Modified polylactic acid aerogel fiber and preparation method thereof

Abstract

The invention relates to a modified polylactic acid aerogel fiber and a preparation method thereof. Specifically, the modified polylactic acid aerogel fiber has a double-layer structure, the outer layer of the double-layer structure is a non-porous outer layer with nano mastoid structures distributed on the smooth outer surface of the outer layer, and the matrix thickness of the non-porous outer layer at the position where the nano mastoid structures are not distributed is 5-50 nm; the radius of the bottom of the nano mastoid structure is 50 nm to 200 nm; the height of the nano mastoid structure is 5 nm to 20 nm; the inner layer of the double-layer structure is an aerogel porous structure layer, and the porosity of the aerogel porous structure layer is 50%-99%; the average pore size is 1-25 nm; the outer layer and the inner layer are of an integrated structure. The invention also relates to a method for preparing the modified polylactic acid aerogel fiber and application of the modified polylactic acid aerogel fiber in preparation of a filter material.

Description

Technical Field

[0001] This invention relates to the field of polylactic acid (PLA) aerogel fiber preparation technology. Specifically, this invention relates to modified PLA aerogel fibers and their preparation methods, particularly modified PLA aerogel fibers with nanopapillary structures and their preparation methods. Background Technology

[0002] Polylactic acid (PLA) fiber is a bio-based synthetic fiber made from renewable plant resources (such as corn, cassava, and sugarcane). Since the 1990s, with the increasing awareness of environmental protection and the popularization of the concept of sustainable development, PLA aerogel fiber has gradually become an ideal substitute for traditional petroleum-based synthetic fibers due to its excellent biodegradability and biocompatibility, showing broad application prospects in textiles, medical care, hygiene, agriculture, and packaging. For example, in the water purification process of ecologically sensitive areas such as wetland restoration and aquaculture, the good biocompatibility and strong degradability of PLA aerogel fiber can avoid secondary pollution problems in specific applications. In the process of industrial wastewater treatment, the excellent surface modification flexibility of PLA aerogel fiber can achieve directional selective adsorption of heavy metal ions, thereby realizing efficient purification of wastewater and secondary recycling of heavy metal ions.

[0003] Traditional polylactic acid (PLA) aerogel fibers, due to their smooth surface and dense structure, are significantly limited in applications requiring high specific surface area and high flux (such as filtration, adsorption, and functional textiles), for example, in terms of purification efficiency in water purification processes. To improve these properties, existing technologies mainly employ strategies such as blending modification, copolymerization modification, irregular cross-section design, and optimized heat treatment processes. For example, loading functional nanoparticles (such as Ti) onto the surface of PLA aerogel fibers... Nanoparticles (such as Ag) effectively increase the specific surface area and number of active sites of the material, thereby increasing the contact area between polylactic acid (PLA) aerogel fibers and pollution sources to improve their purification efficiency and thus enhance their application performance in environmental purification. However, over time, nanoparticles are prone to detachment from the fiber surface, leading to a rapid decrease in the specific surface area of ​​the fiber, and the overall purification performance cannot be effectively guaranteed. In addition, nanoparticles also have the problem of aggregation, resulting in uneven distribution of nanoparticles on the fiber surface. For example, surface etching technology can be used to increase the surface roughness and specific surface area of ​​the fiber, but this process often leads to the destruction of the crystal structure of the fiber surface or the introduction of microcracks, resulting in a significant decrease in mechanical properties and limiting its practical value. For another example, there are PLA aerogel fibers obtained by preparing aerogel structures. These PLA aerogel fibers have nanopores throughout, which not only have the characteristics of large specific surface area, but also significantly increase water flux because water can flow through the inside of the fiber. However, this type of through-pore structure makes it difficult for the fiber to have a complete path for rapid stress dissipation under external forces, similar to smooth and dense fibers, resulting in its mechanical properties being difficult to guarantee. It is evident that although traditional modified polylactic acid aerogel fibers have high specific surface area and excellent fluid permeability, their application is subject to multiple technical limitations: the material itself has insufficient mechanical strength and high brittleness, making it difficult to withstand mechanical stress under normal use conditions; in addition, the preparation process is complex and the raw material cost is high, resulting in high overall production costs and limiting its large-scale production.

[0004] Therefore, how to solve the incompatibility between the high-density surface and mechanical strength of traditional polylactic acid aerogel fibers and the difficulty in large-scale production has become a key issue in this field. Summary of the Invention

[0005] Therefore, the main objective of this invention is to provide an improved modified polylactic acid aerogel fiber and its preparation method, which solves the problem of incompatibility between the high-density surface and mechanical strength of traditional polylactic acid aerogel fibers.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a modified polylactic acid aerogel fiber is provided, characterized in that the modified polylactic acid aerogel fiber has a bilayer structure, wherein: the outer layer of the bilayer structure is a non-porous outer layer with nanopapillary structures distributed on its smooth outer surface, wherein the matrix thickness of the non-porous outer layer at the locations where the nanopapillary structures are not distributed is 5 nm to 50 nm; the bottom radius of the nanopapillary structures is 50 nm to 200 nm; the height of the nanopapillary structures is 5 nm to 20 nm; the inner layer of the bilayer structure is an aerogel porous structure layer, the porosity of the aerogel porous structure layer is 50% to 99%; the average pore size is 1 nm to 25 nm; the outer layer and the inner layer are an integral structure.

[0007] Furthermore, the specific surface area of ​​the non-porous outer layer of the modified polylactic acid aerogel fiber is 200 to 1000 m². 2 / g, with a surface roughness Ra of 100 nm to 200 nm.

[0008] Furthermore, the tensile breaking strength of a single polylactic acid aerogel fiber is 1 GPa to 4 GPa, the strain is 5% to 8%, and the toughness is 25 MJ / m. 3 Up to 70 MJ / m 3 The radius of curvature is 0.1 μm to 1 μm; the aspect ratio of polylactic acid aerogel fibers is 1000 to 2000, and the diameter is 100 to 5000 nm.

[0009] To achieve the above objectives, according to a second aspect of the present invention, a method for preparing modified polylactic acid aerogel fibers according to the first aspect of the present invention is provided, characterized by comprising the following steps: S1: uniformly dissolving polylactic acid in a good solvent of polylactic acid to prepare a homogeneous spinnable solution; S2: electrospinning the homogeneous spinnable solution obtained in S1 to obtain polylactic acid aerogel fibers; S3: receiving the polylactic acid aerogel fibers obtained in S2 onto a first receiving substrate and performing selective swelling treatment by spraying with a non-good solvent of polylactic acid aerogel fibers; S4: moving the polylactic acid aerogel fibers after selective swelling treatment by spraying in S3 onto a second receiving substrate and performing drying treatment to obtain modified polylactic acid aerogel fibers.

[0010] Further, in step (1), the molecular weight of polylactic acid is 50 kDa to 100 kDa, and the concentration of polylactic acid is 5 to 50 wt%; in step (1), the good solvent for polylactic acid is selected from dichloromethane (DCM) and chloroform (CHC). The solvent is selected from one or more of the following: tetrahydrofuran (THF), hexafluoroisopropanol, acetone, dimethyl sulfoxide, and N,N-dimethylformamide (DMF), preferably a mixture of dichloromethane and N,N-dimethylformamide, a mixture of dichloromethane and acetone, a mixture of dichloromethane and methanol, a mixture of chloroform and ethanol, preferably a mixture of dichloromethane and N,N-dimethylformamide in a ratio of 3:7 to 5:5, and more preferably a mixture of dichloromethane and N,N-dimethylformamide in a ratio of 3.5:6.5.

[0011] Further, the electrospinning in step (2) is carried out under the following conditions: ambient temperature of 10 to 40 °C, ambient humidity of 30 to 80%, and the operating parameters of electrospinning in step (2) are: voltage of 5 to 100 kV, distance between the first receiving substrate and the spinning nozzle of 10 to 100 cm, distance between the second receiving substrate and the first receiving substrate of 50 to 100 cm, and infusion rate of 1 to 1000 mL / h. In step (2), the structure of the polylactic acid aerogel fiber obtained is: an aerogel structure with a smooth, non-porous outer layer and an inner layer with nano-connecting pores.

[0012] Furthermore, in step (3), the non-good solvent is selected from methanol, ethanol, and propanol, preferably ethanol; the spraying speed of the non-good solvent droplets is controlled at 0.1 g / cm. 3 ·s -1 Up to 10 g / cm 3 ·s -1 The swelling time should be controlled between 30 and 120 seconds.

[0013] Further, in step (4), the drying temperature is 40 to 55 °C and the drying time is 10 to 60 min; the structure of the modified polylactic acid aerogel fiber in step (4) is: an aerogel structure with a smooth surface and a non-porous outer layer with distributed nanopapillary structures and an inner layer with nano-connecting pores.

