High-strength PLA / PBS nanofiber aerogel and preparation method thereof

Abstract

The application provides a high-strength PLA / PBS nanofiber aerogel and a preparation method thereof, and belongs to the technical field of aerogels, and aims to solve the technical problems of a long preparation period and poor mechanical properties of nanofiber aerogels.The application comprises the following steps: uniformly mixing plasticized polyvinyl alcohol and poly(lactic acid)-poly(butylene succinate); performing melt blending extrusion on the extruded blended strips, stretching the extruded blended strips, and cutting the extruded blended strips into particles to obtain PVA / PLA / PBS blended particles; placing the blended particles into a mold and performing hot pressing to obtain a PVA / PLA / PBS composite material; immersing the composite material in a hot water bath to remove the PVA, and performing freeze-drying after taking out the composite material to obtain a PLA / PBS nanofiber aerogel.The application greatly shortens the preparation period of the nanofiber aerogel, and the prepared PLA / PBS nanofiber aerogel has the advantages of excellent mechanical properties, good biocompatibility, biodegradability and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of aerogels, and particularly relates to a high-strength PLA / PBS nanofiber aerogel and its preparation method. Background Technology

[0002] Aerogels are lightweight three-dimensional solid materials in which the solvent is replaced by air while the pores and network remain unchanged. Various aerogels have been prepared, such as SiO2 aerogels, cellulose aerogels, and carbon aerogels. Due to their low density, high porosity, and large specific surface area, aerogels exhibit excellent optical, thermal, and electrical properties, and have wide applications in filtration, adsorption, and energy fields.

[0003] As a novel type of lightweight functional material, fibrous aerogel materials possess the characteristics of traditional inorganic particle aerogels while also exhibiting the unique advantages of fibrous structures, such as good mechanical flexibility, high pore connectivity, controllable structure, high media transport efficiency, and wide adaptability to raw materials. Due to the higher molecular weight and chain length of polymers, polymer nanofiber aerogels exhibit significantly greater flexibility compared to inorganic fiber aerogels.

[0004] Nanofiber aerogels are typically prepared by dispersing nanofibers in a solvent using ultrasonic or mechanical pulverization methods, followed by freeze-setting and drying. Although the types of nanofibers and preparation processes differ, the preparation parameters and properties of nanofiber aerogels are largely similar. In recent years, many researchers have successfully prepared various polymer nanofiber aerogels, which have broad application prospects in fields such as construction and aerospace. However, nanofiber aerogels suffer from low strength and poor toughness, significantly limiting their application range.

[0005] Polylactic acid (PLA) is a highly promising bio-based, biodegradable, and green polymer material with advantages such as good biocompatibility, good biodegradability, high mechanical strength, and high modulus. It holds promise for widely replacing traditional petroleum-based polymer materials in many fields. In recent years, with the increasing severity of global water pollution, the application of PLA nanofiber aerogels in biological, filtration, and oil-water separation fields has attracted considerable attention from scholars.

[0006] Nanofiber aerogels are typically assembled from nanofibers using a bottom-up strategy. For example, patent publication CN111135771A describes shearing and dispersing nanofibers to obtain a nanofiber dispersion, which is then freeze-dried to produce a nanofiber aerogel. Therefore, nanofiber preparation is a crucial step in nanofiber aerogel production. Techniques for nanofiber preparation mainly include spinning, phase separation, white assembly, and template polymerization. Among these, spinning is considered the most promising method for large-scale preparation of continuous polymer nanofibers, including electrospinning, meltblowing, bicomponent composite spinning, and flash evaporation. Electrospinning is currently the most commonly used method for preparing poly(lactic acid) nanofibers. Numerous reports have documented the use of electrospinning to prepare polylactic acid nanofibers; however, the solvents used in electrospinning are generally toxic, such as chloroform, dichloromethane, and N,N-dimethylformamide. Because these solvents evaporate during fiber preparation, they inevitably cause environmental pollution. While melt electrospinning is not limited by solvents, the high viscosity of molten polymers makes it difficult to obtain fibers with diameters smaller than 500 nm. In addition, due to the significant impact of process and environmental factors on electrospinning, the electrospinning operation is complex, has poor repeatability, and produces nanofibers with high costs.

