A method for preparing highly transparent and highly flexible modified polylactic acid

Abstract

The present invention provides a method for preparing a highly transparent and highly flexible modified polylactic acid, and relates to the technical field of organic polymer compounds. A method for preparing a highly transparent and highly flexible modified polylactic acid includes the steps of preparing a PLA-co-PVL copolymer solution, purifying the PLA-co-PVL copolymer, synthesizing an ATEC-HEA complex, and obtaining a modified polylactic acid composite material; the preparation of the PLA-co-PVL copolymer solution comprises the steps of uniformly mixing L-lactide and δ-valerolactone to obtain a mixed solution, adding a catalyst and an initiator to the mixed solution, and reacting to obtain a PLA-co-PVL copolymer solution; the catalyst is Sn(Oct)2, and the initiator is 1,4-butanediol; the synthesis of the ATEC-HEA complex comprises raw materials including acetyl citrate triethyl, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone; the preparation of the modified polylactic acid composite material comprises raw materials including a PLA-co-PVL solid copolymer, an ATEC-HEA complex, and an antioxidant. The modified polylactic acid of the present invention has high light transmittance and excellent flexibility.

Description

Technical Field

[0001] The present invention relates to the technical field of organic polymer compounds, and in particular to a method for preparing highly transparent and highly flexible modified polylactic acid. Background Art

[0002] Polylactic acid (PLA) is a polymer derived from lactic acid, a readily available and renewable raw material. The production process is pollution-free, and the product is biodegradable, enabling recycling in nature, making it an ideal green polymer material. Modified PLA resins are widely used in the injection molding market. Pure PLA is hard and brittle, and its light transmittance is low. These shortcomings limit its application in injection molding products.

[0003] An existing patent document with publication number CN117946506A discloses a degradable polylactic acid resin and its application in food packaging. This method significantly improves the flexibility of polylactic acid to a certain extent while maintaining a high tensile strength and heat deformation temperature. However, its shortcoming is that it does not mention the regulation of transmittance and haze. The introduction of modified starch and crystallization nucleating agents will cause the transmittance to decrease, thereby limiting its use in some application scenarios that require transmittance. Another existing patent document with publication number CN118562103B discloses a method for preparing polylactic acid for highly transparent food packaging. PLA for highly transparent food packaging is prepared by starch cationization, sulfhydrylation treatment and graft polycondensation. This method utilizes the graft polycondensation of starch and lactic acid to effectively improve the transmittance, excellent heat resistance and mechanical strength of polylactic acid. However, the polylactic acid prepared by this method has obvious deficiencies in flexibility, which limits its wide application in application scenarios that require high deformation capacity, such as flexible packaging and degradable films.

[0004] In summary, although the existing technical solutions have improved certain properties of polylactic acid to a certain extent, the following technical problems still exist: it is impossible to achieve both good flexibility and light transmittance. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a method for preparing highly transparent and highly flexible modified polylactic acid, and achieves the following invention objectives: preparing modified polylactic acid with high light transmittance and excellent flexibility.

[0006] To achieve the above objectives, the technical solutions adopted are as follows:

[0007] A method for preparing highly transparent and highly flexible modified polylactic acid, comprising the steps of preparing a PLA-co-PVL copolymer solution, purifying the PLA-co-PVL copolymer, synthesizing an ATEC-HEA complex, and obtaining a modified polylactic acid composite material;

[0008] Preparation of the PLA-co-PVL copolymer solution: L-lactide and δ-valerolactone are uniformly mixed to obtain a mixed solution; a catalyst and an initiator are added to the mixed solution to react to obtain a PLA-co-PVL copolymer solution; the catalyst is Sn(Oct)2, and the initiator is 1,4-butanediol.

[0009] Purification of the PLA-co-PVL copolymer: adding a PLA-co-PVL copolymer solution into anhydrous methanol to precipitate a precipitate, washing the precipitate with methanol, and drying to obtain a PLA-co-PVL solid copolymer.

[0010] The raw materials used in the synthesis of the ATEC-HEA complex include: acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone;

[0011] The mass ratio of raw materials used in synthesizing the ATEC-HEA complex is: the mass ratio of acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone is 100: (38-40): (0.7-1): (0.3-0.5).

