Modified polylactic acid high-temperature-resistant degradable composite material and preparation method thereof

Abstract

This invention discloses a modified polylactic acid (PLA) high-temperature resistant biodegradable composite material and its preparation method, relating to the field of degradable materials technology. The modified PLA high-temperature resistant biodegradable composite material of this invention comprises at least the following raw materials in parts by weight: 70-80 parts by weight of polylactic acid; 15-25 parts by weight of lignin-PLA-polycaprolactone block copolymer; 5-10 parts by weight of polybutylene terephthalate-adipate; 2-5 parts by weight of stearic acid-modified nano-silica; 0.3-0.8 parts by weight of anti-hydrolysis agent; and 0.2-0.5 parts by weight of antioxidant. The modified PLA high-temperature resistant biodegradable composite material prepared by this invention improves the mechanical properties and high-temperature resistance of PLA composite materials, and the degradation rate can be controlled by the proportion of each component to meet the application requirements of different scenarios.

Description

Technical Field

[0001] This invention relates to the field of degradable materials technology, specifically to a modified polylactic acid high-temperature resistant degradable composite material and its preparation method. Background Technology

[0002] Plastics have been mass-produced and used since the mid-20th century. Compared to other materials, they are strong, durable, and lightweight, and have become an integral part of people's daily lives, used in items such as shopping bags and garbage bags. However, these traditional plastics can persist in the environment for hundreds to thousands of years without degrading, leading to serious plastic pollution problems. The widespread distribution of plastic pollution and its harm to ecosystems and organisms have far exceeded people's imagination. In response to the environmental problems caused by plastics, researchers have been researching and developing biodegradable plastics. Biodegradable plastics can be degraded into water, carbon dioxide (or methane), and other biomass through the enzymatic action of microorganisms in the soil, effectively reducing environmental pollution.

[0003] Currently, common biodegradable plastics are mainly polyesters, including polylactic acid (PLA), polybutylene succinate, polyhydroxyalkanoates, and polybutylene terephthalate / adipate (PBAT). Among them, PLA is a renewable, fully bio-based, and biodegradable aliphatic thermoplastic polymer. Due to its excellent tensile strength (around 45 MPa), thermal stability, and biodegradability, it is widely used in many areas of life. However, PLA has some inherent drawbacks, such as poor toughness and low heat resistance, which limit its large-scale commercial application. Therefore, modification treatments are needed, such as blending modification, copolymerization modification, and nanocomposite modification. PBAT possesses good ductility, tensile properties, and impact resistance, as well as good heat resistance, making it a widely used biodegradable plastic. However, the introduction of aromatic segments affects its biodegradability. Therefore, blending PLA with PBAT can effectively improve the properties of polylactic acid (PLA). However, the poor compatibility between PLA and PBAT leads to a significant reduction in the mechanical strength of the blend, impacting its performance. Filler modification is considered one of the simple and effective methods to improve polymer properties. Blending PLA with nanoparticles is a relatively simple, direct, and effective physical modification method. However, the improvement of PLA properties by using a single filler is limited. Therefore, existing PLA biodegradable materials suffer from poor heat resistance and mechanical properties, severely limiting the application of this technology. Summary of the Invention

[0004] The purpose of this invention is to provide a modified polylactic acid high-temperature resistant and biodegradable composite material and its preparation method, thereby solving the following technical problems:

[0005] Existing polylactic acid biodegradable materials suffer from poor heat resistance and inadequate mechanical properties.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A modified polylactic acid high-temperature resistant and biodegradable composite material, comprising at least the following raw materials in parts by weight:

[0008] 70-80 parts by weight of polylactic acid; 15-25 parts by weight of lignin-polylactic acid-polycaprolactone block copolymer; 5-10 parts by weight of polybutylene terephthalate-adipate; 2-5 parts by weight of stearic acid-modified nano-silica; 0.3-0.8 parts by weight of anti-hydrolysis agent; 0.2-0.5 parts by weight of antioxidant.

