Biodegradable hydrophobic polylactic acid non-woven material and preparation method thereof

Abstract

The invention relates to a biodegradable and hydrophobic polylactic acid non-woven material and a preparation method thereof, and the polylactic acid non-woven material comprises a non-woven fabric for personal protection equipment and a non-woven fabric for a three-layer surgical mask, and comprises a layer of nanofiber membrane and a layer of biodegradable spunbond fabric, and the product accords with the international biodegradation standard EN13432. Wherein the nonwoven fabric for a personal protection device has a breaking strength of at least 45 N, an elongation of at least 15%, and passes the Class 3 Fluid Resistance Test specified in AATCC 42 and AATCC 127.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 601,713, filed on November 21, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] The present invention relates to a biodegradable and hydrophobic polylactic acid nonwoven material and a preparation method thereof, and more specifically, to a hydrophobic polylactic acid nonwoven material having the ability to filter submicron air and liquid barrier properties and good air permeability. Background Art

[0003] Polylactic acid is a biodegradable bio-based polymer that can be obtained from some common renewable resources, such as corn starch or sugar cane. Therefore, nonwoven materials based on polylactic acid are biodegradable and can reduce the generation of plastic waste. They are increasingly attracting attention in various applications, including disposable products. In addition, polylactic acid is non-toxic to the human body and can be safely contacted with the skin, making it suitable for medical and personal protective equipment.

[0004] Polylactic acid nonwoven materials are lightweight, breathable and compostable. Under industrial composting conditions, these materials degrade into carbon dioxide and water. Depending on the end use, polylactic acid nonwoven materials can be prepared by meltblowing or solution methods. Traditionally, the fiber diameters produced by these methods are greater than 1 micron, and it is difficult to achieve ultrafine diameters; for example, when the end use of nonwoven materials is personal protective equipment such as masks, functional hydrophobic additives need to be added to make them have the effect of repelling body fluids, but the addition of hydrophobic additives will also increase the difficulty of achieving ultrafine fiber diameters.

[0005] In the meltblowing process, the polylactic acid resin is first melted, extruded through a series of nozzles to form fibers, and then blown with hot air and deposited on a conveyor belt to form a nonwoven fabric. Typically, the meltblowing process requires a very high melt flow rate, such as up to 1500 g / 10 cm, while the melt flow rate of biodegradable polymers (such as polylactic acid) is generally lower, about 15 g / 10 cm. In addition, the fiber diameter prepared by the meltblowing process is relatively large (>1 μm), resulting in larger pores, so the filtration efficiency of the nonwoven material is low, and additional treatment (such as fiber charging) is usually required to improve the filtration efficiency through electrostatic deposition.

[0006] Alternatively, biodegradable PLA nonwovens can be prepared by a solution process. Electrospinning is a common industry method for drawing ultrafine fibers from a PLA polymer solution using an electric field, where the PLA is first dissolved in a solvent such as chloroform or dichloromethane to form a solution with the desired viscosity; then, a high voltage is applied between the tip of a fine nozzle / needle and a grounded collector to form an electric field that overcomes the surface tension of the polymer solution and pulls it into a fine jet; finally, when the solvent in the fine jet evaporates, the PLA fibers are collected to form a nonwoven mat.

[0007] The electric field forms a "Taylor cone" at the tip of the needle, stretching the solution into a thin jet. When the thin jet is in the air, the solvent is evaporated and leaves behind solidified PLA fibers, which are collected on a grounded collector, which can be flat (forming a uniform mat) or a rotating drum (for aligned fibers). As the fibers accumulate, a nonwoven fabric or web with nano- to micro-scale pores can be formed.

[0008] However, conventional PLA polymers are usually L-isomers with high stereochemical purity, which have poor solubility in common electrospinning organic solvents due to their semi-crystalline and tightly packed structure. Therefore, PLA is usually only soluble in solvents with lower boiling points (such as chloroform and dichloromethane), but these solvents are incompatible with natural / biodegradable hydrophobic additives (highly viscous materials such as insect wax). In addition, the addition of hydrophobic additives to the electrospinning solution will increase its viscosity, thereby reducing spinnability; this will lead to bead defects and larger diameter fibers (>1 micron) during the spinning process, so these fibers have larger pores and lower filtration efficiency.

[0009] Therefore, the art is still seeking a new biodegradable and hydrophobic polylactic acid nonwoven material and a preparation method thereof, which can be used as a hydrophobic filter material that is breathable and has liquid barrier properties. Summary of the invention

[0010] The present invention provides a biodegradable nonwoven alternative material, including a nonwoven fabric for personal protective equipment and a nonwoven fabric for a three-layer surgical mask.

[0011] In one aspect of the biodegradable nonwoven alternative material of the present invention, the nonwoven fabric for personal protective equipment has a breaking strength of at least 45N, an elongation of at least 15%, and passes the third level liquid barrier test of AATCC 42 and AATCC 127.

