Modified polylactic acid and preparation method thereof

Abstract

The invention relates to the field of polylactic acid, and discloses modified polylactic acid and a preparation method thereof. Natural or non-natural amino acid is taken as a raw material, amino of the natural or non-natural amino acid is converted into hydroxy acid to obtain a hydroxy acid compound, an oligomer is prepared under the catalysis of a catalyst, and then the lactide derivative is obtained through depolymerization; and with lactide and a lactide derivative as raw materials, carrying out copolymerization in the presence of a catalyst to obtain the modified polylactic acid. According to the method, firstly, a polymeric monomer is modified, a lactide derivative is synthesized from natural or non-natural amino acid, synthesis of the modified polylactic acid is achieved through copolymerization of the lactide derivative and lactide, and the synthesized polylactic acid has good mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid, and more particularly to a modified polylactic acid and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is a promising biodegradable polymer. Its production process reduces petroleum resource consumption by 30%–50% compared to conventional petroleum-based polymers, and its degradation products are carbon dioxide and water, causing no environmental pollution, making it an environmentally friendly material. PLA has a high modulus, moderate strength, and good chemical inertness, processability, and biocompatibility, making it a highly promising alternative to petroleum-based polymers and attracting widespread attention from scholars both domestically and internationally. Despite its many advantages, PLA also has some performance limitations, such as poor toughness and heat resistance, which restrict its application in certain specific fields.

[0003] Currently, the modification of polylactic acid (PLA) mainly focuses on physical modification, such as improving the performance of PLA materials through physical blending. However, physical modification often faces the problem of poor compatibility, while there are few reports on improving PLA performance by modifying the monomers. Therefore, there is an urgent need in this field to improve the defects in the mechanical properties of PLA from the source by modifying the monomers. Summary of the Invention

[0004] To overcome the poor toughness of polylactic acid (PLA), this invention provides a modified PLA and its preparation method. The invention first modifies the polymer monomers, and then synthesizes the modified PLA through copolymerization of the obtained lactide derivative and lactide. The synthesized modified PLA exhibits good toughness.

[0005] The specific technical solution of this invention is as follows:

[0006] First, this invention provides a modified polylactic acid, the chemical structural formula of which is as follows:

[0007]

[0008] in:

[0009] R is selected from C1-C 10 Alkyl, alkoxy, aryl (heteroaryl), ester, benzyl, amide, or halogen; x takes the value 1.4 * 10 3 -1.6*10 3 The value of y is 26-28.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned modified polylactic acid, comprising the following steps:

[0011] Step a: Using natural or non-natural amino acid S mUsing it as a raw material, hydroxy acid compound S is obtained by converting its amino group into a hydroxy acid. n Oligomers were prepared under the catalysis of a catalyst, and then depolymerized to obtain lactide derivative A.

[0012]

[0013] Step b: Using lactide B and lactide derivative A as raw materials, copolymerize them in the presence of a catalyst to obtain modified polylactic acid C.

[0014]

[0015] Preferably, step a specifically includes: adding natural or non-natural amino acids, sulfuric acid and sodium nitrite to a reaction vessel, stirring the reaction, extracting with ethyl acetate after the reaction is completed, combining the organic phases, and concentrating to obtain a hydroxy acid compound; mixing the hydroxy acid compound with a catalyst and reacting it, distilling under reduced pressure to obtain an oligomer, then heating and distilling under reduced pressure to obtain a crude product of lactide derivative, and recrystallizing it in ethyl acetate to obtain the lactide derivative.

[0016] Further preferred, in step a: the amount of the natural or non-natural amino acid is 350-390 mmol; the concentration of the sulfuric acid solution is 0.8-1.2 M, and the amount is 600-620 mL; the amount of sodium nitrite is 2.3-2.4 mol.

[0017] Further preferably, in step a: the temperature of the stirring reaction is 0-5℃; the temperature of the mixing reaction is 130-180℃; and the temperature of the heating is 200-240℃.