[0014] To achieve the above objectives, according to a third aspect of the present invention, the present invention provides the use of modified polylactic acid aerogel fibers according to the first aspect of the present invention or modified polylactic acid aerogel fibers that can be prepared by the method according to the second aspect of the present invention in the preparation of filter materials.

[0015] The present invention provides an improved polylactic acid (PLA) aerogel fiber and its preparation method. The improved modified PLA aerogel fiber and the fiber membrane prepared therefrom not only possess a large specific surface area but also excellent mechanical properties. On the one hand, it prevents the degradation of the specific surface area of ​​traditional load-modified PLA aerogel fibers over time; on the other hand, it prevents stress concentration-induced structural damage in traditional etch-modified PLA aerogel fibers. This represents a qualitative leap in the comprehensive mechanical properties of PLA aerogel fibers, demonstrating excellent performance in balancing high-density surface area and mechanical strength. This leads to breakthroughs in the application performance boundaries and expansion of application scenarios for PLA aerogel fiber materials. Furthermore, the preparation method of the present invention has no special requirements for raw materials and equipment and can be carried out on mass production equipment. Attached Figure Description

[0016] Figure 1A scanning electron microscope (SEM) image of fibers obtained by electrospinning using the homogeneous spinnable solution prepared in Example 1 of the present invention is shown in 1 μm field of view. The image shows an aerogel structure consisting of a smooth, non-porous outer layer without nanopapillary structures and an inner layer with nanopores.

[0017] Figure 2 A scanning electron microscope (SEM) image of the surface layer of the modified polylactic acid aerogel fiber obtained using Example 1 of the present invention is shown in 2 μm field of view. The image shows that the fiber obtained after swelling-drying treatment possesses a non-porous outer layer with a smooth surface and distributed nanopapillary structures.

[0018] Figure 3 A scanning electron microscope (SEM) image of the surface layer of the modified polylactic acid aerogel fiber obtained using Example 1 of the present invention is shown in 5 μm field of view. The image shows that the fiber obtained after swelling-drying treatment possesses a non-porous outer layer with a smooth surface and distributed nanopapillary structures.

[0019] Figure 4 A scanning electron microscope (SEM) image of a cross-section of modified polylactic acid aerogel fiber obtained using Example 1 of the present invention is shown at a 500 nm field of view. The image reveals that the fiber obtained after swelling-drying treatment possesses an aerogel structure consisting of a smooth, non-porous outer layer with distributed nanopapillary structures and an inner layer with nanoporous interconnections.

[0020] Figure 5 A flowchart of the method of the present invention is shown. Detailed Implementation

[0021] The following description is presented to enable those skilled in the art to obtain and use various embodiments. Descriptions of specific apparatuses, technologies, and applications are provided by way of example only. Various modifications to the embodiments described herein will be apparent to those skilled in the art, and the general principles defined herein can be applied to other instances and applications without departing from the scope of the various embodiments. Therefore, the various embodiments are not intended to be limited to the examples described and shown herein, but are consistent with the scope of the claims. It should be noted that, without conflict, the embodiments and features in the embodiments of this application can be combined with each other. The present invention will now be described in detail with reference to embodiments.

[0022] As described in the background section, the application of traditional polylactic acid aerogel fibers is subject to multiple technical limitations: the material itself has insufficient mechanical strength and high brittleness, making it difficult to withstand mechanical stress under normal use conditions; in addition, the preparation process is complex and the raw material cost is high, resulting in high overall production costs and limiting its large-scale production.

[0023] Due to the aforementioned problems, new polylactic acid aerogel fibers are needed to improve their insufficient mechanical strength and high brittleness. Simultaneously, new methods for preparing polylactic acid aerogel fibers are also required, enabling mass production on advanced equipment.

[0024] To achieve the above objectives, according to a first aspect of the present invention, a modified polylactic acid aerogel fiber is provided, the modified polylactic acid aerogel fiber having a bilayer structure, characterized in that: the outer layer of the bilayer structure is a non-porous outer layer with nanopapillary structures distributed on its smooth outer surface, wherein the matrix thickness of the non-porous outer layer at the locations where the nanopapillary structures are not distributed is 5 nm to 50 nm; the bottom radius of the nanopapillary structures is 50 nm to 200 nm; the height of the nanopapillary structures is 5 nm to 20 nm; the inner layer of the bilayer structure is an aerogel porous structure layer, the porosity of the aerogel porous structure layer is 50% to 99%; the average pore size is 1 to 25 nm; the outer layer and the inner layer are an integral structure.

[0025] In one embodiment, the bilayer structure is formed as follows: First, during the spinning process of the polylactic acid (PLA) spinning solution, water vapor in the air, acting as a non-good solvent, exchanges with the good solvent in the PLA solution jet. As the good solvent evaporates and penetrates deeper into the jet, it triggers phase separation within the PLA solution jet, forming a solvent-rich phase and a non-solvent-rich phase. During this process, due to near-surface contact with air, the solvent evaporates rapidly, and polymer segments quickly accumulate and solidify to form a smooth, non-porous outer layer. The inner layer, with its longer outward diffusion path, experiences a longer solvent retention time. Some solvent escapes through nanopores before the outer layer is fully solidified, while the remainder forms interconnected pathways within through capillary action, maintaining connectivity during solidification and exiting through the fiber ends. This results in PLA aerogel fibers with a smooth, non-porous outer layer and interconnected nanopores within. Further, non-good solvent droplets are sprayed onto the PLA aerogel fibers. Because the solubility parameters of the non-good solvent and PLA are partially matched, and the non-good solvent has a small molecular weight, the surface of the smooth, non-porous outer layer of the PLA aerogel fibers selectively swells. Non-solvents preferentially penetrate the amorphous pores of polylactic acid (PLA), while the tightly packed molecular chains in the crystalline regions hinder diffusion, resulting in swelling without dissolution, thus creating a selective swelling effect. Simultaneously, controlling the spraying and swelling time throughout the process prevents insufficient swelling or adhesion of the PLA aerogel fibers, which could reduce fiber surface roughness or strength. During subsequent drying, the PLA aerogel fibers undergo anisotropic shrinkage, generating compressive stress on the surface and causing localized protrusions, forming nanopapillary structures. The smooth, non-porous outer layer, unswelled, retains its smooth fiber layer structure, referred to as the matrix. The presence of a smooth internal fiber layer (matrix) allows polylactic acid (PLA) aerogel fibers to better dissipate stress under external forces. Compared to porous PLA aerogel fibers, this avoids the inherent defects of porous surfaces acting as crack initiation points, effectively reduces stress concentration points, and increases stress dissipation rate. This results in longer and more tortuous crack propagation paths, requiring more energy to be consumed, thus significantly improving fracture strength, strain, and toughness, exhibiting a macroscopic effect of high mechanical strength. Simultaneously, the presence of nanopapillary structures enables the achievement of a high specific surface area, meeting the application requirements of PLA aerogel fibers in water purification.

[0026] In one embodiment, the matrix thickness of the non-porous outer layer at locations where no nanopapillary structures are distributed is 5 to 50 nm. In another embodiment, the matrix thickness of the non-porous outer layer at locations where no nanopapillary structures are distributed is within the range of the following values ​​or any combination thereof: 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, 40 nm, 41 nm, 42 nm, 43 nm, 44 nm, 45 nm, 46 nm, 47 nm, 48 nm, 49 nm, 50 nm. When the matrix thickness is within the above values ​​or ranges, polylactic acid aerogel fibers exhibit excellent tensile strength, tensile toughness, and flexibility. The resulting fiber membranes inherit the excellent mechanical properties of individual fibers, meeting the application requirements of polylactic acid aerogel fibers in water purification.

