JP2019065159A - Method for reducing molecular weight of polymer component consisting of aliphatic polyester - Google Patents

Abstract

To provide a method for reducing molecular weight of a polymer component consisting of aliphatic polyester such as polylactic acid with suppressing cost at high efficiency.SOLUTION: A solution containing organic acid of 31 to 60 mass% is prepared and a polymer component consisting of aliphatic polyester is input into the solution at an ordinary pressure and heating the same. In the case of hardly hydrolyzable aliphatic polyester such as polylactic acid, polyoxalate is used as a promotion resin for reducing molecular weight for promoting hydrolysis and processing reduction of molecular weight.SELECTED DRAWING: None

Description

  The present invention relates to a method for molecular weight reduction of a polymer component consisting of aliphatic polyester, and more particularly to a method for molecular weight reduction of a polymer component consisting of aliphatic polyester using an organic acid solution of a specific concentration.

  Contaminated soil produced in factories etc. has been transported to a treatment facility for many years and incinerated to render it harmless. Although this method is excellent in that processing can be performed in a short time and processing can be performed regardless of the type of contaminant, there is a drawback in that costs such as transportation costs are required.

  Therefore, recently, soil remediation methods utilizing microorganisms called bioremediation have been actively studied. Bioremediation is the process of decontaminating pollutants and decontaminating soil by causing specific microorganisms to be present in contaminated soil and feeding them.

  In bioremediation, it is widely practiced to spread nutrients such as organic acids to contaminated soil to make the reproduction and activity of microorganisms more active. However, since organic acids are generally liquid at normal temperature, there is a problem that it is difficult to determine the timing and amount of nutrient addition and the workability is poor. In addition, there is also a problem that there is no sustained release, and the effect of nutrient dispersion disappears in a short time.

  In order to solve this problem, Patent Document 1 proposes using a polylactic acid-based resin which is in a solid state and has a weight-average molecular weight of 12,000 or less as a nutrient. In the case of solid state polylactic acid and the like, the workability is greatly improved, and it is possible to accurately determine the timing and amount of nutrient addition. In addition, it gradually decomposes with the passage of time to release an acid such as lactic acid, which functions as a nutrient, and is thus excellent in terms of sustained release.

JP, 2011-104551, A

  However, the polylactic acid-based resin of Patent Document 1 uses a polylactic acid having a large molecular weight as a raw material, and must be manufactured by reducing the molecular weight under pressure using an autoclave or the like, which increases the cost of manufacturing facilities etc. The Furthermore, when it is desired to recover a polylactic acid-based resin having a specific average molecular weight, it is necessary to appropriately sample the solid components in the reaction solution and measure the average molecular weight to confirm the progress of the molecular weight reduction. The method of reducing the molecular weight under pressure is time-consuming and inconvenient for sampling. The present inventors examined production under normal pressure, but there was a problem that the general method took time and the like.

  Accordingly, an object of the present invention is to provide a method for efficiently reducing the molecular weight of a polymer component consisting of aliphatic polyester such as polylactic acid while suppressing the cost.

  According to the present invention, a solution containing 31 to 60% by mass of an organic acid is prepared, and a polymer component consisting of an aliphatic polyester is put into the solution and heated under normal pressure. A molecular weight reduction method is provided.

In the method of the present invention, the following embodiments are preferred.
(1) The aliphatic polyester is polylactic acid.
(2) Use a low molecular weight promoting resin that releases an acid by hydrolysis.
(3) The low molecular weight promoting resin is polyoxalate.
(4) A polymer component comprising the low molecular weight promoting resin and the aliphatic polyester is charged into the solution.
(5) The organic acid is a carboxylic acid.
(6) The organic acid is at least one organic acid selected from the group consisting of lactic acid, acetic acid and citric acid.
(7) The organic acid is lactic acid.
(8) The solution selectively contains the organic acid as a solute.
(9) The heating temperature is 90 ° C. or more.
(10) After heating, the insoluble matter is recovered to obtain a low molecular weight polymer component having a weight average molecular weight of 10,000 to 20,000.
(11) The yield X calculated from the following formula (1) is 90% or more.
X = 100 × (Wf / Wi) (1)
In the formula, Wf represents the mass (g) of the low molecular weight polymer component,
Wi represents the mass (g) of the polymer component before hydrolysis.