[0012] In another aspect of the present invention, the pressure differential of the three-layer surgical mask does not exceed 5 mmH2O / cm2, and the filtration efficiency for particles in the range of 2.7-3.3 μm is at least 95% at a face velocity of 0.27 m / s, and passes the primary liquid barrier test of ASTM F2100.

[0013] In one aspect of the present invention, the biodegradable nonwoven substitute material may include a layer of nanofiber nonwoven film, more particularly, the layer of nanofiber nonwoven film is bonded to a layer of biodegradable spunbond fabric, and the biodegradable nonwoven substitute material complies with the international biodegradation standard EN13432.

[0014] In one aspect of the present invention, the biodegradable spunbond fabric has an average diameter of 1-50 microns and a surface density of 10-200 g / m2.

[0015] In another aspect of the present invention, the biodegradable spunbond fabric further comprises a first biodegradable polymer and a functional additive.

[0016] In one aspect of the present invention, the first biodegradable polymer includes polylactic acid, polycaprolactone, polyhydroxyalkanoate, polybutylene adipate, and the like.

[0017] In another aspect of the present invention, the functional additives include a nucleating agent, a plasticizer, a stabilizer, a water-proofing agent and an antioxidant.

[0018] In one aspect of the present invention, the functional additive is extruded and blended with the first biodegradable polymer through a twin screw to form a spunbond resin, wherein the extrusion temperature is between 170-200° C., the roller temperature is between 45-70° C., and the collector frequency is between 10-50 Hz.

[0019] In another aspect of the present invention, the spunbond resin is formed into a spunbond fabric by spunbonding technology.

[0020] In one aspect of the present invention, the nanofiber membrane has an average diameter of 50-1000 nanometers, a thickness of 2-50 micrometers, and a water contact angle of 110-170°.

[0021] In another aspect of the present invention, the nanofibrous membrane comprises a second biodegradable polymer and a biodegradable hydrophobic additive. Thus, the nanofibrous membrane and the spunbond fabric both comprise biodegradable polymers, but the first and second biodegradable polymers may be of the same type or of different types.

[0022] In one aspect of the present invention, the second biodegradable polymer is a modified biodegradable polymer obtained by melt blending.

[0023] In another aspect of the present invention, melt blending is achieved by extruding the second biodegradable polymer and the plasticizer from a twin screw.

[0024] In one aspect of the present invention, the second biodegradable polymer includes polylactic acid, polycaprolactone, polyhydroxyalkanoate, polybutylene adipate, and the like.

[0025] In another aspect of the present invention, the plasticizer includes epoxidized soybean oil, succinic anhydride, benzoic anhydride, etc., and the added concentration of the plasticizer is in the range of 0.01-5%.

[0026] In one aspect of the present invention, the concentration of the second biodegradable polymer is 10-25%.

[0027] In another aspect of the present invention, the second biodegradable polymer has a molecular weight in the range of 50,000-300,000 g / mole.

[0028] In one aspect of the present invention, the biodegradable hydrophobic additive is a natural hydrophobic additive, including carnauba wax, insect wax, linseed oil, tung oil, etc., and the particle size of the natural hydrophobic additive is between 50-500 microns.

[0029] In another aspect of the present invention, the concentration of the biodegradable hydrophobic additive is 5-15%.

[0030] In one aspect of the present invention, the nanofiber membrane is prepared by a needle nozzle, a multi-nozzle or a wire nozzle electrospinning system, wherein the electrospinning conditions include a voltage between 30-70 kV; a feed rate of the nozzle between 1-200 ml / hour; a distance between the nozzle and the collector between 100-300 mm; a substrate speed between 60-100 mm / min; a temperature between 25-40°C; and a relative humidity between 20-50%.

[0031] The fiber properties of the biodegradable nonwoven substitute material of the present invention meet the specifications of personal protective equipment and surgical masks. The biodegradable nonwoven substitute material includes a nonwoven fabric for personal protective equipment and a nonwoven fabric for surgical masks (such as a three-layer surgical mask), and the two have different properties. For example, the nonwoven fabric for personal protective equipment has a breaking strength of at least 45N, an elongation of at least 15%, and passes the level 3 liquid resistance test of AATCC 42 and AATCC 127; while the pressure difference of the three-layer surgical mask does not exceed 5 mm water column / square centimeter (test area is 4.9 square centimeters, and the flow rate is 8 liters per minute), the filtration efficiency for 0.1 micron particles is at least 95% (flow rate is 28.3 liters per minute), and it passes the ASTM F2100 level 1 liquid resistance test. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] With reference to the accompanying drawings, the embodiments of the present invention will be described in more detail below. It should be noted that the accompanying drawings in the following description are only some implementation examples of the present invention, and those skilled in the art can obtain other accompanying drawings without inventiveness.

