High-strength and high-toughness polylactic acid composite material and preparation method thereof

Abstract

The invention relates to a high-strength and high-toughness polylactic acid composite material and a preparation method thereof, and belongs to the technical field of biodegradable high polymer materials. The formula of the polylactic acid composite material comprises the following components in parts by weight: 70-80 parts of polylactic acid, 5-10 parts of modified cellulose nanocrystals, 3-5 parts of modified montmorillonite, 1-2 parts of a plasticizer and 0.5-1.5 parts of an antioxidant. A preparation method of the modified cellulose nanocrystals comprises the following steps: adding cellulose nanocrystals into deionized water, and carrying out ultrasonic treatment to obtain a dispersion liquid A; and sequentially adding 0.5-1 M tannic acid solution at the temperature of 60 DEG C into the dispersion liquid A, cooling to room temperature, dropwise adding 3 M octadecylamine-ethanol solution, washing with ethanol and deionized water, and carrying out step-by-step freeze-drying treatment to obtain the modified cellulose nanocrystal, the polylactic acid composite material prepared by the preparation method has high strength, high toughness and good high temperature resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of biodegradable polymer materials and relates to a high-strength and high-toughness polylactic acid composite material and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA), a fully biodegradable thermoplastic polyester made from renewable resources such as starch and cellulose, is widely considered an ideal alternative to petroleum-based plastics due to its raw material renewability, biodegradability, and good biocompatibility. However, PLA's inherent defects significantly limit its scope of application. For example, its brittleness is significantly lower than that of general-purpose plastics such as polypropylene, making it difficult to meet the toughness requirements of packaging materials, automotive interiors, etc.; its heat resistance is poor, and it is prone to deformation in hot water or high-temperature environments, which limits its application in areas such as tableware and electronic and electrical components; PLA has low melt strength and is prone to melt fracture during extrusion and injection molding, and is prone to hydrolytic degradation at high temperatures. Although existing modification methods such as blending elastomers or inorganic fillers can partially improve performance, they suffer from problems such as poor compatibility, limited toughening effect, or sacrificed strength.

[0003] Therefore, there is an urgent need to develop a polylactic acid composite material with both high strength and high toughness. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-strength and high-toughness polylactic acid composite material and a preparation method thereof, which has the characteristics of high strength and high toughness.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A high-strength and high-toughness polylactic acid composite material, wherein the polylactic acid composite material has the following formula: in parts by weight, 70-80 parts of polylactic acid, 5-10 parts of modified cellulose nanocrystals, 3-5 parts of modified montmorillonite, 1-2 parts of plasticizer, and 0.5-1.5 parts of antioxidant. The preparation method of modified cellulose nanocrystals is as follows: S1-1: 1 to 3 parts by weight of cellulose nanocrystals are added to 100 parts by weight of deionized water, and ultrasonically treated for 30 to 60 minutes to obtain dispersion A; S1-2: 0.5 to 1 parts by weight of a 0.5 to 1 M tannic acid solution at 60°C were added to the dispersion A in sequence, the pH was adjusted to 8.5 with a 0.1 M NaHCO3 solution, and after cooling to room temperature, 1 to 2 parts by weight of a 3 M octadecylamine-ethanol solution was added dropwise. The mixture was stirred at room temperature for 2 to 3 hours at a stirring speed of 600 to 700 rpm, washed with ethanol and deionized water, and freeze-dried in steps to obtain the modified cellulose nanocrystals.

[0006] As a preferred technical solution of the present invention, the ultrasonic power in S1-1 is 500-600 W.

[0007] As a preferred technical solution of the present invention, the stepwise freeze-drying treatment in S1-2 is pre-freezing at -50°C for 6 to 8 hours, and then freeze-drying at -80°C for 24 hours.

[0008] As a preferred technical solution of the present invention, the preparation method of the modified montmorillonite is as follows: S4-1: Disperse sodium montmorillonite in water to a solid-liquid mass ratio of 1:(20-30), add dodecyl bis(hydroxyethyl)methylammonium chloride, stir at 60-70°C for 1-2 h, wash with deionized water, and freeze-dry at -50°C for 24 h to obtain powder B; S4-2: Powder B was added to a 0.1 M lanthanum nitrate solution so that the solid-liquid mass ratio was 1:50, ultrasonically treated for 4 to 6 hours, and then transferred to a muffle furnace for calcination for 1 to 2 hours to obtain the modified montmorillonite.