[0007] In addition, Pan Wei's group has prepared polymer nanofibers using a melt extrusion-water-soluble exfoliation method, as illustrated in patent publications CN103147159A and CN103243563A. The basic principle is as follows: polyvinyl alcohol (PVA) is fully melt-blended with other thermodynamically incompatible polymers in a twin-screw melt extruder, extruded, and stretched. PVA forms a continuous phase, while the other component forms a dispersed phase. Under the combined action of a stretching flow field and a shear flow field, the dispersed phase forms microfibers with a specific aspect ratio. The dispersed phase nanofibers are then obtained by dissolving and removing the PVA. Compared to other methods for preparing polymer nanofibers, the biggest advantage of this method is its simplicity in equipment and process; conventional polymer melt processing equipment can be used to manufacture nanofibers, thus reducing investment costs. However, the bottom-up strategy used in the above-mentioned nanofiber aerosolization process requires the prior preparation of nanofiber adhesive, resulting in a long cycle time. Furthermore, the lack of inter-fiber bonding during nanofiber aerosolization leads to poor mechanical properties. Summary of the Invention

[0008] To address the technical problems of long preparation cycle and poor mechanical properties of nanofiber aerogels, this invention proposes a high-strength PLA / PBS nanofiber aerogel and its preparation method. This invention significantly shortens the preparation cycle of nanofiber aerogels, and the prepared PLA / PBS nanofiber aerogels have advantages such as excellent mechanical properties, good biocompatibility, and biodegradability.

[0009] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0010] A method for preparing a high-strength PLA / PBS nanofiber aerogel includes the following steps (in parts by weight):

[0011] (1) Add 50-70 parts of polyvinyl alcohol (PVA) and 30-50 parts of glycerol to a high-speed mixer, control the mixing temperature at 50℃-70℃, and mix evenly; melt blend and granulate at 150℃-180℃ using a twin-screw extruder to obtain plasticized polyvinyl alcohol granules.

[0012] (2) Add 70-80 parts of plasticized polyvinyl alcohol, 15-25 parts of polylactic acid and 5-10 parts of polybutylene succinate obtained in step (1) into a high-speed mixer, control the mixing temperature at 50℃-70℃, and mix evenly; melt-blend and extrude at 180℃-200℃ using a twin-screw extruder, and simultaneously stretch 8-12 times through a traction device, and then cut the stretched blend strip into pellets to obtain PVA / PLA / PBS blend pellets.

[0013] (3) Place the PVA / PLA / PBS blended granules obtained in step (2) into a mold, and hot press them in a flat vulcanizing bed for 10-20 minutes at a molding temperature of 140-155℃ and a pressure of 10-20MPa to obtain sheet-like PVA / PLA / PBS composite material.

[0014] 4) Place the sheet-like PVA / PLA / PBS composite material obtained in step (3) in water at 40℃-60℃ for 90-240 minutes to remove PVA. After taking it out, freeze it at -18℃ and freeze-dry it to obtain PLA / PBS nanofiber aerogel.

[0015] The beneficial effects of this invention are:

[0016] (1) This invention first uses PLA, PBS, and plasticized polyvinyl alcohol as raw materials to prepare a composite material with PVA as the matrix and PLA and PBS as the dispersed phases through twin-screw extrusion and stretching. Since PVA, PLA, and PBS are incompatible, PLA and PBS form in-situ microfibers in the PVA matrix due to shearing and stretching effects applied by the continuous phase during the process. Then, the PVA / PLA / PBS composite material is pressed at 140-155℃. This temperature is higher than the melting point of plasticized PVA and PBS but lower than the melting point of PLA. Therefore, during the molding process... PVA and PBS melt while PLA does not, with the non-melting PLA maintaining its micro / nanofiber structure. The molded PVA / PLA / PBS composite material is then placed in water to dissolve the PVA. The PVA-freezed PLA / PBS is then freeze-dried to form a PLA / PBS aerogel. In the aerogel, PLA maintains its nanofiber structure, while PBS no longer retains its nanofiber structure but instead acts as a bonding point between PLA nanofibers. This is equivalent to "welding" adjacent nanofibers together, transforming the originally physically stacked polymer nanofibers into a unified three-dimensional cross-linked network structure. This three-dimensional cross-linked network structure effectively enhances the physical and mechanical properties of the polymer nanofiber aerogel.

[0017] (2) The aerogel of this invention is prepared by melt processing combined with freeze drying to produce PLA / PBS nanofiber aerogel. Compared with other methods for preparing polymer nanofiber aerogels, this method can use conventional industrial polymer melt processing equipment to manufacture nanofiber aerogels, thereby reducing investment costs. No related reports have been found domestically or internationally. The preparation method has the advantages of continuous production, high yield, low cost, and simplicity. It can provide a simple and economical process route for the future large-scale production of polymer nanofiber aerogels.