[0033] Figure 1A The change in the water contact angle of the polylactic acid nanofiber membrane in Example 4 of the present invention is shown.

[0034] Figure 1B The figure shows the change of the water contact angle of the polylactic acid nanofiber membrane in Example 4 of the present invention after a period of time.

[0035] Figure 2A The change in the water contact angle of the polylactic acid nanofiber membrane in Example 5 of the present invention is shown.

[0036] Figure 2B The figure shows the change of the water contact angle of the polylactic acid nanofiber membrane in Example 5 of the present invention after a period of time equal to that in Example 4.

[0037] Figure 3A The change in water contact angle of the polylactic acid nanofiber membrane in Example 6 of the present invention is shown.

[0038] Figure 3B The water contact angle change of the PLA nanofiber membrane in Example 6 of the present invention after the same time as in Example 4 is shown.

[0039] Figure 4 This is a scanning electron microscope image of the polylactic acid nanofiber membrane in Example 4 of the present invention.

[0040] Figure 5 This is a scanning electron microscope image of the polylactic acid nanofiber membrane in Example 7 of the present invention.

[0041] Figure 6 The water contact angle of the spunbonded nonwoven fabric prepared in Comparative Example 2 is shown.

[0042] Figure 7 The water contact angle image of the spunbond nonwoven fabric prepared in Example 10 is shown.

[0043] Figure 8 The process of preparing the polylactic acid particles of the present invention is shown.

[0044] Fig. 9 The spunbonding process of the nonwoven fabric of the present invention is shown.

[0045] Fig.10 The extrusion step of the polylactic acid pellets of the present invention is shown.

[0046] Fig.11 A substrate roll of spunbond material is shown.

[0047] Fig.12 The electrospinning steps are shown schematically.

[0048] Fig.13 Schematic showing the multilayer composite of electrospinning and spunbonding. DETAILED DESCRIPTION

[0049] In one aspect, the present invention provides a polylactic acid-based material that has both biodegradable and hydrophobic properties. Generally, when the water contact angle of a material is greater than 90°, it is considered hydrophobic; conversely, when the water contact angle is less than 90°, it is considered a hydrophilic material. Therefore, the larger the water contact angle, the higher the hydrophobicity of the surface, and the contact angle of a superhydrophobic material can even exceed 150°, and water droplets will only roll on the surface of the superhydrophobic material without penetrating.

[0050] For personal protective equipment such as masks, hydrophobicity is very important to repel water-based aerosols and droplets that may carry pathogens. Ideally, the outer layer of the mask should have a high water contact angle to ensure that external water droplets do not penetrate the mask material. How to balance hydrophobicity and breathability is also very important. Therefore, materials that are hydrophobic enough to repel liquids but allow air to pass through should be used to improve the effectiveness of the equipment and the comfort of the user.

[0051] Therefore, the outer layer of the mask should be hydrophobic (contact angle>90°), but not too extreme to avoid discomfort to the user or reduce its filtration performance. Although polylactic acid has many desirable properties (such as biodegradability and easy processing), it is significantly less hydrophobic than traditional PPE materials (such as polypropylene).

[0052] The water contact angle of unmodified polylactic acid and other biodegradable polymers (such as polycaprolactone, polyhydroxyalkanoate, polybutylene terephthalate) is usually between 65° and 80°, and the actual value depends on the processing and surface conditions, which means that polylactic acid is slightly hydrophilic and its hydrophobic effect is not as good as hydrophobic materials such as polypropylene. Therefore, in the untreated state, polylactic acid with low hydrophobicity is not suitable as a biodegradable personal protective equipment material; in addition, as mentioned above, if biodegradable additives are added during the preparation step, the filtration level will be reduced.

[0053] In order to make the polylactic acid fabric more suitable for personal protective equipment applications, the present invention provides a biodegradable hydrophobic additive that can increase the water contact angle of polylactic acid to at least about 110°, thereby making the fabric effectively repel liquids such as body fluids such as blood and saliva. The polylactic acid biodegradable polymer can be used alone or mixed with other biodegradable polymers, including polycaprolactone (PCL), polyhydroxyalkanoate (PHA) or polybutylene terephthalate (PBAT) with a molecular weight of 50,000-300,000 g / mol.

[0054] In addition to the hydrophobic additive, a biodegradable plasticizer can be added to improve the processing properties of polylactic acid, which is beneficial for subsequent processing into fibers for personal protective equipment. In the personal protective equipment material, the polylactic acid fibers of different layers can have different sizes to optimize the balance between filtration efficiency and air permeability. Other optional additives include nucleating agents, stabilizers and antioxidants.