[0027] In one embodiment, the bottom radius of the nanopapillary structure is 50 nm to 200 nm. In one embodiment, the base radius of the nanopapillary structure is within the range of the following values ​​or any combination thereof: 50 nm, 51 nm, 52 nm, 53 nm, 54 nm, 55 nm, 56 nm, 57 nm, 58 nm, 59 nm, 60 nm, 61 nm, 62 nm, 63 nm, 64 nm, 65 nm, 66 nm, 67 nm, 68 nm, 69 nm, 70 nm, 71 nm, 72 nm, 73 nm, 74 nm, 75 nm, 76 nm, 77 nm, 78 nm, 79 nm, 80 nm, 81 nm, 82 nm, 83 nm, 84 nm, 85 nm, 86 nm, 87 nm, 88 nm, 89 nm, 90 nm, 91 nm, 92 nm, 93 nm, 94 nm, 95 nm, 96 nm, 97 nm, 98 nm, 99 nm, 100 nm, 101 nm, 102 nm, 103 nm, 104 nm. nm, 105 nm, 106 nm, 107 nm, 108 nm, 109 nm, 110 nm, 111 nm, 112 nm, 113 nm, 114 nm, 115 nm, 116 nm, 117 nm, 118 nm, 119 nm, 120 nm, 121 nm, 122 nm, 123 nm, 124 nm, 125 nm, 126 nm, 127 nm, 128 nm, 129 nm, 130 nm, 131 nm, 132 nm, 133 nm, 134 nm, 135 nm, 136 nm, 137 nm, 138 nm, 139 nm, 140 nm, 141 nm, 142 nm, 143 nm, 144 nm, 145 nm, 146 nm, 147 nm, 148 nm, 149 nm, 150 nm, 151 nm, 152 nm, 153 nm, 154 nm, 155 nm, 156 nm, 157 nm, 158 nm, 159 nm, 160 nm, 161 nm, 162 nm, 163 nm, 164 nm, 165 nm, 166 nm, 167 nm, 168 nm, 169 nm, 170 nm, 171 nm, 172 nm, 173 nm, 174 nm, 175 nm, 176 nm, 177 nm, 178 nm, 179 nm, 180 nm, 181 nm, 182 nm, 183 nm, 184 nm, 185 nm, 186 nm, 187 nm, 188 nm, 189nm, 190 nm, 191 nm, 192 nm, 193 nm, 194 nm, 195 nm, 196 nm, 197 nm, 198 nm, 199 nm, 200 nm. In one embodiment, the height of the nanopapillary structure is from 5 nm to 20 nm. In one embodiment, the height of the nanopapillary structure is within the range of the following values ​​or any combination thereof: 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm. When the bottom radius and height of the nanopapillary structure are within the above values, ideal surface roughness and ideal specific surface area can be obtained, thereby meeting the application requirements of polylactic acid aerogel fibers in the field of water purification. Meanwhile, since the nanopapillary structure and the internal smooth fiber layer (matrix) are integrated, the problem of uneven distribution caused by the easy shedding of modified nanoparticles from the fiber surface or the aggregation of nanoparticles in traditional modified polylactic acid aerogel fibers is effectively avoided. It can also effectively avoid the problem of damaging the crystal structure of the fiber or causing microcracks and thus significantly reducing the mechanical strength of the fiber caused by increasing the surface roughness of polylactic acid aerogel fibers through surface etching. This effectively ensures the overall purification performance and structural integrity.

[0028] In one embodiment, the porosity of the aerogel porous structure layer (inner layer) is 50% to 99%. In one embodiment, the porosity of the aerogel porous structure layer (inner layer) is within the range of the following point values ​​or any combination of the following point values: 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%. In one embodiment, the average pore size of the aerogel porous structure layer (inner layer) is from 1 nm to 25 nm. In another embodiment, the average pore size of the aerogel porous structure layer (inner layer) is within the range of the following values ​​or any combination thereof: 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm. Through the pores with porosity and pore size, water can flow through the interior of the fiber, significantly increasing water flux, thereby meeting the application requirements of polylactic acid aerogel fibers in the field of water purification.

[0029] In one embodiment, the specific surface area of ​​the non-porous outer layer is 200 to 1000 m². 2 / g. In one embodiment, the specific surface area of ​​the non-porous outer layer is within the range of the following point values ​​or any combination of the following point values: 200 m² / g, 250 m² / g, 270 m² / g, 300 m² / g, 320 m² / g, 340 m² / g, 360 m² / g, 380 m² / g, 400 m² / g, 420 m² / g, 440 m² / g, 460 m² / g, 480 m² / g, 500 m² / g, 520 m² / g, 540 m² / g, 550 m² / g, 560 m² / g, 580 m² / g. 600 m² / g, 620 m² / g, 640 m² / g, 650 m² / g, 660 m² / g, 680 m² / g, 700 m² / g, 720 m² / g, 740 m² / g, 760 m² / g, 780 m² / g, 800 m² / g, 804 m² / g, 810 m² / g, 820 m² / g, 840 m² / g, 860 m² / g, 880 m² / g, 900 m² / g, 920 m² / g, 940 m² / g, 960 m² / g, 980 m² / g, 1000 m² / g. In one embodiment, the surface roughness Ra of the non-porous outer layer is 100 nm to 200 nm. In one embodiment, the surface roughness Ra of the non-porous outer layer is within the range of the following point values ​​or any combination thereof: 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, and 200 nm. Due to the presence of the nanopapillary structure, ideal surface roughness and ideal specific surface area can be obtained, thereby meeting the application requirements of polylactic acid aerogel fibers in the field of water purification. Meanwhile, since the nanopapillary structure and the internal smooth fiber layer (matrix) are integrated, the problem of uneven distribution caused by the easy shedding of modified nanoparticles from the fiber surface or the aggregation of nanoparticles in traditional modified polylactic acid aerogel fibers is effectively avoided. It can also effectively avoid the problem of damaging the crystal structure of the fiber or causing microcracks and thus significantly reducing the mechanical strength of the fiber caused by increasing the surface roughness of polylactic acid aerogel fibers through surface etching. This effectively ensures the overall purification performance and structural integrity.

[0030] In one embodiment, the tensile breaking strength of a single polylactic acid aerogel fiber is from 1 GPa to 4 GPa. In another embodiment, the tensile breaking strength of a single polylactic acid aerogel fiber is within the range of the following values ​​or any combination thereof: 1.0 GPa, 1.1 GPa, 1.2 GPa, 1.3 GPa, 1.4 GPa, 1.5 GPa, 1.6 GPa, 1.7 GPa, 1.8 GPa, 1.9 GPa, 2.0 GPa, 2.1 GPa, 2.2 GPa, 2.3 GPa, 2.4 GPa, 2.5 GPa, 2.6 GPa, 2.7 GPa, 2.8 GPa, 2.9 GPa, 3.0 GPa, 3.1 GPa, 3.2 GPa, 3.3 GPa, 3.4 GPa, 3.5 GPa, 3.6 GPa, 3.7 GPa, 3.8 GPa, 3.9 GPa, and 4.0 GPa. In one embodiment, the strain of a single polylactic acid aerogel fiber is 5% to 8%. In another embodiment, the strain of a single polylactic acid aerogel fiber is within the range of the following values ​​or any combination thereof: 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%. In one embodiment, the toughness of a single polylactic acid aerogel fiber is 25 MJ / m. 3 Up to 70 MJ / m 3In one embodiment, the toughness of a single polylactic acid aerogel fiber is within the range of the following values ​​or any combination thereof: 25 MJ / m³, 26 MJ / m³, 27 MJ / m³, 28 MJ / m³, 29 MJ / m³, 30 MJ / m³, 31 MJ / m³, 32 MJ / m³, 33 MJ / m³, 34 MJ / m³, 35 MJ / m³, 36 MJ / m³, 37 MJ / m³, 38 MJ / m³, 39 MJ / m³, 40 MJ / m³, 41 MJ / m³, 42 MJ / m³, 43 MJ / m³, 44 MJ / m³, 45 MJ / m³, 46 MJ / m³, 47 MJ / m³, 48 MJ / m³, 49 MJ / m³, 50 MJ / m³, 51 ... MJ / m³, 52 MJ / m³, 53 MJ / m³, 54 MJ / m³, 55 MJ / m³, 56 MJ / m³, 57 MJ / m³, 58 MJ / m³, 59 MJ / m³, 60 MJ / m³, 61 MJ / m³, 62 MJ / m³, 63 MJ / m³, 64 MJ / m³, 65 MJ / m³, 66 MJ / m³, 67 MJ / m³, 68 MJ / m³, 69 MJ / m³, 70 MJ / m³. In one embodiment, the radius of curvature of a single polylactic acid aerogel fiber is from 0.1 μm to 1 μm. In one embodiment, the radius of curvature of a single polylactic acid aerogel fiber is within the range of the following values ​​or any combination thereof: 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, and 1.0 μm. In one embodiment, the aspect ratio of the polylactic acid aerogel fiber is from 1000 to 2000. In one embodiment, the aspect ratio of the polylactic acid aerogel fiber is within the range of the following values ​​or any combination thereof: 1000, 1050, 1100, 1150, 1200, 1240, 1250, 1300, 1340, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1660, 1700, 1750, 1800, 1850, 1900, 1950, 2000. In one embodiment, the diameter of a single polylactic acid aerogel fiber is from 100 to 5000 nm.In one embodiment, the diameter of a single polylactic acid aerogel fiber is within the range of the following values ​​or any combination thereof: 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, 2000 nm, 2100 nm, 2200 nm, 2300 nm, 2400 nm, 2500 nm, 2600 nm, 2700 nm, 2800 nm, 2900 nm, 3000 nm, 2 ... The aspect ratios and diameters of the polylactic acid aerogel fibers are 3100 nm, 3200 nm, 3300 nm, 3400 nm, 3500 nm, 3600 nm, 3700 nm, 3800 nm, 3900 nm, 4000 nm, 4100 nm, 4200 nm, 4300 nm, 4400 nm, 4500 nm, 4600 nm, 4700 nm, 4800 nm, 4900 nm, and 5000 nm. These aspect ratios and diameters provide sufficient structural stability for the polylactic acid aerogel fibers.