[0009] As a further aspect of the present invention, the method for preparing the stearic acid-modified nano-silica includes the following steps:

[0010] Nano-silica and 3-aminopropyltriethoxysilane were added to toluene, centrifuged, washed and freeze-dried to obtain amino-modified nano-silica;

[0011] The amino-modified nano-silica was added to dimethyl sulfoxide, then to a stearic acid / dimethyl sulfoxide solution, and 1-ethyl(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added to activate the carboxyl groups to form a mixture. The mixture was reacted, centrifuged, washed, and freeze-dried to obtain stearic acid-modified nano-silica.

[0012] As a further aspect of the present invention: the mass ratio of the nano-silica to the 3-aminopropyltriethoxysilane is 1:1.2-1.5.

[0013] As a further aspect of the present invention: the mass ratio of the amino-modified nano silica, the stearic acid, the 1-ethyl(3-dimethylaminopropyl)carbodiimide and the N-hydroxysuccinimide in the mixture is 1:1-1.5:1.2-1.4:0.8-1.

[0014] As a further aspect of the present invention, the preparation method of the lignin-polylactic acid-polycaprolactone block copolymer includes at least the following preparation steps:

[0015] Lignin, L-lactide, and stannous octoate catalyst were reacted under N2 atmosphere, and then ε-caprolactone was added to react to obtain lignin-polylactic acid-polycaprolactone block copolymer.

[0016] As a further aspect of the present invention: the mass ratio of lignin, L-lactide and ε-caprolactone is 1:7-9:5-7.

[0017] As a further aspect of the present invention, the number-average molecular weight of the lignin-polylactic acid-polycaprolactone block copolymer is 25,000-35,000 g / mol.

[0018] As a further aspect of the present invention: the anti-hydrolysis agent is one or a mixture of several of polycarbodiimide compounds, monocarbodiimide compounds, or acrylic copolymers with epoxy groups; and the antioxidant is one or a mixture of several of antioxidant 1010, antioxidant 168, antioxidant 1076, or antioxidant 3114.

[0019] A method for preparing a modified polylactic acid high-temperature resistant and biodegradable composite material as described in any of the above claims, comprising at least the following preparation steps:

[0020] Dry polylactic acid, lignin-polylactic acid-polycaprolactone block copolymer, polybutylene terephthalate-adipate, stearic acid-modified nano silica, anti-hydrolysis agent and antioxidant are added to a high-speed mixer and mixed until uniform to obtain a premix.

[0021] The premixed material is added to the hopper of a twin-screw extruder, and then extruded after a melt-blending reaction in the twin-screw extruder to obtain a molten material.

[0022] The molten material is drawn into strips and cooled by air or water. Then it is fed into a pelletizer for slicing and granulation. After drying, a modified polylactic acid high-temperature resistant and biodegradable composite material is obtained.

[0023] The beneficial effects of this invention are:

[0024] The modified polylactic acid (PLA) high-temperature resistant and biodegradable composite material prepared by this invention has significant advantages in terms of excellent comprehensive performance and wide range of applications, improving the mechanical properties and high-temperature resistance of PLA composite materials. This invention achieves a performance breakthrough that is difficult to achieve with single materials by blending lignin-PLA-polycaprolactone block copolymer, polybutylene terephthalate (PET), and PLA, and adding stearic acid-modified nano-silica for synergistic effect. The compatibilizing effect of lignin-polylactic acid-polycaprolactone block copolymer lays the foundation for the compatibility of polybutylene terephthalate (PET) and polylactic acid (PLA), allowing the flexibility of PET and the rigidity of PLA to be fully utilized. Stearic acid-modified nano-silica is uniformly dispersed in this compatible system, simultaneously improving the strength and toughness of the composite material through a "rigidity enhancement + interface strengthening" effect, avoiding the increased brittleness caused by traditional reinforcing agents. Regarding high-temperature resistance, the aromatic ring structure of lignin and the physical barrier effect of nano-silica contribute to... The three components work synergistically to inhibit the degradation and migration of polymer molecular chains at high temperatures, while the presence of polybutylene terephthalate (PET) can alleviate the risk of cracking caused by the excessive rigidity of polylactic acid (PLA) at high temperatures. In terms of degradation performance, the rapid degradation characteristics of PET can first form pores on the material surface, providing channels for microorganisms and moisture to enter, promoting the hydrolysis of PLA and the biodegradation of lignin. The "degradation relay" formed by the three components ensures that the composite material can be completely degraded in the natural environment, and the degradation rate can be adjusted by the proportion of each component to meet the needs of different application scenarios.