[0055] Examples of hydrophobic additives include natural waxes and oils, such as carnauba wax, insect wax, linseed oil, and tung oil. The particle size of the hydrophobic additive ranges from 50 to 500 microns, and the addition amount is about 5% to 15%. Examples of plasticizers include epoxidized soybean oil, succinic anhydride, benzoic anhydride, and the addition amount is about 0.01% to 5%.

[0056] For example, a hydrophobic additive and a plasticizer are added to a biodegradable polymer and mixed thoroughly during the extrusion process, so that the extruded mixed uniform particles are modified hydrophobic biodegradable polymer particles. These particles can be used as starting materials for nanofiber electrospinning because they have good solubility in organic solvents and are conducive to preparing electrospinning solutions. In addition, these particles can also be used as starting materials for spunbond processes.

[0057] like Fig.13 As shown, in one aspect of the present invention, the biodegradable material comprises a first layer 10 of spunbonded nonwoven material, and the first layer 10 is combined with a nanofiber material layer 20, and the combination of the two does not require the use of an additional adhesive; in addition, a second nanofiber material layer 30 can be selectively combined on the other side of the layer 10. Fig.13 In an embodiment, the average diameter of the nanofiber material is between 50-1000 nanometers, the thickness is between 2-50 microns, and the water contact angle is between 110° and 170°.

[0058] It is worth noting that the spunbond layer 10 is a nonwoven layer formed by a spunbond process. In the spunbond process, the biodegradable polymer is melted and extruded through a fine nozzle to form continuous filaments with a diameter between 1 and 50 microns; the filaments are spread on a conveyor belt to form a loose fiber web, which is then stretched by gas (high-speed airflow) or mechanical means to align and stretch the fibers. The fiber web can usually be combined by heat, chemical and / or mechanical means (such as heat pressing) to form a continuous nonwoven spunbond fabric. The surface density of the formed spunbond nonwoven material is between 10 and 200 grams per square meter.

[0059] like Fig.12 As shown in the schematic diagram, the nanofiber layer can be prepared by an electrospinning system of a needle nozzle, a multi-nozzle or a silk nozzle. Compared with some synthetic polymers (such as polypropylene), polylactic acid and other biodegradable polymers have lower elasticity. Therefore, the present invention increases the flexibility of the polymer filaments by adding plasticizer additives and optional polymers, and reduces the possibility of breakage, so as to facilitate subsequent electrospinning.

[0060] During electrospinning, a high voltage charge is applied to the polymer solution to stretch it and form fine fibers, and a layer of spunbond nonwoven material is placed on a grounded collection platform to directly receive the nanofibers. Generally speaking, electrospinning conditions include: voltage range of 30-70kV; nozzle feed rate range of 1-200 ml / hour; nozzle-collector distance range of 100-300 mm; substrate speed range of 60-100 mm / minute; temperature range of 25-40°C; relative humidity range of 20-50%.

[0061] The nonwoven fabric prepared by the composition and method of the present invention has a breaking strength of at least 45N, an elongation of at least 15%, and passes the 3rd level liquid resistance test of AATCC 42 and AATCC 127. In addition, the three-layer material composed of spunbond and electrospun fabrics has a differential pressure of no more than 5 mm H2O / cm2 (test area of ​​4.9 cm2 and flow rate of 8 liters per minute), a filtration efficiency of at least 95% for 0.1 micron particles at a flow rate of 28.3 liters per minute, and passes the ASTM F2100 first level liquid resistance test. In addition, the biodegradable nonwoven composite material meets the international biodegradability standard EN13432.

[0062] On the other hand, a biodegradable spunbond fabric can be prepared by first granulating and extruding and then spunbonding. Taking one of the embodiments as an example, the method for preparing a biodegradable spunbond fabric layer includes the following steps: mixing a biodegradable polymer (such as a biodegradable resin, including but not limited to polylactic acid, polycaprolactone, polyhydroxyalkanoate, poly(succinate terephthalate)) with a functional additive, and feeding the mixture into a twin-screw extruder and extruding granules; feeding the resulting granules into a spunbond machine, and processing the biodegradable fibers into fabrics through spunbonding technology. In the above-mentioned extrusion processing step, the extrusion temperature range is 170-200°C, the roller temperature range is 45-70°C, and the collector frequency range is 10-50Hz.

[0063] The addition of a biodegradable hydrophobic additive can improve the hydrophobicity of the biodegradable nonwoven fabric. As described above, the biodegradable nonwoven fabric can be prepared by spunbonding and solution electrospinning, and no surfactant is added to the electrospinning solution. The electrospinning solution is prepared at room temperature using the above-mentioned modified biodegradable polymer with higher solubility. In the solution electrospinning process, the solution electrospinning can be performed by a needle nozzle, a multi-nozzle or a commercially available silk nozzle electrospinning system.