[0031] To achieve the above objectives, according to a second aspect of the present invention, a method for preparing modified polylactic acid aerogel fibers according to the first aspect of the present invention is provided, characterized by comprising the following steps:

[0032] S1: Prepare a homogeneous spinnable solution by uniformly dissolving polylactic acid in a good solvent for polylactic acid;

[0033] S2: Electrospinning the homogeneous spinnable solution obtained in S1 to obtain polylactic acid aerogel fiber.

[0034] S3: The polylactic acid aerogel fiber obtained in S2 is received onto the first receiving substrate and selectively swollen by spraying the polylactic acid aerogel fiber with a non-good solvent.

[0035] S4: Move the polylactic acid aerogel fibers that have undergone selective swelling treatment by spraying in S3 to the second receiving substrate and dry them to obtain modified polylactic acid aerogel fibers.

[0036] In one embodiment, in S1, polylactic acid is uniformly dissolved in a good solvent for polylactic acid to prepare a homogeneous spinnable solution. In one embodiment, the molecular weight of polylactic acid is 50 kDa to 100 kDa. In one embodiment, the molecular weight of polylactic acid is within the range of the following point values ​​or any combination thereof: 50 kDa, 51 kDa, 52 kDa, 53 kDa, 54 kDa, 55 kDa, 56 kDa, 57 kDa, 58 kDa, 59 kDa, 60 kDa, 61 kDa, 62 kDa, 63 kDa, 64 kDa, 65 kDa, 66 kDa, 67 kDa, 68 kDa, 69 kDa, 70 kDa, 71 kDa, 72 kDa, 73 kDa, 74 kDa, 75 kDa, 76 kDa, 77 kDa, 78 kDa, 79 kDa, 80 kDa, 81 kDa, 82 kDa, 83 kDa, 84 kDa, 85 kDa, 86 kDa, 87 kDa, 88 kDa, 89 kDa, 90 kDa, 91 kDa, 92 kDa, 93 kDa, 94 kDa, 95 kDa, 96 kDa, 97 kDa, 98 kDa, 99 kDa, 100 kDa. Using the above provides the best balance between performance and processability: ensuring sufficient strength while possessing good processability and sustainability.

[0037] In one embodiment, the concentration of polylactic acid is 5 to 50 wt%. In one embodiment, the concentration of polylactic acid is within the range of the following values ​​or any combination thereof: 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%. %, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%. The above concentration range of polylactic acid achieves a good balance between product performance and cost.

[0038] In one embodiment, a good solvent for polylactic acid is selected from dichloromethane (DCM) and chloroform (CHC). The solvent for polylactic acid (PLA) is selected from one or more of dichloromethane and N,N-dimethylformamide (DMF), tetrahydrofuran (THF), hexafluoroisopropanol, acetone, dimethyl sulfoxide, and N,N-dimethylformamide (DMF). In one embodiment, a good solvent for PLA is a mixture of dichloromethane and N,N-dimethylformamide in a ratio of 3:7 to 5:5. In another embodiment, a good solvent for PLA is a mixture of dichloromethane and N,N-dimethylformamide in a ratio of 3.5:6.5. Generally, halogenated hydrocarbon solvents have the strongest dissolving power, ether solvents, ketone solvents, and ester solvents have moderate dissolving power but low toxicity, and amide solvents have strong polarity and high boiling points. Therefore, mixed solvent systems are often used to achieve synergistic effects.

[0039] In one embodiment, polylactic acid is dissolved in a good solvent and stirred thoroughly to prepare a homogeneous spinnable solution.

[0040] In one embodiment, in S2, the homogeneous spinnable solution obtained in S1 is electrospun to obtain polylactic acid aerogel fibers. In one embodiment, the voltage for electrospinning is 5 to 100 kV. In one embodiment, the voltage for electrospinning is within the range of the following values ​​or any combination thereof: 5 kV, 10 kV, 15 kV, 20 kV, 25 kV, 30 kV, 35 kV, 40 kV, 45 kV, 50 kV, 55 kV, 60 kV, 65 kV, 70 kV, 75 kV, 80 kV, 85 kV, 90 kV, 95 kV, 100 kV. In one embodiment, the infusion rate for electrospinning is 1 to 1000 mL / h.In one embodiment, the perfusion speed of electrospinning is 1 mL / h, 2 mL / h, 3 mL / h, 4 mL / h, 5 mL / h, 6 mL / h, 7 mL / h, 8 mL / h, 9 mL / h, 10 mL / h, 11 mL / h, 12 mL / h, 13 mL / h, 14 mL / h, 15 mL / h, 16 mL / h, 17mL / h, 18 mL / h, 19 mL / h, 20 mL / h, 21 mL / h, 22 mL / h, 23 mL / h, 24 mL / h, 25 mL / h, 26 mL / h, 27 mL / h, 28 mL / h, 29 mL / h, 30 mL / h, 31 mL / h, 32 mL / h, 33 mL / h, 34 mL / h, 35 mL / h, 36mL / h, 37 mL / h, 38 mL / h, 39 mL / h, 40 mL / h, 41 mL / h, 42 mL / h, 43 mL / h, 44 mL / h, 45 mL / h, 46 mL / h, 47 mL / h, 48 mL / h, 49 mL / h, 50 mL / h, 51 mL / h, 52 mL / h, 53 mL / h, 54 mL / h, 55mL / h, 56 mL / h, 57 mL / h, 58 mL / h, 59 mL / h, 60 mL / h, 61 mL / h, 62 mL / h, 63 mL / h, 64 mL / h, 65 mL / h, 66 mL / h, 67 mL / h, 68 mL / h, 69 mL / h, 70 mL / h, 71 mL / h, 72 mL / h, 73 mL / h, 74mL / h, 75 mL / h, 76 mL / h, 77 mL / h, 78 mL / h, 79 mL / h, 80 mL / h, 81 mL / h, 82 mL / h, 83 mL / h, 84 mL / h, 85 mL / h, 86 mL / h, 87 mL / h, 88 mL / h, 89 mL / h, 90 mL / h, 91 mL / h, 92 mL / h, 93mL / h, 94 mL / h, 95 mL / h, 96 mL / h, 97 mL / h, 98 mL / h, 99 mL / h, 100 mL / h, 200 mL / h, 300mL / h, 400 mL / h, 500 mL / h, 600 mL / h, 700 mL / h, 800 mL / h, 900 mL / h, 1000 mL / h. During the spinning process of polylactic acid spinning solution, water vapor in the air, acting as a non-good solvent, exchanges with the good solvent in the polylactic acid spinning solution jet. As the good solvent evaporates and penetrates into the jet, it causes phase separation in the polylactic acid spinning solution jet, forming a solvent-enriched phase and a non-solvent-enriched phase.In this process, due to near-surface contact with air, the solvent evaporates rapidly, and polymer segments quickly accumulate and solidify to form a smooth, non-porous outer layer. Inside, due to the long outward diffusion path, the solvent remains for a longer time, allowing some of the nanopores remaining during the incomplete solidification of the non-porous outer layer to escape. After complete solidification, the nanopores disappear, and the remaining solvent can only form interconnected pathways within the fiber through capillary effects. These pathways remain connected during solidification, and the remaining solvent eventually escapes through the fiber ends. This results in polylactic acid aerogel fibers with an aerogel structure of a smooth, non-porous outer layer and an inner layer with interconnected nanopores. By controlling the spinning process parameters, the structural parameters of the obtained polylactic acid aerogel fibers can be adjusted, such as fiber diameter, tensile strength, fiber collection efficiency, and fiber orientation. Adjusting these parameters is within the capabilities of those skilled in the art.

