Method for preparing PLA / TPU (polylactic acid / thermoplastic polyurethane) fiber membrane based on spiral airflow liquid spraying

Abstract

The invention provides a method for preparing a PLA / TPU (polylactic acid / thermoplastic polyurethane) fiber membrane based on spiral airflow liquid spraying, which comprises the following steps: S1, mixing DMC (dimethyl carbonate) and DMAc (dimethylacetamide) to obtain a mixed solvent, adding PLA particles and TPU particles into the mixed solvent, and heating and stirring to obtain a spinning precursor solution; s2, the spinning precursor solution is injected into an injector of a liquid spraying assembly, the spinning precursor solution is pushed to be sprayed towards a spinneret plate under the air pressure condition of 0.1-0.2 Mpa to form a fiber membrane, and a spiral opening gas nozzle is arranged on the liquid spraying assembly; and S3, treating the fiber membrane on the receiving plate in a constant-temperature drying oven to obtain a PLA / TPU fiber membrane, introducing spiral airflow on the basis of liquid spraying, so that the airflow acts on the polymer solution in a rotating or vortex form, and further preparing the PLA / TPU fiber membrane with both strength and toughness.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, and in particular to a method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying. Background Technology

[0002] Polylactic acid (PLA), as a bio-based biodegradable polymer, possesses excellent biocompatibility, processability, and high mechanical strength, showing broad application prospects in biomedical materials, filtration and separation, and environmentally friendly packaging. However, the PLA molecular chain itself has a high rigidity and low flexibility, resulting in inherent brittleness, low elongation at break, and poor impact resistance and fatigue resistance. This makes it unable to meet the requirements for high toughness and high resilience in flexible applications, severely restricting its large-scale application in high-end fields. To improve the insufficient toughness of PLA, the mainstream approach in the industry is to use elastomer blending modification. Among them, thermoplastic polyurethane (TPU), with its excellent elastic deformation capacity, wear resistance, flexibility, and interfacial compatibility, has become one of the preferred elastomer materials for PLA toughening modification. By blending PLA and TPU to prepare composite fiber membranes, it is expected to achieve synergistic regulation of tensile strength and toughness, breaking through the performance bottleneck of single polymers.

[0003] Currently, the mainstream preparation technologies for PLA / TPU composite fiber membranes mainly include three categories: melt spinning, meltblown spinning, and electrospinning. However, for meltblown or melt spinning, PLA and TPU are thermodynamically incompatible, and simple blending easily leads to macroscopic phase separation, forming a rough and uneven structure, creating stress defect points, and causing the material to fracture prematurely under stress, resulting in low toughening efficiency. While electrospinning technology can be used to prepare PLA / TPU fiber membranes, it generally suffers from low production efficiency and insufficient fiber membrane strength. The resulting fiber membranes often have poor mechanical properties or limited improvement in toughness, failing to meet the stringent mechanical performance requirements of applications.

[0004] To address the aforementioned technical bottlenecks, solution jet spinning (SJS) technology has gradually gained industry attention. This technology relies on high-speed airflow to rapidly draw the polymer precursor solution extruded from the spinneret, with the solvent rapidly evaporating to solidify into fibers. Compared to melt spinning / meltblowing, SJS can complete the fiber formation process at room temperature to medium-low temperatures, has lower requirements for polymer thermal stability, effectively avoids polymer thermal degradation, and the rapid solvent evaporation can significantly suppress macroscopic phase separation in PLA / TPU blends, achieving uniform dispersion of blend components. Compared to electrospinning, SJS relies on high-speed airflow, eliminating the need for a high-voltage electrostatic field, resulting in higher production safety, increased spinning efficiency by 2-3 orders of magnitude, and good applicability to low-conductivity polymer solutions. It also has a wider range of raw material compatibility and possesses the potential for large-scale industrial application.