[0064] example

[0065] The present invention provides the following Examples 1-5, which respectively show the experimental results of applying various biodegradable particles to electrospinning. Specifically, the performance of nanofiber layers containing natural waxes of different concentrations in terms of fluid resistance is shown, and the filtration performance of polylactic acid nanofibers of different diameters and thicknesses, as well as the hydrophobicity of different spunbond nonwoven fabrics are tested.

[0066] Example 1 includes Comparative Example 1 and Examples 1-3 to compare the electrospinning properties of the biodegradable particles of the present invention. In Comparative Example 1, the commercially available polylactic acid resin was not dried or mixed with epoxidized soybean oil. The polylactic acid particles mentioned later refer to the polylactic acid particles modified with additives according to the present invention, and the electrospinning properties of the biodegradable particles are evaluated by the needle clogging during electrospinning and the fiber formation effect.

[0067] Comparative Example 1

[0068] 1.5 g of polylactic acid resin (with 1.4% D-lactic acid content) was added to a mixed solution of dichloromethane (DCM) and dimethylformamide (DMF) in a volume ratio of 1:1, and stirred at room temperature until the polylactic acid resin was completely dissolved. The mixed solution was then injected into the electrospinning device, and the operating conditions were set as follows: voltage 30 kV; feed rate 1 ml / h; distance between needle tip and collector 210 mm.

[0069] Example 1

[0070] Before mixing, the polylactic acid resin was dried at 70°C for 3 hours; then 380 grams of polylactic acid resin (with 1.4% D-lactic acid content) was mixed with 20 grams of epoxidized soybean oil and fed into a twin-screw extruder at an extrusion temperature of 170-180°C. Then, 1.8 grams of extruded particles were added to a mixed solution of dichloromethane and dimethylformamide in a volume ratio of 1:1, and stirred at room temperature until the polylactic acid resin was completely dissolved. The mixed solution was then injected into the electrospinning equipment, and the operating conditions were set as follows: voltage 30kV; feed rate 1 ml / hour; needle tip and collector distance 210 mm.

[0071] Example 2

[0072] Before mixing, the polylactic acid resin was dried at 70°C for 3 hours; then 380 grams of polylactic acid resin (with 12% D-lactic acid content) was mixed with 20 grams of epoxidized soybean oil and fed into a twin-screw extruder at an extrusion temperature of 170-180°C. Then, 1.8 grams of the extruded particles were added to a mixed solution of dichloromethane and dimethylformamide in a volume ratio of 1:1, and stirred at room temperature until the polylactic acid resin was completely dissolved. The mixed solution was then injected into the electrospinning equipment, and the operating conditions were set as follows: voltage 30kV; feed rate 1 ml / hour; needle tip and collector distance 210 mm.

[0073] Example 3

[0074] Before mixing, the polylactic acid resin was dried at 70°C for 3 hours; then 395 grams of polylactic acid resin (with 12% D-lactic acid content) was mixed with 5 grams of epoxidized soybean oil and fed into a twin-screw extruder at an extrusion temperature of 170-180°C. Then, 1.5 grams of the extruded particles were added to a mixed solution of dichloromethane and dimethylformamide in a volume ratio of 1:1, and stirred at room temperature until the polylactic acid resin was completely dissolved. The mixed solution was then injected into the electrospinning equipment, and the operating conditions were set as follows: voltage 30kV; feed rate 1 ml / hour; needle tip and collector distance 210 mm.

[0075] Table 1 shows the evaluation results of the electrospinning performance of the polylactic acid particles prepared in Comparative Example 1 and Examples 1-3. According to Table 1, compared with Comparative Example 1, the polylactic acid particles prepared in Examples 1-3 have better electrospinning performance.

[0076] Table 1. Evaluation results of electrospinning performance of polylactic acid particles

[0077] Example 2 includes Examples 4-6, and compares the fluid resistance properties of polylactic acid nanofiber membranes with different concentrations of natural wax, wherein the fluid resistance properties are mainly detected by measuring the water contact angle that changes with time.

[0078] Example 4

[0079] 1.8 g of polylactic acid particles were dissolved in 10 ml of a mixed solvent of dimethylformamide and acetone (volume ratio of 1:1) and stirred at room temperature until a clear and uniform solution was obtained. Next, the polylactic acid solution was injected into the electrospinning device and the operating conditions were set as follows: voltage 45 kV; nozzle to collector distance 210 mm; feed rate 16 ml / h; substrate speed 80 mm / min. Finally, a polylactic acid nanofiber membrane was obtained. FIG1 shows the change in the water contact angle of the polylactic acid nanofiber membrane (without natural wax) prepared in Example 4.