[0012] The modified polylactic acid composite material is prepared by using raw materials including: PLA-co-PVL solid copolymer, ATEC-HEA compound, and antioxidant;

[0013] The antioxidant is Irganox1010.

[0014] The mass ratio of raw materials used in preparing the modified polylactic acid composite material is: the mass ratio of PLA-co-PVL solid copolymer, ATEC-HEA compound, and antioxidant is (85-90): (10-15):0.2.

[0015] The molar ratio of L-lactide to δ-valerolactone is (4-5):1, the catalyst accounts for 0.05-0.1% of the total mass of L-lactide and δ-valerolactone, and the initiator accounts for 0.1-0.2% of the total mass of L-lactide and δ-valerolactone.

[0016] Furthermore, the PLA-co-PVL copolymer solution is prepared by uniformly mixing L-lactide and δ-valerolactone to obtain a mixed solution. Nitrogen is introduced to replace air 3-4 times, and then a catalyst and an initiator are added to the mixed solution and stirred uniformly. The mixture is heated to 130-150°C and reacted for 2-3 hours, then heated to 160-180°C and reacted for 4-8 hours. Nitrogen is continuously introduced during the reaction at a flow rate of 50-60 mL / min. After the reaction is completed, the mixture is cooled to room temperature to obtain a PLA-co-PVL copolymer solution.

[0017] Furthermore, the PLA-co-PVL copolymer is purified by adding the PLA-co-PVL copolymer solution to anhydrous methanol at a mass ratio of 1:(8-10). The mixture is stirred at 500-800 rpm to precipitate the copolymer. The precipitate is collected by filtration, washed 2-3 times with methanol, and dried under vacuum at 50-60°C for 22-24 hours to obtain a solid PLA-co-PVL copolymer.

[0018] Furthermore, the synthesis of the ATEC-HEA complex: acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone are stirred until completely dissolved, nitrogen is introduced to replace the air for 5-10 minutes, and the oil bath is heated to 120-130°C and reacted for 3-4 hours. After the reaction is completed, it is cooled to room temperature and the reaction liquid is subjected to rotary evaporation at a rotary evaporation temperature of 60-70°C, a rotary evaporation vacuum of 0.08-0.09 MPa, and a rotary evaporation time of 7-8 hours. After the rotary evaporation is completed, it is dried under reduced pressure, with the temperature set at 40-50°C, the pressure set at 0.090-0.095 MPa, and the drying time being 2-2.5 hours. After drying, the ATEC-HEA complex is obtained.

[0019] Furthermore, the modified polylactic acid composite material is prepared by uniformly mixing a PLA-co-PVL solid copolymer, an ATEC-HEA compound, and an antioxidant to obtain a mixture. The mixture is then fed into a twin-screw extruder with the following extruder parameters: feed zone temperature 160-165°C, melt zone temperature 170-175°C, mixing zone temperature 175-180°C, die head temperature 170-175°C, screw speed 80-100 rpm, and feed rate 3-5 kg / h. After extrusion, the mixture is water-cooled and pelletized to obtain pellets with a diameter of 4±0.5 mm. The pellets are then vacuum-dried at 50-60°C for 11-12 hours to obtain the modified polylactic acid composite material.

[0020] The beneficial effects of the present invention are as follows:

[0021] (1) The highly transparent and highly flexible modified polylactic acid of the present invention has excellent optical properties. The transmittance reaches 94.14-94.58%, and the haze reaches 3.87-4.46%. The higher transmittance and lower haze mean that the prepared modified polylactic acid has better optical properties and higher light transmission uniformity.