[0041] In one embodiment, the polylactic acid aerogel fibers obtained in S2 are received onto a first receiving substrate and selectively swollen using a non-good solvent spray. In one embodiment, the distance between the first receiving substrate and the spinning nozzle is 10 to 100 cm. In one embodiment, the distance between the first receiving substrate of the electrospinning process and the spinning nozzle is within the range of the following values ​​or any combination thereof: 10 cm, 11 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, 19 cm, 20 cm, 21 cm, 22 cm, 23 cm, 24 cm, 25 cm, 26 cm, 27 cm, 28 cm, 29 cm, 30 cm, 31 cm, 32 cm, 33 cm, 34 cm, 35 cm, 36 cm, 37 cm, 38 cm, 39 cm, 40 cm, 41 cm, 42 cm, 43 cm, 44 cm, 45 cm, 46 cm, 47 cm, 48 cm, 49 cm, 50 cm, 51 cm, 52 cm, 53 cm, 54 cm, 55 cm, 56 cm, 57 cm, 58 cm, 59 cm, 60 cm, 61 cm, 62 cm, 63 cm. cm, 64 cm, 65 cm, 66 cm, 67 cm, 68 cm, 69 cm, 70 cm, 71 cm, 72 cm, 73 cm, 74 cm, 75 cm, 76 cm, 77 cm, 78 cm, 79 cm, 80 cm, 81 cm, 82 cm, 83 cm, 84 cm, 85 cm, 86 cm, 87 cm, 88 cm, 89 cm, 90 cm, 91 cm, 92 cm, 93 cm, 94 cm, 95 cm, 96 cm, 97 cm, 98 cm, 99 cm, 100 cm. In one embodiment, the non-good solvent is selected from methanol, ethanol, and propanol. In one embodiment, the non-good solvent in step (3) is ethanol. Because the solubility parameters of the non-good solvent (e.g., ethanol δ ≈ 26.5 MPa¹ / ²) and polylactic acid (PLA) are partially matched (δ ≈ 20.5 MPa¹ / ²), and the molecular weight of the non-good solvent is small (e.g., ethanol 46), the non-good solvent preferentially penetrates the amorphous pores of PLA, while the tightly packed molecular chains in the crystalline regions hinder diffusion and only swell without dissolving, thus creating a selective swelling effect. In one embodiment, the spray velocity of the non-good solvent droplets is controlled at 0.1 g / cm³. 3 ·s -1 Up to 10 g / cm 3 ·s -1In one embodiment, the spray rate of the non-good solvent droplets is controlled to be within the range of the following values ​​or any combination thereof: 0.1 g / cm³. ¹、0.2 g / cm³· ¹、0.3 g / cm³· ¹、0.4 g / cm³· ¹、0.5 g / cm³· ¹、0.6 g / cm³· ¹、0.7 g / cm³· ¹、0.8 g / cm³· ¹、0.9 g / cm³· ¹、1.0 g / cm³· ¹、1.1 g / cm³· ¹、1.2 g / cm³· ¹、1.3 g / cm³· ¹、1.4 g / cm³· ¹、1.5 g / cm³· ¹、1.6 g / cm³· ¹、1.7 g / cm³· ¹、1.8 g / cm³· ¹、1.9 g / cm³· ¹、2.0 g / cm³· ¹、2.1 g / cm³· ¹、2.2 g / cm³· ¹、2.3 g / cm³· ¹、2.4 g / cm³· ¹、2.5 g / cm³· ¹、2.6 g / cm³· ¹、2.7 g / cm³· ¹、2.8 g / cm³· ¹、2.9 g / cm³· ¹、3.0 g / cm³· ¹、3.1 g / cm³· ¹、3.2 g / cm³· ¹、3.3 g / cm³· ¹、3.4 g / cm³· ¹、3.5 g / cm³· ¹、3.6 g / cm³· ¹、3.7 g / cm³· ¹、3.8 g / cm³· ¹、3.9 g / cm³· ¹、4.0 g / cm³· ¹、4.1 g / cm³· ¹、4.2 g / cm³· ¹、4.3 g / cm³· ¹、4.4 g / cm³· ¹、4.5 g / cm³· ¹、4.6 g / cm³· ¹、4.7 g / cm³· ¹、4.8 g / cm³· ¹、4.9 g / cm³· ¹、5.0 g / cm³· ¹、5.5 g / cm³· ¹、6.0 g / cm³· ¹、6.5 g / cm³· ¹、7.0 g / cm³· ¹、7.5 g / cm³· ¹、8.0 g / cm³· ¹、8.5 g / cm³· ¹、9.0 g / cm³· ¹、9.5 g / cm³· ¹、10.0 g / cm³· ¹. In one embodiment, the swelling time is controlled between 30 and 120 s. In one embodiment, the swelling time is controlled within the range of the following values ​​or any combination thereof: 30 s, 35 s, 40 s, 45 s, 50 s, 55 s, 60 s, 65 s, 70 s, 71 s, 72 s, 73 s, 74 s, 75 s, 76 s, 77 s, 78 s, 79 s, 80 s, 81 s, 82 s, 83 s, 84 s, 85 s, 86 s, 87 s, 88 s, 89 s, 90 s, 95 s, 100 s, 105 s, 110 s, 115 s, 120 s. Controlling the spraying and swelling time throughout the process can prevent insufficient swelling or adhesion of the polylactic acid aerogel fibers, which could reduce fiber surface roughness or fiber strength.

[0042] In one embodiment, the polylactic acid aerogel fibers, after selective swelling treatment by spraying in step S3, are moved to a second receiving substrate and dried to obtain modified polylactic acid aerogel fibers. During the drying process, the polylactic acid aerogel fibers undergo anisotropic shrinkage, generating compressive stress on the surface, and local areas bulge, thereby forming a rough nanopapillary structure. In one embodiment, the distance between the second receiving substrate and the first receiving substrate in the electrospinning process is 50 to 100 cm. In one embodiment, the distance between the second receiving substrate and the first receiving substrate in electrospinning is within the range of the following point values ​​or any combination of the following point values: 50 cm, 51 cm, 52 cm, 53 cm, 54 cm, 55 cm, 56 cm, 57 cm, 58 cm, 59 cm, 60 cm, 61 cm, 62 cm, 63 cm, 64 cm, 65 cm, 66 cm, 67 cm, 68 cm, 69 cm, 70 cm, 71 cm, 72 cm, 73 cm, 74 cm, 75 cm, 76 cm, 77 cm, 78 cm, 79 cm, 80 cm, 81 cm, 82 cm, 83 cm, 84 cm, 85 cm, 86 cm, 87 cm, 88 cm, 89 cm, 90 cm, 91 cm, 92 cm, 93 cm, 94 cm, 95 cm, 96 cm, 97 cm, 98 cm, 99 cm, 100 cm. In one embodiment, the drying temperature is 40 to 55 °C. In another embodiment, the drying temperature is within the range of the following values ​​or any combination thereof: 40 °C, 41 °C, 42 °C, 43 °C, 44 °C, 45 °C, 46 °C, 47 °C, 48 °C, 49 °C, 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C. In one embodiment, the drying time is 10 to 60 minutes.In one embodiment, the drying time is within the range of the following point values ​​or any combination of the following point values: 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, 40 min, 41 min, 42 min, 43 min, 44 min, 45 min, 46 min, 47 min, 48 min, 49 min, 50 min, 51 min, 52 min, 53 min, 54 min, 55 min, 56 min, 57 min, 58 min, 59 min, 60 min. By controlling the drying temperature and duration, anisotropic shrinkage of polylactic acid aerogel fibers can be achieved, generating compressive stress on the surface and causing localized protrusions, thus forming a rough nanopapillary structure. Inside the smooth layer, since it is not swollen, it retains its smooth structure. Therefore, the structure of the obtained modified polylactic acid aerogel fiber is: an aerogel structure consisting of a smooth, non-porous outer layer with distributed nanopapillary structures and an inner layer with interconnected nanopores.

[0043] To achieve the above objectives, according to a third aspect of the present invention, the use of modified polylactic acid aerogel fibers according to the first aspect of the present invention or modified polylactic acid aerogel fibers that can be prepared according to the second aspect of the present invention in the preparation of filter materials is provided.

[0044] In one embodiment, the filter material is a modified polylactic acid aerogel fiber membrane. In one embodiment, the filter material is used for air purification. In one embodiment, the filter material is used for water purification. In one embodiment, the filter material is used to remove heavy metals and organic pollutants from water.

[0045] The present invention will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention.

[0046] Example 1

[0047] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0048] S1: Polylactic acid (PLA) was dissolved in a mixed solvent of dichloromethane and N,N-dimethylformamide and stirred thoroughly to prepare a homogeneous spinnable solution. The PLA had a molecular weight of 50 kDa, a concentration of 20 wt.%, and a ratio of dichloromethane to N,N-dimethylformamide of 3.5:6.5.

[0049] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 25 °C, ambient humidity 30%, voltage 20 kV, the distance between the first receiving substrate and the spinning nozzle is 50 cm, the distance between the second receiving substrate and the first receiving substrate is 60 cm, and the injection rate is 20 mL / h.

[0050] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 1 g / cm. 3 s -1 The swelling time should be controlled within 60 seconds;

[0051] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 45 °C, and the drying time is 30 min.

[0052] The obtained single, rough nanopapillary structure of polylactic acid aerogel fiber has an aspect ratio of 1500, a diameter of 2000 nm, and a specific surface area of ​​300 m². 2 / g, surface roughness Ra is 120 nm; the average radius of the base of a single papilla is 50 nm, the average height is 5 nm, the average thickness of the superficial smooth and dense fiber skin is 20 nm; the porosity of the inner aerogel porous structure is 75%, the average pore size is 15 nm, the tensile breaking strength of a single polylactic acid aerogel fiber is 1.2 GPa, strain is 7%, and toughness is 35 MJ / m 3 The fiber membrane composed of polylactic acid aerogel fibers has a radius of curvature of 0.8 μm and a tensile breaking strength of 10 MPa. It can withstand 1000 cycles of cyclic buckling at 50% strain without breaking, and the surface roughness Ra is still 120 nm when tested again.