[0025] This invention prepares a lignin-polylactic acid-polycaprolactone block copolymer via ring-opening polymerization using lignin, L-lactide, and ε-caprolactone as raw materials. The lignin-polylactic acid-polycaprolactone block copolymer plays a dual core role in the system, acting as both a "bridge" and a "reinforcement." On one hand, the polylactic acid blocks in its molecular structure can form tight entanglements with the polylactic acid molecular chains in the matrix, while the polycaprolactone blocks exhibit good compatibility with the aliphatic ester bond structure of polybutylene terephthalate (PET). Furthermore, the lignin units, with their rigid framework and abundant functional groups, provide heat-resistant support for the composite material (the aromatic ring structure of lignin can increase the material's heat distortion temperature) and inhibit phase separation between polylactic acid and PET through interfacial interactions. This effectively solves the problem of mechanical property fluctuations caused by poor compatibility in traditional polylactic acid / PET blends. On the other hand, after lignin is modified with polylactic acid / polycaprolactone block, it overcomes the defect of easy aggregation of unmodified lignin. Its dispersed phase can play the role of "stress concentration point" when the composite material is subjected to external force, induce the generation of crazes and absorb energy, and significantly improve the impact resistance of the material.

[0026] This invention uses the silane coupling agent 3-aminopropyltriethoxysilane to react with nano-silica to obtain amino-modified nano-silica. This nano-silica is then further reacted with stearic acid to obtain stearic acid-grafted modified nano-silica. The surface of the nano-silica is grafted with the silane coupling agent and stearic acid segments, improving the interfacial compatibility between the silica and the polylactic acid matrix. After dispersion, the stearic acid-modified nano-silica forms "rigid support points" in the composite material, significantly improving the tensile strength, flexural strength, and heat resistance. The stearic acid modification layer reduces the surface energy of the nanoparticles, decreasing agglomeration. Simultaneously, its long-chain alkyl groups can generate van der Waals forces with the flexible segments of polybutylene terephthalate (PET) and polycaprolactone blocks, further strengthening the interfacial bonding. This allows the composite material to maintain stable melt viscosity during high-temperature processing, improving molding accuracy. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1: The preparation method of stearic acid modified nano-silica includes the following steps:

[0029] Weigh 10g of nano silica and 14g of 3-aminopropyltriethoxysilane and add them to 200ml of toluene. Heat and stir at 90℃ for 24h. Collect the precipitate by centrifugation. Redisperse the precipitate in anhydrous ethanol for washing and centrifugation. Repeat the operation three times to remove unreacted 3-aminopropyltriethoxysilane. Freeze-dry at -40℃ for 12h to obtain amino-modified nano silica powder.

[0030] 10g of stearic acid was weighed and added to 40ml of dimethyl sulfoxide (DMSO). The mixture was heated at 50°C until the stearic acid was completely dissolved, yielding a stearic acid / DMSO solution. The 10g of amino-modified nano-silica powder was dispersed in DMSO and then added to the stearic acid / DMSO solution cooled to room temperature. 12g of 1-ethyl(3-dimethylaminopropyl)carbodiimide and 8g of N-hydroxysuccinimide were added to activate the carboxyl groups. The mixture was stirred at room temperature for 24 hours. The mixture was centrifuged to obtain a white precipitate. The precipitate was washed with anhydrous ethanol and then freeze-dried to obtain stearic acid-modified nano-silica.

