Preparation method of high-efficiency water electret polylactic acid melt-blown cloth

Abstract

The application relates to a preparation method of high-efficiency water-electrodeposited polylactic acid melt-blown cloth, and the high-efficiency water-electrodeposited polylactic acid melt-blown cloth is prepared by water-column electrode treatment on polylactic acid melt-blown cloth made of polylactic acid water-column electrode master batch; the polylactic acid water-column electrode master batch is obtained by uniformly mixing polylactic acid, nano inorganic electret particles and ethylene bis-stearamide and then melt-extruding; under a flow rate of 32L / min, the filtration efficiency of the high-efficiency water-electrodeposited polylactic acid melt-blown cloth on sodium chloride particles with an average diameter of 0.3mu is 99.70% to 99.97%; under a flow rate of 85L / min, the filtration efficiency of the high-efficiency water-electrodeposited polylactic acid melt-blown cloth on sodium chloride particles with an average diameter of 0.3mu is 98% to 98.50%. The preparation method of the high-efficiency water-electrodeposited polylactic acid melt-blown cloth can increase the number of dipole charges and space charges of the water-electrodeposited polylactic acid melt-blown material and increase the charge storage stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of melt-blown cloth, and relates to a preparation method of high-efficiency water-electret polylactic acid melt-blown cloth. BACKGROUND

[0002] Bacteria and viruses in the air can seriously affect people's health. In addition, with the continuous development of industrialization, the number of particulate pollutants in the atmospheric environment is increasing, and fine particulate matter can seriously harm the respiratory tract of the human body. Therefore, the demand for air filtration products such as masks and air purifiers, which can effectively block the spread of viruses and the inhalation of particulate matter, continues to grow.

[0003] Melt-blown cloth has the advantages of ultra-fine fibers, small pore size and high porosity, and is the core material of most air filtration products at present. However, most melt-blown cloth is made of polypropylene. Polypropylene is made from fossil energy such as petroleum and is not renewable, which seriously wastes fossil energy; its degradation period is very long, and toxic substances are released during the degradation process. The microplastics produced by discarded polypropylene melt-blown cloth can seriously damage the ecological environment. At present, people's environmental protection awareness is increasing, and a series of policies have been issued by the international and domestic communities for environmental protection. It is the trend of the times to develop green, ecological and environmentally friendly air filtration products.

[0004] Polylactic acid is a biodegradable and eco-friendly material made from renewable starch such as corn and wheat, and the waste of polylactic acid can be decomposed into carbon dioxide and water under the action of microorganisms in soil and seawater, which is non-toxic and harmless to the environment. Therefore, it is urgent to develop polylactic acid melt-blown cloth air filtration material to meet the current green and environmentally friendly development trend of air filtration products. However, melt-blown cloth needs to be charged by electret treatment before it can be used for air filtration. The current electret process mostly uses corona electret, which uses high-voltage electricity and produces a large amount of ozone affecting the environment. Moreover, the charge of the corona electret product is mostly stored on the surface of the product, and the storage is greatly affected by the environment temperature and humidity. With the passage of time, the charge on the surface of the product decays significantly, greatly reducing the filtration efficiency. Water electret is a kind of electret technology that uses high-pressure water flow to generate friction with melt-blown cloth, making the surface and interior of the melt-blown cloth charged with static electricity. The process is safe and environmentally friendly. Moreover, water-electret melt-blown cloth can balance high filtration efficiency and low filtration resistance, and its performance is superior to that of electric-electret melt-blown cloth.

[0005] Document 1 (Biodegradable hydro-charging polylactic acid melt-blown nonwovens with efficient PM0.3 removal [J]. Chemical Engineering Journal, 2023, 458(2): 141412.) by adjusting process parameters such as water pressure, a water-electret polylactic acid melt-blown cloth is prepared, and the filtration efficiency of sodium chloride particles with an average diameter of 0.3 μm is 94.63% at a flow rate of 32 L / min. It is well known that a high discharge peak current in the TSD curve indicates that the amount of charge stored in the material is greater, and the height of the discharge peak temperature indicates the pros and cons of the charge storage stability of the material. The higher the temperature corresponding to the discharge peak, the better the charge storage stability of the material. The peak current of the discharge peak in the TSD curve in document 1 is less than 1.5 pA, and the discharge peak is less, indicating that the amount of charge storage is small. At the same time, the highest temperature corresponding to the discharge peak is less than 100 degrees, and the charge storage stability is poor.

[0006] Document 2 ( Polylactic Acid / Calcium Stearate Hydrocharging Melt-Blown Nonwoven Fabrics for Respirator Applications [J]. ACS Applied Polymer Materials, 2023, 5(6): 4372-4379.) by adding calcium stearate to polylactic acid, a water-electret polylactic acid melt-blown cloth is prepared, and the filtration efficiency of sodium chloride particles with an average diameter of 0.3 μm is 96.78% at a flow rate of 85 L / min. The peak current of the discharge peak in the TSD curve in document 2 is less than 1.5 pA, and the discharge peak is less, indicating that the amount of charge storage is small. At the same time, the highest temperature corresponding to the discharge peak is less than 100 degrees, and the charge storage stability is poor.

