A polylactic acid composite and a method for preparing the same

Abstract

The application discloses a kind of polylactic acid composite and preparation method thereof, wherein the polylactic acid composite includes the following components according to weight parts: modified polylactic acid 85-97 parts;Modified PBAT 1-6 parts;Ethylene-vinyl acetate 1-6 parts;Acetyl citric acid tri-n-butyl ester 2-5 parts;Lubricant 0.5-4 parts;Nucleating agent 0.1-0.5 parts;Anti-hydrolysis agent 0.5-2 parts, wherein the modified polylactic acid is prepared by glycidyl methacrylate modification of polylactic acid, and the modified PBAT is prepared by polyethylene glycol modification of PBAT.The application aims to provide a kind of polylactic acid composite with high toughness, high transparency, high temperature resistance and high biodegradability.

Description

Technical Field

[0001] This invention relates to the field of biodegradable composite materials technology, and in particular to a polylactic acid composite material and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is currently a novel biomaterial with good biocompatibility and biodegradability, as well as excellent gloss, transparency, and tensile strength. It is widely used in food packaging, medical materials, and 3D printing materials. However, PLA products are brittle (elongation at break ≤10%) and have poor temperature resistance (glass transition temperature only 55℃~60℃) due to its low melt strength, slow crystallization rate, and low heat distortion temperature (HDT), thus limiting its application range. Therefore, PLA currently requires pre-modification treatment before use, primarily focusing on improving brittleness, toughness, and heat resistance.

[0003] Among them, the existing invention patent with publication number CN114854186A discloses a heat-resistant modified polylactic acid fully degradable material for tableware. This material modifies polylactic acid with PBAT, natural plant fibers, and modified gelatinized starch to improve its heat resistance, and also adds organic bentonite. While this improves the material's heat resistance, the resulting material has low transparency, failing to meet the requirement for transparent tableware. Another existing invention patent with publication number CN112080115BA discloses a high-toughness polylactic acid composite material for environmentally friendly tableware and its preparation method. This method involves melt-blending adipic acid-modified plant fibers and polyethylene glycol with polylactic acid. Although this significantly improves the material's heat resistance and toughness, the hygroscopic nature of plant fibers makes the resulting composite material unsuitable for use in wet environments and also limits its reprocessing and reuse. Therefore, there is an urgent need for a high-toughness, high-transparency, and high-temperature-resistant modified polylactic acid composite material. Summary of the Invention

[0004] The main objective of this invention is to provide a polylactic acid composite material and its preparation method, aiming to solve the technical problem that existing polylactic acid composite materials cannot achieve high toughness, high transparency, and high temperature resistance.

[0005] To achieve the above objectives, the present invention provides a polylactic acid composite material, comprising the following components by weight:

[0006] 85-97 parts of modified polylactic acid;

[0007] 1-6 parts of modified PBAT;

[0008] 1 to 6 parts of ethylene-vinyl acetate;

[0009] 2-5 parts of tributyl acetyl citrate;

[0010] Lubricant 0.5 to 4 parts;

[0011] Nucleating agent 0.1–0.5 parts;

[0012] The anti-hydrolysis agent is 0.5 to 1 part, wherein the modified polylactic acid is obtained by modifying polylactic acid with glycidyl methacrylate, and the modified PBAT is obtained by modifying PBAT with polyethylene glycol.

[0013] Optionally, the product may also include the following components, in parts by weight:

[0014] 85 parts of modified polylactic acid;

[0015] 4 portions of modified PBAT;

[0016] 4 parts of ethylene-vinyl acetate;

[0017] 3 parts of tributyl acetyl citrate;

[0018] 2 parts lubricant;

[0019] Nucleating agent 0.5 parts;

[0020] 1.5 parts of anti-hydrolysis agent.

[0021] Optionally, the molecular weight of the modified polylactic acid material is in the range of 150,000 to 200,000.