[0053] Example 2

[0054] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0055] S1: Polylactic acid (PLA) was dissolved in chloroform and stirred thoroughly to prepare a homogeneous spinnable solution. The molecular weight of PLA was 75 kDa, and the concentration of PLA was 12 wt.%.

[0056] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 22 °C, ambient humidity 65%, voltage 80 kV, the distance between the first receiving substrate and the spinning nozzle is 70 cm, the distance between the second receiving substrate and the first receiving substrate is 80 cm, and the injection rate is 75 mL / h.

[0057] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 5 g / cm. 3 s -1 The swelling time should be controlled within 100 seconds;

[0058] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 48 °C, and the drying time is 25 min.

[0059] The obtained polylactic acid aerogel fibers with a single rough nanopapillary structure have an aspect ratio of 1700, a diameter of 350 nm, and a specific surface area of ​​270 m². 2 / g, surface roughness Ra is 125 nm; the average radius of the base of a single papilla is 60 nm, the average height is 7 nm, the average thickness of the superficial smooth and dense fiber skin is 13 nm; the porosity of the inner aerogel porous structure is 79%, the average pore size is 15 nm, the tensile breaking strength of a single polylactic acid aerogel fiber is 1 GPa, strain is 5%, and toughness is 25 MJ / m. 3 The fiber membrane composed of polylactic acid aerogel fibers with a radius of curvature of 1 μm has a tensile breaking strength of 6.5 MPa, and can withstand 1000 cycles of cyclic buckling at 50% strain without breaking. Furthermore, the surface roughness Ra is still 125 nm when tested at this time.

[0060] Example 3

[0061] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0062] S1: Polylactic acid (PLA) was dissolved in tetrahydrofuran and stirred thoroughly to prepare a homogeneous spinnable solution. The molecular weight of PLA was 51 kDa, and the concentration of PLA was 50 wt.%.

[0063] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 40 °C, ambient humidity 78%, voltage 95 kV, the distance between the first receiving substrate and the spinning nozzle is 100 cm, the distance between the second receiving substrate and the first receiving substrate is 100 cm, and the injection rate is 50 mL / h.

[0064] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 7 g / cm. 3 s -1 The swelling time is controlled at 110 seconds;

[0065] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 52 °C, and the drying time is 38 min.

[0066] The obtained single-strand coarse nanopapillary structure of polylactic acid aerogel fiber has an aspect ratio of 1200, a diameter of 3000 nm, and a specific surface area of ​​320 m². 2 / g, surface roughness Ra is 114 nm; the average radius of the base of a single papilla is 102 nm, the average height is 10 nm, and the average thickness of the shallow, smooth, dense fiber skin is 50 nm; the porosity of the inner aerogel porous structure is 88%, the average pore size is 19 nm, and the tensile breaking strength of a single polylactic acid aerogel fiber is 1.8 GPa, strain is 6.8%, and toughness is 38 MJ / m. 3 The fiber membrane composed of polylactic acid aerogel fibers has a radius of curvature of 0.75 μm and a tensile breaking strength of 5.5 MPa. It can withstand 1000 cycles of cyclic buckling at 50% strain without breaking, and the surface roughness Ra is still 114 nm when tested again.

[0067] Example 4

[0068] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0069] S1: Polylactic acid (PLA) was dissolved in hexafluoroisopropanol and stirred thoroughly to prepare a homogeneous spinnable solution. The molecular weight of PLA was 86 kDa, and the concentration of PLA was 33 wt.%.

[0070] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 30 °C, ambient humidity 48%, voltage 25 kV, the distance between the first receiving substrate and the spinning nozzle is 70 cm, the distance between the second receiving substrate and the first receiving substrate is 75 cm, and the injection rate is 62 mL / h.

[0071] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 10 g / cm. 3 s -1 The swelling time should be controlled within 70 seconds;

[0072] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 42 °C, and the drying time is 55 min.

[0073] The obtained single, rough nanopapillary structure of polylactic acid aerogel fiber has an aspect ratio of 1100, a diameter of 4500 nm, and a specific surface area of ​​550 m². 2 / g, surface roughness Ra is 134 nm; the average radius of the base of a single papilla is 152 nm, the average height is 17 nm, the average thickness of the shallow, smooth, dense fiber skin is 30 nm; the porosity of the inner aerogel porous structure is 79%, the average pore size is 15 nm, the tensile breaking strength of a single polylactic acid aerogel fiber is 2 GPa, the strain is 6.5%, and the toughness is 42 MJ / m. 3 The fiber membrane composed of polylactic acid aerogel fibers has a radius of curvature of 0.9 μm and a tensile breaking strength of 6.2 MPa. It does not break after 1000 cycles of cyclic buckling at 50% strain, and the surface roughness Ra is still 134 nm when tested again.

[0074] Example 5

[0075] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0076] S1: Polylactic acid (PLA) was dissolved in acetone and stirred thoroughly to prepare a homogeneous spinnable solution. The molecular weight of PLA was 63 kDa, and the concentration of PLA was 21 wt.%.

[0077] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 38 °C, ambient humidity 56%, voltage 39 kV, the distance between the first receiving substrate and the spinning nozzle is 61 cm, the distance between the second receiving substrate and the first receiving substrate is 85 cm, and the injection rate is 76 mL / h.

[0078] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 1.8 g / cm. 3 s -1 The swelling time should be controlled within 60 seconds;

[0079] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 48 °C, and the drying time is 57 min.

[0080] The obtained single-strand coarse nanopapillary structure of polylactic acid aerogel fiber has an aspect ratio of 1340, a diameter of 3400 nm, and a specific surface area of ​​650 m².2 / g, surface roughness Ra is 124 nm; the average radius of the base of a single papilla is 112 nm, the average height is 12 nm, and the average thickness of the shallow, smooth, dense fiber skin is 41 nm; the porosity of the inner aerogel porous structure is 50%, the average pore size is 15 nm, and the tensile breaking strength of a single polylactic acid aerogel fiber is 2.8 GPa, strain is 5.5%, and toughness is 57 MJ / m. 3 The fiber membrane composed of polylactic acid aerogel fibers has a radius of curvature of 0.6 μm and a tensile breaking strength of 5.4 MPa. It can withstand 1000 cycles of cyclic buckling at 50% strain without breaking, and the surface roughness Ra is still 124 nm when tested again.

[0081] Example 6

[0082] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0083] S1: Polylactic acid (PLA) was dissolved in dimethyl sulfoxide and stirred thoroughly to prepare a homogeneous spinnable solution. The molecular weight of PLA was 88 kDa, and the concentration of PLA was 12 wt.%.

[0084] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 32 °C, ambient humidity 66%, voltage 43 kV, the distance between the first receiving substrate and the spinning nozzle is 74 cm, the distance between the second receiving substrate and the first receiving substrate is 91 cm, and the injection rate is 83 mL / h.

[0085] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 2.5 g / cm. 3 s -1 The swelling time is controlled at 72 seconds;

[0086] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 51 °C, and the drying time is 60 min.

[0087] The obtained polylactic acid aerogel fiber with a single rough nanopapillary structure has an aspect ratio of 1240, a diameter of 4800 nm, and a specific surface area of ​​720 m². 2 / g, surface roughness Ra is 131 nm; the average radius of the base of a single papilla is 122 nm, the average height is 14 nm, the average thickness of the shallow, smooth, dense fiber skin is 34 nm; the porosity of the inner aerogel porous structure is 62%, the average pore size is 18 nm, the tensile breaking strength of a single polylactic acid aerogel fiber is 1.2 GPa, the strain is 6.5%, and the toughness is 28 MJ / m. 3 The fiber membrane composed of polylactic acid aerogel fibers with a radius of curvature of 0.5 μm has a tensile breaking strength of 7.4 MPa, and can withstand 1000 cycles of cyclic buckling at 50% strain without breaking. Furthermore, the surface roughness Ra is still 131 nm when tested at this time.

[0088] Example 7

[0089] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0090] S1: Polylactic acid (PLA) was dissolved in N,N-dimethylformamide and stirred thoroughly to prepare a homogeneous spinnable solution. The molecular weight of PLA was 91 kDa, and the concentration of PLA was 5 wt.%.

[0091] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 22 °C, ambient humidity 71%, voltage 56 kV, the distance between the first receiving substrate and the spinning nozzle is 84 cm, the distance between the second receiving substrate and the first receiving substrate is 51 cm, and the injection rate is 63 mL / h.

[0092] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 3.8 g / cm. 3 s -1 The swelling time is controlled at 83 seconds;

[0093] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 49 °C, and the drying time is 48 min.