[0022] (2) The highly transparent and highly flexible modified polylactic acid of the present invention has excellent flexibility. The notched impact strength reaches 7.8-8.6 kJ / m 2, the notched impact strength is higher, indicating a stronger ability to resist fracture; the elongation at break reaches 135-173%, and a higher elongation at break directly reflects better flexibility and ductility; the flexural modulus reaches 2.3-2.8GPa, and a lower flexural modulus means a stronger ability to resist elastic bending deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Attachment Figure 1 is a Fourier transform infrared spectrum of the PLA-co-PVL copolymer in the step of "preparation of PLA-co-PVL copolymer solution" in Example 1;

[0024] Attachment Figure 2 This is the Fourier transform infrared spectrum of the ATEC-HEA complex in the step of “Synthesis of ATEC-HEA complex” in Example 1. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0026] Example 1 A method for preparing highly transparent and highly flexible modified polylactic acid

[0027] A method for preparing highly transparent and highly flexible modified polylactic acid comprises the following steps:

[0028] Step 1: Preparation of PLA-co-PVL copolymer solution

[0029] L-lactide and δ-valerolactone were mixed uniformly at a molar ratio of 4:1 to obtain a mixture. Nitrogen was introduced three times to displace the air. A catalyst and initiator were then added to the mixture and stirred uniformly, with the catalyst comprising 0.05% of the total weight of the mixture and the initiator comprising 0.1% of the total weight of the mixture. The mixture was heated to 130°C and reacted for 3 hours, then to 160°C and reacted for 8 hours. Nitrogen was continuously introduced at a flow rate of 50 mL / min throughout the reaction. After the reaction, the mixture was cooled to room temperature to obtain a PLA-co-PVL copolymer solution. The catalyst was Sn(Oct)2, and the initiator was 1,4-butanediol.

[0030] The FT-IR spectra were characterized at 883 cm -1 The CC skeleton structure characteristic peak appears at 1216cm -1 The characteristic peak of ester bond appears at 1745cm -1 The ester carbonyl characteristic peak appeared at , proving that PLA-co-PVL copolymer was obtained. Figure 1 .

[0031] Step 2: Purification of PLA-co-PVL copolymer

[0032] The PLA-co-PVL copolymer solution was added to anhydrous methanol at a mass ratio of 1:8. The copolymer was stirred at 500 rpm to precipitate. The precipitate was collected by filtration, washed twice with methanol, and dried under vacuum at 50°C for 24 hours to obtain a PLA-co-PVL solid copolymer.

[0033] Step 3: Synthesis of ATEC-HEA complex

[0034] Acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone were stirred until completely dissolved. The mass ratio of acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone was 100:38:0.7:0.3. Nitrogen was introduced to displace the air for 5 minutes, and the mixture was heated in an oil bath to 120°C and allowed to react for 4 hours. After the reaction, the mixture was cooled to room temperature and subjected to rotary evaporation at 60°C, a vacuum of 0.09 MPa, and a time of 8 hours. Following the evaporation, the mixture was dried under reduced pressure at 40°C, a pressure of 0.095 MPa, and a time of 2.5 hours to obtain the ATEC-HEA complex.

[0035] The FT-IR spectra were characterized at 964 cm -1 、1636cm -1 、3040cm -1 The characteristic peak of HEA double bond structure appears at 1710 cm -1 The ester carbonyl characteristic peak appears at the reaction, proving that the ATEC-HEA complex is obtained. Figure 2 .

[0036] Step 4: Prepare modified polylactic acid composite material

[0037] PLA-co-PVL solid copolymer, ATEC-HEA complex, and antioxidant were uniformly mixed to form a composite. The mass ratio of PLA-co-PVL solid copolymer, ATEC-HEA complex, and antioxidant was 85:15:0.2. The composite was then fed into a twin-screw extruder with the following extruder parameters: feed zone temperature of 160°C, melt zone temperature of 170°C, mixing zone temperature of 175°C, die temperature of 170°C, screw speed of 80 rpm, and feed rate of 3 kg / h. After extrusion, the composite was water-cooled and pelletized to obtain pellets with a diameter of 4±0.5 mm. The pellets were then vacuum-dried at 50°C for 12 hours to obtain a modified polylactic acid composite.