  In the present invention, the polymer component mainly composed of aliphatic polyester is reduced in molecular weight by hydrolysis in an organic acid solution under normal pressure, but surprisingly, the organic acid concentration of the solution used is within a specific range (polymer component The polymer component can be reduced to a desired degree with high efficiency at a high efficiency while suppressing the cost by a simple means of adjusting to 31 to 60% by mass) before introduction. In particular, a low molecular weight polymer component having a weight average molecular weight (hereinafter sometimes referred to as an average molecular weight) of 10,000 to 20,000 has been successfully obtained in the solid state with high efficiency.

  In fact, referring to the examples described below, when prepared as a polymer component, a kneaded product of polylactic acid or polylactic acid and polyoxalate is hydrolyzed in an aqueous solution of 50% by weight organic acid, and it is 10 hours from the start Low molecular weight polylactic acid having an average molecular weight of 10,000 to 20,000 can be recovered below. Moreover, when the insoluble matter in the reaction solution is sampled at appropriate time intervals, the average molecular weight is measured, and the time course of hydrolysis is observed, it is in the time period when the average molecular weight reaches 10,000 to 20,000. Since the rate of hydrolysis is slow, the time for which the target low molecular weight polymer component can be recovered is long. If the recoverable time is long, even if it takes time for sampling or measurement at a site such as a factory, there is no concern that the timing of recovery will be missed, which is extremely advantageous in industry.

  On the other hand, when pure water is prepared as in Comparative Example 1 and polylactic acid is hydrolyzed in this, low-molecular weight polylactic acid having an average molecular weight of 10,000 to 20,000 is recovered even if heat treatment is performed for 10 hours. I can not do it, and the manufacturing time is long.

  Moreover, when an organic acid aqueous solution with a high concentration (90 mass%) is used as in Comparative Example 2 and Comparative Example 3, the hydrolysis proceeds fast, which is preferable. However, since the acid in these aqueous solutions has a high affinity to polylactic acid, especially polylactic acid having an average molecular weight of 20,000 or less dissolves in a high concentration aqueous solution of organic acid immediately after formation. Therefore, it is difficult to recover the target low molecular weight polymer component in a solid state.

  Therefore, it is possible to efficiently recover the polymer component which has been reduced in molecular weight to a desired degree in the solid state only by using an organic acid solution of a specific concentration as in the present invention.

  Moreover, since the method of the present invention does not use a low-boiling acid such as an inorganic acid, there is no need to worry about the volatilization of the acid during the reaction, which is safe and does not provide equipment for the volatilized acid. It is also good. In addition, since the molecular weight reduction can proceed at a sufficient speed even under normal pressure, a large scale apparatus such as an autoclave is not necessary. Therefore, molecular weight reduction can be performed at low cost.

It is a graph which shows the relationship of the heat processing time in Example 4 and Comparative Example 6, and the weight average molecular weight of a solid component.

  In the present invention, a solution in which an organic acid is dissolved is prepared, and a polymer component consisting of an aliphatic polyester is put into the solution and hydrolyzed while being heated to lower the molecular weight of the polymer component.

  As aliphatic polyester contained in a polymer component, a well-known thing can be used without any restriction. For example, poly (α-hydroxy acid), poly (β-hydroxyalkanoate), poly (ω-hydroxyalkanoate), polyalkylene dicarboxylate and the like can be mentioned.

  These may be used singly or in combination of two or more. Moreover, although it may be a homopolymer, it may be in the form of a copolymer together with the copolymerization component under the condition that the effect of the present invention is not impaired.

  As a component to form a copolymer, for example, polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, polyethylene glycol and the like; Acids, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, dicarboxylic acids such as anthracenedicarboxylic acid and diesters thereof; glycolic acid, L-lactic acid, D-lactic acid, hydroxypropion Hydroxycarboxylic acids such as acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, mandelic acid, hydroxybenzoic acid, etc .; glycolide, caprolactone , Butyrolactone, valerolactone, propiolactone, lactones such undecalactone; and the like.

  As aliphatic polyesters, poly (α-hydroxy acids) are preferred in view of easy availability, and polylactic acid is particularly preferred. The polylactic acid may be either 100% poly-L-lactic acid or 100% poly-D-lactic acid, or a melt blend of poly-L-lactic acid and poly-D-lactic acid. It may be a random copolymer or block copolymer of lactic acid and D-lactic acid.

  20,000 or more are preferable, as for the weight average molecular weight of aliphatic polyester, 20,000-300,000 are more preferable, and 100,000-300,000 are especially preferable. According to the study of the present inventors, it is confirmed that various reaction conditions and behavior (such as speed) of reduction of molecular weight are substantially the same in the case of aliphatic polyester of such molecular weight.