[0022] Optionally, the lubricant is one or two of polyethylene wax, N,N-ethylene bis-stearamide, glyceryl trihydroxystearate, and n-butyl stearate; the nucleating agent is TMC-300, which belongs to the acylhydrazine nucleating agent class; and the anti-hydrolysis agent is 2,2',6,6'-tetraisopropyldiphenylcarbodiimide.

[0023] Optionally, the deformation temperature of the composite material is above 90°C.

[0024] Optionally, the polyethylene glycol has an average molecular weight of 3600 to 8500.

[0025] Furthermore, to achieve the above objectives, the present invention also provides a method for preparing any of the polylactic acid composite materials described above, the method comprising the following steps:

[0026] Step 10: Add a certain mass ratio of modified polylactic acid, modified PBAT and ethylene-vinyl acetate to a high-speed mixer and stir until homogeneous to obtain mixture A;

[0027] Step 20: Add a certain amount of tributyl acetyl citrate to mixture A obtained in step 10 and stir until homogeneous to obtain mixture B;

[0028] Step 30: Add a certain amount of nucleating agent, anti-hydrolysis agent and lubricant to the mixture B obtained in step 20, and stir evenly to obtain mixture C;

[0029] Step 40: Add the mixture C from step 30 to a twin-screw extruder, melt and granulate to obtain the target composite material. The extrusion temperature of the twin-screw extruder is controlled at 130-190°C, the screw speed is 70-110 r / min, and the screw length-to-diameter ratio is (25-35):1.

[0030] Optionally, the method for preparing the modified polylactic acid includes the following steps:

[0031] A certain amount of glycidyl methacrylate and benzoyl peroxide are dissolved in acetone solution;

[0032] Then it is mixed with polylactic acid, dried, melted and mixed evenly through the mixing head of a torque rheometer, cooled and pelletized. The melt index of the polylactic acid resin is 3-5 g / 10 min. The amount of glycidyl methacrylate added is 1%-4% of polylactic acid, the amount of benzoyl peroxide added is 1%-3% of polylactic acid, and the melting temperature is 185℃.

[0033] Optionally, the preparation method of the modified PBAT includes the following steps:

[0034] Vacuum-dried PBAT and polyethylene glycol (PEG) are placed in dichloroethane, heated and stirred until completely dissolved, wherein the amount of PEG added is 4%-8% of PBAT;

[0035] The above solution was placed in a three-necked flask, and silane coupling agent and catalyst stannous octoate were added successively and stirred. A reflux condenser was installed on the three-necked flask, and the reaction was heated by an oil bath at 70-80°C.

[0036] After reacting for 10–20 h, the reaction solution was dissolved in chloroform and precipitated with methanol. After standing, the precipitate was filtered and then dried in a vacuum oven at 90 °C to obtain the PBAT / PEG block copolymer.

[0037] Optionally, the amount of glycidyl methacrylate added is 1% of polylactic acid, the amount of benzoyl peroxide added is 1.5% of polylactic acid; the amount of polyethylene glycol added is 5% of PBAT, the amount of coupling agent added is 0.1-0.5% of PBAT, and the amount of catalyst added is 0.1-0.3% of PBAT.

[0038] Beneficial effects:

[0039] 1. The modified polylactic acid of this invention improves the toughness of the material without affecting its transparency. The principle is that the modified polylactic acid is obtained by graft polymerization of glycidyl methacrylate and polylactic acid under the action of benzoyl peroxide initiator. The epoxy groups on the glycidyl methacrylate molecular chain undergo esterification reaction with the carboxyl groups on the polylactic acid molecular chain, and the two molecular chains are linked together to form a large molecular chain, thereby increasing the molecular weight of polylactic acid and enhancing the mobility of molecular chain segments, so as to improve the toughness of the material without affecting its transparency.

[0040] 2. The modified PBAT of this invention is obtained by polyethylene glycol block copolymerization to obtain powdered block copolymer, which greatly improves the interfacial compatibility between modified PBAT and polylactic acid, thereby improving the toughness and impact strength of the composite material.

