A method for preparing a polylactic acid aerogel by casting

Abstract

The application discloses a method for preparing polylactic acid aerogel by pouring, which comprises the steps of pouring a polylactic acid solution into a mold and then performing cooling treatment to obtain a polylactic acid aerogel precursor, wherein the polylactic acid solution contains polylactic acid, divalent inorganic salt, N,N-dimethylformamide and ethanol in a mass ratio of 1-20:0.1-5:50-90:10-50. The application adds appropriate amounts of divalent inorganic salt and ethanol into the polylactic acid solution, combines one divalent inorganic salt molecule with multiple ethanol molecules through a complex reaction, forms a hydrogen bond between the hydroxyl group of ethanol and the ester bond of the polylactic acid molecule, and constructs a dynamic network structure, so that the prepared polylactic acid solution has the characteristics of being capable of being cooled and solidified and being capable of being melted by heating. The polylactic acid aerogel prepared by the method has a density less than 0.08 g / cm 3 , a specific surface area greater than 47 m 2 / g, and a contact angle of 114° or above, and has excellent hydrophobicity.

Description

Technical Field

[0001] This invention belongs to the field of new material preparation and relates to a method for preparing polylactic acid aerogel by casting. Background Technology

[0002] Polylactic acid (PLA) is a biodegradable polymer composed of lactic acid molecules linked by ester bonds. It can be prepared through microbial fermentation or chemical synthesis. PLA possesses excellent biocompatibility and biodegradability, and is therefore widely used in medical, food packaging, and agricultural fields.

[0003] Polymer aerogels are an emerging type of porous material characterized by low density, light weight, and large specific surface area, making them widely used in aerospace, automotive, and construction industries. Their porous structure also endows them with excellent thermal insulation and adsorption properties, giving them significant application value in thermal insulation, water treatment, and gas separation. Polymer aerogels can also be combined with technologies such as mold casting and 3D printing to prepare aerogels of more shapes and better suited to various application conditions. Currently, there are two main methods for preparing polymer aerogels: one is to solidify the polymer solution through chemical reaction or low-temperature curing, and then prepare the aerogel through solvent evaporation or freeze-drying; the other is to directly react the polymer monomers with chemical substances using methods such as chemical vapor deposition or electron beam irradiation. For polymers like polylactic acid (PLA), which lack reactive functional groups and whose solvents have very low freezing points, preparing aerogels is even more challenging. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the object of the present invention is to provide a method for preparing polylactic acid aerogel by means of a polylactic acid solution that can be cooled and solidified and heated and melted, through solution casting-cooling, solvent replacement and freeze drying.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] In a first aspect, the present invention provides a method for preparing polylactic acid aerogel by casting. The method includes the step of casting a polylactic acid solution into a mold and then cooling it to obtain a polylactic acid aerogel precursor. The polylactic acid solution contains polylactic acid, divalent inorganic salt, N,N-dimethylformamide, and ethanol in a mass ratio of 1-20:0.1-5:50-90:10-50.

[0007] In the above technical solution, the mass ratio of polylactic acid, divalent inorganic salt, N,N-dimethylformamide, and ethanol in the polylactic acid solution is 1-20:0.1-5:50-90:10-50, preferably 5-15:2-4:50-90:10-40, and more preferably 10:1:80:20. The ethanol is analytical grade high-concentration ethanol with a concentration of 99.9%. If low-concentration ethanol, such as 50% ethanol or 75% ethanol, is used, it is converted to 100% ethanol and then added according to the above-mentioned mass ratio to prepare the polylactic acid solution.

[0008] In the above technical solution, the divalent inorganic salt is one or more of calcium chloride, copper chloride, magnesium chloride, and copper bromide. In this invention, the divalent inorganic salt molecule combines with multiple ethanol molecules through a complexation reaction, and then utilizes the hydroxyl groups of ethanol to form hydrogen bonds with the ester bonds of polylactic acid molecules to construct a dynamic network structure, thereby preparing a polylactic acid solution that can solidify upon cooling and melt upon heating. Therefore, any divalent inorganic salt that can combine with multiple ethanol molecules through a complexation reaction can be used in this invention. That is, the divalent inorganic salt of this invention may also include strontium chloride, zinc chloride, ferrous chloride, calcium bromide, zinc bromide, and magnesium bromide.