  The aliphatic polyester is preferably used in an amount of 100 g to 2 kg per liter of the organic acid aqueous solution from the viewpoint of the balance between the reaction rate and the cost.

  As the polymer component, if necessary, known plasticizers, heat stabilizers, light stabilizers, antioxidants, UV absorbers, flame retardants, colorants, pigments, fillers, fillers, release agents, antistatic agents Additives such as agents, perfumes, lubricants, foaming agents, antibacterial and antifungal agents, nucleating agents, carboxyl group-binding compounds and the like may further be included. Although the compounding quantity of an additive is suitably determined on the conditions of not impairing the effect of this invention, Usually, it is 5 mass parts or less per 100 mass parts of aliphatic polyester.

  In addition, the polymer component is less susceptible to hydrolysis than the above-mentioned aliphatic polyester and is a resin which releases an acid by hydrolysis, ie, a resin which is easily hydrolyzed to release an acid when mixed with water. It may be contained as a molecular weight promoting resin. In particular, when using a poorly hydrolyzable aliphatic polyester such as polylactic acid as a raw material, in order to promote the hydrolysis of such aliphatic polyester to advance the molecular weight reduction, the low molecular weight promoting resin is preferably used. used. As the acid released from the low molecular weight promoting resin, it is particularly preferable that the pH (25 ° C.) in an aqueous solution or aqueous dispersion having a concentration of 0.005 g / ml indicates 4 or less, particularly 3 or less. Acids released include oxalic acid and glycolic acid.

  Examples of the low molecular weight promoting resin include polyoxalate and polyglycolic acid, but polyoxalate is preferable. These may be used in the form of a copolymer. Moreover, you may use individually by 1 type and may be used combining 2 or more types. As a component which forms a copolymer, the component which forms the copolymer mentioned by description of the aliphatic polyester of a raw material can be employ | adopted.

  The weight average molecular weight of the low molecular weight promoting resin is generally 1,000 to 200,000.

  The compounding amount of the low molecular weight promoting resin is not particularly limited, but is preferably 1 part by mass or more and less than 100 parts by weight with respect to 100 parts by mass of the aliphatic polyester. More than 1 mass part and less than 50 mass parts are more preferred, and more than 1 mass part and less than 30 mass parts are especially preferred.

  The low molecular weight promoting resin may be used alone as an injection into the organic acid solution, as needed, instead of being mixed with the polymer component.

  Examples of the form of the polymer component include a film or sheet, a cut form of the film or sheet, pellets, particles and the like, and particles are preferable. When the particulate polymer component is used, the solid content (polymer component after molecular weight reduction) finally obtained is also in the form of particles, and there is an advantage that it can be directly used as a nutrient for microorganisms.

  In the present invention, it is important to use an organic acid. The use of solutes other than acids (eg, basic substances) results in low yields. Low-boiling acids represented by inorganic acids are volatilized by heating, which makes the equipment expensive. In addition, because hydrolysis is too fast, it is difficult to complete the molecular weight reduction to the desired degree, and the yield is also lower than in the case of organic acids.

  The organic acid is preferably a carboxylic acid, more preferably at least one selected from the group consisting of lactic acid, acetic acid and citric acid, and particularly preferably lactic acid.

  As a solvent, water is preferable from the viewpoint of handleability. You may use alcohol together as needed. The alcohol may be appropriately selected from known ones in consideration of the type of solute and the like.

  In the organic acid solution, other solutes such as inorganic acids, alkali metals, and basic substances may be dissolved as long as the effects of the present invention are not impaired, but from the viewpoint of environmental consideration and cost, as a solute It is preferable that the organic acid be selectively contained, in other words, that no other solute be contained.

  In the present invention, it is also important that the concentration of the organic acid in the organic acid solution is 31 to 60% by mass before the polymer component is charged. When the concentration of the organic acid is too low, the rate of hydrolysis is slow. If the concentration of the organic acid is too high, the affinity between the organic acid and the aliphatic polyester in the solution is high, and thus the low molecular weight polymer component dissolves and is difficult to recover in the solid state, in particular, the average molecular weight is 10,000 to With 20,000 low molecular weight polymer components, it can not be substantially recovered.

  In the present invention, a polymer component is usually charged into an organic acid solution under normal pressure (approximately 1 atm) using a reaction apparatus equipped with a reaction vessel, a heating device and a stirring device, and stirring and heating are performed. The heating temperature is determined by the composition of the solution, the type of aliphatic polyester used, and the like, but is usually 90 ° C. or more. When the heating temperature is too low, the hydrolysis rate is slow.