[0018] (3) This invention uses polyvinyl alcohol, polybutylene succinate, and polylactic acid as raw materials. Polyvinyl alcohol, polybutylene succinate, and polylactic acid all have good biocompatibility and biodegradability, and there is no chemical cross-linking during the preparation of the aerogel, which meets the requirements of economy and environmental protection. The prepared composite aerogel has broad application prospects in thermal insulation materials, energy-saving materials, sound insulation materials, adsorbents, etc. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the preparation process of the PLA / PBS aerogel described in this patent.

[0021] Figure 2 This is a scanning electron microscope image of the nanofiber aerogel obtained in Example 1.

[0022] Figure 3 for Figure 2 Scanning electron microscope image of a partially magnified nanofiber aerogel.

[0023] Figure 4 These are stress-strain curves of Example 1 and Comparative Example 1. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The polyvinyl alcohol used in the following examples is selected from PVA1799; the polylactic acid and polybutylene succinate used are conventional melt spinning particles.

[0026] Example 1

[0027] A method for preparing high-strength PLA / PBS nanofiber aerogel, the preparation route is as follows: Figure 1 As shown, PLA, PBS, and plasticized PVA are extruded, stretched, and pelletized using a twin-screw extruder. PLA and PBS form in-situ microfibers within the PVA matrix. The PVA / PLA / PBS particles are then bed-pressed to form a composite material at a temperature below the melting point of PLA, allowing PLA to maintain its micro / nanofiber structure. The resulting PVA / PLA / PBS composite is then dissolved in water to remove the PVA. The PVA-freezed PLA / PBS is then freeze-dried to form a PLA / PBS aerogel. Within the aerogel, PLA maintains its nanofiber structure, while PBS acts as a bonding point for the PLA nanofibers. Simultaneously... Figure 1 The physical image also shows that the PLA / PBS aerogel prepared in this patent is soft and flexible.

[0028] The specific steps include: Adding 500g of polyvinyl alcohol and 500g of glycerol to a high-speed mixer, controlling the mixing temperature at 70℃, and mixing evenly; then melt-blending and granulating at 160℃ using a twin-screw extruder to obtain plasticized polyvinyl alcohol granules. The melting point of the plasticized polyvinyl alcohol is 119℃. Adding 700g of plasticized polyvinyl alcohol, 200g of polylactic acid, and 100g of polybutylene succinate to a high-speed mixer, controlling the mixing temperature at 70℃, and mixing evenly; then melt-blending and extruding at 180℃ using a twin-screw extruder, while simultaneously stretching the blend by 10 times using a traction device, and then granulating the stretched blend strips. Placing the PVA / PLA / PBS blend granules into a mold, and hot-pressing in a flat vulcanizing bed for 10 minutes at a molding temperature of 155℃ and a pressure of 10MPa, to obtain sheet-like PVA / PLA / PBS composite materials. The obtained sheet-like PVA / PLA / PBS composite material was placed in water at 60℃ for 240 minutes to remove PVA. After removal, it was frozen at -18℃ and freeze-dried to obtain PLA / PBS nanofiber aerogel.

[0029] The scanning electron microscope (SEM) image of the nanofiber aerogel prepared in this embodiment is shown below. Figure 2 As shown, from Figure 2 As can be seen, the aerogel exhibits a porous structure with a three-dimensional network. Figure 3 for Figure 2 A magnified scanning electron microscope image of nanofiber aerogel in region A of the image. Figure 3 As can be seen, the aerogel sheets are formed by PLA nanofibers bonding together. Furthermore, the nanofiber aerogel has a tensile strength of 15.8 MPa and an elongation at break of 121%.

[0030] Comparative Example 1

[0031] 500g of polyvinyl alcohol (PVA) and 500g of glycerol (GGE) were added to a high-speed mixer, and the mixing temperature was controlled at 70℃ until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder at 160℃ to obtain plasticized PVA granules. The melting point of the plasticized PVA was 119℃. 700g of plasticized PVA and 300g of polylactic acid (PLA) were added to a high-speed mixer, and the mixing temperature was controlled at 70℃ until homogeneous. The mixture was then melt-blended and extruded using a twin-screw extruder at 180℃, while simultaneously stretching the blend by 10 times using a traction device. The stretched blend was then granulated. The PVA / PLA / PBS blend granules were placed in a mold and hot-pressed in a flat vulcanizing bed at a molding temperature of 155℃ and a pressure of 10MPa for 10 minutes to obtain sheet-like PVA / PLA composite material. The obtained sheet-like PVA / PLA composite material was placed in water at 60℃ for 240 minutes to remove PVA. After removal, it was freeze-formed at -18℃ and freeze-dried to obtain PLA nanofiber aerogel.