[0009] In the above technical solution, the preparation method of the polylactic acid solution is as follows: polylactic acid, divalent inorganic salt, N,N-dimethylformamide, and ethanol are mixed in a mass ratio of 1-20:0.1-5:50-90:10-50, and allowed to stand for 20-60 minutes to allow the polylactic acid and divalent inorganic salt to fully swell. Then, the temperature is raised to 20°C-80°C, and mechanical stirring is performed to completely dissolve the polylactic acid and divalent inorganic salt. The mixture is then kept at a constant temperature for 20-60 minutes to obtain the polylactic acid solution.

[0010] In the above technical solution, the polylactic acid (PLA) solution is poured into a mold pre-adjusted to 20°C–40°C, and then the mold temperature is lowered to -20°C–5°C and allowed to stand for 1–8 hours to obtain the PLA aerogel precursor. The temperature of the PLA solution used for pouring is maintained at 20°C–80°C to ensure that the PLA solution remains in a fluid state. Preferably, a silicone mold can be used, and the mold is dried before pouring, with the mold temperature adjusted to 20°C–40°C to prevent the PLA solution from solidifying first at the contact area with the mold, which would cause the PLA aerogel precursor to delaminate after demolding. Furthermore, adding an appropriate amount of a non-solvent phase (such as silicone oil) to the PLA solution before pouring makes it easier to demold after cooling. Moreover, during solvent displacement, the non-solvent phase detaches from the PLA aerogel precursor, creating pores, thus achieving a dual effect of demolding and pore formation. The amount of non-solvent phase added is 0.5% of the total mass of the solution, so as to facilitate the removal of polylactic acid from the mold after solidification (demolding). In actual operation, the amount of non-solvent phase added can be adjusted appropriately according to the actual situation, preferably around 0.5% of the total mass of the solution.

[0011] In the above technical solution, the method for preparing polylactic acid aerogel by casting further includes the step of: placing the polylactic acid aerogel precursor in water for solvent replacement treatment, and then performing freeze-drying treatment to obtain polylactic acid aerogel.

[0012] In the above technical solution, the solvent replacement treatment step includes: placing the polylactic acid aerogel precursor in water, i.e., water as the replacement medium, at a replacement temperature of 1℃ to 30℃, and for a replacement time of 12h to 48h. In this solvent replacement treatment step, the polylactic acid aerogel precursor is placed in water for an appropriate period. Utilizing the principle of "like dissolves like," N,N-dimethylformamide, ethanol, and dimethyl inorganic salts in the polylactic acid aerogel precursor are replaced. The remaining polylactic acid solidifies upon contact with water, forming a void structure within the polylactic acid precursor. Therefore, the replacement time determines whether the polylactic acid aerogel possesses an excellent microstructure.

[0013] In the above technical solution, the freeze-drying step includes: freezing the polylactic acid aerogel precursor after solvent replacement treatment to -80℃ to -1℃, and then freeze-drying it at a freeze-drying temperature of -50℃ to -20℃ for 12h to 48h. Preferably, the polylactic acid aerogel precursor after solvent replacement treatment is frozen to -50℃ to -20℃, more preferably -40℃ to -20℃, and even more preferably -30℃. The freeze-drying temperature is preferably -40℃ to -20℃, and even more preferably -25℃ or -20℃. By adopting appropriate freeze-drying conditions for the polylactic acid aerogel precursor, moisture can be effectively removed while protecting the internal structure of the polylactic acid aerogel.

[0014] A second aspect of the present invention provides a polylactic acid aerogel prepared by the above-described method for preparing polylactic acid aerogel by casting. The density of the polylactic acid aerogel is less than 0.08 g / cm³. 3 Specific surface area greater than 47m² 2 / g, with a contact angle of 114.2°~119.8°. In some embodiments of the present invention, the density of the polylactic acid aerogel is 0.06g / cm³. 3 ~0.08g / cm 3 However, the density of polylactic acid aerogel prepared by the method of the present invention can also reach 0.06 g / cm³. 3 The density of polylactic acid aerogel can be adjusted by changing the mass fraction of polylactic acid in the solution.