  The upper limit of the heating temperature is usually below the boiling point of the solution. The boiling point of the solution means the boiling point of the solution before the polymer component is charged. Depending on the composition of the solution, the boiling point may not be clearly identified, but in such a case, the upper limit may be set to 140 ° C. In any case, if the heating temperature is too high, there is a possibility that the organic acid and the solvent may be volatilized.

  The time for the molecular weight reduction treatment varies depending on the degree of molecular weight reduction, the composition of the solution, the scale of the apparatus, the heating temperature, etc. Therefore, solid components in the reaction solution are sampled at appropriate time intervals and the weight average molecular weight is measured. The reaction may be terminated when the average molecular weight reaches the desired value. The time for the molecular weight reduction treatment is preferably as short as possible, for example, in the case of obtaining a low molecular weight polymer component having an average molecular weight of 10,000 to 20,000, preferably within 10 hours, more preferably within 8 hours, further preferably Within 6 hours.

  After completion of the reaction, insoluble matter in the reaction solution is recovered by filtration or the like, and appropriately washed and dried.

According to the process of the present invention, a low molecular weight polymer component having a weight average molecular weight of 10,000 to 20,000, in particular, is produced in high yield. For example, in the examples described below, it is shown that the yield exceeds 90%. The yield is calculated by the following equation.
Yield (%) = {W _f / W _i } × 100
In the formula, W _f represents the mass (g) of the low molecular weight polymer component,
W _i represents the mass (g) of the polymer component before hydrolysis.

  There are no particular limitations on the application of the produced low molecular weight polymer component, that is, it may be applied to the desired application.

  For example, a low molecular weight polymer component having an average molecular weight of 10,000 to 20,000 obtained by hydrolyzing a polymer component mainly containing polylactic acid is pulverized into a powder, which is used in the field of bioremediation. It is useful as a nutrient. Such a nutrient is solid, so the workability is good, and it is easy to accurately determine the timing and amount of nutrient dripping. Furthermore, it is easy to pulverize and excellent in sustained release.

  Alternatively, such low molecular weight polymer components can also be applied to fishing net additives and ship bottom paint additives. As a result, it is difficult for waterborne pests such as barnacles to adhere to fishing nets and ship bottoms. Alternatively, in the field of resource mining such as shale gas, addition to fracturing fluid, finishing fluid, drilling fluid and the like can be applied. In particular, in the field of resource mining, where pulverizability and hydrolyzability are required, such low molecular weight polymer components are naturally shrunk as long as the pulverization to the desired particle size is good and there is even water in the underground environment. It can be hydrolyzed.

  The invention is illustrated by the following examples.

<Material used>
As PLA (polylactic acid resin), REVODE 101 (d-lactic acid 4.62%) manufactured by Kaisei Bio-Materials Co., Ltd. was used. The molecular weight of this PLA was measured by the method described later and found to be in the range of 120,000 <Mw <170,000.
Musashino Chemical Laboratory manufactured Musashino lactic acid 50F (50 mass%) and Musashino lactic acid 90F (90 mass%) were used for 50% lactic acid and 90% lactic acid.
50% acetic acid and 90% acetic acid were prepared by treating Wako Pure Chemical Industries, Ltd. reagent special grade acetic acid (purity 99.7 +%) as 100% acetic acid and diluting each with arbitrary pure water.
50% citric acid was prepared by dissolving a reagent special grade citric acid (purity 98.0% or more) manufactured by Wako Pure Chemical Industries, Ltd. in heated pure water.
The 35% hydrochloric acid used Wako Pure Chemical Industries, Ltd. reagent special grade hydrochloric acid (35.0% to 37.0%).

As polyethylene oxalate (PEOx) which is a low molecular weight promoting resin, one polymerized by the following method was used.
In a 1 L separable flask equipped with a mantle heater, a liquid temperature thermometer, a stirrer, a nitrogen inlet tube and a distillation column, 354 g (3 mol) of dimethyl oxalate, 201 g (3.24 mol) of ethylene glycol and 0. 15 g was charged, and the liquid temperature in the flask was heated to 110 ° C. under a nitrogen stream to carry out atmospheric pressure polymerization. After the start of distilling off of methanol, it was kept for 1 hour to react. After 1 hour, the temperature was raised to 150 ° C. at a temperature rising rate of 10 ° C./30 minutes to carry out atmospheric pressure polymerization. At 150 ° C., 32.4 g (0.36 mol) of 1,4-butanediol was added and allowed to react for 1 hour. Thereafter, the temperature was raised to 180 ° C. at 10 ° C./30 minutes. The recovered liquid volume was 192 g.
Thereafter, the liquid temperature in the flask was reduced at a reduced pressure of 190 ° C. and 0.1 kPa to 0.8 kPa, and the obtained polymer was taken out. The mixture was crystallized by heat treatment under vacuum at 90 ° C. for 2 hours and at 120 ° C. for 2 hours. The weight average molecular weight of the thus-obtained PEOx was measured by the method described later and was 100,000.