[0007] In addition, with the continuous development of industrialization, the concentration of particulate pollutants in the atmospheric environment is increasing, and the spread of bacteria and viruses in the air is becoming easier, and people urgently need high-efficiency masks or air purifiers to protect their health, so people's requirements for the filtration efficiency of materials are becoming higher and higher.

[0008] Therefore, it is extremely important to study a preparation method of a high-efficiency water-electret polylactic acid melt-blown cloth to improve the filtration efficiency of the melt-blown cloth and increase the charge storage stability. SUMMARY

[0009] To solve the problems in the prior art, the present application provides a preparation method of a high-efficiency water-electret polylactic acid melt-blown cloth.

[0010] To achieve the above object, the scheme adopted by the present application is as follows:

[0011] A preparation method of high-efficiency water-polarized polylactic acid melt-blown cloth, which comprises the following steps: preparing polylactic acid melt-blown cloth made of polylactic acid water-column polar granules, and processing the polylactic acid melt-blown cloth by water-column polarization to obtain high-efficiency water-polarized polylactic acid melt-blown cloth.

[0012] The polylactic acid water-column polar granules are obtained by uniformly mixing polylactic acid, nano-inorganic polar particle and ethylene bis-stearamide, and then melt-extruding.

[0013] As a preferred technical scheme:

[0014] The preparation method of high-efficiency water-polarized polylactic acid melt-blown cloth as described above has the following advantages: under a flow rate of 32 L / min, the filtration efficiency of the high-efficiency water-polarized polylactic acid melt-blown cloth on sodium chloride particles with an average diameter of 0.3 μm is 99.70% to 99.97%; and under a flow rate of 85 L / min, the filtration efficiency of the high-efficiency water-polarized polylactic acid melt-blown cloth on sodium chloride particles with an average diameter of 0.3 μm is 98% to 98.50%.

[0015] In the TSD spectrum of the high-efficiency low-resistance water-polarized polylactic acid melt-blown cloth, the peak current of the discharge peak is greater than 1.5 pA, and the highest temperature corresponding to the discharge peak is greater than 120℃.

[0016] The preparation method of high-efficiency water-polarized polylactic acid melt-blown cloth as described above has the following advantages: under a flow rate of 32 L / min, the filtration efficiency of the high-efficiency water-polarized polylactic acid melt-blown cloth on sodium chloride particles with an average diameter of 0.3 μm is 99.70% to 99.97%; and under a flow rate of 85 L / min, the filtration efficiency of the high-efficiency water-polarized polylactic acid melt-blown cloth on sodium chloride particles with an average diameter of 0.3 μm is 98% to 98.50%.

[0017] (1) Preparation of polylactic acid water-polarized granules: uniformly mix the polylactic acid granules, nano-inorganic polar particles and ethylene bis-stearamide after being sufficiently dried, and then put them into a double-screw extruder to melt-extrude a sample in the screw area, and then sequentially perform water cooling and granulation to obtain polylactic acid water-polarized granules.

[0018] (2) Preparation of polylactic acid melt-blown cloth: after the polylactic acid water-polarized granules are sufficiently dried, they are put into a melt-blown device to prepare polylactic acid melt-blown cloth with an average fiber diameter of 1.5 to 3 μm.

[0019] (3) Water-polarization treatment of polylactic acid melt-blown cloth: deliver pure water with a resistivity greater than 15 MΩ·cm to a fan-shaped nozzle through a high-pressure water pump, place the polylactic acid melt-blown cloth on a conveying net curtain below the fan-shaped nozzle, set the water pressure to 1 to 4 MPa and the cloth conveying speed to 1 to 4 m / min, make the water flow pierce the polylactic acid melt-blown cloth, and fully rub the polylactic acid melt-blown cloth to generate tribocharging, so that the melt-blown cloth is charged with a large amount of electric charge, and then the high-efficiency water-polarized polylactic acid melt-blown cloth is obtained after drying.

[0020] The preparation method of the high-efficiency water-electret polylactic acid meltblown fabric as described above, in step (1), the drying temperature is 80-100℃, the drying time is 12-14h, and the water content of the fully dried polylactic acid masterbatch is less than 0.01%.

[0021] The preparation method of the high-efficiency water-electret polylactic acid meltblown fabric as described above, in step (1), the nano-inorganic electret particles are barium titanate, silicon dioxide, calcium titanate, silicon carbide, tourmaline or titanium dioxide, and the mass ratio of fully dried polylactic acid masterbatch, nano-inorganic electret particles and ethylene bis-stearamide is 95-99:0.5-4:0.5-4.

[0022] As described above, in the preparation method of a high-efficiency water-electret polylactic acid meltblown fabric, the drying temperature in step (2) is 80-100℃ and the drying time is 12-14h. The water content of the fully dried polylactic acid water-electret masterbatch is less than 0.01%. Since polylactic acid itself has a certain moisture regain rate, it will produce hydrolysis and carbonization when it is melted and extruded at high temperature. Therefore, it needs to be dried before preparation.