[0031] Example 2: The preparation method of stearic acid modified nano-silica includes the following steps:

[0032] Weigh 10g of nano silica and 15g of 3-aminopropyltriethoxysilane and add them to 200ml of toluene. Heat and stir at 90℃ for 24h. Collect the precipitate by centrifugation. Redisperse the precipitate in anhydrous ethanol, wash and centrifuge. Repeat the operation three times to remove unreacted 3-aminopropyltriethoxysilane. Freeze-dry at -40℃ for 12h to obtain amino-modified nano silica powder.

[0033] 15g of stearic acid was weighed and added to 40ml of dimethyl sulfoxide (DMSO). The mixture was heated at 50°C until the stearic acid was completely dissolved, yielding a stearic acid / DMSO solution. 10g of the aforementioned amino-modified nano-silica powder was dispersed in DMSO and then added to the stearic acid / DMSO solution cooled to room temperature. 14g of 1-ethyl(3-dimethylaminopropyl)carbodiimide and 10g of N-hydroxysuccinimide were added to activate the carboxyl groups. The mixture was stirred at room temperature for 24 hours. The mixture was centrifuged to obtain a white precipitate. The precipitate was washed with anhydrous ethanol and then freeze-dried to obtain stearic acid-modified nano-silica.

[0034] Example 3: The preparation method of lignin-polylactic acid-polycaprolactone block copolymer includes the following steps:

[0035] 10g of lignin with a hydroxyl content of 11mmol / g, 80g of L-lactide and 0.4g of catalyst stannous octoate were reacted at 130℃ for 12h under a nitrogen atmosphere. Then, 60g of ε-caprolactone was added to the reaction vessel and the reaction was continued for 12h to obtain a lignin-polylactic acid-polycaprolactone block copolymer with an average molecular weight of 13200g / mol.

[0036] Example 4: A method for preparing a modified polylactic acid high-temperature resistant and biodegradable composite material includes the following steps:

[0037] 75 parts by weight of polylactic acid (PLA 4032D), 20 parts by weight of lignin-polylactic acid-polycaprolactone block copolymer, 7 parts by weight of polybutylene terephthalate-adipate, 3 parts by weight of stearic acid modified nano silica prepared in Example 1, 0.5 parts by weight of hydrolysis inhibitor polycarbodiimide compound, 0.2 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were dried and added to a high-speed mixer and mixed until uniform. The high-speed mixer speed was 800 rpm and the mixing time was 5-25 min to obtain a premix.

[0038] The above premixed material is added to the hopper of a twin-screw extruder. The speed of the twin-screw extruder is controlled at 250 rpm and the vacuum degree is -0.08 MPa. Temperature gradients of 165°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 185°C in zone 5 are set. After the material undergoes melt blending reaction in the twin-screw extruder, it is extruded to obtain molten material.

[0039] The molten material is drawn into strips and cooled by air or water. Then it is fed into a pelletizer for slicing and granulation. After drying, a modified polylactic acid high-temperature resistant and biodegradable composite material is obtained.

[0040] Example 5: A method for preparing a modified polylactic acid high-temperature resistant and biodegradable composite material includes the following steps:

[0041] 75 parts by weight of polylactic acid (PLA 4032D), 20 parts by weight of lignin-polylactic acid-polycaprolactone block copolymer, 7 parts by weight of polybutylene terephthalate-adipate, 3 parts by weight of stearic acid modified nano-silica prepared in Example 2, 0.5 parts by weight of hydrolysis inhibitor polycarbodiimide compound, 0.2 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were dried and added to a high-speed mixer and mixed until uniform. The high-speed mixer speed was 800 rpm and the mixing time was 5-25 min to obtain a premix.

[0042] The above premixed material is added to the hopper of a twin-screw extruder. The speed of the twin-screw extruder is controlled at 250 rpm and the vacuum degree is -0.08 MPa. Temperature gradients of 165°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 185°C in zone 5 are set. After the material undergoes melt blending reaction in the twin-screw extruder, it is extruded to obtain molten material.