[0080] Example 5

[0081] Take 0.3 g of natural wax and add it to 5 ml of acetone. After stirring overnight at a specific temperature, add 1.8 g of polylactic acid particles and 5 ml of dimethylformamide, and stir until the polylactic acid particles are completely dissolved. Inject the polylactic acid / natural wax solution into the electrospinning equipment, and set the operating conditions as follows: voltage 45 kV; nozzle to collector distance 210 mm; feed rate 16 ml / hour; substrate speed 80 mm / min. The prepared product is a polylactic acid / natural wax nanofiber membrane. Figure 2 shows the change in water contact angle of the polylactic acid nanofiber membrane (containing 3% natural wax) prepared in Example 5.

[0082] Example 6

[0083] Take 0.6 grams of natural wax and add it to 5 milliliters of acetone. After stirring overnight at a specific temperature, add 1.8 grams of polylactic acid particles and 5 milliliters of dimethylformamide, and stir until the polylactic acid particles are completely dissolved. Inject the polylactic acid / natural wax solution into the electrospinning equipment, and set the operating conditions as follows: voltage 45kV; nozzle to collector distance 210 mm; feed rate 16 ml / hour; substrate speed 80 mm / min. The prepared polylactic acid / natural wax nanofiber membrane is obtained. Figure 3A-3B The change in water contact angle of the polylactic acid nanofiber membrane (containing 6% natural wax) prepared in Example 6 is shown in FIG.

[0084] According to the measurement results of water contact angle, as the natural wax content increases, the change between the initial water contact angle and the water contact angle measured after a few minutes (for example, 5 minutes) becomes smaller; and the fluid resistance performance of the polylactic acid nanofiber membrane also improves with the increase of natural wax content.

[0085] Example 3 includes Example 4 and Example 7, and compares the fiber diameter and filtration performance of the polylactic acid nanofiber membranes prepared according to Example 4 and Example 7.

[0086] Example 7

[0087] 1.8 g of polylactic acid particles were dissolved in 10 ml of a mixed solvent of dimethylformamide and acetone (volume ratio of 1:1) and stirred at room temperature until a clear and uniform solution was obtained. Then, the polylactic acid solution was injected into the electrospinning device and the operating conditions were set as follows: voltage 50 kV; nozzle to collector distance 270 mm; feed rate 8 ml / h; substrate speed 60-100 mm / min. Finally, the polylactic acid nanofiber membrane was obtained.

[0088] The nanofiber membrane prepared according to Example 4 has an average diameter of about 450 nanometers, a filtration efficiency of 99.1% for 0.1 micron particles, and a differential pressure of 3.1 mmH2O / cm2. The nanofiber membrane prepared according to Example 7 has an average diameter of about 219 nanometers, a filtration efficiency of 99.99% for 0.1 micron particles, and a differential pressure greater than 5 mmH2O / cm2. By adjusting the electrospinning parameters (such as voltage, feed rate, and distance from the nozzle to the collector), the diameter of the nanofiber can be adjusted to control its filtration performance. Table 2 shows the filtration performance of the above two nanofiber membranes. In addition, Figure 4 The scanning electron microscope image of the polylactic acid nanofiber membrane prepared according to Example 4 is shown; and Figure 5 The scanning electron microscope image of the polylactic acid nanofiber membrane prepared according to Example 7 is shown.

[0089] Table 2. Filtration performance of nanofiber membrane

[0090] Example 4 includes Example 8 and Example 9, and compares the thickness and filtration performance of the polylactic acid nanofiber membranes prepared according to Example 4, Example 8 and Example 9.

[0091] Example 8

[0092] 1.8 g of polylactic acid particles were dissolved in 10 ml of a mixed solvent of dimethylformamide and acetone (volume ratio of 1:1) and stirred at room temperature until a clear and uniform solution was obtained. Then, the polylactic acid solution was injected into the electrospinning device and the operating conditions were set as follows: voltage 45 kV; nozzle to collector distance 210 mm; feed rate 16 ml / h; substrate speed 70 mm / min. The polylactic acid nanofiber membrane was obtained.

[0093] Example 9

[0094] 1.8 g of polylactic acid particles were dissolved in 10 ml of a mixed solvent of dimethylformamide and acetone (volume ratio of 1:1) and stirred at room temperature until a clear and uniform solution was obtained. Then, the polylactic acid solution was injected into the electrospinning device and the operating conditions were set as follows: voltage 45 kV; nozzle to collector distance 210 mm; feed rate 16 ml / h; substrate speed 60 mm / min. The polylactic acid nanofiber membrane was obtained.

[0095] The results show that the average diameter of the polylactic acid nanofiber membranes prepared according to Example 4, Example 8 and Example 9 is 450 nanometers, and the thickness is 18 micrometers, 22 micrometers and 29 micrometers respectively. Table 3 further shows the filtration performance of the three nanofiber membranes.