[0023] The preparation method of the high-efficiency water-electret polylactic acid meltblown fabric described above, wherein the process parameters of the meltblown equipment in step (2) are as follows: Zone 1 temperature 170-180℃, Zone 2 temperature 185-195℃, Zone 3 temperature 200-215℃, Zone 4 temperature 215-225℃, Zone 5 temperature 230-240℃, Die head temperature 230-240℃, Hot air temperature 235-250℃, Metering pump frequency 8-22Hz, Air pressure 0.1-0.25MPa, Web laying frequency 5-10Hz, Winding frequency 5.5-10.5Hz, Receiving distance 20-25cm. The Zone 1 temperature is set slightly higher than the melting point of polylactic acid to allow the polylactic acid to flow in the screw extruder; when the Zone 5 temperature and the die head temperature are lower, the flowability of polylactic acid will decrease, resulting in coarser fibers, and the fibers will not have enough residual heat to bond together when they reach the conveyor screen, thus failing to form a web; higher temperatures will lead to an increase in broken fibers during meltblowing. Suitable hot air temperature and pressure can stretch polylactic acid into fibers of appropriate thickness.

[0024] In the preparation method of the high-efficiency water-electret polylactic acid meltblown fabric described above, the drying temperature in step (3) is 40-60℃ and the time is 15-40min.

[0025] The principle of this invention is:

[0026] Polypropylene, the most commonly used meltblown raw material, is a nonpolar molecule with a uniform charge distribution within its molecules. The centers of positive and negative charges coincide, resulting in a dipole moment of zero. Water-electret polypropylene materials do not exhibit dipole charges formed by molecular dipoles. Polylactic acid (PLA), on the other hand, is a polar molecule with non-coincident positive and negative charge centers, resulting in a non-zero dipole moment. The electric field created by the space charge induces polarization of PLA molecular dipoles, thus water-electret PLA meltblown materials exhibit dipole charges. Nano-inorganic electret particles and ethylene bis-stearamide can simultaneously act as heterogeneous nucleating agents for PLA, providing numerous nucleation sites to induce PLA crystallization, promoting the formation of small spherulites, and constructing numerous charge traps in the crystalline and amorphous regions of PLA. However, the aggregation of nanoparticles can cause shielding effects, preventing the complete release of electrostatic effects and reducing the interfacial area, creating electron movement channels and promoting charge dissipation. Ethylene bis-stearamide can also act as a dispersant, ensuring uniform dispersion of the nano-inorganic electret particles and reducing the negative effects caused by their aggregation.

[0027] An inorganic-organic heterogeneous two-phase interface is formed between the nano-inorganic electret particles and ethylene bis-stearamide. Due to the difference in conductivity between the two and the higher dielectric constant of the nano-inorganic electret particles, a charge barrier is generated, causing charge to accumulate at the interface and generating interfacial charge. An inorganic-organic heterogeneous interface also forms between the nano-inorganic electret particles and polylactic acid (PLA), generating interfacial charge. These interfacial charges are deep-trapped space charges, increasing charge storage capacity and stability. Simultaneously, ethylene bis-stearamide can insert into the intermolecular junctions of PLA, weakening intermolecular interactions and increasing the fluidity of PLA molecular chains. Under the shearing action of the high-temperature, high-speed gas flow field of meltblown printing, the ordered arrangement of PLA molecular chains becomes easier, facilitating the formation of a regular and ordered oriented arrangement at the nano-electret particle-PLA inorganic-organic interface, promoting the orientation of PLA molecular dipoles, and increasing the number of dipole charges. The synergistic effect of the nano-inorganic electret particles and ethylene bis-stearamide increases the number of space charges and dipole charges, thereby significantly increasing the filtration efficiency of electrostatic adsorption.

[0028] Beneficial effects

[0029] The present invention provides a method for preparing high-efficiency water-electret polylactic acid meltblown fabric, which can increase the number of dipole charges and space charges in the water-electret polylactic acid meltblown material and increase charge storage stability. Attached Figure Description

[0030] Figure 1 The TSD diagram for Example 1;

[0031] Figure 2 This is the TSD plot for Comparative Example 1;

[0032] Figure 3 This is the TSD plot for Comparative Example 2. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0034] The testing methods used in this embodiment are as follows:

[0035] Filtration efficiency: Tested using a TSI8130 automatic filter media tester, with the flow rate of sodium chloride particles with an average diameter of 0.3 microns set at 32L / min or 85L / min (generally, the test flow rate for air filtration equipment is 32L / min, and the test flow rate for personal protective masks is 85L / min).