[0032] This aerogel has a tensile strength of 5.3 MPa and an elongation at break of 89%. Figure 4 The stress-strain curves show that the tensile strength and elongation at break of Example 1 are significantly improved compared to Comparative Example 1.

[0033] Example 2

[0034] A method for preparing a high-strength PLA / PBS nanofiber aerogel includes the following steps:

[0035] 700g of polyvinyl alcohol (PVA) and 300g of glycerol were added to a high-speed mixer, and the mixing temperature was controlled at 70℃ until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder at 180℃ to obtain plasticized PVA granules. The melting point of the plasticized PVA was 130℃. 700g of plasticized PVA, 250g of polylactic acid (PLA), and 50g of polybutylene succinate (PBS) were added to a high-speed mixer, and the mixing temperature was controlled at 50℃ until homogeneous. The mixture was then melt-blended and extruded using a twin-screw extruder at 180℃, while simultaneously being stretched 8 times using a traction device. The stretched blend was then granulated. The PVA / PLA / PBS blend granules were placed in a mold and hot-pressed in a flat vulcanizing bed for 20 minutes at a molding temperature of 140℃ and a pressure of 20MPa to obtain sheet-like PVA / PLA / PBS composite materials. The obtained sheet-like PVA / PLA / PBS composite material was placed in water at 40℃ for 240 minutes to remove PVA. After removal, it was frozen at -18℃ and freeze-dried to obtain PLA / PBS nanofiber aerogel. The tensile strength of this aerogel was 12.2 MPa and the elongation at break was 98%.

[0036] Example 3

[0037] A method for preparing a high-strength PLA / PBS nanofiber aerogel includes the following steps:

[0038] 600g of polyvinyl alcohol (PVA) and 400g of glycerol (GGE) were added to a high-speed mixer, and the mixing temperature was controlled at 60℃ until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder at 150℃ to obtain plasticized PVA granules. The melting point of the plasticized PVA was 125℃. 800g of plasticized PVA, 150g of polylactic acid (PLA), and 50g of polybutylene succinate (PBS) were added to a high-speed mixer, and the mixing temperature was controlled at 60℃ until homogeneous. The mixture was then melt-blended and extruded using a twin-screw extruder at 200℃, while simultaneously being stretched 12 times using a traction device. The stretched blend was then granulated. The PVA / PLA / PBS blend granules were placed in a mold and hot-pressed in a flat vulcanizing bed for 10 minutes at a molding temperature of 150℃ and a pressure of 10MPa to obtain sheet-like PVA / PLA / PBS composite materials. The obtained sheet-like PVA / PLA / PBS composite material was placed in water at 60℃ for 90 minutes to remove PVA. After removal, it was frozen at -18℃ and freeze-dried to obtain PLA / PBS nanofiber aerogel. The tensile strength of this aerogel was 17.4 MPa and the elongation at break was 83%.

[0039] Example 4

[0040] A method for preparing a high-strength PLA / PBS nanofiber aerogel includes the following steps:

[0041] 650g of polyvinyl alcohol (PVA) and 350g of glycerol (GEPCO) were added to a high-speed mixer, and the mixing temperature was controlled at 65℃ until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder at 175℃ to obtain plasticized PVA granules. The melting point of the plasticized PVA was 123℃. 750g of plasticized PVA, 200g of polylactic acid (PLA), and 50g of polybutylene succinate (PBS) were added to a high-speed mixer, and the mixing temperature was controlled at 55℃ until homogeneous. The mixture was then melt-blended and extruded using a twin-screw extruder at 190℃, while simultaneously stretching the mixture 10 times using a traction device. The stretched blend was then granulated. The PVA / PLA / PBS blend granules were placed in a mold and hot-pressed in a flat vulcanizing bed for 16 minutes at a molding temperature of 145℃ and a pressure of 15MPa to obtain sheet-like PVA / PLA / PBS composite materials. The obtained sheet-like PVA / PLA / PBS composite material was placed in water at 55℃ for 120 minutes to remove PVA. After removal, it was frozen at -18℃ and freeze-dried to obtain PLA / PBS nanofiber aerogel. The tensile strength of this aerogel was 16.4 MPa and the elongation at break was 103%.

