A method for degrading polylactic acid to obtain menthyl lactate

Abstract

The application discloses a method for degrading polylactic acid to obtain menthyl lactate, and belongs to the technical field of depolymerization and recycling of high polymer composite materials. The polylactic acid is degraded to become menthyl lactate in a targeted manner. In the application, the polylactic acid is dissolved in an organic solvent or without adding other solvents under the catalysis of a metal amide catalyst and in the protection of inert gas under normal pressure, and the polylactic acid is depolymerized under the action of menthol. The polylactic acid molecular chain is depolymerized under mild conditions, and the obtained menthyl lactate can be directly reused, so that the industrial production steps and industrial cost are reduced, and the sustainable development principle is met.

Description

TECHNICAL FIELD

[0001] The application relates to a method for degrading polylactic acid into menthyl lactate, and belongs to the technical field of depolymerization and recycling of high polymer composite materials. BACKGROUND

[0002] Polylactic acid (PLA) is the most concerned biodegradable plastic, which has been paid much attention and developed in recent years. However, a large amount of polylactic acid waste is also generated. Although polylactic acid can be degraded into water and carbon dioxide in the natural environment, the period is extremely long, and the environmental conditions are harsh. Therefore, recycling of polylactic acid can not only avoid pollution of the environment by these wastes, but also utilize the waste resources for value-added utilization, which is a key measure to realize sustainable development under the condition of limited resources.

[0003] Menthyl lactate is a chemical substance that can be used in food additives, daily chemical products and medicines, and is recognized as an excellent cooling agent without adverse reactions such as burning, irritation and stinging. It is usually prepared from lactic acid and menthol or menthol, but this process usually needs strong acid catalysis, the reaction conditions are harsh, and the existence of by-products increases the purification cost, so it is of great significance to develop a synthesis process under mild conditions.

[0004] Therefore, it is seen that how to effectively combine the recycling of polylactic acid waste and the preparation of menthyl lactate has high research value. The combination of the two not only utilizes the fixed resources in the waste polylactic acid, but also realizes the synthesis of important chemical products in a “kill two birds with one stone” way, which is really “turning waste into treasure”, and will contribute to our pursuit of more sustainable development and greener future. SUMMARY

[0005] In order to realize the directional degradation of polylactic acid into menthyl lactate, the application provides a method for degrading polylactic acid into menthyl lactate.

[0006] The technical scheme of the application is as follows:

[0007] One of the purposes of the application is to provide a method for degrading polylactic acid into menthyl lactate, which comprises: under the catalysis of a metal amide catalyst at normal pressure and a certain temperature, polylactic acid is dissolved in an organic solvent or without adding a solvent, and the depolymerization of polylactic acid is carried out under the action of menthol to obtain menthyl lactate.

[0008] Further limited, the metal amide is selected from one of the following structures:

[0009]

[0010] In the formula, R1 is an alkyl group.

[0011] More specifically, R1 is methyl.

[0012] More specifically, the metal amide is added in an amount of 0.1-50 wt.% of the polylactic acid content.

[0013] More specifically, the menthol is added in an amount of 10-500 wt.% of the polylactic acid content.

[0014] More specifically, the number average molecular weight of the polylactic acid is 10 2 -10 7 g / mol.

[0015] More specifically, the depolymerization temperature is 20-300℃.

[0016] More specifically, the depolymerization temperature is room temperature.

[0017] More specifically, the organic solvent is one or a mixture of several of benzene, toluene, xylene, chlorobenzene, dichloromethane, trichloromethane, tetrahydrofuran, 2-methyltetrahydrofuran, ethyl acetate.

[0018] More specifically, the concentration of the polylactic acid in the presence of the organic solvent is 0.01-100 M.

[0019] Advantages:

[0020] The present application realizes the directional recovery of menthyl lactate from polylactic acid under the action of a depolymerization reagent, and realizes the chemical recycling of polylactic acid and the efficient preparation of menthyl lactate. Compared with the prior art, the present application has the following advantages:

[0021] (1) The present application realizes the depolymerization of the molecular chain of polylactic acid under mild conditions, and the obtained menthyl lactate can be directly reused, reducing the industrial steps and cost of menthyl lactate preparation, and meeting the principle of sustainable development.