[0041] 3. The addition of tributyl acetyl citrate to the modified polylactic acid, modified PBAT, and ethylene-vinyl acetate of the present invention can increase the compatibility of the three components and increase the toughness without affecting the transparency of polylactic acid.

[0042] 4. The heat distortion temperature of the polylactic acid composite material prepared by this invention is above 90℃;

[0043] 5. As the content of PBAT and vinyl acetate decreases, the transparency gradually increases, and the light transmittance can reach 95%.

[0044] 6. The amide nucleating agent used in this invention can effectively reduce the crystal size of PLA, increase the crystallization rate, thereby increasing the crystallization temperature and crystallinity, and improving its heat resistance.

[0045] 7. The polylactic acid composite material of the present invention has better toughness, higher impact strength, stronger heat resistance, and a heat distortion temperature of over 90°C than pure polylactic acid. It also has high transparency, reaching over 86%, which is of great guiding significance for the development of transparent, heat-resistant, and biodegradable products. Attached Figure Description

[0046] Figure 1 This is a schematic flowchart of an embodiment of the preparation method of polylactic acid composite material of the present invention.

[0047] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0048] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0049] Reference Figure 1This invention provides a schematic flowchart of an embodiment of a method for preparing polylactic acid composite materials, the method comprising the following steps:

[0050] Step 1: Modified polylactic acid, modified PBAT, and ethylene-vinyl acetate in a certain mass ratio are added to a high-speed mixer and stirred until homogeneous to obtain mixture A. The modified polylactic acid is obtained by modifying polylactic acid with glycidyl methacrylate, and the modified PBAT is obtained by modifying PBAT with polyethylene glycol. The mass ratio of modified polylactic acid, modified PBAT, and ethylene-vinyl acetate is: 85-97 parts modified polylactic acid; 1-6 parts modified PBAT; 1-6 parts ethylene-vinyl acetate.

[0051] Step 20: Add a certain amount of tributyl acetyl citrate to mixture A obtained in step 10 and stir for 2-3 minutes until the mixture is homogeneous to obtain mixture B; wherein the mass ratio of the added component is 2-5 parts of tributyl acetyl citrate.

[0052] Step 30: Add a certain amount of nucleating agent, anti-hydrolysis agent and lubricant to the mixture B obtained in step 20, and stir for 15 to 30 minutes until the mixture is uniform to obtain mixture C; wherein the mass ratio of the added components is 0.1 to 0.5 parts of nucleating agent, 0.5 to 2 parts of anti-hydrolysis agent and 0.5 to 4 parts of lubricant.

[0053] Step 40: Add the mixture C from step 30 into a twin-screw extruder. After melt granulation, a target composite material with a light transmittance of over 86% and a deformation temperature of over 90℃ is obtained. At the same time, based on the biodegradability of polylactic acid, it still has high degradation performance after modification. Therefore, the composite material is non-toxic, completely biodegradable, and can be widely used in environmentally friendly tableware, food packaging and other fields.

[0054] Furthermore, during the granulation process, the extrusion temperature of the twin-screw extruder is controlled to be 130–190°C, the screw speed to be 70–110 r / min, and the screw length-to-diameter ratio to be (25–35):1.

[0055] Furthermore, the preparation method of the modified polylactic acid includes the following steps:

[0056] A certain amount of glycidyl methacrylate and benzoyl peroxide are dissolved in acetone solution; then mixed with dried polylactic acid, dried further, and melt-mixed evenly through a torque rheometer mixing head, cooled and pelletized. The amount of glycidyl methacrylate added is 1% to 4% of polylactic acid, the amount of benzoyl peroxide added is 1% to 3% of polylactic acid, and the melting temperature is 185°C.

