-malic acid copolymer (PML) In a 500 ml glass reactor equipped with a stirrer and a degassing port, 13.4 g (0. 1 mol), 100.2 g (1.0 mol) of 90% L-lactic acid manufactured by Purac was charged. The reactor was immersed in an oil bath and polymerized while flowing nitrogen at 135 ° C. and 1.33 kPa (10 mmHg). The obtained colorless and transparent solid was pulverized to obtain a powdery polymer (PML). About obtained PML, the weight average molecular weight measured by the above-mentioned method was 3500.

<Production Example 2> Production of Lactic Acid-Aspartic Acid Copolymer (PAL) 39.9 g (0.3 mol) of Wako Pure Chemical Industries L-aspartic acid was added to a 500 ml glass reactor equipped with a stirrer and a degassing port. ), 300.3 g (3.0 mol) of 90% L-lactic acid manufactured by Purac was charged. The reactor was immersed in an oil bath and subjected to dehydration polymerization for 7 hours while flowing nitrogen at 180 ° C. The obtained colorless and transparent solid was pulverized to obtain a powdery polymer (PAL). About the obtained PAL, the weight average molecular weight measured by the above-mentioned method was 3500.

<Comparative Example 1>
80 parts of polylactic acid (manufactured by Mitsui Chemicals, Inc., trade name “Lacia H400”, Mw = 240,000) and 20 parts of PML prepared in Production Example 1 were manufactured by Labo Plast Mill (manufactured by Toyo Seiki Seisakusho Co., Ltd., trade name “ A segment mixer (manufactured by Toyo Seiki Seisakusho, trade name “TOYOSEIKI, KF-70V2”) was attached to TOYOSEIKI, 4M150 ”, and kneaded at 50 rpm and 175 ° C. for 5 minutes. The obtained composition was hot-pressed at 170 ° C. and quenched at 0 ° C. to obtain a press film 1. When the crystallinity was measured by the method described above, the crystallinity was 7.9%. The obtained film was subjected to a hydrolysis test by the method described above. The test results at each pH are shown in Tables 1 and 2.

<Comparative example 2>
PML was changed to PAL prepared in Production Example 2, and the same procedure as in Comparative Example 1 was carried out except that the kneading temperature was 180 ° C. and the hot press temperature was 180 ° C., and a press film 2 was obtained. When the crystallinity was measured by the method described above, the crystallinity was 6.8%. The obtained film was subjected to a hydrolysis test by the method described above. The test results at each pH are shown in Tables 1 and 2.

<Example 1>
The press film 1 obtained in Comparative Example 1 was heat-treated for 10 minutes at a crystallization temperature (105 ° C.) observed by DSC measurement in Comparative Example 1 under reduced pressure by hot pressing, and crystallized to obtain the crystallized composition of the present invention. Product 1 was obtained. When the crystallinity was measured by the method described above, the crystallinity was 43.3%. The obtained film was subjected to a hydrolysis test by the method described above. The test results at each pH are shown in Tables 1 and 2.

<Example 2>
The press film 2 obtained in Comparative Example 2 was heat-treated for 10 minutes at a crystallization temperature (110 ° C.) observed by DSC measurement in Comparative Example 2 under reduced pressure by hot pressing to obtain a crystallized composition 2 of the present invention. It was. When the crystallinity was measured by the method described above, the crystallinity was 41.6%. The obtained film was subjected to a hydrolysis test by the method described above. The test results at each pH are shown in Tables 1 and 2.

<Comparative Example 3>
Polylactic acid (trade name “Lacia H400” manufactured by Mitsui Chemicals, Inc.) was hot-pressed at 180 ° C. and rapidly cooled at 0 ° C. to obtain a press film 3. When the crystallinity was measured by the method described above, the crystallinity was 1.9%.

<Comparative example 4>
The press film 3 obtained in Comparative Example 3 was heat-treated for 1 hour at a crystallization temperature (120 ° C.) observed by DSC measurement in Comparative Example 3 under reduced pressure by hot pressing, and crystals containing no hydrolysis accelerator (B) A modified PLA film was obtained. When the crystallinity was measured by the method described above, the crystallinity was 52.1%.

From Tables 1 and 2, it was found that when crystallized, the rate of weight loss was faster than that of a rapidly cooled film. In particular, it can be seen that polylactic acid can be completely decomposed in an extremely short time in an alkaline aqueous solution despite crystallization.
Usually, polylactic acid is decomposed slowly by crystallization (Non-patent Documents 1 and 2). Contrary to the conventional case, the crystallized composition of the present invention is crystallized to accelerate the mass loss accompanying decomposition. This is because the hydrolysis accelerator (B) according to the present invention is easily collected in the amorphous part by crystallization, and as a result, acceleration of the decomposition of the amorphous part is accelerated, thereby reducing the weight of the entire composition. It is thought that it accelerates and contributes to the collapse of the crystal region.

The resin composition (C) according to the present invention is, for example, a film, a food packaging material, a sanitary ware packaging material, an agricultural and horticultural material, a fiber, a nonwoven fabric, a sustained-release drug, etc. Applicable to. Moreover, the hydrolysis method which concerns on this invention can hydrolyze the resin composition (C) which concerns on this invention simply and rapidly by using basic aqueous solution.
This application claims priority based on Japanese Patent Application No. 2016-2111778 filed on Oct. 28, 2016, the entire disclosure of which is incorporated herein.

Claims

A resin composition containing a hydrolyzable crystalline polymer (A) and a hydrolysis accelerator (B), wherein the crystallinity of the resin composition is 15% or more and 60% or less. The resin composition (C) characterized by these.
The resin composition (C) according to claim 1, wherein the crystalline polymer (A) is a polyester.
The resin composition (C) according to claim 1, wherein the crystalline polymer (A) is polylactic acid.
The crystalline polymer (A) contains a structural unit (a-1) derived from hydroxycarboxylic acid,
2. The hydrolysis accelerator (B) contains a structural unit (a-2) derived from a hydroxycarboxylic acid and a structural unit (b-1) derived from a polyvalent carboxylic acid. (C).
The resin composition (C) according to any one of claims 1 to 4, wherein a mass ratio of the crystalline polymer (A) to the hydrolysis accelerator (B) is 95/5 to 50/50. .
A hydrolysis method comprising hydrolyzing the resin composition (C) according to any one of claims 1 to 5 in an aqueous solution having a pH higher than 7.
The hydrolysis method according to claim 6, wherein the temperature of the aqueous solution is 30 ° C or higher and lower than the melting point of the resin composition (C).