[0038] Example 2 A method for preparing highly transparent and highly flexible modified polylactic acid

[0039] A method for preparing highly transparent and highly flexible modified polylactic acid comprises the following steps:

[0040] Step 1: Preparation of PLA-co-PVL copolymer solution

[0041] L-lactide and δ-valerolactone were mixed uniformly at a molar ratio of 5:1 to obtain a mixture. Nitrogen was introduced three times to displace the air. A catalyst and initiator were then added to the mixture and stirred uniformly, with the catalyst accounting for 0.05% of the total weight of the mixture and the initiator for 0.1%. The mixture was heated to 140°C and reacted for 2.5 hours, then to 170°C and reacted for 6 hours. Nitrogen was continuously introduced at a flow rate of 50 mL / min throughout the reaction. After the reaction, the mixture was cooled to room temperature to obtain a PLA-co-PVL copolymer solution. The catalyst was Sn(Oct)2, and the initiator was 1,4-butanediol.

[0042] Step 2: Purification of PLA-co-PVL copolymer

[0043] The PLA-co-PVL copolymer solution was added to anhydrous methanol at a mass ratio of 1:10. The copolymer was stirred at 800 rpm to precipitate. The precipitate was collected by filtration, washed three times with methanol, and dried under vacuum at 60°C for 24 hours to obtain a PLA-co-PVL solid copolymer.

[0044] Step 3: Synthesis of ATEC-HEA complex

[0045] Acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone were stirred until completely dissolved. The mass ratio of acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone was 100:38:0.8:0.4. Nitrogen was introduced to displace the air for 5 minutes, and the mixture was heated in an oil bath to 120°C and allowed to react for 3 hours. After the reaction, the mixture was cooled to room temperature and subjected to rotary evaporation at 60°C, a vacuum of 0.09 MPa, and a time of 8 hours. Following the evaporation, the mixture was dried under reduced pressure at 50°C, 0.095 MPa, and a time of 2 hours to obtain the ATEC-HEA complex.

[0046] Step 4: Prepare modified polylactic acid composite material

[0047] PLA-co-PVL solid copolymer, ATEC-HEA complex, and antioxidant were uniformly mixed to form a composite. The mass ratio of PLA-co-PVL solid copolymer, ATEC-HEA complex, and antioxidant was 88:12:0.2. The composite was then fed into a twin-screw extruder with the following extruder parameters: feed zone temperature 160°C, melt zone temperature 170°C, mixing zone temperature 175°C, die temperature 170°C, screw speed 100 rpm, and feed rate 3 kg / h. After extrusion, the composite was water-cooled and pelletized to obtain pellets with a diameter of 4±0.5 mm. The pellets were then vacuum-dried at 60°C for 12 hours to obtain a modified polylactic acid composite.

[0048] Example 3 A method for preparing highly transparent and highly flexible modified polylactic acid

[0049] A method for preparing highly transparent and highly flexible modified polylactic acid comprises the following steps:

[0050] Step 1: Preparation of PLA-co-PVL copolymer solution

[0051] L-lactide and δ-valerolactone were mixed uniformly at a molar ratio of 5:1 to obtain a mixed solution. Nitrogen was introduced to displace the air four times, and then a catalyst and initiator were added to the mixture and stirred uniformly. The catalyst accounted for 0.1% of the total weight of the mixture, and the initiator accounted for 0.2% of the total weight of the mixture. The mixture was heated to 150°C and reacted for 2 hours, then to 180°C and reacted for 4 hours. Nitrogen was continuously introduced at a flow rate of 60 mL / min throughout the reaction. After the reaction, the mixture was cooled to room temperature to obtain a PLA-co-PVL copolymer solution. The catalyst was Sn(Oct)2, and the initiator was 1,4-butanediol.

[0052] Step 2: Purification of PLA-co-PVL copolymer

[0053] The PLA-co-PVL copolymer solution was added to anhydrous methanol at a mass ratio of 1:10. The copolymer was stirred at 800 rpm to precipitate. The precipitate was collected by filtration, washed three times with methanol, and dried under vacuum at 60°C for 22 hours to obtain a PLA-co-PVL solid copolymer.

[0054] Step 3: Synthesis of ATEC-HEA complex

[0055] Acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone were stirred until completely dissolved. The mass ratio of acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone was 100:40:1:0.5. Nitrogen was introduced to displace the air for 10 minutes, and the mixture was heated in an oil bath to 130°C and allowed to react for 3 hours. After the reaction, the mixture was cooled to room temperature and subjected to rotary evaporation at 70°C, a vacuum of 0.08 MPa, and a time of 7 hours. Following the evaporation, the mixture was dried under reduced pressure at 50°C, 0.090 MPa, and a time of 2 hours to obtain the ATEC-HEA complex.