[0015] This invention demonstrates through extensive applied fundamental experiments that adding ethanol and divalent inorganic salts enables polylactic acid (PLA) solutions to exhibit the ability to solidify upon cooling and melt upon heating. This is because divalent inorganic salt molecules in the solution combine with multiple ethanol molecules through complexation reactions, and then hydrogen bonds are formed between the hydroxyl groups of ethanol and the ester bonds of PLA molecules, constructing a dynamic network structure. Heating accelerates the movement of PLA molecules, disrupting the hydrogen bond structure between them and ethanol molecules, thus increasing the solution's fluidity; cooling slows down the movement of PLA molecules, restoring the hydrogen bond structure between them and ethanol molecules, thus reducing the solution's fluidity. Therefore, PLA solutions exhibit the phenomenon of solidification upon cooling and melting upon heating. Since ethanol and divalent inorganic salts are the reasons for the PLA solution's ability to solidify upon cooling and melt upon heating, the solidification temperature and rate of the PLA solution can be adjusted by changing the ratio of ethanol to divalent inorganic salts in the PLA solution, achieving structural control in the preparation of PLA aerogels. This PLA solution, combined with casting technology, enriches the diversity of PLA aerogel products. Therefore, the preparation of polylactic acid aerogels from this polylactic acid solution via casting-cooling, solvent replacement, and freeze-drying is a novel and effective method.

[0016] This invention utilizes complexation reactions and intermolecular hydrogen bonds to construct a dynamic network structure in polylactic acid (PLA) solution, thereby increasing the freezing point of the PLA solution. After the PLA solution solidifies, PLA aerogels are prepared through solvent displacement and freeze-drying.

[0017] The beneficial effects of this invention are:

[0018] (1) This invention is the first to use polylactic acid solution that is cooled and solidified and heated and melted as raw material to prepare polylactic acid aerogel through casting-cooling, solution replacement and freeze drying, and develops a brand-new method for preparing polylactic acid aerogel;

[0019] (2) This invention is the first to prepare a polylactic acid (PLA) solution that can solidify upon cooling and melt upon heating by constructing a dynamic network structure. The preparation method is simple and reliable. Additives can also be added to the PLA solution, which means that PLA aerogels can be endowed with more functions and more flexible and convenient applications. For example, adding an appropriate amount of carbon nanotubes to the PLA solution can significantly improve the thermal stability of the PLA aerogel, enabling its application in air batteries.

[0020] (3) The process for preparing polylactic acid aerogels in this invention is highly adjustable. The solidification temperature of the polylactic acid solution can be adjusted by regulating the concentration of divalent inorganic salts and ethanol. The density of the aerogel can be adjusted by regulating the mass fraction of polylactic acid in the solution. Based on the experimental objectives and environment, a reasonable experimental scheme can be designed to prepare polylactic acid aerogels of the desired shape and density.

[0021] (4) The polylactic acid aerogel prepared by the present invention using the casting technique has a density of less than 0.08 g / cm³. 3 Specific surface area greater than 47m² 2 / g, the fine pores on the surface and inside give it a rich microstructure, which makes the polylactic acid aerogel more flexible and more hydrophobic, meaning that the polylactic acid aerogel can be applied to more and wider fields.

[0022] (5) The process of preparing polylactic acid aerogel involved in this invention is a physical process, which does not change the original molecular structure of polylactic acid and perfectly preserves the biocompatibility and degradability of polylactic acid. Attached Figure Description

[0023] Figure 1 Optical photographs of polylactic acid solutions prepared according to embodiments of the present invention are shown, wherein (a) shows an optical photograph of an unsolidified polylactic acid solution, and (b) shows an optical photograph of a solidified polylactic acid solution.

[0024] Figure 2 An optical photograph of the polylactic acid aerogel prepared according to an embodiment of the present invention is shown.

[0025] Figure 3 The image shown is a scanning electron microscope image of the polylactic acid aerogel prepared according to an embodiment of the present invention.

[0026] Figure 4 The water contact angle of the polylactic acid aerogel prepared according to an embodiment of the present invention is shown.

[0027] Figure 5 The results of the compressive strength test of the polylactic acid aerogel prepared according to the embodiments of the present invention are shown.

[0028] Figure 6 The infrared spectrum of the polylactic acid aerogel prepared according to an embodiment of the present invention is shown. Detailed Implementation

[0029] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the materials and reagents used can be purchased from biological or chemical companies.

[0030] The following are the raw materials used in the examples:

[0031] Polylactic acid: purchased from Aladdin Chemical Reagent Co., Ltd., product standard number: GB / T29284-2012.

[0032] Magnesium chloride: purchased from Aladdin Chemical Reagent Co., Ltd., product standard number: QB / T2605-2003.