[0009] As a preferred technical solution of the present invention, the addition amount of dodecyl bis(hydroxyethyl)methylammonium chloride in S4-1 is 10-20% of the mass of sodium montmorillonite.

[0010] As a preferred technical solution of the present invention, the calcination temperature in S4-2 is 350-400°C.

[0011] As a preferred technical solution of the present invention, the plasticizer is one or more of tributyl citrate, epoxy soybean oil and dioctyl terephthalate.

[0012] As a preferred technical solution of the present invention, the antioxidant is one or more of antioxidant 1010, antioxidant 1076 and antioxidant 168.

[0013] A method for preparing a high-strength and high-toughness polylactic acid composite material, the specific steps of the preparation method are as follows: S9-1: Add polylactic acid, modified cellulose nanocrystals, modified montmorillonite, plasticizer, and antioxidant into a high-speed mixer according to the formula ratio, and stir at 500-700 rpm for 10-30 min at room temperature to obtain a premix; S9-2: melt blending is performed using a twin-screw extruder at a rotation speed of 150 to 250 rpm and a residence time of 5 to 7 minutes. The extruded strip is cooled in a water tank and then pelletized to obtain the high-strength and high-toughness polylactic acid composite material.

[0014] As a preferred technical solution of the present invention, the melt blending temperatures in S9-2 are set to 170-175°C, 175-178°C and 180-185°C from the feeding section to the die head, respectively.

[0015] Tannic acid, a polyphenolic compound containing multiple catechol groups, can adsorb onto the surface of cellulose nanocrystals through non-covalent interactions such as hydrogen bonding and π-π stacking, forming a modified layer. Its hydroxyl groups can form strong hydrogen bonds with the hydroxyl groups of cellulose nanocrystals, enhancing interfacial adhesion. Octadecylamine contains long-chain alkyl and amino groups, which can undergo Michael addition reactions with the phenolic hydroxyl groups of tannic acid to form covalent bonds. The long-chain alkyl groups impart hydrophobicity to the cellulose nanocrystal surface and generate van der Waals interactions with the non-polar groups of polylactic acid, significantly improving compatibility.

[0016] The nanometer size and high aspect ratio of cellulose nanocrystals effectively transmit stress, inhibit crack propagation in the polylactic acid matrix, and significantly enhance tensile strength. The flexible chain segments of octadecylamine form a buffer layer on the surface of the cellulose nanocrystals to absorb impact energy, effectively improving elongation at break. Furthermore, the nanoscale effect of cellulose nanocrystals can retard the thermal degradation of PLA. The hydrophobicity of modified cellulose nanocrystals reduces their effect on the viscosity of the PLA melt, thereby reducing the melt flow rate. Tannic acid and octadecylamine are both bio-based compounds and their derivatives, conforming to the principles of green chemistry. Stepwise freeze-drying maintains the nanostructure of the cellulose nanocrystals, preventing agglomeration, and eliminates the need for high-temperature treatment, resulting in low energy consumption.

[0017] In the preparation of modified montmorillonite, dodecylbis(hydroxyethyl)methylammonium chloride is inserted into the interlayers of the montmorillonite through an ion exchange reaction, expanding the interlayer spacing. This expanded interlayer spacing allows for the insertion of PLA molecular chains, significantly improving interfacial bonding. Lanthanum nitrate solution is ultrasonically treated to penetrate the interlayers of the montmorillonite or adsorb onto the surface. After calcination, it decomposes into lanthanum oxide, forming a montmorillonite composite structure. Lanthanum oxide acts as a Lewis acid catalyst, promoting the stereocomplexation of poly(D-lactic acid) and poly(L-lactic acid) during the PLA melt blending process, significantly increasing the heat deformation temperature. Furthermore, lanthanum oxide can capture free radicals generated by the thermal degradation of PLA, further enhancing the thermal stability of the composite.

[0018] In addition, the lamellar structure of montmorillonite and the needle-like structure of cellulose nanocrystals form an interlocking network, inhibiting crack propagation and further optimizing mechanical properties.