[0056] Step 4: Prepare modified polylactic acid composite material

[0057] PLA-co-PVL solid copolymer, ATEC-HEA complex, and antioxidant were uniformly mixed to form a composite. The mass ratio of PLA-co-PVL solid copolymer, ATEC-HEA complex, and antioxidant was 90:10:0.2. The composite was then fed into a twin-screw extruder with the following extruder parameters: feed zone temperature 165°C, melt zone temperature 175°C, mixing zone temperature 180°C, die temperature 175°C, screw speed 100 rpm, and feed rate 5 kg / h. After extrusion, the composite was water-cooled and pelletized to obtain pellets with a diameter of 4±0.5 mm. The pellets were then vacuum-dried at 60°C for 11 hours to obtain a modified polylactic acid composite.

[0058] Comparative Example 1

[0059] A method for preparing polylactic acid comprises the following steps:

[0060] Step 1: Preparation of PLA-co-PVL copolymer solution

[0061] L-lactide and δ-valerolactone were mixed uniformly at a molar ratio of 5:1 to obtain a mixture. Nitrogen was introduced three times to displace the air. A catalyst and initiator were then added to the mixture and stirred uniformly, with the catalyst accounting for 0.05% of the total weight of the mixture and the initiator for 0.1%. The mixture was heated to 140°C and reacted for 2.5 hours, then to 170°C and reacted for 6 hours. Nitrogen was continuously introduced at a flow rate of 50 mL / min throughout the reaction. After the reaction, the mixture was cooled to room temperature to obtain a PLA-co-PVL copolymer solution. The catalyst was Sn(Oct)2, and the initiator was 1,4-butanediol.

[0062] Step 2: Purification of PLA-co-PVL copolymer

[0063] The PLA-co-PVL copolymer solution was added to anhydrous methanol at a mass ratio of 1:9. The copolymer was stirred at 800 rpm to precipitate. The precipitate was collected by filtration, washed three times with methanol, and dried under vacuum at 60°C for 24 hours to obtain a PLA-co-PVL solid copolymer.

[0064] Step 3: Prepare modified polylactic acid composite material

[0065] PLA-co-PVL solid copolymer, acetyl triethyl citrate, and an antioxidant were uniformly mixed to form a composite. The mass ratio of PLA-co-PVL solid copolymer, acetyl triethyl citrate, and antioxidant was 88:12:0.2. The composite was then fed into a twin-screw extruder with the following extruder parameters: feed zone temperature 160°C, melt zone temperature 170°C, mixing zone temperature 175°C, die temperature 170°C, screw speed 100 rpm, and feed rate 3 kg / h. After extrusion, the composite was water-cooled and pelletized to obtain pellets with a diameter of 4±0.5 mm. The pellets were then vacuum-dried at 60°C for 12 hours to obtain a modified polylactic acid composite. The antioxidant was Irganox 1010.

[0066] Comparative Example 2

[0067] A method for preparing polylactic acid comprises the following steps:

[0068] Step 1: Preparation of PLA solution

[0069] L-lactide was stirred evenly, and nitrogen was introduced three times to replace the air. The catalyst and initiator were then added to the L-lactide and stirred evenly. The catalyst accounted for 0.05% of the L-lactide by weight, and the initiator accounted for 0.1% of the L-lactide by weight. The temperature was raised to 140°C and the reaction was continued for 2.5 hours. The temperature was then raised to 170°C and the reaction was continued for 6 hours. Nitrogen was continuously introduced at a flow rate of 50 mL / min during the reaction. After the reaction, the mixture was cooled to room temperature to obtain a PLA solution. The catalyst was Sn(Oct)2, and the initiator was 1,4-butanediol.

[0070] Step 2: PLA purification

[0071] The PLA solution was added to anhydrous methanol at a mass ratio of 1:9 for the PLA-co-PVL copolymer solution to anhydrous methanol. The copolymer was stirred at 800 rpm to precipitate. The precipitate was collected by filtration, washed three times with methanol, and dried under vacuum at 60°C for 24 hours to obtain a PLA solid.