[0096] Table 3. Filtration performance of nanofiber membrane

[0097] The test results are shown in Table 3. The filtration efficiency of all the tested samples exceeded 99%. As the thickness decreased, the pressure difference also decreased. Therefore, the filtration performance of the nanofiber membrane can be adjusted by adjusting its thickness.

[0098] Example 5 includes Comparative Example 2 and Example 9, and the water contact angles of the spunbonded nonwoven fabrics prepared according to Comparative Example 2 and Example 10 were measured to evaluate their hydrophobicity. Figure 6 ] shows a water contact angle image of the spunbonded nonwoven fabric prepared according to Comparative Example 2; Figure 7 The water contact angle image of the spunbond nonwoven fabric prepared according to Example 10 is shown. Figure 6-7 It can be seen that the water contact angle of the sample in Example 10 is larger, indicating that it has better hydrophobicity.

[0099] Comparative Example 2

[0100] The polylactic acid particles are used for spunbonding to produce a spunbonded nonwoven fabric, wherein the polylactic acid particles are processed in a spunbonding machine at a spinning temperature of 180-230° C. and a bonding temperature of 70° C.

[0101] Example 10

[0102] Polylactic acid particles were extruded through a twin screw extruder and spunbonded to make a spunbonded nonwoven fabric. First, 958 g of polylactic acid was mixed with 2 g of epoxidized soybean oil, 10 g of silane-modified calcium carbonate, and 7 g of an additive (such as 3988), 5 g antioxidants (such as ) after mixing, it is injected into a twin-screw extruder and granulated at a temperature of 170-180°C; then, the granules are sent to a spunbond machine and processed at a spinning temperature of 180-230°C and a bonding temperature of 70°C.

[0103] Figure 8 The method for preparing nanofiber membrane in the present invention includes the preparation of polylactic acid particles, and the steps are as follows: mixing polylactic acid resin having D-lactic acid with a plasticizer, wherein the plasticizer includes but is not limited to epoxidized soybean oil, succinic anhydride, benzoic anhydride, etc.; injecting the mixture into a twin-screw extruder, and generating polylactic acid particles after melting and homogenization, cooling and granulation.

[0104] Fig. 9 The spunbond method for preparing nonwoven fabrics in the present invention comprises the following steps: melting raw materials; spinning and stretching the molten raw materials; forming a web; bonding or embossing the web by means of double hot rollers; and connecting the bonded webs in series and winding them into shape.

[0105] Fig.10 The preparation method of the present invention is as follows: preparing polylactic acid particles by extrusion, adding the extruded polylactic acid particles to a mixture of an organic solvent (such as dichloromethane and dimethylformamide); stirring the mixture at room temperature until the polylactic acid particles are completely dissolved; injecting the mixture into an electrospinning device for fiber spinning; depositing the fibers and bonding and winding them to obtain the spunbonded nonwoven fabric of the present invention.

[0106] Fig.11 A substrate roll of a spunbond material of the present invention is shown.

[0107] Fig.12 The electrospinning method of the present invention is shown, which mainly adopts an electrospinning device, injects a polylactic acid solution into the electrospinning device, and operates under specific electrospinning conditions, including: High voltage power supply: 30-70kV; Nozzle feed rate: 1-200 ml / h; Distance between nozzle and collector: 100-300 mm; Substrate speed: 60-100 mm / min; Temperature: 25-40℃; Relative humidity: 20-50%. The syringe containing the polylactic acid solution is installed on the electrospinning machine, and the polylactic acid solution is injected into the platform with a needle and a high-voltage power supply through a silicone connecting tube by a syringe pump; after fiber injection, polylactic acid nanofibers are obtained on a grounded collection platform.

[0108] The present invention provides a method for preparing a biodegradable and hydrophobic polylactic acid nonwoven material, which comprises the following steps: The degradable polylactic acid polymer is mixed with an additive in an organic solvent to be modified; Adjusting the polymer-solvent matrix to achieve the appropriate viscosity; During the electrospinning process, concentrated polymer chains are separated by a high voltage difference; Improving the conductivity of polymer solutions facilitates the separation of concentrated polymer chains.

[0109] Through the above method, a biodegradable polylactic acid nanofiber with a diameter of about 150 nanometers can be prepared, which is thinner than the existing biodegradable polylactic acid nanofiber. Utilizing the characteristics of this fiber, the air permeability and filtration performance requirements of surgical masks and personal protective equipment that meet the ASTM F2100 Grade 1 standard can be achieved, and the fluid resistance requirements can be met.

[0110] The hydrophobicity of the biodegradable nonwoven fabric can be increased by adding a hydrophobic additive, so that the polymer can be modified by melt blending without using two polymers. In addition, the nonwoven fabric is prepared by spunbonding and electrospinning, so that the nonwoven fabric has two different diameter ranges of fibers, wherein the fiber diameter of the spunbond fabric is 1-50 microns and the fiber diameter of the nanofiber fabric is 50-1000 nanometers.