[0022] (2) The depolymerization method provided by the present application has good universality of solvents and conditions, and has good depolymerization effect under various solvents and depolymerization conditions, and can efficiently recover the directional product.

[0023] (3) The present application uses a catalyst with extremely high catalytic efficiency, which can realize catalysis under the condition of relatively low addition amount, has high product yield, few side reactions, and good economic benefit.

[0024] (4) The present application proposes a new depolymerization strategy to realize the chemical recycling of waste polylactic acid, which has important guiding significance for the recycling of waste materials and the preparation of menthyl lactate. DETAILED DESCRIPTION

[0025] In order to make the above objectives, features and advantages of the present application more obvious and comprehensible, the specific embodiments of the present application will be described in detail below with reference to the description and examples.

[0026] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other manners different from those described herein, and those skilled in the art can make similar generalizations without departing from the concept of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0027] Secondly, "one embodiment" or "an embodiment" referred to herein means that a specific feature, structure or characteristic can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent of or mutually exclusive with other embodiments.

[0028] The experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained by commercial channels by those skilled in the art.

[0029] Example 1

[0030] The reaction process for depolymerization of polylactic acid material in this embodiment is as follows:

[0031]

[0032] The experimental process includes the following steps:

[0033] (1) Take a 150 mL Schlenk flask, evacuate and replace with argon, then in the glove box, add 2.88 g (40 mmol of polymer repeating units) of polylactic acid (Mn=29.4 kg / mol, D=1.73), add 4 mL of LiHMDS catalyst (4 mmol, 1 mol% relative to polymer repeating units), add 20 mL of DCM and 77 g of menthol, and stir the reaction at room temperature in a fume hood. n = 29.4 kg / mol, D = 1.73), 4 mL of LiHMDS catalyst (4 mmol, 1 mol% relative to polymer repeating units), 20 mL of DCM and 77 g of menthol, and stir the reaction at room temperature in a fume hood.

[0034] (2) After 5 minutes of reaction, sample for NMR detection, the results show that the conversion rate of PLA is 100% and the yield of menthyl lactate is 100%.

[0035] (3) After separation of the reaction product, 8.5 g of menthyl lactate is obtained with a yield of 93%.

[0036] Example 2

[0037] The reaction process for depolymerization of polylactic acid material in this embodiment is as follows:

[0038]

[0039] The experimental process includes the following steps:

[0040] (1) Take 150 mL of Schlenk bottle, vacuum and replace argon, then add 2.88 g (40 mmol of polymer repeat units) of polylactic acid (M n = 29.4 kg / mol, D = 1.73), add 4 mL of NaHMDS catalyst (4 mmol, 1 mol% relative to polymer repeat units), add 20 mL of DCM and 77 g of menthol, and stir the reaction at room temperature in the fume hood.

[0041] (2) After 5 min of reaction, sample NMR detection, the results show that the conversion rate of PLA is 100%, and the yield of menthyl lactate is 98.8%.

[0042] (3) After separation of the reaction product, 8.9 g of menthyl lactate is obtained, with a yield of 97%.

[0043] Example 3:

[0044] The reaction process for depolymerization of polylactic acid material in this example is as follows:

[0045]

[0046] The experimental process includes the following steps:

[0047] (1) Take 150 mL of Schlenk bottle, vacuum and replace argon, then add 2.88 g (40 mmol of polymer repeat units) of polylactic acid (M n = 29.4 kg / mol, D = 1.73), add 4 mL of KHMDS catalyst (4 mmol, 1 mol% relative to polymer repeat units), add 20 mL of DCM and 77 g of menthol, and stir the reaction at room temperature in the fume hood.

[0048] (2) After 5 min of reaction, sample NMR detection, the results show that the conversion rate of PLA is 100%, and the yield of menthyl lactate is 96.9%.

[0049] (3) After separation of the reaction product, 8.7 g of menthyl lactate is obtained, with a yield of 95%.