[0072] Step 3: Synthesis of ATEC-HEA complex

[0073] Acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone were stirred until completely dissolved. The mass ratio of acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone was 100:38:0.8:0.4. Nitrogen was introduced to displace the air for 5 minutes, and the mixture was heated in an oil bath to 120°C and allowed to react for 3 hours. After the reaction, the mixture was cooled to room temperature and subjected to rotary evaporation at 60°C, a vacuum of 0.09 MPa, and a time of 8 hours. Following the evaporation, the mixture was dried under reduced pressure at 50°C, 0.095 MPa, and a time of 2 hours to obtain the ATEC-HEA complex.

[0074] Step 4: Prepare polylactic acid composite material

[0075] PLA solid, ATEC-HEA composite, and antioxidant were uniformly mixed to form a mixture. The mass ratio of PLA solid, ATEC-HEA composite, and antioxidant was 90:10:0.2. The mixture was then fed into a twin-screw extruder with the following extruder parameters: feed zone temperature 160°C, melt zone temperature 170°C, mixing zone temperature 175°C, die temperature 170°C, screw speed 100 rpm, and feed rate 3 kg / h. After extrusion, the mixture was water-cooled and pelletized to obtain pellets with a diameter of 4±0.5 mm. The pellets were then vacuum-dried at 60°C for 12 hours to obtain a polylactic acid composite material. The antioxidant was Irganox 1010.

[0076] Example 4 Performance Test

[0077] (I) The light transmittance and haze properties of the polylactic acid prepared in Examples 1-3 and Comparative Examples 1-2 were tested according to the test method in GB / T 2410-2008. The specific test results are shown in Table 1.

[0078] Table 1

[0079] The test results in Table 1 show that the polylactic acid prepared in Examples 1-3 has high transmittance, reaching 94.14-94.58%. Compared with the comparative example, the haze is significantly reduced, reaching 3.87-4.46%. The high transmittance and low haze indicate that the modified polylactic acid prepared in this invention has better optical properties and higher light transmission uniformity.

[0080] (II) The polylactic acid prepared in Examples 1-3 and Comparative Examples 1-2 was tested for tensile strength and notched impact strength according to the test methods in GB / T 29284-2012; elongation at break was tested according to the test methods in GB / T 1040.1-2018; and flexural strength and flexural modulus were tested according to the test methods in GB / T 9341-2008. The specific test results are shown in Table 2.

[0081] Table 2

[0082] From the test results in Table 2, it can be seen that the notched impact strength and elongation at break of the polylactic acid prepared in Examples 1-3 are significantly improved, and the notched impact strength reaches 7.8-8.6 kJ / m 2 , the notched impact strength is higher, indicating a stronger ability to resist fracture, and the elongation at break reaches 135-173%. The higher elongation at break directly reflects better flexibility and ductility; the tensile strength and flexural strength of the polylactic acid prepared in Examples 1-3 are significantly lower than those of the polylactic acid prepared in Comparative Example 1, and significantly higher than those of the polylactic acid prepared in Comparative Example 2, with a tensile strength of 43.25-48.95 MPa and a flexural strength of 72.5-81.4 MPa; the flexural modulus of the polylactic acid prepared in Examples 1-3 is significantly reduced, reaching 2.3-2.8 GPa. A lower flexural modulus means a stronger ability to resist elastic bending deformation. In summary, the modified polylactic acid prepared in the present invention has excellent flexibility.

[0083] Obviously, there are many specific implementation methods that can be changed under the concept of the present invention. Here, it should be stated that any changes made under the inventive concept of the present invention will fall within the scope of protection of the present invention.