[0057] Specifically, the dried polylactic acid (PLA) refers to the PLA raw material being vacuum-dried at 40°C for 24–36 hours, and the melt index of the PLA resin is 3–5 g / 10 min. Simultaneously, the above-mentioned PLA modification is obtained by graft polymerization of glycidyl methacrylate and PLA under the action of the initiator benzoyl peroxide. The principle is that the epoxy groups on the glycidyl methacrylate molecular chain undergo an esterification reaction with the carboxyl groups on the PLA molecular chain, thereby increasing the molecular weight of PLA, enhancing the mobility of molecular chain segments, improving the toughness of the material, and without affecting the transparency of the composite material. The final modified PLA material has a molecular weight range of 150,000–200,000.

[0058] Furthermore, the preparation method of the modified PBAT includes the following steps:

[0059] Vacuum-dried PBAT and polyethylene glycol (PEG) were placed in dichloroethane, heated, and stirred until completely dissolved. The amount of PEG added was 4%–8% of the PBAT. The solution was then placed in a three-necked flask, and a silane coupling agent and a catalyst, stannous octoate (Sc(Oct2)), were added and stirred. A reflux condenser was installed on the three-necked flask, and nitrogen gas was introduced for protection. The reaction was carried out by heating in an oil bath at 70–80°C. After reacting for 10–20 hours, the reaction solution was poured into trichloromethane to dissolve, and precipitation was carried out with methanol. After standing, the mixture was filtered, and the precipitate was then vacuum-dried at 90°C to obtain the PBAT / PEG block copolymer. The amount of the coupling agent added was 0.1–0.5% of the PBAT, and the amount of the catalyst added was 0.1–0.3% of the PBAT.

[0060] Specifically, the PBAT is a copolymer of butylene adipate and butylene terephthalate, and the average molecular weight of the polyethylene glycol is 3600-8500. Preferably, the polyethylene glycol is one or two of PEG-4000, PEG-6000, and PEG-8000. If the average molecular weight of the polyethylene glycol is less than 3600, although the plasticizing effect of the resulting composite material is significant, the crystallization temperature and crystallinity of the composite material decrease, thus reducing the heat resistance of the composite material. If the average molecular weight of the polyethylene glycol is larger than 8500, although the crystallization temperature and crystallinity of the composite material increase, the plasticizing effect decreases, i.e., the tensile strength and heat resistance increase, but the toughness is poor. Meanwhile, the addition of coupling agents and catalysts can accelerate the reaction rate and increase the degree of reaction. The mechanism lies in the modification of PBAT through polyethylene glycol block copolymerization to obtain a powdered block copolymer, which greatly improves the interfacial compatibility between modified PBAT and polylactic acid, thereby improving the toughness and impact strength of the composite material.

[0061] Furthermore, the lubricant is one of polyethylene wax, N,N-ethylene bis-stearamide, glyceryl trihydroxystearate, and n-butyl stearate.

[0062] Furthermore, the nucleating agent is an amide nucleating agent or an acylhydrazine nucleating agent; preferably, one of amide nucleating agent-328 and acylhydrazine nucleating agent-300 is used. The acylhydrazine nucleating agent used in this embodiment can provide more nucleation sites, significantly improve the crystallization rate, effectively reduce the crystal size of PLA, thereby increasing the crystallization temperature and crystallinity, and improving its heat resistance.

[0063] Furthermore, the anti-hydrolysis agent is 2,2',6,6'-tetraisopropyldiphenylcarbodiimide.

[0064] To further understand the purpose, technical means, and technical effects of the present invention, the following description is provided in conjunction with specific embodiments and comparative examples:

[0065] Example 1

[0066] A method for preparing a polylactic acid composite material includes the following raw materials in parts by weight: 85 parts modified polylactic acid, 4 parts modified PBAT, 4 parts ethylene-vinyl acetate, 3 parts tri-n-butyl acetyl citrate, 2 parts lubricant, 0.5 parts nucleating agent, and 1.5 parts anti-hydrolysis agent.