[0036] Example 1

[0037] A method for preparing high-efficiency water-electret polylactic acid meltblown fabric, the specific steps of which are as follows:

[0038] (1) Preparation of polylactic acid water electret masterbatch: Polylactic acid masterbatch (Anhui Fengyuan FY201) was dried at 80℃ for 12h to obtain polylactic acid masterbatch with a water content of 0.008%; the fully dried polylactic acid masterbatch was mixed with barium titanate nanoparticles (average particle size of 200 nm) and ethylene bis-stearamide at a mass ratio of 97:1.5:1.5 and fed into a twin-screw extruder. The mixture was melt-extruded in the screw area to form a sample strip, and then water-cooled and pelletized in sequence to obtain polylactic acid water electret masterbatch;

[0039] (2) Preparation of polylactic acid meltblown fabric: After the polylactic acid water electret masterbatch is fully dried, a polylactic acid water electret masterbatch with a water content of 0.008% is obtained. The masterbatch is then fed into a meltblown equipment to prepare a polylactic acid meltblown fabric with an average fiber diameter of 2.2 μm.

[0040] The process parameters of the meltblown equipment are as follows: Zone 1 temperature 170℃, Zone 2 temperature 185℃, Zone 3 temperature 200℃, Zone 4 temperature 220℃, Zone 5 temperature 230℃, Die head temperature 230℃, Hot air temperature 235℃, Metering pump frequency 20Hz, Air pressure 0.18MPa, Web laying frequency 6Hz, Winding frequency 6.5Hz, Receiving distance 22cm;

[0041] (3) Water electret treatment of polylactic acid meltblown fabric: Pure water with a resistivity of 15.5 MΩ·cm is pumped to a fan-shaped nozzle by a high-pressure water pump. Polylactic acid meltblown fabric is placed on the conveyor screen below the fan-shaped nozzle. The water pressure is set to 2 MPa and the fabric speed is 2 m / min. The water flow pierces the polylactic acid meltblown fabric and rubs against it. Then, it is dried at 50°C for 30 min to obtain high-efficiency water electret polylactic acid meltblown fabric.

[0042] At a flow rate of 32 L / min, the high-efficiency water-electret polylactic acid meltblown fabric achieved a filtration efficiency of 99.91% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the filtration efficiency was 98.42% for the same particles. Figure 1 As shown, the discharge peaks near and before the glass transition temperature of the polymer are mainly formed by the release of dipole charges, while the discharge peaks after the glass transition temperature are formed by the release of space charges. The glass transition temperature of polylactic acid is between 60 and 65 °C. In the TSD spectrum of high-efficiency, low-resistivity water-electret polylactic acid meltblown fabric, the peak current of the discharge peak is 1.7 pA, which indicates an increase in the amount of dipole charge stored. The highest temperature corresponding to the discharge peak is 124.5 °C, indicating high charge storage stability.

[0043] Comparative Example 1

[0044] A method for preparing meltblown fabric is basically the same as in Example 1, except that in step (1), polylactic acid masterbatch of equal mass is used instead of ethylene bis-stearamide (i.e., polylactic acid masterbatch and nano barium titanate in a mass ratio of 98.5:1.5).

[0045] At a flow rate of 32 L / min, the meltblown fabric achieved a filtration efficiency of 97.80% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the filtration efficiency was 92.60%. Figure 2 As shown, in the TSD spectrum of meltblown fabric, the peak current of the discharge peak is 0.86pA, and the highest temperature corresponding to the discharge peak is 85.8℃.

[0046] Comparing Comparative Example 1 and Example 1, it can be found that the filtration efficiency, peak current, and the highest temperature corresponding to the current peak are reduced. This is because the dipole charge is formed by the oriented arrangement of polylactic acid (PLA) molecular chains. Since nano-barium titanate cannot promote the orientation of PLA molecular chains, it cannot increase the number of dipole charges, and its dipole charge storage capacity is less than that of Example 1. Meanwhile, Comparative Example 1 only added nano-barium titanate, which, as an electret, can capture charges and also acts as a heterogeneous nucleating agent for PLA, constructing a large number of nanoscale charge traps in the crystalline and amorphous regions of PLA to capture space charges. However, it will aggregate, causing a shielding effect, preventing the complete release of electrostatic effects, and reducing the interface area, creating electron movement channels, and promoting charge dissipation. Comparative Example 1 lacks ethylene bis-stearamide, and therefore does not have the synergistic effect of nano-barium titanate and ethylene bis-stearamide as in Example 1. In Example 1, barium titanate nanoparticles and ethylene bis-stearamide not only simultaneously induce polylactic acid crystallization, but the ethylene bis-stearamide also ensures uniform dispersion of the inorganic electret nanoparticles, reducing the negative effects caused by the agglomeration of barium titanate nanoparticles. Furthermore, a heterogeneous inorganic-organic two-phase interface is formed between barium titanate nanoparticles, ethylene bis-stearamide, and polylactic acid, creating a charge barrier. Charge accumulates at the interface, generating interfacial charge and increasing the space charge storage capacity. Therefore, the dipole charge and space charge storage capacity in Comparative Example 1 are both lower than in Example 1, resulting in a lower total charge storage capacity. Charge can adsorb sodium chloride particles; Comparative Example 1 has a lower charge storage capacity and therefore adsorbs fewer sodium chloride particles. Filtration efficiency measures a material's ability to adsorb particles; therefore, Comparative Example 1 has a lower filtration efficiency than Example 1.