Claims

1. A method for preparing highly transparent and highly flexible modified polylactic acid, characterized in that: The method includes the steps of preparing a PLA-co-PVL copolymer solution, purifying the PLA-co-PVL copolymer, synthesizing an ATEC-HEA complex, and preparing a modified polylactic acid composite material; Preparation of the PLA-co-PVL copolymer solution: L-lactide and δ-valerolactone are uniformly mixed to obtain a mixed solution, a catalyst and an initiator are added to the mixed solution, and the reaction is performed to obtain a PLA-co-PVL copolymer solution; the catalyst is Sn(Oct)2, and the initiator is 1,4-butanediol; The raw materials used in the synthesis of the ATEC-HEA complex include: acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone; The modified polylactic acid composite material is prepared using raw materials including: PLA-co-PVL solid copolymer, ATEC-HEA compound, and antioxidant.

2. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 1, wherein: The mass ratio of raw materials used in preparing the modified polylactic acid composite material is: the mass ratio of PLA-co-PVL solid copolymer, ATEC-HEA compound, and antioxidant is (85-90): (10-15):0.

2.

3. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 1, wherein: The molar ratio of L-lactide to δ-valerolactone is (4-5):1; the catalyst accounts for 0.05-0.1% of the total mass of L-lactide and δ-valerolactone, and the initiator accounts for 0.1-0.2% of the total mass of L-lactide and δ-valerolactone.

4. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 1, wherein: The mass ratio of raw materials used in synthesizing the ATEC-HEA complex is: the mass ratio of acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone is 100: (38-40): (0.7-1): (0.3-0.5).

5. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 1, wherein: The PLA-co-PVL copolymer solution is prepared by uniformly mixing L-lactide and δ-valerolactone to obtain a mixed solution; introducing nitrogen to replace air 3-4 times, then adding a catalyst and an initiator to the mixed solution and stirring evenly; heating to 130-150° C., reacting for 2-3 hours, then heating to 160-180° C., reacting for 4-8 hours; and cooling to room temperature after the reaction to obtain a PLA-co-PVL copolymer solution.

6. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 5, wherein: In the step of preparing the PLA-co-PVL copolymer solution, nitrogen is continuously introduced during the reaction at a flow rate of 50-60 mL / min.

7. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 1, wherein: The PLA-co-PVL copolymer is purified by adding a PLA-co-PVL copolymer solution into anhydrous methanol, wherein the mass ratio of the PLA-co-PVL copolymer solution to the anhydrous methanol is 1:(8-10); stirring at 500-800 rpm to precipitate the copolymer, collecting the precipitate by filtration, washing the precipitate with methanol 2-3 times, and vacuum drying the precipitate at 50-60° C. for 22-24 hours to obtain a PLA-co-PVL solid copolymer.

8. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 1, wherein: The method for synthesizing the ATEC-HEA complex comprises stirring acetyl triethyl citrate, hydroxyethyl acrylate, p-toluenesulfonic acid, and hydroquinone until completely dissolved, introducing nitrogen to replace the air for 5-10 minutes, heating the mixture in an oil bath to 120-130° C., and reacting the mixture for 3-4 hours. After the reaction, the mixture is cooled to room temperature, and the reaction solution is subjected to rotary evaporation at a temperature of 60-70° C., a vacuum degree of 0.08-0.09 MPa, and a time of 7-8 hours. After the reaction, the mixture is dried under reduced pressure at a temperature of 40-50° C., a pressure of 0.090-0.095 MPa, and a drying time of 2-2.5 hours to obtain the ATEC-HEA complex.

9. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 1, wherein: The modified polylactic acid composite material is prepared by uniformly mixing a PLA-co-PVL solid copolymer, an ATEC-HEA compound, and an antioxidant to obtain a mixture; then adding the mixture to a twin-screw extruder, extruding the mixture through the twin-screw extruder, and then water-cooling and pelletizing to obtain pellets with a diameter of 4±0.5 mm, and then vacuum drying at 50-60°C for 11-12 hours to obtain the modified polylactic acid composite material; the antioxidant is Irganox 1010.

10. The method for preparing a highly transparent and highly flexible modified polylactic acid according to claim 9, wherein: In the step of preparing the modified polylactic acid composite material, the parameters of the twin-screw extruder are set as follows: feed section temperature 160-165°C, melting section temperature 170-175°C, mixing section temperature 175-180°C, die head temperature 170-175°C, screw speed 80-100 rpm, and feeding rate 3-5 kg / h.

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