[0067] Specifically, the preparation steps of polylactic acid composite material include: adding the weighed modified polylactic acid, modified PBAT and ethylene-vinyl acetate into a high-speed mixer and stirring evenly, then adding tributyl acetyl citrate and stirring for 2-3 minutes, finally adding nucleating agent, anti-hydrolysis agent and lubricant and stirring for 15-30 minutes, then adding the evenly mixed material C1 into a twin-screw extruder for melt blending, extrusion and granulation to obtain polylactic acid composite material.

[0068] The preparation method of modified polylactic acid includes the following specific steps: 1 part glycidyl methacrylate and 1.5 parts benzoyl peroxide are dissolved in acetone solution, then mixed with 100 parts polylactic acid that has been vacuum dried at 40℃ for 24 hours, dried, melt-mixed uniformly through a torque rheometer mixer head, cooled, and then pelletized. The torque rheometer mixer head temperature is 185℃, the rotation speed is 43 r / min, and the running time is 10 min.

[0069] The preparation method of modified PBAT includes: placing 100 parts of vacuum-dried PBAT and 5 parts of polyethylene glycol (PEG) in dichloroethane, heating and stirring until completely dissolved, then placing the solution in a three-necked flask, adding 0.5 parts of silane coupling agent and 0.3 parts of catalyst stannous octoate, stirring, and installing a reflux condenser on the three-necked flask, and reacting by heating in an oil bath at 70-80°C. After reacting for 10 hours, the reaction solution is poured into chloroform to dissolve, and precipitated with methanol. After standing, the precipitate is filtered, and then vacuum-dried at 90°C to obtain the PBAT / PEG block copolymer.

[0070] Example 2

[0071] A method for preparing a polylactic acid (PLA) composite material includes the following raw materials in parts by weight: 92 parts modified PLA, 2 parts modified PBAT, 3 parts ethylene-vinyl acetate, 1 part tri-n-butyl acetyl citrate, 1 part lubricant, 0.5 parts nucleating agent, and 0.5 parts anti-hydrolysis agent. The preparation steps of the PLA composite material are the same as in Example 1, specifically referring to Example 1. The preparation method of the modified PLA is also the same as in Example 1, specifically referring to Example 1, except that 1 part glycidyl methacrylate is replaced with 2 parts glycidyl methacrylate. The preparation method of the modified PBAT is also the same as in Example 1, specifically referring to Example 1.

[0072] Example 3

[0073] A method for preparing a polylactic acid (PLA) composite material includes the following raw materials in parts by weight: 92 parts modified PLA, 2 parts modified PBAT, 3 parts ethylene-vinyl acetate, 1 part tri-n-butyl acetyl citrate, 1 part lubricant, 0.5 parts nucleating agent, and 0.5 parts anti-hydrolysis agent. The preparation steps of the PLA composite material are the same as in Example 1, specifically referring to Example 1. The difference is that the lubricant is replaced with polyethylene wax instead of N,N-ethylene bis-stearamide (i.e., lubricant). The preparation method of the modified PLA is the same as in Example 1, specifically referring to Example 1, except that 1 part glycidyl methacrylate is replaced with 4 parts glycidyl methacrylate; and the preparation method of the modified PBAT is the same as in Example 1, specifically referring to Example 1.

[0074] Example 4

[0075] A method for preparing a polylactic acid (PLA) composite material includes the following raw materials in parts by weight: 96 parts modified PLA, 1 part modified PBAT, 1 part ethylene-vinyl acetate, 0.5 parts tri-n-butyl acetylacetic acid, 0.5 parts lubricant, 0.5 parts nucleating agent, and 0.5 parts anti-hydrolysis agent. The preparation steps of the PLA composite material are the same as in Example 1, specifically referring to Example 1. The preparation method of the modified PLA is the same as in Example 1, specifically referring to Example 1, and the preparation method of the modified PBAT is the same as in Example 3, specifically referring to Example 3.

[0076] Comparative Example 1

[0077] The raw materials and preparation method of the polylactic acid composite material are the same as those in Example 2, specifically referring to Example 2. The difference is that formyl peroxide was not added to the modified polylactic acid in this comparative example.