[0047] Comparative Example 2

[0048] A method for preparing meltblown fabric is basically the same as in Example 1, except that in step (1), an equal mass of polylactic acid masterbatch is used to replace barium titanate nanoparticles (i.e., polylactic acid masterbatch and ethylene bis-stearamide in a mass ratio of 98.5:1.5).

[0049] At a flow rate of 32 L / min, the meltblown fabric achieved a filtration efficiency of 96.80% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the filtration efficiency was 91.30%. Figure 3 As shown, in the TSD spectrum of meltblown fabric, the peak current of the discharge peak is 0.93pA, and the highest temperature corresponding to the discharge peak is 86.6℃.

[0050] Comparing Comparative Example 2 and Example 1, the filtration efficiency, peak current, and the highest temperature corresponding to the current peak are lower. This is because Comparative Example 2 only contains ethylene bis-stearamide. The dipole charge is formed by the oriented arrangement of polylactic acid (PLA) molecular chains. Ethylene bis-stearamide can increase the fluidity of PLA molecular chains, and under the shearing action of the high-temperature, high-speed airflow field of meltblown, it can increase the number of dipole charges. However, since there are no nano-inorganic electret particles, Comparative Example 2 lacks the inorganic-organic interface found in Example 1. Example 1 more easily forms a regular and ordered oriented arrangement at the inorganic-organic interface of nano-electret particles and PLA, promoting the orientation of PLA molecular dipoles, resulting in a greater number of dipole charges than Comparative Example 2. Furthermore, although ethylene bis-stearamide in Comparative Example 2 can promote PLA crystallization and increase the interface between crystalline and amorphous regions to capture space charges, it is not an electret, and its ability to capture space charges is weaker than that of nano-inorganic electret particles. Furthermore, in Example 1, a heterogeneous inorganic-organic two-phase interface was formed between the nano-barium titanate, ethylene bis-stearamide, and polylactic acid, creating a charge barrier. Charge accumulates at the interface, generating interfacial charge and increasing the space charge storage capacity. Therefore, the dipole charge and space charge storage capacity in Comparative Example 2 are both less than in Example 1, and the total charge storage capacity is also less than in Example 1. Charge can adsorb sodium chloride particles; Comparative Example 2 has a lower charge storage capacity and thus adsorbs fewer sodium chloride particles. Filtration efficiency measures a material's ability to adsorb particles; therefore, the filtration efficiency of Comparative Example 2 is lower than that of Example 1.

[0051] Comparing Comparative Example 2 and Comparative Example 1, the peak current of the discharge peak in Comparative Example 2 is greater than that in Comparative Example 1, indicating that Comparative Example 2 has a greater number of dipole charges. This is because dipole charges are formed by the oriented arrangement of polylactic acid (PLA) molecular chains. Ethylene bis-stearamide can increase the fluidity of PLA molecular chains. Under the shearing action of the high-temperature, high-speed gas flow field of meltblown, the ordered arrangement of PLA molecular chains becomes easier, which can increase the number of PLA dipole charges. The current corresponding to the highest temperature of the discharge peak in Comparative Example 2 is lower than that in Comparative Example 1, indicating that Comparative Example 2 has a greater number of space charges than Comparative Example 1. This is because ethylene bis-stearamide is an organic nucleating agent for PLA, which can promote the increase of the interface between crystalline and amorphous regions. It also contains nitrogen elements and amide groups with high electronegativity, which capture space charges. However, since it is not an electret, its charge-capturing ability is less than that of nano-barium titanate, and the amount of space charge captured is relatively small.

[0052] Example 2

[0053] A method for preparing high-efficiency water-electret polylactic acid meltblown fabric, the specific steps of which are as follows:

[0054] (1) Preparation of polylactic acid water electret masterbatch: Polylactic acid masterbatch (Anhui Fengyuan FY201) was dried at 90℃ for 12.5h to obtain polylactic acid masterbatch with a water content of 0.006%; the fully dried polylactic acid masterbatch was mixed with nano silica (average particle size of 200 nm) and ethylene bis-stearamide at a mass ratio of 98:1:1, and fed into a twin-screw extruder. The mixture was melt-extruded in the screw area to form a sample strip, and then water-cooled and pelletized in sequence to obtain polylactic acid water electret masterbatch;

[0055] (2) Preparation of polylactic acid meltblown fabric: After the polylactic acid water electret masterbatch is fully dried, a polylactic acid water electret masterbatch with a water content of 0.006% is obtained. The masterbatch is then fed into a meltblown equipment to prepare a polylactic acid meltblown fabric with an average fiber diameter of 1.5 μm.