[0005] However, existing conventional direct-injection solution jet spinning technology still has significant technical drawbacks: Firstly, conventional straight high-speed airflow has a single stretching effect on polymer jets, with limited stretching efficiency, making it difficult to achieve stable and controllable preparation of submicron-sized ultrafine fibers. Furthermore, the jet is prone to divergence and turbulence in high-speed airflow fields, resulting in a wide fiber diameter distribution and poor uniformity. Secondly, the fibers obtained by conventional liquid spraying are mostly linear structures, and the fiber membranes are prone to problems such as tight stacking, low porosity, insufficient air permeability and specific surface area, which cannot meet the requirements of high-end filtration, medical dressing and other fields for high bulkiness and high porosity of materials. Third, the entanglement between linear fibers is weak, making it difficult to simultaneously improve the mechanical strength and resilience of the fiber membrane. This makes it impossible to achieve synergistic optimization of the tensile strength and toughness of the PLA / TPU composite system, and it is difficult to break through the performance bottleneck of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying. The method introduces spiral airflow on the basis of liquid spraying, so that the airflow acts on the polymer solution in the form of rotation or vortex, thereby preparing PLA / TPU fiber membranes with both stiffness and toughness.

[0007] To achieve the above objectives, this technical solution provides a method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying, comprising the following steps: S1: Mix DMC and DMAc to obtain a mixed solvent, add PLA particles and TPU particles to the mixed solvent and heat and stir to obtain a spinning precursor solution; S2: The spinning precursor solution is injected into the syringe of the liquid spraying assembly, and the spinning precursor liquid is pushed toward the spinneret to form a fiber film under a gas pressure of 0.1~0.2Mpa. The liquid spraying assembly is equipped with a spiral gas nozzle. S3: Place the fiber membrane on the receiving plate in a constant temperature oven to obtain PLA / TPU fiber membrane.

[0008] This solution adds a spiral gas nozzle to the liquid spraying process, upgrading the linear air blowing to a spiral swirling flow field. This enables the spinning jet to form a continuous and uniform three-dimensional spiral stretching force, significantly improving the stretch ratio of the spinning jet and helping to produce ultrafine fibers with finer diameters and narrower diameter distributions. This solves the problems of coarse fibers and poor uniformity in traditional liquid spraying. At the same time, the spiral airflow forms a radial binding force on the spinning jet, effectively preventing the spinning jet from diverging and becoming disordered during flight. In addition, the spiral rotating airflow causes the fibers to interweave and become tightly entangled during deposition. This structure endows the fiber membrane with higher porosity, larger specific surface area, and excellent air permeability, perfectly matching the core requirements of high-end filtration, medical dressings, and other fields for material bulkiness and permeability.

[0009] In some embodiments, DMC and DMAc are used as a mixed solvent, wherein DMC provides the core dissolving power to ensure that PLA particles and TPU particles can fully swell even at low temperatures, and DMC, as a regulating component, can dilute the viscosity of the overall system.

[0010] Preferably, the proportion of DMC in the mixed solvent is 60-90%.

[0011] In some embodiments, PLA particles and TPU particles are added to the mixed solvent, wherein the mass percentage of PLA particles and TPU particles in the total content of the mixed solvent is 8 wt% to 15 wt%.

[0012] In some embodiments, the mass ratio of PLA particles to TPU particles is (3.5~4.5):(5.5~6.5).

[0013] Preferably, the mass ratio of PLA particles to TPU particles is 4:6.

[0014] Furthermore, PLA particles and TPU particles are added to the mixed solvent and then placed in a water bath magnetic stirrer at 60~80 ℃ and heated and stirred at a speed of 200~300 r / min for 1.5~3 h.

[0015] Preferably, after adding PLA particles and TPU particles to the mixed solvent, the mixture is placed in a water bath magnetic stirrer at 60 °C and heated and stirred at 250 r / min for 2 h.

[0016] like Figure 4 As shown, after preparing a spinning precursor solution containing TPU and PLA, this method employs a uniquely designed liquid-jet assembly for liquid-jet spinning. Specifically, the liquid-jet assembly includes a push pump, a syringe, and a spiral-shaped gas nozzle. The syringe is placed inside the push pump with its injection outlet facing the spiral-shaped gas nozzle, which faces the receiving plate.

[0017] Specifically, the spinning precursor solution is loaded into an injection pump and then placed inside a push pump. Gas is then ejected using a spiral-shaped gas nozzle under a pressure of 0.1~0.2 MPa. It should be noted that an airflow pressure above 0.1 MPa is required to fully draw the solution into fibers, preventing filament pulling and sticking; a pressure below 0.2 MPa is used to avoid directly breaking or blowing away the fibers.