[0078] Comparative Example 2

[0079] The raw materials and preparation method of the polylactic acid composite material are the same as those in Example 2, specifically referring to Example 2. The difference is that the PBAT in this comparative example was not modified with polyethylene glycol.

[0080] Comparative Example 3

[0081] The raw materials and preparation method of the polylactic acid composite material are the same as those in Example 2, specifically referring to Example 2. The difference is that ethylene-vinyl acetate was not added in this comparative example.

[0082] Comparative Example 4

[0083] The raw materials and preparation method of the polylactic acid composite material are the same as those in Example 2, specifically referring to Example 2. The difference is that no nucleating agent was added in this comparative example.

[0084] The polylactic acid composite materials prepared according to Examples 1-4 and Comparative Examples 1-4 are shown in Table 1. Mechanical properties, heat distortion temperature, and light transmittance were tested, and the results are shown in Table 2.

[0085] Table 1. Raw material composition of composite materials in the examples and comparative examples.

[0086]

[0087]

[0088] Table 2. Test results of mechanical properties, heat distortion temperature, and light transmittance of polylactic acid composite materials.

[0089]

[0090] 1. According to the test results of the mechanical properties of polylactic acid composite materials in Table 2 above, the tensile strength of Examples 1 to 4 is 48.2–68.6 MPa and the impact strength is 7.7–9.3 kJ / m. 2 The elongation at break ranges from 8.3% to 23%, and the mechanical property parameters in Examples 1-4 are all greater than those in Comparative Example 1. Therefore, it can be concluded that the polylactic acid modified with glycidyl methacrylate peroxide in this invention improves the strength and toughness of the polylactic acid composite material. Furthermore, a comparison between Comparative Example 2 and Example 2 shows that PBAT modified with polyethylene glycol improves the strength, toughness, and high-temperature resistance of the polylactic acid composite material. And a comparison between Comparative Example 3 and Example 2 shows that the addition of ethylene-vinyl acetate to the polylactic acid composite material can correspondingly improve its strength and toughness.

[0091] 2. The composite materials obtained in Examples 1-4 and Comparative Examples 1-4 were injection molded into plates with a thickness of 0.15±0.05cm, and their heat distortion temperature was tested. As can be seen from the heat distortion temperature in Table 2 above, the heat distortion temperature of the polylactic acid composite materials in Examples 1-4 is above 95℃, while the heat distortion temperature of the comparative examples 1-4 is lower than that in the embodiments of the present invention. It can be seen that the polylactic acid composite material prepared by the present invention has excellent high temperature resistance.

[0092] 3. The fully degradable composite materials prepared in Examples 1-4 and Comparative Examples 1-4 were extruded and stretched into sheets to obtain sheets with a thickness of 0.3 mm ± 0.02 mm. The transmittance of these sheets was tested. The transmittance of the polylactic acid composite materials in Examples 1-4 was all above 85%, and the transparency gradually increased as the content of PBAT and ethylene-vinyl acetate decreased.

[0093] 4. Comparing Example 2 with Comparative Examples 1-4, it was found that: Comparative Example 1 did not add benzoyl peroxide, the initiator required for polylactic acid modification, resulting in a lower elongation at break of the polylactic acid composite material; Comparative Example 2 did not add polyethylene glycol to PBAT for modification, resulting in a lower heat distortion temperature and elongation at break of the polylactic acid composite material compared to Example 2; Comparative Example 3 did not add ethylene-vinyl acetate, which improved the transparency of the composite material, but its elongation at break, impact strength, and tensile strength were all lower than the corresponding values ​​in Example 2; and Comparative Example 4 did not add a nucleating agent, resulting in a lower heat distortion temperature of the polylactic acid composite material.