[0056] The process parameters of the meltblown equipment are as follows: Zone 1 temperature 172℃, Zone 2 temperature 188℃, Zone 3 temperature 203℃, Zone 4 temperature 215℃, Zone 5 temperature 230℃, Die head temperature 230℃, Hot air temperature 235℃, Metering pump frequency 22Hz, Air pressure 0.1MPa, Web laying frequency 5Hz, Winding frequency 5.5Hz, Receiving distance 25cm;

[0057] (3) Water electret treatment of polylactic acid meltblown fabric: Pure water with a resistivity of 16 MΩ·cm is pumped to the fan-shaped nozzle through a high-pressure water pump. Polylactic acid meltblown fabric is placed on the conveyor screen below the fan-shaped nozzle. The water pressure is set to 4 MPa and the fabric speed is 1 m / min. The water flow pierces the polylactic acid meltblown fabric and rubs against it. Then, it is dried at 50°C for 20 min to obtain high-efficiency water electret polylactic acid meltblown fabric.

[0058] At a flow rate of 32 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 99.97% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 98.50% for sodium chloride particles with an average diameter of 0.3 μm; in the TSD spectrum of the high-efficiency low-resistivity water-electret polylactic acid meltblown fabric, the peak current of the discharge peak is 1.8 pA, and the highest temperature corresponding to the discharge peak is 125 °C.

[0059] Example 3

[0060] A method for preparing high-efficiency water-electret polylactic acid meltblown fabric, the specific steps of which are as follows:

[0061] (1) Preparation of polylactic acid water electret masterbatch: Polylactic acid masterbatch (Anhui Fengyuan FY201) was dried at 100℃ for 13h to obtain polylactic acid masterbatch with a water content of 0.005%; the fully dried polylactic acid masterbatch was mixed with nano calcium titanate (average particle size of 200 nm) and ethylene bis-stearamide at a mass ratio of 99:0.5:0.5 and fed into a twin-screw extruder. The mixture was melt-extruded in the screw area to form a sample strip, and then water-cooled and pelletized in sequence to obtain polylactic acid water electret masterbatch;

[0062] (2) Preparation of polylactic acid meltblown fabric: After the polylactic acid water electret masterbatch is fully dried, a polylactic acid water electret masterbatch with a water content of 0.005% is obtained. The masterbatch is then fed into a meltblown equipment to prepare a polylactic acid meltblown fabric with an average fiber diameter of 1.7 μm.

[0063] The process parameters of the meltblown equipment are as follows: Zone 1 temperature 174℃, Zone 2 temperature 190℃, Zone 3 temperature 205℃, Zone 4 temperature 218℃, Zone 5 temperature 233℃, Die head temperature 233℃, Hot air temperature 238℃, Metering pump frequency 15Hz, Air pressure 0.2MPa, Web laying frequency 8Hz, Winding frequency 8.5Hz, Receiving distance 24cm.

[0064] (3) Water electret treatment of polylactic acid meltblown fabric: Pure water with a resistivity of 16.5 MΩ·cm is pumped to a fan-shaped nozzle by a high-pressure water pump. Polylactic acid meltblown fabric is placed on the conveyor screen below the fan-shaped nozzle. The water pressure is set to 2.5 MPa and the fabric speed is 2.5 m / min. The water flow pierces the polylactic acid meltblown fabric and rubs against it. Then, it is dried at 45°C for 35 min to obtain high-efficiency water electret polylactic acid meltblown fabric.

[0065] At a flow rate of 32 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 99.81% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 98.22% for sodium chloride particles with an average diameter of 0.3 μm; in the TSD spectrum of the high-efficiency low-resistivity water-electret polylactic acid meltblown fabric, the peak current of the discharge peak is 1.63 pA, and the highest temperature corresponding to the discharge peak is 122℃.

[0066] Example 4

[0067] A method for preparing high-efficiency water-electret polylactic acid meltblown fabric, the specific steps of which are as follows:

[0068] (1) Preparation of polylactic acid water electret masterbatch: Polylactic acid masterbatch (Anhui Fengyuan FY201) was dried at 100℃ for 14h to obtain polylactic acid masterbatch with a water content of 0.004%; the fully dried polylactic acid masterbatch was mixed with nano silicon carbide (average particle size of 200 nm) and ethylene bis-stearamide at a mass ratio of 96.5:1.5:2 and fed into a twin-screw extruder. The mixture was melt-extruded in the screw area to form a sample strip, and then water-cooled and pelletized to obtain polylactic acid water electret masterbatch.

[0069] (2) Preparation of polylactic acid meltblown fabric: After the polylactic acid water electret masterbatch is fully dried, a polylactic acid water electret masterbatch with a water content of 0.004% is obtained. The masterbatch is then fed into a meltblown equipment to prepare a polylactic acid meltblown fabric with an average fiber diameter of 2μm.

[0070] The process parameters of the meltblown equipment are as follows: Zone 1 temperature 175℃, Zone 2 temperature 192℃, Zone 3 temperature 208℃, Zone 4 temperature 220℃, Zone 5 temperature 235℃, die head temperature 235℃, hot air temperature 240℃, metering pump frequency 18Hz, air pressure 0.21MPa, web laying frequency 7Hz, winding frequency 7.5Hz, and receiving distance 23cm.