[0033] Copper chloride: purchased from Tianjin Damao Chemical Reagent Factory, product standard number: GB / T15901-1995.

[0034] Copper bromide: purchased from Sinopharm Chemical Reagent Co., Ltd., product standard number: Q / CYDZ 773-2005.

[0035] Calcium chloride: purchased from Tianjin Kemei Chemical Reagent Co., Ltd., product standard number: HG / T 5349-2018.

[0036] N,N-Dimethylformamide: Purchased from Tianjin Kemei Chemical Reagent Co., Ltd., product standard number: GB / T17521-1998.

[0037] Ethanol: Purchased from Tianjin Fuyu Fine Chemical Co., Ltd., product standard number: GB / T13-011-14001.

[0038] Freeze dryer: purchased from Ningbo Xinzhi Biotechnology Co., Ltd., model: SCIENTZ-12N.

[0039] Example 1

[0040] (1) Mix polylactic acid, calcium chloride, N,N-dimethylformamide and ethanol in a weight ratio of 9:1:90:10, let stand for 40 minutes to allow polylactic acid and calcium chloride to fully swell, then heat to 60°C and mechanically stir to completely dissolve polylactic acid and calcium chloride, and let stand at a constant temperature for 40 minutes to obtain a polylactic acid solution.

[0041] (2) The polylactic acid solution is poured into a mold. The mold is dried before pouring. The temperature of the mold is 25°C and the temperature of the polylactic acid solution is 60°C during pouring. After pouring, the mold is cooled to -10°C and left to stand for 6 hours to obtain the polylactic acid aerogel precursor.

[0042] (3) The aerogel precursor was placed in water for solvent displacement at 10°C for 12 hours. Utilizing the principle of "like dissolves like," N,N-dimethylformamide, ethanol, and calcium chloride were fully displaced from the polylactic acid aerogel precursor. The remaining polylactic acid solidified upon contact with water, forming a void structure within the polylactic acid precursor. The displaced polylactic acid precursor was then frozen at -20°C and freeze-dried at -30°C for 12 hours to obtain polylactic acid aerogel.

[0043] Example 2

[0044] (1) Mix polylactic acid, copper chloride, N,N-dimethylformamide and ethanol in a weight ratio of 9:1:90:10, let stand for 40 minutes to allow polylactic acid and copper chloride to fully swell, then heat to 60°C and mechanically stir to completely dissolve polylactic acid and copper chloride, and let stand at a constant temperature for 40 minutes to obtain a polylactic acid solution.

[0045] (2) The polylactic acid solution is poured into a mold. The mold is dried before pouring. The temperature of the mold is 25°C and the temperature of the polylactic acid solution is 60°C during pouring. After pouring, the mold is cooled to -10°C and left to stand for 6 hours to obtain the polylactic acid aerogel precursor.

[0046] (3) The aerogel precursor was placed in water for solvent replacement at 10°C for 12 hours. Utilizing the principle of "like dissolves like," N,N-dimethylformamide, ethanol, and copper chloride were fully replaced from the polylactic acid aerogel precursor. The remaining polylactic acid solidified upon contact with water, forming a void structure within the polylactic acid precursor. The replaced polylactic acid precursor was then frozen at -20°C and freeze-dried at -30°C for 12 hours to obtain polylactic acid aerogel.

[0047] Example 3

[0048] (1) Mix polylactic acid, magnesium chloride, N,N-dimethylformamide and ethanol in a weight ratio of 9:1:90:10, let stand for 40 minutes to allow polylactic acid and magnesium chloride to fully swell, then heat to 60°C and mechanically stir to completely dissolve polylactic acid and magnesium chloride, and let stand at a constant temperature for 40 minutes to obtain a polylactic acid solution.

[0049] (2) The polylactic acid solution is poured into a mold. The mold is dried before pouring. The temperature of the mold is 25°C and the temperature of the polylactic acid solution is 60°C during pouring. After pouring, the mold is cooled to -10°C and left to stand for 6 hours to obtain the polylactic acid aerogel precursor.

[0050] (3) The aerogel precursor was placed in water for solvent displacement at 10°C for 12 hours. Utilizing the principle of "like dissolves like," N,N-dimethylformamide, ethanol, and magnesium chloride were fully displaced from the polylactic acid aerogel precursor. The remaining polylactic acid solidified upon contact with water, forming a void structure within the polylactic acid precursor. The displaced polylactic acid precursor was then frozen at -20°C and freeze-dried at -30°C for 12 hours to obtain polylactic acid aerogel.