[0111] The terms "one embodiment", "this / this embodiment" or "one or more embodiments" used herein refer to a combination of specific features, structures or characteristics in the embodiments that may occur in at least one embodiment. In addition, it is worth noting that the examples of "in an embodiment" used herein do not necessarily refer to the same embodiment.

[0112] The above description and examples are not intended to limit the meaning or scope of the terms in the claims for protection in the present invention, but on the contrary, are intended to assist in understanding the various embodiments. It is anticipated that there may be non-substantial changes in structure, function or results in the future, but all of these changes should be covered in the claims of the present invention. Therefore, although the description and description of the preferred embodiments are provided in the present invention, it should be understood by those skilled in the art that many changes and modifications can be made without departing from the present invention. In addition, although the term "the present invention" is sometimes used in the singular form herein, it should be understood that it includes and protects multiple inventions.

Claims

1. A hydrophobic biodegradable nonwoven fabric, characterized in that: include: a nonwoven spunbond layer having fibers having a diameter of 1 to 50 microns; an electrospun nonwoven layer having fibers with a diameter of 10-1000 nanometers, and the electrospun nonwoven layer is bonded to the nonwoven spunbond layer, wherein the electrospun fibers include at least one first biodegradable polymer selected from polylactic acid, polycaprolactone, polyhydroxyalkanoate or polybutylene succinate, one or more plasticizers and one or more hydrophobic additives; The hydrophobic biodegradable nonwoven fabric has a water contact angle of at least 110°, a breaking strength of at least 45N, an elongation of at least 15%, and passes the level 3 fluid resistance test specified by AATCC 42 and AATCC 127.

2. The hydrophobic biodegradable nonwoven fabric according to claim 1, which has a surface density of 10-200 g / m2. 3 . The hydrophobic biodegradable nonwoven fabric according to claim 1 , wherein the hydrophobic additive is one or more of carnauba wax, insect wax, linseed oil and tung oil.

4. The hydrophobic biodegradable nonwoven fabric according to claim 3, wherein the particle size of the hydrophobic additive is in the range of 50-500 microns.

5. The hydrophobic biodegradable nonwoven fabric according to claim 1, wherein the electrospun fibers comprise a second biodegradable polymer selected from polylactic acid, polycaprolactone, polyhydroxyalkanoate or polybutylene succinate, having a molecular weight of 50,000-300,000 g / mol and a content of 10-25%.

6. The hydrophobic biodegradable nonwoven fabric according to claim 1, wherein the spunbond fibers comprise at least one biodegradable polymer selected from the group consisting of polylactic acid, polycaprolactone, polyhydroxyalkanoate, and polybutylene succinate. 7 . The hydrophobic biodegradable nonwoven fabric according to claim 1 , which complies with the biodegradation standard of EN13432.

8. The hydrophobic biodegradable nonwoven fabric according to claim 1, wherein the content of the plasticizer is 0.01-5%.

9. The hydrophobic biodegradable nonwoven fabric according to claim 1, wherein the content of the hydrophobic additive is 5-15%.

10. The hydrophobic biodegradable nonwoven fabric according to claim 1, further comprising a third nonwoven layer, and the nonwoven fabric has a pressure drop of less than or equal to 5 mm H2O / cm2 (8 liters per minute / 4.9 cm2), has a filtration efficiency of at least 95% for 0.1 micron particles (at a flow rate of 28.3 liters per minute), and meets the fluid resistance test requirements of ASTM F2100 Level 1.

11. A method for preparing the hydrophobic biodegradable nonwoven fabric according to claim 1, characterized in that: include: Mixing and extruding a first biodegradable polymer selected from at least one of polylactic acid, polycaprolactone, polyhydroxyalkanoate or polybutylene succinate, one or more plasticizers and one or more hydrophobic additives to form modified hydrophobic biodegradable polymer particles; dissolving the modified hydrophobic biodegradable polymer particles in a solvent to form a modified hydrophobic biodegradable polymer solution; and The modified hydrophobic biodegradable polymer solution is electrospun to form an electrospun nonwoven layer on the spunbond layer.

12. The method of claim 11, wherein forming the modified hydrophobic biodegradable polymer particles comprises adding the plasticizer and the hydrophobic additive into a twin-screw extruder at an extrusion temperature of 170-200°C.

13. The method according to claim 11, wherein the electrospinning adopts a needle nozzle, a multi-nozzle or a linear nozzle electrospinning system, wherein the electrospinning voltage is 30-70 kV; the nozzle feed rate is 1-200 ml / hour; the distance from the nozzle to the collector is 100-300 mm; the substrate speed is 60-100 mm / min; the temperature is 25-40°C; the relative humidity is 20-50%; the drum temperature is 45-70°C; and the collector frequency is 10-50 Hz.

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