[0094] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0095] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0096] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A polylactic acid composite material, characterized in that, Based on parts by weight, it includes the following components: 85-97 parts of modified polylactic acid; 1-6 parts of modified PBAT; 1-6 parts of ethylene-vinyl acetate; The mixture comprises 2-5 parts of tributyl acetylacetic acid; 0.5-4 parts of lubricant; 0.1-0.5 parts of nucleating agent; and 0.5-2 parts of anti-hydrolysis agent. The nucleating agent is an amide-based or hydrazide-based nucleating agent. The modified polylactic acid is obtained by grafting polylactic acid with glycidyl methacrylate. The modified PBAT is obtained by modifying PBAT with polyethylene glycol. The preparation method of the polylactic acid composite material includes the following steps: Step 10: Add the modified polylactic acid, modified PBAT and ethylene-vinyl acetate in a preset mass ratio to a high-speed mixer and stir until homogeneous to obtain mixture A; Step 20: Add a predetermined amount of tributyl acetyl citrate to mixture A obtained in step 10 and stir until homogeneous to obtain mixture B; Step 30: Add nucleating agent, anti-hydrolysis agent and lubricant to mixture B obtained in step 20, and stir evenly to obtain mixture C; Step 40: Add the mixture C from step 30 into a twin-screw extruder, melt and granulate to obtain the target composite material. The extrusion temperature of the twin-screw extruder is controlled at 130-190°C, the screw speed is 70-110 r / min, and the screw length-to-diameter ratio is (25-35):

1. The preparation method of the modified PBAT includes the following steps: Vacuum-dried PBAT and polyethylene glycol are placed in dichloroethane, heated and stirred until completely dissolved, wherein the amount of polyethylene glycol added is 4-8% of PBAT; The solution was then placed in a three-necked flask, and silane coupling agent and catalyst stannous octoate were added successively and stirred. A reflux condenser was installed on the three-necked flask, and the reaction was heated in an oil bath at 70-80°C. The amount of the coupling agent added was 0.1-0.5% of PBAT, and the amount of the catalyst added was 0.1-0.3% of PBAT. After reacting for 10–20 h, the reaction solution was dissolved in chloroform and precipitated with methanol. After standing, the precipitate was filtered and then dried under vacuum at 90 °C to obtain the PBAT / PEG block copolymer.

2. The polylactic acid composite material according to claim 1, characterized in that, Based on parts by weight, it includes the following components: 85 parts modified polylactic acid; 4 parts modified PBAT; 4 parts ethylene-vinyl acetate; 3 parts of tributyl acetylic acid citrate; 2 parts of lubricant; 0.5 parts of nucleating agent; 1.5 parts of anti-hydrolysis agent.

3. The polylactic acid composite material according to claim 1 or 2, characterized in that, The molecular weight range of the modified polylactic acid material is 150,000 to 200,000.

4. The polylactic acid composite material according to claim 3, characterized in that, The lubricant is one or two of polyethylene wax, N,N-ethylene bis-stearamide, glyceryl trihydroxystearate, and n-butyl stearate; the anti-hydrolysis agent is 2,2',6,6'-tetraisopropyldiphenylcarbodiimide.

5. The polylactic acid composite material according to claim 3, characterized in that, The heat distortion temperature of the composite material is above 90℃.

6. The polylactic acid composite material according to claim 4 or 5, characterized in that, The average molecular weight of the polyethylene glycol is 3600 to 8500.

7. The polylactic acid composite material according to claim 1, characterized in that, The preparation method of the modified polylactic acid includes the following steps: A certain amount of glycidyl methacrylate and benzoyl peroxide were dissolved in an acetone solution; Then it is mixed with polylactic acid, dried, melted and mixed evenly through the mixing head of a torque rheometer, cooled and granulated. The melt index of the polylactic acid is 3-5 g / 10 min. The amount of glycidyl methacrylate added is 1-4% of the polylactic acid, the amount of benzoyl peroxide added is 1%-3% of the polylactic acid, and the melting temperature is 185℃.

8. The polylactic acid composite material according to claim 7, characterized in that, The amount of glycidyl methacrylate added is 1% of polylactic acid, the amount of benzoyl peroxide added is 1.5% of polylactic acid, and the amount of polyethylene glycol added is 5% of PBAT.

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