[0071] (3) Water electret treatment of polylactic acid meltblown fabric: Pure water with a resistivity of 17 MΩ·cm is pumped to the fan-shaped nozzle through a high-pressure water pump. Polylactic acid meltblown fabric is placed on the conveyor screen below the fan-shaped nozzle. The water pressure is set to 3 MPa and the fabric speed is 3 m / min. The water flow pierces the polylactic acid meltblown fabric and rubs against it. Then, it is dried at 55°C for 25 min to obtain high-efficiency water electret polylactic acid meltblown fabric.

[0072] At a flow rate of 32 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 99.86% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 98.31% for sodium chloride particles with an average diameter of 0.3 μm; in the TSD spectrum of the high-efficiency low-resistivity water-electret polylactic acid meltblown fabric, the peak current of the discharge peak is 1.68 pA, and the highest temperature corresponding to the discharge peak is 123.6℃.

[0073] Example 5

[0074] A method for preparing high-efficiency water-electret polylactic acid meltblown fabric, the specific steps of which are as follows:

[0075] (1) Preparation of polylactic acid water electret masterbatch: Polylactic acid masterbatch (Anhui Fengyuan FY201) was dried at 80℃ for 12.5h to obtain polylactic acid masterbatch with a water content of 0.007%; the fully dried polylactic acid masterbatch was mixed with nano tourmaline (average particle size of 300 nm) and ethylene bis-stearamide in a mass ratio of 95.5:0.5:4 and fed into a twin-screw extruder. The mixture was melt-extruded in the screw area to form a sample strip, and then water-cooled and pelletized in sequence to obtain polylactic acid water electret masterbatch;

[0076] (2) Preparation of polylactic acid meltblown fabric: After the polylactic acid water electret masterbatch is fully dried, a polylactic acid water electret masterbatch with a water content of 0.007% is obtained. The masterbatch is then fed into a meltblown equipment to prepare a polylactic acid meltblown fabric with an average fiber diameter of 2.6 μm.

[0077] The process parameters of the meltblown equipment are as follows: Zone 1 temperature 178℃, Zone 2 temperature 194℃, Zone 3 temperature 210℃, Zone 4 temperature 223℃, Zone 5 temperature 238℃, Die head temperature 238℃, Hot air temperature 245℃, Metering pump frequency 12Hz, Air pressure 0.23MPa, Web laying frequency 9Hz, Winding frequency 9.5Hz, Receiving distance 21cm;

[0078] (3) Water electret treatment of polylactic acid meltblown fabric: Pure water with a resistivity of 17.5 MΩ·cm is pumped to a fan-shaped nozzle by a high-pressure water pump. Polylactic acid meltblown fabric is placed on the conveyor screen below the fan-shaped nozzle. The water pressure is set to 3.5 MPa and the fabric speed is 3.5 m / min. The water flow pierces the polylactic acid meltblown fabric and rubs against it. Then, it is dried at 40°C for 40 min to obtain high-efficiency water electret polylactic acid meltblown fabric.

[0079] At a flow rate of 32 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 99.74% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 98.10% for sodium chloride particles with an average diameter of 0.3 μm; in the TSD spectrum of the high-efficiency low-resistivity water-electret polylactic acid meltblown fabric, the discharge peak current is 1.6 pA, and the highest temperature corresponding to the discharge peak is 121℃.

[0080] Example 6

[0081] A method for preparing high-efficiency water-electret polylactic acid meltblown fabric, the specific steps of which are as follows:

[0082] (1) Preparation of polylactic acid water electret masterbatch: Polylactic acid masterbatch (Anhui Fengyuan FY201) was dried at 100℃ for 12h to obtain polylactic acid masterbatch with a water content of 0.006%; the fully dried polylactic acid masterbatch was mixed with nano titanium dioxide (average particle size of 200 nm) and ethylene bis-stearamide at a mass ratio of 95:4:1, and fed into a twin-screw extruder. The mixture was melt-extruded in the screw area to form a sample strip, and then water-cooled and pelletized in sequence to obtain polylactic acid water electret masterbatch;

[0083] (2) Preparation of polylactic acid meltblown fabric: After the polylactic acid water electret masterbatch is fully dried, a polylactic acid water electret masterbatch with a water content of 0.006% is obtained. The masterbatch is then fed into a meltblown equipment to prepare a polylactic acid meltblown fabric with an average fiber diameter of 3μm.

[0084] The process parameters of the meltblown equipment are as follows: Zone 1 temperature 180℃, Zone 2 temperature 195℃, Zone 3 temperature 215℃, Zone 4 temperature 225℃, Zone 5 temperature 240℃, Die head temperature 240℃, Hot air temperature 250℃, Metering pump frequency 8Hz, Air pressure 0.25MPa, Web laying frequency 10Hz, Winding frequency 10.5Hz, Receiving distance 20cm.