[0043] The molten material is drawn into strips and cooled by air or water. Then it is fed into a pelletizer for slicing and granulation. After drying, a modified polylactic acid high-temperature resistant and biodegradable composite material is obtained.

[0044] Example 6 A method for preparing a modified polylactic acid high-temperature resistant and biodegradable composite material includes the following steps:

[0045] 75 parts by weight of polylactic acid (PLA 4032D), 25 parts by weight of lignin-polylactic acid-polycaprolactone block copolymer, 8 parts by weight of polybutylene terephthalate-adipate, 4 parts by weight of stearic acid modified nano-silica prepared in Example 1, 0.7 parts by weight of hydrolysis inhibitor polycarbodiimide compound, 0.2 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were dried and added to a high-speed mixer and mixed until uniform. The high-speed mixer speed was 800 rpm and the mixing time was 5-25 min to obtain a premix.

[0046] The above premixed material is added to the hopper of a twin-screw extruder. The speed of the twin-screw extruder is controlled at 250 rpm and the vacuum degree is -0.08 MPa. Temperature gradients of 165°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 185°C in zone 5 are set. After the material undergoes melt blending reaction in the twin-screw extruder, it is extruded to obtain molten material.

[0047] The molten material is drawn into strips and cooled by air or water. Then it is fed into a pelletizer for slicing and granulation. After drying, a modified polylactic acid high-temperature resistant and biodegradable composite material is obtained.

[0048] Example 7 A method for preparing a modified polylactic acid high-temperature resistant and biodegradable composite material includes the following steps:

[0049] 75 parts by weight of polylactic acid (PLA 4032D), 25 parts by weight of lignin-polylactic acid-polycaprolactone block copolymer, 8 parts by weight of polybutylene terephthalate-adipate, 4 parts by weight of stearic acid modified nano silica prepared in Example 2, 0.7 parts by weight of hydrolysis inhibitor polycarbodiimide compound, 0.2 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were dried and added to a high-speed mixer and mixed until uniform. The high-speed mixer speed was 800 rpm and the mixing time was 5-25 min to obtain a premix.

[0050] The above premixed material is added to the hopper of a twin-screw extruder. The speed of the twin-screw extruder is controlled at 250 rpm and the vacuum degree is -0.08 MPa. Temperature gradients of 165°C in zone 1, 170°C in zone 2, 180°C in zone 3, 185°C in zone 4, and 185°C in zone 5 are set. After the material undergoes melt blending reaction in the twin-screw extruder, it is extruded to obtain molten material.

[0051] The molten material is drawn into strips and cooled by air or water. Then it is fed into a pelletizer for slicing and granulation. After drying, a modified polylactic acid high-temperature resistant and biodegradable composite material is obtained.

[0052] Compared with Example 4, Comparative Example 1 only replaced the stearic acid modified nano silica prepared in Example 1 with amino modified nano silica powder prepared in Example 1. The remaining components and preparation methods were completely the same as those in Example 4.

[0053] Compared with Example 4, Comparative Example 2 only replaced the stearic acid modified nano-silica prepared in Example 1 with unmodified nano-silica in the same mass as in Example 4. The other components and preparation methods were completely the same as in Example 4.

[0054] Compared with Example 4, Comparative Example 3 only replaced the lignin-polylactic acid-polycaprolactone block copolymer prepared in Example 3 with polybutylene terephthalate in equal mass. The remaining components and preparation methods were completely the same as those in Example 4.

[0055] Compared with Example 4, Comparative Example 4 only replaced the added polybutylene terephthalate (PET) with the lignin-polylactic acid-polycaprolactone (PLA) block copolymer prepared in Example 3. The remaining components and preparation methods were completely the same as those in Example 4.