<Measurement of Molecular Weight of PLA and PEOx 10% PLA>
The molecular weight of PLA was measured using GPC under the conditions shown below.
Device: gel permeation chromatograph GPC
Detector: Differential Refractive Index Detector RI
Column: SuperMultipore HZ-M (2)
Solvent: chloroform flow rate: 0.5 mL / min
Column temperature: 40 ° C
Sample preparation: 3 mL of a solvent was added to about 10 mg of a sample and left at room temperature.
After dissolution was visually confirmed, the solution was filtered through a 0.45 μm filter.
The standard used polystyrene.

<Measurement of molecular weight of PEOx>
Device: gel permeation chromatograph GPC
Detector: Differential Refractive Index Detector RI
Column: Shodex HFIP-LG (one), HFIP-806M (two)
(Showa Denko)
Solvent: Hexafluoroisopropanol (5 mM sodium trifluoroacetate added)
Flow rate: 0.5mL / min
Column temperature: 40 ° C
Sample preparation: 5 mL of the solvent was added to about 1.5 mg of the sample and gently stirred at room temperature (sample concentration
About 0.03%).
After dissolution was visually confirmed, the solution was filtered through a 0.45 μm filter.
The standard used polymethyl methacrylate.

Example 1
In a 20 mL vial, 1.0 g of PLA was immersed in 10 mL of 50% lactic acid and allowed to stand for 10 hours while being heated to 95 ° C.

(Example 2)
In a 20-mL vial, 1.0 g of PLA was immersed in 10 mL of 50% acetic acid, and allowed to stand in a heated state at 95 ° C. for 6 hours.

(Example 3)
In a 20 mL vial, 1.0 g of PLA was immersed in 10 mL of 50% citric acid and allowed to stand at 95 ° C. for 10 hours while being heated.

(Comparative example 1)
In a 20 mL vial, 1.0 g of PLA was immersed in 10 mL of pure water and allowed to stand in a heated state at 95 ° C. for 10 hours.

(Comparative example 2)
In a 500 mL separable flask, 50 g of PLA was immersed in 300 mL of 90% lactic acid, and heated to 120 ° C. while stirring with a mechanical stirrer of 130 rpm for 5 hours.

(Comparative example 3)
In a 20 mL vial, 1.0 g of PLA was immersed in 10 mL of 90% acetic acid and allowed to stand at 95 ° C. for 2 hours while being heated.

(Comparative example 4)
In a 20-mL vial, 1.0 g of PLA was immersed in 10 mL of 35% hydrochloric acid and allowed to stand in a heated state at 95 ° C. for 2 hours.

After heat treatment of any sample, the solution was removed with a Pasteur pipette and washed twice with 20 mL of pure water. It heat-dried at 95 degreeC for 1 hour, and measured mass ( _Wf ) after that. The yield (%) was calculated as a percentage (100 × (W _f / W _i )) with the mass (W _i ) of the raw material PLA. It was also measured weight average molecular weight (Mw) from drying and mass (W _f) specimen after the measurement. The molecular weight and the yield are shown in Table 1.

As can be seen from Table 1, the treatment with 50% lactic acid, 50% acetic acid and 50% citric acid reached a molecular weight of 10,000 to 20,000 with a heat treatment of 6 to 10 hours.
In the same treatment with pure water, the molecular weight did not reach 20,000 even after 10 hours.
Treatment with 90% lactic acid and 90% acetic acid proceeded to hydrolysis rapidly, but with 90% lactic acid the molecular weight decreased to 20,000 with 4 hours of treatment and the solids dissolved in 5 hours of treatment. Treatment with 90% acetic acid also reduced the molecular weight to 30,000 in 2 hours of treatment and lost solid form and dissolved in 3 hours of treatment. It is difficult to recover the low molecular weight aliphatic polyester as a solid at the actual production site as the solid dissolves after only one hour.
Even with 35% hydrochloric acid, the 2 hour treatment reduced the molecular weight to 8,800 and the 4 hour treatment lost the solid form. If the molecular weight is less than 10,000 in just 2 hours of treatment, it is difficult to recover solids in the molecular weight range of 10,000 to 20,000.