[0019] Beneficial effects of the present invention: By synergistically modifying cellulose nanocrystals with tannic acid and octadecylamine, their compatibility and dispersibility with PLA are significantly improved, and the composite material has high strength, high toughness and good heat resistance while maintaining biodegradability. The preparation process is environmentally friendly and cost-controllable.

[0020] The modified montmorillonite expands the interlayer spacing through quaternary ammonium salt intercalation, promoting the intercalation bonding of PLA molecular chains; lanthanum nitrate is ultrasonically infiltrated and calcined to generate lanthanum oxide, which improves the high temperature resistance of the composite material; in addition, the lamellar structure of the modified montmorillonite and the needle-like structure of the cellulose nanocrystal form an interlocking network, synergistically inhibiting crack propagation and achieving a simultaneous improvement in strength and toughness. DETAILED DESCRIPTION

[0021] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0022] In the Examples and Comparative Examples of the present invention: Polylactic acid: purchased from Beijing Thompson Biotechnology Co., Ltd. Dodecyl bis(hydroxyethyl)methylammonium chloride: purchased from Shanghai Boyun New Materials Co., Ltd., CAS No. 22340-01-8; Cellulose nanocrystals were purchased from Jiangsu Xingkeyuan Information Technology Co., Ltd. Sodium montmorillonite: purchased from Lingyuan Beibiansen Biotechnology Co., Ltd., with a specific surface area of ​​240m 2 / g; Tannic acid: purchased from Zhangjiajie Jiurui Biotechnology Co., Ltd., with a purity of 98%; Octadecylamine: purchased from Shandong Longhui Chemical Co., Ltd. Lanthanum nitrate: purchased from Nanjing Kangmanlin Chemical Industry Co., Ltd. Tributyl citrate: purchased from Shanghai MacLean Biochemical Technology Co., Ltd. Epoxidized soybean oil: purchased from Shanghai Rongli Chemical Technology Co., Ltd. Dioctyl terephthalate: purchased from Shanghai MacLean Biochemical Technology Co., Ltd. Antioxidant 1010: purchased from Guangzhou Dayin New Materials Co., Ltd. Antioxidant 1076: purchased from Qingdao Zhenguang Functional Materials Technology Co., Ltd. Antioxidant 168 was purchased from Changzhou Qingmu Biotechnology Co., Ltd.

[0023] Example 1

[0024] A high-strength and high-toughness polylactic acid composite material, wherein the polylactic acid composite material has the following formula: in parts by weight, 75 parts of polylactic acid, 8 parts of modified cellulose nanocrystals, 4 parts of modified montmorillonite, 1.5 parts of tributyl citrate, 0.5 parts of antioxidant 1010, and 0.5 parts of antioxidant 168. The preparation method of modified cellulose nanocrystals is as follows: S1-1: 2 parts by weight of cellulose nanocrystals were added to 100 parts by weight of deionized water, and ultrasonicated for 45 min at an ultrasonic power of 550 W to obtain dispersion A; S1-2: 0.8 parts by weight of a 0.5 M tannic acid solution at 60°C was added to dispersion A in sequence, the pH was adjusted to 8.5 using a 0.1 M NaHCO3 solution, and after cooling to room temperature, 1.5 parts by weight of a 3 M octadecylamine-ethanol solution was added dropwise. The mixture was stirred at room temperature for 2.5 h at a stirring speed of 650 rpm, washed with ethanol and deionized water, pre-frozen at -50°C for 7 h, and then freeze-dried at -80°C for 24 h to obtain the modified cellulose nanocrystals.

[0025] The preparation method of the modified montmorillonite is as follows: S4-1: Disperse sodium montmorillonite in water to a solid-liquid mass ratio of 1:25, add 15% of the mass of sodium montmorillonite in dodecyl bis(hydroxyethyl)methylammonium chloride, stir at 65°C for 1.5 h, wash with deionized water, and freeze-dry at -50°C for 24 h to obtain powder B; S4-2: Powder B was added to a 0.1 M lanthanum nitrate solution so that the solid-liquid mass ratio was 1:50, and ultrasonically treated for 5 h. The powder was then transferred to a muffle furnace and calcined for 1.5 h at a calcination temperature of 370° C. to obtain the modified montmorillonite.