[0042] Example 5

[0043] A method for preparing a high-strength PLA / PBS nanofiber aerogel includes the following steps:

[0044] 550g of polyvinyl alcohol (PVA) and 450g of glycerol (Glycerol) were added to a high-speed mixer, and the mixing temperature was controlled at 50℃ until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder at 155℃ to obtain plasticized PVA granules. The melting point of the plasticized PVA was 121℃. 710g of plasticized PVA, 230g of polylactic acid (PLA), and 60g of polybutylene succinate (PBS) were added to a high-speed mixer, and the mixing temperature was controlled at 53℃ until homogeneous. The mixture was then melt-blended and extruded using a twin-screw extruder at 194℃, while simultaneously undergoing a 9-fold stretching process using a traction device. The stretched blend was then granulated. The PVA / PLA / PBS blend granules were placed in a mold and hot-pressed in a flat vulcanizing bed for 18 minutes at a molding temperature of 147℃ and a pressure of 18MPa to obtain sheet-like PVA / PLA / PBS composite materials. The obtained sheet-like PVA / PLA / PBS composite material was placed in water at 46℃ for 230 minutes to remove PVA. After removal, it was frozen at -18℃ and freeze-dried to obtain PLA / PBS nanofiber aerogel. The tensile strength of this aerogel was 14.7 MPa and the elongation at break was 115%.

[0045] Example 6

[0046] A method for preparing a high-strength PLA / PBS nanofiber aerogel includes the following steps:

[0047] 690 g of polyvinyl alcohol (PVA) and 310 g of glycerol (GEPCO) were added to a high-speed mixer, and the mixing temperature was controlled at 62°C until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder at 175°C to obtain plasticized PVA granules. The melting point of the plasticized PVA was 124°C. 740 g of plasticized PVA, 250 g of polylactic acid (PLA), and 80 g of polybutylene succinate (PBS) were added to a high-speed mixer, and the mixing temperature was controlled at 53°C until homogeneous. The mixture was then melt-blended and extruded using a twin-screw extruder at 194°C, while simultaneously undergoing 11 times stretching using a traction device. The stretched blend was then granulated. The PVA / PLA / PBS blend granules were placed in a mold and hot-pressed in a flat vulcanizing bed at a molding temperature of 152°C and a pressure of 16 MPa for 12 minutes to obtain sheet-like PVA / PLA / PBS composite materials. The obtained sheet-like PVA / PLA / PBS composite material was placed in water at 49℃ for 210 minutes to remove PVA. After removal, it was frozen at -18℃ and freeze-dried to obtain PLA / PBS nanofiber aerogel. The tensile strength of this aerogel was 15.7 MPa and the elongation at break was 105%.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-strength PLA / PBS nanofiber porous material, characterized in that, Includes the following steps: (1) Plasticized polyvinyl alcohol, polylactic acid and polybutylene succinate are mixed evenly, and then melt-blended and extruded. At the same time, the extruded blend strips are stretched and granulated to obtain PVA / PLA / PBS blended granules. (2) Place the PVA / PLA / PBS blended granules into a mold and heat-press to shape them to obtain the PVA / PLA / PBS composite material; (3) PVA / PLA / PBS composite material is immersed in a hot water bath to remove PVA, and then freeze-dried to obtain PLA / PBS nanofiber porous material; The raw material ratio in step (1) is as follows: 70-80 parts plasticized polyvinyl alcohol, 15-25 parts polylactic acid, and 5-10 parts polybutylene succinate; The preparation method of the plasticized polyvinyl alcohol is as follows: polyvinyl alcohol and glycerol are mixed evenly at 50℃-70℃; melt-blended and granulated at 150℃-180℃ to obtain plasticized polyvinyl alcohol particles; The melting and blending temperature in step (1) is 180℃-200℃; In step (1), the stretching ratio of the co-mixed strip is 8-12 times; The conditions for hot pressing in step (2) are: molding temperature of 140-155℃, pressure of 10-20MPa, and hot pressing time of 10-20 minutes.

2. The method for preparing high-strength PLA / PBS nanofiber porous material according to claim 1, characterized in that, In step (1), the mixing temperature of plasticized polyvinyl alcohol, polylactic acid and polybutylene succinate is 50℃-70℃.

3. The method for preparing high-strength PLA / PBS nanofiber porous material according to claim 2, characterized in that, The temperature of the hot water bath is 40℃-60℃, and the soaking time is 90-240 minutes.

4. The method for preparing high-strength PLA / PBS nanofiber porous material according to claim 3, characterized in that, The raw materials for preparing the plasticized polyvinyl alcohol are as follows (in parts by weight): 50-70 parts polyvinyl alcohol and 30-50 parts glycerol.

5. High-strength PLA / PBS nanofiber porous material prepared by the method according to any one of claims 1-4.

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