[0056] Performance testing

[0057] Injection Molding for Specimen Preparation: The modified polylactic acid high-temperature resistant and biodegradable composite materials prepared in Examples 4-7 and Comparative Examples 1-4 were prepared into long strip-shaped tensile specimens using a MiniJet Pro micro-injection molding machine. The specimen specifications and dimensions were 80mm×10mm×4mm. The injection molding process parameters were as follows: barrel temperature 155℃, mold temperature 60℃, injection pressure 40MPa, injection time 10s, injection rate 150mm / s, holding pressure 25MPa, and holding time 12s.

[0058] Tensile property test: Dumbbell-shaped specimens were cut using a Type I standard cutter. The tensile speed was 5 mm / min. The laboratory temperature was 23±2℃, the relative humidity was 50±5%, and the air pressure was 86-106 kPa. The static mechanical properties of the test specimens, such as tensile strength and elongation at break, were tested according to the standard GB / T1040.2-2006. The test results are shown in Table 1.

[0059] Impact performance testing: The ratio of the energy absorbed by a notched specimen during cantilever beam impact failure to the initial cross-sectional area of ​​the notch is called the notched impact strength, and the unit is kJ / m². 2 During the experiment, the pendulum impacts the notched side of the specimen. The test specimen is milled into an 80mm × 10mm × 4mm notched impact specimen with a notch length of 2mm. A pendulum with an energy of 1J impacts the specimen. The cantilever beam impact strength α of the notched specimen is... iN (kJ / m 2 ), calculate using the following formula:

[0060] a iN =W / hb N ×10 3

[0061] In the formula, W represents the energy absorbed by the sample after impact, in J.

[0062] h - Sample thickness, mm;

[0063] b N - Remaining width at the bottom of the sample notch, mm;

[0064] The standard test temperature is 23±2℃, and the impact strength of the specimen is measured. Reference standard: GB / T1843-2008; test results are shown in Table 1.

[0065] Heat Deflection Temperature (HDT) Test: The heat deflection temperature (HDT) was measured using the Vicat-HDT-Tester. The sample was heated from room temperature to 230°C, held for 3 minutes to allow complete melting, and then rapidly cooled to 120°C. According to ISO 306 / 75HDT-A standard, the applied stress was 1.8 MPa, and the final deflection was 0.68 mm. The silicone oil was heated at a rate of 2°C / min, with an initial temperature of 30°C and an initial immersion time of 5 minutes. Measurements were repeated three times, and the average value was taken. The test results are shown in Table 1.

[0066] Degradation performance test: Small test pieces measuring 1.5mm × 1.5mm were cut from the test strips, dried, weighed, and their mass recorded. Then, samples with different numbers were covered on both sides with a layer of gauze and buried in soil at a depth of approximately 10cm. After 6 months, the samples were examined. The samples were removed, rinsed with tap water and distilled water to remove surface soil, rinsed with 75% (volume fraction) ethanol to remove further microbial action, and finally rinsed thoroughly with distilled water. The samples were dried in a vacuum drying oven at 40℃ until constant weight, and the mass was recorded. The above experimental steps were repeated, and the mass change of the test pieces was observed. The sample degradation mass loss rate was calculated using the following formula:

[0067] Quality loss rate = (W0 - W) t ) / W0×100%

[0068] In the formula, W0 is the mass of the sample before degradation, in g;

[0069] W t - Mass of the degraded sample, g; Detection results are shown in Table 1;

[0070] Table 1: Statistical table of performance test data of specimens from Examples 4-7 and Comparative Examples 1-4

[0071]

[0072] As shown in Table 1, the modified polylactic acid high-temperature degradable composite material prepared by this invention has excellent mechanical and heat resistance properties, while also considering service life and environmental friendliness. The amino-modified nano-silica added in Comparative Example 1 has high surface polarity and poor compatibility with the polylactic acid matrix, and the unmodified nano-silica added in Comparative Example 2 is prone to agglomeration, leading to a decrease in mechanical and heat resistance properties. The resulting composite material exhibits decreased mechanical properties and a lower heat distortion temperature. In Comparative Example 3, no block copolymer was added, resulting in poor compatibility between polybutylene terephthalate (PET) and polylactic acid, leading to a sharp drop in tensile strength and a lower heat distortion temperature. In Comparative Example 4, the absence of PET resulted in insufficient toughness and a lower degradation rate.