[0018] Further preferred, in step a: the catalyst is zinc oxide.

[0019] Preferably, step b specifically includes: adding the obtained lactide derivative and lactide into a reaction vessel, adding a catalyst and stirring the reaction, dissolving the crude product with dichloromethane, adding methanol to precipitate the product, filtering, and vacuum drying.

[0020] Further preferably, in step b: the amount of the lactide derivative is 1 to 10 wt% of the lactide, most preferably 5 wt%.

[0021] Further preferred, in step b: the catalyst is Sn(Oct)2, SnCl2, Sn(C6H6)4, with Sn(Oct)2 being the most preferred; the molar ratio of the catalyst to the total amount of the polymerizing monomer is 1:(1000-4000), with 1:3000 being the most preferred.

[0022] Preferably, in step b, the reaction temperature of the stirring reaction is 100-150℃, and the reaction time is 6-24h.

[0023] Preferably, in step b, the vacuum drying temperature is 70-90℃ and the time is 20-30h.

[0024] Compared with the prior art, the beneficial effects of the present invention are: the present invention first modifies the polymer monomer, and then synthesizes modified polylactic acid by copolymerizing the obtained lactide derivative with lactide. The synthesized modified polylactic acid has good toughness. Detailed Implementation

[0025] The present invention will be further described below with reference to embodiments.

[0026] Example 1

[0027] 1) Preparation of new monomers:

[0028]

[0029] Add amino acid derivative S to a 1L three-necked flask 1 (50 g, 370 mmol) was added, followed by the addition of a pre-prepared H2SO4 solution (600 mL, 1 M). Sodium nitrite (160 g, 2.3 mol) was added at 0 °C, and the reaction was allowed to proceed for 12 h. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phases were combined, dried, and concentrated to obtain the target product S. 2 Product S 2 100 mmol was added to a 250 mL four-necked flask, along with 2 wt% ZnO catalyst. The mixture was then distilled under reduced pressure at 160 °C with stirring to generate oligomers. The reaction was stopped when the temperature at the condenser inlet began to drop and no more water flowed from the receiving flask. The receiving apparatus was replaced, and the receiving flask was placed in a low-temperature environment. The reaction system was then rapidly heated to 220 °C, followed by rapid depressurization to below 600 Pa. Vacuum distillation yielded the crude monomer product, which was recrystallized from ethyl acetate to obtain A. 1 .

[0030] 2) Preparation of modified polylactic acid:

[0031]

[0032] B (4g, 28mmol), A 1 (5wt%) was weighed into a reaction flask, and catalyst Sn(Oct)₂ (0.03mol%) was added. The reaction was carried out at 120℃ for 12 h. After the reaction was completed, dichloromethane was added to dissolve the product, and then a large amount of methanol was added to precipitate the product. The product was filtered and dried under vacuum to obtain product C. 1 In the structural formula, x is approximately 1.4 * 10^6. 3 y is approximately 26.

[0033] Example 2

[0034] 1) Preparation of new monomers:

[0035]

[0036] Add amino acid derivative S to a 1L three-necked flask 3 (50 g, 381 mmol) was added, followed by the addition of a pre-prepared H2SO4 solution (620 mL, 1 M). Sodium nitrite (165 g, 2.4 mol) was added at 0 °C, and the reaction was allowed to proceed for 12 h. After the reaction was complete, the mixture was extracted with ethyl acetate, and the organic phases were combined, dried, and concentrated to obtain the target product S. 4 Product S 4 100 mmol was added to a 250 mL four-necked flask, along with 2 wt% ZnO catalyst. The mixture was then distilled under reduced pressure at 160 °C with stirring to generate oligomers. The reaction was stopped when the temperature at the condenser inlet began to drop and no more water flowed from the receiving flask. The receiving apparatus was replaced, and the receiving flask was placed in a low-temperature environment. The reaction system was then rapidly heated to 230 °C, followed by rapid depressurization to below 600 Pa. Distillation under reduced pressure yielded the crude monomer product, which was recrystallized in ethyl acetate to obtain A. 2 .