[0094] The obtained polylactic acid aerogel fibers with a single rough nanopapillary structure have an aspect ratio of 1660, a diameter of 1400 nm, and a specific surface area of ​​804 m². 2 / g, surface roughness Ra is 121 nm; the average radius of the base of a single papilla is 102 nm, the average height is 11 nm, the average thickness of the shallow, smooth, dense fiber skin is 27 nm; the porosity of the inner aerogel porous structure is 72%, the average pore size is 15 nm, the tensile breaking strength of a single polylactic acid aerogel fiber is 2.6 GPa, the strain is 7.2%, and the toughness is 38 MJ / m. 3 The fiber membrane composed of polylactic acid aerogel fibers has a radius of curvature of 0.7 μm and a tensile breaking strength of 10.4 MPa. It does not break after 1000 cycles of cyclic buckling at 50% strain, and the surface roughness Ra is still 121 nm when tested again.

[0095] Example 8

[0096] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0097] S1: Polylactic acid (PLA) was dissolved in a mixed solvent of dichloromethane and N,N-dimethylformamide and stirred thoroughly to prepare a homogeneous spinnable solution. The molecular weight of PLA was 51 kDa, the concentration of PLA was 24 wt.%, and the ratio of dichloromethane to N,N-dimethylformamide was 5:5.

[0098] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 28 °C, ambient humidity 65%, voltage 60 kV, the distance between the first receiving substrate and the spinning nozzle is 80 cm, the distance between the second receiving substrate and the first receiving substrate is 80 cm, and the injection rate is 35 mL / h.

[0099] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 4.5 g / cm. 3 s -1 The swelling time should be controlled within 75 seconds;

[0100] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 45 °C, and the drying time is 50 min.

[0101] The obtained single, rough nanopapillary structure of polylactic acid aerogel fiber has an aspect ratio of 1700, a diameter of 500 nm, and a specific surface area of ​​810 m². 2 / g, surface roughness Ra is 131 nm; the average radius of the base of a single papilla is 52 nm, the average height is 8 nm, the average thickness of the superficial smooth and dense fiber skin is 12 nm; the porosity of the inner aerogel porous structure is 85%, the average pore size is 17 nm, the tensile breaking strength of a single polylactic acid aerogel fiber is 3.3 GPa, strain is 7%, and toughness is 66 MJ / m 3 The fiber membrane composed of polylactic acid aerogel fibers has a radius of curvature of 0.7 μm and a tensile breaking strength of 7.4 MPa. It does not break after 1000 cycles of cyclic buckling at 50% strain, and the surface roughness Ra is still 131 nm when tested again.

[0102] Example 9

[0103] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0104] S1: Polylactic acid (PLA) was dissolved in a mixed solvent of dichloromethane and N,N-dimethylformamide and stirred thoroughly to prepare a homogeneous spinnable solution. The PLA had a molecular weight of 60 kDa, a concentration of 18 wt.%, and a ratio of dichloromethane to N,N-dimethylformamide of 3:7.

[0105] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 10 °C, ambient humidity 80%, voltage 100 kV, the distance between the first receiving substrate and the spinning nozzle is 100 cm, the distance between the second receiving substrate and the first receiving substrate is 100 cm, and the injection rate is 100 mL / h.

[0106] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 1 g / cm. 3 s -1 The swelling time should be controlled within 120 seconds;

[0107] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 55 °C, and the drying time is 10 min.

[0108] The obtained single, rough nanopapillary structure of polylactic acid aerogel fiber has an aspect ratio of 1200, a diameter of 100 nm, and a specific surface area of ​​1000 m². 2 / g, surface roughness Ra is 150 nm; the average radius of the base of a single papilla is 50 nm, the average height is 5 nm, and the average thickness of the superficial smooth and dense fiber skin is 5 nm; the porosity of the inner aerogel porous structure is 99%, the average pore size is 5 nm, and the tensile breaking strength of a single polylactic acid aerogel fiber is 1.1 GPa, strain is 5.4%, and toughness is 26 MJ / m. 3 The fiber membrane composed of polylactic acid aerogel fibers has a curvature radius of 0.1 μm and a tensile breaking strength of 5 MPa. It can withstand 1000 cycles of cyclic buckling at 50% strain without breaking, and the surface roughness Ra is still 150 nm when tested again.

[0109] Example 10

[0110] The modified polylactic acid aerogel fiber of this embodiment was prepared by the following steps:

[0111] S1: Polylactic acid (PLA) was dissolved in dichloromethane and stirred thoroughly to prepare a homogeneous spinnable solution. The PLA had a molecular weight of 100 kDa and a concentration of 5 wt.%.

[0112] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 40 °C, ambient humidity 30%, voltage 5 kV, the distance between the first receiving substrate and the spinning nozzle is 50 cm, the distance between the second receiving substrate and the first receiving substrate is 50 cm, and the injection rate is 1 mL / h.

[0113] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 0.1 g / cm. 3 s -1 The swelling time should be controlled within 30 seconds;

[0114] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 40 °C, and the drying time is 10 min.

[0115] The obtained single, rough nanopapillary structure of polylactic acid aerogel fiber has an aspect ratio of 1000, a diameter of 5000 nm, and a specific surface area of ​​200 m². 2 / g, surface roughness Ra is 100 nm; the average radius of the base of a single papilla is 150 nm, the average height is 15 nm, the average thickness of the superficial smooth and dense fiber skin is 50 nm; the porosity of the inner aerogel porous structure is 80%, the average pore size is 20 nm, the tensile breaking strength of a single polylactic acid aerogel fiber is 1.9 GPa, strain is 7%, and toughness is 32 MJ / m3 The fiber membrane composed of polylactic acid aerogel fibers has a radius of curvature of 0.8 μm and a tensile breaking strength of 7 MPa. It can withstand 1000 cycles of cyclic buckling at 50% strain without breaking, and the surface roughness Ra is still 100 nm when tested again.

[0116] Example 11

[0117] The steps for preparing polylactic acid aerogel fibers with a rough nanopapillary structure in this embodiment are as follows:

[0118] S1: Polylactic acid (PLA) was dissolved in chloroform and stirred thoroughly to prepare a homogeneous spinnable solution. The molecular weight of PLA was 60 kDa, and the concentration of PLA was 15 wt.%.

[0119] S2: Electrospin the spinning solution obtained in S1. The relevant process parameters are: ambient temperature 22 °C, ambient humidity 55%, voltage 70 kV, the distance between the first receiving substrate and the spinning nozzle is 60 cm, the distance between the second receiving substrate and the first receiving substrate is 70 cm, and the injection rate is 65 mL / h.

[0120] S3: The polylactic acid aerogel fiber membrane obtained from spinning is received onto the first receiving substrate and subjected to ethanol droplet spraying treatment. The spraying speed is controlled at 3 g / cm. 3 ·s -1 The swelling time should be controlled within 90 seconds;

[0121] S4: The polylactic acid aerogel fiber membrane, after selective swelling treatment by spraying, is moved to the second receiving substrate for drying. The drying temperature is 45 °C, and the drying time is 25 min.

[0122] The obtained single-strand coarse nanopapillary structure of polylactic acid aerogel fiber has an aspect ratio of 1800, a diameter of 450 nm, and a specific surface area of ​​280 m². 2 / g, surface roughness Ra is 125 nm; the average radius of the base of a single papilla is 55 nm, the average height is 6 nm, the average thickness of the superficial smooth and dense fiber skin is 10 nm; the porosity of the inner aerogel porous structure is 76%, the average pore size is 15 nm, the tensile breaking strength of a single polylactic acid aerogel fiber is 1.1 GPa, strain is 3%, and toughness is 30 MJ / m 3 The fiber membrane composed of polylactic acid aerogel fibers has a radius of curvature of 0.9 μm and a tensile breaking strength of 7 MPa. It can withstand 1000 cycles of cyclic buckling at 50% strain without breaking, and the roughness is still 125 nm when tested again.

[0123] Comparative Example 1

[0124] The existing techniques for preparing modified polylactic acid aerogel fiber membranes by loading nanoparticles are as follows:

[0125] Step 1: Dissolve polylactic acid (PLA) in dichloromethane and stir thoroughly to prepare a homogeneous spinnable solution. The PLA has a molecular weight of 80 kDa and a concentration of 12 wt.%.

[0126] Step 2: Electrospin the spinning solution obtained in Step 1. The relevant process parameters are: ambient temperature 30 °C, ambient humidity 50%, voltage 10 kV, distance between the receiving substrate and the spinning nozzle 50 cm, and injection rate 1 mL / h.

[0127] Step 3: Immerse the polylactic acid aerogel fiber membrane in a 2 wt.% aqueous solution of titanium dioxide nanoparticles for 30 min, wherein the particle size of a single titanium dioxide nanoparticle is 40 nm.

[0128] Step 4: Dry the impregnated modified polylactic acid aerogel fiber membrane. The drying temperature is 40 °C, and the drying time is 10 min.