[0026] A method for preparing a high-strength and high-toughness polylactic acid composite material, the specific steps of the preparation method are as follows: S9-1: Add polylactic acid, modified cellulose nanocrystals, modified montmorillonite, plasticizer, and antioxidant into a high-speed mixer according to the formula ratio, and stir at 600 rpm for 20 min at room temperature to obtain a premix; S9-2: A twin-screw extruder was used for melt blending, with the temperature settings from the feeding section to the die head being 172°C, 177°C, and 182°C, respectively. The rotation speed was 200 rpm, and the residence time was 6 min. The extruded strips were cooled in a water tank and then pelletized to obtain the high-strength and high-toughness polylactic acid composite material.

[0027] Example 2

[0028] A high-strength and high-toughness polylactic acid composite material, the polylactic acid composite material has the following formula: in parts by weight, 70 parts of polylactic acid, 5 parts of modified cellulose nanocrystals, 3 parts of modified montmorillonite, 1 part of epoxidized soybean oil, 0.5 parts of antioxidant 1076, and 0.5 parts of antioxidant 168 The preparation method of modified cellulose nanocrystals is as follows: S1-1: 1 part by weight of cellulose nanocrystals was added to 100 parts by weight of deionized water, and ultrasonicated for 30 min at an ultrasonic power of 500 W to obtain dispersion A; S1-2: 0.5 parts by weight of a 0.5 M tannic acid solution at 60°C was added to dispersion A in sequence, the pH was adjusted to 8.5 using a 0.1 M NaHCO3 solution, and after cooling to room temperature, 1 part by weight of a 3 M octadecylamine-ethanol solution was added dropwise. The mixture was stirred at room temperature for 2 h at a stirring speed of 600 rpm, washed with ethanol and deionized water, and pre-frozen at -50°C for 6 h, and then freeze-dried at -80°C for 24 h to obtain the modified cellulose nanocrystals.

[0029] The preparation method of the modified montmorillonite is as follows: S4-1: Disperse sodium montmorillonite in water to a solid-liquid mass ratio of 1:20, add dodecyl bis(hydroxyethyl)methylammonium chloride (10% by mass of sodium montmorillonite), stir at 60°C for 1 h, wash with deionized water, and freeze-dry at -50°C for 24 h to obtain powder B; S4-2: Powder B was added to a 0.1 M lanthanum nitrate solution so that the solid-liquid mass ratio was 1:50, ultrasonically treated for 4 h, and then transferred to a muffle furnace and calcined for 1 h at a calcination temperature of 350° C. to obtain the modified montmorillonite.

[0030] A method for preparing a high-strength and high-toughness polylactic acid composite material, the specific steps of the preparation method are as follows: S9-1: Add polylactic acid, modified cellulose nanocrystals, modified montmorillonite, plasticizer, and antioxidant into a high-speed mixer according to the formula ratio, and stir at 500 rpm for 10 min at room temperature to obtain a premix; S9-2: A twin-screw extruder was used for melt blending, with the temperature settings from the feeding section to the die head being 170°C, 175°C, and 180°C, respectively, the rotation speed being 150 rpm, and the residence time being 5 min. The extruded strips were cooled in a water tank and then pelletized to obtain the high-strength and high-toughness polylactic acid composite material.

[0031] Example 3

[0032] A high-strength and high-toughness polylactic acid composite material, wherein the polylactic acid composite material has the following formula: in parts by weight, 80 parts of polylactic acid, 10 parts of modified cellulose nanocrystals, 5 parts of modified montmorillonite, 2 parts of dioctyl terephthalate, and 10101 parts of an antioxidant. The preparation method of modified cellulose nanocrystals is as follows: S1-1: 3 parts by weight of cellulose nanocrystals were added to 100 parts by weight of deionized water, and ultrasonicated for 60 min at an ultrasonic power of 600 W to obtain dispersion A; S1-2: 1 part by weight of a 1 M tannic acid solution at 60°C was added to dispersion A in sequence, the pH was adjusted to 8.5 using a 0.1 M NaHCO3 solution, and after cooling to room temperature, 2 parts by weight of a 3 M octadecylamine-ethanol solution was added dropwise. The mixture was stirred at room temperature for 3 h at a stirring speed of 700 rpm, washed with ethanol and deionized water, and pre-frozen at -50°C for 8 h, and then freeze-dried at -80°C for 24 h to obtain the modified cellulose nanocrystals.