[0018] In some embodiments, the spiral gas nozzle includes a liquid injection channel and a swirling guide air channel surrounding the liquid injection channel, wherein the air channel opening is arranged around the liquid injection port, and the airflow is ejected from the air channel opening in the form of a rotating vortex through the swirling guide air channel, and forms a spiral stretching and constraint on the spinning jet ejected through the liquid injection port, thereby preparing a fiber membrane with a spiral structure.

[0019] In some embodiments, the liquid spray nozzle protrudes from the plane where the air passage is located, and the air passages are evenly spaced around the outer periphery of the liquid spray nozzle, with the annulus formed by the multiple air passages being concentrically arranged with the nozzle.

[0020] Preferably, the nozzle orifice has a diameter of 0.5 mm, the air passage orifice has a diameter of 0.3 mm, and the angle between the swirling guide air passage and the air passage orifice is 45°.

[0021] In some embodiments, the receiving distance between the nozzle and the receiving plate is set to 15~25cm, the rotation speed is set to 100~200 r / min, the spinning environment temperature is set to 35~45 ℃, and the humidity is below 40%.

[0022] Preferably, the receiving distance between the spiral gas nozzle and the receiving plate is 10cm, the rotation speed is set to 150 r / min, the spinning environment temperature is set to 30 ℃, and the humidity is below 40%.

[0023] In some embodiments, after the liquid spinning of the pre-spinning precursor is completed, the fiber membrane on the receiving plate is quickly removed and placed in a horizontal temperature oven at 60°C to remove residual solvent from the fiber membrane and maintain the spatial network structure of the fiber membrane.

[0024] In some embodiments, the tensile strength of the prepared PLA / TPU fiber membrane is 8.11 MPa.

[0025] In some embodiments, the fracture strain of the prepared PLA / TPU fiber membrane is 178.02%.

[0026] Compared with existing technologies, this technical solution has the following characteristics and beneficial effects: This method employs a spiral airflow jetting technique to prepare PLA / TPU fiber membranes. Compared to meltblown spinning and melt spinning, jetting offers advantages such as lower requirements for polymer thermal stability and melt flow index, faster solvent evaporation during spinning, reduced macroscopic phase separation in the blended system, and finer fiber diameters, enabling the production of submicron-sized fibers. Compared to traditional electrospinning, jetting utilizes high-speed airflow to stretch the fibers, resulting in higher production efficiency, wider raw material applicability, and the potential for large-scale industrialization. More importantly, by introducing a spiral airflow into the jetting process, the fibers undergo micro-bending and twisting during stretching, forming a fluffy, high-porosity spiral fiber network structure. This not only increases the specific surface area and air permeability of the fiber membrane but also enhances its mechanical strength through appropriate fiber entanglement. Attached Figure Description

[0027] Figure 1 This is a SEM image of the PLA / TPU fiber membrane prepared in Example 1.

[0028] Figure 2 This is a SEM image of the PLA / TPU fiber membrane prepared in Comparative Example 1.

[0029] Figure 3 These are the tensile stress-strain curves of the PLA / TPU fiber membranes prepared in Example 1 and Comparative Example 1.

[0030] Figure 4 This is a schematic diagram of the process for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying. Detailed Implementation

[0031] This section provides a more detailed description of the technical solution of the present invention through specific embodiments, but does not limit the invention to the following embodiments. Any obvious substitutions without departing from the concept of the invention fall within the protection scope of the invention. In the embodiments of the present invention, unless otherwise specified, the raw materials and reagents used are all commercially available conventional products, and the methods used are all conventional experimental methods in the art.

[0032] Example 1 Step 1: Mix DMC and DMAc in a reagent bottle at a ratio of 80:20 to obtain a mixed solvent. Add PLA particles and TPU particles to the mixed solvent, wherein the PLA particles and TPU particles account for 12 wt% of the total content of the mixed solvent. Place the reagent bottle in a water bath magnetic stirrer at 60 ℃ and heat and stir at a speed of 250 r / min. After about 2 hours, a uniform and clear solution is obtained.