[0051] Example 4

[0052] (1) Mix polylactic acid, copper bromide, N,N-dimethylformamide and ethanol in a weight ratio of 9:1:90:10, let stand for 40 minutes to allow polylactic acid and copper bromide to fully swell, then heat to 60°C and mechanically stir to completely dissolve polylactic acid and copper bromide, and let stand at a constant temperature for 40 minutes to obtain a polylactic acid solution.

[0053] (2) The polylactic acid solution is poured into a mold. The mold is dried before pouring. The temperature of the mold is 25°C and the temperature of the polylactic acid solution is 60°C during pouring. After pouring, the mold is cooled to -10°C and left to stand for 6 hours to obtain the polylactic acid aerogel precursor.

[0054] (3) The aerogel precursor was placed in water for solvent displacement at 10°C for 12 hours. Utilizing the principle of "like dissolves like," N,N-dimethylformamide, ethanol, and copper bromide were fully displaced from the polylactic acid aerogel precursor. The remaining polylactic acid solidified upon contact with water, forming a void structure within the polylactic acid precursor. The displaced polylactic acid precursor was then frozen at -20°C and freeze-dried at -30°C for 12 hours to obtain polylactic acid aerogel.

[0055] Example 5

[0056] 1. Performance testing of polylactic acid solution

[0057] Figure 1 Images a and b are optical images of the polylactic acid (PLA) solutions prepared in Examples 1-4 before and after freezing, respectively. It can be seen that the PLA solution has the ability to solidify upon cooling and melt upon heating. Before solidification, the PLA solution has high transparency, allowing objects behind it to be clearly seen. After solidification, the transparency of the PLA solution decreases, and the solution does not flow when the ampoule is inverted.

[0058] 2. Morphology of polylactic acid aerogel

[0059] The polylactic acid aerogels prepared in Examples 1 to 4 were observed using an optical microscope (1x magnification) and a scanning electron microscope (10,000x magnification), respectively.

[0060] Figure 2 a to d are optical microscope images of the polylactic acid aerogels prepared in Examples 1 to 4, respectively. It can be seen that the polylactic acid aerogels are shaped like bananas, apples, and grapes. Their surfaces are smooth and there are no obvious defects, which shows that the polylactic acid aerogel preparation method of the present invention can successfully produce polylactic acid aerogels of any shape and can be easily demolded.

[0061] Figure 3 Images a through d are SEM images of the polylactic acid aerogels prepared in Examples 1 through 4, respectively. It can be seen that the microstructure of the polylactic acid aerogel prepared by this invention differs from that of aerogels typically prepared by freeze-drying; its interior is composed of three-dimensional fibers, indicating that the theory proposed in this invention for constructing a dynamic network structure in a polylactic acid solution is reasonable. Low-temperature freezing causes the polylactic acid molecular chains to form a dense network structure in the solution. Subsequently, during solvent replacement, the solvent N,N-dimethylformamide and the divalent inorganic salts and ethanol acting as network nodes dissolve in water and are displaced, while the polylactic acid molecules solidify upon contact with water, thus retaining their network structure.

[0062] 3. Determination of the water contact angle of polylactic acid aerogel

[0063] Measurement method: The water contact angle of polylactic acid aerogel was measured using a contact angle meter (DSA-25, KRUSS, Germany). The extruded droplet size was 2 μL.

[0064] Measurement results: such as Figure 4 The water contact angles of the polylactic acid aerogels prepared in Examples 1 to 4 were 116.5°, 119.6°, 119.8°, and 114.2°, respectively, indicating that the microstructure of the polylactic acid aerogel surface and the intrinsic hydrophobicity of polylactic acid give it excellent hydrophobic properties.

[0065] 4. Determination of the density of polylactic acid aerogel

[0066] Measurement method: Measure the volume and weight of the polylactic acid (PLA) aerogel. Calculate the density of the PLA aerogel using Formula 1.

[0067] ρ=m / v, (1)

[0068] In the formula, v is the volume of polylactic acid aerogel (cm). 3 m is the mass of polylactic acid aerogel (g); ρ is the density of polylactic acid aerogel (g / cm³). 3 )

[0069] Measurement results: The density of the polylactic acid aerogels prepared in Examples 1-4 was 0.06 g / cm³. 3 ~0.08g / cm 3 This demonstrates that the polylactic acid aerogel of the present invention has a low density and is a lightweight material. This allows the polylactic acid aerogel to provide a lightweight solution in many applications, reducing weight and improving portability.