[0033] The preparation method of the modified montmorillonite is as follows: S4-1: Disperse sodium montmorillonite in water to a solid-liquid mass ratio of 1:30, add 20% of the mass of sodium montmorillonite in dodecyl bis(hydroxyethyl)methylammonium chloride, stir at 70°C for 2 h, wash with deionized water, and freeze-dry at -50°C for 24 h to obtain powder B. S4-2: Powder B was added to a 0.1 M lanthanum nitrate solution so that the solid-liquid mass ratio was 1:50, and ultrasonic treatment was performed for 6 h. The powder was then transferred to a muffle furnace and calcined for 2 h at a calcination temperature of 400° C. to obtain the modified montmorillonite.

[0034] A method for preparing a high-strength and high-toughness polylactic acid composite material, the specific steps of the preparation method are as follows: S9-1: Add polylactic acid, modified cellulose nanocrystals, modified montmorillonite, plasticizer, and antioxidant into a high-speed mixer according to the formula ratio, and stir at 700 rpm for 30 min at room temperature to obtain a premix; S9-2: A twin-screw extruder was used for melt blending, with the temperature settings from the feeding section to the die head being 175°C, 178°C, and 185°C, respectively. The rotation speed was 250 rpm, and the residence time was 7 min. The extruded strips were cooled in a water tank and then pelletized to obtain the high-strength and high-toughness polylactic acid composite material.

[0035] Comparative Example 1 Unmodified montmorillonite was used instead of the modified montmorillonite, and the remaining steps were the same as those in Example 1.

[0036] Comparative Example 2 Unmodified cellulose nanocrystals were used instead of modified cellulose nanocrystals, and the remaining steps were consistent with those in Example 1.

[0037] Comparative Example 3 Unmodified montmorillonite was used instead of modified montmorillonite, and unmodified cellulose nanocrystals were used instead of modified cellulose nanocrystals. The remaining steps were the same as those in Example 1.

[0038] Comparative Example 4 Tannic acid was not added during the preparation of modified cellulose nanocrystals, and the remaining steps were the same as those in Example 1.

[0039] Comparative Example 5 The octadecylamine-ethanol solution was not added during the preparation of the modified cellulose nanocrystals, and the remaining steps were the same as those in Example 1.

[0040] Comparative Example 6 In the preparation of modified montmorillonite, dodecyl bis(hydroxyethyl)methylammonium chloride was not added, and the remaining steps were the same as those in Example 1.

[0041] Comparative Example 7 Lanthanum nitrate was not added during the preparation of the modified montmorillonite, and the remaining steps were the same as those in Example 1.

[0042] Mechanical properties testing The tensile strength is determined by referring to the method in GB / T 1040 at a tensile speed of 50 mm / min. The elongation at break is determined by referring to the method in GB / T 1040 at a tensile speed of 50 mm / min. The impact strength is determined by referring to the method in GB / T 1843 at an energy of 5.5 J and a speed of 3.5 m / s.

[0043] Heat deformation temperature test The heat deformation temperature of the composite materials prepared in the examples and comparative examples was measured using a heat deformation temperature tester. The load was 1.82 MPa, the heating rate was 120°C / h, the sample size was 120 mm × 12 mm × 3 mm, and the temperature at which the deflection at the center of the sample reached 0.34 mm was measured.

[0044] Group Tensile strength (MPa) Elongation at break (%) <![CDATA[Impact strength (KJ / m 2 )]]> HDT (℃) Example 1 41 16.8 90 95 Example 2 39 16.2 34.9 90 Example 3 38 16.5 34.5 90 Comparative Example 1 24 10.3 28.0 70 Comparative Example 2 18 11.0 27.1 72 Comparative Example 3 11 9.2 18.3 67 Comparative Example 4 27 13.2 29.8 82 Comparative Example 5 30 12.6 30.2 87 Comparative Example 6 15 11.7 23.3 62 Comparative Example 7 21 11.2 25.1 65 The above data show that the tensile strength, elongation at break, impact strength and HDT of Examples 1 to 3 are all higher than those of the comparative example, indicating that the composite materials prepared by the present invention have high strength, high toughness and heat resistance. The modified montmorillonite and modified cellulose nanocrystals significantly improve the strength, toughness and heat resistance of the material through interface reinforcement and lattice regulation.