[0085] (3) Water electret treatment of polylactic acid meltblown fabric: Pure water with a resistivity of 18 MΩ·cm is pumped to the fan-shaped nozzle by a high-pressure water pump. Polylactic acid meltblown fabric is placed on the conveyor screen below the fan-shaped nozzle. The water pressure is set to 1 MPa and the fabric speed is 4 m / min. The water flow pierces the polylactic acid meltblown fabric and rubs against it. Then, it is dried at 60°C for 15 min to obtain high-efficiency water electret polylactic acid meltblown fabric.

[0086] At a flow rate of 32 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 99.70% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 98% for sodium chloride particles with an average diameter of 0.3 μm; in the TSD spectrum of the high-efficiency low-resistivity water-electret polylactic acid meltblown fabric, the peak current of the discharge peak is 1.52 pA, and the highest temperature corresponding to the discharge peak is 120.1℃.

Claims

1. A method for preparing a high-efficiency water-electret polylactic acid meltblown fabric, characterized in that: High-efficiency water-electrode polylactic acid meltblown fabric is obtained by subjecting polylactic acid meltblown fabric made from polylactic acid water column electrode masterbatch to water column electrode treatment. Polylactic acid water column masterbatch is obtained by melt extrusion after uniformly mixing polylactic acid, nano-inorganic electret particles and ethylene bis-stearamide. The mass ratio of polylactic acid, nano-inorganic electret particles, and ethylene bis-stearamide is 95–99:0.5–4:0.5–4.

2. The method for preparing a high-efficiency water-electret polylactic acid meltblown fabric according to claim 1, characterized in that, At a flow rate of 32 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 99.70%–99.97% for sodium chloride particles with an average diameter of 0.3 μm; at a flow rate of 85 L / min, the high-efficiency water-electret polylactic acid meltblown fabric has a filtration efficiency of 98%–98.50% for sodium chloride particles with an average diameter of 0.3 μm. In the TSD spectrum of high-efficiency, low-resistivity water-electret polylactic acid meltblown fabric, the peak current of the discharge peak is greater than 1.5pA, and the highest temperature corresponding to the discharge peak is greater than 120℃.

3. The method for preparing a high-efficiency water-electret polylactic acid meltblown fabric according to claim 1, characterized in that, The specific steps are as follows: (1) Preparation of polylactic acid water electret masterbatch: The fully dried polylactic acid masterbatch is mixed evenly with nano-inorganic electret particles and ethylene bis-stearamide, and fed into a twin-screw extruder. The mixture is melt-extruded in the screw area to form a sample strip, and then water-cooled and pelletized in sequence to obtain polylactic acid water electret masterbatch. (2) Preparation of polylactic acid meltblown fabric: After the polylactic acid water electret masterbatch is fully dried, it is put into the meltblown equipment to prepare polylactic acid meltblown fabric with an average fiber diameter of 1.5 to 3 μm; (3) Water electret treatment of polylactic acid meltblown fabric: Pure water with a resistivity greater than 15 MΩ·cm is pumped to a fan-shaped nozzle by a high-pressure water pump. Polylactic acid meltblown fabric is placed on the conveyor screen below the fan-shaped nozzle. The water pressure is set to 1-4 MPa and the fabric speed is 1-4 m / min. The water flow pierces the polylactic acid meltblown fabric and rubs against it. Then it is dried to obtain high-efficiency water electret polylactic acid meltblown fabric.

4. The method for preparing a high-efficiency water-electret polylactic acid meltblown fabric according to claim 3, characterized in that, The moisture content of the polylactic acid masterbatch after thorough drying in step (1) is less than 0.01%.

5. The method for preparing a high-efficiency water-electret polylactic acid meltblown fabric according to claim 3, characterized in that, In step (1), the nano-inorganic electret particles are barium titanate, silicon dioxide, calcium titanate, silicon carbide, tourmaline, or titanium dioxide.

6. The method for preparing a high-efficiency water-electret polylactic acid meltblown fabric according to claim 3, characterized in that, The water content of the polylactic acid water electret masterbatch after thorough drying in step (2) is less than 0.01%.

7. The method for preparing a high-efficiency water-electret polylactic acid meltblown fabric according to claim 3, characterized in that, The process parameters of the meltblown equipment in step (2) are as follows: Zone 1 temperature 170-180℃, Zone 2 temperature 185-195℃, Zone 3 temperature 200-215℃, Zone 4 temperature 215-225℃, Zone 5 temperature 230-240℃, Die head temperature 230-240℃, Hot air temperature 235-250℃, Metering pump frequency 8-22Hz, Air pressure 0.1-0.25MPa, Web laying frequency 5-10Hz, Winding frequency 5.5-10.5Hz, Receiving distance 20-25cm.

8. The method for preparing a high-efficiency water-electret polylactic acid meltblown fabric according to claim 3, characterized in that, In step (3), the drying temperature is 40-60℃ and the time is 15-40 min.

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