[0073] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0074] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A modified polylactic acid high-temperature resistant and biodegradable composite material, characterized in that, It shall include at least the following parts by weight of raw materials: 70-80 parts by weight of polylactic acid; 15-25 parts by weight of lignin-polylactic acid-polycaprolactone block copolymer; 5-10 parts by weight of polybutylene terephthalate-adipate; 2-5 parts by weight of stearic acid-modified nano-silica; 0.3-0.8 parts by weight of anti-hydrolysis agent; 0.2-0.5 parts by weight of antioxidant; The preparation method of the stearic acid modified nano-silica includes the following steps: Nano-silica and 3-aminopropyltriethoxysilane were added to toluene, centrifuged, washed and freeze-dried to obtain amino-modified nano-silica; The amino-modified nano-silica was added to dimethyl sulfoxide, then to a stearic acid / dimethyl sulfoxide solution, and 1-ethyl(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added to activate the carboxyl groups to form a mixture. The mixture was reacted, centrifuged, washed, and freeze-dried to obtain stearic acid-modified nano-silica.

2. The modified polylactic acid high-temperature resistant and biodegradable composite material according to claim 1, characterized in that, The mass ratio of the nano-silica to the 3-aminopropyltriethoxysilane is 1:1.2-1.

5.

3. The modified polylactic acid high-temperature resistant and biodegradable composite material according to claim 1, characterized in that, The mass ratio of the amino-modified nano silica, the stearic acid, the 1-ethyl(3-dimethylaminopropyl)carbodiimide and the N-hydroxysuccinimide in the mixture is 1:1-1.5:1.2-1.4:0.8-1.

4. The modified polylactic acid high-temperature resistant and biodegradable composite material according to claim 1, characterized in that, The preparation method of the lignin-polylactic acid-polycaprolactone block copolymer includes at least the following preparation steps: Lignin, L-lactide, and stannous octoate catalyst were reacted under N2 atmosphere, and then ε-caprolactone was added to react to obtain lignin-polylactic acid-polycaprolactone block copolymer.

5. The modified polylactic acid high-temperature resistant and biodegradable composite material according to claim 4, characterized in that, The mass ratio of lignin, L-lactide and ε-caprolactone is 1:7-9:5-7.

6. The modified polylactic acid high-temperature resistant and biodegradable composite material according to claim 4, characterized in that, The number-average molecular weight of the lignin-polylactic acid-polycaprolactone block copolymer is 25,000-35,000 g / mol.

7. The modified polylactic acid high-temperature resistant and biodegradable composite material according to claim 1, characterized in that, The anti-hydrolysis agent is one or a mixture of several of polycarbodiimide compounds, monocarbodiimide compounds, or epoxy-containing acrylic copolymers, and the antioxidant is one or a mixture of several of antioxidant 1010, antioxidant 168, antioxidant 1076, or antioxidant 3114.

8. A method for preparing a modified polylactic acid high-temperature resistant and biodegradable composite material as described in any one of claims 1-7, characterized in that, It includes at least the following preparation steps: Dry polylactic acid, lignin-polylactic acid-polycaprolactone block copolymer, polybutylene terephthalate-adipate, stearic acid-modified nano silica, anti-hydrolysis agent and antioxidant are added to a high-speed mixer and mixed until uniform to obtain a premix. The premixed material is added to the hopper of a twin-screw extruder, and then extruded after a melt-blending reaction in the twin-screw extruder to obtain a molten material. The molten material is drawn into strips and cooled by air or water. Then it is fed into a pelletizer for slicing and granulation. After drying, a modified polylactic acid high-temperature resistant and biodegradable composite material is obtained.

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