[0037] 2) Preparation of modified polylactic acid:

[0038]

[0039] B (4g, 28mmol), A 2 (5wt%) of the crude product was weighed into a reaction flask and catalyst Sn(Oct)₂ (0.03mol%) was added. The reaction was carried out at 120℃ for 12 h. After the reaction was completed, the mixture was cooled to room temperature, and dichloromethane was added to dissolve the crude product. Then, a large amount of methanol was added to precipitate the product. The product was filtered and dried under vacuum to obtain product C. 2 In the structural formula, x is approximately 1.5 * 10^6. 3 y is approximately 28.

[0040] Performance testing

[0041] The performance of the products obtained in each embodiment was tested, and the results are shown in the table below:

[0042]

[0043] As shown in the table above, the tensile strength, elongation at break, tensile modulus, and impact strength of modified polylactic acid materials are significantly higher than those of pure polylactic acid. Chemical modification of polylactic acid can improve some of the mechanical defects of polylactic acid from the source.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A modified polylactic acid, characterized in that: The chemical structural formula is as follows: in: R is selected from C1-C 10 Alkyl, alkoxy, aryl (heteroaryl), ester, benzyl, amide, or halogen; The value of x is between 1400 and 1600. The value of y is 26-28.

2. A method for preparing modified polylactic acid as described in claim 1, characterized in that... Includes the following steps: Step a: Using natural or non-natural amino acid S m Using it as a raw material, hydroxy acid compound S is obtained by converting its amino group into a hydroxy acid. n Oligomers were prepared under the catalysis of a catalyst, and then depolymerized to obtain lactide derivative A; Step b: Using lactide B and lactide derivative A as raw materials, copolymerize them under the catalysis of a catalyst to obtain modified polylactic acid C; 3. The preparation method according to claim 2, characterized in that... Specifically, it includes: Step a: Add natural or non-natural amino acids, sulfuric acid and sodium nitrite to the reaction vessel, stir the reaction, extract with ethyl acetate after the reaction is completed, combine the organic phases, and concentrate to obtain hydroxy acid compound; mix the hydroxy acid compound with the catalyst and react, distill under reduced pressure to obtain oligomer, then heat and distill under reduced pressure to obtain crude lactide derivative product, recrystallize in ethyl acetate to obtain lactide derivative. Step b: Add the obtained lactide derivative and lactide to the reaction vessel, add the catalyst and stir the reaction, dissolve the crude product with dichloromethane, add methanol to precipitate the product, filter, and vacuum dry.

4. The preparation method according to claim 3, characterized in that: In step a: The amount of the natural or non-natural amino acids used is 350-390 mmol; The concentration of the sulfuric acid solution is 0.8-1.2M, and the volume used is 600-620mL; The amount of sodium nitrite used is 2.3 to 2.4 mol.

5. The preparation method according to claim 3, characterized in that: In step a: The temperature of the stirring reaction is 0-5℃; The temperature of the mixing reaction is 130–180°C; The temperature for the heating is 200–240°C.

6. The preparation method according to claim 3, characterized in that: In step a: the catalyst is zinc oxide.

7. The preparation method according to claim 3, characterized in that: In step b: the amount of the lactide derivative used is 1 to 10 wt% of lactide.

8. The preparation method according to claim 3, characterized in that: In step b: The catalyst is Sn(Oct)2, SnCl2, or Sn(C6H6)4. The molar ratio of the catalyst to the total amount of polymer monomers is 1:(1000-4000).

9. The preparation method according to claim 3, characterized in that: In step b: the reaction temperature of the stirring reaction is 100-150℃, and the reaction time is 6-24h.

10. The preparation method according to claim 3, characterized in that: In step b: the vacuum drying temperature is 70-90℃ and the time is 20-30h.

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