  As described above, it has been shown that the solid polyester and reduced molecular weight aliphatic polyester can be obtained in a short time while preventing mass loss due to dissolution by the method of the present invention.

  Next, an example of a particulate kneaded product (PEOx 10% PLA) in which 10% by mass of polyethylene oxalate (PEOx), which is a low molecular weight promoting resin, is kneaded with polylactic acid is shown.

(Example 4)
In a 3 L separable flask, 1500 g of PEOx10% PLA was immersed in 1800 g of 50% lactic acid and heated to 98 ° C. while stirring with a mechanical stirrer of 200 rpm.

(Comparative example 5)
In a 500 mL separable flask, 28 g of PEOx10% PLA was immersed in 200 g of 30% lactic acid and heated to 98 ° C. while stirring with a mechanical stirrer of 200 rpm.

(Comparative example 6)
In a 500 mL separable flask, 200 g of PEOx10% PLA was immersed in 300 g of pure water and heated to 98 ° C. while being stirred by a mechanical stirrer at 170 rpm.

In each example and comparative example, solid content was once collected for several hours, and Mw was measured. The heat treatment was ended when the Mw reached 10,000 to 20,000. Thereafter, the solution was separated by filtration and washed with an equal amount of pure water three or more times. The samples obtained in Example 4 and Comparative Example 5 were dried by heating at 80 ° C. for 3 hours, and the samples obtained in Comparative Example 6 were dried at 50 ° C. for 3 hours. The subsequent mass (W _f ) was measured. The yield (%) was calculated by the percentage [100 × (W _f / W _i )] of the mass (W _i ) of PEOx 10% PLA before hydrolysis. The results are shown in Table 2 below.

  From Table 2, when heat-processing with 50% lactic acid, molecular weight could be reduced to Mw 13,300 in just 5 hours. This time is about half that when treated with pure water to the same molecular weight. The yield at this time was 93%, which was equal to or higher than 91% of the pure water treatment. In addition, when treated with 30% lactic acid, reduction in molecular weight proceeded at a slightly faster rate than pure water, but the yield was low.

  Furthermore, the molecular weight change at the time of the heat processing with 50% lactic acid and pure water is shown in FIG. As can be seen from FIG. 1, in the heat treatment with 50% lactic acid, the Mw reaches 20,000 or less in less than 4 hours, whereas the water treatment reaches the Mw 20,000 or less. Was as slow as 7.5 hours.

  As described above, according to the method of the present invention, it is shown that also when PEOx is mixed with polylactic acid, a solid and low-molecular-weighted aliphatic polyester can be obtained quickly while preventing mass loss due to dissolution. The

Claims (12)

Prepare a solution containing 31 to 60% by mass of an organic acid,
A method for reducing the molecular weight of a polymer component, which comprises adding a polymer component comprising an aliphatic polyester to the solution and heating it under normal pressure.   The method according to claim 1, wherein the aliphatic polyester is polylactic acid.   The method according to claim 2, wherein a low molecular weight promoting resin which releases an acid by hydrolysis is used.   The method according to claim 3, wherein the low molecular weight promoting resin is a polyoxalate.   The method according to any one of claims 3 or 4, wherein a polymer component consisting of said low molecular weight promoting resin and said aliphatic polyester is added to said solution.   The method according to any one of claims 1 to 5, wherein the organic acid is a carboxylic acid.   The method according to any one of claims 1 to 6, wherein the organic acid is at least one organic acid selected from the group consisting of lactic acid, acetic acid and citric acid.   The method according to any one of claims 1 to 7, wherein the organic acid is lactic acid.   The method according to any one of claims 1 to 8, wherein the solution selectively contains the organic acid as a solute.   The method according to any one of claims 1 to 9, wherein the heating temperature is 90 ° C or higher.   The method according to any one of claims 1 to 10, wherein after heating, the insoluble matter is recovered to obtain a low molecular weight polymer component having a weight average molecular weight of 10,000 to 20,000. The method according to claim 11, wherein the yield X calculated from the following formula (1) is 90% or more.
X = 100 × (Wf / Wi) (1)
In the formula, W _f represents the mass (g) of the low molecular weight polymer component,
W _i represents the mass (g) of the polymer component before hydrolysis.