[0033] Step 2: Load the obtained precursor solution into a syringe, then place it into a push pump to provide a gas pressure of 0.15 MPa. Use a spiral gas nozzle to spray the gas, set the receiving distance to 20 cm, the rotation speed to 250 r / min, the spinning environment temperature to 40 ℃, and the humidity to below 40%. After the spinning solution is sprayed, quickly remove the fiber membrane and place it in a constant temperature oven at 60 ℃ to remove the residual solvent in the fiber membrane and maintain the spatial network structure of the fiber membrane.

[0034] Comparative Example 1: Step 1: Mix DMC and DMAc in a reagent bottle at a ratio of 80:20 to obtain a mixed solvent. Add PLA particles and TPU particles to the mixed solvent, wherein the PLA particles and TPU particles account for 12 wt% of the total content of the mixed solvent. Place the reagent bottle in a water bath magnetic stirrer at 60 ℃ and heat and stir at a speed of 250 r / min. After about 2 hours, a uniform and clear solution is obtained.

[0035] Step 2: Load the obtained precursor solution into a syringe, then place it into a push pump to provide a gas pressure of 0.15 MPa. Use a common circular nozzle for gas spraying, set the receiving distance to 20 cm, the rotation speed to 250 r / min, the spinning environment temperature to 40 ℃, and the humidity to below 40%. After the spinning solution is sprayed, quickly remove the fiber membrane and place it in a constant temperature oven at 60 ℃ to remove residual solvent from the fiber membrane and maintain the spatial network structure of the fiber membrane.

[0036] Comparative Example 2: Step 1: Mix DMC and DMAc in a reagent bottle at a ratio of 80:20 to obtain a mixed solvent. Add PLA particles to the mixed solvent, wherein the PLA particles account for 12 wt% of the total content of the mixed solvent. Place the reagent bottle in a water bath magnetic stirrer at 60 ℃ and heat and stir at a speed of 250 r / min. After about 2 hours, a uniform and clear solution is obtained.

[0037] Step 2: Load the obtained precursor solution into a syringe, then place it into a push pump to provide a gas pressure of 0.15 MPa. Use a common circular nozzle for gas spraying, set the receiving distance to 20 cm, the rotation speed to 250 r / min, the spinning environment temperature to 40 ℃, and the humidity to below 40%. After the spinning solution is sprayed, quickly remove the fiber membrane and place it in a constant temperature oven at 60 ℃ to remove residual solvent from the fiber membrane and maintain the spatial network structure of the fiber membrane.

[0038] Comparative Example 3: Step 1: Mix DMC and DMAc in a reagent bottle at a ratio of 80:20 to obtain a mixed solvent. Add TPU particles to the mixed solvent, wherein the TPU particles account for 12 wt% of the total content of the mixed solvent. Place the reagent bottle in a water bath magnetic stirrer at 60 ℃ and heat and stir at a speed of 250 r / min. After about 2 hours, a uniform and clear solution is obtained.

[0039] Step 2: Load the obtained precursor solution into a syringe, then place it into a push pump to provide a gas pressure of 0.15 MPa. Use a common circular nozzle for gas spraying, set the receiving distance to 20 cm, the rotation speed to 250 r / min, the spinning environment temperature to 40 ℃, and the humidity to below 40%. After the spinning solution is sprayed, quickly remove the fiber membrane and place it in a constant temperature oven at 60 ℃ to remove residual solvent from the fiber membrane and maintain the spatial network structure of the fiber membrane.

[0040] Comparative Example 4: Step 1: Mix DMC and DMAc in a reagent bottle at a ratio of 80:20 to obtain a mixed solvent. Add PLA particles and TPU particles to the mixed solvent, wherein the PLA particles and TPU particles account for 12 wt% of the total content of the mixed solvent. Place the reagent bottle in a water bath magnetic stirrer at 60 ℃ and heat and stir at a speed of 250 r / min. After about 2 hours, a uniform and clear solution is obtained.