[0045] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A high-strength and high-toughness polylactic acid composite material, characterized in that: The PLA composite material has the following formula: in parts by weight, 70-80 parts of PLA, 5-10 parts of modified cellulose nanocrystals, 3-5 parts of modified montmorillonite, 1-2 parts of plasticizer and 0.5-1.5 parts of antioxidant. The preparation method of modified cellulose nanocrystals is as follows: S1-1: 1 to 3 parts by weight of cellulose nanocrystals are added to 100 parts by weight of deionized water, and ultrasonically treated for 30 to 60 minutes to obtain dispersion A; S1-2: 0.5 to 1 parts by weight of a 0.5 to 1 M tannic acid solution at 60°C were added to the dispersion A in sequence, the pH was adjusted to 8.5 with a 0.1 M NaHCO3 solution, and after cooling to room temperature, 1 to 2 parts by weight of a 3 M octadecylamine-ethanol solution was added dropwise. The mixture was stirred at room temperature for 2 to 3 hours at a stirring speed of 600 to 700 rpm, washed with ethanol and deionized water, and freeze-dried in steps to obtain the modified cellulose nanocrystals.

2. The high-strength and high-toughness polylactic acid composite material according to claim 1, characterized in that: The ultrasonic power in S1-1 is 500-600 W.

3. The high-strength and high-toughness polylactic acid composite material according to claim 1, characterized in that: The stepwise freeze-drying process in S1-2 comprises pre-freezing at -50°C for 6 to 8 hours and then freeze-drying at -80°C for 24 hours.

4. The high-strength and high-toughness polylactic acid composite material according to claim 1, characterized in that: The preparation method of the modified montmorillonite is as follows: S4-1: Disperse sodium montmorillonite in water to a solid-liquid mass ratio of 1:(20-30), add dodecyl bis(hydroxyethyl)methylammonium chloride, stir at 60-70°C for 1-2 h, wash with deionized water, and freeze-dry at -50°C for 24 h to obtain powder B; S4-2: Powder B was added to a 0.1 M lanthanum nitrate solution so that the solid-liquid mass ratio was 1:50, ultrasonically treated for 4 to 6 hours, and then transferred to a muffle furnace for calcination for 1 to 2 hours to obtain the modified montmorillonite.

5. The high-strength and high-toughness polylactic acid composite material according to claim 4, characterized in that: The addition amount of dodecyl bis(hydroxyethyl)methylammonium chloride in S4-1 is 10-20% of the mass of sodium montmorillonite.

6. The high-strength and high-toughness polylactic acid composite material according to claim 4, characterized in that: The calcination temperature in S4-2 is 350-400°C.

7. The high-strength and high-toughness polylactic acid composite material according to claim 1, characterized in that: The plasticizer is one or more of tributyl citrate, epoxidized soybean oil and dioctyl terephthalate.

8. The high-strength and high-toughness polylactic acid composite material according to claim 1, characterized in that: The antioxidant is one or more of antioxidant 1010 , antioxidant 1076 and antioxidant 168 .

9. A method for preparing a high-strength and high-toughness polylactic acid composite material according to any one of claims 1 to 8, characterized in that: The specific steps of the preparation method are as follows: S9-1: Add polylactic acid, modified cellulose nanocrystals, modified montmorillonite, plasticizer, and antioxidant into a high-speed mixer according to the formula ratio, and stir at 500-700 rpm for 10-30 min at room temperature to obtain a premix; S9-2: melt blending is performed using a twin-screw extruder at a rotation speed of 150 to 250 rpm and a residence time of 5 to 7 min. The extruded strip is cooled in a water tank and then pelletized to obtain the high-strength and high-toughness polylactic acid composite material.

10. The method for preparing a high-strength and high-toughness polylactic acid composite material according to claim 9, characterized in that: The melt blending temperatures in S9-2 are set to 170-175°C, 175-178°C and 180-185°C from the feeding section to the die head, respectively.