[0070] 5. Determination of specific surface area of ​​polylactic acid aerogel

[0071] Measurement method: The specific surface area of ​​polylactic acid aerogel was measured using a high-speed automated specific surface area and porosity analyzer (Tristar 3020, Micromeritics, USA).

[0072] Measurement results: The specific surface areas of the four polylactic acid aerogels prepared in Examples 1-4 were 47.01 m², respectively. 2 / g, 47.5m 2 / g, 48.7m 2 / g, 49.2m 2 / g indicates that the polylactic acid aerogel of the present invention has a porous structure and a large specific surface area, which enables it to be widely used in fields such as heat insulation, adsorption and filtration.

[0073] 6. Determination of compressive strength of polylactic acid aerogel

[0074] Test method: The compressive strength of polylactic acid aerogel under 10% deformation was measured using a compression testing machine (YT-YS5000A, Hangzhou Yante Technology Co., Ltd., China).

[0075] Test results: The 3D fiber network structure of polylactic acid (PLA) aerogel can uniformly transfer stress, giving PLA aerogel excellent compressive strength. The pressures required for 10% deformation of the four aerogels prepared in Examples 1-4 were 0.19 MPa, 0.25 MPa, 0.16 MPa, and 0.19 MPa, respectively.

[0076] 7. Figure 6 The infrared spectrum of the polylactic acid aerogel prepared by the method of the present invention is shown. It can be seen that at approximately 3665 cm⁻¹... -1 The absorption peak at 2953 cm⁻¹ represents the stretching vibration of -OH. -1 The band observed at 1762 cm⁻¹ is due to HCH asymmetric stretching, while at 1762 cm⁻¹... -1 The band observed at this location is C=O stretching. This occurs in the 1000–1500 cm⁻¹ range. -1 The nearby wavelengths can be attributed to the stretching of the ester group (-COC-), while in the 800–1000 cm⁻¹ range... -1The wavelength range between these bands is caused by the tensile vibration of -CC-. This indicates that the casting method for preparing polylactic acid aerogels according to the present invention does not affect the polylactic acid molecular chain, perfectly preserving the original properties of polylactic acid and facilitating subsequent development and application.

[0077] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing polylactic acid aerogel by casting, characterized in that, The process includes the steps of pouring a polylactic acid (PLA) solution into a mold and then cooling it at a temperature of -20°C to 5°C to obtain a PLA aerogel precursor; placing the PLA aerogel precursor in water for solvent displacement treatment; and then freeze-drying it. The PLA solution contains PLA, divalent inorganic salts, N,N-dimethylformamide, and ethanol in a mass ratio of 1~20:0.1~5:50~90:10~50. The divalent inorganic salt is one or more of calcium chloride, magnesium chloride, copper chloride, and copper bromide. The solvent replacement treatment step includes: placing the polylactic acid aerogel precursor in water and leaving it at a temperature of 1℃~30℃ for 12h~48h. The freeze-drying process includes: freezing the polylactic acid aerogel precursor after solvent replacement treatment to -80℃ to -1℃, and then freeze-drying it at a freeze-drying temperature of -50℃ to -20℃ for 12h to 48h.

2. The method for preparing polylactic acid aerogel by casting according to claim 1, characterized in that, The method for preparing the polylactic acid solution includes: mixing polylactic acid, divalent inorganic salt, N,N-dimethylformamide, and ethanol in the mass ratio specified above, allowing it to stand for 20 min to 60 min, heating it to 20°C to 80°C, stirring to dissolve it, and then allowing it to stand to obtain the polylactic acid solution.

3. The method for preparing polylactic acid aerogel by casting according to claim 1, characterized in that, After pouring the polylactic acid solution into a mold pre-adjusted to 20℃~40℃, the temperature of the mold is cooled to the cooling temperature and left to stand for 1h~8h to obtain the polylactic acid aerogel precursor.

4. A polylactic acid aerogel, characterized in that, The polylactic acid aerogel is prepared by any one of claims 1 to 3.

5. The polylactic acid aerogel according to claim 4, characterized in that, The density of the polylactic acid aerogel is less than 0.08 g / cm³. 3 Specific surface area greater than 47m² 2 / g, with a contact angle of 114.2°~119.8°.

Images