[0129] The resulting polylactic acid aerogel fibers have an aspect ratio of 1300, a diameter of 800 nm, and a specific surface area of ​​350 m². 2 The tensile breaking strength of a single polylactic acid aerogel fiber is 0.8 GPa, strain is 4.5%, and toughness is 18 MJ / m. 3 The fiber membrane, composed of polylactic acid aerogel fibers with a radius of curvature of 1.5 μm, has a tensile breaking strength of 1.5 MPa and breaks after 300 cycles of cyclic buckling at 50% strain.

[0130] Comparative Example 2

[0131] The existing technology for preparing modified polylactic acid fiber membranes by loading nanoparticles involves the following steps:

[0132] Step 1: Dissolve polylactic acid (PLA) in dichloromethane and stir thoroughly to prepare a homogeneous spinnable solution. The PLA has a molecular weight of 70 kDa and a concentration of 10 wt.%.

[0133] Step 2: Electrospin the spinning solution obtained in Step 1. The relevant process parameters are: ambient temperature 30 °C, ambient humidity 52%, voltage 15 kV, distance between the receiving substrate and the spinning nozzle 45 cm, and injection rate 2 mL / h.

[0134] Step 3: Immerse the polylactic acid aerogel fiber membrane in a 2.5 wt.% aqueous solution of titanium dioxide nanoparticles for 40 min, wherein the particle size of a single titanium dioxide nanoparticle is 35 nm.

[0135] Step 4: Dry the impregnated modified polylactic acid aerogel fiber membrane. The drying temperature is 45 °C, and the drying time is 20 min.

[0136] The resulting polylactic acid aerogel fibers have an aspect ratio of 1500, a diameter of 800 nm, a roughness Ra of 150 nm, and a specific surface area of ​​370 m². 2 The tensile breaking strength of a single polylactic acid aerogel fiber is 0.75 GPa, strain is 4.5%, and toughness is 15 MJ / m. 3 The fiber membrane, composed of polylactic acid aerogel fibers with a radius of curvature of 1.5 μm, exhibited a tensile breaking strength of 1.2 MPa and fractured after 300 cyclic buckling cycles at 50% strain. The post-fracture roughness was measured to be Ra 32 nm.

[0137] Comparative Example 3

[0138] The existing technique for preparing modified polylactic acid aerogel fiber membranes by etching involves the following steps:

[0139] Step 1: Dissolve polylactic acid (PLA) in dichloromethane and stir thoroughly to prepare a homogeneous spinnable solution. The PLA has a molecular weight of 80 kDa and a concentration of 12 wt.%.

[0140] Step 2: Electrospin the spinning solution obtained in Step 1. The relevant process parameters are: ambient temperature 30 °C, ambient humidity 50%, voltage 10 kV, distance between the receiving substrate and the spinning nozzle 50 cm, and injection rate 1 mL / h.

[0141] Step 3: The polylactic acid aerogel fiber membrane is immersed in an aqueous sodium hydroxide solution for chemical etching at a concentration of 3 mol / L, a temperature of 50 °C, and a time of 1 h.

[0142] Step 4: Dry the chemically etched modified polylactic acid aerogel fiber membrane. The drying temperature is 60 °C, and the drying time is 120 min.

[0143] The resulting polylactic acid aerogel fibers have an aspect ratio of 1300, a diameter of 800 nm, and a specific surface area of ​​450 m². 2 The tensile breaking strength of a single polylactic acid aerogel fiber is 0.65 GPa, strain is 3.7%, and toughness is 13.5 MJ / m. 3 The fiber membrane, composed of polylactic acid aerogel fibers with a radius of curvature of 2.1 μm, has a tensile breaking strength of 0.9 MPa and breaks after 150 cycles of cyclic buckling at 50% strain.

[0144] The results of the above examples and comparative examples demonstrate that the improved modified polylactic acid aerogel fiber and the fiber membrane prepared therefrom of the present invention not only possess a large specific surface area but also exhibit excellent mechanical properties. On the one hand, it prevents the degradation of the specific surface area of ​​traditional load-modified polylactic acid aerogel fibers over time; on the other hand, it prevents stress concentration-induced structural damage in traditional etch-modified polylactic acid aerogel fibers. Furthermore, the preparation method of the present invention has no special requirements for raw materials and equipment and can be carried out on mass production equipment.

Claims

1. A modified polylactic acid aerogel fiber, wherein the modified polylactic acid aerogel fiber has a bilayer structure, characterized in that: The outer layer of the bilayer structure is a non-porous outer layer with nanopapillary structures distributed on its smooth outer surface. The thickness of the matrix of the non-porous outer layer at the locations where the nanopapillary structures are not distributed is 5 nm to 50 nm; the bottom radius of the nanopapillary structures is 50 nm to 200 nm; and the height of the nanopapillary structures is 5 nm to 20 nm. The inner layer of the double-layer structure is an aerogel porous structure layer with a porosity of 50% to 99% and an average pore size of 1 nm to 25 nm. The outer layer and the inner layer are an integral structure.

2. The modified polylactic acid aerogel fiber according to claim 1, characterized in that: The specific surface area of ​​the non-porous outer layer is 200 to 1000 m². 2 / g, with a surface roughness Ra of 100 nm to 200 nm.

3. The modified polylactic acid aerogel fiber according to claim 1, characterized in that: The tensile breaking strength of a single polylactic acid aerogel fiber is 1 GPa to 4 GPa, the strain is 5% to 8%, and the toughness is 25 MJ / m. 3 Up to 70 MJ / m 3 The radius of curvature is 0.1 μm to 1 μm; The polylactic acid aerogel fiber has an aspect ratio of 1000 to 2000 and a diameter of 100 to 5000 nm.

4. A method for preparing modified polylactic acid aerogel fibers according to any one of claims 1 to 3, characterized in that... Includes the following steps: S1: Prepare a homogeneous spinnable solution by uniformly dissolving polylactic acid in a good solvent for polylactic acid; S2: Electrospin the homogeneous spinnable solution obtained in S1 to obtain polylactic acid aerogel fiber. S3: The polylactic acid aerogel fiber obtained in S2 is received onto the first receiving substrate and selectively swollen by spraying the polylactic acid aerogel fiber with a non-good solvent. S4: Move the polylactic acid aerogel fibers that have undergone the selective swelling treatment by spraying in S3 to the second receiving substrate and dry them to obtain the modified polylactic acid aerogel fibers.

5. The method according to claim 4, characterized in that: In step (1), the polylactic acid has a molecular weight of 50 kDa to 100 kDa and a concentration of 5 to 50 wt%. In step (1), the good solvent for polylactic acid is selected from dichloromethane (DCM) and chloroform (CHC). The solvent is selected from one or more of the following: tetrahydrofuran (THF), hexafluoroisopropanol, acetone, dimethyl sulfoxide, and N,N-dimethylformamide (DMF), preferably a mixture of dichloromethane and N,N-dimethylformamide, a mixture of dichloromethane and acetone, a mixture of dichloromethane and methanol, a mixture of chloroform and ethanol, preferably a mixture of dichloromethane and N,N-dimethylformamide in a ratio of 3:7 to 5:5, and more preferably a mixture of dichloromethane and N,N-dimethylformamide in a ratio of 3.5:6.

5.

6. The method according to claim 4, characterized in that: The electrospinning in step (2) is carried out under the following conditions: ambient temperature of 10 to 40 °C and ambient humidity of 30 to 80%. The electrospinning operation parameters in step (2) are: voltage 5 to 100 kV, distance between the first receiving substrate and the spinning nozzle 10 to 100 cm, distance between the second receiving substrate and the first receiving substrate 50 to 100 cm, and injection speed 1 to 1000 mL / h. In step (2), the structure of the obtained polylactic acid aerogel fiber is: an aerogel structure with a smooth, non-porous outer layer and an inner layer with nano-connected pores.

7. The method according to claim 4, characterized in that: The non-good solvent mentioned in step (3) is selected from methanol, ethanol, and propanol, preferably ethanol; the spraying speed of the non-good solvent droplets is controlled at 0.1 g / cm. 3 ·s -1 Up to 10 g / cm 3 ·s -1 The swelling time is controlled between 30 and 120 seconds.

8. The polylactic acid aerogel fiber according to claim 1, characterized in that: The drying temperature in step (4) is 40 to 55 °C, and the drying time is 10 to 60 min; The modified polylactic acid aerogel fiber described in step (4) has the following structure: an aerogel structure consisting of a smooth, non-porous outer layer with distributed nanopapillary structures and an inner layer with nano-connecting pores.

9. Use of the modified polylactic acid aerogel fiber according to any one of claims 1 to 3 or the modified polylactic acid aerogel fiber that can be prepared by the method according to any one of claims 4 to 8 in the preparation of filter materials.

10. The use according to claim 9, wherein, The filter material is used for air purification or water purification, especially for removing heavy metals and organic pollutants from water.

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