[0041] Step 2: Load the obtained precursor solution into a syringe, then into a push pump. Apply a positive pressure of 10 kV at the nozzle and a negative pressure of -2 kV at the roller. Set the receiving distance to 20 cm, the rotation speed to 250 r / min, the spinning environment temperature to 40 ℃, and the humidity to below 40%. After the spinning solution is sprayed out, quickly remove the fiber membrane and place it in a constant temperature oven at 60 ℃ to remove the residual solvent in the fiber membrane and maintain the spatial network structure of the fiber membrane.

[0042] Test Implementation Example: (1) Microscopic morphology characterization: The surface morphology, diameter and distribution of fibers in Example 1 and Comparative Example 1 were observed by scanning electron microscopy (SEM). The diameter of at least 100 fibers was randomly measured using image analysis software (such as ImageJ), and the average diameter and standard deviation of the fibers were calculated.

[0043] SEM images of the fibers prepared in Example 1 are shown below. Figure 1 As shown, the fibers are relatively thin and have a helical structure; the SEM image of the fibers prepared in Comparative Example 1 is shown below. Figure 2 As shown, the fibers obtained in Comparative Example 1 are straight and relatively thick.

[0044] Furthermore, the average diameter and standard deviation of the fibers prepared in Example 1 were (116.88 nm and 44.57 mm), while those in Comparative Example 1 were (322.81 nm and 126.47 mm). This demonstrates that, compared to conventional air-jet spinning, the spiral air-jet spinning method employed in this invention significantly refines the fiber diameter and greatly improves fiber uniformity. Spiral air-jet spinning technology has significant advantages in preparing fine-diameter, highly uniform nanofibers.

[0045] (2) Mechanical property test: The fiber membranes prepared in Example 1 and Comparative Example 1 were cut into standard strip samples (refer to standard GB / T 3923.1-2013). The tensile strength, elongation at break and elastic recovery rate were measured using a universal testing machine. The tensile rate was set to 50-100 mm / min.

[0046] The tensile stress-strain curves of the PLA / TPU fiber membranes prepared in Example 1 and Comparative Example 1 are shown below. Figure 3 As shown, Figure 3 The results show that the spiral airflow spinning method used in this invention significantly improves the strength and toughness of the material.

[0047] Those skilled in the art should understand that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0048] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying, characterized in that, Includes the following steps: S1: Mix DMC and DMAc to obtain a mixed solvent, add PLA particles and TPU particles to the mixed solvent and heat and stir to obtain a spinning precursor solution; S2: The spinning precursor solution is injected into the syringe of the liquid spraying assembly, and the spinning precursor liquid is pushed toward the spinneret to form a fiber film under a gas pressure of 0.1~0.2Mpa. The liquid spraying assembly is equipped with a spiral gas nozzle. S3: Place the fiber membrane on the receiving plate in a constant temperature oven to obtain PLA / TPU fiber membrane.

2. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 1, characterized in that, The spiral gas nozzle includes a liquid injection channel and a swirling guide air channel surrounding the liquid injection channel. The air channel opening is arranged around the liquid injection port of the liquid injection channel. The airflow is ejected from the air channel opening in the form of a rotating vortex through the swirling guide air channel, and forms a spiral stretching and constraint on the spinning jet ejected through the liquid injection port.

3. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 2, characterized in that, The liquid injection nozzle protrudes from the plane where the airway opening is located.

4. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 2, characterized in that, The diameter of the liquid spray nozzle is 0.5 mm, the diameter of the air passage is 0.3 mm, and the angle between the swirling guide air passage and the air passage is 45 degrees.

5. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 1, characterized in that, The receiving distance between the nozzle and the receiving plate is set to 15~25cm.

6. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 1, characterized in that, The spinning speed is set to 100~200 r / min, and the spinning environment temperature is set to 35~45 ℃.

7. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 1, characterized in that, Humidity is below 40%.

8. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 1, characterized in that, The proportion of DMC in the mixed solvent is 60-90%.

9. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 1, characterized in that, The mass percentage of PLA particles and TPU particles in the total content of the mixed solvent is 8 wt% to 15 wt%.

10. The method for preparing PLA / TPU fiber membranes based on spiral airflow liquid spraying according to claim 1, characterized in that, After the liquid precursor of the spinning process is completed, the fiber membrane on the receiving plate is quickly removed and placed in a horizontal temperature oven at 60°C.

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