[0050] Example 4:

[0051] The reaction process for depolymerization of polylactic acid material in this example is as follows:

[0052]

[0053] The experimental process includes the following steps:

[0054] (1) Take 150 mL of Schlenk bottle, vacuum and replace argon, then add 2.88 g (40 mmol of polymer repeat units) of polylactic acid (M n = 29.4 kg / mol, D = 1.73), add 4 mL of LiHMDS catalyst (4 mmol, 1 mol% relative to polymer repeat units), add 20 mL of toluene and 77 g of menthol, and stir the reaction at 50°C in a fume hood.

[0055] (2) After 10 min of reaction, sample NMR detection, the results show that the conversion rate of PLA is 100%, and the yield of menthyl lactate is 98.4%.

[0056] (3) After separation, 8.9 g of menthyl lactate is obtained, with a yield of 98%.

[0057] Example 5:

[0058] The reaction process for depolymerization of polylactic acid material in this example is as follows:

[0059]

[0060] The experimental process includes the following steps:

[0061] (1) Take 150 mL of Schlenk bottle, vacuum and replace argon, then add 2.88 g (40 mmol of polymer repeat units) of polylactic acid (M n = 32.4 kg / mol, D = 1.53), add 4 mL of NaHMDS catalyst (4 mmol, 1 mol% relative to polymer repeat units), add 20 mL of toluene and 77 g of menthol, and stir the reaction at 50°C in a fume hood.

[0062] (2) After 10 min of reaction, sample NMR detection, the results show that the conversion rate of PLA is 100%, and the yield of menthyl lactate is 96.5%.

[0063] (3) After separation, 8.5 g of menthyl lactate is obtained, with a yield of 93%.

[0064] Example 6:

[0065] The reaction process for depolymerization of polylactic acid material in this example is as follows:

[0066]

[0067] The experimental process includes the following steps:

[0068] (1) Take 150 mL of Schlenk bottle, pump and replace argon, then add 2.88 g (40 mmol of polymer repeat units) of polylactic acid (M n = 32.4 kg / mol, D = 1.53), add 4 mL of KHMDS catalyst (4 mmol, 1 mol% relative to polymer repeat units), add 20 mL of xylene and 77 g of menthol, and stir the reaction at 100°C in a fume hood.

[0069] (2) After 5 min of reaction, sample for NMR detection, the results show that the conversion of PLA is 100% and the yield of menthyl lactate is 99.3%.

[0070] (3) After the reaction product is separated, 8.7 g of menthyl lactate is obtained with a yield of 95%.

[0071] Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make various modifications and modifications without departing from the spirit and scope of the present application, therefore the protection scope of the present application should be defined by the claims.

Claims

1. A method for degrading polylactic acid to obtain menthyl lactate, characterized by, The method is: under normal pressure, a certain temperature, and catalysis of a metal amide catalyst, polylactic acid is dissolved in an organic solvent or without adding a solvent, and then depolymerization of polylactic acid is carried out under the action of menthol to obtain menthyl lactate; The metal amide is selected from one of the following structures. In the formula, R1 is an alkyl group.

2. The method of claim 1, wherein, R1 is a methyl group.

3. The method of claim 1, wherein, The added amount of the metal amide is 0.1-50 wt.% of the content of polylactic acid.

4. The method of claim 1, wherein, The added amount of menthol is 10-500 wt.% of the content of polylactic acid.

5. The method of claim 1, wherein, The number average molecular weight of the polylactic acid is 10 2 - 10 7 g / mol.

6. The method of claim 1, wherein, The temperature is 20-300 DEG C.

7. The method of claim 6, wherein, The temperature is room temperature.

8. The method of claim 1, wherein, The organic solvent is one or a mixture of several of benzene, toluene, xylene, chlorobenzene, dichloromethane, trichloromethane, tetrahydrofuran, 2-methyltetrahydrofuran, and ethyl acetate.

9. The method of claim 1, wherein, In the presence of the organic solvent, the concentration of polylactic acid is 0.01-100 M.

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